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START-INFO-DIR-ENTRY
* gcc: (gcc). The GNU Compiler Collection.
END-INFO-DIR-ENTRY
This file documents the use of the GNU compilers.
Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "Funding Free
Software", the Front-Cover texts being (a) (see below), and with the
Back-Cover Texts being (b) (see below). A copy of the license is
included in the section entitled "GNU Free Documentation License".
(a) The FSF's Front-Cover Text is:
A GNU Manual
(b) The FSF's Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU
software. Copies published by the Free Software Foundation raise
funds for GNU development.
File: gcc.info, Node: Top, Next: G++ and GCC, Up: (DIR)
Introduction
************
This manual documents how to use the GNU compilers, as well as their
features and incompatibilities, and how to report bugs. It corresponds
to GCC version 4.2.1. The internals of the GNU compilers, including
how to port them to new targets and some information about how to write
front ends for new languages, are documented in a separate manual.
*Note Introduction: (gccint)Top.
* Menu:
* G++ and GCC:: You can compile C or C++ programs.
* Standards:: Language standards supported by GCC.
* Invoking GCC:: Command options supported by `gcc'.
* C Implementation:: How GCC implements the ISO C specification.
* C Extensions:: GNU extensions to the C language family.
* C++ Extensions:: GNU extensions to the C++ language.
* Objective-C:: GNU Objective-C runtime features.
* Compatibility:: Binary Compatibility
* Gcov:: `gcov'---a test coverage program.
* Trouble:: If you have trouble using GCC.
* Bugs:: How, why and where to report bugs.
* Service:: How to find suppliers of support for GCC.
* Contributing:: How to contribute to testing and developing GCC.
* Funding:: How to help assure funding for free software.
* GNU Project:: The GNU Project and GNU/Linux.
* Copying:: GNU General Public License says
how you can copy and share GCC.
* GNU Free Documentation License:: How you can copy and share this manual.
* Contributors:: People who have contributed to GCC.
* Option Index:: Index to command line options.
* Keyword Index:: Index of concepts and symbol names.
File: gcc.info, Node: G++ and GCC, Next: Standards, Prev: Top, Up: Top
1 Programming Languages Supported by GCC
****************************************
GCC stands for "GNU Compiler Collection". GCC is an integrated
distribution of compilers for several major programming languages.
These languages currently include C, C++, Objective-C, Objective-C++,
Java, Fortran, and Ada.
The abbreviation "GCC" has multiple meanings in common use. The
current official meaning is "GNU Compiler Collection", which refers
generically to the complete suite of tools. The name historically stood
for "GNU C Compiler", and this usage is still common when the emphasis
is on compiling C programs. Finally, the name is also used when
speaking of the "language-independent" component of GCC: code shared
among the compilers for all supported languages.
The language-independent component of GCC includes the majority of the
optimizers, as well as the "back ends" that generate machine code for
various processors.
The part of a compiler that is specific to a particular language is
called the "front end". In addition to the front ends that are
integrated components of GCC, there are several other front ends that
are maintained separately. These support languages such as Pascal,
Mercury, and COBOL. To use these, they must be built together with GCC
proper.
Most of the compilers for languages other than C have their own names.
The C++ compiler is G++, the Ada compiler is GNAT, and so on. When we
talk about compiling one of those languages, we might refer to that
compiler by its own name, or as GCC. Either is correct.
Historically, compilers for many languages, including C++ and Fortran,
have been implemented as "preprocessors" which emit another high level
language such as C. None of the compilers included in GCC are
implemented this way; they all generate machine code directly. This
sort of preprocessor should not be confused with the "C preprocessor",
which is an integral feature of the C, C++, Objective-C and
Objective-C++ languages.
File: gcc.info, Node: Standards, Next: Invoking GCC, Prev: G++ and GCC, Up: Top
2 Language Standards Supported by GCC
*************************************
For each language compiled by GCC for which there is a standard, GCC
attempts to follow one or more versions of that standard, possibly with
some exceptions, and possibly with some extensions.
GCC supports three versions of the C standard, although support for
the most recent version is not yet complete.
The original ANSI C standard (X3.159-1989) was ratified in 1989 and
published in 1990. This standard was ratified as an ISO standard
(ISO/IEC 9899:1990) later in 1990. There were no technical differences
between these publications, although the sections of the ANSI standard
were renumbered and became clauses in the ISO standard. This standard,
in both its forms, is commonly known as "C89", or occasionally as
"C90", from the dates of ratification. The ANSI standard, but not the
ISO standard, also came with a Rationale document. To select this
standard in GCC, use one of the options `-ansi', `-std=c89' or
`-std=iso9899:1990'; to obtain all the diagnostics required by the
standard, you should also specify `-pedantic' (or `-pedantic-errors' if
you want them to be errors rather than warnings). *Note Options
Controlling C Dialect: C Dialect Options.
Errors in the 1990 ISO C standard were corrected in two Technical
Corrigenda published in 1994 and 1996. GCC does not support the
uncorrected version.
An amendment to the 1990 standard was published in 1995. This
amendment added digraphs and `__STDC_VERSION__' to the language, but
otherwise concerned the library. This amendment is commonly known as
"AMD1"; the amended standard is sometimes known as "C94" or "C95". To
select this standard in GCC, use the option `-std=iso9899:199409'
(with, as for other standard versions, `-pedantic' to receive all
required diagnostics).
A new edition of the ISO C standard was published in 1999 as ISO/IEC
9899:1999, and is commonly known as "C99". GCC has incomplete support
for this standard version; see
`http://gcc.gnu.org/gcc-4.2/c99status.html' for details. To select this
standard, use `-std=c99' or `-std=iso9899:1999'. (While in
development, drafts of this standard version were referred to as "C9X".)
Errors in the 1999 ISO C standard were corrected in two Technical
Corrigenda published in 2001 and 2004. GCC does not support the
uncorrected version.
By default, GCC provides some extensions to the C language that on
rare occasions conflict with the C standard. *Note Extensions to the C
Language Family: C Extensions. Use of the `-std' options listed above
will disable these extensions where they conflict with the C standard
version selected. You may also select an extended version of the C
language explicitly with `-std=gnu89' (for C89 with GNU extensions) or
`-std=gnu99' (for C99 with GNU extensions). The default, if no C
language dialect options are given, is `-std=gnu89'; this will change to
`-std=gnu99' in some future release when the C99 support is complete.
Some features that are part of the C99 standard are accepted as
extensions in C89 mode.
The ISO C standard defines (in clause 4) two classes of conforming
implementation. A "conforming hosted implementation" supports the
whole standard including all the library facilities; a "conforming
freestanding implementation" is only required to provide certain
library facilities: those in `<float.h>', `<limits.h>', `<stdarg.h>',
and `<stddef.h>'; since AMD1, also those in `<iso646.h>'; and in C99,
also those in `<stdbool.h>' and `<stdint.h>'. In addition, complex
types, added in C99, are not required for freestanding implementations.
The standard also defines two environments for programs, a
"freestanding environment", required of all implementations and which
may not have library facilities beyond those required of freestanding
implementations, where the handling of program startup and termination
are implementation-defined, and a "hosted environment", which is not
required, in which all the library facilities are provided and startup
is through a function `int main (void)' or `int main (int, char *[])'.
An OS kernel would be a freestanding environment; a program using the
facilities of an operating system would normally be in a hosted
implementation.
GCC aims towards being usable as a conforming freestanding
implementation, or as the compiler for a conforming hosted
implementation. By default, it will act as the compiler for a hosted
implementation, defining `__STDC_HOSTED__' as `1' and presuming that
when the names of ISO C functions are used, they have the semantics
defined in the standard. To make it act as a conforming freestanding
implementation for a freestanding environment, use the option
`-ffreestanding'; it will then define `__STDC_HOSTED__' to `0' and not
make assumptions about the meanings of function names from the standard
library, with exceptions noted below. To build an OS kernel, you may
well still need to make your own arrangements for linking and startup.
*Note Options Controlling C Dialect: C Dialect Options.
GCC does not provide the library facilities required only of hosted
implementations, nor yet all the facilities required by C99 of
freestanding implementations; to use the facilities of a hosted
environment, you will need to find them elsewhere (for example, in the
GNU C library). *Note Standard Libraries: Standard Libraries.
Most of the compiler support routines used by GCC are present in
`libgcc', but there are a few exceptions. GCC requires the
freestanding environment provide `memcpy', `memmove', `memset' and
`memcmp'. Finally, if `__builtin_trap' is used, and the target does
not implement the `trap' pattern, then GCC will emit a call to `abort'.
For references to Technical Corrigenda, Rationale documents and
information concerning the history of C that is available online, see
`http://gcc.gnu.org/readings.html'
There is no formal written standard for Objective-C or Objective-C++.
The most authoritative manual is "Object-Oriented Programming and the
Objective-C Language", available at a number of web sites:
*
`http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/'
is a recent (and periodically updated) version;
* `http://www.toodarkpark.org/computers/objc/' is an older example;
* `http://www.gnustep.org' and `http://gcc.gnu.org/readings.html'
have additional useful information.
There is no standard for treelang, which is a sample language front end
for GCC. Its only purpose is as a sample for people wishing to write a
new language for GCC. The language is documented in
`gcc/treelang/treelang.texi' which can be turned into info or HTML
format.
*Note GNAT Reference Manual: (gnat_rm)Top, for information on standard
conformance and compatibility of the Ada compiler.
*Note Standards: (gfortran)Standards, for details of standards
supported by GNU Fortran.
*Note Compatibility with the Java Platform: (gcj)Compatibility, for
details of compatibility between `gcj' and the Java Platform.
File: gcc.info, Node: Invoking GCC, Next: C Implementation, Prev: Standards, Up: Top
3 GCC Command Options
*********************
When you invoke GCC, it normally does preprocessing, compilation,
assembly and linking. The "overall options" allow you to stop this
process at an intermediate stage. For example, the `-c' option says
not to run the linker. Then the output consists of object files output
by the assembler.
Other options are passed on to one stage of processing. Some options
control the preprocessor and others the compiler itself. Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.
Most of the command line options that you can use with GCC are useful
for C programs; when an option is only useful with another language
(usually C++), the explanation says so explicitly. If the description
for a particular option does not mention a source language, you can use
that option with all supported languages.
*Note Compiling C++ Programs: Invoking G++, for a summary of special
options for compiling C++ programs.
The `gcc' program accepts options and file names as operands. Many
options have multi-letter names; therefore multiple single-letter
options may _not_ be grouped: `-dr' is very different from `-d -r'.
You can mix options and other arguments. For the most part, the order
you use doesn't matter. Order does matter when you use several options
of the same kind; for example, if you specify `-L' more than once, the
directories are searched in the order specified.
Many options have long names starting with `-f' or with `-W'--for
example, `-fmove-loop-invariants', `-Wformat' and so on. Most of these
have both positive and negative forms; the negative form of `-ffoo'
would be `-fno-foo'. This manual documents only one of these two
forms, whichever one is not the default.
*Note Option Index::, for an index to GCC's options.
* Menu:
* Option Summary:: Brief list of all options, without explanations.
* Overall Options:: Controlling the kind of output:
an executable, object files, assembler files,
or preprocessed source.
* Invoking G++:: Compiling C++ programs.
* C Dialect Options:: Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
and Objective-C++.
* Language Independent Options:: Controlling how diagnostics should be
formatted.
* Warning Options:: How picky should the compiler be?
* Debugging Options:: Symbol tables, measurements, and debugging dumps.
* Optimize Options:: How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
Also, getting dependency information for Make.
* Assembler Options:: Passing options to the assembler.
* Link Options:: Specifying libraries and so on.
* Directory Options:: Where to find header files and libraries.
Where to find the compiler executable files.
* Spec Files:: How to pass switches to sub-processes.
* Target Options:: Running a cross-compiler, or an old version of GCC.
* Submodel Options:: Specifying minor hardware or convention variations,
such as 68010 vs 68020.
* Code Gen Options:: Specifying conventions for function calls, data layout
and register usage.
* Environment Variables:: Env vars that affect GCC.
* Precompiled Headers:: Compiling a header once, and using it many times.
* Running Protoize:: Automatically adding or removing function prototypes.
File: gcc.info, Node: Option Summary, Next: Overall Options, Up: Invoking GCC
3.1 Option Summary
==================
Here is a summary of all the options, grouped by type. Explanations are
in the following sections.
_Overall Options_
*Note Options Controlling the Kind of Output: Overall Options.
-c -S -E -o FILE -combine -pipe -pass-exit-codes
-x LANGUAGE -v -### --help --target-help --version @FILE
_C Language Options_
*Note Options Controlling C Dialect: C Dialect Options.
-ansi -std=STANDARD -fgnu89-inline
-aux-info FILENAME
-fno-asm -fno-builtin -fno-builtin-FUNCTION
-fhosted -ffreestanding -fopenmp -fms-extensions
-trigraphs -no-integrated-cpp -traditional -traditional-cpp
-fallow-single-precision -fcond-mismatch
-fsigned-bitfields -fsigned-char
-funsigned-bitfields -funsigned-char
_C++ Language Options_
*Note Options Controlling C++ Dialect: C++ Dialect Options.
-fabi-version=N -fno-access-control -fcheck-new
-fconserve-space -ffriend-injection
-fno-elide-constructors
-fno-enforce-eh-specs
-ffor-scope -fno-for-scope -fno-gnu-keywords
-fno-implicit-templates
-fno-implicit-inline-templates
-fno-implement-inlines -fms-extensions
-fno-nonansi-builtins -fno-operator-names
-fno-optional-diags -fpermissive
-frepo -fno-rtti -fstats -ftemplate-depth-N
-fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++
-fno-default-inline -fvisibility-inlines-hidden
-Wabi -Wctor-dtor-privacy
-Wnon-virtual-dtor -Wreorder
-Weffc++ -Wno-deprecated -Wstrict-null-sentinel
-Wno-non-template-friend -Wold-style-cast
-Woverloaded-virtual -Wno-pmf-conversions
-Wsign-promo
_Objective-C and Objective-C++ Language Options_
*Note Options Controlling Objective-C and Objective-C++ Dialects:
Objective-C and Objective-C++ Dialect Options.
-fconstant-string-class=CLASS-NAME
-fgnu-runtime -fnext-runtime
-fno-nil-receivers
-fobjc-call-cxx-cdtors
-fobjc-direct-dispatch
-fobjc-exceptions
-fobjc-gc
-freplace-objc-classes
-fzero-link
-gen-decls
-Wassign-intercept
-Wno-protocol -Wselector
-Wstrict-selector-match
-Wundeclared-selector
_Language Independent Options_
*Note Options to Control Diagnostic Messages Formatting: Language
Independent Options.
-fmessage-length=N
-fdiagnostics-show-location=[once|every-line]
-fdiagnostics-show-option
_Warning Options_
*Note Options to Request or Suppress Warnings: Warning Options.
-fsyntax-only -pedantic -pedantic-errors
-w -Wextra -Wall -Waddress -Waggregate-return -Wno-attributes
-Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment
-Wconversion -Wno-deprecated-declarations
-Wdisabled-optimization -Wno-div-by-zero -Wno-endif-labels
-Werror -Werror=* -Werror-implicit-function-declaration
-Wfatal-errors -Wfloat-equal -Wformat -Wformat=2
-Wno-format-extra-args -Wformat-nonliteral
-Wformat-security -Wformat-y2k
-Wimplicit -Wimplicit-function-declaration -Wimplicit-int
-Wimport -Wno-import -Winit-self -Winline
-Wno-int-to-pointer-cast
-Wno-invalid-offsetof -Winvalid-pch
-Wlarger-than-LEN -Wunsafe-loop-optimizations -Wlong-long
-Wmain -Wmissing-braces -Wmissing-field-initializers
-Wmissing-format-attribute -Wmissing-include-dirs
-Wmissing-noreturn
-Wno-multichar -Wnonnull -Wno-overflow
-Woverlength-strings -Wpacked -Wpadded
-Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast
-Wredundant-decls
-Wreturn-type -Wsequence-point -Wshadow
-Wsign-compare -Wstack-protector
-Wstrict-aliasing -Wstrict-aliasing=2
-Wstrict-overflow -Wstrict-overflow=N
-Wswitch -Wswitch-default -Wswitch-enum
-Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized
-Wunknown-pragmas -Wno-pragmas -Wunreachable-code
-Wunused -Wunused-function -Wunused-label -Wunused-parameter
-Wunused-value -Wunused-variable -Wvariadic-macros
-Wvolatile-register-var -Wwrite-strings
_C-only Warning Options_
-Wbad-function-cast -Wmissing-declarations
-Wmissing-prototypes -Wnested-externs -Wold-style-definition
-Wstrict-prototypes -Wtraditional
-Wdeclaration-after-statement -Wpointer-sign
_Debugging Options_
*Note Options for Debugging Your Program or GCC: Debugging Options.
-dLETTERS -dumpspecs -dumpmachine -dumpversion
-fdump-noaddr -fdump-unnumbered -fdump-translation-unit[-N]
-fdump-class-hierarchy[-N]
-fdump-ipa-all -fdump-ipa-cgraph
-fdump-tree-all
-fdump-tree-original[-N]
-fdump-tree-optimized[-N]
-fdump-tree-inlined[-N]
-fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias
-fdump-tree-ch
-fdump-tree-ssa[-N] -fdump-tree-pre[-N]
-fdump-tree-ccp[-N] -fdump-tree-dce[-N]
-fdump-tree-gimple[-raw] -fdump-tree-mudflap[-N]
-fdump-tree-dom[-N]
-fdump-tree-dse[-N]
-fdump-tree-phiopt[-N]
-fdump-tree-forwprop[-N]
-fdump-tree-copyrename[-N]
-fdump-tree-nrv -fdump-tree-vect
-fdump-tree-sink
-fdump-tree-sra[-N]
-fdump-tree-salias
-fdump-tree-fre[-N]
-fdump-tree-vrp[-N]
-ftree-vectorizer-verbose=N
-fdump-tree-storeccp[-N]
-feliminate-dwarf2-dups -feliminate-unused-debug-types
-feliminate-unused-debug-symbols -femit-class-debug-always
-fmem-report -fprofile-arcs
-frandom-seed=STRING -fsched-verbose=N
-ftest-coverage -ftime-report -fvar-tracking
-g -gLEVEL -gcoff -gdwarf-2
-ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+
-p -pg -print-file-name=LIBRARY -print-libgcc-file-name
-print-multi-directory -print-multi-lib
-print-prog-name=PROGRAM -print-search-dirs -Q
-save-temps -time
_Optimization Options_
*Note Options that Control Optimization: Optimize Options.
-falign-functions=N -falign-jumps=N
-falign-labels=N -falign-loops=N
-fbounds-check -fmudflap -fmudflapth -fmudflapir
-fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize
-fbranch-target-load-optimize2 -fbtr-bb-exclusive
-fcaller-saves -fcprop-registers -fcse-follow-jumps
-fcse-skip-blocks -fcx-limited-range -fdata-sections
-fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining
-fexpensive-optimizations -ffast-math -ffloat-store
-fforce-addr -ffunction-sections
-fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload
-fcrossjumping -fif-conversion -fif-conversion2
-finline-functions -finline-functions-called-once
-finline-limit=N -fkeep-inline-functions
-fkeep-static-consts -fmerge-constants -fmerge-all-constants
-fmodulo-sched -fno-branch-count-reg
-fno-default-inline -fno-defer-pop -fmove-loop-invariants
-fno-function-cse -fno-guess-branch-probability
-fno-inline -fno-math-errno -fno-peephole -fno-peephole2
-funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss
-fomit-frame-pointer -foptimize-register-move
-foptimize-sibling-calls -fprefetch-loop-arrays
-fprofile-generate -fprofile-use
-fregmove -frename-registers
-freorder-blocks -freorder-blocks-and-partition -freorder-functions
-frerun-cse-after-loop
-frounding-math -frtl-abstract-sequences
-fschedule-insns -fschedule-insns2
-fno-sched-interblock -fno-sched-spec -fsched-spec-load
-fsched-spec-load-dangerous
-fsched-stalled-insns=N -fsched-stalled-insns-dep=N
-fsched2-use-superblocks
-fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops
-fsection-anchors -fsignaling-nans -fsingle-precision-constant
-fstack-protector -fstack-protector-all
-fstrict-aliasing -fstrict-overflow -ftracer -fthread-jumps
-funroll-all-loops -funroll-loops -fpeel-loops
-fsplit-ivs-in-unroller -funswitch-loops
-fvariable-expansion-in-unroller
-ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize
-ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts
-ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink
-ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize
-ftree-vect-loop-version -ftree-salias -fipa-pta -fweb
-ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program
--param NAME=VALUE
-O -O0 -O1 -O2 -O3 -Os
_Preprocessor Options_
*Note Options Controlling the Preprocessor: Preprocessor Options.
-AQUESTION=ANSWER
-A-QUESTION[=ANSWER]
-C -dD -dI -dM -dN
-DMACRO[=DEFN] -E -H
-idirafter DIR
-include FILE -imacros FILE
-iprefix FILE -iwithprefix DIR
-iwithprefixbefore DIR -isystem DIR
-imultilib DIR -isysroot DIR
-M -MM -MF -MG -MP -MQ -MT -nostdinc
-P -fworking-directory -remap
-trigraphs -undef -UMACRO -Wp,OPTION
-Xpreprocessor OPTION
_Assembler Option_
*Note Passing Options to the Assembler: Assembler Options.
-Wa,OPTION -Xassembler OPTION
_Linker Options_
*Note Options for Linking: Link Options.
OBJECT-FILE-NAME -lLIBRARY
-nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic
-s -static -static-libgcc -shared -shared-libgcc -symbolic
-Wl,OPTION -Xlinker OPTION
-u SYMBOL
_Directory Options_
*Note Options for Directory Search: Directory Options.
-BPREFIX -IDIR -iquoteDIR -LDIR
-specs=FILE -I- --sysroot=DIR
_Target Options_
*Note Target Options::.
-V VERSION -b MACHINE
_Machine Dependent Options_
*Note Hardware Models and Configurations: Submodel Options.
_ARC Options_
-EB -EL
-mmangle-cpu -mcpu=CPU -mtext=TEXT-SECTION
-mdata=DATA-SECTION -mrodata=READONLY-DATA-SECTION
_ARM Options_
-mapcs-frame -mno-apcs-frame
-mabi=NAME
-mapcs-stack-check -mno-apcs-stack-check
-mapcs-float -mno-apcs-float
-mapcs-reentrant -mno-apcs-reentrant
-msched-prolog -mno-sched-prolog
-mlittle-endian -mbig-endian -mwords-little-endian
-mfloat-abi=NAME -msoft-float -mhard-float -mfpe
-mthumb-interwork -mno-thumb-interwork
-mcpu=NAME -march=NAME -mfpu=NAME
-mstructure-size-boundary=N
-mabort-on-noreturn
-mlong-calls -mno-long-calls
-msingle-pic-base -mno-single-pic-base
-mpic-register=REG
-mnop-fun-dllimport
-mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns
-mpoke-function-name
-mthumb -marm
-mtpcs-frame -mtpcs-leaf-frame
-mcaller-super-interworking -mcallee-super-interworking
-mtp=NAME
_AVR Options_
-mmcu=MCU -msize -minit-stack=N -mno-interrupts
-mcall-prologues -mno-tablejump -mtiny-stack -mint8
_Blackfin Options_
-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer
-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly
-mlow-64k -mno-low64k -mid-shared-library
-mno-id-shared-library -mshared-library-id=N
-mlong-calls -mno-long-calls
_CRIS Options_
-mcpu=CPU -march=CPU -mtune=CPU
-mmax-stack-frame=N -melinux-stacksize=N
-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects
-mstack-align -mdata-align -mconst-align
-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt
-melf -maout -melinux -mlinux -sim -sim2
-mmul-bug-workaround -mno-mul-bug-workaround
_CRX Options_
-mmac -mpush-args
_Darwin Options_
-all_load -allowable_client -arch -arch_errors_fatal
-arch_only -bind_at_load -bundle -bundle_loader
-client_name -compatibility_version -current_version
-dead_strip
-dependency-file -dylib_file -dylinker_install_name
-dynamic -dynamiclib -exported_symbols_list
-filelist -flat_namespace -force_cpusubtype_ALL
-force_flat_namespace -headerpad_max_install_names
-image_base -init -install_name -keep_private_externs
-multi_module -multiply_defined -multiply_defined_unused
-noall_load -no_dead_strip_inits_and_terms
-nofixprebinding -nomultidefs -noprebind -noseglinkedit
-pagezero_size -prebind -prebind_all_twolevel_modules
-private_bundle -read_only_relocs -sectalign
-sectobjectsymbols -whyload -seg1addr
-sectcreate -sectobjectsymbols -sectorder
-segaddr -segs_read_only_addr -segs_read_write_addr
-seg_addr_table -seg_addr_table_filename -seglinkedit
-segprot -segs_read_only_addr -segs_read_write_addr
-single_module -static -sub_library -sub_umbrella
-twolevel_namespace -umbrella -undefined
-unexported_symbols_list -weak_reference_mismatches
-whatsloaded -F -gused -gfull -mmacosx-version-min=VERSION
-mkernel -mone-byte-bool
_DEC Alpha Options_
-mno-fp-regs -msoft-float -malpha-as -mgas
-mieee -mieee-with-inexact -mieee-conformant
-mfp-trap-mode=MODE -mfp-rounding-mode=MODE
-mtrap-precision=MODE -mbuild-constants
-mcpu=CPU-TYPE -mtune=CPU-TYPE
-mbwx -mmax -mfix -mcix
-mfloat-vax -mfloat-ieee
-mexplicit-relocs -msmall-data -mlarge-data
-msmall-text -mlarge-text
-mmemory-latency=TIME
_DEC Alpha/VMS Options_
-mvms-return-codes
_FRV Options_
-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64
-mhard-float -msoft-float
-malloc-cc -mfixed-cc -mdword -mno-dword
-mdouble -mno-double
-mmedia -mno-media -mmuladd -mno-muladd
-mfdpic -minline-plt -mgprel-ro -multilib-library-pic
-mlinked-fp -mlong-calls -malign-labels
-mlibrary-pic -macc-4 -macc-8
-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move
-moptimize-membar -mno-optimize-membar
-mscc -mno-scc -mcond-exec -mno-cond-exec
-mvliw-branch -mno-vliw-branch
-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec
-mno-nested-cond-exec -mtomcat-stats
-mTLS -mtls
-mcpu=CPU
_GNU/Linux Options_
-muclibc
_H8/300 Options_
-mrelax -mh -ms -mn -mint32 -malign-300
_HPPA Options_
-march=ARCHITECTURE-TYPE
-mbig-switch -mdisable-fpregs -mdisable-indexing
-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld
-mfixed-range=REGISTER-RANGE
-mjump-in-delay -mlinker-opt -mlong-calls
-mlong-load-store -mno-big-switch -mno-disable-fpregs
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas
-mno-jump-in-delay -mno-long-load-store
-mno-portable-runtime -mno-soft-float
-mno-space-regs -msoft-float -mpa-risc-1-0
-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime
-mschedule=CPU-TYPE -mspace-regs -msio -mwsio
-munix=UNIX-STD -nolibdld -static -threads
_i386 and x86-64 Options_
-mtune=CPU-TYPE -march=CPU-TYPE
-mfpmath=UNIT
-masm=DIALECT -mno-fancy-math-387
-mno-fp-ret-in-387 -msoft-float -msvr3-shlib
-mno-wide-multiply -mrtd -malign-double
-mpreferred-stack-boundary=NUM
-mmmx -msse -msse2 -msse3 -m3dnow
-mthreads -mno-align-stringops -minline-all-stringops
-mpush-args -maccumulate-outgoing-args -m128bit-long-double
-m96bit-long-double -mregparm=NUM -msseregparm
-mstackrealign
-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs
-mcmodel=CODE-MODEL
-m32 -m64 -mlarge-data-threshold=NUM
_IA-64 Options_
-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic
-mvolatile-asm-stop -mregister-names -mno-sdata
-mconstant-gp -mauto-pic -minline-float-divide-min-latency
-minline-float-divide-max-throughput
-minline-int-divide-min-latency
-minline-int-divide-max-throughput
-minline-sqrt-min-latency -minline-sqrt-max-throughput
-mno-dwarf2-asm -mearly-stop-bits
-mfixed-range=REGISTER-RANGE -mtls-size=TLS-SIZE
-mtune=CPU-TYPE -mt -pthread -milp32 -mlp64
-mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec
-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec
-msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose
-mno-sched-prefer-non-data-spec-insns
-mno-sched-prefer-non-control-spec-insns
-mno-sched-count-spec-in-critical-path
_M32R/D Options_
-m32r2 -m32rx -m32r
-mdebug
-malign-loops -mno-align-loops
-missue-rate=NUMBER
-mbranch-cost=NUMBER
-mmodel=CODE-SIZE-MODEL-TYPE
-msdata=SDATA-TYPE
-mno-flush-func -mflush-func=NAME
-mno-flush-trap -mflush-trap=NUMBER
-G NUM
_M32C Options_
-mcpu=CPU -msim -memregs=NUMBER
_M680x0 Options_
-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040
-m68060 -mcpu32 -m5200 -mcfv4e -m68881 -mbitfield
-mc68000 -mc68020
-mnobitfield -mrtd -mshort -msoft-float -mpcrel
-malign-int -mstrict-align -msep-data -mno-sep-data
-mshared-library-id=n -mid-shared-library -mno-id-shared-library
_M68hc1x Options_
-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12
-mauto-incdec -minmax -mlong-calls -mshort
-msoft-reg-count=COUNT
_MCore Options_
-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates
-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields
-m4byte-functions -mno-4byte-functions -mcallgraph-data
-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment
_MIPS Options_
-EL -EB -march=ARCH -mtune=ARCH
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64
-mips16 -mno-mips16 -mabi=ABI -mabicalls -mno-abicalls
-mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64
-mfp32 -mfp64 -mhard-float -msoft-float
-msingle-float -mdouble-float -mdsp -mpaired-single -mips3d
-mlong64 -mlong32 -msym32 -mno-sym32
-GNUM -membedded-data -mno-embedded-data
-muninit-const-in-rodata -mno-uninit-const-in-rodata
-msplit-addresses -mno-split-addresses
-mexplicit-relocs -mno-explicit-relocs
-mcheck-zero-division -mno-check-zero-division
-mdivide-traps -mdivide-breaks
-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls
-mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp
-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400
-mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130
-mfix-sb1 -mno-fix-sb1
-mflush-func=FUNC -mno-flush-func
-mbranch-likely -mno-branch-likely
-mfp-exceptions -mno-fp-exceptions
-mvr4130-align -mno-vr4130-align
_MMIX Options_
-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu
-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols
-melf -mbranch-predict -mno-branch-predict -mbase-addresses
-mno-base-addresses -msingle-exit -mno-single-exit
_MN10300 Options_
-mmult-bug -mno-mult-bug
-mam33 -mno-am33
-mam33-2 -mno-am33-2
-mreturn-pointer-on-d0
-mno-crt0 -mrelax
_MT Options_
-mno-crt0 -mbacc -msim
-march=CPU-TYPE
_PDP-11 Options_
-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10
-mbcopy -mbcopy-builtin -mint32 -mno-int16
-mint16 -mno-int32 -mfloat32 -mno-float64
-mfloat64 -mno-float32 -mabshi -mno-abshi
-mbranch-expensive -mbranch-cheap
-msplit -mno-split -munix-asm -mdec-asm
_PowerPC Options_ See RS/6000 and PowerPC Options.
_RS/6000 and PowerPC Options_
-mcpu=CPU-TYPE
-mtune=CPU-TYPE
-mpower -mno-power -mpower2 -mno-power2
-mpowerpc -mpowerpc64 -mno-powerpc
-maltivec -mno-altivec
-mpowerpc-gpopt -mno-powerpc-gpopt
-mpowerpc-gfxopt -mno-powerpc-gfxopt
-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd
-mnew-mnemonics -mold-mnemonics
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc
-m64 -m32 -mxl-compat -mno-xl-compat -mpe
-malign-power -malign-natural
-msoft-float -mhard-float -mmultiple -mno-multiple
-mstring -mno-string -mupdate -mno-update
-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align
-mstrict-align -mno-strict-align -mrelocatable
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian
-mdynamic-no-pic -maltivec -mswdiv
-mprioritize-restricted-insns=PRIORITY
-msched-costly-dep=DEPENDENCE_TYPE
-minsert-sched-nops=SCHEME
-mcall-sysv -mcall-netbsd
-maix-struct-return -msvr4-struct-return
-mabi=ABI-TYPE -msecure-plt -mbss-plt
-misel -mno-isel
-misel=yes -misel=no
-mspe -mno-spe
-mspe=yes -mspe=no
-mvrsave -mno-vrsave
-mmulhw -mno-mulhw
-mdlmzb -mno-dlmzb
-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double
-mprototype -mno-prototype
-msim -mmvme -mads -myellowknife -memb -msdata
-msdata=OPT -mvxworks -mwindiss -G NUM -pthread
_S/390 and zSeries Options_
-mtune=CPU-TYPE -march=CPU-TYPE
-mhard-float -msoft-float -mlong-double-64 -mlong-double-128
-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack
-msmall-exec -mno-small-exec -mmvcle -mno-mvcle
-m64 -m31 -mdebug -mno-debug -mesa -mzarch
-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd
-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard
_Score Options_
-meb -mel
-mnhwloop
-muls
-mmac
-mscore5 -mscore5u -mscore7 -mscore7d
_SH Options_
-m1 -m2 -m2e -m3 -m3e
-m4-nofpu -m4-single-only -m4-single -m4
-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al
-m5-64media -m5-64media-nofpu
-m5-32media -m5-32media-nofpu
-m5-compact -m5-compact-nofpu
-mb -ml -mdalign -mrelax
-mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave
-mieee -misize -mpadstruct -mspace
-mprefergot -musermode -multcost=NUMBER -mdiv=STRATEGY
-mdivsi3_libfunc=NAME
-madjust-unroll -mindexed-addressing -mgettrcost=NUMBER -mpt-fixed
-minvalid-symbols
_SPARC Options_
-mcpu=CPU-TYPE
-mtune=CPU-TYPE
-mcmodel=CODE-MODEL
-m32 -m64 -mapp-regs -mno-app-regs
-mfaster-structs -mno-faster-structs
-mfpu -mno-fpu -mhard-float -msoft-float
-mhard-quad-float -msoft-quad-float
-mimpure-text -mno-impure-text -mlittle-endian
-mstack-bias -mno-stack-bias
-munaligned-doubles -mno-unaligned-doubles
-mv8plus -mno-v8plus -mvis -mno-vis
-threads -pthreads -pthread
_System V Options_
-Qy -Qn -YP,PATHS -Ym,DIR
_TMS320C3x/C4x Options_
-mcpu=CPU -mbig -msmall -mregparm -mmemparm
-mfast-fix -mmpyi -mbk -mti -mdp-isr-reload
-mrpts=COUNT -mrptb -mdb -mloop-unsigned
-mparallel-insns -mparallel-mpy -mpreserve-float
_V850 Options_
-mlong-calls -mno-long-calls -mep -mno-ep
-mprolog-function -mno-prolog-function -mspace
-mtda=N -msda=N -mzda=N
-mapp-regs -mno-app-regs
-mdisable-callt -mno-disable-callt
-mv850e1
-mv850e
-mv850 -mbig-switch
_VAX Options_
-mg -mgnu -munix
_x86-64 Options_ See i386 and x86-64 Options.
_Xstormy16 Options_
-msim
_Xtensa Options_
-mconst16 -mno-const16
-mfused-madd -mno-fused-madd
-mtext-section-literals -mno-text-section-literals
-mtarget-align -mno-target-align
-mlongcalls -mno-longcalls
_zSeries Options_ See S/390 and zSeries Options.
_Code Generation Options_
*Note Options for Code Generation Conventions: Code Gen Options.
-fcall-saved-REG -fcall-used-REG
-ffixed-REG -fexceptions
-fnon-call-exceptions -funwind-tables
-fasynchronous-unwind-tables
-finhibit-size-directive -finstrument-functions
-fno-common -fno-ident
-fpcc-struct-return -fpic -fPIC -fpie -fPIE
-fno-jump-tables
-freg-struct-return -fshort-enums
-fshort-double -fshort-wchar
-fverbose-asm -fpack-struct[=N] -fstack-check
-fstack-limit-register=REG -fstack-limit-symbol=SYM
-fargument-alias -fargument-noalias
-fargument-noalias-global -fargument-noalias-anything
-fleading-underscore -ftls-model=MODEL
-ftrapv -fwrapv -fbounds-check
-fvisibility
* Menu:
* Overall Options:: Controlling the kind of output:
an executable, object files, assembler files,
or preprocessed source.
* C Dialect Options:: Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
and Objective-C++.
* Language Independent Options:: Controlling how diagnostics should be
formatted.
* Warning Options:: How picky should the compiler be?
* Debugging Options:: Symbol tables, measurements, and debugging dumps.
* Optimize Options:: How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
Also, getting dependency information for Make.
* Assembler Options:: Passing options to the assembler.
* Link Options:: Specifying libraries and so on.
* Directory Options:: Where to find header files and libraries.
Where to find the compiler executable files.
* Spec Files:: How to pass switches to sub-processes.
* Target Options:: Running a cross-compiler, or an old version of GCC.
File: gcc.info, Node: Overall Options, Next: Invoking G++, Prev: Option Summary, Up: Invoking GCC
3.2 Options Controlling the Kind of Output
==========================================
Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order. GCC is capable of
preprocessing and compiling several files either into several assembler
input files, or into one assembler input file; then each assembler
input file produces an object file, and linking combines all the object
files (those newly compiled, and those specified as input) into an
executable file.
For any given input file, the file name suffix determines what kind of
compilation is done:
`FILE.c'
C source code which must be preprocessed.
`FILE.i'
C source code which should not be preprocessed.
`FILE.ii'
C++ source code which should not be preprocessed.
`FILE.m'
Objective-C source code. Note that you must link with the
`libobjc' library to make an Objective-C program work.
`FILE.mi'
Objective-C source code which should not be preprocessed.
`FILE.mm'
`FILE.M'
Objective-C++ source code. Note that you must link with the
`libobjc' library to make an Objective-C++ program work. Note
that `.M' refers to a literal capital M.
`FILE.mii'
Objective-C++ source code which should not be preprocessed.
`FILE.h'
C, C++, Objective-C or Objective-C++ header file to be turned into
a precompiled header.
`FILE.cc'
`FILE.cp'
`FILE.cxx'
`FILE.cpp'
`FILE.CPP'
`FILE.c++'
`FILE.C'
C++ source code which must be preprocessed. Note that in `.cxx',
the last two letters must both be literally `x'. Likewise, `.C'
refers to a literal capital C.
`FILE.mm'
`FILE.M'
Objective-C++ source code which must be preprocessed.
`FILE.mii'
Objective-C++ source code which should not be preprocessed.
`FILE.hh'
`FILE.H'
C++ header file to be turned into a precompiled header.
`FILE.f'
`FILE.for'
`FILE.FOR'
Fixed form Fortran source code which should not be preprocessed.
`FILE.F'
`FILE.fpp'
`FILE.FPP'
Fixed form Fortran source code which must be preprocessed (with
the traditional preprocessor).
`FILE.f90'
`FILE.f95'
Free form Fortran source code which should not be preprocessed.
`FILE.F90'
`FILE.F95'
Free form Fortran source code which must be preprocessed (with the
traditional preprocessor).
`FILE.ads'
Ada source code file which contains a library unit declaration (a
declaration of a package, subprogram, or generic, or a generic
instantiation), or a library unit renaming declaration (a package,
generic, or subprogram renaming declaration). Such files are also
called "specs".
`FILE.adb'
Ada source code file containing a library unit body (a subprogram
or package body). Such files are also called "bodies".
`FILE.s'
Assembler code.
`FILE.S'
Assembler code which must be preprocessed.
`OTHER'
An object file to be fed straight into linking. Any file name
with no recognized suffix is treated this way.
You can specify the input language explicitly with the `-x' option:
`-x LANGUAGE'
Specify explicitly the LANGUAGE for the following input files
(rather than letting the compiler choose a default based on the
file name suffix). This option applies to all following input
files until the next `-x' option. Possible values for LANGUAGE
are:
c c-header c-cpp-output
c++ c++-header c++-cpp-output
objective-c objective-c-header objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output
assembler assembler-with-cpp
ada
f95 f95-cpp-input
java
treelang
`-x none'
Turn off any specification of a language, so that subsequent files
are handled according to their file name suffixes (as they are if
`-x' has not been used at all).
`-pass-exit-codes'
Normally the `gcc' program will exit with the code of 1 if any
phase of the compiler returns a non-success return code. If you
specify `-pass-exit-codes', the `gcc' program will instead return
with numerically highest error produced by any phase that returned
an error indication. The C, C++, and Fortran frontends return 4,
if an internal compiler error is encountered.
If you only want some of the stages of compilation, you can use `-x'
(or filename suffixes) to tell `gcc' where to start, and one of the
options `-c', `-S', or `-E' to say where `gcc' is to stop. Note that
some combinations (for example, `-x cpp-output -E') instruct `gcc' to
do nothing at all.
`-c'
Compile or assemble the source files, but do not link. The linking
stage simply is not done. The ultimate output is in the form of an
object file for each source file.
By default, the object file name for a source file is made by
replacing the suffix `.c', `.i', `.s', etc., with `.o'.
Unrecognized input files, not requiring compilation or assembly,
are ignored.
`-S'
Stop after the stage of compilation proper; do not assemble. The
output is in the form of an assembler code file for each
non-assembler input file specified.
By default, the assembler file name for a source file is made by
replacing the suffix `.c', `.i', etc., with `.s'.
Input files that don't require compilation are ignored.
`-E'
Stop after the preprocessing stage; do not run the compiler
proper. The output is in the form of preprocessed source code,
which is sent to the standard output.
Input files which don't require preprocessing are ignored.
`-o FILE'
Place output in file FILE. This applies regardless to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.
If `-o' is not specified, the default is to put an executable file
in `a.out', the object file for `SOURCE.SUFFIX' in `SOURCE.o', its
assembler file in `SOURCE.s', a precompiled header file in
`SOURCE.SUFFIX.gch', and all preprocessed C source on standard
output.
`-v'
Print (on standard error output) the commands executed to run the
stages of compilation. Also print the version number of the
compiler driver program and of the preprocessor and the compiler
proper.
`-###'
Like `-v' except the commands are not executed and all command
arguments are quoted. This is useful for shell scripts to capture
the driver-generated command lines.
`-pipe'
Use pipes rather than temporary files for communication between the
various stages of compilation. This fails to work on some systems
where the assembler is unable to read from a pipe; but the GNU
assembler has no trouble.
`-combine'
If you are compiling multiple source files, this option tells the
driver to pass all the source files to the compiler at once (for
those languages for which the compiler can handle this). This
will allow intermodule analysis (IMA) to be performed by the
compiler. Currently the only language for which this is supported
is C. If you pass source files for multiple languages to the
driver, using this option, the driver will invoke the compiler(s)
that support IMA once each, passing each compiler all the source
files appropriate for it. For those languages that do not support
IMA this option will be ignored, and the compiler will be invoked
once for each source file in that language. If you use this
option in conjunction with `-save-temps', the compiler will
generate multiple pre-processed files (one for each source file),
but only one (combined) `.o' or `.s' file.
`--help'
Print (on the standard output) a description of the command line
options understood by `gcc'. If the `-v' option is also specified
then `--help' will also be passed on to the various processes
invoked by `gcc', so that they can display the command line options
they accept. If the `-Wextra' option is also specified then
command line options which have no documentation associated with
them will also be displayed.
`--target-help'
Print (on the standard output) a description of target specific
command line options for each tool.
`--version'
Display the version number and copyrights of the invoked GCC.
`@FILE'
Read command-line options from FILE. The options read are
inserted in place of the original @FILE option. If FILE does not
exist, or cannot be read, then the option will be treated
literally, and not removed.
Options in FILE are separated by whitespace. A whitespace
character may be included in an option by surrounding the entire
option in either single or double quotes. Any character
(including a backslash) may be included by prefixing the character
to be included with a backslash. The FILE may itself contain
additional @FILE options; any such options will be processed
recursively.
File: gcc.info, Node: Invoking G++, Next: C Dialect Options, Prev: Overall Options, Up: Invoking GCC
3.3 Compiling C++ Programs
==========================
C++ source files conventionally use one of the suffixes `.C', `.cc',
`.cpp', `.CPP', `.c++', `.cp', or `.cxx'; C++ header files often use
`.hh' or `.H'; and preprocessed C++ files use the suffix `.ii'. GCC
recognizes files with these names and compiles them as C++ programs
even if you call the compiler the same way as for compiling C programs
(usually with the name `gcc').
However, the use of `gcc' does not add the C++ library. `g++' is a
program that calls GCC and treats `.c', `.h' and `.i' files as C++
source files instead of C source files unless `-x' is used, and
automatically specifies linking against the C++ library. This program
is also useful when precompiling a C header file with a `.h' extension
for use in C++ compilations. On many systems, `g++' is also installed
with the name `c++'.
When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs. *Note
Options Controlling C Dialect: C Dialect Options, for explanations of
options for languages related to C. *Note Options Controlling C++
Dialect: C++ Dialect Options, for explanations of options that are
meaningful only for C++ programs.
File: gcc.info, Node: C Dialect Options, Next: C++ Dialect Options, Prev: Invoking G++, Up: Invoking GCC
3.4 Options Controlling C Dialect
=================================
The following options control the dialect of C (or languages derived
from C, such as C++, Objective-C and Objective-C++) that the compiler
accepts:
`-ansi'
In C mode, support all ISO C90 programs. In C++ mode, remove GNU
extensions that conflict with ISO C++.
This turns off certain features of GCC that are incompatible with
ISO C90 (when compiling C code), or of standard C++ (when
compiling C++ code), such as the `asm' and `typeof' keywords, and
predefined macros such as `unix' and `vax' that identify the type
of system you are using. It also enables the undesirable and
rarely used ISO trigraph feature. For the C compiler, it disables
recognition of C++ style `//' comments as well as the `inline'
keyword.
The alternate keywords `__asm__', `__extension__', `__inline__'
and `__typeof__' continue to work despite `-ansi'. You would not
want to use them in an ISO C program, of course, but it is useful
to put them in header files that might be included in compilations
done with `-ansi'. Alternate predefined macros such as `__unix__'
and `__vax__' are also available, with or without `-ansi'.
The `-ansi' option does not cause non-ISO programs to be rejected
gratuitously. For that, `-pedantic' is required in addition to
`-ansi'. *Note Warning Options::.
The macro `__STRICT_ANSI__' is predefined when the `-ansi' option
is used. Some header files may notice this macro and refrain from
declaring certain functions or defining certain macros that the
ISO standard doesn't call for; this is to avoid interfering with
any programs that might use these names for other things.
Functions which would normally be built in but do not have
semantics defined by ISO C (such as `alloca' and `ffs') are not
built-in functions with `-ansi' is used. *Note Other built-in
functions provided by GCC: Other Builtins, for details of the
functions affected.
`-std='
Determine the language standard. This option is currently only
supported when compiling C or C++. A value for this option must be
provided; possible values are
`c89'
`iso9899:1990'
ISO C90 (same as `-ansi').
`iso9899:199409'
ISO C90 as modified in amendment 1.
`c99'
`c9x'
`iso9899:1999'
`iso9899:199x'
ISO C99. Note that this standard is not yet fully supported;
see `http://gcc.gnu.org/gcc-4.2/c99status.html' for more
information. The names `c9x' and `iso9899:199x' are
deprecated.
`gnu89'
Default, ISO C90 plus GNU extensions (including some C99
features).
`gnu99'
`gnu9x'
ISO C99 plus GNU extensions. When ISO C99 is fully
implemented in GCC, this will become the default. The name
`gnu9x' is deprecated.
`c++98'
The 1998 ISO C++ standard plus amendments.
`gnu++98'
The same as `-std=c++98' plus GNU extensions. This is the
default for C++ code.
Even when this option is not specified, you can still use some of
the features of newer standards in so far as they do not conflict
with previous C standards. For example, you may use
`__restrict__' even when `-std=c99' is not specified.
The `-std' options specifying some version of ISO C have the same
effects as `-ansi', except that features that were not in ISO C90
but are in the specified version (for example, `//' comments and
the `inline' keyword in ISO C99) are not disabled.
*Note Language Standards Supported by GCC: Standards, for details
of these standard versions.
`-fgnu89-inline'
The option `-fgnu89-inline' tells GCC to use the traditional GNU
semantics for `inline' functions when in C99 mode. *Note An
Inline Function is As Fast As a Macro: Inline. Using this option
is roughly equivalent to adding the `gnu_inline' function
attribute to all inline functions (*note Function Attributes::).
This option is accepted by GCC versions 4.1.3 and up. In GCC
versions prior to 4.3, C99 inline semantics are not supported, and
thus this option is effectively assumed to be present regardless
of whether or not it is specified; the only effect of specifying
it explicitly is to disable warnings about using inline functions
in C99 mode. Likewise, the option `-fno-gnu89-inline' is not
supported in versions of GCC before 4.3. It will be supported
only in C99 or gnu99 mode, not in C89 or gnu89 mode.
The preprocesor macros `__GNUC_GNU_INLINE__' and
`__GNUC_STDC_INLINE__' may be used to check which semantics are in
effect for `inline' functions. *Note Common Predefined Macros:
(cpp)Common Predefined Macros.
`-aux-info FILENAME'
Output to the given filename prototyped declarations for all
functions declared and/or defined in a translation unit, including
those in header files. This option is silently ignored in any
language other than C.
Besides declarations, the file indicates, in comments, the origin
of each declaration (source file and line), whether the
declaration was implicit, prototyped or unprototyped (`I', `N' for
new or `O' for old, respectively, in the first character after the
line number and the colon), and whether it came from a declaration
or a definition (`C' or `F', respectively, in the following
character). In the case of function definitions, a K&R-style list
of arguments followed by their declarations is also provided,
inside comments, after the declaration.
`-fno-asm'
Do not recognize `asm', `inline' or `typeof' as a keyword, so that
code can use these words as identifiers. You can use the keywords
`__asm__', `__inline__' and `__typeof__' instead. `-ansi' implies
`-fno-asm'.
In C++, this switch only affects the `typeof' keyword, since `asm'
and `inline' are standard keywords. You may want to use the
`-fno-gnu-keywords' flag instead, which has the same effect. In
C99 mode (`-std=c99' or `-std=gnu99'), this switch only affects
the `asm' and `typeof' keywords, since `inline' is a standard
keyword in ISO C99.
`-fno-builtin'
`-fno-builtin-FUNCTION'
Don't recognize built-in functions that do not begin with
`__builtin_' as prefix. *Note Other built-in functions provided
by GCC: Other Builtins, for details of the functions affected,
including those which are not built-in functions when `-ansi' or
`-std' options for strict ISO C conformance are used because they
do not have an ISO standard meaning.
GCC normally generates special code to handle certain built-in
functions more efficiently; for instance, calls to `alloca' may
become single instructions that adjust the stack directly, and
calls to `memcpy' may become inline copy loops. The resulting
code is often both smaller and faster, but since the function
calls no longer appear as such, you cannot set a breakpoint on
those calls, nor can you change the behavior of the functions by
linking with a different library. In addition, when a function is
recognized as a built-in function, GCC may use information about
that function to warn about problems with calls to that function,
or to generate more efficient code, even if the resulting code
still contains calls to that function. For example, warnings are
given with `-Wformat' for bad calls to `printf', when `printf' is
built in, and `strlen' is known not to modify global memory.
With the `-fno-builtin-FUNCTION' option only the built-in function
FUNCTION is disabled. FUNCTION must not begin with `__builtin_'.
If a function is named this is not built-in in this version of
GCC, this option is ignored. There is no corresponding
`-fbuiltin-FUNCTION' option; if you wish to enable built-in
functions selectively when using `-fno-builtin' or
`-ffreestanding', you may define macros such as:
#define abs(n) __builtin_abs ((n))
#define strcpy(d, s) __builtin_strcpy ((d), (s))
`-fhosted'
Assert that compilation takes place in a hosted environment. This
implies `-fbuiltin'. A hosted environment is one in which the
entire standard library is available, and in which `main' has a
return type of `int'. Examples are nearly everything except a
kernel. This is equivalent to `-fno-freestanding'.
`-ffreestanding'
Assert that compilation takes place in a freestanding environment.
This implies `-fno-builtin'. A freestanding environment is one
in which the standard library may not exist, and program startup
may not necessarily be at `main'. The most obvious example is an
OS kernel. This is equivalent to `-fno-hosted'.
*Note Language Standards Supported by GCC: Standards, for details
of freestanding and hosted environments.
`-fopenmp'
Enable handling of OpenMP directives `#pragma omp' in C/C++ and
`!$omp' in Fortran. When `-fopenmp' is specified, the compiler
generates parallel code according to the OpenMP Application
Program Interface v2.5 `http://www.openmp.org/'.
`-fms-extensions'
Accept some non-standard constructs used in Microsoft header files.
Some cases of unnamed fields in structures and unions are only
accepted with this option. *Note Unnamed struct/union fields
within structs/unions: Unnamed Fields, for details.
`-trigraphs'
Support ISO C trigraphs. The `-ansi' option (and `-std' options
for strict ISO C conformance) implies `-trigraphs'.
`-no-integrated-cpp'
Performs a compilation in two passes: preprocessing and compiling.
This option allows a user supplied "cc1", "cc1plus", or "cc1obj"
via the `-B' option. The user supplied compilation step can then
add in an additional preprocessing step after normal preprocessing
but before compiling. The default is to use the integrated cpp
(internal cpp)
The semantics of this option will change if "cc1", "cc1plus", and
"cc1obj" are merged.
`-traditional'
`-traditional-cpp'
Formerly, these options caused GCC to attempt to emulate a
pre-standard C compiler. They are now only supported with the
`-E' switch. The preprocessor continues to support a pre-standard
mode. See the GNU CPP manual for details.
`-fcond-mismatch'
Allow conditional expressions with mismatched types in the second
and third arguments. The value of such an expression is void.
This option is not supported for C++.
`-funsigned-char'
Let the type `char' be unsigned, like `unsigned char'.
Each kind of machine has a default for what `char' should be. It
is either like `unsigned char' by default or like `signed char' by
default.
Ideally, a portable program should always use `signed char' or
`unsigned char' when it depends on the signedness of an object.
But many programs have been written to use plain `char' and expect
it to be signed, or expect it to be unsigned, depending on the
machines they were written for. This option, and its inverse, let
you make such a program work with the opposite default.
The type `char' is always a distinct type from each of `signed
char' or `unsigned char', even though its behavior is always just
like one of those two.
`-fsigned-char'
Let the type `char' be signed, like `signed char'.
Note that this is equivalent to `-fno-unsigned-char', which is the
negative form of `-funsigned-char'. Likewise, the option
`-fno-signed-char' is equivalent to `-funsigned-char'.
`-fsigned-bitfields'
`-funsigned-bitfields'
`-fno-signed-bitfields'
`-fno-unsigned-bitfields'
These options control whether a bit-field is signed or unsigned,
when the declaration does not use either `signed' or `unsigned'.
By default, such a bit-field is signed, because this is
consistent: the basic integer types such as `int' are signed types.
File: gcc.info, Node: C++ Dialect Options, Next: Objective-C and Objective-C++ Dialect Options, Prev: C Dialect Options, Up: Invoking GCC
3.5 Options Controlling C++ Dialect
===================================
This section describes the command-line options that are only meaningful
for C++ programs; but you can also use most of the GNU compiler options
regardless of what language your program is in. For example, you might
compile a file `firstClass.C' like this:
g++ -g -frepo -O -c firstClass.C
In this example, only `-frepo' is an option meant only for C++
programs; you can use the other options with any language supported by
GCC.
Here is a list of options that are _only_ for compiling C++ programs:
`-fabi-version=N'
Use version N of the C++ ABI. Version 2 is the version of the C++
ABI that first appeared in G++ 3.4. Version 1 is the version of
the C++ ABI that first appeared in G++ 3.2. Version 0 will always
be the version that conforms most closely to the C++ ABI
specification. Therefore, the ABI obtained using version 0 will
change as ABI bugs are fixed.
The default is version 2.
`-fno-access-control'
Turn off all access checking. This switch is mainly useful for
working around bugs in the access control code.
`-fcheck-new'
Check that the pointer returned by `operator new' is non-null
before attempting to modify the storage allocated. This check is
normally unnecessary because the C++ standard specifies that
`operator new' will only return `0' if it is declared `throw()',
in which case the compiler will always check the return value even
without this option. In all other cases, when `operator new' has
a non-empty exception specification, memory exhaustion is
signalled by throwing `std::bad_alloc'. See also `new (nothrow)'.
`-fconserve-space'
Put uninitialized or runtime-initialized global variables into the
common segment, as C does. This saves space in the executable at
the cost of not diagnosing duplicate definitions. If you compile
with this flag and your program mysteriously crashes after
`main()' has completed, you may have an object that is being
destroyed twice because two definitions were merged.
This option is no longer useful on most targets, now that support
has been added for putting variables into BSS without making them
common.
`-ffriend-injection'
Inject friend functions into the enclosing namespace, so that they
are visible outside the scope of the class in which they are
declared. Friend functions were documented to work this way in
the old Annotated C++ Reference Manual, and versions of G++ before
4.1 always worked that way. However, in ISO C++ a friend function
which is not declared in an enclosing scope can only be found
using argument dependent lookup. This option causes friends to be
injected as they were in earlier releases.
This option is for compatibility, and may be removed in a future
release of G++.
`-fno-elide-constructors'
The C++ standard allows an implementation to omit creating a
temporary which is only used to initialize another object of the
same type. Specifying this option disables that optimization, and
forces G++ to call the copy constructor in all cases.
`-fno-enforce-eh-specs'
Don't generate code to check for violation of exception
specifications at runtime. This option violates the C++ standard,
but may be useful for reducing code size in production builds,
much like defining `NDEBUG'. This does not give user code
permission to throw exceptions in violation of the exception
specifications; the compiler will still optimize based on the
specifications, so throwing an unexpected exception will result in
undefined behavior.
`-ffor-scope'
`-fno-for-scope'
If `-ffor-scope' is specified, the scope of variables declared in
a for-init-statement is limited to the `for' loop itself, as
specified by the C++ standard. If `-fno-for-scope' is specified,
the scope of variables declared in a for-init-statement extends to
the end of the enclosing scope, as was the case in old versions of
G++, and other (traditional) implementations of C++.
The default if neither flag is given to follow the standard, but
to allow and give a warning for old-style code that would
otherwise be invalid, or have different behavior.
`-fno-gnu-keywords'
Do not recognize `typeof' as a keyword, so that code can use this
word as an identifier. You can use the keyword `__typeof__'
instead. `-ansi' implies `-fno-gnu-keywords'.
`-fno-implicit-templates'
Never emit code for non-inline templates which are instantiated
implicitly (i.e. by use); only emit code for explicit
instantiations. *Note Template Instantiation::, for more
information.
`-fno-implicit-inline-templates'
Don't emit code for implicit instantiations of inline templates,
either. The default is to handle inlines differently so that
compiles with and without optimization will need the same set of
explicit instantiations.
`-fno-implement-inlines'
To save space, do not emit out-of-line copies of inline functions
controlled by `#pragma implementation'. This will cause linker
errors if these functions are not inlined everywhere they are
called.
`-fms-extensions'
Disable pedantic warnings about constructs used in MFC, such as
implicit int and getting a pointer to member function via
non-standard syntax.
`-fno-nonansi-builtins'
Disable built-in declarations of functions that are not mandated by
ANSI/ISO C. These include `ffs', `alloca', `_exit', `index',
`bzero', `conjf', and other related functions.
`-fno-operator-names'
Do not treat the operator name keywords `and', `bitand', `bitor',
`compl', `not', `or' and `xor' as synonyms as keywords.
`-fno-optional-diags'
Disable diagnostics that the standard says a compiler does not
need to issue. Currently, the only such diagnostic issued by G++
is the one for a name having multiple meanings within a class.
`-fpermissive'
Downgrade some diagnostics about nonconformant code from errors to
warnings. Thus, using `-fpermissive' will allow some
nonconforming code to compile.
`-frepo'
Enable automatic template instantiation at link time. This option
also implies `-fno-implicit-templates'. *Note Template
Instantiation::, for more information.
`-fno-rtti'
Disable generation of information about every class with virtual
functions for use by the C++ runtime type identification features
(`dynamic_cast' and `typeid'). If you don't use those parts of
the language, you can save some space by using this flag. Note
that exception handling uses the same information, but it will
generate it as needed. The `dynamic_cast' operator can still be
used for casts that do not require runtime type information, i.e.
casts to `void *' or to unambiguous base classes.
`-fstats'
Emit statistics about front-end processing at the end of the
compilation. This information is generally only useful to the G++
development team.
`-ftemplate-depth-N'
Set the maximum instantiation depth for template classes to N. A
limit on the template instantiation depth is needed to detect
endless recursions during template class instantiation. ANSI/ISO
C++ conforming programs must not rely on a maximum depth greater
than 17.
`-fno-threadsafe-statics'
Do not emit the extra code to use the routines specified in the C++
ABI for thread-safe initialization of local statics. You can use
this option to reduce code size slightly in code that doesn't need
to be thread-safe.
`-fuse-cxa-atexit'
Register destructors for objects with static storage duration with
the `__cxa_atexit' function rather than the `atexit' function.
This option is required for fully standards-compliant handling of
static destructors, but will only work if your C library supports
`__cxa_atexit'.
`-fno-use-cxa-get-exception-ptr'
Don't use the `__cxa_get_exception_ptr' runtime routine. This
will cause `std::uncaught_exception' to be incorrect, but is
necessary if the runtime routine is not available.
`-fvisibility-inlines-hidden'
This switch declares that the user does not attempt to compare
pointers to inline methods where the addresses of the two functions
were taken in different shared objects.
The effect of this is that GCC may, effectively, mark inline
methods with `__attribute__ ((visibility ("hidden")))' so that
they do not appear in the export table of a DSO and do not require
a PLT indirection when used within the DSO. Enabling this option
can have a dramatic effect on load and link times of a DSO as it
massively reduces the size of the dynamic export table when the
library makes heavy use of templates.
The behaviour of this switch is not quite the same as marking the
methods as hidden directly, because it does not affect static
variables local to the function or cause the compiler to deduce
that the function is defined in only one shared object.
You may mark a method as having a visibility explicitly to negate
the effect of the switch for that method. For example, if you do
want to compare pointers to a particular inline method, you might
mark it as having default visibility. Marking the enclosing class
with explicit visibility will have no effect.
Explicitly instantiated inline methods are unaffected by this
option as their linkage might otherwise cross a shared library
boundary. *Note Template Instantiation::.
`-fno-weak'
Do not use weak symbol support, even if it is provided by the
linker. By default, G++ will use weak symbols if they are
available. This option exists only for testing, and should not be
used by end-users; it will result in inferior code and has no
benefits. This option may be removed in a future release of G++.
`-nostdinc++'
Do not search for header files in the standard directories
specific to C++, but do still search the other standard
directories. (This option is used when building the C++ library.)
In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:
`-fno-default-inline'
Do not assume `inline' for functions defined inside a class scope.
*Note Options That Control Optimization: Optimize Options. Note
that these functions will have linkage like inline functions; they
just won't be inlined by default.
`-Wabi (C++ only)'
Warn when G++ generates code that is probably not compatible with
the vendor-neutral C++ ABI. Although an effort has been made to
warn about all such cases, there are probably some cases that are
not warned about, even though G++ is generating incompatible code.
There may also be cases where warnings are emitted even though
the code that is generated will be compatible.
You should rewrite your code to avoid these warnings if you are
concerned about the fact that code generated by G++ may not be
binary compatible with code generated by other compilers.
The known incompatibilities at this point include:
* Incorrect handling of tail-padding for bit-fields. G++ may
attempt to pack data into the same byte as a base class. For
example:
struct A { virtual void f(); int f1 : 1; };
struct B : public A { int f2 : 1; };
In this case, G++ will place `B::f2' into the same byte
as`A::f1'; other compilers will not. You can avoid this
problem by explicitly padding `A' so that its size is a
multiple of the byte size on your platform; that will cause
G++ and other compilers to layout `B' identically.
* Incorrect handling of tail-padding for virtual bases. G++
does not use tail padding when laying out virtual bases. For
example:
struct A { virtual void f(); char c1; };
struct B { B(); char c2; };
struct C : public A, public virtual B {};
In this case, G++ will not place `B' into the tail-padding for
`A'; other compilers will. You can avoid this problem by
explicitly padding `A' so that its size is a multiple of its
alignment (ignoring virtual base classes); that will cause
G++ and other compilers to layout `C' identically.
* Incorrect handling of bit-fields with declared widths greater
than that of their underlying types, when the bit-fields
appear in a union. For example:
union U { int i : 4096; };
Assuming that an `int' does not have 4096 bits, G++ will make
the union too small by the number of bits in an `int'.
* Empty classes can be placed at incorrect offsets. For
example:
struct A {};
struct B {
A a;
virtual void f ();
};
struct C : public B, public A {};
G++ will place the `A' base class of `C' at a nonzero offset;
it should be placed at offset zero. G++ mistakenly believes
that the `A' data member of `B' is already at offset zero.
* Names of template functions whose types involve `typename' or
template template parameters can be mangled incorrectly.
template <typename Q>
void f(typename Q::X) {}
template <template <typename> class Q>
void f(typename Q<int>::X) {}
Instantiations of these templates may be mangled incorrectly.
`-Wctor-dtor-privacy (C++ only)'
Warn when a class seems unusable because all the constructors or
destructors in that class are private, and it has neither friends
nor public static member functions.
`-Wnon-virtual-dtor (C++ only)'
Warn when a class appears to be polymorphic, thereby requiring a
virtual destructor, yet it declares a non-virtual one. This
warning is also enabled if -Weffc++ is specified.
`-Wreorder (C++ only)'
Warn when the order of member initializers given in the code does
not match the order in which they must be executed. For instance:
struct A {
int i;
int j;
A(): j (0), i (1) { }
};
The compiler will rearrange the member initializers for `i' and
`j' to match the declaration order of the members, emitting a
warning to that effect. This warning is enabled by `-Wall'.
The following `-W...' options are not affected by `-Wall'.
`-Weffc++ (C++ only)'
Warn about violations of the following style guidelines from Scott
Meyers' `Effective C++' book:
* Item 11: Define a copy constructor and an assignment
operator for classes with dynamically allocated memory.
* Item 12: Prefer initialization to assignment in constructors.
* Item 14: Make destructors virtual in base classes.
* Item 15: Have `operator=' return a reference to `*this'.
* Item 23: Don't try to return a reference when you must
return an object.
Also warn about violations of the following style guidelines from
Scott Meyers' `More Effective C++' book:
* Item 6: Distinguish between prefix and postfix forms of
increment and decrement operators.
* Item 7: Never overload `&&', `||', or `,'.
When selecting this option, be aware that the standard library
headers do not obey all of these guidelines; use `grep -v' to
filter out those warnings.
`-Wno-deprecated (C++ only)'
Do not warn about usage of deprecated features. *Note Deprecated
Features::.
`-Wstrict-null-sentinel (C++ only)'
Warn also about the use of an uncasted `NULL' as sentinel. When
compiling only with GCC this is a valid sentinel, as `NULL' is
defined to `__null'. Although it is a null pointer constant not a
null pointer, it is guaranteed to of the same size as a pointer.
But this use is not portable across different compilers.
`-Wno-non-template-friend (C++ only)'
Disable warnings when non-templatized friend functions are declared
within a template. Since the advent of explicit template
specification support in G++, if the name of the friend is an
unqualified-id (i.e., `friend foo(int)'), the C++ language
specification demands that the friend declare or define an
ordinary, nontemplate function. (Section 14.5.3). Before G++
implemented explicit specification, unqualified-ids could be
interpreted as a particular specialization of a templatized
function. Because this non-conforming behavior is no longer the
default behavior for G++, `-Wnon-template-friend' allows the
compiler to check existing code for potential trouble spots and is
on by default. This new compiler behavior can be turned off with
`-Wno-non-template-friend' which keeps the conformant compiler code
but disables the helpful warning.
`-Wold-style-cast (C++ only)'
Warn if an old-style (C-style) cast to a non-void type is used
within a C++ program. The new-style casts (`dynamic_cast',
`static_cast', `reinterpret_cast', and `const_cast') are less
vulnerable to unintended effects and much easier to search for.
`-Woverloaded-virtual (C++ only)'
Warn when a function declaration hides virtual functions from a
base class. For example, in:
struct A {
virtual void f();
};
struct B: public A {
void f(int);
};
the `A' class version of `f' is hidden in `B', and code like:
B* b;
b->f();
will fail to compile.
`-Wno-pmf-conversions (C++ only)'
Disable the diagnostic for converting a bound pointer to member
function to a plain pointer.
`-Wsign-promo (C++ only)'
Warn when overload resolution chooses a promotion from unsigned or
enumerated type to a signed type, over a conversion to an unsigned
type of the same size. Previous versions of G++ would try to
preserve unsignedness, but the standard mandates the current
behavior.
struct A {
operator int ();
A& operator = (int);
};
main ()
{
A a,b;
a = b;
}
In this example, G++ will synthesize a default `A& operator =
(const A&);', while cfront will use the user-defined `operator ='.
File: gcc.info, Node: Objective-C and Objective-C++ Dialect Options, Next: Language Independent Options, Prev: C++ Dialect Options, Up: Invoking GCC
3.6 Options Controlling Objective-C and Objective-C++ Dialects
==============================================================
(NOTE: This manual does not describe the Objective-C and Objective-C++
languages themselves. See *Note Language Standards Supported by GCC:
Standards, for references.)
This section describes the command-line options that are only
meaningful for Objective-C and Objective-C++ programs, but you can also
use most of the language-independent GNU compiler options. For
example, you might compile a file `some_class.m' like this:
gcc -g -fgnu-runtime -O -c some_class.m
In this example, `-fgnu-runtime' is an option meant only for
Objective-C and Objective-C++ programs; you can use the other options
with any language supported by GCC.
Note that since Objective-C is an extension of the C language,
Objective-C compilations may also use options specific to the C
front-end (e.g., `-Wtraditional'). Similarly, Objective-C++
compilations may use C++-specific options (e.g., `-Wabi').
Here is a list of options that are _only_ for compiling Objective-C
and Objective-C++ programs:
`-fconstant-string-class=CLASS-NAME'
Use CLASS-NAME as the name of the class to instantiate for each
literal string specified with the syntax `@"..."'. The default
class name is `NXConstantString' if the GNU runtime is being used,
and `NSConstantString' if the NeXT runtime is being used (see
below). The `-fconstant-cfstrings' option, if also present, will
override the `-fconstant-string-class' setting and cause `@"..."'
literals to be laid out as constant CoreFoundation strings.
`-fgnu-runtime'
Generate object code compatible with the standard GNU Objective-C
runtime. This is the default for most types of systems.
`-fnext-runtime'
Generate output compatible with the NeXT runtime. This is the
default for NeXT-based systems, including Darwin and Mac OS X.
The macro `__NEXT_RUNTIME__' is predefined if (and only if) this
option is used.
`-fno-nil-receivers'
Assume that all Objective-C message dispatches (e.g., `[receiver
message:arg]') in this translation unit ensure that the receiver
is not `nil'. This allows for more efficient entry points in the
runtime to be used. Currently, this option is only available in
conjunction with the NeXT runtime on Mac OS X 10.3 and later.
`-fobjc-call-cxx-cdtors'
For each Objective-C class, check if any of its instance variables
is a C++ object with a non-trivial default constructor. If so,
synthesize a special `- (id) .cxx_construct' instance method that
will run non-trivial default constructors on any such instance
variables, in order, and then return `self'. Similarly, check if
any instance variable is a C++ object with a non-trivial
destructor, and if so, synthesize a special `- (void)
.cxx_destruct' method that will run all such default destructors,
in reverse order.
The `- (id) .cxx_construct' and/or `- (void) .cxx_destruct' methods
thusly generated will only operate on instance variables declared
in the current Objective-C class, and not those inherited from
superclasses. It is the responsibility of the Objective-C runtime
to invoke all such methods in an object's inheritance hierarchy.
The `- (id) .cxx_construct' methods will be invoked by the runtime
immediately after a new object instance is allocated; the `-
(void) .cxx_destruct' methods will be invoked immediately before
the runtime deallocates an object instance.
As of this writing, only the NeXT runtime on Mac OS X 10.4 and
later has support for invoking the `- (id) .cxx_construct' and `-
(void) .cxx_destruct' methods.
`-fobjc-direct-dispatch'
Allow fast jumps to the message dispatcher. On Darwin this is
accomplished via the comm page.
`-fobjc-exceptions'
Enable syntactic support for structured exception handling in
Objective-C, similar to what is offered by C++ and Java. This
option is unavailable in conjunction with the NeXT runtime on Mac
OS X 10.2 and earlier.
@try {
...
@throw expr;
...
}
@catch (AnObjCClass *exc) {
...
@throw expr;
...
@throw;
...
}
@catch (AnotherClass *exc) {
...
}
@catch (id allOthers) {
...
}
@finally {
...
@throw expr;
...
}
The `@throw' statement may appear anywhere in an Objective-C or
Objective-C++ program; when used inside of a `@catch' block, the
`@throw' may appear without an argument (as shown above), in which
case the object caught by the `@catch' will be rethrown.
Note that only (pointers to) Objective-C objects may be thrown and
caught using this scheme. When an object is thrown, it will be
caught by the nearest `@catch' clause capable of handling objects
of that type, analogously to how `catch' blocks work in C++ and
Java. A `@catch(id ...)' clause (as shown above) may also be
provided to catch any and all Objective-C exceptions not caught by
previous `@catch' clauses (if any).
The `@finally' clause, if present, will be executed upon exit from
the immediately preceding `@try ... @catch' section. This will
happen regardless of whether any exceptions are thrown, caught or
rethrown inside the `@try ... @catch' section, analogously to the
behavior of the `finally' clause in Java.
There are several caveats to using the new exception mechanism:
* Although currently designed to be binary compatible with
`NS_HANDLER'-style idioms provided by the `NSException'
class, the new exceptions can only be used on Mac OS X 10.3
(Panther) and later systems, due to additional functionality
needed in the (NeXT) Objective-C runtime.
* As mentioned above, the new exceptions do not support handling
types other than Objective-C objects. Furthermore, when
used from Objective-C++, the Objective-C exception model does
not interoperate with C++ exceptions at this time. This
means you cannot `@throw' an exception from Objective-C and
`catch' it in C++, or vice versa (i.e., `throw ... @catch').
The `-fobjc-exceptions' switch also enables the use of
synchronization blocks for thread-safe execution:
@synchronized (ObjCClass *guard) {
...
}
Upon entering the `@synchronized' block, a thread of execution
shall first check whether a lock has been placed on the
corresponding `guard' object by another thread. If it has, the
current thread shall wait until the other thread relinquishes its
lock. Once `guard' becomes available, the current thread will
place its own lock on it, execute the code contained in the
`@synchronized' block, and finally relinquish the lock (thereby
making `guard' available to other threads).
Unlike Java, Objective-C does not allow for entire methods to be
marked `@synchronized'. Note that throwing exceptions out of
`@synchronized' blocks is allowed, and will cause the guarding
object to be unlocked properly.
`-fobjc-gc'
Enable garbage collection (GC) in Objective-C and Objective-C++
programs.
`-freplace-objc-classes'
Emit a special marker instructing `ld(1)' not to statically link in
the resulting object file, and allow `dyld(1)' to load it in at
run time instead. This is used in conjunction with the
Fix-and-Continue debugging mode, where the object file in question
may be recompiled and dynamically reloaded in the course of
program execution, without the need to restart the program itself.
Currently, Fix-and-Continue functionality is only available in
conjunction with the NeXT runtime on Mac OS X 10.3 and later.
`-fzero-link'
When compiling for the NeXT runtime, the compiler ordinarily
replaces calls to `objc_getClass("...")' (when the name of the
class is known at compile time) with static class references that
get initialized at load time, which improves run-time performance.
Specifying the `-fzero-link' flag suppresses this behavior and
causes calls to `objc_getClass("...")' to be retained. This is
useful in Zero-Link debugging mode, since it allows for individual
class implementations to be modified during program execution.
`-gen-decls'
Dump interface declarations for all classes seen in the source
file to a file named `SOURCENAME.decl'.
`-Wassign-intercept'
Warn whenever an Objective-C assignment is being intercepted by the
garbage collector.
`-Wno-protocol'
If a class is declared to implement a protocol, a warning is
issued for every method in the protocol that is not implemented by
the class. The default behavior is to issue a warning for every
method not explicitly implemented in the class, even if a method
implementation is inherited from the superclass. If you use the
`-Wno-protocol' option, then methods inherited from the superclass
are considered to be implemented, and no warning is issued for
them.
`-Wselector'
Warn if multiple methods of different types for the same selector
are found during compilation. The check is performed on the list
of methods in the final stage of compilation. Additionally, a
check is performed for each selector appearing in a
`@selector(...)' expression, and a corresponding method for that
selector has been found during compilation. Because these checks
scan the method table only at the end of compilation, these
warnings are not produced if the final stage of compilation is not
reached, for example because an error is found during compilation,
or because the `-fsyntax-only' option is being used.
`-Wstrict-selector-match'
Warn if multiple methods with differing argument and/or return
types are found for a given selector when attempting to send a
message using this selector to a receiver of type `id' or `Class'.
When this flag is off (which is the default behavior), the
compiler will omit such warnings if any differences found are
confined to types which share the same size and alignment.
`-Wundeclared-selector'
Warn if a `@selector(...)' expression referring to an undeclared
selector is found. A selector is considered undeclared if no
method with that name has been declared before the
`@selector(...)' expression, either explicitly in an `@interface'
or `@protocol' declaration, or implicitly in an `@implementation'
section. This option always performs its checks as soon as a
`@selector(...)' expression is found, while `-Wselector' only
performs its checks in the final stage of compilation. This also
enforces the coding style convention that methods and selectors
must be declared before being used.
`-print-objc-runtime-info'
Generate C header describing the largest structure that is passed
by value, if any.
File: gcc.info, Node: Language Independent Options, Next: Warning Options, Prev: Objective-C and Objective-C++ Dialect Options, Up: Invoking GCC
3.7 Options to Control Diagnostic Messages Formatting
=====================================================
Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g. its width, ...). The options described
below can be used to control the diagnostic messages formatting
algorithm, e.g. how many characters per line, how often source location
information should be reported. Right now, only the C++ front end can
honor these options. However it is expected, in the near future, that
the remaining front ends would be able to digest them correctly.
`-fmessage-length=N'
Try to format error messages so that they fit on lines of about N
characters. The default is 72 characters for `g++' and 0 for the
rest of the front ends supported by GCC. If N is zero, then no
line-wrapping will be done; each error message will appear on a
single line.
`-fdiagnostics-show-location=once'
Only meaningful in line-wrapping mode. Instructs the diagnostic
messages reporter to emit _once_ source location information; that
is, in case the message is too long to fit on a single physical
line and has to be wrapped, the source location won't be emitted
(as prefix) again, over and over, in subsequent continuation
lines. This is the default behavior.
`-fdiagnostics-show-location=every-line'
Only meaningful in line-wrapping mode. Instructs the diagnostic
messages reporter to emit the same source location information (as
prefix) for physical lines that result from the process of breaking
a message which is too long to fit on a single line.
`-fdiagnostics-show-option'
This option instructs the diagnostic machinery to add text to each
diagnostic emitted, which indicates which command line option
directly controls that diagnostic, when such an option is known to
the diagnostic machinery.
File: gcc.info, Node: Warning Options, Next: Debugging Options, Prev: Language Independent Options, Up: Invoking GCC
3.8 Options to Request or Suppress Warnings
===========================================
Warnings are diagnostic messages that report constructions which are
not inherently erroneous but which are risky or suggest there may have
been an error.
You can request many specific warnings with options beginning `-W',
for example `-Wimplicit' to request warnings on implicit declarations.
Each of these specific warning options also has a negative form
beginning `-Wno-' to turn off warnings; for example, `-Wno-implicit'.
This manual lists only one of the two forms, whichever is not the
default.
The following options control the amount and kinds of warnings produced
by GCC; for further, language-specific options also refer to *Note C++
Dialect Options:: and *Note Objective-C and Objective-C++ Dialect
Options::.
`-fsyntax-only'
Check the code for syntax errors, but don't do anything beyond
that.
`-pedantic'
Issue all the warnings demanded by strict ISO C and ISO C++;
reject all programs that use forbidden extensions, and some other
programs that do not follow ISO C and ISO C++. For ISO C, follows
the version of the ISO C standard specified by any `-std' option
used.
Valid ISO C and ISO C++ programs should compile properly with or
without this option (though a rare few will require `-ansi' or a
`-std' option specifying the required version of ISO C). However,
without this option, certain GNU extensions and traditional C and
C++ features are supported as well. With this option, they are
rejected.
`-pedantic' does not cause warning messages for use of the
alternate keywords whose names begin and end with `__'. Pedantic
warnings are also disabled in the expression that follows
`__extension__'. However, only system header files should use
these escape routes; application programs should avoid them.
*Note Alternate Keywords::.
Some users try to use `-pedantic' to check programs for strict ISO
C conformance. They soon find that it does not do quite what they
want: it finds some non-ISO practices, but not all--only those for
which ISO C _requires_ a diagnostic, and some others for which
diagnostics have been added.
A feature to report any failure to conform to ISO C might be
useful in some instances, but would require considerable
additional work and would be quite different from `-pedantic'. We
don't have plans to support such a feature in the near future.
Where the standard specified with `-std' represents a GNU extended
dialect of C, such as `gnu89' or `gnu99', there is a corresponding
"base standard", the version of ISO C on which the GNU extended
dialect is based. Warnings from `-pedantic' are given where they
are required by the base standard. (It would not make sense for
such warnings to be given only for features not in the specified
GNU C dialect, since by definition the GNU dialects of C include
all features the compiler supports with the given option, and
there would be nothing to warn about.)
`-pedantic-errors'
Like `-pedantic', except that errors are produced rather than
warnings.
`-w'
Inhibit all warning messages.
`-Wno-import'
Inhibit warning messages about the use of `#import'.
`-Wchar-subscripts'
Warn if an array subscript has type `char'. This is a common cause
of error, as programmers often forget that this type is signed on
some machines. This warning is enabled by `-Wall'.
`-Wcomment'
Warn whenever a comment-start sequence `/*' appears in a `/*'
comment, or whenever a Backslash-Newline appears in a `//' comment.
This warning is enabled by `-Wall'.
`-Wfatal-errors'
This option causes the compiler to abort compilation on the first
error occurred rather than trying to keep going and printing
further error messages.
`-Wformat'
Check calls to `printf' and `scanf', etc., to make sure that the
arguments supplied have types appropriate to the format string
specified, and that the conversions specified in the format string
make sense. This includes standard functions, and others
specified by format attributes (*note Function Attributes::), in
the `printf', `scanf', `strftime' and `strfmon' (an X/Open
extension, not in the C standard) families (or other
target-specific families). Which functions are checked without
format attributes having been specified depends on the standard
version selected, and such checks of functions without the
attribute specified are disabled by `-ffreestanding' or
`-fno-builtin'.
The formats are checked against the format features supported by
GNU libc version 2.2. These include all ISO C90 and C99 features,
as well as features from the Single Unix Specification and some
BSD and GNU extensions. Other library implementations may not
support all these features; GCC does not support warning about
features that go beyond a particular library's limitations.
However, if `-pedantic' is used with `-Wformat', warnings will be
given about format features not in the selected standard version
(but not for `strfmon' formats, since those are not in any version
of the C standard). *Note Options Controlling C Dialect: C
Dialect Options.
Since `-Wformat' also checks for null format arguments for several
functions, `-Wformat' also implies `-Wnonnull'.
`-Wformat' is included in `-Wall'. For more control over some
aspects of format checking, the options `-Wformat-y2k',
`-Wno-format-extra-args', `-Wno-format-zero-length',
`-Wformat-nonliteral', `-Wformat-security', and `-Wformat=2' are
available, but are not included in `-Wall'.
`-Wformat-y2k'
If `-Wformat' is specified, also warn about `strftime' formats
which may yield only a two-digit year.
`-Wno-format-extra-args'
If `-Wformat' is specified, do not warn about excess arguments to a
`printf' or `scanf' format function. The C standard specifies
that such arguments are ignored.
Where the unused arguments lie between used arguments that are
specified with `$' operand number specifications, normally
warnings are still given, since the implementation could not know
what type to pass to `va_arg' to skip the unused arguments.
However, in the case of `scanf' formats, this option will suppress
the warning if the unused arguments are all pointers, since the
Single Unix Specification says that such unused arguments are
allowed.
`-Wno-format-zero-length'
If `-Wformat' is specified, do not warn about zero-length formats.
The C standard specifies that zero-length formats are allowed.
`-Wformat-nonliteral'
If `-Wformat' is specified, also warn if the format string is not a
string literal and so cannot be checked, unless the format function
takes its format arguments as a `va_list'.
`-Wformat-security'
If `-Wformat' is specified, also warn about uses of format
functions that represent possible security problems. At present,
this warns about calls to `printf' and `scanf' functions where the
format string is not a string literal and there are no format
arguments, as in `printf (foo);'. This may be a security hole if
the format string came from untrusted input and contains `%n'.
(This is currently a subset of what `-Wformat-nonliteral' warns
about, but in future warnings may be added to `-Wformat-security'
that are not included in `-Wformat-nonliteral'.)
`-Wformat=2'
Enable `-Wformat' plus format checks not included in `-Wformat'.
Currently equivalent to `-Wformat -Wformat-nonliteral
-Wformat-security -Wformat-y2k'.
`-Wnonnull'
Warn about passing a null pointer for arguments marked as
requiring a non-null value by the `nonnull' function attribute.
`-Wnonnull' is included in `-Wall' and `-Wformat'. It can be
disabled with the `-Wno-nonnull' option.
`-Winit-self (C, C++, Objective-C and Objective-C++ only)'
Warn about uninitialized variables which are initialized with
themselves. Note this option can only be used with the
`-Wuninitialized' option, which in turn only works with `-O1' and
above.
For example, GCC will warn about `i' being uninitialized in the
following snippet only when `-Winit-self' has been specified:
int f()
{
int i = i;
return i;
}
`-Wimplicit-int'
Warn when a declaration does not specify a type. This warning is
enabled by `-Wall'.
`-Wimplicit-function-declaration'
`-Werror-implicit-function-declaration'
Give a warning (or error) whenever a function is used before being
declared. The form `-Wno-error-implicit-function-declaration' is
not supported. This warning is enabled by `-Wall' (as a warning,
not an error).
`-Wimplicit'
Same as `-Wimplicit-int' and `-Wimplicit-function-declaration'.
This warning is enabled by `-Wall'.
`-Wmain'
Warn if the type of `main' is suspicious. `main' should be a
function with external linkage, returning int, taking either zero
arguments, two, or three arguments of appropriate types. This
warning is enabled by `-Wall'.
`-Wmissing-braces'
Warn if an aggregate or union initializer is not fully bracketed.
In the following example, the initializer for `a' is not fully
bracketed, but that for `b' is fully bracketed.
int a[2][2] = { 0, 1, 2, 3 };
int b[2][2] = { { 0, 1 }, { 2, 3 } };
This warning is enabled by `-Wall'.
`-Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)'
Warn if a user-supplied include directory does not exist.
`-Wparentheses'
Warn if parentheses are omitted in certain contexts, such as when
there is an assignment in a context where a truth value is
expected, or when operators are nested whose precedence people
often get confused about. Only the warning for an assignment used
as a truth value is supported when compiling C++; the other
warnings are only supported when compiling C.
Also warn if a comparison like `x<=y<=z' appears; this is
equivalent to `(x<=y ? 1 : 0) <= z', which is a different
interpretation from that of ordinary mathematical notation.
Also warn about constructions where there may be confusion to which
`if' statement an `else' branch belongs. Here is an example of
such a case:
{
if (a)
if (b)
foo ();
else
bar ();
}
In C, every `else' branch belongs to the innermost possible `if'
statement, which in this example is `if (b)'. This is often not
what the programmer expected, as illustrated in the above example
by indentation the programmer chose. When there is the potential
for this confusion, GCC will issue a warning when this flag is
specified. To eliminate the warning, add explicit braces around
the innermost `if' statement so there is no way the `else' could
belong to the enclosing `if'. The resulting code would look like
this:
{
if (a)
{
if (b)
foo ();
else
bar ();
}
}
This warning is enabled by `-Wall'.
`-Wsequence-point'
Warn about code that may have undefined semantics because of
violations of sequence point rules in the C and C++ standards.
The C and C++ standards defines the order in which expressions in
a C/C++ program are evaluated in terms of "sequence points", which
represent a partial ordering between the execution of parts of the
program: those executed before the sequence point, and those
executed after it. These occur after the evaluation of a full
expression (one which is not part of a larger expression), after
the evaluation of the first operand of a `&&', `||', `? :' or `,'
(comma) operator, before a function is called (but after the
evaluation of its arguments and the expression denoting the called
function), and in certain other places. Other than as expressed
by the sequence point rules, the order of evaluation of
subexpressions of an expression is not specified. All these rules
describe only a partial order rather than a total order, since,
for example, if two functions are called within one expression
with no sequence point between them, the order in which the
functions are called is not specified. However, the standards
committee have ruled that function calls do not overlap.
It is not specified when between sequence points modifications to
the values of objects take effect. Programs whose behavior
depends on this have undefined behavior; the C and C++ standards
specify that "Between the previous and next sequence point an
object shall have its stored value modified at most once by the
evaluation of an expression. Furthermore, the prior value shall
be read only to determine the value to be stored.". If a program
breaks these rules, the results on any particular implementation
are entirely unpredictable.
Examples of code with undefined behavior are `a = a++;', `a[n] =
b[n++]' and `a[i++] = i;'. Some more complicated cases are not
diagnosed by this option, and it may give an occasional false
positive result, but in general it has been found fairly effective
at detecting this sort of problem in programs.
The standard is worded confusingly, therefore there is some debate
over the precise meaning of the sequence point rules in subtle
cases. Links to discussions of the problem, including proposed
formal definitions, may be found on the GCC readings page, at
`http://gcc.gnu.org/readings.html'.
This warning is enabled by `-Wall' for C and C++.
`-Wreturn-type'
Warn whenever a function is defined with a return-type that
defaults to `int'. Also warn about any `return' statement with no
return-value in a function whose return-type is not `void'.
For C, also warn if the return type of a function has a type
qualifier such as `const'. Such a type qualifier has no effect,
since the value returned by a function is not an lvalue. ISO C
prohibits qualified `void' return types on function definitions,
so such return types always receive a warning even without this
option.
For C++, a function without return type always produces a
diagnostic message, even when `-Wno-return-type' is specified.
The only exceptions are `main' and functions defined in system
headers.
This warning is enabled by `-Wall'.
`-Wswitch'
Warn whenever a `switch' statement has an index of enumerated type
and lacks a `case' for one or more of the named codes of that
enumeration. (The presence of a `default' label prevents this
warning.) `case' labels outside the enumeration range also
provoke warnings when this option is used. This warning is
enabled by `-Wall'.
`-Wswitch-default'
Warn whenever a `switch' statement does not have a `default' case.
`-Wswitch-enum'
Warn whenever a `switch' statement has an index of enumerated type
and lacks a `case' for one or more of the named codes of that
enumeration. `case' labels outside the enumeration range also
provoke warnings when this option is used.
`-Wtrigraphs'
Warn if any trigraphs are encountered that might change the
meaning of the program (trigraphs within comments are not warned
about). This warning is enabled by `-Wall'.
`-Wunused-function'
Warn whenever a static function is declared but not defined or a
non-inline static function is unused. This warning is enabled by
`-Wall'.
`-Wunused-label'
Warn whenever a label is declared but not used. This warning is
enabled by `-Wall'.
To suppress this warning use the `unused' attribute (*note
Variable Attributes::).
`-Wunused-parameter'
Warn whenever a function parameter is unused aside from its
declaration.
To suppress this warning use the `unused' attribute (*note
Variable Attributes::).
`-Wunused-variable'
Warn whenever a local variable or non-constant static variable is
unused aside from its declaration. This warning is enabled by
`-Wall'.
To suppress this warning use the `unused' attribute (*note
Variable Attributes::).
`-Wunused-value'
Warn whenever a statement computes a result that is explicitly not
used. This warning is enabled by `-Wall'.
To suppress this warning cast the expression to `void'.
`-Wunused'
All the above `-Wunused' options combined.
In order to get a warning about an unused function parameter, you
must either specify `-Wextra -Wunused' (note that `-Wall' implies
`-Wunused'), or separately specify `-Wunused-parameter'.
`-Wuninitialized'
Warn if an automatic variable is used without first being
initialized or if a variable may be clobbered by a `setjmp' call.
These warnings are possible only in optimizing compilation,
because they require data flow information that is computed only
when optimizing. If you do not specify `-O', you will not get
these warnings. Instead, GCC will issue a warning about
`-Wuninitialized' requiring `-O'.
If you want to warn about code which uses the uninitialized value
of the variable in its own initializer, use the `-Winit-self'
option.
These warnings occur for individual uninitialized or clobbered
elements of structure, union or array variables as well as for
variables which are uninitialized or clobbered as a whole. They do
not occur for variables or elements declared `volatile'. Because
these warnings depend on optimization, the exact variables or
elements for which there are warnings will depend on the precise
optimization options and version of GCC used.
Note that there may be no warning about a variable that is used
only to compute a value that itself is never used, because such
computations may be deleted by data flow analysis before the
warnings are printed.
These warnings are made optional because GCC is not smart enough
to see all the reasons why the code might be correct despite
appearing to have an error. Here is one example of how this can
happen:
{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}
If the value of `y' is always 1, 2 or 3, then `x' is always
initialized, but GCC doesn't know this. Here is another common
case:
{
int save_y;
if (change_y) save_y = y, y = new_y;
...
if (change_y) y = save_y;
}
This has no bug because `save_y' is used only if it is set.
This option also warns when a non-volatile automatic variable
might be changed by a call to `longjmp'. These warnings as well
are possible only in optimizing compilation.
The compiler sees only the calls to `setjmp'. It cannot know
where `longjmp' will be called; in fact, a signal handler could
call it at any point in the code. As a result, you may get a
warning even when there is in fact no problem because `longjmp'
cannot in fact be called at the place which would cause a problem.
Some spurious warnings can be avoided if you declare all the
functions you use that never return as `noreturn'. *Note Function
Attributes::.
This warning is enabled by `-Wall'.
`-Wunknown-pragmas'
Warn when a #pragma directive is encountered which is not
understood by GCC. If this command line option is used, warnings
will even be issued for unknown pragmas in system header files.
This is not the case if the warnings were only enabled by the
`-Wall' command line option.
`-Wno-pragmas'
Do not warn about misuses of pragmas, such as incorrect parameters,
invalid syntax, or conflicts between pragmas. See also
`-Wunknown-pragmas'.
`-Wstrict-aliasing'
This option is only active when `-fstrict-aliasing' is active. It
warns about code which might break the strict aliasing rules that
the compiler is using for optimization. The warning does not
catch all cases, but does attempt to catch the more common
pitfalls. It is included in `-Wall'.
`-Wstrict-aliasing=2'
This option is only active when `-fstrict-aliasing' is active. It
warns about code which might break the strict aliasing rules that
the compiler is using for optimization. This warning catches more
cases than `-Wstrict-aliasing', but it will also give a warning
for some ambiguous cases that are safe.
`-Wstrict-overflow'
`-Wstrict-overflow=N'
This option is only active when `-fstrict-overflow' is active. It
warns about cases where the compiler optimizes based on the
assumption that signed overflow does not occur. Note that it does
not warn about all cases where the code might overflow: it only
warns about cases where the compiler implements some optimization.
Thus this warning depends on the optimization level.
An optimization which assumes that signed overflow does not occur
is perfectly safe if the values of the variables involved are such
that overflow never does, in fact, occur. Therefore this warning
can easily give a false positive: a warning about code which is not
actually a problem. To help focus on important issues, several
warning levels are defined. No warnings are issued for the use of
undefined signed overflow when estimating how many iterations a
loop will require, in particular when determining whether a loop
will be executed at all.
`-Wstrict-overflow=1'
Warn about cases which are both questionable and easy to
avoid. For example: `x + 1 > x'; with `-fstrict-overflow',
the compiler will simplify this to `1'. This level of
`-Wstrict-overflow' is enabled by `-Wall'; higher levels are
not, and must be explicitly requested.
`-Wstrict-overflow=2'
Also warn about other cases where a comparison is simplified
to a constant. For example: `abs (x) >= 0'. This can only be
simplified when `-fstrict-overflow' is in effect, because
`abs (INT_MIN)' overflows to `INT_MIN', which is less than
zero. `-Wstrict-overflow' (with no level) is the same as
`-Wstrict-overflow=2'.
`-Wstrict-overflow=3'
Also warn about other cases where a comparison is simplified.
For example: `x + 1 > 1' will be simplified to `x > 0'.
`-Wstrict-overflow=4'
Also warn about other simplifications not covered by the
above cases. For example: `(x * 10) / 5' will be simplified
to `x * 2'.
`-Wstrict-overflow=5'
Also warn about cases where the compiler reduces the
magnitude of a constant involved in a comparison. For
example: `x + 2 > y' will be simplified to `x + 1 >= y'.
This is reported only at the highest warning level because
this simplification applies to many comparisons, so this
warning level will give a very large number of false
positives.
`-Wall'
All of the above `-W' options combined. This enables all the
warnings about constructions that some users consider
questionable, and that are easy to avoid (or modify to prevent the
warning), even in conjunction with macros. This also enables some
language-specific warnings described in *Note C++ Dialect
Options:: and *Note Objective-C and Objective-C++ Dialect
Options::.
The following `-W...' options are not implied by `-Wall'. Some of
them warn about constructions that users generally do not consider
questionable, but which occasionally you might wish to check for;
others warn about constructions that are necessary or hard to avoid in
some cases, and there is no simple way to modify the code to suppress
the warning.
`-Wextra'
(This option used to be called `-W'. The older name is still
supported, but the newer name is more descriptive.) Print extra
warning messages for these events:
* A function can return either with or without a value.
(Falling off the end of the function body is considered
returning without a value.) For example, this function would
evoke such a warning:
foo (a)
{
if (a > 0)
return a;
}
* An expression-statement or the left-hand side of a comma
expression contains no side effects. To suppress the
warning, cast the unused expression to void. For example, an
expression such as `x[i,j]' will cause a warning, but
`x[(void)i,j]' will not.
* An unsigned value is compared against zero with `<' or `>='.
* Storage-class specifiers like `static' are not the first
things in a declaration. According to the C Standard, this
usage is obsolescent.
* If `-Wall' or `-Wunused' is also specified, warn about unused
arguments.
* A comparison between signed and unsigned values could produce
an incorrect result when the signed value is converted to
unsigned. (But don't warn if `-Wno-sign-compare' is also
specified.)
* An aggregate has an initializer which does not initialize all
members. This warning can be independently controlled by
`-Wmissing-field-initializers'.
* An initialized field without side effects is overridden when
using designated initializers (*note Designated Initializers:
Designated Inits.). This warning can be independently
controlled by `-Woverride-init'.
* A function parameter is declared without a type specifier in
K&R-style functions:
void foo(bar) { }
* An empty body occurs in an `if' or `else' statement.
* A pointer is compared against integer zero with `<', `<=',
`>', or `>='.
* A variable might be changed by `longjmp' or `vfork'.
* (C++ only) An enumerator and a non-enumerator both appear in
a conditional expression.
* (C++ only) A non-static reference or non-static `const'
member appears in a class without constructors.
* (C++ only) Ambiguous virtual bases.
* (C++ only) Subscripting an array which has been declared
`register'.
* (C++ only) Taking the address of a variable which has been
declared `register'.
* (C++ only) A base class is not initialized in a derived
class' copy constructor.
`-Wno-div-by-zero'
Do not warn about compile-time integer division by zero. Floating
point division by zero is not warned about, as it can be a
legitimate way of obtaining infinities and NaNs.
`-Wsystem-headers'
Print warning messages for constructs found in system header files.
Warnings from system headers are normally suppressed, on the
assumption that they usually do not indicate real problems and
would only make the compiler output harder to read. Using this
command line option tells GCC to emit warnings from system headers
as if they occurred in user code. However, note that using
`-Wall' in conjunction with this option will _not_ warn about
unknown pragmas in system headers--for that, `-Wunknown-pragmas'
must also be used.
`-Wfloat-equal'
Warn if floating point values are used in equality comparisons.
The idea behind this is that sometimes it is convenient (for the
programmer) to consider floating-point values as approximations to
infinitely precise real numbers. If you are doing this, then you
need to compute (by analyzing the code, or in some other way) the
maximum or likely maximum error that the computation introduces,
and allow for it when performing comparisons (and when producing
output, but that's a different problem). In particular, instead
of testing for equality, you would check to see whether the two
values have ranges that overlap; and this is done with the
relational operators, so equality comparisons are probably
mistaken.
`-Wtraditional (C only)'
Warn about certain constructs that behave differently in
traditional and ISO C. Also warn about ISO C constructs that have
no traditional C equivalent, and/or problematic constructs which
should be avoided.
* Macro parameters that appear within string literals in the
macro body. In traditional C macro replacement takes place
within string literals, but does not in ISO C.
* In traditional C, some preprocessor directives did not exist.
Traditional preprocessors would only consider a line to be a
directive if the `#' appeared in column 1 on the line.
Therefore `-Wtraditional' warns about directives that
traditional C understands but would ignore because the `#'
does not appear as the first character on the line. It also
suggests you hide directives like `#pragma' not understood by
traditional C by indenting them. Some traditional
implementations would not recognize `#elif', so it suggests
avoiding it altogether.
* A function-like macro that appears without arguments.
* The unary plus operator.
* The `U' integer constant suffix, or the `F' or `L' floating
point constant suffixes. (Traditional C does support the `L'
suffix on integer constants.) Note, these suffixes appear in
macros defined in the system headers of most modern systems,
e.g. the `_MIN'/`_MAX' macros in `<limits.h>'. Use of these
macros in user code might normally lead to spurious warnings,
however GCC's integrated preprocessor has enough context to
avoid warning in these cases.
* A function declared external in one block and then used after
the end of the block.
* A `switch' statement has an operand of type `long'.
* A non-`static' function declaration follows a `static' one.
This construct is not accepted by some traditional C
compilers.
* The ISO type of an integer constant has a different width or
signedness from its traditional type. This warning is only
issued if the base of the constant is ten. I.e. hexadecimal
or octal values, which typically represent bit patterns, are
not warned about.
* Usage of ISO string concatenation is detected.
* Initialization of automatic aggregates.
* Identifier conflicts with labels. Traditional C lacks a
separate namespace for labels.
* Initialization of unions. If the initializer is zero, the
warning is omitted. This is done under the assumption that
the zero initializer in user code appears conditioned on e.g.
`__STDC__' to avoid missing initializer warnings and relies
on default initialization to zero in the traditional C case.
* Conversions by prototypes between fixed/floating point values
and vice versa. The absence of these prototypes when
compiling with traditional C would cause serious problems.
This is a subset of the possible conversion warnings, for the
full set use `-Wconversion'.
* Use of ISO C style function definitions. This warning
intentionally is _not_ issued for prototype declarations or
variadic functions because these ISO C features will appear
in your code when using libiberty's traditional C
compatibility macros, `PARAMS' and `VPARAMS'. This warning
is also bypassed for nested functions because that feature is
already a GCC extension and thus not relevant to traditional
C compatibility.
`-Wdeclaration-after-statement (C only)'
Warn when a declaration is found after a statement in a block.
This construct, known from C++, was introduced with ISO C99 and is
by default allowed in GCC. It is not supported by ISO C90 and was
not supported by GCC versions before GCC 3.0. *Note Mixed
Declarations::.
`-Wundef'
Warn if an undefined identifier is evaluated in an `#if' directive.
`-Wno-endif-labels'
Do not warn whenever an `#else' or an `#endif' are followed by
text.
`-Wshadow'
Warn whenever a local variable shadows another local variable,
parameter or global variable or whenever a built-in function is
shadowed.
`-Wlarger-than-LEN'
Warn whenever an object of larger than LEN bytes is defined.
`-Wunsafe-loop-optimizations'
Warn if the loop cannot be optimized because the compiler could not
assume anything on the bounds of the loop indices. With
`-funsafe-loop-optimizations' warn if the compiler made such
assumptions.
`-Wpointer-arith'
Warn about anything that depends on the "size of" a function type
or of `void'. GNU C assigns these types a size of 1, for
convenience in calculations with `void *' pointers and pointers to
functions.
`-Wbad-function-cast (C only)'
Warn whenever a function call is cast to a non-matching type. For
example, warn if `int malloc()' is cast to `anything *'.
`-Wc++-compat'
Warn about ISO C constructs that are outside of the common subset
of ISO C and ISO C++, e.g. request for implicit conversion from
`void *' to a pointer to non-`void' type.
`-Wcast-qual'
Warn whenever a pointer is cast so as to remove a type qualifier
from the target type. For example, warn if a `const char *' is
cast to an ordinary `char *'.
`-Wcast-align'
Warn whenever a pointer is cast such that the required alignment
of the target is increased. For example, warn if a `char *' is
cast to an `int *' on machines where integers can only be accessed
at two- or four-byte boundaries.
`-Wwrite-strings'
When compiling C, give string constants the type `const
char[LENGTH]' so that copying the address of one into a
non-`const' `char *' pointer will get a warning; when compiling
C++, warn about the deprecated conversion from string literals to
`char *'. This warning, by default, is enabled for C++ programs.
These warnings will help you find at compile time code that can
try to write into a string constant, but only if you have been
very careful about using `const' in declarations and prototypes.
Otherwise, it will just be a nuisance; this is why we did not make
`-Wall' request these warnings.
`-Wconversion'
Warn if a prototype causes a type conversion that is different
from what would happen to the same argument in the absence of a
prototype. This includes conversions of fixed point to floating
and vice versa, and conversions changing the width or signedness
of a fixed point argument except when the same as the default
promotion.
Also, warn if a negative integer constant expression is implicitly
converted to an unsigned type. For example, warn about the
assignment `x = -1' if `x' is unsigned. But do not warn about
explicit casts like `(unsigned) -1'.
`-Wsign-compare'
Warn when a comparison between signed and unsigned values could
produce an incorrect result when the signed value is converted to
unsigned. This warning is also enabled by `-Wextra'; to get the
other warnings of `-Wextra' without this warning, use `-Wextra
-Wno-sign-compare'.
`-Waddress'
Warn about suspicious uses of memory addresses. These include using
the address of a function in a conditional expression, such as
`void func(void); if (func)', and comparisons against the memory
address of a string literal, such as `if (x == "abc")'. Such uses
typically indicate a programmer error: the address of a function
always evaluates to true, so their use in a conditional usually
indicate that the programmer forgot the parentheses in a function
call; and comparisons against string literals result in unspecified
behavior and are not portable in C, so they usually indicate that
the programmer intended to use `strcmp'. This warning is enabled
by `-Wall'.
`-Waggregate-return'
Warn if any functions that return structures or unions are defined
or called. (In languages where you can return an array, this also
elicits a warning.)
`-Wno-attributes'
Do not warn if an unexpected `__attribute__' is used, such as
unrecognized attributes, function attributes applied to variables,
etc. This will not stop errors for incorrect use of supported
attributes.
`-Wstrict-prototypes (C only)'
Warn if a function is declared or defined without specifying the
argument types. (An old-style function definition is permitted
without a warning if preceded by a declaration which specifies the
argument types.)
`-Wold-style-definition (C only)'
Warn if an old-style function definition is used. A warning is
given even if there is a previous prototype.
`-Wmissing-prototypes (C only)'
Warn if a global function is defined without a previous prototype
declaration. This warning is issued even if the definition itself
provides a prototype. The aim is to detect global functions that
fail to be declared in header files.
`-Wmissing-declarations (C only)'
Warn if a global function is defined without a previous
declaration. Do so even if the definition itself provides a
prototype. Use this option to detect global functions that are
not declared in header files.
`-Wmissing-field-initializers'
Warn if a structure's initializer has some fields missing. For
example, the following code would cause such a warning, because
`x.h' is implicitly zero:
struct s { int f, g, h; };
struct s x = { 3, 4 };
This option does not warn about designated initializers, so the
following modification would not trigger a warning:
struct s { int f, g, h; };
struct s x = { .f = 3, .g = 4 };
This warning is included in `-Wextra'. To get other `-Wextra'
warnings without this one, use `-Wextra
-Wno-missing-field-initializers'.
`-Wmissing-noreturn'
Warn about functions which might be candidates for attribute
`noreturn'. Note these are only possible candidates, not absolute
ones. Care should be taken to manually verify functions actually
do not ever return before adding the `noreturn' attribute,
otherwise subtle code generation bugs could be introduced. You
will not get a warning for `main' in hosted C environments.
`-Wmissing-format-attribute'
Warn about function pointers which might be candidates for `format'
attributes. Note these are only possible candidates, not absolute
ones. GCC will guess that function pointers with `format'
attributes that are used in assignment, initialization, parameter
passing or return statements should have a corresponding `format'
attribute in the resulting type. I.e. the left-hand side of the
assignment or initialization, the type of the parameter variable,
or the return type of the containing function respectively should
also have a `format' attribute to avoid the warning.
GCC will also warn about function definitions which might be
candidates for `format' attributes. Again, these are only
possible candidates. GCC will guess that `format' attributes
might be appropriate for any function that calls a function like
`vprintf' or `vscanf', but this might not always be the case, and
some functions for which `format' attributes are appropriate may
not be detected.
`-Wno-multichar'
Do not warn if a multicharacter constant (`'FOOF'') is used.
Usually they indicate a typo in the user's code, as they have
implementation-defined values, and should not be used in portable
code.
`-Wnormalized=<none|id|nfc|nfkc>'
In ISO C and ISO C++, two identifiers are different if they are
different sequences of characters. However, sometimes when
characters outside the basic ASCII character set are used, you can
have two different character sequences that look the same. To
avoid confusion, the ISO 10646 standard sets out some
"normalization rules" which when applied ensure that two sequences
that look the same are turned into the same sequence. GCC can
warn you if you are using identifiers which have not been
normalized; this option controls that warning.
There are four levels of warning that GCC supports. The default is
`-Wnormalized=nfc', which warns about any identifier which is not
in the ISO 10646 "C" normalized form, "NFC". NFC is the
recommended form for most uses.
Unfortunately, there are some characters which ISO C and ISO C++
allow in identifiers that when turned into NFC aren't allowable as
identifiers. That is, there's no way to use these symbols in
portable ISO C or C++ and have all your identifiers in NFC.
`-Wnormalized=id' suppresses the warning for these characters. It
is hoped that future versions of the standards involved will
correct this, which is why this option is not the default.
You can switch the warning off for all characters by writing
`-Wnormalized=none'. You would only want to do this if you were
using some other normalization scheme (like "D"), because
otherwise you can easily create bugs that are literally impossible
to see.
Some characters in ISO 10646 have distinct meanings but look
identical in some fonts or display methodologies, especially once
formatting has been applied. For instance `\u207F', "SUPERSCRIPT
LATIN SMALL LETTER N", will display just like a regular `n' which
has been placed in a superscript. ISO 10646 defines the "NFKC"
normalization scheme to convert all these into a standard form as
well, and GCC will warn if your code is not in NFKC if you use
`-Wnormalized=nfkc'. This warning is comparable to warning about
every identifier that contains the letter O because it might be
confused with the digit 0, and so is not the default, but may be
useful as a local coding convention if the programming environment
is unable to be fixed to display these characters distinctly.
`-Wno-deprecated-declarations'
Do not warn about uses of functions (*note Function Attributes::),
variables (*note Variable Attributes::), and types (*note Type
Attributes::) marked as deprecated by using the `deprecated'
attribute.
`-Wno-overflow'
Do not warn about compile-time overflow in constant expressions.
`-Woverride-init'
Warn if an initialized field without side effects is overridden
when using designated initializers (*note Designated Initializers:
Designated Inits.).
This warning is included in `-Wextra'. To get other `-Wextra'
warnings without this one, use `-Wextra -Wno-override-init'.
`-Wpacked'
Warn if a structure is given the packed attribute, but the packed
attribute has no effect on the layout or size of the structure.
Such structures may be mis-aligned for little benefit. For
instance, in this code, the variable `f.x' in `struct bar' will be
misaligned even though `struct bar' does not itself have the
packed attribute:
struct foo {
int x;
char a, b, c, d;
} __attribute__((packed));
struct bar {
char z;
struct foo f;
};
`-Wpadded'
Warn if padding is included in a structure, either to align an
element of the structure or to align the whole structure.
Sometimes when this happens it is possible to rearrange the fields
of the structure to reduce the padding and so make the structure
smaller.
`-Wredundant-decls'
Warn if anything is declared more than once in the same scope,
even in cases where multiple declaration is valid and changes
nothing.
`-Wnested-externs (C only)'
Warn if an `extern' declaration is encountered within a function.
`-Wunreachable-code'
Warn if the compiler detects that code will never be executed.
This option is intended to warn when the compiler detects that at
least a whole line of source code will never be executed, because
some condition is never satisfied or because it is after a
procedure that never returns.
It is possible for this option to produce a warning even though
there are circumstances under which part of the affected line can
be executed, so care should be taken when removing
apparently-unreachable code.
For instance, when a function is inlined, a warning may mean that
the line is unreachable in only one inlined copy of the function.
This option is not made part of `-Wall' because in a debugging
version of a program there is often substantial code which checks
correct functioning of the program and is, hopefully, unreachable
because the program does work. Another common use of unreachable
code is to provide behavior which is selectable at compile-time.
`-Winline'
Warn if a function can not be inlined and it was declared as
inline. Even with this option, the compiler will not warn about
failures to inline functions declared in system headers.
The compiler uses a variety of heuristics to determine whether or
not to inline a function. For example, the compiler takes into
account the size of the function being inlined and the amount of
inlining that has already been done in the current function.
Therefore, seemingly insignificant changes in the source program
can cause the warnings produced by `-Winline' to appear or
disappear.
`-Wno-invalid-offsetof (C++ only)'
Suppress warnings from applying the `offsetof' macro to a non-POD
type. According to the 1998 ISO C++ standard, applying `offsetof'
to a non-POD type is undefined. In existing C++ implementations,
however, `offsetof' typically gives meaningful results even when
applied to certain kinds of non-POD types. (Such as a simple
`struct' that fails to be a POD type only by virtue of having a
constructor.) This flag is for users who are aware that they are
writing nonportable code and who have deliberately chosen to
ignore the warning about it.
The restrictions on `offsetof' may be relaxed in a future version
of the C++ standard.
`-Wno-int-to-pointer-cast (C only)'
Suppress warnings from casts to pointer type of an integer of a
different size.
`-Wno-pointer-to-int-cast (C only)'
Suppress warnings from casts from a pointer to an integer type of a
different size.
`-Winvalid-pch'
Warn if a precompiled header (*note Precompiled Headers::) is
found in the search path but can't be used.
`-Wlong-long'
Warn if `long long' type is used. This is default. To inhibit
the warning messages, use `-Wno-long-long'. Flags `-Wlong-long'
and `-Wno-long-long' are taken into account only when `-pedantic'
flag is used.
`-Wvariadic-macros'
Warn if variadic macros are used in pedantic ISO C90 mode, or the
GNU alternate syntax when in pedantic ISO C99 mode. This is
default. To inhibit the warning messages, use
`-Wno-variadic-macros'.
`-Wvolatile-register-var'
Warn if a register variable is declared volatile. The volatile
modifier does not inhibit all optimizations that may eliminate
reads and/or writes to register variables.
`-Wdisabled-optimization'
Warn if a requested optimization pass is disabled. This warning
does not generally indicate that there is anything wrong with your
code; it merely indicates that GCC's optimizers were unable to
handle the code effectively. Often, the problem is that your code
is too big or too complex; GCC will refuse to optimize programs
when the optimization itself is likely to take inordinate amounts
of time.
`-Wpointer-sign'
Warn for pointer argument passing or assignment with different
signedness. This option is only supported for C and Objective-C.
It is implied by `-Wall' and by `-pedantic', which can be disabled
with `-Wno-pointer-sign'.
`-Werror'
Make all warnings into errors.
`-Werror='
Make the specified warning into an errors. The specifier for a
warning is appended, for example `-Werror=switch' turns the
warnings controlled by `-Wswitch' into errors. This switch takes
a negative form, to be used to negate `-Werror' for specific
warnings, for example `-Wno-error=switch' makes `-Wswitch'
warnings not be errors, even when `-Werror' is in effect. You can
use the `-fdiagnostics-show-option' option to have each
controllable warning amended with the option which controls it, to
determine what to use with this option.
Note that specifying `-Werror='FOO automatically implies `-W'FOO.
However, `-Wno-error='FOO does not imply anything.
`-Wstack-protector'
This option is only active when `-fstack-protector' is active. It
warns about functions that will not be protected against stack
smashing.
`-Woverlength-strings'
Warn about string constants which are longer than the "minimum
maximum" length specified in the C standard. Modern compilers
generally allow string constants which are much longer than the
standard's minimum limit, but very portable programs should avoid
using longer strings.
The limit applies _after_ string constant concatenation, and does
not count the trailing NUL. In C89, the limit was 509 characters;
in C99, it was raised to 4095. C++98 does not specify a normative
minimum maximum, so we do not diagnose overlength strings in C++.
This option is implied by `-pedantic', and can be disabled with
`-Wno-overlength-strings'.
File: gcc.info, Node: Debugging Options, Next: Optimize Options, Prev: Warning Options, Up: Invoking GCC
3.9 Options for Debugging Your Program or GCC
=============================================
GCC has various special options that are used for debugging either your
program or GCC:
`-g'
Produce debugging information in the operating system's native
format (stabs, COFF, XCOFF, or DWARF 2). GDB can work with this
debugging information.
On most systems that use stabs format, `-g' enables use of extra
debugging information that only GDB can use; this extra information
makes debugging work better in GDB but will probably make other
debuggers crash or refuse to read the program. If you want to
control for certain whether to generate the extra information, use
`-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', or `-gvms' (see
below).
GCC allows you to use `-g' with `-O'. The shortcuts taken by
optimized code may occasionally produce surprising results: some
variables you declared may not exist at all; flow of control may
briefly move where you did not expect it; some statements may not
be executed because they compute constant results or their values
were already at hand; some statements may execute in different
places because they were moved out of loops.
Nevertheless it proves possible to debug optimized output. This
makes it reasonable to use the optimizer for programs that might
have bugs.
The following options are useful when GCC is generated with the
capability for more than one debugging format.
`-ggdb'
Produce debugging information for use by GDB. This means to use
the most expressive format available (DWARF 2, stabs, or the
native format if neither of those are supported), including GDB
extensions if at all possible.
`-gstabs'
Produce debugging information in stabs format (if that is
supported), without GDB extensions. This is the format used by
DBX on most BSD systems. On MIPS, Alpha and System V Release 4
systems this option produces stabs debugging output which is not
understood by DBX or SDB. On System V Release 4 systems this
option requires the GNU assembler.
`-feliminate-unused-debug-symbols'
Produce debugging information in stabs format (if that is
supported), for only symbols that are actually used.
`-femit-class-debug-always'
Instead of emitting debugging information for a C++ class in only
one object file, emit it in all object files using the class.
This option should be used only with debuggers that are unable to
handle the way GCC normally emits debugging information for
classes because using this option will increase the size of
debugging information by as much as a factor of two.
`-gstabs+'
Produce debugging information in stabs format (if that is
supported), using GNU extensions understood only by the GNU
debugger (GDB). The use of these extensions is likely to make
other debuggers crash or refuse to read the program.
`-gcoff'
Produce debugging information in COFF format (if that is
supported). This is the format used by SDB on most System V
systems prior to System V Release 4.
`-gxcoff'
Produce debugging information in XCOFF format (if that is
supported). This is the format used by the DBX debugger on IBM
RS/6000 systems.
`-gxcoff+'
Produce debugging information in XCOFF format (if that is
supported), using GNU extensions understood only by the GNU
debugger (GDB). The use of these extensions is likely to make
other debuggers crash or refuse to read the program, and may cause
assemblers other than the GNU assembler (GAS) to fail with an
error.
`-gdwarf-2'
Produce debugging information in DWARF version 2 format (if that is
supported). This is the format used by DBX on IRIX 6. With this
option, GCC uses features of DWARF version 3 when they are useful;
version 3 is upward compatible with version 2, but may still cause
problems for older debuggers.
`-gvms'
Produce debugging information in VMS debug format (if that is
supported). This is the format used by DEBUG on VMS systems.
`-gLEVEL'
`-ggdbLEVEL'
`-gstabsLEVEL'
`-gcoffLEVEL'
`-gxcoffLEVEL'
`-gvmsLEVEL'
Request debugging information and also use LEVEL to specify how
much information. The default level is 2.
Level 1 produces minimal information, enough for making backtraces
in parts of the program that you don't plan to debug. This
includes descriptions of functions and external variables, but no
information about local variables and no line numbers.
Level 3 includes extra information, such as all the macro
definitions present in the program. Some debuggers support macro
expansion when you use `-g3'.
`-gdwarf-2' does not accept a concatenated debug level, because
GCC used to support an option `-gdwarf' that meant to generate
debug information in version 1 of the DWARF format (which is very
different from version 2), and it would have been too confusing.
That debug format is long obsolete, but the option cannot be
changed now. Instead use an additional `-gLEVEL' option to change
the debug level for DWARF2.
`-feliminate-dwarf2-dups'
Compress DWARF2 debugging information by eliminating duplicated
information about each symbol. This option only makes sense when
generating DWARF2 debugging information with `-gdwarf-2'.
`-p'
Generate extra code to write profile information suitable for the
analysis program `prof'. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
`-pg'
Generate extra code to write profile information suitable for the
analysis program `gprof'. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
`-Q'
Makes the compiler print out each function name as it is compiled,
and print some statistics about each pass when it finishes.
`-ftime-report'
Makes the compiler print some statistics about the time consumed
by each pass when it finishes.
`-fmem-report'
Makes the compiler print some statistics about permanent memory
allocation when it finishes.
`-fprofile-arcs'
Add code so that program flow "arcs" are instrumented. During
execution the program records how many times each branch and call
is executed and how many times it is taken or returns. When the
compiled program exits it saves this data to a file called
`AUXNAME.gcda' for each source file. The data may be used for
profile-directed optimizations (`-fbranch-probabilities'), or for
test coverage analysis (`-ftest-coverage'). Each object file's
AUXNAME is generated from the name of the output file, if
explicitly specified and it is not the final executable, otherwise
it is the basename of the source file. In both cases any suffix
is removed (e.g. `foo.gcda' for input file `dir/foo.c', or
`dir/foo.gcda' for output file specified as `-o dir/foo.o').
*Note Cross-profiling::.
`--coverage'
This option is used to compile and link code instrumented for
coverage analysis. The option is a synonym for `-fprofile-arcs'
`-ftest-coverage' (when compiling) and `-lgcov' (when linking).
See the documentation for those options for more details.
* Compile the source files with `-fprofile-arcs' plus
optimization and code generation options. For test coverage
analysis, use the additional `-ftest-coverage' option. You
do not need to profile every source file in a program.
* Link your object files with `-lgcov' or `-fprofile-arcs' (the
latter implies the former).
* Run the program on a representative workload to generate the
arc profile information. This may be repeated any number of
times. You can run concurrent instances of your program, and
provided that the file system supports locking, the data
files will be correctly updated. Also `fork' calls are
detected and correctly handled (double counting will not
happen).
* For profile-directed optimizations, compile the source files
again with the same optimization and code generation options
plus `-fbranch-probabilities' (*note Options that Control
Optimization: Optimize Options.).
* For test coverage analysis, use `gcov' to produce human
readable information from the `.gcno' and `.gcda' files.
Refer to the `gcov' documentation for further information.
With `-fprofile-arcs', for each function of your program GCC
creates a program flow graph, then finds a spanning tree for the
graph. Only arcs that are not on the spanning tree have to be
instrumented: the compiler adds code to count the number of times
that these arcs are executed. When an arc is the only exit or
only entrance to a block, the instrumentation code can be added to
the block; otherwise, a new basic block must be created to hold
the instrumentation code.
`-ftest-coverage'
Produce a notes file that the `gcov' code-coverage utility (*note
`gcov'--a Test Coverage Program: Gcov.) can use to show program
coverage. Each source file's note file is called `AUXNAME.gcno'.
Refer to the `-fprofile-arcs' option above for a description of
AUXNAME and instructions on how to generate test coverage data.
Coverage data will match the source files more closely, if you do
not optimize.
`-dLETTERS'
`-fdump-rtl-PASS'
Says to make debugging dumps during compilation at times specified
by LETTERS. This is used for debugging the RTL-based passes of
the compiler. The file names for most of the dumps are made by
appending a pass number and a word to the DUMPNAME. DUMPNAME is
generated from the name of the output file, if explicitly
specified and it is not an executable, otherwise it is the
basename of the source file.
Most debug dumps can be enabled either passing a letter to the `-d'
option, or with a long `-fdump-rtl' switch; here are the possible
letters for use in LETTERS and PASS, and their meanings:
`-dA'
Annotate the assembler output with miscellaneous debugging
information.
`-dB'
`-fdump-rtl-bbro'
Dump after block reordering, to `FILE.148r.bbro'.
`-dc'
`-fdump-rtl-combine'
Dump after instruction combination, to the file
`FILE.129r.combine'.
`-dC'
`-fdump-rtl-ce1'
`-fdump-rtl-ce2'
`-dC' and `-fdump-rtl-ce1' enable dumping after the first if
conversion, to the file `FILE.117r.ce1'. `-dC' and
`-fdump-rtl-ce2' enable dumping after the second if
conversion, to the file `FILE.130r.ce2'.
`-dd'
`-fdump-rtl-btl'
`-fdump-rtl-dbr'
`-dd' and `-fdump-rtl-btl' enable dumping after branch target
load optimization, to `FILE.31.btl'. `-dd' and
`-fdump-rtl-dbr' enable dumping after delayed branch
scheduling, to `FILE.36.dbr'.
`-dD'
Dump all macro definitions, at the end of preprocessing, in
addition to normal output.
`-dE'
`-fdump-rtl-ce3'
Dump after the third if conversion, to `FILE.146r.ce3'.
`-df'
`-fdump-rtl-cfg'
`-fdump-rtl-life'
`-df' and `-fdump-rtl-cfg' enable dumping after control and
data flow analysis, to `FILE.116r.cfg'. `-df' and
`-fdump-rtl-cfg' enable dumping dump after life analysis, to
`FILE.128r.life1' and `FILE.135r.life2'.
`-dg'
`-fdump-rtl-greg'
Dump after global register allocation, to `FILE.139r.greg'.
`-dG'
`-fdump-rtl-gcse'
`-fdump-rtl-bypass'
`-dG' and `-fdump-rtl-gcse' enable dumping after GCSE, to
`FILE.114r.gcse'. `-dG' and `-fdump-rtl-bypass' enable
dumping after jump bypassing and control flow optimizations,
to `FILE.115r.bypass'.
`-dh'
`-fdump-rtl-eh'
Dump after finalization of EH handling code, to `FILE.02.eh'.
`-di'
`-fdump-rtl-sibling'
Dump after sibling call optimizations, to `FILE.106r.sibling'.
`-dj'
`-fdump-rtl-jump'
Dump after the first jump optimization, to `FILE.112r.jump'.
`-dk'
`-fdump-rtl-stack'
Dump after conversion from registers to stack, to
`FILE.152r.stack'.
`-dl'
`-fdump-rtl-lreg'
Dump after local register allocation, to `FILE.138r.lreg'.
`-dL'
`-fdump-rtl-loop2'
`-dL' and `-fdump-rtl-loop2' enable dumping after the loop
optimization pass, to `FILE.119r.loop2',
`FILE.120r.loop2_init', `FILE.121r.loop2_invariant', and
`FILE.125r.loop2_done'.
`-dm'
`-fdump-rtl-sms'
Dump after modulo scheduling, to `FILE.136r.sms'.
`-dM'
`-fdump-rtl-mach'
Dump after performing the machine dependent reorganization
pass, to `FILE.155r.mach'.
`-dn'
`-fdump-rtl-rnreg'
Dump after register renumbering, to `FILE.147r.rnreg'.
`-dN'
`-fdump-rtl-regmove'
Dump after the register move pass, to `FILE.132r.regmove'.
`-do'
`-fdump-rtl-postreload'
Dump after post-reload optimizations, to `FILE.24.postreload'.
`-dr'
`-fdump-rtl-expand'
Dump after RTL generation, to `FILE.104r.expand'.
`-dR'
`-fdump-rtl-sched2'
Dump after the second scheduling pass, to `FILE.150r.sched2'.
`-ds'
`-fdump-rtl-cse'
Dump after CSE (including the jump optimization that
sometimes follows CSE), to `FILE.113r.cse'.
`-dS'
`-fdump-rtl-sched'
Dump after the first scheduling pass, to `FILE.21.sched'.
`-dt'
`-fdump-rtl-cse2'
Dump after the second CSE pass (including the jump
optimization that sometimes follows CSE), to `FILE.127r.cse2'.
`-dT'
`-fdump-rtl-tracer'
Dump after running tracer, to `FILE.118r.tracer'.
`-dV'
`-fdump-rtl-vpt'
`-fdump-rtl-vartrack'
`-dV' and `-fdump-rtl-vpt' enable dumping after the value
profile transformations, to `FILE.10.vpt'. `-dV' and
`-fdump-rtl-vartrack' enable dumping after variable tracking,
to `FILE.154r.vartrack'.
`-dw'
`-fdump-rtl-flow2'
Dump after the second flow pass, to `FILE.142r.flow2'.
`-dz'
`-fdump-rtl-peephole2'
Dump after the peephole pass, to `FILE.145r.peephole2'.
`-dZ'
`-fdump-rtl-web'
Dump after live range splitting, to `FILE.126r.web'.
`-da'
`-fdump-rtl-all'
Produce all the dumps listed above.
`-dH'
Produce a core dump whenever an error occurs.
`-dm'
Print statistics on memory usage, at the end of the run, to
standard error.
`-dp'
Annotate the assembler output with a comment indicating which
pattern and alternative was used. The length of each
instruction is also printed.
`-dP'
Dump the RTL in the assembler output as a comment before each
instruction. Also turns on `-dp' annotation.
`-dv'
For each of the other indicated dump files (either with `-d'
or `-fdump-rtl-PASS'), dump a representation of the control
flow graph suitable for viewing with VCG to `FILE.PASS.vcg'.
`-dx'
Just generate RTL for a function instead of compiling it.
Usually used with `r' (`-fdump-rtl-expand').
`-dy'
Dump debugging information during parsing, to standard error.
`-fdump-noaddr'
When doing debugging dumps (see `-d' option above), suppress
address output. This makes it more feasible to use diff on
debugging dumps for compiler invocations with different compiler
binaries and/or different text / bss / data / heap / stack / dso
start locations.
`-fdump-unnumbered'
When doing debugging dumps (see `-d' option above), suppress
instruction numbers, line number note and address output. This
makes it more feasible to use diff on debugging dumps for compiler
invocations with different options, in particular with and without
`-g'.
`-fdump-translation-unit (C++ only)'
`-fdump-translation-unit-OPTIONS (C++ only)'
Dump a representation of the tree structure for the entire
translation unit to a file. The file name is made by appending
`.tu' to the source file name. If the `-OPTIONS' form is used,
OPTIONS controls the details of the dump as described for the
`-fdump-tree' options.
`-fdump-class-hierarchy (C++ only)'
`-fdump-class-hierarchy-OPTIONS (C++ only)'
Dump a representation of each class's hierarchy and virtual
function table layout to a file. The file name is made by
appending `.class' to the source file name. If the `-OPTIONS'
form is used, OPTIONS controls the details of the dump as
described for the `-fdump-tree' options.
`-fdump-ipa-SWITCH'
Control the dumping at various stages of inter-procedural analysis
language tree to a file. The file name is generated by appending
a switch specific suffix to the source file name. The following
dumps are possible:
`all'
Enables all inter-procedural analysis dumps; currently the
only produced dump is the `cgraph' dump.
`cgraph'
Dumps information about call-graph optimization, unused
function removal, and inlining decisions.
`-fdump-tree-SWITCH'
`-fdump-tree-SWITCH-OPTIONS'
Control the dumping at various stages of processing the
intermediate language tree to a file. The file name is generated
by appending a switch specific suffix to the source file name. If
the `-OPTIONS' form is used, OPTIONS is a list of `-' separated
options that control the details of the dump. Not all options are
applicable to all dumps, those which are not meaningful will be
ignored. The following options are available
`address'
Print the address of each node. Usually this is not
meaningful as it changes according to the environment and
source file. Its primary use is for tying up a dump file
with a debug environment.
`slim'
Inhibit dumping of members of a scope or body of a function
merely because that scope has been reached. Only dump such
items when they are directly reachable by some other path.
When dumping pretty-printed trees, this option inhibits
dumping the bodies of control structures.
`raw'
Print a raw representation of the tree. By default, trees are
pretty-printed into a C-like representation.
`details'
Enable more detailed dumps (not honored by every dump option).
`stats'
Enable dumping various statistics about the pass (not honored
by every dump option).
`blocks'
Enable showing basic block boundaries (disabled in raw dumps).
`vops'
Enable showing virtual operands for every statement.
`lineno'
Enable showing line numbers for statements.
`uid'
Enable showing the unique ID (`DECL_UID') for each variable.
`all'
Turn on all options, except `raw', `slim' and `lineno'.
The following tree dumps are possible:
`original'
Dump before any tree based optimization, to `FILE.original'.
`optimized'
Dump after all tree based optimization, to `FILE.optimized'.
`inlined'
Dump after function inlining, to `FILE.inlined'.
`gimple'
Dump each function before and after the gimplification pass
to a file. The file name is made by appending `.gimple' to
the source file name.
`cfg'
Dump the control flow graph of each function to a file. The
file name is made by appending `.cfg' to the source file name.
`vcg'
Dump the control flow graph of each function to a file in VCG
format. The file name is made by appending `.vcg' to the
source file name. Note that if the file contains more than
one function, the generated file cannot be used directly by
VCG. You will need to cut and paste each function's graph
into its own separate file first.
`ch'
Dump each function after copying loop headers. The file name
is made by appending `.ch' to the source file name.
`ssa'
Dump SSA related information to a file. The file name is
made by appending `.ssa' to the source file name.
`salias'
Dump structure aliasing variable information to a file. This
file name is made by appending `.salias' to the source file
name.
`alias'
Dump aliasing information for each function. The file name
is made by appending `.alias' to the source file name.
`ccp'
Dump each function after CCP. The file name is made by
appending `.ccp' to the source file name.
`storeccp'
Dump each function after STORE-CCP. The file name is made by
appending `.storeccp' to the source file name.
`pre'
Dump trees after partial redundancy elimination. The file
name is made by appending `.pre' to the source file name.
`fre'
Dump trees after full redundancy elimination. The file name
is made by appending `.fre' to the source file name.
`copyprop'
Dump trees after copy propagation. The file name is made by
appending `.copyprop' to the source file name.
`store_copyprop'
Dump trees after store copy-propagation. The file name is
made by appending `.store_copyprop' to the source file name.
`dce'
Dump each function after dead code elimination. The file
name is made by appending `.dce' to the source file name.
`mudflap'
Dump each function after adding mudflap instrumentation. The
file name is made by appending `.mudflap' to the source file
name.
`sra'
Dump each function after performing scalar replacement of
aggregates. The file name is made by appending `.sra' to the
source file name.
`sink'
Dump each function after performing code sinking. The file
name is made by appending `.sink' to the source file name.
`dom'
Dump each function after applying dominator tree
optimizations. The file name is made by appending `.dom' to
the source file name.
`dse'
Dump each function after applying dead store elimination.
The file name is made by appending `.dse' to the source file
name.
`phiopt'
Dump each function after optimizing PHI nodes into
straightline code. The file name is made by appending
`.phiopt' to the source file name.
`forwprop'
Dump each function after forward propagating single use
variables. The file name is made by appending `.forwprop' to
the source file name.
`copyrename'
Dump each function after applying the copy rename
optimization. The file name is made by appending
`.copyrename' to the source file name.
`nrv'
Dump each function after applying the named return value
optimization on generic trees. The file name is made by
appending `.nrv' to the source file name.
`vect'
Dump each function after applying vectorization of loops.
