1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.1 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @file{gcc}, or
57 @w{@uref{http://gcc.gnu.org/thanks.html}}, for contributors to GCC@.
62 @chapter GCC Command Options
63 @cindex GCC command options
64 @cindex command options
65 @cindex options, GCC command
67 @c man begin DESCRIPTION
69 When you invoke GCC, it normally does preprocessing, compilation,
70 assembly and linking. The ``overall options'' allow you to stop this
71 process at an intermediate stage. For example, the @option{-c} option
72 says not to run the linker. Then the output consists of object files
73 output by the assembler.
75 Other options are passed on to one stage of processing. Some options
76 control the preprocessor and others the compiler itself. Yet other
77 options control the assembler and linker; most of these are not
78 documented here, since you rarely need to use any of them.
80 @cindex C compilation options
81 Most of the command line options that you can use with GCC are useful
82 for C programs; when an option is only useful with another language
83 (usually C++), the explanation says so explicitly. If the description
84 for a particular option does not mention a source language, you can use
85 that option with all supported languages.
87 @cindex C++ compilation options
88 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
89 options for compiling C++ programs.
91 @cindex grouping options
92 @cindex options, grouping
93 The @command{gcc} program accepts options and file names as operands. Many
94 options have multi-letter names; therefore multiple single-letter options
95 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
98 @cindex order of options
99 @cindex options, order
100 You can mix options and other arguments. For the most part, the order
101 you use doesn't matter. Order does matter when you use several options
102 of the same kind; for example, if you specify @option{-L} more than once,
103 the directories are searched in the order specified.
105 Many options have long names starting with @samp{-f} or with
106 @samp{-W}---for example, @option{-fforce-mem},
107 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
108 these have both positive and negative forms; the negative form of
109 @option{-ffoo} would be @option{-fno-foo}. This manual documents
110 only one of these two forms, whichever one is not the default.
114 @xref{Option Index}, for an index to GCC's options.
117 * Option Summary:: Brief list of all options, without explanations.
118 * Overall Options:: Controlling the kind of output:
119 an executable, object files, assembler files,
120 or preprocessed source.
121 * Invoking G++:: Compiling C++ programs.
122 * C Dialect Options:: Controlling the variant of C language compiled.
123 * C++ Dialect Options:: Variations on C++.
124 * Objective-C Dialect Options:: Variations on Objective-C.
125 * Language Independent Options:: Controlling how diagnostics should be
127 * Warning Options:: How picky should the compiler be?
128 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
129 * Optimize Options:: How much optimization?
130 * Preprocessor Options:: Controlling header files and macro definitions.
131 Also, getting dependency information for Make.
132 * Assembler Options:: Passing options to the assembler.
133 * Link Options:: Specifying libraries and so on.
134 * Directory Options:: Where to find header files and libraries.
135 Where to find the compiler executable files.
136 * Spec Files:: How to pass switches to sub-processes.
137 * Target Options:: Running a cross-compiler, or an old version of GCC.
138 * Submodel Options:: Specifying minor hardware or convention variations,
139 such as 68010 vs 68020.
140 * Code Gen Options:: Specifying conventions for function calls, data layout
142 * Environment Variables:: Env vars that affect GCC.
143 * Running Protoize:: Automatically adding or removing function prototypes.
149 @section Option Summary
151 Here is a summary of all the options, grouped by type. Explanations are
152 in the following sections.
155 @item Overall Options
156 @xref{Overall Options,,Options Controlling the Kind of Output}.
158 -c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol
159 -v --target-help --help}
161 @item C Language Options
162 @xref{C Dialect Options,,Options Controlling C Dialect}.
164 -ansi -std=@var{standard} -aux-info @var{filename} @gol
165 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
166 -fhosted -ffreestanding @gol
167 -trigraphs -traditional -traditional-cpp @gol
168 -fallow-single-precision -fcond-mismatch @gol
169 -fsigned-bitfields -fsigned-char @gol
170 -funsigned-bitfields -funsigned-char @gol
171 -fwritable-strings -fshort-wchar}
173 @item C++ Language Options
174 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
176 -fno-access-control -fcheck-new -fconserve-space @gol
177 -fno-const-strings -fdollars-in-identifiers @gol
178 -fno-elide-constructors @gol
179 -fno-enforce-eh-specs -fexternal-templates @gol
180 -falt-external-templates @gol
181 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
182 -fno-implicit-templates @gol
183 -fno-implicit-inline-templates @gol
184 -fno-implement-inlines -fms-extensions @gol
185 -fno-nonansi-builtins -fno-operator-names @gol
186 -fno-optional-diags -fpermissive @gol
187 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
188 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
189 -fno-default-inline -Wctor-dtor-privacy @gol
190 -Wnon-virtual-dtor -Wreorder @gol
191 -Weffc++ -Wno-deprecated @gol
192 -Wno-non-template-friend -Wold-style-cast @gol
193 -Woverloaded-virtual -Wno-pmf-conversions @gol
194 -Wsign-promo -Wsynth}
196 @item Objective-C Language Options
197 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
199 -fconstant-string-class=@var{class-name} @gol
200 -fgnu-runtime -fnext-runtime -gen-decls @gol
201 -Wno-protocol -Wselector}
203 @item Language Independent Options
204 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
206 -fmessage-length=@var{n} @gol
207 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
209 @item Warning Options
210 @xref{Warning Options,,Options to Request or Suppress Warnings}.
212 -fsyntax-only -pedantic -pedantic-errors @gol
213 -w -W -Wall -Waggregate-return @gol
214 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
215 -Wconversion -Wdisabled-optimization -Wdiv-by-zero -Werror @gol
216 -Wfloat-equal -Wformat -Wformat=2 @gol
217 -Wformat-nonliteral -Wformat-security @gol
218 -Wimplicit -Wimplicit-int @gol
219 -Wimplicit-function-declaration @gol
220 -Werror-implicit-function-declaration @gol
221 -Wimport -Winline @gol
222 -Wlarger-than-@var{len} -Wlong-long @gol
223 -Wmain -Wmissing-braces -Wmissing-declarations @gol
224 -Wmissing-format-attribute -Wmissing-noreturn @gol
225 -Wmultichar -Wno-format-extra-args -Wno-format-y2k @gol
226 -Wno-import -Wpacked -Wpadded @gol
227 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
228 -Wreturn-type -Wsequence-point -Wshadow @gol
229 -Wsign-compare -Wswitch -Wsystem-headers @gol
230 -Wtrigraphs -Wundef -Wuninitialized @gol
231 -Wunknown-pragmas -Wunreachable-code @gol
232 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
233 -Wunused-value -Wunused-variable -Wwrite-strings}
235 @item C-only Warning Options
237 -Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol
238 -Wstrict-prototypes -Wtraditional}
240 @item Debugging Options
241 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
243 -d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
245 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
246 -fdump-tree-original@r{[}-@var{n}@r{]} -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
247 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
248 -fmem-report -fpretend-float @gol
249 -fprofile-arcs -ftest-coverage -ftime-report @gol
250 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
251 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
252 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
253 -print-multi-directory -print-multi-lib @gol
254 -print-prog-name=@var{program} -print-search-dirs -Q @gol
257 @item Optimization Options
258 @xref{Optimize Options,,Options that Control Optimization}.
260 -falign-functions=@var{n} -falign-jumps=@var{n} @gol
261 -falign-labels=@var{n} -falign-loops=@var{n} @gol
262 -fbranch-probabilities -fcaller-saves -fcprop-registers @gol
263 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
264 -fdelayed-branch -fdelete-null-pointer-checks @gol
265 -fexpensive-optimizations -ffast-math -ffloat-store @gol
266 -fforce-addr -fforce-mem -ffunction-sections @gol
267 -fgcse -fgcse-lm -fgcse-sm @gol
268 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
269 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
270 -fmove-all-movables -fno-default-inline -fno-defer-pop @gol
271 -fno-function-cse -fno-guess-branch-probability @gol
272 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
273 -funsafe-math-optimizations -fno-trapping-math @gol
274 -fomit-frame-pointer -foptimize-register-move @gol
275 -foptimize-sibling-calls -fprefetch-loop-arrays -freduce-all-givs @gol
276 -fregmove -frename-registers @gol
277 -frerun-cse-after-loop -frerun-loop-opt @gol
278 -fschedule-insns -fschedule-insns2 @gol
279 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
280 -fstrength-reduce -fstrict-aliasing -fthread-jumps -ftrapv @gol
281 -funroll-all-loops -funroll-loops @gol
282 --param @var{name}=@var{value}
283 -O -O0 -O1 -O2 -O3 -Os}
285 @item Preprocessor Options
286 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
288 -$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
289 -C -dD -dI -dM -dN @gol
290 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
291 -idirafter @var{dir} @gol
292 -include @var{file} -imacros @var{file} @gol
293 -iprefix @var{file} -iwithprefix @var{dir} @gol
294 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
295 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
296 -trigraphs -undef -U@var{macro} -Wp,@var{option}}
298 @item Assembler Option
299 @xref{Assembler Options,,Passing Options to the Assembler}.
304 @xref{Link Options,,Options for Linking}.
306 @var{object-file-name} -l@var{library} @gol
307 -nostartfiles -nodefaultlibs -nostdlib @gol
308 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
309 -Wl,@var{option} -Xlinker @var{option} @gol
312 @item Directory Options
313 @xref{Directory Options,,Options for Directory Search}.
315 -B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
318 @c I wrote this xref this way to avoid overfull hbox. -- rms
319 @xref{Target Options}.
321 -b @var{machine} -V @var{version}}
323 @item Machine Dependent Options
324 @xref{Submodel Options,,Hardware Models and Configurations}.
325 @emph{M680x0 Options}
327 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
328 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
329 -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
330 -malign-int -mstrict-align}
332 @emph{M68hc1x Options}
334 -m6811 -m6812 -m68hc11 -m68hc12 @gol
335 -mauto-incdec -mshort -msoft-reg-count=@var{count}}
343 -mcpu=@var{cpu-type} @gol
344 -mtune=@var{cpu-type} @gol
345 -mcmodel=@var{code-model} @gol
347 -mapp-regs -mbroken-saverestore -mcypress @gol
348 -mepilogue -mfaster-structs -mflat @gol
349 -mfpu -mhard-float -mhard-quad-float @gol
350 -mimpure-text -mlive-g0 -mno-app-regs @gol
351 -mno-epilogue -mno-faster-structs -mno-flat -mno-fpu @gol
352 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
353 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
354 -msupersparc -munaligned-doubles -mv8}
356 @emph{Convex Options}
358 -mc1 -mc2 -mc32 -mc34 -mc38 @gol
359 -margcount -mnoargcount @gol
360 -mlong32 -mlong64 @gol
361 -mvolatile-cache -mvolatile-nocache}
363 @emph{AMD29K Options}
365 -m29000 -m29050 -mbw -mnbw -mdw -mndw @gol
366 -mlarge -mnormal -msmall @gol
367 -mkernel-registers -mno-reuse-arg-regs @gol
368 -mno-stack-check -mno-storem-bug @gol
369 -mreuse-arg-regs -msoft-float -mstack-check @gol
370 -mstorem-bug -muser-registers}
374 -mapcs-frame -mno-apcs-frame @gol
375 -mapcs-26 -mapcs-32 @gol
376 -mapcs-stack-check -mno-apcs-stack-check @gol
377 -mapcs-float -mno-apcs-float @gol
378 -mapcs-reentrant -mno-apcs-reentrant @gol
379 -msched-prolog -mno-sched-prolog @gol
380 -mlittle-endian -mbig-endian -mwords-little-endian @gol
381 -malignment-traps -mno-alignment-traps @gol
382 -msoft-float -mhard-float -mfpe @gol
383 -mthumb-interwork -mno-thumb-interwork @gol
384 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
385 -mstructure-size-boundary=@var{n} @gol
386 -mbsd -mxopen -mno-symrename @gol
387 -mabort-on-noreturn @gol
388 -mlong-calls -mno-long-calls @gol
389 -msingle-pic-base -mno-single-pic-base @gol
390 -mpic-register=@var{reg} @gol
391 -mnop-fun-dllimport @gol
392 -mpoke-function-name @gol
394 -mtpcs-frame -mtpcs-leaf-frame @gol
395 -mcaller-super-interworking -mcallee-super-interworking }
397 @emph{MN10200 Options}
401 @emph{MN10300 Options}
403 -mmult-bug -mno-mult-bug @gol
404 -mam33 -mno-am33 @gol
407 @emph{M32R/D Options}
409 -m32rx -m32r -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol
414 -m88000 -m88100 -m88110 -mbig-pic @gol
415 -mcheck-zero-division -mhandle-large-shift @gol
416 -midentify-revision -mno-check-zero-division @gol
417 -mno-ocs-debug-info -mno-ocs-frame-position @gol
418 -mno-optimize-arg-area -mno-serialize-volatile @gol
419 -mno-underscores -mocs-debug-info @gol
420 -mocs-frame-position -moptimize-arg-area @gol
421 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
422 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
423 -mversion-03.00 -mwarn-passed-structs}
425 @emph{RS/6000 and PowerPC Options}
427 -mcpu=@var{cpu-type} @gol
428 -mtune=@var{cpu-type} @gol
429 -mpower -mno-power -mpower2 -mno-power2 @gol
430 -mpowerpc -mpowerpc64 -mno-powerpc @gol
431 -maltivec -mno-altivec @gol
432 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
433 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
434 -mnew-mnemonics -mold-mnemonics @gol
435 -mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc @gol
436 -m64 -m32 -mxl-call -mno-xl-call -mthreads -mpe @gol
437 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
438 -mstring -mno-string -mupdate -mno-update @gol
439 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
440 -mstrict-align -mno-strict-align -mrelocatable @gol
441 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
442 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
443 -mcall-aix -mcall-sysv -mcall-netbsd @gol
444 -maix-struct-return -msvr4-struct-return
446 -mprototype -mno-prototype @gol
447 -msim -mmvme -mads -myellowknife -memb -msdata @gol
448 -msdata=@var{opt} -mvxworks -G @var{num}}
452 -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
453 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
454 -mminimum-fp-blocks -mnohc-struct-return}
458 -mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
459 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
460 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
461 -mgas -mgp32 -mgp64 @gol
462 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
463 -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
464 -mmips-as -mmips-tfile -mno-abicalls @gol
465 -mno-embedded-data -mno-uninit-const-in-rodata @gol
466 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
467 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
468 -mrnames -msoft-float @gol
469 -m4650 -msingle-float -mmad @gol
470 -mstats -EL -EB -G @var{num} -nocpp @gol
471 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol
472 -mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func}
474 @emph{i386 and x86-64 Options}
476 -mcpu=@var{cpu-type} -march=@var{cpu-type} @gol
477 -mintel-syntax -mieee-fp -mno-fancy-math-387 @gol
478 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
479 -mno-wide-multiply -mrtd -malign-double @gol
480 -mpreferred-stack-boundary=@var{num} @gol
481 -mmmx -msse -m3dnow @gol
482 -mthreads -mno-align-stringops -minline-all-stringops @gol
483 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
484 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
490 -march=@var{architecture-type} @gol
491 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
492 -mfast-indirect-calls -mgas -mjump-in-delay @gol
493 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
494 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
495 -mno-jump-in-delay -mno-long-load-store @gol
496 -mno-portable-runtime -mno-soft-float @gol
497 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
498 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
499 -mschedule=@var{cpu-type} -mspace-regs}
501 @emph{Intel 960 Options}
503 -m@var{cpu-type} -masm-compat -mclean-linkage @gol
504 -mcode-align -mcomplex-addr -mleaf-procedures @gol
505 -mic-compat -mic2.0-compat -mic3.0-compat @gol
506 -mintel-asm -mno-clean-linkage -mno-code-align @gol
507 -mno-complex-addr -mno-leaf-procedures @gol
508 -mno-old-align -mno-strict-align -mno-tail-call @gol
509 -mnumerics -mold-align -msoft-float -mstrict-align @gol
512 @emph{DEC Alpha Options}
514 -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float @gol
515 -malpha-as -mgas @gol
516 -mieee -mieee-with-inexact -mieee-conformant @gol
517 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
518 -mtrap-precision=@var{mode} -mbuild-constants @gol
519 -mcpu=@var{cpu-type} @gol
520 -mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max @gol
521 -mmemory-latency=@var{time}}
523 @emph{DEC Alpha/VMS Options}
527 @emph{Clipper Options}
531 @emph{H8/300 Options}
533 -mrelax -mh -ms -mint32 -malign-300}
537 -m1 -m2 -m3 -m3e @gol
538 -m4-nofpu -m4-single-only -m4-single -m4 @gol
539 -mb -ml -mdalign -mrelax @gol
540 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
541 -mieee -misize -mpadstruct -mspace @gol
542 -mprefergot -musermode}
544 @emph{System V Options}
546 -Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
551 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
552 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
554 @emph{TMS320C3x/C4x Options}
556 -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
557 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
558 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
559 -mparallel-insns -mparallel-mpy -mpreserve-float}
563 -mlong-calls -mno-long-calls -mep -mno-ep @gol
564 -mprolog-function -mno-prolog-function -mspace @gol
565 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
570 -m32032 -m32332 -m32532 -m32081 -m32381 @gol
571 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
572 -mregparam -mnoregparam -msb -mnosb @gol
573 -mbitfield -mnobitfield -mhimem -mnohimem}
577 -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
578 -mcall-prologues -mno-tablejump -mtiny-stack}
582 -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
583 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
584 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
585 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
586 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
590 -mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
591 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
596 -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
597 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
598 -mconstant-gp -mauto-pic -minline-divide-min-latency @gol
599 -minline-divide-max-throughput -mno-dwarf2-asm @gol
600 -mfixed-range=@var{register-range}}
602 @emph{S/390 and zSeries Options}
604 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
605 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
606 -m64 -m31 -mdebug -mno-debug}
610 -mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
611 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
612 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
613 -mstack-align -mdata-align -mconst-align @gol
614 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
615 -melf -maout -melinux -mlinux -sim -sim2}
617 @item Code Generation Options
618 @xref{Code Gen Options,,Options for Code Generation Conventions}.
620 -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
621 -ffixed-@var{reg} -fexceptions @gol
622 -fnon-call-exceptions -funwind-tables -fasynchronous-unwind-tables @gol
623 -finhibit-size-directive -finstrument-functions @gol
624 -fno-common -fno-ident -fno-gnu-linker @gol
625 -fpcc-struct-return -fpic -fPIC @gol
626 -freg-struct-return -fshared-data -fshort-enums @gol
627 -fshort-double -fvolatile @gol
628 -fvolatile-global -fvolatile-static @gol
629 -fverbose-asm -fpack-struct -fstack-check @gol
630 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
631 -fargument-alias -fargument-noalias @gol
632 -fargument-noalias-global -fleading-underscore}
636 * Overall Options:: Controlling the kind of output:
637 an executable, object files, assembler files,
638 or preprocessed source.
639 * C Dialect Options:: Controlling the variant of C language compiled.
640 * C++ Dialect Options:: Variations on C++.
641 * Objective-C Dialect Options:: Variations on Objective-C.
642 * Language Independent Options:: Controlling how diagnostics should be
644 * Warning Options:: How picky should the compiler be?
645 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
646 * Optimize Options:: How much optimization?
647 * Preprocessor Options:: Controlling header files and macro definitions.
648 Also, getting dependency information for Make.
649 * Assembler Options:: Passing options to the assembler.
650 * Link Options:: Specifying libraries and so on.
651 * Directory Options:: Where to find header files and libraries.
652 Where to find the compiler executable files.
653 * Spec Files:: How to pass switches to sub-processes.
654 * Target Options:: Running a cross-compiler, or an old version of GCC.
657 @node Overall Options
658 @section Options Controlling the Kind of Output
660 Compilation can involve up to four stages: preprocessing, compilation
661 proper, assembly and linking, always in that order. The first three
662 stages apply to an individual source file, and end by producing an
663 object file; linking combines all the object files (those newly
664 compiled, and those specified as input) into an executable file.
666 @cindex file name suffix
667 For any given input file, the file name suffix determines what kind of
672 C source code which must be preprocessed.
675 C source code which should not be preprocessed.
678 C++ source code which should not be preprocessed.
681 Objective-C source code. Note that you must link with the library
682 @file{libobjc.a} to make an Objective-C program work.
685 Objective-C source code which should not be preprocessed.
688 C header file (not to be compiled or linked).
692 @itemx @var{file}.cxx
693 @itemx @var{file}.cpp
694 @itemx @var{file}.c++
696 C++ source code which must be preprocessed. Note that in @samp{.cxx},
697 the last two letters must both be literally @samp{x}. Likewise,
698 @samp{.C} refers to a literal capital C@.
701 @itemx @var{file}.for
702 @itemx @var{file}.FOR
703 Fortran source code which should not be preprocessed.
706 @itemx @var{file}.fpp
707 @itemx @var{file}.FPP
708 Fortran source code which must be preprocessed (with the traditional
712 Fortran source code which must be preprocessed with a RATFOR
713 preprocessor (not included with GCC)@.
715 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
716 Using and Porting GNU Fortran}, for more details of the handling of
719 @c FIXME: Descriptions of Java file types.
726 Ada source code file which contains a library unit declaration (a
727 declaration of a package, subprogram, or generic, or a generic
728 instantiation), or a library unit renaming declaration (a package,
729 generic, or subprogram renaming declaration). Such files are also
732 @itemx @var{file}.adb
733 Ada source code file containing a library unit body (a subprogram or
734 package body). Such files are also called @dfn{bodies}.
736 @c GCC also knows about some suffixes for languages not yet included:
742 @itemx @var{file}.chi
743 CHILL source code (preprocessed with the traditional preprocessor).
749 Assembler code which must be preprocessed.
752 An object file to be fed straight into linking.
753 Any file name with no recognized suffix is treated this way.
757 You can specify the input language explicitly with the @option{-x} option:
760 @item -x @var{language}
761 Specify explicitly the @var{language} for the following input files
762 (rather than letting the compiler choose a default based on the file
763 name suffix). This option applies to all following input files until
764 the next @option{-x} option. Possible values for @var{language} are:
766 c c-header cpp-output
768 objective-c objc-cpp-output
769 assembler assembler-with-cpp
772 f77 f77-cpp-input ratfor
777 Turn off any specification of a language, so that subsequent files are
778 handled according to their file name suffixes (as they are if @option{-x}
779 has not been used at all).
781 @item -pass-exit-codes
782 @opindex pass-exit-codes
783 Normally the @command{gcc} program will exit with the code of 1 if any
784 phase of the compiler returns a non-success return code. If you specify
785 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
786 numerically highest error produced by any phase that returned an error
790 If you only want some of the stages of compilation, you can use
791 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
792 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
793 @command{gcc} is to stop. Note that some combinations (for example,
794 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
799 Compile or assemble the source files, but do not link. The linking
800 stage simply is not done. The ultimate output is in the form of an
801 object file for each source file.
803 By default, the object file name for a source file is made by replacing
804 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
806 Unrecognized input files, not requiring compilation or assembly, are
811 Stop after the stage of compilation proper; do not assemble. The output
812 is in the form of an assembler code file for each non-assembler input
815 By default, the assembler file name for a source file is made by
816 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
818 Input files that don't require compilation are ignored.
822 Stop after the preprocessing stage; do not run the compiler proper. The
823 output is in the form of preprocessed source code, which is sent to the
826 Input files which don't require preprocessing are ignored.
828 @cindex output file option
831 Place output in file @var{file}. This applies regardless to whatever
832 sort of output is being produced, whether it be an executable file,
833 an object file, an assembler file or preprocessed C code.
835 Since only one output file can be specified, it does not make sense to
836 use @option{-o} when compiling more than one input file, unless you are
837 producing an executable file as output.
839 If @option{-o} is not specified, the default is to put an executable file
840 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
841 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
842 all preprocessed C source on standard output.
846 Print (on standard error output) the commands executed to run the stages
847 of compilation. Also print the version number of the compiler driver
848 program and of the preprocessor and the compiler proper.
852 Use pipes rather than temporary files for communication between the
853 various stages of compilation. This fails to work on some systems where
854 the assembler is unable to read from a pipe; but the GNU assembler has
859 Print (on the standard output) a description of the command line options
860 understood by @command{gcc}. If the @option{-v} option is also specified
861 then @option{--help} will also be passed on to the various processes
862 invoked by @command{gcc}, so that they can display the command line options
863 they accept. If the @option{-W} option is also specified then command
864 line options which have no documentation associated with them will also
869 Print (on the standard output) a description of target specific command
870 line options for each tool.
874 @section Compiling C++ Programs
876 @cindex suffixes for C++ source
877 @cindex C++ source file suffixes
878 C++ source files conventionally use one of the suffixes @samp{.C},
879 @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx};
880 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
881 files with these names and compiles them as C++ programs even if you
882 call the compiler the same way as for compiling C programs (usually with
883 the name @command{gcc}).
887 However, C++ programs often require class libraries as well as a
888 compiler that understands the C++ language---and under some
889 circumstances, you might want to compile programs from standard input,
890 or otherwise without a suffix that flags them as C++ programs.
891 @command{g++} is a program that calls GCC with the default language
892 set to C++, and automatically specifies linking against the C++
893 library. On many systems, @command{g++} is also
894 installed with the name @command{c++}.
896 @cindex invoking @command{g++}
897 When you compile C++ programs, you may specify many of the same
898 command-line options that you use for compiling programs in any
899 language; or command-line options meaningful for C and related
900 languages; or options that are meaningful only for C++ programs.
901 @xref{C Dialect Options,,Options Controlling C Dialect}, for
902 explanations of options for languages related to C@.
903 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
904 explanations of options that are meaningful only for C++ programs.
906 @node C Dialect Options
907 @section Options Controlling C Dialect
908 @cindex dialect options
909 @cindex language dialect options
910 @cindex options, dialect
912 The following options control the dialect of C (or languages derived
913 from C, such as C++ and Objective-C) that the compiler accepts:
920 In C mode, support all ISO C89 programs. In C++ mode,
921 remove GNU extensions that conflict with ISO C++.
923 This turns off certain features of GCC that are incompatible with ISO
924 C89 (when compiling C code), or of standard C++ (when compiling C++ code),
925 such as the @code{asm} and @code{typeof} keywords, and
926 predefined macros such as @code{unix} and @code{vax} that identify the
927 type of system you are using. It also enables the undesirable and
928 rarely used ISO trigraph feature. For the C compiler,
929 it disables recognition of C++ style @samp{//} comments as well as
930 the @code{inline} keyword.
932 The alternate keywords @code{__asm__}, @code{__extension__},
933 @code{__inline__} and @code{__typeof__} continue to work despite
934 @option{-ansi}. You would not want to use them in an ISO C program, of
935 course, but it is useful to put them in header files that might be included
936 in compilations done with @option{-ansi}. Alternate predefined macros
937 such as @code{__unix__} and @code{__vax__} are also available, with or
938 without @option{-ansi}.
940 The @option{-ansi} option does not cause non-ISO programs to be
941 rejected gratuitously. For that, @option{-pedantic} is required in
942 addition to @option{-ansi}. @xref{Warning Options}.
944 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
945 option is used. Some header files may notice this macro and refrain
946 from declaring certain functions or defining certain macros that the
947 ISO standard doesn't call for; this is to avoid interfering with any
948 programs that might use these names for other things.
950 Functions which would normally be built in but do not have semantics
951 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
952 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
953 built-in functions provided by GCC}, for details of the functions
958 Determine the language standard. This option is currently only
959 supported when compiling C@. A value for this option must be provided;
965 ISO C89 (same as @option{-ansi}).
968 ISO C89 as modified in amendment 1.
974 ISO C99. Note that this standard is not yet fully supported; see
975 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
976 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
979 Default, ISO C89 plus GNU extensions (including some C99 features).
983 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
984 this will become the default. The name @samp{gnu9x} is deprecated.
988 Even when this option is not specified, you can still use some of the
989 features of newer standards in so far as they do not conflict with
990 previous C standards. For example, you may use @code{__restrict__} even
991 when @option{-std=c99} is not specified.
993 The @option{-std} options specifying some version of ISO C have the same
994 effects as @option{-ansi}, except that features that were not in ISO C89
995 but are in the specified version (for example, @samp{//} comments and
996 the @code{inline} keyword in ISO C99) are not disabled.
998 @xref{Standards,,Language Standards Supported by GCC}, for details of
999 these standard versions.
1001 @item -aux-info @var{filename}
1003 Output to the given filename prototyped declarations for all functions
1004 declared and/or defined in a translation unit, including those in header
1005 files. This option is silently ignored in any language other than C@.
1007 Besides declarations, the file indicates, in comments, the origin of
1008 each declaration (source file and line), whether the declaration was
1009 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1010 @samp{O} for old, respectively, in the first character after the line
1011 number and the colon), and whether it came from a declaration or a
1012 definition (@samp{C} or @samp{F}, respectively, in the following
1013 character). In the case of function definitions, a K&R-style list of
1014 arguments followed by their declarations is also provided, inside
1015 comments, after the declaration.
1019 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1020 keyword, so that code can use these words as identifiers. You can use
1021 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1022 instead. @option{-ansi} implies @option{-fno-asm}.
1024 In C++, this switch only affects the @code{typeof} keyword, since
1025 @code{asm} and @code{inline} are standard keywords. You may want to
1026 use the @option{-fno-gnu-keywords} flag instead, which has the same
1027 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1028 switch only affects the @code{asm} and @code{typeof} keywords, since
1029 @code{inline} is a standard keyword in ISO C99.
1032 @itemx -fno-builtin-@var{function} @r{(C and Objective-C only)}
1033 @opindex fno-builtin
1034 @cindex built-in functions
1035 Don't recognize built-in functions that do not begin with
1036 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1037 functions provided by GCC}, for details of the functions affected,
1038 including those which are not built-in functions when @option{-ansi} or
1039 @option{-std} options for strict ISO C conformance are used because they
1040 do not have an ISO standard meaning.
1042 GCC normally generates special code to handle certain built-in functions
1043 more efficiently; for instance, calls to @code{alloca} may become single
1044 instructions that adjust the stack directly, and calls to @code{memcpy}
1045 may become inline copy loops. The resulting code is often both smaller
1046 and faster, but since the function calls no longer appear as such, you
1047 cannot set a breakpoint on those calls, nor can you change the behavior
1048 of the functions by linking with a different library.
1050 In C++, @option{-fno-builtin} is always in effect. The @option{-fbuiltin}
1051 option has no effect. Therefore, in C++, the only way to get the
1052 optimization benefits of built-in functions is to call the function
1053 using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses
1054 built-in functions to implement many functions (like
1055 @code{std::strchr}), so that you automatically get efficient code.
1057 With the @option{-fno-builtin-@var{function}} option, not available
1058 when compiling C++, only the built-in function @var{function} is
1059 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1060 function is named this is not built-in in this version of GCC, this
1061 option is ignored. There is no corresponding
1062 @option{-fbuiltin-@var{function}} option; if you wish to enable
1063 built-in functions selectively when using @option{-fno-builtin} or
1064 @option{-ffreestanding}, you may define macros such as:
1067 #define abs(n) __builtin_abs ((n))
1068 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1073 @cindex hosted environment
1075 Assert that compilation takes place in a hosted environment. This implies
1076 @option{-fbuiltin}. A hosted environment is one in which the
1077 entire standard library is available, and in which @code{main} has a return
1078 type of @code{int}. Examples are nearly everything except a kernel.
1079 This is equivalent to @option{-fno-freestanding}.
1081 @item -ffreestanding
1082 @opindex ffreestanding
1083 @cindex hosted environment
1085 Assert that compilation takes place in a freestanding environment. This
1086 implies @option{-fno-builtin}. A freestanding environment
1087 is one in which the standard library may not exist, and program startup may
1088 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1089 This is equivalent to @option{-fno-hosted}.
1091 @xref{Standards,,Language Standards Supported by GCC}, for details of
1092 freestanding and hosted environments.
1096 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1097 options for strict ISO C conformance) implies @option{-trigraphs}.
1099 @cindex traditional C language
1100 @cindex C language, traditional
1102 @opindex traditional
1103 Attempt to support some aspects of traditional C compilers.
1108 All @code{extern} declarations take effect globally even if they
1109 are written inside of a function definition. This includes implicit
1110 declarations of functions.
1113 The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const}
1114 and @code{volatile} are not recognized. (You can still use the
1115 alternative keywords such as @code{__typeof__}, @code{__inline__}, and
1119 Comparisons between pointers and integers are always allowed.
1122 Integer types @code{unsigned short} and @code{unsigned char} promote
1123 to @code{unsigned int}.
1126 Out-of-range floating point literals are not an error.
1129 Certain constructs which ISO regards as a single invalid preprocessing
1130 number, such as @samp{0xe-0xd}, are treated as expressions instead.
1133 String ``constants'' are not necessarily constant; they are stored in
1134 writable space, and identical looking constants are allocated
1135 separately. (This is the same as the effect of
1136 @option{-fwritable-strings}.)
1138 @cindex @code{longjmp} and automatic variables
1140 All automatic variables not declared @code{register} are preserved by
1141 @code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables
1142 not declared @code{volatile} may be clobbered.
1147 @cindex escape sequences, traditional
1148 The character escape sequences @samp{\x} and @samp{\a} evaluate as the
1149 literal characters @samp{x} and @samp{a} respectively. Without
1150 @w{@option{-traditional}}, @samp{\x} is a prefix for the hexadecimal
1151 representation of a character, and @samp{\a} produces a bell.
1154 This option is deprecated and may be removed.
1156 You may wish to use @option{-fno-builtin} as well as @option{-traditional}
1157 if your program uses names that are normally GNU C built-in functions for
1158 other purposes of its own.
1160 You cannot use @option{-traditional} if you include any header files that
1161 rely on ISO C features. Some vendors are starting to ship systems with
1162 ISO C header files and you cannot use @option{-traditional} on such
1163 systems to compile files that include any system headers.
1165 The @option{-traditional} option also enables @option{-traditional-cpp}.
1167 @item -traditional-cpp
1168 @opindex traditional-cpp
1169 Attempt to support some aspects of traditional C preprocessors.
1170 See the GNU CPP manual for details.
1172 @item -fcond-mismatch
1173 @opindex fcond-mismatch
1174 Allow conditional expressions with mismatched types in the second and
1175 third arguments. The value of such an expression is void. This option
1176 is not supported for C++.
1178 @item -funsigned-char
1179 @opindex funsigned-char
1180 Let the type @code{char} be unsigned, like @code{unsigned char}.
1182 Each kind of machine has a default for what @code{char} should
1183 be. It is either like @code{unsigned char} by default or like
1184 @code{signed char} by default.
1186 Ideally, a portable program should always use @code{signed char} or
1187 @code{unsigned char} when it depends on the signedness of an object.
1188 But many programs have been written to use plain @code{char} and
1189 expect it to be signed, or expect it to be unsigned, depending on the
1190 machines they were written for. This option, and its inverse, let you
1191 make such a program work with the opposite default.
1193 The type @code{char} is always a distinct type from each of
1194 @code{signed char} or @code{unsigned char}, even though its behavior
1195 is always just like one of those two.
1198 @opindex fsigned-char
1199 Let the type @code{char} be signed, like @code{signed char}.
1201 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1202 the negative form of @option{-funsigned-char}. Likewise, the option
1203 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1205 @item -fsigned-bitfields
1206 @itemx -funsigned-bitfields
1207 @itemx -fno-signed-bitfields
1208 @itemx -fno-unsigned-bitfields
1209 @opindex fsigned-bitfields
1210 @opindex funsigned-bitfields
1211 @opindex fno-signed-bitfields
1212 @opindex fno-unsigned-bitfields
1213 These options control whether a bit-field is signed or unsigned, when the
1214 declaration does not use either @code{signed} or @code{unsigned}. By
1215 default, such a bit-field is signed, because this is consistent: the
1216 basic integer types such as @code{int} are signed types.
1218 However, when @option{-traditional} is used, bit-fields are all unsigned
1221 @item -fwritable-strings
1222 @opindex fwritable-strings
1223 Store string constants in the writable data segment and don't uniquize
1224 them. This is for compatibility with old programs which assume they can
1225 write into string constants. The option @option{-traditional} also has
1228 Writing into string constants is a very bad idea; ``constants'' should
1231 @item -fallow-single-precision
1232 @opindex fallow-single-precision
1233 Do not promote single precision math operations to double precision,
1234 even when compiling with @option{-traditional}.
1236 Traditional K&R C promotes all floating point operations to double
1237 precision, regardless of the sizes of the operands. On the
1238 architecture for which you are compiling, single precision may be faster
1239 than double precision. If you must use @option{-traditional}, but want
1240 to use single precision operations when the operands are single
1241 precision, use this option. This option has no effect when compiling
1242 with ISO or GNU C conventions (the default).
1245 @opindex fshort-wchar
1246 Override the underlying type for @samp{wchar_t} to be @samp{short
1247 unsigned int} instead of the default for the target. This option is
1248 useful for building programs to run under WINE@.
1251 @node C++ Dialect Options
1252 @section Options Controlling C++ Dialect
1254 @cindex compiler options, C++
1255 @cindex C++ options, command line
1256 @cindex options, C++
1257 This section describes the command-line options that are only meaningful
1258 for C++ programs; but you can also use most of the GNU compiler options
1259 regardless of what language your program is in. For example, you
1260 might compile a file @code{firstClass.C} like this:
1263 g++ -g -frepo -O -c firstClass.C
1267 In this example, only @option{-frepo} is an option meant
1268 only for C++ programs; you can use the other options with any
1269 language supported by GCC@.
1271 Here is a list of options that are @emph{only} for compiling C++ programs:
1274 @item -fno-access-control
1275 @opindex fno-access-control
1276 Turn off all access checking. This switch is mainly useful for working
1277 around bugs in the access control code.
1281 Check that the pointer returned by @code{operator new} is non-null
1282 before attempting to modify the storage allocated. The current Working
1283 Paper requires that @code{operator new} never return a null pointer, so
1284 this check is normally unnecessary.
1286 An alternative to using this option is to specify that your
1287 @code{operator new} does not throw any exceptions; if you declare it
1288 @samp{throw()}, G++ will check the return value. See also @samp{new
1291 @item -fconserve-space
1292 @opindex fconserve-space
1293 Put uninitialized or runtime-initialized global variables into the
1294 common segment, as C does. This saves space in the executable at the
1295 cost of not diagnosing duplicate definitions. If you compile with this
1296 flag and your program mysteriously crashes after @code{main()} has
1297 completed, you may have an object that is being destroyed twice because
1298 two definitions were merged.
1300 This option is no longer useful on most targets, now that support has
1301 been added for putting variables into BSS without making them common.
1303 @item -fno-const-strings
1304 @opindex fno-const-strings
1305 Give string constants type @code{char *} instead of type @code{const
1306 char *}. By default, G++ uses type @code{const char *} as required by
1307 the standard. Even if you use @option{-fno-const-strings}, you cannot
1308 actually modify the value of a string constant, unless you also use
1309 @option{-fwritable-strings}.
1311 This option might be removed in a future release of G++. For maximum
1312 portability, you should structure your code so that it works with
1313 string constants that have type @code{const char *}.
1315 @item -fdollars-in-identifiers
1316 @opindex fdollars-in-identifiers
1317 Accept @samp{$} in identifiers. You can also explicitly prohibit use of
1318 @samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows
1319 @samp{$} by default on most target systems, but there are a few exceptions.)
1320 Traditional C allowed the character @samp{$} to form part of
1321 identifiers. However, ISO C and C++ forbid @samp{$} in identifiers.
1323 @item -fno-elide-constructors
1324 @opindex fno-elide-constructors
1325 The C++ standard allows an implementation to omit creating a temporary
1326 which is only used to initialize another object of the same type.
1327 Specifying this option disables that optimization, and forces G++ to
1328 call the copy constructor in all cases.
1330 @item -fno-enforce-eh-specs
1331 @opindex fno-enforce-eh-specs
1332 Don't check for violation of exception specifications at runtime. This
1333 option violates the C++ standard, but may be useful for reducing code
1334 size in production builds, much like defining @samp{NDEBUG}. The compiler
1335 will still optimize based on the exception specifications.
