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START-INFO-DIR-ENTRY
* As: (as). The GNU assembler.
* Gas: (as). The GNU assembler.
END-INFO-DIR-ENTRY
This file documents the GNU Assembler "as".
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002
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 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
File: as.info, Node: Top, Next: Overview, Up: (dir)
Using as
********
This file is a user guide to the GNU assembler `as' version 2.16.
This document is distributed under the terms of the GNU Free
Documentation License. A copy of the license is included in the
section entitled "GNU Free Documentation License".
* Menu:
* Overview:: Overview
* Invoking:: Command-Line Options
* Syntax:: Syntax
* Sections:: Sections and Relocation
* Symbols:: Symbols
* Expressions:: Expressions
* Pseudo Ops:: Assembler Directives
* Machine Dependencies:: Machine Dependent Features
* Reporting Bugs:: Reporting Bugs
* Acknowledgements:: Who Did What
* GNU Free Documentation License:: GNU Free Documentation License
* Index:: Index
File: as.info, Node: Overview, Next: Invoking, Prev: Top, Up: Top
1 Overview
**********
Here is a brief summary of how to invoke `as'. For details, *note
Command-Line Options: Invoking.
as [-a[cdhlns][=FILE]] [-alternate] [-D]
[-defsym SYM=VAL] [-f] [-g] [-gstabs] [-gstabs+]
[-gdwarf-2] [-help] [-I DIR] [-J] [-K] [-L]
[-listing-lhs-width=NUM] [-listing-lhs-width2=NUM]
[-listing-rhs-width=NUM] [-listing-cont-lines=NUM]
[-keep-locals] [-o OBJFILE] [-R] [-statistics] [-v]
[-version] [-version] [-W] [-warn] [-fatal-warnings]
[-w] [-x] [-Z] [-target-help] [TARGET-OPTIONS]
[-|FILES ...]
_Target Alpha options:_
[-mCPU]
[-mdebug | -no-mdebug]
[-relax] [-g] [-GSIZE]
[-F] [-32addr]
_Target ARC options:_
[-marc[5|6|7|8]]
[-EB|-EL]
_Target ARM options:_
[-mcpu=PROCESSOR[+EXTENSION...]]
[-march=ARCHITECTURE[+EXTENSION...]]
[-mfpu=FLOATING-POINT-FORMAT]
[-mfloat-abi=ABI]
[-meabi=VER]
[-mthumb]
[-EB|-EL]
[-mapcs-32|-mapcs-26|-mapcs-float|
-mapcs-reentrant]
[-mthumb-interwork] [-k]
_Target CRIS options:_
[-underscore | -no-underscore]
[-pic] [-N]
[-emulation=criself | -emulation=crisaout]
[-march=v0_v10 | -march=v10 | -march=v32 | -march=common_v10_v32]
_Target D10V options:_
[-O]
_Target D30V options:_
[-O|-n|-N]
_Target i386 options:_
[-32|-64] [-n]
_Target i960 options:_
[-ACA|-ACA_A|-ACB|-ACC|-AKA|-AKB|
-AKC|-AMC]
[-b] [-no-relax]
_Target IA-64 options:_
[-mconstant-gp|-mauto-pic]
[-milp32|-milp64|-mlp64|-mp64]
[-mle|mbe]
[-munwind-check=warning|-munwind-check=error]
[-mhint.b=ok|-mhint.b=warning|-mhint.b=error]
[-x|-xexplicit] [-xauto] [-xdebug]
_Target IP2K options:_
[-mip2022|-mip2022ext]
_Target M32R options:_
[-m32rx|-[no-]warn-explicit-parallel-conflicts|
-W[n]p]
_Target M680X0 options:_
[-l] [-m68000|-m68010|-m68020|...]
_Target M68HC11 options:_
[-m68hc11|-m68hc12|-m68hcs12]
[-mshort|-mlong]
[-mshort-double|-mlong-double]
[-force-long-branchs] [-short-branchs]
[-strict-direct-mode] [-print-insn-syntax]
[-print-opcodes] [-generate-example]
_Target MCORE options:_
[-jsri2bsr] [-sifilter] [-relax]
[-mcpu=[210|340]]
_Target MIPS options:_
[-nocpp] [-EL] [-EB] [-O[OPTIMIZATION LEVEL]]
[-g[DEBUG LEVEL]] [-G NUM] [-KPIC] [-call_shared]
[-non_shared] [-xgot]
[-mabi=ABI] [-32] [-n32] [-64] [-mfp32] [-mgp32]
[-march=CPU] [-mtune=CPU] [-mips1] [-mips2]
[-mips3] [-mips4] [-mips5] [-mips32] [-mips32r2]
[-mips64] [-mips64r2]
[-construct-floats] [-no-construct-floats]
[-trap] [-no-break] [-break] [-no-trap]
[-mfix7000] [-mno-fix7000]
[-mips16] [-no-mips16]
[-mips3d] [-no-mips3d]
[-mdmx] [-no-mdmx]
[-mdebug] [-no-mdebug]
[-mpdr] [-mno-pdr]
_Target MMIX options:_
[-fixed-special-register-names] [-globalize-symbols]
[-gnu-syntax] [-relax] [-no-predefined-symbols]
[-no-expand] [-no-merge-gregs] [-x]
[-linker-allocated-gregs]
_Target PDP11 options:_
[-mpic|-mno-pic] [-mall] [-mno-extensions]
[-mEXTENSION|-mno-EXTENSION]
[-mCPU] [-mMACHINE]
_Target picoJava options:_
[-mb|-me]
_Target PowerPC options:_
[-mpwrx|-mpwr2|-mpwr|-m601|-mppc|-mppc32|-m603|-m604|
-m403|-m405|-mppc64|-m620|-mppc64bridge|-mbooke|
-mbooke32|-mbooke64]
[-mcom|-many|-maltivec] [-memb]
[-mregnames|-mno-regnames]
[-mrelocatable|-mrelocatable-lib]
[-mlittle|-mlittle-endian|-mbig|-mbig-endian]
[-msolaris|-mno-solaris]
_Target SPARC options:_
[-Av6|-Av7|-Av8|-Asparclet|-Asparclite
-Av8plus|-Av8plusa|-Av9|-Av9a]
[-xarch=v8plus|-xarch=v8plusa] [-bump]
[-32|-64]
_Target TIC54X options:_
[-mcpu=54[123589]|-mcpu=54[56]lp] [-mfar-mode|-mf]
[-merrors-to-file <FILENAME>|-me <FILENAME>]
_Target Xtensa options:_
[-[no-]text-section-literals] [-[no-]absolute-literals]
[-[no-]target-align] [-[no-]longcalls]
[-[no-]transform]
[-rename-section OLDNAME=NEWNAME]
`-a[cdhlmns]'
Turn on listings, in any of a variety of ways:
`-ac'
omit false conditionals
`-ad'
omit debugging directives
`-ah'
include high-level source
`-al'
include assembly
`-am'
include macro expansions
`-an'
omit forms processing
`-as'
include symbols
`=file'
set the name of the listing file
You may combine these options; for example, use `-aln' for assembly
listing without forms processing. The `=file' option, if used,
must be the last one. By itself, `-a' defaults to `-ahls'.
`--alternate'
Begin in alternate macro mode, see *Note `.altmacro': Altmacro.
`-D'
Ignored. This option is accepted for script compatibility with
calls to other assemblers.
`--defsym SYM=VALUE'
Define the symbol SYM to be VALUE before assembling the input file.
VALUE must be an integer constant. As in C, a leading `0x'
indicates a hexadecimal value, and a leading `0' indicates an
octal value.
`-f'
"fast"--skip whitespace and comment preprocessing (assume source is
compiler output).
`-g'
`--gen-debug'
Generate debugging information for each assembler source line
using whichever debug format is preferred by the target. This
currently means either STABS, ECOFF or DWARF2.
`--gstabs'
Generate stabs debugging information for each assembler line. This
may help debugging assembler code, if the debugger can handle it.
`--gstabs+'
Generate stabs debugging information for each assembler line, with
GNU extensions that probably only gdb can handle, and that could
make other debuggers crash or refuse to read your program. This
may help debugging assembler code. Currently the only GNU
extension is the location of the current working directory at
assembling time.
`--gdwarf-2'
Generate DWARF2 debugging information for each assembler line.
This may help debugging assembler code, if the debugger can handle
it. Note--this option is only supported by some targets, not all
of them.
`--help'
Print a summary of the command line options and exit.
`--target-help'
Print a summary of all target specific options and exit.
`-I DIR'
Add directory DIR to the search list for `.include' directives.
`-J'
Don't warn about signed overflow.
`-K'
Issue warnings when difference tables altered for long
displacements.
`-L'
`--keep-locals'
Keep (in the symbol table) local symbols. On traditional a.out
systems these start with `L', but different systems have different
local label prefixes.
`--listing-lhs-width=NUMBER'
Set the maximum width, in words, of the output data column for an
assembler listing to NUMBER.
`--listing-lhs-width2=NUMBER'
Set the maximum width, in words, of the output data column for
continuation lines in an assembler listing to NUMBER.
`--listing-rhs-width=NUMBER'
Set the maximum width of an input source line, as displayed in a
listing, to NUMBER bytes.
`--listing-cont-lines=NUMBER'
Set the maximum number of lines printed in a listing for a single
line of input to NUMBER + 1.
`-o OBJFILE'
Name the object-file output from `as' OBJFILE.
`-R'
Fold the data section into the text section.
`--statistics'
Print the maximum space (in bytes) and total time (in seconds)
used by assembly.
`--strip-local-absolute'
Remove local absolute symbols from the outgoing symbol table.
`-v'
`-version'
Print the `as' version.
`--version'
Print the `as' version and exit.
`-W'
`--no-warn'
Suppress warning messages.
`--fatal-warnings'
Treat warnings as errors.
`--warn'
Don't suppress warning messages or treat them as errors.
`-w'
Ignored.
`-x'
Ignored.
`-Z'
Generate an object file even after errors.
`-- | FILES ...'
Standard input, or source files to assemble.
The following options are available when as is configured for an ARC
processor.
`-marc[5|6|7|8]'
This option selects the core processor variant.
`-EB | -EL'
Select either big-endian (-EB) or little-endian (-EL) output.
The following options are available when as is configured for the ARM
processor family.
`-mcpu=PROCESSOR[+EXTENSION...]'
Specify which ARM processor variant is the target.
`-march=ARCHITECTURE[+EXTENSION...]'
Specify which ARM architecture variant is used by the target.
`-mfpu=FLOATING-POINT-FORMAT'
Select which Floating Point architecture is the target.
`-mfloat-abi=ABI'
Select which floating point ABI is in use.
`-mthumb'
Enable Thumb only instruction decoding.
`-mapcs-32 | -mapcs-26 | -mapcs-float | -mapcs-reentrant'
Select which procedure calling convention is in use.
`-EB | -EL'
Select either big-endian (-EB) or little-endian (-EL) output.
`-mthumb-interwork'
Specify that the code has been generated with interworking between
Thumb and ARM code in mind.
`-k'
Specify that PIC code has been generated.
See the info pages for documentation of the CRIS-specific options.
The following options are available when as is configured for a D10V
processor.
`-O'
Optimize output by parallelizing instructions.
The following options are available when as is configured for a D30V
processor.
`-O'
Optimize output by parallelizing instructions.
`-n'
Warn when nops are generated.
`-N'
Warn when a nop after a 32-bit multiply instruction is generated.
The following options are available when as is configured for the
Intel 80960 processor.
`-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC'
Specify which variant of the 960 architecture is the target.
`-b'
Add code to collect statistics about branches taken.
`-no-relax'
Do not alter compare-and-branch instructions for long
displacements; error if necessary.
The following options are available when as is configured for the
Ubicom IP2K series.
`-mip2022ext'
Specifies that the extended IP2022 instructions are allowed.
`-mip2022'
Restores the default behaviour, which restricts the permitted
instructions to just the basic IP2022 ones.
The following options are available when as is configured for the
Renesas M32R (formerly Mitsubishi M32R) series.
`--m32rx'
Specify which processor in the M32R family is the target. The
default is normally the M32R, but this option changes it to the
M32RX.
`--warn-explicit-parallel-conflicts or --Wp'
Produce warning messages when questionable parallel constructs are
encountered.
`--no-warn-explicit-parallel-conflicts or --Wnp'
Do not produce warning messages when questionable parallel
constructs are encountered.
The following options are available when as is configured for the
Motorola 68000 series.
`-l'
Shorten references to undefined symbols, to one word instead of
two.
`-m68000 | -m68008 | -m68010 | -m68020 | -m68030'
`| -m68040 | -m68060 | -m68302 | -m68331 | -m68332'
`| -m68333 | -m68340 | -mcpu32 | -m5200'
Specify what processor in the 68000 family is the target. The
default is normally the 68020, but this can be changed at
configuration time.
`-m68881 | -m68882 | -mno-68881 | -mno-68882'
The target machine does (or does not) have a floating-point
coprocessor. The default is to assume a coprocessor for 68020,
68030, and cpu32. Although the basic 68000 is not compatible with
the 68881, a combination of the two can be specified, since it's
possible to do emulation of the coprocessor instructions with the
main processor.
`-m68851 | -mno-68851'
The target machine does (or does not) have a memory-management
unit coprocessor. The default is to assume an MMU for 68020 and
up.
For details about the PDP-11 machine dependent features options, see
*Note PDP-11-Options::.
`-mpic | -mno-pic'
Generate position-independent (or position-dependent) code. The
default is `-mpic'.
`-mall'
`-mall-extensions'
Enable all instruction set extensions. This is the default.
`-mno-extensions'
Disable all instruction set extensions.
`-mEXTENSION | -mno-EXTENSION'
Enable (or disable) a particular instruction set extension.
`-mCPU'
Enable the instruction set extensions supported by a particular
CPU, and disable all other extensions.
`-mMACHINE'
Enable the instruction set extensions supported by a particular
machine model, and disable all other extensions.
The following options are available when as is configured for a
picoJava processor.
`-mb'
Generate "big endian" format output.
`-ml'
Generate "little endian" format output.
The following options are available when as is configured for the
Motorola 68HC11 or 68HC12 series.
`-m68hc11 | -m68hc12 | -m68hcs12'
Specify what processor is the target. The default is defined by
the configuration option when building the assembler.
`-mshort'
Specify to use the 16-bit integer ABI.
`-mlong'
Specify to use the 32-bit integer ABI.
`-mshort-double'
Specify to use the 32-bit double ABI.
`-mlong-double'
Specify to use the 64-bit double ABI.
`--force-long-branchs'
Relative branches are turned into absolute ones. This concerns
conditional branches, unconditional branches and branches to a sub
routine.
`-S | --short-branchs'
Do not turn relative branchs into absolute ones when the offset is
out of range.
`--strict-direct-mode'
Do not turn the direct addressing mode into extended addressing
mode when the instruction does not support direct addressing mode.
`--print-insn-syntax'
Print the syntax of instruction in case of error.
`--print-opcodes'
print the list of instructions with syntax and then exit.
`--generate-example'
print an example of instruction for each possible instruction and
then exit. This option is only useful for testing `as'.
The following options are available when `as' is configured for the
SPARC architecture:
`-Av6 | -Av7 | -Av8 | -Asparclet | -Asparclite'
`-Av8plus | -Av8plusa | -Av9 | -Av9a'
Explicitly select a variant of the SPARC architecture.
`-Av8plus' and `-Av8plusa' select a 32 bit environment. `-Av9'
and `-Av9a' select a 64 bit environment.
`-Av8plusa' and `-Av9a' enable the SPARC V9 instruction set with
UltraSPARC extensions.
`-xarch=v8plus | -xarch=v8plusa'
For compatibility with the Solaris v9 assembler. These options are
equivalent to -Av8plus and -Av8plusa, respectively.
`-bump'
Warn when the assembler switches to another architecture.
The following options are available when as is configured for the
'c54x architecture.
`-mfar-mode'
Enable extended addressing mode. All addresses and relocations
will assume extended addressing (usually 23 bits).
`-mcpu=CPU_VERSION'
Sets the CPU version being compiled for.
`-merrors-to-file FILENAME'
Redirect error output to a file, for broken systems which don't
support such behaviour in the shell.
The following options are available when as is configured for a MIPS
processor.
`-G NUM'
This option sets the largest size of an object that can be
referenced implicitly with the `gp' register. It is only accepted
for targets that use ECOFF format, such as a DECstation running
Ultrix. The default value is 8.
`-EB'
Generate "big endian" format output.
`-EL'
Generate "little endian" format output.
`-mips1'
`-mips2'
`-mips3'
`-mips4'
`-mips5'
`-mips32'
`-mips32r2'
`-mips64'
`-mips64r2'
Generate code for a particular MIPS Instruction Set Architecture
level. `-mips1' is an alias for `-march=r3000', `-mips2' is an
alias for `-march=r6000', `-mips3' is an alias for `-march=r4000'
and `-mips4' is an alias for `-march=r8000'. `-mips5', `-mips32',
`-mips32r2', `-mips64', and `-mips64r2' correspond to generic
`MIPS V', `MIPS32', `MIPS32 Release 2', `MIPS64', and `MIPS64
Release 2' ISA processors, respectively.
`-march=CPU'
Generate code for a particular MIPS cpu.
`-mtune=CPU'
Schedule and tune for a particular MIPS cpu.
`-mfix7000'
`-mno-fix7000'
Cause nops to be inserted if the read of the destination register
of an mfhi or mflo instruction occurs in the following two
instructions.
`-mdebug'
`-no-mdebug'
Cause stabs-style debugging output to go into an ECOFF-style
.mdebug section instead of the standard ELF .stabs sections.
`-mpdr'
`-mno-pdr'
Control generation of `.pdr' sections.
`-mgp32'
`-mfp32'
The register sizes are normally inferred from the ISA and ABI, but
these flags force a certain group of registers to be treated as 32
bits wide at all times. `-mgp32' controls the size of
general-purpose registers and `-mfp32' controls the size of
floating-point registers.
`-mips16'
`-no-mips16'
Generate code for the MIPS 16 processor. This is equivalent to
putting `.set mips16' at the start of the assembly file.
`-no-mips16' turns off this option.
`-mips3d'
`-no-mips3d'
Generate code for the MIPS-3D Application Specific Extension.
This tells the assembler to accept MIPS-3D instructions.
`-no-mips3d' turns off this option.
`-mdmx'
`-no-mdmx'
Generate code for the MDMX Application Specific Extension. This
tells the assembler to accept MDMX instructions. `-no-mdmx' turns
off this option.
`--construct-floats'
`--no-construct-floats'
The `--no-construct-floats' option disables the construction of
double width floating point constants by loading the two halves of
the value into the two single width floating point registers that
make up the double width register. By default
`--construct-floats' is selected, allowing construction of these
floating point constants.
`--emulation=NAME'
This option causes `as' to emulate `as' configured for some other
target, in all respects, including output format (choosing between
ELF and ECOFF only), handling of pseudo-opcodes which may generate
debugging information or store symbol table information, and
default endianness. The available configuration names are:
`mipsecoff', `mipself', `mipslecoff', `mipsbecoff', `mipslelf',
`mipsbelf'. The first two do not alter the default endianness
from that of the primary target for which the assembler was
configured; the others change the default to little- or big-endian
as indicated by the `b' or `l' in the name. Using `-EB' or `-EL'
will override the endianness selection in any case.
This option is currently supported only when the primary target
`as' is configured for is a MIPS ELF or ECOFF target.
Furthermore, the primary target or others specified with
`--enable-targets=...' at configuration time must include support
for the other format, if both are to be available. For example,
the Irix 5 configuration includes support for both.
Eventually, this option will support more configurations, with more
fine-grained control over the assembler's behavior, and will be
supported for more processors.
`-nocpp'
`as' ignores this option. It is accepted for compatibility with
the native tools.
`--trap'
`--no-trap'
`--break'
`--no-break'
Control how to deal with multiplication overflow and division by
zero. `--trap' or `--no-break' (which are synonyms) take a trap
exception (and only work for Instruction Set Architecture level 2
and higher); `--break' or `--no-trap' (also synonyms, and the
default) take a break exception.
`-n'
When this option is used, `as' will issue a warning every time it
generates a nop instruction from a macro.
The following options are available when as is configured for an
MCore processor.
`-jsri2bsr'
`-nojsri2bsr'
Enable or disable the JSRI to BSR transformation. By default this
is enabled. The command line option `-nojsri2bsr' can be used to
disable it.
`-sifilter'
`-nosifilter'
Enable or disable the silicon filter behaviour. By default this
is disabled. The default can be overridden by the `-sifilter'
command line option.
`-relax'
Alter jump instructions for long displacements.
`-mcpu=[210|340]'
Select the cpu type on the target hardware. This controls which
instructions can be assembled.
`-EB'
Assemble for a big endian target.
`-EL'
Assemble for a little endian target.
See the info pages for documentation of the MMIX-specific options.
The following options are available when as is configured for an
Xtensa processor.
`--text-section-literals | --no-text-section-literals'
With `--text-section-literals', literal pools are interspersed in
the text section. The default is `--no-text-section-literals',
which places literals in a separate section in the output file.
These options only affect literals referenced via PC-relative
`L32R' instructions; literals for absolute mode `L32R'
instructions are handled separately.
`--absolute-literals | --no-absolute-literals'
Indicate to the assembler whether `L32R' instructions use absolute
or PC-relative addressing. The default is to assume absolute
addressing if the Xtensa processor includes the absolute `L32R'
addressing option. Otherwise, only the PC-relative `L32R' mode
can be used.
`--target-align | --no-target-align'
Enable or disable automatic alignment to reduce branch penalties
at the expense of some code density. The default is
`--target-align'.
`--longcalls | --no-longcalls'
Enable or disable transformation of call instructions to allow
calls across a greater range of addresses. The default is
`--no-longcalls'.
`--transform | --no-transform'
Enable or disable all assembler transformations of Xtensa
instructions. The default is `--transform'; `--no-transform'
should be used only in the rare cases when the instructions must
be exactly as specified in the assembly source.
* Menu:
* Manual:: Structure of this Manual
* GNU Assembler:: The GNU Assembler
* Object Formats:: Object File Formats
* Command Line:: Command Line
* Input Files:: Input Files
* Object:: Output (Object) File
* Errors:: Error and Warning Messages
File: as.info, Node: Manual, Next: GNU Assembler, Up: Overview
1.1 Structure of this Manual
============================
This manual is intended to describe what you need to know to use GNU
`as'. We cover the syntax expected in source files, including notation
for symbols, constants, and expressions; the directives that `as'
understands; and of course how to invoke `as'.
This manual also describes some of the machine-dependent features of
various flavors of the assembler.
On the other hand, this manual is _not_ intended as an introduction
to programming in assembly language--let alone programming in general!
In a similar vein, we make no attempt to introduce the machine
architecture; we do _not_ describe the instruction set, standard
mnemonics, registers or addressing modes that are standard to a
particular architecture. You may want to consult the manufacturer's
machine architecture manual for this information.
File: as.info, Node: GNU Assembler, Next: Object Formats, Prev: Manual, Up: Overview
1.2 The GNU Assembler
=====================
GNU `as' is really a family of assemblers. If you use (or have used)
the GNU assembler on one architecture, you should find a fairly similar
environment when you use it on another architecture. Each version has
much in common with the others, including object file formats, most
assembler directives (often called "pseudo-ops") and assembler syntax.
`as' is primarily intended to assemble the output of the GNU C
compiler `gcc' for use by the linker `ld'. Nevertheless, we've tried
to make `as' assemble correctly everything that other assemblers for
the same machine would assemble. Any exceptions are documented
explicitly (*note Machine Dependencies::). This doesn't mean `as'
always uses the same syntax as another assembler for the same
architecture; for example, we know of several incompatible versions of
680x0 assembly language syntax.
Unlike older assemblers, `as' is designed to assemble a source
program in one pass of the source file. This has a subtle impact on the
`.org' directive (*note `.org': Org.).
File: as.info, Node: Object Formats, Next: Command Line, Prev: GNU Assembler, Up: Overview
1.3 Object File Formats
=======================
The GNU assembler can be configured to produce several alternative
object file formats. For the most part, this does not affect how you
write assembly language programs; but directives for debugging symbols
are typically different in different file formats. *Note Symbol
Attributes: Symbol Attributes.
File: as.info, Node: Command Line, Next: Input Files, Prev: Object Formats, Up: Overview
1.4 Command Line
================
After the program name `as', the command line may contain options and
file names. Options may appear in any order, and may be before, after,
or between file names. The order of file names is significant.
`--' (two hyphens) by itself names the standard input file
explicitly, as one of the files for `as' to assemble.
Except for `--' any command line argument that begins with a hyphen
(`-') is an option. Each option changes the behavior of `as'. No
option changes the way another option works. An option is a `-'
followed by one or more letters; the case of the letter is important.
All options are optional.
Some options expect exactly one file name to follow them. The file
name may either immediately follow the option's letter (compatible with
older assemblers) or it may be the next command argument (GNU
standard). These two command lines are equivalent:
as -o my-object-file.o mumble.s
as -omy-object-file.o mumble.s
File: as.info, Node: Input Files, Next: Object, Prev: Command Line, Up: Overview
1.5 Input Files
===============
We use the phrase "source program", abbreviated "source", to describe
the program input to one run of `as'. The program may be in one or
more files; how the source is partitioned into files doesn't change the
meaning of the source.
The source program is a concatenation of the text in all the files,
in the order specified.
Each time you run `as' it assembles exactly one source program. The
source program is made up of one or more files. (The standard input is
also a file.)
You give `as' a command line that has zero or more input file names.
The input files are read (from left file name to right). A command
line argument (in any position) that has no special meaning is taken to
be an input file name.
If you give `as' no file names it attempts to read one input file
from the `as' standard input, which is normally your terminal. You may
have to type <ctl-D> to tell `as' there is no more program to assemble.
Use `--' if you need to explicitly name the standard input file in
your command line.
If the source is empty, `as' produces a small, empty object file.
Filenames and Line-numbers
--------------------------
There are two ways of locating a line in the input file (or files) and
either may be used in reporting error messages. One way refers to a
line number in a physical file; the other refers to a line number in a
"logical" file. *Note Error and Warning Messages: Errors.
"Physical files" are those files named in the command line given to
`as'.
"Logical files" are simply names declared explicitly by assembler
directives; they bear no relation to physical files. Logical file
names help error messages reflect the original source file, when `as'
source is itself synthesized from other files. `as' understands the
`#' directives emitted by the `gcc' preprocessor. See also *Note
`.file': File.
File: as.info, Node: Object, Next: Errors, Prev: Input Files, Up: Overview
1.6 Output (Object) File
========================
Every time you run `as' it produces an output file, which is your
assembly language program translated into numbers. This file is the
object file. Its default name is `a.out', or `b.out' when `as' is
configured for the Intel 80960. You can give it another name by using
the `-o' option. Conventionally, object file names end with `.o'. The
default name is used for historical reasons: older assemblers were
capable of assembling self-contained programs directly into a runnable
program. (For some formats, this isn't currently possible, but it can
be done for the `a.out' format.)
The object file is meant for input to the linker `ld'. It contains
assembled program code, information to help `ld' integrate the
assembled program into a runnable file, and (optionally) symbolic
information for the debugger.
File: as.info, Node: Errors, Prev: Object, Up: Overview
1.7 Error and Warning Messages
==============================
`as' may write warnings and error messages to the standard error file
(usually your terminal). This should not happen when a compiler runs
`as' automatically. Warnings report an assumption made so that `as'
could keep assembling a flawed program; errors report a grave problem
that stops the assembly.
Warning messages have the format
file_name:NNN:Warning Message Text
(where NNN is a line number). If a logical file name has been given
(*note `.file': File.) it is used for the filename, otherwise the name
of the current input file is used. If a logical line number was given
(*note `.line': Line.) then it is used to calculate the number printed,
otherwise the actual line in the current source file is printed. The
message text is intended to be self explanatory (in the grand Unix
tradition).
Error messages have the format
file_name:NNN:FATAL:Error Message Text
The file name and line number are derived as for warning messages.
The actual message text may be rather less explanatory because many of
them aren't supposed to happen.
File: as.info, Node: Invoking, Next: Syntax, Prev: Overview, Up: Top
2 Command-Line Options
**********************
This chapter describes command-line options available in _all_ versions
of the GNU assembler; *note Machine Dependencies::, for options specific
to particular machine architectures.
If you are invoking `as' via the GNU C compiler, you can use the
`-Wa' option to pass arguments through to the assembler. The assembler
arguments must be separated from each other (and the `-Wa') by commas.
For example:
gcc -c -g -O -Wa,-alh,-L file.c
This passes two options to the assembler: `-alh' (emit a listing to
standard output with high-level and assembly source) and `-L' (retain
local symbols in the symbol table).
Usually you do not need to use this `-Wa' mechanism, since many
compiler command-line options are automatically passed to the assembler
by the compiler. (You can call the GNU compiler driver with the `-v'
option to see precisely what options it passes to each compilation
pass, including the assembler.)
* Menu:
* a:: -a[cdhlns] enable listings
* alternate:: --alternate enable alternate macro syntax
* D:: -D for compatibility
* f:: -f to work faster
* I:: -I for .include search path
* K:: -K for difference tables
* L:: -L to retain local labels
* listing:: --listing-XXX to configure listing output
* M:: -M or --mri to assemble in MRI compatibility mode
* MD:: --MD for dependency tracking
* o:: -o to name the object file
* R:: -R to join data and text sections
* statistics:: --statistics to see statistics about assembly
* traditional-format:: --traditional-format for compatible output
* v:: -v to announce version
* W:: -W, --no-warn, --warn, --fatal-warnings to control warnings
* Z:: -Z to make object file even after errors
File: as.info, Node: a, Next: alternate, Up: Invoking
2.1 Enable Listings: `-a[cdhlns]'
=================================
These options enable listing output from the assembler. By itself,
`-a' requests high-level, assembly, and symbols listing. You can use
other letters to select specific options for the list: `-ah' requests a
high-level language listing, `-al' requests an output-program assembly
listing, and `-as' requests a symbol table listing. High-level
listings require that a compiler debugging option like `-g' be used,
and that assembly listings (`-al') be requested also.
Use the `-ac' option to omit false conditionals from a listing. Any
lines which are not assembled because of a false `.if' (or `.ifdef', or
any other conditional), or a true `.if' followed by an `.else', will be
omitted from the listing.
Use the `-ad' option to omit debugging directives from the listing.
Once you have specified one of these options, you can further control
listing output and its appearance using the directives `.list',
`.nolist', `.psize', `.eject', `.title', and `.sbttl'. The `-an'
option turns off all forms processing. If you do not request listing
output with one of the `-a' options, the listing-control directives
have no effect.
The letters after `-a' may be combined into one option, _e.g._,
`-aln'.
Note if the assembler source is coming from the standard input (eg
because it is being created by `gcc' and the `-pipe' command line switch
is being used) then the listing will not contain any comments or
preprocessor directives. This is because the listing code buffers
input source lines from stdin only after they have been preprocessed by
the assembler. This reduces memory usage and makes the code more
efficient.
File: as.info, Node: alternate, Next: D, Prev: a, Up: Invoking
2.2 `--alternate'
=================
Begin in alternate macro mode, see *Note `.altmacro': Altmacro.
File: as.info, Node: D, Next: f, Prev: alternate, Up: Invoking
2.3 `-D'
========
This option has no effect whatsoever, but it is accepted to make it more
likely that scripts written for other assemblers also work with `as'.
File: as.info, Node: f, Next: I, Prev: D, Up: Invoking
2.4 Work Faster: `-f'
=====================
`-f' should only be used when assembling programs written by a
(trusted) compiler. `-f' stops the assembler from doing whitespace and
comment preprocessing on the input file(s) before assembling them.
*Note Preprocessing: Preprocessing.
_Warning:_ if you use `-f' when the files actually need to be
preprocessed (if they contain comments, for example), `as' does
not work correctly.
File: as.info, Node: I, Next: K, Prev: f, Up: Invoking
2.5 `.include' Search Path: `-I' PATH
=====================================
Use this option to add a PATH to the list of directories `as' searches
for files specified in `.include' directives (*note `.include':
Include.). You may use `-I' as many times as necessary to include a
variety of paths. The current working directory is always searched
first; after that, `as' searches any `-I' directories in the same order
as they were specified (left to right) on the command line.
File: as.info, Node: K, Next: L, Prev: I, Up: Invoking
2.6 Difference Tables: `-K'
===========================
`as' sometimes alters the code emitted for directives of the form
`.word SYM1-SYM2'; *note `.word': Word. You can use the `-K' option if
you want a warning issued when this is done.
