1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003 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, 2002, 2003 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.2 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), g77(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{g77}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @command{gcc}, or
57 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
58 for contributors to GCC@.
63 @chapter GCC Command Options
64 @cindex GCC command options
65 @cindex command options
66 @cindex options, GCC command
68 @c man begin DESCRIPTION
69 When you invoke GCC, it normally does preprocessing, compilation,
70 assembly and linking. The ``overall options'' allow you to stop this
71 process at an intermediate stage. For example, the @option{-c} option
72 says not to run the linker. Then the output consists of object files
73 output by the assembler.
75 Other options are passed on to one stage of processing. Some options
76 control the preprocessor and others the compiler itself. Yet other
77 options control the assembler and linker; most of these are not
78 documented here, since you rarely need to use any of them.
80 @cindex C compilation options
81 Most of the command line options that you can use with GCC are useful
82 for C programs; when an option is only useful with another language
83 (usually C++), the explanation says so explicitly. If the description
84 for a particular option does not mention a source language, you can use
85 that option with all supported languages.
87 @cindex C++ compilation options
88 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
89 options for compiling C++ programs.
91 @cindex grouping options
92 @cindex options, grouping
93 The @command{gcc} program accepts options and file names as operands. Many
94 options have multi-letter names; therefore multiple single-letter options
95 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
98 @cindex order of options
99 @cindex options, order
100 You can mix options and other arguments. For the most part, the order
101 you use doesn't matter. Order does matter when you use several options
102 of the same kind; for example, if you specify @option{-L} more than once,
103 the directories are searched in the order specified.
105 Many options have long names starting with @samp{-f} or with
106 @samp{-W}---for example, @option{-fforce-mem},
107 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
108 these have both positive and negative forms; the negative form of
109 @option{-ffoo} would be @option{-fno-foo}. This manual documents
110 only one of these two forms, whichever one is not the default.
114 @xref{Option Index}, for an index to GCC's options.
117 * Option Summary:: Brief list of all options, without explanations.
118 * Overall Options:: Controlling the kind of output:
119 an executable, object files, assembler files,
120 or preprocessed source.
121 * Invoking G++:: Compiling C++ programs.
122 * C Dialect Options:: Controlling the variant of C language compiled.
123 * C++ Dialect Options:: Variations on C++.
124 * Objective-C Dialect Options:: Variations on Objective-C.
125 * Language Independent Options:: Controlling how diagnostics should be
127 * Warning Options:: How picky should the compiler be?
128 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
129 * Optimize Options:: How much optimization?
130 * Preprocessor Options:: Controlling header files and macro definitions.
131 Also, getting dependency information for Make.
132 * Assembler Options:: Passing options to the assembler.
133 * Link Options:: Specifying libraries and so on.
134 * Directory Options:: Where to find header files and libraries.
135 Where to find the compiler executable files.
136 * Spec Files:: How to pass switches to sub-processes.
137 * Target Options:: Running a cross-compiler, or an old version of GCC.
138 * Submodel Options:: Specifying minor hardware or convention variations,
139 such as 68010 vs 68020.
140 * Code Gen Options:: Specifying conventions for function calls, data layout
142 * Environment Variables:: Env vars that affect GCC.
143 * Precompiled Headers:: Compiling a header once, and using it many times.
144 * Running Protoize:: Automatically adding or removing function prototypes.
150 @section Option Summary
152 Here is a summary of all the options, grouped by type. Explanations are
153 in the following sections.
156 @item Overall Options
157 @xref{Overall Options,,Options Controlling the Kind of Output}.
158 @gccoptlist{-c -S -E -o @var{file} -pipe -pass-exit-codes @gol
159 -x @var{language} -v -### --help --target-help --version}
161 @item C Language Options
162 @xref{C Dialect Options,,Options Controlling C Dialect}.
163 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
164 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
165 -fhosted -ffreestanding -fms-extensions @gol
166 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
167 -fallow-single-precision -fcond-mismatch @gol
168 -fsigned-bitfields -fsigned-char @gol
169 -funsigned-bitfields -funsigned-char @gol
172 @item C++ Language Options
173 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
174 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
175 -fconserve-space -fno-const-strings @gol
176 -fno-elide-constructors @gol
177 -fno-enforce-eh-specs -fexternal-templates @gol
178 -falt-external-templates @gol
179 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
180 -fno-implicit-templates @gol
181 -fno-implicit-inline-templates @gol
182 -fno-implement-inlines -fms-extensions @gol
183 -fno-nonansi-builtins -fno-operator-names @gol
184 -fno-optional-diags -fpermissive @gol
185 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
186 -fuse-cxa-atexit -fvtable-gc -fno-weak -nostdinc++ @gol
187 -fno-default-inline -Wabi -Wctor-dtor-privacy @gol
188 -Wnon-virtual-dtor -Wreorder @gol
189 -Weffc++ -Wno-deprecated @gol
190 -Wno-non-template-friend -Wold-style-cast @gol
191 -Woverloaded-virtual -Wno-pmf-conversions @gol
192 -Wsign-promo -Wsynth}
194 @item Objective-C Language Options
195 @xref{Objective-C Dialect Options,,Options Controlling Objective-C Dialect}.
196 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
197 -fgnu-runtime -fnext-runtime -gen-decls @gol
198 -Wno-protocol -Wselector -Wundeclared-selector}
200 @item Language Independent Options
201 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
202 @gccoptlist{-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}.
207 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
208 -w -Wextra -Wall -Waggregate-return @gol
209 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
210 -Wconversion -Wno-deprecated-declarations @gol
211 -Wdisabled-optimization -Wno-div-by-zero -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 -Winvalid-pch -Wno-endif-labels @gol
218 -Wno-invalid-offsetof @gol
219 -Wlarger-than-@var{len} -Wlong-long @gol
220 -Wmain -Wmissing-braces @gol
221 -Wmissing-format-attribute -Wmissing-noreturn @gol
222 -Wno-multichar -Wno-format-extra-args -Wno-format-y2k @gol
223 -Wno-import -Wnonnull -Wpacked -Wpadded @gol
224 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
225 -Wreturn-type -Wsequence-point -Wshadow @gol
226 -Wsign-compare -Wstrict-aliasing @gol
227 -Wswitch -Wswitch-default -Wswitch-enum @gol
228 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
229 -Wunknown-pragmas -Wunreachable-code @gol
230 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
231 -Wunused-value -Wunused-variable -Wwrite-strings}
233 @item C-only Warning Options
234 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
235 -Wmissing-prototypes -Wnested-externs @gol
236 -Wstrict-prototypes -Wtraditional}
238 @item Debugging Options
239 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
240 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
241 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
242 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
243 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
244 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
245 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
246 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
247 -fmem-report -fprofile-arcs @gol
248 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
249 -ftest-coverage -ftime-report @gol
250 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
251 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
252 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
253 -print-multi-directory -print-multi-lib @gol
254 -print-prog-name=@var{program} -print-search-dirs -Q @gol
257 @item Optimization Options
258 @xref{Optimize Options,,Options that Control Optimization}.
259 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
260 -falign-labels=@var{n} -falign-loops=@var{n} @gol
261 -fbranch-probabilities -fbranch-target-load-optimize @gol
262 -fbranch-target-load-optimize2 -fcaller-saves -fcprop-registers @gol
263 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
264 -fdelayed-branch -fdelete-null-pointer-checks @gol
265 -fexpensive-optimizations -ffast-math -ffloat-store @gol
266 -fforce-addr -fforce-mem -ffunction-sections @gol
267 -fgcse -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping @gol
268 -fif-conversion -fif-conversion2 @gol
269 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
270 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
271 -fmove-all-movables -fnew-ra -fno-branch-count-reg @gol
272 -fno-default-inline -fno-defer-pop @gol
273 -fno-function-cse -fno-guess-branch-probability @gol
274 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
275 -funsafe-math-optimizations -ffinite-math-only @gol
276 -fno-trapping-math -fno-zero-initialized-in-bss @gol
277 -fomit-frame-pointer -foptimize-register-move @gol
278 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
279 -freduce-all-givs -fregmove -frename-registers @gol
280 -freorder-blocks -freorder-functions @gol
281 -frerun-cse-after-loop -frerun-loop-opt @gol
282 -fschedule-insns -fschedule-insns2 @gol
283 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
284 -fsched-spec-load-dangerous -fsched2-use-superblocks @gol
285 -fsched2-use-traces -fsignaling-nans @gol
286 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
287 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
288 -funroll-all-loops -funroll-loops -fpeel-loops @gol
289 -funswitch-loops -fold-unroll-loops -fold-unroll-all-loops @gol
290 --param @var{name}=@var{value}
291 -O -O0 -O1 -O2 -O3 -Os}
293 @item Preprocessor Options
294 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
295 @gccoptlist{-A@var{question}=@var{answer} @gol
296 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
297 -C -dD -dI -dM -dN @gol
298 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
299 -idirafter @var{dir} @gol
300 -include @var{file} -imacros @var{file} @gol
301 -iprefix @var{file} -iwithprefix @var{dir} @gol
302 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
303 -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -remap @gol
304 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
305 -Xpreprocessor @var{option}}
307 @item Assembler Option
308 @xref{Assembler Options,,Passing Options to the Assembler}.
309 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
312 @xref{Link Options,,Options for Linking}.
313 @gccoptlist{@var{object-file-name} -l@var{library} @gol
314 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
315 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
316 -Wl,@var{option} -Xlinker @var{option} @gol
319 @item Directory Options
320 @xref{Directory Options,,Options for Directory Search}.
321 @gccoptlist{-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
324 @c I wrote this xref this way to avoid overfull hbox. -- rms
325 @xref{Target Options}.
326 @gccoptlist{-V @var{version} -b @var{machine}}
328 @item Machine Dependent Options
329 @xref{Submodel Options,,Hardware Models and Configurations}.
331 @emph{M680x0 Options}
332 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
333 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
334 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
335 -malign-int -mstrict-align}
337 @emph{M68hc1x Options}
338 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
339 -mauto-incdec -minmax -mlong-calls -mshort @gol
340 -msoft-reg-count=@var{count}}
343 @gccoptlist{-mg -mgnu -munix}
346 @gccoptlist{-mcpu=@var{cpu-type} @gol
347 -mtune=@var{cpu-type} @gol
348 -mcmodel=@var{code-model} @gol
350 -mapp-regs -mbroken-saverestore -mcypress @gol
351 -mfaster-structs -mflat @gol
352 -mfpu -mhard-float -mhard-quad-float @gol
353 -mimpure-text -mlive-g0 -mno-app-regs @gol
354 -mno-faster-structs -mno-flat -mno-fpu @gol
355 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
356 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
357 -msupersparc -munaligned-doubles -mv8}
360 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
361 -mapcs-26 -mapcs-32 @gol
362 -mapcs-stack-check -mno-apcs-stack-check @gol
363 -mapcs-float -mno-apcs-float @gol
364 -mapcs-reentrant -mno-apcs-reentrant @gol
365 -msched-prolog -mno-sched-prolog @gol
366 -mlittle-endian -mbig-endian -mwords-little-endian @gol
367 -malignment-traps -mno-alignment-traps @gol
368 -msoft-float -mhard-float -mfpe @gol
369 -mthumb-interwork -mno-thumb-interwork @gol
370 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
371 -mstructure-size-boundary=@var{n} @gol
372 -mabort-on-noreturn @gol
373 -mlong-calls -mno-long-calls @gol
374 -msingle-pic-base -mno-single-pic-base @gol
375 -mpic-register=@var{reg} @gol
376 -mnop-fun-dllimport @gol
377 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
378 -mpoke-function-name @gol
380 -mtpcs-frame -mtpcs-leaf-frame @gol
381 -mcaller-super-interworking -mcallee-super-interworking}
383 @emph{MN10200 Options}
386 @emph{MN10300 Options}
387 @gccoptlist{-mmult-bug -mno-mult-bug @gol
388 -mam33 -mno-am33 @gol
391 @emph{M32R/D Options}
392 @gccoptlist{-m32rx -m32r -mcode-model=@var{model-type} @gol
393 -msdata=@var{sdata-type} -G @var{num}}
396 @gccoptlist{-m88000 -m88100 -m88110 -mbig-pic @gol
397 -mcheck-zero-division -mhandle-large-shift @gol
398 -midentify-revision -mno-check-zero-division @gol
399 -mno-ocs-debug-info -mno-ocs-frame-position @gol
400 -mno-optimize-arg-area -mno-serialize-volatile @gol
401 -mno-underscores -mocs-debug-info @gol
402 -mocs-frame-position -moptimize-arg-area @gol
403 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
404 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
405 -mversion-03.00 -mwarn-passed-structs}
407 @emph{RS/6000 and PowerPC Options}
408 @gccoptlist{-mcpu=@var{cpu-type} @gol
409 -mtune=@var{cpu-type} @gol
410 -mpower -mno-power -mpower2 -mno-power2 @gol
411 -mpowerpc -mpowerpc64 -mno-powerpc @gol
412 -maltivec -mno-altivec @gol
413 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
414 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
415 -mnew-mnemonics -mold-mnemonics @gol
416 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
417 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
418 -malign-power -malign-natural @gol
419 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
420 -mstring -mno-string -mupdate -mno-update @gol
421 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
422 -mstrict-align -mno-strict-align -mrelocatable @gol
423 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
424 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
425 -mdynamic-no-pic @gol
426 -mcall-sysv -mcall-netbsd @gol
427 -maix-struct-return -msvr4-struct-return @gol
428 -mabi=altivec -mabi=no-altivec @gol
429 -mabi=spe -mabi=no-spe @gol
430 -misel=yes -misel=no @gol
431 -mspe=yes -mspe=no @gol
432 -mfloat-gprs=yes -mfloat-gprs=no @gol
433 -mprototype -mno-prototype @gol
434 -msim -mmvme -mads -myellowknife -memb -msdata @gol
435 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
437 @emph{Darwin Options}
438 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
439 -arch_only -bind_at_load -bundle -bundle_loader @gol
440 -client_name -compatibility_version -current_version @gol
441 -dependency-file -dylib_file -dylinker_install_name @gol
442 -dynamic -dynamiclib -exported_symbols_list @gol
443 -filelist -flat_namespace -force_cpusubtype_ALL @gol
444 -force_flat_namespace -headerpad_max_install_names @gol
445 -image_base -init -install_name -keep_private_externs @gol
446 -multi_module -multiply_defined -multiply_defined_unused @gol
447 -noall_load -nomultidefs -noprebind -noseglinkedit @gol
448 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
449 -private_bundle -read_only_relocs -sectalign @gol
450 -sectobjectsymbols -whyload -seg1addr @gol
451 -sectcreate -sectobjectsymbols -sectorder @gol
452 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
453 -segprot -segs_read_only_addr -segs_read_write_addr @gol
454 -single_module -static -sub_library -sub_umbrella @gol
455 -twolevel_namespace -umbrella -undefined @gol
456 -unexported_symbols_list -weak_reference_mismatches @gol