1337 @item -fexternal-templates
1338 @opindex fexternal-templates
1340 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1341 template instantiation; template instances are emitted or not according
1342 to the location of the template definition. @xref{Template
1343 Instantiation}, for more information.
1345 This option is deprecated.
1347 @item -falt-external-templates
1348 @opindex falt-external-templates
1349 Similar to @option{-fexternal-templates}, but template instances are
1350 emitted or not according to the place where they are first instantiated.
1351 @xref{Template Instantiation}, for more information.
1353 This option is deprecated.
1356 @itemx -fno-for-scope
1358 @opindex fno-for-scope
1359 If @option{-ffor-scope} is specified, the scope of variables declared in
1360 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1361 as specified by the C++ standard.
1362 If @option{-fno-for-scope} is specified, the scope of variables declared in
1363 a @i{for-init-statement} extends to the end of the enclosing scope,
1364 as was the case in old versions of G++, and other (traditional)
1365 implementations of C++.
1367 The default if neither flag is given to follow the standard,
1368 but to allow and give a warning for old-style code that would
1369 otherwise be invalid, or have different behavior.
1371 @item -fno-gnu-keywords
1372 @opindex fno-gnu-keywords
1373 Do not recognize @code{typeof} as a keyword, so that code can use this
1374 word as an identifier. You can use the keyword @code{__typeof__} instead.
1375 @option{-ansi} implies @option{-fno-gnu-keywords}.
1377 @item -fno-implicit-templates
1378 @opindex fno-implicit-templates
1379 Never emit code for non-inline templates which are instantiated
1380 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1381 @xref{Template Instantiation}, for more information.
1383 @item -fno-implicit-inline-templates
1384 @opindex fno-implicit-inline-templates
1385 Don't emit code for implicit instantiations of inline templates, either.
1386 The default is to handle inlines differently so that compiles with and
1387 without optimization will need the same set of explicit instantiations.
1389 @item -fno-implement-inlines
1390 @opindex fno-implement-inlines
1391 To save space, do not emit out-of-line copies of inline functions
1392 controlled by @samp{#pragma implementation}. This will cause linker
1393 errors if these functions are not inlined everywhere they are called.
1395 @item -fms-extensions
1396 @opindex fms-extensions
1397 Disable pedantic warnings about constructs used in MFC, such as implicit
1398 int and getting a pointer to member function via non-standard syntax.
1400 @item -fno-nonansi-builtins
1401 @opindex fno-nonansi-builtins
1402 Disable built-in declarations of functions that are not mandated by
1403 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1404 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1406 @item -fno-operator-names
1407 @opindex fno-operator-names
1408 Do not treat the operator name keywords @code{and}, @code{bitand},
1409 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1410 synonyms as keywords.
1412 @item -fno-optional-diags
1413 @opindex fno-optional-diags
1414 Disable diagnostics that the standard says a compiler does not need to
1415 issue. Currently, the only such diagnostic issued by G++ is the one for
1416 a name having multiple meanings within a class.
1419 @opindex fpermissive
1420 Downgrade messages about nonconformant code from errors to warnings. By
1421 default, G++ effectively sets @option{-pedantic-errors} without
1422 @option{-pedantic}; this option reverses that. This behavior and this
1423 option are superseded by @option{-pedantic}, which works as it does for GNU C@.
1427 Enable automatic template instantiation at link time. This option also
1428 implies @option{-fno-implicit-templates}. @xref{Template
1429 Instantiation}, for more information.
1433 Disable generation of information about every class with virtual
1434 functions for use by the C++ runtime type identification features
1435 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1436 of the language, you can save some space by using this flag. Note that
1437 exception handling uses the same information, but it will generate it as
1442 Emit statistics about front-end processing at the end of the compilation.
1443 This information is generally only useful to the G++ development team.
1445 @item -ftemplate-depth-@var{n}
1446 @opindex ftemplate-depth
1447 Set the maximum instantiation depth for template classes to @var{n}.
1448 A limit on the template instantiation depth is needed to detect
1449 endless recursions during template class instantiation. ANSI/ISO C++
1450 conforming programs must not rely on a maximum depth greater than 17.
1452 @item -fuse-cxa-atexit
1453 @opindex fuse-cxa-atexit
1454 Register destructors for objects with static storage duration with the
1455 @code{__cxa_atexit} function rather than the @code{atexit} function.
1456 This option is required for fully standards-compliant handling of static
1457 destructors, but will only work if your C library supports
1458 @code{__cxa_atexit}.
1462 Emit special relocations for vtables and virtual function references
1463 so that the linker can identify unused virtual functions and zero out
1464 vtable slots that refer to them. This is most useful with
1465 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1466 also discard the functions themselves.
1468 This optimization requires GNU as and GNU ld. Not all systems support
1469 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1473 Do not use weak symbol support, even if it is provided by the linker.
1474 By default, G++ will use weak symbols if they are available. This
1475 option exists only for testing, and should not be used by end-users;
1476 it will result in inferior code and has no benefits. This option may
1477 be removed in a future release of G++.
1481 Do not search for header files in the standard directories specific to
1482 C++, but do still search the other standard directories. (This option
1483 is used when building the C++ library.)
1486 In addition, these optimization, warning, and code generation options
1487 have meanings only for C++ programs:
1490 @item -fno-default-inline
1491 @opindex fno-default-inline
1492 Do not assume @samp{inline} for functions defined inside a class scope.
1493 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1494 functions will have linkage like inline functions; they just won't be
1497 @item -Wctor-dtor-privacy @r{(C++ only)}
1498 @opindex Wctor-dtor-privacy
1499 Warn when a class seems unusable, because all the constructors or
1500 destructors in a class are private and the class has no friends or
1501 public static member functions.
1503 @item -Wnon-virtual-dtor @r{(C++ only)}
1504 @opindex Wnon-virtual-dtor
1505 Warn when a class declares a non-virtual destructor that should probably
1506 be virtual, because it looks like the class will be used polymorphically.
1508 @item -Wreorder @r{(C++ only)}
1510 @cindex reordering, warning
1511 @cindex warning for reordering of member initializers
1512 Warn when the order of member initializers given in the code does not
1513 match the order in which they must be executed. For instance:
1519 A(): j (0), i (1) @{ @}
1523 Here the compiler will warn that the member initializers for @samp{i}
1524 and @samp{j} will be rearranged to match the declaration order of the
1528 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1531 @item -Weffc++ @r{(C++ only)}
1533 Warn about violations of various style guidelines from Scott Meyers'
1534 @cite{Effective C++} books. If you use this option, you should be aware
1535 that the standard library headers do not obey all of these guidelines;
1536 you can use @samp{grep -v} to filter out those warnings.
1538 @item -Wno-deprecated @r{(C++ only)}
1539 @opindex Wno-deprecated
1540 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1542 @item -Wno-non-template-friend @r{(C++ only)}
1543 @opindex Wno-non-template-friend
1544 Disable warnings when non-templatized friend functions are declared
1545 within a template. With the advent of explicit template specification
1546 support in G++, if the name of the friend is an unqualified-id (i.e.,
1547 @samp{friend foo(int)}), the C++ language specification demands that the
1548 friend declare or define an ordinary, nontemplate function. (Section
1549 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1550 could be interpreted as a particular specialization of a templatized
1551 function. Because this non-conforming behavior is no longer the default
1552 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1553 check existing code for potential trouble spots, and is on by default.
1554 This new compiler behavior can be turned off with
1555 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1556 but disables the helpful warning.
1558 @item -Wold-style-cast @r{(C++ only)}
1559 @opindex Wold-style-cast
1560 Warn if an old-style (C-style) cast is used within a C++ program. The
1561 new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and
1562 @samp{const_cast}) are less vulnerable to unintended effects, and much
1565 @item -Woverloaded-virtual @r{(C++ only)}
1566 @opindex Woverloaded-virtual
1567 @cindex overloaded virtual fn, warning
1568 @cindex warning for overloaded virtual fn
1569 Warn when a function declaration hides virtual functions from a
1570 base class. For example, in:
1577 struct B: public A @{
1582 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1590 will fail to compile.
1592 @item -Wno-pmf-conversions @r{(C++ only)}
1593 @opindex Wno-pmf-conversions
1594 Disable the diagnostic for converting a bound pointer to member function
1597 @item -Wsign-promo @r{(C++ only)}
1598 @opindex Wsign-promo
1599 Warn when overload resolution chooses a promotion from unsigned or
1600 enumeral type to a signed type over a conversion to an unsigned type of
1601 the same size. Previous versions of G++ would try to preserve
1602 unsignedness, but the standard mandates the current behavior.
1604 @item -Wsynth @r{(C++ only)}
1606 @cindex warning for synthesized methods
1607 @cindex synthesized methods, warning
1608 Warn when G++'s synthesis behavior does not match that of cfront. For
1614 A& operator = (int);
1624 In this example, G++ will synthesize a default @samp{A& operator =
1625 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1628 @node Objective-C Dialect Options
1629 @section Options Controlling Objective-C Dialect
1631 @cindex compiler options, Objective-C
1632 @cindex Objective-C options, command line
1633 @cindex options, Objective-C
1634 This section describes the command-line options that are only meaningful
1635 for Objective-C programs; but you can also use most of the GNU compiler
1636 options regardless of what language your program is in. For example,
1637 you might compile a file @code{some_class.m} like this:
1640 gcc -g -fgnu-runtime -O -c some_class.m
1644 In this example, only @option{-fgnu-runtime} is an option meant only for
1645 Objective-C programs; you can use the other options with any language
1648 Here is a list of options that are @emph{only} for compiling Objective-C
1652 @item -fconstant-string-class=@var{class-name}
1653 @opindex fconstant-string-class
1654 Use @var{class-name} as the name of the class to instantiate for each
1655 literal string specified with the syntax @code{@@"@dots{}"}. The default
1656 class name is @code{NXConstantString}.
1659 @opindex fgnu-runtime
1660 Generate object code compatible with the standard GNU Objective-C
1661 runtime. This is the default for most types of systems.
1663 @item -fnext-runtime
1664 @opindex fnext-runtime
1665 Generate output compatible with the NeXT runtime. This is the default
1666 for NeXT-based systems, including Darwin and Mac OS X@.
1670 Dump interface declarations for all classes seen in the source file to a
1671 file named @file{@var{sourcename}.decl}.
1674 @opindex Wno-protocol
1675 Do not warn if methods required by a protocol are not implemented
1676 in the class adopting it.
1680 Warn if a selector has multiple methods of different types defined.
1682 @c not documented because only avail via -Wp
1683 @c @item -print-objc-runtime-info
1687 @node Language Independent Options
1688 @section Options to Control Diagnostic Messages Formatting
1689 @cindex options to control diagnostics formatting
1690 @cindex diagnostic messages
1691 @cindex message formatting
1693 Traditionally, diagnostic messages have been formatted irrespective of
1694 the output device's aspect (e.g.@: its width, @dots{}). The options described
1695 below can be used to control the diagnostic messages formatting
1696 algorithm, e.g.@: how many characters per line, how often source location
1697 information should be reported. Right now, only the C++ front end can
1698 honor these options. However it is expected, in the near future, that
1699 the remaining front ends would be able to digest them correctly.
1702 @item -fmessage-length=@var{n}
1703 @opindex fmessage-length
1704 Try to format error messages so that they fit on lines of about @var{n}
1705 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1706 the front ends supported by GCC@. If @var{n} is zero, then no
1707 line-wrapping will be done; each error message will appear on a single
1710 @opindex fdiagnostics-show-location
1711 @item -fdiagnostics-show-location=once
1712 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1713 reporter to emit @emph{once} source location information; that is, in
1714 case the message is too long to fit on a single physical line and has to
1715 be wrapped, the source location won't be emitted (as prefix) again,
1716 over and over, in subsequent continuation lines. This is the default
1719 @item -fdiagnostics-show-location=every-line
1720 Only meaningful in line-wrapping mode. Instructs the diagnostic
1721 messages reporter to emit the same source location information (as
1722 prefix) for physical lines that result from the process of breaking
1723 a message which is too long to fit on a single line.
1727 @node Warning Options
1728 @section Options to Request or Suppress Warnings
1729 @cindex options to control warnings
1730 @cindex warning messages
1731 @cindex messages, warning
1732 @cindex suppressing warnings
1734 Warnings are diagnostic messages that report constructions which
1735 are not inherently erroneous but which are risky or suggest there
1736 may have been an error.
1738 You can request many specific warnings with options beginning @samp{-W},
1739 for example @option{-Wimplicit} to request warnings on implicit
1740 declarations. Each of these specific warning options also has a
1741 negative form beginning @samp{-Wno-} to turn off warnings;
1742 for example, @option{-Wno-implicit}. This manual lists only one of the
1743 two forms, whichever is not the default.
1745 These options control the amount and kinds of warnings produced by GCC:
1748 @cindex syntax checking
1750 @opindex fsyntax-only
1751 Check the code for syntax errors, but don't do anything beyond that.
1755 Issue all the warnings demanded by strict ISO C and ISO C++;
1756 reject all programs that use forbidden extensions, and some other
1757 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1758 version of the ISO C standard specified by any @option{-std} option used.
1760 Valid ISO C and ISO C++ programs should compile properly with or without
1761 this option (though a rare few will require @option{-ansi} or a
1762 @option{-std} option specifying the required version of ISO C)@. However,
1763 without this option, certain GNU extensions and traditional C and C++
1764 features are supported as well. With this option, they are rejected.
1766 @option{-pedantic} does not cause warning messages for use of the
1767 alternate keywords whose names begin and end with @samp{__}. Pedantic
1768 warnings are also disabled in the expression that follows
1769 @code{__extension__}. However, only system header files should use
1770 these escape routes; application programs should avoid them.
1771 @xref{Alternate Keywords}.
1773 Some users try to use @option{-pedantic} to check programs for strict ISO
1774 C conformance. They soon find that it does not do quite what they want:
1775 it finds some non-ISO practices, but not all---only those for which
1776 ISO C @emph{requires} a diagnostic, and some others for which
1777 diagnostics have been added.
1779 A feature to report any failure to conform to ISO C might be useful in
1780 some instances, but would require considerable additional work and would
1781 be quite different from @option{-pedantic}. We don't have plans to
1782 support such a feature in the near future.
1784 Where the standard specified with @option{-std} represents a GNU
1785 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1786 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1787 extended dialect is based. Warnings from @option{-pedantic} are given
1788 where they are required by the base standard. (It would not make sense
1789 for such warnings to be given only for features not in the specified GNU
1790 C dialect, since by definition the GNU dialects of C include all
1791 features the compiler supports with the given option, and there would be
1792 nothing to warn about.)
1794 @item -pedantic-errors
1795 @opindex pedantic-errors
1796 Like @option{-pedantic}, except that errors are produced rather than
1801 Inhibit all warning messages.
1805 Inhibit warning messages about the use of @samp{#import}.
1807 @item -Wchar-subscripts
1808 @opindex Wchar-subscripts
1809 Warn if an array subscript has type @code{char}. This is a common cause
1810 of error, as programmers often forget that this type is signed on some
1815 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1816 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1820 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1821 the arguments supplied have types appropriate to the format string
1822 specified, and that the conversions specified in the format string make
1823 sense. This includes standard functions, and others specified by format
1824 attributes (@pxref{Function Attributes}), in the @code{printf},
1825 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1826 not in the C standard) families.
1828 The formats are checked against the format features supported by GNU
1829 libc version 2.2. These include all ISO C89 and C99 features, as well
1830 as features from the Single Unix Specification and some BSD and GNU
1831 extensions. Other library implementations may not support all these
1832 features; GCC does not support warning about features that go beyond a
1833 particular library's limitations. However, if @option{-pedantic} is used
1834 with @option{-Wformat}, warnings will be given about format features not
1835 in the selected standard version (but not for @code{strfmon} formats,
1836 since those are not in any version of the C standard). @xref{C Dialect
1837 Options,,Options Controlling C Dialect}.
1839 @option{-Wformat} is included in @option{-Wall}. For more control over some
1840 aspects of format checking, the options @option{-Wno-format-y2k},
1841 @option{-Wno-format-extra-args}, @option{-Wformat-nonliteral},
1842 @option{-Wformat-security} and @option{-Wformat=2} are available, but are
1843 not included in @option{-Wall}.
1845 @item -Wno-format-y2k
1846 @opindex Wno-format-y2k
1847 If @option{-Wformat} is specified, do not warn about @code{strftime}
1848 formats which may yield only a two-digit year.
1850 @item -Wno-format-extra-args
1851 @opindex Wno-format-extra-args
1852 If @option{-Wformat} is specified, do not warn about excess arguments to a
1853 @code{printf} or @code{scanf} format function. The C standard specifies
1854 that such arguments are ignored.
1856 Where the unused arguments lie between used arguments that are
1857 specified with @samp{$} operand number specifications, normally
1858 warnings are still given, since the implementation could not know what
1859 type to pass to @code{va_arg} to skip the unused arguments. However,
1860 in the case of @code{scanf} formats, this option will suppress the
1861 warning if the unused arguments are all pointers, since the Single
1862 Unix Specification says that such unused arguments are allowed.
1864 @item -Wformat-nonliteral
1865 @opindex Wformat-nonliteral
1866 If @option{-Wformat} is specified, also warn if the format string is not a
1867 string literal and so cannot be checked, unless the format function
1868 takes its format arguments as a @code{va_list}.
1870 @item -Wformat-security
1871 @opindex Wformat-security
1872 If @option{-Wformat} is specified, also warn about uses of format
1873 functions that represent possible security problems. At present, this
1874 warns about calls to @code{printf} and @code{scanf} functions where the
1875 format string is not a string literal and there are no format arguments,
1876 as in @code{printf (foo);}. This may be a security hole if the format
1877 string came from untrusted input and contains @samp{%n}. (This is
1878 currently a subset of what @option{-Wformat-nonliteral} warns about, but
1879 in future warnings may be added to @option{-Wformat-security} that are not
1880 included in @option{-Wformat-nonliteral}.)
1884 Enable @option{-Wformat} plus format checks not included in
1885 @option{-Wformat}. Currently equivalent to @samp{-Wformat
1886 -Wformat-nonliteral -Wformat-security}.
1888 @item -Wimplicit-int
1889 @opindex Wimplicit-int
1890 Warn when a declaration does not specify a type.
1892 @item -Wimplicit-function-declaration
1893 @itemx -Werror-implicit-function-declaration
1894 @opindex Wimplicit-function-declaration
1895 @opindex Werror-implicit-function-declaration
1896 Give a warning (or error) whenever a function is used before being
1901 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
1905 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
1906 function with external linkage, returning int, taking either zero
1907 arguments, two, or three arguments of appropriate types.
1909 @item -Wmissing-braces
1910 @opindex Wmissing-braces
1911 Warn if an aggregate or union initializer is not fully bracketed. In
1912 the following example, the initializer for @samp{a} is not fully
1913 bracketed, but that for @samp{b} is fully bracketed.
1916 int a[2][2] = @{ 0, 1, 2, 3 @};
1917 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
1921 @opindex Wparentheses
1922 Warn if parentheses are omitted in certain contexts, such
1923 as when there is an assignment in a context where a truth value
1924 is expected, or when operators are nested whose precedence people
1925 often get confused about.
1927 Also warn about constructions where there may be confusion to which
1928 @code{if} statement an @code{else} branch belongs. Here is an example of
1943 In C, every @code{else} branch belongs to the innermost possible @code{if}
1944 statement, which in this example is @code{if (b)}. This is often not
1945 what the programmer expected, as illustrated in the above example by
1946 indentation the programmer chose. When there is the potential for this
1947 confusion, GCC will issue a warning when this flag is specified.
1948 To eliminate the warning, add explicit braces around the innermost
1949 @code{if} statement so there is no way the @code{else} could belong to
1950 the enclosing @code{if}. The resulting code would look like this:
1966 @item -Wsequence-point
1967 @opindex Wsequence-point
1968 Warn about code that may have undefined semantics because of violations
1969 of sequence point rules in the C standard.
1971 The C standard defines the order in which expressions in a C program are
1972 evaluated in terms of @dfn{sequence points}, which represent a partial
1973 ordering between the execution of parts of the program: those executed
1974 before the sequence point, and those executed after it. These occur
1975 after the evaluation of a full expression (one which is not part of a
1976 larger expression), after the evaluation of the first operand of a
1977 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
1978 function is called (but after the evaluation of its arguments and the
1979 expression denoting the called function), and in certain other places.
1980 Other than as expressed by the sequence point rules, the order of
1981 evaluation of subexpressions of an expression is not specified. All
1982 these rules describe only a partial order rather than a total order,
1983 since, for example, if two functions are called within one expression
1984 with no sequence point between them, the order in which the functions
1985 are called is not specified. However, the standards committee have
1986 ruled that function calls do not overlap.
1988 It is not specified when between sequence points modifications to the
1989 values of objects take effect. Programs whose behavior depends on this
1990 have undefined behavior; the C standard specifies that ``Between the
1991 previous and next sequence point an object shall have its stored value
1992 modified at most once by the evaluation of an expression. Furthermore,
1993 the prior value shall be read only to determine the value to be
1994 stored.''. If a program breaks these rules, the results on any
1995 particular implementation are entirely unpredictable.
1997 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
1998 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
1999 diagnosed by this option, and it may give an occasional false positive
2000 result, but in general it has been found fairly effective at detecting
2001 this sort of problem in programs.
2003 The present implementation of this option only works for C programs. A
2004 future implementation may also work for C++ programs.
2006 The C standard is worded confusingly, therefore there is some debate
2007 over the precise meaning of the sequence point rules in subtle cases.
2008 Links to discussions of the problem, including proposed formal
2009 definitions, may be found on our readings page, at
2010 @w{@uref{http://gcc.gnu.org/readings.html}}.
2013 @opindex Wreturn-type
2014 Warn whenever a function is defined with a return-type that defaults to
2015 @code{int}. Also warn about any @code{return} statement with no
2016 return-value in a function whose return-type is not @code{void}.
2018 For C++, a function without return type always produces a diagnostic
2019 message, even when @option{-Wno-return-type} is specified. The only
2020 exceptions are @samp{main} and functions defined in system headers.
2024 Warn whenever a @code{switch} statement has an index of enumeral type
2025 and lacks a @code{case} for one or more of the named codes of that
2026 enumeration. (The presence of a @code{default} label prevents this
2027 warning.) @code{case} labels outside the enumeration range also
2028 provoke warnings when this option is used.
2032 Warn if any trigraphs are encountered that might change the meaning of
2033 the program (trigraphs within comments are not warned about).
2035 @item -Wunused-function
2036 @opindex Wunused-function
2037 Warn whenever a static function is declared but not defined or a
2038 non\-inline static function is unused.
2040 @item -Wunused-label
2041 @opindex Wunused-label
2042 Warn whenever a label is declared but not used.
2044 To suppress this warning use the @samp{unused} attribute
2045 (@pxref{Variable Attributes}).
2047 @item -Wunused-parameter
2048 @opindex Wunused-parameter
2049 Warn whenever a function parameter is unused aside from its declaration.
2051 To suppress this warning use the @samp{unused} attribute
2052 (@pxref{Variable Attributes}).
2054 @item -Wunused-variable
2055 @opindex Wunused-variable
2056 Warn whenever a local variable or non-constant static variable is unused
2057 aside from its declaration
2059 To suppress this warning use the @samp{unused} attribute
2060 (@pxref{Variable Attributes}).
2062 @item -Wunused-value
2063 @opindex Wunused-value
2064 Warn whenever a statement computes a result that is explicitly not used.
2066 To suppress this warning cast the expression to @samp{void}.
2070 All all the above @option{-Wunused} options combined.
2072 In order to get a warning about an unused function parameter, you must
2073 either specify @samp{-W -Wunused} or separately specify
2074 @option{-Wunused-parameter}.
2076 @item -Wuninitialized
2077 @opindex Wuninitialized
2078 Warn if an automatic variable is used without first being initialized or
2079 if a variable may be clobbered by a @code{setjmp} call.
2081 These warnings are possible only in optimizing compilation,
2082 because they require data flow information that is computed only
2083 when optimizing. If you don't specify @option{-O}, you simply won't
2086 These warnings occur only for variables that are candidates for
2087 register allocation. Therefore, they do not occur for a variable that
2088 is declared @code{volatile}, or whose address is taken, or whose size
2089 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2090 structures, unions or arrays, even when they are in registers.
2092 Note that there may be no warning about a variable that is used only
2093 to compute a value that itself is never used, because such
2094 computations may be deleted by data flow analysis before the warnings
2097 These warnings are made optional because GCC is not smart
2098 enough to see all the reasons why the code might be correct
2099 despite appearing to have an error. Here is one example of how
2120 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2121 always initialized, but GCC doesn't know this. Here is
2122 another common case:
2127 if (change_y) save_y = y, y = new_y;
2129 if (change_y) y = save_y;
2134 This has no bug because @code{save_y} is used only if it is set.
2136 @cindex @code{longjmp} warnings
2137 This option also warns when a non-volatile automatic variable might be
2138 changed by a call to @code{longjmp}. These warnings as well are possible
2139 only in optimizing compilation.
2141 The compiler sees only the calls to @code{setjmp}. It cannot know
2142 where @code{longjmp} will be called; in fact, a signal handler could
2143 call it at any point in the code. As a result, you may get a warning
2144 even when there is in fact no problem because @code{longjmp} cannot
2145 in fact be called at the place which would cause a problem.
2147 Some spurious warnings can be avoided if you declare all the functions
2148 you use that never return as @code{noreturn}. @xref{Function
2151 @item -Wreorder @r{(C++ only)}
2153 @cindex reordering, warning
2154 @cindex warning for reordering of member initializers
2155 Warn when the order of member initializers given in the code does not
2156 match the order in which they must be executed. For instance:
2158 @item -Wunknown-pragmas
2159 @opindex Wunknown-pragmas
2160 @cindex warning for unknown pragmas
2161 @cindex unknown pragmas, warning
2162 @cindex pragmas, warning of unknown
2163 Warn when a #pragma directive is encountered which is not understood by
2164 GCC@. If this command line option is used, warnings will even be issued
2165 for unknown pragmas in system header files. This is not the case if
2166 the warnings were only enabled by the @option{-Wall} command line option.
2170 All of the above @samp{-W} options combined. This enables all the
2171 warnings about constructions that some users consider questionable, and
2172 that are easy to avoid (or modify to prevent the warning), even in
2173 conjunction with macros.
2176 @opindex Wno-div-by-zero
2177 @opindex Wdiv-by-zero
2178 Warn about compile-time integer division by zero. This is default. To
2179 inhibit the warning messages, use @option{-Wno-div-by-zero}. Floating
2180 point division by zero is not warned about, as it can be a legitimate
2181 way of obtaining infinities and NaNs.
2184 @opindex Wno-multichar
2186 Warn if a multicharacter constant (@samp{'FOOF'}) is used. This is
2187 default. To inhibit the warning messages, use @option{-Wno-multichar}.
2188 Usually they indicate a typo in the user's code, as they have
2189 implementation-defined values, and should not be used in portable code.
2191 @item -Wsystem-headers
2192 @opindex Wsystem-headers
2193 @cindex warnings from system headers
2194 @cindex system headers, warnings from
2195 Print warning messages for constructs found in system header files.
2196 Warnings from system headers are normally suppressed, on the assumption
2197 that they usually do not indicate real problems and would only make the
2198 compiler output harder to read. Using this command line option tells
2199 GCC to emit warnings from system headers as if they occurred in user
2200 code. However, note that using @option{-Wall} in conjunction with this
2201 option will @emph{not} warn about unknown pragmas in system
2202 headers---for that, @option{-Wunknown-pragmas} must also be used.
2205 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2206 Some of them warn about constructions that users generally do not
2207 consider questionable, but which occasionally you might wish to check
2208 for; others warn about constructions that are necessary or hard to avoid
2209 in some cases, and there is no simple way to modify the code to suppress
2215 Print extra warning messages for these events:
2219 A function can return either with or without a value. (Falling
2220 off the end of the function body is considered returning without
2221 a value.) For example, this function would evoke such a
2235 An expression-statement or the left-hand side of a comma expression
2236 contains no side effects.
2237 To suppress the warning, cast the unused expression to void.
2238 For example, an expression such as @samp{x[i,j]} will cause a warning,
2239 but @samp{x[(void)i,j]} will not.
2242 An unsigned value is compared against zero with @samp{<} or @samp{<=}.
2245 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2246 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2247 that of ordinary mathematical notation.
2250 Storage-class specifiers like @code{static} are not the first things in
2251 a declaration. According to the C Standard, this usage is obsolescent.
2254 The return type of a function has a type qualifier such as @code{const}.
2255 Such a type qualifier has no effect, since the value returned by a
2256 function is not an lvalue. (But don't warn about the GNU extension of
2257 @code{volatile void} return types. That extension will be warned about
2258 if @option{-pedantic} is specified.)
2261 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2265 A comparison between signed and unsigned values could produce an
2266 incorrect result when the signed value is converted to unsigned.
2267 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2270 An aggregate has a partly bracketed initializer.
2271 For example, the following code would evoke such a warning,
2272 because braces are missing around the initializer for @code{x.h}:
2275 struct s @{ int f, g; @};
2276 struct t @{ struct s h; int i; @};
2277 struct t x = @{ 1, 2, 3 @};
2281 An aggregate has an initializer which does not initialize all members.
2282 For example, the following code would cause such a warning, because
2283 @code{x.h} would be implicitly initialized to zero:
2286 struct s @{ int f, g, h; @};
2287 struct s x = @{ 3, 4 @};
2292 @opindex Wfloat-equal
2293 Warn if floating point values are used in equality comparisons.
2295 The idea behind this is that sometimes it is convenient (for the
2296 programmer) to consider floating-point values as approximations to
2297 infinitely precise real numbers. If you are doing this, then you need
2298 to compute (by analysing the code, or in some other way) the maximum or
2299 likely maximum error that the computation introduces, and allow for it
2300 when performing comparisons (and when producing output, but that's a
2301 different problem). In particular, instead of testing for equality, you
2302 would check to see whether the two values have ranges that overlap; and
2303 this is done with the relational operators, so equality comparisons are
2306 @item -Wtraditional @r{(C only)}
2307 @opindex Wtraditional
2308 Warn about certain constructs that behave differently in traditional and
2309 ISO C@. Also warn about ISO C constructs that have no traditional C
2310 equivalent, and/or problematic constructs which should be avoided.
2314 Macro parameters that appear within string literals in the macro body.
2315 In traditional C macro replacement takes place within string literals,
2316 but does not in ISO C@.
2319 In traditional C, some preprocessor directives did not exist.
2320 Traditional preprocessors would only consider a line to be a directive
2321 if the @samp{#} appeared in column 1 on the line. Therefore
2322 @option{-Wtraditional} warns about directives that traditional C
2323 understands but would ignore because the @samp{#} does not appear as the
2324 first character on the line. It also suggests you hide directives like
2325 @samp{#pragma} not understood by traditional C by indenting them. Some
2326 traditional implementations would not recognize @samp{#elif}, so it
2327 suggests avoiding it altogether.
2330 A function-like macro that appears without arguments.
2333 The unary plus operator.
2336 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2337 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2338 constants.) Note, these suffixes appear in macros defined in the system
2339 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2340 Use of these macros in user code might normally lead to spurious
2341 warnings, however gcc's integrated preprocessor has enough context to
2342 avoid warning in these cases.
2345 A function declared external in one block and then used after the end of
2349 A @code{switch} statement has an operand of type @code{long}.
2352 A non-@code{static} function declaration follows a @code{static} one.
2353 This construct is not accepted by some traditional C compilers.
2356 The ISO type of an integer constant has a different width or
2357 signedness from its traditional type. This warning is only issued if
2358 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2359 typically represent bit patterns, are not warned about.
2362 Usage of ISO string concatenation is detected.
2365 Initialization of automatic aggregates.
2368 Identifier conflicts with labels. Traditional C lacks a separate
2369 namespace for labels.
2372 Initialization of unions. If the initializer is zero, the warning is
2373 omitted. This is done under the assumption that the zero initializer in
2374 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2375 initializer warnings and relies on default initialization to zero in the
2379 Conversions by prototypes between fixed/floating point values and vice
2380 versa. The absence of these prototypes when compiling with traditional
2381 C would cause serious problems. This is a subset of the possible
2382 conversion warnings, for the full set use @option{-Wconversion}.
2387 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2391 Warn whenever a local variable shadows another local variable, parameter or
2392 global variable or whenever a built-in function is shadowed.
2394 @item -Wlarger-than-@var{len}
2395 @opindex Wlarger-than
2396 Warn whenever an object of larger than @var{len} bytes is defined.
2398 @item -Wpointer-arith
2399 @opindex Wpointer-arith
2400 Warn about anything that depends on the ``size of'' a function type or
2401 of @code{void}. GNU C assigns these types a size of 1, for
2402 convenience in calculations with @code{void *} pointers and pointers
2405 @item -Wbad-function-cast @r{(C only)}
2406 @opindex Wbad-function-cast
2407 Warn whenever a function call is cast to a non-matching type.
2408 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2412 Warn whenever a pointer is cast so as to remove a type qualifier from
2413 the target type. For example, warn if a @code{const char *} is cast
2414 to an ordinary @code{char *}.
2417 @opindex Wcast-align
2418 Warn whenever a pointer is cast such that the required alignment of the
2419 target is increased. For example, warn if a @code{char *} is cast to
2420 an @code{int *} on machines where integers can only be accessed at
2421 two- or four-byte boundaries.
2423 @item -Wwrite-strings
2424 @opindex Wwrite-strings
2425 When compiling C, give string constants the type @code{const
2426 char[@var{length}]} so that
2427 copying the address of one into a non-@code{const} @code{char *}
2428 pointer will get a warning; when compiling C++, warn about the
2429 deprecated conversion from string constants to @code{char *}.
2430 These warnings will help you find at
2431 compile time code that can try to write into a string constant, but
2432 only if you have been very careful about using @code{const} in
2433 declarations and prototypes. Otherwise, it will just be a nuisance;
2434 this is why we did not make @option{-Wall} request these warnings.
2437 @opindex Wconversion
2438 Warn if a prototype causes a type conversion that is different from what
2439 would happen to the same argument in the absence of a prototype. This
2440 includes conversions of fixed point to floating and vice versa, and
2441 conversions changing the width or signedness of a fixed point argument
2442 except when the same as the default promotion.
2444 Also, warn if a negative integer constant expression is implicitly
2445 converted to an unsigned type. For example, warn about the assignment
2446 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2447 casts like @code{(unsigned) -1}.
2449 @item -Wsign-compare
2450 @opindex Wsign-compare
2451 @cindex warning for comparison of signed and unsigned values
2452 @cindex comparison of signed and unsigned values, warning
2453 @cindex signed and unsigned values, comparison warning
2454 Warn when a comparison between signed and unsigned values could produce
2455 an incorrect result when the signed value is converted to unsigned.
2456 This warning is also enabled by @option{-W}; to get the other warnings
2457 of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}.
2459 @item -Waggregate-return
2460 @opindex Waggregate-return
2461 Warn if any functions that return structures or unions are defined or
2462 called. (In languages where you can return an array, this also elicits
2465 @item -Wstrict-prototypes @r{(C only)}
2466 @opindex Wstrict-prototypes
2467 Warn if a function is declared or defined without specifying the
2468 argument types. (An old-style function definition is permitted without
2469 a warning if preceded by a declaration which specifies the argument
2472 @item -Wmissing-prototypes @r{(C only)}
2473 @opindex Wmissing-prototypes
2474 Warn if a global function is defined without a previous prototype
2475 declaration. This warning is issued even if the definition itself
2476 provides a prototype. The aim is to detect global functions that fail
2477 to be declared in header files.
2479 @item -Wmissing-declarations
2480 @opindex Wmissing-declarations
2481 Warn if a global function is defined without a previous declaration.
2482 Do so even if the definition itself provides a prototype.
2483 Use this option to detect global functions that are not declared in
2486 @item -Wmissing-noreturn
2487 @opindex Wmissing-noreturn
2488 Warn about functions which might be candidates for attribute @code{noreturn}.
2489 Note these are only possible candidates, not absolute ones. Care should
2490 be taken to manually verify functions actually do not ever return before
2491 adding the @code{noreturn} attribute, otherwise subtle code generation
2492 bugs could be introduced. You will not get a warning for @code{main} in
2493 hosted C environments.
2495 @item -Wmissing-format-attribute
2496 @opindex Wmissing-format-attribute
2498 If @option{-Wformat} is enabled, also warn about functions which might be
2499 candidates for @code{format} attributes. Note these are only possible
2500 candidates, not absolute ones. GCC will guess that @code{format}
2501 attributes might be appropriate for any function that calls a function
2502 like @code{vprintf} or @code{vscanf}, but this might not always be the
2503 case, and some functions for which @code{format} attributes are
2504 appropriate may not be detected. This option has no effect unless
2505 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2509 Warn if a structure is given the packed attribute, but the packed
2510 attribute has no effect on the layout or size of the structure.
2511 Such structures may be mis-aligned for little benefit. For
2512 instance, in this code, the variable @code{f.x} in @code{struct bar}
2513 will be misaligned even though @code{struct bar} does not itself
2514 have the packed attribute:
2521 @} __attribute__((packed));
2531 Warn if padding is included in a structure, either to align an element
2532 of the structure or to align the whole structure. Sometimes when this
2533 happens it is possible to rearrange the fields of the structure to
2534 reduce the padding and so make the structure smaller.
2536 @item -Wredundant-decls
2537 @opindex Wredundant-decls
2538 Warn if anything is declared more than once in the same scope, even in
2539 cases where multiple declaration is valid and changes nothing.
2541 @item -Wnested-externs @r{(C only)}
2542 @opindex Wnested-externs
2543 Warn if an @code{extern} declaration is encountered within a function.
2545 @item -Wunreachable-code
2546 @opindex Wunreachable-code
2547 Warn if the compiler detects that code will never be executed.
2549 This option is intended to warn when the compiler detects that at
2550 least a whole line of source code will never be executed, because
2551 some condition is never satisfied or because it is after a
2552 procedure that never returns.
2554 It is possible for this option to produce a warning even though there
2555 are circumstances under which part of the affected line can be executed,
2556 so care should be taken when removing apparently-unreachable code.
2558 For instance, when a function is inlined, a warning may mean that the
2559 line is unreachable in only one inlined copy of the function.
2561 This option is not made part of @option{-Wall} because in a debugging
2562 version of a program there is often substantial code which checks
2563 correct functioning of the program and is, hopefully, unreachable
2564 because the program does work. Another common use of unreachable
2565 code is to provide behavior which is selectable at compile-time.
2569 Warn if a function can not be inlined and it was declared as inline.
2573 @opindex Wno-long-long
2574 Warn if @samp{long long} type is used. This is default. To inhibit
2575 the warning messages, use @option{-Wno-long-long}. Flags
2576 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2577 only when @option{-pedantic} flag is used.
2579 @item -Wdisabled-optimization
2580 @opindex Wdisabled-optimization
2581 Warn if a requested optimization pass is disabled. This warning does
2582 not generally indicate that there is anything wrong with your code; it
2583 merely indicates that GCC's optimizers were unable to handle the code
2584 effectively. Often, the problem is that your code is too big or too
2585 complex; GCC will refuse to optimize programs when the optimization
2586 itself is likely to take inordinate amounts of time.
2590 Make all warnings into errors.
2593 @node Debugging Options
2594 @section Options for Debugging Your Program or GCC
2595 @cindex options, debugging
2596 @cindex debugging information options
2598 GCC has various special options that are used for debugging
2599 either your program or GCC:
2604 Produce debugging information in the operating system's native format
2605 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2608 On most systems that use stabs format, @option{-g} enables use of extra
2609 debugging information that only GDB can use; this extra information
2610 makes debugging work better in GDB but will probably make other debuggers
2612 refuse to read the program. If you want to control for certain whether
2613 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2614 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2615 or @option{-gvms} (see below).
2617 Unlike most other C compilers, GCC allows you to use @option{-g} with
2618 @option{-O}. The shortcuts taken by optimized code may occasionally
2619 produce surprising results: some variables you declared may not exist
2620 at all; flow of control may briefly move where you did not expect it;
2621 some statements may not be executed because they compute constant
2622 results or their values were already at hand; some statements may
2623 execute in different places because they were moved out of loops.