File: as.info, Node: L, Next: listing, Prev: K, Up: Invoking
2.7 Include Local Labels: `-L'
==============================
Labels beginning with `L' (upper case only) are called "local labels".
*Note Symbol Names::. Normally you do not see such labels when
debugging, because they are intended for the use of programs (like
compilers) that compose assembler programs, not for your notice.
Normally both `as' and `ld' discard such labels, so you do not normally
debug with them.
This option tells `as' to retain those `L...' symbols in the object
file. Usually if you do this you also tell the linker `ld' to preserve
symbols whose names begin with `L'.
By default, a local label is any label beginning with `L', but each
target is allowed to redefine the local label prefix. On the HPPA
local labels begin with `L$'.
File: as.info, Node: listing, Next: M, Prev: L, Up: Invoking
2.8 Configuring listing output: `--listing'
===========================================
The listing feature of the assembler can be enabled via the command
line switch `-a' (*note a::). This feature combines the input source
file(s) with a hex dump of the corresponding locations in the output
object file, and displays them as a listing file. The format of this
listing can be controlled by pseudo ops inside the assembler source
(*note List:: *note Title:: *note Sbttl:: *note Psize:: *note Eject::)
and also by the following switches:
`--listing-lhs-width=`number''
Sets the maximum width, in words, of the first line of the hex
byte dump. This dump appears on the left hand side of the listing
output.
`--listing-lhs-width2=`number''
Sets the maximum width, in words, of any further lines of the hex
byte dump for a given input source line. If this value is not
specified, it defaults to being the same as the value specified
for `--listing-lhs-width'. If neither switch is used the default
is to one.
`--listing-rhs-width=`number''
Sets the maximum width, in characters, of the source line that is
displayed alongside the hex dump. The default value for this
parameter is 100. The source line is displayed on the right hand
side of the listing output.
`--listing-cont-lines=`number''
Sets the maximum number of continuation lines of hex dump that
will be displayed for a given single line of source input. The
default value is 4.
File: as.info, Node: M, Next: MD, Prev: listing, Up: Invoking
2.9 Assemble in MRI Compatibility Mode: `-M'
============================================
The `-M' or `--mri' option selects MRI compatibility mode. This
changes the syntax and pseudo-op handling of `as' to make it compatible
with the `ASM68K' or the `ASM960' (depending upon the configured
target) assembler from Microtec Research. The exact nature of the MRI
syntax will not be documented here; see the MRI manuals for more
information. Note in particular that the handling of macros and macro
arguments is somewhat different. The purpose of this option is to
permit assembling existing MRI assembler code using `as'.
The MRI compatibility is not complete. Certain operations of the
MRI assembler depend upon its object file format, and can not be
supported using other object file formats. Supporting these would
require enhancing each object file format individually. These are:
* global symbols in common section
The m68k MRI assembler supports common sections which are merged
by the linker. Other object file formats do not support this.
`as' handles common sections by treating them as a single common
symbol. It permits local symbols to be defined within a common
section, but it can not support global symbols, since it has no
way to describe them.
* complex relocations
The MRI assemblers support relocations against a negated section
address, and relocations which combine the start addresses of two
or more sections. These are not support by other object file
formats.
* `END' pseudo-op specifying start address
The MRI `END' pseudo-op permits the specification of a start
address. This is not supported by other object file formats. The
start address may instead be specified using the `-e' option to
the linker, or in a linker script.
* `IDNT', `.ident' and `NAME' pseudo-ops
The MRI `IDNT', `.ident' and `NAME' pseudo-ops assign a module
name to the output file. This is not supported by other object
file formats.
* `ORG' pseudo-op
The m68k MRI `ORG' pseudo-op begins an absolute section at a given
address. This differs from the usual `as' `.org' pseudo-op, which
changes the location within the current section. Absolute
sections are not supported by other object file formats. The
address of a section may be assigned within a linker script.
There are some other features of the MRI assembler which are not
supported by `as', typically either because they are difficult or
because they seem of little consequence. Some of these may be
supported in future releases.
* EBCDIC strings
EBCDIC strings are not supported.
* packed binary coded decimal
Packed binary coded decimal is not supported. This means that the
`DC.P' and `DCB.P' pseudo-ops are not supported.
* `FEQU' pseudo-op
The m68k `FEQU' pseudo-op is not supported.
* `NOOBJ' pseudo-op
The m68k `NOOBJ' pseudo-op is not supported.
* `OPT' branch control options
The m68k `OPT' branch control options--`B', `BRS', `BRB', `BRL',
and `BRW'--are ignored. `as' automatically relaxes all branches,
whether forward or backward, to an appropriate size, so these
options serve no purpose.
* `OPT' list control options
The following m68k `OPT' list control options are ignored: `C',
`CEX', `CL', `CRE', `E', `G', `I', `M', `MEX', `MC', `MD', `X'.
* other `OPT' options
The following m68k `OPT' options are ignored: `NEST', `O', `OLD',
`OP', `P', `PCO', `PCR', `PCS', `R'.
* `OPT' `D' option is default
The m68k `OPT' `D' option is the default, unlike the MRI assembler.
`OPT NOD' may be used to turn it off.
* `XREF' pseudo-op.
The m68k `XREF' pseudo-op is ignored.
* `.debug' pseudo-op
The i960 `.debug' pseudo-op is not supported.
* `.extended' pseudo-op
The i960 `.extended' pseudo-op is not supported.
* `.list' pseudo-op.
The various options of the i960 `.list' pseudo-op are not
supported.
* `.optimize' pseudo-op
The i960 `.optimize' pseudo-op is not supported.
* `.output' pseudo-op
The i960 `.output' pseudo-op is not supported.
* `.setreal' pseudo-op
The i960 `.setreal' pseudo-op is not supported.
File: as.info, Node: MD, Next: o, Prev: M, Up: Invoking
2.10 Dependency Tracking: `--MD'
================================
`as' can generate a dependency file for the file it creates. This file
consists of a single rule suitable for `make' describing the
dependencies of the main source file.
The rule is written to the file named in its argument.
This feature is used in the automatic updating of makefiles.
File: as.info, Node: o, Next: R, Prev: MD, Up: Invoking
2.11 Name the Object File: `-o'
===============================
There is always one object file output when you run `as'. By default
it has the name `a.out' (or `b.out', for Intel 960 targets only). You
use this option (which takes exactly one filename) to give the object
file a different name.
Whatever the object file is called, `as' overwrites any existing
file of the same name.
File: as.info, Node: R, Next: statistics, Prev: o, Up: Invoking
2.12 Join Data and Text Sections: `-R'
======================================
`-R' tells `as' to write the object file as if all data-section data
lives in the text section. This is only done at the very last moment:
your binary data are the same, but data section parts are relocated
differently. The data section part of your object file is zero bytes
long because all its bytes are appended to the text section. (*Note
Sections and Relocation: Sections.)
When you specify `-R' it would be possible to generate shorter
address displacements (because we do not have to cross between text and
data section). We refrain from doing this simply for compatibility with
older versions of `as'. In future, `-R' may work this way.
When `as' is configured for COFF or ELF output, this option is only
useful if you use sections named `.text' and `.data'.
`-R' is not supported for any of the HPPA targets. Using `-R'
generates a warning from `as'.
File: as.info, Node: statistics, Next: traditional-format, Prev: R, Up: Invoking
2.13 Display Assembly Statistics: `--statistics'
================================================
Use `--statistics' to display two statistics about the resources used by
`as': the maximum amount of space allocated during the assembly (in
bytes), and the total execution time taken for the assembly (in CPU
seconds).
File: as.info, Node: traditional-format, Next: v, Prev: statistics, Up: Invoking
2.14 Compatible Output: `--traditional-format'
==============================================
For some targets, the output of `as' is different in some ways from the
output of some existing assembler. This switch requests `as' to use
the traditional format instead.
For example, it disables the exception frame optimizations which
`as' normally does by default on `gcc' output.
File: as.info, Node: v, Next: W, Prev: traditional-format, Up: Invoking
2.15 Announce Version: `-v'
===========================
You can find out what version of as is running by including the option
`-v' (which you can also spell as `-version') on the command line.
File: as.info, Node: W, Next: Z, Prev: v, Up: Invoking
2.16 Control Warnings: `-W', `--warn', `--no-warn', `--fatal-warnings'
======================================================================
`as' should never give a warning or error message when assembling
compiler output. But programs written by people often cause `as' to
give a warning that a particular assumption was made. All such
warnings are directed to the standard error file.
If you use the `-W' and `--no-warn' options, no warnings are issued.
This only affects the warning messages: it does not change any
particular of how `as' assembles your file. Errors, which stop the
assembly, are still reported.
If you use the `--fatal-warnings' option, `as' considers files that
generate warnings to be in error.
You can switch these options off again by specifying `--warn', which
causes warnings to be output as usual.
File: as.info, Node: Z, Prev: W, Up: Invoking
2.17 Generate Object File in Spite of Errors: `-Z'
==================================================
After an error message, `as' normally produces no output. If for some
reason you are interested in object file output even after `as' gives
an error message on your program, use the `-Z' option. If there are
any errors, `as' continues anyways, and writes an object file after a
final warning message of the form `N errors, M warnings, generating bad
object file.'
File: as.info, Node: Syntax, Next: Sections, Prev: Invoking, Up: Top
3 Syntax
********
This chapter describes the machine-independent syntax allowed in a
source file. `as' syntax is similar to what many other assemblers use;
it is inspired by the BSD 4.2 assembler, except that `as' does not
assemble Vax bit-fields.
* Menu:
* Preprocessing:: Preprocessing
* Whitespace:: Whitespace
* Comments:: Comments
* Symbol Intro:: Symbols
* Statements:: Statements
* Constants:: Constants
File: as.info, Node: Preprocessing, Next: Whitespace, Up: Syntax
3.1 Preprocessing
=================
The `as' internal preprocessor:
* adjusts and removes extra whitespace. It leaves one space or tab
before the keywords on a line, and turns any other whitespace on
the line into a single space.
* removes all comments, replacing them with a single space, or an
appropriate number of newlines.
* converts character constants into the appropriate numeric values.
It does not do macro processing, include file handling, or anything
else you may get from your C compiler's preprocessor. You can do
include file processing with the `.include' directive (*note
`.include': Include.). You can use the GNU C compiler driver to get
other "CPP" style preprocessing by giving the input file a `.S' suffix.
*Note Options Controlling the Kind of Output: (gcc.info)Overall
Options.
Excess whitespace, comments, and character constants cannot be used
in the portions of the input text that are not preprocessed.
If the first line of an input file is `#NO_APP' or if you use the
`-f' option, whitespace and comments are not removed from the input
file. Within an input file, you can ask for whitespace and comment
removal in specific portions of the by putting a line that says `#APP'
before the text that may contain whitespace or comments, and putting a
line that says `#NO_APP' after this text. This feature is mainly
intend to support `asm' statements in compilers whose output is
otherwise free of comments and whitespace.
File: as.info, Node: Whitespace, Next: Comments, Prev: Preprocessing, Up: Syntax
3.2 Whitespace
==============
"Whitespace" is one or more blanks or tabs, in any order. Whitespace
is used to separate symbols, and to make programs neater for people to
read. Unless within character constants (*note Character Constants:
Characters.), any whitespace means the same as exactly one space.
File: as.info, Node: Comments, Next: Symbol Intro, Prev: Whitespace, Up: Syntax
3.3 Comments
============
There are two ways of rendering comments to `as'. In both cases the
comment is equivalent to one space.
Anything from `/*' through the next `*/' is a comment. This means
you may not nest these comments.
/*
The only way to include a newline ('\n') in a comment
is to use this sort of comment.
*/
/* This sort of comment does not nest. */
Anything from the "line comment" character to the next newline is
considered a comment and is ignored. The line comment character is `;'
for the AMD 29K family; `;' on the ARC; `@' on the ARM; `;' for the
H8/300 family; `!' for the H8/500 family; `;' for the HPPA; `#' on the
i386 and x86-64; `#' on the i960; `;' for the PDP-11; `;' for picoJava;
`#' for Motorola PowerPC; `!' for the Renesas / SuperH SH; `!' on the
SPARC; `#' on the ip2k; `#' on the m32r; `|' on the 680x0; `#' on the
68HC11 and 68HC12; `;' on the M880x0; `#' on the Vax; `!' for the Z8000;
`#' on the V850; `#' for Xtensa systems; see *Note Machine
Dependencies::.
On some machines there are two different line comment characters.
One character only begins a comment if it is the first non-whitespace
character on a line, while the other always begins a comment.
The V850 assembler also supports a double dash as starting a comment
that extends to the end of the line.
`--';
To be compatible with past assemblers, lines that begin with `#'
have a special interpretation. Following the `#' should be an absolute
expression (*note Expressions::): the logical line number of the _next_
line. Then a string (*note Strings: Strings.) is allowed: if present
it is a new logical file name. The rest of the line, if any, should be
whitespace.
If the first non-whitespace characters on the line are not numeric,
the line is ignored. (Just like a comment.)
# This is an ordinary comment.
# 42-6 "new_file_name" # New logical file name
# This is logical line # 36.
This feature is deprecated, and may disappear from future versions
of `as'.
File: as.info, Node: Symbol Intro, Next: Statements, Prev: Comments, Up: Syntax
3.4 Symbols
===========
A "symbol" is one or more characters chosen from the set of all letters
(both upper and lower case), digits and the three characters `_.$'. On
most machines, you can also use `$' in symbol names; exceptions are
noted in *Note Machine Dependencies::. No symbol may begin with a
digit. Case is significant. There is no length limit: all characters
are significant. Symbols are delimited by characters not in that set,
or by the beginning of a file (since the source program must end with a
newline, the end of a file is not a possible symbol delimiter). *Note
Symbols::.
File: as.info, Node: Statements, Next: Constants, Prev: Symbol Intro, Up: Syntax
3.5 Statements
==============
A "statement" ends at a newline character (`\n') or line separator
character. (The line separator is usually `;', unless this conflicts
with the comment character; *note Machine Dependencies::.) The newline
or separator character is considered part of the preceding statement.
Newlines and separators within character constants are an exception:
they do not end statements.
It is an error to end any statement with end-of-file: the last
character of any input file should be a newline.
An empty statement is allowed, and may include whitespace. It is
ignored.
A statement begins with zero or more labels, optionally followed by a
key symbol which determines what kind of statement it is. The key
symbol determines the syntax of the rest of the statement. If the
symbol begins with a dot `.' then the statement is an assembler
directive: typically valid for any computer. If the symbol begins with
a letter the statement is an assembly language "instruction": it
assembles into a machine language instruction. Different versions of
`as' for different computers recognize different instructions. In
fact, the same symbol may represent a different instruction in a
different computer's assembly language.
A label is a symbol immediately followed by a colon (`:').
Whitespace before a label or after a colon is permitted, but you may not
have whitespace between a label's symbol and its colon. *Note Labels::.
For HPPA targets, labels need not be immediately followed by a
colon, but the definition of a label must begin in column zero. This
also implies that only one label may be defined on each line.
label: .directive followed by something
another_label: # This is an empty statement.
instruction operand_1, operand_2, ...
File: as.info, Node: Constants, Prev: Statements, Up: Syntax
3.6 Constants
=============
A constant is a number, written so that its value is known by
inspection, without knowing any context. Like this:
.byte 74, 0112, 092, 0x4A, 0X4a, 'J, '\J # All the same value.
.ascii "Ring the bell\7" # A string constant.
.octa 0x123456789abcdef0123456789ABCDEF0 # A bignum.
.float 0f-314159265358979323846264338327\
95028841971.693993751E-40 # - pi, a flonum.
* Menu:
* Characters:: Character Constants
* Numbers:: Number Constants
File: as.info, Node: Characters, Next: Numbers, Up: Constants
3.6.1 Character Constants
-------------------------
There are two kinds of character constants. A "character" stands for
one character in one byte and its value may be used in numeric
expressions. String constants (properly called string _literals_) are
potentially many bytes and their values may not be used in arithmetic
expressions.
* Menu:
* Strings:: Strings
* Chars:: Characters
File: as.info, Node: Strings, Next: Chars, Up: Characters
3.6.1.1 Strings
...............
A "string" is written between double-quotes. It may contain
double-quotes or null characters. The way to get special characters
into a string is to "escape" these characters: precede them with a
backslash `\' character. For example `\\' represents one backslash:
the first `\' is an escape which tells `as' to interpret the second
character literally as a backslash (which prevents `as' from
recognizing the second `\' as an escape character). The complete list
of escapes follows.
`\b'
Mnemonic for backspace; for ASCII this is octal code 010.
`\f'
Mnemonic for FormFeed; for ASCII this is octal code 014.
`\n'
Mnemonic for newline; for ASCII this is octal code 012.
`\r'
Mnemonic for carriage-Return; for ASCII this is octal code 015.
`\t'
Mnemonic for horizontal Tab; for ASCII this is octal code 011.
`\ DIGIT DIGIT DIGIT'
An octal character code. The numeric code is 3 octal digits. For
compatibility with other Unix systems, 8 and 9 are accepted as
digits: for example, `\008' has the value 010, and `\009' the
value 011.
`\`x' HEX-DIGITS...'
A hex character code. All trailing hex digits are combined.
Either upper or lower case `x' works.
`\\'
Represents one `\' character.
`\"'
Represents one `"' character. Needed in strings to represent this
character, because an unescaped `"' would end the string.
`\ ANYTHING-ELSE'
Any other character when escaped by `\' gives a warning, but
assembles as if the `\' was not present. The idea is that if you
used an escape sequence you clearly didn't want the literal
interpretation of the following character. However `as' has no
other interpretation, so `as' knows it is giving you the wrong
code and warns you of the fact.
Which characters are escapable, and what those escapes represent,
varies widely among assemblers. The current set is what we think the
BSD 4.2 assembler recognizes, and is a subset of what most C compilers
recognize. If you are in doubt, do not use an escape sequence.
File: as.info, Node: Chars, Prev: Strings, Up: Characters
3.6.1.2 Characters
..................
A single character may be written as a single quote immediately
followed by that character. The same escapes apply to characters as to
strings. So if you want to write the character backslash, you must
write `'\\' where the first `\' escapes the second `\'. As you can
see, the quote is an acute accent, not a grave accent. A newline
immediately following an acute accent is taken as a literal character
and does not count as the end of a statement. The value of a character
constant in a numeric expression is the machine's byte-wide code for
that character. `as' assumes your character code is ASCII: `'A' means
65, `'B' means 66, and so on.
File: as.info, Node: Numbers, Prev: Characters, Up: Constants
3.6.2 Number Constants
----------------------
`as' distinguishes three kinds of numbers according to how they are
stored in the target machine. _Integers_ are numbers that would fit
into an `int' in the C language. _Bignums_ are integers, but they are
stored in more than 32 bits. _Flonums_ are floating point numbers,
described below.
* Menu:
* Integers:: Integers
* Bignums:: Bignums
* Flonums:: Flonums
File: as.info, Node: Integers, Next: Bignums, Up: Numbers
3.6.2.1 Integers
................
A binary integer is `0b' or `0B' followed by zero or more of the binary
digits `01'.
An octal integer is `0' followed by zero or more of the octal digits
(`01234567').
A decimal integer starts with a non-zero digit followed by zero or
more digits (`0123456789').
A hexadecimal integer is `0x' or `0X' followed by one or more
hexadecimal digits chosen from `0123456789abcdefABCDEF'.
Integers have the usual values. To denote a negative integer, use
the prefix operator `-' discussed under expressions (*note Prefix
Operators: Prefix Ops.).
File: as.info, Node: Bignums, Next: Flonums, Prev: Integers, Up: Numbers
3.6.2.2 Bignums
...............
A "bignum" has the same syntax and semantics as an integer except that
the number (or its negative) takes more than 32 bits to represent in
binary. The distinction is made because in some places integers are
permitted while bignums are not.
File: as.info, Node: Flonums, Prev: Bignums, Up: Numbers
3.6.2.3 Flonums
...............
A "flonum" represents a floating point number. The translation is
indirect: a decimal floating point number from the text is converted by
`as' to a generic binary floating point number of more than sufficient
precision. This generic floating point number is converted to a
particular computer's floating point format (or formats) by a portion
of `as' specialized to that computer.
A flonum is written by writing (in order)
* The digit `0'. (`0' is optional on the HPPA.)
* A letter, to tell `as' the rest of the number is a flonum. `e' is
recommended. Case is not important.
On the H8/300, H8/500, Renesas / SuperH SH, and AMD 29K
architectures, the letter must be one of the letters `DFPRSX' (in
upper or lower case).
On the ARC, the letter must be one of the letters `DFRS' (in upper
or lower case).
On the Intel 960 architecture, the letter must be one of the
letters `DFT' (in upper or lower case).
On the HPPA architecture, the letter must be `E' (upper case only).
* An optional sign: either `+' or `-'.
* An optional "integer part": zero or more decimal digits.
* An optional "fractional part": `.' followed by zero or more
decimal digits.
* An optional exponent, consisting of:
* An `E' or `e'.
* Optional sign: either `+' or `-'.
* One or more decimal digits.
At least one of the integer part or the fractional part must be
present. The floating point number has the usual base-10 value.
`as' does all processing using integers. Flonums are computed
independently of any floating point hardware in the computer running
`as'.
File: as.info, Node: Sections, Next: Symbols, Prev: Syntax, Up: Top
4 Sections and Relocation
*************************
* Menu:
* Secs Background:: Background
* Ld Sections:: Linker Sections
* As Sections:: Assembler Internal Sections
* Sub-Sections:: Sub-Sections
* bss:: bss Section
File: as.info, Node: Secs Background, Next: Ld Sections, Up: Sections
4.1 Background
==============
Roughly, a section is a range of addresses, with no gaps; all data "in"
those addresses is treated the same for some particular purpose. For
example there may be a "read only" section.
The linker `ld' reads many object files (partial programs) and
combines their contents to form a runnable program. When `as' emits an
object file, the partial program is assumed to start at address 0.
`ld' assigns the final addresses for the partial program, so that
different partial programs do not overlap. This is actually an
oversimplification, but it suffices to explain how `as' uses sections.
`ld' moves blocks of bytes of your program to their run-time
addresses. These blocks slide to their run-time addresses as rigid
units; their length does not change and neither does the order of bytes
within them. Such a rigid unit is called a _section_. Assigning
run-time addresses to sections is called "relocation". It includes the
task of adjusting mentions of object-file addresses so they refer to
the proper run-time addresses. For the H8/300 and H8/500, and for the
Renesas / SuperH SH, `as' pads sections if needed to ensure they end on
a word (sixteen bit) boundary.
An object file written by `as' has at least three sections, any of
which may be empty. These are named "text", "data" and "bss" sections.
When it generates COFF or ELF output, `as' can also generate
whatever other named sections you specify using the `.section'
directive (*note `.section': Section.). If you do not use any
directives that place output in the `.text' or `.data' sections, these
sections still exist, but are empty.
When `as' generates SOM or ELF output for the HPPA, `as' can also
generate whatever other named sections you specify using the `.space'
and `.subspace' directives. See `HP9000 Series 800 Assembly Language
Reference Manual' (HP 92432-90001) for details on the `.space' and
`.subspace' assembler directives.
Additionally, `as' uses different names for the standard text, data,
and bss sections when generating SOM output. Program text is placed
into the `$CODE$' section, data into `$DATA$', and BSS into `$BSS$'.
Within the object file, the text section starts at address `0', the
data section follows, and the bss section follows the data section.
When generating either SOM or ELF output files on the HPPA, the text
section starts at address `0', the data section at address `0x4000000',
and the bss section follows the data section.
To let `ld' know which data changes when the sections are relocated,
and how to change that data, `as' also writes to the object file
details of the relocation needed. To perform relocation `ld' must
know, each time an address in the object file is mentioned:
* Where in the object file is the beginning of this reference to an
address?
* How long (in bytes) is this reference?
* Which section does the address refer to? What is the numeric
value of
(ADDRESS) - (START-ADDRESS OF SECTION)?
* Is the reference to an address "Program-Counter relative"?
In fact, every address `as' ever uses is expressed as
(SECTION) + (OFFSET INTO SECTION)
Further, most expressions `as' computes have this section-relative
nature. (For some object formats, such as SOM for the HPPA, some
expressions are symbol-relative instead.)
In this manual we use the notation {SECNAME N} to mean "offset N
into section SECNAME."
Apart from text, data and bss sections you need to know about the
"absolute" section. When `ld' mixes partial programs, addresses in the
absolute section remain unchanged. For example, address `{absolute 0}'
is "relocated" to run-time address 0 by `ld'. Although the linker
never arranges two partial programs' data sections with overlapping
addresses after linking, _by definition_ their absolute sections must
overlap. Address `{absolute 239}' in one part of a program is always
the same address when the program is running as address `{absolute
239}' in any other part of the program.
The idea of sections is extended to the "undefined" section. Any
address whose section is unknown at assembly time is by definition
rendered {undefined U}--where U is filled in later. Since numbers are
always defined, the only way to generate an undefined address is to
mention an undefined symbol. A reference to a named common block would
be such a symbol: its value is unknown at assembly time so it has
section _undefined_.
By analogy the word _section_ is used to describe groups of sections
in the linked program. `ld' puts all partial programs' text sections
in contiguous addresses in the linked program. It is customary to
refer to the _text section_ of a program, meaning all the addresses of
all partial programs' text sections. Likewise for data and bss
sections.
Some sections are manipulated by `ld'; others are invented for use
of `as' and have no meaning except during assembly.
File: as.info, Node: Ld Sections, Next: As Sections, Prev: Secs Background, Up: Sections
4.2 Linker Sections
===================
`ld' deals with just four kinds of sections, summarized below.
*named sections*
*text section*
*data section*
These sections hold your program. `as' and `ld' treat them as
separate but equal sections. Anything you can say of one section
is true of another. When the program is running, however, it is
customary for the text section to be unalterable. The text
section is often shared among processes: it contains instructions,
constants and the like. The data section of a running program is
usually alterable: for example, C variables would be stored in the
data section.
*bss section*
This section contains zeroed bytes when your program begins
running. It is used to hold uninitialized variables or common
storage. The length of each partial program's bss section is
important, but because it starts out containing zeroed bytes there
is no need to store explicit zero bytes in the object file. The
bss section was invented to eliminate those explicit zeros from
object files.
*absolute section*
Address 0 of this section is always "relocated" to runtime address
0. This is useful if you want to refer to an address that `ld'
must not change when relocating. In this sense we speak of
absolute addresses being "unrelocatable": they do not change
during relocation.
*undefined section*
This "section" is a catch-all for address references to objects
not in the preceding sections.
An idealized example of three relocatable sections follows. The
example uses the traditional section names `.text' and `.data'. Memory
addresses are on the horizontal axis.
+-----+----+--+
partial program # 1: |ttttt|dddd|00|
+-----+----+--+
text data bss
seg. seg. seg.
+---+---+---+
partial program # 2: |TTT|DDD|000|
+---+---+---+
+--+---+-----+--+----+---+-----+~~
linked program: | |TTT|ttttt| |dddd|DDD|00000|
+--+---+-----+--+----+---+-----+~~
addresses: 0 ...
File: as.info, Node: As Sections, Next: Sub-Sections, Prev: Ld Sections, Up: Sections
4.3 Assembler Internal Sections
===============================
These sections are meant only for the internal use of `as'. They have
no meaning at run-time. You do not really need to know about these
sections for most purposes; but they can be mentioned in `as' warning
messages, so it might be helpful to have an idea of their meanings to
`as'. These sections are used to permit the value of every expression
in your assembly language program to be a section-relative address.
ASSEMBLER-INTERNAL-LOGIC-ERROR!
An internal assembler logic error has been found. This means
there is a bug in the assembler.
expr section
The assembler stores complex expression internally as combinations
of symbols. When it needs to represent an expression as a symbol,
it puts it in the expr section.
File: as.info, Node: Sub-Sections, Next: bss, Prev: As Sections, Up: Sections
4.4 Sub-Sections
================
Assembled bytes conventionally fall into two sections: text and data.
You may have separate groups of data in named sections that you want to
end up near to each other in the object file, even though they are not
contiguous in the assembler source. `as' allows you to use
"subsections" for this purpose. Within each section, there can be
numbered subsections with values from 0 to 8192. Objects assembled
into the same subsection go into the object file together with other
objects in the same subsection. For example, a compiler might want to
store constants in the text section, but might not want to have them
interspersed with the program being assembled. In this case, the
compiler could issue a `.text 0' before each section of code being
output, and a `.text 1' before each group of constants being output.
Subsections are optional. If you do not use subsections, everything
goes in subsection number zero.
Each subsection is zero-padded up to a multiple of four bytes.
(Subsections may be padded a different amount on different flavors of
`as'.)
Subsections appear in your object file in numeric order, lowest
numbered to highest. (All this to be compatible with other people's
assemblers.) The object file contains no representation of
subsections; `ld' and other programs that manipulate object files see
no trace of them. They just see all your text subsections as a text
section, and all your data subsections as a data section.
To specify which subsection you want subsequent statements assembled
into, use a numeric argument to specify it, in a `.text EXPRESSION' or
a `.data EXPRESSION' statement. When generating COFF output, you can
also use an extra subsection argument with arbitrary named sections:
`.section NAME, EXPRESSION'. When generating ELF output, you can also
use the `.subsection' directive (*note SubSection::) to specify a
subsection: `.subsection EXPRESSION'. EXPRESSION should be an absolute
expression. (*Note Expressions::.) If you just say `.text' then
`.text 0' is assumed. Likewise `.data' means `.data 0'. Assembly
begins in `text 0'. For instance:
.text 0 # The default subsection is text 0 anyway.
.ascii "This lives in the first text subsection. *"
.text 1
.ascii "But this lives in the second text subsection."
.data 0
.ascii "This lives in the data section,"
.ascii "in the first data subsection."
.text 0
.ascii "This lives in the first text section,"
.ascii "immediately following the asterisk (*)."
Each section has a "location counter" incremented by one for every
byte assembled into that section. Because subsections are merely a
convenience restricted to `as' there is no concept of a subsection
location counter. There is no way to directly manipulate a location
counter--but the `.align' directive changes it, and any label
definition captures its current value. The location counter of the
section where statements are being assembled is said to be the "active"
location counter.
File: as.info, Node: bss, Prev: Sub-Sections, Up: Sections
4.5 bss Section
===============
The bss section is used for local common variable storage. You may
allocate address space in the bss section, but you may not dictate data
to load into it before your program executes. When your program starts
running, all the contents of the bss section are zeroed bytes.
The `.lcomm' pseudo-op defines a symbol in the bss section; see
*Note `.lcomm': Lcomm.
The `.comm' pseudo-op may be used to declare a common symbol, which
is another form of uninitialized symbol; see *Note `.comm': Comm.
When assembling for a target which supports multiple sections, such
as ELF or COFF, you may switch into the `.bss' section and define
symbols as usual; see *Note `.section': Section. You may only assemble
zero values into the section. Typically the section will only contain
symbol definitions and `.skip' directives (*note `.skip': Skip.).
File: as.info, Node: Symbols, Next: Expressions, Prev: Sections, Up: Top
5 Symbols
*********
Symbols are a central concept: the programmer uses symbols to name
things, the linker uses symbols to link, and the debugger uses symbols
to debug.
_Warning:_ `as' does not place symbols in the object file in the
same order they were declared. This may break some debuggers.
* Menu:
* Labels:: Labels
* Setting Symbols:: Giving Symbols Other Values
* Symbol Names:: Symbol Names
* Dot:: The Special Dot Symbol
* Symbol Attributes:: Symbol Attributes
File: as.info, Node: Labels, Next: Setting Symbols, Up: Symbols
5.1 Labels
==========
A "label" is written as a symbol immediately followed by a colon `:'.
The symbol then represents the current value of the active location
counter, and is, for example, a suitable instruction operand. You are
warned if you use the same symbol to represent two different locations:
the first definition overrides any other definitions.
On the HPPA, the usual form for a label need not be immediately
followed by a colon, but instead must start in column zero. Only one
label may be defined on a single line. To work around this, the HPPA
version of `as' also provides a special directive `.label' for defining
labels more flexibly.
File: as.info, Node: Setting Symbols, Next: Symbol Names, Prev: Labels, Up: Symbols
5.2 Giving Symbols Other Values
===============================
A symbol can be given an arbitrary value by writing a symbol, followed
by an equals sign `=', followed by an expression (*note Expressions::).
This is equivalent to using the `.set' directive. *Note `.set': Set.
