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diff --git a/man-pages/gcc3.1 b/man-pages/gcc3.1 new file mode 100644 index 00000000000..35d83929541 --- /dev/null +++ b/man-pages/gcc3.1 @@ -0,0 +1,5764 @@ +.\" Automatically generated by Pod::Man version 1.15 +.\" Wed Jun 19 19:36:28 2002 +.\" +.\" 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 Ip \" List item +.br +.ie \\n(.$>=3 .ne \\$3 +.el .ne 3 +.IP "\\$1" \\$2 +.. +.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. Always turn off hyphenation; it +.\" makes way too many mistakes in technical documents. +.hy 0 +.if n .na +.\" +.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). +.\" Fear. Run. Save yourself. No user-serviceable parts. +.bd B 3 +. \" 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 "gcc-3.1" "2002-06-19" "GNU" +.UC +.SH "NAME" +gcc \- \s-1GNU\s0 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 \-### \-\-target-help \-\-help\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) +\&\-fno-asm \-fno-builtin \-fno-builtin-\fR\fIfunction\fR +\&\fB\-fhosted \-ffreestanding +\&\-trigraphs \-no-integrated-cpp \-traditional \-traditional-cpp +\&\-fallow-single-precision \-fcond-mismatch +\&\-fconstant-cfstrings (\s-1APPLE\s0 \s-1ONLY\s0) +\&\-fsigned-bitfields \-fsigned-char +\&\-funsigned-bitfields \-funsigned-char +\&\-fwritable-strings \-fshort-wchar +\&\-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)\fR +.Ip "\fI\*(C+ Language Options\fR" 4 +.IX Item " Language Options" +\&\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 \-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\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 \-Wdiv-by-zero \-Werror +\&\-Wfloat-equal \-Wformat \-Wformat=2 +\&\-Wformat-nonliteral \-Wformat-security +\&\-Wimplicit \-Wimplicit-int +\&\-Wimplicit-function-declaration +\&\-Werror-implicit-function-declaration +\&\-Wimport \-Winline +\&\-Wlarger-than-\fR\fIlen\fR +\&\fB\-Wno-long-double (\s-1APPLE\s0 \s-1ONLY\s0) +\&\-Wlong-long +\&\-Wmain \-Wmissing-braces \-Wmissing-declarations +\&\-Wmissing-format-attribute \-Wmissing-noreturn +\&\-Wmost (\s-1APPLE\s0 \s-1ONLY\s0) +\&\-Wmultichar \-Wno-format-extra-args \-Wno-format-y2k +\&\-Wno-import \-Wpacked \-Wpadded +\&\-Wparentheses \-Wpointer-arith \-Wredundant-decls +\&\-Wreturn-type \-Wsequence-point \-Wshadow +\&\-Wsign-compare \-Wswitch \-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-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\-fmem-report \-fpretend-float +\&\-fprofile-arcs \-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\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\-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 +\&\-finline-functions \-finline-limit=\fR\fIn\fR \fB\-fkeep-inline-functions +\&\-fkeep-static-consts \-fmerge-constants \-fmerge-all-constants +\&\-fmove-all-movables \-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 \-fno-trapping-math +\&\-fomit-frame-pointer \-foptimize-register-move +\&\-foptimize-sibling-calls \-fprefetch-loop-arrays +\&\-freduce-all-givs \-fregmove \-frename-registers +\&\-frerun-cse-after-loop \-frerun-loop-opt +\&\-fschedule-insns \-fschedule-insns2 +\&\-fsingle-precision-constant \-fssa \-fssa-ccp \-fssa-dce +\&\-fstrength-reduce \-fstrict-aliasing \-fthread-jumps \-ftrapv +\&\-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) +\&\-\-dump-pch\fR \fIname\fR \fB(\s-1APPLE\s0 \s-1ONLY\s0) \-\-load-pch\fR \fIname\fR \fB(\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\-b\fR \fImachine\fR \fB\-V\fR \fIversion\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 +\&\-mprototype \-mno-prototype +\&\-msim \-mmvme \-mads \-myellowknife \-memb \-msdata +\&\-msdata=\fR\fIopt\fR \fB\-mvxworks \-G\fR \fInum\fR \fB\-pthread\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 \-msse-math \-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 +\&\-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 \-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\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 header file (not to be compiled or linked). +.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.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 8 +\& c c-header cpp-output +\& c++ c++-cpp-output +\& objective-c objc-cpp-output +\& objective-c++ (APPLE ONLY) +\& assembler assembler-with-cpp +\& ada +\& f77 f77-cpp-input ratfor +\& java +.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. +.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.c++\fR, \fB.cp\fR, or \fB.cxx\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 from standard input, +or otherwise without a suffix that flags them as \*(C+ programs. +\&\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 C89 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 +C89 (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. 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 C89 (same as \fB\-ansi\fR). +.Ip "\fBiso9899:199409\fR" 4 +.IX Item "iso9899:199409" +\&\s-1ISO\s0 C89 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-3.1/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 C89 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. +.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 C89 +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\-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\fB \fR(C and Objective-C only)" 4 +.IX Item "-fno-builtin-function (C and Objective-C only)" +.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 +In \*(C+, \fB\-fno-builtin\fR is always in effect. The \fB\-fbuiltin\fR +option has no effect. Therefore, in \*(C+, the only way to get the +optimization benefits of built-in functions is to call the function +using the \fB_\|_builtin_\fR prefix. The \s-1GNU\s0 \*(C+ Standard Library uses +built-in functions to implement many functions (like +\&\f(CW\*(C`std::strchr\*(C'\fR), so that you automatically get efficient code. +.Sp +With the \fB\-fno-builtin-\fR\fIfunction\fR option, not available +when compiling \*(C+, 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\-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" +Invoke the external cpp during compilation. The default is to use the +integrated cpp (internal cpp). This option also allows a +user-supplied cpp via the \fB\-B\fR option. This flag is applicable +in both C and \*(C+ modes. +.Sp +We do not guarantee to retain this option in future, and we may change +its semantics. +.Ip "\fB\*(--dump-pch\fR \fIname\fR" 4 +.IX Item "dump-pch name" +Dump the state of the compiler into a directory named \fIname\fR, after +processing all the other arguments. This is useful for creating +precompiled headers. (\s-1APPLE\s0 \s-1ONLY\s0) +.Ip "\fB\*(--load-pch\fR \fIname\fR" 4 +.IX Item "load-pch name" +Restore the state of the compiler from the directory \fIname\fR before +processing the other arguments. The net effect is similar to +\&\fB\-include\fR, but it happens much more quickly. (\s-1APPLE\s0 \s-1ONLY\s0) +.Sp +So for instance if the file \fImyprefix.c\fR #includes various +headers that are useful to all files in your program, you can do +.Sp +.Vb 5 +\& gcc --dump-pch foo -c myprefix.c +\& gcc --load-pch foo myfile1.c +\& gcc --load-pch foo myfile2.c +\& gcc --load-pch foo myfile2.c +\& ... +.Ve +.Ip "\fB\-traditional\fR" 4 +.IX Item "-traditional" +Attempt to support some aspects of traditional C compilers. +Specifically: +.RS 4 +.Ip "\(bu" 4 +All \f(CW\*(C`extern\*(C'\fR declarations take effect globally even if they +are written inside of a function definition. This includes implicit +declarations of functions. +.Ip "\(bu" 4 +The newer keywords \f(CW\*(C`typeof\*(C'\fR, \f(CW\*(C`inline\*(C'\fR, \f(CW\*(C`signed\*(C'\fR, \f(CW\*(C`const\*(C'\fR +and \f(CW\*(C`volatile\*(C'\fR are not recognized. (You can still use the +alternative keywords such as \f(CW\*(C`_\|_typeof_\|_\*(C'\fR, \f(CW\*(C`_\|_inline_\|_\*(C'\fR, and +so on.) +.Ip "\(bu" 4 +Comparisons between pointers and integers are always allowed. +.Ip "\(bu" 4 +Integer types \f(CW\*(C`unsigned short\*(C'\fR and \f(CW\*(C`unsigned char\*(C'\fR promote +to \f(CW\*(C`unsigned int\*(C'\fR. +.Ip "\(bu" 4 +Out-of-range floating point literals are not an error. +.Ip "\(bu" 4 +Certain constructs which \s-1ISO\s0 regards as a single invalid preprocessing +number, such as \fB0xe-0xd\fR, are treated as expressions instead. +.Ip "\(bu" 4 +String ``constants'' are not necessarily constant; they are stored in +writable space, and identical looking constants are allocated +separately. (This is the same as the effect of +\&\fB\-fwritable-strings\fR.) +.Ip "\(bu" 4 +All automatic variables not declared \f(CW\*(C`register\*(C'\fR are preserved by +\&\f(CW\*(C`longjmp\*(C'\fR. Ordinarily, \s-1GNU\s0 C follows \s-1ISO\s0 C: automatic variables +not declared \f(CW\*(C`volatile\*(C'\fR may be clobbered. +.Ip "\(bu" 4 +The character escape sequences \fB\ex\fR and \fB\ea\fR evaluate as the +literal characters \fBx\fR and \fBa\fR respectively. Without +\&\fB\-traditional\fR, \fB\ex\fR is a prefix for the hexadecimal +representation of a character, and \fB\ea\fR produces a bell. +.RE +.RS 4 +.Sp +This option is deprecated and may be removed. +.Sp +You may wish to use \fB\-fno-builtin\fR as well as \fB\-traditional\fR +if your program uses names that are normally \s-1GNU\s0 C built-in functions for +other purposes of its own. +.Sp +You cannot use \fB\-traditional\fR if you include any header files that +rely on \s-1ISO\s0 C features. Some vendors are starting to ship systems with +\&\s-1ISO\s0 C header files and you cannot use \fB\-traditional\fR on such +systems to compile files that include any system headers. +.Sp +The \fB\-traditional\fR option also enables \fB\-traditional-cpp\fR. +.RE +.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\-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. +.Sp +However, when \fB\-traditional\fR is used, bit-fields are all unsigned +no matter what. +.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. The option \fB\-traditional\fR also has +this effect. +.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\-fallow-single-precision\fR" 4 +.IX Item "-fallow-single-precision" +Do not promote single precision math operations to double precision, +even when compiling with \fB\-traditional\fR. +.Sp +Traditional K&R C promotes all floating point operations to double +precision, regardless of the sizes of the operands. On the +architecture for which you are compiling, single precision may be faster +than double precision. If you must use \fB\-traditional\fR, but want +to use single precision operations when the operands are single +precision, use this option. This option has no effect when compiling +with \s-1ISO\s0 or \s-1GNU\s0 C conventions (the default). +.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. +.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 +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\-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 built using older compilers, and is required +to build any Darwin kernel extension. (\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\-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. +.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. +.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 +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. +.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\*(C`*this\*(C'\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: +.RS 4 +.RE +.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 +.Vb 3 +\& struct B: public A { +\& void f(int); +\& }; +.Ve +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 +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 +.Vb 5 +\& main () +\& { +\& A a,b; +\& a = b; +\& } +.Ve +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 +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. +.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" +Do not warn if methods required by a protocol are not implemented +in the class adopting it. +.Ip "\fB\-Wselector\fR" 4 +.IX Item "-Wselector" +Warn if a selector has multiple methods of different types defined. +.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 C89 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 +\&\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\-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\-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\-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 +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\-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 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 +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 +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\-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: +.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\-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. +.Ip "\fB\-Wmost\fR" 4 +.IX Item "-Wmost" +This is equivalent to \-Wall \-Wno-parentheses. (\s-1APPLE\s0 \s-1ONLY\s0) +.Ip "\fB\-Wdiv-by-zero\fR" 4 +.IX Item "-Wdiv-by-zero" +Warn about compile-time integer division by zero. This is default. To +inhibit the warning messages, use \fB\-Wno-div-by-zero\fR. Floating +point division by zero is not warned about, as it can be a legitimate +way of obtaining infinities and NaNs. +.Ip "\fB\-Wmultichar\fR" 4 +.IX Item "-Wmultichar" +Warn if a multicharacter constant (\fB'\s-1FOOF\s0'\fR) is used. This is +default. To inhibit the warning messages, use \fB\-Wno-multichar\fR. +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\-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. +.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\-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 analysing 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. +.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\-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-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-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\-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. +.Ip "\fB\-p\fR" 4 +.IX Item "-p" +Generate extra code to write profile information suitable for the +analysis program \f(CW\*(C`prof\*(C'\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 \f(CW\*(C`gprof\*(C'\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\-a\fR" 4 +.IX Item "-a" +Generate extra code to write profile information for basic blocks, which will +record the number of times each basic block is executed, the basic block start +address, and the function name containing the basic block. If \fB\-g\fR is +used, the line number and filename of the start of the basic block will also be +recorded. If not overridden by the machine description, the default action is +to append to the text file \fIbb.out\fR. +.Sp +This data could be analyzed by a program like \f(CW\*(C`tcov\*(C'\fR. Note, +however, that the format of the data is not what \f(CW\*(C`tcov\*(C'\fR expects. +Eventually \s-1GNU\s0 \f(CW\*(C`gprof\*(C'\fR should be extended to process this data. +.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\fIsourcename\fI.da\fR for each source file. +.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 \f(CW\*(C`gcov\*(C'\fR, +when it is used with the \fB\-ftest-coverage\fR option. \s-1GCC\s0 +supports two methods of determining code coverage: the options that +support \f(CW\*(C`gcov\*(C'\fR, and options \fB\-a\fR and \fB\-ax\fR, which +write information to text files. The options that support \f(CW\*(C`gcov\*(C'\fR +do not need to instrument every arc in the program, so a program compiled +with them runs faster than a program compiled with \fB\-a\fR, which +adds instrumentation code to every basic block in the program. The +tradeoff: since \f(CW\*(C`gcov\*(C'\fR does not have execution counts for all +branches, it must start with the execution counts for the instrumented +branches, and then iterate over the program flow graph until the entire +graph has been solved. Hence, \f(CW\*(C`gcov\*(C'\fR runs a little more slowly than +a program which uses information from \fB\-a\fR and \fB\-ax\fR. +.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. +.Sp +This option makes it possible to estimate branch probabilities and to +calculate basic block execution counts. In general, basic block +execution counts as provided by \fB\-a\fR do not give enough +information to estimate all branch probabilities. +.Ip "\fB\-ftest-coverage\fR" 4 +.IX Item "-ftest-coverage" +Create data files for the \f(CW\*(C`gcov\*(C'\fR code-coverage utility. +The data file names begin with the name of your source file: +.RS 4 +.Ip "\fIsourcename\fR\fB.bb\fR" 4 +.IX Item "sourcename.bb" +A mapping from basic blocks to line numbers, which \f(CW\*(C`gcov\*(C'\fR uses to +associate basic block execution counts with line numbers. +.Ip "\fIsourcename\fR\fB.bbg\fR" 4 +.IX Item "sourcename.bbg" +A list of all arcs in the program flow graph. This allows \f(CW\*(C`gcov\*(C'\fR +to reconstruct the program flow graph, so that it can compute all basic +block and arc execution counts from the information in the +\&\f(CW\*(C`\f(CIsourcename\f(CW.da\*(C'\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: +.RS 4 +.RE +.Ip "\fIsourcename\fR\fB.da\fR" 4 +.IX Item "sourcename.da" +Runtime arc execution counts, used in conjunction with the arc +information in the file \f(CW\*(C`\f(CIsourcename\f(CW.bbg\*(C'\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 source file name (e.g. \fIfoo.c.00.rtl\fR or \fIfoo.c.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.29.bbro\fR. +.Ip "\fBc\fR" 4 +.IX Item "c" +Dump after instruction combination, to the file \fI\fIfile\fI.16.combine\fR. +.Ip "\fBC\fR" 4 +.IX Item "C" +Dump after the first if conversion, to the file \fI\fIfile\fI.17.ce\fR. +.Ip "\fBd\fR" 4 +.IX Item "d" +Dump after delayed branch scheduling, to \fI\fIfile\fI.31.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.26.ce2\fR. +.Ip "\fBf\fR" 4 +.IX Item "f" +Dump after life analysis, to \fI\fIfile\fI.15.life\fR. +.Ip "\fBF\fR" 4 +.IX Item "F" +Dump after purging \f(CW\*(C`ADDRESSOF\*(C'\fR codes, to \fI\fIfile\fI.09.addressof\fR. +.Ip "\fBg\fR" 4 +.IX Item "g" +Dump after global register allocation, to \fI\fIfile\fI.21.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.28.stack\fR. +.Ip "\fBo\fR" 4 +.IX Item "o" +Dump after post-reload optimizations, to \fI\fIfile\fI.22.postreload\fR. +.Ip "\fBG\fR" 4 +.IX Item "G" +Dump after \s-1GCSE\s0, to \fI\fIfile\fI.10.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.32.stack\fR. +.Ip "\fBl\fR" 4 +.IX Item "l" +Dump after local register allocation, to \fI\fIfile\fI.20.lreg\fR. +.Ip "\fBL\fR" 4 +.IX Item "L" +Dump after loop optimization, to \fI\fIfile\fI.11.loop\fR. +.Ip "\fBM\fR" 4 +.IX Item "M" +Dump after performing the machine dependent reorganisation pass, to +\&\fI\fIfile\fI.30.mach\fR. +.Ip "\fBn\fR" 4 +.IX Item "n" +Dump after register renumbering, to \fI\fIfile\fI.25.rnreg\fR. +.Ip "\fBN\fR" 4 +.IX Item "N" +Dump after the register move pass, to \fI\fIfile\fI.18.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.27.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.08.cse\fR. +.Ip "\fBS\fR" 4 +.IX Item "S" +Dump after the first scheduling pass, to \fI\fIfile\fI.19.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.12.cse2\fR. +.Ip "\fBw\fR" 4 +.IX Item "w" +Dump after the second flow pass, to \fI\fIfile\fI.23.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.24.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: +.RS 4 +.RE +.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\-fpretend-float\fR" 4 +.IX Item "-fpretend-float" +When running a cross-compiler, pretend that the target machine uses the +same floating point format as the host machine. This causes incorrect +output of the actual floating constants, but the actual instruction +sequence will probably be the same as \s-1GCC\s0 would make when running on +the target machine. +.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 +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\-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: +.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 +Without \fB\-O\fR, 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. +.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 +When you specify \fB\-O\fR, the compiler turns on \fB\-fthread-jumps\fR +and \fB\-fdefer-pop\fR on all machines. The compiler turns on +\&\fB\-fdelayed-branch\fR on machines that have delay slots, and +\&\fB\-fomit-frame-pointer\fR on machines that can support debugging even +without a frame pointer. On some machines the compiler also turns +on other flags. +.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 optional optimizations except for loop unrolling, +function inlining, and register renaming. It also turns on the +\&\fB\-fforce-mem\fR option on all machines and frame pointer elimination +on machines where doing so does not interfere with debugging. +.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. +.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 +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 which is not the default. +You can figure out the other form by either removing \fBno-\fR or +adding it. +.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\-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. +.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. The \fB\-O2\fR option turns on this option. +.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. +.Ip "\fB\-foptimize-sibling-calls\fR" 4 +.IX Item "-foptimize-sibling-calls" +Optimize sibling and tail recursive calls. +.Ip "\fB\-ftrapv\fR" 4 +.IX Item "-ftrapv" +This option generates traps for signed overflow on addition, subtraction, +multiplication operations. +.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. +.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 (ie 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 +\&\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. +.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) accross compilation units. +.Sp +This option is default for optimized compilation if assembler and linker +support it. Use \fB\-fno-merge-constants\fR to inhibit this behavior. +.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-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. +.Ip "\fB\-ffast-math\fR" 4 +.IX Item "-ffast-math" +Sets \fB\-fno-math-errno\fR, \fB\-funsafe-math-optimizations\fR, and \fB\-fno-trapping-math\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\-fno-trapping-math\fR" 4 +.IX Item "-fno-trapping-math" +Compile code assuming that floating-point operations cannot generate +user-visible traps. 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. +.PP +The following options control specific optimizations. The \fB\-O2\fR +option turns on all of these optimizations except \fB\-funroll-loops\fR +and \fB\-funroll-all-loops\fR. On most machines, the \fB\-O\fR option +turns on the \fB\-fthread-jumps\fR and \fB\-fdelayed-branch\fR options, +but specific machines may handle it differently. +.PP +You can use the following flags in the rare cases when ``fine-tuning'' +of optimizations to be performed is desired. +.PP +Not all of the optimizations performed by \s-1GCC\s0 have \fB\-f\fR options +to control them. +.Ip "\fB\-fstrength-reduce\fR" 4 +.IX Item "-fstrength-reduce" +Perform the optimizations of loop strength reduction and +elimination of iteration variables. +.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. +.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. +.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. +.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. +.Ip "\fB\-frerun-loop-opt\fR" 4 +.IX Item "-frerun-loop-opt" +Run the loop optimizer twice. +.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 elmination pass by adding +\&\fB\-fno-gcse\fR to the command line. +.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. +.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. +.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. +.Ip "\fB\-fexpensive-optimizations\fR" 4 +.IX Item "-fexpensive-optimizations" +Perform a number of minor optimizations that are relatively expensive. +.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. \s-1GCC\s0 enables this optimization by default with \fB\-O2\fR +or higher. +.Sp +Note \fB\-fregmove\fR and \fB\-foptimize-register-move\fR are the same +optimization. +.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. +.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. +.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. +.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 \s-1HP-UX\s0 and Sparc 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\-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 +For all machines, optimization level 2 and higher enables this flag by +default. +.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. +.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. +.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_EXEC_COUNT\s0\fR +note on the first instruction of each basic block, and 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\-fno-guess-branch-probability\fR" 4 +.IX Item "-fno-guess-branch-probability" +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. +.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 +.Vb 5 +\& int f() { +\& a_union t; +\& t.d = 3.0; +\& return t.i; +\& } +.Ve +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 +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. +.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. +.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 +This option does not work on Mac \s-1OS\s0 X. +.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. +.Sp +If \fIn\fR is not specified, use a machine-dependent default. +.Sp +This option does not work on Mac \s-1OS\s0 X. +.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. +.Sp +If \fIn\fR is not specified, use a machine-dependent default. +.Sp +This option does not work on Mac \s-1OS\s0 X. +.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\-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. +.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''. +.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. +.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\fR" 4 +.IX Item "max-inline-insns" +If an function contains more than this many instructions, it +will not be inlined. This option is precisely equivalent to +\&\fB\-finline-limit\fR. +.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(CW\*(C`1\*(C'\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. +.Sp +It is dangerous to specify a standard system include directory in an +\&\fB\-I\fR option. This defeats the special treatment of system +headers +\&. It can also defeat the repairs to buggy system headers which \s-1GCC\s0 +makes when it is installed. +.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\-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. +.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" +When used with \fB\-M\fR or \fB\-MM\fR, \fB\-MG\fR says to treat missing +header files as generated files and assume they live in the same +directory as the source file. It suppresses preprocessed output, as a +missing header file is ordinarily an error. +.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 +.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 +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\-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 cpp +only knows about the standards for C; other language standards will be +added in the future. +.Sp +\&\fIstandard\fR +may be one of: +.RS 4 +.if n .Ip "\f(CW""""iso9899:1990""""\fR" 4 +.el .Ip "\f(CWiso9899:1990\fR" 4 +.IX Item "iso9899:1990" +.PD 0 +.if n .Ip "\f(CW""""c89""""\fR" 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. +.if n .Ip "\f(CW""""iso9899:199409""""\fR" 4 +.el .Ip "\f(CWiso9899:199409\fR" 4 +.IX Item "iso9899:199409" +The 1990 C standard, as amended in 1994. +.if n .Ip "\f(CW""""iso9899:1999""""\fR" 4 +.el .Ip "\f(CWiso9899:1999\fR" 4 +.IX Item "iso9899:1999" +.PD 0 +.if n .Ip "\f(CW""""c99""""\fR" 4 +.el .Ip "\f(CWc99\fR" 4 +.IX Item "c99" +.if n .Ip "\f(CW""""iso9899:199x""""\fR" 4 +.el .Ip "\f(CWiso9899:199x\fR" 4 +.IX Item "iso9899:199x" +.if n .Ip "\f(CW""""c9x""""\fR" 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. +.if n .Ip "\f(CW""""gnu89""""\fR" 4 +.el .Ip "\f(CWgnu89\fR" 4 +.IX Item "gnu89" +The 1990 C standard plus \s-1GNU\s0 extensions. This is the default. +.if n .Ip "\f(CW""""gnu99""""\fR" 4 +.el .Ip "\f(CWgnu99\fR" 4 +.IX Item "gnu99" +.PD 0 +.if n .Ip "\f(CW""""gnu9x""""\fR" 4 +.el .Ip "\f(CWgnu9x\fR" 4 +.IX Item "gnu9x" +.PD +The 1999 C standard plus \s-1GNU\s0 extensions. +.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 +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\-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\fR" 4 +.IX Item "-traditional" +Try to imitate the behavior of old-fashioned C, as opposed to \s-1ISO\s0 +C. +.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\-$\fR" 4 +.IX Item "-$" +Forbid the use of \fB$\fR in identifiers. The C standard allows +implementations to define extra characters that can appear in +identifiers. By default \s-1GNU\s0 \s-1CPP\s0 permits \fB$\fR, a common extension. +.Ip "\fB\-h\fR" 4 +.IX Item "-h" +.PD 0 +.Ip "\fB\*(--help\fR" 4 +.IX Item "help" +.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. +.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, it will be +searched only in the position requested by \fB\-I\fR. Also, it will +not be considered a system include directory. If that directory really +does contain system headers, there is a good chance that they will +break. For instance, if \s-1GCC\s0's installation procedure edited the headers +in \fI/usr/include\fR to fix bugs, \fB\-I/usr/include\fR will cause the +original, buggy headers to be found instead of the corrected ones. \s-1GCC\s0 +will issue a warning when a system include directory is hidden in this +way. +.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" +By default, \s-1GCC\s0 compiles code for the same type of machine that you +are using. However, it can also be installed as a cross-compiler, to +compile for some other type of machine. In fact, several different +configurations of \s-1GCC\s0, for different target machines, can be +installed side by side. Then you specify which one to use with the +\&\fB\-b\fR option. +.PP +In addition, older and newer versions of \s-1GCC\s0 can be installed side +by side. One of them (probably the newest) will be the default, but +you may sometimes wish to use another. +.Ip "\fB\-b\fR \fImachine\fR" 4 +.IX Item "-b machine" +The argument \fImachine\fR specifies the target machine for compilation. +This is useful when you have installed \s-1GCC\s0 as a cross-compiler. +.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. +.Sp +When you do not specify \fB\-b\fR, it normally means to compile for +the same type of machine that you are using. +.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. +.Sp +The default version, when you do not specify \fB\-V\fR, is the last +version of \s-1GCC\s0 that you installed. +.PP +The \fB\-b\fR and \fB\-V\fR options actually work by controlling part of +the file name used for the executable files and libraries used for +compilation. A given version of \s-1GCC\s0, for a given target machine, is +normally kept in the directory \fI/usr/local/lib/gcc-lib/\fImachine\fI/\fIversion\fI\fR. +.PP +Thus, sites can customize the effect of \fB\-b\fR or \fB\-V\fR either by +changing the names of these directories or adding alternate names (or +symbolic links). If in directory \fI/usr/local/lib/gcc-lib/\fR the +file \fI80386\fR is a link to the file \fIi386v\fR, then \fB\-b +80386\fR becomes an alias for \fB\-b i386v\fR. +.PP +In one respect, the \fB\-b\fR or \fB\-V\fR do not completely change +to a different compiler: the top-level driver program \fBgcc\fR +that you originally invoked continues to run and invoke the other +executables (preprocessor, compiler per se, assembler and linker) +that do the real work. However, since no real work is done in the +driver program, it usually does not matter that the driver program +in use is not the one for the specified target. It is common for the +interface to the other executables to change incompatibly between +compiler versions, so unless the version specified is very close to that +of the driver (for example, \fB\-V 3.0\fR with a driver program from \s-1GCC\s0 +version 3.0.1), use of \fB\-V\fR may not work; for example, using +\&\fB\-V 2.95.2\fR will not work with a driver program from \s-1GCC\s0 3.0. +.PP +The only way that the driver program depends on the target machine is +in the parsing and handling of special machine-specific options. +However, this is controlled by a file which is found, along with the +other executables, in the directory for the specified version and +target machine. As a result, a single installed driver program adapts +to any specified target machine, and sufficiently similar compiler +versions. +.PP +The driver program executable does control one significant thing, +however: the default version and target machine. Therefore, you can +install different instances of the driver program, compiled for +different targets or versions, under different names. +.PP +For example, if the driver for version 2.0 is installed as \fBogcc\fR +and that for version 2.1 is installed as \fBgcc\fR, then the command +\&\fBgcc\fR will use version 2.1 by default, while \fBogcc\fR will use +2.0 by default. However, you can choose either version with either +command with the \fB\-V\fR option. +.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 +.I "\s-1IBM\s0 \s-1RS/6000\s0 and PowerPC Options" +.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-powerc\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\-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\-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\-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 +.I "Intel 386 and \s-1AMD\s0 x86\-64 Options" +.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 +and \fBathlon-mp\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 precesion 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 effectivly 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. +.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. +.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. +.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\-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. +.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. +.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. +.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. +.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. +.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 Sparc, 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 Sparc. +.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. Usually you would +not want to use this option, since it makes the code suboptimal, and +the offsets of structure members won't agree with system libraries. +.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 +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 +Be warned that you should know what you are doing when invoking this +option, and that not all targets provide complete support for it. +.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. The 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. +.Ip "\fB\s-1DEPENDENCIES_OUTPUT\s0\fR" 4 +.IX Item "DEPENDENCIES_OUTPUT" +@anchor{\s-1DEPENDENCIES_OUTPUT\s0} +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 the environment variable +\&\fB\s-1DEPENDENCIES_OUTPUT\s0\fR, except that +system header files are not ignored, so it implies \fB\-M\fR rather +than \fB\-MM\fR. +.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 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 1.1 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 +(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 |