2625 Nevertheless it proves possible to debug optimized output. This makes
2626 it reasonable to use the optimizer for programs that might have bugs.
2628 The following options are useful when GCC is generated with the
2629 capability for more than one debugging format.
2633 Produce debugging information for use by GDB@. This means to use the
2634 most expressive format available (DWARF 2, stabs, or the native format
2635 if neither of those are supported), including GDB extensions if at all
2640 Produce debugging information in stabs format (if that is supported),
2641 without GDB extensions. This is the format used by DBX on most BSD
2642 systems. On MIPS, Alpha and System V Release 4 systems this option
2643 produces stabs debugging output which is not understood by DBX or SDB@.
2644 On System V Release 4 systems this option requires the GNU assembler.
2648 Produce debugging information in stabs format (if that is supported),
2649 using GNU extensions understood only by the GNU debugger (GDB)@. The
2650 use of these extensions is likely to make other debuggers crash or
2651 refuse to read the program.
2655 Produce debugging information in COFF format (if that is supported).
2656 This is the format used by SDB on most System V systems prior to
2661 Produce debugging information in XCOFF format (if that is supported).
2662 This is the format used by the DBX debugger on IBM RS/6000 systems.
2666 Produce debugging information in XCOFF format (if that is supported),
2667 using GNU extensions understood only by the GNU debugger (GDB)@. The
2668 use of these extensions is likely to make other debuggers crash or
2669 refuse to read the program, and may cause assemblers other than the GNU
2670 assembler (GAS) to fail with an error.
2674 Produce debugging information in DWARF version 1 format (if that is
2675 supported). This is the format used by SDB on most System V Release 4
2680 Produce debugging information in DWARF version 1 format (if that is
2681 supported), using GNU extensions understood only by the GNU debugger
2682 (GDB)@. The use of these extensions is likely to make other debuggers
2683 crash or refuse to read the program.
2687 Produce debugging information in DWARF version 2 format (if that is
2688 supported). This is the format used by DBX on IRIX 6.
2692 Produce debugging information in VMS debug format (if that is
2693 supported). This is the format used by DEBUG on VMS systems.
2696 @itemx -ggdb@var{level}
2697 @itemx -gstabs@var{level}
2698 @itemx -gcoff@var{level}
2699 @itemx -gxcoff@var{level}
2700 @itemx -gdwarf@var{level}
2701 @itemx -gdwarf-2@var{level}
2702 @itemx -gvms@var{level}
2703 Request debugging information and also use @var{level} to specify how
2704 much information. The default level is 2.
2706 Level 1 produces minimal information, enough for making backtraces in
2707 parts of the program that you don't plan to debug. This includes
2708 descriptions of functions and external variables, but no information
2709 about local variables and no line numbers.
2711 Level 3 includes extra information, such as all the macro definitions
2712 present in the program. Some debuggers support macro expansion when
2713 you use @option{-g3}.
2718 Generate extra code to write profile information suitable for the
2719 analysis program @code{prof}. You must use this option when compiling
2720 the source files you want data about, and you must also use it when
2723 @cindex @code{gprof}
2726 Generate extra code to write profile information suitable for the
2727 analysis program @code{gprof}. You must use this option when compiling
2728 the source files you want data about, and you must also use it when
2734 Generate extra code to write profile information for basic blocks, which will
2735 record the number of times each basic block is executed, the basic block start
2736 address, and the function name containing the basic block. If @option{-g} is
2737 used, the line number and filename of the start of the basic block will also be
2738 recorded. If not overridden by the machine description, the default action is
2739 to append to the text file @file{bb.out}.
2741 This data could be analyzed by a program like @code{tcov}. Note,
2742 however, that the format of the data is not what @code{tcov} expects.
2743 Eventually GNU @code{gprof} should be extended to process this data.
2747 Makes the compiler print out each function name as it is compiled, and
2748 print some statistics about each pass when it finishes.
2751 @opindex ftime-report
2752 Makes the compiler print some statistics about the time consumed by each
2753 pass when it finishes.
2756 @opindex fmem-report
2757 Makes the compiler print some statistics about permanent memory
2758 allocation when it finishes.
2760 @item -fprofile-arcs
2761 @opindex fprofile-arcs
2762 Instrument @dfn{arcs} during compilation to generate coverage data
2763 or for profile-directed block ordering. During execution the program
2764 records how many times each branch is executed and how many times it is
2765 taken. When the compiled program exits it saves this data to a file
2766 called @file{@var{sourcename}.da} for each source file.
2768 For profile-directed block ordering, compile the program with
2769 @option{-fprofile-arcs} plus optimization and code generation options,
2770 generate the arc profile information by running the program on a
2771 selected workload, and then compile the program again with the same
2772 optimization and code generation options plus
2773 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
2774 Control Optimization}).
2776 The other use of @option{-fprofile-arcs} is for use with @code{gcov},
2777 when it is used with the @option{-ftest-coverage} option. GCC
2778 supports two methods of determining code coverage: the options that
2779 support @code{gcov}, and options @option{-a} and @option{-ax}, which
2780 write information to text files. The options that support @code{gcov}
2781 do not need to instrument every arc in the program, so a program compiled
2782 with them runs faster than a program compiled with @option{-a}, which
2783 adds instrumentation code to every basic block in the program. The
2784 tradeoff: since @code{gcov} does not have execution counts for all
2785 branches, it must start with the execution counts for the instrumented
2786 branches, and then iterate over the program flow graph until the entire
2787 graph has been solved. Hence, @code{gcov} runs a little more slowly than
2788 a program which uses information from @option{-a} and @option{-ax}.
2790 With @option{-fprofile-arcs}, for each function of your program GCC
2791 creates a program flow graph, then finds a spanning tree for the graph.
2792 Only arcs that are not on the spanning tree have to be instrumented: the
2793 compiler adds code to count the number of times that these arcs are
2794 executed. When an arc is the only exit or only entrance to a block, the
2795 instrumentation code can be added to the block; otherwise, a new basic
2796 block must be created to hold the instrumentation code.
2798 This option makes it possible to estimate branch probabilities and to
2799 calculate basic block execution counts. In general, basic block
2800 execution counts as provided by @option{-a} do not give enough
2801 information to estimate all branch probabilities.
2804 @item -ftest-coverage
2805 @opindex ftest-coverage
2806 Create data files for the @code{gcov} code-coverage utility
2807 (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}).
2808 The data file names begin with the name of your source file:
2811 @item @var{sourcename}.bb
2812 A mapping from basic blocks to line numbers, which @code{gcov} uses to
2813 associate basic block execution counts with line numbers.
2815 @item @var{sourcename}.bbg
2816 A list of all arcs in the program flow graph. This allows @code{gcov}
2817 to reconstruct the program flow graph, so that it can compute all basic
2818 block and arc execution counts from the information in the
2819 @code{@var{sourcename}.da} file.
2822 Use @option{-ftest-coverage} with @option{-fprofile-arcs}; the latter
2823 option adds instrumentation to the program, which then writes
2824 execution counts to another data file:
2827 @item @var{sourcename}.da
2828 Runtime arc execution counts, used in conjunction with the arc
2829 information in the file @code{@var{sourcename}.bbg}.
2832 Coverage data will map better to the source files if
2833 @option{-ftest-coverage} is used without optimization.
2835 @item -d@var{letters}
2837 Says to make debugging dumps during compilation at times specified by
2838 @var{letters}. This is used for debugging the compiler. The file names
2839 for most of the dumps are made by appending a pass number and a word to
2840 the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}).
2841 Here are the possible letters for use in @var{letters}, and their meanings:
2846 Annotate the assembler output with miscellaneous debugging information.
2849 Dump after computing branch probabilities, to @file{@var{file}.14.bp}.
2852 Dump after block reordering, to @file{@var{file}.28.bbro}.
2855 Dump after instruction combination, to the file @file{@var{file}.16.combine}.
2858 Dump after the first if conversion, to the file @file{@var{file}.17.ce}.
2861 Dump after delayed branch scheduling, to @file{@var{file}.31.dbr}.
2864 Dump all macro definitions, at the end of preprocessing, in addition to
2868 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
2869 @file{@var{file}.07.ussa}.
2872 Dump after the second if conversion, to @file{@var{file}.26.ce2}.
2875 Dump after life analysis, to @file{@var{file}.15.life}.
2878 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.09.addressof}.
2881 Dump after global register allocation, to @file{@var{file}.21.greg}.
2884 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
2887 Dump after post-reload optimizations, to @file{@var{file}.22.postreload}.
2890 Dump after GCSE, to @file{@var{file}.10.gcse}.
2893 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
2896 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
2899 Dump after conversion from registers to stack, to @file{@var{file}.32.stack}.
2902 Dump after local register allocation, to @file{@var{file}.20.lreg}.
2905 Dump after loop optimization, to @file{@var{file}.11.loop}.
2908 Dump after performing the machine dependent reorganisation pass, to
2909 @file{@var{file}.30.mach}.
2912 Dump after register renumbering, to @file{@var{file}.25.rnreg}.
2915 Dump after the register move pass, to @file{@var{file}.18.regmove}.
2918 Dump after RTL generation, to @file{@var{file}.00.rtl}.
2921 Dump after the second scheduling pass, to @file{@var{file}.27.sched2}.
2924 Dump after CSE (including the jump optimization that sometimes follows
2925 CSE), to @file{@var{file}.08.cse}.
2928 Dump after the first scheduling pass, to @file{@var{file}.19.sched}.
2931 Dump after the second CSE pass (including the jump optimization that
2932 sometimes follows CSE), to @file{@var{file}.12.cse2}.
2935 Dump after the second flow pass, to @file{@var{file}.23.flow2}.
2938 Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}.
2941 Dump after the peephole pass, to @file{@var{file}.24.peephole2}.
2944 Produce all the dumps listed above.
2947 Print statistics on memory usage, at the end of the run, to
2951 Annotate the assembler output with a comment indicating which
2952 pattern and alternative was used. The length of each instruction is
2956 Dump the RTL in the assembler output as a comment before each instruction.
2957 Also turns on @option{-dp} annotation.
2960 For each of the other indicated dump files (except for
2961 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
2962 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
2965 Just generate RTL for a function instead of compiling it. Usually used
2969 Dump debugging information during parsing, to standard error.
2972 @item -fdump-unnumbered
2973 @opindex fdump-unnumbered
2974 When doing debugging dumps (see @option{-d} option above), suppress instruction
2975 numbers and line number note output. This makes it more feasible to
2976 use diff on debugging dumps for compiler invocations with different
2977 options, in particular with and without @option{-g}.
2979 @item -fdump-class-hierarchy @r{(C++ only)}
2980 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
2981 @opindex fdump-class-hierarchy
2982 Dump a representation of each class's hierarchy and virtual function
2983 table layout to a file. The file name is made by appending @file{.class}
2984 to the source file name. If the @samp{-@var{options}} form is used,
2985 @var{options} controls the details of the dump as described for the
2986 @option{-fdump-tree} options.
2988 @item -fdump-tree-@var{switch} @r{(C++ only)}
2989 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
2991 Control the dumping at various stages of processing the intermediate
2992 language tree to a file. The file name is generated by appending a switch
2993 specific suffix to the source file name. If the @samp{-@var{options}}
2994 form is used, @var{options} is a list of @samp{-} separated options that
2995 control the details of the dump. Not all options are applicable to all
2996 dumps, those which are not meaningful will be ignored. The following
2997 options are available
3001 Print the address of each node. Usually this is not meaningful as it
3002 changes according to the environment and source file. Its primary use
3003 is for tying up a dump file with a debug environment.
3005 Inhibit dumping of members of a scope or body of a function merely
3006 because that scope has been reached. Only dump such items when they
3007 are directly reachable by some other path.
3009 Turn on all options.
3012 The following tree dumps are possible:
3015 Dump before any tree based optimization, to @file{@var{file}.original}.
3017 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3019 Dump after function inlining, to @file{@var{file}.inlined}.
3022 @item -fpretend-float
3023 @opindex fpretend-float
3024 When running a cross-compiler, pretend that the target machine uses the
3025 same floating point format as the host machine. This causes incorrect
3026 output of the actual floating constants, but the actual instruction
3027 sequence will probably be the same as GCC would make when running on
3032 Store the usual ``temporary'' intermediate files permanently; place them
3033 in the current directory and name them based on the source file. Thus,
3034 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3035 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3036 preprocessed @file{foo.i} output file even though the compiler now
3037 normally uses an integrated preprocessor.
3041 Report the CPU time taken by each subprocess in the compilation
3042 sequence. For C source files, this is the compiler proper and assembler
3043 (plus the linker if linking is done). The output looks like this:
3050 The first number on each line is the ``user time,'' that is time spent
3051 executing the program itself. The second number is ``system time,''
3052 time spent executing operating system routines on behalf of the program.
3053 Both numbers are in seconds.
3055 @item -print-file-name=@var{library}
3056 @opindex print-file-name
3057 Print the full absolute name of the library file @var{library} that
3058 would be used when linking---and don't do anything else. With this
3059 option, GCC does not compile or link anything; it just prints the
3062 @item -print-multi-directory
3063 @opindex print-multi-directory
3064 Print the directory name corresponding to the multilib selected by any
3065 other switches present in the command line. This directory is supposed
3066 to exist in @env{GCC_EXEC_PREFIX}.
3068 @item -print-multi-lib
3069 @opindex print-multi-lib
3070 Print the mapping from multilib directory names to compiler switches
3071 that enable them. The directory name is separated from the switches by
3072 @samp{;}, and each switch starts with an @samp{@@} instead of the
3073 @samp{-}, without spaces between multiple switches. This is supposed to
3074 ease shell-processing.
3076 @item -print-prog-name=@var{program}
3077 @opindex print-prog-name
3078 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3080 @item -print-libgcc-file-name
3081 @opindex print-libgcc-file-name
3082 Same as @option{-print-file-name=libgcc.a}.
3084 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3085 but you do want to link with @file{libgcc.a}. You can do
3088 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3091 @item -print-search-dirs
3092 @opindex print-search-dirs
3093 Print the name of the configured installation directory and a list of
3094 program and library directories gcc will search---and don't do anything else.
3096 This is useful when gcc prints the error message
3097 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3098 To resolve this you either need to put @file{cpp0} and the other compiler
3099 components where gcc expects to find them, or you can set the environment
3100 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3101 Don't forget the trailing '/'.
3102 @xref{Environment Variables}.
3105 @opindex dumpmachine
3106 Print the compiler's target machine (for example,
3107 @samp{i686-pc-linux-gnu})---and don't do anything else.
3110 @opindex dumpversion
3111 Print the compiler version (for example, @samp{3.0})---and don't do
3116 Print the compiler's built-in specs---and don't do anything else. (This
3117 is used when GCC itself is being built.) @xref{Spec Files}.
3120 @node Optimize Options
3121 @section Options That Control Optimization
3122 @cindex optimize options
3123 @cindex options, optimization
3125 These options control various sorts of optimizations:
3132 Optimize. Optimizing compilation takes somewhat more time, and a lot
3133 more memory for a large function.
3135 Without @option{-O}, the compiler's goal is to reduce the cost of
3136 compilation and to make debugging produce the expected results.
3137 Statements are independent: if you stop the program with a breakpoint
3138 between statements, you can then assign a new value to any variable or
3139 change the program counter to any other statement in the function and
3140 get exactly the results you would expect from the source code.
3142 With @option{-O}, the compiler tries to reduce code size and execution
3143 time, without performing any optimizations that take a great deal of
3148 Optimize even more. GCC performs nearly all supported optimizations
3149 that do not involve a space-speed tradeoff. The compiler does not
3150 perform loop unrolling or function inlining when you specify @option{-O2}.
3151 As compared to @option{-O}, this option increases both compilation time
3152 and the performance of the generated code.
3154 @option{-O2} turns on all optional optimizations except for loop unrolling,
3155 function inlining, and register renaming. It also turns on the
3156 @option{-fforce-mem} option on all machines and frame pointer elimination
3157 on machines where doing so does not interfere with debugging.
3159 Please note the warning under @option{-fgcse} about
3160 invoking @option{-O2} on programs that use computed gotos.
3164 Optimize yet more. @option{-O3} turns on all optimizations specified by
3165 @option{-O2} and also turns on the @option{-finline-functions} and
3166 @option{-frename-registers} options.
3174 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3175 do not typically increase code size. It also performs further
3176 optimizations designed to reduce code size.
3178 If you use multiple @option{-O} options, with or without level numbers,
3179 the last such option is the one that is effective.
3182 Options of the form @option{-f@var{flag}} specify machine-independent
3183 flags. Most flags have both positive and negative forms; the negative
3184 form of @option{-ffoo} would be @option{-fno-foo}. In the table below,
3185 only one of the forms is listed---the one which is not the default.
3186 You can figure out the other form by either removing @samp{no-} or
3191 @opindex ffloat-store
3192 Do not store floating point variables in registers, and inhibit other
3193 options that might change whether a floating point value is taken from a
3196 @cindex floating point precision
3197 This option prevents undesirable excess precision on machines such as
3198 the 68000 where the floating registers (of the 68881) keep more
3199 precision than a @code{double} is supposed to have. Similarly for the
3200 x86 architecture. For most programs, the excess precision does only
3201 good, but a few programs rely on the precise definition of IEEE floating
3202 point. Use @option{-ffloat-store} for such programs, after modifying
3203 them to store all pertinent intermediate computations into variables.
3205 @item -fno-default-inline
3206 @opindex fno-default-inline
3207 Do not make member functions inline by default merely because they are
3208 defined inside the class scope (C++ only). Otherwise, when you specify
3209 @w{@option{-O}}, member functions defined inside class scope are compiled
3210 inline by default; i.e., you don't need to add @samp{inline} in front of
3211 the member function name.
3213 @item -fno-defer-pop
3214 @opindex fno-defer-pop
3215 Always pop the arguments to each function call as soon as that function
3216 returns. For machines which must pop arguments after a function call,
3217 the compiler normally lets arguments accumulate on the stack for several
3218 function calls and pops them all at once.
3222 Force memory operands to be copied into registers before doing
3223 arithmetic on them. This produces better code by making all memory
3224 references potential common subexpressions. When they are not common
3225 subexpressions, instruction combination should eliminate the separate
3226 register-load. The @option{-O2} option turns on this option.
3229 @opindex fforce-addr
3230 Force memory address constants to be copied into registers before
3231 doing arithmetic on them. This may produce better code just as
3232 @option{-fforce-mem} may.
3234 @item -fomit-frame-pointer
3235 @opindex fomit-frame-pointer
3236 Don't keep the frame pointer in a register for functions that
3237 don't need one. This avoids the instructions to save, set up and
3238 restore frame pointers; it also makes an extra register available
3239 in many functions. @strong{It also makes debugging impossible on
3243 On some machines, such as the VAX, this flag has no effect, because
3244 the standard calling sequence automatically handles the frame pointer
3245 and nothing is saved by pretending it doesn't exist. The
3246 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3247 whether a target machine supports this flag. @xref{Registers}.
3250 On some machines, such as the VAX, this flag has no effect, because
3251 the standard calling sequence automatically handles the frame pointer
3252 and nothing is saved by pretending it doesn't exist. The
3253 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3254 whether a target machine supports this flag. @xref{Registers,,Register
3255 Usage, gcc.info, Using and Porting GCC}.
3258 @item -foptimize-sibling-calls
3259 @opindex foptimize-sibling-calls
3260 Optimize sibling and tail recursive calls.
3264 This option generates traps for signed overflow on addition, subtraction,
3265 multiplication operations.
3269 Don't pay attention to the @code{inline} keyword. Normally this option
3270 is used to keep the compiler from expanding any functions inline.
3271 Note that if you are not optimizing, no functions can be expanded inline.
3273 @item -finline-functions
3274 @opindex finline-functions
3275 Integrate all simple functions into their callers. The compiler
3276 heuristically decides which functions are simple enough to be worth
3277 integrating in this way.
3279 If all calls to a given function are integrated, and the function is
3280 declared @code{static}, then the function is normally not output as
3281 assembler code in its own right.
3283 @item -finline-limit=@var{n}
3284 @opindex finline-limit
3285 By default, gcc limits the size of functions that can be inlined. This flag
3286 allows the control of this limit for functions that are explicitly marked as
3287 inline (ie marked with the inline keyword or defined within the class
3288 definition in c++). @var{n} is the size of functions that can be inlined in
3289 number of pseudo instructions (not counting parameter handling). The default
3290 value of @var{n} is 600.
3291 Increasing this value can result in more inlined code at
3292 the cost of compilation time and memory consumption. Decreasing usually makes
3293 the compilation faster and less code will be inlined (which presumably
3294 means slower programs). This option is particularly useful for programs that
3295 use inlining heavily such as those based on recursive templates with C++.
3297 @emph{Note:} pseudo instruction represents, in this particular context, an
3298 abstract measurement of function's size. In no way, it represents a count
3299 of assembly instructions and as such its exact meaning might change from one
3300 release to an another.
3302 @item -fkeep-inline-functions
3303 @opindex fkeep-inline-functions
3304 Even if all calls to a given function are integrated, and the function
3305 is declared @code{static}, nevertheless output a separate run-time
3306 callable version of the function. This switch does not affect
3307 @code{extern inline} functions.
3309 @item -fkeep-static-consts
3310 @opindex fkeep-static-consts
3311 Emit variables declared @code{static const} when optimization isn't turned
3312 on, even if the variables aren't referenced.
3314 GCC enables this option by default. If you want to force the compiler to
3315 check if the variable was referenced, regardless of whether or not
3316 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3318 @item -fmerge-constants
3319 Attempt to merge identical constants (string constants and floating point
3320 constants) accross compilation units.
3322 This option is default for optimized compilation if assembler and linker
3323 support it. Use @option{-fno-merge-constants} to inhibit this behavior.
3325 @item -fmerge-all-constants
3326 Attempt to merge identical constants and identical variables.
3328 This option implies @option{-fmerge-constants}. In addition to
3329 @option{-fmerge-constants} this considers e.g. even constant initialized
3330 arrays or initialized constant variables with integral or floating point
3331 types. Languages like C or C++ require each non-automatic variable to
3332 have distinct location, so using this option will result in non-conforming
3335 @item -fno-function-cse
3336 @opindex fno-function-cse
3337 Do not put function addresses in registers; make each instruction that
3338 calls a constant function contain the function's address explicitly.
3340 This option results in less efficient code, but some strange hacks
3341 that alter the assembler output may be confused by the optimizations
3342 performed when this option is not used.
3346 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, and @*
3347 @option{-fno-trapping-math}.
3349 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
3351 This option should never be turned on by any @option{-O} option since
3352 it can result in incorrect output for programs which depend on
3353 an exact implementation of IEEE or ISO rules/specifications for
3356 @item -fno-math-errno
3357 @opindex fno-math-errno
3358 Do not set ERRNO after calling math functions that are executed
3359 with a single instruction, e.g., sqrt. A program that relies on
3360 IEEE exceptions for math error handling may want to use this flag
3361 for speed while maintaining IEEE arithmetic compatibility.
3363 This option should never be turned on by any @option{-O} option since
3364 it can result in incorrect output for programs which depend on
3365 an exact implementation of IEEE or ISO rules/specifications for
3368 The default is @option{-fmath-errno}.
3370 @item -funsafe-math-optimizations
3371 @opindex funsafe-math-optimizations
3372 Allow optimizations for floating-point arithmetic that (a) assume
3373 that arguments and results are valid and (b) may violate IEEE or
3374 ANSI standards. When used at link-time, it may include libraries
3375 or startup files that change the default FPU control word or other
3376 similar optimizations.
3378 This option should never be turned on by any @option{-O} option since
3379 it can result in incorrect output for programs which depend on
3380 an exact implementation of IEEE or ISO rules/specifications for
3383 The default is @option{-fno-unsafe-math-optimizations}.
3385 @item -fno-trapping-math
3386 @opindex fno-trapping-math
3387 Compile code assuming that floating-point operations cannot generate
3388 user-visible traps. Setting this option may allow faster code
3389 if one relies on ``non-stop'' IEEE arithmetic, for example.
3391 This option should never be turned on by any @option{-O} option since
3392 it can result in incorrect output for programs which depend on
3393 an exact implementation of IEEE or ISO rules/specifications for
3396 The default is @option{-ftrapping-math}.
3399 The following options control specific optimizations. The @option{-O2}
3400 option turns on all of these optimizations except @option{-funroll-loops}
3401 and @option{-funroll-all-loops}. On most machines, the @option{-O} option
3402 turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
3403 but specific machines may handle it differently.
3405 You can use the following flags in the rare cases when ``fine-tuning''
3406 of optimizations to be performed is desired.
3408 Not all of the optimizations performed by GCC have @option{-f} options
3412 @item -fstrength-reduce
3413 @opindex fstrength-reduce
3414 Perform the optimizations of loop strength reduction and
3415 elimination of iteration variables.
3417 @item -fthread-jumps
3418 @opindex fthread-jumps
3419 Perform optimizations where we check to see if a jump branches to a
3420 location where another comparison subsumed by the first is found. If
3421 so, the first branch is redirected to either the destination of the
3422 second branch or a point immediately following it, depending on whether
3423 the condition is known to be true or false.
3425 @item -fcse-follow-jumps
3426 @opindex fcse-follow-jumps
3427 In common subexpression elimination, scan through jump instructions
3428 when the target of the jump is not reached by any other path. For
3429 example, when CSE encounters an @code{if} statement with an
3430 @code{else} clause, CSE will follow the jump when the condition
3433 @item -fcse-skip-blocks
3434 @opindex fcse-skip-blocks
3435 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3436 follow jumps which conditionally skip over blocks. When CSE
3437 encounters a simple @code{if} statement with no else clause,
3438 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3439 body of the @code{if}.
3441 @item -frerun-cse-after-loop
3442 @opindex frerun-cse-after-loop
3443 Re-run common subexpression elimination after loop optimizations has been
3446 @item -frerun-loop-opt
3447 @opindex frerun-loop-opt
3448 Run the loop optimizer twice.
3452 Perform a global common subexpression elimination pass.
3453 This pass also performs global constant and copy propagation.
3455 @emph{Note:} When compiling a program using computed gotos, a GCC
3456 extension, you may get better runtime performance if you disable
3457 the global common subexpression elmination pass by adding
3458 @option{-fno-gcse} to the command line.
3462 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3463 attempt to move loads which are only killed by stores into themselves. This
3464 allows a loop containing a load/store sequence to be changed to a load outside
3465 the loop, and a copy/store within the loop.
3469 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3470 subexpression elimination. This pass will attempt to move stores out of loops.
3471 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3472 can be changed to a load before the loop and a store after the loop.
3474 @item -fdelete-null-pointer-checks
3475 @opindex fdelete-null-pointer-checks
3476 Use global dataflow analysis to identify and eliminate useless checks
3477 for null pointers. The compiler assumes that dereferencing a null
3478 pointer would have halted the program. If a pointer is checked after
3479 it has already been dereferenced, it cannot be null.
3481 In some environments, this assumption is not true, and programs can
3482 safely dereference null pointers. Use
3483 @option{-fno-delete-null-pointer-checks} to disable this optimization
3484 for programs which depend on that behavior.
3486 @item -fexpensive-optimizations
3487 @opindex fexpensive-optimizations
3488 Perform a number of minor optimizations that are relatively expensive.
3490 @item -foptimize-register-move
3492 @opindex foptimize-register-move
3494 Attempt to reassign register numbers in move instructions and as
3495 operands of other simple instructions in order to maximize the amount of
3496 register tying. This is especially helpful on machines with two-operand
3497 instructions. GCC enables this optimization by default with @option{-O2}
3500 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3503 @item -fdelayed-branch
3504 @opindex fdelayed-branch
3505 If supported for the target machine, attempt to reorder instructions
3506 to exploit instruction slots available after delayed branch
3509 @item -fschedule-insns
3510 @opindex fschedule-insns
3511 If supported for the target machine, attempt to reorder instructions to
3512 eliminate execution stalls due to required data being unavailable. This
3513 helps machines that have slow floating point or memory load instructions
3514 by allowing other instructions to be issued until the result of the load
3515 or floating point instruction is required.
3517 @item -fschedule-insns2
3518 @opindex fschedule-insns2
3519 Similar to @option{-fschedule-insns}, but requests an additional pass of
3520 instruction scheduling after register allocation has been done. This is
3521 especially useful on machines with a relatively small number of
3522 registers and where memory load instructions take more than one cycle.
3524 @item -ffunction-sections
3525 @itemx -fdata-sections
3526 @opindex ffunction-sections
3527 @opindex fdata-sections
3528 Place each function or data item into its own section in the output
3529 file if the target supports arbitrary sections. The name of the
3530 function or the name of the data item determines the section's name
3533 Use these options on systems where the linker can perform optimizations
3534 to improve locality of reference in the instruction space. HPPA
3535 processors running HP-UX and Sparc processors running Solaris 2 have
3536 linkers with such optimizations. Other systems using the ELF object format
3537 as well as AIX may have these optimizations in the future.
3539 Only use these options when there are significant benefits from doing
3540 so. When you specify these options, the assembler and linker will
3541 create larger object and executable files and will also be slower.
3542 You will not be able to use @code{gprof} on all systems if you
3543 specify this option and you may have problems with debugging if
3544 you specify both this option and @option{-g}.
3546 @item -fcaller-saves
3547 @opindex fcaller-saves
3548 Enable values to be allocated in registers that will be clobbered by
3549 function calls, by emitting extra instructions to save and restore the
3550 registers around such calls. Such allocation is done only when it
3551 seems to result in better code than would otherwise be produced.
3553 This option is always enabled by default on certain machines, usually
3554 those which have no call-preserved registers to use instead.
3556 For all machines, optimization level 2 and higher enables this flag by
3559 @item -funroll-loops
3560 @opindex funroll-loops
3561 Unroll loops whose number of iterations can be determined at compile
3562 time or upon entry to the loop. @option{-funroll-loops} implies both
3563 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
3564 option makes code larger, and may or may not make it run faster.
3566 @item -funroll-all-loops
3567 @opindex funroll-all-loops
3568 Unroll all loops, even if their number of iterations is uncertain when
3569 the loop is entered. This usually makes programs run more slowly.
3570 @option{-funroll-all-loops} implies the same options as
3571 @option{-funroll-loops},
3573 @item -fprefetch-loop-arrays
3574 @opindex fprefetch-loop-arrays
3575 If supported by the target machine, generate instructions to prefetch
3576 memory to improve the performance of loops that access large arrays.
3578 @item -fmove-all-movables
3579 @opindex fmove-all-movables
3580 Forces all invariant computations in loops to be moved
3583 @item -freduce-all-givs
3584 @opindex freduce-all-givs
3585 Forces all general-induction variables in loops to be
3588 @emph{Note:} When compiling programs written in Fortran,
3589 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3590 by default when you use the optimizer.
3592 These options may generate better or worse code; results are highly
3593 dependent on the structure of loops within the source code.
3595 These two options are intended to be removed someday, once
3596 they have helped determine the efficacy of various
3597 approaches to improving loop optimizations.
3599 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
3600 know how use of these options affects
3601 the performance of your production code.
3602 We're very interested in code that runs @emph{slower}
3603 when these options are @emph{enabled}.
3606 @itemx -fno-peephole2
3607 @opindex fno-peephole
3608 @opindex fno-peephole2
3609 Disable any machine-specific peephole optimizations. The difference
3610 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
3611 are implemented in the compiler; some targets use one, some use the
3612 other, a few use both.
3614 @item -fbranch-probabilities
3615 @opindex fbranch-probabilities
3616 After running a program compiled with @option{-fprofile-arcs}
3617 (@pxref{Debugging Options,, Options for Debugging Your Program or
3618 @command{gcc}}), you can compile it a second time using
3619 @option{-fbranch-probabilities}, to improve optimizations based on
3620 the number of times each branch was taken. When the program
3621 compiled with @option{-fprofile-arcs} exits it saves arc execution
3622 counts to a file called @file{@var{sourcename}.da} for each source
3623 file The information in this data file is very dependent on the
3624 structure of the generated code, so you must use the same source code
3625 and the same optimization options for both compilations.
3628 With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
3629 note on the first instruction of each basic block, and a
3630 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
3631 These can be used to improve optimization. Currently, they are only
3632 used in one place: in @file{reorg.c}, instead of guessing which path a
3633 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
3634 exactly determine which path is taken more often.
3637 @item -fno-guess-branch-probability
3638 @opindex fno-guess-branch-probability
3639 Do not guess branch probabilities using a randomized model.
3641 Sometimes gcc will opt to use a randomized model to guess branch
3642 probabilities, when none are available from either profiling feedback
3643 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
3644 different runs of the compiler on the same program may produce different
3647 In a hard real-time system, people don't want different runs of the
3648 compiler to produce code that has different behavior; minimizing
3649 non-determinism is of paramount import. This switch allows users to
3650 reduce non-determinism, possibly at the expense of inferior
3653 @item -fstrict-aliasing
3654 @opindex fstrict-aliasing
3655 Allows the compiler to assume the strictest aliasing rules applicable to
3656 the language being compiled. For C (and C++), this activates
3657 optimizations based on the type of expressions. In particular, an
3658 object of one type is assumed never to reside at the same address as an
3659 object of a different type, unless the types are almost the same. For
3660 example, an @code{unsigned int} can alias an @code{int}, but not a
3661 @code{void*} or a @code{double}. A character type may alias any other
3664 Pay special attention to code like this:
3677 The practice of reading from a different union member than the one most
3678 recently written to (called ``type-punning'') is common. Even with
3679 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
3680 is accessed through the union type. So, the code above will work as
3681 expected. However, this code might not:
3693 Every language that wishes to perform language-specific alias analysis
3694 should define a function that computes, given an @code{tree}
3695 node, an alias set for the node. Nodes in different alias sets are not
3696 allowed to alias. For an example, see the C front-end function
3697 @code{c_get_alias_set}.
3700 @item -falign-functions
3701 @itemx -falign-functions=@var{n}
3702 @opindex falign-functions
3703 Align the start of functions to the next power-of-two greater than
3704 @var{n}, skipping up to @var{n} bytes. For instance,
3705 @option{-falign-functions=32} aligns functions to the next 32-byte
3706 boundary, but @option{-falign-functions=24} would align to the next
3707 32-byte boundary only if this can be done by skipping 23 bytes or less.
3709 @option{-fno-align-functions} and @option{-falign-functions=1} are
3710 equivalent and mean that functions will not be aligned.
3712 Some assemblers only support this flag when @var{n} is a power of two;
3713 in that case, it is rounded up.
3715 If @var{n} is not specified, use a machine-dependent default.
3717 @item -falign-labels
3718 @itemx -falign-labels=@var{n}
3719 @opindex falign-labels
3720 Align all branch targets to a power-of-two boundary, skipping up to
3721 @var{n} bytes like @option{-falign-functions}. This option can easily
3722 make code slower, because it must insert dummy operations for when the
3723 branch target is reached in the usual flow of the code.
3725 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
3726 are greater than this value, then their values are used instead.
3728 If @var{n} is not specified, use a machine-dependent default which is
3729 very likely to be @samp{1}, meaning no alignment.
3732 @itemx -falign-loops=@var{n}
3733 @opindex falign-loops
3734 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
3735 like @option{-falign-functions}. The hope is that the loop will be
3736 executed many times, which will make up for any execution of the dummy
3739 If @var{n} is not specified, use a machine-dependent default.
3742 @itemx -falign-jumps=@var{n}
3743 @opindex falign-jumps
3744 Align branch targets to a power-of-two boundary, for branch targets
3745 where the targets can only be reached by jumping, skipping up to @var{n}
3746 bytes like @option{-falign-functions}. In this case, no dummy operations
3749 If @var{n} is not specified, use a machine-dependent default.
3753 Perform optimizations in static single assignment form. Each function's
3754 flow graph is translated into SSA form, optimizations are performed, and
3755 the flow graph is translated back from SSA form. Users should not
3756 specify this option, since it is not yet ready for production use.
3760 Perform Sparse Conditional Constant Propagation in SSA form. Requires
3761 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
3765 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
3766 Like @option{-fssa}, this is an experimental feature.
3768 @item -fsingle-precision-constant
3769 @opindex fsingle-precision-constant
3770 Treat floating point constant as single precision constant instead of
3771 implicitly converting it to double precision constant.
3773 @item -frename-registers
3774 @opindex frename-registers
3775 Attempt to avoid false dependencies in scheduled code by making use
3776 of registers left over after register allocation. This optimization
3777 will most benefit processors with lots of registers. It can, however,
3778 make debugging impossible, since variables will no longer stay in
3779 a ``home register''.
3781 @item -fno-cprop-registers
3782 @opindex fno-cprop-registers
3783 After register allocation and post-register allocation instruction splitting,
3784 we perform a copy-propagation pass to try to reduce scheduling dependencies
3785 and occasionally eliminate the copy.
3787 @item --param @var{name}=@var{value}
3789 In some places, GCC uses various constants to control the amount of
3790 optimization that is done. For example, GCC will not inline functions
3791 that contain more that a certain number of instructions. You can
3792 control some of these constants on the command-line using the
3793 @option{--param} option.
3795 In each case, the @var{value} is an integer. The allowable choices for
3796 @var{name} are given in the following table:
3799 @item max-delay-slot-insn-search
3800 The maximum number of instructions to consider when looking for an
3801 instruction to fill a delay slot. If more than this arbitrary number of
3802 instructions is searched, the time savings from filling the delay slot
3803 will be minimal so stop searching. Increasing values mean more
3804 aggressive optimization, making the compile time increase with probably
3805 small improvement in executable run time.
3807 @item max-delay-slot-live-search
3808 When trying to fill delay slots, the maximum number of instructions to
3809 consider when searching for a block with valid live register
3810 information. Increasing this arbitrarily chosen value means more
3811 aggressive optimization, increasing the compile time. This parameter
3812 should be removed when the delay slot code is rewritten to maintain the
3815 @item max-gcse-memory
3816 The approximate maximum amount of memory that will be allocated in
3817 order to perform the global common subexpression elimination
3818 optimization. If more memory than specified is required, the
3819 optimization will not be done.
3821 @item max-gcse-passes
3822 The maximum number of passes of GCSE to run.
3824 @item max-pending-list-length
3825 The maximum number of pending dependencies scheduling will allow
3826 before flushing the current state and starting over. Large functions
3827 with few branches or calls can create excessively large lists which
3828 needlessly consume memory and resources.
3830 @item max-inline-insns
3831 If an function contains more than this many instructions, it
3832 will not be inlined. This option is precisely equivalent to
3833 @option{-finline-limit}.
3838 @node Preprocessor Options
3839 @section Options Controlling the Preprocessor
3840 @cindex preprocessor options
3841 @cindex options, preprocessor
3843 These options control the C preprocessor, which is run on each C source
3844 file before actual compilation.
3846 If you use the @option{-E} option, nothing is done except preprocessing.
3847 Some of these options make sense only together with @option{-E} because
3848 they cause the preprocessor output to be unsuitable for actual
3852 @item -include @var{file}
3854 Process @var{file} as input before processing the regular input file.
3855 In effect, the contents of @var{file} are compiled first. Any @option{-D}
3856 and @option{-U} options on the command line are always processed before
3857 @option{-include @var{file}}, regardless of the order in which they are
3858 written. All the @option{-include} and @option{-imacros} options are
3859 processed in the order in which they are written.
3861 @item -imacros @var{file}
3863 Process @var{file} as input, discarding the resulting output, before
3864 processing the regular input file. Because the output generated from
3865 @var{file} is discarded, the only effect of @option{-imacros @var{file}}
3866 is to make the macros defined in @var{file} available for use in the
3867 main input. All the @option{-include} and @option{-imacros} options are
3868 processed in the order in which they are written.
3870 @item -idirafter @var{dir}
3872 @cindex second include path
3873 Add the directory @var{dir} to the second include path. The directories
3874 on the second include path are searched when a header file is not found
3875 in any of the directories in the main include path (the one that
3876 @option{-I} adds to).
3878 @item -iprefix @var{prefix}
3880 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
3883 @item -iwithprefix @var{dir}
3884 @opindex iwithprefix
3885 Add a directory to the second include path. The directory's name is
3886 made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was
3887 specified previously with @option{-iprefix}. If you have not specified a
3888 prefix yet, the directory containing the installed passes of the
3889 compiler is used as the default.