File: as.info, Node: Symbol Names, Next: Dot, Prev: Setting Symbols, Up: Symbols
5.3 Symbol Names
================
Symbol names begin with a letter or with one of `._'. On most
machines, you can also use `$' in symbol names; exceptions are noted in
*Note Machine Dependencies::. That character may be followed by any
string of digits, letters, dollar signs (unless otherwise noted in
*Note Machine Dependencies::), and underscores. For the AMD 29K
family, `?' is also allowed in the body of a symbol name, though not at
its beginning.
Case of letters is significant: `foo' is a different symbol name than
`Foo'.
Each symbol has exactly one name. Each name in an assembly language
program refers to exactly one symbol. You may use that symbol name any
number of times in a program.
Local Symbol Names
------------------
Local symbols help compilers and programmers use names temporarily.
They create symbols which are guaranteed to be unique over the entire
scope of the input source code and which can be referred to by a simple
notation. To define a local symbol, write a label of the form `N:'
(where N represents any positive integer). To refer to the most recent
previous definition of that symbol write `Nb', using the same number as
when you defined the label. To refer to the next definition of a local
label, write `Nf'-- The `b' stands for"backwards" and the `f' stands
for "forwards".
There is no restriction on how you can use these labels, and you can
reuse them too. So that it is possible to repeatedly define the same
local label (using the same number `N'), although you can only refer to
the most recently defined local label of that number (for a backwards
reference) or the next definition of a specific local label for a
forward reference. It is also worth noting that the first 10 local
labels (`0:'...`9:') are implemented in a slightly more efficient
manner than the others.
Here is an example:
1: branch 1f
2: branch 1b
1: branch 2f
2: branch 1b
Which is the equivalent of:
label_1: branch label_3
label_2: branch label_1
label_3: branch label_4
label_4: branch label_3
Local symbol names are only a notational device. They are
immediately transformed into more conventional symbol names before the
assembler uses them. The symbol names stored in the symbol table,
appearing in error messages and optionally emitted to the object file.
The names are constructed using these parts:
`L'
All local labels begin with `L'. Normally both `as' and `ld'
forget symbols that start with `L'. These labels are used for
symbols you are never intended to see. If you use the `-L' option
then `as' retains these symbols in the object file. If you also
instruct `ld' to retain these symbols, you may use them in
debugging.
`NUMBER'
This is the number that was used in the local label definition.
So if the label is written `55:' then the number is `55'.
`C-B'
This unusual character is included so you do not accidentally
invent a symbol of the same name. The character has ASCII value
of `\002' (control-B).
`_ordinal number_'
This is a serial number to keep the labels distinct. The first
definition of `0:' gets the number `1'. The 15th definition of
`0:' gets the number `15', and so on. Likewise the first
definition of `1:' gets the number `1' and its 15th defintion gets
`15' as well.
So for example, the first `1:' is named `L1C-B1', the 44th `3:' is
named `L3C-B44'.
Dollar Local Labels
-------------------
`as' also supports an even more local form of local labels called
dollar labels. These labels go out of scope (ie they become undefined)
as soon as a non-local label is defined. Thus they remain valid for
only a small region of the input source code. Normal local labels, by
contrast, remain in scope for the entire file, or until they are
redefined by another occurrence of the same local label.
Dollar labels are defined in exactly the same way as ordinary local
labels, except that instead of being terminated by a colon, they are
terminated by a dollar sign. eg `55$'.
They can also be distinguished from ordinary local labels by their
transformed name which uses ASCII character `\001' (control-A) as the
magic character to distinguish them from ordinary labels. Thus the 5th
defintion of `6$' is named `L6C-A5'.
File: as.info, Node: Dot, Next: Symbol Attributes, Prev: Symbol Names, Up: Symbols
5.4 The Special Dot Symbol
==========================
The special symbol `.' refers to the current address that `as' is
assembling into. Thus, the expression `melvin: .long .' defines
`melvin' to contain its own address. Assigning a value to `.' is
treated the same as a `.org' directive. Thus, the expression `.=.+4'
is the same as saying `.space 4'.
File: as.info, Node: Symbol Attributes, Prev: Dot, Up: Symbols
5.5 Symbol Attributes
=====================
Every symbol has, as well as its name, the attributes "Value" and
"Type". Depending on output format, symbols can also have auxiliary
attributes.
If you use a symbol without defining it, `as' assumes zero for all
these attributes, and probably won't warn you. This makes the symbol
an externally defined symbol, which is generally what you would want.
* Menu:
* Symbol Value:: Value
* Symbol Type:: Type
* a.out Symbols:: Symbol Attributes: `a.out'
* COFF Symbols:: Symbol Attributes for COFF
* SOM Symbols:: Symbol Attributes for SOM
File: as.info, Node: Symbol Value, Next: Symbol Type, Up: Symbol Attributes
5.5.1 Value
-----------
The value of a symbol is (usually) 32 bits. For a symbol which labels a
location in the text, data, bss or absolute sections the value is the
number of addresses from the start of that section to the label.
Naturally for text, data and bss sections the value of a symbol changes
as `ld' changes section base addresses during linking. Absolute
symbols' values do not change during linking: that is why they are
called absolute.
The value of an undefined symbol is treated in a special way. If it
is 0 then the symbol is not defined in this assembler source file, and
`ld' tries to determine its value from other files linked into the same
program. You make this kind of symbol simply by mentioning a symbol
name without defining it. A non-zero value represents a `.comm' common
declaration. The value is how much common storage to reserve, in bytes
(addresses). The symbol refers to the first address of the allocated
storage.
File: as.info, Node: Symbol Type, Next: a.out Symbols, Prev: Symbol Value, Up: Symbol Attributes
5.5.2 Type
----------
The type attribute of a symbol contains relocation (section)
information, any flag settings indicating that a symbol is external, and
(optionally), other information for linkers and debuggers. The exact
format depends on the object-code output format in use.
File: as.info, Node: a.out Symbols, Next: COFF Symbols, Prev: Symbol Type, Up: Symbol Attributes
5.5.3 Symbol Attributes: `a.out'
--------------------------------
* Menu:
* Symbol Desc:: Descriptor
* Symbol Other:: Other
File: as.info, Node: Symbol Desc, Next: Symbol Other, Up: a.out Symbols
5.5.3.1 Descriptor
..................
This is an arbitrary 16-bit value. You may establish a symbol's
descriptor value by using a `.desc' statement (*note `.desc': Desc.).
A descriptor value means nothing to `as'.
File: as.info, Node: Symbol Other, Prev: Symbol Desc, Up: a.out Symbols
5.5.3.2 Other
.............
This is an arbitrary 8-bit value. It means nothing to `as'.
File: as.info, Node: COFF Symbols, Next: SOM Symbols, Prev: a.out Symbols, Up: Symbol Attributes
5.5.4 Symbol Attributes for COFF
--------------------------------
The COFF format supports a multitude of auxiliary symbol attributes;
like the primary symbol attributes, they are set between `.def' and
`.endef' directives.
5.5.4.1 Primary Attributes
..........................
The symbol name is set with `.def'; the value and type, respectively,
with `.val' and `.type'.
5.5.4.2 Auxiliary Attributes
............................
The `as' directives `.dim', `.line', `.scl', `.size', `.tag', and
`.weak' can generate auxiliary symbol table information for COFF.
File: as.info, Node: SOM Symbols, Prev: COFF Symbols, Up: Symbol Attributes
5.5.5 Symbol Attributes for SOM
-------------------------------
The SOM format for the HPPA supports a multitude of symbol attributes
set with the `.EXPORT' and `.IMPORT' directives.
The attributes are described in `HP9000 Series 800 Assembly Language
Reference Manual' (HP 92432-90001) under the `IMPORT' and `EXPORT'
assembler directive documentation.
File: as.info, Node: Expressions, Next: Pseudo Ops, Prev: Symbols, Up: Top
6 Expressions
*************
An "expression" specifies an address or numeric value. Whitespace may
precede and/or follow an expression.
The result of an expression must be an absolute number, or else an
offset into a particular section. If an expression is not absolute,
and there is not enough information when `as' sees the expression to
know its section, a second pass over the source program might be
necessary to interpret the expression--but the second pass is currently
not implemented. `as' aborts with an error message in this situation.
* Menu:
* Empty Exprs:: Empty Expressions
* Integer Exprs:: Integer Expressions
File: as.info, Node: Empty Exprs, Next: Integer Exprs, Up: Expressions
6.1 Empty Expressions
=====================
An empty expression has no value: it is just whitespace or null.
Wherever an absolute expression is required, you may omit the
expression, and `as' assumes a value of (absolute) 0. This is
compatible with other assemblers.
File: as.info, Node: Integer Exprs, Prev: Empty Exprs, Up: Expressions
6.2 Integer Expressions
=======================
An "integer expression" is one or more _arguments_ delimited by
_operators_.
* Menu:
* Arguments:: Arguments
* Operators:: Operators
* Prefix Ops:: Prefix Operators
* Infix Ops:: Infix Operators
File: as.info, Node: Arguments, Next: Operators, Up: Integer Exprs
6.2.1 Arguments
---------------
"Arguments" are symbols, numbers or subexpressions. In other contexts
arguments are sometimes called "arithmetic operands". In this manual,
to avoid confusing them with the "instruction operands" of the machine
language, we use the term "argument" to refer to parts of expressions
only, reserving the word "operand" to refer only to machine instruction
operands.
Symbols are evaluated to yield {SECTION NNN} where SECTION is one of
text, data, bss, absolute, or undefined. NNN is a signed, 2's
complement 32 bit integer.
Numbers are usually integers.
A number can be a flonum or bignum. In this case, you are warned
that only the low order 32 bits are used, and `as' pretends these 32
bits are an integer. You may write integer-manipulating instructions
that act on exotic constants, compatible with other assemblers.
Subexpressions are a left parenthesis `(' followed by an integer
expression, followed by a right parenthesis `)'; or a prefix operator
followed by an argument.
File: as.info, Node: Operators, Next: Prefix Ops, Prev: Arguments, Up: Integer Exprs
6.2.2 Operators
---------------
"Operators" are arithmetic functions, like `+' or `%'. Prefix
operators are followed by an argument. Infix operators appear between
their arguments. Operators may be preceded and/or followed by
whitespace.
File: as.info, Node: Prefix Ops, Next: Infix Ops, Prev: Operators, Up: Integer Exprs
6.2.3 Prefix Operator
---------------------
`as' has the following "prefix operators". They each take one
argument, which must be absolute.
`-'
"Negation". Two's complement negation.
`~'
"Complementation". Bitwise not.
File: as.info, Node: Infix Ops, Prev: Prefix Ops, Up: Integer Exprs
6.2.4 Infix Operators
---------------------
"Infix operators" take two arguments, one on either side. Operators
have precedence, but operations with equal precedence are performed left
to right. Apart from `+' or `-', both arguments must be absolute, and
the result is absolute.
1. Highest Precedence
`*'
"Multiplication".
`/'
"Division". Truncation is the same as the C operator `/'
`%'
"Remainder".
`<'
`<<'
"Shift Left". Same as the C operator `<<'.
`>'
`>>'
"Shift Right". Same as the C operator `>>'.
2. Intermediate precedence
`|'
"Bitwise Inclusive Or".
`&'
"Bitwise And".
`^'
"Bitwise Exclusive Or".
`!'
"Bitwise Or Not".
3. Low Precedence
`+'
"Addition". If either argument is absolute, the result has
the section of the other argument. You may not add together
arguments from different sections.
`-'
"Subtraction". If the right argument is absolute, the result
has the section of the left argument. If both arguments are
in the same section, the result is absolute. You may not
subtract arguments from different sections.
`=='
"Is Equal To"
`<>'
"Is Not Equal To"
`<'
"Is Less Than"
`>'
"Is Greater Than"
`>='
"Is Greater Than Or Equal To"
`<='
"Is Less Than Or Equal To"
The comparison operators can be used as infix operators. A
true results has a value of -1 whereas a false result has a
value of 0. Note, these operators perform signed
comparisons.
4. Lowest Precedence
`&&'
"Logical And".
`||'
"Logical Or".
These two logical operations can be used to combine the
results of sub expressions. Note, unlike the comparison
operators a true result returns a value of 1 but a false
results does still return 0. Also note that the logical or
operator has a slightly lower precedence than logical and.
In short, it's only meaningful to add or subtract the _offsets_ in an
address; you can only have a defined section in one of the two
arguments.
File: as.info, Node: Pseudo Ops, Next: Machine Dependencies, Prev: Expressions, Up: Top
7 Assembler Directives
**********************
All assembler directives have names that begin with a period (`.').
The rest of the name is letters, usually in lower case.
This chapter discusses directives that are available regardless of
the target machine configuration for the GNU assembler. Some machine
configurations provide additional directives. *Note Machine
Dependencies::.
* Menu:
* Abort:: `.abort'
* ABORT:: `.ABORT'
* Align:: `.align ABS-EXPR , ABS-EXPR'
* Altmacro:: `.altmacro'
* Ascii:: `.ascii "STRING"'...
* Asciz:: `.asciz "STRING"'...
* Balign:: `.balign ABS-EXPR , ABS-EXPR'
* Byte:: `.byte EXPRESSIONS'
* Comm:: `.comm SYMBOL , LENGTH '
* CFI directives:: `.cfi_startproc', `.cfi_endproc', etc.
* Data:: `.data SUBSECTION'
* Def:: `.def NAME'
* Desc:: `.desc SYMBOL, ABS-EXPRESSION'
* Dim:: `.dim'
* Double:: `.double FLONUMS'
* Eject:: `.eject'
* Else:: `.else'
* Elseif:: `.elseif'
* End:: `.end'
* Endef:: `.endef'
* Endfunc:: `.endfunc'
* Endif:: `.endif'
* Equ:: `.equ SYMBOL, EXPRESSION'
* Equiv:: `.equiv SYMBOL, EXPRESSION'
* Err:: `.err'
* Error:: `.error STRING'
* Exitm:: `.exitm'
* Extern:: `.extern'
* Fail:: `.fail'
* File:: `.file STRING'
* Fill:: `.fill REPEAT , SIZE , VALUE'
* Float:: `.float FLONUMS'
* Func:: `.func'
* Global:: `.global SYMBOL', `.globl SYMBOL'
* Hidden:: `.hidden NAMES'
* hword:: `.hword EXPRESSIONS'
* Ident:: `.ident'
* If:: `.if ABSOLUTE EXPRESSION'
* Incbin:: `.incbin "FILE"[,SKIP[,COUNT]]'
* Include:: `.include "FILE"'
* Int:: `.int EXPRESSIONS'
* Internal:: `.internal NAMES'
* Irp:: `.irp SYMBOL,VALUES'...
* Irpc:: `.irpc SYMBOL,VALUES'...
* Lcomm:: `.lcomm SYMBOL , LENGTH'
* Lflags:: `.lflags'
* Line:: `.line LINE-NUMBER'
* Ln:: `.ln LINE-NUMBER'
* Linkonce:: `.linkonce [TYPE]'
* List:: `.list'
* Long:: `.long EXPRESSIONS'
* Macro:: `.macro NAME ARGS'...
* MRI:: `.mri VAL'
* Noaltmacro:: `.noaltmacro'
* Nolist:: `.nolist'
* Octa:: `.octa BIGNUMS'
* Org:: `.org NEW-LC , FILL'
* P2align:: `.p2align ABS-EXPR , ABS-EXPR'
* PopSection:: `.popsection'
* Previous:: `.previous'
* Print:: `.print STRING'
* Protected:: `.protected NAMES'
* Psize:: `.psize LINES, COLUMNS'
* Purgem:: `.purgem NAME'
* PushSection:: `.pushsection NAME'
* Quad:: `.quad BIGNUMS'
* Rept:: `.rept COUNT'
* Sbttl:: `.sbttl "SUBHEADING"'
* Scl:: `.scl CLASS'
* Section:: `.section NAME'
* Set:: `.set SYMBOL, EXPRESSION'
* Short:: `.short EXPRESSIONS'
* Single:: `.single FLONUMS'
* Size:: `.size [NAME , EXPRESSION]'
* Skip:: `.skip SIZE , FILL'
* Sleb128:: `.sleb128 EXPRESSIONS'
* Space:: `.space SIZE , FILL'
* Stab:: `.stabd, .stabn, .stabs'
* String:: `.string "STR"'
* Struct:: `.struct EXPRESSION'
* SubSection:: `.subsection'
* Symver:: `.symver NAME,NAME2@NODENAME'
* Tag:: `.tag STRUCTNAME'
* Text:: `.text SUBSECTION'
* Title:: `.title "HEADING"'
* Type:: `.type <INT | NAME , TYPE DESCRIPTION>'
* Uleb128:: `.uleb128 EXPRESSIONS'
* Val:: `.val ADDR'
* Version:: `.version "STRING"'
* VTableEntry:: `.vtable_entry TABLE, OFFSET'
* VTableInherit:: `.vtable_inherit CHILD, PARENT'
* Warning:: `.warning STRING'
* Weak:: `.weak NAMES'
* Word:: `.word EXPRESSIONS'
* Deprecated:: Deprecated Directives
File: as.info, Node: Abort, Next: ABORT, Up: Pseudo Ops
7.1 `.abort'
============
This directive stops the assembly immediately. It is for compatibility
with other assemblers. The original idea was that the assembly
language source would be piped into the assembler. If the sender of
the source quit, it could use this directive tells `as' to quit also.
One day `.abort' will not be supported.
File: as.info, Node: ABORT, Next: Align, Prev: Abort, Up: Pseudo Ops
7.2 `.ABORT'
============
When producing COFF output, `as' accepts this directive as a synonym
for `.abort'.
When producing `b.out' output, `as' accepts this directive, but
ignores it.
File: as.info, Node: Align, Next: Altmacro, Prev: ABORT, Up: Pseudo Ops
7.3 `.align ABS-EXPR, ABS-EXPR, ABS-EXPR'
=========================================
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
alignment required, as described below.
The second expression (also absolute) gives the fill value to be
stored in the padding bytes. It (and the comma) may be omitted. If it
is omitted, the padding bytes are normally zero. However, on some
systems, if the section is marked as containing code and the fill value
is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it
is present, it is the maximum number of bytes that should be skipped by
this alignment directive. If doing the alignment would require
skipping more bytes than the specified maximum, then the alignment is
not done at all. You can omit the fill value (the second argument)
entirely by simply using two commas after the required alignment; this
can be useful if you want the alignment to be filled with no-op
instructions when appropriate.
The way the required alignment is specified varies from system to
system. For the a29k, arc, hppa, i386 using ELF, i860, iq2000, m68k,
m88k, or32, s390, sparc, tic4x, tic80 and xtensa, the first expression
is the alignment request in bytes. For example `.align 8' advances the
location counter until it is a multiple of 8. If the location counter
is already a multiple of 8, no change is needed. For the tic54x, the
first expression is the alignment request in words.
For other systems, including the i386 using a.out format, and the
arm and strongarm, it is the number of low-order zero bits the location
counter must have after advancement. For example `.align 3' advances
the location counter until it a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
This inconsistency is due to the different behaviors of the various
native assemblers for these systems which GAS must emulate. GAS also
provides `.balign' and `.p2align' directives, described later, which
have a consistent behavior across all architectures (but are specific
to GAS).
File: as.info, Node: Ascii, Next: Asciz, Prev: Altmacro, Up: Pseudo Ops
7.4 `.ascii "STRING"'...
========================
`.ascii' expects zero or more string literals (*note Strings::)
separated by commas. It assembles each string (with no automatic
trailing zero byte) into consecutive addresses.
File: as.info, Node: Asciz, Next: Balign, Prev: Ascii, Up: Pseudo Ops
7.5 `.asciz "STRING"'...
========================
`.asciz' is just like `.ascii', but each string is followed by a zero
byte. The "z" in `.asciz' stands for "zero".
File: as.info, Node: Balign, Next: Byte, Prev: Asciz, Up: Pseudo Ops
7.6 `.balign[wl] ABS-EXPR, ABS-EXPR, ABS-EXPR'
==============================================
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
alignment request in bytes. For example `.balign 8' advances the
location counter until it is a multiple of 8. If the location counter
is already a multiple of 8, no change is needed.
The second expression (also absolute) gives the fill value to be
stored in the padding bytes. It (and the comma) may be omitted. If it
is omitted, the padding bytes are normally zero. However, on some
systems, if the section is marked as containing code and the fill value
is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it
is present, it is the maximum number of bytes that should be skipped by
this alignment directive. If doing the alignment would require
skipping more bytes than the specified maximum, then the alignment is
not done at all. You can omit the fill value (the second argument)
entirely by simply using two commas after the required alignment; this
can be useful if you want the alignment to be filled with no-op
instructions when appropriate.
The `.balignw' and `.balignl' directives are variants of the
`.balign' directive. The `.balignw' directive treats the fill pattern
as a two byte word value. The `.balignl' directives treats the fill
pattern as a four byte longword value. For example, `.balignw
4,0x368d' will align to a multiple of 4. If it skips two bytes, they
will be filled in with the value 0x368d (the exact placement of the
bytes depends upon the endianness of the processor). If it skips 1 or
3 bytes, the fill value is undefined.
File: as.info, Node: Byte, Next: Comm, Prev: Balign, Up: Pseudo Ops
7.7 `.byte EXPRESSIONS'
=======================
`.byte' expects zero or more expressions, separated by commas. Each
expression is assembled into the next byte.
File: as.info, Node: Comm, Next: CFI directives, Prev: Byte, Up: Pseudo Ops
7.8 `.comm SYMBOL , LENGTH '
============================
`.comm' declares a common symbol named SYMBOL. When linking, a common
symbol in one object file may be merged with a defined or common symbol
of the same name in another object file. If `ld' does not see a
definition for the symbol-just one or more common symbols-then it will
allocate LENGTH bytes of uninitialized memory. LENGTH must be an
absolute expression. If `ld' sees multiple common symbols with the
same name, and they do not all have the same size, it will allocate
space using the largest size.
When using ELF, the `.comm' directive takes an optional third
argument. This is the desired alignment of the symbol, specified as a
byte boundary (for example, an alignment of 16 means that the least
significant 4 bits of the address should be zero). The alignment must
be an absolute expression, and it must be a power of two. If `ld'
allocates uninitialized memory for the common symbol, it will use the
alignment when placing the symbol. If no alignment is specified, `as'
will set the alignment to the largest power of two less than or equal
to the size of the symbol, up to a maximum of 16.
The syntax for `.comm' differs slightly on the HPPA. The syntax is
`SYMBOL .comm, LENGTH'; SYMBOL is optional.
File: as.info, Node: CFI directives, Next: Data, Prev: Comm, Up: Pseudo Ops
7.9 `.cfi_startproc'
====================
`.cfi_startproc' is used at the beginning of each function that should
have an entry in `.eh_frame'. It initializes some internal data
structures and emits architecture dependent initial CFI instructions.
Don't forget to close the function by `.cfi_endproc'.
7.10 `.cfi_endproc'
===================
`.cfi_endproc' is used at the end of a function where it closes its
unwind entry previously opened by `.cfi_startproc'. and emits it to
`.eh_frame'.
7.11 `.cfi_def_cfa REGISTER, OFFSET'
====================================
`.cfi_def_cfa' defines a rule for computing CFA as: take address from
REGISTER and add OFFSET to it.
7.12 `.cfi_def_cfa_register REGISTER'
=====================================
`.cfi_def_cfa_register' modifies a rule for computing CFA. From now on
REGISTER will be used instead of the old one. Offset remains the same.
7.13 `.cfi_def_cfa_offset OFFSET'
=================================
`.cfi_def_cfa_offset' modifies a rule for computing CFA. Register
remains the same, but OFFSET is new. Note that it is the absolute
offset that will be added to a defined register to compute CFA address.
7.14 `.cfi_adjust_cfa_offset OFFSET'
====================================
Same as `.cfi_def_cfa_offset' but OFFSET is a relative value that is
added/substracted from the previous offset.
7.15 `.cfi_offset REGISTER, OFFSET'
===================================
Previous value of REGISTER is saved at offset OFFSET from CFA.
7.16 `.cfi_rel_offset REGISTER, OFFSET'
=======================================
Previous value of REGISTER is saved at offset OFFSET from the current
CFA register. This is transformed to `.cfi_offset' using the known
displacement of the CFA register from the CFA. This is often easier to
use, because the number will match the code it's annotating.
7.17 `.cfi_window_save'
=======================
SPARC register window has been saved.
7.18 `.cfi_escape' EXPRESSION[, ...]
====================================
Allows the user to add arbitrary bytes to the unwind info. One might
use this to add OS-specific CFI opcodes, or generic CFI opcodes that
GAS does not yet support.
File: as.info, Node: Data, Next: Def, Prev: CFI directives, Up: Pseudo Ops
7.19 `.data SUBSECTION'
=======================
`.data' tells `as' to assemble the following statements onto the end of
the data subsection numbered SUBSECTION (which is an absolute
expression). If SUBSECTION is omitted, it defaults to zero.
File: as.info, Node: Def, Next: Desc, Prev: Data, Up: Pseudo Ops
7.20 `.def NAME'
================
Begin defining debugging information for a symbol NAME; the definition
extends until the `.endef' directive is encountered.
This directive is only observed when `as' is configured for COFF
format output; when producing `b.out', `.def' is recognized, but
ignored.
File: as.info, Node: Desc, Next: Dim, Prev: Def, Up: Pseudo Ops
7.21 `.desc SYMBOL, ABS-EXPRESSION'
===================================
This directive sets the descriptor of the symbol (*note Symbol
Attributes::) to the low 16 bits of an absolute expression.
The `.desc' directive is not available when `as' is configured for
COFF output; it is only for `a.out' or `b.out' object format. For the
sake of compatibility, `as' accepts it, but produces no output, when
configured for COFF.
File: as.info, Node: Dim, Next: Double, Prev: Desc, Up: Pseudo Ops
7.22 `.dim'
===========
This directive is generated by compilers to include auxiliary debugging
information in the symbol table. It is only permitted inside
`.def'/`.endef' pairs.
`.dim' is only meaningful when generating COFF format output; when
`as' is generating `b.out', it accepts this directive but ignores it.
File: as.info, Node: Double, Next: Eject, Prev: Dim, Up: Pseudo Ops
7.23 `.double FLONUMS'
======================
`.double' expects zero or more flonums, separated by commas. It
assembles floating point numbers. The exact kind of floating point
numbers emitted depends on how `as' is configured. *Note Machine
Dependencies::.
File: as.info, Node: Eject, Next: Else, Prev: Double, Up: Pseudo Ops
7.24 `.eject'
=============
Force a page break at this point, when generating assembly listings.
File: as.info, Node: Else, Next: Elseif, Prev: Eject, Up: Pseudo Ops
7.25 `.else'
============
`.else' is part of the `as' support for conditional assembly; *note
`.if': If. It marks the beginning of a section of code to be assembled
if the condition for the preceding `.if' was false.
File: as.info, Node: Elseif, Next: End, Prev: Else, Up: Pseudo Ops
7.26 `.elseif'
==============
`.elseif' is part of the `as' support for conditional assembly; *note
`.if': If. It is shorthand for beginning a new `.if' block that would
otherwise fill the entire `.else' section.
File: as.info, Node: End, Next: Endef, Prev: Elseif, Up: Pseudo Ops
7.27 `.end'
===========
`.end' marks the end of the assembly file. `as' does not process
anything in the file past the `.end' directive.
File: as.info, Node: Endef, Next: Endfunc, Prev: End, Up: Pseudo Ops
7.28 `.endef'
=============
This directive flags the end of a symbol definition begun with `.def'.
`.endef' is only meaningful when generating COFF format output; if
`as' is configured to generate `b.out', it accepts this directive but
ignores it.
File: as.info, Node: Endfunc, Next: Endif, Prev: Endef, Up: Pseudo Ops
7.29 `.endfunc'
===============
`.endfunc' marks the end of a function specified with `.func'.
File: as.info, Node: Endif, Next: Equ, Prev: Endfunc, Up: Pseudo Ops
7.30 `.endif'
=============
`.endif' is part of the `as' support for conditional assembly; it marks
the end of a block of code that is only assembled conditionally. *Note
`.if': If.
File: as.info, Node: Equ, Next: Equiv, Prev: Endif, Up: Pseudo Ops
7.31 `.equ SYMBOL, EXPRESSION'
==============================
This directive sets the value of SYMBOL to EXPRESSION. It is
synonymous with `.set'; *note `.set': Set.
The syntax for `equ' on the HPPA is `SYMBOL .equ EXPRESSION'.
File: as.info, Node: Equiv, Next: Err, Prev: Equ, Up: Pseudo Ops
7.32 `.equiv SYMBOL, EXPRESSION'
================================
The `.equiv' directive is like `.equ' and `.set', except that the
assembler will signal an error if SYMBOL is already defined. Note a
symbol which has been referenced but not actually defined is considered
to be undefined.
Except for the contents of the error message, this is roughly
equivalent to
.ifdef SYM
.err
.endif
.equ SYM,VAL
File: as.info, Node: Err, Next: Error, Prev: Equiv, Up: Pseudo Ops
7.33 `.err'
===========
If `as' assembles a `.err' directive, it will print an error message
and, unless the `-Z' option was used, it will not generate an object
file. This can be used to signal error an conditionally compiled code.
File: as.info, Node: Error, Next: Exitm, Prev: Err, Up: Pseudo Ops
7.34 `.error "STRING"'
======================
Similarly to `.err', this directive emits an error, but you can specify
a string that will be emitted as the error message. If you don't
specify the message, it defaults to `".error directive invoked in
source file"'. *Note Error and Warning Messages: Errors.
.error "This code has not been assembled and tested."
File: as.info, Node: Exitm, Next: Extern, Prev: Error, Up: Pseudo Ops
7.35 `.exitm'
=============
Exit early from the current macro definition. *Note Macro::.
File: as.info, Node: Extern, Next: Fail, Prev: Exitm, Up: Pseudo Ops
7.36 `.extern'
==============
`.extern' is accepted in the source program--for compatibility with
other assemblers--but it is ignored. `as' treats all undefined symbols
as external.
File: as.info, Node: Fail, Next: File, Prev: Extern, Up: Pseudo Ops
7.37 `.fail EXPRESSION'
=======================
Generates an error or a warning. If the value of the EXPRESSION is 500
or more, `as' will print a warning message. If the value is less than
500, `as' will print an error message. The message will include the
value of EXPRESSION. This can occasionally be useful inside complex
nested macros or conditional assembly.
File: as.info, Node: File, Next: Fill, Prev: Fail, Up: Pseudo Ops
7.38 `.file STRING'
===================
`.file' tells `as' that we are about to start a new logical file.
STRING is the new file name. In general, the filename is recognized
whether or not it is surrounded by quotes `"'; but if you wish to
specify an empty file name, you must give the quotes-`""'. This
statement may go away in future: it is only recognized to be compatible
with old `as' programs. In some configurations of `as', `.file' has
already been removed to avoid conflicts with other assemblers. *Note
Machine Dependencies::.
File: as.info, Node: Fill, Next: Float, Prev: File, Up: Pseudo Ops
7.39 `.fill REPEAT , SIZE , VALUE'
==================================
REPEAT, SIZE and VALUE are absolute expressions. This emits REPEAT
copies of SIZE bytes. REPEAT may be zero or more. SIZE may be zero or
more, but if it is more than 8, then it is deemed to have the value 8,
compatible with other people's assemblers. The contents of each REPEAT
bytes is taken from an 8-byte number. The highest order 4 bytes are
zero. The lowest order 4 bytes are VALUE rendered in the byte-order of
an integer on the computer `as' is assembling for. Each SIZE bytes in
a repetition is taken from the lowest order SIZE bytes of this number.
Again, this bizarre behavior is compatible with other people's
assemblers.
SIZE and VALUE are optional. If the second comma and VALUE are
absent, VALUE is assumed zero. If the first comma and following tokens
are absent, SIZE is assumed to be 1.
File: as.info, Node: Float, Next: Func, Prev: Fill, Up: Pseudo Ops
7.40 `.float FLONUMS'
=====================
This directive assembles zero or more flonums, separated by commas. It
has the same effect as `.single'. The exact kind of floating point
numbers emitted depends on how `as' is configured. *Note Machine
Dependencies::.
File: as.info, Node: Func, Next: Global, Prev: Float, Up: Pseudo Ops
7.41 `.func NAME[,LABEL]'
=========================
`.func' emits debugging information to denote function NAME, and is
ignored unless the file is assembled with debugging enabled. Only
`--gstabs[+]' is currently supported. LABEL is the entry point of the
function and if omitted NAME prepended with the `leading char' is used.
`leading char' is usually `_' or nothing, depending on the target. All
functions are currently defined to have `void' return type. The
function must be terminated with `.endfunc'.