460 @gccoptlist{-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
461 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
462 -mminimum-fp-blocks -mnohc-struct-return}
465 @gccoptlist{-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
466 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
467 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
468 -mgas -mgp32 -mgp64 @gol
469 -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 @gol
470 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
471 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
472 -mmips-as -mmips-tfile -mno-abicalls @gol
473 -mno-embedded-data -mno-uninit-const-in-rodata @gol
474 -mno-embedded-pic -mno-gpopt -mno-long-calls @gol
475 -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats @gol
476 -mrnames -msoft-float @gol
477 -m4650 -msingle-float -mmad @gol
478 -EL -EB -G @var{num} -nocpp @gol
479 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi -mabi-fake-default @gol
480 -mfix7000 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
481 -mbranch-likely -mno-branch-likely}
483 @emph{i386 and x86-64 Options}
484 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
485 -mfpmath=@var{unit} @gol
486 -masm=@var{dialect} -mno-fancy-math-387 @gol
487 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
488 -mno-wide-multiply -mrtd -malign-double @gol
489 -mpreferred-stack-boundary=@var{num} @gol
490 -mmmx -msse -msse2 -m3dnow @gol
491 -mthreads -mno-align-stringops -minline-all-stringops @gol
492 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
493 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
494 -mno-red-zone -mno-tls-direct-seg-refs @gol
495 -mcmodel=@var{code-model} @gol
499 @gccoptlist{-march=@var{architecture-type} @gol
500 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
501 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
502 -mjump-in-delay -mlinker-opt -mlong-calls @gol
503 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
504 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
505 -mno-jump-in-delay -mno-long-load-store @gol
506 -mno-portable-runtime -mno-soft-float @gol
507 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
508 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
509 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
510 -nolibdld -static -threads}
512 @emph{Intel 960 Options}
513 @gccoptlist{-m@var{cpu-type} -masm-compat -mclean-linkage @gol
514 -mcode-align -mcomplex-addr -mleaf-procedures @gol
515 -mic-compat -mic2.0-compat -mic3.0-compat @gol
516 -mintel-asm -mno-clean-linkage -mno-code-align @gol
517 -mno-complex-addr -mno-leaf-procedures @gol
518 -mno-old-align -mno-strict-align -mno-tail-call @gol
519 -mnumerics -mold-align -msoft-float -mstrict-align @gol
522 @emph{DEC Alpha Options}
523 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
524 -mieee -mieee-with-inexact -mieee-conformant @gol
525 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
526 -mtrap-precision=@var{mode} -mbuild-constants @gol
527 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
528 -mbwx -mmax -mfix -mcix @gol
529 -mfloat-vax -mfloat-ieee @gol
530 -mexplicit-relocs -msmall-data -mlarge-data @gol
531 -msmall-text -mlarge-text @gol
532 -mmemory-latency=@var{time}}
534 @emph{DEC Alpha/VMS Options}
535 @gccoptlist{-mvms-return-codes}
537 @emph{H8/300 Options}
538 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
541 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
542 -m4-nofpu -m4-single-only -m4-single -m4 @gol
543 -m5-64media -m5-64media-nofpu @gol
544 -m5-32media -m5-32media-nofpu @gol
545 -m5-compact -m5-compact-nofpu @gol
546 -mb -ml -mdalign -mrelax @gol
547 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
548 -mieee -misize -mpadstruct -mspace @gol
549 -mprefergot -musermode}
551 @emph{System V Options}
552 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
555 @gccoptlist{-EB -EL @gol
556 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
557 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
559 @emph{TMS320C3x/C4x Options}
560 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
561 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
562 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
563 -mparallel-insns -mparallel-mpy -mpreserve-float}
566 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
567 -mprolog-function -mno-prolog-function -mspace @gol
568 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
569 -mapp-regs -mno-app-regs @gol
570 -mdisable-callt -mno-disable-callt @gol
575 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
576 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
577 -mregparam -mnoregparam -msb -mnosb @gol
578 -mbitfield -mnobitfield -mhimem -mnohimem}
581 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
582 -mcall-prologues -mno-tablejump -mtiny-stack}
585 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
586 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
587 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
588 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
589 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
592 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
593 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
594 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
595 -mno-base-addresses -msingle-exit -mno-single-exit}
598 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
599 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
600 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
601 -minline-float-divide-max-throughput @gol
602 -minline-int-divide-min-latency @gol
603 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
604 -mfixed-range=@var{register-range}}
607 @gccoptlist{-mextmem -mextmemory -monchip -mno-asm-optimize @gol
608 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
610 @emph{S/390 and zSeries Options}
611 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
612 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
613 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
614 -m64 -m31 -mdebug -mno-debug -mesa -mzarch}
617 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
618 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
619 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
620 -mstack-align -mdata-align -mconst-align @gol
621 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
622 -melf -maout -melinux -mlinux -sim -sim2}
624 @emph{PDP-11 Options}
625 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
626 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
627 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
628 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
629 -mbranch-expensive -mbranch-cheap @gol
630 -msplit -mno-split -munix-asm -mdec-asm}
632 @emph{Xstormy16 Options}
635 @emph{Xtensa Options}
636 @gccoptlist{-mbig-endian -mlittle-endian @gol
637 -mdensity -mno-density @gol
638 -mconst16 -mno-const16 @gol
640 -maddx -mno-addx @gol
641 -mmac16 -mno-mac16 @gol
642 -mmul16 -mno-mul16 @gol
643 -mmul32 -mno-mul32 @gol
645 -mminmax -mno-minmax @gol
646 -msext -mno-sext @gol
647 -mbooleans -mno-booleans @gol
648 -mhard-float -msoft-float @gol
649 -mfused-madd -mno-fused-madd @gol
650 -mtext-section-literals -mno-text-section-literals @gol
651 -mtarget-align -mno-target-align @gol
652 -mlongcalls -mno-longcalls}
655 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
656 -mhard-float -msoft-float @gol
657 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
658 -mdouble -mno-double @gol
659 -mmedia -mno-media -mmuladd -mno-muladd @gol
660 -mlibrary-pic -macc-4 -macc-8 @gol
661 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
662 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
663 -mvliw-branch -mno-vliw-branch @gol
664 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
665 -mno-nested-cond-exec -mtomcat-stats @gol
668 @item Code Generation Options
669 @xref{Code Gen Options,,Options for Code Generation Conventions}.
670 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
671 -ffixed-@var{reg} -fexceptions @gol
672 -fnon-call-exceptions -funwind-tables @gol
673 -fasynchronous-unwind-tables @gol
674 -finhibit-size-directive -finstrument-functions @gol
675 -fno-common -fno-ident -fno-gnu-linker @gol
676 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
677 -freg-struct-return -fshared-data -fshort-enums @gol
678 -fshort-double -fshort-wchar @gol
679 -fverbose-asm -fpack-struct -fstack-check @gol
680 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
681 -fargument-alias -fargument-noalias @gol
682 -fargument-noalias-global -fleading-underscore @gol
683 -ftls-model=@var{model} @gol
684 -ftrapv -fwrapv -fbounds-check}
688 * Overall Options:: Controlling the kind of output:
689 an executable, object files, assembler files,
690 or preprocessed source.
691 * C Dialect Options:: Controlling the variant of C language compiled.
692 * C++ Dialect Options:: Variations on C++.
693 * Objective-C Dialect Options:: Variations on Objective-C.
694 * Language Independent Options:: Controlling how diagnostics should be
696 * Warning Options:: How picky should the compiler be?
697 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
698 * Optimize Options:: How much optimization?
699 * Preprocessor Options:: Controlling header files and macro definitions.
700 Also, getting dependency information for Make.
701 * Assembler Options:: Passing options to the assembler.
702 * Link Options:: Specifying libraries and so on.
703 * Directory Options:: Where to find header files and libraries.
704 Where to find the compiler executable files.
705 * Spec Files:: How to pass switches to sub-processes.
706 * Target Options:: Running a cross-compiler, or an old version of GCC.
709 @node Overall Options
710 @section Options Controlling the Kind of Output
712 Compilation can involve up to four stages: preprocessing, compilation
713 proper, assembly and linking, always in that order. The first three
714 stages apply to an individual source file, and end by producing an
715 object file; linking combines all the object files (those newly
716 compiled, and those specified as input) into an executable file.
718 @cindex file name suffix
719 For any given input file, the file name suffix determines what kind of
724 C source code which must be preprocessed.
727 C source code which should not be preprocessed.
730 C++ source code which should not be preprocessed.
733 Objective-C source code. Note that you must link with the library
734 @file{libobjc.a} to make an Objective-C program work.
737 Objective-C source code which should not be preprocessed.
740 C or C++ header file to be turned into a precompiled header.
744 @itemx @var{file}.cxx
745 @itemx @var{file}.cpp
746 @itemx @var{file}.CPP
747 @itemx @var{file}.c++
749 C++ source code which must be preprocessed. Note that in @samp{.cxx},
750 the last two letters must both be literally @samp{x}. Likewise,
751 @samp{.C} refers to a literal capital C@.
755 C++ header file to be turned into a precompiled header.
758 @itemx @var{file}.for
759 @itemx @var{file}.FOR
760 Fortran source code which should not be preprocessed.
763 @itemx @var{file}.fpp
764 @itemx @var{file}.FPP
765 Fortran source code which must be preprocessed (with the traditional
769 Fortran source code which must be preprocessed with a RATFOR
770 preprocessor (not included with GCC)@.
772 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
773 Using and Porting GNU Fortran}, for more details of the handling of
776 @c FIXME: Descriptions of Java file types.
783 Ada source code file which contains a library unit declaration (a
784 declaration of a package, subprogram, or generic, or a generic
785 instantiation), or a library unit renaming declaration (a package,
786 generic, or subprogram renaming declaration). Such files are also
789 @itemx @var{file}.adb
790 Ada source code file containing a library unit body (a subprogram or
791 package body). Such files are also called @dfn{bodies}.
793 @c GCC also knows about some suffixes for languages not yet included:
802 Assembler code which must be preprocessed.
805 An object file to be fed straight into linking.
806 Any file name with no recognized suffix is treated this way.
810 You can specify the input language explicitly with the @option{-x} option:
813 @item -x @var{language}
814 Specify explicitly the @var{language} for the following input files
815 (rather than letting the compiler choose a default based on the file
816 name suffix). This option applies to all following input files until
817 the next @option{-x} option. Possible values for @var{language} are:
819 c c-header cpp-output
820 c++ c++-header c++-cpp-output
821 objective-c objective-c-header objc-cpp-output
822 assembler assembler-with-cpp
824 f77 f77-cpp-input ratfor
830 Turn off any specification of a language, so that subsequent files are
831 handled according to their file name suffixes (as they are if @option{-x}
832 has not been used at all).
834 @item -pass-exit-codes
835 @opindex pass-exit-codes
836 Normally the @command{gcc} program will exit with the code of 1 if any
837 phase of the compiler returns a non-success return code. If you specify
838 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
839 numerically highest error produced by any phase that returned an error
843 If you only want some of the stages of compilation, you can use
844 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
845 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
846 @command{gcc} is to stop. Note that some combinations (for example,
847 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
852 Compile or assemble the source files, but do not link. The linking
853 stage simply is not done. The ultimate output is in the form of an
854 object file for each source file.
856 By default, the object file name for a source file is made by replacing
857 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
859 Unrecognized input files, not requiring compilation or assembly, are
864 Stop after the stage of compilation proper; do not assemble. The output
865 is in the form of an assembler code file for each non-assembler input
868 By default, the assembler file name for a source file is made by
869 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
871 Input files that don't require compilation are ignored.
875 Stop after the preprocessing stage; do not run the compiler proper. The
876 output is in the form of preprocessed source code, which is sent to the
879 Input files which don't require preprocessing are ignored.
881 @cindex output file option
884 Place output in file @var{file}. This applies regardless to whatever
885 sort of output is being produced, whether it be an executable file,
886 an object file, an assembler file or preprocessed C code.
888 Since only one output file can be specified, it does not make sense to
889 use @option{-o} when compiling more than one input file, unless you are
890 producing an executable file as output.
892 If @option{-o} is not specified, the default is to put an executable file
893 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
894 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
895 all preprocessed C source on standard output.
899 Print (on standard error output) the commands executed to run the stages
900 of compilation. Also print the version number of the compiler driver
901 program and of the preprocessor and the compiler proper.
905 Like @option{-v} except the commands are not executed and all command
906 arguments are quoted. This is useful for shell scripts to capture the
907 driver-generated command lines.
911 Use pipes rather than temporary files for communication between the
912 various stages of compilation. This fails to work on some systems where
913 the assembler is unable to read from a pipe; but the GNU assembler has
918 Print (on the standard output) a description of the command line options
919 understood by @command{gcc}. If the @option{-v} option is also specified
920 then @option{--help} will also be passed on to the various processes
921 invoked by @command{gcc}, so that they can display the command line options
922 they accept. If the @option{-Wextra} option is also specified then command
923 line options which have no documentation associated with them will also
928 Print (on the standard output) a description of target specific command
929 line options for each tool.
933 Display the version number and copyrights of the invoked GCC.
937 @section Compiling C++ Programs
939 @cindex suffixes for C++ source
940 @cindex C++ source file suffixes
941 C++ source files conventionally use one of the suffixes @samp{.C},
942 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
943 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
944 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
945 files with these names and compiles them as C++ programs even if you
946 call the compiler the same way as for compiling C programs (usually
947 with the name @command{gcc}).
951 However, C++ programs often require class libraries as well as a
952 compiler that understands the C++ language---and under some
953 circumstances, you might want to compile programs or header files from
954 standard input, or otherwise without a suffix that flags them as C++
955 programs. You might also like to precompile a C header file with a
956 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
957 program that calls GCC with the default language set to C++, and
958 automatically specifies linking against the C++ library. On many
959 systems, @command{g++} is also installed with the name @command{c++}.
961 @cindex invoking @command{g++}
962 When you compile C++ programs, you may specify many of the same
963 command-line options that you use for compiling programs in any
964 language; or command-line options meaningful for C and related
965 languages; or options that are meaningful only for C++ programs.
966 @xref{C Dialect Options,,Options Controlling C Dialect}, for
967 explanations of options for languages related to C@.
968 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
969 explanations of options that are meaningful only for C++ programs.
971 @node C Dialect Options
972 @section Options Controlling C Dialect
973 @cindex dialect options
974 @cindex language dialect options
975 @cindex options, dialect
977 The following options control the dialect of C (or languages derived
978 from C, such as C++ and Objective-C) that the compiler accepts:
985 In C mode, support all ISO C90 programs. In C++ mode,
986 remove GNU extensions that conflict with ISO C++.
988 This turns off certain features of GCC that are incompatible with ISO
989 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
990 such as the @code{asm} and @code{typeof} keywords, and
991 predefined macros such as @code{unix} and @code{vax} that identify the
992 type of system you are using. It also enables the undesirable and
993 rarely used ISO trigraph feature. For the C compiler,
994 it disables recognition of C++ style @samp{//} comments as well as
995 the @code{inline} keyword.
997 The alternate keywords @code{__asm__}, @code{__extension__},
998 @code{__inline__} and @code{__typeof__} continue to work despite
999 @option{-ansi}. You would not want to use them in an ISO C program, of
1000 course, but it is useful to put them in header files that might be included
1001 in compilations done with @option{-ansi}. Alternate predefined macros
1002 such as @code{__unix__} and @code{__vax__} are also available, with or
1003 without @option{-ansi}.
1005 The @option{-ansi} option does not cause non-ISO programs to be
1006 rejected gratuitously. For that, @option{-pedantic} is required in
1007 addition to @option{-ansi}. @xref{Warning Options}.
1009 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1010 option is used. Some header files may notice this macro and refrain
1011 from declaring certain functions or defining certain macros that the
1012 ISO standard doesn't call for; this is to avoid interfering with any
1013 programs that might use these names for other things.
1015 Functions which would normally be built in but do not have semantics
1016 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1017 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1018 built-in functions provided by GCC}, for details of the functions
1023 Determine the language standard. This option is currently only
1024 supported when compiling C or C++. A value for this option must be
1025 provided; possible values are
1030 ISO C90 (same as @option{-ansi}).
1032 @item iso9899:199409
1033 ISO C90 as modified in amendment 1.
1039 ISO C99. Note that this standard is not yet fully supported; see
1040 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1041 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1044 Default, ISO C90 plus GNU extensions (including some C99 features).
1048 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1049 this will become the default. The name @samp{gnu9x} is deprecated.
1052 The 1998 ISO C++ standard plus amendments.
1055 The same as @option{-std=c++98} plus GNU extensions. This is the
1056 default for C++ code.
1059 Even when this option is not specified, you can still use some of the
1060 features of newer standards in so far as they do not conflict with
1061 previous C standards. For example, you may use @code{__restrict__} even
1062 when @option{-std=c99} is not specified.
1064 The @option{-std} options specifying some version of ISO C have the same
1065 effects as @option{-ansi}, except that features that were not in ISO C90
1066 but are in the specified version (for example, @samp{//} comments and
1067 the @code{inline} keyword in ISO C99) are not disabled.
1069 @xref{Standards,,Language Standards Supported by GCC}, for details of
1070 these standard versions.
1072 @item -aux-info @var{filename}
1074 Output to the given filename prototyped declarations for all functions
1075 declared and/or defined in a translation unit, including those in header
1076 files. This option is silently ignored in any language other than C@.
1078 Besides declarations, the file indicates, in comments, the origin of
1079 each declaration (source file and line), whether the declaration was
1080 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1081 @samp{O} for old, respectively, in the first character after the line
1082 number and the colon), and whether it came from a declaration or a
1083 definition (@samp{C} or @samp{F}, respectively, in the following
1084 character). In the case of function definitions, a K&R-style list of
1085 arguments followed by their declarations is also provided, inside
1086 comments, after the declaration.
1090 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1091 keyword, so that code can use these words as identifiers. You can use
1092 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1093 instead. @option{-ansi} implies @option{-fno-asm}.
1095 In C++, this switch only affects the @code{typeof} keyword, since
1096 @code{asm} and @code{inline} are standard keywords. You may want to
1097 use the @option{-fno-gnu-keywords} flag instead, which has the same
1098 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1099 switch only affects the @code{asm} and @code{typeof} keywords, since
1100 @code{inline} is a standard keyword in ISO C99.
1103 @itemx -fno-builtin-@var{function}
1104 @opindex fno-builtin
1105 @cindex built-in functions
1106 Don't recognize built-in functions that do not begin with
1107 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1108 functions provided by GCC}, for details of the functions affected,
1109 including those which are not built-in functions when @option{-ansi} or
1110 @option{-std} options for strict ISO C conformance are used because they
1111 do not have an ISO standard meaning.
1113 GCC normally generates special code to handle certain built-in functions
1114 more efficiently; for instance, calls to @code{alloca} may become single
1115 instructions that adjust the stack directly, and calls to @code{memcpy}
1116 may become inline copy loops. The resulting code is often both smaller
1117 and faster, but since the function calls no longer appear as such, you
1118 cannot set a breakpoint on those calls, nor can you change the behavior
1119 of the functions by linking with a different library.
1121 With the @option{-fno-builtin-@var{function}} option
1122 only the built-in function @var{function} is
1123 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1124 function is named this is not built-in in this version of GCC, this
1125 option is ignored. There is no corresponding
1126 @option{-fbuiltin-@var{function}} option; if you wish to enable
1127 built-in functions selectively when using @option{-fno-builtin} or
1128 @option{-ffreestanding}, you may define macros such as:
1131 #define abs(n) __builtin_abs ((n))
1132 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1137 @cindex hosted environment
1139 Assert that compilation takes place in a hosted environment. This implies
1140 @option{-fbuiltin}. A hosted environment is one in which the
1141 entire standard library is available, and in which @code{main} has a return
1142 type of @code{int}. Examples are nearly everything except a kernel.
1143 This is equivalent to @option{-fno-freestanding}.
1145 @item -ffreestanding
1146 @opindex ffreestanding
1147 @cindex hosted environment
1149 Assert that compilation takes place in a freestanding environment. This
1150 implies @option{-fno-builtin}. A freestanding environment
1151 is one in which the standard library may not exist, and program startup may
1152 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1153 This is equivalent to @option{-fno-hosted}.
1155 @xref{Standards,,Language Standards Supported by GCC}, for details of
1156 freestanding and hosted environments.
1158 @item -fms-extensions
1159 @opindex fms-extensions
1160 Accept some non-standard constructs used in Microsoft header files.
1164 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1165 options for strict ISO C conformance) implies @option{-trigraphs}.
1167 @item -no-integrated-cpp
1168 @opindex no-integrated-cpp
1169 Performs a compilation in two passes: preprocessing and compiling. This
1170 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1171 @option{-B} option. The user supplied compilation step can then add in
1172 an additional preprocessing step after normal preprocessing but before
1173 compiling. The default is to use the integrated cpp (internal cpp)
1175 The semantics of this option will change if "cc1", "cc1plus", and
1176 "cc1obj" are merged.
1178 @cindex traditional C language
1179 @cindex C language, traditional
1181 @itemx -traditional-cpp
1182 @opindex traditional-cpp
1183 @opindex traditional
1184 Formerly, these options caused GCC to attempt to emulate a pre-standard
1185 C compiler. They are now only supported with the @option{-E} switch.
1186 The preprocessor continues to support a pre-standard mode. See the GNU
1187 CPP manual for details.
1189 @item -fcond-mismatch
1190 @opindex fcond-mismatch
1191 Allow conditional expressions with mismatched types in the second and
1192 third arguments. The value of such an expression is void. This option
1193 is not supported for C++.
1195 @item -funsigned-char
1196 @opindex funsigned-char
1197 Let the type @code{char} be unsigned, like @code{unsigned char}.
1199 Each kind of machine has a default for what @code{char} should
1200 be. It is either like @code{unsigned char} by default or like
1201 @code{signed char} by default.
1203 Ideally, a portable program should always use @code{signed char} or
1204 @code{unsigned char} when it depends on the signedness of an object.
1205 But many programs have been written to use plain @code{char} and
1206 expect it to be signed, or expect it to be unsigned, depending on the
1207 machines they were written for. This option, and its inverse, let you
1208 make such a program work with the opposite default.
1210 The type @code{char} is always a distinct type from each of
1211 @code{signed char} or @code{unsigned char}, even though its behavior
1212 is always just like one of those two.
1215 @opindex fsigned-char
1216 Let the type @code{char} be signed, like @code{signed char}.
1218 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1219 the negative form of @option{-funsigned-char}. Likewise, the option
1220 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1222 @item -fsigned-bitfields
1223 @itemx -funsigned-bitfields
1224 @itemx -fno-signed-bitfields
1225 @itemx -fno-unsigned-bitfields
1226 @opindex fsigned-bitfields
1227 @opindex funsigned-bitfields
1228 @opindex fno-signed-bitfields
1229 @opindex fno-unsigned-bitfields
1230 These options control whether a bit-field is signed or unsigned, when the
1231 declaration does not use either @code{signed} or @code{unsigned}. By
1232 default, such a bit-field is signed, because this is consistent: the
1233 basic integer types such as @code{int} are signed types.
1235 @item -fwritable-strings
1236 @opindex fwritable-strings
1237 Store string constants in the writable data segment and don't uniquize
1238 them. This is for compatibility with old programs which assume they can
1239 write into string constants.
1241 Writing into string constants is a very bad idea; ``constants'' should
1245 @node C++ Dialect Options
1246 @section Options Controlling C++ Dialect
1248 @cindex compiler options, C++
1249 @cindex C++ options, command line
1250 @cindex options, C++
1251 This section describes the command-line options that are only meaningful
1252 for C++ programs; but you can also use most of the GNU compiler options
1253 regardless of what language your program is in. For example, you
1254 might compile a file @code{firstClass.C} like this:
1257 g++ -g -frepo -O -c firstClass.C
1261 In this example, only @option{-frepo} is an option meant
1262 only for C++ programs; you can use the other options with any
1263 language supported by GCC@.
1265 Here is a list of options that are @emph{only} for compiling C++ programs:
1269 @item -fabi-version=@var{n}
1270 @opindex fabi-version
1271 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1272 ABI that first appeared in G++ 3.2. Version 0 will always be the
1273 version that conforms most closely to the C++ ABI specification.
1274 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1277 The default is version 1.
1279 @item -fno-access-control
1280 @opindex fno-access-control
1281 Turn off all access checking. This switch is mainly useful for working
1282 around bugs in the access control code.
1286 Check that the pointer returned by @code{operator new} is non-null
1287 before attempting to modify the storage allocated. This check is
1288 normally unnecessary because the C++ standard specifies that
1289 @code{operator new} will only return @code{0} if it is declared
1290 @samp{throw()}, in which case the compiler will always check the
1291 return value even without this option. In all other cases, when
1292 @code{operator new} has a non-empty exception specification, memory
1293 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1294 @samp{new (nothrow)}.
1296 @item -fconserve-space
1297 @opindex fconserve-space
1298 Put uninitialized or runtime-initialized global variables into the
1299 common segment, as C does. This saves space in the executable at the
1300 cost of not diagnosing duplicate definitions. If you compile with this
1301 flag and your program mysteriously crashes after @code{main()} has
1302 completed, you may have an object that is being destroyed twice because
1303 two definitions were merged.
1305 This option is no longer useful on most targets, now that support has
1306 been added for putting variables into BSS without making them common.
1308 @item -fno-const-strings
1309 @opindex fno-const-strings
1310 Give string constants type @code{char *} instead of type @code{const
1311 char *}. By default, G++ uses type @code{const char *} as required by
1312 the standard. Even if you use @option{-fno-const-strings}, you cannot
1313 actually modify the value of a string constant, unless you also use
1314 @option{-fwritable-strings}.
1316 This option might be removed in a future release of G++. For maximum
1317 portability, you should structure your code so that it works with
1318 string constants that have type @code{const char *}.
1320 @item -fno-elide-constructors
1321 @opindex fno-elide-constructors
1322 The C++ standard allows an implementation to omit creating a temporary
1323 which is only used to initialize another object of the same type.
1324 Specifying this option disables that optimization, and forces G++ to
1325 call the copy constructor in all cases.
1327 @item -fno-enforce-eh-specs
1328 @opindex fno-enforce-eh-specs
1329 Don't check for violation of exception specifications at runtime. This
1330 option violates the C++ standard, but may be useful for reducing code
1331 size in production builds, much like defining @samp{NDEBUG}. The compiler
1332 will still optimize based on the exception specifications.
1334 @item -fexternal-templates
1335 @opindex fexternal-templates
1337 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1338 template instantiation; template instances are emitted or not according
1339 to the location of the template definition. @xref{Template
1340 Instantiation}, for more information.
1342 This option is deprecated.
1344 @item -falt-external-templates
1345 @opindex falt-external-templates
1346 Similar to @option{-fexternal-templates}, but template instances are
1347 emitted or not according to the place where they are first instantiated.
1348 @xref{Template Instantiation}, for more information.
1350 This option is deprecated.
1353 @itemx -fno-for-scope
1355 @opindex fno-for-scope
1356 If @option{-ffor-scope} is specified, the scope of variables declared in
1357 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1358 as specified by the C++ standard.
1359 If @option{-fno-for-scope} is specified, the scope of variables declared in
1360 a @i{for-init-statement} extends to the end of the enclosing scope,
1361 as was the case in old versions of G++, and other (traditional)
1362 implementations of C++.
1364 The default if neither flag is given to follow the standard,
1365 but to allow and give a warning for old-style code that would
1366 otherwise be invalid, or have different behavior.
1368 @item -fno-gnu-keywords
1369 @opindex fno-gnu-keywords
1370 Do not recognize @code{typeof} as a keyword, so that code can use this
1371 word as an identifier. You can use the keyword @code{__typeof__} instead.
1372 @option{-ansi} implies @option{-fno-gnu-keywords}.
1374 @item -fno-implicit-templates
1375 @opindex fno-implicit-templates
1376 Never emit code for non-inline templates which are instantiated
1377 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1378 @xref{Template Instantiation}, for more information.
1380 @item -fno-implicit-inline-templates
1381 @opindex fno-implicit-inline-templates
1382 Don't emit code for implicit instantiations of inline templates, either.
1383 The default is to handle inlines differently so that compiles with and
1384 without optimization will need the same set of explicit instantiations.
1386 @item -fno-implement-inlines
1387 @opindex fno-implement-inlines
1388 To save space, do not emit out-of-line copies of inline functions
1389 controlled by @samp{#pragma implementation}. This will cause linker
1390 errors if these functions are not inlined everywhere they are called.
1392 @item -fms-extensions
1393 @opindex fms-extensions
1394 Disable pedantic warnings about constructs used in MFC, such as implicit
1395 int and getting a pointer to member function via non-standard syntax.
1397 @item -fno-nonansi-builtins
1398 @opindex fno-nonansi-builtins
1399 Disable built-in declarations of functions that are not mandated by
1400 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1401 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1403 @item -fno-operator-names
1404 @opindex fno-operator-names
1405 Do not treat the operator name keywords @code{and}, @code{bitand},
1406 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1407 synonyms as keywords.
1409 @item -fno-optional-diags
1410 @opindex fno-optional-diags
1411 Disable diagnostics that the standard says a compiler does not need to
1412 issue. Currently, the only such diagnostic issued by G++ is the one for
1413 a name having multiple meanings within a class.
1416 @opindex fpermissive
1417 Downgrade messages about nonconformant code from errors to warnings. By
1418 default, G++ effectively sets @option{-pedantic-errors} without
1419 @option{-pedantic}; this option reverses that. This behavior and this
1420 option are superseded by @option{-pedantic}, which works as it does for GNU C@.
1424 Enable automatic template instantiation at link time. This option also
1425 implies @option{-fno-implicit-templates}. @xref{Template
1426 Instantiation}, for more information.
1430 Disable generation of information about every class with virtual
1431 functions for use by the C++ runtime type identification features
1432 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1433 of the language, you can save some space by using this flag. Note that
1434 exception handling uses the same information, but it will generate it as
1439 Emit statistics about front-end processing at the end of the compilation.
1440 This information is generally only useful to the G++ development team.
1442 @item -ftemplate-depth-@var{n}
1443 @opindex ftemplate-depth
1444 Set the maximum instantiation depth for template classes to @var{n}.
1445 A limit on the template instantiation depth is needed to detect
1446 endless recursions during template class instantiation. ANSI/ISO C++
1447 conforming programs must not rely on a maximum depth greater than 17.
1449 @item -fuse-cxa-atexit
1450 @opindex fuse-cxa-atexit
1451 Register destructors for objects with static storage duration with the
1452 @code{__cxa_atexit} function rather than the @code{atexit} function.
1453 This option is required for fully standards-compliant handling of static
1454 destructors, but will only work if your C library supports
1455 @code{__cxa_atexit}.
1459 Emit special relocations for vtables and virtual function references
1460 so that the linker can identify unused virtual functions and zero out
1461 vtable slots that refer to them. This is most useful with
1462 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1463 also discard the functions themselves.
1465 This optimization requires GNU as and GNU ld. Not all systems support
1466 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1470 Do not use weak symbol support, even if it is provided by the linker.
1471 By default, G++ will use weak symbols if they are available. This
1472 option exists only for testing, and should not be used by end-users;
1473 it will result in inferior code and has no benefits. This option may
1474 be removed in a future release of G++.
1478 Do not search for header files in the standard directories specific to
1479 C++, but do still search the other standard directories. (This option
1480 is used when building the C++ library.)
1483 In addition, these optimization, warning, and code generation options
1484 have meanings only for C++ programs:
1487 @item -fno-default-inline
1488 @opindex fno-default-inline
1489 Do not assume @samp{inline} for functions defined inside a class scope.
1490 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1491 functions will have linkage like inline functions; they just won't be
1494 @item -Wabi @r{(C++ only)}
1496 Warn when G++ generates code that is probably not compatible with the
1497 vendor-neutral C++ ABI. Although an effort has been made to warn about
1498 all such cases, there are probably some cases that are not warned about,
1499 even though G++ is generating incompatible code. There may also be
1500 cases where warnings are emitted even though the code that is generated
1503 You should rewrite your code to avoid these warnings if you are
1504 concerned about the fact that code generated by G++ may not be binary
1505 compatible with code generated by other compilers.
1507 The known incompatibilities at this point include:
1512 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1513 pack data into the same byte as a base class. For example:
1516 struct A @{ virtual void f(); int f1 : 1; @};
1517 struct B : public A @{ int f2 : 1; @};
1521 In this case, G++ will place @code{B::f2} into the same byte
1522 as@code{A::f1}; other compilers will not. You can avoid this problem
1523 by explicitly padding @code{A} so that its size is a multiple of the
1524 byte size on your platform; that will cause G++ and other compilers to
1525 layout @code{B} identically.
1528 Incorrect handling of tail-padding for virtual bases. G++ does not use
1529 tail padding when laying out virtual bases. For example:
1532 struct A @{ virtual void f(); char c1; @};
1533 struct B @{ B(); char c2; @};
1534 struct C : public A, public virtual B @{@};
1538 In this case, G++ will not place @code{B} into the tail-padding for
1539 @code{A}; other compilers will. You can avoid this problem by
1540 explicitly padding @code{A} so that its size is a multiple of its
1541 alignment (ignoring virtual base classes); that will cause G++ and other
1542 compilers to layout @code{C} identically.
1545 Incorrect handling of bit-fields with declared widths greater than that
1546 of their underlying types, when the bit-fields appear in a union. For
1550 union U @{ int i : 4096; @};
1554 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1555 union too small by the number of bits in an @code{int}.
1558 Empty classes can be placed at incorrect offsets. For example:
1568 struct C : public B, public A @{@};
1572 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1573 it should be placed at offset zero. G++ mistakenly believes that the
1574 @code{A} data member of @code{B} is already at offset zero.
1577 Names of template functions whose types involve @code{typename} or
1578 template template parameters can be mangled incorrectly.
1581 template <typename Q>
1582 void f(typename Q::X) @{@}
1584 template <template <typename> class Q>
1585 void f(typename Q<int>::X) @{@}
1589 Instantiations of these templates may be mangled incorrectly.
1593 @item -Wctor-dtor-privacy @r{(C++ only)}
1594 @opindex Wctor-dtor-privacy
1595 Warn when a class seems unusable, because all the constructors or
1596 destructors in a class are private and the class has no friends or
1597 public static member functions.
1599 @item -Wnon-virtual-dtor @r{(C++ only)}
1600 @opindex Wnon-virtual-dtor
1601 Warn when a class declares a non-virtual destructor that should probably
1602 be virtual, because it looks like the class will be used polymorphically.
1603 This warning is enabled by @option{-Wall}.
1605 @item -Wreorder @r{(C++ only)}
1607 @cindex reordering, warning
1608 @cindex warning for reordering of member initializers
1609 Warn when the order of member initializers given in the code does not
1610 match the order in which they must be executed. For instance:
1616 A(): j (0), i (1) @{ @}
1620 Here the compiler will warn that the member initializers for @samp{i}
1621 and @samp{j} will be rearranged to match the declaration order of the
1622 members. This warning is enabled by @option{-Wall}.
1625 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1628 @item -Weffc++ @r{(C++ only)}
1630 Warn about violations of the following style guidelines from Scott Meyers'
1631 @cite{Effective C++} book:
1635 Item 11: Define a copy constructor and an assignment operator for classes
1636 with dynamically allocated memory.
1639 Item 12: Prefer initialization to assignment in constructors.
1642 Item 14: Make destructors virtual in base classes.
1645 Item 15: Have @code{operator=} return a reference to @code{*this}.
1648 Item 23: Don't try to return a reference when you must return an object.
1652 and about violations of the following style guidelines from Scott Meyers'
1653 @cite{More Effective C++} book:
1657 Item 6: Distinguish between prefix and postfix forms of increment and
1658 decrement operators.
1661 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1665 If you use this option, you should be aware that the standard library
1666 headers do not obey all of these guidelines; you can use @samp{grep -v}
1667 to filter out those warnings.
1669 @item -Wno-deprecated @r{(C++ only)}
1670 @opindex Wno-deprecated
1671 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1673 @item -Wno-non-template-friend @r{(C++ only)}
1674 @opindex Wno-non-template-friend
1675 Disable warnings when non-templatized friend functions are declared
1676 within a template. With the advent of explicit template specification
1677 support in G++, if the name of the friend is an unqualified-id (i.e.,
1678 @samp{friend foo(int)}), the C++ language specification demands that the
1679 friend declare or define an ordinary, nontemplate function. (Section
1680 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1681 could be interpreted as a particular specialization of a templatized
1682 function. Because this non-conforming behavior is no longer the default
1683 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1684 check existing code for potential trouble spots, and is on by default.
1685 This new compiler behavior can be turned off with
1686 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1687 but disables the helpful warning.
1689 @item -Wold-style-cast @r{(C++ only)}
1690 @opindex Wold-style-cast
1691 Warn if an old-style (C-style) cast to a non-void type is used within
1692 a C++ program. The new-style casts (@samp{static_cast},
1693 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1694 unintended effects, and much easier to grep for.
1696 @item -Woverloaded-virtual @r{(C++ only)}
1697 @opindex Woverloaded-virtual
1698 @cindex overloaded virtual fn, warning
1699 @cindex warning for overloaded virtual fn
1700 Warn when a function declaration hides virtual functions from a
1701 base class. For example, in:
1708 struct B: public A @{
1713 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1721 will fail to compile.
1723 @item -Wno-pmf-conversions @r{(C++ only)}
1724 @opindex Wno-pmf-conversions
1725 Disable the diagnostic for converting a bound pointer to member function
1728 @item -Wsign-promo @r{(C++ only)}
1729 @opindex Wsign-promo
1730 Warn when overload resolution chooses a promotion from unsigned or
1731 enumeral type to a signed type over a conversion to an unsigned type of
1732 the same size. Previous versions of G++ would try to preserve
1733 unsignedness, but the standard mandates the current behavior.
1735 @item -Wsynth @r{(C++ only)}
1737 @cindex warning for synthesized methods
1738 @cindex synthesized methods, warning
1739 Warn when G++'s synthesis behavior does not match that of cfront. For
1745 A& operator = (int);
1755 In this example, G++ will synthesize a default @samp{A& operator =
1756 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1759 @node Objective-C Dialect Options
1760 @section Options Controlling Objective-C Dialect
1762 @cindex compiler options, Objective-C
1763 @cindex Objective-C options, command line
1764 @cindex options, Objective-C
1765 This section describes the command-line options that are only meaningful
1766 for Objective-C programs; but you can also use most of the GNU compiler
1767 options regardless of what language your program is in. For example,
1768 you might compile a file @code{some_class.m} like this:
1771 gcc -g -fgnu-runtime -O -c some_class.m
1775 In this example, only @option{-fgnu-runtime} is an option meant only for
1776 Objective-C programs; you can use the other options with any language
1779 Here is a list of options that are @emph{only} for compiling Objective-C
1783 @item -fconstant-string-class=@var{class-name}
1784 @opindex fconstant-string-class
1785 Use @var{class-name} as the name of the class to instantiate for each
1786 literal string specified with the syntax @code{@@"@dots{}"}. The default
1787 class name is @code{NXConstantString}.
1790 @opindex fgnu-runtime
1791 Generate object code compatible with the standard GNU Objective-C
1792 runtime. This is the default for most types of systems.
1794 @item -fnext-runtime
1795 @opindex fnext-runtime
1796 Generate output compatible with the NeXT runtime. This is the default
1797 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1798 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1803 Dump interface declarations for all classes seen in the source file to a
1804 file named @file{@var{sourcename}.decl}.
1807 @opindex Wno-protocol
1808 If a class is declared to implement a protocol, a warning is issued for
1809 every method in the protocol that is not implemented by the class. The
1810 default behavior is to issue a warning for every method not explicitly
1811 implemented in the class, even if a method implementation is inherited
1812 from the superclass. If you use the @code{-Wno-protocol} option, then
1813 methods inherited from the superclass are considered to be implemented,
1814 and no warning is issued for them.
1818 Warn if multiple methods of different types for the same selector are
1819 found during compilation. The check is performed on the list of methods
1820 in the final stage of compilation. Additionally, a check is performed
1821 that for each selector appearing in a @code{@@selector(@dots{})}
1822 expression, a corresponding method with that selector has been found
1823 during compilation. Because these checks scan the method table only at
1824 the end of compilation, these warnings are not produced if the final
1825 stage of compilation is not reached, for example because an error is
1826 found during compilation, or because the @code{-fsyntax-only} option is
1829 @item -Wundeclared-selector
1830 @opindex Wundeclared-selector
1831 Warn if a @code{@@selector(@dots{})} expression referring to an
1832 undeclared selector is found. A selector is considered undeclared if no
1833 method with that name has been declared (explicitly, in an
1834 @code{@@interface} or @code{@@protocol} declaration, or implicitly, in
1835 an @code{@@implementation} section) before the
1836 @code{@@selector(@dots{})} expression. This option always performs its
1837 checks as soon as a @code{@@selector(@dots{})} expression is found
1838 (while @code{-Wselector} only performs its checks in the final stage of
1839 compilation), and so additionally enforces the coding style convention
1840 that methods and selectors must be declared before being used.
1842 @c not documented because only avail via -Wp
1843 @c @item -print-objc-runtime-info
1847 @node Language Independent Options
1848 @section Options to Control Diagnostic Messages Formatting
1849 @cindex options to control diagnostics formatting
1850 @cindex diagnostic messages
1851 @cindex message formatting
1853 Traditionally, diagnostic messages have been formatted irrespective of
1854 the output device's aspect (e.g.@: its width, @dots{}). The options described
1855 below can be used to control the diagnostic messages formatting
1856 algorithm, e.g.@: how many characters per line, how often source location
1857 information should be reported. Right now, only the C++ front end can
1858 honor these options. However it is expected, in the near future, that
1859 the remaining front ends would be able to digest them correctly.
1862 @item -fmessage-length=@var{n}
1863 @opindex fmessage-length
1864 Try to format error messages so that they fit on lines of about @var{n}
1865 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1866 the front ends supported by GCC@. If @var{n} is zero, then no
1867 line-wrapping will be done; each error message will appear on a single
1870 @opindex fdiagnostics-show-location
1871 @item -fdiagnostics-show-location=once
1872 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1873 reporter to emit @emph{once} source location information; that is, in
1874 case the message is too long to fit on a single physical line and has to
1875 be wrapped, the source location won't be emitted (as prefix) again,
1876 over and over, in subsequent continuation lines. This is the default
1879 @item -fdiagnostics-show-location=every-line
1880 Only meaningful in line-wrapping mode. Instructs the diagnostic
1881 messages reporter to emit the same source location information (as
1882 prefix) for physical lines that result from the process of breaking
1883 a message which is too long to fit on a single line.
1887 @node Warning Options
1888 @section Options to Request or Suppress Warnings
1889 @cindex options to control warnings
1890 @cindex warning messages
1891 @cindex messages, warning
1892 @cindex suppressing warnings
1894 Warnings are diagnostic messages that report constructions which
1895 are not inherently erroneous but which are risky or suggest there
1896 may have been an error.
1898 You can request many specific warnings with options beginning @samp{-W},
1899 for example @option{-Wimplicit} to request warnings on implicit
1900 declarations. Each of these specific warning options also has a
1901 negative form beginning @samp{-Wno-} to turn off warnings;
1902 for example, @option{-Wno-implicit}. This manual lists only one of the
1903 two forms, whichever is not the default.
1905 The following options control the amount and kinds of warnings produced
1906 by GCC; for further, language-specific options also refer to
1907 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
1910 @cindex syntax checking
1912 @opindex fsyntax-only
1913 Check the code for syntax errors, but don't do anything beyond that.
1917 Issue all the warnings demanded by strict ISO C and ISO C++;
1918 reject all programs that use forbidden extensions, and some other
1919 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1920 version of the ISO C standard specified by any @option{-std} option used.
1922 Valid ISO C and ISO C++ programs should compile properly with or without
1923 this option (though a rare few will require @option{-ansi} or a
1924 @option{-std} option specifying the required version of ISO C)@. However,
1925 without this option, certain GNU extensions and traditional C and C++
1926 features are supported as well. With this option, they are rejected.
1928 @option{-pedantic} does not cause warning messages for use of the
1929 alternate keywords whose names begin and end with @samp{__}. Pedantic
1930 warnings are also disabled in the expression that follows
1931 @code{__extension__}. However, only system header files should use
1932 these escape routes; application programs should avoid them.
1933 @xref{Alternate Keywords}.
1935 Some users try to use @option{-pedantic} to check programs for strict ISO
1936 C conformance. They soon find that it does not do quite what they want:
1937 it finds some non-ISO practices, but not all---only those for which
1938 ISO C @emph{requires} a diagnostic, and some others for which
1939 diagnostics have been added.
1941 A feature to report any failure to conform to ISO C might be useful in
1942 some instances, but would require considerable additional work and would
1943 be quite different from @option{-pedantic}. We don't have plans to
1944 support such a feature in the near future.
1946 Where the standard specified with @option{-std} represents a GNU
1947 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1948 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1949 extended dialect is based. Warnings from @option{-pedantic} are given
1950 where they are required by the base standard. (It would not make sense
1951 for such warnings to be given only for features not in the specified GNU
1952 C dialect, since by definition the GNU dialects of C include all
1953 features the compiler supports with the given option, and there would be
1954 nothing to warn about.)
1956 @item -pedantic-errors
1957 @opindex pedantic-errors
1958 Like @option{-pedantic}, except that errors are produced rather than
1963 Inhibit all warning messages.
1967 Inhibit warning messages about the use of @samp{#import}.
1969 @item -Wchar-subscripts
1970 @opindex Wchar-subscripts
1971 Warn if an array subscript has type @code{char}. This is a common cause
1972 of error, as programmers often forget that this type is signed on some
1977 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1978 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1982 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1983 the arguments supplied have types appropriate to the format string
1984 specified, and that the conversions specified in the format string make
1985 sense. This includes standard functions, and others specified by format
1986 attributes (@pxref{Function Attributes}), in the @code{printf},
1987 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1988 not in the C standard) families.
1990 The formats are checked against the format features supported by GNU
1991 libc version 2.2. These include all ISO C90 and C99 features, as well
1992 as features from the Single Unix Specification and some BSD and GNU
1993 extensions. Other library implementations may not support all these
1994 features; GCC does not support warning about features that go beyond a
1995 particular library's limitations. However, if @option{-pedantic} is used
1996 with @option{-Wformat}, warnings will be given about format features not
1997 in the selected standard version (but not for @code{strfmon} formats,
1998 since those are not in any version of the C standard). @xref{C Dialect
1999 Options,,Options Controlling C Dialect}.
2001 Since @option{-Wformat} also checks for null format arguments for
2002 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2004 @option{-Wformat} is included in @option{-Wall}. For more control over some
2005 aspects of format checking, the options @option{-Wno-format-y2k},
2006 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2007 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2008 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2010 @item -Wno-format-y2k
2011 @opindex Wno-format-y2k
2012 If @option{-Wformat} is specified, do not warn about @code{strftime}
2013 formats which may yield only a two-digit year.
2015 @item -Wno-format-extra-args
2016 @opindex Wno-format-extra-args
2017 If @option{-Wformat} is specified, do not warn about excess arguments to a
2018 @code{printf} or @code{scanf} format function. The C standard specifies
2019 that such arguments are ignored.
2021 Where the unused arguments lie between used arguments that are
2022 specified with @samp{$} operand number specifications, normally
2023 warnings are still given, since the implementation could not know what
2024 type to pass to @code{va_arg} to skip the unused arguments. However,
2025 in the case of @code{scanf} formats, this option will suppress the
2026 warning if the unused arguments are all pointers, since the Single
2027 Unix Specification says that such unused arguments are allowed.
2029 @item -Wno-format-zero-length
2030 @opindex Wno-format-zero-length
2031 If @option{-Wformat} is specified, do not warn about zero-length formats.
2032 The C standard specifies that zero-length formats are allowed.
2034 @item -Wformat-nonliteral
2035 @opindex Wformat-nonliteral
2036 If @option{-Wformat} is specified, also warn if the format string is not a
2037 string literal and so cannot be checked, unless the format function
2038 takes its format arguments as a @code{va_list}.
2040 @item -Wformat-security
2041 @opindex Wformat-security
2042 If @option{-Wformat} is specified, also warn about uses of format
2043 functions that represent possible security problems. At present, this
2044 warns about calls to @code{printf} and @code{scanf} functions where the
2045 format string is not a string literal and there are no format arguments,
2046 as in @code{printf (foo);}. This may be a security hole if the format
2047 string came from untrusted input and contains @samp{%n}. (This is
2048 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2049 in future warnings may be added to @option{-Wformat-security} that are not
2050 included in @option{-Wformat-nonliteral}.)
2054 Enable @option{-Wformat} plus format checks not included in
2055 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2056 -Wformat-nonliteral -Wformat-security}.
2060 Enable warning about passing a null pointer for arguments marked as
2061 requiring a non-null value by the @code{nonnull} function attribute.
2063 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2064 can be disabled with the @option{-Wno-nonnull} option.
2066 @item -Wimplicit-int
2067 @opindex Wimplicit-int
2068 Warn when a declaration does not specify a type.
2070 @item -Wimplicit-function-declaration
2071 @itemx -Werror-implicit-function-declaration
2072 @opindex Wimplicit-function-declaration
2073 @opindex Werror-implicit-function-declaration
2074 Give a warning (or error) whenever a function is used before being
2079 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2083 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2084 function with external linkage, returning int, taking either zero
2085 arguments, two, or three arguments of appropriate types.
2087 @item -Wmissing-braces
2088 @opindex Wmissing-braces
2089 Warn if an aggregate or union initializer is not fully bracketed. In
2090 the following example, the initializer for @samp{a} is not fully
2091 bracketed, but that for @samp{b} is fully bracketed.
2094 int a[2][2] = @{ 0, 1, 2, 3 @};
2095 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2099 @opindex Wparentheses
2100 Warn if parentheses are omitted in certain contexts, such
2101 as when there is an assignment in a context where a truth value
2102 is expected, or when operators are nested whose precedence people
2103 often get confused about.
2105 Also warn about constructions where there may be confusion to which
2106 @code{if} statement an @code{else} branch belongs. Here is an example of
2121 In C, every @code{else} branch belongs to the innermost possible @code{if}
2122 statement, which in this example is @code{if (b)}. This is often not
2123 what the programmer expected, as illustrated in the above example by
2124 indentation the programmer chose. When there is the potential for this
2125 confusion, GCC will issue a warning when this flag is specified.
2126 To eliminate the warning, add explicit braces around the innermost
2127 @code{if} statement so there is no way the @code{else} could belong to
2128 the enclosing @code{if}. The resulting code would look like this:
2144 @item -Wsequence-point
2145 @opindex Wsequence-point
2146 Warn about code that may have undefined semantics because of violations
2147 of sequence point rules in the C standard.
2149 The C standard defines the order in which expressions in a C program are
2150 evaluated in terms of @dfn{sequence points}, which represent a partial
2151 ordering between the execution of parts of the program: those executed
2152 before the sequence point, and those executed after it. These occur
2153 after the evaluation of a full expression (one which is not part of a
2154 larger expression), after the evaluation of the first operand of a
2155 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2156 function is called (but after the evaluation of its arguments and the
2157 expression denoting the called function), and in certain other places.
2158 Other than as expressed by the sequence point rules, the order of
2159 evaluation of subexpressions of an expression is not specified. All
2160 these rules describe only a partial order rather than a total order,
2161 since, for example, if two functions are called within one expression
2162 with no sequence point between them, the order in which the functions
2163 are called is not specified. However, the standards committee have
2164 ruled that function calls do not overlap.
2166 It is not specified when between sequence points modifications to the
2167 values of objects take effect. Programs whose behavior depends on this
2168 have undefined behavior; the C standard specifies that ``Between the
2169 previous and next sequence point an object shall have its stored value
2170 modified at most once by the evaluation of an expression. Furthermore,
2171 the prior value shall be read only to determine the value to be
2172 stored.''. If a program breaks these rules, the results on any
2173 particular implementation are entirely unpredictable.
2175 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2176 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2177 diagnosed by this option, and it may give an occasional false positive
2178 result, but in general it has been found fairly effective at detecting
2179 this sort of problem in programs.
2181 The present implementation of this option only works for C programs. A
2182 future implementation may also work for C++ programs.
2184 The C standard is worded confusingly, therefore there is some debate
2185 over the precise meaning of the sequence point rules in subtle cases.
2186 Links to discussions of the problem, including proposed formal
2187 definitions, may be found on our readings page, at
2188 @w{@uref{http://gcc.gnu.org/readings.html}}.
2191 @opindex Wreturn-type
2192 Warn whenever a function is defined with a return-type that defaults to
2193 @code{int}. Also warn about any @code{return} statement with no
2194 return-value in a function whose return-type is not @code{void}.
2196 For C++, a function without return type always produces a diagnostic
2197 message, even when @option{-Wno-return-type} is specified. The only
2198 exceptions are @samp{main} and functions defined in system headers.
2202 Warn whenever a @code{switch} statement has an index of enumeral type
2203 and lacks a @code{case} for one or more of the named codes of that
2204 enumeration. (The presence of a @code{default} label prevents this
2205 warning.) @code{case} labels outside the enumeration range also
2206 provoke warnings when this option is used.
2208 @item -Wswitch-default
2209 @opindex Wswitch-switch
2210 Warn whenever a @code{switch} statement does not have a @code{default}
2214 @opindex Wswitch-enum
2215 Warn whenever a @code{switch} statement has an index of enumeral type
2216 and lacks a @code{case} for one or more of the named codes of that
2217 enumeration. @code{case} labels outside the enumeration range also
2218 provoke warnings when this option is used.
2222 Warn if any trigraphs are encountered that might change the meaning of
2223 the program (trigraphs within comments are not warned about).
2225 @item -Wunused-function
2226 @opindex Wunused-function
2227 Warn whenever a static function is declared but not defined or a
2228 non\-inline static function is unused.
2230 @item -Wunused-label
2231 @opindex Wunused-label
2232 Warn whenever a label is declared but not used.
2234 To suppress this warning use the @samp{unused} attribute
2235 (@pxref{Variable Attributes}).
2237 @item -Wunused-parameter
2238 @opindex Wunused-parameter
2239 Warn whenever a function parameter is unused aside from its declaration.
2241 To suppress this warning use the @samp{unused} attribute
2242 (@pxref{Variable Attributes}).
2244 @item -Wunused-variable
2245 @opindex Wunused-variable
2246 Warn whenever a local variable or non-constant static variable is unused
2247 aside from its declaration
2249 To suppress this warning use the @samp{unused} attribute
2250 (@pxref{Variable Attributes}).
2252 @item -Wunused-value
2253 @opindex Wunused-value
2254 Warn whenever a statement computes a result that is explicitly not used.
2256 To suppress this warning cast the expression to @samp{void}.
2260 All the above @option{-Wunused} options combined.
2262 In order to get a warning about an unused function parameter, you must
2263 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2264 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2266 @item -Wuninitialized
2267 @opindex Wuninitialized
2268 Warn if an automatic variable is used without first being initialized or
2269 if a variable may be clobbered by a @code{setjmp} call.
2271 These warnings are possible only in optimizing compilation,
2272 because they require data flow information that is computed only
2273 when optimizing. If you don't specify @option{-O}, you simply won't
2276 These warnings occur only for variables that are candidates for
2277 register allocation. Therefore, they do not occur for a variable that
2278 is declared @code{volatile}, or whose address is taken, or whose size
2279 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2280 structures, unions or arrays, even when they are in registers.
2282 Note that there may be no warning about a variable that is used only
2283 to compute a value that itself is never used, because such
2284 computations may be deleted by data flow analysis before the warnings
2287 These warnings are made optional because GCC is not smart
2288 enough to see all the reasons why the code might be correct
2289 despite appearing to have an error. Here is one example of how
2310 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2311 always initialized, but GCC doesn't know this. Here is
2312 another common case:
2317 if (change_y) save_y = y, y = new_y;
2319 if (change_y) y = save_y;
2324 This has no bug because @code{save_y} is used only if it is set.
2326 @cindex @code{longjmp} warnings
2327 This option also warns when a non-volatile automatic variable might be
2328 changed by a call to @code{longjmp}. These warnings as well are possible
2329 only in optimizing compilation.
2331 The compiler sees only the calls to @code{setjmp}. It cannot know
2332 where @code{longjmp} will be called; in fact, a signal handler could
2333 call it at any point in the code. As a result, you may get a warning
2334 even when there is in fact no problem because @code{longjmp} cannot
2335 in fact be called at the place which would cause a problem.
2337 Some spurious warnings can be avoided if you declare all the functions
2338 you use that never return as @code{noreturn}. @xref{Function
2341 @item -Wunknown-pragmas
2342 @opindex Wunknown-pragmas
2343 @cindex warning for unknown pragmas
2344 @cindex unknown pragmas, warning
2345 @cindex pragmas, warning of unknown
2346 Warn when a #pragma directive is encountered which is not understood by
2347 GCC@. If this command line option is used, warnings will even be issued
2348 for unknown pragmas in system header files. This is not the case if
2349 the warnings were only enabled by the @option{-Wall} command line option.
2351 @item -Wstrict-aliasing
2352 @opindex Wstrict-aliasing
2353 This option is only active when @option{-fstrict-aliasing} is active.
2354 It warns about code which might break the strict aliasing rules that the
2355 compiler is using for optimization. The warning does not catch all
2356 cases, but does attempt to catch the more common pitfalls. It is
2357 included in @option{-Wall}.
2361 All of the above @samp{-W} options combined. This enables all the
2362 warnings about constructions that some users consider questionable, and
2363 that are easy to avoid (or modify to prevent the warning), even in
2364 conjunction with macros. This also enables some language-specific
2365 warnings described in @ref{C++ Dialect Options} and
2366 @ref{Objective-C Dialect Options}.
2369 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2370 Some of them warn about constructions that users generally do not
2371 consider questionable, but which occasionally you might wish to check
2372 for; others warn about constructions that are necessary or hard to avoid
2373 in some cases, and there is no simple way to modify the code to suppress
2380 (This option used to be called @option{-W}. The older name is still
2381 supported, but the newer name is more descriptive.) Print extra warning
2382 messages for these events:
2386 A function can return either with or without a value. (Falling
2387 off the end of the function body is considered returning without
2388 a value.) For example, this function would evoke such a
2402 An expression-statement or the left-hand side of a comma expression
2403 contains no side effects.
2404 To suppress the warning, cast the unused expression to void.
2405 For example, an expression such as @samp{x[i,j]} will cause a warning,
2406 but @samp{x[(void)i,j]} will not.
2409 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2412 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2413 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2414 that of ordinary mathematical notation.
2417 Storage-class specifiers like @code{static} are not the first things in
2418 a declaration. According to the C Standard, this usage is obsolescent.
2421 The return type of a function has a type qualifier such as @code{const}.
2422 Such a type qualifier has no effect, since the value returned by a
2423 function is not an lvalue. (But don't warn about the GNU extension of
2424 @code{volatile void} return types. That extension will be warned about
2425 if @option{-pedantic} is specified.)
2428 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2432 A comparison between signed and unsigned values could produce an
2433 incorrect result when the signed value is converted to unsigned.
2434 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2437 An aggregate has an initializer which does not initialize all members.
2438 For example, the following code would cause such a warning, because
2439 @code{x.h} would be implicitly initialized to zero:
2442 struct s @{ int f, g, h; @};
2443 struct s x = @{ 3, 4 @};
2447 A function parameter is declared without a type specifier in K&R-style
2455 An empty body occurs in an @samp{if} or @samp{else} statement.
2458 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2459 @samp{>}, or @samp{>=}.
2462 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2465 Any of several floating-point events that often indicate errors, such as
2466 overflow, underflow, loss of precision, etc.
2468 @item @r{(C++ only)}
2469 An enumerator and a non-enumerator both appear in a conditional expression.
2471 @item @r{(C++ only)}
2472 A non-static reference or non-static @samp{const} member appears in a
2473 class without constructors.
2475 @item @r{(C++ only)}
2476 Ambiguous virtual bases.
2478 @item @r{(C++ only)}
2479 Subscripting an array which has been declared @samp{register}.
2481 @item @r{(C++ only)}
2482 Taking the address of a variable which has been declared @samp{register}.
2484 @item @r{(C++ only)}
2485 A base class is not initialized in a derived class' copy constructor.
2488 @item -Wno-div-by-zero
2489 @opindex Wno-div-by-zero
2490 @opindex Wdiv-by-zero
2491 Do not warn about compile-time integer division by zero. Floating point
2492 division by zero is not warned about, as it can be a legitimate way of
2493 obtaining infinities and NaNs.
2495 @item -Wsystem-headers
2496 @opindex Wsystem-headers
2497 @cindex warnings from system headers
2498 @cindex system headers, warnings from
2499 Print warning messages for constructs found in system header files.
2500 Warnings from system headers are normally suppressed, on the assumption
2501 that they usually do not indicate real problems and would only make the
2502 compiler output harder to read. Using this command line option tells
2503 GCC to emit warnings from system headers as if they occurred in user
2504 code. However, note that using @option{-Wall} in conjunction with this
2505 option will @emph{not} warn about unknown pragmas in system
2506 headers---for that, @option{-Wunknown-pragmas} must also be used.
2509 @opindex Wfloat-equal
2510 Warn if floating point values are used in equality comparisons.
2512 The idea behind this is that sometimes it is convenient (for the
2513 programmer) to consider floating-point values as approximations to
2514 infinitely precise real numbers. If you are doing this, then you need
2515 to compute (by analyzing the code, or in some other way) the maximum or
2516 likely maximum error that the computation introduces, and allow for it
2517 when performing comparisons (and when producing output, but that's a
2518 different problem). In particular, instead of testing for equality, you
2519 would check to see whether the two values have ranges that overlap; and
2520 this is done with the relational operators, so equality comparisons are
2523 @item -Wtraditional @r{(C only)}
2524 @opindex Wtraditional
2525 Warn about certain constructs that behave differently in traditional and
2526 ISO C@. Also warn about ISO C constructs that have no traditional C
2527 equivalent, and/or problematic constructs which should be avoided.
2531 Macro parameters that appear within string literals in the macro body.
2532 In traditional C macro replacement takes place within string literals,
2533 but does not in ISO C@.
2536 In traditional C, some preprocessor directives did not exist.
2537 Traditional preprocessors would only consider a line to be a directive
2538 if the @samp{#} appeared in column 1 on the line. Therefore
2539 @option{-Wtraditional} warns about directives that traditional C
2540 understands but would ignore because the @samp{#} does not appear as the
2541 first character on the line. It also suggests you hide directives like
2542 @samp{#pragma} not understood by traditional C by indenting them. Some
2543 traditional implementations would not recognize @samp{#elif}, so it
2544 suggests avoiding it altogether.
2547 A function-like macro that appears without arguments.
2550 The unary plus operator.
2553 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2554 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2555 constants.) Note, these suffixes appear in macros defined in the system
2556 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2557 Use of these macros in user code might normally lead to spurious
2558 warnings, however gcc's integrated preprocessor has enough context to
2559 avoid warning in these cases.
2562 A function declared external in one block and then used after the end of
2566 A @code{switch} statement has an operand of type @code{long}.
2569 A non-@code{static} function declaration follows a @code{static} one.
2570 This construct is not accepted by some traditional C compilers.
2573 The ISO type of an integer constant has a different width or
2574 signedness from its traditional type. This warning is only issued if
2575 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2576 typically represent bit patterns, are not warned about.
2579 Usage of ISO string concatenation is detected.
2582 Initialization of automatic aggregates.
2585 Identifier conflicts with labels. Traditional C lacks a separate
2586 namespace for labels.
2589 Initialization of unions. If the initializer is zero, the warning is
2590 omitted. This is done under the assumption that the zero initializer in
2591 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2592 initializer warnings and relies on default initialization to zero in the
2596 Conversions by prototypes between fixed/floating point values and vice
2597 versa. The absence of these prototypes when compiling with traditional
2598 C would cause serious problems. This is a subset of the possible
2599 conversion warnings, for the full set use @option{-Wconversion}.
2602 Use of ISO C style function definitions. This warning intentionally is
2603 @emph{not} issued for prototype declarations or variadic functions
2604 because these ISO C features will appear in your code when using
2605 libiberty's traditional C compatibility macros, @code{PARAMS} and
2606 @code{VPARAMS}. This warning is also bypassed for nested functions
2607 because that feature is already a gcc extension and thus not relevant to
2608 traditional C compatibility.
2613 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2615 @item -Wendif-labels
2616 @opindex Wendif-labels
2617 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2621 Warn whenever a local variable shadows another local variable, parameter or
2622 global variable or whenever a built-in function is shadowed.
2624 @item -Wlarger-than-@var{len}
2625 @opindex Wlarger-than
2626 Warn whenever an object of larger than @var{len} bytes is defined.
2628 @item -Wpointer-arith
2629 @opindex Wpointer-arith
2630 Warn about anything that depends on the ``size of'' a function type or
2631 of @code{void}. GNU C assigns these types a size of 1, for
2632 convenience in calculations with @code{void *} pointers and pointers
2635 @item -Wbad-function-cast @r{(C only)}
2636 @opindex Wbad-function-cast
2637 Warn whenever a function call is cast to a non-matching type.
2638 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2642 Warn whenever a pointer is cast so as to remove a type qualifier from
2643 the target type. For example, warn if a @code{const char *} is cast
2644 to an ordinary @code{char *}.
2647 @opindex Wcast-align
2648 Warn whenever a pointer is cast such that the required alignment of the
2649 target is increased. For example, warn if a @code{char *} is cast to
2650 an @code{int *} on machines where integers can only be accessed at
2651 two- or four-byte boundaries.
2653 @item -Wwrite-strings
2654 @opindex Wwrite-strings
2655 When compiling C, give string constants the type @code{const
2656 char[@var{length}]} so that
2657 copying the address of one into a non-@code{const} @code{char *}
2658 pointer will get a warning; when compiling C++, warn about the
2659 deprecated conversion from string constants to @code{char *}.
2660 These warnings will help you find at
2661 compile time code that can try to write into a string constant, but
2662 only if you have been very careful about using @code{const} in
2663 declarations and prototypes. Otherwise, it will just be a nuisance;
2664 this is why we did not make @option{-Wall} request these warnings.
2667 @opindex Wconversion
2668 Warn if a prototype causes a type conversion that is different from what
2669 would happen to the same argument in the absence of a prototype. This
2670 includes conversions of fixed point to floating and vice versa, and
2671 conversions changing the width or signedness of a fixed point argument
2672 except when the same as the default promotion.
2674 Also, warn if a negative integer constant expression is implicitly
2675 converted to an unsigned type. For example, warn about the assignment
2676 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2677 casts like @code{(unsigned) -1}.
2679 @item -Wsign-compare
2680 @opindex Wsign-compare
2681 @cindex warning for comparison of signed and unsigned values
2682 @cindex comparison of signed and unsigned values, warning
2683 @cindex signed and unsigned values, comparison warning
2684 Warn when a comparison between signed and unsigned values could produce
2685 an incorrect result when the signed value is converted to unsigned.
2686 This warning is also enabled by @option{-Wextra}; to get the other warnings
2687 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2689 @item -Waggregate-return
2690 @opindex Waggregate-return
2691 Warn if any functions that return structures or unions are defined or
2692 called. (In languages where you can return an array, this also elicits
2695 @item -Wstrict-prototypes @r{(C only)}
2696 @opindex Wstrict-prototypes
2697 Warn if a function is declared or defined without specifying the
2698 argument types. (An old-style function definition is permitted without
2699 a warning if preceded by a declaration which specifies the argument
2702 @item -Wmissing-prototypes @r{(C only)}
2703 @opindex Wmissing-prototypes
2704 Warn if a global function is defined without a previous prototype
2705 declaration. This warning is issued even if the definition itself
2706 provides a prototype. The aim is to detect global functions that fail
2707 to be declared in header files.
2709 @item -Wmissing-declarations @r{(C only)}
2710 @opindex Wmissing-declarations
2711 Warn if a global function is defined without a previous declaration.
2712 Do so even if the definition itself provides a prototype.
2713 Use this option to detect global functions that are not declared in
2716 @item -Wmissing-noreturn
2717 @opindex Wmissing-noreturn
2718 Warn about functions which might be candidates for attribute @code{noreturn}.
2719 Note these are only possible candidates, not absolute ones. Care should
2720 be taken to manually verify functions actually do not ever return before
2721 adding the @code{noreturn} attribute, otherwise subtle code generation
2722 bugs could be introduced. You will not get a warning for @code{main} in
2723 hosted C environments.
2725 @item -Wmissing-format-attribute
2726 @opindex Wmissing-format-attribute
2728 If @option{-Wformat} is enabled, also warn about functions which might be
2729 candidates for @code{format} attributes. Note these are only possible
2730 candidates, not absolute ones. GCC will guess that @code{format}
2731 attributes might be appropriate for any function that calls a function
2732 like @code{vprintf} or @code{vscanf}, but this might not always be the
2733 case, and some functions for which @code{format} attributes are
2734 appropriate may not be detected. This option has no effect unless
2735 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2737 @item -Wno-multichar
2738 @opindex Wno-multichar
2740 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2741 Usually they indicate a typo in the user's code, as they have
2742 implementation-defined values, and should not be used in portable code.
2744 @item -Wno-deprecated-declarations
2745 @opindex Wno-deprecated-declarations
2746 Do not warn about uses of functions, variables, and types marked as
2747 deprecated by using the @code{deprecated} attribute.
2748 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2749 @pxref{Type Attributes}.)
2753 Warn if a structure is given the packed attribute, but the packed
2754 attribute has no effect on the layout or size of the structure.