3891 @item -iwithprefixbefore @var{dir}
3892 @opindex iwithprefixbefore
3893 Add a directory to the main include path. The directory's name is made
3894 by concatenating @var{prefix} and @var{dir}, as in the case of
3895 @option{-iwithprefix}.
3897 @item -isystem @var{dir}
3899 Add a directory to the beginning of the second include path, marking it
3900 as a system directory, so that it gets the same special treatment as
3901 is applied to the standard system directories.
3905 Do not search the standard system directories for header files. Only
3906 the directories you have specified with @option{-I} options (and the
3907 current directory, if appropriate) are searched. @xref{Directory
3908 Options}, for information on @option{-I}.
3910 By using both @option{-nostdinc} and @option{-I-}, you can limit the include-file
3911 search path to only those directories you specify explicitly.
3915 When searching for a header file in a directory, remap file names if a
3916 file named @file{header.gcc} exists in that directory. This can be used
3917 to work around limitations of file systems with file name restrictions.
3918 The @file{header.gcc} file should contain a series of lines with two
3919 tokens on each line: the first token is the name to map, and the second
3920 token is the actual name to use.
3924 Do not predefine any nonstandard macros. (Including architecture flags).
3928 Run only the C preprocessor. Preprocess all the C source files
3929 specified and output the results to standard output or to the
3930 specified output file.
3934 Tell the preprocessor not to discard comments. Used with the
3939 Tell the preprocessor not to generate @samp{#line} directives.
3940 Used with the @option{-E} option.
3943 @cindex dependencies, make
3946 Instead of outputting the result of preprocessing, output a rule
3947 suitable for @code{make} describing the dependencies of the main source
3948 file. The preprocessor outputs one @code{make} rule containing the
3949 object file name for that source file, a colon, and the names of all the
3950 included files. Unless overridden explicitly, the object file name
3951 consists of the basename of the source file with any suffix replaced with
3952 object file suffix. If there are many included files then the
3953 rule is split into several lines using @samp{\}-newline.
3955 @option{-M} implies @option{-E}.
3959 Like @option{-M}, but mention only the files included with @samp{#include
3960 "@var{file}"}. System header files included with @samp{#include
3961 <@var{file}>} are omitted.
3965 Like @option{-M} but the dependency information is written to a file
3966 rather than stdout. @code{gcc} will use the same file name and
3967 directory as the object file, but with the suffix @file{.d} instead.
3969 This is in addition to compiling the main file as specified---@option{-MD}
3970 does not inhibit ordinary compilation the way @option{-M} does,
3971 unless you also specify @option{-MG}.
3973 With Mach, you can use the utility @code{md} to merge multiple
3974 dependency files into a single dependency file suitable for using with
3975 the @samp{make} command.
3979 Like @option{-MD} except mention only user header files, not system
3982 @item -MF @var{file}
3984 When used with @option{-M} or @option{-MM}, specifies a file to write the
3985 dependencies to. This allows the preprocessor to write the preprocessed
3986 file to stdout normally. If no @option{-MF} switch is given, CPP sends
3987 the rules to stdout and suppresses normal preprocessed output.
3989 Another way to specify output of a @code{make} rule is by setting
3990 the environment variable @env{DEPENDENCIES_OUTPUT} (@pxref{Environment
3995 When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing
3996 header files as generated files and assume they live in the same
3997 directory as the source file. It suppresses preprocessed output, as a
3998 missing header file is ordinarily an error.
4000 This feature is used in automatic updating of makefiles.
4004 This option instructs CPP to add a phony target for each dependency
4005 other than the main file, causing each to depend on nothing. These
4006 dummy rules work around errors @code{make} gives if you remove header
4007 files without updating the @code{Makefile} to match.
4009 This is typical output:-
4012 /tmp/test.o: /tmp/test.c /tmp/test.h
4017 @item -MQ @var{target}
4018 @item -MT @var{target}
4021 By default CPP uses the main file name, including any path, and appends
4022 the object suffix, normally ``.o'', to it to obtain the name of the
4023 target for dependency generation. With @option{-MT} you can specify a
4024 target yourself, overriding the default one.
4026 If you want multiple targets, you can specify them as a single argument
4027 to @option{-MT}, or use multiple @option{-MT} options.
4029 The targets you specify are output in the order they appear on the
4030 command line. @option{-MQ} is identical to @option{-MT}, except that the
4031 target name is quoted for Make, but with @option{-MT} it isn't. For
4032 example, @option{-MT '$(objpfx)foo.o'} gives
4035 $(objpfx)foo.o: /tmp/foo.c
4038 but @option{-MQ '$(objpfx)foo.o'} gives
4041 $$(objpfx)foo.o: /tmp/foo.c
4044 The default target is automatically quoted, as if it were given with
4049 Print the name of each header file used, in addition to other normal
4052 @item -A@var{question}(@var{answer})
4054 Assert the answer @var{answer} for @var{question}, in case it is tested
4055 with a preprocessing conditional such as @samp{#if
4056 #@var{question}(@var{answer})}. @option{-A-} disables the standard
4057 assertions that normally describe the target machine.
4061 Define macro @var{macro} with the string @samp{1} as its definition.
4063 @item -D@var{macro}=@var{defn}
4064 Define macro @var{macro} as @var{defn}. All instances of @option{-D} on
4065 the command line are processed before any @option{-U} options.
4067 Any @option{-D} and @option{-U} options on the command line are processed in
4068 order, and always before @option{-imacros @var{file}}, regardless of the
4069 order in which they are written.
4073 Undefine macro @var{macro}. @option{-U} options are evaluated after all
4074 @option{-D} options, but before any @option{-include} and @option{-imacros}
4077 Any @option{-D} and @option{-U} options on the command line are processed in
4078 order, and always before @option{-imacros @var{file}}, regardless of the
4079 order in which they are written.
4083 Tell the preprocessor to output only a list of the macro definitions
4084 that are in effect at the end of preprocessing. Used with the @option{-E}
4089 Tell the preprocessing to pass all macro definitions into the output, in
4090 their proper sequence in the rest of the output.
4094 Like @option{-dD} except that the macro arguments and contents are omitted.
4095 Only @samp{#define @var{name}} is included in the output.
4099 Output @samp{#include} directives in addition to the result of
4102 @item -fpreprocessed
4103 @opindex fpreprocessed
4104 Indicate to the preprocessor that the input file has already been
4105 preprocessed. This suppresses things like macro expansion, trigraph
4106 conversion, escaped newline splicing, and processing of most directives.
4107 The preprocessor still recognizes and removes comments, so that you can
4108 pass a file preprocessed with @option{-C} to the compiler without
4109 problems. In this mode the integrated preprocessor is little more than
4110 a tokenizer for the front ends.
4112 @option{-fpreprocessed} is implicit if the input file has one of the
4113 extensions @samp{i}, @samp{ii} or @samp{mi}. These are the extensions
4114 that GCC uses for preprocessed files created by @option{-save-temps}.
4118 Process ISO standard trigraph sequences. These are three-character
4119 sequences, all starting with @samp{??}, that are defined by ISO C to
4120 stand for single characters. For example, @samp{??/} stands for
4121 @samp{\}, so @samp{'??/n'} is a character constant for a newline. By
4122 default, GCC ignores trigraphs, but in standard-conforming modes it
4123 converts them. See the @option{-std} and @option{-ansi} options.
4125 The nine trigraph sequences are
4128 @expansion{} @samp{[}
4131 @expansion{} @samp{]}
4134 @expansion{} @samp{@{}
4137 @expansion{} @samp{@}}
4140 @expansion{} @samp{#}
4143 @expansion{} @samp{\}
4146 @expansion{} @samp{^}
4149 @expansion{} @samp{|}
4152 @expansion{} @samp{~}
4156 Trigraph support is not popular, so many compilers do not implement it
4157 properly. Portable code should not rely on trigraphs being either
4158 converted or ignored.
4160 @item -Wp,@var{option}
4162 Pass @var{option} as an option to the preprocessor. If @var{option}
4163 contains commas, it is split into multiple options at the commas.
4166 @node Assembler Options
4167 @section Passing Options to the Assembler
4169 @c prevent bad page break with this line
4170 You can pass options to the assembler.
4173 @item -Wa,@var{option}
4175 Pass @var{option} as an option to the assembler. If @var{option}
4176 contains commas, it is split into multiple options at the commas.
4180 @section Options for Linking
4181 @cindex link options
4182 @cindex options, linking
4184 These options come into play when the compiler links object files into
4185 an executable output file. They are meaningless if the compiler is
4186 not doing a link step.
4190 @item @var{object-file-name}
4191 A file name that does not end in a special recognized suffix is
4192 considered to name an object file or library. (Object files are
4193 distinguished from libraries by the linker according to the file
4194 contents.) If linking is done, these object files are used as input
4203 If any of these options is used, then the linker is not run, and
4204 object file names should not be used as arguments. @xref{Overall
4208 @item -l@var{library}
4209 @itemx -l @var{library}
4211 Search the library named @var{library} when linking. (The second
4212 alternative with the library as a separate argument is only for
4213 POSIX compliance and is not recommended.)
4215 It makes a difference where in the command you write this option; the
4216 linker searches and processes libraries and object files in the order they
4217 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4218 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4219 to functions in @samp{z}, those functions may not be loaded.
4221 The linker searches a standard list of directories for the library,
4222 which is actually a file named @file{lib@var{library}.a}. The linker
4223 then uses this file as if it had been specified precisely by name.
4225 The directories searched include several standard system directories
4226 plus any that you specify with @option{-L}.
4228 Normally the files found this way are library files---archive files
4229 whose members are object files. The linker handles an archive file by
4230 scanning through it for members which define symbols that have so far
4231 been referenced but not defined. But if the file that is found is an
4232 ordinary object file, it is linked in the usual fashion. The only
4233 difference between using an @option{-l} option and specifying a file name
4234 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4235 and searches several directories.
4239 You need this special case of the @option{-l} option in order to
4240 link an Objective-C program.
4243 @opindex nostartfiles
4244 Do not use the standard system startup files when linking.
4245 The standard system libraries are used normally, unless @option{-nostdlib}
4246 or @option{-nodefaultlibs} is used.
4248 @item -nodefaultlibs
4249 @opindex nodefaultlibs
4250 Do not use the standard system libraries when linking.
4251 Only the libraries you specify will be passed to the linker.
4252 The standard startup files are used normally, unless @option{-nostartfiles}
4253 is used. The compiler may generate calls to memcmp, memset, and memcpy
4254 for System V (and ISO C) environments or to bcopy and bzero for
4255 BSD environments. These entries are usually resolved by entries in
4256 libc. These entry points should be supplied through some other
4257 mechanism when this option is specified.
4261 Do not use the standard system startup files or libraries when linking.
4262 No startup files and only the libraries you specify will be passed to
4263 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4264 for System V (and ISO C) environments or to bcopy and bzero for
4265 BSD environments. These entries are usually resolved by entries in
4266 libc. These entry points should be supplied through some other
4267 mechanism when this option is specified.
4269 @cindex @option{-lgcc}, use with @option{-nostdlib}
4270 @cindex @option{-nostdlib} and unresolved references
4271 @cindex unresolved references and @option{-nostdlib}
4272 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4273 @cindex @option{-nodefaultlibs} and unresolved references
4274 @cindex unresolved references and @option{-nodefaultlibs}
4275 One of the standard libraries bypassed by @option{-nostdlib} and
4276 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4277 that GCC uses to overcome shortcomings of particular machines, or special
4278 needs for some languages.
4280 (@xref{Interface,,Interfacing to GCC Output}, for more discussion of
4284 (@xref{Interface,,Interfacing to GCC Output,gcc.info,Porting GCC},
4285 for more discussion of @file{libgcc.a}.)
4287 In most cases, you need @file{libgcc.a} even when you want to avoid
4288 other standard libraries. In other words, when you specify @option{-nostdlib}
4289 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4290 This ensures that you have no unresolved references to internal GCC
4291 library subroutines. (For example, @samp{__main}, used to ensure C++
4292 constructors will be called; @pxref{Collect2,,@command{collect2}}.)
4296 Remove all symbol table and relocation information from the executable.
4300 On systems that support dynamic linking, this prevents linking with the shared
4301 libraries. On other systems, this option has no effect.
4305 Produce a shared object which can then be linked with other objects to
4306 form an executable. Not all systems support this option. For predictable
4307 results, you must also specify the same set of options that were used to
4308 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4309 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4310 needs to build supplementary stub code for constructors to work. On
4311 multi-libbed systems, @samp{gcc -shared} must select the correct support
4312 libraries to link against. Failing to supply the correct flags may lead
4313 to subtle defects. Supplying them in cases where they are not necessary
4316 @item -shared-libgcc
4317 @itemx -static-libgcc
4318 @opindex shared-libgcc
4319 @opindex static-libgcc
4320 On systems that provide @file{libgcc} as a shared library, these options
4321 force the use of either the shared or static version respectively.
4322 If no shared version of @file{libgcc} was built when the compiler was
4323 configured, these options have no effect.
4325 There are several situations in which an application should use the
4326 shared @file{libgcc} instead of the static version. The most common
4327 of these is when the application wishes to throw and catch exceptions
4328 across different shared libraries. In that case, each of the libraries
4329 as well as the application itself should use the shared @file{libgcc}.
4331 Therefore, whenever you specify the @option{-shared} option, the GCC
4332 driver automatically adds @option{-shared-libgcc}, unless you explicitly
4333 specify @option{-static-libgcc}. The G++ driver automatically adds
4334 @option{-shared-libgcc} when you build a main executable as well because
4335 for C++ programs that is typically the right thing to do.
4336 (Exception-handling will not work reliably otherwise.)
4338 However, when linking a main executable written in C, you must
4339 explicitly say @option{-shared-libgcc} if you want to use the shared
4344 Bind references to global symbols when building a shared object. Warn
4345 about any unresolved references (unless overridden by the link editor
4346 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4349 @item -Xlinker @var{option}
4351 Pass @var{option} as an option to the linker. You can use this to
4352 supply system-specific linker options which GCC does not know how to
4355 If you want to pass an option that takes an argument, you must use
4356 @option{-Xlinker} twice, once for the option and once for the argument.
4357 For example, to pass @option{-assert definitions}, you must write
4358 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4359 @option{-Xlinker "-assert definitions"}, because this passes the entire
4360 string as a single argument, which is not what the linker expects.
4362 @item -Wl,@var{option}
4364 Pass @var{option} as an option to the linker. If @var{option} contains
4365 commas, it is split into multiple options at the commas.
4367 @item -u @var{symbol}
4369 Pretend the symbol @var{symbol} is undefined, to force linking of
4370 library modules to define it. You can use @option{-u} multiple times with
4371 different symbols to force loading of additional library modules.
4374 @node Directory Options
4375 @section Options for Directory Search
4376 @cindex directory options
4377 @cindex options, directory search
4380 These options specify directories to search for header files, for
4381 libraries and for parts of the compiler:
4386 Add the directory @var{dir} to the head of the list of directories to be
4387 searched for header files. This can be used to override a system header
4388 file, substituting your own version, since these directories are
4389 searched before the system header file directories. However, you should
4390 not use this option to add directories that contain vendor-supplied
4391 system header files (use @option{-isystem} for that). If you use more than
4392 one @option{-I} option, the directories are scanned in left-to-right
4393 order; the standard system directories come after.
4395 If a standard system include directory, or a directory specified with
4396 @option{-isystem}, is also specified with @option{-I}, it will be
4397 searched only in the position requested by @option{-I}. Also, it will
4398 not be considered a system include directory. If that directory really
4399 does contain system headers, there is a good chance that they will
4400 break. For instance, if GCC's installation procedure edited the headers
4401 in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the
4402 original, buggy headers to be found instead of the corrected ones. GCC
4403 will issue a warning when a system include directory is hidden in this
4408 Any directories you specify with @option{-I} options before the @option{-I-}
4409 option are searched only for the case of @samp{#include "@var{file}"};
4410 they are not searched for @samp{#include <@var{file}>}.
4412 If additional directories are specified with @option{-I} options after
4413 the @option{-I-}, these directories are searched for all @samp{#include}
4414 directives. (Ordinarily @emph{all} @option{-I} directories are used
4417 In addition, the @option{-I-} option inhibits the use of the current
4418 directory (where the current input file came from) as the first search
4419 directory for @samp{#include "@var{file}"}. There is no way to
4420 override this effect of @option{-I-}. With @option{-I.} you can specify
4421 searching the directory which was current when the compiler was
4422 invoked. That is not exactly the same as what the preprocessor does
4423 by default, but it is often satisfactory.
4425 @option{-I-} does not inhibit the use of the standard system directories
4426 for header files. Thus, @option{-I-} and @option{-nostdinc} are
4431 Add directory @var{dir} to the list of directories to be searched
4434 @item -B@var{prefix}
4436 This option specifies where to find the executables, libraries,
4437 include files, and data files of the compiler itself.
4439 The compiler driver program runs one or more of the subprograms
4440 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
4441 @var{prefix} as a prefix for each program it tries to run, both with and
4442 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
4444 For each subprogram to be run, the compiler driver first tries the
4445 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
4446 was not specified, the driver tries two standard prefixes, which are
4447 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
4448 those results in a file name that is found, the unmodified program
4449 name is searched for using the directories specified in your
4450 @env{PATH} environment variable.
4452 The compiler will check to see if the path provided by the @option{-B}
4453 refers to a directory, and if necessary it will add a directory
4454 separator character at the end of the path.
4456 @option{-B} prefixes that effectively specify directory names also apply
4457 to libraries in the linker, because the compiler translates these
4458 options into @option{-L} options for the linker. They also apply to
4459 includes files in the preprocessor, because the compiler translates these
4460 options into @option{-isystem} options for the preprocessor. In this case,
4461 the compiler appends @samp{include} to the prefix.
4463 The run-time support file @file{libgcc.a} can also be searched for using
4464 the @option{-B} prefix, if needed. If it is not found there, the two
4465 standard prefixes above are tried, and that is all. The file is left
4466 out of the link if it is not found by those means.
4468 Another way to specify a prefix much like the @option{-B} prefix is to use
4469 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
4472 As a special kludge, if the path provided by @option{-B} is
4473 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
4474 9, then it will be replaced by @file{[dir/]include}. This is to help
4475 with boot-strapping the compiler.
4477 @item -specs=@var{file}
4479 Process @var{file} after the compiler reads in the standard @file{specs}
4480 file, in order to override the defaults that the @file{gcc} driver
4481 program uses when determining what switches to pass to @file{cc1},
4482 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
4483 @option{-specs=@var{file}} can be specified on the command line, and they
4484 are processed in order, from left to right.
4490 @section Specifying subprocesses and the switches to pass to them
4492 @command{gcc} is a driver program. It performs its job by invoking a
4493 sequence of other programs to do the work of compiling, assembling and
4494 linking. GCC interprets its command-line parameters and uses these to
4495 deduce which programs it should invoke, and which command-line options
4496 it ought to place on their command lines. This behavior is controlled
4497 by @dfn{spec strings}. In most cases there is one spec string for each
4498 program that GCC can invoke, but a few programs have multiple spec
4499 strings to control their behavior. The spec strings built into GCC can
4500 be overridden by using the @option{-specs=} command-line switch to specify
4503 @dfn{Spec files} are plaintext files that are used to construct spec
4504 strings. They consist of a sequence of directives separated by blank
4505 lines. The type of directive is determined by the first non-whitespace
4506 character on the line and it can be one of the following:
4509 @item %@var{command}
4510 Issues a @var{command} to the spec file processor. The commands that can
4514 @item %include <@var{file}>
4516 Search for @var{file} and insert its text at the current point in the
4519 @item %include_noerr <@var{file}>
4520 @cindex %include_noerr
4521 Just like @samp{%include}, but do not generate an error message if the include
4522 file cannot be found.
4524 @item %rename @var{old_name} @var{new_name}
4526 Rename the spec string @var{old_name} to @var{new_name}.
4530 @item *[@var{spec_name}]:
4531 This tells the compiler to create, override or delete the named spec
4532 string. All lines after this directive up to the next directive or
4533 blank line are considered to be the text for the spec string. If this
4534 results in an empty string then the spec will be deleted. (Or, if the
4535 spec did not exist, then nothing will happened.) Otherwise, if the spec
4536 does not currently exist a new spec will be created. If the spec does
4537 exist then its contents will be overridden by the text of this
4538 directive, unless the first character of that text is the @samp{+}
4539 character, in which case the text will be appended to the spec.
4541 @item [@var{suffix}]:
4542 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
4543 and up to the next directive or blank line are considered to make up the
4544 spec string for the indicated suffix. When the compiler encounters an
4545 input file with the named suffix, it will processes the spec string in
4546 order to work out how to compile that file. For example:
4553 This says that any input file whose name ends in @samp{.ZZ} should be
4554 passed to the program @samp{z-compile}, which should be invoked with the
4555 command-line switch @option{-input} and with the result of performing the
4556 @samp{%i} substitution. (See below.)
4558 As an alternative to providing a spec string, the text that follows a
4559 suffix directive can be one of the following:
4562 @item @@@var{language}
4563 This says that the suffix is an alias for a known @var{language}. This is
4564 similar to using the @option{-x} command-line switch to GCC to specify a
4565 language explicitly. For example:
4572 Says that .ZZ files are, in fact, C++ source files.
4575 This causes an error messages saying:
4578 @var{name} compiler not installed on this system.
4582 GCC already has an extensive list of suffixes built into it.
4583 This directive will add an entry to the end of the list of suffixes, but
4584 since the list is searched from the end backwards, it is effectively
4585 possible to override earlier entries using this technique.
4589 GCC has the following spec strings built into it. Spec files can
4590 override these strings or create their own. Note that individual
4591 targets can also add their own spec strings to this list.
4594 asm Options to pass to the assembler
4595 asm_final Options to pass to the assembler post-processor
4596 cpp Options to pass to the C preprocessor
4597 cc1 Options to pass to the C compiler
4598 cc1plus Options to pass to the C++ compiler
4599 endfile Object files to include at the end of the link
4600 link Options to pass to the linker
4601 lib Libraries to include on the command line to the linker
4602 libgcc Decides which GCC support library to pass to the linker
4603 linker Sets the name of the linker
4604 predefines Defines to be passed to the C preprocessor
4605 signed_char Defines to pass to CPP to say whether @code{char} is signed
4607 startfile Object files to include at the start of the link
4610 Here is a small example of a spec file:
4616 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
4619 This example renames the spec called @samp{lib} to @samp{old_lib} and
4620 then overrides the previous definition of @samp{lib} with a new one.
4621 The new definition adds in some extra command-line options before
4622 including the text of the old definition.
4624 @dfn{Spec strings} are a list of command-line options to be passed to their
4625 corresponding program. In addition, the spec strings can contain
4626 @samp{%}-prefixed sequences to substitute variable text or to
4627 conditionally insert text into the command line. Using these constructs
4628 it is possible to generate quite complex command lines.
4630 Here is a table of all defined @samp{%}-sequences for spec
4631 strings. Note that spaces are not generated automatically around the
4632 results of expanding these sequences. Therefore you can concatenate them
4633 together or combine them with constant text in a single argument.
4637 Substitute one @samp{%} into the program name or argument.
4640 Substitute the name of the input file being processed.
4643 Substitute the basename of the input file being processed.
4644 This is the substring up to (and not including) the last period
4645 and not including the directory.
4648 This is the same as @samp{%b}, but include the file suffix (text after
4652 Marks the argument containing or following the @samp{%d} as a
4653 temporary file name, so that that file will be deleted if GCC exits
4654 successfully. Unlike @samp{%g}, this contributes no text to the
4657 @item %g@var{suffix}
4658 Substitute a file name that has suffix @var{suffix} and is chosen
4659 once per compilation, and mark the argument in the same way as
4660 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
4661 name is now chosen in a way that is hard to predict even when previously
4662 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
4663 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
4664 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
4665 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
4666 was simply substituted with a file name chosen once per compilation,
4667 without regard to any appended suffix (which was therefore treated
4668 just like ordinary text), making such attacks more likely to succeed.
4670 @item %u@var{suffix}
4671 Like @samp{%g}, but generates a new temporary file name even if
4672 @samp{%u@var{suffix}} was already seen.
4674 @item %U@var{suffix}
4675 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
4676 new one if there is no such last file name. In the absence of any
4677 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
4678 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
4679 would involve the generation of two distinct file names, one
4680 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
4681 simply substituted with a file name chosen for the previous @samp{%u},
4682 without regard to any appended suffix.
4684 @item %j@var{SUFFIX}
4685 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
4686 writable, and if save-temps is off; otherwise, substitute the name
4687 of a temporary file, just like @samp{%u}. This temporary file is not
4688 meant for communication between processes, but rather as a junk
4691 @item %.@var{SUFFIX}
4692 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
4693 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
4694 terminated by the next space or %.
4697 Marks the argument containing or following the @samp{%w} as the
4698 designated output file of this compilation. This puts the argument
4699 into the sequence of arguments that @samp{%o} will substitute later.
4702 Substitutes the names of all the output files, with spaces
4703 automatically placed around them. You should write spaces
4704 around the @samp{%o} as well or the results are undefined.
4705 @samp{%o} is for use in the specs for running the linker.
4706 Input files whose names have no recognized suffix are not compiled
4707 at all, but they are included among the output files, so they will
4711 Substitutes the suffix for object files. Note that this is
4712 handled specially when it immediately follows @samp{%g, %u, or %U},
4713 because of the need for those to form complete file names. The
4714 handling is such that @samp{%O} is treated exactly as if it had already
4715 been substituted, except that @samp{%g, %u, and %U} do not currently
4716 support additional @var{suffix} characters following @samp{%O} as they would
4717 following, for example, @samp{.o}.
4720 Substitutes the standard macro predefinitions for the
4721 current target machine. Use this when running @code{cpp}.
4724 Like @samp{%p}, but puts @samp{__} before and after the name of each
4725 predefined macro, except for macros that start with @samp{__} or with
4726 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
4730 Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}.
4733 Current argument is the name of a library or startup file of some sort.
4734 Search for that file in a standard list of directories and substitute
4735 the full name found.
4738 Print @var{str} as an error message. @var{str} is terminated by a newline.
4739 Use this when inconsistent options are detected.
4742 Output @samp{-} if the input for the current command is coming from a pipe.
4745 Substitute the contents of spec string @var{name} at this point.
4748 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
4750 @item %x@{@var{option}@}
4751 Accumulate an option for @samp{%X}.
4754 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
4758 Output the accumulated assembler options specified by @option{-Wa}.
4761 Output the accumulated preprocessor options specified by @option{-Wp}.
4764 Substitute the major version number of GCC@.
4765 (For version 2.9.5, this is 2.)
4768 Substitute the minor version number of GCC@.
4769 (For version 2.9.5, this is 9.)
4772 Substitute the patch level number of GCC@.
4773 (For version 2.9.5, this is 5.)
4776 Process the @code{asm} spec. This is used to compute the
4777 switches to be passed to the assembler.
4780 Process the @code{asm_final} spec. This is a spec string for
4781 passing switches to an assembler post-processor, if such a program is
4785 Process the @code{link} spec. This is the spec for computing the
4786 command line passed to the linker. Typically it will make use of the
4787 @samp{%L %G %S %D and %E} sequences.
4790 Dump out a @option{-L} option for each directory that GCC believes might
4791 contain startup files. If the target supports multilibs then the
4792 current multilib directory will be prepended to each of these paths.
4795 Output the multilib directory with directory separators replaced with
4796 @samp{_}. If multilib directories are not set, or the multilib directory is
4797 @file{.} then this option emits nothing.
4800 Process the @code{lib} spec. This is a spec string for deciding which
4801 libraries should be included on the command line to the linker.
4804 Process the @code{libgcc} spec. This is a spec string for deciding
4805 which GCC support library should be included on the command line to the linker.
4808 Process the @code{startfile} spec. This is a spec for deciding which
4809 object files should be the first ones passed to the linker. Typically
4810 this might be a file named @file{crt0.o}.
4813 Process the @code{endfile} spec. This is a spec string that specifies
4814 the last object files that will be passed to the linker.
4817 Process the @code{cpp} spec. This is used to construct the arguments
4818 to be passed to the C preprocessor.
4821 Process the @code{signed_char} spec. This is intended to be used
4822 to tell cpp whether a char is signed. It typically has the definition:
4824 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
4828 Process the @code{cc1} spec. This is used to construct the options to be
4829 passed to the actual C compiler (@samp{cc1}).
4832 Process the @code{cc1plus} spec. This is used to construct the options to be
4833 passed to the actual C++ compiler (@samp{cc1plus}).
4836 Substitute the variable part of a matched option. See below.
4837 Note that each comma in the substituted string is replaced by
4841 Substitutes the @code{-S} switch, if that switch was given to GCC@.
4842 If that switch was not specified, this substitutes nothing. Note that
4843 the leading dash is omitted when specifying this option, and it is
4844 automatically inserted if the substitution is performed. Thus the spec
4845 string @samp{%@{foo@}} would match the command-line option @option{-foo}
4846 and would output the command line option @option{-foo}.
4848 @item %W@{@code{S}@}
4849 Like %@{@code{S}@} but mark last argument supplied within as a file to be
4852 @item %@{@code{S}*@}
4853 Substitutes all the switches specified to GCC whose names start
4854 with @code{-S}, but which also take an argument. This is used for
4855 switches like @option{-o}, @option{-D}, @option{-I}, etc.
4856 GCC considers @option{-o foo} as being
4857 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
4858 text, including the space. Thus two arguments would be generated.
4860 @item %@{^@code{S}*@}
4861 Like %@{@code{S}*@}, but don't put a blank between a switch and its
4862 argument. Thus %@{^o*@} would only generate one argument, not two.
4864 @item %@{@code{S}*&@code{T}*@}
4865 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
4866 (the order of @code{S} and @code{T} in the spec is not significant).
4867 There can be any number of ampersand-separated variables; for each the
4868 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
4870 @item %@{<@code{S}@}
4871 Remove all occurrences of @code{-S} from the command line. Note---this
4872 command is position dependent. @samp{%} commands in the spec string
4873 before this option will see @code{-S}, @samp{%} commands in the spec
4874 string after this option will not.
4876 @item %@{@code{S}*:@code{X}@}
4877 Substitutes @code{X} if one or more switches whose names start with
4878 @code{-S} are specified to GCC@. Note that the tail part of the
4879 @code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted
4880 for each occurrence of @samp{%*} within @code{X}.
4882 @item %@{@code{S}:@code{X}@}
4883 Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@.
4885 @item %@{!@code{S}:@code{X}@}
4886 Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@.
4888 @item %@{|@code{S}:@code{X}@}
4889 Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}.
4891 @item %@{|!@code{S}:@code{X}@}
4892 Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}.
4894 @item %@{.@code{S}:@code{X}@}
4895 Substitutes @code{X}, but only if processing a file with suffix @code{S}.
4897 @item %@{!.@code{S}:@code{X}@}
4898 Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}.
4900 @item %@{@code{S}|@code{P}:@code{X}@}
4901 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be
4902 combined with @samp{!} and @samp{.} sequences as well, although they
4903 have a stronger binding than the @samp{|}. For example a spec string
4907 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
4910 will output the following command-line options from the following input
4911 command-line options:
4916 -d fred.c -foo -baz -boggle
4917 -d jim.d -bar -baz -boggle
4922 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or
4923 %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs
4924 or spaces, or even newlines. They are processed as usual, as described
4927 The @option{-O}, @option{-f}, @option{-m}, and @option{-W}
4928 switches are handled specifically in these
4929 constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or
4930 @option{-W} switch is found later in the command line, the earlier switch
4931 value is ignored, except with @{@code{S}*@} where @code{S} is just one
4932 letter, which passes all matching options.
4934 The character @samp{|} at the beginning of the predicate text is used to indicate
4935 that a command should be piped to the following command, but only if @option{-pipe}
4938 It is built into GCC which switches take arguments and which do not.
4939 (You might think it would be useful to generalize this to allow each
4940 compiler's spec to say which switches take arguments. But this cannot
4941 be done in a consistent fashion. GCC cannot even decide which input
4942 files have been specified without knowing which switches take arguments,
4943 and it must know which input files to compile in order to tell which
4946 GCC also knows implicitly that arguments starting in @option{-l} are to be
4947 treated as compiler output files, and passed to the linker in their
4948 proper position among the other output files.
4950 @c man begin OPTIONS
4952 @node Target Options
4953 @section Specifying Target Machine and Compiler Version
4954 @cindex target options
4955 @cindex cross compiling
4956 @cindex specifying machine version
4957 @cindex specifying compiler version and target machine
4958 @cindex compiler version, specifying
4959 @cindex target machine, specifying
4961 By default, GCC compiles code for the same type of machine that you
4962 are using. However, it can also be installed as a cross-compiler, to
4963 compile for some other type of machine. In fact, several different
4964 configurations of GCC, for different target machines, can be
4965 installed side by side. Then you specify which one to use with the
4968 In addition, older and newer versions of GCC can be installed side
4969 by side. One of them (probably the newest) will be the default, but
4970 you may sometimes wish to use another.
4973 @item -b @var{machine}
4975 The argument @var{machine} specifies the target machine for compilation.
4976 This is useful when you have installed GCC as a cross-compiler.
4978 The value to use for @var{machine} is the same as was specified as the
4979 machine type when configuring GCC as a cross-compiler. For
4980 example, if a cross-compiler was configured with @samp{configure
4981 i386v}, meaning to compile for an 80386 running System V, then you
4982 would specify @option{-b i386v} to run that cross compiler.
4984 When you do not specify @option{-b}, it normally means to compile for
4985 the same type of machine that you are using.
4987 @item -V @var{version}
4989 The argument @var{version} specifies which version of GCC to run.
4990 This is useful when multiple versions are installed. For example,
4991 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
4993 The default version, when you do not specify @option{-V}, is the last
4994 version of GCC that you installed.
4997 The @option{-b} and @option{-V} options actually work by controlling part of
4998 the file name used for the executable files and libraries used for
4999 compilation. A given version of GCC, for a given target machine, is
5000 normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}.
5002 Thus, sites can customize the effect of @option{-b} or @option{-V} either by
5003 changing the names of these directories or adding alternate names (or
5004 symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the
5005 file @file{80386} is a link to the file @file{i386v}, then @option{-b
5006 80386} becomes an alias for @option{-b i386v}.
5008 In one respect, the @option{-b} or @option{-V} do not completely change
5009 to a different compiler: the top-level driver program @command{gcc}
5010 that you originally invoked continues to run and invoke the other
5011 executables (preprocessor, compiler per se, assembler and linker)
5012 that do the real work. However, since no real work is done in the
5013 driver program, it usually does not matter that the driver program
5014 in use is not the one for the specified target. It is common for the
5015 interface to the other executables to change incompatibly between
5016 compiler versions, so unless the version specified is very close to that
5017 of the driver (for example, @option{-V 3.0} with a driver program from GCC
5018 version 3.0.1), use of @option{-V} may not work; for example, using
5019 @option{-V 2.95.2} will not work with a driver program from GCC 3.0.
5021 The only way that the driver program depends on the target machine is
5022 in the parsing and handling of special machine-specific options.
5023 However, this is controlled by a file which is found, along with the
5024 other executables, in the directory for the specified version and
5025 target machine. As a result, a single installed driver program adapts
5026 to any specified target machine, and sufficiently similar compiler
5029 The driver program executable does control one significant thing,
5030 however: the default version and target machine. Therefore, you can
5031 install different instances of the driver program, compiled for
5032 different targets or versions, under different names.
5034 For example, if the driver for version 2.0 is installed as @command{ogcc}
5035 and that for version 2.1 is installed as @command{gcc}, then the command
5036 @command{gcc} will use version 2.1 by default, while @command{ogcc} will use
5037 2.0 by default. However, you can choose either version with either
5038 command with the @option{-V} option.
5040 @node Submodel Options
5041 @section Hardware Models and Configurations
5042 @cindex submodel options
5043 @cindex specifying hardware config
5044 @cindex hardware models and configurations, specifying
5045 @cindex machine dependent options
5047 Earlier we discussed the standard option @option{-b} which chooses among
5048 different installed compilers for completely different target
5049 machines, such as VAX vs.@: 68000 vs.@: 80386.
5051 In addition, each of these target machine types can have its own
5052 special options, starting with @samp{-m}, to choose among various
5053 hardware models or configurations---for example, 68010 vs 68020,
5054 floating coprocessor or none. A single installed version of the
5055 compiler can compile for any model or configuration, according to the
5058 Some configurations of the compiler also support additional special
5059 options, usually for compatibility with other compilers on the same
5063 These options are defined by the macro @code{TARGET_SWITCHES} in the
5064 machine description. The default for the options is also defined by
5065 that macro, which enables you to change the defaults.
5080 * RS/6000 and PowerPC Options::
5083 * i386 and x86-64 Options::
5085 * Intel 960 Options::
5086 * DEC Alpha Options::
5087 * DEC Alpha/VMS Options::
5091 * System V Options::
5092 * TMS320C3x/C4x Options::
5100 * S/390 and zSeries Options::
5105 @node M680x0 Options
5106 @subsection M680x0 Options
5107 @cindex M680x0 options
5109 These are the @samp{-m} options defined for the 68000 series. The default
5110 values for these options depends on which style of 68000 was selected when
5111 the compiler was configured; the defaults for the most common choices are
5119 Generate output for a 68000. This is the default
5120 when the compiler is configured for 68000-based systems.
5122 Use this option for microcontrollers with a 68000 or EC000 core,
5123 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5129 Generate output for a 68020. This is the default
5130 when the compiler is configured for 68020-based systems.
5134 Generate output containing 68881 instructions for floating point.
5135 This is the default for most 68020 systems unless @option{--nfp} was
5136 specified when the compiler was configured.
5140 Generate output for a 68030. This is the default when the compiler is
5141 configured for 68030-based systems.
5145 Generate output for a 68040. This is the default when the compiler is
5146 configured for 68040-based systems.
5148 This option inhibits the use of 68881/68882 instructions that have to be
5149 emulated by software on the 68040. Use this option if your 68040 does not
5150 have code to emulate those instructions.
5154 Generate output for a 68060. This is the default when the compiler is
5155 configured for 68060-based systems.
5157 This option inhibits the use of 68020 and 68881/68882 instructions that
5158 have to be emulated by software on the 68060. Use this option if your 68060
5159 does not have code to emulate those instructions.
5163 Generate output for a CPU32. This is the default
5164 when the compiler is configured for CPU32-based systems.
5166 Use this option for microcontrollers with a
5167 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5168 68336, 68340, 68341, 68349 and 68360.
5172 Generate output for a 520X ``coldfire'' family cpu. This is the default
5173 when the compiler is configured for 520X-based systems.
5175 Use this option for microcontroller with a 5200 core, including
5176 the MCF5202, MCF5203, MCF5204 and MCF5202.
5181 Generate output for a 68040, without using any of the new instructions.
5182 This results in code which can run relatively efficiently on either a
5183 68020/68881 or a 68030 or a 68040. The generated code does use the
5184 68881 instructions that are emulated on the 68040.
5188 Generate output for a 68060, without using any of the new instructions.
5189 This results in code which can run relatively efficiently on either a
5190 68020/68881 or a 68030 or a 68040. The generated code does use the
5191 68881 instructions that are emulated on the 68060.
5195 Generate output containing Sun FPA instructions for floating point.
5198 @opindex msoft-float
5199 Generate output containing library calls for floating point.
5200 @strong{Warning:} the requisite libraries are not available for all m68k
5201 targets. Normally the facilities of the machine's usual C compiler are
5202 used, but this can't be done directly in cross-compilation. You must
5203 make your own arrangements to provide suitable library functions for
5204 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5205 @samp{m68k-*-coff} do provide software floating point support.
5209 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5212 @opindex mnobitfield
5213 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5214 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5218 Do use the bit-field instructions. The @option{-m68020} option implies
5219 @option{-mbitfield}. This is the default if you use a configuration
5220 designed for a 68020.
5224 Use a different function-calling convention, in which functions
5225 that take a fixed number of arguments return with the @code{rtd}
5226 instruction, which pops their arguments while returning. This
5227 saves one instruction in the caller since there is no need to pop
5228 the arguments there.