File: as.info, Node: Global, Next: Hidden, Prev: Func, Up: Pseudo Ops
7.42 `.global SYMBOL', `.globl SYMBOL'
======================================
`.global' makes the symbol visible to `ld'. If you define SYMBOL in
your partial program, its value is made available to other partial
programs that are linked with it. Otherwise, SYMBOL takes its
attributes from a symbol of the same name from another file linked into
the same program.
Both spellings (`.globl' and `.global') are accepted, for
compatibility with other assemblers.
On the HPPA, `.global' is not always enough to make it accessible to
other partial programs. You may need the HPPA-only `.EXPORT' directive
as well. *Note HPPA Assembler Directives: HPPA Directives.
File: as.info, Node: Hidden, Next: hword, Prev: Global, Up: Pseudo Ops
7.43 `.hidden NAMES'
====================
This is one of the ELF visibility directives. The other two are
`.internal' (*note `.internal': Internal.) and `.protected' (*note
`.protected': Protected.).
This directive overrides the named symbols default visibility (which
is set by their binding: local, global or weak). The directive sets
the visibility to `hidden' which means that the symbols are not visible
to other components. Such symbols are always considered to be
`protected' as well.
File: as.info, Node: hword, Next: Ident, Prev: Hidden, Up: Pseudo Ops
7.44 `.hword EXPRESSIONS'
=========================
This expects zero or more EXPRESSIONS, and emits a 16 bit number for
each.
This directive is a synonym for `.short'; depending on the target
architecture, it may also be a synonym for `.word'.
File: as.info, Node: Ident, Next: If, Prev: hword, Up: Pseudo Ops
7.45 `.ident'
=============
This directive is used by some assemblers to place tags in object files.
`as' simply accepts the directive for source-file compatibility with
such assemblers, but does not actually emit anything for it.
File: as.info, Node: If, Next: Incbin, Prev: Ident, Up: Pseudo Ops
7.46 `.if ABSOLUTE EXPRESSION'
==============================
`.if' marks the beginning of a section of code which is only considered
part of the source program being assembled if the argument (which must
be an ABSOLUTE EXPRESSION) is non-zero. The end of the conditional
section of code must be marked by `.endif' (*note `.endif': Endif.);
optionally, you may include code for the alternative condition, flagged
by `.else' (*note `.else': Else.). If you have several conditions to
check, `.elseif' may be used to avoid nesting blocks if/else within
each subsequent `.else' block.
The following variants of `.if' are also supported:
`.ifdef SYMBOL'
Assembles the following section of code if the specified SYMBOL
has been defined. Note a symbol which has been referenced but not
yet defined is considered to be undefined.
`.ifc STRING1,STRING2'
Assembles the following section of code if the two strings are the
same. The strings may be optionally quoted with single quotes.
If they are not quoted, the first string stops at the first comma,
and the second string stops at the end of the line. Strings which
contain whitespace should be quoted. The string comparison is
case sensitive.
`.ifeq ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is zero.
`.ifeqs STRING1,STRING2'
Another form of `.ifc'. The strings must be quoted using double
quotes.
`.ifge ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is greater
than or equal to zero.
`.ifgt ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is greater
than zero.
`.ifle ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is less
than or equal to zero.
`.iflt ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is less
than zero.
`.ifnc STRING1,STRING2.'
Like `.ifc', but the sense of the test is reversed: this assembles
the following section of code if the two strings are not the same.
`.ifndef SYMBOL'
`.ifnotdef SYMBOL'
Assembles the following section of code if the specified SYMBOL
has not been defined. Both spelling variants are equivalent.
Note a symbol which has been referenced but not yet defined is
considered to be undefined.
`.ifne ABSOLUTE EXPRESSION'
Assembles the following section of code if the argument is not
equal to zero (in other words, this is equivalent to `.if').
`.ifnes STRING1,STRING2'
Like `.ifeqs', but the sense of the test is reversed: this
assembles the following section of code if the two strings are not
the same.
File: as.info, Node: Incbin, Next: Include, Prev: If, Up: Pseudo Ops
7.47 `.incbin "FILE"[,SKIP[,COUNT]]'
====================================
The `incbin' directive includes FILE verbatim at the current location.
You can control the search paths used with the `-I' command-line option
(*note Command-Line Options: Invoking.). Quotation marks are required
around FILE.
The SKIP argument skips a number of bytes from the start of the
FILE. The COUNT argument indicates the maximum number of bytes to
read. Note that the data is not aligned in any way, so it is the user's
responsibility to make sure that proper alignment is provided both
before and after the `incbin' directive.
File: as.info, Node: Include, Next: Int, Prev: Incbin, Up: Pseudo Ops
7.48 `.include "FILE"'
======================
This directive provides a way to include supporting files at specified
points in your source program. The code from FILE is assembled as if
it followed the point of the `.include'; when the end of the included
file is reached, assembly of the original file continues. You can
control the search paths used with the `-I' command-line option (*note
Command-Line Options: Invoking.). Quotation marks are required around
FILE.
File: as.info, Node: Int, Next: Internal, Prev: Include, Up: Pseudo Ops
7.49 `.int EXPRESSIONS'
=======================
Expect zero or more EXPRESSIONS, of any section, separated by commas.
For each expression, emit a number that, at run time, is the value of
that expression. The byte order and bit size of the number depends on
what kind of target the assembly is for.
File: as.info, Node: Internal, Next: Irp, Prev: Int, Up: Pseudo Ops
7.50 `.internal NAMES'
======================
This is one of the ELF visibility directives. The other two are
`.hidden' (*note `.hidden': Hidden.) and `.protected' (*note
`.protected': Protected.).
This directive overrides the named symbols default visibility (which
is set by their binding: local, global or weak). The directive sets
the visibility to `internal' which means that the symbols are
considered to be `hidden' (i.e., not visible to other components), and
that some extra, processor specific processing must also be performed
upon the symbols as well.
File: as.info, Node: Irp, Next: Irpc, Prev: Internal, Up: Pseudo Ops
7.51 `.irp SYMBOL,VALUES'...
============================
Evaluate a sequence of statements assigning different values to SYMBOL.
The sequence of statements starts at the `.irp' directive, and is
terminated by an `.endr' directive. For each VALUE, SYMBOL is set to
VALUE, and the sequence of statements is assembled. If no VALUE is
listed, the sequence of statements is assembled once, with SYMBOL set
to the null string. To refer to SYMBOL within the sequence of
statements, use \SYMBOL.
For example, assembling
.irp param,1,2,3
move d\param,sp@-
.endr
is equivalent to assembling
move d1,sp@-
move d2,sp@-
move d3,sp@-
File: as.info, Node: Irpc, Next: Lcomm, Prev: Irp, Up: Pseudo Ops
7.52 `.irpc SYMBOL,VALUES'...
=============================
Evaluate a sequence of statements assigning different values to SYMBOL.
The sequence of statements starts at the `.irpc' directive, and is
terminated by an `.endr' directive. For each character in VALUE,
SYMBOL is set to the character, and the sequence of statements is
assembled. If no VALUE is listed, the sequence of statements is
assembled once, with SYMBOL set to the null string. To refer to SYMBOL
within the sequence of statements, use \SYMBOL.
For example, assembling
.irpc param,123
move d\param,sp@-
.endr
is equivalent to assembling
move d1,sp@-
move d2,sp@-
move d3,sp@-
File: as.info, Node: Lcomm, Next: Lflags, Prev: Irpc, Up: Pseudo Ops
7.53 `.lcomm SYMBOL , LENGTH'
=============================
Reserve LENGTH (an absolute expression) bytes for a local common
denoted by SYMBOL. The section and value of SYMBOL are those of the
new local common. The addresses are allocated in the bss section, so
that at run-time the bytes start off zeroed. SYMBOL is not declared
global (*note `.global': Global.), so is normally not visible to `ld'.
Some targets permit a third argument to be used with `.lcomm'. This
argument specifies the desired alignment of the symbol in the bss
section.
The syntax for `.lcomm' differs slightly on the HPPA. The syntax is
`SYMBOL .lcomm, LENGTH'; SYMBOL is optional.
File: as.info, Node: Lflags, Next: Line, Prev: Lcomm, Up: Pseudo Ops
7.54 `.lflags'
==============
`as' accepts this directive, for compatibility with other assemblers,
but ignores it.
File: as.info, Node: Line, Next: Ln, Prev: Lflags, Up: Pseudo Ops
7.55 `.line LINE-NUMBER'
========================
Change the logical line number. LINE-NUMBER must be an absolute
expression. The next line has that logical line number. Therefore any
other statements on the current line (after a statement separator
character) are reported as on logical line number LINE-NUMBER - 1. One
day `as' will no longer support this directive: it is recognized only
for compatibility with existing assembler programs.
_Warning:_ In the AMD29K configuration of as, this command is not
available; use the synonym `.ln' in that context.
Even though this is a directive associated with the `a.out' or
`b.out' object-code formats, `as' still recognizes it when producing
COFF output, and treats `.line' as though it were the COFF `.ln' _if_
it is found outside a `.def'/`.endef' pair.
Inside a `.def', `.line' is, instead, one of the directives used by
compilers to generate auxiliary symbol information for debugging.
File: as.info, Node: Linkonce, Next: List, Prev: Ln, Up: Pseudo Ops
7.56 `.linkonce [TYPE]'
=======================
Mark the current section so that the linker only includes a single copy
of it. This may be used to include the same section in several
different object files, but ensure that the linker will only include it
once in the final output file. The `.linkonce' pseudo-op must be used
for each instance of the section. Duplicate sections are detected
based on the section name, so it should be unique.
This directive is only supported by a few object file formats; as of
this writing, the only object file format which supports it is the
Portable Executable format used on Windows NT.
The TYPE argument is optional. If specified, it must be one of the
following strings. For example:
.linkonce same_size
Not all types may be supported on all object file formats.
`discard'
Silently discard duplicate sections. This is the default.
`one_only'
Warn if there are duplicate sections, but still keep only one copy.
`same_size'
Warn if any of the duplicates have different sizes.
`same_contents'
Warn if any of the duplicates do not have exactly the same
contents.
File: as.info, Node: Ln, Next: Linkonce, Prev: Line, Up: Pseudo Ops
7.57 `.ln LINE-NUMBER'
======================
`.ln' is a synonym for `.line'.
File: as.info, Node: MRI, Next: Noaltmacro, Prev: Macro, Up: Pseudo Ops
7.58 `.mri VAL'
===============
If VAL is non-zero, this tells `as' to enter MRI mode. If VAL is zero,
this tells `as' to exit MRI mode. This change affects code assembled
until the next `.mri' directive, or until the end of the file. *Note
MRI mode: M.
File: as.info, Node: List, Next: Long, Prev: Linkonce, Up: Pseudo Ops
7.59 `.list'
============
Control (in conjunction with the `.nolist' directive) whether or not
assembly listings are generated. These two directives maintain an
internal counter (which is zero initially). `.list' increments the
counter, and `.nolist' decrements it. Assembly listings are generated
whenever the counter is greater than zero.
By default, listings are disabled. When you enable them (with the
`-a' command line option; *note Command-Line Options: Invoking.), the
initial value of the listing counter is one.
File: as.info, Node: Long, Next: Macro, Prev: List, Up: Pseudo Ops
7.60 `.long EXPRESSIONS'
========================
`.long' is the same as `.int', *note `.int': Int.
File: as.info, Node: Macro, Next: MRI, Prev: Long, Up: Pseudo Ops
7.61 `.macro'
=============
The commands `.macro' and `.endm' allow you to define macros that
generate assembly output. For example, this definition specifies a
macro `sum' that puts a sequence of numbers into memory:
.macro sum from=0, to=5
.long \from
.if \to-\from
sum "(\from+1)",\to
.endif
.endm
With that definition, `SUM 0,5' is equivalent to this assembly input:
.long 0
.long 1
.long 2
.long 3
.long 4
.long 5
`.macro MACNAME'
`.macro MACNAME MACARGS ...'
Begin the definition of a macro called MACNAME. If your macro
definition requires arguments, specify their names after the macro
name, separated by commas or spaces. You can supply a default
value for any macro argument by following the name with `=DEFLT'.
You cannot define two macros with the same MACNAME unless it has
been subject to the `.purgem' directive (*Note Purgem::.) between
the two definitions. For example, these are all valid `.macro'
statements:
`.macro comm'
Begin the definition of a macro called `comm', which takes no
arguments.
`.macro plus1 p, p1'
`.macro plus1 p p1'
Either statement begins the definition of a macro called
`plus1', which takes two arguments; within the macro
definition, write `\p' or `\p1' to evaluate the arguments.
`.macro reserve_str p1=0 p2'
Begin the definition of a macro called `reserve_str', with two
arguments. The first argument has a default value, but not
the second. After the definition is complete, you can call
the macro either as `reserve_str A,B' (with `\p1' evaluating
to A and `\p2' evaluating to B), or as `reserve_str ,B' (with
`\p1' evaluating as the default, in this case `0', and `\p2'
evaluating to B).
When you call a macro, you can specify the argument values either
by position, or by keyword. For example, `sum 9,17' is equivalent
to `sum to=17, from=9'.
`.endm'
Mark the end of a macro definition.
`.exitm'
Exit early from the current macro definition.
`\@'
`as' maintains a counter of how many macros it has executed in
this pseudo-variable; you can copy that number to your output with
`\@', but _only within a macro definition_.
`LOCAL NAME [ , ... ]'
_Warning: `LOCAL' is only available if you select "alternate macro
syntax" with `--alternate' or `.altmacro'._ *Note `.altmacro':
Altmacro.
File: as.info, Node: Altmacro, Next: Ascii, Prev: Align, Up: Pseudo Ops
7.62 `.altmacro'
================
Enable alternate macro mode, enabling:
`LOCAL NAME [ , ... ]'
One additional directive, `LOCAL', is available. It is used to
generate a string replacement for each of the NAME arguments, and
replace any instances of NAME in each macro expansion. The
replacement string is unique in the assembly, and different for
each separate macro expansion. `LOCAL' allows you to write macros
that define symbols, without fear of conflict between separate
macro expansions.
`String delimiters'
You can write strings delimited in these other ways besides
`"STRING"':
`'STRING''
You can delimit strings with single-quote charaters.
`<STRING>'
You can delimit strings with matching angle brackets.
`single-character string escape'
To include any single character literally in a string (even if the
character would otherwise have some special meaning), you can
prefix the character with `!' (an exclamation mark). For example,
you can write `<4.3 !> 5.4!!>' to get the literal text `4.3 >
5.4!'.
`Expression results as strings'
You can write `%EXPR' to evaluate the expression EXPR and use the
result as a string.
File: as.info, Node: Noaltmacro, Next: Nolist, Prev: MRI, Up: Pseudo Ops
7.63 `.noaltmacro'
==================
Disable alternate macro mode. *Note Altmacro::
File: as.info, Node: Nolist, Next: Octa, Prev: Noaltmacro, Up: Pseudo Ops
7.64 `.nolist'
==============
Control (in conjunction with the `.list' directive) whether or not
assembly listings are generated. These two directives maintain an
internal counter (which is zero initially). `.list' increments the
counter, and `.nolist' decrements it. Assembly listings are generated
whenever the counter is greater than zero.
File: as.info, Node: Octa, Next: Org, Prev: Nolist, Up: Pseudo Ops
7.65 `.octa BIGNUMS'
====================
This directive expects zero or more bignums, separated by commas. For
each bignum, it emits a 16-byte integer.
The term "octa" comes from contexts in which a "word" is two bytes;
hence _octa_-word for 16 bytes.
File: as.info, Node: Org, Next: P2align, Prev: Octa, Up: Pseudo Ops
7.66 `.org NEW-LC , FILL'
=========================
Advance the location counter of the current section to NEW-LC. NEW-LC
is either an absolute expression or an expression with the same section
as the current subsection. That is, you can't use `.org' to cross
sections: if NEW-LC has the wrong section, the `.org' directive is
ignored. To be compatible with former assemblers, if the section of
NEW-LC is absolute, `as' issues a warning, then pretends the section of
NEW-LC is the same as the current subsection.
`.org' may only increase the location counter, or leave it
unchanged; you cannot use `.org' to move the location counter backwards.
Because `as' tries to assemble programs in one pass, NEW-LC may not
be undefined. If you really detest this restriction we eagerly await a
chance to share your improved assembler.
Beware that the origin is relative to the start of the section, not
to the start of the subsection. This is compatible with other people's
assemblers.
When the location counter (of the current subsection) is advanced,
the intervening bytes are filled with FILL which should be an absolute
expression. If the comma and FILL are omitted, FILL defaults to zero.
File: as.info, Node: P2align, Next: PopSection, Prev: Org, Up: Pseudo Ops
7.67 `.p2align[wl] ABS-EXPR, ABS-EXPR, ABS-EXPR'
================================================
Pad the location counter (in the current subsection) to a particular
storage boundary. The first expression (which must be absolute) is the
number of low-order zero bits the location counter must have after
advancement. For example `.p2align 3' advances the location counter
until it a multiple of 8. If the location counter is already a
multiple of 8, no change is needed.
The second expression (also absolute) gives the fill value to be
stored in the padding bytes. It (and the comma) may be omitted. If it
is omitted, the padding bytes are normally zero. However, on some
systems, if the section is marked as containing code and the fill value
is omitted, the space is filled with no-op instructions.
The third expression is also absolute, and is also optional. If it
is present, it is the maximum number of bytes that should be skipped by
this alignment directive. If doing the alignment would require
skipping more bytes than the specified maximum, then the alignment is
not done at all. You can omit the fill value (the second argument)
entirely by simply using two commas after the required alignment; this
can be useful if you want the alignment to be filled with no-op
instructions when appropriate.
The `.p2alignw' and `.p2alignl' directives are variants of the
`.p2align' directive. The `.p2alignw' directive treats the fill
pattern as a two byte word value. The `.p2alignl' directives treats the
fill pattern as a four byte longword value. For example, `.p2alignw
2,0x368d' will align to a multiple of 4. If it skips two bytes, they
will be filled in with the value 0x368d (the exact placement of the
bytes depends upon the endianness of the processor). If it skips 1 or
3 bytes, the fill value is undefined.
File: as.info, Node: Previous, Next: Print, Prev: PopSection, Up: Pseudo Ops
7.68 `.previous'
================
This is one of the ELF section stack manipulation directives. The
others are `.section' (*note Section::), `.subsection' (*note
SubSection::), `.pushsection' (*note PushSection::), and `.popsection'
(*note PopSection::).
This directive swaps the current section (and subsection) with most
recently referenced section (and subsection) prior to this one.
Multiple `.previous' directives in a row will flip between two sections
(and their subsections).
In terms of the section stack, this directive swaps the current
section with the top section on the section stack.
File: as.info, Node: PopSection, Next: Previous, Prev: P2align, Up: Pseudo Ops
7.69 `.popsection'
==================
This is one of the ELF section stack manipulation directives. The
others are `.section' (*note Section::), `.subsection' (*note
SubSection::), `.pushsection' (*note PushSection::), and `.previous'
(*note Previous::).
This directive replaces the current section (and subsection) with
the top section (and subsection) on the section stack. This section is
popped off the stack.
File: as.info, Node: Print, Next: Protected, Prev: Previous, Up: Pseudo Ops
7.70 `.print STRING'
====================
`as' will print STRING on the standard output during assembly. You
must put STRING in double quotes.
File: as.info, Node: Protected, Next: Psize, Prev: Print, Up: Pseudo Ops
7.71 `.protected NAMES'
=======================
This is one of the ELF visibility directives. The other two are
`.hidden' (*note Hidden::) and `.internal' (*note Internal::).
This directive overrides the named symbols default visibility (which
is set by their binding: local, global or weak). The directive sets
the visibility to `protected' which means that any references to the
symbols from within the components that defines them must be resolved
to the definition in that component, even if a definition in another
component would normally preempt this.
File: as.info, Node: Psize, Next: Purgem, Prev: Protected, Up: Pseudo Ops
7.72 `.psize LINES , COLUMNS'
=============================
Use this directive to declare the number of lines--and, optionally, the
number of columns--to use for each page, when generating listings.
If you do not use `.psize', listings use a default line-count of 60.
You may omit the comma and COLUMNS specification; the default width is
200 columns.
`as' generates formfeeds whenever the specified number of lines is
exceeded (or whenever you explicitly request one, using `.eject').
If you specify LINES as `0', no formfeeds are generated save those
explicitly specified with `.eject'.
File: as.info, Node: Purgem, Next: PushSection, Prev: Psize, Up: Pseudo Ops
7.73 `.purgem NAME'
===================
Undefine the macro NAME, so that later uses of the string will not be
expanded. *Note Macro::.
File: as.info, Node: PushSection, Next: Quad, Prev: Purgem, Up: Pseudo Ops
7.74 `.pushsection NAME , SUBSECTION'
=====================================
This is one of the ELF section stack manipulation directives. The
others are `.section' (*note Section::), `.subsection' (*note
SubSection::), `.popsection' (*note PopSection::), and `.previous'
(*note Previous::).
This directive pushes the current section (and subsection) onto the
top of the section stack, and then replaces the current section and
subsection with `name' and `subsection'.
File: as.info, Node: Quad, Next: Rept, Prev: PushSection, Up: Pseudo Ops
7.75 `.quad BIGNUMS'
====================
`.quad' expects zero or more bignums, separated by commas. For each
bignum, it emits an 8-byte integer. If the bignum won't fit in 8
bytes, it prints a warning message; and just takes the lowest order 8
bytes of the bignum.
The term "quad" comes from contexts in which a "word" is two bytes;
hence _quad_-word for 8 bytes.
File: as.info, Node: Rept, Next: Sbttl, Prev: Quad, Up: Pseudo Ops
7.76 `.rept COUNT'
==================
Repeat the sequence of lines between the `.rept' directive and the next
`.endr' directive COUNT times.
For example, assembling
.rept 3
.long 0
.endr
is equivalent to assembling
.long 0
.long 0
.long 0
File: as.info, Node: Sbttl, Next: Scl, Prev: Rept, Up: Pseudo Ops
7.77 `.sbttl "SUBHEADING"'
==========================
Use SUBHEADING as the title (third line, immediately after the title
line) when generating assembly listings.
This directive affects subsequent pages, as well as the current page
if it appears within ten lines of the top of a page.
File: as.info, Node: Scl, Next: Section, Prev: Sbttl, Up: Pseudo Ops
7.78 `.scl CLASS'
=================
Set the storage-class value for a symbol. This directive may only be
used inside a `.def'/`.endef' pair. Storage class may flag whether a
symbol is static or external, or it may record further symbolic
debugging information.
The `.scl' directive is primarily associated with COFF output; when
configured to generate `b.out' output format, `as' accepts this
directive but ignores it.
File: as.info, Node: Section, Next: Set, Prev: Scl, Up: Pseudo Ops
7.79 `.section NAME'
====================
Use the `.section' directive to assemble the following code into a
section named NAME.
This directive is only supported for targets that actually support
arbitrarily named sections; on `a.out' targets, for example, it is not
accepted, even with a standard `a.out' section name.
COFF Version
------------
For COFF targets, the `.section' directive is used in one of the
following ways:
.section NAME[, "FLAGS"]
.section NAME[, SUBSEGMENT]
If the optional argument is quoted, it is taken as flags to use for
the section. Each flag is a single character. The following flags are
recognized:
`b'
bss section (uninitialized data)
`n'
section is not loaded
`w'
writable section
`d'
data section
`r'
read-only section
`x'
executable section
`s'
shared section (meaningful for PE targets)
`a'
ignored. (For compatibility with the ELF version)
If no flags are specified, the default flags depend upon the section
name. If the section name is not recognized, the default will be for
the section to be loaded and writable. Note the `n' and `w' flags
remove attributes from the section, rather than adding them, so if they
are used on their own it will be as if no flags had been specified at
all.
If the optional argument to the `.section' directive is not quoted,
it is taken as a subsegment number (*note Sub-Sections::).
ELF Version
-----------
This is one of the ELF section stack manipulation directives. The
others are `.subsection' (*note SubSection::), `.pushsection' (*note
PushSection::), `.popsection' (*note PopSection::), and `.previous'
(*note Previous::).
For ELF targets, the `.section' directive is used like this:
.section NAME [, "FLAGS"[, @TYPE[,FLAG_SPECIFIC_ARGUMENTS]]
The optional FLAGS argument is a quoted string which may contain any
combination of the following characters:
`a'
section is allocatable
`w'
section is writable
`x'
section is executable
`M'
section is mergeable
`S'
section contains zero terminated strings
`G'
section is a member of a section group
`T'
section is used for thread-local-storage
The optional TYPE argument may contain one of the following
constants:
`@progbits'
section contains data
`@nobits'
section does not contain data (i.e., section only occupies space)
`@note'
section contains data which is used by things other than the
program
`@init_array'
section contains an array of pointers to init functions
`@fini_array'
section contains an array of pointers to finish functions
`@preinit_array'
section contains an array of pointers to pre-init functions
Many targets only support the first three section types.
Note on targets where the `@' character is the start of a comment (eg
ARM) then another character is used instead. For example the ARM port
uses the `%' character.
If FLAGS contains the `M' symbol then the TYPE argument must be
specified as well as an extra argument - ENTSIZE - like this:
.section NAME , "FLAGS"M, @TYPE, ENTSIZE
Sections with the `M' flag but not `S' flag must contain fixed size
constants, each ENTSIZE octets long. Sections with both `M' and `S'
must contain zero terminated strings where each character is ENTSIZE
bytes long. The linker may remove duplicates within sections with the
same name, same entity size and same flags. ENTSIZE must be an
absolute expression.
If FLAGS contains the `G' symbol then the TYPE argument must be
present along with an additional field like this:
.section NAME , "FLAGS"G, @TYPE, GROUPNAME[, LINKAGE]
The GROUPNAME field specifies the name of the section group to which
this particular section belongs. The optional linkage field can
contain:
`comdat'
indicates that only one copy of this section should be retained
`.gnu.linkonce'
an alias for comdat
Note - if both the M and G flags are present then the fields for the
Merge flag should come first, like this:
.section NAME , "FLAGS"MG, @TYPE, ENTSIZE, GROUPNAME[, LINKAGE]
If no flags are specified, the default flags depend upon the section
name. If the section name is not recognized, the default will be for
the section to have none of the above flags: it will not be allocated
in memory, nor writable, nor executable. The section will contain data.
For ELF targets, the assembler supports another type of `.section'
directive for compatibility with the Solaris assembler:
.section "NAME"[, FLAGS...]
Note that the section name is quoted. There may be a sequence of
comma separated flags:
`#alloc'
section is allocatable
`#write'
section is writable
`#execinstr'
section is executable
`#tls'
section is used for thread local storage
This directive replaces the current section and subsection. See the
contents of the gas testsuite directory `gas/testsuite/gas/elf' for
some examples of how this directive and the other section stack
directives work.
File: as.info, Node: Set, Next: Short, Prev: Section, Up: Pseudo Ops
7.80 `.set SYMBOL, EXPRESSION'
==============================
Set the value of SYMBOL to EXPRESSION. This changes SYMBOL's value and
type to conform to EXPRESSION. If SYMBOL was flagged as external, it
remains flagged (*note Symbol Attributes::).
You may `.set' a symbol many times in the same assembly.
If you `.set' a global symbol, the value stored in the object file
is the last value stored into it.
The syntax for `set' on the HPPA is `SYMBOL .set EXPRESSION'.
File: as.info, Node: Short, Next: Single, Prev: Set, Up: Pseudo Ops
7.81 `.short EXPRESSIONS'
=========================
`.short' is normally the same as `.word'. *Note `.word': Word.
In some configurations, however, `.short' and `.word' generate
numbers of different lengths; *note Machine Dependencies::.
File: as.info, Node: Single, Next: Size, Prev: Short, Up: Pseudo Ops
7.82 `.single FLONUMS'
======================
This directive assembles zero or more flonums, separated by commas. It
has the same effect as `.float'. The exact kind of floating point
numbers emitted depends on how `as' is configured. *Note Machine
Dependencies::.
File: as.info, Node: Size, Next: Skip, Prev: Single, Up: Pseudo Ops
7.83 `.size'
============
This directive is used to set the size associated with a symbol.
COFF Version
------------
For COFF targets, the `.size' directive is only permitted inside
`.def'/`.endef' pairs. It is used like this:
.size EXPRESSION
`.size' is only meaningful when generating COFF format output; when
`as' is generating `b.out', it accepts this directive but ignores it.
ELF Version
-----------
For ELF targets, the `.size' directive is used like this:
.size NAME , EXPRESSION
This directive sets the size associated with a symbol NAME. The
size in bytes is computed from EXPRESSION which can make use of label
arithmetic. This directive is typically used to set the size of
function symbols.
File: as.info, Node: Sleb128, Next: Space, Prev: Skip, Up: Pseudo Ops
7.84 `.sleb128 EXPRESSIONS'
===========================
SLEB128 stands for "signed little endian base 128." This is a compact,
variable length representation of numbers used by the DWARF symbolic
debugging format. *Note `.uleb128': Uleb128.
File: as.info, Node: Skip, Next: Sleb128, Prev: Size, Up: Pseudo Ops
7.85 `.skip SIZE , FILL'
========================
This directive emits SIZE bytes, each of value FILL. Both SIZE and
FILL are absolute expressions. If the comma and FILL are omitted, FILL
is assumed to be zero. This is the same as `.space'.
File: as.info, Node: Space, Next: Stab, Prev: Sleb128, Up: Pseudo Ops
7.86 `.space SIZE , FILL'
=========================
This directive emits SIZE bytes, each of value FILL. Both SIZE and
FILL are absolute expressions. If the comma and FILL are omitted, FILL
is assumed to be zero. This is the same as `.skip'.
_Warning:_ `.space' has a completely different meaning for HPPA
targets; use `.block' as a substitute. See `HP9000 Series 800
Assembly Language Reference Manual' (HP 92432-90001) for the
meaning of the `.space' directive. *Note HPPA Assembler
Directives: HPPA Directives, for a summary.
On the AMD 29K, this directive is ignored; it is accepted for
compatibility with other AMD 29K assemblers.
_Warning:_ In most versions of the GNU assembler, the directive
`.space' has the effect of `.block' *Note Machine Dependencies::.
File: as.info, Node: Stab, Next: String, Prev: Space, Up: Pseudo Ops
7.87 `.stabd, .stabn, .stabs'
=============================
There are three directives that begin `.stab'. All emit symbols (*note
Symbols::), for use by symbolic debuggers. The symbols are not entered
in the `as' hash table: they cannot be referenced elsewhere in the
source file. Up to five fields are required:
STRING
This is the symbol's name. It may contain any character except
`\000', so is more general than ordinary symbol names. Some
debuggers used to code arbitrarily complex structures into symbol
names using this field.
TYPE
An absolute expression. The symbol's type is set to the low 8
bits of this expression. Any bit pattern is permitted, but `ld'
and debuggers choke on silly bit patterns.
OTHER
An absolute expression. The symbol's "other" attribute is set to
the low 8 bits of this expression.
DESC
An absolute expression. The symbol's descriptor is set to the low
16 bits of this expression.
VALUE
An absolute expression which becomes the symbol's value.
If a warning is detected while reading a `.stabd', `.stabn', or
`.stabs' statement, the symbol has probably already been created; you
get a half-formed symbol in your object file. This is compatible with
earlier assemblers!
`.stabd TYPE , OTHER , DESC'
The "name" of the symbol generated is not even an empty string.
It is a null pointer, for compatibility. Older assemblers used a
null pointer so they didn't waste space in object files with empty
strings.
The symbol's value is set to the location counter, relocatably.
When your program is linked, the value of this symbol is the
address of the location counter when the `.stabd' was assembled.
`.stabn TYPE , OTHER , DESC , VALUE'
The name of the symbol is set to the empty string `""'.
`.stabs STRING , TYPE , OTHER , DESC , VALUE'
All five fields are specified.
File: as.info, Node: String, Next: Struct, Prev: Stab, Up: Pseudo Ops
7.88 `.string' "STR"
====================
Copy the characters in STR to the object file. You may specify more
than one string to copy, separated by commas. Unless otherwise
specified for a particular machine, the assembler marks the end of each
string with a 0 byte. You can use any of the escape sequences
described in *Note Strings: Strings.
File: as.info, Node: Struct, Next: SubSection, Prev: String, Up: Pseudo Ops
7.89 `.struct EXPRESSION'
=========================
Switch to the absolute section, and set the section offset to
EXPRESSION, which must be an absolute expression. You might use this
as follows:
.struct 0
field1:
.struct field1 + 4
field2:
.struct field2 + 4
field3:
This would define the symbol `field1' to have the value 0, the symbol
`field2' to have the value 4, and the symbol `field3' to have the value
8. Assembly would be left in the absolute section, and you would need
to use a `.section' directive of some sort to change to some other
section before further assembly.