The file name is made by appending `.vect' to the source file
name.
`vrp'
Dump each function after Value Range Propagation (VRP). The
file name is made by appending `.vrp' to the source file name.
`all'
Enable all the available tree dumps with the flags provided
in this option.
`-ftree-vectorizer-verbose=N'
This option controls the amount of debugging output the vectorizer
prints. This information is written to standard error, unless
`-fdump-tree-all' or `-fdump-tree-vect' is specified, in which
case it is output to the usual dump listing file, `.vect'. For
N=0 no diagnostic information is reported. If N=1 the vectorizer
reports each loop that got vectorized, and the total number of
loops that got vectorized. If N=2 the vectorizer also reports
non-vectorized loops that passed the first analysis phase
(vect_analyze_loop_form) - i.e. countable, inner-most, single-bb,
single-entry/exit loops. This is the same verbosity level that
`-fdump-tree-vect-stats' uses. Higher verbosity levels mean
either more information dumped for each reported loop, or same
amount of information reported for more loops: If N=3, alignment
related information is added to the reports. If N=4,
data-references related information (e.g. memory dependences,
memory access-patterns) is added to the reports. If N=5, the
vectorizer reports also non-vectorized inner-most loops that did
not pass the first analysis phase (i.e. may not be countable, or
may have complicated control-flow). If N=6, the vectorizer
reports also non-vectorized nested loops. For N=7, all the
information the vectorizer generates during its analysis and
transformation is reported. This is the same verbosity level that
`-fdump-tree-vect-details' uses.
`-frandom-seed=STRING'
This option provides a seed that GCC uses when it would otherwise
use random numbers. It is used to generate certain symbol names
that have to be different in every compiled file. It is also used
to place unique stamps in coverage data files and the object files
that produce them. You can use the `-frandom-seed' option to
produce reproducibly identical object files.
The STRING should be different for every file you compile.
`-fsched-verbose=N'
On targets that use instruction scheduling, this option controls
the amount of debugging output the scheduler prints. This
information is written to standard error, unless `-dS' or `-dR' is
specified, in which case it is output to the usual dump listing
file, `.sched' or `.sched2' respectively. However for N greater
than nine, the output is always printed to standard error.
For N greater than zero, `-fsched-verbose' outputs the same
information as `-dRS'. For N greater than one, it also output
basic block probabilities, detailed ready list information and
unit/insn info. For N greater than two, it includes RTL at abort
point, control-flow and regions info. And for N over four,
`-fsched-verbose' also includes dependence info.
`-save-temps'
Store the usual "temporary" intermediate files permanently; place
them in the current directory and name them based on the source
file. Thus, compiling `foo.c' with `-c -save-temps' would produce
files `foo.i' and `foo.s', as well as `foo.o'. This creates a
preprocessed `foo.i' output file even though the compiler now
normally uses an integrated preprocessor.
When used in combination with the `-x' command line option,
`-save-temps' is sensible enough to avoid over writing an input
source file with the same extension as an intermediate file. The
corresponding intermediate file may be obtained by renaming the
source file before using `-save-temps'.
`-time'
Report the CPU time taken by each subprocess in the compilation
sequence. For C source files, this is the compiler proper and
assembler (plus the linker if linking is done). The output looks
like this:
# cc1 0.12 0.01
# as 0.00 0.01
The first number on each line is the "user time", that is time
spent executing the program itself. The second number is "system
time", time spent executing operating system routines on behalf of
the program. Both numbers are in seconds.
`-fvar-tracking'
Run variable tracking pass. It computes where variables are
stored at each position in code. Better debugging information is
then generated (if the debugging information format supports this
information).
It is enabled by default when compiling with optimization (`-Os',
`-O', `-O2', ...), debugging information (`-g') and the debug info
format supports it.
`-print-file-name=LIBRARY'
Print the full absolute name of the library file LIBRARY that
would be used when linking--and don't do anything else. With this
option, GCC does not compile or link anything; it just prints the
file name.
`-print-multi-directory'
Print the directory name corresponding to the multilib selected by
any other switches present in the command line. This directory is
supposed to exist in `GCC_EXEC_PREFIX'.
`-print-multi-lib'
Print the mapping from multilib directory names to compiler
switches that enable them. The directory name is separated from
the switches by `;', and each switch starts with an `@' instead of
the `-', without spaces between multiple switches. This is
supposed to ease shell-processing.
`-print-prog-name=PROGRAM'
Like `-print-file-name', but searches for a program such as `cpp'.
`-print-libgcc-file-name'
Same as `-print-file-name=libgcc.a'.
This is useful when you use `-nostdlib' or `-nodefaultlibs' but
you do want to link with `libgcc.a'. You can do
gcc -nostdlib FILES... `gcc -print-libgcc-file-name`
`-print-search-dirs'
Print the name of the configured installation directory and a list
of program and library directories `gcc' will search--and don't do
anything else.
This is useful when `gcc' prints the error message `installation
problem, cannot exec cpp0: No such file or directory'. To resolve
this you either need to put `cpp0' and the other compiler
components where `gcc' expects to find them, or you can set the
environment variable `GCC_EXEC_PREFIX' to the directory where you
installed them. Don't forget the trailing `/'. *Note Environment
Variables::.
`-dumpmachine'
Print the compiler's target machine (for example,
`i686-pc-linux-gnu')--and don't do anything else.
`-dumpversion'
Print the compiler version (for example, `3.0')--and don't do
anything else.
`-dumpspecs'
Print the compiler's built-in specs--and don't do anything else.
(This is used when GCC itself is being built.) *Note Spec Files::.
`-feliminate-unused-debug-types'
Normally, when producing DWARF2 output, GCC will emit debugging
information for all types declared in a compilation unit,
regardless of whether or not they are actually used in that
compilation unit. Sometimes this is useful, such as if, in the
debugger, you want to cast a value to a type that is not actually
used in your program (but is declared). More often, however, this
results in a significant amount of wasted space. With this
option, GCC will avoid producing debug symbol output for types
that are nowhere used in the source file being compiled.
File: gcc.info, Node: Optimize Options, Next: Preprocessor Options, Prev: Debugging Options, Up: Invoking GCC
3.10 Options That Control Optimization
======================================
These options control various sorts of optimizations.
Without any optimization option, the compiler's goal is to reduce the
cost of compilation and to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you would expect from the source code.
Turning on optimization flags makes the compiler attempt to improve
the performance and/or code size at the expense of compilation time and
possibly the ability to debug the program.
The compiler performs optimization based on the knowledge it has of
the program. Optimization levels `-O' and above, in particular, enable
_unit-at-a-time_ mode, which allows the compiler to consider
information gained from later functions in the file when compiling a
function. Compiling multiple files at once to a single output file in
_unit-at-a-time_ mode allows the compiler to use information gained
from all of the files when compiling each of them.
Not all optimizations are controlled directly by a flag. Only
optimizations that have a flag are listed.
`-O'
`-O1'
Optimize. Optimizing compilation takes somewhat more time, and a
lot more memory for a large function.
With `-O', the compiler tries to reduce code size and execution
time, without performing any optimizations that take a great deal
of compilation time.
`-O' turns on the following optimization flags:
-fdefer-pop
-fdelayed-branch
-fguess-branch-probability
-fcprop-registers
-fif-conversion
-fif-conversion2
-ftree-ccp
-ftree-dce
-ftree-dominator-opts
-ftree-dse
-ftree-ter
-ftree-lrs
-ftree-sra
-ftree-copyrename
-ftree-fre
-ftree-ch
-funit-at-a-time
-fmerge-constants
`-O' also turns on `-fomit-frame-pointer' on machines where doing
so does not interfere with debugging.
`-O2'
Optimize even more. GCC performs nearly all supported
optimizations that do not involve a space-speed tradeoff. The
compiler does not perform loop unrolling or function inlining when
you specify `-O2'. As compared to `-O', this option increases
both compilation time and the performance of the generated code.
`-O2' turns on all optimization flags specified by `-O'. It also
turns on the following optimization flags:
-fthread-jumps
-fcrossjumping
-foptimize-sibling-calls
-fcse-follow-jumps -fcse-skip-blocks
-fgcse -fgcse-lm
-fexpensive-optimizations
-frerun-cse-after-loop
-fcaller-saves
-fpeephole2
-fschedule-insns -fschedule-insns2
-fsched-interblock -fsched-spec
-fregmove
-fstrict-aliasing -fstrict-overflow
-fdelete-null-pointer-checks
-freorder-blocks -freorder-functions
-falign-functions -falign-jumps
-falign-loops -falign-labels
-ftree-vrp
-ftree-pre
Please note the warning under `-fgcse' about invoking `-O2' on
programs that use computed gotos.
`-O2' doesn't turn on `-ftree-vrp' for the Ada compiler. This
option must be explicitly specified on the command line to be
enabled for the Ada compiler.
`-O3'
Optimize yet more. `-O3' turns on all optimizations specified by
`-O2' and also turns on the `-finline-functions',
`-funswitch-loops' and `-fgcse-after-reload' options.
`-O0'
Do not optimize. This is the default.
`-Os'
Optimize for size. `-Os' enables all `-O2' optimizations that do
not typically increase code size. It also performs further
optimizations designed to reduce code size.
`-Os' disables the following optimization flags:
-falign-functions -falign-jumps -falign-loops
-falign-labels -freorder-blocks -freorder-blocks-and-partition
-fprefetch-loop-arrays -ftree-vect-loop-version
If you use multiple `-O' options, with or without level numbers,
the last such option is the one that is effective.
Options of the form `-fFLAG' specify machine-independent flags. Most
flags have both positive and negative forms; the negative form of
`-ffoo' would be `-fno-foo'. In the table below, only one of the forms
is listed--the one you typically will use. You can figure out the
other form by either removing `no-' or adding it.
The following options control specific optimizations. They are either
activated by `-O' options or are related to ones that are. You can use
the following flags in the rare cases when "fine-tuning" of
optimizations to be performed is desired.
`-fno-default-inline'
Do not make member functions inline by default merely because they
are defined inside the class scope (C++ only). Otherwise, when
you specify `-O', member functions defined inside class scope are
compiled inline by default; i.e., you don't need to add `inline'
in front of the member function name.
`-fno-defer-pop'
Always pop the arguments to each function call as soon as that
function returns. For machines which must pop arguments after a
function call, the compiler normally lets arguments accumulate on
the stack for several function calls and pops them all at once.
Disabled at levels `-O', `-O2', `-O3', `-Os'.
`-fforce-mem'
Force memory operands to be copied into registers before doing
arithmetic on them. This produces better code by making all memory
references potential common subexpressions. When they are not
common subexpressions, instruction combination should eliminate
the separate register-load. This option is now a nop and will be
removed in 4.3.
`-fforce-addr'
Force memory address constants to be copied into registers before
doing arithmetic on them.
`-fomit-frame-pointer'
Don't keep the frame pointer in a register for functions that
don't need one. This avoids the instructions to save, set up and
restore frame pointers; it also makes an extra register available
in many functions. *It also makes debugging impossible on some
machines.*
On some machines, such as the VAX, this flag has no effect, because
the standard calling sequence automatically handles the frame
pointer and nothing is saved by pretending it doesn't exist. The
machine-description macro `FRAME_POINTER_REQUIRED' controls
whether a target machine supports this flag. *Note Register
Usage: (gccint)Registers.
Enabled at levels `-O', `-O2', `-O3', `-Os'.
`-foptimize-sibling-calls'
Optimize sibling and tail recursive calls.
Enabled at levels `-O2', `-O3', `-Os'.
`-fno-inline'
Don't pay attention to the `inline' keyword. Normally this option
is used to keep the compiler from expanding any functions inline.
Note that if you are not optimizing, no functions can be expanded
inline.
`-finline-functions'
Integrate all simple functions into their callers. The compiler
heuristically decides which functions are simple enough to be worth
integrating in this way.
If all calls to a given function are integrated, and the function
is declared `static', then the function is normally not output as
assembler code in its own right.
Enabled at level `-O3'.
`-finline-functions-called-once'
Consider all `static' functions called once for inlining into their
caller even if they are not marked `inline'. If a call to a given
function is integrated, then the function is not output as
assembler code in its own right.
Enabled if `-funit-at-a-time' is enabled.
`-fearly-inlining'
Inline functions marked by `always_inline' and functions whose
body seems smaller than the function call overhead early before
doing `-fprofile-generate' instrumentation and real inlining pass.
Doing so makes profiling significantly cheaper and usually
inlining faster on programs having large chains of nested wrapper
functions.
Enabled by default.
`-finline-limit=N'
By default, GCC limits the size of functions that can be inlined.
This flag allows the control of this limit for functions that are
explicitly marked as inline (i.e., marked with the inline keyword
or defined within the class definition in c++). N is the size of
functions that can be inlined in number of pseudo instructions
(not counting parameter handling). The default value of N is 600.
Increasing this value can result in more inlined code at the cost
of compilation time and memory consumption. Decreasing usually
makes the compilation faster and less code will be inlined (which
presumably means slower programs). This option is particularly
useful for programs that use inlining heavily such as those based
on recursive templates with C++.
Inlining is actually controlled by a number of parameters, which
may be specified individually by using `--param NAME=VALUE'. The
`-finline-limit=N' option sets some of these parameters as follows:
`max-inline-insns-single'
is set to N/2.
`max-inline-insns-auto'
is set to N/2.
`min-inline-insns'
is set to 130 or N/4, whichever is smaller.
`max-inline-insns-rtl'
is set to N.
See below for a documentation of the individual parameters
controlling inlining.
_Note:_ pseudo instruction represents, in this particular context,
an abstract measurement of function's size. In no way does it
represent a count of assembly instructions and as such its exact
meaning might change from one release to an another.
`-fkeep-inline-functions'
In C, emit `static' functions that are declared `inline' into the
object file, even if the function has been inlined into all of its
callers. This switch does not affect functions using the `extern
inline' extension in GNU C. In C++, emit any and all inline
functions into the object file.
`-fkeep-static-consts'
Emit variables declared `static const' when optimization isn't
turned on, even if the variables aren't referenced.
GCC enables this option by default. If you want to force the
compiler to check if the variable was referenced, regardless of
whether or not optimization is turned on, use the
`-fno-keep-static-consts' option.
`-fmerge-constants'
Attempt to merge identical constants (string constants and
floating point constants) across compilation units.
This option is the default for optimized compilation if the
assembler and linker support it. Use `-fno-merge-constants' to
inhibit this behavior.
Enabled at levels `-O', `-O2', `-O3', `-Os'.
`-fmerge-all-constants'
Attempt to merge identical constants and identical variables.
This option implies `-fmerge-constants'. In addition to
`-fmerge-constants' this considers e.g. even constant initialized
arrays or initialized constant variables with integral or floating
point types. Languages like C or C++ require each non-automatic
variable to have distinct location, so using this option will
result in non-conforming behavior.
`-fmodulo-sched'
Perform swing modulo scheduling immediately before the first
scheduling pass. This pass looks at innermost loops and reorders
their instructions by overlapping different iterations.
`-fno-branch-count-reg'
Do not use "decrement and branch" instructions on a count register,
but instead generate a sequence of instructions that decrement a
register, compare it against zero, then branch based upon the
result. This option is only meaningful on architectures that
support such instructions, which include x86, PowerPC, IA-64 and
S/390.
The default is `-fbranch-count-reg'.
`-fno-function-cse'
Do not put function addresses in registers; make each instruction
that calls a constant function contain the function's address
explicitly.
This option results in less efficient code, but some strange hacks
that alter the assembler output may be confused by the
optimizations performed when this option is not used.
The default is `-ffunction-cse'
`-fno-zero-initialized-in-bss'
If the target supports a BSS section, GCC by default puts
variables that are initialized to zero into BSS. This can save
space in the resulting code.
This option turns off this behavior because some programs
explicitly rely on variables going to the data section. E.g., so
that the resulting executable can find the beginning of that
section and/or make assumptions based on that.
The default is `-fzero-initialized-in-bss'.
`-fbounds-check'
For front-ends that support it, generate additional code to check
that indices used to access arrays are within the declared range.
This is currently only supported by the Java and Fortran
front-ends, where this option defaults to true and false
respectively.
`-fmudflap -fmudflapth -fmudflapir'
For front-ends that support it (C and C++), instrument all risky
pointer/array dereferencing operations, some standard library
string/heap functions, and some other associated constructs with
range/validity tests. Modules so instrumented should be immune to
buffer overflows, invalid heap use, and some other classes of C/C++
programming errors. The instrumentation relies on a separate
runtime library (`libmudflap'), which will be linked into a
program if `-fmudflap' is given at link time. Run-time behavior
of the instrumented program is controlled by the `MUDFLAP_OPTIONS'
environment variable. See `env MUDFLAP_OPTIONS=-help a.out' for
its options.
Use `-fmudflapth' instead of `-fmudflap' to compile and to link if
your program is multi-threaded. Use `-fmudflapir', in addition to
`-fmudflap' or `-fmudflapth', if instrumentation should ignore
pointer reads. This produces less instrumentation (and therefore
faster execution) and still provides some protection against
outright memory corrupting writes, but allows erroneously read
data to propagate within a program.
`-fthread-jumps'
Perform optimizations where we check to see if a jump branches to a
location where another comparison subsumed by the first is found.
If so, the first branch is redirected to either the destination of
the second branch or a point immediately following it, depending
on whether the condition is known to be true or false.
Enabled at levels `-O2', `-O3', `-Os'.
`-fcse-follow-jumps'
In common subexpression elimination, scan through jump instructions
when the target of the jump is not reached by any other path. For
example, when CSE encounters an `if' statement with an `else'
clause, CSE will follow the jump when the condition tested is
false.
Enabled at levels `-O2', `-O3', `-Os'.
`-fcse-skip-blocks'
This is similar to `-fcse-follow-jumps', but causes CSE to follow
jumps which conditionally skip over blocks. When CSE encounters a
simple `if' statement with no else clause, `-fcse-skip-blocks'
causes CSE to follow the jump around the body of the `if'.
Enabled at levels `-O2', `-O3', `-Os'.
`-frerun-cse-after-loop'
Re-run common subexpression elimination after loop optimizations
has been performed.
Enabled at levels `-O2', `-O3', `-Os'.
`-fgcse'
Perform a global common subexpression elimination pass. This pass
also performs global constant and copy propagation.
_Note:_ When compiling a program using computed gotos, a GCC
extension, you may get better runtime performance if you disable
the global common subexpression elimination pass by adding
`-fno-gcse' to the command line.
Enabled at levels `-O2', `-O3', `-Os'.
`-fgcse-lm'
When `-fgcse-lm' is enabled, global common subexpression
elimination will attempt to move loads which are only killed by
stores into themselves. This allows a loop containing a
load/store sequence to be changed to a load outside the loop, and
a copy/store within the loop.
Enabled by default when gcse is enabled.
`-fgcse-sm'
When `-fgcse-sm' is enabled, a store motion pass is run after
global common subexpression elimination. This pass will attempt
to move stores out of loops. When used in conjunction with
`-fgcse-lm', loops containing a load/store sequence can be changed
to a load before the loop and a store after the loop.
Not enabled at any optimization level.
`-fgcse-las'
When `-fgcse-las' is enabled, the global common subexpression
elimination pass eliminates redundant loads that come after stores
to the same memory location (both partial and full redundancies).
Not enabled at any optimization level.
`-fgcse-after-reload'
When `-fgcse-after-reload' is enabled, a redundant load elimination
pass is performed after reload. The purpose of this pass is to
cleanup redundant spilling.
`-funsafe-loop-optimizations'
If given, the loop optimizer will assume that loop indices do not
overflow, and that the loops with nontrivial exit condition are not
infinite. This enables a wider range of loop optimizations even if
the loop optimizer itself cannot prove that these assumptions are
valid. Using `-Wunsafe-loop-optimizations', the compiler will
warn you if it finds this kind of loop.
`-fcrossjumping'
Perform cross-jumping transformation. This transformation unifies
equivalent code and save code size. The resulting code may or may
not perform better than without cross-jumping.
Enabled at levels `-O2', `-O3', `-Os'.
`-fif-conversion'
Attempt to transform conditional jumps into branch-less
equivalents. This include use of conditional moves, min, max, set
flags and abs instructions, and some tricks doable by standard
arithmetics. The use of conditional execution on chips where it
is available is controlled by `if-conversion2'.
Enabled at levels `-O', `-O2', `-O3', `-Os'.
`-fif-conversion2'
Use conditional execution (where available) to transform
conditional jumps into branch-less equivalents.
Enabled at levels `-O', `-O2', `-O3', `-Os'.
`-fdelete-null-pointer-checks'
Use global dataflow analysis to identify and eliminate useless
checks for null pointers. The compiler assumes that dereferencing
a null pointer would have halted the program. If a pointer is
checked after it has already been dereferenced, it cannot be null.
In some environments, this assumption is not true, and programs can
safely dereference null pointers. Use
`-fno-delete-null-pointer-checks' to disable this optimization for
programs which depend on that behavior.
Enabled at levels `-O2', `-O3', `-Os'.
`-fexpensive-optimizations'
Perform a number of minor optimizations that are relatively
expensive.
Enabled at levels `-O2', `-O3', `-Os'.
`-foptimize-register-move'
`-fregmove'
Attempt to reassign register numbers in move instructions and as
operands of other simple instructions in order to maximize the
amount of register tying. This is especially helpful on machines
with two-operand instructions.
Note `-fregmove' and `-foptimize-register-move' are the same
optimization.
Enabled at levels `-O2', `-O3', `-Os'.
`-fdelayed-branch'
If supported for the target machine, attempt to reorder
instructions to exploit instruction slots available after delayed
branch instructions.
Enabled at levels `-O', `-O2', `-O3', `-Os'.
`-fschedule-insns'
If supported for the target machine, attempt to reorder
instructions to eliminate execution stalls due to required data
being unavailable. This helps machines that have slow floating
point or memory load instructions by allowing other instructions
to be issued until the result of the load or floating point
instruction is required.
Enabled at levels `-O2', `-O3', `-Os'.
`-fschedule-insns2'
Similar to `-fschedule-insns', but requests an additional pass of
instruction scheduling after register allocation has been done.
This is especially useful on machines with a relatively small
number of registers and where memory load instructions take more
than one cycle.
Enabled at levels `-O2', `-O3', `-Os'.
`-fno-sched-interblock'
Don't schedule instructions across basic blocks. This is normally
enabled by default when scheduling before register allocation, i.e.
with `-fschedule-insns' or at `-O2' or higher.
`-fno-sched-spec'
Don't allow speculative motion of non-load instructions. This is
normally enabled by default when scheduling before register
allocation, i.e. with `-fschedule-insns' or at `-O2' or higher.
`-fsched-spec-load'
Allow speculative motion of some load instructions. This only
makes sense when scheduling before register allocation, i.e. with
`-fschedule-insns' or at `-O2' or higher.
`-fsched-spec-load-dangerous'
Allow speculative motion of more load instructions. This only
makes sense when scheduling before register allocation, i.e. with
`-fschedule-insns' or at `-O2' or higher.
`-fsched-stalled-insns=N'
Define how many insns (if any) can be moved prematurely from the
queue of stalled insns into the ready list, during the second
scheduling pass.
`-fsched-stalled-insns-dep=N'
Define how many insn groups (cycles) will be examined for a
dependency on a stalled insn that is candidate for premature
removal from the queue of stalled insns. Has an effect only
during the second scheduling pass, and only if
`-fsched-stalled-insns' is used and its value is not zero.
`-fsched2-use-superblocks'
When scheduling after register allocation, do use superblock
scheduling algorithm. Superblock scheduling allows motion across
basic block boundaries resulting on faster schedules. This option
is experimental, as not all machine descriptions used by GCC model
the CPU closely enough to avoid unreliable results from the
algorithm.
This only makes sense when scheduling after register allocation,
i.e. with `-fschedule-insns2' or at `-O2' or higher.
`-fsched2-use-traces'
Use `-fsched2-use-superblocks' algorithm when scheduling after
register allocation and additionally perform code duplication in
order to increase the size of superblocks using tracer pass. See
`-ftracer' for details on trace formation.
This mode should produce faster but significantly longer programs.
Also without `-fbranch-probabilities' the traces constructed may
not match the reality and hurt the performance. This only makes
sense when scheduling after register allocation, i.e. with
`-fschedule-insns2' or at `-O2' or higher.
`-fsee'
Eliminates redundant extension instructions and move the non
redundant ones to optimal placement using LCM.
`-freschedule-modulo-scheduled-loops'
The modulo scheduling comes before the traditional scheduling, if
a loop was modulo scheduled we may want to prevent the later
scheduling passes from changing its schedule, we use this option
to control that.
`-fcaller-saves'
Enable values to be allocated in registers that will be clobbered
by function calls, by emitting extra instructions to save and
restore the registers around such calls. Such allocation is done
only when it seems to result in better code than would otherwise
be produced.
This option is always enabled by default on certain machines,
usually those which have no call-preserved registers to use
instead.
Enabled at levels `-O2', `-O3', `-Os'.
`-ftree-pre'
Perform Partial Redundancy Elimination (PRE) on trees. This flag
is enabled by default at `-O2' and `-O3'.
`-ftree-fre'
Perform Full Redundancy Elimination (FRE) on trees. The difference
between FRE and PRE is that FRE only considers expressions that
are computed on all paths leading to the redundant computation.
This analysis faster than PRE, though it exposes fewer
redundancies. This flag is enabled by default at `-O' and higher.
`-ftree-copy-prop'
Perform copy propagation on trees. This pass eliminates
unnecessary copy operations. This flag is enabled by default at
`-O' and higher.
`-ftree-store-copy-prop'
Perform copy propagation of memory loads and stores. This pass
eliminates unnecessary copy operations in memory references
(structures, global variables, arrays, etc). This flag is enabled
by default at `-O2' and higher.
`-ftree-salias'
Perform structural alias analysis on trees. This flag is enabled
by default at `-O' and higher.
`-fipa-pta'
Perform interprocedural pointer analysis.
`-ftree-sink'
Perform forward store motion on trees. This flag is enabled by
default at `-O' and higher.
`-ftree-ccp'
Perform sparse conditional constant propagation (CCP) on trees.
This pass only operates on local scalar variables and is enabled
by default at `-O' and higher.
`-ftree-store-ccp'
Perform sparse conditional constant propagation (CCP) on trees.
This pass operates on both local scalar variables and memory
stores and loads (global variables, structures, arrays, etc).
This flag is enabled by default at `-O2' and higher.
`-ftree-dce'
Perform dead code elimination (DCE) on trees. This flag is
enabled by default at `-O' and higher.
`-ftree-dominator-opts'
Perform a variety of simple scalar cleanups (constant/copy
propagation, redundancy elimination, range propagation and
expression simplification) based on a dominator tree traversal.
This also performs jump threading (to reduce jumps to jumps). This
flag is enabled by default at `-O' and higher.
`-ftree-ch'
Perform loop header copying on trees. This is beneficial since it
increases effectiveness of code motion optimizations. It also
saves one jump. This flag is enabled by default at `-O' and
higher. It is not enabled for `-Os', since it usually increases
code size.
`-ftree-loop-optimize'
Perform loop optimizations on trees. This flag is enabled by
default at `-O' and higher.
`-ftree-loop-linear'
Perform linear loop transformations on tree. This flag can
improve cache performance and allow further loop optimizations to
take place.
`-ftree-loop-im'
Perform loop invariant motion on trees. This pass moves only
invariants that would be hard to handle at RTL level (function
calls, operations that expand to nontrivial sequences of insns).
With `-funswitch-loops' it also moves operands of conditions that
are invariant out of the loop, so that we can use just trivial
invariantness analysis in loop unswitching. The pass also includes
store motion.
`-ftree-loop-ivcanon'
Create a canonical counter for number of iterations in the loop
for that determining number of iterations requires complicated
analysis. Later optimizations then may determine the number
easily. Useful especially in connection with unrolling.
`-fivopts'
Perform induction variable optimizations (strength reduction,
induction variable merging and induction variable elimination) on
trees.
`-ftree-sra'
Perform scalar replacement of aggregates. This pass replaces
structure references with scalars to prevent committing structures
to memory too early. This flag is enabled by default at `-O' and
higher.
`-ftree-copyrename'
Perform copy renaming on trees. This pass attempts to rename
compiler temporaries to other variables at copy locations, usually
resulting in variable names which more closely resemble the
original variables. This flag is enabled by default at `-O' and
higher.
`-ftree-ter'
Perform temporary expression replacement during the SSA->normal
phase. Single use/single def temporaries are replaced at their
use location with their defining expression. This results in
non-GIMPLE code, but gives the expanders much more complex trees
to work on resulting in better RTL generation. This is enabled by
default at `-O' and higher.
`-ftree-lrs'
Perform live range splitting during the SSA->normal phase.
Distinct live ranges of a variable are split into unique
variables, allowing for better optimization later. This is
enabled by default at `-O' and higher.
`-ftree-vectorize'
Perform loop vectorization on trees.
`-ftree-vect-loop-version'
Perform loop versioning when doing loop vectorization on trees.
When a loop appears to be vectorizable except that data alignment
or data dependence cannot be determined at compile time then
vectorized and non-vectorized versions of the loop are generated
along with runtime checks for alignment or dependence to control
which version is executed. This option is enabled by default
except at level `-Os' where it is disabled.
`-ftree-vrp'
Perform Value Range Propagation on trees. This is similar to the
constant propagation pass, but instead of values, ranges of values
are propagated. This allows the optimizers to remove unnecessary
range checks like array bound checks and null pointer checks.
This is enabled by default at `-O2' and higher. Null pointer check
elimination is only done if `-fdelete-null-pointer-checks' is
enabled.
`-ftracer'
Perform tail duplication to enlarge superblock size. This
transformation simplifies the control flow of the function
allowing other optimizations to do better job.
`-funroll-loops'
Unroll loops whose number of iterations can be determined at
compile time or upon entry to the loop. `-funroll-loops' implies
`-frerun-cse-after-loop'. This option makes code larger, and may
or may not make it run faster.
`-funroll-all-loops'
Unroll all loops, even if their number of iterations is uncertain
when the loop is entered. This usually makes programs run more
slowly. `-funroll-all-loops' implies the same options as
`-funroll-loops',
`-fsplit-ivs-in-unroller'
Enables expressing of values of induction variables in later
iterations of the unrolled loop using the value in the first
iteration. This breaks long dependency chains, thus improving
efficiency of the scheduling passes.
Combination of `-fweb' and CSE is often sufficient to obtain the
same effect. However in cases the loop body is more complicated
than a single basic block, this is not reliable. It also does not
work at all on some of the architectures due to restrictions in
the CSE pass.
This optimization is enabled by default.
`-fvariable-expansion-in-unroller'
With this option, the compiler will create multiple copies of some
local variables when unrolling a loop which can result in superior
code.
`-fprefetch-loop-arrays'
If supported by the target machine, generate instructions to
prefetch memory to improve the performance of loops that access
large arrays.
This option may generate better or worse code; results are highly
dependent on the structure of loops within the source code.
Disabled at level `-Os'.
`-fno-peephole'
`-fno-peephole2'
Disable any machine-specific peephole optimizations. The
difference between `-fno-peephole' and `-fno-peephole2' is in how
they are implemented in the compiler; some targets use one, some
use the other, a few use both.
`-fpeephole' is enabled by default. `-fpeephole2' enabled at
levels `-O2', `-O3', `-Os'.
`-fno-guess-branch-probability'
Do not guess branch probabilities using heuristics.
GCC will use heuristics to guess branch probabilities if they are
not provided by profiling feedback (`-fprofile-arcs'). These
heuristics are based on the control flow graph. If some branch
probabilities are specified by `__builtin_expect', then the
heuristics will be used to guess branch probabilities for the rest
of the control flow graph, taking the `__builtin_expect' info into
account. The interactions between the heuristics and
`__builtin_expect' can be complex, and in some cases, it may be
useful to disable the heuristics so that the effects of
`__builtin_expect' are easier to understand.
The default is `-fguess-branch-probability' at levels `-O', `-O2',
`-O3', `-Os'.
`-freorder-blocks'
Reorder basic blocks in the compiled function in order to reduce
number of taken branches and improve code locality.
Enabled at levels `-O2', `-O3'.
`-freorder-blocks-and-partition'
In addition to reordering basic blocks in the compiled function,
in order to reduce number of taken branches, partitions hot and
cold basic blocks into separate sections of the assembly and .o
files, to improve paging and cache locality performance.
This optimization is automatically turned off in the presence of
exception handling, for linkonce sections, for functions with a
user-defined section attribute and on any architecture that does
not support named sections.
`-freorder-functions'
Reorder functions in the object file in order to improve code
locality. This is implemented by using special subsections
`.text.hot' for most frequently executed functions and
`.text.unlikely' for unlikely executed functions. Reordering is
done by the linker so object file format must support named
sections and linker must place them in a reasonable way.
Also profile feedback must be available in to make this option
effective. See `-fprofile-arcs' for details.
Enabled at levels `-O2', `-O3', `-Os'.
`-fstrict-aliasing'
Allows the compiler to assume the strictest aliasing rules
applicable to the language being compiled. For C (and C++), this
activates optimizations based on the type of expressions. In
particular, an object of one type is assumed never to reside at
the same address as an object of a different type, unless the
types are almost the same. For example, an `unsigned int' can
alias an `int', but not a `void*' or a `double'. A character type
may alias any other type.
Pay special attention to code like this:
union a_union {
int i;
double d;
};
int f() {
a_union t;
t.d = 3.0;
return t.i;
}
The practice of reading from a different union member than the one
most recently written to (called "type-punning") is common. Even
with `-fstrict-aliasing', type-punning is allowed, provided the
memory is accessed through the union type. So, the code above
will work as expected. However, this code might not:
int f() {
a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
return *ip;
}
Every language that wishes to perform language-specific alias
analysis should define a function that computes, given an `tree'
node, an alias set for the node. Nodes in different alias sets
are not allowed to alias. For an example, see the C front-end
function `c_get_alias_set'.
Enabled at levels `-O2', `-O3', `-Os'.
`-fstrict-overflow'
Allow the compiler to assume strict signed overflow rules,
depending on the language being compiled. For C (and C++) this
means that overflow when doing arithmetic with signed numbers is
undefined, which means that the compiler may assume that it will
not happen. This permits various optimizations. For example, the
compiler will assume that an expression like `i + 10 > i' will
always be true for signed `i'. This assumption is only valid if
signed overflow is undefined, as the expression is false if `i +
10' overflows when using twos complement arithmetic. When this
option is in effect any attempt to determine whether an operation
on signed numbers will overflow must be written carefully to not
actually involve overflow.
See also the `-fwrapv' option. Using `-fwrapv' means that signed
overflow is fully defined: it wraps. When `-fwrapv' is used,
there is no difference between `-fstrict-overflow' and
`-fno-strict-overflow'. With `-fwrapv' certain types of overflow
are permitted. For example, if the compiler gets an overflow when
doing arithmetic on constants, the overflowed value can still be
used with `-fwrapv', but not otherwise.
The `-fstrict-overflow' option is enabled at levels `-O2', `-O3',
`-Os'.
`-falign-functions'
`-falign-functions=N'
Align the start of functions to the next power-of-two greater than
N, skipping up to N bytes. For instance, `-falign-functions=32'
aligns functions to the next 32-byte boundary, but
`-falign-functions=24' would align to the next 32-byte boundary
only if this can be done by skipping 23 bytes or less.
`-fno-align-functions' and `-falign-functions=1' are equivalent
and mean that functions will not be aligned.
Some assemblers only support this flag when N is a power of two;
in that case, it is rounded up.
If N is not specified or is zero, use a machine-dependent default.
Enabled at levels `-O2', `-O3'.
`-falign-labels'
`-falign-labels=N'
Align all branch targets to a power-of-two boundary, skipping up to
N bytes like `-falign-functions'. This option can easily make
code slower, because it must insert dummy operations for when the
branch target is reached in the usual flow of the code.
`-fno-align-labels' and `-falign-labels=1' are equivalent and mean
that labels will not be aligned.
If `-falign-loops' or `-falign-jumps' are applicable and are
greater than this value, then their values are used instead.
If N is not specified or is zero, use a machine-dependent default
which is very likely to be `1', meaning no alignment.
Enabled at levels `-O2', `-O3'.
`-falign-loops'
`-falign-loops=N'
Align loops to a power-of-two boundary, skipping up to N bytes
like `-falign-functions'. The hope is that the loop will be
executed many times, which will make up for any execution of the
dummy operations.
`-fno-align-loops' and `-falign-loops=1' are equivalent and mean
that loops will not be aligned.
If N is not specified or is zero, use a machine-dependent default.
Enabled at levels `-O2', `-O3'.
`-falign-jumps'
`-falign-jumps=N'
Align branch targets to a power-of-two boundary, for branch targets
where the targets can only be reached by jumping, skipping up to N
bytes like `-falign-functions'. In this case, no dummy operations
need be executed.
`-fno-align-jumps' and `-falign-jumps=1' are equivalent and mean
that loops will not be aligned.
If N is not specified or is zero, use a machine-dependent default.
Enabled at levels `-O2', `-O3'.
`-funit-at-a-time'
Parse the whole compilation unit before starting to produce code.
This allows some extra optimizations to take place but consumes
more memory (in general). There are some compatibility issues
with _unit-at-a-time_ mode:
* enabling _unit-at-a-time_ mode may change the order in which
functions, variables, and top-level `asm' statements are
emitted, and will likely break code relying on some particular
ordering. The majority of such top-level `asm' statements,
though, can be replaced by `section' attributes. The
`fno-toplevel-reorder' option may be used to keep the ordering
used in the input file, at the cost of some optimizations.
* _unit-at-a-time_ mode removes unreferenced static variables
and functions. This may result in undefined references when
an `asm' statement refers directly to variables or functions
that are otherwise unused. In that case either the
variable/function shall be listed as an operand of the `asm'
statement operand or, in the case of top-level `asm'
statements the attribute `used' shall be used on the
declaration.
* Static functions now can use non-standard passing conventions
that may break `asm' statements calling functions directly.
Again, attribute `used' will prevent this behavior.
As a temporary workaround, `-fno-unit-at-a-time' can be used, but
this scheme may not be supported by future releases of GCC.
Enabled at levels `-O', `-O2', `-O3', `-Os'.
`-fno-toplevel-reorder'
Do not reorder top-level functions, variables, and `asm'
statements. Output them in the same order that they appear in the
input file. When this option is used, unreferenced static
variables will not be removed. This option is intended to support
existing code which relies on a particular ordering. For new
code, it is better to use attributes.
`-fweb'
Constructs webs as commonly used for register allocation purposes
and assign each web individual pseudo register. This allows the
register allocation pass to operate on pseudos directly, but also
strengthens several other optimization passes, such as CSE, loop
optimizer and trivial dead code remover. It can, however, make
debugging impossible, since variables will no longer stay in a
"home register".
Enabled by default with `-funroll-loops'.
`-fwhole-program'
Assume that the current compilation unit represents whole program
being compiled. All public functions and variables with the
exception of `main' and those merged by attribute
`externally_visible' become static functions and in a affect gets
more aggressively optimized by interprocedural optimizers. While
this option is equivalent to proper use of `static' keyword for
programs consisting of single file, in combination with option
`--combine' this flag can be used to compile most of smaller scale
C programs since the functions and variables become local for the
whole combined compilation unit, not for the single source file
itself.
`-fno-cprop-registers'
After register allocation and post-register allocation instruction
splitting, we perform a copy-propagation pass to try to reduce
scheduling dependencies and occasionally eliminate the copy.
Disabled at levels `-O', `-O2', `-O3', `-Os'.
`-fprofile-generate'
Enable options usually used for instrumenting application to
produce profile useful for later recompilation with profile
feedback based optimization. You must use `-fprofile-generate'
both when compiling and when linking your program.
The following options are enabled: `-fprofile-arcs',
`-fprofile-values', `-fvpt'.
`-fprofile-use'
Enable profile feedback directed optimizations, and optimizations
generally profitable only with profile feedback available.
The following options are enabled: `-fbranch-probabilities',
`-fvpt', `-funroll-loops', `-fpeel-loops', `-ftracer'
The following options control compiler behavior regarding floating
point arithmetic. These options trade off between speed and
correctness. All must be specifically enabled.
`-ffloat-store'
Do not store floating point variables in registers, and inhibit
other options that might change whether a floating point value is
taken from a register or memory.
This option prevents undesirable excess precision on machines such
as the 68000 where the floating registers (of the 68881) keep more
precision than a `double' is supposed to have. Similarly for the
x86 architecture. For most programs, the excess precision does
only good, but a few programs rely on the precise definition of
IEEE floating point. Use `-ffloat-store' for such programs, after
modifying them to store all pertinent intermediate computations
into variables.
`-ffast-math'
Sets `-fno-math-errno', `-funsafe-math-optimizations',
`-fno-trapping-math', `-ffinite-math-only', `-fno-rounding-math',
`-fno-signaling-nans' and `fcx-limited-range'.
This option causes the preprocessor macro `__FAST_MATH__' to be
defined.
This option should never be turned on by any `-O' option since it
can result in incorrect output for programs which depend on an
exact implementation of IEEE or ISO rules/specifications for math
functions.
`-fno-math-errno'
Do not set ERRNO after calling math functions that are executed
with a single instruction, e.g., sqrt. A program that relies on
IEEE exceptions for math error handling may want to use this flag
for speed while maintaining IEEE arithmetic compatibility.
This option should never be turned on by any `-O' option since it
can result in incorrect output for programs which depend on an
exact implementation of IEEE or ISO rules/specifications for math
functions.
The default is `-fmath-errno'.
On Darwin systems, the math library never sets `errno'. There is
therefore no reason for the compiler to consider the possibility
that it might, and `-fno-math-errno' is the default.
`-funsafe-math-optimizations'
Allow optimizations for floating-point arithmetic that (a) assume
that arguments and results are valid and (b) may violate IEEE or
ANSI standards. When used at link-time, it may include libraries
or startup files that change the default FPU control word or other
similar optimizations.
This option should never be turned on by any `-O' option since it
can result in incorrect output for programs which depend on an
exact implementation of IEEE or ISO rules/specifications for math
functions.
The default is `-fno-unsafe-math-optimizations'.
`-ffinite-math-only'
Allow optimizations for floating-point arithmetic that assume that
arguments and results are not NaNs or +-Infs.
This option should never be turned on by any `-O' option since it
can result in incorrect output for programs which depend on an
exact implementation of IEEE or ISO rules/specifications.
The default is `-fno-finite-math-only'.
`-fno-trapping-math'
Compile code assuming that floating-point operations cannot
generate user-visible traps. These traps include division by
zero, overflow, underflow, inexact result and invalid operation.
This option implies `-fno-signaling-nans'. Setting this option
may allow faster code if one relies on "non-stop" IEEE arithmetic,
for example.
This option should never be turned on by any `-O' option since it
can result in incorrect output for programs which depend on an
exact implementation of IEEE or ISO rules/specifications for math
functions.
The default is `-ftrapping-math'.
`-frounding-math'
Disable transformations and optimizations that assume default
floating point rounding behavior. This is round-to-zero for all
floating point to integer conversions, and round-to-nearest for
all other arithmetic truncations. This option should be specified
for programs that change the FP rounding mode dynamically, or that
may be executed with a non-default rounding mode. This option
disables constant folding of floating point expressions at
compile-time (which may be affected by rounding mode) and
arithmetic transformations that are unsafe in the presence of
sign-dependent rounding modes.
The default is `-fno-rounding-math'.
This option is experimental and does not currently guarantee to
disable all GCC optimizations that are affected by rounding mode.
Future versions of GCC may provide finer control of this setting
using C99's `FENV_ACCESS' pragma. This command line option will
be used to specify the default state for `FENV_ACCESS'.
`-frtl-abstract-sequences'
It is a size optimization method. This option is to find identical
sequences of code, which can be turned into pseudo-procedures and
then replace all occurrences with calls to the newly created
subroutine. It is kind of an opposite of `-finline-functions'.
This optimization runs at RTL level.
`-fsignaling-nans'
Compile code assuming that IEEE signaling NaNs may generate
user-visible traps during floating-point operations. Setting this
option disables optimizations that may change the number of
exceptions visible with signaling NaNs. This option implies
`-ftrapping-math'.
This option causes the preprocessor macro `__SUPPORT_SNAN__' to be
defined.
The default is `-fno-signaling-nans'.
This option is experimental and does not currently guarantee to
disable all GCC optimizations that affect signaling NaN behavior.
`-fsingle-precision-constant'
Treat floating point constant as single precision constant instead
of implicitly converting it to double precision constant.
`-fcx-limited-range'
`-fno-cx-limited-range'
When enabled, this option states that a range reduction step is not
needed when performing complex division. The default is
`-fno-cx-limited-range', but is enabled by `-ffast-math'.
This option controls the default setting of the ISO C99
`CX_LIMITED_RANGE' pragma. Nevertheless, the option applies to
all languages.
The following options control optimizations that may improve
performance, but are not enabled by any `-O' options. This section
includes experimental options that may produce broken code.
`-fbranch-probabilities'
After running a program compiled with `-fprofile-arcs' (*note
Options for Debugging Your Program or `gcc': Debugging Options.),
you can compile it a second time using `-fbranch-probabilities',
to improve optimizations based on the number of times each branch
was taken. When the program compiled with `-fprofile-arcs' exits
it saves arc execution counts to a file called `SOURCENAME.gcda'
for each source file The information in this data file is very
dependent on the structure of the generated code, so you must use
the same source code and the same optimization options for both
compilations.
With `-fbranch-probabilities', GCC puts a `REG_BR_PROB' note on
each `JUMP_INSN' and `CALL_INSN'. These can be used to improve
optimization. Currently, they are only used in one place: in
`reorg.c', instead of guessing which path a branch is mostly to
take, the `REG_BR_PROB' values are used to exactly determine which
path is taken more often.
`-fprofile-values'
If combined with `-fprofile-arcs', it adds code so that some data
about values of expressions in the program is gathered.
With `-fbranch-probabilities', it reads back the data gathered
from profiling values of expressions and adds `REG_VALUE_PROFILE'
notes to instructions for their later usage in optimizations.
Enabled with `-fprofile-generate' and `-fprofile-use'.
`-fvpt'
If combined with `-fprofile-arcs', it instructs the compiler to add
a code to gather information about values of expressions.
With `-fbranch-probabilities', it reads back the data gathered and
actually performs the optimizations based on them. Currently the
optimizations include specialization of division operation using
the knowledge about the value of the denominator.
`-frename-registers'
Attempt to avoid false dependencies in scheduled code by making use
of registers left over after register allocation. This
optimization will most benefit processors with lots of registers.
Depending on the debug information format adopted by the target,
however, it can make debugging impossible, since variables will no
longer stay in a "home register".
Enabled by default with `-funroll-loops'.
`-ftracer'
Perform tail duplication to enlarge superblock size. This
transformation simplifies the control flow of the function
allowing other optimizations to do better job.
Enabled with `-fprofile-use'.
`-funroll-loops'
Unroll loops whose number of iterations can be determined at
compile time or upon entry to the loop. `-funroll-loops' implies
`-frerun-cse-after-loop', `-fweb' and `-frename-registers'. It
also turns on complete loop peeling (i.e. complete removal of
loops with small constant number of iterations). This option
makes code larger, and may or may not make it run faster.
Enabled with `-fprofile-use'.
`-funroll-all-loops'
Unroll all loops, even if their number of iterations is uncertain
when the loop is entered. This usually makes programs run more
slowly. `-funroll-all-loops' implies the same options as
`-funroll-loops'.
`-fpeel-loops'
Peels the loops for that there is enough information that they do
not roll much (from profile feedback). It also turns on complete
loop peeling (i.e. complete removal of loops with small constant
number of iterations).
Enabled with `-fprofile-use'.
`-fmove-loop-invariants'
Enables the loop invariant motion pass in the RTL loop optimizer.
Enabled at level `-O1'
`-funswitch-loops'
Move branches with loop invariant conditions out of the loop, with
duplicates of the loop on both branches (modified according to
result of the condition).
`-ffunction-sections'
`-fdata-sections'
Place each function or data item into its own section in the output
file if the target supports arbitrary sections. The name of the
function or the name of the data item determines the section's name
in the output file.
Use these options on systems where the linker can perform
optimizations to improve locality of reference in the instruction
space. Most systems using the ELF object format and SPARC
processors running Solaris 2 have linkers with such optimizations.
AIX may have these optimizations in the future.
Only use these options when there are significant benefits from
doing so. When you specify these options, the assembler and
linker will create larger object and executable files and will
also be slower. You will not be able to use `gprof' on all
systems if you specify this option and you may have problems with
debugging if you specify both this option and `-g'.
`-fbranch-target-load-optimize'
Perform branch target register load optimization before prologue /
epilogue threading. The use of target registers can typically be
exposed only during reload, thus hoisting loads out of loops and
doing inter-block scheduling needs a separate optimization pass.
`-fbranch-target-load-optimize2'
Perform branch target register load optimization after prologue /
epilogue threading.
`-fbtr-bb-exclusive'
When performing branch target register load optimization, don't
reuse branch target registers in within any basic block.
`-fstack-protector'
Emit extra code to check for buffer overflows, such as stack
smashing attacks. This is done by adding a guard variable to
functions with vulnerable objects. This includes functions that
call alloca, and functions with buffers larger than 8 bytes. The
guards are initialized when a function is entered and then checked
when the function exits. If a guard check fails, an error message
is printed and the program exits.
`-fstack-protector-all'
Like `-fstack-protector' except that all functions are protected.
`-fsection-anchors'
Try to reduce the number of symbolic address calculations by using
shared "anchor" symbols to address nearby objects. This
transformation can help to reduce the number of GOT entries and
GOT accesses on some targets.
For example, the implementation of the following function `foo':
static int a, b, c;
int foo (void) { return a + b + c; }
would usually calculate the addresses of all three variables, but
if you compile it with `-fsection-anchors', it will access the
variables from a common anchor point instead. The effect is
similar to the following pseudocode (which isn't valid C):
int foo (void)
{
register int *xr = &x;
return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
}
Not all targets support this option.
`--param NAME=VALUE'
In some places, GCC uses various constants to control the amount of
optimization that is done. For example, GCC will not inline
functions that contain more that a certain number of instructions.
You can control some of these constants on the command-line using
the `--param' option.
The names of specific parameters, and the meaning of the values,
are tied to the internals of the compiler, and are subject to
change without notice in future releases.
In each case, the VALUE is an integer. The allowable choices for
NAME are given in the following table:
`salias-max-implicit-fields'
The maximum number of fields in a variable without direct
structure accesses for which structure aliasing will consider
trying to track each field. The default is 5
`salias-max-array-elements'
The maximum number of elements an array can have and its
elements still be tracked individually by structure aliasing.
The default is 4
`sra-max-structure-size'
The maximum structure size, in bytes, at which the scalar
replacement of aggregates (SRA) optimization will perform
block copies. The default value, 0, implies that GCC will
select the most appropriate size itself.
`sra-field-structure-ratio'
The threshold ratio (as a percentage) between instantiated
fields and the complete structure size. We say that if the
ratio of the number of bytes in instantiated fields to the
number of bytes in the complete structure exceeds this
parameter, then block copies are not used. The default is 75.
`max-crossjump-edges'
The maximum number of incoming edges to consider for
crossjumping. The algorithm used by `-fcrossjumping' is
O(N^2) in the number of edges incoming to each block.
Increasing values mean more aggressive optimization, making
the compile time increase with probably small improvement in
executable size.
`min-crossjump-insns'
The minimum number of instructions which must be matched at
the end of two blocks before crossjumping will be performed
on them. This value is ignored in the case where all
instructions in the block being crossjumped from are matched.
The default value is 5.
`max-grow-copy-bb-insns'
The maximum code size expansion factor when copying basic
blocks instead of jumping. The expansion is relative to a
jump instruction. The default value is 8.
`max-goto-duplication-insns'
The maximum number of instructions to duplicate to a block
that jumps to a computed goto. To avoid O(N^2) behavior in a
number of passes, GCC factors computed gotos early in the
compilation process, and unfactors them as late as possible.
Only computed jumps at the end of a basic blocks with no more
than max-goto-duplication-insns are unfactored. The default
value is 8.
`max-delay-slot-insn-search'
The maximum number of instructions to consider when looking
for an instruction to fill a delay slot. If more than this
arbitrary number of instructions is searched, the time
savings from filling the delay slot will be minimal so stop
searching. Increasing values mean more aggressive
optimization, making the compile time increase with probably
small improvement in executable run time.
`max-delay-slot-live-search'
When trying to fill delay slots, the maximum number of
instructions to consider when searching for a block with
valid live register information. Increasing this arbitrarily
chosen value means more aggressive optimization, increasing
the compile time. This parameter should be removed when the
delay slot code is rewritten to maintain the control-flow
graph.
`max-gcse-memory'
The approximate maximum amount of memory that will be
allocated in order to perform the global common subexpression
elimination optimization. If more memory than specified is
required, the optimization will not be done.
`max-gcse-passes'
The maximum number of passes of GCSE to run. The default is
1.
`max-pending-list-length'
The maximum number of pending dependencies scheduling will
allow before flushing the current state and starting over.
Large functions with few branches or calls can create
excessively large lists which needlessly consume memory and
resources.
`max-inline-insns-single'
Several parameters control the tree inliner used in gcc.
This number sets the maximum number of instructions (counted
in GCC's internal representation) in a single function that
the tree inliner will consider for inlining. This only
affects functions declared inline and methods implemented in
a class declaration (C++). The default value is 450.
`max-inline-insns-auto'
When you use `-finline-functions' (included in `-O3'), a lot
of functions that would otherwise not be considered for
inlining by the compiler will be investigated. To those
functions, a different (more restrictive) limit compared to
functions declared inline can be applied. The default value
is 90.
`large-function-insns'
The limit specifying really large functions. For functions
larger than this limit after inlining inlining is constrained
by `--param large-function-growth'. This parameter is useful
primarily to avoid extreme compilation time caused by
non-linear algorithms used by the backend. This parameter is
ignored when `-funit-at-a-time' is not used. The default
value is 2700.
`large-function-growth'
Specifies maximal growth of large function caused by inlining
in percents. This parameter is ignored when
`-funit-at-a-time' is not used. The default value is 100
which limits large function growth to 2.0 times the original
size.
`large-unit-insns'
The limit specifying large translation unit. Growth caused
by inlining of units larger than this limit is limited by
`--param inline-unit-growth'. For small units this might be
too tight (consider unit consisting of function A that is
inline and B that just calls A three time. If B is small
relative to A, the growth of unit is 300\% and yet such
inlining is very sane. For very large units consisting of
small inlininable functions however the overall unit growth
limit is needed to avoid exponential explosion of code size.
Thus for smaller units, the size is increased to `--param
large-unit-insns' before applying `--param
inline-unit-growth'. The default is 10000
`inline-unit-growth'
Specifies maximal overall growth of the compilation unit
caused by inlining. This parameter is ignored when
`-funit-at-a-time' is not used. The default value is 50
which limits unit growth to 1.5 times the original size.
`max-inline-insns-recursive'
`max-inline-insns-recursive-auto'
Specifies maximum number of instructions out-of-line copy of
self recursive inline function can grow into by performing
recursive inlining.
For functions declared inline `--param
max-inline-insns-recursive' is taken into account. For
function not declared inline, recursive inlining happens only
when `-finline-functions' (included in `-O3') is enabled and
`--param max-inline-insns-recursive-auto' is used. The
default value is 450.
`max-inline-recursive-depth'
`max-inline-recursive-depth-auto'
Specifies maximum recursion depth used by the recursive
inlining.
For functions declared inline `--param
max-inline-recursive-depth' is taken into account. For
function not declared inline, recursive inlining happens only
when `-finline-functions' (included in `-O3') is enabled and
`--param max-inline-recursive-depth-auto' is used. The
default value is 450.
`min-inline-recursive-probability'
Recursive inlining is profitable only for function having
deep recursion in average and can hurt for function having
little recursion depth by increasing the prologue size or
complexity of function body to other optimizers.
When profile feedback is available (see `-fprofile-generate')
the actual recursion depth can be guessed from probability
that function will recurse via given call expression. This
parameter limits inlining only to call expression whose
probability exceeds given threshold (in percents). The
default value is 10.
`inline-call-cost'
Specify cost of call instruction relative to simple
arithmetics operations (having cost of 1). Increasing this
cost disqualifies inlining of non-leaf functions and at the
same time increases size of leaf function that is believed to
reduce function size by being inlined. In effect it
increases amount of inlining for code having large
abstraction penalty (many functions that just pass the
arguments to other functions) and decrease inlining for code
with low abstraction penalty. The default value is 16.
`max-unrolled-insns'
The maximum number of instructions that a loop should have if
that loop is unrolled, and if the loop is unrolled, it
determines how many times the loop code is unrolled.
`max-average-unrolled-insns'
The maximum number of instructions biased by probabilities of
their execution that a loop should have if that loop is
unrolled, and if the loop is unrolled, it determines how many
times the loop code is unrolled.
`max-unroll-times'
The maximum number of unrollings of a single loop.
`max-peeled-insns'
The maximum number of instructions that a loop should have if
that loop is peeled, and if the loop is peeled, it determines
how many times the loop code is peeled.
`max-peel-times'
The maximum number of peelings of a single loop.
`max-completely-peeled-insns'
The maximum number of insns of a completely peeled loop.
`max-completely-peel-times'
The maximum number of iterations of a loop to be suitable for
complete peeling.
`max-unswitch-insns'
The maximum number of insns of an unswitched loop.
`max-unswitch-level'
The maximum number of branches unswitched in a single loop.
`lim-expensive'
The minimum cost of an expensive expression in the loop
invariant motion.
`iv-consider-all-candidates-bound'
Bound on number of candidates for induction variables below
that all candidates are considered for each use in induction
variable optimizations. Only the most relevant candidates
are considered if there are more candidates, to avoid
quadratic time complexity.
`iv-max-considered-uses'
The induction variable optimizations give up on loops that
contain more induction variable uses.
`iv-always-prune-cand-set-bound'
If number of candidates in the set is smaller than this value,
we always try to remove unnecessary ivs from the set during
its optimization when a new iv is added to the set.
`scev-max-expr-size'
Bound on size of expressions used in the scalar evolutions
analyzer. Large expressions slow the analyzer.
`vect-max-version-checks'
The maximum number of runtime checks that can be performed
when doing loop versioning in the vectorizer. See option
ftree-vect-loop-version for more information.
`max-iterations-to-track'
The maximum number of iterations of a loop the brute force
algorithm for analysis of # of iterations of the loop tries
to evaluate.
`hot-bb-count-fraction'
Select fraction of the maximal count of repetitions of basic
block in program given basic block needs to have to be
considered hot.
`hot-bb-frequency-fraction'
Select fraction of the maximal frequency of executions of
basic block in function given basic block needs to have to be
considered hot
`max-predicted-iterations'
The maximum number of loop iterations we predict statically.
This is useful in cases where function contain single loop
with known bound and other loop with unknown. We predict the
known number of iterations correctly, while the unknown
number of iterations average to roughly 10. This means that
the loop without bounds would appear artificially cold
relative to the other one.
`tracer-dynamic-coverage'
`tracer-dynamic-coverage-feedback'
This value is used to limit superblock formation once the
given percentage of executed instructions is covered. This
limits unnecessary code size expansion.
The `tracer-dynamic-coverage-feedback' is used only when
profile feedback is available. The real profiles (as opposed
to statically estimated ones) are much less balanced allowing
the threshold to be larger value.
`tracer-max-code-growth'
Stop tail duplication once code growth has reached given
percentage. This is rather hokey argument, as most of the
duplicates will be eliminated later in cross jumping, so it
may be set to much higher values than is the desired code
growth.
`tracer-min-branch-ratio'
Stop reverse growth when the reverse probability of best edge
is less than this threshold (in percent).
`tracer-min-branch-ratio'
`tracer-min-branch-ratio-feedback'
Stop forward growth if the best edge do have probability
lower than this threshold.
Similarly to `tracer-dynamic-coverage' two values are
present, one for compilation for profile feedback and one for
compilation without. The value for compilation with profile
feedback needs to be more conservative (higher) in order to
make tracer effective.
`max-cse-path-length'
Maximum number of basic blocks on path that cse considers.
The default is 10.
`max-cse-insns'
The maximum instructions CSE process before flushing. The
default is 1000.
`global-var-threshold'
Counts the number of function calls (N) and the number of
call-clobbered variables (V). If NxV is larger than this
limit, a single artificial variable will be created to
represent all the call-clobbered variables at function call
sites. This artificial variable will then be made to alias
every call-clobbered variable. (done as `int * size_t' on
the host machine; beware overflow).
`max-aliased-vops'
Maximum number of virtual operands allowed to represent
aliases before triggering the alias grouping heuristic.
Alias grouping reduces compile times and memory consumption
needed for aliasing at the expense of precision loss in alias
information.
`ggc-min-expand'
GCC uses a garbage collector to manage its own memory
allocation. This parameter specifies the minimum percentage
by which the garbage collector's heap should be allowed to
expand between collections. Tuning this may improve
compilation speed; it has no effect on code generation.
The default is 30% + 70% * (RAM/1GB) with an upper bound of
100% when RAM >= 1GB. If `getrlimit' is available, the
notion of "RAM" is the smallest of actual RAM and
`RLIMIT_DATA' or `RLIMIT_AS'. If GCC is not able to
calculate RAM on a particular platform, the lower bound of
30% is used. Setting this parameter and `ggc-min-heapsize'
to zero causes a full collection to occur at every
opportunity. This is extremely slow, but can be useful for
debugging.
`ggc-min-heapsize'
Minimum size of the garbage collector's heap before it begins
bothering to collect garbage. The first collection occurs
after the heap expands by `ggc-min-expand'% beyond
`ggc-min-heapsize'. Again, tuning this may improve
compilation speed, and has no effect on code generation.
The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
which tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
exceeded, but with a lower bound of 4096 (four megabytes) and
an upper bound of 131072 (128 megabytes). If GCC is not able
to calculate RAM on a particular platform, the lower bound is
used. Setting this parameter very large effectively disables
garbage collection. Setting this parameter and
`ggc-min-expand' to zero causes a full collection to occur at
every opportunity.
`max-reload-search-insns'
The maximum number of instruction reload should look backward
for equivalent register. Increasing values mean more
aggressive optimization, making the compile time increase
with probably slightly better performance. The default value
is 100.
`max-cselib-memory-locations'
The maximum number of memory locations cselib should take
into account. Increasing values mean more aggressive
optimization, making the compile time increase with probably
slightly better performance. The default value is 500.
`max-flow-memory-locations'
Similar as `max-cselib-memory-locations' but for dataflow
liveness. The default value is 100.
`reorder-blocks-duplicate'
`reorder-blocks-duplicate-feedback'
Used by basic block reordering pass to decide whether to use
unconditional branch or duplicate the code on its
destination. Code is duplicated when its estimated size is
smaller than this value multiplied by the estimated size of
unconditional jump in the hot spots of the program.
The `reorder-block-duplicate-feedback' is used only when
profile feedback is available and may be set to higher values
than `reorder-block-duplicate' since information about the
hot spots is more accurate.
`max-sched-ready-insns'
The maximum number of instructions ready to be issued the
scheduler should consider at any given time during the first
scheduling pass. Increasing values mean more thorough
searches, making the compilation time increase with probably
little benefit. The default value is 100.
`max-sched-region-blocks'
The maximum number of blocks in a region to be considered for
interblock scheduling. The default value is 10.
`max-sched-region-insns'
The maximum number of insns in a region to be considered for
interblock scheduling. The default value is 100.
`min-spec-prob'
The minimum probability (in percents) of reaching a source
block for interblock speculative scheduling. The default
value is 40.
`max-sched-extend-regions-iters'
The maximum number of iterations through CFG to extend
regions. 0 - disable region extension, N - do at most N
iterations. The default value is 0.
`max-sched-insn-conflict-delay'
The maximum conflict delay for an insn to be considered for
speculative motion. The default value is 3.
`sched-spec-prob-cutoff'
The minimal probability of speculation success (in percents),
so that speculative insn will be scheduled. The default
value is 40.
`max-last-value-rtl'
The maximum size measured as number of RTLs that can be
recorded in an expression in combiner for a pseudo register
as last known value of that register. The default is 10000.
`integer-share-limit'
Small integer constants can use a shared data structure,
reducing the compiler's memory usage and increasing its
speed. This sets the maximum value of a shared integer
constant's. The default value is 256.
`min-virtual-mappings'
Specifies the minimum number of virtual mappings in the
incremental SSA updater that should be registered to trigger
the virtual mappings heuristic defined by
virtual-mappings-ratio. The default value is 100.
`virtual-mappings-ratio'
If the number of virtual mappings is virtual-mappings-ratio
bigger than the number of virtual symbols to be updated, then
the incremental SSA updater switches to a full update for
those symbols. The default ratio is 3.
`ssp-buffer-size'
The minimum size of buffers (i.e. arrays) that will receive
stack smashing protection when `-fstack-protection' is used.
`max-jump-thread-duplication-stmts'
Maximum number of statements allowed in a block that needs to
be duplicated when threading jumps.
`max-fields-for-field-sensitive'
Maximum number of fields in a structure we will treat in a
field sensitive manner during pointer analysis.
File: gcc.info, Node: Preprocessor Options, Next: Assembler Options, Prev: Optimize Options, Up: Invoking GCC
3.11 Options Controlling the Preprocessor
=========================================
These options control the C preprocessor, which is run on each C source
file before actual compilation.
If you use the `-E' option, nothing is done except preprocessing.
Some of these options make sense only together with `-E' because they
cause the preprocessor output to be unsuitable for actual compilation.
You can use `-Wp,OPTION' to bypass the compiler driver and pass
OPTION directly through to the preprocessor. If OPTION contains
commas, it is split into multiple options at the commas. However,
many options are modified, translated or interpreted by the
compiler driver before being passed to the preprocessor, and `-Wp'
forcibly bypasses this phase. The preprocessor's direct interface
is undocumented and subject to change, so whenever possible you
should avoid using `-Wp' and let the driver handle the options
instead.
`-Xpreprocessor OPTION'
Pass OPTION as an option to the preprocessor. You can use this to
supply system-specific preprocessor options which GCC does not
know how to recognize.
If you want to pass an option that takes an argument, you must use
`-Xpreprocessor' twice, once for the option and once for the
argument.
`-D NAME'
Predefine NAME as a macro, with definition `1'.
`-D NAME=DEFINITION'
The contents of DEFINITION are tokenized and processed as if they
appeared during translation phase three in a `#define' directive.
In particular, the definition will be truncated by embedded
newline characters.
If you are invoking the preprocessor from a shell or shell-like
program you may need to use the shell's quoting syntax to protect
characters such as spaces that have a meaning in the shell syntax.
If you wish to define a function-like macro on the command line,
write its argument list with surrounding parentheses before the
equals sign (if any). Parentheses are meaningful to most shells,
so you will need to quote the option. With `sh' and `csh',
`-D'NAME(ARGS...)=DEFINITION'' works.
`-D' and `-U' options are processed in the order they are given on
the command line. All `-imacros FILE' and `-include FILE' options
are processed after all `-D' and `-U' options.
`-U NAME'
Cancel any previous definition of NAME, either built in or
provided with a `-D' option.
`-undef'
Do not predefine any system-specific or GCC-specific macros. The
standard predefined macros remain defined.
`-I DIR'
Add the directory DIR to the list of directories to be searched
for header files. Directories named by `-I' are searched before
the standard system include directories. If the directory DIR is
a standard system include directory, the option is ignored to
ensure that the default search order for system directories and
the special treatment of system headers are not defeated .
`-o FILE'
Write output to FILE. This is the same as specifying FILE as the
second non-option argument to `cpp'. `gcc' has a different
interpretation of a second non-option argument, so you must use
`-o' to specify the output file.
`-Wall'
Turns on all optional warnings which are desirable for normal code.
At present this is `-Wcomment', `-Wtrigraphs', `-Wmultichar' and a
warning about integer promotion causing a change of sign in `#if'
expressions. Note that many of the preprocessor's warnings are on
by default and have no options to control them.
`-Wcomment'
`-Wcomments'
Warn whenever a comment-start sequence `/*' appears in a `/*'
comment, or whenever a backslash-newline appears in a `//' comment.
(Both forms have the same effect.)
`-Wtrigraphs'
Most trigraphs in comments cannot affect the meaning of the
program. However, a trigraph that would form an escaped newline
(`??/' at the end of a line) can, by changing where the comment
begins or ends. Therefore, only trigraphs that would form escaped
newlines produce warnings inside a comment.
This option is implied by `-Wall'. If `-Wall' is not given, this
option is still enabled unless trigraphs are enabled. To get
trigraph conversion without warnings, but get the other `-Wall'
warnings, use `-trigraphs -Wall -Wno-trigraphs'.
`-Wtraditional'
Warn about certain constructs that behave differently in
traditional and ISO C. Also warn about ISO C constructs that have
no traditional C equivalent, and problematic constructs which
should be avoided.
`-Wimport'
Warn the first time `#import' is used.
`-Wundef'
Warn whenever an identifier which is not a macro is encountered in
an `#if' directive, outside of `defined'. Such identifiers are
replaced with zero.
`-Wunused-macros'
Warn about macros defined in the main file that are unused. A
macro is "used" if it is expanded or tested for existence at least
once. The preprocessor will also warn if the macro has not been
used at the time it is redefined or undefined.
Built-in macros, macros defined on the command line, and macros
defined in include files are not warned about.
_Note:_ If a macro is actually used, but only used in skipped
conditional blocks, then CPP will report it as unused. To avoid
the warning in such a case, you might improve the scope of the
macro's definition by, for example, moving it into the first
skipped block. Alternatively, you could provide a dummy use with
something like:
#if defined the_macro_causing_the_warning
#endif
`-Wendif-labels'
Warn whenever an `#else' or an `#endif' are followed by text.
This usually happens in code of the form
#if FOO
...
#else FOO
...
#endif FOO
The second and third `FOO' should be in comments, but often are not
in older programs. This warning is on by default.
`-Werror'
Make all warnings into hard errors. Source code which triggers
warnings will be rejected.
`-Wsystem-headers'
Issue warnings for code in system headers. These are normally
unhelpful in finding bugs in your own code, therefore suppressed.
If you are responsible for the system library, you may want to see
them.
`-w'
Suppress all warnings, including those which GNU CPP issues by
default.
`-pedantic'
Issue all the mandatory diagnostics listed in the C standard.
Some of them are left out by default, since they trigger
frequently on harmless code.
`-pedantic-errors'
Issue all the mandatory diagnostics, and make all mandatory
diagnostics into errors. This includes mandatory diagnostics that
GCC issues without `-pedantic' but treats as warnings.
`-M'
Instead of outputting the result of preprocessing, output a rule
suitable for `make' describing the dependencies of the main source
file. The preprocessor outputs one `make' rule containing the
object file name for that source file, a colon, and the names of
all the included files, including those coming from `-include' or
`-imacros' command line options.
Unless specified explicitly (with `-MT' or `-MQ'), the object file
name consists of the basename of the source file with any suffix
replaced with object file suffix. If there are many included
files then the rule is split into several lines using `\'-newline.
The rule has no commands.
This option does not suppress the preprocessor's debug output,
such as `-dM'. To avoid mixing such debug output with the
dependency rules you should explicitly specify the dependency
output file with `-MF', or use an environment variable like
`DEPENDENCIES_OUTPUT' (*note Environment Variables::). Debug
output will still be sent to the regular output stream as normal.
Passing `-M' to the driver implies `-E', and suppresses warnings
with an implicit `-w'.
`-MM'
Like `-M' but do not mention header files that are found in system
header directories, nor header files that are included, directly
or indirectly, from such a header.
This implies that the choice of angle brackets or double quotes in
an `#include' directive does not in itself determine whether that
header will appear in `-MM' dependency output. This is a slight
change in semantics from GCC versions 3.0 and earlier.
`-MF FILE'
When used with `-M' or `-MM', specifies a file to write the
dependencies to. If no `-MF' switch is given the preprocessor
sends the rules to the same place it would have sent preprocessed
output.
When used with the driver options `-MD' or `-MMD', `-MF' overrides
the default dependency output file.
`-MG'
In conjunction with an option such as `-M' requesting dependency
generation, `-MG' assumes missing header files are generated files
and adds them to the dependency list without raising an error.
The dependency filename is taken directly from the `#include'
directive without prepending any path. `-MG' also suppresses
preprocessed output, as a missing header file renders this useless.
This feature is used in automatic updating of makefiles.
`-MP'
This option instructs CPP to add a phony target for each dependency
other than the main file, causing each to depend on nothing. These
dummy rules work around errors `make' gives if you remove header
files without updating the `Makefile' to match.
This is typical output:
test.o: test.c test.h
test.h:
`-MT TARGET'
Change the target of the rule emitted by dependency generation. By
default CPP takes the name of the main input file, including any
path, deletes any file suffix such as `.c', and appends the
platform's usual object suffix. The result is the target.
An `-MT' option will set the target to be exactly the string you
specify. If you want multiple targets, you can specify them as a
single argument to `-MT', or use multiple `-MT' options.
For example, `-MT '$(objpfx)foo.o'' might give
$(objpfx)foo.o: foo.c
`-MQ TARGET'
Same as `-MT', but it quotes any characters which are special to
Make. `-MQ '$(objpfx)foo.o'' gives
$$(objpfx)foo.o: foo.c
The default target is automatically quoted, as if it were given
with `-MQ'.
`-MD'
`-MD' is equivalent to `-M -MF FILE', except that `-E' is not
implied. The driver determines FILE based on whether an `-o'
option is given. If it is, the driver uses its argument but with
a suffix of `.d', otherwise it take the basename of the input file
and applies a `.d' suffix.
If `-MD' is used in conjunction with `-E', any `-o' switch is
understood to specify the dependency output file (*note -MF:
dashMF.), but if used without `-E', each `-o' is understood to
specify a target object file.
Since `-E' is not implied, `-MD' can be used to generate a
dependency output file as a side-effect of the compilation process.
`-MMD'
Like `-MD' except mention only user header files, not system
header files.
`-fpch-deps'
When using precompiled headers (*note Precompiled Headers::), this
flag will cause the dependency-output flags to also list the files
from the precompiled header's dependencies. If not specified only
the precompiled header would be listed and not the files that were
used to create it because those files are not consulted when a
precompiled header is used.
`-fpch-preprocess'
This option allows use of a precompiled header (*note Precompiled
Headers::) together with `-E'. It inserts a special `#pragma',
`#pragma GCC pch_preprocess "<filename>"' in the output to mark
the place where the precompiled header was found, and its
filename. When `-fpreprocessed' is in use, GCC recognizes this
`#pragma' and loads the PCH.
This option is off by default, because the resulting preprocessed
output is only really suitable as input to GCC. It is switched on
by `-save-temps'.
You should not write this `#pragma' in your own code, but it is
safe to edit the filename if the PCH file is available in a
different location. The filename may be absolute or it may be
relative to GCC's current directory.
`-x c'
`-x c++'
`-x objective-c'
`-x assembler-with-cpp'
Specify the source language: C, C++, Objective-C, or assembly.
This has nothing to do with standards conformance or extensions;
it merely selects which base syntax to expect. If you give none
of these options, cpp will deduce the language from the extension
of the source file: `.c', `.cc', `.m', or `.S'. Some other common
extensions for C++ and assembly are also recognized. If cpp does
not recognize the extension, it will treat the file as C; this is
the most generic mode.
_Note:_ Previous versions of cpp accepted a `-lang' option which
selected both the language and the standards conformance level.
This option has been removed, because it conflicts with the `-l'
option.
`-std=STANDARD'
`-ansi'
Specify the standard to which the code should conform. Currently
CPP knows about C and C++ standards; others may be added in the
future.
STANDARD may be one of:
`iso9899:1990'
`c89'
The ISO C standard from 1990. `c89' is the customary
shorthand for this version of the standard.
The `-ansi' option is equivalent to `-std=c89'.
`iso9899:199409'
The 1990 C standard, as amended in 1994.
`iso9899:1999'
`c99'
`iso9899:199x'
`c9x'
The revised ISO C standard, published in December 1999.
Before publication, this was known as C9X.
`gnu89'
The 1990 C standard plus GNU extensions. This is the default.
`gnu99'
`gnu9x'
The 1999 C standard plus GNU extensions.
`c++98'
The 1998 ISO C++ standard plus amendments.
`gnu++98'
The same as `-std=c++98' plus GNU extensions. This is the
default for C++ code.
`-I-'
Split the include path. Any directories specified with `-I'
options before `-I-' are searched only for headers requested with
`#include "FILE"'; they are not searched for `#include <FILE>'.
If additional directories are specified with `-I' options after
the `-I-', those directories are searched for all `#include'
directives.
In addition, `-I-' inhibits the use of the directory of the current
file directory as the first search directory for `#include "FILE"'.
This option has been deprecated.
`-nostdinc'
Do not search the standard system directories for header files.
Only the directories you have specified with `-I' options (and the
directory of the current file, if appropriate) are searched.
`-nostdinc++'
Do not search for header files in the C++-specific standard
directories, but do still search the other standard directories.
(This option is used when building the C++ library.)
`-include FILE'
Process FILE as if `#include "file"' appeared as the first line of
the primary source file. However, the first directory searched
for FILE is the preprocessor's working directory _instead of_ the
directory containing the main source file. If not found there, it
is searched for in the remainder of the `#include "..."' search
chain as normal.
If multiple `-include' options are given, the files are included
in the order they appear on the command line.
`-imacros FILE'
Exactly like `-include', except that any output produced by
scanning FILE is thrown away. Macros it defines remain defined.
This allows you to acquire all the macros from a header without
also processing its declarations.
All files specified by `-imacros' are processed before all files
specified by `-include'.
`-idirafter DIR'
Search DIR for header files, but do it _after_ all directories
specified with `-I' and the standard system directories have been
exhausted. DIR is treated as a system include directory.
`-iprefix PREFIX'
Specify PREFIX as the prefix for subsequent `-iwithprefix'
options. If the prefix represents a directory, you should include
the final `/'.
`-iwithprefix DIR'
`-iwithprefixbefore DIR'
Append DIR to the prefix specified previously with `-iprefix', and
add the resulting directory to the include search path.
`-iwithprefixbefore' puts it in the same place `-I' would;
`-iwithprefix' puts it where `-idirafter' would.
`-isysroot DIR'
This option is like the `--sysroot' option, but applies only to
header files. See the `--sysroot' option for more information.
`-imultilib DIR'
Use DIR as a subdirectory of the directory containing
target-specific C++ headers.
`-isystem DIR'
Search DIR for header files, after all directories specified by
`-I' but before the standard system directories. Mark it as a
system directory, so that it gets the same special treatment as is
applied to the standard system directories.
`-iquote DIR'
Search DIR only for header files requested with `#include "FILE"';
they are not searched for `#include <FILE>', before all
directories specified by `-I' and before the standard system
directories.
`-fdollars-in-identifiers'
Accept `$' in identifiers.
`-fextended-identifiers'
Accept universal character names in identifiers. This option is
experimental; in a future version of GCC, it will be enabled by
default for C99 and C++.
`-fpreprocessed'
Indicate to the preprocessor that the input file has already been
preprocessed. This suppresses things like macro expansion,
trigraph conversion, escaped newline splicing, and processing of
most directives. The preprocessor still recognizes and removes
comments, so that you can pass a file preprocessed with `-C' to
the compiler without problems. In this mode the integrated
preprocessor is little more than a tokenizer for the front ends.
`-fpreprocessed' is implicit if the input file has one of the
extensions `.i', `.ii' or `.mi'. These are the extensions that
GCC uses for preprocessed files created by `-save-temps'.
`-ftabstop=WIDTH'
Set the distance between tab stops. This helps the preprocessor
report correct column numbers in warnings or errors, even if tabs
appear on the line. If the value is less than 1 or greater than
100, the option is ignored. The default is 8.
`-fexec-charset=CHARSET'
Set the execution character set, used for string and character
constants. The default is UTF-8. CHARSET can be any encoding
supported by the system's `iconv' library routine.
`-fwide-exec-charset=CHARSET'
Set the wide execution character set, used for wide string and
character constants. The default is UTF-32 or UTF-16, whichever
corresponds to the width of `wchar_t'. As with `-fexec-charset',
CHARSET can be any encoding supported by the system's `iconv'
library routine; however, you will have problems with encodings
that do not fit exactly in `wchar_t'.
`-finput-charset=CHARSET'
Set the input character set, used for translation from the
character set of the input file to the source character set used
by GCC. If the locale does not specify, or GCC cannot get this
information from the locale, the default is UTF-8. This can be
overridden by either the locale or this command line option.
Currently the command line option takes precedence if there's a
conflict. CHARSET can be any encoding supported by the system's
`iconv' library routine.
`-fworking-directory'
Enable generation of linemarkers in the preprocessor output that
will let the compiler know the current working directory at the
time of preprocessing. When this option is enabled, the
preprocessor will emit, after the initial linemarker, a second
linemarker with the current working directory followed by two
slashes. GCC will use this directory, when it's present in the
preprocessed input, as the directory emitted as the current
working directory in some debugging information formats. This
option is implicitly enabled if debugging information is enabled,
but this can be inhibited with the negated form
`-fno-working-directory'. If the `-P' flag is present in the
command line, this option has no effect, since no `#line'
directives are emitted whatsoever.
`-fno-show-column'
Do not print column numbers in diagnostics. This may be necessary
if diagnostics are being scanned by a program that does not
understand the column numbers, such as `dejagnu'.
`-A PREDICATE=ANSWER'
Make an assertion with the predicate PREDICATE and answer ANSWER.
This form is preferred to the older form `-A PREDICATE(ANSWER)',
which is still supported, because it does not use shell special
characters.
`-A -PREDICATE=ANSWER'
Cancel an assertion with the predicate PREDICATE and answer ANSWER.
`-dCHARS'
CHARS is a sequence of one or more of the following characters,
and must not be preceded by a space. Other characters are
interpreted by the compiler proper, or reserved for future
versions of GCC, and so are silently ignored. If you specify
characters whose behavior conflicts, the result is undefined.
`M'
Instead of the normal output, generate a list of `#define'
directives for all the macros defined during the execution of
the preprocessor, including predefined macros. This gives
you a way of finding out what is predefined in your version
of the preprocessor. Assuming you have no file `foo.h', the
command
touch foo.h; cpp -dM foo.h
will show all the predefined macros.
`D'
Like `M' except in two respects: it does _not_ include the
predefined macros, and it outputs _both_ the `#define'
directives and the result of preprocessing. Both kinds of
output go to the standard output file.
`N'
Like `D', but emit only the macro names, not their expansions.
`I'
Output `#include' directives in addition to the result of
preprocessing.
`-P'
Inhibit generation of linemarkers in the output from the
preprocessor. This might be useful when running the preprocessor
on something that is not C code, and will be sent to a program
which might be confused by the linemarkers.
`-C'
Do not discard comments. All comments are passed through to the
output file, except for comments in processed directives, which
are deleted along with the directive.
You should be prepared for side effects when using `-C'; it causes
the preprocessor to treat comments as tokens in their own right.
For example, comments appearing at the start of what would be a
directive line have the effect of turning that line into an
ordinary source line, since the first token on the line is no
longer a `#'.
`-CC'
Do not discard comments, including during macro expansion. This is
like `-C', except that comments contained within macros are also
passed through to the output file where the macro is expanded.
In addition to the side-effects of the `-C' option, the `-CC'
option causes all C++-style comments inside a macro to be
converted to C-style comments. This is to prevent later use of
that macro from inadvertently commenting out the remainder of the
source line.
The `-CC' option is generally used to support lint comments.
`-traditional-cpp'
Try to imitate the behavior of old-fashioned C preprocessors, as
opposed to ISO C preprocessors.
`-trigraphs'
Process trigraph sequences. These are three-character sequences,
all starting with `??', that are defined by ISO C to stand for
single characters. For example, `??/' stands for `\', so `'??/n''
is a character constant for a newline. By default, GCC ignores
trigraphs, but in standard-conforming modes it converts them. See
the `-std' and `-ansi' options.
The nine trigraphs and their replacements are
Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??-
Replacement: [ ] { } # \ ^ | ~
`-remap'
Enable special code to work around file systems which only permit
very short file names, such as MS-DOS.
`--help'
`--target-help'
Print text describing all the command line options instead of
preprocessing anything.
`-v'
Verbose mode. Print out GNU CPP's version number at the beginning
of execution, and report the final form of the include path.
`-H'
Print the name of each header file used, in addition to other
normal activities. Each name is indented to show how deep in the
`#include' stack it is. Precompiled header files are also
printed, even if they are found to be invalid; an invalid
precompiled header file is printed with `...x' and a valid one
with `...!' .
`-version'
`--version'
Print out GNU CPP's version number. With one dash, proceed to
preprocess as normal. With two dashes, exit immediately.
File: gcc.info, Node: Assembler Options, Next: Link Options, Prev: Preprocessor Options, Up: Invoking GCC
3.12 Passing Options to the Assembler
=====================================
You can pass options to the assembler.
`-Wa,OPTION'
Pass OPTION as an option to the assembler. If OPTION contains
commas, it is split into multiple options at the commas.
`-Xassembler OPTION'
Pass OPTION as an option to the assembler. You can use this to
supply system-specific assembler options which GCC does not know
how to recognize.
If you want to pass an option that takes an argument, you must use
`-Xassembler' twice, once for the option and once for the argument.
File: gcc.info, Node: Link Options, Next: Directory Options, Prev: Assembler Options, Up: Invoking GCC
3.13 Options for Linking
========================
These options come into play when the compiler links object files into
an executable output file. They are meaningless if the compiler is not
doing a link step.
`OBJECT-FILE-NAME'
A file name that does not end in a special recognized suffix is
considered to name an object file or library. (Object files are
distinguished from libraries by the linker according to the file
contents.) If linking is done, these object files are used as
input to the linker.
`-c'
`-S'
`-E'
If any of these options is used, then the linker is not run, and
object file names should not be used as arguments. *Note Overall
Options::.
`-lLIBRARY'
`-l LIBRARY'
Search the library named LIBRARY when linking. (The second
alternative with the library as a separate argument is only for
POSIX compliance and is not recommended.)
It makes a difference where in the command you write this option;
the linker searches and processes libraries and object files in
the order they are specified. Thus, `foo.o -lz bar.o' searches
library `z' after file `foo.o' but before `bar.o'. If `bar.o'
refers to functions in `z', those functions may not be loaded.
The linker searches a standard list of directories for the library,
which is actually a file named `libLIBRARY.a'. The linker then
uses this file as if it had been specified precisely by name.
The directories searched include several standard system
directories plus any that you specify with `-L'.
Normally the files found this way are library files--archive files
whose members are object files. The linker handles an archive
file by scanning through it for members which define symbols that
have so far been referenced but not defined. But if the file that
is found is an ordinary object file, it is linked in the usual
fashion. The only difference between using an `-l' option and
specifying a file name is that `-l' surrounds LIBRARY with `lib'
and `.a' and searches several directories.
`-lobjc'
You need this special case of the `-l' option in order to link an
Objective-C or Objective-C++ program.
`-nostartfiles'
Do not use the standard system startup files when linking. The
standard system libraries are used normally, unless `-nostdlib' or
`-nodefaultlibs' is used.
`-nodefaultlibs'
Do not use the standard system libraries when linking. Only the
libraries you specify will be passed to the linker. The standard
startup files are used normally, unless `-nostartfiles' is used.
The compiler may generate calls to `memcmp', `memset', `memcpy'
and `memmove'. These entries are usually resolved by entries in
libc. These entry points should be supplied through some other
mechanism when this option is specified.
`-nostdlib'
Do not use the standard system startup files or libraries when
linking. No startup files and only the libraries you specify will
be passed to the linker. The compiler may generate calls to
`memcmp', `memset', `memcpy' and `memmove'. These entries are
usually resolved by entries in libc. These entry points should be
supplied through some other mechanism when this option is
specified.
One of the standard libraries bypassed by `-nostdlib' and
`-nodefaultlibs' is `libgcc.a', a library of internal subroutines
that GCC uses to overcome shortcomings of particular machines, or
special needs for some languages. (*Note Interfacing to GCC
Output: (gccint)Interface, for more discussion of `libgcc.a'.) In
most cases, you need `libgcc.a' even when you want to avoid other
standard libraries. In other words, when you specify `-nostdlib'
or `-nodefaultlibs' you should usually specify `-lgcc' as well.
This ensures that you have no unresolved references to internal GCC
library subroutines. (For example, `__main', used to ensure C++
constructors will be called; *note `collect2': (gccint)Collect2.)
`-pie'
Produce a position independent executable on targets which support
it. For predictable results, you must also specify the same set
of options that were used to generate code (`-fpie', `-fPIE', or
model suboptions) when you specify this option.
`-rdynamic'
Pass the flag `-export-dynamic' to the ELF linker, on targets that
support it. This instructs the linker to add all symbols, not only
used ones, to the dynamic symbol table. This option is needed for
some uses of `dlopen' or to allow obtaining backtraces from within
a program.
`-s'
Remove all symbol table and relocation information from the
executable.
`-static'
On systems that support dynamic linking, this prevents linking
with the shared libraries. On other systems, this option has no
effect.
`-shared'
Produce a shared object which can then be linked with other
objects to form an executable. Not all systems support this
option. For predictable results, you must also specify the same
set of options that were used to generate code (`-fpic', `-fPIC',
or model suboptions) when you specify this option.(1)
`-shared-libgcc'
`-static-libgcc'
On systems that provide `libgcc' as a shared library, these options
force the use of either the shared or static version respectively.
If no shared version of `libgcc' was built when the compiler was
configured, these options have no effect.
There are several situations in which an application should use the
shared `libgcc' instead of the static version. The most common of
these is when the application wishes to throw and catch exceptions
across different shared libraries. In that case, each of the
libraries as well as the application itself should use the shared
`libgcc'.
Therefore, the G++ and GCJ drivers automatically add
`-shared-libgcc' whenever you build a shared library or a main
executable, because C++ and Java programs typically use
exceptions, so this is the right thing to do.
If, instead, you use the GCC driver to create shared libraries,
you may find that they will not always be linked with the shared
`libgcc'. If GCC finds, at its configuration time, that you have
a non-GNU linker or a GNU linker that does not support option
`--eh-frame-hdr', it will link the shared version of `libgcc' into
shared libraries by default. Otherwise, it will take advantage of
the linker and optimize away the linking with the shared version
of `libgcc', linking with the static version of libgcc by default.
This allows exceptions to propagate through such shared
libraries, without incurring relocation costs at library load time.
However, if a library or main executable is supposed to throw or
catch exceptions, you must link it using the G++ or GCJ driver, as
appropriate for the languages used in the program, or using the
option `-shared-libgcc', such that it is linked with the shared
`libgcc'.
`-symbolic'
Bind references to global symbols when building a shared object.
Warn about any unresolved references (unless overridden by the
link editor option `-Xlinker -z -Xlinker defs'). Only a few
systems support this option.
`-Xlinker OPTION'
Pass OPTION as an option to the linker. You can use this to
supply system-specific linker options which GCC does not know how
to recognize.
If you want to pass an option that takes an argument, you must use
`-Xlinker' twice, once for the option and once for the argument.
For example, to pass `-assert definitions', you must write
`-Xlinker -assert -Xlinker definitions'. It does not work to write
`-Xlinker "-assert definitions"', because this passes the entire
string as a single argument, which is not what the linker expects.
`-Wl,OPTION'
Pass OPTION as an option to the linker. If OPTION contains
commas, it is split into multiple options at the commas.
`-u SYMBOL'
Pretend the symbol SYMBOL is undefined, to force linking of
library modules to define it. You can use `-u' multiple times with
different symbols to force loading of additional library modules.
---------- Footnotes ----------
(1) On some systems, `gcc -shared' needs to build supplementary stub
code for constructors to work. On multi-libbed systems, `gcc -shared'
must select the correct support libraries to link against. Failing to
supply the correct flags may lead to subtle defects. Supplying them in
cases where they are not necessary is innocuous.
File: gcc.info, Node: Directory Options, Next: Spec Files, Prev: Link Options, Up: Invoking GCC
3.14 Options for Directory Search
=================================
These options specify directories to search for header files, for
libraries and for parts of the compiler:
`-IDIR'
Add the directory DIR to the head of the list of directories to be
searched for header files. This can be used to override a system
header file, substituting your own version, since these
directories are searched before the system header file
directories. However, you should not use this option to add
directories that contain vendor-supplied system header files (use
`-isystem' for that). If you use more than one `-I' option, the
directories are scanned in left-to-right order; the standard
system directories come after.
If a standard system include directory, or a directory specified
with `-isystem', is also specified with `-I', the `-I' option will
be ignored. The directory will still be searched but as a system
directory at its normal position in the system include chain.
This is to ensure that GCC's procedure to fix buggy system headers
and the ordering for the include_next directive are not
inadvertently changed. If you really need to change the search
order for system directories, use the `-nostdinc' and/or
`-isystem' options.
`-iquoteDIR'
Add the directory DIR to the head of the list of directories to be
searched for header files only for the case of `#include "FILE"';
they are not searched for `#include <FILE>', otherwise just like
`-I'.
`-LDIR'
Add directory DIR to the list of directories to be searched for
`-l'.
`-BPREFIX'
This option specifies where to find the executables, libraries,
include files, and data files of the compiler itself.
The compiler driver program runs one or more of the subprograms
`cpp', `cc1', `as' and `ld'. It tries PREFIX as a prefix for each
program it tries to run, both with and without `MACHINE/VERSION/'
(*note Target Options::).
For each subprogram to be run, the compiler driver first tries the
`-B' prefix, if any. If that name is not found, or if `-B' was
not specified, the driver tries two standard prefixes, which are
`/usr/lib/gcc/' and `/usr/local/lib/gcc/'. If neither of those
results in a file name that is found, the unmodified program name
is searched for using the directories specified in your `PATH'
environment variable.
The compiler will check to see if the path provided by the `-B'
refers to a directory, and if necessary it will add a directory
separator character at the end of the path.
`-B' prefixes that effectively specify directory names also apply
to libraries in the linker, because the compiler translates these
options into `-L' options for the linker. They also apply to
includes files in the preprocessor, because the compiler
translates these options into `-isystem' options for the
preprocessor. In this case, the compiler appends `include' to the
prefix.
The run-time support file `libgcc.a' can also be searched for using
the `-B' prefix, if needed. If it is not found there, the two
standard prefixes above are tried, and that is all. The file is
left out of the link if it is not found by those means.
Another way to specify a prefix much like the `-B' prefix is to use
the environment variable `GCC_EXEC_PREFIX'. *Note Environment
Variables::.
As a special kludge, if the path provided by `-B' is
`[dir/]stageN/', where N is a number in the range 0 to 9, then it
will be replaced by `[dir/]include'. This is to help with
boot-strapping the compiler.
`-specs=FILE'
Process FILE after the compiler reads in the standard `specs'
file, in order to override the defaults that the `gcc' driver
program uses when determining what switches to pass to `cc1',
`cc1plus', `as', `ld', etc. More than one `-specs=FILE' can be
specified on the command line, and they are processed in order,
from left to right.
`--sysroot=DIR'
Use DIR as the logical root directory for headers and libraries.
For example, if the compiler would normally search for headers in
`/usr/include' and libraries in `/usr/lib', it will instead search
`DIR/usr/include' and `DIR/usr/lib'.
If you use both this option and the `-isysroot' option, then the
`--sysroot' option will apply to libraries, but the `-isysroot'
option will apply to header files.
The GNU linker (beginning with version 2.16) has the necessary
support for this option. If your linker does not support this
option, the header file aspect of `--sysroot' will still work, but
the library aspect will not.
`-I-'
This option has been deprecated. Please use `-iquote' instead for
`-I' directories before the `-I-' and remove the `-I-'. Any
directories you specify with `-I' options before the `-I-' option
are searched only for the case of `#include "FILE"'; they are not
searched for `#include <FILE>'.
If additional directories are specified with `-I' options after
the `-I-', these directories are searched for all `#include'
directives. (Ordinarily _all_ `-I' directories are used this way.)
In addition, the `-I-' option inhibits the use of the current
directory (where the current input file came from) as the first
search directory for `#include "FILE"'. There is no way to
override this effect of `-I-'. With `-I.' you can specify
searching the directory which was current when the compiler was
invoked. That is not exactly the same as what the preprocessor
does by default, but it is often satisfactory.
`-I-' does not inhibit the use of the standard system directories
for header files. Thus, `-I-' and `-nostdinc' are independent.
File: gcc.info, Node: Spec Files, Next: Target Options, Prev: Directory Options, Up: Invoking GCC
3.15 Specifying subprocesses and the switches to pass to them
=============================================================
`gcc' is a driver program. It performs its job by invoking a sequence
of other programs to do the work of compiling, assembling and linking.
GCC interprets its command-line parameters and uses these to deduce
which programs it should invoke, and which command-line options it
ought to place on their command lines. This behavior is controlled by
"spec strings". In most cases there is one spec string for each
program that GCC can invoke, but a few programs have multiple spec
strings to control their behavior. The spec strings built into GCC can
be overridden by using the `-specs=' command-line switch to specify a
spec file.
"Spec files" are plaintext files that are used to construct spec
strings. They consist of a sequence of directives separated by blank
lines. The type of directive is determined by the first non-whitespace
character on the line and it can be one of the following:
`%COMMAND'
Issues a COMMAND to the spec file processor. The commands that can
appear here are:
`%include <FILE>'
Search for FILE and insert its text at the current point in
the specs file.
`%include_noerr <FILE>'
Just like `%include', but do not generate an error message if
the include file cannot be found.
`%rename OLD_NAME NEW_NAME'
Rename the spec string OLD_NAME to NEW_NAME.
`*[SPEC_NAME]:'
This tells the compiler to create, override or delete the named
spec string. All lines after this directive up to the next
directive or blank line are considered to be the text for the spec
string. If this results in an empty string then the spec will be
deleted. (Or, if the spec did not exist, then nothing will
happened.) Otherwise, if the spec does not currently exist a new
spec will be created. If the spec does exist then its contents
will be overridden by the text of this directive, unless the first
character of that text is the `+' character, in which case the
text will be appended to the spec.
`[SUFFIX]:'
Creates a new `[SUFFIX] spec' pair. All lines after this directive
and up to the next directive or blank line are considered to make
up the spec string for the indicated suffix. When the compiler
encounters an input file with the named suffix, it will processes
the spec string in order to work out how to compile that file.
For example:
.ZZ:
z-compile -input %i
This says that any input file whose name ends in `.ZZ' should be
passed to the program `z-compile', which should be invoked with the
command-line switch `-input' and with the result of performing the
`%i' substitution. (See below.)
As an alternative to providing a spec string, the text that
follows a suffix directive can be one of the following:
`@LANGUAGE'
This says that the suffix is an alias for a known LANGUAGE.
This is similar to using the `-x' command-line switch to GCC
to specify a language explicitly. For example:
.ZZ:
@c++
Says that .ZZ files are, in fact, C++ source files.
`#NAME'
This causes an error messages saying:
NAME compiler not installed on this system.
GCC already has an extensive list of suffixes built into it. This
directive will add an entry to the end of the list of suffixes, but
since the list is searched from the end backwards, it is
effectively possible to override earlier entries using this
technique.
GCC has the following spec strings built into it. Spec files can
override these strings or create their own. Note that individual
targets can also add their own spec strings to this list.
asm Options to pass to the assembler
asm_final Options to pass to the assembler post-processor
cpp Options to pass to the C preprocessor
cc1 Options to pass to the C compiler
cc1plus Options to pass to the C++ compiler
endfile Object files to include at the end of the link
link Options to pass to the linker
lib Libraries to include on the command line to the linker
libgcc Decides which GCC support library to pass to the linker
linker Sets the name of the linker
predefines Defines to be passed to the C preprocessor
signed_char Defines to pass to CPP to say whether `char' is signed
by default
startfile Object files to include at the start of the link
Here is a small example of a spec file:
%rename lib old_lib
*lib:
--start-group -lgcc -lc -leval1 --end-group %(old_lib)
This example renames the spec called `lib' to `old_lib' and then
overrides the previous definition of `lib' with a new one. The new
definition adds in some extra command-line options before including the
text of the old definition.
"Spec strings" are a list of command-line options to be passed to their
corresponding program. In addition, the spec strings can contain
`%'-prefixed sequences to substitute variable text or to conditionally
insert text into the command line. Using these constructs it is
possible to generate quite complex command lines.
Here is a table of all defined `%'-sequences for spec strings. Note
that spaces are not generated automatically around the results of
expanding these sequences. Therefore you can concatenate them together
or combine them with constant text in a single argument.
`%%'
Substitute one `%' into the program name or argument.
`%i'
Substitute the name of the input file being processed.
`%b'
Substitute the basename of the input file being processed. This
is the substring up to (and not including) the last period and not
including the directory.
`%B'
This is the same as `%b', but include the file suffix (text after
the last period).
`%d'
Marks the argument containing or following the `%d' as a temporary
file name, so that that file will be deleted if GCC exits
successfully. Unlike `%g', this contributes no text to the
argument.
`%gSUFFIX'
Substitute a file name that has suffix SUFFIX and is chosen once
per compilation, and mark the argument in the same way as `%d'.
To reduce exposure to denial-of-service attacks, the file name is
now chosen in a way that is hard to predict even when previously
chosen file names are known. For example, `%g.s ... %g.o ... %g.s'
might turn into `ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s'. SUFFIX
matches the regexp `[.A-Za-z]*' or the special string `%O', which
is treated exactly as if `%O' had been preprocessed. Previously,
`%g' was simply substituted with a file name chosen once per
compilation, without regard to any appended suffix (which was
therefore treated just like ordinary text), making such attacks
more likely to succeed.
`%uSUFFIX'
Like `%g', but generates a new temporary file name even if
`%uSUFFIX' was already seen.
`%USUFFIX'
Substitutes the last file name generated with `%uSUFFIX',
generating a new one if there is no such last file name. In the
absence of any `%uSUFFIX', this is just like `%gSUFFIX', except
they don't share the same suffix _space_, so `%g.s ... %U.s ...
%g.s ... %U.s' would involve the generation of two distinct file
names, one for each `%g.s' and another for each `%U.s'.
Previously, `%U' was simply substituted with a file name chosen
for the previous `%u', without regard to any appended suffix.
`%jSUFFIX'
Substitutes the name of the `HOST_BIT_BUCKET', if any, and if it is
writable, and if save-temps is off; otherwise, substitute the name
of a temporary file, just like `%u'. This temporary file is not
meant for communication between processes, but rather as a junk
disposal mechanism.
`%|SUFFIX'
`%mSUFFIX'
Like `%g', except if `-pipe' is in effect. In that case `%|'
substitutes a single dash and `%m' substitutes nothing at all.
These are the two most common ways to instruct a program that it
should read from standard input or write to standard output. If
you need something more elaborate you can use an `%{pipe:`X'}'
construct: see for example `f/lang-specs.h'.
`%.SUFFIX'
Substitutes .SUFFIX for the suffixes of a matched switch's args
when it is subsequently output with `%*'. SUFFIX is terminated by
the next space or %.
`%w'
Marks the argument containing or following the `%w' as the
designated output file of this compilation. This puts the argument
into the sequence of arguments that `%o' will substitute later.
`%o'
Substitutes the names of all the output files, with spaces
automatically placed around them. You should write spaces around
the `%o' as well or the results are undefined. `%o' is for use in
the specs for running the linker. Input files whose names have no
recognized suffix are not compiled at all, but they are included
among the output files, so they will be linked.
`%O'
Substitutes the suffix for object files. Note that this is
handled specially when it immediately follows `%g, %u, or %U',
because of the need for those to form complete file names. The
handling is such that `%O' is treated exactly as if it had already
been substituted, except that `%g, %u, and %U' do not currently
support additional SUFFIX characters following `%O' as they would
following, for example, `.o'.
`%p'
Substitutes the standard macro predefinitions for the current
target machine. Use this when running `cpp'.
`%P'
Like `%p', but puts `__' before and after the name of each
predefined macro, except for macros that start with `__' or with
`_L', where L is an uppercase letter. This is for ISO C.
`%I'
Substitute any of `-iprefix' (made from `GCC_EXEC_PREFIX'),
`-isysroot' (made from `TARGET_SYSTEM_ROOT'), `-isystem' (made
from `COMPILER_PATH' and `-B' options) and `-imultilib' as
necessary.
`%s'
Current argument is the name of a library or startup file of some
sort. Search for that file in a standard list of directories and
substitute the full name found.
`%eSTR'
Print STR as an error message. STR is terminated by a newline.
Use this when inconsistent options are detected.
`%(NAME)'
Substitute the contents of spec string NAME at this point.
`%[NAME]'
Like `%(...)' but put `__' around `-D' arguments.
`%x{OPTION}'
Accumulate an option for `%X'.
`%X'
Output the accumulated linker options specified by `-Wl' or a `%x'
spec string.
`%Y'
Output the accumulated assembler options specified by `-Wa'.
`%Z'
Output the accumulated preprocessor options specified by `-Wp'.
`%a'
Process the `asm' spec. This is used to compute the switches to
be passed to the assembler.
`%A'
Process the `asm_final' spec. This is a spec string for passing
switches to an assembler post-processor, if such a program is
needed.
`%l'
Process the `link' spec. This is the spec for computing the
command line passed to the linker. Typically it will make use of
the `%L %G %S %D and %E' sequences.
`%D'
Dump out a `-L' option for each directory that GCC believes might
contain startup files. If the target supports multilibs then the
current multilib directory will be prepended to each of these
paths.
`%L'
Process the `lib' spec. This is a spec string for deciding which
libraries should be included on the command line to the linker.
`%G'
Process the `libgcc' spec. This is a spec string for deciding
which GCC support library should be included on the command line
to the linker.
`%S'
Process the `startfile' spec. This is a spec for deciding which
object files should be the first ones passed to the linker.
Typically this might be a file named `crt0.o'.
`%E'
Process the `endfile' spec. This is a spec string that specifies
the last object files that will be passed to the linker.
`%C'
Process the `cpp' spec. This is used to construct the arguments
to be passed to the C preprocessor.
`%1'
Process the `cc1' spec. This is used to construct the options to
be passed to the actual C compiler (`cc1').
`%2'
Process the `cc1plus' spec. This is used to construct the options
to be passed to the actual C++ compiler (`cc1plus').
`%*'
Substitute the variable part of a matched option. See below.
Note that each comma in the substituted string is replaced by a
single space.
`%<`S''
Remove all occurrences of `-S' from the command line. Note--this
command is position dependent. `%' commands in the spec string
before this one will see `-S', `%' commands in the spec string
after this one will not.
`%:FUNCTION(ARGS)'
Call the named function FUNCTION, passing it ARGS. ARGS is first
processed as a nested spec string, then split into an argument
vector in the usual fashion. The function returns a string which
is processed as if it had appeared literally as part of the
current spec.
The following built-in spec functions are provided:
``if-exists''
The `if-exists' spec function takes one argument, an absolute
pathname to a file. If the file exists, `if-exists' returns
the pathname. Here is a small example of its usage:
*startfile:
crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
``if-exists-else''
The `if-exists-else' spec function is similar to the
`if-exists' spec function, except that it takes two
arguments. The first argument is an absolute pathname to a
file. If the file exists, `if-exists-else' returns the
pathname. If it does not exist, it returns the second
argument. This way, `if-exists-else' can be used to select
one file or another, based on the existence of the first.
Here is a small example of its usage:
*startfile:
crt0%O%s %:if-exists(crti%O%s) \
%:if-exists-else(crtbeginT%O%s crtbegin%O%s)
``replace-outfile''
The `replace-outfile' spec function takes two arguments. It
looks for the first argument in the outfiles array and
replaces it with the second argument. Here is a small
example of its usage:
%{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)}
`%{`S'}'
Substitutes the `-S' switch, if that switch was given to GCC. If
that switch was not specified, this substitutes nothing. Note that
the leading dash is omitted when specifying this option, and it is
automatically inserted if the substitution is performed. Thus the
spec string `%{foo}' would match the command-line option `-foo'
and would output the command line option `-foo'.
`%W{`S'}'
Like %{`S'} but mark last argument supplied within as a file to be
deleted on failure.
`%{`S'*}'
Substitutes all the switches specified to GCC whose names start
with `-S', but which also take an argument. This is used for
switches like `-o', `-D', `-I', etc. GCC considers `-o foo' as
being one switch whose names starts with `o'. %{o*} would
substitute this text, including the space. Thus two arguments
would be generated.
`%{`S'*&`T'*}'
Like %{`S'*}, but preserve order of `S' and `T' options (the order
of `S' and `T' in the spec is not significant). There can be any
number of ampersand-separated variables; for each the wild card is
optional. Useful for CPP as `%{D*&U*&A*}'.
`%{`S':`X'}'
Substitutes `X', if the `-S' switch was given to GCC.
`%{!`S':`X'}'
Substitutes `X', if the `-S' switch was _not_ given to GCC.
`%{`S'*:`X'}'
Substitutes `X' if one or more switches whose names start with
`-S' are specified to GCC. Normally `X' is substituted only once,
no matter how many such switches appeared. However, if `%*'
appears somewhere in `X', then `X' will be substituted once for
each matching switch, with the `%*' replaced by the part of that
switch that matched the `*'.
`%{.`S':`X'}'
Substitutes `X', if processing a file with suffix `S'.
`%{!.`S':`X'}'
Substitutes `X', if _not_ processing a file with suffix `S'.
`%{`S'|`P':`X'}'
Substitutes `X' if either `-S' or `-P' was given to GCC. This may
be combined with `!', `.', and `*' sequences as well, although
they have a stronger binding than the `|'. If `%*' appears in
`X', all of the alternatives must be starred, and only the first
matching alternative is substituted.
For example, a spec string like this:
%{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}
will output the following command-line options from the following
input command-line options:
fred.c -foo -baz
jim.d -bar -boggle
-d fred.c -foo -baz -boggle
-d jim.d -bar -baz -boggle
`%{S:X; T:Y; :D}'
If `S' was given to GCC, substitutes `X'; else if `T' was given to
GCC, substitutes `Y'; else substitutes `D'. There can be as many
clauses as you need. This may be combined with `.', `!', `|', and
`*' as needed.
The conditional text `X' in a %{`S':`X'} or similar construct may
contain other nested `%' constructs or spaces, or even newlines. They
are processed as usual, as described above. Trailing white space in
`X' is ignored. White space may also appear anywhere on the left side
of the colon in these constructs, except between `.' or `*' and the
corresponding word.
The `-O', `-f', `-m', and `-W' switches are handled specifically in
these constructs. If another value of `-O' or the negated form of a
`-f', `-m', or `-W' switch is found later in the command line, the
earlier switch value is ignored, except with {`S'*} where `S' is just
one letter, which passes all matching options.
The character `|' at the beginning of the predicate text is used to
indicate that a command should be piped to the following command, but
only if `-pipe' is specified.
It is built into GCC which switches take arguments and which do not.
(You might think it would be useful to generalize this to allow each
compiler's spec to say which switches take arguments. But this cannot
be done in a consistent fashion. GCC cannot even decide which input
files have been specified without knowing which switches take arguments,
and it must know which input files to compile in order to tell which
compilers to run).
GCC also knows implicitly that arguments starting in `-l' are to be
treated as compiler output files, and passed to the linker in their
proper position among the other output files.
File: gcc.info, Node: Target Options, Next: Submodel Options, Prev: Spec Files, Up: Invoking GCC
3.16 Specifying Target Machine and Compiler Version
===================================================
The usual way to run GCC is to run the executable called `gcc', or
`<machine>-gcc' when cross-compiling, or `<machine>-gcc-<version>' to
run a version other than the one that was installed last. Sometimes
this is inconvenient, so GCC provides options that will switch to
another cross-compiler or version.
`-b MACHINE'
The argument MACHINE specifies the target machine for compilation.
The value to use for MACHINE is the same as was specified as the
machine type when configuring GCC as a cross-compiler. For
example, if a cross-compiler was configured with `configure
arm-elf', meaning to compile for an arm processor with elf
binaries, then you would specify `-b arm-elf' to run that cross
compiler. Because there are other options beginning with `-b', the
configuration must contain a hyphen.
`-V VERSION'
The argument VERSION specifies which version of GCC to run. This
is useful when multiple versions are installed. For example,
VERSION might be `4.0', meaning to run GCC version 4.0.
The `-V' and `-b' options work by running the
`<machine>-gcc-<version>' executable, so there's no real reason to use
them if you can just run that directly.
File: gcc.info, Node: Submodel Options, Next: Code Gen Options, Prev: Target Options, Up: Invoking GCC
3.17 Hardware Models and Configurations
=======================================
Earlier we discussed the standard option `-b' which chooses among
different installed compilers for completely different target machines,
such as VAX vs. 68000 vs. 80386.
In addition, each of these target machine types can have its own
special options, starting with `-m', to choose among various hardware
models or configurations--for example, 68010 vs 68020, floating
coprocessor or none. A single installed version of the compiler can
compile for any model or configuration, according to the options
specified.
Some configurations of the compiler also support additional special
options, usually for compatibility with other compilers on the same
platform.
* Menu:
* ARC Options::
* ARM Options::
* AVR Options::
* Blackfin Options::
* CRIS Options::
* CRX Options::
* Darwin Options::
* DEC Alpha Options::
* DEC Alpha/VMS Options::
* FRV Options::
* GNU/Linux Options::
* H8/300 Options::
* HPPA Options::
* i386 and x86-64 Options::
* IA-64 Options::
* M32C Options::
* M32R/D Options::
* M680x0 Options::
* M68hc1x Options::
* MCore Options::
* MIPS Options::
* MMIX Options::
* MN10300 Options::
* MT Options::
* PDP-11 Options::
* PowerPC Options::
* RS/6000 and PowerPC Options::
* S/390 and zSeries Options::
* Score Options::
* SH Options::
* SPARC Options::
* System V Options::
* TMS320C3x/C4x Options::
* V850 Options::
* VAX Options::
* x86-64 Options::
* Xstormy16 Options::
* Xtensa Options::
* zSeries Options::
File: gcc.info, Node: ARC Options, Next: ARM Options, Up: Submodel Options
3.17.1 ARC Options
------------------
These options are defined for ARC implementations:
`-EL'
Compile code for little endian mode. This is the default.
`-EB'
Compile code for big endian mode.
`-mmangle-cpu'
Prepend the name of the cpu to all public symbol names. In
multiple-processor systems, there are many ARC variants with
different instruction and register set characteristics. This flag
prevents code compiled for one cpu to be linked with code compiled
for another. No facility exists for handling variants that are
"almost identical". This is an all or nothing option.
`-mcpu=CPU'
Compile code for ARC variant CPU. Which variants are supported
depend on the configuration. All variants support `-mcpu=base',
this is the default.
`-mtext=TEXT-SECTION'
`-mdata=DATA-SECTION'
`-mrodata=READONLY-DATA-SECTION'
Put functions, data, and readonly data in TEXT-SECTION,
DATA-SECTION, and READONLY-DATA-SECTION respectively by default.
This can be overridden with the `section' attribute. *Note
Variable Attributes::.
File: gcc.info, Node: ARM Options, Next: AVR Options, Prev: ARC Options, Up: Submodel Options
3.17.2 ARM Options
------------------
These `-m' options are defined for Advanced RISC Machines (ARM)
architectures:
`-mabi=NAME'
Generate code for the specified ABI. Permissible values are:
`apcs-gnu', `atpcs', `aapcs', `aapcs-linux' and `iwmmxt'.
`-mapcs-frame'
Generate a stack frame that is compliant with the ARM Procedure
Call Standard for all functions, even if this is not strictly
necessary for correct execution of the code. Specifying
`-fomit-frame-pointer' with this option will cause the stack
frames not to be generated for leaf functions. The default is
`-mno-apcs-frame'.
`-mapcs'
This is a synonym for `-mapcs-frame'.
`-mthumb-interwork'
Generate code which supports calling between the ARM and Thumb
instruction sets. Without this option the two instruction sets
cannot be reliably used inside one program. The default is
`-mno-thumb-interwork', since slightly larger code is generated
when `-mthumb-interwork' is specified.
`-mno-sched-prolog'
Prevent the reordering of instructions in the function prolog, or
the merging of those instruction with the instructions in the
function's body. This means that all functions will start with a
recognizable set of instructions (or in fact one of a choice from
a small set of different function prologues), and this information
can be used to locate the start if functions inside an executable
piece of code. The default is `-msched-prolog'.
`-mhard-float'
Generate output containing floating point instructions. This is
the default.
`-msoft-float'
Generate output containing library calls for floating point.
*Warning:* the requisite libraries are not available for all ARM
targets. Normally the facilities of the machine's usual C
compiler are used, but this cannot be done directly in
cross-compilation. You must make your own arrangements to provide
suitable library functions for cross-compilation.
`-msoft-float' changes the calling convention in the output file;
therefore, it is only useful if you compile _all_ of a program with
this option. In particular, you need to compile `libgcc.a', the
library that comes with GCC, with `-msoft-float' in order for this
to work.
`-mfloat-abi=NAME'
Specifies which ABI to use for floating point values. Permissible
values are: `soft', `softfp' and `hard'.
`soft' and `hard' are equivalent to `-msoft-float' and
`-mhard-float' respectively. `softfp' allows the generation of
floating point instructions, but still uses the soft-float calling
conventions.
`-mlittle-endian'
Generate code for a processor running in little-endian mode. This
is the default for all standard configurations.
`-mbig-endian'
Generate code for a processor running in big-endian mode; the
default is to compile code for a little-endian processor.
`-mwords-little-endian'
This option only applies when generating code for big-endian
processors. Generate code for a little-endian word order but a
big-endian byte order. That is, a byte order of the form
`32107654'. Note: this option should only be used if you require
compatibility with code for big-endian ARM processors generated by
versions of the compiler prior to 2.8.
`-mcpu=NAME'
This specifies the name of the target ARM processor. GCC uses
this name to determine what kind of instructions it can emit when
generating assembly code. Permissible names are: `arm2', `arm250',
`arm3', `arm6', `arm60', `arm600', `arm610', `arm620', `arm7',
`arm7m', `arm7d', `arm7dm', `arm7di', `arm7dmi', `arm70', `arm700',
`arm700i', `arm710', `arm710c', `arm7100', `arm7500', `arm7500fe',
`arm7tdmi', `arm7tdmi-s', `arm8', `strongarm', `strongarm110',
`strongarm1100', `arm8', `arm810', `arm9', `arm9e', `arm920',
`arm920t', `arm922t', `arm946e-s', `arm966e-s', `arm968e-s',
`arm926ej-s', `arm940t', `arm9tdmi', `arm10tdmi', `arm1020t',
`arm1026ej-s', `arm10e', `arm1020e', `arm1022e', `arm1136j-s',
`arm1136jf-s', `mpcore', `mpcorenovfp', `arm1176jz-s',
`arm1176jzf-s', `xscale', `iwmmxt', `ep9312'.
`-mtune=NAME'
This option is very similar to the `-mcpu=' option, except that
instead of specifying the actual target processor type, and hence
restricting which instructions can be used, it specifies that GCC
should tune the performance of the code as if the target were of
the type specified in this option, but still choosing the
instructions that it will generate based on the cpu specified by a
`-mcpu=' option. For some ARM implementations better performance
can be obtained by using this option.
`-march=NAME'
This specifies the name of the target ARM architecture. GCC uses
this name to determine what kind of instructions it can emit when
generating assembly code. This option can be used in conjunction
with or instead of the `-mcpu=' option. Permissible names are:
`armv2', `armv2a', `armv3', `armv3m', `armv4', `armv4t', `armv5',
`armv5t', `armv5te', `armv6', `armv6j', `iwmmxt', `ep9312'.
`-mfpu=NAME'
`-mfpe=NUMBER'
`-mfp=NUMBER'
This specifies what floating point hardware (or hardware
emulation) is available on the target. Permissible names are:
`fpa', `fpe2', `fpe3', `maverick', `vfp'. `-mfp' and `-mfpe' are
synonyms for `-mfpu'=`fpe'NUMBER, for compatibility with older
versions of GCC.
If `-msoft-float' is specified this specifies the format of
floating point values.
`-mstructure-size-boundary=N'
The size of all structures and unions will be rounded up to a
multiple of the number of bits set by this option. Permissible
values are 8, 32 and 64. The default value varies for different
toolchains. For the COFF targeted toolchain the default value is
8. A value of 64 is only allowed if the underlying ABI supports
it.
Specifying the larger number can produce faster, more efficient
code, but can also increase the size of the program. Different
values are potentially incompatible. Code compiled with one value
cannot necessarily expect to work with code or libraries compiled
with another value, if they exchange information using structures
or unions.
`-mabort-on-noreturn'
Generate a call to the function `abort' at the end of a `noreturn'
function. It will be executed if the function tries to return.
`-mlong-calls'
`-mno-long-calls'
Tells the compiler to perform function calls by first loading the
address of the function into a register and then performing a
subroutine call on this register. This switch is needed if the
target function will lie outside of the 64 megabyte addressing
range of the offset based version of subroutine call instruction.
Even if this switch is enabled, not all function calls will be
turned into long calls. The heuristic is that static functions,
functions which have the `short-call' attribute, functions that
are inside the scope of a `#pragma no_long_calls' directive and
functions whose definitions have already been compiled within the
current compilation unit, will not be turned into long calls. The
exception to this rule is that weak function definitions,
functions with the `long-call' attribute or the `section'
attribute, and functions that are within the scope of a `#pragma
long_calls' directive, will always be turned into long calls.
This feature is not enabled by default. Specifying
`-mno-long-calls' will restore the default behavior, as will
placing the function calls within the scope of a `#pragma
long_calls_off' directive. Note these switches have no effect on
how the compiler generates code to handle function calls via
function pointers.
`-mnop-fun-dllimport'
Disable support for the `dllimport' attribute.
`-msingle-pic-base'
Treat the register used for PIC addressing as read-only, rather
than loading it in the prologue for each function. The run-time
system is responsible for initializing this register with an
appropriate value before execution begins.
`-mpic-register=REG'
Specify the register to be used for PIC addressing. The default
is R10 unless stack-checking is enabled, when R9 is used.
`-mcirrus-fix-invalid-insns'
Insert NOPs into the instruction stream to in order to work around
problems with invalid Maverick instruction combinations. This
option is only valid if the `-mcpu=ep9312' option has been used to
enable generation of instructions for the Cirrus Maverick floating
point co-processor. This option is not enabled by default, since
the problem is only present in older Maverick implementations.
The default can be re-enabled by use of the
`-mno-cirrus-fix-invalid-insns' switch.
`-mpoke-function-name'
Write the name of each function into the text section, directly
preceding the function prologue. The generated code is similar to
this:
t0
.ascii "arm_poke_function_name", 0
.align
t1
.word 0xff000000 + (t1 - t0)
arm_poke_function_name
mov ip, sp
stmfd sp!, {fp, ip, lr, pc}
sub fp, ip, #4
When performing a stack backtrace, code can inspect the value of
`pc' stored at `fp + 0'. If the trace function then looks at
location `pc - 12' and the top 8 bits are set, then we know that
there is a function name embedded immediately preceding this
location and has length `((pc[-3]) & 0xff000000)'.
`-mthumb'
Generate code for the 16-bit Thumb instruction set. The default
is to use the 32-bit ARM instruction set.
`-mtpcs-frame'
Generate a stack frame that is compliant with the Thumb Procedure
Call Standard for all non-leaf functions. (A leaf function is one
that does not call any other functions.) The default is
`-mno-tpcs-frame'.
`-mtpcs-leaf-frame'
Generate a stack frame that is compliant with the Thumb Procedure
Call Standard for all leaf functions. (A leaf function is one
that does not call any other functions.) The default is
`-mno-apcs-leaf-frame'.
`-mcallee-super-interworking'
Gives all externally visible functions in the file being compiled
an ARM instruction set header which switches to Thumb mode before
executing the rest of the function. This allows these functions
to be called from non-interworking code.
`-mcaller-super-interworking'
Allows calls via function pointers (including virtual functions) to
execute correctly regardless of whether the target code has been
compiled for interworking or not. There is a small overhead in
the cost of executing a function pointer if this option is enabled.
`-mtp=NAME'
Specify the access model for the thread local storage pointer.
The valid models are `soft', which generates calls to
`__aeabi_read_tp', `cp15', which fetches the thread pointer from
`cp15' directly (supported in the arm6k architecture), and `auto',
which uses the best available method for the selected processor.
The default setting is `auto'.
File: gcc.info, Node: AVR Options, Next: Blackfin Options, Prev: ARM Options, Up: Submodel Options
3.17.3 AVR Options
------------------
These options are defined for AVR implementations:
`-mmcu=MCU'
Specify ATMEL AVR instruction set or MCU type.
Instruction set avr1 is for the minimal AVR core, not supported by
the C compiler, only for assembler programs (MCU types: at90s1200,
attiny10, attiny11, attiny12, attiny15, attiny28).
Instruction set avr2 (default) is for the classic AVR core with up
to 8K program memory space (MCU types: at90s2313, at90s2323,
attiny22, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434,
at90s8515, at90c8534, at90s8535).
Instruction set avr3 is for the classic AVR core with up to 128K
program memory space (MCU types: atmega103, atmega603, at43usb320,
at76c711).
Instruction set avr4 is for the enhanced AVR core with up to 8K
program memory space (MCU types: atmega8, atmega83, atmega85).
Instruction set avr5 is for the enhanced AVR core with up to 128K
program memory space (MCU types: atmega16, atmega161, atmega163,
atmega32, atmega323, atmega64, atmega128, at43usb355, at94k).
`-msize'
Output instruction sizes to the asm file.
`-minit-stack=N'
Specify the initial stack address, which may be a symbol or
numeric value, `__stack' is the default.
`-mno-interrupts'
Generated code is not compatible with hardware interrupts. Code
size will be smaller.
`-mcall-prologues'
Functions prologues/epilogues expanded as call to appropriate
subroutines. Code size will be smaller.
`-mno-tablejump'
Do not generate tablejump insns which sometimes increase code size.
`-mtiny-stack'
Change only the low 8 bits of the stack pointer.
`-mint8'
Assume int to be 8 bit integer. This affects the sizes of all
types: A char will be 1 byte, an int will be 1 byte, an long will
be 2 bytes and long long will be 4 bytes. Please note that this
option does not comply to the C standards, but it will provide you
with smaller code size.
File: gcc.info, Node: Blackfin Options, Next: CRIS Options, Prev: AVR Options, Up: Submodel Options
3.17.4 Blackfin Options
-----------------------
`-momit-leaf-frame-pointer'
Don't keep the frame pointer in a register for leaf functions.
This avoids the instructions to save, set up and restore frame
pointers and makes an extra register available in leaf functions.
The option `-fomit-frame-pointer' removes the frame pointer for
all functions which might make debugging harder.
`-mspecld-anomaly'
When enabled, the compiler will ensure that the generated code
does not contain speculative loads after jump instructions. This
option is enabled by default.
`-mno-specld-anomaly'
Don't generate extra code to prevent speculative loads from
occurring.
`-mcsync-anomaly'
When enabled, the compiler will ensure that the generated code
does not contain CSYNC or SSYNC instructions too soon after
conditional branches. This option is enabled by default.
`-mno-csync-anomaly'
Don't generate extra code to prevent CSYNC or SSYNC instructions
from occurring too soon after a conditional branch.
`-mlow-64k'
When enabled, the compiler is free to take advantage of the
knowledge that the entire program fits into the low 64k of memory.
`-mno-low-64k'
Assume that the program is arbitrarily large. This is the default.
`-mid-shared-library'
Generate code that supports shared libraries via the library ID
method. This allows for execute in place and shared libraries in
an environment without virtual memory management. This option
implies `-fPIC'.
`-mno-id-shared-library'
Generate code that doesn't assume ID based shared libraries are
being used. This is the default.
`-mshared-library-id=n'
Specified the identification number of the ID based shared library
being compiled. Specifying a value of 0 will generate more
compact code, specifying other values will force the allocation of
that number to the current library but is no more space or time
efficient than omitting this option.
`-mlong-calls'
`-mno-long-calls'
Tells the compiler to perform function calls by first loading the
address of the function into a register and then performing a
subroutine call on this register. This switch is needed if the
target function will lie outside of the 24 bit addressing range of
the offset based version of subroutine call instruction.
This feature is not enabled by default. Specifying
`-mno-long-calls' will restore the default behavior. Note these
switches have no effect on how the compiler generates code to
handle function calls via function pointers.
File: gcc.info, Node: CRIS Options, Next: CRX Options, Prev: Blackfin Options, Up: Submodel Options
3.17.5 CRIS Options
-------------------
These options are defined specifically for the CRIS ports.
`-march=ARCHITECTURE-TYPE'
`-mcpu=ARCHITECTURE-TYPE'
Generate code for the specified architecture. The choices for
ARCHITECTURE-TYPE are `v3', `v8' and `v10' for respectively
ETRAX 4, ETRAX 100, and ETRAX 100 LX. Default is `v0' except for
cris-axis-linux-gnu, where the default is `v10'.
`-mtune=ARCHITECTURE-TYPE'
Tune to ARCHITECTURE-TYPE everything applicable about the generated
code, except for the ABI and the set of available instructions.
The choices for ARCHITECTURE-TYPE are the same as for
`-march=ARCHITECTURE-TYPE'.
`-mmax-stack-frame=N'
Warn when the stack frame of a function exceeds N bytes.
`-melinux-stacksize=N'
Only available with the `cris-axis-aout' target. Arranges for
indications in the program to the kernel loader that the stack of
the program should be set to N bytes.
`-metrax4'
`-metrax100'
The options `-metrax4' and `-metrax100' are synonyms for
`-march=v3' and `-march=v8' respectively.
`-mmul-bug-workaround'
`-mno-mul-bug-workaround'
Work around a bug in the `muls' and `mulu' instructions for CPU
models where it applies. This option is active by default.
`-mpdebug'
Enable CRIS-specific verbose debug-related information in the
assembly code. This option also has the effect to turn off the
`#NO_APP' formatted-code indicator to the assembler at the
beginning of the assembly file.
`-mcc-init'
Do not use condition-code results from previous instruction;
always emit compare and test instructions before use of condition
codes.
`-mno-side-effects'
Do not emit instructions with side-effects in addressing modes
other than post-increment.
`-mstack-align'
`-mno-stack-align'
`-mdata-align'
`-mno-data-align'
`-mconst-align'
`-mno-const-align'
These options (no-options) arranges (eliminate arrangements) for
the stack-frame, individual data and constants to be aligned for
the maximum single data access size for the chosen CPU model. The
default is to arrange for 32-bit alignment. ABI details such as
structure layout are not affected by these options.
`-m32-bit'
`-m16-bit'
`-m8-bit'
Similar to the stack- data- and const-align options above, these
options arrange for stack-frame, writable data and constants to
all be 32-bit, 16-bit or 8-bit aligned. The default is 32-bit
alignment.
`-mno-prologue-epilogue'
`-mprologue-epilogue'
With `-mno-prologue-epilogue', the normal function prologue and
epilogue that sets up the stack-frame are omitted and no return
instructions or return sequences are generated in the code. Use
this option only together with visual inspection of the compiled
code: no warnings or errors are generated when call-saved
registers must be saved, or storage for local variable needs to be
allocated.
`-mno-gotplt'
`-mgotplt'
With `-fpic' and `-fPIC', don't generate (do generate) instruction
sequences that load addresses for functions from the PLT part of
the GOT rather than (traditional on other architectures) calls to
the PLT. The default is `-mgotplt'.
`-maout'
Legacy no-op option only recognized with the cris-axis-aout target.
`-melf'
Legacy no-op option only recognized with the cris-axis-elf and
cris-axis-linux-gnu targets.
`-melinux'
Only recognized with the cris-axis-aout target, where it selects a
GNU/linux-like multilib, include files and instruction set for
`-march=v8'.
`-mlinux'
Legacy no-op option only recognized with the cris-axis-linux-gnu
target.
`-sim'
This option, recognized for the cris-axis-aout and cris-axis-elf
arranges to link with input-output functions from a simulator
library. Code, initialized data and zero-initialized data are
allocated consecutively.
`-sim2'
Like `-sim', but pass linker options to locate initialized data at
0x40000000 and zero-initialized data at 0x80000000.
File: gcc.info, Node: CRX Options, Next: Darwin Options, Prev: CRIS Options, Up: Submodel Options
3.17.6 CRX Options
------------------
These options are defined specifically for the CRX ports.
`-mmac'
Enable the use of multiply-accumulate instructions. Disabled by
default.
`-mpush-args'
Push instructions will be used to pass outgoing arguments when
functions are called. Enabled by default.
File: gcc.info, Node: Darwin Options, Next: DEC Alpha Options, Prev: CRX Options, Up: Submodel Options
3.17.7 Darwin Options
---------------------
These options are defined for all architectures running the Darwin
operating system.
FSF GCC on Darwin does not create "fat" object files; it will create
an object file for the single architecture that it was built to target.
Apple's GCC on Darwin does create "fat" files if multiple `-arch'
options are used; it does so by running the compiler or linker multiple
times and joining the results together with `lipo'.
The subtype of the file created (like `ppc7400' or `ppc970' or `i686')
is determined by the flags that specify the ISA that GCC is targetting,
like `-mcpu' or `-march'. The `-force_cpusubtype_ALL' option can be
used to override this.
The Darwin tools vary in their behavior when presented with an ISA
mismatch. The assembler, `as', will only permit instructions to be
used that are valid for the subtype of the file it is generating, so
you cannot put 64-bit instructions in an `ppc750' object file. The
linker for shared libraries, `/usr/bin/libtool', will fail and print an
error if asked to create a shared library with a less restrictive
subtype than its input files (for instance, trying to put a `ppc970'
object file in a `ppc7400' library). The linker for executables, `ld',
will quietly give the executable the most restrictive subtype of any of
its input files.
`-FDIR'
Add the framework directory DIR to the head of the list of
directories to be searched for header files. These directories are
interleaved with those specified by `-I' options and are scanned
in a left-to-right order.
A framework directory is a directory with frameworks in it. A
framework is a directory with a `"Headers"' and/or
`"PrivateHeaders"' directory contained directly in it that ends in
`".framework"'. The name of a framework is the name of this
directory excluding the `".framework"'. Headers associated with
the framework are found in one of those two directories, with
`"Headers"' being searched first. A subframework is a framework
directory that is in a framework's `"Frameworks"' directory.
Includes of subframework headers can only appear in a header of a
framework that contains the subframework, or in a sibling
subframework header. Two subframeworks are siblings if they occur
in the same framework. A subframework should not have the same
name as a framework, a warning will be issued if this is violated.
Currently a subframework cannot have subframeworks, in the
future, the mechanism may be extended to support this. The
standard frameworks can be found in `"/System/Library/Frameworks"'
and `"/Library/Frameworks"'. An example include looks like
`#include <Framework/header.h>', where `Framework' denotes the
name of the framework and header.h is found in the
`"PrivateHeaders"' or `"Headers"' directory.
`-gused'
Emit debugging information for symbols that are used. For STABS
debugging format, this enables `-feliminate-unused-debug-symbols'.
This is by default ON.
`-gfull'
Emit debugging information for all symbols and types.
`-mmacosx-version-min=VERSION'
The earliest version of MacOS X that this executable will run on
is VERSION. Typical values of VERSION include `10.1', `10.2', and
`10.3.9'.
The default for this option is to make choices that seem to be most
useful.
`-mkernel'
Enable kernel development mode. The `-mkernel' option sets
`-static', `-fno-common', `-fno-cxa-atexit', `-fno-exceptions',
`-fno-non-call-exceptions', `-fapple-kext', `-fno-weak' and
`-fno-rtti' where applicable. This mode also sets `-mno-altivec',
`-msoft-float', `-fno-builtin' and `-mlong-branch' for PowerPC
targets.
`-mone-byte-bool'
Override the defaults for `bool' so that `sizeof(bool)==1'. By
default `sizeof(bool)' is `4' when compiling for Darwin/PowerPC
and `1' when compiling for Darwin/x86, so this option has no
effect on x86.
*Warning:* The `-mone-byte-bool' switch causes GCC to generate
code that is not binary compatible with code generated without
that switch. Using this switch may require recompiling all other
modules in a program, including system libraries. Use this switch
to conform to a non-default data model.
`-mfix-and-continue'
`-ffix-and-continue'
`-findirect-data'
Generate code suitable for fast turn around development. Needed to
enable gdb to dynamically load `.o' files into already running
programs. `-findirect-data' and `-ffix-and-continue' are provided
for backwards compatibility.
`-all_load'
Loads all members of static archive libraries. See man ld(1) for
more information.
`-arch_errors_fatal'
Cause the errors having to do with files that have the wrong
architecture to be fatal.
