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 make and distribute verbatim copies of this
12 manual provided the copyright notice and this permission notice are
13 preserved on all copies.
15 Permission is granted to copy and distribute modified versions of this
16 manual under the conditions for verbatim copying, provided also that the
17 entire resulting derived work is distributed under the terms of a
18 permission notice identical to this one.
20 Permission is granted to copy and distribute translations of this manual
21 into another language, under the above conditions for modified versions,
22 except that this permission notice may be included in translations
23 approved by the Free Software Foundation instead of in the original
26 @c Set file name and title for the man page.
28 @settitle GNU project C and C++ compiler
30 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
31 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
32 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
33 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
34 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
35 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
36 [@option{-o} @var{outfile}] @var{infile}@dots{}
38 Only the most useful options are listed here; see below for the
39 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
42 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
43 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
44 @file{ld}, @file{binutils} and @file{gdb}.
47 For instructions on reporting bugs, see
48 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
49 script to report bugs is recommended.
52 See the Info entry for @file{gcc}, or
53 @w{@uref{http://gcc.gnu.org/thanks.html}}, for contributors to GCC@.
58 @chapter GCC Command Options
59 @cindex GCC command options
60 @cindex command options
61 @cindex options, GCC command
63 @c man begin DESCRIPTION
65 When you invoke GCC, it normally does preprocessing, compilation,
66 assembly and linking. The ``overall options'' allow you to stop this
67 process at an intermediate stage. For example, the @option{-c} option
68 says not to run the linker. Then the output consists of object files
69 output by the assembler.
71 Other options are passed on to one stage of processing. Some options
72 control the preprocessor and others the compiler itself. Yet other
73 options control the assembler and linker; most of these are not
74 documented here, since you rarely need to use any of them.
76 @cindex C compilation options
77 Most of the command line options that you can use with GCC are useful
78 for C programs; when an option is only useful with another language
79 (usually C++), the explanation says so explicitly. If the description
80 for a particular option does not mention a source language, you can use
81 that option with all supported languages.
83 @cindex C++ compilation options
84 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
85 options for compiling C++ programs.
87 @cindex grouping options
88 @cindex options, grouping
89 The @command{gcc} program accepts options and file names as operands. Many
90 options have multi-letter names; therefore multiple single-letter options
91 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
94 @cindex order of options
95 @cindex options, order
96 You can mix options and other arguments. For the most part, the order
97 you use doesn't matter. Order does matter when you use several options
98 of the same kind; for example, if you specify @option{-L} more than once,
99 the directories are searched in the order specified.
101 Many options have long names starting with @samp{-f} or with
102 @samp{-W}---for example, @option{-fforce-mem},
103 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
104 these have both positive and negative forms; the negative form of
105 @option{-ffoo} would be @option{-fno-foo}. This manual documents
106 only one of these two forms, whichever one is not the default.
110 @xref{Option Index}, for an index to GCC's options.
113 * Option Summary:: Brief list of all options, without explanations.
114 * Overall Options:: Controlling the kind of output:
115 an executable, object files, assembler files,
116 or preprocessed source.
117 * Invoking G++:: Compiling C++ programs.
118 * C Dialect Options:: Controlling the variant of C language compiled.
119 * C++ Dialect Options:: Variations on C++.
120 * Objective-C Dialect Options:: Variations on Objective-C.
121 * Language Independent Options:: Controlling how diagnostics should be
123 * Warning Options:: How picky should the compiler be?
124 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
125 * Optimize Options:: How much optimization?
126 * Preprocessor Options:: Controlling header files and macro definitions.
127 Also, getting dependency information for Make.
128 * Assembler Options:: Passing options to the assembler.
129 * Link Options:: Specifying libraries and so on.
130 * Directory Options:: Where to find header files and libraries.
131 Where to find the compiler executable files.
132 * Spec Files:: How to pass switches to sub-processes.
133 * Target Options:: Running a cross-compiler, or an old version of GCC.
134 * Submodel Options:: Specifying minor hardware or convention variations,
135 such as 68010 vs 68020.
136 * Code Gen Options:: Specifying conventions for function calls, data layout
138 * Environment Variables:: Env vars that affect GCC.
139 * Running Protoize:: Automatically adding or removing function prototypes.
145 @section Option Summary
147 Here is a summary of all the options, grouped by type. Explanations are
148 in the following sections.
151 @item Overall Options
152 @xref{Overall Options,,Options Controlling the Kind of Output}.
154 -c -S -E -o @var{file} -pipe -pass-exit-codes -x @var{language} @gol
155 -v --target-help --help}
157 @item C Language Options
158 @xref{C Dialect Options,,Options Controlling C Dialect}.
160 -ansi -std=@var{standard} -aux-info @var{filename} @gol
161 -fno-asm -fno-builtin @gol
162 -fhosted -ffreestanding @gol
163 -trigraphs -traditional -traditional-cpp @gol
164 -fallow-single-precision -fcond-mismatch @gol
165 -fsigned-bitfields -fsigned-char @gol
166 -funsigned-bitfields -funsigned-char @gol
167 -fwritable-strings -fshort-wchar}
169 @item C++ Language Options
170 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
172 -fno-access-control -fcheck-new -fconserve-space @gol
173 -fno-const-strings -fdollars-in-identifiers @gol
174 -fno-elide-constructors @gol
175 -fno-enforce-eh-specs -fexternal-templates @gol
176 -falt-external-templates @gol
177 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
178 -fno-implicit-templates @gol
179 -fno-implicit-inline-templates @gol
180 -fno-implement-inlines -fms-extensions @gol
181 -fno-nonansi-builtins -fno-operator-names @gol
182 -fno-optional-diags -fpermissive @gol
183 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
184 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
185 -fno-default-inline -Wctor-dtor-privacy @gol
186 -Wnon-virtual-dtor -Wreorder @gol
187 -Weffc++ -Wno-deprecated @gol
188 -Wno-non-template-friend -Wold-style-cast @gol
189 -Woverloaded-virtual -Wno-pmf-conversions @gol
190 -Wsign-promo -Wsynth}
192 @item Objective-C Language Options
193 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
195 -fconstant-string-class=@var{class-name} @gol
196 -fgnu-runtime -fnext-runtime -gen-decls @gol
197 -Wno-protocol -Wselector}
199 @item Language Independent Options
200 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
202 -fmessage-length=@var{n} @gol
203 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
205 @item Warning Options
206 @xref{Warning Options,,Options to Request or Suppress Warnings}.
208 -fsyntax-only -pedantic -pedantic-errors @gol
209 -w -W -Wall -Waggregate-return @gol
210 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
211 -Wconversion -Wdisabled-optimization -Werror @gol
212 -Wfloat-equal -Wformat -Wformat=2 @gol
213 -Wformat-nonliteral -Wformat-security @gol
214 -Wimplicit -Wimplicit-int @gol
215 -Wimplicit-function-declaration @gol
216 -Werror-implicit-function-declaration @gol
217 -Wimport -Winline @gol
218 -Wlarger-than-@var{len} -Wlong-long @gol
219 -Wmain -Wmissing-braces -Wmissing-declarations @gol
220 -Wmissing-format-attribute -Wmissing-noreturn @gol
221 -Wmultichar -Wno-format-extra-args -Wno-format-y2k @gol
222 -Wno-import -Wpacked -Wpadded @gol
223 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
224 -Wreturn-type -Wsequence-point -Wshadow @gol
225 -Wsign-compare -Wswitch -Wsystem-headers @gol
226 -Wtrigraphs -Wundef -Wuninitialized @gol
227 -Wunknown-pragmas -Wunreachable-code @gol
228 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
229 -Wunused-value -Wunused-variable -Wwrite-strings}
231 @item C-only Warning Options
233 -Wbad-function-cast -Wmissing-prototypes -Wnested-externs @gol
234 -Wstrict-prototypes -Wtraditional}
236 @item Debugging Options
237 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
239 -a -ax -d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
241 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
242 -fdump-tree-original@r{[}-@var{n}@r{]} -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
243 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
244 -fmem-report -fpretend-float @gol
245 -fprofile-arcs -ftest-coverage -ftime-report @gol
246 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
247 -ggdb -gstabs -gstabs+ -gxcoff -gxcoff+ @gol
248 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
249 -print-multi-directory -print-multi-lib @gol
250 -print-prog-name=@var{program} -print-search-dirs -Q @gol
253 @item Optimization Options
254 @xref{Optimize Options,,Options that Control Optimization}.
256 -falign-functions=@var{n} -falign-jumps=@var{n} @gol
257 -falign-labels=@var{n} -falign-loops=@var{n} @gol
258 -fbranch-probabilities -fcaller-saves @gol
259 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
260 -fdelayed-branch -fdelete-null-pointer-checks @gol
261 -fexpensive-optimizations -ffast-math -ffloat-store @gol
262 -fforce-addr -fforce-mem -ffunction-sections @gol
263 -fgcse -fgcse-lm -fgcse-sm @gol
264 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
265 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
266 -fmove-all-movables -fno-default-inline -fno-defer-pop @gol
267 -fno-function-cse -fno-guess-branch-probability @gol
268 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
269 -funsafe-math-optimizations -fno-trapping-math @gol
270 -fomit-frame-pointer -foptimize-register-move @gol
271 -foptimize-sibling-calls -freduce-all-givs @gol
272 -fregmove -frename-registers @gol
273 -frerun-cse-after-loop -frerun-loop-opt @gol
274 -fschedule-insns -fschedule-insns2 @gol
275 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
276 -fstrength-reduce -fstrict-aliasing -fthread-jumps -ftrapv @gol
277 -funroll-all-loops -funroll-loops @gol
278 --param @var{name}=@var{value}
279 -O -O0 -O1 -O2 -O3 -Os}
281 @item Preprocessor Options
282 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
284 -$ -A@var{question}=@var{answer} -A-@var{question}@r{[}=@var{answer}@r{]} @gol
285 -C -dD -dI -dM -dN @gol
286 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
287 -idirafter @var{dir} @gol
288 -include @var{file} -imacros @var{file} @gol
289 -iprefix @var{file} -iwithprefix @var{dir} @gol
290 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
291 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
292 -trigraphs -undef -U@var{macro} -Wp,@var{option}}
294 @item Assembler Option
295 @xref{Assembler Options,,Passing Options to the Assembler}.
300 @xref{Link Options,,Options for Linking}.
302 @var{object-file-name} -l@var{library} @gol
303 -nostartfiles -nodefaultlibs -nostdlib @gol
304 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
305 -Wl,@var{option} -Xlinker @var{option} @gol
308 @item Directory Options
309 @xref{Directory Options,,Options for Directory Search}.
311 -B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
314 @c I wrote this xref this way to avoid overfull hbox. -- rms
315 @xref{Target Options}.
317 -b @var{machine} -V @var{version}}
319 @item Machine Dependent Options
320 @xref{Submodel Options,,Hardware Models and Configurations}.
321 @emph{M680x0 Options}
323 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
324 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
325 -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
326 -malign-int -mstrict-align}
328 @emph{M68hc1x Options}
330 -m6811 -m6812 -m68hc11 -m68hc12 @gol
331 -mauto-incdec -mshort -msoft-reg-count=@var{count}}
339 -mcpu=@var{cpu-type} @gol
340 -mtune=@var{cpu-type} @gol
341 -mcmodel=@var{code-model} @gol
343 -mapp-regs -mbroken-saverestore -mcypress @gol
344 -mepilogue -mfaster-structs -mflat @gol
345 -mfpu -mhard-float -mhard-quad-float @gol
346 -mimpure-text -mlive-g0 -mno-app-regs @gol
347 -mno-epilogue -mno-faster-structs -mno-flat -mno-fpu @gol
348 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
349 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
350 -msupersparc -munaligned-doubles -mv8}
352 @emph{Convex Options}
354 -mc1 -mc2 -mc32 -mc34 -mc38 @gol
355 -margcount -mnoargcount @gol
356 -mlong32 -mlong64 @gol
357 -mvolatile-cache -mvolatile-nocache}
359 @emph{AMD29K Options}
361 -m29000 -m29050 -mbw -mnbw -mdw -mndw @gol
362 -mlarge -mnormal -msmall @gol
363 -mkernel-registers -mno-reuse-arg-regs @gol
364 -mno-stack-check -mno-storem-bug @gol
365 -mreuse-arg-regs -msoft-float -mstack-check @gol
366 -mstorem-bug -muser-registers}
370 -mapcs-frame -mno-apcs-frame @gol
371 -mapcs-26 -mapcs-32 @gol
372 -mapcs-stack-check -mno-apcs-stack-check @gol
373 -mapcs-float -mno-apcs-float @gol
374 -mapcs-reentrant -mno-apcs-reentrant @gol
375 -msched-prolog -mno-sched-prolog @gol
376 -mlittle-endian -mbig-endian -mwords-little-endian @gol
377 -malignment-traps -mno-alignment-traps @gol
378 -msoft-float -mhard-float -mfpe @gol
379 -mthumb-interwork -mno-thumb-interwork @gol
380 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
381 -mstructure-size-boundary=@var{n} @gol
382 -mbsd -mxopen -mno-symrename @gol
383 -mabort-on-noreturn @gol
384 -mlong-calls -mno-long-calls @gol
385 -msingle-pic-base -mno-single-pic-base @gol
386 -mpic-register=@var{reg} @gol
387 -mnop-fun-dllimport @gol
388 -mpoke-function-name @gol
390 -mtpcs-frame -mtpcs-leaf-frame @gol
391 -mcaller-super-interworking -mcallee-super-interworking }
393 @emph{MN10200 Options}
397 @emph{MN10300 Options}
399 -mmult-bug -mno-mult-bug @gol
400 -mam33 -mno-am33 @gol
403 @emph{M32R/D Options}
405 -mcode-model=@var{model-type} -msdata=@var{sdata-type} @gol
410 -m88000 -m88100 -m88110 -mbig-pic @gol
411 -mcheck-zero-division -mhandle-large-shift @gol
412 -midentify-revision -mno-check-zero-division @gol
413 -mno-ocs-debug-info -mno-ocs-frame-position @gol
414 -mno-optimize-arg-area -mno-serialize-volatile @gol
415 -mno-underscores -mocs-debug-info @gol
416 -mocs-frame-position -moptimize-arg-area @gol
417 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
418 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
419 -mversion-03.00 -mwarn-passed-structs}
421 @emph{RS/6000 and PowerPC Options}
423 -mcpu=@var{cpu-type} @gol
424 -mtune=@var{cpu-type} @gol
425 -mpower -mno-power -mpower2 -mno-power2 @gol
426 -mpowerpc -mpowerpc64 -mno-powerpc @gol
427 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
428 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
429 -mnew-mnemonics -mold-mnemonics @gol
430 -mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc @gol
431 -m64 -m32 -mxl-call -mno-xl-call -mthreads -mpe @gol
432 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
433 -mstring -mno-string -mupdate -mno-update @gol
434 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
435 -mstrict-align -mno-strict-align -mrelocatable @gol
436 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
437 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
438 -mcall-aix -mcall-sysv -mcall-netbsd @gol
439 -mprototype -mno-prototype @gol
440 -msim -mmvme -mads -myellowknife -memb -msdata @gol
441 -msdata=@var{opt} -mvxworks -G @var{num}}
445 -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
446 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
447 -mminimum-fp-blocks -mnohc-struct-return}
451 -mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
452 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
453 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
454 -mgas -mgp32 -mgp64 @gol
455 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
456 -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
457 -mmips-as -mmips-tfile -mno-abicalls @gol
458 -mno-embedded-data -mno-uninit-const-in-rodata @gol
459 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
460 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
461 -mrnames -msoft-float @gol
462 -m4650 -msingle-float -mmad @gol
463 -mstats -EL -EB -G @var{num} -nocpp @gol
464 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol
467 @emph{i386 and x86-64 Options}
469 -mcpu=@var{cpu-type} -march=@var{cpu-type} @gol
470 -mintel-syntax -mieee-fp -mno-fancy-math-387 @gol
471 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
472 -mno-wide-multiply -mrtd -malign-double @gol
473 -mpreferred-stack-boundary=@var{num} @gol
474 -mmmx -msse -m3dnow @gol
475 -mthreads -mno-align-stringops -minline-all-stringops @gol
476 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
477 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
483 -march=@var{architecture-type} @gol
484 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
485 -mfast-indirect-calls -mgas -mjump-in-delay @gol
486 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
487 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
488 -mno-jump-in-delay -mno-long-load-store @gol
489 -mno-portable-runtime -mno-soft-float @gol
490 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
491 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
492 -mschedule=@var{cpu-type} -mspace-regs}
494 @emph{Intel 960 Options}
496 -m@var{cpu-type} -masm-compat -mclean-linkage @gol
497 -mcode-align -mcomplex-addr -mleaf-procedures @gol
498 -mic-compat -mic2.0-compat -mic3.0-compat @gol
499 -mintel-asm -mno-clean-linkage -mno-code-align @gol
500 -mno-complex-addr -mno-leaf-procedures @gol
501 -mno-old-align -mno-strict-align -mno-tail-call @gol
502 -mnumerics -mold-align -msoft-float -mstrict-align @gol
505 @emph{DEC Alpha Options}
507 -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float @gol
508 -malpha-as -mgas @gol
509 -mieee -mieee-with-inexact -mieee-conformant @gol
510 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
511 -mtrap-precision=@var{mode} -mbuild-constants @gol
512 -mcpu=@var{cpu-type} @gol
513 -mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max @gol
514 -mmemory-latency=@var{time}}
516 @emph{Clipper Options}
520 @emph{H8/300 Options}
522 -mrelax -mh -ms -mint32 -malign-300}
526 -m1 -m2 -m3 -m3e @gol
527 -m4-nofpu -m4-single-only -m4-single -m4 @gol
528 -mb -ml -mdalign -mrelax @gol
529 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
530 -mieee -misize -mpadstruct -mspace @gol
531 -mprefergot -musermode}
533 @emph{System V Options}
535 -Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
540 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
541 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
543 @emph{TMS320C3x/C4x Options}
545 -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
546 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
547 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
548 -mparallel-insns -mparallel-mpy -mpreserve-float}
552 -mlong-calls -mno-long-calls -mep -mno-ep @gol
553 -mprolog-function -mno-prolog-function -mspace @gol
554 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
559 -m32032 -m32332 -m32532 -m32081 -m32381 @gol
560 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
561 -mregparam -mnoregparam -msb -mnosb @gol
562 -mbitfield -mnobitfield -mhimem -mnohimem}
566 -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
567 -mcall-prologues -mno-tablejump -mtiny-stack}
571 -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
572 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
573 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
574 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
575 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
579 -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
580 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
581 -mconstant-gp -mauto-pic -minline-divide-min-latency @gol
582 -minline-divide-max-throughput -mno-dwarf2-asm @gol
583 -mfixed-range=@var{register-range}}
585 @emph{S/390 and zSeries Options}
587 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
588 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
589 -m64 -m31 -mdebug -mno-debug}
593 -mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
594 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
595 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
596 -mstack-align -mdata-align -mconst-align @gol
597 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
598 -melf -maout -melinux -mlinux -sim -sim2}
600 @item Code Generation Options
601 @xref{Code Gen Options,,Options for Code Generation Conventions}.
603 -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
604 -ffixed-@var{reg} -fexceptions @gol
605 -fnon-call-exceptions -funwind-tables -fasynchronous-unwind-tables @gol
606 -finhibit-size-directive -finstrument-functions @gol
607 -fcheck-memory-usage -fprefix-function-name @gol
608 -fno-common -fno-ident -fno-gnu-linker @gol
609 -fpcc-struct-return -fpic -fPIC @gol
610 -freg-struct-return -fshared-data -fshort-enums @gol
611 -fshort-double -fvolatile @gol
612 -fvolatile-global -fvolatile-static @gol
613 -fverbose-asm -fpack-struct -fstack-check @gol
614 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
615 -fargument-alias -fargument-noalias @gol
616 -fargument-noalias-global -fleading-underscore}
620 * Overall Options:: Controlling the kind of output:
621 an executable, object files, assembler files,
622 or preprocessed source.
623 * C Dialect Options:: Controlling the variant of C language compiled.
624 * C++ Dialect Options:: Variations on C++.
625 * Objective-C Dialect Options:: Variations on Objective-C.
626 * Language Independent Options:: Controlling how diagnostics should be
628 * Warning Options:: How picky should the compiler be?
629 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
630 * Optimize Options:: How much optimization?
631 * Preprocessor Options:: Controlling header files and macro definitions.
632 Also, getting dependency information for Make.
633 * Assembler Options:: Passing options to the assembler.
634 * Link Options:: Specifying libraries and so on.
635 * Directory Options:: Where to find header files and libraries.
636 Where to find the compiler executable files.
637 * Spec Files:: How to pass switches to sub-processes.
638 * Target Options:: Running a cross-compiler, or an old version of GCC.
641 @node Overall Options
642 @section Options Controlling the Kind of Output
644 Compilation can involve up to four stages: preprocessing, compilation
645 proper, assembly and linking, always in that order. The first three
646 stages apply to an individual source file, and end by producing an
647 object file; linking combines all the object files (those newly
648 compiled, and those specified as input) into an executable file.
650 @cindex file name suffix
651 For any given input file, the file name suffix determines what kind of
656 C source code which must be preprocessed.
659 C source code which should not be preprocessed.
662 C++ source code which should not be preprocessed.
665 Objective-C source code. Note that you must link with the library
666 @file{libobjc.a} to make an Objective-C program work.
669 Objective-C source code which should not be preprocessed.
672 C header file (not to be compiled or linked).
676 @itemx @var{file}.cxx
677 @itemx @var{file}.cpp
678 @itemx @var{file}.c++
680 C++ source code which must be preprocessed. Note that in @samp{.cxx},
681 the last two letters must both be literally @samp{x}. Likewise,
682 @samp{.C} refers to a literal capital C@.
685 @itemx @var{file}.for
686 @itemx @var{file}.FOR
687 Fortran source code which should not be preprocessed.
690 @itemx @var{file}.fpp
691 @itemx @var{file}.FPP
692 Fortran source code which must be preprocessed (with the traditional
696 Fortran source code which must be preprocessed with a RATFOR
697 preprocessor (not included with GCC)@.
699 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
700 Using and Porting GNU Fortran}, for more details of the handling of
703 @c FIXME: Descriptions of Java file types.
709 @c GCC also knows about some suffixes for languages not yet included:
719 @itemx @var{file}.chi
720 CHILL source code (preprocessed with the traditional preprocessor).
726 Assembler code which must be preprocessed.
729 An object file to be fed straight into linking.
730 Any file name with no recognized suffix is treated this way.
734 You can specify the input language explicitly with the @option{-x} option:
737 @item -x @var{language}
738 Specify explicitly the @var{language} for the following input files
739 (rather than letting the compiler choose a default based on the file
740 name suffix). This option applies to all following input files until
741 the next @option{-x} option. Possible values for @var{language} are:
743 c c-header cpp-output
745 objective-c objc-cpp-output
746 assembler assembler-with-cpp
747 f77 f77-cpp-input ratfor
750 @c Also f77-version, for internal use only.
753 Turn off any specification of a language, so that subsequent files are
754 handled according to their file name suffixes (as they are if @option{-x}
755 has not been used at all).
757 @item -pass-exit-codes
758 @opindex pass-exit-codes
759 Normally the @command{gcc} program will exit with the code of 1 if any
760 phase of the compiler returns a non-success return code. If you specify
761 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
762 numerically highest error produced by any phase that returned an error
766 If you only want some of the stages of compilation, you can use
767 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
768 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
769 @command{gcc} is to stop. Note that some combinations (for example,
770 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
775 Compile or assemble the source files, but do not link. The linking
776 stage simply is not done. The ultimate output is in the form of an
777 object file for each source file.
779 By default, the object file name for a source file is made by replacing
780 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
782 Unrecognized input files, not requiring compilation or assembly, are
787 Stop after the stage of compilation proper; do not assemble. The output
788 is in the form of an assembler code file for each non-assembler input
791 By default, the assembler file name for a source file is made by
792 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
794 Input files that don't require compilation are ignored.
798 Stop after the preprocessing stage; do not run the compiler proper. The
799 output is in the form of preprocessed source code, which is sent to the
802 Input files which don't require preprocessing are ignored.
804 @cindex output file option
807 Place output in file @var{file}. This applies regardless to whatever
808 sort of output is being produced, whether it be an executable file,
809 an object file, an assembler file or preprocessed C code.
811 Since only one output file can be specified, it does not make sense to
812 use @option{-o} when compiling more than one input file, unless you are
813 producing an executable file as output.
815 If @option{-o} is not specified, the default is to put an executable file
816 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
817 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
818 all preprocessed C source on standard output.
822 Print (on standard error output) the commands executed to run the stages
823 of compilation. Also print the version number of the compiler driver
824 program and of the preprocessor and the compiler proper.
828 Use pipes rather than temporary files for communication between the
829 various stages of compilation. This fails to work on some systems where
830 the assembler is unable to read from a pipe; but the GNU assembler has
835 Print (on the standard output) a description of the command line options
836 understood by @command{gcc}. If the @option{-v} option is also specified
837 then @option{--help} will also be passed on to the various processes
838 invoked by @command{gcc}, so that they can display the command line options
839 they accept. If the @option{-W} option is also specified then command
840 line options which have no documentation associated with them will also
845 Print (on the standard output) a description of target specific command
846 line options for each tool.
850 @section Compiling C++ Programs
852 @cindex suffixes for C++ source
853 @cindex C++ source file suffixes
854 C++ source files conventionally use one of the suffixes @samp{.C},
855 @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx};
856 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
857 files with these names and compiles them as C++ programs even if you
858 call the compiler the same way as for compiling C programs (usually with
859 the name @command{gcc}).
863 However, C++ programs often require class libraries as well as a
864 compiler that understands the C++ language---and under some
865 circumstances, you might want to compile programs from standard input,
866 or otherwise without a suffix that flags them as C++ programs.
867 @command{g++} is a program that calls GCC with the default language
868 set to C++, and automatically specifies linking against the C++
869 library. On many systems, @command{g++} is also
870 installed with the name @command{c++}.
872 @cindex invoking @command{g++}
873 When you compile C++ programs, you may specify many of the same
874 command-line options that you use for compiling programs in any
875 language; or command-line options meaningful for C and related
876 languages; or options that are meaningful only for C++ programs.
877 @xref{C Dialect Options,,Options Controlling C Dialect}, for
878 explanations of options for languages related to C@.
879 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
880 explanations of options that are meaningful only for C++ programs.
882 @node C Dialect Options
883 @section Options Controlling C Dialect
884 @cindex dialect options
885 @cindex language dialect options
886 @cindex options, dialect
888 The following options control the dialect of C (or languages derived
889 from C, such as C++ and Objective-C) that the compiler accepts:
896 In C mode, support all ISO C89 programs. In C++ mode,
897 remove GNU extensions that conflict with ISO C++.
899 This turns off certain features of GCC that are incompatible with ISO
900 C89 (when compiling C code), or of standard C++ (when compiling C++ code),
901 such as the @code{asm} and @code{typeof} keywords, and
902 predefined macros such as @code{unix} and @code{vax} that identify the
903 type of system you are using. It also enables the undesirable and
904 rarely used ISO trigraph feature. For the C compiler,
905 it disables recognition of C++ style @samp{//} comments as well as
906 the @code{inline} keyword.
908 The alternate keywords @code{__asm__}, @code{__extension__},
909 @code{__inline__} and @code{__typeof__} continue to work despite
910 @option{-ansi}. You would not want to use them in an ISO C program, of
911 course, but it is useful to put them in header files that might be included
912 in compilations done with @option{-ansi}. Alternate predefined macros
913 such as @code{__unix__} and @code{__vax__} are also available, with or
914 without @option{-ansi}.
916 The @option{-ansi} option does not cause non-ISO programs to be
917 rejected gratuitously. For that, @option{-pedantic} is required in
918 addition to @option{-ansi}. @xref{Warning Options}.
920 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
921 option is used. Some header files may notice this macro and refrain
922 from declaring certain functions or defining certain macros that the
923 ISO standard doesn't call for; this is to avoid interfering with any
924 programs that might use these names for other things.
926 Functions which would normally be built in but do not have semantics
927 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
928 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
929 built-in functions provided by GCC}, for details of the functions
934 Determine the language standard. This option is currently only
935 supported when compiling C@. A value for this option must be provided;
941 ISO C89 (same as @option{-ansi}).
944 ISO C89 as modified in amendment 1.
950 ISO C99. Note that this standard is not yet fully supported; see
951 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
952 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
955 Default, ISO C89 plus GNU extensions (including some C99 features).
959 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
960 this will become the default. The name @samp{gnu9x} is deprecated.
964 Even when this option is not specified, you can still use some of the
965 features of newer standards in so far as they do not conflict with
966 previous C standards. For example, you may use @code{__restrict__} even
967 when @option{-std=c99} is not specified.
969 The @option{-std} options specifying some version of ISO C have the same
970 effects as @option{-ansi}, except that features that were not in ISO C89
971 but are in the specified version (for example, @samp{//} comments and
972 the @code{inline} keyword in ISO C99) are not disabled.
974 @xref{Standards,,Language Standards Supported by GCC}, for details of
975 these standard versions.
977 @item -aux-info @var{filename}
979 Output to the given filename prototyped declarations for all functions
980 declared and/or defined in a translation unit, including those in header
981 files. This option is silently ignored in any language other than C@.
983 Besides declarations, the file indicates, in comments, the origin of
984 each declaration (source file and line), whether the declaration was
985 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
986 @samp{O} for old, respectively, in the first character after the line
987 number and the colon), and whether it came from a declaration or a
988 definition (@samp{C} or @samp{F}, respectively, in the following
989 character). In the case of function definitions, a K&R-style list of
990 arguments followed by their declarations is also provided, inside
991 comments, after the declaration.
995 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
996 keyword, so that code can use these words as identifiers. You can use
997 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
998 instead. @option{-ansi} implies @option{-fno-asm}.
1000 In C++, this switch only affects the @code{typeof} keyword, since
1001 @code{asm} and @code{inline} are standard keywords. You may want to
1002 use the @option{-fno-gnu-keywords} flag instead, which has the same
1003 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1004 switch only affects the @code{asm} and @code{typeof} keywords, since
1005 @code{inline} is a standard keyword in ISO C99.
1008 @opindex fno-builtin
1009 @cindex built-in functions
1010 Don't recognize built-in functions that do not begin with
1011 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1012 functions provided by GCC}, for details of the functions affected,
1013 including those which are not built-in functions when @option{-ansi} or
1014 @option{-std} options for strict ISO C conformance are used because they
1015 do not have an ISO standard meaning.
1017 GCC normally generates special code to handle certain built-in functions
1018 more efficiently; for instance, calls to @code{alloca} may become single
1019 instructions that adjust the stack directly, and calls to @code{memcpy}
1020 may become inline copy loops. The resulting code is often both smaller
1021 and faster, but since the function calls no longer appear as such, you
1022 cannot set a breakpoint on those calls, nor can you change the behavior
1023 of the functions by linking with a different library.
1025 In C++, @option{-fno-builtin} is always in effect. The @option{-fbuiltin}
1026 option has no effect. Therefore, in C++, the only way to get the
1027 optimization benefits of built-in functions is to call the function
1028 using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses
1029 built-in functions to implement many functions (like
1030 @code{std::strchr}), so that you automatically get efficient code.
1034 @cindex hosted environment
1036 Assert that compilation takes place in a hosted environment. This implies
1037 @option{-fbuiltin}. A hosted environment is one in which the
1038 entire standard library is available, and in which @code{main} has a return
1039 type of @code{int}. Examples are nearly everything except a kernel.
1040 This is equivalent to @option{-fno-freestanding}.
1042 @item -ffreestanding
1043 @opindex ffreestanding
1044 @cindex hosted environment
1046 Assert that compilation takes place in a freestanding environment. This
1047 implies @option{-fno-builtin}. A freestanding environment
1048 is one in which the standard library may not exist, and program startup may
1049 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1050 This is equivalent to @option{-fno-hosted}.
1052 @xref{Standards,,Language Standards Supported by GCC}, for details of
1053 freestanding and hosted environments.
1057 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1058 options for strict ISO C conformance) implies @option{-trigraphs}.
1060 @cindex traditional C language
1061 @cindex C language, traditional
1063 @opindex traditional
1064 Attempt to support some aspects of traditional C compilers.
1069 All @code{extern} declarations take effect globally even if they
1070 are written inside of a function definition. This includes implicit
1071 declarations of functions.
1074 The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const}
1075 and @code{volatile} are not recognized. (You can still use the
1076 alternative keywords such as @code{__typeof__}, @code{__inline__}, and
1080 Comparisons between pointers and integers are always allowed.
1083 Integer types @code{unsigned short} and @code{unsigned char} promote
1084 to @code{unsigned int}.
1087 Out-of-range floating point literals are not an error.
1090 Certain constructs which ISO regards as a single invalid preprocessing
1091 number, such as @samp{0xe-0xd}, are treated as expressions instead.
1094 String ``constants'' are not necessarily constant; they are stored in
1095 writable space, and identical looking constants are allocated
1096 separately. (This is the same as the effect of
1097 @option{-fwritable-strings}.)
1099 @cindex @code{longjmp} and automatic variables
1101 All automatic variables not declared @code{register} are preserved by
1102 @code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables
1103 not declared @code{volatile} may be clobbered.
1108 @cindex escape sequences, traditional
1109 The character escape sequences @samp{\x} and @samp{\a} evaluate as the
1110 literal characters @samp{x} and @samp{a} respectively. Without
1111 @w{@option{-traditional}}, @samp{\x} is a prefix for the hexadecimal
1112 representation of a character, and @samp{\a} produces a bell.
1115 You may wish to use @option{-fno-builtin} as well as @option{-traditional}
1116 if your program uses names that are normally GNU C built-in functions for
1117 other purposes of its own.
1119 You cannot use @option{-traditional} if you include any header files that
1120 rely on ISO C features. Some vendors are starting to ship systems with
1121 ISO C header files and you cannot use @option{-traditional} on such
1122 systems to compile files that include any system headers.
1124 The @option{-traditional} option also enables @option{-traditional-cpp}.
1126 @item -traditional-cpp
1127 @opindex traditional-cpp
1128 Attempt to support some aspects of traditional C preprocessors.
1129 See the GNU CPP manual for details.
1131 @item -fcond-mismatch
1132 @opindex fcond-mismatch
1133 Allow conditional expressions with mismatched types in the second and
1134 third arguments. The value of such an expression is void. This option
1135 is not supported for C++.
1137 @item -funsigned-char
1138 @opindex funsigned-char
1139 Let the type @code{char} be unsigned, like @code{unsigned char}.
1141 Each kind of machine has a default for what @code{char} should
1142 be. It is either like @code{unsigned char} by default or like
1143 @code{signed char} by default.
1145 Ideally, a portable program should always use @code{signed char} or
1146 @code{unsigned char} when it depends on the signedness of an object.
1147 But many programs have been written to use plain @code{char} and
1148 expect it to be signed, or expect it to be unsigned, depending on the
1149 machines they were written for. This option, and its inverse, let you
1150 make such a program work with the opposite default.
1152 The type @code{char} is always a distinct type from each of
1153 @code{signed char} or @code{unsigned char}, even though its behavior
1154 is always just like one of those two.
1157 @opindex fsigned-char
1158 Let the type @code{char} be signed, like @code{signed char}.
1160 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1161 the negative form of @option{-funsigned-char}. Likewise, the option
1162 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1164 @item -fsigned-bitfields
1165 @itemx -funsigned-bitfields
1166 @itemx -fno-signed-bitfields
1167 @itemx -fno-unsigned-bitfields
1168 @opindex fsigned-bitfields
1169 @opindex funsigned-bitfields
1170 @opindex fno-signed-bitfields
1171 @opindex fno-unsigned-bitfields
1172 These options control whether a bit-field is signed or unsigned, when the
1173 declaration does not use either @code{signed} or @code{unsigned}. By
1174 default, such a bit-field is signed, because this is consistent: the
1175 basic integer types such as @code{int} are signed types.
1177 However, when @option{-traditional} is used, bit-fields are all unsigned
1180 @item -fwritable-strings
1181 @opindex fwritable-strings
1182 Store string constants in the writable data segment and don't uniquize
1183 them. This is for compatibility with old programs which assume they can
1184 write into string constants. The option @option{-traditional} also has
1187 Writing into string constants is a very bad idea; ``constants'' should
1190 @item -fallow-single-precision
1191 @opindex fallow-single-precision
1192 Do not promote single precision math operations to double precision,
1193 even when compiling with @option{-traditional}.
1195 Traditional K&R C promotes all floating point operations to double
1196 precision, regardless of the sizes of the operands. On the
1197 architecture for which you are compiling, single precision may be faster
1198 than double precision. If you must use @option{-traditional}, but want
1199 to use single precision operations when the operands are single
1200 precision, use this option. This option has no effect when compiling
1201 with ISO or GNU C conventions (the default).
1204 @opindex fshort-wchar
1205 Override the underlying type for @samp{wchar_t} to be @samp{short
1206 unsigned int} instead of the default for the target. This option is
1207 useful for building programs to run under WINE@.
1210 @node C++ Dialect Options
1211 @section Options Controlling C++ Dialect
1213 @cindex compiler options, C++
1214 @cindex C++ options, command line
1215 @cindex options, C++
1216 This section describes the command-line options that are only meaningful
1217 for C++ programs; but you can also use most of the GNU compiler options
1218 regardless of what language your program is in. For example, you
1219 might compile a file @code{firstClass.C} like this:
1222 g++ -g -frepo -O -c firstClass.C
1226 In this example, only @option{-frepo} is an option meant
1227 only for C++ programs; you can use the other options with any
1228 language supported by GCC@.
1230 Here is a list of options that are @emph{only} for compiling C++ programs:
1233 @item -fno-access-control
1234 @opindex fno-access-control
1235 Turn off all access checking. This switch is mainly useful for working
1236 around bugs in the access control code.
1240 Check that the pointer returned by @code{operator new} is non-null
1241 before attempting to modify the storage allocated. The current Working
1242 Paper requires that @code{operator new} never return a null pointer, so
1243 this check is normally unnecessary.
1245 An alternative to using this option is to specify that your
1246 @code{operator new} does not throw any exceptions; if you declare it
1247 @samp{throw()}, G++ will check the return value. See also @samp{new
1250 @item -fconserve-space
1251 @opindex fconserve-space
1252 Put uninitialized or runtime-initialized global variables into the
1253 common segment, as C does. This saves space in the executable at the
1254 cost of not diagnosing duplicate definitions. If you compile with this
1255 flag and your program mysteriously crashes after @code{main()} has
1256 completed, you may have an object that is being destroyed twice because
1257 two definitions were merged.
1259 This option is no longer useful on most targets, now that support has
1260 been added for putting variables into BSS without making them common.
1262 @item -fno-const-strings
1263 @opindex fno-const-strings
1264 Give string constants type @code{char *} instead of type @code{const
1265 char *}. By default, G++ uses type @code{const char *} as required by
1266 the standard. Even if you use @option{-fno-const-strings}, you cannot
1267 actually modify the value of a string constant, unless you also use
1268 @option{-fwritable-strings}.
1270 This option might be removed in a future release of G++. For maximum
1271 portability, you should structure your code so that it works with
1272 string constants that have type @code{const char *}.
1274 @item -fdollars-in-identifiers
1275 @opindex fdollars-in-identifiers
1276 Accept @samp{$} in identifiers. You can also explicitly prohibit use of
1277 @samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows
1278 @samp{$} by default on most target systems, but there are a few exceptions.)
1279 Traditional C allowed the character @samp{$} to form part of
1280 identifiers. However, ISO C and C++ forbid @samp{$} in identifiers.
1282 @item -fno-elide-constructors
1283 @opindex fno-elide-constructors
1284 The C++ standard allows an implementation to omit creating a temporary
1285 which is only used to initialize another object of the same type.
1286 Specifying this option disables that optimization, and forces G++ to
1287 call the copy constructor in all cases.
1289 @item -fno-enforce-eh-specs
1290 @opindex fno-enforce-eh-specs
1291 Don't check for violation of exception specifications at runtime. This
1292 option violates the C++ standard, but may be useful for reducing code
1293 size in production builds, much like defining @samp{NDEBUG}. The compiler
1294 will still optimize based on the exception specifications.