File: as.info, Node: SubSection, Next: Symver, Prev: Struct, Up: Pseudo Ops
7.90 `.subsection NAME'
=======================
This is one of the ELF section stack manipulation directives. The
others are `.section' (*note Section::), `.pushsection' (*note
PushSection::), `.popsection' (*note PopSection::), and `.previous'
(*note Previous::).
This directive replaces the current subsection with `name'. The
current section is not changed. The replaced subsection is put onto
the section stack in place of the then current top of stack subsection.
File: as.info, Node: Symver, Next: Tag, Prev: SubSection, Up: Pseudo Ops
7.91 `.symver'
==============
Use the `.symver' directive to bind symbols to specific version nodes
within a source file. This is only supported on ELF platforms, and is
typically used when assembling files to be linked into a shared library.
There are cases where it may make sense to use this in objects to be
bound into an application itself so as to override a versioned symbol
from a shared library.
For ELF targets, the `.symver' directive can be used like this:
.symver NAME, NAME2@NODENAME
If the symbol NAME is defined within the file being assembled, the
`.symver' directive effectively creates a symbol alias with the name
NAME2@NODENAME, and in fact the main reason that we just don't try and
create a regular alias is that the @ character isn't permitted in
symbol names. The NAME2 part of the name is the actual name of the
symbol by which it will be externally referenced. The name NAME itself
is merely a name of convenience that is used so that it is possible to
have definitions for multiple versions of a function within a single
source file, and so that the compiler can unambiguously know which
version of a function is being mentioned. The NODENAME portion of the
alias should be the name of a node specified in the version script
supplied to the linker when building a shared library. If you are
attempting to override a versioned symbol from a shared library, then
NODENAME should correspond to the nodename of the symbol you are trying
to override.
If the symbol NAME is not defined within the file being assembled,
all references to NAME will be changed to NAME2@NODENAME. If no
reference to NAME is made, NAME2@NODENAME will be removed from the
symbol table.
Another usage of the `.symver' directive is:
.symver NAME, NAME2@@NODENAME
In this case, the symbol NAME must exist and be defined within the
file being assembled. It is similar to NAME2@NODENAME. The difference
is NAME2@@NODENAME will also be used to resolve references to NAME2 by
the linker.
The third usage of the `.symver' directive is:
.symver NAME, NAME2@@@NODENAME
When NAME is not defined within the file being assembled, it is
treated as NAME2@NODENAME. When NAME is defined within the file being
assembled, the symbol name, NAME, will be changed to NAME2@@NODENAME.
File: as.info, Node: Tag, Next: Text, Prev: Symver, Up: Pseudo Ops
7.92 `.tag STRUCTNAME'
======================
This directive is generated by compilers to include auxiliary debugging
information in the symbol table. It is only permitted inside
`.def'/`.endef' pairs. Tags are used to link structure definitions in
the symbol table with instances of those structures.
`.tag' is only used when generating COFF format output; when `as' is
generating `b.out', it accepts this directive but ignores it.
File: as.info, Node: Text, Next: Title, Prev: Tag, Up: Pseudo Ops
7.93 `.text SUBSECTION'
=======================
Tells `as' to assemble the following statements onto the end of the
text subsection numbered SUBSECTION, which is an absolute expression.
If SUBSECTION is omitted, subsection number zero is used.
File: as.info, Node: Title, Next: Type, Prev: Text, Up: Pseudo Ops
7.94 `.title "HEADING"'
=======================
Use HEADING as the title (second line, immediately after the source
file name and pagenumber) when generating assembly listings.
This directive affects subsequent pages, as well as the current page
if it appears within ten lines of the top of a page.
File: as.info, Node: Type, Next: Uleb128, Prev: Title, Up: Pseudo Ops
7.95 `.type'
============
This directive is used to set the type of a symbol.
COFF Version
------------
For COFF targets, this directive is permitted only within
`.def'/`.endef' pairs. It is used like this:
.type INT
This records the integer INT as the type attribute of a symbol table
entry.
`.type' is associated only with COFF format output; when `as' is
configured for `b.out' output, it accepts this directive but ignores it.
ELF Version
-----------
For ELF targets, the `.type' directive is used like this:
.type NAME , TYPE DESCRIPTION
This sets the type of symbol NAME to be either a function symbol or
an object symbol. There are five different syntaxes supported for the
TYPE DESCRIPTION field, in order to provide compatibility with various
other assemblers. The syntaxes supported are:
.type <name>,#function
.type <name>,#object
.type <name>,@function
.type <name>,@object
.type <name>,%function
.type <name>,%object
.type <name>,"function"
.type <name>,"object"
.type <name> STT_FUNCTION
.type <name> STT_OBJECT
File: as.info, Node: Uleb128, Next: Val, Prev: Type, Up: Pseudo Ops
7.96 `.uleb128 EXPRESSIONS'
===========================
ULEB128 stands for "unsigned little endian base 128." This is a
compact, variable length representation of numbers used by the DWARF
symbolic debugging format. *Note `.sleb128': Sleb128.
File: as.info, Node: Val, Next: Version, Prev: Uleb128, Up: Pseudo Ops
7.97 `.val ADDR'
================
This directive, permitted only within `.def'/`.endef' pairs, records
the address ADDR as the value attribute of a symbol table entry.
`.val' is used only for COFF output; when `as' is configured for
`b.out', it accepts this directive but ignores it.
File: as.info, Node: Version, Next: VTableEntry, Prev: Val, Up: Pseudo Ops
7.98 `.version "STRING"'
========================
This directive creates a `.note' section and places into it an ELF
formatted note of type NT_VERSION. The note's name is set to `string'.
File: as.info, Node: VTableEntry, Next: VTableInherit, Prev: Version, Up: Pseudo Ops
7.99 `.vtable_entry TABLE, OFFSET'
==================================
This directive finds or creates a symbol `table' and creates a
`VTABLE_ENTRY' relocation for it with an addend of `offset'.
File: as.info, Node: VTableInherit, Next: Warning, Prev: VTableEntry, Up: Pseudo Ops
7.100 `.vtable_inherit CHILD, PARENT'
=====================================
This directive finds the symbol `child' and finds or creates the symbol
`parent' and then creates a `VTABLE_INHERIT' relocation for the parent
whose addend is the value of the child symbol. As a special case the
parent name of `0' is treated as refering the `*ABS*' section.
File: as.info, Node: Warning, Next: Weak, Prev: VTableInherit, Up: Pseudo Ops
7.101 `.warning "STRING"'
=========================
Similar to the directive `.error' (*note `.error "STRING"': Error.),
but just emits a warning.
File: as.info, Node: Weak, Next: Word, Prev: Warning, Up: Pseudo Ops
7.102 `.weak NAMES'
===================
This directive sets the weak attribute on the comma separated list of
symbol `names'. If the symbols do not already exist, they will be
created.
On COFF targets other than PE, weak symbols are a GNU extension.
This directive sets the weak attribute on the comma separated list of
symbol `names'. If the symbols do not already exist, they will be
created.
On the PE target, weak symbols are supported natively as weak
aliases. When a weak symbol is created that is not an alias, GAS
creates an alternate symbol to hold the default value.
File: as.info, Node: Word, Next: Deprecated, Prev: Weak, Up: Pseudo Ops
7.103 `.word EXPRESSIONS'
=========================
This directive expects zero or more EXPRESSIONS, of any section,
separated by commas.
The size of the number emitted, and its byte order, depend on what
target computer the assembly is for.
_Warning: Special Treatment to support Compilers_
Machines with a 32-bit address space, but that do less than 32-bit
addressing, require the following special treatment. If the machine of
interest to you does 32-bit addressing (or doesn't require it; *note
Machine Dependencies::), you can ignore this issue.
In order to assemble compiler output into something that works, `as'
occasionally does strange things to `.word' directives. Directives of
the form `.word sym1-sym2' are often emitted by compilers as part of
jump tables. Therefore, when `as' assembles a directive of the form
`.word sym1-sym2', and the difference between `sym1' and `sym2' does
not fit in 16 bits, `as' creates a "secondary jump table", immediately
before the next label. This secondary jump table is preceded by a
short-jump to the first byte after the secondary table. This
short-jump prevents the flow of control from accidentally falling into
the new table. Inside the table is a long-jump to `sym2'. The
original `.word' contains `sym1' minus the address of the long-jump to
`sym2'.
If there were several occurrences of `.word sym1-sym2' before the
secondary jump table, all of them are adjusted. If there was a `.word
sym3-sym4', that also did not fit in sixteen bits, a long-jump to
`sym4' is included in the secondary jump table, and the `.word'
directives are adjusted to contain `sym3' minus the address of the
long-jump to `sym4'; and so on, for as many entries in the original
jump table as necessary.
File: as.info, Node: Deprecated, Prev: Word, Up: Pseudo Ops
7.104 Deprecated Directives
===========================
One day these directives won't work. They are included for
compatibility with older assemblers.
.abort
.line
File: as.info, Node: Machine Dependencies, Next: Reporting Bugs, Prev: Pseudo Ops, Up: Top
8 Machine Dependent Features
****************************
The machine instruction sets are (almost by definition) different on
each machine where `as' runs. Floating point representations vary as
well, and `as' often supports a few additional directives or
command-line options for compatibility with other assemblers on a
particular platform. Finally, some versions of `as' support special
pseudo-instructions for branch optimization.
This chapter discusses most of these differences, though it does not
include details on any machine's instruction set. For details on that
subject, see the hardware manufacturer's manual.
* Menu:
* AMD29K-Dependent:: AMD 29K Dependent Features
* Alpha-Dependent:: Alpha Dependent Features
* ARC-Dependent:: ARC Dependent Features
* ARM-Dependent:: ARM Dependent Features
* CRIS-Dependent:: CRIS Dependent Features
* D10V-Dependent:: D10V Dependent Features
* D30V-Dependent:: D30V Dependent Features
* H8/300-Dependent:: Renesas H8/300 Dependent Features
* H8/500-Dependent:: Renesas H8/500 Dependent Features
* HPPA-Dependent:: HPPA Dependent Features
* ESA/390-Dependent:: IBM ESA/390 Dependent Features
* i386-Dependent:: Intel 80386 and AMD x86-64 Dependent Features
* i860-Dependent:: Intel 80860 Dependent Features
* i960-Dependent:: Intel 80960 Dependent Features
* IA-64-Dependent:: Intel IA-64 Dependent Features
* IP2K-Dependent:: IP2K Dependent Features
* M32R-Dependent:: M32R Dependent Features
* M68K-Dependent:: M680x0 Dependent Features
* M68HC11-Dependent:: M68HC11 and 68HC12 Dependent Features
* M88K-Dependent:: M880x0 Dependent Features
* MIPS-Dependent:: MIPS Dependent Features
* MMIX-Dependent:: MMIX Dependent Features
* MSP430-Dependent:: MSP430 Dependent Features
* SH-Dependent:: Renesas / SuperH SH Dependent Features
* SH64-Dependent:: SuperH SH64 Dependent Features
* PDP-11-Dependent:: PDP-11 Dependent Features
* PJ-Dependent:: picoJava Dependent Features
* PPC-Dependent:: PowerPC Dependent Features
* Sparc-Dependent:: SPARC Dependent Features
* TIC54X-Dependent:: TI TMS320C54x Dependent Features
* V850-Dependent:: V850 Dependent Features
* Xtensa-Dependent:: Xtensa Dependent Features
* Z8000-Dependent:: Z8000 Dependent Features
* Vax-Dependent:: VAX Dependent Features
File: as.info, Node: AMD29K-Dependent, Next: Alpha-Dependent, Up: Machine Dependencies
8.1 AMD 29K Dependent Features
==============================
* Menu:
* AMD29K Options:: Options
* AMD29K Syntax:: Syntax
* AMD29K Floating Point:: Floating Point
* AMD29K Directives:: AMD 29K Machine Directives
* AMD29K Opcodes:: Opcodes
File: as.info, Node: AMD29K Options, Next: AMD29K Syntax, Up: AMD29K-Dependent
8.1.1 Options
-------------
`as' has no additional command-line options for the AMD 29K family.
File: as.info, Node: AMD29K Syntax, Next: AMD29K Floating Point, Prev: AMD29K Options, Up: AMD29K-Dependent
8.1.2 Syntax
------------
* Menu:
* AMD29K-Macros:: Macros
* AMD29K-Chars:: Special Characters
* AMD29K-Regs:: Register Names
File: as.info, Node: AMD29K-Macros, Next: AMD29K-Chars, Up: AMD29K Syntax
8.1.2.1 Macros
..............
The macro syntax used on the AMD 29K is like that described in the AMD
29K Family Macro Assembler Specification. Normal `as' macros should
still work.
File: as.info, Node: AMD29K-Chars, Next: AMD29K-Regs, Prev: AMD29K-Macros, Up: AMD29K Syntax
8.1.2.2 Special Characters
..........................
`;' is the line comment character.
The character `?' is permitted in identifiers (but may not begin an
identifier).
File: as.info, Node: AMD29K-Regs, Prev: AMD29K-Chars, Up: AMD29K Syntax
8.1.2.3 Register Names
......................
General-purpose registers are represented by predefined symbols of the
form `GRNNN' (for global registers) or `LRNNN' (for local registers),
where NNN represents a number between `0' and `127', written with no
leading zeros. The leading letters may be in either upper or lower
case; for example, `gr13' and `LR7' are both valid register names.
You may also refer to general-purpose registers by specifying the
register number as the result of an expression (prefixed with `%%' to
flag the expression as a register number):
%%EXPRESSION
--where EXPRESSION must be an absolute expression evaluating to a
number between `0' and `255'. The range [0, 127] refers to global
registers, and the range [128, 255] to local registers.
In addition, `as' understands the following protected
special-purpose register names for the AMD 29K family:
vab chd pc0
ops chc pc1
cps rbp pc2
cfg tmc mmu
cha tmr lru
These unprotected special-purpose register names are also recognized:
ipc alu fpe
ipa bp inte
ipb fc fps
q cr exop
File: as.info, Node: AMD29K Floating Point, Next: AMD29K Directives, Prev: AMD29K Syntax, Up: AMD29K-Dependent
8.1.3 Floating Point
--------------------
The AMD 29K family uses IEEE floating-point numbers.
File: as.info, Node: AMD29K Directives, Next: AMD29K Opcodes, Prev: AMD29K Floating Point, Up: AMD29K-Dependent
8.1.4 AMD 29K Machine Directives
--------------------------------
`.block SIZE , FILL'
This directive emits SIZE bytes, each of value FILL. Both SIZE
and FILL are absolute expressions. If the comma and FILL are
omitted, FILL is assumed to be zero.
In other versions of the GNU assembler, this directive is called
`.space'.
`.cputype'
This directive is ignored; it is accepted for compatibility with
other AMD 29K assemblers.
`.file'
This directive is ignored; it is accepted for compatibility with
other AMD 29K assemblers.
_Warning:_ in other versions of the GNU assembler, `.file' is
used for the directive called `.app-file' in the AMD 29K
support.
`.line'
This directive is ignored; it is accepted for compatibility with
other AMD 29K assemblers.
`.sect'
This directive is ignored; it is accepted for compatibility with
other AMD 29K assemblers.
`.use SECTION NAME'
Establishes the section and subsection for the following code;
SECTION NAME may be one of `.text', `.data', `.data1', or `.lit'.
With one of the first three SECTION NAME options, `.use' is
equivalent to the machine directive SECTION NAME; the remaining
case, `.use .lit', is the same as `.data 200'.
File: as.info, Node: AMD29K Opcodes, Prev: AMD29K Directives, Up: AMD29K-Dependent
8.1.5 Opcodes
-------------
`as' implements all the standard AMD 29K opcodes. No additional
pseudo-instructions are needed on this family.
For information on the 29K machine instruction set, see `Am29000
User's Manual', Advanced Micro Devices, Inc.
File: as.info, Node: Alpha-Dependent, Next: ARC-Dependent, Prev: AMD29K-Dependent, Up: Machine Dependencies
8.2 Alpha Dependent Features
============================
* Menu:
* Alpha Notes:: Notes
* Alpha Options:: Options
* Alpha Syntax:: Syntax
* Alpha Floating Point:: Floating Point
* Alpha Directives:: Alpha Machine Directives
* Alpha Opcodes:: Opcodes
File: as.info, Node: Alpha Notes, Next: Alpha Options, Up: Alpha-Dependent
8.2.1 Notes
-----------
The documentation here is primarily for the ELF object format. `as'
also supports the ECOFF and EVAX formats, but features specific to
these formats are not yet documented.
File: as.info, Node: Alpha Options, Next: Alpha Syntax, Prev: Alpha Notes, Up: Alpha-Dependent
8.2.2 Options
-------------
`-mCPU'
This option specifies the target processor. If an attempt is made
to assemble an instruction which will not execute on the target
processor, the assembler may either expand the instruction as a
macro or issue an error message. This option is equivalent to the
`.arch' directive.
The following processor names are recognized: `21064', `21064a',
`21066', `21068', `21164', `21164a', `21164pc', `21264', `21264a',
`21264b', `ev4', `ev5', `lca45', `ev5', `ev56', `pca56', `ev6',
`ev67', `ev68'. The special name `all' may be used to allow the
assembler to accept instructions valid for any Alpha processor.
In order to support existing practice in OSF/1 with respect to
`.arch', and existing practice within `MILO' (the Linux ARC
bootloader), the numbered processor names (e.g. 21064) enable the
processor-specific PALcode instructions, while the
"electro-vlasic" names (e.g. `ev4') do not.
`-mdebug'
`-no-mdebug'
Enables or disables the generation of `.mdebug' encapsulation for
stabs directives and procedure descriptors. The default is to
automatically enable `.mdebug' when the first stabs directive is
seen.
`-relax'
This option forces all relocations to be put into the object file,
instead of saving space and resolving some relocations at assembly
time. Note that this option does not propagate all symbol
arithmetic into the object file, because not all symbol arithmetic
can be represented. However, the option can still be useful in
specific applications.
`-g'
This option is used when the compiler generates debug information.
When `gcc' is using `mips-tfile' to generate debug information
for ECOFF, local labels must be passed through to the object file.
Otherwise this option has no effect.
`-GSIZE'
A local common symbol larger than SIZE is placed in `.bss', while
smaller symbols are placed in `.sbss'.
`-F'
`-32addr'
These options are ignored for backward compatibility.
File: as.info, Node: Alpha Syntax, Next: Alpha Floating Point, Prev: Alpha Options, Up: Alpha-Dependent
8.2.3 Syntax
------------
The assembler syntax closely follow the Alpha Reference Manual;
assembler directives and general syntax closely follow the OSF/1 and
OpenVMS syntax, with a few differences for ELF.
* Menu:
* Alpha-Chars:: Special Characters
* Alpha-Regs:: Register Names
* Alpha-Relocs:: Relocations
File: as.info, Node: Alpha-Chars, Next: Alpha-Regs, Up: Alpha Syntax
8.2.3.1 Special Characters
..........................
`#' is the line comment character.
`;' can be used instead of a newline to separate statements.
File: as.info, Node: Alpha-Regs, Next: Alpha-Relocs, Prev: Alpha-Chars, Up: Alpha Syntax
8.2.3.2 Register Names
......................
The 32 integer registers are referred to as `$N' or `$rN'. In
addition, registers 15, 28, 29, and 30 may be referred to by the
symbols `$fp', `$at', `$gp', and `$sp' respectively.
The 32 floating-point registers are referred to as `$fN'.
File: as.info, Node: Alpha-Relocs, Prev: Alpha-Regs, Up: Alpha Syntax
8.2.3.3 Relocations
...................
Some of these relocations are available for ECOFF, but mostly only for
ELF. They are modeled after the relocation format introduced in
Digital Unix 4.0, but there are additions.
The format is `!TAG' or `!TAG!NUMBER' where TAG is the name of the
relocation. In some cases NUMBER is used to relate specific
instructions.
The relocation is placed at the end of the instruction like so:
ldah $0,a($29) !gprelhigh
lda $0,a($0) !gprellow
ldq $1,b($29) !literal!100
ldl $2,0($1) !lituse_base!100
`!literal'
`!literal!N'
Used with an `ldq' instruction to load the address of a symbol
from the GOT.
A sequence number N is optional, and if present is used to pair
`lituse' relocations with this `literal' relocation. The `lituse'
relocations are used by the linker to optimize the code based on
the final location of the symbol.
Note that these optimizations are dependent on the data flow of the
program. Therefore, if _any_ `lituse' is paired with a `literal'
relocation, then _all_ uses of the register set by the `literal'
instruction must also be marked with `lituse' relocations. This
is because the original `literal' instruction may be deleted or
transformed into another instruction.
Also note that there may be a one-to-many relationship between
`literal' and `lituse', but not a many-to-one. That is, if there
are two code paths that load up the same address and feed the
value to a single use, then the use may not use a `lituse'
relocation.
`!lituse_base!N'
Used with any memory format instruction (e.g. `ldl') to indicate
that the literal is used for an address load. The offset field of
the instruction must be zero. During relaxation, the code may be
altered to use a gp-relative load.
`!lituse_jsr!N'
Used with a register branch format instruction (e.g. `jsr') to
indicate that the literal is used for a call. During relaxation,
the code may be altered to use a direct branch (e.g. `bsr').
`!lituse_bytoff!N'
Used with a byte mask instruction (e.g. `extbl') to indicate that
only the low 3 bits of the address are relevant. During
relaxation, the code may be altered to use an immediate instead of
a register shift.
`!lituse_addr!N'
Used with any other instruction to indicate that the original
address is in fact used, and the original `ldq' instruction may
not be altered or deleted. This is useful in conjunction with
`lituse_jsr' to test whether a weak symbol is defined.
ldq $27,foo($29) !literal!1
beq $27,is_undef !lituse_addr!1
jsr $26,($27),foo !lituse_jsr!1
`!lituse_tlsgd!N'
Used with a register branch format instruction to indicate that the
literal is the call to `__tls_get_addr' used to compute the
address of the thread-local storage variable whose descriptor was
loaded with `!tlsgd!N'.
`!lituse_tlsldm!N'
Used with a register branch format instruction to indicate that the
literal is the call to `__tls_get_addr' used to compute the
address of the base of the thread-local storage block for the
current module. The descriptor for the module must have been
loaded with `!tlsldm!N'.
`!gpdisp!N'
Used with `ldah' and `lda' to load the GP from the current
address, a-la the `ldgp' macro. The source register for the
`ldah' instruction must contain the address of the `ldah'
instruction. There must be exactly one `lda' instruction paired
with the `ldah' instruction, though it may appear anywhere in the
instruction stream. The immediate operands must be zero.
bsr $26,foo
ldah $29,0($26) !gpdisp!1
lda $29,0($29) !gpdisp!1
`!gprelhigh'
Used with an `ldah' instruction to add the high 16 bits of a
32-bit displacement from the GP.
`!gprellow'
Used with any memory format instruction to add the low 16 bits of a
32-bit displacement from the GP.
`!gprel'
Used with any memory format instruction to add a 16-bit
displacement from the GP.
`!samegp'
Used with any branch format instruction to skip the GP load at the
target address. The referenced symbol must have the same GP as the
source object file, and it must be declared to either not use `$27'
or perform a standard GP load in the first two instructions via the
`.prologue' directive.
`!tlsgd'
`!tlsgd!N'
Used with an `lda' instruction to load the address of a TLS
descriptor for a symbol in the GOT.
The sequence number N is optional, and if present it used to pair
the descriptor load with both the `literal' loading the address of
the `__tls_get_addr' function and the `lituse_tlsgd' marking the
call to that function.
For proper relaxation, both the `tlsgd', `literal' and `lituse'
relocations must be in the same extended basic block. That is,
the relocation with the lowest address must be executed first at
runtime.
`!tlsldm'
`!tlsldm!N'
Used with an `lda' instruction to load the address of a TLS
descriptor for the current module in the GOT.
Similar in other respects to `tlsgd'.
`!gotdtprel'
Used with an `ldq' instruction to load the offset of the TLS
symbol within its module's thread-local storage block. Also known
as the dynamic thread pointer offset or dtp-relative offset.
`!dtprelhi'
`!dtprello'
`!dtprel'
Like `gprel' relocations except they compute dtp-relative offsets.
`!gottprel'
Used with an `ldq' instruction to load the offset of the TLS
symbol from the thread pointer. Also known as the tp-relative
offset.
`!tprelhi'
`!tprello'
`!tprel'
Like `gprel' relocations except they compute tp-relative offsets.
File: as.info, Node: Alpha Floating Point, Next: Alpha Directives, Prev: Alpha Syntax, Up: Alpha-Dependent
8.2.4 Floating Point
--------------------
The Alpha family uses both IEEE and VAX floating-point numbers.
File: as.info, Node: Alpha Directives, Next: Alpha Opcodes, Prev: Alpha Floating Point, Up: Alpha-Dependent
8.2.5 Alpha Assembler Directives
--------------------------------
`as' for the Alpha supports many additional directives for
compatibility with the native assembler. This section describes them
only briefly.
These are the additional directives in `as' for the Alpha:
`.arch CPU'
Specifies the target processor. This is equivalent to the `-mCPU'
command-line option. *Note Options: Alpha Options, for a list of
values for CPU.
`.ent FUNCTION[, N]'
Mark the beginning of FUNCTION. An optional number may follow for
compatibility with the OSF/1 assembler, but is ignored. When
generating `.mdebug' information, this will create a procedure
descriptor for the function. In ELF, it will mark the symbol as a
function a-la the generic `.type' directive.
`.end FUNCTION'
Mark the end of FUNCTION. In ELF, it will set the size of the
symbol a-la the generic `.size' directive.
`.mask MASK, OFFSET'
Indicate which of the integer registers are saved in the current
function's stack frame. MASK is interpreted a bit mask in which
bit N set indicates that register N is saved. The registers are
saved in a block located OFFSET bytes from the "canonical frame
address" (CFA) which is the value of the stack pointer on entry to
the function. The registers are saved sequentially, except that
the return address register (normally `$26') is saved first.
This and the other directives that describe the stack frame are
currently only used when generating `.mdebug' information. They
may in the future be used to generate DWARF2 `.debug_frame' unwind
information for hand written assembly.
`.fmask MASK, OFFSET'
Indicate which of the floating-point registers are saved in the
current stack frame. The MASK and OFFSET parameters are
interpreted as with `.mask'.
`.frame FRAMEREG, FRAMEOFFSET, RETREG[, ARGOFFSET]'
Describes the shape of the stack frame. The frame pointer in use
is FRAMEREG; normally this is either `$fp' or `$sp'. The frame
pointer is FRAMEOFFSET bytes below the CFA. The return address is
initially located in RETREG until it is saved as indicated in
`.mask'. For compatibility with OSF/1 an optional ARGOFFSET
parameter is accepted and ignored. It is believed to indicate the
offset from the CFA to the saved argument registers.
`.prologue N'
Indicate that the stack frame is set up and all registers have been
spilled. The argument N indicates whether and how the function
uses the incoming "procedure vector" (the address of the called
function) in `$27'. 0 indicates that `$27' is not used; 1
indicates that the first two instructions of the function use `$27'
to perform a load of the GP register; 2 indicates that `$27' is
used in some non-standard way and so the linker cannot elide the
load of the procedure vector during relaxation.
`.usepv FUNCTION, WHICH'
Used to indicate the use of the `$27' register, similar to
`.prologue', but without the other semantics of needing to be
inside an open `.ent'/`.end' block.
The WHICH argument should be either `no', indicating that `$27' is
not used, or `std', indicating that the first two instructions of
the function perform a GP load.
One might use this directive instead of `.prologue' if you are
also using dwarf2 CFI directives.
`.gprel32 EXPRESSION'
Computes the difference between the address in EXPRESSION and the
GP for the current object file, and stores it in 4 bytes. In
addition to being smaller than a full 8 byte address, this also
does not require a dynamic relocation when used in a shared
library.
`.t_floating EXPRESSION'
Stores EXPRESSION as an IEEE double precision value.
`.s_floating EXPRESSION'
Stores EXPRESSION as an IEEE single precision value.
`.f_floating EXPRESSION'
Stores EXPRESSION as a VAX F format value.
`.g_floating EXPRESSION'
Stores EXPRESSION as a VAX G format value.
`.d_floating EXPRESSION'
Stores EXPRESSION as a VAX D format value.
`.set FEATURE'
Enables or disables various assembler features. Using the positive
name of the feature enables while using `noFEATURE' disables.
`at'
Indicates that macro expansions may clobber the "assembler
temporary" (`$at' or `$28') register. Some macros may not be
expanded without this and will generate an error message if
`noat' is in effect. When `at' is in effect, a warning will
be generated if `$at' is used by the programmer.
`macro'
Enables the expansion of macro instructions. Note that
variants of real instructions, such as `br label' vs `br
$31,label' are considered alternate forms and not macros.
`move'
`reorder'
`volatile'
These control whether and how the assembler may re-order
instructions. Accepted for compatibility with the OSF/1
assembler, but `as' does not do instruction scheduling, so
these features are ignored.
The following directives are recognized for compatibility with the
OSF/1 assembler but are ignored.
.proc .aproc
.reguse .livereg
.option .aent
.ugen .eflag
.alias .noalias
File: as.info, Node: Alpha Opcodes, Prev: Alpha Directives, Up: Alpha-Dependent
8.2.6 Opcodes
-------------
For detailed information on the Alpha machine instruction set, see the
Alpha Architecture Handbook
(ftp://ftp.digital.com/pub/Digital/info/semiconductor/literature/alphaahb.pdf).
File: as.info, Node: ARC-Dependent, Next: ARM-Dependent, Prev: Alpha-Dependent, Up: Machine Dependencies
8.3 ARC Dependent Features
==========================
* Menu:
* ARC Options:: Options
* ARC Syntax:: Syntax
* ARC Floating Point:: Floating Point
* ARC Directives:: ARC Machine Directives
* ARC Opcodes:: Opcodes
File: as.info, Node: ARC Options, Next: ARC Syntax, Up: ARC-Dependent
8.3.1 Options
-------------
`-marc[5|6|7|8]'
This option selects the core processor variant. Using `-marc' is
the same as `-marc6', which is also the default.
`arc5'
Base instruction set.
`arc6'
Jump-and-link (jl) instruction. No requirement of an
instruction between setting flags and conditional jump. For
example:
mov.f r0,r1
beq foo
`arc7'
Break (brk) and sleep (sleep) instructions.
`arc8'
Software interrupt (swi) instruction.
Note: the `.option' directive can to be used to select a core
variant from within assembly code.
`-EB'
This option specifies that the output generated by the assembler
should be marked as being encoded for a big-endian processor.
`-EL'
This option specifies that the output generated by the assembler
should be marked as being encoded for a little-endian processor -
this is the default.
File: as.info, Node: ARC Syntax, Next: ARC Floating Point, Prev: ARC Options, Up: ARC-Dependent
8.3.2 Syntax
------------
* Menu:
* ARC-Chars:: Special Characters
* ARC-Regs:: Register Names
File: as.info, Node: ARC-Chars, Next: ARC-Regs, Up: ARC Syntax
8.3.2.1 Special Characters
..........................
*TODO*
File: as.info, Node: ARC-Regs, Prev: ARC-Chars, Up: ARC Syntax
8.3.2.2 Register Names
......................
*TODO*
File: as.info, Node: ARC Floating Point, Next: ARC Directives, Prev: ARC Syntax, Up: ARC-Dependent
8.3.3 Floating Point
--------------------
The ARC core does not currently have hardware floating point support.
Software floating point support is provided by `GCC' and uses IEEE
floating-point numbers.
File: as.info, Node: ARC Directives, Next: ARC Opcodes, Prev: ARC Floating Point, Up: ARC-Dependent
8.3.4 ARC Machine Directives
----------------------------
The ARC version of `as' supports the following additional machine
directives:
`.2byte EXPRESSIONS'
*TODO*
`.3byte EXPRESSIONS'
*TODO*
`.4byte EXPRESSIONS'
*TODO*
`.extAuxRegister NAME,ADDRESS,MODE'
The ARCtangent A4 has extensible auxiliary register space. The
auxiliary registers can be defined in the assembler source code by
using this directive. The first parameter is the NAME of the new
auxiallry register. The second parameter is the ADDRESS of the
register in the auxiliary register memory map for the variant of
the ARC. The third parameter specifies the MODE in which the
register can be operated is and it can be one of:
`r (readonly)'
`w (write only)'
`r|w (read or write)'
For example:
.extAuxRegister mulhi,0x12,w
This specifies an extension auxiliary register called _mulhi_
which is at address 0x12 in the memory space and which is only
writable.