5230 This calling convention is incompatible with the one normally
5231 used on Unix, so you cannot use it if you need to call libraries
5232 compiled with the Unix compiler.
5234 Also, you must provide function prototypes for all functions that
5235 take variable numbers of arguments (including @code{printf});
5236 otherwise incorrect code will be generated for calls to those
5239 In addition, seriously incorrect code will result if you call a
5240 function with too many arguments. (Normally, extra arguments are
5241 harmlessly ignored.)
5243 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5244 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5247 @itemx -mno-align-int
5249 @opindex mno-align-int
5250 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5251 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5252 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5253 Aligning variables on 32-bit boundaries produces code that runs somewhat
5254 faster on processors with 32-bit busses at the expense of more memory.
5256 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5257 align structures containing the above types differently than
5258 most published application binary interface specifications for the m68k.
5262 Use the pc-relative addressing mode of the 68000 directly, instead of
5263 using a global offset table. At present, this option implies @option{-fpic},
5264 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5265 not presently supported with @option{-mpcrel}, though this could be supported for
5266 68020 and higher processors.
5268 @item -mno-strict-align
5269 @itemx -mstrict-align
5270 @opindex mno-strict-align
5271 @opindex mstrict-align
5272 Do not (do) assume that unaligned memory references will be handled by
5277 @node M68hc1x Options
5278 @subsection M68hc1x Options
5279 @cindex M68hc1x options
5281 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5282 microcontrollers. The default values for these options depends on
5283 which style of microcontroller was selected when the compiler was configured;
5284 the defaults for the most common choices are given below.
5291 Generate output for a 68HC11. This is the default
5292 when the compiler is configured for 68HC11-based systems.
5298 Generate output for a 68HC12. This is the default
5299 when the compiler is configured for 68HC12-based systems.
5302 @opindex mauto-incdec
5303 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5308 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5310 @item -msoft-reg-count=@var{count}
5311 @opindex msoft-reg-count
5312 Specify the number of pseudo-soft registers which are used for the
5313 code generation. The maximum number is 32. Using more pseudo-soft
5314 register may or may not result in better code depending on the program.
5315 The default is 4 for 68HC11 and 2 for 68HC12.
5320 @subsection VAX Options
5323 These @samp{-m} options are defined for the VAX:
5328 Do not output certain jump instructions (@code{aobleq} and so on)
5329 that the Unix assembler for the VAX cannot handle across long
5334 Do output those jump instructions, on the assumption that you
5335 will assemble with the GNU assembler.
5339 Output code for g-format floating point numbers instead of d-format.
5343 @subsection SPARC Options
5344 @cindex SPARC options
5346 These @samp{-m} switches are supported on the SPARC:
5351 @opindex mno-app-regs
5353 Specify @option{-mapp-regs} to generate output using the global registers
5354 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5357 To be fully SVR4 ABI compliant at the cost of some performance loss,
5358 specify @option{-mno-app-regs}. You should compile libraries and system
5359 software with this option.
5364 @opindex mhard-float
5365 Generate output containing floating point instructions. This is the
5371 @opindex msoft-float
5372 Generate output containing library calls for floating point.
5373 @strong{Warning:} the requisite libraries are not available for all SPARC
5374 targets. Normally the facilities of the machine's usual C compiler are
5375 used, but this cannot be done directly in cross-compilation. You must make
5376 your own arrangements to provide suitable library functions for
5377 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5378 @samp{sparclite-*-*} do provide software floating point support.
5380 @option{-msoft-float} changes the calling convention in the output file;
5381 therefore, it is only useful if you compile @emph{all} of a program with
5382 this option. In particular, you need to compile @file{libgcc.a}, the
5383 library that comes with GCC, with @option{-msoft-float} in order for
5386 @item -mhard-quad-float
5387 @opindex mhard-quad-float
5388 Generate output containing quad-word (long double) floating point
5391 @item -msoft-quad-float
5392 @opindex msoft-quad-float
5393 Generate output containing library calls for quad-word (long double)
5394 floating point instructions. The functions called are those specified
5395 in the SPARC ABI@. This is the default.
5397 As of this writing, there are no sparc implementations that have hardware
5398 support for the quad-word floating point instructions. They all invoke
5399 a trap handler for one of these instructions, and then the trap handler
5400 emulates the effect of the instruction. Because of the trap handler overhead,
5401 this is much slower than calling the ABI library routines. Thus the
5402 @option{-msoft-quad-float} option is the default.
5406 @opindex mno-epilogue
5408 With @option{-mepilogue} (the default), the compiler always emits code for
5409 function exit at the end of each function. Any function exit in
5410 the middle of the function (such as a return statement in C) will
5411 generate a jump to the exit code at the end of the function.
5413 With @option{-mno-epilogue}, the compiler tries to emit exit code inline
5414 at every function exit.
5420 With @option{-mflat}, the compiler does not generate save/restore instructions
5421 and will use a ``flat'' or single register window calling convention.
5422 This model uses %i7 as the frame pointer and is compatible with the normal
5423 register window model. Code from either may be intermixed.
5424 The local registers and the input registers (0--5) are still treated as
5425 ``call saved'' registers and will be saved on the stack as necessary.
5427 With @option{-mno-flat} (the default), the compiler emits save/restore
5428 instructions (except for leaf functions) and is the normal mode of operation.
5430 @item -mno-unaligned-doubles
5431 @itemx -munaligned-doubles
5432 @opindex mno-unaligned-doubles
5433 @opindex munaligned-doubles
5434 Assume that doubles have 8 byte alignment. This is the default.
5436 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
5437 alignment only if they are contained in another type, or if they have an
5438 absolute address. Otherwise, it assumes they have 4 byte alignment.
5439 Specifying this option avoids some rare compatibility problems with code
5440 generated by other compilers. It is not the default because it results
5441 in a performance loss, especially for floating point code.
5443 @item -mno-faster-structs
5444 @itemx -mfaster-structs
5445 @opindex mno-faster-structs
5446 @opindex mfaster-structs
5447 With @option{-mfaster-structs}, the compiler assumes that structures
5448 should have 8 byte alignment. This enables the use of pairs of
5449 @code{ldd} and @code{std} instructions for copies in structure
5450 assignment, in place of twice as many @code{ld} and @code{st} pairs.
5451 However, the use of this changed alignment directly violates the Sparc
5452 ABI@. Thus, it's intended only for use on targets where the developer
5453 acknowledges that their resulting code will not be directly in line with
5454 the rules of the ABI@.
5460 These two options select variations on the SPARC architecture.
5462 By default (unless specifically configured for the Fujitsu SPARClite),
5463 GCC generates code for the v7 variant of the SPARC architecture.
5465 @option{-mv8} will give you SPARC v8 code. The only difference from v7
5466 code is that the compiler emits the integer multiply and integer
5467 divide instructions which exist in SPARC v8 but not in SPARC v7.
5469 @option{-msparclite} will give you SPARClite code. This adds the integer
5470 multiply, integer divide step and scan (@code{ffs}) instructions which
5471 exist in SPARClite but not in SPARC v7.
5473 These options are deprecated and will be deleted in a future GCC release.
5474 They have been replaced with @option{-mcpu=xxx}.
5479 @opindex msupersparc
5480 These two options select the processor for which the code is optimized.
5482 With @option{-mcypress} (the default), the compiler optimizes code for the
5483 Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series.
5484 This is also appropriate for the older SparcStation 1, 2, IPX etc.
5486 With @option{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as
5487 used in the SparcStation 10, 1000 and 2000 series. This flag also enables use
5488 of the full SPARC v8 instruction set.
5490 These options are deprecated and will be deleted in a future GCC release.
5491 They have been replaced with @option{-mcpu=xxx}.
5493 @item -mcpu=@var{cpu_type}
5495 Set the instruction set, register set, and instruction scheduling parameters
5496 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
5497 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
5498 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
5499 @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}.
5501 Default instruction scheduling parameters are used for values that select
5502 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
5503 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
5505 Here is a list of each supported architecture and their supported
5510 v8: supersparc, hypersparc
5511 sparclite: f930, f934, sparclite86x
5516 @item -mtune=@var{cpu_type}
5518 Set the instruction scheduling parameters for machine type
5519 @var{cpu_type}, but do not set the instruction set or register set that the
5520 option @option{-mcpu=@var{cpu_type}} would.
5522 The same values for @option{-mcpu=@var{cpu_type}} can be used for
5523 @option{-mtune=@var{cpu_type}}, but the only useful values are those
5524 that select a particular cpu implementation. Those are @samp{cypress},
5525 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
5526 @samp{sparclite86x}, @samp{tsc701}, and @samp{ultrasparc}.
5530 These @samp{-m} switches are supported in addition to the above
5531 on the SPARCLET processor.
5534 @item -mlittle-endian
5535 @opindex mlittle-endian
5536 Generate code for a processor running in little-endian mode.
5540 Treat register @code{%g0} as a normal register.
5541 GCC will continue to clobber it as necessary but will not assume
5542 it always reads as 0.
5544 @item -mbroken-saverestore
5545 @opindex mbroken-saverestore
5546 Generate code that does not use non-trivial forms of the @code{save} and
5547 @code{restore} instructions. Early versions of the SPARCLET processor do
5548 not correctly handle @code{save} and @code{restore} instructions used with
5549 arguments. They correctly handle them used without arguments. A @code{save}
5550 instruction used without arguments increments the current window pointer
5551 but does not allocate a new stack frame. It is assumed that the window
5552 overflow trap handler will properly handle this case as will interrupt
5556 These @samp{-m} switches are supported in addition to the above
5557 on SPARC V9 processors in 64-bit environments.
5560 @item -mlittle-endian
5561 @opindex mlittle-endian
5562 Generate code for a processor running in little-endian mode.
5568 Generate code for a 32-bit or 64-bit environment.
5569 The 32-bit environment sets int, long and pointer to 32 bits.
5570 The 64-bit environment sets int to 32 bits and long and pointer
5573 @item -mcmodel=medlow
5574 @opindex mcmodel=medlow
5575 Generate code for the Medium/Low code model: the program must be linked
5576 in the low 32 bits of the address space. Pointers are 64 bits.
5577 Programs can be statically or dynamically linked.
5579 @item -mcmodel=medmid
5580 @opindex mcmodel=medmid
5581 Generate code for the Medium/Middle code model: the program must be linked
5582 in the low 44 bits of the address space, the text segment must be less than
5583 2G bytes, and data segment must be within 2G of the text segment.
5584 Pointers are 64 bits.
5586 @item -mcmodel=medany
5587 @opindex mcmodel=medany
5588 Generate code for the Medium/Anywhere code model: the program may be linked
5589 anywhere in the address space, the text segment must be less than
5590 2G bytes, and data segment must be within 2G of the text segment.
5591 Pointers are 64 bits.
5593 @item -mcmodel=embmedany
5594 @opindex mcmodel=embmedany
5595 Generate code for the Medium/Anywhere code model for embedded systems:
5596 assume a 32-bit text and a 32-bit data segment, both starting anywhere
5597 (determined at link time). Register %g4 points to the base of the
5598 data segment. Pointers are still 64 bits.
5599 Programs are statically linked, PIC is not supported.
5602 @itemx -mno-stack-bias
5603 @opindex mstack-bias
5604 @opindex mno-stack-bias
5605 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
5606 frame pointer if present, are offset by @minus{}2047 which must be added back
5607 when making stack frame references.
5608 Otherwise, assume no such offset is present.
5611 @node Convex Options
5612 @subsection Convex Options
5613 @cindex Convex options
5615 These @samp{-m} options are defined for Convex:
5620 Generate output for C1. The code will run on any Convex machine.
5621 The preprocessor symbol @code{__convex__c1__} is defined.
5625 Generate output for C2. Uses instructions not available on C1.
5626 Scheduling and other optimizations are chosen for max performance on C2.
5627 The preprocessor symbol @code{__convex_c2__} is defined.
5631 Generate output for C32xx. Uses instructions not available on C1.
5632 Scheduling and other optimizations are chosen for max performance on C32.
5633 The preprocessor symbol @code{__convex_c32__} is defined.
5637 Generate output for C34xx. Uses instructions not available on C1.
5638 Scheduling and other optimizations are chosen for max performance on C34.
5639 The preprocessor symbol @code{__convex_c34__} is defined.
5643 Generate output for C38xx. Uses instructions not available on C1.
5644 Scheduling and other optimizations are chosen for max performance on C38.
5645 The preprocessor symbol @code{__convex_c38__} is defined.
5649 Generate code which puts an argument count in the word preceding each
5650 argument list. This is compatible with regular CC, and a few programs
5651 may need the argument count word. GDB and other source-level debuggers
5652 do not need it; this info is in the symbol table.
5655 @opindex mnoargcount
5656 Omit the argument count word. This is the default.
5658 @item -mvolatile-cache
5659 @opindex mvolatile-cache
5660 Allow volatile references to be cached. This is the default.
5662 @item -mvolatile-nocache
5663 @opindex mvolatile-nocache
5664 Volatile references bypass the data cache, going all the way to memory.
5665 This is only needed for multi-processor code that does not use standard
5666 synchronization instructions. Making non-volatile references to volatile
5667 locations will not necessarily work.
5671 Type long is 32 bits, the same as type int. This is the default.
5675 Type long is 64 bits, the same as type long long. This option is useless,
5676 because no library support exists for it.
5679 @node AMD29K Options
5680 @subsection AMD29K Options
5681 @cindex AMD29K options
5683 These @samp{-m} options are defined for the AMD Am29000:
5688 @cindex DW bit (29k)
5689 Generate code that assumes the @code{DW} bit is set, i.e., that byte and
5690 halfword operations are directly supported by the hardware. This is the
5695 Generate code that assumes the @code{DW} bit is not set.
5699 @cindex byte writes (29k)
5700 Generate code that assumes the system supports byte and halfword write
5701 operations. This is the default.
5705 Generate code that assumes the systems does not support byte and
5706 halfword write operations. @option{-mnbw} implies @option{-mndw}.
5710 @cindex memory model (29k)
5711 Use a small memory model that assumes that all function addresses are
5712 either within a single 256 KB segment or at an absolute address of less
5713 than 256k. This allows the @code{call} instruction to be used instead
5714 of a @code{const}, @code{consth}, @code{calli} sequence.
5718 Use the normal memory model: Generate @code{call} instructions only when
5719 calling functions in the same file and @code{calli} instructions
5720 otherwise. This works if each file occupies less than 256 KB but allows
5721 the entire executable to be larger than 256 KB@. This is the default.
5725 Always use @code{calli} instructions. Specify this option if you expect
5726 a single file to compile into more than 256 KB of code.
5730 @cindex processor selection (29k)
5731 Generate code for the Am29050.
5735 Generate code for the Am29000. This is the default.
5737 @item -mkernel-registers
5738 @opindex mkernel-registers
5739 @cindex kernel and user registers (29k)
5740 Generate references to registers @code{gr64-gr95} instead of to
5741 registers @code{gr96-gr127}. This option can be used when compiling
5742 kernel code that wants a set of global registers disjoint from that used
5745 Note that when this option is used, register names in @samp{-f} flags
5746 must use the normal, user-mode, names.
5748 @item -muser-registers
5749 @opindex muser-registers
5750 Use the normal set of global registers, @code{gr96-gr127}. This is the
5754 @itemx -mno-stack-check
5755 @opindex mstack-check
5756 @opindex mno-stack-check
5757 @cindex stack checks (29k)
5758 Insert (or do not insert) a call to @code{__msp_check} after each stack
5759 adjustment. This is often used for kernel code.
5762 @itemx -mno-storem-bug
5763 @opindex mstorem-bug
5764 @opindex mno-storem-bug
5765 @cindex storem bug (29k)
5766 @option{-mstorem-bug} handles 29k processors which cannot handle the
5767 separation of a mtsrim insn and a storem instruction (most 29000 chips
5768 to date, but not the 29050).
5770 @item -mno-reuse-arg-regs
5771 @itemx -mreuse-arg-regs
5772 @opindex mno-reuse-arg-regs
5773 @opindex mreuse-arg-regs
5774 @option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument
5775 registers for copying out arguments. This helps detect calling a function
5776 with fewer arguments than it was declared with.
5778 @item -mno-impure-text
5779 @itemx -mimpure-text
5780 @opindex mno-impure-text
5781 @opindex mimpure-text
5782 @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to
5783 not pass @option{-assert pure-text} to the linker when linking a shared object.
5786 @opindex msoft-float
5787 Generate output containing library calls for floating point.
5788 @strong{Warning:} the requisite libraries are not part of GCC@.
5789 Normally the facilities of the machine's usual C compiler are used, but
5790 this can't be done directly in cross-compilation. You must make your
5791 own arrangements to provide suitable library functions for
5796 Do not generate multm or multmu instructions. This is useful for some embedded
5797 systems which do not have trap handlers for these instructions.
5801 @subsection ARM Options
5804 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
5809 @opindex mapcs-frame
5810 Generate a stack frame that is compliant with the ARM Procedure Call
5811 Standard for all functions, even if this is not strictly necessary for
5812 correct execution of the code. Specifying @option{-fomit-frame-pointer}
5813 with this option will cause the stack frames not to be generated for
5814 leaf functions. The default is @option{-mno-apcs-frame}.
5818 This is a synonym for @option{-mapcs-frame}.
5822 Generate code for a processor running with a 26-bit program counter,
5823 and conforming to the function calling standards for the APCS 26-bit
5824 option. This option replaces the @option{-m2} and @option{-m3} options
5825 of previous releases of the compiler.
5829 Generate code for a processor running with a 32-bit program counter,
5830 and conforming to the function calling standards for the APCS 32-bit
5831 option. This option replaces the @option{-m6} option of previous releases
5835 @c not currently implemented
5836 @item -mapcs-stack-check
5837 @opindex mapcs-stack-check
5838 Generate code to check the amount of stack space available upon entry to
5839 every function (that actually uses some stack space). If there is
5840 insufficient space available then either the function
5841 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
5842 called, depending upon the amount of stack space required. The run time
5843 system is required to provide these functions. The default is
5844 @option{-mno-apcs-stack-check}, since this produces smaller code.
5846 @c not currently implemented
5848 @opindex mapcs-float
5849 Pass floating point arguments using the float point registers. This is
5850 one of the variants of the APCS@. This option is recommended if the
5851 target hardware has a floating point unit or if a lot of floating point
5852 arithmetic is going to be performed by the code. The default is
5853 @option{-mno-apcs-float}, since integer only code is slightly increased in
5854 size if @option{-mapcs-float} is used.
5856 @c not currently implemented
5857 @item -mapcs-reentrant
5858 @opindex mapcs-reentrant
5859 Generate reentrant, position independent code. The default is
5860 @option{-mno-apcs-reentrant}.
5863 @item -mthumb-interwork
5864 @opindex mthumb-interwork
5865 Generate code which supports calling between the ARM and Thumb
5866 instruction sets. Without this option the two instruction sets cannot
5867 be reliably used inside one program. The default is
5868 @option{-mno-thumb-interwork}, since slightly larger code is generated
5869 when @option{-mthumb-interwork} is specified.
5871 @item -mno-sched-prolog
5872 @opindex mno-sched-prolog
5873 Prevent the reordering of instructions in the function prolog, or the
5874 merging of those instruction with the instructions in the function's
5875 body. This means that all functions will start with a recognizable set
5876 of instructions (or in fact one of a choice from a small set of
5877 different function prologues), and this information can be used to
5878 locate the start if functions inside an executable piece of code. The
5879 default is @option{-msched-prolog}.
5882 @opindex mhard-float
5883 Generate output containing floating point instructions. This is the
5887 @opindex msoft-float
5888 Generate output containing library calls for floating point.
5889 @strong{Warning:} the requisite libraries are not available for all ARM
5890 targets. Normally the facilities of the machine's usual C compiler are
5891 used, but this cannot be done directly in cross-compilation. You must make
5892 your own arrangements to provide suitable library functions for
5895 @option{-msoft-float} changes the calling convention in the output file;
5896 therefore, it is only useful if you compile @emph{all} of a program with
5897 this option. In particular, you need to compile @file{libgcc.a}, the
5898 library that comes with GCC, with @option{-msoft-float} in order for
5901 @item -mlittle-endian
5902 @opindex mlittle-endian
5903 Generate code for a processor running in little-endian mode. This is
5904 the default for all standard configurations.
5907 @opindex mbig-endian
5908 Generate code for a processor running in big-endian mode; the default is
5909 to compile code for a little-endian processor.
5911 @item -mwords-little-endian
5912 @opindex mwords-little-endian
5913 This option only applies when generating code for big-endian processors.
5914 Generate code for a little-endian word order but a big-endian byte
5915 order. That is, a byte order of the form @samp{32107654}. Note: this
5916 option should only be used if you require compatibility with code for
5917 big-endian ARM processors generated by versions of the compiler prior to
5920 @item -malignment-traps
5921 @opindex malignment-traps
5922 Generate code that will not trap if the MMU has alignment traps enabled.
5923 On ARM architectures prior to ARMv4, there were no instructions to
5924 access half-word objects stored in memory. However, when reading from
5925 memory a feature of the ARM architecture allows a word load to be used,
5926 even if the address is unaligned, and the processor core will rotate the
5927 data as it is being loaded. This option tells the compiler that such
5928 misaligned accesses will cause a MMU trap and that it should instead
5929 synthesise the access as a series of byte accesses. The compiler can
5930 still use word accesses to load half-word data if it knows that the
5931 address is aligned to a word boundary.
5933 This option is ignored when compiling for ARM architecture 4 or later,
5934 since these processors have instructions to directly access half-word
5937 @item -mno-alignment-traps
5938 @opindex mno-alignment-traps
5939 Generate code that assumes that the MMU will not trap unaligned
5940 accesses. This produces better code when the target instruction set
5941 does not have half-word memory operations (i.e.@: implementations prior to
5944 Note that you cannot use this option to access unaligned word objects,
5945 since the processor will only fetch one 32-bit aligned object from
5948 The default setting for most targets is @option{-mno-alignment-traps}, since
5949 this produces better code when there are no half-word memory
5950 instructions available.
5952 @item -mshort-load-bytes
5953 @itemx -mno-short-load-words
5954 @opindex mshort-load-bytes
5955 @opindex mno-short-load-words
5956 These are deprecated aliases for @option{-malignment-traps}.
5958 @item -mno-short-load-bytes
5959 @itemx -mshort-load-words
5960 @opindex mno-short-load-bytes
5961 @opindex mshort-load-words
5962 This are deprecated aliases for @option{-mno-alignment-traps}.
5966 This option only applies to RISC iX@. Emulate the native BSD-mode
5967 compiler. This is the default if @option{-ansi} is not specified.
5971 This option only applies to RISC iX@. Emulate the native X/Open-mode
5974 @item -mno-symrename
5975 @opindex mno-symrename
5976 This option only applies to RISC iX@. Do not run the assembler
5977 post-processor, @samp{symrename}, after code has been assembled.
5978 Normally it is necessary to modify some of the standard symbols in
5979 preparation for linking with the RISC iX C library; this option
5980 suppresses this pass. The post-processor is never run when the
5981 compiler is built for cross-compilation.
5983 @item -mcpu=@var{name}
5985 This specifies the name of the target ARM processor. GCC uses this name
5986 to determine what kind of instructions it can emit when generating
5987 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
5988 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
5989 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
5990 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
5991 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
5992 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
5993 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
5994 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
5995 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
5996 @samp{arm1020t}, @samp{xscale}.
5998 @itemx -mtune=@var{name}
6000 This option is very similar to the @option{-mcpu=} option, except that
6001 instead of specifying the actual target processor type, and hence
6002 restricting which instructions can be used, it specifies that GCC should
6003 tune the performance of the code as if the target were of the type
6004 specified in this option, but still choosing the instructions that it
6005 will generate based on the cpu specified by a @option{-mcpu=} option.
6006 For some ARM implementations better performance can be obtained by using
6009 @item -march=@var{name}
6011 This specifies the name of the target ARM architecture. GCC uses this
6012 name to determine what kind of instructions it can emit when generating
6013 assembly code. This option can be used in conjunction with or instead
6014 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6015 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6016 @samp{armv5}, @samp{armv5t}, @samp{armv5te}.
6018 @item -mfpe=@var{number}
6019 @itemx -mfp=@var{number}
6022 This specifies the version of the floating point emulation available on
6023 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6024 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6026 @item -mstructure-size-boundary=@var{n}
6027 @opindex mstructure-size-boundary
6028 The size of all structures and unions will be rounded up to a multiple
6029 of the number of bits set by this option. Permissible values are 8 and
6030 32. The default value varies for different toolchains. For the COFF
6031 targeted toolchain the default value is 8. Specifying the larger number
6032 can produce faster, more efficient code, but can also increase the size
6033 of the program. The two values are potentially incompatible. Code
6034 compiled with one value cannot necessarily expect to work with code or
6035 libraries compiled with the other value, if they exchange information
6036 using structures or unions.
6038 @item -mabort-on-noreturn
6039 @opindex mabort-on-noreturn
6040 Generate a call to the function @code{abort} at the end of a
6041 @code{noreturn} function. It will be executed if the function tries to
6045 @itemx -mno-long-calls
6046 @opindex mlong-calls
6047 @opindex mno-long-calls
6048 Tells the compiler to perform function calls by first loading the
6049 address of the function into a register and then performing a subroutine
6050 call on this register. This switch is needed if the target function
6051 will lie outside of the 64 megabyte addressing range of the offset based
6052 version of subroutine call instruction.
6054 Even if this switch is enabled, not all function calls will be turned
6055 into long calls. The heuristic is that static functions, functions
6056 which have the @samp{short-call} attribute, functions that are inside
6057 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6058 definitions have already been compiled within the current compilation
6059 unit, will not be turned into long calls. The exception to this rule is
6060 that weak function definitions, functions with the @samp{long-call}
6061 attribute or the @samp{section} attribute, and functions that are within
6062 the scope of a @samp{#pragma long_calls} directive, will always be
6063 turned into long calls.
6065 This feature is not enabled by default. Specifying
6066 @option{-mno-long-calls} will restore the default behavior, as will
6067 placing the function calls within the scope of a @samp{#pragma
6068 long_calls_off} directive. Note these switches have no effect on how
6069 the compiler generates code to handle function calls via function
6072 @item -mnop-fun-dllimport
6073 @opindex mnop-fun-dllimport
6074 Disable support for the @code{dllimport} attribute.
6076 @item -msingle-pic-base
6077 @opindex msingle-pic-base
6078 Treat the register used for PIC addressing as read-only, rather than
6079 loading it in the prologue for each function. The run-time system is
6080 responsible for initializing this register with an appropriate value
6081 before execution begins.
6083 @item -mpic-register=@var{reg}
6084 @opindex mpic-register
6085 Specify the register to be used for PIC addressing. The default is R10
6086 unless stack-checking is enabled, when R9 is used.
6088 @item -mpoke-function-name
6089 @opindex mpoke-function-name
6090 Write the name of each function into the text section, directly
6091 preceding the function prologue. The generated code is similar to this:
6095 .ascii "arm_poke_function_name", 0
6098 .word 0xff000000 + (t1 - t0)
6099 arm_poke_function_name
6101 stmfd sp!, @{fp, ip, lr, pc@}
6105 When performing a stack backtrace, code can inspect the value of
6106 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6107 location @code{pc - 12} and the top 8 bits are set, then we know that
6108 there is a function name embedded immediately preceding this location
6109 and has length @code{((pc[-3]) & 0xff000000)}.
6113 Generate code for the 16-bit Thumb instruction set. The default is to
6114 use the 32-bit ARM instruction set.
6117 @opindex mtpcs-frame
6118 Generate a stack frame that is compliant with the Thumb Procedure Call
6119 Standard for all non-leaf functions. (A leaf function is one that does
6120 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6122 @item -mtpcs-leaf-frame
6123 @opindex mtpcs-leaf-frame
6124 Generate a stack frame that is compliant with the Thumb Procedure Call
6125 Standard for all leaf functions. (A leaf function is one that does
6126 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6128 @item -mcallee-super-interworking
6129 @opindex mcallee-super-interworking
6130 Gives all externally visible functions in the file being compiled an ARM
6131 instruction set header which switches to Thumb mode before executing the
6132 rest of the function. This allows these functions to be called from
6133 non-interworking code.
6135 @item -mcaller-super-interworking
6136 @opindex mcaller-super-interworking
6137 Allows calls via function pointers (including virtual functions) to
6138 execute correctly regardless of whether the target code has been
6139 compiled for interworking or not. There is a small overhead in the cost
6140 of executing a function pointer if this option is enabled.
6144 @node MN10200 Options
6145 @subsection MN10200 Options
6146 @cindex MN10200 options
6147 These @option{-m} options are defined for Matsushita MN10200 architectures:
6152 Indicate to the linker that it should perform a relaxation optimization pass
6153 to shorten branches, calls and absolute memory addresses. This option only
6154 has an effect when used on the command line for the final link step.
6156 This option makes symbolic debugging impossible.
6159 @node MN10300 Options
6160 @subsection MN10300 Options
6161 @cindex MN10300 options
6162 These @option{-m} options are defined for Matsushita MN10300 architectures:
6167 Generate code to avoid bugs in the multiply instructions for the MN10300
6168 processors. This is the default.
6171 @opindex mno-mult-bug
6172 Do not generate code to avoid bugs in the multiply instructions for the
6177 Generate code which uses features specific to the AM33 processor.
6181 Do not generate code which uses features specific to the AM33 processor. This
6186 Do not link in the C run-time initialization object file.
6190 Indicate to the linker that it should perform a relaxation optimization pass
6191 to shorten branches, calls and absolute memory addresses. This option only
6192 has an effect when used on the command line for the final link step.
6194 This option makes symbolic debugging impossible.
6198 @node M32R/D Options
6199 @subsection M32R/D Options
6200 @cindex M32R/D options
6202 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6207 Generate code for the M32R/X@.
6211 Generate code for the M32R@. This is the default.
6213 @item -mcode-model=small
6214 @opindex mcode-model=small
6215 Assume all objects live in the lower 16MB of memory (so that their addresses
6216 can be loaded with the @code{ld24} instruction), and assume all subroutines
6217 are reachable with the @code{bl} instruction.
6218 This is the default.
6220 The addressability of a particular object can be set with the
6221 @code{model} attribute.
6223 @item -mcode-model=medium
6224 @opindex mcode-model=medium
6225 Assume objects may be anywhere in the 32-bit address space (the compiler
6226 will generate @code{seth/add3} instructions to load their addresses), and
6227 assume all subroutines are reachable with the @code{bl} instruction.
6229 @item -mcode-model=large
6230 @opindex mcode-model=large
6231 Assume objects may be anywhere in the 32-bit address space (the compiler
6232 will generate @code{seth/add3} instructions to load their addresses), and
6233 assume subroutines may not be reachable with the @code{bl} instruction
6234 (the compiler will generate the much slower @code{seth/add3/jl}
6235 instruction sequence).
6238 @opindex msdata=none
6239 Disable use of the small data area. Variables will be put into
6240 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6241 @code{section} attribute has been specified).
6242 This is the default.
6244 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6245 Objects may be explicitly put in the small data area with the
6246 @code{section} attribute using one of these sections.
6249 @opindex msdata=sdata
6250 Put small global and static data in the small data area, but do not
6251 generate special code to reference them.
6255 Put small global and static data in the small data area, and generate
6256 special instructions to reference them.
6260 @cindex smaller data references
6261 Put global and static objects less than or equal to @var{num} bytes
6262 into the small data or bss sections instead of the normal data or bss
6263 sections. The default value of @var{num} is 8.
6264 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6265 for this option to have any effect.
6267 All modules should be compiled with the same @option{-G @var{num}} value.
6268 Compiling with different values of @var{num} may or may not work; if it
6269 doesn't the linker will give an error message---incorrect code will not be
6275 @subsection M88K Options
6276 @cindex M88k options
6278 These @samp{-m} options are defined for Motorola 88k architectures:
6283 Generate code that works well on both the m88100 and the
6288 Generate code that works best for the m88100, but that also
6293 Generate code that works best for the m88110, and may not run
6298 Obsolete option to be removed from the next revision.
6301 @item -midentify-revision
6302 @opindex midentify-revision
6303 @cindex identifying source, compiler (88k)
6304 Include an @code{ident} directive in the assembler output recording the
6305 source file name, compiler name and version, timestamp, and compilation
6308 @item -mno-underscores
6309 @opindex mno-underscores
6310 @cindex underscores, avoiding (88k)
6311 In assembler output, emit symbol names without adding an underscore
6312 character at the beginning of each name. The default is to use an
6313 underscore as prefix on each name.
6315 @item -mocs-debug-info
6316 @itemx -mno-ocs-debug-info
6317 @opindex mocs-debug-info
6318 @opindex mno-ocs-debug-info
6320 @cindex debugging, 88k OCS
6321 Include (or omit) additional debugging information (about registers used
6322 in each stack frame) as specified in the 88open Object Compatibility
6323 Standard, ``OCS''@. This extra information allows debugging of code that
6324 has had the frame pointer eliminated. The default for DG/UX, SVr4, and
6325 Delta 88 SVr3.2 is to include this information; other 88k configurations
6326 omit this information by default.
6328 @item -mocs-frame-position
6329 @opindex mocs-frame-position
6330 @cindex register positions in frame (88k)
6331 When emitting COFF debugging information for automatic variables and
6332 parameters stored on the stack, use the offset from the canonical frame
6333 address, which is the stack pointer (register 31) on entry to the
6334 function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
6335 @option{-mocs-frame-position}; other 88k configurations have the default
6336 @option{-mno-ocs-frame-position}.
6338 @item -mno-ocs-frame-position
6339 @opindex mno-ocs-frame-position
6340 @cindex register positions in frame (88k)
6341 When emitting COFF debugging information for automatic variables and
6342 parameters stored on the stack, use the offset from the frame pointer
6343 register (register 30). When this option is in effect, the frame
6344 pointer is not eliminated when debugging information is selected by the
6347 @item -moptimize-arg-area
6348 @opindex moptimize-arg-area
6349 @cindex arguments in frame (88k)
6350 Save space by reorganizing the stack frame. This option generates code
6351 that does not agree with the 88open specifications, but uses less
6354 @itemx -mno-optimize-arg-area
6355 @opindex mno-optimize-arg-area
6356 Do not reorganize the stack frame to save space. This is the default.
6357 The generated conforms to the specification, but uses more memory.
6359 @item -mshort-data-@var{num}
6360 @opindex mshort-data
6361 @cindex smaller data references (88k)
6362 @cindex r0-relative references (88k)
6363 Generate smaller data references by making them relative to @code{r0},
6364 which allows loading a value using a single instruction (rather than the
6365 usual two). You control which data references are affected by
6366 specifying @var{num} with this option. For example, if you specify
6367 @option{-mshort-data-512}, then the data references affected are those
6368 involving displacements of less than 512 bytes.
6369 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6372 @item -mserialize-volatile
6373 @opindex mserialize-volatile
6374 @itemx -mno-serialize-volatile
6375 @opindex mno-serialize-volatile
6376 @cindex sequential consistency on 88k
6377 Do, or don't, generate code to guarantee sequential consistency
6378 of volatile memory references. By default, consistency is
6381 The order of memory references made by the MC88110 processor does
6382 not always match the order of the instructions requesting those
6383 references. In particular, a load instruction may execute before
6384 a preceding store instruction. Such reordering violates
6385 sequential consistency of volatile memory references, when there
6386 are multiple processors. When consistency must be guaranteed,
6387 GCC generates special instructions, as needed, to force
6388 execution in the proper order.
6390 The MC88100 processor does not reorder memory references and so
6391 always provides sequential consistency. However, by default, GCC
6392 generates the special instructions to guarantee consistency
6393 even when you use @option{-m88100}, so that the code may be run on an
6394 MC88110 processor. If you intend to run your code only on the
6395 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6397 The extra code generated to guarantee consistency may affect the
6398 performance of your application. If you know that you can safely
6399 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6405 @cindex assembler syntax, 88k
6407 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6408 related to System V release 4 (SVr4). This controls the following:
6412 Which variant of the assembler syntax to emit.
6414 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6415 that is used on System V release 4.
6417 @option{-msvr4} makes GCC issue additional declaration directives used in
6421 @option{-msvr4} is the default for the m88k-motorola-sysv4 and
6422 m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all
6423 other m88k configurations.
6425 @item -mversion-03.00
6426 @opindex mversion-03.00
6427 This option is obsolete, and is ignored.
6428 @c ??? which asm syntax better for GAS? option there too?
6430 @item -mno-check-zero-division
6431 @itemx -mcheck-zero-division
6432 @opindex mno-check-zero-division
6433 @opindex mcheck-zero-division
6434 @cindex zero division on 88k
6435 Do, or don't, generate code to guarantee that integer division by
6436 zero will be detected. By default, detection is guaranteed.
6438 Some models of the MC88100 processor fail to trap upon integer
6439 division by zero under certain conditions. By default, when
6440 compiling code that might be run on such a processor, GCC
6441 generates code that explicitly checks for zero-valued divisors
6442 and traps with exception number 503 when one is detected. Use of
6443 @option{-mno-check-zero-division} suppresses such checking for code
6444 generated to run on an MC88100 processor.
6446 GCC assumes that the MC88110 processor correctly detects all instances
6447 of integer division by zero. When @option{-m88110} is specified, no
6448 explicit checks for zero-valued divisors are generated, and both
6449 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6452 @item -muse-div-instruction
6453 @opindex muse-div-instruction
6454 @cindex divide instruction, 88k
6455 Use the div instruction for signed integer division on the
6456 MC88100 processor. By default, the div instruction is not used.
6458 On the MC88100 processor the signed integer division instruction
6459 div) traps to the operating system on a negative operand. The
6460 operating system transparently completes the operation, but at a
6461 large cost in execution time. By default, when compiling code
6462 that might be run on an MC88100 processor, GCC emulates signed
6463 integer division using the unsigned integer division instruction
6464 divu), thereby avoiding the large penalty of a trap to the
6465 operating system. Such emulation has its own, smaller, execution
6466 cost in both time and space. To the extent that your code's
6467 important signed integer division operations are performed on two
6468 nonnegative operands, it may be desirable to use the div
6469 instruction directly.
6471 On the MC88110 processor the div instruction (also known as the
6472 divs instruction) processes negative operands without trapping to
6473 the operating system. When @option{-m88110} is specified,
6474 @option{-muse-div-instruction} is ignored, and the div instruction is used
6475 for signed integer division.
6477 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6478 particular, the behavior of such a division with and without
6479 @option{-muse-div-instruction} may differ.
6481 @item -mtrap-large-shift
6482 @itemx -mhandle-large-shift
6483 @opindex mtrap-large-shift
6484 @opindex mhandle-large-shift
6485 @cindex bit shift overflow (88k)
6486 @cindex large bit shifts (88k)
6487 Include code to detect bit-shifts of more than 31 bits; respectively,
6488 trap such shifts or emit code to handle them properly. By default GCC
6489 makes no special provision for large bit shifts.
6491 @item -mwarn-passed-structs
6492 @opindex mwarn-passed-structs
6493 @cindex structure passing (88k)
6494 Warn when a function passes a struct as an argument or result.
6495 Structure-passing conventions have changed during the evolution of the C
6496 language, and are often the source of portability problems. By default,
6497 GCC issues no such warning.
6500 @c break page here to avoid unsightly interparagraph stretch.
6504 @node RS/6000 and PowerPC Options
6505 @subsection IBM RS/6000 and PowerPC Options
6506 @cindex RS/6000 and PowerPC Options
6507 @cindex IBM RS/6000 and PowerPC Options
6509 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6517 @itemx -mpowerpc-gpopt
6518 @itemx -mno-powerpc-gpopt
6519 @itemx -mpowerpc-gfxopt
6520 @itemx -mno-powerpc-gfxopt
6522 @itemx -mno-powerpc64
6528 @opindex mno-powerpc
6529 @opindex mpowerpc-gpopt
6530 @opindex mno-powerpc-gpopt
6531 @opindex mpowerpc-gfxopt
6532 @opindex mno-powerpc-gfxopt
6534 @opindex mno-powerpc64
6535 GCC supports two related instruction set architectures for the
6536 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6537 instructions supported by the @samp{rios} chip set used in the original
6538 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6539 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6540 the IBM 4xx microprocessors.