1296 @item -fexternal-templates
1297 @opindex fexternal-templates
1299 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1300 template instantiation; template instances are emitted or not according
1301 to the location of the template definition. @xref{Template
1302 Instantiation}, for more information.
1304 This option is deprecated.
1306 @item -falt-external-templates
1307 @opindex falt-external-templates
1308 Similar to @option{-fexternal-templates}, but template instances are
1309 emitted or not according to the place where they are first instantiated.
1310 @xref{Template Instantiation}, for more information.
1312 This option is deprecated.
1315 @itemx -fno-for-scope
1317 @opindex fno-for-scope
1318 If @option{-ffor-scope} is specified, the scope of variables declared in
1319 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1320 as specified by the C++ standard.
1321 If @option{-fno-for-scope} is specified, the scope of variables declared in
1322 a @i{for-init-statement} extends to the end of the enclosing scope,
1323 as was the case in old versions of G++, and other (traditional)
1324 implementations of C++.
1326 The default if neither flag is given to follow the standard,
1327 but to allow and give a warning for old-style code that would
1328 otherwise be invalid, or have different behavior.
1330 @item -fno-gnu-keywords
1331 @opindex fno-gnu-keywords
1332 Do not recognize @code{typeof} as a keyword, so that code can use this
1333 word as an identifier. You can use the keyword @code{__typeof__} instead.
1334 @option{-ansi} implies @option{-fno-gnu-keywords}.
1336 @item -fno-implicit-templates
1337 @opindex fno-implicit-templates
1338 Never emit code for non-inline templates which are instantiated
1339 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1340 @xref{Template Instantiation}, for more information.
1342 @item -fno-implicit-inline-templates
1343 @opindex fno-implicit-inline-templates
1344 Don't emit code for implicit instantiations of inline templates, either.
1345 The default is to handle inlines differently so that compiles with and
1346 without optimization will need the same set of explicit instantiations.
1348 @item -fno-implement-inlines
1349 @opindex fno-implement-inlines
1350 To save space, do not emit out-of-line copies of inline functions
1351 controlled by @samp{#pragma implementation}. This will cause linker
1352 errors if these functions are not inlined everywhere they are called.
1354 @item -fms-extensions
1355 @opindex fms-extensions
1356 Disable pedantic warnings about constructs used in MFC, such as implicit
1357 int and getting a pointer to member function via non-standard syntax.
1359 @item -fno-nonansi-builtins
1360 @opindex fno-nonansi-builtins
1361 Disable built-in declarations of functions that are not mandated by
1362 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1363 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1365 @item -fno-operator-names
1366 @opindex fno-operator-names
1367 Do not treat the operator name keywords @code{and}, @code{bitand},
1368 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1369 synonyms as keywords.
1371 @item -fno-optional-diags
1372 @opindex fno-optional-diags
1373 Disable diagnostics that the standard says a compiler does not need to
1374 issue. Currently, the only such diagnostic issued by G++ is the one for
1375 a name having multiple meanings within a class.
1378 @opindex fpermissive
1379 Downgrade messages about nonconformant code from errors to warnings. By
1380 default, G++ effectively sets @option{-pedantic-errors} without
1381 @option{-pedantic}; this option reverses that. This behavior and this
1382 option are superseded by @option{-pedantic}, which works as it does for GNU C@.
1386 Enable automatic template instantiation at link time. This option also
1387 implies @option{-fno-implicit-templates}. @xref{Template
1388 Instantiation}, for more information.
1392 Disable generation of information about every class with virtual
1393 functions for use by the C++ runtime type identification features
1394 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1395 of the language, you can save some space by using this flag. Note that
1396 exception handling uses the same information, but it will generate it as
1401 Emit statistics about front-end processing at the end of the compilation.
1402 This information is generally only useful to the G++ development team.
1404 @item -ftemplate-depth-@var{n}
1405 @opindex ftemplate-depth
1406 Set the maximum instantiation depth for template classes to @var{n}.
1407 A limit on the template instantiation depth is needed to detect
1408 endless recursions during template class instantiation. ANSI/ISO C++
1409 conforming programs must not rely on a maximum depth greater than 17.
1411 @item -fuse-cxa-atexit
1412 @opindex fuse-cxa-atexit
1413 Register destructors for objects with static storage duration with the
1414 @code{__cxa_atexit} function rather than the @code{atexit} function.
1415 This option is required for fully standards-compliant handling of static
1416 destructors, but will only work if your C library supports
1417 @code{__cxa_atexit}.
1421 Emit special relocations for vtables and virtual function references
1422 so that the linker can identify unused virtual functions and zero out
1423 vtable slots that refer to them. This is most useful with
1424 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1425 also discard the functions themselves.
1427 This optimization requires GNU as and GNU ld. Not all systems support
1428 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1432 Do not use weak symbol support, even if it is provided by the linker.
1433 By default, G++ will use weak symbols if they are available. This
1434 option exists only for testing, and should not be used by end-users;
1435 it will result in inferior code and has no benefits. This option may
1436 be removed in a future release of G++.
1440 Do not search for header files in the standard directories specific to
1441 C++, but do still search the other standard directories. (This option
1442 is used when building the C++ library.)
1445 In addition, these optimization, warning, and code generation options
1446 have meanings only for C++ programs:
1449 @item -fno-default-inline
1450 @opindex fno-default-inline
1451 Do not assume @samp{inline} for functions defined inside a class scope.
1452 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1453 functions will have linkage like inline functions; they just won't be
1456 @item -Wctor-dtor-privacy @r{(C++ only)}
1457 @opindex Wctor-dtor-privacy
1458 Warn when a class seems unusable, because all the constructors or
1459 destructors in a class are private and the class has no friends or
1460 public static member functions.
1462 @item -Wnon-virtual-dtor @r{(C++ only)}
1463 @opindex Wnon-virtual-dtor
1464 Warn when a class declares a non-virtual destructor that should probably
1465 be virtual, because it looks like the class will be used polymorphically.
1467 @item -Wreorder @r{(C++ only)}
1469 @cindex reordering, warning
1470 @cindex warning for reordering of member initializers
1471 Warn when the order of member initializers given in the code does not
1472 match the order in which they must be executed. For instance:
1478 A(): j (0), i (1) @{ @}
1482 Here the compiler will warn that the member initializers for @samp{i}
1483 and @samp{j} will be rearranged to match the declaration order of the
1487 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1490 @item -Weffc++ @r{(C++ only)}
1492 Warn about violations of various style guidelines from Scott Meyers'
1493 @cite{Effective C++} books. If you use this option, you should be aware
1494 that the standard library headers do not obey all of these guidelines;
1495 you can use @samp{grep -v} to filter out those warnings.
1497 @item -Wno-deprecated @r{(C++ only)}
1498 @opindex Wno-deprecated
1499 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1501 @item -Wno-non-template-friend @r{(C++ only)}
1502 @opindex Wno-non-template-friend
1503 Disable warnings when non-templatized friend functions are declared
1504 within a template. With the advent of explicit template specification
1505 support in G++, if the name of the friend is an unqualified-id (i.e.,
1506 @samp{friend foo(int)}), the C++ language specification demands that the
1507 friend declare or define an ordinary, nontemplate function. (Section
1508 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1509 could be interpreted as a particular specialization of a templatized
1510 function. Because this non-conforming behavior is no longer the default
1511 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1512 check existing code for potential trouble spots, and is on by default.
1513 This new compiler behavior can be turned off with
1514 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1515 but disables the helpful warning.
1517 @item -Wold-style-cast @r{(C++ only)}
1518 @opindex Wold-style-cast
1519 Warn if an old-style (C-style) cast is used within a C++ program. The
1520 new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and
1521 @samp{const_cast}) are less vulnerable to unintended effects, and much
1524 @item -Woverloaded-virtual @r{(C++ only)}
1525 @opindex Woverloaded-virtual
1526 @cindex overloaded virtual fn, warning
1527 @cindex warning for overloaded virtual fn
1528 Warn when a function declaration hides virtual functions from a
1529 base class. For example, in:
1536 struct B: public A @{
1541 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1549 will fail to compile.
1551 @item -Wno-pmf-conversions @r{(C++ only)}
1552 @opindex Wno-pmf-conversions
1553 Disable the diagnostic for converting a bound pointer to member function
1556 @item -Wsign-promo @r{(C++ only)}
1557 @opindex Wsign-promo
1558 Warn when overload resolution chooses a promotion from unsigned or
1559 enumeral type to a signed type over a conversion to an unsigned type of
1560 the same size. Previous versions of G++ would try to preserve
1561 unsignedness, but the standard mandates the current behavior.
1563 @item -Wsynth @r{(C++ only)}
1565 @cindex warning for synthesized methods
1566 @cindex synthesized methods, warning
1567 Warn when G++'s synthesis behavior does not match that of cfront. For
1573 A& operator = (int);
1583 In this example, G++ will synthesize a default @samp{A& operator =
1584 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1587 @node Objective-C Dialect Options
1588 @section Options Controlling Objective-C Dialect
1590 @cindex compiler options, Objective-C
1591 @cindex Objective-C options, command line
1592 @cindex options, Objective-C
1593 This section describes the command-line options that are only meaningful
1594 for Objective-C programs; but you can also use most of the GNU compiler
1595 options regardless of what language your program is in. For example,
1596 you might compile a file @code{some_class.m} like this:
1599 gcc -g -fgnu-runtime -O -c some_class.m
1603 In this example, only @option{-fgnu-runtime} is an option meant only for
1604 Objective-C programs; you can use the other options with any language
1607 Here is a list of options that are @emph{only} for compiling Objective-C
1611 @item -fconstant-string-class=@var{class-name}
1612 @opindex fconstant-string-class
1613 Use @var{class-name} as the name of the class to instantiate for each
1614 literal string specified with the syntax @code{@@"@dots{}"}. The default
1615 class name is @code{NXConstantString}.
1618 @opindex fgnu-runtime
1619 Generate object code compatible with the standard GNU Objective-C
1620 runtime. This is the default for most types of systems.
1622 @item -fnext-runtime
1623 @opindex fnext-runtime
1624 Generate output compatible with the NeXT runtime. This is the default
1625 for NeXT-based systems, including Darwin and Mac OS X@.
1629 Dump interface declarations for all classes seen in the source file to a
1630 file named @file{@var{sourcename}.decl}.
1633 @opindex Wno-protocol
1634 Do not warn if methods required by a protocol are not implemented
1635 in the class adopting it.
1639 Warn if a selector has multiple methods of different types defined.
1641 @c not documented because only avail via -Wp
1642 @c @item -print-objc-runtime-info
1646 @node Language Independent Options
1647 @section Options to Control Diagnostic Messages Formatting
1648 @cindex options to control diagnostics formatting
1649 @cindex diagnostic messages
1650 @cindex message formatting
1652 Traditionally, diagnostic messages have been formatted irrespective of
1653 the output device's aspect (e.g.@: its width, @dots{}). The options described
1654 below can be used to control the diagnostic messages formatting
1655 algorithm, e.g.@: how many characters per line, how often source location
1656 information should be reported. Right now, only the C++ front end can
1657 honor these options. However it is expected, in the near future, that
1658 the remaining front ends would be able to digest them correctly.
1661 @item -fmessage-length=@var{n}
1662 @opindex fmessage-length
1663 Try to format error messages so that they fit on lines of about @var{n}
1664 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1665 the front ends supported by GCC@. If @var{n} is zero, then no
1666 line-wrapping will be done; each error message will appear on a single
1669 @opindex fdiagnostics-show-location
1670 @item -fdiagnostics-show-location=once
1671 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1672 reporter to emit @emph{once} source location information; that is, in
1673 case the message is too long to fit on a single physical line and has to
1674 be wrapped, the source location won't be emitted (as prefix) again,
1675 over and over, in subsequent continuation lines. This is the default
1678 @item -fdiagnostics-show-location=every-line
1679 Only meaningful in line-wrapping mode. Instructs the diagnostic
1680 messages reporter to emit the same source location information (as
1681 prefix) for physical lines that result from the process of breaking
1682 a message which is too long to fit on a single line.
1686 @node Warning Options
1687 @section Options to Request or Suppress Warnings
1688 @cindex options to control warnings
1689 @cindex warning messages
1690 @cindex messages, warning
1691 @cindex suppressing warnings
1693 Warnings are diagnostic messages that report constructions which
1694 are not inherently erroneous but which are risky or suggest there
1695 may have been an error.
1697 You can request many specific warnings with options beginning @samp{-W},
1698 for example @option{-Wimplicit} to request warnings on implicit
1699 declarations. Each of these specific warning options also has a
1700 negative form beginning @samp{-Wno-} to turn off warnings;
1701 for example, @option{-Wno-implicit}. This manual lists only one of the
1702 two forms, whichever is not the default.
1704 These options control the amount and kinds of warnings produced by GCC:
1707 @cindex syntax checking
1709 @opindex fsyntax-only
1710 Check the code for syntax errors, but don't do anything beyond that.
1714 Issue all the warnings demanded by strict ISO C and ISO C++;
1715 reject all programs that use forbidden extensions, and some other
1716 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1717 version of the ISO C standard specified by any @option{-std} option used.
1719 Valid ISO C and ISO C++ programs should compile properly with or without
1720 this option (though a rare few will require @option{-ansi} or a
1721 @option{-std} option specifying the required version of ISO C)@. However,
1722 without this option, certain GNU extensions and traditional C and C++
1723 features are supported as well. With this option, they are rejected.
1725 @option{-pedantic} does not cause warning messages for use of the
1726 alternate keywords whose names begin and end with @samp{__}. Pedantic
1727 warnings are also disabled in the expression that follows
1728 @code{__extension__}. However, only system header files should use
1729 these escape routes; application programs should avoid them.
1730 @xref{Alternate Keywords}.
1732 Some users try to use @option{-pedantic} to check programs for strict ISO
1733 C conformance. They soon find that it does not do quite what they want:
1734 it finds some non-ISO practices, but not all---only those for which
1735 ISO C @emph{requires} a diagnostic, and some others for which
1736 diagnostics have been added.
1738 A feature to report any failure to conform to ISO C might be useful in
1739 some instances, but would require considerable additional work and would
1740 be quite different from @option{-pedantic}. We don't have plans to
1741 support such a feature in the near future.
1743 Where the standard specified with @option{-std} represents a GNU
1744 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1745 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1746 extended dialect is based. Warnings from @option{-pedantic} are given
1747 where they are required by the base standard. (It would not make sense
1748 for such warnings to be given only for features not in the specified GNU
1749 C dialect, since by definition the GNU dialects of C include all
1750 features the compiler supports with the given option, and there would be
1751 nothing to warn about.)
1753 @item -pedantic-errors
1754 @opindex pedantic-errors
1755 Like @option{-pedantic}, except that errors are produced rather than
1760 Inhibit all warning messages.
1764 Inhibit warning messages about the use of @samp{#import}.
1766 @item -Wchar-subscripts
1767 @opindex Wchar-subscripts
1768 Warn if an array subscript has type @code{char}. This is a common cause
1769 of error, as programmers often forget that this type is signed on some
1774 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1775 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1779 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1780 the arguments supplied have types appropriate to the format string
1781 specified, and that the conversions specified in the format string make
1782 sense. This includes standard functions, and others specified by format
1783 attributes (@pxref{Function Attributes}), in the @code{printf},
1784 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1785 not in the C standard) families.
1787 The formats are checked against the format features supported by GNU
1788 libc version 2.2. These include all ISO C89 and C99 features, as well
1789 as features from the Single Unix Specification and some BSD and GNU
1790 extensions. Other library implementations may not support all these
1791 features; GCC does not support warning about features that go beyond a
1792 particular library's limitations. However, if @option{-pedantic} is used
1793 with @option{-Wformat}, warnings will be given about format features not
1794 in the selected standard version (but not for @code{strfmon} formats,
1795 since those are not in any version of the C standard). @xref{C Dialect
1796 Options,,Options Controlling C Dialect}.
1798 @option{-Wformat} is included in @option{-Wall}. For more control over some
1799 aspects of format checking, the options @option{-Wno-format-y2k},
1800 @option{-Wno-format-extra-args}, @option{-Wformat-nonliteral},
1801 @option{-Wformat-security} and @option{-Wformat=2} are available, but are
1802 not included in @option{-Wall}.
1804 @item -Wno-format-y2k
1805 @opindex Wno-format-y2k
1806 If @option{-Wformat} is specified, do not warn about @code{strftime}
1807 formats which may yield only a two-digit year.
1809 @item -Wno-format-extra-args
1810 @opindex Wno-format-extra-args
1811 If @option{-Wformat} is specified, do not warn about excess arguments to a
1812 @code{printf} or @code{scanf} format function. The C standard specifies
1813 that such arguments are ignored.
1815 @item -Wformat-nonliteral
1816 @opindex Wformat-nonliteral
1817 If @option{-Wformat} is specified, also warn if the format string is not a
1818 string literal and so cannot be checked, unless the format function
1819 takes its format arguments as a @code{va_list}.
1821 @item -Wformat-security
1822 @opindex Wformat-security
1823 If @option{-Wformat} is specified, also warn about uses of format
1824 functions that represent possible security problems. At present, this
1825 warns about calls to @code{printf} and @code{scanf} functions where the
1826 format string is not a string literal and there are no format arguments,
1827 as in @code{printf (foo);}. This may be a security hole if the format
1828 string came from untrusted input and contains @samp{%n}. (This is
1829 currently a subset of what @option{-Wformat-nonliteral} warns about, but
1830 in future warnings may be added to @option{-Wformat-security} that are not
1831 included in @option{-Wformat-nonliteral}.)
1835 Enable @option{-Wformat} plus format checks not included in
1836 @option{-Wformat}. Currently equivalent to @samp{-Wformat
1837 -Wformat-nonliteral -Wformat-security}.
1839 @item -Wimplicit-int
1840 @opindex Wimplicit-int
1841 Warn when a declaration does not specify a type.
1843 @item -Wimplicit-function-declaration
1844 @itemx -Werror-implicit-function-declaration
1845 @opindex Wimplicit-function-declaration
1846 @opindex Werror-implicit-function-declaration
1847 Give a warning (or error) whenever a function is used before being
1852 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
1856 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
1857 function with external linkage, returning int, taking either zero
1858 arguments, two, or three arguments of appropriate types.
1860 @item -Wmissing-braces
1861 @opindex Wmissing-braces
1862 Warn if an aggregate or union initializer is not fully bracketed. In
1863 the following example, the initializer for @samp{a} is not fully
1864 bracketed, but that for @samp{b} is fully bracketed.
1867 int a[2][2] = @{ 0, 1, 2, 3 @};
1868 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
1873 Warn if a multicharacter constant (@samp{'FOOF'}) is used. Usually they
1874 indicate a typo in the user's code, as they have implementation-defined
1875 values, and should not be used in portable code.
1878 @opindex Wparentheses
1879 Warn if parentheses are omitted in certain contexts, such
1880 as when there is an assignment in a context where a truth value
1881 is expected, or when operators are nested whose precedence people
1882 often get confused about.
1884 Also warn about constructions where there may be confusion to which
1885 @code{if} statement an @code{else} branch belongs. Here is an example of
1900 In C, every @code{else} branch belongs to the innermost possible @code{if}
1901 statement, which in this example is @code{if (b)}. This is often not
1902 what the programmer expected, as illustrated in the above example by
1903 indentation the programmer chose. When there is the potential for this
1904 confusion, GCC will issue a warning when this flag is specified.
1905 To eliminate the warning, add explicit braces around the innermost
1906 @code{if} statement so there is no way the @code{else} could belong to
1907 the enclosing @code{if}. The resulting code would look like this:
1923 @item -Wsequence-point
1924 @opindex Wsequence-point
1925 Warn about code that may have undefined semantics because of violations
1926 of sequence point rules in the C standard.
1928 The C standard defines the order in which expressions in a C program are
1929 evaluated in terms of @dfn{sequence points}, which represent a partial
1930 ordering between the execution of parts of the program: those executed
1931 before the sequence point, and those executed after it. These occur
1932 after the evaluation of a full expression (one which is not part of a
1933 larger expression), after the evaluation of the first operand of a
1934 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
1935 function is called (but after the evaluation of its arguments and the
1936 expression denoting the called function), and in certain other places.
1937 Other than as expressed by the sequence point rules, the order of
1938 evaluation of subexpressions of an expression is not specified. All
1939 these rules describe only a partial order rather than a total order,
1940 since, for example, if two functions are called within one expression
1941 with no sequence point between them, the order in which the functions
1942 are called is not specified. However, the standards committee have
1943 ruled that function calls do not overlap.
1945 It is not specified when between sequence points modifications to the
1946 values of objects take effect. Programs whose behavior depends on this
1947 have undefined behavior; the C standard specifies that ``Between the
1948 previous and next sequence point an object shall have its stored value
1949 modified at most once by the evaluation of an expression. Furthermore,
1950 the prior value shall be read only to determine the value to be
1951 stored.''. If a program breaks these rules, the results on any
1952 particular implementation are entirely unpredictable.
1954 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
1955 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
1956 diagnosed by this option, and it may give an occasional false positive
1957 result, but in general it has been found fairly effective at detecting
1958 this sort of problem in programs.
1960 The present implementation of this option only works for C programs. A
1961 future implementation may also work for C++ programs.
1963 The C standard is worded confusingly, therefore there is some debate
1964 over the precise meaning of the sequence point rules in subtle cases.
1965 Links to discussions of the problem, including proposed formal
1966 definitions, may be found on our readings page, at
1967 @w{@uref{http://gcc.gnu.org/readings.html}}.
1970 @opindex Wreturn-type
1971 Warn whenever a function is defined with a return-type that defaults to
1972 @code{int}. Also warn about any @code{return} statement with no
1973 return-value in a function whose return-type is not @code{void}.
1975 For C++, a function without return type always produces a diagnostic
1976 message, even when @option{-Wno-return-type} is specified. The only
1977 exceptions are @samp{main} and functions defined in system headers.
1981 Warn whenever a @code{switch} statement has an index of enumeral type
1982 and lacks a @code{case} for one or more of the named codes of that
1983 enumeration. (The presence of a @code{default} label prevents this
1984 warning.) @code{case} labels outside the enumeration range also
1985 provoke warnings when this option is used.
1989 Warn if any trigraphs are encountered that might change the meaning of
1990 the program (trigraphs within comments are not warned about).
1992 @item -Wunused-function
1993 @opindex Wunused-function
1994 Warn whenever a static function is declared but not defined or a
1995 non\-inline static function is unused.
1997 @item -Wunused-label
1998 @opindex Wunused-label
1999 Warn whenever a label is declared but not used.
2001 To suppress this warning use the @samp{unused} attribute
2002 (@pxref{Variable Attributes}).
2004 @item -Wunused-parameter
2005 @opindex Wunused-parameter
2006 Warn whenever a function parameter is unused aside from its declaration.
2008 To suppress this warning use the @samp{unused} attribute
2009 (@pxref{Variable Attributes}).
2011 @item -Wunused-variable
2012 @opindex Wunused-variable
2013 Warn whenever a local variable or non-constant static variable is unused
2014 aside from its declaration
2016 To suppress this warning use the @samp{unused} attribute
2017 (@pxref{Variable Attributes}).
2019 @item -Wunused-value
2020 @opindex Wunused-value
2021 Warn whenever a statement computes a result that is explicitly not used.
2023 To suppress this warning cast the expression to @samp{void}.
2027 All all the above @option{-Wunused} options combined.
2029 In order to get a warning about an unused function parameter, you must
2030 either specify @samp{-W -Wunused} or separately specify
2031 @option{-Wunused-parameter}.
2033 @item -Wuninitialized
2034 @opindex Wuninitialized
2035 Warn if an automatic variable is used without first being initialized or
2036 if a variable may be clobbered by a @code{setjmp} call.
2038 These warnings are possible only in optimizing compilation,
2039 because they require data flow information that is computed only
2040 when optimizing. If you don't specify @option{-O}, you simply won't
2043 These warnings occur only for variables that are candidates for
2044 register allocation. Therefore, they do not occur for a variable that
2045 is declared @code{volatile}, or whose address is taken, or whose size
2046 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2047 structures, unions or arrays, even when they are in registers.
2049 Note that there may be no warning about a variable that is used only
2050 to compute a value that itself is never used, because such
2051 computations may be deleted by data flow analysis before the warnings
2054 These warnings are made optional because GCC is not smart
2055 enough to see all the reasons why the code might be correct
2056 despite appearing to have an error. Here is one example of how
2077 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2078 always initialized, but GCC doesn't know this. Here is
2079 another common case:
2084 if (change_y) save_y = y, y = new_y;
2086 if (change_y) y = save_y;
2091 This has no bug because @code{save_y} is used only if it is set.
2093 @cindex @code{longjmp} warnings
2094 This option also warns when a non-volatile automatic variable might be
2095 changed by a call to @code{longjmp}. These warnings as well are possible
2096 only in optimizing compilation.
2098 The compiler sees only the calls to @code{setjmp}. It cannot know
2099 where @code{longjmp} will be called; in fact, a signal handler could
2100 call it at any point in the code. As a result, you may get a warning
2101 even when there is in fact no problem because @code{longjmp} cannot
2102 in fact be called at the place which would cause a problem.
2104 Some spurious warnings can be avoided if you declare all the functions
2105 you use that never return as @code{noreturn}. @xref{Function
2108 @item -Wreorder @r{(C++ only)}
2110 @cindex reordering, warning
2111 @cindex warning for reordering of member initializers
2112 Warn when the order of member initializers given in the code does not
2113 match the order in which they must be executed. For instance:
2115 @item -Wunknown-pragmas
2116 @opindex Wunknown-pragmas
2117 @cindex warning for unknown pragmas
2118 @cindex unknown pragmas, warning
2119 @cindex pragmas, warning of unknown
2120 Warn when a #pragma directive is encountered which is not understood by
2121 GCC@. If this command line option is used, warnings will even be issued
2122 for unknown pragmas in system header files. This is not the case if
2123 the warnings were only enabled by the @option{-Wall} command line option.
2127 All of the above @samp{-W} options combined. This enables all the
2128 warnings about constructions that some users consider questionable, and
2129 that are easy to avoid (or modify to prevent the warning), even in
2130 conjunction with macros.
2132 @item -Wsystem-headers
2133 @opindex Wsystem-headers
2134 @cindex warnings from system headers
2135 @cindex system headers, warnings from
2136 Print warning messages for constructs found in system header files.
2137 Warnings from system headers are normally suppressed, on the assumption
2138 that they usually do not indicate real problems and would only make the
2139 compiler output harder to read. Using this command line option tells
2140 GCC to emit warnings from system headers as if they occurred in user
2141 code. However, note that using @option{-Wall} in conjunction with this
2142 option will @emph{not} warn about unknown pragmas in system
2143 headers---for that, @option{-Wunknown-pragmas} must also be used.
2146 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2147 Some of them warn about constructions that users generally do not
2148 consider questionable, but which occasionally you might wish to check
2149 for; others warn about constructions that are necessary or hard to avoid
2150 in some cases, and there is no simple way to modify the code to suppress
2156 Print extra warning messages for these events:
2160 A function can return either with or without a value. (Falling
2161 off the end of the function body is considered returning without
2162 a value.) For example, this function would evoke such a
2176 An expression-statement or the left-hand side of a comma expression
2177 contains no side effects.
2178 To suppress the warning, cast the unused expression to void.
2179 For example, an expression such as @samp{x[i,j]} will cause a warning,
2180 but @samp{x[(void)i,j]} will not.
2183 An unsigned value is compared against zero with @samp{<} or @samp{<=}.
2186 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2187 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2188 that of ordinary mathematical notation.
2191 Storage-class specifiers like @code{static} are not the first things in
2192 a declaration. According to the C Standard, this usage is obsolescent.
2195 The return type of a function has a type qualifier such as @code{const}.
2196 Such a type qualifier has no effect, since the value returned by a
2197 function is not an lvalue. (But don't warn about the GNU extension of
2198 @code{volatile void} return types. That extension will be warned about
2199 if @option{-pedantic} is specified.)
2202 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2206 A comparison between signed and unsigned values could produce an
2207 incorrect result when the signed value is converted to unsigned.
2208 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2211 An aggregate has a partly bracketed initializer.
2212 For example, the following code would evoke such a warning,
2213 because braces are missing around the initializer for @code{x.h}:
2216 struct s @{ int f, g; @};
2217 struct t @{ struct s h; int i; @};
2218 struct t x = @{ 1, 2, 3 @};
2222 An aggregate has an initializer which does not initialize all members.
2223 For example, the following code would cause such a warning, because
2224 @code{x.h} would be implicitly initialized to zero:
2227 struct s @{ int f, g, h; @};
2228 struct s x = @{ 3, 4 @};
2233 @opindex Wfloat-equal
2234 Warn if floating point values are used in equality comparisons.
2236 The idea behind this is that sometimes it is convenient (for the
2237 programmer) to consider floating-point values as approximations to
2238 infinitely precise real numbers. If you are doing this, then you need
2239 to compute (by analysing the code, or in some other way) the maximum or
2240 likely maximum error that the computation introduces, and allow for it
2241 when performing comparisons (and when producing output, but that's a
2242 different problem). In particular, instead of testing for equality, you
2243 would check to see whether the two values have ranges that overlap; and
2244 this is done with the relational operators, so equality comparisons are
2247 @item -Wtraditional @r{(C only)}
2248 @opindex Wtraditional
2249 Warn about certain constructs that behave differently in traditional and
2250 ISO C@. Also warn about ISO C constructs that have no traditional C
2251 equivalent, and/or problematic constructs which should be avoided.
2255 Macro parameters that appear within string literals in the macro body.
2256 In traditional C macro replacement takes place within string literals,
2257 but does not in ISO C@.
2260 In traditional C, some preprocessor directives did not exist.
2261 Traditional preprocessors would only consider a line to be a directive
2262 if the @samp{#} appeared in column 1 on the line. Therefore
2263 @option{-Wtraditional} warns about directives that traditional C
2264 understands but would ignore because the @samp{#} does not appear as the
2265 first character on the line. It also suggests you hide directives like
2266 @samp{#pragma} not understood by traditional C by indenting them. Some
2267 traditional implementations would not recognise @samp{#elif}, so it
2268 suggests avoiding it altogether.
2271 A function-like macro that appears without arguments.
2274 The unary plus operator.
2277 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2278 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2279 constants.) Note, these suffixes appear in macros defined in the system
2280 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2281 Use of these macros in user code might normally lead to spurious
2282 warnings, however gcc's integrated preprocessor has enough context to
2283 avoid warning in these cases.
2286 A function declared external in one block and then used after the end of
2290 A @code{switch} statement has an operand of type @code{long}.
2293 A non-@code{static} function declaration follows a @code{static} one.
2294 This construct is not accepted by some traditional C compilers.
2297 The ISO type of an integer constant has a different width or
2298 signedness from its traditional type. This warning is only issued if
2299 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2300 typically represent bit patterns, are not warned about.
2303 Usage of ISO string concatenation is detected.
2306 Initialization of automatic aggregates.
2309 Identifier conflicts with labels. Traditional C lacks a separate
2310 namespace for labels.
2313 Initialization of unions. If the initializer is zero, the warning is
2314 omitted. This is done under the assumption that the zero initializer in
2315 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2316 initializer warnings and relies on default initialization to zero in the
2320 Conversions by prototypes between fixed/floating point values and vice
2321 versa. The absence of these prototypes when compiling with traditional
2322 C would cause serious problems. This is a subset of the possible
2323 conversion warnings, for the full set use @option{-Wconversion}.
2328 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2332 Warn whenever a local variable shadows another local variable, parameter or
2333 global variable or whenever a built-in function is shadowed.
2335 @item -Wlarger-than-@var{len}
2336 @opindex Wlarger-than
2337 Warn whenever an object of larger than @var{len} bytes is defined.
2339 @item -Wpointer-arith
2340 @opindex Wpointer-arith
2341 Warn about anything that depends on the ``size of'' a function type or
2342 of @code{void}. GNU C assigns these types a size of 1, for
2343 convenience in calculations with @code{void *} pointers and pointers
2346 @item -Wbad-function-cast @r{(C only)}
2347 @opindex Wbad-function-cast
2348 Warn whenever a function call is cast to a non-matching type.
2349 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2353 Warn whenever a pointer is cast so as to remove a type qualifier from
2354 the target type. For example, warn if a @code{const char *} is cast
2355 to an ordinary @code{char *}.
2358 @opindex Wcast-align
2359 Warn whenever a pointer is cast such that the required alignment of the
2360 target is increased. For example, warn if a @code{char *} is cast to
2361 an @code{int *} on machines where integers can only be accessed at
2362 two- or four-byte boundaries.
2364 @item -Wwrite-strings
2365 @opindex Wwrite-strings
2366 When compiling C, give string constants the type @code{const
2367 char[@var{length}]} so that
2368 copying the address of one into a non-@code{const} @code{char *}
2369 pointer will get a warning; when compiling C++, warn about the
2370 deprecated conversion from string constants to @code{char *}.
2371 These warnings will help you find at
2372 compile time code that can try to write into a string constant, but
2373 only if you have been very careful about using @code{const} in
2374 declarations and prototypes. Otherwise, it will just be a nuisance;
2375 this is why we did not make @option{-Wall} request these warnings.
2378 @opindex Wconversion
2379 Warn if a prototype causes a type conversion that is different from what
2380 would happen to the same argument in the absence of a prototype. This
2381 includes conversions of fixed point to floating and vice versa, and
2382 conversions changing the width or signedness of a fixed point argument
2383 except when the same as the default promotion.
2385 Also, warn if a negative integer constant expression is implicitly
2386 converted to an unsigned type. For example, warn about the assignment
2387 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2388 casts like @code{(unsigned) -1}.
2390 @item -Wsign-compare
2391 @opindex Wsign-compare
2392 @cindex warning for comparison of signed and unsigned values
2393 @cindex comparison of signed and unsigned values, warning
2394 @cindex signed and unsigned values, comparison warning
2395 Warn when a comparison between signed and unsigned values could produce
2396 an incorrect result when the signed value is converted to unsigned.
2397 This warning is also enabled by @option{-W}; to get the other warnings
2398 of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}.
2400 @item -Waggregate-return
2401 @opindex Waggregate-return
2402 Warn if any functions that return structures or unions are defined or
2403 called. (In languages where you can return an array, this also elicits
2406 @item -Wstrict-prototypes @r{(C only)}
2407 @opindex Wstrict-prototypes
2408 Warn if a function is declared or defined without specifying the
2409 argument types. (An old-style function definition is permitted without
2410 a warning if preceded by a declaration which specifies the argument
2413 @item -Wmissing-prototypes @r{(C only)}
2414 @opindex Wmissing-prototypes
2415 Warn if a global function is defined without a previous prototype
2416 declaration. This warning is issued even if the definition itself
2417 provides a prototype. The aim is to detect global functions that fail
2418 to be declared in header files.
2420 @item -Wmissing-declarations
2421 @opindex Wmissing-declarations
2422 Warn if a global function is defined without a previous declaration.
2423 Do so even if the definition itself provides a prototype.
2424 Use this option to detect global functions that are not declared in
2427 @item -Wmissing-noreturn
2428 @opindex Wmissing-noreturn
2429 Warn about functions which might be candidates for attribute @code{noreturn}.
2430 Note these are only possible candidates, not absolute ones. Care should
2431 be taken to manually verify functions actually do not ever return before
2432 adding the @code{noreturn} attribute, otherwise subtle code generation
2433 bugs could be introduced. You will not get a warning for @code{main} in
2434 hosted C environments.
2436 @item -Wmissing-format-attribute
2437 @opindex Wmissing-format-attribute
2439 If @option{-Wformat} is enabled, also warn about functions which might be
2440 candidates for @code{format} attributes. Note these are only possible
2441 candidates, not absolute ones. GCC will guess that @code{format}
2442 attributes might be appropriate for any function that calls a function
2443 like @code{vprintf} or @code{vscanf}, but this might not always be the
2444 case, and some functions for which @code{format} attributes are
2445 appropriate may not be detected. This option has no effect unless
2446 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2450 Warn if a structure is given the packed attribute, but the packed
2451 attribute has no effect on the layout or size of the structure.
2452 Such structures may be mis-aligned for little benefit. For
2453 instance, in this code, the variable @code{f.x} in @code{struct bar}
2454 will be misaligned even though @code{struct bar} does not itself
2455 have the packed attribute:
2462 @} __attribute__((packed));
2472 Warn if padding is included in a structure, either to align an element
2473 of the structure or to align the whole structure. Sometimes when this
2474 happens it is possible to rearrange the fields of the structure to
2475 reduce the padding and so make the structure smaller.
2477 @item -Wredundant-decls
2478 @opindex Wredundant-decls
2479 Warn if anything is declared more than once in the same scope, even in
2480 cases where multiple declaration is valid and changes nothing.
2482 @item -Wnested-externs @r{(C only)}
2483 @opindex Wnested-externs
2484 Warn if an @code{extern} declaration is encountered within a function.
2486 @item -Wunreachable-code
2487 @opindex Wunreachable-code
2488 Warn if the compiler detects that code will never be executed.
2490 This option is intended to warn when the compiler detects that at
2491 least a whole line of source code will never be executed, because
2492 some condition is never satisfied or because it is after a
2493 procedure that never returns.
2495 It is possible for this option to produce a warning even though there
2496 are circumstances under which part of the affected line can be executed,
2497 so care should be taken when removing apparently-unreachable code.
2499 For instance, when a function is inlined, a warning may mean that the
2500 line is unreachable in only one inlined copy of the function.
2502 This option is not made part of @option{-Wall} because in a debugging
2503 version of a program there is often substantial code which checks
2504 correct functioning of the program and is, hopefully, unreachable
2505 because the program does work. Another common use of unreachable
2506 code is to provide behaviour which is selectable at compile-time.
2510 Warn if a function can not be inlined and it was declared as inline.
2514 @opindex Wno-long-long
2515 Warn if @samp{long long} type is used. This is default. To inhibit
2516 the warning messages, use @option{-Wno-long-long}. Flags
2517 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2518 only when @option{-pedantic} flag is used.
2520 @item -Wdisabled-optimization
2521 @opindex Wdisabled-optimization
2522 Warn if a requested optimization pass is disabled. This warning does
2523 not generally indicate that there is anything wrong with your code; it
2524 merely indicates that GCC's optimizers were unable to handle the code
2525 effectively. Often, the problem is that your code is too big or too
2526 complex; GCC will refuse to optimize programs when the optimization
2527 itself is likely to take inordinate amounts of time.
2531 Make all warnings into errors.
2534 @node Debugging Options
2535 @section Options for Debugging Your Program or GCC
2536 @cindex options, debugging
2537 @cindex debugging information options
2539 GCC has various special options that are used for debugging
2540 either your program or GCC:
2545 Produce debugging information in the operating system's native format
2546 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2549 On most systems that use stabs format, @option{-g} enables use of extra
2550 debugging information that only GDB can use; this extra information
2551 makes debugging work better in GDB but will probably make other debuggers
2553 refuse to read the program. If you want to control for certain whether
2554 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2555 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, or @option{-gdwarf-1}
2558 Unlike most other C compilers, GCC allows you to use @option{-g} with
2559 @option{-O}. The shortcuts taken by optimized code may occasionally
2560 produce surprising results: some variables you declared may not exist
2561 at all; flow of control may briefly move where you did not expect it;
2562 some statements may not be executed because they compute constant
2563 results or their values were already at hand; some statements may
2564 execute in different places because they were moved out of loops.
2566 Nevertheless it proves possible to debug optimized output. This makes
2567 it reasonable to use the optimizer for programs that might have bugs.
2569 The following options are useful when GCC is generated with the
2570 capability for more than one debugging format.
2574 Produce debugging information for use by GDB@. This means to use the
2575 most expressive format available (DWARF 2, stabs, or the native format
2576 if neither of those are supported), including GDB extensions if at all
2581 Produce debugging information in stabs format (if that is supported),
2582 without GDB extensions. This is the format used by DBX on most BSD
2583 systems. On MIPS, Alpha and System V Release 4 systems this option
2584 produces stabs debugging output which is not understood by DBX or SDB@.
2585 On System V Release 4 systems this option requires the GNU assembler.
2589 Produce debugging information in stabs format (if that is supported),
2590 using GNU extensions understood only by the GNU debugger (GDB)@. The
2591 use of these extensions is likely to make other debuggers crash or
2592 refuse to read the program.