`.extCondCode SUFFIX,VALUE'
The condition codes on the ARCtangent A4 are extensible and can be
specified by means of this assembler directive. They are specified
by the suffix and the value for the condition code. They can be
used to specify extra condition codes with any values. For
example:
.extCondCode is_busy,0x14
add.is_busy r1,r2,r3
bis_busy _main
`.extCoreRegister NAME,REGNUM,MODE,SHORTCUT'
Specifies an extension core register NAME for the application.
This allows a register NAME with a valid REGNUM between 0 and 60,
with the following as valid values for MODE
`_r_ (readonly)'
`_w_ (write only)'
`_r|w_ (read or write)'
The other parameter gives a description of the register having a
SHORTCUT in the pipeline. The valid values are:
`can_shortcut'
`cannot_shortcut'
For example:
.extCoreRegister mlo,57,r,can_shortcut
This defines an extension core register mlo with the value 57 which
can shortcut the pipeline.
`.extInstruction NAME,OPCODE,SUBOPCODE,SUFFIXCLASS,SYNTAXCLASS'
The ARCtangent A4 allows the user to specify extension
instructions. The extension instructions are not macros. The
assembler creates encodings for use of these instructions
according to the specification by the user. The parameters are:
*NAME
Name of the extension instruction
*OPCODE
Opcode to be used. (Bits 27:31 in the encoding). Valid values
0x10-0x1f or 0x03
*SUBOPCODE
Subopcode to be used. Valid values are from 0x09-0x3f.
However the correct value also depends on SYNTAXCLASS
*SUFFIXCLASS
Determines the kinds of suffixes to be allowed. Valid values
are `SUFFIX_NONE', `SUFFIX_COND', `SUFFIX_FLAG' which
indicates the absence or presence of conditional suffixes and
flag setting by the extension instruction. It is also
possible to specify that an instruction sets the flags and is
conditional by using `SUFFIX_CODE' | `SUFFIX_FLAG'.
*SYNTAXCLASS
Determines the syntax class for the instruction. It can have
the following values:
``SYNTAX_2OP':'
2 Operand Instruction
``SYNTAX_3OP':'
3 Operand Instruction
In addition there could be modifiers for the syntax class as
described below:
Syntax Class Modifiers are:
- `OP1_MUST_BE_IMM': Modifies syntax class SYNTAX_3OP,
specifying that the first operand of a three-operand
instruction must be an immediate (i.e. the result is
discarded). OP1_MUST_BE_IMM is used by bitwise ORing it
with SYNTAX_3OP as given in the example below. This
could usually be used to set the flags using specific
instructions and not retain results.
- `OP1_IMM_IMPLIED': Modifies syntax class SYNTAX_20P, it
specifies that there is an implied immediate destination
operand which does not appear in the syntax. For
example, if the source code contains an instruction like:
inst r1,r2
it really means that the first argument is an implied
immediate (that is, the result is discarded). This is
the same as though the source code were: inst 0,r1,r2.
You use OP1_IMM_IMPLIED by bitwise ORing it with
SYNTAX_20P.
For example, defining 64-bit multiplier with immediate operands:
.extInstruction mp64,0x14,0x0,SUFFIX_COND | SUFFIX_FLAG ,
SYNTAX_3OP|OP1_MUST_BE_IMM
The above specifies an extension instruction called mp64 which has
3 operands, sets the flags, can be used with a condition code, for
which the first operand is an immediate. (Equivalent to
discarding the result of the operation).
.extInstruction mul64,0x14,0x00,SUFFIX_COND, SYNTAX_2OP|OP1_IMM_IMPLIED
This describes a 2 operand instruction with an implicit first
immediate operand. The result of this operation would be
discarded.
`.half EXPRESSIONS'
*TODO*
`.long EXPRESSIONS'
*TODO*
`.option ARC|ARC5|ARC6|ARC7|ARC8'
The `.option' directive must be followed by the desired core
version. Again `arc' is an alias for `arc6'.
Note: the `.option' directive overrides the command line option
`-marc'; a warning is emitted when the version is not consistent
between the two - even for the implicit default core version
(arc6).
`.short EXPRESSIONS'
*TODO*
`.word EXPRESSIONS'
*TODO*
File: as.info, Node: ARC Opcodes, Prev: ARC Directives, Up: ARC-Dependent
8.3.5 Opcodes
-------------
For information on the ARC instruction set, see `ARC Programmers
Reference Manual', ARC International (www.arc.com)
File: as.info, Node: ARM-Dependent, Next: CRIS-Dependent, Prev: ARC-Dependent, Up: Machine Dependencies
8.4 ARM Dependent Features
==========================
* Menu:
* ARM Options:: Options
* ARM Syntax:: Syntax
* ARM Floating Point:: Floating Point
* ARM Directives:: ARM Machine Directives
* ARM Opcodes:: Opcodes
* ARM Mapping Symbols:: Mapping Symbols
File: as.info, Node: ARM Options, Next: ARM Syntax, Up: ARM-Dependent
8.4.1 Options
-------------
`-mcpu=PROCESSOR[+EXTENSION...]'
This option specifies the target processor. The assembler will
issue an error message if an attempt is made to assemble an
instruction which will not execute on the target processor. The
following processor names are recognized: `arm1', `arm2', `arm250',
`arm3', `arm6', `arm60', `arm600', `arm610', `arm620', `arm7',
`arm7m', `arm7d', `arm7dm', `arm7di', `arm7dmi', `arm70', `arm700',
`arm700i', `arm710', `arm710t', `arm720', `arm720t', `arm740t',
`arm710c', `arm7100', `arm7500', `arm7500fe', `arm7t', `arm7tdmi',
`arm7tdmi-s', `arm8', `arm810', `strongarm', `strongarm1',
`strongarm110', `strongarm1100', `strongarm1110', `arm9', `arm920',
`arm920t', `arm922t', `arm940t', `arm9tdmi', `arm9e', `arm926e',
`arm926ej-s', `arm946e-r0', `arm946e', `arm966e-r0', `arm966e',
`arm10t', `arm10e', `arm1020', `arm1020t', `arm1020e',
`arm1026ej-s', `arm1136j-s', `arm1136jf-s', `arm1176jz-s',
`arm1176jzf-s', `mpcore', `mpcorenovfp', `ep9312' (ARM920 with
Cirrus Maverick coprocessor), `i80200' (Intel XScale processor)
`iwmmxt' (Intel(r) XScale processor with Wireless MMX(tm)
technology coprocessor) and `xscale'. The special name `all' may
be used to allow the assembler to accept instructions valid for
any ARM processor.
In addition to the basic instruction set, the assembler can be
told to accept various extension mnemonics that extend the
processor using the co-processor instruction space. For example,
`-mcpu=arm920+maverick' is equivalent to specifying
`-mcpu=ep9312'. The following extensions are currently supported:
`+maverick' `+iwmmxt' and `+xscale'.
`-march=ARCHITECTURE[+EXTENSION...]'
This option specifies the target architecture. The assembler will
issue an error message if an attempt is made to assemble an
instruction which will not execute on the target architecture.
The following architecture names are recognized: `armv1', `armv2',
`armv2a', `armv2s', `armv3', `armv3m', `armv4', `armv4xm',
`armv4t', `armv4txm', `armv5', `armv5t', `armv5txm', `armv5te',
`armv5texp', `armv6', `armv6j', `armv6k', `armv6z', `armv6zk',
`iwmmxt' and `xscale'. If both `-mcpu' and `-march' are
specified, the assembler will use the setting for `-mcpu'.
The architecture option can be extended with the same instruction
set extension options as the `-mcpu' option.
`-mfpu=FLOATING-POINT-FORMAT'
This option specifies the floating point format to assemble for.
The assembler will issue an error message if an attempt is made to
assemble an instruction which will not execute on the target
floating point unit. The following format options are recognized:
`softfpa', `fpe', `fpe2', `fpe3', `fpa', `fpa10', `fpa11',
`arm7500fe', `softvfp', `softvfp+vfp', `vfp', `vfp10', `vfp10-r0',
`vfp9', `vfpxd', `arm1020t', `arm1020e', `arm1136jf-s' and
`maverick'.
In addition to determining which instructions are assembled, this
option also affects the way in which the `.double' assembler
directive behaves when assembling little-endian code.
The default is dependent on the processor selected. For
Architecture 5 or later, the default is to assembler for VFP
instructions; for earlier architectures the default is to assemble
for FPA instructions.
`-mthumb'
This option specifies that the assembler should start assembling
Thumb instructions; that is, it should behave as though the file
starts with a `.code 16' directive.
`-mthumb-interwork'
This option specifies that the output generated by the assembler
should be marked as supporting interworking.
`-mapcs `[26|32]''
This option specifies that the output generated by the assembler
should be marked as supporting the indicated version of the Arm
Procedure. Calling Standard.
`-matpcs'
This option specifies that the output generated by the assembler
should be marked as supporting the Arm/Thumb Procedure Calling
Standard. If enabled this option will cause the assembler to
create an empty debugging section in the object file called
.arm.atpcs. Debuggers can use this to determine the ABI being
used by.
`-mapcs-float'
This indicates the floating point variant of the APCS should be
used. In this variant floating point arguments are passed in FP
registers rather than integer registers.
`-mapcs-reentrant'
This indicates that the reentrant variant of the APCS should be
used. This variant supports position independent code.
`-mfloat-abi=ABI'
This option specifies that the output generated by the assembler
should be marked as using specified floating point ABI. The
following values are recognized: `soft', `softfp' and `hard'.
`-meabi=VER'
This option specifies which EABI version the produced object files
should conform to. The following values are recognised: `gnu' and
`4'.
`-EB'
This option specifies that the output generated by the assembler
should be marked as being encoded for a big-endian processor.
`-EL'
This option specifies that the output generated by the assembler
should be marked as being encoded for a little-endian processor.
`-k'
This option specifies that the output of the assembler should be
marked as position-independent code (PIC).
File: as.info, Node: ARM Syntax, Next: ARM Floating Point, Prev: ARM Options, Up: ARM-Dependent
8.4.2 Syntax
------------
* Menu:
* ARM-Chars:: Special Characters
* ARM-Regs:: Register Names
File: as.info, Node: ARM-Chars, Next: ARM-Regs, Up: ARM Syntax
8.4.2.1 Special Characters
..........................
The presence of a `@' on a line indicates the start of a comment that
extends to the end of the current line. If a `#' appears as the first
character of a line, the whole line is treated as a comment.
The `;' character can be used instead of a newline to separate
statements.
Either `#' or `$' can be used to indicate immediate operands.
*TODO* Explain about /data modifier on symbols.
File: as.info, Node: ARM-Regs, Prev: ARM-Chars, Up: ARM Syntax
8.4.2.2 Register Names
......................
*TODO* Explain about ARM register naming, and the predefined names.
File: as.info, Node: ARM Floating Point, Next: ARM Directives, Prev: ARM Syntax, Up: ARM-Dependent
8.4.3 Floating Point
--------------------
The ARM family uses IEEE floating-point numbers.
File: as.info, Node: ARM Directives, Next: ARM Opcodes, Prev: ARM Floating Point, Up: ARM-Dependent
8.4.4 ARM Machine Directives
----------------------------
`.align EXPRESSION [, EXPRESSION]'
This is the generic .ALIGN directive. For the ARM however if the
first argument is zero (ie no alignment is needed) the assembler
will behave as if the argument had been 2 (ie pad to the next four
byte boundary). This is for compatibility with ARM's own
assembler.
`NAME .req REGISTER NAME'
This creates an alias for REGISTER NAME called NAME. For example:
foo .req r0
`.unreq ALIAS-NAME'
This undefines a register alias which was previously defined using
the `req' directive. For example:
foo .req r0
.unreq foo
An error occurs if the name is undefined. Note - this pseudo op
can be used to delete builtin in register name aliases (eg 'r0').
This should only be done if it is really necessary.
`.code `[16|32]''
This directive selects the instruction set being generated. The
value 16 selects Thumb, with the value 32 selecting ARM.
`.thumb'
This performs the same action as .CODE 16.
`.arm'
This performs the same action as .CODE 32.
`.force_thumb'
This directive forces the selection of Thumb instructions, even if
the target processor does not support those instructions
`.thumb_func'
This directive specifies that the following symbol is the name of a
Thumb encoded function. This information is necessary in order to
allow the assembler and linker to generate correct code for
interworking between Arm and Thumb instructions and should be used
even if interworking is not going to be performed. The presence
of this directive also implies `.thumb'
`.thumb_set'
This performs the equivalent of a `.set' directive in that it
creates a symbol which is an alias for another symbol (possibly
not yet defined). This directive also has the added property in
that it marks the aliased symbol as being a thumb function entry
point, in the same way that the `.thumb_func' directive does.
`.ltorg'
This directive causes the current contents of the literal pool to
be dumped into the current section (which is assumed to be the
.text section) at the current location (aligned to a word
boundary). `GAS' maintains a separate literal pool for each
section and each sub-section. The `.ltorg' directive will only
affect the literal pool of the current section and sub-section.
At the end of assembly all remaining, un-empty literal pools will
automatically be dumped.
Note - older versions of `GAS' would dump the current literal pool
any time a section change occurred. This is no longer done, since
it prevents accurate control of the placement of literal pools.
`.pool'
This is a synonym for .ltorg.
`.unwind_fnstart'
Marks the start of a function with an unwind table entry.
`.unwind_fnend'
Marks the end of a function with an unwind table entry. The
unwind index table entry is created when this directive is
processed.
If no personality routine has been specified then standard
personality routine 0 or 1 will be used, depending on the number
of unwind opcodes required.
`.cantunwind'
Prevents unwinding through the current function. No personality
routine or exception table data is required or permitted.
`.personality NAME'
Sets the personality routine for the current function to NAME.
`.personalityindex INDEX'
Sets the personality routine for the current function to the EABI
standard routine number INDEX
`.handlerdata'
Marks the end of the current function, and the start of the
exception table entry for that function. Anything between this
directive and the `.fnend' directive will be added to the
exception table entry.
Must be preceded by a `.personality' or `.personalityindex'
directive.
`.save REGLIST'
Generate unwinder annotations to restore the registers in REGLIST.
The format of REGLIST is the same as the corresponding
store-multiple instruction.
_core registers_
.save {r4, r5, r6, lr}
stmfd sp!, {r4, r5, r6, lr}
_FPA registers_
.save f4, 2
sfmfd f4, 2, [sp]!
_VFP registers_
.save {d8, d9, d10}
fstmdf sp!, {d8, d9, d10}
_iWMMXt registers_
.save {wr10, wr11}
wstrd wr11, [sp, #-8]!
wstrd wr10, [sp, #-8]!
or
.save wr11
wstrd wr11, [sp, #-8]!
.save wr10
wstrd wr10, [sp, #-8]!
`.pad #COUNT'
Generate unwinder annotations for a stack adjustment of COUNT
bytes. A positive value indicates the function prologue allocated
stack space by decrementing the stack pointer.
`.movsp REG'
Tell the unwinder that REG contains the current stack pointer.
`.setfp FPREG, SPREG [, #OFFSET]'
Make all unwinder annotations relaive to a frame pointer. Without
this the unwinder will use offsets from the stack pointer.
The syntax of this directive is the same as the `sub' or `mov'
instruction used to set the frame pointer. SPREG must be either
`sp' or mentioned in a previous `.movsp' directive.
.movsp ip
mov ip, sp
...
.setfp fp, ip, #4
sub fp, ip, #4
`.raw OFFSET, BYTE1, ...'
Insert one of more arbitary unwind opcode bytes, which are known
to adjust the stack pointer by OFFSET bytes.
For example `.unwind_raw 4, 0xb1, 0x01' is equivalent to `.save
{r0}'
File: as.info, Node: ARM Opcodes, Next: ARM Mapping Symbols, Prev: ARM Directives, Up: ARM-Dependent
8.4.5 Opcodes
-------------
`as' implements all the standard ARM opcodes. It also implements
several pseudo opcodes, including several synthetic load instructions.
`NOP'
nop
This pseudo op will always evaluate to a legal ARM instruction
that does nothing. Currently it will evaluate to MOV r0, r0.
`LDR'
ldr <register> , = <expression>
If expression evaluates to a numeric constant then a MOV or MVN
instruction will be used in place of the LDR instruction, if the
constant can be generated by either of these instructions.
Otherwise the constant will be placed into the nearest literal
pool (if it not already there) and a PC relative LDR instruction
will be generated.
`ADR'
adr <register> <label>
This instruction will load the address of LABEL into the indicated
register. The instruction will evaluate to a PC relative ADD or
SUB instruction depending upon where the label is located. If the
label is out of range, or if it is not defined in the same file
(and section) as the ADR instruction, then an error will be
generated. This instruction will not make use of the literal pool.
`ADRL'
adrl <register> <label>
This instruction will load the address of LABEL into the indicated
register. The instruction will evaluate to one or two PC relative
ADD or SUB instructions depending upon where the label is located.
If a second instruction is not needed a NOP instruction will be
generated in its place, so that this instruction is always 8 bytes
long.
If the label is out of range, or if it is not defined in the same
file (and section) as the ADRL instruction, then an error will be
generated. This instruction will not make use of the literal pool.
For information on the ARM or Thumb instruction sets, see `ARM
Software Development Toolkit Reference Manual', Advanced RISC Machines
Ltd.
File: as.info, Node: ARM Mapping Symbols, Prev: ARM Opcodes, Up: ARM-Dependent
8.4.6 Mapping Symbols
---------------------
The ARM ELF specification requires that special symbols be inserted
into object files to mark certain features:
`$a'
At the start of a region of code containing ARM instructions.
`$t'
At the start of a region of code containing THUMB instructions.
`$d'
At the start of a region of data.
The assembler will automatically insert these symbols for you - there
is no need to code them yourself. Support for tagging symbols ($b, $f,
$p and $m) which is also mentioned in the current ARM ELF specification
is not implemented. This is because they have been dropped from the
new EABI and so tools cannot rely upon their presence.
File: as.info, Node: CRIS-Dependent, Next: D10V-Dependent, Prev: ARM-Dependent, Up: Machine Dependencies
8.5 CRIS Dependent Features
===========================
* Menu:
* CRIS-Opts:: Command-line Options
* CRIS-Expand:: Instruction expansion
* CRIS-Symbols:: Symbols
* CRIS-Syntax:: Syntax
File: as.info, Node: CRIS-Opts, Next: CRIS-Expand, Up: CRIS-Dependent
8.5.1 Command-line Options
--------------------------
The CRIS version of `as' has these machine-dependent command-line
options.
The format of the generated object files can be either ELF or a.out,
specified by the command-line options `--emulation=crisaout' and
`--emulation=criself'. The default is ELF (criself), unless `as' has
been configured specifically for a.out by using the configuration name
`cris-axis-aout'.
There are two different link-incompatible ELF object file variants
for CRIS, for use in environments where symbols are expected to be
prefixed by a leading `_' character and for environments without such a
symbol prefix. The variant used for GNU/Linux port has no symbol
prefix. Which variant to produce is specified by either of the options
`--underscore' and `--no-underscore'. The default is `--underscore'.
Since symbols in CRIS a.out objects are expected to have a `_' prefix,
specifying `--no-underscore' when generating a.out objects is an error.
Besides the object format difference, the effect of this option is to
parse register names differently (*note crisnous::). The
`--no-underscore' option makes a `$' register prefix mandatory.
The option `--pic' must be passed to `as' in order to recognize the
symbol syntax used for ELF (SVR4 PIC) position-independent-code (*note
crispic::). This will also affect expansion of instructions. The
expansion with `--pic' will use PC-relative rather than (slightly
faster) absolute addresses in those expansions.
The option `--march=ARCHITECTURE' specifies the recognized
instruction set and recognized register names. It also controls the
architecture type of the object file. Valid values for ARCHITECTURE
are:
`v0_v10'
All instructions and register names for any architecture variant
in the set v0...v10 are recognized. This is the default if the
target is configured as cris-*.
`v10'
Only instructions and register names for CRIS v10 (as found in
ETRAX 100 LX) are recognized. This is the default if the target
is configured as crisv10-*.
`v32'
Only instructions and register names for CRIS v32 (code name
Guinness) are recognized. This is the default if the target is
configured as crisv32-*. This value implies `--no-mul-bug-abort'.
(A subsequent `--mul-bug-abort' will turn it back on.)
`common_v10_v32'
Only instructions with register names and addressing modes with
opcodes common to the v10 and v32 are recognized.
When `-N' is specified, `as' will emit a warning when a 16-bit
branch instruction is expanded into a 32-bit multiple-instruction
construct (*note CRIS-Expand::).
Some versions of the CRIS v10, for example in the Etrax 100 LX,
contain a bug that causes destabilizing memory accesses when a multiply
instruction is executed with certain values in the first operand just
before a cache-miss. When the `--mul-bug-abort' command line option is
active (the default value), `as' will refuse to assemble a file
containing a multiply instruction at a dangerous offset, one that could
be the last on a cache-line, or is in a section with insufficient
alignment. This placement checking does not catch any case where the
multiply instruction is dangerously placed because it is located in a
delay-slot. The `--mul-bug-abort' command line option turns off the
checking.
File: as.info, Node: CRIS-Expand, Next: CRIS-Symbols, Prev: CRIS-Opts, Up: CRIS-Dependent
8.5.2 Instruction expansion
---------------------------
`as' will silently choose an instruction that fits the operand size for
`[register+constant]' operands. For example, the offset `127' in
`move.d [r3+127],r4' fits in an instruction using a signed-byte offset.
Similarly, `move.d [r2+32767],r1' will generate an instruction using a
16-bit offset. For symbolic expressions and constants that do not fit
in 16 bits including the sign bit, a 32-bit offset is generated.
For branches, `as' will expand from a 16-bit branch instruction into
a sequence of instructions that can reach a full 32-bit address. Since
this does not correspond to a single instruction, such expansions can
optionally be warned about. *Note CRIS-Opts::.
If the operand is found to fit the range, a `lapc' mnemonic will
translate to a `lapcq' instruction. Use `lapc.d' to force the 32-bit
`lapc' instruction.
Similarly, the `addo' mnemonic will translate to the shortest
fitting instruction of `addoq', `addo.w' and `addo.d', when used with a
operand that is a constant known at assembly time.
File: as.info, Node: CRIS-Symbols, Next: CRIS-Syntax, Prev: CRIS-Expand, Up: CRIS-Dependent
8.5.3 Symbols
-------------
Some symbols are defined by the assembler. They're intended to be used
in conditional assembly, for example:
.if ..asm.arch.cris.v32
CODE FOR CRIS V32
.elseif ..asm.arch.cris.common_v10_v32
CODE COMMON TO CRIS V32 AND CRIS V10
.elseif ..asm.arch.cris.v10 | ..asm.arch.cris.any_v0_v10
CODE FOR V10
.else
.error "Code needs to be added here."
.endif
These symbols are defined in the assembler, reflecting command-line
options, either when specified or the default. They are always
defined, to 0 or 1.
`..asm.arch.cris.any_v0_v10'
This symbol is non-zero when `--march=v0_v10' is specified or the
default.
`..asm.arch.cris.common_v10_v32'
Set according to the option `--march=common_v10_v32'.
`..asm.arch.cris.v10'
Reflects the option `--march=v10'.
`..asm.arch.cris.v32'
Corresponds to `--march=v10'.
Speaking of symbols, when a symbol is used in code, it can have a
suffix modifying its value for use in position-independent code. *Note
CRIS-Pic::.
File: as.info, Node: CRIS-Syntax, Prev: CRIS-Symbols, Up: CRIS-Dependent
8.5.4 Syntax
------------
There are different aspects of the CRIS assembly syntax.
* Menu:
* CRIS-Chars:: Special Characters
* CRIS-Pic:: Position-Independent Code Symbols
* CRIS-Regs:: Register Names
* CRIS-Pseudos:: Assembler Directives
File: as.info, Node: CRIS-Chars, Next: CRIS-Pic, Up: CRIS-Syntax
8.5.4.1 Special Characters
..........................
The character `#' is a line comment character. It starts a comment if
and only if it is placed at the beginning of a line.
A `;' character starts a comment anywhere on the line, causing all
characters up to the end of the line to be ignored.
A `@' character is handled as a line separator equivalent to a
logical new-line character (except in a comment), so separate
instructions can be specified on a single line.
File: as.info, Node: CRIS-Pic, Next: CRIS-Regs, Prev: CRIS-Chars, Up: CRIS-Syntax
8.5.4.2 Symbols in position-independent code
............................................
When generating position-independent code (SVR4 PIC) for use in
cris-axis-linux-gnu or crisv32-axis-linux-gnu shared libraries, symbol
suffixes are used to specify what kind of run-time symbol lookup will
be used, expressed in the object as different _relocation types_.
Usually, all absolute symbol values must be located in a table, the
_global offset table_, leaving the code position-independent;
independent of values of global symbols and independent of the address
of the code. The suffix modifies the value of the symbol, into for
example an index into the global offset table where the real symbol
value is entered, or a PC-relative value, or a value relative to the
start of the global offset table. All symbol suffixes start with the
character `:' (omitted in the list below). Every symbol use in code or
a read-only section must therefore have a PIC suffix to enable a useful
shared library to be created. Usually, these constructs must not be
used with an additive constant offset as is usually allowed, i.e. no 4
as in `symbol + 4' is allowed. This restriction is checked at
link-time, not at assembly-time.
`GOT'
Attaching this suffix to a symbol in an instruction causes the
symbol to be entered into the global offset table. The value is a
32-bit index for that symbol into the global offset table. The
name of the corresponding relocation is `R_CRIS_32_GOT'. Example:
`move.d [$r0+extsym:GOT],$r9'
`GOT16'
Same as for `GOT', but the value is a 16-bit index into the global
offset table. The corresponding relocation is `R_CRIS_16_GOT'.
Example: `move.d [$r0+asymbol:GOT16],$r10'
`PLT'
This suffix is used for function symbols. It causes a _procedure
linkage table_, an array of code stubs, to be created at the time
the shared object is created or linked against, together with a
global offset table entry. The value is a pc-relative offset to
the corresponding stub code in the procedure linkage table. This
arrangement causes the run-time symbol resolver to be called to
look up and set the value of the symbol the first time the
function is called (at latest; depending environment variables).
It is only safe to leave the symbol unresolved this way if all
references are function calls. The name of the relocation is
`R_CRIS_32_PLT_PCREL'. Example: `add.d fnname:PLT,$pc'
`PLTG'
Like PLT, but the value is relative to the beginning of the global
offset table. The relocation is `R_CRIS_32_PLT_GOTREL'. Example:
`move.d fnname:PLTG,$r3'
`GOTPLT'
Similar to `PLT', but the value of the symbol is a 32-bit index
into the global offset table. This is somewhat of a mix between
the effect of the `GOT' and the `PLT' suffix; the difference to
`GOT' is that there will be a procedure linkage table entry
created, and that the symbol is assumed to be a function entry and
will be resolved by the run-time resolver as with `PLT'. The
relocation is `R_CRIS_32_GOTPLT'. Example: `jsr
[$r0+fnname:GOTPLT]'
`GOTPLT16'
A variant of `GOTPLT' giving a 16-bit value. Its relocation name
is `R_CRIS_16_GOTPLT'. Example: `jsr [$r0+fnname:GOTPLT16]'
`GOTOFF'
This suffix must only be attached to a local symbol, but may be
used in an expression adding an offset. The value is the address
of the symbol relative to the start of the global offset table.
The relocation name is `R_CRIS_32_GOTREL'. Example: `move.d
[$r0+localsym:GOTOFF],r3'
File: as.info, Node: CRIS-Regs, Next: CRIS-Pseudos, Prev: CRIS-Pic, Up: CRIS-Syntax
8.5.4.3 Register names
......................
A `$' character may always prefix a general or special register name in
an instruction operand but is mandatory when the option
`--no-underscore' is specified or when the `.syntax register_prefix'
directive is in effect (*note crisnous::). Register names are
case-insensitive.
File: as.info, Node: CRIS-Pseudos, Prev: CRIS-Regs, Up: CRIS-Syntax
8.5.4.4 Assembler Directives
............................
There are a few CRIS-specific pseudo-directives in addition to the
generic ones. *Note Pseudo Ops::. Constants emitted by
pseudo-directives are in little-endian order for CRIS. There is no
support for floating-point-specific directives for CRIS.
`.dword EXPRESSIONS'
The `.dword' directive is a synonym for `.int', expecting zero or
more EXPRESSIONS, separated by commas. For each expression, a
32-bit little-endian constant is emitted.
`.syntax ARGUMENT'
The `.syntax' directive takes as ARGUMENT one of the following
case-sensitive choices.
`no_register_prefix'
The `.syntax no_register_prefix' directive makes a `$'
character prefix on all registers optional. It overrides a
previous setting, including the corresponding effect of the
option `--no-underscore'. If this directive is used when
ordinary symbols do not have a `_' character prefix, care
must be taken to avoid ambiguities whether an operand is a
register or a symbol; using symbols with names the same as
general or special registers then invoke undefined behavior.
`register_prefix'
This directive makes a `$' character prefix on all registers
mandatory. It overrides a previous setting, including the
corresponding effect of the option `--underscore'.
`leading_underscore'
This is an assertion directive, emitting an error if the
`--no-underscore' option is in effect.
`no_leading_underscore'
This is the opposite of the `.syntax leading_underscore'
directive and emits an error if the option `--underscore' is
in effect.
`.arch ARGUMENT'
This is an assertion directive, giving an error if the specified
ARGUMENT is not the same as the specified or default value for the
`--march=ARCHITECTURE' option (*note march-option::).
File: as.info, Node: D10V-Dependent, Next: D30V-Dependent, Prev: CRIS-Dependent, Up: Machine Dependencies
8.6 D10V Dependent Features
===========================
* Menu:
* D10V-Opts:: D10V Options
* D10V-Syntax:: Syntax
* D10V-Float:: Floating Point
* D10V-Opcodes:: Opcodes
File: as.info, Node: D10V-Opts, Next: D10V-Syntax, Up: D10V-Dependent
8.6.1 D10V Options
------------------
The Mitsubishi D10V version of `as' has a few machine dependent options.
`-O'
The D10V can often execute two sub-instructions in parallel. When
this option is used, `as' will attempt to optimize its output by
detecting when instructions can be executed in parallel.
`--nowarnswap'
To optimize execution performance, `as' will sometimes swap the
order of instructions. Normally this generates a warning. When
this option is used, no warning will be generated when
instructions are swapped.
`--gstabs-packing'
`--no-gstabs-packing'
`as' packs adjacent short instructions into a single packed
instruction. `--no-gstabs-packing' turns instruction packing off if
`--gstabs' is specified as well; `--gstabs-packing' (the default)
turns instruction packing on even when `--gstabs' is specified.
File: as.info, Node: D10V-Syntax, Next: D10V-Float, Prev: D10V-Opts, Up: D10V-Dependent
8.6.2 Syntax
------------
The D10V syntax is based on the syntax in Mitsubishi's D10V
architecture manual. The differences are detailed below.
* Menu:
* D10V-Size:: Size Modifiers
* D10V-Subs:: Sub-Instructions
* D10V-Chars:: Special Characters
* D10V-Regs:: Register Names
* D10V-Addressing:: Addressing Modes
* D10V-Word:: @WORD Modifier
File: as.info, Node: D10V-Size, Next: D10V-Subs, Up: D10V-Syntax
8.6.2.1 Size Modifiers
......................
The D10V version of `as' uses the instruction names in the D10V
Architecture Manual. However, the names in the manual are sometimes
ambiguous. There are instruction names that can assemble to a short or
long form opcode. How does the assembler pick the correct form? `as'
will always pick the smallest form if it can. When dealing with a
symbol that is not defined yet when a line is being assembled, it will
always use the long form. If you need to force the assembler to use
either the short or long form of the instruction, you can append either
`.s' (short) or `.l' (long) to it. For example, if you are writing an
assembly program and you want to do a branch to a symbol that is
defined later in your program, you can write `bra.s foo'. Objdump
and GDB will always append `.s' or `.l' to instructions which have both
short and long forms.
File: as.info, Node: D10V-Subs, Next: D10V-Chars, Prev: D10V-Size, Up: D10V-Syntax
8.6.2.2 Sub-Instructions
........................
The D10V assembler takes as input a series of instructions, either
one-per-line, or in the special two-per-line format described in the
next section. Some of these instructions will be short-form or
sub-instructions. These sub-instructions can be packed into a single
instruction. The assembler will do this automatically. It will also
detect when it should not pack instructions. For example, when a label
is defined, the next instruction will never be packaged with the
previous one. Whenever a branch and link instruction is called, it
will not be packaged with the next instruction so the return address
will be valid. Nops are automatically inserted when necessary.
If you do not want the assembler automatically making these
decisions, you can control the packaging and execution type (parallel
or sequential) with the special execution symbols described in the next
section.