`-bind_at_load'
Causes the output file to be marked such that the dynamic linker
will bind all undefined references when the file is loaded or
launched.
`-bundle'
Produce a Mach-o bundle format file. See man ld(1) for more
information.
`-bundle_loader EXECUTABLE'
This option specifies the EXECUTABLE that will be loading the build
output file being linked. See man ld(1) for more information.
`-dynamiclib'
When passed this option, GCC will produce a dynamic library
instead of an executable when linking, using the Darwin `libtool'
command.
`-force_cpusubtype_ALL'
This causes GCC's output file to have the ALL subtype, instead of
one controlled by the `-mcpu' or `-march' option.
`-allowable_client CLIENT_NAME'
`-client_name'
`-compatibility_version'
`-current_version'
`-dead_strip'
`-dependency-file'
`-dylib_file'
`-dylinker_install_name'
`-dynamic'
`-exported_symbols_list'
`-filelist'
`-flat_namespace'
`-force_flat_namespace'
`-headerpad_max_install_names'
`-image_base'
`-init'
`-install_name'
`-keep_private_externs'
`-multi_module'
`-multiply_defined'
`-multiply_defined_unused'
`-noall_load'
`-no_dead_strip_inits_and_terms'
`-nofixprebinding'
`-nomultidefs'
`-noprebind'
`-noseglinkedit'
`-pagezero_size'
`-prebind'
`-prebind_all_twolevel_modules'
`-private_bundle'
`-read_only_relocs'
`-sectalign'
`-sectobjectsymbols'
`-whyload'
`-seg1addr'
`-sectcreate'
`-sectobjectsymbols'
`-sectorder'
`-segaddr'
`-segs_read_only_addr'
`-segs_read_write_addr'
`-seg_addr_table'
`-seg_addr_table_filename'
`-seglinkedit'
`-segprot'
`-segs_read_only_addr'
`-segs_read_write_addr'
`-single_module'
`-static'
`-sub_library'
`-sub_umbrella'
`-twolevel_namespace'
`-umbrella'
`-undefined'
`-unexported_symbols_list'
`-weak_reference_mismatches'
`-whatsloaded'
These options are passed to the Darwin linker. The Darwin linker
man page describes them in detail.
File: gcc.info, Node: DEC Alpha Options, Next: DEC Alpha/VMS Options, Prev: Darwin Options, Up: Submodel Options
3.17.8 DEC Alpha Options
------------------------
These `-m' options are defined for the DEC Alpha implementations:
`-mno-soft-float'
`-msoft-float'
Use (do not use) the hardware floating-point instructions for
floating-point operations. When `-msoft-float' is specified,
functions in `libgcc.a' will be used to perform floating-point
operations. Unless they are replaced by routines that emulate the
floating-point operations, or compiled in such a way as to call
such emulations routines, these routines will issue floating-point
operations. If you are compiling for an Alpha without
floating-point operations, you must ensure that the library is
built so as not to call them.
Note that Alpha implementations without floating-point operations
are required to have floating-point registers.
`-mfp-reg'
`-mno-fp-regs'
Generate code that uses (does not use) the floating-point register
set. `-mno-fp-regs' implies `-msoft-float'. If the floating-point
register set is not used, floating point operands are passed in
integer registers as if they were integers and floating-point
results are passed in `$0' instead of `$f0'. This is a
non-standard calling sequence, so any function with a
floating-point argument or return value called by code compiled
with `-mno-fp-regs' must also be compiled with that option.
A typical use of this option is building a kernel that does not
use, and hence need not save and restore, any floating-point
registers.
`-mieee'
The Alpha architecture implements floating-point hardware
optimized for maximum performance. It is mostly compliant with
the IEEE floating point standard. However, for full compliance,
software assistance is required. This option generates code fully
IEEE compliant code _except_ that the INEXACT-FLAG is not
maintained (see below). If this option is turned on, the
preprocessor macro `_IEEE_FP' is defined during compilation. The
resulting code is less efficient but is able to correctly support
denormalized numbers and exceptional IEEE values such as
not-a-number and plus/minus infinity. Other Alpha compilers call
this option `-ieee_with_no_inexact'.
`-mieee-with-inexact'
This is like `-mieee' except the generated code also maintains the
IEEE INEXACT-FLAG. Turning on this option causes the generated
code to implement fully-compliant IEEE math. In addition to
`_IEEE_FP', `_IEEE_FP_EXACT' is defined as a preprocessor macro.
On some Alpha implementations the resulting code may execute
significantly slower than the code generated by default. Since
there is very little code that depends on the INEXACT-FLAG, you
should normally not specify this option. Other Alpha compilers
call this option `-ieee_with_inexact'.
`-mfp-trap-mode=TRAP-MODE'
This option controls what floating-point related traps are enabled.
Other Alpha compilers call this option `-fptm TRAP-MODE'. The
trap mode can be set to one of four values:
`n'
This is the default (normal) setting. The only traps that
are enabled are the ones that cannot be disabled in software
(e.g., division by zero trap).
`u'
In addition to the traps enabled by `n', underflow traps are
enabled as well.
`su'
Like `u', but the instructions are marked to be safe for
software completion (see Alpha architecture manual for
details).
`sui'
Like `su', but inexact traps are enabled as well.
`-mfp-rounding-mode=ROUNDING-MODE'
Selects the IEEE rounding mode. Other Alpha compilers call this
option `-fprm ROUNDING-MODE'. The ROUNDING-MODE can be one of:
`n'
Normal IEEE rounding mode. Floating point numbers are
rounded towards the nearest machine number or towards the
even machine number in case of a tie.
`m'
Round towards minus infinity.
`c'
Chopped rounding mode. Floating point numbers are rounded
towards zero.
`d'
Dynamic rounding mode. A field in the floating point control
register (FPCR, see Alpha architecture reference manual)
controls the rounding mode in effect. The C library
initializes this register for rounding towards plus infinity.
Thus, unless your program modifies the FPCR, `d' corresponds
to round towards plus infinity.
`-mtrap-precision=TRAP-PRECISION'
In the Alpha architecture, floating point traps are imprecise.
This means without software assistance it is impossible to recover
from a floating trap and program execution normally needs to be
terminated. GCC can generate code that can assist operating
system trap handlers in determining the exact location that caused
a floating point trap. Depending on the requirements of an
application, different levels of precisions can be selected:
`p'
Program precision. This option is the default and means a
trap handler can only identify which program caused a
floating point exception.
`f'
Function precision. The trap handler can determine the
function that caused a floating point exception.
`i'
Instruction precision. The trap handler can determine the
exact instruction that caused a floating point exception.
Other Alpha compilers provide the equivalent options called
`-scope_safe' and `-resumption_safe'.
`-mieee-conformant'
This option marks the generated code as IEEE conformant. You must
not use this option unless you also specify `-mtrap-precision=i'
and either `-mfp-trap-mode=su' or `-mfp-trap-mode=sui'. Its only
effect is to emit the line `.eflag 48' in the function prologue of
the generated assembly file. Under DEC Unix, this has the effect
that IEEE-conformant math library routines will be linked in.
`-mbuild-constants'
Normally GCC examines a 32- or 64-bit integer constant to see if
it can construct it from smaller constants in two or three
instructions. If it cannot, it will output the constant as a
literal and generate code to load it from the data segment at
runtime.
Use this option to require GCC to construct _all_ integer constants
using code, even if it takes more instructions (the maximum is
six).
You would typically use this option to build a shared library
dynamic loader. Itself a shared library, it must relocate itself
in memory before it can find the variables and constants in its
own data segment.
`-malpha-as'
`-mgas'
Select whether to generate code to be assembled by the
vendor-supplied assembler (`-malpha-as') or by the GNU assembler
`-mgas'.
`-mbwx'
`-mno-bwx'
`-mcix'
`-mno-cix'
`-mfix'
`-mno-fix'
`-mmax'
`-mno-max'
Indicate whether GCC should generate code to use the optional BWX,
CIX, FIX and MAX instruction sets. The default is to use the
instruction sets supported by the CPU type specified via `-mcpu='
option or that of the CPU on which GCC was built if none was
specified.
`-mfloat-vax'
`-mfloat-ieee'
Generate code that uses (does not use) VAX F and G floating point
arithmetic instead of IEEE single and double precision.
`-mexplicit-relocs'
`-mno-explicit-relocs'
Older Alpha assemblers provided no way to generate symbol
relocations except via assembler macros. Use of these macros does
not allow optimal instruction scheduling. GNU binutils as of
version 2.12 supports a new syntax that allows the compiler to
explicitly mark which relocations should apply to which
instructions. This option is mostly useful for debugging, as GCC
detects the capabilities of the assembler when it is built and
sets the default accordingly.
`-msmall-data'
`-mlarge-data'
When `-mexplicit-relocs' is in effect, static data is accessed via
"gp-relative" relocations. When `-msmall-data' is used, objects 8
bytes long or smaller are placed in a "small data area" (the
`.sdata' and `.sbss' sections) and are accessed via 16-bit
relocations off of the `$gp' register. This limits the size of
the small data area to 64KB, but allows the variables to be
directly accessed via a single instruction.
The default is `-mlarge-data'. With this option the data area is
limited to just below 2GB. Programs that require more than 2GB of
data must use `malloc' or `mmap' to allocate the data in the heap
instead of in the program's data segment.
When generating code for shared libraries, `-fpic' implies
`-msmall-data' and `-fPIC' implies `-mlarge-data'.
`-msmall-text'
`-mlarge-text'
When `-msmall-text' is used, the compiler assumes that the code of
the entire program (or shared library) fits in 4MB, and is thus
reachable with a branch instruction. When `-msmall-data' is used,
the compiler can assume that all local symbols share the same
`$gp' value, and thus reduce the number of instructions required
for a function call from 4 to 1.
The default is `-mlarge-text'.
`-mcpu=CPU_TYPE'
Set the instruction set and instruction scheduling parameters for
machine type CPU_TYPE. You can specify either the `EV' style name
or the corresponding chip number. GCC supports scheduling
parameters for the EV4, EV5 and EV6 family of processors and will
choose the default values for the instruction set from the
processor you specify. If you do not specify a processor type,
GCC will default to the processor on which the compiler was built.
Supported values for CPU_TYPE are
`ev4'
`ev45'
`21064'
Schedules as an EV4 and has no instruction set extensions.
`ev5'
`21164'
Schedules as an EV5 and has no instruction set extensions.
`ev56'
`21164a'
Schedules as an EV5 and supports the BWX extension.
`pca56'
`21164pc'
`21164PC'
Schedules as an EV5 and supports the BWX and MAX extensions.
`ev6'
`21264'
Schedules as an EV6 and supports the BWX, FIX, and MAX
extensions.
`ev67'
`21264a'
Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
extensions.
`-mtune=CPU_TYPE'
Set only the instruction scheduling parameters for machine type
CPU_TYPE. The instruction set is not changed.
`-mmemory-latency=TIME'
Sets the latency the scheduler should assume for typical memory
references as seen by the application. This number is highly
dependent on the memory access patterns used by the application
and the size of the external cache on the machine.
Valid options for TIME are
`NUMBER'
A decimal number representing clock cycles.
`L1'
`L2'
`L3'
`main'
The compiler contains estimates of the number of clock cycles
for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
(also called Dcache, Scache, and Bcache), as well as to main
memory. Note that L3 is only valid for EV5.
File: gcc.info, Node: DEC Alpha/VMS Options, Next: FRV Options, Prev: DEC Alpha Options, Up: Submodel Options
3.17.9 DEC Alpha/VMS Options
----------------------------
These `-m' options are defined for the DEC Alpha/VMS implementations:
`-mvms-return-codes'
Return VMS condition codes from main. The default is to return
POSIX style condition (e.g. error) codes.
File: gcc.info, Node: FRV Options, Next: GNU/Linux Options, Prev: DEC Alpha/VMS Options, Up: Submodel Options
3.17.10 FRV Options
-------------------
`-mgpr-32'
Only use the first 32 general purpose registers.
`-mgpr-64'
Use all 64 general purpose registers.
`-mfpr-32'
Use only the first 32 floating point registers.
`-mfpr-64'
Use all 64 floating point registers
`-mhard-float'
Use hardware instructions for floating point operations.
`-msoft-float'
Use library routines for floating point operations.
`-malloc-cc'
Dynamically allocate condition code registers.
`-mfixed-cc'
Do not try to dynamically allocate condition code registers, only
use `icc0' and `fcc0'.
`-mdword'
Change ABI to use double word insns.
`-mno-dword'
Do not use double word instructions.
`-mdouble'
Use floating point double instructions.
`-mno-double'
Do not use floating point double instructions.
`-mmedia'
Use media instructions.
`-mno-media'
Do not use media instructions.
`-mmuladd'
Use multiply and add/subtract instructions.
`-mno-muladd'
Do not use multiply and add/subtract instructions.
`-mfdpic'
Select the FDPIC ABI, that uses function descriptors to represent
pointers to functions. Without any PIC/PIE-related options, it
implies `-fPIE'. With `-fpic' or `-fpie', it assumes GOT entries
and small data are within a 12-bit range from the GOT base
address; with `-fPIC' or `-fPIE', GOT offsets are computed with 32
bits.
`-minline-plt'
Enable inlining of PLT entries in function calls to functions that
are not known to bind locally. It has no effect without `-mfdpic'.
It's enabled by default if optimizing for speed and compiling for
shared libraries (i.e., `-fPIC' or `-fpic'), or when an
optimization option such as `-O3' or above is present in the
command line.
`-mTLS'
Assume a large TLS segment when generating thread-local code.
`-mtls'
Do not assume a large TLS segment when generating thread-local
code.
`-mgprel-ro'
Enable the use of `GPREL' relocations in the FDPIC ABI for data
that is known to be in read-only sections. It's enabled by
default, except for `-fpic' or `-fpie': even though it may help
make the global offset table smaller, it trades 1 instruction for
4. With `-fPIC' or `-fPIE', it trades 3 instructions for 4, one
of which may be shared by multiple symbols, and it avoids the need
for a GOT entry for the referenced symbol, so it's more likely to
be a win. If it is not, `-mno-gprel-ro' can be used to disable it.
`-multilib-library-pic'
Link with the (library, not FD) pic libraries. It's implied by
`-mlibrary-pic', as well as by `-fPIC' and `-fpic' without
`-mfdpic'. You should never have to use it explicitly.
`-mlinked-fp'
Follow the EABI requirement of always creating a frame pointer
whenever a stack frame is allocated. This option is enabled by
default and can be disabled with `-mno-linked-fp'.
`-mlong-calls'
Use indirect addressing to call functions outside the current
compilation unit. This allows the functions to be placed anywhere
within the 32-bit address space.
`-malign-labels'
Try to align labels to an 8-byte boundary by inserting nops into
the previous packet. This option only has an effect when VLIW
packing is enabled. It doesn't create new packets; it merely adds
nops to existing ones.
`-mlibrary-pic'
Generate position-independent EABI code.
`-macc-4'
Use only the first four media accumulator registers.
`-macc-8'
Use all eight media accumulator registers.
`-mpack'
Pack VLIW instructions.
`-mno-pack'
Do not pack VLIW instructions.
`-mno-eflags'
Do not mark ABI switches in e_flags.
`-mcond-move'
Enable the use of conditional-move instructions (default).
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mno-cond-move'
Disable the use of conditional-move instructions.
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mscc'
Enable the use of conditional set instructions (default).
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mno-scc'
Disable the use of conditional set instructions.
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mcond-exec'
Enable the use of conditional execution (default).
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mno-cond-exec'
Disable the use of conditional execution.
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mvliw-branch'
Run a pass to pack branches into VLIW instructions (default).
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mno-vliw-branch'
Do not run a pass to pack branches into VLIW instructions.
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mmulti-cond-exec'
Enable optimization of `&&' and `||' in conditional execution
(default).
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mno-multi-cond-exec'
Disable optimization of `&&' and `||' in conditional execution.
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mnested-cond-exec'
Enable nested conditional execution optimizations (default).
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-mno-nested-cond-exec'
Disable nested conditional execution optimizations.
This switch is mainly for debugging the compiler and will likely
be removed in a future version.
`-moptimize-membar'
This switch removes redundant `membar' instructions from the
compiler generated code. It is enabled by default.
`-mno-optimize-membar'
This switch disables the automatic removal of redundant `membar'
instructions from the generated code.
`-mtomcat-stats'
Cause gas to print out tomcat statistics.
`-mcpu=CPU'
Select the processor type for which to generate code. Possible
values are `frv', `fr550', `tomcat', `fr500', `fr450', `fr405',
`fr400', `fr300' and `simple'.
File: gcc.info, Node: GNU/Linux Options, Next: H8/300 Options, Prev: FRV Options, Up: Submodel Options
3.17.11 GNU/Linux Options
-------------------------
These `-m' options are defined for GNU/Linux targets:
`-mglibc'
Use the GNU C library instead of uClibc. This is the default
except on `*-*-linux-*uclibc*' targets.
`-muclibc'
Use uClibc instead of the GNU C library. This is the default on
`*-*-linux-*uclibc*' targets.
File: gcc.info, Node: H8/300 Options, Next: HPPA Options, Prev: GNU/Linux Options, Up: Submodel Options
3.17.12 H8/300 Options
----------------------
These `-m' options are defined for the H8/300 implementations:
`-mrelax'
Shorten some address references at link time, when possible; uses
the linker option `-relax'. *Note `ld' and the H8/300:
(ld)H8/300, for a fuller description.
`-mh'
Generate code for the H8/300H.
`-ms'
Generate code for the H8S.
`-mn'
Generate code for the H8S and H8/300H in the normal mode. This
switch must be used either with `-mh' or `-ms'.
`-ms2600'
Generate code for the H8S/2600. This switch must be used with
`-ms'.
`-mint32'
Make `int' data 32 bits by default.
`-malign-300'
On the H8/300H and H8S, use the same alignment rules as for the
H8/300. The default for the H8/300H and H8S is to align longs and
floats on 4 byte boundaries. `-malign-300' causes them to be
aligned on 2 byte boundaries. This option has no effect on the
H8/300.
File: gcc.info, Node: HPPA Options, Next: i386 and x86-64 Options, Prev: H8/300 Options, Up: Submodel Options
3.17.13 HPPA Options
--------------------
These `-m' options are defined for the HPPA family of computers:
`-march=ARCHITECTURE-TYPE'
Generate code for the specified architecture. The choices for
ARCHITECTURE-TYPE are `1.0' for PA 1.0, `1.1' for PA 1.1, and
`2.0' for PA 2.0 processors. Refer to `/usr/lib/sched.models' on
an HP-UX system to determine the proper architecture option for
your machine. Code compiled for lower numbered architectures will
run on higher numbered architectures, but not the other way around.
`-mpa-risc-1-0'
`-mpa-risc-1-1'
`-mpa-risc-2-0'
Synonyms for `-march=1.0', `-march=1.1', and `-march=2.0'
respectively.
`-mbig-switch'
Generate code suitable for big switch tables. Use this option
only if the assembler/linker complain about out of range branches
within a switch table.
`-mjump-in-delay'
Fill delay slots of function calls with unconditional jump
instructions by modifying the return pointer for the function call
to be the target of the conditional jump.
`-mdisable-fpregs'
Prevent floating point registers from being used in any manner.
This is necessary for compiling kernels which perform lazy context
switching of floating point registers. If you use this option and
attempt to perform floating point operations, the compiler will
abort.
`-mdisable-indexing'
Prevent the compiler from using indexing address modes. This
avoids some rather obscure problems when compiling MIG generated
code under MACH.
`-mno-space-regs'
Generate code that assumes the target has no space registers.
This allows GCC to generate faster indirect calls and use unscaled
index address modes.
Such code is suitable for level 0 PA systems and kernels.
`-mfast-indirect-calls'
Generate code that assumes calls never cross space boundaries.
This allows GCC to emit code which performs faster indirect calls.
This option will not work in the presence of shared libraries or
nested functions.
`-mfixed-range=REGISTER-RANGE'
Generate code treating the given register range as fixed registers.
A fixed register is one that the register allocator can not use.
This is useful when compiling kernel code. A register range is
specified as two registers separated by a dash. Multiple register
ranges can be specified separated by a comma.
`-mlong-load-store'
Generate 3-instruction load and store sequences as sometimes
required by the HP-UX 10 linker. This is equivalent to the `+k'
option to the HP compilers.
`-mportable-runtime'
Use the portable calling conventions proposed by HP for ELF
systems.
`-mgas'
Enable the use of assembler directives only GAS understands.
`-mschedule=CPU-TYPE'
Schedule code according to the constraints for the machine type
CPU-TYPE. The choices for CPU-TYPE are `700' `7100', `7100LC',
`7200', `7300' and `8000'. Refer to `/usr/lib/sched.models' on an
HP-UX system to determine the proper scheduling option for your
machine. The default scheduling is `8000'.
`-mlinker-opt'
Enable the optimization pass in the HP-UX linker. Note this makes
symbolic debugging impossible. It also triggers a bug in the
HP-UX 8 and HP-UX 9 linkers in which they give bogus error
messages when linking some programs.
`-msoft-float'
Generate output containing library calls for floating point.
*Warning:* the requisite libraries are not available for all HPPA
targets. Normally the facilities of the machine's usual C
compiler are used, but this cannot be done directly in
cross-compilation. You must make your own arrangements to provide
suitable library functions for cross-compilation. The embedded
target `hppa1.1-*-pro' does provide software floating point
support.
`-msoft-float' changes the calling convention in the output file;
therefore, it is only useful if you compile _all_ of a program with
this option. In particular, you need to compile `libgcc.a', the
library that comes with GCC, with `-msoft-float' in order for this
to work.
`-msio'
Generate the predefine, `_SIO', for server IO. The default is
`-mwsio'. This generates the predefines, `__hp9000s700',
`__hp9000s700__' and `_WSIO', for workstation IO. These options
are available under HP-UX and HI-UX.
`-mgnu-ld'
Use GNU ld specific options. This passes `-shared' to ld when
building a shared library. It is the default when GCC is
configured, explicitly or implicitly, with the GNU linker. This
option does not have any affect on which ld is called, it only
changes what parameters are passed to that ld. The ld that is
called is determined by the `--with-ld' configure option, GCC's
program search path, and finally by the user's `PATH'. The linker
used by GCC can be printed using `which `gcc
-print-prog-name=ld`'. This option is only available on the 64
bit HP-UX GCC, i.e. configured with `hppa*64*-*-hpux*'.
`-mhp-ld'
Use HP ld specific options. This passes `-b' to ld when building
a shared library and passes `+Accept TypeMismatch' to ld on all
links. It is the default when GCC is configured, explicitly or
implicitly, with the HP linker. This option does not have any
affect on which ld is called, it only changes what parameters are
passed to that ld. The ld that is called is determined by the
`--with-ld' configure option, GCC's program search path, and
finally by the user's `PATH'. The linker used by GCC can be
printed using `which `gcc -print-prog-name=ld`'. This option is
only available on the 64 bit HP-UX GCC, i.e. configured with
`hppa*64*-*-hpux*'.
`-mlong-calls'
Generate code that uses long call sequences. This ensures that a
call is always able to reach linker generated stubs. The default
is to generate long calls only when the distance from the call
site to the beginning of the function or translation unit, as the
case may be, exceeds a predefined limit set by the branch type
being used. The limits for normal calls are 7,600,000 and 240,000
bytes, respectively for the PA 2.0 and PA 1.X architectures.
Sibcalls are always limited at 240,000 bytes.
Distances are measured from the beginning of functions when using
the `-ffunction-sections' option, or when using the `-mgas' and
`-mno-portable-runtime' options together under HP-UX with the SOM
linker.
It is normally not desirable to use this option as it will degrade
performance. However, it may be useful in large applications,
particularly when partial linking is used to build the application.
The types of long calls used depends on the capabilities of the
assembler and linker, and the type of code being generated. The
impact on systems that support long absolute calls, and long pic
symbol-difference or pc-relative calls should be relatively small.
However, an indirect call is used on 32-bit ELF systems in pic code
and it is quite long.
`-munix=UNIX-STD'
Generate compiler predefines and select a startfile for the
specified UNIX standard. The choices for UNIX-STD are `93', `95'
and `98'. `93' is supported on all HP-UX versions. `95' is
available on HP-UX 10.10 and later. `98' is available on HP-UX
11.11 and later. The default values are `93' for HP-UX 10.00,
`95' for HP-UX 10.10 though to 11.00, and `98' for HP-UX 11.11 and
later.
`-munix=93' provides the same predefines as GCC 3.3 and 3.4.
`-munix=95' provides additional predefines for `XOPEN_UNIX' and
`_XOPEN_SOURCE_EXTENDED', and the startfile `unix95.o'.
`-munix=98' provides additional predefines for `_XOPEN_UNIX',
`_XOPEN_SOURCE_EXTENDED', `_INCLUDE__STDC_A1_SOURCE' and
`_INCLUDE_XOPEN_SOURCE_500', and the startfile `unix98.o'.
It is _important_ to note that this option changes the interfaces
for various library routines. It also affects the operational
behavior of the C library. Thus, _extreme_ care is needed in
using this option.
Library code that is intended to operate with more than one UNIX
standard must test, set and restore the variable
__XPG4_EXTENDED_MASK as appropriate. Most GNU software doesn't
provide this capability.
`-nolibdld'
Suppress the generation of link options to search libdld.sl when
the `-static' option is specified on HP-UX 10 and later.
`-static'
The HP-UX implementation of setlocale in libc has a dependency on
libdld.sl. There isn't an archive version of libdld.sl. Thus,
when the `-static' option is specified, special link options are
needed to resolve this dependency.
On HP-UX 10 and later, the GCC driver adds the necessary options to
link with libdld.sl when the `-static' option is specified. This
causes the resulting binary to be dynamic. On the 64-bit port,
the linkers generate dynamic binaries by default in any case. The
`-nolibdld' option can be used to prevent the GCC driver from
adding these link options.
`-threads'
Add support for multithreading with the "dce thread" library under
HP-UX. This option sets flags for both the preprocessor and
linker.
File: gcc.info, Node: i386 and x86-64 Options, Next: IA-64 Options, Prev: HPPA Options, Up: Submodel Options
3.17.14 Intel 386 and AMD x86-64 Options
----------------------------------------
These `-m' options are defined for the i386 and x86-64 family of
computers:
`-mtune=CPU-TYPE'
Tune to CPU-TYPE everything applicable about the generated code,
except for the ABI and the set of available instructions. The
choices for CPU-TYPE are:
_generic_
Produce code optimized for the most common IA32/AMD64/EM64T
processors. If you know the CPU on which your code will run,
then you should use the corresponding `-mtune' option instead
of `-mtune=generic'. But, if you do not know exactly what
CPU users of your application will have, then you should use
this option.
As new processors are deployed in the marketplace, the
behavior of this option will change. Therefore, if you
upgrade to a newer version of GCC, the code generated option
will change to reflect the processors that were most common
when that version of GCC was released.
There is no `-march=generic' option because `-march'
indicates the instruction set the compiler can use, and there
is no generic instruction set applicable to all processors.
In contrast, `-mtune' indicates the processor (or, in this
case, collection of processors) for which the code is
optimized.
_native_
This selects the CPU to tune for at compilation time by
determining the processor type of the compiling machine.
Using `-mtune=native' will produce code optimized for the
local machine under the constraints of the selected
instruction set. Using `-march=native' will enable all
instruction subsets supported by the local machine (hence the
result might not run on different machines).
_i386_
Original Intel's i386 CPU.
_i486_
Intel's i486 CPU. (No scheduling is implemented for this
chip.)
_i586, pentium_
Intel Pentium CPU with no MMX support.
_pentium-mmx_
Intel PentiumMMX CPU based on Pentium core with MMX
instruction set support.
_pentiumpro_
Intel PentiumPro CPU.
_i686_
Same as `generic', but when used as `march' option, PentiumPro
instruction set will be used, so the code will run on all
i686 family chips.
_pentium2_
Intel Pentium2 CPU based on PentiumPro core with MMX
instruction set support.
_pentium3, pentium3m_
Intel Pentium3 CPU based on PentiumPro core with MMX and SSE
instruction set support.
_pentium-m_
Low power version of Intel Pentium3 CPU with MMX, SSE and
SSE2 instruction set support. Used by Centrino notebooks.
_pentium4, pentium4m_
Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set
support.
_prescott_
Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2
and SSE3 instruction set support.
_nocona_
Improved version of Intel Pentium4 CPU with 64-bit
extensions, MMX, SSE, SSE2 and SSE3 instruction set support.
_k6_
AMD K6 CPU with MMX instruction set support.
_k6-2, k6-3_
Improved versions of AMD K6 CPU with MMX and 3dNOW!
instruction set support.
_athlon, athlon-tbird_
AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE
prefetch instructions support.
_athlon-4, athlon-xp, athlon-mp_
Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and
full SSE instruction set support.
_k8, opteron, athlon64, athlon-fx_
AMD K8 core based CPUs with x86-64 instruction set support.
(This supersets MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and
64-bit instruction set extensions.)
_winchip-c6_
IDT Winchip C6 CPU, dealt in same way as i486 with additional
MMX instruction set support.
_winchip2_
IDT Winchip2 CPU, dealt in same way as i486 with additional
MMX and 3dNOW! instruction set support.
_c3_
Via C3 CPU with MMX and 3dNOW! instruction set support. (No
scheduling is implemented for this chip.)
_c3-2_
Via C3-2 CPU with MMX and SSE instruction set support. (No
scheduling is implemented for this chip.)
While picking a specific CPU-TYPE will schedule things
appropriately for that particular chip, the compiler will not
generate any code that does not run on the i386 without the
`-march=CPU-TYPE' option being used.
`-march=CPU-TYPE'
Generate instructions for the machine type CPU-TYPE. The choices
for CPU-TYPE are the same as for `-mtune'. Moreover, specifying
`-march=CPU-TYPE' implies `-mtune=CPU-TYPE'.
`-mcpu=CPU-TYPE'
A deprecated synonym for `-mtune'.
`-m386'
`-m486'
`-mpentium'
`-mpentiumpro'
These options are synonyms for `-mtune=i386', `-mtune=i486',
`-mtune=pentium', and `-mtune=pentiumpro' respectively. These
synonyms are deprecated.
`-mfpmath=UNIT'
Generate floating point arithmetics for selected unit UNIT. The
choices for UNIT are:
`387'
Use the standard 387 floating point coprocessor present
majority of chips and emulated otherwise. Code compiled with
this option will run almost everywhere. The temporary
results are computed in 80bit precision instead of precision
specified by the type resulting in slightly different results
compared to most of other chips. See `-ffloat-store' for
more detailed description.
This is the default choice for i386 compiler.
`sse'
Use scalar floating point instructions present in the SSE
instruction set. This instruction set is supported by
Pentium3 and newer chips, in the AMD line by Athlon-4,
Athlon-xp and Athlon-mp chips. The earlier version of SSE
instruction set supports only single precision arithmetics,
thus the double and extended precision arithmetics is still
done using 387. Later version, present only in Pentium4 and
the future AMD x86-64 chips supports double precision
arithmetics too.
For the i386 compiler, you need to use `-march=CPU-TYPE',
`-msse' or `-msse2' switches to enable SSE extensions and
make this option effective. For the x86-64 compiler, these
extensions are enabled by default.
The resulting code should be considerably faster in the
majority of cases and avoid the numerical instability
problems of 387 code, but may break some existing code that
expects temporaries to be 80bit.
This is the default choice for the x86-64 compiler.
`sse,387'
Attempt to utilize both instruction sets at once. This
effectively double the amount of available registers and on
chips with separate execution units for 387 and SSE the
execution resources too. Use this option with care, as it is
still experimental, because the GCC register allocator does
not model separate functional units well resulting in
instable performance.
`-masm=DIALECT'
Output asm instructions using selected DIALECT. Supported choices
are `intel' or `att' (the default one). Darwin does not support
`intel'.
`-mieee-fp'
`-mno-ieee-fp'
Control whether or not the compiler uses IEEE floating point
comparisons. These handle correctly the case where the result of a
comparison is unordered.
`-msoft-float'
Generate output containing library calls for floating point.
*Warning:* the requisite libraries are not part of GCC. Normally
the facilities of the machine's usual C compiler are used, but
this can't be done directly in cross-compilation. You must make
your own arrangements to provide suitable library functions for
cross-compilation.
On machines where a function returns floating point results in the
80387 register stack, some floating point opcodes may be emitted
even if `-msoft-float' is used.
`-mno-fp-ret-in-387'
Do not use the FPU registers for return values of functions.
The usual calling convention has functions return values of types
`float' and `double' in an FPU register, even if there is no FPU.
The idea is that the operating system should emulate an FPU.
The option `-mno-fp-ret-in-387' causes such values to be returned
in ordinary CPU registers instead.
`-mno-fancy-math-387'
Some 387 emulators do not support the `sin', `cos' and `sqrt'
instructions for the 387. Specify this option to avoid generating
those instructions. This option is the default on FreeBSD,
OpenBSD and NetBSD. This option is overridden when `-march'
indicates that the target cpu will always have an FPU and so the
instruction will not need emulation. As of revision 2.6.1, these
instructions are not generated unless you also use the
`-funsafe-math-optimizations' switch.
`-malign-double'
`-mno-align-double'
Control whether GCC aligns `double', `long double', and `long
long' variables on a two word boundary or a one word boundary.
Aligning `double' variables on a two word boundary will produce
code that runs somewhat faster on a `Pentium' at the expense of
more memory.
On x86-64, `-malign-double' is enabled by default.
*Warning:* if you use the `-malign-double' switch, structures
containing the above types will be aligned differently than the
published application binary interface specifications for the 386
and will not be binary compatible with structures in code compiled
without that switch.
`-m96bit-long-double'
`-m128bit-long-double'
These switches control the size of `long double' type. The i386
application binary interface specifies the size to be 96 bits, so
`-m96bit-long-double' is the default in 32 bit mode.
Modern architectures (Pentium and newer) would prefer `long double'
to be aligned to an 8 or 16 byte boundary. In arrays or structures
conforming to the ABI, this would not be possible. So specifying a
`-m128bit-long-double' will align `long double' to a 16 byte
boundary by padding the `long double' with an additional 32 bit
zero.
In the x86-64 compiler, `-m128bit-long-double' is the default
choice as its ABI specifies that `long double' is to be aligned on
16 byte boundary.
Notice that neither of these options enable any extra precision
over the x87 standard of 80 bits for a `long double'.
*Warning:* if you override the default value for your target ABI,
the structures and arrays containing `long double' variables will
change their size as well as function calling convention for
function taking `long double' will be modified. Hence they will
not be binary compatible with arrays or structures in code
compiled without that switch.
`-mmlarge-data-threshold=NUMBER'
When `-mcmodel=medium' is specified, the data greater than
THRESHOLD are placed in large data section. This value must be the
same across all object linked into the binary and defaults to
65535.
`-msvr3-shlib'
`-mno-svr3-shlib'
Control whether GCC places uninitialized local variables into the
`bss' or `data' segments. `-msvr3-shlib' places them into `bss'.
These options are meaningful only on System V Release 3.
`-mrtd'
Use a different function-calling convention, in which functions
that take a fixed number of arguments return with the `ret' NUM
instruction, which pops their arguments while returning. This
saves one instruction in the caller since there is no need to pop
the arguments there.
You can specify that an individual function is called with this
calling sequence with the function attribute `stdcall'. You can
also override the `-mrtd' option by using the function attribute
`cdecl'. *Note Function Attributes::.
*Warning:* this calling convention is incompatible with the one
normally used on Unix, so you cannot use it if you need to call
libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including `printf'); otherwise
incorrect code will be generated for calls to those functions.
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
`-mregparm=NUM'
Control how many registers are used to pass integer arguments. By
default, no registers are used to pass arguments, and at most 3
registers can be used. You can control this behavior for a
specific function by using the function attribute `regparm'.
*Note Function Attributes::.
*Warning:* if you use this switch, and NUM is nonzero, then you
must build all modules with the same value, including any
libraries. This includes the system libraries and startup modules.
`-msseregparm'
Use SSE register passing conventions for float and double arguments
and return values. You can control this behavior for a specific
function by using the function attribute `sseregparm'. *Note
Function Attributes::.
*Warning:* if you use this switch then you must build all modules
with the same value, including any libraries. This includes the
system libraries and startup modules.
`-mstackrealign'
Realign the stack at entry. On the Intel x86, the
`-mstackrealign' option will generate an alternate prologue and
epilogue that realigns the runtime stack. This supports mixing
legacy codes that keep a 4-byte aligned stack with modern codes
that keep a 16-byte stack for SSE compatibility. The alternate
prologue and epilogue are slower and bigger than the regular ones,
and the alternate prologue requires an extra scratch register;
this lowers the number of registers available if used in
conjunction with the `regparm' attribute. The `-mstackrealign'
option is incompatible with the nested function prologue; this is
considered a hard error. See also the attribute
`force_align_arg_pointer', applicable to individual functions.
`-mpreferred-stack-boundary=NUM'
Attempt to keep the stack boundary aligned to a 2 raised to NUM
byte boundary. If `-mpreferred-stack-boundary' is not specified,
the default is 4 (16 bytes or 128 bits).
On Pentium and PentiumPro, `double' and `long double' values
should be aligned to an 8 byte boundary (see `-malign-double') or
suffer significant run time performance penalties. On Pentium
III, the Streaming SIMD Extension (SSE) data type `__m128' may not
work properly if it is not 16 byte aligned.
To ensure proper alignment of this values on the stack, the stack
boundary must be as aligned as that required by any value stored
on the stack. Further, every function must be generated such that
it keeps the stack aligned. Thus calling a function compiled with
a higher preferred stack boundary from a function compiled with a
lower preferred stack boundary will most likely misalign the
stack. It is recommended that libraries that use callbacks always
use the default setting.
This extra alignment does consume extra stack space, and generally
increases code size. Code that is sensitive to stack space usage,
such as embedded systems and operating system kernels, may want to
reduce the preferred alignment to `-mpreferred-stack-boundary=2'.
`-mmmx'
`-mno-mmx'
`-msse'
`-mno-sse'
`-msse2'
`-mno-sse2'
`-msse3'
`-mno-sse3'
`-m3dnow'
`-mno-3dnow'
These switches enable or disable the use of instructions in the
MMX, SSE, SSE2 or 3DNow! extended instruction sets. These
extensions are also available as built-in functions: see *Note X86
Built-in Functions::, for details of the functions enabled and
disabled by these switches.
To have SSE/SSE2 instructions generated automatically from
floating-point code (as opposed to 387 instructions), see
`-mfpmath=sse'.
These options will enable GCC to use these extended instructions in
generated code, even without `-mfpmath=sse'. Applications which
perform runtime CPU detection must compile separate files for each
supported architecture, using the appropriate flags. In
particular, the file containing the CPU detection code should be
compiled without these options.
`-mpush-args'
`-mno-push-args'
Use PUSH operations to store outgoing parameters. This method is
shorter and usually equally fast as method using SUB/MOV
operations and is enabled by default. In some cases disabling it
may improve performance because of improved scheduling and reduced
dependencies.
`-maccumulate-outgoing-args'
If enabled, the maximum amount of space required for outgoing
arguments will be computed in the function prologue. This is
faster on most modern CPUs because of reduced dependencies,
improved scheduling and reduced stack usage when preferred stack
boundary is not equal to 2. The drawback is a notable increase in
code size. This switch implies `-mno-push-args'.
`-mthreads'
Support thread-safe exception handling on `Mingw32'. Code that
relies on thread-safe exception handling must compile and link all
code with the `-mthreads' option. When compiling, `-mthreads'
defines `-D_MT'; when linking, it links in a special thread helper
library `-lmingwthrd' which cleans up per thread exception
handling data.
`-mno-align-stringops'
Do not align destination of inlined string operations. This
switch reduces code size and improves performance in case the
destination is already aligned, but GCC doesn't know about it.
`-minline-all-stringops'
By default GCC inlines string operations only when destination is
known to be aligned at least to 4 byte boundary. This enables
more inlining, increase code size, but may improve performance of
code that depends on fast memcpy, strlen and memset for short
lengths.
`-momit-leaf-frame-pointer'
Don't keep the frame pointer in a register for leaf functions.
This avoids the instructions to save, set up and restore frame
pointers and makes an extra register available in leaf functions.
The option `-fomit-frame-pointer' removes the frame pointer for
all functions which might make debugging harder.
`-mtls-direct-seg-refs'
`-mno-tls-direct-seg-refs'
Controls whether TLS variables may be accessed with offsets from
the TLS segment register (`%gs' for 32-bit, `%fs' for 64-bit), or
whether the thread base pointer must be added. Whether or not this
is legal depends on the operating system, and whether it maps the
segment to cover the entire TLS area.
For systems that use GNU libc, the default is on.
These `-m' switches are supported in addition to the above on AMD
x86-64 processors in 64-bit environments.
`-m32'
`-m64'
Generate code for a 32-bit or 64-bit environment. The 32-bit
environment sets int, long and pointer to 32 bits and generates
code that runs on any i386 system. The 64-bit environment sets
int to 32 bits and long and pointer to 64 bits and generates code
for AMD's x86-64 architecture. For darwin only the -m64 option
turns off the `-fno-pic' and `-mdynamic-no-pic' options.
`-mno-red-zone'
Do not use a so called red zone for x86-64 code. The red zone is
mandated by the x86-64 ABI, it is a 128-byte area beyond the
location of the stack pointer that will not be modified by signal
or interrupt handlers and therefore can be used for temporary data
without adjusting the stack pointer. The flag `-mno-red-zone'
disables this red zone.
`-mcmodel=small'
Generate code for the small code model: the program and its
symbols must be linked in the lower 2 GB of the address space.
Pointers are 64 bits. Programs can be statically or dynamically
linked. This is the default code model.
`-mcmodel=kernel'
Generate code for the kernel code model. The kernel runs in the
negative 2 GB of the address space. This model has to be used for
Linux kernel code.
`-mcmodel=medium'
Generate code for the medium model: The program is linked in the
lower 2 GB of the address space but symbols can be located
anywhere in the address space. Programs can be statically or
dynamically linked, but building of shared libraries are not
supported with the medium model.
`-mcmodel=large'
Generate code for the large model: This model makes no assumptions
about addresses and sizes of sections. Currently GCC does not
implement this model.
File: gcc.info, Node: IA-64 Options, Next: M32C Options, Prev: i386 and x86-64 Options, Up: Submodel Options
3.17.15 IA-64 Options
---------------------
These are the `-m' options defined for the Intel IA-64 architecture.
`-mbig-endian'
Generate code for a big endian target. This is the default for
HP-UX.
`-mlittle-endian'
Generate code for a little endian target. This is the default for
AIX5 and GNU/Linux.
`-mgnu-as'
`-mno-gnu-as'
Generate (or don't) code for the GNU assembler. This is the
default.
`-mgnu-ld'
`-mno-gnu-ld'
Generate (or don't) code for the GNU linker. This is the default.
`-mno-pic'
Generate code that does not use a global pointer register. The
result is not position independent code, and violates the IA-64
ABI.
`-mvolatile-asm-stop'
`-mno-volatile-asm-stop'
Generate (or don't) a stop bit immediately before and after
volatile asm statements.
`-mregister-names'
`-mno-register-names'
Generate (or don't) `in', `loc', and `out' register names for the
stacked registers. This may make assembler output more readable.
`-mno-sdata'
`-msdata'
Disable (or enable) optimizations that use the small data section.
This may be useful for working around optimizer bugs.
`-mconstant-gp'
Generate code that uses a single constant global pointer value.
This is useful when compiling kernel code.
`-mauto-pic'
Generate code that is self-relocatable. This implies
`-mconstant-gp'. This is useful when compiling firmware code.
`-minline-float-divide-min-latency'
Generate code for inline divides of floating point values using
the minimum latency algorithm.
`-minline-float-divide-max-throughput'
Generate code for inline divides of floating point values using
the maximum throughput algorithm.
`-minline-int-divide-min-latency'
Generate code for inline divides of integer values using the
minimum latency algorithm.
`-minline-int-divide-max-throughput'
Generate code for inline divides of integer values using the
maximum throughput algorithm.
`-minline-sqrt-min-latency'
Generate code for inline square roots using the minimum latency
algorithm.
`-minline-sqrt-max-throughput'
Generate code for inline square roots using the maximum throughput
algorithm.
`-mno-dwarf2-asm'
`-mdwarf2-asm'
Don't (or do) generate assembler code for the DWARF2 line number
debugging info. This may be useful when not using the GNU
assembler.
`-mearly-stop-bits'
`-mno-early-stop-bits'
Allow stop bits to be placed earlier than immediately preceding the
instruction that triggered the stop bit. This can improve
instruction scheduling, but does not always do so.
`-mfixed-range=REGISTER-RANGE'
Generate code treating the given register range as fixed registers.
A fixed register is one that the register allocator can not use.
This is useful when compiling kernel code. A register range is
specified as two registers separated by a dash. Multiple register
ranges can be specified separated by a comma.
`-mtls-size=TLS-SIZE'
Specify bit size of immediate TLS offsets. Valid values are 14,
22, and 64.
`-mtune=CPU-TYPE'
Tune the instruction scheduling for a particular CPU, Valid values
are itanium, itanium1, merced, itanium2, and mckinley.
`-mt'
`-pthread'
Add support for multithreading using the POSIX threads library.
This option sets flags for both the preprocessor and linker. It
does not affect the thread safety of object code produced by the
compiler or that of libraries supplied with it. These are HP-UX
specific flags.
`-milp32'
`-mlp64'
Generate code for a 32-bit or 64-bit environment. The 32-bit
environment sets int, long and pointer to 32 bits. The 64-bit
environment sets int to 32 bits and long and pointer to 64 bits.
These are HP-UX specific flags.
`-mno-sched-br-data-spec'
`-msched-br-data-spec'
(Dis/En)able data speculative scheduling before reload. This will
result in generation of the ld.a instructions and the
corresponding check instructions (ld.c / chk.a). The default is
'disable'.
`-msched-ar-data-spec'
`-mno-sched-ar-data-spec'
(En/Dis)able data speculative scheduling after reload. This will
result in generation of the ld.a instructions and the
corresponding check instructions (ld.c / chk.a). The default is
'enable'.
`-mno-sched-control-spec'
`-msched-control-spec'
(Dis/En)able control speculative scheduling. This feature is
available only during region scheduling (i.e. before reload).
This will result in generation of the ld.s instructions and the
corresponding check instructions chk.s . The default is 'disable'.
`-msched-br-in-data-spec'
`-mno-sched-br-in-data-spec'
(En/Dis)able speculative scheduling of the instructions that are
dependent on the data speculative loads before reload. This is
effective only with `-msched-br-data-spec' enabled. The default
is 'enable'.
`-msched-ar-in-data-spec'
`-mno-sched-ar-in-data-spec'
(En/Dis)able speculative scheduling of the instructions that are
dependent on the data speculative loads after reload. This is
effective only with `-msched-ar-data-spec' enabled. The default
is 'enable'.
`-msched-in-control-spec'
`-mno-sched-in-control-spec'
(En/Dis)able speculative scheduling of the instructions that are
dependent on the control speculative loads. This is effective
only with `-msched-control-spec' enabled. The default is 'enable'.
`-msched-ldc'
`-mno-sched-ldc'
(En/Dis)able use of simple data speculation checks ld.c . If
disabled, only chk.a instructions will be emitted to check data
speculative loads. The default is 'enable'.
`-mno-sched-control-ldc'
`-msched-control-ldc'
(Dis/En)able use of ld.c instructions to check control speculative
loads. If enabled, in case of control speculative load with no
speculatively scheduled dependent instructions this load will be
emitted as ld.sa and ld.c will be used to check it. The default
is 'disable'.
`-mno-sched-spec-verbose'
`-msched-spec-verbose'
(Dis/En)able printing of the information about speculative motions.
`-mno-sched-prefer-non-data-spec-insns'
`-msched-prefer-non-data-spec-insns'
If enabled, data speculative instructions will be chosen for
schedule only if there are no other choices at the moment. This
will make the use of the data speculation much more conservative.
The default is 'disable'.
`-mno-sched-prefer-non-control-spec-insns'
`-msched-prefer-non-control-spec-insns'
If enabled, control speculative instructions will be chosen for
schedule only if there are no other choices at the moment. This
will make the use of the control speculation much more
conservative. The default is 'disable'.
`-mno-sched-count-spec-in-critical-path'
`-msched-count-spec-in-critical-path'
If enabled, speculative dependencies will be considered during
computation of the instructions priorities. This will make the
use of the speculation a bit more conservative. The default is
'disable'.
File: gcc.info, Node: M32C Options, Next: M32R/D Options, Prev: IA-64 Options, Up: Submodel Options
3.17.16 M32C Options
--------------------
`-mcpu=NAME'
Select the CPU for which code is generated. NAME may be one of
`r8c' for the R8C/Tiny series, `m16c' for the M16C (up to /60)
series, `m32cm' for the M16C/80 series, or `m32c' for the M32C/80
series.
`-msim'
Specifies that the program will be run on the simulator. This
causes an alternate runtime library to be linked in which
supports, for example, file I/O. You must not use this option
when generating programs that will run on real hardware; you must
provide your own runtime library for whatever I/O functions are
needed.
`-memregs=NUMBER'
Specifies the number of memory-based pseudo-registers GCC will use
during code generation. These pseudo-registers will be used like
real registers, so there is a tradeoff between GCC's ability to
fit the code into available registers, and the performance penalty
of using memory instead of registers. Note that all modules in a
program must be compiled with the same value for this option.
Because of that, you must not use this option with the default
runtime libraries gcc builds.
File: gcc.info, Node: M32R/D Options, Next: M680x0 Options, Prev: M32C Options, Up: Submodel Options
3.17.17 M32R/D Options
----------------------
These `-m' options are defined for Renesas M32R/D architectures:
`-m32r2'
Generate code for the M32R/2.
`-m32rx'
Generate code for the M32R/X.
`-m32r'
Generate code for the M32R. This is the default.
`-mmodel=small'
Assume all objects live in the lower 16MB of memory (so that their
addresses can be loaded with the `ld24' instruction), and assume
all subroutines are reachable with the `bl' instruction. This is
the default.
The addressability of a particular object can be set with the
`model' attribute.
`-mmodel=medium'
Assume objects may be anywhere in the 32-bit address space (the
compiler will generate `seth/add3' instructions to load their
addresses), and assume all subroutines are reachable with the `bl'
instruction.
`-mmodel=large'
Assume objects may be anywhere in the 32-bit address space (the
compiler will generate `seth/add3' instructions to load their
addresses), and assume subroutines may not be reachable with the
`bl' instruction (the compiler will generate the much slower
`seth/add3/jl' instruction sequence).
`-msdata=none'
Disable use of the small data area. Variables will be put into
one of `.data', `bss', or `.rodata' (unless the `section'
attribute has been specified). This is the default.
The small data area consists of sections `.sdata' and `.sbss'.
Objects may be explicitly put in the small data area with the
`section' attribute using one of these sections.
`-msdata=sdata'
Put small global and static data in the small data area, but do not
generate special code to reference them.
`-msdata=use'
Put small global and static data in the small data area, and
generate special instructions to reference them.
`-G NUM'
Put global and static objects less than or equal to NUM bytes into
the small data or bss sections instead of the normal data or bss
sections. The default value of NUM is 8. The `-msdata' option
must be set to one of `sdata' or `use' for this option to have any
effect.
All modules should be compiled with the same `-G NUM' value.
Compiling with different values of NUM may or may not work; if it
doesn't the linker will give an error message--incorrect code will
not be generated.
`-mdebug'
Makes the M32R specific code in the compiler display some
statistics that might help in debugging programs.
`-malign-loops'
Align all loops to a 32-byte boundary.
`-mno-align-loops'
Do not enforce a 32-byte alignment for loops. This is the default.
`-missue-rate=NUMBER'
Issue NUMBER instructions per cycle. NUMBER can only be 1 or 2.
`-mbranch-cost=NUMBER'
NUMBER can only be 1 or 2. If it is 1 then branches will be
preferred over conditional code, if it is 2, then the opposite will
apply.
`-mflush-trap=NUMBER'
Specifies the trap number to use to flush the cache. The default
is 12. Valid numbers are between 0 and 15 inclusive.
`-mno-flush-trap'
Specifies that the cache cannot be flushed by using a trap.
`-mflush-func=NAME'
Specifies the name of the operating system function to call to
flush the cache. The default is __flush_cache_, but a function
call will only be used if a trap is not available.
`-mno-flush-func'
Indicates that there is no OS function for flushing the cache.
File: gcc.info, Node: M680x0 Options, Next: M68hc1x Options, Prev: M32R/D Options, Up: Submodel Options
3.17.18 M680x0 Options
----------------------
These are the `-m' options defined for the 68000 series. The default
values for these options depends on which style of 68000 was selected
when the compiler was configured; the defaults for the most common
choices are given below.
`-m68000'
`-mc68000'
Generate output for a 68000. This is the default when the
compiler is configured for 68000-based systems.
Use this option for microcontrollers with a 68000 or EC000 core,
including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
`-m68020'
`-mc68020'
Generate output for a 68020. This is the default when the
compiler is configured for 68020-based systems.
`-m68881'
Generate output containing 68881 instructions for floating point.
This is the default for most 68020 systems unless `--nfp' was
specified when the compiler was configured.
`-m68030'
Generate output for a 68030. This is the default when the
compiler is configured for 68030-based systems.
`-m68040'
Generate output for a 68040. This is the default when the
compiler is configured for 68040-based systems.
This option inhibits the use of 68881/68882 instructions that have
to be emulated by software on the 68040. Use this option if your
68040 does not have code to emulate those instructions.
`-m68060'
Generate output for a 68060. This is the default when the
compiler is configured for 68060-based systems.
This option inhibits the use of 68020 and 68881/68882 instructions
that have to be emulated by software on the 68060. Use this
option if your 68060 does not have code to emulate those
instructions.
`-mcpu32'
Generate output for a CPU32. This is the default when the
compiler is configured for CPU32-based systems.
Use this option for microcontrollers with a CPU32 or CPU32+ core,
including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
68341, 68349 and 68360.
`-m5200'
Generate output for a 520X "coldfire" family cpu. This is the
default when the compiler is configured for 520X-based systems.
Use this option for microcontroller with a 5200 core, including
the MCF5202, MCF5203, MCF5204 and MCF5202.
`-mcfv4e'
Generate output for a ColdFire V4e family cpu (e.g. 547x/548x).
This includes use of hardware floating point instructions.
`-m68020-40'
Generate output for a 68040, without using any of the new
instructions. This results in code which can run relatively
efficiently on either a 68020/68881 or a 68030 or a 68040. The
generated code does use the 68881 instructions that are emulated
on the 68040.
`-m68020-60'
Generate output for a 68060, without using any of the new
instructions. This results in code which can run relatively
efficiently on either a 68020/68881 or a 68030 or a 68040. The
generated code does use the 68881 instructions that are emulated
on the 68060.
`-msoft-float'
Generate output containing library calls for floating point.
*Warning:* the requisite libraries are not available for all m68k
targets. Normally the facilities of the machine's usual C
compiler are used, but this can't be done directly in
cross-compilation. You must make your own arrangements to provide
suitable library functions for cross-compilation. The embedded
targets `m68k-*-aout' and `m68k-*-coff' do provide software
floating point support.
`-mshort'
Consider type `int' to be 16 bits wide, like `short int'.
Additionally, parameters passed on the stack are also aligned to a
16-bit boundary even on targets whose API mandates promotion to
32-bit.
`-mnobitfield'
Do not use the bit-field instructions. The `-m68000', `-mcpu32'
and `-m5200' options imply `-mnobitfield'.
`-mbitfield'
Do use the bit-field instructions. The `-m68020' option implies
`-mbitfield'. This is the default if you use a configuration
designed for a 68020.
`-mrtd'
Use a different function-calling convention, in which functions
that take a fixed number of arguments return with the `rtd'
instruction, which pops their arguments while returning. This
saves one instruction in the caller since there is no need to pop
the arguments there.
This calling convention is incompatible with the one normally used
on Unix, so you cannot use it if you need to call libraries
compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that
take variable numbers of arguments (including `printf'); otherwise
incorrect code will be generated for calls to those functions.
In addition, seriously incorrect code will result if you call a
function with too many arguments. (Normally, extra arguments are
harmlessly ignored.)
The `rtd' instruction is supported by the 68010, 68020, 68030,
68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
`-malign-int'
`-mno-align-int'
Control whether GCC aligns `int', `long', `long long', `float',
`double', and `long double' variables on a 32-bit boundary
(`-malign-int') or a 16-bit boundary (`-mno-align-int'). Aligning
variables on 32-bit boundaries produces code that runs somewhat
faster on processors with 32-bit busses at the expense of more
memory.
*Warning:* if you use the `-malign-int' switch, GCC will align
structures containing the above types differently than most
published application binary interface specifications for the m68k.
`-mpcrel'
Use the pc-relative addressing mode of the 68000 directly, instead
of using a global offset table. At present, this option implies
`-fpic', allowing at most a 16-bit offset for pc-relative
addressing. `-fPIC' is not presently supported with `-mpcrel',
though this could be supported for 68020 and higher processors.
`-mno-strict-align'
`-mstrict-align'
Do not (do) assume that unaligned memory references will be
handled by the system.
`-msep-data'
Generate code that allows the data segment to be located in a
different area of memory from the text segment. This allows for
execute in place in an environment without virtual memory
management. This option implies `-fPIC'.
`-mno-sep-data'
Generate code that assumes that the data segment follows the text
segment. This is the default.
`-mid-shared-library'
Generate code that supports shared libraries via the library ID
method. This allows for execute in place and shared libraries in
an environment without virtual memory management. This option
implies `-fPIC'.
`-mno-id-shared-library'
Generate code that doesn't assume ID based shared libraries are
being used. This is the default.
`-mshared-library-id=n'
Specified the identification number of the ID based shared library
being compiled. Specifying a value of 0 will generate more
compact code, specifying other values will force the allocation of
that number to the current library but is no more space or time
efficient than omitting this option.
File: gcc.info, Node: M68hc1x Options, Next: MCore Options, Prev: M680x0 Options, Up: Submodel Options
3.17.19 M68hc1x Options
-----------------------
These are the `-m' options defined for the 68hc11 and 68hc12
microcontrollers. The default values for these options depends on
which style of microcontroller was selected when the compiler was
configured; the defaults for the most common choices are given below.
`-m6811'
`-m68hc11'
Generate output for a 68HC11. This is the default when the
compiler is configured for 68HC11-based systems.
`-m6812'
`-m68hc12'
Generate output for a 68HC12. This is the default when the
compiler is configured for 68HC12-based systems.
`-m68S12'
`-m68hcs12'
Generate output for a 68HCS12.
`-mauto-incdec'
Enable the use of 68HC12 pre and post auto-increment and
auto-decrement addressing modes.
`-minmax'
`-nominmax'
Enable the use of 68HC12 min and max instructions.
`-mlong-calls'
`-mno-long-calls'
Treat all calls as being far away (near). If calls are assumed to
be far away, the compiler will use the `call' instruction to call
a function and the `rtc' instruction for returning.
`-mshort'
Consider type `int' to be 16 bits wide, like `short int'.
`-msoft-reg-count=COUNT'
Specify the number of pseudo-soft registers which are used for the
code generation. The maximum number is 32. Using more pseudo-soft
register may or may not result in better code depending on the
program. The default is 4 for 68HC11 and 2 for 68HC12.
File: gcc.info, Node: MCore Options, Next: MIPS Options, Prev: M68hc1x Options, Up: Submodel Options
3.17.20 MCore Options
---------------------
These are the `-m' options defined for the Motorola M*Core processors.
`-mhardlit'
`-mno-hardlit'
Inline constants into the code stream if it can be done in two
instructions or less.
`-mdiv'
`-mno-div'
Use the divide instruction. (Enabled by default).
`-mrelax-immediate'
`-mno-relax-immediate'
Allow arbitrary sized immediates in bit operations.
`-mwide-bitfields'
`-mno-wide-bitfields'
Always treat bit-fields as int-sized.
`-m4byte-functions'
`-mno-4byte-functions'
Force all functions to be aligned to a four byte boundary.
`-mcallgraph-data'
`-mno-callgraph-data'
Emit callgraph information.
`-mslow-bytes'
`-mno-slow-bytes'
Prefer word access when reading byte quantities.
`-mlittle-endian'
`-mbig-endian'
Generate code for a little endian target.
`-m210'
`-m340'
Generate code for the 210 processor.
File: gcc.info, Node: MIPS Options, Next: MMIX Options, Prev: MCore Options, Up: Submodel Options
3.17.21 MIPS Options
--------------------
`-EB'
Generate big-endian code.
`-EL'
Generate little-endian code. This is the default for `mips*el-*-*'
configurations.
`-march=ARCH'
Generate code that will run on ARCH, which can be the name of a
generic MIPS ISA, or the name of a particular processor. The ISA
names are: `mips1', `mips2', `mips3', `mips4', `mips32',
`mips32r2', and `mips64'. The processor names are: `4kc', `4km',
`4kp', `5kc', `5kf', `20kc', `24k', `24kc', `24kf', `24kx', `m4k',
`orion', `r2000', `r3000', `r3900', `r4000', `r4400', `r4600',
`r4650', `r6000', `r8000', `rm7000', `rm9000', `sb1', `sr71000',
`vr4100', `vr4111', `vr4120', `vr4130', `vr4300', `vr5000',
`vr5400' and `vr5500'. The special value `from-abi' selects the
most compatible architecture for the selected ABI (that is,
`mips1' for 32-bit ABIs and `mips3' for 64-bit ABIs).
In processor names, a final `000' can be abbreviated as `k' (for
example, `-march=r2k'). Prefixes are optional, and `vr' may be
written `r'.
GCC defines two macros based on the value of this option. The
first is `_MIPS_ARCH', which gives the name of target
architecture, as a string. The second has the form
`_MIPS_ARCH_FOO', where FOO is the capitalized value of
`_MIPS_ARCH'. For example, `-march=r2000' will set `_MIPS_ARCH'
to `"r2000"' and define the macro `_MIPS_ARCH_R2000'.
Note that the `_MIPS_ARCH' macro uses the processor names given
above. In other words, it will have the full prefix and will not
abbreviate `000' as `k'. In the case of `from-abi', the macro
names the resolved architecture (either `"mips1"' or `"mips3"').
It names the default architecture when no `-march' option is given.
`-mtune=ARCH'
Optimize for ARCH. Among other things, this option controls the
way instructions are scheduled, and the perceived cost of
arithmetic operations. The list of ARCH values is the same as for
`-march'.
When this option is not used, GCC will optimize for the processor
specified by `-march'. By using `-march' and `-mtune' together,
it is possible to generate code that will run on a family of
processors, but optimize the code for one particular member of
that family.
`-mtune' defines the macros `_MIPS_TUNE' and `_MIPS_TUNE_FOO',
which work in the same way as the `-march' ones described above.
`-mips1'
Equivalent to `-march=mips1'.
`-mips2'
Equivalent to `-march=mips2'.
`-mips3'
Equivalent to `-march=mips3'.
`-mips4'
Equivalent to `-march=mips4'.
`-mips32'
Equivalent to `-march=mips32'.
`-mips32r2'
Equivalent to `-march=mips32r2'.
`-mips64'
Equivalent to `-march=mips64'.
`-mips16'
`-mno-mips16'
Generate (do not generate) MIPS16 code. If GCC is targetting a
MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE.
`-mabi=32'
`-mabi=o64'
`-mabi=n32'
`-mabi=64'
`-mabi=eabi'
Generate code for the given ABI.
Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
generates 64-bit code when you select a 64-bit architecture, but
you can use `-mgp32' to get 32-bit code instead.
For information about the O64 ABI, see
`http://gcc.gnu.org/projects/mipso64-abi.html'.
`-mabicalls'
`-mno-abicalls'
Generate (do not generate) code that is suitable for SVR4-style
dynamic objects. `-mabicalls' is the default for SVR4-based
systems.
`-mshared'
`-mno-shared'
Generate (do not generate) code that is fully position-independent,
and that can therefore be linked into shared libraries. This
option only affects `-mabicalls'.
All `-mabicalls' code has traditionally been position-independent,
regardless of options like `-fPIC' and `-fpic'. However, as an
extension, the GNU toolchain allows executables to use absolute
accesses for locally-binding symbols. It can also use shorter GP
initialization sequences and generate direct calls to
locally-defined functions. This mode is selected by `-mno-shared'.
`-mno-shared' depends on binutils 2.16 or higher and generates
objects that can only be linked by the GNU linker. However, the
option does not affect the ABI of the final executable; it only
affects the ABI of relocatable objects. Using `-mno-shared' will
generally make executables both smaller and quicker.
`-mshared' is the default.
`-mxgot'
`-mno-xgot'
Lift (do not lift) the usual restrictions on the size of the global
offset table.
GCC normally uses a single instruction to load values from the GOT.
While this is relatively efficient, it will only work if the GOT
is smaller than about 64k. Anything larger will cause the linker
to report an error such as:
relocation truncated to fit: R_MIPS_GOT16 foobar
If this happens, you should recompile your code with `-mxgot'. It
should then work with very large GOTs, although it will also be
less efficient, since it will take three instructions to fetch the
value of a global symbol.
Note that some linkers can create multiple GOTs. If you have such
a linker, you should only need to use `-mxgot' when a single object
file accesses more than 64k's worth of GOT entries. Very few do.
These options have no effect unless GCC is generating position
independent code.
`-mgp32'
Assume that general-purpose registers are 32 bits wide.
`-mgp64'
Assume that general-purpose registers are 64 bits wide.
`-mfp32'
Assume that floating-point registers are 32 bits wide.
`-mfp64'
Assume that floating-point registers are 64 bits wide.
`-mhard-float'
Use floating-point coprocessor instructions.
`-msoft-float'
Do not use floating-point coprocessor instructions. Implement
floating-point calculations using library calls instead.
`-msingle-float'
Assume that the floating-point coprocessor only supports
single-precision operations.
`-mdouble-float'
Assume that the floating-point coprocessor supports
double-precision operations. This is the default.
`-mdsp'
`-mno-dsp'
Use (do not use) the MIPS DSP ASE. *Note MIPS DSP Built-in
Functions::.
`-mpaired-single'
`-mno-paired-single'
Use (do not use) paired-single floating-point instructions. *Note
MIPS Paired-Single Support::. This option can only be used when
generating 64-bit code and requires hardware floating-point
support to be enabled.
`-mips3d'
`-mno-mips3d'
Use (do not use) the MIPS-3D ASE. *Note MIPS-3D Built-in
Functions::. The option `-mips3d' implies `-mpaired-single'.
`-mlong64'
Force `long' types to be 64 bits wide. See `-mlong32' for an
explanation of the default and the way that the pointer size is
determined.
`-mlong32'
Force `long', `int', and pointer types to be 32 bits wide.
The default size of `int's, `long's and pointers depends on the
ABI. All the supported ABIs use 32-bit `int's. The n64 ABI uses
64-bit `long's, as does the 64-bit EABI; the others use 32-bit
`long's. Pointers are the same size as `long's, or the same size
as integer registers, whichever is smaller.
`-msym32'
`-mno-sym32'
Assume (do not assume) that all symbols have 32-bit values,
regardless of the selected ABI. This option is useful in
combination with `-mabi=64' and `-mno-abicalls' because it allows
GCC to generate shorter and faster references to symbolic
addresses.
`-G NUM'
Put global and static items less than or equal to NUM bytes into
the small data or bss section instead of the normal data or bss
section. This allows the data to be accessed using a single
instruction.
All modules should be compiled with the same `-G NUM' value.
`-membedded-data'
`-mno-embedded-data'
Allocate variables to the read-only data section first if
possible, then next in the small data section if possible,
otherwise in data. This gives slightly slower code than the
default, but reduces the amount of RAM required when executing,
and thus may be preferred for some embedded systems.
`-muninit-const-in-rodata'
`-mno-uninit-const-in-rodata'
Put uninitialized `const' variables in the read-only data section.
This option is only meaningful in conjunction with
`-membedded-data'.
`-msplit-addresses'
`-mno-split-addresses'
Enable (disable) use of the `%hi()' and `%lo()' assembler
relocation operators. This option has been superseded by
`-mexplicit-relocs' but is retained for backwards compatibility.
`-mexplicit-relocs'
`-mno-explicit-relocs'
Use (do not use) assembler relocation operators when dealing with
symbolic addresses. The alternative, selected by
`-mno-explicit-relocs', is to use assembler macros instead.
`-mexplicit-relocs' is the default if GCC was configured to use an
assembler that supports relocation operators.
`-mcheck-zero-division'
`-mno-check-zero-division'
Trap (do not trap) on integer division by zero. The default is
`-mcheck-zero-division'.
`-mdivide-traps'
`-mdivide-breaks'
MIPS systems check for division by zero by generating either a
conditional trap or a break instruction. Using traps results in
smaller code, but is only supported on MIPS II and later. Also,
some versions of the Linux kernel have a bug that prevents trap
from generating the proper signal (`SIGFPE'). Use
`-mdivide-traps' to allow conditional traps on architectures that
support them and `-mdivide-breaks' to force the use of breaks.
The default is usually `-mdivide-traps', but this can be
overridden at configure time using `--with-divide=breaks'.
Divide-by-zero checks can be completely disabled using
`-mno-check-zero-division'.
`-mmemcpy'
`-mno-memcpy'
Force (do not force) the use of `memcpy()' for non-trivial block
moves. The default is `-mno-memcpy', which allows GCC to inline
most constant-sized copies.
`-mlong-calls'
`-mno-long-calls'
Disable (do not disable) use of the `jal' instruction. Calling
functions using `jal' is more efficient but requires the caller
and callee to be in the same 256 megabyte segment.
This option has no effect on abicalls code. The default is
`-mno-long-calls'.
`-mmad'
`-mno-mad'
Enable (disable) use of the `mad', `madu' and `mul' instructions,
as provided by the R4650 ISA.
`-mfused-madd'
`-mno-fused-madd'
Enable (disable) use of the floating point multiply-accumulate
instructions, when they are available. The default is
`-mfused-madd'.
When multiply-accumulate instructions are used, the intermediate
product is calculated to infinite precision and is not subject to
the FCSR Flush to Zero bit. This may be undesirable in some
circumstances.
`-nocpp'
Tell the MIPS assembler to not run its preprocessor over user
assembler files (with a `.s' suffix) when assembling them.
`-mfix-r4000'
`-mno-fix-r4000'
Work around certain R4000 CPU errata:
- A double-word or a variable shift may give an incorrect
result if executed immediately after starting an integer
division.
- A double-word or a variable shift may give an incorrect
result if executed while an integer multiplication is in
progress.
- An integer division may give an incorrect result if started
in a delay slot of a taken branch or a jump.
`-mfix-r4400'
`-mno-fix-r4400'
Work around certain R4400 CPU errata:
- A double-word or a variable shift may give an incorrect
result if executed immediately after starting an integer
division.
`-mfix-vr4120'
`-mno-fix-vr4120'
Work around certain VR4120 errata:
- `dmultu' does not always produce the correct result.
- `div' and `ddiv' do not always produce the correct result if
one of the operands is negative.
The workarounds for the division errata rely on special functions
in `libgcc.a'. At present, these functions are only provided by
the `mips64vr*-elf' configurations.
Other VR4120 errata require a nop to be inserted between certain
pairs of instructions. These errata are handled by the assembler,
not by GCC itself.
`-mfix-vr4130'
Work around the VR4130 `mflo'/`mfhi' errata. The workarounds are
implemented by the assembler rather than by GCC, although GCC will
avoid using `mflo' and `mfhi' if the VR4130 `macc', `macchi',
`dmacc' and `dmacchi' instructions are available instead.
`-mfix-sb1'
`-mno-fix-sb1'
Work around certain SB-1 CPU core errata. (This flag currently
works around the SB-1 revision 2 "F1" and "F2" floating point
errata.)
`-mflush-func=FUNC'
`-mno-flush-func'
Specifies the function to call to flush the I and D caches, or to
not call any such function. If called, the function must take the
same arguments as the common `_flush_func()', that is, the address
of the memory range for which the cache is being flushed, the size
of the memory range, and the number 3 (to flush both caches). The
default depends on the target GCC was configured for, but commonly
is either `_flush_func' or `__cpu_flush'.
`-mbranch-likely'
`-mno-branch-likely'
Enable or disable use of Branch Likely instructions, regardless of
the default for the selected architecture. By default, Branch
Likely instructions may be generated if they are supported by the
selected architecture. An exception is for the MIPS32 and MIPS64
architectures and processors which implement those architectures;
for those, Branch Likely instructions will not be generated by
default because the MIPS32 and MIPS64 architectures specifically
deprecate their use.
`-mfp-exceptions'
`-mno-fp-exceptions'
Specifies whether FP exceptions are enabled. This affects how we
schedule FP instructions for some processors. The default is that
FP exceptions are enabled.
For instance, on the SB-1, if FP exceptions are disabled, and we
are emitting 64-bit code, then we can use both FP pipes.
Otherwise, we can only use one FP pipe.
`-mvr4130-align'
`-mno-vr4130-align'
The VR4130 pipeline is two-way superscalar, but can only issue two
instructions together if the first one is 8-byte aligned. When
this option is enabled, GCC will align pairs of instructions that
it thinks should execute in parallel.
This option only has an effect when optimizing for the VR4130. It
normally makes code faster, but at the expense of making it bigger.
It is enabled by default at optimization level `-O3'.
File: gcc.info, Node: MMIX Options, Next: MN10300 Options, Prev: MIPS Options, Up: Submodel Options
3.17.22 MMIX Options
--------------------
These options are defined for the MMIX:
`-mlibfuncs'
`-mno-libfuncs'
Specify that intrinsic library functions are being compiled,
passing all values in registers, no matter the size.
`-mepsilon'
`-mno-epsilon'
Generate floating-point comparison instructions that compare with
respect to the `rE' epsilon register.
`-mabi=mmixware'
`-mabi=gnu'
Generate code that passes function parameters and return values
that (in the called function) are seen as registers `$0' and up,
as opposed to the GNU ABI which uses global registers `$231' and
up.
`-mzero-extend'
`-mno-zero-extend'
When reading data from memory in sizes shorter than 64 bits, use
(do not use) zero-extending load instructions by default, rather
than sign-extending ones.
`-mknuthdiv'
`-mno-knuthdiv'
Make the result of a division yielding a remainder have the same
sign as the divisor. With the default, `-mno-knuthdiv', the sign
of the remainder follows the sign of the dividend. Both methods
are arithmetically valid, the latter being almost exclusively used.
`-mtoplevel-symbols'
`-mno-toplevel-symbols'
Prepend (do not prepend) a `:' to all global symbols, so the
assembly code can be used with the `PREFIX' assembly directive.
`-melf'
Generate an executable in the ELF format, rather than the default
`mmo' format used by the `mmix' simulator.
`-mbranch-predict'
`-mno-branch-predict'
Use (do not use) the probable-branch instructions, when static
branch prediction indicates a probable branch.
`-mbase-addresses'
`-mno-base-addresses'
Generate (do not generate) code that uses _base addresses_. Using
a base address automatically generates a request (handled by the
assembler and the linker) for a constant to be set up in a global
register. The register is used for one or more base address
requests within the range 0 to 255 from the value held in the
register. The generally leads to short and fast code, but the
number of different data items that can be addressed is limited.
This means that a program that uses lots of static data may
require `-mno-base-addresses'.
`-msingle-exit'
`-mno-single-exit'
Force (do not force) generated code to have a single exit point in
each function.
File: gcc.info, Node: MN10300 Options, Next: MT Options, Prev: MMIX Options, Up: Submodel Options
3.17.23 MN10300 Options
-----------------------
These `-m' options are defined for Matsushita MN10300 architectures:
`-mmult-bug'
Generate code to avoid bugs in the multiply instructions for the
MN10300 processors. This is the default.
`-mno-mult-bug'
Do not generate code to avoid bugs in the multiply instructions
for the MN10300 processors.
`-mam33'
Generate code which uses features specific to the AM33 processor.
`-mno-am33'
Do not generate code which uses features specific to the AM33
processor. This is the default.
`-mreturn-pointer-on-d0'
When generating a function which returns a pointer, return the
pointer in both `a0' and `d0'. Otherwise, the pointer is returned
only in a0, and attempts to call such functions without a prototype
would result in errors. Note that this option is on by default;
use `-mno-return-pointer-on-d0' to disable it.
`-mno-crt0'
Do not link in the C run-time initialization object file.
`-mrelax'
Indicate to the linker that it should perform a relaxation
optimization pass to shorten branches, calls and absolute memory
addresses. This option only has an effect when used on the
command line for the final link step.
This option makes symbolic debugging impossible.
File: gcc.info, Node: MT Options, Next: PDP-11 Options, Prev: MN10300 Options, Up: Submodel Options
3.17.24 MT Options
------------------
These `-m' options are defined for Morpho MT architectures:
`-march=CPU-TYPE'
Generate code that will run on CPU-TYPE, which is the name of a
system representing a certain processor type. Possible values for
CPU-TYPE are `ms1-64-001', `ms1-16-002', `ms1-16-003' and `ms2'.
When this option is not used, the default is `-march=ms1-16-002'.
`-mbacc'
Use byte loads and stores when generating code.
`-mno-bacc'
Do not use byte loads and stores when generating code.
`-msim'
Use simulator runtime
`-mno-crt0'
Do not link in the C run-time initialization object file `crti.o'.
Other run-time initialization and termination files such as
`startup.o' and `exit.o' are still included on the linker command
line.
File: gcc.info, Node: PDP-11 Options, Next: PowerPC Options, Prev: MT Options, Up: Submodel Options
3.17.25 PDP-11 Options
----------------------
These options are defined for the PDP-11:
`-mfpu'
Use hardware FPP floating point. This is the default. (FIS
floating point on the PDP-11/40 is not supported.)
`-msoft-float'
Do not use hardware floating point.
`-mac0'
Return floating-point results in ac0 (fr0 in Unix assembler
syntax).
`-mno-ac0'
Return floating-point results in memory. This is the default.
`-m40'
Generate code for a PDP-11/40.
`-m45'
Generate code for a PDP-11/45. This is the default.
`-m10'
Generate code for a PDP-11/10.
`-mbcopy-builtin'
Use inline `movmemhi' patterns for copying memory. This is the
default.
`-mbcopy'
Do not use inline `movmemhi' patterns for copying memory.
`-mint16'
`-mno-int32'
Use 16-bit `int'. This is the default.
`-mint32'
`-mno-int16'
Use 32-bit `int'.
`-mfloat64'
`-mno-float32'
Use 64-bit `float'. This is the default.
`-mfloat32'
`-mno-float64'
Use 32-bit `float'.
`-mabshi'
Use `abshi2' pattern. This is the default.
`-mno-abshi'
Do not use `abshi2' pattern.
`-mbranch-expensive'
Pretend that branches are expensive. This is for experimenting
with code generation only.
`-mbranch-cheap'
Do not pretend that branches are expensive. This is the default.
`-msplit'
Generate code for a system with split I&D.
`-mno-split'
Generate code for a system without split I&D. This is the default.
`-munix-asm'
Use Unix assembler syntax. This is the default when configured for
`pdp11-*-bsd'.
`-mdec-asm'
Use DEC assembler syntax. This is the default when configured for
any PDP-11 target other than `pdp11-*-bsd'.
File: gcc.info, Node: PowerPC Options, Next: RS/6000 and PowerPC Options, Prev: PDP-11 Options, Up: Submodel Options
3.17.26 PowerPC Options
-----------------------
These are listed under *Note RS/6000 and PowerPC Options::.
File: gcc.info, Node: RS/6000 and PowerPC Options, Next: S/390 and zSeries Options, Prev: PowerPC Options, Up: Submodel Options
3.17.27 IBM RS/6000 and PowerPC Options
---------------------------------------
These `-m' options are defined for the IBM RS/6000 and PowerPC:
`-mpower'
`-mno-power'
`-mpower2'
`-mno-power2'
`-mpowerpc'
`-mno-powerpc'
`-mpowerpc-gpopt'
`-mno-powerpc-gpopt'
`-mpowerpc-gfxopt'
`-mno-powerpc-gfxopt'
`-mpowerpc64'
`-mno-powerpc64'
`-mmfcrf'
`-mno-mfcrf'
`-mpopcntb'
`-mno-popcntb'
`-mfprnd'
`-mno-fprnd'
GCC supports two related instruction set architectures for the
RS/6000 and PowerPC. The "POWER" instruction set are those
instructions supported by the `rios' chip set used in the original
RS/6000 systems and the "PowerPC" instruction set is the
architecture of the Freescale MPC5xx, MPC6xx, MPC8xx
microprocessors, and the IBM 4xx, 6xx, and follow-on
microprocessors.
Neither architecture is a subset of the other. However there is a
large common subset of instructions supported by both. An MQ
register is included in processors supporting the POWER
architecture.
You use these options to specify which instructions are available
on the processor you are using. The default value of these
options is determined when configuring GCC. Specifying the
`-mcpu=CPU_TYPE' overrides the specification of these options. We
recommend you use the `-mcpu=CPU_TYPE' option rather than the
options listed above.
The `-mpower' option allows GCC to generate instructions that are
found only in the POWER architecture and to use the MQ register.
Specifying `-mpower2' implies `-power' and also allows GCC to
generate instructions that are present in the POWER2 architecture
but not the original POWER architecture.
The `-mpowerpc' option allows GCC to generate instructions that
are found only in the 32-bit subset of the PowerPC architecture.
Specifying `-mpowerpc-gpopt' implies `-mpowerpc' and also allows
GCC to use the optional PowerPC architecture instructions in the
General Purpose group, including floating-point square root.
Specifying `-mpowerpc-gfxopt' implies `-mpowerpc' and also allows
GCC to use the optional PowerPC architecture instructions in the
Graphics group, including floating-point select.
The `-mmfcrf' option allows GCC to generate the move from
condition register field instruction implemented on the POWER4
processor and other processors that support the PowerPC V2.01
architecture. The `-mpopcntb' option allows GCC to generate the
popcount and double precision FP reciprocal estimate instruction
implemented on the POWER5 processor and other processors that
support the PowerPC V2.02 architecture. The `-mfprnd' option
allows GCC to generate the FP round to integer instructions
implemented on the POWER5+ processor and other processors that
support the PowerPC V2.03 architecture.
The `-mpowerpc64' option allows GCC to generate the additional
64-bit instructions that are found in the full PowerPC64
architecture and to treat GPRs as 64-bit, doubleword quantities.
GCC defaults to `-mno-powerpc64'.
If you specify both `-mno-power' and `-mno-powerpc', GCC will use
only the instructions in the common subset of both architectures
plus some special AIX common-mode calls, and will not use the MQ
register. Specifying both `-mpower' and `-mpowerpc' permits GCC
to use any instruction from either architecture and to allow use
of the MQ register; specify this for the Motorola MPC601.
`-mnew-mnemonics'
`-mold-mnemonics'
Select which mnemonics to use in the generated assembler code.
With `-mnew-mnemonics', GCC uses the assembler mnemonics defined
for the PowerPC architecture. With `-mold-mnemonics' it uses the
assembler mnemonics defined for the POWER architecture.
Instructions defined in only one architecture have only one
mnemonic; GCC uses that mnemonic irrespective of which of these
options is specified.
GCC defaults to the mnemonics appropriate for the architecture in
use. Specifying `-mcpu=CPU_TYPE' sometimes overrides the value of
these option. Unless you are building a cross-compiler, you
should normally not specify either `-mnew-mnemonics' or
`-mold-mnemonics', but should instead accept the default.
`-mcpu=CPU_TYPE'
Set architecture type, register usage, choice of mnemonics, and
instruction scheduling parameters for machine type CPU_TYPE.
Supported values for CPU_TYPE are `401', `403', `405', `405fp',
`440', `440fp', `505', `601', `602', `603', `603e', `604', `604e',
`620', `630', `740', `7400', `7450', `750', `801', `821', `823',
`860', `970', `8540', `ec603e', `G3', `G4', `G5', `power',
`power2', `power3', `power4', `power5', `power5+', `power6',
`common', `powerpc', `powerpc64', `rios', `rios1', `rios2', `rsc',
and `rs64'.
`-mcpu=common' selects a completely generic processor. Code
generated under this option will run on any POWER or PowerPC
processor. GCC will use only the instructions in the common
subset of both architectures, and will not use the MQ register.
GCC assumes a generic processor model for scheduling purposes.
`-mcpu=power', `-mcpu=power2', `-mcpu=powerpc', and
`-mcpu=powerpc64' specify generic POWER, POWER2, pure 32-bit
PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
types, with an appropriate, generic processor model assumed for
scheduling purposes.
The other options specify a specific processor. Code generated
under those options will run best on that processor, and may not
run at all on others.
The `-mcpu' options automatically enable or disable the following
options: `-maltivec', `-mfprnd', `-mhard-float', `-mmfcrf',
`-mmultiple', `-mnew-mnemonics', `-mpopcntb', `-mpower',
`-mpower2', `-mpowerpc64', `-mpowerpc-gpopt', `-mpowerpc-gfxopt',
`-mstring', `-mmulhw', `-mdlmzb'. The particular options set for
any particular CPU will vary between compiler versions, depending
on what setting seems to produce optimal code for that CPU; it
doesn't necessarily reflect the actual hardware's capabilities. If
you wish to set an individual option to a particular value, you may
specify it after the `-mcpu' option, like `-mcpu=970 -mno-altivec'.
On AIX, the `-maltivec' and `-mpowerpc64' options are not enabled
or disabled by the `-mcpu' option at present because AIX does not
have full support for these options. You may still enable or
disable them individually if you're sure it'll work in your
environment.
`-mtune=CPU_TYPE'
Set the instruction scheduling parameters for machine type
CPU_TYPE, but do not set the architecture type, register usage, or
choice of mnemonics, as `-mcpu=CPU_TYPE' would. The same values
for CPU_TYPE are used for `-mtune' as for `-mcpu'. If both are
specified, the code generated will use the architecture,
registers, and mnemonics set by `-mcpu', but the scheduling
parameters set by `-mtune'.
`-mswdiv'
`-mno-swdiv'
Generate code to compute division as reciprocal estimate and
iterative refinement, creating opportunities for increased
throughput. This feature requires: optional PowerPC Graphics
instruction set for single precision and FRE instruction for
double precision, assuming divides cannot generate user-visible
traps, and the domain values not include Infinities, denormals or
zero denominator.
`-maltivec'
`-mno-altivec'
Generate code that uses (does not use) AltiVec instructions, and
also enable the use of built-in functions that allow more direct
access to the AltiVec instruction set. You may also need to set
`-mabi=altivec' to adjust the current ABI with AltiVec ABI
enhancements.
`-mvrsave'
`-mno-vrsave'
Generate VRSAVE instructions when generating AltiVec code.
`-msecure-plt'
Generate code that allows ld and ld.so to build executables and
shared libraries with non-exec .plt and .got sections. This is a
PowerPC 32-bit SYSV ABI option.
`-mbss-plt'
Generate code that uses a BSS .plt section that ld.so fills in, and
requires .plt and .got sections that are both writable and
executable. This is a PowerPC 32-bit SYSV ABI option.
`-misel'
`-mno-isel'
This switch enables or disables the generation of ISEL
instructions.
`-misel=YES/NO'
This switch has been deprecated. Use `-misel' and `-mno-isel'
instead.
`-mspe'
`-mno-spe'
This switch enables or disables the generation of SPE simd
instructions.
`-mspe=YES/NO'
This option has been deprecated. Use `-mspe' and `-mno-spe'
instead.
`-mfloat-gprs=YES/SINGLE/DOUBLE/NO'
`-mfloat-gprs'
This switch enables or disables the generation of floating point
operations on the general purpose registers for architectures that
support it.
The argument YES or SINGLE enables the use of single-precision
floating point operations.
The argument DOUBLE enables the use of single and double-precision
floating point operations.
The argument NO disables floating point operations on the general
purpose registers.
This option is currently only available on the MPC854x.
`-m32'
`-m64'
Generate code for 32-bit or 64-bit environments of Darwin and SVR4
targets (including GNU/Linux). The 32-bit environment sets int,
long and pointer to 32 bits and generates code that runs on any
PowerPC variant. The 64-bit environment sets int to 32 bits and
long and pointer to 64 bits, and generates code for PowerPC64, as
for `-mpowerpc64'.
`-mfull-toc'
`-mno-fp-in-toc'
`-mno-sum-in-toc'
`-mminimal-toc'
Modify generation of the TOC (Table Of Contents), which is created
for every executable file. The `-mfull-toc' option is selected by
default. In that case, GCC will allocate at least one TOC entry
for each unique non-automatic variable reference in your program.
GCC will also place floating-point constants in the TOC. However,
only 16,384 entries are available in the TOC.
If you receive a linker error message that saying you have
overflowed the available TOC space, you can reduce the amount of
TOC space used with the `-mno-fp-in-toc' and `-mno-sum-in-toc'
options. `-mno-fp-in-toc' prevents GCC from putting floating-point
constants in the TOC and `-mno-sum-in-toc' forces GCC to generate
code to calculate the sum of an address and a constant at run-time
instead of putting that sum into the TOC. You may specify one or
both of these options. Each causes GCC to produce very slightly
slower and larger code at the expense of conserving TOC space.
If you still run out of space in the TOC even when you specify
both of these options, specify `-mminimal-toc' instead. This
option causes GCC to make only one TOC entry for every file. When
you specify this option, GCC will produce code that is slower and
larger but which uses extremely little TOC space. You may wish to
use this option only on files that contain less frequently
executed code.
`-maix64'
`-maix32'
Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
64-bit `long' type, and the infrastructure needed to support them.
Specifying `-maix64' implies `-mpowerpc64' and `-mpowerpc', while
`-maix32' disables the 64-bit ABI and implies `-mno-powerpc64'.
GCC defaults to `-maix32'.
`-mxl-compat'
`-mno-xl-compat'
Produce code that conforms more closely to IBM XL compiler
semantics when using AIX-compatible ABI. Pass floating-point
arguments to prototyped functions beyond the register save area
(RSA) on the stack in addition to argument FPRs. Do not assume
that most significant double in 128-bit long double value is
properly rounded when comparing values and converting to double.
Use XL symbol names for long double support routines.
The AIX calling convention was extended but not initially
documented to handle an obscure K&R C case of calling a function
that takes the address of its arguments with fewer arguments than
declared. IBM XL compilers access floating point arguments which
do not fit in the RSA from the stack when a subroutine is compiled
without optimization. Because always storing floating-point
arguments on the stack is inefficient and rarely needed, this
option is not enabled by default and only is necessary when
calling subroutines compiled by IBM XL compilers without
optimization.
`-mpe'
Support "IBM RS/6000 SP" "Parallel Environment" (PE). Link an
application written to use message passing with special startup
code to enable the application to run. The system must have PE
installed in the standard location (`/usr/lpp/ppe.poe/'), or the
`specs' file must be overridden with the `-specs=' option to
specify the appropriate directory location. The Parallel
Environment does not support threads, so the `-mpe' option and the
`-pthread' option are incompatible.
`-malign-natural'
`-malign-power'
On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
`-malign-natural' overrides the ABI-defined alignment of larger
types, such as floating-point doubles, on their natural size-based
boundary. The option `-malign-power' instructs GCC to follow the
ABI-specified alignment rules. GCC defaults to the standard
alignment defined in the ABI.
On 64-bit Darwin, natural alignment is the default, and
`-malign-power' is not supported.
`-msoft-float'
`-mhard-float'
Generate code that does not use (uses) the floating-point register
set. Software floating point emulation is provided if you use the
`-msoft-float' option, and pass the option to GCC when linking.
`-mmultiple'
`-mno-multiple'
Generate code that uses (does not use) the load multiple word
instructions and the store multiple word instructions. These
instructions are generated by default on POWER systems, and not
generated on PowerPC systems. Do not use `-mmultiple' on little
endian PowerPC systems, since those instructions do not work when
the processor is in little endian mode. The exceptions are PPC740
and PPC750 which permit the instructions usage in little endian
mode.
`-mstring'
`-mno-string'
Generate code that uses (does not use) the load string instructions
and the store string word instructions to save multiple registers
and do small block moves. These instructions are generated by
default on POWER systems, and not generated on PowerPC systems.
Do not use `-mstring' on little endian PowerPC systems, since those
instructions do not work when the processor is in little endian
mode. The exceptions are PPC740 and PPC750 which permit the
instructions usage in little endian mode.
`-mupdate'
`-mno-update'
Generate code that uses (does not use) the load or store
instructions that update the base register to the address of the
calculated memory location. These instructions are generated by
default. If you use `-mno-update', there is a small window
between the time that the stack pointer is updated and the address
of the previous frame is stored, which means code that walks the
stack frame across interrupts or signals may get corrupted data.
`-mfused-madd'
`-mno-fused-madd'
Generate code that uses (does not use) the floating point multiply
and accumulate instructions. These instructions are generated by
default if hardware floating is used.
`-mmulhw'
`-mno-mulhw'
Generate code that uses (does not use) the half-word multiply and
multiply-accumulate instructions on the IBM 405 and 440 processors.
These instructions are generated by default when targetting those
processors.
`-mdlmzb'
`-mno-dlmzb'
Generate code that uses (does not use) the string-search `dlmzb'
instruction on the IBM 405 and 440 processors. This instruction is
generated by default when targetting those processors.
`-mno-bit-align'
`-mbit-align'
On System V.4 and embedded PowerPC systems do not (do) force
structures and unions that contain bit-fields to be aligned to the
base type of the bit-field.
For example, by default a structure containing nothing but 8
`unsigned' bit-fields of length 1 would be aligned to a 4 byte
boundary and have a size of 4 bytes. By using `-mno-bit-align',
the structure would be aligned to a 1 byte boundary and be one
byte in size.
`-mno-strict-align'
`-mstrict-align'
On System V.4 and embedded PowerPC systems do not (do) assume that
unaligned memory references will be handled by the system.
`-mrelocatable'
`-mno-relocatable'
On embedded PowerPC systems generate code that allows (does not
allow) the program to be relocated to a different address at
runtime. If you use `-mrelocatable' on any module, all objects
linked together must be compiled with `-mrelocatable' or
`-mrelocatable-lib'.
`-mrelocatable-lib'
`-mno-relocatable-lib'
On embedded PowerPC systems generate code that allows (does not
allow) the program to be relocated to a different address at
runtime. Modules compiled with `-mrelocatable-lib' can be linked
with either modules compiled without `-mrelocatable' and
`-mrelocatable-lib' or with modules compiled with the
`-mrelocatable' options.
`-mno-toc'
`-mtoc'
On System V.4 and embedded PowerPC systems do not (do) assume that
register 2 contains a pointer to a global area pointing to the
addresses used in the program.
`-mlittle'
`-mlittle-endian'
On System V.4 and embedded PowerPC systems compile code for the
processor in little endian mode. The `-mlittle-endian' option is
the same as `-mlittle'.
`-mbig'
`-mbig-endian'
On System V.4 and embedded PowerPC systems compile code for the
processor in big endian mode. The `-mbig-endian' option is the
same as `-mbig'.
`-mdynamic-no-pic'
On Darwin and Mac OS X systems, compile code so that it is not
relocatable, but that its external references are relocatable. The
resulting code is suitable for applications, but not shared
libraries.
`-mprioritize-restricted-insns=PRIORITY'
This option controls the priority that is assigned to
dispatch-slot restricted instructions during the second scheduling
pass. The argument PRIORITY takes the value 0/1/2 to assign
NO/HIGHEST/SECOND-HIGHEST priority to dispatch slot restricted
instructions.
`-msched-costly-dep=DEPENDENCE_TYPE'
This option controls which dependences are considered costly by
the target during instruction scheduling. The argument
DEPENDENCE_TYPE takes one of the following values: NO: no
dependence is costly, ALL: all dependences are costly,
TRUE_STORE_TO_LOAD: a true dependence from store to load is costly,
STORE_TO_LOAD: any dependence from store to load is costly,
NUMBER: any dependence which latency >= NUMBER is costly.
`-minsert-sched-nops=SCHEME'
This option controls which nop insertion scheme will be used during
the second scheduling pass. The argument SCHEME takes one of the
following values: NO: Don't insert nops. PAD: Pad with nops any
dispatch group which has vacant issue slots, according to the
scheduler's grouping. REGROUP_EXACT: Insert nops to force costly
dependent insns into separate groups. Insert exactly as many nops
as needed to force an insn to a new group, according to the
estimated processor grouping. NUMBER: Insert nops to force costly
dependent insns into separate groups. Insert NUMBER nops to force
an insn to a new group.
`-mcall-sysv'
On System V.4 and embedded PowerPC systems compile code using
calling conventions that adheres to the March 1995 draft of the
System V Application Binary Interface, PowerPC processor
supplement. This is the default unless you configured GCC using
`powerpc-*-eabiaix'.
`-mcall-sysv-eabi'
Specify both `-mcall-sysv' and `-meabi' options.
`-mcall-sysv-noeabi'
Specify both `-mcall-sysv' and `-mno-eabi' options.
`-mcall-solaris'
On System V.4 and embedded PowerPC systems compile code for the
Solaris operating system.
`-mcall-linux'
On System V.4 and embedded PowerPC systems compile code for the
Linux-based GNU system.
`-mcall-gnu'
On System V.4 and embedded PowerPC systems compile code for the
Hurd-based GNU system.
`-mcall-netbsd'
On System V.4 and embedded PowerPC systems compile code for the
NetBSD operating system.
`-maix-struct-return'
Return all structures in memory (as specified by the AIX ABI).
`-msvr4-struct-return'
Return structures smaller than 8 bytes in registers (as specified
by the SVR4 ABI).
`-mabi=ABI-TYPE'
Extend the current ABI with a particular extension, or remove such
extension. Valid values are ALTIVEC, NO-ALTIVEC, SPE, NO-SPE,
IBMLONGDOUBLE, IEEELONGDOUBLE.
`-mabi=spe'
Extend the current ABI with SPE ABI extensions. This does not
change the default ABI, instead it adds the SPE ABI extensions to
the current ABI.
`-mabi=no-spe'
Disable Booke SPE ABI extensions for the current ABI.
`-mabi=ibmlongdouble'
Change the current ABI to use IBM extended precision long double.
This is a PowerPC 32-bit SYSV ABI option.
`-mabi=ieeelongdouble'
Change the current ABI to use IEEE extended precision long double.
This is a PowerPC 32-bit Linux ABI option.
`-mprototype'
`-mno-prototype'
On System V.4 and embedded PowerPC systems assume that all calls to
variable argument functions are properly prototyped. Otherwise,
the compiler must insert an instruction before every non
prototyped call to set or clear bit 6 of the condition code
register (CR) to indicate whether floating point values were
passed in the floating point registers in case the function takes
a variable arguments. With `-mprototype', only calls to
prototyped variable argument functions will set or clear the bit.
`-msim'
On embedded PowerPC systems, assume that the startup module is
called `sim-crt0.o' and that the standard C libraries are
`libsim.a' and `libc.a'. This is the default for
`powerpc-*-eabisim'. configurations.
`-mmvme'
On embedded PowerPC systems, assume that the startup module is
called `crt0.o' and the standard C libraries are `libmvme.a' and
`libc.a'.
`-mads'
On embedded PowerPC systems, assume that the startup module is
called `crt0.o' and the standard C libraries are `libads.a' and
`libc.a'.
`-myellowknife'
On embedded PowerPC systems, assume that the startup module is
called `crt0.o' and the standard C libraries are `libyk.a' and
`libc.a'.
`-mvxworks'
On System V.4 and embedded PowerPC systems, specify that you are
compiling for a VxWorks system.
`-mwindiss'
Specify that you are compiling for the WindISS simulation
environment.
`-memb'
On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
header to indicate that `eabi' extended relocations are used.
`-meabi'
`-mno-eabi'
On System V.4 and embedded PowerPC systems do (do not) adhere to
the Embedded Applications Binary Interface (eabi) which is a set of
modifications to the System V.4 specifications. Selecting `-meabi'
means that the stack is aligned to an 8 byte boundary, a function
`__eabi' is called to from `main' to set up the eabi environment,
and the `-msdata' option can use both `r2' and `r13' to point to
two separate small data areas. Selecting `-mno-eabi' means that
the stack is aligned to a 16 byte boundary, do not call an
initialization function from `main', and the `-msdata' option will
only use `r13' to point to a single small data area. The `-meabi'
option is on by default if you configured GCC using one of the
`powerpc*-*-eabi*' options.
`-msdata=eabi'
On System V.4 and embedded PowerPC systems, put small initialized
`const' global and static data in the `.sdata2' section, which is
pointed to by register `r2'. Put small initialized non-`const'
global and static data in the `.sdata' section, which is pointed
to by register `r13'. Put small uninitialized global and static
data in the `.sbss' section, which is adjacent to the `.sdata'
section. The `-msdata=eabi' option is incompatible with the
`-mrelocatable' option. The `-msdata=eabi' option also sets the
`-memb' option.
`-msdata=sysv'
On System V.4 and embedded PowerPC systems, put small global and
static data in the `.sdata' section, which is pointed to by
register `r13'. Put small uninitialized global and static data in
the `.sbss' section, which is adjacent to the `.sdata' section.
The `-msdata=sysv' option is incompatible with the `-mrelocatable'
option.
`-msdata=default'
`-msdata'
On System V.4 and embedded PowerPC systems, if `-meabi' is used,
compile code the same as `-msdata=eabi', otherwise compile code the
same as `-msdata=sysv'.
`-msdata-data'
On System V.4 and embedded PowerPC systems, put small global data
in the `.sdata' section. Put small uninitialized global data in
the `.sbss' section. Do not use register `r13' to address small
data however. This is the default behavior unless other `-msdata'
options are used.
`-msdata=none'
`-mno-sdata'
On embedded PowerPC systems, put all initialized global and static
data in the `.data' section, and all uninitialized data in the
`.bss' section.
`-G NUM'
On embedded PowerPC systems, put global and static items less than
or equal to NUM bytes into the small data or bss sections instead
of the normal data or bss section. By default, NUM is 8. The `-G
NUM' switch is also passed to the linker. All modules should be
compiled with the same `-G NUM' value.
`-mregnames'
`-mno-regnames'
On System V.4 and embedded PowerPC systems do (do not) emit
register names in the assembly language output using symbolic
forms.
`-mlongcall'
`-mno-longcall'
By default assume that all calls are far away so that a longer more
expensive calling sequence is required. This is required for calls
further than 32 megabytes (33,554,432 bytes) from the current
location. A short call will be generated if the compiler knows
the call cannot be that far away. This setting can be overridden
by the `shortcall' function attribute, or by `#pragma longcall(0)'.
Some linkers are capable of detecting out-of-range calls and
generating glue code on the fly. On these systems, long calls are
unnecessary and generate slower code. As of this writing, the AIX
linker can do this, as can the GNU linker for PowerPC/64. It is
planned to add this feature to the GNU linker for 32-bit PowerPC
systems as well.
On Darwin/PPC systems, `#pragma longcall' will generate "jbsr
callee, L42", plus a "branch island" (glue code). The two target
addresses represent the callee and the "branch island". The
Darwin/PPC linker will prefer the first address and generate a "bl
callee" if the PPC "bl" instruction will reach the callee directly;
otherwise, the linker will generate "bl L42" to call the "branch
island". The "branch island" is appended to the body of the
calling function; it computes the full 32-bit address of the callee
and jumps to it.
On Mach-O (Darwin) systems, this option directs the compiler emit
to the glue for every direct call, and the Darwin linker decides
whether to use or discard it.
In the future, we may cause GCC to ignore all longcall
specifications when the linker is known to generate glue.
`-pthread'
Adds support for multithreading with the "pthreads" library. This
option sets flags for both the preprocessor and linker.
File: gcc.info, Node: S/390 and zSeries Options, Next: Score Options, Prev: RS/6000 and PowerPC Options, Up: Submodel Options
3.17.28 S/390 and zSeries Options
---------------------------------
These are the `-m' options defined for the S/390 and zSeries
architecture.
`-mhard-float'
`-msoft-float'
Use (do not use) the hardware floating-point instructions and
registers for floating-point operations. When `-msoft-float' is
specified, functions in `libgcc.a' will be used to perform
floating-point operations. When `-mhard-float' is specified, the
compiler generates IEEE floating-point instructions. This is the
default.
`-mlong-double-64'
`-mlong-double-128'
These switches control the size of `long double' type. A size of
64bit makes the `long double' type equivalent to the `double'
type. This is the default.
`-mbackchain'
`-mno-backchain'
Store (do not store) the address of the caller's frame as
backchain pointer into the callee's stack frame. A backchain may
be needed to allow debugging using tools that do not understand
DWARF-2 call frame information. When `-mno-packed-stack' is in
effect, the backchain pointer is stored at the bottom of the stack
frame; when `-mpacked-stack' is in effect, the backchain is placed
into the topmost word of the 96/160 byte register save area.
In general, code compiled with `-mbackchain' is call-compatible
with code compiled with `-mmo-backchain'; however, use of the
backchain for debugging purposes usually requires that the whole
binary is built with `-mbackchain'. Note that the combination of
`-mbackchain', `-mpacked-stack' and `-mhard-float' is not
supported. In order to build a linux kernel use `-msoft-float'.
The default is to not maintain the backchain.
`-mpacked-stack'
`-mno-packed-stack'
Use (do not use) the packed stack layout. When
`-mno-packed-stack' is specified, the compiler uses the all fields
of the 96/160 byte register save area only for their default
purpose; unused fields still take up stack space. When
`-mpacked-stack' is specified, register save slots are densely
packed at the top of the register save area; unused space is
reused for other purposes, allowing for more efficient use of the
available stack space. However, when `-mbackchain' is also in
effect, the topmost word of the save area is always used to store
the backchain, and the return address register is always saved two
words below the backchain.
As long as the stack frame backchain is not used, code generated
with `-mpacked-stack' is call-compatible with code generated with
`-mno-packed-stack'. Note that some non-FSF releases of GCC 2.95
for S/390 or zSeries generated code that uses the stack frame
backchain at run time, not just for debugging purposes. Such code
is not call-compatible with code compiled with `-mpacked-stack'.
Also, note that the combination of `-mbackchain', `-mpacked-stack'
and `-mhard-float' is not supported. In order to build a linux
kernel use `-msoft-float'.
The default is to not use the packed stack layout.
`-msmall-exec'
`-mno-small-exec'
Generate (or do not generate) code using the `bras' instruction to
do subroutine calls. This only works reliably if the total
executable size does not exceed 64k. The default is to use the
`basr' instruction instead, which does not have this limitation.
`-m64'
`-m31'
When `-m31' is specified, generate code compliant to the GNU/Linux
for S/390 ABI. When `-m64' is specified, generate code compliant
to the GNU/Linux for zSeries ABI. This allows GCC in particular
to generate 64-bit instructions. For the `s390' targets, the
default is `-m31', while the `s390x' targets default to `-m64'.
`-mzarch'
`-mesa'
When `-mzarch' is specified, generate code using the instructions
available on z/Architecture. When `-mesa' is specified, generate
code using the instructions available on ESA/390. Note that
`-mesa' is not possible with `-m64'. When generating code
compliant to the GNU/Linux for S/390 ABI, the default is `-mesa'.
When generating code compliant to the GNU/Linux for zSeries ABI,
the default is `-mzarch'.
`-mmvcle'
`-mno-mvcle'
Generate (or do not generate) code using the `mvcle' instruction
to perform block moves. When `-mno-mvcle' is specified, use a
`mvc' loop instead. This is the default unless optimizing for
size.
`-mdebug'
`-mno-debug'
Print (or do not print) additional debug information when
compiling. The default is to not print debug information.
`-march=CPU-TYPE'
Generate code that will run on CPU-TYPE, which is the name of a
system representing a certain processor type. Possible values for
CPU-TYPE are `g5', `g6', `z900', and `z990'. When generating code
using the instructions available on z/Architecture, the default is
`-march=z900'. Otherwise, the default is `-march=g5'.
`-mtune=CPU-TYPE'
Tune to CPU-TYPE everything applicable about the generated code,
except for the ABI and the set of available instructions. The
list of CPU-TYPE values is the same as for `-march'. The default
is the value used for `-march'.
`-mtpf-trace'
`-mno-tpf-trace'
Generate code that adds (does not add) in TPF OS specific branches
to trace routines in the operating system. This option is off by
default, even when compiling for the TPF OS.
`-mfused-madd'
`-mno-fused-madd'
Generate code that uses (does not use) the floating point multiply
and accumulate instructions. These instructions are generated by
default if hardware floating point is used.
`-mwarn-framesize=FRAMESIZE'
Emit a warning if the current function exceeds the given frame
size. Because this is a compile time check it doesn't need to be
a real problem when the program runs. It is intended to identify
functions which most probably cause a stack overflow. It is
useful to be used in an environment with limited stack size e.g.
the linux kernel.
`-mwarn-dynamicstack'
Emit a warning if the function calls alloca or uses dynamically
sized arrays. This is generally a bad idea with a limited stack
size.
`-mstack-guard=STACK-GUARD'
`-mstack-size=STACK-SIZE'
These arguments always have to be used in conjunction. If they
are present the s390 back end emits additional instructions in the
function prologue which trigger a trap if the stack size is
STACK-GUARD bytes above the STACK-SIZE (remember that the stack on
s390 grows downward). These options are intended to be used to
help debugging stack overflow problems. The additionally emitted
code causes only little overhead and hence can also be used in
production like systems without greater performance degradation.
The given values have to be exact powers of 2 and STACK-SIZE has
to be greater than STACK-GUARD without exceeding 64k. In order to
be efficient the extra code makes the assumption that the stack
starts at an address aligned to the value given by STACK-SIZE.
File: gcc.info, Node: Score Options, Next: SH Options, Prev: S/390 and zSeries Options, Up: Submodel Options
3.17.29 Score Options
---------------------
These options are defined for Score implementations:
`-meb'
Compile code for big endian mode. This is the default.
`-mel'
Compile code for little endian mode.
`-mnhwloop'
Disable generate bcnz instruction.
`-muls'
Enable generate unaligned load and store instruction.
`-mmac'
Enable the use of multiply-accumulate instructions. Disabled by
default.
`-mscore5'
Specify the SCORE5 as the target architecture.
`-mscore5u'
Specify the SCORE5U of the target architecture.
`-mscore7'
Specify the SCORE7 as the target architecture. This is the default.
`-mscore7d'
Specify the SCORE7D as the target architecture.
File: gcc.info, Node: SH Options, Next: SPARC Options, Prev: Score Options, Up: Submodel Options
3.17.30 SH Options
------------------
These `-m' options are defined for the SH implementations:
`-m1'
Generate code for the SH1.
`-m2'
Generate code for the SH2.
`-m2e'
Generate code for the SH2e.
`-m3'
Generate code for the SH3.
`-m3e'
Generate code for the SH3e.
`-m4-nofpu'
Generate code for the SH4 without a floating-point unit.
`-m4-single-only'
Generate code for the SH4 with a floating-point unit that only
supports single-precision arithmetic.
`-m4-single'
Generate code for the SH4 assuming the floating-point unit is in
single-precision mode by default.
`-m4'
Generate code for the SH4.
`-m4a-nofpu'
Generate code for the SH4al-dsp, or for a SH4a in such a way that
the floating-point unit is not used.
`-m4a-single-only'
Generate code for the SH4a, in such a way that no double-precision
floating point operations are used.
`-m4a-single'
Generate code for the SH4a assuming the floating-point unit is in
single-precision mode by default.
`-m4a'
Generate code for the SH4a.
`-m4al'
Same as `-m4a-nofpu', except that it implicitly passes `-dsp' to
the assembler. GCC doesn't generate any DSP instructions at the
moment.
`-mb'
Compile code for the processor in big endian mode.
`-ml'
Compile code for the processor in little endian mode.
`-mdalign'
Align doubles at 64-bit boundaries. Note that this changes the
calling conventions, and thus some functions from the standard C
library will not work unless you recompile it first with
`-mdalign'.
`-mrelax'
Shorten some address references at link time, when possible; uses
the linker option `-relax'.
`-mbigtable'
Use 32-bit offsets in `switch' tables. The default is to use
16-bit offsets.
`-mfmovd'
Enable the use of the instruction `fmovd'.
`-mhitachi'
Comply with the calling conventions defined by Renesas.
`-mrenesas'
Comply with the calling conventions defined by Renesas.
`-mno-renesas'
Comply with the calling conventions defined for GCC before the
Renesas conventions were available. This option is the default
for all targets of the SH toolchain except for `sh-symbianelf'.
`-mnomacsave'
Mark the `MAC' register as call-clobbered, even if `-mhitachi' is
given.
`-mieee'
Increase IEEE-compliance of floating-point code. At the moment,
this is equivalent to `-fno-finite-math-only'. When generating 16
bit SH opcodes, getting IEEE-conforming results for comparisons of
NANs / infinities incurs extra overhead in every floating point
comparison, therefore the default is set to `-ffinite-math-only'.
`-misize'
Dump instruction size and location in the assembly code.
`-mpadstruct'
This option is deprecated. It pads structures to multiple of 4
bytes, which is incompatible with the SH ABI.
`-mspace'
Optimize for space instead of speed. Implied by `-Os'.
`-mprefergot'
When generating position-independent code, emit function calls
using the Global Offset Table instead of the Procedure Linkage
Table.
`-musermode'
Generate a library function call to invalidate instruction cache
entries, after fixing up a trampoline. This library function call
doesn't assume it can write to the whole memory address space.
This is the default when the target is `sh-*-linux*'.
`-multcost=NUMBER'
Set the cost to assume for a multiply insn.
`-mdiv=STRATEGY'
Set the division strategy to use for SHmedia code. STRATEGY must
be one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l,
inv:call, inv:call2, inv:fp . "fp" performs the operation in
floating point. This has a very high latency, but needs only a
few instructions, so it might be a good choice if your code has
enough easily exploitable ILP to allow the compiler to schedule
the floating point instructions together with other instructions.
Division by zero causes a floating point exception. "inv" uses
integer operations to calculate the inverse of the divisor, and
then multiplies the dividend with the inverse. This strategy
allows cse and hoisting of the inverse calculation. Division by
zero calculates an unspecified result, but does not trap.
"inv:minlat" is a variant of "inv" where if no cse / hoisting
opportunities have been found, or if the entire operation has been
hoisted to the same place, the last stages of the inverse
calculation are intertwined with the final multiply to reduce the
overall latency, at the expense of using a few more instructions,
and thus offering fewer scheduling opportunities with other code.
"call" calls a library function that usually implements the
inv:minlat strategy. This gives high code density for
m5-*media-nofpu compilations. "call2" uses a different entry
point of the same library function, where it assumes that a
pointer to a lookup table has already been set up, which exposes
the pointer load to cse / code hoisting optimizations.
"inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm
for initial code generation, but if the code stays unoptimized,
revert to the "call", "call2", or "fp" strategies, respectively.
Note that the potentially-trapping side effect of division by zero
is carried by a separate instruction, so it is possible that all
the integer instructions are hoisted out, but the marker for the
side effect stays where it is. A recombination to fp operations
or a call is not possible in that case. "inv20u" and "inv20l" are
variants of the "inv:minlat" strategy. In the case that the
inverse calculation was nor separated from the multiply, they speed
up division where the dividend fits into 20 bits (plus sign where
applicable), by inserting a test to skip a number of operations in
this case; this test slows down the case of larger dividends.
inv20u assumes the case of a such a small dividend to be unlikely,
and inv20l assumes it to be likely.
`-mdivsi3_libfunc=NAME'
Set the name of the library function used for 32 bit signed
division to NAME. This only affect the name used in the call and
inv:call division strategies, and the compiler will still expect
the same sets of input/output/clobbered registers as if this
option was not present.
`-madjust-unroll'
Throttle unrolling to avoid thrashing target registers. This
option only has an effect if the gcc code base supports the
TARGET_ADJUST_UNROLL_MAX target hook.
`-mindexed-addressing'
Enable the use of the indexed addressing mode for
SHmedia32/SHcompact. This is only safe if the hardware and/or OS
implement 32 bit wrap-around semantics for the indexed addressing
mode. The architecture allows the implementation of processors
with 64 bit MMU, which the OS could use to get 32 bit addressing,
but since no current hardware implementation supports this or any
other way to make the indexed addressing mode safe to use in the
32 bit ABI, the default is -mno-indexed-addressing.
`-mgettrcost=NUMBER'
Set the cost assumed for the gettr instruction to NUMBER. The
default is 2 if `-mpt-fixed' is in effect, 100 otherwise.
`-mpt-fixed'
Assume pt* instructions won't trap. This will generally generate
better scheduled code, but is unsafe on current hardware. The
current architecture definition says that ptabs and ptrel trap
when the target anded with 3 is 3. This has the unintentional
effect of making it unsafe to schedule ptabs / ptrel before a
branch, or hoist it out of a loop. For example,
__do_global_ctors, a part of libgcc that runs constructors at
program startup, calls functions in a list which is delimited by
-1. With the -mpt-fixed option, the ptabs will be done before
testing against -1. That means that all the constructors will be
run a bit quicker, but when the loop comes to the end of the list,
the program crashes because ptabs loads -1 into a target register.
Since this option is unsafe for any hardware implementing the
current architecture specification, the default is -mno-pt-fixed.
Unless the user specifies a specific cost with `-mgettrcost',
-mno-pt-fixed also implies `-mgettrcost=100'; this deters register
allocation using target registers for storing ordinary integers.
`-minvalid-symbols'
Assume symbols might be invalid. Ordinary function symbols
generated by the compiler will always be valid to load with
movi/shori/ptabs or movi/shori/ptrel, but with assembler and/or
linker tricks it is possible to generate symbols that will cause
ptabs / ptrel to trap. This option is only meaningful when
`-mno-pt-fixed' is in effect. It will then prevent
cross-basic-block cse, hoisting and most scheduling of symbol
loads. The default is `-mno-invalid-symbols'.
File: gcc.info, Node: SPARC Options, Next: System V Options, Prev: SH Options, Up: Submodel Options
3.17.31 SPARC Options
---------------------
These `-m' options are supported on the SPARC:
`-mno-app-regs'
`-mapp-regs'
Specify `-mapp-regs' to generate output using the global registers
2 through 4, which the SPARC SVR4 ABI reserves for applications.
This is the default.
To be fully SVR4 ABI compliant at the cost of some performance
loss, specify `-mno-app-regs'. You should compile libraries and
system software with this option.
`-mfpu'
`-mhard-float'
Generate output containing floating point instructions. This is
the default.
`-mno-fpu'
`-msoft-float'
Generate output containing library calls for floating point.
*Warning:* the requisite libraries are not available for all SPARC
targets. Normally the facilities of the machine's usual C
compiler are used, but this cannot be done directly in
cross-compilation. You must make your own arrangements to provide
suitable library functions for cross-compilation. The embedded
targets `sparc-*-aout' and `sparclite-*-*' do provide software
floating point support.
`-msoft-float' changes the calling convention in the output file;
therefore, it is only useful if you compile _all_ of a program with
this option. In particular, you need to compile `libgcc.a', the
library that comes with GCC, with `-msoft-float' in order for this
to work.
`-mhard-quad-float'
Generate output containing quad-word (long double) floating point
instructions.
`-msoft-quad-float'
Generate output containing library calls for quad-word (long
double) floating point instructions. The functions called are
those specified in the SPARC ABI. This is the default.
As of this writing, there are no SPARC implementations that have
hardware support for the quad-word floating point instructions.
They all invoke a trap handler for one of these instructions, and
then the trap handler emulates the effect of the instruction.
Because of the trap handler overhead, this is much slower than
calling the ABI library routines. Thus the `-msoft-quad-float'
option is the default.
`-mno-unaligned-doubles'
`-munaligned-doubles'
Assume that doubles have 8 byte alignment. This is the default.
With `-munaligned-doubles', GCC assumes that doubles have 8 byte
alignment only if they are contained in another type, or if they
have an absolute address. Otherwise, it assumes they have 4 byte
alignment. Specifying this option avoids some rare compatibility
problems with code generated by other compilers. It is not the
default because it results in a performance loss, especially for
floating point code.
`-mno-faster-structs'
`-mfaster-structs'
With `-mfaster-structs', the compiler assumes that structures
should have 8 byte alignment. This enables the use of pairs of
`ldd' and `std' instructions for copies in structure assignment,
in place of twice as many `ld' and `st' pairs. However, the use
of this changed alignment directly violates the SPARC ABI. Thus,
it's intended only for use on targets where the developer
acknowledges that their resulting code will not be directly in
line with the rules of the ABI.
`-mimpure-text'
`-mimpure-text', used in addition to `-shared', tells the compiler
to not pass `-z text' to the linker when linking a shared object.
Using this option, you can link position-dependent code into a
shared object.
`-mimpure-text' suppresses the "relocations remain against
allocatable but non-writable sections" linker error message.
However, the necessary relocations will trigger copy-on-write, and
the shared object is not actually shared across processes.
Instead of using `-mimpure-text', you should compile all source
code with `-fpic' or `-fPIC'.
This option is only available on SunOS and Solaris.
`-mcpu=CPU_TYPE'
Set the instruction set, register set, and instruction scheduling
parameters for machine type CPU_TYPE. Supported values for
CPU_TYPE are `v7', `cypress', `v8', `supersparc', `sparclite',
`f930', `f934', `hypersparc', `sparclite86x', `sparclet',
`tsc701', `v9', `ultrasparc', `ultrasparc3', and `niagara'.
Default instruction scheduling parameters are used for values that
select an architecture and not an implementation. These are `v7',
`v8', `sparclite', `sparclet', `v9'.
Here is a list of each supported architecture and their supported
implementations.
v7: cypress
v8: supersparc, hypersparc
sparclite: f930, f934, sparclite86x
sparclet: tsc701
v9: ultrasparc, ultrasparc3, niagara
By default (unless configured otherwise), GCC generates code for
the V7 variant of the SPARC architecture. With `-mcpu=cypress',
the compiler additionally optimizes it for the Cypress CY7C602
chip, as used in the SPARCStation/SPARCServer 3xx series. This is
also appropriate for the older SPARCStation 1, 2, IPX etc.
With `-mcpu=v8', GCC generates code for the V8 variant of the SPARC
architecture. The only difference from V7 code is that the
compiler emits the integer multiply and integer divide
instructions which exist in SPARC-V8 but not in SPARC-V7. With
`-mcpu=supersparc', the compiler additionally optimizes it for the
SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
series.
With `-mcpu=sparclite', GCC generates code for the SPARClite
variant of the SPARC architecture. This adds the integer
multiply, integer divide step and scan (`ffs') instructions which
exist in SPARClite but not in SPARC-V7. With `-mcpu=f930', the
compiler additionally optimizes it for the Fujitsu MB86930 chip,
which is the original SPARClite, with no FPU. With `-mcpu=f934',
the compiler additionally optimizes it for the Fujitsu MB86934
chip, which is the more recent SPARClite with FPU.
With `-mcpu=sparclet', GCC generates code for the SPARClet variant
of the SPARC architecture. This adds the integer multiply,
multiply/accumulate, integer divide step and scan (`ffs')
instructions which exist in SPARClet but not in SPARC-V7. With
`-mcpu=tsc701', the compiler additionally optimizes it for the
TEMIC SPARClet chip.
With `-mcpu=v9', GCC generates code for the V9 variant of the SPARC
architecture. This adds 64-bit integer and floating-point move
instructions, 3 additional floating-point condition code registers
and conditional move instructions. With `-mcpu=ultrasparc', the
compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
chips. With `-mcpu=ultrasparc3', the compiler additionally
optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+
chips. With `-mcpu=niagara', the compiler additionally optimizes
it for Sun UltraSPARC T1 chips.
`-mtune=CPU_TYPE'
Set the instruction scheduling parameters for machine type
CPU_TYPE, but do not set the instruction set or register set that
the option `-mcpu=CPU_TYPE' would.
The same values for `-mcpu=CPU_TYPE' can be used for
`-mtune=CPU_TYPE', but the only useful values are those that
select a particular cpu implementation. Those are `cypress',
`supersparc', `hypersparc', `f930', `f934', `sparclite86x',
`tsc701', `ultrasparc', `ultrasparc3', and `niagara'.
`-mv8plus'
`-mno-v8plus'
With `-mv8plus', GCC generates code for the SPARC-V8+ ABI. The
difference from the V8 ABI is that the global and out registers are
considered 64-bit wide. This is enabled by default on Solaris in
32-bit mode for all SPARC-V9 processors.
`-mvis'
`-mno-vis'
With `-mvis', GCC generates code that takes advantage of the
UltraSPARC Visual Instruction Set extensions. The default is
`-mno-vis'.
These `-m' options are supported in addition to the above on SPARC-V9
processors in 64-bit environments:
`-mlittle-endian'
Generate code for a processor running in little-endian mode. It
is only available for a few configurations and most notably not on
Solaris and Linux.
`-m32'
`-m64'
Generate code for a 32-bit or 64-bit environment. The 32-bit
environment sets int, long and pointer to 32 bits. The 64-bit
environment sets int to 32 bits and long and pointer to 64 bits.
`-mcmodel=medlow'
Generate code for the Medium/Low code model: 64-bit addresses,
programs must be linked in the low 32 bits of memory. Programs
can be statically or dynamically linked.
`-mcmodel=medmid'
Generate code for the Medium/Middle code model: 64-bit addresses,
programs must be linked in the low 44 bits of memory, the text and
data segments must be less than 2GB in size and the data segment
must be located within 2GB of the text segment.
`-mcmodel=medany'
Generate code for the Medium/Anywhere code model: 64-bit
addresses, programs may be linked anywhere in memory, the text and
data segments must be less than 2GB in size and the data segment
must be located within 2GB of the text segment.
`-mcmodel=embmedany'
Generate code for the Medium/Anywhere code model for embedded
systems: 64-bit addresses, the text and data segments must be less
than 2GB in size, both starting anywhere in memory (determined at
link time). The global register %g4 points to the base of the
data segment. Programs are statically linked and PIC is not
supported.
`-mstack-bias'
`-mno-stack-bias'
With `-mstack-bias', GCC assumes that the stack pointer, and frame
pointer if present, are offset by -2047 which must be added back
when making stack frame references. This is the default in 64-bit
mode. Otherwise, assume no such offset is present.
These switches are supported in addition to the above on Solaris:
`-threads'
Add support for multithreading using the Solaris threads library.
This option sets flags for both the preprocessor and linker. This
option does not affect the thread safety of object code produced
by the compiler or that of libraries supplied with it.
`-pthreads'
Add support for multithreading using the POSIX threads library.
This option sets flags for both the preprocessor and linker. This
option does not affect the thread safety of object code produced
by the compiler or that of libraries supplied with it.
`-pthread'
This is a synonym for `-pthreads'.
File: gcc.info, Node: System V Options, Next: TMS320C3x/C4x Options, Prev: SPARC Options, Up: Submodel Options
3.17.32 Options for System V
----------------------------
These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:
`-G'
Create a shared object. It is recommended that `-symbolic' or
`-shared' be used instead.
`-Qy'
Identify the versions of each tool used by the compiler, in a
`.ident' assembler directive in the output.
`-Qn'
Refrain from adding `.ident' directives to the output file (this is
the default).
`-YP,DIRS'
Search the directories DIRS, and no others, for libraries
specified with `-l'.
`-Ym,DIR'
Look in the directory DIR to find the M4 preprocessor. The
assembler uses this option.
File: gcc.info, Node: TMS320C3x/C4x Options, Next: V850 Options, Prev: System V Options, Up: Submodel Options
3.17.33 TMS320C3x/C4x Options
-----------------------------
These `-m' options are defined for TMS320C3x/C4x implementations:
`-mcpu=CPU_TYPE'
Set the instruction set, register set, and instruction scheduling
parameters for machine type CPU_TYPE. Supported values for
CPU_TYPE are `c30', `c31', `c32', `c40', and `c44'. The default
is `c40' to generate code for the TMS320C40.
`-mbig-memory'
`-mbig'
`-msmall-memory'
`-msmall'
Generates code for the big or small memory model. The small memory
model assumed that all data fits into one 64K word page. At
run-time the data page (DP) register must be set to point to the
64K page containing the .bss and .data program sections. The big
memory model is the default and requires reloading of the DP
register for every direct memory access.
`-mbk'
`-mno-bk'
Allow (disallow) allocation of general integer operands into the
block count register BK.
`-mdb'
`-mno-db'
Enable (disable) generation of code using decrement and branch,
DBcond(D), instructions. This is enabled by default for the C4x.
To be on the safe side, this is disabled for the C3x, since the
maximum iteration count on the C3x is 2^23 + 1 (but who iterates
loops more than 2^23 times on the C3x?). Note that GCC will try
to reverse a loop so that it can utilize the decrement and branch
instruction, but will give up if there is more than one memory
reference in the loop. Thus a loop where the loop counter is
decremented can generate slightly more efficient code, in cases
where the RPTB instruction cannot be utilized.
`-mdp-isr-reload'
`-mparanoid'
Force the DP register to be saved on entry to an interrupt service
routine (ISR), reloaded to point to the data section, and restored
on exit from the ISR. This should not be required unless someone
has violated the small memory model by modifying the DP register,
say within an object library.
`-mmpyi'
`-mno-mpyi'
For the C3x use the 24-bit MPYI instruction for integer multiplies
instead of a library call to guarantee 32-bit results. Note that
if one of the operands is a constant, then the multiplication will
be performed using shifts and adds. If the `-mmpyi' option is not
specified for the C3x, then squaring operations are performed
inline instead of a library call.
`-mfast-fix'
`-mno-fast-fix'
The C3x/C4x FIX instruction to convert a floating point value to an
integer value chooses the nearest integer less than or equal to the
floating point value rather than to the nearest integer. Thus if
the floating point number is negative, the result will be
incorrectly truncated an additional code is necessary to detect
and correct this case. This option can be used to disable
generation of the additional code required to correct the result.
`-mrptb'
`-mno-rptb'
Enable (disable) generation of repeat block sequences using the
RPTB instruction for zero overhead looping. The RPTB construct is
only used for innermost loops that do not call functions or jump
across the loop boundaries. There is no advantage having nested
RPTB loops due to the overhead required to save and restore the
RC, RS, and RE registers. This is enabled by default with `-O2'.
`-mrpts=COUNT'
`-mno-rpts'
Enable (disable) the use of the single instruction repeat
instruction RPTS. If a repeat block contains a single
instruction, and the loop count can be guaranteed to be less than
the value COUNT, GCC will emit a RPTS instruction instead of a
RPTB. If no value is specified, then a RPTS will be emitted even
if the loop count cannot be determined at compile time. Note that
the repeated instruction following RPTS does not have to be
reloaded from memory each iteration, thus freeing up the CPU buses
for operands. However, since interrupts are blocked by this
instruction, it is disabled by default.
`-mloop-unsigned'
`-mno-loop-unsigned'
The maximum iteration count when using RPTS and RPTB (and DB on
the C40) is 2^31 + 1 since these instructions test if the
iteration count is negative to terminate the loop. If the
iteration count is unsigned there is a possibility than the 2^31 +
1 maximum iteration count may be exceeded. This switch allows an
unsigned iteration count.
`-mti'
Try to emit an assembler syntax that the TI assembler (asm30) is
happy with. This also enforces compatibility with the API
employed by the TI C3x C compiler. For example, long doubles are
passed as structures rather than in floating point registers.
`-mregparm'
`-mmemparm'
Generate code that uses registers (stack) for passing arguments to
functions. By default, arguments are passed in registers where
possible rather than by pushing arguments on to the stack.
`-mparallel-insns'
`-mno-parallel-insns'
Allow the generation of parallel instructions. This is enabled by
default with `-O2'.
`-mparallel-mpy'
`-mno-parallel-mpy'
Allow the generation of MPY||ADD and MPY||SUB parallel
instructions, provided `-mparallel-insns' is also specified.
These instructions have tight register constraints which can
pessimize the code generation of large functions.
File: gcc.info, Node: V850 Options, Next: VAX Options, Prev: TMS320C3x/C4x Options, Up: Submodel Options
3.17.34 V850 Options
--------------------
These `-m' options are defined for V850 implementations:
`-mlong-calls'
`-mno-long-calls'
Treat all calls as being far away (near). If calls are assumed to
be far away, the compiler will always load the functions address
up into a register, and call indirect through the pointer.
`-mno-ep'
`-mep'
Do not optimize (do optimize) basic blocks that use the same index
pointer 4 or more times to copy pointer into the `ep' register, and
use the shorter `sld' and `sst' instructions. The `-mep' option
is on by default if you optimize.
`-mno-prolog-function'
`-mprolog-function'
Do not use (do use) external functions to save and restore
registers at the prologue and epilogue of a function. The
external functions are slower, but use less code space if more
than one function saves the same number of registers. The
`-mprolog-function' option is on by default if you optimize.
`-mspace'
Try to make the code as small as possible. At present, this just
turns on the `-mep' and `-mprolog-function' options.
`-mtda=N'
Put static or global variables whose size is N bytes or less into
the tiny data area that register `ep' points to. The tiny data
area can hold up to 256 bytes in total (128 bytes for byte
references).
`-msda=N'
Put static or global variables whose size is N bytes or less into
the small data area that register `gp' points to. The small data
area can hold up to 64 kilobytes.
`-mzda=N'
Put static or global variables whose size is N bytes or less into
the first 32 kilobytes of memory.
`-mv850'
Specify that the target processor is the V850.
`-mbig-switch'
Generate code suitable for big switch tables. Use this option
only if the assembler/linker complain about out of range branches
within a switch table.
`-mapp-regs'
This option will cause r2 and r5 to be used in the code generated
by the compiler. This setting is the default.
`-mno-app-regs'
This option will cause r2 and r5 to be treated as fixed registers.
`-mv850e1'
Specify that the target processor is the V850E1. The preprocessor
constants `__v850e1__' and `__v850e__' will be defined if this
option is used.
`-mv850e'
Specify that the target processor is the V850E. The preprocessor
constant `__v850e__' will be defined if this option is used.
If neither `-mv850' nor `-mv850e' nor `-mv850e1' are defined then
a default target processor will be chosen and the relevant
`__v850*__' preprocessor constant will be defined.
The preprocessor constants `__v850' and `__v851__' are always
defined, regardless of which processor variant is the target.
`-mdisable-callt'
This option will suppress generation of the CALLT instruction for
the v850e and v850e1 flavors of the v850 architecture. The
default is `-mno-disable-callt' which allows the CALLT instruction
to be used.
File: gcc.info, Node: VAX Options, Next: x86-64 Options, Prev: V850 Options, Up: Submodel Options
3.17.35 VAX Options
-------------------
These `-m' options are defined for the VAX:
`-munix'
Do not output certain jump instructions (`aobleq' and so on) that
the Unix assembler for the VAX cannot handle across long ranges.
`-mgnu'
Do output those jump instructions, on the assumption that you will
assemble with the GNU assembler.
`-mg'
Output code for g-format floating point numbers instead of
d-format.
File: gcc.info, Node: x86-64 Options, Next: Xstormy16 Options, Prev: VAX Options, Up: Submodel Options
3.17.36 x86-64 Options
----------------------
These are listed under *Note i386 and x86-64 Options::.
File: gcc.info, Node: Xstormy16 Options, Next: Xtensa Options, Prev: x86-64 Options, Up: Submodel Options
3.17.37 Xstormy16 Options
-------------------------
These options are defined for Xstormy16:
`-msim'
Choose startup files and linker script suitable for the simulator.
File: gcc.info, Node: Xtensa Options, Next: zSeries Options, Prev: Xstormy16 Options, Up: Submodel Options
3.17.38 Xtensa Options
----------------------
These options are supported for Xtensa targets:
`-mconst16'
`-mno-const16'
Enable or disable use of `CONST16' instructions for loading
constant values. The `CONST16' instruction is currently not a
standard option from Tensilica. When enabled, `CONST16'
instructions are always used in place of the standard `L32R'
instructions. The use of `CONST16' is enabled by default only if
the `L32R' instruction is not available.
`-mfused-madd'
`-mno-fused-madd'
Enable or disable use of fused multiply/add and multiply/subtract
instructions in the floating-point option. This has no effect if
the floating-point option is not also enabled. Disabling fused
multiply/add and multiply/subtract instructions forces the
compiler to use separate instructions for the multiply and
add/subtract operations. This may be desirable in some cases
where strict IEEE 754-compliant results are required: the fused
multiply add/subtract instructions do not round the intermediate
result, thereby producing results with _more_ bits of precision
than specified by the IEEE standard. Disabling fused multiply
add/subtract instructions also ensures that the program output is
not sensitive to the compiler's ability to combine multiply and
add/subtract operations.
`-mtext-section-literals'
`-mno-text-section-literals'
Control the treatment of literal pools. The default is
`-mno-text-section-literals', which places literals in a separate
section in the output file. This allows the literal pool to be
placed in a data RAM/ROM, and it also allows the linker to combine
literal pools from separate object files to remove redundant
literals and improve code size. With `-mtext-section-literals',
the literals are interspersed in the text section in order to keep
them as close as possible to their references. This may be
necessary for large assembly files.