6542 Neither architecture is a subset of the other. However there is a
6543 large common subset of instructions supported by both. An MQ
6544 register is included in processors supporting the POWER architecture.
6546 You use these options to specify which instructions are available on the
6547 processor you are using. The default value of these options is
6548 determined when configuring GCC@. Specifying the
6549 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6550 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6551 rather than the options listed above.
6553 The @option{-mpower} option allows GCC to generate instructions that
6554 are found only in the POWER architecture and to use the MQ register.
6555 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6556 to generate instructions that are present in the POWER2 architecture but
6557 not the original POWER architecture.
6559 The @option{-mpowerpc} option allows GCC to generate instructions that
6560 are found only in the 32-bit subset of the PowerPC architecture.
6561 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6562 GCC to use the optional PowerPC architecture instructions in the
6563 General Purpose group, including floating-point square root. Specifying
6564 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6565 use the optional PowerPC architecture instructions in the Graphics
6566 group, including floating-point select.
6568 The @option{-mpowerpc64} option allows GCC to generate the additional
6569 64-bit instructions that are found in the full PowerPC64 architecture
6570 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6571 @option{-mno-powerpc64}.
6573 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6574 will use only the instructions in the common subset of both
6575 architectures plus some special AIX common-mode calls, and will not use
6576 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6577 permits GCC to use any instruction from either architecture and to
6578 allow use of the MQ register; specify this for the Motorola MPC601.
6580 @item -mnew-mnemonics
6581 @itemx -mold-mnemonics
6582 @opindex mnew-mnemonics
6583 @opindex mold-mnemonics
6584 Select which mnemonics to use in the generated assembler code. With
6585 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
6586 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
6587 assembler mnemonics defined for the POWER architecture. Instructions
6588 defined in only one architecture have only one mnemonic; GCC uses that
6589 mnemonic irrespective of which of these options is specified.
6591 GCC defaults to the mnemonics appropriate for the architecture in
6592 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6593 value of these option. Unless you are building a cross-compiler, you
6594 should normally not specify either @option{-mnew-mnemonics} or
6595 @option{-mold-mnemonics}, but should instead accept the default.
6597 @item -mcpu=@var{cpu_type}
6599 Set architecture type, register usage, choice of mnemonics, and
6600 instruction scheduling parameters for machine type @var{cpu_type}.
6601 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6602 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6603 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6604 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
6605 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
6606 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
6608 @option{-mcpu=common} selects a completely generic processor. Code
6609 generated under this option will run on any POWER or PowerPC processor.
6610 GCC will use only the instructions in the common subset of both
6611 architectures, and will not use the MQ register. GCC assumes a generic
6612 processor model for scheduling purposes.
6614 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
6615 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
6616 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
6617 types, with an appropriate, generic processor model assumed for
6618 scheduling purposes.
6620 The other options specify a specific processor. Code generated under
6621 those options will run best on that processor, and may not run at all on
6624 The @option{-mcpu} options automatically enable or disable other
6625 @option{-m} options as follows:
6629 @option{-mno-power}, @option{-mno-powerc}
6636 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
6651 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6654 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6659 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
6662 @item -mtune=@var{cpu_type}
6664 Set the instruction scheduling parameters for machine type
6665 @var{cpu_type}, but do not set the architecture type, register usage, or
6666 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
6667 values for @var{cpu_type} are used for @option{-mtune} as for
6668 @option{-mcpu}. If both are specified, the code generated will use the
6669 architecture, registers, and mnemonics set by @option{-mcpu}, but the
6670 scheduling parameters set by @option{-mtune}.
6675 @opindex mno-altivec
6676 These switches enable or disable the use of built-in functions that
6677 allow access to the AltiVec instruction set. You may also need to set
6678 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
6682 @itemx -mno-fp-in-toc
6683 @itemx -mno-sum-in-toc
6684 @itemx -mminimal-toc
6686 @opindex mno-fp-in-toc
6687 @opindex mno-sum-in-toc
6688 @opindex mminimal-toc
6689 Modify generation of the TOC (Table Of Contents), which is created for
6690 every executable file. The @option{-mfull-toc} option is selected by
6691 default. In that case, GCC will allocate at least one TOC entry for
6692 each unique non-automatic variable reference in your program. GCC
6693 will also place floating-point constants in the TOC@. However, only
6694 16,384 entries are available in the TOC@.
6696 If you receive a linker error message that saying you have overflowed
6697 the available TOC space, you can reduce the amount of TOC space used
6698 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
6699 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
6700 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
6701 generate code to calculate the sum of an address and a constant at
6702 run-time instead of putting that sum into the TOC@. You may specify one
6703 or both of these options. Each causes GCC to produce very slightly
6704 slower and larger code at the expense of conserving TOC space.
6706 If you still run out of space in the TOC even when you specify both of
6707 these options, specify @option{-mminimal-toc} instead. This option causes
6708 GCC to make only one TOC entry for every file. When you specify this
6709 option, GCC will produce code that is slower and larger but which
6710 uses extremely little TOC space. You may wish to use this option
6711 only on files that contain less frequently executed code.
6717 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
6718 @code{long} type, and the infrastructure needed to support them.
6719 Specifying @option{-maix64} implies @option{-mpowerpc64} and
6720 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
6721 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
6726 @opindex mno-xl-call
6727 On AIX, pass floating-point arguments to prototyped functions beyond the
6728 register save area (RSA) on the stack in addition to argument FPRs. The
6729 AIX calling convention was extended but not initially documented to
6730 handle an obscure K&R C case of calling a function that takes the
6731 address of its arguments with fewer arguments than declared. AIX XL
6732 compilers access floating point arguments which do not fit in the
6733 RSA from the stack when a subroutine is compiled without
6734 optimization. Because always storing floating-point arguments on the
6735 stack is inefficient and rarely needed, this option is not enabled by
6736 default and only is necessary when calling subroutines compiled by AIX
6737 XL compilers without optimization.
6741 Support @dfn{AIX Threads}. Link an application written to use
6742 @dfn{pthreads} with special libraries and startup code to enable the
6747 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
6748 application written to use message passing with special startup code to
6749 enable the application to run. The system must have PE installed in the
6750 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
6751 must be overridden with the @option{-specs=} option to specify the
6752 appropriate directory location. The Parallel Environment does not
6753 support threads, so the @option{-mpe} option and the @option{-mthreads}
6754 option are incompatible.
6758 @opindex msoft-float
6759 @opindex mhard-float
6760 Generate code that does not use (uses) the floating-point register set.
6761 Software floating point emulation is provided if you use the
6762 @option{-msoft-float} option, and pass the option to GCC when linking.
6765 @itemx -mno-multiple
6767 @opindex mno-multiple
6768 Generate code that uses (does not use) the load multiple word
6769 instructions and the store multiple word instructions. These
6770 instructions are generated by default on POWER systems, and not
6771 generated on PowerPC systems. Do not use @option{-mmultiple} on little
6772 endian PowerPC systems, since those instructions do not work when the
6773 processor is in little endian mode. The exceptions are PPC740 and
6774 PPC750 which permit the instructions usage in little endian mode.
6780 Generate code that uses (does not use) the load string instructions
6781 and the store string word instructions to save multiple registers and
6782 do small block moves. These instructions are generated by default on
6783 POWER systems, and not generated on PowerPC systems. Do not use
6784 @option{-mstring} on little endian PowerPC systems, since those
6785 instructions do not work when the processor is in little endian mode.
6786 The exceptions are PPC740 and PPC750 which permit the instructions
6787 usage in little endian mode.
6793 Generate code that uses (does not use) the load or store instructions
6794 that update the base register to the address of the calculated memory
6795 location. These instructions are generated by default. If you use
6796 @option{-mno-update}, there is a small window between the time that the
6797 stack pointer is updated and the address of the previous frame is
6798 stored, which means code that walks the stack frame across interrupts or
6799 signals may get corrupted data.
6802 @itemx -mno-fused-madd
6803 @opindex mfused-madd
6804 @opindex mno-fused-madd
6805 Generate code that uses (does not use) the floating point multiply and
6806 accumulate instructions. These instructions are generated by default if
6807 hardware floating is used.
6809 @item -mno-bit-align
6811 @opindex mno-bit-align
6813 On System V.4 and embedded PowerPC systems do not (do) force structures
6814 and unions that contain bit-fields to be aligned to the base type of the
6817 For example, by default a structure containing nothing but 8
6818 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
6819 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
6820 the structure would be aligned to a 1 byte boundary and be one byte in
6823 @item -mno-strict-align
6824 @itemx -mstrict-align
6825 @opindex mno-strict-align
6826 @opindex mstrict-align
6827 On System V.4 and embedded PowerPC systems do not (do) assume that
6828 unaligned memory references will be handled by the system.
6831 @itemx -mno-relocatable
6832 @opindex mrelocatable
6833 @opindex mno-relocatable
6834 On embedded PowerPC systems generate code that allows (does not allow)
6835 the program to be relocated to a different address at runtime. If you
6836 use @option{-mrelocatable} on any module, all objects linked together must
6837 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
6839 @item -mrelocatable-lib
6840 @itemx -mno-relocatable-lib
6841 @opindex mrelocatable-lib
6842 @opindex mno-relocatable-lib
6843 On embedded PowerPC systems generate code that allows (does not allow)
6844 the program to be relocated to a different address at runtime. Modules
6845 compiled with @option{-mrelocatable-lib} can be linked with either modules
6846 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
6847 with modules compiled with the @option{-mrelocatable} options.
6853 On System V.4 and embedded PowerPC systems do not (do) assume that
6854 register 2 contains a pointer to a global area pointing to the addresses
6855 used in the program.
6858 @itemx -mlittle-endian
6860 @opindex mlittle-endian
6861 On System V.4 and embedded PowerPC systems compile code for the
6862 processor in little endian mode. The @option{-mlittle-endian} option is
6863 the same as @option{-mlittle}.
6868 @opindex mbig-endian
6869 On System V.4 and embedded PowerPC systems compile code for the
6870 processor in big endian mode. The @option{-mbig-endian} option is
6871 the same as @option{-mbig}.
6875 On System V.4 and embedded PowerPC systems compile code using calling
6876 conventions that adheres to the March 1995 draft of the System V
6877 Application Binary Interface, PowerPC processor supplement. This is the
6878 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
6880 @item -mcall-sysv-eabi
6881 @opindex mcall-sysv-eabi
6882 Specify both @option{-mcall-sysv} and @option{-meabi} options.
6884 @item -mcall-sysv-noeabi
6885 @opindex mcall-sysv-noeabi
6886 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
6890 On System V.4 and embedded PowerPC systems compile code using calling
6891 conventions that are similar to those used on AIX@. This is the
6892 default if you configured GCC using @samp{powerpc-*-eabiaix}.
6894 @item -mcall-solaris
6895 @opindex mcall-solaris
6896 On System V.4 and embedded PowerPC systems compile code for the Solaris
6900 @opindex mcall-linux
6901 On System V.4 and embedded PowerPC systems compile code for the
6902 Linux-based GNU system.
6905 @opindex mcall-netbsd
6906 On System V.4 and embedded PowerPC systems compile code for the
6907 NetBSD operating system.
6909 @item -maix-struct-return
6910 @opindex maix-struct-return
6911 Return all structures in memory (as specified by the AIX ABI)@.
6913 @item -msvr4-struct-return
6914 @opindex msvr4-struct-return
6915 Return structures smaller than 8 bytes in registers (as specified by the
6919 @opindex mabi=altivec
6920 Extend the current ABI with AltiVec ABI extensions. This does not
6921 change the default ABI, instead it adds the AltiVec ABI extensions to
6925 @itemx -mno-prototype
6927 @opindex mno-prototype
6928 On System V.4 and embedded PowerPC systems assume that all calls to
6929 variable argument functions are properly prototyped. Otherwise, the
6930 compiler must insert an instruction before every non prototyped call to
6931 set or clear bit 6 of the condition code register (@var{CR}) to
6932 indicate whether floating point values were passed in the floating point
6933 registers in case the function takes a variable arguments. With
6934 @option{-mprototype}, only calls to prototyped variable argument functions
6935 will set or clear the bit.
6939 On embedded PowerPC systems, assume that the startup module is called
6940 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
6941 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
6946 On embedded PowerPC systems, assume that the startup module is called
6947 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
6952 On embedded PowerPC systems, assume that the startup module is called
6953 @file{crt0.o} and the standard C libraries are @file{libads.a} and
6957 @opindex myellowknife
6958 On embedded PowerPC systems, assume that the startup module is called
6959 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
6964 On System V.4 and embedded PowerPC systems, specify that you are
6965 compiling for a VxWorks system.
6969 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
6970 header to indicate that @samp{eabi} extended relocations are used.
6976 On System V.4 and embedded PowerPC systems do (do not) adhere to the
6977 Embedded Applications Binary Interface (eabi) which is a set of
6978 modifications to the System V.4 specifications. Selecting @option{-meabi}
6979 means that the stack is aligned to an 8 byte boundary, a function
6980 @code{__eabi} is called to from @code{main} to set up the eabi
6981 environment, and the @option{-msdata} option can use both @code{r2} and
6982 @code{r13} to point to two separate small data areas. Selecting
6983 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
6984 do not call an initialization function from @code{main}, and the
6985 @option{-msdata} option will only use @code{r13} to point to a single
6986 small data area. The @option{-meabi} option is on by default if you
6987 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
6990 @opindex msdata=eabi
6991 On System V.4 and embedded PowerPC systems, put small initialized
6992 @code{const} global and static data in the @samp{.sdata2} section, which
6993 is pointed to by register @code{r2}. Put small initialized
6994 non-@code{const} global and static data in the @samp{.sdata} section,
6995 which is pointed to by register @code{r13}. Put small uninitialized
6996 global and static data in the @samp{.sbss} section, which is adjacent to
6997 the @samp{.sdata} section. The @option{-msdata=eabi} option is
6998 incompatible with the @option{-mrelocatable} option. The
6999 @option{-msdata=eabi} option also sets the @option{-memb} option.
7002 @opindex msdata=sysv
7003 On System V.4 and embedded PowerPC systems, put small global and static
7004 data in the @samp{.sdata} section, which is pointed to by register
7005 @code{r13}. Put small uninitialized global and static data in the
7006 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7007 The @option{-msdata=sysv} option is incompatible with the
7008 @option{-mrelocatable} option.
7010 @item -msdata=default
7012 @opindex msdata=default
7014 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7015 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7016 same as @option{-msdata=sysv}.
7019 @opindex msdata-data
7020 On System V.4 and embedded PowerPC systems, put small global and static
7021 data in the @samp{.sdata} section. Put small uninitialized global and
7022 static data in the @samp{.sbss} section. Do not use register @code{r13}
7023 to address small data however. This is the default behavior unless
7024 other @option{-msdata} options are used.
7028 @opindex msdata=none
7030 On embedded PowerPC systems, put all initialized global and static data
7031 in the @samp{.data} section, and all uninitialized data in the
7032 @samp{.bss} section.
7036 @cindex smaller data references (PowerPC)
7037 @cindex .sdata/.sdata2 references (PowerPC)
7038 On embedded PowerPC systems, put global and static items less than or
7039 equal to @var{num} bytes into the small data or bss sections instead of
7040 the normal data or bss section. By default, @var{num} is 8. The
7041 @option{-G @var{num}} switch is also passed to the linker.
7042 All modules should be compiled with the same @option{-G @var{num}} value.
7045 @itemx -mno-regnames
7047 @opindex mno-regnames
7048 On System V.4 and embedded PowerPC systems do (do not) emit register
7049 names in the assembly language output using symbolic forms.
7054 @subsection IBM RT Options
7056 @cindex IBM RT options
7058 These @samp{-m} options are defined for the IBM RT PC:
7062 @opindex min-line-mul
7063 Use an in-line code sequence for integer multiplies. This is the
7066 @item -mcall-lib-mul
7067 @opindex mcall-lib-mul
7068 Call @code{lmul$$} for integer multiples.
7070 @item -mfull-fp-blocks
7071 @opindex mfull-fp-blocks
7072 Generate full-size floating point data blocks, including the minimum
7073 amount of scratch space recommended by IBM@. This is the default.
7075 @item -mminimum-fp-blocks
7076 @opindex mminimum-fp-blocks
7077 Do not include extra scratch space in floating point data blocks. This
7078 results in smaller code, but slower execution, since scratch space must
7079 be allocated dynamically.
7081 @cindex @file{varargs.h} and RT PC
7082 @cindex @file{stdarg.h} and RT PC
7083 @item -mfp-arg-in-fpregs
7084 @opindex mfp-arg-in-fpregs
7085 Use a calling sequence incompatible with the IBM calling convention in
7086 which floating point arguments are passed in floating point registers.
7087 Note that @code{varargs.h} and @code{stdarg.h} will not work with
7088 floating point operands if this option is specified.
7090 @item -mfp-arg-in-gregs
7091 @opindex mfp-arg-in-gregs
7092 Use the normal calling convention for floating point arguments. This is
7095 @item -mhc-struct-return
7096 @opindex mhc-struct-return
7097 Return structures of more than one word in memory, rather than in a
7098 register. This provides compatibility with the MetaWare HighC (hc)
7099 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7100 with the Portable C Compiler (pcc).
7102 @item -mnohc-struct-return
7103 @opindex mnohc-struct-return
7104 Return some structures of more than one word in registers, when
7105 convenient. This is the default. For compatibility with the
7106 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7107 option @option{-mhc-struct-return}.
7111 @subsection MIPS Options
7112 @cindex MIPS options
7114 These @samp{-m} options are defined for the MIPS family of computers:
7118 @item -march=@var{cpu-type}
7120 Assume the defaults for the machine type @var{cpu-type} when generating
7121 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7122 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7123 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7124 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7125 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7126 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc.
7128 @item -mtune=@var{cpu-type}
7130 Assume the defaults for the machine type @var{cpu-type} when scheduling
7131 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7132 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7133 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7134 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7135 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7136 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific
7137 @var{cpu-type} will schedule things appropriately for that particular
7138 chip, the compiler will not generate any code that does not meet level 1
7139 of the MIPS ISA (instruction set architecture) without a @option{-mipsX}
7140 or @option{-mabi} switch being used.
7142 @item -mcpu=@var{cpu-type}
7144 This is identical to specifying both @option{-march} and @option{-mtune}.
7148 Issue instructions from level 1 of the MIPS ISA@. This is the default.
7149 @samp{r3000} is the default @var{cpu-type} at this ISA level.
7153 Issue instructions from level 2 of the MIPS ISA (branch likely, square
7154 root instructions). @samp{r6000} is the default @var{cpu-type} at this
7159 Issue instructions from level 3 of the MIPS ISA (64-bit instructions).
7160 @samp{r4000} is the default @var{cpu-type} at this ISA level.
7164 Issue instructions from level 4 of the MIPS ISA (conditional move,
7165 prefetch, enhanced FPU instructions). @samp{r8000} is the default
7166 @var{cpu-type} at this ISA level.
7170 Assume that 32 32-bit floating point registers are available. This is
7175 Assume that 32 64-bit floating point registers are available. This is
7176 the default when the @option{-mips3} option is used.
7179 @itemx -mno-fused-madd
7180 @opindex mfused-madd
7181 @opindex mno-fused-madd
7182 Generate code that uses (does not use) the floating point multiply and
7183 accumulate instructions, when they are available. These instructions
7184 are generated by default if they are available, but this may be
7185 undesirable if the extra precision causes problems or on certain chips
7186 in the mode where denormals are rounded to zero where denormals
7187 generated by multiply and accumulate instructions cause exceptions
7192 Assume that 32 32-bit general purpose registers are available. This is
7197 Assume that 32 64-bit general purpose registers are available. This is
7198 the default when the @option{-mips3} option is used.
7202 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7203 explanation of the default, and the width of pointers.
7207 Force long types to be 64 bits wide. See @option{-mlong32} for an
7208 explanation of the default, and the width of pointers.
7212 Force long, int, and pointer types to be 32 bits wide.
7214 If none of @option{-mlong32}, @option{-mlong64}, or @option{-mint64} are set,
7215 the size of ints, longs, and pointers depends on the ABI and ISA chosen.
7216 For @option{-mabi=32}, and @option{-mabi=n32}, ints and longs are 32 bits
7217 wide. For @option{-mabi=64}, ints are 32 bits, and longs are 64 bits wide.
7218 For @option{-mabi=eabi} and either @option{-mips1} or @option{-mips2}, ints
7219 and longs are 32 bits wide. For @option{-mabi=eabi} and higher ISAs, ints
7220 are 32 bits, and longs are 64 bits wide. The width of pointer types is
7221 the smaller of the width of longs or the width of general purpose
7222 registers (which in turn depends on the ISA)@.
7234 Generate code for the indicated ABI@. The default instruction level is
7235 @option{-mips1} for @samp{32}, @option{-mips3} for @samp{n32}, and
7236 @option{-mips4} otherwise. Conversely, with @option{-mips1} or
7237 @option{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI
7242 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7243 add normal debug information. This is the default for all
7244 platforms except for the OSF/1 reference platform, using the OSF/rose
7245 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7246 switches are used, the @file{mips-tfile} program will encapsulate the
7247 stabs within MIPS ECOFF@.
7251 Generate code for the GNU assembler. This is the default on the OSF/1
7252 reference platform, using the OSF/rose object format. Also, this is
7253 the default if the configure option @option{--with-gnu-as} is used.
7255 @item -msplit-addresses
7256 @itemx -mno-split-addresses
7257 @opindex msplit-addresses
7258 @opindex mno-split-addresses
7259 Generate code to load the high and low parts of address constants separately.
7260 This allows GCC to optimize away redundant loads of the high order
7261 bits of addresses. This optimization requires GNU as and GNU ld.
7262 This optimization is enabled by default for some embedded targets where
7263 GNU as and GNU ld are standard.
7269 The @option{-mrnames} switch says to output code using the MIPS software
7270 names for the registers, instead of the hardware names (ie, @var{a0}
7271 instead of @var{$4}). The only known assembler that supports this option
7272 is the Algorithmics assembler.
7278 The @option{-mgpopt} switch says to write all of the data declarations
7279 before the instructions in the text section, this allows the MIPS
7280 assembler to generate one word memory references instead of using two
7281 words for short global or static data items. This is on by default if
7282 optimization is selected.
7288 For each non-inline function processed, the @option{-mstats} switch
7289 causes the compiler to emit one line to the standard error file to
7290 print statistics about the program (number of registers saved, stack
7297 The @option{-mmemcpy} switch makes all block moves call the appropriate
7298 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7299 generating inline code.
7302 @itemx -mno-mips-tfile
7303 @opindex mmips-tfile
7304 @opindex mno-mips-tfile
7305 The @option{-mno-mips-tfile} switch causes the compiler not
7306 postprocess the object file with the @file{mips-tfile} program,
7307 after the MIPS assembler has generated it to add debug support. If
7308 @file{mips-tfile} is not run, then no local variables will be
7309 available to the debugger. In addition, @file{stage2} and
7310 @file{stage3} objects will have the temporary file names passed to the
7311 assembler embedded in the object file, which means the objects will
7312 not compare the same. The @option{-mno-mips-tfile} switch should only
7313 be used when there are bugs in the @file{mips-tfile} program that
7314 prevents compilation.
7317 @opindex msoft-float
7318 Generate output containing library calls for floating point.
7319 @strong{Warning:} the requisite libraries are not part of GCC@.
7320 Normally the facilities of the machine's usual C compiler are used, but
7321 this can't be done directly in cross-compilation. You must make your
7322 own arrangements to provide suitable library functions for
7326 @opindex mhard-float
7327 Generate output containing floating point instructions. This is the
7328 default if you use the unmodified sources.
7331 @itemx -mno-abicalls
7333 @opindex mno-abicalls
7334 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7335 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7336 position independent code.
7339 @itemx -mno-long-calls
7340 @opindex mlong-calls
7341 @opindex mno-long-calls
7342 Do all calls with the @samp{JALR} instruction, which requires
7343 loading up a function's address into a register before the call.
7344 You need to use this switch, if you call outside of the current
7345 512 megabyte segment to functions that are not through pointers.
7348 @itemx -mno-half-pic
7350 @opindex mno-half-pic
7351 Put pointers to extern references into the data section and load them
7352 up, rather than put the references in the text section.
7354 @item -membedded-pic
7355 @itemx -mno-embedded-pic
7356 @opindex membedded-pic
7357 @opindex mno-embedded-pic
7358 Generate PIC code suitable for some embedded systems. All calls are
7359 made using PC relative address, and all data is addressed using the $gp
7360 register. No more than 65536 bytes of global data may be used. This
7361 requires GNU as and GNU ld which do most of the work. This currently
7362 only works on targets which use ECOFF; it does not work with ELF@.
7364 @item -membedded-data
7365 @itemx -mno-embedded-data
7366 @opindex membedded-data
7367 @opindex mno-embedded-data
7368 Allocate variables to the read-only data section first if possible, then
7369 next in the small data section if possible, otherwise in data. This gives
7370 slightly slower code than the default, but reduces the amount of RAM required
7371 when executing, and thus may be preferred for some embedded systems.
7373 @item -muninit-const-in-rodata
7374 @itemx -mno-uninit-const-in-rodata
7375 @opindex muninit-const-in-rodata
7376 @opindex mno-uninit-const-in-rodata
7377 When used together with @option{-membedded-data}, it will always store uninitialized
7378 const variables in the read-only data section.
7380 @item -msingle-float
7381 @itemx -mdouble-float
7382 @opindex msingle-float
7383 @opindex mdouble-float
7384 The @option{-msingle-float} switch tells gcc to assume that the floating
7385 point coprocessor only supports single precision operations, as on the
7386 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
7387 double precision operations. This is the default.
7393 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
7394 as on the @samp{r4650} chip.
7398 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
7399 @option{-mcpu=r4650}.
7405 Enable 16-bit instructions.
7409 Use the entry and exit pseudo ops. This option can only be used with
7414 Compile code for the processor in little endian mode.
7415 The requisite libraries are assumed to exist.
7419 Compile code for the processor in big endian mode.
7420 The requisite libraries are assumed to exist.
7424 @cindex smaller data references (MIPS)
7425 @cindex gp-relative references (MIPS)
7426 Put global and static items less than or equal to @var{num} bytes into
7427 the small data or bss sections instead of the normal data or bss
7428 section. This allows the assembler to emit one word memory reference
7429 instructions based on the global pointer (@var{gp} or @var{$28}),
7430 instead of the normal two words used. By default, @var{num} is 8 when
7431 the MIPS assembler is used, and 0 when the GNU assembler is used. The
7432 @option{-G @var{num}} switch is also passed to the assembler and linker.
7433 All modules should be compiled with the same @option{-G @var{num}}
7438 Tell the MIPS assembler to not run its preprocessor over user
7439 assembler files (with a @samp{.s} suffix) when assembling them.
7443 Pass an option to gas which will cause nops to be inserted if
7444 the read of the destination register of an mfhi or mflo instruction
7445 occurs in the following two instructions.
7449 Do not include the default crt0.
7451 @item -mflush-func=@var{func}
7452 @itemx -mno-flush-func
7453 @opindex mflush-func
7454 Specifies the function to call to flush the I and D caches, or to not
7455 call any such function. If called, the function must take the same
7456 arguments as the common @code{_flush_func()}, that is, the address of the
7457 memory range for which the cache is being flushed, the size of the
7458 memory range, and the number 3 (to flush both caches). The default
7459 depends on the target gcc was configured for, but commonly is either
7460 @samp{_flush_func} or @samp{__cpu_flush}.
7464 These options are defined by the macro
7465 @code{TARGET_SWITCHES} in the machine description. The default for the
7466 options is also defined by that macro, which enables you to change the
7470 @node i386 and x86-64 Options
7471 @subsection Intel 386 and AMD x86-64 Options
7472 @cindex i386 Options
7473 @cindex x86-64 Options
7474 @cindex Intel 386 Options
7475 @cindex AMD x86-64 Options
7477 These @samp{-m} options are defined for the i386 and x86-64 family of
7481 @item -mcpu=@var{cpu-type}
7483 Tune to @var{cpu-type} everything applicable about the generated code, except
7484 for the ABI and the set of available instructions. The choices for
7485 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
7486 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
7487 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
7488 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp}
7489 and @samp{athlon-mp}.
7491 While picking a specific @var{cpu-type} will schedule things appropriately
7492 for that particular chip, the compiler will not generate any code that
7493 does not run on the i386 without the @option{-march=@var{cpu-type}} option
7494 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
7495 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
7496 AMD chips as opposed to the Intel ones.
7498 @item -march=@var{cpu-type}
7500 Generate instructions for the machine type @var{cpu-type}. The choices
7501 for @var{cpu-type} are the same as for @option{-mcpu}. Moreover,
7502 specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}.
7511 @opindex mpentiumpro
7512 These options are synonyms for @option{-mcpu=i386}, @option{-mcpu=i486},
7513 @option{-mcpu=pentium}, and @option{-mcpu=pentiumpro} respectively.
7514 These synonyms are deprecated.
7516 @item -mintel-syntax
7517 @opindex mintel-syntax
7518 Emit assembly using Intel syntax opcodes instead of AT&T syntax.
7523 @opindex mno-ieee-fp
7524 Control whether or not the compiler uses IEEE floating point
7525 comparisons. These handle correctly the case where the result of a
7526 comparison is unordered.
7529 @opindex msoft-float
7530 Generate output containing library calls for floating point.
7531 @strong{Warning:} the requisite libraries are not part of GCC@.
7532 Normally the facilities of the machine's usual C compiler are used, but
7533 this can't be done directly in cross-compilation. You must make your
7534 own arrangements to provide suitable library functions for
7537 On machines where a function returns floating point results in the 80387
7538 register stack, some floating point opcodes may be emitted even if
7539 @option{-msoft-float} is used.
7541 @item -mno-fp-ret-in-387
7542 @opindex mno-fp-ret-in-387
7543 Do not use the FPU registers for return values of functions.
7545 The usual calling convention has functions return values of types
7546 @code{float} and @code{double} in an FPU register, even if there
7547 is no FPU@. The idea is that the operating system should emulate
7550 The option @option{-mno-fp-ret-in-387} causes such values to be returned
7551 in ordinary CPU registers instead.
7553 @item -mno-fancy-math-387
7554 @opindex mno-fancy-math-387
7555 Some 387 emulators do not support the @code{sin}, @code{cos} and
7556 @code{sqrt} instructions for the 387. Specify this option to avoid
7557 generating those instructions. This option is the default on FreeBSD@.
7558 As of revision 2.6.1, these instructions are not generated unless you
7559 also use the @option{-funsafe-math-optimizations} switch.
7561 @item -malign-double
7562 @itemx -mno-align-double
7563 @opindex malign-double
7564 @opindex mno-align-double
7565 Control whether GCC aligns @code{double}, @code{long double}, and
7566 @code{long long} variables on a two word boundary or a one word
7567 boundary. Aligning @code{double} variables on a two word boundary will
7568 produce code that runs somewhat faster on a @samp{Pentium} at the
7569 expense of more memory.
7571 @item -m128bit-long-double
7572 @opindex m128bit-long-double
7573 Control the size of @code{long double} type. i386 application binary interface
7574 specify the size to be 12 bytes, while modern architectures (Pentium and newer)
7575 prefer @code{long double} aligned to 8 or 16 byte boundary. This is
7576 impossible to reach with 12 byte long doubles in the array accesses.
7578 @strong{Warning:} if you use the @option{-m128bit-long-double} switch, the
7579 structures and arrays containing @code{long double} will change their size as
7580 well as function calling convention for function taking @code{long double}
7583 @item -m96bit-long-double
7584 @opindex m96bit-long-double
7585 Set the size of @code{long double} to 96 bits as required by the i386
7586 application binary interface. This is the default.
7589 @itemx -mno-svr3-shlib
7590 @opindex msvr3-shlib
7591 @opindex mno-svr3-shlib
7592 Control whether GCC places uninitialized local variables into the
7593 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
7594 into @code{bss}. These options are meaningful only on System V Release 3.
7598 Use a different function-calling convention, in which functions that
7599 take a fixed number of arguments return with the @code{ret} @var{num}
7600 instruction, which pops their arguments while returning. This saves one
7601 instruction in the caller since there is no need to pop the arguments
7604 You can specify that an individual function is called with this calling
7605 sequence with the function attribute @samp{stdcall}. You can also
7606 override the @option{-mrtd} option by using the function attribute
7607 @samp{cdecl}. @xref{Function Attributes}.
7609 @strong{Warning:} this calling convention is incompatible with the one
7610 normally used on Unix, so you cannot use it if you need to call
7611 libraries compiled with the Unix compiler.
7613 Also, you must provide function prototypes for all functions that
7614 take variable numbers of arguments (including @code{printf});
7615 otherwise incorrect code will be generated for calls to those
7618 In addition, seriously incorrect code will result if you call a
7619 function with too many arguments. (Normally, extra arguments are
7620 harmlessly ignored.)
7622 @item -mregparm=@var{num}
7624 Control how many registers are used to pass integer arguments. By
7625 default, no registers are used to pass arguments, and at most 3
7626 registers can be used. You can control this behavior for a specific
7627 function by using the function attribute @samp{regparm}.
7628 @xref{Function Attributes}.
7630 @strong{Warning:} if you use this switch, and
7631 @var{num} is nonzero, then you must build all modules with the same
7632 value, including any libraries. This includes the system libraries and
7635 @item -mpreferred-stack-boundary=@var{num}
7636 @opindex mpreferred-stack-boundary
7637 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
7638 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
7639 the default is 4 (16 bytes or 128 bits), except when optimizing for code
7640 size (@option{-Os}), in which case the default is the minimum correct
7641 alignment (4 bytes for x86, and 8 bytes for x86-64).
7643 On Pentium and PentiumPro, @code{double} and @code{long double} values
7644 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
7645 suffer significant run time performance penalties. On Pentium III, the
7646 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
7647 penalties if it is not 16 byte aligned.
7649 To ensure proper alignment of this values on the stack, the stack boundary
7650 must be as aligned as that required by any value stored on the stack.
7651 Further, every function must be generated such that it keeps the stack
7652 aligned. Thus calling a function compiled with a higher preferred
7653 stack boundary from a function compiled with a lower preferred stack
7654 boundary will most likely misalign the stack. It is recommended that
7655 libraries that use callbacks always use the default setting.
7657 This extra alignment does consume extra stack space, and generally
7658 increases code size. Code that is sensitive to stack space usage, such
7659 as embedded systems and operating system kernels, may want to reduce the
7660 preferred alignment to @option{-mpreferred-stack-boundary=2}.
7674 These switches enable or disable the use of built-in functions that allow
7675 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
7677 The following machine modes are available for use with MMX built-in functions
7678 (@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32 bit integers,
7679 @code{V4HI} for a vector of four 16 bit integers, and @code{V8QI} for a
7680 vector of eight 8 bit integers. Some of the built-in functions operate on
7681 MMX registers as a whole 64 bit entity, these use @code{DI} as their mode.
7683 If 3Dnow extensions are enabled, @code{V2SF} is used as a mode for a vector
7684 of two 32 bit floating point values.
7686 If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32 bit
7687 floating point values. Some instructions use a vector of four 32 bit
7688 integers, these use @code{V4SI}. Finally, some instructions operate on an
7689 entire vector register, interpreting it as a 128 bit integer, these use mode
7692 The following built-in functions are made available by @option{-mmmx}:
7694 @item v8qi __builtin_ia32_paddb (v8qi, v8qi)
7695 Generates the @code{paddb} machine instruction.
7696 @item v4hi __builtin_ia32_paddw (v4hi, v4hi)
7697 Generates the @code{paddw} machine instruction.
7698 @item v2si __builtin_ia32_paddd (v2si, v2si)
7699 Generates the @code{paddd} machine instruction.
7700 @item v8qi __builtin_ia32_psubb (v8qi, v8qi)
7701 Generates the @code{psubb} machine instruction.
7702 @item v4hi __builtin_ia32_psubw (v4hi, v4hi)
7703 Generates the @code{psubw} machine instruction.
7704 @item v2si __builtin_ia32_psubd (v2si, v2si)
7705 Generates the @code{psubd} machine instruction.
7707 @item v8qi __builtin_ia32_paddsb (v8qi, v8qi)
7708 Generates the @code{paddsb} machine instruction.
7709 @item v4hi __builtin_ia32_paddsw (v4hi, v4hi)
7710 Generates the @code{paddsw} machine instruction.
7711 @item v8qi __builtin_ia32_psubsb (v8qi, v8qi)
7712 Generates the @code{psubsb} machine instruction.
7713 @item v4hi __builtin_ia32_psubsw (v4hi, v4hi)
7714 Generates the @code{psubsw} machine instruction.
7716 @item v8qi __builtin_ia32_paddusb (v8qi, v8qi)
7717 Generates the @code{paddusb} machine instruction.
7718 @item v4hi __builtin_ia32_paddusw (v4hi, v4hi)
7719 Generates the @code{paddusw} machine instruction.
7720 @item v8qi __builtin_ia32_psubusb (v8qi, v8qi)
7721 Generates the @code{psubusb} machine instruction.
7722 @item v4hi __builtin_ia32_psubusw (v4hi, v4hi)
7723 Generates the @code{psubusw} machine instruction.
7725 @item v4hi __builtin_ia32_pmullw (v4hi, v4hi)
7726 Generates the @code{pmullw} machine instruction.
7727 @item v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
7728 Generates the @code{pmulhw} machine instruction.
7730 @item di __builtin_ia32_pand (di, di)
7731 Generates the @code{pand} machine instruction.
7732 @item di __builtin_ia32_pandn (di,di)
7733 Generates the @code{pandn} machine instruction.
7734 @item di __builtin_ia32_por (di, di)
7735 Generates the @code{por} machine instruction.
7736 @item di __builtin_ia32_pxor (di, di)
7737 Generates the @code{pxor} machine instruction.
7739 @item v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
7740 Generates the @code{pcmpeqb} machine instruction.
7741 @item v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
7742 Generates the @code{pcmpeqw} machine instruction.
7743 @item v2si __builtin_ia32_pcmpeqd (v2si, v2si)
7744 Generates the @code{pcmpeqd} machine instruction.
7745 @item v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
7746 Generates the @code{pcmpgtb} machine instruction.
7747 @item v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
7748 Generates the @code{pcmpgtw} machine instruction.
7749 @item v2si __builtin_ia32_pcmpgtd (v2si, v2si)
7750 Generates the @code{pcmpgtd} machine instruction.
7752 @item v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
7753 Generates the @code{punpckhbw} machine instruction.
7754 @item v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
7755 Generates the @code{punpckhwd} machine instruction.
7756 @item v2si __builtin_ia32_punpckhdq (v2si, v2si)
7757 Generates the @code{punpckhdq} machine instruction.
7758 @item v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
7759 Generates the @code{punpcklbw} machine instruction.
7760 @item v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
7761 Generates the @code{punpcklwd} machine instruction.
7762 @item v2si __builtin_ia32_punpckldq (v2si, v2si)
7763 Generates the @code{punpckldq} machine instruction.
7765 @item v8qi __builtin_ia32_packsswb (v4hi, v4hi)
7766 Generates the @code{packsswb} machine instruction.
7767 @item v4hi __builtin_ia32_packssdw (v2si, v2si)
7768 Generates the @code{packssdw} machine instruction.
7769 @item v8qi __builtin_ia32_packuswb (v4hi, v4hi)
7770 Generates the @code{packuswb} machine instruction.
7774 The following built-in functions are made available either with @option{-msse}, or
7775 with a combination of @option{-m3dnow} and @option{-march=athlon}.