2596 Produce debugging information in COFF format (if that is supported).
2597 This is the format used by SDB on most System V systems prior to
2602 Produce debugging information in XCOFF format (if that is supported).
2603 This is the format used by the DBX debugger on IBM RS/6000 systems.
2607 Produce debugging information in XCOFF format (if that is supported),
2608 using GNU extensions understood only by the GNU debugger (GDB)@. The
2609 use of these extensions is likely to make other debuggers crash or
2610 refuse to read the program, and may cause assemblers other than the GNU
2611 assembler (GAS) to fail with an error.
2615 Produce debugging information in DWARF version 1 format (if that is
2616 supported). This is the format used by SDB on most System V Release 4
2621 Produce debugging information in DWARF version 1 format (if that is
2622 supported), using GNU extensions understood only by the GNU debugger
2623 (GDB)@. The use of these extensions is likely to make other debuggers
2624 crash or refuse to read the program.
2628 Produce debugging information in DWARF version 2 format (if that is
2629 supported). This is the format used by DBX on IRIX 6.
2632 @itemx -ggdb@var{level}
2633 @itemx -gstabs@var{level}
2634 @itemx -gcoff@var{level}
2635 @itemx -gxcoff@var{level}
2636 @itemx -gdwarf@var{level}
2637 @itemx -gdwarf-2@var{level}
2638 Request debugging information and also use @var{level} to specify how
2639 much information. The default level is 2.
2641 Level 1 produces minimal information, enough for making backtraces in
2642 parts of the program that you don't plan to debug. This includes
2643 descriptions of functions and external variables, but no information
2644 about local variables and no line numbers.
2646 Level 3 includes extra information, such as all the macro definitions
2647 present in the program. Some debuggers support macro expansion when
2648 you use @option{-g3}.
2653 Generate extra code to write profile information suitable for the
2654 analysis program @code{prof}. You must use this option when compiling
2655 the source files you want data about, and you must also use it when
2658 @cindex @code{gprof}
2661 Generate extra code to write profile information suitable for the
2662 analysis program @code{gprof}. You must use this option when compiling
2663 the source files you want data about, and you must also use it when
2669 Generate extra code to write profile information for basic blocks, which will
2670 record the number of times each basic block is executed, the basic block start
2671 address, and the function name containing the basic block. If @option{-g} is
2672 used, the line number and filename of the start of the basic block will also be
2673 recorded. If not overridden by the machine description, the default action is
2674 to append to the text file @file{bb.out}.
2676 This data could be analyzed by a program like @code{tcov}. Note,
2677 however, that the format of the data is not what @code{tcov} expects.
2678 Eventually GNU @code{gprof} should be extended to process this data.
2682 Makes the compiler print out each function name as it is compiled, and
2683 print some statistics about each pass when it finishes.
2686 @opindex ftime-report
2687 Makes the compiler print some statistics about the time consumed by each
2688 pass when it finishes.
2691 @opindex fmem-report
2692 Makes the compiler print some statistics about permanent memory
2693 allocation when it finishes.
2697 Generate extra code to profile basic blocks. Your executable will
2698 produce output that is a superset of that produced when @option{-a} is
2699 used. Additional output is the source and target address of the basic
2700 blocks where a jump takes place, the number of times a jump is executed,
2701 and (optionally) the complete sequence of basic blocks being executed.
2702 The output is appended to file @file{bb.out}.
2704 You can examine different profiling aspects without recompilation. Your
2705 executable will read a list of function names from file @file{bb.in}.
2706 Profiling starts when a function on the list is entered and stops when
2707 that invocation is exited. To exclude a function from profiling, prefix
2708 its name with @samp{-}. If a function name is not unique, you can
2709 disambiguate it by writing it in the form
2710 @samp{/path/filename.d:functionname}. Your executable will write the
2711 available paths and filenames in file @file{bb.out}.
2713 Several function names have a special meaning:
2716 Write source, target and frequency of jumps to file @file{bb.out}.
2717 @item __bb_hidecall__
2718 Exclude function calls from frequency count.
2719 @item __bb_showret__
2720 Include function returns in frequency count.
2722 Write the sequence of basic blocks executed to file @file{bbtrace.gz}.
2723 The file will be compressed using the program @samp{gzip}, which must
2724 exist in your @env{PATH}. On systems without the @samp{popen}
2725 function, the file will be named @file{bbtrace} and will not be
2726 compressed. @strong{Profiling for even a few seconds on these systems
2727 will produce a very large file.} Note: @code{__bb_hidecall__} and
2728 @code{__bb_showret__} will not affect the sequence written to
2732 Here's a short example using different profiling parameters
2733 in file @file{bb.in}. Assume function @code{foo} consists of basic blocks
2734 1 and 2 and is called twice from block 3 of function @code{main}. After
2735 the calls, block 3 transfers control to block 4 of @code{main}.
2737 With @code{__bb_trace__} and @code{main} contained in file @file{bb.in},
2738 the following sequence of blocks is written to file @file{bbtrace.gz}:
2739 0 3 1 2 1 2 4. The return from block 2 to block 3 is not shown, because
2740 the return is to a point inside the block and not to the top. The
2741 block address 0 always indicates, that control is transferred
2742 to the trace from somewhere outside the observed functions. With
2743 @samp{-foo} added to @file{bb.in}, the blocks of function
2744 @code{foo} are removed from the trace, so only 0 3 4 remains.
2746 With @code{__bb_jumps__} and @code{main} contained in file @file{bb.in},
2747 jump frequencies will be written to file @file{bb.out}. The
2748 frequencies are obtained by constructing a trace of blocks
2749 and incrementing a counter for every neighbouring pair of blocks
2750 in the trace. The trace 0 3 1 2 1 2 4 displays the following
2754 Jump from block 0x0 to block 0x3 executed 1 time(s)
2755 Jump from block 0x3 to block 0x1 executed 1 time(s)
2756 Jump from block 0x1 to block 0x2 executed 2 time(s)
2757 Jump from block 0x2 to block 0x1 executed 1 time(s)
2758 Jump from block 0x2 to block 0x4 executed 1 time(s)
2761 With @code{__bb_hidecall__}, control transfer due to call instructions
2762 is removed from the trace, that is the trace is cut into three parts: 0
2763 3 4, 0 1 2 and 0 1 2. With @code{__bb_showret__}, control transfer due
2764 to return instructions is added to the trace. The trace becomes: 0 3 1
2765 2 3 1 2 3 4. Note, that this trace is not the same, as the sequence
2766 written to @file{bbtrace.gz}. It is solely used for counting jump
2769 @item -fprofile-arcs
2770 @opindex fprofile-arcs
2771 Instrument @dfn{arcs} during compilation to generate coverage data
2772 or for profile-directed block ordering. During execution the program
2773 records how many times each branch is executed and how many times it is
2774 taken. When the compiled program exits it saves this data to a file
2775 called @file{@var{sourcename}.da} for each source file.
2777 For profile-directed block ordering, compile the program with
2778 @option{-fprofile-arcs} plus optimization and code generation options,
2779 generate the arc profile information by running the program on a
2780 selected workload, and then compile the program again with the same
2781 optimization and code generation options plus
2782 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
2783 Control Optimization}).
2785 The other use of @option{-fprofile-arcs} is for use with @code{gcov},
2786 when it is used with the @option{-ftest-coverage} option. GCC
2787 supports two methods of determining code coverage: the options that
2788 support @code{gcov}, and options @option{-a} and @option{-ax}, which
2789 write information to text files. The options that support @code{gcov}
2790 do not need to instrument every arc in the program, so a program compiled
2791 with them runs faster than a program compiled with @option{-a}, which
2792 adds instrumentation code to every basic block in the program. The
2793 tradeoff: since @code{gcov} does not have execution counts for all
2794 branches, it must start with the execution counts for the instrumented
2795 branches, and then iterate over the program flow graph until the entire
2796 graph has been solved. Hence, @code{gcov} runs a little more slowly than
2797 a program which uses information from @option{-a} and @option{-ax}.
2799 With @option{-fprofile-arcs}, for each function of your program GCC
2800 creates a program flow graph, then finds a spanning tree for the graph.
2801 Only arcs that are not on the spanning tree have to be instrumented: the
2802 compiler adds code to count the number of times that these arcs are
2803 executed. When an arc is the only exit or only entrance to a block, the
2804 instrumentation code can be added to the block; otherwise, a new basic
2805 block must be created to hold the instrumentation code.
2807 This option makes it possible to estimate branch probabilities and to
2808 calculate basic block execution counts. In general, basic block
2809 execution counts as provided by @option{-a} do not give enough
2810 information to estimate all branch probabilities.
2813 @item -ftest-coverage
2814 @opindex ftest-coverage
2815 Create data files for the @code{gcov} code-coverage utility
2816 (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}).
2817 The data file names begin with the name of your source file:
2820 @item @var{sourcename}.bb
2821 A mapping from basic blocks to line numbers, which @code{gcov} uses to
2822 associate basic block execution counts with line numbers.
2824 @item @var{sourcename}.bbg
2825 A list of all arcs in the program flow graph. This allows @code{gcov}
2826 to reconstruct the program flow graph, so that it can compute all basic
2827 block and arc execution counts from the information in the
2828 @code{@var{sourcename}.da} file.
2831 Use @option{-ftest-coverage} with @option{-fprofile-arcs}; the latter
2832 option adds instrumentation to the program, which then writes
2833 execution counts to another data file:
2836 @item @var{sourcename}.da
2837 Runtime arc execution counts, used in conjunction with the arc
2838 information in the file @code{@var{sourcename}.bbg}.
2841 Coverage data will map better to the source files if
2842 @option{-ftest-coverage} is used without optimization.
2844 @item -d@var{letters}
2846 Says to make debugging dumps during compilation at times specified by
2847 @var{letters}. This is used for debugging the compiler. The file names
2848 for most of the dumps are made by appending a pass number and a word to
2849 the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}).
2850 Here are the possible letters for use in @var{letters}, and their meanings:
2855 Annotate the assembler output with miscellaneous debugging information.
2858 Dump after computing branch probabilities, to @file{@var{file}.14.bp}.
2861 Dump after block reordering, to @file{@var{file}.28.bbro}.
2864 Dump after instruction combination, to the file @file{@var{file}.16.combine}.
2867 Dump after the first if conversion, to the file @file{@var{file}.17.ce}.
2870 Dump after delayed branch scheduling, to @file{@var{file}.31.dbr}.
2873 Dump all macro definitions, at the end of preprocessing, in addition to
2877 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
2878 @file{@var{file}.07.ussa}.
2881 Dump after the second if conversion, to @file{@var{file}.26.ce2}.
2884 Dump after life analysis, to @file{@var{file}.15.life}.
2887 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.09.addressof}.
2890 Dump after global register allocation, to @file{@var{file}.21.greg}.
2893 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
2896 Dump after post-reload optimizations, to @file{@var{file}.22.postreload}.
2899 Dump after GCSE, to @file{@var{file}.10.gcse}.
2902 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
2905 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
2908 Dump after conversion from registers to stack, to @file{@var{file}.32.stack}.
2911 Dump after local register allocation, to @file{@var{file}.20.lreg}.
2914 Dump after loop optimization, to @file{@var{file}.11.loop}.
2917 Dump after performing the machine dependent reorganisation pass, to
2918 @file{@var{file}.30.mach}.
2921 Dump after register renumbering, to @file{@var{file}.25.rnreg}.
2924 Dump after the register move pass, to @file{@var{file}.18.regmove}.
2927 Dump after RTL generation, to @file{@var{file}.00.rtl}.
2930 Dump after the second scheduling pass, to @file{@var{file}.27.sched2}.
2933 Dump after CSE (including the jump optimization that sometimes follows
2934 CSE), to @file{@var{file}.08.cse}.
2937 Dump after the first scheduling pass, to @file{@var{file}.19.sched}.
2940 Dump after the second CSE pass (including the jump optimization that
2941 sometimes follows CSE), to @file{@var{file}.12.cse2}.
2944 Dump after the second flow pass, to @file{@var{file}.23.flow2}.
2947 Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}.
2950 Dump after the peephole pass, to @file{@var{file}.24.peephole2}.
2953 Produce all the dumps listed above.
2956 Print statistics on memory usage, at the end of the run, to
2960 Annotate the assembler output with a comment indicating which
2961 pattern and alternative was used. The length of each instruction is
2965 Dump the RTL in the assembler output as a comment before each instruction.
2966 Also turns on @option{-dp} annotation.
2969 For each of the other indicated dump files (except for
2970 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
2971 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
2974 Just generate RTL for a function instead of compiling it. Usually used
2978 Dump debugging information during parsing, to standard error.
2981 @item -fdump-unnumbered
2982 @opindex fdump-unnumbered
2983 When doing debugging dumps (see @option{-d} option above), suppress instruction
2984 numbers and line number note output. This makes it more feasible to
2985 use diff on debugging dumps for compiler invocations with different
2986 options, in particular with and without @option{-g}.
2988 @item -fdump-class-hierarchy @r{(C++ only)}
2989 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
2990 @opindex fdump-class-hierarchy
2991 Dump a representation of each class's hierarchy and virtual function
2992 table layout to a file. The file name is made by appending @file{.class}
2993 to the source file name. If the @samp{-@var{options}} form is used,
2994 @var{options} controls the details of the dump as described for the
2995 @option{-fdump-tree} options.
2997 @item -fdump-tree-@var{switch} @r{(C++ only)}
2998 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3000 Control the dumping at various stages of processing the intermediate
3001 language tree to a file. The file name is generated by appending a switch
3002 specific suffix to the source file name. If the @samp{-@var{options}}
3003 form is used, @var{options} is a list of @samp{-} separated options that
3004 control the details of the dump. Not all options are applicable to all
3005 dumps, those which are not meaningful will be ignored. The following
3006 options are available
3010 Print the address of each node. Usually this is not meaningful as it
3011 changes according to the environment and source file. Its primary use
3012 is for tying up a dump file with a debug environment.
3014 Inhibit dumping of members of a scope or body of a function merely
3015 because that scope has been reached. Only dump such items when they
3016 are directly reachable by some other path.
3018 Turn on all options.
3021 The following tree dumps are possible:
3024 Dump before any tree based optimization, to @file{@var{file}.original}.
3026 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3028 Dump after function inlining, to @file{@var{file}.inlined}.
3031 @item -fpretend-float
3032 @opindex fpretend-float
3033 When running a cross-compiler, pretend that the target machine uses the
3034 same floating point format as the host machine. This causes incorrect
3035 output of the actual floating constants, but the actual instruction
3036 sequence will probably be the same as GCC would make when running on
3041 Store the usual ``temporary'' intermediate files permanently; place them
3042 in the current directory and name them based on the source file. Thus,
3043 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3044 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3045 preprocessed @file{foo.i} output file even though the compiler now
3046 normally uses an integrated preprocessor.
3050 Report the CPU time taken by each subprocess in the compilation
3051 sequence. For C source files, this is the compiler proper and assembler
3052 (plus the linker if linking is done). The output looks like this:
3059 The first number on each line is the ``user time,'' that is time spent
3060 executing the program itself. The second number is ``system time,''
3061 time spent executing operating system routines on behalf of the program.
3062 Both numbers are in seconds.
3064 @item -print-file-name=@var{library}
3065 @opindex print-file-name
3066 Print the full absolute name of the library file @var{library} that
3067 would be used when linking---and don't do anything else. With this
3068 option, GCC does not compile or link anything; it just prints the
3071 @item -print-multi-directory
3072 @opindex print-multi-directory
3073 Print the directory name corresponding to the multilib selected by any
3074 other switches present in the command line. This directory is supposed
3075 to exist in @env{GCC_EXEC_PREFIX}.
3077 @item -print-multi-lib
3078 @opindex print-multi-lib
3079 Print the mapping from multilib directory names to compiler switches
3080 that enable them. The directory name is separated from the switches by
3081 @samp{;}, and each switch starts with an @samp{@@} instead of the
3082 @samp{-}, without spaces between multiple switches. This is supposed to
3083 ease shell-processing.
3085 @item -print-prog-name=@var{program}
3086 @opindex print-prog-name
3087 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3089 @item -print-libgcc-file-name
3090 @opindex print-libgcc-file-name
3091 Same as @option{-print-file-name=libgcc.a}.
3093 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3094 but you do want to link with @file{libgcc.a}. You can do
3097 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3100 @item -print-search-dirs
3101 @opindex print-search-dirs
3102 Print the name of the configured installation directory and a list of
3103 program and library directories gcc will search---and don't do anything else.
3105 This is useful when gcc prints the error message
3106 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3107 To resolve this you either need to put @file{cpp0} and the other compiler
3108 components where gcc expects to find them, or you can set the environment
3109 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3110 Don't forget the trailing '/'.
3111 @xref{Environment Variables}.
3114 @opindex dumpmachine
3115 Print the compiler's target machine (for example,
3116 @samp{i686-pc-linux-gnu})---and don't do anything else.
3119 @opindex dumpversion
3120 Print the compiler version (for example, @samp{3.0})---and don't do
3125 Print the compiler's built-in specs---and don't do anything else. (This
3126 is used when GCC itself is being built.) @xref{Spec Files}.
3129 @node Optimize Options
3130 @section Options That Control Optimization
3131 @cindex optimize options
3132 @cindex options, optimization
3134 These options control various sorts of optimizations:
3141 Optimize. Optimizing compilation takes somewhat more time, and a lot
3142 more memory for a large function.
3144 Without @option{-O}, the compiler's goal is to reduce the cost of
3145 compilation and to make debugging produce the expected results.
3146 Statements are independent: if you stop the program with a breakpoint
3147 between statements, you can then assign a new value to any variable or
3148 change the program counter to any other statement in the function and
3149 get exactly the results you would expect from the source code.
3151 With @option{-O}, the compiler tries to reduce code size and execution
3152 time, without performing any optimizations that take a great deal of
3157 Optimize even more. GCC performs nearly all supported optimizations
3158 that do not involve a space-speed tradeoff. The compiler does not
3159 perform loop unrolling or function inlining when you specify @option{-O2}.
3160 As compared to @option{-O}, this option increases both compilation time
3161 and the performance of the generated code.
3163 @option{-O2} turns on all optional optimizations except for loop unrolling,
3164 function inlining, and register renaming. It also turns on the
3165 @option{-fforce-mem} option on all machines and frame pointer elimination
3166 on machines where doing so does not interfere with debugging.
3168 Please note the warning under @option{-fgcse} about
3169 invoking @option{-O2} on programs that use computed gotos.
3173 Optimize yet more. @option{-O3} turns on all optimizations specified by
3174 @option{-O2} and also turns on the @option{-finline-functions} and
3175 @option{-frename-registers} options.
3183 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3184 do not typically increase code size. It also performs further
3185 optimizations designed to reduce code size.
3187 If you use multiple @option{-O} options, with or without level numbers,
3188 the last such option is the one that is effective.
3191 Options of the form @option{-f@var{flag}} specify machine-independent
3192 flags. Most flags have both positive and negative forms; the negative
3193 form of @option{-ffoo} would be @option{-fno-foo}. In the table below,
3194 only one of the forms is listed---the one which is not the default.
3195 You can figure out the other form by either removing @samp{no-} or
3200 @opindex ffloat-store
3201 Do not store floating point variables in registers, and inhibit other
3202 options that might change whether a floating point value is taken from a
3205 @cindex floating point precision
3206 This option prevents undesirable excess precision on machines such as
3207 the 68000 where the floating registers (of the 68881) keep more
3208 precision than a @code{double} is supposed to have. Similarly for the
3209 x86 architecture. For most programs, the excess precision does only
3210 good, but a few programs rely on the precise definition of IEEE floating
3211 point. Use @option{-ffloat-store} for such programs, after modifying
3212 them to store all pertinent intermediate computations into variables.
3214 @item -fno-default-inline
3215 @opindex fno-default-inline
3216 Do not make member functions inline by default merely because they are
3217 defined inside the class scope (C++ only). Otherwise, when you specify
3218 @w{@option{-O}}, member functions defined inside class scope are compiled
3219 inline by default; i.e., you don't need to add @samp{inline} in front of
3220 the member function name.
3222 @item -fno-defer-pop
3223 @opindex fno-defer-pop
3224 Always pop the arguments to each function call as soon as that function
3225 returns. For machines which must pop arguments after a function call,
3226 the compiler normally lets arguments accumulate on the stack for several
3227 function calls and pops them all at once.
3231 Force memory operands to be copied into registers before doing
3232 arithmetic on them. This produces better code by making all memory
3233 references potential common subexpressions. When they are not common
3234 subexpressions, instruction combination should eliminate the separate
3235 register-load. The @option{-O2} option turns on this option.
3238 @opindex fforce-addr
3239 Force memory address constants to be copied into registers before
3240 doing arithmetic on them. This may produce better code just as
3241 @option{-fforce-mem} may.
3243 @item -fomit-frame-pointer
3244 @opindex fomit-frame-pointer
3245 Don't keep the frame pointer in a register for functions that
3246 don't need one. This avoids the instructions to save, set up and
3247 restore frame pointers; it also makes an extra register available
3248 in many functions. @strong{It also makes debugging impossible on
3252 On some machines, such as the VAX, this flag has no effect, because
3253 the standard calling sequence automatically handles the frame pointer
3254 and nothing is saved by pretending it doesn't exist. The
3255 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3256 whether a target machine supports this flag. @xref{Registers}.
3259 On some machines, such as the VAX, this flag has no effect, because
3260 the standard calling sequence automatically handles the frame pointer
3261 and nothing is saved by pretending it doesn't exist. The
3262 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3263 whether a target machine supports this flag. @xref{Registers,,Register
3264 Usage, gcc.info, Using and Porting GCC}.
3267 @item -foptimize-sibling-calls
3268 @opindex foptimize-sibling-calls
3269 Optimize sibling and tail recursive calls.
3273 This option generates traps for signed overflow on addition, subtraction,
3274 multiplication operations.
3278 Don't pay attention to the @code{inline} keyword. Normally this option
3279 is used to keep the compiler from expanding any functions inline.
3280 Note that if you are not optimizing, no functions can be expanded inline.
3282 @item -finline-functions
3283 @opindex finline-functions
3284 Integrate all simple functions into their callers. The compiler
3285 heuristically decides which functions are simple enough to be worth
3286 integrating in this way.
3288 If all calls to a given function are integrated, and the function is
3289 declared @code{static}, then the function is normally not output as
3290 assembler code in its own right.
3292 @item -finline-limit=@var{n}
3293 @opindex finline-limit
3294 By default, gcc limits the size of functions that can be inlined. This flag
3295 allows the control of this limit for functions that are explicitly marked as
3296 inline (ie marked with the inline keyword or defined within the class
3297 definition in c++). @var{n} is the size of functions that can be inlined in
3298 number of pseudo instructions (not counting parameter handling). The default
3299 value of @var{n} is 600.
3300 Increasing this value can result in more inlined code at
3301 the cost of compilation time and memory consumption. Decreasing usually makes
3302 the compilation faster and less code will be inlined (which presumably
3303 means slower programs). This option is particularly useful for programs that
3304 use inlining heavily such as those based on recursive templates with C++.
3306 @emph{Note:} pseudo instruction represents, in this particular context, an
3307 abstract measurement of function's size. In no way, it represents a count
3308 of assembly instructions and as such its exact meaning might change from one
3309 release to an another.
3311 @item -fkeep-inline-functions
3312 @opindex fkeep-inline-functions
3313 Even if all calls to a given function are integrated, and the function
3314 is declared @code{static}, nevertheless output a separate run-time
3315 callable version of the function. This switch does not affect
3316 @code{extern inline} functions.
3318 @item -fkeep-static-consts
3319 @opindex fkeep-static-consts
3320 Emit variables declared @code{static const} when optimization isn't turned
3321 on, even if the variables aren't referenced.
3323 GCC enables this option by default. If you want to force the compiler to
3324 check if the variable was referenced, regardless of whether or not
3325 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3327 @item -fmerge-constants
3328 Attempt to merge identical constants (string constants and floating point
3329 constants) accross compilation units.
3331 This option is default for optimized compilation if assembler and linker
3332 support it. Use @option{-fno-merge-constants} to inhibit this behaviour.
3334 @item -fmerge-all-constants
3335 Attempt to merge identical constants and identical variables.
3337 This option implies @option{-fmerge-constants}. In addition to
3338 @option{-fmerge-constants} this considers e.g. even constant initialized
3339 arrays or initialized constant variables with integral or floating point
3340 types. Languages like C or C++ require each non-automatic variable to
3341 have distinct location, so using this option will result in non-conforming
3344 @item -fno-function-cse
3345 @opindex fno-function-cse
3346 Do not put function addresses in registers; make each instruction that
3347 calls a constant function contain the function's address explicitly.
3349 This option results in less efficient code, but some strange hacks
3350 that alter the assembler output may be confused by the optimizations
3351 performed when this option is not used.
3355 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, and @*
3356 @option{-fno-trapping-math}.
3358 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
3360 This option should never be turned on by any @option{-O} option since
3361 it can result in incorrect output for programs which depend on
3362 an exact implementation of IEEE or ISO rules/specifications for
3365 @item -fno-math-errno
3366 @opindex fno-math-errno
3367 Do not set ERRNO after calling math functions that are executed
3368 with a single instruction, e.g., sqrt. A program that relies on
3369 IEEE exceptions for math error handling may want to use this flag
3370 for speed while maintaining IEEE arithmetic compatibility.
3372 This option should never be turned on by any @option{-O} option since
3373 it can result in incorrect output for programs which depend on
3374 an exact implementation of IEEE or ISO rules/specifications for
3377 The default is @option{-fmath-errno}.
3379 @item -funsafe-math-optimizations
3380 @opindex funsafe-math-optimizations
3381 Allow optimizations for floating-point arithmetic that (a) assume
3382 that arguments and results are valid and (b) may violate IEEE or
3383 ANSI standards. When used at link-time, it may include libraries
3384 or startup files that change the default FPU control word or other
3385 similar optimizations.
3387 This option should never be turned on by any @option{-O} option since
3388 it can result in incorrect output for programs which depend on
3389 an exact implementation of IEEE or ISO rules/specifications for
3392 The default is @option{-fno-unsafe-math-optimizations}.
3394 @item -fno-trapping-math
3395 @opindex fno-trapping-math
3396 Compile code assuming that floating-point operations cannot generate
3397 user-visible traps. Setting this option may allow faster code
3398 if one relies on ``non-stop'' IEEE arithmetic, for example.
3400 This option should never be turned on by any @option{-O} option since
3401 it can result in incorrect output for programs which depend on
3402 an exact implementation of IEEE or ISO rules/specifications for
3405 The default is @option{-ftrapping-math}.
3408 The following options control specific optimizations. The @option{-O2}
3409 option turns on all of these optimizations except @option{-funroll-loops}
3410 and @option{-funroll-all-loops}. On most machines, the @option{-O} option
3411 turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
3412 but specific machines may handle it differently.
3414 You can use the following flags in the rare cases when ``fine-tuning''
3415 of optimizations to be performed is desired.
3417 Not all of the optimizations performed by GCC have @option{-f} options
3421 @item -fstrength-reduce
3422 @opindex fstrength-reduce
3423 Perform the optimizations of loop strength reduction and
3424 elimination of iteration variables.
3426 @item -fthread-jumps
3427 @opindex fthread-jumps
3428 Perform optimizations where we check to see if a jump branches to a
3429 location where another comparison subsumed by the first is found. If
3430 so, the first branch is redirected to either the destination of the
3431 second branch or a point immediately following it, depending on whether
3432 the condition is known to be true or false.
3434 @item -fcse-follow-jumps
3435 @opindex fcse-follow-jumps
3436 In common subexpression elimination, scan through jump instructions
3437 when the target of the jump is not reached by any other path. For
3438 example, when CSE encounters an @code{if} statement with an
3439 @code{else} clause, CSE will follow the jump when the condition
3442 @item -fcse-skip-blocks
3443 @opindex fcse-skip-blocks
3444 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3445 follow jumps which conditionally skip over blocks. When CSE
3446 encounters a simple @code{if} statement with no else clause,
3447 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3448 body of the @code{if}.
3450 @item -frerun-cse-after-loop
3451 @opindex frerun-cse-after-loop
3452 Re-run common subexpression elimination after loop optimizations has been
3455 @item -frerun-loop-opt
3456 @opindex frerun-loop-opt
3457 Run the loop optimizer twice.
3461 Perform a global common subexpression elimination pass.
3462 This pass also performs global constant and copy propagation.
3464 @emph{Note:} When compiling a program using computed gotos, a GCC
3465 extension, you may get better runtime performance if you disable
3466 the global common subexpression elmination pass by adding
3467 @option{-fno-gcse} to the command line.
3471 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3472 attempt to move loads which are only killed by stores into themselves. This
3473 allows a loop containing a load/store sequence to be changed to a load outside
3474 the loop, and a copy/store within the loop.
3478 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3479 subexpression elimination. This pass will attempt to move stores out of loops.
3480 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3481 can be changed to a load before the loop and a store after the loop.
3483 @item -fdelete-null-pointer-checks
3484 @opindex fdelete-null-pointer-checks
3485 Use global dataflow analysis to identify and eliminate useless checks
3486 for null pointers. The compiler assumes that dereferencing a null
3487 pointer would have halted the program. If a pointer is checked after
3488 it has already been dereferenced, it cannot be null.
3490 In some environments, this assumption is not true, and programs can
3491 safely dereference null pointers. Use
3492 @option{-fno-delete-null-pointer-checks} to disable this optimization
3493 for programs which depend on that behavior.
3495 @item -fexpensive-optimizations
3496 @opindex fexpensive-optimizations
3497 Perform a number of minor optimizations that are relatively expensive.
3499 @item -foptimize-register-move
3501 @opindex foptimize-register-move
3503 Attempt to reassign register numbers in move instructions and as
3504 operands of other simple instructions in order to maximize the amount of
3505 register tying. This is especially helpful on machines with two-operand
3506 instructions. GCC enables this optimization by default with @option{-O2}
3509 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3512 @item -fdelayed-branch
3513 @opindex fdelayed-branch
3514 If supported for the target machine, attempt to reorder instructions
3515 to exploit instruction slots available after delayed branch
3518 @item -fschedule-insns
3519 @opindex fschedule-insns
3520 If supported for the target machine, attempt to reorder instructions to
3521 eliminate execution stalls due to required data being unavailable. This
3522 helps machines that have slow floating point or memory load instructions
3523 by allowing other instructions to be issued until the result of the load
3524 or floating point instruction is required.
3526 @item -fschedule-insns2
3527 @opindex fschedule-insns2
3528 Similar to @option{-fschedule-insns}, but requests an additional pass of
3529 instruction scheduling after register allocation has been done. This is
3530 especially useful on machines with a relatively small number of
3531 registers and where memory load instructions take more than one cycle.
3533 @item -ffunction-sections
3534 @itemx -fdata-sections
3535 @opindex ffunction-sections
3536 @opindex fdata-sections
3537 Place each function or data item into its own section in the output
3538 file if the target supports arbitrary sections. The name of the
3539 function or the name of the data item determines the section's name
3542 Use these options on systems where the linker can perform optimizations
3543 to improve locality of reference in the instruction space. HPPA
3544 processors running HP-UX and Sparc processors running Solaris 2 have
3545 linkers with such optimizations. Other systems using the ELF object format
3546 as well as AIX may have these optimizations in the future.
3548 Only use these options when there are significant benefits from doing
3549 so. When you specify these options, the assembler and linker will
3550 create larger object and executable files and will also be slower.
3551 You will not be able to use @code{gprof} on all systems if you
3552 specify this option and you may have problems with debugging if
3553 you specify both this option and @option{-g}.
3555 @item -fcaller-saves
3556 @opindex fcaller-saves
3557 Enable values to be allocated in registers that will be clobbered by
3558 function calls, by emitting extra instructions to save and restore the
3559 registers around such calls. Such allocation is done only when it
3560 seems to result in better code than would otherwise be produced.
3562 This option is always enabled by default on certain machines, usually
3563 those which have no call-preserved registers to use instead.
3565 For all machines, optimization level 2 and higher enables this flag by
3568 @item -funroll-loops
3569 @opindex funroll-loops
3570 Unroll loops whose number of iterations can be determined at compile
3571 time or upon entry to the loop. @option{-funroll-loops} implies both
3572 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
3573 option makes code larger, and may or may not make it run faster.
3575 @item -funroll-all-loops
3576 @opindex funroll-all-loops
3577 Unroll all loops, even if their number of iterations is uncertain when
3578 the loop is entered. This usually makes programs run more slowly.
3579 @option{-funroll-all-loops} implies the same options as
3580 @option{-funroll-loops},
3583 @item -fmove-all-movables
3584 @opindex fmove-all-movables
3585 Forces all invariant computations in loops to be moved
3588 @item -freduce-all-givs
3589 @opindex freduce-all-givs
3590 Forces all general-induction variables in loops to be
3593 @emph{Note:} When compiling programs written in Fortran,
3594 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3595 by default when you use the optimizer.
3597 These options may generate better or worse code; results are highly
3598 dependent on the structure of loops within the source code.
3600 These two options are intended to be removed someday, once
3601 they have helped determine the efficacy of various
3602 approaches to improving loop optimizations.
3604 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
3605 know how use of these options affects
3606 the performance of your production code.
3607 We're very interested in code that runs @emph{slower}
3608 when these options are @emph{enabled}.
3611 @itemx -fno-peephole2
3612 @opindex fno-peephole
3613 @opindex fno-peephole2
3614 Disable any machine-specific peephole optimizations. The difference
3615 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
3616 are implemented in the compiler; some targets use one, some use the
3617 other, a few use both.
3619 @item -fbranch-probabilities
3620 @opindex fbranch-probabilities
3621 After running a program compiled with @option{-fprofile-arcs}
3622 (@pxref{Debugging Options,, Options for Debugging Your Program or
3623 @command{gcc}}), you can compile it a second time using
3624 @option{-fbranch-probabilities}, to improve optimizations based on
3625 the number of times each branch was taken. When the program
3626 compiled with @option{-fprofile-arcs} exits it saves arc execution
3627 counts to a file called @file{@var{sourcename}.da} for each source
3628 file The information in this data file is very dependent on the
3629 structure of the generated code, so you must use the same source code
3630 and the same optimization options for both compilations.
3633 With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
3634 note on the first instruction of each basic block, and a
3635 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
3636 These can be used to improve optimization. Currently, they are only
3637 used in one place: in @file{reorg.c}, instead of guessing which path a
3638 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
3639 exactly determine which path is taken more often.
3642 @item -fno-guess-branch-probability
3643 @opindex fno-guess-branch-probability
3644 Do not guess branch probabilities using a randomized model.
3646 Sometimes gcc will opt to use a randomized model to guess branch
3647 probabilities, when none are available from either profiling feedback
3648 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
3649 different runs of the compiler on the same program may produce different
3652 In a hard real-time system, people don't want different runs of the
3653 compiler to produce code that has different behavior; minimizing
3654 non-determinism is of paramount import. This switch allows users to
3655 reduce non-determinism, possibly at the expense of inferior
3658 @item -fstrict-aliasing
3659 @opindex fstrict-aliasing
3660 Allows the compiler to assume the strictest aliasing rules applicable to
3661 the language being compiled. For C (and C++), this activates
3662 optimizations based on the type of expressions. In particular, an
3663 object of one type is assumed never to reside at the same address as an
3664 object of a different type, unless the types are almost the same. For
3665 example, an @code{unsigned int} can alias an @code{int}, but not a
3666 @code{void*} or a @code{double}. A character type may alias any other
3669 Pay special attention to code like this:
3682 The practice of reading from a different union member than the one most
3683 recently written to (called ``type-punning'') is common. Even with
3684 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
3685 is accessed through the union type. So, the code above will work as
3686 expected. However, this code might not:
3698 Every language that wishes to perform language-specific alias analysis
3699 should define a function that computes, given an @code{tree}
3700 node, an alias set for the node. Nodes in different alias sets are not
3701 allowed to alias. For an example, see the C front-end function
3702 @code{c_get_alias_set}.
3705 @item -falign-functions
3706 @itemx -falign-functions=@var{n}
3707 @opindex falign-functions
3708 Align the start of functions to the next power-of-two greater than
3709 @var{n}, skipping up to @var{n} bytes. For instance,
3710 @option{-falign-functions=32} aligns functions to the next 32-byte
3711 boundary, but @option{-falign-functions=24} would align to the next
3712 32-byte boundary only if this can be done by skipping 23 bytes or less.
3714 @option{-fno-align-functions} and @option{-falign-functions=1} are
3715 equivalent and mean that functions will not be aligned.
3717 Some assemblers only support this flag when @var{n} is a power of two;
3718 in that case, it is rounded up.
3720 If @var{n} is not specified, use a machine-dependent default.
3722 @item -falign-labels
3723 @itemx -falign-labels=@var{n}
3724 @opindex falign-labels
3725 Align all branch targets to a power-of-two boundary, skipping up to
3726 @var{n} bytes like @option{-falign-functions}. This option can easily
3727 make code slower, because it must insert dummy operations for when the
3728 branch target is reached in the usual flow of the code.
3730 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
3731 are greater than this value, then their values are used instead.
3733 If @var{n} is not specified, use a machine-dependent default which is
3734 very likely to be @samp{1}, meaning no alignment.
3737 @itemx -falign-loops=@var{n}
3738 @opindex falign-loops
3739 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
3740 like @option{-falign-functions}. The hope is that the loop will be
3741 executed many times, which will make up for any execution of the dummy
3744 If @var{n} is not specified, use a machine-dependent default.
3747 @itemx -falign-jumps=@var{n}
3748 @opindex falign-jumps
3749 Align branch targets to a power-of-two boundary, for branch targets
3750 where the targets can only be reached by jumping, skipping up to @var{n}
3751 bytes like @option{-falign-functions}. In this case, no dummy operations
3754 If @var{n} is not specified, use a machine-dependent default.
3758 Perform optimizations in static single assignment form. Each function's
3759 flow graph is translated into SSA form, optimizations are performed, and
3760 the flow graph is translated back from SSA form. Users should not
3761 specify this option, since it is not yet ready for production use.
3765 Perform Sparse Conditional Constant Propagation in SSA form. Requires
3766 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
3770 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
3771 Like @option{-fssa}, this is an experimental feature.
3773 @item -fsingle-precision-constant
3774 @opindex fsingle-precision-constant
3775 Treat floating point constant as single precision constant instead of
3776 implicitly converting it to double precision constant.
3778 @item -frename-registers
3779 @opindex frename-registers
3780 Attempt to avoid false dependencies in scheduled code by making use
3781 of registers left over after register allocation. This optimization
3782 will most benefit processors with lots of registers. It can, however,
3783 make debugging impossible, since variables will no longer stay in
3784 a ``home register''.
3786 @item --param @var{name}=@var{value}
3788 In some places, GCC uses various constants to control the amount of
3789 optimization that is done. For example, GCC will not inline functions
3790 that contain more that a certain number of instructions. You can
3791 control some of these constants on the command-line using the
3792 @option{--param} option.
3794 In each case, the @var{value} is an integer. The allowable choices for
3795 @var{name} are given in the following table:
3798 @item max-delay-slot-insn-search
3799 The maximum number of instructions to consider when looking for an
3800 instruction to fill a delay slot. If more than this arbitrary number of
3801 instructions is searched, the time savings from filling the delay slot
3802 will be minimal so stop searching. Increasing values mean more
3803 aggressive optimization, making the compile time increase with probably
3804 small improvement in executable run time.
3806 @item max-delay-slot-live-search
3807 When trying to fill delay slots, the maximum number of instructions to
3808 consider when searching for a block with valid live register
3809 information. Increasing this arbitrarily chosen value means more
3810 aggressive optimization, increasing the compile time. This parameter
3811 should be removed when the delay slot code is rewritten to maintain the
3814 @item max-gcse-memory
3815 The approximate maximum amount of memory that will be allocated in
3816 order to perform the global common subexpression elimination
3817 optimization. If more memory than specified is required, the
3818 optimization will not be done.
3820 @item max-gcse-passes
3821 The maximum number of passes of GCSE to run.
3823 @item max-pending-list-length
3824 The maximum number of pending dependancies scheduling will allow
3825 before flushing the current state and starting over. Large functions
3826 with few branches or calls can create excessively large lists which
3827 needlessly consume memory and resources.
3829 @item max-inline-insns
3830 If an function contains more than this many instructions, it
3831 will not be inlined. This option is precisely equivalent to
3832 @option{-finline-limit}.
3837 @node Preprocessor Options
3838 @section Options Controlling the Preprocessor
3839 @cindex preprocessor options
3840 @cindex options, preprocessor
3842 These options control the C preprocessor, which is run on each C source
3843 file before actual compilation.