File: as.info, Node: D10V-Chars, Next: D10V-Regs, Prev: D10V-Subs, Up: D10V-Syntax
8.6.2.3 Special Characters
..........................
`;' and `#' are the line comment characters. Sub-instructions may be
executed in order, in reverse-order, or in parallel. Instructions
listed in the standard one-per-line format will be executed
sequentially. To specify the executing order, use the following
symbols:
`->'
Sequential with instruction on the left first.
`<-'
Sequential with instruction on the right first.
`||'
Parallel
The D10V syntax allows either one instruction per line, one
instruction per line with the execution symbol, or two instructions per
line. For example
`abs a1 -> abs r0'
Execute these sequentially. The instruction on the right is in
the right container and is executed second.
`abs r0 <- abs a1'
Execute these reverse-sequentially. The instruction on the right
is in the right container, and is executed first.
`ld2w r2,@r8+ || mac a0,r0,r7'
Execute these in parallel.
`ld2w r2,@r8+ ||'
`mac a0,r0,r7'
Two-line format. Execute these in parallel.
`ld2w r2,@r8+'
`mac a0,r0,r7'
Two-line format. Execute these sequentially. Assembler will put
them in the proper containers.
`ld2w r2,@r8+ ->'
`mac a0,r0,r7'
Two-line format. Execute these sequentially. Same as above but
second instruction will always go into right container.
Since `$' has no special meaning, you may use it in symbol names.
File: as.info, Node: D10V-Regs, Next: D10V-Addressing, Prev: D10V-Chars, Up: D10V-Syntax
8.6.2.4 Register Names
......................
You can use the predefined symbols `r0' through `r15' to refer to the
D10V registers. You can also use `sp' as an alias for `r15'. The
accumulators are `a0' and `a1'. There are special register-pair names
that may optionally be used in opcodes that require even-numbered
registers. Register names are not case sensitive.
Register Pairs
`r0-r1'
`r2-r3'
`r4-r5'
`r6-r7'
`r8-r9'
`r10-r11'
`r12-r13'
`r14-r15'
The D10V also has predefined symbols for these control registers and
status bits:
`psw'
Processor Status Word
`bpsw'
Backup Processor Status Word
`pc'
Program Counter
`bpc'
Backup Program Counter
`rpt_c'
Repeat Count
`rpt_s'
Repeat Start address
`rpt_e'
Repeat End address
`mod_s'
Modulo Start address
`mod_e'
Modulo End address
`iba'
Instruction Break Address
`f0'
Flag 0
`f1'
Flag 1
`c'
Carry flag
File: as.info, Node: D10V-Addressing, Next: D10V-Word, Prev: D10V-Regs, Up: D10V-Syntax
8.6.2.5 Addressing Modes
........................
`as' understands the following addressing modes for the D10V. `RN' in
the following refers to any of the numbered registers, but _not_ the
control registers.
`RN'
Register direct
`@RN'
Register indirect
`@RN+'
Register indirect with post-increment
`@RN-'
Register indirect with post-decrement
`@-SP'
Register indirect with pre-decrement
`@(DISP, RN)'
Register indirect with displacement
`ADDR'
PC relative address (for branch or rep).
`#IMM'
Immediate data (the `#' is optional and ignored)
File: as.info, Node: D10V-Word, Prev: D10V-Addressing, Up: D10V-Syntax
8.6.2.6 @WORD Modifier
......................
Any symbol followed by `@word' will be replaced by the symbol's value
shifted right by 2. This is used in situations such as loading a
register with the address of a function (or any other code fragment).
For example, if you want to load a register with the location of the
function `main' then jump to that function, you could do it as follows:
ldi r2, main@word
jmp r2
File: as.info, Node: D10V-Float, Next: D10V-Opcodes, Prev: D10V-Syntax, Up: D10V-Dependent
8.6.3 Floating Point
--------------------
The D10V has no hardware floating point, but the `.float' and `.double'
directives generates IEEE floating-point numbers for compatibility with
other development tools.
File: as.info, Node: D10V-Opcodes, Prev: D10V-Float, Up: D10V-Dependent
8.6.4 Opcodes
-------------
For detailed information on the D10V machine instruction set, see `D10V
Architecture: A VLIW Microprocessor for Multimedia Applications'
(Mitsubishi Electric Corp.). `as' implements all the standard D10V
opcodes. The only changes are those described in the section on size
modifiers
File: as.info, Node: D30V-Dependent, Next: H8/300-Dependent, Prev: D10V-Dependent, Up: Machine Dependencies
8.7 D30V Dependent Features
===========================
* Menu:
* D30V-Opts:: D30V Options
* D30V-Syntax:: Syntax
* D30V-Float:: Floating Point
* D30V-Opcodes:: Opcodes
File: as.info, Node: D30V-Opts, Next: D30V-Syntax, Up: D30V-Dependent
8.7.1 D30V Options
------------------
The Mitsubishi D30V version of `as' has a few machine dependent options.
`-O'
The D30V can often execute two sub-instructions in parallel. When
this option is used, `as' will attempt to optimize its output by
detecting when instructions can be executed in parallel.
`-n'
When this option is used, `as' will issue a warning every time it
adds a nop instruction.
`-N'
When this option is used, `as' will issue a warning if it needs to
insert a nop after a 32-bit multiply before a load or 16-bit
multiply instruction.
File: as.info, Node: D30V-Syntax, Next: D30V-Float, Prev: D30V-Opts, Up: D30V-Dependent
8.7.2 Syntax
------------
The D30V syntax is based on the syntax in Mitsubishi's D30V
architecture manual. The differences are detailed below.
* Menu:
* D30V-Size:: Size Modifiers
* D30V-Subs:: Sub-Instructions
* D30V-Chars:: Special Characters
* D30V-Guarded:: Guarded Execution
* D30V-Regs:: Register Names
* D30V-Addressing:: Addressing Modes
File: as.info, Node: D30V-Size, Next: D30V-Subs, Up: D30V-Syntax
8.7.2.1 Size Modifiers
......................
The D30V version of `as' uses the instruction names in the D30V
Architecture Manual. However, the names in the manual are sometimes
ambiguous. There are instruction names that can assemble to a short or
long form opcode. How does the assembler pick the correct form? `as'
will always pick the smallest form if it can. When dealing with a
symbol that is not defined yet when a line is being assembled, it will
always use the long form. If you need to force the assembler to use
either the short or long form of the instruction, you can append either
`.s' (short) or `.l' (long) to it. For example, if you are writing an
assembly program and you want to do a branch to a symbol that is
defined later in your program, you can write `bra.s foo'. Objdump and
GDB will always append `.s' or `.l' to instructions which have both
short and long forms.
File: as.info, Node: D30V-Subs, Next: D30V-Chars, Prev: D30V-Size, Up: D30V-Syntax
8.7.2.2 Sub-Instructions
........................
The D30V assembler takes as input a series of instructions, either
one-per-line, or in the special two-per-line format described in the
next section. Some of these instructions will be short-form or
sub-instructions. These sub-instructions can be packed into a single
instruction. The assembler will do this automatically. It will also
detect when it should not pack instructions. For example, when a label
is defined, the next instruction will never be packaged with the
previous one. Whenever a branch and link instruction is called, it
will not be packaged with the next instruction so the return address
will be valid. Nops are automatically inserted when necessary.
If you do not want the assembler automatically making these
decisions, you can control the packaging and execution type (parallel
or sequential) with the special execution symbols described in the next
section.
File: as.info, Node: D30V-Chars, Next: D30V-Guarded, Prev: D30V-Subs, Up: D30V-Syntax
8.7.2.3 Special Characters
..........................
`;' and `#' are the line comment characters. Sub-instructions may be
executed in order, in reverse-order, or in parallel. Instructions
listed in the standard one-per-line format will be executed
sequentially unless you use the `-O' option.
To specify the executing order, use the following symbols:
`->'
Sequential with instruction on the left first.
`<-'
Sequential with instruction on the right first.
`||'
Parallel
The D30V syntax allows either one instruction per line, one
instruction per line with the execution symbol, or two instructions per
line. For example
`abs r2,r3 -> abs r4,r5'
Execute these sequentially. The instruction on the right is in
the right container and is executed second.
`abs r2,r3 <- abs r4,r5'
Execute these reverse-sequentially. The instruction on the right
is in the right container, and is executed first.
`abs r2,r3 || abs r4,r5'
Execute these in parallel.
`ldw r2,@(r3,r4) ||'
`mulx r6,r8,r9'
Two-line format. Execute these in parallel.
`mulx a0,r8,r9'
`stw r2,@(r3,r4)'
Two-line format. Execute these sequentially unless `-O' option is
used. If the `-O' option is used, the assembler will determine if
the instructions could be done in parallel (the above two
instructions can be done in parallel), and if so, emit them as
parallel instructions. The assembler will put them in the proper
containers. In the above example, the assembler will put the
`stw' instruction in left container and the `mulx' instruction in
the right container.
`stw r2,@(r3,r4) ->'
`mulx a0,r8,r9'
Two-line format. Execute the `stw' instruction followed by the
`mulx' instruction sequentially. The first instruction goes in the
left container and the second instruction goes into right
container. The assembler will give an error if the machine
ordering constraints are violated.
`stw r2,@(r3,r4) <-'
`mulx a0,r8,r9'
Same as previous example, except that the `mulx' instruction is
executed before the `stw' instruction.
Since `$' has no special meaning, you may use it in symbol names.
File: as.info, Node: D30V-Guarded, Next: D30V-Regs, Prev: D30V-Chars, Up: D30V-Syntax
8.7.2.4 Guarded Execution
.........................
`as' supports the full range of guarded execution directives for each
instruction. Just append the directive after the instruction proper.
The directives are:
`/tx'
Execute the instruction if flag f0 is true.
`/fx'
Execute the instruction if flag f0 is false.
`/xt'
Execute the instruction if flag f1 is true.
`/xf'
Execute the instruction if flag f1 is false.
`/tt'
Execute the instruction if both flags f0 and f1 are true.
`/tf'
Execute the instruction if flag f0 is true and flag f1 is false.
File: as.info, Node: D30V-Regs, Next: D30V-Addressing, Prev: D30V-Guarded, Up: D30V-Syntax
8.7.2.5 Register Names
......................
You can use the predefined symbols `r0' through `r63' to refer to the
D30V registers. You can also use `sp' as an alias for `r63' and `link'
as an alias for `r62'. The accumulators are `a0' and `a1'.
The D30V also has predefined symbols for these control registers and
status bits:
`psw'
Processor Status Word
`bpsw'
Backup Processor Status Word
`pc'
Program Counter
`bpc'
Backup Program Counter
`rpt_c'
Repeat Count
`rpt_s'
Repeat Start address
`rpt_e'
Repeat End address
`mod_s'
Modulo Start address
`mod_e'
Modulo End address
`iba'
Instruction Break Address
`f0'
Flag 0
`f1'
Flag 1
`f2'
Flag 2
`f3'
Flag 3
`f4'
Flag 4
`f5'
Flag 5
`f6'
Flag 6
`f7'
Flag 7
`s'
Same as flag 4 (saturation flag)
`v'
Same as flag 5 (overflow flag)
`va'
Same as flag 6 (sticky overflow flag)
`c'
Same as flag 7 (carry/borrow flag)
`b'
Same as flag 7 (carry/borrow flag)
File: as.info, Node: D30V-Addressing, Prev: D30V-Regs, Up: D30V-Syntax
8.7.2.6 Addressing Modes
........................
`as' understands the following addressing modes for the D30V. `RN' in
the following refers to any of the numbered registers, but _not_ the
control registers.
`RN'
Register direct
`@RN'
Register indirect
`@RN+'
Register indirect with post-increment
`@RN-'
Register indirect with post-decrement
`@-SP'
Register indirect with pre-decrement
`@(DISP, RN)'
Register indirect with displacement
`ADDR'
PC relative address (for branch or rep).
`#IMM'
Immediate data (the `#' is optional and ignored)
File: as.info, Node: D30V-Float, Next: D30V-Opcodes, Prev: D30V-Syntax, Up: D30V-Dependent
8.7.3 Floating Point
--------------------
The D30V has no hardware floating point, but the `.float' and `.double'
directives generates IEEE floating-point numbers for compatibility with
other development tools.
File: as.info, Node: D30V-Opcodes, Prev: D30V-Float, Up: D30V-Dependent
8.7.4 Opcodes
-------------
For detailed information on the D30V machine instruction set, see `D30V
Architecture: A VLIW Microprocessor for Multimedia Applications'
(Mitsubishi Electric Corp.). `as' implements all the standard D30V
opcodes. The only changes are those described in the section on size
modifiers
File: as.info, Node: H8/300-Dependent, Next: H8/500-Dependent, Prev: D30V-Dependent, Up: Machine Dependencies
8.8 H8/300 Dependent Features
=============================
* Menu:
* H8/300 Options:: Options
* H8/300 Syntax:: Syntax
* H8/300 Floating Point:: Floating Point
* H8/300 Directives:: H8/300 Machine Directives
* H8/300 Opcodes:: Opcodes
File: as.info, Node: H8/300 Options, Next: H8/300 Syntax, Up: H8/300-Dependent
8.8.1 Options
-------------
`as' has no additional command-line options for the Renesas (formerly
Hitachi) H8/300 family.
File: as.info, Node: H8/300 Syntax, Next: H8/300 Floating Point, Prev: H8/300 Options, Up: H8/300-Dependent
8.8.2 Syntax
------------
* Menu:
* H8/300-Chars:: Special Characters
* H8/300-Regs:: Register Names
* H8/300-Addressing:: Addressing Modes
File: as.info, Node: H8/300-Chars, Next: H8/300-Regs, Up: H8/300 Syntax
8.8.2.1 Special Characters
..........................
`;' is the line comment character.
`$' can be used instead of a newline to separate statements.
Therefore _you may not use `$' in symbol names_ on the H8/300.
File: as.info, Node: H8/300-Regs, Next: H8/300-Addressing, Prev: H8/300-Chars, Up: H8/300 Syntax
8.8.2.2 Register Names
......................
You can use predefined symbols of the form `rNh' and `rNl' to refer to
the H8/300 registers as sixteen 8-bit general-purpose registers. N is
a digit from `0' to `7'); for instance, both `r0h' and `r7l' are valid
register names.
You can also use the eight predefined symbols `rN' to refer to the
H8/300 registers as 16-bit registers (you must use this form for
addressing).
On the H8/300H, you can also use the eight predefined symbols `erN'
(`er0' ... `er7') to refer to the 32-bit general purpose registers.
The two control registers are called `pc' (program counter; a 16-bit
register, except on the H8/300H where it is 24 bits) and `ccr'
(condition code register; an 8-bit register). `r7' is used as the
stack pointer, and can also be called `sp'.
File: as.info, Node: H8/300-Addressing, Prev: H8/300-Regs, Up: H8/300 Syntax
8.8.2.3 Addressing Modes
........................
as understands the following addressing modes for the H8/300:
`rN'
Register direct
`@rN'
Register indirect
`@(D, rN)'
`@(D:16, rN)'
`@(D:24, rN)'
Register indirect: 16-bit or 24-bit displacement D from register
N. (24-bit displacements are only meaningful on the H8/300H.)
`@rN+'
Register indirect with post-increment
`@-rN'
Register indirect with pre-decrement
``@'AA'
``@'AA:8'
``@'AA:16'
``@'AA:24'
Absolute address `aa'. (The address size `:24' only makes sense
on the H8/300H.)
`#XX'
`#XX:8'
`#XX:16'
`#XX:32'
Immediate data XX. You may specify the `:8', `:16', or `:32' for
clarity, if you wish; but `as' neither requires this nor uses
it--the data size required is taken from context.
``@'`@'AA'
``@'`@'AA:8'
Memory indirect. You may specify the `:8' for clarity, if you
wish; but `as' neither requires this nor uses it.
File: as.info, Node: H8/300 Floating Point, Next: H8/300 Directives, Prev: H8/300 Syntax, Up: H8/300-Dependent
8.8.3 Floating Point
--------------------
The H8/300 family has no hardware floating point, but the `.float'
directive generates IEEE floating-point numbers for compatibility with
other development tools.
File: as.info, Node: H8/300 Directives, Next: H8/300 Opcodes, Prev: H8/300 Floating Point, Up: H8/300-Dependent
8.8.4 H8/300 Machine Directives
-------------------------------
`as' has the following machine-dependent directives for the H8/300:
`.h8300h'
Recognize and emit additional instructions for the H8/300H
variant, and also make `.int' emit 32-bit numbers rather than the
usual (16-bit) for the H8/300 family.
`.h8300s'
Recognize and emit additional instructions for the H8S variant, and
also make `.int' emit 32-bit numbers rather than the usual (16-bit)
for the H8/300 family.
`.h8300hn'
Recognize and emit additional instructions for the H8/300H variant
in normal mode, and also make `.int' emit 32-bit numbers rather
than the usual (16-bit) for the H8/300 family.
`.h8300sn'
Recognize and emit additional instructions for the H8S variant in
normal mode, and also make `.int' emit 32-bit numbers rather than
the usual (16-bit) for the H8/300 family.
On the H8/300 family (including the H8/300H) `.word' directives
generate 16-bit numbers.
File: as.info, Node: H8/300 Opcodes, Prev: H8/300 Directives, Up: H8/300-Dependent
8.8.5 Opcodes
-------------
For detailed information on the H8/300 machine instruction set, see
`H8/300 Series Programming Manual'. For information specific to the
H8/300H, see `H8/300H Series Programming Manual' (Renesas).
`as' implements all the standard H8/300 opcodes. No additional
pseudo-instructions are needed on this family.
The following table summarizes the H8/300 opcodes, and their
arguments. Entries marked `*' are opcodes used only on the H8/300H.
Legend:
Rs source register
Rd destination register
abs absolute address
imm immediate data
disp:N N-bit displacement from a register
pcrel:N N-bit displacement relative to program counter
add.b #imm,rd * andc #imm,ccr
add.b rs,rd band #imm,rd
add.w rs,rd band #imm,@rd
* add.w #imm,rd band #imm,@abs:8
* add.l rs,rd bra pcrel:8
* add.l #imm,rd * bra pcrel:16
adds #imm,rd bt pcrel:8
addx #imm,rd * bt pcrel:16
addx rs,rd brn pcrel:8
and.b #imm,rd * brn pcrel:16
and.b rs,rd bf pcrel:8
* and.w rs,rd * bf pcrel:16
* and.w #imm,rd bhi pcrel:8
* and.l #imm,rd * bhi pcrel:16
* and.l rs,rd bls pcrel:8
* bls pcrel:16 bld #imm,rd
bcc pcrel:8 bld #imm,@rd
* bcc pcrel:16 bld #imm,@abs:8
bhs pcrel:8 bnot #imm,rd
* bhs pcrel:16 bnot #imm,@rd
bcs pcrel:8 bnot #imm,@abs:8
* bcs pcrel:16 bnot rs,rd
blo pcrel:8 bnot rs,@rd
* blo pcrel:16 bnot rs,@abs:8
bne pcrel:8 bor #imm,rd
* bne pcrel:16 bor #imm,@rd
beq pcrel:8 bor #imm,@abs:8
* beq pcrel:16 bset #imm,rd
bvc pcrel:8 bset #imm,@rd
* bvc pcrel:16 bset #imm,@abs:8
bvs pcrel:8 bset rs,rd
* bvs pcrel:16 bset rs,@rd
bpl pcrel:8 bset rs,@abs:8
* bpl pcrel:16 bsr pcrel:8
bmi pcrel:8 bsr pcrel:16
* bmi pcrel:16 bst #imm,rd
bge pcrel:8 bst #imm,@rd
* bge pcrel:16 bst #imm,@abs:8
blt pcrel:8 btst #imm,rd
* blt pcrel:16 btst #imm,@rd
bgt pcrel:8 btst #imm,@abs:8
* bgt pcrel:16 btst rs,rd
ble pcrel:8 btst rs,@rd
* ble pcrel:16 btst rs,@abs:8
bclr #imm,rd bxor #imm,rd
bclr #imm,@rd bxor #imm,@rd
bclr #imm,@abs:8 bxor #imm,@abs:8
bclr rs,rd cmp.b #imm,rd
bclr rs,@rd cmp.b rs,rd
bclr rs,@abs:8 cmp.w rs,rd
biand #imm,rd cmp.w rs,rd
biand #imm,@rd * cmp.w #imm,rd
biand #imm,@abs:8 * cmp.l #imm,rd
bild #imm,rd * cmp.l rs,rd
bild #imm,@rd daa rs
bild #imm,@abs:8 das rs
bior #imm,rd dec.b rs
bior #imm,@rd * dec.w #imm,rd
bior #imm,@abs:8 * dec.l #imm,rd
bist #imm,rd divxu.b rs,rd
bist #imm,@rd * divxu.w rs,rd
bist #imm,@abs:8 * divxs.b rs,rd
bixor #imm,rd * divxs.w rs,rd
bixor #imm,@rd eepmov
bixor #imm,@abs:8 * eepmovw
* exts.w rd mov.w rs,@abs:16
* exts.l rd * mov.l #imm,rd
* extu.w rd * mov.l rs,rd
* extu.l rd * mov.l @rs,rd
inc rs * mov.l @(disp:16,rs),rd
* inc.w #imm,rd * mov.l @(disp:24,rs),rd
* inc.l #imm,rd * mov.l @rs+,rd
jmp @rs * mov.l @abs:16,rd
jmp abs * mov.l @abs:24,rd
jmp @@abs:8 * mov.l rs,@rd
jsr @rs * mov.l rs,@(disp:16,rd)
jsr abs * mov.l rs,@(disp:24,rd)
jsr @@abs:8 * mov.l rs,@-rd
ldc #imm,ccr * mov.l rs,@abs:16
ldc rs,ccr * mov.l rs,@abs:24
* ldc @abs:16,ccr movfpe @abs:16,rd
* ldc @abs:24,ccr movtpe rs,@abs:16
* ldc @(disp:16,rs),ccr mulxu.b rs,rd
* ldc @(disp:24,rs),ccr * mulxu.w rs,rd
* ldc @rs+,ccr * mulxs.b rs,rd
* ldc @rs,ccr * mulxs.w rs,rd
* mov.b @(disp:24,rs),rd neg.b rs
* mov.b rs,@(disp:24,rd) * neg.w rs
mov.b @abs:16,rd * neg.l rs
mov.b rs,rd nop
mov.b @abs:8,rd not.b rs
mov.b rs,@abs:8 * not.w rs
mov.b rs,rd * not.l rs
mov.b #imm,rd or.b #imm,rd
mov.b @rs,rd or.b rs,rd
mov.b @(disp:16,rs),rd * or.w #imm,rd
mov.b @rs+,rd * or.w rs,rd
mov.b @abs:8,rd * or.l #imm,rd
mov.b rs,@rd * or.l rs,rd
mov.b rs,@(disp:16,rd) orc #imm,ccr
mov.b rs,@-rd pop.w rs
mov.b rs,@abs:8 * pop.l rs
mov.w rs,@rd push.w rs
* mov.w @(disp:24,rs),rd * push.l rs
* mov.w rs,@(disp:24,rd) rotl.b rs
* mov.w @abs:24,rd * rotl.w rs
* mov.w rs,@abs:24 * rotl.l rs
mov.w rs,rd rotr.b rs
mov.w #imm,rd * rotr.w rs
mov.w @rs,rd * rotr.l rs
mov.w @(disp:16,rs),rd rotxl.b rs
mov.w @rs+,rd * rotxl.w rs
mov.w @abs:16,rd * rotxl.l rs
mov.w rs,@(disp:16,rd) rotxr.b rs
mov.w rs,@-rd * rotxr.w rs
* rotxr.l rs * stc ccr,@(disp:24,rd)
bpt * stc ccr,@-rd
rte * stc ccr,@abs:16
rts * stc ccr,@abs:24
shal.b rs sub.b rs,rd
* shal.w rs sub.w rs,rd
* shal.l rs * sub.w #imm,rd
shar.b rs * sub.l rs,rd
* shar.w rs * sub.l #imm,rd
* shar.l rs subs #imm,rd
shll.b rs subx #imm,rd
* shll.w rs subx rs,rd
* shll.l rs * trapa #imm
shlr.b rs xor #imm,rd
* shlr.w rs xor rs,rd
* shlr.l rs * xor.w #imm,rd
sleep * xor.w rs,rd
stc ccr,rd * xor.l #imm,rd
* stc ccr,@rs * xor.l rs,rd
* stc ccr,@(disp:16,rd) xorc #imm,ccr
Four H8/300 instructions (`add', `cmp', `mov', `sub') are defined
with variants using the suffixes `.b', `.w', and `.l' to specify the
size of a memory operand. `as' supports these suffixes, but does not
require them; since one of the operands is always a register, `as' can
deduce the correct size.
For example, since `r0' refers to a 16-bit register,
mov r0,@foo
is equivalent to
mov.w r0,@foo
If you use the size suffixes, `as' issues a warning when the suffix
and the register size do not match.
File: as.info, Node: H8/500-Dependent, Next: HPPA-Dependent, Prev: H8/300-Dependent, Up: Machine Dependencies
8.9 H8/500 Dependent Features
=============================
* Menu:
* H8/500 Options:: Options
* H8/500 Syntax:: Syntax
* H8/500 Floating Point:: Floating Point
* H8/500 Directives:: H8/500 Machine Directives
* H8/500 Opcodes:: Opcodes
File: as.info, Node: H8/500 Options, Next: H8/500 Syntax, Up: H8/500-Dependent
8.9.1 Options
-------------
`as' has no additional command-line options for the Renesas (formerly
Hitachi) H8/500 family.
File: as.info, Node: H8/500 Syntax, Next: H8/500 Floating Point, Prev: H8/500 Options, Up: H8/500-Dependent
8.9.2 Syntax
------------
* Menu:
* H8/500-Chars:: Special Characters
* H8/500-Regs:: Register Names
* H8/500-Addressing:: Addressing Modes
File: as.info, Node: H8/500-Chars, Next: H8/500-Regs, Up: H8/500 Syntax
8.9.2.1 Special Characters
..........................
`!' is the line comment character.
`;' can be used instead of a newline to separate statements.
Since `$' has no special meaning, you may use it in symbol names.
File: as.info, Node: H8/500-Regs, Next: H8/500-Addressing, Prev: H8/500-Chars, Up: H8/500 Syntax
8.9.2.2 Register Names
......................
You can use the predefined symbols `r0', `r1', `r2', `r3', `r4', `r5',
`r6', and `r7' to refer to the H8/500 registers.
The H8/500 also has these control registers:
`cp'
code pointer
`dp'
data pointer
`bp'
base pointer
`tp'
stack top pointer
`ep'
extra pointer
`sr'
status register
`ccr'
condition code register
All registers are 16 bits long. To represent 32 bit numbers, use two
adjacent registers; for distant memory addresses, use one of the segment
pointers (`cp' for the program counter; `dp' for `r0'-`r3'; `ep' for
`r4' and `r5'; and `tp' for `r6' and `r7'.
File: as.info, Node: H8/500-Addressing, Prev: H8/500-Regs, Up: H8/500 Syntax
8.9.2.3 Addressing Modes
........................
as understands the following addressing modes for the H8/500:
`RN'
Register direct
`@RN'
Register indirect
`@(d:8, RN)'
Register indirect with 8 bit signed displacement
`@(d:16, RN)'
Register indirect with 16 bit signed displacement
`@-RN'
Register indirect with pre-decrement
`@RN+'
Register indirect with post-increment
`@AA:8'
8 bit absolute address
`@AA:16'
16 bit absolute address
`#XX:8'
8 bit immediate
`#XX:16'
16 bit immediate
File: as.info, Node: H8/500 Floating Point, Next: H8/500 Directives, Prev: H8/500 Syntax, Up: H8/500-Dependent
8.9.3 Floating Point
--------------------
The H8/500 family has no hardware floating point, but the `.float'
directive generates IEEE floating-point numbers for compatibility with
other development tools.
File: as.info, Node: H8/500 Directives, Next: H8/500 Opcodes, Prev: H8/500 Floating Point, Up: H8/500-Dependent
8.9.4 H8/500 Machine Directives
-------------------------------
`as' has no machine-dependent directives for the H8/500. However, on
this platform the `.int' and `.word' directives generate 16-bit numbers.
File: as.info, Node: H8/500 Opcodes, Prev: H8/500 Directives, Up: H8/500-Dependent
8.9.5 Opcodes
-------------
For detailed information on the H8/500 machine instruction set, see
`H8/500 Series Programming Manual' (Renesas M21T001).
`as' implements all the standard H8/500 opcodes. No additional
pseudo-instructions are needed on this family.
The following table summarizes H8/500 opcodes and their operands:
Legend:
abs8 8-bit absolute address
abs16 16-bit absolute address
abs24 24-bit absolute address
crb `ccr', `br', `ep', `dp', `tp', `dp'
disp8 8-bit displacement
ea `rn', `@rn', `@(d:8, rn)', `@(d:16, rn)',
`@-rn', `@rn+', `@aa:8', `@aa:16',
`#xx:8', `#xx:16'
ea_mem `@rn', `@(d:8, rn)', `@(d:16, rn)',
`@-rn', `@rn+', `@aa:8', `@aa:16'
ea_noimm `rn', `@rn', `@(d:8, rn)', `@(d:16, rn)',
`@-rn', `@rn+', `@aa:8', `@aa:16'
fp r6
imm4 4-bit immediate data
imm8 8-bit immediate data
imm16 16-bit immediate data
pcrel8 8-bit offset from program counter
pcrel16 16-bit offset from program counter
qim `-2', `-1', `1', `2'
rd any register
rs a register distinct from rd
rlist comma-separated list of registers in parentheses;
register ranges `rd-rs' are allowed
sp stack pointer (`r7')
sr status register
sz size; `.b' or `.w'. If omitted, default `.w'
ldc[.b] ea,crb bcc[.w] pcrel16
ldc[.w] ea,sr bcc[.b] pcrel8
add[:q] sz qim,ea_noimm bhs[.w] pcrel16
add[:g] sz ea,rd bhs[.b] pcrel8
adds sz ea,rd bcs[.w] pcrel16
addx sz ea,rd bcs[.b] pcrel8
and sz ea,rd blo[.w] pcrel16
andc[.b] imm8,crb blo[.b] pcrel8
andc[.w] imm16,sr bne[.w] pcrel16
bpt bne[.b] pcrel8
bra[.w] pcrel16 beq[.w] pcrel16
bra[.b] pcrel8 beq[.b] pcrel8
bt[.w] pcrel16 bvc[.w] pcrel16
bt[.b] pcrel8 bvc[.b] pcrel8
brn[.w] pcrel16 bvs[.w] pcrel16
brn[.b] pcrel8 bvs[.b] pcrel8
bf[.w] pcrel16 bpl[.w] pcrel16
bf[.b] pcrel8 bpl[.b] pcrel8
bhi[.w] pcrel16 bmi[.w] pcrel16
bhi[.b] pcrel8 bmi[.b] pcrel8
bls[.w] pcrel16 bge[.w] pcrel16
bls[.b] pcrel8 bge[.b] pcrel8
blt[.w] pcrel16 mov[:g][.b] imm8,ea_mem
blt[.b] pcrel8 mov[:g][.w] imm16,ea_mem
bgt[.w] pcrel16 movfpe[.b] ea,rd
bgt[.b] pcrel8 movtpe[.b] rs,ea_noimm
ble[.w] pcrel16 mulxu sz ea,rd
ble[.b] pcrel8 neg sz ea
bclr sz imm4,ea_noimm nop
bclr sz rs,ea_noimm not sz ea
bnot sz imm4,ea_noimm or sz ea,rd
bnot sz rs,ea_noimm orc[.b] imm8,crb
bset sz imm4,ea_noimm orc[.w] imm16,sr
bset sz rs,ea_noimm pjmp abs24
bsr[.b] pcrel8 pjmp @rd
bsr[.w] pcrel16 pjsr abs24
btst sz imm4,ea_noimm pjsr @rd
btst sz rs,ea_noimm prtd imm8
clr sz ea prtd imm16
cmp[:e][.b] imm8,rd prts
cmp[:i][.w] imm16,rd rotl sz ea
cmp[:g].b imm8,ea_noimm rotr sz ea
cmp[:g][.w] imm16,ea_noimm rotxl sz ea
Cmp[:g] sz ea,rd rotxr sz ea
dadd rs,rd rtd imm8
divxu sz ea,rd rtd imm16
dsub rs,rd rts
exts[.b] rd scb/f rs,pcrel8
extu[.b] rd scb/ne rs,pcrel8
jmp @rd scb/eq rs,pcrel8
jmp @(imm8,rd) shal sz ea
jmp @(imm16,rd) shar sz ea
jmp abs16 shll sz ea
jsr @rd shlr sz ea
jsr @(imm8,rd) sleep
jsr @(imm16,rd) stc[.b] crb,ea_noimm
jsr abs16 stc[.w] sr,ea_noimm
ldm @sp+,(rlist) stm (rlist),@-sp
link fp,imm8 sub sz ea,rd
link fp,imm16 subs sz ea,rd
mov[:e][.b] imm8,rd subx sz ea,rd
mov[:i][.w] imm16,rd swap[.b] rd
mov[:l][.w] abs8,rd tas[.b] ea
mov[:l].b abs8,rd trapa imm4
mov[:s][.w] rs,abs8 trap/vs
mov[:s].b rs,abs8 tst sz ea
mov[:f][.w] @(disp8,fp),rd unlk fp
mov[:f][.w] rs,@(disp8,fp) xch[.w] rs,rd
mov[:f].b @(disp8,fp),rd xor sz ea,rd
mov[:f].b rs,@(disp8,fp) xorc.b imm8,crb
mov[:g] sz rs,ea_mem xorc.w imm16,sr
mov[:g] sz ea,rd
File: as.info, Node: HPPA-Dependent, Next: ESA/390-Dependent, Prev: H8/500-Dependent, Up: Machine Dependencies
8.10 HPPA Dependent Features
============================
* Menu:
* HPPA Notes:: Notes
* HPPA Options:: Options
* HPPA Syntax:: Syntax
* HPPA Floating Point:: Floating Point
* HPPA Directives:: HPPA Machine Directives
* HPPA Opcodes:: Opcodes
File: as.info, Node: HPPA Notes, Next: HPPA Options, Up: HPPA-Dependent
8.10.1 Notes
------------
As a back end for GNU CC `as' has been throughly tested and should work
extremely well. We have tested it only minimally on hand written
assembly code and no one has tested it much on the assembly output from
the HP compilers.
