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 -fno-honor-std @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
240 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
241 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
242 -fdump-ast-original@r{[}-@var{n}@r{]} -fdump-ast-optimized@r{[}-@var{n}@r{]} @gol
243 -fdump-ast-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 -fmove-all-movables @gol
266 -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 -mprototype -mno-prototype @gol
439 -msim -mmvme -mads -myellowknife -memb -msdata @gol
440 -msdata=@var{opt} -mvxworks -G @var{num}}
444 -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
445 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
446 -mminimum-fp-blocks -mnohc-struct-return}
450 -mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
451 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
452 -membedded-pic -mfp32 -mfp64 -mgas -mgp32 -mgp64 @gol
453 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
454 -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
455 -mmips-as -mmips-tfile -mno-abicalls @gol
456 -mno-embedded-data -mno-uninit-const-in-rodata @gol
457 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
458 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
459 -mrnames -msoft-float @gol
460 -m4650 -msingle-float -mmad @gol
461 -mstats -EL -EB -G @var{num} -nocpp @gol
462 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi @gol
467 -mcpu=@var{cpu-type} -march=@var{cpu-type} @gol
468 -mintel-syntax -mieee-fp -mno-fancy-math-387 @gol
469 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
470 -mno-wide-multiply -mrtd -malign-double @gol
471 -mpreferred-stack-boundary=@var{num} @gol
472 -mthreads -mno-align-stringops -minline-all-stringops @gol
473 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
474 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer}
478 -march=@var{architecture-type} @gol
479 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
480 -mfast-indirect-calls -mgas -mjump-in-delay @gol
481 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
482 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
483 -mno-jump-in-delay -mno-long-load-store @gol
484 -mno-portable-runtime -mno-soft-float @gol
485 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
486 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
487 -mschedule=@var{cpu-type} -mspace-regs}
489 @emph{Intel 960 Options}
491 -m@var{cpu-type} -masm-compat -mclean-linkage @gol
492 -mcode-align -mcomplex-addr -mleaf-procedures @gol
493 -mic-compat -mic2.0-compat -mic3.0-compat @gol
494 -mintel-asm -mno-clean-linkage -mno-code-align @gol
495 -mno-complex-addr -mno-leaf-procedures @gol
496 -mno-old-align -mno-strict-align -mno-tail-call @gol
497 -mnumerics -mold-align -msoft-float -mstrict-align @gol
500 @emph{DEC Alpha Options}
502 -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float @gol
503 -malpha-as -mgas @gol
504 -mieee -mieee-with-inexact -mieee-conformant @gol
505 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
506 -mtrap-precision=@var{mode} -mbuild-constants @gol
507 -mcpu=@var{cpu-type} @gol
508 -mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max @gol
509 -mmemory-latency=@var{time}}
511 @emph{Clipper Options}
515 @emph{H8/300 Options}
517 -mrelax -mh -ms -mint32 -malign-300}
521 -m1 -m2 -m3 -m3e @gol
522 -m4-nofpu -m4-single-only -m4-single -m4 @gol
523 -mb -ml -mdalign -mrelax @gol
524 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
525 -mieee -misize -mpadstruct -mspace @gol
526 -mprefergot -musermode}
528 @emph{System V Options}
530 -Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
535 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
536 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
538 @emph{TMS320C3x/C4x Options}
540 -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
541 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
542 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
543 -mparallel-insns -mparallel-mpy -mpreserve-float}
547 -mlong-calls -mno-long-calls -mep -mno-ep @gol
548 -mprolog-function -mno-prolog-function -mspace @gol
549 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
554 -m32032 -m32332 -m32532 -m32081 -m32381 @gol
555 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
556 -mregparam -mnoregparam -msb -mnosb @gol
557 -mbitfield -mnobitfield -mhimem -mnohimem}
561 -mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
562 -mcall-prologues -mno-tablejump -mtiny-stack}
566 -mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
567 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
568 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
569 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
570 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
574 -mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
575 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
576 -mconstant-gp -mauto-pic -minline-divide-min-latency @gol
577 -minline-divide-max-throughput -mno-dwarf2-asm @gol
578 -mfixed-range=@var{register-range}}
580 @item Code Generation Options
581 @xref{Code Gen Options,,Options for Code Generation Conventions}.
583 -fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
584 -ffixed-@var{reg} -fexceptions @gol
585 -fnon-call-exceptions -funwind-tables @gol
586 -finhibit-size-directive -finstrument-functions @gol
587 -fcheck-memory-usage -fprefix-function-name @gol
588 -fno-common -fno-ident -fno-gnu-linker @gol
589 -fpcc-struct-return -fpic -fPIC @gol
590 -freg-struct-return -fshared-data -fshort-enums @gol
591 -fshort-double -fvolatile @gol
592 -fvolatile-global -fvolatile-static @gol
593 -fverbose-asm -fpack-struct -fstack-check @gol
594 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
595 -fargument-alias -fargument-noalias @gol
596 -fargument-noalias-global -fleading-underscore}
600 * Overall Options:: Controlling the kind of output:
601 an executable, object files, assembler files,
602 or preprocessed source.
603 * C Dialect Options:: Controlling the variant of C language compiled.
604 * C++ Dialect Options:: Variations on C++.
605 * Objective-C Dialect Options:: Variations on Objective-C.
606 * Language Independent Options:: Controlling how diagnostics should be
608 * Warning Options:: How picky should the compiler be?
609 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
610 * Optimize Options:: How much optimization?
611 * Preprocessor Options:: Controlling header files and macro definitions.
612 Also, getting dependency information for Make.
613 * Assembler Options:: Passing options to the assembler.
614 * Link Options:: Specifying libraries and so on.
615 * Directory Options:: Where to find header files and libraries.
616 Where to find the compiler executable files.
617 * Spec Files:: How to pass switches to sub-processes.
618 * Target Options:: Running a cross-compiler, or an old version of GCC.
621 @node Overall Options
622 @section Options Controlling the Kind of Output
624 Compilation can involve up to four stages: preprocessing, compilation
625 proper, assembly and linking, always in that order. The first three
626 stages apply to an individual source file, and end by producing an
627 object file; linking combines all the object files (those newly
628 compiled, and those specified as input) into an executable file.
630 @cindex file name suffix
631 For any given input file, the file name suffix determines what kind of
636 C source code which must be preprocessed.
639 C source code which should not be preprocessed.
642 C++ source code which should not be preprocessed.
645 Objective-C source code. Note that you must link with the library
646 @file{libobjc.a} to make an Objective-C program work.
649 Objective-C source code which should not be preprocessed.
652 C header file (not to be compiled or linked).
656 @itemx @var{file}.cxx
657 @itemx @var{file}.cpp
658 @itemx @var{file}.c++
660 C++ source code which must be preprocessed. Note that in @samp{.cxx},
661 the last two letters must both be literally @samp{x}. Likewise,
662 @samp{.C} refers to a literal capital C@.
665 @itemx @var{file}.for
666 @itemx @var{file}.FOR
667 Fortran source code which should not be preprocessed.
670 @itemx @var{file}.fpp
671 @itemx @var{file}.FPP
672 Fortran source code which must be preprocessed (with the traditional
676 Fortran source code which must be preprocessed with a RATFOR
677 preprocessor (not included with GCC)@.
679 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
680 Using and Porting GNU Fortran}, for more details of the handling of
683 @c FIXME: Descriptions of Java file types.
689 @c GCC also knows about some suffixes for languages not yet included:
699 @itemx @var{file}.chi
700 CHILL source code (preprocessed with the traditional preprocessor).
706 Assembler code which must be preprocessed.
709 An object file to be fed straight into linking.
710 Any file name with no recognized suffix is treated this way.
714 You can specify the input language explicitly with the @option{-x} option:
717 @item -x @var{language}
718 Specify explicitly the @var{language} for the following input files
719 (rather than letting the compiler choose a default based on the file
720 name suffix). This option applies to all following input files until
721 the next @option{-x} option. Possible values for @var{language} are:
723 c c-header cpp-output
725 objective-c objc-cpp-output
726 assembler assembler-with-cpp
727 f77 f77-cpp-input ratfor
730 @c Also f77-version, for internal use only.
733 Turn off any specification of a language, so that subsequent files are
734 handled according to their file name suffixes (as they are if @option{-x}
735 has not been used at all).
737 @item -pass-exit-codes
738 @opindex pass-exit-codes
739 Normally the @command{gcc} program will exit with the code of 1 if any
740 phase of the compiler returns a non-success return code. If you specify
741 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
742 numerically highest error produced by any phase that returned an error
746 If you only want some of the stages of compilation, you can use
747 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
748 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
749 @command{gcc} is to stop. Note that some combinations (for example,
750 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
755 Compile or assemble the source files, but do not link. The linking
756 stage simply is not done. The ultimate output is in the form of an
757 object file for each source file.
759 By default, the object file name for a source file is made by replacing
760 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
762 Unrecognized input files, not requiring compilation or assembly, are
767 Stop after the stage of compilation proper; do not assemble. The output
768 is in the form of an assembler code file for each non-assembler input
771 By default, the assembler file name for a source file is made by
772 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
774 Input files that don't require compilation are ignored.
778 Stop after the preprocessing stage; do not run the compiler proper. The
779 output is in the form of preprocessed source code, which is sent to the
782 Input files which don't require preprocessing are ignored.
784 @cindex output file option
787 Place output in file @var{file}. This applies regardless to whatever
788 sort of output is being produced, whether it be an executable file,
789 an object file, an assembler file or preprocessed C code.
791 Since only one output file can be specified, it does not make sense to
792 use @option{-o} when compiling more than one input file, unless you are
793 producing an executable file as output.
795 If @option{-o} is not specified, the default is to put an executable file
796 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
797 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
798 all preprocessed C source on standard output.
802 Print (on standard error output) the commands executed to run the stages
803 of compilation. Also print the version number of the compiler driver
804 program and of the preprocessor and the compiler proper.
808 Use pipes rather than temporary files for communication between the
809 various stages of compilation. This fails to work on some systems where
810 the assembler is unable to read from a pipe; but the GNU assembler has
815 Print (on the standard output) a description of the command line options
816 understood by @command{gcc}. If the @option{-v} option is also specified
817 then @option{--help} will also be passed on to the various processes
818 invoked by @command{gcc}, so that they can display the command line options
819 they accept. If the @option{-W} option is also specified then command
820 line options which have no documentation associated with them will also
825 Print (on the standard output) a description of target specific command
826 line options for each tool.
830 @section Compiling C++ Programs
832 @cindex suffixes for C++ source
833 @cindex C++ source file suffixes
834 C++ source files conventionally use one of the suffixes @samp{.C},
835 @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx};
836 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
837 files with these names and compiles them as C++ programs even if you
838 call the compiler the same way as for compiling C programs (usually with
839 the name @command{gcc}).
843 However, C++ programs often require class libraries as well as a
844 compiler that understands the C++ language---and under some
845 circumstances, you might want to compile programs from standard input,
846 or otherwise without a suffix that flags them as C++ programs.
847 @command{g++} is a program that calls GCC with the default language
848 set to C++, and automatically specifies linking against the C++
849 library. On many systems, @command{g++} is also
850 installed with the name @command{c++}.
852 @cindex invoking @command{g++}
853 When you compile C++ programs, you may specify many of the same
854 command-line options that you use for compiling programs in any
855 language; or command-line options meaningful for C and related
856 languages; or options that are meaningful only for C++ programs.
857 @xref{C Dialect Options,,Options Controlling C Dialect}, for
858 explanations of options for languages related to C@.
859 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
860 explanations of options that are meaningful only for C++ programs.
862 @node C Dialect Options
863 @section Options Controlling C Dialect
864 @cindex dialect options
865 @cindex language dialect options
866 @cindex options, dialect
868 The following options control the dialect of C (or languages derived
869 from C, such as C++ and Objective-C) that the compiler accepts:
876 In C mode, support all ISO C89 programs. In C++ mode,
877 remove GNU extensions that conflict with ISO C++.
879 This turns off certain features of GCC that are incompatible with ISO
880 C89 (when compiling C code), or of standard C++ (when compiling C++ code),
881 such as the @code{asm} and @code{typeof} keywords, and
882 predefined macros such as @code{unix} and @code{vax} that identify the
883 type of system you are using. It also enables the undesirable and
884 rarely used ISO trigraph feature. For the C compiler,
885 it disables recognition of C++ style @samp{//} comments as well as
886 the @code{inline} keyword.
888 The alternate keywords @code{__asm__}, @code{__extension__},
889 @code{__inline__} and @code{__typeof__} continue to work despite
890 @option{-ansi}. You would not want to use them in an ISO C program, of
891 course, but it is useful to put them in header files that might be included
892 in compilations done with @option{-ansi}. Alternate predefined macros
893 such as @code{__unix__} and @code{__vax__} are also available, with or
894 without @option{-ansi}.
896 The @option{-ansi} option does not cause non-ISO programs to be
897 rejected gratuitously. For that, @option{-pedantic} is required in
898 addition to @option{-ansi}. @xref{Warning Options}.
900 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
901 option is used. Some header files may notice this macro and refrain
902 from declaring certain functions or defining certain macros that the
903 ISO standard doesn't call for; this is to avoid interfering with any
904 programs that might use these names for other things.
906 Functions which would normally be built in but do not have semantics
907 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
908 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
909 built-in functions provided by GCC}, for details of the functions
914 Determine the language standard. This option is currently only
915 supported when compiling C@. A value for this option must be provided;
921 ISO C89 (same as @option{-ansi}).
924 ISO C89 as modified in amendment 1.
930 ISO C99. Note that this standard is not yet fully supported; see
931 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
932 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
935 Default, ISO C89 plus GNU extensions (including some C99 features).
939 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
940 this will become the default. The name @samp{gnu9x} is deprecated.
944 Even when this option is not specified, you can still use some of the
945 features of newer standards in so far as they do not conflict with
946 previous C standards. For example, you may use @code{__restrict__} even
947 when @option{-std=c99} is not specified.
949 The @option{-std} options specifying some version of ISO C have the same
950 effects as @option{-ansi}, except that features that were not in ISO C89
951 but are in the specified version (for example, @samp{//} comments and
952 the @code{inline} keyword in ISO C99) are not disabled.
954 @xref{Standards,,Language Standards Supported by GCC}, for details of
955 these standard versions.
957 @item -aux-info @var{filename}
959 Output to the given filename prototyped declarations for all functions
960 declared and/or defined in a translation unit, including those in header
961 files. This option is silently ignored in any language other than C@.
963 Besides declarations, the file indicates, in comments, the origin of
964 each declaration (source file and line), whether the declaration was
965 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
966 @samp{O} for old, respectively, in the first character after the line
967 number and the colon), and whether it came from a declaration or a
968 definition (@samp{C} or @samp{F}, respectively, in the following
969 character). In the case of function definitions, a K&R-style list of
970 arguments followed by their declarations is also provided, inside
971 comments, after the declaration.
975 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
976 keyword, so that code can use these words as identifiers. You can use
977 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
978 instead. @option{-ansi} implies @option{-fno-asm}.
980 In C++, this switch only affects the @code{typeof} keyword, since
981 @code{asm} and @code{inline} are standard keywords. You may want to
982 use the @option{-fno-gnu-keywords} flag instead, which has the same
983 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
984 switch only affects the @code{asm} and @code{typeof} keywords, since
985 @code{inline} is a standard keyword in ISO C99.
989 @cindex built-in functions
990 Don't recognize built-in functions that do not begin with
991 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
992 functions provided by GCC}, for details of the functions affected,
993 including those which are not built-in functions when @option{-ansi} or
994 @option{-std} options for strict ISO C conformance are used because they
995 do not have an ISO standard meaning.
997 GCC normally generates special code to handle certain built-in functions
998 more efficiently; for instance, calls to @code{alloca} may become single
999 instructions that adjust the stack directly, and calls to @code{memcpy}
1000 may become inline copy loops. The resulting code is often both smaller
1001 and faster, but since the function calls no longer appear as such, you
1002 cannot set a breakpoint on those calls, nor can you change the behavior
1003 of the functions by linking with a different library.
1005 In C++, @option{-fno-builtin} is always in effect. The @option{-fbuiltin}
1006 option has no effect. Therefore, in C++, the only way to get the
1007 optimization benefits of built-in functions is to call the function
1008 using the @samp{__builtin_} prefix. The GNU C++ Standard Library uses
1009 built-in functions to implement many functions (like
1010 @code{std::strchr}), so that you automatically get efficient code.
1014 @cindex hosted environment
1016 Assert that compilation takes place in a hosted environment. This implies
1017 @option{-fbuiltin}. A hosted environment is one in which the
1018 entire standard library is available, and in which @code{main} has a return
1019 type of @code{int}. Examples are nearly everything except a kernel.
1020 This is equivalent to @option{-fno-freestanding}.
1022 @item -ffreestanding
1023 @opindex ffreestanding
1024 @cindex hosted environment
1026 Assert that compilation takes place in a freestanding environment. This
1027 implies @option{-fno-builtin}. A freestanding environment
1028 is one in which the standard library may not exist, and program startup may
1029 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1030 This is equivalent to @option{-fno-hosted}.
1032 @xref{Standards,,Language Standards Supported by GCC}, for details of
1033 freestanding and hosted environments.
1037 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1038 options for strict ISO C conformance) implies @option{-trigraphs}.
1040 @cindex traditional C language
1041 @cindex C language, traditional
1043 @opindex traditional
1044 Attempt to support some aspects of traditional C compilers.
1049 All @code{extern} declarations take effect globally even if they
1050 are written inside of a function definition. This includes implicit
1051 declarations of functions.
1054 The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const}
1055 and @code{volatile} are not recognized. (You can still use the
1056 alternative keywords such as @code{__typeof__}, @code{__inline__}, and
1060 Comparisons between pointers and integers are always allowed.
1063 Integer types @code{unsigned short} and @code{unsigned char} promote
1064 to @code{unsigned int}.
1067 Out-of-range floating point literals are not an error.
1070 Certain constructs which ISO regards as a single invalid preprocessing
1071 number, such as @samp{0xe-0xd}, are treated as expressions instead.
1074 String ``constants'' are not necessarily constant; they are stored in
1075 writable space, and identical looking constants are allocated
1076 separately. (This is the same as the effect of
1077 @option{-fwritable-strings}.)
1079 @cindex @code{longjmp} and automatic variables
1081 All automatic variables not declared @code{register} are preserved by
1082 @code{longjmp}. Ordinarily, GNU C follows ISO C: automatic variables
1083 not declared @code{volatile} may be clobbered.
1088 @cindex escape sequences, traditional
1089 The character escape sequences @samp{\x} and @samp{\a} evaluate as the
1090 literal characters @samp{x} and @samp{a} respectively. Without
1091 @w{@option{-traditional}}, @samp{\x} is a prefix for the hexadecimal
1092 representation of a character, and @samp{\a} produces a bell.
1095 You may wish to use @option{-fno-builtin} as well as @option{-traditional}
1096 if your program uses names that are normally GNU C built-in functions for
1097 other purposes of its own.
1099 You cannot use @option{-traditional} if you include any header files that
1100 rely on ISO C features. Some vendors are starting to ship systems with
1101 ISO C header files and you cannot use @option{-traditional} on such
1102 systems to compile files that include any system headers.
1104 The @option{-traditional} option also enables @option{-traditional-cpp},
1105 which is described next.
1107 @item -traditional-cpp
1108 @opindex traditional-cpp
1109 Attempt to support some aspects of traditional C preprocessors.
1114 Comments convert to nothing at all, rather than to a space. This allows
1115 traditional token concatenation.
1118 In a preprocessing directive, the @samp{#} symbol must appear as the first
1119 character of a line.
1122 Macro arguments are recognized within string constants in a macro
1123 definition (and their values are stringified, though without additional
1124 quote marks, when they appear in such a context). The preprocessor
1125 always considers a string constant to end at a newline.
1128 @cindex detecting @w{@option{-traditional}}
1129 The predefined macro @code{__STDC__} is not defined when you use
1130 @option{-traditional}, but @code{__GNUC__} is (since the GNU extensions
1131 which @code{__GNUC__} indicates are not affected by
1132 @option{-traditional}). If you need to write header files that work
1133 differently depending on whether @option{-traditional} is in use, by
1134 testing both of these predefined macros you can distinguish four
1135 situations: GNU C, traditional GNU C, other ISO C compilers, and other
1136 old C compilers. The predefined macro @code{__STDC_VERSION__} is also
1137 not defined when you use @option{-traditional}. @xref{Standard
1138 Predefined,,Standard Predefined Macros,cpp.info,The C Preprocessor},
1139 for more discussion of these and other predefined macros.
1142 @cindex string constants vs newline
1143 @cindex newline vs string constants
1144 The preprocessor considers a string constant to end at a newline (unless
1145 the newline is escaped with @samp{\}). (Without @w{@option{-traditional}},
1146 string constants can contain the newline character as typed.)
1149 @item -fcond-mismatch
1150 @opindex fcond-mismatch
1151 Allow conditional expressions with mismatched types in the second and
1152 third arguments. The value of such an expression is void. This option
1153 is not supported for C++.
1155 @item -funsigned-char
1156 @opindex funsigned-char
1157 Let the type @code{char} be unsigned, like @code{unsigned char}.
1159 Each kind of machine has a default for what @code{char} should
1160 be. It is either like @code{unsigned char} by default or like
1161 @code{signed char} by default.
1163 Ideally, a portable program should always use @code{signed char} or
1164 @code{unsigned char} when it depends on the signedness of an object.
1165 But many programs have been written to use plain @code{char} and
1166 expect it to be signed, or expect it to be unsigned, depending on the
1167 machines they were written for. This option, and its inverse, let you
1168 make such a program work with the opposite default.
1170 The type @code{char} is always a distinct type from each of
1171 @code{signed char} or @code{unsigned char}, even though its behavior
1172 is always just like one of those two.
1175 @opindex fsigned-char
1176 Let the type @code{char} be signed, like @code{signed char}.
1178 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1179 the negative form of @option{-funsigned-char}. Likewise, the option
1180 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1182 @item -fsigned-bitfields
1183 @itemx -funsigned-bitfields
1184 @itemx -fno-signed-bitfields
1185 @itemx -fno-unsigned-bitfields
1186 @opindex fsigned-bitfields
1187 @opindex funsigned-bitfields
1188 @opindex fno-signed-bitfields
1189 @opindex fno-unsigned-bitfields
1190 These options control whether a bit-field is signed or unsigned, when the
1191 declaration does not use either @code{signed} or @code{unsigned}. By
1192 default, such a bit-field is signed, because this is consistent: the
1193 basic integer types such as @code{int} are signed types.
1195 However, when @option{-traditional} is used, bit-fields are all unsigned
1198 @item -fwritable-strings
1199 @opindex fwritable-strings
1200 Store string constants in the writable data segment and don't uniquize
1201 them. This is for compatibility with old programs which assume they can
1202 write into string constants. The option @option{-traditional} also has
1205 Writing into string constants is a very bad idea; ``constants'' should
1208 @item -fallow-single-precision
1209 @opindex fallow-single-precision
1210 Do not promote single precision math operations to double precision,
1211 even when compiling with @option{-traditional}.
1213 Traditional K&R C promotes all floating point operations to double
1214 precision, regardless of the sizes of the operands. On the
1215 architecture for which you are compiling, single precision may be faster
1216 than double precision. If you must use @option{-traditional}, but want
1217 to use single precision operations when the operands are single
1218 precision, use this option. This option has no effect when compiling
1219 with ISO or GNU C conventions (the default).
1222 @opindex fshort-wchar
1223 Override the underlying type for @samp{wchar_t} to be @samp{short
1224 unsigned int} instead of the default for the target. This option is
1225 useful for building programs to run under WINE@.
1228 @node C++ Dialect Options
1229 @section Options Controlling C++ Dialect
1231 @cindex compiler options, C++
1232 @cindex C++ options, command line
1233 @cindex options, C++
1234 This section describes the command-line options that are only meaningful
1235 for C++ programs; but you can also use most of the GNU compiler options
1236 regardless of what language your program is in. For example, you
1237 might compile a file @code{firstClass.C} like this:
1240 g++ -g -frepo -O -c firstClass.C
1244 In this example, only @option{-frepo} is an option meant
1245 only for C++ programs; you can use the other options with any
1246 language supported by GCC@.
1248 Here is a list of options that are @emph{only} for compiling C++ programs:
1251 @item -fno-access-control
1252 @opindex fno-access-control
1253 Turn off all access checking. This switch is mainly useful for working
1254 around bugs in the access control code.
1258 Check that the pointer returned by @code{operator new} is non-null
1259 before attempting to modify the storage allocated. The current Working
1260 Paper requires that @code{operator new} never return a null pointer, so
1261 this check is normally unnecessary.
1263 An alternative to using this option is to specify that your
1264 @code{operator new} does not throw any exceptions; if you declare it
1265 @samp{throw()}, G++ will check the return value. See also @samp{new
1268 @item -fconserve-space
1269 @opindex fconserve-space
1270 Put uninitialized or runtime-initialized global variables into the
1271 common segment, as C does. This saves space in the executable at the
1272 cost of not diagnosing duplicate definitions. If you compile with this
1273 flag and your program mysteriously crashes after @code{main()} has
1274 completed, you may have an object that is being destroyed twice because
1275 two definitions were merged.
1277 This option is no longer useful on most targets, now that support has
1278 been added for putting variables into BSS without making them common.
1280 @item -fno-const-strings
1281 @opindex fno-const-strings
1282 Give string constants type @code{char *} instead of type @code{const
1283 char *}. By default, G++ uses type @code{const char *} as required by
1284 the standard. Even if you use @option{-fno-const-strings}, you cannot
1285 actually modify the value of a string constant, unless you also use
1286 @option{-fwritable-strings}.
1288 This option might be removed in a future release of G++. For maximum
1289 portability, you should structure your code so that it works with
1290 string constants that have type @code{const char *}.
1292 @item -fdollars-in-identifiers
1293 @opindex fdollars-in-identifiers
1294 Accept @samp{$} in identifiers. You can also explicitly prohibit use of
1295 @samp{$} with the option @option{-fno-dollars-in-identifiers}. (GNU C allows
1296 @samp{$} by default on most target systems, but there are a few exceptions.)
1297 Traditional C allowed the character @samp{$} to form part of
1298 identifiers. However, ISO C and C++ forbid @samp{$} in identifiers.
1300 @item -fno-elide-constructors
1301 @opindex fno-elide-constructors
1302 The C++ standard allows an implementation to omit creating a temporary
1303 which is only used to initialize another object of the same type.
1304 Specifying this option disables that optimization, and forces G++ to
1305 call the copy constructor in all cases.
1307 @item -fno-enforce-eh-specs
1308 @opindex fno-enforce-eh-specs
1309 Don't check for violation of exception specifications at runtime. This
1310 option violates the C++ standard, but may be useful for reducing code
1311 size in production builds, much like defining @samp{NDEBUG}. The compiler
1312 will still optimize based on the exception specifications.
1314 @item -fexternal-templates
1315 @opindex fexternal-templates
1316 Cause template instantiations to obey @samp{#pragma interface} and
1317 @samp{implementation}; template instances are emitted or not according
1318 to the location of the template definition. @xref{Template
1319 Instantiation}, for more information.
1321 This option is deprecated.
1323 @item -falt-external-templates
1324 @opindex falt-external-templates
1325 Similar to @option{-fexternal-templates}, but template instances are emitted or
1326 not according to the place where they are first instantiated.
1327 @xref{Template Instantiation}, for more information.
1329 This option is deprecated.
1332 @itemx -fno-for-scope
1334 @opindex fno-for-scope
1335 If @option{-ffor-scope} is specified, the scope of variables declared in
1336 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1337 as specified by the C++ standard.
1338 If @option{-fno-for-scope} is specified, the scope of variables declared in
1339 a @i{for-init-statement} extends to the end of the enclosing scope,
1340 as was the case in old versions of G++, and other (traditional)
1341 implementations of C++.
1343 The default if neither flag is given to follow the standard,
1344 but to allow and give a warning for old-style code that would
1345 otherwise be invalid, or have different behavior.
1347 @item -fno-gnu-keywords
1348 @opindex fno-gnu-keywords
1349 Do not recognize @code{typeof} as a keyword, so that code can use this
1350 word as an identifier. You can use the keyword @code{__typeof__} instead.
1351 @option{-ansi} implies @option{-fno-gnu-keywords}.
1353 @item -fno-honor-std
1354 @opindex fno-honor-std
1355 Ignore @code{namespace std}, instead of treating it as a real namespace.
1356 With this switch, the compiler will ignore
1357 @code{namespace-declarations}, @code{using-declarations},
1358 @code{using-directives}, and @code{namespace-names}, if they involve
1361 This option is only useful if you have manually compiled the C++
1362 run-time library with the same switch. Otherwise, your programs will
1363 not link. The use of this option is not recommended, and the option may
1364 be removed from a future version of G++.
1366 @item -fno-implicit-templates
1367 @opindex fno-implicit-templates
1368 Never emit code for non-inline templates which are instantiated
1369 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1370 @xref{Template Instantiation}, for more information.
1372 @item -fno-implicit-inline-templates
1373 @opindex fno-implicit-inline-templates
1374 Don't emit code for implicit instantiations of inline templates, either.
1375 The default is to handle inlines differently so that compiles with and
1376 without optimization will need the same set of explicit instantiations.
1378 @item -fno-implement-inlines
1379 @opindex fno-implement-inlines
1380 To save space, do not emit out-of-line copies of inline functions
1381 controlled by @samp{#pragma implementation}. This will cause linker
1382 errors if these functions are not inlined everywhere they are called.
1384 @item -fms-extensions
1385 @opindex fms-extensions
1386 Disable pedantic warnings about constructs used in MFC, such as implicit
1387 int and getting a pointer to member function via non-standard syntax.
1389 @item -fno-nonansi-builtins
1390 @opindex fno-nonansi-builtins
1391 Disable built-in declarations of functions that are not mandated by
1392 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1393 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1395 @item -fno-operator-names
1396 @opindex fno-operator-names
1397 Do not treat the operator name keywords @code{and}, @code{bitand},
1398 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1399 synonyms as keywords.
1401 @item -fno-optional-diags
1402 @opindex fno-optional-diags
1403 Disable diagnostics that the standard says a compiler does not need to
1404 issue. Currently, the only such diagnostic issued by G++ is the one for
1405 a name having multiple meanings within a class.
1408 @opindex fpermissive
1409 Downgrade messages about nonconformant code from errors to warnings. By
1410 default, G++ effectively sets @option{-pedantic-errors} without
1411 @option{-pedantic}; this option reverses that. This behavior and this
1412 option are superseded by @option{-pedantic}, which works as it does for GNU C@.
1416 Enable automatic template instantiation. This option also implies
1417 @option{-fno-implicit-templates}. @xref{Template Instantiation}, for more
1422 Disable generation of information about every class with virtual
1423 functions for use by the C++ runtime type identification features
1424 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1425 of the language, you can save some space by using this flag. Note that
1426 exception handling uses the same information, but it will generate it as
1431 Emit statistics about front-end processing at the end of the compilation.
1432 This information is generally only useful to the G++ development team.
1434 @item -ftemplate-depth-@var{n}
1435 @opindex ftemplate-depth
1436 Set the maximum instantiation depth for template classes to @var{n}.
1437 A limit on the template instantiation depth is needed to detect
1438 endless recursions during template class instantiation. ANSI/ISO C++
1439 conforming programs must not rely on a maximum depth greater than 17.
1441 @item -fuse-cxa-atexit
1442 @opindex fuse-cxa-atexit
1443 Register destructors for objects with static storage duration with the
1444 @code{__cxa_atexit} function rather than the @code{atexit} function.
1445 This option is required for fully standards-compliant handling of static
1446 destructors, but will only work if your C library supports
1447 @code{__cxa_atexit}.
1451 Emit special relocations for vtables and virtual function references
1452 so that the linker can identify unused virtual functions and zero out
1453 vtable slots that refer to them. This is most useful with
1454 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1455 also discard the functions themselves.
1457 This optimization requires GNU as and GNU ld. Not all systems support
1458 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1462 Do not use weak symbol support, even if it is provided by the linker.
1463 By default, G++ will use weak symbols if they are available. This
1464 option exists only for testing, and should not be used by end-users;
1465 it will result in inferior code and has no benefits. This option may
1466 be removed in a future release of G++.
1470 Do not search for header files in the standard directories specific to
1471 C++, but do still search the other standard directories. (This option
1472 is used when building the C++ library.)
1475 In addition, these optimization, warning, and code generation options
1476 have meanings only for C++ programs:
1479 @item -fno-default-inline
1480 @opindex fno-default-inline
1481 Do not assume @samp{inline} for functions defined inside a class scope.
1482 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1483 functions will have linkage like inline functions; they just won't be
1486 @item -Wctor-dtor-privacy @r{(C++ only)}
1487 @opindex Wctor-dtor-privacy
1488 Warn when a class seems unusable, because all the constructors or
1489 destructors in a class are private and the class has no friends or
1490 public static member functions.
1492 @item -Wnon-virtual-dtor @r{(C++ only)}
1493 @opindex Wnon-virtual-dtor
1494 Warn when a class declares a non-virtual destructor that should probably
1495 be virtual, because it looks like the class will be used polymorphically.
1497 @item -Wreorder @r{(C++ only)}
1499 @cindex reordering, warning
1500 @cindex warning for reordering of member initializers
1501 Warn when the order of member initializers given in the code does not
1502 match the order in which they must be executed. For instance:
1508 A(): j (0), i (1) @{ @}
1512 Here the compiler will warn that the member initializers for @samp{i}
1513 and @samp{j} will be rearranged to match the declaration order of the
1517 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1520 @item -Weffc++ @r{(C++ only)}
1522 Warn about violations of various style guidelines from Scott Meyers'
1523 @cite{Effective C++} books. If you use this option, you should be aware
1524 that the standard library headers do not obey all of these guidelines;
1525 you can use @samp{grep -v} to filter out those warnings.
1527 @item -Wno-deprecated @r{(C++ only)}
1528 @opindex Wno-deprecated
1529 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1531 @item -Wno-non-template-friend @r{(C++ only)}
1532 @opindex Wno-non-template-friend
1533 Disable warnings when non-templatized friend functions are declared
1534 within a template. With the advent of explicit template specification
1535 support in G++, if the name of the friend is an unqualified-id (i.e.,
1536 @samp{friend foo(int)}), the C++ language specification demands that the
1537 friend declare or define an ordinary, nontemplate function. (Section
1538 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1539 could be interpreted as a particular specialization of a templatized
1540 function. Because this non-conforming behavior is no longer the default
1541 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1542 check existing code for potential trouble spots, and is on by default.
1543 This new compiler behavior can be turned off with
1544 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1545 but disables the helpful warning.
1547 @item -Wold-style-cast @r{(C++ only)}
1548 @opindex Wold-style-cast
1549 Warn if an old-style (C-style) cast is used within a C++ program. The
1550 new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and
1551 @samp{const_cast}) are less vulnerable to unintended effects, and much
1554 @item -Woverloaded-virtual @r{(C++ only)}
1555 @opindex Woverloaded-virtual
1556 @cindex overloaded virtual fn, warning
1557 @cindex warning for overloaded virtual fn
1558 Warn when a function declaration hides virtual functions from a
1559 base class. For example, in:
1566 struct B: public A @{
1571 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1579 will fail to compile.
1581 @item -Wno-pmf-conversions @r{(C++ only)}
1582 @opindex Wno-pmf-conversions
1583 Disable the diagnostic for converting a bound pointer to member function
1586 @item -Wsign-promo @r{(C++ only)}
1587 @opindex Wsign-promo
1588 Warn when overload resolution chooses a promotion from unsigned or
1589 enumeral type to a signed type over a conversion to an unsigned type of
1590 the same size. Previous versions of G++ would try to preserve
1591 unsignedness, but the standard mandates the current behavior.
1593 @item -Wsynth @r{(C++ only)}
1595 @cindex warning for synthesized methods
1596 @cindex synthesized methods, warning
1597 Warn when G++'s synthesis behavior does not match that of cfront. For
1603 A& operator = (int);
1613 In this example, G++ will synthesize a default @samp{A& operator =
1614 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1617 @node Objective-C Dialect Options
1618 @section Options Controlling Objective-C Dialect
1620 @cindex compiler options, Objective-C
1621 @cindex Objective-C options, command line
1622 @cindex options, Objective-C
1623 This section describes the command-line options that are only meaningful
1624 for Objective-C programs; but you can also use most of the GNU compiler
1625 options regardless of what language your program is in. For example,
1626 you might compile a file @code{some_class.m} like this:
1629 gcc -g -fgnu-runtime -O -c some_class.m
1633 In this example, only @option{-fgnu-runtime} is an option meant only for
1634 Objective-C programs; you can use the other options with any language
1637 Here is a list of options that are @emph{only} for compiling Objective-C
1641 @item -fconstant-string-class=@var{class-name}
1642 @opindex fconstant-string-class
1643 Use @var{class-name} as the name of the class to instantiate for each
1644 literal string specified with the syntax @code{@@"@dots{}"}. The default
1645 class name is @code{NXConstantString}.
1648 @opindex fgnu-runtime
1649 Generate object code compatible with the standard GNU Objective-C
1650 runtime. This is the default for most types of systems.
1652 @item -fnext-runtime
1653 @opindex fnext-runtime
1654 Generate output compatible with the NeXT runtime. This is the default
1655 for NeXT-based systems, including Darwin and Mac OS X@.
1659 Dump interface declarations for all classes seen in the source file to a
1660 file named @file{@var{sourcename}.decl}.
1663 @opindex Wno-protocol
1664 Do not warn if methods required by a protocol are not implemented
1665 in the class adopting it.
1669 Warn if a selector has multiple methods of different types defined.
1671 @c not documented because only avail via -Wp
1672 @c @item -print-objc-runtime-info
1676 @node Language Independent Options
1677 @section Options to Control Diagnostic Messages Formatting
1678 @cindex options to control diagnostics formatting
1679 @cindex diagnostic messages
1680 @cindex message formatting
1682 Traditionally, diagnostic messages have been formatted irrespective of
1683 the output device's aspect (e.g.@: its width, @dots{}). The options described
1684 below can be used to control the diagnostic messages formatting
1685 algorithm, e.g.@: how many characters per line, how often source location
1686 information should be reported. Right now, only the C++ front end can
1687 honor these options. However it is expected, in the near future, that
1688 the remaining front ends would be able to digest them correctly.
1691 @item -fmessage-length=@var{n}
1692 @opindex fmessage-length
1693 Try to format error messages so that they fit on lines of about @var{n}
1694 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1695 the front ends supported by GCC@. If @var{n} is zero, then no
1696 line-wrapping will be done; each error message will appear on a single
1699 @opindex fdiagnostics-show-location
1700 @item -fdiagnostics-show-location=once
1701 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1702 reporter to emit @emph{once} source location information; that is, in
1703 case the message is too long to fit on a single physical line and has to
1704 be wrapped, the source location won't be emitted (as prefix) again,
1705 over and over, in subsequent continuation lines. This is the default
1708 @item -fdiagnostics-show-location=every-line
1709 Only meaningful in line-wrapping mode. Instructs the diagnostic
1710 messages reporter to emit the same source location information (as
1711 prefix) for physical lines that result from the process of breaking a
1712 a message which is too long to fit on a single line.
1716 @node Warning Options
1717 @section Options to Request or Suppress Warnings
1718 @cindex options to control warnings
1719 @cindex warning messages
1720 @cindex messages, warning
1721 @cindex suppressing warnings
1723 Warnings are diagnostic messages that report constructions which
1724 are not inherently erroneous but which are risky or suggest there
1725 may have been an error.
1727 You can request many specific warnings with options beginning @samp{-W},
1728 for example @option{-Wimplicit} to request warnings on implicit
1729 declarations. Each of these specific warning options also has a
1730 negative form beginning @samp{-Wno-} to turn off warnings;
1731 for example, @option{-Wno-implicit}. This manual lists only one of the
1732 two forms, whichever is not the default.
1734 These options control the amount and kinds of warnings produced by GCC:
1737 @cindex syntax checking
1739 @opindex fsyntax-only
1740 Check the code for syntax errors, but don't do anything beyond that.
1744 Issue all the warnings demanded by strict ISO C and ISO C++;
1745 reject all programs that use forbidden extensions, and some other
1746 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1747 version of the ISO C standard specified by any @option{-std} option used.
1749 Valid ISO C and ISO C++ programs should compile properly with or without
1750 this option (though a rare few will require @option{-ansi} or a
1751 @option{-std} option specifying the required version of ISO C)@. However,
1752 without this option, certain GNU extensions and traditional C and C++
1753 features are supported as well. With this option, they are rejected.
1755 @option{-pedantic} does not cause warning messages for use of the
1756 alternate keywords whose names begin and end with @samp{__}. Pedantic
1757 warnings are also disabled in the expression that follows
1758 @code{__extension__}. However, only system header files should use
1759 these escape routes; application programs should avoid them.
1760 @xref{Alternate Keywords}.
1762 Some users try to use @option{-pedantic} to check programs for strict ISO
1763 C conformance. They soon find that it does not do quite what they want:
1764 it finds some non-ISO practices, but not all---only those for which
1765 ISO C @emph{requires} a diagnostic, and some others for which
1766 diagnostics have been added.
1768 A feature to report any failure to conform to ISO C might be useful in
1769 some instances, but would require considerable additional work and would
1770 be quite different from @option{-pedantic}. We don't have plans to
1771 support such a feature in the near future.
1773 Where the standard specified with @option{-std} represents a GNU
1774 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1775 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1776 extended dialect is based. Warnings from @option{-pedantic} are given
1777 where they are required by the base standard. (It would not make sense
1778 for such warnings to be given only for features not in the specified GNU
1779 C dialect, since by definition the GNU dialects of C include all
1780 features the compiler supports with the given option, and there would be
1781 nothing to warn about.)
1783 @item -pedantic-errors
1784 @opindex pedantic-errors
1785 Like @option{-pedantic}, except that errors are produced rather than
1790 Inhibit all warning messages.
1794 Inhibit warning messages about the use of @samp{#import}.
1796 @item -Wchar-subscripts
1797 @opindex Wchar-subscripts
1798 Warn if an array subscript has type @code{char}. This is a common cause
1799 of error, as programmers often forget that this type is signed on some
1804 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1805 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1809 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1810 the arguments supplied have types appropriate to the format string
1811 specified, and that the conversions specified in the format string make
1812 sense. This includes standard functions, and others specified by format
1813 attributes (@pxref{Function Attributes}), in the @code{printf},
1814 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1815 not in the C standard) families.
1817 The formats are checked against the format features supported by GNU
1818 libc version 2.2. These include all ISO C89 and C99 features, as well
1819 as features from the Single Unix Specification and some BSD and GNU
1820 extensions. Other library implementations may not support all these
1821 features; GCC does not support warning about features that go beyond a
1822 particular library's limitations. However, if @option{-pedantic} is used
1823 with @option{-Wformat}, warnings will be given about format features not
1824 in the selected standard version (but not for @code{strfmon} formats,
1825 since those are not in any version of the C standard). @xref{C Dialect
1826 Options,,Options Controlling C Dialect}.
1828 @option{-Wformat} is included in @option{-Wall}. For more control over some
1829 aspects of format checking, the options @option{-Wno-format-y2k},
1830 @option{-Wno-format-extra-args}, @option{-Wformat-nonliteral},
1831 @option{-Wformat-security} and @option{-Wformat=2} are available, but are
1832 not included in @option{-Wall}.
1834 @item -Wno-format-y2k
1835 @opindex Wno-format-y2k
1836 If @option{-Wformat} is specified, do not warn about @code{strftime}
1837 formats which may yield only a two-digit year.
1839 @item -Wno-format-extra-args
1840 @opindex Wno-format-extra-args
1841 If @option{-Wformat} is specified, do not warn about excess arguments to a
1842 @code{printf} or @code{scanf} format function. The C standard specifies
1843 that such arguments are ignored.
1845 @item -Wformat-nonliteral
1846 @opindex Wformat-nonliteral
1847 If @option{-Wformat} is specified, also warn if the format string is not a
1848 string literal and so cannot be checked, unless the format function
1849 takes its format arguments as a @code{va_list}.
1851 @item -Wformat-security
1852 @opindex Wformat-security
1853 If @option{-Wformat} is specified, also warn about uses of format
1854 functions that represent possible security problems. At present, this
1855 warns about calls to @code{printf} and @code{scanf} functions where the
1856 format string is not a string literal and there are no format arguments,
1857 as in @code{printf (foo);}. This may be a security hole if the format
1858 string came from untrusted input and contains @samp{%n}. (This is
1859 currently a subset of what @option{-Wformat-nonliteral} warns about, but
1860 in future warnings may be added to @option{-Wformat-security} that are not
1861 included in @option{-Wformat-nonliteral}.)
1865 Enable @option{-Wformat} plus format checks not included in
1866 @option{-Wformat}. Currently equivalent to @samp{-Wformat
1867 -Wformat-nonliteral -Wformat-security}.
1869 @item -Wimplicit-int
1870 @opindex Wimplicit-int
1871 Warn when a declaration does not specify a type.
1873 @item -Wimplicit-function-declaration
1874 @itemx -Werror-implicit-function-declaration
1875 @opindex Wimplicit-function-declaration
1876 @opindex Werror-implicit-function-declaration
1877 Give a warning (or error) whenever a function is used before being
1882 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
1886 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
1887 function with external linkage, returning int, taking either zero
1888 arguments, two, or three arguments of appropriate types.
1890 @item -Wmissing-braces
1891 @opindex Wmissing-braces
1892 Warn if an aggregate or union initializer is not fully bracketed. In
1893 the following example, the initializer for @samp{a} is not fully
1894 bracketed, but that for @samp{b} is fully bracketed.
1897 int a[2][2] = @{ 0, 1, 2, 3 @};
1898 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
1903 Warn if a multicharacter constant (@samp{'FOOF'}) is used. Usually they
1904 indicate a typo in the user's code, as they have implementation-defined
1905 values, and should not be used in portable code.
1908 @opindex Wparentheses
1909 Warn if parentheses are omitted in certain contexts, such
1910 as when there is an assignment in a context where a truth value
1911 is expected, or when operators are nested whose precedence people
1912 often get confused about.
1914 Also warn about constructions where there may be confusion to which
1915 @code{if} statement an @code{else} branch belongs. Here is an example of
1930 In C, every @code{else} branch belongs to the innermost possible @code{if}
1931 statement, which in this example is @code{if (b)}. This is often not
1932 what the programmer expected, as illustrated in the above example by
1933 indentation the programmer chose. When there is the potential for this
1934 confusion, GCC will issue a warning when this flag is specified.
1935 To eliminate the warning, add explicit braces around the innermost
1936 @code{if} statement so there is no way the @code{else} could belong to
1937 the enclosing @code{if}. The resulting code would look like this:
1953 @item -Wsequence-point
1954 @opindex Wsequence-point
1955 Warn about code that may have undefined semantics because of violations
1956 of sequence point rules in the C standard.
1958 The C standard defines the order in which expressions in a C program are
1959 evaluated in terms of @dfn{sequence points}, which represent a partial
1960 ordering between the execution of parts of the program: those executed
1961 before the sequence point, and those executed after it. These occur
1962 after the evaluation of a full expression (one which is not part of a
1963 larger expression), after the evaluation of the first operand of a
1964 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
1965 function is called (but after the evaluation of its arguments and the
1966 expression denoting the called function), and in certain other places.
1967 Other than as expressed by the sequence point rules, the order of
1968 evaluation of subexpressions of an expression is not specified. All
1969 these rules describe only a partial order rather than a total order,
1970 since, for example, if two functions are called within one expression
1971 with no sequence point between them, the order in which the functions
1972 are called is not specified. However, the standards committee have
1973 ruled that function calls do not overlap.
1975 It is not specified when between sequence points modifications to the
1976 values of objects take effect. Programs whose behavior depends on this
1977 have undefined behavior; the C standard specifies that ``Between the
1978 previous and next sequence point an object shall have its stored value
1979 modified at most once by the evaluation of an expression. Furthermore,
1980 the prior value shall be read only to determine the value to be
1981 stored.''. If a program breaks these rules, the results on any
1982 particular implementation are entirely unpredictable.
1984 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
1985 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
1986 diagnosed by this option, and it may give an occasional false positive
1987 result, but in general it has been found fairly effective at detecting
1988 this sort of problem in programs.
1990 The present implementation of this option only works for C programs. A
1991 future implementation may also work for C++ programs.
1993 There is some controversy over the precise meaning of the sequence point
1994 rules in subtle cases. Links to papers with alternative formal definitions
1995 and other related discussions may be found on our readings page
1996 @w{@uref{http://gcc.gnu.org/readings.html}}.
1999 @opindex Wreturn-type
2000 Warn whenever a function is defined with a return-type that defaults to
2001 @code{int}. Also warn about any @code{return} statement with no
2002 return-value in a function whose return-type is not @code{void}.
2004 For C++, a function without return type always produces a diagnostic
2005 message, even when @option{-Wno-return-type} is specified. The only
2006 exceptions are @samp{main} and functions defined in system headers.
2010 Warn whenever a @code{switch} statement has an index of enumeral type
2011 and lacks a @code{case} for one or more of the named codes of that
2012 enumeration. (The presence of a @code{default} label prevents this
2013 warning.) @code{case} labels outside the enumeration range also
2014 provoke warnings when this option is used.
2018 Warn if any trigraphs are encountered that might change the meaning of
2019 the program (trigraphs within comments are not warned about).
2021 @item -Wunused-function
2022 @opindex Wunused-function
2023 Warn whenever a static function is declared but not defined or a
2024 non\-inline static function is unused.
2026 @item -Wunused-label
2027 @opindex Wunused-label
2028 Warn whenever a label is declared but not used.
2030 To suppress this warning use the @samp{unused} attribute
2031 (@pxref{Variable Attributes}).
2033 @item -Wunused-parameter
2034 @opindex Wunused-parameter
2035 Warn whenever a function parameter is unused aside from its declaration.
2037 To suppress this warning use the @samp{unused} attribute
2038 (@pxref{Variable Attributes}).
2040 @item -Wunused-variable
2041 @opindex Wunused-variable
2042 Warn whenever a local variable or non-constant static variable is unused
2043 aside from its declaration
2045 To suppress this warning use the @samp{unused} attribute
2046 (@pxref{Variable Attributes}).
2048 @item -Wunused-value
2049 @opindex Wunused-value
2050 Warn whenever a statement computes a result that is explicitly not used.
2052 To suppress this warning cast the expression to @samp{void}.
2056 All all the above @option{-Wunused} options combined.
2058 In order to get a warning about an unused function parameter, you must
2059 either specify @samp{-W -Wunused} or separately specify
2060 @option{-Wunused-parameter}.
2062 @item -Wuninitialized
2063 @opindex Wuninitialized
2064 Warn if an automatic variable is used without first being initialized or
2065 if a variable may be clobbered by a @code{setjmp} call.
2067 These warnings are possible only in optimizing compilation,
2068 because they require data flow information that is computed only
2069 when optimizing. If you don't specify @option{-O}, you simply won't
2072 These warnings occur only for variables that are candidates for
2073 register allocation. Therefore, they do not occur for a variable that
2074 is declared @code{volatile}, or whose address is taken, or whose size
2075 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2076 structures, unions or arrays, even when they are in registers.
2078 Note that there may be no warning about a variable that is used only
2079 to compute a value that itself is never used, because such
2080 computations may be deleted by data flow analysis before the warnings
2083 These warnings are made optional because GCC is not smart
2084 enough to see all the reasons why the code might be correct
2085 despite appearing to have an error. Here is one example of how
2106 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2107 always initialized, but GCC doesn't know this. Here is
2108 another common case:
2113 if (change_y) save_y = y, y = new_y;
2115 if (change_y) y = save_y;
2120 This has no bug because @code{save_y} is used only if it is set.
2122 @cindex @code{longjmp} warnings
2123 This option also warns when a non-volatile automatic variable might be
2124 changed by a call to @code{longjmp}. These warnings as well are possible
2125 only in optimizing compilation.
2127 The compiler sees only the calls to @code{setjmp}. It cannot know
2128 where @code{longjmp} will be called; in fact, a signal handler could
2129 call it at any point in the code. As a result, you may get a warning
2130 even when there is in fact no problem because @code{longjmp} cannot
2131 in fact be called at the place which would cause a problem.
2133 Some spurious warnings can be avoided if you declare all the functions
2134 you use that never return as @code{noreturn}. @xref{Function
2137 @item -Wreorder @r{(C++ only)}
2139 @cindex reordering, warning
2140 @cindex warning for reordering of member initializers
2141 Warn when the order of member initializers given in the code does not
2142 match the order in which they must be executed. For instance:
2144 @item -Wunknown-pragmas
2145 @opindex Wunknown-pragmas
2146 @cindex warning for unknown pragmas
2147 @cindex unknown pragmas, warning
2148 @cindex pragmas, warning of unknown
2149 Warn when a #pragma directive is encountered which is not understood by
2150 GCC@. If this command line option is used, warnings will even be issued
2151 for unknown pragmas in system header files. This is not the case if
2152 the warnings were only enabled by the @option{-Wall} command line option.
2156 All of the above @samp{-W} options combined. This enables all the
2157 warnings about constructions that some users consider questionable, and
2158 that are easy to avoid (or modify to prevent the warning), even in
2159 conjunction with macros.
2161 @item -Wsystem-headers
2162 @opindex Wsystem-headers
2163 @cindex warnings from system headers
2164 @cindex system headers, warnings from
2165 Print warning messages for constructs found in system header files.
2166 Warnings from system headers are normally suppressed, on the assumption
2167 that they usually do not indicate real problems and would only make the
2168 compiler output harder to read. Using this command line option tells
2169 GCC to emit warnings from system headers as if they occurred in user
2170 code. However, note that using @option{-Wall} in conjunction with this
2171 option will @emph{not} warn about unknown pragmas in system
2172 headers---for that, @option{-Wunknown-pragmas} must also be used.
2175 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2176 Some of them warn about constructions that users generally do not
2177 consider questionable, but which occasionally you might wish to check
2178 for; others warn about constructions that are necessary or hard to avoid
2179 in some cases, and there is no simple way to modify the code to suppress
2185 Print extra warning messages for these events:
2189 A function can return either with or without a value. (Falling
2190 off the end of the function body is considered returning without
2191 a value.) For example, this function would evoke such a
2205 An expression-statement or the left-hand side of a comma expression
2206 contains no side effects.
2207 To suppress the warning, cast the unused expression to void.
2208 For example, an expression such as @samp{x[i,j]} will cause a warning,
2209 but @samp{x[(void)i,j]} will not.
2212 An unsigned value is compared against zero with @samp{<} or @samp{<=}.
2215 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2216 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2217 that of ordinary mathematical notation.
2220 Storage-class specifiers like @code{static} are not the first things in
2221 a declaration. According to the C Standard, this usage is obsolescent.
2224 The return type of a function has a type qualifier such as @code{const}.
2225 Such a type qualifier has no effect, since the value returned by a
2226 function is not an lvalue. (But don't warn about the GNU extension of
2227 @code{volatile void} return types. That extension will be warned about
2228 if @option{-pedantic} is specified.)
2231 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2235 A comparison between signed and unsigned values could produce an
2236 incorrect result when the signed value is converted to unsigned.
2237 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2240 An aggregate has a partly bracketed initializer.
2241 For example, the following code would evoke such a warning,
2242 because braces are missing around the initializer for @code{x.h}:
2245 struct s @{ int f, g; @};
2246 struct t @{ struct s h; int i; @};
2247 struct t x = @{ 1, 2, 3 @};
2251 An aggregate has an initializer which does not initialize all members.
2252 For example, the following code would cause such a warning, because
2253 @code{x.h} would be implicitly initialized to zero:
2256 struct s @{ int f, g, h; @};
2257 struct s x = @{ 3, 4 @};
2262 @opindex Wfloat-equal
2263 Warn if floating point values are used in equality comparisons.
2265 The idea behind this is that sometimes it is convenient (for the
2266 programmer) to consider floating-point values as approximations to
2267 infinitely precise real numbers. If you are doing this, then you need
2268 to compute (by analysing the code, or in some other way) the maximum or
2269 likely maximum error that the computation introduces, and allow for it
2270 when performing comparisons (and when producing output, but that's a
2271 different problem). In particular, instead of testing for equality, you
2272 would check to see whether the two values have ranges that overlap; and
2273 this is done with the relational operators, so equality comparisons are
2276 @item -Wtraditional @r{(C only)}
2277 @opindex Wtraditional
2278 Warn about certain constructs that behave differently in traditional and
2279 ISO C@. Also warn about ISO C constructs that have no traditional C
2280 equivalent, and/or problematic constructs which should be avoided.
2284 Macro parameters that appear within string literals in the macro body.
2285 In traditional C macro replacement takes place within string literals,
2286 but does not in ISO C@.
2289 In traditional C, some preprocessor directives did not exist.
2290 Traditional preprocessors would only consider a line to be a directive
2291 if the @samp{#} appeared in column 1 on the line. Therefore
2292 @option{-Wtraditional} warns about directives that traditional C
2293 understands but would ignore because the @samp{#} does not appear as the
2294 first character on the line. It also suggests you hide directives like
2295 @samp{#pragma} not understood by traditional C by indenting them. Some
2296 traditional implementations would not recognise @samp{#elif}, so it
2297 suggests avoiding it altogether.
2300 A function-like macro that appears without arguments.
2303 The unary plus operator.
2306 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2307 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2308 constants.) Note, these suffixes appear in macros defined in the system
2309 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2310 Use of these macros in user code might normally lead to spurious
2311 warnings, however gcc's integrated preprocessor has enough context to
2312 avoid warning in these cases.
2315 A function declared external in one block and then used after the end of
2319 A @code{switch} statement has an operand of type @code{long}.
2322 A non-@code{static} function declaration follows a @code{static} one.
2323 This construct is not accepted by some traditional C compilers.
2326 The ISO type of an integer constant has a different width or
2327 signedness from its traditional type. This warning is only issued if
2328 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2329 typically represent bit patterns, are not warned about.
2332 Usage of ISO string concatenation is detected.
2335 Initialization of automatic aggregates.
2338 Identifier conflicts with labels. Traditional C lacks a separate
2339 namespace for labels.
2342 Initialization of unions. If the initializer is zero, the warning is
2343 omitted. This is done under the assumption that the zero initializer in
2344 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2345 initializer warnings and relies on default initialization to zero in the
2349 Conversions by prototypes between fixed/floating point values and vice
2350 versa. The absence of these prototypes when compiling with traditional
2351 C would cause serious problems. This is a subset of the possible
2352 conversion warnings, for the full set use @option{-Wconversion}.
2357 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2361 Warn whenever a local variable shadows another local variable, parameter or
2362 global variable or whenever a built-in function is shadowed.
2364 @item -Wlarger-than-@var{len}
2365 @opindex Wlarger-than
2366 Warn whenever an object of larger than @var{len} bytes is defined.
2368 @item -Wpointer-arith
2369 @opindex Wpointer-arith
2370 Warn about anything that depends on the ``size of'' a function type or
2371 of @code{void}. GNU C assigns these types a size of 1, for
2372 convenience in calculations with @code{void *} pointers and pointers
2375 @item -Wbad-function-cast @r{(C only)}
2376 @opindex Wbad-function-cast
2377 Warn whenever a function call is cast to a non-matching type.
2378 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2382 Warn whenever a pointer is cast so as to remove a type qualifier from
2383 the target type. For example, warn if a @code{const char *} is cast
2384 to an ordinary @code{char *}.
2387 @opindex Wcast-align
2388 Warn whenever a pointer is cast such that the required alignment of the
2389 target is increased. For example, warn if a @code{char *} is cast to
2390 an @code{int *} on machines where integers can only be accessed at
2391 two- or four-byte boundaries.
2393 @item -Wwrite-strings
2394 @opindex Wwrite-strings
2395 When compiling C, give string constants the type @code{const
2396 char[@var{length}]} so that
2397 copying the address of one into a non-@code{const} @code{char *}
2398 pointer will get a warning; when compiling C++, warn about the
2399 deprecated conversion from string constants to @code{char *}.
2400 These warnings will help you find at
2401 compile time code that can try to write into a string constant, but
2402 only if you have been very careful about using @code{const} in
2403 declarations and prototypes. Otherwise, it will just be a nuisance;
2404 this is why we did not make @option{-Wall} request these warnings.
2407 @opindex Wconversion
2408 Warn if a prototype causes a type conversion that is different from what
2409 would happen to the same argument in the absence of a prototype. This
2410 includes conversions of fixed point to floating and vice versa, and
2411 conversions changing the width or signedness of a fixed point argument
2412 except when the same as the default promotion.
2414 Also, warn if a negative integer constant expression is implicitly
2415 converted to an unsigned type. For example, warn about the assignment
2416 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2417 casts like @code{(unsigned) -1}.
2419 @item -Wsign-compare
2420 @opindex Wsign-compare
2421 @cindex warning for comparison of signed and unsigned values
2422 @cindex comparison of signed and unsigned values, warning
2423 @cindex signed and unsigned values, comparison warning
2424 Warn when a comparison between signed and unsigned values could produce
2425 an incorrect result when the signed value is converted to unsigned.
2426 This warning is also enabled by @option{-W}; to get the other warnings
2427 of @option{-W} without this warning, use @samp{-W -Wno-sign-compare}.
2429 @item -Waggregate-return
2430 @opindex Waggregate-return
2431 Warn if any functions that return structures or unions are defined or
2432 called. (In languages where you can return an array, this also elicits
2435 @item -Wstrict-prototypes @r{(C only)}
2436 @opindex Wstrict-prototypes
2437 Warn if a function is declared or defined without specifying the
2438 argument types. (An old-style function definition is permitted without
2439 a warning if preceded by a declaration which specifies the argument
2442 @item -Wmissing-prototypes @r{(C only)}
2443 @opindex Wmissing-prototypes
2444 Warn if a global function is defined without a previous prototype
2445 declaration. This warning is issued even if the definition itself
2446 provides a prototype. The aim is to detect global functions that fail
2447 to be declared in header files.
2449 @item -Wmissing-declarations
2450 @opindex Wmissing-declarations
2451 Warn if a global function is defined without a previous declaration.
2452 Do so even if the definition itself provides a prototype.
2453 Use this option to detect global functions that are not declared in
2456 @item -Wmissing-noreturn
2457 @opindex Wmissing-noreturn
2458 Warn about functions which might be candidates for attribute @code{noreturn}.
2459 Note these are only possible candidates, not absolute ones. Care should
2460 be taken to manually verify functions actually do not ever return before
2461 adding the @code{noreturn} attribute, otherwise subtle code generation
2462 bugs could be introduced. You will not get a warning for @code{main} in
2463 hosted C environments.
2465 @item -Wmissing-format-attribute
2466 @opindex Wmissing-format-attribute
2468 If @option{-Wformat} is enabled, also warn about functions which might be
2469 candidates for @code{format} attributes. Note these are only possible
2470 candidates, not absolute ones. GCC will guess that @code{format}
2471 attributes might be appropriate for any function that calls a function
2472 like @code{vprintf} or @code{vscanf}, but this might not always be the
2473 case, and some functions for which @code{format} attributes are
2474 appropriate may not be detected. This option has no effect unless
2475 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2479 Warn if a structure is given the packed attribute, but the packed
2480 attribute has no effect on the layout or size of the structure.
2481 Such structures may be mis-aligned for little benefit. For
2482 instance, in this code, the variable @code{f.x} in @code{struct bar}
2483 will be misaligned even though @code{struct bar} does not itself
2484 have the packed attribute:
2491 @} __attribute__((packed));
2501 Warn if padding is included in a structure, either to align an element
2502 of the structure or to align the whole structure. Sometimes when this
2503 happens it is possible to rearrange the fields of the structure to
2504 reduce the padding and so make the structure smaller.
2506 @item -Wredundant-decls
2507 @opindex Wredundant-decls
2508 Warn if anything is declared more than once in the same scope, even in
2509 cases where multiple declaration is valid and changes nothing.
2511 @item -Wnested-externs @r{(C only)}
2512 @opindex Wnested-externs
2513 Warn if an @code{extern} declaration is encountered within a function.
2515 @item -Wunreachable-code
2516 @opindex Wunreachable-code
2517 Warn if the compiler detects that code will never be executed.
2519 This option is intended to warn when the compiler detects that at
2520 least a whole line of source code will never be executed, because
2521 some condition is never satisfied or because it is after a
2522 procedure that never returns.
2524 It is possible for this option to produce a warning even though there
2525 are circumstances under which part of the affected line can be executed,
2526 so care should be taken when removing apparently-unreachable code.
2528 For instance, when a function is inlined, a warning may mean that the
2529 line is unreachable in only one inlined copy of the function.
2531 This option is not made part of @option{-Wall} because in a debugging
2532 version of a program there is often substantial code which checks
2533 correct functioning of the program and is, hopefully, unreachable
2534 because the program does work. Another common use of unreachable
2535 code is to provide behaviour which is selectable at compile-time.
2539 Warn if a function can not be inlined and it was declared as inline.
2543 @opindex Wno-long-long
2544 Warn if @samp{long long} type is used. This is default. To inhibit
2545 the warning messages, use @option{-Wno-long-long}. Flags
2546 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2547 only when @option{-pedantic} flag is used.
2549 @item -Wdisabled-optimization
2550 @opindex Wdisabled-optimization
2551 Warn if a requested optimization pass is disabled. This warning does
2552 not generally indicate that there is anything wrong with your code; it
2553 merely indicates that GCC's optimizers were unable to handle the code
2554 effectively. Often, the problem is that your code is too big or too
2555 complex; GCC will refuse to optimize programs when the optimization
2556 itself is likely to take inordinate amounts of time.
2560 Make all warnings into errors.
2563 @node Debugging Options
2564 @section Options for Debugging Your Program or GCC
2565 @cindex options, debugging
2566 @cindex debugging information options
2568 GCC has various special options that are used for debugging
2569 either your program or GCC:
2574 Produce debugging information in the operating system's native format
2575 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2578 On most systems that use stabs format, @option{-g} enables use of extra
2579 debugging information that only GDB can use; this extra information
2580 makes debugging work better in GDB but will probably make other debuggers
2582 refuse to read the program. If you want to control for certain whether
2583 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2584 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, or @option{-gdwarf-1}
2587 Unlike most other C compilers, GCC allows you to use @option{-g} with
2588 @option{-O}. The shortcuts taken by optimized code may occasionally
2589 produce surprising results: some variables you declared may not exist
2590 at all; flow of control may briefly move where you did not expect it;
2591 some statements may not be executed because they compute constant
2592 results or their values were already at hand; some statements may
2593 execute in different places because they were moved out of loops.
2595 Nevertheless it proves possible to debug optimized output. This makes
2596 it reasonable to use the optimizer for programs that might have bugs.
2598 The following options are useful when GCC is generated with the
2599 capability for more than one debugging format.
2603 Produce debugging information for use by GDB@. This means to use the
2604 most expressive format available (DWARF 2, stabs, or the native format
2605 if neither of those are supported), including GDB extensions if at all
2610 Produce debugging information in stabs format (if that is supported),
2611 without GDB extensions. This is the format used by DBX on most BSD
2612 systems. On MIPS, Alpha and System V Release 4 systems this option
2613 produces stabs debugging output which is not understood by DBX or SDB@.
2614 On System V Release 4 systems this option requires the GNU assembler.
2618 Produce debugging information in stabs format (if that is supported),
2619 using GNU extensions understood only by the GNU debugger (GDB)@. The
2620 use of these extensions is likely to make other debuggers crash or
2621 refuse to read the program.
2625 Produce debugging information in COFF format (if that is supported).
2626 This is the format used by SDB on most System V systems prior to
2631 Produce debugging information in XCOFF format (if that is supported).
2632 This is the format used by the DBX debugger on IBM RS/6000 systems.
2636 Produce debugging information in XCOFF format (if that is supported),
2637 using GNU extensions understood only by the GNU debugger (GDB)@. The
2638 use of these extensions is likely to make other debuggers crash or
2639 refuse to read the program, and may cause assemblers other than the GNU
2640 assembler (GAS) to fail with an error.
2644 Produce debugging information in DWARF version 1 format (if that is
2645 supported). This is the format used by SDB on most System V Release 4
2650 Produce debugging information in DWARF version 1 format (if that is
2651 supported), using GNU extensions understood only by the GNU debugger
2652 (GDB)@. The use of these extensions is likely to make other debuggers
2653 crash or refuse to read the program.
2657 Produce debugging information in DWARF version 2 format (if that is
2658 supported). This is the format used by DBX on IRIX 6.
2661 @itemx -ggdb@var{level}
2662 @itemx -gstabs@var{level}
2663 @itemx -gcoff@var{level}
2664 @itemx -gxcoff@var{level}
2665 @itemx -gdwarf@var{level}
2666 @itemx -gdwarf-2@var{level}
2667 Request debugging information and also use @var{level} to specify how
2668 much information. The default level is 2.
2670 Level 1 produces minimal information, enough for making backtraces in
2671 parts of the program that you don't plan to debug. This includes
2672 descriptions of functions and external variables, but no information
2673 about local variables and no line numbers.
2675 Level 3 includes extra information, such as all the macro definitions
2676 present in the program. Some debuggers support macro expansion when
2677 you use @option{-g3}.
2682 Generate extra code to write profile information suitable for the
2683 analysis program @code{prof}. You must use this option when compiling
2684 the source files you want data about, and you must also use it when
2687 @cindex @code{gprof}
2690 Generate extra code to write profile information suitable for the
2691 analysis program @code{gprof}. You must use this option when compiling
2692 the source files you want data about, and you must also use it when
2698 Generate extra code to write profile information for basic blocks, which will
2699 record the number of times each basic block is executed, the basic block start
2700 address, and the function name containing the basic block. If @option{-g} is
2701 used, the line number and filename of the start of the basic block will also be
2702 recorded. If not overridden by the machine description, the default action is
2703 to append to the text file @file{bb.out}.
2705 This data could be analyzed by a program like @code{tcov}. Note,
2706 however, that the format of the data is not what @code{tcov} expects.
2707 Eventually GNU @code{gprof} should be extended to process this data.
2711 Makes the compiler print out each function name as it is compiled, and
2712 print some statistics about each pass when it finishes.
2715 @opindex ftime-report
2716 Makes the compiler print some statistics about the time consumed by each
2717 pass when it finishes.
2720 @opindex fmem-report
2721 Makes the compiler print some statistics about permanent memory
2722 allocation when it finishes.
2726 Generate extra code to profile basic blocks. Your executable will
2727 produce output that is a superset of that produced when @option{-a} is
2728 used. Additional output is the source and target address of the basic
2729 blocks where a jump takes place, the number of times a jump is executed,
2730 and (optionally) the complete sequence of basic blocks being executed.
2731 The output is appended to file @file{bb.out}.
2733 You can examine different profiling aspects without recompilation. Your
2734 executable will read a list of function names from file @file{bb.in}.
2735 Profiling starts when a function on the list is entered and stops when
2736 that invocation is exited. To exclude a function from profiling, prefix
2737 its name with @samp{-}. If a function name is not unique, you can
2738 disambiguate it by writing it in the form
2739 @samp{/path/filename.d:functionname}. Your executable will write the
2740 available paths and filenames in file @file{bb.out}.
2742 Several function names have a special meaning:
2745 Write source, target and frequency of jumps to file @file{bb.out}.
2746 @item __bb_hidecall__
2747 Exclude function calls from frequency count.
2748 @item __bb_showret__
2749 Include function returns in frequency count.
2751 Write the sequence of basic blocks executed to file @file{bbtrace.gz}.
2752 The file will be compressed using the program @samp{gzip}, which must
2753 exist in your @env{PATH}. On systems without the @samp{popen}
2754 function, the file will be named @file{bbtrace} and will not be
2755 compressed. @strong{Profiling for even a few seconds on these systems
2756 will produce a very large file.} Note: @code{__bb_hidecall__} and
2757 @code{__bb_showret__} will not affect the sequence written to
2761 Here's a short example using different profiling parameters
2762 in file @file{bb.in}. Assume function @code{foo} consists of basic blocks
2763 1 and 2 and is called twice from block 3 of function @code{main}. After
2764 the calls, block 3 transfers control to block 4 of @code{main}.
2766 With @code{__bb_trace__} and @code{main} contained in file @file{bb.in},
2767 the following sequence of blocks is written to file @file{bbtrace.gz}:
2768 0 3 1 2 1 2 4. The return from block 2 to block 3 is not shown, because
2769 the return is to a point inside the block and not to the top. The
2770 block address 0 always indicates, that control is transferred
2771 to the trace from somewhere outside the observed functions. With
2772 @samp{-foo} added to @file{bb.in}, the blocks of function
2773 @code{foo} are removed from the trace, so only 0 3 4 remains.
2775 With @code{__bb_jumps__} and @code{main} contained in file @file{bb.in},
2776 jump frequencies will be written to file @file{bb.out}. The
2777 frequencies are obtained by constructing a trace of blocks
2778 and incrementing a counter for every neighbouring pair of blocks
2779 in the trace. The trace 0 3 1 2 1 2 4 displays the following
2783 Jump from block 0x0 to block 0x3 executed 1 time(s)
2784 Jump from block 0x3 to block 0x1 executed 1 time(s)
2785 Jump from block 0x1 to block 0x2 executed 2 time(s)
2786 Jump from block 0x2 to block 0x1 executed 1 time(s)
2787 Jump from block 0x2 to block 0x4 executed 1 time(s)
2790 With @code{__bb_hidecall__}, control transfer due to call instructions
2791 is removed from the trace, that is the trace is cut into three parts: 0
2792 3 4, 0 1 2 and 0 1 2. With @code{__bb_showret__}, control transfer due
2793 to return instructions is added to the trace. The trace becomes: 0 3 1
2794 2 3 1 2 3 4. Note, that this trace is not the same, as the sequence
2795 written to @file{bbtrace.gz}. It is solely used for counting jump
2798 @item -fprofile-arcs
2799 @opindex fprofile-arcs
2800 Instrument @dfn{arcs} during compilation. For each function of your
2801 program, GCC creates a program flow graph, then finds a spanning tree
2802 for the graph. Only arcs that are not on the spanning tree have to be
2803 instrumented: the compiler adds code to count the number of times that these
2804 arcs are executed. When an arc is the only exit or only entrance to a
2805 block, the instrumentation code can be added to the block; otherwise, a
2806 new basic block must be created to hold the instrumentation code.
2808 Since not every arc in the program must be instrumented, programs
2809 compiled with this option run faster than programs compiled with
2810 @option{-a}, which adds instrumentation code to every basic block in the
2811 program. The tradeoff: since @code{gcov} does not have
2812 execution counts for all branches, it must start with the execution
2813 counts for the instrumented branches, and then iterate over the program
2814 flow graph until the entire graph has been solved. Hence, @code{gcov}
2815 runs a little more slowly than a program which uses information from
2818 @option{-fprofile-arcs} also makes it possible to estimate branch
2819 probabilities, and to calculate basic block execution counts. In
2820 general, basic block execution counts do not give enough information to
2821 estimate all branch probabilities. When the compiled program exits, it
2822 saves the arc execution counts to a file called
2823 @file{@var{sourcename}.da}. Use the compiler option
2824 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
2825 Control Optimization}) when recompiling, to optimize using estimated
2826 branch probabilities.
2829 @item -ftest-coverage
2830 @opindex ftest-coverage
2831 Create data files for the @code{gcov} code-coverage utility
2832 (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}).
2833 The data file names begin with the name of your source file:
2836 @item @var{sourcename}.bb
2837 A mapping from basic blocks to line numbers, which @code{gcov} uses to
2838 associate basic block execution counts with line numbers.
2840 @item @var{sourcename}.bbg
2841 A list of all arcs in the program flow graph. This allows @code{gcov}
2842 to reconstruct the program flow graph, so that it can compute all basic
2843 block and arc execution counts from the information in the
2844 @code{@var{sourcename}.da} file (this last file is the output from
2845 @option{-fprofile-arcs}).
2848 @item -d@var{letters}
2850 Says to make debugging dumps during compilation at times specified by
2851 @var{letters}. This is used for debugging the compiler. The file names
2852 for most of the dumps are made by appending a pass number and a word to
2853 the source file name (e.g. @file{foo.c.00.rtl} or @file{foo.c.01.sibling}).
2854 Here are the possible letters for use in @var{letters}, and their meanings:
2859 Annotate the assembler output with miscellaneous debugging information.
2862 Dump after computing branch probabilities, to @file{@var{file}.14.bp}.
2865 Dump after block reordering, to @file{@var{file}.28.bbro}.
2868 Dump after instruction combination, to the file @file{@var{file}.16.combine}.
2871 Dump after the first if conversion, to the file @file{@var{file}.17.ce}.
2874 Dump after delayed branch scheduling, to @file{@var{file}.31.dbr}.
2877 Dump all macro definitions, at the end of preprocessing, in addition to
2881 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
2882 @file{@var{file}.07.ussa}.
2885 Dump after the second if conversion, to @file{@var{file}.26.ce2}.
2888 Dump after life analysis, to @file{@var{file}.15.life}.
2891 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.09.addressof}.
2894 Dump after global register allocation, to @file{@var{file}.21.greg}.
2897 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
2901 Dump after post-reload CSE and other optimizations, to @file{@var{file}.22.postreload}.
2904 Dump after GCSE, to @file{@var{file}.10.gcse}.
2907 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
2910 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
2913 Dump after the last jump optimization, to @file{@var{file}.29.jump2}.
2916 Dump after conversion from registers to stack, to @file{@var{file}.32.stack}.
2919 Dump after local register allocation, to @file{@var{file}.20.lreg}.
2922 Dump after loop optimization, to @file{@var{file}.11.loop}.
2925 Dump after performing the machine dependent reorganisation pass, to
2926 @file{@var{file}.30.mach}.
2929 Dump after register renumbering, to @file{@var{file}.25.rnreg}.
2932 Dump after the register move pass, to @file{@var{file}.18.regmove}.
2935 Dump after RTL generation, to @file{@var{file}.00.rtl}.
2938 Dump after the second instruction scheduling pass, to
2939 @file{@var{file}.27.sched2}.
2942 Dump after CSE (including the jump optimization that sometimes follows
2943 CSE), to @file{@var{file}.08.cse}.
2946 Dump after the first instruction scheduling pass, to
2947 @file{@var{file}.19.sched}.
2950 Dump after the second CSE pass (including the jump optimization that
2951 sometimes follows CSE), to @file{@var{file}.12.cse2}.
2954 Dump after the second flow pass, to @file{@var{file}.23.flow2}.
2957 Dump after SSA aggressive dead code elimination, to @file{@var{file}.06.ssadce}.
2960 Dump after the peephole pass, to @file{@var{file}.24.peephole2}.
2963 Produce all the dumps listed above.
2966 Print statistics on memory usage, at the end of the run, to
2970 Annotate the assembler output with a comment indicating which
2971 pattern and alternative was used. The length of each instruction is
2975 Dump the RTL in the assembler output as a comment before each instruction.
2976 Also turns on @option{-dp} annotation.
2979 For each of the other indicated dump files (except for
2980 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
2981 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
2984 Just generate RTL for a function instead of compiling it. Usually used
2988 Dump debugging information during parsing, to standard error.
2991 @item -fdump-unnumbered
2992 @opindex fdump-unnumbered
2993 When doing debugging dumps (see @option{-d} option above), suppress instruction
2994 numbers and line number note output. This makes it more feasible to
2995 use diff on debugging dumps for compiler invocations with different
2996 options, in particular with and without @option{-g}.
2998 @item -fdump-translation-unit @r{(C and C++ only)}
2999 @itemx -fdump-translation-unit-@var{number} @r{(C and C++ only)}
3000 @opindex fdump-translation-unit
3001 Dump a representation of the tree structure for the entire translation
3002 unit to a file. The file name is made by appending @file{.tu} to the
3003 source file name. If the @samp{-@var{number}} form is used, @var{number}
3004 controls the details of the dump as described for the @option{-fdump-tree} options.
3006 @item -fdump-class-hierarchy @r{(C++ only)}
3007 @itemx -fdump-class-hierarchy-@var{number} @r{(C++ only)}
3008 @opindex fdump-class-hierarchy
3009 Dump a representation of each class's hierarchy and virtual function
3010 table layout to a file. The file name is made by appending @file{.class}
3011 to the source file name. If the @samp{-@var{number}} form is used, @var{number}
3012 controls the details of the dump as described for the @option{-fdump-tree}
3015 @item -fdump-ast-@var{switch} @r{(C++ only)}
3016 @itemx -fdump-ast-@var{switch}-@var{number} @r{(C++ only)}
3018 Control the dumping at various stages of processing the abstract syntax
3019 tree to a file. The file name is generated by appending a switch
3020 specific suffix to the source file name. If the @samp{-@var{number}} form is
3021 used, @var{number} is a bit mask which controls the details of the
3022 dump. The following bits are meaningful (these are not set symbolically,
3023 as the primary function of these dumps is for debugging gcc itself):
3027 Print the address of each node. Usually this is not meaningful as it
3028 changes according to the environment and source file.
3030 Inhibit dumping of members of a scope or body of a function, unless they
3031 are reachable by some other path.
3034 The following tree dumps are possible:
3037 Dump before any tree based optimization, to @file{@var{file}.original}.
3039 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3041 Dump after inlining within the body of the function, to
3042 @file{@var{file}.inlined}.
3045 @item -fpretend-float
3046 @opindex fpretend-float
3047 When running a cross-compiler, pretend that the target machine uses the
3048 same floating point format as the host machine. This causes incorrect
3049 output of the actual floating constants, but the actual instruction
3050 sequence will probably be the same as GCC would make when running on
3055 Store the usual ``temporary'' intermediate files permanently; place them
3056 in the current directory and name them based on the source file. Thus,
3057 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3058 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3059 preprocessed @file{foo.i} output file even though the compiler now
3060 normally uses an integrated preprocessor.
3064 Report the CPU time taken by each subprocess in the compilation
3065 sequence. For C source files, this is the compiler proper and assembler
3066 (plus the linker if linking is done). The output looks like this:
3073 The first number on each line is the ``user time,'' that is time spent
3074 executing the program itself. The second number is ``system time,''
3075 time spent executing operating system routines on behalf of the program.
3076 Both numbers are in seconds.
3078 @item -print-file-name=@var{library}
3079 @opindex print-file-name
3080 Print the full absolute name of the library file @var{library} that
3081 would be used when linking---and don't do anything else. With this
3082 option, GCC does not compile or link anything; it just prints the
3085 @item -print-multi-directory
3086 @opindex print-multi-directory
3087 Print the directory name corresponding to the multilib selected by any
3088 other switches present in the command line. This directory is supposed
3089 to exist in @env{GCC_EXEC_PREFIX}.
3091 @item -print-multi-lib
3092 @opindex print-multi-lib
3093 Print the mapping from multilib directory names to compiler switches
3094 that enable them. The directory name is separated from the switches by
3095 @samp{;}, and each switch starts with an @samp{@@} instead of the
3096 @samp{-}, without spaces between multiple switches. This is supposed to
3097 ease shell-processing.
3099 @item -print-prog-name=@var{program}
3100 @opindex print-prog-name
3101 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3103 @item -print-libgcc-file-name
3104 @opindex print-libgcc-file-name
3105 Same as @option{-print-file-name=libgcc.a}.
3107 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3108 but you do want to link with @file{libgcc.a}. You can do
3111 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3114 @item -print-search-dirs
3115 @opindex print-search-dirs
3116 Print the name of the configured installation directory and a list of
3117 program and library directories gcc will search---and don't do anything else.
3119 This is useful when gcc prints the error message
3120 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3121 To resolve this you either need to put @file{cpp0} and the other compiler
3122 components where gcc expects to find them, or you can set the environment
3123 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3124 Don't forget the trailing '/'.
3125 @xref{Environment Variables}.
3128 @opindex dumpmachine
3129 Print the compiler's target machine (for example,
3130 @samp{i686-pc-linux-gnu})---and don't do anything else.
3133 @opindex dumpversion
3134 Print the compiler version (for example, @samp{3.0})---and don't do
3139 Print the compiler's built-in specs---and don't do anything else. (This
3140 is used when GCC itself is being built.) @xref{Spec Files}.
3143 @node Optimize Options
3144 @section Options That Control Optimization
3145 @cindex optimize options
3146 @cindex options, optimization
3148 These options control various sorts of optimizations:
3155 Optimize. Optimizing compilation takes somewhat more time, and a lot
3156 more memory for a large function.
3158 Without @option{-O}, the compiler's goal is to reduce the cost of
3159 compilation and to make debugging produce the expected results.
3160 Statements are independent: if you stop the program with a breakpoint
3161 between statements, you can then assign a new value to any variable or
3162 change the program counter to any other statement in the function and
3163 get exactly the results you would expect from the source code.
3165 Without @option{-O}, the compiler only allocates variables declared
3166 @code{register} in registers. The resulting compiled code is a little
3167 worse than produced by PCC without @option{-O}.
3169 With @option{-O}, the compiler tries to reduce code size and execution
3172 When you specify @option{-O}, the compiler turns on @option{-fthread-jumps}
3173 and @option{-fdefer-pop} on all machines. The compiler turns on
3174 @option{-fdelayed-branch} on machines that have delay slots, and
3175 @option{-fomit-frame-pointer} on machines that can support debugging even
3176 without a frame pointer. On some machines the compiler also turns
3181 Optimize even more. GCC performs nearly all supported optimizations
3182 that do not involve a space-speed tradeoff. The compiler does not
3183 perform loop unrolling or function inlining when you specify @option{-O2}.
3184 As compared to @option{-O}, this option increases both compilation time
3185 and the performance of the generated code.
3187 @option{-O2} turns on all optional optimizations except for loop unrolling,
3188 function inlining, and register renaming. It also turns on the
3189 @option{-fforce-mem} option on all machines and frame pointer elimination
3190 on machines where doing so does not interfere with debugging.
3192 Please note the warning under @option{-fgcse} about
3193 invoking @option{-O2} on programs that use computed gotos.
3197 Optimize yet more. @option{-O3} turns on all optimizations specified by
3198 @option{-O2} and also turns on the @option{-finline-functions} and
3199 @option{-frename-registers} options.
3207 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3208 do not typically increase code size. It also performs further
3209 optimizations designed to reduce code size.
3211 If you use multiple @option{-O} options, with or without level numbers,
3212 the last such option is the one that is effective.
3215 Options of the form @option{-f@var{flag}} specify machine-independent
3216 flags. Most flags have both positive and negative forms; the negative
3217 form of @option{-ffoo} would be @option{-fno-foo}. In the table below,
3218 only one of the forms is listed---the one which is not the default.
3219 You can figure out the other form by either removing @samp{no-} or
3224 @opindex ffloat-store
3225 Do not store floating point variables in registers, and inhibit other
3226 options that might change whether a floating point value is taken from a
3229 @cindex floating point precision
3230 This option prevents undesirable excess precision on machines such as
3231 the 68000 where the floating registers (of the 68881) keep more
3232 precision than a @code{double} is supposed to have. Similarly for the
3233 x86 architecture. For most programs, the excess precision does only
3234 good, but a few programs rely on the precise definition of IEEE floating
3235 point. Use @option{-ffloat-store} for such programs, after modifying
3236 them to store all pertinent intermediate computations into variables.
3238 @item -fno-default-inline
3239 @opindex fno-default-inline
3240 Do not make member functions inline by default merely because they are
3241 defined inside the class scope (C++ only). Otherwise, when you specify
3242 @w{@option{-O}}, member functions defined inside class scope are compiled
3243 inline by default; i.e., you don't need to add @samp{inline} in front of
3244 the member function name.
3246 @item -fno-defer-pop
3247 @opindex fno-defer-pop
3248 Always pop the arguments to each function call as soon as that function
3249 returns. For machines which must pop arguments after a function call,
3250 the compiler normally lets arguments accumulate on the stack for several
3251 function calls and pops them all at once.
3255 Force memory operands to be copied into registers before doing
3256 arithmetic on them. This produces better code by making all memory
3257 references potential common subexpressions. When they are not common
3258 subexpressions, instruction combination should eliminate the separate
3259 register-load. The @option{-O2} option turns on this option.
3262 @opindex fforce-addr
3263 Force memory address constants to be copied into registers before
3264 doing arithmetic on them. This may produce better code just as
3265 @option{-fforce-mem} may.
3267 @item -fomit-frame-pointer
3268 @opindex fomit-frame-pointer
3269 Don't keep the frame pointer in a register for functions that
3270 don't need one. This avoids the instructions to save, set up and
3271 restore frame pointers; it also makes an extra register available
3272 in many functions. @strong{It also makes debugging impossible on
3276 On some machines, such as the Vax, this flag has no effect, because
3277 the standard calling sequence automatically handles the frame pointer
3278 and nothing is saved by pretending it doesn't exist. The
3279 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3280 whether a target machine supports this flag. @xref{Registers}.
3283 On some machines, such as the Vax, this flag has no effect, because
3284 the standard calling sequence automatically handles the frame pointer
3285 and nothing is saved by pretending it doesn't exist. The
3286 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3287 whether a target machine supports this flag. @xref{Registers,,Register
3288 Usage, gcc.info, Using and Porting GCC}.
3291 @item -foptimize-sibling-calls
3292 @opindex foptimize-sibling-calls
3293 Optimize sibling and tail recursive calls.
3297 This option generates traps for signed overflow on addition, subtraction,
3298 multiplication operations.
3302 Don't pay attention to the @code{inline} keyword. Normally this option
3303 is used to keep the compiler from expanding any functions inline.
3304 Note that if you are not optimizing, no functions can be expanded inline.
3306 @item -finline-functions
3307 @opindex finline-functions
3308 Integrate all simple functions into their callers. The compiler
3309 heuristically decides which functions are simple enough to be worth
3310 integrating in this way.
3312 If all calls to a given function are integrated, and the function is
3313 declared @code{static}, then the function is normally not output as
3314 assembler code in its own right.
3316 @item -finline-limit=@var{n}
3317 @opindex finline-limit
3318 By default, gcc limits the size of functions that can be inlined. This flag
3319 allows the control of this limit for functions that are explicitly marked as
3320 inline (ie marked with the inline keyword or defined within the class
3321 definition in c++). @var{n} is the size of functions that can be inlined in
3322 number of pseudo instructions (not counting parameter handling). The default
3323 value of @var{n} is 10000. Increasing this value can result in more inlined code at
3324 the cost of compilation time and memory consumption. Decreasing usually makes
3325 the compilation faster and less code will be inlined (which presumably
3326 means slower programs). This option is particularly useful for programs that
3327 use inlining heavily such as those based on recursive templates with C++.
3329 @emph{Note:} pseudo instruction represents, in this particular context, an
3330 abstract measurement of function's size. In no way, it represents a count
3331 of assembly instructions and as such its exact meaning might change from one
3332 release to an another.
3334 @item -fkeep-inline-functions
3335 @opindex fkeep-inline-functions
3336 Even if all calls to a given function are integrated, and the function
3337 is declared @code{static}, nevertheless output a separate run-time
3338 callable version of the function. This switch does not affect
3339 @code{extern inline} functions.
3341 @item -fkeep-static-consts
3342 @opindex fkeep-static-consts
3343 Emit variables declared @code{static const} when optimization isn't turned
3344 on, even if the variables aren't referenced.
3346 GCC enables this option by default. If you want to force the compiler to
3347 check if the variable was referenced, regardless of whether or not
3348 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3350 @item -fno-function-cse
3351 @opindex fno-function-cse
3352 Do not put function addresses in registers; make each instruction that
3353 calls a constant function contain the function's address explicitly.
3355 This option results in less efficient code, but some strange hacks
3356 that alter the assembler output may be confused by the optimizations
3357 performed when this option is not used.
3361 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
3362 and @option{-fno-trapping-math}.
3364 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
3366 This option should never be turned on by any @option{-O} option since
3367 it can result in incorrect output for programs which depend on
3368 an exact implementation of IEEE or ISO rules/specifications for
3371 @item -fno-math-errno
3372 @opindex fno-math-errno
3373 Do not set ERRNO after calling math functions that are executed
3374 with a single instruction, e.g., sqrt. A program that relies on
3375 IEEE exceptions for math error handling may want to use this flag
3376 for speed while maintaining IEEE arithmetic compatibility.
3378 This option should never be turned on by any @option{-O} option since
3379 it can result in incorrect output for programs which depend on
3380 an exact implementation of IEEE or ISO rules/specifications for
3383 The default is @option{-fmath-errno}. The @option{-ffast-math} option
3384 sets @option{-fno-math-errno}.
3386 @item -funsafe-math-optimizations
3387 @opindex funsafe-math-optimizations
3388 Allow optimizations for floating-point arithmetic that (a) assume
3389 that arguments and results are valid and (b) may violate IEEE or
3390 ANSI standards. When used at link-time, it may include libraries
3391 or startup files that change the default FPU control word or other
3392 similar optimizations.
3394 This option should never be turned on by any @option{-O} option since
3395 it can result in incorrect output for programs which depend on
3396 an exact implementation of IEEE or ISO rules/specifications for
3399 The default is @option{-fno-unsafe-math-optimizations}. The
3400 @option{-ffast-math} option sets @option{-funsafe-math-optimizations}.
3402 @item -fno-trapping-math
3403 @opindex fno-trapping-math
3404 Compile code assuming that floating-point operations cannot generate
3405 user-visible traps. Setting this option may allow faster code
3406 if one relies on ``non-stop'' IEEE arithmetic, for example.
3408 This option should never be turned on by any @option{-O} option since
3409 it can result in incorrect output for programs which depend on
3410 an exact implementation of IEEE or ISO rules/specifications for
3413 The default is @option{-ftrapping-math}. The @option{-ffast-math}
3414 option sets @option{-fno-trapping-math}.
3417 @c following causes underfulls.. they don't look great, but we deal.
3419 The following options control specific optimizations. The @option{-O2}
3420 option turns on all of these optimizations except @option{-funroll-loops}
3421 and @option{-funroll-all-loops}. On most machines, the @option{-O} option
3422 turns on the @option{-fthread-jumps} and @option{-fdelayed-branch} options,
3423 but specific machines may handle it differently.
3425 You can use the following flags in the rare cases when ``fine-tuning''
3426 of optimizations to be performed is desired.
3429 @item -fstrength-reduce
3430 @opindex fstrength-reduce
3431 Perform the optimizations of loop strength reduction and
3432 elimination of iteration variables.
3434 @item -fthread-jumps
3435 @opindex fthread-jumps
3436 Perform optimizations where we check to see if a jump branches to a
3437 location where another comparison subsumed by the first is found. If
3438 so, the first branch is redirected to either the destination of the
3439 second branch or a point immediately following it, depending on whether
3440 the condition is known to be true or false.
3442 @item -fcse-follow-jumps
3443 @opindex fcse-follow-jumps
3444 In common subexpression elimination, scan through jump instructions
3445 when the target of the jump is not reached by any other path. For
3446 example, when CSE encounters an @code{if} statement with an
3447 @code{else} clause, CSE will follow the jump when the condition
3450 @item -fcse-skip-blocks
3451 @opindex fcse-skip-blocks
3452 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3453 follow jumps which conditionally skip over blocks. When CSE
3454 encounters a simple @code{if} statement with no else clause,
3455 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3456 body of the @code{if}.
3458 @item -frerun-cse-after-loop
3459 @opindex frerun-cse-after-loop
3460 Re-run common subexpression elimination after loop optimizations has been
3463 @item -frerun-loop-opt
3464 @opindex frerun-loop-opt
3465 Run the loop optimizer twice.
3469 Perform a global common subexpression elimination pass.
3470 This pass also performs global constant and copy propagation.
3472 @emph{Note:} When compiling a program using computed gotos, a GCC
3473 extension, you may get better runtime performance if you disable
3474 the global common subexpression elmination pass by adding
3475 @option{-fno-gcse} to the command line.
3479 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3480 attempt to move loads which are only killed by stores into themselves. This
3481 allows a loop containing a load/store sequence to be changed to a load outside
3482 the loop, and a copy/store within the loop.
3486 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3487 subexpression elimination. This pass will attempt to move stores out of loops.
3488 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3489 can be changed to a load before the loop and a store after the loop.
3491 @item -fdelete-null-pointer-checks
3492 @opindex fdelete-null-pointer-checks
3493 Use global dataflow analysis to identify and eliminate useless null
3494 pointer checks. Programs which rely on NULL pointer dereferences @emph{not}
3495 halting the program may not work properly with this option. Use
3496 @option{-fno-delete-null-pointer-checks} to disable this optimizing for programs
3497 which depend on that behavior.
3499 @item -fexpensive-optimizations
3500 @opindex fexpensive-optimizations
3501 Perform a number of minor optimizations that are relatively expensive.
3503 @item -foptimize-register-move
3505 @opindex foptimize-register-move
3507 Attempt to reassign register numbers in move instructions and as
3508 operands of other simple instructions in order to maximize the amount of
3509 register tying. This is especially helpful on machines with two-operand
3510 instructions. GCC enables this optimization by default with @option{-O2}
3513 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3516 @item -fdelayed-branch
3517 @opindex fdelayed-branch
3518 If supported for the target machine, attempt to reorder instructions
3519 to exploit instruction slots available after delayed branch
3522 @item -fschedule-insns
3523 @opindex fschedule-insns
3524 If supported for the target machine, attempt to reorder instructions to
3525 eliminate execution stalls due to required data being unavailable. This
3526 helps machines that have slow floating point or memory load instructions
3527 by allowing other instructions to be issued until the result of the load
3528 or floating point instruction is required.
3530 @item -fschedule-insns2
3531 @opindex fschedule-insns2
3532 Similar to @option{-fschedule-insns}, but requests an additional pass of
3533 instruction scheduling after register allocation has been done. This is
3534 especially useful on machines with a relatively small number of
3535 registers and where memory load instructions take more than one cycle.
3537 @item -ffunction-sections
3538 @itemx -fdata-sections
3539 @opindex ffunction-sections
3540 @opindex fdata-sections
3541 Place each function or data item into its own section in the output
3542 file if the target supports arbitrary sections. The name of the
3543 function or the name of the data item determines the section's name
3546 Use these options on systems where the linker can perform optimizations
3547 to improve locality of reference in the instruction space. HPPA
3548 processors running HP-UX and Sparc processors running Solaris 2 have
3549 linkers with such optimizations. Other systems using the ELF object format
3550 as well as AIX may have these optimizations in the future.
3552 Only use these options when there are significant benefits from doing
3553 so. When you specify these options, the assembler and linker will
3554 create larger object and executable files and will also be slower.
3555 You will not be able to use @code{gprof} on all systems if you
3556 specify this option and you may have problems with debugging if
3557 you specify both this option and @option{-g}.
3559 @item -fcaller-saves
3560 @opindex fcaller-saves
3561 Enable values to be allocated in registers that will be clobbered by
3562 function calls, by emitting extra instructions to save and restore the
3563 registers around such calls. Such allocation is done only when it
3564 seems to result in better code than would otherwise be produced.
3566 This option is always enabled by default on certain machines, usually
3567 those which have no call-preserved registers to use instead.
3569 For all machines, optimization level 2 and higher enables this flag by
3572 @item -funroll-loops
3573 @opindex funroll-loops
3574 Perform the optimization of loop unrolling. This is only done for loops
3575 whose number of iterations can be determined at compile time or run time.
3576 @option{-funroll-loops} implies both @option{-fstrength-reduce} and
3577 @option{-frerun-cse-after-loop}.
3579 @item -funroll-all-loops
3580 @opindex funroll-all-loops
3581 Perform the optimization of loop unrolling. This is done for all loops
3582 and usually makes programs run more slowly. @option{-funroll-all-loops}
3583 implies @option{-fstrength-reduce} as well as @option{-frerun-cse-after-loop}.
3585 @item -fmove-all-movables
3586 @opindex fmove-all-movables
3587 Forces all invariant computations in loops to be moved
3590 @item -freduce-all-givs
3591 @opindex freduce-all-givs
3592 Forces all general-induction variables in loops to be
3595 @emph{Note:} When compiling programs written in Fortran,
3596 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3597 by default when you use the optimizer.
3599 These options may generate better or worse code; results are highly
3600 dependent on the structure of loops within the source code.
3602 These two options are intended to be removed someday, once
3603 they have helped determine the efficacy of various
3604 approaches to improving loop optimizations.
3606 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
3607 know how use of these options affects
3608 the performance of your production code.
3609 We're very interested in code that runs @emph{slower}
3610 when these options are @emph{enabled}.
3613 @itemx -fno-peephole2
3614 @opindex fno-peephole
3615 @opindex fno-peephole2
3616 Disable any machine-specific peephole optimizations. The difference
3617 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
3618 are implemented in the compiler; some targets use one, some use the
3619 other, a few use both.
3621 @item -fbranch-probabilities
3622 @opindex fbranch-probabilities
3623 After running a program compiled with @option{-fprofile-arcs}
3624 (@pxref{Debugging Options,, Options for Debugging Your Program or
3625 @command{gcc}}), you can compile it a second time using
3626 @option{-fbranch-probabilities}, to improve optimizations based on
3627 guessing the path a branch might take.
3630 With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
3631 note on the first instruction of each basic block, and a
3632 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
3633 These can be used to improve optimization. Currently, they are only
3634 used in one place: in @file{reorg.c}, instead of guessing which path a
3635 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
3636 exactly determine which path is taken more often.
3639 @item -fno-guess-branch-probability
3640 @opindex fno-guess-branch-probability
3641 Sometimes gcc will opt to guess branch probabilities when none are
3642 available from either profile directed feedback (@option{-fprofile-arcs})
3643 or @samp{__builtin_expect}. In a hard real-time system, people don't
3644 want different runs of the compiler to produce code that has different
3645 behavior; minimizing non-determinism is of paramount import. This
3646 switch allows users to reduce non-determinism, possibly at the expense
3647 of inferior optimization.
3649 @item -fstrict-aliasing
3650 @opindex fstrict-aliasing
3651 Allows the compiler to assume the strictest aliasing rules applicable to
3652 the language being compiled. For C (and C++), this activates
3653 optimizations based on the type of expressions. In particular, an
3654 object of one type is assumed never to reside at the same address as an
3655 object of a different type, unless the types are almost the same. For
3656 example, an @code{unsigned int} can alias an @code{int}, but not a
3657 @code{void*} or a @code{double}. A character type may alias any other
3660 Pay special attention to code like this:
3673 The practice of reading from a different union member than the one most
3674 recently written to (called ``type-punning'') is common. Even with
3675 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
3676 is accessed through the union type. So, the code above will work as
3677 expected. However, this code might not:
3689 Every language that wishes to perform language-specific alias analysis
3690 should define a function that computes, given an @code{tree}
3691 node, an alias set for the node. Nodes in different alias sets are not
3692 allowed to alias. For an example, see the C front-end function
3693 @code{c_get_alias_set}.
3696 @item -falign-functions
3697 @itemx -falign-functions=@var{n}
3698 @opindex falign-functions
3699 Align the start of functions to the next power-of-two greater than
3700 @var{n}, skipping up to @var{n} bytes. For instance,
3701 @option{-falign-functions=32} aligns functions to the next 32-byte
3702 boundary, but @option{-falign-functions=24} would align to the next
3703 32-byte boundary only if this can be done by skipping 23 bytes or less.
3705 @option{-fno-align-functions} and @option{-falign-functions=1} are
3706 equivalent and mean that functions will not be aligned.
3708 Some assemblers only support this flag when @var{n} is a power of two;
3709 in that case, it is rounded up.
3711 If @var{n} is not specified, use a machine-dependent default.
3713 @item -falign-labels
3714 @itemx -falign-labels=@var{n}
3715 @opindex falign-labels
3716 Align all branch targets to a power-of-two boundary, skipping up to
3717 @var{n} bytes like @option{-falign-functions}. This option can easily
3718 make code slower, because it must insert dummy operations for when the
3719 branch target is reached in the usual flow of the code.
3721 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
3722 are greater than this value, then their values are used instead.
3724 If @var{n} is not specified, use a machine-dependent default which is
3725 very likely to be @samp{1}, meaning no alignment.
3728 @itemx -falign-loops=@var{n}
3729 @opindex falign-loops
3730 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
3731 like @option{-falign-functions}. The hope is that the loop will be
3732 executed many times, which will make up for any execution of the dummy
3735 If @var{n} is not specified, use a machine-dependent default.
3738 @itemx -falign-jumps=@var{n}
3739 @opindex falign-jumps
3740 Align branch targets to a power-of-two boundary, for branch targets
3741 where the targets can only be reached by jumping, skipping up to @var{n}
3742 bytes like @option{-falign-functions}. In this case, no dummy operations
3745 If @var{n} is not specified, use a machine-dependent default.
3749 Perform optimizations in static single assignment form. Each function's
3750 flow graph is translated into SSA form, optimizations are performed, and
3751 the flow graph is translated back from SSA form. Users should not
3752 specify this option, since it is not yet ready for production use.
3756 Perform Sparse Conditional Constant Propagation in SSA form. Requires
3757 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
3761 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
3762 Like @option{-fssa}, this is an experimental feature.
3764 @item -fsingle-precision-constant
3765 @opindex fsingle-precision-constant
3766 Treat floating point constant as single precision constant instead of
3767 implicitly converting it to double precision constant.
3769 @item -frename-registers
3770 @opindex frename-registers
3771 Attempt to avoid false dependencies in scheduled code by making use
3772 of registers left over after register allocation. This optimization
3773 will most benefit processors with lots of registers. It can, however,
3774 make debugging impossible, since variables will no longer stay in
3775 a ``home register''.
3777 @item --param @var{name}=@var{value}
3779 In some places, GCC uses various constants to control the amount of
3780 optimization that is done. For example, GCC will not inline functions
3781 that contain more that a certain number of instructions. You can
3782 control some of these constants on the command-line using the
3783 @option{--param} option.
3785 In each case, the @var{value} is a integer. The allowable choices for
3786 @var{name} are given in the following table:
3789 @item max-delay-slot-insn-search
3790 The maximum number of instructions to consider when looking for an
3791 instruction to fill a delay slot. If more than this arbitrary number of
3792 instructions is searched, the time savings from filling the delay slot
3793 will be minimal so stop searching. Increasing values mean more
3794 aggressive optimization, making the compile time increase with probably
3795 small improvement in executable run time.
3797 @item max-delay-slot-live-search
3798 When trying to fill delay slots, the maximum number of instructions to
3799 consider when searching for a block with valid live register
3800 information. Increasing this arbitrarily chosen value means more
3801 aggressive optimization, increasing the compile time. This parameter
3802 should be removed when the delay slot code is rewritten to maintain the
3805 @item max-gcse-memory
3806 The approximate maximum amount of memory that will be allocated in
3807 order to perform the global common subexpression elimination
3808 optimization. If more memory than specified is required, the
3809 optimization will not be done.
3811 @item max-gcse-passes
3812 The maximum number of passes of GCSE to run.
3814 @item max-inline-insns
3815 If an function contains more than this many instructions, it
3816 will not be inlined. This option is precisely equivalent to
3817 @option{-finline-limit}.
3822 @node Preprocessor Options
3823 @section Options Controlling the Preprocessor
3824 @cindex preprocessor options
3825 @cindex options, preprocessor
3827 These options control the C preprocessor, which is run on each C source
3828 file before actual compilation.
3830 If you use the @option{-E} option, nothing is done except preprocessing.
3831 Some of these options make sense only together with @option{-E} because
3832 they cause the preprocessor output to be unsuitable for actual
3836 @item -include @var{file}
3838 Process @var{file} as input before processing the regular input file.
3839 In effect, the contents of @var{file} are compiled first. Any @option{-D}
3840 and @option{-U} options on the command line are always processed before
3841 @option{-include @var{file}}, regardless of the order in which they are
3842 written. All the @option{-include} and @option{-imacros} options are
3843 processed in the order in which they are written.
3845 @item -imacros @var{file}
3847 Process @var{file} as input, discarding the resulting output, before
3848 processing the regular input file. Because the output generated from
3849 @var{file} is discarded, the only effect of @option{-imacros @var{file}}
3850 is to make the macros defined in @var{file} available for use in the
3851 main input. All the @option{-include} and @option{-imacros} options are
3852 processed in the order in which they are written.
3854 @item -idirafter @var{dir}
3856 @cindex second include path
3857 Add the directory @var{dir} to the second include path. The directories
3858 on the second include path are searched when a header file is not found
3859 in any of the directories in the main include path (the one that
3860 @option{-I} adds to).
3862 @item -iprefix @var{prefix}
3864 Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix}
3867 @item -iwithprefix @var{dir}
3868 @opindex iwithprefix
3869 Add a directory to the second include path. The directory's name is
3870 made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was
3871 specified previously with @option{-iprefix}. If you have not specified a
3872 prefix yet, the directory containing the installed passes of the
3873 compiler is used as the default.
3875 @item -iwithprefixbefore @var{dir}
3876 @opindex iwithprefixbefore
3877 Add a directory to the main include path. The directory's name is made
3878 by concatenating @var{prefix} and @var{dir}, as in the case of
3879 @option{-iwithprefix}.
3881 @item -isystem @var{dir}
3883 Add a directory to the beginning of the second include path, marking it
3884 as a system directory, so that it gets the same special treatment as
3885 is applied to the standard system directories.
3889 Do not search the standard system directories for header files. Only
3890 the directories you have specified with @option{-I} options (and the
3891 current directory, if appropriate) are searched. @xref{Directory
3892 Options}, for information on @option{-I}.
3894 By using both @option{-nostdinc} and @option{-I-}, you can limit the include-file
3895 search path to only those directories you specify explicitly.
3899 When searching for a header file in a directory, remap file names if a
3900 file named @file{header.gcc} exists in that directory. This can be used
3901 to work around limitations of file systems with file name restrictions.
3902 The @file{header.gcc} file should contain a series of lines with two
3903 tokens on each line: the first token is the name to map, and the second
3904 token is the actual name to use.
3908 Do not predefine any nonstandard macros. (Including architecture flags).
3912 Run only the C preprocessor. Preprocess all the C source files
3913 specified and output the results to standard output or to the
3914 specified output file.
3918 Tell the preprocessor not to discard comments. Used with the
3923 Tell the preprocessor not to generate @samp{#line} directives.
3924 Used with the @option{-E} option.
3927 @cindex dependencies, make
3930 Instead of outputting the result of preprocessing, output a rule
3931 suitable for @code{make} describing the dependencies of the main source
3932 file. The preprocessor outputs one @code{make} rule containing the
3933 object file name for that source file, a colon, and the names of all the
3934 included files. Unless overridden explicitly, the object file name
3935 consists of the basename of the source file with any suffix replaced with
3936 object file suffix. If there are many included files then the
3937 rule is split into several lines using @samp{\}-newline.
3939 @option{-M} implies @option{-E}.
3943 Like @option{-M}, but mention only the files included with @samp{#include
3944 "@var{file}"}. System header files included with @samp{#include
3945 <@var{file}>} are omitted.
3949 Like @option{-M} but the dependency information is written to a file
3950 rather than stdout. @code{gcc} will use the same file name and
3951 directory as the object file, but with the suffix @file{.d} instead.
3953 This is in addition to compiling the main file as specified---@option{-MD}
3954 does not inhibit ordinary compilation the way @option{-M} does,
3955 unless you also specify @option{-MG}.
3957 With Mach, you can use the utility @code{md} to merge multiple
3958 dependency files into a single dependency file suitable for using with
3959 the @samp{make} command.
3963 Like @option{-MD} except mention only user header files, not system
3966 @item -MF @var{file}
3968 When used with @option{-M} or @option{-MM}, specifies a file to write the
3969 dependencies to. This allows the preprocessor to write the preprocessed
3970 file to stdout normally. If no @option{-MF} switch is given, CPP sends
3971 the rules to stdout and suppresses normal preprocessed output.
3973 Another way to specify output of a @code{make} rule is by setting
3974 the environment variable @env{DEPENDENCIES_OUTPUT} (@pxref{Environment
3979 When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing
3980 header files as generated files and assume they live in the same
3981 directory as the source file. It suppresses preprocessed output, as a
3982 missing header file is ordinarily an error.
3984 This feature is used in automatic updating of makefiles.
3988 This option instructs CPP to add a phony target for each dependency
3989 other than the main file, causing each to depend on nothing. These
3990 dummy rules work around errors @code{make} gives if you remove header
3991 files without updating the @code{Makefile} to match.
3993 This is typical output:-
3996 /tmp/test.o: /tmp/test.c /tmp/test.h
4001 @item -MQ @var{target}
4002 @item -MT @var{target}
4005 By default CPP uses the main file name, including any path, and appends
4006 the object suffix, normally ``.o'', to it to obtain the name of the
4007 target for dependency generation. With @option{-MT} you can specify a
4008 target yourself, overriding the default one.
4010 If you want multiple targets, you can specify them as a single argument
4011 to @option{-MT}, or use multiple @option{-MT} options.
4013 The targets you specify are output in the order they appear on the
4014 command line. @option{-MQ} is identical to @option{-MT}, except that the
4015 target name is quoted for Make, but with @option{-MT} it isn't. For
4016 example, @option{-MT '$(objpfx)foo.o'} gives
4019 $(objpfx)foo.o: /tmp/foo.c
4022 but @option{-MQ '$(objpfx)foo.o'} gives
4025 $$(objpfx)foo.o: /tmp/foo.c
4028 The default target is automatically quoted, as if it were given with
4033 Print the name of each header file used, in addition to other normal
4036 @item -A@var{question}(@var{answer})
4038 Assert the answer @var{answer} for @var{question}, in case it is tested
4039 with a preprocessing conditional such as @samp{#if
4040 #@var{question}(@var{answer})}. @option{-A-} disables the standard
4041 assertions that normally describe the target machine.
4045 Define macro @var{macro} with the string @samp{1} as its definition.
4047 @item -D@var{macro}=@var{defn}
4048 Define macro @var{macro} as @var{defn}. All instances of @option{-D} on
4049 the command line are processed before any @option{-U} options.
4051 Any @option{-D} and @option{-U} options on the command line are processed in
4052 order, and always before @option{-imacros @var{file}}, regardless of the
4053 order in which they are written.
4057 Undefine macro @var{macro}. @option{-U} options are evaluated after all
4058 @option{-D} options, but before any @option{-include} and @option{-imacros}
4061 Any @option{-D} and @option{-U} options on the command line are processed in
4062 order, and always before @option{-imacros @var{file}}, regardless of the
4063 order in which they are written.
4067 Tell the preprocessor to output only a list of the macro definitions
4068 that are in effect at the end of preprocessing. Used with the @option{-E}
4073 Tell the preprocessing to pass all macro definitions into the output, in
4074 their proper sequence in the rest of the output.
4078 Like @option{-dD} except that the macro arguments and contents are omitted.
4079 Only @samp{#define @var{name}} is included in the output.
4083 Output @samp{#include} directives in addition to the result of
4086 @item -fpreprocessed
4087 @opindex fpreprocessed
4088 Indicate to the preprocessor that the input file has already been
4089 preprocessed. This suppresses things like macro expansion, trigraph
4090 conversion, escaped newline splicing, and processing of most directives.
4091 The preprocessor still recognizes and removes comments, so that you can
4092 pass a file preprocessed with @option{-C} to the compiler without
4093 problems. In this mode the integrated preprocessor is little more than
4094 a tokenizer for the front ends.
4096 @option{-fpreprocessed} is implicit if the input file has one of the
4097 extensions @samp{i}, @samp{ii} or @samp{mi}. These are the extensions
4098 that GCC uses for preprocessed files created by @option{-save-temps}.
4102 Process ISO standard trigraph sequences. These are three-character
4103 sequences, all starting with @samp{??}, that are defined by ISO C to
4104 stand for single characters. For example, @samp{??/} stands for
4105 @samp{\}, so @samp{'??/n'} is a character constant for a newline. By
4106 default, GCC ignores trigraphs, but in standard-conforming modes it
4107 converts them. See the @option{-std} and @option{-ansi} options.
4109 The nine trigraph sequences are
4112 @expansion{} @samp{[}
4115 @expansion{} @samp{]}
4118 @expansion{} @samp{@{}
4121 @expansion{} @samp{@}}
4124 @expansion{} @samp{#}
4127 @expansion{} @samp{\}
4130 @expansion{} @samp{^}
4133 @expansion{} @samp{|}
4136 @expansion{} @samp{~}
4140 Trigraph support is not popular, so many compilers do not implement it
4141 properly. Portable code should not rely on trigraphs being either
4142 converted or ignored.
4144 @item -Wp,@var{option}
4146 Pass @var{option} as an option to the preprocessor. If @var{option}
4147 contains commas, it is split into multiple options at the commas.
4150 @node Assembler Options
4151 @section Passing Options to the Assembler
4153 @c prevent bad page break with this line
4154 You can pass options to the assembler.
4157 @item -Wa,@var{option}
4159 Pass @var{option} as an option to the assembler. If @var{option}
4160 contains commas, it is split into multiple options at the commas.
4164 @section Options for Linking
4165 @cindex link options
4166 @cindex options, linking
4168 These options come into play when the compiler links object files into
4169 an executable output file. They are meaningless if the compiler is
4170 not doing a link step.
4174 @item @var{object-file-name}
4175 A file name that does not end in a special recognized suffix is
4176 considered to name an object file or library. (Object files are
4177 distinguished from libraries by the linker according to the file
4178 contents.) If linking is done, these object files are used as input
4187 If any of these options is used, then the linker is not run, and
4188 object file names should not be used as arguments. @xref{Overall
4192 @item -l@var{library}
4193 @itemx -l @var{library}
4195 Search the library named @var{library} when linking. (The second
4196 alternative with the library as a separate argument is only for
4197 POSIX compliance and is not recommended.)
4199 It makes a difference where in the command you write this option; the
4200 linker searches and processes libraries and object files in the order they
4201 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4202 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4203 to functions in @samp{z}, those functions may not be loaded.
4205 The linker searches a standard list of directories for the library,
4206 which is actually a file named @file{lib@var{library}.a}. The linker
4207 then uses this file as if it had been specified precisely by name.
4209 The directories searched include several standard system directories
4210 plus any that you specify with @option{-L}.
4212 Normally the files found this way are library files---archive files
4213 whose members are object files. The linker handles an archive file by
4214 scanning through it for members which define symbols that have so far
4215 been referenced but not defined. But if the file that is found is an
4216 ordinary object file, it is linked in the usual fashion. The only
4217 difference between using an @option{-l} option and specifying a file name
4218 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4219 and searches several directories.
4223 You need this special case of the @option{-l} option in order to
4224 link an Objective-C program.
4227 @opindex nostartfiles
4228 Do not use the standard system startup files when linking.
4229 The standard system libraries are used normally, unless @option{-nostdlib}
4230 or @option{-nodefaultlibs} is used.
4232 @item -nodefaultlibs
4233 @opindex nodefaultlibs
4234 Do not use the standard system libraries when linking.
4235 Only the libraries you specify will be passed to the linker.
4236 The standard startup files are used normally, unless @option{-nostartfiles}
4237 is used. The compiler may generate calls to memcmp, memset, and memcpy
4238 for System V (and ISO C) environments or to bcopy and bzero for
4239 BSD environments. These entries are usually resolved by entries in
4240 libc. These entry points should be supplied through some other
4241 mechanism when this option is specified.
4245 Do not use the standard system startup files or libraries when linking.
4246 No startup files and only the libraries you specify will be passed to
4247 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4248 for System V (and ISO C) environments or to bcopy and bzero for
4249 BSD environments. These entries are usually resolved by entries in
4250 libc. These entry points should be supplied through some other
4251 mechanism when this option is specified.
4253 @cindex @option{-lgcc}, use with @option{-nostdlib}
4254 @cindex @option{-nostdlib} and unresolved references
4255 @cindex unresolved references and @option{-nostdlib}
4256 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4257 @cindex @option{-nodefaultlibs} and unresolved references
4258 @cindex unresolved references and @option{-nodefaultlibs}
4259 One of the standard libraries bypassed by @option{-nostdlib} and
4260 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4261 that GCC uses to overcome shortcomings of particular machines, or special
4262 needs for some languages.
4264 (@xref{Interface,,Interfacing to GCC Output}, for more discussion of
4268 (@xref{Interface,,Interfacing to GCC Output,gcc.info,Porting GCC},
4269 for more discussion of @file{libgcc.a}.)
4271 In most cases, you need @file{libgcc.a} even when you want to avoid
4272 other standard libraries. In other words, when you specify @option{-nostdlib}
4273 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4274 This ensures that you have no unresolved references to internal GCC
4275 library subroutines. (For example, @samp{__main}, used to ensure C++
4276 constructors will be called; @pxref{Collect2,,@command{collect2}}.)
4280 Remove all symbol table and relocation information from the executable.
4284 On systems that support dynamic linking, this prevents linking with the shared
4285 libraries. On other systems, this option has no effect.
4289 Produce a shared object which can then be linked with other objects to
4290 form an executable. Not all systems support this option. For predictable
4291 results, you must also specify the same set of options that were used to
4292 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4293 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4294 needs to build supplementary stub code for constructors to work. On
4295 multi-libbed systems, @samp{gcc -shared} must select the correct support
4296 libraries to link against. Failing to supply the correct flags may lead
4297 to subtle defects. Supplying them in cases where they are not necessary
4300 @item -shared-libgcc
4301 @itemx -static-libgcc
4302 @opindex shared-libgcc
4303 @opindex static-libgcc
4304 On systems that provide @file{libgcc} as a shared library, these options
4305 force the use of either the shared or static version respectively.
4306 If no shared version of @file{libgcc} was built when the compiler was
4307 configured, these options have no effect.
4309 There are several situations in which an application should use the
4310 shared @file{libgcc} instead of the static version. The most common
4311 of these is when the application wishes to throw and catch exceptions
4312 across different shared libraries. In that case, each of the libraries
4313 as well as the application itself should use the shared @file{libgcc}.
4315 Therefore, whenever you specify the @option{-shared} option, the GCC
4316 driver automatically adds @option{-shared-libgcc}, unless you explicitly
4317 specify @option{-static-libgcc}. The G++ driver automatically adds
4318 @option{-shared-libgcc} when you build a main executable as well because
4319 for C++ programs that is typically the right thing to do.
4320 (Exception-handling will not work reliably otherwise.)
4322 However, when linking a main executable written in C, you must
4323 explicitly say @option{-shared-libgcc} if you want to use the shared
4328 Bind references to global symbols when building a shared object. Warn
4329 about any unresolved references (unless overridden by the link editor
4330 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4333 @item -Xlinker @var{option}
4335 Pass @var{option} as an option to the linker. You can use this to
4336 supply system-specific linker options which GCC does not know how to
4339 If you want to pass an option that takes an argument, you must use
4340 @option{-Xlinker} twice, once for the option and once for the argument.
4341 For example, to pass @option{-assert definitions}, you must write
4342 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4343 @option{-Xlinker "-assert definitions"}, because this passes the entire
4344 string as a single argument, which is not what the linker expects.
4346 @item -Wl,@var{option}
4348 Pass @var{option} as an option to the linker. If @var{option} contains
4349 commas, it is split into multiple options at the commas.
4351 @item -u @var{symbol}
4353 Pretend the symbol @var{symbol} is undefined, to force linking of
4354 library modules to define it. You can use @option{-u} multiple times with
4355 different symbols to force loading of additional library modules.
4358 @node Directory Options
4359 @section Options for Directory Search
4360 @cindex directory options
4361 @cindex options, directory search
4364 These options specify directories to search for header files, for
4365 libraries and for parts of the compiler:
4370 Add the directory @var{dir} to the head of the list of directories to be
4371 searched for header files. This can be used to override a system header
4372 file, substituting your own version, since these directories are
4373 searched before the system header file directories. However, you should
4374 not use this option to add directories that contain vendor-supplied
4375 system header files (use @option{-isystem} for that). If you use more than
4376 one @option{-I} option, the directories are scanned in left-to-right
4377 order; the standard system directories come after.
4379 If a standard system include directory, or a directory specified with
4380 @option{-isystem}, is also specified with @option{-I}, it will be
4381 searched only in the position requested by @option{-I}. Also, it will
4382 not be considered a system include directory. If that directory really
4383 does contain system headers, there is a good chance that they will
4384 break. For instance, if GCC's installation procedure edited the headers
4385 in @file{/usr/include} to fix bugs, @samp{-I/usr/include} will cause the
4386 original, buggy headers to be found instead of the corrected ones. GCC
4387 will issue a warning when a system include directory is hidden in this
4392 Any directories you specify with @option{-I} options before the @option{-I-}
4393 option are searched only for the case of @samp{#include "@var{file}"};
4394 they are not searched for @samp{#include <@var{file}>}.
4396 If additional directories are specified with @option{-I} options after
4397 the @option{-I-}, these directories are searched for all @samp{#include}
4398 directives. (Ordinarily @emph{all} @option{-I} directories are used
4401 In addition, the @option{-I-} option inhibits the use of the current
4402 directory (where the current input file came from) as the first search
4403 directory for @samp{#include "@var{file}"}. There is no way to
4404 override this effect of @option{-I-}. With @option{-I.} you can specify
4405 searching the directory which was current when the compiler was
4406 invoked. That is not exactly the same as what the preprocessor does
4407 by default, but it is often satisfactory.
4409 @option{-I-} does not inhibit the use of the standard system directories
4410 for header files. Thus, @option{-I-} and @option{-nostdinc} are
4415 Add directory @var{dir} to the list of directories to be searched
4418 @item -B@var{prefix}
4420 This option specifies where to find the executables, libraries,
4421 include files, and data files of the compiler itself.
4423 The compiler driver program runs one or more of the subprograms
4424 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
4425 @var{prefix} as a prefix for each program it tries to run, both with and
4426 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
4428 For each subprogram to be run, the compiler driver first tries the
4429 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
4430 was not specified, the driver tries two standard prefixes, which are
4431 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
4432 those results in a file name that is found, the unmodified program
4433 name is searched for using the directories specified in your
4434 @env{PATH} environment variable.
4436 The compiler will check to see if the path provided by the @option{-B}
4437 refers to a directory, and if necessary it will add a directory
4438 separator character at the end of the path.
4440 @option{-B} prefixes that effectively specify directory names also apply
4441 to libraries in the linker, because the compiler translates these
4442 options into @option{-L} options for the linker. They also apply to
4443 includes files in the preprocessor, because the compiler translates these
4444 options into @option{-isystem} options for the preprocessor. In this case,
4445 the compiler appends @samp{include} to the prefix.
4447 The run-time support file @file{libgcc.a} can also be searched for using
4448 the @option{-B} prefix, if needed. If it is not found there, the two
4449 standard prefixes above are tried, and that is all. The file is left
4450 out of the link if it is not found by those means.
4452 Another way to specify a prefix much like the @option{-B} prefix is to use
4453 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
4456 As a special kludge, if the path provided by @option{-B} is
4457 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
4458 9, then it will be replaced by @file{[dir/]include}. This is to help
4459 with boot-strapping the compiler.
4461 @item -specs=@var{file}
4463 Process @var{file} after the compiler reads in the standard @file{specs}
4464 file, in order to override the defaults that the @file{gcc} driver
4465 program uses when determining what switches to pass to @file{cc1},
4466 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
4467 @option{-specs=@var{file}} can be specified on the command line, and they
4468 are processed in order, from left to right.
4474 @section Specifying subprocesses and the switches to pass to them
4476 @command{gcc} is a driver program. It performs its job by invoking a
4477 sequence of other programs to do the work of compiling, assembling and
4478 linking. GCC interprets its command-line parameters and uses these to
4479 deduce which programs it should invoke, and which command-line options
4480 it ought to place on their command lines. This behaviour is controlled
4481 by @dfn{spec strings}. In most cases there is one spec string for each
4482 program that GCC can invoke, but a few programs have multiple spec
4483 strings to control their behaviour. The spec strings built into GCC can
4484 be overridden by using the @option{-specs=} command-line switch to specify
4487 @dfn{Spec files} are plaintext files that are used to construct spec
4488 strings. They consist of a sequence of directives separated by blank
4489 lines. The type of directive is determined by the first non-whitespace
4490 character on the line and it can be one of the following:
4493 @item %@var{command}
4494 Issues a @var{command} to the spec file processor. The commands that can
4498 @item %include <@var{file}>
4500 Search for @var{file} and insert its text at the current point in the
4503 @item %include_noerr <@var{file}>
4504 @cindex %include_noerr
4505 Just like @samp{%include}, but do not generate an error message if the include
4506 file cannot be found.
4508 @item %rename @var{old_name} @var{new_name}
4510 Rename the spec string @var{old_name} to @var{new_name}.
4514 @item *[@var{spec_name}]:
4515 This tells the compiler to create, override or delete the named spec
4516 string. All lines after this directive up to the next directive or
4517 blank line are considered to be the text for the spec string. If this
4518 results in an empty string then the spec will be deleted. (Or, if the
4519 spec did not exist, then nothing will happened.) Otherwise, if the spec
4520 does not currently exist a new spec will be created. If the spec does
4521 exist then its contents will be overridden by the text of this
4522 directive, unless the first character of that text is the @samp{+}
4523 character, in which case the text will be appended to the spec.
4525 @item [@var{suffix}]:
4526 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
4527 and up to the next directive or blank line are considered to make up the
4528 spec string for the indicated suffix. When the compiler encounters an
4529 input file with the named suffix, it will processes the spec string in
4530 order to work out how to compile that file. For example:
4537 This says that any input file whose name ends in @samp{.ZZ} should be
4538 passed to the program @samp{z-compile}, which should be invoked with the
4539 command-line switch @option{-input} and with the result of performing the
4540 @samp{%i} substitution. (See below.)
4542 As an alternative to providing a spec string, the text that follows a
4543 suffix directive can be one of the following:
4546 @item @@@var{language}
4547 This says that the suffix is an alias for a known @var{language}. This is
4548 similar to using the @option{-x} command-line switch to GCC to specify a
4549 language explicitly. For example:
4556 Says that .ZZ files are, in fact, C++ source files.
4559 This causes an error messages saying:
4562 @var{name} compiler not installed on this system.
4566 GCC already has an extensive list of suffixes built into it.
4567 This directive will add an entry to the end of the list of suffixes, but
4568 since the list is searched from the end backwards, it is effectively
4569 possible to override earlier entries using this technique.
4573 GCC has the following spec strings built into it. Spec files can
4574 override these strings or create their own. Note that individual
4575 targets can also add their own spec strings to this list.
4578 asm Options to pass to the assembler
4579 asm_final Options to pass to the assembler post-processor
4580 cpp Options to pass to the C preprocessor
4581 cc1 Options to pass to the C compiler
4582 cc1plus Options to pass to the C++ compiler
4583 endfile Object files to include at the end of the link
4584 link Options to pass to the linker
4585 lib Libraries to include on the command line to the linker
4586 libgcc Decides which GCC support library to pass to the linker
4587 linker Sets the name of the linker
4588 predefines Defines to be passed to the C preprocessor
4589 signed_char Defines to pass to CPP to say whether @code{char} is signed
4591 startfile Object files to include at the start of the link
4594 Here is a small example of a spec file:
4600 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
4603 This example renames the spec called @samp{lib} to @samp{old_lib} and
4604 then overrides the previous definition of @samp{lib} with a new one.
4605 The new definition adds in some extra command-line options before
4606 including the text of the old definition.
4608 @dfn{Spec strings} are a list of command-line options to be passed to their
4609 corresponding program. In addition, the spec strings can contain
4610 @samp{%}-prefixed sequences to substitute variable text or to
4611 conditionally insert text into the command line. Using these constructs
4612 it is possible to generate quite complex command lines.
4614 Here is a table of all defined @samp{%}-sequences for spec
4615 strings. Note that spaces are not generated automatically around the
4616 results of expanding these sequences. Therefore you can concatenate them
4617 together or combine them with constant text in a single argument.
4621 Substitute one @samp{%} into the program name or argument.
4624 Substitute the name of the input file being processed.
4627 Substitute the basename of the input file being processed.
4628 This is the substring up to (and not including) the last period
4629 and not including the directory.
4632 This is the same as @samp{%b}, but include the file suffix (text after
4636 Marks the argument containing or following the @samp{%d} as a
4637 temporary file name, so that that file will be deleted if GCC exits
4638 successfully. Unlike @samp{%g}, this contributes no text to the
4641 @item %g@var{suffix}
4642 Substitute a file name that has suffix @var{suffix} and is chosen
4643 once per compilation, and mark the argument in the same way as
4644 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
4645 name is now chosen in a way that is hard to predict even when previously
4646 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
4647 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
4648 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
4649 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
4650 was simply substituted with a file name chosen once per compilation,
4651 without regard to any appended suffix (which was therefore treated
4652 just like ordinary text), making such attacks more likely to succeed.
4654 @item %u@var{suffix}
4655 Like @samp{%g}, but generates a new temporary file name even if
4656 @samp{%u@var{suffix}} was already seen.
4658 @item %U@var{suffix}
4659 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
4660 new one if there is no such last file name. In the absence of any
4661 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
4662 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
4663 would involve the generation of two distinct file names, one
4664 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
4665 simply substituted with a file name chosen for the previous @samp{%u},
4666 without regard to any appended suffix.
4668 @item %j@var{SUFFIX}
4669 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
4670 writable, and if save-temps is off; otherwise, substitute the name
4671 of a temporary file, just like @samp{%u}. This temporary file is not
4672 meant for communication between processes, but rather as a junk
4675 @item %.@var{SUFFIX}
4676 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
4677 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
4678 terminated by the next space or %.
4681 Marks the argument containing or following the @samp{%w} as the
4682 designated output file of this compilation. This puts the argument
4683 into the sequence of arguments that @samp{%o} will substitute later.
4686 Substitutes the names of all the output files, with spaces
4687 automatically placed around them. You should write spaces
4688 around the @samp{%o} as well or the results are undefined.
4689 @samp{%o} is for use in the specs for running the linker.
4690 Input files whose names have no recognized suffix are not compiled
4691 at all, but they are included among the output files, so they will
4695 Substitutes the suffix for object files. Note that this is
4696 handled specially when it immediately follows @samp{%g, %u, or %U},
4697 because of the need for those to form complete file names. The
4698 handling is such that @samp{%O} is treated exactly as if it had already
4699 been substituted, except that @samp{%g, %u, and %U} do not currently
4700 support additional @var{suffix} characters following @samp{%O} as they would
4701 following, for example, @samp{.o}.
4704 Substitutes the standard macro predefinitions for the
4705 current target machine. Use this when running @code{cpp}.
4708 Like @samp{%p}, but puts @samp{__} before and after the name of each
4709 predefined macro, except for macros that start with @samp{__} or with
4710 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
4714 Substitute a @option{-iprefix} option made from @env{GCC_EXEC_PREFIX}.
4717 Current argument is the name of a library or startup file of some sort.
4718 Search for that file in a standard list of directories and substitute
4719 the full name found.
4722 Print @var{str} as an error message. @var{str} is terminated by a newline.
4723 Use this when inconsistent options are detected.
4726 Output @samp{-} if the input for the current command is coming from a pipe.
4729 Substitute the contents of spec string @var{name} at this point.
4732 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
4734 @item %x@{@var{option}@}
4735 Accumulate an option for @samp{%X}.
4738 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
4742 Output the accumulated assembler options specified by @option{-Wa}.
4745 Output the accumulated preprocessor options specified by @option{-Wp}.
4748 Substitute the major version number of GCC@.
4749 (For version 2.9.5, this is 2.)
4752 Substitute the minor version number of GCC@.
4753 (For version 2.9.5, this is 9.)
4756 Substitute the patch level number of GCC@.
4757 (For version 2.9.5, this is 5.)
4760 Process the @code{asm} spec. This is used to compute the
4761 switches to be passed to the assembler.
4764 Process the @code{asm_final} spec. This is a spec string for
4765 passing switches to an assembler post-processor, if such a program is
4769 Process the @code{link} spec. This is the spec for computing the
4770 command line passed to the linker. Typically it will make use of the
4771 @samp{%L %G %S %D and %E} sequences.
4774 Dump out a @option{-L} option for each directory that GCC believes might
4775 contain startup files. If the target supports multilibs then the
4776 current multilib directory will be prepended to each of these paths.
4779 Output the multilib directory with directory separators replaced with
4780 @samp{_}. If multilib directories are not set, or the multilib directory is
4781 @file{.} then this option emits nothing.
4784 Process the @code{lib} spec. This is a spec string for deciding which
4785 libraries should be included on the command line to the linker.
4788 Process the @code{libgcc} spec. This is a spec string for deciding
4789 which GCC support library should be included on the command line to the linker.
4792 Process the @code{startfile} spec. This is a spec for deciding which
4793 object files should be the first ones passed to the linker. Typically
4794 this might be a file named @file{crt0.o}.
4797 Process the @code{endfile} spec. This is a spec string that specifies
4798 the last object files that will be passed to the linker.
4801 Process the @code{cpp} spec. This is used to construct the arguments
4802 to be passed to the C preprocessor.
4805 Process the @code{signed_char} spec. This is intended to be used
4806 to tell cpp whether a char is signed. It typically has the definition:
4808 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
4812 Process the @code{cc1} spec. This is used to construct the options to be
4813 passed to the actual C compiler (@samp{cc1}).
4816 Process the @code{cc1plus} spec. This is used to construct the options to be
4817 passed to the actual C++ compiler (@samp{cc1plus}).
4820 Substitute the variable part of a matched option. See below.
4821 Note that each comma in the substituted string is replaced by
4825 Substitutes the @code{-S} switch, if that switch was given to GCC@.
4826 If that switch was not specified, this substitutes nothing. Note that
4827 the leading dash is omitted when specifying this option, and it is
4828 automatically inserted if the substitution is performed. Thus the spec
4829 string @samp{%@{foo@}} would match the command-line option @option{-foo}
4830 and would output the command line option @option{-foo}.
4832 @item %W@{@code{S}@}
4833 Like %@{@code{S}@} but mark last argument supplied within as a file to be
4836 @item %@{@code{S}*@}
4837 Substitutes all the switches specified to GCC whose names start
4838 with @code{-S}, but which also take an argument. This is used for
4839 switches like @option{-o}, @option{-D}, @option{-I}, etc.
4840 GCC considers @option{-o foo} as being
4841 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
4842 text, including the space. Thus two arguments would be generated.
4844 @item %@{^@code{S}*@}
4845 Like %@{@code{S}*@}, but don't put a blank between a switch and its
4846 argument. Thus %@{^o*@} would only generate one argument, not two.
4848 @item %@{@code{S}*&@code{T}*@}
4849 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
4850 (the order of @code{S} and @code{T} in the spec is not significant).
4851 There can be any number of ampersand-separated variables; for each the
4852 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
4854 @item %@{<@code{S}@}
4855 Remove all occurrences of @code{-S} from the command line. Note---this
4856 command is position dependent. @samp{%} commands in the spec string
4857 before this option will see @code{-S}, @samp{%} commands in the spec
4858 string after this option will not.
4860 @item %@{@code{S}*:@code{X}@}
4861 Substitutes @code{X} if one or more switches whose names start with
4862 @code{-S} are specified to GCC@. Note that the tail part of the
4863 @code{-S} option (i.e.@: the part matched by the @samp{*}) will be substituted
4864 for each occurrence of @samp{%*} within @code{X}.
4866 @item %@{@code{S}:@code{X}@}
4867 Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC@.
4869 @item %@{!@code{S}:@code{X}@}
4870 Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC@.
4872 @item %@{|@code{S}:@code{X}@}
4873 Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}.
4875 @item %@{|!@code{S}:@code{X}@}
4876 Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}.
4878 @item %@{.@code{S}:@code{X}@}
4879 Substitutes @code{X}, but only if processing a file with suffix @code{S}.
4881 @item %@{!.@code{S}:@code{X}@}
4882 Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}.
4884 @item %@{@code{S}|@code{P}:@code{X}@}
4885 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@. This may be
4886 combined with @samp{!} and @samp{.} sequences as well, although they
4887 have a stronger binding than the @samp{|}. For example a spec string
4891 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
4894 will output the following command-line options from the following input
4895 command-line options:
4900 -d fred.c -foo -baz -boggle
4901 -d jim.d -bar -baz -boggle
4906 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or
4907 %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs
4908 or spaces, or even newlines. They are processed as usual, as described
4911 The @option{-O}, @option{-f}, @option{-m}, and @option{-W}
4912 switches are handled specifically in these
4913 constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or
4914 @option{-W} switch is found later in the command line, the earlier switch
4915 value is ignored, except with @{@code{S}*@} where @code{S} is just one
4916 letter, which passes all matching options.
4918 The character @samp{|} at the beginning of the predicate text is used to indicate
4919 that a command should be piped to the following command, but only if @option{-pipe}
4922 It is built into GCC which switches take arguments and which do not.
4923 (You might think it would be useful to generalize this to allow each
4924 compiler's spec to say which switches take arguments. But this cannot
4925 be done in a consistent fashion. GCC cannot even decide which input
4926 files have been specified without knowing which switches take arguments,
4927 and it must know which input files to compile in order to tell which
4930 GCC also knows implicitly that arguments starting in @option{-l} are to be
4931 treated as compiler output files, and passed to the linker in their
4932 proper position among the other output files.
4934 @c man begin OPTIONS
4936 @node Target Options
4937 @section Specifying Target Machine and Compiler Version
4938 @cindex target options
4939 @cindex cross compiling
4940 @cindex specifying machine version
4941 @cindex specifying compiler version and target machine
4942 @cindex compiler version, specifying
4943 @cindex target machine, specifying
4945 By default, GCC compiles code for the same type of machine that you
4946 are using. However, it can also be installed as a cross-compiler, to
4947 compile for some other type of machine. In fact, several different
4948 configurations of GCC, for different target machines, can be
4949 installed side by side. Then you specify which one to use with the
4952 In addition, older and newer versions of GCC can be installed side
4953 by side. One of them (probably the newest) will be the default, but
4954 you may sometimes wish to use another.
4957 @item -b @var{machine}
4959 The argument @var{machine} specifies the target machine for compilation.
4960 This is useful when you have installed GCC as a cross-compiler.
4962 The value to use for @var{machine} is the same as was specified as the
4963 machine type when configuring GCC as a cross-compiler. For
4964 example, if a cross-compiler was configured with @samp{configure
4965 i386v}, meaning to compile for an 80386 running System V, then you
4966 would specify @option{-b i386v} to run that cross compiler.
4968 When you do not specify @option{-b}, it normally means to compile for
4969 the same type of machine that you are using.
4971 @item -V @var{version}
4973 The argument @var{version} specifies which version of GCC to run.
4974 This is useful when multiple versions are installed. For example,
4975 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
4977 The default version, when you do not specify @option{-V}, is the last
4978 version of GCC that you installed.
4981 The @option{-b} and @option{-V} options actually work by controlling part of
4982 the file name used for the executable files and libraries used for
4983 compilation. A given version of GCC, for a given target machine, is
4984 normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}.
4986 Thus, sites can customize the effect of @option{-b} or @option{-V} either by
4987 changing the names of these directories or adding alternate names (or
4988 symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the
4989 file @file{80386} is a link to the file @file{i386v}, then @option{-b
4990 80386} becomes an alias for @option{-b i386v}.
4992 In one respect, the @option{-b} or @option{-V} do not completely change
4993 to a different compiler: the top-level driver program @command{gcc}
4994 that you originally invoked continues to run and invoke the other
4995 executables (preprocessor, compiler per se, assembler and linker)
4996 that do the real work. However, since no real work is done in the
4997 driver program, it usually does not matter that the driver program
4998 in use is not the one for the specified target. It is common for the
4999 interface to the other executables to change incompatibly between
5000 compiler versions, so unless the version specified is very close to that
5001 of the driver (for example, @option{-V 3.0} with a driver program from GCC
5002 version 3.0.1), use of @option{-V} may not work; for example, using
5003 @option{-V 2.95.2} will not work with a driver program from GCC 3.0.
5005 The only way that the driver program depends on the target machine is
5006 in the parsing and handling of special machine-specific options.
5007 However, this is controlled by a file which is found, along with the
5008 other executables, in the directory for the specified version and
5009 target machine. As a result, a single installed driver program adapts
5010 to any specified target machine, and sufficiently similar compiler
5013 The driver program executable does control one significant thing,
5014 however: the default version and target machine. Therefore, you can
5015 install different instances of the driver program, compiled for
5016 different targets or versions, under different names.
5018 For example, if the driver for version 2.0 is installed as @command{ogcc}
5019 and that for version 2.1 is installed as @command{gcc}, then the command
5020 @command{gcc} will use version 2.1 by default, while @command{ogcc} will use
5021 2.0 by default. However, you can choose either version with either
5022 command with the @option{-V} option.
5024 @node Submodel Options
5025 @section Hardware Models and Configurations
5026 @cindex submodel options
5027 @cindex specifying hardware config
5028 @cindex hardware models and configurations, specifying
5029 @cindex machine dependent options
5031 Earlier we discussed the standard option @option{-b} which chooses among
5032 different installed compilers for completely different target
5033 machines, such as Vax vs.@: 68000 vs.@: 80386.
5035 In addition, each of these target machine types can have its own
5036 special options, starting with @samp{-m}, to choose among various
5037 hardware models or configurations---for example, 68010 vs 68020,
5038 floating coprocessor or none. A single installed version of the
5039 compiler can compile for any model or configuration, according to the
5042 Some configurations of the compiler also support additional special
5043 options, usually for compatibility with other compilers on the same
5047 These options are defined by the macro @code{TARGET_SWITCHES} in the
5048 machine description. The default for the options is also defined by
5049 that macro, which enables you to change the defaults.
5064 * RS/6000 and PowerPC Options::
5069 * Intel 960 Options::
5070 * DEC Alpha Options::
5074 * System V Options::
5075 * TMS320C3x/C4x Options::
5085 @node M680x0 Options
5086 @subsection M680x0 Options
5087 @cindex M680x0 options
5089 These are the @samp{-m} options defined for the 68000 series. The default
5090 values for these options depends on which style of 68000 was selected when
5091 the compiler was configured; the defaults for the most common choices are
5099 Generate output for a 68000. This is the default
5100 when the compiler is configured for 68000-based systems.
5102 Use this option for microcontrollers with a 68000 or EC000 core,
5103 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5109 Generate output for a 68020. This is the default
5110 when the compiler is configured for 68020-based systems.
5114 Generate output containing 68881 instructions for floating point.
5115 This is the default for most 68020 systems unless @option{--nfp} was
5116 specified when the compiler was configured.
5120 Generate output for a 68030. This is the default when the compiler is
5121 configured for 68030-based systems.
5125 Generate output for a 68040. This is the default when the compiler is
5126 configured for 68040-based systems.
5128 This option inhibits the use of 68881/68882 instructions that have to be
5129 emulated by software on the 68040. Use this option if your 68040 does not
5130 have code to emulate those instructions.
5134 Generate output for a 68060. This is the default when the compiler is
5135 configured for 68060-based systems.
5137 This option inhibits the use of 68020 and 68881/68882 instructions that
5138 have to be emulated by software on the 68060. Use this option if your 68060
5139 does not have code to emulate those instructions.
5143 Generate output for a CPU32. This is the default
5144 when the compiler is configured for CPU32-based systems.
5146 Use this option for microcontrollers with a
5147 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5148 68336, 68340, 68341, 68349 and 68360.
5152 Generate output for a 520X ``coldfire'' family cpu. This is the default
5153 when the compiler is configured for 520X-based systems.
5155 Use this option for microcontroller with a 5200 core, including
5156 the MCF5202, MCF5203, MCF5204 and MCF5202.
5161 Generate output for a 68040, without using any of the new instructions.
5162 This results in code which can run relatively efficiently on either a
5163 68020/68881 or a 68030 or a 68040. The generated code does use the
5164 68881 instructions that are emulated on the 68040.
5168 Generate output for a 68060, without using any of the new instructions.
5169 This results in code which can run relatively efficiently on either a
5170 68020/68881 or a 68030 or a 68040. The generated code does use the
5171 68881 instructions that are emulated on the 68060.
5175 Generate output containing Sun FPA instructions for floating point.
5178 @opindex msoft-float
5179 Generate output containing library calls for floating point.
5180 @strong{Warning:} the requisite libraries are not available for all m68k
5181 targets. Normally the facilities of the machine's usual C compiler are
5182 used, but this can't be done directly in cross-compilation. You must
5183 make your own arrangements to provide suitable library functions for
5184 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5185 @samp{m68k-*-coff} do provide software floating point support.
5189 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5192 @opindex mnobitfield
5193 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5194 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5198 Do use the bit-field instructions. The @option{-m68020} option implies
5199 @option{-mbitfield}. This is the default if you use a configuration
5200 designed for a 68020.
5204 Use a different function-calling convention, in which functions
5205 that take a fixed number of arguments return with the @code{rtd}
5206 instruction, which pops their arguments while returning. This
5207 saves one instruction in the caller since there is no need to pop
5208 the arguments there.
5210 This calling convention is incompatible with the one normally
5211 used on Unix, so you cannot use it if you need to call libraries
5212 compiled with the Unix compiler.
5214 Also, you must provide function prototypes for all functions that
5215 take variable numbers of arguments (including @code{printf});
5216 otherwise incorrect code will be generated for calls to those
5219 In addition, seriously incorrect code will result if you call a
5220 function with too many arguments. (Normally, extra arguments are
5221 harmlessly ignored.)
5223 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5224 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5227 @itemx -mno-align-int
5229 @opindex mno-align-int
5230 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5231 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5232 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5233 Aligning variables on 32-bit boundaries produces code that runs somewhat
5234 faster on processors with 32-bit busses at the expense of more memory.
5236 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5237 align structures containing the above types differently than
5238 most published application binary interface specifications for the m68k.
5242 Use the pc-relative addressing mode of the 68000 directly, instead of
5243 using a global offset table. At present, this option implies @option{-fpic},
5244 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5245 not presently supported with @option{-mpcrel}, though this could be supported for
5246 68020 and higher processors.
5248 @item -mno-strict-align
5249 @itemx -mstrict-align
5250 @opindex mno-strict-align
5251 @opindex mstrict-align
5252 Do not (do) assume that unaligned memory references will be handled by
5257 @node M68hc1x Options
5258 @subsection M68hc1x Options
5259 @cindex M68hc1x options
5261 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5262 microcontrollers. The default values for these options depends on
5263 which style of microcontroller was selected when the compiler was configured;
5264 the defaults for the most common choices are given below.
5271 Generate output for a 68HC11. This is the default
5272 when the compiler is configured for 68HC11-based systems.
5278 Generate output for a 68HC12. This is the default
5279 when the compiler is configured for 68HC12-based systems.
5282 @opindex mauto-incdec
5283 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5288 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5290 @item -msoft-reg-count=@var{count}
5291 @opindex msoft-reg-count
5292 Specify the number of pseudo-soft registers which are used for the
5293 code generation. The maximum number is 32. Using more pseudo-soft
5294 register may or may not result in better code depending on the program.
5295 The default is 4 for 68HC11 and 2 for 68HC12.
5300 @subsection VAX Options
5303 These @samp{-m} options are defined for the Vax:
5308 Do not output certain jump instructions (@code{aobleq} and so on)
5309 that the Unix assembler for the Vax cannot handle across long
5314 Do output those jump instructions, on the assumption that you
5315 will assemble with the GNU assembler.
5319 Output code for g-format floating point numbers instead of d-format.
5323 @subsection SPARC Options
5324 @cindex SPARC options
5326 These @samp{-m} switches are supported on the SPARC:
5331 @opindex mno-app-regs
5333 Specify @option{-mapp-regs} to generate output using the global registers
5334 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5337 To be fully SVR4 ABI compliant at the cost of some performance loss,
5338 specify @option{-mno-app-regs}. You should compile libraries and system
5339 software with this option.
5344 @opindex mhard-float
5345 Generate output containing floating point instructions. This is the
5351 @opindex msoft-float
5352 Generate output containing library calls for floating point.
5353 @strong{Warning:} the requisite libraries are not available for all SPARC
5354 targets. Normally the facilities of the machine's usual C compiler are
5355 used, but this cannot be done directly in cross-compilation. You must make
5356 your own arrangements to provide suitable library functions for
5357 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5358 @samp{sparclite-*-*} do provide software floating point support.
5360 @option{-msoft-float} changes the calling convention in the output file;
5361 therefore, it is only useful if you compile @emph{all} of a program with
5362 this option. In particular, you need to compile @file{libgcc.a}, the
5363 library that comes with GCC, with @option{-msoft-float} in order for
5366 @item -mhard-quad-float
5367 @opindex mhard-quad-float
5368 Generate output containing quad-word (long double) floating point
5371 @item -msoft-quad-float
5372 @opindex msoft-quad-float
5373 Generate output containing library calls for quad-word (long double)
5374 floating point instructions. The functions called are those specified
5375 in the SPARC ABI@. This is the default.
5377 As of this writing, there are no sparc implementations that have hardware
5378 support for the quad-word floating point instructions. They all invoke
5379 a trap handler for one of these instructions, and then the trap handler
5380 emulates the effect of the instruction. Because of the trap handler overhead,
5381 this is much slower than calling the ABI library routines. Thus the
5382 @option{-msoft-quad-float} option is the default.
5386 @opindex mno-epilogue
5388 With @option{-mepilogue} (the default), the compiler always emits code for
5389 function exit at the end of each function. Any function exit in
5390 the middle of the function (such as a return statement in C) will
5391 generate a jump to the exit code at the end of the function.
5393 With @option{-mno-epilogue}, the compiler tries to emit exit code inline
5394 at every function exit.
5400 With @option{-mflat}, the compiler does not generate save/restore instructions
5401 and will use a ``flat'' or single register window calling convention.
5402 This model uses %i7 as the frame pointer and is compatible with the normal
5403 register window model. Code from either may be intermixed.
5404 The local registers and the input registers (0--5) are still treated as
5405 ``call saved'' registers and will be saved on the stack as necessary.
5407 With @option{-mno-flat} (the default), the compiler emits save/restore
5408 instructions (except for leaf functions) and is the normal mode of operation.
5410 @item -mno-unaligned-doubles
5411 @itemx -munaligned-doubles
5412 @opindex mno-unaligned-doubles
5413 @opindex munaligned-doubles
5414 Assume that doubles have 8 byte alignment. This is the default.
5416 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
5417 alignment only if they are contained in another type, or if they have an
5418 absolute address. Otherwise, it assumes they have 4 byte alignment.
5419 Specifying this option avoids some rare compatibility problems with code
5420 generated by other compilers. It is not the default because it results
5421 in a performance loss, especially for floating point code.
5423 @item -mno-faster-structs
5424 @itemx -mfaster-structs
5425 @opindex mno-faster-structs
5426 @opindex mfaster-structs
5427 With @option{-mfaster-structs}, the compiler assumes that structures
5428 should have 8 byte alignment. This enables the use of pairs of
5429 @code{ldd} and @code{std} instructions for copies in structure
5430 assignment, in place of twice as many @code{ld} and @code{st} pairs.
5431 However, the use of this changed alignment directly violates the Sparc
5432 ABI@. Thus, it's intended only for use on targets where the developer
5433 acknowledges that their resulting code will not be directly in line with
5434 the rules of the ABI@.
5440 These two options select variations on the SPARC architecture.
5442 By default (unless specifically configured for the Fujitsu SPARClite),
5443 GCC generates code for the v7 variant of the SPARC architecture.
5445 @option{-mv8} will give you SPARC v8 code. The only difference from v7
5446 code is that the compiler emits the integer multiply and integer
5447 divide instructions which exist in SPARC v8 but not in SPARC v7.
5449 @option{-msparclite} will give you SPARClite code. This adds the integer
5450 multiply, integer divide step and scan (@code{ffs}) instructions which
5451 exist in SPARClite but not in SPARC v7.
5453 These options are deprecated and will be deleted in a future GCC release.
5454 They have been replaced with @option{-mcpu=xxx}.
5459 @opindex msupersparc
5460 These two options select the processor for which the code is optimised.
5462 With @option{-mcypress} (the default), the compiler optimizes code for the
5463 Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series.
5464 This is also appropriate for the older SparcStation 1, 2, IPX etc.
5466 With @option{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as
5467 used in the SparcStation 10, 1000 and 2000 series. This flag also enables use
5468 of the full SPARC v8 instruction set.
5470 These options are deprecated and will be deleted in a future GCC release.
5471 They have been replaced with @option{-mcpu=xxx}.
5473 @item -mcpu=@var{cpu_type}
5475 Set the instruction set, register set, and instruction scheduling parameters
5476 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
5477 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
5478 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
5479 @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}.
5481 Default instruction scheduling parameters are used for values that select
5482 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
5483 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
5485 Here is a list of each supported architecture and their supported
5490 v8: supersparc, hypersparc
5491 sparclite: f930, f934, sparclite86x
5496 @item -mtune=@var{cpu_type}
5498 Set the instruction scheduling parameters for machine type
5499 @var{cpu_type}, but do not set the instruction set or register set that the
5500 option @option{-mcpu=@var{cpu_type}} would.
5502 The same values for @option{-mcpu=@var{cpu_type}} are used for
5503 @option{-mtune=@var{cpu_type}}, though the only useful values are those that
5504 select a particular cpu implementation: @samp{cypress}, @samp{supersparc},
5505 @samp{hypersparc}, @samp{f930}, @samp{f934}, @samp{sparclite86x},
5506 @samp{tsc701}, @samp{ultrasparc}.
5510 These @samp{-m} switches are supported in addition to the above
5511 on the SPARCLET processor.
5514 @item -mlittle-endian
5515 @opindex mlittle-endian
5516 Generate code for a processor running in little-endian mode.
5520 Treat register @code{%g0} as a normal register.
5521 GCC will continue to clobber it as necessary but will not assume
5522 it always reads as 0.
5524 @item -mbroken-saverestore
5525 @opindex mbroken-saverestore
5526 Generate code that does not use non-trivial forms of the @code{save} and
5527 @code{restore} instructions. Early versions of the SPARCLET processor do
5528 not correctly handle @code{save} and @code{restore} instructions used with
5529 arguments. They correctly handle them used without arguments. A @code{save}
5530 instruction used without arguments increments the current window pointer
5531 but does not allocate a new stack frame. It is assumed that the window
5532 overflow trap handler will properly handle this case as will interrupt
5536 These @samp{-m} switches are supported in addition to the above
5537 on SPARC V9 processors in 64-bit environments.
5540 @item -mlittle-endian
5541 @opindex mlittle-endian
5542 Generate code for a processor running in little-endian mode.
5548 Generate code for a 32-bit or 64-bit environment.
5549 The 32-bit environment sets int, long and pointer to 32 bits.
5550 The 64-bit environment sets int to 32 bits and long and pointer
5553 @item -mcmodel=medlow
5554 @opindex mcmodel=medlow
5555 Generate code for the Medium/Low code model: the program must be linked
5556 in the low 32 bits of the address space. Pointers are 64 bits.
5557 Programs can be statically or dynamically linked.
5559 @item -mcmodel=medmid
5560 @opindex mcmodel=medmid
5561 Generate code for the Medium/Middle code model: the program must be linked
5562 in the low 44 bits of the address space, the text segment must be less than
5563 2G bytes, and data segment must be within 2G of the text segment.
5564 Pointers are 64 bits.
5566 @item -mcmodel=medany
5567 @opindex mcmodel=medany
5568 Generate code for the Medium/Anywhere code model: the program may be linked
5569 anywhere in the address space, the text segment must be less than
5570 2G bytes, and data segment must be within 2G of the text segment.
5571 Pointers are 64 bits.
5573 @item -mcmodel=embmedany
5574 @opindex mcmodel=embmedany
5575 Generate code for the Medium/Anywhere code model for embedded systems:
5576 assume a 32-bit text and a 32-bit data segment, both starting anywhere
5577 (determined at link time). Register %g4 points to the base of the
5578 data segment. Pointers are still 64 bits.
5579 Programs are statically linked, PIC is not supported.
5582 @itemx -mno-stack-bias
5583 @opindex mstack-bias
5584 @opindex mno-stack-bias
5585 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
5586 frame pointer if present, are offset by @minus{}2047 which must be added back
5587 when making stack frame references.
5588 Otherwise, assume no such offset is present.
5591 @node Convex Options
5592 @subsection Convex Options
5593 @cindex Convex options
5595 These @samp{-m} options are defined for Convex:
5600 Generate output for C1. The code will run on any Convex machine.
5601 The preprocessor symbol @code{__convex__c1__} is defined.
5605 Generate output for C2. Uses instructions not available on C1.
5606 Scheduling and other optimizations are chosen for max performance on C2.
5607 The preprocessor symbol @code{__convex_c2__} is defined.
5611 Generate output for C32xx. Uses instructions not available on C1.
5612 Scheduling and other optimizations are chosen for max performance on C32.
5613 The preprocessor symbol @code{__convex_c32__} is defined.
5617 Generate output for C34xx. Uses instructions not available on C1.
5618 Scheduling and other optimizations are chosen for max performance on C34.
5619 The preprocessor symbol @code{__convex_c34__} is defined.
5623 Generate output for C38xx. Uses instructions not available on C1.
5624 Scheduling and other optimizations are chosen for max performance on C38.
5625 The preprocessor symbol @code{__convex_c38__} is defined.
5629 Generate code which puts an argument count in the word preceding each
5630 argument list. This is compatible with regular CC, and a few programs
5631 may need the argument count word. GDB and other source-level debuggers
5632 do not need it; this info is in the symbol table.
5635 @opindex mnoargcount
5636 Omit the argument count word. This is the default.
5638 @item -mvolatile-cache
5639 @opindex mvolatile-cache
5640 Allow volatile references to be cached. This is the default.
5642 @item -mvolatile-nocache
5643 @opindex mvolatile-nocache
5644 Volatile references bypass the data cache, going all the way to memory.
5645 This is only needed for multi-processor code that does not use standard
5646 synchronization instructions. Making non-volatile references to volatile
5647 locations will not necessarily work.
5651 Type long is 32 bits, the same as type int. This is the default.
5655 Type long is 64 bits, the same as type long long. This option is useless,
5656 because no library support exists for it.
5659 @node AMD29K Options
5660 @subsection AMD29K Options
5661 @cindex AMD29K options
5663 These @samp{-m} options are defined for the AMD Am29000:
5668 @cindex DW bit (29k)
5669 Generate code that assumes the @code{DW} bit is set, i.e., that byte and
5670 halfword operations are directly supported by the hardware. This is the
5675 Generate code that assumes the @code{DW} bit is not set.
5679 @cindex byte writes (29k)
5680 Generate code that assumes the system supports byte and halfword write
5681 operations. This is the default.
5685 Generate code that assumes the systems does not support byte and
5686 halfword write operations. @option{-mnbw} implies @option{-mndw}.
5690 @cindex memory model (29k)
5691 Use a small memory model that assumes that all function addresses are
5692 either within a single 256 KB segment or at an absolute address of less
5693 than 256k. This allows the @code{call} instruction to be used instead
5694 of a @code{const}, @code{consth}, @code{calli} sequence.
5698 Use the normal memory model: Generate @code{call} instructions only when
5699 calling functions in the same file and @code{calli} instructions
5700 otherwise. This works if each file occupies less than 256 KB but allows
5701 the entire executable to be larger than 256 KB@. This is the default.
5705 Always use @code{calli} instructions. Specify this option if you expect
5706 a single file to compile into more than 256 KB of code.
5710 @cindex processor selection (29k)
5711 Generate code for the Am29050.
5715 Generate code for the Am29000. This is the default.
5717 @item -mkernel-registers
5718 @opindex mkernel-registers
5719 @cindex kernel and user registers (29k)
5720 Generate references to registers @code{gr64-gr95} instead of to
5721 registers @code{gr96-gr127}. This option can be used when compiling
5722 kernel code that wants a set of global registers disjoint from that used
5725 Note that when this option is used, register names in @samp{-f} flags
5726 must use the normal, user-mode, names.
5728 @item -muser-registers
5729 @opindex muser-registers
5730 Use the normal set of global registers, @code{gr96-gr127}. This is the
5734 @itemx -mno-stack-check
5735 @opindex mstack-check
5736 @opindex mno-stack-check
5737 @cindex stack checks (29k)
5738 Insert (or do not insert) a call to @code{__msp_check} after each stack
5739 adjustment. This is often used for kernel code.
5742 @itemx -mno-storem-bug
5743 @opindex mstorem-bug
5744 @opindex mno-storem-bug
5745 @cindex storem bug (29k)
5746 @option{-mstorem-bug} handles 29k processors which cannot handle the
5747 separation of a mtsrim insn and a storem instruction (most 29000 chips
5748 to date, but not the 29050).
5750 @item -mno-reuse-arg-regs
5751 @itemx -mreuse-arg-regs
5752 @opindex mno-reuse-arg-regs
5753 @opindex mreuse-arg-regs
5754 @option{-mno-reuse-arg-regs} tells the compiler to only use incoming argument
5755 registers for copying out arguments. This helps detect calling a function
5756 with fewer arguments than it was declared with.
5758 @item -mno-impure-text
5759 @itemx -mimpure-text
5760 @opindex mno-impure-text
5761 @opindex mimpure-text
5762 @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to
5763 not pass @option{-assert pure-text} to the linker when linking a shared object.
5766 @opindex msoft-float
5767 Generate output containing library calls for floating point.
5768 @strong{Warning:} the requisite libraries are not part of GCC@.
5769 Normally the facilities of the machine's usual C compiler are used, but
5770 this can't be done directly in cross-compilation. You must make your
5771 own arrangements to provide suitable library functions for
5776 Do not generate multm or multmu instructions. This is useful for some embedded
5777 systems which do not have trap handlers for these instructions.
5781 @subsection ARM Options
5784 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
5789 @opindex mapcs-frame
5790 Generate a stack frame that is compliant with the ARM Procedure Call
5791 Standard for all functions, even if this is not strictly necessary for
5792 correct execution of the code. Specifying @option{-fomit-frame-pointer}
5793 with this option will cause the stack frames not to be generated for
5794 leaf functions. The default is @option{-mno-apcs-frame}.
5798 This is a synonym for @option{-mapcs-frame}.
5802 Generate code for a processor running with a 26-bit program counter,
5803 and conforming to the function calling standards for the APCS 26-bit
5804 option. This option replaces the @option{-m2} and @option{-m3} options
5805 of previous releases of the compiler.
5809 Generate code for a processor running with a 32-bit program counter,
5810 and conforming to the function calling standards for the APCS 32-bit
5811 option. This option replaces the @option{-m6} option of previous releases
5815 @c not currently implemented
5816 @item -mapcs-stack-check
5817 @opindex mapcs-stack-check
5818 Generate code to check the amount of stack space available upon entry to
5819 every function (that actually uses some stack space). If there is
5820 insufficient space available then either the function
5821 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
5822 called, depending upon the amount of stack space required. The run time
5823 system is required to provide these functions. The default is
5824 @option{-mno-apcs-stack-check}, since this produces smaller code.
5826 @c not currently implemented
5828 @opindex mapcs-float
5829 Pass floating point arguments using the float point registers. This is
5830 one of the variants of the APCS@. This option is recommended if the
5831 target hardware has a floating point unit or if a lot of floating point
5832 arithmetic is going to be performed by the code. The default is
5833 @option{-mno-apcs-float}, since integer only code is slightly increased in
5834 size if @option{-mapcs-float} is used.
5836 @c not currently implemented
5837 @item -mapcs-reentrant
5838 @opindex mapcs-reentrant
5839 Generate reentrant, position independent code. The default is
5840 @option{-mno-apcs-reentrant}.
5843 @item -mthumb-interwork
5844 @opindex mthumb-interwork
5845 Generate code which supports calling between the ARM and Thumb
5846 instruction sets. Without this option the two instruction sets cannot
5847 be reliably used inside one program. The default is
5848 @option{-mno-thumb-interwork}, since slightly larger code is generated
5849 when @option{-mthumb-interwork} is specified.
5851 @item -mno-sched-prolog
5852 @opindex mno-sched-prolog
5853 Prevent the reordering of instructions in the function prolog, or the
5854 merging of those instruction with the instructions in the function's
5855 body. This means that all functions will start with a recognizable set
5856 of instructions (or in fact one of a choice from a small set of
5857 different function prologues), and this information can be used to
5858 locate the start if functions inside an executable piece of code. The
5859 default is @option{-msched-prolog}.
5862 @opindex mhard-float
5863 Generate output containing floating point instructions. This is the
5867 @opindex msoft-float
5868 Generate output containing library calls for floating point.
5869 @strong{Warning:} the requisite libraries are not available for all ARM
5870 targets. Normally the facilities of the machine's usual C compiler are
5871 used, but this cannot be done directly in cross-compilation. You must make
5872 your own arrangements to provide suitable library functions for
5875 @option{-msoft-float} changes the calling convention in the output file;
5876 therefore, it is only useful if you compile @emph{all} of a program with
5877 this option. In particular, you need to compile @file{libgcc.a}, the
5878 library that comes with GCC, with @option{-msoft-float} in order for
5881 @item -mlittle-endian
5882 @opindex mlittle-endian
5883 Generate code for a processor running in little-endian mode. This is
5884 the default for all standard configurations.
5887 @opindex mbig-endian
5888 Generate code for a processor running in big-endian mode; the default is
5889 to compile code for a little-endian processor.
5891 @item -mwords-little-endian
5892 @opindex mwords-little-endian
5893 This option only applies when generating code for big-endian processors.
5894 Generate code for a little-endian word order but a big-endian byte
5895 order. That is, a byte order of the form @samp{32107654}. Note: this
5896 option should only be used if you require compatibility with code for
5897 big-endian ARM processors generated by versions of the compiler prior to
5900 @item -malignment-traps
5901 @opindex malignment-traps
5902 Generate code that will not trap if the MMU has alignment traps enabled.
5903 On ARM architectures prior to ARMv4, there were no instructions to
5904 access half-word objects stored in memory. However, when reading from
5905 memory a feature of the ARM architecture allows a word load to be used,
5906 even if the address is unaligned, and the processor core will rotate the
5907 data as it is being loaded. This option tells the compiler that such
5908 misaligned accesses will cause a MMU trap and that it should instead
5909 synthesise the access as a series of byte accesses. The compiler can
5910 still use word accesses to load half-word data if it knows that the
5911 address is aligned to a word boundary.
5913 This option is ignored when compiling for ARM architecture 4 or later,
5914 since these processors have instructions to directly access half-word
5917 @item -mno-alignment-traps
5918 @opindex mno-alignment-traps
5919 Generate code that assumes that the MMU will not trap unaligned
5920 accesses. This produces better code when the target instruction set
5921 does not have half-word memory operations (i.e.@: implementations prior to
5924 Note that you cannot use this option to access unaligned word objects,
5925 since the processor will only fetch one 32-bit aligned object from
5928 The default setting for most targets is @option{-mno-alignment-traps}, since
5929 this produces better code when there are no half-word memory
5930 instructions available.
5932 @item -mshort-load-bytes
5933 @itemx -mno-short-load-words
5934 @opindex mshort-load-bytes
5935 @opindex mno-short-load-words
5936 These are deprecated aliases for @option{-malignment-traps}.
5938 @item -mno-short-load-bytes
5939 @itemx -mshort-load-words
5940 @opindex mno-short-load-bytes
5941 @opindex mshort-load-words
5942 This are deprecated aliases for @option{-mno-alignment-traps}.
5946 This option only applies to RISC iX@. Emulate the native BSD-mode
5947 compiler. This is the default if @option{-ansi} is not specified.
5951 This option only applies to RISC iX@. Emulate the native X/Open-mode
5954 @item -mno-symrename
5955 @opindex mno-symrename
5956 This option only applies to RISC iX@. Do not run the assembler
5957 post-processor, @samp{symrename}, after code has been assembled.
5958 Normally it is necessary to modify some of the standard symbols in
5959 preparation for linking with the RISC iX C library; this option
5960 suppresses this pass. The post-processor is never run when the
5961 compiler is built for cross-compilation.
5963 @item -mcpu=@var{name}
5965 This specifies the name of the target ARM processor. GCC uses this name
5966 to determine what kind of instructions it can emit when generating
5967 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
5968 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
5969 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
5970 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
5971 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
5972 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
5973 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
5974 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
5975 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
5976 @samp{arm1020t}, @samp{xscale}.
5978 @itemx -mtune=@var{name}
5980 This option is very similar to the @option{-mcpu=} option, except that
5981 instead of specifying the actual target processor type, and hence
5982 restricting which instructions can be used, it specifies that GCC should
5983 tune the performance of the code as if the target were of the type
5984 specified in this option, but still choosing the instructions that it
5985 will generate based on the cpu specified by a @option{-mcpu=} option.
5986 For some ARM implementations better performance can be obtained by using
5989 @item -march=@var{name}
5991 This specifies the name of the target ARM architecture. GCC uses this
5992 name to determine what kind of instructions it can emit when generating
5993 assembly code. This option can be used in conjunction with or instead
5994 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
5995 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
5996 @samp{armv5}, @samp{armv5t}, @samp{armv5te}.
5998 @item -mfpe=@var{number}
5999 @itemx -mfp=@var{number}
6002 This specifies the version of the floating point emulation available on
6003 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6004 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6006 @item -mstructure-size-boundary=@var{n}
6007 @opindex mstructure-size-boundary
6008 The size of all structures and unions will be rounded up to a multiple
6009 of the number of bits set by this option. Permissible values are 8 and
6010 32. The default value varies for different toolchains. For the COFF
6011 targeted toolchain the default value is 8. Specifying the larger number
6012 can produce faster, more efficient code, but can also increase the size
6013 of the program. The two values are potentially incompatible. Code
6014 compiled with one value cannot necessarily expect to work with code or
6015 libraries compiled with the other value, if they exchange information
6016 using structures or unions.
6018 @item -mabort-on-noreturn
6019 @opindex mabort-on-noreturn
6020 Generate a call to the function @code{abort} at the end of a
6021 @code{noreturn} function. It will be executed if the function tries to
6025 @itemx -mno-long-calls
6026 @opindex mlong-calls
6027 @opindex mno-long-calls
6028 Tells the compiler to perform function calls by first loading the
6029 address of the function into a register and then performing a subroutine
6030 call on this register. This switch is needed if the target function
6031 will lie outside of the 64 megabyte addressing range of the offset based
6032 version of subroutine call instruction.
6034 Even if this switch is enabled, not all function calls will be turned
6035 into long calls. The heuristic is that static functions, functions
6036 which have the @samp{short-call} attribute, functions that are inside
6037 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6038 definitions have already been compiled within the current compilation
6039 unit, will not be turned into long calls. The exception to this rule is
6040 that weak function definitions, functions with the @samp{long-call}
6041 attribute or the @samp{section} attribute, and functions that are within
6042 the scope of a @samp{#pragma long_calls} directive, will always be
6043 turned into long calls.
6045 This feature is not enabled by default. Specifying
6046 @option{-mno-long-calls} will restore the default behaviour, as will
6047 placing the function calls within the scope of a @samp{#pragma
6048 long_calls_off} directive. Note these switches have no effect on how
6049 the compiler generates code to handle function calls via function
6052 @item -mnop-fun-dllimport
6053 @opindex mnop-fun-dllimport
6054 Disable support for the @code{dllimport} attribute.
6056 @item -msingle-pic-base
6057 @opindex msingle-pic-base
6058 Treat the register used for PIC addressing as read-only, rather than
6059 loading it in the prologue for each function. The run-time system is
6060 responsible for initialising this register with an appropriate value
6061 before execution begins.
6063 @item -mpic-register=@var{reg}
6064 @opindex mpic-register
6065 Specify the register to be used for PIC addressing. The default is R10
6066 unless stack-checking is enabled, when R9 is used.
6068 @item -mpoke-function-name
6069 @opindex mpoke-function-name
6070 Write the name of each function into the text section, directly
6071 preceding the function prologue. The generated code is similar to this:
6075 .ascii "arm_poke_function_name", 0
6078 .word 0xff000000 + (t1 - t0)
6079 arm_poke_function_name
6081 stmfd sp!, @{fp, ip, lr, pc@}
6085 When performing a stack backtrace, code can inspect the value of
6086 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6087 location @code{pc - 12} and the top 8 bits are set, then we know that
6088 there is a function name embedded immediately preceding this location
6089 and has length @code{((pc[-3]) & 0xff000000)}.
6093 Generate code for the 16-bit Thumb instruction set. The default is to
6094 use the 32-bit ARM instruction set.
6097 @opindex mtpcs-frame
6098 Generate a stack frame that is compliant with the Thumb Procedure Call
6099 Standard for all non-leaf functions. (A leaf function is one that does
6100 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6102 @item -mtpcs-leaf-frame
6103 @opindex mtpcs-leaf-frame
6104 Generate a stack frame that is compliant with the Thumb Procedure Call
6105 Standard for all leaf functions. (A leaf function is one that does
6106 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6108 @item -mcallee-super-interworking
6109 @opindex mcallee-super-interworking
6110 Gives all externally visible functions in the file being compiled an ARM
6111 instruction set header which switches to Thumb mode before executing the
6112 rest of the function. This allows these functions to be called from
6113 non-interworking code.
6115 @item -mcaller-super-interworking
6116 @opindex mcaller-super-interworking
6117 Allows calls via function pointers (including virtual functions) to
6118 execute correctly regardless of whether the target code has been
6119 compiled for interworking or not. There is a small overhead in the cost
6120 of executing a function pointer if this option is enabled.
6124 @node MN10200 Options
6125 @subsection MN10200 Options
6126 @cindex MN10200 options
6127 These @option{-m} options are defined for Matsushita MN10200 architectures:
6132 Indicate to the linker that it should perform a relaxation optimization pass
6133 to shorten branches, calls and absolute memory addresses. This option only
6134 has an effect when used on the command line for the final link step.
6136 This option makes symbolic debugging impossible.
6139 @node MN10300 Options
6140 @subsection MN10300 Options
6141 @cindex MN10300 options
6142 These @option{-m} options are defined for Matsushita MN10300 architectures:
6147 Generate code to avoid bugs in the multiply instructions for the MN10300
6148 processors. This is the default.
6151 @opindex mno-mult-bug
6152 Do not generate code to avoid bugs in the multiply instructions for the
6157 Generate code which uses features specific to the AM33 processor.
6161 Do not generate code which uses features specific to the AM33 processor. This
6166 Do not link in the C run-time initialization object file.
6170 Indicate to the linker that it should perform a relaxation optimization pass
6171 to shorten branches, calls and absolute memory addresses. This option only
6172 has an effect when used on the command line for the final link step.
6174 This option makes symbolic debugging impossible.
6178 @node M32R/D Options
6179 @subsection M32R/D Options
6180 @cindex M32R/D options
6182 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6185 @item -mcode-model=small
6186 @opindex mcode-model=small
6187 Assume all objects live in the lower 16MB of memory (so that their addresses
6188 can be loaded with the @code{ld24} instruction), and assume all subroutines
6189 are reachable with the @code{bl} instruction.
6190 This is the default.
6192 The addressability of a particular object can be set with the
6193 @code{model} attribute.
6195 @item -mcode-model=medium
6196 @opindex mcode-model=medium
6197 Assume objects may be anywhere in the 32-bit address space (the compiler
6198 will generate @code{seth/add3} instructions to load their addresses), and
6199 assume all subroutines are reachable with the @code{bl} instruction.
6201 @item -mcode-model=large
6202 @opindex mcode-model=large
6203 Assume objects may be anywhere in the 32-bit address space (the compiler
6204 will generate @code{seth/add3} instructions to load their addresses), and
6205 assume subroutines may not be reachable with the @code{bl} instruction
6206 (the compiler will generate the much slower @code{seth/add3/jl}
6207 instruction sequence).
6210 @opindex msdata=none
6211 Disable use of the small data area. Variables will be put into
6212 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6213 @code{section} attribute has been specified).
6214 This is the default.
6216 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6217 Objects may be explicitly put in the small data area with the
6218 @code{section} attribute using one of these sections.
6221 @opindex msdata=sdata
6222 Put small global and static data in the small data area, but do not
6223 generate special code to reference them.
6227 Put small global and static data in the small data area, and generate
6228 special instructions to reference them.
6232 @cindex smaller data references
6233 Put global and static objects less than or equal to @var{num} bytes
6234 into the small data or bss sections instead of the normal data or bss
6235 sections. The default value of @var{num} is 8.
6236 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6237 for this option to have any effect.
6239 All modules should be compiled with the same @option{-G @var{num}} value.
6240 Compiling with different values of @var{num} may or may not work; if it
6241 doesn't the linker will give an error message---incorrect code will not be
6247 @subsection M88K Options
6248 @cindex M88k options
6250 These @samp{-m} options are defined for Motorola 88k architectures:
6255 Generate code that works well on both the m88100 and the
6260 Generate code that works best for the m88100, but that also
6265 Generate code that works best for the m88110, and may not run
6270 Obsolete option to be removed from the next revision.
6273 @item -midentify-revision
6274 @opindex midentify-revision
6275 @cindex identifying source, compiler (88k)
6276 Include an @code{ident} directive in the assembler output recording the
6277 source file name, compiler name and version, timestamp, and compilation
6280 @item -mno-underscores
6281 @opindex mno-underscores
6282 @cindex underscores, avoiding (88k)
6283 In assembler output, emit symbol names without adding an underscore
6284 character at the beginning of each name. The default is to use an
6285 underscore as prefix on each name.
6287 @item -mocs-debug-info
6288 @itemx -mno-ocs-debug-info
6289 @opindex mocs-debug-info
6290 @opindex mno-ocs-debug-info
6292 @cindex debugging, 88k OCS
6293 Include (or omit) additional debugging information (about registers used
6294 in each stack frame) as specified in the 88open Object Compatibility
6295 Standard, ``OCS''@. This extra information allows debugging of code that
6296 has had the frame pointer eliminated. The default for DG/UX, SVr4, and
6297 Delta 88 SVr3.2 is to include this information; other 88k configurations
6298 omit this information by default.
6300 @item -mocs-frame-position
6301 @opindex mocs-frame-position
6302 @cindex register positions in frame (88k)
6303 When emitting COFF debugging information for automatic variables and
6304 parameters stored on the stack, use the offset from the canonical frame
6305 address, which is the stack pointer (register 31) on entry to the
6306 function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use
6307 @option{-mocs-frame-position}; other 88k configurations have the default
6308 @option{-mno-ocs-frame-position}.
6310 @item -mno-ocs-frame-position
6311 @opindex mno-ocs-frame-position
6312 @cindex register positions in frame (88k)
6313 When emitting COFF debugging information for automatic variables and
6314 parameters stored on the stack, use the offset from the frame pointer
6315 register (register 30). When this option is in effect, the frame
6316 pointer is not eliminated when debugging information is selected by the
6319 @item -moptimize-arg-area
6320 @itemx -mno-optimize-arg-area
6321 @opindex moptimize-arg-area
6322 @opindex mno-optimize-arg-area
6323 @cindex arguments in frame (88k)
6324 Control how function arguments are stored in stack frames.
6325 @option{-moptimize-arg-area} saves space by optimizing them, but this
6326 conflicts with the 88open specifications. The opposite alternative,
6327 @option{-mno-optimize-arg-area}, agrees with 88open standards. By default
6328 GCC does not optimize the argument area.
6330 @item -mshort-data-@var{num}
6331 @opindex mshort-data
6332 @cindex smaller data references (88k)
6333 @cindex r0-relative references (88k)
6334 Generate smaller data references by making them relative to @code{r0},
6335 which allows loading a value using a single instruction (rather than the
6336 usual two). You control which data references are affected by
6337 specifying @var{num} with this option. For example, if you specify
6338 @option{-mshort-data-512}, then the data references affected are those
6339 involving displacements of less than 512 bytes.
6340 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6343 @item -mserialize-volatile
6344 @opindex mserialize-volatile
6345 @itemx -mno-serialize-volatile
6346 @opindex mno-serialize-volatile
6347 @cindex sequential consistency on 88k
6348 Do, or don't, generate code to guarantee sequential consistency
6349 of volatile memory references. By default, consistency is
6352 The order of memory references made by the MC88110 processor does
6353 not always match the order of the instructions requesting those
6354 references. In particular, a load instruction may execute before
6355 a preceding store instruction. Such reordering violates
6356 sequential consistency of volatile memory references, when there
6357 are multiple processors. When consistency must be guaranteed,
6358 GCC generates special instructions, as needed, to force
6359 execution in the proper order.
6361 The MC88100 processor does not reorder memory references and so
6362 always provides sequential consistency. However, by default, GCC
6363 generates the special instructions to guarantee consistency
6364 even when you use @option{-m88100}, so that the code may be run on an
6365 MC88110 processor. If you intend to run your code only on the
6366 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6368 The extra code generated to guarantee consistency may affect the
6369 performance of your application. If you know that you can safely
6370 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6376 @cindex assembler syntax, 88k
6378 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6379 related to System V release 4 (SVr4). This controls the following:
6383 Which variant of the assembler syntax to emit.
6385 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6386 that is used on System V release 4.
6388 @option{-msvr4} makes GCC issue additional declaration directives used in
6392 @option{-msvr4} is the default for the m88k-motorola-sysv4 and
6393 m88k-dg-dgux m88k configurations. @option{-msvr3} is the default for all
6394 other m88k configurations.
6396 @item -mversion-03.00
6397 @opindex mversion-03.00
6398 This option is obsolete, and is ignored.
6399 @c ??? which asm syntax better for GAS? option there too?
6401 @item -mno-check-zero-division
6402 @itemx -mcheck-zero-division
6403 @opindex mno-check-zero-division
6404 @opindex mcheck-zero-division
6405 @cindex zero division on 88k
6406 Do, or don't, generate code to guarantee that integer division by
6407 zero will be detected. By default, detection is guaranteed.
6409 Some models of the MC88100 processor fail to trap upon integer
6410 division by zero under certain conditions. By default, when
6411 compiling code that might be run on such a processor, GCC
6412 generates code that explicitly checks for zero-valued divisors
6413 and traps with exception number 503 when one is detected. Use of
6414 mno-check-zero-division suppresses such checking for code
6415 generated to run on an MC88100 processor.
6417 GCC assumes that the MC88110 processor correctly detects all
6418 instances of integer division by zero. When @option{-m88110} is
6419 specified, both @option{-mcheck-zero-division} and
6420 @option{-mno-check-zero-division} are ignored, and no explicit checks for
6421 zero-valued divisors are generated.
6423 @item -muse-div-instruction
6424 @opindex muse-div-instruction
6425 @cindex divide instruction, 88k
6426 Use the div instruction for signed integer division on the
6427 MC88100 processor. By default, the div instruction is not used.
6429 On the MC88100 processor the signed integer division instruction
6430 div) traps to the operating system on a negative operand. The
6431 operating system transparently completes the operation, but at a
6432 large cost in execution time. By default, when compiling code
6433 that might be run on an MC88100 processor, GCC emulates signed
6434 integer division using the unsigned integer division instruction
6435 divu), thereby avoiding the large penalty of a trap to the
6436 operating system. Such emulation has its own, smaller, execution
6437 cost in both time and space. To the extent that your code's
6438 important signed integer division operations are performed on two
6439 nonnegative operands, it may be desirable to use the div
6440 instruction directly.
6442 On the MC88110 processor the div instruction (also known as the
6443 divs instruction) processes negative operands without trapping to
6444 the operating system. When @option{-m88110} is specified,
6445 @option{-muse-div-instruction} is ignored, and the div instruction is used
6446 for signed integer division.
6448 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6449 particular, the behavior of such a division with and without
6450 @option{-muse-div-instruction} may differ.
6452 @item -mtrap-large-shift
6453 @itemx -mhandle-large-shift
6454 @opindex mtrap-large-shift
6455 @opindex mhandle-large-shift
6456 @cindex bit shift overflow (88k)
6457 @cindex large bit shifts (88k)
6458 Include code to detect bit-shifts of more than 31 bits; respectively,
6459 trap such shifts or emit code to handle them properly. By default GCC
6460 makes no special provision for large bit shifts.
6462 @item -mwarn-passed-structs
6463 @opindex mwarn-passed-structs
6464 @cindex structure passing (88k)
6465 Warn when a function passes a struct as an argument or result.
6466 Structure-passing conventions have changed during the evolution of the C
6467 language, and are often the source of portability problems. By default,
6468 GCC issues no such warning.
6471 @node RS/6000 and PowerPC Options
6472 @subsection IBM RS/6000 and PowerPC Options
6473 @cindex RS/6000 and PowerPC Options
6474 @cindex IBM RS/6000 and PowerPC Options
6476 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6484 @itemx -mpowerpc-gpopt
6485 @itemx -mno-powerpc-gpopt
6486 @itemx -mpowerpc-gfxopt
6487 @itemx -mno-powerpc-gfxopt
6489 @itemx -mno-powerpc64
6495 @opindex mno-powerpc
6496 @opindex mpowerpc-gpopt
6497 @opindex mno-powerpc-gpopt
6498 @opindex mpowerpc-gfxopt
6499 @opindex mno-powerpc-gfxopt
6501 @opindex mno-powerpc64
6502 GCC supports two related instruction set architectures for the
6503 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6504 instructions supported by the @samp{rios} chip set used in the original
6505 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6506 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6507 the IBM 4xx microprocessors.
6509 Neither architecture is a subset of the other. However there is a
6510 large common subset of instructions supported by both. An MQ
6511 register is included in processors supporting the POWER architecture.
6513 You use these options to specify which instructions are available on the
6514 processor you are using. The default value of these options is
6515 determined when configuring GCC@. Specifying the
6516 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6517 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6518 rather than the options listed above.
6520 The @option{-mpower} option allows GCC to generate instructions that
6521 are found only in the POWER architecture and to use the MQ register.
6522 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6523 to generate instructions that are present in the POWER2 architecture but
6524 not the original POWER architecture.
6526 The @option{-mpowerpc} option allows GCC to generate instructions that
6527 are found only in the 32-bit subset of the PowerPC architecture.
6528 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6529 GCC to use the optional PowerPC architecture instructions in the
6530 General Purpose group, including floating-point square root. Specifying
6531 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6532 use the optional PowerPC architecture instructions in the Graphics
6533 group, including floating-point select.
6535 The @option{-mpowerpc64} option allows GCC to generate the additional
6536 64-bit instructions that are found in the full PowerPC64 architecture
6537 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6538 @option{-mno-powerpc64}.
6540 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6541 will use only the instructions in the common subset of both
6542 architectures plus some special AIX common-mode calls, and will not use
6543 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6544 permits GCC to use any instruction from either architecture and to
6545 allow use of the MQ register; specify this for the Motorola MPC601.
6547 @item -mnew-mnemonics
6548 @itemx -mold-mnemonics
6549 @opindex mnew-mnemonics
6550 @opindex mold-mnemonics
6551 Select which mnemonics to use in the generated assembler code.
6552 @option{-mnew-mnemonics} requests output that uses the assembler mnemonics
6553 defined for the PowerPC architecture, while @option{-mold-mnemonics}
6554 requests the assembler mnemonics defined for the POWER architecture.
6555 Instructions defined in only one architecture have only one mnemonic;
6556 GCC uses that mnemonic irrespective of which of these options is
6559 GCC defaults to the mnemonics appropriate for the architecture in
6560 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6561 value of these option. Unless you are building a cross-compiler, you
6562 should normally not specify either @option{-mnew-mnemonics} or
6563 @option{-mold-mnemonics}, but should instead accept the default.
6565 @item -mcpu=@var{cpu_type}
6567 Set architecture type, register usage, choice of mnemonics, and
6568 instruction scheduling parameters for machine type @var{cpu_type}.
6569 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6570 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6571 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6572 @samp{630}, @samp{740}, @samp{750}, @samp{power}, @samp{power2},
6573 @samp{powerpc}, @samp{403}, @samp{505}, @samp{801}, @samp{821},
6574 @samp{823}, and @samp{860} and @samp{common}. @option{-mcpu=power},
6575 @option{-mcpu=power2}, @option{-mcpu=powerpc}, and @option{-mcpu=powerpc64}
6576 specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not MPC601),
6577 and 64-bit PowerPC architecture machine types, with an appropriate,
6578 generic processor model assumed for scheduling purposes.
6580 Specifying any of the following options:
6581 @option{-mcpu=rios1}, @option{-mcpu=rios2}, @option{-mcpu=rsc},
6582 @option{-mcpu=power}, or @option{-mcpu=power2}
6583 enables the @option{-mpower} option and disables the @option{-mpowerpc} option;
6584 @option{-mcpu=601} enables both the @option{-mpower} and @option{-mpowerpc} options.
6585 All of @option{-mcpu=rs64a}, @option{-mcpu=602}, @option{-mcpu=603},
6586 @option{-mcpu=603e}, @option{-mcpu=604}, @option{-mcpu=620}, @option{-mcpu=630},
6587 @option{-mcpu=740}, and @option{-mcpu=750}
6588 enable the @option{-mpowerpc} option and disable the @option{-mpower} option.
6589 Exactly similarly, all of @option{-mcpu=403},
6590 @option{-mcpu=505}, @option{-mcpu=821}, @option{-mcpu=860} and @option{-mcpu=powerpc}
6591 enable the @option{-mpowerpc} option and disable the @option{-mpower} option.
6592 @option{-mcpu=common} disables both the
6593 @option{-mpower} and @option{-mpowerpc} options.
6595 AIX versions 4 or greater selects @option{-mcpu=common} by default, so
6596 that code will operate on all members of the RS/6000 POWER and PowerPC
6597 families. In that case, GCC will use only the instructions in the
6598 common subset of both architectures plus some special AIX common-mode
6599 calls, and will not use the MQ register. GCC assumes a generic
6600 processor model for scheduling purposes.
6602 Specifying any of the options @option{-mcpu=rios1}, @option{-mcpu=rios2},
6603 @option{-mcpu=rsc}, @option{-mcpu=power}, or @option{-mcpu=power2} also
6604 disables the @samp{new-mnemonics} option. Specifying @option{-mcpu=601},
6605 @option{-mcpu=602}, @option{-mcpu=603}, @option{-mcpu=603e}, @option{-mcpu=604},
6606 @option{-mcpu=620}, @option{-mcpu=630}, @option{-mcpu=403}, @option{-mcpu=505},
6607 @option{-mcpu=821}, @option{-mcpu=860} or @option{-mcpu=powerpc} also enables
6608 the @samp{new-mnemonics} option.
6610 Specifying @option{-mcpu=403}, @option{-mcpu=821}, or @option{-mcpu=860} also
6611 enables the @option{-msoft-float} option.
6613 @item -mtune=@var{cpu_type}
6615 Set the instruction scheduling parameters for machine type
6616 @var{cpu_type}, but do not set the architecture type, register usage,
6617 choice of mnemonics like @option{-mcpu=@var{cpu_type}} would. The same
6618 values for @var{cpu_type} are used for @option{-mtune=@var{cpu_type}} as
6619 for @option{-mcpu=@var{cpu_type}}. The @option{-mtune=@var{cpu_type}}
6620 option overrides the @option{-mcpu=@var{cpu_type}} option in terms of
6621 instruction scheduling parameters.
6624 @itemx -mno-fp-in-toc
6625 @itemx -mno-sum-in-toc
6626 @itemx -mminimal-toc
6628 @opindex mno-fp-in-toc
6629 @opindex mno-sum-in-toc
6630 @opindex mminimal-toc
6631 Modify generation of the TOC (Table Of Contents), which is created for
6632 every executable file. The @option{-mfull-toc} option is selected by
6633 default. In that case, GCC will allocate at least one TOC entry for
6634 each unique non-automatic variable reference in your program. GCC
6635 will also place floating-point constants in the TOC@. However, only
6636 16,384 entries are available in the TOC@.
6638 If you receive a linker error message that saying you have overflowed
6639 the available TOC space, you can reduce the amount of TOC space used
6640 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
6641 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
6642 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
6643 generate code to calculate the sum of an address and a constant at
6644 run-time instead of putting that sum into the TOC@. You may specify one
6645 or both of these options. Each causes GCC to produce very slightly
6646 slower and larger code at the expense of conserving TOC space.
6648 If you still run out of space in the TOC even when you specify both of
6649 these options, specify @option{-mminimal-toc} instead. This option causes
6650 GCC to make only one TOC entry for every file. When you specify this
6651 option, GCC will produce code that is slower and larger but which
6652 uses extremely little TOC space. You may wish to use this option
6653 only on files that contain less frequently executed code.
6659 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
6660 @code{long} type, and the infrastructure needed to support them.
6661 Specifying @option{-maix64} implies @option{-mpowerpc64} and
6662 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
6663 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
6668 @opindex mno-xl-call
6669 On AIX, pass floating-point arguments to prototyped functions beyond the
6670 register save area (RSA) on the stack in addition to argument FPRs. The
6671 AIX calling convention was extended but not initially documented to
6672 handle an obscure K&R C case of calling a function that takes the
6673 address of its arguments with fewer arguments than declared. AIX XL
6674 compilers access floating point arguments which do not fit in the
6675 RSA from the stack when a subroutine is compiled without
6676 optimization. Because always storing floating-point arguments on the
6677 stack is inefficient and rarely needed, this option is not enabled by
6678 default and only is necessary when calling subroutines compiled by AIX
6679 XL compilers without optimization.
6683 Support @dfn{AIX Threads}. Link an application written to use
6684 @dfn{pthreads} with special libraries and startup code to enable the
6689 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
6690 application written to use message passing with special startup code to
6691 enable the application to run. The system must have PE installed in the
6692 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
6693 must be overridden with the @option{-specs=} option to specify the
6694 appropriate directory location. The Parallel Environment does not
6695 support threads, so the @option{-mpe} option and the @option{-mthreads}
6696 option are incompatible.
6700 @opindex msoft-float
6701 @opindex mhard-float
6702 Generate code that does not use (uses) the floating-point register set.
6703 Software floating point emulation is provided if you use the
6704 @option{-msoft-float} option, and pass the option to GCC when linking.
6707 @itemx -mno-multiple
6709 @opindex mno-multiple
6710 Generate code that uses (does not use) the load multiple word
6711 instructions and the store multiple word instructions. These
6712 instructions are generated by default on POWER systems, and not
6713 generated on PowerPC systems. Do not use @option{-mmultiple} on little
6714 endian PowerPC systems, since those instructions do not work when the
6715 processor is in little endian mode. The exceptions are PPC740 and
6716 PPC750 which permit the instructions usage in little endian mode.
6722 Generate code that uses (does not use) the load string instructions
6723 and the store string word instructions to save multiple registers and
6724 do small block moves. These instructions are generated by default on
6725 POWER systems, and not generated on PowerPC systems. Do not use
6726 @option{-mstring} on little endian PowerPC systems, since those
6727 instructions do not work when the processor is in little endian mode.
6728 The exceptions are PPC740 and PPC750 which permit the instructions
6729 usage in little endian mode.
6735 Generate code that uses (does not use) the load or store instructions
6736 that update the base register to the address of the calculated memory
6737 location. These instructions are generated by default. If you use
6738 @option{-mno-update}, there is a small window between the time that the
6739 stack pointer is updated and the address of the previous frame is
6740 stored, which means code that walks the stack frame across interrupts or
6741 signals may get corrupted data.
6744 @itemx -mno-fused-madd
6745 @opindex mfused-madd
6746 @opindex mno-fused-madd
6747 Generate code that uses (does not use) the floating point multiply and
6748 accumulate instructions. These instructions are generated by default if
6749 hardware floating is used.
6751 @item -mno-bit-align
6753 @opindex mno-bit-align
6755 On System V.4 and embedded PowerPC systems do not (do) force structures
6756 and unions that contain bit-fields to be aligned to the base type of the
6759 For example, by default a structure containing nothing but 8
6760 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
6761 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
6762 the structure would be aligned to a 1 byte boundary and be one byte in
6765 @item -mno-strict-align
6766 @itemx -mstrict-align
6767 @opindex mno-strict-align
6768 @opindex mstrict-align
6769 On System V.4 and embedded PowerPC systems do not (do) assume that
6770 unaligned memory references will be handled by the system.
6773 @itemx -mno-relocatable
6774 @opindex mrelocatable
6775 @opindex mno-relocatable
6776 On embedded PowerPC systems generate code that allows (does not allow)
6777 the program to be relocated to a different address at runtime. If you
6778 use @option{-mrelocatable} on any module, all objects linked together must
6779 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
6781 @item -mrelocatable-lib
6782 @itemx -mno-relocatable-lib
6783 @opindex mrelocatable-lib
6784 @opindex mno-relocatable-lib
6785 On embedded PowerPC systems generate code that allows (does not allow)
6786 the program to be relocated to a different address at runtime. Modules
6787 compiled with @option{-mrelocatable-lib} can be linked with either modules
6788 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
6789 with modules compiled with the @option{-mrelocatable} options.
6795 On System V.4 and embedded PowerPC systems do not (do) assume that
6796 register 2 contains a pointer to a global area pointing to the addresses
6797 used in the program.
6800 @itemx -mlittle-endian
6802 @opindex mlittle-endian
6803 On System V.4 and embedded PowerPC systems compile code for the
6804 processor in little endian mode. The @option{-mlittle-endian} option is
6805 the same as @option{-mlittle}.
6810 @opindex mbig-endian
6811 On System V.4 and embedded PowerPC systems compile code for the
6812 processor in big endian mode. The @option{-mbig-endian} option is
6813 the same as @option{-mbig}.
6817 On System V.4 and embedded PowerPC systems compile code using calling
6818 conventions that adheres to the March 1995 draft of the System V
6819 Application Binary Interface, PowerPC processor supplement. This is the
6820 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
6822 @item -mcall-sysv-eabi
6823 @opindex mcall-sysv-eabi
6824 Specify both @option{-mcall-sysv} and @option{-meabi} options.
6826 @item -mcall-sysv-noeabi
6827 @opindex mcall-sysv-noeabi
6828 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
6832 On System V.4 and embedded PowerPC systems compile code using calling
6833 conventions that are similar to those used on AIX@. This is the
6834 default if you configured GCC using @samp{powerpc-*-eabiaix}.
6836 @item -mcall-solaris
6837 @opindex mcall-solaris
6838 On System V.4 and embedded PowerPC systems compile code for the Solaris
6842 @opindex mcall-linux
6843 On System V.4 and embedded PowerPC systems compile code for the
6844 Linux-based GNU system.
6847 @itemx -mno-prototype
6849 @opindex mno-prototype
6850 On System V.4 and embedded PowerPC systems assume that all calls to
6851 variable argument functions are properly prototyped. Otherwise, the
6852 compiler must insert an instruction before every non prototyped call to
6853 set or clear bit 6 of the condition code register (@var{CR}) to
6854 indicate whether floating point values were passed in the floating point
6855 registers in case the function takes a variable arguments. With
6856 @option{-mprototype}, only calls to prototyped variable argument functions
6857 will set or clear the bit.
6861 On embedded PowerPC systems, assume that the startup module is called
6862 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
6863 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
6868 On embedded PowerPC systems, assume that the startup module is called
6869 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
6874 On embedded PowerPC systems, assume that the startup module is called
6875 @file{crt0.o} and the standard C libraries are @file{libads.a} and
6879 @opindex myellowknife
6880 On embedded PowerPC systems, assume that the startup module is called
6881 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
6886 On System V.4 and embedded PowerPC systems, specify that you are
6887 compiling for a VxWorks system.
6891 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
6892 header to indicate that @samp{eabi} extended relocations are used.
6898 On System V.4 and embedded PowerPC systems do (do not) adhere to the
6899 Embedded Applications Binary Interface (eabi) which is a set of
6900 modifications to the System V.4 specifications. Selecting @option{-meabi}
6901 means that the stack is aligned to an 8 byte boundary, a function
6902 @code{__eabi} is called to from @code{main} to set up the eabi
6903 environment, and the @option{-msdata} option can use both @code{r2} and
6904 @code{r13} to point to two separate small data areas. Selecting
6905 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
6906 do not call an initialization function from @code{main}, and the
6907 @option{-msdata} option will only use @code{r13} to point to a single
6908 small data area. The @option{-meabi} option is on by default if you
6909 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
6912 @opindex msdata=eabi
6913 On System V.4 and embedded PowerPC systems, put small initialized
6914 @code{const} global and static data in the @samp{.sdata2} section, which
6915 is pointed to by register @code{r2}. Put small initialized
6916 non-@code{const} global and static data in the @samp{.sdata} section,
6917 which is pointed to by register @code{r13}. Put small uninitialized
6918 global and static data in the @samp{.sbss} section, which is adjacent to
6919 the @samp{.sdata} section. The @option{-msdata=eabi} option is
6920 incompatible with the @option{-mrelocatable} option. The
6921 @option{-msdata=eabi} option also sets the @option{-memb} option.
6924 @opindex msdata=sysv
6925 On System V.4 and embedded PowerPC systems, put small global and static
6926 data in the @samp{.sdata} section, which is pointed to by register
6927 @code{r13}. Put small uninitialized global and static data in the
6928 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
6929 The @option{-msdata=sysv} option is incompatible with the
6930 @option{-mrelocatable} option.
6932 @item -msdata=default
6934 @opindex msdata=default
6936 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
6937 compile code the same as @option{-msdata=eabi}, otherwise compile code the
6938 same as @option{-msdata=sysv}.
6941 @opindex msdata-data
6942 On System V.4 and embedded PowerPC systems, put small global and static
6943 data in the @samp{.sdata} section. Put small uninitialized global and
6944 static data in the @samp{.sbss} section. Do not use register @code{r13}
6945 to address small data however. This is the default behavior unless
6946 other @option{-msdata} options are used.
6950 @opindex msdata=none
6952 On embedded PowerPC systems, put all initialized global and static data
6953 in the @samp{.data} section, and all uninitialized data in the
6954 @samp{.bss} section.
6958 @cindex smaller data references (PowerPC)
6959 @cindex .sdata/.sdata2 references (PowerPC)
6960 On embedded PowerPC systems, put global and static items less than or
6961 equal to @var{num} bytes into the small data or bss sections instead of
6962 the normal data or bss section. By default, @var{num} is 8. The
6963 @option{-G @var{num}} switch is also passed to the linker.
6964 All modules should be compiled with the same @option{-G @var{num}} value.
6967 @itemx -mno-regnames
6969 @opindex mno-regnames
6970 On System V.4 and embedded PowerPC systems do (do not) emit register
6971 names in the assembly language output using symbolic forms.
6976 @subsection IBM RT Options
6978 @cindex IBM RT options
6980 These @samp{-m} options are defined for the IBM RT PC:
6984 @opindex min-line-mul
6985 Use an in-line code sequence for integer multiplies. This is the
6988 @item -mcall-lib-mul
6989 @opindex mcall-lib-mul
6990 Call @code{lmul$$} for integer multiples.
6992 @item -mfull-fp-blocks
6993 @opindex mfull-fp-blocks
6994 Generate full-size floating point data blocks, including the minimum
6995 amount of scratch space recommended by IBM@. This is the default.
6997 @item -mminimum-fp-blocks
6998 @opindex mminimum-fp-blocks
6999 Do not include extra scratch space in floating point data blocks. This
7000 results in smaller code, but slower execution, since scratch space must
7001 be allocated dynamically.
7003 @cindex @file{varargs.h} and RT PC
7004 @cindex @file{stdarg.h} and RT PC
7005 @item -mfp-arg-in-fpregs
7006 @opindex mfp-arg-in-fpregs
7007 Use a calling sequence incompatible with the IBM calling convention in
7008 which floating point arguments are passed in floating point registers.
7009 Note that @code{varargs.h} and @code{stdarg.h} will not work with
7010 floating point operands if this option is specified.
7012 @item -mfp-arg-in-gregs
7013 @opindex mfp-arg-in-gregs
7014 Use the normal calling convention for floating point arguments. This is
7017 @item -mhc-struct-return
7018 @opindex mhc-struct-return
7019 Return structures of more than one word in memory, rather than in a
7020 register. This provides compatibility with the MetaWare HighC (hc)
7021 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7022 with the Portable C Compiler (pcc).
7024 @item -mnohc-struct-return
7025 @opindex mnohc-struct-return
7026 Return some structures of more than one word in registers, when
7027 convenient. This is the default. For compatibility with the
7028 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7029 option @option{-mhc-struct-return}.
7033 @subsection MIPS Options
7034 @cindex MIPS options
7036 These @samp{-m} options are defined for the MIPS family of computers:
7040 @item -march=@var{cpu-type}
7042 Assume the defaults for the machine type @var{cpu-type} when generating
7043 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7044 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7045 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7046 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7047 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7048 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc.
7050 @item -mtune=@var{cpu-type}
7052 Assume the defaults for the machine type @var{cpu-type} when scheduling
7053 instructions. The choices for @var{cpu-type} are @samp{r2000}, @samp{r3000},
7054 @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400},
7055 @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000},
7056 and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000},
7057 @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as
7058 @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific
7059 @var{cpu-type} will schedule things appropriately for that particular
7060 chip, the compiler will not generate any code that does not meet level 1
7061 of the MIPS ISA (instruction set architecture) without a @option{-mipsX}
7062 or @option{-mabi} switch being used.
7064 @item -mcpu=@var{cpu-type}
7066 This is identical to specifying both @option{-march} and @option{-mtune}.
7070 Issue instructions from level 1 of the MIPS ISA@. This is the default.
7071 @samp{r3000} is the default @var{cpu-type} at this ISA level.
7075 Issue instructions from level 2 of the MIPS ISA (branch likely, square
7076 root instructions). @samp{r6000} is the default @var{cpu-type} at this
7081 Issue instructions from level 3 of the MIPS ISA (64-bit instructions).
7082 @samp{r4000} is the default @var{cpu-type} at this ISA level.
7086 Issue instructions from level 4 of the MIPS ISA (conditional move,
7087 prefetch, enhanced FPU instructions). @samp{r8000} is the default
7088 @var{cpu-type} at this ISA level.
7092 Assume that 32 32-bit floating point registers are available. This is
7097 Assume that 32 64-bit floating point registers are available. This is
7098 the default when the @option{-mips3} option is used.
7102 Assume that 32 32-bit general purpose registers are available. This is
7107 Assume that 32 64-bit general purpose registers are available. This is
7108 the default when the @option{-mips3} option is used.
7112 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7113 explanation of the default, and the width of pointers.
7117 Force long types to be 64 bits wide. See @option{-mlong32} for an
7118 explanation of the default, and the width of pointers.
7122 Force long, int, and pointer types to be 32 bits wide.
7124 If none of @option{-mlong32}, @option{-mlong64}, or @option{-mint64} are set,
7125 the size of ints, longs, and pointers depends on the ABI and ISA chosen.
7126 For @option{-mabi=32}, and @option{-mabi=n32}, ints and longs are 32 bits
7127 wide. For @option{-mabi=64}, ints are 32 bits, and longs are 64 bits wide.
7128 For @option{-mabi=eabi} and either @option{-mips1} or @option{-mips2}, ints
7129 and longs are 32 bits wide. For @option{-mabi=eabi} and higher ISAs, ints
7130 are 32 bits, and longs are 64 bits wide. The width of pointer types is
7131 the smaller of the width of longs or the width of general purpose
7132 registers (which in turn depends on the ISA)@.
7144 Generate code for the indicated ABI@. The default instruction level is
7145 @option{-mips1} for @samp{32}, @option{-mips3} for @samp{n32}, and
7146 @option{-mips4} otherwise. Conversely, with @option{-mips1} or
7147 @option{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI
7152 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7153 add normal debug information. This is the default for all
7154 platforms except for the OSF/1 reference platform, using the OSF/rose
7155 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7156 switches are used, the @file{mips-tfile} program will encapsulate the
7157 stabs within MIPS ECOFF@.
7161 Generate code for the GNU assembler. This is the default on the OSF/1
7162 reference platform, using the OSF/rose object format. Also, this is
7163 the default if the configure option @option{--with-gnu-as} is used.
7165 @item -msplit-addresses
7166 @itemx -mno-split-addresses
7167 @opindex msplit-addresses
7168 @opindex mno-split-addresses
7169 Generate code to load the high and low parts of address constants separately.
7170 This allows GCC to optimize away redundant loads of the high order
7171 bits of addresses. This optimization requires GNU as and GNU ld.
7172 This optimization is enabled by default for some embedded targets where
7173 GNU as and GNU ld are standard.
7179 The @option{-mrnames} switch says to output code using the MIPS software
7180 names for the registers, instead of the hardware names (ie, @var{a0}
7181 instead of @var{$4}). The only known assembler that supports this option
7182 is the Algorithmics assembler.
7188 The @option{-mgpopt} switch says to write all of the data declarations
7189 before the instructions in the text section, this allows the MIPS
7190 assembler to generate one word memory references instead of using two
7191 words for short global or static data items. This is on by default if
7192 optimization is selected.
7198 For each non-inline function processed, the @option{-mstats} switch
7199 causes the compiler to emit one line to the standard error file to
7200 print statistics about the program (number of registers saved, stack
7207 The @option{-mmemcpy} switch makes all block moves call the appropriate
7208 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7209 generating inline code.
7212 @itemx -mno-mips-tfile
7213 @opindex mmips-tfile
7214 @opindex mno-mips-tfile
7215 The @option{-mno-mips-tfile} switch causes the compiler not
7216 postprocess the object file with the @file{mips-tfile} program,
7217 after the MIPS assembler has generated it to add debug support. If
7218 @file{mips-tfile} is not run, then no local variables will be
7219 available to the debugger. In addition, @file{stage2} and
7220 @file{stage3} objects will have the temporary file names passed to the
7221 assembler embedded in the object file, which means the objects will
7222 not compare the same. The @option{-mno-mips-tfile} switch should only
7223 be used when there are bugs in the @file{mips-tfile} program that
7224 prevents compilation.
7227 @opindex msoft-float
7228 Generate output containing library calls for floating point.
7229 @strong{Warning:} the requisite libraries are not part of GCC@.
7230 Normally the facilities of the machine's usual C compiler are used, but
7231 this can't be done directly in cross-compilation. You must make your
7232 own arrangements to provide suitable library functions for
7236 @opindex mhard-float
7237 Generate output containing floating point instructions. This is the
7238 default if you use the unmodified sources.
7241 @itemx -mno-abicalls
7243 @opindex mno-abicalls
7244 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7245 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7246 position independent code.
7249 @itemx -mno-long-calls
7250 @opindex mlong-calls
7251 @opindex mno-long-calls
7252 Do all calls with the @samp{JALR} instruction, which requires
7253 loading up a function's address into a register before the call.
7254 You need to use this switch, if you call outside of the current
7255 512 megabyte segment to functions that are not through pointers.
7258 @itemx -mno-half-pic
7260 @opindex mno-half-pic
7261 Put pointers to extern references into the data section and load them
7262 up, rather than put the references in the text section.
7264 @item -membedded-pic
7265 @itemx -mno-embedded-pic
7266 @opindex membedded-pic
7267 @opindex mno-embedded-pic
7268 Generate PIC code suitable for some embedded systems. All calls are
7269 made using PC relative address, and all data is addressed using the $gp
7270 register. No more than 65536 bytes of global data may be used. This
7271 requires GNU as and GNU ld which do most of the work. This currently
7272 only works on targets which use ECOFF; it does not work with ELF@.
7274 @item -membedded-data
7275 @itemx -mno-embedded-data
7276 @opindex membedded-data
7277 @opindex mno-embedded-data
7278 Allocate variables to the read-only data section first if possible, then
7279 next in the small data section if possible, otherwise in data. This gives
7280 slightly slower code than the default, but reduces the amount of RAM required
7281 when executing, and thus may be preferred for some embedded systems.
7283 @item -muninit-const-in-rodata
7284 @itemx -mno-uninit-const-in-rodata
7285 @opindex muninit-const-in-rodata
7286 @opindex mno-uninit-const-in-rodata
7287 When used together with @option{-membedded-data}, it will always store uninitialized
7288 const variables in the read-only data section.
7290 @item -msingle-float
7291 @itemx -mdouble-float
7292 @opindex msingle-float
7293 @opindex mdouble-float
7294 The @option{-msingle-float} switch tells gcc to assume that the floating
7295 point coprocessor only supports single precision operations, as on the
7296 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
7297 double precision operations. This is the default.
7303 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
7304 as on the @samp{r4650} chip.
7308 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
7309 @option{-mcpu=r4650}.
7315 Enable 16-bit instructions.
7319 Use the entry and exit pseudo ops. This option can only be used with
7324 Compile code for the processor in little endian mode.
7325 The requisite libraries are assumed to exist.
7329 Compile code for the processor in big endian mode.
7330 The requisite libraries are assumed to exist.
7334 @cindex smaller data references (MIPS)
7335 @cindex gp-relative references (MIPS)
7336 Put global and static items less than or equal to @var{num} bytes into
7337 the small data or bss sections instead of the normal data or bss
7338 section. This allows the assembler to emit one word memory reference
7339 instructions based on the global pointer (@var{gp} or @var{$28}),
7340 instead of the normal two words used. By default, @var{num} is 8 when
7341 the MIPS assembler is used, and 0 when the GNU assembler is used. The
7342 @option{-G @var{num}} switch is also passed to the assembler and linker.
7343 All modules should be compiled with the same @option{-G @var{num}}
7348 Tell the MIPS assembler to not run its preprocessor over user
7349 assembler files (with a @samp{.s} suffix) when assembling them.
7353 Pass an option to gas which will cause nops to be inserted if
7354 the read of the destination register of an mfhi or mflo instruction
7355 occurs in the following two instructions.
7359 Do not include the default crt0.
7363 These options are defined by the macro
7364 @code{TARGET_SWITCHES} in the machine description. The default for the
7365 options is also defined by that macro, which enables you to change the
7370 @subsection Intel 386 Options
7371 @cindex i386 Options
7372 @cindex Intel 386 Options
7374 These @samp{-m} options are defined for the i386 family of computers:
7377 @item -mcpu=@var{cpu-type}
7379 Assume the defaults for the machine type @var{cpu-type} when scheduling
7380 instructions. The choices for @var{cpu-type} are @samp{i386},
7381 @samp{i486}, @samp{i586}, @samp{i686}, @samp{pentium},
7382 @samp{pentiumpro}, @samp{pentium4}, @samp{k6}, and @samp{athlon}
7384 While picking a specific @var{cpu-type} will schedule things appropriately
7385 for that particular chip, the compiler will not generate any code that
7386 does not run on the i386 without the @option{-march=@var{cpu-type}} option
7387 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
7388 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
7389 AMD chips as opposed to the Intel ones.
7391 @item -march=@var{cpu-type}
7393 Generate instructions for the machine type @var{cpu-type}. The choices
7394 for @var{cpu-type} are the same as for @option{-mcpu}. Moreover,
7395 specifying @option{-march=@var{cpu-type}} implies @option{-mcpu=@var{cpu-type}}.
7404 @opindex mpentiumpro
7405 Synonyms for @option{-mcpu=i386}, @option{-mcpu=i486}, @option{-mcpu=pentium}, and @option{-mcpu=pentiumpro}
7406 respectively. These synonyms are deprecated.
7408 @item -mintel-syntax
7409 @opindex mintel-syntax
7410 Emit assembly using Intel syntax opcodes instead of AT&T syntax.
7415 @opindex mno-ieee-fp
7416 Control whether or not the compiler uses IEEE floating point
7417 comparisons. These handle correctly the case where the result of a
7418 comparison is unordered.
7421 @opindex msoft-float
7422 Generate output containing library calls for floating point.
7423 @strong{Warning:} the requisite libraries are not part of GCC@.
7424 Normally the facilities of the machine's usual C compiler are used, but
7425 this can't be done directly in cross-compilation. You must make your
7426 own arrangements to provide suitable library functions for
7429 On machines where a function returns floating point results in the 80387
7430 register stack, some floating point opcodes may be emitted even if
7431 @option{-msoft-float} is used.
7433 @item -mno-fp-ret-in-387
7434 @opindex mno-fp-ret-in-387
7435 Do not use the FPU registers for return values of functions.
7437 The usual calling convention has functions return values of types
7438 @code{float} and @code{double} in an FPU register, even if there
7439 is no FPU@. The idea is that the operating system should emulate
7442 The option @option{-mno-fp-ret-in-387} causes such values to be returned
7443 in ordinary CPU registers instead.
7445 @item -mno-fancy-math-387
7446 @opindex mno-fancy-math-387
7447 Some 387 emulators do not support the @code{sin}, @code{cos} and
7448 @code{sqrt} instructions for the 387. Specify this option to avoid
7449 generating those instructions. This option is the default on FreeBSD@.
7450 As of revision 2.6.1, these instructions are not generated unless you
7451 also use the @option{-funsafe-math-optimizations} switch.
7453 @item -malign-double
7454 @itemx -mno-align-double
7455 @opindex malign-double
7456 @opindex mno-align-double
7457 Control whether GCC aligns @code{double}, @code{long double}, and
7458 @code{long long} variables on a two word boundary or a one word
7459 boundary. Aligning @code{double} variables on a two word boundary will
7460 produce code that runs somewhat faster on a @samp{Pentium} at the
7461 expense of more memory.
7463 @item -m128bit-long-double
7464 @itemx -m128bit-long-double
7465 @opindex m128bit-long-double
7466 @opindex m128bit-long-double
7467 Control the size of @code{long double} type. i386 application binary interface
7468 specify the size to be 12 bytes, while modern architectures (Pentium and newer)
7469 prefer @code{long double} aligned to 8 or 16 byte boundary. This is
7470 impossible to reach with 12 byte long doubles in the array accesses.
7472 @strong{Warning:} if you use the @option{-m128bit-long-double} switch, the
7473 structures and arrays containing @code{long double} will change their size as
7474 well as function calling convention for function taking @code{long double}
7477 @item -m96bit-long-double
7478 @itemx -m96bit-long-double
7479 @opindex m96bit-long-double
7480 @opindex m96bit-long-double
7481 Set the size of @code{long double} to 96 bits as required by the i386
7482 application binary interface. This is the default.
7485 @itemx -mno-svr3-shlib
7486 @opindex msvr3-shlib
7487 @opindex mno-svr3-shlib
7488 Control whether GCC places uninitialized locals into @code{bss} or
7489 @code{data}. @option{-msvr3-shlib} places these locals into @code{bss}.
7490 These options are meaningful only on System V Release 3.
7492 @item -mno-wide-multiply
7493 @itemx -mwide-multiply
7494 @opindex mno-wide-multiply
7495 @opindex mwide-multiply
7496 Control whether GCC uses the @code{mul} and @code{imul} that produce
7497 64-bit results in @code{eax:edx} from 32-bit operands to do @code{long
7498 long} multiplies and 32-bit division by constants.
7502 Use a different function-calling convention, in which functions that
7503 take a fixed number of arguments return with the @code{ret} @var{num}
7504 instruction, which pops their arguments while returning. This saves one
7505 instruction in the caller since there is no need to pop the arguments
7508 You can specify that an individual function is called with this calling
7509 sequence with the function attribute @samp{stdcall}. You can also
7510 override the @option{-mrtd} option by using the function attribute
7511 @samp{cdecl}. @xref{Function Attributes}.
7513 @strong{Warning:} this calling convention is incompatible with the one
7514 normally used on Unix, so you cannot use it if you need to call
7515 libraries compiled with the Unix compiler.
7517 Also, you must provide function prototypes for all functions that
7518 take variable numbers of arguments (including @code{printf});
7519 otherwise incorrect code will be generated for calls to those
7522 In addition, seriously incorrect code will result if you call a
7523 function with too many arguments. (Normally, extra arguments are
7524 harmlessly ignored.)
7526 @item -mregparm=@var{num}
7528 Control how many registers are used to pass integer arguments. By
7529 default, no registers are used to pass arguments, and at most 3
7530 registers can be used. You can control this behavior for a specific
7531 function by using the function attribute @samp{regparm}.
7532 @xref{Function Attributes}.
7534 @strong{Warning:} if you use this switch, and
7535 @var{num} is nonzero, then you must build all modules with the same
7536 value, including any libraries. This includes the system libraries and
7539 @item -mpreferred-stack-boundary=@var{num}
7540 @opindex mpreferred-stack-boundary
7541 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
7542 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
7543 the default is 4 (16 bytes or 128 bits).
7545 The stack is required to be aligned on a 4 byte boundary. On Pentium
7546 and PentiumPro, @code{double} and @code{long double} values should be
7547 aligned to an 8 byte boundary (see @option{-malign-double}) or suffer
7548 significant run time performance penalties. On Pentium III, the
7549 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
7550 penalties if it is not 16 byte aligned.
7552 To ensure proper alignment of this values on the stack, the stack boundary
7553 must be as aligned as that required by any value stored on the stack.
7554 Further, every function must be generated such that it keeps the stack
7555 aligned. Thus calling a function compiled with a higher preferred
7556 stack boundary from a function compiled with a lower preferred stack
7557 boundary will most likely misalign the stack. It is recommended that
7558 libraries that use callbacks always use the default setting.
7560 This extra alignment does consume extra stack space. Code that is sensitive
7561 to stack space usage, such as embedded systems and operating system kernels,
7562 may want to reduce the preferred alignment to
7563 @option{-mpreferred-stack-boundary=2}.
7567 Use PUSH operations to store outgoing parameters. This method is shorter
7568 and usually equally fast as method using SUB/MOV operations and is enabled
7569 by default. In some cases disabling it may improve performance because of
7570 improved scheduling and reduced dependencies.
7572 @item -maccumulate-outgoing-args
7573 @opindex maccumulate-outgoing-args
7574 If enabled, the maximum amount of space required for outgoing arguments will be
7575 computed in the function prologue. This in faster on most modern CPUs
7576 because of reduced dependencies, improved scheduling and reduced stack usage
7577 when preferred stack boundary is not equal to 2. The drawback is a notable
7578 increase in code size. This switch implies @option{-mno-push-args}.
7582 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
7583 on thread-safe exception handling must compile and link all code with the
7584 @option{-mthreads} option. When compiling, @option{-mthreads} defines
7585 @option{-D_MT}; when linking, it links in a special thread helper library
7586 @option{-lmingwthrd} which cleans up per thread exception handling data.
7588 @item -mno-align-stringops
7589 @opindex mno-align-stringops
7590 Do not align destination of inlined string operations. This switch reduces
7591 code size and improves performance in case the destination is already aligned,
7592 but gcc don't know about it.
7594 @item -minline-all-stringops
7595 @opindex minline-all-stringops
7596 By default GCC inlines string operations only when destination is known to be
7597 aligned at least to 4 byte boundary. This enables more inlining, increase code
7598 size, but may improve performance of code that depends on fast memcpy, strlen
7599 and memset for short lengths.
7601 @item -momit-leaf-frame-pointer
7602 @opindex momit-leaf-frame-pointer
7603 Don't keep the frame pointer in a register for leaf functions. This
7604 avoids the instructions to save, set up and restore frame pointers and
7605 makes an extra register available in leaf functions. The option
7606 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7607 which might make debugging harder.
7611 @subsection HPPA Options
7612 @cindex HPPA Options
7614 These @samp{-m} options are defined for the HPPA family of computers:
7617 @item -march=@var{architecture-type}
7619 Generate code for the specified architecture. The choices for
7620 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
7621 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
7622 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
7623 architecture option for your machine. Code compiled for lower numbered
7624 architectures will run on higher numbered architectures, but not the
7627 PA 2.0 support currently requires gas snapshot 19990413 or later. The
7628 next release of binutils (current is 2.9.1) will probably contain PA 2.0
7632 @itemx -mpa-risc-1-1
7633 @itemx -mpa-risc-2-0
7634 @opindex mpa-risc-1-0
7635 @opindex mpa-risc-1-1
7636 @opindex mpa-risc-2-0
7637 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
7640 @opindex mbig-switch
7641 Generate code suitable for big switch tables. Use this option only if
7642 the assembler/linker complain about out of range branches within a switch
7645 @item -mjump-in-delay
7646 @opindex mjump-in-delay
7647 Fill delay slots of function calls with unconditional jump instructions
7648 by modifying the return pointer for the function call to be the target
7649 of the conditional jump.
7651 @item -mdisable-fpregs
7652 @opindex mdisable-fpregs
7653 Prevent floating point registers from being used in any manner. This is
7654 necessary for compiling kernels which perform lazy context switching of
7655 floating point registers. If you use this option and attempt to perform
7656 floating point operations, the compiler will abort.
7658 @item -mdisable-indexing
7659 @opindex mdisable-indexing
7660 Prevent the compiler from using indexing address modes. This avoids some
7661 rather obscure problems when compiling MIG generated code under MACH@.
7663 @item -mno-space-regs
7664 @opindex mno-space-regs
7665 Generate code that assumes the target has no space registers. This allows
7666 GCC to generate faster indirect calls and use unscaled index address modes.
7668 Such code is suitable for level 0 PA systems and kernels.
7670 @item -mfast-indirect-calls
7671 @opindex mfast-indirect-calls
7672 Generate code that assumes calls never cross space boundaries. This
7673 allows GCC to emit code which performs faster indirect calls.
7675 This option will not work in the presence of shared libraries or nested
7678 @item -mlong-load-store
7679 @opindex mlong-load-store
7680 Generate 3-instruction load and store sequences as sometimes required by
7681 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
7684 @item -mportable-runtime
7685 @opindex mportable-runtime
7686 Use the portable calling conventions proposed by HP for ELF systems.
7690 Enable the use of assembler directives only GAS understands.
7692 @item -mschedule=@var{cpu-type}
7694 Schedule code according to the constraints for the machine type
7695 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
7696 @samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to
7697 @file{/usr/lib/sched.models} on an HP-UX system to determine the
7698 proper scheduling option for your machine.
7701 @opindex mlinker-opt
7702 Enable the optimization pass in the HPUX linker. Note this makes symbolic
7703 debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers
7704 in which they give bogus error messages when linking some programs.
7707 @opindex msoft-float
7708 Generate output containing library calls for floating point.
7709 @strong{Warning:} the requisite libraries are not available for all HPPA
7710 targets. Normally the facilities of the machine's usual C compiler are
7711 used, but this cannot be done directly in cross-compilation. You must make
7712 your own arrangements to provide suitable library functions for
7713 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
7714 does provide software floating point support.
7716 @option{-msoft-float} changes the calling convention in the output file;
7717 therefore, it is only useful if you compile @emph{all} of a program with
7718 this option. In particular, you need to compile @file{libgcc.a}, the
7719 library that comes with GCC, with @option{-msoft-float} in order for
7723 @node Intel 960 Options
7724 @subsection Intel 960 Options
7726 These @samp{-m} options are defined for the Intel 960 implementations:
7729 @item -m@var{cpu-type}
7737 Assume the defaults for the machine type @var{cpu-type} for some of
7738 the other options, including instruction scheduling, floating point
7739 support, and addressing modes. The choices for @var{cpu-type} are
7740 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
7741 @samp{sa}, and @samp{sb}.
7748 @opindex msoft-float
7749 The @option{-mnumerics} option indicates that the processor does support
7750 floating-point instructions. The @option{-msoft-float} option indicates
7751 that floating-point support should not be assumed.
7753 @item -mleaf-procedures
7754 @itemx -mno-leaf-procedures
7755 @opindex mleaf-procedures
7756 @opindex mno-leaf-procedures
7757 Do (or do not) attempt to alter leaf procedures to be callable with the
7758 @code{bal} instruction as well as @code{call}. This will result in more
7759 efficient code for explicit calls when the @code{bal} instruction can be
7760 substituted by the assembler or linker, but less efficient code in other
7761 cases, such as calls via function pointers, or using a linker that doesn't
7762 support this optimization.
7765 @itemx -mno-tail-call
7767 @opindex mno-tail-call
7768 Do (or do not) make additional attempts (beyond those of the
7769 machine-independent portions of the compiler) to optimize tail-recursive
7770 calls into branches. You may not want to do this because the detection of
7771 cases where this is not valid is not totally complete. The default is
7772 @option{-mno-tail-call}.
7774 @item -mcomplex-addr
7775 @itemx -mno-complex-addr
7776 @opindex mcomplex-addr
7777 @opindex mno-complex-addr
7778 Assume (or do not assume) that the use of a complex addressing mode is a
7779 win on this implementation of the i960. Complex addressing modes may not
7780 be worthwhile on the K-series, but they definitely are on the C-series.
7781 The default is currently @option{-mcomplex-addr} for all processors except
7785 @itemx -mno-code-align
7786 @opindex mcode-align
7787 @opindex mno-code-align
7788 Align code to 8-byte boundaries for faster fetching (or don't bother).
7789 Currently turned on by default for C-series implementations only.
7792 @item -mclean-linkage
7793 @itemx -mno-clean-linkage
7794 @opindex mclean-linkage
7795 @opindex mno-clean-linkage
7796 These options are not fully implemented.
7800 @itemx -mic2.0-compat
7801 @itemx -mic3.0-compat
7803 @opindex mic2.0-compat
7804 @opindex mic3.0-compat
7805 Enable compatibility with iC960 v2.0 or v3.0.
7809 @opindex masm-compat
7811 Enable compatibility with the iC960 assembler.
7813 @item -mstrict-align
7814 @itemx -mno-strict-align
7815 @opindex mstrict-align
7816 @opindex mno-strict-align
7817 Do not permit (do permit) unaligned accesses.
7821 Enable structure-alignment compatibility with Intel's gcc release version
7822 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
7824 @item -mlong-double-64
7825 @opindex mlong-double-64
7826 Implement type @samp{long double} as 64-bit floating point numbers.
7827 Without the option @samp{long double} is implemented by 80-bit
7828 floating point numbers. The only reason we have it because there is
7829 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
7830 is only useful for people using soft-float targets. Otherwise, we
7831 should recommend against use of it.
7835 @node DEC Alpha Options
7836 @subsection DEC Alpha Options
7838 These @samp{-m} options are defined for the DEC Alpha implementations:
7841 @item -mno-soft-float
7843 @opindex mno-soft-float
7844 @opindex msoft-float
7845 Use (do not use) the hardware floating-point instructions for
7846 floating-point operations. When @option{-msoft-float} is specified,
7847 functions in @file{libgcc.a} will be used to perform floating-point
7848 operations. Unless they are replaced by routines that emulate the
7849 floating-point operations, or compiled in such a way as to call such
7850 emulations routines, these routines will issue floating-point
7851 operations. If you are compiling for an Alpha without floating-point
7852 operations, you must ensure that the library is built so as not to call
7855 Note that Alpha implementations without floating-point operations are
7856 required to have floating-point registers.
7861 @opindex mno-fp-regs
7862 Generate code that uses (does not use) the floating-point register set.
7863 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
7864 register set is not used, floating point operands are passed in integer
7865 registers as if they were integers and floating-point results are passed
7866 in $0 instead of $f0. This is a non-standard calling sequence, so any
7867 function with a floating-point argument or return value called by code
7868 compiled with @option{-mno-fp-regs} must also be compiled with that
7871 A typical use of this option is building a kernel that does not use,
7872 and hence need not save and restore, any floating-point registers.
7876 The Alpha architecture implements floating-point hardware optimized for
7877 maximum performance. It is mostly compliant with the IEEE floating
7878 point standard. However, for full compliance, software assistance is
7879 required. This option generates code fully IEEE compliant code
7880 @emph{except} that the @var{inexact-flag} is not maintained (see below).
7881 If this option is turned on, the CPP macro @code{_IEEE_FP} is defined
7882 during compilation. The option is a shorthand for: @option{-D_IEEE_FP
7883 -mfp-trap-mode=su -mtrap-precision=i -mieee-conformant}. The resulting
7884 code is less efficient but is able to correctly support denormalized
7885 numbers and exceptional IEEE values such as not-a-number and plus/minus
7886 infinity. Other Alpha compilers call this option
7887 @option{-ieee_with_no_inexact}.
7889 @item -mieee-with-inexact
7890 @opindex mieee-with-inexact
7891 @c overfull hbox here --bob 22 jul96
7892 @c original text between ignore ... end ignore
7894 This is like @option{-mieee} except the generated code also maintains the
7895 IEEE @var{inexact-flag}. Turning on this option causes the generated
7896 code to implement fully-compliant IEEE math. The option is a shorthand
7897 for @option{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus @option{-mieee-conformant},
7898 @option{-mfp-trap-mode=sui}, and @option{-mtrap-precision=i}. On some Alpha
7899 implementations the resulting code may execute significantly slower than
7900 the code generated by default. Since there is very little code that
7901 depends on the @var{inexact-flag}, you should normally not specify this
7902 option. Other Alpha compilers call this option
7903 @option{-ieee_with_inexact}.
7905 @c changed paragraph
7906 This is like @option{-mieee} except the generated code also maintains the
7907 IEEE @var{inexact-flag}. Turning on this option causes the generated
7908 code to implement fully-compliant IEEE math. The option is a shorthand
7909 for @option{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus the three following:
7910 @option{-mieee-conformant},
7911 @option{-mfp-trap-mode=sui},
7912 and @option{-mtrap-precision=i}.
7913 On some Alpha implementations the resulting code may execute
7914 significantly slower than the code generated by default. Since there
7915 is very little code that depends on the @var{inexact-flag}, you should
7916 normally not specify this option. Other Alpha compilers call this
7917 option @option{-ieee_with_inexact}.
7918 @c end changes to prevent overfull hboxes
7920 @item -mfp-trap-mode=@var{trap-mode}
7921 @opindex mfp-trap-mode
7922 This option controls what floating-point related traps are enabled.
7923 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
7924 The trap mode can be set to one of four values:
7928 This is the default (normal) setting. The only traps that are enabled
7929 are the ones that cannot be disabled in software (e.g., division by zero
7933 In addition to the traps enabled by @samp{n}, underflow traps are enabled
7937 Like @samp{su}, but the instructions are marked to be safe for software
7938 completion (see Alpha architecture manual for details).
7941 Like @samp{su}, but inexact traps are enabled as well.
7944 @item -mfp-rounding-mode=@var{rounding-mode}
7945 @opindex mfp-rounding-mode
7946 Selects the IEEE rounding mode. Other Alpha compilers call this option
7947 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
7952 Normal IEEE rounding mode. Floating point numbers are rounded towards
7953 the nearest machine number or towards the even machine number in case
7957 Round towards minus infinity.
7960 Chopped rounding mode. Floating point numbers are rounded towards zero.
7963 Dynamic rounding mode. A field in the floating point control register
7964 (@var{fpcr}, see Alpha architecture reference manual) controls the
7965 rounding mode in effect. The C library initializes this register for
7966 rounding towards plus infinity. Thus, unless your program modifies the
7967 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
7970 @item -mtrap-precision=@var{trap-precision}
7971 @opindex mtrap-precision
7972 In the Alpha architecture, floating point traps are imprecise. This
7973 means without software assistance it is impossible to recover from a
7974 floating trap and program execution normally needs to be terminated.
7975 GCC can generate code that can assist operating system trap handlers
7976 in determining the exact location that caused a floating point trap.
7977 Depending on the requirements of an application, different levels of
7978 precisions can be selected:
7982 Program precision. This option is the default and means a trap handler
7983 can only identify which program caused a floating point exception.
7986 Function precision. The trap handler can determine the function that
7987 caused a floating point exception.
7990 Instruction precision. The trap handler can determine the exact
7991 instruction that caused a floating point exception.
7994 Other Alpha compilers provide the equivalent options called
7995 @option{-scope_safe} and @option{-resumption_safe}.
7997 @item -mieee-conformant
7998 @opindex mieee-conformant
7999 This option marks the generated code as IEEE conformant. You must not
8000 use this option unless you also specify @option{-mtrap-precision=i} and either
8001 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8002 is to emit the line @samp{.eflag 48} in the function prologue of the
8003 generated assembly file. Under DEC Unix, this has the effect that
8004 IEEE-conformant math library routines will be linked in.
8006 @item -mbuild-constants
8007 @opindex mbuild-constants
8008 Normally GCC examines a 32- or 64-bit integer constant to
8009 see if it can construct it from smaller constants in two or three
8010 instructions. If it cannot, it will output the constant as a literal and
8011 generate code to load it from the data segment at runtime.
8013 Use this option to require GCC to construct @emph{all} integer constants
8014 using code, even if it takes more instructions (the maximum is six).
8016 You would typically use this option to build a shared library dynamic
8017 loader. Itself a shared library, it must relocate itself in memory
8018 before it can find the variables and constants in its own data segment.
8024 Select whether to generate code to be assembled by the vendor-supplied
8025 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8039 Indicate whether GCC should generate code to use the optional BWX,
8040 CIX, and MAX instruction sets. The default is to use the instruction sets
8041 supported by the CPU type specified via @option{-mcpu=} option or that
8042 of the CPU on which GCC was built if none was specified.
8044 @item -mcpu=@var{cpu_type}
8046 Set the instruction set, register set, and instruction scheduling
8047 parameters for machine type @var{cpu_type}. You can specify either the
8048 @samp{EV} style name or the corresponding chip number. GCC
8049 supports scheduling parameters for the EV4 and EV5 family of processors
8050 and will choose the default values for the instruction set from
8051 the processor you specify. If you do not specify a processor type,
8052 GCC will default to the processor on which the compiler was built.
8054 Supported values for @var{cpu_type} are
8059 Schedules as an EV4 and has no instruction set extensions.
8063 Schedules as an EV5 and has no instruction set extensions.
8067 Schedules as an EV5 and supports the BWX extension.
8072 Schedules as an EV5 and supports the BWX and MAX extensions.
8076 Schedules as an EV5 (until Digital releases the scheduling parameters
8077 for the EV6) and supports the BWX, CIX, and MAX extensions.
8080 @item -mmemory-latency=@var{time}
8081 @opindex mmemory-latency
8082 Sets the latency the scheduler should assume for typical memory
8083 references as seen by the application. This number is highly
8084 dependent on the memory access patterns used by the application
8085 and the size of the external cache on the machine.
8087 Valid options for @var{time} are
8091 A decimal number representing clock cycles.
8097 The compiler contains estimates of the number of clock cycles for
8098 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8099 (also called Dcache, Scache, and Bcache), as well as to main memory.
8100 Note that L3 is only valid for EV5.
8105 @node Clipper Options
8106 @subsection Clipper Options
8108 These @samp{-m} options are defined for the Clipper implementations:
8113 Produce code for a C300 Clipper processor. This is the default.
8117 Produce code for a C400 Clipper processor i.e.@: use floating point
8121 @node H8/300 Options
8122 @subsection H8/300 Options
8124 These @samp{-m} options are defined for the H8/300 implementations:
8129 Shorten some address references at link time, when possible; uses the
8130 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8131 ld.info, Using ld}, for a fuller description.
8135 Generate code for the H8/300H@.
8139 Generate code for the H8/S@.
8143 Generate code for the H8/S2600. This switch must be used with @option{-ms}.
8147 Make @code{int} data 32 bits by default.
8151 On the H8/300H and H8/S, use the same alignment rules as for the H8/300.
8152 The default for the H8/300H and H8/S is to align longs and floats on 4
8154 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8155 This option has no effect on the H8/300.
8159 @subsection SH Options
8161 These @samp{-m} options are defined for the SH implementations:
8166 Generate code for the SH1.
8170 Generate code for the SH2.
8174 Generate code for the SH3.
8178 Generate code for the SH3e.
8182 Generate code for the SH4 without a floating-point unit.
8184 @item -m4-single-only
8185 @opindex m4-single-only
8186 Generate code for the SH4 with a floating-point unit that only
8187 supports single-precision arithmetic.
8191 Generate code for the SH4 assuming the floating-point unit is in
8192 single-precision mode by default.
8196 Generate code for the SH4.
8200 Compile code for the processor in big endian mode.
8204 Compile code for the processor in little endian mode.
8208 Align doubles at 64-bit boundaries. Note that this changes the calling
8209 conventions, and thus some functions from the standard C library will
8210 not work unless you recompile it first with @option{-mdalign}.
8214 Shorten some address references at link time, when possible; uses the
8215 linker option @option{-relax}.
8219 Use 32-bit offsets in @code{switch} tables. The default is to use
8224 Enable the use of the instruction @code{fmovd}.
8228 Comply with the calling conventions defined by Hitachi.
8232 Mark the @code{MAC} register as call-clobbered, even if
8233 @option{-mhitachi} is given.
8237 Increase IEEE-compliance of floating-point code.
8241 Dump instruction size and location in the assembly code.
8245 This option is deprecated. It pads structures to multiple of 4 bytes,
8246 which is incompatible with the SH ABI@.
8250 Optimize for space instead of speed. Implied by @option{-Os}.
8254 When generating position-independent code, emit function calls using
8255 the Global Offset Table instead of the Procedure Linkage Table.
8259 Generate a library function call to invalidate instruction cache
8260 entries, after fixing up a trampoline. This library function call
8261 doesn't assume it can write to the whole memory address space. This
8262 is the default when the target is @code{sh-*-linux*}.
8265 @node System V Options
8266 @subsection Options for System V
8268 These additional options are available on System V Release 4 for
8269 compatibility with other compilers on those systems:
8274 Create a shared object.
8275 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
8279 Identify the versions of each tool used by the compiler, in a
8280 @code{.ident} assembler directive in the output.
8284 Refrain from adding @code{.ident} directives to the output file (this is
8287 @item -YP,@var{dirs}
8289 Search the directories @var{dirs}, and no others, for libraries
8290 specified with @option{-l}.
8294 Look in the directory @var{dir} to find the M4 preprocessor.
8295 The assembler uses this option.
8296 @c This is supposed to go with a -Yd for predefined M4 macro files, but
8297 @c the generic assembler that comes with Solaris takes just -Ym.
8300 @node TMS320C3x/C4x Options
8301 @subsection TMS320C3x/C4x Options
8302 @cindex TMS320C3x/C4x Options
8304 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
8308 @item -mcpu=@var{cpu_type}
8310 Set the instruction set, register set, and instruction scheduling
8311 parameters for machine type @var{cpu_type}. Supported values for
8312 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
8313 @samp{c44}. The default is @samp{c40} to generate code for the
8318 @itemx -msmall-memory
8320 @opindex mbig-memory
8322 @opindex msmall-memory
8324 Generates code for the big or small memory model. The small memory
8325 model assumed that all data fits into one 64K word page. At run-time
8326 the data page (DP) register must be set to point to the 64K page
8327 containing the .bss and .data program sections. The big memory model is
8328 the default and requires reloading of the DP register for every direct
8335 Allow (disallow) allocation of general integer operands into the block
8342 Enable (disable) generation of code using decrement and branch,
8343 DBcond(D), instructions. This is enabled by default for the C4x. To be
8344 on the safe side, this is disabled for the C3x, since the maximum
8345 iteration count on the C3x is @math{2^23 + 1} (but who iterates loops more than
8346 @math{2^23} times on the C3x?). Note that GCC will try to reverse a loop so
8347 that it can utilise the decrement and branch instruction, but will give
8348 up if there is more than one memory reference in the loop. Thus a loop
8349 where the loop counter is decremented can generate slightly more
8350 efficient code, in cases where the RPTB instruction cannot be utilised.
8352 @item -mdp-isr-reload
8354 @opindex mdp-isr-reload
8356 Force the DP register to be saved on entry to an interrupt service
8357 routine (ISR), reloaded to point to the data section, and restored on
8358 exit from the ISR@. This should not be required unless someone has
8359 violated the small memory model by modifying the DP register, say within
8366 For the C3x use the 24-bit MPYI instruction for integer multiplies
8367 instead of a library call to guarantee 32-bit results. Note that if one
8368 of the operands is a constant, then the multiplication will be performed
8369 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
8370 then squaring operations are performed inline instead of a library call.
8373 @itemx -mno-fast-fix
8375 @opindex mno-fast-fix
8376 The C3x/C4x FIX instruction to convert a floating point value to an
8377 integer value chooses the nearest integer less than or equal to the
8378 floating point value rather than to the nearest integer. Thus if the
8379 floating point number is negative, the result will be incorrectly
8380 truncated an additional code is necessary to detect and correct this
8381 case. This option can be used to disable generation of the additional
8382 code required to correct the result.
8388 Enable (disable) generation of repeat block sequences using the RPTB
8389 instruction for zero overhead looping. The RPTB construct is only used
8390 for innermost loops that do not call functions or jump across the loop
8391 boundaries. There is no advantage having nested RPTB loops due to the
8392 overhead required to save and restore the RC, RS, and RE registers.
8393 This is enabled by default with @option{-O2}.
8395 @item -mrpts=@var{count}
8399 Enable (disable) the use of the single instruction repeat instruction
8400 RPTS@. If a repeat block contains a single instruction, and the loop
8401 count can be guaranteed to be less than the value @var{count}, GCC will
8402 emit a RPTS instruction instead of a RPTB@. If no value is specified,
8403 then a RPTS will be emitted even if the loop count cannot be determined
8404 at compile time. Note that the repeated instruction following RPTS does
8405 not have to be reloaded from memory each iteration, thus freeing up the
8406 CPU buses for operands. However, since interrupts are blocked by this
8407 instruction, it is disabled by default.
8409 @item -mloop-unsigned
8410 @itemx -mno-loop-unsigned
8411 @opindex mloop-unsigned
8412 @opindex mno-loop-unsigned
8413 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
8414 is @math{2^31 + 1} since these instructions test if the iteration count is
8415 negative to terminate the loop. If the iteration count is unsigned
8416 there is a possibility than the @math{2^31 + 1} maximum iteration count may be
8417 exceeded. This switch allows an unsigned iteration count.
8421 Try to emit an assembler syntax that the TI assembler (asm30) is happy
8422 with. This also enforces compatibility with the API employed by the TI
8423 C3x C compiler. For example, long doubles are passed as structures
8424 rather than in floating point registers.
8430 Generate code that uses registers (stack) for passing arguments to functions.
8431 By default, arguments are passed in registers where possible rather
8432 than by pushing arguments on to the stack.
8434 @item -mparallel-insns
8435 @itemx -mno-parallel-insns
8436 @opindex mparallel-insns
8437 @opindex mno-parallel-insns
8438 Allow the generation of parallel instructions. This is enabled by
8439 default with @option{-O2}.
8441 @item -mparallel-mpy
8442 @itemx -mno-parallel-mpy
8443 @opindex mparallel-mpy
8444 @opindex mno-parallel-mpy
8445 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
8446 provided @option{-mparallel-insns} is also specified. These instructions have
8447 tight register constraints which can pessimize the code generation
8453 @subsection V850 Options
8454 @cindex V850 Options
8456 These @samp{-m} options are defined for V850 implementations:
8460 @itemx -mno-long-calls
8461 @opindex mlong-calls
8462 @opindex mno-long-calls
8463 Treat all calls as being far away (near). If calls are assumed to be
8464 far away, the compiler will always load the functions address up into a
8465 register, and call indirect through the pointer.
8471 Do not optimize (do optimize) basic blocks that use the same index
8472 pointer 4 or more times to copy pointer into the @code{ep} register, and
8473 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
8474 option is on by default if you optimize.
8476 @item -mno-prolog-function
8477 @itemx -mprolog-function
8478 @opindex mno-prolog-function
8479 @opindex mprolog-function
8480 Do not use (do use) external functions to save and restore registers at
8481 the prolog and epilog of a function. The external functions are slower,
8482 but use less code space if more than one function saves the same number
8483 of registers. The @option{-mprolog-function} option is on by default if
8488 Try to make the code as small as possible. At present, this just turns
8489 on the @option{-mep} and @option{-mprolog-function} options.
8493 Put static or global variables whose size is @var{n} bytes or less into
8494 the tiny data area that register @code{ep} points to. The tiny data
8495 area can hold up to 256 bytes in total (128 bytes for byte references).
8499 Put static or global variables whose size is @var{n} bytes or less into
8500 the small data area that register @code{gp} points to. The small data
8501 area can hold up to 64 kilobytes.
8505 Put static or global variables whose size is @var{n} bytes or less into
8506 the first 32 kilobytes of memory.
8510 Specify that the target processor is the V850.
8513 @opindex mbig-switch
8514 Generate code suitable for big switch tables. Use this option only if
8515 the assembler/linker complain about out of range branches within a switch
8520 @subsection ARC Options
8523 These options are defined for ARC implementations:
8528 Compile code for little endian mode. This is the default.
8532 Compile code for big endian mode.
8535 @opindex mmangle-cpu
8536 Prepend the name of the cpu to all public symbol names.
8537 In multiple-processor systems, there are many ARC variants with different
8538 instruction and register set characteristics. This flag prevents code
8539 compiled for one cpu to be linked with code compiled for another.
8540 No facility exists for handling variants that are ``almost identical''.
8541 This is an all or nothing option.
8543 @item -mcpu=@var{cpu}
8545 Compile code for ARC variant @var{cpu}.
8546 Which variants are supported depend on the configuration.
8547 All variants support @option{-mcpu=base}, this is the default.
8549 @item -mtext=@var{text-section}
8550 @itemx -mdata=@var{data-section}
8551 @itemx -mrodata=@var{readonly-data-section}
8555 Put functions, data, and readonly data in @var{text-section},
8556 @var{data-section}, and @var{readonly-data-section} respectively
8557 by default. This can be overridden with the @code{section} attribute.
8558 @xref{Variable Attributes}.
8563 @subsection NS32K Options
8564 @cindex NS32K options
8566 These are the @samp{-m} options defined for the 32000 series. The default
8567 values for these options depends on which style of 32000 was selected when
8568 the compiler was configured; the defaults for the most common choices are
8576 Generate output for a 32032. This is the default
8577 when the compiler is configured for 32032 and 32016 based systems.
8583 Generate output for a 32332. This is the default
8584 when the compiler is configured for 32332-based systems.
8590 Generate output for a 32532. This is the default
8591 when the compiler is configured for 32532-based systems.
8595 Generate output containing 32081 instructions for floating point.
8596 This is the default for all systems.
8600 Generate output containing 32381 instructions for floating point. This
8601 also implies @option{-m32081}. The 32381 is only compatible with the 32332
8602 and 32532 cpus. This is the default for the pc532-netbsd configuration.
8606 Try and generate multiply-add floating point instructions @code{polyF}
8607 and @code{dotF}. This option is only available if the @option{-m32381}
8608 option is in effect. Using these instructions requires changes to to
8609 register allocation which generally has a negative impact on
8610 performance. This option should only be enabled when compiling code
8611 particularly likely to make heavy use of multiply-add instructions.
8614 @opindex mnomulti-add
8615 Do not try and generate multiply-add floating point instructions
8616 @code{polyF} and @code{dotF}. This is the default on all platforms.
8619 @opindex msoft-float
8620 Generate output containing library calls for floating point.
8621 @strong{Warning:} the requisite libraries may not be available.
8624 @opindex mnobitfield
8625 Do not use the bit-field instructions. On some machines it is faster to
8626 use shifting and masking operations. This is the default for the pc532.
8630 Do use the bit-field instructions. This is the default for all platforms
8635 Use a different function-calling convention, in which functions
8636 that take a fixed number of arguments return pop their
8637 arguments on return with the @code{ret} instruction.
8639 This calling convention is incompatible with the one normally
8640 used on Unix, so you cannot use it if you need to call libraries
8641 compiled with the Unix compiler.
8643 Also, you must provide function prototypes for all functions that
8644 take variable numbers of arguments (including @code{printf});
8645 otherwise incorrect code will be generated for calls to those
8648 In addition, seriously incorrect code will result if you call a
8649 function with too many arguments. (Normally, extra arguments are
8650 harmlessly ignored.)
8652 This option takes its name from the 680x0 @code{rtd} instruction.
8657 Use a different function-calling convention where the first two arguments
8658 are passed in registers.
8660 This calling convention is incompatible with the one normally
8661 used on Unix, so you cannot use it if you need to call libraries
8662 compiled with the Unix compiler.
8665 @opindex mnoregparam
8666 Do not pass any arguments in registers. This is the default for all
8671 It is OK to use the sb as an index register which is always loaded with
8672 zero. This is the default for the pc532-netbsd target.
8676 The sb register is not available for use or has not been initialized to
8677 zero by the run time system. This is the default for all targets except
8678 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
8679 @option{-fpic} is set.
8683 Many ns32000 series addressing modes use displacements of up to 512MB@.
8684 If an address is above 512MB then displacements from zero can not be used.
8685 This option causes code to be generated which can be loaded above 512MB@.
8686 This may be useful for operating systems or ROM code.
8690 Assume code will be loaded in the first 512MB of virtual address space.
8691 This is the default for all platforms.
8697 @subsection AVR Options
8700 These options are defined for AVR implementations:
8703 @item -mmcu=@var{mcu}
8705 Specify ATMEL AVR instruction set or MCU type.
8707 Instruction set avr1 is for the minimal AVR core, not supported by the C
8708 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
8709 attiny11, attiny12, attiny15, attiny28).
8711 Instruction set avr2 (default) is for the classic AVR core with up to
8712 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
8713 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
8714 at90c8534, at90s8535).
8716 Instruction set avr3 is for the classic AVR core with up to 128K program
8717 memory space (MCU types: atmega103, atmega603).
8719 Instruction set avr4 is for the enhanced AVR core with up to 8K program
8720 memory space (MCU types: atmega83, atmega85).
8722 Instruction set avr5 is for the enhanced AVR core with up to 128K program
8723 memory space (MCU types: atmega161, atmega163, atmega32, at94k).
8727 Output instruction sizes to the asm file.
8729 @item -minit-stack=@var{N}
8730 @opindex minit-stack
8731 Specify the initial stack address, which may be a symbol or numeric value,
8732 @samp{__stack} is the default.
8734 @item -mno-interrupts
8735 @opindex mno-interrupts
8736 Generated code is not compatible with hardware interrupts.
8737 Code size will be smaller.
8739 @item -mcall-prologues
8740 @opindex mcall-prologues
8741 Functions prologues/epilogues expanded as call to appropriate
8742 subroutines. Code size will be smaller.
8744 @item -mno-tablejump
8745 @opindex mno-tablejump
8746 Do not generate tablejump insns which sometimes increase code size.
8749 @opindex mtiny-stack
8750 Change only the low 8 bits of the stack pointer.
8754 @subsection MCore Options
8755 @cindex MCore options
8757 These are the @samp{-m} options defined for the Motorola M*Core
8767 @opindex mno-hardlit
8768 Inline constants into the code stream if it can be done in two
8769 instructions or less.
8777 Use the divide instruction. (Enabled by default).
8779 @item -mrelax-immediate
8780 @itemx -mrelax-immediate
8781 @itemx -mno-relax-immediate
8782 @opindex mrelax-immediate
8783 @opindex mrelax-immediate
8784 @opindex mno-relax-immediate
8785 Allow arbitrary sized immediates in bit operations.
8787 @item -mwide-bitfields
8788 @itemx -mwide-bitfields
8789 @itemx -mno-wide-bitfields
8790 @opindex mwide-bitfields
8791 @opindex mwide-bitfields
8792 @opindex mno-wide-bitfields
8793 Always treat bit-fields as int-sized.
8795 @item -m4byte-functions
8796 @itemx -m4byte-functions
8797 @itemx -mno-4byte-functions
8798 @opindex m4byte-functions
8799 @opindex m4byte-functions
8800 @opindex mno-4byte-functions
8801 Force all functions to be aligned to a four byte boundary.
8803 @item -mcallgraph-data
8804 @itemx -mcallgraph-data
8805 @itemx -mno-callgraph-data
8806 @opindex mcallgraph-data
8807 @opindex mcallgraph-data
8808 @opindex mno-callgraph-data
8809 Emit callgraph information.
8813 @itemx -mno-slow-bytes
8814 @opindex mslow-bytes
8815 @opindex mslow-bytes
8816 @opindex mno-slow-bytes
8817 Prefer word access when reading byte quantities.
8819 @item -mlittle-endian
8820 @itemx -mlittle-endian
8822 @opindex mlittle-endian
8823 @opindex mlittle-endian
8824 @opindex mbig-endian
8825 Generate code for a little endian target.
8833 Generate code for the 210 processor.
8837 @subsection IA-64 Options
8838 @cindex IA-64 Options
8840 These are the @samp{-m} options defined for the Intel IA-64 architecture.
8844 @opindex mbig-endian
8845 Generate code for a big endian target. This is the default for HPUX@.
8847 @item -mlittle-endian
8848 @opindex mlittle-endian
8849 Generate code for a little endian target. This is the default for AIX5
8856 Generate (or don't) code for the GNU assembler. This is the default.
8857 @c Also, this is the default if the configure option @option{--with-gnu-as}
8864 Generate (or don't) code for the GNU linker. This is the default.
8865 @c Also, this is the default if the configure option @option{--with-gnu-ld}
8870 Generate code that does not use a global pointer register. The result
8871 is not position independent code, and violates the IA-64 ABI@.
8873 @item -mvolatile-asm-stop
8874 @itemx -mno-volatile-asm-stop
8875 @opindex mvolatile-asm-stop
8876 @opindex mno-volatile-asm-stop
8877 Generate (or don't) a stop bit immediately before and after volatile asm
8882 Generate code that works around Itanium B step errata.
8884 @item -mregister-names
8885 @itemx -mno-register-names
8886 @opindex mregister-names
8887 @opindex mno-register-names
8888 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
8889 the stacked registers. This may make assembler output more readable.
8895 Disable (or enable) optimizations that use the small data section. This may
8896 be useful for working around optimizer bugs.
8899 @opindex mconstant-gp
8900 Generate code that uses a single constant global pointer value. This is
8901 useful when compiling kernel code.
8905 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
8906 This is useful when compiling firmware code.
8908 @item -minline-divide-min-latency
8909 @opindex minline-divide-min-latency
8910 Generate code for inline divides using the minimum latency algorithm.
8912 @item -minline-divide-max-throughput
8913 @opindex minline-divide-max-throughput
8914 Generate code for inline divides using the maximum throughput algorithm.
8916 @item -mno-dwarf2-asm
8918 @opindex mno-dwarf2-asm
8919 @opindex mdwarf2-asm
8920 Don't (or do) generate assembler code for the DWARF2 line number debugging
8921 info. This may be useful when not using the GNU assembler.
8923 @item -mfixed-range=@var{register-range}
8924 @opindex mfixed-range
8925 Generate code treating the given register range as fixed registers.
8926 A fixed register is one that the register allocator can not use. This is
8927 useful when compiling kernel code. A register range is specified as
8928 two registers separated by a dash. Multiple register ranges can be
8929 specified separated by a comma.
8933 @subsection D30V Options
8934 @cindex D30V Options
8936 These @samp{-m} options are defined for D30V implementations:
8941 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
8942 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
8943 memory, which starts at location @code{0x80000000}.
8947 Same as the @option{-mextmem} switch.
8951 Link the @samp{.text} section into onchip text memory, which starts at
8952 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
8953 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
8954 into onchip data memory, which starts at location @code{0x20000000}.
8956 @item -mno-asm-optimize
8957 @itemx -masm-optimize
8958 @opindex mno-asm-optimize
8959 @opindex masm-optimize
8960 Disable (enable) passing @option{-O} to the assembler when optimizing.
8961 The assembler uses the @option{-O} option to automatically parallelize
8962 adjacent short instructions where possible.
8964 @item -mbranch-cost=@var{n}
8965 @opindex mbranch-cost
8966 Increase the internal costs of branches to @var{n}. Higher costs means
8967 that the compiler will issue more instructions to avoid doing a branch.
8970 @item -mcond-exec=@var{n}
8972 Specify the maximum number of conditionally executed instructions that
8973 replace a branch. The default is 4.
8976 @node Code Gen Options
8977 @section Options for Code Generation Conventions
8978 @cindex code generation conventions
8979 @cindex options, code generation
8980 @cindex run-time options
8982 These machine-independent options control the interface conventions
8983 used in code generation.
8985 Most of them have both positive and negative forms; the negative form
8986 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
8987 one of the forms is listed---the one which is not the default. You
8988 can figure out the other form by either removing @samp{no-} or adding
8993 @opindex fexceptions
8994 Enable exception handling. Generates extra code needed to propagate
8995 exceptions. For some targets, this implies GCC will generate frame
8996 unwind information for all functions, which can produce significant data
8997 size overhead, although it does not affect execution. If you do not
8998 specify this option, GCC will enable it by default for languages like
8999 C++ which normally require exception handling, and disable it for
9000 languages like C that do not normally require it. However, you may need
9001 to enable this option when compiling C code that needs to interoperate
9002 properly with exception handlers written in C++. You may also wish to
9003 disable this option if you are compiling older C++ programs that don't
9004 use exception handling.
9006 @item -fnon-call-exceptions
9007 @opindex fnon-call-exceptions
9008 Generate code that allows trapping instructions to throw exceptions.
9009 Note that this requires platform-specific runtime support that does
9010 not exist everywhere. Moreover, it only allows @emph{trapping}
9011 instructions to throw exceptions, i.e.@: memory references or floating
9012 point instructions. It does not allow exceptions to be thrown from
9013 arbitrary signal handlers such as @code{SIGALRM}.
9015 @item -funwind-tables
9016 @opindex funwind-tables
9017 Similar to @option{-fexceptions}, except that it will just generate any needed
9018 static data, but will not affect the generated code in any other way.
9019 You will normally not enable this option; instead, a language processor
9020 that needs this handling would enable it on your behalf.
9022 @item -fpcc-struct-return
9023 @opindex fpcc-struct-return
9024 Return ``short'' @code{struct} and @code{union} values in memory like
9025 longer ones, rather than in registers. This convention is less
9026 efficient, but it has the advantage of allowing intercallability between
9027 GCC-compiled files and files compiled with other compilers.
9029 The precise convention for returning structures in memory depends
9030 on the target configuration macros.
9032 Short structures and unions are those whose size and alignment match
9033 that of some integer type.
9035 @item -freg-struct-return
9036 @opindex freg-struct-return
9037 Use the convention that @code{struct} and @code{union} values are
9038 returned in registers when possible. This is more efficient for small
9039 structures than @option{-fpcc-struct-return}.
9041 If you specify neither @option{-fpcc-struct-return} nor its contrary
9042 @option{-freg-struct-return}, GCC defaults to whichever convention is
9043 standard for the target. If there is no standard convention, GCC
9044 defaults to @option{-fpcc-struct-return}, except on targets where GCC
9045 is the principal compiler. In those cases, we can choose the standard,
9046 and we chose the more efficient register return alternative.
9049 @opindex fshort-enums
9050 Allocate to an @code{enum} type only as many bytes as it needs for the
9051 declared range of possible values. Specifically, the @code{enum} type
9052 will be equivalent to the smallest integer type which has enough room.
9054 @item -fshort-double
9055 @opindex fshort-double
9056 Use the same size for @code{double} as for @code{float}.
9059 @opindex fshared-data
9060 Requests that the data and non-@code{const} variables of this
9061 compilation be shared data rather than private data. The distinction
9062 makes sense only on certain operating systems, where shared data is
9063 shared between processes running the same program, while private data
9064 exists in one copy per process.
9068 In C, allocate even uninitialized global variables in the data section of the
9069 object file, rather than generating them as common blocks. This has the
9070 effect that if the same variable is declared (without @code{extern}) in
9071 two different compilations, you will get an error when you link them.
9072 The only reason this might be useful is if you wish to verify that the
9073 program will work on other systems which always work this way.
9077 Ignore the @samp{#ident} directive.
9079 @item -fno-gnu-linker
9080 @opindex fno-gnu-linker
9081 Do not output global initializations (such as C++ constructors and
9082 destructors) in the form used by the GNU linker (on systems where the GNU
9083 linker is the standard method of handling them). Use this option when
9084 you want to use a non-GNU linker, which also requires using the
9085 @command{collect2} program to make sure the system linker includes
9086 constructors and destructors. (@command{collect2} is included in the GCC
9087 distribution.) For systems which @emph{must} use @command{collect2}, the
9088 compiler driver @command{gcc} is configured to do this automatically.
9090 @item -finhibit-size-directive
9091 @opindex finhibit-size-directive
9092 Don't output a @code{.size} assembler directive, or anything else that
9093 would cause trouble if the function is split in the middle, and the
9094 two halves are placed at locations far apart in memory. This option is
9095 used when compiling @file{crtstuff.c}; you should not need to use it
9099 @opindex fverbose-asm
9100 Put extra commentary information in the generated assembly code to
9101 make it more readable. This option is generally only of use to those
9102 who actually need to read the generated assembly code (perhaps while
9103 debugging the compiler itself).
9105 @option{-fno-verbose-asm}, the default, causes the
9106 extra information to be omitted and is useful when comparing two assembler
9111 Consider all memory references through pointers to be volatile.
9113 @item -fvolatile-global
9114 @opindex fvolatile-global
9115 Consider all memory references to extern and global data items to
9116 be volatile. GCC does not consider static data items to be volatile
9117 because of this switch.
9119 @item -fvolatile-static
9120 @opindex fvolatile-static
9121 Consider all memory references to static data to be volatile.
9125 @cindex global offset table
9127 Generate position-independent code (PIC) suitable for use in a shared
9128 library, if supported for the target machine. Such code accesses all
9129 constant addresses through a global offset table (GOT)@. The dynamic
9130 loader resolves the GOT entries when the program starts (the dynamic
9131 loader is not part of GCC; it is part of the operating system). If
9132 the GOT size for the linked executable exceeds a machine-specific
9133 maximum size, you get an error message from the linker indicating that
9134 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
9135 instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k
9136 on the m68k and RS/6000. The 386 has no such limit.)
9138 Position-independent code requires special support, and therefore works
9139 only on certain machines. For the 386, GCC supports PIC for System V
9140 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
9141 position-independent.
9145 If supported for the target machine, emit position-independent code,
9146 suitable for dynamic linking and avoiding any limit on the size of the
9147 global offset table. This option makes a difference on the m68k, m88k,
9150 Position-independent code requires special support, and therefore works
9151 only on certain machines.
9153 @item -ffixed-@var{reg}
9155 Treat the register named @var{reg} as a fixed register; generated code
9156 should never refer to it (except perhaps as a stack pointer, frame
9157 pointer or in some other fixed role).
9159 @var{reg} must be the name of a register. The register names accepted
9160 are machine-specific and are defined in the @code{REGISTER_NAMES}
9161 macro in the machine description macro file.
9163 This flag does not have a negative form, because it specifies a
9166 @item -fcall-used-@var{reg}
9168 Treat the register named @var{reg} as an allocable register that is
9169 clobbered by function calls. It may be allocated for temporaries or
9170 variables that do not live across a call. Functions compiled this way
9171 will not save and restore the register @var{reg}.
9173 It is an error to used this flag with the frame pointer or stack pointer.
9174 Use of this flag for other registers that have fixed pervasive roles in
9175 the machine's execution model will produce disastrous results.
9177 This flag does not have a negative form, because it specifies a
9180 @item -fcall-saved-@var{reg}
9181 @opindex fcall-saved
9182 Treat the register named @var{reg} as an allocable register saved by
9183 functions. It may be allocated even for temporaries or variables that
9184 live across a call. Functions compiled this way will save and restore
9185 the register @var{reg} if they use it.
9187 It is an error to used this flag with the frame pointer or stack pointer.
9188 Use of this flag for other registers that have fixed pervasive roles in
9189 the machine's execution model will produce disastrous results.
9191 A different sort of disaster will result from the use of this flag for
9192 a register in which function values may be returned.
9194 This flag does not have a negative form, because it specifies a
9198 @opindex fpack-struct
9199 Pack all structure members together without holes. Usually you would
9200 not want to use this option, since it makes the code suboptimal, and
9201 the offsets of structure members won't agree with system libraries.
9203 @item -fcheck-memory-usage
9204 @opindex fcheck-memory-usage
9205 Generate extra code to check each memory access. GCC will generate
9206 code that is suitable for a detector of bad memory accesses such as
9209 Normally, you should compile all, or none, of your code with this option.
9211 If you do mix code compiled with and without this option,
9212 you must ensure that all code that has side effects
9213 and that is called by code compiled with this option
9214 is, itself, compiled with this option.
9215 If you do not, you might get erroneous messages from the detector.
9217 If you use functions from a library that have side-effects (such as
9218 @code{read}), you might not be able to recompile the library and
9219 specify this option. In that case, you can enable the
9220 @option{-fprefix-function-name} option, which requests GCC to encapsulate
9221 your code and make other functions look as if they were compiled with
9222 @option{-fcheck-memory-usage}. This is done by calling ``stubs'',
9223 which are provided by the detector. If you cannot find or build
9224 stubs for every function you call, you might have to specify
9225 @option{-fcheck-memory-usage} without @option{-fprefix-function-name}.
9227 If you specify this option, you can not use the @code{asm} or
9228 @code{__asm__} keywords in functions with memory checking enabled. GCC
9229 cannot understand what the @code{asm} statement may do, and therefore
9230 cannot generate the appropriate code, so it will reject it. However, if
9231 you specify the function attribute @code{no_check_memory_usage}
9232 (@pxref{Function Attributes}), GCC will disable memory checking within a
9233 function; you may use @code{asm} statements inside such functions. You
9234 may have an inline expansion of a non-checked function within a checked
9235 function; in that case GCC will not generate checks for the inlined
9236 function's memory accesses.
9238 If you move your @code{asm} statements to non-checked inline functions
9239 and they do access memory, you can add calls to the support code in your
9240 inline function, to indicate any reads, writes, or copies being done.
9241 These calls would be similar to those done in the stubs described above.
9243 @item -fprefix-function-name
9244 @opindex fprefix-function-name
9245 Request GCC to add a prefix to the symbols generated for function names.
9246 GCC adds a prefix to the names of functions defined as well as
9247 functions called. Code compiled with this option and code compiled
9248 without the option can't be linked together, unless stubs are used.
9250 If you compile the following code with @option{-fprefix-function-name}
9252 extern void bar (int);
9261 GCC will compile the code as if it was written:
9263 extern void prefix_bar (int);
9267 return prefix_bar (a + 5);
9270 This option is designed to be used with @option{-fcheck-memory-usage}.
9272 @item -finstrument-functions
9273 @opindex finstrument-functions
9274 Generate instrumentation calls for entry and exit to functions. Just
9275 after function entry and just before function exit, the following
9276 profiling functions will be called with the address of the current
9277 function and its call site. (On some platforms,
9278 @code{__builtin_return_address} does not work beyond the current
9279 function, so the call site information may not be available to the
9280 profiling functions otherwise.)
9283 void __cyg_profile_func_enter (void *this_fn,
9285 void __cyg_profile_func_exit (void *this_fn,
9289 The first argument is the address of the start of the current function,
9290 which may be looked up exactly in the symbol table.
9292 This instrumentation is also done for functions expanded inline in other
9293 functions. The profiling calls will indicate where, conceptually, the
9294 inline function is entered and exited. This means that addressable
9295 versions of such functions must be available. If all your uses of a
9296 function are expanded inline, this may mean an additional expansion of
9297 code size. If you use @samp{extern inline} in your C code, an
9298 addressable version of such functions must be provided. (This is
9299 normally the case anyways, but if you get lucky and the optimizer always
9300 expands the functions inline, you might have gotten away without
9301 providing static copies.)
9303 A function may be given the attribute @code{no_instrument_function}, in
9304 which case this instrumentation will not be done. This can be used, for
9305 example, for the profiling functions listed above, high-priority
9306 interrupt routines, and any functions from which the profiling functions
9307 cannot safely be called (perhaps signal handlers, if the profiling
9308 routines generate output or allocate memory).
9311 @opindex fstack-check
9312 Generate code to verify that you do not go beyond the boundary of the
9313 stack. You should specify this flag if you are running in an
9314 environment with multiple threads, but only rarely need to specify it in
9315 a single-threaded environment since stack overflow is automatically
9316 detected on nearly all systems if there is only one stack.
9318 Note that this switch does not actually cause checking to be done; the
9319 operating system must do that. The switch causes generation of code
9320 to ensure that the operating system sees the stack being extended.
9322 @item -fstack-limit-register=@var{reg}
9323 @itemx -fstack-limit-symbol=@var{sym}
9324 @itemx -fno-stack-limit
9325 @opindex fstack-limit-register
9326 @opindex fstack-limit-symbol
9327 @opindex fno-stack-limit
9328 Generate code to ensure that the stack does not grow beyond a certain value,
9329 either the value of a register or the address of a symbol. If the stack
9330 would grow beyond the value, a signal is raised. For most targets,
9331 the signal is raised before the stack overruns the boundary, so
9332 it is possible to catch the signal without taking special precautions.
9334 For instance, if the stack starts at address @samp{0x80000000} and grows
9335 downwards you can use the flags
9336 @samp{-fstack-limit-symbol=__stack_limit
9337 -Wl,--defsym,__stack_limit=0x7ffe0000} which will enforce a stack
9340 @cindex aliasing of parameters
9341 @cindex parameters, aliased
9342 @item -fargument-alias
9343 @itemx -fargument-noalias
9344 @itemx -fargument-noalias-global
9345 @opindex fargument-alias
9346 @opindex fargument-noalias
9347 @opindex fargument-noalias-global
9348 Specify the possible relationships among parameters and between
9349 parameters and global data.
9351 @option{-fargument-alias} specifies that arguments (parameters) may
9352 alias each other and may alias global storage.
9353 @option{-fargument-noalias} specifies that arguments do not alias
9354 each other, but may alias global storage.
9355 @option{-fargument-noalias-global} specifies that arguments do not
9356 alias each other and do not alias global storage.
9358 Each language will automatically use whatever option is required by
9359 the language standard. You should not need to use these options yourself.
9361 @item -fleading-underscore
9362 @opindex fleading-underscore
9363 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
9364 change the way C symbols are represented in the object file. One use
9365 is to help link with legacy assembly code.
9367 Be warned that you should know what you are doing when invoking this
9368 option, and that not all targets provide complete support for it.
9373 @node Environment Variables
9374 @section Environment Variables Affecting GCC
9375 @cindex environment variables
9377 @c man begin ENVIRONMENT
9379 This section describes several environment variables that affect how GCC
9380 operates. Some of them work by specifying directories or prefixes to use
9381 when searching for various kinds of files. Some are used to specify other
9382 aspects of the compilation environment.
9385 Note that you can also specify places to search using options such as
9386 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
9387 take precedence over places specified using environment variables, which
9388 in turn take precedence over those specified by the configuration of GCC@.
9392 Note that you can also specify places to search using options such as
9393 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
9394 take precedence over places specified using environment variables, which
9395 in turn take precedence over those specified by the configuration of GCC@.
9402 @c @itemx LC_COLLATE
9404 @c @itemx LC_MONETARY
9405 @c @itemx LC_NUMERIC
9410 @c @findex LC_COLLATE
9412 @c @findex LC_MONETARY
9413 @c @findex LC_NUMERIC
9417 These environment variables control the way that GCC uses
9418 localization information that allow GCC to work with different
9419 national conventions. GCC inspects the locale categories
9420 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
9421 so. These locale categories can be set to any value supported by your
9422 installation. A typical value is @samp{en_UK} for English in the United
9425 The @env{LC_CTYPE} environment variable specifies character
9426 classification. GCC uses it to determine the character boundaries in
9427 a string; this is needed for some multibyte encodings that contain quote
9428 and escape characters that would otherwise be interpreted as a string
9431 The @env{LC_MESSAGES} environment variable specifies the language to
9432 use in diagnostic messages.
9434 If the @env{LC_ALL} environment variable is set, it overrides the value
9435 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
9436 and @env{LC_MESSAGES} default to the value of the @env{LANG}
9437 environment variable. If none of these variables are set, GCC
9438 defaults to traditional C English behavior.
9442 If @env{TMPDIR} is set, it specifies the directory to use for temporary
9443 files. GCC uses temporary files to hold the output of one stage of
9444 compilation which is to be used as input to the next stage: for example,
9445 the output of the preprocessor, which is the input to the compiler
9448 @item GCC_EXEC_PREFIX
9449 @findex GCC_EXEC_PREFIX
9450 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
9451 names of the subprograms executed by the compiler. No slash is added
9452 when this prefix is combined with the name of a subprogram, but you can
9453 specify a prefix that ends with a slash if you wish.
9455 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
9456 an appropriate prefix to use based on the pathname it was invoked with.
9458 If GCC cannot find the subprogram using the specified prefix, it
9459 tries looking in the usual places for the subprogram.
9461 The default value of @env{GCC_EXEC_PREFIX} is
9462 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
9463 of @code{prefix} when you ran the @file{configure} script.
9465 Other prefixes specified with @option{-B} take precedence over this prefix.
9467 This prefix is also used for finding files such as @file{crt0.o} that are
9470 In addition, the prefix is used in an unusual way in finding the
9471 directories to search for header files. For each of the standard
9472 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
9473 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
9474 replacing that beginning with the specified prefix to produce an
9475 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
9476 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
9477 These alternate directories are searched first; the standard directories
9481 @findex COMPILER_PATH
9482 The value of @env{COMPILER_PATH} is a colon-separated list of
9483 directories, much like @env{PATH}. GCC tries the directories thus
9484 specified when searching for subprograms, if it can't find the
9485 subprograms using @env{GCC_EXEC_PREFIX}.
9488 @findex LIBRARY_PATH
9489 The value of @env{LIBRARY_PATH} is a colon-separated list of
9490 directories, much like @env{PATH}. When configured as a native compiler,
9491 GCC tries the directories thus specified when searching for special
9492 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
9493 using GCC also uses these directories when searching for ordinary
9494 libraries for the @option{-l} option (but directories specified with
9495 @option{-L} come first).
9497 @item C_INCLUDE_PATH
9498 @itemx CPLUS_INCLUDE_PATH
9499 @itemx OBJC_INCLUDE_PATH
9500 @findex C_INCLUDE_PATH
9501 @findex CPLUS_INCLUDE_PATH
9502 @findex OBJC_INCLUDE_PATH
9503 @c @itemx OBJCPLUS_INCLUDE_PATH
9504 These environment variables pertain to particular languages. Each
9505 variable's value is a colon-separated list of directories, much like
9506 @env{PATH}. When GCC searches for header files, it tries the
9507 directories listed in the variable for the language you are using, after
9508 the directories specified with @option{-I} but before the standard header
9511 @item DEPENDENCIES_OUTPUT
9512 @findex DEPENDENCIES_OUTPUT
9513 @cindex dependencies for make as output
9514 If this variable is set, its value specifies how to output dependencies
9515 for Make based on the header files processed by the compiler. This
9516 output looks much like the output from the @option{-M} option
9517 (@pxref{Preprocessor Options}), but it goes to a separate file, and is
9518 in addition to the usual results of compilation.
9520 The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in
9521 which case the Make rules are written to that file, guessing the target
9522 name from the source file name. Or the value can have the form
9523 @samp{@var{file} @var{target}}, in which case the rules are written to
9524 file @var{file} using @var{target} as the target name.
9528 @cindex locale definition
9529 This variable is used to pass locale information to the compiler. One way in
9530 which this information is used is to determine the character set to be used
9531 when character literals, string literals and comments are parsed in C and C++.
9532 When the compiler is configured to allow multibyte characters,
9533 the following values for @env{LANG} are recognized:
9537 Recognize JIS characters.
9539 Recognize SJIS characters.
9541 Recognize EUCJP characters.
9544 If @env{LANG} is not defined, or if it has some other value, then the
9545 compiler will use mblen and mbtowc as defined by the default locale to
9546 recognize and translate multibyte characters.
9551 @node Running Protoize
9552 @section Running Protoize
9554 The program @code{protoize} is an optional part of GCC@. You can use
9555 it to add prototypes to a program, thus converting the program to ISO
9556 C in one respect. The companion program @code{unprotoize} does the
9557 reverse: it removes argument types from any prototypes that are found.
9559 When you run these programs, you must specify a set of source files as
9560 command line arguments. The conversion programs start out by compiling
9561 these files to see what functions they define. The information gathered
9562 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
9564 After scanning comes actual conversion. The specified files are all
9565 eligible to be converted; any files they include (whether sources or
9566 just headers) are eligible as well.
9568 But not all the eligible files are converted. By default,
9569 @code{protoize} and @code{unprotoize} convert only source and header
9570 files in the current directory. You can specify additional directories
9571 whose files should be converted with the @option{-d @var{directory}}
9572 option. You can also specify particular files to exclude with the
9573 @option{-x @var{file}} option. A file is converted if it is eligible, its
9574 directory name matches one of the specified directory names, and its
9575 name within the directory has not been excluded.
9577 Basic conversion with @code{protoize} consists of rewriting most
9578 function definitions and function declarations to specify the types of
9579 the arguments. The only ones not rewritten are those for varargs
9582 @code{protoize} optionally inserts prototype declarations at the
9583 beginning of the source file, to make them available for any calls that
9584 precede the function's definition. Or it can insert prototype
9585 declarations with block scope in the blocks where undeclared functions
9588 Basic conversion with @code{unprotoize} consists of rewriting most
9589 function declarations to remove any argument types, and rewriting
9590 function definitions to the old-style pre-ISO form.
9592 Both conversion programs print a warning for any function declaration or
9593 definition that they can't convert. You can suppress these warnings
9596 The output from @code{protoize} or @code{unprotoize} replaces the
9597 original source file. The original file is renamed to a name ending
9598 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
9599 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
9600 for DOS) file already exists, then the source file is simply discarded.
9602 @code{protoize} and @code{unprotoize} both depend on GCC itself to
9603 scan the program and collect information about the functions it uses.
9604 So neither of these programs will work until GCC is installed.
9606 Here is a table of the options you can use with @code{protoize} and
9607 @code{unprotoize}. Each option works with both programs unless
9611 @item -B @var{directory}
9612 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
9613 usual directory (normally @file{/usr/local/lib}). This file contains
9614 prototype information about standard system functions. This option
9615 applies only to @code{protoize}.
9617 @item -c @var{compilation-options}
9618 Use @var{compilation-options} as the options when running @code{gcc} to
9619 produce the @samp{.X} files. The special option @option{-aux-info} is
9620 always passed in addition, to tell @code{gcc} to write a @samp{.X} file.
9622 Note that the compilation options must be given as a single argument to
9623 @code{protoize} or @code{unprotoize}. If you want to specify several
9624 @code{gcc} options, you must quote the entire set of compilation options
9625 to make them a single word in the shell.
9627 There are certain @code{gcc} arguments that you cannot use, because they
9628 would produce the wrong kind of output. These include @option{-g},
9629 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
9630 the @var{compilation-options}, they are ignored.
9633 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
9634 systems) instead of @samp{.c}. This is convenient if you are converting
9635 a C program to C++. This option applies only to @code{protoize}.
9638 Add explicit global declarations. This means inserting explicit
9639 declarations at the beginning of each source file for each function
9640 that is called in the file and was not declared. These declarations
9641 precede the first function definition that contains a call to an
9642 undeclared function. This option applies only to @code{protoize}.
9644 @item -i @var{string}
9645 Indent old-style parameter declarations with the string @var{string}.
9646 This option applies only to @code{protoize}.
9648 @code{unprotoize} converts prototyped function definitions to old-style
9649 function definitions, where the arguments are declared between the
9650 argument list and the initial @samp{@{}. By default, @code{unprotoize}
9651 uses five spaces as the indentation. If you want to indent with just
9652 one space instead, use @option{-i " "}.
9655 Keep the @samp{.X} files. Normally, they are deleted after conversion
9659 Add explicit local declarations. @code{protoize} with @option{-l} inserts
9660 a prototype declaration for each function in each block which calls the
9661 function without any declaration. This option applies only to
9665 Make no real changes. This mode just prints information about the conversions
9666 that would have been done without @option{-n}.
9669 Make no @samp{.save} files. The original files are simply deleted.
9670 Use this option with caution.
9672 @item -p @var{program}
9673 Use the program @var{program} as the compiler. Normally, the name
9677 Work quietly. Most warnings are suppressed.
9680 Print the version number, just like @option{-v} for @code{gcc}.
9683 If you need special compiler options to compile one of your program's
9684 source files, then you should generate that file's @samp{.X} file
9685 specially, by running @code{gcc} on that source file with the
9686 appropriate options and the option @option{-aux-info}. Then run
9687 @code{protoize} on the entire set of files. @code{protoize} will use
9688 the existing @samp{.X} file because it is newer than the source file.
9692 gcc -Dfoo=bar file1.c -aux-info file1.X
9697 You need to include the special files along with the rest in the
9698 @code{protoize} command, even though their @samp{.X} files already
9699 exist, because otherwise they won't get converted.
9701 @xref{Protoize Caveats}, for more information on how to use
9702 @code{protoize} successfully.