3845 If you use the @option{-E} option, nothing is done except preprocessing.
3846 Some of these options make sense only together with @option{-E} because
3847 they cause the preprocessor output to be unsuitable for actual
3851 @item -include @var{file}
3853 Process @var{file} as input before processing the regular input file.
3854 In effect, the contents of @var{file} are compiled first. Any @option{-D}
3855 and @option{-U} options on the command line are always processed before
3856 @option{-include @var{file}}, regardless of the order in which they are
3857 written. All the @option{-include} and @option{-imacros} options are
3858 processed in the order in which they are written.
3860 @item -imacros @var{file}
3862 Process @var{file} as input, discarding the resulting output, before
3863 processing the regular input file. Because the output generated from
3864 @var{file} is discarded, the only effect of @option{-imacros @var{file}}
3865 is to make the macros defined in @var{file} available for use in the
3866 main input. All the @option{-include} and @option{-imacros} options are
3867 processed in the order in which they are written.
3869 @item -idirafter @var{dir}
3871 @cindex second include path
3872 Add the directory @var{dir} to the second include path. The directories
3873 on the second include path are searched when a header file is not found
3874 in any of the directories in the main include path (the one that
3875 @option{-I} adds to).
3877 @item -iprefix @var{prefix}
3879 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
3882 @item -iwithprefix @var{dir}
3883 @opindex iwithprefix
3884 Add a directory to the second include path. The directory's name is
3885 made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was
3886 specified previously with @option{-iprefix}. If you have not specified a
3887 prefix yet, the directory containing the installed passes of the
3888 compiler is used as the default.
3890 @item -iwithprefixbefore @var{dir}
3891 @opindex iwithprefixbefore
3892 Add a directory to the main include path. The directory's name is made
3893 by concatenating @var{prefix} and @var{dir}, as in the case of
3894 @option{-iwithprefix}.
3896 @item -isystem @var{dir}
3898 Add a directory to the beginning of the second include path, marking it
3899 as a system directory, so that it gets the same special treatment as
3900 is applied to the standard system directories.
3904 Do not search the standard system directories for header files. Only
3905 the directories you have specified with @option{-I} options (and the
3906 current directory, if appropriate) are searched. @xref{Directory
3907 Options}, for information on @option{-I}.
3909 By using both @option{-nostdinc} and @option{-I-}, you can limit the include-file
3910 search path to only those directories you specify explicitly.
3914 When searching for a header file in a directory, remap file names if a
3915 file named @file{header.gcc} exists in that directory. This can be used
3916 to work around limitations of file systems with file name restrictions.
3917 The @file{header.gcc} file should contain a series of lines with two
3918 tokens on each line: the first token is the name to map, and the second
3919 token is the actual name to use.
3923 Do not predefine any nonstandard macros. (Including architecture flags).
3927 Run only the C preprocessor. Preprocess all the C source files
3928 specified and output the results to standard output or to the
3929 specified output file.
3933 Tell the preprocessor not to discard comments. Used with the
3938 Tell the preprocessor not to generate @samp{#line} directives.
3939 Used with the @option{-E} option.
3942 @cindex dependencies, make
3945 Instead of outputting the result of preprocessing, output a rule
3946 suitable for @code{make} describing the dependencies of the main source
3947 file. The preprocessor outputs one @code{make} rule containing the
3948 object file name for that source file, a colon, and the names of all the
3949 included files. Unless overridden explicitly, the object file name
3950 consists of the basename of the source file with any suffix replaced with
3951 object file suffix. If there are many included files then the
3952 rule is split into several lines using @samp{\}-newline.
3954 @option{-M} implies @option{-E}.
3958 Like @option{-M}, but mention only the files included with @samp{#include
3959 "@var{file}"}. System header files included with @samp{#include
3960 <@var{file}>} are omitted.
3964 Like @option{-M} but the dependency information is written to a file
3965 rather than stdout. @code{gcc} will use the same file name and
3966 directory as the object file, but with the suffix @file{.d} instead.
3968 This is in addition to compiling the main file as specified---@option{-MD}
3969 does not inhibit ordinary compilation the way @option{-M} does,
3970 unless you also specify @option{-MG}.
3972 With Mach, you can use the utility @code{md} to merge multiple
3973 dependency files into a single dependency file suitable for using with
3974 the @samp{make} command.
3978 Like @option{-MD} except mention only user header files, not system
3981 @item -MF @var{file}
3983 When used with @option{-M} or @option{-MM}, specifies a file to write the
3984 dependencies to. This allows the preprocessor to write the preprocessed
3985 file to stdout normally. If no @option{-MF} switch is given, CPP sends
3986 the rules to stdout and suppresses normal preprocessed output.
3988 Another way to specify output of a @code{make} rule is by setting
3989 the environment variable @env{DEPENDENCIES_OUTPUT} (@pxref{Environment
3994 When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing
3995 header files as generated files and assume they live in the same
3996 directory as the source file. It suppresses preprocessed output, as a
3997 missing header file is ordinarily an error.
3999 This feature is used in automatic updating of makefiles.
4003 This option instructs CPP to add a phony target for each dependency
4004 other than the main file, causing each to depend on nothing. These
4005 dummy rules work around errors @code{make} gives if you remove header
4006 files without updating the @code{Makefile} to match.
4008 This is typical output:-
4011 /tmp/test.o: /tmp/test.c /tmp/test.h
4016 @item -MQ @var{target}
4017 @item -MT @var{target}
4020 By default CPP uses the main file name, including any path, and appends
4021 the object suffix, normally ``.o'', to it to obtain the name of the
4022 target for dependency generation. With @option{-MT} you can specify a
4023 target yourself, overriding the default one.
4025 If you want multiple targets, you can specify them as a single argument
4026 to @option{-MT}, or use multiple @option{-MT} options.
4028 The targets you specify are output in the order they appear on the
4029 command line. @option{-MQ} is identical to @option{-MT}, except that the
4030 target name is quoted for Make, but with @option{-MT} it isn't. For
4031 example, @option{-MT '$(objpfx)foo.o'} gives
4034 $(objpfx)foo.o: /tmp/foo.c
4037 but @option{-MQ '$(objpfx)foo.o'} gives
4040 $$(objpfx)foo.o: /tmp/foo.c
4043 The default target is automatically quoted, as if it were given with
4048 Print the name of each header file used, in addition to other normal
4051 @item -A@var{question}(@var{answer})
4053 Assert the answer @var{answer} for @var{question}, in case it is tested
4054 with a preprocessing conditional such as @samp{#if
4055 #@var{question}(@var{answer})}. @option{-A-} disables the standard
4056 assertions that normally describe the target machine.
4060 Define macro @var{macro} with the string @samp{1} as its definition.
4062 @item -D@var{macro}=@var{defn}
4063 Define macro @var{macro} as @var{defn}. All instances of @option{-D} on
4064 the command line are processed before any @option{-U} options.
4066 Any @option{-D} and @option{-U} options on the command line are processed in
4067 order, and always before @option{-imacros @var{file}}, regardless of the
4068 order in which they are written.
4072 Undefine macro @var{macro}. @option{-U} options are evaluated after all
4073 @option{-D} options, but before any @option{-include} and @option{-imacros}
4076 Any @option{-D} and @option{-U} options on the command line are processed in
4077 order, and always before @option{-imacros @var{file}}, regardless of the
4078 order in which they are written.
4082 Tell the preprocessor to output only a list of the macro definitions
4083 that are in effect at the end of preprocessing. Used with the @option{-E}
4088 Tell the preprocessing to pass all macro definitions into the output, in
4089 their proper sequence in the rest of the output.
4093 Like @option{-dD} except that the macro arguments and contents are omitted.
4094 Only @samp{#define @var{name}} is included in the output.
4098 Output @samp{#include} directives in addition to the result of
4101 @item -fpreprocessed
4102 @opindex fpreprocessed
4103 Indicate to the preprocessor that the input file has already been
4104 preprocessed. This suppresses things like macro expansion, trigraph
4105 conversion, escaped newline splicing, and processing of most directives.
4106 The preprocessor still recognizes and removes comments, so that you can
4107 pass a file preprocessed with @option{-C} to the compiler without
4108 problems. In this mode the integrated preprocessor is little more than
4109 a tokenizer for the front ends.
4111 @option{-fpreprocessed} is implicit if the input file has one of the
4112 extensions @samp{i}, @samp{ii} or @samp{mi}. These are the extensions
4113 that GCC uses for preprocessed files created by @option{-save-temps}.
4117 Process ISO standard trigraph sequences. These are three-character
4118 sequences, all starting with @samp{??}, that are defined by ISO C to
4119 stand for single characters. For example, @samp{??/} stands for
4120 @samp{\}, so @samp{'??/n'} is a character constant for a newline. By
4121 default, GCC ignores trigraphs, but in standard-conforming modes it
4122 converts them. See the @option{-std} and @option{-ansi} options.
4124 The nine trigraph sequences are
4127 @expansion{} @samp{[}
4130 @expansion{} @samp{]}
4133 @expansion{} @samp{@{}
4136 @expansion{} @samp{@}}
4139 @expansion{} @samp{#}
4142 @expansion{} @samp{\}
4145 @expansion{} @samp{^}
4148 @expansion{} @samp{|}
4151 @expansion{} @samp{~}
4155 Trigraph support is not popular, so many compilers do not implement it
4156 properly. Portable code should not rely on trigraphs being either
4157 converted or ignored.
4159 @item -Wp,@var{option}
4161 Pass @var{option} as an option to the preprocessor. If @var{option}
4162 contains commas, it is split into multiple options at the commas.
4165 @node Assembler Options
4166 @section Passing Options to the Assembler
4168 @c prevent bad page break with this line
4169 You can pass options to the assembler.
4172 @item -Wa,@var{option}
4174 Pass @var{option} as an option to the assembler. If @var{option}
4175 contains commas, it is split into multiple options at the commas.
4179 @section Options for Linking
4180 @cindex link options
4181 @cindex options, linking
4183 These options come into play when the compiler links object files into
4184 an executable output file. They are meaningless if the compiler is
4185 not doing a link step.
4189 @item @var{object-file-name}
4190 A file name that does not end in a special recognized suffix is
4191 considered to name an object file or library. (Object files are
4192 distinguished from libraries by the linker according to the file
4193 contents.) If linking is done, these object files are used as input
4202 If any of these options is used, then the linker is not run, and
4203 object file names should not be used as arguments. @xref{Overall
4207 @item -l@var{library}
4208 @itemx -l @var{library}
4210 Search the library named @var{library} when linking. (The second
4211 alternative with the library as a separate argument is only for
4212 POSIX compliance and is not recommended.)
4214 It makes a difference where in the command you write this option; the
4215 linker searches and processes libraries and object files in the order they
4216 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4217 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4218 to functions in @samp{z}, those functions may not be loaded.
4220 The linker searches a standard list of directories for the library,
4221 which is actually a file named @file{lib@var{library}.a}. The linker
4222 then uses this file as if it had been specified precisely by name.
4224 The directories searched include several standard system directories
4225 plus any that you specify with @option{-L}.
4227 Normally the files found this way are library files---archive files
4228 whose members are object files. The linker handles an archive file by
4229 scanning through it for members which define symbols that have so far
4230 been referenced but not defined. But if the file that is found is an
4231 ordinary object file, it is linked in the usual fashion. The only
4232 difference between using an @option{-l} option and specifying a file name
4233 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4234 and searches several directories.
4238 You need this special case of the @option{-l} option in order to
4239 link an Objective-C program.
4242 @opindex nostartfiles
4243 Do not use the standard system startup files when linking.
4244 The standard system libraries are used normally, unless @option{-nostdlib}
4245 or @option{-nodefaultlibs} is used.
4247 @item -nodefaultlibs
4248 @opindex nodefaultlibs
4249 Do not use the standard system libraries when linking.
4250 Only the libraries you specify will be passed to the linker.
4251 The standard startup files are used normally, unless @option{-nostartfiles}
4252 is used. The compiler may generate calls to memcmp, memset, and memcpy
4253 for System V (and ISO C) environments or to bcopy and bzero for
4254 BSD environments. These entries are usually resolved by entries in
4255 libc. These entry points should be supplied through some other
4256 mechanism when this option is specified.
4260 Do not use the standard system startup files or libraries when linking.
4261 No startup files and only the libraries you specify will be passed to
4262 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4263 for System V (and ISO C) environments or to bcopy and bzero for
4264 BSD environments. These entries are usually resolved by entries in
4265 libc. These entry points should be supplied through some other
4266 mechanism when this option is specified.
4268 @cindex @option{-lgcc}, use with @option{-nostdlib}
4269 @cindex @option{-nostdlib} and unresolved references
4270 @cindex unresolved references and @option{-nostdlib}
4271 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4272 @cindex @option{-nodefaultlibs} and unresolved references
4273 @cindex unresolved references and @option{-nodefaultlibs}
4274 One of the standard libraries bypassed by @option{-nostdlib} and
4275 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4276 that GCC uses to overcome shortcomings of particular machines, or special
4277 needs for some languages.
4279 (@xref{Interface,,Interfacing to GCC Output}, for more discussion of
4283 (@xref{Interface,,Interfacing to GCC Output,gcc.info,Porting GCC},
4284 for more discussion of @file{libgcc.a}.)
4286 In most cases, you need @file{libgcc.a} even when you want to avoid
4287 other standard libraries. In other words, when you specify @option{-nostdlib}
4288 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4289 This ensures that you have no unresolved references to internal GCC
4290 library subroutines. (For example, @samp{__main}, used to ensure C++
4291 constructors will be called; @pxref{Collect2,,@command{collect2}}.)
4295 Remove all symbol table and relocation information from the executable.
4299 On systems that support dynamic linking, this prevents linking with the shared
4300 libraries. On other systems, this option has no effect.
4304 Produce a shared object which can then be linked with other objects to
4305 form an executable. Not all systems support this option. For predictable
4306 results, you must also specify the same set of options that were used to
4307 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4308 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4309 needs to build supplementary stub code for constructors to work. On
4310 multi-libbed systems, @samp{gcc -shared} must select the correct support
4311 libraries to link against. Failing to supply the correct flags may lead
4312 to subtle defects. Supplying them in cases where they are not necessary
4315 @item -shared-libgcc
4316 @itemx -static-libgcc
4317 @opindex shared-libgcc
4318 @opindex static-libgcc
4319 On systems that provide @file{libgcc} as a shared library, these options
4320 force the use of either the shared or static version respectively.
4321 If no shared version of @file{libgcc} was built when the compiler was
4322 configured, these options have no effect.
4324 There are several situations in which an application should use the
4325 shared @file{libgcc} instead of the static version. The most common
4326 of these is when the application wishes to throw and catch exceptions
4327 across different shared libraries. In that case, each of the libraries
4328 as well as the application itself should use the shared @file{libgcc}.
4330 Therefore, whenever you specify the @option{-shared} option, the GCC
4331 driver automatically adds @option{-shared-libgcc}, unless you explicitly
4332 specify @option{-static-libgcc}. The G++ driver automatically adds
4333 @option{-shared-libgcc} when you build a main executable as well because
4334 for C++ programs that is typically the right thing to do.
4335 (Exception-handling will not work reliably otherwise.)
4337 However, when linking a main executable written in C, you must
4338 explicitly say @option{-shared-libgcc} if you want to use the shared
4343 Bind references to global symbols when building a shared object. Warn
4344 about any unresolved references (unless overridden by the link editor
4345 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4348 @item -Xlinker @var{option}
4350 Pass @var{option} as an option to the linker. You can use this to
4351 supply system-specific linker options which GCC does not know how to
4354 If you want to pass an option that takes an argument, you must use
4355 @option{-Xlinker} twice, once for the option and once for the argument.
4356 For example, to pass @option{-assert definitions}, you must write
4357 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4358 @option{-Xlinker "-assert definitions"}, because this passes the entire
4359 string as a single argument, which is not what the linker expects.
4361 @item -Wl,@var{option}
4363 Pass @var{option} as an option to the linker. If @var{option} contains
4364 commas, it is split into multiple options at the commas.
4366 @item -u @var{symbol}
4368 Pretend the symbol @var{symbol} is undefined, to force linking of
4369 library modules to define it. You can use @option{-u} multiple times with
4370 different symbols to force loading of additional library modules.
4373 @node Directory Options
4374 @section Options for Directory Search
4375 @cindex directory options
4376 @cindex options, directory search
4379 These options specify directories to search for header files, for
4380 libraries and for parts of the compiler:
4385 Add the directory @var{dir} to the head of the list of directories to be
4386 searched for header files. This can be used to override a system header
4387 file, substituting your own version, since these directories are
4388 searched before the system header file directories. However, you should
4389 not use this option to add directories that contain vendor-supplied
4390 system header files (use @option{-isystem} for that). If you use more than
4391 one @option{-I} option, the directories are scanned in left-to-right
4392 order; the standard system directories come after.
4394 If a standard system include directory, or a directory specified with
4395 @option{-isystem}, is also specified with @option{-I}, it will be
4396 searched only in the position requested by @option{-I}. Also, it will
4397 not be considered a system include directory. If that directory really
4398 does contain system headers, there is a good chance that they will
4399 break. For instance, if GCC's installation procedure edited the headers
4400 in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the
4401 original, buggy headers to be found instead of the corrected ones. GCC
4402 will issue a warning when a system include directory is hidden in this
4407 Any directories you specify with @option{-I} options before the @option{-I-}
4408 option are searched only for the case of @samp{#include "@var{file}"};
4409 they are not searched for @samp{#include <@var{file}>}.
4411 If additional directories are specified with @option{-I} options after
4412 the @option{-I-}, these directories are searched for all @samp{#include}
4413 directives. (Ordinarily @emph{all} @option{-I} directories are used
4416 In addition, the @option{-I-} option inhibits the use of the current
4417 directory (where the current input file came from) as the first search
4418 directory for @samp{#include "@var{file}"}. There is no way to
4419 override this effect of @option{-I-}. With @option{-I.} you can specify
4420 searching the directory which was current when the compiler was
4421 invoked. That is not exactly the same as what the preprocessor does
4422 by default, but it is often satisfactory.
4424 @option{-I-} does not inhibit the use of the standard system directories
4425 for header files. Thus, @option{-I-} and @option{-nostdinc} are
4430 Add directory @var{dir} to the list of directories to be searched
4433 @item -B@var{prefix}
4435 This option specifies where to find the executables, libraries,
4436 include files, and data files of the compiler itself.
4438 The compiler driver program runs one or more of the subprograms
4439 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
4440 @var{prefix} as a prefix for each program it tries to run, both with and
4441 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
4443 For each subprogram to be run, the compiler driver first tries the
4444 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
4445 was not specified, the driver tries two standard prefixes, which are
4446 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
4447 those results in a file name that is found, the unmodified program
4448 name is searched for using the directories specified in your
4449 @env{PATH} environment variable.
4451 The compiler will check to see if the path provided by the @option{-B}
4452 refers to a directory, and if necessary it will add a directory
4453 separator character at the end of the path.
4455 @option{-B} prefixes that effectively specify directory names also apply
4456 to libraries in the linker, because the compiler translates these
4457 options into @option{-L} options for the linker. They also apply to
4458 includes files in the preprocessor, because the compiler translates these
4459 options into @option{-isystem} options for the preprocessor. In this case,
4460 the compiler appends @samp{include} to the prefix.
4462 The run-time support file @file{libgcc.a} can also be searched for using
4463 the @option{-B} prefix, if needed. If it is not found there, the two
4464 standard prefixes above are tried, and that is all. The file is left
4465 out of the link if it is not found by those means.
4467 Another way to specify a prefix much like the @option{-B} prefix is to use
4468 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
4471 As a special kludge, if the path provided by @option{-B} is
4472 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
4473 9, then it will be replaced by @file{[dir/]include}. This is to help
4474 with boot-strapping the compiler.
4476 @item -specs=@var{file}
4478 Process @var{file} after the compiler reads in the standard @file{specs}
4479 file, in order to override the defaults that the @file{gcc} driver
4480 program uses when determining what switches to pass to @file{cc1},
4481 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
4482 @option{-specs=@var{file}} can be specified on the command line, and they
4483 are processed in order, from left to right.
4489 @section Specifying subprocesses and the switches to pass to them
4491 @command{gcc} is a driver program. It performs its job by invoking a
4492 sequence of other programs to do the work of compiling, assembling and
4493 linking. GCC interprets its command-line parameters and uses these to
4494 deduce which programs it should invoke, and which command-line options
4495 it ought to place on their command lines. This behaviour is controlled
4496 by @dfn{spec strings}. In most cases there is one spec string for each
4497 program that GCC can invoke, but a few programs have multiple spec
4498 strings to control their behaviour. The spec strings built into GCC can
4499 be overridden by using the @option{-specs=} command-line switch to specify
4502 @dfn{Spec files} are plaintext files that are used to construct spec
4503 strings. They consist of a sequence of directives separated by blank
4504 lines. The type of directive is determined by the first non-whitespace
4505 character on the line and it can be one of the following:
4508 @item %@var{command}
4509 Issues a @var{command} to the spec file processor. The commands that can
4513 @item %include <@var{file}>
4515 Search for @var{file} and insert its text at the current point in the
4518 @item %include_noerr <@var{file}>
4519 @cindex %include_noerr
4520 Just like @samp{%include}, but do not generate an error message if the include
4521 file cannot be found.
4523 @item %rename @var{old_name} @var{new_name}
4525 Rename the spec string @var{old_name} to @var{new_name}.
4529 @item *[@var{spec_name}]:
4530 This tells the compiler to create, override or delete the named spec
4531 string. All lines after this directive up to the next directive or
4532 blank line are considered to be the text for the spec string. If this
4533 results in an empty string then the spec will be deleted. (Or, if the
4534 spec did not exist, then nothing will happened.) Otherwise, if the spec
4535 does not currently exist a new spec will be created. If the spec does
4536 exist then its contents will be overridden by the text of this
4537 directive, unless the first character of that text is the @samp{+}
4538 character, in which case the text will be appended to the spec.
4540 @item [@var{suffix}]:
4541 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
4542 and up to the next directive or blank line are considered to make up the
4543 spec string for the indicated suffix. When the compiler encounters an
4544 input file with the named suffix, it will processes the spec string in
4545 order to work out how to compile that file. For example:
4552 This says that any input file whose name ends in @samp{.ZZ} should be
4553 passed to the program @samp{z-compile}, which should be invoked with the
4554 command-line switch @option{-input} and with the result of performing the
4555 @samp{%i} substitution. (See below.)
4557 As an alternative to providing a spec string, the text that follows a
4558 suffix directive can be one of the following:
4561 @item @@@var{language}
4562 This says that the suffix is an alias for a known @var{language}. This is
4563 similar to using the @option{-x} command-line switch to GCC to specify a
4564 language explicitly. For example:
4571 Says that .ZZ files are, in fact, C++ source files.
4574 This causes an error messages saying:
4577 @var{name} compiler not installed on this system.
4581 GCC already has an extensive list of suffixes built into it.
4582 This directive will add an entry to the end of the list of suffixes, but
4583 since the list is searched from the end backwards, it is effectively
4584 possible to override earlier entries using this technique.
4588 GCC has the following spec strings built into it. Spec files can
4589 override these strings or create their own. Note that individual
4590 targets can also add their own spec strings to this list.
4593 asm Options to pass to the assembler
4594 asm_final Options to pass to the assembler post-processor
4595 cpp Options to pass to the C preprocessor
4596 cc1 Options to pass to the C compiler
4597 cc1plus Options to pass to the C++ compiler
4598 endfile Object files to include at the end of the link
4599 link Options to pass to the linker
4600 lib Libraries to include on the command line to the linker
4601 libgcc Decides which GCC support library to pass to the linker
4602 linker Sets the name of the linker
4603 predefines Defines to be passed to the C preprocessor
4604 signed_char Defines to pass to CPP to say whether @code{char} is signed
4606 startfile Object files to include at the start of the link
4609 Here is a small example of a spec file:
4615 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
4618 This example renames the spec called @samp{lib} to @samp{old_lib} and
4619 then overrides the previous definition of @samp{lib} with a new one.
4620 The new definition adds in some extra command-line options before
4621 including the text of the old definition.
4623 @dfn{Spec strings} are a list of command-line options to be passed to their
4624 corresponding program. In addition, the spec strings can contain
4625 @samp{%}-prefixed sequences to substitute variable text or to
4626 conditionally insert text into the command line. Using these constructs
4627 it is possible to generate quite complex command lines.
4629 Here is a table of all defined @samp{%}-sequences for spec
4630 strings. Note that spaces are not generated automatically around the
4631 results of expanding these sequences. Therefore you can concatenate them
4632 together or combine them with constant text in a single argument.
4636 Substitute one @samp{%} into the program name or argument.
4639 Substitute the name of the input file being processed.
4642 Substitute the basename of the input file being processed.
4643 This is the substring up to (and not including) the last period
4644 and not including the directory.
4647 This is the same as @samp{%b}, but include the file suffix (text after
4651 Marks the argument containing or following the @samp{%d} as a
4652 temporary file name, so that that file will be deleted if GCC exits
4653 successfully. Unlike @samp{%g}, this contributes no text to the
4656 @item %g@var{suffix}
4657 Substitute a file name that has suffix @var{suffix} and is chosen
4658 once per compilation, and mark the argument in the same way as
4659 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
4660 name is now chosen in a way that is hard to predict even when previously
4661 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
4662 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
4663 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
4664 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
4665 was simply substituted with a file name chosen once per compilation,
4666 without regard to any appended suffix (which was therefore treated
4667 just like ordinary text), making such attacks more likely to succeed.
4669 @item %u@var{suffix}
4670 Like @samp{%g}, but generates a new temporary file name even if
4671 @samp{%u@var{suffix}} was already seen.
4673 @item %U@var{suffix}
4674 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
4675 new one if there is no such last file name. In the absence of any
4676 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
4677 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
4678 would involve the generation of two distinct file names, one
4679 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
4680 simply substituted with a file name chosen for the previous @samp{%u},
4681 without regard to any appended suffix.
4683 @item %j@var{SUFFIX}
4684 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
4685 writable, and if save-temps is off; otherwise, substitute the name
4686 of a temporary file, just like @samp{%u}. This temporary file is not
4687 meant for communication between processes, but rather as a junk
4690 @item %.@var{SUFFIX}
4691 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
4692 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
4693 terminated by the next space or %.
4696 Marks the argument containing or following the @samp{%w} as the
4697 designated output file of this compilation. This puts the argument
4698 into the sequence of arguments that @samp{%o} will substitute later.
4701 Substitutes the names of all the output files, with spaces
4702 automatically placed around them. You should write spaces
4703 around the @samp{%o} as well or the results are undefined.
4704 @samp{%o} is for use in the specs for running the linker.
4705 Input files whose names have no recognized suffix are not compiled
4706 at all, but they are included among the output files, so they will
4710 Substitutes the suffix for object files. Note that this is
4711 handled specially when it immediately follows @samp{%g, %u, or %U},
4712 because of the need for those to form complete file names. The
4713 handling is such that @samp{%O} is treated exactly as if it had already
4714 been substituted, except that @samp{%g, %u, and %U} do not currently
4715 support additional @var{suffix} characters following @samp{%O} as they would
4716 following, for example, @samp{.o}.
4719 Substitutes the standard macro predefinitions for the
4720 current target machine. Use this when running @code{cpp}.
4723 Like @samp{%p}, but puts @samp{__} before and after the name of each
4724 predefined macro, except for macros that start with @samp{__} or with
4725 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
4729 Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}.
4732 Current argument is the name of a library or startup file of some sort.
4733 Search for that file in a standard list of directories and substitute
4734 the full name found.
4737 Print @var{str} as an error message. @var{str} is terminated by a newline.
4738 Use this when inconsistent options are detected.
4741 Output @samp{-} if the input for the current command is coming from a pipe.
4744 Substitute the contents of spec string @var{name} at this point.
4747 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
4749 @item %x@{@var{option}@}
4750 Accumulate an option for @samp{%X}.
4753 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
4757 Output the accumulated assembler options specified by @option{-Wa}.
4760 Output the accumulated preprocessor options specified by @option{-Wp}.
4763 Substitute the major version number of GCC@.
4764 (For version 2.9.5, this is 2.)
4767 Substitute the minor version number of GCC@.
4768 (For version 2.9.5, this is 9.)
4771 Substitute the patch level number of GCC@.
4772 (For version 2.9.5, this is 5.)
4775 Process the @code{asm} spec. This is used to compute the
4776 switches to be passed to the assembler.
4779 Process the @code{asm_final} spec. This is a spec string for
4780 passing switches to an assembler post-processor, if such a program is
4784 Process the @code{link} spec. This is the spec for computing the
4785 command line passed to the linker. Typically it will make use of the
4786 @samp{%L %G %S %D and %E} sequences.
4789 Dump out a @option{-L} option for each directory that GCC believes might
4790 contain startup files. If the target supports multilibs then the
4791 current multilib directory will be prepended to each of these paths.
4794 Output the multilib directory with directory separators replaced with
4795 @samp{_}. If multilib directories are not set, or the multilib directory is
4796 @file{.} then this option emits nothing.
4799 Process the @code{lib} spec. This is a spec string for deciding which
4800 libraries should be included on the command line to the linker.
4803 Process the @code{libgcc} spec. This is a spec string for deciding
4804 which GCC support library should be included on the command line to the linker.
4807 Process the @code{startfile} spec. This is a spec for deciding which
4808 object files should be the first ones passed to the linker. Typically
4809 this might be a file named @file{crt0.o}.
4812 Process the @code{endfile} spec. This is a spec string that specifies
4813 the last object files that will be passed to the linker.
4816 Process the @code{cpp} spec. This is used to construct the arguments
4817 to be passed to the C preprocessor.
4820 Process the @code{signed_char} spec. This is intended to be used
4821 to tell cpp whether a char is signed. It typically has the definition:
4823 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
4827 Process the @code{cc1} spec. This is used to construct the options to be
4828 passed to the actual C compiler (@samp{cc1}).
4831 Process the @code{cc1plus} spec. This is used to construct the options to be
4832 passed to the actual C++ compiler (@samp{cc1plus}).
4835 Substitute the variable part of a matched option. See below.
4836 Note that each comma in the substituted string is replaced by
4840 Substitutes the @code{-S} switch, if that switch was given to GCC@.
4841 If that switch was not specified, this substitutes nothing. Note that
4842 the leading dash is omitted when specifying this option, and it is
4843 automatically inserted if the substitution is performed. Thus the spec
4844 string @samp{%@{foo@}} would match the command-line option @option{-foo}
4845 and would output the command line option @option{-foo}.
4847 @item %W@{@code{S}@}
4848 Like %@{@code{S}@} but mark last argument supplied within as a file to be
4851 @item %@{@code{S}*@}
4852 Substitutes all the switches specified to GCC whose names start
4853 with @code{-S}, but which also take an argument. This is used for
4854 switches like @option{-o}, @option{-D}, @option{-I}, etc.
4855 GCC considers @option{-o foo} as being
4856 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
4857 text, including the space. Thus two arguments would be generated.
4859 @item %@{^@code{S}*@}
4860 Like %@{@code{S}*@}, but don't put a blank between a switch and its
4861 argument. Thus %@{^o*@} would only generate one argument, not two.
4863 @item %@{@code{S}*&@code{T}*@}
4864 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
4865 (the order of @code{S} and @code{T} in the spec is not significant).
4866 There can be any number of ampersand-separated variables; for each the
4867 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
4869 @item %@{<@code{S}@}
4870 Remove all occurrences of @code{-S} from the command line. Note---this
4871 command is position dependent. @samp{%} commands in the spec string
4872 before this option will see @code{-S}, @samp{%} commands in the spec
4873 string after this option will not.
4875 @item %@{@code{S}*:@code{X}@}
4876 Substitutes @code{X} if one or more switches whose names start with
4877 @code{-S} are specified to GCC@. Note that the tail part of the
4878 @code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted
4879 for each occurrence of @samp{%*} within @code{X}.
4881 @item %@{@code{S}:@code{X}@}
4882 Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@.
4884 @item %@{!@code{S}:@code{X}@}
4885 Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@.
4887 @item %@{|@code{S}:@code{X}@}
4888 Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}.
4890 @item %@{|!@code{S}:@code{X}@}
4891 Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}.
4893 @item %@{.@code{S}:@code{X}@}
4894 Substitutes @code{X}, but only if processing a file with suffix @code{S}.
4896 @item %@{!.@code{S}:@code{X}@}
4897 Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}.
4899 @item %@{@code{S}|@code{P}:@code{X}@}
4900 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be
4901 combined with @samp{!} and @samp{.} sequences as well, although they
4902 have a stronger binding than the @samp{|}. For example a spec string
4906 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
4909 will output the following command-line options from the following input
4910 command-line options:
4915 -d fred.c -foo -baz -boggle
4916 -d jim.d -bar -baz -boggle
4921 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or
4922 %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs
4923 or spaces, or even newlines. They are processed as usual, as described
4926 The @option{-O}, @option{-f}, @option{-m}, and @option{-W}
4927 switches are handled specifically in these
4928 constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or
4929 @option{-W} switch is found later in the command line, the earlier switch
4930 value is ignored, except with @{@code{S}*@} where @code{S} is just one
4931 letter, which passes all matching options.
4933 The character @samp{|} at the beginning of the predicate text is used to indicate
4934 that a command should be piped to the following command, but only if @option{-pipe}
4937 It is built into GCC which switches take arguments and which do not.
4938 (You might think it would be useful to generalize this to allow each
4939 compiler's spec to say which switches take arguments. But this cannot
4940 be done in a consistent fashion. GCC cannot even decide which input
4941 files have been specified without knowing which switches take arguments,
4942 and it must know which input files to compile in order to tell which
4945 GCC also knows implicitly that arguments starting in @option{-l} are to be
4946 treated as compiler output files, and passed to the linker in their
4947 proper position among the other output files.
4949 @c man begin OPTIONS
4951 @node Target Options
4952 @section Specifying Target Machine and Compiler Version
4953 @cindex target options
4954 @cindex cross compiling
4955 @cindex specifying machine version
4956 @cindex specifying compiler version and target machine
4957 @cindex compiler version, specifying
4958 @cindex target machine, specifying
4960 By default, GCC compiles code for the same type of machine that you
4961 are using. However, it can also be installed as a cross-compiler, to
4962 compile for some other type of machine. In fact, several different
4963 configurations of GCC, for different target machines, can be
4964 installed side by side. Then you specify which one to use with the
4967 In addition, older and newer versions of GCC can be installed side
4968 by side. One of them (probably the newest) will be the default, but
4969 you may sometimes wish to use another.
4972 @item -b @var{machine}
4974 The argument @var{machine} specifies the target machine for compilation.
4975 This is useful when you have installed GCC as a cross-compiler.
4977 The value to use for @var{machine} is the same as was specified as the
4978 machine type when configuring GCC as a cross-compiler. For
4979 example, if a cross-compiler was configured with @samp{configure
4980 i386v}, meaning to compile for an 80386 running System V, then you
4981 would specify @option{-b i386v} to run that cross compiler.
4983 When you do not specify @option{-b}, it normally means to compile for
4984 the same type of machine that you are using.
4986 @item -V @var{version}
4988 The argument @var{version} specifies which version of GCC to run.
4989 This is useful when multiple versions are installed. For example,
4990 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
4992 The default version, when you do not specify @option{-V}, is the last
4993 version of GCC that you installed.
4996 The @option{-b} and @option{-V} options actually work by controlling part of
4997 the file name used for the executable files and libraries used for
4998 compilation. A given version of GCC, for a given target machine, is
4999 normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}.
5001 Thus, sites can customize the effect of @option{-b} or @option{-V} either by
5002 changing the names of these directories or adding alternate names (or
5003 symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the
5004 file @file{80386} is a link to the file @file{i386v}, then @option{-b
5005 80386} becomes an alias for @option{-b i386v}.
5007 In one respect, the @option{-b} or @option{-V} do not completely change
5008 to a different compiler: the top-level driver program @command{gcc}
5009 that you originally invoked continues to run and invoke the other
5010 executables (preprocessor, compiler per se, assembler and linker)
5011 that do the real work. However, since no real work is done in the
5012 driver program, it usually does not matter that the driver program
5013 in use is not the one for the specified target. It is common for the
5014 interface to the other executables to change incompatibly between
5015 compiler versions, so unless the version specified is very close to that
5016 of the driver (for example, @option{-V 3.0} with a driver program from GCC
5017 version 3.0.1), use of @option{-V} may not work; for example, using
5018 @option{-V 2.95.2} will not work with a driver program from GCC 3.0.
5020 The only way that the driver program depends on the target machine is
5021 in the parsing and handling of special machine-specific options.
5022 However, this is controlled by a file which is found, along with the
5023 other executables, in the directory for the specified version and
5024 target machine. As a result, a single installed driver program adapts
5025 to any specified target machine, and sufficiently similar compiler
5028 The driver program executable does control one significant thing,
5029 however: the default version and target machine. Therefore, you can
5030 install different instances of the driver program, compiled for
5031 different targets or versions, under different names.
5033 For example, if the driver for version 2.0 is installed as @command{ogcc}
5034 and that for version 2.1 is installed as @command{gcc}, then the command
5035 @command{gcc} will use version 2.1 by default, while @command{ogcc} will use
5036 2.0 by default. However, you can choose either version with either
5037 command with the @option{-V} option.
5039 @node Submodel Options
5040 @section Hardware Models and Configurations
5041 @cindex submodel options
5042 @cindex specifying hardware config
5043 @cindex hardware models and configurations, specifying
5044 @cindex machine dependent options
5046 Earlier we discussed the standard option @option{-b} which chooses among
5047 different installed compilers for completely different target
5048 machines, such as VAX vs.@: 68000 vs.@: 80386.
5050 In addition, each of these target machine types can have its own
5051 special options, starting with @samp{-m}, to choose among various
5052 hardware models or configurations---for example, 68010 vs 68020,
5053 floating coprocessor or none. A single installed version of the
5054 compiler can compile for any model or configuration, according to the
5057 Some configurations of the compiler also support additional special
5058 options, usually for compatibility with other compilers on the same
5062 These options are defined by the macro @code{TARGET_SWITCHES} in the
5063 machine description. The default for the options is also defined by
5064 that macro, which enables you to change the defaults.
5079 * RS/6000 and PowerPC Options::
5082 * i386 and x86-64 Options::
5084 * Intel 960 Options::
5085 * DEC Alpha Options::
5089 * System V Options::
5090 * TMS320C3x/C4x Options::
5098 * S/390 and zSeries Options::
5102 @node M680x0 Options
5103 @subsection M680x0 Options
5104 @cindex M680x0 options
5106 These are the @samp{-m} options defined for the 68000 series. The default
5107 values for these options depends on which style of 68000 was selected when
5108 the compiler was configured; the defaults for the most common choices are
5116 Generate output for a 68000. This is the default
5117 when the compiler is configured for 68000-based systems.
5119 Use this option for microcontrollers with a 68000 or EC000 core,
5120 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5126 Generate output for a 68020. This is the default
5127 when the compiler is configured for 68020-based systems.
5131 Generate output containing 68881 instructions for floating point.
5132 This is the default for most 68020 systems unless @option{--nfp} was
5133 specified when the compiler was configured.
5137 Generate output for a 68030. This is the default when the compiler is
5138 configured for 68030-based systems.
5142 Generate output for a 68040. This is the default when the compiler is
5143 configured for 68040-based systems.
5145 This option inhibits the use of 68881/68882 instructions that have to be
5146 emulated by software on the 68040. Use this option if your 68040 does not
5147 have code to emulate those instructions.
5151 Generate output for a 68060. This is the default when the compiler is
5152 configured for 68060-based systems.
5154 This option inhibits the use of 68020 and 68881/68882 instructions that
5155 have to be emulated by software on the 68060. Use this option if your 68060
5156 does not have code to emulate those instructions.
5160 Generate output for a CPU32. This is the default
5161 when the compiler is configured for CPU32-based systems.
5163 Use this option for microcontrollers with a
5164 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5165 68336, 68340, 68341, 68349 and 68360.
5169 Generate output for a 520X ``coldfire'' family cpu. This is the default
5170 when the compiler is configured for 520X-based systems.
5172 Use this option for microcontroller with a 5200 core, including
5173 the MCF5202, MCF5203, MCF5204 and MCF5202.
5178 Generate output for a 68040, without using any of the new instructions.
5179 This results in code which can run relatively efficiently on either a
5180 68020/68881 or a 68030 or a 68040. The generated code does use the
5181 68881 instructions that are emulated on the 68040.
5185 Generate output for a 68060, without using any of the new instructions.
5186 This results in code which can run relatively efficiently on either a
5187 68020/68881 or a 68030 or a 68040. The generated code does use the
5188 68881 instructions that are emulated on the 68060.
5192 Generate output containing Sun FPA instructions for floating point.
5195 @opindex msoft-float
5196 Generate output containing library calls for floating point.
5197 @strong{Warning:} the requisite libraries are not available for all m68k
5198 targets. Normally the facilities of the machine's usual C compiler are
5199 used, but this can't be done directly in cross-compilation. You must
5200 make your own arrangements to provide suitable library functions for
5201 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5202 @samp{m68k-*-coff} do provide software floating point support.
5206 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5209 @opindex mnobitfield
5210 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5211 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5215 Do use the bit-field instructions. The @option{-m68020} option implies
5216 @option{-mbitfield}. This is the default if you use a configuration
5217 designed for a 68020.
5221 Use a different function-calling convention, in which functions
5222 that take a fixed number of arguments return with the @code{rtd}
5223 instruction, which pops their arguments while returning. This
5224 saves one instruction in the caller since there is no need to pop
5225 the arguments there.
5227 This calling convention is incompatible with the one normally
5228 used on Unix, so you cannot use it if you need to call libraries
5229 compiled with the Unix compiler.
5231 Also, you must provide function prototypes for all functions that
5232 take variable numbers of arguments (including @code{printf});
5233 otherwise incorrect code will be generated for calls to those
5236 In addition, seriously incorrect code will result if you call a
5237 function with too many arguments. (Normally, extra arguments are
5238 harmlessly ignored.)
5240 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5241 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5244 @itemx -mno-align-int
5246 @opindex mno-align-int
5247 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5248 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5249 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5250 Aligning variables on 32-bit boundaries produces code that runs somewhat
5251 faster on processors with 32-bit busses at the expense of more memory.
5253 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5254 align structures containing the above types differently than
5255 most published application binary interface specifications for the m68k.
5259 Use the pc-relative addressing mode of the 68000 directly, instead of
5260 using a global offset table. At present, this option implies @option{-fpic},
5261 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5262 not presently supported with @option{-mpcrel}, though this could be supported for
5263 68020 and higher processors.
5265 @item -mno-strict-align
5266 @itemx -mstrict-align
5267 @opindex mno-strict-align
5268 @opindex mstrict-align
5269 Do not (do) assume that unaligned memory references will be handled by
5274 @node M68hc1x Options
5275 @subsection M68hc1x Options
5276 @cindex M68hc1x options
5278 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5279 microcontrollers. The default values for these options depends on
5280 which style of microcontroller was selected when the compiler was configured;
5281 the defaults for the most common choices are given below.
5288 Generate output for a 68HC11. This is the default
5289 when the compiler is configured for 68HC11-based systems.
5295 Generate output for a 68HC12. This is the default
5296 when the compiler is configured for 68HC12-based systems.
5299 @opindex mauto-incdec
5300 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5305 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5307 @item -msoft-reg-count=@var{count}
5308 @opindex msoft-reg-count
5309 Specify the number of pseudo-soft registers which are used for the
5310 code generation. The maximum number is 32. Using more pseudo-soft
5311 register may or may not result in better code depending on the program.
5312 The default is 4 for 68HC11 and 2 for 68HC12.
5317 @subsection VAX Options
5320 These @samp{-m} options are defined for the VAX:
5325 Do not output certain jump instructions (@code{aobleq} and so on)
5326 that the Unix assembler for the VAX cannot handle across long
5331 Do output those jump instructions, on the assumption that you
5332 will assemble with the GNU assembler.
5336 Output code for g-format floating point numbers instead of d-format.
5340 @subsection SPARC Options
5341 @cindex SPARC options
5343 These @samp{-m} switches are supported on the SPARC:
5348 @opindex mno-app-regs
5350 Specify @option{-mapp-regs} to generate output using the global registers
5351 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5354 To be fully SVR4 ABI compliant at the cost of some performance loss,
5355 specify @option{-mno-app-regs}. You should compile libraries and system
5356 software with this option.
5361 @opindex mhard-float
5362 Generate output containing floating point instructions. This is the
5368 @opindex msoft-float
5369 Generate output containing library calls for floating point.
5370 @strong{Warning:} the requisite libraries are not available for all SPARC
5371 targets. Normally the facilities of the machine's usual C compiler are
5372 used, but this cannot be done directly in cross-compilation. You must make
5373 your own arrangements to provide suitable library functions for
5374 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5375 @samp{sparclite-*-*} do provide software floating point support.
5377 @option{-msoft-float} changes the calling convention in the output file;
5378 therefore, it is only useful if you compile @emph{all} of a program with
5379 this option. In particular, you need to compile @file{libgcc.a}, the
5380 library that comes with GCC, with @option{-msoft-float} in order for
5383 @item -mhard-quad-float
5384 @opindex mhard-quad-float
5385 Generate output containing quad-word (long double) floating point
5388 @item -msoft-quad-float
5389 @opindex msoft-quad-float
5390 Generate output containing library calls for quad-word (long double)
5391 floating point instructions. The functions called are those specified
5392 in the SPARC ABI@. This is the default.
5394 As of this writing, there are no sparc implementations that have hardware
5395 support for the quad-word floating point instructions. They all invoke
5396 a trap handler for one of these instructions, and then the trap handler
5397 emulates the effect of the instruction. Because of the trap handler overhead,
5398 this is much slower than calling the ABI library routines. Thus the
5399 @option{-msoft-quad-float} option is the default.
5403 @opindex mno-epilogue
5405 With @option{-mepilogue} (the default), the compiler always emits code for
5406 function exit at the end of each function. Any function exit in
5407 the middle of the function (such as a return statement in C) will
5408 generate a jump to the exit code at the end of the function.
5410 With @option{-mno-epilogue}, the compiler tries to emit exit code inline
5411 at every function exit.
5417 With @option{-mflat}, the compiler does not generate save/restore instructions
5418 and will use a ``flat'' or single register window calling convention.
5419 This model uses %i7 as the frame pointer and is compatible with the normal
5420 register window model. Code from either may be intermixed.
5421 The local registers and the input registers (0--5) are still treated as
5422 ``call saved'' registers and will be saved on the stack as necessary.
5424 With @option{-mno-flat} (the default), the compiler emits save/restore
5425 instructions (except for leaf functions) and is the normal mode of operation.
5427 @item -mno-unaligned-doubles
5428 @itemx -munaligned-doubles
5429 @opindex mno-unaligned-doubles
5430 @opindex munaligned-doubles
5431 Assume that doubles have 8 byte alignment. This is the default.
5433 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
5434 alignment only if they are contained in another type, or if they have an
5435 absolute address. Otherwise, it assumes they have 4 byte alignment.
5436 Specifying this option avoids some rare compatibility problems with code
5437 generated by other compilers. It is not the default because it results
5438 in a performance loss, especially for floating point code.
5440 @item -mno-faster-structs
5441 @itemx -mfaster-structs
5442 @opindex mno-faster-structs
5443 @opindex mfaster-structs
5444 With @option{-mfaster-structs}, the compiler assumes that structures
5445 should have 8 byte alignment. This enables the use of pairs of
5446 @code{ldd} and @code{std} instructions for copies in structure
5447 assignment, in place of twice as many @code{ld} and @code{st} pairs.
5448 However, the use of this changed alignment directly violates the Sparc
5449 ABI@. Thus, it's intended only for use on targets where the developer
5450 acknowledges that their resulting code will not be directly in line with
5451 the rules of the ABI@.
5457 These two options select variations on the SPARC architecture.
5459 By default (unless specifically configured for the Fujitsu SPARClite),
5460 GCC generates code for the v7 variant of the SPARC architecture.
5462 @option{-mv8} will give you SPARC v8 code. The only difference from v7
5463 code is that the compiler emits the integer multiply and integer
5464 divide instructions which exist in SPARC v8 but not in SPARC v7.
5466 @option{-msparclite} will give you SPARClite code. This adds the integer
5467 multiply, integer divide step and scan (@code{ffs}) instructions which
5468 exist in SPARClite but not in SPARC v7.
5470 These options are deprecated and will be deleted in a future GCC release.
5471 They have been replaced with @option{-mcpu=xxx}.
5476 @opindex msupersparc
5477 These two options select the processor for which the code is optimised.
5479 With @option{-mcypress} (the default), the compiler optimizes code for the
5480 Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series.
5481 This is also appropriate for the older SparcStation 1, 2, IPX etc.
5483 With @option{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as
5484 used in the SparcStation 10, 1000 and 2000 series. This flag also enables use
5485 of the full SPARC v8 instruction set.
5487 These options are deprecated and will be deleted in a future GCC release.
5488 They have been replaced with @option{-mcpu=xxx}.
5490 @item -mcpu=@var{cpu_type}
5492 Set the instruction set, register set, and instruction scheduling parameters
5493 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
5494 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
5495 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
5496 @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}.
5498 Default instruction scheduling parameters are used for values that select
5499 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
5500 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
5502 Here is a list of each supported architecture and their supported
5507 v8: supersparc, hypersparc
5508 sparclite: f930, f934, sparclite86x
5513 @item -mtune=@var{cpu_type}
5515 Set the instruction scheduling parameters for machine type
5516 @var{cpu_type}, but do not set the instruction set or register set that the
5517 option @option{-mcpu=@var{cpu_type}} would.
5519 The same values for @option{-mcpu=@var{cpu_type}} can be used for
5520 @option{-mtune=@var{cpu_type}}, but the only useful values are those
5521 that select a particular cpu implementation. Those are @samp{cypress},
5522 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
5523 @samp{sparclite86x}, @samp{tsc701}, and @samp{ultrasparc}.
5527 These @samp{-m} switches are supported in addition to the above
5528 on the SPARCLET processor.
5531 @item -mlittle-endian
5532 @opindex mlittle-endian
5533 Generate code for a processor running in little-endian mode.
5537 Treat register @code{%g0} as a normal register.
5538 GCC will continue to clobber it as necessary but will not assume
5539 it always reads as 0.
5541 @item -mbroken-saverestore
5542 @opindex mbroken-saverestore
5543 Generate code that does not use non-trivial forms of the @code{save} and
5544 @code{restore} instructions. Early versions of the SPARCLET processor do
5545 not correctly handle @code{save} and @code{restore} instructions used with
5546 arguments. They correctly handle them used without arguments. A @code{save}
5547 instruction used without arguments increments the current window pointer
5548 but does not allocate a new stack frame. It is assumed that the window
5549 overflow trap handler will properly handle this case as will interrupt
5553 These @samp{-m} switches are supported in addition to the above
5554 on SPARC V9 processors in 64-bit environments.
5557 @item -mlittle-endian
5558 @opindex mlittle-endian
5559 Generate code for a processor running in little-endian mode.
5565 Generate code for a 32-bit or 64-bit environment.
5566 The 32-bit environment sets int, long and pointer to 32 bits.
5567 The 64-bit environment sets int to 32 bits and long and pointer
5570 @item -mcmodel=medlow
5571 @opindex mcmodel=medlow
5572 Generate code for the Medium/Low code model: the program must be linked
5573 in the low 32 bits of the address space. Pointers are 64 bits.
5574 Programs can be statically or dynamically linked.
5576 @item -mcmodel=medmid
5577 @opindex mcmodel=medmid
5578 Generate code for the Medium/Middle code model: the program must be linked
5579 in the low 44 bits of the address space, the text segment must be less than
5580 2G bytes, and data segment must be within 2G of the text segment.
5581 Pointers are 64 bits.
5583 @item -mcmodel=medany
5584 @opindex mcmodel=medany
5585 Generate code for the Medium/Anywhere code model: the program may be linked
5586 anywhere in the address space, the text segment must be less than
5587 2G bytes, and data segment must be within 2G of the text segment.
5588 Pointers are 64 bits.
5590 @item -mcmodel=embmedany
5591 @opindex mcmodel=embmedany
5592 Generate code for the Medium/Anywhere code model for embedded systems:
5593 assume a 32-bit text and a 32-bit data segment, both starting anywhere
5594 (determined at link time). Register %g4 points to the base of the
5595 data segment. Pointers are still 64 bits.
5596 Programs are statically linked, PIC is not supported.
5599 @itemx -mno-stack-bias
5600 @opindex mstack-bias
5601 @opindex mno-stack-bias
5602 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
5603 frame pointer if present, are offset by @minus{}2047 which must be added back
5604 when making stack frame references.
5605 Otherwise, assume no such offset is present.
5608 @node Convex Options
5609 @subsection Convex Options
5610 @cindex Convex options
5612 These @samp{-m} options are defined for Convex:
5617 Generate output for C1. The code will run on any Convex machine.
5618 The preprocessor symbol @code{__convex__c1__} is defined.
5622 Generate output for C2. Uses instructions not available on C1.
5623 Scheduling and other optimizations are chosen for max performance on C2.
5624 The preprocessor symbol @code{__convex_c2__} is defined.
5628 Generate output for C32xx. Uses instructions not available on C1.
5629 Scheduling and other optimizations are chosen for max performance on C32.
5630 The preprocessor symbol @code{__convex_c32__} is defined.
5634 Generate output for C34xx. Uses instructions not available on C1.
5635 Scheduling and other optimizations are chosen for max performance on C34.
5636 The preprocessor symbol @code{__convex_c34__} is defined.
5640 Generate output for C38xx. Uses instructions not available on C1.
5641 Scheduling and other optimizations are chosen for max performance on C38.
5642 The preprocessor symbol @code{__convex_c38__} is defined.
5646 Generate code which puts an argument count in the word preceding each
5647 argument list. This is compatible with regular CC, and a few programs
5648 may need the argument count word. GDB and other source-level debuggers
5649 do not need it; this info is in the symbol table.
5652 @opindex mnoargcount
5653 Omit the argument count word. This is the default.
5655 @item -mvolatile-cache
5656 @opindex mvolatile-cache
5657 Allow volatile references to be cached. This is the default.
5659 @item -mvolatile-nocache
5660 @opindex mvolatile-nocache
5661 Volatile references bypass the data cache, going all the way to memory.
5662 This is only needed for multi-processor code that does not use standard
5663 synchronization instructions. Making non-volatile references to volatile
5664 locations will not necessarily work.
5668 Type long is 32 bits, the same as type int. This is the default.
5672 Type long is 64 bits, the same as type long long. This option is useless,
5673 because no library support exists for it.
5676 @node AMD29K Options
5677 @subsection AMD29K Options
5678 @cindex AMD29K options
5680 These @samp{-m} options are defined for the AMD Am29000:
5685 @cindex DW bit (29k)
5686 Generate code that assumes the @code{DW} bit is set, i.e., that byte and
5687 halfword operations are directly supported by the hardware. This is the
5692 Generate code that assumes the @code{DW} bit is not set.
5696 @cindex byte writes (29k)
5697 Generate code that assumes the system supports byte and halfword write
5698 operations. This is the default.
5702 Generate code that assumes the systems does not support byte and
5703 halfword write operations. @option{-mnbw} implies @option{-mndw}.
5707 @cindex memory model (29k)
5708 Use a small memory model that assumes that all function addresses are
5709 either within a single 256 KB segment or at an absolute address of less
5710 than 256k. This allows the @code{call} instruction to be used instead
5711 of a @code{const}, @code{consth}, @code{calli} sequence.
5715 Use the normal memory model: Generate @code{call} instructions only when
5716 calling functions in the same file and @code{calli} instructions
5717 otherwise. This works if each file occupies less than 256 KB but allows
5718 the entire executable to be larger than 256 KB@. This is the default.
5722 Always use @code{calli} instructions. Specify this option if you expect
5723 a single file to compile into more than 256 KB of code.
5727 @cindex processor selection (29k)
5728 Generate code for the Am29050.
5732 Generate code for the Am29000. This is the default.
5734 @item -mkernel-registers
5735 @opindex mkernel-registers
5736 @cindex kernel and user registers (29k)
5737 Generate references to registers @code{gr64-gr95} instead of to
5738 registers @code{gr96-gr127}. This option can be used when compiling
5739 kernel code that wants a set of global registers disjoint from that used
5742 Note that when this option is used, register names in @samp{-f} flags
5743 must use the normal, user-mode, names.
5745 @item -muser-registers
5746 @opindex muser-registers
5747 Use the normal set of global registers, @code{gr96-gr127}. This is the
5751 @itemx -mno-stack-check
5752 @opindex mstack-check
5753 @opindex mno-stack-check
5754 @cindex stack checks (29k)
5755 Insert (or do not insert) a call to @code{__msp_check} after each stack
5756 adjustment. This is often used for kernel code.
5759 @itemx -mno-storem-bug
5760 @opindex mstorem-bug
5761 @opindex mno-storem-bug
5762 @cindex storem bug (29k)
5763 @option{-mstorem-bug} handles 29k processors which cannot handle the
5764 separation of a mtsrim insn and a storem instruction (most 29000 chips
5765 to date, but not the 29050).
5767 @item -mno-reuse-arg-regs
5768 @itemx -mreuse-arg-regs
5769 @opindex mno-reuse-arg-regs
5770 @opindex mreuse-arg-regs
5771 @option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument
5772 registers for copying out arguments. This helps detect calling a function
5773 with fewer arguments than it was declared with.
5775 @item -mno-impure-text
5776 @itemx -mimpure-text
5777 @opindex mno-impure-text
5778 @opindex mimpure-text
5779 @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to
5780 not pass @option{-assert pure-text} to the linker when linking a shared object.
5783 @opindex msoft-float
5784 Generate output containing library calls for floating point.
5785 @strong{Warning:} the requisite libraries are not part of GCC@.
5786 Normally the facilities of the machine's usual C compiler are used, but
5787 this can't be done directly in cross-compilation. You must make your
5788 own arrangements to provide suitable library functions for
5793 Do not generate multm or multmu instructions. This is useful for some embedded
5794 systems which do not have trap handlers for these instructions.
5798 @subsection ARM Options
5801 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
5806 @opindex mapcs-frame
5807 Generate a stack frame that is compliant with the ARM Procedure Call
5808 Standard for all functions, even if this is not strictly necessary for
5809 correct execution of the code. Specifying @option{-fomit-frame-pointer}
5810 with this option will cause the stack frames not to be generated for
5811 leaf functions. The default is @option{-mno-apcs-frame}.
5815 This is a synonym for @option{-mapcs-frame}.
5819 Generate code for a processor running with a 26-bit program counter,
5820 and conforming to the function calling standards for the APCS 26-bit
5821 option. This option replaces the @option{-m2} and @option{-m3} options
5822 of previous releases of the compiler.
5826 Generate code for a processor running with a 32-bit program counter,
5827 and conforming to the function calling standards for the APCS 32-bit
5828 option. This option replaces the @option{-m6} option of previous releases
5832 @c not currently implemented
5833 @item -mapcs-stack-check
5834 @opindex mapcs-stack-check
5835 Generate code to check the amount of stack space available upon entry to
5836 every function (that actually uses some stack space). If there is
5837 insufficient space available then either the function
5838 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
5839 called, depending upon the amount of stack space required. The run time
5840 system is required to provide these functions. The default is
5841 @option{-mno-apcs-stack-check}, since this produces smaller code.
5843 @c not currently implemented
5845 @opindex mapcs-float
5846 Pass floating point arguments using the float point registers. This is
5847 one of the variants of the APCS@. This option is recommended if the
5848 target hardware has a floating point unit or if a lot of floating point
5849 arithmetic is going to be performed by the code. The default is
5850 @option{-mno-apcs-float}, since integer only code is slightly increased in
5851 size if @option{-mapcs-float} is used.
5853 @c not currently implemented
5854 @item -mapcs-reentrant
5855 @opindex mapcs-reentrant
5856 Generate reentrant, position independent code. The default is
5857 @option{-mno-apcs-reentrant}.
5860 @item -mthumb-interwork
5861 @opindex mthumb-interwork
5862 Generate code which supports calling between the ARM and Thumb
5863 instruction sets. Without this option the two instruction sets cannot
5864 be reliably used inside one program. The default is
5865 @option{-mno-thumb-interwork}, since slightly larger code is generated
5866 when @option{-mthumb-interwork} is specified.
5868 @item -mno-sched-prolog
5869 @opindex mno-sched-prolog
5870 Prevent the reordering of instructions in the function prolog, or the
5871 merging of those instruction with the instructions in the function's
5872 body. This means that all functions will start with a recognizable set
5873 of instructions (or in fact one of a choice from a small set of
5874 different function prologues), and this information can be used to
5875 locate the start if functions inside an executable piece of code. The
5876 default is @option{-msched-prolog}.
5879 @opindex mhard-float
5880 Generate output containing floating point instructions. This is the
5884 @opindex msoft-float
5885 Generate output containing library calls for floating point.
5886 @strong{Warning:} the requisite libraries are not available for all ARM
5887 targets. Normally the facilities of the machine's usual C compiler are
5888 used, but this cannot be done directly in cross-compilation. You must make
5889 your own arrangements to provide suitable library functions for
5892 @option{-msoft-float} changes the calling convention in the output file;
5893 therefore, it is only useful if you compile @emph{all} of a program with
5894 this option. In particular, you need to compile @file{libgcc.a}, the
5895 library that comes with GCC, with @option{-msoft-float} in order for
5898 @item -mlittle-endian
5899 @opindex mlittle-endian
5900 Generate code for a processor running in little-endian mode. This is
5901 the default for all standard configurations.
5904 @opindex mbig-endian
5905 Generate code for a processor running in big-endian mode; the default is
5906 to compile code for a little-endian processor.
5908 @item -mwords-little-endian
5909 @opindex mwords-little-endian
5910 This option only applies when generating code for big-endian processors.
5911 Generate code for a little-endian word order but a big-endian byte
5912 order. That is, a byte order of the form @samp{32107654}. Note: this
5913 option should only be used if you require compatibility with code for
5914 big-endian ARM processors generated by versions of the compiler prior to
5917 @item -malignment-traps
5918 @opindex malignment-traps
5919 Generate code that will not trap if the MMU has alignment traps enabled.
5920 On ARM architectures prior to ARMv4, there were no instructions to
5921 access half-word objects stored in memory. However, when reading from
5922 memory a feature of the ARM architecture allows a word load to be used,
5923 even if the address is unaligned, and the processor core will rotate the
5924 data as it is being loaded. This option tells the compiler that such
5925 misaligned accesses will cause a MMU trap and that it should instead
5926 synthesise the access as a series of byte accesses. The compiler can
5927 still use word accesses to load half-word data if it knows that the
5928 address is aligned to a word boundary.
5930 This option is ignored when compiling for ARM architecture 4 or later,
5931 since these processors have instructions to directly access half-word
5934 @item -mno-alignment-traps
5935 @opindex mno-alignment-traps
5936 Generate code that assumes that the MMU will not trap unaligned
5937 accesses. This produces better code when the target instruction set
5938 does not have half-word memory operations (i.e.@: implementations prior to
5941 Note that you cannot use this option to access unaligned word objects,
5942 since the processor will only fetch one 32-bit aligned object from
5945 The default setting for most targets is @option{-mno-alignment-traps}, since
5946 this produces better code when there are no half-word memory
5947 instructions available.
5949 @item -mshort-load-bytes
5950 @itemx -mno-short-load-words
5951 @opindex mshort-load-bytes
5952 @opindex mno-short-load-words
5953 These are deprecated aliases for @option{-malignment-traps}.
5955 @item -mno-short-load-bytes
5956 @itemx -mshort-load-words
5957 @opindex mno-short-load-bytes
5958 @opindex mshort-load-words
5959 This are deprecated aliases for @option{-mno-alignment-traps}.
5963 This option only applies to RISC iX@. Emulate the native BSD-mode
5964 compiler. This is the default if @option{-ansi} is not specified.
5968 This option only applies to RISC iX@. Emulate the native X/Open-mode
5971 @item -mno-symrename
5972 @opindex mno-symrename
5973 This option only applies to RISC iX@. Do not run the assembler
5974 post-processor, @samp{symrename}, after code has been assembled.
5975 Normally it is necessary to modify some of the standard symbols in
5976 preparation for linking with the RISC iX C library; this option
5977 suppresses this pass. The post-processor is never run when the
5978 compiler is built for cross-compilation.
5980 @item -mcpu=@var{name}
5982 This specifies the name of the target ARM processor. GCC uses this name
5983 to determine what kind of instructions it can emit when generating
5984 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
5985 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
5986 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
5987 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
5988 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
5989 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
5990 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
5991 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
5992 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
5993 @samp{arm1020t}, @samp{xscale}.
5995 @itemx -mtune=@var{name}
5997 This option is very similar to the @option{-mcpu=} option, except that
5998 instead of specifying the actual target processor type, and hence
5999 restricting which instructions can be used, it specifies that GCC should
6000 tune the performance of the code as if the target were of the type
6001 specified in this option, but still choosing the instructions that it
6002 will generate based on the cpu specified by a @option{-mcpu=} option.
6003 For some ARM implementations better performance can be obtained by using
6006 @item -march=@var{name}
6008 This specifies the name of the target ARM architecture. GCC uses this
6009 name to determine what kind of instructions it can emit when generating
6010 assembly code. This option can be used in conjunction with or instead
6011 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6012 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6013 @samp{armv5}, @samp{armv5t}, @samp{armv5te}.
6015 @item -mfpe=@var{number}
6016 @itemx -mfp=@var{number}
6019 This specifies the version of the floating point emulation available on
6020 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6021 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6023 @item -mstructure-size-boundary=@var{n}
6024 @opindex mstructure-size-boundary
6025 The size of all structures and unions will be rounded up to a multiple
6026 of the number of bits set by this option. Permissible values are 8 and
6027 32. The default value varies for different toolchains. For the COFF
6028 targeted toolchain the default value is 8. Specifying the larger number
6029 can produce faster, more efficient code, but can also increase the size
6030 of the program. The two values are potentially incompatible. Code
6031 compiled with one value cannot necessarily expect to work with code or
6032 libraries compiled with the other value, if they exchange information
6033 using structures or unions.
6035 @item -mabort-on-noreturn
6036 @opindex mabort-on-noreturn
6037 Generate a call to the function @code{abort} at the end of a
6038 @code{noreturn} function. It will be executed if the function tries to
6042 @itemx -mno-long-calls
6043 @opindex mlong-calls
6044 @opindex mno-long-calls
6045 Tells the compiler to perform function calls by first loading the
6046 address of the function into a register and then performing a subroutine
6047 call on this register. This switch is needed if the target function
6048 will lie outside of the 64 megabyte addressing range of the offset based
6049 version of subroutine call instruction.
6051 Even if this switch is enabled, not all function calls will be turned
6052 into long calls. The heuristic is that static functions, functions
6053 which have the @samp{short-call} attribute, functions that are inside
6054 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6055 definitions have already been compiled within the current compilation
6056 unit, will not be turned into long calls. The exception to this rule is
6057 that weak function definitions, functions with the @samp{long-call}
6058 attribute or the @samp{section} attribute, and functions that are within
6059 the scope of a @samp{#pragma long_calls} directive, will always be
6060 turned into long calls.
6062 This feature is not enabled by default. Specifying
6063 @option{-mno-long-calls} will restore the default behaviour, as will
6064 placing the function calls within the scope of a @samp{#pragma
6065 long_calls_off} directive. Note these switches have no effect on how
6066 the compiler generates code to handle function calls via function
6069 @item -mnop-fun-dllimport
6070 @opindex mnop-fun-dllimport
6071 Disable support for the @code{dllimport} attribute.
6073 @item -msingle-pic-base
6074 @opindex msingle-pic-base
6075 Treat the register used for PIC addressing as read-only, rather than
6076 loading it in the prologue for each function. The run-time system is
6077 responsible for initialising this register with an appropriate value
6078 before execution begins.
6080 @item -mpic-register=@var{reg}
6081 @opindex mpic-register
6082 Specify the register to be used for PIC addressing. The default is R10
6083 unless stack-checking is enabled, when R9 is used.
6085 @item -mpoke-function-name
6086 @opindex mpoke-function-name
6087 Write the name of each function into the text section, directly
6088 preceding the function prologue. The generated code is similar to this:
6092 .ascii "arm_poke_function_name", 0
6095 .word 0xff000000 + (t1 - t0)
6096 arm_poke_function_name
6098 stmfd sp!, @{fp, ip, lr, pc@}
6102 When performing a stack backtrace, code can inspect the value of
6103 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6104 location @code{pc - 12} and the top 8 bits are set, then we know that
6105 there is a function name embedded immediately preceding this location
6106 and has length @code{((pc[-3]) & 0xff000000)}.
6110 Generate code for the 16-bit Thumb instruction set. The default is to
6111 use the 32-bit ARM instruction set.
6114 @opindex mtpcs-frame
6115 Generate a stack frame that is compliant with the Thumb Procedure Call
6116 Standard for all non-leaf functions. (A leaf function is one that does
6117 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6119 @item -mtpcs-leaf-frame
6120 @opindex mtpcs-leaf-frame
6121 Generate a stack frame that is compliant with the Thumb Procedure Call
6122 Standard for all leaf functions. (A leaf function is one that does
6123 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6125 @item -mcallee-super-interworking
6126 @opindex mcallee-super-interworking
6127 Gives all externally visible functions in the file being compiled an ARM
6128 instruction set header which switches to Thumb mode before executing the
6129 rest of the function. This allows these functions to be called from
6130 non-interworking code.
6132 @item -mcaller-super-interworking
6133 @opindex mcaller-super-interworking
6134 Allows calls via function pointers (including virtual functions) to
6135 execute correctly regardless of whether the target code has been
6136 compiled for interworking or not. There is a small overhead in the cost
6137 of executing a function pointer if this option is enabled.
6141 @node MN10200 Options
6142 @subsection MN10200 Options
6143 @cindex MN10200 options
6144 These @option{-m} options are defined for Matsushita MN10200 architectures:
6149 Indicate to the linker that it should perform a relaxation optimization pass
6150 to shorten branches, calls and absolute memory addresses. This option only
6151 has an effect when used on the command line for the final link step.
6153 This option makes symbolic debugging impossible.
6156 @node MN10300 Options
6157 @subsection MN10300 Options
6158 @cindex MN10300 options
6159 These @option{-m} options are defined for Matsushita MN10300 architectures:
6164 Generate code to avoid bugs in the multiply instructions for the MN10300
6165 processors. This is the default.
6168 @opindex mno-mult-bug
6169 Do not generate code to avoid bugs in the multiply instructions for the
6174 Generate code which uses features specific to the AM33 processor.
6178 Do not generate code which uses features specific to the AM33 processor. This
6183 Do not link in the C run-time initialization object file.
6187 Indicate to the linker that it should perform a relaxation optimization pass
6188 to shorten branches, calls and absolute memory addresses. This option only
6189 has an effect when used on the command line for the final link step.
6191 This option makes symbolic debugging impossible.
6195 @node M32R/D Options
6196 @subsection M32R/D Options
6197 @cindex M32R/D options
6199 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6202 @item -mcode-model=small
6203 @opindex mcode-model=small
6204 Assume all objects live in the lower 16MB of memory (so that their addresses
6205 can be loaded with the @code{ld24} instruction), and assume all subroutines
6206 are reachable with the @code{bl} instruction.
6207 This is the default.
6209 The addressability of a particular object can be set with the
6210 @code{model} attribute.
6212 @item -mcode-model=medium
6213 @opindex mcode-model=medium
6214 Assume objects may be anywhere in the 32-bit address space (the compiler
6215 will generate @code{seth/add3} instructions to load their addresses), and
6216 assume all subroutines are reachable with the @code{bl} instruction.
6218 @item -mcode-model=large
6219 @opindex mcode-model=large
6220 Assume objects may be anywhere in the 32-bit address space (the compiler
6221 will generate @code{seth/add3} instructions to load their addresses), and
6222 assume subroutines may not be reachable with the @code{bl} instruction
6223 (the compiler will generate the much slower @code{seth/add3/jl}
6224 instruction sequence).
6227 @opindex msdata=none
6228 Disable use of the small data area. Variables will be put into
6229 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6230 @code{section} attribute has been specified).
6231 This is the default.
6233 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6234 Objects may be explicitly put in the small data area with the
6235 @code{section} attribute using one of these sections.
6238 @opindex msdata=sdata
6239 Put small global and static data in the small data area, but do not
6240 generate special code to reference them.
6244 Put small global and static data in the small data area, and generate
6245 special instructions to reference them.
6249 @cindex smaller data references
6250 Put global and static objects less than or equal to @var{num} bytes
6251 into the small data or bss sections instead of the normal data or bss
6252 sections. The default value of @var{num} is 8.
6253 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6254 for this option to have any effect.
6256 All modules should be compiled with the same @option{-G @var{num}} value.
6257 Compiling with different values of @var{num} may or may not work; if it
6258 doesn't the linker will give an error message---incorrect code will not be
6264 @subsection M88K Options
6265 @cindex M88k options
6267 These @samp{-m} options are defined for Motorola 88k architectures:
6272 Generate code that works well on both the m88100 and the
6277 Generate code that works best for the m88100, but that also
6282 Generate code that works best for the m88110, and may not run
6287 Obsolete option to be removed from the next revision.
6290 @item -midentify-revision
6291 @opindex midentify-revision
6292 @cindex identifying source, compiler (88k)
6293 Include an @code{ident} directive in the assembler output recording the
6294 source file name, compiler name and version, timestamp, and compilation
6297 @item -mno-underscores
6298 @opindex mno-underscores
6299 @cindex underscores, avoiding (88k)
6300 In assembler output, emit symbol names without adding an underscore
6301 character at the beginning of each name. The default is to use an
6302 underscore as prefix on each name.
6304 @item -mocs-debug-info
6305 @itemx -mno-ocs-debug-info
6306 @opindex mocs-debug-info
6307 @opindex mno-ocs-debug-info
6309 @cindex debugging, 88k OCS
6310 Include (or omit) additional debugging information (about registers used
6311 in each stack frame) as specified in the 88open Object Compatibility
6312 Standard, ``OCS''@. This extra information allows debugging of code that
6313 has had the frame pointer eliminated. The default for DG/UX, SVr4, and
6314 Delta 88 SVr3.2 is to include this information; other 88k configurations
6315 omit this information by default.
6317 @item -mocs-frame-position
6318 @opindex mocs-frame-position
6319 @cindex register positions in frame (88k)
6320 When emitting COFF debugging information for automatic variables and
6321 parameters stored on the stack, use the offset from the canonical frame
6322 address, which is the stack pointer (register 31) on entry to the
6323 function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
6324 @option{-mocs-frame-position}; other 88k configurations have the default
6325 @option{-mno-ocs-frame-position}.
6327 @item -mno-ocs-frame-position
6328 @opindex mno-ocs-frame-position
6329 @cindex register positions in frame (88k)
6330 When emitting COFF debugging information for automatic variables and
6331 parameters stored on the stack, use the offset from the frame pointer
6332 register (register 30). When this option is in effect, the frame
6333 pointer is not eliminated when debugging information is selected by the
6336 @item -moptimize-arg-area
6337 @opindex moptimize-arg-area
6338 @cindex arguments in frame (88k)
6339 Save space by reorganizing the stack frame. This option generates code
6340 that does not agree with the 88open specifications, but uses less
6343 @itemx -mno-optimize-arg-area
6344 @opindex mno-optimize-arg-area
6345 Do not reorganize the stack frame to save space. This is the default.
6346 The generated conforms to the specification, but uses more memory.
6348 @item -mshort-data-@var{num}
6349 @opindex mshort-data
6350 @cindex smaller data references (88k)
6351 @cindex r0-relative references (88k)
6352 Generate smaller data references by making them relative to @code{r0},
6353 which allows loading a value using a single instruction (rather than the
6354 usual two). You control which data references are affected by
6355 specifying @var{num} with this option. For example, if you specify
6356 @option{-mshort-data-512}, then the data references affected are those
6357 involving displacements of less than 512 bytes.
6358 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6361 @item -mserialize-volatile
6362 @opindex mserialize-volatile
6363 @itemx -mno-serialize-volatile
6364 @opindex mno-serialize-volatile
6365 @cindex sequential consistency on 88k
6366 Do, or don't, generate code to guarantee sequential consistency
6367 of volatile memory references. By default, consistency is
6370 The order of memory references made by the MC88110 processor does
6371 not always match the order of the instructions requesting those
6372 references. In particular, a load instruction may execute before
6373 a preceding store instruction. Such reordering violates
6374 sequential consistency of volatile memory references, when there
6375 are multiple processors. When consistency must be guaranteed,
6376 GCC generates special instructions, as needed, to force
6377 execution in the proper order.
6379 The MC88100 processor does not reorder memory references and so
6380 always provides sequential consistency. However, by default, GCC
6381 generates the special instructions to guarantee consistency
6382 even when you use @option{-m88100}, so that the code may be run on an
6383 MC88110 processor. If you intend to run your code only on the
6384 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6386 The extra code generated to guarantee consistency may affect the
6387 performance of your application. If you know that you can safely
6388 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6394 @cindex assembler syntax, 88k
6396 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6397 related to System V release 4 (SVr4). This controls the following:
6401 Which variant of the assembler syntax to emit.
6403 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6404 that is used on System V release 4.
6406 @option{-msvr4} makes GCC issue additional declaration directives used in
6410 @option{-msvr4} is the default for the m88k-motorola-sysv4 and
6411 m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all
6412 other m88k configurations.
6414 @item -mversion-03.00
6415 @opindex mversion-03.00
6416 This option is obsolete, and is ignored.
6417 @c ??? which asm syntax better for GAS? option there too?
6419 @item -mno-check-zero-division
6420 @itemx -mcheck-zero-division
6421 @opindex mno-check-zero-division
6422 @opindex mcheck-zero-division
6423 @cindex zero division on 88k
6424 Do, or don't, generate code to guarantee that integer division by
6425 zero will be detected. By default, detection is guaranteed.
6427 Some models of the MC88100 processor fail to trap upon integer
6428 division by zero under certain conditions. By default, when
6429 compiling code that might be run on such a processor, GCC
6430 generates code that explicitly checks for zero-valued divisors
6431 and traps with exception number 503 when one is detected. Use of
6432 @option{-mno-check-zero-division} suppresses such checking for code
6433 generated to run on an MC88100 processor.
6435 GCC assumes that the MC88110 processor correctly detects all instances
6436 of integer division by zero. When @option{-m88110} is specified, no
6437 explicit checks for zero-valued divisors are generated, and both
6438 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6441 @item -muse-div-instruction
6442 @opindex muse-div-instruction
6443 @cindex divide instruction, 88k
6444 Use the div instruction for signed integer division on the
6445 MC88100 processor. By default, the div instruction is not used.
6447 On the MC88100 processor the signed integer division instruction
6448 div) traps to the operating system on a negative operand. The
6449 operating system transparently completes the operation, but at a
6450 large cost in execution time. By default, when compiling code
6451 that might be run on an MC88100 processor, GCC emulates signed
6452 integer division using the unsigned integer division instruction
6453 divu), thereby avoiding the large penalty of a trap to the
6454 operating system. Such emulation has its own, smaller, execution
6455 cost in both time and space. To the extent that your code's
6456 important signed integer division operations are performed on two
6457 nonnegative operands, it may be desirable to use the div
6458 instruction directly.
6460 On the MC88110 processor the div instruction (also known as the
6461 divs instruction) processes negative operands without trapping to
6462 the operating system. When @option{-m88110} is specified,
6463 @option{-muse-div-instruction} is ignored, and the div instruction is used
6464 for signed integer division.
6466 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6467 particular, the behavior of such a division with and without
6468 @option{-muse-div-instruction} may differ.
6470 @item -mtrap-large-shift
6471 @itemx -mhandle-large-shift
6472 @opindex mtrap-large-shift
6473 @opindex mhandle-large-shift
6474 @cindex bit shift overflow (88k)
6475 @cindex large bit shifts (88k)
6476 Include code to detect bit-shifts of more than 31 bits; respectively,
6477 trap such shifts or emit code to handle them properly. By default GCC
6478 makes no special provision for large bit shifts.
6480 @item -mwarn-passed-structs
6481 @opindex mwarn-passed-structs
6482 @cindex structure passing (88k)
6483 Warn when a function passes a struct as an argument or result.
6484 Structure-passing conventions have changed during the evolution of the C
6485 language, and are often the source of portability problems. By default,
6486 GCC issues no such warning.
6489 @c break page here to avoid unsightly interparagraph stretch.
6493 @node RS/6000 and PowerPC Options
6494 @subsection IBM RS/6000 and PowerPC Options
6495 @cindex RS/6000 and PowerPC Options
6496 @cindex IBM RS/6000 and PowerPC Options
6498 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6506 @itemx -mpowerpc-gpopt
6507 @itemx -mno-powerpc-gpopt
6508 @itemx -mpowerpc-gfxopt
6509 @itemx -mno-powerpc-gfxopt
6511 @itemx -mno-powerpc64
6517 @opindex mno-powerpc
6518 @opindex mpowerpc-gpopt
6519 @opindex mno-powerpc-gpopt
6520 @opindex mpowerpc-gfxopt
6521 @opindex mno-powerpc-gfxopt
6523 @opindex mno-powerpc64
6524 GCC supports two related instruction set architectures for the
6525 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6526 instructions supported by the @samp{rios} chip set used in the original
6527 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6528 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6529 the IBM 4xx microprocessors.
6531 Neither architecture is a subset of the other. However there is a
6532 large common subset of instructions supported by both. An MQ
6533 register is included in processors supporting the POWER architecture.
6535 You use these options to specify which instructions are available on the
6536 processor you are using. The default value of these options is
6537 determined when configuring GCC@. Specifying the
6538 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6539 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6540 rather than the options listed above.
6542 The @option{-mpower} option allows GCC to generate instructions that
6543 are found only in the POWER architecture and to use the MQ register.
6544 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6545 to generate instructions that are present in the POWER2 architecture but
6546 not the original POWER architecture.
6548 The @option{-mpowerpc} option allows GCC to generate instructions that
6549 are found only in the 32-bit subset of the PowerPC architecture.
6550 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6551 GCC to use the optional PowerPC architecture instructions in the
6552 General Purpose group, including floating-point square root. Specifying
6553 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6554 use the optional PowerPC architecture instructions in the Graphics
6555 group, including floating-point select.
6557 The @option{-mpowerpc64} option allows GCC to generate the additional
6558 64-bit instructions that are found in the full PowerPC64 architecture
6559 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6560 @option{-mno-powerpc64}.
6562 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6563 will use only the instructions in the common subset of both
6564 architectures plus some special AIX common-mode calls, and will not use
6565 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6566 permits GCC to use any instruction from either architecture and to
6567 allow use of the MQ register; specify this for the Motorola MPC601.
6569 @item -mnew-mnemonics
6570 @itemx -mold-mnemonics
6571 @opindex mnew-mnemonics
6572 @opindex mold-mnemonics
6573 Select which mnemonics to use in the generated assembler code. With
6574 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
6575 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
6576 assembler mnemonics defined for the POWER architecture. Instructions
6577 defined in only one architecture have only one mnemonic; GCC uses that
6578 mnemonic irrespective of which of these options is specified.
6580 GCC defaults to the mnemonics appropriate for the architecture in
6581 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6582 value of these option. Unless you are building a cross-compiler, you
6583 should normally not specify either @option{-mnew-mnemonics} or
6584 @option{-mold-mnemonics}, but should instead accept the default.
6586 @item -mcpu=@var{cpu_type}
6588 Set architecture type, register usage, choice of mnemonics, and
6589 instruction scheduling parameters for machine type @var{cpu_type}.
6590 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6591 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6592 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6593 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
6594 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
6595 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
6597 @option{-mcpu=common} selects a completely generic processor. Code
6598 generated under this option will run on any POWER or PowerPC processor.
6599 GCC will use only the instructions in the common subset of both
6600 architectures, and will not use the MQ register. GCC assumes a generic
6601 processor model for scheduling purposes.
6603 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
6604 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
6605 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
6606 types, with an appropriate, generic processor model assumed for
6607 scheduling purposes.
6609 The other options specify a specific processor. Code generated under
6610 those options will run best on that processor, and may not run at all on
6613 The @option{-mcpu} options automatically enable or disable other
6614 @option{-m} options as follows:
6618 @option{-mno-power}, @option{-mno-powerc}
6625 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
6640 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6643 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
6648 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
6651 @item -mtune=@var{cpu_type}
6653 Set the instruction scheduling parameters for machine type
6654 @var{cpu_type}, but do not set the architecture type, register usage, or
6655 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
6656 values for @var{cpu_type} are used for @option{-mtune} as for
6657 @option{-mcpu}. If both are specified, the code generated will use the
6658 architecture, registers, and mnemonics set by @option{-mcpu}, but the
6659 scheduling parameters set by @option{-mtune}.
6662 @itemx -mno-fp-in-toc
6663 @itemx -mno-sum-in-toc
6664 @itemx -mminimal-toc
6666 @opindex mno-fp-in-toc
6667 @opindex mno-sum-in-toc
6668 @opindex mminimal-toc
6669 Modify generation of the TOC (Table Of Contents), which is created for
6670 every executable file. The @option{-mfull-toc} option is selected by
6671 default. In that case, GCC will allocate at least one TOC entry for
6672 each unique non-automatic variable reference in your program. GCC
6673 will also place floating-point constants in the TOC@. However, only
6674 16,384 entries are available in the TOC@.
6676 If you receive a linker error message that saying you have overflowed
6677 the available TOC space, you can reduce the amount of TOC space used
6678 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
6679 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
6680 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
6681 generate code to calculate the sum of an address and a constant at
6682 run-time instead of putting that sum into the TOC@. You may specify one
6683 or both of these options. Each causes GCC to produce very slightly
6684 slower and larger code at the expense of conserving TOC space.
6686 If you still run out of space in the TOC even when you specify both of
6687 these options, specify @option{-mminimal-toc} instead. This option causes
6688 GCC to make only one TOC entry for every file. When you specify this
6689 option, GCC will produce code that is slower and larger but which
6690 uses extremely little TOC space. You may wish to use this option
6691 only on files that contain less frequently executed code.
6697 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
6698 @code{long} type, and the infrastructure needed to support them.
6699 Specifying @option{-maix64} implies @option{-mpowerpc64} and
6700 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
6701 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
6706 @opindex mno-xl-call
6707 On AIX, pass floating-point arguments to prototyped functions beyond the
6708 register save area (RSA) on the stack in addition to argument FPRs. The
6709 AIX calling convention was extended but not initially documented to
6710 handle an obscure K&R C case of calling a function that takes the
6711 address of its arguments with fewer arguments than declared. AIX XL
6712 compilers access floating point arguments which do not fit in the
6713 RSA from the stack when a subroutine is compiled without
6714 optimization. Because always storing floating-point arguments on the
6715 stack is inefficient and rarely needed, this option is not enabled by
6716 default and only is necessary when calling subroutines compiled by AIX
6717 XL compilers without optimization.
6721 Support @dfn{AIX Threads}. Link an application written to use
6722 @dfn{pthreads} with special libraries and startup code to enable the
6727 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
6728 application written to use message passing with special startup code to
6729 enable the application to run. The system must have PE installed in the
6730 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
6731 must be overridden with the @option{-specs=} option to specify the
6732 appropriate directory location. The Parallel Environment does not
6733 support threads, so the @option{-mpe} option and the @option{-mthreads}
6734 option are incompatible.
6738 @opindex msoft-float
6739 @opindex mhard-float
6740 Generate code that does not use (uses) the floating-point register set.
6741 Software floating point emulation is provided if you use the
6742 @option{-msoft-float} option, and pass the option to GCC when linking.
6745 @itemx -mno-multiple
6747 @opindex mno-multiple
6748 Generate code that uses (does not use) the load multiple word
6749 instructions and the store multiple word instructions. These
6750 instructions are generated by default on POWER systems, and not
6751 generated on PowerPC systems. Do not use @option{-mmultiple} on little
6752 endian PowerPC systems, since those instructions do not work when the
6753 processor is in little endian mode. The exceptions are PPC740 and
6754 PPC750 which permit the instructions usage in little endian mode.
6760 Generate code that uses (does not use) the load string instructions
6761 and the store string word instructions to save multiple registers and
6762 do small block moves. These instructions are generated by default on
6763 POWER systems, and not generated on PowerPC systems. Do not use
6764 @option{-mstring} on little endian PowerPC systems, since those
6765 instructions do not work when the processor is in little endian mode.
6766 The exceptions are PPC740 and PPC750 which permit the instructions
6767 usage in little endian mode.
6773 Generate code that uses (does not use) the load or store instructions
6774 that update the base register to the address of the calculated memory
6775 location. These instructions are generated by default. If you use
6776 @option{-mno-update}, there is a small window between the time that the
6777 stack pointer is updated and the address of the previous frame is
6778 stored, which means code that walks the stack frame across interrupts or
6779 signals may get corrupted data.
6782 @itemx -mno-fused-madd
6783 @opindex mfused-madd
6784 @opindex mno-fused-madd
6785 Generate code that uses (does not use) the floating point multiply and
6786 accumulate instructions. These instructions are generated by default if
6787 hardware floating is used.
6789 @item -mno-bit-align
6791 @opindex mno-bit-align
6793 On System V.4 and embedded PowerPC systems do not (do) force structures
6794 and unions that contain bit-fields to be aligned to the base type of the
6797 For example, by default a structure containing nothing but 8
6798 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
6799 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
6800 the structure would be aligned to a 1 byte boundary and be one byte in
6803 @item -mno-strict-align
6804 @itemx -mstrict-align
6805 @opindex mno-strict-align
6806 @opindex mstrict-align
6807 On System V.4 and embedded PowerPC systems do not (do) assume that
6808 unaligned memory references will be handled by the system.
6811 @itemx -mno-relocatable
6812 @opindex mrelocatable
6813 @opindex mno-relocatable
6814 On embedded PowerPC systems generate code that allows (does not allow)
6815 the program to be relocated to a different address at runtime. If you
6816 use @option{-mrelocatable} on any module, all objects linked together must
6817 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
6819 @item -mrelocatable-lib
6820 @itemx -mno-relocatable-lib
6821 @opindex mrelocatable-lib
6822 @opindex mno-relocatable-lib
6823 On embedded PowerPC systems generate code that allows (does not allow)
6824 the program to be relocated to a different address at runtime. Modules
6825 compiled with @option{-mrelocatable-lib} can be linked with either modules
6826 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
6827 with modules compiled with the @option{-mrelocatable} options.
6833 On System V.4 and embedded PowerPC systems do not (do) assume that
6834 register 2 contains a pointer to a global area pointing to the addresses
6835 used in the program.
6838 @itemx -mlittle-endian
6840 @opindex mlittle-endian
6841 On System V.4 and embedded PowerPC systems compile code for the
6842 processor in little endian mode. The @option{-mlittle-endian} option is
6843 the same as @option{-mlittle}.
6848 @opindex mbig-endian
6849 On System V.4 and embedded PowerPC systems compile code for the
6850 processor in big endian mode. The @option{-mbig-endian} option is
6851 the same as @option{-mbig}.
6855 On System V.4 and embedded PowerPC systems compile code using calling
6856 conventions that adheres to the March 1995 draft of the System V
6857 Application Binary Interface, PowerPC processor supplement. This is the
6858 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
6860 @item -mcall-sysv-eabi
6861 @opindex mcall-sysv-eabi
6862 Specify both @option{-mcall-sysv} and @option{-meabi} options.
6864 @item -mcall-sysv-noeabi
6865 @opindex mcall-sysv-noeabi
6866 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
6870 On System V.4 and embedded PowerPC systems compile code using calling
6871 conventions that are similar to those used on AIX@. This is the
6872 default if you configured GCC using @samp{powerpc-*-eabiaix}.
6874 @item -mcall-solaris
6875 @opindex mcall-solaris
6876 On System V.4 and embedded PowerPC systems compile code for the Solaris
6880 @opindex mcall-linux
6881 On System V.4 and embedded PowerPC systems compile code for the
6882 Linux-based GNU system.
6885 @opindex mcall-netbsd
6886 On System V.4 and embedded PowerPC systems compile code for the
6887 NetBSD operating system.
6890 @itemx -mno-prototype
6892 @opindex mno-prototype
6893 On System V.4 and embedded PowerPC systems assume that all calls to
6894 variable argument functions are properly prototyped. Otherwise, the
6895 compiler must insert an instruction before every non prototyped call to
6896 set or clear bit 6 of the condition code register (@var{CR}) to
6897 indicate whether floating point values were passed in the floating point
6898 registers in case the function takes a variable arguments. With
6899 @option{-mprototype}, only calls to prototyped variable argument functions
6900 will set or clear the bit.
6904 On embedded PowerPC systems, assume that the startup module is called
6905 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
6906 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
6911 On embedded PowerPC systems, assume that the startup module is called
6912 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
6917 On embedded PowerPC systems, assume that the startup module is called
6918 @file{crt0.o} and the standard C libraries are @file{libads.a} and
6922 @opindex myellowknife
6923 On embedded PowerPC systems, assume that the startup module is called
6924 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
6929 On System V.4 and embedded PowerPC systems, specify that you are
6930 compiling for a VxWorks system.
6934 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
6935 header to indicate that @samp{eabi} extended relocations are used.
6941 On System V.4 and embedded PowerPC systems do (do not) adhere to the
6942 Embedded Applications Binary Interface (eabi) which is a set of
6943 modifications to the System V.4 specifications. Selecting @option{-meabi}
6944 means that the stack is aligned to an 8 byte boundary, a function
6945 @code{__eabi} is called to from @code{main} to set up the eabi
6946 environment, and the @option{-msdata} option can use both @code{r2} and
6947 @code{r13} to point to two separate small data areas. Selecting
6948 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
6949 do not call an initialization function from @code{main}, and the
6950 @option{-msdata} option will only use @code{r13} to point to a single
6951 small data area. The @option{-meabi} option is on by default if you
6952 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
6955 @opindex msdata=eabi
6956 On System V.4 and embedded PowerPC systems, put small initialized
6957 @code{const} global and static data in the @samp{.sdata2} section, which
6958 is pointed to by register @code{r2}. Put small initialized
6959 non-@code{const} global and static data in the @samp{.sdata} section,
6960 which is pointed to by register @code{r13}. Put small uninitialized
6961 global and static data in the @samp{.sbss} section, which is adjacent to
6962 the @samp{.sdata} section. The @option{-msdata=eabi} option is
6963 incompatible with the @option{-mrelocatable} option. The
6964 @option{-msdata=eabi} option also sets the @option{-memb} option.
6967 @opindex msdata=sysv
6968 On System V.4 and embedded PowerPC systems, put small global and static
6969 data in the @samp{.sdata} section, which is pointed to by register
6970 @code{r13}. Put small uninitialized global and static data in the
6971 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
6972 The @option{-msdata=sysv} option is incompatible with the
6973 @option{-mrelocatable} option.
6975 @item -msdata=default
6977 @opindex msdata=default
6979 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
6980 compile code the same as @option{-msdata=eabi}, otherwise compile code the
6981 same as @option{-msdata=sysv}.
6984 @opindex msdata-data
6985 On System V.4 and embedded PowerPC systems, put small global and static
6986 data in the @samp{.sdata} section. Put small uninitialized global and
6987 static data in the @samp{.sbss} section. Do not use register @code{r13}
6988 to address small data however. This is the default behavior unless
6989 other @option{-msdata} options are used.
6993 @opindex msdata=none
6995 On embedded PowerPC systems, put all initialized global and static data
6996 in the @samp{.data} section, and all uninitialized data in the
6997 @samp{.bss} section.
7001 @cindex smaller data references (PowerPC)
7002 @cindex .sdata/.sdata2 references (PowerPC)
7003 On embedded PowerPC systems, put global and static items less than or
7004 equal to @var{num} bytes into the small data or bss sections instead of
7005 the normal data or bss section. By default, @var{num} is 8. The
7006 @option{-G @var{num}} switch is also passed to the linker.
7007 All modules should be compiled with the same @option{-G @var{num}} value.
7010 @itemx -mno-regnames
7012 @opindex mno-regnames
7013 On System V.4 and embedded PowerPC systems do (do not) emit register
7014 names in the assembly language output using symbolic forms.
7019 @subsection IBM RT Options
7021 @cindex IBM RT options
7023 These @samp{-m} options are defined for the IBM RT PC:
7027 @opindex min-line-mul
7028 Use an in-line code sequence for integer multiplies. This is the
7031 @item -mcall-lib-mul
7032 @opindex mcall-lib-mul
7033 Call @code{lmul$$} for integer multiples.
7035 @item -mfull-fp-blocks
7036 @opindex mfull-fp-blocks
7037 Generate full-size floating point data blocks, including the minimum
7038 amount of scratch space recommended by IBM@. This is the default.
7040 @item -mminimum-fp-blocks
7041 @opindex mminimum-fp-blocks
7042 Do not include extra scratch space in floating point data blocks. This
7043 results in smaller code, but slower execution, since scratch space must
7044 be allocated dynamically.
7046 @cindex @file{varargs.h} and RT PC
7047 @cindex @file{stdarg.h} and RT PC
7048 @item -mfp-arg-in-fpregs
7049 @opindex mfp-arg-in-fpregs
7050 Use a calling sequence incompatible with the IBM calling convention in
7051 which floating point arguments are passed in floating point registers.
7052 Note that @code{varargs.h} and @code{stdarg.h} will not work with
7053 floating point operands if this option is specified.
7055 @item -mfp-arg-in-gregs
7056 @opindex mfp-arg-in-gregs
7057 Use the normal calling convention for floating point arguments. This is
7060 @item -mhc-struct-return
7061 @opindex mhc-struct-return
7062 Return structures of more than one word in memory, rather than in a
7063 register. This provides compatibility with the MetaWare HighC (hc)
7064 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7065 with the Portable C Compiler (pcc).
7067 @item -mnohc-struct-return
7068 @opindex mnohc-struct-return
7069 Return some structures of more than one word in registers, when
7070 convenient. This is the default. For compatibility with the
7071 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7072 option @option{-mhc-struct-return}.
7076 @subsection MIPS Options
7077 @cindex MIPS options
7079 These @samp{-m} options are defined for the MIPS family of computers:
7083 @item -march=@var{cpu-type}
7085 Assume the defaults for the machine type @var{cpu-type} when generating
7086 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7087 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7088 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7089 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7090 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7091 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc.
7093 @item -mtune=@var{cpu-type}
7095 Assume the defaults for the machine type @var{cpu-type} when scheduling
7096 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7097 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7098 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7099 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7100 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7101 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific
7102 @var{cpu-type} will schedule things appropriately for that particular
7103 chip, the compiler will not generate any code that does not meet level 1
7104 of the MIPS ISA (instruction set architecture) without a @option{-mipsX}
7105 or @option{-mabi} switch being used.
7107 @item -mcpu=@var{cpu-type}
7109 This is identical to specifying both @option{-march} and @option{-mtune}.
7113 Issue instructions from level 1 of the MIPS ISA@. This is the default.
7114 @samp{r3000} is the default @var{cpu-type} at this ISA level.
7118 Issue instructions from level 2 of the MIPS ISA (branch likely, square
7119 root instructions). @samp{r6000} is the default @var{cpu-type} at this
7124 Issue instructions from level 3 of the MIPS ISA (64-bit instructions).
7125 @samp{r4000} is the default @var{cpu-type} at this ISA level.
7129 Issue instructions from level 4 of the MIPS ISA (conditional move,
7130 prefetch, enhanced FPU instructions). @samp{r8000} is the default
7131 @var{cpu-type} at this ISA level.
7135 Assume that 32 32-bit floating point registers are available. This is
7140 Assume that 32 64-bit floating point registers are available. This is
7141 the default when the @option{-mips3} option is used.
7144 @itemx -mno-fused-madd
7145 @opindex mfused-madd
7146 @opindex mno-fused-madd
7147 Generate code that uses (does not use) the floating point multiply and
7148 accumulate instructions, when they are available. These instructions
7149 are generated by default if they are available, but this may be
7150 undesirable if the extra precision causes problems or on certain chips
7151 in the mode where denormals are rounded to zero where denormals
7152 generated by multiply and accumulate instructions cause exceptions
7157 Assume that 32 32-bit general purpose registers are available. This is
7162 Assume that 32 64-bit general purpose registers are available. This is
7163 the default when the @option{-mips3} option is used.
7167 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7168 explanation of the default, and the width of pointers.
7172 Force long types to be 64 bits wide. See @option{-mlong32} for an
7173 explanation of the default, and the width of pointers.
7177 Force long, int, and pointer types to be 32 bits wide.
7179 If none of @option{-mlong32}, @option{-mlong64}, or @option{-mint64} are set,
7180 the size of ints, longs, and pointers depends on the ABI and ISA chosen.
7181 For @option{-mabi=32}, and @option{-mabi=n32}, ints and longs are 32 bits
7182 wide. For @option{-mabi=64}, ints are 32 bits, and longs are 64 bits wide.
7183 For @option{-mabi=eabi} and either @option{-mips1} or @option{-mips2}, ints
7184 and longs are 32 bits wide. For @option{-mabi=eabi} and higher ISAs, ints
7185 are 32 bits, and longs are 64 bits wide. The width of pointer types is
7186 the smaller of the width of longs or the width of general purpose
7187 registers (which in turn depends on the ISA)@.
7199 Generate code for the indicated ABI@. The default instruction level is
7200 @option{-mips1} for @samp{32}, @option{-mips3} for @samp{n32}, and
7201 @option{-mips4} otherwise. Conversely, with @option{-mips1} or
7202 @option{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI
7207 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7208 add normal debug information. This is the default for all
7209 platforms except for the OSF/1 reference platform, using the OSF/rose
7210 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7211 switches are used, the @file{mips-tfile} program will encapsulate the
7212 stabs within MIPS ECOFF@.
7216 Generate code for the GNU assembler. This is the default on the OSF/1
7217 reference platform, using the OSF/rose object format. Also, this is
7218 the default if the configure option @option{--with-gnu-as} is used.
7220 @item -msplit-addresses
7221 @itemx -mno-split-addresses
7222 @opindex msplit-addresses
7223 @opindex mno-split-addresses
7224 Generate code to load the high and low parts of address constants separately.
7225 This allows GCC to optimize away redundant loads of the high order
7226 bits of addresses. This optimization requires GNU as and GNU ld.
7227 This optimization is enabled by default for some embedded targets where
7228 GNU as and GNU ld are standard.
7234 The @option{-mrnames} switch says to output code using the MIPS software
7235 names for the registers, instead of the hardware names (ie, @var{a0}
7236 instead of @var{$4}). The only known assembler that supports this option
7237 is the Algorithmics assembler.
7243 The @option{-mgpopt} switch says to write all of the data declarations
7244 before the instructions in the text section, this allows the MIPS
7245 assembler to generate one word memory references instead of using two
7246 words for short global or static data items. This is on by default if
7247 optimization is selected.
7253 For each non-inline function processed, the @option{-mstats} switch
7254 causes the compiler to emit one line to the standard error file to
7255 print statistics about the program (number of registers saved, stack
7262 The @option{-mmemcpy} switch makes all block moves call the appropriate
7263 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7264 generating inline code.
7267 @itemx -mno-mips-tfile
7268 @opindex mmips-tfile
7269 @opindex mno-mips-tfile
7270 The @option{-mno-mips-tfile} switch causes the compiler not
7271 postprocess the object file with the @file{mips-tfile} program,
7272 after the MIPS assembler has generated it to add debug support. If
7273 @file{mips-tfile} is not run, then no local variables will be
7274 available to the debugger. In addition, @file{stage2} and
7275 @file{stage3} objects will have the temporary file names passed to the
7276 assembler embedded in the object file, which means the objects will
7277 not compare the same. The @option{-mno-mips-tfile} switch should only
7278 be used when there are bugs in the @file{mips-tfile} program that
7279 prevents compilation.
7282 @opindex msoft-float
7283 Generate output containing library calls for floating point.
7284 @strong{Warning:} the requisite libraries are not part of GCC@.
7285 Normally the facilities of the machine's usual C compiler are used, but
7286 this can't be done directly in cross-compilation. You must make your
7287 own arrangements to provide suitable library functions for
7291 @opindex mhard-float
7292 Generate output containing floating point instructions. This is the
7293 default if you use the unmodified sources.
7296 @itemx -mno-abicalls
7298 @opindex mno-abicalls
7299 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7300 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7301 position independent code.
7304 @itemx -mno-long-calls
7305 @opindex mlong-calls
7306 @opindex mno-long-calls
7307 Do all calls with the @samp{JALR} instruction, which requires
7308 loading up a function's address into a register before the call.
7309 You need to use this switch, if you call outside of the current
7310 512 megabyte segment to functions that are not through pointers.
7313 @itemx -mno-half-pic
7315 @opindex mno-half-pic
7316 Put pointers to extern references into the data section and load them
7317 up, rather than put the references in the text section.
7319 @item -membedded-pic
7320 @itemx -mno-embedded-pic
7321 @opindex membedded-pic
7322 @opindex mno-embedded-pic
7323 Generate PIC code suitable for some embedded systems. All calls are
7324 made using PC relative address, and all data is addressed using the $gp
7325 register. No more than 65536 bytes of global data may be used. This
7326 requires GNU as and GNU ld which do most of the work. This currently
7327 only works on targets which use ECOFF; it does not work with ELF@.
7329 @item -membedded-data
7330 @itemx -mno-embedded-data
7331 @opindex membedded-data
7332 @opindex mno-embedded-data
7333 Allocate variables to the read-only data section first if possible, then
7334 next in the small data section if possible, otherwise in data. This gives
7335 slightly slower code than the default, but reduces the amount of RAM required
7336 when executing, and thus may be preferred for some embedded systems.
7338 @item -muninit-const-in-rodata
7339 @itemx -mno-uninit-const-in-rodata
7340 @opindex muninit-const-in-rodata
7341 @opindex mno-uninit-const-in-rodata
7342 When used together with @option{-membedded-data}, it will always store uninitialized
7343 const variables in the read-only data section.
7345 @item -msingle-float
7346 @itemx -mdouble-float
7347 @opindex msingle-float
7348 @opindex mdouble-float
7349 The @option{-msingle-float} switch tells gcc to assume that the floating
7350 point coprocessor only supports single precision operations, as on the
7351 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
7352 double precision operations. This is the default.
7358 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
7359 as on the @samp{r4650} chip.
7363 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
7364 @option{-mcpu=r4650}.
7370 Enable 16-bit instructions.
7374 Use the entry and exit pseudo ops. This option can only be used with
7379 Compile code for the processor in little endian mode.
7380 The requisite libraries are assumed to exist.
7384 Compile code for the processor in big endian mode.
7385 The requisite libraries are assumed to exist.
7389 @cindex smaller data references (MIPS)
7390 @cindex gp-relative references (MIPS)
7391 Put global and static items less than or equal to @var{num} bytes into
7392 the small data or bss sections instead of the normal data or bss
7393 section. This allows the assembler to emit one word memory reference
7394 instructions based on the global pointer (@var{gp} or @var{$28}),
7395 instead of the normal two words used. By default, @var{num} is 8 when
7396 the MIPS assembler is used, and 0 when the GNU assembler is used. The
7397 @option{-G @var{num}} switch is also passed to the assembler and linker.
7398 All modules should be compiled with the same @option{-G @var{num}}
7403 Tell the MIPS assembler to not run its preprocessor over user
7404 assembler files (with a @samp{.s} suffix) when assembling them.
7408 Pass an option to gas which will cause nops to be inserted if
7409 the read of the destination register of an mfhi or mflo instruction
7410 occurs in the following two instructions.
7414 Do not include the default crt0.
7418 These options are defined by the macro
7419 @code{TARGET_SWITCHES} in the machine description. The default for the
7420 options is also defined by that macro, which enables you to change the
7424 @node i386 and x86-64 Options
7425 @subsection Intel 386 and AMD x86-64 Options
7426 @cindex i386 Options
7427 @cindex x86-64 Options
7428 @cindex Intel 386 Options
7429 @cindex AMD x86-64 Options
7431 These @samp{-m} options are defined for the i386 and x86-64 family of
7435 @item -mcpu=@var{cpu-type}
7437 Assume the defaults for the machine type @var{cpu-type} when scheduling
7438 instructions. The choices for @var{cpu-type} are @samp{i386},
7439 @samp{i486}, @samp{i586}, @samp{i686}, @samp{pentium},
7440 @samp{pentiumpro}, @samp{pentium4}, @samp{k6}, and @samp{athlon}
7442 While picking a specific @var{cpu-type} will schedule things appropriately
7443 for that particular chip, the compiler will not generate any code that
7444 does not run on the i386 without the @option{-march=@var{cpu-type}} option
7445 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
7446 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
7447 AMD chips as opposed to the Intel ones.
7449 @item -march=@var{cpu-type}
7451 Generate instructions for the machine type @var{cpu-type}. The choices
7452 for @var{cpu-type} are the same as for @option{-mcpu}. Moreover,
7453 specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}.
7462 @opindex mpentiumpro
7463 These options are synonyms for @option{-mcpu=i386}, @option{-mcpu=i486},
7464 @option{-mcpu=pentium}, and @option{-mcpu=pentiumpro} respectively.
7465 These synonyms are deprecated.
7467 @item -mintel-syntax
7468 @opindex mintel-syntax
7469 Emit assembly using Intel syntax opcodes instead of AT&T syntax.
7474 @opindex mno-ieee-fp
7475 Control whether or not the compiler uses IEEE floating point
7476 comparisons. These handle correctly the case where the result of a
7477 comparison is unordered.
7480 @opindex msoft-float
7481 Generate output containing library calls for floating point.
7482 @strong{Warning:} the requisite libraries are not part of GCC@.
7483 Normally the facilities of the machine's usual C compiler are used, but
7484 this can't be done directly in cross-compilation. You must make your
7485 own arrangements to provide suitable library functions for
7488 On machines where a function returns floating point results in the 80387
7489 register stack, some floating point opcodes may be emitted even if
7490 @option{-msoft-float} is used.
7492 @item -mno-fp-ret-in-387
7493 @opindex mno-fp-ret-in-387
7494 Do not use the FPU registers for return values of functions.
7496 The usual calling convention has functions return values of types
7497 @code{float} and @code{double} in an FPU register, even if there
7498 is no FPU@. The idea is that the operating system should emulate
7501 The option @option{-mno-fp-ret-in-387} causes such values to be returned
7502 in ordinary CPU registers instead.
7504 @item -mno-fancy-math-387
7505 @opindex mno-fancy-math-387
7506 Some 387 emulators do not support the @code{sin}, @code{cos} and
7507 @code{sqrt} instructions for the 387. Specify this option to avoid
7508 generating those instructions. This option is the default on FreeBSD@.
7509 As of revision 2.6.1, these instructions are not generated unless you
7510 also use the @option{-funsafe-math-optimizations} switch.
7512 @item -malign-double
7513 @itemx -mno-align-double
7514 @opindex malign-double
7515 @opindex mno-align-double
7516 Control whether GCC aligns @code{double}, @code{long double}, and
7517 @code{long long} variables on a two word boundary or a one word
7518 boundary. Aligning @code{double} variables on a two word boundary will
7519 produce code that runs somewhat faster on a @samp{Pentium} at the
7520 expense of more memory.
7522 @item -m128bit-long-double
7523 @opindex m128bit-long-double
7524 Control the size of @code{long double} type. i386 application binary interface
7525 specify the size to be 12 bytes, while modern architectures (Pentium and newer)
7526 prefer @code{long double} aligned to 8 or 16 byte boundary. This is
7527 impossible to reach with 12 byte long doubles in the array accesses.
7529 @strong{Warning:} if you use the @option{-m128bit-long-double} switch, the
7530 structures and arrays containing @code{long double} will change their size as
7531 well as function calling convention for function taking @code{long double}
7534 @item -m96bit-long-double
7535 @opindex m96bit-long-double
7536 Set the size of @code{long double} to 96 bits as required by the i386
7537 application binary interface. This is the default.
7540 @itemx -mno-svr3-shlib
7541 @opindex msvr3-shlib
7542 @opindex mno-svr3-shlib
7543 Control whether GCC places uninitialized local variables into the
7544 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
7545 into @code{bss}. These options are meaningful only on System V Release 3.
7549 Use a different function-calling convention, in which functions that
7550 take a fixed number of arguments return with the @code{ret} @var{num}
7551 instruction, which pops their arguments while returning. This saves one
7552 instruction in the caller since there is no need to pop the arguments
7555 You can specify that an individual function is called with this calling
7556 sequence with the function attribute @samp{stdcall}. You can also
7557 override the @option{-mrtd} option by using the function attribute
7558 @samp{cdecl}. @xref{Function Attributes}.
7560 @strong{Warning:} this calling convention is incompatible with the one
7561 normally used on Unix, so you cannot use it if you need to call
7562 libraries compiled with the Unix compiler.
7564 Also, you must provide function prototypes for all functions that
7565 take variable numbers of arguments (including @code{printf});
7566 otherwise incorrect code will be generated for calls to those
7569 In addition, seriously incorrect code will result if you call a
7570 function with too many arguments. (Normally, extra arguments are
7571 harmlessly ignored.)
7573 @item -mregparm=@var{num}
7575 Control how many registers are used to pass integer arguments. By
7576 default, no registers are used to pass arguments, and at most 3
7577 registers can be used. You can control this behavior for a specific
7578 function by using the function attribute @samp{regparm}.
7579 @xref{Function Attributes}.
7581 @strong{Warning:} if you use this switch, and
7582 @var{num} is nonzero, then you must build all modules with the same
7583 value, including any libraries. This includes the system libraries and
7586 @item -mpreferred-stack-boundary=@var{num}
7587 @opindex mpreferred-stack-boundary
7588 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
7589 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
7590 the default is 4 (16 bytes or 128 bits).
7592 The stack is required to be aligned on a 4 byte boundary. On Pentium
7593 and PentiumPro, @code{double} and @code{long double} values should be
7594 aligned to an 8 byte boundary (see @option{-malign-double}) or suffer
7595 significant run time performance penalties. On Pentium III, the
7596 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
7597 penalties if it is not 16 byte aligned.
7599 To ensure proper alignment of this values on the stack, the stack boundary
7600 must be as aligned as that required by any value stored on the stack.
7601 Further, every function must be generated such that it keeps the stack
7602 aligned. Thus calling a function compiled with a higher preferred
7603 stack boundary from a function compiled with a lower preferred stack
7604 boundary will most likely misalign the stack. It is recommended that
7605 libraries that use callbacks always use the default setting.
7607 This extra alignment does consume extra stack space. Code that is sensitive
7608 to stack space usage, such as embedded systems and operating system kernels,
7609 may want to reduce the preferred alignment to
7610 @option{-mpreferred-stack-boundary=2}.
7624 These switches enable or disable the use of built-in functions that allow
7625 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
7627 The following machine modes are available for use with MMX built-in functions
7628 (@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32 bit integers,
7629 @code{V4HI} for a vector of four 16 bit integers, and @code{V8QI} for a
7630 vector of eight 8 bit integers. Some of the built-in functions operate on
7631 MMX registers as a whole 64 bit entity, these use @code{DI} as their mode.
7633 If 3Dnow extensions are enabled, @code{V2SF} is used as a mode for a vector
7634 of two 32 bit floating point values.
7636 If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32 bit
7637 floating point values. Some instructions use a vector of four 32 bit
7638 integers, these use @code{V4SI}. Finally, some instructions operate on an
7639 entire vector register, interpreting it as a 128 bit integer, these use mode
7642 The following built-in functions are made available by @option{-mmmx}:
7644 @item v8qi __builtin_ia32_paddb (v8qi, v8qi)
7645 Generates the @code{paddb} machine instruction.
7646 @item v4hi __builtin_ia32_paddw (v4hi, v4hi)
7647 Generates the @code{paddw} machine instruction.
7648 @item v2si __builtin_ia32_paddd (v2si, v2si)
7649 Generates the @code{paddd} machine instruction.
7650 @item v8qi __builtin_ia32_psubb (v8qi, v8qi)
7651 Generates the @code{psubb} machine instruction.
7652 @item v4hi __builtin_ia32_psubw (v4hi, v4hi)
7653 Generates the @code{psubw} machine instruction.
7654 @item v2si __builtin_ia32_psubd (v2si, v2si)
7655 Generates the @code{psubd} machine instruction.
7657 @item v8qi __builtin_ia32_paddsb (v8qi, v8qi)
7658 Generates the @code{paddsb} machine instruction.
7659 @item v4hi __builtin_ia32_paddsw (v4hi, v4hi)
7660 Generates the @code{paddsw} machine instruction.
7661 @item v8qi __builtin_ia32_psubsb (v8qi, v8qi)
7662 Generates the @code{psubsb} machine instruction.
7663 @item v4hi __builtin_ia32_psubsw (v4hi, v4hi)
7664 Generates the @code{psubsw} machine instruction.
7666 @item v8qi __builtin_ia32_paddusb (v8qi, v8qi)
7667 Generates the @code{paddusb} machine instruction.
7668 @item v4hi __builtin_ia32_paddusw (v4hi, v4hi)
7669 Generates the @code{paddusw} machine instruction.
7670 @item v8qi __builtin_ia32_psubusb (v8qi, v8qi)
7671 Generates the @code{psubusb} machine instruction.
7672 @item v4hi __builtin_ia32_psubusw (v4hi, v4hi)
7673 Generates the @code{psubusw} machine instruction.
7675 @item v4hi __builtin_ia32_pmullw (v4hi, v4hi)
7676 Generates the @code{pmullw} machine instruction.
7677 @item v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
7678 Generates the @code{pmulhw} machine instruction.
7680 @item di __builtin_ia32_pand (di, di)
7681 Generates the @code{pand} machine instruction.
7682 @item di __builtin_ia32_pandn (di,di)
7683 Generates the @code{pandn} machine instruction.
7684 @item di __builtin_ia32_por (di, di)
7685 Generates the @code{por} machine instruction.
7686 @item di __builtin_ia32_pxor (di, di)
7687 Generates the @code{pxor} machine instruction.
7689 @item v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
7690 Generates the @code{pcmpeqb} machine instruction.
7691 @item v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
7692 Generates the @code{pcmpeqw} machine instruction.
7693 @item v2si __builtin_ia32_pcmpeqd (v2si, v2si)
7694 Generates the @code{pcmpeqd} machine instruction.
7695 @item v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
7696 Generates the @code{pcmpgtb} machine instruction.
7697 @item v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
7698 Generates the @code{pcmpgtw} machine instruction.
7699 @item v2si __builtin_ia32_pcmpgtd (v2si, v2si)
7700 Generates the @code{pcmpgtd} machine instruction.
7702 @item v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
7703 Generates the @code{punpckhbw} machine instruction.
7704 @item v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
7705 Generates the @code{punpckhwd} machine instruction.
7706 @item v2si __builtin_ia32_punpckhdq (v2si, v2si)
7707 Generates the @code{punpckhdq} machine instruction.
7708 @item v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
7709 Generates the @code{punpcklbw} machine instruction.
7710 @item v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
7711 Generates the @code{punpcklwd} machine instruction.
7712 @item v2si __builtin_ia32_punpckldq (v2si, v2si)
7713 Generates the @code{punpckldq} machine instruction.
7715 @item v8qi __builtin_ia32_packsswb (v4hi, v4hi)
7716 Generates the @code{packsswb} machine instruction.
7717 @item v4hi __builtin_ia32_packssdw (v2si, v2si)
7718 Generates the @code{packssdw} machine instruction.
7719 @item v8qi __builtin_ia32_packuswb (v4hi, v4hi)
7720 Generates the @code{packuswb} machine instruction.
7724 The following built-in functions are made available either with @option{-msse}, or
7725 with a combination of @option{-m3dnow} and @option{-march=athlon}.
7728 @item v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
7729 Generates the @code{pmulhuw} machine instruction.
7731 @item v8qi __builtin_ia32_pavgb (v8qi, v8qi)
7732 Generates the @code{pavgb} machine instruction.
7733 @item v4hi __builtin_ia32_pavgw (v4hi, v4hi)
7734 Generates the @code{pavgw} machine instruction.
7735 @item v4hi __builtin_ia32_psadbw (v8qi, v8qi)
7736 Generates the @code{psadbw} machine instruction.
7738 @item v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
7739 Generates the @code{pmaxub} machine instruction.
7740 @item v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
7741 Generates the @code{pmaxsw} machine instruction.
7742 @item v8qi __builtin_ia32_pminub (v8qi, v8qi)
7743 Generates the @code{pminub} machine instruction.
7744 @item v4hi __builtin_ia32_pminsw (v4hi, v4hi)
7745 Generates the @code{pminsw} machine instruction.
7747 @item int __builtin_ia32_pextrw (v4hi, int)
7748 Generates the @code{pextrw} machine instruction.
7749 @item v4hi __builtin_ia32_pinsrw (v4hi, int, int)
7750 Generates the @code{pinsrw} machine instruction.
7752 @item int __builtin_ia32_pmovmskb (v8qi)
7753 Generates the @code{pmovmskb} machine instruction.
7754 @item void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
7755 Generates the @code{maskmovq} machine instruction.
7756 @item void __builtin_ia32_movntq (di *, di)
7757 Generates the @code{movntq} machine instruction.
7758 @item void __builtin_ia32_sfence (void)
7759 Generates the @code{sfence} machine instruction.
7760 @item void __builtin_ia32_prefetch (char *, int selector)
7761 Generates a prefetch machine instruction, depending on the value of
7762 selector. If @code{selector} is 0, it generates @code{prefetchnta}; for
7763 a value of 1, it generates @code{prefetcht0}; for a value of 2, it generates
7764 @code{prefetcht1}; and for a value of 3 it generates @code{prefetcht2}.
7768 The following built-in functions are available when @option{-msse} is used.
7771 @item int __builtin_ia32_comieq (v4sf, v4sf)
7772 Generates the @code{comiss} machine instruction and performs an equality
7773 comparison. The return value is the truth value of that comparison.
7774 @item int __builtin_ia32_comineq (v4sf, v4sf)
7775 Generates the @code{comiss} machine instruction and performs an inequality
7776 comparison. The return value is the truth value of that comparison.
7777 @item int __builtin_ia32_comilt (v4sf, v4sf)
7778 Generates the @code{comiss} machine instruction and performs a ``less than''
7779 comparison. The return value is the truth value of that comparison.
7780 @item int __builtin_ia32_comile (v4sf, v4sf)
7781 Generates the @code{comiss} machine instruction and performs a ``less or
7782 equal'' comparison. The return value is the truth value of that comparison.
7783 @item int __builtin_ia32_comigt (v4sf, v4sf)
7784 Generates the @code{comiss} machine instruction and performs a ``greater than''
7785 comparison. The return value is the truth value of that comparison.
7786 @item int __builtin_ia32_comige (v4sf, v4sf)
7787 Generates the @code{comiss} machine instruction and performs a ``greater or
7788 equal'' comparison. The return value is the truth value of that comparison.
7790 @item int __builtin_ia32_ucomieq (v4sf, v4sf)
7791 Generates the @code{ucomiss} machine instruction and performs an equality
7792 comparison. The return value is the truth value of that comparison.
7793 @item int __builtin_ia32_ucomineq (v4sf, v4sf)
7794 Generates the @code{ucomiss} machine instruction and performs an inequality
7795 comparison. The return value is the truth value of that comparison.
7796 @item int __builtin_ia32_ucomilt (v4sf, v4sf)
7797 Generates the @code{ucomiss} machine instruction and performs a ``less than''
7798 comparison. The return value is the truth value of that comparison.
7799 @item int __builtin_ia32_ucomile (v4sf, v4sf)
7800 Generates the @code{ucomiss} machine instruction and performs a ``less or
7801 equal'' comparison. The return value is the truth value of that comparison.
7802 @item int __builtin_ia32_ucomigt (v4sf, v4sf)
7803 Generates the @code{ucomiss} machine instruction and performs a ``greater than''
7804 comparison. The return value is the truth value of that comparison.
7805 @item int __builtin_ia32_ucomige (v4sf, v4sf)
7806 Generates the @code{ucomiss} machine instruction and performs a ``greater or
7807 equal'' comparison. The return value is the truth value of that comparison.
7809 @item v4sf __builtin_ia32_addps (v4sf, v4sf)
7810 Generates the @code{addps} machine instruction.
7811 @item v4sf __builtin_ia32_addss (v4sf, v4sf)
7812 Generates the @code{addss} machine instruction.
7813 @item v4sf __builtin_ia32_subps (v4sf, v4sf)
7814 Generates the @code{subps} machine instruction.
7815 @item v4sf __builtin_ia32_subss (v4sf, v4sf)
7816 Generates the @code{subss} machine instruction.
7817 @item v4sf __builtin_ia32_mulps (v4sf, v4sf)
7818 Generates the @code{mulps} machine instruction.
7819 @item v4sf __builtin_ia32_mulss (v4sf, v4sf)
7820 Generates the @code{mulss} machine instruction.
7821 @item v4sf __builtin_ia32_divps (v4sf, v4sf)
7822 Generates the @code{divps} machine instruction.
7823 @item v4sf __builtin_ia32_divss (v4sf, v4sf)
7824 Generates the @code{divss} machine instruction.
7826 @item v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
7827 Generates the @code{cmpeqps} machine instruction.
7828 @item v4si __builtin_ia32_cmplts (v4sf, v4sf)
7829 Generates the @code{cmpltps} machine instruction.
7830 @item v4si __builtin_ia32_cmpleps (v4sf, v4sf)
7831 Generates the @code{cmpleps} machine instruction.
7832 @item v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
7833 Generates the @code{cmpgtps} machine instruction.
7834 @item v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
7835 Generates the @code{cmpgeps} machine instruction.
7836 @item v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
7837 Generates the @code{cmpunodps} machine instruction.
7838 @item v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
7839 Generates the @code{cmpeqps} machine instruction.
7840 @item v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
7841 Generates the @code{cmpltps} machine instruction.
7842 @item v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
7843 Generates the @code{cmpleps} machine instruction.
7844 @item v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
7845 Generates the @code{cmpgtps} machine instruction.
7846 @item v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
7847 Generates the @code{cmpgeps} machine instruction.
7848 @item v4si __builtin_ia32_cmpordps (v4sf, v4sf)
7849 Generates the @code{cmpunodps} machine instruction.
7851 @item v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
7852 Generates the @code{cmpeqss} machine instruction.
7853 @item v4si __builtin_ia32_cmpltss (v4sf, v4sf)
7854 Generates the @code{cmpltss} machine instruction.
7855 @item v4si __builtin_ia32_cmpless (v4sf, v4sf)
7856 Generates the @code{cmpless} machine instruction.
7857 @item v4si __builtin_ia32_cmpgtss (v4sf, v4sf)
7858 Generates the @code{cmpgtss} machine instruction.
7859 @item v4si __builtin_ia32_cmpgess (v4sf, v4sf)
7860 Generates the @code{cmpgess} machine instruction.
7861 @item v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
7862 Generates the @code{cmpunodss} machine instruction.
7863 @item v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
7864 Generates the @code{cmpeqss} machine instruction.
7865 @item v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
7866 Generates the @code{cmpltss} machine instruction.
7867 @item v4si __builtin_ia32_cmpnless (v4sf, v4sf)
7868 Generates the @code{cmpless} machine instruction.
7869 @item v4si __builtin_ia32_cmpngtss (v4sf, v4sf)
7870 Generates the @code{cmpgtss} machine instruction.
7871 @item v4si __builtin_ia32_cmpngess (v4sf, v4sf)
7872 Generates the @code{cmpgess} machine instruction.
7873 @item v4si __builtin_ia32_cmpordss (v4sf, v4sf)
7874 Generates the @code{cmpunodss} machine instruction.
7876 @item v4sf __builtin_ia32_maxps (v4sf, v4sf)
7877 Generates the @code{maxps} machine instruction.
7878 @item v4sf __builtin_ia32_maxsss (v4sf, v4sf)
7879 Generates the @code{maxss} machine instruction.
7880 @item v4sf __builtin_ia32_minps (v4sf, v4sf)
7881 Generates the @code{minps} machine instruction.
7882 @item v4sf __builtin_ia32_minsss (v4sf, v4sf)
7883 Generates the @code{minss} machine instruction.
7885 @item ti __builtin_ia32_andps (ti, ti)
7886 Generates the @code{andps} machine instruction.
7887 @item ti __builtin_ia32_andnps (ti, ti)
7888 Generates the @code{andnps} machine instruction.
7889 @item ti __builtin_ia32_orps (ti, ti)
7890 Generates the @code{orps} machine instruction.
7891 @item ti __builtin_ia32_xorps (ti, ti)
7892 Generates the @code{xorps} machine instruction.
7894 @item v4sf __builtin_ia32_movps (v4sf, v4sf)
7895 Generates the @code{movps} machine instruction.
7896 @item v4sf __builtin_ia32_movhlps (v4sf, v4sf)
7897 Generates the @code{movhlps} machine instruction.
7898 @item v4sf __builtin_ia32_movlhps (v4sf, v4sf)
7899 Generates the @code{movlhps} machine instruction.
7900 @item v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
7901 Generates the @code{unpckhps} machine instruction.
7902 @item v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
7903 Generates the @code{unpcklps} machine instruction.
7905 @item v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
7906 Generates the @code{cvtpi2ps} machine instruction.
7907 @item v2si __builtin_ia32_cvtps2pi (v4sf)
7908 Generates the @code{cvtps2pi} machine instruction.
7909 @item v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
7910 Generates the @code{cvtsi2ss} machine instruction.
7911 @item int __builtin_ia32_cvtss2si (v4sf)
7912 Generates the @code{cvtsi2ss} machine instruction.
7913 @item v2si __builtin_ia32_cvttps2pi (v4sf)
7914 Generates the @code{cvttps2pi} machine instruction.
7915 @item int __builtin_ia32_cvttss2si (v4sf)
7916 Generates the @code{cvttsi2ss} machine instruction.
7918 @item v4sf __builtin_ia32_rcpps (v4sf)
7919 Generates the @code{rcpps} machine instruction.
7920 @item v4sf __builtin_ia32_rsqrtps (v4sf)
7921 Generates the @code{rsqrtps} machine instruction.
7922 @item v4sf __builtin_ia32_sqrtps (v4sf)
7923 Generates the @code{sqrtps} machine instruction.
7924 @item v4sf __builtin_ia32_rcpss (v4sf)
7925 Generates the @code{rcpss} machine instruction.
7926 @item v4sf __builtin_ia32_rsqrtss (v4sf)
7927 Generates the @code{rsqrtss} machine instruction.
7928 @item v4sf __builtin_ia32_sqrtss (v4sf)
7929 Generates the @code{sqrtss} machine instruction.
7931 @item v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
7932 Generates the @code{shufps} machine instruction.
7934 @item v4sf __builtin_ia32_loadaps (float *)
7935 Generates the @code{movaps} machine instruction as a load from memory.
7936 @item void __builtin_ia32_storeaps (float *, v4sf)
7937 Generates the @code{movaps} machine instruction as a store to memory.
7938 @item v4sf __builtin_ia32_loadups (float *)
7939 Generates the @code{movups} machine instruction as a load from memory.
7940 @item void __builtin_ia32_storeups (float *, v4sf)
7941 Generates the @code{movups} machine instruction as a store to memory.
7942 @item v4sf __builtin_ia32_loadsss (float *)
7943 Generates the @code{movss} machine instruction as a load from memory.
7944 @item void __builtin_ia32_storess (float *, v4sf)
7945 Generates the @code{movss} machine instruction as a store to memory.
7947 @item v4sf __builtin_ia32_loadhps (v4sf, v2si *)
7948 Generates the @code{movhps} machine instruction as a load from memory.
7949 @item v4sf __builtin_ia32_loadlps (v4sf, v2si *)
7950 Generates the @code{movlps} machine instruction as a load from memory
7951 @item void __builtin_ia32_storehps (v4sf, v2si *)
7952 Generates the @code{movhps} machine instruction as a store to memory.
7953 @item void __builtin_ia32_storelps (v4sf, v2si *)
7954 Generates the @code{movlps} machine instruction as a store to memory.
7956 @item void __builtin_ia32_movntps (float *, v4sf)
7957 Generates the @code{movntps} machine instruction.
7958 @item int __builtin_ia32_movmskps (v4sf)
7959 Generates the @code{movntps} machine instruction.
7961 @item void __builtin_ia32_storeps1 (float *, v4sf)
7962 Generates the @code{movaps} machine instruction as a store to memory.
7963 Before storing, the value is modified with a @code{shufps} instruction
7964 so that the lowest of the four floating point elements is replicated
7965 across the entire vector that is stored.
7966 @item void __builtin_ia32_storerps (float *, v4sf)
7967 Generates the @code{movaps} machine instruction as a store to memory.
7968 Before storing, the value is modified with a @code{shufps} instruction
7969 so that the order of the four floating point elements in the vector is
7971 @item v4sf __builtin_ia32_loadps1 (float *)
7972 Generates a @code{movss} machine instruction to load a floating point
7973 value from memory, and a @code{shufps} instruction to replicate the
7974 loaded value across all four elements of the result vector.
7975 @item v4sf __builtin_ia32_loadrps (float *)
7976 Generates a @code{movaps} machine instruction to load a vector from
7977 memory, and a @code{shufps} instruction to reverse the order of the
7978 four floating point elements in the result vector.
7979 @item v4sf __builtin_ia32_setps (float, float, float, float)
7980 Constructs a vector from four single floating point values. The return
7981 value is equal to the value that would result from storing the four
7982 arguments into consecutive memory locations and then executing a
7983 @code{movaps} to load the vector from memory.
7984 @item v4sf __builtin_ia32_setps1 (float)
7985 Constructs a vector from a single floating point value by replicating
7986 it across all four elements of the result vector.
7990 @itemx -mno-push-args
7992 @opindex mno-push-args
7993 Use PUSH operations to store outgoing parameters. This method is shorter
7994 and usually equally fast as method using SUB/MOV operations and is enabled
7995 by default. In some cases disabling it may improve performance because of
7996 improved scheduling and reduced dependencies.
7998 @item -maccumulate-outgoing-args
7999 @opindex maccumulate-outgoing-args
8000 If enabled, the maximum amount of space required for outgoing arguments will be
8001 computed in the function prologue. This is faster on most modern CPUs
8002 because of reduced dependencies, improved scheduling and reduced stack usage
8003 when preferred stack boundary is not equal to 2. The drawback is a notable
8004 increase in code size. This switch implies @option{-mno-push-args}.
8008 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8009 on thread-safe exception handling must compile and link all code with the
8010 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8011 @option{-D_MT}; when linking, it links in a special thread helper library
8012 @option{-lmingwthrd} which cleans up per thread exception handling data.
8014 @item -mno-align-stringops
8015 @opindex mno-align-stringops
8016 Do not align destination of inlined string operations. This switch reduces
8017 code size and improves performance in case the destination is already aligned,
8018 but gcc don't know about it.
8020 @item -minline-all-stringops
8021 @opindex minline-all-stringops
8022 By default GCC inlines string operations only when destination is known to be
8023 aligned at least to 4 byte boundary. This enables more inlining, increase code
8024 size, but may improve performance of code that depends on fast memcpy, strlen
8025 and memset for short lengths.
8027 @item -momit-leaf-frame-pointer
8028 @opindex momit-leaf-frame-pointer
8029 Don't keep the frame pointer in a register for leaf functions. This
8030 avoids the instructions to save, set up and restore frame pointers and
8031 makes an extra register available in leaf functions. The option
8032 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8033 which might make debugging harder.
8036 These @samp{-m} switches are supported in addition to the above
8037 on AMD x86-64 processors in 64-bit environments.
8044 Generate code for a 32-bit or 64-bit environment.
8045 The 32-bit environment sets int, long and pointer to 32 bits and
8046 generates code that runs on any i386 system.
8047 The 64-bit environment sets int to 32 bits and long and pointer
8048 to 64 bits and generates code for AMD's x86-64 architecture.
8051 @opindex no-red-zone
8052 Do not use a so called red zone for x86-64 code. The red zone is mandated
8053 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8054 stack pointer that will not be modified by signal or interrupt handlers
8055 and therefore can be used for temporary data without adjusting the stack
8056 pointer. The flag @option{-mno-red-zone} disables this red zone.
8060 @subsection HPPA Options
8061 @cindex HPPA Options
8063 These @samp{-m} options are defined for the HPPA family of computers:
8066 @item -march=@var{architecture-type}
8068 Generate code for the specified architecture. The choices for
8069 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8070 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8071 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8072 architecture option for your machine. Code compiled for lower numbered
8073 architectures will run on higher numbered architectures, but not the
8076 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8077 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8081 @itemx -mpa-risc-1-1
8082 @itemx -mpa-risc-2-0
8083 @opindex mpa-risc-1-0
8084 @opindex mpa-risc-1-1
8085 @opindex mpa-risc-2-0
8086 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8089 @opindex mbig-switch
8090 Generate code suitable for big switch tables. Use this option only if
8091 the assembler/linker complain about out of range branches within a switch
8094 @item -mjump-in-delay
8095 @opindex mjump-in-delay
8096 Fill delay slots of function calls with unconditional jump instructions
8097 by modifying the return pointer for the function call to be the target
8098 of the conditional jump.
8100 @item -mdisable-fpregs
8101 @opindex mdisable-fpregs
8102 Prevent floating point registers from being used in any manner. This is
8103 necessary for compiling kernels which perform lazy context switching of
8104 floating point registers. If you use this option and attempt to perform
8105 floating point operations, the compiler will abort.
8107 @item -mdisable-indexing
8108 @opindex mdisable-indexing
8109 Prevent the compiler from using indexing address modes. This avoids some
8110 rather obscure problems when compiling MIG generated code under MACH@.
8112 @item -mno-space-regs
8113 @opindex mno-space-regs
8114 Generate code that assumes the target has no space registers. This allows
8115 GCC to generate faster indirect calls and use unscaled index address modes.
8117 Such code is suitable for level 0 PA systems and kernels.
8119 @item -mfast-indirect-calls
8120 @opindex mfast-indirect-calls
8121 Generate code that assumes calls never cross space boundaries. This
8122 allows GCC to emit code which performs faster indirect calls.
8124 This option will not work in the presence of shared libraries or nested
8127 @item -mlong-load-store
8128 @opindex mlong-load-store
8129 Generate 3-instruction load and store sequences as sometimes required by
8130 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8133 @item -mportable-runtime
8134 @opindex mportable-runtime
8135 Use the portable calling conventions proposed by HP for ELF systems.
8139 Enable the use of assembler directives only GAS understands.
8141 @item -mschedule=@var{cpu-type}
8143 Schedule code according to the constraints for the machine type
8144 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8145 @samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to
8146 @file{/usr/lib/sched.models} on an HP-UX system to determine the
8147 proper scheduling option for your machine.
8150 @opindex mlinker-opt
8151 Enable the optimization pass in the HPUX linker. Note this makes symbolic
8152 debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers
8153 in which they give bogus error messages when linking some programs.
8156 @opindex msoft-float
8157 Generate output containing library calls for floating point.
8158 @strong{Warning:} the requisite libraries are not available for all HPPA
8159 targets. Normally the facilities of the machine's usual C compiler are
8160 used, but this cannot be done directly in cross-compilation. You must make
8161 your own arrangements to provide suitable library functions for
8162 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8163 does provide software floating point support.
8165 @option{-msoft-float} changes the calling convention in the output file;
8166 therefore, it is only useful if you compile @emph{all} of a program with
8167 this option. In particular, you need to compile @file{libgcc.a}, the
8168 library that comes with GCC, with @option{-msoft-float} in order for
8172 @node Intel 960 Options
8173 @subsection Intel 960 Options
8175 These @samp{-m} options are defined for the Intel 960 implementations:
8178 @item -m@var{cpu-type}
8186 Assume the defaults for the machine type @var{cpu-type} for some of
8187 the other options, including instruction scheduling, floating point
8188 support, and addressing modes. The choices for @var{cpu-type} are
8189 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8190 @samp{sa}, and @samp{sb}.
8197 @opindex msoft-float
8198 The @option{-mnumerics} option indicates that the processor does support
8199 floating-point instructions. The @option{-msoft-float} option indicates
8200 that floating-point support should not be assumed.
8202 @item -mleaf-procedures
8203 @itemx -mno-leaf-procedures
8204 @opindex mleaf-procedures
8205 @opindex mno-leaf-procedures
8206 Do (or do not) attempt to alter leaf procedures to be callable with the
8207 @code{bal} instruction as well as @code{call}. This will result in more
8208 efficient code for explicit calls when the @code{bal} instruction can be
8209 substituted by the assembler or linker, but less efficient code in other
8210 cases, such as calls via function pointers, or using a linker that doesn't
8211 support this optimization.
8214 @itemx -mno-tail-call
8216 @opindex mno-tail-call
8217 Do (or do not) make additional attempts (beyond those of the
8218 machine-independent portions of the compiler) to optimize tail-recursive
8219 calls into branches. You may not want to do this because the detection of
8220 cases where this is not valid is not totally complete. The default is
8221 @option{-mno-tail-call}.
8223 @item -mcomplex-addr
8224 @itemx -mno-complex-addr
8225 @opindex mcomplex-addr
8226 @opindex mno-complex-addr
8227 Assume (or do not assume) that the use of a complex addressing mode is a
8228 win on this implementation of the i960. Complex addressing modes may not
8229 be worthwhile on the K-series, but they definitely are on the C-series.
8230 The default is currently @option{-mcomplex-addr} for all processors except
8234 @itemx -mno-code-align
8235 @opindex mcode-align
8236 @opindex mno-code-align
8237 Align code to 8-byte boundaries for faster fetching (or don't bother).
8238 Currently turned on by default for C-series implementations only.
8241 @item -mclean-linkage
8242 @itemx -mno-clean-linkage
8243 @opindex mclean-linkage
8244 @opindex mno-clean-linkage
8245 These options are not fully implemented.
8249 @itemx -mic2.0-compat
8250 @itemx -mic3.0-compat
8252 @opindex mic2.0-compat
8253 @opindex mic3.0-compat
8254 Enable compatibility with iC960 v2.0 or v3.0.
8258 @opindex masm-compat
8260 Enable compatibility with the iC960 assembler.
8262 @item -mstrict-align
8263 @itemx -mno-strict-align
8264 @opindex mstrict-align
8265 @opindex mno-strict-align
8266 Do not permit (do permit) unaligned accesses.
8270 Enable structure-alignment compatibility with Intel's gcc release version
8271 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8273 @item -mlong-double-64
8274 @opindex mlong-double-64
8275 Implement type @samp{long double} as 64-bit floating point numbers.
8276 Without the option @samp{long double} is implemented by 80-bit
8277 floating point numbers. The only reason we have it because there is
8278 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8279 is only useful for people using soft-float targets. Otherwise, we
8280 should recommend against use of it.
8284 @node DEC Alpha Options
8285 @subsection DEC Alpha Options
8287 These @samp{-m} options are defined for the DEC Alpha implementations:
8290 @item -mno-soft-float
8292 @opindex mno-soft-float
8293 @opindex msoft-float
8294 Use (do not use) the hardware floating-point instructions for
8295 floating-point operations. When @option{-msoft-float} is specified,
8296 functions in @file{libgcc.a} will be used to perform floating-point
8297 operations. Unless they are replaced by routines that emulate the
8298 floating-point operations, or compiled in such a way as to call such
8299 emulations routines, these routines will issue floating-point
8300 operations. If you are compiling for an Alpha without floating-point
8301 operations, you must ensure that the library is built so as not to call
8304 Note that Alpha implementations without floating-point operations are
8305 required to have floating-point registers.
8310 @opindex mno-fp-regs
8311 Generate code that uses (does not use) the floating-point register set.
8312 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8313 register set is not used, floating point operands are passed in integer
8314 registers as if they were integers and floating-point results are passed
8315 in $0 instead of $f0. This is a non-standard calling sequence, so any
8316 function with a floating-point argument or return value called by code
8317 compiled with @option{-mno-fp-regs} must also be compiled with that
8320 A typical use of this option is building a kernel that does not use,
8321 and hence need not save and restore, any floating-point registers.
8325 The Alpha architecture implements floating-point hardware optimized for
8326 maximum performance. It is mostly compliant with the IEEE floating
8327 point standard. However, for full compliance, software assistance is
8328 required. This option generates code fully IEEE compliant code
8329 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8330 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8331 defined during compilation. The resulting code is less efficient but is
8332 able to correctly support denormalized numbers and exceptional IEEE
8333 values such as not-a-number and plus/minus infinity. Other Alpha
8334 compilers call this option @option{-ieee_with_no_inexact}.
8336 @item -mieee-with-inexact
8337 @opindex mieee-with-inexact
8338 This is like @option{-mieee} except the generated code also maintains
8339 the IEEE @var{inexact-flag}. Turning on this option causes the
8340 generated code to implement fully-compliant IEEE math. In addition to
8341 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8342 macro. On some Alpha implementations the resulting code may execute
8343 significantly slower than the code generated by default. Since there is
8344 very little code that depends on the @var{inexact-flag}, you should
8345 normally not specify this option. Other Alpha compilers call this
8346 option @option{-ieee_with_inexact}.
8348 @item -mfp-trap-mode=@var{trap-mode}
8349 @opindex mfp-trap-mode
8350 This option controls what floating-point related traps are enabled.
8351 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8352 The trap mode can be set to one of four values:
8356 This is the default (normal) setting. The only traps that are enabled
8357 are the ones that cannot be disabled in software (e.g., division by zero
8361 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8365 Like @samp{su}, but the instructions are marked to be safe for software
8366 completion (see Alpha architecture manual for details).
8369 Like @samp{su}, but inexact traps are enabled as well.
8372 @item -mfp-rounding-mode=@var{rounding-mode}
8373 @opindex mfp-rounding-mode
8374 Selects the IEEE rounding mode. Other Alpha compilers call this option
8375 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8380 Normal IEEE rounding mode. Floating point numbers are rounded towards
8381 the nearest machine number or towards the even machine number in case
8385 Round towards minus infinity.
8388 Chopped rounding mode. Floating point numbers are rounded towards zero.
8391 Dynamic rounding mode. A field in the floating point control register
8392 (@var{fpcr}, see Alpha architecture reference manual) controls the
8393 rounding mode in effect. The C library initializes this register for
8394 rounding towards plus infinity. Thus, unless your program modifies the
8395 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8398 @item -mtrap-precision=@var{trap-precision}
8399 @opindex mtrap-precision
8400 In the Alpha architecture, floating point traps are imprecise. This
8401 means without software assistance it is impossible to recover from a
8402 floating trap and program execution normally needs to be terminated.
8403 GCC can generate code that can assist operating system trap handlers
8404 in determining the exact location that caused a floating point trap.
8405 Depending on the requirements of an application, different levels of
8406 precisions can be selected:
8410 Program precision. This option is the default and means a trap handler
8411 can only identify which program caused a floating point exception.
8414 Function precision. The trap handler can determine the function that
8415 caused a floating point exception.
8418 Instruction precision. The trap handler can determine the exact
8419 instruction that caused a floating point exception.
8422 Other Alpha compilers provide the equivalent options called
8423 @option{-scope_safe} and @option{-resumption_safe}.
8425 @item -mieee-conformant
8426 @opindex mieee-conformant
8427 This option marks the generated code as IEEE conformant. You must not
8428 use this option unless you also specify @option{-mtrap-precision=i} and either
8429 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8430 is to emit the line @samp{.eflag 48} in the function prologue of the
8431 generated assembly file. Under DEC Unix, this has the effect that
8432 IEEE-conformant math library routines will be linked in.
8434 @item -mbuild-constants
8435 @opindex mbuild-constants
8436 Normally GCC examines a 32- or 64-bit integer constant to
8437 see if it can construct it from smaller constants in two or three
8438 instructions. If it cannot, it will output the constant as a literal and
8439 generate code to load it from the data segment at runtime.
8441 Use this option to require GCC to construct @emph{all} integer constants
8442 using code, even if it takes more instructions (the maximum is six).
8444 You would typically use this option to build a shared library dynamic
8445 loader. Itself a shared library, it must relocate itself in memory
8446 before it can find the variables and constants in its own data segment.
8452 Select whether to generate code to be assembled by the vendor-supplied
8453 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8467 Indicate whether GCC should generate code to use the optional BWX,
8468 CIX, and MAX instruction sets. The default is to use the instruction sets
8469 supported by the CPU type specified via @option{-mcpu=} option or that
8470 of the CPU on which GCC was built if none was specified.
8472 @item -mcpu=@var{cpu_type}
8474 Set the instruction set, register set, and instruction scheduling
8475 parameters for machine type @var{cpu_type}. You can specify either the
8476 @samp{EV} style name or the corresponding chip number. GCC
8477 supports scheduling parameters for the EV4 and EV5 family of processors
8478 and will choose the default values for the instruction set from
8479 the processor you specify. If you do not specify a processor type,
8480 GCC will default to the processor on which the compiler was built.
8482 Supported values for @var{cpu_type} are
8487 Schedules as an EV4 and has no instruction set extensions.
8491 Schedules as an EV5 and has no instruction set extensions.
8495 Schedules as an EV5 and supports the BWX extension.
8500 Schedules as an EV5 and supports the BWX and MAX extensions.
8504 Schedules as an EV5 (until Digital releases the scheduling parameters
8505 for the EV6) and supports the BWX, CIX, and MAX extensions.
8508 @item -mmemory-latency=@var{time}
8509 @opindex mmemory-latency
8510 Sets the latency the scheduler should assume for typical memory
8511 references as seen by the application. This number is highly
8512 dependent on the memory access patterns used by the application
8513 and the size of the external cache on the machine.
8515 Valid options for @var{time} are
8519 A decimal number representing clock cycles.
8525 The compiler contains estimates of the number of clock cycles for
8526 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8527 (also called Dcache, Scache, and Bcache), as well as to main memory.
8528 Note that L3 is only valid for EV5.
8533 @node Clipper Options
8534 @subsection Clipper Options
8536 These @samp{-m} options are defined for the Clipper implementations:
8541 Produce code for a C300 Clipper processor. This is the default.
8545 Produce code for a C400 Clipper processor, i.e.@: use floating point
8549 @node H8/300 Options
8550 @subsection H8/300 Options
8552 These @samp{-m} options are defined for the H8/300 implementations:
8557 Shorten some address references at link time, when possible; uses the
8558 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8559 ld.info, Using ld}, for a fuller description.
8563 Generate code for the H8/300H@.
8567 Generate code for the H8/S@.
8571 Generate code for the H8/S2600. This switch must be used with @option{-ms}.
8575 Make @code{int} data 32 bits by default.
8579 On the H8/300H and H8/S, use the same alignment rules as for the H8/300.
8580 The default for the H8/300H and H8/S is to align longs and floats on 4
8582 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8583 This option has no effect on the H8/300.
8587 @subsection SH Options
8589 These @samp{-m} options are defined for the SH implementations:
8594 Generate code for the SH1.
8598 Generate code for the SH2.
8602 Generate code for the SH3.
8606 Generate code for the SH3e.
8610 Generate code for the SH4 without a floating-point unit.
8612 @item -m4-single-only
8613 @opindex m4-single-only
8614 Generate code for the SH4 with a floating-point unit that only
8615 supports single-precision arithmetic.
8619 Generate code for the SH4 assuming the floating-point unit is in
8620 single-precision mode by default.
8624 Generate code for the SH4.
8628 Compile code for the processor in big endian mode.
8632 Compile code for the processor in little endian mode.
8636 Align doubles at 64-bit boundaries. Note that this changes the calling
8637 conventions, and thus some functions from the standard C library will
8638 not work unless you recompile it first with @option{-mdalign}.
8642 Shorten some address references at link time, when possible; uses the
8643 linker option @option{-relax}.
8647 Use 32-bit offsets in @code{switch} tables. The default is to use
8652 Enable the use of the instruction @code{fmovd}.
8656 Comply with the calling conventions defined by Hitachi.
8660 Mark the @code{MAC} register as call-clobbered, even if
8661 @option{-mhitachi} is given.
8665 Increase IEEE-compliance of floating-point code.
8669 Dump instruction size and location in the assembly code.
8673 This option is deprecated. It pads structures to multiple of 4 bytes,
8674 which is incompatible with the SH ABI@.
8678 Optimize for space instead of speed. Implied by @option{-Os}.
8682 When generating position-independent code, emit function calls using
8683 the Global Offset Table instead of the Procedure Linkage Table.
8687 Generate a library function call to invalidate instruction cache
8688 entries, after fixing up a trampoline. This library function call
8689 doesn't assume it can write to the whole memory address space. This
8690 is the default when the target is @code{sh-*-linux*}.
8693 @node System V Options
8694 @subsection Options for System V
8696 These additional options are available on System V Release 4 for
8697 compatibility with other compilers on those systems:
8702 Create a shared object.
8703 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
8707 Identify the versions of each tool used by the compiler, in a
8708 @code{.ident} assembler directive in the output.
8712 Refrain from adding @code{.ident} directives to the output file (this is
8715 @item -YP,@var{dirs}
8717 Search the directories @var{dirs}, and no others, for libraries
8718 specified with @option{-l}.
8722 Look in the directory @var{dir} to find the M4 preprocessor.
8723 The assembler uses this option.
8724 @c This is supposed to go with a -Yd for predefined M4 macro files, but
8725 @c the generic assembler that comes with Solaris takes just -Ym.
8728 @node TMS320C3x/C4x Options
8729 @subsection TMS320C3x/C4x Options
8730 @cindex TMS320C3x/C4x Options
8732 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
8736 @item -mcpu=@var{cpu_type}
8738 Set the instruction set, register set, and instruction scheduling
8739 parameters for machine type @var{cpu_type}. Supported values for
8740 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
8741 @samp{c44}. The default is @samp{c40} to generate code for the
8746 @itemx -msmall-memory
8748 @opindex mbig-memory
8750 @opindex msmall-memory
8752 Generates code for the big or small memory model. The small memory
8753 model assumed that all data fits into one 64K word page. At run-time
8754 the data page (DP) register must be set to point to the 64K page
8755 containing the .bss and .data program sections. The big memory model is
8756 the default and requires reloading of the DP register for every direct
8763 Allow (disallow) allocation of general integer operands into the block
8770 Enable (disable) generation of code using decrement and branch,
8771 DBcond(D), instructions. This is enabled by default for the C4x. To be
8772 on the safe side, this is disabled for the C3x, since the maximum
8773 iteration count on the C3x is @math{2^23 + 1} (but who iterates loops more than
8774 @math{2^23} times on the C3x?). Note that GCC will try to reverse a loop so
8775 that it can utilise the decrement and branch instruction, but will give
8776 up if there is more than one memory reference in the loop. Thus a loop
8777 where the loop counter is decremented can generate slightly more
8778 efficient code, in cases where the RPTB instruction cannot be utilised.
8780 @item -mdp-isr-reload
8782 @opindex mdp-isr-reload
8784 Force the DP register to be saved on entry to an interrupt service
8785 routine (ISR), reloaded to point to the data section, and restored on
8786 exit from the ISR@. This should not be required unless someone has
8787 violated the small memory model by modifying the DP register, say within
8794 For the C3x use the 24-bit MPYI instruction for integer multiplies
8795 instead of a library call to guarantee 32-bit results. Note that if one
8796 of the operands is a constant, then the multiplication will be performed
8797 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
8798 then squaring operations are performed inline instead of a library call.
8801 @itemx -mno-fast-fix
8803 @opindex mno-fast-fix
8804 The C3x/C4x FIX instruction to convert a floating point value to an
8805 integer value chooses the nearest integer less than or equal to the
8806 floating point value rather than to the nearest integer. Thus if the
8807 floating point number is negative, the result will be incorrectly
8808 truncated an additional code is necessary to detect and correct this
8809 case. This option can be used to disable generation of the additional
8810 code required to correct the result.
8816 Enable (disable) generation of repeat block sequences using the RPTB
8817 instruction for zero overhead looping. The RPTB construct is only used
8818 for innermost loops that do not call functions or jump across the loop
8819 boundaries. There is no advantage having nested RPTB loops due to the
8820 overhead required to save and restore the RC, RS, and RE registers.
8821 This is enabled by default with @option{-O2}.
8823 @item -mrpts=@var{count}
8827 Enable (disable) the use of the single instruction repeat instruction
8828 RPTS@. If a repeat block contains a single instruction, and the loop
8829 count can be guaranteed to be less than the value @var{count}, GCC will
8830 emit a RPTS instruction instead of a RPTB@. If no value is specified,
8831 then a RPTS will be emitted even if the loop count cannot be determined
8832 at compile time. Note that the repeated instruction following RPTS does
8833 not have to be reloaded from memory each iteration, thus freeing up the
8834 CPU buses for operands. However, since interrupts are blocked by this
8835 instruction, it is disabled by default.
8837 @item -mloop-unsigned
8838 @itemx -mno-loop-unsigned
8839 @opindex mloop-unsigned
8840 @opindex mno-loop-unsigned
8841 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
8842 is @math{2^31 + 1} since these instructions test if the iteration count is
8843 negative to terminate the loop. If the iteration count is unsigned
8844 there is a possibility than the @math{2^31 + 1} maximum iteration count may be
8845 exceeded. This switch allows an unsigned iteration count.
8849 Try to emit an assembler syntax that the TI assembler (asm30) is happy
8850 with. This also enforces compatibility with the API employed by the TI
8851 C3x C compiler. For example, long doubles are passed as structures
8852 rather than in floating point registers.
8858 Generate code that uses registers (stack) for passing arguments to functions.
8859 By default, arguments are passed in registers where possible rather
8860 than by pushing arguments on to the stack.
8862 @item -mparallel-insns
8863 @itemx -mno-parallel-insns
8864 @opindex mparallel-insns
8865 @opindex mno-parallel-insns
8866 Allow the generation of parallel instructions. This is enabled by
8867 default with @option{-O2}.
8869 @item -mparallel-mpy
8870 @itemx -mno-parallel-mpy
8871 @opindex mparallel-mpy
8872 @opindex mno-parallel-mpy
8873 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
8874 provided @option{-mparallel-insns} is also specified. These instructions have
8875 tight register constraints which can pessimize the code generation
8881 @subsection V850 Options
8882 @cindex V850 Options
8884 These @samp{-m} options are defined for V850 implementations:
8888 @itemx -mno-long-calls
8889 @opindex mlong-calls
8890 @opindex mno-long-calls
8891 Treat all calls as being far away (near). If calls are assumed to be
8892 far away, the compiler will always load the functions address up into a
8893 register, and call indirect through the pointer.
8899 Do not optimize (do optimize) basic blocks that use the same index
8900 pointer 4 or more times to copy pointer into the @code{ep} register, and
8901 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
8902 option is on by default if you optimize.
8904 @item -mno-prolog-function
8905 @itemx -mprolog-function
8906 @opindex mno-prolog-function
8907 @opindex mprolog-function
8908 Do not use (do use) external functions to save and restore registers at
8909 the prolog and epilog of a function. The external functions are slower,
8910 but use less code space if more than one function saves the same number
8911 of registers. The @option{-mprolog-function} option is on by default if
8916 Try to make the code as small as possible. At present, this just turns
8917 on the @option{-mep} and @option{-mprolog-function} options.
8921 Put static or global variables whose size is @var{n} bytes or less into
8922 the tiny data area that register @code{ep} points to. The tiny data
8923 area can hold up to 256 bytes in total (128 bytes for byte references).
8927 Put static or global variables whose size is @var{n} bytes or less into
8928 the small data area that register @code{gp} points to. The small data
8929 area can hold up to 64 kilobytes.
8933 Put static or global variables whose size is @var{n} bytes or less into
8934 the first 32 kilobytes of memory.
8938 Specify that the target processor is the V850.
8941 @opindex mbig-switch
8942 Generate code suitable for big switch tables. Use this option only if
8943 the assembler/linker complain about out of range branches within a switch
8948 @subsection ARC Options
8951 These options are defined for ARC implementations:
8956 Compile code for little endian mode. This is the default.
8960 Compile code for big endian mode.
8963 @opindex mmangle-cpu
8964 Prepend the name of the cpu to all public symbol names.
8965 In multiple-processor systems, there are many ARC variants with different
8966 instruction and register set characteristics. This flag prevents code
8967 compiled for one cpu to be linked with code compiled for another.
8968 No facility exists for handling variants that are ``almost identical''.
8969 This is an all or nothing option.
8971 @item -mcpu=@var{cpu}
8973 Compile code for ARC variant @var{cpu}.
8974 Which variants are supported depend on the configuration.
8975 All variants support @option{-mcpu=base}, this is the default.
8977 @item -mtext=@var{text-section}
8978 @itemx -mdata=@var{data-section}
8979 @itemx -mrodata=@var{readonly-data-section}
8983 Put functions, data, and readonly data in @var{text-section},
8984 @var{data-section}, and @var{readonly-data-section} respectively
8985 by default. This can be overridden with the @code{section} attribute.
8986 @xref{Variable Attributes}.