The format of the debugging sections has changed since the original
`as' port (version 1.3X) was released; therefore, you must rebuild all
HPPA objects and libraries with the new assembler so that you can debug
the final executable.
The HPPA `as' port generates a small subset of the relocations
available in the SOM and ELF object file formats. Additional relocation
support will be added as it becomes necessary.
File: as.info, Node: HPPA Options, Next: HPPA Syntax, Prev: HPPA Notes, Up: HPPA-Dependent
8.10.2 Options
--------------
`as' has no machine-dependent command-line options for the HPPA.
File: as.info, Node: HPPA Syntax, Next: HPPA Floating Point, Prev: HPPA Options, Up: HPPA-Dependent
8.10.3 Syntax
-------------
The assembler syntax closely follows the HPPA instruction set reference
manual; assembler directives and general syntax closely follow the HPPA
assembly language reference manual, with a few noteworthy differences.
First, a colon may immediately follow a label definition. This is
simply for compatibility with how most assembly language programmers
write code.
Some obscure expression parsing problems may affect hand written
code which uses the `spop' instructions, or code which makes significant
use of the `!' line separator.
`as' is much less forgiving about missing arguments and other
similar oversights than the HP assembler. `as' notifies you of missing
arguments as syntax errors; this is regarded as a feature, not a bug.
Finally, `as' allows you to use an external symbol without
explicitly importing the symbol. _Warning:_ in the future this will be
an error for HPPA targets.
Special characters for HPPA targets include:
`;' is the line comment character.
`!' can be used instead of a newline to separate statements.
Since `$' has no special meaning, you may use it in symbol names.
File: as.info, Node: HPPA Floating Point, Next: HPPA Directives, Prev: HPPA Syntax, Up: HPPA-Dependent
8.10.4 Floating Point
---------------------
The HPPA family uses IEEE floating-point numbers.
File: as.info, Node: HPPA Directives, Next: HPPA Opcodes, Prev: HPPA Floating Point, Up: HPPA-Dependent
8.10.5 HPPA Assembler Directives
--------------------------------
`as' for the HPPA supports many additional directives for compatibility
with the native assembler. This section describes them only briefly.
For detailed information on HPPA-specific assembler directives, see
`HP9000 Series 800 Assembly Language Reference Manual' (HP 92432-90001).
`as' does _not_ support the following assembler directives described
in the HP manual:
.endm .liston
.enter .locct
.leave .macro
.listoff
Beyond those implemented for compatibility, `as' supports one
additional assembler directive for the HPPA: `.param'. It conveys
register argument locations for static functions. Its syntax closely
follows the `.export' directive.
These are the additional directives in `as' for the HPPA:
`.block N'
`.blockz N'
Reserve N bytes of storage, and initialize them to zero.
`.call'
Mark the beginning of a procedure call. Only the special case
with _no arguments_ is allowed.
`.callinfo [ PARAM=VALUE, ... ] [ FLAG, ... ]'
Specify a number of parameters and flags that define the
environment for a procedure.
PARAM may be any of `frame' (frame size), `entry_gr' (end of
general register range), `entry_fr' (end of float register range),
`entry_sr' (end of space register range).
The values for FLAG are `calls' or `caller' (proc has
subroutines), `no_calls' (proc does not call subroutines),
`save_rp' (preserve return pointer), `save_sp' (proc preserves
stack pointer), `no_unwind' (do not unwind this proc), `hpux_int'
(proc is interrupt routine).
`.code'
Assemble into the standard section called `$TEXT$', subsection
`$CODE$'.
`.copyright "STRING"'
In the SOM object format, insert STRING into the object code,
marked as a copyright string.
`.copyright "STRING"'
In the ELF object format, insert STRING into the object code,
marked as a version string.
`.enter'
Not yet supported; the assembler rejects programs containing this
directive.
`.entry'
Mark the beginning of a procedure.
`.exit'
Mark the end of a procedure.
`.export NAME [ ,TYP ] [ ,PARAM=R ]'
Make a procedure NAME available to callers. TYP, if present, must
be one of `absolute', `code' (ELF only, not SOM), `data', `entry',
`data', `entry', `millicode', `plabel', `pri_prog', or `sec_prog'.
PARAM, if present, provides either relocation information for the
procedure arguments and result, or a privilege level. PARAM may be
`argwN' (where N ranges from `0' to `3', and indicates one of four
one-word arguments); `rtnval' (the procedure's result); or
`priv_lev' (privilege level). For arguments or the result, R
specifies how to relocate, and must be one of `no' (not
relocatable), `gr' (argument is in general register), `fr' (in
floating point register), or `fu' (upper half of float register).
For `priv_lev', R is an integer.
`.half N'
Define a two-byte integer constant N; synonym for the portable
`as' directive `.short'.
`.import NAME [ ,TYP ]'
Converse of `.export'; make a procedure available to call. The
arguments use the same conventions as the first two arguments for
`.export'.
`.label NAME'
Define NAME as a label for the current assembly location.
`.leave'
Not yet supported; the assembler rejects programs containing this
directive.
`.origin LC'
Advance location counter to LC. Synonym for the `as' portable
directive `.org'.
`.param NAME [ ,TYP ] [ ,PARAM=R ]'
Similar to `.export', but used for static procedures.
`.proc'
Use preceding the first statement of a procedure.
`.procend'
Use following the last statement of a procedure.
`LABEL .reg EXPR'
Synonym for `.equ'; define LABEL with the absolute expression EXPR
as its value.
`.space SECNAME [ ,PARAMS ]'
Switch to section SECNAME, creating a new section by that name if
necessary. You may only use PARAMS when creating a new section,
not when switching to an existing one. SECNAME may identify a
section by number rather than by name.
If specified, the list PARAMS declares attributes of the section,
identified by keywords. The keywords recognized are `spnum=EXP'
(identify this section by the number EXP, an absolute expression),
`sort=EXP' (order sections according to this sort key when linking;
EXP is an absolute expression), `unloadable' (section contains no
loadable data), `notdefined' (this section defined elsewhere), and
`private' (data in this section not available to other programs).
`.spnum SECNAM'
Allocate four bytes of storage, and initialize them with the
section number of the section named SECNAM. (You can define the
section number with the HPPA `.space' directive.)
`.string "STR"'
Copy the characters in the string STR to the object file. *Note
Strings: Strings, for information on escape sequences you can use
in `as' strings.
_Warning!_ The HPPA version of `.string' differs from the usual
`as' definition: it does _not_ write a zero byte after copying STR.
`.stringz "STR"'
Like `.string', but appends a zero byte after copying STR to object
file.
`.subspa NAME [ ,PARAMS ]'
`.nsubspa NAME [ ,PARAMS ]'
Similar to `.space', but selects a subsection NAME within the
current section. You may only specify PARAMS when you create a
subsection (in the first instance of `.subspa' for this NAME).
If specified, the list PARAMS declares attributes of the
subsection, identified by keywords. The keywords recognized are
`quad=EXPR' ("quadrant" for this subsection), `align=EXPR'
(alignment for beginning of this subsection; a power of two),
`access=EXPR' (value for "access rights" field), `sort=EXPR'
(sorting order for this subspace in link), `code_only' (subsection
contains only code), `unloadable' (subsection cannot be loaded
into memory), `comdat' (subsection is comdat), `common'
(subsection is common block), `dup_comm' (subsection may have
duplicate names), or `zero' (subsection is all zeros, do not write
in object file).
`.nsubspa' always creates a new subspace with the given name, even
if one with the same name already exists.
`comdat', `common' and `dup_comm' can be used to implement various
flavors of one-only support when using the SOM linker. The SOM
linker only supports specific combinations of these flags. The
details are not documented. A brief description is provided here.
`comdat' provides a form of linkonce support. It is useful for
both code and data subspaces. A `comdat' subspace has a key symbol
marked by the `is_comdat' flag or `ST_COMDAT'. Only the first
subspace for any given key is selected. The key symbol becomes
universal in shared links. This is similar to the behavior of
`secondary_def' symbols.
`common' provides Fortran named common support. It is only useful
for data subspaces. Symbols with the flag `is_common' retain this
flag in shared links. Referencing a `is_common' symbol in a shared
library from outside the library doesn't work. Thus, `is_common'
symbols must be output whenever they are needed.
`common' and `dup_comm' together provide Cobol common support.
The subspaces in this case must all be the same length.
Otherwise, this support is similar to the Fortran common support.
`dup_comm' by itself provides a type of one-only support for code.
Only the first `dup_comm' subspace is selected. There is a rather
complex algorithm to compare subspaces. Code symbols marked with
the `dup_common' flag are hidden. This support was intended for
"C++ duplicate inlines".
A simplified technique is used to mark the flags of symbols based
on the flags of their subspace. A symbol with the scope
SS_UNIVERSAL and type ST_ENTRY, ST_CODE or ST_DATA is marked with
the corresponding settings of `comdat', `common' and `dup_comm'
from the subspace, respectively. This avoids having to introduce
additional directives to mark these symbols. The HP assembler
sets `is_common' from `common'. However, it doesn't set the
`dup_common' from `dup_comm'. It doesn't have `comdat' support.
`.version "STR"'
Write STR as version identifier in object code.
File: as.info, Node: HPPA Opcodes, Prev: HPPA Directives, Up: HPPA-Dependent
8.10.6 Opcodes
--------------
For detailed information on the HPPA machine instruction set, see
`PA-RISC Architecture and Instruction Set Reference Manual' (HP
09740-90039).
File: as.info, Node: ESA/390-Dependent, Next: i386-Dependent, Prev: HPPA-Dependent, Up: Machine Dependencies
8.11 ESA/390 Dependent Features
===============================
* Menu:
* ESA/390 Notes:: Notes
* ESA/390 Options:: Options
* ESA/390 Syntax:: Syntax
* ESA/390 Floating Point:: Floating Point
* ESA/390 Directives:: ESA/390 Machine Directives
* ESA/390 Opcodes:: Opcodes
File: as.info, Node: ESA/390 Notes, Next: ESA/390 Options, Up: ESA/390-Dependent
8.11.1 Notes
------------
The ESA/390 `as' port is currently intended to be a back-end for the
GNU CC compiler. It is not HLASM compatible, although it does support
a subset of some of the HLASM directives. The only supported binary
file format is ELF; none of the usual MVS/VM/OE/USS object file
formats, such as ESD or XSD, are supported.
When used with the GNU CC compiler, the ESA/390 `as' will produce
correct, fully relocated, functional binaries, and has been used to
compile and execute large projects. However, many aspects should still
be considered experimental; these include shared library support,
dynamically loadable objects, and any relocation other than the 31-bit
relocation.
File: as.info, Node: ESA/390 Options, Next: ESA/390 Syntax, Prev: ESA/390 Notes, Up: ESA/390-Dependent
8.11.2 Options
--------------
`as' has no machine-dependent command-line options for the ESA/390.
File: as.info, Node: ESA/390 Syntax, Next: ESA/390 Floating Point, Prev: ESA/390 Options, Up: ESA/390-Dependent
8.11.3 Syntax
-------------
The opcode/operand syntax follows the ESA/390 Principles of Operation
manual; assembler directives and general syntax are loosely based on the
prevailing AT&T/SVR4/ELF/Solaris style notation. HLASM-style directives
are _not_ supported for the most part, with the exception of those
described herein.
A leading dot in front of directives is optional, and the case of
directives is ignored; thus for example, .using and USING have the same
effect.
A colon may immediately follow a label definition. This is simply
for compatibility with how most assembly language programmers write
code.
`#' is the line comment character.
`;' can be used instead of a newline to separate statements.
Since `$' has no special meaning, you may use it in symbol names.
Registers can be given the symbolic names r0..r15, fp0, fp2, fp4,
fp6. By using thesse symbolic names, `as' can detect simple syntax
errors. The name rarg or r.arg is a synonym for r11, rtca or r.tca for
r12, sp, r.sp, dsa r.dsa for r13, lr or r.lr for r14, rbase or r.base
for r3 and rpgt or r.pgt for r4.
`*' is the current location counter. Unlike `.' it is always
relative to the last USING directive. Note that this means that
expressions cannot use multiplication, as any occurrence of `*' will be
interpreted as a location counter.
All labels are relative to the last USING. Thus, branches to a label
always imply the use of base+displacement.
Many of the usual forms of address constants / address literals are
supported. Thus,
.using *,r3
L r15,=A(some_routine)
LM r6,r7,=V(some_longlong_extern)
A r1,=F'12'
AH r0,=H'42'
ME r6,=E'3.1416'
MD r6,=D'3.14159265358979'
O r6,=XL4'cacad0d0'
.ltorg
should all behave as expected: that is, an entry in the literal pool
will be created (or reused if it already exists), and the instruction
operands will be the displacement into the literal pool using the
current base register (as last declared with the `.using' directive).
File: as.info, Node: ESA/390 Floating Point, Next: ESA/390 Directives, Prev: ESA/390 Syntax, Up: ESA/390-Dependent
8.11.4 Floating Point
---------------------
The assembler generates only IEEE floating-point numbers. The older
floating point formats are not supported.
File: as.info, Node: ESA/390 Directives, Next: ESA/390 Opcodes, Prev: ESA/390 Floating Point, Up: ESA/390-Dependent
8.11.5 ESA/390 Assembler Directives
-----------------------------------
`as' for the ESA/390 supports all of the standard ELF/SVR4 assembler
directives that are documented in the main part of this documentation.
Several additional directives are supported in order to implement the
ESA/390 addressing model. The most important of these are `.using' and
`.ltorg'
These are the additional directives in `as' for the ESA/390:
`.dc'
A small subset of the usual DC directive is supported.
`.drop REGNO'
Stop using REGNO as the base register. The REGNO must have been
previously declared with a `.using' directive in the same section
as the current section.
`.ebcdic STRING'
Emit the EBCDIC equivalent of the indicated string. The emitted
string will be null terminated. Note that the directives
`.string' etc. emit ascii strings by default.
`EQU'
The standard HLASM-style EQU directive is not supported; however,
the standard `as' directive .equ can be used to the same effect.
`.ltorg'
Dump the literal pool accumulated so far; begin a new literal pool.
The literal pool will be written in the current section; in order
to generate correct assembly, a `.using' must have been previously
specified in the same section.
`.using EXPR,REGNO'
Use REGNO as the base register for all subsequent RX, RS, and SS
form instructions. The EXPR will be evaluated to obtain the base
address; usually, EXPR will merely be `*'.
This assembler allows two `.using' directives to be simultaneously
outstanding, one in the `.text' section, and one in another section
(typically, the `.data' section). This feature allows dynamically
loaded objects to be implemented in a relatively straightforward
way. A `.using' directive must always be specified in the `.text'
section; this will specify the base register that will be used for
branches in the `.text' section. A second `.using' may be
specified in another section; this will specify the base register
that is used for non-label address literals. When a second
`.using' is specified, then the subsequent `.ltorg' must be put in
the same section; otherwise an error will result.
Thus, for example, the following code uses `r3' to address branch
targets and `r4' to address the literal pool, which has been
written to the `.data' section. The is, the constants
`=A(some_routine)', `=H'42'' and `=E'3.1416'' will all appear in
the `.data' section.
.data
.using LITPOOL,r4
.text
BASR r3,0
.using *,r3
B START
.long LITPOOL
START:
L r4,4(,r3)
L r15,=A(some_routine)
LTR r15,r15
BNE LABEL
AH r0,=H'42'
LABEL:
ME r6,=E'3.1416'
.data
LITPOOL:
.ltorg
Note that this dual-`.using' directive semantics extends and is
not compatible with HLASM semantics. Note that this assembler
directive does not support the full range of HLASM semantics.
File: as.info, Node: ESA/390 Opcodes, Prev: ESA/390 Directives, Up: ESA/390-Dependent
8.11.6 Opcodes
--------------
For detailed information on the ESA/390 machine instruction set, see
`ESA/390 Principles of Operation' (IBM Publication Number DZ9AR004).
File: as.info, Node: i386-Dependent, Next: i860-Dependent, Prev: ESA/390-Dependent, Up: Machine Dependencies
8.12 80386 Dependent Features
=============================
The i386 version `as' supports both the original Intel 386
architecture in both 16 and 32-bit mode as well as AMD x86-64
architecture extending the Intel architecture to 64-bits.
* Menu:
* i386-Options:: Options
* i386-Syntax:: AT&T Syntax versus Intel Syntax
* i386-Mnemonics:: Instruction Naming
* i386-Regs:: Register Naming
* i386-Prefixes:: Instruction Prefixes
* i386-Memory:: Memory References
* i386-Jumps:: Handling of Jump Instructions
* i386-Float:: Floating Point
* i386-SIMD:: Intel's MMX and AMD's 3DNow! SIMD Operations
* i386-16bit:: Writing 16-bit Code
* i386-Arch:: Specifying an x86 CPU architecture
* i386-Bugs:: AT&T Syntax bugs
* i386-Notes:: Notes
File: as.info, Node: i386-Options, Next: i386-Syntax, Up: i386-Dependent
8.12.1 Options
--------------
The i386 version of `as' has a few machine dependent options:
`--32 | --64'
Select the word size, either 32 bits or 64 bits. Selecting 32-bit
implies Intel i386 architecture, while 64-bit implies AMD x86-64
architecture.
These options are only available with the ELF object file format,
and require that the necessary BFD support has been included (on a
32-bit platform you have to add -enable-64-bit-bfd to configure
enable 64-bit usage and use x86-64 as target platform).
`-n'
By default, x86 GAS replaces multiple nop instructions used for
alignment within code sections with multi-byte nop instructions
such as leal 0(%esi,1),%esi. This switch disables the
optimization.
File: as.info, Node: i386-Syntax, Next: i386-Mnemonics, Prev: i386-Options, Up: i386-Dependent
8.12.2 AT&T Syntax versus Intel Syntax
--------------------------------------
`as' now supports assembly using Intel assembler syntax.
`.intel_syntax' selects Intel mode, and `.att_syntax' switches back to
the usual AT&T mode for compatibility with the output of `gcc'. Either
of these directives may have an optional argument, `prefix', or
`noprefix' specifying whether registers require a `%' prefix. AT&T
System V/386 assembler syntax is quite different from Intel syntax. We
mention these differences because almost all 80386 documents use Intel
syntax. Notable differences between the two syntaxes are:
* AT&T immediate operands are preceded by `$'; Intel immediate
operands are undelimited (Intel `push 4' is AT&T `pushl $4').
AT&T register operands are preceded by `%'; Intel register operands
are undelimited. AT&T absolute (as opposed to PC relative)
jump/call operands are prefixed by `*'; they are undelimited in
Intel syntax.
* AT&T and Intel syntax use the opposite order for source and
destination operands. Intel `add eax, 4' is `addl $4, %eax'. The
`source, dest' convention is maintained for compatibility with
previous Unix assemblers. Note that instructions with more than
one source operand, such as the `enter' instruction, do _not_ have
reversed order. *Note i386-Bugs::.
* In AT&T syntax the size of memory operands is determined from the
last character of the instruction mnemonic. Mnemonic suffixes of
`b', `w', `l' and `q' specify byte (8-bit), word (16-bit), long
(32-bit) and quadruple word (64-bit) memory references. Intel
syntax accomplishes this by prefixing memory operands (_not_ the
instruction mnemonics) with `byte ptr', `word ptr', `dword ptr'
and `qword ptr'. Thus, Intel `mov al, byte ptr FOO' is `movb FOO,
%al' in AT&T syntax.
* Immediate form long jumps and calls are `lcall/ljmp $SECTION,
$OFFSET' in AT&T syntax; the Intel syntax is `call/jmp far
SECTION:OFFSET'. Also, the far return instruction is `lret
$STACK-ADJUST' in AT&T syntax; Intel syntax is `ret far
STACK-ADJUST'.
* The AT&T assembler does not provide support for multiple section
programs. Unix style systems expect all programs to be single
sections.
File: as.info, Node: i386-Mnemonics, Next: i386-Regs, Prev: i386-Syntax, Up: i386-Dependent
8.12.3 Instruction Naming
-------------------------
Instruction mnemonics are suffixed with one character modifiers which
specify the size of operands. The letters `b', `w', `l' and `q'
specify byte, word, long and quadruple word operands. If no suffix is
specified by an instruction then `as' tries to fill in the missing
suffix based on the destination register operand (the last one by
convention). Thus, `mov %ax, %bx' is equivalent to `movw %ax, %bx';
also, `mov $1, %bx' is equivalent to `movw $1, bx'. Note that this is
incompatible with the AT&T Unix assembler which assumes that a missing
mnemonic suffix implies long operand size. (This incompatibility does
not affect compiler output since compilers always explicitly specify
the mnemonic suffix.)
Almost all instructions have the same names in AT&T and Intel format.
There are a few exceptions. The sign extend and zero extend
instructions need two sizes to specify them. They need a size to
sign/zero extend _from_ and a size to zero extend _to_. This is
accomplished by using two instruction mnemonic suffixes in AT&T syntax.
Base names for sign extend and zero extend are `movs...' and `movz...'
in AT&T syntax (`movsx' and `movzx' in Intel syntax). The instruction
mnemonic suffixes are tacked on to this base name, the _from_ suffix
before the _to_ suffix. Thus, `movsbl %al, %edx' is AT&T syntax for
"move sign extend _from_ %al _to_ %edx." Possible suffixes, thus, are
`bl' (from byte to long), `bw' (from byte to word), `wl' (from word to
long), `bq' (from byte to quadruple word), `wq' (from word to quadruple
word), and `lq' (from long to quadruple word).
The Intel-syntax conversion instructions
* `cbw' -- sign-extend byte in `%al' to word in `%ax',
* `cwde' -- sign-extend word in `%ax' to long in `%eax',
* `cwd' -- sign-extend word in `%ax' to long in `%dx:%ax',
* `cdq' -- sign-extend dword in `%eax' to quad in `%edx:%eax',
* `cdqe' -- sign-extend dword in `%eax' to quad in `%rax' (x86-64
only),
* `cqo' -- sign-extend quad in `%rax' to octuple in `%rdx:%rax'
(x86-64 only),
are called `cbtw', `cwtl', `cwtd', `cltd', `cltq', and `cqto' in AT&T
naming. `as' accepts either naming for these instructions.
Far call/jump instructions are `lcall' and `ljmp' in AT&T syntax,
but are `call far' and `jump far' in Intel convention.
File: as.info, Node: i386-Regs, Next: i386-Prefixes, Prev: i386-Mnemonics, Up: i386-Dependent
8.12.4 Register Naming
----------------------
Register operands are always prefixed with `%'. The 80386 registers
consist of
* the 8 32-bit registers `%eax' (the accumulator), `%ebx', `%ecx',
`%edx', `%edi', `%esi', `%ebp' (the frame pointer), and `%esp'
(the stack pointer).
* the 8 16-bit low-ends of these: `%ax', `%bx', `%cx', `%dx', `%di',
`%si', `%bp', and `%sp'.
* the 8 8-bit registers: `%ah', `%al', `%bh', `%bl', `%ch', `%cl',
`%dh', and `%dl' (These are the high-bytes and low-bytes of `%ax',
`%bx', `%cx', and `%dx')
* the 6 section registers `%cs' (code section), `%ds' (data
section), `%ss' (stack section), `%es', `%fs', and `%gs'.
* the 3 processor control registers `%cr0', `%cr2', and `%cr3'.
* the 6 debug registers `%db0', `%db1', `%db2', `%db3', `%db6', and
`%db7'.
* the 2 test registers `%tr6' and `%tr7'.
* the 8 floating point register stack `%st' or equivalently
`%st(0)', `%st(1)', `%st(2)', `%st(3)', `%st(4)', `%st(5)',
`%st(6)', and `%st(7)'. These registers are overloaded by 8 MMX
registers `%mm0', `%mm1', `%mm2', `%mm3', `%mm4', `%mm5', `%mm6'
and `%mm7'.
* the 8 SSE registers registers `%xmm0', `%xmm1', `%xmm2', `%xmm3',
`%xmm4', `%xmm5', `%xmm6' and `%xmm7'.
The AMD x86-64 architecture extends the register set by:
* enhancing the 8 32-bit registers to 64-bit: `%rax' (the
accumulator), `%rbx', `%rcx', `%rdx', `%rdi', `%rsi', `%rbp' (the
frame pointer), `%rsp' (the stack pointer)
* the 8 extended registers `%r8'-`%r15'.
* the 8 32-bit low ends of the extended registers: `%r8d'-`%r15d'
* the 8 16-bit low ends of the extended registers: `%r8w'-`%r15w'
* the 8 8-bit low ends of the extended registers: `%r8b'-`%r15b'
* the 4 8-bit registers: `%sil', `%dil', `%bpl', `%spl'.
* the 8 debug registers: `%db8'-`%db15'.
* the 8 SSE registers: `%xmm8'-`%xmm15'.
File: as.info, Node: i386-Prefixes, Next: i386-Memory, Prev: i386-Regs, Up: i386-Dependent
8.12.5 Instruction Prefixes
---------------------------
Instruction prefixes are used to modify the following instruction. They
are used to repeat string instructions, to provide section overrides, to
perform bus lock operations, and to change operand and address sizes.
(Most instructions that normally operate on 32-bit operands will use
16-bit operands if the instruction has an "operand size" prefix.)
Instruction prefixes are best written on the same line as the
instruction they act upon. For example, the `scas' (scan string)
instruction is repeated with:
repne scas %es:(%edi),%al
You may also place prefixes on the lines immediately preceding the
instruction, but this circumvents checks that `as' does with prefixes,
and will not work with all prefixes.
Here is a list of instruction prefixes:
* Section override prefixes `cs', `ds', `ss', `es', `fs', `gs'.
These are automatically added by specifying using the
SECTION:MEMORY-OPERAND form for memory references.
* Operand/Address size prefixes `data16' and `addr16' change 32-bit
operands/addresses into 16-bit operands/addresses, while `data32'
and `addr32' change 16-bit ones (in a `.code16' section) into
32-bit operands/addresses. These prefixes _must_ appear on the
same line of code as the instruction they modify. For example, in
a 16-bit `.code16' section, you might write:
addr32 jmpl *(%ebx)
* The bus lock prefix `lock' inhibits interrupts during execution of
the instruction it precedes. (This is only valid with certain
instructions; see a 80386 manual for details).
* The wait for coprocessor prefix `wait' waits for the coprocessor to
complete the current instruction. This should never be needed for
the 80386/80387 combination.
* The `rep', `repe', and `repne' prefixes are added to string
instructions to make them repeat `%ecx' times (`%cx' times if the
current address size is 16-bits).
* The `rex' family of prefixes is used by x86-64 to encode
extensions to i386 instruction set. The `rex' prefix has four
bits -- an operand size overwrite (`64') used to change operand
size from 32-bit to 64-bit and X, Y and Z extensions bits used to
extend the register set.
You may write the `rex' prefixes directly. The `rex64xyz'
instruction emits `rex' prefix with all the bits set. By omitting
the `64', `x', `y' or `z' you may write other prefixes as well.
Normally, there is no need to write the prefixes explicitly, since
gas will automatically generate them based on the instruction
operands.
File: as.info, Node: i386-Memory, Next: i386-Jumps, Prev: i386-Prefixes, Up: i386-Dependent
8.12.6 Memory References
------------------------
An Intel syntax indirect memory reference of the form
SECTION:[BASE + INDEX*SCALE + DISP]
is translated into the AT&T syntax
SECTION:DISP(BASE, INDEX, SCALE)
where BASE and INDEX are the optional 32-bit base and index registers,
DISP is the optional displacement, and SCALE, taking the values 1, 2,
4, and 8, multiplies INDEX to calculate the address of the operand. If
no SCALE is specified, SCALE is taken to be 1. SECTION specifies the
optional section register for the memory operand, and may override the
default section register (see a 80386 manual for section register
defaults). Note that section overrides in AT&T syntax _must_ be
preceded by a `%'. If you specify a section override which coincides
with the default section register, `as' does _not_ output any section
register override prefixes to assemble the given instruction. Thus,
section overrides can be specified to emphasize which section register
is used for a given memory operand.
Here are some examples of Intel and AT&T style memory references:
AT&T: `-4(%ebp)', Intel: `[ebp - 4]'
BASE is `%ebp'; DISP is `-4'. SECTION is missing, and the default
section is used (`%ss' for addressing with `%ebp' as the base
register). INDEX, SCALE are both missing.
AT&T: `foo(,%eax,4)', Intel: `[foo + eax*4]'
INDEX is `%eax' (scaled by a SCALE 4); DISP is `foo'. All other
fields are missing. The section register here defaults to `%ds'.
AT&T: `foo(,1)'; Intel `[foo]'
This uses the value pointed to by `foo' as a memory operand. Note
that BASE and INDEX are both missing, but there is only _one_ `,'.
This is a syntactic exception.
AT&T: `%gs:foo'; Intel `gs:foo'
This selects the contents of the variable `foo' with section
register SECTION being `%gs'.
Absolute (as opposed to PC relative) call and jump operands must be
prefixed with `*'. If no `*' is specified, `as' always chooses PC
relative addressing for jump/call labels.
Any instruction that has a memory operand, but no register operand,
_must_ specify its size (byte, word, long, or quadruple) with an
instruction mnemonic suffix (`b', `w', `l' or `q', respectively).
The x86-64 architecture adds an RIP (instruction pointer relative)
addressing. This addressing mode is specified by using `rip' as a base
register. Only constant offsets are valid. For example:
AT&T: `1234(%rip)', Intel: `[rip + 1234]'
Points to the address 1234 bytes past the end of the current
instruction.
AT&T: `symbol(%rip)', Intel: `[rip + symbol]'
Points to the `symbol' in RIP relative way, this is shorter than
the default absolute addressing.
Other addressing modes remain unchanged in x86-64 architecture,
except registers used are 64-bit instead of 32-bit.
File: as.info, Node: i386-Jumps, Next: i386-Float, Prev: i386-Memory, Up: i386-Dependent
8.12.7 Handling of Jump Instructions
------------------------------------
Jump instructions are always optimized to use the smallest possible
displacements. This is accomplished by using byte (8-bit) displacement
jumps whenever the target is sufficiently close. If a byte displacement
is insufficient a long displacement is used. We do not support word
(16-bit) displacement jumps in 32-bit mode (i.e. prefixing the jump
instruction with the `data16' instruction prefix), since the 80386
insists upon masking `%eip' to 16 bits after the word displacement is
added. (See also *note i386-Arch::)
Note that the `jcxz', `jecxz', `loop', `loopz', `loope', `loopnz'
and `loopne' instructions only come in byte displacements, so that if
you use these instructions (`gcc' does not use them) you may get an
error message (and incorrect code). The AT&T 80386 assembler tries to
get around this problem by expanding `jcxz foo' to
jcxz cx_zero
jmp cx_nonzero
cx_zero: jmp foo
cx_nonzero: