.\" Automatically generated by Pod::Man v1.34, Pod::Parser v1.13 .\" .\" Standard preamble: .\" ======================================================================== .de Sh \" Subsection heading .br .if t .Sp .ne 5 .PP \fB\\$1\fR .PP .. .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. | will give a .\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used to .\" do unbreakable dashes and therefore won't be available. \*(C` and \*(C' .\" expand to `' in nroff, nothing in troff, for use with C<>. .tr \(*W-|\(bv\*(Tr .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} .el\{\ . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' 'br\} .\" .\" If the F register is turned on, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .if \nF \{\ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . nr % 0 . rr F .\} .\" .\" For nroff, turn off justification. 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No user-serviceable parts. . \" fudge factors for nroff and troff .if n \{\ . ds #H 0 . ds #V .8m . ds #F .3m . ds #[ \f1 . ds #] \fP .\} .if t \{\ . ds #H ((1u-(\\\\n(.fu%2u))*.13m) . ds #V .6m . ds #F 0 . ds #[ \& . ds #] \& .\} . \" simple accents for nroff and troff .if n \{\ . ds ' \& . ds ` \& . ds ^ \& . ds , \& . ds ~ ~ . ds / .\} .if t \{\ . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u" . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u' . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u' . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u' . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u' . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u' .\} . \" troff and (daisy-wheel) nroff accents .ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V' .ds 8 \h'\*(#H'\(*b\h'-\*(#H' .ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#] .ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H' .ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u' .ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#] .ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#] .ds ae a\h'-(\w'a'u*4/10)'e .ds Ae A\h'-(\w'A'u*4/10)'E . \" corrections for vroff .if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u' .if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u' . \" for low resolution devices (crt and lpr) .if \n(.H>23 .if \n(.V>19 \ \{\ . ds : e . ds 8 ss . ds o a . ds d- d\h'-1'\(ga . ds D- D\h'-1'\(hy . ds th \o'bp' . ds Th \o'LP' . ds ae ae . ds Ae AE .\} .rm #[ #] #H #V #F C .\" ======================================================================== .\" .IX Title "GCC 1" .TH GCC 1 "2003-05-22" "gcc-3.3" "GNU" .SH "NAME" gcc \- GNU project C and C++ compiler .SH "SYNOPSIS" .IX Header "SYNOPSIS" gcc [\fB\-c\fR|\fB\-S\fR|\fB\-E\fR] [\fB\-std=\fR\fIstandard\fR] [\fB\-g\fR] [\fB\-pg\fR] [\fB\-O\fR\fIlevel\fR] [\fB\-W\fR\fIwarn\fR...] [\fB\-pedantic\fR] [\fB\-I\fR\fIdir\fR...] [\fB\-L\fR\fIdir\fR...] [\fB\-D\fR\fImacro\fR[=\fIdefn\fR]...] [\fB\-U\fR\fImacro\fR] [\fB\-f\fR\fIoption\fR...] [\fB\-m\fR\fImachine-option\fR...] [\fB\-o\fR \fIoutfile\fR] \fIinfile\fR... .PP Only the most useful options are listed here; see below for the remainder. \fBg++\fR accepts mostly the same options as \fBgcc\fR. .PP In Apple's version of \s-1GCC\s0, both \fBcc\fR and \fBgcc\fR are actually symbolic links to \fBgcc3\fR, while \fBc++\fR and \fBg++\fR are links to \fBg++3\fR. .PP Note that Apple's \s-1GCC\s0 includes a number of extensions to standard \s-1GCC\s0 (flagged below with ``\s-1APPLE\s0 \s-1ONLY\s0''), and that not all generic \s-1GCC\s0 options are available or supported on Darwin / Mac \s-1OS\s0 X. In particular, Apple does not currently support the compilation of Fortran, Ada, or Java, although there are third parties who have made these work. .SH "DESCRIPTION" .IX Header "DESCRIPTION" When you invoke \s-1GCC\s0, it normally does preprocessing, compilation, assembly and linking. The ``overall options'' allow you to stop this process at an intermediate stage. For example, the \fB\-c\fR option says not to run the linker. Then the output consists of object files output by the assembler. .PP Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them. .PP Most of the command line options that you can use with \s-1GCC\s0 are useful for C programs; when an option is only useful with another language (usually \*(C+), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages. .PP The \fBgcc\fR program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may \fInot\fR be grouped: \fB\-dr\fR is very different from \fB\-d\ \-r\fR. .PP You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify \fB\-L\fR more than once, the directories are searched in the order specified. .PP Many options have long names starting with \fB\-f\fR or with \&\fB\-W\fR\-\-\-for example, \fB\-fforce\-mem\fR, \&\fB\-fstrength\-reduce\fR, \fB\-Wformat\fR and so on. Most of these have both positive and negative forms; the negative form of \&\fB\-ffoo\fR would be \fB\-fno\-foo\fR. This manual documents only one of these two forms, whichever one is not the default. .SH "OPTIONS" .IX Header "OPTIONS" .Sh "Option Summary" .IX Subsection "Option Summary" Here is a summary of all the options, grouped by type. Explanations are in the following sections. .IP "\fIOverall Options\fR" 4 .IX Item "Overall Options" \&\fB\-c \-S \-E \-o\fR \fIfile\fR \fB\-pipe \-pass\-exit\-codes \-x\fR \fIlanguage\fR \&\fB\-ObjC (\s-1APPLE\s0 \s-1ONLY\s0) \-ObjC++ (\s-1APPLE\s0 \s-1ONLY\s0) \&\-arch\fR \fIarch\fR \fB(\s-1APPLE\s0 \s-1ONLY\s0) \&\-v \-### \-\-help \-\-target\-help \-\-version\fR .IP "\fIC Language Options\fR" 4 .IX Item "C Language Options" \&\fB\-ansi \-std=\fR\fIstandard\fR \fB\-aux\-info\fR \fIfilename\fR \&\fB\-faltivec (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fasm\-blocks (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fno\-asm \-fno\-builtin \-fno\-builtin\-\fR\fIfunction\fR \&\fB\-fhosted \-ffreestanding \-fms\-extensions \&\-trigraphs \-no\-integrated\-cpp \-traditional \-traditional\-cpp \&\-fallow\-single\-precision \-fcond\-mismatch \&\-fconstant\-cfstrings (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fpch\-preprocess (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fsigned\-bitfields \-fsigned\-char \&\-funsigned\-bitfields \-funsigned\-char \&\-fpascal\-strings (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fcoalesce (\s-1APPLE\s0 \s-1ONLY\s0) \-fweak\-coalesced (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wno\-#warnings (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wextra\-tokens (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wpragma\-once (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wnewline\-eof (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wno\-altivec\-long\-deprecated (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fwritable\-strings\fR .IP "\fI\*(C+ Language Options\fR" 4 .IX Item " Language Options" \&\fB\-fabi\-version=\fR\fIn\fR \fB\-fno\-access\-control \-fcheck\-new \&\-fconserve\-space \-fno\-const\-strings \-fdollars\-in\-identifiers \&\-fno\-elide\-constructors \&\-fno\-enforce\-eh\-specs \-fexternal\-templates \&\-falt\-external\-templates \&\-ffor\-scope \-fno\-for\-scope \-fno\-gnu\-keywords \&\-fno\-implicit\-templates \&\-fno\-implicit\-inline\-templates \&\-fno\-implement\-inlines \&\-findirect\-virtual\-calls (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fapple\-kext (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fcoalesce\-templates (\s-1APPLE\s0 \s-1ONLY\s0) \&\-fms\-extensions \&\-fno\-nonansi\-builtins \-fno\-operator\-names \&\-fno\-optional\-diags \-fpermissive \&\-frepo \-fno\-rtti \-fstats \-ftemplate\-depth\-\fR\fIn\fR \&\fB\-fuse\-cxa\-atexit \-fvtable\-gc \-fno\-weak \-nostdinc++ \&\-fno\-default\-inline \-Wabi \-Wctor\-dtor\-privacy \&\-Wnon\-virtual\-dtor \-Wreorder \&\-Weffc++ \-Wno\-deprecated \&\-Wno\-non\-template\-friend \-Wold\-style\-cast \&\-Woverloaded\-virtual \-Wno\-pmf\-conversions \&\-Wsign\-promo \-Wsynth\fR .IP "\fIObjective-C Language Options\fR" 4 .IX Item "Objective-C Language Options" \&\fB\-fconstant\-string\-class=\fR\fIclass-name\fR \&\fB\-fgnu\-runtime \-fnext\-runtime \-gen\-decls \&\-Wno\-protocol \-Wselector \-Wundeclared\-selector\fR .IP "\fILanguage Independent Options\fR" 4 .IX Item "Language Independent Options" \&\fB\-fmessage\-length=\fR\fIn\fR \&\fB\-fdiagnostics\-show\-location=\fR[\fBonce\fR|\fBevery-line\fR] .IP "\fIWarning Options\fR" 4 .IX Item "Warning Options" \&\fB\-fsyntax\-only \-pedantic \-pedantic\-errors \&\-w \-W \-Wall \-Waggregate\-return \&\-Wcast\-align \-Wcast\-qual \-Wchar\-subscripts \-Wcomment \&\-Wconversion \-Wno\-deprecated\-declarations \&\-Wdisabled\-optimization \-Wno\-div\-by\-zero \-Werror \&\-Wfloat\-equal \-Wformat \-Wformat=2 \&\-Wformat\-nonliteral \-Wformat\-security \&\-Wimplicit \-Wimplicit\-int \&\-Wimplicit\-function\-declaration \&\-Werror\-implicit\-function\-declaration \&\-Wimport \-Winline \-Winvalid\-pch \-Wno\-endif\-labels \&\-Wno\-invalid\-offsetof (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wlarger\-than\-\fR\fIlen\fR \fB\-Wlong\-long \&\-Wno\-long\-double (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wmain \-Wmissing\-braces \&\-Wmissing\-format\-attribute \-Wmissing\-noreturn \&\-Wmost (\s-1APPLE\s0 \s-1ONLY\s0) \&\-Wno\-multichar \-Wno\-format\-extra\-args \-Wno\-format\-y2k \&\-Wno\-import \-Wnonnull \-Wpacked \-Wpadded \&\-Wparentheses \-Wpointer\-arith \-Wredundant\-decls \&\-Wreturn\-type \-Wsequence\-point \-Wshadow \&\-Wsign\-compare \-Wstrict\-aliasing \&\-Wswitch \-Wswitch\-default \-Wswitch\-enum \&\-Wsystem\-headers \-Wtrigraphs \-Wundef \-Wuninitialized \&\-Wunknown\-pragmas \-Wunreachable\-code \&\-Wunused \-Wunused\-function \-Wunused\-label \-Wunused\-parameter \&\-Wunused\-value \-Wunused\-variable \-Wwrite\-strings\fR .IP "\fIC\-only Warning Options\fR" 4 .IX Item "C-only Warning Options" \&\fB\-Wbad\-function\-cast \-Wmissing\-declarations \&\-Wmissing\-prototypes \-Wnested\-externs \&\-Wstrict\-prototypes \-Wtraditional\fR .IP "\fIDebugging Options\fR" 4 .IX Item "Debugging Options" \&\fB\-d\fR\fIletters\fR \fB\-dumpspecs \-dumpmachine \-dumpversion \&\-fdump\-unnumbered \-fdump\-translation\-unit\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-class\-hierarchy\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-original\fR[\fB\-\fR\fIn\fR] \fB\-fdump\-tree\-optimized\fR[\fB\-\fR\fIn\fR] \&\fB\-fdump\-tree\-inlined\fR[\fB\-\fR\fIn\fR] \&\fB\-feliminate\-dwarf2\-dups \-fmem\-report \&\-fprofile\-arcs \-fsched\-verbose=\fR\fIn\fR \&\fB\-ftest\-coverage \-ftime\-report \&\-g \-g\fR\fIlevel\fR \fB\-gcoff \-gdwarf \-gdwarf\-1 \-gdwarf\-1+ \-gdwarf\-2 \&\-ggdb \-gstabs \-gstabs+ \-gvms \-gxcoff \-gxcoff+ \&\-p \-pg \-print\-file\-name=\fR\fIlibrary\fR \fB\-print\-libgcc\-file\-name \&\-print\-multi\-directory \-print\-multi\-lib \&\-print\-prog\-name=\fR\fIprogram\fR \fB\-print\-search\-dirs \-Q \&\-save\-temps \-time \-fsave\-repository=\fR\fIlocation\fR \fB\-grepository\fR .IP "\fIOptimization Options\fR" 4 .IX Item "Optimization Options" \&\fB\-falign\-functions=\fR\fIn\fR \fB\-falign\-jumps=\fR\fIn\fR \&\fB\-falign\-labels=\fR\fIn\fR \fB\-falign\-loops=\fR\fIn\fR \&\fB\-falign\-loops\-max\-skip=\fR\fIn\fR \fB\-falign\-jumps\-max\-skip=\fR\fIn\fR \&\fB\-fbranch\-probabilities \-fcaller\-saves \-fcprop\-registers \&\-fcse\-follow\-jumps \-fcse\-skip\-blocks \-fdata\-sections \&\-fdelayed\-branch \-fdelete\-null\-pointer\-checks \&\-fexpensive\-optimizations \-ffast\-math \-ffloat\-store \&\-fforce\-addr \-fforce\-mem \-ffunction\-sections \&\-fgcse \-fgcse\-lm \-fgcse\-sm \-floop\-optimize \-fcrossjumping \&\-fif\-conversion \-fif\-conversion2 \&\-finline\-functions \-finline\-limit=\fR\fIn\fR \fB\-fkeep\-inline\-functions \&\-fkeep\-static\-consts \-fmerge\-constants \-fmerge\-all\-constants \&\-fmove\-all\-movables \-fnew\-ra \-fno\-branch\-count\-reg \&\-fno\-default\-inline \-fno\-defer\-pop \&\-fno\-function\-cse \-fno\-guess\-branch\-probability \&\-fno\-inline \-fno\-math\-errno \-fno\-peephole \-fno\-peephole2 \&\-funsafe\-math\-optimizations \-ffinite\-math\-only \&\-fno\-trapping\-math \-fno\-zero\-initialized\-in\-bss \&\-fomit\-frame\-pointer \-foptimize\-register\-move \&\-foptimize\-sibling\-calls \-fprefetch\-loop\-arrays \&\-freduce\-all\-givs \-fregmove \-frename\-registers \&\-freorder\-blocks \-freorder\-functions \&\-frerun\-cse\-after\-loop \-frerun\-loop\-opt \&\-fschedule\-insns \-fschedule\-insns2 \&\-fno\-sched\-interblock \-fno\-sched\-spec \-fsched\-spec\-load \&\-fsched\-spec\-load\-dangerous \-fsignaling\-nans \&\-fsingle\-precision\-constant \-fssa \-fssa\-ccp \-fssa\-dce \&\-fstrength\-reduce \-fstrict\-aliasing \-ftracer \-fthread\-jumps \&\-funroll\-all\-loops \-funroll\-loops \&\-\-param\fR \fIname\fR\fB=\fR\fIvalue\fR \&\fB\-O \-O0 \-O1 \-O2 \-O3 \-Os\fR .IP "\fIPreprocessor Options\fR" 4 .IX Item "Preprocessor Options" \&\fB\-$ \-A\fR\fIquestion\fR\fB=\fR\fIanswer\fR \fB\-A\-\fR\fIquestion\fR[\fB=\fR\fIanswer\fR] \&\fB\-C \-dD \-dI \-dM \-dN \&\-D\fR\fImacro\fR[\fB=\fR\fIdefn\fR] \fB\-E \-H \&\-idirafter\fR \fIdir\fR \&\fB\-include\fR \fIfile\fR \fB\-imacros\fR \fIfile\fR \&\fB\-iprefix\fR \fIfile\fR \fB\-iwithprefix\fR \fIdir\fR \&\fB\-iwithprefixbefore\fR \fIdir\fR \fB\-isystem\fR \fIdir\fR \&\fB\-M \-MM \-MF \-MG \-MP \-MQ \-MT \-nostdinc \-P \-remap \&\-dependency\-file (\s-1APPLE\s0 \s-1ONLY\s0) \&\-trigraphs \-undef \-U\fR\fImacro\fR \fB\-Wp,\fR\fIoption\fR .IP "\fIAssembler Option\fR" 4 .IX Item "Assembler Option" \&\fB\-Wa,\fR\fIoption\fR .IP "\fILinker Options\fR" 4 .IX Item "Linker Options" \&\fB \&\fR\fIobject-file-name\fR \fB\-l\fR\fIlibrary\fR \&\fB\-nostartfiles \-nodefaultlibs \-nostdlib \-no\-c++filt (\s-1APPLE\s0 \s-1ONLY\s0) \&\-s \-static \-static\-libgcc \-shared \-shared\-libgcc \-symbolic \&\-Wl,\fR\fIoption\fR \fB\-Xlinker\fR \fIoption\fR \&\fB\-u\fR \fIsymbol\fR .IP "\fIDirectory Options\fR" 4 .IX Item "Directory Options" \&\fB\-B\fR\fIprefix\fR \fB\-I\fR\fIdir\fR \fB\-I\- \&\-F\fR\fIdir\fR \fB(\s-1APPLE\s0 \s-1ONLY\s0) \&\-L\fR\fIdir\fR \fB\-specs=\fR\fIfile\fR .IP "\fITarget Options\fR" 4 .IX Item "Target Options" \&\fB\-V\fR \fIversion\fR \fB\-b\fR \fImachine\fR .IP "\fIMachine Dependent Options\fR" 4 .IX Item "Machine Dependent Options" \&\fI\s-1RS/6000\s0 and PowerPC Options\fR .Sp \&\fB\-mcpu=\fR\fIcpu-type\fR \&\fB\-mtune=\fR\fIcpu-type\fR \&\fB\-mpower \-mno\-power \-mpower2 \-mno\-power2 \&\-mpowerpc \-mpowerpc64 \-mno\-powerpc \&\-maltivec \-mno\-altivec \&\-mpowerpc\-gpopt \-mno\-powerpc\-gpopt \&\-mpowerpc\-gfxopt \-mno\-powerpc\-gfxopt \&\-mnew\-mnemonics \-mold\-mnemonics \&\-mfull\-toc \-mminimal\-toc \-mno\-fp\-in\-toc \-mno\-sum\-in\-toc \&\-m64 \-m32 \-mxl\-call \-mno\-xl\-call \-mpe \&\-malign\-mac68k (\s-1APPLE\s0 \s-1ONLY\s0) \&\-malign\-power (\s-1APPLE\s0 \s-1ONLY\s0) \&\-malign\-natural (\s-1APPLE\s0 \s-1ONLY\s0) \&\-msoft\-float \-mhard\-float \-mmultiple \-mno\-multiple \&\-mstring \-mno\-string \-mupdate \-mno\-update \&\-mfused\-madd \-mno\-fused\-madd \-mbit\-align \-mno\-bit\-align \&\-mstrict\-align \-mno\-strict\-align \-mrelocatable \&\-mno\-relocatable \-mrelocatable\-lib \-mno\-relocatable\-lib \&\-mtoc \-mno\-toc \-mlittle \-mlittle\-endian \-mbig \-mbig\-endian \&\-mdynamic\-no\-pic (\s-1APPLE\s0 \s-1ONLY\s0) \&\-mlong\-branch (\s-1APPLE\s0 \s-1ONLY\s0) \&\-mcall\-aix \-mcall\-sysv \-mcall\-netbsd \&\-maix\-struct\-return \-msvr4\-struct\-return \&\-mabi=altivec \-mabi=no\-altivec \&\-mabi=spe \-mabi=no\-spe \&\-misel=yes \-misel=no \&\-mprototype \-mno\-prototype \&\-msim \-mmvme \-mads \-myellowknife \-memb \-msdata \&\-msdata=\fR\fIopt\fR \fB\-mvxworks \-mwindiss \-G\fR \fInum\fR \fB\-pthread\fR .Sp \&\fIDarwin Options\fR .Sp \&\fB\-all_load \-allowable_client \-arch \-arch_errors_fatal \&\-arch_only \-bind_at_load \-bundle \-bundle_loader \&\-client_name \-compatibility_version \-current_version \&\-dependency\-file \-dylib_file \-dylinker_install_name \&\-dynamic \-dynamiclib \-exported_symbols_list \&\-filelist \-flat_namespace \-force_cpusubtype_ALL \&\-force_flat_namespace \-headerpad_max_install_names \&\-image_base \-init \-install_name \-keep_private_externs \&\-multi_module \-multiply_defined \-multiply_defined_unused \&\-noall_load \-nomultidefs \-noprebind \-noseglinkedit \&\-pagezero_size \-prebind \-prebind_all_twolevel_modules \&\-private_bundle \-read_only_relocs \-sectalign \&\-sectobjectsymbols \-whyload \-seg1addr \&\-sectcreate \-sectobjectsymbols \-sectorder \&\-seg_addr_table \-seg_addr_table_filename \-seglinkedit \&\-segprot \-segs_read_only_addr \-segs_read_write_addr \&\-single_module \-static \-sub_library \-sub_umbrella \&\-twolevel_namespace \-umbrella \-undefined \&\-unexported_symbols_list \-weak_reference_mismatches \-whatsloaded\fR .Sp \&\fIi386 and x86\-64 Options\fR .Sp \&\fB\-mcpu=\fR\fIcpu-type\fR \fB\-march=\fR\fIcpu-type\fR \fB\-mfpmath=\fR\fIunit\fR \&\fB\-masm=\fR\fIdialect\fR \fB\-mno\-fancy\-math\-387 \&\-mno\-fp\-ret\-in\-387 \-msoft\-float \-msvr3\-shlib \&\-mno\-wide\-multiply \-mrtd \-malign\-double \&\-mpreferred\-stack\-boundary=\fR\fInum\fR \&\fB\-mmmx \-msse \-msse2 \-m3dnow \&\-mthreads \-mno\-align\-stringops \-minline\-all\-stringops \&\-mpush\-args \-maccumulate\-outgoing\-args \-m128bit\-long\-double \&\-m96bit\-long\-double \-mregparm=\fR\fInum\fR \fB\-momit\-leaf\-frame\-pointer \&\-mno\-red\-zone \&\-mcmodel=\fR\fIcode-model\fR \&\fB\-m32 \-m64\fR .IP "\fICode Generation Options\fR" 4 .IX Item "Code Generation Options" \&\fB\-fcall\-saved\-\fR\fIreg\fR \fB\-fcall\-used\-\fR\fIreg\fR \&\fB\-ffixed\-\fR\fIreg\fR \fB\-fexceptions \&\-fnon\-call\-exceptions \-funwind\-tables \&\-fasynchronous\-unwind\-tables \&\-finhibit\-size\-directive \-finstrument\-functions \&\-fno\-common \-fno\-ident \-fno\-gnu\-linker \&\-fpcc\-struct\-return \-fpic \-fPIC \&\-freg\-struct\-return \-fshared\-data \-fshort\-enums \&\-fshort\-double \-fshort\-wchar \-fvolatile \&\-fvolatile\-global \-fvolatile\-static \&\-fverbose\-asm \-fpack\-struct \-fstack\-check \&\-fstack\-limit\-register=\fR\fIreg\fR \fB\-fstack\-limit\-symbol=\fR\fIsym\fR \&\fB\-fargument\-alias \-fargument\-noalias \&\-fargument\-noalias\-global \-fleading\-underscore \&\-ftls\-model=\fR\fImodel\fR \&\fB\-ftrapv \-fbounds\-check\fR .Sh "Options Controlling the Kind of Output" .IX Subsection "Options Controlling the Kind of Output" Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. The first three stages apply to an individual source file, and end by producing an object file; linking combines all the object files (those newly compiled, and those specified as input) into an executable file. .PP For any given input file, the file name suffix determines what kind of compilation is done: .IP "\fIfile\fR\fB.c\fR" 4 .IX Item "file.c" C source code which must be preprocessed. .IP "\fIfile\fR\fB.i\fR" 4 .IX Item "file.i" C source code which should not be preprocessed. .IP "\fIfile\fR\fB.ii\fR" 4 .IX Item "file.ii" \&\*(C+ source code which should not be preprocessed. .IP "\fIfile\fR\fB.m\fR" 4 .IX Item "file.m" Objective-C source code. Note that you must link with the library \&\fIlibobjc.a\fR to make an Objective-C program work. .IP "\fIfile\fR\fB.mi\fR" 4 .IX Item "file.mi" Objective-C source code which should not be preprocessed. .IP "\fIfile\fR\fB.h\fR" 4 .IX Item "file.h" C or \*(C+ header file to be turned into a precompiled header. .IP "\fIfile\fR\fB.cc\fR" 4 .IX Item "file.cc" .PD 0 .IP "\fIfile\fR\fB.cp\fR" 4 .IX Item "file.cp" .IP "\fIfile\fR\fB.cxx\fR" 4 .IX Item "file.cxx" .IP "\fIfile\fR\fB.cpp\fR" 4 .IX Item "file.cpp" .IP "\fIfile\fR\fB.c++\fR" 4 .IX Item "file.c++" .IP "\fIfile\fR\fB.C\fR" 4 .IX Item "file.C" .PD \&\*(C+ source code which must be preprocessed. Note that in \fB.cxx\fR, the last two letters must both be literally \fBx\fR. Likewise, \&\fB.C\fR refers to a literal capital C. .IP "\fIfile\fR\fB.mm\fR" 4 .IX Item "file.mm" .PD 0 .IP "\fIfile\fR\fB.M\fR" 4 .IX Item "file.M" .PD Objective\-\*(C+ source code which must be preprocessed. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fIfile\fR\fB.mii\fR" 4 .IX Item "file.mii" Objective\-\*(C+ source code which should not be preprocessed. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fIfile\fR\fB.hh\fR" 4 .IX Item "file.hh" .PD 0 .IP "\fIfile\fR\fB.H\fR" 4 .IX Item "file.H" .PD \&\*(C+ header file to be turned into a precompiled header. .IP "\fIfile\fR\fB.f\fR" 4 .IX Item "file.f" .PD 0 .IP "\fIfile\fR\fB.for\fR" 4 .IX Item "file.for" .IP "\fIfile\fR\fB.FOR\fR" 4 .IX Item "file.FOR" .PD Fortran source code which should not be preprocessed. .IP "\fIfile\fR\fB.F\fR" 4 .IX Item "file.F" .PD 0 .IP "\fIfile\fR\fB.fpp\fR" 4 .IX Item "file.fpp" .IP "\fIfile\fR\fB.FPP\fR" 4 .IX Item "file.FPP" .PD Fortran source code which must be preprocessed (with the traditional preprocessor). .IP "\fIfile\fR\fB.r\fR" 4 .IX Item "file.r" Fortran source code which must be preprocessed with a \s-1RATFOR\s0 preprocessor (not included with \s-1GCC\s0). .IP "\fIfile\fR\fB.ads\fR" 4 .IX Item "file.ads" Ada source code file which contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called \fIspecs\fR. .IP "\fIfile\fR\fB.adb\fR" 4 .IX Item "file.adb" Ada source code file containing a library unit body (a subprogram or package body). Such files are also called \fIbodies\fR. .IP "\fIfile\fR\fB.s\fR" 4 .IX Item "file.s" Assembler code. Apple's version of \s-1GCC\s0 runs the preprocessor on these files as well as those ending in \fB.S\fR. .IP "\fIfile\fR\fB.S\fR" 4 .IX Item "file.S" Assembler code which must be preprocessed. .IP "\fIother\fR" 4 .IX Item "other" An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. .PP You can specify the input language explicitly with the \fB\-x\fR option: .IP "\fB\-x\fR \fIlanguage\fR" 4 .IX Item "-x language" Specify explicitly the \fIlanguage\fR for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next \fB\-x\fR option. Possible values for \fIlanguage\fR are: .Sp .Vb 9 \& c c-header cpp-output \& c++ c++-header c++-cpp-output \& objective-c objective-c-header objc-cpp-output \& objective-c++ (APPLE ONLY) objective-c++-header (APPLE ONLY) \& assembler assembler-with-cpp \& ada \& f77 f77-cpp-input ratfor \& java \& treelang .Ve .IP "\fB\-x none\fR" 4 .IX Item "-x none" Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if \fB\-x\fR has not been used at all). .IP "\fB\-ObjC\fR" 4 .IX Item "-ObjC" .PD 0 .IP "\fB\-ObjC++\fR" 4 .IX Item "-ObjC++" .PD These are similar in effect to \fB\-x objective-c\fR and \fB\-x objective\-c++\fR, but affect only the choice of compiler for files already identified as source files. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-arch\fR \fIarch\fR" 4 .IX Item "-arch arch" Compile for the specified target architecture \fIarch\fR. The allowable values are \fBi386\fR and \fBppc\fR. Multiple options work, and direct the compiler to produce ``fat'' binaries including object code for each architecture specified with \fB\-arch\fR. This option only works if assembler and libraries are available for each architecture specified. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-pass\-exit\-codes\fR" 4 .IX Item "-pass-exit-codes" Normally the \fBgcc\fR program will exit with the code of 1 if any phase of the compiler returns a non-success return code. If you specify \&\fB\-pass\-exit\-codes\fR, the \fBgcc\fR program will instead return with numerically highest error produced by any phase that returned an error indication. .PP If you only want some of the stages of compilation, you can use \&\fB\-x\fR (or filename suffixes) to tell \fBgcc\fR where to start, and one of the options \fB\-c\fR, \fB\-S\fR, or \fB\-E\fR to say where \&\fBgcc\fR is to stop. Note that some combinations (for example, \&\fB\-x cpp-output \-E\fR) instruct \fBgcc\fR to do nothing at all. .IP "\fB\-c\fR" 4 .IX Item "-c" Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. .Sp By default, the object file name for a source file is made by replacing the suffix \fB.c\fR, \fB.i\fR, \fB.s\fR, etc., with \fB.o\fR. .Sp Unrecognized input files, not requiring compilation or assembly, are ignored. .IP "\fB\-S\fR" 4 .IX Item "-S" Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified. .Sp By default, the assembler file name for a source file is made by replacing the suffix \fB.c\fR, \fB.i\fR, etc., with \fB.s\fR. .Sp Input files that don't require compilation are ignored. .IP "\fB\-E\fR" 4 .IX Item "-E" Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. .Sp Input files which don't require preprocessing are ignored. .IP "\fB\-o\fR \fIfile\fR" 4 .IX Item "-o file" Place output in file \fIfile\fR. This applies regardless to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. .Sp Since only one output file can be specified, it does not make sense to use \fB\-o\fR when compiling more than one input file, unless you are producing an executable file as output. .Sp If \fB\-o\fR is not specified, the default is to put an executable file in \fIa.out\fR, the object file for \fI\fIsource\fI.\fIsuffix\fI\fR in \&\fI\fIsource\fI.o\fR, its assembler file in \fI\fIsource\fI.s\fR, and all preprocessed C source on standard output. .IP "\fB\-v\fR" 4 .IX Item "-v" Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper. .IP "\fB\-###\fR" 4 .IX Item "-###" Like \fB\-v\fR except the commands are not executed and all command arguments are quoted. This is useful for shell scripts to capture the driver-generated command lines. .IP "\fB\-pipe\fR" 4 .IX Item "-pipe" Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the \s-1GNU\s0 assembler has no trouble. .IP "\fB\-\-help\fR" 4 .IX Item "--help" Print (on the standard output) a description of the command line options understood by \fBgcc\fR. If the \fB\-v\fR option is also specified then \fB\-\-help\fR will also be passed on to the various processes invoked by \fBgcc\fR, so that they can display the command line options they accept. If the \fB\-W\fR option is also specified then command line options which have no documentation associated with them will also be displayed. .IP "\fB\-\-target\-help\fR" 4 .IX Item "--target-help" Print (on the standard output) a description of target specific command line options for each tool. .IP "\fB\-\-version\fR" 4 .IX Item "--version" Display the version number and copyrights of the invoked \s-1GCC\s0. .Sh "Compiling \*(C+ Programs" .IX Subsection "Compiling Programs" \&\*(C+ source files conventionally use one of the suffixes \fB.C\fR, \&\fB.cc\fR, \fB.cpp\fR, \fB.CPP\fR, \fB.c++\fR, \fB.cp\fR, or \&\fB.cxx\fR; \*(C+ header files often use \fB.hh\fR or \fB.H\fR; preprocessed \*(C+ files use the suffix \fB.ii\fR. \s-1GCC\s0 recognizes files with these names and compiles them as \*(C+ programs even if you call the compiler the same way as for compiling C programs (usually with the name \fBgcc\fR). .PP However, \*(C+ programs often require class libraries as well as a compiler that understands the \*(C+ language\-\-\-and under some circumstances, you might want to compile programs or header files from standard input, or otherwise without a suffix that flags them as \*(C+ programs. You might also like to precompile a C header file with a \&\fB.h\fR extension to be used in \*(C+ compilations. \fBg++\fR is a program that calls \s-1GCC\s0 with the default language set to \*(C+, and automatically specifies linking against the \*(C+ library. On many systems, \fBg++\fR is also installed with the name \fBc++\fR. .PP When you compile \*(C+ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for \*(C+ programs. .Sh "Options Controlling C Dialect" .IX Subsection "Options Controlling C Dialect" The following options control the dialect of C (or languages derived from C, such as \*(C+ and Objective\-C) that the compiler accepts: .IP "\fB\-ansi\fR" 4 .IX Item "-ansi" In C mode, support all \s-1ISO\s0 C90 programs. In \*(C+ mode, remove \s-1GNU\s0 extensions that conflict with \s-1ISO\s0 \*(C+. .Sp This turns off certain features of \s-1GCC\s0 that are incompatible with \s-1ISO\s0 C90 (when compiling C code), or of standard \*(C+ (when compiling \*(C+ code), such as the \f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`typeof\*(C'\fR keywords, and predefined macros such as \f(CW\*(C`unix\*(C'\fR and \f(CW\*(C`vax\*(C'\fR that identify the type of system you are using. It also enables the undesirable and rarely used \s-1ISO\s0 trigraph feature. For the C compiler, it disables recognition of \*(C+ style \fB//\fR comments as well as the \f(CW\*(C`inline\*(C'\fR keyword. .Sp The alternate keywords \f(CW\*(C`_\|_asm_\|_\*(C'\fR, \f(CW\*(C`_\|_extension_\|_\*(C'\fR, \&\f(CW\*(C`_\|_inline_\|_\*(C'\fR and \f(CW\*(C`_\|_typeof_\|_\*(C'\fR continue to work despite \&\fB\-ansi\fR. You would not want to use them in an \s-1ISO\s0 C program, of course, but it is useful to put them in header files that might be included in compilations done with \fB\-ansi\fR. Alternate predefined macros such as \f(CW\*(C`_\|_unix_\|_\*(C'\fR and \f(CW\*(C`_\|_vax_\|_\*(C'\fR are also available, with or without \fB\-ansi\fR. .Sp The \fB\-ansi\fR option does not cause non-ISO programs to be rejected gratuitously. For that, \fB\-pedantic\fR is required in addition to \fB\-ansi\fR. .Sp The macro \f(CW\*(C`_\|_STRICT_ANSI_\|_\*(C'\fR is predefined when the \fB\-ansi\fR option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the \&\s-1ISO\s0 standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. .Sp Functions which would normally be built in but do not have semantics defined by \s-1ISO\s0 C (such as \f(CW\*(C`alloca\*(C'\fR and \f(CW\*(C`ffs\*(C'\fR) are not built-in functions with \fB\-ansi\fR is used. .IP "\fB\-std=\fR" 4 .IX Item "-std=" Determine the language standard. This option is currently only supported when compiling C or \*(C+. A value for this option must be provided; possible values are .RS 4 .IP "\fBc89\fR" 4 .IX Item "c89" .PD 0 .IP "\fBiso9899:1990\fR" 4 .IX Item "iso9899:1990" .PD \&\s-1ISO\s0 C90 (same as \fB\-ansi\fR). .IP "\fBiso9899:199409\fR" 4 .IX Item "iso9899:199409" \&\s-1ISO\s0 C90 as modified in amendment 1. .IP "\fBc99\fR" 4 .IX Item "c99" .PD 0 .IP "\fBc9x\fR" 4 .IX Item "c9x" .IP "\fBiso9899:1999\fR" 4 .IX Item "iso9899:1999" .IP "\fBiso9899:199x\fR" 4 .IX Item "iso9899:199x" .PD \&\s-1ISO\s0 C99. Note that this standard is not yet fully supported; see <\fBhttp://gcc.gnu.org/gcc\-3.3/c99status.html\fR> for more information. The names \fBc9x\fR and \fBiso9899:199x\fR are deprecated. .IP "\fBgnu89\fR" 4 .IX Item "gnu89" Default, \s-1ISO\s0 C90 plus \s-1GNU\s0 extensions (including some C99 features). .IP "\fBgnu99\fR" 4 .IX Item "gnu99" .PD 0 .IP "\fBgnu9x\fR" 4 .IX Item "gnu9x" .PD \&\s-1ISO\s0 C99 plus \s-1GNU\s0 extensions. When \s-1ISO\s0 C99 is fully implemented in \s-1GCC\s0, this will become the default. The name \fBgnu9x\fR is deprecated. .IP "\fBc++98\fR" 4 .IX Item "c++98" The 1998 \s-1ISO\s0 \*(C+ standard plus amendments. .IP "\fBgnu++98\fR" 4 .IX Item "gnu++98" The same as \fB\-std=c++98\fR plus \s-1GNU\s0 extensions. This is the default for \*(C+ code. .RE .RS 4 .Sp Even when this option is not specified, you can still use some of the features of newer standards in so far as they do not conflict with previous C standards. For example, you may use \f(CW\*(C`_\|_restrict_\|_\*(C'\fR even when \fB\-std=c99\fR is not specified. .Sp The \fB\-std\fR options specifying some version of \s-1ISO\s0 C have the same effects as \fB\-ansi\fR, except that features that were not in \s-1ISO\s0 C90 but are in the specified version (for example, \fB//\fR comments and the \f(CW\*(C`inline\*(C'\fR keyword in \s-1ISO\s0 C99) are not disabled. .RE .IP "\fB\-aux\-info\fR \fIfilename\fR" 4 .IX Item "-aux-info filename" Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C. .Sp Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (\fBI\fR, \fBN\fR for new or \&\fBO\fR for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (\fBC\fR or \fBF\fR, respectively, in the following character). In the case of function definitions, a K&R\-style list of arguments followed by their declarations is also provided, inside comments, after the declaration. .IP "\fB\-faltivec\fR" 4 .IX Item "-faltivec" Enable the AltiVec language extensions, as defined in Motorola's AltiVec \&\s-1PIM\s0. This includes the recognition of \f(CW\*(C`vector\*(C'\fR and \f(CW\*(C`pixel\*(C'\fR as (context\-dependent) keywords, the definition of built-in functions such as \f(CW\*(C`vec_add\*(C'\fR, and other extensions. Note that unlike the option \&\fB\-maltivec\fR, the extensions do not require the inclusion of any special header files. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-fasm\-blocks\fR" 4 .IX Item "-fasm-blocks" Enable the use of blocks and entire functions of assembly code within a C or \*(C+ file. The syntax follows that used in CodeWarrior. (\s-1APPLE\s0 \&\s-1ONLY\s0) .IP "\fB\-fno\-asm\fR" 4 .IX Item "-fno-asm" Do not recognize \f(CW\*(C`asm\*(C'\fR, \f(CW\*(C`inline\*(C'\fR or \f(CW\*(C`typeof\*(C'\fR as a keyword, so that code can use these words as identifiers. You can use the keywords \f(CW\*(C`_\|_asm_\|_\*(C'\fR, \f(CW\*(C`_\|_inline_\|_\*(C'\fR and \f(CW\*(C`_\|_typeof_\|_\*(C'\fR instead. \fB\-ansi\fR implies \fB\-fno\-asm\fR. .Sp In \*(C+, this switch only affects the \f(CW\*(C`typeof\*(C'\fR keyword, since \&\f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`inline\*(C'\fR are standard keywords. You may want to use the \fB\-fno\-gnu\-keywords\fR flag instead, which has the same effect. In C99 mode (\fB\-std=c99\fR or \fB\-std=gnu99\fR), this switch only affects the \f(CW\*(C`asm\*(C'\fR and \f(CW\*(C`typeof\*(C'\fR keywords, since \&\f(CW\*(C`inline\*(C'\fR is a standard keyword in \s-1ISO\s0 C99. .IP "\fB\-fno\-builtin\fR" 4 .IX Item "-fno-builtin" .PD 0 .IP "\fB\-fno\-builtin\-\fR\fIfunction\fR" 4 .IX Item "-fno-builtin-function" .PD Don't recognize built-in functions that do not begin with \&\fB_\|_builtin_\fR as prefix. .Sp \&\s-1GCC\s0 normally generates special code to handle certain built-in functions more efficiently; for instance, calls to \f(CW\*(C`alloca\*(C'\fR may become single instructions that adjust the stack directly, and calls to \f(CW\*(C`memcpy\*(C'\fR may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. .Sp With the \fB\-fno\-builtin\-\fR\fIfunction\fR option only the built-in function \fIfunction\fR is disabled. \fIfunction\fR must not begin with \fB_\|_builtin_\fR. If a function is named this is not built-in in this version of \s-1GCC\s0, this option is ignored. There is no corresponding \&\fB\-fbuiltin\-\fR\fIfunction\fR option; if you wish to enable built-in functions selectively when using \fB\-fno\-builtin\fR or \&\fB\-ffreestanding\fR, you may define macros such as: .Sp .Vb 2 \& #define abs(n) __builtin_abs ((n)) \& #define strcpy(d, s) __builtin_strcpy ((d), (s)) .Ve .IP "\fB\-fhosted\fR" 4 .IX Item "-fhosted" Assert that compilation takes place in a hosted environment. This implies \&\fB\-fbuiltin\fR. A hosted environment is one in which the entire standard library is available, and in which \f(CW\*(C`main\*(C'\fR has a return type of \f(CW\*(C`int\*(C'\fR. Examples are nearly everything except a kernel. This is equivalent to \fB\-fno\-freestanding\fR. .IP "\fB\-ffreestanding\fR" 4 .IX Item "-ffreestanding" Assert that compilation takes place in a freestanding environment. This implies \fB\-fno\-builtin\fR. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at \f(CW\*(C`main\*(C'\fR. The most obvious example is an \s-1OS\s0 kernel. This is equivalent to \fB\-fno\-hosted\fR. .IP "\fB\-fms\-extensions\fR" 4 .IX Item "-fms-extensions" Accept some non-standard constructs used in Microsoft header files. .IP "\fB\-trigraphs\fR" 4 .IX Item "-trigraphs" Support \s-1ISO\s0 C trigraphs. The \fB\-ansi\fR option (and \fB\-std\fR options for strict \s-1ISO\s0 C conformance) implies \fB\-trigraphs\fR. .IP "\fB\-no\-integrated\-cpp\fR" 4 .IX Item "-no-integrated-cpp" Performs a compilation in two passes: preprocessing and compiling. This option allows a user supplied \*(L"cc1\*(R", \*(L"cc1plus\*(R", or \*(L"cc1obj\*(R" via the \&\fB\-B\fR option. The user supplied compilation step can then add in an additional preprocessing step after normal preprocessing but before compiling. The default is to use the integrated cpp (internal cpp) .Sp The semantics of this option will change if \*(L"cc1\*(R", \*(L"cc1plus\*(R", and \&\*(L"cc1obj\*(R" are merged. .IP "\fB\-traditional\fR" 4 .IX Item "-traditional" .PD 0 .IP "\fB\-traditional\-cpp\fR" 4 .IX Item "-traditional-cpp" .PD Formerly, these options caused \s-1GCC\s0 to attempt to emulate a pre-standard C compiler. They are now only supported with the \fB\-E\fR switch. The preprocessor continues to support a pre-standard mode. See the \s-1GNU\s0 \&\s-1CPP\s0 manual for details. .IP "\fB\-fcond\-mismatch\fR" 4 .IX Item "-fcond-mismatch" Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for \*(C+. .IP "\fB\-fpch\-preprocess\fR" 4 .IX Item "-fpch-preprocess" Enable \s-1PCH\s0 processing even when \fB\-E\fR or \fB\-save\-temps\fR is used. .IP "\fB\-funsigned\-char\fR" 4 .IX Item "-funsigned-char" Let the type \f(CW\*(C`char\*(C'\fR be unsigned, like \f(CW\*(C`unsigned char\*(C'\fR. .Sp Each kind of machine has a default for what \f(CW\*(C`char\*(C'\fR should be. It is either like \f(CW\*(C`unsigned char\*(C'\fR by default or like \&\f(CW\*(C`signed char\*(C'\fR by default. .Sp Ideally, a portable program should always use \f(CW\*(C`signed char\*(C'\fR or \&\f(CW\*(C`unsigned char\*(C'\fR when it depends on the signedness of an object. But many programs have been written to use plain \f(CW\*(C`char\*(C'\fR and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. .Sp The type \f(CW\*(C`char\*(C'\fR is always a distinct type from each of \&\f(CW\*(C`signed char\*(C'\fR or \f(CW\*(C`unsigned char\*(C'\fR, even though its behavior is always just like one of those two. .IP "\fB\-fsigned\-char\fR" 4 .IX Item "-fsigned-char" Let the type \f(CW\*(C`char\*(C'\fR be signed, like \f(CW\*(C`signed char\*(C'\fR. .Sp Note that this is equivalent to \fB\-fno\-unsigned\-char\fR, which is the negative form of \fB\-funsigned\-char\fR. Likewise, the option \&\fB\-fno\-signed\-char\fR is equivalent to \fB\-funsigned\-char\fR. .IP "\fB\-fsigned\-bitfields\fR" 4 .IX Item "-fsigned-bitfields" .PD 0 .IP "\fB\-funsigned\-bitfields\fR" 4 .IX Item "-funsigned-bitfields" .IP "\fB\-fno\-signed\-bitfields\fR" 4 .IX Item "-fno-signed-bitfields" .IP "\fB\-fno\-unsigned\-bitfields\fR" 4 .IX Item "-fno-unsigned-bitfields" .PD These options control whether a bit-field is signed or unsigned, when the declaration does not use either \f(CW\*(C`signed\*(C'\fR or \f(CW\*(C`unsigned\*(C'\fR. By default, such a bit-field is signed, because this is consistent: the basic integer types such as \f(CW\*(C`int\*(C'\fR are signed types. .IP "\fB\-fwritable\-strings\fR" 4 .IX Item "-fwritable-strings" Store string constants in the writable data segment and don't uniquize them. This is for compatibility with old programs which assume they can write into string constants. .Sp Writing into string constants is a very bad idea; ``constants'' should be constant. .IP "\fB\-fconstant\-cfstrings\fR" 4 .IX Item "-fconstant-cfstrings" Enable the automatic creation of a CoreFoundation-type constant string whenever a special builtin \f(CW\*(C`_\|_builtin_\|_CFStringMakeConstantString\*(C'\fR is called on a literal string. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-fpascal\-strings\fR" 4 .IX Item "-fpascal-strings" Allow Pascal-style string literals to be constructed. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-fcoalesce\fR" 4 .IX Item "-fcoalesce" Coalesce duplicated functions and data. The linker will discard all but one, saving space. Enabled by default. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-fweak\-coalesced\fR" 4 .IX Item "-fweak-coalesced" Use the new \s-1OS\s0 X \*(L"weak_definitions\*(R" section attribute for coalesced items. A single \*(L"normal\*(R" definition will be chosen by the linker over any number of weakly-coalesced ones. (\s-1APPLE\s0 \s-1ONLY\s0) .Sh "Options Controlling \*(C+ Dialect" .IX Subsection "Options Controlling Dialect" This section describes the command-line options that are only meaningful for \*(C+ programs; but you can also use most of the \s-1GNU\s0 compiler options regardless of what language your program is in. For example, you might compile a file \f(CW\*(C`firstClass.C\*(C'\fR like this: .PP .Vb 1 \& g++ -g -frepo -O -c firstClass.C .Ve .PP In this example, only \fB\-frepo\fR is an option meant only for \*(C+ programs; you can use the other options with any language supported by \s-1GCC\s0. .PP Here is a list of options that are \fIonly\fR for compiling \*(C+ programs: .IP "\fB\-fabi\-version=\fR\fIn\fR" 4 .IX Item "-fabi-version=n" Use version \fIn\fR of the \*(C+ \s-1ABI\s0. Version 1 is the version of the \*(C+ \&\s-1ABI\s0 that first appeared in G++ 3.2. Version 0 will always be the version that conforms most closely to the \*(C+ \s-1ABI\s0 specification. Therefore, the \s-1ABI\s0 obtained using version 0 will change as \s-1ABI\s0 bugs are fixed. .Sp The default is version 1. .IP "\fB\-fno\-access\-control\fR" 4 .IX Item "-fno-access-control" Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. .IP "\fB\-fcheck\-new\fR" 4 .IX Item "-fcheck-new" Check that the pointer returned by \f(CW\*(C`operator new\*(C'\fR is non-null before attempting to modify the storage allocated. The current Working Paper requires that \f(CW\*(C`operator new\*(C'\fR never return a null pointer, so this check is normally unnecessary. .Sp An alternative to using this option is to specify that your \&\f(CW\*(C`operator new\*(C'\fR does not throw any exceptions; if you declare it \&\fB\f(BIthrow()\fB\fR, G++ will check the return value. See also \fBnew (nothrow)\fR. .IP "\fB\-fconserve\-space\fR" 4 .IX Item "-fconserve-space" Put uninitialized or runtime-initialized global variables into the common segment, as C does. This saves space in the executable at the cost of not diagnosing duplicate definitions. If you compile with this flag and your program mysteriously crashes after \f(CW\*(C`main()\*(C'\fR has completed, you may have an object that is being destroyed twice because two definitions were merged. .Sp This option is no longer useful on most targets, now that support has been added for putting variables into \s-1BSS\s0 without making them common. .IP "\fB\-fno\-const\-strings\fR" 4 .IX Item "-fno-const-strings" Give string constants type \f(CW\*(C`char *\*(C'\fR instead of type \f(CW\*(C`const char *\*(C'\fR. By default, G++ uses type \f(CW\*(C`const char *\*(C'\fR as required by the standard. Even if you use \fB\-fno\-const\-strings\fR, you cannot actually modify the value of a string constant, unless you also use \&\fB\-fwritable\-strings\fR. .Sp This option might be removed in a future release of G++. For maximum portability, you should structure your code so that it works with string constants that have type \f(CW\*(C`const char *\*(C'\fR. .IP "\fB\-fdollars\-in\-identifiers\fR" 4 .IX Item "-fdollars-in-identifiers" Accept \fB$\fR in identifiers. You can also explicitly prohibit use of \&\fB$\fR with the option \fB\-fno\-dollars\-in\-identifiers\fR. (\s-1GNU\s0 C allows \&\fB$\fR by default on most target systems, but there are a few exceptions.) Traditional C allowed the character \fB$\fR to form part of identifiers. However, \s-1ISO\s0 C and \*(C+ forbid \fB$\fR in identifiers. .IP "\fB\-fno\-elide\-constructors\fR" 4 .IX Item "-fno-elide-constructors" The \*(C+ standard allows an implementation to omit creating a temporary which is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. .IP "\fB\-fno\-enforce\-eh\-specs\fR" 4 .IX Item "-fno-enforce-eh-specs" Don't check for violation of exception specifications at runtime. This option violates the \*(C+ standard, but may be useful for reducing code size in production builds, much like defining \fB\s-1NDEBUG\s0\fR. The compiler will still optimize based on the exception specifications. .IP "\fB\-fexternal\-templates\fR" 4 .IX Item "-fexternal-templates" Cause \fB#pragma interface\fR and \fBimplementation\fR to apply to template instantiation; template instances are emitted or not according to the location of the template definition. .Sp This option is deprecated. .IP "\fB\-falt\-external\-templates\fR" 4 .IX Item "-falt-external-templates" Similar to \fB\-fexternal\-templates\fR, but template instances are emitted or not according to the place where they are first instantiated. .Sp This option is deprecated. .IP "\fB\-ffor\-scope\fR" 4 .IX Item "-ffor-scope" .PD 0 .IP "\fB\-fno\-for\-scope\fR" 4 .IX Item "-fno-for-scope" .PD If \fB\-ffor\-scope\fR is specified, the scope of variables declared in a \fIfor-init-statement\fR is limited to the \fBfor\fR loop itself, as specified by the \*(C+ standard. If \fB\-fno\-for\-scope\fR is specified, the scope of variables declared in a \fIfor-init-statement\fR extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of \*(C+. .Sp The default if neither flag is given to follow the standard, but to allow and give a warning for old-style code that would otherwise be invalid, or have different behavior. .IP "\fB\-fno\-gnu\-keywords\fR" 4 .IX Item "-fno-gnu-keywords" Do not recognize \f(CW\*(C`typeof\*(C'\fR as a keyword, so that code can use this word as an identifier. You can use the keyword \f(CW\*(C`_\|_typeof_\|_\*(C'\fR instead. \&\fB\-ansi\fR implies \fB\-fno\-gnu\-keywords\fR. .IP "\fB\-fno\-implicit\-templates\fR" 4 .IX Item "-fno-implicit-templates" Never emit code for non-inline templates which are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. .IP "\fB\-fno\-implicit\-inline\-templates\fR" 4 .IX Item "-fno-implicit-inline-templates" Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization will need the same set of explicit instantiations. .IP "\fB\-fno\-implement\-inlines\fR" 4 .IX Item "-fno-implement-inlines" To save space, do not emit out-of-line copies of inline functions controlled by \fB#pragma implementation\fR. This will cause linker errors if these functions are not inlined everywhere they are called. .IP "\fB\-findirect\-virtual\-calls\fR" 4 .IX Item "-findirect-virtual-calls" Do not make direct calls to virtual functions; instead, always go through the vtable. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-fapple\-kext\fR" 4 .IX Item "-fapple-kext" Alter vtables, destructors, and other implementation details to more closely resemble the \s-1GCC\s0 2.95 \s-1ABI\s0. This is to make kernel extensions loadable by Darwin kernels, and is required to build any Darwin kernel extension. \fB\-fno\-exceptions\fR and \fB\-static\fR must also be used with this flag. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-fcoalesce\-templates\fR" 4 .IX Item "-fcoalesce-templates" Mark instantiated templates as \*(L"coalesced\*(R": the linker will discard all but one, thus saving space. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-fms\-extensions\fR" 4 .IX Item "-fms-extensions" Disable pedantic warnings about constructs used in \s-1MFC\s0, such as implicit int and getting a pointer to member function via non-standard syntax. .IP "\fB\-fno\-nonansi\-builtins\fR" 4 .IX Item "-fno-nonansi-builtins" Disable built-in declarations of functions that are not mandated by \&\s-1ANSI/ISO\s0 C. These include \f(CW\*(C`ffs\*(C'\fR, \f(CW\*(C`alloca\*(C'\fR, \f(CW\*(C`_exit\*(C'\fR, \&\f(CW\*(C`index\*(C'\fR, \f(CW\*(C`bzero\*(C'\fR, \f(CW\*(C`conjf\*(C'\fR, and other related functions. .IP "\fB\-fno\-operator\-names\fR" 4 .IX Item "-fno-operator-names" Do not treat the operator name keywords \f(CW\*(C`and\*(C'\fR, \f(CW\*(C`bitand\*(C'\fR, \&\f(CW\*(C`bitor\*(C'\fR, \f(CW\*(C`compl\*(C'\fR, \f(CW\*(C`not\*(C'\fR, \f(CW\*(C`or\*(C'\fR and \f(CW\*(C`xor\*(C'\fR as synonyms as keywords. .IP "\fB\-fno\-optional\-diags\fR" 4 .IX Item "-fno-optional-diags" Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a class. .IP "\fB\-fpermissive\fR" 4 .IX Item "-fpermissive" Downgrade messages about nonconformant code from errors to warnings. By default, G++ effectively sets \fB\-pedantic\-errors\fR without \&\fB\-pedantic\fR; this option reverses that. This behavior and this option are superseded by \fB\-pedantic\fR, which works as it does for \s-1GNU\s0 C. .IP "\fB\-frepo\fR" 4 .IX Item "-frepo" Enable automatic template instantiation at link time. This option also implies \fB\-fno\-implicit\-templates\fR. .IP "\fB\-fno\-rtti\fR" 4 .IX Item "-fno-rtti" Disable generation of information about every class with virtual functions for use by the \*(C+ runtime type identification features (\fBdynamic_cast\fR and \fBtypeid\fR). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but it will generate it as needed. .IP "\fB\-fstats\fR" 4 .IX Item "-fstats" Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team. .IP "\fB\-ftemplate\-depth\-\fR\fIn\fR" 4 .IX Item "-ftemplate-depth-n" Set the maximum instantiation depth for template classes to \fIn\fR. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. \s-1ANSI/ISO\s0 \*(C+ conforming programs must not rely on a maximum depth greater than 17. .IP "\fB\-fuse\-cxa\-atexit\fR" 4 .IX Item "-fuse-cxa-atexit" Register destructors for objects with static storage duration with the \&\f(CW\*(C`_\|_cxa_atexit\*(C'\fR function rather than the \f(CW\*(C`atexit\*(C'\fR function. This option is required for fully standards-compliant handling of static destructors, but will only work if your C library supports \&\f(CW\*(C`_\|_cxa_atexit\*(C'\fR. This option is not supported on Mac \s-1OS\s0 X. .IP "\fB\-fvtable\-gc\fR" 4 .IX Item "-fvtable-gc" Emit special relocations for vtables and virtual function references so that the linker can identify unused virtual functions and zero out vtable slots that refer to them. This is most useful with \&\fB\-ffunction\-sections\fR and \fB\-Wl,\-\-gc\-sections\fR, in order to also discard the functions themselves. .Sp This optimization requires \s-1GNU\s0 as and \s-1GNU\s0 ld. Not all systems support this option. \fB\-Wl,\-\-gc\-sections\fR is ignored without \fB\-static\fR. .IP "\fB\-fno\-weak\fR" 4 .IX Item "-fno-weak" Do not use weak symbol support, even if it is provided by the linker. By default, G++ will use weak symbols if they are available. This option exists only for testing, and should not be used by end\-users; it will result in inferior code and has no benefits. This option may be removed in a future release of G++. .IP "\fB\-nostdinc++\fR" 4 .IX Item "-nostdinc++" Do not search for header files in the standard directories specific to \&\*(C+, but do still search the other standard directories. (This option is used when building the \*(C+ library.) .PP In addition, these optimization, warning, and code generation options have meanings only for \*(C+ programs: .IP "\fB\-fno\-default\-inline\fR" 4 .IX Item "-fno-default-inline" Do not assume \fBinline\fR for functions defined inside a class scope. Note that these functions will have linkage like inline functions; they just won't be inlined by default. .IP "\fB\-Wabi\fR (\*(C+ only)" 4 .IX Item "-Wabi ( only)" Warn when G++ generates code that is probably not compatible with the vendor-neutral \*(C+ \s-1ABI\s0. Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated will be compatible. .Sp You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers. .Sp The known incompatibilities at this point include: .RS 4 .IP "\(bu" 4 Incorrect handling of tail-padding for bit\-fields. G++ may attempt to pack data into the same byte as a base class. For example: .Sp .Vb 2 \& struct A { virtual void f(); int f1 : 1; }; \& struct B : public A { int f2 : 1; }; .Ve .Sp In this case, G++ will place \f(CW\*(C`B::f2\*(C'\fR into the same byte as\f(CW\*(C`A::f1\*(C'\fR; other compilers will not. You can avoid this problem by explicitly padding \f(CW\*(C`A\*(C'\fR so that its size is a multiple of the byte size on your platform; that will cause G++ and other compilers to layout \f(CW\*(C`B\*(C'\fR identically. .IP "\(bu" 4 Incorrect handling of tail-padding for virtual bases. G++ does not use tail padding when laying out virtual bases. For example: .Sp .Vb 3 \& struct A { virtual void f(); char c1; }; \& struct B { B(); char c2; }; \& struct C : public A, public virtual B {}; .Ve .Sp In this case, G++ will not place \f(CW\*(C`B\*(C'\fR into the tail-padding for \&\f(CW\*(C`A\*(C'\fR; other compilers will. You can avoid this problem by explicitly padding \f(CW\*(C`A\*(C'\fR so that its size is a multiple of its alignment (ignoring virtual base classes); that will cause G++ and other compilers to layout \f(CW\*(C`C\*(C'\fR identically. .IP "\(bu" 4 Incorrect handling of bit-fields with declared widths greater than that of their underlying types, when the bit-fields appear in a union. For example: .Sp .Vb 1 \& union U { int i : 4096; }; .Ve .Sp Assuming that an \f(CW\*(C`int\*(C'\fR does not have 4096 bits, G++ will make the union too small by the number of bits in an \f(CW\*(C`int\*(C'\fR. .IP "\(bu" 4 Empty classes can be placed at incorrect offsets. For example: .Sp .Vb 1 \& struct A {}; .Ve .Sp .Vb 4 \& struct B { \& A a; \& virtual void f (); \& }; .Ve .Sp .Vb 1 \& struct C : public B, public A {}; .Ve .Sp G++ will place the \f(CW\*(C`A\*(C'\fR base class of \f(CW\*(C`C\*(C'\fR at a nonzero offset; it should be placed at offset zero. G++ mistakenly believes that the \&\f(CW\*(C`A\*(C'\fR data member of \f(CW\*(C`B\*(C'\fR is already at offset zero. .IP "\(bu" 4 Names of template functions whose types involve \f(CW\*(C`typename\*(C'\fR or template template parameters can be mangled incorrectly. .Sp .Vb 2 \& template <typename Q> \& void f(typename Q::X) {} .Ve .Sp .Vb 2 \& template <template <typename> class Q> \& void f(typename Q<int>::X) {} .Ve .Sp Instantiations of these templates may be mangled incorrectly. .RE .RS 4 .RE .IP "\fB\-Wctor\-dtor\-privacy\fR (\*(C+ only)" 4 .IX Item "-Wctor-dtor-privacy ( only)" Warn when a class seems unusable, because all the constructors or destructors in a class are private and the class has no friends or public static member functions. This warning is enabled by default. .IP "\fB\-Wnon\-virtual\-dtor\fR (\*(C+ only)" 4 .IX Item "-Wnon-virtual-dtor ( only)" Warn when a class declares a non-virtual destructor that should probably be virtual, because it looks like the class will be used polymorphically. This warning is enabled by \fB\-Wall\fR. .IP "\fB\-Wreorder\fR (\*(C+ only)" 4 .IX Item "-Wreorder ( only)" Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: .Sp .Vb 5 \& struct A { \& int i; \& int j; \& A(): j (0), i (1) { } \& }; .Ve .Sp Here the compiler will warn that the member initializers for \fBi\fR and \fBj\fR will be rearranged to match the declaration order of the members. This warning is enabled by \fB\-Wall\fR. .PP The following \fB\-W...\fR options are not affected by \fB\-Wall\fR. .IP "\fB\-Weffc++\fR (\*(C+ only)" 4 .IX Item "-Weffc++ ( only)" Warn about violations of the following style guidelines from Scott Meyers' \&\fIEffective \*(C+\fR book: .RS 4 .IP "\(bu" 4 Item 11: Define a copy constructor and an assignment operator for classes with dynamically allocated memory. .IP "\(bu" 4 Item 12: Prefer initialization to assignment in constructors. .IP "\(bu" 4 Item 14: Make destructors virtual in base classes. .IP "\(bu" 4 Item 15: Have \f(CW\*(C`operator=\*(C'\fR return a reference to \f(CW*this\fR. .IP "\(bu" 4 Item 23: Don't try to return a reference when you must return an object. .RE .RS 4 .Sp and about violations of the following style guidelines from Scott Meyers' \&\fIMore Effective \*(C+\fR book: .IP "\(bu" 4 Item 6: Distinguish between prefix and postfix forms of increment and decrement operators. .IP "\(bu" 4 Item 7: Never overload \f(CW\*(C`&&\*(C'\fR, \f(CW\*(C`||\*(C'\fR, or \f(CW\*(C`,\*(C'\fR. .RE .RS 4 .Sp If you use this option, you should be aware that the standard library headers do not obey all of these guidelines; you can use \fBgrep \-v\fR to filter out those warnings. .RE .IP "\fB\-Wno\-deprecated\fR (\*(C+ only)" 4 .IX Item "-Wno-deprecated ( only)" Do not warn about usage of deprecated features. .IP "\fB\-Wno\-non\-template\-friend\fR (\*(C+ only)" 4 .IX Item "-Wno-non-template-friend ( only)" Disable warnings when non-templatized friend functions are declared within a template. With the advent of explicit template specification support in G++, if the name of the friend is an unqualified-id (i.e., \&\fBfriend foo(int)\fR), the \*(C+ language specification demands that the friend declare or define an ordinary, nontemplate function. (Section 14.5.3). Before G++ implemented explicit specification, unqualified-ids could be interpreted as a particular specialization of a templatized function. Because this non-conforming behavior is no longer the default behavior for G++, \fB\-Wnon\-template\-friend\fR allows the compiler to check existing code for potential trouble spots, and is on by default. This new compiler behavior can be turned off with \&\fB\-Wno\-non\-template\-friend\fR which keeps the conformant compiler code but disables the helpful warning. .IP "\fB\-Wold\-style\-cast\fR (\*(C+ only)" 4 .IX Item "-Wold-style-cast ( only)" Warn if an old-style (C\-style) cast to a non-void type is used within a \*(C+ program. The new-style casts (\fBstatic_cast\fR, \&\fBreinterpret_cast\fR, and \fBconst_cast\fR) are less vulnerable to unintended effects, and much easier to grep for. .IP "\fB\-Woverloaded\-virtual\fR (\*(C+ only)" 4 .IX Item "-Woverloaded-virtual ( only)" Warn when a function declaration hides virtual functions from a base class. For example, in: .Sp .Vb 3 \& struct A { \& virtual void f(); \& }; .Ve .Sp .Vb 3 \& struct B: public A { \& void f(int); \& }; .Ve .Sp the \f(CW\*(C`A\*(C'\fR class version of \f(CW\*(C`f\*(C'\fR is hidden in \f(CW\*(C`B\*(C'\fR, and code like this: .Sp .Vb 2 \& B* b; \& b->f(); .Ve .Sp will fail to compile. .IP "\fB\-Wno\-pmf\-conversions\fR (\*(C+ only)" 4 .IX Item "-Wno-pmf-conversions ( only)" Disable the diagnostic for converting a bound pointer to member function to a plain pointer. .IP "\fB\-Wsign\-promo\fR (\*(C+ only)" 4 .IX Item "-Wsign-promo ( only)" Warn when overload resolution chooses a promotion from unsigned or enumeral type to a signed type over a conversion to an unsigned type of the same size. Previous versions of G++ would try to preserve unsignedness, but the standard mandates the current behavior. .IP "\fB\-Wsynth\fR (\*(C+ only)" 4 .IX Item "-Wsynth ( only)" Warn when G++'s synthesis behavior does not match that of cfront. For instance: .Sp .Vb 4 \& struct A { \& operator int (); \& A& operator = (int); \& }; .Ve .Sp .Vb 5 \& main () \& { \& A a,b; \& a = b; \& } .Ve .Sp In this example, G++ will synthesize a default \fBA& operator = (const A&);\fR, while cfront will use the user-defined \fBoperator =\fR. .Sh "Options Controlling Objective-C Dialect" .IX Subsection "Options Controlling Objective-C Dialect" This section describes the command-line options that are only meaningful for Objective-C programs; but you can also use most of the \s-1GNU\s0 compiler options regardless of what language your program is in. For example, you might compile a file \f(CW\*(C`some_class.m\*(C'\fR like this: .PP .Vb 1 \& gcc -g -fgnu-runtime -O -c some_class.m .Ve .PP In this example, only \fB\-fgnu\-runtime\fR is an option meant only for Objective-C programs; you can use the other options with any language supported by \s-1GCC\s0. .PP Here is a list of options that are \fIonly\fR for compiling Objective-C programs: .IP "\fB\-fconstant\-string\-class=\fR\fIclass-name\fR" 4 .IX Item "-fconstant-string-class=class-name" Use \fIclass-name\fR as the name of the class to instantiate for each literal string specified with the syntax \f(CW\*(C`@"..."\*(C'\fR. The default class name is \f(CW\*(C`NXConstantString\*(C'\fR. .IP "\fB\-fgnu\-runtime\fR" 4 .IX Item "-fgnu-runtime" Generate object code compatible with the standard \s-1GNU\s0 Objective-C runtime. This is the default for most types of systems. .IP "\fB\-fnext\-runtime\fR" 4 .IX Item "-fnext-runtime" Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac \s-1OS\s0 X. The macro \&\f(CW\*(C`_\|_NEXT_RUNTIME_\|_\*(C'\fR is predefined if (and only if) this option is used. .IP "\fB\-gen\-decls\fR" 4 .IX Item "-gen-decls" Dump interface declarations for all classes seen in the source file to a file named \fI\fIsourcename\fI.decl\fR. .IP "\fB\-Wno\-protocol\fR" 4 .IX Item "-Wno-protocol" If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the \f(CW\*(C`\-Wno\-protocol\*(C'\fR option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. .IP "\fB\-Wselector\fR" 4 .IX Item "-Wselector" Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. Additionally, a check is performed that for each selector appearing in a \f(CW\*(C`@selector(...)\*(C'\fR expression, a corresponding method with that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the \f(CW\*(C`\-fsyntax\-only\*(C'\fR option is being used. .IP "\fB\-Wundeclared\-selector\fR" 4 .IX Item "-Wundeclared-selector" Warn if a \f(CW\*(C`@selector(...)\*(C'\fR expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared (explicitly, in an \&\f(CW@interface\fR or \f(CW@protocol\fR declaration, or implicitly, in an \f(CW@implementation\fR section) before the \&\f(CW\*(C`@selector(...)\*(C'\fR expression. This option always performs its checks as soon as a \f(CW\*(C`@selector(...)\*(C'\fR expression is found (while \f(CW\*(C`\-Wselector\*(C'\fR only performs its checks in the final stage of compilation), and so additionally enforces the coding style convention that methods and selectors must be declared before being used. .Sh "Options to Control Diagnostic Messages Formatting" .IX Subsection "Options to Control Diagnostic Messages Formatting" Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g. its width, ...). The options described below can be used to control the diagnostic messages formatting algorithm, e.g. how many characters per line, how often source location information should be reported. Right now, only the \*(C+ front end can honor these options. However it is expected, in the near future, that the remaining front ends would be able to digest them correctly. .IP "\fB\-fmessage\-length=\fR\fIn\fR" 4 .IX Item "-fmessage-length=n" Try to format error messages so that they fit on lines of about \fIn\fR characters. The default is 72 characters for \fBg++\fR and 0 for the rest of the front ends supported by \s-1GCC\s0. If \fIn\fR is zero, then no line-wrapping will be done; each error message will appear on a single line. .IP "\fB\-fdiagnostics\-show\-location=once\fR" 4 .IX Item "-fdiagnostics-show-location=once" Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit \fIonce\fR source location information; that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior. .IP "\fB\-fdiagnostics\-show\-location=every\-line\fR" 4 .IX Item "-fdiagnostics-show-location=every-line" Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line. .Sh "Options to Request or Suppress Warnings" .IX Subsection "Options to Request or Suppress Warnings" Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there may have been an error. .PP You can request many specific warnings with options beginning \fB\-W\fR, for example \fB\-Wimplicit\fR to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning \fB\-Wno\-\fR to turn off warnings; for example, \fB\-Wno\-implicit\fR. This manual lists only one of the two forms, whichever is not the default. .PP The following options control the amount and kinds of warnings produced by \s-1GCC\s0; for further, language-specific options also refer to \&\f(CW@ref\fR{\*(C+ Dialect Options} and \f(CW@ref\fR{Objective\-C Dialect Options}. .IP "\fB\-fsyntax\-only\fR" 4 .IX Item "-fsyntax-only" Check the code for syntax errors, but don't do anything beyond that. .IP "\fB\-pedantic\fR" 4 .IX Item "-pedantic" Issue all the warnings demanded by strict \s-1ISO\s0 C and \s-1ISO\s0 \*(C+; reject all programs that use forbidden extensions, and some other programs that do not follow \s-1ISO\s0 C and \s-1ISO\s0 \*(C+. For \s-1ISO\s0 C, follows the version of the \s-1ISO\s0 C standard specified by any \fB\-std\fR option used. .Sp Valid \s-1ISO\s0 C and \s-1ISO\s0 \*(C+ programs should compile properly with or without this option (though a rare few will require \fB\-ansi\fR or a \&\fB\-std\fR option specifying the required version of \s-1ISO\s0 C). However, without this option, certain \s-1GNU\s0 extensions and traditional C and \*(C+ features are supported as well. With this option, they are rejected. .Sp \&\fB\-pedantic\fR does not cause warning messages for use of the alternate keywords whose names begin and end with \fB_\|_\fR. Pedantic warnings are also disabled in the expression that follows \&\f(CW\*(C`_\|_extension_\|_\*(C'\fR. However, only system header files should use these escape routes; application programs should avoid them. .Sp Some users try to use \fB\-pedantic\fR to check programs for strict \s-1ISO\s0 C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all\-\-\-only those for which \&\s-1ISO\s0 C \fIrequires\fR a diagnostic, and some others for which diagnostics have been added. .Sp A feature to report any failure to conform to \s-1ISO\s0 C might be useful in some instances, but would require considerable additional work and would be quite different from \fB\-pedantic\fR. We don't have plans to support such a feature in the near future. .Sp Where the standard specified with \fB\-std\fR represents a \s-1GNU\s0 extended dialect of C, such as \fBgnu89\fR or \fBgnu99\fR, there is a corresponding \fIbase standard\fR, the version of \s-1ISO\s0 C on which the \s-1GNU\s0 extended dialect is based. Warnings from \fB\-pedantic\fR are given where they are required by the base standard. (It would not make sense for such warnings to be given only for features not in the specified \s-1GNU\s0 C dialect, since by definition the \s-1GNU\s0 dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.) .IP "\fB\-pedantic\-errors\fR" 4 .IX Item "-pedantic-errors" Like \fB\-pedantic\fR, except that errors are produced rather than warnings. .IP "\fB\-w\fR" 4 .IX Item "-w" Inhibit all warning messages. .IP "\fB\-Wno\-import\fR" 4 .IX Item "-Wno-import" Inhibit warning messages about the use of \fB#import\fR. .IP "\fB\-Wno\-#warnings\fR" 4 .IX Item "-Wno-#warnings" Inhibit warning messages issued by \fB#warning\fR. .IP "\fB\-Wpragma\-once\fR" 4 .IX Item "-Wpragma-once" Warn about the use of \fB#pragma once\fR. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-Wextra\-tokens\fR" 4 .IX Item "-Wextra-tokens" Warn about extra tokens at the end of prepreprocessor directives. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-Wnewline\-eof\fR" 4 .IX Item "-Wnewline-eof" Warn about files missing a newline at the end of the file. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-Wno\-altivec\-long\-deprecated\fR" 4 .IX Item "-Wno-altivec-long-deprecated" Do not warn about the use of the deprecated 'long' keyword in AltiVec data types. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-Wchar\-subscripts\fR" 4 .IX Item "-Wchar-subscripts" Warn if an array subscript has type \f(CW\*(C`char\*(C'\fR. This is a common cause of error, as programmers often forget that this type is signed on some machines. .IP "\fB\-Wcomment\fR" 4 .IX Item "-Wcomment" Warn whenever a comment-start sequence \fB/*\fR appears in a \fB/*\fR comment, or whenever a Backslash-Newline appears in a \fB//\fR comment. .IP "\fB\-Wformat\fR" 4 .IX Item "-Wformat" Check calls to \f(CW\*(C`printf\*(C'\fR and \f(CW\*(C`scanf\*(C'\fR, etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format string make sense. This includes standard functions, and others specified by format attributes, in the \f(CW\*(C`printf\*(C'\fR, \&\f(CW\*(C`scanf\*(C'\fR, \f(CW\*(C`strftime\*(C'\fR and \f(CW\*(C`strfmon\*(C'\fR (an X/Open extension, not in the C standard) families. .Sp The formats are checked against the format features supported by \s-1GNU\s0 libc version 2.2. These include all \s-1ISO\s0 C90 and C99 features, as well as features from the Single Unix Specification and some \s-1BSD\s0 and \s-1GNU\s0 extensions. Other library implementations may not support all these features; \s-1GCC\s0 does not support warning about features that go beyond a particular library's limitations. However, if \fB\-pedantic\fR is used with \fB\-Wformat\fR, warnings will be given about format features not in the selected standard version (but not for \f(CW\*(C`strfmon\*(C'\fR formats, since those are not in any version of the C standard). .Sp Since \fB\-Wformat\fR also checks for null format arguments for several functions, \fB\-Wformat\fR also implies \fB\-Wnonnull\fR. .Sp \&\fB\-Wformat\fR is included in \fB\-Wall\fR. For more control over some aspects of format checking, the options \fB\-Wno\-format\-y2k\fR, \&\fB\-Wno\-format\-extra\-args\fR, \fB\-Wno\-format\-zero\-length\fR, \&\fB\-Wformat\-nonliteral\fR, \fB\-Wformat\-security\fR, and \&\fB\-Wformat=2\fR are available, but are not included in \fB\-Wall\fR. .IP "\fB\-Wno\-format\-y2k\fR" 4 .IX Item "-Wno-format-y2k" If \fB\-Wformat\fR is specified, do not warn about \f(CW\*(C`strftime\*(C'\fR formats which may yield only a two-digit year. .IP "\fB\-Wno\-format\-extra\-args\fR" 4 .IX Item "-Wno-format-extra-args" If \fB\-Wformat\fR is specified, do not warn about excess arguments to a \&\f(CW\*(C`printf\*(C'\fR or \f(CW\*(C`scanf\*(C'\fR format function. The C standard specifies that such arguments are ignored. .Sp Where the unused arguments lie between used arguments that are specified with \fB$\fR operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to \f(CW\*(C`va_arg\*(C'\fR to skip the unused arguments. However, in the case of \f(CW\*(C`scanf\*(C'\fR formats, this option will suppress the warning if the unused arguments are all pointers, since the Single Unix Specification says that such unused arguments are allowed. .IP "\fB\-Wno\-format\-zero\-length\fR" 4 .IX Item "-Wno-format-zero-length" If \fB\-Wformat\fR is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed. .IP "\fB\-Wformat\-nonliteral\fR" 4 .IX Item "-Wformat-nonliteral" If \fB\-Wformat\fR is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a \f(CW\*(C`va_list\*(C'\fR. .IP "\fB\-Wformat\-security\fR" 4 .IX Item "-Wformat-security" If \fB\-Wformat\fR is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to \f(CW\*(C`printf\*(C'\fR and \f(CW\*(C`scanf\*(C'\fR functions where the format string is not a string literal and there are no format arguments, as in \f(CW\*(C`printf (foo);\*(C'\fR. This may be a security hole if the format string came from untrusted input and contains \fB%n\fR. (This is currently a subset of what \fB\-Wformat\-nonliteral\fR warns about, but in future warnings may be added to \fB\-Wformat\-security\fR that are not included in \fB\-Wformat\-nonliteral\fR.) .IP "\fB\-Wformat=2\fR" 4 .IX Item "-Wformat=2" Enable \fB\-Wformat\fR plus format checks not included in \&\fB\-Wformat\fR. Currently equivalent to \fB\-Wformat \&\-Wformat\-nonliteral \-Wformat\-security\fR. .IP "\fB\-Wnonnull\fR" 4 .IX Item "-Wnonnull" Enable warning about passing a null pointer for arguments marked as requiring a non-null value by the \f(CW\*(C`nonnull\*(C'\fR function attribute. .Sp \&\fB\-Wnonnull\fR is included in \fB\-Wall\fR and \fB\-Wformat\fR. It can be disabled with the \fB\-Wno\-nonnull\fR option. .IP "\fB\-Wimplicit\-int\fR" 4 .IX Item "-Wimplicit-int" Warn when a declaration does not specify a type. .IP "\fB\-Wimplicit\-function\-declaration\fR" 4 .IX Item "-Wimplicit-function-declaration" .PD 0 .IP "\fB\-Werror\-implicit\-function\-declaration\fR" 4 .IX Item "-Werror-implicit-function-declaration" .PD Give a warning (or error) whenever a function is used before being declared. .IP "\fB\-Wimplicit\fR" 4 .IX Item "-Wimplicit" Same as \fB\-Wimplicit\-int\fR and \fB\-Wimplicit\-function\-declaration\fR. .IP "\fB\-Wmain\fR" 4 .IX Item "-Wmain" Warn if the type of \fBmain\fR is suspicious. \fBmain\fR should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. .IP "\fB\-Wmissing\-braces\fR" 4 .IX Item "-Wmissing-braces" Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for \fBa\fR is not fully bracketed, but that for \fBb\fR is fully bracketed. .Sp .Vb 2 \& int a[2][2] = { 0, 1, 2, 3 }; \& int b[2][2] = { { 0, 1 }, { 2, 3 } }; .Ve .IP "\fB\-Wparentheses\fR" 4 .IX Item "-Wparentheses" Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about. .Sp Also warn about constructions where there may be confusion to which \&\f(CW\*(C`if\*(C'\fR statement an \f(CW\*(C`else\*(C'\fR branch belongs. Here is an example of such a case: .Sp .Vb 7 \& { \& if (a) \& if (b) \& foo (); \& else \& bar (); \& } .Ve .Sp In C, every \f(CW\*(C`else\*(C'\fR branch belongs to the innermost possible \f(CW\*(C`if\*(C'\fR statement, which in this example is \f(CW\*(C`if (b)\*(C'\fR. This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, \s-1GCC\s0 will issue a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost \&\f(CW\*(C`if\*(C'\fR statement so there is no way the \f(CW\*(C`else\*(C'\fR could belong to the enclosing \f(CW\*(C`if\*(C'\fR. The resulting code would look like this: .Sp .Vb 9 \& { \& if (a) \& { \& if (b) \& foo (); \& else \& bar (); \& } \& } .Ve .IP "\fB\-Wsequence\-point\fR" 4 .IX Item "-Wsequence-point" Warn about code that may have undefined semantics because of violations of sequence point rules in the C standard. .Sp The C standard defines the order in which expressions in a C program are evaluated in terms of \fIsequence points\fR, which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a \&\f(CW\*(C`&&\*(C'\fR, \f(CW\*(C`||\*(C'\fR, \f(CW\*(C`? :\*(C'\fR or \f(CW\*(C`,\*(C'\fR (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. .Sp It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C standard specifies that ``Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.''. If a program breaks these rules, the results on any particular implementation are entirely unpredictable. .Sp Examples of code with undefined behavior are \f(CW\*(C`a = a++;\*(C'\fR, \f(CW\*(C`a[n] = b[n++]\*(C'\fR and \f(CW\*(C`a[i++] = i;\*(C'\fR. Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. .Sp The present implementation of this option only works for C programs. A future implementation may also work for \*(C+ programs. .Sp The C standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on our readings page, at <\fBhttp://gcc.gnu.org/readings.html\fR>. .IP "\fB\-Wreturn\-type\fR" 4 .IX Item "-Wreturn-type" Warn whenever a function is defined with a return-type that defaults to \&\f(CW\*(C`int\*(C'\fR. Also warn about any \f(CW\*(C`return\*(C'\fR statement with no return-value in a function whose return-type is not \f(CW\*(C`void\*(C'\fR. .Sp For \*(C+, a function without return type always produces a diagnostic message, even when \fB\-Wno\-return\-type\fR is specified. The only exceptions are \fBmain\fR and functions defined in system headers. .IP "\fB\-Wswitch\fR" 4 .IX Item "-Wswitch" Warn whenever a \f(CW\*(C`switch\*(C'\fR statement has an index of enumeral type and lacks a \f(CW\*(C`case\*(C'\fR for one or more of the named codes of that enumeration. (The presence of a \f(CW\*(C`default\*(C'\fR label prevents this warning.) \f(CW\*(C`case\*(C'\fR labels outside the enumeration range also provoke warnings when this option is used. .IP "\fB\-Wswitch\-default\fR" 4 .IX Item "-Wswitch-default" Warn whenever a \f(CW\*(C`switch\*(C'\fR statement does not have a \f(CW\*(C`default\*(C'\fR case. .IP "\fB\-Wswitch\-enum\fR" 4 .IX Item "-Wswitch-enum" Warn whenever a \f(CW\*(C`switch\*(C'\fR statement has an index of enumeral type and lacks a \f(CW\*(C`case\*(C'\fR for one or more of the named codes of that enumeration. \f(CW\*(C`case\*(C'\fR labels outside the enumeration range also provoke warnings when this option is used. .IP "\fB\-Wtrigraphs\fR" 4 .IX Item "-Wtrigraphs" Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). .IP "\fB\-Wunused\-function\fR" 4 .IX Item "-Wunused-function" Warn whenever a static function is declared but not defined or a non\e\-inline static function is unused. .IP "\fB\-Wunused\-label\fR" 4 .IX Item "-Wunused-label" Warn whenever a label is declared but not used. .Sp To suppress this warning use the \fBunused\fR attribute. .IP "\fB\-Wunused\-parameter\fR" 4 .IX Item "-Wunused-parameter" Warn whenever a function parameter is unused aside from its declaration. .Sp To suppress this warning use the \fBunused\fR attribute. .IP "\fB\-Wunused\-variable\fR" 4 .IX Item "-Wunused-variable" Warn whenever a local variable or non-constant static variable is unused aside from its declaration .Sp To suppress this warning use the \fBunused\fR attribute. .IP "\fB\-Wunused\-value\fR" 4 .IX Item "-Wunused-value" Warn whenever a statement computes a result that is explicitly not used. .Sp To suppress this warning cast the expression to \fBvoid\fR. .IP "\fB\-Wunused\fR" 4 .IX Item "-Wunused" All the above \fB\-Wunused\fR options combined. .Sp In order to get a warning about an unused function parameter, you must either specify \fB\-W \-Wunused\fR or separately specify \&\fB\-Wunused\-parameter\fR. .IP "\fB\-Wuninitialized\fR" 4 .IX Item "-Wuninitialized" Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a \f(CW\*(C`setjmp\*(C'\fR call. .Sp These warnings are possible only in optimizing compilation, because they require data flow information that is computed only when optimizing. If you don't specify \fB\-O\fR, you simply won't get these warnings. .Sp These warnings occur only for variables that are candidates for register allocation. Therefore, they do not occur for a variable that is declared \f(CW\*(C`volatile\*(C'\fR, or whose address is taken, or whose size is other than 1, 2, 4 or 8 bytes. Also, they do not occur for structures, unions or arrays, even when they are in registers. .Sp Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed. .Sp These warnings are made optional because \s-1GCC\s0 is not smart enough to see all the reasons why the code might be correct despite appearing to have an error. Here is one example of how this can happen: .Sp .Vb 12 \& { \& int x; \& switch (y) \& { \& case 1: x = 1; \& break; \& case 2: x = 4; \& break; \& case 3: x = 5; \& } \& foo (x); \& } .Ve .Sp If the value of \f(CW\*(C`y\*(C'\fR is always 1, 2 or 3, then \f(CW\*(C`x\*(C'\fR is always initialized, but \s-1GCC\s0 doesn't know this. Here is another common case: .Sp .Vb 6 \& { \& int save_y; \& if (change_y) save_y = y, y = new_y; \& ... \& if (change_y) y = save_y; \& } .Ve .Sp This has no bug because \f(CW\*(C`save_y\*(C'\fR is used only if it is set. .Sp This option also warns when a non-volatile automatic variable might be changed by a call to \f(CW\*(C`longjmp\*(C'\fR. These warnings as well are possible only in optimizing compilation. .Sp The compiler sees only the calls to \f(CW\*(C`setjmp\*(C'\fR. It cannot know where \f(CW\*(C`longjmp\*(C'\fR will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because \f(CW\*(C`longjmp\*(C'\fR cannot in fact be called at the place which would cause a problem. .Sp Some spurious warnings can be avoided if you declare all the functions you use that never return as \f(CW\*(C`noreturn\*(C'\fR. .IP "\fB\-Wunknown\-pragmas\fR" 4 .IX Item "-Wunknown-pragmas" Warn when a #pragma directive is encountered which is not understood by \&\s-1GCC\s0. If this command line option is used, warnings will even be issued for unknown pragmas in system header files. This is not the case if the warnings were only enabled by the \fB\-Wall\fR command line option. .IP "\fB\-Wstrict\-aliasing\fR" 4 .IX Item "-Wstrict-aliasing" This option is only active when \fB\-fstrict\-aliasing\fR is active. It warns about code which might break the strict aliasing rules that the compiler is using for optimization. The warning does not catch all cases, but does attempt to catch the more common pitfalls. It is included in \fB\-Wall\fR. .IP "\fB\-Wall\fR" 4 .IX Item "-Wall" All of the above \fB\-W\fR options combined. This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This also enables some language-specific warnings described in \f(CW@ref\fR{\*(C+ Dialect Options} and \&\f(CW@ref\fR{Objective\-C Dialect Options}. .IP "\fB\-Wmost\fR" 4 .IX Item "-Wmost" This is equivalent to \-Wall \-Wno\-parentheses. (\s-1APPLE\s0 \s-1ONLY\s0) .PP The following \fB\-W...\fR options are not implied by \fB\-Wall\fR. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. .IP "\fB\-W\fR" 4 .IX Item "-W" Print extra warning messages for these events: .RS 4 .IP "\(bu" 4 A function can return either with or without a value. (Falling off the end of the function body is considered returning without a value.) For example, this function would evoke such a warning: .Sp .Vb 5 \& foo (a) \& { \& if (a > 0) \& return a; \& } .Ve .IP "\(bu" 4 An expression-statement or the left-hand side of a comma expression contains no side effects. To suppress the warning, cast the unused expression to void. For example, an expression such as \fBx[i,j]\fR will cause a warning, but \fBx[(void)i,j]\fR will not. .IP "\(bu" 4 An unsigned value is compared against zero with \fB<\fR or \fB<=\fR. .IP "\(bu" 4 A comparison like \fBx<=y<=z\fR appears; this is equivalent to \&\fB(x<=y ? 1 : 0) <= z\fR, which is a different interpretation from that of ordinary mathematical notation. .IP "\(bu" 4 Storage-class specifiers like \f(CW\*(C`static\*(C'\fR are not the first things in a declaration. According to the C Standard, this usage is obsolescent. .IP "\(bu" 4 The return type of a function has a type qualifier such as \f(CW\*(C`const\*(C'\fR. Such a type qualifier has no effect, since the value returned by a function is not an lvalue. (But don't warn about the \s-1GNU\s0 extension of \&\f(CW\*(C`volatile void\*(C'\fR return types. That extension will be warned about if \fB\-pedantic\fR is specified.) .IP "\(bu" 4 If \fB\-Wall\fR or \fB\-Wunused\fR is also specified, warn about unused arguments. .IP "\(bu" 4 A comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. (But don't warn if \fB\-Wno\-sign\-compare\fR is also specified.) .IP "\(bu" 4 An aggregate has a partly bracketed initializer. For example, the following code would evoke such a warning, because braces are missing around the initializer for \f(CW\*(C`x.h\*(C'\fR: .Sp .Vb 3 \& struct s { int f, g; }; \& struct t { struct s h; int i; }; \& struct t x = { 1, 2, 3 }; .Ve .IP "\(bu" 4 An aggregate has an initializer which does not initialize all members. For example, the following code would cause such a warning, because \&\f(CW\*(C`x.h\*(C'\fR would be implicitly initialized to zero: .Sp .Vb 2 \& struct s { int f, g, h; }; \& struct s x = { 3, 4 }; .Ve .RE .RS 4 .RE .IP "\fB\-Wno\-div\-by\-zero\fR" 4 .IX Item "-Wno-div-by-zero" Do not warn about compile-time integer division by zero. Floating point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs. .IP "\fB\-Wsystem\-headers\fR" 4 .IX Item "-Wsystem-headers" Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command line option tells \&\s-1GCC\s0 to emit warnings from system headers as if they occurred in user code. However, note that using \fB\-Wall\fR in conjunction with this option will \fInot\fR warn about unknown pragmas in system headers\-\-\-for that, \fB\-Wunknown\-pragmas\fR must also be used. .IP "\fB\-Wfloat\-equal\fR" 4 .IX Item "-Wfloat-equal" Warn if floating point values are used in equality comparisons. .Sp The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but that's a different problem). In particular, instead of testing for equality, you would check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken. .IP "\fB\-Wtraditional\fR (C only)" 4 .IX Item "-Wtraditional (C only)" Warn about certain constructs that behave differently in traditional and \&\s-1ISO\s0 C. Also warn about \s-1ISO\s0 C constructs that have no traditional C equivalent, and/or problematic constructs which should be avoided. .RS 4 .IP "\(bu" 4 Macro parameters that appear within string literals in the macro body. In traditional C macro replacement takes place within string literals, but does not in \s-1ISO\s0 C. .IP "\(bu" 4 In traditional C, some preprocessor directives did not exist. Traditional preprocessors would only consider a line to be a directive if the \fB#\fR appeared in column 1 on the line. Therefore \&\fB\-Wtraditional\fR warns about directives that traditional C understands but would ignore because the \fB#\fR does not appear as the first character on the line. It also suggests you hide directives like \&\fB#pragma\fR not understood by traditional C by indenting them. Some traditional implementations would not recognize \fB#elif\fR, so it suggests avoiding it altogether. .IP "\(bu" 4 A function-like macro that appears without arguments. .IP "\(bu" 4 The unary plus operator. .IP "\(bu" 4 The \fBU\fR integer constant suffix, or the \fBF\fR or \fBL\fR floating point constant suffixes. (Traditional C does support the \fBL\fR suffix on integer constants.) Note, these suffixes appear in macros defined in the system headers of most modern systems, e.g. the \fB_MIN\fR/\fB_MAX\fR macros in \f(CW\*(C`<limits.h>\*(C'\fR. Use of these macros in user code might normally lead to spurious warnings, however gcc's integrated preprocessor has enough context to avoid warning in these cases. .IP "\(bu" 4 A function declared external in one block and then used after the end of the block. .IP "\(bu" 4 A \f(CW\*(C`switch\*(C'\fR statement has an operand of type \f(CW\*(C`long\*(C'\fR. .IP "\(bu" 4 A non\-\f(CW\*(C`static\*(C'\fR function declaration follows a \f(CW\*(C`static\*(C'\fR one. This construct is not accepted by some traditional C compilers. .IP "\(bu" 4 The \s-1ISO\s0 type of an integer constant has a different width or signedness from its traditional type. This warning is only issued if the base of the constant is ten. I.e. hexadecimal or octal values, which typically represent bit patterns, are not warned about. .IP "\(bu" 4 Usage of \s-1ISO\s0 string concatenation is detected. .IP "\(bu" 4 Initialization of automatic aggregates. .IP "\(bu" 4 Identifier conflicts with labels. Traditional C lacks a separate namespace for labels. .IP "\(bu" 4 Initialization of unions. If the initializer is zero, the warning is omitted. This is done under the assumption that the zero initializer in user code appears conditioned on e.g. \f(CW\*(C`_\|_STDC_\|_\*(C'\fR to avoid missing initializer warnings and relies on default initialization to zero in the traditional C case. .IP "\(bu" 4 Conversions by prototypes between fixed/floating point values and vice versa. The absence of these prototypes when compiling with traditional C would cause serious problems. This is a subset of the possible conversion warnings, for the full set use \fB\-Wconversion\fR. .IP "\(bu" 4 Use of \s-1ISO\s0 C style function definitions. This warning intentionally is \&\fInot\fR issued for prototype declarations or variadic functions because these \s-1ISO\s0 C features will appear in your code when using libiberty's traditional C compatibility macros, \f(CW\*(C`PARAMS\*(C'\fR and \&\f(CW\*(C`VPARAMS\*(C'\fR. This warning is also bypassed for nested functions because that feature is already a gcc extension and thus not relevant to traditional C compatibility. .RE .RS 4 .RE .IP "\fB\-Wundef\fR" 4 .IX Item "-Wundef" Warn if an undefined identifier is evaluated in an \fB#if\fR directive. .IP "\fB\-Wendif\-labels\fR" 4 .IX Item "-Wendif-labels" Warn whenever an \fB#else\fR or an \fB#endif\fR are followed by text. .IP "\fB\-Wshadow\fR" 4 .IX Item "-Wshadow" Warn whenever a local variable shadows another local variable, parameter or global variable or whenever a built-in function is shadowed. .IP "\fB\-Wlarger\-than\-\fR\fIlen\fR" 4 .IX Item "-Wlarger-than-len" Warn whenever an object of larger than \fIlen\fR bytes is defined. .IP "\fB\-Wpointer\-arith\fR" 4 .IX Item "-Wpointer-arith" Warn about anything that depends on the ``size of'' a function type or of \f(CW\*(C`void\*(C'\fR. \s-1GNU\s0 C assigns these types a size of 1, for convenience in calculations with \f(CW\*(C`void *\*(C'\fR pointers and pointers to functions. .IP "\fB\-Wbad\-function\-cast\fR (C only)" 4 .IX Item "-Wbad-function-cast (C only)" Warn whenever a function call is cast to a non-matching type. For example, warn if \f(CW\*(C`int malloc()\*(C'\fR is cast to \f(CW\*(C`anything *\*(C'\fR. .IP "\fB\-Wcast\-qual\fR" 4 .IX Item "-Wcast-qual" Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a \f(CW\*(C`const char *\*(C'\fR is cast to an ordinary \f(CW\*(C`char *\*(C'\fR. .IP "\fB\-Wcast\-align\fR" 4 .IX Item "-Wcast-align" Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a \f(CW\*(C`char *\*(C'\fR is cast to an \f(CW\*(C`int *\*(C'\fR on machines where integers can only be accessed at two\- or four-byte boundaries. .IP "\fB\-Wwrite\-strings\fR" 4 .IX Item "-Wwrite-strings" When compiling C, give string constants the type \f(CW\*(C`const char[\f(CIlength\f(CW]\*(C'\fR so that copying the address of one into a non\-\f(CW\*(C`const\*(C'\fR \f(CW\*(C`char *\*(C'\fR pointer will get a warning; when compiling \*(C+, warn about the deprecated conversion from string constants to \f(CW\*(C`char *\*(C'\fR. These warnings will help you find at compile time code that can try to write into a string constant, but only if you have been very careful about using \f(CW\*(C`const\*(C'\fR in declarations and prototypes. Otherwise, it will just be a nuisance; this is why we did not make \fB\-Wall\fR request these warnings. .IP "\fB\-Wconversion\fR" 4 .IX Item "-Wconversion" Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to floating and vice versa, and conversions changing the width or signedness of a fixed point argument except when the same as the default promotion. .Sp Also, warn if a negative integer constant expression is implicitly converted to an unsigned type. For example, warn about the assignment \&\f(CW\*(C`x = \-1\*(C'\fR if \f(CW\*(C`x\*(C'\fR is unsigned. But do not warn about explicit casts like \f(CW\*(C`(unsigned) \-1\*(C'\fR. .IP "\fB\-Wsign\-compare\fR" 4 .IX Item "-Wsign-compare" Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. This warning is also enabled by \fB\-W\fR; to get the other warnings of \fB\-W\fR without this warning, use \fB\-W \-Wno\-sign\-compare\fR. .IP "\fB\-Waggregate\-return\fR" 4 .IX Item "-Waggregate-return" Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.) .IP "\fB\-Wstrict\-prototypes\fR (C only)" 4 .IX Item "-Wstrict-prototypes (C only)" Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration which specifies the argument types.) .IP "\fB\-Wmissing\-prototypes\fR (C only)" 4 .IX Item "-Wmissing-prototypes (C only)" Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. The aim is to detect global functions that fail to be declared in header files. .IP "\fB\-Wmissing\-declarations\fR" 4 .IX Item "-Wmissing-declarations" Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. .IP "\fB\-Wmissing\-noreturn\fR" 4 .IX Item "-Wmissing-noreturn" Warn about functions which might be candidates for attribute \f(CW\*(C`noreturn\*(C'\fR. Note these are only possible candidates, not absolute ones. Care should be taken to manually verify functions actually do not ever return before adding the \f(CW\*(C`noreturn\*(C'\fR attribute, otherwise subtle code generation bugs could be introduced. You will not get a warning for \f(CW\*(C`main\*(C'\fR in hosted C environments. .IP "\fB\-Wmissing\-format\-attribute\fR" 4 .IX Item "-Wmissing-format-attribute" If \fB\-Wformat\fR is enabled, also warn about functions which might be candidates for \f(CW\*(C`format\*(C'\fR attributes. Note these are only possible candidates, not absolute ones. \s-1GCC\s0 will guess that \f(CW\*(C`format\*(C'\fR attributes might be appropriate for any function that calls a function like \f(CW\*(C`vprintf\*(C'\fR or \f(CW\*(C`vscanf\*(C'\fR, but this might not always be the case, and some functions for which \f(CW\*(C`format\*(C'\fR attributes are appropriate may not be detected. This option has no effect unless \&\fB\-Wformat\fR is enabled (possibly by \fB\-Wall\fR). .IP "\fB\-Wno\-multichar\fR" 4 .IX Item "-Wno-multichar" Do not warn if a multicharacter constant (\fB'\s-1FOOF\s0'\fR) is used. Usually they indicate a typo in the user's code, as they have implementation-defined values, and should not be used in portable code. .IP "\fB\-Wno\-deprecated\-declarations\fR" 4 .IX Item "-Wno-deprecated-declarations" Do not warn about uses of functions, variables, and types marked as deprecated by using the \f(CW\*(C`deprecated\*(C'\fR attribute. (@pxref{Function Attributes}, \f(CW@pxref\fR{Variable Attributes}, \&\f(CW@pxref\fR{Type Attributes}.) .IP "\fB\-Wpacked\fR" 4 .IX Item "-Wpacked" Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For instance, in this code, the variable \f(CW\*(C`f.x\*(C'\fR in \f(CW\*(C`struct bar\*(C'\fR will be misaligned even though \f(CW\*(C`struct bar\*(C'\fR does not itself have the packed attribute: .Sp .Vb 8 \& struct foo { \& int x; \& char a, b, c, d; \& } __attribute__((packed)); \& struct bar { \& char z; \& struct foo f; \& }; .Ve .IP "\fB\-Wpadded\fR" 4 .IX Item "-Wpadded" Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller. .IP "\fB\-Wredundant\-decls\fR" 4 .IX Item "-Wredundant-decls" Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing. .IP "\fB\-Wnested\-externs\fR (C only)" 4 .IX Item "-Wnested-externs (C only)" Warn if an \f(CW\*(C`extern\*(C'\fR declaration is encountered within a function. .IP "\fB\-Wunreachable\-code\fR" 4 .IX Item "-Wunreachable-code" Warn if the compiler detects that code will never be executed. .Sp This option is intended to warn when the compiler detects that at least a whole line of source code will never be executed, because some condition is never satisfied or because it is after a procedure that never returns. .Sp It is possible for this option to produce a warning even though there are circumstances under which part of the affected line can be executed, so care should be taken when removing apparently-unreachable code. .Sp For instance, when a function is inlined, a warning may mean that the line is unreachable in only one inlined copy of the function. .Sp This option is not made part of \fB\-Wall\fR because in a debugging version of a program there is often substantial code which checks correct functioning of the program and is, hopefully, unreachable because the program does work. Another common use of unreachable code is to provide behavior which is selectable at compile\-time. .IP "\fB\-Winline\fR" 4 .IX Item "-Winline" Warn if a function can not be inlined and it was declared as inline. .IP "\fB\-Wno\-invalid\-offsetof\fR (\*(C+ only)" 4 .IX Item "-Wno-invalid-offsetof ( only)" Suppress warnings from applying the \fBoffsetof\fR macro to a non-POD type. .IP "\fB\-Wno\-long\-double\fR" 4 .IX Item "-Wno-long-double" Inhibit warning if the \fBlong double\fR type is used. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-Winvalid\-pch\fR" 4 .IX Item "-Winvalid-pch" Warn if a precompiled header is found in the search path but can't be used. .IP "\fB\-Wlong\-long\fR" 4 .IX Item "-Wlong-long" Warn if \fBlong long\fR type is used. This is default. To inhibit the warning messages, use \fB\-Wno\-long\-long\fR. Flags \&\fB\-Wlong\-long\fR and \fB\-Wno\-long\-long\fR are taken into account only when \fB\-pedantic\fR flag is used. .IP "\fB\-Wdisabled\-optimization\fR" 4 .IX Item "-Wdisabled-optimization" Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that \s-1GCC\s0's optimizers were unable to handle the code effectively. Often, the problem is that your code is too big or too complex; \s-1GCC\s0 will refuse to optimize programs when the optimization itself is likely to take inordinate amounts of time. .IP "\fB\-Werror\fR" 4 .IX Item "-Werror" Make all warnings into errors. .Sh "Options for Debugging Your Program or \s-1GCC\s0" .IX Subsection "Options for Debugging Your Program or GCC" \&\s-1GCC\s0 has various special options that are used for debugging either your program or \s-1GCC:\s0 .IP "\fB\-g\fR" 4 .IX Item "-g" Produce debugging information in the operating system's native format (stabs, \s-1COFF\s0, \s-1XCOFF\s0, or \s-1DWARF\s0). \s-1GDB\s0 can work with this debugging information. .Sp On most systems that use stabs format, \fB\-g\fR enables use of extra debugging information that only \s-1GDB\s0 can use; this extra information makes debugging work better in \s-1GDB\s0 but will probably make other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use \fB\-gstabs+\fR or \fB\-gstabs\fR (see below). .Sp Unlike most other C compilers, \s-1GCC\s0 allows you to use \fB\-g\fR with \&\fB\-O\fR. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values were already at hand; some statements may execute in different places because they were moved out of loops. .Sp Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs. .Sp The following options are useful when \s-1GCC\s0 is generated with the capability for more than one debugging format. .IP "\fB\-ggdb\fR" 4 .IX Item "-ggdb" Produce debugging information for use by \s-1GDB\s0. This means to use the most expressive format available (\s-1DWARF\s0 2, stabs, or the native format if neither of those are supported), including \s-1GDB\s0 extensions if at all possible. .IP "\fB\-gstabs\fR" 4 .IX Item "-gstabs" Produce debugging information in stabs format (if that is supported), without \s-1GDB\s0 extensions. This is the format used by \s-1DBX\s0 on most \s-1BSD\s0 systems. On \s-1MIPS\s0, Alpha and System V Release 4 systems this option produces stabs debugging output which is not understood by \s-1DBX\s0 or \s-1SDB\s0. On System V Release 4 systems this option requires the \s-1GNU\s0 assembler. .IP "\fB\-gstabs+\fR" 4 .IX Item "-gstabs+" Produce debugging information in stabs format (if that is supported), using \s-1GNU\s0 extensions understood only by the \s-1GNU\s0 debugger (\s-1GDB\s0). The use of these extensions is likely to make other debuggers crash or refuse to read the program. .Sp (Other debug formats, such as \fB\-gcoff\fR, are not supported in Darwin or Mac \s-1OS\s0 X.) .IP "\fB\-g\fR\fIlevel\fR" 4 .IX Item "-glevel" .PD 0 .IP "\fB\-ggdb\fR\fIlevel\fR" 4 .IX Item "-ggdblevel" .IP "\fB\-gstabs\fR\fIlevel\fR" 4 .IX Item "-gstabslevel" .PD Request debugging information and also use \fIlevel\fR to specify how much information. The default level is 2. .Sp Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, but no information about local variables and no line numbers. .Sp Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use \fB\-g3\fR. .Sp Note that in order to avoid confusion between \s-1DWARF1\s0 debug level 2, and \s-1DWARF2\s0, neither \fB\-gdwarf\fR nor \fB\-gdwarf\-2\fR accept a concatenated debug level. Instead use an additional \fB\-g\fR\fIlevel\fR option to change the debug level for \s-1DWARF1\s0 or \s-1DWARF2\s0. .IP "\fB\-feliminate\-dwarf2\-dups\fR" 4 .IX Item "-feliminate-dwarf2-dups" Compress \s-1DWARF2\s0 debugging information by eliminating duplicated information about each symbol. This option only makes sense when generating \s-1DWARF2\s0 debugging information with \fB\-gdwarf\-2\fR. .IP "\fB\-p\fR" 4 .IX Item "-p" Generate extra code to write profile information suitable for the analysis program \fBprof\fR. You must use this option when compiling the source files you want data about, and you must also use it when linking. .IP "\fB\-pg\fR" 4 .IX Item "-pg" Generate extra code to write profile information suitable for the analysis program \fBgprof\fR. You must use this option when compiling the source files you want data about, and you must also use it when linking. .IP "\fB\-Q\fR" 4 .IX Item "-Q" Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes. .IP "\fB\-ftime\-report\fR" 4 .IX Item "-ftime-report" Makes the compiler print some statistics about the time consumed by each pass when it finishes. .IP "\fB\-fmem\-report\fR" 4 .IX Item "-fmem-report" Makes the compiler print some statistics about permanent memory allocation when it finishes. .IP "\fB\-fprofile\-arcs\fR" 4 .IX Item "-fprofile-arcs" Instrument \fIarcs\fR during compilation to generate coverage data or for profile-directed block ordering. During execution the program records how many times each branch is executed and how many times it is taken. When the compiled program exits it saves this data to a file called \fI\fIauxname\fI.da\fR for each source file. \fIauxname\fR is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. \fIfoo.da\fR for input file \fIdir/foo.c\fR, or \fIdir/foo.da\fR for output file specified as \fB\-o dir/foo.o\fR). .Sp For profile-directed block ordering, compile the program with \&\fB\-fprofile\-arcs\fR plus optimization and code generation options, generate the arc profile information by running the program on a selected workload, and then compile the program again with the same optimization and code generation options plus \&\fB\-fbranch\-probabilities\fR. .Sp The other use of \fB\-fprofile\-arcs\fR is for use with \fBgcov\fR, when it is used with the \fB\-ftest\-coverage\fR option. .Sp With \fB\-fprofile\-arcs\fR, for each function of your program \s-1GCC\s0 creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code. .IP "\fB\-ftest\-coverage\fR" 4 .IX Item "-ftest-coverage" Create data files for the \fBgcov\fR code-coverage utility. See \&\fB\-fprofile\-arcs\fR option above for a description of \fIauxname\fR. .RS 4 .IP "\fIauxname\fR\fB.bb\fR" 4 .IX Item "auxname.bb" A mapping from basic blocks to line numbers, which \fBgcov\fR uses to associate basic block execution counts with line numbers. .IP "\fIauxname\fR\fB.bbg\fR" 4 .IX Item "auxname.bbg" A list of all arcs in the program flow graph. This allows \fBgcov\fR to reconstruct the program flow graph, so that it can compute all basic block and arc execution counts from the information in the \&\fI\fIauxname\fI.da\fR file. .RE .RS 4 .Sp Use \fB\-ftest\-coverage\fR with \fB\-fprofile\-arcs\fR; the latter option adds instrumentation to the program, which then writes execution counts to another data file: .IP "\fIauxname\fR\fB.da\fR" 4 .IX Item "auxname.da" Runtime arc execution counts, used in conjunction with the arc information in the file \fI\fIauxname\fI.bbg\fR. .RE .RS 4 .Sp Coverage data will map better to the source files if \&\fB\-ftest\-coverage\fR is used without optimization. .RE .IP "\fB\-d\fR\fIletters\fR" 4 .IX Item "-dletters" Says to make debugging dumps during compilation at times specified by \&\fIletters\fR. This is used for debugging the compiler. The file names for most of the dumps are made by appending a pass number and a word to the \fIdumpname\fR. \fIdumpname\fR is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. \fIfoo.00.rtl\fR or \fIfoo.01.sibling\fR). Here are the possible letters for use in \fIletters\fR, and their meanings: .RS 4 .IP "\fBA\fR" 4 .IX Item "A" Annotate the assembler output with miscellaneous debugging information. .IP "\fBb\fR" 4 .IX Item "b" Dump after computing branch probabilities, to \fI\fIfile\fI.14.bp\fR. .IP "\fBB\fR" 4 .IX Item "B" Dump after block reordering, to \fI\fIfile\fI.32.bbro\fR. .IP "\fBc\fR" 4 .IX Item "c" Dump after instruction combination, to the file \fI\fIfile\fI.19.combine\fR. .IP "\fBC\fR" 4 .IX Item "C" Dump after the first if conversion, to the file \fI\fIfile\fI.15.ce1\fR. .IP "\fBd\fR" 4 .IX Item "d" Dump after delayed branch scheduling, to \fI\fIfile\fI.34.dbr\fR. .IP "\fBD\fR" 4 .IX Item "D" Dump all macro definitions, at the end of preprocessing, in addition to normal output. .IP "\fBe\fR" 4 .IX Item "e" Dump after \s-1SSA\s0 optimizations, to \fI\fIfile\fI.04.ssa\fR and \&\fI\fIfile\fI.07.ussa\fR. .IP "\fBE\fR" 4 .IX Item "E" Dump after the second if conversion, to \fI\fIfile\fI.29.ce3\fR. .IP "\fBf\fR" 4 .IX Item "f" Dump after life analysis, to \fI\fIfile\fI.18.life\fR. .IP "\fBF\fR" 4 .IX Item "F" Dump after purging \f(CW\*(C`ADDRESSOF\*(C'\fR codes, to \fI\fIfile\fI.10.addressof\fR. .IP "\fBg\fR" 4 .IX Item "g" Dump after global register allocation, to \fI\fIfile\fI.24.greg\fR. .IP "\fBh\fR" 4 .IX Item "h" Dump after finalization of \s-1EH\s0 handling code, to \fI\fIfile\fI.02.eh\fR. .IP "\fBk\fR" 4 .IX Item "k" Dump after reg-to-stack conversion, to \fI\fIfile\fI.31.stack\fR. .IP "\fBo\fR" 4 .IX Item "o" Dump after post-reload optimizations, to \fI\fIfile\fI.25.postreload\fR. .IP "\fBG\fR" 4 .IX Item "G" Dump after \s-1GCSE\s0, to \fI\fIfile\fI.11.gcse\fR. .IP "\fBi\fR" 4 .IX Item "i" Dump after sibling call optimizations, to \fI\fIfile\fI.01.sibling\fR. .IP "\fBj\fR" 4 .IX Item "j" Dump after the first jump optimization, to \fI\fIfile\fI.03.jump\fR. .IP "\fBk\fR" 4 .IX Item "k" Dump after conversion from registers to stack, to \fI\fIfile\fI.31.stack\fR. .IP "\fBl\fR" 4 .IX Item "l" Dump after local register allocation, to \fI\fIfile\fI.23.lreg\fR. .IP "\fBL\fR" 4 .IX Item "L" Dump after loop optimization, to \fI\fIfile\fI.12.loop\fR. .IP "\fBM\fR" 4 .IX Item "M" Dump after performing the machine dependent reorganization pass, to \&\fI\fIfile\fI.33.mach\fR. .IP "\fBn\fR" 4 .IX Item "n" Dump after register renumbering, to \fI\fIfile\fI.28.rnreg\fR. .IP "\fBN\fR" 4 .IX Item "N" Dump after the register move pass, to \fI\fIfile\fI.21.regmove\fR. .IP "\fBr\fR" 4 .IX Item "r" Dump after \s-1RTL\s0 generation, to \fI\fIfile\fI.00.rtl\fR. .IP "\fBR\fR" 4 .IX Item "R" Dump after the second scheduling pass, to \fI\fIfile\fI.30.sched2\fR. .IP "\fBs\fR" 4 .IX Item "s" Dump after \s-1CSE\s0 (including the jump optimization that sometimes follows \&\s-1CSE\s0), to \fI\fIfile\fI.09.cse\fR. .IP "\fBS\fR" 4 .IX Item "S" Dump after the first scheduling pass, to \fI\fIfile\fI.22.sched\fR. .IP "\fBt\fR" 4 .IX Item "t" Dump after the second \s-1CSE\s0 pass (including the jump optimization that sometimes follows \s-1CSE\s0), to \fI\fIfile\fI.17.cse2\fR. .IP "\fBu\fR" 4 .IX Item "u" Dump after null pointer elimination pass to \fI\fIfile\fI.08.null\fR. .IP "\fBw\fR" 4 .IX Item "w" Dump after the second flow pass, to \fI\fIfile\fI.26.flow2\fR. .IP "\fBX\fR" 4 .IX Item "X" Dump after \s-1SSA\s0 dead code elimination, to \fI\fIfile\fI.06.ssadce\fR. .IP "\fBz\fR" 4 .IX Item "z" Dump after the peephole pass, to \fI\fIfile\fI.27.peephole2\fR. .IP "\fBa\fR" 4 .IX Item "a" Produce all the dumps listed above. .IP "\fBm\fR" 4 .IX Item "m" Print statistics on memory usage, at the end of the run, to standard error. .IP "\fBp\fR" 4 .IX Item "p" Annotate the assembler output with a comment indicating which pattern and alternative was used. The length of each instruction is also printed. .IP "\fBP\fR" 4 .IX Item "P" Dump the \s-1RTL\s0 in the assembler output as a comment before each instruction. Also turns on \fB\-dp\fR annotation. .IP "\fBv\fR" 4 .IX Item "v" For each of the other indicated dump files (except for \&\fI\fIfile\fI.00.rtl\fR), dump a representation of the control flow graph suitable for viewing with \s-1VCG\s0 to \fI\fIfile\fI.\fIpass\fI.vcg\fR. .IP "\fBx\fR" 4 .IX Item "x" Just generate \s-1RTL\s0 for a function instead of compiling it. Usually used with \fBr\fR. .IP "\fBy\fR" 4 .IX Item "y" Dump debugging information during parsing, to standard error. .RE .RS 4 .RE .IP "\fB\-fdump\-unnumbered\fR" 4 .IX Item "-fdump-unnumbered" When doing debugging dumps (see \fB\-d\fR option above), suppress instruction numbers and line number note output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without \fB\-g\fR. .IP "\fB\-fdump\-translation\-unit\fR (C and \*(C+ only)" 4 .IX Item "-fdump-translation-unit (C and only)" .PD 0 .IP "\fB\-fdump\-translation\-unit\-\fR\fIoptions\fR\fB \fR(C and \*(C+ only)" 4 .IX Item "-fdump-translation-unit-options (C and only)" .PD Dump a representation of the tree structure for the entire translation unit to a file. The file name is made by appending \fI.tu\fR to the source file name. If the \fB\-\fR\fIoptions\fR form is used, \fIoptions\fR controls the details of the dump as described for the \&\fB\-fdump\-tree\fR options. .IP "\fB\-fdump\-class\-hierarchy\fR (\*(C+ only)" 4 .IX Item "-fdump-class-hierarchy ( only)" .PD 0 .IP "\fB\-fdump\-class\-hierarchy\-\fR\fIoptions\fR\fB \fR(\*(C+ only)" 4 .IX Item "-fdump-class-hierarchy-options ( only)" .PD Dump a representation of each class's hierarchy and virtual function table layout to a file. The file name is made by appending \fI.class\fR to the source file name. If the \fB\-\fR\fIoptions\fR form is used, \&\fIoptions\fR controls the details of the dump as described for the \&\fB\-fdump\-tree\fR options. .IP "\fB\-fdump\-tree\-\fR\fIswitch\fR\fB \fR(\*(C+ only)" 4 .IX Item "-fdump-tree-switch ( only)" .PD 0 .IP "\fB\-fdump\-tree\-\fR\fIswitch\fR\fB\-\fR\fIoptions\fR\fB \fR(\*(C+ only)" 4 .IX Item "-fdump-tree-switch-options ( only)" .PD Control the dumping at various stages of processing the intermediate language tree to a file. The file name is generated by appending a switch specific suffix to the source file name. If the \fB\-\fR\fIoptions\fR form is used, \fIoptions\fR is a list of \fB\-\fR separated options that control the details of the dump. Not all options are applicable to all dumps, those which are not meaningful will be ignored. The following options are available .RS 4 .IP "\fBaddress\fR" 4 .IX Item "address" Print the address of each node. Usually this is not meaningful as it changes according to the environment and source file. Its primary use is for tying up a dump file with a debug environment. .IP "\fBslim\fR" 4 .IX Item "slim" Inhibit dumping of members of a scope or body of a function merely because that scope has been reached. Only dump such items when they are directly reachable by some other path. .IP "\fBall\fR" 4 .IX Item "all" Turn on all options. .RE .RS 4 .Sp The following tree dumps are possible: .IP "\fBoriginal\fR" 4 .IX Item "original" Dump before any tree based optimization, to \fI\fIfile\fI.original\fR. .IP "\fBoptimized\fR" 4 .IX Item "optimized" Dump after all tree based optimization, to \fI\fIfile\fI.optimized\fR. .IP "\fBinlined\fR" 4 .IX Item "inlined" Dump after function inlining, to \fI\fIfile\fI.inlined\fR. .RE .RS 4 .RE .IP "\fB\-fsched\-verbose=\fR\fIn\fR" 4 .IX Item "-fsched-verbose=n" On targets that use instruction scheduling, this option controls the amount of debugging output the scheduler prints. This information is written to standard error, unless \fB\-dS\fR or \fB\-dR\fR is specified, in which case it is output to the usual dump listing file, \fI.sched\fR or \fI.sched2\fR respectively. However for \fIn\fR greater than nine, the output is always printed to standard error. .Sp For \fIn\fR greater than zero, \fB\-fsched\-verbose\fR outputs the same information as \fB\-dRS\fR. For \fIn\fR greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For \fIn\fR greater than two, it includes \s-1RTL\s0 at abort point, control-flow and regions info. And for \fIn\fR over four, \fB\-fsched\-verbose\fR also includes dependence info. .IP "\fB\-save\-temps\fR" 4 .IX Item "-save-temps" Store the usual ``temporary'' intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling \fIfoo.c\fR with \fB\-c \-save\-temps\fR would produce files \&\fIfoo.i\fR and \fIfoo.s\fR, as well as \fIfoo.o\fR. This creates a preprocessed \fIfoo.i\fR output file even though the compiler now normally uses an integrated preprocessor. .IP "\fB\-time\fR" 4 .IX Item "-time" Report the \s-1CPU\s0 time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). The output looks like this: .Sp .Vb 2 \& # cc1 0.12 0.01 \& # as 0.00 0.01 .Ve .Sp The first number on each line is the ``user time,'' that is time spent executing the program itself. The second number is ``system time,'' time spent executing operating system routines on behalf of the program. Both numbers are in seconds. .IP "\fB\-fsave\-repository=\fR\fIlocation\fR" 4 .IX Item "-fsave-repository=location" Creates separate symbol repository at \fIlocation\fR for given input header file. Separate repository contains only debugging symbols in stabs format. .IP "\fB\-grepository\fR" 4 .IX Item "-grepository" Instructs compiler to use separate symbol repository with debugging symbols. Compiler searches for such repositories in include paths. .IP "\fB\-print\-file\-name=\fR\fIlibrary\fR" 4 .IX Item "-print-file-name=library" Print the full absolute name of the library file \fIlibrary\fR that would be used when linking\-\-\-and don't do anything else. With this option, \s-1GCC\s0 does not compile or link anything; it just prints the file name. .IP "\fB\-print\-multi\-directory\fR" 4 .IX Item "-print-multi-directory" Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in \fB\s-1GCC_EXEC_PREFIX\s0\fR. .IP "\fB\-print\-multi\-lib\fR" 4 .IX Item "-print-multi-lib" Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by \&\fB;\fR, and each switch starts with an \fB@} instead of the \&\f(CB@samp\fB{\-\fR, without spaces between multiple switches. This is supposed to ease shell\-processing. .IP "\fB\-print\-prog\-name=\fR\fIprogram\fR" 4 .IX Item "-print-prog-name=program" Like \fB\-print\-file\-name\fR, but searches for a program such as \fBcpp\fR. .IP "\fB\-print\-libgcc\-file\-name\fR" 4 .IX Item "-print-libgcc-file-name" Same as \fB\-print\-file\-name=libgcc.a\fR. .Sp This is useful when you use \fB\-nostdlib\fR or \fB\-nodefaultlibs\fR but you do want to link with \fIlibgcc.a\fR. You can do .Sp .Vb 1 \& gcc -nostdlib <files>... `gcc -print-libgcc-file-name` .Ve .IP "\fB\-print\-search\-dirs\fR" 4 .IX Item "-print-search-dirs" Print the name of the configured installation directory and a list of program and library directories gcc will search\-\-\-and don't do anything else. .Sp This is useful when gcc prints the error message \&\fBinstallation problem, cannot exec cpp0: No such file or directory\fR. To resolve this you either need to put \fIcpp0\fR and the other compiler components where gcc expects to find them, or you can set the environment variable \fB\s-1GCC_EXEC_PREFIX\s0\fR to the directory where you installed them. Don't forget the trailing '/'. .IP "\fB\-dumpmachine\fR" 4 .IX Item "-dumpmachine" Print the compiler's target machine (for example, \&\fBi686\-pc\-linux\-gnu\fR)\-\-\-and don't do anything else. .IP "\fB\-dumpversion\fR" 4 .IX Item "-dumpversion" Print the compiler version (for example, \fB3.0\fR)\-\-\-and don't do anything else. .IP "\fB\-dumpspecs\fR" 4 .IX Item "-dumpspecs" Print the compiler's built-in specs\-\-\-and don't do anything else. (This is used when \s-1GCC\s0 itself is being built.) .Sh "Options That Control Optimization" .IX Subsection "Options That Control Optimization" These options control various sorts of optimizations. .PP Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you would expect from the source code. .PP Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program. .PP Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed. .IP "\fB\-O\fR" 4 .IX Item "-O" .PD 0 .IP "\fB\-O1\fR" 4 .IX Item "-O1" .PD Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. .Sp With \fB\-O\fR, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. .Sp In Apple's version of \s-1GCC\s0, \fB\-fstrict\-aliasing\fR, \&\fB\-freorder\-blocks\fR, and \fB\-fsched\-interblock\fR are disabled by default when optimizing. .IP "\fB\-O2\fR" 4 .IX Item "-O2" Optimize even more. \s-1GCC\s0 performs nearly all supported optimizations that do not involve a space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when you specify \fB\-O2\fR. As compared to \fB\-O\fR, this option increases both compilation time and the performance of the generated code. .Sp \&\fB\-O2\fR turns on all optimization flags specified by \fB\-O\fR. It also turns on the following optimization flags: \&\fB\-fforce\-mem \&\-foptimize\-sibling\-calls \&\-fstrength\-reduce \&\-fcse\-follow\-jumps \-fcse\-skip\-blocks \&\-frerun\-cse\-after\-loop \-frerun\-loop\-opt \&\-fgcse \-fgcse\-lm \-fgcse\-sm \&\-fdelete\-null\-pointer\-checks \&\-fexpensive\-optimizations \&\-fregmove \&\-fschedule\-insns \-fschedule\-insns2 \&\-fsched\-interblock \-fsched\-spec \&\-fcaller\-saves \&\-fpeephole2 \&\-freorder\-blocks \-freorder\-functions \&\-fstrict\-aliasing \&\-falign\-functions \-falign\-jumps \&\-falign\-loops \-falign\-labels\fR .Sp Please note the warning under \fB\-fgcse\fR about invoking \fB\-O2\fR on programs that use computed gotos. .IP "\fB\-O3\fR" 4 .IX Item "-O3" Optimize yet more. \fB\-O3\fR turns on all optimizations specified by \&\fB\-O2\fR and also turns on the \fB\-finline\-functions\fR and \&\fB\-frename\-registers\fR options. .IP "\fB\-O0\fR" 4 .IX Item "-O0" Do not optimize. This is the default. .IP "\fB\-Os\fR" 4 .IX Item "-Os" Optimize for size. \fB\-Os\fR enables all \fB\-O2\fR optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size. .Sp \&\fB\-Os\fR disables the following optimization flags: \&\fB\-falign\-functions \-falign\-jumps \-falign\-loops \&\-falign\-labels \-freorder\-blocks \-fprefetch\-loop\-arrays\fR .Sp If you use multiple \fB\-O\fR options, with or without level numbers, the last such option is the one that is effective. .PP Options of the form \fB\-f\fR\fIflag\fR specify machine-independent flags. Most flags have both positive and negative forms; the negative form of \fB\-ffoo\fR would be \fB\-fno\-foo\fR. In the table below, only one of the forms is listed\-\-\-the one you typically will use. You can figure out the other form by either removing \fBno\-\fR or adding it. .PP The following options control specific optimizations. They are either activated by \fB\-O\fR options or are related to ones that are. You can use the following flags in the rare cases when ``fine\-tuning'' of optimizations to be performed is desired. .IP "\fB\-fno\-default\-inline\fR" 4 .IX Item "-fno-default-inline" Do not make member functions inline by default merely because they are defined inside the class scope (\*(C+ only). Otherwise, when you specify \&\fB\-O\fR, member functions defined inside class scope are compiled inline by default; i.e., you don't need to add \fBinline\fR in front of the member function name. .IP "\fB\-fno\-defer\-pop\fR" 4 .IX Item "-fno-defer-pop" Always pop the arguments to each function call as soon as that function returns. For machines which must pop arguments after a function call, the compiler normally lets arguments accumulate on the stack for several function calls and pops them all at once. .Sp Disabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fforce\-mem\fR" 4 .IX Item "-fforce-mem" Force memory operands to be copied into registers before doing arithmetic on them. This produces better code by making all memory references potential common subexpressions. When they are not common subexpressions, instruction combination should eliminate the separate register\-load. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fforce\-addr\fR" 4 .IX Item "-fforce-addr" Force memory address constants to be copied into registers before doing arithmetic on them. This may produce better code just as \&\fB\-fforce\-mem\fR may. .IP "\fB\-fomit\-frame\-pointer\fR" 4 .IX Item "-fomit-frame-pointer" Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. \fBIt also makes debugging impossible on some machines.\fR .Sp On some machines, such as the \s-1VAX\s0, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesn't exist. The machine-description macro \f(CW\*(C`FRAME_POINTER_REQUIRED\*(C'\fR controls whether a target machine supports this flag. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-foptimize\-sibling\-calls\fR" 4 .IX Item "-foptimize-sibling-calls" Optimize sibling and tail recursive calls. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fno\-inline\fR" 4 .IX Item "-fno-inline" Don't pay attention to the \f(CW\*(C`inline\*(C'\fR keyword. Normally this option is used to keep the compiler from expanding any functions inline. Note that if you are not optimizing, no functions can be expanded inline. .IP "\fB\-finline\-functions\fR" 4 .IX Item "-finline-functions" Integrate all simple functions into their callers. The compiler heuristically decides which functions are simple enough to be worth integrating in this way. .Sp If all calls to a given function are integrated, and the function is declared \f(CW\*(C`static\*(C'\fR, then the function is normally not output as assembler code in its own right. .Sp Enabled at level \fB\-O3\fR. .IP "\fB\-finline\-limit=\fR\fIn\fR" 4 .IX Item "-finline-limit=n" By default, gcc limits the size of functions that can be inlined. This flag allows the control of this limit for functions that are explicitly marked as inline (i.e., marked with the inline keyword or defined within the class definition in c++). \fIn\fR is the size of functions that can be inlined in number of pseudo instructions (not counting parameter handling). The default value of \fIn\fR is 600. Increasing this value can result in more inlined code at the cost of compilation time and memory consumption. Decreasing usually makes the compilation faster and less code will be inlined (which presumably means slower programs). This option is particularly useful for programs that use inlining heavily such as those based on recursive templates with \*(C+. .Sp Inlining is actually controlled by a number of parameters, which may be specified individually by using \fB\-\-param\fR \fIname\fR\fB=\fR\fIvalue\fR. The \fB\-finline\-limit=\fR\fIn\fR option sets some of these parameters as follows: .RS 4 .Sp .Vb 10 \& @item max-inline-insns \& is set to I<n>. \& @item max-inline-insns-single \& is set to I<n>/2. \& @item max-inline-insns-single-auto \& is set to I<n>/2. \& @item min-inline-insns \& is set to 130 or I<n>/4, whichever is smaller. \& @item max-inline-insns-rtl \& is set to I<n>. .Ve .RE .RS 4 .Sp Using \fB\-finline\-limit=600\fR thus results in the default settings for these parameters. See below for a documentation of the individual parameters controlling inlining. .Sp \&\fINote:\fR pseudo instruction represents, in this particular context, an abstract measurement of function's size. In no way, it represents a count of assembly instructions and as such its exact meaning might change from one release to an another. .RE .IP "\fB\-fkeep\-inline\-functions\fR" 4 .IX Item "-fkeep-inline-functions" Even if all calls to a given function are integrated, and the function is declared \f(CW\*(C`static\*(C'\fR, nevertheless output a separate run-time callable version of the function. This switch does not affect \&\f(CW\*(C`extern inline\*(C'\fR functions. .IP "\fB\-fkeep\-static\-consts\fR" 4 .IX Item "-fkeep-static-consts" Emit variables declared \f(CW\*(C`static const\*(C'\fR when optimization isn't turned on, even if the variables aren't referenced. .Sp \&\s-1GCC\s0 enables this option by default. If you want to force the compiler to check if the variable was referenced, regardless of whether or not optimization is turned on, use the \fB\-fno\-keep\-static\-consts\fR option. .IP "\fB\-fmerge\-constants\fR" 4 .IX Item "-fmerge-constants" Attempt to merge identical constants (string constants and floating point constants) across compilation units. .Sp This option is the default for optimized compilation if the assembler and linker support it. Use \fB\-fno\-merge\-constants\fR to inhibit this behavior. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fmerge\-all\-constants\fR" 4 .IX Item "-fmerge-all-constants" Attempt to merge identical constants and identical variables. .Sp This option implies \fB\-fmerge\-constants\fR. In addition to \&\fB\-fmerge\-constants\fR this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating point types. Languages like C or \*(C+ require each non-automatic variable to have distinct location, so using this option will result in non-conforming behavior. .IP "\fB\-fno\-branch\-count\-reg\fR" 4 .IX Item "-fno-branch-count-reg" Do not use ``decrement and branch'' instructions on a count register, but instead generate a sequence of instructions that decrement a register, compare it against zero, then branch based upon the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, \s-1IA\-64\s0 and S/390. .Sp The default is \fB\-fbranch\-count\-reg\fR, enabled when \&\fB\-fstrength\-reduce\fR is enabled. .IP "\fB\-fno\-function\-cse\fR" 4 .IX Item "-fno-function-cse" Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. .Sp This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. .Sp The default is \fB\-ffunction\-cse\fR .IP "\fB\-fno\-zero\-initialized\-in\-bss\fR" 4 .IX Item "-fno-zero-initialized-in-bss" If the target supports a \s-1BSS\s0 section, \s-1GCC\s0 by default puts variables that are initialized to zero into \s-1BSS\s0. This can save space in the resulting code. .Sp This option turns off this behavior because some programs explicitly rely on variables going to the data section. E.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that. .Sp The default is \fB\-fzero\-initialized\-in\-bss\fR. .IP "\fB\-fstrength\-reduce\fR" 4 .IX Item "-fstrength-reduce" Perform the optimizations of loop strength reduction and elimination of iteration variables. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fthread\-jumps\fR" 4 .IX Item "-fthread-jumps" Perform optimizations where we check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fcse\-follow\-jumps\fR" 4 .IX Item "-fcse-follow-jumps" In common subexpression elimination, scan through jump instructions when the target of the jump is not reached by any other path. For example, when \s-1CSE\s0 encounters an \f(CW\*(C`if\*(C'\fR statement with an \&\f(CW\*(C`else\*(C'\fR clause, \s-1CSE\s0 will follow the jump when the condition tested is false. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fcse\-skip\-blocks\fR" 4 .IX Item "-fcse-skip-blocks" This is similar to \fB\-fcse\-follow\-jumps\fR, but causes \s-1CSE\s0 to follow jumps which conditionally skip over blocks. When \s-1CSE\s0 encounters a simple \f(CW\*(C`if\*(C'\fR statement with no else clause, \&\fB\-fcse\-skip\-blocks\fR causes \s-1CSE\s0 to follow the jump around the body of the \f(CW\*(C`if\*(C'\fR. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-frerun\-cse\-after\-loop\fR" 4 .IX Item "-frerun-cse-after-loop" Re-run common subexpression elimination after loop optimizations has been performed. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-frerun\-loop\-opt\fR" 4 .IX Item "-frerun-loop-opt" Run the loop optimizer twice. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fgcse\fR" 4 .IX Item "-fgcse" Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. .Sp \&\fINote:\fR When compiling a program using computed gotos, a \s-1GCC\s0 extension, you may get better runtime performance if you disable the global common subexpression elimination pass by adding \&\fB\-fno\-gcse\fR to the command line. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fgcse\-lm\fR" 4 .IX Item "-fgcse-lm" When \fB\-fgcse\-lm\fR is enabled, global common subexpression elimination will attempt to move loads which are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop. .Sp Enabled by default when gcse is enabled. .IP "\fB\-fgcse\-sm\fR" 4 .IX Item "-fgcse-sm" When \fB\-fgcse\-sm\fR is enabled, A store motion pass is run after global common subexpression elimination. This pass will attempt to move stores out of loops. When used in conjunction with \fB\-fgcse\-lm\fR, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop. .Sp Enabled by default when gcse is enabled. .IP "\fB\-floop\-optimize\fR" 4 .IX Item "-floop-optimize" Perform loop optimizations: move constant expressions out of loops, simplify exit test conditions and optionally do strength-reduction and loop unrolling as well. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fcrossjumping\fR" 4 .IX Item "-fcrossjumping" Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The resulting code may or may not perform better than without cross\-jumping. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fif\-conversion\fR" 4 .IX Item "-fif-conversion" Attempt to transform conditional jumps into branch-less equivalents. This include use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard arithmetics. The use of conditional execution on chips where it is available is controlled by \f(CW\*(C`if\-conversion2\*(C'\fR. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fif\-conversion2\fR" 4 .IX Item "-fif-conversion2" Use conditional execution (where available) to transform conditional jumps into branch-less equivalents. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fdelete\-null\-pointer\-checks\fR" 4 .IX Item "-fdelete-null-pointer-checks" Use global dataflow analysis to identify and eliminate useless checks for null pointers. The compiler assumes that dereferencing a null pointer would have halted the program. If a pointer is checked after it has already been dereferenced, it cannot be null. .Sp In some environments, this assumption is not true, and programs can safely dereference null pointers. Use \&\fB\-fno\-delete\-null\-pointer\-checks\fR to disable this optimization for programs which depend on that behavior. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fexpensive\-optimizations\fR" 4 .IX Item "-fexpensive-optimizations" Perform a number of minor optimizations that are relatively expensive. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-foptimize\-register\-move\fR" 4 .IX Item "-foptimize-register-move" .PD 0 .IP "\fB\-fregmove\fR" 4 .IX Item "-fregmove" .PD Attempt to reassign register numbers in move instructions and as operands of other simple instructions in order to maximize the amount of register tying. This is especially helpful on machines with two-operand instructions. .Sp Note \fB\-fregmove\fR and \fB\-foptimize\-register\-move\fR are the same optimization. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fdelayed\-branch\fR" 4 .IX Item "-fdelayed-branch" If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. .Sp Enabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fschedule\-insns\fR" 4 .IX Item "-fschedule-insns" If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating point instruction is required. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fschedule\-insns2\fR" 4 .IX Item "-fschedule-insns2" Similar to \fB\-fschedule\-insns\fR, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fno\-sched\-interblock\fR" 4 .IX Item "-fno-sched-interblock" Don't schedule instructions across basic blocks. This is normally enabled by default when scheduling before register allocation, i.e. with \fB\-fschedule\-insns\fR or at \fB\-O2\fR or higher. .IP "\fB\-fno\-sched\-spec\fR" 4 .IX Item "-fno-sched-spec" Don't allow speculative motion of non-load instructions. This is normally enabled by default when scheduling before register allocation, i.e. with \fB\-fschedule\-insns\fR or at \fB\-O2\fR or higher. .IP "\fB\-fsched\-spec\-load\fR" 4 .IX Item "-fsched-spec-load" Allow speculative motion of some load instructions. This only makes sense when scheduling before register allocation, i.e. with \&\fB\-fschedule\-insns\fR or at \fB\-O2\fR or higher. .IP "\fB\-fsched\-spec\-load\-dangerous\fR" 4 .IX Item "-fsched-spec-load-dangerous" Allow speculative motion of more load instructions. This only makes sense when scheduling before register allocation, i.e. with \&\fB\-fschedule\-insns\fR or at \fB\-O2\fR or higher. .IP "\fB\-fcaller\-saves\fR" 4 .IX Item "-fcaller-saves" Enable values to be allocated in registers that will be clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code than would otherwise be produced. .Sp This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fmove\-all\-movables\fR" 4 .IX Item "-fmove-all-movables" Forces all invariant computations in loops to be moved outside the loop. .IP "\fB\-freduce\-all\-givs\fR" 4 .IX Item "-freduce-all-givs" Forces all general-induction variables in loops to be strength\-reduced. .Sp \&\fINote:\fR When compiling programs written in Fortran, \&\fB\-fmove\-all\-movables\fR and \fB\-freduce\-all\-givs\fR are enabled by default when you use the optimizer. .Sp These options may generate better or worse code; results are highly dependent on the structure of loops within the source code. .Sp These two options are intended to be removed someday, once they have helped determine the efficacy of various approaches to improving loop optimizations. .Sp Please let us (<\fBgcc@gcc.gnu.org\fR> and <\fBfortran@gnu.org\fR>) know how use of these options affects the performance of your production code. We're very interested in code that runs \fIslower\fR when these options are \fIenabled\fR. .IP "\fB\-fno\-peephole\fR" 4 .IX Item "-fno-peephole" .PD 0 .IP "\fB\-fno\-peephole2\fR" 4 .IX Item "-fno-peephole2" .PD Disable any machine-specific peephole optimizations. The difference between \fB\-fno\-peephole\fR and \fB\-fno\-peephole2\fR is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. .Sp \&\fB\-fpeephole\fR is enabled by default. \&\fB\-fpeephole2\fR enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fbranch\-probabilities\fR" 4 .IX Item "-fbranch-probabilities" .PD 0 .IP "\fB\-fno\-guess\-branch\-probability\fR" 4 .IX Item "-fno-guess-branch-probability" .PD Do not guess branch probabilities using a randomized model. .Sp Sometimes gcc will opt to use a randomized model to guess branch probabilities, when none are available from either profiling feedback (\fB\-fprofile\-arcs\fR) or \fB_\|_builtin_expect\fR. This means that different runs of the compiler on the same program may produce different object code. .Sp In a hard real-time system, people don't want different runs of the compiler to produce code that has different behavior; minimizing non-determinism is of paramount import. This switch allows users to reduce non\-determinism, possibly at the expense of inferior optimization. .Sp The default is \fB\-fguess\-branch\-probability\fR at levels \&\fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-freorder\-blocks\fR" 4 .IX Item "-freorder-blocks" Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-freorder\-functions\fR" 4 .IX Item "-freorder-functions" Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. This is implemented by using special subsections \f(CW\*(C`text.hot\*(C'\fR for most frequently executed functions and \&\f(CW\*(C`text.unlikely\*(C'\fR for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way. .Sp Also profile feedback must be available in to make this option effective. See \&\fB\-fprofile\-arcs\fR for details. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-fstrict\-aliasing\fR" 4 .IX Item "-fstrict-aliasing" Allows the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and \*(C+), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an \f(CW\*(C`unsigned int\*(C'\fR can alias an \f(CW\*(C`int\*(C'\fR, but not a \&\f(CW\*(C`void*\*(C'\fR or a \f(CW\*(C`double\*(C'\fR. A character type may alias any other type. .Sp Pay special attention to code like this: .Sp .Vb 4 \& union a_union { \& int i; \& double d; \& }; .Ve .Sp .Vb 5 \& int f() { \& a_union t; \& t.d = 3.0; \& return t.i; \& } .Ve .Sp The practice of reading from a different union member than the one most recently written to (called ``type\-punning'') is common. Even with \&\fB\-fstrict\-aliasing\fR, type-punning is allowed, provided the memory is accessed through the union type. So, the code above will work as expected. However, this code might not: .Sp .Vb 7 \& int f() { \& a_union t; \& int* ip; \& t.d = 3.0; \& ip = &t.i; \& return *ip; \& } .Ve .Sp Every language that wishes to perform language-specific alias analysis should define a function that computes, given an \f(CW\*(C`tree\*(C'\fR node, an alias set for the node. Nodes in different alias sets are not allowed to alias. For an example, see the C front-end function \&\f(CW\*(C`c_get_alias_set\*(C'\fR. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .IP "\fB\-falign\-functions\fR" 4 .IX Item "-falign-functions" .PD 0 .IP "\fB\-falign\-functions=\fR\fIn\fR" 4 .IX Item "-falign-functions=n" .PD Align the start of functions to the next power-of-two greater than \&\fIn\fR, skipping up to \fIn\fR bytes. For instance, \&\fB\-falign\-functions=32\fR aligns functions to the next 32\-byte boundary, but \fB\-falign\-functions=24\fR would align to the next 32\-byte boundary only if this can be done by skipping 23 bytes or less. .Sp \&\fB\-fno\-align\-functions\fR and \fB\-falign\-functions=1\fR are equivalent and mean that functions will not be aligned. .Sp Some assemblers only support this flag when \fIn\fR is a power of two; in that case, it is rounded up. .Sp If \fIn\fR is not specified, use a machine-dependent default. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR. .IP "\fB\-falign\-labels\fR" 4 .IX Item "-falign-labels" .PD 0 .IP "\fB\-falign\-labels=\fR\fIn\fR" 4 .IX Item "-falign-labels=n" .PD Align all branch targets to a power-of-two boundary, skipping up to \&\fIn\fR bytes like \fB\-falign\-functions\fR. This option can easily make code slower, because it must insert dummy operations for when the branch target is reached in the usual flow of the code. .Sp If \fB\-falign\-loops\fR or \fB\-falign\-jumps\fR are applicable and are greater than this value, then their values are used instead. .Sp If \fIn\fR is not specified, use a machine-dependent default which is very likely to be \fB1\fR, meaning no alignment. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR. .IP "\fB\-falign\-loops\fR" 4 .IX Item "-falign-loops" .PD 0 .IP "\fB\-falign\-loops=\fR\fIn\fR" 4 .IX Item "-falign-loops=n" .PD Align loops to a power-of-two boundary, skipping up to \fIn\fR bytes like \fB\-falign\-functions\fR. The hope is that the loop will be executed many times, which will make up for any execution of the dummy operations. .IP "\fB\-falign\-loops\-max\-skip\fR" 4 .IX Item "-falign-loops-max-skip" .PD 0 .IP "\fB\-falign\-loops\-max\-skip=\fR\fIn\fR" 4 .IX Item "-falign-loops-max-skip=n" .PD When aligning loops to a power-of-two boundary, only do so if can skip by up to \fIn\fR bytes. .Sp If \fIn\fR is not specified, use a machine-dependent default. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR. .IP "\fB\-falign\-jumps\fR" 4 .IX Item "-falign-jumps" .PD 0 .IP "\fB\-falign\-jumps=\fR\fIn\fR" 4 .IX Item "-falign-jumps=n" .PD Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping, skipping up to \fIn\fR bytes like \fB\-falign\-functions\fR. In this case, no dummy operations need be executed. .IP "\fB\-falign\-jumps\-max\-skip\fR" 4 .IX Item "-falign-jumps-max-skip" .PD 0 .IP "\fB\-falign\-jumps\-max\-skip=\fR\fIn\fR" 4 .IX Item "-falign-jumps-max-skip=n" .PD When aligning branch targets to a power-of-two boundary, only do so if can skip by up to \fIn\fR bytes. .Sp If \fIn\fR is not specified, use a machine-dependent default. .Sp Enabled at levels \fB\-O2\fR, \fB\-O3\fR. .IP "\fB\-frename\-registers\fR" 4 .IX Item "-frename-registers" Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization will most benefit processors with lots of registers. It can, however, make debugging impossible, since variables will no longer stay in a ``home register''. .Sp Enabled at levels \fB\-O3\fR. .IP "\fB\-fno\-cprop\-registers\fR" 4 .IX Item "-fno-cprop-registers" After register allocation and post-register allocation instruction splitting, we perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. .Sp Disabled at levels \fB\-O\fR, \fB\-O2\fR, \fB\-O3\fR, \fB\-Os\fR. .PP The following options control compiler behavior regarding floating point arithmetic. These options trade off between speed and correctness. All must be specifically enabled. .IP "\fB\-ffloat\-store\fR" 4 .IX Item "-ffloat-store" Do not store floating point variables in registers, and inhibit other options that might change whether a floating point value is taken from a register or memory. .Sp This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a \f(CW\*(C`double\*(C'\fR is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of \s-1IEEE\s0 floating point. Use \fB\-ffloat\-store\fR for such programs, after modifying them to store all pertinent intermediate computations into variables. .IP "\fB\-ffast\-math\fR" 4 .IX Item "-ffast-math" Sets \fB\-fno\-math\-errno\fR, \fB\-funsafe\-math\-optimizations\fR, \fB\-fno\-trapping\-math\fR, \fB\-ffinite\-math\-only\fR and \fB\-fno\-signaling\-nans\fR. .Sp This option causes the preprocessor macro \f(CW\*(C`_\|_FAST_MATH_\|_\*(C'\fR to be defined. .Sp This option should never be turned on by any \fB\-O\fR option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. .IP "\fB\-fno\-math\-errno\fR" 4 .IX Item "-fno-math-errno" Do not set \s-1ERRNO\s0 after calling math functions that are executed with a single instruction, e.g., sqrt. A program that relies on \&\s-1IEEE\s0 exceptions for math error handling may want to use this flag for speed while maintaining \s-1IEEE\s0 arithmetic compatibility. .Sp This option should never be turned on by any \fB\-O\fR option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. .Sp The default is \fB\-fmath\-errno\fR. .IP "\fB\-funsafe\-math\-optimizations\fR" 4 .IX Item "-funsafe-math-optimizations" Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate \s-1IEEE\s0 or \&\s-1ANSI\s0 standards. When used at link\-time, it may include libraries or startup files that change the default \s-1FPU\s0 control word or other similar optimizations. .Sp This option should never be turned on by any \fB\-O\fR option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. .Sp The default is \fB\-fno\-unsafe\-math\-optimizations\fR. .IP "\fB\-ffinite\-math\-only\fR" 4 .IX Item "-ffinite-math-only" Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +\-Infs. .Sp This option should never be turned on by any \fB\-O\fR option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications. .Sp The default is \fB\-fno\-finite\-math\-only\fR. .IP "\fB\-fno\-trapping\-math\fR" 4 .IX Item "-fno-trapping-math" Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. This option implies \&\fB\-fno\-signaling\-nans\fR. Setting this option may allow faster code if one relies on ``non\-stop'' \s-1IEEE\s0 arithmetic, for example. .Sp This option should never be turned on by any \fB\-O\fR option since it can result in incorrect output for programs which depend on an exact implementation of \s-1IEEE\s0 or \s-1ISO\s0 rules/specifications for math functions. .Sp The default is \fB\-ftrapping\-math\fR. .IP "\fB\-fsignaling\-nans\fR" 4 .IX Item "-fsignaling-nans" Compile code assuming that \s-1IEEE\s0 signaling NaNs may generate user-visible traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs. This option implies \fB\-ftrapping\-math\fR. .Sp This option causes the preprocessor macro \f(CW\*(C`_\|_SUPPORT_SNAN_\|_\*(C'\fR to be defined. .Sp The default is \fB\-fno\-signaling\-nans\fR. .Sp This option is experimental and does not currently guarantee to disable all \s-1GCC\s0 optimizations that affect signaling NaN behavior. .IP "\fB\-fsingle\-precision\-constant\fR" 4 .IX Item "-fsingle-precision-constant" Treat floating point constant as single precision constant instead of implicitly converting it to double precision constant. .PP The following options control optimizations that may improve performance, but are not enabled by any \fB\-O\fR options. This section includes experimental options that may produce broken code. .IP "\fB\-fbranch\-probabilities\fR" 4 .IX Item "-fbranch-probabilities" After running a program compiled with \fB\-fprofile\-arcs\fR, you can compile it a second time using \&\fB\-fbranch\-probabilities\fR, to improve optimizations based on the number of times each branch was taken. When the program compiled with \fB\-fprofile\-arcs\fR exits it saves arc execution counts to a file called \fI\fIsourcename\fI.da\fR for each source file The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations. .Sp With \fB\-fbranch\-probabilities\fR, \s-1GCC\s0 puts a \&\fB\s-1REG_BR_PROB\s0\fR note on each \fB\s-1JUMP_INSN\s0\fR and \fB\s-1CALL_INSN\s0\fR. These can be used to improve optimization. Currently, they are only used in one place: in \fIreorg.c\fR, instead of guessing which path a branch is mostly to take, the \fB\s-1REG_BR_PROB\s0\fR values are used to exactly determine which path is taken more often. .IP "\fB\-fnew\-ra\fR" 4 .IX Item "-fnew-ra" Use a graph coloring register allocator. Currently this option is meant for testing, so we are interested to hear about miscompilations with \&\fB\-fnew\-ra\fR. .IP "\fB\-ftracer\fR" 4 .IX Item "-ftracer" Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do better job. .IP "\fB\-funroll\-loops\fR" 4 .IX Item "-funroll-loops" Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. \fB\-funroll\-loops\fR implies both \&\fB\-fstrength\-reduce\fR and \fB\-frerun\-cse\-after\-loop\fR. This option makes code larger, and may or may not make it run faster. .IP "\fB\-funroll\-all\-loops\fR" 4 .IX Item "-funroll-all-loops" Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. \&\fB\-funroll\-all\-loops\fR implies the same options as \&\fB\-funroll\-loops\fR, .IP "\fB\-fprefetch\-loop\-arrays\fR" 4 .IX Item "-fprefetch-loop-arrays" If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. .Sp Disabled at level \fB\-Os\fR. .IP "\fB\-ffunction\-sections\fR" 4 .IX Item "-ffunction-sections" .PD 0 .IP "\fB\-fdata\-sections\fR" 4 .IX Item "-fdata-sections" .PD Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the section's name in the output file. .Sp Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. \s-1HPPA\s0 processors running HP-UX and \s-1SPARC\s0 processors running Solaris 2 have linkers with such optimizations. Other systems using the \s-1ELF\s0 object format as well as \s-1AIX\s0 may have these optimizations in the future. .Sp Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker will create larger object and executable files and will also be slower. You will not be able to use \f(CW\*(C`gprof\*(C'\fR on all systems if you specify this option and you may have problems with debugging if you specify both this option and \fB\-g\fR. .IP "\fB\-fssa\fR" 4 .IX Item "-fssa" Perform optimizations in static single assignment form. Each function's flow graph is translated into \s-1SSA\s0 form, optimizations are performed, and the flow graph is translated back from \s-1SSA\s0 form. Users should not specify this option, since it is not yet ready for production use. .IP "\fB\-fssa\-ccp\fR" 4 .IX Item "-fssa-ccp" Perform Sparse Conditional Constant Propagation in \s-1SSA\s0 form. Requires \&\fB\-fssa\fR. Like \fB\-fssa\fR, this is an experimental feature. .IP "\fB\-fssa\-dce\fR" 4 .IX Item "-fssa-dce" Perform aggressive dead-code elimination in \s-1SSA\s0 form. Requires \fB\-fssa\fR. Like \fB\-fssa\fR, this is an experimental feature. .IP "\fB\-\-param\fR \fIname\fR\fB=\fR\fIvalue\fR" 4 .IX Item "--param name=value" In some places, \s-1GCC\s0 uses various constants to control the amount of optimization that is done. For example, \s-1GCC\s0 will not inline functions that contain more that a certain number of instructions. You can control some of these constants on the command-line using the \&\fB\-\-param\fR option. .Sp In each case, the \fIvalue\fR is an integer. The allowable choices for \&\fIname\fR are given in the following table: .RS 4 .IP "\fBmax-delay-slot-insn-search\fR" 4 .IX Item "max-delay-slot-insn-search" The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions is searched, the time savings from filling the delay slot will be minimal so stop searching. Increasing values mean more aggressive optimization, making the compile time increase with probably small improvement in executable run time. .IP "\fBmax-delay-slot-live-search\fR" 4 .IX Item "max-delay-slot-live-search" When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compile time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph. .IP "\fBmax-gcse-memory\fR" 4 .IX Item "max-gcse-memory" The approximate maximum amount of memory that will be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization will not be done. .IP "\fBmax-gcse-passes\fR" 4 .IX Item "max-gcse-passes" The maximum number of passes of \s-1GCSE\s0 to run. .IP "\fBmax-pending-list-length\fR" 4 .IX Item "max-pending-list-length" The maximum number of pending dependencies scheduling will allow before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources. .IP "\fBmax-inline-insns-single\fR" 4 .IX Item "max-inline-insns-single" Several parameters control the tree inliner used in gcc. This number sets the maximum number of instructions (counted in gcc's internal representation) in a single function that the tree inliner will consider for inlining. This only affects functions declared inline and methods implemented in a class declaration (\*(C+). The default value is 300. .IP "\fBmax-inline-insns-auto\fR" 4 .IX Item "max-inline-insns-auto" When you use \fB\-finline\-functions\fR (included in \fB\-O3\fR), a lot of functions that would otherwise not be considered for inlining by the compiler will be investigated. To those functions, a different (more restrictive) limit compared to functions declared inline can be applied. The default value is 300. .IP "\fBmax-inline-insns\fR" 4 .IX Item "max-inline-insns" The tree inliner does decrease the allowable size for single functions to be inlined after we already inlined the number of instructions given here by repeated inlining. This number should be a factor of two or more larger than the single function limit. Higher numbers result in better runtime performance, but incur higher compile-time resource (\s-1CPU\s0 time, memory) requirements and result in larger binaries. Very high values are not advisable, as too large binaries may adversely affect runtime performance. The default value is 600. .IP "\fBmax-inline-slope\fR" 4 .IX Item "max-inline-slope" After exceeding the maximum number of inlined instructions by repeated inlining, a linear function is used to decrease the allowable size for single functions. The slope of that function is the negative reciprocal of the number specified here. The default value is 32. .IP "\fBmin-inline-insns\fR" 4 .IX Item "min-inline-insns" The repeated inlining is throttled more and more by the linear function after exceeding the limit. To avoid too much throttling, a minimum for this function is specified here to allow repeated inlining for very small functions even when a lot of repeated inlining already has been done. The default value is 130. .IP "\fBmax-inline-insns-rtl\fR" 4 .IX Item "max-inline-insns-rtl" For languages that use the \s-1RTL\s0 inliner (this happens at a later stage than tree inlining), you can set the maximum allowable size (counted in \s-1RTL\s0 instructions) for the \s-1RTL\s0 inliner with this parameter. The default value is 600. .IP "\fBmax-unrolled-insns\fR" 4 .IX Item "max-unrolled-insns" The maximum number of instructions that a loop should have if that loop is unrolled, and if the loop is unrolled, it determines how many times the loop code is unrolled. .IP "\fBhot-bb-count-fraction\fR" 4 .IX Item "hot-bb-count-fraction" Select fraction of the maximal count of repetitions of basic block in program given basic block needs to have to be considered hot. .IP "\fBhot-bb-frequency-fraction\fR" 4 .IX Item "hot-bb-frequency-fraction" Select fraction of the maximal frequency of executions of basic block in function given basic block needs to have to be considered hot .IP "\fBtracer-dynamic-coverage\fR" 4 .IX Item "tracer-dynamic-coverage" .PD 0 .IP "\fBtracer-dynamic-coverage-feedback\fR" 4 .IX Item "tracer-dynamic-coverage-feedback" .PD This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary code size expansion. .Sp The \fBtracer-dynamic-coverage-feedback\fR is used only when profile feedback is available. The real profiles (as opposed to statically estimated ones) are much less balanced allowing the threshold to be larger value. .IP "\fBtracer-max-code-growth\fR" 4 .IX Item "tracer-max-code-growth" Stop tail duplication once code growth has reached given percentage. This is rather hokey argument, as most of the duplicates will be eliminated later in cross jumping, so it may be set to much higher values than is the desired code growth. .IP "\fBtracer-min-branch-ratio\fR" 4 .IX Item "tracer-min-branch-ratio" Stop reverse growth when the reverse probability of best edge is less than this threshold (in percent). .IP "\fBtracer-min-branch-ratio\fR" 4 .IX Item "tracer-min-branch-ratio" .PD 0 .IP "\fBtracer-min-branch-ratio-feedback\fR" 4 .IX Item "tracer-min-branch-ratio-feedback" .PD Stop forward growth if the best edge do have probability lower than this threshold. .Sp Similarly to \fBtracer-dynamic-coverage\fR two values are present, one for compilation for profile feedback and one for compilation without. The value for compilation with profile feedback needs to be more conservative (higher) in order to make tracer effective. .IP "\fBggc-min-expand\fR" 4 .IX Item "ggc-min-expand" \&\s-1GCC\s0 uses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which the garbage collector's heap should be allowed to expand between collections. Tuning this may improve compilation speed; it has no effect on code generation. .Sp The default is 30% + 70% * (\s-1RAM/1GB\s0) with an upper bound of 100% when \&\s-1RAM\s0 >= 1GB. If \f(CW\*(C`getrlimit\*(C'\fR is available, the notion of \*(L"\s-1RAM\s0\*(R" is the smallest of actual \s-1RAM\s0, \s-1RLIMIT_RSS\s0, \s-1RLIMIT_DATA\s0 and \s-1RLIMIT_AS\s0. If \&\s-1GCC\s0 is not able to calculate \s-1RAM\s0 on a particular platform, the lower bound of 30% is used. Setting this parameter and \&\fBggc-min-heapsize\fR to zero causes a full collection to occur at every opportunity. This is extremely slow, but can be useful for debugging. .IP "\fBggc-min-heapsize\fR" 4 .IX Item "ggc-min-heapsize" Minimum size of the garbage collector's heap before it begins bothering to collect garbage. The first collection occurs after the heap expands by \fBggc-min-expand\fR% beyond \fBggc-min-heapsize\fR. Again, tuning this may improve compilation speed, and has no effect on code generation. .Sp The default is \s-1RAM/8\s0, with a lower bound of 4096 (four megabytes) and an upper bound of 131072 (128 megabytes). If \f(CW\*(C`getrlimit\*(C'\fR is available, the notion of \*(L"\s-1RAM\s0\*(R" is the smallest of actual \s-1RAM\s0, \&\s-1RLIMIT_RSS\s0, \s-1RLIMIT_DATA\s0 and \s-1RLIMIT_AS\s0. If \s-1GCC\s0 is not able to calculate \&\s-1RAM\s0 on a particular platform, the lower bound is used. Setting this parameter very large effectively disables garbage collection. Setting this parameter and \fBggc-min-expand\fR to zero causes a full collection to occur at every opportunity. .RE .RS 4 .RE .Sh "Options Controlling the Preprocessor" .IX Subsection "Options Controlling the Preprocessor" These options control the C preprocessor, which is run on each C source file before actual compilation. .PP If you use the \fB\-E\fR option, nothing is done except preprocessing. Some of these options make sense only together with \fB\-E\fR because they cause the preprocessor output to be unsuitable for actual compilation. .PP You can use \fB\-Wp,\fR\fIoption\fR to bypass the compiler driver and pass \fIoption\fR directly through to the preprocessor. If \&\fIoption\fR contains commas, it is split into multiple options at the commas. However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and \&\fB\-Wp\fR forcibly bypasses this phase. The preprocessor's direct interface is undocumented and subject to change, so whenever possible you should avoid using \fB\-Wp\fR and let the driver handle the options instead. .IP "\fB\-D\fR \fIname\fR" 4 .IX Item "-D name" Predefine \fIname\fR as a macro, with definition \f(CW1\fR. .IP "\fB\-D\fR \fIname\fR\fB=\fR\fIdefinition\fR" 4 .IX Item "-D name=definition" Predefine \fIname\fR as a macro, with definition \fIdefinition\fR. There are no restrictions on the contents of \fIdefinition\fR, but if you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax. .Sp If you wish to define a function-like macro on the command line, write its argument list with surrounding parentheses before the equals sign (if any). Parentheses are meaningful to most shells, so you will need to quote the option. With \fBsh\fR and \fBcsh\fR, \&\fB\-D'\fR\fIname\fR\fB(\fR\fIargs...\fR\fB)=\fR\fIdefinition\fR\fB'\fR works. .Sp \&\fB\-D\fR and \fB\-U\fR options are processed in the order they are given on the command line. All \fB\-imacros\fR \fIfile\fR and \&\fB\-include\fR \fIfile\fR options are processed after all \&\fB\-D\fR and \fB\-U\fR options. .IP "\fB\-U\fR \fIname\fR" 4 .IX Item "-U name" Cancel any previous definition of \fIname\fR, either built in or provided with a \fB\-D\fR option. .IP "\fB\-undef\fR" 4 .IX Item "-undef" Do not predefine any system-specific macros. The common predefined macros remain defined. .IP "\fB\-I\fR \fIdir\fR" 4 .IX Item "-I dir" Add the directory \fIdir\fR to the list of directories to be searched for header files. Directories named by \fB\-I\fR are searched before the standard system include directories. If the directory \fIdir\fR is a standard system include directory, the option is ignored to ensure that the default search order for system directories and the special treatment of system headers are not defeated \&. .IP "\fB\-o\fR \fIfile\fR" 4 .IX Item "-o file" Write output to \fIfile\fR. This is the same as specifying \fIfile\fR as the second non-option argument to \fBcpp\fR. \fBgcc\fR has a different interpretation of a second non-option argument, so you must use \fB\-o\fR to specify the output file. .IP "\fB\-Wall\fR" 4 .IX Item "-Wall" Turns on all optional warnings which are desirable for normal code. At present this is \fB\-Wcomment\fR and \fB\-Wtrigraphs\fR. Note that many of the preprocessor's warnings are on by default and have no options to control them. .IP "\fB\-Wcomment\fR" 4 .IX Item "-Wcomment" .PD 0 .IP "\fB\-Wcomments\fR" 4 .IX Item "-Wcomments" .PD Warn whenever a comment-start sequence \fB/*\fR appears in a \fB/*\fR comment, or whenever a backslash-newline appears in a \fB//\fR comment. (Both forms have the same effect.) .IP "\fB\-Wtrigraphs\fR" 4 .IX Item "-Wtrigraphs" Warn if any trigraphs are encountered. This option used to take effect only if \fB\-trigraphs\fR was also specified, but now works independently. Warnings are not given for trigraphs within comments, as they do not affect the meaning of the program. .IP "\fB\-Wtraditional\fR" 4 .IX Item "-Wtraditional" Warn about certain constructs that behave differently in traditional and \&\s-1ISO\s0 C. Also warn about \s-1ISO\s0 C constructs that have no traditional C equivalent, and problematic constructs which should be avoided. .IP "\fB\-Wimport\fR" 4 .IX Item "-Wimport" Warn the first time \fB#import\fR is used. .IP "\fB\-Wundef\fR" 4 .IX Item "-Wundef" Warn whenever an identifier which is not a macro is encountered in an \&\fB#if\fR directive, outside of \fBdefined\fR. Such identifiers are replaced with zero. .IP "\fB\-Wunused\-macros\fR" 4 .IX Item "-Wunused-macros" Warn about macros defined in the main file that are unused. A macro is \fIused\fR if it is expanded or tested for existence at least once. The preprocessor will also warn if the macro has not been used at the time it is redefined or undefined. .Sp Built-in macros, macros defined on the command line, and macros defined in include files are not warned about. .Sp \&\fBNote:\fR If a macro is actually used, but only used in skipped conditional blocks, then \s-1CPP\s0 will report it as unused. To avoid the warning in such a case, you might improve the scope of the macro's definition by, for example, moving it into the first skipped block. Alternatively, you could provide a dummy use with something like: .Sp .Vb 2 \& #if defined the_macro_causing_the_warning \& #endif .Ve .IP "\fB\-Wendif\-labels\fR" 4 .IX Item "-Wendif-labels" Warn whenever an \fB#else\fR or an \fB#endif\fR are followed by text. This usually happens in code of the form .Sp .Vb 5 \& #if FOO \& ... \& #else FOO \& ... \& #endif FOO .Ve .Sp The second and third \f(CW\*(C`FOO\*(C'\fR should be in comments, but often are not in older programs. This warning is on by default. .IP "\fB\-Werror\fR" 4 .IX Item "-Werror" Make all warnings into hard errors. Source code which triggers warnings will be rejected. .IP "\fB\-Wsystem\-headers\fR" 4 .IX Item "-Wsystem-headers" Issue warnings for code in system headers. These are normally unhelpful in finding bugs in your own code, therefore suppressed. If you are responsible for the system library, you may want to see them. .IP "\fB\-w\fR" 4 .IX Item "-w" Suppress all warnings, including those which \s-1GNU\s0 \s-1CPP\s0 issues by default. .IP "\fB\-pedantic\fR" 4 .IX Item "-pedantic" Issue all the mandatory diagnostics listed in the C standard. Some of them are left out by default, since they trigger frequently on harmless code. .IP "\fB\-pedantic\-errors\fR" 4 .IX Item "-pedantic-errors" Issue all the mandatory diagnostics, and make all mandatory diagnostics into errors. This includes mandatory diagnostics that \s-1GCC\s0 issues without \fB\-pedantic\fR but treats as warnings. .IP "\fB\-M\fR" 4 .IX Item "-M" Instead of outputting the result of preprocessing, output a rule suitable for \fBmake\fR describing the dependencies of the main source file. The preprocessor outputs one \fBmake\fR rule containing the object file name for that source file, a colon, and the names of all the included files, including those coming from \fB\-include\fR or \&\fB\-imacros\fR command line options. .Sp Unless specified explicitly (with \fB\-MT\fR or \fB\-MQ\fR), the object file name consists of the basename of the source file with any suffix replaced with object file suffix. If there are many included files then the rule is split into several lines using \fB\e\fR\-newline. The rule has no commands. .Sp This option does not suppress the preprocessor's debug output, such as \&\fB\-dM\fR. To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output file with \&\fB\-MF\fR, or use an environment variable like \&\fB\s-1DEPENDENCIES_OUTPUT\s0\fR. Debug output will still be sent to the regular output stream as normal. .Sp Passing \fB\-M\fR to the driver implies \fB\-E\fR, and suppresses warnings with an implicit \fB\-w\fR. .IP "\fB\-MM\fR" 4 .IX Item "-MM" Like \fB\-M\fR but do not mention header files that are found in system header directories, nor header files that are included, directly or indirectly, from such a header. .Sp This implies that the choice of angle brackets or double quotes in an \&\fB#include\fR directive does not in itself determine whether that header will appear in \fB\-MM\fR dependency output. This is a slight change in semantics from \s-1GCC\s0 versions 3.0 and earlier. .IP "\fB\-MF\fR \fIfile\fR" 4 .IX Item "-MF file" @anchor{\-MF} When used with \fB\-M\fR or \fB\-MM\fR, specifies a file to write the dependencies to. If no \fB\-MF\fR switch is given the preprocessor sends the rules to the same place it would have sent preprocessed output. .Sp When used with the driver options \fB\-MD\fR or \fB\-MMD\fR, \&\fB\-MF\fR overrides the default dependency output file. .IP "\fB\-dependency\-file\fR" 4 .IX Item "-dependency-file" Like \fB\-MF\fR. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-MG\fR" 4 .IX Item "-MG" In conjunction with an option such as \fB\-M\fR requesting dependency generation, \fB\-MG\fR assumes missing header files are generated files and adds them to the dependency list without raising an error. The dependency filename is taken directly from the \&\f(CW\*(C`#include\*(C'\fR directive without prepending any path. \fB\-MG\fR also suppresses preprocessed output, as a missing header file renders this useless. .Sp This feature is used in automatic updating of makefiles. .IP "\fB\-MP\fR" 4 .IX Item "-MP" This option instructs \s-1CPP\s0 to add a phony target for each dependency other than the main file, causing each to depend on nothing. These dummy rules work around errors \fBmake\fR gives if you remove header files without updating the \fIMakefile\fR to match. .Sp This is typical output: .Sp .Vb 1 \& test.o: test.c test.h .Ve .Sp .Vb 1 \& test.h: .Ve .IP "\fB\-MT\fR \fItarget\fR" 4 .IX Item "-MT target" Change the target of the rule emitted by dependency generation. By default \s-1CPP\s0 takes the name of the main input file, including any path, deletes any file suffix such as \fB.c\fR, and appends the platform's usual object suffix. The result is the target. .Sp An \fB\-MT\fR option will set the target to be exactly the string you specify. If you want multiple targets, you can specify them as a single argument to \fB\-MT\fR, or use multiple \fB\-MT\fR options. .Sp For example, \fB\-MT\ '$(objpfx)foo.o'\fR might give .Sp .Vb 1 \& $(objpfx)foo.o: foo.c .Ve .IP "\fB\-MQ\fR \fItarget\fR" 4 .IX Item "-MQ target" Same as \fB\-MT\fR, but it quotes any characters which are special to Make. \fB\-MQ\ '$(objpfx)foo.o'\fR gives .Sp .Vb 1 \& $$(objpfx)foo.o: foo.c .Ve .Sp The default target is automatically quoted, as if it were given with \&\fB\-MQ\fR. .IP "\fB\-MD\fR" 4 .IX Item "-MD" \&\fB\-MD\fR is equivalent to \fB\-M \-MF\fR \fIfile\fR, except that \&\fB\-E\fR is not implied. The driver determines \fIfile\fR based on whether an \fB\-o\fR option is given. If it is, the driver uses its argument but with a suffix of \fI.d\fR, otherwise it take the basename of the input file and applies a \fI.d\fR suffix. .Sp If \fB\-MD\fR is used in conjunction with \fB\-E\fR, any \&\fB\-o\fR switch is understood to specify the dependency output file (but \f(CW@pxref\fR{\-MF}), but if used without \fB\-E\fR, each \fB\-o\fR is understood to specify a target object file. .Sp Since \fB\-E\fR is not implied, \fB\-MD\fR can be used to generate a dependency output file as a side-effect of the compilation process. .IP "\fB\-MMD\fR" 4 .IX Item "-MMD" Like \fB\-MD\fR except mention only user header files, not system \&\-header files. .IP "\fB\-fpch\-deps\fR" 4 .IX Item "-fpch-deps" When using precompiled headers, this flag will cause the dependency-output flags to also list the files from the precompiled header's dependencies. If not specified only the precompiled header would be listed and not the files that were used to create it because those files are not consulted when a precompiled header is used. .IP "\fB\-x c\fR" 4 .IX Item "-x c" .PD 0 .IP "\fB\-x c++\fR" 4 .IX Item "-x c++" .IP "\fB\-x objective-c\fR" 4 .IX Item "-x objective-c" .IP "\fB\-x objective\-c++\fR" 4 .IX Item "-x objective-c++" .IP "\fB\-x assembler-with-cpp\fR" 4 .IX Item "-x assembler-with-cpp" .PD Specify the source language: C, \*(C+, Objective\-C, Objective\-\*(C+, or assembly. This has nothing to do with standards conformance or extensions; it merely selects which base syntax to expect. If you give none of these options, cpp will deduce the language from the extension of the source file: \&\fB.c\fR, \fB.cc\fR, \fB.m\fR, \fB.mm\fR, or \fB.S\fR. Some other common extensions for \*(C+ and assembly are also recognized. If cpp does not recognize the extension, it will treat the file as C; this is the most generic mode. .Sp \&\fBNote:\fR Previous versions of cpp accepted a \fB\-lang\fR option which selected both the language and the standards conformance level. This option has been removed, because it conflicts with the \fB\-l\fR option. .IP "\fB\-std=\fR\fIstandard\fR" 4 .IX Item "-std=standard" .PD 0 .IP "\fB\-ansi\fR" 4 .IX Item "-ansi" .PD Specify the standard to which the code should conform. Currently \s-1CPP\s0 knows about C and \*(C+ standards; others may be added in the future. .Sp \&\fIstandard\fR may be one of: .RS 4 .ie n .IP """iso9899:1990""" 4 .el .IP "\f(CWiso9899:1990\fR" 4 .IX Item "iso9899:1990" .PD 0 .ie n .IP """c89""" 4 .el .IP "\f(CWc89\fR" 4 .IX Item "c89" .PD The \s-1ISO\s0 C standard from 1990. \fBc89\fR is the customary shorthand for this version of the standard. .Sp The \fB\-ansi\fR option is equivalent to \fB\-std=c89\fR. .ie n .IP """iso9899:199409""" 4 .el .IP "\f(CWiso9899:199409\fR" 4 .IX Item "iso9899:199409" The 1990 C standard, as amended in 1994. .ie n .IP """iso9899:1999""" 4 .el .IP "\f(CWiso9899:1999\fR" 4 .IX Item "iso9899:1999" .PD 0 .ie n .IP """c99""" 4 .el .IP "\f(CWc99\fR" 4 .IX Item "c99" .ie n .IP """iso9899:199x""" 4 .el .IP "\f(CWiso9899:199x\fR" 4 .IX Item "iso9899:199x" .ie n .IP """c9x""" 4 .el .IP "\f(CWc9x\fR" 4 .IX Item "c9x" .PD The revised \s-1ISO\s0 C standard, published in December 1999. Before publication, this was known as C9X. .ie n .IP """gnu89""" 4 .el .IP "\f(CWgnu89\fR" 4 .IX Item "gnu89" The 1990 C standard plus \s-1GNU\s0 extensions. This is the default. .ie n .IP """gnu99""" 4 .el .IP "\f(CWgnu99\fR" 4 .IX Item "gnu99" .PD 0 .ie n .IP """gnu9x""" 4 .el .IP "\f(CWgnu9x\fR" 4 .IX Item "gnu9x" .PD The 1999 C standard plus \s-1GNU\s0 extensions. .ie n .IP """c++98""" 4 .el .IP "\f(CWc++98\fR" 4 .IX Item "c++98" The 1998 \s-1ISO\s0 \*(C+ standard plus amendments. .ie n .IP """gnu++98""" 4 .el .IP "\f(CWgnu++98\fR" 4 .IX Item "gnu++98" The same as \fB\-std=c++98\fR plus \s-1GNU\s0 extensions. This is the default for \*(C+ code. .RE .RS 4 .RE .IP "\fB\-I\-\fR" 4 .IX Item "-I-" Split the include path. Any directories specified with \fB\-I\fR options before \fB\-I\-\fR are searched only for headers requested with \&\f(CW\*(C`#include\ "\f(CIfile\f(CW"\*(C'\fR; they are not searched for \&\f(CW\*(C`#include\ <\f(CIfile\f(CW>\*(C'\fR. If additional directories are specified with \fB\-I\fR options after the \fB\-I\-\fR, those directories are searched for all \fB#include\fR directives. .Sp In addition, \fB\-I\-\fR inhibits the use of the directory of the current file directory as the first search directory for \f(CW\*(C`#include\ "\f(CIfile\f(CW"\*(C'\fR. .IP "\fB\-nostdinc\fR" 4 .IX Item "-nostdinc" Do not search the standard system directories for header files. Only the directories you have specified with \fB\-I\fR options (and the directory of the current file, if appropriate) are searched. .IP "\fB\-nostdinc++\fR" 4 .IX Item "-nostdinc++" Do not search for header files in the \*(C+\-specific standard directories, but do still search the other standard directories. (This option is used when building the \*(C+ library.) .IP "\fB\-include\fR \fIfile\fR" 4 .IX Item "-include file" Process \fIfile\fR as if \f(CW\*(C`#include "file"\*(C'\fR appeared as the first line of the primary source file. However, the first directory searched for \fIfile\fR is the preprocessor's working directory \fIinstead of\fR the directory containing the main source file. If not found there, it is searched for in the remainder of the \f(CW\*(C`#include "..."\*(C'\fR search chain as normal. .Sp If multiple \fB\-include\fR options are given, the files are included in the order they appear on the command line. .IP "\fB\-imacros\fR \fIfile\fR" 4 .IX Item "-imacros file" Exactly like \fB\-include\fR, except that any output produced by scanning \fIfile\fR is thrown away. Macros it defines remain defined. This allows you to acquire all the macros from a header without also processing its declarations. .Sp All files specified by \fB\-imacros\fR are processed before all files specified by \fB\-include\fR. .IP "\fB\-idirafter\fR \fIdir\fR" 4 .IX Item "-idirafter dir" Search \fIdir\fR for header files, but do it \fIafter\fR all directories specified with \fB\-I\fR and the standard system directories have been exhausted. \fIdir\fR is treated as a system include directory. .IP "\fB\-iprefix\fR \fIprefix\fR" 4 .IX Item "-iprefix prefix" Specify \fIprefix\fR as the prefix for subsequent \fB\-iwithprefix\fR options. If the prefix represents a directory, you should include the final \fB/\fR. .IP "\fB\-iwithprefix\fR \fIdir\fR" 4 .IX Item "-iwithprefix dir" .PD 0 .IP "\fB\-iwithprefixbefore\fR \fIdir\fR" 4 .IX Item "-iwithprefixbefore dir" .PD Append \fIdir\fR to the prefix specified previously with \&\fB\-iprefix\fR, and add the resulting directory to the include search path. \fB\-iwithprefixbefore\fR puts it in the same place \fB\-I\fR would; \fB\-iwithprefix\fR puts it where \fB\-idirafter\fR would. .Sp Use of these options is discouraged. .IP "\fB\-isystem\fR \fIdir\fR" 4 .IX Item "-isystem dir" Search \fIdir\fR for header files, after all directories specified by \&\fB\-I\fR but before the standard system directories. Mark it as a system directory, so that it gets the same special treatment as is applied to the standard system directories. .IP "\fB\-fpreprocessed\fR" 4 .IX Item "-fpreprocessed" Indicate to the preprocessor that the input file has already been preprocessed. This suppresses things like macro expansion, trigraph conversion, escaped newline splicing, and processing of most directives. The preprocessor still recognizes and removes comments, so that you can pass a file preprocessed with \fB\-C\fR to the compiler without problems. In this mode the integrated preprocessor is little more than a tokenizer for the front ends. .Sp \&\fB\-fpreprocessed\fR is implicit if the input file has one of the extensions \fB.i\fR, \fB.ii\fR or \fB.mi\fR. These are the extensions that \s-1GCC\s0 uses for preprocessed files created by \&\fB\-save\-temps\fR. .IP "\fB\-ftabstop=\fR\fIwidth\fR" 4 .IX Item "-ftabstop=width" Set the distance between tab stops. This helps the preprocessor report correct column numbers in warnings or errors, even if tabs appear on the line. If the value is less than 1 or greater than 100, the option is ignored. The default is 8. .IP "\fB\-fno\-show\-column\fR" 4 .IX Item "-fno-show-column" Do not print column numbers in diagnostics. This may be necessary if diagnostics are being scanned by a program that does not understand the column numbers, such as \fBdejagnu\fR. .IP "\fB\-A\fR \fIpredicate\fR\fB=\fR\fIanswer\fR" 4 .IX Item "-A predicate=answer" Make an assertion with the predicate \fIpredicate\fR and answer \&\fIanswer\fR. This form is preferred to the older form \fB\-A\fR \&\fIpredicate\fR\fB(\fR\fIanswer\fR\fB)\fR, which is still supported, because it does not use shell special characters. .IP "\fB\-A \-\fR\fIpredicate\fR\fB=\fR\fIanswer\fR" 4 .IX Item "-A -predicate=answer" Cancel an assertion with the predicate \fIpredicate\fR and answer \&\fIanswer\fR. .IP "\fB\-A\-\fR" 4 .IX Item "-A-" Cancel all predefined assertions and all assertions preceding it on the command line. Also, undefine all predefined macros and all macros preceding it on the command line. (This is a historical wart and may change in the future.) .IP "\fB\-dCHARS\fR" 4 .IX Item "-dCHARS" \&\fI\s-1CHARS\s0\fR is a sequence of one or more of the following characters, and must not be preceded by a space. Other characters are interpreted by the compiler proper, or reserved for future versions of \s-1GCC\s0, and so are silently ignored. If you specify characters whose behavior conflicts, the result is undefined. .RS 4 .IP "\fBM\fR" 4 .IX Item "M" Instead of the normal output, generate a list of \fB#define\fR directives for all the macros defined during the execution of the preprocessor, including predefined macros. This gives you a way of finding out what is predefined in your version of the preprocessor. Assuming you have no file \fIfoo.h\fR, the command .Sp .Vb 1 \& touch foo.h; cpp -dM foo.h .Ve .Sp will show all the predefined macros. .IP "\fBD\fR" 4 .IX Item "D" Like \fBM\fR except in two respects: it does \fInot\fR include the predefined macros, and it outputs \fIboth\fR the \fB#define\fR directives and the result of preprocessing. Both kinds of output go to the standard output file. .IP "\fBN\fR" 4 .IX Item "N" Like \fBD\fR, but emit only the macro names, not their expansions. .IP "\fBI\fR" 4 .IX Item "I" Output \fB#include\fR directives in addition to the result of preprocessing. .RE .RS 4 .RE .IP "\fB\-P\fR" 4 .IX Item "-P" Inhibit generation of linemarkers in the output from the preprocessor. This might be useful when running the preprocessor on something that is not C code, and will be sent to a program which might be confused by the linemarkers. .IP "\fB\-C\fR" 4 .IX Item "-C" Do not discard comments. All comments are passed through to the output file, except for comments in processed directives, which are deleted along with the directive. .Sp You should be prepared for side effects when using \fB\-C\fR; it causes the preprocessor to treat comments as tokens in their own right. For example, comments appearing at the start of what would be a directive line have the effect of turning that line into an ordinary source line, since the first token on the line is no longer a \fB#\fR. .IP "\fB\-CC\fR" 4 .IX Item "-CC" Do not discard comments, including during macro expansion. This is like \fB\-C\fR, except that comments contained within macros are also passed through to the output file where the macro is expanded. .Sp In addition to the side-effects of the \fB\-C\fR option, the \&\fB\-CC\fR option causes all \*(C+\-style comments inside a macro to be converted to C\-style comments. This is to prevent later use of that macro from inadvertently commenting out the remainder of the source line. .Sp The \fB\-CC\fR option is generally used to support lint comments. .IP "\fB\-gcc\fR" 4 .IX Item "-gcc" Define the macros _\|_GNUC_\|_, _\|_GNUC_MINOR_\|_ and _\|_GNUC_PATCHLEVEL_\|_. These are defined automatically when you use \&\fBgcc \-E\fR; you can turn them off in that case with \&\fB\-no\-gcc\fR. .IP "\fB\-traditional\-cpp\fR" 4 .IX Item "-traditional-cpp" Try to imitate the behavior of old-fashioned C preprocessors, as opposed to \s-1ISO\s0 C preprocessors. .IP "\fB\-trigraphs\fR" 4 .IX Item "-trigraphs" Process trigraph sequences. These are three-character sequences, all starting with \fB??\fR, that are defined by \s-1ISO\s0 C to stand for single characters. For example, \&\fB??/\fR stands for \fB\e\fR, so \fB'??/n'\fR is a character constant for a newline. By default, \s-1GCC\s0 ignores trigraphs, but in standard-conforming modes it converts them. See the \fB\-std\fR and \&\fB\-ansi\fR options. .Sp The nine trigraphs and their replacements are .Sp .Vb 2 \& Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- \& Replacement: [ ] { } # \e ^ | ~ .Ve .IP "\fB\-remap\fR" 4 .IX Item "-remap" Enable special code to work around file systems which only permit very short file names, such as \s-1MS\-DOS\s0. .IP "\fB\-\-help\fR" 4 .IX Item "--help" .PD 0 .IP "\fB\-\-target\-help\fR" 4 .IX Item "--target-help" .PD Print text describing all the command line options instead of preprocessing anything. .IP "\fB\-v\fR" 4 .IX Item "-v" Verbose mode. Print out \s-1GNU\s0 \s-1CPP\s0's version number at the beginning of execution, and report the final form of the include path. .IP "\fB\-H\fR" 4 .IX Item "-H" Print the name of each header file used, in addition to other normal activities. Each name is indented to show how deep in the \&\fB#include\fR stack it is. Precompiled header files are also printed, even if they are found to be invalid; an invalid precompiled header file is printed with \fB...x\fR and a valid one with \fB...!\fR . .IP "\fB\-version\fR" 4 .IX Item "-version" .PD 0 .IP "\fB\-\-version\fR" 4 .IX Item "--version" .PD Print out \s-1GNU\s0 \s-1CPP\s0's version number. With one dash, proceed to preprocess as normal. With two dashes, exit immediately. .Sh "Passing Options to the Assembler" .IX Subsection "Passing Options to the Assembler" You can pass options to the assembler. .IP "\fB\-Wa,\fR\fIoption\fR" 4 .IX Item "-Wa,option" Pass \fIoption\fR as an option to the assembler. If \fIoption\fR contains commas, it is split into multiple options at the commas. .Sh "Options for Linking" .IX Subsection "Options for Linking" These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step. .PP In addition to the options listed below, Apple's \s-1GCC\s0 also accepts and passes nearly all of the options defined by the linker \fBld\fR and by the library tool \fBlibtool\fR. Common options include \&\fB\-framework\fR, \fB\-dynamic\fR, \fB\-bundle\fR, \&\fB\-flat_namespace\fR, and so forth. See the ld and libtool man pages for further details. .IP "\fIobject-file-name\fR" 4 .IX Item "object-file-name" A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker. .IP "\fB\-c\fR" 4 .IX Item "-c" .PD 0 .IP "\fB\-S\fR" 4 .IX Item "-S" .IP "\fB\-E\fR" 4 .IX Item "-E" .PD If any of these options is used, then the linker is not run, and object file names should not be used as arguments. .IP "\fB\-l\fR\fIlibrary\fR" 4 .IX Item "-llibrary" .PD 0 .IP "\fB\-l\fR \fIlibrary\fR" 4 .IX Item "-l library" .PD Search the library named \fIlibrary\fR when linking. (The second alternative with the library as a separate argument is only for \&\s-1POSIX\s0 compliance and is not recommended.) .Sp It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, \fBfoo.o \-lz bar.o\fR searches library \fBz\fR after file \fIfoo.o\fR but before \fIbar.o\fR. If \fIbar.o\fR refers to functions in \fBz\fR, those functions may not be loaded. .Sp The linker searches a standard list of directories for the library, which is actually a file named \fIlib\fIlibrary\fI.a\fR. The linker then uses this file as if it had been specified precisely by name. .Sp The directories searched include several standard system directories plus any that you specify with \fB\-L\fR. .Sp Normally the files found this way are library files\-\-\-archive files whose members are object files. The linker handles an archive file by scanning through it for members which define symbols that have so far been referenced but not defined. But if the file that is found is an ordinary object file, it is linked in the usual fashion. The only difference between using an \fB\-l\fR option and specifying a file name is that \fB\-l\fR surrounds \fIlibrary\fR with \fBlib\fR and \fB.a\fR and searches several directories. .IP "\fB\-lobjc\fR" 4 .IX Item "-lobjc" You need this special case of the \fB\-l\fR option in order to link an Objective-C program. .IP "\fB\-nostartfiles\fR" 4 .IX Item "-nostartfiles" Do not use the standard system startup files when linking. The standard system libraries are used normally, unless \fB\-nostdlib\fR or \fB\-nodefaultlibs\fR is used. .IP "\fB\-nodefaultlibs\fR" 4 .IX Item "-nodefaultlibs" Do not use the standard system libraries when linking. Only the libraries you specify will be passed to the linker. The standard startup files are used normally, unless \fB\-nostartfiles\fR is used. The compiler may generate calls to memcmp, memset, and memcpy for System V (and \s-1ISO\s0 C) environments or to bcopy and bzero for \&\s-1BSD\s0 environments. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. .IP "\fB\-nostdlib\fR" 4 .IX Item "-nostdlib" Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify will be passed to the linker. The compiler may generate calls to memcmp, memset, and memcpy for System V (and \s-1ISO\s0 C) environments or to bcopy and bzero for \&\s-1BSD\s0 environments. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. .IP "\fB\-no\-c++filt\fR" 4 .IX Item "-no-c++filt" By default all linker diagnostic output is piped through c++filt. This option suppresses that behavior. (\s-1APPLE\s0 \s-1ONLY\s0) .Sp One of the standard libraries bypassed by \fB\-nostdlib\fR and \&\fB\-nodefaultlibs\fR is \fIlibgcc.a\fR, a library of internal subroutines that \s-1GCC\s0 uses to overcome shortcomings of particular machines, or special needs for some languages. .Sp In most cases, you need \fIlibgcc.a\fR even when you want to avoid other standard libraries. In other words, when you specify \fB\-nostdlib\fR or \fB\-nodefaultlibs\fR you should usually specify \fB\-lgcc\fR as well. This ensures that you have no unresolved references to internal \s-1GCC\s0 library subroutines. (For example, \fB_\|_main\fR, used to ensure \*(C+ constructors will be called.) .IP "\fB\-s\fR" 4 .IX Item "-s" Remove all symbol table and relocation information from the executable. .IP "\fB\-static\fR" 4 .IX Item "-static" On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect. .Sp This option will not work on Mac \s-1OS\s0 X unless all of your libraries (including \fIlibgcc.a\fR) have also been compiled with \&\fB\-static\fR. .IP "\fB\-shared\fR" 4 .IX Item "-shared" Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options that were used to generate code (\fB\-fpic\fR, \fB\-fPIC\fR, or model suboptions) when you specify this option.[1] .Sp This option is not supported on Mac \s-1OS\s0 X. .IP "\fB\-shared\-libgcc\fR" 4 .IX Item "-shared-libgcc" .PD 0 .IP "\fB\-static\-libgcc\fR" 4 .IX Item "-static-libgcc" .PD On systems that provide \fIlibgcc\fR as a shared library, these options force the use of either the shared or static version respectively. If no shared version of \fIlibgcc\fR was built when the compiler was configured, these options have no effect. .Sp There are several situations in which an application should use the shared \fIlibgcc\fR instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared \fIlibgcc\fR. .Sp Therefore, the G++ and \s-1GCJ\s0 drivers automatically add \&\fB\-shared\-libgcc\fR whenever you build a shared library or a main executable, because \*(C+ and Java programs typically use exceptions, so this is the right thing to do. .Sp If, instead, you use the \s-1GCC\s0 driver to create shared libraries, you may find that they will not always be linked with the shared \fIlibgcc\fR. If \s-1GCC\s0 finds, at its configuration time, that you have a \s-1GNU\s0 linker that does not support option \fB\-\-eh\-frame\-hdr\fR, it will link the shared version of \fIlibgcc\fR into shared libraries by default. Otherwise, it will take advantage of the linker and optimize away the linking with the shared version of \fIlibgcc\fR, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time. .Sp However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ or \s-1GCJ\s0 driver, as appropriate for the languages used in the program, or using the option \&\fB\-shared\-libgcc\fR, such that it is linked with the shared \&\fIlibgcc\fR. .IP "\fB\-symbolic\fR" 4 .IX Item "-symbolic" Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option \fB\-Xlinker \-z \-Xlinker defs\fR). Only a few systems support this option. .IP "\fB\-Xlinker\fR \fIoption\fR" 4 .IX Item "-Xlinker option" Pass \fIoption\fR as an option to the linker. You can use this to supply system-specific linker options which \s-1GCC\s0 does not know how to recognize. .Sp If you want to pass an option that takes an argument, you must use \&\fB\-Xlinker\fR twice, once for the option and once for the argument. For example, to pass \fB\-assert definitions\fR, you must write \&\fB\-Xlinker \-assert \-Xlinker definitions\fR. It does not work to write \&\fB\-Xlinker \*(L"\-assert definitions\*(R"\fR, because this passes the entire string as a single argument, which is not what the linker expects. .IP "\fB\-Wl,\fR\fIoption\fR" 4 .IX Item "-Wl,option" Pass \fIoption\fR as an option to the linker. If \fIoption\fR contains commas, it is split into multiple options at the commas. .IP "\fB\-u\fR \fIsymbol\fR" 4 .IX Item "-u symbol" Pretend the symbol \fIsymbol\fR is undefined, to force linking of library modules to define it. You can use \fB\-u\fR multiple times with different symbols to force loading of additional library modules. .Sh "Options for Directory Search" .IX Subsection "Options for Directory Search" These options specify directories to search for header files, for libraries and for parts of the compiler: .IP "\fB\-I\fR\fIdir\fR" 4 .IX Item "-Idir" Add the directory \fIdir\fR to the head of the list of directories to be searched for header files. This can be used to override a system header file, substituting your own version, since these directories are searched before the system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files (use \fB\-isystem\fR for that). If you use more than one \fB\-I\fR option, the directories are scanned in left-to-right order; the standard system directories come after. .Sp If a standard system include directory, or a directory specified with \&\fB\-isystem\fR, is also specified with \fB\-I\fR, the \fB\-I\fR option will be ignored. The directory will still be searched but as a system directory at its normal position in the system include chain. This is to ensure that \s-1GCC\s0's procedure to fix buggy system headers and the ordering for the include_next directive are not inadvertently changed. If you really need to change the search order for system directories, use the \fB\-nostdinc\fR and/or \fB\-isystem\fR options. .IP "\fB\-I\-\fR" 4 .IX Item "-I-" Any directories you specify with \fB\-I\fR options before the \fB\-I\-\fR option are searched only for the case of \fB#include "\fR\fIfile\fR\fB"\fR; they are not searched for \fB#include <\fR\fIfile\fR\fB>\fR. .Sp If additional directories are specified with \fB\-I\fR options after the \fB\-I\-\fR, these directories are searched for all \fB#include\fR directives. (Ordinarily \fIall\fR \fB\-I\fR directories are used this way.) .Sp In addition, the \fB\-I\-\fR option inhibits the use of the current directory (where the current input file came from) as the first search directory for \fB#include "\fR\fIfile\fR\fB"\fR. There is no way to override this effect of \fB\-I\-\fR. With \fB\-I.\fR you can specify searching the directory which was current when the compiler was invoked. That is not exactly the same as what the preprocessor does by default, but it is often satisfactory. .Sp \&\fB\-I\-\fR does not inhibit the use of the standard system directories for header files. Thus, \fB\-I\-\fR and \fB\-nostdinc\fR are independent. .IP "\fB\-L\fR\fIdir\fR" 4 .IX Item "-Ldir" Add directory \fIdir\fR to the list of directories to be searched for \fB\-l\fR. .IP "\fB\-F\fR\fIdir\fR" 4 .IX Item "-Fdir" In Apple's version of \s-1GCC\s0 only, add the directory \fIdir\fR to the head of the list of directories to be searched for frameworks. .Sp The framework search algorithm is, for an inclusion of \&\fB<Fmwk/Header.h>\fR, to look for files named \&\fI\fIpath\fI/Fmwk.framework/Headers/Header.h\fR or \&\fI\fIpath\fI/Fmwk.framework/PrivateHeaders/Header.h\fR where \&\fIpath\fR includes \fI/System/Library/Frameworks/\fR \&\fI/Library/Frameworks/\fR, and \fI/Local/Library/Frameworks/\fR, plus any additional paths specified by \fB\-F\fR. .Sp All the \fB\-F\fR options are also passed to the linker. .IP "\fB\-B\fR\fIprefix\fR" 4 .IX Item "-Bprefix" This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. .Sp The compiler driver program runs one or more of the subprograms \&\fIcpp\fR, \fIcc1\fR, \fIas\fR and \fIld\fR. It tries \&\fIprefix\fR as a prefix for each program it tries to run, both with and without \fImachine\fR\fB/\fR\fIversion\fR\fB/\fR. .Sp For each subprogram to be run, the compiler driver first tries the \&\fB\-B\fR prefix, if any. If that name is not found, or if \fB\-B\fR was not specified, the driver tries two standard prefixes, which are \&\fI/usr/lib/gcc/\fR and \fI/usr/local/lib/gcc\-lib/\fR. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your \&\fB\s-1PATH\s0\fR environment variable. .Sp The compiler will check to see if the path provided by the \fB\-B\fR refers to a directory, and if necessary it will add a directory separator character at the end of the path. .Sp \&\fB\-B\fR prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into \fB\-L\fR options for the linker. They also apply to includes files in the preprocessor, because the compiler translates these options into \fB\-isystem\fR options for the preprocessor. In this case, the compiler appends \fBinclude\fR to the prefix. .Sp The run-time support file \fIlibgcc.a\fR can also be searched for using the \fB\-B\fR prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. .Sp Another way to specify a prefix much like the \fB\-B\fR prefix is to use the environment variable \fB\s-1GCC_EXEC_PREFIX\s0\fR. .Sp As a special kludge, if the path provided by \fB\-B\fR is \&\fI[dir/]stage\fIN\fI/\fR, where \fIN\fR is a number in the range 0 to 9, then it will be replaced by \fI[dir/]include\fR. This is to help with boot-strapping the compiler. .IP "\fB\-specs=\fR\fIfile\fR" 4 .IX Item "-specs=file" Process \fIfile\fR after the compiler reads in the standard \fIspecs\fR file, in order to override the defaults that the \fIgcc\fR driver program uses when determining what switches to pass to \fIcc1\fR, \&\fIcc1plus\fR, \fIas\fR, \fIld\fR, etc. More than one \&\fB\-specs=\fR\fIfile\fR can be specified on the command line, and they are processed in order, from left to right. .Sh "Specifying Target Machine and Compiler Version" .IX Subsection "Specifying Target Machine and Compiler Version" The usual way to run \s-1GCC\s0 is to run the executable called \fIgcc\fR, or \&\fI<machine>\-gcc\fR when cross\-compiling, or \&\fI<machine>\-gcc\-<version>\fR to run a version other than the one that was installed last. Sometimes this is inconvenient, so \s-1GCC\s0 provides options that will switch to another cross-compiler or version. .IP "\fB\-b\fR \fImachine\fR" 4 .IX Item "-b machine" The argument \fImachine\fR specifies the target machine for compilation. .Sp The value to use for \fImachine\fR is the same as was specified as the machine type when configuring \s-1GCC\s0 as a cross\-compiler. For example, if a cross-compiler was configured with \fBconfigure i386v\fR, meaning to compile for an 80386 running System V, then you would specify \fB\-b i386v\fR to run that cross compiler. .IP "\fB\-V\fR \fIversion\fR" 4 .IX Item "-V version" The argument \fIversion\fR specifies which version of \s-1GCC\s0 to run. This is useful when multiple versions are installed. For example, \&\fIversion\fR might be \fB2.0\fR, meaning to run \s-1GCC\s0 version 2.0. .PP The \fB\-V\fR and \fB\-b\fR options work by running the \&\fI<machine>\-gcc\-<version>\fR executable, so there's no real reason to use them if you can just run that directly. .Sh "Hardware Models and Configurations" .IX Subsection "Hardware Models and Configurations" Earlier we discussed the standard option \fB\-b\fR which chooses among different installed compilers for completely different target machines, such as \s-1VAX\s0 vs. 68000 vs. 80386. .PP In addition, each of these target machine types can have its own special options, starting with \fB\-m\fR, to choose among various hardware models or configurations\-\-\-for example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or configuration, according to the options specified. .PP Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform. .PP These options are defined by the macro \f(CW\*(C`TARGET_SWITCHES\*(C'\fR in the machine description. The default for the options is also defined by that macro, which enables you to change the defaults. .PP \fI\s-1IBM\s0 \s-1RS/6000\s0 and PowerPC Options\fR .IX Subsection "IBM RS/6000 and PowerPC Options" .PP These \fB\-m\fR options are defined for the \s-1IBM\s0 \s-1RS/6000\s0 and PowerPC: .IP "\fB\-mpower\fR" 4 .IX Item "-mpower" .PD 0 .IP "\fB\-mno\-power\fR" 4 .IX Item "-mno-power" .IP "\fB\-mpower2\fR" 4 .IX Item "-mpower2" .IP "\fB\-mno\-power2\fR" 4 .IX Item "-mno-power2" .IP "\fB\-mpowerpc\fR" 4 .IX Item "-mpowerpc" .IP "\fB\-mno\-powerpc\fR" 4 .IX Item "-mno-powerpc" .IP "\fB\-mpowerpc\-gpopt\fR" 4 .IX Item "-mpowerpc-gpopt" .IP "\fB\-mno\-powerpc\-gpopt\fR" 4 .IX Item "-mno-powerpc-gpopt" .IP "\fB\-mpowerpc\-gfxopt\fR" 4 .IX Item "-mpowerpc-gfxopt" .IP "\fB\-mno\-powerpc\-gfxopt\fR" 4 .IX Item "-mno-powerpc-gfxopt" .IP "\fB\-mpowerpc64\fR" 4 .IX Item "-mpowerpc64" .IP "\fB\-mno\-powerpc64\fR" 4 .IX Item "-mno-powerpc64" .PD \&\s-1GCC\s0 supports two related instruction set architectures for the \&\s-1RS/6000\s0 and PowerPC. The \fI\s-1POWER\s0\fR instruction set are those instructions supported by the \fBrios\fR chip set used in the original \&\s-1RS/6000\s0 systems and the \fIPowerPC\fR instruction set is the architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and the \s-1IBM\s0 4xx microprocessors. .Sp Neither architecture is a subset of the other. However there is a large common subset of instructions supported by both. An \s-1MQ\s0 register is included in processors supporting the \s-1POWER\s0 architecture. .Sp You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring \s-1GCC\s0. Specifying the \&\fB\-mcpu=\fR\fIcpu_type\fR overrides the specification of these options. We recommend you use the \fB\-mcpu=\fR\fIcpu_type\fR option rather than the options listed above. .Sp The \fB\-mpower\fR option allows \s-1GCC\s0 to generate instructions that are found only in the \s-1POWER\s0 architecture and to use the \s-1MQ\s0 register. Specifying \fB\-mpower2\fR implies \fB\-power\fR and also allows \s-1GCC\s0 to generate instructions that are present in the \s-1POWER2\s0 architecture but not the original \s-1POWER\s0 architecture. .Sp The \fB\-mpowerpc\fR option allows \s-1GCC\s0 to generate instructions that are found only in the 32\-bit subset of the PowerPC architecture. Specifying \fB\-mpowerpc\-gpopt\fR implies \fB\-mpowerpc\fR and also allows \&\s-1GCC\s0 to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying \&\fB\-mpowerpc\-gfxopt\fR implies \fB\-mpowerpc\fR and also allows \s-1GCC\s0 to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. .Sp The \fB\-mpowerpc64\fR option allows \s-1GCC\s0 to generate the additional 64\-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64\-bit, doubleword quantities. \s-1GCC\s0 defaults to \&\fB\-mno\-powerpc64\fR. .Sp If you specify both \fB\-mno\-power\fR and \fB\-mno\-powerpc\fR, \s-1GCC\s0 will use only the instructions in the common subset of both architectures plus some special \s-1AIX\s0 common-mode calls, and will not use the \s-1MQ\s0 register. Specifying both \fB\-mpower\fR and \fB\-mpowerpc\fR permits \s-1GCC\s0 to use any instruction from either architecture and to allow use of the \s-1MQ\s0 register; specify this for the Motorola \s-1MPC601\s0. .IP "\fB\-mnew\-mnemonics\fR" 4 .IX Item "-mnew-mnemonics" .PD 0 .IP "\fB\-mold\-mnemonics\fR" 4 .IX Item "-mold-mnemonics" .PD Select which mnemonics to use in the generated assembler code. With \&\fB\-mnew\-mnemonics\fR, \s-1GCC\s0 uses the assembler mnemonics defined for the PowerPC architecture. With \fB\-mold\-mnemonics\fR it uses the assembler mnemonics defined for the \s-1POWER\s0 architecture. Instructions defined in only one architecture have only one mnemonic; \s-1GCC\s0 uses that mnemonic irrespective of which of these options is specified. .Sp \&\s-1GCC\s0 defaults to the mnemonics appropriate for the architecture in use. Specifying \fB\-mcpu=\fR\fIcpu_type\fR sometimes overrides the value of these option. Unless you are building a cross\-compiler, you should normally not specify either \fB\-mnew\-mnemonics\fR or \&\fB\-mold\-mnemonics\fR, but should instead accept the default. .IP "\fB\-mcpu=\fR\fIcpu_type\fR" 4 .IX Item "-mcpu=cpu_type" Set architecture type, register usage, choice of mnemonics, and instruction scheduling parameters for machine type \fIcpu_type\fR. Supported values for \fIcpu_type\fR are \fBrios\fR, \fBrios1\fR, \&\fBrsc\fR, \fBrios2\fR, \fBrs64a\fR, \fB601\fR, \fB602\fR, \&\fB603\fR, \fB603e\fR, \fB604\fR, \fB604e\fR, \fB620\fR, \&\fB630\fR, \fB740\fR, \fB7400\fR, \fB7450\fR, \fB750\fR, \&\fBpower\fR, \fBpower2\fR, \fBpowerpc\fR, \fB403\fR, \fB505\fR, \&\fB801\fR, \fB821\fR, \fB823\fR, and \fB860\fR and \fBcommon\fR. .Sp \&\fB\-mcpu=common\fR selects a completely generic processor. Code generated under this option will run on any \s-1POWER\s0 or PowerPC processor. \&\s-1GCC\s0 will use only the instructions in the common subset of both architectures, and will not use the \s-1MQ\s0 register. \s-1GCC\s0 assumes a generic processor model for scheduling purposes. .Sp \&\fB\-mcpu=power\fR, \fB\-mcpu=power2\fR, \fB\-mcpu=powerpc\fR, and \&\fB\-mcpu=powerpc64\fR specify generic \s-1POWER\s0, \s-1POWER2\s0, pure 32\-bit PowerPC (i.e., not \s-1MPC601\s0), and 64\-bit PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes. .Sp The other options specify a specific processor. Code generated under those options will run best on that processor, and may not run at all on others. .Sp The \fB\-mcpu\fR options automatically enable or disable other \&\fB\-m\fR options as follows: .RS 4 .IP "\fBcommon\fR" 4 .IX Item "common" \&\fB\-mno\-power\fR, \fB\-mno\-powerpc\fR .IP "\fBpower\fR" 4 .IX Item "power" .PD 0 .IP "\fBpower2\fR" 4 .IX Item "power2" .IP "\fBrios1\fR" 4 .IX Item "rios1" .IP "\fBrios2\fR" 4 .IX Item "rios2" .IP "\fBrsc\fR" 4 .IX Item "rsc" .PD \&\fB\-mpower\fR, \fB\-mno\-powerpc\fR, \fB\-mno\-new\-mnemonics\fR .IP "\fBpowerpc\fR" 4 .IX Item "powerpc" .PD 0 .IP "\fBrs64a\fR" 4 .IX Item "rs64a" .IP "\fB602\fR" 4 .IX Item "602" .IP "\fB603\fR" 4 .IX Item "603" .IP "\fB603e\fR" 4 .IX Item "603e" .IP "\fB604\fR" 4 .IX Item "604" .IP "\fB620\fR" 4 .IX Item "620" .IP "\fB630\fR" 4 .IX Item "630" .IP "\fB740\fR" 4 .IX Item "740" .IP "\fB7400\fR" 4 .IX Item "7400" .IP "\fB7450\fR" 4 .IX Item "7450" .IP "\fB750\fR" 4 .IX Item "750" .IP "\fB505\fR" 4 .IX Item "505" .PD \&\fB\-mno\-power\fR, \fB\-mpowerpc\fR, \fB\-mnew\-mnemonics\fR .IP "\fB601\fR" 4 .IX Item "601" \&\fB\-mpower\fR, \fB\-mpowerpc\fR, \fB\-mnew\-mnemonics\fR .IP "\fB403\fR" 4 .IX Item "403" .PD 0 .IP "\fB821\fR" 4 .IX Item "821" .IP "\fB860\fR" 4 .IX Item "860" .PD \&\fB\-mno\-power\fR, \fB\-mpowerpc\fR, \fB\-mnew\-mnemonics\fR, \fB\-msoft\-float\fR .RE .RS 4 .RE .IP "\fB\-mtune=\fR\fIcpu_type\fR" 4 .IX Item "-mtune=cpu_type" Set the instruction scheduling parameters for machine type \&\fIcpu_type\fR, but do not set the architecture type, register usage, or choice of mnemonics, as \fB\-mcpu=\fR\fIcpu_type\fR would. The same values for \fIcpu_type\fR are used for \fB\-mtune\fR as for \&\fB\-mcpu\fR. If both are specified, the code generated will use the architecture, registers, and mnemonics set by \fB\-mcpu\fR, but the scheduling parameters set by \fB\-mtune\fR. .IP "\fB\-maltivec\fR" 4 .IX Item "-maltivec" .PD 0 .IP "\fB\-mno\-altivec\fR" 4 .IX Item "-mno-altivec" .PD These switches enable or disable the use of built-in functions that allow access to the AltiVec instruction set. You may also need to set \&\fB\-mabi=altivec\fR to adjust the current \s-1ABI\s0 with AltiVec \s-1ABI\s0 enhancements. .Sp This option is not supported on Mac \s-1OS\s0 X; use \fB\-faltivec\fR instead. .IP "\fB\-mabi=spe\fR" 4 .IX Item "-mabi=spe" Extend the current \s-1ABI\s0 with \s-1SPE\s0 \s-1ABI\s0 extensions. This does not change the default \s-1ABI\s0, instead it adds the \s-1SPE\s0 \s-1ABI\s0 extensions to the current \&\s-1ABI\s0. .IP "\fB\-mabi=no\-spe\fR" 4 .IX Item "-mabi=no-spe" Disable Booke \s-1SPE\s0 \s-1ABI\s0 extensions for the current \s-1ABI\s0. .IP "\fB\-misel=\fR\fIyes/no\fR" 4 .IX Item "-misel=yes/no" .PD 0 .IP "\fB\-misel\fR" 4 .IX Item "-misel" .PD This switch enables or disables the generation of \s-1ISEL\s0 instructions. .IP "\fB\-mfull\-toc\fR" 4 .IX Item "-mfull-toc" .PD 0 .IP "\fB\-mno\-fp\-in\-toc\fR" 4 .IX Item "-mno-fp-in-toc" .IP "\fB\-mno\-sum\-in\-toc\fR" 4 .IX Item "-mno-sum-in-toc" .IP "\fB\-mminimal\-toc\fR" 4 .IX Item "-mminimal-toc" .PD Modify generation of the \s-1TOC\s0 (Table Of Contents), which is created for every executable file. The \fB\-mfull\-toc\fR option is selected by default. In that case, \s-1GCC\s0 will allocate at least one \s-1TOC\s0 entry for each unique non-automatic variable reference in your program. \s-1GCC\s0 will also place floating-point constants in the \s-1TOC\s0. However, only 16,384 entries are available in the \s-1TOC\s0. .Sp If you receive a linker error message that saying you have overflowed the available \s-1TOC\s0 space, you can reduce the amount of \s-1TOC\s0 space used with the \fB\-mno\-fp\-in\-toc\fR and \fB\-mno\-sum\-in\-toc\fR options. \&\fB\-mno\-fp\-in\-toc\fR prevents \s-1GCC\s0 from putting floating-point constants in the \s-1TOC\s0 and \fB\-mno\-sum\-in\-toc\fR forces \s-1GCC\s0 to generate code to calculate the sum of an address and a constant at run-time instead of putting that sum into the \s-1TOC\s0. You may specify one or both of these options. Each causes \s-1GCC\s0 to produce very slightly slower and larger code at the expense of conserving \s-1TOC\s0 space. .Sp If you still run out of space in the \s-1TOC\s0 even when you specify both of these options, specify \fB\-mminimal\-toc\fR instead. This option causes \&\s-1GCC\s0 to make only one \s-1TOC\s0 entry for every file. When you specify this option, \s-1GCC\s0 will produce code that is slower and larger but which uses extremely little \s-1TOC\s0 space. You may wish to use this option only on files that contain less frequently executed code. .IP "\fB\-maix64\fR" 4 .IX Item "-maix64" .PD 0 .IP "\fB\-maix32\fR" 4 .IX Item "-maix32" .PD Enable 64\-bit \s-1AIX\s0 \s-1ABI\s0 and calling convention: 64\-bit pointers, 64\-bit \&\f(CW\*(C`long\*(C'\fR type, and the infrastructure needed to support them. Specifying \fB\-maix64\fR implies \fB\-mpowerpc64\fR and \&\fB\-mpowerpc\fR, while \fB\-maix32\fR disables the 64\-bit \s-1ABI\s0 and implies \fB\-mno\-powerpc64\fR. \s-1GCC\s0 defaults to \fB\-maix32\fR. .IP "\fB\-mxl\-call\fR" 4 .IX Item "-mxl-call" .PD 0 .IP "\fB\-mno\-xl\-call\fR" 4 .IX Item "-mno-xl-call" .PD On \s-1AIX\s0, pass floating-point arguments to prototyped functions beyond the register save area (\s-1RSA\s0) on the stack in addition to argument FPRs. The \&\s-1AIX\s0 calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. \s-1AIX\s0 \s-1XL\s0 compilers access floating point arguments which do not fit in the \&\s-1RSA\s0 from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by \s-1AIX\s0 \&\s-1XL\s0 compilers without optimization. .IP "\fB\-mpe\fR" 4 .IX Item "-mpe" Support \fI\s-1IBM\s0 \s-1RS/6000\s0 \s-1SP\s0\fR \fIParallel Environment\fR (\s-1PE\s0). Link an application written to use message passing with special startup code to enable the application to run. The system must have \s-1PE\s0 installed in the standard location (\fI/usr/lpp/ppe.poe/\fR), or the \fIspecs\fR file must be overridden with the \fB\-specs=\fR option to specify the appropriate directory location. The Parallel Environment does not support threads, so the \fB\-mpe\fR option and the \fB\-pthread\fR option are incompatible. .IP "\fB\-malign\-mac68k\fR" 4 .IX Item "-malign-mac68k" .PD 0 .IP "\fB\-malign\-power\fR" 4 .IX Item "-malign-power" .IP "\fB\-malign\-natural\fR" 4 .IX Item "-malign-natural" .PD The option \fB\-malign\-mac68k\fR causes structure fields to be aligned on 2\-byte boundaries, in order to be compatible with m68k compiler output. The option \fB\-malign\-power\fR is the standard alignment mode for the PowerPC. The option \fB\-malign\-natural\fR is an extension of PowerPC alignment that aligns larger data types such as doubles on their natural boundaries. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-msoft\-float\fR" 4 .IX Item "-msoft-float" .PD 0 .IP "\fB\-mhard\-float\fR" 4 .IX Item "-mhard-float" .PD Generate code that does not use (uses) the floating-point register set. Software floating point emulation is provided if you use the \&\fB\-msoft\-float\fR option, and pass the option to \s-1GCC\s0 when linking. .IP "\fB\-mmultiple\fR" 4 .IX Item "-mmultiple" .PD 0 .IP "\fB\-mno\-multiple\fR" 4 .IX Item "-mno-multiple" .PD Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on \s-1POWER\s0 systems, and not generated on PowerPC systems. Do not use \fB\-mmultiple\fR on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. The exceptions are \s-1PPC740\s0 and \&\s-1PPC750\s0 which permit the instructions usage in little endian mode. .IP "\fB\-mstring\fR" 4 .IX Item "-mstring" .PD 0 .IP "\fB\-mno\-string\fR" 4 .IX Item "-mno-string" .PD Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on \&\s-1POWER\s0 systems, and not generated on PowerPC systems. Do not use \&\fB\-mstring\fR on little endian PowerPC systems, since those instructions do not work when the processor is in little endian mode. The exceptions are \s-1PPC740\s0 and \s-1PPC750\s0 which permit the instructions usage in little endian mode. .IP "\fB\-mupdate\fR" 4 .IX Item "-mupdate" .PD 0 .IP "\fB\-mno\-update\fR" 4 .IX Item "-mno-update" .PD Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use \&\fB\-mno\-update\fR, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data. .IP "\fB\-mfused\-madd\fR" 4 .IX Item "-mfused-madd" .PD 0 .IP "\fB\-mno\-fused\-madd\fR" 4 .IX Item "-mno-fused-madd" .PD Generate code that uses (does not use) the floating point multiply and accumulate instructions. These instructions are generated by default if hardware floating is used. .IP "\fB\-mno\-bit\-align\fR" 4 .IX Item "-mno-bit-align" .PD 0 .IP "\fB\-mbit\-align\fR" 4 .IX Item "-mbit-align" .PD On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit\-field. .Sp For example, by default a structure containing nothing but 8 \&\f(CW\*(C`unsigned\*(C'\fR bit-fields of length 1 would be aligned to a 4 byte boundary and have a size of 4 bytes. By using \fB\-mno\-bit\-align\fR, the structure would be aligned to a 1 byte boundary and be one byte in size. .IP "\fB\-mno\-strict\-align\fR" 4 .IX Item "-mno-strict-align" .PD 0 .IP "\fB\-mstrict\-align\fR" 4 .IX Item "-mstrict-align" .PD On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references will be handled by the system. .IP "\fB\-mrelocatable\fR" 4 .IX Item "-mrelocatable" .PD 0 .IP "\fB\-mno\-relocatable\fR" 4 .IX Item "-mno-relocatable" .PD On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. If you use \fB\-mrelocatable\fR on any module, all objects linked together must be compiled with \fB\-mrelocatable\fR or \fB\-mrelocatable\-lib\fR. .IP "\fB\-mrelocatable\-lib\fR" 4 .IX Item "-mrelocatable-lib" .PD 0 .IP "\fB\-mno\-relocatable\-lib\fR" 4 .IX Item "-mno-relocatable-lib" .PD On embedded PowerPC systems generate code that allows (does not allow) the program to be relocated to a different address at runtime. Modules compiled with \fB\-mrelocatable\-lib\fR can be linked with either modules compiled without \fB\-mrelocatable\fR and \fB\-mrelocatable\-lib\fR or with modules compiled with the \fB\-mrelocatable\fR options. .IP "\fB\-mno\-toc\fR" 4 .IX Item "-mno-toc" .PD 0 .IP "\fB\-mtoc\fR" 4 .IX Item "-mtoc" .PD On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program. .IP "\fB\-mlittle\fR" 4 .IX Item "-mlittle" .PD 0 .IP "\fB\-mlittle\-endian\fR" 4 .IX Item "-mlittle-endian" .PD On System V.4 and embedded PowerPC systems compile code for the processor in little endian mode. The \fB\-mlittle\-endian\fR option is the same as \fB\-mlittle\fR. .IP "\fB\-mbig\fR" 4 .IX Item "-mbig" .PD 0 .IP "\fB\-mbig\-endian\fR" 4 .IX Item "-mbig-endian" .PD On System V.4 and embedded PowerPC systems compile code for the processor in big endian mode. The \fB\-mbig\-endian\fR option is the same as \fB\-mbig\fR. .IP "\fB\-mdynamic\-no\-pic\fR" 4 .IX Item "-mdynamic-no-pic" On Darwin and Mac \s-1OS\s0 X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-mlong\-branch\fR" 4 .IX Item "-mlong-branch" On Darwin and Mac \s-1OS\s0 X systems, compile calls to use a 32\-bit destination address. This is to support kernel extensions, which may load anywhere within the kernel address space. (\s-1APPLE\s0 \s-1ONLY\s0) .IP "\fB\-mcall\-sysv\fR" 4 .IX Item "-mcall-sysv" On System V.4 and embedded PowerPC systems compile code using calling conventions that adheres to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured \s-1GCC\s0 using \fBpowerpc\-*\-eabiaix\fR. .IP "\fB\-mcall\-sysv\-eabi\fR" 4 .IX Item "-mcall-sysv-eabi" Specify both \fB\-mcall\-sysv\fR and \fB\-meabi\fR options. .IP "\fB\-mcall\-sysv\-noeabi\fR" 4 .IX Item "-mcall-sysv-noeabi" Specify both \fB\-mcall\-sysv\fR and \fB\-mno\-eabi\fR options. .IP "\fB\-mcall\-aix\fR" 4 .IX Item "-mcall-aix" On System V.4 and embedded PowerPC systems compile code using calling conventions that are similar to those used on \s-1AIX\s0. This is the default if you configured \s-1GCC\s0 using \fBpowerpc\-*\-eabiaix\fR. .IP "\fB\-mcall\-solaris\fR" 4 .IX Item "-mcall-solaris" On System V.4 and embedded PowerPC systems compile code for the Solaris operating system. .IP "\fB\-mcall\-linux\fR" 4 .IX Item "-mcall-linux" On System V.4 and embedded PowerPC systems compile code for the Linux-based \s-1GNU\s0 system. .IP "\fB\-mcall\-gnu\fR" 4 .IX Item "-mcall-gnu" On System V.4 and embedded PowerPC systems compile code for the Hurd-based \s-1GNU\s0 system. .IP "\fB\-mcall\-netbsd\fR" 4 .IX Item "-mcall-netbsd" On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system. .IP "\fB\-maix\-struct\-return\fR" 4 .IX Item "-maix-struct-return" Return all structures in memory (as specified by the \s-1AIX\s0 \s-1ABI\s0). .IP "\fB\-msvr4\-struct\-return\fR" 4 .IX Item "-msvr4-struct-return" Return structures smaller than 8 bytes in registers (as specified by the \&\s-1SVR4\s0 \s-1ABI\s0). .IP "\fB\-mabi=altivec\fR" 4 .IX Item "-mabi=altivec" Extend the current \s-1ABI\s0 with AltiVec \s-1ABI\s0 extensions. This does not change the default \s-1ABI\s0, instead it adds the AltiVec \s-1ABI\s0 extensions to the current \s-1ABI\s0. .Sp This option is effectively permanently enabled on Mac \s-1OS\s0 X. .IP "\fB\-mabi=no\-altivec\fR" 4 .IX Item "-mabi=no-altivec" Disable AltiVec \s-1ABI\s0 extensions for the current \s-1ABI\s0. .Sp This option will not work on Mac \s-1OS\s0 X. .IP "\fB\-mprototype\fR" 4 .IX Item "-mprototype" .PD 0 .IP "\fB\-mno\-prototype\fR" 4 .IX Item "-mno-prototype" .PD On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non prototyped call to set or clear bit 6 of the condition code register (\fI\s-1CR\s0\fR) to indicate whether floating point values were passed in the floating point registers in case the function takes a variable arguments. With \&\fB\-mprototype\fR, only calls to prototyped variable argument functions will set or clear the bit. .IP "\fB\-msim\fR" 4 .IX Item "-msim" On embedded PowerPC systems, assume that the startup module is called \&\fIsim\-crt0.o\fR and that the standard C libraries are \fIlibsim.a\fR and \&\fIlibc.a\fR. This is the default for \fBpowerpc\-*\-eabisim\fR. configurations. .IP "\fB\-mmvme\fR" 4 .IX Item "-mmvme" On embedded PowerPC systems, assume that the startup module is called \&\fIcrt0.o\fR and the standard C libraries are \fIlibmvme.a\fR and \&\fIlibc.a\fR. .IP "\fB\-mads\fR" 4 .IX Item "-mads" On embedded PowerPC systems, assume that the startup module is called \&\fIcrt0.o\fR and the standard C libraries are \fIlibads.a\fR and \&\fIlibc.a\fR. .IP "\fB\-myellowknife\fR" 4 .IX Item "-myellowknife" On embedded PowerPC systems, assume that the startup module is called \&\fIcrt0.o\fR and the standard C libraries are \fIlibyk.a\fR and \&\fIlibc.a\fR. .IP "\fB\-mvxworks\fR" 4 .IX Item "-mvxworks" On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system. .IP "\fB\-mwindiss\fR" 4 .IX Item "-mwindiss" Specify that you are compiling for the WindISS simulation environment. .IP "\fB\-memb\fR" 4 .IX Item "-memb" On embedded PowerPC systems, set the \fI\s-1PPC_EMB\s0\fR bit in the \s-1ELF\s0 flags header to indicate that \fBeabi\fR extended relocations are used. .IP "\fB\-meabi\fR" 4 .IX Item "-meabi" .PD 0 .IP "\fB\-mno\-eabi\fR" 4 .IX Item "-mno-eabi" .PD On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (eabi) which is a set of modifications to the System V.4 specifications. Selecting \fB\-meabi\fR means that the stack is aligned to an 8 byte boundary, a function \&\f(CW\*(C`_\|_eabi\*(C'\fR is called to from \f(CW\*(C`main\*(C'\fR to set up the eabi environment, and the \fB\-msdata\fR option can use both \f(CW\*(C`r2\*(C'\fR and \&\f(CW\*(C`r13\*(C'\fR to point to two separate small data areas. Selecting \&\fB\-mno\-eabi\fR means that the stack is aligned to a 16 byte boundary, do not call an initialization function from \f(CW\*(C`main\*(C'\fR, and the \&\fB\-msdata\fR option will only use \f(CW\*(C`r13\*(C'\fR to point to a single small data area. The \fB\-meabi\fR option is on by default if you configured \s-1GCC\s0 using one of the \fBpowerpc*\-*\-eabi*\fR options. .IP "\fB\-msdata=eabi\fR" 4 .IX Item "-msdata=eabi" On System V.4 and embedded PowerPC systems, put small initialized \&\f(CW\*(C`const\*(C'\fR global and static data in the \fB.sdata2\fR section, which is pointed to by register \f(CW\*(C`r2\*(C'\fR. Put small initialized non\-\f(CW\*(C`const\*(C'\fR global and static data in the \fB.sdata\fR section, which is pointed to by register \f(CW\*(C`r13\*(C'\fR. Put small uninitialized global and static data in the \fB.sbss\fR section, which is adjacent to the \fB.sdata\fR section. The \fB\-msdata=eabi\fR option is incompatible with the \fB\-mrelocatable\fR option. The \&\fB\-msdata=eabi\fR option also sets the \fB\-memb\fR option. .IP "\fB\-msdata=sysv\fR" 4 .IX Item "-msdata=sysv" On System V.4 and embedded PowerPC systems, put small global and static data in the \fB.sdata\fR section, which is pointed to by register \&\f(CW\*(C`r13\*(C'\fR. Put small uninitialized global and static data in the \&\fB.sbss\fR section, which is adjacent to the \fB.sdata\fR section. The \fB\-msdata=sysv\fR option is incompatible with the \&\fB\-mrelocatable\fR option. .IP "\fB\-msdata=default\fR" 4 .IX Item "-msdata=default" .PD 0 .IP "\fB\-msdata\fR" 4 .IX Item "-msdata" .PD On System V.4 and embedded PowerPC systems, if \fB\-meabi\fR is used, compile code the same as \fB\-msdata=eabi\fR, otherwise compile code the same as \fB\-msdata=sysv\fR. .IP "\fB\-msdata\-data\fR" 4 .IX Item "-msdata-data" On System V.4 and embedded PowerPC systems, put small global and static data in the \fB.sdata\fR section. Put small uninitialized global and static data in the \fB.sbss\fR section. Do not use register \f(CW\*(C`r13\*(C'\fR to address small data however. This is the default behavior unless other \fB\-msdata\fR options are used. .IP "\fB\-msdata=none\fR" 4 .IX Item "-msdata=none" .PD 0 .IP "\fB\-mno\-sdata\fR" 4 .IX Item "-mno-sdata" .PD On embedded PowerPC systems, put all initialized global and static data in the \fB.data\fR section, and all uninitialized data in the \&\fB.bss\fR section. .IP "\fB\-G\fR \fInum\fR" 4 .IX Item "-G num" On embedded PowerPC systems, put global and static items less than or equal to \fInum\fR bytes into the small data or bss sections instead of the normal data or bss section. By default, \fInum\fR is 8. The \&\fB\-G\fR \fInum\fR switch is also passed to the linker. All modules should be compiled with the same \fB\-G\fR \fInum\fR value. .IP "\fB\-mregnames\fR" 4 .IX Item "-mregnames" .PD 0 .IP "\fB\-mno\-regnames\fR" 4 .IX Item "-mno-regnames" .PD On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms. .IP "\fB\-mlongcall\fR" 4 .IX Item "-mlongcall" .PD 0 .IP "\fB\-mno\-longcall\fR" 4 .IX Item "-mno-longcall" .PD Default to making all function calls via pointers, so that functions which reside further than 64 megabytes (67,108,864 bytes) from the current location can be called. This setting can be overridden by the \&\f(CW\*(C`shortcall\*(C'\fR function attribute, or by \f(CW\*(C`#pragma longcall(0)\*(C'\fR. .Sp Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the \s-1AIX\s0 linker can do this, as can the \s-1GNU\s0 linker for PowerPC/64. It is planned to add this feature to the \s-1GNU\s0 linker for 32\-bit PowerPC systems as well. .Sp In the future, we may cause \s-1GCC\s0 to ignore all longcall specifications when the linker is known to generate glue. .IP "\fB\-pthread\fR" 4 .IX Item "-pthread" Adds support for multithreading with the \fIpthreads\fR library. This option sets flags for both the preprocessor and linker. .PP \fIDarwin Options\fR .IX Subsection "Darwin Options" .IP "\fB\-all_load\fR" 4 .IX Item "-all_load" Loads all members of static archive libraries. See man \fIld\fR\|(1) for more information. .IP "\fB\-arch_errors_fatal\fR" 4 .IX Item "-arch_errors_fatal" Cause the errors having to do with files that have the wrong architecture to be fatal. .IP "\fB\-bind_at_load\fR" 4 .IX Item "-bind_at_load" Causes the output file to be marked such that the dynamic linker will bind all undefined references when the file is loaded or launched. .IP "\fB\-bundle\fR" 4 .IX Item "-bundle" Produce a Mach-o bundle format file. See man \fIld\fR\|(1) for more information. .IP "\fB\-bundle_loader\fR \fIexecutable\fR" 4 .IX Item "-bundle_loader executable" This specifies the \fIexecutable\fR that will be loading the build output file being linked. See man \fIld\fR\|(1) for more information. .IP "\fB\-allowable_client\fR \fIclient_name\fR" 4 .IX Item "-allowable_client client_name" .PD 0 .IP "\fB\-arch_only\fR" 4 .IX Item "-arch_only" .IP "\fB\-client_name\fR" 4 .IX Item "-client_name" .IP "\fB\-compatibility_version\fR" 4 .IX Item "-compatibility_version" .IP "\fB\-current_version\fR" 4 .IX Item "-current_version" .IP "\fB\-dependency\-file\fR" 4 .IX Item "-dependency-file" .IP "\fB\-dylib_file\fR" 4 .IX Item "-dylib_file" .IP "\fB\-dylinker_install_name\fR" 4 .IX Item "-dylinker_install_name" .IP "\fB\-dynamic\fR" 4 .IX Item "-dynamic" .IP "\fB\-dynamiclib\fR" 4 .IX Item "-dynamiclib" .IP "\fB\-exported_symbols_list\fR" 4 .IX Item "-exported_symbols_list" .IP "\fB\-filelist\fR" 4 .IX Item "-filelist" .IP "\fB\-flat_namespace\fR" 4 .IX Item "-flat_namespace" .IP "\fB\-force_cpusubtype_ALL\fR" 4 .IX Item "-force_cpusubtype_ALL" .IP "\fB\-force_flat_namespace\fR" 4 .IX Item "-force_flat_namespace" .IP "\fB\-headerpad_max_install_names\fR" 4 .IX Item "-headerpad_max_install_names" .IP "\fB\-image_base\fR" 4 .IX Item "-image_base" .IP "\fB\-init\fR" 4 .IX Item "-init" .IP "\fB\-install_name\fR" 4 .IX Item "-install_name" .IP "\fB\-keep_private_externs\fR" 4 .IX Item "-keep_private_externs" .IP "\fB\-multi_module\fR" 4 .IX Item "-multi_module" .IP "\fB\-multiply_defined\fR" 4 .IX Item "-multiply_defined" .IP "\fB\-multiply_defined_unused\fR" 4 .IX Item "-multiply_defined_unused" .IP "\fB\-noall_load\fR" 4 .IX Item "-noall_load" .IP "\fB\-nomultidefs\fR" 4 .IX Item "-nomultidefs" .IP "\fB\-noprebind\fR" 4 .IX Item "-noprebind" .IP "\fB\-noseglinkedit\fR" 4 .IX Item "-noseglinkedit" .IP "\fB\-pagezero_size\fR" 4 .IX Item "-pagezero_size" .IP "\fB\-prebind\fR" 4 .IX Item "-prebind" .IP "\fB\-prebind_all_twolevel_modules\fR" 4 .IX Item "-prebind_all_twolevel_modules" .IP "\fB\-private_bundle\fR" 4 .IX Item "-private_bundle" .IP "\fB\-read_only_relocs\fR" 4 .IX Item "-read_only_relocs" .IP "\fB\-sectalign\fR" 4 .IX Item "-sectalign" .IP "\fB\-sectobjectsymbols\fR" 4 .IX Item "-sectobjectsymbols" .IP "\fB\-whyload\fR" 4 .IX Item "-whyload" .IP "\fB\-seg1addr\fR" 4 .IX Item "-seg1addr" .IP "\fB\-sectcreate\fR" 4 .IX Item "-sectcreate" .IP "\fB\-sectobjectsymbols\fR" 4 .IX Item "-sectobjectsymbols" .IP "\fB\-sectorder\fR" 4 .IX Item "-sectorder" .IP "\fB\-seg_addr_table\fR" 4 .IX Item "-seg_addr_table" .IP "\fB\-seg_addr_table_filename\fR" 4 .IX Item "-seg_addr_table_filename" .IP "\fB\-seglinkedit\fR" 4 .IX Item "-seglinkedit" .IP "\fB\-segprot\fR" 4 .IX Item "-segprot" .IP "\fB\-segs_read_only_addr\fR" 4 .IX Item "-segs_read_only_addr" .IP "\fB\-segs_read_write_addr\fR" 4 .IX Item "-segs_read_write_addr" .IP "\fB\-single_module\fR" 4 .IX Item "-single_module" .IP "\fB\-static\fR" 4 .IX Item "-static" .IP "\fB\-sub_library\fR" 4 .IX Item "-sub_library" .IP "\fB\-sub_umbrella\fR" 4 .IX Item "-sub_umbrella" .IP "\fB\-twolevel_namespace\fR" 4 .IX Item "-twolevel_namespace" .IP "\fB\-umbrella\fR" 4 .IX Item "-umbrella" .IP "\fB\-undefined\fR" 4 .IX Item "-undefined" .IP "\fB\-unexported_symbols_list\fR" 4 .IX Item "-unexported_symbols_list" .IP "\fB\-weak_reference_mismatches\fR" 4 .IX Item "-weak_reference_mismatches" .IP "\fB\-whatsloaded\fR" 4 .IX Item "-whatsloaded" .PD This options are available for Darwin linker. Darwin linker man page describes them in detail. .PP \fIIntel 386 and \s-1AMD\s0 x86\-64 Options\fR .IX Subsection "Intel 386 and AMD x86-64 Options" .PP These \fB\-m\fR options are defined for the i386 and x86\-64 family of computers: .IP "\fB\-mcpu=\fR\fIcpu-type\fR" 4 .IX Item "-mcpu=cpu-type" Tune to \fIcpu-type\fR everything applicable about the generated code, except for the \s-1ABI\s0 and the set of available instructions. The choices for \&\fIcpu-type\fR are \fBi386\fR, \fBi486\fR, \fBi586\fR, \fBi686\fR, \&\fBpentium\fR, \fBpentium-mmx\fR, \fBpentiumpro\fR, \fBpentium2\fR, \&\fBpentium3\fR, \fBpentium4\fR, \fBk6\fR, \fBk6\-2\fR, \fBk6\-3\fR, \&\fBathlon\fR, \fBathlon-tbird\fR, \fBathlon\-4\fR, \fBathlon-xp\fR, \&\fBathlon-mp\fR, \fBwinchip\-c6\fR, \fBwinchip2\fR and \fBc3\fR. .Sp While picking a specific \fIcpu-type\fR will schedule things appropriately for that particular chip, the compiler will not generate any code that does not run on the i386 without the \fB\-march=\fR\fIcpu-type\fR option being used. \fBi586\fR is equivalent to \fBpentium\fR and \fBi686\fR is equivalent to \fBpentiumpro\fR. \fBk6\fR and \fBathlon\fR are the \&\s-1AMD\s0 chips as opposed to the Intel ones. .IP "\fB\-march=\fR\fIcpu-type\fR" 4 .IX Item "-march=cpu-type" Generate instructions for the machine type \fIcpu-type\fR. The choices for \fIcpu-type\fR are the same as for \fB\-mcpu\fR. Moreover, specifying \fB\-march=\fR\fIcpu-type\fR implies \fB\-mcpu=\fR\fIcpu-type\fR. .IP "\fB\-m386\fR" 4 .IX Item "-m386" .PD 0 .IP "\fB\-m486\fR" 4 .IX Item "-m486" .IP "\fB\-mpentium\fR" 4 .IX Item "-mpentium" .IP "\fB\-mpentiumpro\fR" 4 .IX Item "-mpentiumpro" .PD These options are synonyms for \fB\-mcpu=i386\fR, \fB\-mcpu=i486\fR, \&\fB\-mcpu=pentium\fR, and \fB\-mcpu=pentiumpro\fR respectively. These synonyms are deprecated. .IP "\fB\-mfpmath=\fR\fIunit\fR" 4 .IX Item "-mfpmath=unit" generate floating point arithmetics for selected unit \fIunit\fR. the choices for \fIunit\fR are: .RS 4 .IP "\fB387\fR" 4 .IX Item "387" Use the standard 387 floating point coprocessor present majority of chips and emulated otherwise. Code compiled with this option will run almost everywhere. The temporary results are computed in 80bit precision instead of precision specified by the type resulting in slightly different results compared to most of other chips. See \fB\-ffloat\-store\fR for more detailed description. .Sp This is the default choice for i386 compiler. .IP "\fBsse\fR" 4 .IX Item "sse" Use scalar floating point instructions present in the \s-1SSE\s0 instruction set. This instruction set is supported by Pentium3 and newer chips, in the \s-1AMD\s0 line by Athlon\-4, Athlon-xp and Athlon-mp chips. The earlier version of \s-1SSE\s0 instruction set supports only single precision arithmetics, thus the double and extended precision arithmetics is still done using 387. Later version, present only in Pentium4 and the future \s-1AMD\s0 x86\-64 chips supports double precision arithmetics too. .Sp For i387 you need to use \fB\-march=\fR\fIcpu-type\fR, \fB\-msse\fR or \&\fB\-msse2\fR switches to enable \s-1SSE\s0 extensions and make this option effective. For x86\-64 compiler, these extensions are enabled by default. .Sp The resulting code should be considerably faster in majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects temporaries to be 80bit. .Sp This is the default choice for x86\-64 compiler. .IP "\fBsse,387\fR" 4 .IX Item "sse,387" Attempt to utilize both instruction sets at once. This effectively double the amount of available registers and on chips with separate execution units for 387 and \s-1SSE\s0 the execution resources too. Use this option with care, as it is still experimental, because gcc register allocator does not model separate functional units well resulting in instable performance. .RE .RS 4 .RE .IP "\fB\-masm=\fR\fIdialect\fR" 4 .IX Item "-masm=dialect" Output asm instructions using selected \fIdialect\fR. Supported choices are \&\fBintel\fR or \fBatt\fR (the default one). .IP "\fB\-mieee\-fp\fR" 4 .IX Item "-mieee-fp" .PD 0 .IP "\fB\-mno\-ieee\-fp\fR" 4 .IX Item "-mno-ieee-fp" .PD Control whether or not the compiler uses \s-1IEEE\s0 floating point comparisons. These handle correctly the case where the result of a comparison is unordered. .IP "\fB\-msoft\-float\fR" 4 .IX Item "-msoft-float" Generate output containing library calls for floating point. \&\fBWarning:\fR the requisite libraries are not part of \s-1GCC\s0. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross\-compilation. You must make your own arrangements to provide suitable library functions for cross\-compilation. .Sp On machines where a function returns floating point results in the 80387 register stack, some floating point opcodes may be emitted even if \&\fB\-msoft\-float\fR is used. .IP "\fB\-mno\-fp\-ret\-in\-387\fR" 4 .IX Item "-mno-fp-ret-in-387" Do not use the \s-1FPU\s0 registers for return values of functions. .Sp The usual calling convention has functions return values of types \&\f(CW\*(C`float\*(C'\fR and \f(CW\*(C`double\*(C'\fR in an \s-1FPU\s0 register, even if there is no \s-1FPU\s0. The idea is that the operating system should emulate an \s-1FPU\s0. .Sp The option \fB\-mno\-fp\-ret\-in\-387\fR causes such values to be returned in ordinary \s-1CPU\s0 registers instead. .IP "\fB\-mno\-fancy\-math\-387\fR" 4 .IX Item "-mno-fancy-math-387" Some 387 emulators do not support the \f(CW\*(C`sin\*(C'\fR, \f(CW\*(C`cos\*(C'\fR and \&\f(CW\*(C`sqrt\*(C'\fR instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on FreeBSD, OpenBSD and NetBSD. This option is overridden when \fB\-march\fR indicates that the target cpu will always have an \s-1FPU\s0 and so the instruction will not need emulation. As of revision 2.6.1, these instructions are not generated unless you also use the \&\fB\-funsafe\-math\-optimizations\fR switch. .IP "\fB\-malign\-double\fR" 4 .IX Item "-malign-double" .PD 0 .IP "\fB\-mno\-align\-double\fR" 4 .IX Item "-mno-align-double" .PD Control whether \s-1GCC\s0 aligns \f(CW\*(C`double\*(C'\fR, \f(CW\*(C`long double\*(C'\fR, and \&\f(CW\*(C`long long\*(C'\fR variables on a two word boundary or a one word boundary. Aligning \f(CW\*(C`double\*(C'\fR variables on a two word boundary will produce code that runs somewhat faster on a \fBPentium\fR at the expense of more memory. .Sp \&\fBWarning:\fR if you use the \fB\-malign\-double\fR switch, structures containing the above types will be aligned differently than the published application binary interface specifications for the 386 and will not be binary compatible with structures in code compiled without that switch. .IP "\fB\-m128bit\-long\-double\fR" 4 .IX Item "-m128bit-long-double" Control the size of \f(CW\*(C`long double\*(C'\fR type. i386 application binary interface specify the size to be 12 bytes, while modern architectures (Pentium and newer) prefer \f(CW\*(C`long double\*(C'\fR aligned to 8 or 16 byte boundary. This is impossible to reach with 12 byte long doubles in the array accesses. .Sp \&\fBWarning:\fR if you use the \fB\-m128bit\-long\-double\fR switch, the structures and arrays containing \f(CW\*(C`long double\*(C'\fR will change their size as well as function calling convention for function taking \f(CW\*(C`long double\*(C'\fR will be modified. .IP "\fB\-m96bit\-long\-double\fR" 4 .IX Item "-m96bit-long-double" Set the size of \f(CW\*(C`long double\*(C'\fR to 96 bits as required by the i386 application binary interface. This is the default. .IP "\fB\-msvr3\-shlib\fR" 4 .IX Item "-msvr3-shlib" .PD 0 .IP "\fB\-mno\-svr3\-shlib\fR" 4 .IX Item "-mno-svr3-shlib" .PD Control whether \s-1GCC\s0 places uninitialized local variables into the \&\f(CW\*(C`bss\*(C'\fR or \f(CW\*(C`data\*(C'\fR segments. \fB\-msvr3\-shlib\fR places them into \f(CW\*(C`bss\*(C'\fR. These options are meaningful only on System V Release 3. .IP "\fB\-mrtd\fR" 4 .IX Item "-mrtd" Use a different function-calling convention, in which functions that take a fixed number of arguments return with the \f(CW\*(C`ret\*(C'\fR \fInum\fR instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. .Sp You can specify that an individual function is called with this calling sequence with the function attribute \fBstdcall\fR. You can also override the \fB\-mrtd\fR option by using the function attribute \&\fBcdecl\fR. .Sp \&\fBWarning:\fR this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. .Sp Also, you must provide function prototypes for all functions that take variable numbers of arguments (including \f(CW\*(C`printf\*(C'\fR); otherwise incorrect code will be generated for calls to those functions. .Sp In addition, seriously incorrect code will result if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) .IP "\fB\-mregparm=\fR\fInum\fR" 4 .IX Item "-mregparm=num" Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a specific function by using the function attribute \fBregparm\fR. .Sp \&\fBWarning:\fR if you use this switch, and \&\fInum\fR is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. .IP "\fB\-mpreferred\-stack\-boundary=\fR\fInum\fR" 4 .IX Item "-mpreferred-stack-boundary=num" Attempt to keep the stack boundary aligned to a 2 raised to \fInum\fR byte boundary. If \fB\-mpreferred\-stack\-boundary\fR is not specified, the default is 4 (16 bytes or 128 bits), except when optimizing for code size (\fB\-Os\fR), in which case the default is the minimum correct alignment (4 bytes for x86, and 8 bytes for x86\-64). .Sp On Pentium and PentiumPro, \f(CW\*(C`double\*(C'\fR and \f(CW\*(C`long double\*(C'\fR values should be aligned to an 8 byte boundary (see \fB\-malign\-double\fR) or suffer significant run time performance penalties. On Pentium \s-1III\s0, the Streaming \s-1SIMD\s0 Extension (\s-1SSE\s0) data type \f(CW\*(C`_\|_m128\*(C'\fR suffers similar penalties if it is not 16 byte aligned. .Sp To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary will most likely misalign the stack. It is recommended that libraries that use callbacks always use the default setting. .Sp This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, may want to reduce the preferred alignment to \fB\-mpreferred\-stack\-boundary=2\fR. .IP "\fB\-mmmx\fR" 4 .IX Item "-mmmx" .PD 0 .IP "\fB\-mno\-mmx\fR" 4 .IX Item "-mno-mmx" .IP "\fB\-msse\fR" 4 .IX Item "-msse" .IP "\fB\-mno\-sse\fR" 4 .IX Item "-mno-sse" .IP "\fB\-msse2\fR" 4 .IX Item "-msse2" .IP "\fB\-mno\-sse2\fR" 4 .IX Item "-mno-sse2" .IP "\fB\-m3dnow\fR" 4 .IX Item "-m3dnow" .IP "\fB\-mno\-3dnow\fR" 4 .IX Item "-mno-3dnow" .PD These switches enable or disable the use of built-in functions that allow direct access to the \s-1MMX\s0, \s-1SSE\s0 and 3Dnow extensions of the instruction set. .Sp To have \s-1SSE/SSE2\s0 instructions generated automatically from floating-point code, see \fB\-mfpmath=sse\fR. .IP "\fB\-mpush\-args\fR" 4 .IX Item "-mpush-args" .PD 0 .IP "\fB\-mno\-push\-args\fR" 4 .IX Item "-mno-push-args" .PD Use \s-1PUSH\s0 operations to store outgoing parameters. This method is shorter and usually equally fast as method using \s-1SUB/MOV\s0 operations and is enabled by default. In some cases disabling it may improve performance because of improved scheduling and reduced dependencies. .IP "\fB\-maccumulate\-outgoing\-args\fR" 4 .IX Item "-maccumulate-outgoing-args" If enabled, the maximum amount of space required for outgoing arguments will be computed in the function prologue. This is faster on most modern CPUs because of reduced dependencies, improved scheduling and reduced stack usage when preferred stack boundary is not equal to 2. The drawback is a notable increase in code size. This switch implies \fB\-mno\-push\-args\fR. .IP "\fB\-mthreads\fR" 4 .IX Item "-mthreads" Support thread-safe exception handling on \fBMingw32\fR. Code that relies on thread-safe exception handling must compile and link all code with the \&\fB\-mthreads\fR option. When compiling, \fB\-mthreads\fR defines \&\fB\-D_MT\fR; when linking, it links in a special thread helper library \&\fB\-lmingwthrd\fR which cleans up per thread exception handling data. .IP "\fB\-mno\-align\-stringops\fR" 4 .IX Item "-mno-align-stringops" Do not align destination of inlined string operations. This switch reduces code size and improves performance in case the destination is already aligned, but gcc don't know about it. .IP "\fB\-minline\-all\-stringops\fR" 4 .IX Item "-minline-all-stringops" By default \s-1GCC\s0 inlines string operations only when destination is known to be aligned at least to 4 byte boundary. This enables more inlining, increase code size, but may improve performance of code that depends on fast memcpy, strlen and memset for short lengths. .IP "\fB\-momit\-leaf\-frame\-pointer\fR" 4 .IX Item "-momit-leaf-frame-pointer" Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions. The option \&\fB\-fomit\-frame\-pointer\fR removes the frame pointer for all functions which might make debugging harder. .PP These \fB\-m\fR switches are supported in addition to the above on \s-1AMD\s0 x86\-64 processors in 64\-bit environments. .IP "\fB\-m32\fR" 4 .IX Item "-m32" .PD 0 .IP "\fB\-m64\fR" 4 .IX Item "-m64" .PD Generate code for a 32\-bit or 64\-bit environment. The 32\-bit environment sets int, long and pointer to 32 bits and generates code that runs on any i386 system. The 64\-bit environment sets int to 32 bits and long and pointer to 64 bits and generates code for \s-1AMD\s0's x86\-64 architecture. .IP "\fB\-mno\-red\-zone\fR" 4 .IX Item "-mno-red-zone" Do not use a so called red zone for x86\-64 code. The red zone is mandated by the x86\-64 \s-1ABI\s0, it is a 128\-byte area beyond the location of the stack pointer that will not be modified by signal or interrupt handlers and therefore can be used for temporary data without adjusting the stack pointer. The flag \fB\-mno\-red\-zone\fR disables this red zone. .IP "\fB\-mcmodel=small\fR" 4 .IX Item "-mcmodel=small" Generate code for the small code model: the program and its symbols must be linked in the lower 2 \s-1GB\s0 of the address space. Pointers are 64 bits. Programs can be statically or dynamically linked. This is the default code model. .IP "\fB\-mcmodel=kernel\fR" 4 .IX Item "-mcmodel=kernel" Generate code for the kernel code model. The kernel runs in the negative 2 \s-1GB\s0 of the address space. This model has to be used for Linux kernel code. .IP "\fB\-mcmodel=medium\fR" 4 .IX Item "-mcmodel=medium" Generate code for the medium model: The program is linked in the lower 2 \&\s-1GB\s0 of the address space but symbols can be located anywhere in the address space. Programs can be statically or dynamically linked, but building of shared libraries are not supported with the medium model. .IP "\fB\-mcmodel=large\fR" 4 .IX Item "-mcmodel=large" Generate code for the large model: This model makes no assumptions about addresses and sizes of sections. Currently \s-1GCC\s0 does not implement this model. .Sh "Options for Code Generation Conventions" .IX Subsection "Options for Code Generation Conventions" These machine-independent options control the interface conventions used in code generation. .PP Most of them have both positive and negative forms; the negative form of \fB\-ffoo\fR would be \fB\-fno\-foo\fR. In the table below, only one of the forms is listed\-\-\-the one which is not the default. You can figure out the other form by either removing \fBno\-\fR or adding it. .IP "\fB\-fbounds\-check\fR" 4 .IX Item "-fbounds-check" For front-ends that support it, generate additional code to check that indices used to access arrays are within the declared range. This is currently only supported by the Java and Fortran 77 front\-ends, where this option defaults to true and false respectively. .IP "\fB\-ftrapv\fR" 4 .IX Item "-ftrapv" This option generates traps for signed overflow on addition, subtraction, multiplication operations. .IP "\fB\-fexceptions\fR" 4 .IX Item "-fexceptions" Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies \s-1GCC\s0 will generate frame unwind information for all functions, which can produce significant data size overhead, although it does not affect execution. If you do not specify this option, \s-1GCC\s0 will enable it by default for languages like \&\*(C+ which normally require exception handling, and disable it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in \*(C+. You may also wish to disable this option if you are compiling older \*(C+ programs that don't use exception handling. .IP "\fB\-fnon\-call\-exceptions\fR" 4 .IX Item "-fnon-call-exceptions" Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows \fItrapping\fR instructions to throw exceptions, i.e. memory references or floating point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as \f(CW\*(C`SIGALRM\*(C'\fR. .IP "\fB\-funwind\-tables\fR" 4 .IX Item "-funwind-tables" Similar to \fB\-fexceptions\fR, except that it will just generate any needed static data, but will not affect the generated code in any other way. You will normally not enable this option; instead, a language processor that needs this handling would enable it on your behalf. .IP "\fB\-fasynchronous\-unwind\-tables\fR" 4 .IX Item "-fasynchronous-unwind-tables" Generate unwind table in dwarf2 format, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events (such as debugger or garbage collector). .IP "\fB\-fpcc\-struct\-return\fR" 4 .IX Item "-fpcc-struct-return" Return ``short'' \f(CW\*(C`struct\*(C'\fR and \f(CW\*(C`union\*(C'\fR values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GCC-compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc). .Sp The precise convention for returning structures in memory depends on the target configuration macros. .Sp Short structures and unions are those whose size and alignment match that of some integer type. .Sp \&\fBWarning:\fR code compiled with the \fB\-fpcc\-struct\-return\fR switch is not binary compatible with code compiled with the \&\fB\-freg\-struct\-return\fR switch. Use it to conform to a non-default application binary interface. .IP "\fB\-freg\-struct\-return\fR" 4 .IX Item "-freg-struct-return" Return \f(CW\*(C`struct\*(C'\fR and \f(CW\*(C`union\*(C'\fR values in registers when possible. This is more efficient for small structures than \&\fB\-fpcc\-struct\-return\fR. .Sp If you specify neither \fB\-fpcc\-struct\-return\fR nor \&\fB\-freg\-struct\-return\fR, \s-1GCC\s0 defaults to whichever convention is standard for the target. If there is no standard convention, \s-1GCC\s0 defaults to \fB\-fpcc\-struct\-return\fR, except on targets where \s-1GCC\s0 is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. .Sp \&\fBWarning:\fR code compiled with the \fB\-freg\-struct\-return\fR switch is not binary compatible with code compiled with the \&\fB\-fpcc\-struct\-return\fR switch. Use it to conform to a non-default application binary interface. .IP "\fB\-fshort\-enums\fR" 4 .IX Item "-fshort-enums" Allocate to an \f(CW\*(C`enum\*(C'\fR type only as many bytes as it needs for the declared range of possible values. Specifically, the \f(CW\*(C`enum\*(C'\fR type will be equivalent to the smallest integer type which has enough room. .Sp \&\fBWarning:\fR the \fB\-fshort\-enums\fR switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. .IP "\fB\-fshort\-double\fR" 4 .IX Item "-fshort-double" Use the same size for \f(CW\*(C`double\*(C'\fR as for \f(CW\*(C`float\*(C'\fR. .Sp \&\fBWarning:\fR the \fB\-fshort\-double\fR switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. .IP "\fB\-fshort\-wchar\fR" 4 .IX Item "-fshort-wchar" Override the underlying type for \fBwchar_t\fR to be \fBshort unsigned int\fR instead of the default for the target. This option is useful for building programs to run under \s-1WINE\s0. .Sp \&\fBWarning:\fR the \fB\-fshort\-wchar\fR switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. .IP "\fB\-fshared\-data\fR" 4 .IX Item "-fshared-data" Requests that the data and non\-\f(CW\*(C`const\*(C'\fR variables of this compilation be shared data rather than private data. The distinction makes sense only on certain operating systems, where shared data is shared between processes running the same program, while private data exists in one copy per process. .IP "\fB\-fno\-common\fR" 4 .IX Item "-fno-common" In C, allocate even uninitialized global variables in the data section of the object file, rather than generating them as common blocks. This has the effect that if the same variable is declared (without \f(CW\*(C`extern\*(C'\fR) in two different compilations, you will get an error when you link them. The only reason this might be useful is if you wish to verify that the program will work on other systems which always work this way. .IP "\fB\-fno\-ident\fR" 4 .IX Item "-fno-ident" Ignore the \fB#ident\fR directive. .IP "\fB\-fno\-gnu\-linker\fR" 4 .IX Item "-fno-gnu-linker" Do not output global initializations (such as \*(C+ constructors and destructors) in the form used by the \s-1GNU\s0 linker (on systems where the \s-1GNU\s0 linker is the standard method of handling them). Use this option when you want to use a non-GNU linker, which also requires using the \&\fBcollect2\fR program to make sure the system linker includes constructors and destructors. (\fBcollect2\fR is included in the \s-1GCC\s0 distribution.) For systems which \fImust\fR use \fBcollect2\fR, the compiler driver \fBgcc\fR is configured to do this automatically. .IP "\fB\-finhibit\-size\-directive\fR" 4 .IX Item "-finhibit-size-directive" Don't output a \f(CW\*(C`.size\*(C'\fR assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling \fIcrtstuff.c\fR; you should not need to use it for anything else. .IP "\fB\-fverbose\-asm\fR" 4 .IX Item "-fverbose-asm" Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). .Sp \&\fB\-fno\-verbose\-asm\fR, the default, causes the extra information to be omitted and is useful when comparing two assembler files. .IP "\fB\-fvolatile\fR" 4 .IX Item "-fvolatile" Consider all memory references through pointers to be volatile. .IP "\fB\-fvolatile\-global\fR" 4 .IX Item "-fvolatile-global" Consider all memory references to extern and global data items to be volatile. \s-1GCC\s0 does not consider static data items to be volatile because of this switch. .IP "\fB\-fvolatile\-static\fR" 4 .IX Item "-fvolatile-static" Consider all memory references to static data to be volatile. .IP "\fB\-fpic\fR" 4 .IX Item "-fpic" Generate position-independent code (\s-1PIC\s0) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table (\s-1GOT\s0). The dynamic loader resolves the \s-1GOT\s0 entries when the program starts (the dynamic loader is not part of \s-1GCC\s0; it is part of the operating system). If the \s-1GOT\s0 size for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that \&\fB\-fpic\fR does not work; in that case, recompile with \fB\-fPIC\fR instead. (These maximums are 16k on the m88k, 8k on the \s-1SPARC\s0, and 32k on the m68k and \s-1RS/6000\s0. The 386 has no such limit.) .Sp Position-independent code requires special support, and therefore works only on certain machines. For the 386, \s-1GCC\s0 supports \s-1PIC\s0 for System V but not for the Sun 386i. Code generated for the \s-1IBM\s0 \s-1RS/6000\s0 is always position\-independent. .Sp \&\fB\-fpic\fR is not supported on Mac \s-1OS\s0 X. .IP "\fB\-fPIC\fR" 4 .IX Item "-fPIC" If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on the m68k, m88k, and the \s-1SPARC\s0. .Sp Position-independent code requires special support, and therefore works only on certain machines. .Sp \&\fB\-fPIC\fR is the default on Darwin and Mac \s-1OS\s0 X. .IP "\fB\-ffixed\-\fR\fIreg\fR" 4 .IX Item "-ffixed-reg" Treat the register named \fIreg\fR as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). .Sp \&\fIreg\fR must be the name of a register. The register names accepted are machine-specific and are defined in the \f(CW\*(C`REGISTER_NAMES\*(C'\fR macro in the machine description macro file. .Sp This flag does not have a negative form, because it specifies a three-way choice. .IP "\fB\-fcall\-used\-\fR\fIreg\fR" 4 .IX Item "-fcall-used-reg" Treat the register named \fIreg\fR as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way will not save and restore the register \fIreg\fR. .Sp It is an error to used this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model will produce disastrous results. .Sp This flag does not have a negative form, because it specifies a three-way choice. .IP "\fB\-fcall\-saved\-\fR\fIreg\fR" 4 .IX Item "-fcall-saved-reg" Treat the register named \fIreg\fR as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way will save and restore the register \fIreg\fR if they use it. .Sp It is an error to used this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model will produce disastrous results. .Sp A different sort of disaster will result from the use of this flag for a register in which function values may be returned. .Sp This flag does not have a negative form, because it specifies a three-way choice. .IP "\fB\-fpack\-struct\fR" 4 .IX Item "-fpack-struct" Pack all structure members together without holes. .Sp \&\fBWarning:\fR the \fB\-fpack\-struct\fR switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface. .IP "\fB\-finstrument\-functions\fR" 4 .IX Item "-finstrument-functions" Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions will be called with the address of the current function and its call site. (On some platforms, \&\f(CW\*(C`_\|_builtin_return_address\*(C'\fR does not work beyond the current function, so the call site information may not be available to the profiling functions otherwise.) .Sp .Vb 4 \& void __cyg_profile_func_enter (void *this_fn, \& void *call_site); \& void __cyg_profile_func_exit (void *this_fn, \& void *call_site); .Ve .Sp The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table. .Sp This instrumentation is also done for functions expanded inline in other functions. The profiling calls will indicate where, conceptually, the inline function is entered and exited. This means that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use \fBextern inline\fR in your C code, an addressable version of such functions must be provided. (This is normally the case anyways, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static copies.) .Sp A function may be given the attribute \f(CW\*(C`no_instrument_function\*(C'\fR, in which case this instrumentation will not be done. This can be used, for example, for the profiling functions listed above, high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate memory). .IP "\fB\-fstack\-check\fR" 4 .IX Item "-fstack-check" Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. .Sp Note that this switch does not actually cause checking to be done; the operating system must do that. The switch causes generation of code to ensure that the operating system sees the stack being extended. .IP "\fB\-fstack\-limit\-register=\fR\fIreg\fR" 4 .IX Item "-fstack-limit-register=reg" .PD 0 .IP "\fB\-fstack\-limit\-symbol=\fR\fIsym\fR" 4 .IX Item "-fstack-limit-symbol=sym" .IP "\fB\-fno\-stack\-limit\fR" 4 .IX Item "-fno-stack-limit" .PD Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If the stack would grow beyond the value, a signal is raised. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions. .Sp For instance, if the stack starts at absolute address \fB0x80000000\fR and grows downwards, you can use the flags \&\fB\-fstack\-limit\-symbol=_\|_stack_limit\fR and \&\fB\-Wl,\-\-defsym,_\|_stack_limit=0x7ffe0000\fR to enforce a stack limit of 128KB. Note that this may only work with the \s-1GNU\s0 linker. .IP "\fB\-fargument\-alias\fR" 4 .IX Item "-fargument-alias" .PD 0 .IP "\fB\-fargument\-noalias\fR" 4 .IX Item "-fargument-noalias" .IP "\fB\-fargument\-noalias\-global\fR" 4 .IX Item "-fargument-noalias-global" .PD Specify the possible relationships among parameters and between parameters and global data. .Sp \&\fB\-fargument\-alias\fR specifies that arguments (parameters) may alias each other and may alias global storage.\fB\-fargument\-noalias\fR specifies that arguments do not alias each other, but may alias global storage.\fB\-fargument\-noalias\-global\fR specifies that arguments do not alias each other and do not alias global storage. .Sp Each language will automatically use whatever option is required by the language standard. You should not need to use these options yourself. .IP "\fB\-fleading\-underscore\fR" 4 .IX Item "-fleading-underscore" This option and its counterpart, \fB\-fno\-leading\-underscore\fR, forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code. .Sp \&\fBWarning:\fR the \fB\-fleading\-underscore\fR switch causes \s-1GCC\s0 to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Not all targets provide complete support for this switch. .IP "\fB\-ftls\-model=\fR\fImodel\fR" 4 .IX Item "-ftls-model=model" Alter the thread-local storage model to be used. The \fImodel\fR argument should be one of \f(CW\*(C`global\-dynamic\*(C'\fR, \&\f(CW\*(C`local\-dynamic\*(C'\fR, \f(CW\*(C`initial\-exec\*(C'\fR or \f(CW\*(C`local\-exec\*(C'\fR. .Sp The default without \fB\-fpic\fR is \f(CW\*(C`initial\-exec\*(C'\fR; with \&\fB\-fpic\fR the default is \f(CW\*(C`global\-dynamic\*(C'\fR. .SH "ENVIRONMENT" .IX Header "ENVIRONMENT" This section describes several environment variables that affect how \s-1GCC\s0 operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment. .PP Note that you can also specify places to search using options such as \&\fB\-B\fR, \fB\-I\fR and \fB\-L\fR. These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of \s-1GCC\s0. .IP "\fB\s-1LANG\s0\fR" 4 .IX Item "LANG" .PD 0 .IP "\fB\s-1LC_CTYPE\s0\fR" 4 .IX Item "LC_CTYPE" .IP "\fB\s-1LC_MESSAGES\s0\fR" 4 .IX Item "LC_MESSAGES" .IP "\fB\s-1LC_ALL\s0\fR" 4 .IX Item "LC_ALL" .PD These environment variables control the way that \s-1GCC\s0 uses localization information that allow \s-1GCC\s0 to work with different national conventions. \s-1GCC\s0 inspects the locale categories \&\fB\s-1LC_CTYPE\s0\fR and \fB\s-1LC_MESSAGES\s0\fR if it has been configured to do so. These locale categories can be set to any value supported by your installation. A typical value is \fBen_UK\fR for English in the United Kingdom. .Sp The \fB\s-1LC_CTYPE\s0\fR environment variable specifies character classification. \s-1GCC\s0 uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain quote and escape characters that would otherwise be interpreted as a string end or escape. .Sp The \fB\s-1LC_MESSAGES\s0\fR environment variable specifies the language to use in diagnostic messages. .Sp If the \fB\s-1LC_ALL\s0\fR environment variable is set, it overrides the value of \fB\s-1LC_CTYPE\s0\fR and \fB\s-1LC_MESSAGES\s0\fR; otherwise, \fB\s-1LC_CTYPE\s0\fR and \fB\s-1LC_MESSAGES\s0\fR default to the value of the \fB\s-1LANG\s0\fR environment variable. If none of these variables are set, \s-1GCC\s0 defaults to traditional C English behavior. .IP "\fB\s-1TMPDIR\s0\fR" 4 .IX Item "TMPDIR" If \fB\s-1TMPDIR\s0\fR is set, it specifies the directory to use for temporary files. \s-1GCC\s0 uses temporary files to hold the output of one stage of compilation which is to be used as input to the next stage: for example, the output of the preprocessor, which is the input to the compiler proper. .IP "\fB\s-1GCC_EXEC_PREFIX\s0\fR" 4 .IX Item "GCC_EXEC_PREFIX" If \fB\s-1GCC_EXEC_PREFIX\s0\fR is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a subprogram, but you can specify a prefix that ends with a slash if you wish. .Sp If \fB\s-1GCC_EXEC_PREFIX\s0\fR is not set, \s-1GCC\s0 will attempt to figure out an appropriate prefix to use based on the pathname it was invoked with. .Sp If \s-1GCC\s0 cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram. .Sp The default value of \fB\s-1GCC_EXEC_PREFIX\s0\fR is \&\fI\fIprefix\fI/lib/gcc\-lib/\fR where \fIprefix\fR is the value of \f(CW\*(C`prefix\*(C'\fR when you ran the \fIconfigure\fR script. .Sp Other prefixes specified with \fB\-B\fR take precedence over this prefix. .Sp This prefix is also used for finding files such as \fIcrt0.o\fR that are used for linking. .Sp In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with \fB/usr/local/lib/gcc\-lib\fR (more precisely, with the value of \fB\s-1GCC_INCLUDE_DIR\s0\fR), \s-1GCC\s0 tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with \fB\-Bfoo/\fR, \s-1GCC\s0 will search \&\fIfoo/bar\fR where it would normally search \fI/usr/local/lib/bar\fR. These alternate directories are searched first; the standard directories come next. .IP "\fB\s-1COMPILER_PATH\s0\fR" 4 .IX Item "COMPILER_PATH" The value of \fB\s-1COMPILER_PATH\s0\fR is a colon-separated list of directories, much like \fB\s-1PATH\s0\fR. \s-1GCC\s0 tries the directories thus specified when searching for subprograms, if it can't find the subprograms using \fB\s-1GCC_EXEC_PREFIX\s0\fR. .IP "\fB\s-1LIBRARY_PATH\s0\fR" 4 .IX Item "LIBRARY_PATH" The value of \fB\s-1LIBRARY_PATH\s0\fR is a colon-separated list of directories, much like \fB\s-1PATH\s0\fR. When configured as a native compiler, \&\s-1GCC\s0 tries the directories thus specified when searching for special linker files, if it can't find them using \fB\s-1GCC_EXEC_PREFIX\s0\fR. Linking using \s-1GCC\s0 also uses these directories when searching for ordinary libraries for the \fB\-l\fR option (but directories specified with \&\fB\-L\fR come first). .IP "\fB\s-1LANG\s0\fR" 4 .IX Item "LANG" This variable is used to pass locale information to the compiler. One way in which this information is used is to determine the character set to be used when character literals, string literals and comments are parsed in C and \*(C+. When the compiler is configured to allow multibyte characters, the following values for \fB\s-1LANG\s0\fR are recognized: .RS 4 .IP "\fBC\-JIS\fR" 4 .IX Item "C-JIS" Recognize \s-1JIS\s0 characters. .IP "\fBC\-SJIS\fR" 4 .IX Item "C-SJIS" Recognize \s-1SJIS\s0 characters. .IP "\fBC\-EUCJP\fR" 4 .IX Item "C-EUCJP" Recognize \s-1EUCJP\s0 characters. .RE .RS 4 .Sp If \fB\s-1LANG\s0\fR is not defined, or if it has some other value, then the compiler will use mblen and mbtowc as defined by the default locale to recognize and translate multibyte characters. .RE .PP Some additional environments variables affect the behavior of the preprocessor. .IP "\fB\s-1CPATH\s0\fR" 4 .IX Item "CPATH" .PD 0 .IP "\fBC_INCLUDE_PATH\fR" 4 .IX Item "C_INCLUDE_PATH" .IP "\fB\s-1CPLUS_INCLUDE_PATH\s0\fR" 4 .IX Item "CPLUS_INCLUDE_PATH" .IP "\fB\s-1OBJC_INCLUDE_PATH\s0\fR" 4 .IX Item "OBJC_INCLUDE_PATH" .PD Each variable's value is a list of directories separated by a special character, much like \fB\s-1PATH\s0\fR, in which to look for header files. The special character, \f(CW\*(C`PATH_SEPARATOR\*(C'\fR, is target-dependent and determined at \s-1GCC\s0 build time. For Windows-based targets it is a semicolon, and for almost all other targets it is a colon. .Sp \&\fB\s-1CPATH\s0\fR specifies a list of directories to be searched as if specified with \fB\-I\fR, but after any paths given with \fB\-I\fR options on the command line. This environment variable is used regardless of which language is being preprocessed. .Sp The remaining environment variables apply only when preprocessing the particular language indicated. Each specifies a list of directories to be searched as if specified with \fB\-isystem\fR, but after any paths given with \fB\-isystem\fR options on the command line. .Sp In all these variables, an empty element instructs the compiler to search its current working directory. Empty elements can appear at the beginning or end of a path. For instance, if the value of \&\fB\s-1CPATH\s0\fR is \f(CW\*(C`:/special/include\*(C'\fR, that has the same effect as \fB\-I.\ \-I/special/include\fR. .IP "\fB\s-1DEPENDENCIES_OUTPUT\s0\fR" 4 .IX Item "DEPENDENCIES_OUTPUT" If this variable is set, its value specifies how to output dependencies for Make based on the non-system header files processed by the compiler. System header files are ignored in the dependency output. .Sp The value of \fB\s-1DEPENDENCIES_OUTPUT\s0\fR can be just a file name, in which case the Make rules are written to that file, guessing the target name from the source file name. Or the value can have the form \&\fIfile\fR\fB \fR\fItarget\fR, in which case the rules are written to file \fIfile\fR using \fItarget\fR as the target name. .Sp In other words, this environment variable is equivalent to combining the options \fB\-MM\fR and \fB\-MF\fR, with an optional \fB\-MT\fR switch too. .IP "\fB\s-1SUNPRO_DEPENDENCIES\s0\fR" 4 .IX Item "SUNPRO_DEPENDENCIES" This variable is the same as \fB\s-1DEPENDENCIES_OUTPUT\s0\fR (see above), except that system header files are not ignored, so it implies \&\fB\-M\fR rather than \fB\-MM\fR. However, the dependence on the main input file is omitted. .SH "BUGS" .IX Header "BUGS" To report bugs to Apple, see <\fBhttp://developer.apple.com/bugreporter\fR>. .SH "FOOTNOTES" .IX Header "FOOTNOTES" .IP "1." 4 On some systems, \fBgcc \-shared\fR needs to build supplementary stub code for constructors to work. On multi-libbed systems, \fBgcc \-shared\fR must select the correct support libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf\-funding\fR\|(7), \&\fIcpp\fR\|(1), \fIgcov\fR\|(1), \fIg77\fR\|(1), \fIas\fR\|(1), \fIld\fR\|(1), \fIgdb\fR\|(1), \fIadb\fR\|(1), \fIdbx\fR\|(1), \fIsdb\fR\|(1) and the Info entries for \fIgcc\fR, \fIcpp\fR, \fIg77\fR, \fIas\fR, \&\fIld\fR, \fIbinutils\fR and \fIgdb\fR. .SH "AUTHOR" .IX Header "AUTHOR" See the Info entry for \fBgcc\fR, or <\fBhttp://gcc.gnu.org/onlinedocs/gcc/Contributors.html\fR>, for contributors to \s-1GCC\s0. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright (c) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc. .PP Permission is granted to copy, distribute and/or modify this document under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being ``\s-1GNU\s0 General Public License'' and ``Funding Free Software'', the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the \fIgfdl\fR\|(7) man page. .PP (a) The \s-1FSF\s0's Front-Cover Text is: .PP .Vb 1 \& A GNU Manual .Ve .PP (b) The \s-1FSF\s0's Back-Cover Text is: .PP .Vb 3 \& You have freedom to copy and modify this GNU Manual, like GNU \& software. Copies published by the Free Software Foundation raise \& funds for GNU development. .Ve