8991 @subsection NS32K Options
8992 @cindex NS32K options
8994 These are the @samp{-m} options defined for the 32000 series. The default
8995 values for these options depends on which style of 32000 was selected when
8996 the compiler was configured; the defaults for the most common choices are
9004 Generate output for a 32032. This is the default
9005 when the compiler is configured for 32032 and 32016 based systems.
9011 Generate output for a 32332. This is the default
9012 when the compiler is configured for 32332-based systems.
9018 Generate output for a 32532. This is the default
9019 when the compiler is configured for 32532-based systems.
9023 Generate output containing 32081 instructions for floating point.
9024 This is the default for all systems.
9028 Generate output containing 32381 instructions for floating point. This
9029 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9030 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9034 Try and generate multiply-add floating point instructions @code{polyF}
9035 and @code{dotF}. This option is only available if the @option{-m32381}
9036 option is in effect. Using these instructions requires changes to
9037 register allocation which generally has a negative impact on
9038 performance. This option should only be enabled when compiling code
9039 particularly likely to make heavy use of multiply-add instructions.
9042 @opindex mnomulti-add
9043 Do not try and generate multiply-add floating point instructions
9044 @code{polyF} and @code{dotF}. This is the default on all platforms.
9047 @opindex msoft-float
9048 Generate output containing library calls for floating point.
9049 @strong{Warning:} the requisite libraries may not be available.
9052 @opindex mnobitfield
9053 Do not use the bit-field instructions. On some machines it is faster to
9054 use shifting and masking operations. This is the default for the pc532.
9058 Do use the bit-field instructions. This is the default for all platforms
9063 Use a different function-calling convention, in which functions
9064 that take a fixed number of arguments return pop their
9065 arguments on return with the @code{ret} instruction.
9067 This calling convention is incompatible with the one normally
9068 used on Unix, so you cannot use it if you need to call libraries
9069 compiled with the Unix compiler.
9071 Also, you must provide function prototypes for all functions that
9072 take variable numbers of arguments (including @code{printf});
9073 otherwise incorrect code will be generated for calls to those
9076 In addition, seriously incorrect code will result if you call a
9077 function with too many arguments. (Normally, extra arguments are
9078 harmlessly ignored.)
9080 This option takes its name from the 680x0 @code{rtd} instruction.
9085 Use a different function-calling convention where the first two arguments
9086 are passed in registers.
9088 This calling convention is incompatible with the one normally
9089 used on Unix, so you cannot use it if you need to call libraries
9090 compiled with the Unix compiler.
9093 @opindex mnoregparam
9094 Do not pass any arguments in registers. This is the default for all
9099 It is OK to use the sb as an index register which is always loaded with
9100 zero. This is the default for the pc532-netbsd target.
9104 The sb register is not available for use or has not been initialized to
9105 zero by the run time system. This is the default for all targets except
9106 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9107 @option{-fpic} is set.
9111 Many ns32000 series addressing modes use displacements of up to 512MB@.
9112 If an address is above 512MB then displacements from zero can not be used.
9113 This option causes code to be generated which can be loaded above 512MB@.
9114 This may be useful for operating systems or ROM code.
9118 Assume code will be loaded in the first 512MB of virtual address space.
9119 This is the default for all platforms.
9125 @subsection AVR Options
9128 These options are defined for AVR implementations:
9131 @item -mmcu=@var{mcu}
9133 Specify ATMEL AVR instruction set or MCU type.
9135 Instruction set avr1 is for the minimal AVR core, not supported by the C
9136 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9137 attiny11, attiny12, attiny15, attiny28).
9139 Instruction set avr2 (default) is for the classic AVR core with up to
9140 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9141 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9142 at90c8534, at90s8535).
9144 Instruction set avr3 is for the classic AVR core with up to 128K program
9145 memory space (MCU types: atmega103, atmega603).
9147 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9148 memory space (MCU types: atmega83, atmega85).
9150 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9151 memory space (MCU types: atmega161, atmega163, atmega32, at94k).
9155 Output instruction sizes to the asm file.
9157 @item -minit-stack=@var{N}
9158 @opindex minit-stack
9159 Specify the initial stack address, which may be a symbol or numeric value,
9160 @samp{__stack} is the default.
9162 @item -mno-interrupts
9163 @opindex mno-interrupts
9164 Generated code is not compatible with hardware interrupts.
9165 Code size will be smaller.
9167 @item -mcall-prologues
9168 @opindex mcall-prologues
9169 Functions prologues/epilogues expanded as call to appropriate
9170 subroutines. Code size will be smaller.
9172 @item -mno-tablejump
9173 @opindex mno-tablejump
9174 Do not generate tablejump insns which sometimes increase code size.
9177 @opindex mtiny-stack
9178 Change only the low 8 bits of the stack pointer.
9182 @subsection MCore Options
9183 @cindex MCore options
9185 These are the @samp{-m} options defined for the Motorola M*Core
9195 @opindex mno-hardlit
9196 Inline constants into the code stream if it can be done in two
9197 instructions or less.
9205 Use the divide instruction. (Enabled by default).
9207 @item -mrelax-immediate
9208 @itemx -mrelax-immediate
9209 @itemx -mno-relax-immediate
9210 @opindex mrelax-immediate
9211 @opindex mrelax-immediate
9212 @opindex mno-relax-immediate
9213 Allow arbitrary sized immediates in bit operations.
9215 @item -mwide-bitfields
9216 @itemx -mwide-bitfields
9217 @itemx -mno-wide-bitfields
9218 @opindex mwide-bitfields
9219 @opindex mwide-bitfields
9220 @opindex mno-wide-bitfields
9221 Always treat bit-fields as int-sized.
9223 @item -m4byte-functions
9224 @itemx -m4byte-functions
9225 @itemx -mno-4byte-functions
9226 @opindex m4byte-functions
9227 @opindex m4byte-functions
9228 @opindex mno-4byte-functions
9229 Force all functions to be aligned to a four byte boundary.
9231 @item -mcallgraph-data
9232 @itemx -mcallgraph-data
9233 @itemx -mno-callgraph-data
9234 @opindex mcallgraph-data
9235 @opindex mcallgraph-data
9236 @opindex mno-callgraph-data
9237 Emit callgraph information.
9241 @itemx -mno-slow-bytes
9242 @opindex mslow-bytes
9243 @opindex mslow-bytes
9244 @opindex mno-slow-bytes
9245 Prefer word access when reading byte quantities.
9247 @item -mlittle-endian
9248 @itemx -mlittle-endian
9250 @opindex mlittle-endian
9251 @opindex mlittle-endian
9252 @opindex mbig-endian
9253 Generate code for a little endian target.
9261 Generate code for the 210 processor.
9265 @subsection IA-64 Options
9266 @cindex IA-64 Options
9268 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9272 @opindex mbig-endian
9273 Generate code for a big endian target. This is the default for HPUX@.
9275 @item -mlittle-endian
9276 @opindex mlittle-endian
9277 Generate code for a little endian target. This is the default for AIX5
9284 Generate (or don't) code for the GNU assembler. This is the default.
9285 @c Also, this is the default if the configure option @option{--with-gnu-as}
9292 Generate (or don't) code for the GNU linker. This is the default.
9293 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9298 Generate code that does not use a global pointer register. The result
9299 is not position independent code, and violates the IA-64 ABI@.
9301 @item -mvolatile-asm-stop
9302 @itemx -mno-volatile-asm-stop
9303 @opindex mvolatile-asm-stop
9304 @opindex mno-volatile-asm-stop
9305 Generate (or don't) a stop bit immediately before and after volatile asm
9310 Generate code that works around Itanium B step errata.
9312 @item -mregister-names
9313 @itemx -mno-register-names
9314 @opindex mregister-names
9315 @opindex mno-register-names
9316 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9317 the stacked registers. This may make assembler output more readable.
9323 Disable (or enable) optimizations that use the small data section. This may
9324 be useful for working around optimizer bugs.
9327 @opindex mconstant-gp
9328 Generate code that uses a single constant global pointer value. This is
9329 useful when compiling kernel code.
9333 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9334 This is useful when compiling firmware code.
9336 @item -minline-divide-min-latency
9337 @opindex minline-divide-min-latency
9338 Generate code for inline divides using the minimum latency algorithm.
9340 @item -minline-divide-max-throughput
9341 @opindex minline-divide-max-throughput
9342 Generate code for inline divides using the maximum throughput algorithm.
9344 @item -mno-dwarf2-asm
9346 @opindex mno-dwarf2-asm
9347 @opindex mdwarf2-asm
9348 Don't (or do) generate assembler code for the DWARF2 line number debugging
9349 info. This may be useful when not using the GNU assembler.
9351 @item -mfixed-range=@var{register-range}
9352 @opindex mfixed-range
9353 Generate code treating the given register range as fixed registers.
9354 A fixed register is one that the register allocator can not use. This is
9355 useful when compiling kernel code. A register range is specified as
9356 two registers separated by a dash. Multiple register ranges can be
9357 specified separated by a comma.
9361 @subsection D30V Options
9362 @cindex D30V Options
9364 These @samp{-m} options are defined for D30V implementations:
9369 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
9370 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
9371 memory, which starts at location @code{0x80000000}.
9375 Same as the @option{-mextmem} switch.
9379 Link the @samp{.text} section into onchip text memory, which starts at
9380 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
9381 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
9382 into onchip data memory, which starts at location @code{0x20000000}.
9384 @item -mno-asm-optimize
9385 @itemx -masm-optimize
9386 @opindex mno-asm-optimize
9387 @opindex masm-optimize
9388 Disable (enable) passing @option{-O} to the assembler when optimizing.
9389 The assembler uses the @option{-O} option to automatically parallelize
9390 adjacent short instructions where possible.
9392 @item -mbranch-cost=@var{n}
9393 @opindex mbranch-cost
9394 Increase the internal costs of branches to @var{n}. Higher costs means
9395 that the compiler will issue more instructions to avoid doing a branch.
9398 @item -mcond-exec=@var{n}
9400 Specify the maximum number of conditionally executed instructions that
9401 replace a branch. The default is 4.
9404 @node S/390 and zSeries Options
9405 @subsection S/390 and zSeries Options
9406 @cindex S/390 and zSeries Options
9408 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
9413 @opindex mhard-float
9414 @opindex msoft-float
9415 Use (do not use) the hardware floating-point instructions and registers
9416 for floating-point operations. When @option{-msoft-float} is specified,
9417 functions in @file{libgcc.a} will be used to perform floating-point
9418 operations. When @option{-mhard-float} is specified, the compiler
9419 generates IEEE floating-point instructions. This is the default.
9422 @itemx -mno-backchain
9424 @opindex mno-backchain
9425 Generate (or do not generate) code which maintains an explicit
9426 backchain within the stack frame that points to the caller's frame.
9427 This is currently needed to allow debugging. The default is to
9428 generate the backchain.
9431 @itemx -mno-small-exec
9432 @opindex msmall-exec
9433 @opindex mno-small-exec
9434 Generate (or do not generate) code using the @code{bras} instruction
9435 to do subroutine calls.
9436 This only works reliably if the total executable size does not
9437 exceed 64k. The default is to use the @code{basr} instruction instead,
9438 which does not have this limitation.
9444 When @option{-m31} is specified, generate code compliant to the
9445 Linux for S/390 ABI@. When @option{-m64} is specified, generate
9446 code compliant to the Linux for zSeries ABI@. This allows GCC in
9447 particular to generate 64-bit instructions. For the @samp{s390}
9448 targets, the default is @option{-m31}, while the @samp{s390x}
9449 targets default to @option{-m64}.
9455 Generate (or do not generate) code using the @code{mvcle} instruction
9456 to perform block moves. When @option{-mno-mvcle} is specifed,
9457 use a @code{mvc} loop instead. This is the default.
9463 Print (or do not print) additional debug information when compiling.
9464 The default is to not print debug information.
9469 @subsection CRIS Options
9470 @cindex CRIS Options
9472 These options are defined specifically for the CRIS ports.
9475 @item -march=@var{architecture-type}
9476 @itemx -mcpu=@var{architecture-type}
9479 Generate code for the specified architecture. The choices for
9480 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9481 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
9482 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9485 @item -mtune=@var{architecture-type}
9487 Tune to @var{architecture-type} everything applicable about the generated
9488 code, except for the ABI and the set of available instructions. The
9489 choices for @var{architecture-type} are the same as for
9490 @option{-march=@var{architecture-type}}.
9492 @item -mmax-stack-frame=@var{n}
9493 @opindex mmax-stack-frame
9494 Warn when the stack frame of a function exceeds @var{n} bytes.
9496 @item -melinux-stacksize=@var{n}
9497 @opindex melinux-stacksize
9498 Only available with the @samp{cris-axis-aout} target. Arranges for
9499 indications in the program to the kernel loader that the stack of the
9500 program should be set to @var{n} bytes.
9506 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9507 @option{-march=v3} and @option{-march=v8} respectively.
9511 Enable CRIS-specific verbose debug-related information in the assembly
9512 code. This option also has the effect to turn off the @samp{#NO_APP}
9513 formatted-code indicator to the assembler at the beginning of the
9518 Do not use condition-code results from previous instruction; always emit
9519 compare and test instructions before use of condition codes.
9521 @item -mno-side-effects
9522 @opindex mno-side-effects
9523 Do not emit instructions with side-effects in addressing modes other than
9527 @itemx -mno-stack-align
9529 @itemx -mno-data-align
9530 @itemx -mconst-align
9531 @itemx -mno-const-align
9532 @opindex mstack-align
9533 @opindex mno-stack-align
9534 @opindex mdata-align
9535 @opindex mno-data-align
9536 @opindex mconst-align
9537 @opindex mno-const-align
9538 These options (no-options) arranges (eliminate arrangements) for the
9539 stack-frame, individual data and constants to be aligned for the maximum
9540 single data access size for the chosen CPU model. The default is to
9541 arrange for 32-bit alignment. ABI details such as structure layout are
9542 not affected by these options.
9550 Similar to the stack- data- and const-align options above, these options
9551 arrange for stack-frame, writable data and constants to all be 32-bit,
9552 16-bit or 8-bit aligned. The default is 32-bit alignment.
9554 @item -mno-prologue-epilogue
9555 @itemx -mprologue-epilogue
9556 @opindex mno-prologue-epilogue
9557 @opindex mprologue-epilogue
9558 With @option{-mno-prologue-epilogue}, the normal function prologue and
9559 epilogue that sets up the stack-frame are omitted and no return
9560 instructions or return sequences are generated in the code. Use this
9561 option only together with visual inspection of the compiled code: no
9562 warnings or errors are generated when call-saved registers must be saved,
9563 or storage for local variable needs to be allocated.
9569 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9570 instruction sequences that load addresses for functions from the PLT part
9571 of the GOT rather than (traditional on other architectures) calls to the
9572 PLT. The default is @option{-mgotplt}.
9576 Legacy no-op option only recognized with the cris-axis-aout target.
9580 Legacy no-op option only recognized with the cris-axis-elf and
9581 cris-axis-linux-gnu targets.
9585 Only recognized with the cris-axis-aout target, where it selects a
9586 GNU/linux-like multilib, include files and instruction set for
9591 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9595 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
9596 to link with input-output functions from a simulator library. Code,
9597 initialized data and zero-initialized data are allocated consecutively.
9601 Like @option{-sim}, but pass linker options to locate initialized data at
9602 0x40000000 and zero-initialized data at 0x80000000.
9606 @node Code Gen Options
9607 @section Options for Code Generation Conventions
9608 @cindex code generation conventions
9609 @cindex options, code generation
9610 @cindex run-time options
9612 These machine-independent options control the interface conventions
9613 used in code generation.
9615 Most of them have both positive and negative forms; the negative form
9616 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
9617 one of the forms is listed---the one which is not the default. You
9618 can figure out the other form by either removing @samp{no-} or adding
9623 @opindex fexceptions
9624 Enable exception handling. Generates extra code needed to propagate
9625 exceptions. For some targets, this implies GCC will generate frame
9626 unwind information for all functions, which can produce significant data
9627 size overhead, although it does not affect execution. If you do not
9628 specify this option, GCC will enable it by default for languages like
9629 C++ which normally require exception handling, and disable it for
9630 languages like C that do not normally require it. However, you may need
9631 to enable this option when compiling C code that needs to interoperate
9632 properly with exception handlers written in C++. You may also wish to
9633 disable this option if you are compiling older C++ programs that don't
9634 use exception handling.
9636 @item -fnon-call-exceptions
9637 @opindex fnon-call-exceptions
9638 Generate code that allows trapping instructions to throw exceptions.
9639 Note that this requires platform-specific runtime support that does
9640 not exist everywhere. Moreover, it only allows @emph{trapping}
9641 instructions to throw exceptions, i.e.@: memory references or floating
9642 point instructions. It does not allow exceptions to be thrown from
9643 arbitrary signal handlers such as @code{SIGALRM}.
9645 @item -funwind-tables
9646 @opindex funwind-tables
9647 Similar to @option{-fexceptions}, except that it will just generate any needed
9648 static data, but will not affect the generated code in any other way.
9649 You will normally not enable this option; instead, a language processor
9650 that needs this handling would enable it on your behalf.
9652 @item -fasynchronous-unwind-tables
9653 @opindex funwind-tables
9654 Generate unwind table in dwarf2 format, if supported by target machine. The
9655 table is exact at each instruction boundary, so it can be used for stack
9656 unwinding from asynchronous events (such as debugger or garbage collector).
9658 @item -fpcc-struct-return
9659 @opindex fpcc-struct-return
9660 Return ``short'' @code{struct} and @code{union} values in memory like
9661 longer ones, rather than in registers. This convention is less
9662 efficient, but it has the advantage of allowing intercallability between
9663 GCC-compiled files and files compiled with other compilers.
9665 The precise convention for returning structures in memory depends
9666 on the target configuration macros.
9668 Short structures and unions are those whose size and alignment match
9669 that of some integer type.
9671 @item -freg-struct-return
9672 @opindex freg-struct-return
9673 Return @code{struct} and @code{union} values in registers when possible.
9674 This is more efficient for small structures than
9675 @option{-fpcc-struct-return}.
9677 If you specify neither @option{-fpcc-struct-return} nor
9678 @option{-freg-struct-return}, GCC defaults to whichever convention is
9679 standard for the target. If there is no standard convention, GCC
9680 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
9681 the principal compiler. In those cases, we can choose the standard, and
9682 we chose the more efficient register return alternative.
9685 @opindex fshort-enums
9686 Allocate to an @code{enum} type only as many bytes as it needs for the
9687 declared range of possible values. Specifically, the @code{enum} type
9688 will be equivalent to the smallest integer type which has enough room.
9690 @item -fshort-double
9691 @opindex fshort-double
9692 Use the same size for @code{double} as for @code{float}.
9695 @opindex fshared-data
9696 Requests that the data and non-@code{const} variables of this
9697 compilation be shared data rather than private data. The distinction
9698 makes sense only on certain operating systems, where shared data is
9699 shared between processes running the same program, while private data
9700 exists in one copy per process.
9704 In C, allocate even uninitialized global variables in the data section of the
9705 object file, rather than generating them as common blocks. This has the
9706 effect that if the same variable is declared (without @code{extern}) in
9707 two different compilations, you will get an error when you link them.
9708 The only reason this might be useful is if you wish to verify that the
9709 program will work on other systems which always work this way.
9713 Ignore the @samp{#ident} directive.
9715 @item -fno-gnu-linker
9716 @opindex fno-gnu-linker
9717 Do not output global initializations (such as C++ constructors and
9718 destructors) in the form used by the GNU linker (on systems where the GNU
9719 linker is the standard method of handling them). Use this option when
9720 you want to use a non-GNU linker, which also requires using the
9721 @command{collect2} program to make sure the system linker includes
9722 constructors and destructors. (@command{collect2} is included in the GCC
9723 distribution.) For systems which @emph{must} use @command{collect2}, the
9724 compiler driver @command{gcc} is configured to do this automatically.
9726 @item -finhibit-size-directive
9727 @opindex finhibit-size-directive
9728 Don't output a @code{.size} assembler directive, or anything else that
9729 would cause trouble if the function is split in the middle, and the
9730 two halves are placed at locations far apart in memory. This option is
9731 used when compiling @file{crtstuff.c}; you should not need to use it
9735 @opindex fverbose-asm
9736 Put extra commentary information in the generated assembly code to
9737 make it more readable. This option is generally only of use to those
9738 who actually need to read the generated assembly code (perhaps while
9739 debugging the compiler itself).
9741 @option{-fno-verbose-asm}, the default, causes the
9742 extra information to be omitted and is useful when comparing two assembler
9747 Consider all memory references through pointers to be volatile.
9749 @item -fvolatile-global
9750 @opindex fvolatile-global
9751 Consider all memory references to extern and global data items to
9752 be volatile. GCC does not consider static data items to be volatile
9753 because of this switch.
9755 @item -fvolatile-static
9756 @opindex fvolatile-static
9757 Consider all memory references to static data to be volatile.
9761 @cindex global offset table
9763 Generate position-independent code (PIC) suitable for use in a shared
9764 library, if supported for the target machine. Such code accesses all
9765 constant addresses through a global offset table (GOT)@. The dynamic
9766 loader resolves the GOT entries when the program starts (the dynamic
9767 loader is not part of GCC; it is part of the operating system). If
9768 the GOT size for the linked executable exceeds a machine-specific
9769 maximum size, you get an error message from the linker indicating that
9770 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
9771 instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k
9772 on the m68k and RS/6000. The 386 has no such limit.)
9774 Position-independent code requires special support, and therefore works
9775 only on certain machines. For the 386, GCC supports PIC for System V
9776 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
9777 position-independent.
9781 If supported for the target machine, emit position-independent code,
9782 suitable for dynamic linking and avoiding any limit on the size of the
9783 global offset table. This option makes a difference on the m68k, m88k,
9786 Position-independent code requires special support, and therefore works
9787 only on certain machines.
9789 @item -ffixed-@var{reg}
9791 Treat the register named @var{reg} as a fixed register; generated code
9792 should never refer to it (except perhaps as a stack pointer, frame
9793 pointer or in some other fixed role).
9795 @var{reg} must be the name of a register. The register names accepted
9796 are machine-specific and are defined in the @code{REGISTER_NAMES}
9797 macro in the machine description macro file.
9799 This flag does not have a negative form, because it specifies a
9802 @item -fcall-used-@var{reg}
9804 Treat the register named @var{reg} as an allocable register that is
9805 clobbered by function calls. It may be allocated for temporaries or
9806 variables that do not live across a call. Functions compiled this way
9807 will not save and restore the register @var{reg}.
9809 It is an error to used this flag with the frame pointer or stack pointer.
9810 Use of this flag for other registers that have fixed pervasive roles in
9811 the machine's execution model will produce disastrous results.
9813 This flag does not have a negative form, because it specifies a
9816 @item -fcall-saved-@var{reg}
9817 @opindex fcall-saved
9818 Treat the register named @var{reg} as an allocable register saved by
9819 functions. It may be allocated even for temporaries or variables that
9820 live across a call. Functions compiled this way will save and restore
9821 the register @var{reg} if they use it.
9823 It is an error to used this flag with the frame pointer or stack pointer.
9824 Use of this flag for other registers that have fixed pervasive roles in
9825 the machine's execution model will produce disastrous results.
9827 A different sort of disaster will result from the use of this flag for
9828 a register in which function values may be returned.
9830 This flag does not have a negative form, because it specifies a
9834 @opindex fpack-struct
9835 Pack all structure members together without holes. Usually you would
9836 not want to use this option, since it makes the code suboptimal, and
9837 the offsets of structure members won't agree with system libraries.
9839 @item -fcheck-memory-usage
9840 @opindex fcheck-memory-usage
9841 Generate extra code to check each memory access. GCC will generate
9842 code that is suitable for a detector of bad memory accesses such as
9845 Normally, you should compile all, or none, of your code with this option.
9847 If you do mix code compiled with and without this option,
9848 you must ensure that all code that has side effects
9849 and that is called by code compiled with this option
9850 is, itself, compiled with this option.
9851 If you do not, you might get erroneous messages from the detector.
9853 If you use functions from a library that have side-effects (such as
9854 @code{read}), you might not be able to recompile the library and
9855 specify this option. In that case, you can enable the
9856 @option{-fprefix-function-name} option, which requests GCC to encapsulate
9857 your code and make other functions look as if they were compiled with
9858 @option{-fcheck-memory-usage}. This is done by calling ``stubs'',
9859 which are provided by the detector. If you cannot find or build
9860 stubs for every function you call, you might have to specify
9861 @option{-fcheck-memory-usage} without @option{-fprefix-function-name}.
9863 If you specify this option, you can not use the @code{asm} or
9864 @code{__asm__} keywords in functions with memory checking enabled. GCC
9865 cannot understand what the @code{asm} statement may do, and therefore
9866 cannot generate the appropriate code, so it will reject it. However, if
9867 you specify the function attribute @code{no_check_memory_usage}
9868 (@pxref{Function Attributes}), GCC will disable memory checking within a
9869 function; you may use @code{asm} statements inside such functions. You
9870 may have an inline expansion of a non-checked function within a checked
9871 function; in that case GCC will not generate checks for the inlined
9872 function's memory accesses.
9874 If you move your @code{asm} statements to non-checked inline functions
9875 and they do access memory, you can add calls to the support code in your
9876 inline function, to indicate any reads, writes, or copies being done.
9877 These calls would be similar to those done in the stubs described above.
9879 @item -fprefix-function-name
9880 @opindex fprefix-function-name
9881 Request GCC to add a prefix to the symbols generated for function names.
9882 GCC adds a prefix to the names of functions defined as well as
9883 functions called. Code compiled with this option and code compiled
9884 without the option can't be linked together, unless stubs are used.
9886 If you compile the following code with @option{-fprefix-function-name}
9888 extern void bar (int);
9897 GCC will compile the code as if it was written:
9899 extern void prefix_bar (int);
9903 return prefix_bar (a + 5);
9906 This option is designed to be used with @option{-fcheck-memory-usage}.
9908 @item -finstrument-functions
9909 @opindex finstrument-functions
9910 Generate instrumentation calls for entry and exit to functions. Just
9911 after function entry and just before function exit, the following
9912 profiling functions will be called with the address of the current
9913 function and its call site. (On some platforms,
9914 @code{__builtin_return_address} does not work beyond the current
9915 function, so the call site information may not be available to the
9916 profiling functions otherwise.)
9919 void __cyg_profile_func_enter (void *this_fn,
9921 void __cyg_profile_func_exit (void *this_fn,
9925 The first argument is the address of the start of the current function,
9926 which may be looked up exactly in the symbol table.
9928 This instrumentation is also done for functions expanded inline in other
9929 functions. The profiling calls will indicate where, conceptually, the
9930 inline function is entered and exited. This means that addressable
9931 versions of such functions must be available. If all your uses of a
9932 function are expanded inline, this may mean an additional expansion of
9933 code size. If you use @samp{extern inline} in your C code, an
9934 addressable version of such functions must be provided. (This is
9935 normally the case anyways, but if you get lucky and the optimizer always
9936 expands the functions inline, you might have gotten away without
9937 providing static copies.)
9939 A function may be given the attribute @code{no_instrument_function}, in
9940 which case this instrumentation will not be done. This can be used, for
9941 example, for the profiling functions listed above, high-priority
9942 interrupt routines, and any functions from which the profiling functions
9943 cannot safely be called (perhaps signal handlers, if the profiling
9944 routines generate output or allocate memory).
9947 @opindex fstack-check
9948 Generate code to verify that you do not go beyond the boundary of the
9949 stack. You should specify this flag if you are running in an
9950 environment with multiple threads, but only rarely need to specify it in
9951 a single-threaded environment since stack overflow is automatically
9952 detected on nearly all systems if there is only one stack.
9954 Note that this switch does not actually cause checking to be done; the
9955 operating system must do that. The switch causes generation of code
9956 to ensure that the operating system sees the stack being extended.
9958 @item -fstack-limit-register=@var{reg}
9959 @itemx -fstack-limit-symbol=@var{sym}
9960 @itemx -fno-stack-limit
9961 @opindex fstack-limit-register
9962 @opindex fstack-limit-symbol
9963 @opindex fno-stack-limit
9964 Generate code to ensure that the stack does not grow beyond a certain value,
9965 either the value of a register or the address of a symbol. If the stack
9966 would grow beyond the value, a signal is raised. For most targets,
9967 the signal is raised before the stack overruns the boundary, so
9968 it is possible to catch the signal without taking special precautions.
9970 For instance, if the stack starts at absolute address @samp{0x80000000}
9971 and grows downwards, you can use the flags
9972 @option{-fstack-limit-symbol=__stack_limit} and
9973 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
9974 of 128KB@. Note that this may only work with the GNU linker.
9976 @cindex aliasing of parameters
9977 @cindex parameters, aliased
9978 @item -fargument-alias
9979 @itemx -fargument-noalias
9980 @itemx -fargument-noalias-global
9981 @opindex fargument-alias
9982 @opindex fargument-noalias
9983 @opindex fargument-noalias-global
9984 Specify the possible relationships among parameters and between
9985 parameters and global data.
9987 @option{-fargument-alias} specifies that arguments (parameters) may
9988 alias each other and may alias global storage.@*
9989 @option{-fargument-noalias} specifies that arguments do not alias
9990 each other, but may alias global storage.@*
9991 @option{-fargument-noalias-global} specifies that arguments do not
9992 alias each other and do not alias global storage.
9994 Each language will automatically use whatever option is required by
9995 the language standard. You should not need to use these options yourself.
9997 @item -fleading-underscore
9998 @opindex fleading-underscore
9999 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
10000 change the way C symbols are represented in the object file. One use
10001 is to help link with legacy assembly code.
10003 Be warned that you should know what you are doing when invoking this
10004 option, and that not all targets provide complete support for it.
10009 @node Environment Variables
10010 @section Environment Variables Affecting GCC
10011 @cindex environment variables
10013 @c man begin ENVIRONMENT
10015 This section describes several environment variables that affect how GCC
10016 operates. Some of them work by specifying directories or prefixes to use
10017 when searching for various kinds of files. Some are used to specify other
10018 aspects of the compilation environment.
10021 Note that you can also specify places to search using options such as
10022 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
10023 take precedence over places specified using environment variables, which
10024 in turn take precedence over those specified by the configuration of GCC@.
10028 Note that you can also specify places to search using options such as
10029 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
10030 take precedence over places specified using environment variables, which
10031 in turn take precedence over those specified by the configuration of GCC@.
10038 @c @itemx LC_COLLATE
10040 @c @itemx LC_MONETARY
10041 @c @itemx LC_NUMERIC
10046 @c @findex LC_COLLATE
10047 @findex LC_MESSAGES
10048 @c @findex LC_MONETARY
10049 @c @findex LC_NUMERIC
10053 These environment variables control the way that GCC uses
10054 localization information that allow GCC to work with different
10055 national conventions. GCC inspects the locale categories
10056 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
10057 so. These locale categories can be set to any value supported by your
10058 installation. A typical value is @samp{en_UK} for English in the United
10061 The @env{LC_CTYPE} environment variable specifies character
10062 classification. GCC uses it to determine the character boundaries in
10063 a string; this is needed for some multibyte encodings that contain quote
10064 and escape characters that would otherwise be interpreted as a string
10067 The @env{LC_MESSAGES} environment variable specifies the language to
10068 use in diagnostic messages.
10070 If the @env{LC_ALL} environment variable is set, it overrides the value
10071 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
10072 and @env{LC_MESSAGES} default to the value of the @env{LANG}
10073 environment variable. If none of these variables are set, GCC
10074 defaults to traditional C English behavior.
10078 If @env{TMPDIR} is set, it specifies the directory to use for temporary
10079 files. GCC uses temporary files to hold the output of one stage of
10080 compilation which is to be used as input to the next stage: for example,
10081 the output of the preprocessor, which is the input to the compiler
10084 @item GCC_EXEC_PREFIX
10085 @findex GCC_EXEC_PREFIX
10086 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
10087 names of the subprograms executed by the compiler. No slash is added
10088 when this prefix is combined with the name of a subprogram, but you can
10089 specify a prefix that ends with a slash if you wish.
10091 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
10092 an appropriate prefix to use based on the pathname it was invoked with.
10094 If GCC cannot find the subprogram using the specified prefix, it
10095 tries looking in the usual places for the subprogram.
10097 The default value of @env{GCC_EXEC_PREFIX} is
10098 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
10099 of @code{prefix} when you ran the @file{configure} script.
10101 Other prefixes specified with @option{-B} take precedence over this prefix.
10103 This prefix is also used for finding files such as @file{crt0.o} that are
10106 In addition, the prefix is used in an unusual way in finding the
10107 directories to search for header files. For each of the standard
10108 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
10109 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
10110 replacing that beginning with the specified prefix to produce an
10111 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
10112 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
10113 These alternate directories are searched first; the standard directories
10116 @item COMPILER_PATH
10117 @findex COMPILER_PATH
10118 The value of @env{COMPILER_PATH} is a colon-separated list of
10119 directories, much like @env{PATH}. GCC tries the directories thus
10120 specified when searching for subprograms, if it can't find the
10121 subprograms using @env{GCC_EXEC_PREFIX}.
10124 @findex LIBRARY_PATH
10125 The value of @env{LIBRARY_PATH} is a colon-separated list of
10126 directories, much like @env{PATH}. When configured as a native compiler,
10127 GCC tries the directories thus specified when searching for special
10128 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
10129 using GCC also uses these directories when searching for ordinary
10130 libraries for the @option{-l} option (but directories specified with
10131 @option{-L} come first).
10133 @item C_INCLUDE_PATH
10134 @itemx CPLUS_INCLUDE_PATH
10135 @itemx OBJC_INCLUDE_PATH
10136 @findex C_INCLUDE_PATH
10137 @findex CPLUS_INCLUDE_PATH
10138 @findex OBJC_INCLUDE_PATH
10139 @c @itemx OBJCPLUS_INCLUDE_PATH
10140 These environment variables pertain to particular languages. Each
10141 variable's value is a colon-separated list of directories, much like
10142 @env{PATH}. When GCC searches for header files, it tries the
10143 directories listed in the variable for the language you are using, after
10144 the directories specified with @option{-I} but before the standard header
10147 @item DEPENDENCIES_OUTPUT
10148 @findex DEPENDENCIES_OUTPUT
10149 @cindex dependencies for make as output
10150 If this variable is set, its value specifies how to output dependencies
10151 for Make based on the header files processed by the compiler. This
10152 output looks much like the output from the @option{-M} option
10153 (@pxref{Preprocessor Options}), but it goes to a separate file, and is
10154 in addition to the usual results of compilation.
10156 The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in
10157 which case the Make rules are written to that file, guessing the target
10158 name from the source file name. Or the value can have the form
10159 @samp{@var{file} @var{target}}, in which case the rules are written to
10160 file @var{file} using @var{target} as the target name.
10164 @cindex locale definition
10165 This variable is used to pass locale information to the compiler. One way in
10166 which this information is used is to determine the character set to be used
10167 when character literals, string literals and comments are parsed in C and C++.
10168 When the compiler is configured to allow multibyte characters,
10169 the following values for @env{LANG} are recognized:
10173 Recognize JIS characters.
10175 Recognize SJIS characters.
10177 Recognize EUCJP characters.
10180 If @env{LANG} is not defined, or if it has some other value, then the
10181 compiler will use mblen and mbtowc as defined by the default locale to
10182 recognize and translate multibyte characters.
10187 @node Running Protoize
10188 @section Running Protoize
10190 The program @code{protoize} is an optional part of GCC@. You can use
10191 it to add prototypes to a program, thus converting the program to ISO
10192 C in one respect. The companion program @code{unprotoize} does the
10193 reverse: it removes argument types from any prototypes that are found.
10195 When you run these programs, you must specify a set of source files as
10196 command line arguments. The conversion programs start out by compiling
10197 these files to see what functions they define. The information gathered
10198 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
10200 After scanning comes actual conversion. The specified files are all
10201 eligible to be converted; any files they include (whether sources or
10202 just headers) are eligible as well.
10204 But not all the eligible files are converted. By default,
10205 @code{protoize} and @code{unprotoize} convert only source and header
10206 files in the current directory. You can specify additional directories
10207 whose files should be converted with the @option{-d @var{directory}}
10208 option. You can also specify particular files to exclude with the
10209 @option{-x @var{file}} option. A file is converted if it is eligible, its
10210 directory name matches one of the specified directory names, and its
10211 name within the directory has not been excluded.
10213 Basic conversion with @code{protoize} consists of rewriting most
10214 function definitions and function declarations to specify the types of
10215 the arguments. The only ones not rewritten are those for varargs
10218 @code{protoize} optionally inserts prototype declarations at the
10219 beginning of the source file, to make them available for any calls that
10220 precede the function's definition. Or it can insert prototype
10221 declarations with block scope in the blocks where undeclared functions
10224 Basic conversion with @code{unprotoize} consists of rewriting most
10225 function declarations to remove any argument types, and rewriting
10226 function definitions to the old-style pre-ISO form.
10228 Both conversion programs print a warning for any function declaration or
10229 definition that they can't convert. You can suppress these warnings
10232 The output from @code{protoize} or @code{unprotoize} replaces the
10233 original source file. The original file is renamed to a name ending
10234 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
10235 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
10236 for DOS) file already exists, then the source file is simply discarded.
10238 @code{protoize} and @code{unprotoize} both depend on GCC itself to
10239 scan the program and collect information about the functions it uses.
10240 So neither of these programs will work until GCC is installed.
10242 Here is a table of the options you can use with @code{protoize} and
10243 @code{unprotoize}. Each option works with both programs unless
10247 @item -B @var{directory}
10248 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
10249 usual directory (normally @file{/usr/local/lib}). This file contains
10250 prototype information about standard system functions. This option
10251 applies only to @code{protoize}.
10253 @item -c @var{compilation-options}
10254 Use @var{compilation-options} as the options when running @code{gcc} to
10255 produce the @samp{.X} files. The special option @option{-aux-info} is
10256 always passed in addition, to tell @code{gcc} to write a @samp{.X} file.
10258 Note that the compilation options must be given as a single argument to
10259 @code{protoize} or @code{unprotoize}. If you want to specify several
10260 @code{gcc} options, you must quote the entire set of compilation options
10261 to make them a single word in the shell.
10263 There are certain @code{gcc} arguments that you cannot use, because they
10264 would produce the wrong kind of output. These include @option{-g},
10265 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
10266 the @var{compilation-options}, they are ignored.
10269 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
10270 systems) instead of @samp{.c}. This is convenient if you are converting
10271 a C program to C++. This option applies only to @code{protoize}.
10274 Add explicit global declarations. This means inserting explicit
10275 declarations at the beginning of each source file for each function
10276 that is called in the file and was not declared. These declarations
10277 precede the first function definition that contains a call to an
10278 undeclared function. This option applies only to @code{protoize}.
10280 @item -i @var{string}
10281 Indent old-style parameter declarations with the string @var{string}.
10282 This option applies only to @code{protoize}.
10284 @code{unprotoize} converts prototyped function definitions to old-style
10285 function definitions, where the arguments are declared between the
10286 argument list and the initial @samp{@{}. By default, @code{unprotoize}
10287 uses five spaces as the indentation. If you want to indent with just
10288 one space instead, use @option{-i " "}.
10291 Keep the @samp{.X} files. Normally, they are deleted after conversion
10295 Add explicit local declarations. @code{protoize} with @option{-l} inserts
10296 a prototype declaration for each function in each block which calls the
10297 function without any declaration. This option applies only to
10301 Make no real changes. This mode just prints information about the conversions
10302 that would have been done without @option{-n}.
10305 Make no @samp{.save} files. The original files are simply deleted.
10306 Use this option with caution.
10308 @item -p @var{program}
10309 Use the program @var{program} as the compiler. Normally, the name
10310 @file{gcc} is used.
10313 Work quietly. Most warnings are suppressed.
10316 Print the version number, just like @option{-v} for @code{gcc}.
10319 If you need special compiler options to compile one of your program's
10320 source files, then you should generate that file's @samp{.X} file
10321 specially, by running @code{gcc} on that source file with the
10322 appropriate options and the option @option{-aux-info}. Then run
10323 @code{protoize} on the entire set of files. @code{protoize} will use
10324 the existing @samp{.X} file because it is newer than the source file.
10328 gcc -Dfoo=bar file1.c -aux-info file1.X
10333 You need to include the special files along with the rest in the
10334 @code{protoize} command, even though their @samp{.X} files already
10335 exist, because otherwise they won't get converted.
10337 @xref{Protoize Caveats}, for more information on how to use
10338 @code{protoize} successfully.