`-mtarget-align'
`-mno-target-align'
When this option is enabled, GCC instructs the assembler to
automatically align instructions to reduce branch penalties at the
expense of some code density. The assembler attempts to widen
density instructions to align branch targets and the instructions
following call instructions. If there are not enough preceding
safe density instructions to align a target, no widening will be
performed. The default is `-mtarget-align'. These options do not
affect the treatment of auto-aligned instructions like `LOOP',
which the assembler will always align, either by widening density
instructions or by inserting no-op instructions.
`-mlongcalls'
`-mno-longcalls'
When this option is enabled, GCC instructs the assembler to
translate direct calls to indirect calls unless it can determine
that the target of a direct call is in the range allowed by the
call instruction. This translation typically occurs for calls to
functions in other source files. Specifically, the assembler
translates a direct `CALL' instruction into an `L32R' followed by
a `CALLX' instruction. The default is `-mno-longcalls'. This
option should be used in programs where the call target can
potentially be out of range. This option is implemented in the
assembler, not the compiler, so the assembly code generated by GCC
will still show direct call instructions--look at the disassembled
object code to see the actual instructions. Note that the
assembler will use an indirect call for every cross-file call, not
just those that really will be out of range.
File: gcc.info, Node: zSeries Options, Prev: Xtensa Options, Up: Submodel Options
3.17.39 zSeries Options
-----------------------
These are listed under *Note S/390 and zSeries Options::.
File: gcc.info, Node: Code Gen Options, Next: Environment Variables, Prev: Submodel Options, Up: Invoking GCC
3.18 Options for Code Generation Conventions
============================================
These machine-independent options control the interface conventions
used in code generation.
Most of them have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'. In the table below, only one of the
forms is listed--the one which is not the default. You can figure out
the other form by either removing `no-' or adding it.
`-fbounds-check'
For front-ends that support it, generate additional code to check
that indices used to access arrays are within the declared range.
This is currently only supported by the Java and Fortran
front-ends, where this option defaults to true and false
respectively.
`-ftrapv'
This option generates traps for signed overflow on addition,
subtraction, multiplication operations.
`-fwrapv'
This option instructs the compiler to assume that signed arithmetic
overflow of addition, subtraction and multiplication wraps around
using twos-complement representation. This flag enables some
optimizations and disables others. This option is enabled by
default for the Java front-end, as required by the Java language
specification.
`-fexceptions'
Enable exception handling. Generates extra code needed to
propagate exceptions. For some targets, this implies GCC will
generate frame unwind information for all functions, which can
produce significant data size overhead, although it does not
affect execution. If you do not specify this option, GCC will
enable it by default for languages like C++ which normally require
exception handling, and disable it for languages like C that do
not normally require it. However, you may need to enable this
option when compiling C code that needs to interoperate properly
with exception handlers written in C++. You may also wish to
disable this option if you are compiling older C++ programs that
don't use exception handling.
`-fnon-call-exceptions'
Generate code that allows trapping instructions to throw
exceptions. Note that this requires platform-specific runtime
support that does not exist everywhere. Moreover, it only allows
_trapping_ instructions to throw exceptions, i.e. memory
references or floating point instructions. It does not allow
exceptions to be thrown from arbitrary signal handlers such as
`SIGALRM'.
`-funwind-tables'
Similar to `-fexceptions', except that it will just generate any
needed static data, but will not affect the generated code in any
other way. You will normally not enable this option; instead, a
language processor that needs this handling would enable it on
your behalf.
`-fasynchronous-unwind-tables'
Generate unwind table in dwarf2 format, if supported by target
machine. The table is exact at each instruction boundary, so it
can be used for stack unwinding from asynchronous events (such as
debugger or garbage collector).
`-fpcc-struct-return'
Return "short" `struct' and `union' values in memory like longer
ones, rather than in registers. This convention is less
efficient, but it has the advantage of allowing intercallability
between GCC-compiled files and files compiled with other
compilers, particularly the Portable C Compiler (pcc).
The precise convention for returning structures in memory depends
on the target configuration macros.
Short structures and unions are those whose size and alignment
match that of some integer type.
*Warning:* code compiled with the `-fpcc-struct-return' switch is
not binary compatible with code compiled with the
`-freg-struct-return' switch. Use it to conform to a non-default
application binary interface.
`-freg-struct-return'
Return `struct' and `union' values in registers when possible.
This is more efficient for small structures than
`-fpcc-struct-return'.
If you specify neither `-fpcc-struct-return' nor
`-freg-struct-return', GCC defaults to whichever convention is
standard for the target. If there is no standard convention, GCC
defaults to `-fpcc-struct-return', except on targets where GCC is
the principal compiler. In those cases, we can choose the
standard, and we chose the more efficient register return
alternative.
*Warning:* code compiled with the `-freg-struct-return' switch is
not binary compatible with code compiled with the
`-fpcc-struct-return' switch. Use it to conform to a non-default
application binary interface.
`-fshort-enums'
Allocate to an `enum' type only as many bytes as it needs for the
declared range of possible values. Specifically, the `enum' type
will be equivalent to the smallest integer type which has enough
room.
*Warning:* the `-fshort-enums' switch causes GCC to generate code
that is not binary compatible with code generated without that
switch. Use it to conform to a non-default application binary
interface.
`-fshort-double'
Use the same size for `double' as for `float'.
*Warning:* the `-fshort-double' switch causes GCC to generate code
that is not binary compatible with code generated without that
switch. Use it to conform to a non-default application binary
interface.
`-fshort-wchar'
Override the underlying type for `wchar_t' to be `short unsigned
int' instead of the default for the target. This option is useful
for building programs to run under WINE.
*Warning:* the `-fshort-wchar' switch causes GCC to generate code
that is not binary compatible with code generated without that
switch. Use it to conform to a non-default application binary
interface.
`-fno-common'
In C, allocate even uninitialized global variables in the data
section of the object file, rather than generating them as common
blocks. This has the effect that if the same variable is declared
(without `extern') in two different compilations, you will get an
error when you link them. The only reason this might be useful is
if you wish to verify that the program will work on other systems
which always work this way.
`-fno-ident'
Ignore the `#ident' directive.
`-finhibit-size-directive'
Don't output a `.size' assembler directive, or anything else that
would cause trouble if the function is split in the middle, and the
two halves are placed at locations far apart in memory. This
option is used when compiling `crtstuff.c'; you should not need to
use it for anything else.
`-fverbose-asm'
Put extra commentary information in the generated assembly code to
make it more readable. This option is generally only of use to
those who actually need to read the generated assembly code
(perhaps while debugging the compiler itself).
`-fno-verbose-asm', the default, causes the extra information to
be omitted and is useful when comparing two assembler files.
`-fpic'
Generate position-independent code (PIC) suitable for use in a
shared library, if supported for the target machine. Such code
accesses all constant addresses through a global offset table
(GOT). The dynamic loader resolves the GOT entries when the
program starts (the dynamic loader is not part of GCC; it is part
of the operating system). If the GOT size for the linked
executable exceeds a machine-specific maximum size, you get an
error message from the linker indicating that `-fpic' does not
work; in that case, recompile with `-fPIC' instead. (These
maximums are 8k on the SPARC and 32k on the m68k and RS/6000. The
386 has no such limit.)
Position-independent code requires special support, and therefore
works only on certain machines. For the 386, GCC supports PIC for
System V but not for the Sun 386i. Code generated for the IBM
RS/6000 is always position-independent.
When this flag is set, the macros `__pic__' and `__PIC__' are
defined to 1.
`-fPIC'
If supported for the target machine, emit position-independent
code, suitable for dynamic linking and avoiding any limit on the
size of the global offset table. This option makes a difference
on the m68k, PowerPC and SPARC.
Position-independent code requires special support, and therefore
works only on certain machines.
When this flag is set, the macros `__pic__' and `__PIC__' are
defined to 2.
`-fpie'
`-fPIE'
These options are similar to `-fpic' and `-fPIC', but generated
position independent code can be only linked into executables.
Usually these options are used when `-pie' GCC option will be used
during linking.
`-fno-jump-tables'
Do not use jump tables for switch statements even where it would be
more efficient than other code generation strategies. This option
is of use in conjunction with `-fpic' or `-fPIC' for building code
which forms part of a dynamic linker and cannot reference the
address of a jump table. On some targets, jump tables do not
require a GOT and this option is not needed.
`-ffixed-REG'
Treat the register named REG as a fixed register; generated code
should never refer to it (except perhaps as a stack pointer, frame
pointer or in some other fixed role).
REG must be the name of a register. The register names accepted
are machine-specific and are defined in the `REGISTER_NAMES' macro
in the machine description macro file.
This flag does not have a negative form, because it specifies a
three-way choice.
`-fcall-used-REG'
Treat the register named REG as an allocable register that is
clobbered by function calls. It may be allocated for temporaries
or variables that do not live across a call. Functions compiled
this way will not save and restore the register REG.
It is an error to used this flag with the frame pointer or stack
pointer. Use of this flag for other registers that have fixed
pervasive roles in the machine's execution model will produce
disastrous results.
This flag does not have a negative form, because it specifies a
three-way choice.
`-fcall-saved-REG'
Treat the register named REG as an allocable register saved by
functions. It may be allocated even for temporaries or variables
that live across a call. Functions compiled this way will save
and restore the register REG if they use it.
It is an error to used this flag with the frame pointer or stack
pointer. Use of this flag for other registers that have fixed
pervasive roles in the machine's execution model will produce
disastrous results.
A different sort of disaster will result from the use of this flag
for a register in which function values may be returned.
This flag does not have a negative form, because it specifies a
three-way choice.
`-fpack-struct[=N]'
Without a value specified, pack all structure members together
without holes. When a value is specified (which must be a small
power of two), pack structure members according to this value,
representing the maximum alignment (that is, objects with default
alignment requirements larger than this will be output potentially
unaligned at the next fitting location.
*Warning:* the `-fpack-struct' switch causes GCC to generate code
that is not binary compatible with code generated without that
switch. Additionally, it makes the code suboptimal. Use it to
conform to a non-default application binary interface.
`-finstrument-functions'
Generate instrumentation calls for entry and exit to functions.
Just after function entry and just before function exit, the
following profiling functions will be called with the address of
the current function and its call site. (On some platforms,
`__builtin_return_address' does not work beyond the current
function, so the call site information may not be available to the
profiling functions otherwise.)
void __cyg_profile_func_enter (void *this_fn,
void *call_site);
void __cyg_profile_func_exit (void *this_fn,
void *call_site);
The first argument is the address of the start of the current
function, which may be looked up exactly in the symbol table.
This instrumentation is also done for functions expanded inline in
other functions. The profiling calls will indicate where,
conceptually, the inline function is entered and exited. This
means that addressable versions of such functions must be
available. If all your uses of a function are expanded inline,
this may mean an additional expansion of code size. If you use
`extern inline' in your C code, an addressable version of such
functions must be provided. (This is normally the case anyways,
but if you get lucky and the optimizer always expands the
functions inline, you might have gotten away without providing
static copies.)
A function may be given the attribute `no_instrument_function', in
which case this instrumentation will not be done. This can be
used, for example, for the profiling functions listed above,
high-priority interrupt routines, and any functions from which the
profiling functions cannot safely be called (perhaps signal
handlers, if the profiling routines generate output or allocate
memory).
`-fstack-check'
Generate code to verify that you do not go beyond the boundary of
the stack. You should specify this flag if you are running in an
environment with multiple threads, but only rarely need to specify
it in a single-threaded environment since stack overflow is
automatically detected on nearly all systems if there is only one
stack.
Note that this switch does not actually cause checking to be done;
the operating system must do that. The switch causes generation
of code to ensure that the operating system sees the stack being
extended.
`-fstack-limit-register=REG'
`-fstack-limit-symbol=SYM'
`-fno-stack-limit'
Generate code to ensure that the stack does not grow beyond a
certain value, either the value of a register or the address of a
symbol. If the stack would grow beyond the value, a signal is
raised. For most targets, the signal is raised before the stack
overruns the boundary, so it is possible to catch the signal
without taking special precautions.
For instance, if the stack starts at absolute address `0x80000000'
and grows downwards, you can use the flags
`-fstack-limit-symbol=__stack_limit' and
`-Wl,--defsym,__stack_limit=0x7ffe0000' to enforce a stack limit
of 128KB. Note that this may only work with the GNU linker.
`-fargument-alias'
`-fargument-noalias'
`-fargument-noalias-global'
`-fargument-noalias-anything'
Specify the possible relationships among parameters and between
parameters and global data.
`-fargument-alias' specifies that arguments (parameters) may alias
each other and may alias global storage.
`-fargument-noalias' specifies that arguments do not alias each
other, but may alias global storage.
`-fargument-noalias-global' specifies that arguments do not alias
each other and do not alias global storage.
`-fargument-noalias-anything' specifies that arguments do not
alias any other storage.
Each language will automatically use whatever option is required by
the language standard. You should not need to use these options
yourself.
`-fleading-underscore'
This option and its counterpart, `-fno-leading-underscore',
forcibly change the way C symbols are represented in the object
file. One use is to help link with legacy assembly code.
*Warning:* the `-fleading-underscore' switch causes GCC to
generate code that is not binary compatible with code generated
without that switch. Use it to conform to a non-default
application binary interface. Not all targets provide complete
support for this switch.
`-ftls-model=MODEL'
Alter the thread-local storage model to be used (*note
Thread-Local::). The MODEL argument should be one of
`global-dynamic', `local-dynamic', `initial-exec' or `local-exec'.
The default without `-fpic' is `initial-exec'; with `-fpic' the
default is `global-dynamic'.
`-fvisibility=DEFAULT|INTERNAL|HIDDEN|PROTECTED'
Set the default ELF image symbol visibility to the specified
option--all symbols will be marked with this unless overridden
within the code. Using this feature can very substantially
improve linking and load times of shared object libraries, produce
more optimized code, provide near-perfect API export and prevent
symbol clashes. It is *strongly* recommended that you use this in
any shared objects you distribute.
Despite the nomenclature, `default' always means public ie;
available to be linked against from outside the shared object.
`protected' and `internal' are pretty useless in real-world usage
so the only other commonly used option will be `hidden'. The
default if `-fvisibility' isn't specified is `default', i.e., make
every symbol public--this causes the same behavior as previous
versions of GCC.
A good explanation of the benefits offered by ensuring ELF symbols
have the correct visibility is given by "How To Write Shared
Libraries" by Ulrich Drepper (which can be found at
`http://people.redhat.com/~drepper/')--however a superior solution
made possible by this option to marking things hidden when the
default is public is to make the default hidden and mark things
public. This is the norm with DLL's on Windows and with
`-fvisibility=hidden' and `__attribute__
((visibility("default")))' instead of `__declspec(dllexport)' you
get almost identical semantics with identical syntax. This is a
great boon to those working with cross-platform projects.
For those adding visibility support to existing code, you may find
`#pragma GCC visibility' of use. This works by you enclosing the
declarations you wish to set visibility for with (for example)
`#pragma GCC visibility push(hidden)' and `#pragma GCC visibility
pop'. Bear in mind that symbol visibility should be viewed *as
part of the API interface contract* and thus all new code should
always specify visibility when it is not the default ie;
declarations only for use within the local DSO should *always* be
marked explicitly as hidden as so to avoid PLT indirection
overheads--making this abundantly clear also aids readability and
self-documentation of the code. Note that due to ISO C++
specification requirements, operator new and operator delete must
always be of default visibility.
Be aware that headers from outside your project, in particular
system headers and headers from any other library you use, may not
be expecting to be compiled with visibility other than the
default. You may need to explicitly say `#pragma GCC visibility
push(default)' before including any such headers.
`extern' declarations are not affected by `-fvisibility', so a lot
of code can be recompiled with `-fvisibility=hidden' with no
modifications. However, this means that calls to `extern'
functions with no explicit visibility will use the PLT, so it is
more effective to use `__attribute ((visibility))' and/or `#pragma
GCC visibility' to tell the compiler which `extern' declarations
should be treated as hidden.
Note that `-fvisibility' does affect C++ vague linkage entities.
This means that, for instance, an exception class that will be
thrown between DSOs must be explicitly marked with default
visibility so that the `type_info' nodes will be unified between
the DSOs.
An overview of these techniques, their benefits and how to use them
is at `http://gcc.gnu.org/wiki/Visibility'.
File: gcc.info, Node: Environment Variables, Next: Precompiled Headers, Prev: Code Gen Options, Up: Invoking GCC
3.19 Environment Variables Affecting GCC
========================================
This section describes several environment variables that affect how GCC
operates. Some of them work by specifying directories or prefixes to
use when searching for various kinds of files. Some are used to
specify other aspects of the compilation environment.
Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (*note Directory Options::). These take precedence
over places specified using environment variables, which in turn take
precedence over those specified by the configuration of GCC. *Note
Controlling the Compilation Driver `gcc': (gccint)Driver.
`LANG'
`LC_CTYPE'
`LC_MESSAGES'
`LC_ALL'
These environment variables control the way that GCC uses
localization information that allow GCC to work with different
national conventions. GCC inspects the locale categories
`LC_CTYPE' and `LC_MESSAGES' if it has been configured to do so.
These locale categories can be set to any value supported by your
installation. A typical value is `en_GB.UTF-8' for English in the
United Kingdom encoded in UTF-8.
The `LC_CTYPE' environment variable specifies character
classification. GCC uses it to determine the character boundaries
in a string; this is needed for some multibyte encodings that
contain quote and escape characters that would otherwise be
interpreted as a string end or escape.
The `LC_MESSAGES' environment variable specifies the language to
use in diagnostic messages.
If the `LC_ALL' environment variable is set, it overrides the value
of `LC_CTYPE' and `LC_MESSAGES'; otherwise, `LC_CTYPE' and
`LC_MESSAGES' default to the value of the `LANG' environment
variable. If none of these variables are set, GCC defaults to
traditional C English behavior.
`TMPDIR'
If `TMPDIR' is set, it specifies the directory to use for temporary
files. GCC uses temporary files to hold the output of one stage of
compilation which is to be used as input to the next stage: for
example, the output of the preprocessor, which is the input to the
compiler proper.
`GCC_EXEC_PREFIX'
If `GCC_EXEC_PREFIX' is set, it specifies a prefix to use in the
names of the subprograms executed by the compiler. No slash is
added when this prefix is combined with the name of a subprogram,
but you can specify a prefix that ends with a slash if you wish.
If `GCC_EXEC_PREFIX' is not set, GCC will attempt to figure out an
appropriate prefix to use based on the pathname it was invoked
with.
If GCC cannot find the subprogram using the specified prefix, it
tries looking in the usual places for the subprogram.
The default value of `GCC_EXEC_PREFIX' is `PREFIX/lib/gcc/' where
PREFIX is the value of `prefix' when you ran the `configure'
script.
Other prefixes specified with `-B' take precedence over this
prefix.
This prefix is also used for finding files such as `crt0.o' that
are used for linking.
In addition, the prefix is used in an unusual way in finding the
directories to search for header files. For each of the standard
directories whose name normally begins with `/usr/local/lib/gcc'
(more precisely, with the value of `GCC_INCLUDE_DIR'), GCC tries
replacing that beginning with the specified prefix to produce an
alternate directory name. Thus, with `-Bfoo/', GCC will search
`foo/bar' where it would normally search `/usr/local/lib/bar'.
These alternate directories are searched first; the standard
directories come next.
`COMPILER_PATH'
The value of `COMPILER_PATH' is a colon-separated list of
directories, much like `PATH'. GCC tries the directories thus
specified when searching for subprograms, if it can't find the
subprograms using `GCC_EXEC_PREFIX'.
`LIBRARY_PATH'
The value of `LIBRARY_PATH' is a colon-separated list of
directories, much like `PATH'. When configured as a native
compiler, GCC tries the directories thus specified when searching
for special linker files, if it can't find them using
`GCC_EXEC_PREFIX'. Linking using GCC also uses these directories
when searching for ordinary libraries for the `-l' option (but
directories specified with `-L' come first).
`LANG'
This variable is used to pass locale information to the compiler.
One way in which this information is used is to determine the
character set to be used when character literals, string literals
and comments are parsed in C and C++. When the compiler is
configured to allow multibyte characters, the following values for
`LANG' are recognized:
`C-JIS'
Recognize JIS characters.
`C-SJIS'
Recognize SJIS characters.
`C-EUCJP'
Recognize EUCJP characters.
If `LANG' is not defined, or if it has some other value, then the
compiler will use mblen and mbtowc as defined by the default
locale to recognize and translate multibyte characters.
Some additional environments variables affect the behavior of the
preprocessor.
`CPATH'
`C_INCLUDE_PATH'
`CPLUS_INCLUDE_PATH'
`OBJC_INCLUDE_PATH'
Each variable's value is a list of directories separated by a
special character, much like `PATH', in which to look for header
files. The special character, `PATH_SEPARATOR', is
target-dependent and determined at GCC build time. For Microsoft
Windows-based targets it is a semicolon, and for almost all other
targets it is a colon.
`CPATH' specifies a list of directories to be searched as if
specified with `-I', but after any paths given with `-I' options
on the command line. This environment variable is used regardless
of which language is being preprocessed.
The remaining environment variables apply only when preprocessing
the particular language indicated. Each specifies a list of
directories to be searched as if specified with `-isystem', but
after any paths given with `-isystem' options on the command line.
In all these variables, an empty element instructs the compiler to
search its current working directory. Empty elements can appear
at the beginning or end of a path. For instance, if the value of
`CPATH' is `:/special/include', that has the same effect as
`-I. -I/special/include'.
`DEPENDENCIES_OUTPUT'
If this variable is set, its value specifies how to output
dependencies for Make based on the non-system header files
processed by the compiler. System header files are ignored in the
dependency output.
The value of `DEPENDENCIES_OUTPUT' can be just a file name, in
which case the Make rules are written to that file, guessing the
target name from the source file name. Or the value can have the
form `FILE TARGET', in which case the rules are written to file
FILE using TARGET as the target name.
In other words, this environment variable is equivalent to
combining the options `-MM' and `-MF' (*note Preprocessor
Options::), with an optional `-MT' switch too.
`SUNPRO_DEPENDENCIES'
This variable is the same as `DEPENDENCIES_OUTPUT' (see above),
except that system header files are not ignored, so it implies
`-M' rather than `-MM'. However, the dependence on the main input
file is omitted. *Note Preprocessor Options::.
File: gcc.info, Node: Precompiled Headers, Next: Running Protoize, Prev: Environment Variables, Up: Invoking GCC
3.20 Using Precompiled Headers
==============================
Often large projects have many header files that are included in every
source file. The time the compiler takes to process these header files
over and over again can account for nearly all of the time required to
build the project. To make builds faster, GCC allows users to
`precompile' a header file; then, if builds can use the precompiled
header file they will be much faster.
To create a precompiled header file, simply compile it as you would any
other file, if necessary using the `-x' option to make the driver treat
it as a C or C++ header file. You will probably want to use a tool
like `make' to keep the precompiled header up-to-date when the headers
it contains change.
A precompiled header file will be searched for when `#include' is seen
in the compilation. As it searches for the included file (*note Search
Path: (cpp)Search Path.) the compiler looks for a precompiled header in
each directory just before it looks for the include file in that
directory. The name searched for is the name specified in the
`#include' with `.gch' appended. If the precompiled header file can't
be used, it is ignored.
For instance, if you have `#include "all.h"', and you have `all.h.gch'
in the same directory as `all.h', then the precompiled header file will
be used if possible, and the original header will be used otherwise.
Alternatively, you might decide to put the precompiled header file in a
directory and use `-I' to ensure that directory is searched before (or
instead of) the directory containing the original header. Then, if you
want to check that the precompiled header file is always used, you can
put a file of the same name as the original header in this directory
containing an `#error' command.
This also works with `-include'. So yet another way to use
precompiled headers, good for projects not designed with precompiled
header files in mind, is to simply take most of the header files used by
a project, include them from another header file, precompile that header
file, and `-include' the precompiled header. If the header files have
guards against multiple inclusion, they will be skipped because they've
already been included (in the precompiled header).
If you need to precompile the same header file for different
languages, targets, or compiler options, you can instead make a
_directory_ named like `all.h.gch', and put each precompiled header in
the directory, perhaps using `-o'. It doesn't matter what you call the
files in the directory, every precompiled header in the directory will
be considered. The first precompiled header encountered in the
directory that is valid for this compilation will be used; they're
searched in no particular order.
There are many other possibilities, limited only by your imagination,
good sense, and the constraints of your build system.
A precompiled header file can be used only when these conditions apply:
* Only one precompiled header can be used in a particular
compilation.
* A precompiled header can't be used once the first C token is seen.
You can have preprocessor directives before a precompiled header;
you can even include a precompiled header from inside another
header, so long as there are no C tokens before the `#include'.
* The precompiled header file must be produced for the same language
as the current compilation. You can't use a C precompiled header
for a C++ compilation.
* The precompiled header file must have been produced by the same
compiler binary as the current compilation is using.
* Any macros defined before the precompiled header is included must
either be defined in the same way as when the precompiled header
was generated, or must not affect the precompiled header, which
usually means that they don't appear in the precompiled header at
all.
The `-D' option is one way to define a macro before a precompiled
header is included; using a `#define' can also do it. There are
also some options that define macros implicitly, like `-O' and
`-Wdeprecated'; the same rule applies to macros defined this way.
* If debugging information is output when using the precompiled
header, using `-g' or similar, the same kind of debugging
information must have been output when building the precompiled
header. However, a precompiled header built using `-g' can be
used in a compilation when no debugging information is being
output.
* The same `-m' options must generally be used when building and
using the precompiled header. *Note Submodel Options::, for any
cases where this rule is relaxed.
* Each of the following options must be the same when building and
using the precompiled header:
-fexceptions -funit-at-a-time
* Some other command-line options starting with `-f', `-p', or `-O'
must be defined in the same way as when the precompiled header was
generated. At present, it's not clear which options are safe to
change and which are not; the safest choice is to use exactly the
same options when generating and using the precompiled header.
The following are known to be safe:
-fmessage-length= -fpreprocessed
-fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
-fsched-verbose=<number> -fschedule-insns -fvisibility=
-pedantic-errors
For all of these except the last, the compiler will automatically
ignore the precompiled header if the conditions aren't met. If you
find an option combination that doesn't work and doesn't cause the
precompiled header to be ignored, please consider filing a bug report,
see *Note Bugs::.
If you do use differing options when generating and using the
precompiled header, the actual behavior will be a mixture of the
behavior for the options. For instance, if you use `-g' to generate
the precompiled header but not when using it, you may or may not get
debugging information for routines in the precompiled header.
File: gcc.info, Node: Running Protoize, Prev: Precompiled Headers, Up: Invoking GCC
3.21 Running Protoize
=====================
The program `protoize' is an optional part of GCC. You can use it to
add prototypes to a program, thus converting the program to ISO C in
one respect. The companion program `unprotoize' does the reverse: it
removes argument types from any prototypes that are found.
When you run these programs, you must specify a set of source files as
command line arguments. The conversion programs start out by compiling
these files to see what functions they define. The information gathered
about a file FOO is saved in a file named `FOO.X'.
After scanning comes actual conversion. The specified files are all
eligible to be converted; any files they include (whether sources or
just headers) are eligible as well.
But not all the eligible files are converted. By default, `protoize'
and `unprotoize' convert only source and header files in the current
directory. You can specify additional directories whose files should
be converted with the `-d DIRECTORY' option. You can also specify
particular files to exclude with the `-x FILE' option. A file is
converted if it is eligible, its directory name matches one of the
specified directory names, and its name within the directory has not
been excluded.
Basic conversion with `protoize' consists of rewriting most function
definitions and function declarations to specify the types of the
arguments. The only ones not rewritten are those for varargs functions.
`protoize' optionally inserts prototype declarations at the beginning
of the source file, to make them available for any calls that precede
the function's definition. Or it can insert prototype declarations
with block scope in the blocks where undeclared functions are called.
Basic conversion with `unprotoize' consists of rewriting most function
declarations to remove any argument types, and rewriting function
definitions to the old-style pre-ISO form.
Both conversion programs print a warning for any function declaration
or definition that they can't convert. You can suppress these warnings
with `-q'.
The output from `protoize' or `unprotoize' replaces the original
source file. The original file is renamed to a name ending with
`.save' (for DOS, the saved filename ends in `.sav' without the
original `.c' suffix). If the `.save' (`.sav' for DOS) file already
exists, then the source file is simply discarded.
`protoize' and `unprotoize' both depend on GCC itself to scan the
program and collect information about the functions it uses. So
neither of these programs will work until GCC is installed.
Here is a table of the options you can use with `protoize' and
`unprotoize'. Each option works with both programs unless otherwise
stated.
`-B DIRECTORY'
Look for the file `SYSCALLS.c.X' in DIRECTORY, instead of the
usual directory (normally `/usr/local/lib'). This file contains
prototype information about standard system functions. This option
applies only to `protoize'.
`-c COMPILATION-OPTIONS'
Use COMPILATION-OPTIONS as the options when running `gcc' to
produce the `.X' files. The special option `-aux-info' is always
passed in addition, to tell `gcc' to write a `.X' file.
Note that the compilation options must be given as a single
argument to `protoize' or `unprotoize'. If you want to specify
several `gcc' options, you must quote the entire set of
compilation options to make them a single word in the shell.
There are certain `gcc' arguments that you cannot use, because they
would produce the wrong kind of output. These include `-g', `-O',
`-c', `-S', and `-o' If you include these in the
COMPILATION-OPTIONS, they are ignored.
`-C'
Rename files to end in `.C' (`.cc' for DOS-based file systems)
instead of `.c'. This is convenient if you are converting a C
program to C++. This option applies only to `protoize'.
`-g'
Add explicit global declarations. This means inserting explicit
declarations at the beginning of each source file for each function
that is called in the file and was not declared. These
declarations precede the first function definition that contains a
call to an undeclared function. This option applies only to
`protoize'.
`-i STRING'
Indent old-style parameter declarations with the string STRING.
This option applies only to `protoize'.
`unprotoize' converts prototyped function definitions to old-style
function definitions, where the arguments are declared between the
argument list and the initial `{'. By default, `unprotoize' uses
five spaces as the indentation. If you want to indent with just
one space instead, use `-i " "'.
`-k'
Keep the `.X' files. Normally, they are deleted after conversion
is finished.
`-l'
Add explicit local declarations. `protoize' with `-l' inserts a
prototype declaration for each function in each block which calls
the function without any declaration. This option applies only to
`protoize'.
`-n'
Make no real changes. This mode just prints information about the
conversions that would have been done without `-n'.
`-N'
Make no `.save' files. The original files are simply deleted.
Use this option with caution.
`-p PROGRAM'
Use the program PROGRAM as the compiler. Normally, the name `gcc'
is used.
`-q'
Work quietly. Most warnings are suppressed.
`-v'
Print the version number, just like `-v' for `gcc'.
If you need special compiler options to compile one of your program's
source files, then you should generate that file's `.X' file specially,
by running `gcc' on that source file with the appropriate options and
the option `-aux-info'. Then run `protoize' on the entire set of
files. `protoize' will use the existing `.X' file because it is newer
than the source file. For example:
gcc -Dfoo=bar file1.c -aux-info file1.X
protoize *.c
You need to include the special files along with the rest in the
`protoize' command, even though their `.X' files already exist, because
otherwise they won't get converted.
*Note Protoize Caveats::, for more information on how to use
`protoize' successfully.
File: gcc.info, Node: C Implementation, Next: C Extensions, Prev: Invoking GCC, Up: Top
4 C Implementation-defined behavior
***********************************
A conforming implementation of ISO C is required to document its choice
of behavior in each of the areas that are designated "implementation
defined". The following lists all such areas, along with the section
numbers from the ISO/IEC 9899:1990 and ISO/IEC 9899:1999 standards.
Some areas are only implementation-defined in one version of the
standard.
Some choices depend on the externally determined ABI for the platform
(including standard character encodings) which GCC follows; these are
listed as "determined by ABI" below. *Note Binary Compatibility:
Compatibility, and `http://gcc.gnu.org/readings.html'. Some choices
are documented in the preprocessor manual. *Note
Implementation-defined behavior: (cpp)Implementation-defined behavior.
Some choices are made by the library and operating system (or other
environment when compiling for a freestanding environment); refer to
their documentation for details.
* Menu:
* Translation implementation::
* Environment implementation::
* Identifiers implementation::
* Characters implementation::
* Integers implementation::
* Floating point implementation::
* Arrays and pointers implementation::
* Hints implementation::
* Structures unions enumerations and bit-fields implementation::
* Qualifiers implementation::
* Declarators implementation::
* Statements implementation::
* Preprocessing directives implementation::
* Library functions implementation::
* Architecture implementation::
* Locale-specific behavior implementation::
File: gcc.info, Node: Translation implementation, Next: Environment implementation, Up: C Implementation
4.1 Translation
===============
* `How a diagnostic is identified (C90 3.7, C99 3.10, C90 and C99
5.1.1.3).'
Diagnostics consist of all the output sent to stderr by GCC.
* `Whether each nonempty sequence of white-space characters other
than new-line is retained or replaced by one space character in
translation phase 3 (C90 and C99 5.1.1.2).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
File: gcc.info, Node: Environment implementation, Next: Identifiers implementation, Prev: Translation implementation, Up: C Implementation
4.2 Environment
===============
The behavior of most of these points are dependent on the implementation
of the C library, and are not defined by GCC itself.
* `The mapping between physical source file multibyte characters and
the source character set in translation phase 1 (C90 and C99
5.1.1.2).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
File: gcc.info, Node: Identifiers implementation, Next: Characters implementation, Prev: Environment implementation, Up: C Implementation
4.3 Identifiers
===============
* `Which additional multibyte characters may appear in identifiers
and their correspondence to universal character names (C99 6.4.2).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
* `The number of significant initial characters in an identifier
(C90 6.1.2, C90 and C99 5.2.4.1, C99 6.4.2).'
For internal names, all characters are significant. For external
names, the number of significant characters are defined by the
linker; for almost all targets, all characters are significant.
* `Whether case distinctions are significant in an identifier with
external linkage (C90 6.1.2).'
This is a property of the linker. C99 requires that case
distinctions are always significant in identifiers with external
linkage and systems without this property are not supported by GCC.
File: gcc.info, Node: Characters implementation, Next: Integers implementation, Prev: Identifiers implementation, Up: C Implementation
4.4 Characters
==============
* `The number of bits in a byte (C90 3.4, C99 3.6).'
Determined by ABI.
* `The values of the members of the execution character set (C90 and
C99 5.2.1).'
Determined by ABI.
* `The unique value of the member of the execution character set
produced for each of the standard alphabetic escape sequences (C90
and C99 5.2.2).'
Determined by ABI.
* `The value of a `char' object into which has been stored any
character other than a member of the basic execution character set
(C90 6.1.2.5, C99 6.2.5).'
Determined by ABI.
* `Which of `signed char' or `unsigned char' has the same range,
representation, and behavior as "plain" `char' (C90 6.1.2.5, C90
6.2.1.1, C99 6.2.5, C99 6.3.1.1).'
Determined by ABI. The options `-funsigned-char' and
`-fsigned-char' change the default. *Note Options Controlling C
Dialect: C Dialect Options.
* `The mapping of members of the source character set (in character
constants and string literals) to members of the execution
character set (C90 6.1.3.4, C99 6.4.4.4, C90 and C99 5.1.1.2).'
Determined by ABI.
* `The value of an integer character constant containing more than
one character or containing a character or escape sequence that
does not map to a single-byte execution character (C90 6.1.3.4,
C99 6.4.4.4).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
* `The value of a wide character constant containing more than one
multibyte character, or containing a multibyte character or escape
sequence not represented in the extended execution character set
(C90 6.1.3.4, C99 6.4.4.4).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
* `The current locale used to convert a wide character constant
consisting of a single multibyte character that maps to a member
of the extended execution character set into a corresponding wide
character code (C90 6.1.3.4, C99 6.4.4.4).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
* `The current locale used to convert a wide string literal into
corresponding wide character codes (C90 6.1.4, C99 6.4.5).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
* `The value of a string literal containing a multibyte character or
escape sequence not represented in the execution character set
(C90 6.1.4, C99 6.4.5).'
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior.
File: gcc.info, Node: Integers implementation, Next: Floating point implementation, Prev: Characters implementation, Up: C Implementation
4.5 Integers
============
* `Any extended integer types that exist in the implementation (C99
6.2.5).'
GCC does not support any extended integer types.
* `Whether signed integer types are represented using sign and
magnitude, two's complement, or one's complement, and whether the
extraordinary value is a trap representation or an ordinary value
(C99 6.2.6.2).'
GCC supports only two's complement integer types, and all bit
patterns are ordinary values.
* `The rank of any extended integer type relative to another extended
integer type with the same precision (C99 6.3.1.1).'
GCC does not support any extended integer types.
* `The result of, or the signal raised by, converting an integer to a
signed integer type when the value cannot be represented in an
object of that type (C90 6.2.1.2, C99 6.3.1.3).'
For conversion to a type of width N, the value is reduced modulo
2^N to be within range of the type; no signal is raised.
* `The results of some bitwise operations on signed integers (C90
6.3, C99 6.5).'
Bitwise operators act on the representation of the value including
both the sign and value bits, where the sign bit is considered
immediately above the highest-value value bit. Signed `>>' acts
on negative numbers by sign extension.
GCC does not use the latitude given in C99 only to treat certain
aspects of signed `<<' as undefined, but this is subject to change.
* `The sign of the remainder on integer division (C90 6.3.5).'
GCC always follows the C99 requirement that the result of division
is truncated towards zero.
File: gcc.info, Node: Floating point implementation, Next: Arrays and pointers implementation, Prev: Integers implementation, Up: C Implementation
4.6 Floating point
==================
* `The accuracy of the floating-point operations and of the library
functions in `<math.h>' and `<complex.h>' that return
floating-point results (C90 and C99 5.2.4.2.2).'
The accuracy is unknown.
* `The rounding behaviors characterized by non-standard values of
`FLT_ROUNDS' (C90 and C99 5.2.4.2.2).'
GCC does not use such values.
* `The evaluation methods characterized by non-standard negative
values of `FLT_EVAL_METHOD' (C99 5.2.4.2.2).'
GCC does not use such values.
* `The direction of rounding when an integer is converted to a
floating-point number that cannot exactly represent the original
value (C90 6.2.1.3, C99 6.3.1.4).'
C99 Annex F is followed.
* `The direction of rounding when a floating-point number is
converted to a narrower floating-point number (C90 6.2.1.4, C99
6.3.1.5).'
C99 Annex F is followed.
* `How the nearest representable value or the larger or smaller
representable value immediately adjacent to the nearest
representable value is chosen for certain floating constants (C90
6.1.3.1, C99 6.4.4.2).'
C99 Annex F is followed.
* `Whether and how floating expressions are contracted when not
disallowed by the `FP_CONTRACT' pragma (C99 6.5).'
Expressions are currently only contracted if
`-funsafe-math-optimizations' or `-ffast-math' are used. This is
subject to change.
* `The default state for the `FENV_ACCESS' pragma (C99 7.6.1).'
This pragma is not implemented, but the default is to "off" unless
`-frounding-math' is used in which case it is "on".
* `Additional floating-point exceptions, rounding modes,
environments, and classifications, and their macro names (C99 7.6,
C99 7.12).'
This is dependent on the implementation of the C library, and is
not defined by GCC itself.
* `The default state for the `FP_CONTRACT' pragma (C99 7.12.2).'
This pragma is not implemented. Expressions are currently only
contracted if `-funsafe-math-optimizations' or `-ffast-math' are
used. This is subject to change.
* `Whether the "inexact" floating-point exception can be raised when
the rounded result actually does equal the mathematical result in
an IEC 60559 conformant implementation (C99 F.9).'
This is dependent on the implementation of the C library, and is
not defined by GCC itself.
* `Whether the "underflow" (and "inexact") floating-point exception
can be raised when a result is tiny but not inexact in an IEC
60559 conformant implementation (C99 F.9).'
This is dependent on the implementation of the C library, and is
not defined by GCC itself.
File: gcc.info, Node: Arrays and pointers implementation, Next: Hints implementation, Prev: Floating point implementation, Up: C Implementation
4.7 Arrays and pointers
=======================
* `The result of converting a pointer to an integer or vice versa
(C90 6.3.4, C99 6.3.2.3).'
A cast from pointer to integer discards most-significant bits if
the pointer representation is larger than the integer type,
sign-extends(1) if the pointer representation is smaller than the
integer type, otherwise the bits are unchanged.
A cast from integer to pointer discards most-significant bits if
the pointer representation is smaller than the integer type,
extends according to the signedness of the integer type if the
pointer representation is larger than the integer type, otherwise
the bits are unchanged.
When casting from pointer to integer and back again, the resulting
pointer must reference the same object as the original pointer,
otherwise the behavior is undefined. That is, one may not use
integer arithmetic to avoid the undefined behavior of pointer
arithmetic as proscribed in C99 6.5.6/8.
* `The size of the result of subtracting two pointers to elements of
the same array (C90 6.3.6, C99 6.5.6).'
The value is as specified in the standard and the type is
determined by the ABI.
---------- Footnotes ----------
(1) Future versions of GCC may zero-extend, or use a target-defined
`ptr_extend' pattern. Do not rely on sign extension.
File: gcc.info, Node: Hints implementation, Next: Structures unions enumerations and bit-fields implementation, Prev: Arrays and pointers implementation, Up: C Implementation
4.8 Hints
=========
* `The extent to which suggestions made by using the `register'
storage-class specifier are effective (C90 6.5.1, C99 6.7.1).'
The `register' specifier affects code generation only in these
ways:
* When used as part of the register variable extension, see
*Note Explicit Reg Vars::.
* When `-O0' is in use, the compiler allocates distinct stack
memory for all variables that do not have the `register'
storage-class specifier; if `register' is specified, the
variable may have a shorter lifespan than the code would
indicate and may never be placed in memory.
* On some rare x86 targets, `setjmp' doesn't save the registers
in all circumstances. In those cases, GCC doesn't allocate
any variables in registers unless they are marked `register'.
* `The extent to which suggestions made by using the inline function
specifier are effective (C99 6.7.4).'
GCC will not inline any functions if the `-fno-inline' option is
used or if `-O0' is used. Otherwise, GCC may still be unable to
inline a function for many reasons; the `-Winline' option may be
used to determine if a function has not been inlined and why not.
File: gcc.info, Node: Structures unions enumerations and bit-fields implementation, Next: Qualifiers implementation, Prev: Hints implementation, Up: C Implementation
4.9 Structures, unions, enumerations, and bit-fields
====================================================
* `A member of a union object is accessed using a member of a
different type (C90 6.3.2.3).'
The relevant bytes of the representation of the object are treated
as an object of the type used for the access. This may be a trap
representation.
* `Whether a "plain" `int' bit-field is treated as a `signed int'
bit-field or as an `unsigned int' bit-field (C90 6.5.2, C90
6.5.2.1, C99 6.7.2, C99 6.7.2.1).'
By default it is treated as `signed int' but this may be changed
by the `-funsigned-bitfields' option.
* `Allowable bit-field types other than `_Bool', `signed int', and
`unsigned int' (C99 6.7.2.1).'
No other types are permitted in strictly conforming mode.
* `Whether a bit-field can straddle a storage-unit boundary (C90
6.5.2.1, C99 6.7.2.1).'
Determined by ABI.
* `The order of allocation of bit-fields within a unit (C90 6.5.2.1,
C99 6.7.2.1).'
Determined by ABI.
* `The alignment of non-bit-field members of structures (C90
6.5.2.1, C99 6.7.2.1).'
Determined by ABI.
* `The integer type compatible with each enumerated type (C90
6.5.2.2, C99 6.7.2.2).'
Normally, the type is `unsigned int' if there are no negative
values in the enumeration, otherwise `int'. If `-fshort-enums' is
specified, then if there are negative values it is the first of
`signed char', `short' and `int' that can represent all the
values, otherwise it is the first of `unsigned char', `unsigned
short' and `unsigned int' that can represent all the values.
On some targets, `-fshort-enums' is the default; this is
determined by the ABI.
File: gcc.info, Node: Qualifiers implementation, Next: Declarators implementation, Prev: Structures unions enumerations and bit-fields implementation, Up: C Implementation
4.10 Qualifiers
===============
* `What constitutes an access to an object that has
volatile-qualified type (C90 6.5.3, C99 6.7.3).'
Such an object is normally accessed by pointers and used for
accessing hardware. In most expressions, it is intuitively
obvious what is a read and what is a write. For example
volatile int *dst = SOMEVALUE;
volatile int *src = SOMEOTHERVALUE;
*dst = *src;
will cause a read of the volatile object pointed to by SRC and
store the value into the volatile object pointed to by DST. There
is no guarantee that these reads and writes are atomic, especially
for objects larger than `int'.
However, if the volatile storage is not being modified, and the
value of the volatile storage is not used, then the situation is
less obvious. For example
volatile int *src = SOMEVALUE;
*src;
According to the C standard, such an expression is an rvalue whose
type is the unqualified version of its original type, i.e. `int'.
Whether GCC interprets this as a read of the volatile object being
pointed to or only as a request to evaluate the expression for its
side-effects depends on this type.
If it is a scalar type, or on most targets an aggregate type whose
only member object is of a scalar type, or a union type whose
member objects are of scalar types, the expression is interpreted
by GCC as a read of the volatile object; in the other cases, the
expression is only evaluated for its side-effects.
File: gcc.info, Node: Declarators implementation, Next: Statements implementation, Prev: Qualifiers implementation, Up: C Implementation
4.11 Declarators
================
* `The maximum number of declarators that may modify an arithmetic,
structure or union type (C90 6.5.4).'
GCC is only limited by available memory.
File: gcc.info, Node: Statements implementation, Next: Preprocessing directives implementation, Prev: Declarators implementation, Up: C Implementation
4.12 Statements
===============
* `The maximum number of `case' values in a `switch' statement (C90
6.6.4.2).'
GCC is only limited by available memory.
File: gcc.info, Node: Preprocessing directives implementation, Next: Library functions implementation, Prev: Statements implementation, Up: C Implementation
4.13 Preprocessing directives
=============================
*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior, for details of these aspects of implementation-defined
behavior.
* `How sequences in both forms of header names are mapped to headers
or external source file names (C90 6.1.7, C99 6.4.7).'
* `Whether the value of a character constant in a constant expression
that controls conditional inclusion matches the value of the same
character constant in the execution character set (C90 6.8.1, C99
6.10.1).'
* `Whether the value of a single-character character constant in a
constant expression that controls conditional inclusion may have a
negative value (C90 6.8.1, C99 6.10.1).'
* `The places that are searched for an included `<>' delimited
header, and how the places are specified or the header is
identified (C90 6.8.2, C99 6.10.2).'
* `How the named source file is searched for in an included `""'
delimited header (C90 6.8.2, C99 6.10.2).'
* `The method by which preprocessing tokens (possibly resulting from
macro expansion) in a `#include' directive are combined into a
header name (C90 6.8.2, C99 6.10.2).'
* `The nesting limit for `#include' processing (C90 6.8.2, C99
6.10.2).'
* `Whether the `#' operator inserts a `\' character before the `\'
character that begins a universal character name in a character
constant or string literal (C99 6.10.3.2).'
* `The behavior on each recognized non-`STDC #pragma' directive (C90
6.8.6, C99 6.10.6).'
*Note Pragmas: (cpp)Pragmas, for details of pragmas accepted by
GCC on all targets. *Note Pragmas Accepted by GCC: Pragmas, for
details of target-specific pragmas.
* `The definitions for `__DATE__' and `__TIME__' when respectively,
the date and time of translation are not available (C90 6.8.8, C99
6.10.8).'
File: gcc.info, Node: Library functions implementation, Next: Architecture implementation, Prev: Preprocessing directives implementation, Up: C Implementation
4.14 Library functions
======================
The behavior of most of these points are dependent on the implementation
of the C library, and are not defined by GCC itself.
* `The null pointer constant to which the macro `NULL' expands (C90
7.1.6, C99 7.17).'
In `<stddef.h>', `NULL' expands to `((void *)0)'. GCC does not
provide the other headers which define `NULL' and some library
implementations may use other definitions in those headers.
File: gcc.info, Node: Architecture implementation, Next: Locale-specific behavior implementation, Prev: Library functions implementation, Up: C Implementation
4.15 Architecture
=================
* `The values or expressions assigned to the macros specified in the
headers `<float.h>', `<limits.h>', and `<stdint.h>' (C90 and C99
5.2.4.2, C99 7.18.2, C99 7.18.3).'
Determined by ABI.
* `The number, order, and encoding of bytes in any object (when not
explicitly specified in this International Standard) (C99
6.2.6.1).'
Determined by ABI.
* `The value of the result of the `sizeof' operator (C90 6.3.3.4,
C99 6.5.3.4).'
Determined by ABI.
File: gcc.info, Node: Locale-specific behavior implementation, Prev: Architecture implementation, Up: C Implementation
4.16 Locale-specific behavior
=============================
The behavior of these points are dependent on the implementation of the
C library, and are not defined by GCC itself.
File: gcc.info, Node: C Extensions, Next: C++ Extensions, Prev: C Implementation, Up: Top
5 Extensions to the C Language Family
*************************************
GNU C provides several language features not found in ISO standard C.
(The `-pedantic' option directs GCC to print a warning message if any
of these features is used.) To test for the availability of these
features in conditional compilation, check for a predefined macro
`__GNUC__', which is always defined under GCC.
These extensions are available in C and Objective-C. Most of them are
also available in C++. *Note Extensions to the C++ Language: C++
Extensions, for extensions that apply _only_ to C++.
Some features that are in ISO C99 but not C89 or C++ are also, as
extensions, accepted by GCC in C89 mode and in C++.
* Menu:
* Statement Exprs:: Putting statements and declarations inside expressions.
* Local Labels:: Labels local to a block.
* Labels as Values:: Getting pointers to labels, and computed gotos.
* Nested Functions:: As in Algol and Pascal, lexical scoping of functions.
* Constructing Calls:: Dispatching a call to another function.
* Typeof:: `typeof': referring to the type of an expression.
* Conditionals:: Omitting the middle operand of a `?:' expression.
* Long Long:: Double-word integers---`long long int'.
* Complex:: Data types for complex numbers.
* Decimal Float:: Decimal Floating Types.
* Hex Floats:: Hexadecimal floating-point constants.
* Zero Length:: Zero-length arrays.
* Variable Length:: Arrays whose length is computed at run time.
* Empty Structures:: Structures with no members.
* Variadic Macros:: Macros with a variable number of arguments.
* Escaped Newlines:: Slightly looser rules for escaped newlines.
* Subscripting:: Any array can be subscripted, even if not an lvalue.
* Pointer Arith:: Arithmetic on `void'-pointers and function pointers.
* Initializers:: Non-constant initializers.
* Compound Literals:: Compound literals give structures, unions
or arrays as values.
* Designated Inits:: Labeling elements of initializers.
* Cast to Union:: Casting to union type from any member of the union.
* Case Ranges:: `case 1 ... 9' and such.
* Mixed Declarations:: Mixing declarations and code.
* Function Attributes:: Declaring that functions have no side effects,
or that they can never return.
* Attribute Syntax:: Formal syntax for attributes.
* Function Prototypes:: Prototype declarations and old-style definitions.
* C++ Comments:: C++ comments are recognized.
* Dollar Signs:: Dollar sign is allowed in identifiers.
* Character Escapes:: `\e' stands for the character <ESC>.
* Variable Attributes:: Specifying attributes of variables.
* Type Attributes:: Specifying attributes of types.
* Alignment:: Inquiring about the alignment of a type or variable.
* Inline:: Defining inline functions (as fast as macros).
* Extended Asm:: Assembler instructions with C expressions as operands.
(With them you can define ``built-in'' functions.)
* Constraints:: Constraints for asm operands
* Asm Labels:: Specifying the assembler name to use for a C symbol.
* Explicit Reg Vars:: Defining variables residing in specified registers.
* Alternate Keywords:: `__const__', `__asm__', etc., for header files.
* Incomplete Enums:: `enum foo;', with details to follow.
* Function Names:: Printable strings which are the name of the current
function.
* Return Address:: Getting the return or frame address of a function.
* Vector Extensions:: Using vector instructions through built-in functions.
* Offsetof:: Special syntax for implementing `offsetof'.
* Atomic Builtins:: Built-in functions for atomic memory access.
* Object Size Checking:: Built-in functions for limited buffer overflow
checking.
* Other Builtins:: Other built-in functions.
* Target Builtins:: Built-in functions specific to particular targets.
* Target Format Checks:: Format checks specific to particular targets.
* Pragmas:: Pragmas accepted by GCC.
* Unnamed Fields:: Unnamed struct/union fields within structs/unions.
* Thread-Local:: Per-thread variables.
File: gcc.info, Node: Statement Exprs, Next: Local Labels, Up: C Extensions
5.1 Statements and Declarations in Expressions
==============================================
A compound statement enclosed in parentheses may appear as an expression
in GNU C. This allows you to use loops, switches, and local variables
within an expression.
Recall that a compound statement is a sequence of statements surrounded
by braces; in this construct, parentheses go around the braces. For
example:
({ int y = foo (); int z;
if (y > 0) z = y;
else z = - y;
z; })
is a valid (though slightly more complex than necessary) expression for
the absolute value of `foo ()'.
The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct. (If you use some other kind of statement
last within the braces, the construct has type `void', and thus
effectively no value.)
This feature is especially useful in making macro definitions "safe"
(so that they evaluate each operand exactly once). For example, the
"maximum" function is commonly defined as a macro in standard C as
follows:
#define max(a,b) ((a) > (b) ? (a) : (b))
But this definition computes either A or B twice, with bad results if
the operand has side effects. In GNU C, if you know the type of the
operands (here taken as `int'), you can define the macro safely as
follows:
#define maxint(a,b) \
({int _a = (a), _b = (b); _a > _b ? _a : _b; })
Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit-field, or the
initial value of a static variable.
If you don't know the type of the operand, you can still do this, but
you must use `typeof' (*note Typeof::).
In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression. For instance, if `A' is a class, then
A a;
({a;}).Foo ()
will construct a temporary `A' object to hold the result of the
statement expression, and that will be used to invoke `Foo'. Therefore
the `this' pointer observed by `Foo' will not be the address of `a'.
Any temporaries created within a statement within a statement
expression will be destroyed at the statement's end. This makes
statement expressions inside macros slightly different from function
calls. In the latter case temporaries introduced during argument
evaluation will be destroyed at the end of the statement that includes
the function call. In the statement expression case they will be
destroyed during the statement expression. For instance,
#define macro(a) ({__typeof__(a) b = (a); b + 3; })
template<typename T> T function(T a) { T b = a; return b + 3; }
void foo ()
{
macro (X ());
function (X ());
}
will have different places where temporaries are destroyed. For the
`macro' case, the temporary `X' will be destroyed just after the
initialization of `b'. In the `function' case that temporary will be
destroyed when the function returns.
These considerations mean that it is probably a bad idea to use
statement-expressions of this form in header files that are designed to
work with C++. (Note that some versions of the GNU C Library contained
header files using statement-expression that lead to precisely this
bug.)
Jumping into a statement expression with `goto' or using a `switch'
statement outside the statement expression with a `case' or `default'
label inside the statement expression is not permitted. Jumping into a
statement expression with a computed `goto' (*note Labels as Values::)
yields undefined behavior. Jumping out of a statement expression is
permitted, but if the statement expression is part of a larger
expression then it is unspecified which other subexpressions of that
expression have been evaluated except where the language definition
requires certain subexpressions to be evaluated before or after the
statement expression. In any case, as with a function call the
evaluation of a statement expression is not interleaved with the
evaluation of other parts of the containing expression. For example,
foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();
will call `foo' and `bar1' and will not call `baz' but may or may not
call `bar2'. If `bar2' is called, it will be called after `foo' and
before `bar1'
File: gcc.info, Node: Local Labels, Next: Labels as Values, Prev: Statement Exprs, Up: C Extensions
5.2 Locally Declared Labels
===========================
GCC allows you to declare "local labels" in any nested block scope. A
local label is just like an ordinary label, but you can only reference
it (with a `goto' statement, or by taking its address) within the block
in which it was declared.
A local label declaration looks like this:
__label__ LABEL;
or
__label__ LABEL1, LABEL2, /* ... */;
Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.
The label declaration defines the label _name_, but does not define
the label itself. You must do this in the usual way, with `LABEL:',
within the statements of the statement expression.
The local label feature is useful for complex macros. If a macro
contains nested loops, a `goto' can be useful for breaking out of them.
However, an ordinary label whose scope is the whole function cannot be
used: if the macro can be expanded several times in one function, the
label will be multiply defined in that function. A local label avoids
this problem. For example:
#define SEARCH(value, array, target) \
do { \
__label__ found; \
typeof (target) _SEARCH_target = (target); \
typeof (*(array)) *_SEARCH_array = (array); \
int i, j; \
int value; \
for (i = 0; i < max; i++) \
for (j = 0; j < max; j++) \
if (_SEARCH_array[i][j] == _SEARCH_target) \
{ (value) = i; goto found; } \
(value) = -1; \
found:; \
} while (0)
This could also be written using a statement-expression:
#define SEARCH(array, target) \
({ \
__label__ found; \
typeof (target) _SEARCH_target = (target); \
typeof (*(array)) *_SEARCH_array = (array); \
int i, j; \
int value; \
for (i = 0; i < max; i++) \
for (j = 0; j < max; j++) \
if (_SEARCH_array[i][j] == _SEARCH_target) \
{ value = i; goto found; } \
value = -1; \
found: \
value; \
})
Local label declarations also make the labels they declare visible to
nested functions, if there are any. *Note Nested Functions::, for
details.
File: gcc.info, Node: Labels as Values, Next: Nested Functions, Prev: Local Labels, Up: C Extensions
5.3 Labels as Values
====================
You can get the address of a label defined in the current function (or
a containing function) with the unary operator `&&'. The value has
type `void *'. This value is a constant and can be used wherever a
constant of that type is valid. For example:
void *ptr;
/* ... */
ptr = &&foo;
To use these values, you need to be able to jump to one. This is done
with the computed goto statement(1), `goto *EXP;'. For example,
goto *ptr;
Any expression of type `void *' is allowed.
One way of using these constants is in initializing a static array that
will serve as a jump table:
static void *array[] = { &&foo, &&bar, &&hack };
Then you can select a label with indexing, like this:
goto *array[i];
Note that this does not check whether the subscript is in bounds--array
indexing in C never does that.
Such an array of label values serves a purpose much like that of the
`switch' statement. The `switch' statement is cleaner, so use that
rather than an array unless the problem does not fit a `switch'
statement very well.
Another use of label values is in an interpreter for threaded code.
The labels within the interpreter function can be stored in the
threaded code for super-fast dispatching.
You may not use this mechanism to jump to code in a different function.
If you do that, totally unpredictable things will happen. The best way
to avoid this is to store the label address only in automatic variables
and never pass it as an argument.
An alternate way to write the above example is
static const int array[] = { &&foo - &&foo, &&bar - &&foo,
&&hack - &&foo };
goto *(&&foo + array[i]);
This is more friendly to code living in shared libraries, as it reduces
the number of dynamic relocations that are needed, and by consequence,
allows the data to be read-only.
---------- Footnotes ----------
(1) The analogous feature in Fortran is called an assigned goto, but
that name seems inappropriate in C, where one can do more than simply
store label addresses in label variables.
File: gcc.info, Node: Nested Functions, Next: Constructing Calls, Prev: Labels as Values, Up: C Extensions
5.4 Nested Functions
====================
A "nested function" is a function defined inside another function.
(Nested functions are not supported for GNU C++.) The nested function's
name is local to the block where it is defined. For example, here we
define a nested function named `square', and call it twice:
foo (double a, double b)
{
double square (double z) { return z * z; }
return square (a) + square (b);
}
The nested function can access all the variables of the containing
function that are visible at the point of its definition. This is
called "lexical scoping". For example, here we show a nested function
which uses an inherited variable named `offset':
bar (int *array, int offset, int size)
{
int access (int *array, int index)
{ return array[index + offset]; }
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
}
Nested function definitions are permitted within functions in the
places where variable definitions are allowed; that is, in any block,
mixed with the other declarations and statements in the block.
It is possible to call the nested function from outside the scope of
its name by storing its address or passing the address to another
function:
hack (int *array, int size)
{
void store (int index, int value)
{ array[index] = value; }
intermediate (store, size);
}
Here, the function `intermediate' receives the address of `store' as
an argument. If `intermediate' calls `store', the arguments given to
`store' are used to store into `array'. But this technique works only
so long as the containing function (`hack', in this example) does not
exit.
If you try to call the nested function through its address after the
containing function has exited, all hell will break loose. If you try
to call it after a containing scope level has exited, and if it refers
to some of the variables that are no longer in scope, you may be lucky,
but it's not wise to take the risk. If, however, the nested function
does not refer to anything that has gone out of scope, you should be
safe.
GCC implements taking the address of a nested function using a
technique called "trampolines". A paper describing them is available as
`http://people.debian.org/~aaronl/Usenix88-lexic.pdf'.
A nested function can jump to a label inherited from a containing
function, provided the label was explicitly declared in the containing
function (*note Local Labels::). Such a jump returns instantly to the
containing function, exiting the nested function which did the `goto'
and any intermediate functions as well. Here is an example:
bar (int *array, int offset, int size)
{
__label__ failure;
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
/* ... */
return 0;
/* Control comes here from `access'
if it detects an error. */
failure:
return -1;
}
A nested function always has no linkage. Declaring one with `extern'
or `static' is erroneous. If you need to declare the nested function
before its definition, use `auto' (which is otherwise meaningless for
function declarations).
bar (int *array, int offset, int size)
{
__label__ failure;
auto int access (int *, int);
/* ... */
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
/* ... */
}
File: gcc.info, Node: Constructing Calls, Next: Typeof, Prev: Nested Functions, Up: C Extensions
5.5 Constructing Function Calls
===============================
Using the built-in functions described below, you can record the
arguments a function received, and call another function with the same
arguments, without knowing the number or types of the arguments.
You can also record the return value of that function call, and later
return that value, without knowing what data type the function tried to
return (as long as your caller expects that data type).
However, these built-in functions may interact badly with some
sophisticated features or other extensions of the language. It is,
therefore, not recommended to use them outside very simple functions
acting as mere forwarders for their arguments.
-- Built-in Function: void * __builtin_apply_args ()
This built-in function returns a pointer to data describing how to
perform a call with the same arguments as were passed to the
current function.
The function saves the arg pointer register, structure value
address, and all registers that might be used to pass arguments to
a function into a block of memory allocated on the stack. Then it
returns the address of that block.
-- Built-in Function: void * __builtin_apply (void (*FUNCTION)(), void
*ARGUMENTS, size_t SIZE)
This built-in function invokes FUNCTION with a copy of the
parameters described by ARGUMENTS and SIZE.
The value of ARGUMENTS should be the value returned by
`__builtin_apply_args'. The argument SIZE specifies the size of
the stack argument data, in bytes.
This function returns a pointer to data describing how to return
whatever value was returned by FUNCTION. The data is saved in a
block of memory allocated on the stack.
It is not always simple to compute the proper value for SIZE. The
value is used by `__builtin_apply' to compute the amount of data
that should be pushed on the stack and copied from the incoming
argument area.
-- Built-in Function: void __builtin_return (void *RESULT)
This built-in function returns the value described by RESULT from
the containing function. You should specify, for RESULT, a value
returned by `__builtin_apply'.
File: gcc.info, Node: Typeof, Next: Conditionals, Prev: Constructing Calls, Up: C Extensions
5.6 Referring to a Type with `typeof'
=====================================
Another way to refer to the type of an expression is with `typeof'.
The syntax of using of this keyword looks like `sizeof', but the
construct acts semantically like a type name defined with `typedef'.
There are two ways of writing the argument to `typeof': with an
expression or with a type. Here is an example with an expression:
typeof (x[0](1))
This assumes that `x' is an array of pointers to functions; the type
described is that of the values of the functions.
Here is an example with a typename as the argument:
typeof (int *)
Here the type described is that of pointers to `int'.
If you are writing a header file that must work when included in ISO C
programs, write `__typeof__' instead of `typeof'. *Note Alternate
Keywords::.
A `typeof'-construct can be used anywhere a typedef name could be
used. For example, you can use it in a declaration, in a cast, or
inside of `sizeof' or `typeof'.
`typeof' is often useful in conjunction with the
statements-within-expressions feature. Here is how the two together can
be used to define a safe "maximum" macro that operates on any
arithmetic type and evaluates each of its arguments exactly once:
#define max(a,b) \
({ typeof (a) _a = (a); \
typeof (b) _b = (b); \
_a > _b ? _a : _b; })
The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within
the expressions that are substituted for `a' and `b'. Eventually we
hope to design a new form of declaration syntax that allows you to
declare variables whose scopes start only after their initializers;
this will be a more reliable way to prevent such conflicts.
Some more examples of the use of `typeof':
* This declares `y' with the type of what `x' points to.
typeof (*x) y;
* This declares `y' as an array of such values.
typeof (*x) y[4];
* This declares `y' as an array of pointers to characters:
typeof (typeof (char *)[4]) y;
It is equivalent to the following traditional C declaration:
char *y[4];
To see the meaning of the declaration using `typeof', and why it
might be a useful way to write, rewrite it with these macros:
#define pointer(T) typeof(T *)
#define array(T, N) typeof(T [N])
Now the declaration can be rewritten this way:
array (pointer (char), 4) y;
Thus, `array (pointer (char), 4)' is the type of arrays of 4
pointers to `char'.
_Compatibility Note:_ In addition to `typeof', GCC 2 supported a more
limited extension which permitted one to write
typedef T = EXPR;
with the effect of declaring T to have the type of the expression EXPR.
This extension does not work with GCC 3 (versions between 3.0 and 3.2
will crash; 3.2.1 and later give an error). Code which relies on it
should be rewritten to use `typeof':
typedef typeof(EXPR) T;
This will work with all versions of GCC.
File: gcc.info, Node: Conditionals, Next: Long Long, Prev: Typeof, Up: C Extensions
5.7 Conditionals with Omitted Operands
======================================
The middle operand in a conditional expression may be omitted. Then if
the first operand is nonzero, its value is the value of the conditional
expression.
Therefore, the expression
x ? : y
has the value of `x' if that is nonzero; otherwise, the value of `y'.
This example is perfectly equivalent to
x ? x : y
In this simple case, the ability to omit the middle operand is not
especially useful. When it becomes useful is when the first operand
does, or may (if it is a macro argument), contain a side effect. Then
repeating the operand in the middle would perform the side effect
twice. Omitting the middle operand uses the value already computed
without the undesirable effects of recomputing it.
File: gcc.info, Node: Long Long, Next: Complex, Prev: Conditionals, Up: C Extensions
5.8 Double-Word Integers
========================
ISO C99 supports data types for integers that are at least 64 bits wide,
and as an extension GCC supports them in C89 mode and in C++. Simply
write `long long int' for a signed integer, or `unsigned long long int'
for an unsigned integer. To make an integer constant of type `long
long int', add the suffix `LL' to the integer. To make an integer
constant of type `unsigned long long int', add the suffix `ULL' to the
integer.
You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines. Multiplication is open-coded
if the machine supports fullword-to-doubleword a widening multiply
instruction. Division and shifts are open-coded only on machines that
provide special support. The operations that are not open-coded use
special library routines that come with GCC.
There may be pitfalls when you use `long long' types for function
arguments, unless you declare function prototypes. If a function
expects type `int' for its argument, and you pass a value of type `long
long int', confusion will result because the caller and the subroutine
will disagree about the number of bytes for the argument. Likewise, if
the function expects `long long int' and you pass `int'. The best way
to avoid such problems is to use prototypes.
File: gcc.info, Node: Complex, Next: Decimal Float, Prev: Long Long, Up: C Extensions
5.9 Complex Numbers
===================
ISO C99 supports complex floating data types, and as an extension GCC
supports them in C89 mode and in C++, and supports complex integer data
types which are not part of ISO C99. You can declare complex types
using the keyword `_Complex'. As an extension, the older GNU keyword
`__complex__' is also supported.
For example, `_Complex double x;' declares `x' as a variable whose
real part and imaginary part are both of type `double'. `_Complex
short int y;' declares `y' to have real and imaginary parts of type
`short int'; this is not likely to be useful, but it shows that the set
of complex types is complete.
To write a constant with a complex data type, use the suffix `i' or
`j' (either one; they are equivalent). For example, `2.5fi' has type
`_Complex float' and `3i' has type `_Complex int'. Such a constant
always has a pure imaginary value, but you can form any complex value
you like by adding one to a real constant. This is a GNU extension; if
you have an ISO C99 conforming C library (such as GNU libc), and want
to construct complex constants of floating type, you should include
`<complex.h>' and use the macros `I' or `_Complex_I' instead.
To extract the real part of a complex-valued expression EXP, write
`__real__ EXP'. Likewise, use `__imag__' to extract the imaginary
part. This is a GNU extension; for values of floating type, you should
use the ISO C99 functions `crealf', `creal', `creall', `cimagf',
`cimag' and `cimagl', declared in `<complex.h>' and also provided as
built-in functions by GCC.
The operator `~' performs complex conjugation when used on a value
with a complex type. This is a GNU extension; for values of floating
type, you should use the ISO C99 functions `conjf', `conj' and `conjl',
declared in `<complex.h>' and also provided as built-in functions by
GCC.
GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice-versa). Only the DWARF2
debug info format can represent this, so use of DWARF2 is recommended.
If you are using the stabs debug info format, GCC describes a
noncontiguous complex variable as if it were two separate variables of
noncomplex type. If the variable's actual name is `foo', the two
fictitious variables are named `foo$real' and `foo$imag'. You can
examine and set these two fictitious variables with your debugger.
File: gcc.info, Node: Decimal Float, Next: Hex Floats, Prev: Complex, Up: C Extensions
5.10 Decimal Floating Types
===========================
As an extension, the GNU C compiler supports decimal floating types as
defined in the N1176 draft of ISO/IEC WDTR24732. Support for decimal
floating types in GCC will evolve as the draft technical report changes.
Calling conventions for any target might also change. Not all targets
support decimal floating types.
The decimal floating types are `_Decimal32', `_Decimal64', and
`_Decimal128'. They use a radix of ten, unlike the floating types
`float', `double', and `long double' whose radix is not specified by
the C standard but is usually two.
Support for decimal floating types includes the arithmetic operators
add, subtract, multiply, divide; unary arithmetic operators; relational
operators; equality operators; and conversions to and from integer and
other floating types. Use a suffix `df' or `DF' in a literal constant
of type `_Decimal32', `dd' or `DD' for `_Decimal64', and `dl' or `DL'
for `_Decimal128'.
GCC support of decimal float as specified by the draft technical report
is incomplete:
* Translation time data type (TTDT) is not supported.
* Characteristics of decimal floating types are defined in header
file `decfloat.h' rather than `float.h'.
* When the value of a decimal floating type cannot be represented in
the integer type to which it is being converted, the result is
undefined rather than the result value specified by the draft
technical report.
Types `_Decimal32', `_Decimal64', and `_Decimal128' are supported by
the DWARF2 debug information format.
File: gcc.info, Node: Hex Floats, Next: Zero Length, Prev: Decimal Float, Up: C Extensions
5.11 Hex Floats
===============
ISO C99 supports floating-point numbers written not only in the usual
decimal notation, such as `1.55e1', but also numbers such as `0x1.fp3'
written in hexadecimal format. As a GNU extension, GCC supports this
in C89 mode (except in some cases when strictly conforming) and in C++.
In that format the `0x' hex introducer and the `p' or `P' exponent
field are mandatory. The exponent is a decimal number that indicates
the power of 2 by which the significant part will be multiplied. Thus
`0x1.f' is 1 15/16, `p3' multiplies it by 8, and the value of `0x1.fp3'
is the same as `1.55e1'.
Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation. Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., `0x1.f'. This
could mean `1.0f' or `1.9375' since `f' is also the extension for
floating-point constants of type `float'.
File: gcc.info, Node: Zero Length, Next: Variable Length, Prev: Hex Floats, Up: C Extensions
5.12 Arrays of Length Zero
==========================
Zero-length arrays are allowed in GNU C. They are very useful as the
last element of a structure which is really a header for a
variable-length object:
struct line {
int length;
char contents[0];
};
struct line *thisline = (struct line *)
malloc (sizeof (struct line) + this_length);
thisline->length = this_length;
In ISO C90, you would have to give `contents' a length of 1, which
means either you waste space or complicate the argument to `malloc'.
In ISO C99, you would use a "flexible array member", which is slightly
different in syntax and semantics:
* Flexible array members are written as `contents[]' without the `0'.
* Flexible array members have incomplete type, and so the `sizeof'
operator may not be applied. As a quirk of the original
implementation of zero-length arrays, `sizeof' evaluates to zero.
* Flexible array members may only appear as the last member of a
`struct' that is otherwise non-empty.
* A structure containing a flexible array member, or a union
containing such a structure (possibly recursively), may not be a
member of a structure or an element of an array. (However, these
uses are permitted by GCC as extensions.)
GCC versions before 3.0 allowed zero-length arrays to be statically
initialized, as if they were flexible arrays. In addition to those
cases that were useful, it also allowed initializations in situations
that would corrupt later data. Non-empty initialization of zero-length
arrays is now treated like any case where there are more initializer
elements than the array holds, in that a suitable warning about "excess
elements in array" is given, and the excess elements (all of them, in
this case) are ignored.
Instead GCC allows static initialization of flexible array members.
This is equivalent to defining a new structure containing the original
structure followed by an array of sufficient size to contain the data.
I.e. in the following, `f1' is constructed as if it were declared like
`f2'.
struct f1 {
int x; int y[];
} f1 = { 1, { 2, 3, 4 } };
struct f2 {
struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } };
The convenience of this extension is that `f1' has the desired type,
eliminating the need to consistently refer to `f2.f1'.
This has symmetry with normal static arrays, in that an array of
unknown size is also written with `[]'.
Of course, this extension only makes sense if the extra data comes at
the end of a top-level object, as otherwise we would be overwriting
data at subsequent offsets. To avoid undue complication and confusion
with initialization of deeply nested arrays, we simply disallow any
non-empty initialization except when the structure is the top-level
object. For example:
struct foo { int x; int y[]; };
struct bar { struct foo z; };
struct foo a = { 1, { 2, 3, 4 } }; // Valid.
struct bar b = { { 1, { 2, 3, 4 } } }; // Invalid.
struct bar c = { { 1, { } } }; // Valid.
struct foo d[1] = { { 1 { 2, 3, 4 } } }; // Invalid.
File: gcc.info, Node: Empty Structures, Next: Variadic Macros, Prev: Variable Length, Up: C Extensions
5.13 Structures With No Members
===============================
GCC permits a C structure to have no members:
struct empty {
};
The structure will have size zero. In C++, empty structures are part
of the language. G++ treats empty structures as if they had a single
member of type `char'.
File: gcc.info, Node: Variable Length, Next: Empty Structures, Prev: Zero Length, Up: C Extensions
5.14 Arrays of Variable Length
==============================
Variable-length automatic arrays are allowed in ISO C99, and as an
extension GCC accepts them in C89 mode and in C++. (However, GCC's
implementation of variable-length arrays does not yet conform in detail
to the ISO C99 standard.) These arrays are declared like any other
automatic arrays, but with a length that is not a constant expression.
The storage is allocated at the point of declaration and deallocated
when the brace-level is exited. For example:
FILE *
concat_fopen (char *s1, char *s2, char *mode)
{
char str[strlen (s1) + strlen (s2) + 1];
strcpy (str, s1);
strcat (str, s2);
return fopen (str, mode);
}
Jumping or breaking out of the scope of the array name deallocates the
storage. Jumping into the scope is not allowed; you get an error
message for it.
You can use the function `alloca' to get an effect much like
variable-length arrays. The function `alloca' is available in many
other C implementations (but not in all). On the other hand,
variable-length arrays are more elegant.
There are other differences between these two methods. Space allocated
with `alloca' exists until the containing _function_ returns. The
space for a variable-length array is deallocated as soon as the array
name's scope ends. (If you use both variable-length arrays and
`alloca' in the same function, deallocation of a variable-length array
will also deallocate anything more recently allocated with `alloca'.)
You can also use variable-length arrays as arguments to functions:
struct entry
tester (int len, char data[len][len])
{
/* ... */
}
The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
`sizeof'.
If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list--another GNU extension.
struct entry
tester (int len; char data[len][len], int len)
{
/* ... */
}
The `int len' before the semicolon is a "parameter forward
declaration", and it serves the purpose of making the name `len' known
when the declaration of `data' is parsed.
You can write any number of such parameter forward declarations in the
parameter list. They can be separated by commas or semicolons, but the
last one must end with a semicolon, which is followed by the "real"
parameter declarations. Each forward declaration must match a "real"
declaration in parameter name and data type. ISO C99 does not support
parameter forward declarations.
File: gcc.info, Node: Variadic Macros, Next: Escaped Newlines, Prev: Empty Structures, Up: C Extensions
5.15 Macros with a Variable Number of Arguments.
================================================
In the ISO C standard of 1999, a macro can be declared to accept a
variable number of arguments much as a function can. The syntax for
defining the macro is similar to that of a function. Here is an
example:
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)
Here `...' is a "variable argument". In the invocation of such a
macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas. This set of
tokens replaces the identifier `__VA_ARGS__' in the macro body wherever
it appears. See the CPP manual for more information.
GCC has long supported variadic macros, and used a different syntax
that allowed you to give a name to the variable arguments just like any
other argument. Here is an example:
#define debug(format, args...) fprintf (stderr, format, args)
This is in all ways equivalent to the ISO C example above, but arguably
more readable and descriptive.
GNU CPP has two further variadic macro extensions, and permits them to
be used with either of the above forms of macro definition.
In standard C, you are not allowed to leave the variable argument out
entirely; but you are allowed to pass an empty argument. For example,
this invocation is invalid in ISO C, because there is no comma after
the string:
debug ("A message")
GNU CPP permits you to completely omit the variable arguments in this
way. In the above examples, the compiler would complain, though since
the expansion of the macro still has the extra comma after the format
string.
To help solve this problem, CPP behaves specially for variable
arguments used with the token paste operator, `##'. If instead you
write
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)
and if the variable arguments are omitted or empty, the `##' operator
causes the preprocessor to remove the comma before it. If you do
provide some variable arguments in your macro invocation, GNU CPP does
not complain about the paste operation and instead places the variable
arguments after the comma. Just like any other pasted macro argument,
these arguments are not macro expanded.
File: gcc.info, Node: Escaped Newlines, Next: Subscripting, Prev: Variadic Macros, Up: C Extensions
5.16 Slightly Looser Rules for Escaped Newlines
===============================================
Recently, the preprocessor has relaxed its treatment of escaped
newlines. Previously, the newline had to immediately follow a
backslash. The current implementation allows whitespace in the form of
spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline. The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line. This works within comments and
tokens, as well as between tokens. Comments are _not_ treated as
whitespace for the purposes of this relaxation, since they have not yet
been replaced with spaces.
File: gcc.info, Node: Subscripting, Next: Pointer Arith, Prev: Escaped Newlines, Up: C Extensions
5.17 Non-Lvalue Arrays May Have Subscripts
==========================================
In ISO C99, arrays that are not lvalues still decay to pointers, and
may be subscripted, although they may not be modified or used after the
next sequence point and the unary `&' operator may not be applied to
them. As an extension, GCC allows such arrays to be subscripted in C89
mode, though otherwise they do not decay to pointers outside C99 mode.
For example, this is valid in GNU C though not valid in C89:
struct foo {int a[4];};
struct foo f();
bar (int index)
{
return f().a[index];
}
File: gcc.info, Node: Pointer Arith, Next: Initializers, Prev: Subscripting, Up: C Extensions
5.18 Arithmetic on `void'- and Function-Pointers
================================================
In GNU C, addition and subtraction operations are supported on pointers
to `void' and on pointers to functions. This is done by treating the
size of a `void' or of a function as 1.
A consequence of this is that `sizeof' is also allowed on `void' and
on function types, and returns 1.
The option `-Wpointer-arith' requests a warning if these extensions
are used.
File: gcc.info, Node: Initializers, Next: Compound Literals, Prev: Pointer Arith, Up: C Extensions
5.19 Non-Constant Initializers
==============================
As in standard C++ and ISO C99, the elements of an aggregate
initializer for an automatic variable are not required to be constant
expressions in GNU C. Here is an example of an initializer with
run-time varying elements:
foo (float f, float g)
{
float beat_freqs[2] = { f-g, f+g };
/* ... */
}
File: gcc.info, Node: Compound Literals, Next: Designated Inits, Prev: Initializers, Up: C Extensions
5.20 Compound Literals
======================
ISO C99 supports compound literals. A compound literal looks like a
cast containing an initializer. Its value is an object of the type
specified in the cast, containing the elements specified in the
initializer; it is an lvalue. As an extension, GCC supports compound
literals in C89 mode and in C++.
Usually, the specified type is a structure. Assume that `struct foo'
and `structure' are declared as shown:
struct foo {int a; char b[2];} structure;
Here is an example of constructing a `struct foo' with a compound
literal:
structure = ((struct foo) {x + y, 'a', 0});
This is equivalent to writing the following:
{
struct foo temp = {x + y, 'a', 0};
structure = temp;
}
You can also construct an array. If all the elements of the compound
literal are (made up of) simple constant expressions, suitable for use
in initializers of objects of static storage duration, then the compound
literal can be coerced to a pointer to its first element and used in
such an initializer, as shown here:
char **foo = (char *[]) { "x", "y", "z" };
Compound literals for scalar types and union types are is also
allowed, but then the compound literal is equivalent to a cast.
As a GNU extension, GCC allows initialization of objects with static
storage duration by compound literals (which is not possible in ISO
C99, because the initializer is not a constant). It is handled as if
the object was initialized only with the bracket enclosed list if the
types of the compound literal and the object match. The initializer
list of the compound literal must be constant. If the object being
initialized has array type of unknown size, the size is determined by
compound literal size.
static struct foo x = (struct foo) {1, 'a', 'b'};
static int y[] = (int []) {1, 2, 3};
static int z[] = (int [3]) {1};
The above lines are equivalent to the following:
static struct foo x = {1, 'a', 'b'};
static int y[] = {1, 2, 3};
static int z[] = {1, 0, 0};
File: gcc.info, Node: Designated Inits, Next: Cast to Union, Prev: Compound Literals, Up: C Extensions
5.21 Designated Initializers
============================
Standard C89 requires the elements of an initializer to appear in a
fixed order, the same as the order of the elements in the array or
structure being initialized.
In ISO C99 you can give the elements in any order, specifying the array
indices or structure field names they apply to, and GNU C allows this as
an extension in C89 mode as well. This extension is not implemented in
GNU C++.
To specify an array index, write `[INDEX] =' before the element value.
For example,
int a[6] = { [4] = 29, [2] = 15 };
is equivalent to
int a[6] = { 0, 0, 15, 0, 29, 0 };
The index values must be constant expressions, even if the array being
initialized is automatic.
An alternative syntax for this which has been obsolete since GCC 2.5
but GCC still accepts is to write `[INDEX]' before the element value,
with no `='.
To initialize a range of elements to the same value, write `[FIRST ...
LAST] = VALUE'. This is a GNU extension. For example,
int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };
If the value in it has side-effects, the side-effects will happen only
once, not for each initialized field by the range initializer.
Note that the length of the array is the highest value specified plus
one.
In a structure initializer, specify the name of a field to initialize
with `.FIELDNAME =' before the element value. For example, given the
following structure,
struct point { int x, y; };
the following initialization
struct point p = { .y = yvalue, .x = xvalue };
is equivalent to
struct point p = { xvalue, yvalue };
Another syntax which has the same meaning, obsolete since GCC 2.5, is
`FIELDNAME:', as shown here:
struct point p = { y: yvalue, x: xvalue };
The `[INDEX]' or `.FIELDNAME' is known as a "designator". You can
also use a designator (or the obsolete colon syntax) when initializing
a union, to specify which element of the union should be used. For
example,
union foo { int i; double d; };
union foo f = { .d = 4 };
will convert 4 to a `double' to store it in the union using the second
element. By contrast, casting 4 to type `union foo' would store it
into the union as the integer `i', since it is an integer. (*Note Cast
to Union::.)
You can combine this technique of naming elements with ordinary C
initialization of successive elements. Each initializer element that
does not have a designator applies to the next consecutive element of
the array or structure. For example,
int a[6] = { [1] = v1, v2, [4] = v4 };
is equivalent to
int a[6] = { 0, v1, v2, 0, v4, 0 };
Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an `enum' type. For
example:
int whitespace[256]
= { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };
You can also write a series of `.FIELDNAME' and `[INDEX]' designators
before an `=' to specify a nested subobject to initialize; the list is
taken relative to the subobject corresponding to the closest
surrounding brace pair. For example, with the `struct point'
declaration above:
struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };
If the same field is initialized multiple times, it will have value from
the last initialization. If any such overridden initialization has
side-effect, it is unspecified whether the side-effect happens or not.
Currently, GCC will discard them and issue a warning.
File: gcc.info, Node: Case Ranges, Next: Mixed Declarations, Prev: Cast to Union, Up: C Extensions
5.22 Case Ranges
================
You can specify a range of consecutive values in a single `case' label,
like this:
case LOW ... HIGH:
This has the same effect as the proper number of individual `case'
labels, one for each integer value from LOW to HIGH, inclusive.
This feature is especially useful for ranges of ASCII character codes:
case 'A' ... 'Z':
*Be careful:* Write spaces around the `...', for otherwise it may be
parsed wrong when you use it with integer values. For example, write
this:
case 1 ... 5:
rather than this:
case 1...5:
File: gcc.info, Node: Cast to Union, Next: Case Ranges, Prev: Designated Inits, Up: C Extensions
5.23 Cast to a Union Type
=========================
A cast to union type is similar to other casts, except that the type
specified is a union type. You can specify the type either with `union
TAG' or with a typedef name. A cast to union is actually a constructor
though, not a cast, and hence does not yield an lvalue like normal
casts. (*Note Compound Literals::.)
The types that may be cast to the union type are those of the members
of the union. Thus, given the following union and variables:
union foo { int i; double d; };
int x;
double y;
both `x' and `y' can be cast to type `union foo'.
Using the cast as the right-hand side of an assignment to a variable of
union type is equivalent to storing in a member of the union:
union foo u;
/* ... */
u = (union foo) x == u.i = x
u = (union foo) y == u.d = y
You can also use the union cast as a function argument:
void hack (union foo);
/* ... */
hack ((union foo) x);
File: gcc.info, Node: Mixed Declarations, Next: Function Attributes, Prev: Case Ranges, Up: C Extensions
5.24 Mixed Declarations and Code
================================
ISO C99 and ISO C++ allow declarations and code to be freely mixed
within compound statements. As an extension, GCC also allows this in
C89 mode. For example, you could do:
int i;
/* ... */
i++;
int j = i + 2;
Each identifier is visible from where it is declared until the end of
the enclosing block.
File: gcc.info, Node: Function Attributes, Next: Attribute Syntax, Prev: Mixed Declarations, Up: C Extensions
5.25 Declaring Attributes of Functions
======================================
In GNU C, you declare certain things about functions called in your
program which help the compiler optimize function calls and check your
code more carefully.
The keyword `__attribute__' allows you to specify special attributes
when making a declaration. This keyword is followed by an attribute
specification inside double parentheses. The following attributes are
currently defined for functions on all targets: `noreturn',
`returns_twice', `noinline', `always_inline', `flatten', `pure',
`const', `nothrow', `sentinel', `format', `format_arg',
`no_instrument_function', `section', `constructor', `destructor',
`used', `unused', `deprecated', `weak', `malloc', `alias',
`warn_unused_result', `nonnull', `gnu_inline' and `externally_visible'.
Several other attributes are defined for functions on particular
target systems. Other attributes, including `section' are supported
for variables declarations (*note Variable Attributes::) and for types
(*note Type Attributes::).
You may also specify attributes with `__' preceding and following each
keyword. This allows you to use them in header files without being
concerned about a possible macro of the same name. For example, you
may use `__noreturn__' instead of `noreturn'.
*Note Attribute Syntax::, for details of the exact syntax for using
attributes.
`alias ("TARGET")'
The `alias' attribute causes the declaration to be emitted as an
alias for another symbol, which must be specified. For instance,
void __f () { /* Do something. */; }
void f () __attribute__ ((weak, alias ("__f")));
defines `f' to be a weak alias for `__f'. In C++, the mangled
name for the target must be used. It is an error if `__f' is not
defined in the same translation unit.
Not all target machines support this attribute.
`always_inline'
Generally, functions are not inlined unless optimization is
specified. For functions declared inline, this attribute inlines
the function even if no optimization level was specified.
`gnu_inline'
This attribute should be used with a function which is also
declared with the `inline' keyword. It directs GCC to treat the
function as if it were defined in gnu89 mode even when compiling
in C99 or gnu99 mode.
If the function is declared `extern', then this definition of the
function is used only for inlining. In no case is the function
compiled as a standalone function, not even if you take its address
explicitly. Such an address becomes an external reference, as if
you had only declared the function, and had not defined it. This
has almost the effect of a macro. The way to use this is to put a
function definition in a header file with this attribute, and put
another copy of the function, without `extern', in a library file.
The definition in the header file will cause most calls to the
function to be inlined. If any uses of the function remain, they
will refer to the single copy in the library. Note that the two
definitions of the functions need not be precisely the same,
although if they do not have the same effect your program may
behave oddly.
If the function is neither `extern' nor `static', then the
function is compiled as a standalone function, as well as being
inlined where possible.
This is how GCC traditionally handled functions declared `inline'.
Since ISO C99 specifies a different semantics for `inline', this
function attribute is provided as a transition measure and as a
useful feature in its own right. This attribute is available in
GCC 4.1.3 and later. It is available if either of the
preprocessor macros `__GNUC_GNU_INLINE__' or
`__GNUC_STDC_INLINE__' are defined. *Note An Inline Function is
As Fast As a Macro: Inline.
Note that since the first version of GCC to support C99 inline
semantics is 4.3, earlier versions of GCC which accept this
attribute effectively assume that it is always present, whether or
not it is given explicitly. In versions prior to 4.3, the only
effect of explicitly including it is to disable warnings about
using inline functions in C99 mode.
`flatten'
Generally, inlining into a function is limited. For a function
marked with this attribute, every call inside this function will
be inlined, if possible. Whether the function itself is
considered for inlining depends on its size and the current
inlining parameters. The `flatten' attribute only works reliably
in unit-at-a-time mode.
`cdecl'
On the Intel 386, the `cdecl' attribute causes the compiler to
assume that the calling function will pop off the stack space used
to pass arguments. This is useful to override the effects of the
`-mrtd' switch.
`const'
Many functions do not examine any values except their arguments,
and have no effects except the return value. Basically this is
just slightly more strict class than the `pure' attribute below,
since function is not allowed to read global memory.
Note that a function that has pointer arguments and examines the
data pointed to must _not_ be declared `const'. Likewise, a
function that calls a non-`const' function usually must not be
`const'. It does not make sense for a `const' function to return
`void'.
The attribute `const' is not implemented in GCC versions earlier
than 2.5. An alternative way to declare that a function has no
side effects, which works in the current version and in some older
versions, is as follows:
typedef int intfn ();
extern const intfn square;
This approach does not work in GNU C++ from 2.6.0 on, since the
language specifies that the `const' must be attached to the return
value.
`constructor'
`destructor'
The `constructor' attribute causes the function to be called
automatically before execution enters `main ()'. Similarly, the
`destructor' attribute causes the function to be called
automatically after `main ()' has completed or `exit ()' has been
called. Functions with these attributes are useful for
initializing data that will be used implicitly during the
execution of the program.
These attributes are not currently implemented for Objective-C.
`deprecated'
The `deprecated' attribute results in a warning if the function is
used anywhere in the source file. This is useful when identifying
functions that are expected to be removed in a future version of a
program. The warning also includes the location of the declaration
of the deprecated function, to enable users to easily find further
information about why the function is deprecated, or what they
should do instead. Note that the warnings only occurs for uses:
int old_fn () __attribute__ ((deprecated));
int old_fn ();
int (*fn_ptr)() = old_fn;
results in a warning on line 3 but not line 2.
The `deprecated' attribute can also be used for variables and
types (*note Variable Attributes::, *note Type Attributes::.)
`dllexport'
On Microsoft Windows targets and Symbian OS targets the
`dllexport' attribute causes the compiler to provide a global
pointer to a pointer in a DLL, so that it can be referenced with
the `dllimport' attribute. On Microsoft Windows targets, the
pointer name is formed by combining `_imp__' and the function or
variable name.
You can use `__declspec(dllexport)' as a synonym for
`__attribute__ ((dllexport))' for compatibility with other
compilers.
On systems that support the `visibility' attribute, this attribute
also implies "default" visibility, unless a `visibility' attribute
is explicitly specified. You should avoid the use of `dllexport'
with "hidden" or "internal" visibility; in the future GCC may
issue an error for those cases.
Currently, the `dllexport' attribute is ignored for inlined
functions, unless the `-fkeep-inline-functions' flag has been
used. The attribute is also ignored for undefined symbols.
When applied to C++ classes, the attribute marks defined
non-inlined member functions and static data members as exports.
Static consts initialized in-class are not marked unless they are
also defined out-of-class.
For Microsoft Windows targets there are alternative methods for
including the symbol in the DLL's export table such as using a
`.def' file with an `EXPORTS' section or, with GNU ld, using the
`--export-all' linker flag.
`dllimport'
On Microsoft Windows and Symbian OS targets, the `dllimport'
attribute causes the compiler to reference a function or variable
via a global pointer to a pointer that is set up by the DLL
exporting the symbol. The attribute implies `extern' storage. On
Microsoft Windows targets, the pointer name is formed by combining
`_imp__' and the function or variable name.
You can use `__declspec(dllimport)' as a synonym for
`__attribute__ ((dllimport))' for compatibility with other
compilers.
Currently, the attribute is ignored for inlined functions. If the
attribute is applied to a symbol _definition_, an error is
reported. If a symbol previously declared `dllimport' is later
defined, the attribute is ignored in subsequent references, and a
warning is emitted. The attribute is also overridden by a
subsequent declaration as `dllexport'.
When applied to C++ classes, the attribute marks non-inlined
member functions and static data members as imports. However, the
attribute is ignored for virtual methods to allow creation of
vtables using thunks.
On the SH Symbian OS target the `dllimport' attribute also has
another affect--it can cause the vtable and run-time type
information for a class to be exported. This happens when the
class has a dllimport'ed constructor or a non-inline, non-pure
virtual function and, for either of those two conditions, the
class also has a inline constructor or destructor and has a key
function that is defined in the current translation unit.
For Microsoft Windows based targets the use of the `dllimport'
attribute on functions is not necessary, but provides a small
performance benefit by eliminating a thunk in the DLL. The use of
the `dllimport' attribute on imported variables was required on
older versions of the GNU linker, but can now be avoided by
passing the `--enable-auto-import' switch to the GNU linker. As
with functions, using the attribute for a variable eliminates a
thunk in the DLL.
One drawback to using this attribute is that a pointer to a
function or variable marked as `dllimport' cannot be used as a
constant address. On Microsoft Windows targets, the attribute can
be disabled for functions by setting the `-mnop-fun-dllimport'
flag.
`eightbit_data'
Use this attribute on the H8/300, H8/300H, and H8S to indicate
that the specified variable should be placed into the eight bit
data section. The compiler will generate more efficient code for
certain operations on data in the eight bit data area. Note the
eight bit data area is limited to 256 bytes of data.
You must use GAS and GLD from GNU binutils version 2.7 or later for
this attribute to work correctly.
`exception_handler'
Use this attribute on the Blackfin to indicate that the specified
function is an exception handler. The compiler will generate
function entry and exit sequences suitable for use in an exception
handler when this attribute is present.
`far'
On 68HC11 and 68HC12 the `far' attribute causes the compiler to
use a calling convention that takes care of switching memory banks
when entering and leaving a function. This calling convention is
also the default when using the `-mlong-calls' option.
On 68HC12 the compiler will use the `call' and `rtc' instructions
to call and return from a function.
On 68HC11 the compiler will generate a sequence of instructions to
invoke a board-specific routine to switch the memory bank and call
the real function. The board-specific routine simulates a `call'.
At the end of a function, it will jump to a board-specific routine
instead of using `rts'. The board-specific return routine
simulates the `rtc'.
`fastcall'
On the Intel 386, the `fastcall' attribute causes the compiler to
pass the first argument (if of integral type) in the register ECX
and the second argument (if of integral type) in the register EDX.
Subsequent and other typed arguments are passed on the stack.
The called function will pop the arguments off the stack. If the
number of arguments is variable all arguments are pushed on the
stack.
`format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)'
The `format' attribute specifies that a function takes `printf',
`scanf', `strftime' or `strfmon' style arguments which should be
type-checked against a format string. For example, the
declaration:
extern int
my_printf (void *my_object, const char *my_format, ...)
__attribute__ ((format (printf, 2, 3)));
causes the compiler to check the arguments in calls to `my_printf'
for consistency with the `printf' style format string argument
`my_format'.
The parameter ARCHETYPE determines how the format string is
interpreted, and should be `printf', `scanf', `strftime' or
`strfmon'. (You can also use `__printf__', `__scanf__',
`__strftime__' or `__strfmon__'.) The parameter STRING-INDEX
specifies which argument is the format string argument (starting
from 1), while FIRST-TO-CHECK is the number of the first argument
to check against the format string. For functions where the
arguments are not available to be checked (such as `vprintf'),
specify the third parameter as zero. In this case the compiler
only checks the format string for consistency. For `strftime'
formats, the third parameter is required to be zero. Since
non-static C++ methods have an implicit `this' argument, the
arguments of such methods should be counted from two, not one, when
giving values for STRING-INDEX and FIRST-TO-CHECK.
In the example above, the format string (`my_format') is the second
argument of the function `my_print', and the arguments to check
start with the third argument, so the correct parameters for the
format attribute are 2 and 3.
The `format' attribute allows you to identify your own functions
which take format strings as arguments, so that GCC can check the
calls to these functions for errors. The compiler always (unless
`-ffreestanding' or `-fno-builtin' is used) checks formats for the
standard library functions `printf', `fprintf', `sprintf',
`scanf', `fscanf', `sscanf', `strftime', `vprintf', `vfprintf' and
`vsprintf' whenever such warnings are requested (using
`-Wformat'), so there is no need to modify the header file
`stdio.h'. In C99 mode, the functions `snprintf', `vsnprintf',
`vscanf', `vfscanf' and `vsscanf' are also checked. Except in
strictly conforming C standard modes, the X/Open function
`strfmon' is also checked as are `printf_unlocked' and
`fprintf_unlocked'. *Note Options Controlling C Dialect: C
Dialect Options.
The target may provide additional types of format checks. *Note
Format Checks Specific to Particular Target Machines: Target
Format Checks.
`format_arg (STRING-INDEX)'
The `format_arg' attribute specifies that a function takes a format
string for a `printf', `scanf', `strftime' or `strfmon' style
function and modifies it (for example, to translate it into
another language), so the result can be passed to a `printf',
`scanf', `strftime' or `strfmon' style function (with the
remaining arguments to the format function the same as they would
have been for the unmodified string). For example, the
declaration:
extern char *
my_dgettext (char *my_domain, const char *my_format)
__attribute__ ((format_arg (2)));
causes the compiler to check the arguments in calls to a `printf',
`scanf', `strftime' or `strfmon' type function, whose format
string argument is a call to the `my_dgettext' function, for
consistency with the format string argument `my_format'. If the
`format_arg' attribute had not been specified, all the compiler
could tell in such calls to format functions would be that the
format string argument is not constant; this would generate a
warning when `-Wformat-nonliteral' is used, but the calls could
not be checked without the attribute.
The parameter STRING-INDEX specifies which argument is the format
string argument (starting from one). Since non-static C++ methods
have an implicit `this' argument, the arguments of such methods
should be counted from two.
The `format-arg' attribute allows you to identify your own
functions which modify format strings, so that GCC can check the
calls to `printf', `scanf', `strftime' or `strfmon' type function
whose operands are a call to one of your own function. The
compiler always treats `gettext', `dgettext', and `dcgettext' in
this manner except when strict ISO C support is requested by
`-ansi' or an appropriate `-std' option, or `-ffreestanding' or
`-fno-builtin' is used. *Note Options Controlling C Dialect: C
Dialect Options.
`function_vector'
Use this attribute on the H8/300, H8/300H, and H8S to indicate
that the specified function should be called through the function
vector. Calling a function through the function vector will
reduce code size, however; the function vector has a limited size
(maximum 128 entries on the H8/300 and 64 entries on the H8/300H
and H8S) and shares space with the interrupt vector.
You must use GAS and GLD from GNU binutils version 2.7 or later for
this attribute to work correctly.
`interrupt'
Use this attribute on the ARM, AVR, C4x, CRX, M32C, M32R/D, MS1,
and Xstormy16 ports to indicate that the specified function is an
interrupt handler. The compiler will generate function entry and
exit sequences suitable for use in an interrupt handler when this
attribute is present.
Note, interrupt handlers for the Blackfin, m68k, H8/300, H8/300H,
H8S, and SH processors can be specified via the
`interrupt_handler' attribute.
Note, on the AVR, interrupts will be enabled inside the function.
Note, for the ARM, you can specify the kind of interrupt to be
handled by adding an optional parameter to the interrupt attribute
like this:
void f () __attribute__ ((interrupt ("IRQ")));
Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT
and UNDEF.
`interrupt_handler'
Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S,
and SH to indicate that the specified function is an interrupt
handler. The compiler will generate function entry and exit
sequences suitable for use in an interrupt handler when this
attribute is present.
`kspisusp'
When used together with `interrupt_handler', `exception_handler'
or `nmi_handler', code will be generated to load the stack pointer
from the USP register in the function prologue.
`long_call/short_call'
This attribute specifies how a particular function is called on
ARM. Both attributes override the `-mlong-calls' (*note ARM
Options::) command line switch and `#pragma long_calls' settings.
The `long_call' attribute indicates that the function might be far
away from the call site and require a different (more expensive)
calling sequence. The `short_call' attribute always places the
offset to the function from the call site into the `BL'
instruction directly.
`longcall/shortcall'
On the Blackfin, RS/6000 and PowerPC, the `longcall' attribute
indicates that the function might be far away from the call site
and require a different (more expensive) calling sequence. The
`shortcall' attribute indicates that the function is always close
enough for the shorter calling sequence to be used. These
attributes override both the `-mlongcall' switch and, on the
RS/6000 and PowerPC, the `#pragma longcall' setting.
*Note RS/6000 and PowerPC Options::, for more information on
whether long calls are necessary.
`long_call'
This attribute specifies how a particular function is called on
MIPS. The attribute overrides the `-mlong-calls' (*note MIPS
Options::) command line switch. This attribute causes the
compiler to always call the function by first loading its address
into a register, and then using the contents of that register.
`malloc'
The `malloc' attribute is used to tell the compiler that a function
may be treated as if any non-`NULL' pointer it returns cannot
alias any other pointer valid when the function returns. This
will often improve optimization. Standard functions with this
property include `malloc' and `calloc'. `realloc'-like functions
have this property as long as the old pointer is never referred to
(including comparing it to the new pointer) after the function
returns a non-`NULL' value.
`model (MODEL-NAME)'
On the M32R/D, use this attribute to set the addressability of an
object, and of the code generated for a function. The identifier
MODEL-NAME is one of `small', `medium', or `large', representing
each of the code models.
Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the `ld24' instruction), and are
callable with the `bl' instruction.
Medium model objects may live anywhere in the 32-bit address space
(the compiler will generate `seth/add3' instructions to load their
addresses), and are callable with the `bl' instruction.
Large model objects may live anywhere in the 32-bit address space
(the compiler will generate `seth/add3' instructions to load their
addresses), and may not be reachable with the `bl' instruction
(the compiler will generate the much slower `seth/add3/jl'
instruction sequence).
On IA-64, use this attribute to set the addressability of an
object. At present, the only supported identifier for MODEL-NAME
is `small', indicating addressability via "small" (22-bit)
addresses (so that their addresses can be loaded with the `addl'
instruction). Caveat: such addressing is by definition not
position independent and hence this attribute must not be used for
objects defined by shared libraries.
`naked'
Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate
that the specified function does not need prologue/epilogue
sequences generated by the compiler. It is up to the programmer
to provide these sequences.
`near'
On 68HC11 and 68HC12 the `near' attribute causes the compiler to
use the normal calling convention based on `jsr' and `rts'. This
attribute can be used to cancel the effect of the `-mlong-calls'
option.
`nesting'
Use this attribute together with `interrupt_handler',
`exception_handler' or `nmi_handler' to indicate that the function
entry code should enable nested interrupts or exceptions.
`nmi_handler'
Use this attribute on the Blackfin to indicate that the specified
function is an NMI handler. The compiler will generate function
entry and exit sequences suitable for use in an NMI handler when
this attribute is present.
`no_instrument_function'
If `-finstrument-functions' is given, profiling function calls will
be generated at entry and exit of most user-compiled functions.
Functions with this attribute will not be so instrumented.
`noinline'
This function attribute prevents a function from being considered
for inlining.
`nonnull (ARG-INDEX, ...)'
The `nonnull' attribute specifies that some function parameters
should be non-null pointers. For instance, the declaration:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull (1, 2)));
causes the compiler to check that, in calls to `my_memcpy',
arguments DEST and SRC are non-null. If the compiler determines
that a null pointer is passed in an argument slot marked as
non-null, and the `-Wnonnull' option is enabled, a warning is
issued. The compiler may also choose to make optimizations based
on the knowledge that certain function arguments will not be null.
If no argument index list is given to the `nonnull' attribute, all
pointer arguments are marked as non-null. To illustrate, the
following declaration is equivalent to the previous example:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull));
`noreturn'
A few standard library functions, such as `abort' and `exit',
cannot return. GCC knows this automatically. Some programs define
their own functions that never return. You can declare them
`noreturn' to tell the compiler this fact. For example,
void fatal () __attribute__ ((noreturn));
void
fatal (/* ... */)
{
/* ... */ /* Print error message. */ /* ... */
exit (1);
}
The `noreturn' keyword tells the compiler to assume that `fatal'
cannot return. It can then optimize without regard to what would
happen if `fatal' ever did return. This makes slightly better
code. More importantly, it helps avoid spurious warnings of
uninitialized variables.
The `noreturn' keyword does not affect the exceptional path when
that applies: a `noreturn'-marked function may still return to the
caller by throwing an exception or calling `longjmp'.
Do not assume that registers saved by the calling function are
restored before calling the `noreturn' function.
It does not make sense for a `noreturn' function to have a return
type other than `void'.
The attribute `noreturn' is not implemented in GCC versions
earlier than 2.5. An alternative way to declare that a function
does not return, which works in the current version and in some
older versions, is as follows:
typedef void voidfn ();
volatile voidfn fatal;
This approach does not work in GNU C++.
`nothrow'
The `nothrow' attribute is used to inform the compiler that a
function cannot throw an exception. For example, most functions in
the standard C library can be guaranteed not to throw an exception
with the notable exceptions of `qsort' and `bsearch' that take
function pointer arguments. The `nothrow' attribute is not
implemented in GCC versions earlier than 3.3.
`pure'
Many functions have no effects except the return value and their
return value depends only on the parameters and/or global
variables. Such a function can be subject to common subexpression
elimination and loop optimization just as an arithmetic operator
would be. These functions should be declared with the attribute
`pure'. For example,
int square (int) __attribute__ ((pure));
says that the hypothetical function `square' is safe to call fewer
times than the program says.
Some of common examples of pure functions are `strlen' or `memcmp'.
Interesting non-pure functions are functions with infinite loops
or those depending on volatile memory or other system resource,
that may change between two consecutive calls (such as `feof' in a
multithreading environment).
The attribute `pure' is not implemented in GCC versions earlier
than 2.96.
`regparm (NUMBER)'
On the Intel 386, the `regparm' attribute causes the compiler to
pass arguments number one to NUMBER if they are of integral type
in registers EAX, EDX, and ECX instead of on the stack. Functions
that take a variable number of arguments will continue to be
passed all of their arguments on the stack.
Beware that on some ELF systems this attribute is unsuitable for
global functions in shared libraries with lazy binding (which is
the default). Lazy binding will send the first call via resolving
code in the loader, which might assume EAX, EDX and ECX can be
clobbered, as per the standard calling conventions. Solaris 8 is
affected by this. GNU systems with GLIBC 2.1 or higher, and
FreeBSD, are believed to be safe since the loaders there save all
registers. (Lazy binding can be disabled with the linker or the
loader if desired, to avoid the problem.)
`sseregparm'
On the Intel 386 with SSE support, the `sseregparm' attribute
causes the compiler to pass up to 3 floating point arguments in
SSE registers instead of on the stack. Functions that take a
variable number of arguments will continue to pass all of their
floating point arguments on the stack.
`force_align_arg_pointer'
On the Intel x86, the `force_align_arg_pointer' attribute may be
applied to individual function definitions, generating an alternate
prologue and epilogue that realigns the runtime stack. This
supports mixing legacy codes that run with a 4-byte aligned stack
with modern codes that keep a 16-byte stack for SSE compatibility.
The alternate prologue and epilogue are slower and bigger than
the regular ones, and the alternate prologue requires a scratch
register; this lowers the number of registers available if used in
conjunction with the `regparm' attribute. The
`force_align_arg_pointer' attribute is incompatible with nested
functions; this is considered a hard error.
`returns_twice'
The `returns_twice' attribute tells the compiler that a function
may return more than one time. The compiler will ensure that all
registers are dead before calling such a function and will emit a
warning about the variables that may be clobbered after the second
return from the function. Examples of such functions are `setjmp'
and `vfork'. The `longjmp'-like counterpart of such function, if
any, might need to be marked with the `noreturn' attribute.
`saveall'
Use this attribute on the Blackfin, H8/300, H8/300H, and H8S to
indicate that all registers except the stack pointer should be
saved in the prologue regardless of whether they are used or not.
`section ("SECTION-NAME")'
Normally, the compiler places the code it generates in the `text'
section. Sometimes, however, you need additional sections, or you
need certain particular functions to appear in special sections.
The `section' attribute specifies that a function lives in a
particular section. For example, the declaration:
extern void foobar (void) __attribute__ ((section ("bar")));
puts the function `foobar' in the `bar' section.
Some file formats do not support arbitrary sections so the
`section' attribute is not available on all platforms. If you
need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.
`sentinel'
This function attribute ensures that a parameter in a function
call is an explicit `NULL'. The attribute is only valid on
variadic functions. By default, the sentinel is located at
position zero, the last parameter of the function call. If an
optional integer position argument P is supplied to the attribute,
the sentinel must be located at position P counting backwards from
the end of the argument list.
__attribute__ ((sentinel))
is equivalent to
__attribute__ ((sentinel(0)))
The attribute is automatically set with a position of 0 for the
built-in functions `execl' and `execlp'. The built-in function
`execle' has the attribute set with a position of 1.
A valid `NULL' in this context is defined as zero with any pointer
type. If your system defines the `NULL' macro with an integer type
then you need to add an explicit cast. GCC replaces `stddef.h'
with a copy that redefines NULL appropriately.
The warnings for missing or incorrect sentinels are enabled with
`-Wformat'.
`short_call'
See long_call/short_call.
`shortcall'
See longcall/shortcall.
`signal'
Use this attribute on the AVR to indicate that the specified
function is a signal handler. The compiler will generate function
entry and exit sequences suitable for use in a signal handler when
this attribute is present. Interrupts will be disabled inside the
function.
`sp_switch'
Use this attribute on the SH to indicate an `interrupt_handler'
function should switch to an alternate stack. It expects a string
argument that names a global variable holding the address of the
alternate stack.
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
sp_switch ("alt_stack")));
`stdcall'
On the Intel 386, the `stdcall' attribute causes the compiler to
assume that the called function will pop off the stack space used
to pass arguments, unless it takes a variable number of arguments.
`tiny_data'
Use this attribute on the H8/300H and H8S to indicate that the
specified variable should be placed into the tiny data section.
The compiler will generate more efficient code for loads and stores
on data in the tiny data section. Note the tiny data area is
limited to slightly under 32kbytes of data.
`trap_exit'
Use this attribute on the SH for an `interrupt_handler' to return
using `trapa' instead of `rte'. This attribute expects an integer
argument specifying the trap number to be used.
`unused'
This attribute, attached to a function, means that the function is
meant to be possibly unused. GCC will not produce a warning for
this function.
`used'
This attribute, attached to a function, means that code must be
emitted for the function even if it appears that the function is
not referenced. This is useful, for example, when the function is
referenced only in inline assembly.
`visibility ("VISIBILITY_TYPE")'
This attribute affects the linkage of the declaration to which it
is attached. There are four supported VISIBILITY_TYPE values:
default, hidden, protected or internal visibility.
void __attribute__ ((visibility ("protected")))
f () { /* Do something. */; }
int i __attribute__ ((visibility ("hidden")));
The possible values of VISIBILITY_TYPE correspond to the
visibility settings in the ELF gABI.
"default"
Default visibility is the normal case for the object file
format. This value is available for the visibility attribute
to override other options that may change the assumed
visibility of entities.
On ELF, default visibility means that the declaration is
visible to other modules and, in shared libraries, means that
the declared entity may be overridden.
On Darwin, default visibility means that the declaration is
visible to other modules.
Default visibility corresponds to "external linkage" in the
language.
"hidden"
Hidden visibility indicates that the entity declared will
have a new form of linkage, which we'll call "hidden
linkage". Two declarations of an object with hidden linkage
refer to the same object if they are in the same shared
object.
"internal"
Internal visibility is like hidden visibility, but with
additional processor specific semantics. Unless otherwise
specified by the psABI, GCC defines internal visibility to
mean that a function is _never_ called from another module.
Compare this with hidden functions which, while they cannot
be referenced directly by other modules, can be referenced
indirectly via function pointers. By indicating that a
function cannot be called from outside the module, GCC may
for instance omit the load of a PIC register since it is known
that the calling function loaded the correct value.
"protected"
Protected visibility is like default visibility except that it
indicates that references within the defining module will
bind to the definition in that module. That is, the declared
entity cannot be overridden by another module.
All visibilities are supported on many, but not all, ELF targets
(supported when the assembler supports the `.visibility'
pseudo-op). Default visibility is supported everywhere. Hidden
visibility is supported on Darwin targets.
The visibility attribute should be applied only to declarations
which would otherwise have external linkage. The attribute should
be applied consistently, so that the same entity should not be
declared with different settings of the attribute.
In C++, the visibility attribute applies to types as well as
functions and objects, because in C++ types have linkage. A class
must not have greater visibility than its non-static data member
types and bases, and class members default to the visibility of
their class. Also, a declaration without explicit visibility is
limited to the visibility of its type.
In C++, you can mark member functions and static member variables
of a class with the visibility attribute. This is useful if if
you know a particular method or static member variable should only
be used from one shared object; then you can mark it hidden while
the rest of the class has default visibility. Care must be taken
to avoid breaking the One Definition Rule; for example, it is
usually not useful to mark an inline method as hidden without
marking the whole class as hidden.
A C++ namespace declaration can also have the visibility attribute.
This attribute applies only to the particular namespace body, not
to other definitions of the same namespace; it is equivalent to
using `#pragma GCC visibility' before and after the namespace
definition (*note Visibility Pragmas::).
In C++, if a template argument has limited visibility, this
restriction is implicitly propagated to the template instantiation.
Otherwise, template instantiations and specializations default to
the visibility of their template.
If both the template and enclosing class have explicit visibility,
the visibility from the template is used.
`warn_unused_result'
The `warn_unused_result' attribute causes a warning to be emitted
if a caller of the function with this attribute does not use its
return value. This is useful for functions where not checking the
result is either a security problem or always a bug, such as
`realloc'.
int fn () __attribute__ ((warn_unused_result));
int foo ()
{
if (fn () < 0) return -1;
fn ();
return 0;
}
results in warning on line 5.
`weak'
The `weak' attribute causes the declaration to be emitted as a weak
symbol rather than a global. This is primarily useful in defining
library functions which can be overridden in user code, though it
can also be used with non-function declarations. Weak symbols are
supported for ELF targets, and also for a.out targets when using
the GNU assembler and linker.
`weakref'
`weakref ("TARGET")'
The `weakref' attribute marks a declaration as a weak reference.
Without arguments, it should be accompanied by an `alias' attribute
naming the target symbol. Optionally, the TARGET may be given as
an argument to `weakref' itself. In either case, `weakref'
implicitly marks the declaration as `weak'. Without a TARGET,
given as an argument to `weakref' or to `alias', `weakref' is
equivalent to `weak'.
static int x() __attribute__ ((weakref ("y")));
/* is equivalent to... */
static int x() __attribute__ ((weak, weakref, alias ("y")));
/* and to... */
static int x() __attribute__ ((weakref));
static int x() __attribute__ ((alias ("y")));
A weak reference is an alias that does not by itself require a
definition to be given for the target symbol. If the target
symbol is only referenced through weak references, then the
becomes a `weak' undefined symbol. If it is directly referenced,
however, then such strong references prevail, and a definition
will be required for the symbol, not necessarily in the same
translation unit.
The effect is equivalent to moving all references to the alias to a
separate translation unit, renaming the alias to the aliased
symbol, declaring it as weak, compiling the two separate
translation units and performing a reloadable link on them.
At present, a declaration to which `weakref' is attached can only
be `static'.
`externally_visible'
This attribute, attached to a global variable or function nullify
effect of `-fwhole-program' command line option, so the object
remain visible outside the current compilation unit
You can specify multiple attributes in a declaration by separating them
by commas within the double parentheses or by immediately following an
attribute declaration with another attribute declaration.
Some people object to the `__attribute__' feature, suggesting that ISO
C's `#pragma' should be used instead. At the time `__attribute__' was
designed, there were two reasons for not doing this.
1. It is impossible to generate `#pragma' commands from a macro.
2. There is no telling what the same `#pragma' might mean in another
compiler.
These two reasons applied to almost any application that might have
been proposed for `#pragma'. It was basically a mistake to use
`#pragma' for _anything_.
The ISO C99 standard includes `_Pragma', which now allows pragmas to
be generated from macros. In addition, a `#pragma GCC' namespace is
now in use for GCC-specific pragmas. However, it has been found
convenient to use `__attribute__' to achieve a natural attachment of
attributes to their corresponding declarations, whereas `#pragma GCC'
is of use for constructs that do not naturally form part of the
grammar. *Note Miscellaneous Preprocessing Directives: (cpp)Other
Directives.
File: gcc.info, Node: Attribute Syntax, Next: Function Prototypes, Prev: Function Attributes, Up: C Extensions
5.26 Attribute Syntax
=====================
This section describes the syntax with which `__attribute__' may be
used, and the constructs to which attribute specifiers bind, for the C
language. Some details may vary for C++ and Objective-C. Because of
infelicities in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.
There are some problems with the semantics of attributes in C++. For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading. Similarly, `typeid' does
not distinguish between types with different attributes. Support for
attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.
*Note Function Attributes::, for details of the semantics of attributes
applying to functions. *Note Variable Attributes::, for details of the
semantics of attributes applying to variables. *Note Type Attributes::,
for details of the semantics of attributes applying to structure, union
and enumerated types.
An "attribute specifier" is of the form `__attribute__
((ATTRIBUTE-LIST))'. An "attribute list" is a possibly empty
comma-separated sequence of "attributes", where each attribute is one
of the following:
* Empty. Empty attributes are ignored.
* A word (which may be an identifier such as `unused', or a reserved
word such as `const').
* A word, followed by, in parentheses, parameters for the attribute.
These parameters take one of the following forms:
* An identifier. For example, `mode' attributes use this form.
* An identifier followed by a comma and a non-empty
comma-separated list of expressions. For example, `format'
attributes use this form.
* A possibly empty comma-separated list of expressions. For
example, `format_arg' attributes use this form with the list
being a single integer constant expression, and `alias'
attributes use this form with the list being a single string
constant.
An "attribute specifier list" is a sequence of one or more attribute
specifiers, not separated by any other tokens.
In GNU C, an attribute specifier list may appear after the colon
following a label, other than a `case' or `default' label. The only
attribute it makes sense to use after a label is `unused'. This
feature is intended for code generated by programs which contains labels
that may be unused but which is compiled with `-Wall'. It would not
normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
contained within an `#ifdef' conditional. GNU C++ does not permit such
placement of attribute lists, as it is permissible for a declaration,
which could begin with an attribute list, to be labelled in C++.
Declarations cannot be labelled in C90 or C99, so the ambiguity does
not arise there.
An attribute specifier list may appear as part of a `struct', `union'
or `enum' specifier. It may go either immediately after the `struct',
`union' or `enum' keyword, or after the closing brace. The former
syntax is preferred. Where attribute specifiers follow the closing
brace, they are considered to relate to the structure, union or
enumerated type defined, not to any enclosing declaration the type
specifier appears in, and the type defined is not complete until after
the attribute specifiers.
Otherwise, an attribute specifier appears as part of a declaration,
counting declarations of unnamed parameters and type names, and relates
to that declaration (which may be nested in another declaration, for
example in the case of a parameter declaration), or to a particular
declarator within a declaration. Where an attribute specifier is
applied to a parameter declared as a function or an array, it should
apply to the function or array rather than the pointer to which the
parameter is implicitly converted, but this is not yet correctly
implemented.
Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers. (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
`section'.) There is one necessary limitation to this syntax: the
first old-style parameter declaration in a function definition cannot
begin with an attribute specifier, because such an attribute applies to
the function instead by syntax described below (which, however, is not
yet implemented in this case). In some other cases, attribute
specifiers are permitted by this grammar but not yet supported by the
compiler. All attribute specifiers in this place relate to the
declaration as a whole. In the obsolescent usage where a type of `int'
is implied by the absence of type specifiers, such a list of specifiers
and qualifiers may be an attribute specifier list with no other
specifiers or qualifiers.
At present, the first parameter in a function prototype must have some
type specifier which is not an attribute specifier; this resolves an
ambiguity in the interpretation of `void f(int (__attribute__((foo))
x))', but is subject to change. At present, if the parentheses of a
function declarator contain only attributes then those attributes are
ignored, rather than yielding an error or warning or implying a single
parameter of type int, but this is subject to change.
An attribute specifier list may appear immediately before a declarator
(other than the first) in a comma-separated list of declarators in a
declaration of more than one identifier using a single list of
specifiers and qualifiers. Such attribute specifiers apply only to the
identifier before whose declarator they appear. For example, in
__attribute__((noreturn)) void d0 (void),
__attribute__((format(printf, 1, 2))) d1 (const char *, ...),
d2 (void)
the `noreturn' attribute applies to all the functions declared; the
`format' attribute only applies to `d1'.
An attribute specifier list may appear immediately before the comma,
`=' or semicolon terminating the declaration of an identifier other
than a function definition. At present, such attribute specifiers apply
to the declared object or function, but in future they may attach to the
outermost adjacent declarator. In simple cases there is no difference,
but, for example, in
void (****f)(void) __attribute__((noreturn));
at present the `noreturn' attribute applies to `f', which causes a
warning since `f' is not a function, but in future it may apply to the
function `****f'. The precise semantics of what attributes in such
cases will apply to are not yet specified. Where an assembler name for
an object or function is specified (*note Asm Labels::), at present the
attribute must follow the `asm' specification; in future, attributes
before the `asm' specification may apply to the adjacent declarator,
and those after it to the declared object or function.
An attribute specifier list may, in future, be permitted to appear
after the declarator in a function definition (before any old-style
parameter declarations or the function body).
Attribute specifiers may be mixed with type qualifiers appearing inside
the `[]' of a parameter array declarator, in the C99 construct by which
such qualifiers are applied to the pointer to which the array is
implicitly converted. Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.
An attribute specifier list may appear at the start of a nested
declarator. At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented. When
attribute specifiers follow the `*' of a pointer declarator, they may
be mixed with any type qualifiers present. The following describes the
formal semantics of this syntax. It will make the most sense if you
are familiar with the formal specification of declarators in the ISO C
standard.
Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration `T D1',
where `T' contains declaration specifiers that specify a type TYPE
(such as `int') and `D1' is a declarator that contains an identifier
IDENT. The type specified for IDENT for derived declarators whose type
does not include an attribute specifier is as in the ISO C standard.
If `D1' has the form `( ATTRIBUTE-SPECIFIER-LIST D )', and the
declaration `T D' specifies the type "DERIVED-DECLARATOR-TYPE-LIST
TYPE" for IDENT, then `T D1' specifies the type
"DERIVED-DECLARATOR-TYPE-LIST ATTRIBUTE-SPECIFIER-LIST TYPE" for IDENT.
If `D1' has the form `* TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST
D', and the declaration `T D' specifies the type
"DERIVED-DECLARATOR-TYPE-LIST TYPE" for IDENT, then `T D1' specifies
the type "DERIVED-DECLARATOR-TYPE-LIST
TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST TYPE" for IDENT.
For example,
void (__attribute__((noreturn)) ****f) (void);
specifies the type "pointer to pointer to pointer to pointer to
non-returning function returning `void'". As another example,
char *__attribute__((aligned(8))) *f;
specifies the type "pointer to 8-byte-aligned pointer to `char'". Note
again that this does not work with most attributes; for example, the
usage of `aligned' and `noreturn' attributes given above is not yet
supported.
For compatibility with existing code written for compiler versions that
did not implement attributes on nested declarators, some laxity is
allowed in the placing of attributes. If an attribute that only applies
to types is applied to a declaration, it will be treated as applying to
the type of that declaration. If an attribute that only applies to
declarations is applied to the type of a declaration, it will be treated
as applying to that declaration; and, for compatibility with code
placing the attributes immediately before the identifier declared, such
an attribute applied to a function return type will be treated as
applying to the function type, and such an attribute applied to an array
element type will be treated as applying to the array type. If an
attribute that only applies to function types is applied to a
pointer-to-function type, it will be treated as applying to the pointer
target type; if such an attribute is applied to a function return type
that is not a pointer-to-function type, it will be treated as applying
to the function type.
File: gcc.info, Node: Function Prototypes, Next: C++ Comments, Prev: Attribute Syntax, Up: C Extensions
5.27 Prototypes and Old-Style Function Definitions
==================================================
GNU C extends ISO C to allow a function prototype to override a later
old-style non-prototype definition. Consider the following example:
/* Use prototypes unless the compiler is old-fashioned. */
#ifdef __STDC__
#define P(x) x
#else
#define P(x) ()
#endif
/* Prototype function declaration. */
int isroot P((uid_t));
/* Old-style function definition. */
int
isroot (x) /* ??? lossage here ??? */
uid_t x;
{
return x == 0;
}
Suppose the type `uid_t' happens to be `short'. ISO C does not allow
this example, because subword arguments in old-style non-prototype
definitions are promoted. Therefore in this example the function
definition's argument is really an `int', which does not match the
prototype argument type of `short'.
This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know
whether the `uid_t' type is `short', `int', or `long'. Therefore, in
cases like these GNU C allows a prototype to override a later old-style
definition. More precisely, in GNU C, a function prototype argument
type overrides the argument type specified by a later old-style
definition if the former type is the same as the latter type before
promotion. Thus in GNU C the above example is equivalent to the
following:
int isroot (uid_t);
int
isroot (uid_t x)
{
return x == 0;
}
GNU C++ does not support old-style function definitions, so this
extension is irrelevant.
File: gcc.info, Node: C++ Comments, Next: Dollar Signs, Prev: Function Prototypes, Up: C Extensions
5.28 C++ Style Comments
=======================
In GNU C, you may use C++ style comments, which start with `//' and
continue until the end of the line. Many other C implementations allow
such comments, and they are included in the 1999 C standard. However,
C++ style comments are not recognized if you specify an `-std' option
specifying a version of ISO C before C99, or `-ansi' (equivalent to
`-std=c89').
File: gcc.info, Node: Dollar Signs, Next: Character Escapes, Prev: C++ Comments, Up: C Extensions
5.29 Dollar Signs in Identifier Names
=====================================
In GNU C, you may normally use dollar signs in identifier names. This
is because many traditional C implementations allow such identifiers.
However, dollar signs in identifiers are not supported on a few target
machines, typically because the target assembler does not allow them.
File: gcc.info, Node: Character Escapes, Next: Variable Attributes, Prev: Dollar Signs, Up: C Extensions
5.30 The Character <ESC> in Constants
=====================================
You can use the sequence `\e' in a string or character constant to
stand for the ASCII character <ESC>.
File: gcc.info, Node: Alignment, Next: Inline, Prev: Type Attributes, Up: C Extensions
5.31 Inquiring on Alignment of Types or Variables
=================================================
The keyword `__alignof__' allows you to inquire about how an object is
aligned, or the minimum alignment usually required by a type. Its
syntax is just like `sizeof'.
For example, if the target machine requires a `double' value to be
aligned on an 8-byte boundary, then `__alignof__ (double)' is 8. This
is true on many RISC machines. On more traditional machine designs,
`__alignof__ (double)' is 4 or even 2.
Some machines never actually require alignment; they allow reference
to any data type even at an odd address. For these machines,
`__alignof__' reports the _recommended_ alignment of a type.
If the operand of `__alignof__' is an lvalue rather than a type, its
value is the required alignment for its type, taking into account any
minimum alignment specified with GCC's `__attribute__' extension (*note
Variable Attributes::). For example, after this declaration:
struct foo { int x; char y; } foo1;
the value of `__alignof__ (foo1.y)' is 1, even though its actual
alignment is probably 2 or 4, the same as `__alignof__ (int)'.
It is an error to ask for the alignment of an incomplete type.
File: gcc.info, Node: Variable Attributes, Next: Type Attributes, Prev: Character Escapes, Up: C Extensions
5.32 Specifying Attributes of Variables
=======================================
The keyword `__attribute__' allows you to specify special attributes of
variables or structure fields. This keyword is followed by an
attribute specification inside double parentheses. Some attributes are
currently defined generically for variables. Other attributes are
defined for variables on particular target systems. Other attributes
are available for functions (*note Function Attributes::) and for types
(*note Type Attributes::). Other front ends might define more
attributes (*note Extensions to the C++ Language: C++ Extensions.).
You may also specify attributes with `__' preceding and following each
keyword. This allows you to use them in header files without being
concerned about a possible macro of the same name. For example, you
may use `__aligned__' instead of `aligned'.
*Note Attribute Syntax::, for details of the exact syntax for using
attributes.
`aligned (ALIGNMENT)'
This attribute specifies a minimum alignment for the variable or
structure field, measured in bytes. For example, the declaration:
int x __attribute__ ((aligned (16))) = 0;
causes the compiler to allocate the global variable `x' on a
16-byte boundary. On a 68040, this could be used in conjunction
with an `asm' expression to access the `move16' instruction which
requires 16-byte aligned operands.
You can also specify the alignment of structure fields. For
example, to create a double-word aligned `int' pair, you could
write:
struct foo { int x[2] __attribute__ ((aligned (8))); };
This is an alternative to creating a union with a `double' member
that forces the union to be double-word aligned.
As in the preceding examples, you can explicitly specify the
alignment (in bytes) that you wish the compiler to use for a given
variable or structure field. Alternatively, you can leave out the
alignment factor and just ask the compiler to align a variable or
field to the maximum useful alignment for the target machine you
are compiling for. For example, you could write:
short array[3] __attribute__ ((aligned));
Whenever you leave out the alignment factor in an `aligned'
attribute specification, the compiler automatically sets the
alignment for the declared variable or field to the largest
alignment which is ever used for any data type on the target
machine you are compiling for. Doing this can often make copy
operations more efficient, because the compiler can use whatever
instructions copy the biggest chunks of memory when performing
copies to or from the variables or fields that you have aligned
this way.
The `aligned' attribute can only increase the alignment; but you
can decrease it by specifying `packed' as well. See below.
Note that the effectiveness of `aligned' attributes may be limited
by inherent limitations in your linker. On many systems, the
linker is only able to arrange for variables to be aligned up to a
certain maximum alignment. (For some linkers, the maximum
supported alignment may be very very small.) If your linker is
only able to align variables up to a maximum of 8 byte alignment,
then specifying `aligned(16)' in an `__attribute__' will still
only provide you with 8 byte alignment. See your linker
documentation for further information.
`cleanup (CLEANUP_FUNCTION)'
The `cleanup' attribute runs a function when the variable goes out
of scope. This attribute can only be applied to auto function
scope variables; it may not be applied to parameters or variables
with static storage duration. The function must take one
parameter, a pointer to a type compatible with the variable. The
return value of the function (if any) is ignored.
If `-fexceptions' is enabled, then CLEANUP_FUNCTION will be run
during the stack unwinding that happens during the processing of
the exception. Note that the `cleanup' attribute does not allow
the exception to be caught, only to perform an action. It is
undefined what happens if CLEANUP_FUNCTION does not return
normally.
`common'
`nocommon'
The `common' attribute requests GCC to place a variable in
"common" storage. The `nocommon' attribute requests the
opposite--to allocate space for it directly.
These attributes override the default chosen by the `-fno-common'
and `-fcommon' flags respectively.
`deprecated'
The `deprecated' attribute results in a warning if the variable is
used anywhere in the source file. This is useful when identifying
variables that are expected to be removed in a future version of a
program. The warning also includes the location of the declaration
of the deprecated variable, to enable users to easily find further
information about why the variable is deprecated, or what they
should do instead. Note that the warning only occurs for uses:
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () { return old_var; }
results in a warning on line 3 but not line 2.
The `deprecated' attribute can also be used for functions and
types (*note Function Attributes::, *note Type Attributes::.)
`mode (MODE)'
This attribute specifies the data type for the
declaration--whichever type corresponds to the mode MODE. This in
effect lets you request an integer or floating point type
according to its width.
You may also specify a mode of `byte' or `__byte__' to indicate
the mode corresponding to a one-byte integer, `word' or `__word__'
for the mode of a one-word integer, and `pointer' or `__pointer__'
for the mode used to represent pointers.
`packed'
The `packed' attribute specifies that a variable or structure field
should have the smallest possible alignment--one byte for a
variable, and one bit for a field, unless you specify a larger
value with the `aligned' attribute.
Here is a structure in which the field `x' is packed, so that it
immediately follows `a':
struct foo
{
char a;
int x[2] __attribute__ ((packed));
};
`section ("SECTION-NAME")'
Normally, the compiler places the objects it generates in sections
like `data' and `bss'. Sometimes, however, you need additional
sections, or you need certain particular variables to appear in
special sections, for example to map to special hardware. The
`section' attribute specifies that a variable (or function) lives
in a particular section. For example, this small program uses
several specific section names:
struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
int init_data __attribute__ ((section ("INITDATA"))) = 0;
main()
{
/* Initialize stack pointer */
init_sp (stack + sizeof (stack));
/* Initialize initialized data */
memcpy (&init_data, &data, &edata - &data);
/* Turn on the serial ports */
init_duart (&a);
init_duart (&b);
}
Use the `section' attribute with an _initialized_ definition of a
_global_ variable, as shown in the example. GCC issues a warning
and otherwise ignores the `section' attribute in uninitialized
variable declarations.
You may only use the `section' attribute with a fully initialized
global definition because of the way linkers work. The linker
requires each object be defined once, with the exception that
uninitialized variables tentatively go in the `common' (or `bss')
section and can be multiply "defined". You can force a variable
to be initialized with the `-fno-common' flag or the `nocommon'
attribute.
Some file formats do not support arbitrary sections so the
`section' attribute is not available on all platforms. If you
need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.
`shared'
On Microsoft Windows, in addition to putting variable definitions
in a named section, the section can also be shared among all
running copies of an executable or DLL. For example, this small
program defines shared data by putting it in a named section
`shared' and marking the section shareable:
int foo __attribute__((section ("shared"), shared)) = 0;
int
main()
{
/* Read and write foo. All running
copies see the same value. */
return 0;
}
You may only use the `shared' attribute along with `section'
attribute with a fully initialized global definition because of
the way linkers work. See `section' attribute for more
information.
The `shared' attribute is only available on Microsoft Windows.
`tls_model ("TLS_MODEL")'
The `tls_model' attribute sets thread-local storage model (*note
Thread-Local::) of a particular `__thread' variable, overriding
`-ftls-model=' command line switch on a per-variable basis. The
TLS_MODEL argument should be one of `global-dynamic',
`local-dynamic', `initial-exec' or `local-exec'.
Not all targets support this attribute.
`unused'
This attribute, attached to a variable, means that the variable is
meant to be possibly unused. GCC will not produce a warning for
this variable.
`used'
This attribute, attached to a variable, means that the variable
must be emitted even if it appears that the variable is not
referenced.
`vector_size (BYTES)'
This attribute specifies the vector size for the variable,
measured in bytes. For example, the declaration:
int foo __attribute__ ((vector_size (16)));
causes the compiler to set the mode for `foo', to be 16 bytes,
divided into `int' sized units. Assuming a 32-bit int (a vector of
4 units of 4 bytes), the corresponding mode of `foo' will be V4SI.
This attribute is only applicable to integral and float scalars,
although arrays, pointers, and function return values are allowed
in conjunction with this construct.
Aggregates with this attribute are invalid, even if they are of
the same size as a corresponding scalar. For example, the
declaration:
struct S { int a; };
struct S __attribute__ ((vector_size (16))) foo;
is invalid even if the size of the structure is the same as the
size of the `int'.
`selectany'
The `selectany' attribute causes an initialized global variable to
have link-once semantics. When multiple definitions of the
variable are encountered by the linker, the first is selected and
the remainder are discarded. Following usage by the Microsoft
compiler, the linker is told _not_ to warn about size or content
differences of the multiple definitions.
Although the primary usage of this attribute is for POD types, the
attribute can also be applied to global C++ objects that are
initialized by a constructor. In this case, the static
initialization and destruction code for the object is emitted in
each translation defining the object, but the calls to the
constructor and destructor are protected by a link-once guard
variable.
The `selectany' attribute is only available on Microsoft Windows
targets. You can use `__declspec (selectany)' as a synonym for
`__attribute__ ((selectany))' for compatibility with other
compilers.
`weak'
The `weak' attribute is described in *Note Function Attributes::.
`dllimport'
The `dllimport' attribute is described in *Note Function
Attributes::.
`dllexport'
The `dllexport' attribute is described in *Note Function
Attributes::.
5.32.1 M32R/D Variable Attributes
---------------------------------
One attribute is currently defined for the M32R/D.
`model (MODEL-NAME)'
Use this attribute on the M32R/D to set the addressability of an
object. The identifier MODEL-NAME is one of `small', `medium', or
`large', representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the `ld24' instruction).
Medium and large model objects may live anywhere in the 32-bit
address space (the compiler will generate `seth/add3' instructions
to load their addresses).
5.32.2 i386 Variable Attributes
-------------------------------
Two attributes are currently defined for i386 configurations:
`ms_struct' and `gcc_struct'
`ms_struct'
`gcc_struct'
If `packed' is used on a structure, or if bit-fields are used it
may be that the Microsoft ABI packs them differently than GCC
would normally pack them. Particularly when moving packed data
between functions compiled with GCC and the native Microsoft
compiler (either via function call or as data in a file), it may
be necessary to access either format.
Currently `-m[no-]ms-bitfields' is provided for the Microsoft
Windows X86 compilers to match the native Microsoft compiler.
The Microsoft structure layout algorithm is fairly simple with the
exception of the bitfield packing:
The padding and alignment of members of structures and whether a
bit field can straddle a storage-unit boundary
1. Structure members are stored sequentially in the order in
which they are declared: the first member has the lowest
memory address and the last member the highest.
2. Every data object has an alignment-requirement. The
alignment-requirement for all data except structures, unions,
and arrays is either the size of the object or the current
packing size (specified with either the aligned attribute or
the pack pragma), whichever is less. For structures, unions,
and arrays, the alignment-requirement is the largest
alignment-requirement of its members. Every object is
allocated an offset so that:
offset % alignment-requirement == 0
3. Adjacent bit fields are packed into the same 1-, 2-, or
4-byte allocation unit if the integral types are the same
size and if the next bit field fits into the current
allocation unit without crossing the boundary imposed by the
common alignment requirements of the bit fields.
Handling of zero-length bitfields:
MSVC interprets zero-length bitfields in the following ways:
1. If a zero-length bitfield is inserted between two bitfields
that would normally be coalesced, the bitfields will not be
coalesced.
For example:
struct
{
unsigned long bf_1 : 12;
unsigned long : 0;
unsigned long bf_2 : 12;
} t1;
The size of `t1' would be 8 bytes with the zero-length
bitfield. If the zero-length bitfield were removed, `t1''s
size would be 4 bytes.
2. If a zero-length bitfield is inserted after a bitfield,
`foo', and the alignment of the zero-length bitfield is
greater than the member that follows it, `bar', `bar' will be
aligned as the type of the zero-length bitfield.
For example:
struct
{
char foo : 4;
short : 0;
char bar;
} t2;
struct
{
char foo : 4;
short : 0;
double bar;
} t3;
For `t2', `bar' will be placed at offset 2, rather than
offset 1. Accordingly, the size of `t2' will be 4. For
`t3', the zero-length bitfield will not affect the alignment
of `bar' or, as a result, the size of the structure.
Taking this into account, it is important to note the
following:
1. If a zero-length bitfield follows a normal bitfield, the
type of the zero-length bitfield may affect the
alignment of the structure as whole. For example, `t2'
has a size of 4 bytes, since the zero-length bitfield
follows a normal bitfield, and is of type short.
2. Even if a zero-length bitfield is not followed by a
normal bitfield, it may still affect the alignment of
the structure:
struct
{
char foo : 6;
long : 0;
} t4;
Here, `t4' will take up 4 bytes.
3. Zero-length bitfields following non-bitfield members are
ignored:
struct
{
char foo;
long : 0;
char bar;
} t5;
Here, `t5' will take up 2 bytes.
5.32.3 PowerPC Variable Attributes
----------------------------------
Three attributes currently are defined for PowerPC configurations:
`altivec', `ms_struct' and `gcc_struct'.
For full documentation of the struct attributes please see the
documentation in the *Note i386 Variable Attributes::, section.
For documentation of `altivec' attribute please see the documentation
in the *Note PowerPC Type Attributes::, section.
5.32.4 Xstormy16 Variable Attributes
------------------------------------
One attribute is currently defined for xstormy16 configurations:
`below100'
`below100'
If a variable has the `below100' attribute (`BELOW100' is allowed
also), GCC will place the variable in the first 0x100 bytes of
memory and use special opcodes to access it. Such variables will
be placed in either the `.bss_below100' section or the
`.data_below100' section.
File: gcc.info, Node: Type Attributes, Next: Alignment, Prev: Variable Attributes, Up: C Extensions
5.33 Specifying Attributes of Types
===================================
The keyword `__attribute__' allows you to specify special attributes of
`struct' and `union' types when you define such types. This keyword is
followed by an attribute specification inside double parentheses.
Seven attributes are currently defined for types: `aligned', `packed',
`transparent_union', `unused', `deprecated', `visibility', and
`may_alias'. Other attributes are defined for functions (*note
Function Attributes::) and for variables (*note Variable Attributes::).
You may also specify any one of these attributes with `__' preceding
and following its keyword. This allows you to use these attributes in
header files without being concerned about a possible macro of the same
name. For example, you may use `__aligned__' instead of `aligned'.
You may specify type attributes either in a `typedef' declaration or
in an enum, struct or union type declaration or definition.
For an enum, struct or union type, you may specify attributes either
between the enum, struct or union tag and the name of the type, or just
past the closing curly brace of the _definition_. The former syntax is
preferred.
*Note Attribute Syntax::, for details of the exact syntax for using
attributes.
`aligned (ALIGNMENT)'
This attribute specifies a minimum alignment (in bytes) for
variables of the specified type. For example, the declarations:
struct S { short f[3]; } __attribute__ ((aligned (8)));
typedef int more_aligned_int __attribute__ ((aligned (8)));
force the compiler to insure (as far as it can) that each variable
whose type is `struct S' or `more_aligned_int' will be allocated
and aligned _at least_ on a 8-byte boundary. On a SPARC, having
all variables of type `struct S' aligned to 8-byte boundaries
allows the compiler to use the `ldd' and `std' (doubleword load and
store) instructions when copying one variable of type `struct S' to
another, thus improving run-time efficiency.
Note that the alignment of any given `struct' or `union' type is
required by the ISO C standard to be at least a perfect multiple of
the lowest common multiple of the alignments of all of the members
of the `struct' or `union' in question. This means that you _can_
effectively adjust the alignment of a `struct' or `union' type by
attaching an `aligned' attribute to any one of the members of such
a type, but the notation illustrated in the example above is a
more obvious, intuitive, and readable way to request the compiler
to adjust the alignment of an entire `struct' or `union' type.
As in the preceding example, you can explicitly specify the
alignment (in bytes) that you wish the compiler to use for a given
`struct' or `union' type. Alternatively, you can leave out the
alignment factor and just ask the compiler to align a type to the
maximum useful alignment for the target machine you are compiling
for. For example, you could write:
struct S { short f[3]; } __attribute__ ((aligned));
Whenever you leave out the alignment factor in an `aligned'
attribute specification, the compiler automatically sets the
alignment for the type to the largest alignment which is ever used
for any data type on the target machine you are compiling for.
Doing this can often make copy operations more efficient, because
the compiler can use whatever instructions copy the biggest chunks
of memory when performing copies to or from the variables which
have types that you have aligned this way.
In the example above, if the size of each `short' is 2 bytes, then
the size of the entire `struct S' type is 6 bytes. The smallest
power of two which is greater than or equal to that is 8, so the
compiler sets the alignment for the entire `struct S' type to 8
bytes.
Note that although you can ask the compiler to select a
time-efficient alignment for a given type and then declare only
individual stand-alone objects of that type, the compiler's
ability to select a time-efficient alignment is primarily useful
only when you plan to create arrays of variables having the
relevant (efficiently aligned) type. If you declare or use arrays
of variables of an efficiently-aligned type, then it is likely
that your program will also be doing pointer arithmetic (or
subscripting, which amounts to the same thing) on pointers to the
relevant type, and the code that the compiler generates for these
pointer arithmetic operations will often be more efficient for
efficiently-aligned types than for other types.
The `aligned' attribute can only increase the alignment; but you
can decrease it by specifying `packed' as well. See below.
Note that the effectiveness of `aligned' attributes may be limited
by inherent limitations in your linker. On many systems, the
linker is only able to arrange for variables to be aligned up to a
certain maximum alignment. (For some linkers, the maximum
supported alignment may be very very small.) If your linker is
only able to align variables up to a maximum of 8 byte alignment,
then specifying `aligned(16)' in an `__attribute__' will still
only provide you with 8 byte alignment. See your linker
documentation for further information.
`packed'
This attribute, attached to `struct' or `union' type definition,
specifies that each member (other than zero-width bitfields) of
the structure or union is placed to minimize the memory required.
When attached to an `enum' definition, it indicates that the
smallest integral type should be used.
Specifying this attribute for `struct' and `union' types is
equivalent to specifying the `packed' attribute on each of the
structure or union members. Specifying the `-fshort-enums' flag
on the line is equivalent to specifying the `packed' attribute on
all `enum' definitions.
In the following example `struct my_packed_struct''s members are
packed closely together, but the internal layout of its `s' member
is not packed--to do that, `struct my_unpacked_struct' would need
to be packed too.
struct my_unpacked_struct
{
char c;
int i;
};
struct __attribute__ ((__packed__)) my_packed_struct
{
char c;
int i;
struct my_unpacked_struct s;
};
You may only specify this attribute on the definition of a `enum',
`struct' or `union', not on a `typedef' which does not also define
the enumerated type, structure or union.
`transparent_union'
This attribute, attached to a `union' type definition, indicates
that any function parameter having that union type causes calls to
that function to be treated in a special way.
First, the argument corresponding to a transparent union type can
be of any type in the union; no cast is required. Also, if the
union contains a pointer type, the corresponding argument can be a
null pointer constant or a void pointer expression; and if the
union contains a void pointer type, the corresponding argument can
be any pointer expression. If the union member type is a pointer,
qualifiers like `const' on the referenced type must be respected,
just as with normal pointer conversions.
Second, the argument is passed to the function using the calling
conventions of the first member of the transparent union, not the
calling conventions of the union itself. All members of the union
must have the same machine representation; this is necessary for
this argument passing to work properly.
Transparent unions are designed for library functions that have
multiple interfaces for compatibility reasons. For example,
suppose the `wait' function must accept either a value of type
`int *' to comply with Posix, or a value of type `union wait *' to
comply with the 4.1BSD interface. If `wait''s parameter were
`void *', `wait' would accept both kinds of arguments, but it
would also accept any other pointer type and this would make
argument type checking less useful. Instead, `<sys/wait.h>' might
define the interface as follows:
typedef union
{
int *__ip;
union wait *__up;
} wait_status_ptr_t __attribute__ ((__transparent_union__));
pid_t wait (wait_status_ptr_t);
This interface allows either `int *' or `union wait *' arguments
to be passed, using the `int *' calling convention. The program
can call `wait' with arguments of either type:
int w1 () { int w; return wait (&w); }
int w2 () { union wait w; return wait (&w); }
With this interface, `wait''s implementation might look like this:
pid_t wait (wait_status_ptr_t p)
{
return waitpid (-1, p.__ip, 0);
}
`unused'
When attached to a type (including a `union' or a `struct'), this
attribute means that variables of that type are meant to appear
possibly unused. GCC will not produce a warning for any variables
of that type, even if the variable appears to do nothing. This is
often the case with lock or thread classes, which are usually
defined and then not referenced, but contain constructors and
destructors that have nontrivial bookkeeping functions.
`deprecated'
The `deprecated' attribute results in a warning if the type is
used anywhere in the source file. This is useful when identifying
types that are expected to be removed in a future version of a
program. If possible, the warning also includes the location of
the declaration of the deprecated type, to enable users to easily
find further information about why the type is deprecated, or what
they should do instead. Note that the warnings only occur for
uses and then only if the type is being applied to an identifier
that itself is not being declared as deprecated.
typedef int T1 __attribute__ ((deprecated));
T1 x;
typedef T1 T2;
T2 y;
typedef T1 T3 __attribute__ ((deprecated));
T3 z __attribute__ ((deprecated));
results in a warning on line 2 and 3 but not lines 4, 5, or 6. No
warning is issued for line 4 because T2 is not explicitly
deprecated. Line 5 has no warning because T3 is explicitly
deprecated. Similarly for line 6.
The `deprecated' attribute can also be used for functions and
variables (*note Function Attributes::, *note Variable
Attributes::.)
`may_alias'
Accesses to objects with types with this attribute are not
subjected to type-based alias analysis, but are instead assumed to
be able to alias any other type of objects, just like the `char'
type. See `-fstrict-aliasing' for more information on aliasing
issues.
Example of use:
typedef short __attribute__((__may_alias__)) short_a;
int
main (void)
{
int a = 0x12345678;
short_a *b = (short_a *) &a;
b[1] = 0;
if (a == 0x12345678)
abort();
exit(0);
}
If you replaced `short_a' with `short' in the variable
declaration, the above program would abort when compiled with
`-fstrict-aliasing', which is on by default at `-O2' or above in
recent GCC versions.
`visibility'
In C++, attribute visibility (*note Function Attributes::) can
also be applied to class, struct, union and enum types. Unlike
other type attributes, the attribute must appear between the
initial keyword and the name of the type; it cannot appear after
the body of the type.
Note that the type visibility is applied to vague linkage entities
associated with the class (vtable, typeinfo node, etc.). In
particular, if a class is thrown as an exception in one shared
object and caught in another, the class must have default
visibility. Otherwise the two shared objects will be unable to
use the same typeinfo node and exception handling will break.
5.33.1 ARM Type Attributes
--------------------------
On those ARM targets that support `dllimport' (such as Symbian
OS), you can use the `notshared' attribute to indicate that the virtual
table and other similar data for a class should not be exported from a
DLL. For example:
class __declspec(notshared) C {
public:
__declspec(dllimport) C();
virtual void f();
}
__declspec(dllexport)
C::C() {}
In this code, `C::C' is exported from the current DLL, but the
virtual table for `C' is not exported. (You can use `__attribute__'
instead of `__declspec' if you prefer, but most Symbian OS code uses
`__declspec'.)
5.33.2 i386 Type Attributes
---------------------------
Two attributes are currently defined for i386 configurations:
`ms_struct' and `gcc_struct'
`ms_struct'
`gcc_struct'
If `packed' is used on a structure, or if bit-fields are used it
may be that the Microsoft ABI packs them differently than GCC
would normally pack them. Particularly when moving packed data
between functions compiled with GCC and the native Microsoft
compiler (either via function call or as data in a file), it may
be necessary to access either format.
Currently `-m[no-]ms-bitfields' is provided for the Microsoft
Windows X86 compilers to match the native Microsoft compiler.
To specify multiple attributes, separate them by commas within the
double parentheses: for example, `__attribute__ ((aligned (16),
packed))'.
5.33.3 PowerPC Type Attributes
------------------------------
Three attributes currently are defined for PowerPC configurations:
`altivec', `ms_struct' and `gcc_struct'.
For full documentation of the struct attributes please see the
documentation in the *Note i386 Type Attributes::, section.
The `altivec' attribute allows one to declare AltiVec vector data
types supported by the AltiVec Programming Interface Manual. The
attribute requires an argument to specify one of three vector types:
`vector__', `pixel__' (always followed by unsigned short), and `bool__'
(always followed by unsigned).
__attribute__((altivec(vector__)))
__attribute__((altivec(pixel__))) unsigned short
__attribute__((altivec(bool__))) unsigned
These attributes mainly are intended to support the `__vector',
`__pixel', and `__bool' AltiVec keywords.
File: gcc.info, Node: Inline, Next: Extended Asm, Prev: Alignment, Up: C Extensions
5.34 An Inline Function is As Fast As a Macro
=============================================
By declaring a function `inline', you can direct GCC to integrate that
function's code into the code for its callers. This makes execution
faster by eliminating the function-call overhead; in addition, if any
of the actual argument values are constant, their known values may
permit simplifications at compile time so that not all of the inline
function's code needs to be included. The effect on code size is less
predictable; object code may be larger or smaller with function
inlining, depending on the particular case. Inlining of functions is an
optimization and it really "works" only in optimizing compilation. If
you don't use `-O', no function is really inline.
Inline functions are included in the ISO C99 standard, but there are
currently substantial differences between what GCC implements and what
the ISO C99 standard requires. GCC will fully support C99 inline
functions in version 4.3. The traditional GCC handling of inline
functions will still be available with `-std=gnu89', `-fgnu89-inline'
or when `gnu_inline' attribute is present on all inline declarations.
The preprocessor macros `__GNUC_GNU_INLINE__' and
`__GNUC_STDC_INLINE__' may be used to determine the handling of
`inline' during a particular compilation (*note Common Predefined
Macros: (cpp)Common Predefined Macros.).
To declare a function inline, use the `inline' keyword in its
declaration, like this:
inline int
inc (int *a)
{
(*a)++;
}
(If you are writing a header file to be included in ISO C programs,
write `__inline__' instead of `inline'. *Note Alternate Keywords::.)
You can also make all "simple enough" functions inline with the option
`-finline-functions'.
Note that certain usages in a function definition can make it
unsuitable for inline substitution. Among these usages are: use of
varargs, use of alloca, use of variable sized data types (*note
Variable Length::), use of computed goto (*note Labels as Values::),
use of nonlocal goto, and nested functions (*note Nested Functions::).
Using `-Winline' will warn when a function marked `inline' could not be
substituted, and will give the reason for the failure.
Note that in C and Objective-C, unlike C++, the `inline' keyword does
not affect the linkage of the function.
GCC automatically inlines member functions defined within the class
body of C++ programs even if they are not explicitly declared `inline'.
(You can override this with `-fno-default-inline'; *note Options
Controlling C++ Dialect: C++ Dialect Options.)
When a function is both inline and `static', if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option `-fkeep-inline-functions'.
Some calls cannot be integrated for various reasons (in particular,
calls that precede the function's definition cannot be integrated, and
neither can recursive calls within the definition). If there is a
nonintegrated call, then the function is compiled to assembler code as
usual. The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.
When an inline function is not `static', then the compiler must assume
that there may be calls from other source files; since a global symbol
can be defined only once in any program, the function must not be
defined in the other source files, so the calls therein cannot be
integrated. Therefore, a non-`static' inline function is always
compiled on its own in the usual fashion.
If you specify both `inline' and `extern' in the function definition,
then the definition is used only for inlining. In no case is the
function compiled on its own, not even if you refer to its address
explicitly. Such an address becomes an external reference, as if you
had only declared the function, and had not defined it.
This combination of `inline' and `extern' has almost the effect of a
macro. The way to use it is to put a function definition in a header
file with these keywords, and put another copy of the definition
(lacking `inline' and `extern') in a library file. The definition in
the header file will cause most calls to the function to be inlined.
If any uses of the function remain, they will refer to the single copy
in the library.
Since GCC 4.3 will implement ISO C99 semantics for inline functions,
it is simplest to use `static inline' only to guarantee compatibility.
(The existing semantics will remain available when `-std=gnu89' is
specified, but eventually the default will be `-std=gnu99'; that will
implement the C99 semantics, though it does not do so in versions of
GCC before 4.3. After the default changes, the existing semantics will
still be available via the `-fgnu89-inline' option or the `gnu_inline'
function attribute.)
GCC does not inline any functions when not optimizing unless you
specify the `always_inline' attribute for the function, like this:
/* Prototype. */
inline void foo (const char) __attribute__((always_inline));
File: gcc.info, Node: Extended Asm, Next: Constraints, Prev: Inline, Up: C Extensions
5.35 Assembler Instructions with C Expression Operands
======================================================
In an assembler instruction using `asm', you can specify the operands
of the instruction using C expressions. This means you need not guess
which registers or memory locations will contain the data you want to
use.
You must specify an assembler instruction template much like what
appears in a machine description, plus an operand constraint string for
each operand.
For example, here is how to use the 68881's `fsinx' instruction:
asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
Here `angle' is the C expression for the input operand while `result'
is that of the output operand. Each has `"f"' as its operand
constraint, saying that a floating point register is required. The `='
in `=f' indicates that the operand is an output; all output operands'
constraints must use `='. The constraints use the same language used
in the machine description (*note Constraints::).
Each operand is described by an operand-constraint string followed by
the C expression in parentheses. A colon separates the assembler
template from the first output operand and another separates the last
output operand from the first input, if any. Commas separate the
operands within each group. The total number of operands is currently
limited to 30; this limitation may be lifted in some future version of
GCC.
If there are no output operands but there are input operands, you must
place two consecutive colons surrounding the place where the output
operands would go.
As of GCC version 3.1, it is also possible to specify input and output
operands using symbolic names which can be referenced within the
assembler code. These names are specified inside square brackets
preceding the constraint string, and can be referenced inside the
assembler code using `%[NAME]' instead of a percentage sign followed by
the operand number. Using named operands the above example could look
like:
asm ("fsinx %[angle],%[output]"
: [output] "=f" (result)
: [angle] "f" (angle));
Note that the symbolic operand names have no relation whatsoever to
other C identifiers. You may use any name you like, even those of
existing C symbols, but you must ensure that no two operands within the
same assembler construct use the same symbolic name.
Output operand expressions must be lvalues; the compiler can check
this. The input operands need not be lvalues. The compiler cannot
check whether the operands have data types that are reasonable for the
instruction being executed. It does not parse the assembler instruction
template and does not know what it means or even whether it is valid
assembler input. The extended `asm' feature is most often used for
machine instructions the compiler itself does not know exist. If the
output expression cannot be directly addressed (for example, it is a
bit-field), your constraint must allow a register. In that case, GCC
will use the register as the output of the `asm', and then store that
register into the output.
The ordinary output operands must be write-only; GCC will assume that
the values in these operands before the instruction are dead and need
not be generated. Extended asm supports input-output or read-write
operands. Use the constraint character `+' to indicate such an operand
and list it with the output operands. You should only use read-write
operands when the constraints for the operand (or the operand in which
only some of the bits are to be changed) allow a register.
You may, as an alternative, logically split its function into two
separate operands, one input operand and one write-only output operand.
The connection between them is expressed by constraints which say they
need to be in the same location when the instruction executes. You can
use the same C expression for both operands, or different expressions.
For example, here we write the (fictitious) `combine' instruction with
`bar' as its read-only source operand and `foo' as its read-write
destination:
asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));
The constraint `"0"' for operand 1 says that it must occupy the same
location as operand 0. A number in constraint is allowed only in an
input operand and it must refer to an output operand.
Only a number in the constraint can guarantee that one operand will be
in the same place as another. The mere fact that `foo' is the value of
both operands is not enough to guarantee that they will be in the same
place in the generated assembler code. The following would not work
reliably:
asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));
Various optimizations or reloading could cause operands 0 and 1 to be
in different registers; GCC knows no reason not to do so. For example,
the compiler might find a copy of the value of `foo' in one register and
use it for operand 1, but generate the output operand 0 in a different
register (copying it afterward to `foo''s own address). Of course,
since the register for operand 1 is not even mentioned in the assembler
code, the result will not work, but GCC can't tell that.
As of GCC version 3.1, one may write `[NAME]' instead of the operand
number for a matching constraint. For example:
asm ("cmoveq %1,%2,%[result]"
: [result] "=r"(result)
: "r" (test), "r"(new), "[result]"(old));
Sometimes you need to make an `asm' operand be a specific register,
but there's no matching constraint letter for that register _by
itself_. To force the operand into that register, use a local variable
for the operand and specify the register in the variable declaration.
*Note Explicit Reg Vars::. Then for the `asm' operand, use any
register constraint letter that matches the register:
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = ...;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
In the above example, beware that a register that is call-clobbered by
the target ABI will be overwritten by any function call in the
assignment, including library calls for arithmetic operators. Assuming
it is a call-clobbered register, this may happen to `r0' above by the
assignment to `p2'. If you have to use such a register, use temporary
variables for expressions between the register assignment and use:
int t1 = ...;
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = t1;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
Some instructions clobber specific hard registers. To describe this,
write a third colon after the input operands, followed by the names of
the clobbered hard registers (given as strings). Here is a realistic
example for the VAX:
asm volatile ("movc3 %0,%1,%2"
: /* no outputs */
: "g" (from), "g" (to), "g" (count)
: "r0", "r1", "r2", "r3", "r4", "r5");
You may not write a clobber description in a way that overlaps with an
input or output operand. For example, you may not have an operand
describing a register class with one member if you mention that register
in the clobber list. Variables declared to live in specific registers
(*note Explicit Reg Vars::), and used as asm input or output operands
must have no part mentioned in the clobber description. There is no
way for you to specify that an input operand is modified without also
specifying it as an output operand. Note that if all the output
operands you specify are for this purpose (and hence unused), you will
then also need to specify `volatile' for the `asm' construct, as
described below, to prevent GCC from deleting the `asm' statement as
unused.
If you refer to a particular hardware register from the assembler code,
you will probably have to list the register after the third colon to
tell the compiler the register's value is modified. In some assemblers,
the register names begin with `%'; to produce one `%' in the assembler
code, you must write `%%' in the input.
If your assembler instruction can alter the condition code register,
add `cc' to the list of clobbered registers. GCC on some machines
represents the condition codes as a specific hardware register; `cc'
serves to name this register. On other machines, the condition code is
handled differently, and specifying `cc' has no effect. But it is
valid no matter what the machine.
If your assembler instructions access memory in an unpredictable
fashion, add `memory' to the list of clobbered registers. This will
cause GCC to not keep memory values cached in registers across the
assembler instruction and not optimize stores or loads to that memory.
You will also want to add the `volatile' keyword if the memory affected
is not listed in the inputs or outputs of the `asm', as the `memory'
clobber does not count as a side-effect of the `asm'. If you know how
large the accessed memory is, you can add it as input or output but if
this is not known, you should add `memory'. As an example, if you
access ten bytes of a string, you can use a memory input like:
{"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.
Note that in the following example the memory input is necessary,
otherwise GCC might optimize the store to `x' away:
int foo ()
{
int x = 42;
int *y = &x;
int result;
asm ("magic stuff accessing an 'int' pointed to by '%1'"
"=&d" (r) : "a" (y), "m" (*y));
return result;
}
You can put multiple assembler instructions together in a single `asm'
template, separated by the characters normally used in assembly code
for the system. A combination that works in most places is a newline
to break the line, plus a tab character to move to the instruction field
(written as `\n\t'). Sometimes semicolons can be used, if the
assembler allows semicolons as a line-breaking character. Note that
some assembler dialects use semicolons to start a comment. The input
operands are guaranteed not to use any of the clobbered registers, and
neither will the output operands' addresses, so you can read and write
the clobbered registers as many times as you like. Here is an example
of multiple instructions in a template; it assumes the subroutine
`_foo' accepts arguments in registers 9 and 10:
asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
: /* no outputs */
: "g" (from), "g" (to)
: "r9", "r10");
Unless an output operand has the `&' constraint modifier, GCC may
allocate it in the same register as an unrelated input operand, on the
assumption the inputs are consumed before the outputs are produced.
This assumption may be false if the assembler code actually consists of
more than one instruction. In such a case, use `&' for each output
operand that may not overlap an input. *Note Modifiers::.
If you want to test the condition code produced by an assembler
instruction, you must include a branch and a label in the `asm'
construct, as follows:
asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
: "g" (result)
: "g" (input));
This assumes your assembler supports local labels, as the GNU assembler
and most Unix assemblers do.
Speaking of labels, jumps from one `asm' to another are not supported.
The compiler's optimizers do not know about these jumps, and therefore
they cannot take account of them when deciding how to optimize.
Usually the most convenient way to use these `asm' instructions is to
encapsulate them in macros that look like functions. For example,
#define sin(x) \
({ double __value, __arg = (x); \
asm ("fsinx %1,%0": "=f" (__value): "f" (__arg)); \
__value; })
Here the variable `__arg' is used to make sure that the instruction
operates on a proper `double' value, and to accept only those arguments
`x' which can convert automatically to a `double'.
Another way to make sure the instruction operates on the correct data
type is to use a cast in the `asm'. This is different from using a
variable `__arg' in that it converts more different types. For
example, if the desired type were `int', casting the argument to `int'
would accept a pointer with no complaint, while assigning the argument
to an `int' variable named `__arg' would warn about using a pointer
unless the caller explicitly casts it.
If an `asm' has output operands, GCC assumes for optimization purposes
the instruction has no side effects except to change the output
operands. This does not mean instructions with a side effect cannot be
used, but you must be careful, because the compiler may eliminate them
if the output operands aren't used, or move them out of loops, or
replace two with one if they constitute a common subexpression. Also,
if your instruction does have a side effect on a variable that otherwise
appears not to change, the old value of the variable may be reused later
if it happens to be found in a register.
You can prevent an `asm' instruction from being deleted by writing the
keyword `volatile' after the `asm'. For example:
#define get_and_set_priority(new) \
({ int __old; \
asm volatile ("get_and_set_priority %0, %1" \
: "=g" (__old) : "g" (new)); \
__old; })
The `volatile' keyword indicates that the instruction has important
side-effects. GCC will not delete a volatile `asm' if it is reachable.
(The instruction can still be deleted if GCC can prove that
control-flow will never reach the location of the instruction.) Note
that even a volatile `asm' instruction can be moved relative to other
code, including across jump instructions. For example, on many targets
there is a system register which can be set to control the rounding
mode of floating point operations. You might try setting it with a
volatile `asm', like this PowerPC example:
asm volatile("mtfsf 255,%0" : : "f" (fpenv));
sum = x + y;
This will not work reliably, as the compiler may move the addition back
before the volatile `asm'. To make it work you need to add an
artificial dependency to the `asm' referencing a variable in the code
you don't want moved, for example:
asm volatile ("mtfsf 255,%1" : "=X"(sum): "f"(fpenv));
sum = x + y;
Similarly, you can't expect a sequence of volatile `asm' instructions
to remain perfectly consecutive. If you want consecutive output, use a
single `asm'. Also, GCC will perform some optimizations across a
volatile `asm' instruction; GCC does not "forget everything" when it
encounters a volatile `asm' instruction the way some other compilers do.
An `asm' instruction without any output operands will be treated
identically to a volatile `asm' instruction.
It is a natural idea to look for a way to give access to the condition
code left by the assembler instruction. However, when we attempted to
implement this, we found no way to make it work reliably. The problem
is that output operands might need reloading, which would result in
additional following "store" instructions. On most machines, these
instructions would alter the condition code before there was time to
test it. This problem doesn't arise for ordinary "test" and "compare"
instructions because they don't have any output operands.
For reasons similar to those described above, it is not possible to
give an assembler instruction access to the condition code left by
previous instructions.
If you are writing a header file that should be includable in ISO C
programs, write `__asm__' instead of `asm'. *Note Alternate Keywords::.
5.35.1 Size of an `asm'
-----------------------
Some targets require that GCC track the size of each instruction used in
order to generate correct code. Because the final length of an `asm'
is only known by the assembler, GCC must make an estimate as to how big
it will be. The estimate is formed by counting the number of
statements in the pattern of the `asm' and multiplying that by the
length of the longest instruction on that processor. Statements in the
`asm' are identified by newline characters and whatever statement
separator characters are supported by the assembler; on most processors
this is the ``;'' character.
Normally, GCC's estimate is perfectly adequate to ensure that correct
code is generated, but it is possible to confuse the compiler if you use
pseudo instructions or assembler macros that expand into multiple real
instructions or if you use assembler directives that expand to more
space in the object file than would be needed for a single instruction.
If this happens then the assembler will produce a diagnostic saying that
a label is unreachable.
5.35.2 i386 floating point asm operands
---------------------------------------
There are several rules on the usage of stack-like regs in asm_operands
insns. These rules apply only to the operands that are stack-like regs:
1. Given a set of input regs that die in an asm_operands, it is
necessary to know which are implicitly popped by the asm, and
which must be explicitly popped by gcc.
An input reg that is implicitly popped by the asm must be
explicitly clobbered, unless it is constrained to match an output
operand.
2. For any input reg that is implicitly popped by an asm, it is
necessary to know how to adjust the stack to compensate for the
pop. If any non-popped input is closer to the top of the
reg-stack than the implicitly popped reg, it would not be possible
to know what the stack looked like--it's not clear how the rest of
the stack "slides up".
All implicitly popped input regs must be closer to the top of the
reg-stack than any input that is not implicitly popped.
It is possible that if an input dies in an insn, reload might use
the input reg for an output reload. Consider this example:
asm ("foo" : "=t" (a) : "f" (b));
This asm says that input B is not popped by the asm, and that the
asm pushes a result onto the reg-stack, i.e., the stack is one
deeper after the asm than it was before. But, it is possible that
reload will think that it can use the same reg for both the input
and the output, if input B dies in this insn.
If any input operand uses the `f' constraint, all output reg
constraints must use the `&' earlyclobber.
The asm above would be written as
asm ("foo" : "=&t" (a) : "f" (b));
3. Some operands need to be in particular places on the stack. All
output operands fall in this category--there is no other way to
know which regs the outputs appear in unless the user indicates
this in the constraints.
Output operands must specifically indicate which reg an output
appears in after an asm. `=f' is not allowed: the operand
constraints must select a class with a single reg.
4. Output operands may not be "inserted" between existing stack regs.
Since no 387 opcode uses a read/write operand, all output operands
are dead before the asm_operands, and are pushed by the
asm_operands. It makes no sense to push anywhere but the top of
the reg-stack.
Output operands must start at the top of the reg-stack: output
operands may not "skip" a reg.
5. Some asm statements may need extra stack space for internal
calculations. This can be guaranteed by clobbering stack registers
unrelated to the inputs and outputs.
Here are a couple of reasonable asms to want to write. This asm takes
one input, which is internally popped, and produces two outputs.
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
This asm takes two inputs, which are popped by the `fyl2xp1' opcode,
and replaces them with one output. The user must code the `st(1)'
clobber for reg-stack.c to know that `fyl2xp1' pops both inputs.
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");
File: gcc.info, Node: Constraints, Next: Asm Labels, Prev: Extended Asm, Up: C Extensions
5.36 Constraints for `asm' Operands
===================================
Here are specific details on what constraint letters you can use with
`asm' operands. Constraints can say whether an operand may be in a
register, and which kinds of register; whether the operand can be a
memory reference, and which kinds of address; whether the operand may
be an immediate constant, and which possible values it may have.
Constraints can also require two operands to match.
* Menu:
* Simple Constraints:: Basic use of constraints.
* Multi-Alternative:: When an insn has two alternative constraint-patterns.
* Modifiers:: More precise control over effects of constraints.
* Machine Constraints:: Special constraints for some particular machines.
File: gcc.info, Node: Simple Constraints, Next: Multi-Alternative, Up: Constraints
5.36.1 Simple Constraints
-------------------------
The simplest kind of constraint is a string full of letters, each of
which describes one kind of operand that is permitted. Here are the
letters that are allowed:
whitespace
Whitespace characters are ignored and can be inserted at any
position except the first. This enables each alternative for
different operands to be visually aligned in the machine
description even if they have different number of constraints and
modifiers.
`m'
A memory operand is allowed, with any kind of address that the
machine supports in general.
`o'
A memory operand is allowed, but only if the address is
"offsettable". This means that adding a small integer (actually,
the width in bytes of the operand, as determined by its machine
mode) may be added to the address and the result is also a valid
memory address.
For example, an address which is constant is offsettable; so is an
address that is the sum of a register and a constant (as long as a
slightly larger constant is also within the range of
address-offsets supported by the machine); but an autoincrement or
autodecrement address is not offsettable. More complicated
indirect/indexed addresses may or may not be offsettable depending
on the other addressing modes that the machine supports.
Note that in an output operand which can be matched by another
operand, the constraint letter `o' is valid only when accompanied
by both `<' (if the target machine has predecrement addressing)
and `>' (if the target machine has preincrement addressing).
`V'
A memory operand that is not offsettable. In other words,
anything that would fit the `m' constraint but not the `o'
constraint.
`<'
A memory operand with autodecrement addressing (either
predecrement or postdecrement) is allowed.
`>'
A memory operand with autoincrement addressing (either
preincrement or postincrement) is allowed.
`r'
A register operand is allowed provided that it is in a general
register.
`i'
An immediate integer operand (one with constant value) is allowed.
This includes symbolic constants whose values will be known only at
assembly time or later.
`n'
An immediate integer operand with a known numeric value is allowed.
Many systems cannot support assembly-time constants for operands
less than a word wide. Constraints for these operands should use
`n' rather than `i'.
`I', `J', `K', ... `P'
Other letters in the range `I' through `P' may be defined in a
machine-dependent fashion to permit immediate integer operands with
explicit integer values in specified ranges. For example, on the
68000, `I' is defined to stand for the range of values 1 to 8.
This is the range permitted as a shift count in the shift
instructions.
`E'
An immediate floating operand (expression code `const_double') is
allowed, but only if the target floating point format is the same
as that of the host machine (on which the compiler is running).
`F'
An immediate floating operand (expression code `const_double' or
`const_vector') is allowed.
`G', `H'
`G' and `H' may be defined in a machine-dependent fashion to
permit immediate floating operands in particular ranges of values.
`s'
An immediate integer operand whose value is not an explicit
integer is allowed.
This might appear strange; if an insn allows a constant operand
with a value not known at compile time, it certainly must allow
any known value. So why use `s' instead of `i'? Sometimes it
allows better code to be generated.
For example, on the 68000 in a fullword instruction it is possible
to use an immediate operand; but if the immediate value is between
-128 and 127, better code results from loading the value into a
register and using the register. This is because the load into
the register can be done with a `moveq' instruction. We arrange
for this to happen by defining the letter `K' to mean "any integer
outside the range -128 to 127", and then specifying `Ks' in the
operand constraints.
`g'
Any register, memory or immediate integer operand is allowed,
except for registers that are not general registers.
`X'
Any operand whatsoever is allowed.
`0', `1', `2', ... `9'
An operand that matches the specified operand number is allowed.
If a digit is used together with letters within the same
alternative, the digit should come last.
This number is allowed to be more than a single digit. If multiple
digits are encountered consecutively, they are interpreted as a
single decimal integer. There is scant chance for ambiguity,
since to-date it has never been desirable that `10' be interpreted
as matching either operand 1 _or_ operand 0. Should this be
desired, one can use multiple alternatives instead.
This is called a "matching constraint" and what it really means is
that the assembler has only a single operand that fills two roles
which `asm' distinguishes. For example, an add instruction uses
two input operands and an output operand, but on most CISC
machines an add instruction really has only two operands, one of
them an input-output operand:
addl #35,r12
Matching constraints are used in these circumstances. More
precisely, the two operands that match must include one input-only
operand and one output-only operand. Moreover, the digit must be a
smaller number than the number of the operand that uses it in the
constraint.
`p'
An operand that is a valid memory address is allowed. This is for
"load address" and "push address" instructions.
`p' in the constraint must be accompanied by `address_operand' as
the predicate in the `match_operand'. This predicate interprets
the mode specified in the `match_operand' as the mode of the memory
reference for which the address would be valid.
OTHER-LETTERS
Other letters can be defined in machine-dependent fashion to stand
for particular classes of registers or other arbitrary operand
types. `d', `a' and `f' are defined on the 68000/68020 to stand
for data, address and floating point registers.
File: gcc.info, Node: Multi-Alternative, Next: Modifiers, Prev: Simple Constraints, Up: Constraints
5.36.2 Multiple Alternative Constraints
---------------------------------------
Sometimes a single instruction has multiple alternative sets of possible
operands. For example, on the 68000, a logical-or instruction can
combine register or an immediate value into memory, or it can combine
any kind of operand into a register; but it cannot combine one memory
location into another.
These constraints are represented as multiple alternatives. An
alternative can be described by a series of letters for each operand.
The overall constraint for an operand is made from the letters for this
operand from the first alternative, a comma, the letters for this
operand from the second alternative, a comma, and so on until the last
alternative.
If all the operands fit any one alternative, the instruction is valid.
Otherwise, for each alternative, the compiler counts how many
instructions must be added to copy the operands so that that
alternative applies. The alternative requiring the least copying is
chosen. If two alternatives need the same amount of copying, the one
that comes first is chosen. These choices can be altered with the `?'
and `!' characters:
`?'
Disparage slightly the alternative that the `?' appears in, as a
choice when no alternative applies exactly. The compiler regards
this alternative as one unit more costly for each `?' that appears
in it.
`!'
Disparage severely the alternative that the `!' appears in. This
alternative can still be used if it fits without reloading, but if
reloading is needed, some other alternative will be used.
File: gcc.info, Node: Modifiers, Next: Machine Constraints, Prev: Multi-Alternative, Up: Constraints
5.36.3 Constraint Modifier Characters
-------------------------------------
Here are constraint modifier characters.
`='
Means that this operand is write-only for this instruction: the
previous value is discarded and replaced by output data.
`+'
Means that this operand is both read and written by the
instruction.
When the compiler fixes up the operands to satisfy the constraints,
it needs to know which operands are inputs to the instruction and
which are outputs from it. `=' identifies an output; `+'
identifies an operand that is both input and output; all other
operands are assumed to be input only.
If you specify `=' or `+' in a constraint, you put it in the first
character of the constraint string.
`&'
Means (in a particular alternative) that this operand is an
"earlyclobber" operand, which is modified before the instruction is
finished using the input operands. Therefore, this operand may
not lie in a register that is used as an input operand or as part
of any memory address.
`&' applies only to the alternative in which it is written. In
constraints with multiple alternatives, sometimes one alternative
requires `&' while others do not. See, for example, the `movdf'
insn of the 68000.
An input operand can be tied to an earlyclobber operand if its only
use as an input occurs before the early result is written. Adding
alternatives of this form often allows GCC to produce better code
when only some of the inputs can be affected by the earlyclobber.
See, for example, the `mulsi3' insn of the ARM.
`&' does not obviate the need to write `='.
`%'
Declares the instruction to be commutative for this operand and the
following operand. This means that the compiler may interchange
the two operands if that is the cheapest way to make all operands
fit the constraints. GCC can only handle one commutative pair in
an asm; if you use more, the compiler may fail. Note that you
need not use the modifier if the two alternatives are strictly
identical; this would only waste time in the reload pass. The
modifier is not operational after register allocation, so the
result of `define_peephole2' and `define_split's performed after
reload cannot rely on `%' to make the intended insn match.
`#'
Says that all following characters, up to the next comma, are to be
ignored as a constraint. They are significant only for choosing
register preferences.
`*'
Says that the following character should be ignored when choosing
register preferences. `*' has no effect on the meaning of the
constraint as a constraint, and no effect on reloading.
File: gcc.info, Node: Machine Constraints, Prev: Modifiers, Up: Constraints
5.36.4 Constraints for Particular Machines
------------------------------------------
Whenever possible, you should use the general-purpose constraint letters
in `asm' arguments, since they will convey meaning more readily to
people reading your code. Failing that, use the constraint letters
that usually have very similar meanings across architectures. The most
commonly used constraints are `m' and `r' (for memory and
general-purpose registers respectively; *note Simple Constraints::), and
`I', usually the letter indicating the most common immediate-constant
format.
Each architecture defines additional constraints. These constraints
are used by the compiler itself for instruction generation, as well as
for `asm' statements; therefore, some of the constraints are not
particularly useful for `asm'. Here is a summary of some of the
machine-dependent constraints available on some particular machines; it
includes both constraints that are useful for `asm' and constraints
that aren't. The compiler source file mentioned in the table heading
for each architecture is the definitive reference for the meanings of
that architecture's constraints.
_ARM family--`config/arm/arm.h'_
`f'
Floating-point register
`w'
VFP floating-point register
`F'
One of the floating-point constants 0.0, 0.5, 1.0, 2.0, 3.0,
4.0, 5.0 or 10.0
`G'
Floating-point constant that would satisfy the constraint `F'
if it were negated
`I'
Integer that is valid as an immediate operand in a data
processing instruction. That is, an integer in the range 0
to 255 rotated by a multiple of 2
`J'
Integer in the range -4095 to 4095
`K'
Integer that satisfies constraint `I' when inverted (ones
complement)
`L'
Integer that satisfies constraint `I' when negated (twos
complement)
`M'
Integer in the range 0 to 32
`Q'
A memory reference where the exact address is in a single
register (``m'' is preferable for `asm' statements)
`R'
An item in the constant pool
`S'
A symbol in the text segment of the current file
`Uv'
A memory reference suitable for VFP load/store insns
(reg+constant offset)
`Uy'
A memory reference suitable for iWMMXt load/store
instructions.
`Uq'
A memory reference suitable for the ARMv4 ldrsb instruction.
_AVR family--`config/avr/constraints.md'_
`l'
Registers from r0 to r15
`a'
Registers from r16 to r23
`d'
Registers from r16 to r31
`w'
Registers from r24 to r31. These registers can be used in
`adiw' command
`e'
Pointer register (r26-r31)
`b'
Base pointer register (r28-r31)
`q'
Stack pointer register (SPH:SPL)
`t'
Temporary register r0
`x'
Register pair X (r27:r26)
`y'
Register pair Y (r29:r28)
`z'
Register pair Z (r31:r30)
`I'
Constant greater than -1, less than 64
`J'
Constant greater than -64, less than 1
`K'
Constant integer 2
`L'
Constant integer 0
`M'
Constant that fits in 8 bits
`N'
Constant integer -1
`O'
Constant integer 8, 16, or 24
`P'
Constant integer 1
`G'
A floating point constant 0.0
_CRX Architecture--`config/crx/crx.h'_
`b'
Registers from r0 to r14 (registers without stack pointer)
`l'
Register r16 (64-bit accumulator lo register)
`h'
Register r17 (64-bit accumulator hi register)
`k'
Register pair r16-r17. (64-bit accumulator lo-hi pair)
`I'
Constant that fits in 3 bits
`J'
Constant that fits in 4 bits
`K'
Constant that fits in 5 bits
`L'
Constant that is one of -1, 4, -4, 7, 8, 12, 16, 20, 32, 48
`G'
Floating point constant that is legal for store immediate
_PowerPC and IBM RS6000--`config/rs6000/rs6000.h'_
`b'
Address base register
`f'
Floating point register
`v'
Vector register
`h'
`MQ', `CTR', or `LINK' register
`q'
`MQ' register
`c'
`CTR' register
`l'
`LINK' register
`x'
`CR' register (condition register) number 0
`y'
`CR' register (condition register)
`z'
`FPMEM' stack memory for FPR-GPR transfers
`I'
Signed 16-bit constant
`J'
Unsigned 16-bit constant shifted left 16 bits (use `L'
instead for `SImode' constants)
`K'
Unsigned 16-bit constant
`L'
Signed 16-bit constant shifted left 16 bits
`M'
Constant larger than 31
`N'
Exact power of 2
`O'
Zero
`P'
Constant whose negation is a signed 16-bit constant
`G'
Floating point constant that can be loaded into a register
with one instruction per word
`Q'
Memory operand that is an offset from a register (`m' is
preferable for `asm' statements)
`R'
AIX TOC entry
`S'
Constant suitable as a 64-bit mask operand
`T'
Constant suitable as a 32-bit mask operand
`U'
System V Release 4 small data area reference
_MorphoTech family--`config/mt/mt.h'_
`I'
Constant for an arithmetic insn (16-bit signed integer).
`J'
The constant 0.
`K'
Constant for a logical insn (16-bit zero-extended integer).
`L'
A constant that can be loaded with `lui' (i.e. the bottom 16
bits are zero).
`M'
A constant that takes two words to load (i.e. not matched by
`I', `K', or `L').
`N'
Negative 16-bit constants other than -65536.
`O'
A 15-bit signed integer constant.
`P'
A positive 16-bit constant.
_Intel 386--`config/i386/constraints.md'_
`R'
Legacy register--the eight integer registers available on all
i386 processors (`a', `b', `c', `d', `si', `di', `bp', `sp').
`q'
Any register accessible as `Rl'. In 32-bit mode, `a', `b',
`c', and `d'; in 64-bit mode, any integer register.
`Q'
Any register accessible as `Rh': `a', `b', `c', and `d'.
`a'
The `a' register.
`b'
The `b' register.
`c'
The `c' register.
`d'
The `d' register.
`S'
The `si' register.
`D'
The `di' register.
`A'
The `a' and `d' registers, as a pair (for instructions that
return half the result in one and half in the other).
`f'
Any 80387 floating-point (stack) register.
`t'
Top of 80387 floating-point stack (`%st(0)').
`u'
Second from top of 80387 floating-point stack (`%st(1)').
`y'
Any MMX register.
`x'
Any SSE register.
`I'
Integer constant in the range 0 ... 31, for 32-bit shifts.
`J'
Integer constant in the range 0 ... 63, for 64-bit shifts.
`K'
Signed 8-bit integer constant.
`L'
`0xFF' or `0xFFFF', for andsi as a zero-extending move.
`M'
0, 1, 2, or 3 (shifts for the `lea' instruction).
`N'
Unsigned 8-bit integer constant (for `in' and `out'
instructions).
`G'
Standard 80387 floating point constant.
`C'
Standard SSE floating point constant.
`e'
32-bit signed integer constant, or a symbolic reference known
to fit that range (for immediate operands in sign-extending
x86-64 instructions).
`Z'
32-bit unsigned integer constant, or a symbolic reference
known to fit that range (for immediate operands in
zero-extending x86-64 instructions).
_Intel IA-64--`config/ia64/ia64.h'_
`a'
General register `r0' to `r3' for `addl' instruction
`b'
Branch register
`c'
Predicate register (`c' as in "conditional")
`d'
Application register residing in M-unit
`e'
Application register residing in I-unit
`f'
Floating-point register
`m'
Memory operand. Remember that `m' allows postincrement and
postdecrement which require printing with `%Pn' on IA-64.
Use `S' to disallow postincrement and postdecrement.
`G'
Floating-point constant 0.0 or 1.0
`I'
14-bit signed integer constant
`J'
22-bit signed integer constant
`K'
8-bit signed integer constant for logical instructions
`L'
8-bit adjusted signed integer constant for compare pseudo-ops
`M'
6-bit unsigned integer constant for shift counts
`N'
9-bit signed integer constant for load and store
postincrements
`O'
The constant zero
`P'
0 or -1 for `dep' instruction
`Q'
Non-volatile memory for floating-point loads and stores
`R'
Integer constant in the range 1 to 4 for `shladd' instruction
`S'
Memory operand except postincrement and postdecrement
_FRV--`config/frv/frv.h'_
`a'
Register in the class `ACC_REGS' (`acc0' to `acc7').
`b'
Register in the class `EVEN_ACC_REGS' (`acc0' to `acc7').
`c'
Register in the class `CC_REGS' (`fcc0' to `fcc3' and `icc0'
to `icc3').
`d'
Register in the class `GPR_REGS' (`gr0' to `gr63').
`e'
Register in the class `EVEN_REGS' (`gr0' to `gr63'). Odd
registers are excluded not in the class but through the use
of a machine mode larger than 4 bytes.
`f'
Register in the class `FPR_REGS' (`fr0' to `fr63').
`h'
Register in the class `FEVEN_REGS' (`fr0' to `fr63'). Odd
registers are excluded not in the class but through the use
of a machine mode larger than 4 bytes.
`l'
Register in the class `LR_REG' (the `lr' register).
`q'
Register in the class `QUAD_REGS' (`gr2' to `gr63').
Register numbers not divisible by 4 are excluded not in the
class but through the use of a machine mode larger than 8
bytes.
`t'
Register in the class `ICC_REGS' (`icc0' to `icc3').
`u'
Register in the class `FCC_REGS' (`fcc0' to `fcc3').
`v'
Register in the class `ICR_REGS' (`cc4' to `cc7').
`w'
Register in the class `FCR_REGS' (`cc0' to `cc3').
`x'
Register in the class `QUAD_FPR_REGS' (`fr0' to `fr63').
Register numbers not divisible by 4 are excluded not in the
class but through the use of a machine mode larger than 8
bytes.
`z'
Register in the class `SPR_REGS' (`lcr' and `lr').
`A'
Register in the class `QUAD_ACC_REGS' (`acc0' to `acc7').
`B'
Register in the class `ACCG_REGS' (`accg0' to `accg7').
`C'
Register in the class `CR_REGS' (`cc0' to `cc7').
`G'
Floating point constant zero
`I'
6-bit signed integer constant
`J'
10-bit signed integer constant
`L'
16-bit signed integer constant
`M'
16-bit unsigned integer constant
`N'
12-bit signed integer constant that is negative--i.e. in the
range of -2048 to -1
`O'
Constant zero
`P'
12-bit signed integer constant that is greater than
zero--i.e. in the range of 1 to 2047.
_Blackfin family--`config/bfin/bfin.h'_
`a'
P register
`d'
D register
`z'
A call clobbered P register.
`D'
Even-numbered D register
`W'
Odd-numbered D register
`e'
Accumulator register.
`A'
Even-numbered accumulator register.
`B'
Odd-numbered accumulator register.
`b'
I register
`v'
B register
`f'
M register
`c'
Registers used for circular buffering, i.e. I, B, or L
registers.
`C'
The CC register.
`t'
LT0 or LT1.
`k'
LC0 or LC1.
`u'
LB0 or LB1.
`x'
Any D, P, B, M, I or L register.
`y'
Additional registers typically used only in prologues and
epilogues: RETS, RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and
USP.
`w'
Any register except accumulators or CC.
`Ksh'
Signed 16 bit integer (in the range -32768 to 32767)
`Kuh'
Unsigned 16 bit integer (in the range 0 to 65535)
`Ks7'
Signed 7 bit integer (in the range -64 to 63)
`Ku7'
Unsigned 7 bit integer (in the range 0 to 127)
`Ku5'
Unsigned 5 bit integer (in the range 0 to 31)
`Ks4'
Signed 4 bit integer (in the range -8 to 7)
`Ks3'
Signed 3 bit integer (in the range -3 to 4)
`Ku3'
Unsigned 3 bit integer (in the range 0 to 7)
`PN'
Constant N, where N is a single-digit constant in the range 0
to 4.
`M1'
Constant 255.
`M2'
Constant 65535.
`J'
An integer constant with exactly a single bit set.
`L'
An integer constant with all bits set except exactly one.
`H'
`Q'
Any SYMBOL_REF.
_M32C--`config/m32c/m32c.c'_
`Rsp'
`Rfb'
`Rsb'
`$sp', `$fb', `$sb'.
`Rcr'
Any control register, when they're 16 bits wide (nothing if
control registers are 24 bits wide)
`Rcl'
Any control register, when they're 24 bits wide.
`R0w'
`R1w'
`R2w'
`R3w'
$r0, $r1, $r2, $r3.
`R02'
$r0 or $r2, or $r2r0 for 32 bit values.
`R13'
$r1 or $r3, or $r3r1 for 32 bit values.
`Rdi'
A register that can hold a 64 bit value.
`Rhl'
$r0 or $r1 (registers with addressable high/low bytes)
`R23'
$r2 or $r3
`Raa'
Address registers
`Raw'
Address registers when they're 16 bits wide.
`Ral'
Address registers when they're 24 bits wide.
`Rqi'
Registers that can hold QI values.
`Rad'
Registers that can be used with displacements ($a0, $a1, $sb).
`Rsi'
Registers that can hold 32 bit values.
`Rhi'
Registers that can hold 16 bit values.
`Rhc'
Registers chat can hold 16 bit values, including all control
registers.
`Rra'
$r0 through R1, plus $a0 and $a1.
`Rfl'
The flags register.
`Rmm'
The memory-based pseudo-registers $mem0 through $mem15.
`Rpi'
Registers that can hold pointers (16 bit registers for r8c,
m16c; 24 bit registers for m32cm, m32c).
`Rpa'
Matches multiple registers in a PARALLEL to form a larger
register. Used to match function return values.
`Is3'
-8 ... 7
`IS1'
-128 ... 127
`IS2'
-32768 ... 32767
`IU2'
0 ... 65535
`In4'
-8 ... -1 or 1 ... 8
`In5'
-16 ... -1 or 1 ... 16
`In6'
-32 ... -1 or 1 ... 32
`IM2'
-65536 ... -1
`Ilb'
An 8 bit value with exactly one bit set.
`Ilw'
A 16 bit value with exactly one bit set.
`Sd'
The common src/dest memory addressing modes.
`Sa'
Memory addressed using $a0 or $a1.
`Si'
Memory addressed with immediate addresses.
`Ss'
Memory addressed using the stack pointer ($sp).
`Sf'
Memory addressed using the frame base register ($fb).
`Ss'
Memory addressed using the small base register ($sb).
`S1'
$r1h
_MIPS--`config/mips/constraints.md'_
`d'
An address register. This is equivalent to `r' unless
generating MIPS16 code.
`f'
A floating-point register (if available).
`h'
The `hi' register.
`l'
The `lo' register.
`x'
The `hi' and `lo' registers.
`c'
A register suitable for use in an indirect jump. This will
always be `$25' for `-mabicalls'.
`y'
Equivalent to `r'; retained for backwards compatibility.
`z'
A floating-point condition code register.
`I'
A signed 16-bit constant (for arithmetic instructions).
`J'
Integer zero.
`K'
An unsigned 16-bit constant (for logic instructions).
`L'
A signed 32-bit constant in which the lower 16 bits are zero.
Such constants can be loaded using `lui'.
`M'
A constant that cannot be loaded using `lui', `addiu' or
`ori'.
`N'
A constant in the range -65535 to -1 (inclusive).
`O'
A signed 15-bit constant.
`P'
A constant in the range 1 to 65535 (inclusive).
`G'
Floating-point zero.
`R'
An address that can be used in a non-macro load or store.
_Motorola 680x0--`config/m68k/m68k.h'_
`a'
Address register
`d'
Data register
`f'
68881 floating-point register, if available
`I'
Integer in the range 1 to 8
`J'
16-bit signed number
`K'
Signed number whose magnitude is greater than 0x80
`L'
Integer in the range -8 to -1
`M'
Signed number whose magnitude is greater than 0x100
`G'
Floating point constant that is not a 68881 constant
_Motorola 68HC11 & 68HC12 families--`config/m68hc11/m68hc11.h'_
`a'
Register `a'
`b'
Register `b'
`d'
Register `d'
`q'
An 8-bit register
`t'
Temporary soft register _.tmp
`u'
A soft register _.d1 to _.d31
`w'
Stack pointer register
`x'
Register `x'
`y'
Register `y'
`z'
Pseudo register `z' (replaced by `x' or `y' at the end)
`A'
An address register: x, y or z
`B'
An address register: x or y
`D'
Register pair (x:d) to form a 32-bit value
`L'
Constants in the range -65536 to 65535
`M'
Constants whose 16-bit low part is zero
`N'
Constant integer 1 or -1
`O'
Constant integer 16
`P'
Constants in the range -8 to 2
_SPARC--`config/sparc/sparc.h'_
`f'
Floating-point register on the SPARC-V8 architecture and
lower floating-point register on the SPARC-V9 architecture.
`e'
Floating-point register. It is equivalent to `f' on the
SPARC-V8 architecture and contains both lower and upper
floating-point registers on the SPARC-V9 architecture.
`c'
Floating-point condition code register.
`d'
Lower floating-point register. It is only valid on the
SPARC-V9 architecture when the Visual Instruction Set is
available.
`b'
Floating-point register. It is only valid on the SPARC-V9
architecture when the Visual Instruction Set is available.
`h'
64-bit global or out register for the SPARC-V8+ architecture.
`I'
Signed 13-bit constant
`J'
Zero
`K'
32-bit constant with the low 12 bits clear (a constant that
can be loaded with the `sethi' instruction)
`L'
A constant in the range supported by `movcc' instructions
`M'
A constant in the range supported by `movrcc' instructions
`N'
Same as `K', except that it verifies that bits that are not
in the lower 32-bit range are all zero. Must be used instead
of `K' for modes wider than `SImode'
`O'
The constant 4096
`G'
Floating-point zero
`H'
Signed 13-bit constant, sign-extended to 32 or 64 bits
`Q'
Floating-point constant whose integral representation can be
moved into an integer register using a single sethi
instruction
`R'
Floating-point constant whose integral representation can be
moved into an integer register using a single mov instruction
`S'
Floating-point constant whose integral representation can be
moved into an integer register using a high/lo_sum
instruction sequence
`T'
Memory address aligned to an 8-byte boundary
`U'
Even register
`W'
Memory address for `e' constraint registers
`Y'
Vector zero
_TMS320C3x/C4x--`config/c4x/c4x.h'_
`a'
Auxiliary (address) register (ar0-ar7)
`b'
Stack pointer register (sp)
`c'
Standard (32-bit) precision integer register
`f'
Extended (40-bit) precision register (r0-r11)
`k'
Block count register (bk)
`q'
Extended (40-bit) precision low register (r0-r7)
`t'
Extended (40-bit) precision register (r0-r1)
`u'
Extended (40-bit) precision register (r2-r3)
`v'
Repeat count register (rc)
`x'
Index register (ir0-ir1)
`y'
Status (condition code) register (st)
`z'
Data page register (dp)
`G'
Floating-point zero
`H'
Immediate 16-bit floating-point constant
`I'
Signed 16-bit constant
`J'
Signed 8-bit constant
`K'
Signed 5-bit constant
`L'
Unsigned 16-bit constant
`M'
Unsigned 8-bit constant
`N'
Ones complement of unsigned 16-bit constant
`O'
High 16-bit constant (32-bit constant with 16 LSBs zero)
`Q'
Indirect memory reference with signed 8-bit or index register
displacement
`R'
Indirect memory reference with unsigned 5-bit displacement
`S'
Indirect memory reference with 1 bit or index register
displacement
`T'
Direct memory reference
`U'
Symbolic address
_S/390 and zSeries--`config/s390/s390.h'_
`a'
Address register (general purpose register except r0)
`c'
Condition code register
`d'
Data register (arbitrary general purpose register)
`f'
Floating-point register
`I'
Unsigned 8-bit constant (0-255)
`J'
Unsigned 12-bit constant (0-4095)
`K'
Signed 16-bit constant (-32768-32767)
`L'
Value appropriate as displacement.
`(0..4095)'
for short displacement
`(-524288..524287)'
for long displacement
`M'
Constant integer with a value of 0x7fffffff.
`N'
Multiple letter constraint followed by 4 parameter letters.
`0..9:'
number of the part counting from most to least
significant
`H,Q:'
mode of the part
`D,S,H:'
mode of the containing operand
`0,F:'
value of the other parts (F--all bits set)
The constraint matches if the specified part of a constant
has a value different from it's other parts.
`Q'
Memory reference without index register and with short
displacement.
`R'
Memory reference with index register and short displacement.
`S'
Memory reference without index register but with long
displacement.
`T'
Memory reference with index register and long displacement.
`U'
Pointer with short displacement.
`W'
Pointer with long displacement.
`Y'
Shift count operand.
_Score family--`config/score/score.h'_
`d'
Registers from r0 to r32.
`e'
Registers from r0 to r16.
`t'
r8--r11 or r22--r27 registers.
`h'
hi register.
`l'
lo register.
`x'
hi + lo register.
`q'
cnt register.
`y'
lcb register.
`z'
scb register.
`a'
cnt + lcb + scb register.
`c'
cr0--cr15 register.
`b'
cp1 registers.
`f'
cp2 registers.
`i'
cp3 registers.
`j'
cp1 + cp2 + cp3 registers.
`I'
High 16-bit constant (32-bit constant with 16 LSBs zero).
`J'
Unsigned 5 bit integer (in the range 0 to 31).
`K'
Unsigned 16 bit integer (in the range 0 to 65535).
`L'
Signed 16 bit integer (in the range -32768 to 32767).
`M'
Unsigned 14 bit integer (in the range 0 to 16383).
`N'
Signed 14 bit integer (in the range -8192 to 8191).
`Z'
Any SYMBOL_REF.
_Xstormy16--`config/stormy16/stormy16.h'_
`a'
Register r0.
`b'
Register r1.
`c'
Register r2.
`d'
Register r8.
`e'
Registers r0 through r7.
`t'
Registers r0 and r1.
`y'
The carry register.
`z'
Registers r8 and r9.
`I'
A constant between 0 and 3 inclusive.
`J'
A constant that has exactly one bit set.
`K'
A constant that has exactly one bit clear.
`L'
A constant between 0 and 255 inclusive.
`M'
A constant between -255 and 0 inclusive.
`N'
A constant between -3 and 0 inclusive.
`O'
A constant between 1 and 4 inclusive.
`P'
A constant between -4 and -1 inclusive.
`Q'
A memory reference that is a stack push.
`R'
A memory reference that is a stack pop.
`S'
A memory reference that refers to a constant address of known
value.
`T'
The register indicated by Rx (not implemented yet).
`U'
A constant that is not between 2 and 15 inclusive.
`Z'
The constant 0.
_Xtensa--`config/xtensa/xtensa.h'_
`a'
General-purpose 32-bit register
`b'
One-bit boolean register
`A'
MAC16 40-bit accumulator register
`I'
Signed 12-bit integer constant, for use in MOVI instructions
`J'
Signed 8-bit integer constant, for use in ADDI instructions
`K'
Integer constant valid for BccI instructions
`L'
Unsigned constant valid for BccUI instructions
File: gcc.info, Node: Asm Labels, Next: Explicit Reg Vars, Prev: Constraints, Up: C Extensions
5.37 Controlling Names Used in Assembler Code
=============================================
You can specify the name to be used in the assembler code for a C
function or variable by writing the `asm' (or `__asm__') keyword after
the declarator as follows:
int foo asm ("myfoo") = 2;
This specifies that the name to be used for the variable `foo' in the
assembler code should be `myfoo' rather than the usual `_foo'.
On systems where an underscore is normally prepended to the name of a C
function or variable, this feature allows you to define names for the
linker that do not start with an underscore.
It does not make sense to use this feature with a non-static local
variable since such variables do not have assembler names. If you are
trying to put the variable in a particular register, see *Note Explicit
Reg Vars::. GCC presently accepts such code with a warning, but will
probably be changed to issue an error, rather than a warning, in the
future.
You cannot use `asm' in this way in a function _definition_; but you
can get the same effect by writing a declaration for the function
before its definition and putting `asm' there, like this:
extern func () asm ("FUNC");
func (x, y)
int x, y;
/* ... */
It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols. Also, you must not use a
register name; that would produce completely invalid assembler code.
GCC does not as yet have the ability to store static variables in
registers. Perhaps that will be added.
File: gcc.info, Node: Explicit Reg Vars, Next: Alternate Keywords, Prev: Asm Labels, Up: C Extensions
5.38 Variables in Specified Registers
=====================================
GNU C allows you to put a few global variables into specified hardware
registers. You can also specify the register in which an ordinary
register variable should be allocated.
* Global register variables reserve registers throughout the program.
This may be useful in programs such as programming language
interpreters which have a couple of global variables that are
accessed very often.
* Local register variables in specific registers do not reserve the
registers, except at the point where they are used as input or
output operands in an `asm' statement and the `asm' statement
itself is not deleted. The compiler's data flow analysis is
capable of determining where the specified registers contain live
values, and where they are available for other uses. Stores into
local register variables may be deleted when they appear to be
dead according to dataflow analysis. References to local register
variables may be deleted or moved or simplified.
These local variables are sometimes convenient for use with the
extended `asm' feature (*note Extended Asm::), if you want to
write one output of the assembler instruction directly into a
particular register. (This will work provided the register you
specify fits the constraints specified for that operand in the
`asm'.)
* Menu:
* Global Reg Vars::
* Local Reg Vars::
File: gcc.info, Node: Global Reg Vars, Next: Local Reg Vars, Up: Explicit Reg Vars
5.38.1 Defining Global Register Variables
-----------------------------------------
You can define a global register variable in GNU C like this:
register int *foo asm ("a5");
Here `a5' is the name of the register which should be used. Choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.
Naturally the register name is cpu-dependent, so you would need to
conditionalize your program according to cpu type. The register `a5'
would be a good choice on a 68000 for a variable of pointer type. On
machines with register windows, be sure to choose a "global" register
that is not affected magically by the function call mechanism.
In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.
Eventually there may be a way of asking the compiler to choose a
register automatically, but first we need to figure out how it should
choose and how to enable you to guide the choice. No solution is
evident.
Defining a global register variable in a certain register reserves that
register entirely for this use, at least within the current compilation.
The register will not be allocated for any other purpose in the
functions in the current compilation. The register will not be saved
and restored by these functions. Stores into this register are never
deleted even if they would appear to be dead, but references may be
deleted or moved or simplified.
It is not safe to access the global register variables from signal
handlers, or from more than one thread of control, because the system
library routines may temporarily use the register for other things
(unless you recompile them specially for the task at hand).
It is not safe for one function that uses a global register variable to
call another such function `foo' by way of a third function `lose' that
was compiled without knowledge of this variable (i.e. in a different
source file in which the variable wasn't declared). This is because
`lose' might save the register and put some other value there. For
example, you can't expect a global register variable to be available in
the comparison-function that you pass to `qsort', since `qsort' might
have put something else in that register. (If you are prepared to
recompile `qsort' with the same global register variable, you can solve
this problem.)
If you want to recompile `qsort' or other source files which do not
actually use your global register variable, so that they will not use
that register for any other purpose, then it suffices to specify the
compiler option `-ffixed-REG'. You need not actually add a global
register declaration to their source code.
A function which can alter the value of a global register variable
cannot safely be called from a function compiled without this variable,
because it could clobber the value the caller expects to find there on
return. Therefore, the function which is the entry point into the part
of the program that uses the global register variable must explicitly
save and restore the value which belongs to its caller.
On most machines, `longjmp' will restore to each global register
variable the value it had at the time of the `setjmp'. On some
machines, however, `longjmp' will not change the value of global
register variables. To be portable, the function that called `setjmp'
should make other arrangements to save the values of the global register
variables, and to restore them in a `longjmp'. This way, the same
thing will happen regardless of what `longjmp' does.
All global register variable declarations must precede all function
definitions. If such a declaration could appear after function
definitions, the declaration would be too late to prevent the register
from being used for other purposes in the preceding functions.
Global register variables may not have initial values, because an
executable file has no means to supply initial contents for a register.
On the SPARC, there are reports that g3 ... g7 are suitable registers,
but certain library functions, such as `getwd', as well as the
subroutines for division and remainder, modify g3 and g4. g1 and g2
are local temporaries.
On the 68000, a2 ... a5 should be suitable, as should d2 ... d7. Of
course, it will not do to use more than a few of those.
File: gcc.info, Node: Local Reg Vars, Prev: Global Reg Vars, Up: Explicit Reg Vars
5.38.2 Specifying Registers for Local Variables
-----------------------------------------------
You can define a local register variable with a specified register like
this:
register int *foo asm ("a5");
Here `a5' is the name of the register which should be used. Note that
this is the same syntax used for defining global register variables,
but for a local variable it would appear within a function.
Naturally the register name is cpu-dependent, but this is not a
problem, since specific registers are most often useful with explicit
assembler instructions (*note Extended Asm::). Both of these things
generally require that you conditionalize your program according to cpu
type.
In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.
Defining such a register variable does not reserve the register; it
remains available for other uses in places where flow control determines
the variable's value is not live.
This option does not guarantee that GCC will generate code that has
this variable in the register you specify at all times. You may not
code an explicit reference to this register in the _assembler
instruction template_ part of an `asm' statement and assume it will
always refer to this variable. However, using the variable as an `asm'
_operand_ guarantees that the specified register is used for the
operand.
Stores into local register variables may be deleted when they appear
to be dead according to dataflow analysis. References to local
register variables may be deleted or moved or simplified.
As for global register variables, it's recommended that you choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it. A common
pitfall is to initialize multiple call-clobbered registers with
arbitrary expressions, where a function call or library call for an
arithmetic operator will overwrite a register value from a previous
assignment, for example `r0' below:
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = ...;
In those cases, a solution is to use a temporary variable for each
arbitrary expression. *Note Example of asm with clobbered asm reg::.
File: gcc.info, Node: Alternate Keywords, Next: Incomplete Enums, Prev: Explicit Reg Vars, Up: C Extensions
5.39 Alternate Keywords
=======================
`-ansi' and the various `-std' options disable certain keywords. This
causes trouble when you want to use GNU C extensions, or a
general-purpose header file that should be usable by all programs,
including ISO C programs. The keywords `asm', `typeof' and `inline'
are not available in programs compiled with `-ansi' or `-std' (although
`inline' can be used in a program compiled with `-std=c99'). The ISO
C99 keyword `restrict' is only available when `-std=gnu99' (which will
eventually be the default) or `-std=c99' (or the equivalent
`-std=iso9899:1999') is used.
The way to solve these problems is to put `__' at the beginning and
end of each problematical keyword. For example, use `__asm__' instead
of `asm', and `__inline__' instead of `inline'.
Other C compilers won't accept these alternative keywords; if you want
to compile with another compiler, you can define the alternate keywords
as macros to replace them with the customary keywords. It looks like
this:
#ifndef __GNUC__
#define __asm__ asm
#endif
`-pedantic' and other options cause warnings for many GNU C extensions.
You can prevent such warnings within one expression by writing
`__extension__' before the expression. `__extension__' has no effect
aside from this.
File: gcc.info, Node: Incomplete Enums, Next: Function Names, Prev: Alternate Keywords, Up: C Extensions
5.40 Incomplete `enum' Types
============================
You can define an `enum' tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
`struct foo' without describing the elements. A later declaration
which does specify the possible values completes the type.
You can't allocate variables or storage using the type while it is
incomplete. However, you can work with pointers to that type.
This extension may not be very useful, but it makes the handling of
`enum' more consistent with the way `struct' and `union' are handled.
This extension is not supported by GNU C++.
File: gcc.info, Node: Function Names, Next: Return Address, Prev: Incomplete Enums, Up: C Extensions
5.41 Function Names as Strings
==============================
GCC provides three magic variables which hold the name of the current
function, as a string. The first of these is `__func__', which is part
of the C99 standard:
The identifier `__func__' is implicitly declared by the translator
as if, immediately following the opening brace of each function
definition, the declaration
static const char __func__[] = "function-name";
appeared, where function-name is the name of the lexically-enclosing
function. This name is the unadorned name of the function.
`__FUNCTION__' is another name for `__func__'. Older versions of GCC
recognize only this name. However, it is not standardized. For
maximum portability, we recommend you use `__func__', but provide a
fallback definition with the preprocessor:
#if __STDC_VERSION__ < 199901L
# if __GNUC__ >= 2
# define __func__ __FUNCTION__
# else
# define __func__ "<unknown>"
# endif
#endif
In C, `__PRETTY_FUNCTION__' is yet another name for `__func__'.
However, in C++, `__PRETTY_FUNCTION__' contains the type signature of
the function as well as its bare name. For example, this program:
extern "C" {
extern int printf (char *, ...);
}
class a {
public:
void sub (int i)
{
printf ("__FUNCTION__ = %s\n", __FUNCTION__);
printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
}
};
int
main (void)
{
a ax;
ax.sub (0);
return 0;
}
gives this output:
__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)
These identifiers are not preprocessor macros. In GCC 3.3 and
earlier, in C only, `__FUNCTION__' and `__PRETTY_FUNCTION__' were
treated as string literals; they could be used to initialize `char'
arrays, and they could be concatenated with other string literals. GCC
3.4 and later treat them as variables, like `__func__'. In C++,
`__FUNCTION__' and `__PRETTY_FUNCTION__' have always been variables.
File: gcc.info, Node: Return Address, Next: Vector Extensions, Prev: Function Names, Up: C Extensions
5.42 Getting the Return or Frame Address of a Function
======================================================
These functions may be used to get information about the callers of a
function.
-- Built-in Function: void * __builtin_return_address (unsigned int
LEVEL)
This function returns the return address of the current function,
or of one of its callers. The LEVEL argument is number of frames
to scan up the call stack. A value of `0' yields the return
address of the current function, a value of `1' yields the return
address of the caller of the current function, and so forth. When
inlining the expected behavior is that the function will return
the address of the function that will be returned to. To work
around this behavior use the `noinline' function attribute.
The LEVEL argument must be a constant integer.
On some machines it may be impossible to determine the return
address of any function other than the current one; in such cases,
or when the top of the stack has been reached, this function will
return `0' or a random value. In addition,
`__builtin_frame_address' may be used to determine if the top of
the stack has been reached.
This function should only be used with a nonzero argument for
debugging purposes.
-- Built-in Function: void * __builtin_frame_address (unsigned int
LEVEL)
This function is similar to `__builtin_return_address', but it
returns the address of the function frame rather than the return
address of the function. Calling `__builtin_frame_address' with a
value of `0' yields the frame address of the current function, a
value of `1' yields the frame address of the caller of the current
function, and so forth.
The frame is the area on the stack which holds local variables and
saved registers. The frame address is normally the address of the
first word pushed on to the stack by the function. However, the
exact definition depends upon the processor and the calling
convention. If the processor has a dedicated frame pointer
register, and the function has a frame, then
`__builtin_frame_address' will return the value of the frame
pointer register.
On some machines it may be impossible to determine the frame
address of any function other than the current one; in such cases,
or when the top of the stack has been reached, this function will
return `0' if the first frame pointer is properly initialized by
the startup code.
This function should only be used with a nonzero argument for
debugging purposes.
File: gcc.info, Node: Vector Extensions, Next: Offsetof, Prev: Return Address, Up: C Extensions
5.43 Using vector instructions through built-in functions
=========================================================
On some targets, the instruction set contains SIMD vector instructions
that operate on multiple values contained in one large register at the
same time. For example, on the i386 the MMX, 3Dnow! and SSE extensions
can be used this way.
The first step in using these extensions is to provide the necessary
data types. This should be done using an appropriate `typedef':
typedef int v4si __attribute__ ((vector_size (16)));
The `int' type specifies the base type, while the attribute specifies
the vector size for the variable, measured in bytes. For example, the
declaration above causes the compiler to set the mode for the `v4si'
type to be 16 bytes wide and divided into `int' sized units. For a
32-bit `int' this means a vector of 4 units of 4 bytes, and the
corresponding mode of `foo' will be V4SI.
The `vector_size' attribute is only applicable to integral and float
scalars, although arrays, pointers, and function return values are
allowed in conjunction with this construct.
All the basic integer types can be used as base types, both as signed
and as unsigned: `char', `short', `int', `long', `long long'. In
addition, `float' and `double' can be used to build floating-point
vector types.
Specifying a combination that is not valid for the current architecture
will cause GCC to synthesize the instructions using a narrower mode.
For example, if you specify a variable of type `V4SI' and your
architecture does not allow for this specific SIMD type, GCC will
produce code that uses 4 `SIs'.
The types defined in this manner can be used with a subset of normal C
operations. Currently, GCC will allow using the following operators on
these types: `+, -, *, /, unary minus, ^, |, &, ~'.
The operations behave like C++ `valarrays'. Addition is defined as
the addition of the corresponding elements of the operands. For
example, in the code below, each of the 4 elements in A will be added
to the corresponding 4 elements in B and the resulting vector will be
stored in C.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a, b, c;
c = a + b;
Subtraction, multiplication, division, and the logical operations
operate in a similar manner. Likewise, the result of using the unary
minus or complement operators on a vector type is a vector whose
elements are the negative or complemented values of the corresponding
elements in the operand.
You can declare variables and use them in function calls and returns,
as well as in assignments and some casts. You can specify a vector
type as a return type for a function. Vector types can also be used as
function arguments. It is possible to cast from one vector type to
another, provided they are of the same size (in fact, you can also cast
vectors to and from other datatypes of the same size).
You cannot operate between vectors of different lengths or different
signedness without a cast.
A port that supports hardware vector operations, usually provides a set
of built-in functions that can be used to operate on vectors. For
example, a function to add two vectors and multiply the result by a
third could look like this:
v4si f (v4si a, v4si b, v4si c)
{
v4si tmp = __builtin_addv4si (a, b);
return __builtin_mulv4si (tmp, c);
}
File: gcc.info, Node: Offsetof, Next: Atomic Builtins, Prev: Vector Extensions, Up: C Extensions
5.44 Offsetof
=============
GCC implements for both C and C++ a syntactic extension to implement
the `offsetof' macro.
primary:
"__builtin_offsetof" "(" `typename' "," offsetof_member_designator ")"
offsetof_member_designator:
`identifier'
| offsetof_member_designator "." `identifier'
| offsetof_member_designator "[" `expr' "]"
This extension is sufficient such that
#define offsetof(TYPE, MEMBER) __builtin_offsetof (TYPE, MEMBER)
is a suitable definition of the `offsetof' macro. In C++, TYPE may be
dependent. In either case, MEMBER may consist of a single identifier,
or a sequence of member accesses and array references.
File: gcc.info, Node: Atomic Builtins, Next: Object Size Checking, Prev: Offsetof, Up: C Extensions
5.45 Built-in functions for atomic memory access
================================================
The following builtins are intended to be compatible with those
described in the `Intel Itanium Processor-specific Application Binary
Interface', section 7.4. As such, they depart from the normal GCC
practice of using the "__builtin_" prefix, and further that they are
overloaded such that they work on multiple types.
The definition given in the Intel documentation allows only for the
use of the types `int', `long', `long long' as well as their unsigned
counterparts. GCC will allow any integral scalar or pointer type that
is 1, 2, 4 or 8 bytes in length.
Not all operations are supported by all target processors. If a
particular operation cannot be implemented on the target processor, a
warning will be generated and a call an external function will be
generated. The external function will carry the same name as the
builtin, with an additional suffix `_N' where N is the size of the data
type.
In most cases, these builtins are considered a "full barrier". That
is, no memory operand will be moved across the operation, either
forward or backward. Further, instructions will be issued as necessary
to prevent the processor from speculating loads across the operation
and from queuing stores after the operation.
All of the routines are are described in the Intel documentation to
take "an optional list of variables protected by the memory barrier".
It's not clear what is meant by that; it could mean that _only_ the
following variables are protected, or it could mean that these variables
should in addition be protected. At present GCC ignores this list and
protects all variables which are globally accessible. If in the future
we make some use of this list, an empty list will continue to mean all
globally accessible variables.
`TYPE __sync_fetch_and_add (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_sub (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_or (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_and (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_xor (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_nand (TYPE *ptr, TYPE value, ...)'
These builtins perform the operation suggested by the name, and
returns the value that had previously been in memory. That is,
{ tmp = *ptr; *ptr OP= value; return tmp; }
{ tmp = *ptr; *ptr = ~tmp & value; return tmp; } // nand
`TYPE __sync_add_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_sub_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_or_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_and_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_xor_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_nand_and_fetch (TYPE *ptr, TYPE value, ...)'
These builtins perform the operation suggested by the name, and
return the new value. That is,
{ *ptr OP= value; return *ptr; }
{ *ptr = ~*ptr & value; return *ptr; } // nand
`bool __sync_bool_compare_and_swap (TYPE *ptr, TYPE oldval TYPE newval, ...)'
`TYPE __sync_val_compare_and_swap (TYPE *ptr, TYPE oldval TYPE newval, ...)'
These builtins perform an atomic compare and swap. That is, if
the current value of `*PTR' is OLDVAL, then write NEWVAL into
`*PTR'.
The "bool" version returns true if the comparison is successful and
NEWVAL was written. The "val" version returns the contents of
`*PTR' before the operation.
`__sync_synchronize (...)'
This builtin issues a full memory barrier.
`TYPE __sync_lock_test_and_set (TYPE *ptr, TYPE value, ...)'
This builtin, as described by Intel, is not a traditional
test-and-set operation, but rather an atomic exchange operation.
It writes VALUE into `*PTR', and returns the previous contents of
`*PTR'.
Many targets have only minimal support for such locks, and do not
support a full exchange operation. In this case, a target may
support reduced functionality here by which the _only_ valid value
to store is the immediate constant 1. The exact value actually
stored in `*PTR' is implementation defined.
This builtin is not a full barrier, but rather an "acquire
barrier". This means that references after the builtin cannot
move to (or be speculated to) before the builtin, but previous
memory stores may not be globally visible yet, and previous memory
loads may not yet be satisfied.
`void __sync_lock_release (TYPE *ptr, ...)'
This builtin releases the lock acquired by
`__sync_lock_test_and_set'. Normally this means writing the
constant 0 to `*PTR'.
This builtin is not a full barrier, but rather a "release barrier".
This means that all previous memory stores are globally visible,
and all previous memory loads have been satisfied, but following
memory reads are not prevented from being speculated to before the
barrier.
File: gcc.info, Node: Object Size Checking, Next: Other Builtins, Prev: Atomic Builtins, Up: C Extensions
5.46 Object Size Checking Builtins
==================================
GCC implements a limited buffer overflow protection mechanism that can
prevent some buffer overflow attacks.
-- Built-in Function: size_t __builtin_object_size (void * PTR, int
TYPE)
is a built-in construct that returns a constant number of bytes
from PTR to the end of the object PTR pointer points to (if known
at compile time). `__builtin_object_size' never evaluates its
arguments for side-effects. If there are any side-effects in
them, it returns `(size_t) -1' for TYPE 0 or 1 and `(size_t) 0'
for TYPE 2 or 3. If there are multiple objects PTR can point to
and all of them are known at compile time, the returned number is
the maximum of remaining byte counts in those objects if TYPE & 2
is 0 and minimum if nonzero. If it is not possible to determine
which objects PTR points to at compile time,
`__builtin_object_size' should return `(size_t) -1' for TYPE 0 or
1 and `(size_t) 0' for TYPE 2 or 3.
TYPE is an integer constant from 0 to 3. If the least significant
bit is clear, objects are whole variables, if it is set, a closest
surrounding subobject is considered the object a pointer points to.
The second bit determines if maximum or minimum of remaining bytes
is computed.
struct V { char buf1[10]; int b; char buf2[10]; } var;
char *p = &var.buf1[1], *q = &var.b;
/* Here the object p points to is var. */
assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
/* The subobject p points to is var.buf1. */
assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
/* The object q points to is var. */
assert (__builtin_object_size (q, 0)
== (char *) (&var + 1) - (char *) &var.b);
/* The subobject q points to is var.b. */
assert (__builtin_object_size (q, 1) == sizeof (var.b));
There are built-in functions added for many common string operation
functions, e.g. for `memcpy' `__builtin___memcpy_chk' built-in is
provided. This built-in has an additional last argument, which is the
number of bytes remaining in object the DEST argument points to or
`(size_t) -1' if the size is not known.
The built-in functions are optimized into the normal string functions
like `memcpy' if the last argument is `(size_t) -1' or if it is known
at compile time that the destination object will not be overflown. If
the compiler can determine at compile time the object will be always
overflown, it issues a warning.
The intended use can be e.g.
#undef memcpy
#define bos0(dest) __builtin_object_size (dest, 0)
#define memcpy(dest, src, n) \
__builtin___memcpy_chk (dest, src, n, bos0 (dest))
char *volatile p;
char buf[10];
/* It is unknown what object p points to, so this is optimized
into plain memcpy - no checking is possible. */
memcpy (p, "abcde", n);
/* Destination is known and length too. It is known at compile
time there will be no overflow. */
memcpy (&buf[5], "abcde", 5);
/* Destination is known, but the length is not known at compile time.
This will result in __memcpy_chk call that can check for overflow
at runtime. */
memcpy (&buf[5], "abcde", n);
/* Destination is known and it is known at compile time there will
be overflow. There will be a warning and __memcpy_chk call that
will abort the program at runtime. */
memcpy (&buf[6], "abcde", 5);
Such built-in functions are provided for `memcpy', `mempcpy',
`memmove', `memset', `strcpy', `stpcpy', `strncpy', `strcat' and
`strncat'.
There are also checking built-in functions for formatted output
functions.
int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
const char *fmt, ...);
int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
va_list ap);
int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
const char *fmt, va_list ap);
The added FLAG argument is passed unchanged to `__sprintf_chk' etc.
functions and can contain implementation specific flags on what
additional security measures the checking function might take, such as
handling `%n' differently.
The OS argument is the object size S points to, like in the other
built-in functions. There is a small difference in the behavior
though, if OS is `(size_t) -1', the built-in functions are optimized
into the non-checking functions only if FLAG is 0, otherwise the
checking function is called with OS argument set to `(size_t) -1'.
In addition to this, there are checking built-in functions
`__builtin___printf_chk', `__builtin___vprintf_chk',
`__builtin___fprintf_chk' and `__builtin___vfprintf_chk'. These have
just one additional argument, FLAG, right before format string FMT. If
the compiler is able to optimize them to `fputc' etc. functions, it
will, otherwise the checking function should be called and the FLAG
argument passed to it.
File: gcc.info, Node: Other Builtins, Next: Target Builtins, Prev: Object Size Checking, Up: C Extensions
5.47 Other built-in functions provided by GCC
=============================================
GCC provides a large number of built-in functions other than the ones
mentioned above. Some of these are for internal use in the processing
of exceptions or variable-length argument lists and will not be
documented here because they may change from time to time; we do not
recommend general use of these functions.
The remaining functions are provided for optimization purposes.
GCC includes built-in versions of many of the functions in the standard
C library. The versions prefixed with `__builtin_' will always be
treated as having the same meaning as the C library function even if you
specify the `-fno-builtin' option. (*note C Dialect Options::) Many of
these functions are only optimized in certain cases; if they are not
optimized in a particular case, a call to the library function will be
emitted.
Outside strict ISO C mode (`-ansi', `-std=c89' or `-std=c99'), the
functions `_exit', `alloca', `bcmp', `bzero', `dcgettext', `dgettext',
`dremf', `dreml', `drem', `exp10f', `exp10l', `exp10', `ffsll', `ffsl',
`ffs', `fprintf_unlocked', `fputs_unlocked', `gammaf', `gammal',
`gamma', `gettext', `index', `isascii', `j0f', `j0l', `j0', `j1f',
`j1l', `j1', `jnf', `jnl', `jn', `mempcpy', `pow10f', `pow10l', `pow10',
`printf_unlocked', `rindex', `scalbf', `scalbl', `scalb', `signbit',
`signbitf', `signbitl', `significandf', `significandl', `significand',
`sincosf', `sincosl', `sincos', `stpcpy', `stpncpy', `strcasecmp',
`strdup', `strfmon', `strncasecmp', `strndup', `toascii', `y0f', `y0l',
`y0', `y1f', `y1l', `y1', `ynf', `ynl' and `yn' may be handled as
built-in functions. All these functions have corresponding versions
prefixed with `__builtin_', which may be used even in strict C89 mode.
The ISO C99 functions `_Exit', `acoshf', `acoshl', `acosh', `asinhf',
`asinhl', `asinh', `atanhf', `atanhl', `atanh', `cabsf', `cabsl',
`cabs', `cacosf', `cacoshf', `cacoshl', `cacosh', `cacosl', `cacos',
`cargf', `cargl', `carg', `casinf', `casinhf', `casinhl', `casinh',
`casinl', `casin', `catanf', `catanhf', `catanhl', `catanh', `catanl',
`catan', `cbrtf', `cbrtl', `cbrt', `ccosf', `ccoshf', `ccoshl',
`ccosh', `ccosl', `ccos', `cexpf', `cexpl', `cexp', `cimagf', `cimagl',
`cimag', `clogf', `clogl', `clog', `conjf', `conjl', `conj',
`copysignf', `copysignl', `copysign', `cpowf', `cpowl', `cpow',
`cprojf', `cprojl', `cproj', `crealf', `creall', `creal', `csinf',
`csinhf', `csinhl', `csinh', `csinl', `csin', `csqrtf', `csqrtl',
`csqrt', `ctanf', `ctanhf', `ctanhl', `ctanh', `ctanl', `ctan',
`erfcf', `erfcl', `erfc', `erff', `erfl', `erf', `exp2f', `exp2l',
`exp2', `expm1f', `expm1l', `expm1', `fdimf', `fdiml', `fdim', `fmaf',
`fmal', `fmaxf', `fmaxl', `fmax', `fma', `fminf', `fminl', `fmin',
`hypotf', `hypotl', `hypot', `ilogbf', `ilogbl', `ilogb', `imaxabs',
`isblank', `iswblank', `lgammaf', `lgammal', `lgamma', `llabs',
`llrintf', `llrintl', `llrint', `llroundf', `llroundl', `llround',
`log1pf', `log1pl', `log1p', `log2f', `log2l', `log2', `logbf',
`logbl', `logb', `lrintf', `lrintl', `lrint', `lroundf', `lroundl',
`lround', `nearbyintf', `nearbyintl', `nearbyint', `nextafterf',
`nextafterl', `nextafter', `nexttowardf', `nexttowardl', `nexttoward',
`remainderf', `remainderl', `remainder', `remquof', `remquol',
`remquo', `rintf', `rintl', `rint', `roundf', `roundl', `round',
`scalblnf', `scalblnl', `scalbln', `scalbnf', `scalbnl', `scalbn',
`snprintf', `tgammaf', `tgammal', `tgamma', `truncf', `truncl', `trunc',
`vfscanf', `vscanf', `vsnprintf' and `vsscanf' are handled as built-in
functions except in strict ISO C90 mode (`-ansi' or `-std=c89').
There are also built-in versions of the ISO C99 functions `acosf',
`acosl', `asinf', `asinl', `atan2f', `atan2l', `atanf', `atanl',
`ceilf', `ceill', `cosf', `coshf', `coshl', `cosl', `expf', `expl',
`fabsf', `fabsl', `floorf', `floorl', `fmodf', `fmodl', `frexpf',
`frexpl', `ldexpf', `ldexpl', `log10f', `log10l', `logf', `logl',
`modfl', `modf', `powf', `powl', `sinf', `sinhf', `sinhl', `sinl',
`sqrtf', `sqrtl', `tanf', `tanhf', `tanhl' and `tanl' that are
recognized in any mode since ISO C90 reserves these names for the
purpose to which ISO C99 puts them. All these functions have
corresponding versions prefixed with `__builtin_'.
The ISO C94 functions `iswalnum', `iswalpha', `iswcntrl', `iswdigit',
`iswgraph', `iswlower', `iswprint', `iswpunct', `iswspace', `iswupper',
`iswxdigit', `towlower' and `towupper' are handled as built-in functions
except in strict ISO C90 mode (`-ansi' or `-std=c89').
The ISO C90 functions `abort', `abs', `acos', `asin', `atan2', `atan',
`calloc', `ceil', `cosh', `cos', `exit', `exp', `fabs', `floor', `fmod',
`fprintf', `fputs', `frexp', `fscanf', `isalnum', `isalpha', `iscntrl',
`isdigit', `isgraph', `islower', `isprint', `ispunct', `isspace',
`isupper', `isxdigit', `tolower', `toupper', `labs', `ldexp', `log10',
`log', `malloc', `memcmp', `memcpy', `memset', `modf', `pow', `printf',
`putchar', `puts', `scanf', `sinh', `sin', `snprintf', `sprintf',
`sqrt', `sscanf', `strcat', `strchr', `strcmp', `strcpy', `strcspn',
`strlen', `strncat', `strncmp', `strncpy', `strpbrk', `strrchr',
`strspn', `strstr', `tanh', `tan', `vfprintf', `vprintf' and `vsprintf'
are all recognized as built-in functions unless `-fno-builtin' is
specified (or `-fno-builtin-FUNCTION' is specified for an individual
function). All of these functions have corresponding versions prefixed
with `__builtin_'.
GCC provides built-in versions of the ISO C99 floating point comparison
macros that avoid raising exceptions for unordered operands. They have
the same names as the standard macros ( `isgreater', `isgreaterequal',
`isless', `islessequal', `islessgreater', and `isunordered') , with
`__builtin_' prefixed. We intend for a library implementor to be able
to simply `#define' each standard macro to its built-in equivalent.
-- Built-in Function: int __builtin_types_compatible_p (TYPE1, TYPE2)
You can use the built-in function `__builtin_types_compatible_p' to
determine whether two types are the same.
This built-in function returns 1 if the unqualified versions of the
types TYPE1 and TYPE2 (which are types, not expressions) are
compatible, 0 otherwise. The result of this built-in function can
be used in integer constant expressions.
This built-in function ignores top level qualifiers (e.g., `const',
`volatile'). For example, `int' is equivalent to `const int'.
The type `int[]' and `int[5]' are compatible. On the other hand,
`int' and `char *' are not compatible, even if the size of their
types, on the particular architecture are the same. Also, the
amount of pointer indirection is taken into account when
determining similarity. Consequently, `short *' is not similar to
`short **'. Furthermore, two types that are typedefed are
considered compatible if their underlying types are compatible.
An `enum' type is not considered to be compatible with another
`enum' type even if both are compatible with the same integer
type; this is what the C standard specifies. For example, `enum
{foo, bar}' is not similar to `enum {hot, dog}'.
You would typically use this function in code whose execution
varies depending on the arguments' types. For example:
#define foo(x) \
({ \
typeof (x) tmp = (x); \
if (__builtin_types_compatible_p (typeof (x), long double)) \
tmp = foo_long_double (tmp); \
else if (__builtin_types_compatible_p (typeof (x), double)) \
tmp = foo_double (tmp); \
else if (__builtin_types_compatible_p (typeof (x), float)) \
tmp = foo_float (tmp); \
else \
abort (); \
tmp; \
})
_Note:_ This construct is only available for C.
-- Built-in Function: TYPE __builtin_choose_expr (CONST_EXP, EXP1,
EXP2)
You can use the built-in function `__builtin_choose_expr' to
evaluate code depending on the value of a constant expression.
This built-in function returns EXP1 if CONST_EXP, which is a
constant expression that must be able to be determined at compile
time, is nonzero. Otherwise it returns 0.
This built-in function is analogous to the `? :' operator in C,
except that the expression returned has its type unaltered by
promotion rules. Also, the built-in function does not evaluate
the expression that was not chosen. For example, if CONST_EXP
evaluates to true, EXP2 is not evaluated even if it has
side-effects.
This built-in function can return an lvalue if the chosen argument
is an lvalue.
If EXP1 is returned, the return type is the same as EXP1's type.
Similarly, if EXP2 is returned, its return type is the same as
EXP2.
Example:
#define foo(x) \
__builtin_choose_expr ( \
__builtin_types_compatible_p (typeof (x), double), \
foo_double (x), \
__builtin_choose_expr ( \
__builtin_types_compatible_p (typeof (x), float), \
foo_float (x), \
/* The void expression results in a compile-time error \
when assigning the result to something. */ \
(void)0))
_Note:_ This construct is only available for C. Furthermore, the
unused expression (EXP1 or EXP2 depending on the value of
CONST_EXP) may still generate syntax errors. This may change in
future revisions.
-- Built-in Function: int __builtin_constant_p (EXP)
You can use the built-in function `__builtin_constant_p' to
determine if a value is known to be constant at compile-time and
hence that GCC can perform constant-folding on expressions
involving that value. The argument of the function is the value
to test. The function returns the integer 1 if the argument is
known to be a compile-time constant and 0 if it is not known to be
a compile-time constant. A return of 0 does not indicate that the
value is _not_ a constant, but merely that GCC cannot prove it is
a constant with the specified value of the `-O' option.
You would typically use this function in an embedded application
where memory was a critical resource. If you have some complex
calculation, you may want it to be folded if it involves
constants, but need to call a function if it does not. For
example:
#define Scale_Value(X) \
(__builtin_constant_p (X) \
? ((X) * SCALE + OFFSET) : Scale (X))
You may use this built-in function in either a macro or an inline
function. However, if you use it in an inlined function and pass
an argument of the function as the argument to the built-in, GCC
will never return 1 when you call the inline function with a
string constant or compound literal (*note Compound Literals::)
and will not return 1 when you pass a constant numeric value to
the inline function unless you specify the `-O' option.
You may also use `__builtin_constant_p' in initializers for static
data. For instance, you can write
static const int table[] = {
__builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
/* ... */
};
This is an acceptable initializer even if EXPRESSION is not a
constant expression. GCC must be more conservative about
evaluating the built-in in this case, because it has no
opportunity to perform optimization.
Previous versions of GCC did not accept this built-in in data
initializers. The earliest version where it is completely safe is
3.0.1.
-- Built-in Function: long __builtin_expect (long EXP, long C)
You may use `__builtin_expect' to provide the compiler with branch
prediction information. In general, you should prefer to use
actual profile feedback for this (`-fprofile-arcs'), as
programmers are notoriously bad at predicting how their programs
actually perform. However, there are applications in which this
data is hard to collect.
The return value is the value of EXP, which should be an integral
expression. The value of C must be a compile-time constant. The
semantics of the built-in are that it is expected that EXP == C.
For example:
if (__builtin_expect (x, 0))
foo ();
would indicate that we do not expect to call `foo', since we
expect `x' to be zero. Since you are limited to integral
expressions for EXP, you should use constructions such as
if (__builtin_expect (ptr != NULL, 1))
error ();
when testing pointer or floating-point values.
-- Built-in Function: void __builtin_prefetch (const void *ADDR, ...)
This function is used to minimize cache-miss latency by moving
data into a cache before it is accessed. You can insert calls to
`__builtin_prefetch' into code for which you know addresses of
data in memory that is likely to be accessed soon. If the target
supports them, data prefetch instructions will be generated. If
the prefetch is done early enough before the access then the data
will be in the cache by the time it is accessed.
The value of ADDR is the address of the memory to prefetch. There
are two optional arguments, RW and LOCALITY. The value of RW is a
compile-time constant one or zero; one means that the prefetch is
preparing for a write to the memory address and zero, the default,
means that the prefetch is preparing for a read. The value
LOCALITY must be a compile-time constant integer between zero and
three. A value of zero means that the data has no temporal
locality, so it need not be left in the cache after the access. A
value of three means that the data has a high degree of temporal
locality and should be left in all levels of cache possible.
Values of one and two mean, respectively, a low or moderate degree
of temporal locality. The default is three.
for (i = 0; i < n; i++)
{
a[i] = a[i] + b[i];
__builtin_prefetch (&a[i+j], 1, 1);
__builtin_prefetch (&b[i+j], 0, 1);
/* ... */
}
Data prefetch does not generate faults if ADDR is invalid, but the
address expression itself must be valid. For example, a prefetch
of `p->next' will not fault if `p->next' is not a valid address,
but evaluation will fault if `p' is not a valid address.
If the target does not support data prefetch, the address
expression is evaluated if it includes side effects but no other
code is generated and GCC does not issue a warning.
-- Built-in Function: double __builtin_huge_val (void)
Returns a positive infinity, if supported by the floating-point
format, else `DBL_MAX'. This function is suitable for
implementing the ISO C macro `HUGE_VAL'.
-- Built-in Function: float __builtin_huge_valf (void)
Similar to `__builtin_huge_val', except the return type is `float'.
-- Built-in Function: long double __builtin_huge_vall (void)
Similar to `__builtin_huge_val', except the return type is `long
double'.
-- Built-in Function: double __builtin_inf (void)
Similar to `__builtin_huge_val', except a warning is generated if
the target floating-point format does not support infinities.
-- Built-in Function: _Decimal32 __builtin_infd32 (void)
Similar to `__builtin_inf', except the return type is `_Decimal32'.
-- Built-in Function: _Decimal64 __builtin_infd64 (void)
Similar to `__builtin_inf', except the return type is `_Decimal64'.
-- Built-in Function: _Decimal128 __builtin_infd128 (void)
Similar to `__builtin_inf', except the return type is
`_Decimal128'.
-- Built-in Function: float __builtin_inff (void)
Similar to `__builtin_inf', except the return type is `float'.
This function is suitable for implementing the ISO C99 macro
`INFINITY'.
-- Built-in Function: long double __builtin_infl (void)
Similar to `__builtin_inf', except the return type is `long
double'.
-- Built-in Function: double __builtin_nan (const char *str)
This is an implementation of the ISO C99 function `nan'.
Since ISO C99 defines this function in terms of `strtod', which we
do not implement, a description of the parsing is in order. The
string is parsed as by `strtol'; that is, the base is recognized by
leading `0' or `0x' prefixes. The number parsed is placed in the
significand such that the least significant bit of the number is
at the least significant bit of the significand. The number is
truncated to fit the significand field provided. The significand
is forced to be a quiet NaN.
This function, if given a string literal all of which would have
been consumed by strtol, is evaluated early enough that it is
considered a compile-time constant.
-- Built-in Function: _Decimal32 __builtin_nand32 (const char *str)
Similar to `__builtin_nan', except the return type is `_Decimal32'.
-- Built-in Function: _Decimal64 __builtin_nand64 (const char *str)
Similar to `__builtin_nan', except the return type is `_Decimal64'.
-- Built-in Function: _Decimal128 __builtin_nand128 (const char *str)
Similar to `__builtin_nan', except the return type is
`_Decimal128'.
-- Built-in Function: float __builtin_nanf (const char *str)
Similar to `__builtin_nan', except the return type is `float'.
-- Built-in Function: long double __builtin_nanl (const char *str)
Similar to `__builtin_nan', except the return type is `long
double'.
-- Built-in Function: double __builtin_nans (const char *str)
Similar to `__builtin_nan', except the significand is forced to be
a signaling NaN. The `nans' function is proposed by WG14 N965.
-- Built-in Function: float __builtin_nansf (const char *str)
Similar to `__builtin_nans', except the return type is `float'.
-- Built-in Function: long double __builtin_nansl (const char *str)
Similar to `__builtin_nans', except the return type is `long
double'.
-- Built-in Function: int __builtin_ffs (unsigned int x)
Returns one plus the index of the least significant 1-bit of X, or
if X is zero, returns zero.
-- Built-in Function: int __builtin_clz (unsigned int x)
Returns the number of leading 0-bits in X, starting at the most
significant bit position. If X is 0, the result is undefined.
-- Built-in Function: int __builtin_ctz (unsigned int x)
Returns the number of trailing 0-bits in X, starting at the least
significant bit position. If X is 0, the result is undefined.
-- Built-in Function: int __builtin_popcount (unsigned int x)
Returns the number of 1-bits in X.
-- Built-in Function: int __builtin_parity (unsigned int x)
Returns the parity of X, i.e. the number of 1-bits in X modulo 2.
-- Built-in Function: int __builtin_ffsl (unsigned long)
Similar to `__builtin_ffs', except the argument type is `unsigned
long'.
-- Built-in Function: int __builtin_clzl (unsigned long)
Similar to `__builtin_clz', except the argument type is `unsigned
long'.
-- Built-in Function: int __builtin_ctzl (unsigned long)
Similar to `__builtin_ctz', except the argument type is `unsigned
long'.
-- Built-in Function: int __builtin_popcountl (unsigned long)
Similar to `__builtin_popcount', except the argument type is
`unsigned long'.
-- Built-in Function: int __builtin_parityl (unsigned long)
Similar to `__builtin_parity', except the argument type is
`unsigned long'.
-- Built-in Function: int __builtin_ffsll (unsigned long long)
Similar to `__builtin_ffs', except the argument type is `unsigned
long long'.
-- Built-in Function: int __builtin_clzll (unsigned long long)
Similar to `__builtin_clz', except the argument type is `unsigned
long long'.
-- Built-in Function: int __builtin_ctzll (unsigned long long)
Similar to `__builtin_ctz', except the argument type is `unsigned
long long'.
-- Built-in Function: int __builtin_popcountll (unsigned long long)
Similar to `__builtin_popcount', except the argument type is
`unsigned long long'.
-- Built-in Function: int __builtin_parityll (unsigned long long)
Similar to `__builtin_parity', except the argument type is
`unsigned long long'.
-- Built-in Function: double __builtin_powi (double, int)
Returns the first argument raised to the power of the second.
Unlike the `pow' function no guarantees about precision and
rounding are made.
-- Built-in Function: float __builtin_powif (float, int)
Similar to `__builtin_powi', except the argument and return types
are `float'.
-- Built-in Function: long double __builtin_powil (long double, int)
Similar to `__builtin_powi', except the argument and return types
are `long double'.
File: gcc.info, Node: Target Builtins, Next: Target Format Checks, Prev: Other Builtins, Up: C Extensions
5.48 Built-in Functions Specific to Particular Target Machines
==============================================================
On some target machines, GCC supports many built-in functions specific
to those machines. Generally these generate calls to specific machine
instructions, but allow the compiler to schedule those calls.
* Menu:
* Alpha Built-in Functions::
* ARM Built-in Functions::
* Blackfin Built-in Functions::
* FR-V Built-in Functions::
* X86 Built-in Functions::
* MIPS DSP Built-in Functions::
* MIPS Paired-Single Support::
* PowerPC AltiVec Built-in Functions::
* SPARC VIS Built-in Functions::
File: gcc.info, Node: Alpha Built-in Functions, Next: ARM Built-in Functions, Up: Target Builtins
5.48.1 Alpha Built-in Functions
-------------------------------
These built-in functions are available for the Alpha family of
processors, depending on the command-line switches used.
The following built-in functions are always available. They all
generate the machine instruction that is part of the name.
long __builtin_alpha_implver (void)
long __builtin_alpha_rpcc (void)
long __builtin_alpha_amask (long)
long __builtin_alpha_cmpbge (long, long)
long __builtin_alpha_extbl (long, long)
long __builtin_alpha_extwl (long, long)
long __builtin_alpha_extll (long, long)
long __builtin_alpha_extql (long, long)
long __builtin_alpha_extwh (long, long)
long __builtin_alpha_extlh (long, long)
long __builtin_alpha_extqh (long, long)
long __builtin_alpha_insbl (long, long)
long __builtin_alpha_inswl (long, long)
long __builtin_alpha_insll (long, long)
long __builtin_alpha_insql (long, long)
long __builtin_alpha_inswh (long, long)
long __builtin_alpha_inslh (long, long)
long __builtin_alpha_insqh (long, long)
long __builtin_alpha_mskbl (long, long)
long __builtin_alpha_mskwl (long, long)
long __builtin_alpha_mskll (long, long)
long __builtin_alpha_mskql (long, long)
long __builtin_alpha_mskwh (long, long)
long __builtin_alpha_msklh (long, long)
long __builtin_alpha_mskqh (long, long)
long __builtin_alpha_umulh (long, long)
long __builtin_alpha_zap (long, long)
long __builtin_alpha_zapnot (long, long)
The following built-in functions are always with `-mmax' or
`-mcpu=CPU' where CPU is `pca56' or later. They all generate the
machine instruction that is part of the name.
long __builtin_alpha_pklb (long)
long __builtin_alpha_pkwb (long)
long __builtin_alpha_unpkbl (long)
long __builtin_alpha_unpkbw (long)
long __builtin_alpha_minub8 (long, long)
long __builtin_alpha_minsb8 (long, long)
long __builtin_alpha_minuw4 (long, long)
long __builtin_alpha_minsw4 (long, long)
long __builtin_alpha_maxub8 (long, long)
long __builtin_alpha_maxsb8 (long, long)
long __builtin_alpha_maxuw4 (long, long)
long __builtin_alpha_maxsw4 (long, long)
long __builtin_alpha_perr (long, long)
The following built-in functions are always with `-mcix' or
`-mcpu=CPU' where CPU is `ev67' or later. They all generate the
machine instruction that is part of the name.
long __builtin_alpha_cttz (long)
long __builtin_alpha_ctlz (long)
long __builtin_alpha_ctpop (long)
The following builtins are available on systems that use the OSF/1
PALcode. Normally they invoke the `rduniq' and `wruniq' PAL calls, but
when invoked with `-mtls-kernel', they invoke `rdval' and `wrval'.
void *__builtin_thread_pointer (void)
void __builtin_set_thread_pointer (void *)
File: gcc.info, Node: ARM Built-in Functions, Next: Blackfin Built-in Functions, Prev: Alpha Built-in Functions, Up: Target Builtins
5.48.2 ARM Built-in Functions
-----------------------------
These built-in functions are available for the ARM family of
processors, when the `-mcpu=iwmmxt' switch is used:
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef char v8qi __attribute__ ((vector_size (8)));
int __builtin_arm_getwcx (int)
void __builtin_arm_setwcx (int, int)
int __builtin_arm_textrmsb (v8qi, int)
int __builtin_arm_textrmsh (v4hi, int)
int __builtin_arm_textrmsw (v2si, int)
int __builtin_arm_textrmub (v8qi, int)
int __builtin_arm_textrmuh (v4hi, int)
int __builtin_arm_textrmuw (v2si, int)
v8qi __builtin_arm_tinsrb (v8qi, int)
v4hi __builtin_arm_tinsrh (v4hi, int)
v2si __builtin_arm_tinsrw (v2si, int)
long long __builtin_arm_tmia (long long, int, int)
long long __builtin_arm_tmiabb (long long, int, int)
long long __builtin_arm_tmiabt (long long, int, int)
long long __builtin_arm_tmiaph (long long, int, int)
long long __builtin_arm_tmiatb (long long, int, int)
long long __builtin_arm_tmiatt (long long, int, int)
int __builtin_arm_tmovmskb (v8qi)
int __builtin_arm_tmovmskh (v4hi)
int __builtin_arm_tmovmskw (v2si)
long long __builtin_arm_waccb (v8qi)
long long __builtin_arm_wacch (v4hi)
long long __builtin_arm_waccw (v2si)
v8qi __builtin_arm_waddb (v8qi, v8qi)
v8qi __builtin_arm_waddbss (v8qi, v8qi)
v8qi __builtin_arm_waddbus (v8qi, v8qi)
v4hi __builtin_arm_waddh (v4hi, v4hi)
v4hi __builtin_arm_waddhss (v4hi, v4hi)
v4hi __builtin_arm_waddhus (v4hi, v4hi)
v2si __builtin_arm_waddw (v2si, v2si)
v2si __builtin_arm_waddwss (v2si, v2si)
v2si __builtin_arm_waddwus (v2si, v2si)
v8qi __builtin_arm_walign (v8qi, v8qi, int)
long long __builtin_arm_wand(long long, long long)
long long __builtin_arm_wandn (long long, long long)
v8qi __builtin_arm_wavg2b (v8qi, v8qi)
v8qi __builtin_arm_wavg2br (v8qi, v8qi)
v4hi __builtin_arm_wavg2h (v4hi, v4hi)
v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
v2si __builtin_arm_wcmpeqw (v2si, v2si)
v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtsw (v2si, v2si)
v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtuw (v2si, v2si)
long long __builtin_arm_wmacs (long long, v4hi, v4hi)
long long __builtin_arm_wmacsz (v4hi, v4hi)
long long __builtin_arm_wmacu (long long, v4hi, v4hi)
long long __builtin_arm_wmacuz (v4hi, v4hi)
v4hi __builtin_arm_wmadds (v4hi, v4hi)
v4hi __builtin_arm_wmaddu (v4hi, v4hi)
v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
v2si __builtin_arm_wmaxsw (v2si, v2si)
v8qi __builtin_arm_wmaxub (v8qi, v8qi)
v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
v2si __builtin_arm_wmaxuw (v2si, v2si)
v8qi __builtin_arm_wminsb (v8qi, v8qi)
v4hi __builtin_arm_wminsh (v4hi, v4hi)
v2si __builtin_arm_wminsw (v2si, v2si)
v8qi __builtin_arm_wminub (v8qi, v8qi)
v4hi __builtin_arm_wminuh (v4hi, v4hi)
v2si __builtin_arm_wminuw (v2si, v2si)
v4hi __builtin_arm_wmulsm (v4hi, v4hi)
v4hi __builtin_arm_wmulul (v4hi, v4hi)
v4hi __builtin_arm_wmulum (v4hi, v4hi)
long long __builtin_arm_wor (long long, long long)
v2si __builtin_arm_wpackdss (long long, long long)
v2si __builtin_arm_wpackdus (long long, long long)
v8qi __builtin_arm_wpackhss (v4hi, v4hi)
v8qi __builtin_arm_wpackhus (v4hi, v4hi)
v4hi __builtin_arm_wpackwss (v2si, v2si)
v4hi __builtin_arm_wpackwus (v2si, v2si)
long long __builtin_arm_wrord (long long, long long)
long long __builtin_arm_wrordi (long long, int)
v4hi __builtin_arm_wrorh (v4hi, long long)
v4hi __builtin_arm_wrorhi (v4hi, int)
v2si __builtin_arm_wrorw (v2si, long long)
v2si __builtin_arm_wrorwi (v2si, int)
v2si __builtin_arm_wsadb (v8qi, v8qi)
v2si __builtin_arm_wsadbz (v8qi, v8qi)
v2si __builtin_arm_wsadh (v4hi, v4hi)
v2si __builtin_arm_wsadhz (v4hi, v4hi)
v4hi __builtin_arm_wshufh (v4hi, int)
long long __builtin_arm_wslld (long long, long long)
long long __builtin_arm_wslldi (long long, int)
v4hi __builtin_arm_wsllh (v4hi, long long)
v4hi __builtin_arm_wsllhi (v4hi, int)
v2si __builtin_arm_wsllw (v2si, long long)
v2si __builtin_arm_wsllwi (v2si, int)
long long __builtin_arm_wsrad (long long, long long)
long long __builtin_arm_wsradi (long long, int)
v4hi __builtin_arm_wsrah (v4hi, long long)
v4hi __builtin_arm_wsrahi (v4hi, int)
v2si __builtin_arm_wsraw (v2si, long long)
v2si __builtin_arm_wsrawi (v2si, int)
long long __builtin_arm_wsrld (long long, long long)
long long __builtin_arm_wsrldi (long long, int)
v4hi __builtin_arm_wsrlh (v4hi, long long)
v4hi __builtin_arm_wsrlhi (v4hi, int)
v2si __builtin_arm_wsrlw (v2si, long long)
v2si __builtin_arm_wsrlwi (v2si, int)
v8qi __builtin_arm_wsubb (v8qi, v8qi)
v8qi __builtin_arm_wsubbss (v8qi, v8qi)
v8qi __builtin_arm_wsubbus (v8qi, v8qi)
v4hi __builtin_arm_wsubh (v4hi, v4hi)
v4hi __builtin_arm_wsubhss (v4hi, v4hi)
v4hi __builtin_arm_wsubhus (v4hi, v4hi)
v2si __builtin_arm_wsubw (v2si, v2si)
v2si __builtin_arm_wsubwss (v2si, v2si)
v2si __builtin_arm_wsubwus (v2si, v2si)
v4hi __builtin_arm_wunpckehsb (v8qi)
v2si __builtin_arm_wunpckehsh (v4hi)
long long __builtin_arm_wunpckehsw (v2si)
v4hi __builtin_arm_wunpckehub (v8qi)
v2si __builtin_arm_wunpckehuh (v4hi)
long long __builtin_arm_wunpckehuw (v2si)
v4hi __builtin_arm_wunpckelsb (v8qi)
v2si __builtin_arm_wunpckelsh (v4hi)
long long __builtin_arm_wunpckelsw (v2si)
v4hi __builtin_arm_wunpckelub (v8qi)
v2si __builtin_arm_wunpckeluh (v4hi)
long long __builtin_arm_wunpckeluw (v2si)
v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
v2si __builtin_arm_wunpckihw (v2si, v2si)
v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
v2si __builtin_arm_wunpckilw (v2si, v2si)
long long __builtin_arm_wxor (long long, long long)
long long __builtin_arm_wzero ()
File: gcc.info, Node: Blackfin Built-in Functions, Next: FR-V Built-in Functions, Prev: ARM Built-in Functions, Up: Target Builtins
5.48.3 Blackfin Built-in Functions
----------------------------------
Currently, there are two Blackfin-specific built-in functions. These
are used for generating `CSYNC' and `SSYNC' machine insns without using
inline assembly; by using these built-in functions the compiler can
automatically add workarounds for hardware errata involving these
instructions. These functions are named as follows:
void __builtin_bfin_csync (void)
void __builtin_bfin_ssync (void)
File: gcc.info, Node: FR-V Built-in Functions, Next: X86 Built-in Functions, Prev: Blackfin Built-in Functions, Up: Target Builtins
5.48.4 FR-V Built-in Functions
------------------------------
GCC provides many FR-V-specific built-in functions. In general, these
functions are intended to be compatible with those described by `FR-V
Family, Softune C/C++ Compiler Manual (V6), Fujitsu Semiconductor'.
The two exceptions are `__MDUNPACKH' and `__MBTOHE', the gcc forms of
which pass 128-bit values by pointer rather than by value.
Most of the functions are named after specific FR-V instructions.
Such functions are said to be "directly mapped" and are summarized here
in tabular form.
* Menu:
* Argument Types::
* Directly-mapped Integer Functions::
* Directly-mapped Media Functions::
* Raw read/write Functions::
* Other Built-in Functions::
File: gcc.info, Node: Argument Types, Next: Directly-mapped Integer Functions, Up: FR-V Built-in Functions
5.48.4.1 Argument Types
.......................
The arguments to the built-in functions can be divided into three
groups: register numbers, compile-time constants and run-time values.
In order to make this classification clear at a glance, the arguments
and return values are given the following pseudo types:
Pseudo type Real C type Constant? Description
`uh' `unsigned short' No an unsigned halfword
`uw1' `unsigned int' No an unsigned word
`sw1' `int' No a signed word
`uw2' `unsigned long long' No an unsigned doubleword
`sw2' `long long' No a signed doubleword
`const' `int' Yes an integer constant
`acc' `int' Yes an ACC register number
`iacc' `int' Yes an IACC register number
These pseudo types are not defined by GCC, they are simply a notational
convenience used in this manual.
Arguments of type `uh', `uw1', `sw1', `uw2' and `sw2' are evaluated at
run time. They correspond to register operands in the underlying FR-V
instructions.
`const' arguments represent immediate operands in the underlying FR-V
instructions. They must be compile-time constants.
`acc' arguments are evaluated at compile time and specify the number
of an accumulator register. For example, an `acc' argument of 2 will
select the ACC2 register.
`iacc' arguments are similar to `acc' arguments but specify the number
of an IACC register. See *note Other Built-in Functions:: for more
details.
File: gcc.info, Node: Directly-mapped Integer Functions, Next: Directly-mapped Media Functions, Prev: Argument Types, Up: FR-V Built-in Functions
5.48.4.2 Directly-mapped Integer Functions
..........................................
The functions listed below map directly to FR-V I-type instructions.
Function prototype Example usage Assembly output
`sw1 __ADDSS (sw1, sw1)' `C = __ADDSS (A, B)' `ADDSS A,B,C'
`sw1 __SCAN (sw1, sw1)' `C = __SCAN (A, B)' `SCAN A,B,C'
`sw1 __SCUTSS (sw1)' `B = __SCUTSS (A)' `SCUTSS A,B'
`sw1 __SLASS (sw1, sw1)' `C = __SLASS (A, B)' `SLASS A,B,C'
`void __SMASS (sw1, sw1)' `__SMASS (A, B)' `SMASS A,B'
`void __SMSSS (sw1, sw1)' `__SMSSS (A, B)' `SMSSS A,B'
`void __SMU (sw1, sw1)' `__SMU (A, B)' `SMU A,B'
`sw2 __SMUL (sw1, sw1)' `C = __SMUL (A, B)' `SMUL A,B,C'
`sw1 __SUBSS (sw1, sw1)' `C = __SUBSS (A, B)' `SUBSS A,B,C'
`uw2 __UMUL (uw1, uw1)' `C = __UMUL (A, B)' `UMUL A,B,C'
File: gcc.info, Node: Directly-mapped Media Functions, Next: Raw read/write Functions, Prev: Directly-mapped Integer Functions, Up: FR-V Built-in Functions
5.48.4.3 Directly-mapped Media Functions
........................................
The functions listed below map directly to FR-V M-type instructions.
Function prototype Example usage Assembly output
`uw1 __MABSHS (sw1)' `B = __MABSHS (A)' `MABSHS A,B'
`void __MADDACCS (acc, acc)' `__MADDACCS (B, A)' `MADDACCS A,B'
`sw1 __MADDHSS (sw1, sw1)' `C = __MADDHSS (A, B)' `MADDHSS A,B,C'
`uw1 __MADDHUS (uw1, uw1)' `C = __MADDHUS (A, B)' `MADDHUS A,B,C'
`uw1 __MAND (uw1, uw1)' `C = __MAND (A, B)' `MAND A,B,C'
`void __MASACCS (acc, acc)' `__MASACCS (B, A)' `MASACCS A,B'
`uw1 __MAVEH (uw1, uw1)' `C = __MAVEH (A, B)' `MAVEH A,B,C'
`uw2 __MBTOH (uw1)' `B = __MBTOH (A)' `MBTOH A,B'
`void __MBTOHE (uw1 *, uw1)' `__MBTOHE (&B, A)' `MBTOHE A,B'
`void __MCLRACC (acc)' `__MCLRACC (A)' `MCLRACC A'
`void __MCLRACCA (void)' `__MCLRACCA ()' `MCLRACCA'
`uw1 __Mcop1 (uw1, uw1)' `C = __Mcop1 (A, B)' `Mcop1 A,B,C'
`uw1 __Mcop2 (uw1, uw1)' `C = __Mcop2 (A, B)' `Mcop2 A,B,C'
`uw1 __MCPLHI (uw2, const)' `C = __MCPLHI (A, B)' `MCPLHI A,#B,C'
`uw1 __MCPLI (uw2, const)' `C = __MCPLI (A, B)' `MCPLI A,#B,C'
`void __MCPXIS (acc, sw1, sw1)' `__MCPXIS (C, A, B)' `MCPXIS A,B,C'
`void __MCPXIU (acc, uw1, uw1)' `__MCPXIU (C, A, B)' `MCPXIU A,B,C'
`void __MCPXRS (acc, sw1, sw1)' `__MCPXRS (C, A, B)' `MCPXRS A,B,C'
`void __MCPXRU (acc, uw1, uw1)' `__MCPXRU (C, A, B)' `MCPXRU A,B,C'
`uw1 __MCUT (acc, uw1)' `C = __MCUT (A, B)' `MCUT A,B,C'
`uw1 __MCUTSS (acc, sw1)' `C = __MCUTSS (A, B)' `MCUTSS A,B,C'
`void __MDADDACCS (acc, acc)' `__MDADDACCS (B, A)' `MDADDACCS A,B'
`void __MDASACCS (acc, acc)' `__MDASACCS (B, A)' `MDASACCS A,B'
`uw2 __MDCUTSSI (acc, const)' `C = __MDCUTSSI (A, B)' `MDCUTSSI A,#B,C'
`uw2 __MDPACKH (uw2, uw2)' `C = __MDPACKH (A, B)' `MDPACKH A,B,C'
`uw2 __MDROTLI (uw2, const)' `C = __MDROTLI (A, B)' `MDROTLI A,#B,C'
`void __MDSUBACCS (acc, acc)' `__MDSUBACCS (B, A)' `MDSUBACCS A,B'
`void __MDUNPACKH (uw1 *, uw2)' `__MDUNPACKH (&B, A)' `MDUNPACKH A,B'
`uw2 __MEXPDHD (uw1, const)' `C = __MEXPDHD (A, B)' `MEXPDHD A,#B,C'
`uw1 __MEXPDHW (uw1, const)' `C = __MEXPDHW (A, B)' `MEXPDHW A,#B,C'
`uw1 __MHDSETH (uw1, const)' `C = __MHDSETH (A, B)' `MHDSETH A,#B,C'
`sw1 __MHDSETS (const)' `B = __MHDSETS (A)' `MHDSETS #A,B'
`uw1 __MHSETHIH (uw1, const)' `B = __MHSETHIH (B, A)' `MHSETHIH #A,B'
`sw1 __MHSETHIS (sw1, const)' `B = __MHSETHIS (B, A)' `MHSETHIS #A,B'
`uw1 __MHSETLOH (uw1, const)' `B = __MHSETLOH (B, A)' `MHSETLOH #A,B'
`sw1 __MHSETLOS (sw1, const)' `B = __MHSETLOS (B, A)' `MHSETLOS #A,B'
`uw1 __MHTOB (uw2)' `B = __MHTOB (A)' `MHTOB A,B'
`void __MMACHS (acc, sw1, sw1)' `__MMACHS (C, A, B)' `MMACHS A,B,C'
`void __MMACHU (acc, uw1, uw1)' `__MMACHU (C, A, B)' `MMACHU A,B,C'
`void __MMRDHS (acc, sw1, sw1)' `__MMRDHS (C, A, B)' `MMRDHS A,B,C'
`void __MMRDHU (acc, uw1, uw1)' `__MMRDHU (C, A, B)' `MMRDHU A,B,C'
`void __MMULHS (acc, sw1, sw1)' `__MMULHS (C, A, B)' `MMULHS A,B,C'
`void __MMULHU (acc, uw1, uw1)' `__MMULHU (C, A, B)' `MMULHU A,B,C'
`void __MMULXHS (acc, sw1, sw1)' `__MMULXHS (C, A, B)' `MMULXHS A,B,C'
`void __MMULXHU (acc, uw1, uw1)' `__MMULXHU (C, A, B)' `MMULXHU A,B,C'
`uw1 __MNOT (uw1)' `B = __MNOT (A)' `MNOT A,B'
`uw1 __MOR (uw1, uw1)' `C = __MOR (A, B)' `MOR A,B,C'
`uw1 __MPACKH (uh, uh)' `C = __MPACKH (A, B)' `MPACKH A,B,C'
`sw2 __MQADDHSS (sw2, sw2)' `C = __MQADDHSS (A, B)' `MQADDHSS A,B,C'
`uw2 __MQADDHUS (uw2, uw2)' `C = __MQADDHUS (A, B)' `MQADDHUS A,B,C'
`void __MQCPXIS (acc, sw2, sw2)' `__MQCPXIS (C, A, B)' `MQCPXIS A,B,C'
`void __MQCPXIU (acc, uw2, uw2)' `__MQCPXIU (C, A, B)' `MQCPXIU A,B,C'
`void __MQCPXRS (acc, sw2, sw2)' `__MQCPXRS (C, A, B)' `MQCPXRS A,B,C'
`void __MQCPXRU (acc, uw2, uw2)' `__MQCPXRU (C, A, B)' `MQCPXRU A,B,C'
`sw2 __MQLCLRHS (sw2, sw2)' `C = __MQLCLRHS (A, B)' `MQLCLRHS A,B,C'
`sw2 __MQLMTHS (sw2, sw2)' `C = __MQLMTHS (A, B)' `MQLMTHS A,B,C'
`void __MQMACHS (acc, sw2, sw2)' `__MQMACHS (C, A, B)' `MQMACHS A,B,C'
`void __MQMACHU (acc, uw2, uw2)' `__MQMACHU (C, A, B)' `MQMACHU A,B,C'
`void __MQMACXHS (acc, sw2, `__MQMACXHS (C, A, B)' `MQMACXHS A,B,C'
sw2)'
`void __MQMULHS (acc, sw2, sw2)' `__MQMULHS (C, A, B)' `MQMULHS A,B,C'
`void __MQMULHU (acc, uw2, uw2)' `__MQMULHU (C, A, B)' `MQMULHU A,B,C'
`void __MQMULXHS (acc, sw2, `__MQMULXHS (C, A, B)' `MQMULXHS A,B,C'
sw2)'
`void __MQMULXHU (acc, uw2, `__MQMULXHU (C, A, B)' `MQMULXHU A,B,C'
uw2)'
`sw2 __MQSATHS (sw2, sw2)' `C = __MQSATHS (A, B)' `MQSATHS A,B,C'
`uw2 __MQSLLHI (uw2, int)' `C = __MQSLLHI (A, B)' `MQSLLHI A,B,C'
`sw2 __MQSRAHI (sw2, int)' `C = __MQSRAHI (A, B)' `MQSRAHI A,B,C'
`sw2 __MQSUBHSS (sw2, sw2)' `C = __MQSUBHSS (A, B)' `MQSUBHSS A,B,C'
`uw2 __MQSUBHUS (uw2, uw2)' `C = __MQSUBHUS (A, B)' `MQSUBHUS A,B,C'
`void __MQXMACHS (acc, sw2, `__MQXMACHS (C, A, B)' `MQXMACHS A,B,C'
sw2)'
`void __MQXMACXHS (acc, sw2, `__MQXMACXHS (C, A, B)' `MQXMACXHS A,B,C'
sw2)'
`uw1 __MRDACC (acc)' `B = __MRDACC (A)' `MRDACC A,B'
`uw1 __MRDACCG (acc)' `B = __MRDACCG (A)' `MRDACCG A,B'
`uw1 __MROTLI (uw1, const)' `C = __MROTLI (A, B)' `MROTLI A,#B,C'
`uw1 __MROTRI (uw1, const)' `C = __MROTRI (A, B)' `MROTRI A,#B,C'
`sw1 __MSATHS (sw1, sw1)' `C = __MSATHS (A, B)' `MSATHS A,B,C'
`uw1 __MSATHU (uw1, uw1)' `C = __MSATHU (A, B)' `MSATHU A,B,C'
`uw1 __MSLLHI (uw1, const)' `C = __MSLLHI (A, B)' `MSLLHI A,#B,C'
`sw1 __MSRAHI (sw1, const)' `C = __MSRAHI (A, B)' `MSRAHI A,#B,C'
`uw1 __MSRLHI (uw1, const)' `C = __MSRLHI (A, B)' `MSRLHI A,#B,C'
`void __MSUBACCS (acc, acc)' `__MSUBACCS (B, A)' `MSUBACCS A,B'
`sw1 __MSUBHSS (sw1, sw1)' `C = __MSUBHSS (A, B)' `MSUBHSS A,B,C'
`uw1 __MSUBHUS (uw1, uw1)' `C = __MSUBHUS (A, B)' `MSUBHUS A,B,C'
`void __MTRAP (void)' `__MTRAP ()' `MTRAP'
`uw2 __MUNPACKH (uw1)' `B = __MUNPACKH (A)' `MUNPACKH A,B'
`uw1 __MWCUT (uw2, uw1)' `C = __MWCUT (A, B)' `MWCUT A,B,C'
`void __MWTACC (acc, uw1)' `__MWTACC (B, A)' `MWTACC A,B'
`void __MWTACCG (acc, uw1)' `__MWTACCG (B, A)' `MWTACCG A,B'
`uw1 __MXOR (uw1, uw1)' `C = __MXOR (A, B)' `MXOR A,B,C'
File: gcc.info, Node: Raw read/write Functions, Next: Other Built-in Functions, Prev: Directly-mapped Media Functions, Up: FR-V Built-in Functions
5.48.4.4 Raw read/write Functions
.................................
This sections describes built-in functions related to read and write
instructions to access memory. These functions generate `membar'
instructions to flush the I/O load and stores where appropriate, as
described in Fujitsu's manual described above.
`unsigned char __builtin_read8 (void *DATA)'
`unsigned short __builtin_read16 (void *DATA)'
`unsigned long __builtin_read32 (void *DATA)'
`unsigned long long __builtin_read64 (void *DATA)'
`void __builtin_write8 (void *DATA, unsigned char DATUM)'
`void __builtin_write16 (void *DATA, unsigned short DATUM)'
`void __builtin_write32 (void *DATA, unsigned long DATUM)'
`void __builtin_write64 (void *DATA, unsigned long long DATUM)'
File: gcc.info, Node: Other Built-in Functions, Prev: Raw read/write Functions, Up: FR-V Built-in Functions
5.48.4.5 Other Built-in Functions
.................................
This section describes built-in functions that are not named after a
specific FR-V instruction.
`sw2 __IACCreadll (iacc REG)'
Return the full 64-bit value of IACC0. The REG argument is
reserved for future expansion and must be 0.
`sw1 __IACCreadl (iacc REG)'
Return the value of IACC0H if REG is 0 and IACC0L if REG is 1.
Other values of REG are rejected as invalid.
`void __IACCsetll (iacc REG, sw2 X)'
Set the full 64-bit value of IACC0 to X. The REG argument is
reserved for future expansion and must be 0.
`void __IACCsetl (iacc REG, sw1 X)'
Set IACC0H to X if REG is 0 and IACC0L to X if REG is 1. Other
values of REG are rejected as invalid.
`void __data_prefetch0 (const void *X)'
Use the `dcpl' instruction to load the contents of address X into
the data cache.
`void __data_prefetch (const void *X)'
Use the `nldub' instruction to load the contents of address X into
the data cache. The instruction will be issued in slot I1.
File: gcc.info, Node: X86 Built-in Functions, Next: MIPS DSP Built-in Functions, Prev: FR-V Built-in Functions, Up: Target Builtins
5.48.5 X86 Built-in Functions
-----------------------------
These built-in functions are available for the i386 and x86-64 family
of computers, depending on the command-line switches used.
Note that, if you specify command-line switches such as `-msse', the
compiler could use the extended instruction sets even if the built-ins
are not used explicitly in the program. For this reason, applications
which perform runtime CPU detection must compile separate files for each
supported architecture, using the appropriate flags. In particular,
the file containing the CPU detection code should be compiled without
these options.
The following machine modes are available for use with MMX built-in
functions (*note Vector Extensions::): `V2SI' for a vector of two
32-bit integers, `V4HI' for a vector of four 16-bit integers, and
`V8QI' for a vector of eight 8-bit integers. Some of the built-in
functions operate on MMX registers as a whole 64-bit entity, these use
`DI' as their mode.
If 3Dnow extensions are enabled, `V2SF' is used as a mode for a vector
of two 32-bit floating point values.
If SSE extensions are enabled, `V4SF' is used for a vector of four
32-bit floating point values. Some instructions use a vector of four
32-bit integers, these use `V4SI'. Finally, some instructions operate
on an entire vector register, interpreting it as a 128-bit integer,
these use mode `TI'.
The following built-in functions are made available by `-mmmx'. All
of them generate the machine instruction that is part of the name.
v8qi __builtin_ia32_paddb (v8qi, v8qi)
v4hi __builtin_ia32_paddw (v4hi, v4hi)
v2si __builtin_ia32_paddd (v2si, v2si)
v8qi __builtin_ia32_psubb (v8qi, v8qi)
v4hi __builtin_ia32_psubw (v4hi, v4hi)
v2si __builtin_ia32_psubd (v2si, v2si)
v8qi __builtin_ia32_paddsb (v8qi, v8qi)
v4hi __builtin_ia32_paddsw (v4hi, v4hi)
v8qi __builtin_ia32_psubsb (v8qi, v8qi)
v4hi __builtin_ia32_psubsw (v4hi, v4hi)
v8qi __builtin_ia32_paddusb (v8qi, v8qi)
v4hi __builtin_ia32_paddusw (v4hi, v4hi)
v8qi __builtin_ia32_psubusb (v8qi, v8qi)
v4hi __builtin_ia32_psubusw (v4hi, v4hi)
v4hi __builtin_ia32_pmullw (v4hi, v4hi)
v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
di __builtin_ia32_pand (di, di)
di __builtin_ia32_pandn (di,di)
di __builtin_ia32_por (di, di)
di __builtin_ia32_pxor (di, di)
v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
v2si __builtin_ia32_pcmpeqd (v2si, v2si)
v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
v2si __builtin_ia32_pcmpgtd (v2si, v2si)
v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
v2si __builtin_ia32_punpckhdq (v2si, v2si)
v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
v2si __builtin_ia32_punpckldq (v2si, v2si)
v8qi __builtin_ia32_packsswb (v4hi, v4hi)
v4hi __builtin_ia32_packssdw (v2si, v2si)
v8qi __builtin_ia32_packuswb (v4hi, v4hi)
The following built-in functions are made available either with
`-msse', or with a combination of `-m3dnow' and `-march=athlon'. All
of them generate the machine instruction that is part of the name.
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
v8qi __builtin_ia32_pavgb (v8qi, v8qi)
v4hi __builtin_ia32_pavgw (v4hi, v4hi)
v4hi __builtin_ia32_psadbw (v8qi, v8qi)
v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
v8qi __builtin_ia32_pminub (v8qi, v8qi)
v4hi __builtin_ia32_pminsw (v4hi, v4hi)
int __builtin_ia32_pextrw (v4hi, int)
v4hi __builtin_ia32_pinsrw (v4hi, int, int)
int __builtin_ia32_pmovmskb (v8qi)
void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
void __builtin_ia32_movntq (di *, di)
void __builtin_ia32_sfence (void)
The following built-in functions are available when `-msse' is used.
All of them generate the machine instruction that is part of the name.
int __builtin_ia32_comieq (v4sf, v4sf)
int __builtin_ia32_comineq (v4sf, v4sf)
int __builtin_ia32_comilt (v4sf, v4sf)
int __builtin_ia32_comile (v4sf, v4sf)
int __builtin_ia32_comigt (v4sf, v4sf)
int __builtin_ia32_comige (v4sf, v4sf)
int __builtin_ia32_ucomieq (v4sf, v4sf)
int __builtin_ia32_ucomineq (v4sf, v4sf)
int __builtin_ia32_ucomilt (v4sf, v4sf)
int __builtin_ia32_ucomile (v4sf, v4sf)
int __builtin_ia32_ucomigt (v4sf, v4sf)
int __builtin_ia32_ucomige (v4sf, v4sf)
v4sf __builtin_ia32_addps (v4sf, v4sf)
v4sf __builtin_ia32_subps (v4sf, v4sf)
v4sf __builtin_ia32_mulps (v4sf, v4sf)
v4sf __builtin_ia32_divps (v4sf, v4sf)
v4sf __builtin_ia32_addss (v4sf, v4sf)
v4sf __builtin_ia32_subss (v4sf, v4sf)
v4sf __builtin_ia32_mulss (v4sf, v4sf)
v4sf __builtin_ia32_divss (v4sf, v4sf)
v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
v4si __builtin_ia32_cmpltps (v4sf, v4sf)
v4si __builtin_ia32_cmpleps (v4sf, v4sf)
v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
v4si __builtin_ia32_cmpordps (v4sf, v4sf)
v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
v4si __builtin_ia32_cmpltss (v4sf, v4sf)
v4si __builtin_ia32_cmpless (v4sf, v4sf)
v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
v4si __builtin_ia32_cmpnless (v4sf, v4sf)
v4si __builtin_ia32_cmpordss (v4sf, v4sf)
v4sf __builtin_ia32_maxps (v4sf, v4sf)
v4sf __builtin_ia32_maxss (v4sf, v4sf)
v4sf __builtin_ia32_minps (v4sf, v4sf)
v4sf __builtin_ia32_minss (v4sf, v4sf)
v4sf __builtin_ia32_andps (v4sf, v4sf)
v4sf __builtin_ia32_andnps (v4sf, v4sf)
v4sf __builtin_ia32_orps (v4sf, v4sf)
v4sf __builtin_ia32_xorps (v4sf, v4sf)
v4sf __builtin_ia32_movss (v4sf, v4sf)
v4sf __builtin_ia32_movhlps (v4sf, v4sf)
v4sf __builtin_ia32_movlhps (v4sf, v4sf)
v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
v2si __builtin_ia32_cvtps2pi (v4sf)
int __builtin_ia32_cvtss2si (v4sf)
v2si __builtin_ia32_cvttps2pi (v4sf)
int __builtin_ia32_cvttss2si (v4sf)
v4sf __builtin_ia32_rcpps (v4sf)
v4sf __builtin_ia32_rsqrtps (v4sf)
v4sf __builtin_ia32_sqrtps (v4sf)
v4sf __builtin_ia32_rcpss (v4sf)
v4sf __builtin_ia32_rsqrtss (v4sf)
v4sf __builtin_ia32_sqrtss (v4sf)
v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
void __builtin_ia32_movntps (float *, v4sf)
int __builtin_ia32_movmskps (v4sf)
The following built-in functions are available when `-msse' is used.
`v4sf __builtin_ia32_loadaps (float *)'
Generates the `movaps' machine instruction as a load from memory.
`void __builtin_ia32_storeaps (float *, v4sf)'
Generates the `movaps' machine instruction as a store to memory.
`v4sf __builtin_ia32_loadups (float *)'
Generates the `movups' machine instruction as a load from memory.
`void __builtin_ia32_storeups (float *, v4sf)'
Generates the `movups' machine instruction as a store to memory.
`v4sf __builtin_ia32_loadsss (float *)'
Generates the `movss' machine instruction as a load from memory.
`void __builtin_ia32_storess (float *, v4sf)'
Generates the `movss' machine instruction as a store to memory.
`v4sf __builtin_ia32_loadhps (v4sf, v2si *)'
Generates the `movhps' machine instruction as a load from memory.
`v4sf __builtin_ia32_loadlps (v4sf, v2si *)'
Generates the `movlps' machine instruction as a load from memory
`void __builtin_ia32_storehps (v4sf, v2si *)'
Generates the `movhps' machine instruction as a store to memory.
`void __builtin_ia32_storelps (v4sf, v2si *)'
Generates the `movlps' machine instruction as a store to memory.
The following built-in functions are available when `-msse2' is used.
All of them generate the machine instruction that is part of the name.
int __builtin_ia32_comisdeq (v2df, v2df)
int __builtin_ia32_comisdlt (v2df, v2df)
int __builtin_ia32_comisdle (v2df, v2df)
int __builtin_ia32_comisdgt (v2df, v2df)
int __builtin_ia32_comisdge (v2df, v2df)
int __builtin_ia32_comisdneq (v2df, v2df)
int __builtin_ia32_ucomisdeq (v2df, v2df)
int __builtin_ia32_ucomisdlt (v2df, v2df)
int __builtin_ia32_ucomisdle (v2df, v2df)
int __builtin_ia32_ucomisdgt (v2df, v2df)
int __builtin_ia32_ucomisdge (v2df, v2df)
int __builtin_ia32_ucomisdneq (v2df, v2df)
v2df __builtin_ia32_cmpeqpd (v2df, v2df)
v2df __builtin_ia32_cmpltpd (v2df, v2df)
v2df __builtin_ia32_cmplepd (v2df, v2df)
v2df __builtin_ia32_cmpgtpd (v2df, v2df)
v2df __builtin_ia32_cmpgepd (v2df, v2df)
v2df __builtin_ia32_cmpunordpd (v2df, v2df)
v2df __builtin_ia32_cmpneqpd (v2df, v2df)
v2df __builtin_ia32_cmpnltpd (v2df, v2df)
v2df __builtin_ia32_cmpnlepd (v2df, v2df)
v2df __builtin_ia32_cmpngtpd (v2df, v2df)
v2df __builtin_ia32_cmpngepd (v2df, v2df)
v2df __builtin_ia32_cmpordpd (v2df, v2df)
v2df __builtin_ia32_cmpeqsd (v2df, v2df)
v2df __builtin_ia32_cmpltsd (v2df, v2df)
v2df __builtin_ia32_cmplesd (v2df, v2df)
v2df __builtin_ia32_cmpunordsd (v2df, v2df)
v2df __builtin_ia32_cmpneqsd (v2df, v2df)
v2df __builtin_ia32_cmpnltsd (v2df, v2df)
v2df __builtin_ia32_cmpnlesd (v2df, v2df)
v2df __builtin_ia32_cmpordsd (v2df, v2df)
v2di __builtin_ia32_paddq (v2di, v2di)
v2di __builtin_ia32_psubq (v2di, v2di)
v2df __builtin_ia32_addpd (v2df, v2df)
v2df __builtin_ia32_subpd (v2df, v2df)
v2df __builtin_ia32_mulpd (v2df, v2df)
v2df __builtin_ia32_divpd (v2df, v2df)
v2df __builtin_ia32_addsd (v2df, v2df)
v2df __builtin_ia32_subsd (v2df, v2df)
v2df __builtin_ia32_mulsd (v2df, v2df)
v2df __builtin_ia32_divsd (v2df, v2df)
v2df __builtin_ia32_minpd (v2df, v2df)
v2df __builtin_ia32_maxpd (v2df, v2df)
v2df __builtin_ia32_minsd (v2df, v2df)
v2df __builtin_ia32_maxsd (v2df, v2df)
v2df __builtin_ia32_andpd (v2df, v2df)
v2df __builtin_ia32_andnpd (v2df, v2df)
v2df __builtin_ia32_orpd (v2df, v2df)
v2df __builtin_ia32_xorpd (v2df, v2df)
v2df __builtin_ia32_movsd (v2df, v2df)
v2df __builtin_ia32_unpckhpd (v2df, v2df)
v2df __builtin_ia32_unpcklpd (v2df, v2df)
v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
v4si __builtin_ia32_paddd128 (v4si, v4si)
v2di __builtin_ia32_paddq128 (v2di, v2di)
v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
v4si __builtin_ia32_psubd128 (v4si, v4si)
v2di __builtin_ia32_psubq128 (v2di, v2di)
v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
v2di __builtin_ia32_pand128 (v2di, v2di)
v2di __builtin_ia32_pandn128 (v2di, v2di)
v2di __builtin_ia32_por128 (v2di, v2di)
v2di __builtin_ia32_pxor128 (v2di, v2di)
v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckldq128 (v4si, v4si)
v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)
v16qi __builtin_ia32_packsswb128 (v16qi, v16qi)
v8hi __builtin_ia32_packssdw128 (v8hi, v8hi)
v16qi __builtin_ia32_packuswb128 (v16qi, v16qi)
v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
void __builtin_ia32_maskmovdqu (v16qi, v16qi)
v2df __builtin_ia32_loadupd (double *)
void __builtin_ia32_storeupd (double *, v2df)
v2df __builtin_ia32_loadhpd (v2df, double *)
v2df __builtin_ia32_loadlpd (v2df, double *)
int __builtin_ia32_movmskpd (v2df)
int __builtin_ia32_pmovmskb128 (v16qi)
void __builtin_ia32_movnti (int *, int)
void __builtin_ia32_movntpd (double *, v2df)
void __builtin_ia32_movntdq (v2df *, v2df)
v4si __builtin_ia32_pshufd (v4si, int)
v8hi __builtin_ia32_pshuflw (v8hi, int)
v8hi __builtin_ia32_pshufhw (v8hi, int)
v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
v2df __builtin_ia32_sqrtpd (v2df)
v2df __builtin_ia32_sqrtsd (v2df)
v2df __builtin_ia32_shufpd (v2df, v2df, int)
v2df __builtin_ia32_cvtdq2pd (v4si)
v4sf __builtin_ia32_cvtdq2ps (v4si)
v4si __builtin_ia32_cvtpd2dq (v2df)
v2si __builtin_ia32_cvtpd2pi (v2df)
v4sf __builtin_ia32_cvtpd2ps (v2df)
v4si __builtin_ia32_cvttpd2dq (v2df)
v2si __builtin_ia32_cvttpd2pi (v2df)
v2df __builtin_ia32_cvtpi2pd (v2si)
int __builtin_ia32_cvtsd2si (v2df)
int __builtin_ia32_cvttsd2si (v2df)
long long __builtin_ia32_cvtsd2si64 (v2df)
long long __builtin_ia32_cvttsd2si64 (v2df)
v4si __builtin_ia32_cvtps2dq (v4sf)
v2df __builtin_ia32_cvtps2pd (v4sf)
v4si __builtin_ia32_cvttps2dq (v4sf)
v2df __builtin_ia32_cvtsi2sd (v2df, int)
v2df __builtin_ia32_cvtsi642sd (v2df, long long)
v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
void __builtin_ia32_clflush (const void *)
void __builtin_ia32_lfence (void)
void __builtin_ia32_mfence (void)
v16qi __builtin_ia32_loaddqu (const char *)
void __builtin_ia32_storedqu (char *, v16qi)
unsigned long long __builtin_ia32_pmuludq (v2si, v2si)
v2di __builtin_ia32_pmuludq128 (v4si, v4si)
v8hi __builtin_ia32_psllw128 (v8hi, v2di)
v4si __builtin_ia32_pslld128 (v4si, v2di)
v2di __builtin_ia32_psllq128 (v4si, v2di)
v8hi __builtin_ia32_psrlw128 (v8hi, v2di)
v4si __builtin_ia32_psrld128 (v4si, v2di)
v2di __builtin_ia32_psrlq128 (v2di, v2di)
v8hi __builtin_ia32_psraw128 (v8hi, v2di)
v4si __builtin_ia32_psrad128 (v4si, v2di)
v2di __builtin_ia32_pslldqi128 (v2di, int)
v8hi __builtin_ia32_psllwi128 (v8hi, int)
v4si __builtin_ia32_pslldi128 (v4si, int)
v2di __builtin_ia32_psllqi128 (v2di, int)
v2di __builtin_ia32_psrldqi128 (v2di, int)
v8hi __builtin_ia32_psrlwi128 (v8hi, int)
v4si __builtin_ia32_psrldi128 (v4si, int)
v2di __builtin_ia32_psrlqi128 (v2di, int)
v8hi __builtin_ia32_psrawi128 (v8hi, int)
v4si __builtin_ia32_psradi128 (v4si, int)
v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi)
The following built-in functions are available when `-msse3' is used.
All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_addsubpd (v2df, v2df)
v4sf __builtin_ia32_addsubps (v4sf, v4sf)
v2df __builtin_ia32_haddpd (v2df, v2df)
v4sf __builtin_ia32_haddps (v4sf, v4sf)
v2df __builtin_ia32_hsubpd (v2df, v2df)
v4sf __builtin_ia32_hsubps (v4sf, v4sf)
v16qi __builtin_ia32_lddqu (char const *)
void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
v2df __builtin_ia32_movddup (v2df)
v4sf __builtin_ia32_movshdup (v4sf)
v4sf __builtin_ia32_movsldup (v4sf)
void __builtin_ia32_mwait (unsigned int, unsigned int)
The following built-in functions are available when `-msse3' is used.
`v2df __builtin_ia32_loadddup (double const *)'
Generates the `movddup' machine instruction as a load from memory.
The following built-in functions are available when `-m3dnow' is used.
All of them generate the machine instruction that is part of the name.
void __builtin_ia32_femms (void)
v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
v2si __builtin_ia32_pf2id (v2sf)
v2sf __builtin_ia32_pfacc (v2sf, v2sf)
v2sf __builtin_ia32_pfadd (v2sf, v2sf)
v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
v2sf __builtin_ia32_pfmax (v2sf, v2sf)
v2sf __builtin_ia32_pfmin (v2sf, v2sf)
v2sf __builtin_ia32_pfmul (v2sf, v2sf)
v2sf __builtin_ia32_pfrcp (v2sf)
v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
v2sf __builtin_ia32_pfrsqrt (v2sf)
v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf)
v2sf __builtin_ia32_pfsub (v2sf, v2sf)
v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
v2sf __builtin_ia32_pi2fd (v2si)
v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)
The following built-in functions are available when both `-m3dnow' and
`-march=athlon' are used. All of them generate the machine instruction
that is part of the name.
v2si __builtin_ia32_pf2iw (v2sf)
v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
v2sf __builtin_ia32_pi2fw (v2si)
v2sf __builtin_ia32_pswapdsf (v2sf)
v2si __builtin_ia32_pswapdsi (v2si)
File: gcc.info, Node: MIPS DSP Built-in Functions, Next: MIPS Paired-Single Support, Prev: X86 Built-in Functions, Up: Target Builtins
5.48.6 MIPS DSP Built-in Functions
----------------------------------
The MIPS DSP Application-Specific Extension (ASE) includes new
instructions that are designed to improve the performance of DSP and
media applications. It provides instructions that operate on packed
8-bit integer data, Q15 fractional data and Q31 fractional data.
GCC supports MIPS DSP operations using both the generic vector
extensions (*note Vector Extensions::) and a collection of
MIPS-specific built-in functions. Both kinds of support are enabled by
the `-mdsp' command-line option.
At present, GCC only provides support for operations on 32-bit
vectors. The vector type associated with 8-bit integer data is usually
called `v4i8' and the vector type associated with Q15 is usually called
`v2q15'. They can be defined in C as follows:
typedef char v4i8 __attribute__ ((vector_size(4)));
typedef short v2q15 __attribute__ ((vector_size(4)));
`v4i8' and `v2q15' values are initialized in the same way as
aggregates. For example:
v4i8 a = {1, 2, 3, 4};
v4i8 b;
b = (v4i8) {5, 6, 7, 8};
v2q15 c = {0x0fcb, 0x3a75};
v2q15 d;
d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};
_Note:_ The CPU's endianness determines the order in which values are
packed. On little-endian targets, the first value is the least
significant and the last value is the most significant. The opposite
order applies to big-endian targets. For example, the code above will
set the lowest byte of `a' to `1' on little-endian targets and `4' on
big-endian targets.
_Note:_ Q15 and Q31 values must be initialized with their integer
representation. As shown in this example, the integer representation
of a Q15 value can be obtained by multiplying the fractional value by
`0x1.0p15'. The equivalent for Q31 values is to multiply by `0x1.0p31'.
The table below lists the `v4i8' and `v2q15' operations for which
hardware support exists. `a' and `b' are `v4i8' values, and `c' and
`d' are `v2q15' values.
C code MIPS instruction
`a + b' `addu.qb'
`c + d' `addq.ph'
`a - b' `subu.qb'
`c - d' `subq.ph'
It is easier to describe the DSP built-in functions if we first define
the following types:
typedef int q31;
typedef int i32;
typedef long long a64;
`q31' and `i32' are actually the same as `int', but we use `q31' to
indicate a Q31 fractional value and `i32' to indicate a 32-bit integer
value. Similarly, `a64' is the same as `long long', but we use `a64'
to indicate values that will be placed in one of the four DSP
accumulators (`$ac0', `$ac1', `$ac2' or `$ac3').
Also, some built-in functions prefer or require immediate numbers as
parameters, because the corresponding DSP instructions accept both
immediate numbers and register operands, or accept immediate numbers
only. The immediate parameters are listed as follows.
imm0_7: 0 to 7.
imm0_15: 0 to 15.
imm0_31: 0 to 31.
imm0_63: 0 to 63.
imm0_255: 0 to 255.
imm_n32_31: -32 to 31.
imm_n512_511: -512 to 511.
The following built-in functions map directly to a particular MIPS DSP
instruction. Please refer to the architecture specification for
details on what each instruction does.
v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
q31 __builtin_mips_addq_s_w (q31, q31)
v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
q31 __builtin_mips_subq_s_w (q31, q31)
v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
i32 __builtin_mips_addsc (i32, i32)
i32 __builtin_mips_addwc (i32, i32)
i32 __builtin_mips_modsub (i32, i32)
i32 __builtin_mips_raddu_w_qb (v4i8)
v2q15 __builtin_mips_absq_s_ph (v2q15)
q31 __builtin_mips_absq_s_w (q31)
v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
v2q15 __builtin_mips_precrq_ph_w (q31, q31)
v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
q31 __builtin_mips_preceq_w_phl (v2q15)
q31 __builtin_mips_preceq_w_phr (v2q15)
v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shll_qb (v4i8, i32)
v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_ph (v2q15, i32)
v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
q31 __builtin_mips_shll_s_w (q31, imm0_31)
q31 __builtin_mips_shll_s_w (q31, i32)
v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shrl_qb (v4i8, i32)
v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_ph (v2q15, i32)
v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
q31 __builtin_mips_shra_r_w (q31, imm0_31)
q31 __builtin_mips_shra_r_w (q31, i32)
v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
i32 __builtin_mips_bitrev (i32)
i32 __builtin_mips_insv (i32, i32)
v4i8 __builtin_mips_repl_qb (imm0_255)
v4i8 __builtin_mips_repl_qb (i32)
v2q15 __builtin_mips_repl_ph (imm_n512_511)
v2q15 __builtin_mips_repl_ph (i32)
void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
void __builtin_mips_cmp_le_ph (v2q15, v2q15)
v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
i32 __builtin_mips_extr_w (a64, imm0_31)
i32 __builtin_mips_extr_w (a64, i32)
i32 __builtin_mips_extr_r_w (a64, imm0_31)
i32 __builtin_mips_extr_s_h (a64, i32)
i32 __builtin_mips_extr_rs_w (a64, imm0_31)
i32 __builtin_mips_extr_rs_w (a64, i32)
i32 __builtin_mips_extr_s_h (a64, imm0_31)
i32 __builtin_mips_extr_r_w (a64, i32)
i32 __builtin_mips_extp (a64, imm0_31)
i32 __builtin_mips_extp (a64, i32)
i32 __builtin_mips_extpdp (a64, imm0_31)
i32 __builtin_mips_extpdp (a64, i32)
a64 __builtin_mips_shilo (a64, imm_n32_31)
a64 __builtin_mips_shilo (a64, i32)
a64 __builtin_mips_mthlip (a64, i32)
void __builtin_mips_wrdsp (i32, imm0_63)
i32 __builtin_mips_rddsp (imm0_63)
i32 __builtin_mips_lbux (void *, i32)
i32 __builtin_mips_lhx (void *, i32)
i32 __builtin_mips_lwx (void *, i32)
i32 __builtin_mips_bposge32 (void)
File: gcc.info, Node: MIPS Paired-Single Support, Next: PowerPC AltiVec Built-in Functions, Prev: MIPS DSP Built-in Functions, Up: Target Builtins
5.48.7 MIPS Paired-Single Support
---------------------------------
The MIPS64 architecture includes a number of instructions that operate
on pairs of single-precision floating-point values. Each pair is
packed into a 64-bit floating-point register, with one element being
designated the "upper half" and the other being designated the "lower
half".
GCC supports paired-single operations using both the generic vector
extensions (*note Vector Extensions::) and a collection of
MIPS-specific built-in functions. Both kinds of support are enabled by
the `-mpaired-single' command-line option.
The vector type associated with paired-single values is usually called
`v2sf'. It can be defined in C as follows:
typedef float v2sf __attribute__ ((vector_size (8)));
`v2sf' values are initialized in the same way as aggregates. For
example:
v2sf a = {1.5, 9.1};
v2sf b;
float e, f;
b = (v2sf) {e, f};
_Note:_ The CPU's endianness determines which value is stored in the
upper half of a register and which value is stored in the lower half.
On little-endian targets, the first value is the lower one and the
second value is the upper one. The opposite order applies to
big-endian targets. For example, the code above will set the lower
half of `a' to `1.5' on little-endian targets and `9.1' on big-endian
targets.
* Menu:
* Paired-Single Arithmetic::
* Paired-Single Built-in Functions::
* MIPS-3D Built-in Functions::
File: gcc.info, Node: Paired-Single Arithmetic, Next: Paired-Single Built-in Functions, Up: MIPS Paired-Single Support
5.48.7.1 Paired-Single Arithmetic
.................................
The table below lists the `v2sf' operations for which hardware support
exists. `a', `b' and `c' are `v2sf' values and `x' is an integral
value.
C code MIPS instruction
`a + b' `add.ps'
`a - b' `sub.ps'
`-a' `neg.ps'
`a * b' `mul.ps'
`a * b + c' `madd.ps'
`a * b - c' `msub.ps'
`-(a * b + c)' `nmadd.ps'
`-(a * b - c)' `nmsub.ps'
`x ? a : b' `movn.ps'/`movz.ps'
Note that the multiply-accumulate instructions can be disabled using
the command-line option `-mno-fused-madd'.
File: gcc.info, Node: Paired-Single Built-in Functions, Next: MIPS-3D Built-in Functions, Prev: Paired-Single Arithmetic, Up: MIPS Paired-Single Support
5.48.7.2 Paired-Single Built-in Functions
.........................................
The following paired-single functions map directly to a particular MIPS
instruction. Please refer to the architecture specification for
details on what each instruction does.
`v2sf __builtin_mips_pll_ps (v2sf, v2sf)'
Pair lower lower (`pll.ps').
`v2sf __builtin_mips_pul_ps (v2sf, v2sf)'
Pair upper lower (`pul.ps').
`v2sf __builtin_mips_plu_ps (v2sf, v2sf)'
Pair lower upper (`plu.ps').
`v2sf __builtin_mips_puu_ps (v2sf, v2sf)'
Pair upper upper (`puu.ps').
`v2sf __builtin_mips_cvt_ps_s (float, float)'
Convert pair to paired single (`cvt.ps.s').
`float __builtin_mips_cvt_s_pl (v2sf)'
Convert pair lower to single (`cvt.s.pl').
`float __builtin_mips_cvt_s_pu (v2sf)'
Convert pair upper to single (`cvt.s.pu').
`v2sf __builtin_mips_abs_ps (v2sf)'
Absolute value (`abs.ps').
`v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)'
Align variable (`alnv.ps').
_Note:_ The value of the third parameter must be 0 or 4 modulo 8,
otherwise the result will be unpredictable. Please read the
instruction description for details.
The following multi-instruction functions are also available. In each
case, COND can be any of the 16 floating-point conditions: `f', `un',
`eq', `ueq', `olt', `ult', `ole', `ule', `sf', `ngle', `seq', `ngl',
`lt', `nge', `le' or `ngt'.
`v2sf __builtin_mips_movt_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)'
`v2sf __builtin_mips_movf_c_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)'
Conditional move based on floating point comparison (`c.COND.ps',
`movt.ps'/`movf.ps').
The `movt' functions return the value X computed by:
c.COND.ps CC,A,B
mov.ps X,C
movt.ps X,D,CC
The `movf' functions are similar but use `movf.ps' instead of
`movt.ps'.
`int __builtin_mips_upper_c_COND_ps (v2sf A, v2sf B)'
`int __builtin_mips_lower_c_COND_ps (v2sf A, v2sf B)'
Comparison of two paired-single values (`c.COND.ps',
`bc1t'/`bc1f').
These functions compare A and B using `c.COND.ps' and return
either the upper or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_c_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_c_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();
File: gcc.info, Node: MIPS-3D Built-in Functions, Prev: Paired-Single Built-in Functions, Up: MIPS Paired-Single Support
5.48.7.3 MIPS-3D Built-in Functions
...................................
The MIPS-3D Application-Specific Extension (ASE) includes additional
paired-single instructions that are designed to improve the performance
of 3D graphics operations. Support for these instructions is controlled
by the `-mips3d' command-line option.
The functions listed below map directly to a particular MIPS-3D
instruction. Please refer to the architecture specification for more
details on what each instruction does.
`v2sf __builtin_mips_addr_ps (v2sf, v2sf)'
Reduction add (`addr.ps').
`v2sf __builtin_mips_mulr_ps (v2sf, v2sf)'
Reduction multiply (`mulr.ps').
`v2sf __builtin_mips_cvt_pw_ps (v2sf)'
Convert paired single to paired word (`cvt.pw.ps').
`v2sf __builtin_mips_cvt_ps_pw (v2sf)'
Convert paired word to paired single (`cvt.ps.pw').
`float __builtin_mips_recip1_s (float)'
`double __builtin_mips_recip1_d (double)'
`v2sf __builtin_mips_recip1_ps (v2sf)'
Reduced precision reciprocal (sequence step 1) (`recip1.FMT').
`float __builtin_mips_recip2_s (float, float)'
`double __builtin_mips_recip2_d (double, double)'
`v2sf __builtin_mips_recip2_ps (v2sf, v2sf)'
Reduced precision reciprocal (sequence step 2) (`recip2.FMT').
`float __builtin_mips_rsqrt1_s (float)'
`double __builtin_mips_rsqrt1_d (double)'
`v2sf __builtin_mips_rsqrt1_ps (v2sf)'
Reduced precision reciprocal square root (sequence step 1)
(`rsqrt1.FMT').
`float __builtin_mips_rsqrt2_s (float, float)'
`double __builtin_mips_rsqrt2_d (double, double)'
`v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)'
Reduced precision reciprocal square root (sequence step 2)
(`rsqrt2.FMT').
The following multi-instruction functions are also available. In each
case, COND can be any of the 16 floating-point conditions: `f', `un',
`eq', `ueq', `olt', `ult', `ole', `ule', `sf', `ngle', `seq', `ngl',
`lt', `nge', `le' or `ngt'.
`int __builtin_mips_cabs_COND_s (float A, float B)'
`int __builtin_mips_cabs_COND_d (double A, double B)'
Absolute comparison of two scalar values (`cabs.COND.FMT',
`bc1t'/`bc1f').
These functions compare A and B using `cabs.COND.s' or
`cabs.COND.d' and return the result as a boolean value. For
example:
float a, b;
if (__builtin_mips_cabs_eq_s (a, b))
true ();
else
false ();
`int __builtin_mips_upper_cabs_COND_ps (v2sf A, v2sf B)'
`int __builtin_mips_lower_cabs_COND_ps (v2sf A, v2sf B)'
Absolute comparison of two paired-single values (`cabs.COND.ps',
`bc1t'/`bc1f').
These functions compare A and B using `cabs.COND.ps' and return
either the upper or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_cabs_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_cabs_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();
`v2sf __builtin_mips_movt_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)'
`v2sf __builtin_mips_movf_cabs_COND_ps (v2sf A, v2sf B, v2sf C, v2sf D)'
Conditional move based on absolute comparison (`cabs.COND.ps',
`movt.ps'/`movf.ps').
The `movt' functions return the value X computed by:
cabs.COND.ps CC,A,B
mov.ps X,C
movt.ps X,D,CC
The `movf' functions are similar but use `movf.ps' instead of
`movt.ps'.
`int __builtin_mips_any_c_COND_ps (v2sf A, v2sf B)'
`int __builtin_mips_all_c_COND_ps (v2sf A, v2sf B)'
`int __builtin_mips_any_cabs_COND_ps (v2sf A, v2sf B)'
`int __builtin_mips_all_cabs_COND_ps (v2sf A, v2sf B)'
Comparison of two paired-single values (`c.COND.ps'/`cabs.COND.ps',
`bc1any2t'/`bc1any2f').
These functions compare A and B using `c.COND.ps' or
`cabs.COND.ps'. The `any' forms return true if either result is
true and the `all' forms return true if both results are true.
For example:
v2sf a, b;
if (__builtin_mips_any_c_eq_ps (a, b))
one_is_true ();
else
both_are_false ();
if (__builtin_mips_all_c_eq_ps (a, b))
both_are_true ();
else
one_is_false ();
`int __builtin_mips_any_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)'
`int __builtin_mips_all_c_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)'
`int __builtin_mips_any_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)'
`int __builtin_mips_all_cabs_COND_4s (v2sf A, v2sf B, v2sf C, v2sf D)'
Comparison of four paired-single values
(`c.COND.ps'/`cabs.COND.ps', `bc1any4t'/`bc1any4f').
These functions use `c.COND.ps' or `cabs.COND.ps' to compare A
with B and to compare C with D. The `any' forms return true if
any of the four results are true and the `all' forms return true
if all four results are true. For example:
v2sf a, b, c, d;
if (__builtin_mips_any_c_eq_4s (a, b, c, d))
some_are_true ();
else
all_are_false ();
if (__builtin_mips_all_c_eq_4s (a, b, c, d))
all_are_true ();
else
some_are_false ();
File: gcc.info, Node: PowerPC AltiVec Built-in Functions, Next: SPARC VIS Built-in Functions, Prev: MIPS Paired-Single Support, Up: Target Builtins
5.48.8 PowerPC AltiVec Built-in Functions
-----------------------------------------
GCC provides an interface for the PowerPC family of processors to access
the AltiVec operations described in Motorola's AltiVec Programming
Interface Manual. The interface is made available by including
`<altivec.h>' and using `-maltivec' and `-mabi=altivec'. The interface
supports the following vector types.
vector unsigned char
vector signed char
vector bool char
vector unsigned short
vector signed short
vector bool short
vector pixel
vector unsigned int
vector signed int
vector bool int
vector float
GCC's implementation of the high-level language interface available
from C and C++ code differs from Motorola's documentation in several
ways.
* A vector constant is a list of constant expressions within curly
braces.
* A vector initializer requires no cast if the vector constant is of
the same type as the variable it is initializing.
* If `signed' or `unsigned' is omitted, the signedness of the vector
type is the default signedness of the base type. The default
varies depending on the operating system, so a portable program
should always specify the signedness.
* Compiling with `-maltivec' adds keywords `__vector', `__pixel',
and `__bool'. Macros `vector', `pixel', and `bool' are defined in
`<altivec.h>' and can be undefined.
* GCC allows using a `typedef' name as the type specifier for a
vector type.
* For C, overloaded functions are implemented with macros so the
following does not work:
vec_add ((vector signed int){1, 2, 3, 4}, foo);
Since `vec_add' is a macro, the vector constant in the example is
treated as four separate arguments. Wrap the entire argument in
parentheses for this to work.
_Note:_ Only the `<altivec.h>' interface is supported. Internally,
GCC uses built-in functions to achieve the functionality in the
aforementioned header file, but they are not supported and are subject
to change without notice.
The following interfaces are supported for the generic and specific
AltiVec operations and the AltiVec predicates. In cases where there is
a direct mapping between generic and specific operations, only the
generic names are shown here, although the specific operations can also
be used.
Arguments that are documented as `const int' require literal integral
values within the range required for that operation.
vector signed char vec_abs (vector signed char);
vector signed short vec_abs (vector signed short);
vector signed int vec_abs (vector signed int);
vector float vec_abs (vector float);
vector signed char vec_abss (vector signed char);
vector signed short vec_abss (vector signed short);
vector signed int vec_abss (vector signed int);
vector signed char vec_add (vector bool char, vector signed char);
vector signed char vec_add (vector signed char, vector bool char);
vector signed char vec_add (vector signed char, vector signed char);
vector unsigned char vec_add (vector bool char, vector unsigned char);
vector unsigned char vec_add (vector unsigned char, vector bool char);
vector unsigned char vec_add (vector unsigned char,
vector unsigned char);
vector signed short vec_add (vector bool short, vector signed short);
vector signed short vec_add (vector signed short, vector bool short);
vector signed short vec_add (vector signed short, vector signed short);
vector unsigned short vec_add (vector bool short,
vector unsigned short);
vector unsigned short vec_add (vector unsigned short,
vector bool short);
vector unsigned short vec_add (vector unsigned short,
vector unsigned short);
vector signed int vec_add (vector bool int, vector signed int);
vector signed int vec_add (vector signed int, vector bool int);
vector signed int vec_add (vector signed int, vector signed int);
vector unsigned int vec_add (vector bool int, vector unsigned int);
vector unsigned int vec_add (vector unsigned int, vector bool int);
vector unsigned int vec_add (vector unsigned int, vector unsigned int);
vector float vec_add (vector float, vector float);
vector float vec_vaddfp (vector float, vector float);
vector signed int vec_vadduwm (vector bool int, vector signed int);
vector signed int vec_vadduwm (vector signed int, vector bool int);
vector signed int vec_vadduwm (vector signed int, vector signed int);
vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
vector unsigned int vec_vadduwm (vector unsigned int,
vector unsigned int);
vector signed short vec_vadduhm (vector bool short,
vector signed short);
vector signed short vec_vadduhm (vector signed short,
vector bool short);
vector signed short vec_vadduhm (vector signed short,
vector signed short);
vector unsigned short vec_vadduhm (vector bool short,
vector unsigned short);
vector unsigned short vec_vadduhm (vector unsigned short,
vector bool short);
vector unsigned short vec_vadduhm (vector unsigned short,
vector unsigned short);
vector signed char vec_vaddubm (vector bool char, vector signed char);
vector signed char vec_vaddubm (vector signed char, vector bool char);
vector signed char vec_vaddubm (vector signed char, vector signed char);
vector unsigned char vec_vaddubm (vector bool char,
vector unsigned char);
vector unsigned char vec_vaddubm (vector unsigned char,
vector bool char);
vector unsigned char vec_vaddubm (vector unsigned char,
vector unsigned char);
vector unsigned int vec_addc (vector unsigned int, vector unsigned int);
vector unsigned char vec_adds (vector bool char, vector unsigned char);
vector unsigned char vec_adds (vector unsigned char, vector bool char);
vector unsigned char vec_adds (vector unsigned char,
vector unsigned char);
vector signed char vec_adds (vector bool char, vector signed char);
vector signed char vec_adds (vector signed char, vector bool char);
vector signed char vec_adds (vector signed char, vector signed char);
vector unsigned short vec_adds (vector bool short,
vector unsigned short);
vector unsigned short vec_adds (vector unsigned short,
vector bool short);
vector unsigned short vec_adds (vector unsigned short,
vector unsigned short);
vector signed short vec_adds (vector bool short, vector signed short);
vector signed short vec_adds (vector signed short, vector bool short);
vector signed short vec_adds (vector signed short, vector signed short);
vector unsigned int vec_adds (vector bool int, vector unsigned int);
vector unsigned int vec_adds (vector unsigned int, vector bool int);
vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
vector signed int vec_adds (vector bool int, vector signed int);
vector signed int vec_adds (vector signed int, vector bool int);
vector signed int vec_adds (vector signed int, vector signed int);
vector signed int vec_vaddsws (vector bool int, vector signed int);
vector signed int vec_vaddsws (vector signed int, vector bool int);
vector signed int vec_vaddsws (vector signed int, vector signed int);
vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
vector unsigned int vec_vadduws (vector unsigned int,
vector unsigned int);
vector signed short vec_vaddshs (vector bool short,
vector signed short);
vector signed short vec_vaddshs (vector signed short,
vector bool short);
vector signed short vec_vaddshs (vector signed short,
vector signed short);
vector unsigned short vec_vadduhs (vector bool short,
vector unsigned short);
vector unsigned short vec_vadduhs (vector unsigned short,
vector bool short);
vector unsigned short vec_vadduhs (vector unsigned short,
vector unsigned short);
vector signed char vec_vaddsbs (vector bool char, vector signed char);
vector signed char vec_vaddsbs (vector signed char, vector bool char);
vector signed char vec_vaddsbs (vector signed char, vector signed char);
vector unsigned char vec_vaddubs (vector bool char,
vector unsigned char);
vector unsigned char vec_vaddubs (vector unsigned char,
vector bool char);
vector unsigned char vec_vaddubs (vector unsigned char,
vector unsigned char);
vector float vec_and (vector float, vector float);
vector float vec_and (vector float, vector bool int);
vector float vec_and (vector bool int, vector float);
vector bool int vec_and (vector bool int, vector bool int);
vector signed int vec_and (vector bool int, vector signed int);
vector signed int vec_and (vector signed int, vector bool int);
vector signed int vec_and (vector signed int, vector signed int);
vector unsigned int vec_and (vector bool int, vector unsigned int);
vector unsigned int vec_and (vector unsigned int, vector bool int);
vector unsigned int vec_and (vector unsigned int, vector unsigned int);
vector bool short vec_and (vector bool short, vector bool short);
vector signed short vec_and (vector bool short, vector signed short);
vector signed short vec_and (vector signed short, vector bool short);
vector signed short vec_and (vector signed short, vector signed short);
vector unsigned short vec_and (vector bool short,
vector unsigned short);
vector unsigned short vec_and (vector unsigned short,
vector bool short);
vector unsigned short vec_and (vector unsigned short,
vector unsigned short);
vector signed char vec_and (vector bool char, vector signed char);
vector bool char vec_and (vector bool char, vector bool char);
vector signed char vec_and (vector signed char, vector bool char);
vector signed char vec_and (vector signed char, vector signed char);
vector unsigned char vec_and (vector bool char, vector unsigned char);
vector unsigned char vec_and (vector unsigned char, vector bool char);
vector unsigned char vec_and (vector unsigned char,
vector unsigned char);
vector float vec_andc (vector float, vector float);
vector float vec_andc (vector float, vector bool int);
vector float vec_andc (vector bool int, vector float);
vector bool int vec_andc (vector bool int, vector bool int);
vector signed int vec_andc (vector bool int, vector signed int);
vector signed int vec_andc (vector signed int, vector bool int);
vector signed int vec_andc (vector signed int, vector signed int);
vector unsigned int vec_andc (vector bool int, vector unsigned int);
vector unsigned int vec_andc (vector unsigned int, vector bool int);
vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
vector bool short vec_andc (vector bool short, vector bool short);
vector signed short vec_andc (vector bool short, vector signed short);
vector signed short vec_andc (vector signed short, vector bool short);
vector signed short vec_andc (vector signed short, vector signed short);
vector unsigned short vec_andc (vector bool short,
vector unsigned short);
vector unsigned short vec_andc (vector unsigned short,
vector bool short);
vector unsigned short vec_andc (vector unsigned short,
vector unsigned short);
vector signed char vec_andc (vector bool char, vector signed char);
vector bool char vec_andc (vector bool char, vector bool char);
vector signed char vec_andc (vector signed char, vector bool char);
vector signed char vec_andc (vector signed char, vector signed char);
vector unsigned char vec_andc (vector bool char, vector unsigned char);
vector unsigned char vec_andc (vector unsigned char, vector bool char);
vector unsigned char vec_andc (vector unsigned char,
vector unsigned char);
vector unsigned char vec_avg (vector unsigned char,
vector unsigned char);
vector signed char vec_avg (vector signed char, vector signed char);
vector unsigned short vec_avg (vector unsigned short,
vector unsigned short);
vector signed short vec_avg (vector signed short, vector signed short);
vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
vector signed int vec_avg (vector signed int, vector signed int);
vector signed int vec_vavgsw (vector signed int, vector signed int);
vector unsigned int vec_vavguw (vector unsigned int,
vector unsigned int);
vector signed short vec_vavgsh (vector signed short,
vector signed short);
vector unsigned short vec_vavguh (vector unsigned short,
vector unsigned short);
vector signed char vec_vavgsb (vector signed char, vector signed char);
vector unsigned char vec_vavgub (vector unsigned char,
vector unsigned char);
vector float vec_ceil (vector float);
vector signed int vec_cmpb (vector float, vector float);
vector bool char vec_cmpeq (vector signed char, vector signed char);
vector bool char vec_cmpeq (vector unsigned char, vector unsigned char);
vector bool short vec_cmpeq (vector signed short, vector signed short);
vector bool short vec_cmpeq (vector unsigned short,
vector unsigned short);
vector bool int vec_cmpeq (vector signed int, vector signed int);
vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
vector bool int vec_cmpeq (vector float, vector float);
vector bool int vec_vcmpeqfp (vector float, vector float);
vector bool int vec_vcmpequw (vector signed int, vector signed int);
vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);
vector bool short vec_vcmpequh (vector signed short,
vector signed short);
vector bool short vec_vcmpequh (vector unsigned short,
vector unsigned short);
vector bool char vec_vcmpequb (vector signed char, vector signed char);
vector bool char vec_vcmpequb (vector unsigned char,
vector unsigned char);
vector bool int vec_cmpge (vector float, vector float);
vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
vector bool char vec_cmpgt (vector signed char, vector signed char);
vector bool short vec_cmpgt (vector unsigned short,
vector unsigned short);
vector bool short vec_cmpgt (vector signed short, vector signed short);
vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
vector bool int vec_cmpgt (vector signed int, vector signed int);
vector bool int vec_cmpgt (vector float, vector float);
vector bool int vec_vcmpgtfp (vector float, vector float);
vector bool int vec_vcmpgtsw (vector signed int, vector signed int);
vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);
vector bool short vec_vcmpgtsh (vector signed short,
vector signed short);
vector bool short vec_vcmpgtuh (vector unsigned short,
vector unsigned short);
vector bool char vec_vcmpgtsb (vector signed char, vector signed char);
vector bool char vec_vcmpgtub (vector unsigned char,
vector unsigned char);
vector bool int vec_cmple (vector float, vector float);
vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
vector bool char vec_cmplt (vector signed char, vector signed char);
vector bool short vec_cmplt (vector unsigned short,
vector unsigned short);
vector bool short vec_cmplt (vector signed short, vector signed short);
vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
vector bool int vec_cmplt (vector signed int, vector signed int);
vector bool int vec_cmplt (vector float, vector float);
vector float vec_ctf (vector unsigned int, const int);
vector float vec_ctf (vector signed int, const int);
vector float vec_vcfsx (vector signed int, const int);
vector float vec_vcfux (vector unsigned int, const int);
vector signed int vec_cts (vector float, const int);
vector unsigned int vec_ctu (vector float, const int);
void vec_dss (const int);
void vec_dssall (void);
void vec_dst (const vector unsigned char *, int, const int);
void vec_dst (const vector signed char *, int, const int);
void vec_dst (const vector bool char *, int, const int);
void vec_dst (const vector unsigned short *, int, const int);
void vec_dst (const vector signed short *, int, const int);
void vec_dst (const vector bool short *, int, const int);
void vec_dst (const vector pixel *, int, const int);
void vec_dst (const vector unsigned int *, int, const int);
void vec_dst (const vector signed int *, int, const int);
void vec_dst (const vector bool int *, int, const int);
void vec_dst (const vector float *, int, const int);
void vec_dst (const unsigned char *, int, const int);
void vec_dst (const signed char *, int, const int);
void vec_dst (const unsigned short *, int, const int);
void vec_dst (const short *, int, const int);
void vec_dst (const unsigned int *, int, const int);
void vec_dst (const int *, int, const int);
void vec_dst (const unsigned long *, int, const int);
void vec_dst (const long *, int, const int);
void vec_dst (const float *, int, const int);
void vec_dstst (const vector unsigned char *, int, const int);
void vec_dstst (const vector signed char *, int, const int);
void vec_dstst (const vector bool char *, int, const int);
void vec_dstst (const vector unsigned short *, int, const int);
void vec_dstst (const vector signed short *, int, const int);
void vec_dstst (const vector bool short *, int, const int);
void vec_dstst (const vector pixel *, int, const int);
void vec_dstst (const vector unsigned int *, int, const int);
void vec_dstst (const vector signed int *, int, const int);
void vec_dstst (const vector bool int *, int, const int);
void vec_dstst (const vector float *, int, const int);
void vec_dstst (const unsigned char *, int, const int);
void vec_dstst (const signed char *, int, const int);
void vec_dstst (const unsigned short *, int, const int);
void vec_dstst (const short *, int, const int);
void vec_dstst (const unsigned int *, int, const int);
void vec_dstst (const int *, int, const int);
void vec_dstst (const unsigned long *, int, const int);
void vec_dstst (const long *, int, const int);
void vec_dstst (const float *, int, const int);
void vec_dststt (const vector unsigned char *, int, const int);
void vec_dststt (const vector signed char *, int, const int);
void vec_dststt (const vector bool char *, int, const int);
void vec_dststt (const vector unsigned short *, int, const int);
void vec_dststt (const vector signed short *, int, const int);
void vec_dststt (const vector bool short *, int, const int);
void vec_dststt (const vector pixel *, int, const int);
void vec_dststt (const vector unsigned int *, int, const int);
void vec_dststt (const vector signed int *, int, const int);
void vec_dststt (const vector bool int *, int, const int);
void vec_dststt (const vector float *, int, const int);
void vec_dststt (const unsigned char *, int, const int);
void vec_dststt (const signed char *, int, const int);
void vec_dststt (const unsigned short *, int, const int);
void vec_dststt (const short *, int, const int);
void vec_dststt (const unsigned int *, int, const int);
void vec_dststt (const int *, int, const int);
void vec_dststt (const unsigned long *, int, const int);
void vec_dststt (const long *, int, const int);
void vec_dststt (const float *, int, const int);
void vec_dstt (const vector unsigned char *, int, const int);
void vec_dstt (const vector signed char *, int, const int);
void vec_dstt (const vector bool char *, int, const int);
void vec_dstt (const vector unsigned short *, int, const int);
void vec_dstt (const vector signed short *, int, const int);
void vec_dstt (const vector bool short *, int, const int);
void vec_dstt (const vector pixel *, int, const int);
void vec_dstt (const vector unsigned int *, int, const int);
void vec_dstt (const vector signed int *, int, const int);
void vec_dstt (const vector bool int *, int, const int);
void vec_dstt (const vector float *, int, const int);
void vec_dstt (const unsigned char *, int, const int);
void vec_dstt (const signed char *, int, const int);
void vec_dstt (const unsigned short *, int, const int);
void vec_dstt (const short *, int, const int);
void vec_dstt (const unsigned int *, int, const int);
void vec_dstt (const int *, int, const int);
void vec_dstt (const unsigned long *, int, const int);
void vec_dstt (const long *, int, const int);
void vec_dstt (const float *, int, const int);
vector float vec_expte (vector float);
vector float vec_floor (vector float);
vector float vec_ld (int, const vector float *);
vector float vec_ld (int, const float *);
vector bool int vec_ld (int, const vector bool int *);
vector signed int vec_ld (int, const vector signed int *);
vector signed int vec_ld (int, const int *);
vector signed int vec_ld (int, const long *);
vector unsigned int vec_ld (int, const vector unsigned int *);
vector unsigned int vec_ld (int, const unsigned int *);
vector unsigned int vec_ld (int, const unsigned long *);
vector bool short vec_ld (int, const vector bool short *);
vector pixel vec_ld (int, const vector pixel *);
vector signed short vec_ld (int, const vector signed short *);
vector signed short vec_ld (int, const short *);
vector unsigned short vec_ld (int, const vector unsigned short *);
vector unsigned short vec_ld (int, const unsigned short *);
vector bool char vec_ld (int, const vector bool char *);
vector signed char vec_ld (int, const vector signed char *);
vector signed char vec_ld (int, const signed char *);
vector unsigned char vec_ld (int, const vector unsigned char *);
vector unsigned char vec_ld (int, const unsigned char *);
vector signed char vec_lde (int, const signed char *);
vector unsigned char vec_lde (int, const unsigned char *);
vector signed short vec_lde (int, const short *);
vector unsigned short vec_lde (int, const unsigned short *);
vector float vec_lde (int, const float *);
vector signed int vec_lde (int, const int *);
vector unsigned int vec_lde (int, const unsigned int *);
vector signed int vec_lde (int, const long *);
vector unsigned int vec_lde (int, const unsigned long *);
vector float vec_lvewx (int, float *);
vector signed int vec_lvewx (int, int *);
vector unsigned int vec_lvewx (int, unsigned int *);
vector signed int vec_lvewx (int, long *);
vector unsigned int vec_lvewx (int, unsigned long *);
vector signed short vec_lvehx (int, short *);
vector unsigned short vec_lvehx (int, unsigned short *);
vector signed char vec_lvebx (int, char *);
vector unsigned char vec_lvebx (int, unsigned char *);
vector float vec_ldl (int, const vector float *);
vector float vec_ldl (int, const float *);
vector bool int vec_ldl (int, const vector bool int *);
vector signed int vec_ldl (int, const vector signed int *);
vector signed int vec_ldl (int, const int *);
vector signed int vec_ldl (int, const long *);
vector unsigned int vec_ldl (int, const vector unsigned int *);
vector unsigned int vec_ldl (int, const unsigned int *);
vector unsigned int vec_ldl (int, const unsigned long *);
vector bool short vec_ldl (int, const vector bool short *);
vector pixel vec_ldl (int, const vector pixel *);
vector signed short vec_ldl (int, const vector signed short *);
vector signed short vec_ldl (int, const short *);
vector unsigned short vec_ldl (int, const vector unsigned short *);
vector unsigned short vec_ldl (int, const unsigned short *);
vector bool char vec_ldl (int, const vector bool char *);
vector signed char vec_ldl (int, const vector signed char *);
vector signed char vec_ldl (int, const signed char *);
vector unsigned char vec_ldl (int, const vector unsigned char *);
vector unsigned char vec_ldl (int, const unsigned char *);
vector float vec_loge (vector float);
vector unsigned char vec_lvsl (int, const volatile unsigned char *);
vector unsigned char vec_lvsl (int, const volatile signed char *);
vector unsigned char vec_lvsl (int, const volatile unsigned short *);
vector unsigned char vec_lvsl (int, const volatile short *);
vector unsigned char vec_lvsl (int, const volatile unsigned int *);
vector unsigned char vec_lvsl (int, const volatile int *);
vector unsigned char vec_lvsl (int, const volatile unsigned long *);
vector unsigned char vec_lvsl (int, const volatile long *);
vector unsigned char vec_lvsl (int, const volatile float *);
vector unsigned char vec_lvsr (int, const volatile unsigned char *);
vector unsigned char vec_lvsr (int, const volatile signed char *);
vector unsigned char vec_lvsr (int, const volatile unsigned short *);
vector unsigned char vec_lvsr (int, const volatile short *);
vector unsigned char vec_lvsr (int, const volatile unsigned int *);
vector unsigned char vec_lvsr (int, const volatile int *);
vector unsigned char vec_lvsr (int, const volatile unsigned long *);
vector unsigned char vec_lvsr (int, const volatile long *);
vector unsigned char vec_lvsr (int, const volatile float *);
vector float vec_madd (vector float, vector float, vector float);
vector signed short vec_madds (vector signed short,
vector signed short,
vector signed short);
vector unsigned char vec_max (vector bool char, vector unsigned char);
vector unsigned char vec_max (vector unsigned char, vector bool char);
vector unsigned char vec_max (vector unsigned char,
vector unsigned char);
vector signed char vec_max (vector bool char, vector signed char);
vector signed char vec_max (vector signed char, vector bool char);
vector signed char vec_max (vector signed char, vector signed char);
vector unsigned short vec_max (vector bool short,
vector unsigned short);
vector unsigned short vec_max (vector unsigned short,
vector bool short);
vector unsigned short vec_max (vector unsigned short,
vector unsigned short);
vector signed short vec_max (vector bool short, vector signed short);
vector signed short vec_max (vector signed short, vector bool short);
vector signed short vec_max (vector signed short, vector signed short);
vector unsigned int vec_max (vector bool int, vector unsigned int);
vector unsigned int vec_max (vector unsigned int, vector bool int);
vector unsigned int vec_max (vector unsigned int, vector unsigned int);
vector signed int vec_max (vector bool int, vector signed int);
vector signed int vec_max (vector signed int, vector bool int);
vector signed int vec_max (vector signed int, vector signed int);
vector float vec_max (vector float, vector float);
vector float vec_vmaxfp (vector float, vector float);
vector signed int vec_vmaxsw (vector bool int, vector signed int);
vector signed int vec_vmaxsw (vector signed int, vector bool int);
vector signed int vec_vmaxsw (vector signed int, vector signed int);
vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
vector unsigned int vec_vmaxuw (vector unsigned int,
vector unsigned int);
vector signed short vec_vmaxsh (vector bool short, vector signed short);
vector signed short vec_vmaxsh (vector signed short, vector bool short);
vector signed short vec_vmaxsh (vector signed short,
vector signed short);
vector unsigned short vec_vmaxuh (vector bool short,
vector unsigned short);
vector unsigned short vec_vmaxuh (vector unsigned short,
vector bool short);
vector unsigned short vec_vmaxuh (vector unsigned short,
vector unsigned short);
vector signed char vec_vmaxsb (vector bool char, vector signed char);
vector signed char vec_vmaxsb (vector signed char, vector bool char);
vector signed char vec_vmaxsb (vector signed char, vector signed char);
vector unsigned char vec_vmaxub (vector bool char,
vector unsigned char);
vector unsigned char vec_vmaxub (vector unsigned char,
vector bool char);
vector unsigned char vec_vmaxub (vector unsigned char,
vector unsigned char);
vector bool char vec_mergeh (vector bool char, vector bool char);
vector signed char vec_mergeh (vector signed char, vector signed char);
vector unsigned char vec_mergeh (vector unsigned char,
vector unsigned char);
vector bool short vec_mergeh (vector bool short, vector bool short);
vector pixel vec_mergeh (vector pixel, vector pixel);
vector signed short vec_mergeh (vector signed short,
vector signed short);
vector unsigned short vec_mergeh (vector unsigned short,
vector unsigned short);
vector float vec_mergeh (vector float, vector float);
vector bool int vec_mergeh (vector bool int, vector bool int);
vector signed int vec_mergeh (vector signed int, vector signed int);
vector unsigned int vec_mergeh (vector unsigned int,
vector unsigned int);
vector float vec_vmrghw (vector float, vector float);
vector bool int vec_vmrghw (vector bool int, vector bool int);
vector signed int vec_vmrghw (vector signed int, vector signed int);
vector unsigned int vec_vmrghw (vector unsigned int,
vector unsigned int);
vector bool short vec_vmrghh (vector bool short, vector bool short);
vector signed short vec_vmrghh (vector signed short,
vector signed short);
vector unsigned short vec_vmrghh (vector unsigned short,
vector unsigned short);
vector pixel vec_vmrghh (vector pixel, vector pixel);
vector bool char vec_vmrghb (vector bool char, vector bool char);
vector signed char vec_vmrghb (vector signed char, vector signed char);
vector unsigned char vec_vmrghb (vector unsigned char,
vector unsigned char);
vector bool char vec_mergel (vector bool char, vector bool char);
vector signed char vec_mergel (vector signed char, vector signed char);
vector unsigned char vec_mergel (vector unsigned char,
vector unsigned char);
vector bool short vec_mergel (vector bool short, vector bool short);
vector pixel vec_mergel (vector pixel, vector pixel);
vector signed short vec_mergel (vector signed short,
vector signed short);
vector unsigned short vec_mergel (vector unsigned short,
vector unsigned short);
vector float vec_mergel (vector float, vector float);
vector bool int vec_mergel (vector bool int, vector bool int);
vector signed int vec_mergel (vector signed int, vector signed int);
vector unsigned int vec_mergel (vector unsigned int,
vector unsigned int);
vector float vec_vmrglw (vector float, vector float);
vector signed int vec_vmrglw (vector signed int, vector signed int);
vector unsigned int vec_vmrglw (vector unsigned int,
vector unsigned int);
vector bool int vec_vmrglw (vector bool int, vector bool int);
vector bool short vec_vmrglh (vector bool short, vector bool short);
vector signed short vec_vmrglh (vector signed short,
vector signed short);
vector unsigned short vec_vmrglh (vector unsigned short,
vector unsigned short);
vector pixel vec_vmrglh (vector pixel, vector pixel);
vector bool char vec_vmrglb (vector bool char, vector bool char);
vector signed char vec_vmrglb (vector signed char, vector signed char);
vector unsigned char vec_vmrglb (vector unsigned char,
vector unsigned char);
vector unsigned short vec_mfvscr (void);
vector unsigned char vec_min (vector bool char, vector unsigned char);
vector unsigned char vec_min (vector unsigned char, vector bool char);
vector unsigned char vec_min (vector unsigned char,
vector unsigned char);
vector signed char vec_min (vector bool char, vector signed char);
vector signed char vec_min (vector signed char, vector bool char);
vector signed char vec_min (vector signed char, vector signed char);
vector unsigned short vec_min (vector bool short,
vector unsigned short);
vector unsigned short vec_min (vector unsigned short,
vector bool short);
vector unsigned short vec_min (vector unsigned short,
vector unsigned short);
vector signed short vec_min (vector bool short, vector signed short);
vector signed short vec_min (vector signed short, vector bool short);
vector signed short vec_min (vector signed short, vector signed short);
vector unsigned int vec_min (vector bool int, vector unsigned int);
vector unsigned int vec_min (vector unsigned int, vector bool int);
vector unsigned int vec_min (vector unsigned int, vector unsigned int);
vector signed int vec_min (vector bool int, vector signed int);
vector signed int vec_min (vector signed int, vector bool int);
vector signed int vec_min (vector signed int, vector signed int);
vector float vec_min (vector float, vector float);
vector float vec_vminfp (vector float, vector float);
vector signed int vec_vminsw (vector bool int, vector signed int);
vector signed int vec_vminsw (vector signed int, vector bool int);
vector signed int vec_vminsw (vector signed int, vector signed int);
vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
vector unsigned int vec_vminuw (vector unsigned int,
vector unsigned int);
vector signed short vec_vminsh (vector bool short, vector signed short);
vector signed short vec_vminsh (vector signed short, vector bool short);
vector signed short vec_vminsh (vector signed short,
vector signed short);
vector unsigned short vec_vminuh (vector bool short,
vector unsigned short);
vector unsigned short vec_vminuh (vector unsigned short,
vector bool short);
vector unsigned short vec_vminuh (vector unsigned short,
vector unsigned short);
vector signed char vec_vminsb (vector bool char, vector signed char);
vector signed char vec_vminsb (vector signed char, vector bool char);
vector signed char vec_vminsb (vector signed char, vector signed char);
vector unsigned char vec_vminub (vector bool char,
vector unsigned char);
vector unsigned char vec_vminub (vector unsigned char,
vector bool char);
vector unsigned char vec_vminub (vector unsigned char,
vector unsigned char);
vector signed short vec_mladd (vector signed short,
vector signed short,
vector signed short);
vector signed short vec_mladd (vector signed short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mladd (vector unsigned short,
vector signed short,
vector signed short);
vector unsigned short vec_mladd (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mradds (vector signed short,
vector signed short,
vector signed short);
vector unsigned int vec_msum (vector unsigned char,
vector unsigned char,
vector unsigned int);
vector signed int vec_msum (vector signed char,
vector unsigned char,
vector signed int);
vector unsigned int vec_msum (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msum (vector signed short,
vector signed short,
vector signed int);
vector signed int vec_vmsumshm (vector signed short,
vector signed short,
vector signed int);
vector unsigned int vec_vmsumuhm (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_vmsummbm (vector signed char,
vector unsigned char,
vector signed int);
vector unsigned int vec_vmsumubm (vector unsigned char,
vector unsigned char,
vector unsigned int);
vector unsigned int vec_msums (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msums (vector signed short,
vector signed short,
vector signed int);
vector signed int vec_vmsumshs (vector signed short,
vector signed short,
vector signed int);
vector unsigned int vec_vmsumuhs (vector unsigned short,
vector unsigned short,
vector unsigned int);
void vec_mtvscr (vector signed int);
void vec_mtvscr (vector unsigned int);
void vec_mtvscr (vector bool int);
void vec_mtvscr (vector signed short);
void vec_mtvscr (vector unsigned short);
void vec_mtvscr (vector bool short);
void vec_mtvscr (vector pixel);
void vec_mtvscr (vector signed char);
void vec_mtvscr (vector unsigned char);
void vec_mtvscr (vector bool char);
vector unsigned short vec_mule (vector unsigned char,
vector unsigned char);
vector signed short vec_mule (vector signed char,
vector signed char);
vector unsigned int vec_mule (vector unsigned short,
vector unsigned short);
vector signed int vec_mule (vector signed short, vector signed short);
vector signed int vec_vmulesh (vector signed short,
vector signed short);
vector unsigned int vec_vmuleuh (vector unsigned short,
vector unsigned short);
vector signed short vec_vmulesb (vector signed char,
vector signed char);
vector unsigned short vec_vmuleub (vector unsigned char,
vector unsigned char);
vector unsigned short vec_mulo (vector unsigned char,
vector unsigned char);
vector signed short vec_mulo (vector signed char, vector signed char);
vector unsigned int vec_mulo (vector unsigned short,
vector unsigned short);
vector signed int vec_mulo (vector signed short, vector signed short);
vector signed int vec_vmulosh (vector signed short,
vector signed short);
vector unsigned int vec_vmulouh (vector unsigned short,
vector unsigned short);
vector signed short vec_vmulosb (vector signed char,
vector signed char);
vector unsigned short vec_vmuloub (vector unsigned char,
vector unsigned char);
vector float vec_nmsub (vector float, vector float, vector float);
vector float vec_nor (vector float, vector float);
vector signed int vec_nor (vector signed int, vector signed int);
vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
vector bool int vec_nor (vector bool int, vector bool int);
vector signed short vec_nor (vector signed short, vector signed short);
vector unsigned short vec_nor (vector unsigned short,
vector unsigned short);
vector bool short vec_nor (vector bool short, vector bool short);
vector signed char vec_nor (vector signed char, vector signed char);
vector unsigned char vec_nor (vector unsigned char,
vector unsigned char);
vector bool char vec_nor (vector bool char, vector bool char);
vector float vec_or (vector float, vector float);
vector float vec_or (vector float, vector bool int);
vector float vec_or (vector bool int, vector float);
vector bool int vec_or (vector bool int, vector bool int);
vector signed int vec_or (vector bool int, vector signed int);
vector signed int vec_or (vector signed int, vector bool int);
vector signed int vec_or (vector signed int, vector signed int);
vector unsigned int vec_or (vector bool int, vector unsigned int);
vector unsigned int vec_or (vector unsigned int, vector bool int);
vector unsigned int vec_or (vector unsigned int, vector unsigned int);
vector bool short vec_or (vector bool short, vector bool short);
vector signed short vec_or (vector bool short, vector signed short);
vector signed short vec_or (vector signed short, vector bool short);
vector signed short vec_or (vector signed short, vector signed short);
vector unsigned short vec_or (vector bool short, vector unsigned short);
vector unsigned short vec_or (vector unsigned short, vector bool short);
vector unsigned short vec_or (vector unsigned short,
vector unsigned short);
vector signed char vec_or (vector bool char, vector signed char);
vector bool char vec_or (vector bool char, vector bool char);
vector signed char vec_or (vector signed char, vector bool char);
vector signed char vec_or (vector signed char, vector signed char);
vector unsigned char vec_or (vector bool char, vector unsigned char);
vector unsigned char vec_or (vector unsigned char, vector bool char);
vector unsigned char vec_or (vector unsigned char,
vector unsigned char);
vector signed char vec_pack (vector signed short, vector signed short);
vector unsigned char vec_pack (vector unsigned short,
vector unsigned short);
vector bool char vec_pack (vector bool short, vector bool short);
vector signed short vec_pack (vector signed int, vector signed int);
vector unsigned short vec_pack (vector unsigned int,
vector unsigned int);
vector bool short vec_pack (vector bool int, vector bool int);
vector bool short vec_vpkuwum (vector bool int, vector bool int);
vector signed short vec_vpkuwum (vector signed int, vector signed int);
vector unsigned short vec_vpkuwum (vector unsigned int,
vector unsigned int);
vector bool char vec_vpkuhum (vector bool short, vector bool short);
vector signed char vec_vpkuhum (vector signed short,
vector signed short);
vector unsigned char vec_vpkuhum (vector unsigned short,
vector unsigned short);
vector pixel vec_packpx (vector unsigned int, vector unsigned int);
vector unsigned char vec_packs (vector unsigned short,
vector unsigned short);
vector signed char vec_packs (vector signed short, vector signed short);
vector unsigned short vec_packs (vector unsigned int,
vector unsigned int);
vector signed short vec_packs (vector signed int, vector signed int);
vector signed short vec_vpkswss (vector signed int, vector signed int);
vector unsigned short vec_vpkuwus (vector unsigned int,
vector unsigned int);
vector signed char vec_vpkshss (vector signed short,
vector signed short);
vector unsigned char vec_vpkuhus (vector unsigned short,
vector unsigned short);
vector unsigned char vec_packsu (vector unsigned short,
vector unsigned short);
vector unsigned char vec_packsu (vector signed short,
vector signed short);
vector unsigned short vec_packsu (vector unsigned int,
vector unsigned int);
vector unsigned short vec_packsu (vector signed int, vector signed int);
vector unsigned short vec_vpkswus (vector signed int,
vector signed int);
vector unsigned char vec_vpkshus (vector signed short,
vector signed short);
vector float vec_perm (vector float,
vector float,
vector unsigned char);
vector signed int vec_perm (vector signed int,
vector signed int,
vector unsigned char);
vector unsigned int vec_perm (vector unsigned int,
vector unsigned int,
vector unsigned char);
vector bool int vec_perm (vector bool int,
vector bool int,
vector unsigned char);
vector signed short vec_perm (vector signed short,
vector signed short,
vector unsigned char);
vector unsigned short vec_perm (vector unsigned short,
vector unsigned short,
vector unsigned char);
vector bool short vec_perm (vector bool short,
vector bool short,
vector unsigned char);
vector pixel vec_perm (vector pixel,
vector pixel,
vector unsigned char);
vector signed char vec_perm (vector signed char,
vector signed char,
vector unsigned char);
vector unsigned char vec_perm (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector bool char vec_perm (vector bool char,
vector bool char,
vector unsigned char);
vector float vec_re (vector float);
vector signed char vec_rl (vector signed char,
vector unsigned char);
vector unsigned char vec_rl (vector unsigned char,
vector unsigned char);
vector signed short vec_rl (vector signed short, vector unsigned short);
vector unsigned short vec_rl (vector unsigned short,
vector unsigned short);
vector signed int vec_rl (vector signed int, vector unsigned int);
vector unsigned int vec_rl (vector unsigned int, vector unsigned int);
vector signed int vec_vrlw (vector signed int, vector unsigned int);
vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);
vector signed short vec_vrlh (vector signed short,
vector unsigned short);
vector unsigned short vec_vrlh (vector unsigned short,
vector unsigned short);
vector signed char vec_vrlb (vector signed char, vector unsigned char);
vector unsigned char vec_vrlb (vector unsigned char,
vector unsigned char);
vector float vec_round (vector float);
vector float vec_rsqrte (vector float);
vector float vec_sel (vector float, vector float, vector bool int);
vector float vec_sel (vector float, vector float, vector unsigned int);
vector signed int vec_sel (vector signed int,
vector signed int,
vector bool int);
vector signed int vec_sel (vector signed int,
vector signed int,
vector unsigned int);
vector unsigned int vec_sel (vector unsigned int,
vector unsigned int,
vector bool int);
vector unsigned int vec_sel (vector unsigned int,
vector unsigned int,
vector unsigned int);
vector bool int vec_sel (vector bool int,
vector bool int,
vector bool int);
vector bool int vec_sel (vector bool int,
vector bool int,
vector unsigned int);
vector signed short vec_sel (vector signed short,
vector signed short,
vector bool short);
vector signed short vec_sel (vector signed short,
vector signed short,
vector unsigned short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector bool short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector bool short vec_sel (vector bool short,
vector bool short,
vector bool short);
vector bool short vec_sel (vector bool short,
vector bool short,
vector unsigned short);
vector signed char vec_sel (vector signed char,
vector signed char,
vector bool char);
vector signed char vec_sel (vector signed char,
vector signed char,
vector unsigned char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector bool char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector bool char vec_sel (vector bool char,
vector bool char,
vector bool char);
vector bool char vec_sel (vector bool char,
vector bool char,
vector unsigned char);
vector signed char vec_sl (vector signed char,
vector unsigned char);
vector unsigned char vec_sl (vector unsigned char,
vector unsigned char);
vector signed short vec_sl (vector signed short, vector unsigned short);
vector unsigned short vec_sl (vector unsigned short,
vector unsigned short);
vector signed int vec_sl (vector signed int, vector unsigned int);
vector unsigned int vec_sl (vector unsigned int, vector unsigned int);
vector signed int vec_vslw (vector signed int, vector unsigned int);
vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);
vector signed short vec_vslh (vector signed short,
vector unsigned short);
vector unsigned short vec_vslh (vector unsigned short,
vector unsigned short);
vector signed char vec_vslb (vector signed char, vector unsigned char);
vector unsigned char vec_vslb (vector unsigned char,
vector unsigned char);
vector float vec_sld (vector float, vector float, const int);
vector signed int vec_sld (vector signed int,
vector signed int,
const int);
vector unsigned int vec_sld (vector unsigned int,
vector unsigned int,
const int);
vector bool int vec_sld (vector bool int,
vector bool int,
const int);
vector signed short vec_sld (vector signed short,
vector signed short,
const int);
vector unsigned short vec_sld (vector unsigned short,
vector unsigned short,
const int);
vector bool short vec_sld (vector bool short,
vector bool short,
const int);
vector pixel vec_sld (vector pixel,
vector pixel,
const int);
vector signed char vec_sld (vector signed char,
vector signed char,
const int);
vector unsigned char vec_sld (vector unsigned char,
vector unsigned char,
const int);
vector bool char vec_sld (vector bool char,
vector bool char,
const int);
vector signed int vec_sll (vector signed int,
vector unsigned int);
vector signed int vec_sll (vector signed int,
vector unsigned short);
vector signed int vec_sll (vector signed int,
vector unsigned char);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned int);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned short);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned char);
vector bool int vec_sll (vector bool int,
vector unsigned int);
vector bool int vec_sll (vector bool int,
vector unsigned short);
vector bool int vec_sll (vector bool int,
vector unsigned char);
vector signed short vec_sll (vector signed short,
vector unsigned int);
vector signed short vec_sll (vector signed short,
vector unsigned short);
vector signed short vec_sll (vector signed short,
vector unsigned char);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned int);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned short);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned char);
vector bool short vec_sll (vector bool short, vector unsigned int);
vector bool short vec_sll (vector bool short, vector unsigned short);
vector bool short vec_sll (vector bool short, vector unsigned char);
vector pixel vec_sll (vector pixel, vector unsigned int);
vector pixel vec_sll (vector pixel, vector unsigned short);
vector pixel vec_sll (vector pixel, vector unsigned char);
vector signed char vec_sll (vector signed char, vector unsigned int);
vector signed char vec_sll (vector signed char, vector unsigned short);
vector signed char vec_sll (vector signed char, vector unsigned char);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned int);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned short);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned char);
vector bool char vec_sll (vector bool char, vector unsigned int);
vector bool char vec_sll (vector bool char, vector unsigned short);
vector bool char vec_sll (vector bool char, vector unsigned char);
vector float vec_slo (vector float, vector signed char);
vector float vec_slo (vector float, vector unsigned char);
vector signed int vec_slo (vector signed int, vector signed char);
vector signed int vec_slo (vector signed int, vector unsigned char);
vector unsigned int vec_slo (vector unsigned int, vector signed char);
vector unsigned int vec_slo (vector unsigned int, vector unsigned char);
vector signed short vec_slo (vector signed short, vector signed char);
vector signed short vec_slo (vector signed short, vector unsigned char);
vector unsigned short vec_slo (vector unsigned short,
vector signed char);
vector unsigned short vec_slo (vector unsigned short,
vector unsigned char);
vector pixel vec_slo (vector pixel, vector signed char);
vector pixel vec_slo (vector pixel, vector unsigned char);
vector signed char vec_slo (vector signed char, vector signed char);
vector signed char vec_slo (vector signed char, vector unsigned char);
vector unsigned char vec_slo (vector unsigned char, vector signed char);
vector unsigned char vec_slo (vector unsigned char,
vector unsigned char);
vector signed char vec_splat (vector signed char, const int);
vector unsigned char vec_splat (vector unsigned char, const int);
vector bool char vec_splat (vector bool char, const int);
vector signed short vec_splat (vector signed short, const int);
vector unsigned short vec_splat (vector unsigned short, const int);
vector bool short vec_splat (vector bool short, const int);
vector pixel vec_splat (vector pixel, const int);
vector float vec_splat (vector float, const int);
vector signed int vec_splat (vector signed int, const int);
vector unsigned int vec_splat (vector unsigned int, const int);
vector bool int vec_splat (vector bool int, const int);
vector float vec_vspltw (vector float, const int);
vector signed int vec_vspltw (vector signed int, const int);
vector unsigned int vec_vspltw (vector unsigned int, const int);
vector bool int vec_vspltw (vector bool int, const int);
vector bool short vec_vsplth (vector bool short, const int);
vector signed short vec_vsplth (vector signed short, const int);
vector unsigned short vec_vsplth (vector unsigned short, const int);
vector pixel vec_vsplth (vector pixel, const int);
vector signed char vec_vspltb (vector signed char, const int);
vector unsigned char vec_vspltb (vector unsigned char, const int);
vector bool char vec_vspltb (vector bool char, const int);
vector signed char vec_splat_s8 (const int);
vector signed short vec_splat_s16 (const int);
vector signed int vec_splat_s32 (const int);
vector unsigned char vec_splat_u8 (const int);
vector unsigned short vec_splat_u16 (const int);
vector unsigned int vec_splat_u32 (const int);
vector signed char vec_sr (vector signed char, vector unsigned char);
vector unsigned char vec_sr (vector unsigned char,
vector unsigned char);
vector signed short vec_sr (vector signed short,
vector unsigned short);
vector unsigned short vec_sr (vector unsigned short,
vector unsigned short);
vector signed int vec_sr (vector signed int, vector unsigned int);
vector unsigned int vec_sr (vector unsigned int, vector unsigned int);
vector signed int vec_vsrw (vector signed int, vector unsigned int);
vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);
vector signed short vec_vsrh (vector signed short,
vector unsigned short);
vector unsigned short vec_vsrh (vector unsigned short,
vector unsigned short);
vector signed char vec_vsrb (vector signed char, vector unsigned char);
vector unsigned char vec_vsrb (vector unsigned char,
vector unsigned char);
vector signed char vec_sra (vector signed char, vector unsigned char);
vector unsigned char vec_sra (vector unsigned char,
vector unsigned char);
vector signed short vec_sra (vector signed short,
vector unsigned short);
vector unsigned short vec_sra (vector unsigned short,
vector unsigned short);
vector signed int vec_sra (vector signed int, vector unsigned int);
vector unsigned int vec_sra (vector unsigned int, vector unsigned int);
vector signed int vec_vsraw (vector signed int, vector unsigned int);
vector unsigned int vec_vsraw (vector unsigned int,
vector unsigned int);
vector signed short vec_vsrah (vector signed short,
vector unsigned short);
vector unsigned short vec_vsrah (vector unsigned short,
vector unsigned short);
vector signed char vec_vsrab (vector signed char, vector unsigned char);
vector unsigned char vec_vsrab (vector unsigned char,
vector unsigned char);
vector signed int vec_srl (vector signed int, vector unsigned int);
vector signed int vec_srl (vector signed int, vector unsigned short);
vector signed int vec_srl (vector signed int, vector unsigned char);
vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
vector unsigned int vec_srl (vector unsigned int,
vector unsigned short);
vector unsigned int vec_srl (vector unsigned int, vector unsigned char);
vector bool int vec_srl (vector bool int, vector unsigned int);
vector bool int vec_srl (vector bool int, vector unsigned short);
vector bool int vec_srl (vector bool int, vector unsigned char);
vector signed short vec_srl (vector signed short, vector unsigned int);
vector signed short vec_srl (vector signed short,
vector unsigned short);
vector signed short vec_srl (vector signed short, vector unsigned char);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned int);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned short);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned char);
vector bool short vec_srl (vector bool short, vector unsigned int);
vector bool short vec_srl (vector bool short, vector unsigned short);
vector bool short vec_srl (vector bool short, vector unsigned char);
vector pixel vec_srl (vector pixel, vector unsigned int);
vector pixel vec_srl (vector pixel, vector unsigned short);
vector pixel vec_srl (vector pixel, vector unsigned char);
vector signed char vec_srl (vector signed char, vector unsigned int);
vector signed char vec_srl (vector signed char, vector unsigned short);
vector signed char vec_srl (vector signed char, vector unsigned char);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned int);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned short);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned char);
vector bool char vec_srl (vector bool char, vector unsigned int);
vector bool char vec_srl (vector bool char, vector unsigned short);
vector bool char vec_srl (vector bool char, vector unsigned char);
vector float vec_sro (vector float, vector signed char);
vector float vec_sro (vector float, vector unsigned char);
vector signed int vec_sro (vector signed int, vector signed char);
vector signed int vec_sro (vector signed int, vector unsigned char);
vector unsigned int vec_sro (vector unsigned int, vector signed char);
vector unsigned int vec_sro (vector unsigned int, vector unsigned char);
vector signed short vec_sro (vector signed short, vector signed char);
vector signed short vec_sro (vector signed short, vector unsigned char);
vector unsigned short vec_sro (vector unsigned short,
vector signed char);
vector unsigned short vec_sro (vector unsigned short,
vector unsigned char);
vector pixel vec_sro (vector pixel, vector signed char);
vector pixel vec_sro (vector pixel, vector unsigned char);
vector signed char vec_sro (vector signed char, vector signed char);
vector signed char vec_sro (vector signed char, vector unsigned char);
vector unsigned char vec_sro (vector unsigned char, vector signed char);
vector unsigned char vec_sro (vector unsigned char,
vector unsigned char);
void vec_st (vector float, int, vector float *);
void vec_st (vector float, int, float *);
void vec_st (vector signed int, int, vector signed int *);
void vec_st (vector signed int, int, int *);
void vec_st (vector unsigned int, int, vector unsigned int *);
void vec_st (vector unsigned int, int, unsigned int *);
void vec_st (vector bool int, int, vector bool int *);
void vec_st (vector bool int, int, unsigned int *);
void vec_st (vector bool int, int, int *);
void vec_st (vector signed short, int, vector signed short *);
void vec_st (vector signed short, int, short *);
void vec_st (vector unsigned short, int, vector unsigned short *);
void vec_st (vector unsigned short, int, unsigned short *);
void vec_st (vector bool short, int, vector bool short *);
void vec_st (vector bool short, int, unsigned short *);
void vec_st (vector pixel, int, vector pixel *);
void vec_st (vector pixel, int, unsigned short *);
void vec_st (vector pixel, int, short *);
void vec_st (vector bool short, int, short *);
void vec_st (vector signed char, int, vector signed char *);
void vec_st (vector signed char, int, signed char *);
void vec_st (vector unsigned char, int, vector unsigned char *);
void vec_st (vector unsigned char, int, unsigned char *);
void vec_st (vector bool char, int, vector bool char *);
void vec_st (vector bool char, int, unsigned char *);
void vec_st (vector bool char, int, signed char *);
void vec_ste (vector signed char, int, signed char *);
void vec_ste (vector unsigned char, int, unsigned char *);
void vec_ste (vector bool char, int, signed char *);
void vec_ste (vector bool char, int, unsigned char *);
void vec_ste (vector signed short, int, short *);
void vec_ste (vector unsigned short, int, unsigned short *);
void vec_ste (vector bool short, int, short *);
void vec_ste (vector bool short, int, unsigned short *);
void vec_ste (vector pixel, int, short *);
void vec_ste (vector pixel, int, unsigned short *);
void vec_ste (vector float, int, float *);
void vec_ste (vector signed int, int, int *);
void vec_ste (vector unsigned int, int, unsigned int *);
void vec_ste (vector bool int, int, int *);
void vec_ste (vector bool int, int, unsigned int *);
void vec_stvewx (vector float, int, float *);
void vec_stvewx (vector signed int, int, int *);
void vec_stvewx (vector unsigned int, int, unsigned int *);
void vec_stvewx (vector bool int, int, int *);
void vec_stvewx (vector bool int, int, unsigned int *);
void vec_stvehx (vector signed short, int, short *);
void vec_stvehx (vector unsigned short, int, unsigned short *);
void vec_stvehx (vector bool short, int, short *);
void vec_stvehx (vector bool short, int, unsigned short *);
void vec_stvehx (vector pixel, int, short *);
void vec_stvehx (vector pixel, int, unsigned short *);
void vec_stvebx (vector signed char, int, signed char *);
void vec_stvebx (vector unsigned char, int, unsigned char *);
void vec_stvebx (vector bool char, int, signed char *);
void vec_stvebx (vector bool char, int, unsigned char *);
void vec_stl (vector float, int, vector float *);
void vec_stl (vector float, int, float *);
void vec_stl (vector signed int, int, vector signed int *);
void vec_stl (vector signed int, int, int *);
void vec_stl (vector unsigned int, int, vector unsigned int *);
void vec_stl (vector unsigned int, int, unsigned int *);
void vec_stl (vector bool int, int, vector bool int *);
void vec_stl (vector bool int, int, unsigned int *);
void vec_stl (vector bool int, int, int *);
void vec_stl (vector signed short, int, vector signed short *);
void vec_stl (vector signed short, int, short *);
void vec_stl (vector unsigned short, int, vector unsigned short *);
void vec_stl (vector unsigned short, int, unsigned short *);
void vec_stl (vector bool short, int, vector bool short *);
void vec_stl (vector bool short, int, unsigned short *);
void vec_stl (vector bool short, int, short *);
void vec_stl (vector pixel, int, vector pixel *);
void vec_stl (vector pixel, int, unsigned short *);
void vec_stl (vector pixel, int, short *);
void vec_stl (vector signed char, int, vector signed char *);
void vec_stl (vector signed char, int, signed char *);
void vec_stl (vector unsigned char, int, vector unsigned char *);
void vec_stl (vector unsigned char, int, unsigned char *);
void vec_stl (vector bool char, int, vector bool char *);
void vec_stl (vector bool char, int, unsigned char *);
void vec_stl (vector bool char, int, signed char *);
vector signed char vec_sub (vector bool char, vector signed char);
vector signed char vec_sub (vector signed char, vector bool char);
vector signed char vec_sub (vector signed char, vector signed char);
vector unsigned char vec_sub (vector bool char, vector unsigned char);
vector unsigned char vec_sub (vector unsigned char, vector bool char);
vector unsigned char vec_sub (vector unsigned char,
vector unsigned char);
vector signed short vec_sub (vector bool short, vector signed short);
vector signed short vec_sub (vector signed short, vector bool short);
vector signed short vec_sub (vector signed short, vector signed short);
vector unsigned short vec_sub (vector bool short,
vector unsigned short);
vector unsigned short vec_sub (vector unsigned short,
vector bool short);
vector unsigned short vec_sub (vector unsigned short,
vector unsigned short);
vector signed int vec_sub (vector bool int, vector signed int);
vector signed int vec_sub (vector signed int, vector bool int);
vector signed int vec_sub (vector signed int, vector signed int);
vector unsigned int vec_sub (vector bool int, vector unsigned int);
vector unsigned int vec_sub (vector unsigned int, vector bool int);
vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
vector float vec_sub (vector float, vector float);
vector float vec_vsubfp (vector float, vector float);
vector signed int vec_vsubuwm (vector bool int, vector signed int);
vector signed int vec_vsubuwm (vector signed int, vector bool int);
vector signed int vec_vsubuwm (vector signed int, vector signed int);
vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuwm (vector unsigned int,
vector unsigned int);
vector signed short vec_vsubuhm (vector bool short,
vector signed short);
vector signed short vec_vsubuhm (vector signed short,
vector bool short);
vector signed short vec_vsubuhm (vector signed short,
vector signed short);
vector unsigned short vec_vsubuhm (vector bool short,
vector unsigned short);
vector unsigned short vec_vsubuhm (vector unsigned short,
vector bool short);
vector unsigned short vec_vsubuhm (vector unsigned short,
vector unsigned short);
vector signed char vec_vsububm (vector bool char, vector signed char);
vector signed char vec_vsububm (vector signed char, vector bool char);
vector signed char vec_vsububm (vector signed char, vector signed char);
vector unsigned char vec_vsububm (vector bool char,
vector unsigned char);
vector unsigned char vec_vsububm (vector unsigned char,
vector bool char);
vector unsigned char vec_vsububm (vector unsigned char,
vector unsigned char);
vector unsigned int vec_subc (vector unsigned int, vector unsigned int);
vector unsigned char vec_subs (vector bool char, vector unsigned char);
vector unsigned char vec_subs (vector unsigned char, vector bool char);
vector unsigned char vec_subs (vector unsigned char,
vector unsigned char);
vector signed char vec_subs (vector bool char, vector signed char);
vector signed char vec_subs (vector signed char, vector bool char);
vector signed char vec_subs (vector signed char, vector signed char);
vector unsigned short vec_subs (vector bool short,
vector unsigned short);
vector unsigned short vec_subs (vector unsigned short,
vector bool short);
vector unsigned short vec_subs (vector unsigned short,
vector unsigned short);
vector signed short vec_subs (vector bool short, vector signed short);
vector signed short vec_subs (vector signed short, vector bool short);
vector signed short vec_subs (vector signed short, vector signed short);
vector unsigned int vec_subs (vector bool int, vector unsigned int);
vector unsigned int vec_subs (vector unsigned int, vector bool int);
vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
vector signed int vec_subs (vector bool int, vector signed int);
vector signed int vec_subs (vector signed int, vector bool int);
vector signed int vec_subs (vector signed int, vector signed int);
vector signed int vec_vsubsws (vector bool int, vector signed int);
vector signed int vec_vsubsws (vector signed int, vector bool int);
vector signed int vec_vsubsws (vector signed int, vector signed int);
vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuws (vector unsigned int,
vector unsigned int);
vector signed short vec_vsubshs (vector bool short,
vector signed short);
vector signed short vec_vsubshs (vector signed short,
vector bool short);
vector signed short vec_vsubshs (vector signed short,
vector signed short);
vector unsigned short vec_vsubuhs (vector bool short,
vector unsigned short);
vector unsigned short vec_vsubuhs (vector unsigned short,
vector bool short);
vector unsigned short vec_vsubuhs (vector unsigned short,
vector unsigned short);
vector signed char vec_vsubsbs (vector bool char, vector signed char);
vector signed char vec_vsubsbs (vector signed char, vector bool char);
vector signed char vec_vsubsbs (vector signed char, vector signed char);
vector unsigned char vec_vsububs (vector bool char,
vector unsigned char);
vector unsigned char vec_vsububs (vector unsigned char,
vector bool char);
vector unsigned char vec_vsububs (vector unsigned char,
vector unsigned char);
vector unsigned int vec_sum4s (vector unsigned char,
vector unsigned int);
vector signed int vec_sum4s (vector signed char, vector signed int);
vector signed int vec_sum4s (vector signed short, vector signed int);
vector signed int vec_vsum4shs (vector signed short, vector signed int);
vector signed int vec_vsum4sbs (vector signed char, vector signed int);
vector unsigned int vec_vsum4ubs (vector unsigned char,
vector unsigned int);
vector signed int vec_sum2s (vector signed int, vector signed int);
vector signed int vec_sums (vector signed int, vector signed int);
vector float vec_trunc (vector float);
vector signed short vec_unpackh (vector signed char);
vector bool short vec_unpackh (vector bool char);
vector signed int vec_unpackh (vector signed short);
vector bool int vec_unpackh (vector bool short);
vector unsigned int vec_unpackh (vector pixel);
vector bool int vec_vupkhsh (vector bool short);
vector signed int vec_vupkhsh (vector signed short);
vector unsigned int vec_vupkhpx (vector pixel);
vector bool short vec_vupkhsb (vector bool char);
vector signed short vec_vupkhsb (vector signed char);
vector signed short vec_unpackl (vector signed char);
vector bool short vec_unpackl (vector bool char);
vector unsigned int vec_unpackl (vector pixel);
vector signed int vec_unpackl (vector signed short);
vector bool int vec_unpackl (vector bool short);
vector unsigned int vec_vupklpx (vector pixel);
vector bool int vec_vupklsh (vector bool short);
vector signed int vec_vupklsh (vector signed short);
vector bool short vec_vupklsb (vector bool char);
vector signed short vec_vupklsb (vector signed char);
vector float vec_xor (vector float, vector float);
vector float vec_xor (vector float, vector bool int);
vector float vec_xor (vector bool int, vector float);
vector bool int vec_xor (vector bool int, vector bool int);
vector signed int vec_xor (vector bool int, vector signed int);
vector signed int vec_xor (vector signed int, vector bool int);
vector signed int vec_xor (vector signed int, vector signed int);
vector unsigned int vec_xor (vector bool int, vector unsigned int);
vector unsigned int vec_xor (vector unsigned int, vector bool int);
vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
vector bool short vec_xor (vector bool short, vector bool short);
vector signed short vec_xor (vector bool short, vector signed short);
vector signed short vec_xor (vector signed short, vector bool short);
vector signed short vec_xor (vector signed short, vector signed short);
vector unsigned short vec_xor (vector bool short,
vector unsigned short);
vector unsigned short vec_xor (vector unsigned short,
vector bool short);
vector unsigned short vec_xor (vector unsigned short,
vector unsigned short);
vector signed char vec_xor (vector bool char, vector signed char);
vector bool char vec_xor (vector bool char, vector bool char);
vector signed char vec_xor (vector signed char, vector bool char);
vector signed char vec_xor (vector signed char, vector signed char);
vector unsigned char vec_xor (vector bool char, vector unsigned char);
vector unsigned char vec_xor (vector unsigned char, vector bool char);
vector unsigned char vec_xor (vector unsigned char,
vector unsigned char);
int vec_all_eq (vector signed char, vector bool char);
int vec_all_eq (vector signed char, vector signed char);
int vec_all_eq (vector unsigned char, vector bool char);
int vec_all_eq (vector unsigned char, vector unsigned char);
int vec_all_eq (vector bool char, vector bool char);
int vec_all_eq (vector bool char, vector unsigned char);
int vec_all_eq (vector bool char, vector signed char);
int vec_all_eq (vector signed short, vector bool short);
int vec_all_eq (vector signed short, vector signed short);
int vec_all_eq (vector unsigned short, vector bool short);
int vec_all_eq (vector unsigned short, vector unsigned short);
int vec_all_eq (vector bool short, vector bool short);
int vec_all_eq (vector bool short, vector unsigned short);
int vec_all_eq (vector bool short, vector signed short);
int vec_all_eq (vector pixel, vector pixel);
int vec_all_eq (vector signed int, vector bool int);
int vec_all_eq (vector signed int, vector signed int);
int vec_all_eq (vector unsigned int, vector bool int);
int vec_all_eq (vector unsigned int, vector unsigned int);
int vec_all_eq (vector bool int, vector bool int);
int vec_all_eq (vector bool int, vector unsigned int);
int vec_all_eq (vector bool int, vector signed int);
int vec_all_eq (vector float, vector float);
int vec_all_ge (vector bool char, vector unsigned char);
int vec_all_ge (vector unsigned char, vector bool char);
int vec_all_ge (vector unsigned char, vector unsigned char);
int vec_all_ge (vector bool char, vector signed char);
int vec_all_ge (vector signed char, vector bool char);
int vec_all_ge (vector signed char, vector signed char);
int vec_all_ge (vector bool short, vector unsigned short);
int vec_all_ge (vector unsigned short, vector bool short);
int vec_all_ge (vector unsigned short, vector unsigned short);
int vec_all_ge (vector signed short, vector signed short);
int vec_all_ge (vector bool short, vector signed short);
int vec_all_ge (vector signed short, vector bool short);
int vec_all_ge (vector bool int, vector unsigned int);
int vec_all_ge (vector unsigned int, vector bool int);
int vec_all_ge (vector unsigned int, vector unsigned int);
int vec_all_ge (vector bool int, vector signed int);
int vec_all_ge (vector signed int, vector bool int);
int vec_all_ge (vector signed int, vector signed int);
int vec_all_ge (vector float, vector float);
int vec_all_gt (vector bool char, vector unsigned char);
int vec_all_gt (vector unsigned char, vector bool char);
int vec_all_gt (vector unsigned char, vector unsigned char);
int vec_all_gt (vector bool char, vector signed char);
int vec_all_gt (vector signed char, vector bool char);
int vec_all_gt (vector signed char, vector signed char);
int vec_all_gt (vector bool short, vector unsigned short);
int vec_all_gt (vector unsigned short, vector bool short);
int vec_all_gt (vector unsigned short, vector unsigned short);
int vec_all_gt (vector bool short, vector signed short);
int vec_all_gt (vector signed short, vector bool short);
int vec_all_gt (vector signed short, vector signed short);
int vec_all_gt (vector bool int, vector unsigned int);
int vec_all_gt (vector unsigned int, vector bool int);
int vec_all_gt (vector unsigned int, vector unsigned int);
int vec_all_gt (vector bool int, vector signed int);
int vec_all_gt (vector signed int, vector bool int);
int vec_all_gt (vector signed int, vector signed int);
int vec_all_gt (vector float, vector float);
int vec_all_in (vector float, vector float);
int vec_all_le (vector bool char, vector unsigned char);
int vec_all_le (vector unsigned char, vector bool char);
int vec_all_le (vector unsigned char, vector unsigned char);
int vec_all_le (vector bool char, vector signed char);
int vec_all_le (vector signed char, vector bool char);
int vec_all_le (vector signed char, vector signed char);
int vec_all_le (vector bool short, vector unsigned short);
int vec_all_le (vector unsigned short, vector bool short);
int vec_all_le (vector unsigned short, vector unsigned short);
int vec_all_le (vector bool short, vector signed short);
int vec_all_le (vector signed short, vector bool short);
int vec_all_le (vector signed short, vector signed short);
int vec_all_le (vector bool int, vector unsigned int);
int vec_all_le (vector unsigned int, vector bool int);
int vec_all_le (vector unsigned int, vector unsigned int);
int vec_all_le (vector bool int, vector signed int);
int vec_all_le (vector signed int, vector bool int);
int vec_all_le (vector signed int, vector signed int);
int vec_all_le (vector float, vector float);
int vec_all_lt (vector bool char, vector unsigned char);
int vec_all_lt (vector unsigned char, vector bool char);
int vec_all_lt (vector unsigned char, vector unsigned char);
int vec_all_lt (vector bool char, vector signed char);
int vec_all_lt (vector signed char, vector bool char);
int vec_all_lt (vector signed char, vector signed char);
int vec_all_lt (vector bool short, vector unsigned short);
int vec_all_lt (vector unsigned short, vector bool short);
int vec_all_lt (vector unsigned short, vector unsigned short);
int vec_all_lt (vector bool short, vector signed short);
int vec_all_lt (vector signed short, vector bool short);
int vec_all_lt (vector signed short, vector signed short);
int vec_all_lt (vector bool int, vector unsigned int);
int vec_all_lt (vector unsigned int, vector bool int);
int vec_all_lt (vector unsigned int, vector unsigned int);
int vec_all_lt (vector bool int, vector signed int);
int vec_all_lt (vector signed int, vector bool int);
int vec_all_lt (vector signed int, vector signed int);
int vec_all_lt (vector float, vector float);
int vec_all_nan (vector float);
int vec_all_ne (vector signed char, vector bool char);
int vec_all_ne (vector signed char, vector signed char);
int vec_all_ne (vector unsigned char, vector bool char);
int vec_all_ne (vector unsigned char, vector unsigned char);
int vec_all_ne (vector bool char, vector bool char);
int vec_all_ne (vector bool char, vector unsigned char);
int vec_all_ne (vector bool char, vector signed char);
int vec_all_ne (vector signed short, vector bool short);
int vec_all_ne (vector signed short, vector signed short);
int vec_all_ne (vector unsigned short, vector bool short);
int vec_all_ne (vector unsigned short, vector unsigned short);
int vec_all_ne (vector bool short, vector bool short);
int vec_all_ne (vector bool short, vector unsigned short);
int vec_all_ne (vector bool short, vector signed short);
int vec_all_ne (vector pixel, vector pixel);
int vec_all_ne (vector signed int, vector bool int);
int vec_all_ne (vector signed int, vector signed int);
int vec_all_ne (vector unsigned int, vector bool int);
int vec_all_ne (vector unsigned int, vector unsigned int);
int vec_all_ne (vector bool int, vector bool int);
int vec_all_ne (vector bool int, vector unsigned int);
int vec_all_ne (vector bool int, vector signed int);
int vec_all_ne (vector float, vector float);
int vec_all_nge (vector float, vector float);
int vec_all_ngt (vector float, vector float);
int vec_all_nle (vector float, vector float);
int vec_all_nlt (vector float, vector float);
int vec_all_numeric (vector float);
int vec_any_eq (vector signed char, vector bool char);
int vec_any_eq (vector signed char, vector signed char);
int vec_any_eq (vector unsigned char, vector bool char);
int vec_any_eq (vector unsigned char, vector unsigned char);
int vec_any_eq (vector bool char, vector bool char);
int vec_any_eq (vector bool char, vector unsigned char);
int vec_any_eq (vector bool char, vector signed char);
int vec_any_eq (vector signed short, vector bool short);
int vec_any_eq (vector signed short, vector signed short);
int vec_any_eq (vector unsigned short, vector bool short);
int vec_any_eq (vector unsigned short, vector unsigned short);
int vec_any_eq (vector bool short, vector bool short);
int vec_any_eq (vector bool short, vector unsigned short);
int vec_any_eq (vector bool short, vector signed short);
int vec_any_eq (vector pixel, vector pixel);
int vec_any_eq (vector signed int, vector bool int);
int vec_any_eq (vector signed int, vector signed int);
int vec_any_eq (vector unsigned int, vector bool int);
int vec_any_eq (vector unsigned int, vector unsigned int);
int vec_any_eq (vector bool int, vector bool int);
int vec_any_eq (vector bool int, vector unsigned int);
int vec_any_eq (vector bool int, vector signed int);
int vec_any_eq (vector float, vector float);
int vec_any_ge (vector signed char, vector bool char);
int vec_any_ge (vector unsigned char, vector bool char);
int vec_any_ge (vector unsigned char, vector unsigned char);
int vec_any_ge (vector signed char, vector signed char);
int vec_any_ge (vector bool char, vector unsigned char);
int vec_any_ge (vector bool char, vector signed char);
int vec_any_ge (vector unsigned short, vector bool short);
int vec_any_ge (vector unsigned short, vector unsigned short);
int vec_any_ge (vector signed short, vector signed short);
int vec_any_ge (vector signed short, vector bool short);
int vec_any_ge (vector bool short, vector unsigned short);
int vec_any_ge (vector bool short, vector signed short);
int vec_any_ge (vector signed int, vector bool int);
int vec_any_ge (vector unsigned int, vector bool int);
int vec_any_ge (vector unsigned int, vector unsigned int);
int vec_any_ge (vector signed int, vector signed int);
int vec_any_ge (vector bool int, vector unsigned int);
int vec_any_ge (vector bool int, vector signed int);
int vec_any_ge (vector float, vector float);
int vec_any_gt (vector bool char, vector unsigned char);
int vec_any_gt (vector unsigned char, vector bool char);
int vec_any_gt (vector unsigned char, vector unsigned char);
int vec_any_gt (vector bool char, vector signed char);
int vec_any_gt (vector signed char, vector bool char);
int vec_any_gt (vector signed char, vector signed char);
int vec_any_gt (vector bool short, vector unsigned short);
int vec_any_gt (vector unsigned short, vector bool short);
int vec_any_gt (vector unsigned short, vector unsigned short);
int vec_any_gt (vector bool short, vector signed short);
int vec_any_gt (vector signed short, vector bool short);
int vec_any_gt (vector signed short, vector signed short);
int vec_any_gt (vector bool int, vector unsigned int);
int vec_any_gt (vector unsigned int, vector bool int);
int vec_any_gt (vector unsigned int, vector unsigned int);
int vec_any_gt (vector bool int, vector signed int);
int vec_any_gt (vector signed int, vector bool int);
int vec_any_gt (vector signed int, vector signed int);
int vec_any_gt (vector float, vector float);
int vec_any_le (vector bool char, vector unsigned char);
int vec_any_le (vector unsigned char, vector bool char);
int vec_any_le (vector unsigned char, vector unsigned char);
int vec_any_le (vector bool char, vector signed char);
int vec_any_le (vector signed char, vector bool char);
int vec_any_le (vector signed char, vector signed char);
int vec_any_le (vector bool short, vector unsigned short);
int vec_any_le (vector unsigned short, vector bool short);
int vec_any_le (vector unsigned short, vector unsigned short);
int vec_any_le (vector bool short, vector signed short);
int vec_any_le (vector signed short, vector bool short);
int vec_any_le (vector signed short, vector signed short);
int vec_any_le (vector bool int, vector unsigned int);
int vec_any_le (vector unsigned int, vector bool int);
int vec_any_le (vector unsigned int, vector unsigned int);
int vec_any_le (vector bool int, vector signed int);
int vec_any_le (vector signed int, vector bool int);
int vec_any_le (vector signed int, vector signed int);
int vec_any_le (vector float, vector float);
int vec_any_lt (vector bool char, vector unsigned char);
int vec_any_lt (vector unsigned char, vector bool char);
int vec_any_lt (vector unsigned char, vector unsigned char);
int vec_any_lt (vector bool char, vector signed char);
int vec_any_lt (vector signed char, vector bool char);
int vec_any_lt (vector signed char, vector signed char);
int vec_any_lt (vector bool short, vector unsigned short);
int vec_any_lt (vector unsigned short, vector bool short);
int vec_any_lt (vector unsigned short, vector unsigned short);
int vec_any_lt (vector bool short, vector signed short);
int vec_any_lt (vector signed short, vector bool short);
int vec_any_lt (vector signed short, vector signed short);
int vec_any_lt (vector bool int, vector unsigned int);
int vec_any_lt (vector unsigned int, vector bool int);
int vec_any_lt (vector unsigned int, vector unsigned int);
int vec_any_lt (vector bool int, vector signed int);
int vec_any_lt (vector signed int, vector bool int);
int vec_any_lt (vector signed int, vector signed int);
int vec_any_lt (vector float, vector float);
int vec_any_nan (vector float);
int vec_any_ne (vector signed char, vector bool char);
int vec_any_ne (vector signed char, vector signed char);
int vec_any_ne (vector unsigned char, vector bool char);
int vec_any_ne (vector unsigned char, vector unsigned char);
int vec_any_ne (vector bool char, vector bool char);
int vec_any_ne (vector bool char, vector unsigned char);
int vec_any_ne (vector bool char, vector signed char);
int vec_any_ne (vector signed short, vector bool short);
int vec_any_ne (vector signed short, vector signed short);
int vec_any_ne (vector unsigned short, vector bool short);
int vec_any_ne (vector unsigned short, vector unsigned short);
int vec_any_ne (vector bool short, vector bool short);
int vec_any_ne (vector bool short, vector unsigned short);
int vec_any_ne (vector bool short, vector signed short);
int vec_any_ne (vector pixel, vector pixel);
int vec_any_ne (vector signed int, vector bool int);
int vec_any_ne (vector signed int, vector signed int);
int vec_any_ne (vector unsigned int, vector bool int);
int vec_any_ne (vector unsigned int, vector unsigned int);
int vec_any_ne (vector bool int, vector bool int);
int vec_any_ne (vector bool int, vector unsigned int);
int vec_any_ne (vector bool int, vector signed int);
int vec_any_ne (vector float, vector float);
int vec_any_nge (vector float, vector float);
int vec_any_ngt (vector float, vector float);
int vec_any_nle (vector float, vector float);
int vec_any_nlt (vector float, vector float);
int vec_any_numeric (vector float);
int vec_any_out (vector float, vector float);
File: gcc.info, Node: SPARC VIS Built-in Functions, Prev: PowerPC AltiVec Built-in Functions, Up: Target Builtins
5.48.9 SPARC VIS Built-in Functions
-----------------------------------
GCC supports SIMD operations on the SPARC using both the generic vector
extensions (*note Vector Extensions::) as well as built-in functions for
the SPARC Visual Instruction Set (VIS). When you use the `-mvis'
switch, the VIS extension is exposed as the following built-in
functions:
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef short v2hi __attribute__ ((vector_size (4)));
typedef char v8qi __attribute__ ((vector_size (8)));
typedef char v4qi __attribute__ ((vector_size (4)));
void * __builtin_vis_alignaddr (void *, long);
int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
v2si __builtin_vis_faligndatav2si (v2si, v2si);
v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);
v4hi __builtin_vis_fexpand (v4qi);
v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
v4hi __builtin_vis_fmul8x16au (v4qi, v4hi);
v4hi __builtin_vis_fmul8x16al (v4qi, v4hi);
v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);
v4qi __builtin_vis_fpack16 (v4hi);
v8qi __builtin_vis_fpack32 (v2si, v2si);
v2hi __builtin_vis_fpackfix (v2si);
v8qi __builtin_vis_fpmerge (v4qi, v4qi);
int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);
File: gcc.info, Node: Target Format Checks, Next: Pragmas, Prev: Target Builtins, Up: C Extensions
5.49 Format Checks Specific to Particular Target Machines
=========================================================
For some target machines, GCC supports additional options to the format
attribute (*note Declaring Attributes of Functions: Function
Attributes.).
* Menu:
* Solaris Format Checks::
File: gcc.info, Node: Solaris Format Checks, Up: Target Format Checks
5.49.1 Solaris Format Checks
----------------------------
Solaris targets support the `cmn_err' (or `__cmn_err__') format check.
`cmn_err' accepts a subset of the standard `printf' conversions, and
the two-argument `%b' conversion for displaying bit-fields. See the
Solaris man page for `cmn_err' for more information.
File: gcc.info, Node: Pragmas, Next: Unnamed Fields, Prev: Target Format Checks, Up: C Extensions
5.50 Pragmas Accepted by GCC
============================
GCC supports several types of pragmas, primarily in order to compile
code originally written for other compilers. Note that in general we
do not recommend the use of pragmas; *Note Function Attributes::, for
further explanation.
* Menu:
* ARM Pragmas::
* M32C Pragmas::
* RS/6000 and PowerPC Pragmas::
* Darwin Pragmas::
* Solaris Pragmas::
* Symbol-Renaming Pragmas::
* Structure-Packing Pragmas::
* Weak Pragmas::
* Diagnostic Pragmas::
* Visibility Pragmas::
File: gcc.info, Node: ARM Pragmas, Next: M32C Pragmas, Up: Pragmas
5.50.1 ARM Pragmas
------------------
The ARM target defines pragmas for controlling the default addition of
`long_call' and `short_call' attributes to functions. *Note Function
Attributes::, for information about the effects of these attributes.
`long_calls'
Set all subsequent functions to have the `long_call' attribute.
`no_long_calls'
Set all subsequent functions to have the `short_call' attribute.
`long_calls_off'
Do not affect the `long_call' or `short_call' attributes of
subsequent functions.
File: gcc.info, Node: M32C Pragmas, Next: RS/6000 and PowerPC Pragmas, Prev: ARM Pragmas, Up: Pragmas
5.50.2 M32C Pragmas
-------------------
`memregs NUMBER'
Overrides the command line option `-memregs=' for the current
file. Use with care! This pragma must be before any function in
the file, and mixing different memregs values in different objects
may make them incompatible. This pragma is useful when a
performance-critical function uses a memreg for temporary values,
as it may allow you to reduce the number of memregs used.
File: gcc.info, Node: RS/6000 and PowerPC Pragmas, Next: Darwin Pragmas, Prev: M32C Pragmas, Up: Pragmas
5.50.3 RS/6000 and PowerPC Pragmas
----------------------------------
The RS/6000 and PowerPC targets define one pragma for controlling
whether or not the `longcall' attribute is added to function
declarations by default. This pragma overrides the `-mlongcall'
option, but not the `longcall' and `shortcall' attributes. *Note
RS/6000 and PowerPC Options::, for more information about when long
calls are and are not necessary.
`longcall (1)'
Apply the `longcall' attribute to all subsequent function
declarations.
`longcall (0)'
Do not apply the `longcall' attribute to subsequent function
declarations.
File: gcc.info, Node: Darwin Pragmas, Next: Solaris Pragmas, Prev: RS/6000 and PowerPC Pragmas, Up: Pragmas
5.50.4 Darwin Pragmas
---------------------
The following pragmas are available for all architectures running the
Darwin operating system. These are useful for compatibility with other
Mac OS compilers.
`mark TOKENS...'
This pragma is accepted, but has no effect.
`options align=ALIGNMENT'
This pragma sets the alignment of fields in structures. The
values of ALIGNMENT may be `mac68k', to emulate m68k alignment, or
`power', to emulate PowerPC alignment. Uses of this pragma nest
properly; to restore the previous setting, use `reset' for the
ALIGNMENT.
`segment TOKENS...'
This pragma is accepted, but has no effect.
`unused (VAR [, VAR]...)'
This pragma declares variables to be possibly unused. GCC will not
produce warnings for the listed variables. The effect is similar
to that of the `unused' attribute, except that this pragma may
appear anywhere within the variables' scopes.
File: gcc.info, Node: Solaris Pragmas, Next: Symbol-Renaming Pragmas, Prev: Darwin Pragmas, Up: Pragmas
5.50.5 Solaris Pragmas
----------------------
The Solaris target supports `#pragma redefine_extname' (*note
Symbol-Renaming Pragmas::). It also supports additional `#pragma'
directives for compatibility with the system compiler.
`align ALIGNMENT (VARIABLE [, VARIABLE]...)'
Increase the minimum alignment of each VARIABLE to ALIGNMENT.
This is the same as GCC's `aligned' attribute *note Variable
Attributes::). Macro expansion occurs on the arguments to this
pragma when compiling C and Objective-C. It does not currently
occur when compiling C++, but this is a bug which may be fixed in
a future release.
`fini (FUNCTION [, FUNCTION]...)'
This pragma causes each listed FUNCTION to be called after main,
or during shared module unloading, by adding a call to the `.fini'
section.
`init (FUNCTION [, FUNCTION]...)'
This pragma causes each listed FUNCTION to be called during
initialization (before `main') or during shared module loading, by
adding a call to the `.init' section.
File: gcc.info, Node: Symbol-Renaming Pragmas, Next: Structure-Packing Pragmas, Prev: Solaris Pragmas, Up: Pragmas
5.50.6 Symbol-Renaming Pragmas
------------------------------
For compatibility with the Solaris and Tru64 UNIX system headers, GCC
supports two `#pragma' directives which change the name used in
assembly for a given declaration. These pragmas are only available on
platforms whose system headers need them. To get this effect on all
platforms supported by GCC, use the asm labels extension (*note Asm
Labels::).
`redefine_extname OLDNAME NEWNAME'
This pragma gives the C function OLDNAME the assembly symbol
NEWNAME. The preprocessor macro `__PRAGMA_REDEFINE_EXTNAME' will
be defined if this pragma is available (currently only on Solaris).
`extern_prefix STRING'
This pragma causes all subsequent external function and variable
declarations to have STRING prepended to their assembly symbols.
This effect may be terminated with another `extern_prefix' pragma
whose argument is an empty string. The preprocessor macro
`__PRAGMA_EXTERN_PREFIX' will be defined if this pragma is
available (currently only on Tru64 UNIX).
These pragmas and the asm labels extension interact in a complicated
manner. Here are some corner cases you may want to be aware of.
1. Both pragmas silently apply only to declarations with external
linkage. Asm labels do not have this restriction.
2. In C++, both pragmas silently apply only to declarations with "C"
linkage. Again, asm labels do not have this restriction.
3. If any of the three ways of changing the assembly name of a
declaration is applied to a declaration whose assembly name has
already been determined (either by a previous use of one of these
features, or because the compiler needed the assembly name in
order to generate code), and the new name is different, a warning
issues and the name does not change.
4. The OLDNAME used by `#pragma redefine_extname' is always the
C-language name.
5. If `#pragma extern_prefix' is in effect, and a declaration occurs
with an asm label attached, the prefix is silently ignored for
that declaration.
6. If `#pragma extern_prefix' and `#pragma redefine_extname' apply to
the same declaration, whichever triggered first wins, and a
warning issues if they contradict each other. (We would like to
have `#pragma redefine_extname' always win, for consistency with
asm labels, but if `#pragma extern_prefix' triggers first we have
no way of knowing that that happened.)
File: gcc.info, Node: Structure-Packing Pragmas, Next: Weak Pragmas, Prev: Symbol-Renaming Pragmas, Up: Pragmas
5.50.7 Structure-Packing Pragmas
--------------------------------
For compatibility with Win32, GCC supports a set of `#pragma'
directives which change the maximum alignment of members of structures
(other than zero-width bitfields), unions, and classes subsequently
defined. The N value below always is required to be a small power of
two and specifies the new alignment in bytes.
1. `#pragma pack(N)' simply sets the new alignment.
2. `#pragma pack()' sets the alignment to the one that was in effect
when compilation started (see also command line option
`-fpack-struct[=<n>]' *note Code Gen Options::).
3. `#pragma pack(push[,N])' pushes the current alignment setting on
an internal stack and then optionally sets the new alignment.
4. `#pragma pack(pop)' restores the alignment setting to the one
saved at the top of the internal stack (and removes that stack
entry). Note that `#pragma pack([N])' does not influence this
internal stack; thus it is possible to have `#pragma pack(push)'
followed by multiple `#pragma pack(N)' instances and finalized by
a single `#pragma pack(pop)'.
Some targets, e.g. i386 and powerpc, support the `ms_struct' `#pragma'
which lays out a structure as the documented `__attribute__
((ms_struct))'.
1. `#pragma ms_struct on' turns on the layout for structures declared.
2. `#pragma ms_struct off' turns off the layout for structures
declared.
3. `#pragma ms_struct reset' goes back to the default layout.
File: gcc.info, Node: Weak Pragmas, Next: Diagnostic Pragmas, Prev: Structure-Packing Pragmas, Up: Pragmas
5.50.8 Weak Pragmas
-------------------
For compatibility with SVR4, GCC supports a set of `#pragma' directives
for declaring symbols to be weak, and defining weak aliases.
`#pragma weak SYMBOL'
This pragma declares SYMBOL to be weak, as if the declaration had
the attribute of the same name. The pragma may appear before or
after the declaration of SYMBOL, but must appear before either its
first use or its definition. It is not an error for SYMBOL to
never be defined at all.
`#pragma weak SYMBOL1 = SYMBOL2'
This pragma declares SYMBOL1 to be a weak alias of SYMBOL2. It is
an error if SYMBOL2 is not defined in the current translation unit.
File: gcc.info, Node: Diagnostic Pragmas, Next: Visibility Pragmas, Prev: Weak Pragmas, Up: Pragmas
5.50.9 Diagnostic Pragmas
-------------------------
GCC allows the user to selectively enable or disable certain types of
diagnostics, and change the kind of the diagnostic. For example, a
project's policy might require that all sources compile with `-Werror'
but certain files might have exceptions allowing specific types of
warnings. Or, a project might selectively enable diagnostics and treat
them as errors depending on which preprocessor macros are defined.
`#pragma GCC diagnostic KIND OPTION'
Modifies the disposition of a diagnostic. Note that not all
diagnostics are modifiable; at the moment only warnings (normally
controlled by `-W...') can be controlled, and not all of them.
Use `-fdiagnostics-show-option' to determine which diagnostics are
controllable and which option controls them.
KIND is `error' to treat this diagnostic as an error, `warning' to
treat it like a warning (even if `-Werror' is in effect), or
`ignored' if the diagnostic is to be ignored. OPTION is a double
quoted string which matches the command line option.
#pragma GCC diagnostic warning "-Wformat"
#pragma GCC diagnostic error "-Wformat"
#pragma GCC diagnostic ignored "-Wformat"
Note that these pragmas override any command line options. Also,
while it is syntactically valid to put these pragmas anywhere in
your sources, the only supported location for them is before any
data or functions are defined. Doing otherwise may result in
unpredictable results depending on how the optimizer manages your
sources. If the same option is listed multiple times, the last
one specified is the one that is in effect. This pragma is not
intended to be a general purpose replacement for command line
options, but for implementing strict control over project policies.
File: gcc.info, Node: Visibility Pragmas, Prev: Diagnostic Pragmas, Up: Pragmas
5.50.10 Visibility Pragmas
--------------------------
`#pragma GCC visibility push(VISIBILITY)'
`#pragma GCC visibility pop'
This pragma allows the user to set the visibility for multiple
declarations without having to give each a visibility attribute
*Note Function Attributes::, for more information about visibility
and the attribute syntax.
In C++, `#pragma GCC visibility' affects only namespace-scope
declarations. Class members and template specializations are not
affected; if you want to override the visibility for a particular
member or instantiation, you must use an attribute.
File: gcc.info, Node: Unnamed Fields, Next: Thread-Local, Prev: Pragmas, Up: C Extensions
5.51 Unnamed struct/union fields within structs/unions
======================================================
For compatibility with other compilers, GCC allows you to define a
structure or union that contains, as fields, structures and unions
without names. For example:
struct {
int a;
union {
int b;
float c;
};
int d;
} foo;
In this example, the user would be able to access members of the
unnamed union with code like `foo.b'. Note that only unnamed structs
and unions are allowed, you may not have, for example, an unnamed `int'.
You must never create such structures that cause ambiguous field
definitions. For example, this structure:
struct {
int a;
struct {
int a;
};
} foo;
It is ambiguous which `a' is being referred to with `foo.a'. Such
constructs are not supported and must be avoided. In the future, such
constructs may be detected and treated as compilation errors.
Unless `-fms-extensions' is used, the unnamed field must be a
structure or union definition without a tag (for example, `struct { int
a; };'). If `-fms-extensions' is used, the field may also be a
definition with a tag such as `struct foo { int a; };', a reference to
a previously defined structure or union such as `struct foo;', or a
reference to a `typedef' name for a previously defined structure or
union type.
File: gcc.info, Node: Thread-Local, Prev: Unnamed Fields, Up: C Extensions
5.52 Thread-Local Storage
=========================
Thread-local storage (TLS) is a mechanism by which variables are
allocated such that there is one instance of the variable per extant
thread. The run-time model GCC uses to implement this originates in
the IA-64 processor-specific ABI, but has since been migrated to other
processors as well. It requires significant support from the linker
(`ld'), dynamic linker (`ld.so'), and system libraries (`libc.so' and
`libpthread.so'), so it is not available everywhere.
At the user level, the extension is visible with a new storage class
keyword: `__thread'. For example:
__thread int i;
extern __thread struct state s;
static __thread char *p;
The `__thread' specifier may be used alone, with the `extern' or
`static' specifiers, but with no other storage class specifier. When
used with `extern' or `static', `__thread' must appear immediately
after the other storage class specifier.
The `__thread' specifier may be applied to any global, file-scoped
static, function-scoped static, or static data member of a class. It
may not be applied to block-scoped automatic or non-static data member.
When the address-of operator is applied to a thread-local variable, it
is evaluated at run-time and returns the address of the current thread's
instance of that variable. An address so obtained may be used by any
thread. When a thread terminates, any pointers to thread-local
variables in that thread become invalid.
No static initialization may refer to the address of a thread-local
variable.
In C++, if an initializer is present for a thread-local variable, it
must be a CONSTANT-EXPRESSION, as defined in 5.19.2 of the ANSI/ISO C++
standard.
See ELF Handling For Thread-Local Storage
(http://people.redhat.com/drepper/tls.pdf) for a detailed explanation of
the four thread-local storage addressing models, and how the run-time
is expected to function.
* Menu:
* C99 Thread-Local Edits::
* C++98 Thread-Local Edits::
File: gcc.info, Node: C99 Thread-Local Edits, Next: C++98 Thread-Local Edits, Up: Thread-Local
5.52.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage
-------------------------------------------------------
The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that
document the exact semantics of the language extension.
* `5.1.2 Execution environments'
Add new text after paragraph 1
Within either execution environment, a "thread" is a flow of
control within a program. It is implementation defined
whether or not there may be more than one thread associated
with a program. It is implementation defined how threads
beyond the first are created, the name and type of the
function called at thread startup, and how threads may be
terminated. However, objects with thread storage duration
shall be initialized before thread startup.
* `6.2.4 Storage durations of objects'
Add new text before paragraph 3
An object whose identifier is declared with the storage-class
specifier `__thread' has "thread storage duration". Its
lifetime is the entire execution of the thread, and its
stored value is initialized only once, prior to thread
startup.
* `6.4.1 Keywords'
Add `__thread'.
* `6.7.1 Storage-class specifiers'
Add `__thread' to the list of storage class specifiers in
paragraph 1.
Change paragraph 2 to
With the exception of `__thread', at most one storage-class
specifier may be given [...]. The `__thread' specifier may
be used alone, or immediately following `extern' or `static'.
Add new text after paragraph 6
The declaration of an identifier for a variable that has
block scope that specifies `__thread' shall also specify
either `extern' or `static'.
The `__thread' specifier shall be used only with variables.
File: gcc.info, Node: C++98 Thread-Local Edits, Prev: C99 Thread-Local Edits, Up: Thread-Local
5.52.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage
--------------------------------------------------------
The following are a set of changes to ISO/IEC 14882:1998 (aka C++98)
that document the exact semantics of the language extension.
* [intro.execution]
New text after paragraph 4
A "thread" is a flow of control within the abstract machine.
It is implementation defined whether or not there may be more
than one thread.
New text after paragraph 7
It is unspecified whether additional action must be taken to
ensure when and whether side effects are visible to other
threads.
* [lex.key]
Add `__thread'.
* [basic.start.main]
Add after paragraph 5
The thread that begins execution at the `main' function is
called the "main thread". It is implementation defined how
functions beginning threads other than the main thread are
designated or typed. A function so designated, as well as
the `main' function, is called a "thread startup function".
It is implementation defined what happens if a thread startup
function returns. It is implementation defined what happens
to other threads when any thread calls `exit'.
* [basic.start.init]
Add after paragraph 4
The storage for an object of thread storage duration shall be
statically initialized before the first statement of the
thread startup function. An object of thread storage
duration shall not require dynamic initialization.
* [basic.start.term]
Add after paragraph 3
The type of an object with thread storage duration shall not
have a non-trivial destructor, nor shall it be an array type
whose elements (directly or indirectly) have non-trivial
destructors.
* [basic.stc]
Add "thread storage duration" to the list in paragraph 1.
Change paragraph 2
Thread, static, and automatic storage durations are
associated with objects introduced by declarations [...].
Add `__thread' to the list of specifiers in paragraph 3.
* [basic.stc.thread]
New section before [basic.stc.static]
The keyword `__thread' applied to a non-local object gives the
object thread storage duration.
A local variable or class data member declared both `static'
and `__thread' gives the variable or member thread storage
duration.
* [basic.stc.static]
Change paragraph 1
All objects which have neither thread storage duration,
dynamic storage duration nor are local [...].
* [dcl.stc]
Add `__thread' to the list in paragraph 1.
Change paragraph 1
With the exception of `__thread', at most one
STORAGE-CLASS-SPECIFIER shall appear in a given
DECL-SPECIFIER-SEQ. The `__thread' specifier may be used
alone, or immediately following the `extern' or `static'
specifiers. [...]
Add after paragraph 5
The `__thread' specifier can be applied only to the names of
objects and to anonymous unions.
* [class.mem]
Add after paragraph 6
Non-`static' members shall not be `__thread'.
File: gcc.info, Node: C++ Extensions, Next: Objective-C, Prev: C Extensions, Up: Top
6 Extensions to the C++ Language
********************************
The GNU compiler provides these extensions to the C++ language (and you
can also use most of the C language extensions in your C++ programs).
If you want to write code that checks whether these features are
available, you can test for the GNU compiler the same way as for C
programs: check for a predefined macro `__GNUC__'. You can also use
`__GNUG__' to test specifically for GNU C++ (*note Predefined Macros:
(cpp)Common Predefined Macros.).
* Menu:
* Volatiles:: What constitutes an access to a volatile object.
* Restricted Pointers:: C99 restricted pointers and references.
* Vague Linkage:: Where G++ puts inlines, vtables and such.
* C++ Interface:: You can use a single C++ header file for both
declarations and definitions.
* Template Instantiation:: Methods for ensuring that exactly one copy of
each needed template instantiation is emitted.
* Bound member functions:: You can extract a function pointer to the
method denoted by a `->*' or `.*' expression.
* C++ Attributes:: Variable, function, and type attributes for C++ only.
* Namespace Association:: Strong using-directives for namespace association.
* Java Exceptions:: Tweaking exception handling to work with Java.
* Deprecated Features:: Things will disappear from g++.
* Backwards Compatibility:: Compatibilities with earlier definitions of C++.
File: gcc.info, Node: Volatiles, Next: Restricted Pointers, Up: C++ Extensions
6.1 When is a Volatile Object Accessed?
=======================================
Both the C and C++ standard have the concept of volatile objects. These
are normally accessed by pointers and used for accessing hardware. The
standards encourage compilers to refrain from optimizations concerning
accesses to volatile objects. The C standard leaves it implementation
defined as to what constitutes a volatile access. The C++ standard
omits to specify this, except to say that C++ should behave in a
similar manner to C with respect to volatiles, where possible. The
minimum either standard specifies is that at a sequence point all
previous accesses to volatile objects have stabilized and no subsequent
accesses have occurred. Thus an implementation is free to reorder and
combine volatile accesses which occur between sequence points, but
cannot do so for accesses across a sequence point. The use of
volatiles does not allow you to violate the restriction on updating
objects multiple times within a sequence point.
*Note Volatile qualifier and the C compiler: Qualifiers implementation.
The behavior differs slightly between C and C++ in the non-obvious
cases:
volatile int *src = SOMEVALUE;
*src;
With C, such expressions are rvalues, and GCC interprets this either
as a read of the volatile object being pointed to or only as request to
evaluate the side-effects. The C++ standard specifies that such
expressions do not undergo lvalue to rvalue conversion, and that the
type of the dereferenced object may be incomplete. The C++ standard
does not specify explicitly that it is this lvalue to rvalue conversion
which may be responsible for causing an access. However, there is
reason to believe that it is, because otherwise certain simple
expressions become undefined. However, because it would surprise most
programmers, G++ treats dereferencing a pointer to volatile object of
complete type when the value is unused as GCC would do for an
equivalent type in C. When the object has incomplete type, G++ issues
a warning; if you wish to force an error, you must force a conversion
to rvalue with, for instance, a static cast.
When using a reference to volatile, G++ does not treat equivalent
expressions as accesses to volatiles, but instead issues a warning that
no volatile is accessed. The rationale for this is that otherwise it
becomes difficult to determine where volatile access occur, and not
possible to ignore the return value from functions returning volatile
references. Again, if you wish to force a read, cast the reference to
an rvalue.
File: gcc.info, Node: Restricted Pointers, Next: Vague Linkage, Prev: Volatiles, Up: C++ Extensions
6.2 Restricting Pointer Aliasing
================================
As with the C front end, G++ understands the C99 feature of restricted
pointers, specified with the `__restrict__', or `__restrict' type
qualifier. Because you cannot compile C++ by specifying the `-std=c99'
language flag, `restrict' is not a keyword in C++.
In addition to allowing restricted pointers, you can specify restricted
references, which indicate that the reference is not aliased in the
local context.
void fn (int *__restrict__ rptr, int &__restrict__ rref)
{
/* ... */
}
In the body of `fn', RPTR points to an unaliased integer and RREF
refers to a (different) unaliased integer.
You may also specify whether a member function's THIS pointer is
unaliased by using `__restrict__' as a member function qualifier.
void T::fn () __restrict__
{
/* ... */
}
Within the body of `T::fn', THIS will have the effective definition `T
*__restrict__ const this'. Notice that the interpretation of a
`__restrict__' member function qualifier is different to that of
`const' or `volatile' qualifier, in that it is applied to the pointer
rather than the object. This is consistent with other compilers which
implement restricted pointers.
As with all outermost parameter qualifiers, `__restrict__' is ignored
in function definition matching. This means you only need to specify
`__restrict__' in a function definition, rather than in a function
prototype as well.
File: gcc.info, Node: Vague Linkage, Next: C++ Interface, Prev: Restricted Pointers, Up: C++ Extensions
6.3 Vague Linkage
=================
There are several constructs in C++ which require space in the object
file but are not clearly tied to a single translation unit. We say that
these constructs have "vague linkage". Typically such constructs are
emitted wherever they are needed, though sometimes we can be more
clever.
Inline Functions
Inline functions are typically defined in a header file which can
be included in many different compilations. Hopefully they can
usually be inlined, but sometimes an out-of-line copy is
necessary, if the address of the function is taken or if inlining
fails. In general, we emit an out-of-line copy in all translation
units where one is needed. As an exception, we only emit inline
virtual functions with the vtable, since it will always require a
copy.
Local static variables and string constants used in an inline
function are also considered to have vague linkage, since they
must be shared between all inlined and out-of-line instances of
the function.
VTables
C++ virtual functions are implemented in most compilers using a
lookup table, known as a vtable. The vtable contains pointers to
the virtual functions provided by a class, and each object of the
class contains a pointer to its vtable (or vtables, in some
multiple-inheritance situations). If the class declares any
non-inline, non-pure virtual functions, the first one is chosen as
the "key method" for the class, and the vtable is only emitted in
the translation unit where the key method is defined.
_Note:_ If the chosen key method is later defined as inline, the
vtable will still be emitted in every translation unit which
defines it. Make sure that any inline virtuals are declared
inline in the class body, even if they are not defined there.
type_info objects
C++ requires information about types to be written out in order to
implement `dynamic_cast', `typeid' and exception handling. For
polymorphic classes (classes with virtual functions), the type_info
object is written out along with the vtable so that `dynamic_cast'
can determine the dynamic type of a class object at runtime. For
all other types, we write out the type_info object when it is
used: when applying `typeid' to an expression, throwing an object,
or referring to a type in a catch clause or exception
specification.
Template Instantiations
Most everything in this section also applies to template
instantiations, but there are other options as well. *Note
Where's the Template?: Template Instantiation.
When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of
these constructs will be discarded at link time. This is known as
COMDAT support.
On targets that don't support COMDAT, but do support weak symbols, GCC
will use them. This way one copy will override all the others, but the
unused copies will still take up space in the executable.
For targets which do not support either COMDAT or weak symbols, most
entities with vague linkage will be emitted as local symbols to avoid
duplicate definition errors from the linker. This will not happen for
local statics in inlines, however, as having multiple copies will
almost certainly break things.
*Note Declarations and Definitions in One Header: C++ Interface, for
another way to control placement of these constructs.
File: gcc.info, Node: C++ Interface, Next: Template Instantiation, Prev: Vague Linkage, Up: C++ Extensions
6.4 #pragma interface and implementation
========================================
`#pragma interface' and `#pragma implementation' provide the user with
a way of explicitly directing the compiler to emit entities with vague
linkage (and debugging information) in a particular translation unit.
_Note:_ As of GCC 2.7.2, these `#pragma's are not useful in most
cases, because of COMDAT support and the "key method" heuristic
mentioned in *Note Vague Linkage::. Using them can actually cause your
program to grow due to unnecessary out-of-line copies of inline
functions. Currently (3.4) the only benefit of these `#pragma's is
reduced duplication of debugging information, and that should be
addressed soon on DWARF 2 targets with the use of COMDAT groups.
`#pragma interface'
`#pragma interface "SUBDIR/OBJECTS.h"'
Use this directive in _header files_ that define object classes,
to save space in most of the object files that use those classes.
Normally, local copies of certain information (backup copies of
inline member functions, debugging information, and the internal
tables that implement virtual functions) must be kept in each
object file that includes class definitions. You can use this
pragma to avoid such duplication. When a header file containing
`#pragma interface' is included in a compilation, this auxiliary
information will not be generated (unless the main input source
file itself uses `#pragma implementation'). Instead, the object
files will contain references to be resolved at link time.
The second form of this directive is useful for the case where you
have multiple headers with the same name in different directories.
If you use this form, you must specify the same string to `#pragma
implementation'.
`#pragma implementation'
`#pragma implementation "OBJECTS.h"'
Use this pragma in a _main input file_, when you want full output
from included header files to be generated (and made globally
visible). The included header file, in turn, should use `#pragma
interface'. Backup copies of inline member functions, debugging
information, and the internal tables used to implement virtual
functions are all generated in implementation files.
If you use `#pragma implementation' with no argument, it applies to
an include file with the same basename(1) as your source file.
For example, in `allclass.cc', giving just `#pragma implementation'
by itself is equivalent to `#pragma implementation "allclass.h"'.
In versions of GNU C++ prior to 2.6.0 `allclass.h' was treated as
an implementation file whenever you would include it from
`allclass.cc' even if you never specified `#pragma
implementation'. This was deemed to be more trouble than it was
worth, however, and disabled.
Use the string argument if you want a single implementation file to
include code from multiple header files. (You must also use
`#include' to include the header file; `#pragma implementation'
only specifies how to use the file--it doesn't actually include
it.)
There is no way to split up the contents of a single header file
into multiple implementation files.
`#pragma implementation' and `#pragma interface' also have an effect
on function inlining.
If you define a class in a header file marked with `#pragma
interface', the effect on an inline function defined in that class is
similar to an explicit `extern' declaration--the compiler emits no code
at all to define an independent version of the function. Its
definition is used only for inlining with its callers.
Conversely, when you include the same header file in a main source file
that declares it as `#pragma implementation', the compiler emits code
for the function itself; this defines a version of the function that
can be found via pointers (or by callers compiled without inlining).
If all calls to the function can be inlined, you can avoid emitting the
function by compiling with `-fno-implement-inlines'. If any calls were
not inlined, you will get linker errors.
---------- Footnotes ----------
(1) A file's "basename" was the name stripped of all leading path
information and of trailing suffixes, such as `.h' or `.C' or `.cc'.
File: gcc.info, Node: Template Instantiation, Next: Bound member functions, Prev: C++ Interface, Up: C++ Extensions
6.5 Where's the Template?
=========================
C++ templates are the first language feature to require more
intelligence from the environment than one usually finds on a UNIX
system. Somehow the compiler and linker have to make sure that each
template instance occurs exactly once in the executable if it is needed,
and not at all otherwise. There are two basic approaches to this
problem, which are referred to as the Borland model and the Cfront
model.
Borland model
Borland C++ solved the template instantiation problem by adding
the code equivalent of common blocks to their linker; the compiler
emits template instances in each translation unit that uses them,
and the linker collapses them together. The advantage of this
model is that the linker only has to consider the object files
themselves; there is no external complexity to worry about. This
disadvantage is that compilation time is increased because the
template code is being compiled repeatedly. Code written for this
model tends to include definitions of all templates in the header
file, since they must be seen to be instantiated.
Cfront model
The AT&T C++ translator, Cfront, solved the template instantiation
problem by creating the notion of a template repository, an
automatically maintained place where template instances are
stored. A more modern version of the repository works as follows:
As individual object files are built, the compiler places any
template definitions and instantiations encountered in the
repository. At link time, the link wrapper adds in the objects in
the repository and compiles any needed instances that were not
previously emitted. The advantages of this model are more optimal
compilation speed and the ability to use the system linker; to
implement the Borland model a compiler vendor also needs to
replace the linker. The disadvantages are vastly increased
complexity, and thus potential for error; for some code this can be
just as transparent, but in practice it can been very difficult to
build multiple programs in one directory and one program in
multiple directories. Code written for this model tends to
separate definitions of non-inline member templates into a
separate file, which should be compiled separately.
When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the
Borland model. On other systems, G++ implements neither automatic
model.
A future version of G++ will support a hybrid model whereby the
compiler will emit any instantiations for which the template definition
is included in the compile, and store template definitions and
instantiation context information into the object file for the rest.
The link wrapper will extract that information as necessary and invoke
the compiler to produce the remaining instantiations. The linker will
then combine duplicate instantiations.
In the mean time, you have the following options for dealing with
template instantiations:
1. Compile your template-using code with `-frepo'. The compiler will
generate files with the extension `.rpo' listing all of the
template instantiations used in the corresponding object files
which could be instantiated there; the link wrapper, `collect2',
will then update the `.rpo' files to tell the compiler where to
place those instantiations and rebuild any affected object files.
The link-time overhead is negligible after the first pass, as the
compiler will continue to place the instantiations in the same
files.
This is your best option for application code written for the
Borland model, as it will just work. Code written for the Cfront
model will need to be modified so that the template definitions
are available at one or more points of instantiation; usually this
is as simple as adding `#include <tmethods.cc>' to the end of each
template header.
For library code, if you want the library to provide all of the
template instantiations it needs, just try to link all of its
object files together; the link will fail, but cause the
instantiations to be generated as a side effect. Be warned,
however, that this may cause conflicts if multiple libraries try
to provide the same instantiations. For greater control, use
explicit instantiation as described in the next option.
2. Compile your code with `-fno-implicit-templates' to disable the
implicit generation of template instances, and explicitly
instantiate all the ones you use. This approach requires more
knowledge of exactly which instances you need than do the others,
but it's less mysterious and allows greater control. You can
scatter the explicit instantiations throughout your program,
perhaps putting them in the translation units where the instances
are used or the translation units that define the templates
themselves; you can put all of the explicit instantiations you
need into one big file; or you can create small files like
#include "Foo.h"
#include "Foo.cc"
template class Foo<int>;
template ostream& operator <<
(ostream&, const Foo<int>&);
for each of the instances you need, and create a template
instantiation library from those.
If you are using Cfront-model code, you can probably get away with
not using `-fno-implicit-templates' when compiling files that don't
`#include' the member template definitions.
If you use one big file to do the instantiations, you may want to
compile it without `-fno-implicit-templates' so you get all of the
instances required by your explicit instantiations (but not by any
other files) without having to specify them as well.
G++ has extended the template instantiation syntax given in the ISO
standard to allow forward declaration of explicit instantiations
(with `extern'), instantiation of the compiler support data for a
template class (i.e. the vtable) without instantiating any of its
members (with `inline'), and instantiation of only the static data
members of a template class, without the support data or member
functions (with (`static'):
extern template int max (int, int);
inline template class Foo<int>;
static template class Foo<int>;
3. Do nothing. Pretend G++ does implement automatic instantiation
management. Code written for the Borland model will work fine, but
each translation unit will contain instances of each of the
templates it uses. In a large program, this can lead to an
unacceptable amount of code duplication.
File: gcc.info, Node: Bound member functions, Next: C++ Attributes, Prev: Template Instantiation, Up: C++ Extensions
6.6 Extracting the function pointer from a bound pointer to member function
===========================================================================
In C++, pointer to member functions (PMFs) are implemented using a wide
pointer of sorts to handle all the possible call mechanisms; the PMF
needs to store information about how to adjust the `this' pointer, and
if the function pointed to is virtual, where to find the vtable, and
where in the vtable to look for the member function. If you are using
PMFs in an inner loop, you should really reconsider that decision. If
that is not an option, you can extract the pointer to the function that
would be called for a given object/PMF pair and call it directly inside
the inner loop, to save a bit of time.
Note that you will still be paying the penalty for the call through a
function pointer; on most modern architectures, such a call defeats the
branch prediction features of the CPU. This is also true of normal
virtual function calls.
The syntax for this extension is
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);
fptr p = (fptr)(a.*fp);
For PMF constants (i.e. expressions of the form `&Klasse::Member'), no
object is needed to obtain the address of the function. They can be
converted to function pointers directly:
fptr p1 = (fptr)(&A::foo);
You must specify `-Wno-pmf-conversions' to use this extension.
File: gcc.info, Node: C++ Attributes, Next: Namespace Association, Prev: Bound member functions, Up: C++ Extensions
6.7 C++-Specific Variable, Function, and Type Attributes
========================================================
Some attributes only make sense for C++ programs.
`init_priority (PRIORITY)'
In Standard C++, objects defined at namespace scope are guaranteed
to be initialized in an order in strict accordance with that of
their definitions _in a given translation unit_. No guarantee is
made for initializations across translation units. However, GNU
C++ allows users to control the order of initialization of objects
defined at namespace scope with the `init_priority' attribute by
specifying a relative PRIORITY, a constant integral expression
currently bounded between 101 and 65535 inclusive. Lower numbers
indicate a higher priority.
In the following example, `A' would normally be created before
`B', but the `init_priority' attribute has reversed that order:
Some_Class A __attribute__ ((init_priority (2000)));
Some_Class B __attribute__ ((init_priority (543)));
Note that the particular values of PRIORITY do not matter; only
their relative ordering.
`java_interface'
This type attribute informs C++ that the class is a Java
interface. It may only be applied to classes declared within an
`extern "Java"' block. Calls to methods declared in this
interface will be dispatched using GCJ's interface table
mechanism, instead of regular virtual table dispatch.
See also *Note Namespace Association::.
File: gcc.info, Node: Namespace Association, Next: Java Exceptions, Prev: C++ Attributes, Up: C++ Extensions
6.8 Namespace Association
=========================
*Caution:* The semantics of this extension are not fully defined.
Users should refrain from using this extension as its semantics may
change subtly over time. It is possible that this extension will be
removed in future versions of G++.
A using-directive with `__attribute ((strong))' is stronger than a
normal using-directive in two ways:
* Templates from the used namespace can be specialized and explicitly
instantiated as though they were members of the using namespace.
* The using namespace is considered an associated namespace of all
templates in the used namespace for purposes of argument-dependent
name lookup.
The used namespace must be nested within the using namespace so that
normal unqualified lookup works properly.
This is useful for composing a namespace transparently from
implementation namespaces. For example:
namespace std {
namespace debug {
template <class T> struct A { };
}
using namespace debug __attribute ((__strong__));
template <> struct A<int> { }; // ok to specialize
template <class T> void f (A<T>);
}
int main()
{
f (std::A<float>()); // lookup finds std::f
f (std::A<int>());
}
File: gcc.info, Node: Java Exceptions, Next: Deprecated Features, Prev: Namespace Association, Up: C++ Extensions
6.9 Java Exceptions
===================
The Java language uses a slightly different exception handling model
from C++. Normally, GNU C++ will automatically detect when you are
writing C++ code that uses Java exceptions, and handle them
appropriately. However, if C++ code only needs to execute destructors
when Java exceptions are thrown through it, GCC will guess incorrectly.
Sample problematic code is:
struct S { ~S(); };
extern void bar(); // is written in Java, and may throw exceptions
void foo()
{
S s;
bar();
}
The usual effect of an incorrect guess is a link failure, complaining of
a missing routine called `__gxx_personality_v0'.
You can inform the compiler that Java exceptions are to be used in a
translation unit, irrespective of what it might think, by writing
`#pragma GCC java_exceptions' at the head of the file. This `#pragma'
must appear before any functions that throw or catch exceptions, or run
destructors when exceptions are thrown through them.
You cannot mix Java and C++ exceptions in the same translation unit.
It is believed to be safe to throw a C++ exception from one file through
another file compiled for the Java exception model, or vice versa, but
there may be bugs in this area.
File: gcc.info, Node: Deprecated Features, Next: Backwards Compatibility, Prev: Java Exceptions, Up: C++ Extensions
6.10 Deprecated Features
========================
In the past, the GNU C++ compiler was extended to experiment with new
features, at a time when the C++ language was still evolving. Now that
the C++ standard is complete, some of those features are superseded by
superior alternatives. Using the old features might cause a warning in
some cases that the feature will be dropped in the future. In other
cases, the feature might be gone already.
While the list below is not exhaustive, it documents some of the
options that are now deprecated:
`-fexternal-templates'
`-falt-external-templates'
These are two of the many ways for G++ to implement template
instantiation. *Note Template Instantiation::. The C++ standard
clearly defines how template definitions have to be organized
across implementation units. G++ has an implicit instantiation
mechanism that should work just fine for standard-conforming code.
`-fstrict-prototype'
`-fno-strict-prototype'
Previously it was possible to use an empty prototype parameter
list to indicate an unspecified number of parameters (like C),
rather than no parameters, as C++ demands. This feature has been
removed, except where it is required for backwards compatibility
*Note Backwards Compatibility::.
G++ allows a virtual function returning `void *' to be overridden by
one returning a different pointer type. This extension to the
covariant return type rules is now deprecated and will be removed from a
future version.
The G++ minimum and maximum operators (`<?' and `>?') and their
compound forms (`<?=') and `>?=') have been deprecated and will be
removed in a future version. Code using these operators should be
modified to use `std::min' and `std::max' instead.
The named return value extension has been deprecated, and is now
removed from G++.
The use of initializer lists with new expressions has been deprecated,
and is now removed from G++.
Floating and complex non-type template parameters have been deprecated,
and are now removed from G++.
The implicit typename extension has been deprecated and is now removed
from G++.
The use of default arguments in function pointers, function typedefs
and other places where they are not permitted by the standard is
deprecated and will be removed from a future version of G++.
G++ allows floating-point literals to appear in integral constant
expressions, e.g. ` enum E { e = int(2.2 * 3.7) } ' This extension is
deprecated and will be removed from a future version.
G++ allows static data members of const floating-point type to be
declared with an initializer in a class definition. The standard only
allows initializers for static members of const integral types and const
enumeration types so this extension has been deprecated and will be
removed from a future version.
File: gcc.info, Node: Backwards Compatibility, Prev: Deprecated Features, Up: C++ Extensions
6.11 Backwards Compatibility
============================
Now that there is a definitive ISO standard C++, G++ has a specification
to adhere to. The C++ language evolved over time, and features that
used to be acceptable in previous drafts of the standard, such as the
ARM [Annotated C++ Reference Manual], are no longer accepted. In order
to allow compilation of C++ written to such drafts, G++ contains some
backwards compatibilities. _All such backwards compatibility features
are liable to disappear in future versions of G++._ They should be
considered deprecated *Note Deprecated Features::.
`For scope'
If a variable is declared at for scope, it used to remain in scope
until the end of the scope which contained the for statement
(rather than just within the for scope). G++ retains this, but
issues a warning, if such a variable is accessed outside the for
scope.
`Implicit C language'
Old C system header files did not contain an `extern "C" {...}'
scope to set the language. On such systems, all header files are
implicitly scoped inside a C language scope. Also, an empty
prototype `()' will be treated as an unspecified number of
arguments, rather than no arguments, as C++ demands.
File: gcc.info, Node: Objective-C, Next: Compatibility, Prev: C++ Extensions, Up: Top
7 GNU Objective-C runtime features
**********************************
This document is meant to describe some of the GNU Objective-C runtime
features. It is not intended to teach you Objective-C, there are
several resources on the Internet that present the language. Questions
and comments about this document to Ovidiu Predescu <ovidiu@cup.hp.com>.
* Menu:
* Executing code before main::
* Type encoding::
* Garbage Collection::
* Constant string objects::
* compatibility_alias::
File: gcc.info, Node: Executing code before main, Next: Type encoding, Prev: Objective-C, Up: Objective-C
7.1 `+load': Executing code before main
=======================================
The GNU Objective-C runtime provides a way that allows you to execute
code before the execution of the program enters the `main' function.
The code is executed on a per-class and a per-category basis, through a
special class method `+load'.
This facility is very useful if you want to initialize global variables
which can be accessed by the program directly, without sending a message
to the class first. The usual way to initialize global variables, in
the `+initialize' method, might not be useful because `+initialize' is
only called when the first message is sent to a class object, which in
some cases could be too late.
Suppose for example you have a `FileStream' class that declares
`Stdin', `Stdout' and `Stderr' as global variables, like below:
FileStream *Stdin = nil;
FileStream *Stdout = nil;
FileStream *Stderr = nil;
@implementation FileStream
+ (void)initialize
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
@end
In this example, the initialization of `Stdin', `Stdout' and `Stderr'
in `+initialize' occurs too late. The programmer can send a message to
one of these objects before the variables are actually initialized,
thus sending messages to the `nil' object. The `+initialize' method
which actually initializes the global variables is not invoked until
the first message is sent to the class object. The solution would
require these variables to be initialized just before entering `main'.
The correct solution of the above problem is to use the `+load' method
instead of `+initialize':
@implementation FileStream
+ (void)load
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
@end
The `+load' is a method that is not overridden by categories. If a
class and a category of it both implement `+load', both methods are
invoked. This allows some additional initializations to be performed in
a category.
This mechanism is not intended to be a replacement for `+initialize'.
You should be aware of its limitations when you decide to use it
instead of `+initialize'.
* Menu:
* What you can and what you cannot do in +load::
File: gcc.info, Node: What you can and what you cannot do in +load, Prev: Executing code before main, Up: Executing code before main
7.1.1 What you can and what you cannot do in `+load'
----------------------------------------------------
The `+load' implementation in the GNU runtime guarantees you the
following things:
* you can write whatever C code you like;
* you can send messages to Objective-C constant strings (`@"this is a
constant string"');
* you can allocate and send messages to objects whose class is
implemented in the same file;
* the `+load' implementation of all super classes of a class are
executed before the `+load' of that class is executed;
* the `+load' implementation of a class is executed before the
`+load' implementation of any category.
In particular, the following things, even if they can work in a
particular case, are not guaranteed:
* allocation of or sending messages to arbitrary objects;
* allocation of or sending messages to objects whose classes have a
category implemented in the same file;
You should make no assumptions about receiving `+load' in sibling
classes when you write `+load' of a class. The order in which sibling
classes receive `+load' is not guaranteed.
The order in which `+load' and `+initialize' are called could be
problematic if this matters. If you don't allocate objects inside
`+load', it is guaranteed that `+load' is called before `+initialize'.
If you create an object inside `+load' the `+initialize' method of
object's class is invoked even if `+load' was not invoked. Note if you
explicitly call `+load' on a class, `+initialize' will be called first.
To avoid possible problems try to implement only one of these methods.
The `+load' method is also invoked when a bundle is dynamically loaded
into your running program. This happens automatically without any
intervening operation from you. When you write bundles and you need to
write `+load' you can safely create and send messages to objects whose
classes already exist in the running program. The same restrictions as
above apply to classes defined in bundle.
File: gcc.info, Node: Type encoding, Next: Garbage Collection, Prev: Executing code before main, Up: Objective-C
7.2 Type encoding
=================
The Objective-C compiler generates type encodings for all the types.
These type encodings are used at runtime to find out information about
selectors and methods and about objects and classes.
The types are encoded in the following way:
`_Bool' `B'
`char' `c'
`unsigned char' `C'
`short' `s'
`unsigned short' `S'
`int' `i'
`unsigned int' `I'
`long' `l'
`unsigned long' `L'
`long long' `q'
`unsigned long `Q'
long'
`float' `f'
`double' `d'
`void' `v'
`id' `@'
`Class' `#'
`SEL' `:'
`char*' `*'
unknown type `?'
Complex types `j' followed by the inner type. For example
`_Complex double' is encoded as "jd".
bit-fields `b' followed by the starting position of the
bit-field, the type of the bit-field and the size of
the bit-field (the bit-fields encoding was changed
from the NeXT's compiler encoding, see below)
The encoding of bit-fields has changed to allow bit-fields to be
properly handled by the runtime functions that compute sizes and
alignments of types that contain bit-fields. The previous encoding
contained only the size of the bit-field. Using only this information
it is not possible to reliably compute the size occupied by the
bit-field. This is very important in the presence of the Boehm's
garbage collector because the objects are allocated using the typed
memory facility available in this collector. The typed memory
allocation requires information about where the pointers are located
inside the object.
The position in the bit-field is the position, counting in bits, of the
bit closest to the beginning of the structure.
The non-atomic types are encoded as follows:
pointers `^' followed by the pointed type.
arrays `[' followed by the number of elements in the array
followed by the type of the elements followed by `]'
structures `{' followed by the name of the structure (or `?' if the
structure is unnamed), the `=' sign, the type of the
members and by `}'
unions `(' followed by the name of the structure (or `?' if the
union is unnamed), the `=' sign, the type of the members
followed by `)'
Here are some types and their encodings, as they are generated by the
compiler on an i386 machine:
Objective-C type Compiler encoding
int a[10]; `[10i]'
struct { `{?=i[3f]b128i3b131i2c}'
int i;
float f[3];
int a:3;
int b:2;
char c;
}
In addition to the types the compiler also encodes the type
specifiers. The table below describes the encoding of the current
Objective-C type specifiers:
Specifier Encoding
`const' `r'
`in' `n'
`inout' `N'
`out' `o'
`bycopy' `O'
`oneway' `V'
The type specifiers are encoded just before the type. Unlike types
however, the type specifiers are only encoded when they appear in method
argument types.
File: gcc.info, Node: Garbage Collection, Next: Constant string objects, Prev: Type encoding, Up: Objective-C
7.3 Garbage Collection
======================
Support for a new memory management policy has been added by using a
powerful conservative garbage collector, known as the
Boehm-Demers-Weiser conservative garbage collector. It is available
from `http://www.hpl.hp.com/personal/Hans_Boehm/gc/'.
To enable the support for it you have to configure the compiler using
an additional argument, `--enable-objc-gc'. You need to have garbage
collector installed before building the compiler. This will build an
additional runtime library which has several enhancements to support
the garbage collector. The new library has a new name, `libobjc_gc.a'
to not conflict with the non-garbage-collected library.
When the garbage collector is used, the objects are allocated using the
so-called typed memory allocation mechanism available in the
Boehm-Demers-Weiser collector. This mode requires precise information
on where pointers are located inside objects. This information is
computed once per class, immediately after the class has been
initialized.
There is a new runtime function `class_ivar_set_gcinvisible()' which
can be used to declare a so-called "weak pointer" reference. Such a
pointer is basically hidden for the garbage collector; this can be
useful in certain situations, especially when you want to keep track of
the allocated objects, yet allow them to be collected. This kind of
pointers can only be members of objects, you cannot declare a global
pointer as a weak reference. Every type which is a pointer type can be
declared a weak pointer, including `id', `Class' and `SEL'.
Here is an example of how to use this feature. Suppose you want to
implement a class whose instances hold a weak pointer reference; the
following class does this:
@interface WeakPointer : Object
{
const void* weakPointer;
}
- initWithPointer:(const void*)p;
- (const void*)weakPointer;
@end
@implementation WeakPointer
+ (void)initialize
{
class_ivar_set_gcinvisible (self, "weakPointer", YES);
}
- initWithPointer:(const void*)p
{
weakPointer = p;
return self;
}
- (const void*)weakPointer
{
return weakPointer;
}
@end
Weak pointers are supported through a new type character specifier
represented by the `!' character. The `class_ivar_set_gcinvisible()'
function adds or removes this specifier to the string type description
of the instance variable named as argument.
File: gcc.info, Node: Constant string objects, Next: compatibility_alias, Prev: Garbage Collection, Up: Objective-C
7.4 Constant string objects
===========================
GNU Objective-C provides constant string objects that are generated
directly by the compiler. You declare a constant string object by
prefixing a C constant string with the character `@':
id myString = @"this is a constant string object";
The constant string objects are by default instances of the
`NXConstantString' class which is provided by the GNU Objective-C
runtime. To get the definition of this class you must include the
`objc/NXConstStr.h' header file.
User defined libraries may want to implement their own constant string
class. To be able to support them, the GNU Objective-C compiler
provides a new command line options
`-fconstant-string-class=CLASS-NAME'. The provided class should adhere
to a strict structure, the same as `NXConstantString''s structure:
@interface MyConstantStringClass
{
Class isa;
char *c_string;
unsigned int len;
}
@end
`NXConstantString' inherits from `Object'; user class libraries may
choose to inherit the customized constant string class from a different
class than `Object'. There is no requirement in the methods the
constant string class has to implement, but the final ivar layout of
the class must be the compatible with the given structure.
When the compiler creates the statically allocated constant string
object, the `c_string' field will be filled by the compiler with the
string; the `length' field will be filled by the compiler with the
string length; the `isa' pointer will be filled with `NULL' by the
compiler, and it will later be fixed up automatically at runtime by the
GNU Objective-C runtime library to point to the class which was set by
the `-fconstant-string-class' option when the object file is loaded (if
you wonder how it works behind the scenes, the name of the class to
use, and the list of static objects to fixup, are stored by the
compiler in the object file in a place where the GNU runtime library
will find them at runtime).
As a result, when a file is compiled with the
`-fconstant-string-class' option, all the constant string objects will
be instances of the class specified as argument to this option. It is
possible to have multiple compilation units referring to different
constant string classes, neither the compiler nor the linker impose any
restrictions in doing this.
File: gcc.info, Node: compatibility_alias, Prev: Constant string objects, Up: Objective-C
7.5 compatibility_alias
=======================
This is a feature of the Objective-C compiler rather than of the
runtime, anyway since it is documented nowhere and its existence was
forgotten, we are documenting it here.
The keyword `@compatibility_alias' allows you to define a class name
as equivalent to another class name. For example:
@compatibility_alias WOApplication GSWApplication;
tells the compiler that each time it encounters `WOApplication' as a
class name, it should replace it with `GSWApplication' (that is,
`WOApplication' is just an alias for `GSWApplication').
There are some constraints on how this can be used--
* `WOApplication' (the alias) must not be an existing class;
* `GSWApplication' (the real class) must be an existing class.
File: gcc.info, Node: Compatibility, Next: Gcov, Prev: Objective-C, Up: Top
8 Binary Compatibility
**********************
Binary compatibility encompasses several related concepts:
"application binary interface (ABI)"
The set of runtime conventions followed by all of the tools that
deal with binary representations of a program, including
compilers, assemblers, linkers, and language runtime support.
Some ABIs are formal with a written specification, possibly
designed by multiple interested parties. Others are simply the
way things are actually done by a particular set of tools.
"ABI conformance"
A compiler conforms to an ABI if it generates code that follows
all of the specifications enumerated by that ABI. A library
conforms to an ABI if it is implemented according to that ABI. An
application conforms to an ABI if it is built using tools that
conform to that ABI and does not contain source code that
specifically changes behavior specified by the ABI.
"calling conventions"
Calling conventions are a subset of an ABI that specify of how
arguments are passed and function results are returned.
"interoperability"
Different sets of tools are interoperable if they generate files
that can be used in the same program. The set of tools includes
compilers, assemblers, linkers, libraries, header files, startup
files, and debuggers. Binaries produced by different sets of
tools are not interoperable unless they implement the same ABI.
This applies to different versions of the same tools as well as
tools from different vendors.
"intercallability"
Whether a function in a binary built by one set of tools can call a
function in a binary built by a different set of tools is a subset
of interoperability.
"implementation-defined features"
Language standards include lists of implementation-defined
features whose behavior can vary from one implementation to
another. Some of these features are normally covered by a
platform's ABI and others are not. The features that are not
covered by an ABI generally affect how a program behaves, but not
intercallability.
"compatibility"
Conformance to the same ABI and the same behavior of
implementation-defined features are both relevant for
compatibility.
The application binary interface implemented by a C or C++ compiler
affects code generation and runtime support for:
* size and alignment of data types
* layout of structured types
* calling conventions
* register usage conventions
* interfaces for runtime arithmetic support
* object file formats
In addition, the application binary interface implemented by a C++
compiler affects code generation and runtime support for:
* name mangling
* exception handling
* invoking constructors and destructors
* layout, alignment, and padding of classes
* layout and alignment of virtual tables
Some GCC compilation options cause the compiler to generate code that
does not conform to the platform's default ABI. Other options cause
different program behavior for implementation-defined features that are
not covered by an ABI. These options are provided for consistency with
other compilers that do not follow the platform's default ABI or the
usual behavior of implementation-defined features for the platform. Be
very careful about using such options.
Most platforms have a well-defined ABI that covers C code, but ABIs
that cover C++ functionality are not yet common.
Starting with GCC 3.2, GCC binary conventions for C++ are based on a
written, vendor-neutral C++ ABI that was designed to be specific to
64-bit Itanium but also includes generic specifications that apply to
any platform. This C++ ABI is also implemented by other compiler
vendors on some platforms, notably GNU/Linux and BSD systems. We have
tried hard to provide a stable ABI that will be compatible with future
GCC releases, but it is possible that we will encounter problems that
make this difficult. Such problems could include different
interpretations of the C++ ABI by different vendors, bugs in the ABI, or
bugs in the implementation of the ABI in different compilers. GCC's
`-Wabi' switch warns when G++ generates code that is probably not
compatible with the C++ ABI.
The C++ library used with a C++ compiler includes the Standard C++
Library, with functionality defined in the C++ Standard, plus language
runtime support. The runtime support is included in a C++ ABI, but
there is no formal ABI for the Standard C++ Library. Two
implementations of that library are interoperable if one follows the
de-facto ABI of the other and if they are both built with the same
compiler, or with compilers that conform to the same ABI for C++
compiler and runtime support.
When G++ and another C++ compiler conform to the same C++ ABI, but the
implementations of the Standard C++ Library that they normally use do
not follow the same ABI for the Standard C++ Library, object files
built with those compilers can be used in the same program only if they
use the same C++ library. This requires specifying the location of the
C++ library header files when invoking the compiler whose usual library
is not being used. The location of GCC's C++ header files depends on
how the GCC build was configured, but can be seen by using the G++ `-v'
option. With default configuration options for G++ 3.3 the compile
line for a different C++ compiler needs to include
-IGCC_INSTALL_DIRECTORY/include/c++/3.3
Similarly, compiling code with G++ that must use a C++ library other
than the GNU C++ library requires specifying the location of the header
files for that other library.
The most straightforward way to link a program to use a particular C++
library is to use a C++ driver that specifies that C++ library by
default. The `g++' driver, for example, tells the linker where to find
GCC's C++ library (`libstdc++') plus the other libraries and startup
files it needs, in the proper order.
If a program must use a different C++ library and it's not possible to
do the final link using a C++ driver that uses that library by default,
it is necessary to tell `g++' the location and name of that library.
It might also be necessary to specify different startup files and other
runtime support libraries, and to suppress the use of GCC's support
libraries with one or more of the options `-nostdlib', `-nostartfiles',
and `-nodefaultlibs'.
File: gcc.info, Node: Gcov, Next: Trouble, Prev: Compatibility, Up: Top
9 `gcov'--a Test Coverage Program
*********************************
`gcov' is a tool you can use in conjunction with GCC to test code
coverage in your programs.
* Menu:
* Gcov Intro:: Introduction to gcov.
* Invoking Gcov:: How to use gcov.
* Gcov and Optimization:: Using gcov with GCC optimization.
* Gcov Data Files:: The files used by gcov.
* Cross-profiling:: Data file relocation.
File: gcc.info, Node: Gcov Intro, Next: Invoking Gcov, Up: Gcov
9.1 Introduction to `gcov'
==========================
`gcov' is a test coverage program. Use it in concert with GCC to
analyze your programs to help create more efficient, faster running
code and to discover untested parts of your program. You can use
`gcov' as a profiling tool to help discover where your optimization
efforts will best affect your code. You can also use `gcov' along with
the other profiling tool, `gprof', to assess which parts of your code
use the greatest amount of computing time.
Profiling tools help you analyze your code's performance. Using a
profiler such as `gcov' or `gprof', you can find out some basic
performance statistics, such as:
* how often each line of code executes
* what lines of code are actually executed
* how much computing time each section of code uses
Once you know these things about how your code works when compiled, you
can look at each module to see which modules should be optimized.
`gcov' helps you determine where to work on optimization.
Software developers also use coverage testing in concert with
testsuites, to make sure software is actually good enough for a release.
Testsuites can verify that a program works as expected; a coverage
program tests to see how much of the program is exercised by the
testsuite. Developers can then determine what kinds of test cases need
to be added to the testsuites to create both better testing and a better
final product.
You should compile your code without optimization if you plan to use
`gcov' because the optimization, by combining some lines of code into
one function, may not give you as much information as you need to look
for `hot spots' where the code is using a great deal of computer time.
Likewise, because `gcov' accumulates statistics by line (at the lowest
resolution), it works best with a programming style that places only
one statement on each line. If you use complicated macros that expand
to loops or to other control structures, the statistics are less
helpful--they only report on the line where the macro call appears. If
your complex macros behave like functions, you can replace them with
inline functions to solve this problem.
`gcov' creates a logfile called `SOURCEFILE.gcov' which indicates how
many times each line of a source file `SOURCEFILE.c' has executed. You
can use these logfiles along with `gprof' to aid in fine-tuning the
performance of your programs. `gprof' gives timing information you can
use along with the information you get from `gcov'.
`gcov' works only on code compiled with GCC. It is not compatible
with any other profiling or test coverage mechanism.
File: gcc.info, Node: Invoking Gcov, Next: Gcov and Optimization, Prev: Gcov Intro, Up: Gcov
9.2 Invoking `gcov'
===================
gcov [OPTIONS] SOURCEFILE
`gcov' accepts the following options:
`-h'
`--help'
Display help about using `gcov' (on the standard output), and exit
without doing any further processing.
`-v'
`--version'
Display the `gcov' version number (on the standard output), and
exit without doing any further processing.
`-a'
`--all-blocks'
Write individual execution counts for every basic block. Normally
gcov outputs execution counts only for the main blocks of a line.
With this option you can determine if blocks within a single line
are not being executed.
`-b'
`--branch-probabilities'
Write branch frequencies to the output file, and write branch
summary info to the standard output. This option allows you to
see how often each branch in your program was taken.
Unconditional branches will not be shown, unless the `-u' option
is given.
`-c'
`--branch-counts'
Write branch frequencies as the number of branches taken, rather
than the percentage of branches taken.
`-n'
`--no-output'
Do not create the `gcov' output file.
`-l'
`--long-file-names'
Create long file names for included source files. For example, if
the header file `x.h' contains code, and was included in the file
`a.c', then running `gcov' on the file `a.c' will produce an
output file called `a.c##x.h.gcov' instead of `x.h.gcov'. This
can be useful if `x.h' is included in multiple source files. If
you use the `-p' option, both the including and included file
names will be complete path names.
`-p'
`--preserve-paths'
Preserve complete path information in the names of generated
`.gcov' files. Without this option, just the filename component is
used. With this option, all directories are used, with `/'
characters translated to `#' characters, `.' directory components
removed and `..' components renamed to `^'. This is useful if
sourcefiles are in several different directories. It also affects
the `-l' option.
`-f'
`--function-summaries'
Output summaries for each function in addition to the file level
summary.
`-o DIRECTORY|FILE'
`--object-directory DIRECTORY'
`--object-file FILE'
Specify either the directory containing the gcov data files, or the
object path name. The `.gcno', and `.gcda' data files are
searched for using this option. If a directory is specified, the
data files are in that directory and named after the source file
name, without its extension. If a file is specified here, the
data files are named after that file, without its extension. If
this option is not supplied, it defaults to the current directory.
`-u'
`--unconditional-branches'
When branch probabilities are given, include those of
unconditional branches. Unconditional branches are normally not
interesting.
`gcov' should be run with the current directory the same as that when
you invoked the compiler. Otherwise it will not be able to locate the
source files. `gcov' produces files called `MANGLEDNAME.gcov' in the
current directory. These contain the coverage information of the
source file they correspond to. One `.gcov' file is produced for each
source file containing code, which was compiled to produce the data
files. The MANGLEDNAME part of the output file name is usually simply
the source file name, but can be something more complicated if the `-l'
or `-p' options are given. Refer to those options for details.
The `.gcov' files contain the `:' separated fields along with program
source code. The format is
EXECUTION_COUNT:LINE_NUMBER:SOURCE LINE TEXT
Additional block information may succeed each line, when requested by
command line option. The EXECUTION_COUNT is `-' for lines containing
no code and `#####' for lines which were never executed. Some lines of
information at the start have LINE_NUMBER of zero.
The preamble lines are of the form
-:0:TAG:VALUE
The ordering and number of these preamble lines will be augmented as
`gcov' development progresses -- do not rely on them remaining
unchanged. Use TAG to locate a particular preamble line.
The additional block information is of the form
TAG INFORMATION
The INFORMATION is human readable, but designed to be simple enough
for machine parsing too.
When printing percentages, 0% and 100% are only printed when the values
are _exactly_ 0% and 100% respectively. Other values which would
conventionally be rounded to 0% or 100% are instead printed as the
nearest non-boundary value.
When using `gcov', you must first compile your program with two
special GCC options: `-fprofile-arcs -ftest-coverage'. This tells the
compiler to generate additional information needed by gcov (basically a
flow graph of the program) and also includes additional code in the
object files for generating the extra profiling information needed by
gcov. These additional files are placed in the directory where the
object file is located.
Running the program will cause profile output to be generated. For
each source file compiled with `-fprofile-arcs', an accompanying
`.gcda' file will be placed in the object file directory.
Running `gcov' with your program's source file names as arguments will
now produce a listing of the code along with frequency of execution for
each line. For example, if your program is called `tmp.c', this is
what you see when you use the basic `gcov' facility:
$ gcc -fprofile-arcs -ftest-coverage tmp.c
$ a.out
$ gcov tmp.c
90.00% of 10 source lines executed in file tmp.c
Creating tmp.c.gcov.
The file `tmp.c.gcov' contains output from `gcov'. Here is a sample:
-: 0:Source:tmp.c
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
1: 4:{
1: 5: int i, total;
-: 6:
1: 7: total = 0;
-: 8:
11: 9: for (i = 0; i < 10; i++)
10: 10: total += i;
-: 11:
1: 12: if (total != 45)
#####: 13: printf ("Failure\n");
-: 14: else
1: 15: printf ("Success\n");
1: 16: return 0;
-: 17:}
When you use the `-a' option, you will get individual block counts,
and the output looks like this:
-: 0:Source:tmp.c
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
1: 4:{
1: 4-block 0
1: 5: int i, total;
-: 6:
1: 7: total = 0;
-: 8:
11: 9: for (i = 0; i < 10; i++)
11: 9-block 0
10: 10: total += i;
10: 10-block 0
-: 11:
1: 12: if (total != 45)
1: 12-block 0
#####: 13: printf ("Failure\n");
$$$$$: 13-block 0
-: 14: else
1: 15: printf ("Success\n");
1: 15-block 0
1: 16: return 0;
1: 16-block 0
-: 17:}
In this mode, each basic block is only shown on one line - the last
line of the block. A multi-line block will only contribute to the
execution count of that last line, and other lines will not be shown to
contain code, unless previous blocks end on those lines. The total
execution count of a line is shown and subsequent lines show the
execution counts for individual blocks that end on that line. After
each block, the branch and call counts of the block will be shown, if
the `-b' option is given.
Because of the way GCC instruments calls, a call count can be shown
after a line with no individual blocks. As you can see, line 13
contains a basic block that was not executed.
When you use the `-b' option, your output looks like this:
$ gcov -b tmp.c
90.00% of 10 source lines executed in file tmp.c
80.00% of 5 branches executed in file tmp.c
80.00% of 5 branches taken at least once in file tmp.c
50.00% of 2 calls executed in file tmp.c
Creating tmp.c.gcov.
Here is a sample of a resulting `tmp.c.gcov' file:
-: 0:Source:tmp.c
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
function main called 1 returned 1 blocks executed 75%
1: 4:{
1: 5: int i, total;
-: 6:
1: 7: total = 0;
-: 8:
11: 9: for (i = 0; i < 10; i++)
branch 0 taken 91% (fallthrough)
branch 1 taken 9%
10: 10: total += i;
-: 11:
1: 12: if (total != 45)
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
#####: 13: printf ("Failure\n");
call 0 never executed
-: 14: else
1: 15: printf ("Success\n");
call 0 called 1 returned 100%
1: 16: return 0;
-: 17:}
For each function, a line is printed showing how many times the
function is called, how many times it returns and what percentage of the
function's blocks were executed.
For each basic block, a line is printed after the last line of the
basic block describing the branch or call that ends the basic block.
There can be multiple branches and calls listed for a single source
line if there are multiple basic blocks that end on that line. In this
case, the branches and calls are each given a number. There is no
simple way to map these branches and calls back to source constructs.
In general, though, the lowest numbered branch or call will correspond
to the leftmost construct on the source line.
For a branch, if it was executed at least once, then a percentage
indicating the number of times the branch was taken divided by the
number of times the branch was executed will be printed. Otherwise, the
message "never executed" is printed.
For a call, if it was executed at least once, then a percentage
indicating the number of times the call returned divided by the number
of times the call was executed will be printed. This will usually be
100%, but may be less for functions that call `exit' or `longjmp', and
thus may not return every time they are called.
The execution counts are cumulative. If the example program were
executed again without removing the `.gcda' file, the count for the
number of times each line in the source was executed would be added to
the results of the previous run(s). This is potentially useful in
several ways. For example, it could be used to accumulate data over a
number of program runs as part of a test verification suite, or to
provide more accurate long-term information over a large number of
program runs.
The data in the `.gcda' files is saved immediately before the program
exits. For each source file compiled with `-fprofile-arcs', the
profiling code first attempts to read in an existing `.gcda' file; if
the file doesn't match the executable (differing number of basic block
counts) it will ignore the contents of the file. It then adds in the
new execution counts and finally writes the data to the file.
File: gcc.info, Node: Gcov and Optimization, Next: Gcov Data Files, Prev: Invoking Gcov, Up: Gcov
9.3 Using `gcov' with GCC Optimization
======================================
If you plan to use `gcov' to help optimize your code, you must first
compile your program with two special GCC options: `-fprofile-arcs
-ftest-coverage'. Aside from that, you can use any other GCC options;
but if you want to prove that every single line in your program was
executed, you should not compile with optimization at the same time.
On some machines the optimizer can eliminate some simple code lines by
combining them with other lines. For example, code like this:
if (a != b)
c = 1;
else
c = 0;
can be compiled into one instruction on some machines. In this case,
there is no way for `gcov' to calculate separate execution counts for
each line because there isn't separate code for each line. Hence the
`gcov' output looks like this if you compiled the program with
optimization:
100: 12:if (a != b)
100: 13: c = 1;
100: 14:else
100: 15: c = 0;
The output shows that this block of code, combined by optimization,
executed 100 times. In one sense this result is correct, because there
was only one instruction representing all four of these lines. However,
the output does not indicate how many times the result was 0 and how
many times the result was 1.
Inlineable functions can create unexpected line counts. Line counts
are shown for the source code of the inlineable function, but what is
shown depends on where the function is inlined, or if it is not inlined
at all.
If the function is not inlined, the compiler must emit an out of line
copy of the function, in any object file that needs it. If `fileA.o'
and `fileB.o' both contain out of line bodies of a particular
inlineable function, they will also both contain coverage counts for
that function. When `fileA.o' and `fileB.o' are linked together, the
linker will, on many systems, select one of those out of line bodies
for all calls to that function, and remove or ignore the other.
Unfortunately, it will not remove the coverage counters for the unused
function body. Hence when instrumented, all but one use of that
function will show zero counts.
If the function is inlined in several places, the block structure in
each location might not be the same. For instance, a condition might
now be calculable at compile time in some instances. Because the
coverage of all the uses of the inline function will be shown for the
same source lines, the line counts themselves might seem inconsistent.
File: gcc.info, Node: Gcov Data Files, Next: Cross-profiling, Prev: Gcov and Optimization, Up: Gcov
9.4 Brief description of `gcov' data files
==========================================
`gcov' uses two files for profiling. The names of these files are
derived from the original _object_ file by substituting the file suffix
with either `.gcno', or `.gcda'. All of these files are placed in the
same directory as the object file, and contain data stored in a
platform-independent format.
The `.gcno' file is generated when the source file is compiled with
the GCC `-ftest-coverage' option. It contains information to
reconstruct the basic block graphs and assign source line numbers to
blocks.
The `.gcda' file is generated when a program containing object files
built with the GCC `-fprofile-arcs' option is executed. A separate
`.gcda' file is created for each object file compiled with this option.
It contains arc transition counts, and some summary information.
The full details of the file format is specified in `gcov-io.h', and
functions provided in that header file should be used to access the
coverage files.
File: gcc.info, Node: Cross-profiling, Prev: Gcov Data Files, Up: Gcov
9.5 Data file relocation to support cross-profiling
===================================================
Running the program will cause profile output to be generated. For each
source file compiled with `-fprofile-arcs', an accompanying `.gcda'
file will be placed in the object file directory. That implicitly
requires running the program on the same system as it was built or
having the same absolute directory structure on the target system. The
program will try to create the needed directory structure, if it is not
already present.
To support cross-profiling, a program compiled with `-fprofile-arcs'
can relocate the data files based on two environment variables:
* GCOV_PREFIX contains the prefix to add to the absolute paths in
the object file. Prefix must be absolute as well, otherwise its
value is ignored. The default is no prefix.
* GCOV_PREFIX_STRIP indicates the how many initial directory names
to strip off the hardwired absolute paths. Default value is 0.
_Note:_ GCOV_PREFIX_STRIP has no effect if GCOV_PREFIX is
undefined, empty or non-absolute.
For example, if the object file `/user/build/foo.o' was built with
`-fprofile-arcs', the final executable will try to create the data file
`/user/build/foo.gcda' when running on the target system. This will
fail if the corresponding directory does not exist and it is unable to
create it. This can be overcome by, for example, setting the
environment as `GCOV_PREFIX=/target/run' and `GCOV_PREFIX_STRIP=1'.
Such a setting will name the data file `/target/run/build/foo.gcda'.
You must move the data files to the expected directory tree in order to
use them for profile directed optimizations (`--use-profile'), or to
use the `gcov' tool.
File: gcc.info, Node: Trouble, Next: Bugs, Prev: Gcov, Up: Top
10 Known Causes of Trouble with GCC
***********************************
This section describes known problems that affect users of GCC. Most
of these are not GCC bugs per se--if they were, we would fix them. But
the result for a user may be like the result of a bug.
Some of these problems are due to bugs in other software, some are
missing features that are too much work to add, and some are places
where people's opinions differ as to what is best.
* Menu:
* Actual Bugs:: Bugs we will fix later.
* Cross-Compiler Problems:: Common problems of cross compiling with GCC.
* Interoperation:: Problems using GCC with other compilers,
and with certain linkers, assemblers and debuggers.
* Incompatibilities:: GCC is incompatible with traditional C.
* Fixed Headers:: GCC uses corrected versions of system header files.
This is necessary, but doesn't always work smoothly.
* Standard Libraries:: GCC uses the system C library, which might not be
compliant with the ISO C standard.
* Disappointments:: Regrettable things we can't change, but not quite bugs.
* C++ Misunderstandings:: Common misunderstandings with GNU C++.
* Protoize Caveats:: Things to watch out for when using `protoize'.
* Non-bugs:: Things we think are right, but some others disagree.
* Warnings and Errors:: Which problems in your code get warnings,
and which get errors.
File: gcc.info, Node: Actual Bugs, Next: Cross-Compiler Problems, Up: Trouble
10.1 Actual Bugs We Haven't Fixed Yet
=====================================
* The `fixincludes' script interacts badly with automounters; if the
directory of system header files is automounted, it tends to be
unmounted while `fixincludes' is running. This would seem to be a
bug in the automounter. We don't know any good way to work around
it.
* The `fixproto' script will sometimes add prototypes for the
`sigsetjmp' and `siglongjmp' functions that reference the
`jmp_buf' type before that type is defined. To work around this,
edit the offending file and place the typedef in front of the
prototypes.
File: gcc.info, Node: Cross-Compiler Problems, Next: Interoperation, Prev: Actual Bugs, Up: Trouble
10.2 Cross-Compiler Problems
============================
You may run into problems with cross compilation on certain machines,
for several reasons.
* At present, the program `mips-tfile' which adds debug support to
object files on MIPS systems does not work in a cross compile
environment.
File: gcc.info, Node: Interoperation, Next: Incompatibilities, Prev: Cross-Compiler Problems, Up: Trouble
10.3 Interoperation
===================
This section lists various difficulties encountered in using GCC
together with other compilers or with the assemblers, linkers,
libraries and debuggers on certain systems.
* On many platforms, GCC supports a different ABI for C++ than do
other compilers, so the object files compiled by GCC cannot be
used with object files generated by another C++ compiler.
An area where the difference is most apparent is name mangling.
The use of different name mangling is intentional, to protect you
from more subtle problems. Compilers differ as to many internal
details of C++ implementation, including: how class instances are
laid out, how multiple inheritance is implemented, and how virtual
function calls are handled. If the name encoding were made the
same, your programs would link against libraries provided from
other compilers--but the programs would then crash when run.
Incompatible libraries are then detected at link time, rather than
at run time.
* On some BSD systems, including some versions of Ultrix, use of
profiling causes static variable destructors (currently used only
in C++) not to be run.
* On some SGI systems, when you use `-lgl_s' as an option, it gets
translated magically to `-lgl_s -lX11_s -lc_s'. Naturally, this
does not happen when you use GCC. You must specify all three
options explicitly.
* On a SPARC, GCC aligns all values of type `double' on an 8-byte
boundary, and it expects every `double' to be so aligned. The Sun
compiler usually gives `double' values 8-byte alignment, with one
exception: function arguments of type `double' may not be aligned.
As a result, if a function compiled with Sun CC takes the address
of an argument of type `double' and passes this pointer of type
`double *' to a function compiled with GCC, dereferencing the
pointer may cause a fatal signal.
One way to solve this problem is to compile your entire program
with GCC. Another solution is to modify the function that is
compiled with Sun CC to copy the argument into a local variable;
local variables are always properly aligned. A third solution is
to modify the function that uses the pointer to dereference it via
the following function `access_double' instead of directly with
`*':
inline double
access_double (double *unaligned_ptr)
{
union d2i { double d; int i[2]; };
union d2i *p = (union d2i *) unaligned_ptr;
union d2i u;
u.i[0] = p->i[0];
u.i[1] = p->i[1];
return u.d;
}
Storing into the pointer can be done likewise with the same union.
* On Solaris, the `malloc' function in the `libmalloc.a' library may
allocate memory that is only 4 byte aligned. Since GCC on the
SPARC assumes that doubles are 8 byte aligned, this may result in a
fatal signal if doubles are stored in memory allocated by the
`libmalloc.a' library.
The solution is to not use the `libmalloc.a' library. Use instead
`malloc' and related functions from `libc.a'; they do not have
this problem.
* On the HP PA machine, ADB sometimes fails to work on functions
compiled with GCC. Specifically, it fails to work on functions
that use `alloca' or variable-size arrays. This is because GCC
doesn't generate HP-UX unwind descriptors for such functions. It
may even be impossible to generate them.
* Debugging (`-g') is not supported on the HP PA machine, unless you
use the preliminary GNU tools.
* Taking the address of a label may generate errors from the HP-UX
PA assembler. GAS for the PA does not have this problem.
* Using floating point parameters for indirect calls to static
functions will not work when using the HP assembler. There simply
is no way for GCC to specify what registers hold arguments for
static functions when using the HP assembler. GAS for the PA does
not have this problem.
* In extremely rare cases involving some very large functions you may
receive errors from the HP linker complaining about an out of
bounds unconditional branch offset. This used to occur more often
in previous versions of GCC, but is now exceptionally rare. If
you should run into it, you can work around by making your
function smaller.
* GCC compiled code sometimes emits warnings from the HP-UX
assembler of the form:
(warning) Use of GR3 when
frame >= 8192 may cause conflict.
These warnings are harmless and can be safely ignored.
* In extremely rare cases involving some very large functions you may
receive errors from the AIX Assembler complaining about a
displacement that is too large. If you should run into it, you
can work around by making your function smaller.
* The `libstdc++.a' library in GCC relies on the SVR4 dynamic linker
semantics which merges global symbols between libraries and
applications, especially necessary for C++ streams functionality.
This is not the default behavior of AIX shared libraries and
dynamic linking. `libstdc++.a' is built on AIX with
"runtime-linking" enabled so that symbol merging can occur. To
utilize this feature, the application linked with `libstdc++.a'
must include the `-Wl,-brtl' flag on the link line. G++ cannot
impose this because this option may interfere with the semantics
of the user program and users may not always use `g++' to link his
or her application. Applications are not required to use the
`-Wl,-brtl' flag on the link line--the rest of the `libstdc++.a'
library which is not dependent on the symbol merging semantics
will continue to function correctly.
* An application can interpose its own definition of functions for
functions invoked by `libstdc++.a' with "runtime-linking" enabled
on AIX. To accomplish this the application must be linked with
"runtime-linking" option and the functions explicitly must be
exported by the application (`-Wl,-brtl,-bE:exportfile').
* AIX on the RS/6000 provides support (NLS) for environments outside
of the United States. Compilers and assemblers use NLS to support
locale-specific representations of various objects including
floating-point numbers (`.' vs `,' for separating decimal
fractions). There have been problems reported where the library
linked with GCC does not produce the same floating-point formats
that the assembler accepts. If you have this problem, set the
`LANG' environment variable to `C' or `En_US'.
* Even if you specify `-fdollars-in-identifiers', you cannot
successfully use `$' in identifiers on the RS/6000 due to a
restriction in the IBM assembler. GAS supports these identifiers.
* On Ultrix, the Fortran compiler expects registers 2 through 5 to
be saved by function calls. However, the C compiler uses
conventions compatible with BSD Unix: registers 2 through 5 may be
clobbered by function calls.
GCC uses the same convention as the Ultrix C compiler. You can use
these options to produce code compatible with the Fortran compiler:
-fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5
File: gcc.info, Node: Incompatibilities, Next: Fixed Headers, Prev: Interoperation, Up: Trouble
10.4 Incompatibilities of GCC
=============================
There are several noteworthy incompatibilities between GNU C and K&R
(non-ISO) versions of C.
* GCC normally makes string constants read-only. If several
identical-looking string constants are used, GCC stores only one
copy of the string.
One consequence is that you cannot call `mktemp' with a string
constant argument. The function `mktemp' always alters the string
its argument points to.
Another consequence is that `sscanf' does not work on some very
old systems when passed a string constant as its format control
string or input. This is because `sscanf' incorrectly tries to
write into the string constant. Likewise `fscanf' and `scanf'.
The solution to these problems is to change the program to use
`char'-array variables with initialization strings for these
purposes instead of string constants.
* `-2147483648' is positive.
This is because 2147483648 cannot fit in the type `int', so
(following the ISO C rules) its data type is `unsigned long int'.
Negating this value yields 2147483648 again.
* GCC does not substitute macro arguments when they appear inside of
string constants. For example, the following macro in GCC
#define foo(a) "a"
will produce output `"a"' regardless of what the argument A is.
* When you use `setjmp' and `longjmp', the only automatic variables
guaranteed to remain valid are those declared `volatile'. This is
a consequence of automatic register allocation. Consider this
function:
jmp_buf j;
foo ()
{
int a, b;
a = fun1 ();
if (setjmp (j))
return a;
a = fun2 ();
/* `longjmp (j)' may occur in `fun3'. */
return a + fun3 ();
}
Here `a' may or may not be restored to its first value when the
`longjmp' occurs. If `a' is allocated in a register, then its
first value is restored; otherwise, it keeps the last value stored
in it.
If you use the `-W' option with the `-O' option, you will get a
warning when GCC thinks such a problem might be possible.
* Programs that use preprocessing directives in the middle of macro
arguments do not work with GCC. For example, a program like this
will not work:
foobar (
#define luser
hack)
ISO C does not permit such a construct.
* K&R compilers allow comments to cross over an inclusion boundary
(i.e. started in an include file and ended in the including file).
* Declarations of external variables and functions within a block
apply only to the block containing the declaration. In other
words, they have the same scope as any other declaration in the
same place.
In some other C compilers, a `extern' declaration affects all the
rest of the file even if it happens within a block.
* In traditional C, you can combine `long', etc., with a typedef
name, as shown here:
typedef int foo;
typedef long foo bar;
In ISO C, this is not allowed: `long' and other type modifiers
require an explicit `int'.
* PCC allows typedef names to be used as function parameters.
* Traditional C allows the following erroneous pair of declarations
to appear together in a given scope:
typedef int foo;
typedef foo foo;
* GCC treats all characters of identifiers as significant.
According to K&R-1 (2.2), "No more than the first eight characters
are significant, although more may be used.". Also according to
K&R-1 (2.2), "An identifier is a sequence of letters and digits;
the first character must be a letter. The underscore _ counts as
a letter.", but GCC also allows dollar signs in identifiers.
* PCC allows whitespace in the middle of compound assignment
operators such as `+='. GCC, following the ISO standard, does not
allow this.
* GCC complains about unterminated character constants inside of
preprocessing conditionals that fail. Some programs have English
comments enclosed in conditionals that are guaranteed to fail; if
these comments contain apostrophes, GCC will probably report an
error. For example, this code would produce an error:
#if 0
You can't expect this to work.
#endif
The best solution to such a problem is to put the text into an
actual C comment delimited by `/*...*/'.
* Many user programs contain the declaration `long time ();'. In the
past, the system header files on many systems did not actually
declare `time', so it did not matter what type your program
declared it to return. But in systems with ISO C headers, `time'
is declared to return `time_t', and if that is not the same as
`long', then `long time ();' is erroneous.
The solution is to change your program to use appropriate system
headers (`<time.h>' on systems with ISO C headers) and not to
declare `time' if the system header files declare it, or failing
that to use `time_t' as the return type of `time'.
* When compiling functions that return `float', PCC converts it to a
double. GCC actually returns a `float'. If you are concerned
with PCC compatibility, you should declare your functions to return
`double'; you might as well say what you mean.
* When compiling functions that return structures or unions, GCC
output code normally uses a method different from that used on most
versions of Unix. As a result, code compiled with GCC cannot call
a structure-returning function compiled with PCC, and vice versa.
The method used by GCC is as follows: a structure or union which is
1, 2, 4 or 8 bytes long is returned like a scalar. A structure or
union with any other size is stored into an address supplied by
the caller (usually in a special, fixed register, but on some
machines it is passed on the stack). The target hook
`TARGET_STRUCT_VALUE_RTX' tells GCC where to pass this address.
By contrast, PCC on most target machines returns structures and
unions of any size by copying the data into an area of static
storage, and then returning the address of that storage as if it
were a pointer value. The caller must copy the data from that
memory area to the place where the value is wanted. GCC does not
use this method because it is slower and nonreentrant.
On some newer machines, PCC uses a reentrant convention for all
structure and union returning. GCC on most of these machines uses
a compatible convention when returning structures and unions in
memory, but still returns small structures and unions in registers.
You can tell GCC to use a compatible convention for all structure
and union returning with the option `-fpcc-struct-return'.
* GCC complains about program fragments such as `0x74ae-0x4000'
which appear to be two hexadecimal constants separated by the minus
operator. Actually, this string is a single "preprocessing token".
Each such token must correspond to one token in C. Since this
does not, GCC prints an error message. Although it may appear
obvious that what is meant is an operator and two values, the ISO
C standard specifically requires that this be treated as erroneous.
A "preprocessing token" is a "preprocessing number" if it begins
with a digit and is followed by letters, underscores, digits,
periods and `e+', `e-', `E+', `E-', `p+', `p-', `P+', or `P-'
character sequences. (In strict C89 mode, the sequences `p+',
`p-', `P+' and `P-' cannot appear in preprocessing numbers.)
To make the above program fragment valid, place whitespace in
front of the minus sign. This whitespace will end the
preprocessing number.
File: gcc.info, Node: Fixed Headers, Next: Standard Libraries, Prev: Incompatibilities, Up: Trouble
10.5 Fixed Header Files
=======================
GCC needs to install corrected versions of some system header files.
This is because most target systems have some header files that won't
work with GCC unless they are changed. Some have bugs, some are
incompatible with ISO C, and some depend on special features of other
compilers.
Installing GCC automatically creates and installs the fixed header
files, by running a program called `fixincludes'. Normally, you don't
need to pay attention to this. But there are cases where it doesn't do
the right thing automatically.
* If you update the system's header files, such as by installing a
new system version, the fixed header files of GCC are not
automatically updated. They can be updated using the `mkheaders'
script installed in `LIBEXECDIR/gcc/TARGET/VERSION/install-tools/'.
* On some systems, header file directories contain machine-specific
symbolic links in certain places. This makes it possible to share
most of the header files among hosts running the same version of
the system on different machine models.
The programs that fix the header files do not understand this
special way of using symbolic links; therefore, the directory of
fixed header files is good only for the machine model used to
build it.
It is possible to make separate sets of fixed header files for the
different machine models, and arrange a structure of symbolic
links so as to use the proper set, but you'll have to do this by
hand.
File: gcc.info, Node: Standard Libraries, Next: Disappointments, Prev: Fixed Headers, Up: Trouble
10.6 Standard Libraries
=======================
GCC by itself attempts to be a conforming freestanding implementation.
*Note Language Standards Supported by GCC: Standards, for details of
what this means. Beyond the library facilities required of such an
implementation, the rest of the C library is supplied by the vendor of
the operating system. If that C library doesn't conform to the C
standards, then your programs might get warnings (especially when using
`-Wall') that you don't expect.
For example, the `sprintf' function on SunOS 4.1.3 returns `char *'
while the C standard says that `sprintf' returns an `int'. The
`fixincludes' program could make the prototype for this function match
the Standard, but that would be wrong, since the function will still
return `char *'.
If you need a Standard compliant library, then you need to find one, as
GCC does not provide one. The GNU C library (called `glibc') provides
ISO C, POSIX, BSD, SystemV and X/Open compatibility for GNU/Linux and
HURD-based GNU systems; no recent version of it supports other systems,
though some very old versions did. Version 2.2 of the GNU C library
includes nearly complete C99 support. You could also ask your
operating system vendor if newer libraries are available.
File: gcc.info, Node: Disappointments, Next: C++ Misunderstandings, Prev: Standard Libraries, Up: Trouble
10.7 Disappointments and Misunderstandings
==========================================
These problems are perhaps regrettable, but we don't know any practical
way around them.
* Certain local variables aren't recognized by debuggers when you
compile with optimization.
This occurs because sometimes GCC optimizes the variable out of
existence. There is no way to tell the debugger how to compute the
value such a variable "would have had", and it is not clear that
would be desirable anyway. So GCC simply does not mention the
eliminated variable when it writes debugging information.
You have to expect a certain amount of disagreement between the
executable and your source code, when you use optimization.
* Users often think it is a bug when GCC reports an error for code
like this:
int foo (struct mumble *);
struct mumble { ... };
int foo (struct mumble *x)
{ ... }
This code really is erroneous, because the scope of `struct
mumble' in the prototype is limited to the argument list
containing it. It does not refer to the `struct mumble' defined
with file scope immediately below--they are two unrelated types
with similar names in different scopes.
But in the definition of `foo', the file-scope type is used
because that is available to be inherited. Thus, the definition
and the prototype do not match, and you get an error.
This behavior may seem silly, but it's what the ISO standard
specifies. It is easy enough for you to make your code work by
moving the definition of `struct mumble' above the prototype.
It's not worth being incompatible with ISO C just to avoid an
error for the example shown above.
* Accesses to bit-fields even in volatile objects works by accessing
larger objects, such as a byte or a word. You cannot rely on what
size of object is accessed in order to read or write the
bit-field; it may even vary for a given bit-field according to the
precise usage.
If you care about controlling the amount of memory that is
accessed, use volatile but do not use bit-fields.
* GCC comes with shell scripts to fix certain known problems in
system header files. They install corrected copies of various
header files in a special directory where only GCC will normally
look for them. The scripts adapt to various systems by searching
all the system header files for the problem cases that we know
about.
If new system header files are installed, nothing automatically
arranges to update the corrected header files. They can be
updated using the `mkheaders' script installed in
`LIBEXECDIR/gcc/TARGET/VERSION/install-tools/'.
* On 68000 and x86 systems, for instance, you can get paradoxical
results if you test the precise values of floating point numbers.
For example, you can find that a floating point value which is not
a NaN is not equal to itself. This results from the fact that the
floating point registers hold a few more bits of precision than
fit in a `double' in memory. Compiled code moves values between
memory and floating point registers at its convenience, and moving
them into memory truncates them.
You can partially avoid this problem by using the `-ffloat-store'
option (*note Optimize Options::).
* On AIX and other platforms without weak symbol support, templates
need to be instantiated explicitly and symbols for static members
of templates will not be generated.
* On AIX, GCC scans object files and library archives for static
constructors and destructors when linking an application before the
linker prunes unreferenced symbols. This is necessary to prevent
the AIX linker from mistakenly assuming that static constructor or
destructor are unused and removing them before the scanning can
occur. All static constructors and destructors found will be
referenced even though the modules in which they occur may not be
used by the program. This may lead to both increased executable
size and unexpected symbol references.
File: gcc.info, Node: C++ Misunderstandings, Next: Protoize Caveats, Prev: Disappointments, Up: Trouble
10.8 Common Misunderstandings with GNU C++
==========================================
C++ is a complex language and an evolving one, and its standard
definition (the ISO C++ standard) was only recently completed. As a
result, your C++ compiler may occasionally surprise you, even when its
behavior is correct. This section discusses some areas that frequently
give rise to questions of this sort.
* Menu:
* Static Definitions:: Static member declarations are not definitions
* Name lookup:: Name lookup, templates, and accessing members of base classes
* Temporaries:: Temporaries may vanish before you expect
* Copy Assignment:: Copy Assignment operators copy virtual bases twice
File: gcc.info, Node: Static Definitions, Next: Name lookup, Up: C++ Misunderstandings
10.8.1 Declare _and_ Define Static Members
------------------------------------------
When a class has static data members, it is not enough to _declare_ the
static member; you must also _define_ it. For example:
class Foo
{
...
void method();
static int bar;
};
This declaration only establishes that the class `Foo' has an `int'
named `Foo::bar', and a member function named `Foo::method'. But you
still need to define _both_ `method' and `bar' elsewhere. According to
the ISO standard, you must supply an initializer in one (and only one)
source file, such as:
int Foo::bar = 0;
Other C++ compilers may not correctly implement the standard behavior.
As a result, when you switch to `g++' from one of these compilers, you
may discover that a program that appeared to work correctly in fact
does not conform to the standard: `g++' reports as undefined symbols
any static data members that lack definitions.
File: gcc.info, Node: Name lookup, Next: Temporaries, Prev: Static Definitions, Up: C++ Misunderstandings
10.8.2 Name lookup, templates, and accessing members of base classes
--------------------------------------------------------------------
The C++ standard prescribes that all names that are not dependent on
template parameters are bound to their present definitions when parsing
a template function or class.(1) Only names that are dependent are
looked up at the point of instantiation. For example, consider
void foo(double);
struct A {
template <typename T>
void f () {
foo (1); // 1
int i = N; // 2
T t;
t.bar(); // 3
foo (t); // 4
}
static const int N;
};
Here, the names `foo' and `N' appear in a context that does not depend
on the type of `T'. The compiler will thus require that they are
defined in the context of use in the template, not only before the
point of instantiation, and will here use `::foo(double)' and `A::N',
respectively. In particular, it will convert the integer value to a
`double' when passing it to `::foo(double)'.
Conversely, `bar' and the call to `foo' in the fourth marked line are
used in contexts that do depend on the type of `T', so they are only
looked up at the point of instantiation, and you can provide
declarations for them after declaring the template, but before
instantiating it. In particular, if you instantiate `A::f<int>', the
last line will call an overloaded `::foo(int)' if one was provided,
even if after the declaration of `struct A'.
This distinction between lookup of dependent and non-dependent names is
called two-stage (or dependent) name lookup. G++ implements it since
version 3.4.
Two-stage name lookup sometimes leads to situations with behavior
different from non-template codes. The most common is probably this:
template <typename T> struct Base {
int i;
};
template <typename T> struct Derived : public Base<T> {
int get_i() { return i; }
};
In `get_i()', `i' is not used in a dependent context, so the compiler
will look for a name declared at the enclosing namespace scope (which
is the global scope here). It will not look into the base class, since
that is dependent and you may declare specializations of `Base' even
after declaring `Derived', so the compiler can't really know what `i'
would refer to. If there is no global variable `i', then you will get
an error message.
In order to make it clear that you want the member of the base class,
you need to defer lookup until instantiation time, at which the base
class is known. For this, you need to access `i' in a dependent
context, by either using `this->i' (remember that `this' is of type
`Derived<T>*', so is obviously dependent), or using `Base<T>::i'.
Alternatively, `Base<T>::i' might be brought into scope by a
`using'-declaration.
Another, similar example involves calling member functions of a base
class:
template <typename T> struct Base {
int f();
};
template <typename T> struct Derived : Base<T> {
int g() { return f(); };
};
Again, the call to `f()' is not dependent on template arguments (there
are no arguments that depend on the type `T', and it is also not
otherwise specified that the call should be in a dependent context).
Thus a global declaration of such a function must be available, since
the one in the base class is not visible until instantiation time. The
compiler will consequently produce the following error message:
x.cc: In member function `int Derived<T>::g()':
x.cc:6: error: there are no arguments to `f' that depend on a template
parameter, so a declaration of `f' must be available
x.cc:6: error: (if you use `-fpermissive', G++ will accept your code, but
allowing the use of an undeclared name is deprecated)
To make the code valid either use `this->f()', or `Base<T>::f()'.
Using the `-fpermissive' flag will also let the compiler accept the
code, by marking all function calls for which no declaration is visible
at the time of definition of the template for later lookup at
instantiation time, as if it were a dependent call. We do not
recommend using `-fpermissive' to work around invalid code, and it will
also only catch cases where functions in base classes are called, not
where variables in base classes are used (as in the example above).
Note that some compilers (including G++ versions prior to 3.4) get
these examples wrong and accept above code without an error. Those
compilers do not implement two-stage name lookup correctly.
---------- Footnotes ----------
(1) The C++ standard just uses the term "dependent" for names that
depend on the type or value of template parameters. This shorter term
will also be used in the rest of this section.
File: gcc.info, Node: Temporaries, Next: Copy Assignment, Prev: Name lookup, Up: C++ Misunderstandings
10.8.3 Temporaries May Vanish Before You Expect
-----------------------------------------------
It is dangerous to use pointers or references to _portions_ of a
temporary object. The compiler may very well delete the object before
you expect it to, leaving a pointer to garbage. The most common place
where this problem crops up is in classes like string classes,
especially ones that define a conversion function to type `char *' or
`const char *'--which is one reason why the standard `string' class
requires you to call the `c_str' member function. However, any class
that returns a pointer to some internal structure is potentially
subject to this problem.
For example, a program may use a function `strfunc' that returns
`string' objects, and another function `charfunc' that operates on
pointers to `char':
string strfunc ();
void charfunc (const char *);
void
f ()
{
const char *p = strfunc().c_str();
...
charfunc (p);
...
charfunc (p);
}
In this situation, it may seem reasonable to save a pointer to the C
string returned by the `c_str' member function and use that rather than
call `c_str' repeatedly. However, the temporary string created by the
call to `strfunc' is destroyed after `p' is initialized, at which point
`p' is left pointing to freed memory.
Code like this may run successfully under some other compilers,
particularly obsolete cfront-based compilers that delete temporaries
along with normal local variables. However, the GNU C++ behavior is
standard-conforming, so if your program depends on late destruction of
temporaries it is not portable.
The safe way to write such code is to give the temporary a name, which
forces it to remain until the end of the scope of the name. For
example:
const string& tmp = strfunc ();
charfunc (tmp.c_str ());
File: gcc.info, Node: Copy Assignment, Prev: Temporaries, Up: C++ Misunderstandings
10.8.4 Implicit Copy-Assignment for Virtual Bases
-------------------------------------------------
When a base class is virtual, only one subobject of the base class
belongs to each full object. Also, the constructors and destructors are
invoked only once, and called from the most-derived class. However,
such objects behave unspecified when being assigned. For example:
struct Base{
char *name;
Base(char *n) : name(strdup(n)){}
Base& operator= (const Base& other){
free (name);
name = strdup (other.name);
}
};
struct A:virtual Base{
int val;
A():Base("A"){}
};
struct B:virtual Base{
int bval;
B():Base("B"){}
};
struct Derived:public A, public B{
Derived():Base("Derived"){}
};
void func(Derived &d1, Derived &d2)
{
d1 = d2;
}
The C++ standard specifies that `Base::Base' is only called once when
constructing or copy-constructing a Derived object. It is unspecified
whether `Base::operator=' is called more than once when the implicit
copy-assignment for Derived objects is invoked (as it is inside `func'
in the example).
G++ implements the "intuitive" algorithm for copy-assignment: assign
all direct bases, then assign all members. In that algorithm, the
virtual base subobject can be encountered more than once. In the
example, copying proceeds in the following order: `val', `name' (via
`strdup'), `bval', and `name' again.
If application code relies on copy-assignment, a user-defined
copy-assignment operator removes any uncertainties. With such an
operator, the application can define whether and how the virtual base
subobject is assigned.
File: gcc.info, Node: Protoize Caveats, Next: Non-bugs, Prev: C++ Misunderstandings, Up: Trouble
10.9 Caveats of using `protoize'
================================
The conversion programs `protoize' and `unprotoize' can sometimes
change a source file in a way that won't work unless you rearrange it.
* `protoize' can insert references to a type name or type tag before
the definition, or in a file where they are not defined.
If this happens, compiler error messages should show you where the
new references are, so fixing the file by hand is straightforward.
* There are some C constructs which `protoize' cannot figure out.
For example, it can't determine argument types for declaring a
pointer-to-function variable; this you must do by hand. `protoize'
inserts a comment containing `???' each time it finds such a
variable; so you can find all such variables by searching for this
string. ISO C does not require declaring the argument types of
pointer-to-function types.
* Using `unprotoize' can easily introduce bugs. If the program
relied on prototypes to bring about conversion of arguments, these
conversions will not take place in the program without prototypes.
One case in which you can be sure `unprotoize' is safe is when you
are removing prototypes that were made with `protoize'; if the
program worked before without any prototypes, it will work again
without them.
You can find all the places where this problem might occur by
compiling the program with the `-Wconversion' option. It prints a
warning whenever an argument is converted.
* Both conversion programs can be confused if there are macro calls
in and around the text to be converted. In other words, the
standard syntax for a declaration or definition must not result
from expanding a macro. This problem is inherent in the design of
C and cannot be fixed. If only a few functions have confusing
macro calls, you can easily convert them manually.
* `protoize' cannot get the argument types for a function whose
definition was not actually compiled due to preprocessing
conditionals. When this happens, `protoize' changes nothing in
regard to such a function. `protoize' tries to detect such
instances and warn about them.
You can generally work around this problem by using `protoize' step
by step, each time specifying a different set of `-D' options for
compilation, until all of the functions have been converted.
There is no automatic way to verify that you have got them all,
however.
* Confusion may result if there is an occasion to convert a function
declaration or definition in a region of source code where there
is more than one formal parameter list present. Thus, attempts to
convert code containing multiple (conditionally compiled) versions
of a single function header (in the same vicinity) may not produce
the desired (or expected) results.
If you plan on converting source files which contain such code, it
is recommended that you first make sure that each conditionally
compiled region of source code which contains an alternative
function header also contains at least one additional follower
token (past the final right parenthesis of the function header).
This should circumvent the problem.
* `unprotoize' can become confused when trying to convert a function
definition or declaration which contains a declaration for a
pointer-to-function formal argument which has the same name as the
function being defined or declared. We recommend you avoid such
choices of formal parameter names.
* You might also want to correct some of the indentation by hand and
break long lines. (The conversion programs don't write lines
longer than eighty characters in any case.)
File: gcc.info, Node: Non-bugs, Next: Warnings and Errors, Prev: Protoize Caveats, Up: Trouble
10.10 Certain Changes We Don't Want to Make
===========================================
This section lists changes that people frequently request, but which we
do not make because we think GCC is better without them.
* Checking the number and type of arguments to a function which has
an old-fashioned definition and no prototype.
Such a feature would work only occasionally--only for calls that
appear in the same file as the called function, following the
definition. The only way to check all calls reliably is to add a
prototype for the function. But adding a prototype eliminates the
motivation for this feature. So the feature is not worthwhile.
* Warning about using an expression whose type is signed as a shift
count.
Shift count operands are probably signed more often than unsigned.
Warning about this would cause far more annoyance than good.
* Warning about assigning a signed value to an unsigned variable.
Such assignments must be very common; warning about them would
cause more annoyance than good.
* Warning when a non-void function value is ignored.
C contains many standard functions that return a value that most
programs choose to ignore. One obvious example is `printf'.
Warning about this practice only leads the defensive programmer to
clutter programs with dozens of casts to `void'. Such casts are
required so frequently that they become visual noise. Writing
those casts becomes so automatic that they no longer convey useful
information about the intentions of the programmer. For functions
where the return value should never be ignored, use the
`warn_unused_result' function attribute (*note Function
Attributes::).
* Making `-fshort-enums' the default.
This would cause storage layout to be incompatible with most other
C compilers. And it doesn't seem very important, given that you
can get the same result in other ways. The case where it matters
most is when the enumeration-valued object is inside a structure,
and in that case you can specify a field width explicitly.
* Making bit-fields unsigned by default on particular machines where
"the ABI standard" says to do so.
The ISO C standard leaves it up to the implementation whether a
bit-field declared plain `int' is signed or not. This in effect
creates two alternative dialects of C.
The GNU C compiler supports both dialects; you can specify the
signed dialect with `-fsigned-bitfields' and the unsigned dialect
with `-funsigned-bitfields'. However, this leaves open the
question of which dialect to use by default.
Currently, the preferred dialect makes plain bit-fields signed,
because this is simplest. Since `int' is the same as `signed int'
in every other context, it is cleanest for them to be the same in
bit-fields as well.
Some computer manufacturers have published Application Binary
Interface standards which specify that plain bit-fields should be
unsigned. It is a mistake, however, to say anything about this
issue in an ABI. This is because the handling of plain bit-fields
distinguishes two dialects of C. Both dialects are meaningful on
every type of machine. Whether a particular object file was
compiled using signed bit-fields or unsigned is of no concern to
other object files, even if they access the same bit-fields in the
same data structures.
A given program is written in one or the other of these two
dialects. The program stands a chance to work on most any machine
if it is compiled with the proper dialect. It is unlikely to work
at all if compiled with the wrong dialect.
Many users appreciate the GNU C compiler because it provides an
environment that is uniform across machines. These users would be
inconvenienced if the compiler treated plain bit-fields
differently on certain machines.
Occasionally users write programs intended only for a particular
machine type. On these occasions, the users would benefit if the
GNU C compiler were to support by default the same dialect as the
other compilers on that machine. But such applications are rare.
And users writing a program to run on more than one type of
machine cannot possibly benefit from this kind of compatibility.
This is why GCC does and will treat plain bit-fields in the same
fashion on all types of machines (by default).
There are some arguments for making bit-fields unsigned by default
on all machines. If, for example, this becomes a universal de
facto standard, it would make sense for GCC to go along with it.
This is something to be considered in the future.
(Of course, users strongly concerned about portability should
indicate explicitly in each bit-field whether it is signed or not.
In this way, they write programs which have the same meaning in
both C dialects.)
* Undefining `__STDC__' when `-ansi' is not used.
Currently, GCC defines `__STDC__' unconditionally. This provides
good results in practice.
Programmers normally use conditionals on `__STDC__' to ask whether
it is safe to use certain features of ISO C, such as function
prototypes or ISO token concatenation. Since plain `gcc' supports
all the features of ISO C, the correct answer to these questions is
"yes".
Some users try to use `__STDC__' to check for the availability of
certain library facilities. This is actually incorrect usage in
an ISO C program, because the ISO C standard says that a conforming
freestanding implementation should define `__STDC__' even though it
does not have the library facilities. `gcc -ansi -pedantic' is a
conforming freestanding implementation, and it is therefore
required to define `__STDC__', even though it does not come with
an ISO C library.
Sometimes people say that defining `__STDC__' in a compiler that
does not completely conform to the ISO C standard somehow violates
the standard. This is illogical. The standard is a standard for
compilers that claim to support ISO C, such as `gcc -ansi'--not
for other compilers such as plain `gcc'. Whatever the ISO C
standard says is relevant to the design of plain `gcc' without
`-ansi' only for pragmatic reasons, not as a requirement.
GCC normally defines `__STDC__' to be 1, and in addition defines
`__STRICT_ANSI__' if you specify the `-ansi' option, or a `-std'
option for strict conformance to some version of ISO C. On some
hosts, system include files use a different convention, where
`__STDC__' is normally 0, but is 1 if the user specifies strict
conformance to the C Standard. GCC follows the host convention
when processing system include files, but when processing user
files it follows the usual GNU C convention.
* Undefining `__STDC__' in C++.
Programs written to compile with C++-to-C translators get the
value of `__STDC__' that goes with the C compiler that is
subsequently used. These programs must test `__STDC__' to
determine what kind of C preprocessor that compiler uses: whether
they should concatenate tokens in the ISO C fashion or in the
traditional fashion.
These programs work properly with GNU C++ if `__STDC__' is defined.
They would not work otherwise.
In addition, many header files are written to provide prototypes
in ISO C but not in traditional C. Many of these header files can
work without change in C++ provided `__STDC__' is defined. If
`__STDC__' is not defined, they will all fail, and will all need
to be changed to test explicitly for C++ as well.
* Deleting "empty" loops.
Historically, GCC has not deleted "empty" loops under the
assumption that the most likely reason you would put one in a
program is to have a delay, so deleting them will not make real
programs run any faster.
However, the rationale here is that optimization of a nonempty loop
cannot produce an empty one. This held for carefully written C
compiled with less powerful optimizers but is not always the case
for carefully written C++ or with more powerful optimizers. Thus
GCC will remove operations from loops whenever it can determine
those operations are not externally visible (apart from the time
taken to execute them, of course). In case the loop can be proved
to be finite, GCC will also remove the loop itself.
Be aware of this when performing timing tests, for instance the
following loop can be completely removed, provided
`some_expression' can provably not change any global state.
{
int sum = 0;
int ix;
for (ix = 0; ix != 10000; ix++)
sum += some_expression;
}
Even though `sum' is accumulated in the loop, no use is made of
that summation, so the accumulation can be removed.
* Making side effects happen in the same order as in some other
compiler.
It is never safe to depend on the order of evaluation of side
effects. For example, a function call like this may very well
behave differently from one compiler to another:
void func (int, int);
int i = 2;
func (i++, i++);
There is no guarantee (in either the C or the C++ standard language
definitions) that the increments will be evaluated in any
particular order. Either increment might happen first. `func'
might get the arguments `2, 3', or it might get `3, 2', or even
`2, 2'.
* Making certain warnings into errors by default.
Some ISO C testsuites report failure when the compiler does not
produce an error message for a certain program.
ISO C requires a "diagnostic" message for certain kinds of invalid
programs, but a warning is defined by GCC to count as a
diagnostic. If GCC produces a warning but not an error, that is
correct ISO C support. If testsuites call this "failure", they
should be run with the GCC option `-pedantic-errors', which will
turn these warnings into errors.
File: gcc.info, Node: Warnings and Errors, Prev: Non-bugs, Up: Trouble
10.11 Warning Messages and Error Messages
=========================================
The GNU compiler can produce two kinds of diagnostics: errors and
warnings. Each kind has a different purpose:
"Errors" report problems that make it impossible to compile your
program. GCC reports errors with the source file name and line
number where the problem is apparent.
"Warnings" report other unusual conditions in your code that _may_
indicate a problem, although compilation can (and does) proceed.
Warning messages also report the source file name and line number,
but include the text `warning:' to distinguish them from error
messages.
Warnings may indicate danger points where you should check to make sure
that your program really does what you intend; or the use of obsolete
features; or the use of nonstandard features of GNU C or C++. Many
warnings are issued only if you ask for them, with one of the `-W'
options (for instance, `-Wall' requests a variety of useful warnings).
GCC always tries to compile your program if possible; it never
gratuitously rejects a program whose meaning is clear merely because
(for instance) it fails to conform to a standard. In some cases,
however, the C and C++ standards specify that certain extensions are
forbidden, and a diagnostic _must_ be issued by a conforming compiler.
The `-pedantic' option tells GCC to issue warnings in such cases;
`-pedantic-errors' says to make them errors instead. This does not
mean that _all_ non-ISO constructs get warnings or errors.
*Note Options to Request or Suppress Warnings: Warning Options, for
more detail on these and related command-line options.
File: gcc.info, Node: Bugs, Next: Service, Prev: Trouble, Up: Top
11 Reporting Bugs
*****************
Your bug reports play an essential role in making GCC reliable.
When you encounter a problem, the first thing to do is to see if it is
already known. *Note Trouble::. If it isn't known, then you should
report the problem.
* Menu:
* Criteria: Bug Criteria. Have you really found a bug?
* Reporting: Bug Reporting. How to report a bug effectively.
* Known: Trouble. Known problems.
* Help: Service. Where to ask for help.
File: gcc.info, Node: Bug Criteria, Next: Bug Reporting, Up: Bugs
11.1 Have You Found a Bug?
==========================
If you are not sure whether you have found a bug, here are some
guidelines:
* If the compiler gets a fatal signal, for any input whatever, that
is a compiler bug. Reliable compilers never crash.
* If the compiler produces invalid assembly code, for any input
whatever (except an `asm' statement), that is a compiler bug,
unless the compiler reports errors (not just warnings) which would
ordinarily prevent the assembler from being run.
* If the compiler produces valid assembly code that does not
correctly execute the input source code, that is a compiler bug.
However, you must double-check to make sure, because you may have a
program whose behavior is undefined, which happened by chance to
give the desired results with another C or C++ compiler.
For example, in many nonoptimizing compilers, you can write `x;'
at the end of a function instead of `return x;', with the same
results. But the value of the function is undefined if `return'
is omitted; it is not a bug when GCC produces different results.
Problems often result from expressions with two increment
operators, as in `f (*p++, *p++)'. Your previous compiler might
have interpreted that expression the way you intended; GCC might
interpret it another way. Neither compiler is wrong. The bug is
in your code.
After you have localized the error to a single source line, it
should be easy to check for these things. If your program is
correct and well defined, you have found a compiler bug.
* If the compiler produces an error message for valid input, that is
a compiler bug.
* If the compiler does not produce an error message for invalid
input, that is a compiler bug. However, you should note that your
idea of "invalid input" might be someone else's idea of "an
extension" or "support for traditional practice".
* If you are an experienced user of one of the languages GCC
supports, your suggestions for improvement of GCC are welcome in
any case.
File: gcc.info, Node: Bug Reporting, Prev: Bug Criteria, Up: Bugs
11.2 How and where to Report Bugs
=================================
Bugs should be reported to the GCC bug database. Please refer to
`http://gcc.gnu.org/bugs.html' for up-to-date instructions how to
submit bug reports. Copies of this file in HTML (`bugs.html') and
plain text (`BUGS') are also part of GCC releases.
File: gcc.info, Node: Service, Next: Contributing, Prev: Bugs, Up: Top
12 How To Get Help with GCC
***************************
If you need help installing, using or changing GCC, there are two ways
to find it:
* Send a message to a suitable network mailing list. First try
<gcc-help@gcc.gnu.org> (for help installing or using GCC), and if
that brings no response, try <gcc@gcc.gnu.org>. For help changing
GCC, ask <gcc@gcc.gnu.org>. If you think you have found a bug in
GCC, please report it following the instructions at *note Bug
Reporting::.
* Look in the service directory for someone who might help you for a
fee. The service directory is found at
`http://www.gnu.org/prep/service.html'.
For further information, see `http://gcc.gnu.org/faq.html#support'.
File: gcc.info, Node: Contributing, Next: Funding, Prev: Service, Up: Top
13 Contributing to GCC Development
**********************************
If you would like to help pretest GCC releases to assure they work well,
current development sources are available by SVN (see
`http://gcc.gnu.org/svn.html'). Source and binary snapshots are also
available for FTP; see `http://gcc.gnu.org/snapshots.html'.
If you would like to work on improvements to GCC, please read the
advice at these URLs:
`http://gcc.gnu.org/contribute.html'
`http://gcc.gnu.org/contributewhy.html'
for information on how to make useful contributions and avoid
duplication of effort. Suggested projects are listed at
`http://gcc.gnu.org/projects/'.
File: gcc.info, Node: Funding, Next: GNU Project, Prev: Contributing, Up: Top
Funding Free Software
*********************
If you want to have more free software a few years from now, it makes
sense for you to help encourage people to contribute funds for its
development. The most effective approach known is to encourage
commercial redistributors to donate.
Users of free software systems can boost the pace of development by
encouraging for-a-fee distributors to donate part of their selling price
to free software developers--the Free Software Foundation, and others.
The way to convince distributors to do this is to demand it and expect
it from them. So when you compare distributors, judge them partly by
how much they give to free software development. Show distributors
they must compete to be the one who gives the most.
To make this approach work, you must insist on numbers that you can
compare, such as, "We will donate ten dollars to the Frobnitz project
for each disk sold." Don't be satisfied with a vague promise, such as
"A portion of the profits are donated," since it doesn't give a basis
for comparison.
Even a precise fraction "of the profits from this disk" is not very
meaningful, since creative accounting and unrelated business decisions
can greatly alter what fraction of the sales price counts as profit.
If the price you pay is $50, ten percent of the profit is probably less
than a dollar; it might be a few cents, or nothing at all.
Some redistributors do development work themselves. This is useful
too; but to keep everyone honest, you need to inquire how much they do,
and what kind. Some kinds of development make much more long-term
difference than others. For example, maintaining a separate version of
a program contributes very little; maintaining the standard version of a
program for the whole community contributes much. Easy new ports
contribute little, since someone else would surely do them; difficult
ports such as adding a new CPU to the GNU Compiler Collection
contribute more; major new features or packages contribute the most.
By establishing the idea that supporting further development is "the
proper thing to do" when distributing free software for a fee, we can
assure a steady flow of resources into making more free software.
Copyright (C) 1994 Free Software Foundation, Inc.
Verbatim copying and redistribution of this section is permitted
without royalty; alteration is not permitted.
File: gcc.info, Node: GNU Project, Next: Copying, Prev: Funding, Up: Top
The GNU Project and GNU/Linux
*****************************
The GNU Project was launched in 1984 to develop a complete Unix-like
operating system which is free software: the GNU system. (GNU is a
recursive acronym for "GNU's Not Unix"; it is pronounced "guh-NEW".)
Variants of the GNU operating system, which use the kernel Linux, are
now widely used; though these systems are often referred to as "Linux",
they are more accurately called GNU/Linux systems.
For more information, see:
`http://www.gnu.org/'
`http://www.gnu.org/gnu/linux-and-gnu.html'
File: gcc.info, Node: Copying, Next: GNU Free Documentation License, Prev: GNU Project, Up: Top
GNU GENERAL PUBLIC LICENSE
**************************
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
Preamble
========
The licenses for most software are designed to take away your freedom
to share and change it. By contrast, the GNU General Public License is
intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users. This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it. (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.) You can apply it to
your programs, too.
When we speak of free software, we are referring to freedom, not
price. Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it in
new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have. You must make sure that they, too, receive or can get the
source code. And you must show them these terms so they know their
rights.
We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software. If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.
Finally, any free program is threatened constantly by software
patents. We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary. To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and
modification follow.
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. This License applies to any program or other work which contains a
notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License. The "Program",
below, refers to any such program or work, and a "work based on
the Program" means either the Program or any derivative work under
copyright law: that is to say, a work containing the Program or a
portion of it, either verbatim or with modifications and/or
translated into another language. (Hereinafter, translation is
included without limitation in the term "modification".) Each
licensee is addressed as "you".
Activities other than copying, distribution and modification are
not covered by this License; they are outside its scope. The act
of running the Program is not restricted, and the output from the
Program is covered only if its contents constitute a work based on
the Program (independent of having been made by running the
Program). Whether that is true depends on what the Program does.
1. You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any
warranty; and give any other recipients of the Program a copy of
this License along with the Program.
You may charge a fee for the physical act of transferring a copy,
and you may at your option offer warranty protection in exchange
for a fee.
2. You may modify your copy or copies of the Program or any portion
of it, thus forming a work based on the Program, and copy and
distribute such modifications or work under the terms of Section 1
above, provided that you also meet all of these conditions:
a. You must cause the modified files to carry prominent notices
stating that you changed the files and the date of any change.
b. You must cause any work that you distribute or publish, that
in whole or in part contains or is derived from the Program
or any part thereof, to be licensed as a whole at no charge
to all third parties under the terms of this License.
c. If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
interactive use in the most ordinary way, to print or display
an announcement including an appropriate copyright notice and
a notice that there is no warranty (or else, saying that you
provide a warranty) and that users may redistribute the
program under these conditions, and telling the user how to
view a copy of this License. (Exception: if the Program
itself is interactive but does not normally print such an
announcement, your work based on the Program is not required
to print an announcement.)
These requirements apply to the modified work as a whole. If
identifiable sections of that work are not derived from the
Program, and can be reasonably considered independent and separate
works in themselves, then this License, and its terms, do not
apply to those sections when you distribute them as separate
works. But when you distribute the same sections as part of a
whole which is a work based on the Program, the distribution of
the whole must be on the terms of this License, whose permissions
for other licensees extend to the entire whole, and thus to each
and every part regardless of who wrote it.
Thus, it is not the intent of this section to claim rights or
contest your rights to work written entirely by you; rather, the
intent is to exercise the right to control the distribution of
derivative or collective works based on the Program.
In addition, mere aggregation of another work not based on the
Program with the Program (or with a work based on the Program) on
a volume of a storage or distribution medium does not bring the
other work under the scope of this License.
3. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms
of Sections 1 and 2 above provided that you also do one of the
following:
a. Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of
Sections 1 and 2 above on a medium customarily used for
software interchange; or,
b. Accompany it with a written offer, valid for at least three
years, to give any third party, for a charge no more than your
cost of physically performing source distribution, a complete
machine-readable copy of the corresponding source code, to be
distributed under the terms of Sections 1 and 2 above on a
medium customarily used for software interchange; or,
c. Accompany it with the information you received as to the offer
to distribute corresponding source code. (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form with
such an offer, in accord with Subsection b above.)
The source code for a work means the preferred form of the work for
making modifications to it. For an executable work, complete
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However, as a special exception, the source code distributed need
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If distribution of executable or object code is made by offering
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access to copy the source code from the same place counts as
distribution of the source code, even though third parties are not
compelled to copy the source along with the object code.
4. You may not copy, modify, sublicense, or distribute the Program
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense or distribute the Program is
void, and will automatically terminate your rights under this
License. However, parties who have received copies, or rights,
from you under this License will not have their licenses
terminated so long as such parties remain in full compliance.
5. You are not required to accept this License, since you have not
signed it. However, nothing else grants you permission to modify
or distribute the Program or its derivative works. These actions
are prohibited by law if you do not accept this License.
Therefore, by modifying or distributing the Program (or any work
based on the Program), you indicate your acceptance of this
License to do so, and all its terms and conditions for copying,
distributing or modifying the Program or works based on it.
6. Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program
subject to these terms and conditions. You may not impose any
further restrictions on the recipients' exercise of the rights
granted herein. You are not responsible for enforcing compliance
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7. If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent
issues), conditions are imposed on you (whether by court order,
agreement or otherwise) that contradict the conditions of this
License, they do not excuse you from the conditions of this
License. If you cannot distribute so as to satisfy simultaneously
your obligations under this License and any other pertinent
obligations, then as a consequence you may not distribute the
Program at all. For example, if a patent license would not permit
royalty-free redistribution of the Program by all those who
receive copies directly or indirectly through you, then the only
way you could satisfy both it and this License would be to refrain
entirely from distribution of the Program.
If any portion of this section is held invalid or unenforceable
under any particular circumstance, the balance of the section is
intended to apply and the section as a whole is intended to apply
in other circumstances.
It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of
any such claims; this section has the sole purpose of protecting
the integrity of the free software distribution system, which is
implemented by public license practices. Many people have made
generous contributions to the wide range of software distributed
through that system in reliance on consistent application of that
system; it is up to the author/donor to decide if he or she is
willing to distribute software through any other system and a
licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed
to be a consequence of the rest of this License.
8. If the distribution and/or use of the Program is restricted in
certain countries either by patents or by copyrighted interfaces,
the original copyright holder who places the Program under this
License may add an explicit geographical distribution limitation
excluding those countries, so that distribution is permitted only
in or among countries not thus excluded. In such case, this
License incorporates the limitation as if written in the body of
this License.
9. The Free Software Foundation may publish revised and/or new
versions of the General Public License from time to time. Such
new versions will be similar in spirit to the present version, but
may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the
Program specifies a version number of this License which applies
to it and "any later version", you have the option of following
the terms and conditions either of that version or of any later
version published by the Free Software Foundation. If the Program
does not specify a version number of this License, you may choose
any version ever published by the Free Software Foundation.
10. If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the
author to ask for permission. For software which is copyrighted
by the Free Software Foundation, write to the Free Software
Foundation; we sometimes make exceptions for this. Our decision
will be guided by the two goals of preserving the free status of
all derivatives of our free software and of promoting the sharing
and reuse of software generally.
NO WARRANTY
11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE
QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
SERVICING, REPAIR OR CORRECTION.
12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
END OF TERMS AND CONDITIONS
Appendix: How to Apply These Terms to Your New Programs
=======================================================
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
Copyright (C) YEAR NAME OF AUTHOR
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
Also add information on how to contact you by electronic and paper
mail.
If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) YEAR NAME OF AUTHOR
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License. Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program
`Gnomovision' (which makes passes at compilers) written by James Hacker.
SIGNATURE OF TY COON, 1 April 1989
Ty Coon, President of Vice
This General Public License does not permit incorporating your program
into proprietary programs. If your program is a subroutine library,
you may consider it more useful to permit linking proprietary
applications with the library. If this is what you want to do, use the
GNU Library General Public License instead of this License.
File: gcc.info, Node: GNU Free Documentation License, Next: Contributors, Prev: Copying, Up: Top
GNU Free Documentation License
******************************
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
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of subject matter or whether it is published as a printed book.
We recommend this License principally for works whose purpose is
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1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
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A section "Entitled XYZ" means a named subunit of the Document
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To "Preserve the Title" of such a section when you modify the
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The Document may include Warranty Disclaimers next to the notice
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2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
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You may also lend copies, under the same conditions stated above,
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3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly
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If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
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If you publish or distribute Opaque copies of the Document
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It is requested, but not required, that you contact the authors of
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4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
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A. Use in the Title Page (and on the covers, if any) a title
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that version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
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from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
the Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
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File: gcc.info, Node: Contributors, Next: Option Index, Prev: GNU Free Documentation License, Up: Top
Contributors to GCC
*******************
The GCC project would like to thank its many contributors. Without
them the project would not have been nearly as successful as it has
been. Any omissions in this list are accidental. Feel free to contact
<law@redhat.com> or <gerald@pfeifer.com> if you have been left out or
some of your contributions are not listed. Please keep this list in
alphabetical order.
* Analog Devices helped implement the support for complex data types
and iterators.
* John David Anglin for threading-related fixes and improvements to
libstdc++-v3, and the HP-UX port.
* James van Artsdalen wrote the code that makes efficient use of the
Intel 80387 register stack.
* Abramo and Roberto Bagnara for the SysV68 Motorola 3300 Delta
Series port.
* Alasdair Baird for various bug fixes.
* Giovanni Bajo for analyzing lots of complicated C++ problem
reports.
* Peter Barada for his work to improve code generation for new
ColdFire cores.
* Gerald Baumgartner added the signature extension to the C++ front
end.
* Godmar Back for his Java improvements and encouragement.
* Scott Bambrough for help porting the Java compiler.
* Wolfgang Bangerth for processing tons of bug reports.
* Jon Beniston for his Microsoft Windows port of Java.
* Daniel Berlin for better DWARF2 support, faster/better
optimizations, improved alias analysis, plus migrating GCC to
Bugzilla.
* Geoff Berry for his Java object serialization work and various
patches.
* Uros Bizjak for the implementation of x87 math built-in functions
and for various middle end and i386 back end improvements and
bugfixes.
* Eric Blake for helping to make GCJ and libgcj conform to the
specifications.
* Janne Blomqvist for contributions to GNU Fortran.
* Segher Boessenkool for various fixes.
* Hans-J. Boehm for his garbage collector, IA-64 libffi port, and
other Java work.
* Neil Booth for work on cpplib, lang hooks, debug hooks and other
miscellaneous clean-ups.
* Steven Bosscher for integrating the GNU Fortran front end into GCC
and for contributing to the tree-ssa branch.
* Eric Botcazou for fixing middle- and backend bugs left and right.
* Per Bothner for his direction via the steering committee and
various improvements to the infrastructure for supporting new
languages. Chill front end implementation. Initial
implementations of cpplib, fix-header, config.guess, libio, and
past C++ library (libg++) maintainer. Dreaming up, designing and
implementing much of GCJ.
* Devon Bowen helped port GCC to the Tahoe.
* Don Bowman for mips-vxworks contributions.
* Dave Brolley for work on cpplib and Chill.
* Paul Brook for work on the ARM architecture and maintaining GNU
Fortran.
* Robert Brown implemented the support for Encore 32000 systems.
* Christian Bruel for improvements to local store elimination.
* Herman A.J. ten Brugge for various fixes.
* Joerg Brunsmann for Java compiler hacking and help with the GCJ
FAQ.
* Joe Buck for his direction via the steering committee.
* Craig Burley for leadership of the G77 Fortran effort.
* Stephan Buys for contributing Doxygen notes for libstdc++.
* Paolo Carlini for libstdc++ work: lots of efficiency improvements
to the C++ strings, streambufs and formatted I/O, hard detective
work on the frustrating localization issues, and keeping up with
the problem reports.
* John Carr for his alias work, SPARC hacking, infrastructure
improvements, previous contributions to the steering committee,
loop optimizations, etc.
* Stephane Carrez for 68HC11 and 68HC12 ports.
* Steve Chamberlain for support for the Renesas SH and H8 processors
and the PicoJava processor, and for GCJ config fixes.
* Glenn Chambers for help with the GCJ FAQ.
* John-Marc Chandonia for various libgcj patches.
* Scott Christley for his Objective-C contributions.
* Eric Christopher for his Java porting help and clean-ups.
* Branko Cibej for more warning contributions.
* The GNU Classpath project for all of their merged runtime code.
* Nick Clifton for arm, mcore, fr30, v850, m32r work, `--help', and
other random hacking.
* Michael Cook for libstdc++ cleanup patches to reduce warnings.
* R. Kelley Cook for making GCC buildable from a read-only directory
as well as other miscellaneous build process and documentation
clean-ups.
* Ralf Corsepius for SH testing and minor bugfixing.
* Stan Cox for care and feeding of the x86 port and lots of behind
the scenes hacking.
* Alex Crain provided changes for the 3b1.
* Ian Dall for major improvements to the NS32k port.
* Paul Dale for his work to add uClinux platform support to the m68k
backend.
* Dario Dariol contributed the four varieties of sample programs
that print a copy of their source.
* Russell Davidson for fstream and stringstream fixes in libstdc++.
* Bud Davis for work on the G77 and GNU Fortran compilers.
* Mo DeJong for GCJ and libgcj bug fixes.
* DJ Delorie for the DJGPP port, build and libiberty maintenance,
various bug fixes, and the M32C port.
* Arnaud Desitter for helping to debug GNU Fortran.
* Gabriel Dos Reis for contributions to G++, contributions and
maintenance of GCC diagnostics infrastructure, libstdc++-v3,
including `valarray<>', `complex<>', maintaining the numerics
library (including that pesky `<limits>' :-) and keeping
up-to-date anything to do with numbers.
* Ulrich Drepper for his work on glibc, testing of GCC using glibc,
ISO C99 support, CFG dumping support, etc., plus support of the
C++ runtime libraries including for all kinds of C interface
issues, contributing and maintaining `complex<>', sanity checking
and disbursement, configuration architecture, libio maintenance,
and early math work.
* Zdenek Dvorak for a new loop unroller and various fixes.
* Richard Earnshaw for his ongoing work with the ARM.
* David Edelsohn for his direction via the steering committee,
ongoing work with the RS6000/PowerPC port, help cleaning up Haifa
loop changes, doing the entire AIX port of libstdc++ with his bare
hands, and for ensuring GCC properly keeps working on AIX.
* Kevin Ediger for the floating point formatting of num_put::do_put
in libstdc++.
* Phil Edwards for libstdc++ work including configuration hackery,
documentation maintainer, chief breaker of the web pages, the
occasional iostream bug fix, and work on shared library symbol
versioning.
* Paul Eggert for random hacking all over GCC.
* Mark Elbrecht for various DJGPP improvements, and for libstdc++
configuration support for locales and fstream-related fixes.
* Vadim Egorov for libstdc++ fixes in strings, streambufs, and
iostreams.
* Christian Ehrhardt for dealing with bug reports.
* Ben Elliston for his work to move the Objective-C runtime into its
own subdirectory and for his work on autoconf.
* Marc Espie for OpenBSD support.
* Doug Evans for much of the global optimization framework, arc,
m32r, and SPARC work.
* Christopher Faylor for his work on the Cygwin port and for caring
and feeding the gcc.gnu.org box and saving its users tons of spam.
* Fred Fish for BeOS support and Ada fixes.
* Ivan Fontes Garcia for the Portuguese translation of the GCJ FAQ.
* Peter Gerwinski for various bug fixes and the Pascal front end.
* Kaveh R. Ghazi for his direction via the steering committee,
amazing work to make `-W -Wall -W* -Werror' useful, and
continuously testing GCC on a plethora of platforms. Kaveh
extends his gratitude to the CAIP Center at Rutgers University for
providing him with computing resources to work on Free Software
since the late 1980s.
* John Gilmore for a donation to the FSF earmarked improving GNU
Java.
* Judy Goldberg for c++ contributions.
* Torbjorn Granlund for various fixes and the c-torture testsuite,
multiply- and divide-by-constant optimization, improved long long
support, improved leaf function register allocation, and his
direction via the steering committee.
* Anthony Green for his `-Os' contributions and Java front end work.
* Stu Grossman for gdb hacking, allowing GCJ developers to debug
Java code.
* Michael K. Gschwind contributed the port to the PDP-11.
* Ron Guilmette implemented the `protoize' and `unprotoize' tools,
the support for Dwarf symbolic debugging information, and much of
the support for System V Release 4. He has also worked heavily on
the Intel 386 and 860 support.
* Mostafa Hagog for Swing Modulo Scheduling (SMS) and post reload
GCSE.
* Bruno Haible for improvements in the runtime overhead for EH, new
warnings and assorted bug fixes.
* Andrew Haley for his amazing Java compiler and library efforts.
* Chris Hanson assisted in making GCC work on HP-UX for the 9000
series 300.
* Michael Hayes for various thankless work he's done trying to get
the c30/c40 ports functional. Lots of loop and unroll
improvements and fixes.
* Dara Hazeghi for wading through myriads of target-specific bug
reports.
* Kate Hedstrom for staking the G77 folks with an initial testsuite.
* Richard Henderson for his ongoing SPARC, alpha, ia32, and ia64
work, loop opts, and generally fixing lots of old problems we've
ignored for years, flow rewrite and lots of further stuff,
including reviewing tons of patches.
* Aldy Hernandez for working on the PowerPC port, SIMD support, and
various fixes.
* Nobuyuki Hikichi of Software Research Associates, Tokyo,
contributed the support for the Sony NEWS machine.
* Kazu Hirata for caring and feeding the Renesas H8/300 port and
various fixes.
* Katherine Holcomb for work on GNU Fortran.
* Manfred Hollstein for his ongoing work to keep the m88k alive, lots
of testing and bug fixing, particularly of GCC configury code.
* Steve Holmgren for MachTen patches.
* Jan Hubicka for his x86 port improvements.
* Falk Hueffner for working on C and optimization bug reports.
* Bernardo Innocenti for his m68k work, including merging of
ColdFire improvements and uClinux support.
* Christian Iseli for various bug fixes.
* Kamil Iskra for general m68k hacking.
* Lee Iverson for random fixes and MIPS testing.
* Andreas Jaeger for testing and benchmarking of GCC and various bug
fixes.
* Jakub Jelinek for his SPARC work and sibling call optimizations as
well as lots of bug fixes and test cases, and for improving the
Java build system.
* Janis Johnson for ia64 testing and fixes, her quality improvement
sidetracks, and web page maintenance.
* Kean Johnston for SCO OpenServer support and various fixes.
* Tim Josling for the sample language treelang based originally on
Richard Kenner's "toy" language.
* Nicolai Josuttis for additional libstdc++ documentation.
* Klaus Kaempf for his ongoing work to make alpha-vms a viable
target.
* Steven G. Kargl for work on GNU Fortran.
* David Kashtan of SRI adapted GCC to VMS.
* Ryszard Kabatek for many, many libstdc++ bug fixes and
optimizations of strings, especially member functions, and for
auto_ptr fixes.
* Geoffrey Keating for his ongoing work to make the PPC work for
GNU/Linux and his automatic regression tester.
* Brendan Kehoe for his ongoing work with G++ and for a lot of early
work in just about every part of libstdc++.
* Oliver M. Kellogg of Deutsche Aerospace contributed the port to the
MIL-STD-1750A.
* Richard Kenner of the New York University Ultracomputer Research
Laboratory wrote the machine descriptions for the AMD 29000, the
DEC Alpha, the IBM RT PC, and the IBM RS/6000 as well as the
support for instruction attributes. He also made changes to
better support RISC processors including changes to common
subexpression elimination, strength reduction, function calling
sequence handling, and condition code support, in addition to
generalizing the code for frame pointer elimination and delay slot
scheduling. Richard Kenner was also the head maintainer of GCC
for several years.
* Mumit Khan for various contributions to the Cygwin and Mingw32
ports and maintaining binary releases for Microsoft Windows hosts,
and for massive libstdc++ porting work to Cygwin/Mingw32.
* Robin Kirkham for cpu32 support.
* Mark Klein for PA improvements.
* Thomas Koenig for various bug fixes.
* Bruce Korb for the new and improved fixincludes code.
* Benjamin Kosnik for his G++ work and for leading the libstdc++-v3
effort.
* Charles LaBrec contributed the support for the Integrated Solutions
68020 system.
* Asher Langton and Mike Kumbera for contributing Cray pointer
support to GNU Fortran, and for other GNU Fortran improvements.
* Jeff Law for his direction via the steering committee,
coordinating the entire egcs project and GCC 2.95, rolling out
snapshots and releases, handling merges from GCC2, reviewing tons
of patches that might have fallen through the cracks else, and
random but extensive hacking.
* Marc Lehmann for his direction via the steering committee and
helping with analysis and improvements of x86 performance.
* Victor Leikehman for work on GNU Fortran.
* Ted Lemon wrote parts of the RTL reader and printer.
* Kriang Lerdsuwanakij for C++ improvements including template as
template parameter support, and many C++ fixes.
* Warren Levy for tremendous work on libgcj (Java Runtime Library)
and random work on the Java front end.
* Alain Lichnewsky ported GCC to the MIPS CPU.
* Oskar Liljeblad for hacking on AWT and his many Java bug reports
and patches.
* Robert Lipe for OpenServer support, new testsuites, testing, etc.
* Weiwen Liu for testing and various bug fixes.
* Dave Love for his ongoing work with the Fortran front end and
runtime libraries.
* Martin von Lo"wis for internal consistency checking infrastructure,
various C++ improvements including namespace support, and tons of
assistance with libstdc++/compiler merges.
* H.J. Lu for his previous contributions to the steering committee,
many x86 bug reports, prototype patches, and keeping the GNU/Linux
ports working.
* Greg McGary for random fixes and (someday) bounded pointers.
* Andrew MacLeod for his ongoing work in building a real EH system,
various code generation improvements, work on the global
optimizer, etc.
* Vladimir Makarov for hacking some ugly i960 problems, PowerPC
hacking improvements to compile-time performance, overall
knowledge and direction in the area of instruction scheduling, and
design and implementation of the automaton based instruction
scheduler.
* Bob Manson for his behind the scenes work on dejagnu.
* Philip Martin for lots of libstdc++ string and vector iterator
fixes and improvements, and string clean up and testsuites.
* All of the Mauve project contributors, for Java test code.
* Bryce McKinlay for numerous GCJ and libgcj fixes and improvements.
* Adam Megacz for his work on the Microsoft Windows port of GCJ.
* Michael Meissner for LRS framework, ia32, m32r, v850, m88k, MIPS,
powerpc, haifa, ECOFF debug support, and other assorted hacking.
* Jason Merrill for his direction via the steering committee and
leading the G++ effort.
* Martin Michlmayr for testing GCC on several architectures using the
entire Debian archive.
* David Miller for his direction via the steering committee, lots of
SPARC work, improvements in jump.c and interfacing with the Linux
kernel developers.
* Gary Miller ported GCC to Charles River Data Systems machines.
* Alfred Minarik for libstdc++ string and ios bug fixes, and turning
the entire libstdc++ testsuite namespace-compatible.
* Mark Mitchell for his direction via the steering committee,
mountains of C++ work, load/store hoisting out of loops, alias
analysis improvements, ISO C `restrict' support, and serving as
release manager for GCC 3.x.
* Alan Modra for various GNU/Linux bits and testing.
* Toon Moene for his direction via the steering committee, Fortran
maintenance, and his ongoing work to make us make Fortran run fast.
* Jason Molenda for major help in the care and feeding of all the
services on the gcc.gnu.org (formerly egcs.cygnus.com)
machine--mail, web services, ftp services, etc etc. Doing all
this work on scrap paper and the backs of envelopes would have
been... difficult.
* Catherine Moore for fixing various ugly problems we have sent her
way, including the haifa bug which was killing the Alpha & PowerPC
Linux kernels.
* Mike Moreton for his various Java patches.
* David Mosberger-Tang for various Alpha improvements, and for the
initial IA-64 port.
* Stephen Moshier contributed the floating point emulator that
assists in cross-compilation and permits support for floating
point numbers wider than 64 bits and for ISO C99 support.
* Bill Moyer for his behind the scenes work on various issues.
* Philippe De Muyter for his work on the m68k port.
* Joseph S. Myers for his work on the PDP-11 port, format checking
and ISO C99 support, and continuous emphasis on (and contributions
to) documentation.
* Nathan Myers for his work on libstdc++-v3: architecture and
authorship through the first three snapshots, including
implementation of locale infrastructure, string, shadow C headers,
and the initial project documentation (DESIGN, CHECKLIST, and so
forth). Later, more work on MT-safe string and shadow headers.
* Felix Natter for documentation on porting libstdc++.
* Nathanael Nerode for cleaning up the configuration/build process.
* NeXT, Inc. donated the front end that supports the Objective-C
language.
* Hans-Peter Nilsson for the CRIS and MMIX ports, improvements to
the search engine setup, various documentation fixes and other
small fixes.
* Geoff Noer for his work on getting cygwin native builds working.
* Diego Novillo for his work on Tree SSA, OpenMP, SPEC performance
tracking web pages and assorted fixes.
* David O'Brien for the FreeBSD/alpha, FreeBSD/AMD x86-64,
FreeBSD/ARM, FreeBSD/PowerPC, and FreeBSD/SPARC64 ports and
related infrastructure improvements.
* Alexandre Oliva for various build infrastructure improvements,
scripts and amazing testing work, including keeping libtool issues
sane and happy.
* Stefan Olsson for work on mt_alloc.
* Melissa O'Neill for various NeXT fixes.
* Rainer Orth for random MIPS work, including improvements to GCC's
o32 ABI support, improvements to dejagnu's MIPS support, Java
configuration clean-ups and porting work, etc.
* Hartmut Penner for work on the s390 port.
* Paul Petersen wrote the machine description for the Alliant FX/8.
* Alexandre Petit-Bianco for implementing much of the Java compiler
and continued Java maintainership.
* Matthias Pfaller for major improvements to the NS32k port.
* Gerald Pfeifer for his direction via the steering committee,
pointing out lots of problems we need to solve, maintenance of the
web pages, and taking care of documentation maintenance in general.
* Andrew Pinski for processing bug reports by the dozen.
* Ovidiu Predescu for his work on the Objective-C front end and
runtime libraries.
* Jerry Quinn for major performance improvements in C++ formatted
I/O.
* Ken Raeburn for various improvements to checker, MIPS ports and
various cleanups in the compiler.
* Rolf W. Rasmussen for hacking on AWT.
* David Reese of Sun Microsystems contributed to the Solaris on
PowerPC port.
* Volker Reichelt for keeping up with the problem reports.
* Joern Rennecke for maintaining the sh port, loop, regmove & reload
hacking.
* Loren J. Rittle for improvements to libstdc++-v3 including the
FreeBSD port, threading fixes, thread-related configury changes,
critical threading documentation, and solutions to really tricky
I/O problems, as well as keeping GCC properly working on FreeBSD
and continuous testing.
* Craig Rodrigues for processing tons of bug reports.
* Ola Ro"nnerup for work on mt_alloc.
* Gavin Romig-Koch for lots of behind the scenes MIPS work.
* David Ronis inspired and encouraged Craig to rewrite the G77
documentation in texinfo format by contributing a first pass at a
translation of the old `g77-0.5.16/f/DOC' file.
* Ken Rose for fixes to GCC's delay slot filling code.
* Paul Rubin wrote most of the preprocessor.
* Pe'tur Runo'lfsson for major performance improvements in C++
formatted I/O and large file support in C++ filebuf.
* Chip Salzenberg for libstdc++ patches and improvements to locales,
traits, Makefiles, libio, libtool hackery, and "long long" support.
* Juha Sarlin for improvements to the H8 code generator.
* Greg Satz assisted in making GCC work on HP-UX for the 9000 series
300.
* Roger Sayle for improvements to constant folding and GCC's RTL
optimizers as well as for fixing numerous bugs.
* Bradley Schatz for his work on the GCJ FAQ.
* Peter Schauer wrote the code to allow debugging to work on the
Alpha.
* William Schelter did most of the work on the Intel 80386 support.
* Tobias Schlu"ter for work on GNU Fortran.
* Bernd Schmidt for various code generation improvements and major
work in the reload pass as well a serving as release manager for
GCC 2.95.3.
* Peter Schmid for constant testing of libstdc++--especially
application testing, going above and beyond what was requested for
the release criteria--and libstdc++ header file tweaks.
* Jason Schroeder for jcf-dump patches.
* Andreas Schwab for his work on the m68k port.
* Lars Segerlund for work on GNU Fortran.
* Joel Sherrill for his direction via the steering committee, RTEMS
contributions and RTEMS testing.
* Nathan Sidwell for many C++ fixes/improvements.
* Jeffrey Siegal for helping RMS with the original design of GCC,
some code which handles the parse tree and RTL data structures,
constant folding and help with the original VAX & m68k ports.
* Kenny Simpson for prompting libstdc++ fixes due to defect reports
from the LWG (thereby keeping GCC in line with updates from the
ISO).
* Franz Sirl for his ongoing work with making the PPC port stable
for GNU/Linux.
* Andrey Slepuhin for assorted AIX hacking.
* Christopher Smith did the port for Convex machines.
* Danny Smith for his major efforts on the Mingw (and Cygwin) ports.
* Randy Smith finished the Sun FPA support.
* Scott Snyder for queue, iterator, istream, and string fixes and
libstdc++ testsuite entries. Also for providing the patch to G77
to add rudimentary support for `INTEGER*1', `INTEGER*2', and
`LOGICAL*1'.
* Brad Spencer for contributions to the GLIBCPP_FORCE_NEW technique.
* Richard Stallman, for writing the original GCC and launching the
GNU project.
* Jan Stein of the Chalmers Computer Society provided support for
Genix, as well as part of the 32000 machine description.
* Nigel Stephens for various mips16 related fixes/improvements.
* Jonathan Stone wrote the machine description for the Pyramid
computer.
* Graham Stott for various infrastructure improvements.
* John Stracke for his Java HTTP protocol fixes.
* Mike Stump for his Elxsi port, G++ contributions over the years
and more recently his vxworks contributions
* Jeff Sturm for Java porting help, bug fixes, and encouragement.
* Shigeya Suzuki for this fixes for the bsdi platforms.
* Ian Lance Taylor for his mips16 work, general configury hacking,
fixincludes, etc.
* Holger Teutsch provided the support for the Clipper CPU.
* Gary Thomas for his ongoing work to make the PPC work for
GNU/Linux.
* Philipp Thomas for random bug fixes throughout the compiler
* Jason Thorpe for thread support in libstdc++ on NetBSD.
* Kresten Krab Thorup wrote the run time support for the Objective-C
language and the fantastic Java bytecode interpreter.
* Michael Tiemann for random bug fixes, the first instruction
scheduler, initial C++ support, function integration, NS32k, SPARC
and M88k machine description work, delay slot scheduling.
* Andreas Tobler for his work porting libgcj to Darwin.
* Teemu Torma for thread safe exception handling support.
* Leonard Tower wrote parts of the parser, RTL generator, and RTL
definitions, and of the VAX machine description.
* Tom Tromey for internationalization support and for his many Java
contributions and libgcj maintainership.
* Lassi Tuura for improvements to config.guess to determine HP
processor types.
* Petter Urkedal for libstdc++ CXXFLAGS, math, and algorithms fixes.
* Andy Vaught for the design and initial implementation of the GNU
Fortran front end.
* Brent Verner for work with the libstdc++ cshadow files and their
associated configure steps.
* Todd Vierling for contributions for NetBSD ports.
* Jonathan Wakely for contributing libstdc++ Doxygen notes and XHTML
guidance.
* Dean Wakerley for converting the install documentation from HTML
to texinfo in time for GCC 3.0.
* Krister Walfridsson for random bug fixes.
* Feng Wang for contributions to GNU Fortran.
* Stephen M. Webb for time and effort on making libstdc++ shadow
files work with the tricky Solaris 8+ headers, and for pushing the
build-time header tree.
* John Wehle for various improvements for the x86 code generator,
related infrastructure improvements to help x86 code generation,
value range propagation and other work, WE32k port.
* Ulrich Weigand for work on the s390 port.
* Zack Weinberg for major work on cpplib and various other bug fixes.
* Matt Welsh for help with Linux Threads support in GCJ.
* Urban Widmark for help fixing java.io.
* Mark Wielaard for new Java library code and his work integrating
with Classpath.
* Dale Wiles helped port GCC to the Tahoe.
* Bob Wilson from Tensilica, Inc. for the Xtensa port.
* Jim Wilson for his direction via the steering committee, tackling
hard problems in various places that nobody else wanted to work
on, strength reduction and other loop optimizations.
* Paul Woegerer and Tal Agmon for the CRX port.
* Carlo Wood for various fixes.
* Tom Wood for work on the m88k port.
* Canqun Yang for work on GNU Fortran.
* Masanobu Yuhara of Fujitsu Laboratories implemented the machine
description for the Tron architecture (specifically, the Gmicro).
* Kevin Zachmann helped port GCC to the Tahoe.
* Ayal Zaks for Swing Modulo Scheduling (SMS).
* Xiaoqiang Zhang for work on GNU Fortran.
* Gilles Zunino for help porting Java to Irix.
The following people are recognized for their contributions to GNAT,
the Ada front end of GCC:
* Bernard Banner
* Romain Berrendonner
* Geert Bosch
* Emmanuel Briot
* Joel Brobecker
* Ben Brosgol
* Vincent Celier
* Arnaud Charlet
* Chien Chieng
* Cyrille Comar
* Cyrille Crozes
* Robert Dewar
* Gary Dismukes
* Robert Duff
* Ed Falis
* Ramon Fernandez
* Sam Figueroa
* Vasiliy Fofanov
* Michael Friess
* Franco Gasperoni
* Ted Giering
* Matthew Gingell
* Laurent Guerby
* Jerome Guitton
* Olivier Hainque
* Jerome Hugues
* Hristian Kirtchev
* Jerome Lambourg
* Bruno Leclerc
* Albert Lee
* Sean McNeil
* Javier Miranda
* Laurent Nana
* Pascal Obry
* Dong-Ik Oh
* Laurent Pautet
* Brett Porter
* Thomas Quinot
* Nicolas Roche
* Pat Rogers
* Jose Ruiz
* Douglas Rupp
* Sergey Rybin
* Gail Schenker
* Ed Schonberg
* Nicolas Setton
* Samuel Tardieu
The following people are recognized for their contributions of new
features, bug reports, testing and integration of classpath/libgcj for
GCC version 4.1:
* Lillian Angel for `JTree' implementation and lots Free Swing
additions and bugfixes.
* Wolfgang Baer for `GapContent' bugfixes.
* Anthony Balkissoon for `JList', Free Swing 1.5 updates and mouse
event fixes, lots of Free Swing work including `JTable' editing.
* Stuart Ballard for RMI constant fixes.
* Goffredo Baroncelli for `HTTPURLConnection' fixes.
* Gary Benson for `MessageFormat' fixes.
* Daniel Bonniot for `Serialization' fixes.
* Chris Burdess for lots of gnu.xml and http protocol fixes, `StAX'
and `DOM xml:id' support.
* Ka-Hing Cheung for `TreePath' and `TreeSelection' fixes.
* Archie Cobbs for build fixes, VM interface updates,
`URLClassLoader' updates.
* Kelley Cook for build fixes.
* Martin Cordova for Suggestions for better `SocketTimeoutException'.
* David Daney for `BitSet' bugfixes, `HttpURLConnection' rewrite and
improvements.
* Thomas Fitzsimmons for lots of upgrades to the gtk+ AWT and Cairo
2D support. Lots of imageio framework additions, lots of AWT and
Free Swing bugfixes.
* Jeroen Frijters for `ClassLoader' and nio cleanups, serialization
fixes, better `Proxy' support, bugfixes and IKVM integration.
* Santiago Gala for `AccessControlContext' fixes.
* Nicolas Geoffray for `VMClassLoader' and `AccessController'
improvements.
* David Gilbert for `basic' and `metal' icon and plaf support and
lots of documenting, Lots of Free Swing and metal theme additions.
`MetalIconFactory' implementation.
* Anthony Green for `MIDI' framework, `ALSA' and `DSSI' providers.
* Andrew Haley for `Serialization' and `URLClassLoader' fixes, gcj
build speedups.
* Kim Ho for `JFileChooser' implementation.
* Andrew John Hughes for `Locale' and net fixes, URI RFC2986
updates, `Serialization' fixes, `Properties' XML support and
generic branch work, VMIntegration guide update.
* Bastiaan Huisman for `TimeZone' bugfixing.
* Andreas Jaeger for mprec updates.
* Paul Jenner for better `-Werror' support.
* Ito Kazumitsu for `NetworkInterface' implementation and updates.
* Roman Kennke for `BoxLayout', `GrayFilter' and `SplitPane', plus
bugfixes all over. Lots of Free Swing work including styled text.
* Simon Kitching for `String' cleanups and optimization suggestions.
* Michael Koch for configuration fixes, `Locale' updates, bug and
build fixes.
* Guilhem Lavaux for configuration, thread and channel fixes and
Kaffe integration. JCL native `Pointer' updates. Logger bugfixes.
* David Lichteblau for JCL support library global/local reference
cleanups.
* Aaron Luchko for JDWP updates and documentation fixes.
* Ziga Mahkovec for `Graphics2D' upgraded to Cairo 0.5 and new regex
features.
* Sven de Marothy for BMP imageio support, CSS and `TextLayout'
fixes. `GtkImage' rewrite, 2D, awt, free swing and date/time fixes
and implementing the Qt4 peers.
* Casey Marshall for crypto algorithm fixes, `FileChannel' lock,
`SystemLogger' and `FileHandler' rotate implementations, NIO
`FileChannel.map' support, security and policy updates.
* Bryce McKinlay for RMI work.
* Audrius Meskauskas for lots of Free Corba, RMI and HTML work plus
testing and documenting.
* Kalle Olavi Niemitalo for build fixes.
* Rainer Orth for build fixes.
* Andrew Overholt for `File' locking fixes.
* Ingo Proetel for `Image', `Logger' and `URLClassLoader' updates.
* Olga Rodimina for `MenuSelectionManager' implementation.
* Jan Roehrich for `BasicTreeUI' and `JTree' fixes.
* Julian Scheid for documentation updates and gjdoc support.
* Christian Schlichtherle for zip fixes and cleanups.
* Robert Schuster for documentation updates and beans fixes,
`TreeNode' enumerations and `ActionCommand' and various fixes, XML
and URL, AWT and Free Swing bugfixes.
* Keith Seitz for lots of JDWP work.
* Christian Thalinger for 64-bit cleanups, Configuration and VM
interface fixes and `CACAO' integration, `fdlibm' updates.
* Gael Thomas for `VMClassLoader' boot packages support suggestions.
* Andreas Tobler for Darwin and Solaris testing and fixing, `Qt4'
support for Darwin/OS X, `Graphics2D' support, `gtk+' updates.
* Dalibor Topic for better `DEBUG' support, build cleanups and Kaffe
integration. `Qt4' build infrastructure, `SHA1PRNG' and
`GdkPixbugDecoder' updates.
* Tom Tromey for Eclipse integration, generics work, lots of bugfixes
and gcj integration including coordinating The Big Merge.
* Mark Wielaard for bugfixes, packaging and release management,
`Clipboard' implementation, system call interrupts and network
timeouts and `GdkPixpufDecoder' fixes.
In addition to the above, all of which also contributed time and
energy in testing GCC, we would like to thank the following for their
contributions to testing:
* Michael Abd-El-Malek
* Thomas Arend
* Bonzo Armstrong
* Steven Ashe
* Chris Baldwin
* David Billinghurst
* Jim Blandy
* Stephane Bortzmeyer
* Horst von Brand
* Frank Braun
* Rodney Brown
* Sidney Cadot
* Bradford Castalia
* Jonathan Corbet
* Ralph Doncaster
* Richard Emberson
* Levente Farkas
* Graham Fawcett
* Mark Fernyhough
* Robert A. French
* Jo"rgen Freyh
* Mark K. Gardner
* Charles-Antoine Gauthier
* Yung Shing Gene
* David Gilbert
* Simon Gornall
* Fred Gray
* John Griffin
* Patrik Hagglund
* Phil Hargett
* Amancio Hasty
* Takafumi Hayashi
* Bryan W. Headley
* Kevin B. Hendricks
* Joep Jansen
* Christian Joensson
* Michel Kern
* David Kidd
* Tobias Kuipers
* Anand Krishnaswamy
* A. O. V. Le Blanc
* llewelly
* Damon Love
* Brad Lucier
* Matthias Klose
* Martin Knoblauch
* Rick Lutowski
* Jesse Macnish
* Stefan Morrell
* Anon A. Mous
* Matthias Mueller
* Pekka Nikander
* Rick Niles
* Jon Olson
* Magnus Persson
* Chris Pollard
* Richard Polton
* Derk Reefman
* David Rees
* Paul Reilly
* Tom Reilly
* Torsten Rueger
* Danny Sadinoff
* Marc Schifer
* Erik Schnetter
* Wayne K. Schroll
* David Schuler
* Vin Shelton
* Tim Souder
* Adam Sulmicki
* Bill Thorson
* George Talbot
* Pedro A. M. Vazquez
* Gregory Warnes
* Ian Watson
* David E. Young
* And many others
And finally we'd like to thank everyone who uses the compiler, submits
bug reports and generally reminds us why we're doing this work in the
first place.
File: gcc.info, Node: Option Index, Next: Keyword Index, Prev: Contributors, Up: Top
Option Index
************
GCC's command line options are indexed here without any initial `-' or
`--'. Where an option has both positive and negative forms (such as
`-fOPTION' and `-fno-OPTION'), relevant entries in the manual are
indexed under the most appropriate form; it may sometimes be useful to
look up both forms.
[index ]
* Menu:
* ###: Overall Options. (line 192)
* A: Preprocessor Options.
(line 510)
* all_load: Darwin Options. (line 103)
* allowable_client: Darwin Options. (line 190)
* ansi <1>: Non-bugs. (line 107)
* ansi <2>: Other Builtins. (line 22)
* ansi <3>: Preprocessor Options.
(line 324)
* ansi <4>: C Dialect Options. (line 11)
* ansi: Standards. (line 13)
* arch_errors_fatal: Darwin Options. (line 107)
* aux-info: C Dialect Options. (line 119)
* b: Target Options. (line 13)
* B: Directory Options. (line 41)
* bcopy-builtin: PDP-11 Options. (line 32)
* bind_at_load: Darwin Options. (line 111)
* bundle: Darwin Options. (line 116)
* bundle_loader: Darwin Options. (line 120)
* c: Link Options. (line 20)
* C: Preprocessor Options.
(line 557)
* c: Overall Options. (line 147)
* client_name: Darwin Options. (line 190)
* combine: Overall Options. (line 203)
* compatibility_version: Darwin Options. (line 190)
* coverage: Debugging Options. (line 169)
* crossjumping: Optimize Options. (line 435)
* current_version: Darwin Options. (line 190)
* D: Preprocessor Options.
(line 33)
* d: Debugging Options. (line 221)
* da: Debugging Options. (line 387)
* dA: Debugging Options. (line 234)
* dB: Debugging Options. (line 239)
* dC: Debugging Options. (line 249)
* dc: Debugging Options. (line 243)
* dD <1>: Preprocessor Options.
(line 538)
* dD: Debugging Options. (line 263)
* dd: Debugging Options. (line 257)
* dE: Debugging Options. (line 268)
* dead_strip: Darwin Options. (line 190)
* dependency-file: Darwin Options. (line 190)
* df: Debugging Options. (line 273)
* dG: Debugging Options. (line 285)
* dg: Debugging Options. (line 280)
* dH: Debugging Options. (line 390)
* dh: Debugging Options. (line 292)
* dI: Preprocessor Options.
(line 547)
* di: Debugging Options. (line 296)
* dj: Debugging Options. (line 300)
* dk: Debugging Options. (line 304)
* dL: Debugging Options. (line 313)
* dl: Debugging Options. (line 309)
* dM: Preprocessor Options.
(line 526)
* dm: Debugging Options. (line 393)
* dM: Debugging Options. (line 324)
* dm: Debugging Options. (line 320)
* dN <1>: Preprocessor Options.
(line 544)
* dN: Debugging Options. (line 333)
* dn: Debugging Options. (line 329)
* do: Debugging Options. (line 337)
* dP: Debugging Options. (line 402)
* dp: Debugging Options. (line 397)
* dR: Debugging Options. (line 345)
* dr: Debugging Options. (line 341)
* dS: Debugging Options. (line 354)
* ds: Debugging Options. (line 349)
* dT: Debugging Options. (line 363)
* dt: Debugging Options. (line 358)
* dumpmachine: Debugging Options. (line 770)
* dumpspecs: Debugging Options. (line 778)
* dumpversion: Debugging Options. (line 774)
* dv: Debugging Options. (line 406)
* dV: Debugging Options. (line 368)
* dw: Debugging Options. (line 375)
* dx: Debugging Options. (line 411)
* dy: Debugging Options. (line 415)
* dylib_file: Darwin Options. (line 190)
* dylinker_install_name: Darwin Options. (line 190)
* dynamic: Darwin Options. (line 190)
* dynamiclib: Darwin Options. (line 124)
* dZ: Debugging Options. (line 383)
* dz: Debugging Options. (line 379)
* E <1>: Link Options. (line 20)
* E: Overall Options. (line 168)
* EB <1>: MIPS Options. (line 7)
* EB: ARC Options. (line 12)
* EL <1>: MIPS Options. (line 10)
* EL: ARC Options. (line 9)
* exported_symbols_list: Darwin Options. (line 190)
* F: Darwin Options. (line 32)
* fabi-version: C++ Dialect Options.
(line 20)
* falign-functions: Optimize Options. (line 902)
* falign-jumps: Optimize Options. (line 952)
* falign-labels: Optimize Options. (line 920)
* falign-loops: Optimize Options. (line 938)
* fargument-alias: Code Gen Options. (line 336)
* fargument-noalias: Code Gen Options. (line 336)
* fargument-noalias-anything: Code Gen Options. (line 336)
* fargument-noalias-global: Code Gen Options. (line 336)
* fasynchronous-unwind-tables: Code Gen Options. (line 64)
* fbounds-check <1>: Code Gen Options. (line 15)
* fbounds-check: Optimize Options. (line 326)
* fbranch-probabilities: Optimize Options. (line 1200)
* fbranch-target-load-optimize: Optimize Options. (line 1308)
* fbranch-target-load-optimize2: Optimize Options. (line 1314)
* fbtr-bb-exclusive: Optimize Options. (line 1318)
* fcall-saved <1>: Interoperation. (line 150)
* fcall-saved: Code Gen Options. (line 237)
* fcall-used: Code Gen Options. (line 223)
* fcaller-saves: Optimize Options. (line 579)
* fcheck-new: C++ Dialect Options.