7778 @item v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
7779 Generates the @code{pmulhuw} machine instruction.
7781 @item v8qi __builtin_ia32_pavgb (v8qi, v8qi)
7782 Generates the @code{pavgb} machine instruction.
7783 @item v4hi __builtin_ia32_pavgw (v4hi, v4hi)
7784 Generates the @code{pavgw} machine instruction.
7785 @item v4hi __builtin_ia32_psadbw (v8qi, v8qi)
7786 Generates the @code{psadbw} machine instruction.
7788 @item v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
7789 Generates the @code{pmaxub} machine instruction.
7790 @item v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
7791 Generates the @code{pmaxsw} machine instruction.
7792 @item v8qi __builtin_ia32_pminub (v8qi, v8qi)
7793 Generates the @code{pminub} machine instruction.
7794 @item v4hi __builtin_ia32_pminsw (v4hi, v4hi)
7795 Generates the @code{pminsw} machine instruction.
7797 @item int __builtin_ia32_pextrw (v4hi, int)
7798 Generates the @code{pextrw} machine instruction.
7799 @item v4hi __builtin_ia32_pinsrw (v4hi, int, int)
7800 Generates the @code{pinsrw} machine instruction.
7802 @item int __builtin_ia32_pmovmskb (v8qi)
7803 Generates the @code{pmovmskb} machine instruction.
7804 @item void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
7805 Generates the @code{maskmovq} machine instruction.
7806 @item void __builtin_ia32_movntq (di *, di)
7807 Generates the @code{movntq} machine instruction.
7808 @item void __builtin_ia32_sfence (void)
7809 Generates the @code{sfence} machine instruction.
7810 @item void __builtin_ia32_prefetch (char *, int selector)
7811 Generates a prefetch machine instruction, depending on the value of
7812 selector. If @code{selector} is 0, it generates @code{prefetchnta}; for
7813 a value of 1, it generates @code{prefetcht0}; for a value of 2, it generates
7814 @code{prefetcht1}; and for a value of 3 it generates @code{prefetcht2}.
7818 The following built-in functions are available when @option{-msse} is used.
7821 @item int __builtin_ia32_comieq (v4sf, v4sf)
7822 Generates the @code{comiss} machine instruction and performs an equality
7823 comparison. The return value is the truth value of that comparison.
7824 @item int __builtin_ia32_comineq (v4sf, v4sf)
7825 Generates the @code{comiss} machine instruction and performs an inequality
7826 comparison. The return value is the truth value of that comparison.
7827 @item int __builtin_ia32_comilt (v4sf, v4sf)
7828 Generates the @code{comiss} machine instruction and performs a ``less than''
7829 comparison. The return value is the truth value of that comparison.
7830 @item int __builtin_ia32_comile (v4sf, v4sf)
7831 Generates the @code{comiss} machine instruction and performs a ``less or
7832 equal'' comparison. The return value is the truth value of that comparison.
7833 @item int __builtin_ia32_comigt (v4sf, v4sf)
7834 Generates the @code{comiss} machine instruction and performs a ``greater than''
7835 comparison. The return value is the truth value of that comparison.
7836 @item int __builtin_ia32_comige (v4sf, v4sf)
7837 Generates the @code{comiss} machine instruction and performs a ``greater or
7838 equal'' comparison. The return value is the truth value of that comparison.
7840 @item int __builtin_ia32_ucomieq (v4sf, v4sf)
7841 Generates the @code{ucomiss} machine instruction and performs an equality
7842 comparison. The return value is the truth value of that comparison.
7843 @item int __builtin_ia32_ucomineq (v4sf, v4sf)
7844 Generates the @code{ucomiss} machine instruction and performs an inequality
7845 comparison. The return value is the truth value of that comparison.
7846 @item int __builtin_ia32_ucomilt (v4sf, v4sf)
7847 Generates the @code{ucomiss} machine instruction and performs a ``less than''
7848 comparison. The return value is the truth value of that comparison.
7849 @item int __builtin_ia32_ucomile (v4sf, v4sf)
7850 Generates the @code{ucomiss} machine instruction and performs a ``less or
7851 equal'' comparison. The return value is the truth value of that comparison.
7852 @item int __builtin_ia32_ucomigt (v4sf, v4sf)
7853 Generates the @code{ucomiss} machine instruction and performs a ``greater than''
7854 comparison. The return value is the truth value of that comparison.
7855 @item int __builtin_ia32_ucomige (v4sf, v4sf)
7856 Generates the @code{ucomiss} machine instruction and performs a ``greater or
7857 equal'' comparison. The return value is the truth value of that comparison.
7859 @item v4sf __builtin_ia32_addps (v4sf, v4sf)
7860 Generates the @code{addps} machine instruction.
7861 @item v4sf __builtin_ia32_addss (v4sf, v4sf)
7862 Generates the @code{addss} machine instruction.
7863 @item v4sf __builtin_ia32_subps (v4sf, v4sf)
7864 Generates the @code{subps} machine instruction.
7865 @item v4sf __builtin_ia32_subss (v4sf, v4sf)
7866 Generates the @code{subss} machine instruction.
7867 @item v4sf __builtin_ia32_mulps (v4sf, v4sf)
7868 Generates the @code{mulps} machine instruction.
7869 @item v4sf __builtin_ia32_mulss (v4sf, v4sf)
7870 Generates the @code{mulss} machine instruction.
7871 @item v4sf __builtin_ia32_divps (v4sf, v4sf)
7872 Generates the @code{divps} machine instruction.
7873 @item v4sf __builtin_ia32_divss (v4sf, v4sf)
7874 Generates the @code{divss} machine instruction.
7876 @item v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
7877 Generates the @code{cmpeqps} machine instruction.
7878 @item v4si __builtin_ia32_cmplts (v4sf, v4sf)
7879 Generates the @code{cmpltps} machine instruction.
7880 @item v4si __builtin_ia32_cmpleps (v4sf, v4sf)
7881 Generates the @code{cmpleps} machine instruction.
7882 @item v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
7883 Generates the @code{cmpgtps} machine instruction.
7884 @item v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
7885 Generates the @code{cmpgeps} machine instruction.
7886 @item v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
7887 Generates the @code{cmpunodps} machine instruction.
7888 @item v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
7889 Generates the @code{cmpeqps} machine instruction.
7890 @item v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
7891 Generates the @code{cmpltps} machine instruction.
7892 @item v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
7893 Generates the @code{cmpleps} machine instruction.
7894 @item v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
7895 Generates the @code{cmpgtps} machine instruction.
7896 @item v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
7897 Generates the @code{cmpgeps} machine instruction.
7898 @item v4si __builtin_ia32_cmpordps (v4sf, v4sf)
7899 Generates the @code{cmpunodps} machine instruction.
7901 @item v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
7902 Generates the @code{cmpeqss} machine instruction.
7903 @item v4si __builtin_ia32_cmpltss (v4sf, v4sf)
7904 Generates the @code{cmpltss} machine instruction.
7905 @item v4si __builtin_ia32_cmpless (v4sf, v4sf)
7906 Generates the @code{cmpless} machine instruction.
7907 @item v4si __builtin_ia32_cmpgtss (v4sf, v4sf)
7908 Generates the @code{cmpgtss} machine instruction.
7909 @item v4si __builtin_ia32_cmpgess (v4sf, v4sf)
7910 Generates the @code{cmpgess} machine instruction.
7911 @item v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
7912 Generates the @code{cmpunodss} machine instruction.
7913 @item v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
7914 Generates the @code{cmpeqss} machine instruction.
7915 @item v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
7916 Generates the @code{cmpltss} machine instruction.
7917 @item v4si __builtin_ia32_cmpnless (v4sf, v4sf)
7918 Generates the @code{cmpless} machine instruction.
7919 @item v4si __builtin_ia32_cmpngtss (v4sf, v4sf)
7920 Generates the @code{cmpgtss} machine instruction.
7921 @item v4si __builtin_ia32_cmpngess (v4sf, v4sf)
7922 Generates the @code{cmpgess} machine instruction.
7923 @item v4si __builtin_ia32_cmpordss (v4sf, v4sf)
7924 Generates the @code{cmpunodss} machine instruction.
7926 @item v4sf __builtin_ia32_maxps (v4sf, v4sf)
7927 Generates the @code{maxps} machine instruction.
7928 @item v4sf __builtin_ia32_maxsss (v4sf, v4sf)
7929 Generates the @code{maxss} machine instruction.
7930 @item v4sf __builtin_ia32_minps (v4sf, v4sf)
7931 Generates the @code{minps} machine instruction.
7932 @item v4sf __builtin_ia32_minsss (v4sf, v4sf)
7933 Generates the @code{minss} machine instruction.
7935 @item ti __builtin_ia32_andps (ti, ti)
7936 Generates the @code{andps} machine instruction.
7937 @item ti __builtin_ia32_andnps (ti, ti)
7938 Generates the @code{andnps} machine instruction.
7939 @item ti __builtin_ia32_orps (ti, ti)
7940 Generates the @code{orps} machine instruction.
7941 @item ti __builtin_ia32_xorps (ti, ti)
7942 Generates the @code{xorps} machine instruction.
7944 @item v4sf __builtin_ia32_movps (v4sf, v4sf)
7945 Generates the @code{movps} machine instruction.
7946 @item v4sf __builtin_ia32_movhlps (v4sf, v4sf)
7947 Generates the @code{movhlps} machine instruction.
7948 @item v4sf __builtin_ia32_movlhps (v4sf, v4sf)
7949 Generates the @code{movlhps} machine instruction.
7950 @item v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
7951 Generates the @code{unpckhps} machine instruction.
7952 @item v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
7953 Generates the @code{unpcklps} machine instruction.
7955 @item v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
7956 Generates the @code{cvtpi2ps} machine instruction.
7957 @item v2si __builtin_ia32_cvtps2pi (v4sf)
7958 Generates the @code{cvtps2pi} machine instruction.
7959 @item v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
7960 Generates the @code{cvtsi2ss} machine instruction.
7961 @item int __builtin_ia32_cvtss2si (v4sf)
7962 Generates the @code{cvtsi2ss} machine instruction.
7963 @item v2si __builtin_ia32_cvttps2pi (v4sf)
7964 Generates the @code{cvttps2pi} machine instruction.
7965 @item int __builtin_ia32_cvttss2si (v4sf)
7966 Generates the @code{cvttsi2ss} machine instruction.
7968 @item v4sf __builtin_ia32_rcpps (v4sf)
7969 Generates the @code{rcpps} machine instruction.
7970 @item v4sf __builtin_ia32_rsqrtps (v4sf)
7971 Generates the @code{rsqrtps} machine instruction.
7972 @item v4sf __builtin_ia32_sqrtps (v4sf)
7973 Generates the @code{sqrtps} machine instruction.
7974 @item v4sf __builtin_ia32_rcpss (v4sf)
7975 Generates the @code{rcpss} machine instruction.
7976 @item v4sf __builtin_ia32_rsqrtss (v4sf)
7977 Generates the @code{rsqrtss} machine instruction.
7978 @item v4sf __builtin_ia32_sqrtss (v4sf)
7979 Generates the @code{sqrtss} machine instruction.
7981 @item v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
7982 Generates the @code{shufps} machine instruction.
7984 @item v4sf __builtin_ia32_loadaps (float *)
7985 Generates the @code{movaps} machine instruction as a load from memory.
7986 @item void __builtin_ia32_storeaps (float *, v4sf)
7987 Generates the @code{movaps} machine instruction as a store to memory.
7988 @item v4sf __builtin_ia32_loadups (float *)
7989 Generates the @code{movups} machine instruction as a load from memory.
7990 @item void __builtin_ia32_storeups (float *, v4sf)
7991 Generates the @code{movups} machine instruction as a store to memory.
7992 @item v4sf __builtin_ia32_loadsss (float *)
7993 Generates the @code{movss} machine instruction as a load from memory.
7994 @item void __builtin_ia32_storess (float *, v4sf)
7995 Generates the @code{movss} machine instruction as a store to memory.
7997 @item v4sf __builtin_ia32_loadhps (v4sf, v2si *)
7998 Generates the @code{movhps} machine instruction as a load from memory.
7999 @item v4sf __builtin_ia32_loadlps (v4sf, v2si *)
8000 Generates the @code{movlps} machine instruction as a load from memory
8001 @item void __builtin_ia32_storehps (v4sf, v2si *)
8002 Generates the @code{movhps} machine instruction as a store to memory.
8003 @item void __builtin_ia32_storelps (v4sf, v2si *)
8004 Generates the @code{movlps} machine instruction as a store to memory.
8006 @item void __builtin_ia32_movntps (float *, v4sf)
8007 Generates the @code{movntps} machine instruction.
8008 @item int __builtin_ia32_movmskps (v4sf)
8009 Generates the @code{movntps} machine instruction.
8011 @item void __builtin_ia32_storeps1 (float *, v4sf)
8012 Generates the @code{movaps} machine instruction as a store to memory.
8013 Before storing, the value is modified with a @code{shufps} instruction
8014 so that the lowest of the four floating point elements is replicated
8015 across the entire vector that is stored.
8016 @item void __builtin_ia32_storerps (float *, v4sf)
8017 Generates the @code{movaps} machine instruction as a store to memory.
8018 Before storing, the value is modified with a @code{shufps} instruction
8019 so that the order of the four floating point elements in the vector is
8021 @item v4sf __builtin_ia32_loadps1 (float *)
8022 Generates a @code{movss} machine instruction to load a floating point
8023 value from memory, and a @code{shufps} instruction to replicate the
8024 loaded value across all four elements of the result vector.
8025 @item v4sf __builtin_ia32_loadrps (float *)
8026 Generates a @code{movaps} machine instruction to load a vector from
8027 memory, and a @code{shufps} instruction to reverse the order of the
8028 four floating point elements in the result vector.
8029 @item v4sf __builtin_ia32_setps (float, float, float, float)
8030 Constructs a vector from four single floating point values. The return
8031 value is equal to the value that would result from storing the four
8032 arguments into consecutive memory locations and then executing a
8033 @code{movaps} to load the vector from memory.
8034 @item v4sf __builtin_ia32_setps1 (float)
8035 Constructs a vector from a single floating point value by replicating
8036 it across all four elements of the result vector.
8040 @itemx -mno-push-args
8042 @opindex mno-push-args
8043 Use PUSH operations to store outgoing parameters. This method is shorter
8044 and usually equally fast as method using SUB/MOV operations and is enabled
8045 by default. In some cases disabling it may improve performance because of
8046 improved scheduling and reduced dependencies.
8048 @item -maccumulate-outgoing-args
8049 @opindex maccumulate-outgoing-args
8050 If enabled, the maximum amount of space required for outgoing arguments will be
8051 computed in the function prologue. This is faster on most modern CPUs
8052 because of reduced dependencies, improved scheduling and reduced stack usage
8053 when preferred stack boundary is not equal to 2. The drawback is a notable
8054 increase in code size. This switch implies @option{-mno-push-args}.
8058 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8059 on thread-safe exception handling must compile and link all code with the
8060 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8061 @option{-D_MT}; when linking, it links in a special thread helper library
8062 @option{-lmingwthrd} which cleans up per thread exception handling data.
8064 @item -mno-align-stringops
8065 @opindex mno-align-stringops
8066 Do not align destination of inlined string operations. This switch reduces
8067 code size and improves performance in case the destination is already aligned,
8068 but gcc don't know about it.
8070 @item -minline-all-stringops
8071 @opindex minline-all-stringops
8072 By default GCC inlines string operations only when destination is known to be
8073 aligned at least to 4 byte boundary. This enables more inlining, increase code
8074 size, but may improve performance of code that depends on fast memcpy, strlen
8075 and memset for short lengths.
8077 @item -momit-leaf-frame-pointer
8078 @opindex momit-leaf-frame-pointer
8079 Don't keep the frame pointer in a register for leaf functions. This
8080 avoids the instructions to save, set up and restore frame pointers and
8081 makes an extra register available in leaf functions. The option
8082 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8083 which might make debugging harder.
8086 These @samp{-m} switches are supported in addition to the above
8087 on AMD x86-64 processors in 64-bit environments.
8094 Generate code for a 32-bit or 64-bit environment.
8095 The 32-bit environment sets int, long and pointer to 32 bits and
8096 generates code that runs on any i386 system.
8097 The 64-bit environment sets int to 32 bits and long and pointer
8098 to 64 bits and generates code for AMD's x86-64 architecture.
8101 @opindex no-red-zone
8102 Do not use a so called red zone for x86-64 code. The red zone is mandated
8103 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8104 stack pointer that will not be modified by signal or interrupt handlers
8105 and therefore can be used for temporary data without adjusting the stack
8106 pointer. The flag @option{-mno-red-zone} disables this red zone.
8110 @subsection HPPA Options
8111 @cindex HPPA Options
8113 These @samp{-m} options are defined for the HPPA family of computers:
8116 @item -march=@var{architecture-type}
8118 Generate code for the specified architecture. The choices for
8119 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8120 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8121 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8122 architecture option for your machine. Code compiled for lower numbered
8123 architectures will run on higher numbered architectures, but not the
8126 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8127 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8131 @itemx -mpa-risc-1-1
8132 @itemx -mpa-risc-2-0
8133 @opindex mpa-risc-1-0
8134 @opindex mpa-risc-1-1
8135 @opindex mpa-risc-2-0
8136 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8139 @opindex mbig-switch
8140 Generate code suitable for big switch tables. Use this option only if
8141 the assembler/linker complain about out of range branches within a switch
8144 @item -mjump-in-delay
8145 @opindex mjump-in-delay
8146 Fill delay slots of function calls with unconditional jump instructions
8147 by modifying the return pointer for the function call to be the target
8148 of the conditional jump.
8150 @item -mdisable-fpregs
8151 @opindex mdisable-fpregs
8152 Prevent floating point registers from being used in any manner. This is
8153 necessary for compiling kernels which perform lazy context switching of
8154 floating point registers. If you use this option and attempt to perform
8155 floating point operations, the compiler will abort.
8157 @item -mdisable-indexing
8158 @opindex mdisable-indexing
8159 Prevent the compiler from using indexing address modes. This avoids some
8160 rather obscure problems when compiling MIG generated code under MACH@.
8162 @item -mno-space-regs
8163 @opindex mno-space-regs
8164 Generate code that assumes the target has no space registers. This allows
8165 GCC to generate faster indirect calls and use unscaled index address modes.
8167 Such code is suitable for level 0 PA systems and kernels.
8169 @item -mfast-indirect-calls
8170 @opindex mfast-indirect-calls
8171 Generate code that assumes calls never cross space boundaries. This
8172 allows GCC to emit code which performs faster indirect calls.
8174 This option will not work in the presence of shared libraries or nested
8177 @item -mlong-load-store
8178 @opindex mlong-load-store
8179 Generate 3-instruction load and store sequences as sometimes required by
8180 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8183 @item -mportable-runtime
8184 @opindex mportable-runtime
8185 Use the portable calling conventions proposed by HP for ELF systems.
8189 Enable the use of assembler directives only GAS understands.
8191 @item -mschedule=@var{cpu-type}
8193 Schedule code according to the constraints for the machine type
8194 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8195 @samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to
8196 @file{/usr/lib/sched.models} on an HP-UX system to determine the
8197 proper scheduling option for your machine.
8200 @opindex mlinker-opt
8201 Enable the optimization pass in the HPUX linker. Note this makes symbolic
8202 debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers
8203 in which they give bogus error messages when linking some programs.
8206 @opindex msoft-float
8207 Generate output containing library calls for floating point.
8208 @strong{Warning:} the requisite libraries are not available for all HPPA
8209 targets. Normally the facilities of the machine's usual C compiler are
8210 used, but this cannot be done directly in cross-compilation. You must make
8211 your own arrangements to provide suitable library functions for
8212 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8213 does provide software floating point support.
8215 @option{-msoft-float} changes the calling convention in the output file;
8216 therefore, it is only useful if you compile @emph{all} of a program with
8217 this option. In particular, you need to compile @file{libgcc.a}, the
8218 library that comes with GCC, with @option{-msoft-float} in order for
8222 @node Intel 960 Options
8223 @subsection Intel 960 Options
8225 These @samp{-m} options are defined for the Intel 960 implementations:
8228 @item -m@var{cpu-type}
8236 Assume the defaults for the machine type @var{cpu-type} for some of
8237 the other options, including instruction scheduling, floating point
8238 support, and addressing modes. The choices for @var{cpu-type} are
8239 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8240 @samp{sa}, and @samp{sb}.
8247 @opindex msoft-float
8248 The @option{-mnumerics} option indicates that the processor does support
8249 floating-point instructions. The @option{-msoft-float} option indicates
8250 that floating-point support should not be assumed.
8252 @item -mleaf-procedures
8253 @itemx -mno-leaf-procedures
8254 @opindex mleaf-procedures
8255 @opindex mno-leaf-procedures
8256 Do (or do not) attempt to alter leaf procedures to be callable with the
8257 @code{bal} instruction as well as @code{call}. This will result in more
8258 efficient code for explicit calls when the @code{bal} instruction can be
8259 substituted by the assembler or linker, but less efficient code in other
8260 cases, such as calls via function pointers, or using a linker that doesn't
8261 support this optimization.
8264 @itemx -mno-tail-call
8266 @opindex mno-tail-call
8267 Do (or do not) make additional attempts (beyond those of the
8268 machine-independent portions of the compiler) to optimize tail-recursive
8269 calls into branches. You may not want to do this because the detection of
8270 cases where this is not valid is not totally complete. The default is
8271 @option{-mno-tail-call}.
8273 @item -mcomplex-addr
8274 @itemx -mno-complex-addr
8275 @opindex mcomplex-addr
8276 @opindex mno-complex-addr
8277 Assume (or do not assume) that the use of a complex addressing mode is a
8278 win on this implementation of the i960. Complex addressing modes may not
8279 be worthwhile on the K-series, but they definitely are on the C-series.
8280 The default is currently @option{-mcomplex-addr} for all processors except
8284 @itemx -mno-code-align
8285 @opindex mcode-align
8286 @opindex mno-code-align
8287 Align code to 8-byte boundaries for faster fetching (or don't bother).
8288 Currently turned on by default for C-series implementations only.
8291 @item -mclean-linkage
8292 @itemx -mno-clean-linkage
8293 @opindex mclean-linkage
8294 @opindex mno-clean-linkage
8295 These options are not fully implemented.
8299 @itemx -mic2.0-compat
8300 @itemx -mic3.0-compat
8302 @opindex mic2.0-compat
8303 @opindex mic3.0-compat
8304 Enable compatibility with iC960 v2.0 or v3.0.
8308 @opindex masm-compat
8310 Enable compatibility with the iC960 assembler.
8312 @item -mstrict-align
8313 @itemx -mno-strict-align
8314 @opindex mstrict-align
8315 @opindex mno-strict-align
8316 Do not permit (do permit) unaligned accesses.
8320 Enable structure-alignment compatibility with Intel's gcc release version
8321 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8323 @item -mlong-double-64
8324 @opindex mlong-double-64
8325 Implement type @samp{long double} as 64-bit floating point numbers.
8326 Without the option @samp{long double} is implemented by 80-bit
8327 floating point numbers. The only reason we have it because there is
8328 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8329 is only useful for people using soft-float targets. Otherwise, we
8330 should recommend against use of it.
8334 @node DEC Alpha Options
8335 @subsection DEC Alpha Options
8337 These @samp{-m} options are defined for the DEC Alpha implementations:
8340 @item -mno-soft-float
8342 @opindex mno-soft-float
8343 @opindex msoft-float
8344 Use (do not use) the hardware floating-point instructions for
8345 floating-point operations. When @option{-msoft-float} is specified,
8346 functions in @file{libgcc.a} will be used to perform floating-point
8347 operations. Unless they are replaced by routines that emulate the
8348 floating-point operations, or compiled in such a way as to call such
8349 emulations routines, these routines will issue floating-point
8350 operations. If you are compiling for an Alpha without floating-point
8351 operations, you must ensure that the library is built so as not to call
8354 Note that Alpha implementations without floating-point operations are
8355 required to have floating-point registers.
8360 @opindex mno-fp-regs
8361 Generate code that uses (does not use) the floating-point register set.
8362 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8363 register set is not used, floating point operands are passed in integer
8364 registers as if they were integers and floating-point results are passed
8365 in $0 instead of $f0. This is a non-standard calling sequence, so any
8366 function with a floating-point argument or return value called by code
8367 compiled with @option{-mno-fp-regs} must also be compiled with that
8370 A typical use of this option is building a kernel that does not use,
8371 and hence need not save and restore, any floating-point registers.
8375 The Alpha architecture implements floating-point hardware optimized for
8376 maximum performance. It is mostly compliant with the IEEE floating
8377 point standard. However, for full compliance, software assistance is
8378 required. This option generates code fully IEEE compliant code
8379 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8380 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8381 defined during compilation. The resulting code is less efficient but is
8382 able to correctly support denormalized numbers and exceptional IEEE
8383 values such as not-a-number and plus/minus infinity. Other Alpha
8384 compilers call this option @option{-ieee_with_no_inexact}.
8386 @item -mieee-with-inexact
8387 @opindex mieee-with-inexact
8388 This is like @option{-mieee} except the generated code also maintains
8389 the IEEE @var{inexact-flag}. Turning on this option causes the
8390 generated code to implement fully-compliant IEEE math. In addition to
8391 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8392 macro. On some Alpha implementations the resulting code may execute
8393 significantly slower than the code generated by default. Since there is
8394 very little code that depends on the @var{inexact-flag}, you should
8395 normally not specify this option. Other Alpha compilers call this
8396 option @option{-ieee_with_inexact}.
8398 @item -mfp-trap-mode=@var{trap-mode}
8399 @opindex mfp-trap-mode
8400 This option controls what floating-point related traps are enabled.
8401 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8402 The trap mode can be set to one of four values:
8406 This is the default (normal) setting. The only traps that are enabled
8407 are the ones that cannot be disabled in software (e.g., division by zero
8411 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8415 Like @samp{su}, but the instructions are marked to be safe for software
8416 completion (see Alpha architecture manual for details).
8419 Like @samp{su}, but inexact traps are enabled as well.
8422 @item -mfp-rounding-mode=@var{rounding-mode}
8423 @opindex mfp-rounding-mode
8424 Selects the IEEE rounding mode. Other Alpha compilers call this option
8425 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8430 Normal IEEE rounding mode. Floating point numbers are rounded towards
8431 the nearest machine number or towards the even machine number in case
8435 Round towards minus infinity.
8438 Chopped rounding mode. Floating point numbers are rounded towards zero.
8441 Dynamic rounding mode. A field in the floating point control register
8442 (@var{fpcr}, see Alpha architecture reference manual) controls the
8443 rounding mode in effect. The C library initializes this register for
8444 rounding towards plus infinity. Thus, unless your program modifies the
8445 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8448 @item -mtrap-precision=@var{trap-precision}
8449 @opindex mtrap-precision
8450 In the Alpha architecture, floating point traps are imprecise. This
8451 means without software assistance it is impossible to recover from a
8452 floating trap and program execution normally needs to be terminated.
8453 GCC can generate code that can assist operating system trap handlers
8454 in determining the exact location that caused a floating point trap.
8455 Depending on the requirements of an application, different levels of
8456 precisions can be selected:
8460 Program precision. This option is the default and means a trap handler
8461 can only identify which program caused a floating point exception.
8464 Function precision. The trap handler can determine the function that
8465 caused a floating point exception.
8468 Instruction precision. The trap handler can determine the exact
8469 instruction that caused a floating point exception.
8472 Other Alpha compilers provide the equivalent options called
8473 @option{-scope_safe} and @option{-resumption_safe}.
8475 @item -mieee-conformant
8476 @opindex mieee-conformant
8477 This option marks the generated code as IEEE conformant. You must not
8478 use this option unless you also specify @option{-mtrap-precision=i} and either
8479 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8480 is to emit the line @samp{.eflag 48} in the function prologue of the
8481 generated assembly file. Under DEC Unix, this has the effect that
8482 IEEE-conformant math library routines will be linked in.
8484 @item -mbuild-constants
8485 @opindex mbuild-constants
8486 Normally GCC examines a 32- or 64-bit integer constant to
8487 see if it can construct it from smaller constants in two or three
8488 instructions. If it cannot, it will output the constant as a literal and
8489 generate code to load it from the data segment at runtime.
8491 Use this option to require GCC to construct @emph{all} integer constants
8492 using code, even if it takes more instructions (the maximum is six).
8494 You would typically use this option to build a shared library dynamic
8495 loader. Itself a shared library, it must relocate itself in memory
8496 before it can find the variables and constants in its own data segment.
8502 Select whether to generate code to be assembled by the vendor-supplied
8503 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8517 Indicate whether GCC should generate code to use the optional BWX,
8518 CIX, and MAX instruction sets. The default is to use the instruction sets
8519 supported by the CPU type specified via @option{-mcpu=} option or that
8520 of the CPU on which GCC was built if none was specified.
8522 @item -mcpu=@var{cpu_type}
8524 Set the instruction set, register set, and instruction scheduling
8525 parameters for machine type @var{cpu_type}. You can specify either the
8526 @samp{EV} style name or the corresponding chip number. GCC
8527 supports scheduling parameters for the EV4 and EV5 family of processors
8528 and will choose the default values for the instruction set from
8529 the processor you specify. If you do not specify a processor type,
8530 GCC will default to the processor on which the compiler was built.
8532 Supported values for @var{cpu_type} are
8537 Schedules as an EV4 and has no instruction set extensions.
8541 Schedules as an EV5 and has no instruction set extensions.
8545 Schedules as an EV5 and supports the BWX extension.
8550 Schedules as an EV5 and supports the BWX and MAX extensions.
8554 Schedules as an EV5 (until Digital releases the scheduling parameters
8555 for the EV6) and supports the BWX, CIX, and MAX extensions.
8558 @item -mmemory-latency=@var{time}
8559 @opindex mmemory-latency
8560 Sets the latency the scheduler should assume for typical memory
8561 references as seen by the application. This number is highly
8562 dependent on the memory access patterns used by the application
8563 and the size of the external cache on the machine.
8565 Valid options for @var{time} are
8569 A decimal number representing clock cycles.
8575 The compiler contains estimates of the number of clock cycles for
8576 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8577 (also called Dcache, Scache, and Bcache), as well as to main memory.
8578 Note that L3 is only valid for EV5.
8583 @node DEC Alpha/VMS Options
8584 @subsection DEC Alpha/VMS Options
8586 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8589 @item -mvms-return-codes
8590 @opindex mvms-return-codes
8591 Return VMS condition codes from main. The default is to return POSIX
8592 style condition (e.g.@ error) codes.
8595 @node Clipper Options
8596 @subsection Clipper Options
8598 These @samp{-m} options are defined for the Clipper implementations:
8603 Produce code for a C300 Clipper processor. This is the default.
8607 Produce code for a C400 Clipper processor, i.e.@: use floating point
8611 @node H8/300 Options
8612 @subsection H8/300 Options
8614 These @samp{-m} options are defined for the H8/300 implementations:
8619 Shorten some address references at link time, when possible; uses the
8620 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8621 ld.info, Using ld}, for a fuller description.
8625 Generate code for the H8/300H@.
8629 Generate code for the H8/S@.
8633 Generate code for the H8/S2600. This switch must be used with @option{-ms}.
8637 Make @code{int} data 32 bits by default.
8641 On the H8/300H and H8/S, use the same alignment rules as for the H8/300.
8642 The default for the H8/300H and H8/S is to align longs and floats on 4
8644 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8645 This option has no effect on the H8/300.
8649 @subsection SH Options
8651 These @samp{-m} options are defined for the SH implementations:
8656 Generate code for the SH1.
8660 Generate code for the SH2.
8664 Generate code for the SH3.
8668 Generate code for the SH3e.
8672 Generate code for the SH4 without a floating-point unit.
8674 @item -m4-single-only
8675 @opindex m4-single-only
8676 Generate code for the SH4 with a floating-point unit that only
8677 supports single-precision arithmetic.
8681 Generate code for the SH4 assuming the floating-point unit is in
8682 single-precision mode by default.
8686 Generate code for the SH4.
8690 Compile code for the processor in big endian mode.
8694 Compile code for the processor in little endian mode.
8698 Align doubles at 64-bit boundaries. Note that this changes the calling
8699 conventions, and thus some functions from the standard C library will
8700 not work unless you recompile it first with @option{-mdalign}.
8704 Shorten some address references at link time, when possible; uses the
8705 linker option @option{-relax}.
8709 Use 32-bit offsets in @code{switch} tables. The default is to use
8714 Enable the use of the instruction @code{fmovd}.
8718 Comply with the calling conventions defined by Hitachi.
8722 Mark the @code{MAC} register as call-clobbered, even if
8723 @option{-mhitachi} is given.
8727 Increase IEEE-compliance of floating-point code.
8731 Dump instruction size and location in the assembly code.
8735 This option is deprecated. It pads structures to multiple of 4 bytes,
8736 which is incompatible with the SH ABI@.
8740 Optimize for space instead of speed. Implied by @option{-Os}.
8744 When generating position-independent code, emit function calls using
8745 the Global Offset Table instead of the Procedure Linkage Table.
8749 Generate a library function call to invalidate instruction cache
8750 entries, after fixing up a trampoline. This library function call
8751 doesn't assume it can write to the whole memory address space. This
8752 is the default when the target is @code{sh-*-linux*}.
8755 @node System V Options
8756 @subsection Options for System V
8758 These additional options are available on System V Release 4 for
8759 compatibility with other compilers on those systems:
8764 Create a shared object.
8765 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
8769 Identify the versions of each tool used by the compiler, in a
8770 @code{.ident} assembler directive in the output.
8774 Refrain from adding @code{.ident} directives to the output file (this is
8777 @item -YP,@var{dirs}
8779 Search the directories @var{dirs}, and no others, for libraries
8780 specified with @option{-l}.
8784 Look in the directory @var{dir} to find the M4 preprocessor.
8785 The assembler uses this option.
8786 @c This is supposed to go with a -Yd for predefined M4 macro files, but
8787 @c the generic assembler that comes with Solaris takes just -Ym.
8790 @node TMS320C3x/C4x Options
8791 @subsection TMS320C3x/C4x Options
8792 @cindex TMS320C3x/C4x Options
8794 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
8798 @item -mcpu=@var{cpu_type}
8800 Set the instruction set, register set, and instruction scheduling
8801 parameters for machine type @var{cpu_type}. Supported values for
8802 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
8803 @samp{c44}. The default is @samp{c40} to generate code for the
8808 @itemx -msmall-memory
8810 @opindex mbig-memory
8812 @opindex msmall-memory
8814 Generates code for the big or small memory model. The small memory
8815 model assumed that all data fits into one 64K word page. At run-time
8816 the data page (DP) register must be set to point to the 64K page
8817 containing the .bss and .data program sections. The big memory model is
8818 the default and requires reloading of the DP register for every direct
8825 Allow (disallow) allocation of general integer operands into the block
8832 Enable (disable) generation of code using decrement and branch,
8833 DBcond(D), instructions. This is enabled by default for the C4x. To be
8834 on the safe side, this is disabled for the C3x, since the maximum
8835 iteration count on the C3x is @math{2^23 + 1} (but who iterates loops more than
8836 @math{2^23} times on the C3x?). Note that GCC will try to reverse a loop so
8837 that it can utilise the decrement and branch instruction, but will give
8838 up if there is more than one memory reference in the loop. Thus a loop
8839 where the loop counter is decremented can generate slightly more
8840 efficient code, in cases where the RPTB instruction cannot be utilised.
8842 @item -mdp-isr-reload
8844 @opindex mdp-isr-reload
8846 Force the DP register to be saved on entry to an interrupt service
8847 routine (ISR), reloaded to point to the data section, and restored on
8848 exit from the ISR@. This should not be required unless someone has
8849 violated the small memory model by modifying the DP register, say within
8856 For the C3x use the 24-bit MPYI instruction for integer multiplies
8857 instead of a library call to guarantee 32-bit results. Note that if one
8858 of the operands is a constant, then the multiplication will be performed
8859 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
8860 then squaring operations are performed inline instead of a library call.
8863 @itemx -mno-fast-fix
8865 @opindex mno-fast-fix
8866 The C3x/C4x FIX instruction to convert a floating point value to an
8867 integer value chooses the nearest integer less than or equal to the
8868 floating point value rather than to the nearest integer. Thus if the
8869 floating point number is negative, the result will be incorrectly
8870 truncated an additional code is necessary to detect and correct this
8871 case. This option can be used to disable generation of the additional
8872 code required to correct the result.
8878 Enable (disable) generation of repeat block sequences using the RPTB
8879 instruction for zero overhead looping. The RPTB construct is only used
8880 for innermost loops that do not call functions or jump across the loop
8881 boundaries. There is no advantage having nested RPTB loops due to the
8882 overhead required to save and restore the RC, RS, and RE registers.
8883 This is enabled by default with @option{-O2}.
8885 @item -mrpts=@var{count}
8889 Enable (disable) the use of the single instruction repeat instruction
8890 RPTS@. If a repeat block contains a single instruction, and the loop
8891 count can be guaranteed to be less than the value @var{count}, GCC will
8892 emit a RPTS instruction instead of a RPTB@. If no value is specified,
8893 then a RPTS will be emitted even if the loop count cannot be determined
8894 at compile time. Note that the repeated instruction following RPTS does
8895 not have to be reloaded from memory each iteration, thus freeing up the
8896 CPU buses for operands. However, since interrupts are blocked by this
8897 instruction, it is disabled by default.
8899 @item -mloop-unsigned
8900 @itemx -mno-loop-unsigned
8901 @opindex mloop-unsigned
8902 @opindex mno-loop-unsigned
8903 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
8904 is @math{2^31 + 1} since these instructions test if the iteration count is
8905 negative to terminate the loop. If the iteration count is unsigned
8906 there is a possibility than the @math{2^31 + 1} maximum iteration count may be
8907 exceeded. This switch allows an unsigned iteration count.
8911 Try to emit an assembler syntax that the TI assembler (asm30) is happy
8912 with. This also enforces compatibility with the API employed by the TI
8913 C3x C compiler. For example, long doubles are passed as structures
8914 rather than in floating point registers.
8920 Generate code that uses registers (stack) for passing arguments to functions.
8921 By default, arguments are passed in registers where possible rather
8922 than by pushing arguments on to the stack.
8924 @item -mparallel-insns
8925 @itemx -mno-parallel-insns
8926 @opindex mparallel-insns
8927 @opindex mno-parallel-insns
8928 Allow the generation of parallel instructions. This is enabled by
8929 default with @option{-O2}.
8931 @item -mparallel-mpy
8932 @itemx -mno-parallel-mpy
8933 @opindex mparallel-mpy
8934 @opindex mno-parallel-mpy
8935 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
8936 provided @option{-mparallel-insns} is also specified. These instructions have
8937 tight register constraints which can pessimize the code generation
8943 @subsection V850 Options
8944 @cindex V850 Options
8946 These @samp{-m} options are defined for V850 implementations:
8950 @itemx -mno-long-calls
8951 @opindex mlong-calls
8952 @opindex mno-long-calls
8953 Treat all calls as being far away (near). If calls are assumed to be
8954 far away, the compiler will always load the functions address up into a
8955 register, and call indirect through the pointer.
8961 Do not optimize (do optimize) basic blocks that use the same index
8962 pointer 4 or more times to copy pointer into the @code{ep} register, and
8963 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
8964 option is on by default if you optimize.
8966 @item -mno-prolog-function
8967 @itemx -mprolog-function
8968 @opindex mno-prolog-function
8969 @opindex mprolog-function
8970 Do not use (do use) external functions to save and restore registers at
8971 the prolog and epilog of a function. The external functions are slower,
8972 but use less code space if more than one function saves the same number
8973 of registers. The @option{-mprolog-function} option is on by default if
8978 Try to make the code as small as possible. At present, this just turns
8979 on the @option{-mep} and @option{-mprolog-function} options.
8983 Put static or global variables whose size is @var{n} bytes or less into
8984 the tiny data area that register @code{ep} points to. The tiny data
8985 area can hold up to 256 bytes in total (128 bytes for byte references).
8989 Put static or global variables whose size is @var{n} bytes or less into
8990 the small data area that register @code{gp} points to. The small data
8991 area can hold up to 64 kilobytes.
8995 Put static or global variables whose size is @var{n} bytes or less into
8996 the first 32 kilobytes of memory.
9000 Specify that the target processor is the V850.
9003 @opindex mbig-switch
9004 Generate code suitable for big switch tables. Use this option only if
9005 the assembler/linker complain about out of range branches within a switch
9010 @subsection ARC Options
9013 These options are defined for ARC implementations:
9018 Compile code for little endian mode. This is the default.
9022 Compile code for big endian mode.
9025 @opindex mmangle-cpu
9026 Prepend the name of the cpu to all public symbol names.
9027 In multiple-processor systems, there are many ARC variants with different
9028 instruction and register set characteristics. This flag prevents code
9029 compiled for one cpu to be linked with code compiled for another.
9030 No facility exists for handling variants that are ``almost identical''.
9031 This is an all or nothing option.
9033 @item -mcpu=@var{cpu}
9035 Compile code for ARC variant @var{cpu}.
9036 Which variants are supported depend on the configuration.
9037 All variants support @option{-mcpu=base}, this is the default.
9039 @item -mtext=@var{text-section}
9040 @itemx -mdata=@var{data-section}
9041 @itemx -mrodata=@var{readonly-data-section}
9045 Put functions, data, and readonly data in @var{text-section},
9046 @var{data-section}, and @var{readonly-data-section} respectively
9047 by default. This can be overridden with the @code{section} attribute.
9048 @xref{Variable Attributes}.
9053 @subsection NS32K Options
9054 @cindex NS32K options
9056 These are the @samp{-m} options defined for the 32000 series. The default
9057 values for these options depends on which style of 32000 was selected when
9058 the compiler was configured; the defaults for the most common choices are
9066 Generate output for a 32032. This is the default
9067 when the compiler is configured for 32032 and 32016 based systems.
9073 Generate output for a 32332. This is the default
9074 when the compiler is configured for 32332-based systems.
9080 Generate output for a 32532. This is the default
9081 when the compiler is configured for 32532-based systems.
9085 Generate output containing 32081 instructions for floating point.
9086 This is the default for all systems.
9090 Generate output containing 32381 instructions for floating point. This
9091 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9092 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9096 Try and generate multiply-add floating point instructions @code{polyF}
9097 and @code{dotF}. This option is only available if the @option{-m32381}
9098 option is in effect. Using these instructions requires changes to
9099 register allocation which generally has a negative impact on
9100 performance. This option should only be enabled when compiling code
9101 particularly likely to make heavy use of multiply-add instructions.
9104 @opindex mnomulti-add
9105 Do not try and generate multiply-add floating point instructions
9106 @code{polyF} and @code{dotF}. This is the default on all platforms.
9109 @opindex msoft-float
9110 Generate output containing library calls for floating point.
9111 @strong{Warning:} the requisite libraries may not be available.
9114 @opindex mnobitfield
9115 Do not use the bit-field instructions. On some machines it is faster to
9116 use shifting and masking operations. This is the default for the pc532.
9120 Do use the bit-field instructions. This is the default for all platforms
9125 Use a different function-calling convention, in which functions
9126 that take a fixed number of arguments return pop their
9127 arguments on return with the @code{ret} instruction.
9129 This calling convention is incompatible with the one normally
9130 used on Unix, so you cannot use it if you need to call libraries
9131 compiled with the Unix compiler.
9133 Also, you must provide function prototypes for all functions that
9134 take variable numbers of arguments (including @code{printf});
9135 otherwise incorrect code will be generated for calls to those
9138 In addition, seriously incorrect code will result if you call a
9139 function with too many arguments. (Normally, extra arguments are
9140 harmlessly ignored.)
9142 This option takes its name from the 680x0 @code{rtd} instruction.
9147 Use a different function-calling convention where the first two arguments
9148 are passed in registers.
9150 This calling convention is incompatible with the one normally
9151 used on Unix, so you cannot use it if you need to call libraries
9152 compiled with the Unix compiler.
9155 @opindex mnoregparam
9156 Do not pass any arguments in registers. This is the default for all
9161 It is OK to use the sb as an index register which is always loaded with
9162 zero. This is the default for the pc532-netbsd target.
9166 The sb register is not available for use or has not been initialized to
9167 zero by the run time system. This is the default for all targets except
9168 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9169 @option{-fpic} is set.
9173 Many ns32000 series addressing modes use displacements of up to 512MB@.
9174 If an address is above 512MB then displacements from zero can not be used.
9175 This option causes code to be generated which can be loaded above 512MB@.
9176 This may be useful for operating systems or ROM code.
9180 Assume code will be loaded in the first 512MB of virtual address space.
9181 This is the default for all platforms.
9187 @subsection AVR Options
9190 These options are defined for AVR implementations:
9193 @item -mmcu=@var{mcu}
9195 Specify ATMEL AVR instruction set or MCU type.
9197 Instruction set avr1 is for the minimal AVR core, not supported by the C
9198 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9199 attiny11, attiny12, attiny15, attiny28).
9201 Instruction set avr2 (default) is for the classic AVR core with up to
9202 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9203 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9204 at90c8534, at90s8535).
9206 Instruction set avr3 is for the classic AVR core with up to 128K program
9207 memory space (MCU types: atmega103, atmega603).
9209 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9210 memory space (MCU types: atmega83, atmega85).
9212 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9213 memory space (MCU types: atmega161, atmega163, atmega32, at94k).
9217 Output instruction sizes to the asm file.
9219 @item -minit-stack=@var{N}
9220 @opindex minit-stack
9221 Specify the initial stack address, which may be a symbol or numeric value,
9222 @samp{__stack} is the default.
9224 @item -mno-interrupts
9225 @opindex mno-interrupts
9226 Generated code is not compatible with hardware interrupts.
9227 Code size will be smaller.
9229 @item -mcall-prologues
9230 @opindex mcall-prologues
9231 Functions prologues/epilogues expanded as call to appropriate
9232 subroutines. Code size will be smaller.
9234 @item -mno-tablejump
9235 @opindex mno-tablejump
9236 Do not generate tablejump insns which sometimes increase code size.
9239 @opindex mtiny-stack
9240 Change only the low 8 bits of the stack pointer.
9244 @subsection MCore Options
9245 @cindex MCore options
9247 These are the @samp{-m} options defined for the Motorola M*Core
9257 @opindex mno-hardlit
9258 Inline constants into the code stream if it can be done in two
9259 instructions or less.
9267 Use the divide instruction. (Enabled by default).
9269 @item -mrelax-immediate
9270 @itemx -mrelax-immediate
9271 @itemx -mno-relax-immediate
9272 @opindex mrelax-immediate
9273 @opindex mrelax-immediate
9274 @opindex mno-relax-immediate
9275 Allow arbitrary sized immediates in bit operations.
9277 @item -mwide-bitfields
9278 @itemx -mwide-bitfields
9279 @itemx -mno-wide-bitfields
9280 @opindex mwide-bitfields
9281 @opindex mwide-bitfields
9282 @opindex mno-wide-bitfields
9283 Always treat bit-fields as int-sized.
9285 @item -m4byte-functions
9286 @itemx -m4byte-functions
9287 @itemx -mno-4byte-functions
9288 @opindex m4byte-functions
9289 @opindex m4byte-functions
9290 @opindex mno-4byte-functions
9291 Force all functions to be aligned to a four byte boundary.
9293 @item -mcallgraph-data
9294 @itemx -mcallgraph-data
9295 @itemx -mno-callgraph-data
9296 @opindex mcallgraph-data
9297 @opindex mcallgraph-data
9298 @opindex mno-callgraph-data
9299 Emit callgraph information.
9303 @itemx -mno-slow-bytes
9304 @opindex mslow-bytes
9305 @opindex mslow-bytes
9306 @opindex mno-slow-bytes
9307 Prefer word access when reading byte quantities.
9309 @item -mlittle-endian
9310 @itemx -mlittle-endian
9312 @opindex mlittle-endian
9313 @opindex mlittle-endian
9314 @opindex mbig-endian
9315 Generate code for a little endian target.
9323 Generate code for the 210 processor.
9327 @subsection IA-64 Options
9328 @cindex IA-64 Options
9330 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9334 @opindex mbig-endian
9335 Generate code for a big endian target. This is the default for HPUX@.
9337 @item -mlittle-endian
9338 @opindex mlittle-endian
9339 Generate code for a little endian target. This is the default for AIX5
9346 Generate (or don't) code for the GNU assembler. This is the default.
9347 @c Also, this is the default if the configure option @option{--with-gnu-as}
9354 Generate (or don't) code for the GNU linker. This is the default.
9355 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9360 Generate code that does not use a global pointer register. The result
9361 is not position independent code, and violates the IA-64 ABI@.
9363 @item -mvolatile-asm-stop
9364 @itemx -mno-volatile-asm-stop
9365 @opindex mvolatile-asm-stop
9366 @opindex mno-volatile-asm-stop
9367 Generate (or don't) a stop bit immediately before and after volatile asm
9372 Generate code that works around Itanium B step errata.
9374 @item -mregister-names
9375 @itemx -mno-register-names
9376 @opindex mregister-names
9377 @opindex mno-register-names
9378 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9379 the stacked registers. This may make assembler output more readable.
9385 Disable (or enable) optimizations that use the small data section. This may
9386 be useful for working around optimizer bugs.
9389 @opindex mconstant-gp
9390 Generate code that uses a single constant global pointer value. This is
9391 useful when compiling kernel code.
9395 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9396 This is useful when compiling firmware code.
9398 @item -minline-divide-min-latency
9399 @opindex minline-divide-min-latency
9400 Generate code for inline divides using the minimum latency algorithm.
9402 @item -minline-divide-max-throughput
9403 @opindex minline-divide-max-throughput
9404 Generate code for inline divides using the maximum throughput algorithm.
9406 @item -mno-dwarf2-asm
9408 @opindex mno-dwarf2-asm
9409 @opindex mdwarf2-asm
9410 Don't (or do) generate assembler code for the DWARF2 line number debugging
9411 info. This may be useful when not using the GNU assembler.
9413 @item -mfixed-range=@var{register-range}
9414 @opindex mfixed-range
9415 Generate code treating the given register range as fixed registers.
9416 A fixed register is one that the register allocator can not use. This is
9417 useful when compiling kernel code. A register range is specified as
9418 two registers separated by a dash. Multiple register ranges can be
9419 specified separated by a comma.
9423 @subsection D30V Options
9424 @cindex D30V Options
9426 These @samp{-m} options are defined for D30V implementations:
9431 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
9432 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
9433 memory, which starts at location @code{0x80000000}.
9437 Same as the @option{-mextmem} switch.
9441 Link the @samp{.text} section into onchip text memory, which starts at
9442 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
9443 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
9444 into onchip data memory, which starts at location @code{0x20000000}.
9446 @item -mno-asm-optimize
9447 @itemx -masm-optimize
9448 @opindex mno-asm-optimize
9449 @opindex masm-optimize
9450 Disable (enable) passing @option{-O} to the assembler when optimizing.
9451 The assembler uses the @option{-O} option to automatically parallelize
9452 adjacent short instructions where possible.
9454 @item -mbranch-cost=@var{n}
9455 @opindex mbranch-cost
9456 Increase the internal costs of branches to @var{n}. Higher costs means
9457 that the compiler will issue more instructions to avoid doing a branch.
9460 @item -mcond-exec=@var{n}
9462 Specify the maximum number of conditionally executed instructions that
9463 replace a branch. The default is 4.
9466 @node S/390 and zSeries Options
9467 @subsection S/390 and zSeries Options
9468 @cindex S/390 and zSeries Options
9470 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
9475 @opindex mhard-float
9476 @opindex msoft-float
9477 Use (do not use) the hardware floating-point instructions and registers
9478 for floating-point operations. When @option{-msoft-float} is specified,
9479 functions in @file{libgcc.a} will be used to perform floating-point
9480 operations. When @option{-mhard-float} is specified, the compiler
9481 generates IEEE floating-point instructions. This is the default.
9484 @itemx -mno-backchain
9486 @opindex mno-backchain
9487 Generate (or do not generate) code which maintains an explicit
9488 backchain within the stack frame that points to the caller's frame.
9489 This is currently needed to allow debugging. The default is to
9490 generate the backchain.
9493 @itemx -mno-small-exec
9494 @opindex msmall-exec
9495 @opindex mno-small-exec
9496 Generate (or do not generate) code using the @code{bras} instruction
9497 to do subroutine calls.
9498 This only works reliably if the total executable size does not
9499 exceed 64k. The default is to use the @code{basr} instruction instead,
9500 which does not have this limitation.
9506 When @option{-m31} is specified, generate code compliant to the
9507 Linux for S/390 ABI@. When @option{-m64} is specified, generate
9508 code compliant to the Linux for zSeries ABI@. This allows GCC in
9509 particular to generate 64-bit instructions. For the @samp{s390}
9510 targets, the default is @option{-m31}, while the @samp{s390x}
9511 targets default to @option{-m64}.
9517 Generate (or do not generate) code using the @code{mvcle} instruction
9518 to perform block moves. When @option{-mno-mvcle} is specifed,
9519 use a @code{mvc} loop instead. This is the default.
9525 Print (or do not print) additional debug information when compiling.
9526 The default is to not print debug information.
9531 @subsection CRIS Options
9532 @cindex CRIS Options
9534 These options are defined specifically for the CRIS ports.
9537 @item -march=@var{architecture-type}
9538 @itemx -mcpu=@var{architecture-type}
9541 Generate code for the specified architecture. The choices for
9542 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9543 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
9544 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9547 @item -mtune=@var{architecture-type}
9549 Tune to @var{architecture-type} everything applicable about the generated
9550 code, except for the ABI and the set of available instructions. The
9551 choices for @var{architecture-type} are the same as for
9552 @option{-march=@var{architecture-type}}.
9554 @item -mmax-stack-frame=@var{n}
9555 @opindex mmax-stack-frame
9556 Warn when the stack frame of a function exceeds @var{n} bytes.
9558 @item -melinux-stacksize=@var{n}
9559 @opindex melinux-stacksize
9560 Only available with the @samp{cris-axis-aout} target. Arranges for
9561 indications in the program to the kernel loader that the stack of the
9562 program should be set to @var{n} bytes.
9568 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9569 @option{-march=v3} and @option{-march=v8} respectively.
9573 Enable CRIS-specific verbose debug-related information in the assembly
9574 code. This option also has the effect to turn off the @samp{#NO_APP}
9575 formatted-code indicator to the assembler at the beginning of the
9580 Do not use condition-code results from previous instruction; always emit
9581 compare and test instructions before use of condition codes.
9583 @item -mno-side-effects
9584 @opindex mno-side-effects
9585 Do not emit instructions with side-effects in addressing modes other than
9589 @itemx -mno-stack-align
9591 @itemx -mno-data-align
9592 @itemx -mconst-align
9593 @itemx -mno-const-align
9594 @opindex mstack-align
9595 @opindex mno-stack-align
9596 @opindex mdata-align
9597 @opindex mno-data-align
9598 @opindex mconst-align
9599 @opindex mno-const-align
9600 These options (no-options) arranges (eliminate arrangements) for the
9601 stack-frame, individual data and constants to be aligned for the maximum
9602 single data access size for the chosen CPU model. The default is to
9603 arrange for 32-bit alignment. ABI details such as structure layout are
9604 not affected by these options.
9612 Similar to the stack- data- and const-align options above, these options
9613 arrange for stack-frame, writable data and constants to all be 32-bit,
9614 16-bit or 8-bit aligned. The default is 32-bit alignment.
9616 @item -mno-prologue-epilogue
9617 @itemx -mprologue-epilogue
9618 @opindex mno-prologue-epilogue
9619 @opindex mprologue-epilogue
9620 With @option{-mno-prologue-epilogue}, the normal function prologue and
9621 epilogue that sets up the stack-frame are omitted and no return
9622 instructions or return sequences are generated in the code. Use this
9623 option only together with visual inspection of the compiled code: no
9624 warnings or errors are generated when call-saved registers must be saved,
9625 or storage for local variable needs to be allocated.
9631 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9632 instruction sequences that load addresses for functions from the PLT part
9633 of the GOT rather than (traditional on other architectures) calls to the
9634 PLT. The default is @option{-mgotplt}.
9638 Legacy no-op option only recognized with the cris-axis-aout target.
9642 Legacy no-op option only recognized with the cris-axis-elf and
9643 cris-axis-linux-gnu targets.
9647 Only recognized with the cris-axis-aout target, where it selects a
9648 GNU/linux-like multilib, include files and instruction set for
9653 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9657 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
9658 to link with input-output functions from a simulator library. Code,
9659 initialized data and zero-initialized data are allocated consecutively.
9663 Like @option{-sim}, but pass linker options to locate initialized data at
9664 0x40000000 and zero-initialized data at 0x80000000.
9668 @subsection MMIX Options
9669 @cindex MMIX Options
9671 These options are defined for the MMIX:
9675 @itemx -mno-libfuncs
9676 Specify that intrinsic library functions are being compiled, passing all
9677 values in registers, no matter the size.
9681 Generate floating-point comparison instructions that compare with respect
9682 to the @code{rE} epsilon register.
9684 @item -mabi=mmixware
9686 Generate code that passes function parameters and return values that (in
9687 the called function) are seen as registers @code{$0} and up, as opposed to
9688 the GNU ABI which uses global registers @code{$231} and up.
9691 @item -mno-zero-extend
9692 When reading data from memory in sizes shorter than 64 bits, use (do not
9693 use) zero-extending load instructions by default, rather than
9694 sign-extending ones.
9697 @itemx -mno-knuthdiv
9698 Make the result of a division yielding a remainder have the same sign as
9699 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
9700 remainder follows the sign of the dividend. Both methods are
9701 arithmetically valid, the latter being almost exclusively used.
9703 @item -mtoplevel-symbols
9704 @itemx -mno-toplevel-symbols
9705 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
9706 code can be used with the @code{PREFIX} assembly directive.
9709 Generate an executable in the ELF format, rather than the default
9710 @samp{mmo} format used by the @command{mmix} simulator.
9713 @node Code Gen Options
9714 @section Options for Code Generation Conventions
9715 @cindex code generation conventions
9716 @cindex options, code generation
9717 @cindex run-time options
9719 These machine-independent options control the interface conventions
9720 used in code generation.
9722 Most of them have both positive and negative forms; the negative form
9723 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
9724 one of the forms is listed---the one which is not the default. You
9725 can figure out the other form by either removing @samp{no-} or adding
9730 @opindex fexceptions
9731 Enable exception handling. Generates extra code needed to propagate
9732 exceptions. For some targets, this implies GCC will generate frame
9733 unwind information for all functions, which can produce significant data
9734 size overhead, although it does not affect execution. If you do not
9735 specify this option, GCC will enable it by default for languages like
9736 C++ which normally require exception handling, and disable it for
9737 languages like C that do not normally require it. However, you may need
9738 to enable this option when compiling C code that needs to interoperate
9739 properly with exception handlers written in C++. You may also wish to
9740 disable this option if you are compiling older C++ programs that don't
9741 use exception handling.
9743 @item -fnon-call-exceptions
9744 @opindex fnon-call-exceptions
9745 Generate code that allows trapping instructions to throw exceptions.
9746 Note that this requires platform-specific runtime support that does
9747 not exist everywhere. Moreover, it only allows @emph{trapping}
9748 instructions to throw exceptions, i.e.@: memory references or floating
9749 point instructions. It does not allow exceptions to be thrown from
9750 arbitrary signal handlers such as @code{SIGALRM}.
9752 @item -funwind-tables
9753 @opindex funwind-tables
9754 Similar to @option{-fexceptions}, except that it will just generate any needed
9755 static data, but will not affect the generated code in any other way.
9756 You will normally not enable this option; instead, a language processor
9757 that needs this handling would enable it on your behalf.
9759 @item -fasynchronous-unwind-tables
9760 @opindex funwind-tables
9761 Generate unwind table in dwarf2 format, if supported by target machine. The
9762 table is exact at each instruction boundary, so it can be used for stack
9763 unwinding from asynchronous events (such as debugger or garbage collector).
9765 @item -fpcc-struct-return
9766 @opindex fpcc-struct-return
9767 Return ``short'' @code{struct} and @code{union} values in memory like
9768 longer ones, rather than in registers. This convention is less
9769 efficient, but it has the advantage of allowing intercallability between
9770 GCC-compiled files and files compiled with other compilers.
9772 The precise convention for returning structures in memory depends
9773 on the target configuration macros.
9775 Short structures and unions are those whose size and alignment match
9776 that of some integer type.
9778 @item -freg-struct-return
9779 @opindex freg-struct-return
9780 Return @code{struct} and @code{union} values in registers when possible.
9781 This is more efficient for small structures than
9782 @option{-fpcc-struct-return}.
9784 If you specify neither @option{-fpcc-struct-return} nor
9785 @option{-freg-struct-return}, GCC defaults to whichever convention is
9786 standard for the target. If there is no standard convention, GCC
9787 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
9788 the principal compiler. In those cases, we can choose the standard, and
9789 we chose the more efficient register return alternative.
9792 @opindex fshort-enums
9793 Allocate to an @code{enum} type only as many bytes as it needs for the
9794 declared range of possible values. Specifically, the @code{enum} type
9795 will be equivalent to the smallest integer type which has enough room.
9797 @item -fshort-double
9798 @opindex fshort-double
9799 Use the same size for @code{double} as for @code{float}.
9802 @opindex fshared-data
9803 Requests that the data and non-@code{const} variables of this
9804 compilation be shared data rather than private data. The distinction
9805 makes sense only on certain operating systems, where shared data is
9806 shared between processes running the same program, while private data
9807 exists in one copy per process.
9811 In C, allocate even uninitialized global variables in the data section of the
9812 object file, rather than generating them as common blocks. This has the
9813 effect that if the same variable is declared (without @code{extern}) in
9814 two different compilations, you will get an error when you link them.
9815 The only reason this might be useful is if you wish to verify that the
9816 program will work on other systems which always work this way.
9820 Ignore the @samp{#ident} directive.
9822 @item -fno-gnu-linker
9823 @opindex fno-gnu-linker
9824 Do not output global initializations (such as C++ constructors and
9825 destructors) in the form used by the GNU linker (on systems where the GNU
9826 linker is the standard method of handling them). Use this option when
9827 you want to use a non-GNU linker, which also requires using the
9828 @command{collect2} program to make sure the system linker includes
9829 constructors and destructors. (@command{collect2} is included in the GCC
9830 distribution.) For systems which @emph{must} use @command{collect2}, the
9831 compiler driver @command{gcc} is configured to do this automatically.
9833 @item -finhibit-size-directive
9834 @opindex finhibit-size-directive
9835 Don't output a @code{.size} assembler directive, or anything else that
9836 would cause trouble if the function is split in the middle, and the
9837 two halves are placed at locations far apart in memory. This option is
9838 used when compiling @file{crtstuff.c}; you should not need to use it
9842 @opindex fverbose-asm
9843 Put extra commentary information in the generated assembly code to
9844 make it more readable. This option is generally only of use to those
9845 who actually need to read the generated assembly code (perhaps while
9846 debugging the compiler itself).
9848 @option{-fno-verbose-asm}, the default, causes the
9849 extra information to be omitted and is useful when comparing two assembler
9854 Consider all memory references through pointers to be volatile.
9856 @item -fvolatile-global
9857 @opindex fvolatile-global
9858 Consider all memory references to extern and global data items to
9859 be volatile. GCC does not consider static data items to be volatile
9860 because of this switch.
9862 @item -fvolatile-static
9863 @opindex fvolatile-static
9864 Consider all memory references to static data to be volatile.
9868 @cindex global offset table
9870 Generate position-independent code (PIC) suitable for use in a shared
9871 library, if supported for the target machine. Such code accesses all
9872 constant addresses through a global offset table (GOT)@. The dynamic
9873 loader resolves the GOT entries when the program starts (the dynamic
9874 loader is not part of GCC; it is part of the operating system). If
9875 the GOT size for the linked executable exceeds a machine-specific
9876 maximum size, you get an error message from the linker indicating that
9877 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
9878 instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k
9879 on the m68k and RS/6000. The 386 has no such limit.)
9881 Position-independent code requires special support, and therefore works
9882 only on certain machines. For the 386, GCC supports PIC for System V
9883 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
9884 position-independent.
9888 If supported for the target machine, emit position-independent code,
9889 suitable for dynamic linking and avoiding any limit on the size of the
9890 global offset table. This option makes a difference on the m68k, m88k,
9893 Position-independent code requires special support, and therefore works
9894 only on certain machines.
9896 @item -ffixed-@var{reg}
9898 Treat the register named @var{reg} as a fixed register; generated code
9899 should never refer to it (except perhaps as a stack pointer, frame
9900 pointer or in some other fixed role).
9902 @var{reg} must be the name of a register. The register names accepted
9903 are machine-specific and are defined in the @code{REGISTER_NAMES}
9904 macro in the machine description macro file.
9906 This flag does not have a negative form, because it specifies a
9909 @item -fcall-used-@var{reg}
9911 Treat the register named @var{reg} as an allocable register that is
9912 clobbered by function calls. It may be allocated for temporaries or
9913 variables that do not live across a call. Functions compiled this way
9914 will not save and restore the register @var{reg}.
9916 It is an error to used this flag with the frame pointer or stack pointer.
9917 Use of this flag for other registers that have fixed pervasive roles in
9918 the machine's execution model will produce disastrous results.
9920 This flag does not have a negative form, because it specifies a
9923 @item -fcall-saved-@var{reg}
9924 @opindex fcall-saved
9925 Treat the register named @var{reg} as an allocable register saved by
9926 functions. It may be allocated even for temporaries or variables that
9927 live across a call. Functions compiled this way will save and restore
9928 the register @var{reg} if they use it.
9930 It is an error to used this flag with the frame pointer or stack pointer.
9931 Use of this flag for other registers that have fixed pervasive roles in
9932 the machine's execution model will produce disastrous results.
9934 A different sort of disaster will result from the use of this flag for
9935 a register in which function values may be returned.
9937 This flag does not have a negative form, because it specifies a
9941 @opindex fpack-struct
9942 Pack all structure members together without holes. Usually you would
9943 not want to use this option, since it makes the code suboptimal, and
9944 the offsets of structure members won't agree with system libraries.
9946 @item -finstrument-functions
9947 @opindex finstrument-functions
9948 Generate instrumentation calls for entry and exit to functions. Just
9949 after function entry and just before function exit, the following
9950 profiling functions will be called with the address of the current
9951 function and its call site. (On some platforms,
9952 @code{__builtin_return_address} does not work beyond the current
9953 function, so the call site information may not be available to the
9954 profiling functions otherwise.)
9957 void __cyg_profile_func_enter (void *this_fn,
9959 void __cyg_profile_func_exit (void *this_fn,
9963 The first argument is the address of the start of the current function,
9964 which may be looked up exactly in the symbol table.
9966 This instrumentation is also done for functions expanded inline in other
9967 functions. The profiling calls will indicate where, conceptually, the
9968 inline function is entered and exited. This means that addressable
9969 versions of such functions must be available. If all your uses of a
9970 function are expanded inline, this may mean an additional expansion of
9971 code size. If you use @samp{extern inline} in your C code, an
9972 addressable version of such functions must be provided. (This is
9973 normally the case anyways, but if you get lucky and the optimizer always
9974 expands the functions inline, you might have gotten away without
9975 providing static copies.)
9977 A function may be given the attribute @code{no_instrument_function}, in
9978 which case this instrumentation will not be done. This can be used, for
9979 example, for the profiling functions listed above, high-priority
9980 interrupt routines, and any functions from which the profiling functions
9981 cannot safely be called (perhaps signal handlers, if the profiling
9982 routines generate output or allocate memory).
9985 @opindex fstack-check
9986 Generate code to verify that you do not go beyond the boundary of the
9987 stack. You should specify this flag if you are running in an
9988 environment with multiple threads, but only rarely need to specify it in
9989 a single-threaded environment since stack overflow is automatically
9990 detected on nearly all systems if there is only one stack.
9992 Note that this switch does not actually cause checking to be done; the
9993 operating system must do that. The switch causes generation of code
9994 to ensure that the operating system sees the stack being extended.
9996 @item -fstack-limit-register=@var{reg}
9997 @itemx -fstack-limit-symbol=@var{sym}
9998 @itemx -fno-stack-limit
9999 @opindex fstack-limit-register
10000 @opindex fstack-limit-symbol
10001 @opindex fno-stack-limit
10002 Generate code to ensure that the stack does not grow beyond a certain value,
10003 either the value of a register or the address of a symbol. If the stack
10004 would grow beyond the value, a signal is raised. For most targets,
10005 the signal is raised before the stack overruns the boundary, so
10006 it is possible to catch the signal without taking special precautions.
10008 For instance, if the stack starts at absolute address @samp{0x80000000}
10009 and grows downwards, you can use the flags
10010 @option{-fstack-limit-symbol=__stack_limit} and
10011 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
10012 of 128KB@. Note that this may only work with the GNU linker.
10014 @cindex aliasing of parameters
10015 @cindex parameters, aliased
10016 @item -fargument-alias
10017 @itemx -fargument-noalias
10018 @itemx -fargument-noalias-global
10019 @opindex fargument-alias
10020 @opindex fargument-noalias
10021 @opindex fargument-noalias-global
10022 Specify the possible relationships among parameters and between
10023 parameters and global data.
10025 @option{-fargument-alias} specifies that arguments (parameters) may
10026 alias each other and may alias global storage.@*
10027 @option{-fargument-noalias} specifies that arguments do not alias
10028 each other, but may alias global storage.@*
10029 @option{-fargument-noalias-global} specifies that arguments do not
10030 alias each other and do not alias global storage.
10032 Each language will automatically use whatever option is required by
10033 the language standard. You should not need to use these options yourself.
10035 @item -fleading-underscore
10036 @opindex fleading-underscore
10037 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
10038 change the way C symbols are represented in the object file. One use
10039 is to help link with legacy assembly code.
10041 Be warned that you should know what you are doing when invoking this
10042 option, and that not all targets provide complete support for it.
10047 @node Environment Variables
10048 @section Environment Variables Affecting GCC
10049 @cindex environment variables
10051 @c man begin ENVIRONMENT
10053 This section describes several environment variables that affect how GCC
10054 operates. Some of them work by specifying directories or prefixes to use
10055 when searching for various kinds of files. Some are used to specify other
10056 aspects of the compilation environment.
10059 Note that you can also specify places to search using options such as
10060 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
10061 take precedence over places specified using environment variables, which
10062 in turn take precedence over those specified by the configuration of GCC@.
10066 Note that you can also specify places to search using options such as
10067 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
10068 take precedence over places specified using environment variables, which
10069 in turn take precedence over those specified by the configuration of GCC@.
10076 @c @itemx LC_COLLATE
10078 @c @itemx LC_MONETARY
10079 @c @itemx LC_NUMERIC
10084 @c @findex LC_COLLATE
10085 @findex LC_MESSAGES
10086 @c @findex LC_MONETARY
10087 @c @findex LC_NUMERIC
10091 These environment variables control the way that GCC uses
10092 localization information that allow GCC to work with different
10093 national conventions. GCC inspects the locale categories
10094 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
10095 so. These locale categories can be set to any value supported by your
10096 installation. A typical value is @samp{en_UK} for English in the United
10099 The @env{LC_CTYPE} environment variable specifies character
10100 classification. GCC uses it to determine the character boundaries in
10101 a string; this is needed for some multibyte encodings that contain quote
10102 and escape characters that would otherwise be interpreted as a string
10105 The @env{LC_MESSAGES} environment variable specifies the language to
10106 use in diagnostic messages.
10108 If the @env{LC_ALL} environment variable is set, it overrides the value
10109 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
10110 and @env{LC_MESSAGES} default to the value of the @env{LANG}
10111 environment variable. If none of these variables are set, GCC
10112 defaults to traditional C English behavior.
10116 If @env{TMPDIR} is set, it specifies the directory to use for temporary
10117 files. GCC uses temporary files to hold the output of one stage of
10118 compilation which is to be used as input to the next stage: for example,
10119 the output of the preprocessor, which is the input to the compiler
10122 @item GCC_EXEC_PREFIX
10123 @findex GCC_EXEC_PREFIX
10124 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
10125 names of the subprograms executed by the compiler. No slash is added
10126 when this prefix is combined with the name of a subprogram, but you can
10127 specify a prefix that ends with a slash if you wish.
10129 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
10130 an appropriate prefix to use based on the pathname it was invoked with.
10132 If GCC cannot find the subprogram using the specified prefix, it
10133 tries looking in the usual places for the subprogram.
10135 The default value of @env{GCC_EXEC_PREFIX} is
10136 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
10137 of @code{prefix} when you ran the @file{configure} script.
10139 Other prefixes specified with @option{-B} take precedence over this prefix.
10141 This prefix is also used for finding files such as @file{crt0.o} that are
10144 In addition, the prefix is used in an unusual way in finding the
10145 directories to search for header files. For each of the standard
10146 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
10147 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
10148 replacing that beginning with the specified prefix to produce an
10149 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
10150 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
10151 These alternate directories are searched first; the standard directories
10154 @item COMPILER_PATH
10155 @findex COMPILER_PATH
10156 The value of @env{COMPILER_PATH} is a colon-separated list of
10157 directories, much like @env{PATH}. GCC tries the directories thus
10158 specified when searching for subprograms, if it can't find the
10159 subprograms using @env{GCC_EXEC_PREFIX}.
10162 @findex LIBRARY_PATH
10163 The value of @env{LIBRARY_PATH} is a colon-separated list of
10164 directories, much like @env{PATH}. When configured as a native compiler,
10165 GCC tries the directories thus specified when searching for special
10166 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
10167 using GCC also uses these directories when searching for ordinary
10168 libraries for the @option{-l} option (but directories specified with
10169 @option{-L} come first).
10171 @item C_INCLUDE_PATH
10172 @itemx CPLUS_INCLUDE_PATH
10173 @itemx OBJC_INCLUDE_PATH
10174 @findex C_INCLUDE_PATH
10175 @findex CPLUS_INCLUDE_PATH
10176 @findex OBJC_INCLUDE_PATH
10177 @c @itemx OBJCPLUS_INCLUDE_PATH
10178 These environment variables pertain to particular languages. Each
10179 variable's value is a colon-separated list of directories, much like
10180 @env{PATH}. When GCC searches for header files, it tries the
10181 directories listed in the variable for the language you are using, after
10182 the directories specified with @option{-I} but before the standard header
10185 @item DEPENDENCIES_OUTPUT
10186 @findex DEPENDENCIES_OUTPUT
10187 @cindex dependencies for make as output
10188 If this variable is set, its value specifies how to output dependencies
10189 for Make based on the header files processed by the compiler. This
10190 output looks much like the output from the @option{-M} option
10191 (@pxref{Preprocessor Options}), but it goes to a separate file, and is
10192 in addition to the usual results of compilation.
10194 The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in
10195 which case the Make rules are written to that file, guessing the target
10196 name from the source file name. Or the value can have the form
10197 @samp{@var{file} @var{target}}, in which case the rules are written to
10198 file @var{file} using @var{target} as the target name.
10202 @cindex locale definition
10203 This variable is used to pass locale information to the compiler. One way in
10204 which this information is used is to determine the character set to be used
10205 when character literals, string literals and comments are parsed in C and C++.
10206 When the compiler is configured to allow multibyte characters,
10207 the following values for @env{LANG} are recognized:
10211 Recognize JIS characters.
10213 Recognize SJIS characters.
10215 Recognize EUCJP characters.
10218 If @env{LANG} is not defined, or if it has some other value, then the
10219 compiler will use mblen and mbtowc as defined by the default locale to
10220 recognize and translate multibyte characters.
10225 @node Running Protoize
10226 @section Running Protoize
10228 The program @code{protoize} is an optional part of GCC@. You can use
10229 it to add prototypes to a program, thus converting the program to ISO
10230 C in one respect. The companion program @code{unprotoize} does the
10231 reverse: it removes argument types from any prototypes that are found.
10233 When you run these programs, you must specify a set of source files as
10234 command line arguments. The conversion programs start out by compiling
10235 these files to see what functions they define. The information gathered
10236 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
10238 After scanning comes actual conversion. The specified files are all
10239 eligible to be converted; any files they include (whether sources or
10240 just headers) are eligible as well.
10242 But not all the eligible files are converted. By default,
10243 @code{protoize} and @code{unprotoize} convert only source and header
10244 files in the current directory. You can specify additional directories
10245 whose files should be converted with the @option{-d @var{directory}}
10246 option. You can also specify particular files to exclude with the
10247 @option{-x @var{file}} option. A file is converted if it is eligible, its
10248 directory name matches one of the specified directory names, and its
10249 name within the directory has not been excluded.
10251 Basic conversion with @code{protoize} consists of rewriting most
10252 function definitions and function declarations to specify the types of
10253 the arguments. The only ones not rewritten are those for varargs
10256 @code{protoize} optionally inserts prototype declarations at the
10257 beginning of the source file, to make them available for any calls that
10258 precede the function's definition. Or it can insert prototype
10259 declarations with block scope in the blocks where undeclared functions
10262 Basic conversion with @code{unprotoize} consists of rewriting most
10263 function declarations to remove any argument types, and rewriting
10264 function definitions to the old-style pre-ISO form.
10266 Both conversion programs print a warning for any function declaration or
10267 definition that they can't convert. You can suppress these warnings
10270 The output from @code{protoize} or @code{unprotoize} replaces the
10271 original source file. The original file is renamed to a name ending
10272 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
10273 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
10274 for DOS) file already exists, then the source file is simply discarded.
10276 @code{protoize} and @code{unprotoize} both depend on GCC itself to
10277 scan the program and collect information about the functions it uses.
10278 So neither of these programs will work until GCC is installed.
10280 Here is a table of the options you can use with @code{protoize} and
10281 @code{unprotoize}. Each option works with both programs unless
10285 @item -B @var{directory}
10286 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
10287 usual directory (normally @file{/usr/local/lib}). This file contains
10288 prototype information about standard system functions. This option
10289 applies only to @code{protoize}.
10291 @item -c @var{compilation-options}
10292 Use @var{compilation-options} as the options when running @code{gcc} to
10293 produce the @samp{.X} files. The special option @option{-aux-info} is
10294 always passed in addition, to tell @code{gcc} to write a @samp{.X} file.
10296 Note that the compilation options must be given as a single argument to
10297 @code{protoize} or @code{unprotoize}. If you want to specify several
10298 @code{gcc} options, you must quote the entire set of compilation options
10299 to make them a single word in the shell.
10301 There are certain @code{gcc} arguments that you cannot use, because they
10302 would produce the wrong kind of output. These include @option{-g},
10303 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
10304 the @var{compilation-options}, they are ignored.
10307 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
10308 systems) instead of @samp{.c}. This is convenient if you are converting
10309 a C program to C++. This option applies only to @code{protoize}.
10312 Add explicit global declarations. This means inserting explicit
10313 declarations at the beginning of each source file for each function
10314 that is called in the file and was not declared. These declarations
10315 precede the first function definition that contains a call to an
10316 undeclared function. This option applies only to @code{protoize}.
10318 @item -i @var{string}
10319 Indent old-style parameter declarations with the string @var{string}.
10320 This option applies only to @code{protoize}.
10322 @code{unprotoize} converts prototyped function definitions to old-style
10323 function definitions, where the arguments are declared between the
10324 argument list and the initial @samp{@{}. By default, @code{unprotoize}
10325 uses five spaces as the indentation. If you want to indent with just
10326 one space instead, use @option{-i " "}.
10329 Keep the @samp{.X} files. Normally, they are deleted after conversion
10333 Add explicit local declarations. @code{protoize} with @option{-l} inserts
10334 a prototype declaration for each function in each block which calls the
10335 function without any declaration. This option applies only to
10339 Make no real changes. This mode just prints information about the conversions
10340 that would have been done without @option{-n}.
10343 Make no @samp{.save} files. The original files are simply deleted.
10344 Use this option with caution.
10346 @item -p @var{program}
10347 Use the program @var{program} as the compiler. Normally, the name
10348 @file{gcc} is used.
10351 Work quietly. Most warnings are suppressed.
10354 Print the version number, just like @option{-v} for @code{gcc}.
10357 If you need special compiler options to compile one of your program's
10358 source files, then you should generate that file's @samp{.X} file
10359 specially, by running @code{gcc} on that source file with the
10360 appropriate options and the option @option{-aux-info}. Then run
10361 @code{protoize} on the entire set of files. @code{protoize} will use
10362 the existing @samp{.X} file because it is newer than the source file.
10366 gcc -Dfoo=bar file1.c -aux-info file1.X
10371 You need to include the special files along with the rest in the
10372 @code{protoize} command, even though their @samp{.X} files already
10373 exist, because otherwise they won't get converted.
10375 @xref{Protoize Caveats}, for more information on how to use
10376 @code{protoize} successfully.