(line 34)
* fcommon: Variable Attributes.
(line 92)
* fcond-mismatch: C Dialect Options. (line 235)
* fconserve-space: C++ Dialect Options.
(line 44)
* fconstant-string-class: Objective-C and Objective-C++ Dialect Options.
(line 30)
* fcse-follow-jumps: Optimize Options. (line 363)
* fcse-skip-blocks: Optimize Options. (line 372)
* fcx-limited-range: Optimize Options. (line 1186)
* fdata-sections: Optimize Options. (line 1289)
* fdelayed-branch: Optimize Options. (line 488)
* fdelete-null-pointer-checks: Optimize Options. (line 457)
* fdiagnostics-show-location: Language Independent Options.
(line 21)
* fdiagnostics-show-option: Language Independent Options.
(line 36)
* fdollars-in-identifiers <1>: Interoperation. (line 146)
* fdollars-in-identifiers: Preprocessor Options.
(line 440)
* fdump-class-hierarchy: Debugging Options. (line 441)
* fdump-ipa: Debugging Options. (line 448)
* fdump-noaddr: Debugging Options. (line 418)
* fdump-rtl-all: Debugging Options. (line 387)
* fdump-rtl-bbro: Debugging Options. (line 239)
* fdump-rtl-btl: Debugging Options. (line 257)
* fdump-rtl-bypass: Debugging Options. (line 285)
* fdump-rtl-ce1: Debugging Options. (line 249)
* fdump-rtl-ce2: Debugging Options. (line 249)
* fdump-rtl-ce3: Debugging Options. (line 268)
* fdump-rtl-cfg: Debugging Options. (line 273)
* fdump-rtl-combine: Debugging Options. (line 243)
* fdump-rtl-cse: Debugging Options. (line 349)
* fdump-rtl-cse2: Debugging Options. (line 358)
* fdump-rtl-dbr: Debugging Options. (line 257)
* fdump-rtl-eh: Debugging Options. (line 292)
* fdump-rtl-expand: Debugging Options. (line 341)
* fdump-rtl-flow2: Debugging Options. (line 375)
* fdump-rtl-gcse: Debugging Options. (line 285)
* fdump-rtl-greg: Debugging Options. (line 280)
* fdump-rtl-jump: Debugging Options. (line 300)
* fdump-rtl-life: Debugging Options. (line 273)
* fdump-rtl-loop2: Debugging Options. (line 313)
* fdump-rtl-lreg: Debugging Options. (line 309)
* fdump-rtl-mach: Debugging Options. (line 324)
* fdump-rtl-peephole2: Debugging Options. (line 379)
* fdump-rtl-postreload: Debugging Options. (line 337)
* fdump-rtl-regmove: Debugging Options. (line 333)
* fdump-rtl-rnreg: Debugging Options. (line 329)
* fdump-rtl-sched: Debugging Options. (line 354)
* fdump-rtl-sched2: Debugging Options. (line 345)
* fdump-rtl-sibling: Debugging Options. (line 296)
* fdump-rtl-sms: Debugging Options. (line 320)
* fdump-rtl-stack: Debugging Options. (line 304)
* fdump-rtl-tracer: Debugging Options. (line 363)
* fdump-rtl-vartrack: Debugging Options. (line 368)
* fdump-rtl-vpt: Debugging Options. (line 368)
* fdump-rtl-web: Debugging Options. (line 383)
* fdump-translation-unit: Debugging Options. (line 433)
* fdump-tree: Debugging Options. (line 463)
* fdump-tree-alias: Debugging Options. (line 551)
* fdump-tree-all: Debugging Options. (line 636)
* fdump-tree-ccp: Debugging Options. (line 555)
* fdump-tree-cfg: Debugging Options. (line 526)
* fdump-tree-ch: Debugging Options. (line 538)
* fdump-tree-copyprop: Debugging Options. (line 571)
* fdump-tree-copyrename: Debugging Options. (line 617)
* fdump-tree-dce: Debugging Options. (line 579)
* fdump-tree-dom: Debugging Options. (line 597)
* fdump-tree-dse: Debugging Options. (line 602)
* fdump-tree-forwprop: Debugging Options. (line 612)
* fdump-tree-fre: Debugging Options. (line 567)
* fdump-tree-gimple: Debugging Options. (line 521)
* fdump-tree-mudflap: Debugging Options. (line 583)
* fdump-tree-nrv: Debugging Options. (line 622)
* fdump-tree-phiopt: Debugging Options. (line 607)
* fdump-tree-pre: Debugging Options. (line 563)
* fdump-tree-salias: Debugging Options. (line 546)
* fdump-tree-sink: Debugging Options. (line 593)
* fdump-tree-sra: Debugging Options. (line 588)
* fdump-tree-ssa: Debugging Options. (line 542)
* fdump-tree-store_copyprop: Debugging Options. (line 575)
* fdump-tree-storeccp: Debugging Options. (line 559)
* fdump-tree-vcg: Debugging Options. (line 530)
* fdump-tree-vect: Debugging Options. (line 627)
* fdump-tree-vrp: Debugging Options. (line 632)
* fdump-unnumbered: Debugging Options. (line 425)
* fearly-inlining: Optimize Options. (line 204)
* feliminate-dwarf2-dups: Debugging Options. (line 125)
* feliminate-unused-debug-symbols: Debugging Options. (line 52)
* feliminate-unused-debug-types: Debugging Options. (line 782)
* fexceptions: Code Gen Options. (line 34)
* fexec-charset: Preprocessor Options.
(line 467)
* fexpensive-optimizations: Optimize Options. (line 470)
* fextended-identifiers: Preprocessor Options.
(line 443)
* ffast-math: Optimize Options. (line 1070)
* ffinite-math-only: Optimize Options. (line 1114)
* ffix-and-continue: Darwin Options. (line 97)
* ffixed: Code Gen Options. (line 211)
* ffloat-store <1>: Disappointments. (line 77)
* ffloat-store: Optimize Options. (line 1056)
* ffor-scope: C++ Dialect Options.
(line 86)
* fforce-addr: Optimize Options. (line 154)
* fforce-mem: Optimize Options. (line 146)
* ffreestanding <1>: Function Attributes.
(line 314)
* ffreestanding <2>: Warning Options. (line 94)
* ffreestanding <3>: C Dialect Options. (line 190)
* ffreestanding: Standards. (line 81)
* ffriend-injection: C++ Dialect Options.
(line 56)
* ffunction-sections: Optimize Options. (line 1289)
* fgcse: Optimize Options. (line 386)
* fgcse-after-reload: Optimize Options. (line 422)
* fgcse-las: Optimize Options. (line 415)
* fgcse-lm: Optimize Options. (line 397)
* fgcse-sm: Optimize Options. (line 406)
* fgnu-runtime: Objective-C and Objective-C++ Dialect Options.
(line 39)
* fgnu89-inline: C Dialect Options. (line 98)
* fhosted: C Dialect Options. (line 183)
* filelist: Darwin Options. (line 190)
* findirect-data: Darwin Options. (line 97)
* finhibit-size-directive: Code Gen Options. (line 147)
* finline-functions: Optimize Options. (line 185)
* finline-functions-called-once: Optimize Options. (line 196)
* finline-limit: Optimize Options. (line 214)
* finput-charset: Preprocessor Options.
(line 480)
* finstrument-functions <1>: Function Attributes.
(line 508)
* finstrument-functions: Code Gen Options. (line 267)
* fkeep-inline-functions <1>: Inline. (line 58)
* fkeep-inline-functions: Optimize Options. (line 252)
* fkeep-static-consts: Optimize Options. (line 259)
* flat_namespace: Darwin Options. (line 190)
* fleading-underscore: Code Gen Options. (line 353)
* fmem-report: Debugging Options. (line 150)
* fmessage-length: Language Independent Options.
(line 15)
* fmodulo-sched: Optimize Options. (line 288)
* fmove-loop-invariants: Optimize Options. (line 1279)
* fms-extensions <1>: Unnamed Fields. (line 37)
* fms-extensions <2>: C++ Dialect Options.
(line 121)
* fms-extensions: C Dialect Options. (line 206)
* fmudflap: Optimize Options. (line 333)
* fmudflapir: Optimize Options. (line 333)
* fmudflapth: Optimize Options. (line 333)
* fnext-runtime: Objective-C and Objective-C++ Dialect Options.
(line 43)
* fno-access-control: C++ Dialect Options.
(line 30)
* fno-asm: C Dialect Options. (line 135)
* fno-branch-count-reg: Optimize Options. (line 293)
* fno-builtin <1>: Other Builtins. (line 14)
* fno-builtin <2>: Function Attributes.
(line 314)
* fno-builtin <3>: Warning Options. (line 94)
* fno-builtin: C Dialect Options. (line 149)
* fno-common <1>: Variable Attributes.
(line 92)
* fno-common: Code Gen Options. (line 135)
* fno-cprop-registers: Optimize Options. (line 1028)
* fno-cx-limited-range: Optimize Options. (line 1186)
* fno-default-inline <1>: Inline. (line 53)
* fno-default-inline <2>: Optimize Options. (line 131)
* fno-default-inline: C++ Dialect Options.
(line 233)
* fno-defer-pop: Optimize Options. (line 138)
* fno-elide-constructors: C++ Dialect Options.
(line 69)
* fno-enforce-eh-specs: C++ Dialect Options.
(line 75)
* fno-for-scope: C++ Dialect Options.
(line 86)
* fno-function-cse: Optimize Options. (line 303)
* fno-gnu-keywords: C++ Dialect Options.
(line 98)
* fno-guess-branch-probability: Optimize Options. (line 787)
* fno-ident: Code Gen Options. (line 144)
* fno-implement-inlines <1>: C++ Interface. (line 75)
* fno-implement-inlines: C++ Dialect Options.
(line 115)
* fno-implicit-inline-templates: C++ Dialect Options.
(line 109)
* fno-implicit-templates <1>: Template Instantiation.
(line 87)
* fno-implicit-templates: C++ Dialect Options.
(line 103)
* fno-inline: Optimize Options. (line 179)
* fno-jump-tables: Code Gen Options. (line 203)
* fno-math-errno: Optimize Options. (line 1083)
* fno-nil-receivers: Objective-C and Objective-C++ Dialect Options.
(line 49)
* fno-nonansi-builtins: C++ Dialect Options.
(line 126)
* fno-operator-names: C++ Dialect Options.
(line 131)
* fno-optional-diags: C++ Dialect Options.
(line 135)
* fno-peephole: Optimize Options. (line 778)
* fno-peephole2: Optimize Options. (line 778)
* fno-rtti: C++ Dialect Options.
(line 150)
* fno-sched-interblock: Optimize Options. (line 514)
* fno-sched-spec: Optimize Options. (line 519)
* fno-show-column: Preprocessor Options.
(line 505)
* fno-signed-bitfields: C Dialect Options. (line 268)
* fno-stack-limit: Code Gen Options. (line 319)
* fno-threadsafe-statics: C++ Dialect Options.
(line 172)
* fno-trapping-math: Optimize Options. (line 1124)
* fno-unsigned-bitfields: C Dialect Options. (line 268)
* fno-use-cxa-get-exception-ptr: C++ Dialect Options.
(line 185)
* fno-weak: C++ Dialect Options.
(line 218)
* fno-working-directory: Preprocessor Options.
(line 490)
* fno-zero-initialized-in-bss: Optimize Options. (line 314)
* fnon-call-exceptions: Code Gen Options. (line 48)
* fobjc-call-cxx-cdtors: Objective-C and Objective-C++ Dialect Options.
(line 56)
* fobjc-direct-dispatch: Objective-C and Objective-C++ Dialect Options.
(line 81)
* fobjc-exceptions: Objective-C and Objective-C++ Dialect Options.
(line 85)
* fobjc-gc: Objective-C and Objective-C++ Dialect Options.
(line 170)
* fomit-frame-pointer: Optimize Options. (line 158)
* fopenmp: C Dialect Options. (line 200)
* foptimize-register-move: Optimize Options. (line 477)
* foptimize-sibling-calls: Optimize Options. (line 174)
* force_cpusubtype_ALL: Darwin Options. (line 129)
* force_flat_namespace: Darwin Options. (line 190)
* fpack-struct: Code Gen Options. (line 254)
* fpcc-struct-return <1>: Incompatibilities. (line 170)
* fpcc-struct-return: Code Gen Options. (line 70)
* fpch-deps: Preprocessor Options.
(line 280)
* fpch-preprocess: Preprocessor Options.
(line 288)
* fpeel-loops: Optimize Options. (line 1271)
* fpermissive: C++ Dialect Options.
(line 140)
* fPIC: Code Gen Options. (line 184)
* fpic: Code Gen Options. (line 163)
* fPIE: Code Gen Options. (line 197)
* fpie: Code Gen Options. (line 197)
* fprefetch-loop-arrays: Optimize Options. (line 767)
* fpreprocessed: Preprocessor Options.
(line 448)
* fprofile-arcs <1>: Other Builtins. (line 236)
* fprofile-arcs: Debugging Options. (line 154)
* fprofile-generate: Optimize Options. (line 1035)
* fprofile-use: Optimize Options. (line 1044)
* fprofile-values: Optimize Options. (line 1219)
* frandom-string: Debugging Options. (line 665)
* freg-struct-return: Code Gen Options. (line 88)
* fregmove: Optimize Options. (line 477)
* frename-registers: Optimize Options. (line 1238)
* freorder-blocks: Optimize Options. (line 804)
* freorder-blocks-and-partition: Optimize Options. (line 810)
* freorder-functions: Optimize Options. (line 821)
* freplace-objc-classes: Objective-C and Objective-C++ Dialect Options.
(line 174)
* frepo <1>: Template Instantiation.
(line 62)
* frepo: C++ Dialect Options.
(line 145)
* frerun-cse-after-loop: Optimize Options. (line 380)
* frounding-math: Optimize Options. (line 1139)
* frtl-abstract-sequences: Optimize Options. (line 1159)
* fsched-spec-load: Optimize Options. (line 524)
* fsched-spec-load-dangerous: Optimize Options. (line 529)
* fsched-stalled-insns: Optimize Options. (line 534)
* fsched-stalled-insns-dep: Optimize Options. (line 539)
* fsched-verbose: Debugging Options. (line 675)
* fsched2-use-superblocks: Optimize Options. (line 546)
* fsched2-use-traces: Optimize Options. (line 557)
* fschedule-insns: Optimize Options. (line 495)
* fschedule-insns2: Optimize Options. (line 505)
* fscheduling-in-modulo-scheduled-loops: Optimize Options. (line 573)
* fsection-anchors: Optimize Options. (line 1334)
* fsee: Optimize Options. (line 569)
* fshort-double: Code Gen Options. (line 117)
* fshort-enums <1>: Non-bugs. (line 42)
* fshort-enums <2>: Type Attributes. (line 112)
* fshort-enums <3>: Structures unions enumerations and bit-fields implementation.
(line 43)
* fshort-enums: Code Gen Options. (line 106)
* fshort-wchar: Code Gen Options. (line 125)
* fsignaling-nans: Optimize Options. (line 1166)
* fsigned-bitfields <1>: Non-bugs. (line 57)
* fsigned-bitfields: C Dialect Options. (line 268)
* fsigned-char <1>: Characters implementation.
(line 31)
* fsigned-char: C Dialect Options. (line 258)
* fsingle-precision-constant: Optimize Options. (line 1181)
* fsplit-ivs-in-unroller: Optimize Options. (line 748)
* fstack-check: Code Gen Options. (line 304)
* fstack-limit-register: Code Gen Options. (line 319)
* fstack-limit-symbol: Code Gen Options. (line 319)
* fstats: C++ Dialect Options.
(line 160)
* fstrict-aliasing: Optimize Options. (line 834)
* fstrict-overflow: Optimize Options. (line 876)
* fsyntax-only: Warning Options. (line 23)
* ftabstop: Preprocessor Options.
(line 461)
* ftemplate-depth: C++ Dialect Options.
(line 165)
* ftest-coverage: Debugging Options. (line 210)
* fthread-jumps: Optimize Options. (line 354)
* ftime-report: Debugging Options. (line 146)
* ftracer: Optimize Options. (line 731)
* ftrapv: Code Gen Options. (line 22)
* ftree-vect-loop-version: Optimize Options. (line 713)
* ftree-vectorizer-verbose: Debugging Options. (line 640)
* funit-at-a-time: Optimize Options. (line 965)
* funroll-all-loops: Optimize Options. (line 742)
* funroll-loops: Optimize Options. (line 736)
* funsafe-loop-optimizations: Optimize Options. (line 427)
* funsafe-math-optimizations: Optimize Options. (line 1100)
* funsigned-bitfields <1>: Non-bugs. (line 57)
* funsigned-bitfields <2>: Structures unions enumerations and bit-fields implementation.
(line 17)
* funsigned-bitfields: C Dialect Options. (line 268)
* funsigned-char <1>: Characters implementation.
(line 31)
* funsigned-char: C Dialect Options. (line 240)
* funswitch-loops: Optimize Options. (line 1283)
* funwind-tables: Code Gen Options. (line 57)
* fuse-cxa-atexit: C++ Dialect Options.
(line 178)
* fvar-tracking: Debugging Options. (line 718)
* fvariable-expansion-in-unroller: Optimize Options. (line 762)
* fverbose-asm: Code Gen Options. (line 154)
* fvisibility: Code Gen Options. (line 372)
* fvisibility-inlines-hidden: C++ Dialect Options.
(line 190)
* fvpt: Optimize Options. (line 1229)
* fweb: Optimize Options. (line 1004)
* fwhole-program: Optimize Options. (line 1015)
* fwide-exec-charset: Preprocessor Options.
(line 472)
* fworking-directory: Preprocessor Options.
(line 490)
* fwrapv: Code Gen Options. (line 26)
* fzero-link: Objective-C and Objective-C++ Dialect Options.
(line 184)
* G <1>: System V Options. (line 10)
* G <2>: RS/6000 and PowerPC Options.
(line 607)
* G <3>: MIPS Options. (line 216)
* G: M32R/D Options. (line 57)
* g: Debugging Options. (line 10)
* gcoff: Debugging Options. (line 70)
* gdwarf-2: Debugging Options. (line 88)
* gen-decls: Objective-C and Objective-C++ Dialect Options.
(line 194)
* gfull: Darwin Options. (line 64)
* ggdb: Debugging Options. (line 38)
* gnu-ld: HPPA Options. (line 113)
* gstabs: Debugging Options. (line 44)
* gstabs+: Debugging Options. (line 64)
* gused: Darwin Options. (line 59)
* gvms: Debugging Options. (line 95)
* gxcoff: Debugging Options. (line 75)
* gxcoff+: Debugging Options. (line 80)
* H: Preprocessor Options.
(line 612)
* headerpad_max_install_names: Darwin Options. (line 190)
* help <1>: Preprocessor Options.
(line 604)
* help: Overall Options. (line 219)
* hp-ld: HPPA Options. (line 125)
* I <1>: Directory Options. (line 10)
* I: Preprocessor Options.
(line 64)
* I- <1>: Directory Options. (line 107)
* I-: Preprocessor Options.
(line 361)
* idirafter: Preprocessor Options.
(line 403)
* if-conversion: Optimize Options. (line 442)
* if-conversion2: Optimize Options. (line 451)
* imacros: Preprocessor Options.
(line 394)
* image_base: Darwin Options. (line 190)
* imultilib: Preprocessor Options.
(line 424)
* include: Preprocessor Options.
(line 383)
* init: Darwin Options. (line 190)
* install_name: Darwin Options. (line 190)
* iprefix: Preprocessor Options.
(line 408)
* iquote <1>: Directory Options. (line 31)
* iquote: Preprocessor Options.
(line 434)
* isysroot: Preprocessor Options.
(line 420)
* isystem: Preprocessor Options.
(line 428)
* iwithprefix: Preprocessor Options.
(line 414)
* iwithprefixbefore: Preprocessor Options.
(line 414)
* keep_private_externs: Darwin Options. (line 190)
* L: Directory Options. (line 37)
* l: Link Options. (line 26)
* lobjc: Link Options. (line 53)
* M: Preprocessor Options.
(line 173)
* m1: SH Options. (line 9)
* m10: PDP-11 Options. (line 29)
* m128bit-long-double: i386 and x86-64 Options.
(line 254)
* m16-bit: CRIS Options. (line 69)
* m2: SH Options. (line 12)
* m210: MCore Options. (line 43)
* m3: SH Options. (line 18)
* m31: S/390 and zSeries Options.
(line 79)
* m32 <1>: SPARC Options. (line 189)
* m32 <2>: RS/6000 and PowerPC Options.
(line 222)
* m32: i386 and x86-64 Options.
(line 464)
* m32-bit: CRIS Options. (line 69)
* m32r: M32R/D Options. (line 15)
* m32r2: M32R/D Options. (line 9)
* m32rx: M32R/D Options. (line 12)
* m340: MCore Options. (line 43)
* m386: i386 and x86-64 Options.
(line 142)
* m3dnow: i386 and x86-64 Options.
(line 389)
* m3e: SH Options. (line 21)
* m4: SH Options. (line 35)
* m4-nofpu: SH Options. (line 24)
* m4-single: SH Options. (line 31)
* m4-single-only: SH Options. (line 27)
* m40: PDP-11 Options. (line 23)
* m45: PDP-11 Options. (line 26)
* m486: i386 and x86-64 Options.
(line 142)
* m4a: SH Options. (line 50)
* m4a-nofpu: SH Options. (line 38)
* m4a-single: SH Options. (line 46)
* m4a-single-only: SH Options. (line 42)
* m4al: SH Options. (line 53)
* m4byte-functions: MCore Options. (line 27)
* m5200: M680x0 Options. (line 59)
* m64 <1>: SPARC Options. (line 189)
* m64 <2>: S/390 and zSeries Options.
(line 79)
* m64 <3>: RS/6000 and PowerPC Options.
(line 222)
* m64: i386 and x86-64 Options.
(line 464)
* m68000: M680x0 Options. (line 13)
* m68020: M680x0 Options. (line 21)
* m68020-40: M680x0 Options. (line 70)
* m68020-60: M680x0 Options. (line 77)
* m68030: M680x0 Options. (line 30)
* m68040: M680x0 Options. (line 34)
* m68060: M680x0 Options. (line 42)
* m6811: M68hc1x Options. (line 13)
* m6812: M68hc1x Options. (line 18)
* m68881: M680x0 Options. (line 25)
* m68hc11: M68hc1x Options. (line 13)
* m68hc12: M68hc1x Options. (line 18)
* m68hcs12: M68hc1x Options. (line 23)
* m68S12: M68hc1x Options. (line 23)
* m8-bit: CRIS Options. (line 69)
* m96bit-long-double: i386 and x86-64 Options.
(line 254)
* mabi <1>: RS/6000 and PowerPC Options.
(line 489)
* mabi: ARM Options. (line 10)
* mabi-mmixware: MMIX Options. (line 20)
* mabi=32: MIPS Options. (line 89)
* mabi=64: MIPS Options. (line 89)
* mabi=eabi: MIPS Options. (line 89)
* mabi=gnu: MMIX Options. (line 20)
* mabi=ibmlongdouble: RS/6000 and PowerPC Options.
(line 502)
* mabi=ieeelongdouble: RS/6000 and PowerPC Options.
(line 506)
* mabi=n32: MIPS Options. (line 89)
* mabi=no-spe: RS/6000 and PowerPC Options.
(line 499)
* mabi=o64: MIPS Options. (line 89)
* mabi=spe: RS/6000 and PowerPC Options.
(line 494)
* mabicalls: MIPS Options. (line 100)
* mabort-on-noreturn: ARM Options. (line 144)
* mabshi: PDP-11 Options. (line 55)
* mac0: PDP-11 Options. (line 16)
* macc-4: FRV Options. (line 113)
* macc-8: FRV Options. (line 116)
* maccumulate-outgoing-args: i386 and x86-64 Options.
(line 415)
* madjust-unroll: SH Options. (line 175)
* mads: RS/6000 and PowerPC Options.
(line 532)
* maix-struct-return: RS/6000 and PowerPC Options.
(line 482)
* maix32: RS/6000 and PowerPC Options.
(line 260)
* maix64: RS/6000 and PowerPC Options.
(line 260)
* malign-300: H8/300 Options. (line 31)
* malign-double: i386 and x86-64 Options.
(line 238)
* malign-int: M680x0 Options. (line 132)
* malign-labels: FRV Options. (line 104)
* malign-loops: M32R/D Options. (line 73)
* malign-natural: RS/6000 and PowerPC Options.
(line 299)
* malign-power: RS/6000 and PowerPC Options.
(line 299)
* malloc-cc: FRV Options. (line 25)
* malpha-as: DEC Alpha Options. (line 159)
* maltivec: RS/6000 and PowerPC Options.
(line 164)
* mam33: MN10300 Options. (line 17)
* maout: CRIS Options. (line 92)
* mapcs: ARM Options. (line 22)
* mapcs-frame: ARM Options. (line 14)
* mapp-regs <1>: V850 Options. (line 57)
* mapp-regs: SPARC Options. (line 10)
* march <1>: S/390 and zSeries Options.
(line 108)
* march <2>: MT Options. (line 9)
* march <3>: MIPS Options. (line 14)
* march <4>: i386 and x86-64 Options.
(line 131)
* march <5>: HPPA Options. (line 9)
* march <6>: CRIS Options. (line 10)
* march: ARM Options. (line 109)
* masm=DIALECT: i386 and x86-64 Options.
(line 194)
* mauto-incdec: M68hc1x Options. (line 26)
* mauto-pic: IA-64 Options. (line 50)
* mb: SH Options. (line 58)
* mbacc: MT Options. (line 16)
* mbackchain: S/390 and zSeries Options.
(line 26)
* mbase-addresses: MMIX Options. (line 54)
* mbcopy: PDP-11 Options. (line 36)
* mbig <1>: TMS320C3x/C4x Options.
(line 18)
* mbig: RS/6000 and PowerPC Options.
(line 414)
* mbig-endian <1>: RS/6000 and PowerPC Options.
(line 414)
* mbig-endian <2>: MCore Options. (line 39)
* mbig-endian <3>: IA-64 Options. (line 9)
* mbig-endian: ARM Options. (line 72)
* mbig-memory: TMS320C3x/C4x Options.
(line 18)
* mbig-switch <1>: V850 Options. (line 52)
* mbig-switch: HPPA Options. (line 23)
* mbigtable: SH Options. (line 74)
* mbit-align: RS/6000 and PowerPC Options.
(line 368)
* mbitfield: M680x0 Options. (line 104)
* mbk: TMS320C3x/C4x Options.
(line 27)
* mbranch-cheap: PDP-11 Options. (line 65)
* mbranch-cost=NUMBER: M32R/D Options. (line 82)
* mbranch-expensive: PDP-11 Options. (line 61)
* mbranch-likely: MIPS Options. (line 367)
* mbranch-predict: MMIX Options. (line 49)
* mbss-plt: RS/6000 and PowerPC Options.
(line 181)
* mbuild-constants: DEC Alpha Options. (line 142)
* mbwx: DEC Alpha Options. (line 171)
* mc68000: M680x0 Options. (line 13)
* mc68020: M680x0 Options. (line 21)
* mcall-gnu: RS/6000 and PowerPC Options.
(line 474)
* mcall-linux: RS/6000 and PowerPC Options.
(line 470)
* mcall-netbsd: RS/6000 and PowerPC Options.
(line 478)
* mcall-prologues: AVR Options. (line 43)
* mcall-solaris: RS/6000 and PowerPC Options.
(line 466)
* mcall-sysv: RS/6000 and PowerPC Options.
(line 453)
* mcall-sysv-eabi: RS/6000 and PowerPC Options.
(line 460)
* mcall-sysv-noeabi: RS/6000 and PowerPC Options.
(line 463)
* mcallee-super-interworking: ARM Options. (line 234)
* mcaller-super-interworking: ARM Options. (line 240)
* mcallgraph-data: MCore Options. (line 31)
* mcc-init: CRIS Options. (line 46)
* mcfv4e: M680x0 Options. (line 66)
* mcheck-zero-division: MIPS Options. (line 254)
* mcirrus-fix-invalid-insns: ARM Options. (line 187)
* mcix: DEC Alpha Options. (line 171)
* mcmodel=embmedany: SPARC Options. (line 211)
* mcmodel=kernel: i386 and x86-64 Options.
(line 486)
* mcmodel=large: i386 and x86-64 Options.
(line 498)
* mcmodel=medany: SPARC Options. (line 205)
* mcmodel=medium: i386 and x86-64 Options.
(line 491)
* mcmodel=medlow: SPARC Options. (line 194)
* mcmodel=medmid: SPARC Options. (line 199)
* mcmodel=small: i386 and x86-64 Options.
(line 480)
* mcond-exec: FRV Options. (line 152)
* mcond-move: FRV Options. (line 128)
* mconst-align: CRIS Options. (line 60)
* mconst16: Xtensa Options. (line 10)
* mconstant-gp: IA-64 Options. (line 46)
* mcpu <1>: TMS320C3x/C4x Options.
(line 9)
* mcpu <2>: SPARC Options. (line 96)
* mcpu <3>: RS/6000 and PowerPC Options.
(line 100)
* mcpu <4>: i386 and x86-64 Options.
(line 136)
* mcpu <5>: FRV Options. (line 212)
* mcpu <6>: DEC Alpha Options. (line 223)
* mcpu <7>: CRIS Options. (line 10)
* mcpu <8>: ARM Options. (line 84)
* mcpu: ARC Options. (line 23)
* mcpu32: M680x0 Options. (line 51)
* mcpu=: M32C Options. (line 7)
* mcsync-anomaly: Blackfin Options. (line 23)
* MD: Preprocessor Options.
(line 261)
* mdalign: SH Options. (line 64)
* mdata: ARC Options. (line 30)
* mdata-align: CRIS Options. (line 60)
* mdb: TMS320C3x/C4x Options.
(line 32)
* mdebug <1>: S/390 and zSeries Options.
(line 104)
* mdebug: M32R/D Options. (line 69)
* mdec-asm: PDP-11 Options. (line 78)
* mdisable-callt: V850 Options. (line 80)
* mdisable-fpregs: HPPA Options. (line 33)
* mdisable-indexing: HPPA Options. (line 40)
* mdiv: MCore Options. (line 15)
* mdiv=STRATEGY: SH Options. (line 127)
* mdivide-breaks: MIPS Options. (line 259)
* mdivide-traps: MIPS Options. (line 259)
* mdivsi3_libfunc=NAME: SH Options. (line 168)
* mdlmzb: RS/6000 and PowerPC Options.
(line 362)
* mdouble: FRV Options. (line 38)
* mdouble-float: MIPS Options. (line 173)
* mdp-isr-reload: TMS320C3x/C4x Options.
(line 45)
* mdsp: MIPS Options. (line 178)
* mdwarf2-asm: IA-64 Options. (line 79)
* mdword: FRV Options. (line 32)
* mdynamic-no-pic: RS/6000 and PowerPC Options.
(line 419)
* meabi: RS/6000 and PowerPC Options.
(line 555)
* mearly-stop-bits: IA-64 Options. (line 85)
* meb: Score Options. (line 9)
* mel: Score Options. (line 12)
* melf <1>: MMIX Options. (line 44)
* melf: CRIS Options. (line 95)
* melinux: CRIS Options. (line 99)
* melinux-stacksize: CRIS Options. (line 25)
* memb: RS/6000 and PowerPC Options.
(line 550)
* membedded-data: MIPS Options. (line 225)
* memregs=: M32C Options. (line 21)
* mep: V850 Options. (line 16)
* mepsilon: MMIX Options. (line 15)
* mesa: S/390 and zSeries Options.
(line 87)
* metrax100: CRIS Options. (line 31)
* metrax4: CRIS Options. (line 31)
* mexplicit-relocs <1>: MIPS Options. (line 245)
* mexplicit-relocs: DEC Alpha Options. (line 184)
* MF: Preprocessor Options.
(line 207)
* mfast-fix: TMS320C3x/C4x Options.
(line 62)
* mfast-indirect-calls: HPPA Options. (line 52)
* mfaster-structs: SPARC Options. (line 71)
* mfdpic: FRV Options. (line 56)
* mfix: DEC Alpha Options. (line 171)
* mfix-and-continue: Darwin Options. (line 97)
* mfix-r4000: MIPS Options. (line 309)
* mfix-r4400: MIPS Options. (line 323)
* mfix-sb1: MIPS Options. (line 351)
* mfix-vr4120: MIPS Options. (line 330)
* mfix-vr4130: MIPS Options. (line 344)
* mfixed-cc: FRV Options. (line 28)
* mfixed-range <1>: IA-64 Options. (line 90)
* mfixed-range: HPPA Options. (line 59)
* mfloat-abi: ARM Options. (line 59)
* mfloat-gprs: RS/6000 and PowerPC Options.
(line 205)
* mfloat-ieee: DEC Alpha Options. (line 179)
* mfloat-vax: DEC Alpha Options. (line 179)
* mfloat32: PDP-11 Options. (line 52)
* mfloat64: PDP-11 Options. (line 48)
* mflush-func: MIPS Options. (line 357)
* mflush-func=NAME: M32R/D Options. (line 94)
* mflush-trap=NUMBER: M32R/D Options. (line 87)
* mfmovd: SH Options. (line 78)
* mfp: ARM Options. (line 119)
* mfp-exceptions: MIPS Options. (line 378)
* mfp-reg: DEC Alpha Options. (line 25)
* mfp-rounding-mode: DEC Alpha Options. (line 85)
* mfp-trap-mode: DEC Alpha Options. (line 63)
* mfp32: MIPS Options. (line 156)
* mfp64: MIPS Options. (line 159)
* mfpe: ARM Options. (line 119)
* mfpr-32: FRV Options. (line 13)
* mfpr-64: FRV Options. (line 16)
* mfprnd: RS/6000 and PowerPC Options.
(line 25)
* mfpu <1>: SPARC Options. (line 20)
* mfpu <2>: PDP-11 Options. (line 9)
* mfpu: ARM Options. (line 119)
* mfull-toc: RS/6000 and PowerPC Options.
(line 233)
* mfused-madd <1>: Xtensa Options. (line 19)
* mfused-madd <2>: S/390 and zSeries Options.
(line 128)
* mfused-madd <3>: RS/6000 and PowerPC Options.
(line 349)
* mfused-madd: MIPS Options. (line 294)
* mg: VAX Options. (line 17)
* MG: Preprocessor Options.
(line 216)
* mgas <1>: HPPA Options. (line 75)
* mgas: DEC Alpha Options. (line 159)
* mgettrcost=NUMBER: SH Options. (line 190)
* mglibc: GNU/Linux Options. (line 9)
* mgnu: VAX Options. (line 13)
* mgnu-as: IA-64 Options. (line 18)
* mgnu-ld: IA-64 Options. (line 23)
* mgotplt: CRIS Options. (line 86)
* mgp32: MIPS Options. (line 150)
* mgp64: MIPS Options. (line 153)
* mgpr-32: FRV Options. (line 7)
* mgpr-64: FRV Options. (line 10)
* mgprel-ro: FRV Options. (line 79)
* mh: H8/300 Options. (line 14)
* mhard-float <1>: SPARC Options. (line 20)
* mhard-float <2>: S/390 and zSeries Options.
(line 11)
* mhard-float <3>: RS/6000 and PowerPC Options.
(line 311)
* mhard-float <4>: MIPS Options. (line 162)
* mhard-float <5>: FRV Options. (line 19)
* mhard-float: ARM Options. (line 41)
* mhard-quad-float: SPARC Options. (line 41)
* mhardlit: MCore Options. (line 10)
* mhitachi: SH Options. (line 81)
* mid-shared-library: Blackfin Options. (line 39)
* mieee <1>: SH Options. (line 96)
* mieee: DEC Alpha Options. (line 39)
* mieee-conformant: DEC Alpha Options. (line 134)
* mieee-fp: i386 and x86-64 Options.
(line 200)
* mieee-with-inexact: DEC Alpha Options. (line 52)
* milp32: IA-64 Options. (line 114)
* mimpure-text: SPARC Options. (line 81)
* mindexed-addressing: SH Options. (line 180)
* minit-stack: AVR Options. (line 35)
* minline-all-stringops: i386 and x86-64 Options.
(line 436)
* minline-float-divide-max-throughput: IA-64 Options. (line 58)
* minline-float-divide-min-latency: IA-64 Options. (line 54)
* minline-int-divide-max-throughput: IA-64 Options. (line 66)
* minline-int-divide-min-latency: IA-64 Options. (line 62)
* minline-plt: FRV Options. (line 64)
* minline-sqrt-max-throughput: IA-64 Options. (line 74)
* minline-sqrt-min-latency: IA-64 Options. (line 70)
* minmax: M68hc1x Options. (line 31)
* minsert-sched-nops: RS/6000 and PowerPC Options.
(line 441)
* mint16: PDP-11 Options. (line 40)
* mint32 <1>: PDP-11 Options. (line 44)
* mint32: H8/300 Options. (line 28)
* mint8: AVR Options. (line 53)
* minvalid-symbols: SH Options. (line 213)
* mips1: MIPS Options. (line 59)
* mips16: MIPS Options. (line 81)
* mips2: MIPS Options. (line 62)
* mips3: MIPS Options. (line 65)
* mips32: MIPS Options. (line 71)
* mips32r2: MIPS Options. (line 74)
* mips3d: MIPS Options. (line 190)
* mips4: MIPS Options. (line 68)
* mips64: MIPS Options. (line 77)
* misel: RS/6000 and PowerPC Options.
(line 187)
* misize: SH Options. (line 103)
* missue-rate=NUMBER: M32R/D Options. (line 79)
* mjump-in-delay: HPPA Options. (line 28)
* mkernel: Darwin Options. (line 75)
* mknuthdiv: MMIX Options. (line 33)
* ml: SH Options. (line 61)
* mlarge-data: DEC Alpha Options. (line 195)
* mlarge-data-threshold=NUMBER: i386 and x86-64 Options.
(line 280)
* mlarge-text: DEC Alpha Options. (line 213)
* mlibfuncs: MMIX Options. (line 10)
* mlibrary-pic: FRV Options. (line 110)
* mlinked-fp: FRV Options. (line 94)
* mlinker-opt: HPPA Options. (line 85)
* mlinux: CRIS Options. (line 104)
* mlittle: RS/6000 and PowerPC Options.
(line 408)
* mlittle-endian <1>: SPARC Options. (line 183)
* mlittle-endian <2>: RS/6000 and PowerPC Options.
(line 408)
* mlittle-endian <3>: MCore Options. (line 39)
* mlittle-endian <4>: IA-64 Options. (line 13)
* mlittle-endian: ARM Options. (line 68)
* mlong-calls <1>: V850 Options. (line 10)
* mlong-calls <2>: MIPS Options. (line 280)
* mlong-calls <3>: M68hc1x Options. (line 35)
* mlong-calls <4>: FRV Options. (line 99)
* mlong-calls <5>: Blackfin Options. (line 57)
* mlong-calls: ARM Options. (line 149)
* mlong-double-128: S/390 and zSeries Options.
(line 20)
* mlong-double-64: S/390 and zSeries Options.
(line 20)
* mlong-load-store: HPPA Options. (line 66)
* mlong32: MIPS Options. (line 199)
* mlong64: MIPS Options. (line 194)
* mlongcall: RS/6000 and PowerPC Options.
(line 621)
* mlongcalls: Xtensa Options. (line 60)
* mloop-unsigned: TMS320C3x/C4x Options.
(line 94)
* mlow-64k: Blackfin Options. (line 32)
* mlp64: IA-64 Options. (line 114)
* MM: Preprocessor Options.
(line 197)
* mmac <1>: Score Options. (line 21)
* mmac: CRX Options. (line 9)
* mmad: MIPS Options. (line 289)
* mmangle-cpu: ARC Options. (line 15)
* mmax: DEC Alpha Options. (line 171)
* mmax-stack-frame: CRIS Options. (line 22)
* mmcu: AVR Options. (line 9)
* MMD: Preprocessor Options.
(line 276)
* mmedia: FRV Options. (line 44)
* mmemcpy: MIPS Options. (line 274)
* mmemory-latency: DEC Alpha Options. (line 266)
* mmemparm: TMS320C3x/C4x Options.
(line 109)
* mmfcrf: RS/6000 and PowerPC Options.
(line 25)
* mminimal-toc: RS/6000 and PowerPC Options.
(line 233)
* mmmx: i386 and x86-64 Options.
(line 389)
* mmodel=large: M32R/D Options. (line 33)
* mmodel=medium: M32R/D Options. (line 27)
* mmodel=small: M32R/D Options. (line 18)
* mmpyi: TMS320C3x/C4x Options.
(line 53)
* mmul-bug-workaround: CRIS Options. (line 36)
* mmuladd: FRV Options. (line 50)
* mmulhw: RS/6000 and PowerPC Options.
(line 355)
* mmult-bug: MN10300 Options. (line 9)
* mmulti-cond-exec: FRV Options. (line 176)
* mmultiple: RS/6000 and PowerPC Options.
(line 317)
* mmvcle: S/390 and zSeries Options.
(line 97)
* mmvme: RS/6000 and PowerPC Options.
(line 527)
* mn: H8/300 Options. (line 20)
* mnested-cond-exec: FRV Options. (line 189)
* mnew-mnemonics: RS/6000 and PowerPC Options.
(line 85)
* mnhwloop: Score Options. (line 15)
* mno-3dnow: i386 and x86-64 Options.
(line 389)
* mno-4byte-functions: MCore Options. (line 27)
* mno-abicalls: MIPS Options. (line 100)
* mno-abshi: PDP-11 Options. (line 58)
* mno-ac0: PDP-11 Options. (line 20)
* mno-align-double: i386 and x86-64 Options.
(line 238)
* mno-align-int: M680x0 Options. (line 132)
* mno-align-loops: M32R/D Options. (line 76)
* mno-align-stringops: i386 and x86-64 Options.
(line 431)
* mno-altivec: RS/6000 and PowerPC Options.
(line 164)
* mno-am33: MN10300 Options. (line 20)
* mno-app-regs <1>: V850 Options. (line 61)
* mno-app-regs: SPARC Options. (line 10)
* mno-bacc: MT Options. (line 19)
* mno-backchain: S/390 and zSeries Options.
(line 26)
* mno-base-addresses: MMIX Options. (line 54)
* mno-bit-align: RS/6000 and PowerPC Options.
(line 368)
* mno-bk: TMS320C3x/C4x Options.
(line 27)
* mno-branch-likely: MIPS Options. (line 367)
* mno-branch-predict: MMIX Options. (line 49)
* mno-bwx: DEC Alpha Options. (line 171)
* mno-callgraph-data: MCore Options. (line 31)
* mno-check-zero-division: MIPS Options. (line 254)
* mno-cirrus-fix-invalid-insns: ARM Options. (line 187)
* mno-cix: DEC Alpha Options. (line 171)
* mno-cond-exec: FRV Options. (line 158)
* mno-cond-move: FRV Options. (line 134)
* mno-const-align: CRIS Options. (line 60)
* mno-const16: Xtensa Options. (line 10)
* mno-crt0 <1>: MT Options. (line 25)
* mno-crt0: MN10300 Options. (line 31)
* mno-csync-anomaly: Blackfin Options. (line 28)
* mno-data-align: CRIS Options. (line 60)
* mno-db: TMS320C3x/C4x Options.
(line 32)
* mno-debug: S/390 and zSeries Options.
(line 104)
* mno-div: MCore Options. (line 15)
* mno-dlmzb: RS/6000 and PowerPC Options.
(line 362)
* mno-double: FRV Options. (line 41)
* mno-dsp: MIPS Options. (line 178)
* mno-dwarf2-asm: IA-64 Options. (line 79)
* mno-dword: FRV Options. (line 35)
* mno-eabi: RS/6000 and PowerPC Options.
(line 555)
* mno-early-stop-bits: IA-64 Options. (line 85)
* mno-eflags: FRV Options. (line 125)
* mno-embedded-data: MIPS Options. (line 225)
* mno-ep: V850 Options. (line 16)
* mno-epsilon: MMIX Options. (line 15)
* mno-explicit-relocs <1>: MIPS Options. (line 245)
* mno-explicit-relocs: DEC Alpha Options. (line 184)
* mno-fancy-math-387: i386 and x86-64 Options.
(line 227)
* mno-fast-fix: TMS320C3x/C4x Options.
(line 62)
* mno-faster-structs: SPARC Options. (line 71)
* mno-fix: DEC Alpha Options. (line 171)
* mno-fix-r4000: MIPS Options. (line 309)
* mno-fix-r4400: MIPS Options. (line 323)
* mno-float32: PDP-11 Options. (line 48)
* mno-float64: PDP-11 Options. (line 52)
* mno-flush-func: M32R/D Options. (line 99)
* mno-flush-trap: M32R/D Options. (line 91)
* mno-fp-in-toc: RS/6000 and PowerPC Options.
(line 233)
* mno-fp-regs: DEC Alpha Options. (line 25)
* mno-fp-ret-in-387: i386 and x86-64 Options.
(line 217)
* mno-fprnd: RS/6000 and PowerPC Options.
(line 25)
* mno-fpu: SPARC Options. (line 25)
* mno-fused-madd <1>: Xtensa Options. (line 19)
* mno-fused-madd <2>: S/390 and zSeries Options.
(line 128)
* mno-fused-madd <3>: RS/6000 and PowerPC Options.
(line 349)
* mno-fused-madd: MIPS Options. (line 294)
* mno-gnu-as: IA-64 Options. (line 18)
* mno-gnu-ld: IA-64 Options. (line 23)
* mno-gotplt: CRIS Options. (line 86)
* mno-hardlit: MCore Options. (line 10)
* mno-id-shared-library: Blackfin Options. (line 45)
* mno-ieee-fp: i386 and x86-64 Options.
(line 200)
* mno-int16: PDP-11 Options. (line 44)
* mno-int32: PDP-11 Options. (line 40)
* mno-interrupts: AVR Options. (line 39)
* mno-isel: RS/6000 and PowerPC Options.
(line 187)
* mno-knuthdiv: MMIX Options. (line 33)
* mno-libfuncs: MMIX Options. (line 10)
* mno-long-calls <1>: V850 Options. (line 10)
* mno-long-calls <2>: MIPS Options. (line 280)
* mno-long-calls <3>: M68hc1x Options. (line 35)
* mno-long-calls <4>: HPPA Options. (line 138)
* mno-long-calls <5>: Blackfin Options. (line 57)
* mno-long-calls: ARM Options. (line 149)
* mno-longcall: RS/6000 and PowerPC Options.
(line 621)
* mno-longcalls: Xtensa Options. (line 60)
* mno-loop-unsigned: TMS320C3x/C4x Options.
(line 94)
* mno-low-64k: Blackfin Options. (line 36)
* mno-mad: MIPS Options. (line 289)
* mno-max: DEC Alpha Options. (line 171)
* mno-media: FRV Options. (line 47)
* mno-memcpy: MIPS Options. (line 274)
* mno-mfcrf: RS/6000 and PowerPC Options.
(line 25)
* mno-mips16: MIPS Options. (line 81)
* mno-mips3d: MIPS Options. (line 190)
* mno-mmx: i386 and x86-64 Options.
(line 389)
* mno-mpyi: TMS320C3x/C4x Options.
(line 53)
* mno-mul-bug-workaround: CRIS Options. (line 36)
* mno-muladd: FRV Options. (line 53)
* mno-mulhw: RS/6000 and PowerPC Options.
(line 355)
* mno-mult-bug: MN10300 Options. (line 13)
* mno-multi-cond-exec: FRV Options. (line 183)
* mno-multiple: RS/6000 and PowerPC Options.
(line 317)
* mno-mvcle: S/390 and zSeries Options.
(line 97)
* mno-nested-cond-exec: FRV Options. (line 195)
* mno-optimize-membar: FRV Options. (line 205)
* mno-pack: FRV Options. (line 122)
* mno-packed-stack: S/390 and zSeries Options.
(line 46)
* mno-paired-single: MIPS Options. (line 183)
* mno-parallel-insns: TMS320C3x/C4x Options.
(line 115)
* mno-parallel-mpy: TMS320C3x/C4x Options.
(line 120)
* mno-pic: IA-64 Options. (line 26)
* mno-popcntb: RS/6000 and PowerPC Options.
(line 25)
* mno-power: RS/6000 and PowerPC Options.
(line 25)
* mno-power2: RS/6000 and PowerPC Options.
(line 25)
* mno-powerpc: RS/6000 and PowerPC Options.
(line 25)
* mno-powerpc-gfxopt: RS/6000 and PowerPC Options.
(line 25)
* mno-powerpc-gpopt: RS/6000 and PowerPC Options.
(line 25)
* mno-powerpc64: RS/6000 and PowerPC Options.
(line 25)
* mno-prolog-function: V850 Options. (line 23)
* mno-prologue-epilogue: CRIS Options. (line 76)
* mno-prototype: RS/6000 and PowerPC Options.
(line 511)
* mno-push-args: i386 and x86-64 Options.
(line 408)
* mno-register-names: IA-64 Options. (line 37)
* mno-regnames: RS/6000 and PowerPC Options.
(line 615)
* mno-relax-immediate: MCore Options. (line 19)
* mno-relocatable: RS/6000 and PowerPC Options.
(line 385)
* mno-relocatable-lib: RS/6000 and PowerPC Options.
(line 393)
* mno-rptb: TMS320C3x/C4x Options.
(line 72)
* mno-rpts: TMS320C3x/C4x Options.
(line 81)
* mno-scc: FRV Options. (line 146)
* mno-sched-ar-data-spec: IA-64 Options. (line 128)
* mno-sched-ar-in-data-spec: IA-64 Options. (line 149)
* mno-sched-br-data-spec: IA-64 Options. (line 121)
* mno-sched-br-in-data-spec: IA-64 Options. (line 142)
* mno-sched-control-ldc: IA-64 Options. (line 168)
* mno-sched-control-spec: IA-64 Options. (line 135)
* mno-sched-count-spec-in-critical-path: IA-64 Options. (line 194)
* mno-sched-in-control-spec: IA-64 Options. (line 156)
* mno-sched-ldc: IA-64 Options. (line 162)
* mno-sched-prefer-non-control-spec-insns: IA-64 Options. (line 187)
* mno-sched-prefer-non-data-spec-insns: IA-64 Options. (line 180)
* mno-sched-prolog: ARM Options. (line 32)
* mno-sched-spec-verbose: IA-64 Options. (line 176)
* mno-sdata <1>: RS/6000 and PowerPC Options.
(line 602)
* mno-sdata: IA-64 Options. (line 42)
* mno-side-effects: CRIS Options. (line 51)
* mno-single-exit: MMIX Options. (line 66)
* mno-slow-bytes: MCore Options. (line 35)
* mno-small-exec: S/390 and zSeries Options.
(line 72)
* mno-soft-float: DEC Alpha Options. (line 10)
* mno-space-regs: HPPA Options. (line 45)
* mno-spe: RS/6000 and PowerPC Options.
(line 196)
* mno-specld-anomaly: Blackfin Options. (line 19)
* mno-split: PDP-11 Options. (line 71)
* mno-split-addresses: MIPS Options. (line 239)
* mno-sse: i386 and x86-64 Options.
(line 389)
* mno-stack-align: CRIS Options. (line 60)
* mno-stack-bias: SPARC Options. (line 220)
* mno-strict-align <1>: RS/6000 and PowerPC Options.
(line 380)
* mno-strict-align: M680x0 Options. (line 152)
* mno-string: RS/6000 and PowerPC Options.
(line 328)
* mno-sum-in-toc: RS/6000 and PowerPC Options.
(line 233)
* mno-svr3-shlib: i386 and x86-64 Options.
(line 287)
* mno-swdiv: RS/6000 and PowerPC Options.
(line 154)
* mno-sym32: MIPS Options. (line 209)
* mno-tablejump: AVR Options. (line 47)
* mno-target-align: Xtensa Options. (line 47)
* mno-text-section-literals: Xtensa Options. (line 35)
* mno-toc: RS/6000 and PowerPC Options.
(line 402)
* mno-toplevel-symbols: MMIX Options. (line 40)
* mno-tpf-trace: S/390 and zSeries Options.
(line 122)
* mno-unaligned-doubles: SPARC Options. (line 59)
* mno-uninit-const-in-rodata: MIPS Options. (line 233)
* mno-update: RS/6000 and PowerPC Options.
(line 339)
* mno-v8plus: SPARC Options. (line 168)
* mno-vis: SPARC Options. (line 175)
* mno-vliw-branch: FRV Options. (line 170)
* mno-volatile-asm-stop: IA-64 Options. (line 32)
* mno-vrsave: RS/6000 and PowerPC Options.
(line 173)
* mno-wide-bitfields: MCore Options. (line 23)
* mno-xgot: MIPS Options. (line 127)
* mno-xl-compat: RS/6000 and PowerPC Options.
(line 268)
* mno-zero-extend: MMIX Options. (line 27)
* mnobitfield: M680x0 Options. (line 100)
* mnomacsave: SH Options. (line 92)
* mnominmax: M68hc1x Options. (line 31)
* mnop-fun-dllimport: ARM Options. (line 174)
* mold-mnemonics: RS/6000 and PowerPC Options.
(line 85)
* momit-leaf-frame-pointer <1>: i386 and x86-64 Options.
(line 443)
* momit-leaf-frame-pointer: Blackfin Options. (line 7)
* mone-byte-bool: Darwin Options. (line 83)
* moptimize-membar: FRV Options. (line 201)
* MP: Preprocessor Options.
(line 226)
* mpa-risc-1-0: HPPA Options. (line 19)
* mpa-risc-1-1: HPPA Options. (line 19)
* mpa-risc-2-0: HPPA Options. (line 19)
* mpack: FRV Options. (line 119)
* mpacked-stack: S/390 and zSeries Options.
(line 46)
* mpadstruct: SH Options. (line 106)
* mpaired-single: MIPS Options. (line 183)
* mparallel-insns: TMS320C3x/C4x Options.
(line 115)
* mparallel-mpy: TMS320C3x/C4x Options.
(line 120)
* mparanoid: TMS320C3x/C4x Options.
(line 45)
* mpcrel: M680x0 Options. (line 144)
* mpdebug: CRIS Options. (line 40)
* mpe: RS/6000 and PowerPC Options.
(line 288)
* mpentium: i386 and x86-64 Options.
(line 142)
* mpentiumpro: i386 and x86-64 Options.
(line 142)
* mpic-register: ARM Options. (line 183)
* mpoke-function-name: ARM Options. (line 197)
* mpopcntb: RS/6000 and PowerPC Options.
(line 25)
* mportable-runtime: HPPA Options. (line 71)
* mpower: RS/6000 and PowerPC Options.
(line 25)
* mpower2: RS/6000 and PowerPC Options.
(line 25)
* mpowerpc: RS/6000 and PowerPC Options.
(line 25)
* mpowerpc-gfxopt: RS/6000 and PowerPC Options.
(line 25)
* mpowerpc-gpopt: RS/6000 and PowerPC Options.
(line 25)
* mpowerpc64: RS/6000 and PowerPC Options.
(line 25)
* mprefergot: SH Options. (line 113)
* mpreferred-stack-boundary: i386 and x86-64 Options.
(line 351)
* mprioritize-restricted-insns: RS/6000 and PowerPC Options.
(line 425)
* mprolog-function: V850 Options. (line 23)
* mprologue-epilogue: CRIS Options. (line 76)
* mprototype: RS/6000 and PowerPC Options.
(line 511)
* mpt-fixed: SH Options. (line 194)
* mpush-args <1>: i386 and x86-64 Options.
(line 408)
* mpush-args: CRX Options. (line 13)
* MQ: Preprocessor Options.
(line 252)
* mregister-names: IA-64 Options. (line 37)
* mregnames: RS/6000 and PowerPC Options.
(line 615)
* mregparm <1>: TMS320C3x/C4x Options.
(line 109)
* mregparm: i386 and x86-64 Options.
(line 316)
* mrelax <1>: SH Options. (line 70)
* mrelax <2>: MN10300 Options. (line 34)
* mrelax: H8/300 Options. (line 9)
* mrelax-immediate: MCore Options. (line 19)
* mrelocatable: RS/6000 and PowerPC Options.
(line 385)
* mrelocatable-lib: RS/6000 and PowerPC Options.
(line 393)
* mreturn-pointer-on-d0: MN10300 Options. (line 24)
* mrodata: ARC Options. (line 30)
* mrptb: TMS320C3x/C4x Options.
(line 72)
* mrpts: TMS320C3x/C4x Options.
(line 81)
* mrtd <1>: Function Attributes.
(line 100)
* mrtd <2>: M680x0 Options. (line 109)
* mrtd: i386 and x86-64 Options.
(line 292)
* ms: H8/300 Options. (line 17)
* ms2600: H8/300 Options. (line 24)
* mscc: FRV Options. (line 140)
* msched-ar-data-spec: IA-64 Options. (line 128)
* msched-ar-in-data-spec: IA-64 Options. (line 149)
* msched-br-data-spec: IA-64 Options. (line 121)
* msched-br-in-data-spec: IA-64 Options. (line 142)
* msched-control-ldc: IA-64 Options. (line 168)
* msched-control-spec: IA-64 Options. (line 135)
* msched-costly-dep: RS/6000 and PowerPC Options.
(line 432)
* msched-count-spec-in-critical-path: IA-64 Options. (line 194)
* msched-in-control-spec: IA-64 Options. (line 156)
* msched-ldc: IA-64 Options. (line 162)
* msched-prefer-non-control-spec-insns: IA-64 Options. (line 187)
* msched-prefer-non-data-spec-insns: IA-64 Options. (line 180)
* msched-spec-verbose: IA-64 Options. (line 176)
* mschedule: HPPA Options. (line 78)
* mscore5: Score Options. (line 25)
* mscore5u: Score Options. (line 28)
* mscore7: Score Options. (line 31)
* mscore7d: Score Options. (line 34)
* msda: V850 Options. (line 40)
* msdata <1>: RS/6000 and PowerPC Options.
(line 589)
* msdata: IA-64 Options. (line 42)
* msdata-data: RS/6000 and PowerPC Options.
(line 594)
* msdata=default: RS/6000 and PowerPC Options.
(line 589)
* msdata=eabi: RS/6000 and PowerPC Options.
(line 569)
* msdata=none <1>: RS/6000 and PowerPC Options.
(line 602)
* msdata=none: M32R/D Options. (line 40)
* msdata=sdata: M32R/D Options. (line 49)
* msdata=sysv: RS/6000 and PowerPC Options.
(line 580)
* msdata=use: M32R/D Options. (line 53)
* msecure-plt: RS/6000 and PowerPC Options.
(line 176)
* mshared-library-id: Blackfin Options. (line 49)
* mshort <1>: M68hc1x Options. (line 40)
* mshort: M680x0 Options. (line 94)
* msim <1>: Xstormy16 Options. (line 9)
* msim <2>: RS/6000 and PowerPC Options.
(line 521)
* msim <3>: MT Options. (line 22)
* msim: M32C Options. (line 13)
* msingle-exit: MMIX Options. (line 66)
* msingle-float: MIPS Options. (line 169)
* msingle-pic-base: ARM Options. (line 177)
* msio: HPPA Options. (line 107)
* msize: AVR Options. (line 32)
* mslow-bytes: MCore Options. (line 35)
* msmall: TMS320C3x/C4x Options.
(line 18)
* msmall-data: DEC Alpha Options. (line 195)
* msmall-exec: S/390 and zSeries Options.
(line 72)
* msmall-memory: TMS320C3x/C4x Options.
(line 18)
* msmall-text: DEC Alpha Options. (line 213)
* msoft-float <1>: SPARC Options. (line 25)
* msoft-float <2>: S/390 and zSeries Options.
(line 11)
* msoft-float <3>: RS/6000 and PowerPC Options.
(line 311)
* msoft-float <4>: PDP-11 Options. (line 13)
* msoft-float <5>: MIPS Options. (line 165)
* msoft-float <6>: M680x0 Options. (line 84)
* msoft-float <7>: i386 and x86-64 Options.
(line 205)
* msoft-float <8>: HPPA Options. (line 91)
* msoft-float <9>: FRV Options. (line 22)
* msoft-float <10>: DEC Alpha Options. (line 10)
* msoft-float: ARM Options. (line 45)
* msoft-quad-float: SPARC Options. (line 45)
* msoft-reg-count: M68hc1x Options. (line 43)
* mspace <1>: V850 Options. (line 30)
* mspace: SH Options. (line 110)
* mspe: RS/6000 and PowerPC Options.
(line 196)
* mspecld-anomaly: Blackfin Options. (line 14)
* msplit: PDP-11 Options. (line 68)
* msplit-addresses: MIPS Options. (line 239)
* msse: i386 and x86-64 Options.
(line 389)
* msseregparm: i386 and x86-64 Options.
(line 327)
* mstack-align: CRIS Options. (line 60)
* mstack-bias: SPARC Options. (line 220)
* mstack-guard: S/390 and zSeries Options.
(line 148)
* mstack-size: S/390 and zSeries Options.
(line 148)
* mstackrealign: i386 and x86-64 Options.
(line 337)
* mstrict-align <1>: RS/6000 and PowerPC Options.
(line 380)
* mstrict-align: M680x0 Options. (line 152)
* mstring: RS/6000 and PowerPC Options.
(line 328)
* mstructure-size-boundary: ARM Options. (line 129)
* msvr3-shlib: i386 and x86-64 Options.
(line 287)
* msvr4-struct-return: RS/6000 and PowerPC Options.
(line 485)
* mswdiv: RS/6000 and PowerPC Options.
(line 154)
* msym32: MIPS Options. (line 209)
* mt: IA-64 Options. (line 106)
* MT: Preprocessor Options.
(line 238)
* mtarget-align: Xtensa Options. (line 47)
* mtda: V850 Options. (line 34)
* mtext: ARC Options. (line 30)
* mtext-section-literals: Xtensa Options. (line 35)
* mthreads: i386 and x86-64 Options.
(line 423)
* mthumb: ARM Options. (line 218)
* mthumb-interwork: ARM Options. (line 25)
* mti: TMS320C3x/C4x Options.
(line 102)
* mtiny-stack: AVR Options. (line 50)
* mtls-direct-seg-refs: i386 and x86-64 Options.
(line 451)
* mtls-size: IA-64 Options. (line 97)
* mtoc: RS/6000 and PowerPC Options.
(line 402)
* mtomcat-stats: FRV Options. (line 209)
* mtoplevel-symbols: MMIX Options. (line 40)
* mtp: ARM Options. (line 246)
* mtpcs-frame: ARM Options. (line 222)
* mtpcs-leaf-frame: ARM Options. (line 228)
* mtpf-trace: S/390 and zSeries Options.
(line 122)
* mtrap-precision: DEC Alpha Options. (line 109)
* mtune <1>: SPARC Options. (line 156)
* mtune <2>: S/390 and zSeries Options.
(line 115)
* mtune <3>: RS/6000 and PowerPC Options.
(line 144)
* mtune <4>: MIPS Options. (line 44)
* mtune <5>: IA-64 Options. (line 101)
* mtune <6>: i386 and x86-64 Options.
(line 10)
* mtune <7>: DEC Alpha Options. (line 262)
* mtune <8>: CRIS Options. (line 16)
* mtune: ARM Options. (line 99)
* muclibc: GNU/Linux Options. (line 13)
* muls: Score Options. (line 18)
* multcost=NUMBER: SH Options. (line 124)
* multi_module: Darwin Options. (line 190)
* multilib-library-pic: FRV Options. (line 89)
* multiply_defined: Darwin Options. (line 190)
* multiply_defined_unused: Darwin Options. (line 190)
* munaligned-doubles: SPARC Options. (line 59)
* muninit-const-in-rodata: MIPS Options. (line 233)
* munix: VAX Options. (line 9)
* munix-asm: PDP-11 Options. (line 74)
* mupdate: RS/6000 and PowerPC Options.
(line 339)
* musermode: SH Options. (line 118)
* mv850: V850 Options. (line 49)
* mv850e: V850 Options. (line 69)
* mv850e1: V850 Options. (line 64)
* mv8plus: SPARC Options. (line 168)
* mvis: SPARC Options. (line 175)
* mvliw-branch: FRV Options. (line 164)
* mvms-return-codes: DEC Alpha/VMS Options.
(line 9)
* mvolatile-asm-stop: IA-64 Options. (line 32)
* mvr4130-align: MIPS Options. (line 388)
* mvrsave: RS/6000 and PowerPC Options.
(line 173)
* mvxworks: RS/6000 and PowerPC Options.
(line 542)
* mwarn-dynamicstack: S/390 and zSeries Options.
(line 141)
* mwarn-framesize: S/390 and zSeries Options.
(line 133)
* mwide-bitfields: MCore Options. (line 23)
* mwindiss: RS/6000 and PowerPC Options.
(line 546)
* mwords-little-endian: ARM Options. (line 76)
* mxgot: MIPS Options. (line 127)
* mxl-compat: RS/6000 and PowerPC Options.
(line 268)
* myellowknife: RS/6000 and PowerPC Options.
(line 537)
* mzarch: S/390 and zSeries Options.
(line 87)
* mzda: V850 Options. (line 45)
* mzero-extend: MMIX Options. (line 27)
* no-integrated-cpp: C Dialect Options. (line 217)
* no-red-zone: i386 and x86-64 Options.
(line 472)
* no_dead_strip_inits_and_terms: Darwin Options. (line 190)
* noall_load: Darwin Options. (line 190)
* nocpp: MIPS Options. (line 304)
* nodefaultlibs: Link Options. (line 62)
* nofixprebinding: Darwin Options. (line 190)
* nolibdld: HPPA Options. (line 190)
* nomultidefs: Darwin Options. (line 190)
* noprebind: Darwin Options. (line 190)
* noseglinkedit: Darwin Options. (line 190)
* nostartfiles: Link Options. (line 57)
* nostdinc: Preprocessor Options.
(line 373)
* nostdinc++ <1>: Preprocessor Options.
(line 378)
* nostdinc++: C++ Dialect Options.
(line 225)
* nostdlib: Link Options. (line 71)
* o: Preprocessor Options.
(line 72)
* O: Optimize Options. (line 32)
* o: Overall Options. (line 175)
* O0: Optimize Options. (line 104)
* O1: Optimize Options. (line 32)
* O2: Optimize Options. (line 63)
* O3: Optimize Options. (line 99)
* Os: Optimize Options. (line 107)
* P: Preprocessor Options.
(line 551)
* p: Debugging Options. (line 130)
* pagezero_size: Darwin Options. (line 190)
* param: Optimize Options. (line 1358)
* pass-exit-codes: Overall Options. (line 133)
* pedantic <1>: Warnings and Errors.
(line 25)
* pedantic <2>: Alternate Keywords. (line 29)
* pedantic <3>: C Extensions. (line 6)
* pedantic <4>: Preprocessor Options.
(line 163)
* pedantic <5>: Warning Options. (line 27)
* pedantic: Standards. (line 13)
* pedantic-errors <1>: Warnings and Errors.
(line 25)
* pedantic-errors <2>: Non-bugs. (line 216)
* pedantic-errors <3>: Preprocessor Options.
(line 168)
* pedantic-errors <4>: Warning Options. (line 69)
* pedantic-errors: Standards. (line 13)
* pg: Debugging Options. (line 136)
* pie: Link Options. (line 92)
* pipe: Overall Options. (line 197)
* prebind: Darwin Options. (line 190)
* prebind_all_twolevel_modules: Darwin Options. (line 190)
* preprocessor: Preprocessor Options.
(line 24)
* print-file-name: Debugging Options. (line 728)
* print-libgcc-file-name: Debugging Options. (line 749)
* print-multi-directory: Debugging Options. (line 734)
* print-multi-lib: Debugging Options. (line 739)
* print-objc-runtime-info: Objective-C and Objective-C++ Dialect Options.
(line 244)
* print-prog-name: Debugging Options. (line 746)
* print-search-dirs: Debugging Options. (line 757)
* private_bundle: Darwin Options. (line 190)
* pthread <1>: SPARC Options. (line 240)
* pthread <2>: RS/6000 and PowerPC Options.
(line 653)
* pthread: IA-64 Options. (line 106)
* pthreads: SPARC Options. (line 234)
* Q: Debugging Options. (line 142)
* Qn: System V Options. (line 18)
* Qy: System V Options. (line 14)
* rdynamic: Link Options. (line 98)
* read_only_relocs: Darwin Options. (line 190)
* remap: Preprocessor Options.
(line 599)
* s: Link Options. (line 105)
* S <1>: Link Options. (line 20)
* S: Overall Options. (line 158)
* save-temps: Debugging Options. (line 690)
* sectalign: Darwin Options. (line 190)
* sectcreate: Darwin Options. (line 190)
* sectobjectsymbols: Darwin Options. (line 190)
* sectorder: Darwin Options. (line 190)
* seg1addr: Darwin Options. (line 190)
* seg_addr_table: Darwin Options. (line 190)
* seg_addr_table_filename: Darwin Options. (line 190)
* segaddr: Darwin Options. (line 190)
* seglinkedit: Darwin Options. (line 190)
* segprot: Darwin Options. (line 190)
* segs_read_only_addr: Darwin Options. (line 190)
* segs_read_write_addr: Darwin Options. (line 190)
* shared: Link Options. (line 114)
* shared-libgcc: Link Options. (line 122)
* sim: CRIS Options. (line 108)
* sim2: CRIS Options. (line 114)
* single_module: Darwin Options. (line 190)
* specs: Directory Options. (line 84)
* static <1>: HPPA Options. (line 194)
* static <2>: Darwin Options. (line 190)
* static: Link Options. (line 109)
* static-libgcc: Link Options. (line 122)
* std <1>: Non-bugs. (line 107)
* std <2>: Other Builtins. (line 22)
* std <3>: C Dialect Options. (line 47)
* std: Standards. (line 13)
* std=: Preprocessor Options.
(line 324)
* sub_library: Darwin Options. (line 190)
* sub_umbrella: Darwin Options. (line 190)
* symbolic: Link Options. (line 157)
* sysroot: Directory Options. (line 92)
* target-help <1>: Preprocessor Options.
(line 604)
* target-help: Overall Options. (line 228)
* threads <1>: SPARC Options. (line 228)
* threads: HPPA Options. (line 207)
* time: Debugging Options. (line 704)
* tls: FRV Options. (line 75)
* TLS: FRV Options. (line 72)
* traditional <1>: Incompatibilities. (line 6)
* traditional: C Dialect Options. (line 229)
* traditional-cpp <1>: Preprocessor Options.
(line 582)
* traditional-cpp: C Dialect Options. (line 229)
* trigraphs <1>: Preprocessor Options.
(line 586)
* trigraphs: C Dialect Options. (line 213)
* twolevel_namespace: Darwin Options. (line 190)
* u: Link Options. (line 179)
* U: Preprocessor Options.
(line 56)
* umbrella: Darwin Options. (line 190)
* undef: Preprocessor Options.
(line 60)
* undefined: Darwin Options. (line 190)
* unexported_symbols_list: Darwin Options. (line 190)
* V: Target Options. (line 24)
* v <1>: Preprocessor Options.
(line 608)
* v: Overall Options. (line 186)
* version <1>: Preprocessor Options.
(line 621)
* version: Overall Options. (line 232)
* W: Incompatibilities. (line 64)
* w: Preprocessor Options.
(line 159)
* W: Warning Options. (line 569)
* w: Warning Options. (line 73)
* Wa: Assembler Options. (line 9)
* Wabi: C++ Dialect Options.
(line 239)
* Waddress: Warning Options. (line 837)
* Waggregate-return: Warning Options. (line 850)
* Wall <1>: Standard Libraries. (line 6)
* Wall <2>: Preprocessor Options.
(line 78)
* Wall: Warning Options. (line 553)
* Wassign-intercept: Objective-C and Objective-C++ Dialect Options.
(line 198)
* Wattributes: Warning Options. (line 855)
* Wbad-function-cast: Warning Options. (line 785)
* Wcast-align: Warning Options. (line 799)
* Wcast-qual: Warning Options. (line 794)
* Wchar-subscripts: Warning Options. (line 79)
* Wcomment <1>: Preprocessor Options.
(line 86)
* Wcomment: Warning Options. (line 84)
* Wcomments: Preprocessor Options.
(line 86)
* Wconversion <1>: Protoize Caveats. (line 31)
* Wconversion: Warning Options. (line 817)
* Wctor-dtor-privacy: C++ Dialect Options.
(line 317)
* Wdeclaration-after-statement: Warning Options. (line 751)
* Wdisabled-optimization: Warning Options. (line 1104)
* Wdiv-by-zero: Warning Options. (line 643)
* weak_reference_mismatches: Darwin Options. (line 190)
* Weffc++: C++ Dialect Options.
(line 343)
* Wendif-labels <1>: Preprocessor Options.
(line 136)
* Wendif-labels: Warning Options. (line 761)
* Werror <1>: Preprocessor Options.
(line 149)
* Werror: Warning Options. (line 1119)
* Werror-implicit-function-declaration: Warning Options. (line 198)
* Werror=: Warning Options. (line 1122)
* Wextra: Warning Options. (line 569)
* Wfatal-errors: Warning Options. (line 89)
* Wfloat-equal: Warning Options. (line 659)
* Wformat <1>: Function Attributes.
(line 281)
* Wformat: Warning Options. (line 94)
* Wformat-nonliteral <1>: Function Attributes.
(line 334)
* Wformat-nonliteral: Warning Options. (line 151)
* Wformat-security: Warning Options. (line 156)
* Wformat-y2k: Warning Options. (line 129)
* Wformat=2: Warning Options. (line 167)
* whatsloaded: Darwin Options. (line 190)
* whyload: Darwin Options. (line 190)
* Wimplicit: Warning Options. (line 204)
* Wimplicit-function-declaration: Warning Options. (line 198)
* Wimplicit-int: Warning Options. (line 193)
* Wimport: Preprocessor Options.
(line 109)
* Winit-self: Warning Options. (line 179)
* Winline <1>: Inline. (line 42)
* Winline: Warning Options. (line 1048)
* Winvalid-pch: Warning Options. (line 1083)
* Wl: Link Options. (line 175)
* Wlarger-than: Warning Options. (line 770)
* Wlong-long: Warning Options. (line 1087)
* Wmain: Warning Options. (line 208)
* Wmissing-braces: Warning Options. (line 214)
* Wmissing-declarations: Warning Options. (line 877)
* Wmissing-field-initializers: Warning Options. (line 883)
* Wmissing-format-attribute: Warning Options. (line 909)
* Wmissing-include-dirs: Warning Options. (line 224)
* Wmissing-noreturn: Warning Options. (line 901)
* Wmissing-prototypes: Warning Options. (line 871)
* Wmultichar: Warning Options. (line 928)
* Wnested-externs: Warning Options. (line 1023)
* Wno-address: Warning Options. (line 837)
* Wno-attributes: Warning Options. (line 855)
* Wno-deprecated: C++ Dialect Options.
(line 373)
* Wno-deprecated-declarations: Warning Options. (line 977)
* Wno-div-by-zero: Warning Options. (line 643)
* Wno-endif-labels: Warning Options. (line 761)
* Wno-format-extra-args: Warning Options. (line 133)
* Wno-format-zero-length: Warning Options. (line 147)
* Wno-import: Warning Options. (line 76)
* Wno-int-to-pointer-cast: Warning Options. (line 1075)
* Wno-invalid-offsetof: Warning Options. (line 1061)
* Wno-long-long: Warning Options. (line 1087)
* Wno-multichar: Warning Options. (line 928)
* Wno-non-template-friend: C++ Dialect Options.
(line 384)
* Wno-overflow: Warning Options. (line 983)
* Wno-pmf-conversions <1>: Bound member functions.
(line 35)
* Wno-pmf-conversions: C++ Dialect Options.
(line 425)
* Wno-pointer-sign: Warning Options. (line 1113)
* Wno-pointer-to-int-cast: Warning Options. (line 1079)
* Wno-pragmas: Warning Options. (line 481)
* Wno-protocol: Objective-C and Objective-C++ Dialect Options.
(line 202)
* Wno-variadic-macros: Warning Options. (line 1093)
* Wno-volatile-register-var: Warning Options. (line 1099)
* Wnon-virtual-dtor: C++ Dialect Options.
(line 322)
* Wnonnull: Warning Options. (line 172)
* Wnormalized: Warning Options. (line 934)
* Wold-style-cast: C++ Dialect Options.
(line 400)
* Wold-style-definition: Warning Options. (line 867)
* Woverlength-strings: Warning Options. (line 1141)
* Woverloaded-virtual: C++ Dialect Options.
(line 406)
* Woverride-init: Warning Options. (line 986)
* Wp: Preprocessor Options.
(line 13)
* Wpacked: Warning Options. (line 994)
* Wpadded: Warning Options. (line 1011)
* Wparentheses: Warning Options. (line 227)
* Wpointer-arith <1>: Pointer Arith. (line 13)
* Wpointer-arith: Warning Options. (line 779)
* Wpointer-sign: Warning Options. (line 1113)
* Wpragmas: Warning Options. (line 481)
* Wredundant-decls: Warning Options. (line 1018)
* Wreorder: C++ Dialect Options.
(line 327)
* Wreturn-type: Warning Options. (line 319)
* Wselector: Objective-C and Objective-C++ Dialect Options.
(line 212)
* Wsequence-point: Warning Options. (line 273)
* Wshadow: Warning Options. (line 765)
* Wsign-compare: Warning Options. (line 830)
* Wsign-promo: C++ Dialect Options.
(line 429)
* Wstack-protector: Warning Options. (line 1136)
* Wstrict-aliasing: Warning Options. (line 486)
* Wstrict-aliasing=2: Warning Options. (line 493)
* Wstrict-null-sentinel: C++ Dialect Options.
(line 377)
* Wstrict-overflow: Warning Options. (line 502)
* Wstrict-prototypes: Warning Options. (line 861)
* Wstrict-selector-match: Objective-C and Objective-C++ Dialect Options.
(line 224)
* Wswitch: Warning Options. (line 338)
* Wswitch-enum: Warning Options. (line 349)
* Wswitch-switch: Warning Options. (line 346)
* Wsystem-headers <1>: Preprocessor Options.
(line 153)
* Wsystem-headers: Warning Options. (line 648)
* Wtraditional <1>: Preprocessor Options.
(line 103)
* Wtraditional: Warning Options. (line 674)
* Wtrigraphs <1>: Preprocessor Options.
(line 91)
* Wtrigraphs: Warning Options. (line 355)
* Wundeclared-selector: Objective-C and Objective-C++ Dialect Options.
(line 232)
* Wundef <1>: Preprocessor Options.
(line 112)
* Wundef: Warning Options. (line 758)
* Wuninitialized: Warning Options. (line 400)
* Wunknown-pragmas: Warning Options. (line 474)
* Wunreachable-code: Warning Options. (line 1026)
* Wunsafe-loop-optimizations: Warning Options. (line 773)
* Wunused: Warning Options. (line 393)
* Wunused-function: Warning Options. (line 360)
* Wunused-label: Warning Options. (line 365)
* Wunused-macros: Preprocessor Options.
(line 117)
* Wunused-parameter: Warning Options. (line 372)
* Wunused-value: Warning Options. (line 387)
* Wunused-variable: Warning Options. (line 379)
* Wvariadic-macros: Warning Options. (line 1093)
* Wvolatile-register-var: Warning Options. (line 1099)
* Wwrite-strings: Warning Options. (line 805)
* x <1>: Preprocessor Options.
(line 308)
* x: Overall Options. (line 109)
* Xassembler: Assembler Options. (line 13)
* Xlinker: Link Options. (line 163)
* Ym: System V Options. (line 26)
* YP: System V Options. (line 22)
File: gcc.info, Node: Keyword Index, Prev: Option Index, Up: Top
Keyword Index
*************
[index ]
* Menu:
* ! in constraint: Multi-Alternative. (line 33)
* # in constraint: Modifiers. (line 57)
* #pragma: Pragmas. (line 6)
* #pragma implementation: C++ Interface. (line 39)
* #pragma implementation, implied: C++ Interface. (line 46)
* #pragma interface: C++ Interface. (line 20)
* #pragma, reason for not using: Function Attributes.
(line 916)
* $: Dollar Signs. (line 6)
* % in constraint: Modifiers. (line 45)
* %include: Spec Files. (line 27)
* %include_noerr: Spec Files. (line 31)
* %rename: Spec Files. (line 35)
* & in constraint: Modifiers. (line 25)
* ': Incompatibilities. (line 116)
* * in constraint: Modifiers. (line 62)
* + in constraint: Modifiers. (line 12)
* -lgcc, use with -nodefaultlibs: Link Options. (line 79)
* -lgcc, use with -nostdlib: Link Options. (line 79)
* -nodefaultlibs and unresolved references: Link Options. (line 79)
* -nostdlib and unresolved references: Link Options. (line 79)
* .sdata/.sdata2 references (PowerPC): RS/6000 and PowerPC Options.
(line 607)
* //: C++ Comments. (line 6)
* 0 in constraint: Simple Constraints. (line 115)
* < in constraint: Simple Constraints. (line 46)
* = in constraint: Modifiers. (line 8)
* > in constraint: Simple Constraints. (line 50)
* ? in constraint: Multi-Alternative. (line 27)
* ?: extensions: Conditionals. (line 6)
* ?: side effect: Conditionals. (line 20)
* _ in variables in macros: Typeof. (line 42)
* __builtin___fprintf_chk: Object Size Checking.
(line 6)
* __builtin___memcpy_chk: Object Size Checking.
(line 6)
* __builtin___memmove_chk: Object Size Checking.
(line 6)
* __builtin___mempcpy_chk: Object Size Checking.
(line 6)
* __builtin___memset_chk: Object Size Checking.
(line 6)
* __builtin___printf_chk: Object Size Checking.
(line 6)
* __builtin___snprintf_chk: Object Size Checking.
(line 6)
* __builtin___sprintf_chk: Object Size Checking.
(line 6)
* __builtin___stpcpy_chk: Object Size Checking.
(line 6)
* __builtin___strcat_chk: Object Size Checking.
(line 6)
* __builtin___strcpy_chk: Object Size Checking.
(line 6)
* __builtin___strncat_chk: Object Size Checking.
(line 6)
* __builtin___strncpy_chk: Object Size Checking.
(line 6)
* __builtin___vfprintf_chk: Object Size Checking.
(line 6)
* __builtin___vprintf_chk: Object Size Checking.
(line 6)
* __builtin___vsnprintf_chk: Object Size Checking.
(line 6)
* __builtin___vsprintf_chk: Object Size Checking.
(line 6)
* __builtin_apply: Constructing Calls. (line 31)
* __builtin_apply_args: Constructing Calls. (line 20)
* __builtin_choose_expr: Other Builtins. (line 150)
* __builtin_clz: Other Builtins. (line 383)
* __builtin_clzl: Other Builtins. (line 401)
* __builtin_clzll: Other Builtins. (line 421)
* __builtin_constant_p: Other Builtins. (line 190)
* __builtin_ctz: Other Builtins. (line 387)
* __builtin_ctzl: Other Builtins. (line 405)
* __builtin_ctzll: Other Builtins. (line 425)
* __builtin_expect: Other Builtins. (line 236)
* __builtin_ffs: Other Builtins. (line 379)
* __builtin_ffsl: Other Builtins. (line 397)
* __builtin_ffsll: Other Builtins. (line 417)
* __builtin_frame_address: Return Address. (line 34)
* __builtin_huge_val: Other Builtins. (line 300)
* __builtin_huge_valf: Other Builtins. (line 305)
* __builtin_huge_vall: Other Builtins. (line 308)
* __builtin_inf: Other Builtins. (line 312)
* __builtin_infd128: Other Builtins. (line 322)
* __builtin_infd32: Other Builtins. (line 316)
* __builtin_infd64: Other Builtins. (line 319)
* __builtin_inff: Other Builtins. (line 326)
* __builtin_infl: Other Builtins. (line 331)
* __builtin_isgreater: Other Builtins. (line 6)
* __builtin_isgreaterequal: Other Builtins. (line 6)
* __builtin_isless: Other Builtins. (line 6)
* __builtin_islessequal: Other Builtins. (line 6)
* __builtin_islessgreater: Other Builtins. (line 6)
* __builtin_isunordered: Other Builtins. (line 6)
* __builtin_nan: Other Builtins. (line 335)
* __builtin_nand128: Other Builtins. (line 357)
* __builtin_nand32: Other Builtins. (line 351)
* __builtin_nand64: Other Builtins. (line 354)
* __builtin_nanf: Other Builtins. (line 361)
* __builtin_nanl: Other Builtins. (line 364)
* __builtin_nans: Other Builtins. (line 368)
* __builtin_nansf: Other Builtins. (line 372)
* __builtin_nansl: Other Builtins. (line 375)
* __builtin_object_size: Object Size Checking.
(line 6)
* __builtin_offsetof: Offsetof. (line 6)
* __builtin_parity: Other Builtins. (line 394)
* __builtin_parityl: Other Builtins. (line 413)
* __builtin_parityll: Other Builtins. (line 433)
* __builtin_popcount: Other Builtins. (line 391)
* __builtin_popcountl: Other Builtins. (line 409)
* __builtin_popcountll: Other Builtins. (line 429)
* __builtin_powi: Other Builtins. (line 6)
* __builtin_powif: Other Builtins. (line 6)
* __builtin_powil: Other Builtins. (line 6)
* __builtin_prefetch: Other Builtins. (line 261)
* __builtin_return: Constructing Calls. (line 48)
* __builtin_return_address: Return Address. (line 11)
* __builtin_types_compatible_p: Other Builtins. (line 104)
* __complex__ keyword: Complex. (line 6)
* __declspec(dllexport): Function Attributes.
(line 161)
* __declspec(dllimport): Function Attributes.
(line 193)
* __extension__: Alternate Keywords. (line 29)
* __func__ identifier: Function Names. (line 6)
* __FUNCTION__ identifier: Function Names. (line 6)
* __imag__ keyword: Complex. (line 27)
* __PRETTY_FUNCTION__ identifier: Function Names. (line 6)
* __real__ keyword: Complex. (line 27)
* __STDC_HOSTED__: Standards. (line 6)
* __sync_add_and_fetch: Atomic Builtins. (line 57)
* __sync_and_and_fetch: Atomic Builtins. (line 57)
* __sync_bool_compare_and_swap: Atomic Builtins. (line 65)
* __sync_fetch_and_add: Atomic Builtins. (line 45)
* __sync_fetch_and_and: Atomic Builtins. (line 45)
* __sync_fetch_and_nand: Atomic Builtins. (line 45)
* __sync_fetch_and_or: Atomic Builtins. (line 45)
* __sync_fetch_and_sub: Atomic Builtins. (line 45)
* __sync_fetch_and_xor: Atomic Builtins. (line 45)
* __sync_lock_release: Atomic Builtins. (line 95)
* __sync_lock_test_and_set: Atomic Builtins. (line 77)
* __sync_nand_and_fetch: Atomic Builtins. (line 57)
* __sync_or_and_fetch: Atomic Builtins. (line 57)
* __sync_sub_and_fetch: Atomic Builtins. (line 57)
* __sync_synchronize: Atomic Builtins. (line 74)
* __sync_val_compare_and_swap: Atomic Builtins. (line 65)
* __sync_xor_and_fetch: Atomic Builtins. (line 57)
* __thread: Thread-Local. (line 6)
* _Complex keyword: Complex. (line 6)
* _Decimal128 data type: Decimal Float. (line 6)
* _Decimal32 data type: Decimal Float. (line 6)
* _Decimal64 data type: Decimal Float. (line 6)
* _exit: Other Builtins. (line 6)
* _Exit: Other Builtins. (line 6)
* ABI: Compatibility. (line 6)
* abort: Other Builtins. (line 6)
* abs: Other Builtins. (line 6)
* accessing volatiles: Volatiles. (line 6)
* acos: Other Builtins. (line 6)
* acosf: Other Builtins. (line 6)
* acosh: Other Builtins. (line 6)
* acoshf: Other Builtins. (line 6)
* acoshl: Other Builtins. (line 6)
* acosl: Other Builtins. (line 6)
* Ada: G++ and GCC. (line 6)
* address constraints: Simple Constraints. (line 142)
* address of a label: Labels as Values. (line 6)
* address_operand: Simple Constraints. (line 146)
* alias attribute: Function Attributes.
(line 33)
* aliasing of parameters: Code Gen Options. (line 332)
* aligned attribute <1>: Type Attributes. (line 30)
* aligned attribute: Variable Attributes.
(line 23)
* alignment: Alignment. (line 6)
* alloca: Other Builtins. (line 6)
* alloca vs variable-length arrays: Variable Length. (line 27)
* Allow nesting in an interrupt handler on the Blackfin processor.: Function Attributes.
(line 497)
* alternate keywords: Alternate Keywords. (line 6)
* always_inline function attribute: Function Attributes.
(line 46)
* AMD x86-64 Options: i386 and x86-64 Options.
(line 6)
* AMD1: Standards. (line 6)
* ANSI C: Standards. (line 6)
* ANSI C standard: Standards. (line 6)
* ANSI C89: Standards. (line 6)
* ANSI support: C Dialect Options. (line 10)
* ANSI X3.159-1989: Standards. (line 6)
* apostrophes: Incompatibilities. (line 116)
* application binary interface: Compatibility. (line 6)
* ARC Options: ARC Options. (line 6)
* ARM [Annotated C++ Reference Manual]: Backwards Compatibility.
(line 6)
* ARM options: ARM Options. (line 6)
* arrays of length zero: Zero Length. (line 6)
* arrays of variable length: Variable Length. (line 6)
* arrays, non-lvalue: Subscripting. (line 6)
* asin: Other Builtins. (line 6)
* asinf: Other Builtins. (line 6)
* asinh: Other Builtins. (line 6)
* asinhf: Other Builtins. (line 6)
* asinhl: Other Builtins. (line 6)
* asinl: Other Builtins. (line 6)
* asm constraints: Constraints. (line 6)
* asm expressions: Extended Asm. (line 6)
* assembler instructions: Extended Asm. (line 6)
* assembler names for identifiers: Asm Labels. (line 6)
* assembly code, invalid: Bug Criteria. (line 12)
* atan: Other Builtins. (line 6)
* atan2: Other Builtins. (line 6)
* atan2f: Other Builtins. (line 6)
* atan2l: Other Builtins. (line 6)
* atanf: Other Builtins. (line 6)
* atanh: Other Builtins. (line 6)
* atanhf: Other Builtins. (line 6)
* atanhl: Other Builtins. (line 6)
* atanl: Other Builtins. (line 6)
* attribute of types: Type Attributes. (line 6)
* attribute of variables: Variable Attributes.
(line 6)
* attribute syntax: Attribute Syntax. (line 6)
* autoincrement/decrement addressing: Simple Constraints. (line 28)
* automatic inline for C++ member fns: Inline. (line 53)
* AVR Options: AVR Options. (line 6)
* Backwards Compatibility: Backwards Compatibility.
(line 6)
* base class members: Name lookup. (line 6)
* bcmp: Other Builtins. (line 6)
* below100 attribute: Variable Attributes.
(line 449)
* binary compatibility: Compatibility. (line 6)
* Blackfin Options: Blackfin Options. (line 6)
* bound pointer to member function: Bound member functions.
(line 6)
* bounds checking: Optimize Options. (line 333)
* bug criteria: Bug Criteria. (line 6)
* bugs: Bugs. (line 6)
* bugs, known: Trouble. (line 6)
* built-in functions <1>: Other Builtins. (line 6)
* built-in functions: C Dialect Options. (line 149)
* bzero: Other Builtins. (line 6)
* C compilation options: Invoking GCC. (line 17)
* C intermediate output, nonexistent: G++ and GCC. (line 35)
* C language extensions: C Extensions. (line 6)
* C language, traditional: C Dialect Options. (line 227)
* C standard: Standards. (line 6)
* C standards: Standards. (line 6)
* c++: Invoking G++. (line 13)
* C++: G++ and GCC. (line 30)
* C++ comments: C++ Comments. (line 6)
* C++ compilation options: Invoking GCC. (line 23)
* C++ interface and implementation headers: C++ Interface. (line 6)
* C++ language extensions: C++ Extensions. (line 6)
* C++ member fns, automatically inline: Inline. (line 53)
* C++ misunderstandings: C++ Misunderstandings.
(line 6)
* C++ options, command line: C++ Dialect Options.
(line 6)
* C++ pragmas, effect on inlining: C++ Interface. (line 66)
* C++ source file suffixes: Invoking G++. (line 6)
* C++ static data, declaring and defining: Static Definitions.
(line 6)
* C89: Standards. (line 6)
* C90: Standards. (line 6)
* C94: Standards. (line 6)
* C95: Standards. (line 6)
* C99: Standards. (line 6)
* C9X: Standards. (line 6)
* C_INCLUDE_PATH: Environment Variables.
(line 124)
* cabs: Other Builtins. (line 6)
* cabsf: Other Builtins. (line 6)
* cabsl: Other Builtins. (line 6)
* cacos: Other Builtins. (line 6)
* cacosf: Other Builtins. (line 6)
* cacosh: Other Builtins. (line 6)
* cacoshf: Other Builtins. (line 6)
* cacoshl: Other Builtins. (line 6)
* cacosl: Other Builtins. (line 6)
* calling functions through the function vector on the H8/300 processors: Function Attributes.
(line 373)
* calloc: Other Builtins. (line 6)
* carg: Other Builtins. (line 6)
* cargf: Other Builtins. (line 6)
* cargl: Other Builtins. (line 6)
* case labels in initializers: Designated Inits. (line 6)
* case ranges: Case Ranges. (line 6)
* casin: Other Builtins. (line 6)
* casinf: Other Builtins. (line 6)
* casinh: Other Builtins. (line 6)
* casinhf: Other Builtins. (line 6)
* casinhl: Other Builtins. (line 6)
* casinl: Other Builtins. (line 6)
* cast to a union: Cast to Union. (line 6)
* catan: Other Builtins. (line 6)
* catanf: Other Builtins. (line 6)
* catanh: Other Builtins. (line 6)
* catanhf: Other Builtins. (line 6)
* catanhl: Other Builtins. (line 6)
* catanl: Other Builtins. (line 6)
* cbrt: Other Builtins. (line 6)
* cbrtf: Other Builtins. (line 6)
* cbrtl: Other Builtins. (line 6)
* ccos: Other Builtins. (line 6)
* ccosf: Other Builtins. (line 6)
* ccosh: Other Builtins. (line 6)
* ccoshf: Other Builtins. (line 6)
* ccoshl: Other Builtins. (line 6)
* ccosl: Other Builtins. (line 6)
* ceil: Other Builtins. (line 6)
* ceilf: Other Builtins. (line 6)
* ceill: Other Builtins. (line 6)
* cexp: Other Builtins. (line 6)
* cexpf: Other Builtins. (line 6)
* cexpl: Other Builtins. (line 6)
* character set, execution: Preprocessor Options.
(line 467)
* character set, input: Preprocessor Options.
(line 480)
* character set, input normalization: Warning Options. (line 934)
* character set, wide execution: Preprocessor Options.
(line 472)
* cimag: Other Builtins. (line 6)
* cimagf: Other Builtins. (line 6)
* cimagl: Other Builtins. (line 6)
* cleanup attribute: Variable Attributes.
(line 76)
* clog: Other Builtins. (line 6)
* clogf: Other Builtins. (line 6)
* clogl: Other Builtins. (line 6)
* COBOL: G++ and GCC. (line 23)
* code generation conventions: Code Gen Options. (line 6)
* code, mixed with declarations: Mixed Declarations. (line 6)
* command options: Invoking GCC. (line 6)
* comments, C++ style: C++ Comments. (line 6)
* common attribute: Variable Attributes.
(line 92)
* comparison of signed and unsigned values, warning: Warning Options.
(line 830)
* compiler bugs, reporting: Bug Reporting. (line 6)
* compiler compared to C++ preprocessor: G++ and GCC. (line 35)
* compiler options, C++: C++ Dialect Options.
(line 6)
* compiler options, Objective-C and Objective-C++: Objective-C and Objective-C++ Dialect Options.
(line 6)
* compiler version, specifying: Target Options. (line 6)
* COMPILER_PATH: Environment Variables.
(line 85)
* complex conjugation: Complex. (line 34)
* complex numbers: Complex. (line 6)
* compound literals: Compound Literals. (line 6)
* computed gotos: Labels as Values. (line 6)
* conditional expressions, extensions: Conditionals. (line 6)
* conflicting types: Disappointments. (line 21)
* conj: Other Builtins. (line 6)
* conjf: Other Builtins. (line 6)
* conjl: Other Builtins. (line 6)
* const applied to function: Function Attributes.
(line 6)
* const function attribute: Function Attributes.
(line 106)
* constants in constraints: Simple Constraints. (line 58)
* constraint modifier characters: Modifiers. (line 6)
* constraint, matching: Simple Constraints. (line 127)
* constraints, asm: Constraints. (line 6)
* constraints, machine specific: Machine Constraints.
(line 6)
* constructing calls: Constructing Calls. (line 6)
* constructor expressions: Compound Literals. (line 6)
* constructor function attribute: Function Attributes.
(line 132)
* contributors: Contributors. (line 6)
* copysign: Other Builtins. (line 6)
* copysignf: Other Builtins. (line 6)
* copysignl: Other Builtins. (line 6)
* core dump: Bug Criteria. (line 9)
* cos: Other Builtins. (line 6)
* cosf: Other Builtins. (line 6)
* cosh: Other Builtins. (line 6)
* coshf: Other Builtins. (line 6)
* coshl: Other Builtins. (line 6)
* cosl: Other Builtins. (line 6)
* CPATH: Environment Variables.
(line 123)
* CPLUS_INCLUDE_PATH: Environment Variables.
(line 125)
* cpow: Other Builtins. (line 6)
* cpowf: Other Builtins. (line 6)
* cpowl: Other Builtins. (line 6)
* cproj: Other Builtins. (line 6)
* cprojf: Other Builtins. (line 6)
* cprojl: Other Builtins. (line 6)
* creal: Other Builtins. (line 6)
* crealf: Other Builtins. (line 6)
* creall: Other Builtins. (line 6)
* CRIS Options: CRIS Options. (line 6)
* cross compiling: Target Options. (line 6)
* CRX Options: CRX Options. (line 6)
* csin: Other Builtins. (line 6)
* csinf: Other Builtins. (line 6)
* csinh: Other Builtins. (line 6)
* csinhf: Other Builtins. (line 6)
* csinhl: Other Builtins. (line 6)
* csinl: Other Builtins. (line 6)
* csqrt: Other Builtins. (line 6)
* csqrtf: Other Builtins. (line 6)
* csqrtl: Other Builtins. (line 6)
* ctan: Other Builtins. (line 6)
* ctanf: Other Builtins. (line 6)
* ctanh: Other Builtins. (line 6)
* ctanhf: Other Builtins. (line 6)
* ctanhl: Other Builtins. (line 6)
* ctanl: Other Builtins. (line 6)
* Darwin options: Darwin Options. (line 6)
* dcgettext: Other Builtins. (line 6)
* DD integer suffix: Decimal Float. (line 6)
* dd integer suffix: Decimal Float. (line 6)
* deallocating variable length arrays: Variable Length. (line 23)
* debugging information options: Debugging Options. (line 6)
* decimal floating types: Decimal Float. (line 6)
* declaration scope: Incompatibilities. (line 80)
* declarations inside expressions: Statement Exprs. (line 6)
* declarations, mixed with code: Mixed Declarations. (line 6)
* declaring attributes of functions: Function Attributes.
(line 6)
* declaring static data in C++: Static Definitions. (line 6)
* defining static data in C++: Static Definitions. (line 6)
* dependencies for make as output: Environment Variables.
(line 151)
* dependencies, make: Preprocessor Options.
(line 173)
* DEPENDENCIES_OUTPUT: Environment Variables.
(line 150)
* dependent name lookup: Name lookup. (line 6)
* deprecated attribute: Variable Attributes.
(line 100)
* deprecated attribute.: Function Attributes.
(line 143)
* designated initializers: Designated Inits. (line 6)
* designator lists: Designated Inits. (line 94)
* designators: Designated Inits. (line 61)
* destructor function attribute: Function Attributes.
(line 132)
* DF integer suffix: Decimal Float. (line 6)
* df integer suffix: Decimal Float. (line 6)
* dgettext: Other Builtins. (line 6)
* diagnostic messages: Language Independent Options.
(line 6)
* dialect options: C Dialect Options. (line 6)
* digits in constraint: Simple Constraints. (line 115)
* directory options: Directory Options. (line 6)
* DL integer suffix: Decimal Float. (line 6)
* dl integer suffix: Decimal Float. (line 6)
* dollar signs in identifier names: Dollar Signs. (line 6)
* double-word arithmetic: Long Long. (line 6)
* downward funargs: Nested Functions. (line 6)
* drem: Other Builtins. (line 6)
* dremf: Other Builtins. (line 6)
* dreml: Other Builtins. (line 6)
* E in constraint: Simple Constraints. (line 77)
* earlyclobber operand: Modifiers. (line 25)
* eight bit data on the H8/300, H8/300H, and H8S: Function Attributes.
(line 240)
* empty structures: Empty Structures. (line 6)
* environment variables: Environment Variables.
(line 6)
* erf: Other Builtins. (line 6)
* erfc: Other Builtins. (line 6)
* erfcf: Other Builtins. (line 6)
* erfcl: Other Builtins. (line 6)
* erff: Other Builtins. (line 6)
* erfl: Other Builtins. (line 6)
* error messages: Warnings and Errors.
(line 6)
* escaped newlines: Escaped Newlines. (line 6)
* exception handler functions on the Blackfin processor: Function Attributes.
(line 250)
* exclamation point: Multi-Alternative. (line 33)
* exit: Other Builtins. (line 6)
* exp: Other Builtins. (line 6)
* exp10: Other Builtins. (line 6)
* exp10f: Other Builtins. (line 6)
* exp10l: Other Builtins. (line 6)
* exp2: Other Builtins. (line 6)
* exp2f: Other Builtins. (line 6)
* exp2l: Other Builtins. (line 6)
* expf: Other Builtins. (line 6)
* expl: Other Builtins. (line 6)
* explicit register variables: Explicit Reg Vars. (line 6)
* expm1: Other Builtins. (line 6)
* expm1f: Other Builtins. (line 6)
* expm1l: Other Builtins. (line 6)
* expressions containing statements: Statement Exprs. (line 6)
* expressions, constructor: Compound Literals. (line 6)
* extended asm: Extended Asm. (line 6)
* extensible constraints: Simple Constraints. (line 151)
* extensions, ?:: Conditionals. (line 6)
* extensions, C language: C Extensions. (line 6)
* extensions, C++ language: C++ Extensions. (line 6)
* external declaration scope: Incompatibilities. (line 80)
* externally_visible attribute.: Function Attributes.
(line 907)
* F in constraint: Simple Constraints. (line 82)
* fabs: Other Builtins. (line 6)
* fabsf: Other Builtins. (line 6)
* fabsl: Other Builtins. (line 6)
* fatal signal: Bug Criteria. (line 9)
* fdim: Other Builtins. (line 6)
* fdimf: Other Builtins. (line 6)
* fdiml: Other Builtins. (line 6)
* FDL, GNU Free Documentation License: GNU Free Documentation License.
(line 6)
* ffs: Other Builtins. (line 6)
* file name suffix: Overall Options. (line 14)
* file names: Link Options. (line 10)
* flatten function attribute: Function Attributes.
(line 91)
* flexible array members: Zero Length. (line 6)
* float as function value type: Incompatibilities. (line 141)
* floating point precision <1>: Disappointments. (line 68)
* floating point precision: Optimize Options. (line 1060)
* floor: Other Builtins. (line 6)
* floorf: Other Builtins. (line 6)
* floorl: Other Builtins. (line 6)
* fma: Other Builtins. (line 6)
* fmaf: Other Builtins. (line 6)
* fmal: Other Builtins. (line 6)
* fmax: Other Builtins. (line 6)
* fmaxf: Other Builtins. (line 6)
* fmaxl: Other Builtins. (line 6)
* fmin: Other Builtins. (line 6)
* fminf: Other Builtins. (line 6)
* fminl: Other Builtins. (line 6)
* fmod: Other Builtins. (line 6)
* fmodf: Other Builtins. (line 6)
* fmodl: Other Builtins. (line 6)
* force_align_arg_pointer attribute: Function Attributes.
(line 636)
* format function attribute: Function Attributes.
(line 281)
* format_arg function attribute: Function Attributes.
(line 334)
* Fortran: G++ and GCC. (line 6)
* forwarding calls: Constructing Calls. (line 6)
* fprintf: Other Builtins. (line 6)
* fprintf_unlocked: Other Builtins. (line 6)
* fputs: Other Builtins. (line 6)
* fputs_unlocked: Other Builtins. (line 6)
* freestanding environment: Standards. (line 6)
* freestanding implementation: Standards. (line 6)
* frexp: Other Builtins. (line 6)
* frexpf: Other Builtins. (line 6)
* frexpl: Other Builtins. (line 6)
* FRV Options: FRV Options. (line 6)
* fscanf: Other Builtins. (line 6)
* fscanf, and constant strings: Incompatibilities. (line 17)
* function addressability on the M32R/D: Function Attributes.
(line 457)
* function attributes: Function Attributes.
(line 6)
* function pointers, arithmetic: Pointer Arith. (line 6)
* function prototype declarations: Function Prototypes.
(line 6)
* function without a prologue/epilogue code: Function Attributes.
(line 485)
* function, size of pointer to: Pointer Arith. (line 6)
* functions called via pointer on the RS/6000 and PowerPC: Function Attributes.
(line 428)
* functions in arbitrary sections: Function Attributes.
(line 6)
* functions that are passed arguments in registers on the 386: Function Attributes.
(line 6)
* functions that behave like malloc: Function Attributes.
(line 6)
* functions that do not pop the argument stack on the 386: Function Attributes.
(line 6)
* functions that do pop the argument stack on the 386: Function Attributes.
(line 100)
* functions that have no side effects: Function Attributes.
(line 6)
* functions that never return: Function Attributes.
(line 6)
* functions that pop the argument stack on the 386: Function Attributes.
(line 6)
* functions that return more than once: Function Attributes.
(line 6)
* functions which do not handle memory bank switching on 68HC11/68HC12: Function Attributes.
(line 491)
* functions which handle memory bank switching: Function Attributes.
(line 256)
* functions with non-null pointer arguments: Function Attributes.
(line 6)
* functions with printf, scanf, strftime or strfmon style arguments: Function Attributes.
(line 6)
* g in constraint: Simple Constraints. (line 108)
* G in constraint: Simple Constraints. (line 86)
* g++: Invoking G++. (line 13)
* G++: G++ and GCC. (line 30)
* gamma: Other Builtins. (line 6)
* gammaf: Other Builtins. (line 6)
* gammal: Other Builtins. (line 6)
* GCC: G++ and GCC. (line 6)
* GCC command options: Invoking GCC. (line 6)
* GCC_EXEC_PREFIX: Environment Variables.
(line 52)
* gcc_struct: Type Attributes. (line 302)
* gcc_struct attribute: Variable Attributes.
(line 313)
* gcov: Debugging Options. (line 168)
* gettext: Other Builtins. (line 6)
* global offset table: Code Gen Options. (line 163)
* global register after longjmp: Global Reg Vars. (line 66)
* global register variables: Global Reg Vars. (line 6)
* GNAT: G++ and GCC. (line 30)
* GNU C Compiler: G++ and GCC. (line 6)
* GNU Compiler Collection: G++ and GCC. (line 6)
* gnu_inline function attribute: Function Attributes.
(line 51)
* goto with computed label: Labels as Values. (line 6)
* gp-relative references (MIPS): MIPS Options. (line 216)
* gprof: Debugging Options. (line 135)
* grouping options: Invoking GCC. (line 26)
* H in constraint: Simple Constraints. (line 86)
* hardware models and configurations, specifying: Submodel Options.
(line 6)
* hex floats: Hex Floats. (line 6)
* hosted environment <1>: C Dialect Options. (line 183)
* hosted environment: Standards. (line 6)
* hosted implementation: Standards. (line 6)
* HPPA Options: HPPA Options. (line 6)
* hypot: Other Builtins. (line 6)
* hypotf: Other Builtins. (line 6)
* hypotl: Other Builtins. (line 6)
* I in constraint: Simple Constraints. (line 69)
* i in constraint: Simple Constraints. (line 58)
* i386 Options: i386 and x86-64 Options.
(line 6)
* IA-64 Options: IA-64 Options. (line 6)
* IBM RS/6000 and PowerPC Options: RS/6000 and PowerPC Options.
(line 6)
* identifier names, dollar signs in: Dollar Signs. (line 6)
* identifiers, names in assembler code: Asm Labels. (line 6)
* ilogb: Other Builtins. (line 6)
* ilogbf: Other Builtins. (line 6)
* ilogbl: Other Builtins. (line 6)
* imaxabs: Other Builtins. (line 6)
* implementation-defined behavior, C language: C Implementation.
(line 6)
* implied #pragma implementation: C++ Interface. (line 46)
* incompatibilities of GCC: Incompatibilities. (line 6)
* increment operators: Bug Criteria. (line 17)
* index: Other Builtins. (line 6)
* indirect calls on ARM: Function Attributes.
(line 418)
* indirect calls on MIPS: Function Attributes.
(line 440)
* init_priority attribute: C++ Attributes. (line 9)
* initializations in expressions: Compound Literals. (line 6)
* initializers with labeled elements: Designated Inits. (line 6)
* initializers, non-constant: Initializers. (line 6)
* inline automatic for C++ member fns: Inline. (line 53)
* inline functions: Inline. (line 6)
* inline functions, omission of: Inline. (line 58)
* inlining and C++ pragmas: C++ Interface. (line 66)
* installation trouble: Trouble. (line 6)
* integrating function code: Inline. (line 6)
* Intel 386 Options: i386 and x86-64 Options.
(line 6)
* interface and implementation headers, C++: C++ Interface. (line 6)
* intermediate C version, nonexistent: G++ and GCC. (line 35)
* interrupt handler functions: Function Attributes.
(line 384)
* interrupt handler functions on the Blackfin, m68k, H8/300 and SH processors: Function Attributes.
(line 406)
* introduction: Top. (line 6)
* invalid assembly code: Bug Criteria. (line 12)
* invalid input: Bug Criteria. (line 42)
* invoking g++: Invoking G++. (line 21)
* isalnum: Other Builtins. (line 6)
* isalpha: Other Builtins. (line 6)
* isascii: Other Builtins. (line 6)
* isblank: Other Builtins. (line 6)
* iscntrl: Other Builtins. (line 6)
* isdigit: Other Builtins. (line 6)
* isgraph: Other Builtins. (line 6)
* islower: Other Builtins. (line 6)
* ISO 9899: Standards. (line 6)
* ISO C: Standards. (line 6)
* ISO C standard: Standards. (line 6)
* ISO C90: Standards. (line 6)
* ISO C94: Standards. (line 6)
* ISO C95: Standards. (line 6)
* ISO C99: Standards. (line 6)
* ISO C9X: Standards. (line 6)
* ISO support: C Dialect Options. (line 10)
* ISO/IEC 9899: Standards. (line 6)
* isprint: Other Builtins. (line 6)
* ispunct: Other Builtins. (line 6)
* isspace: Other Builtins. (line 6)
* isupper: Other Builtins. (line 6)
* iswalnum: Other Builtins. (line 6)
* iswalpha: Other Builtins. (line 6)
* iswblank: Other Builtins. (line 6)
* iswcntrl: Other Builtins. (line 6)
* iswdigit: Other Builtins. (line 6)
* iswgraph: Other Builtins. (line 6)
* iswlower: Other Builtins. (line 6)
* iswprint: Other Builtins. (line 6)
* iswpunct: Other Builtins. (line 6)
* iswspace: Other Builtins. (line 6)
* iswupper: Other Builtins. (line 6)
* iswxdigit: Other Builtins. (line 6)
* isxdigit: Other Builtins. (line 6)
* j0: Other Builtins. (line 6)
* j0f: Other Builtins. (line 6)
* j0l: Other Builtins. (line 6)
* j1: Other Builtins. (line 6)
* j1f: Other Builtins. (line 6)
* j1l: Other Builtins. (line 6)
* Java: G++ and GCC. (line 6)
* java_interface attribute: C++ Attributes. (line 29)
* jn: Other Builtins. (line 6)
* jnf: Other Builtins. (line 6)
* jnl: Other Builtins. (line 6)
* keywords, alternate: Alternate Keywords. (line 6)
* known causes of trouble: Trouble. (line 6)
* labeled elements in initializers: Designated Inits. (line 6)
* labels as values: Labels as Values. (line 6)
* labs: Other Builtins. (line 6)
* LANG: Environment Variables.
(line 21)
* language dialect options: C Dialect Options. (line 6)
* LC_ALL: Environment Variables.
(line 21)
* LC_CTYPE: Environment Variables.
(line 21)
* LC_MESSAGES: Environment Variables.
(line 21)
* ldexp: Other Builtins. (line 6)
* ldexpf: Other Builtins. (line 6)
* ldexpl: Other Builtins. (line 6)
* length-zero arrays: Zero Length. (line 6)
* lgamma: Other Builtins. (line 6)
* lgammaf: Other Builtins. (line 6)
* lgammal: Other Builtins. (line 6)
* Libraries: Link Options. (line 24)
* LIBRARY_PATH: Environment Variables.
(line 91)
* link options: Link Options. (line 6)
* LL integer suffix: Long Long. (line 6)
* llabs: Other Builtins. (line 6)
* llrint: Other Builtins. (line 6)
* llrintf: Other Builtins. (line 6)
* llrintl: Other Builtins. (line 6)
* llround: Other Builtins. (line 6)
* llroundf: Other Builtins. (line 6)
* llroundl: Other Builtins. (line 6)
* load address instruction: Simple Constraints. (line 142)
* local labels: Local Labels. (line 6)
* local variables in macros: Typeof. (line 42)
* local variables, specifying registers: Local Reg Vars. (line 6)
* locale: Environment Variables.
(line 21)
* locale definition: Environment Variables.
(line 100)
* log: Other Builtins. (line 6)
* log10: Other Builtins. (line 6)
* log10f: Other Builtins. (line 6)
* log10l: Other Builtins. (line 6)
* log1p: Other Builtins. (line 6)
* log1pf: Other Builtins. (line 6)
* log1pl: Other Builtins. (line 6)
* log2: Other Builtins. (line 6)
* log2f: Other Builtins. (line 6)
* log2l: Other Builtins. (line 6)
* logb: Other Builtins. (line 6)
* logbf: Other Builtins. (line 6)
* logbl: Other Builtins. (line 6)
* logf: Other Builtins. (line 6)
* logl: Other Builtins. (line 6)
* long long data types: Long Long. (line 6)
* longjmp: Global Reg Vars. (line 66)
* longjmp incompatibilities: Incompatibilities. (line 39)
* longjmp warnings: Warning Options. (line 457)
* lrint: Other Builtins. (line 6)
* lrintf: Other Builtins. (line 6)
* lrintl: Other Builtins. (line 6)
* lround: Other Builtins. (line 6)
* lroundf: Other Builtins. (line 6)
* lroundl: Other Builtins. (line 6)
* m in constraint: Simple Constraints. (line 17)
* M32C options: M32C Options. (line 6)
* M32R/D options: M32R/D Options. (line 6)
* M680x0 options: M680x0 Options. (line 6)
* M68hc1x options: M68hc1x Options. (line 6)
* machine dependent options: Submodel Options. (line 6)
* machine specific constraints: Machine Constraints.
(line 6)
* macro with variable arguments: Variadic Macros. (line 6)
* macros containing asm: Extended Asm. (line 239)
* macros, inline alternative: Inline. (line 6)
* macros, local labels: Local Labels. (line 6)
* macros, local variables in: Typeof. (line 42)
* macros, statements in expressions: Statement Exprs. (line 6)
* macros, types of arguments: Typeof. (line 6)
* make: Preprocessor Options.
(line 173)
* malloc: Other Builtins. (line 6)
* malloc attribute: Function Attributes.
(line 447)
* matching constraint: Simple Constraints. (line 127)
* MCore options: MCore Options. (line 6)
* member fns, automatically inline: Inline. (line 53)
* memcmp: Other Builtins. (line 6)
* memcpy: Other Builtins. (line 6)
* memory references in constraints: Simple Constraints. (line 17)
* mempcpy: Other Builtins. (line 6)
* memset: Other Builtins. (line 6)
* Mercury: G++ and GCC. (line 23)
* message formatting: Language Independent Options.
(line 6)
* messages, warning: Warning Options. (line 6)
* messages, warning and error: Warnings and Errors.
(line 6)
* middle-operands, omitted: Conditionals. (line 6)
* MIPS options: MIPS Options. (line 6)
* misunderstandings in C++: C++ Misunderstandings.
(line 6)
* mixed declarations and code: Mixed Declarations. (line 6)
* mktemp, and constant strings: Incompatibilities. (line 13)
* MMIX Options: MMIX Options. (line 6)
* MN10300 options: MN10300 Options. (line 6)
* mode attribute: Variable Attributes.
(line 118)
* modf: Other Builtins. (line 6)
* modff: Other Builtins. (line 6)
* modfl: Other Builtins. (line 6)
* modifiers in constraints: Modifiers. (line 6)
* ms_struct: Type Attributes. (line 302)
* ms_struct attribute: Variable Attributes.
(line 313)
* MT options: MT Options. (line 6)
* mudflap: Optimize Options. (line 333)
* multiple alternative constraints: Multi-Alternative. (line 6)
* multiprecision arithmetic: Long Long. (line 6)
* n in constraint: Simple Constraints. (line 63)
* names used in assembler code: Asm Labels. (line 6)
* naming convention, implementation headers: C++ Interface. (line 46)
* nearbyint: Other Builtins. (line 6)
* nearbyintf: Other Builtins. (line 6)
* nearbyintl: Other Builtins. (line 6)
* nested functions: Nested Functions. (line 6)
* newlines (escaped): Escaped Newlines. (line 6)
* nextafter: Other Builtins. (line 6)
* nextafterf: Other Builtins. (line 6)
* nextafterl: Other Builtins. (line 6)
* nexttoward: Other Builtins. (line 6)
* nexttowardf: Other Builtins. (line 6)
* nexttowardl: Other Builtins. (line 6)
* NFC: Warning Options. (line 934)
* NFKC: Warning Options. (line 934)
* NMI handler functions on the Blackfin processor: Function Attributes.
(line 502)
* no_instrument_function function attribute: Function Attributes.
(line 508)
* nocommon attribute: Variable Attributes.
(line 92)
* noinline function attribute: Function Attributes.
(line 513)
* non-constant initializers: Initializers. (line 6)
* non-static inline function: Inline. (line 70)
* nonnull function attribute: Function Attributes.
(line 517)
* noreturn function attribute: Function Attributes.
(line 540)
* nothrow function attribute: Function Attributes.
(line 582)
* o in constraint: Simple Constraints. (line 21)
* OBJC_INCLUDE_PATH: Environment Variables.
(line 126)
* Objective-C <1>: Standards. (line 110)
* Objective-C: G++ and GCC. (line 6)
* Objective-C and Objective-C++ options, command line: Objective-C and Objective-C++ Dialect Options.
(line 6)
* Objective-C++ <1>: Standards. (line 110)
* Objective-C++: G++ and GCC. (line 6)
* offsettable address: Simple Constraints. (line 21)
* old-style function definitions: Function Prototypes.
(line 6)
* omitted middle-operands: Conditionals. (line 6)
* open coding: Inline. (line 6)
* openmp parallel: C Dialect Options. (line 200)
* operand constraints, asm: Constraints. (line 6)
* optimize options: Optimize Options. (line 6)
* options to control diagnostics formatting: Language Independent Options.
(line 6)
* options to control warnings: Warning Options. (line 6)
* options, C++: C++ Dialect Options.
(line 6)
* options, code generation: Code Gen Options. (line 6)
* options, debugging: Debugging Options. (line 6)
* options, dialect: C Dialect Options. (line 6)
* options, directory search: Directory Options. (line 6)
* options, GCC command: Invoking GCC. (line 6)
* options, grouping: Invoking GCC. (line 26)
* options, linking: Link Options. (line 6)
* options, Objective-C and Objective-C++: Objective-C and Objective-C++ Dialect Options.
(line 6)
* options, optimization: Optimize Options. (line 6)
* options, order: Invoking GCC. (line 30)
* options, preprocessor: Preprocessor Options.
(line 6)
* order of evaluation, side effects: Non-bugs. (line 196)
* order of options: Invoking GCC. (line 30)
* other register constraints: Simple Constraints. (line 151)
* output file option: Overall Options. (line 174)
* overloaded virtual fn, warning: C++ Dialect Options.
(line 406)
* p in constraint: Simple Constraints. (line 142)
* packed attribute: Variable Attributes.
(line 129)
* parameter forward declaration: Variable Length. (line 60)
* parameters, aliased: Code Gen Options. (line 332)
* Pascal: G++ and GCC. (line 23)
* PDP-11 Options: PDP-11 Options. (line 6)
* PIC: Code Gen Options. (line 163)
* pmf: Bound member functions.
(line 6)
* pointer arguments: Function Attributes.
(line 111)
* pointer to member function: Bound member functions.
(line 6)
* portions of temporary objects, pointers to: Temporaries. (line 6)
* pow: Other Builtins. (line 6)
* pow10: Other Builtins. (line 6)
* pow10f: Other Builtins. (line 6)
* pow10l: Other Builtins. (line 6)
* PowerPC options: PowerPC Options. (line 6)
* powf: Other Builtins. (line 6)
* powl: Other Builtins. (line 6)
* pragma, align: Solaris Pragmas. (line 11)
* pragma, diagnostic: Diagnostic Pragmas. (line 14)
* pragma, extern_prefix: Symbol-Renaming Pragmas.
(line 19)
* pragma, fini: Solaris Pragmas. (line 19)
* pragma, init: Solaris Pragmas. (line 24)
* pragma, long_calls: ARM Pragmas. (line 11)
* pragma, long_calls_off: ARM Pragmas. (line 17)
* pragma, longcall: RS/6000 and PowerPC Pragmas.
(line 14)
* pragma, mark: Darwin Pragmas. (line 11)
* pragma, memregs: M32C Pragmas. (line 7)
* pragma, no_long_calls: ARM Pragmas. (line 14)
* pragma, options align: Darwin Pragmas. (line 14)
* pragma, reason for not using: Function Attributes.
(line 916)
* pragma, redefine_extname: Symbol-Renaming Pragmas.
(line 14)
* pragma, segment: Darwin Pragmas. (line 21)
* pragma, unused: Darwin Pragmas. (line 24)
* pragma, visibility: Visibility Pragmas. (line 8)
* pragma, weak: Weak Pragmas. (line 10)
* pragmas: Pragmas. (line 6)
* pragmas in C++, effect on inlining: C++ Interface. (line 66)
* pragmas, interface and implementation: C++ Interface. (line 6)
* pragmas, warning of unknown: Warning Options. (line 474)
* precompiled headers: Precompiled Headers.
(line 6)
* preprocessing numbers: Incompatibilities. (line 173)
* preprocessing tokens: Incompatibilities. (line 173)
* preprocessor options: Preprocessor Options.
(line 6)
* printf: Other Builtins. (line 6)
* printf_unlocked: Other Builtins. (line 6)
* prof: Debugging Options. (line 129)
* promotion of formal parameters: Function Prototypes.
(line 6)
* pure function attribute: Function Attributes.
(line 590)
* push address instruction: Simple Constraints. (line 142)
* putchar: Other Builtins. (line 6)
* puts: Other Builtins. (line 6)
* qsort, and global register variables: Global Reg Vars. (line 42)
* question mark: Multi-Alternative. (line 27)
* r in constraint: Simple Constraints. (line 54)
* ranges in case statements: Case Ranges. (line 6)
* read-only strings: Incompatibilities. (line 9)
* register variable after longjmp: Global Reg Vars. (line 66)
* registers: Extended Asm. (line 6)
* registers for local variables: Local Reg Vars. (line 6)
* registers in constraints: Simple Constraints. (line 54)
* registers, global allocation: Explicit Reg Vars. (line 6)
* registers, global variables in: Global Reg Vars. (line 6)
* regparm attribute: Function Attributes.
(line 612)
* relocation truncated to fit (MIPS): MIPS Options. (line 135)
* remainder: Other Builtins. (line 6)
* remainderf: Other Builtins. (line 6)
* remainderl: Other Builtins. (line 6)
* remquo: Other Builtins. (line 6)
* remquof: Other Builtins. (line 6)
* remquol: Other Builtins. (line 6)
* reordering, warning: C++ Dialect Options.
(line 327)
* reporting bugs: Bugs. (line 6)
* rest argument (in macro): Variadic Macros. (line 6)
* restricted pointers: Restricted Pointers.
(line 6)
* restricted references: Restricted Pointers.
(line 6)
* restricted this pointer: Restricted Pointers.
(line 6)
* returns_twice attribute: Function Attributes.
(line 649)
* rindex: Other Builtins. (line 6)
* rint: Other Builtins. (line 6)
* rintf: Other Builtins. (line 6)
* rintl: Other Builtins. (line 6)
* round: Other Builtins. (line 6)
* roundf: Other Builtins. (line 6)
* roundl: Other Builtins. (line 6)
* RS/6000 and PowerPC Options: RS/6000 and PowerPC Options.
(line 6)
* RTTI: Vague Linkage. (line 43)
* run-time options: Code Gen Options. (line 6)
* s in constraint: Simple Constraints. (line 90)
* S/390 and zSeries Options: S/390 and zSeries Options.
(line 6)
* save all registers on the Blackfin, H8/300, H8/300H, and H8S: Function Attributes.
(line 658)
* scalb: Other Builtins. (line 6)
* scalbf: Other Builtins. (line 6)
* scalbl: Other Builtins. (line 6)
* scalbln: Other Builtins. (line 6)
* scalblnf: Other Builtins. (line 6)
* scalbn: Other Builtins. (line 6)
* scalbnf: Other Builtins. (line 6)
* scanf, and constant strings: Incompatibilities. (line 17)
* scanfnl: Other Builtins. (line 6)
* scope of a variable length array: Variable Length. (line 23)
* scope of declaration: Disappointments. (line 21)
* scope of external declarations: Incompatibilities. (line 80)
* Score Options: Score Options. (line 6)
* search path: Directory Options. (line 6)
* section function attribute: Function Attributes.
(line 663)
* section variable attribute: Variable Attributes.
(line 144)
* sentinel function attribute: Function Attributes.
(line 679)
* setjmp: Global Reg Vars. (line 66)
* setjmp incompatibilities: Incompatibilities. (line 39)
* shared strings: Incompatibilities. (line 9)
* shared variable attribute: Variable Attributes.
(line 189)
* side effect in ?:: Conditionals. (line 20)
* side effects, macro argument: Statement Exprs. (line 35)
* side effects, order of evaluation: Non-bugs. (line 196)
* signal handler functions on the AVR processors: Function Attributes.
(line 710)
* signbit: Other Builtins. (line 6)
* signbitf: Other Builtins. (line 6)
* signbitl: Other Builtins. (line 6)
* signed and unsigned values, comparison warning: Warning Options.
(line 830)
* significand: Other Builtins. (line 6)
* significandf: Other Builtins. (line 6)
* significandl: Other Builtins. (line 6)
* simple constraints: Simple Constraints. (line 6)
* sin: Other Builtins. (line 6)
* sincos: Other Builtins. (line 6)
* sincosf: Other Builtins. (line 6)
* sincosl: Other Builtins. (line 6)
* sinf: Other Builtins. (line 6)
* sinh: Other Builtins. (line 6)
* sinhf: Other Builtins. (line 6)
* sinhl: Other Builtins. (line 6)
* sinl: Other Builtins. (line 6)
* sizeof: Typeof. (line 6)
* smaller data references: M32R/D Options. (line 57)
* smaller data references (MIPS): MIPS Options. (line 216)
* smaller data references (PowerPC): RS/6000 and PowerPC Options.
(line 607)
* snprintf: Other Builtins. (line 6)
* SPARC options: SPARC Options. (line 6)
* Spec Files: Spec Files. (line 6)
* specified registers: Explicit Reg Vars. (line 6)
* specifying compiler version and target machine: Target Options.
(line 6)
* specifying hardware config: Submodel Options. (line 6)
* specifying machine version: Target Options. (line 6)
* specifying registers for local variables: Local Reg Vars. (line 6)
* speed of compilation: Precompiled Headers.
(line 6)
* sprintf: Other Builtins. (line 6)
* sqrt: Other Builtins. (line 6)
* sqrtf: Other Builtins. (line 6)
* sqrtl: Other Builtins. (line 6)
* sscanf: Other Builtins. (line 6)
* sscanf, and constant strings: Incompatibilities. (line 17)
* sseregparm attribute: Function Attributes.
(line 629)
* statements inside expressions: Statement Exprs. (line 6)
* static data in C++, declaring and defining: Static Definitions.
(line 6)
* stpcpy: Other Builtins. (line 6)
* stpncpy: Other Builtins. (line 6)
* strcasecmp: Other Builtins. (line 6)
* strcat: Other Builtins. (line 6)
* strchr: Other Builtins. (line 6)
* strcmp: Other Builtins. (line 6)
* strcpy: Other Builtins. (line 6)
* strcspn: Other Builtins. (line 6)
* strdup: Other Builtins. (line 6)
* strfmon: Other Builtins. (line 6)
* strftime: Other Builtins. (line 6)
* string constants: Incompatibilities. (line 9)
* strlen: Other Builtins. (line 6)
* strncasecmp: Other Builtins. (line 6)
* strncat: Other Builtins. (line 6)
* strncmp: Other Builtins. (line 6)
* strncpy: Other Builtins. (line 6)
* strndup: Other Builtins. (line 6)
* strpbrk: Other Builtins. (line 6)
* strrchr: Other Builtins. (line 6)
* strspn: Other Builtins. (line 6)
* strstr: Other Builtins. (line 6)
* struct: Unnamed Fields. (line 6)
* structures: Incompatibilities. (line 146)
* structures, constructor expression: Compound Literals. (line 6)
* submodel options: Submodel Options. (line 6)
* subscripting: Subscripting. (line 6)
* subscripting and function values: Subscripting. (line 6)
* suffixes for C++ source: Invoking G++. (line 6)
* SUNPRO_DEPENDENCIES: Environment Variables.
(line 166)
* suppressing warnings: Warning Options. (line 6)
* surprises in C++: C++ Misunderstandings.
(line 6)
* syntax checking: Warning Options. (line 22)
* system headers, warnings from: Warning Options. (line 648)
* tan: Other Builtins. (line 6)
* tanf: Other Builtins. (line 6)
* tanh: Other Builtins. (line 6)
* tanhf: Other Builtins. (line 6)
* tanhl: Other Builtins. (line 6)
* tanl: Other Builtins. (line 6)
* target machine, specifying: Target Options. (line 6)
* target options: Target Options. (line 6)
* TC1: Standards. (line 6)
* TC2: Standards. (line 6)
* Technical Corrigenda: Standards. (line 6)
* Technical Corrigendum 1: Standards. (line 6)
* Technical Corrigendum 2: Standards. (line 6)
* template instantiation: Template Instantiation.
(line 6)
* temporaries, lifetime of: Temporaries. (line 6)
* tgamma: Other Builtins. (line 6)
* tgammaf: Other Builtins. (line 6)
* tgammal: Other Builtins. (line 6)
* Thread-Local Storage: Thread-Local. (line 6)
* thunks: Nested Functions. (line 6)
* tiny data section on the H8/300H and H8S: Function Attributes.
(line 732)
* TLS: Thread-Local. (line 6)
* tls_model attribute: Variable Attributes.
(line 213)
* TMPDIR: Environment Variables.
(line 45)
* TMS320C3x/C4x Options: TMS320C3x/C4x Options.
(line 6)
* toascii: Other Builtins. (line 6)
* tolower: Other Builtins. (line 6)
* toupper: Other Builtins. (line 6)
* towlower: Other Builtins. (line 6)
* towupper: Other Builtins. (line 6)
* traditional C language: C Dialect Options. (line 227)
* treelang <1>: Standards. (line 123)
* treelang: G++ and GCC. (line 6)
* trunc: Other Builtins. (line 6)
* truncf: Other Builtins. (line 6)
* truncl: Other Builtins. (line 6)
* two-stage name lookup: Name lookup. (line 6)
* type alignment: Alignment. (line 6)
* type attributes: Type Attributes. (line 6)
* type_info: Vague Linkage. (line 43)
* typedef names as function parameters: Incompatibilities. (line 97)
* typeof: Typeof. (line 6)
* ULL integer suffix: Long Long. (line 6)
* Ultrix calling convention: Interoperation. (line 150)
* undefined behavior: Bug Criteria. (line 17)
* undefined function value: Bug Criteria. (line 17)
* underscores in variables in macros: Typeof. (line 42)
* union: Unnamed Fields. (line 6)
* union, casting to a: Cast to Union. (line 6)
* unions: Incompatibilities. (line 146)
* unknown pragmas, warning: Warning Options. (line 474)
* unresolved references and -nodefaultlibs: Link Options. (line 79)
* unresolved references and -nostdlib: Link Options. (line 79)
* unused attribute.: Function Attributes.
(line 744)
* used attribute.: Function Attributes.
(line 749)
* User stack pointer in interrupts on the Blackfin: Function Attributes.
(line 413)
* V in constraint: Simple Constraints. (line 41)
* V850 Options: V850 Options. (line 6)
* vague linkage: Vague Linkage. (line 6)
* value after longjmp: Global Reg Vars. (line 66)
* variable addressability on the IA-64: Function Attributes.
(line 457)
* variable addressability on the M32R/D: Variable Attributes.
(line 294)
* variable alignment: Alignment. (line 6)
* variable attributes: Variable Attributes.
(line 6)
* variable number of arguments: Variadic Macros. (line 6)
* variable-length array scope: Variable Length. (line 23)
* variable-length arrays: Variable Length. (line 6)
* variables in specified registers: Explicit Reg Vars. (line 6)
* variables, local, in macros: Typeof. (line 42)
* variadic macros: Variadic Macros. (line 6)
* VAX calling convention: Interoperation. (line 150)
* VAX options: VAX Options. (line 6)
* vfprintf: Other Builtins. (line 6)
* vfscanf: Other Builtins. (line 6)
* visibility attribute: Function Attributes.
(line 755)
* VLAs: Variable Length. (line 6)
* void pointers, arithmetic: Pointer Arith. (line 6)
* void, size of pointer to: Pointer Arith. (line 6)
* volatile access: Volatiles. (line 6)
* volatile applied to function: Function Attributes.
(line 6)
* volatile read: Volatiles. (line 6)
* volatile write: Volatiles. (line 6)
* vprintf: Other Builtins. (line 6)
* vscanf: Other Builtins. (line 6)
* vsnprintf: Other Builtins. (line 6)
* vsprintf: Other Builtins. (line 6)
* vsscanf: Other Builtins. (line 6)
* vtable: Vague Linkage. (line 28)
* warn_unused_result attribute: Function Attributes.
(line 849)
* warning for comparison of signed and unsigned values: Warning Options.
(line 830)
* warning for overloaded virtual fn: C++ Dialect Options.
(line 406)
* warning for reordering of member initializers: C++ Dialect Options.
(line 327)
* warning for unknown pragmas: Warning Options. (line 474)
* warning messages: Warning Options. (line 6)
* warnings from system headers: Warning Options. (line 648)
* warnings vs errors: Warnings and Errors.
(line 6)
* weak attribute: Function Attributes.
(line 866)
* weakref attribute: Function Attributes.
(line 875)
* whitespace: Incompatibilities. (line 112)
* X in constraint: Simple Constraints. (line 112)
* X3.159-1989: Standards. (line 6)
* x86-64 options: x86-64 Options. (line 6)
* x86-64 Options: i386 and x86-64 Options.
(line 6)
* Xstormy16 Options: Xstormy16 Options. (line 6)
* Xtensa Options: Xtensa Options. (line 6)
* y0: Other Builtins. (line 6)
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* yn: Other Builtins. (line 6)
* ynf: Other Builtins. (line 6)
* ynl: Other Builtins. (line 6)
* zero-length arrays: Zero Length. (line 6)
* zero-size structures: Empty Structures. (line 6)
* zSeries options: zSeries Options. (line 6)
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End Tag Table