2755 Such structures may be mis-aligned for little benefit. For
2756 instance, in this code, the variable @code{f.x} in @code{struct bar}
2757 will be misaligned even though @code{struct bar} does not itself
2758 have the packed attribute:
2765 @} __attribute__((packed));
2775 Warn if padding is included in a structure, either to align an element
2776 of the structure or to align the whole structure. Sometimes when this
2777 happens it is possible to rearrange the fields of the structure to
2778 reduce the padding and so make the structure smaller.
2780 @item -Wredundant-decls
2781 @opindex Wredundant-decls
2782 Warn if anything is declared more than once in the same scope, even in
2783 cases where multiple declaration is valid and changes nothing.
2785 @item -Wnested-externs @r{(C only)}
2786 @opindex Wnested-externs
2787 Warn if an @code{extern} declaration is encountered within a function.
2789 @item -Wunreachable-code
2790 @opindex Wunreachable-code
2791 Warn if the compiler detects that code will never be executed.
2793 This option is intended to warn when the compiler detects that at
2794 least a whole line of source code will never be executed, because
2795 some condition is never satisfied or because it is after a
2796 procedure that never returns.
2798 It is possible for this option to produce a warning even though there
2799 are circumstances under which part of the affected line can be executed,
2800 so care should be taken when removing apparently-unreachable code.
2802 For instance, when a function is inlined, a warning may mean that the
2803 line is unreachable in only one inlined copy of the function.
2805 This option is not made part of @option{-Wall} because in a debugging
2806 version of a program there is often substantial code which checks
2807 correct functioning of the program and is, hopefully, unreachable
2808 because the program does work. Another common use of unreachable
2809 code is to provide behavior which is selectable at compile-time.
2813 Warn if a function can not be inlined and it was declared as inline.
2814 Even with this option, the compiler will not warn about failures to
2815 inline functions declared in system headers.
2817 The compiler uses a variety of heuristics to determine whether or not
2818 to inline a function. For example, the compiler takes into account
2819 the size of the function being inlined and the the amount of inlining
2820 that has already been done in the current function. Therefore,
2821 seemingly insignificant changes in the source program can cause the
2822 warnings produced by @option{-Winline} to appear or disappear.
2824 @item -Wno-invalid-offsetof @r{(C++ only)}
2825 @opindex Wno-invalid-offsetof
2826 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2827 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2828 to a non-POD type is undefined. In existing C++ implementations,
2829 however, @samp{offsetof} typically gives meaningful results even when
2830 applied to certain kinds of non-POD types. (Such as a simple
2831 @samp{struct} that fails to be a POD type only by virtue of having a
2832 constructor.) This flag is for users who are aware that they are
2833 writing nonportable code and who have deliberately chosen to ignore the
2836 The restrictions on @samp{offsetof} may be relaxed in a future version
2837 of the C++ standard.
2840 @opindex Winvalid-pch
2841 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2842 the search path but can't be used.
2846 @opindex Wno-long-long
2847 Warn if @samp{long long} type is used. This is default. To inhibit
2848 the warning messages, use @option{-Wno-long-long}. Flags
2849 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2850 only when @option{-pedantic} flag is used.
2852 @item -Wdisabled-optimization
2853 @opindex Wdisabled-optimization
2854 Warn if a requested optimization pass is disabled. This warning does
2855 not generally indicate that there is anything wrong with your code; it
2856 merely indicates that GCC's optimizers were unable to handle the code
2857 effectively. Often, the problem is that your code is too big or too
2858 complex; GCC will refuse to optimize programs when the optimization
2859 itself is likely to take inordinate amounts of time.
2863 Make all warnings into errors.
2866 @node Debugging Options
2867 @section Options for Debugging Your Program or GCC
2868 @cindex options, debugging
2869 @cindex debugging information options
2871 GCC has various special options that are used for debugging
2872 either your program or GCC:
2877 Produce debugging information in the operating system's native format
2878 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2881 On most systems that use stabs format, @option{-g} enables use of extra
2882 debugging information that only GDB can use; this extra information
2883 makes debugging work better in GDB but will probably make other debuggers
2885 refuse to read the program. If you want to control for certain whether
2886 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2887 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2888 or @option{-gvms} (see below).
2890 Unlike most other C compilers, GCC allows you to use @option{-g} with
2891 @option{-O}. The shortcuts taken by optimized code may occasionally
2892 produce surprising results: some variables you declared may not exist
2893 at all; flow of control may briefly move where you did not expect it;
2894 some statements may not be executed because they compute constant
2895 results or their values were already at hand; some statements may
2896 execute in different places because they were moved out of loops.
2898 Nevertheless it proves possible to debug optimized output. This makes
2899 it reasonable to use the optimizer for programs that might have bugs.
2901 The following options are useful when GCC is generated with the
2902 capability for more than one debugging format.
2906 Produce debugging information for use by GDB@. This means to use the
2907 most expressive format available (DWARF 2, stabs, or the native format
2908 if neither of those are supported), including GDB extensions if at all
2913 Produce debugging information in stabs format (if that is supported),
2914 without GDB extensions. This is the format used by DBX on most BSD
2915 systems. On MIPS, Alpha and System V Release 4 systems this option
2916 produces stabs debugging output which is not understood by DBX or SDB@.
2917 On System V Release 4 systems this option requires the GNU assembler.
2921 Produce debugging information in stabs format (if that is supported),
2922 using GNU extensions understood only by the GNU debugger (GDB)@. The
2923 use of these extensions is likely to make other debuggers crash or
2924 refuse to read the program.
2928 Produce debugging information in COFF format (if that is supported).
2929 This is the format used by SDB on most System V systems prior to
2934 Produce debugging information in XCOFF format (if that is supported).
2935 This is the format used by the DBX debugger on IBM RS/6000 systems.
2939 Produce debugging information in XCOFF format (if that is supported),
2940 using GNU extensions understood only by the GNU debugger (GDB)@. The
2941 use of these extensions is likely to make other debuggers crash or
2942 refuse to read the program, and may cause assemblers other than the GNU
2943 assembler (GAS) to fail with an error.
2947 Produce debugging information in DWARF version 1 format (if that is
2948 supported). This is the format used by SDB on most System V Release 4
2951 This option is deprecated.
2955 Produce debugging information in DWARF version 1 format (if that is
2956 supported), using GNU extensions understood only by the GNU debugger
2957 (GDB)@. The use of these extensions is likely to make other debuggers
2958 crash or refuse to read the program.
2960 This option is deprecated.
2964 Produce debugging information in DWARF version 2 format (if that is
2965 supported). This is the format used by DBX on IRIX 6.
2969 Produce debugging information in VMS debug format (if that is
2970 supported). This is the format used by DEBUG on VMS systems.
2973 @itemx -ggdb@var{level}
2974 @itemx -gstabs@var{level}
2975 @itemx -gcoff@var{level}
2976 @itemx -gxcoff@var{level}
2977 @itemx -gvms@var{level}
2978 Request debugging information and also use @var{level} to specify how
2979 much information. The default level is 2.
2981 Level 1 produces minimal information, enough for making backtraces in
2982 parts of the program that you don't plan to debug. This includes
2983 descriptions of functions and external variables, but no information
2984 about local variables and no line numbers.
2986 Level 3 includes extra information, such as all the macro definitions
2987 present in the program. Some debuggers support macro expansion when
2988 you use @option{-g3}.
2990 Note that in order to avoid confusion between DWARF1 debug level 2,
2991 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
2992 a concatenated debug level. Instead use an additional @option{-g@var{level}}
2993 option to change the debug level for DWARF1 or DWARF2.
2995 @item -feliminate-dwarf2-dups
2996 @opindex feliminate-dwarf2-dups
2997 Compress DWARF2 debugging information by eliminating duplicated
2998 information about each symbol. This option only makes sense when
2999 generating DWARF2 debugging information with @option{-gdwarf-2}.
3001 @cindex @command{prof}
3004 Generate extra code to write profile information suitable for the
3005 analysis program @command{prof}. You must use this option when compiling
3006 the source files you want data about, and you must also use it when
3009 @cindex @command{gprof}
3012 Generate extra code to write profile information suitable for the
3013 analysis program @command{gprof}. You must use this option when compiling
3014 the source files you want data about, and you must also use it when
3019 Makes the compiler print out each function name as it is compiled, and
3020 print some statistics about each pass when it finishes.
3023 @opindex ftime-report
3024 Makes the compiler print some statistics about the time consumed by each
3025 pass when it finishes.
3028 @opindex fmem-report
3029 Makes the compiler print some statistics about permanent memory
3030 allocation when it finishes.
3032 @item -fprofile-arcs
3033 @opindex fprofile-arcs
3034 Add code so that program flow @dfn{arcs} are instrumented. During
3035 execution the program records how many times each branch and call is
3036 executed and how many times it is taken or returns. When the compiled
3037 program exits it saves this data to a file called
3038 @file{@var{auxname}.da} for each source file. The data may be used for
3039 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3040 test coverage analysis (@option{-ftest-coverage}). Each object file's
3041 @var{auxname} is generated from the name of the output file, if
3042 explicitly specified and it is not the final executable, otherwise it is
3043 the basename of the source file. In both cases any suffix is removed
3044 (e.g. @file{foo.da} for input file @file{dir/foo.c}, or
3045 @file{dir/foo.da} for output file specified as @option{-o dir/foo.o}).
3050 Compile the source files with @option{-fprofile-arcs} plus optimization
3051 and code generation options. For test coverage analysis, use the
3052 additional @option{-ftest-coverage} option. You do not need to profile
3053 every source file in a program.
3056 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3057 (the latter implies the former).
3060 Run the program on a representative workload to generate the arc profile
3061 information. This may be repeated any number of times. You can run
3062 concurrent instances of your program, and provided that the file system
3063 supports locking, the data files will be correctly updated. Also
3064 @code{fork} calls are detected and correctly handled (double counting
3068 For profile-directed optimizations, compile the source files again with
3069 the same optimization and code generation options plus
3070 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3071 Control Optimization}).
3074 For test coverage analysis, use @command{gcov} to produce human readable
3075 information from the @file{.bbg} and @file{.da} files. Refer to the
3076 @command{gcov} documentation for further information.
3080 With @option{-fprofile-arcs}, for each function of your program GCC
3081 creates a program flow graph, then finds a spanning tree for the graph.
3082 Only arcs that are not on the spanning tree have to be instrumented: the
3083 compiler adds code to count the number of times that these arcs are
3084 executed. When an arc is the only exit or only entrance to a block, the
3085 instrumentation code can be added to the block; otherwise, a new basic
3086 block must be created to hold the instrumentation code.
3089 @item -ftest-coverage
3090 @opindex ftest-coverage
3091 Produce a graph file that the @command{gcov} code-coverage utility
3092 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3093 show program coverage. Each source file's data file is called
3094 @file{@var{auxname}.bbg}. Refer to the @option{-fprofile-arcs} option
3095 above for a description of @var{auxname} and instructions on how to
3096 generate test coverage data. Coverage data will match the source files
3097 more closely, if you do not optimize.
3099 @item -d@var{letters}
3101 Says to make debugging dumps during compilation at times specified by
3102 @var{letters}. This is used for debugging the compiler. The file names
3103 for most of the dumps are made by appending a pass number and a word to
3104 the @var{dumpname}. @var{dumpname} is generated from the name of the
3105 output file, if explicitly specified and it is not an executable,
3106 otherwise it is the basename of the source file. In both cases any
3107 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3108 Here are the possible letters for use in @var{letters}, and their
3114 Annotate the assembler output with miscellaneous debugging information.
3117 Dump after computing branch probabilities, to @file{@var{file}.15.bp}.
3120 Dump after block reordering, to @file{@var{file}.31.bbro}.
3123 Dump after instruction combination, to the file @file{@var{file}.21.combine}.
3126 Dump after the first if conversion, to the file @file{@var{file}.16.ce1}.
3129 Dump after delayed branch scheduling, to @file{@var{file}.36.dbr}.
3132 Dump all macro definitions, at the end of preprocessing, in addition to
3136 Dump after SSA optimizations, to @file{@var{file}.04.ssa} and
3137 @file{@var{file}.07.ussa}.
3140 Dump after the second if conversion, to @file{@var{file}.32.ce3}.
3143 Dump after life analysis, to @file{@var{file}.20.life}.
3146 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.10.addressof}.
3149 Dump after global register allocation, to @file{@var{file}.26.greg}.
3152 Dump after GCSE, to @file{@var{file}.11.gcse}.
3155 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3158 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3161 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3164 Dump after conversion from registers to stack, to @file{@var{file}.35.stack}.
3167 Dump after local register allocation, to @file{@var{file}.25.lreg}.
3170 Dump after loop optimization passes, to @file{@var{file}.12.loop} and
3171 @file{@var{file}.18.loop2}.
3174 Dump after performing the machine dependent reorganization pass, to
3175 @file{@var{file}.36.mach}.
3178 Dump after register renumbering, to @file{@var{file}.30.rnreg}.
3181 Dump after the register move pass, to @file{@var{file}.23.regmove}.
3184 Dump after post-reload optimizations, to @file{@var{file}.27.postreload}.
3187 Dump after RTL generation, to @file{@var{file}.00.rtl}.
3190 Dump after the second scheduling pass, to @file{@var{file}.34.sched2}.
3193 Dump after CSE (including the jump optimization that sometimes follows
3194 CSE), to @file{@var{file}.09.cse}.
3197 Dump after the first scheduling pass, to @file{@var{file}.24.sched}.
3200 Dump after the second CSE pass (including the jump optimization that
3201 sometimes follows CSE), to @file{@var{file}.19.cse2}.
3204 Dump after null pointer elimination pass to @file{@var{file}.08.null}.
3207 Dump after the second flow pass, to @file{@var{file}.28.flow2}.
3210 Dump after SSA dead code elimination, to @file{@var{file}.06.ssadce}.
3213 Dump after the peephole pass, to @file{@var{file}.29.peephole2}.
3216 Produce all the dumps listed above.
3219 Produce a core dump whenever an error occurs.
3222 Print statistics on memory usage, at the end of the run, to
3226 Annotate the assembler output with a comment indicating which
3227 pattern and alternative was used. The length of each instruction is
3231 Dump the RTL in the assembler output as a comment before each instruction.
3232 Also turns on @option{-dp} annotation.
3235 For each of the other indicated dump files (except for
3236 @file{@var{file}.00.rtl}), dump a representation of the control flow graph
3237 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3240 Just generate RTL for a function instead of compiling it. Usually used
3244 Dump debugging information during parsing, to standard error.
3247 @item -fdump-unnumbered
3248 @opindex fdump-unnumbered
3249 When doing debugging dumps (see @option{-d} option above), suppress instruction
3250 numbers and line number note output. This makes it more feasible to
3251 use diff on debugging dumps for compiler invocations with different
3252 options, in particular with and without @option{-g}.
3254 @item -fdump-translation-unit @r{(C and C++ only)}
3255 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3256 @opindex fdump-translation-unit
3257 Dump a representation of the tree structure for the entire translation
3258 unit to a file. The file name is made by appending @file{.tu} to the
3259 source file name. If the @samp{-@var{options}} form is used, @var{options}
3260 controls the details of the dump as described for the
3261 @option{-fdump-tree} options.
3263 @item -fdump-class-hierarchy @r{(C++ only)}
3264 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3265 @opindex fdump-class-hierarchy
3266 Dump a representation of each class's hierarchy and virtual function
3267 table layout to a file. The file name is made by appending @file{.class}
3268 to the source file name. If the @samp{-@var{options}} form is used,
3269 @var{options} controls the details of the dump as described for the
3270 @option{-fdump-tree} options.
3272 @item -fdump-tree-@var{switch} @r{(C++ only)}
3273 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3275 Control the dumping at various stages of processing the intermediate
3276 language tree to a file. The file name is generated by appending a switch
3277 specific suffix to the source file name. If the @samp{-@var{options}}
3278 form is used, @var{options} is a list of @samp{-} separated options that
3279 control the details of the dump. Not all options are applicable to all
3280 dumps, those which are not meaningful will be ignored. The following
3281 options are available
3285 Print the address of each node. Usually this is not meaningful as it
3286 changes according to the environment and source file. Its primary use
3287 is for tying up a dump file with a debug environment.
3289 Inhibit dumping of members of a scope or body of a function merely
3290 because that scope has been reached. Only dump such items when they
3291 are directly reachable by some other path.
3293 Turn on all options.
3296 The following tree dumps are possible:
3299 Dump before any tree based optimization, to @file{@var{file}.original}.
3301 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3303 Dump after function inlining, to @file{@var{file}.inlined}.
3306 @item -frandom-seed=@var{string}
3307 @opindex frandom-string
3308 This option provides a seed that GCC uses when it would otherwise use
3309 random numbers. At present, this is used to generate certain symbol names
3310 that have to be different in every compiled file.
3312 The @var{string} should be different for every file you compile.
3314 @item -fsched-verbose=@var{n}
3315 @opindex fsched-verbose
3316 On targets that use instruction scheduling, this option controls the
3317 amount of debugging output the scheduler prints. This information is
3318 written to standard error, unless @option{-dS} or @option{-dR} is
3319 specified, in which case it is output to the usual dump
3320 listing file, @file{.sched} or @file{.sched2} respectively. However
3321 for @var{n} greater than nine, the output is always printed to standard
3324 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3325 same information as @option{-dRS}. For @var{n} greater than one, it
3326 also output basic block probabilities, detailed ready list information
3327 and unit/insn info. For @var{n} greater than two, it includes RTL
3328 at abort point, control-flow and regions info. And for @var{n} over
3329 four, @option{-fsched-verbose} also includes dependence info.
3333 Store the usual ``temporary'' intermediate files permanently; place them
3334 in the current directory and name them based on the source file. Thus,
3335 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3336 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3337 preprocessed @file{foo.i} output file even though the compiler now
3338 normally uses an integrated preprocessor.
3342 Report the CPU time taken by each subprocess in the compilation
3343 sequence. For C source files, this is the compiler proper and assembler
3344 (plus the linker if linking is done). The output looks like this:
3351 The first number on each line is the ``user time,'' that is time spent
3352 executing the program itself. The second number is ``system time,''
3353 time spent executing operating system routines on behalf of the program.
3354 Both numbers are in seconds.
3356 @item -print-file-name=@var{library}
3357 @opindex print-file-name
3358 Print the full absolute name of the library file @var{library} that
3359 would be used when linking---and don't do anything else. With this
3360 option, GCC does not compile or link anything; it just prints the
3363 @item -print-multi-directory
3364 @opindex print-multi-directory
3365 Print the directory name corresponding to the multilib selected by any
3366 other switches present in the command line. This directory is supposed
3367 to exist in @env{GCC_EXEC_PREFIX}.
3369 @item -print-multi-lib
3370 @opindex print-multi-lib
3371 Print the mapping from multilib directory names to compiler switches
3372 that enable them. The directory name is separated from the switches by
3373 @samp{;}, and each switch starts with an @samp{@@} instead of the
3374 @samp{-}, without spaces between multiple switches. This is supposed to
3375 ease shell-processing.
3377 @item -print-prog-name=@var{program}
3378 @opindex print-prog-name
3379 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3381 @item -print-libgcc-file-name
3382 @opindex print-libgcc-file-name
3383 Same as @option{-print-file-name=libgcc.a}.
3385 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3386 but you do want to link with @file{libgcc.a}. You can do
3389 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3392 @item -print-search-dirs
3393 @opindex print-search-dirs
3394 Print the name of the configured installation directory and a list of
3395 program and library directories gcc will search---and don't do anything else.
3397 This is useful when gcc prints the error message
3398 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3399 To resolve this you either need to put @file{cpp0} and the other compiler
3400 components where gcc expects to find them, or you can set the environment
3401 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3402 Don't forget the trailing '/'.
3403 @xref{Environment Variables}.
3406 @opindex dumpmachine
3407 Print the compiler's target machine (for example,
3408 @samp{i686-pc-linux-gnu})---and don't do anything else.
3411 @opindex dumpversion
3412 Print the compiler version (for example, @samp{3.0})---and don't do
3417 Print the compiler's built-in specs---and don't do anything else. (This
3418 is used when GCC itself is being built.) @xref{Spec Files}.
3420 @item -feliminate-unused-debug-types
3421 @opindex feliminate-unused-debug-types
3422 Normally, when producing DWARF2 output, GCC will emit debugging
3423 information for all types declared in a compilation
3424 unit, regardless of whether or not they are actually used
3425 in that compilation unit. Sometimes this is useful, such as
3426 if, in the debugger, you want to cast a value to a type that is
3427 not actually used in your program (but is declared). More often,
3428 however, this results in a significant amount of wasted space.
3429 With this option, GCC will avoid producing debug symbol output
3430 for types that are nowhere used in the source file being compiled.
3433 @node Optimize Options
3434 @section Options That Control Optimization
3435 @cindex optimize options
3436 @cindex options, optimization
3438 These options control various sorts of optimizations.
3440 Without any optimization option, the compiler's goal is to reduce the
3441 cost of compilation and to make debugging produce the expected
3442 results. Statements are independent: if you stop the program with a
3443 breakpoint between statements, you can then assign a new value to any
3444 variable or change the program counter to any other statement in the
3445 function and get exactly the results you would expect from the source
3448 Turning on optimization flags makes the compiler attempt to improve
3449 the performance and/or code size at the expense of compilation time
3450 and possibly the ability to debug the program.
3452 Not all optimizations are controlled directly by a flag. Only
3453 optimizations that have a flag are listed.
3460 Optimize. Optimizing compilation takes somewhat more time, and a lot
3461 more memory for a large function.
3463 With @option{-O}, the compiler tries to reduce code size and execution
3464 time, without performing any optimizations that take a great deal of
3467 @option{-O} turns on the following optimization flags:
3468 @gccoptlist{-fdefer-pop @gol
3469 -fmerge-constants @gol
3471 -floop-optimize @gol
3473 -fif-conversion @gol
3474 -fif-conversion2 @gol
3475 -fdelayed-branch @gol
3476 -fguess-branch-probability @gol
3479 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3480 where doing so does not interfere with debugging.
3484 Optimize even more. GCC performs nearly all supported optimizations
3485 that do not involve a space-speed tradeoff. The compiler does not
3486 perform loop unrolling or function inlining when you specify @option{-O2}.
3487 As compared to @option{-O}, this option increases both compilation time
3488 and the performance of the generated code.
3490 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3491 also turns on the following optimization flags:
3492 @gccoptlist{-fforce-mem @gol
3493 -foptimize-sibling-calls @gol
3494 -fstrength-reduce @gol
3495 -fcse-follow-jumps -fcse-skip-blocks @gol
3496 -frerun-cse-after-loop -frerun-loop-opt @gol
3497 -fgcse -fgcse-lm -fgcse-sm @gol
3498 -fdelete-null-pointer-checks @gol
3499 -fexpensive-optimizations @gol
3501 -fschedule-insns -fschedule-insns2 @gol
3502 -fsched-interblock -fsched-spec @gol
3505 -freorder-blocks -freorder-functions @gol
3506 -fstrict-aliasing @gol
3507 -falign-functions -falign-jumps @gol
3508 -falign-loops -falign-labels}
3510 Please note the warning under @option{-fgcse} about
3511 invoking @option{-O2} on programs that use computed gotos.
3515 Optimize yet more. @option{-O3} turns on all optimizations specified by
3516 @option{-O2} and also turns on the @option{-finline-functions},
3517 @option{-funit-at-a-time} and @option{-frename-registers} options.
3521 Do not optimize. This is the default.
3525 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3526 do not typically increase code size. It also performs further
3527 optimizations designed to reduce code size.
3529 @option{-Os} disables the following optimization flags:
3530 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3531 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3533 If you use multiple @option{-O} options, with or without level numbers,
3534 the last such option is the one that is effective.
3537 Options of the form @option{-f@var{flag}} specify machine-independent
3538 flags. Most flags have both positive and negative forms; the negative
3539 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3540 below, only one of the forms is listed---the one you typically will
3541 use. You can figure out the other form by either removing @samp{no-}
3544 The following options control specific optimizations. They are either
3545 activated by @option{-O} options or are related to ones that are. You
3546 can use the following flags in the rare cases when ``fine-tuning'' of
3547 optimizations to be performed is desired.
3550 @item -fno-default-inline
3551 @opindex fno-default-inline
3552 Do not make member functions inline by default merely because they are
3553 defined inside the class scope (C++ only). Otherwise, when you specify
3554 @w{@option{-O}}, member functions defined inside class scope are compiled
3555 inline by default; i.e., you don't need to add @samp{inline} in front of
3556 the member function name.
3558 @item -fno-defer-pop
3559 @opindex fno-defer-pop
3560 Always pop the arguments to each function call as soon as that function
3561 returns. For machines which must pop arguments after a function call,
3562 the compiler normally lets arguments accumulate on the stack for several
3563 function calls and pops them all at once.
3565 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3569 Force memory operands to be copied into registers before doing
3570 arithmetic on them. This produces better code by making all memory
3571 references potential common subexpressions. When they are not common
3572 subexpressions, instruction combination should eliminate the separate
3575 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3578 @opindex fforce-addr
3579 Force memory address constants to be copied into registers before
3580 doing arithmetic on them. This may produce better code just as
3581 @option{-fforce-mem} may.
3583 @item -fomit-frame-pointer
3584 @opindex fomit-frame-pointer
3585 Don't keep the frame pointer in a register for functions that
3586 don't need one. This avoids the instructions to save, set up and
3587 restore frame pointers; it also makes an extra register available
3588 in many functions. @strong{It also makes debugging impossible on
3591 On some machines, such as the VAX, this flag has no effect, because
3592 the standard calling sequence automatically handles the frame pointer
3593 and nothing is saved by pretending it doesn't exist. The
3594 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3595 whether a target machine supports this flag. @xref{Registers,,Register
3596 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3598 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3600 @item -foptimize-sibling-calls
3601 @opindex foptimize-sibling-calls
3602 Optimize sibling and tail recursive calls.
3604 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3608 Don't pay attention to the @code{inline} keyword. Normally this option
3609 is used to keep the compiler from expanding any functions inline.
3610 Note that if you are not optimizing, no functions can be expanded inline.
3612 @item -finline-functions
3613 @opindex finline-functions
3614 Integrate all simple functions into their callers. The compiler
3615 heuristically decides which functions are simple enough to be worth
3616 integrating in this way.
3618 If all calls to a given function are integrated, and the function is
3619 declared @code{static}, then the function is normally not output as
3620 assembler code in its own right.
3622 Enabled at level @option{-O3}.
3624 @item -finline-limit=@var{n}
3625 @opindex finline-limit
3626 By default, gcc limits the size of functions that can be inlined. This flag
3627 allows the control of this limit for functions that are explicitly marked as
3628 inline (i.e., marked with the inline keyword or defined within the class
3629 definition in c++). @var{n} is the size of functions that can be inlined in
3630 number of pseudo instructions (not counting parameter handling). The default
3631 value of @var{n} is 600.
3632 Increasing this value can result in more inlined code at
3633 the cost of compilation time and memory consumption. Decreasing usually makes
3634 the compilation faster and less code will be inlined (which presumably
3635 means slower programs). This option is particularly useful for programs that
3636 use inlining heavily such as those based on recursive templates with C++.
3638 Inlining is actually controlled by a number of parameters, which may be
3639 specified individually by using @option{--param @var{name}=@var{value}}.
3640 The @option{-finline-limit=@var{n}} option sets some of these parameters
3644 @item max-inline-insns
3646 @item max-inline-insns-single
3647 is set to @var{n}/2.
3648 @item max-inline-insns-auto
3649 is set to @var{n}/2.
3650 @item min-inline-insns
3651 is set to 130 or @var{n}/4, whichever is smaller.
3652 @item max-inline-insns-rtl
3656 Using @option{-finline-limit=600} thus results in the default settings
3657 for these parameters. See below for a documentation of the individual
3658 parameters controlling inlining.
3660 @emph{Note:} pseudo instruction represents, in this particular context, an
3661 abstract measurement of function's size. In no way, it represents a count
3662 of assembly instructions and as such its exact meaning might change from one
3663 release to an another.
3665 @item -fkeep-inline-functions
3666 @opindex fkeep-inline-functions
3667 Even if all calls to a given function are integrated, and the function
3668 is declared @code{static}, nevertheless output a separate run-time
3669 callable version of the function. This switch does not affect
3670 @code{extern inline} functions.
3672 @item -fkeep-static-consts
3673 @opindex fkeep-static-consts
3674 Emit variables declared @code{static const} when optimization isn't turned
3675 on, even if the variables aren't referenced.
3677 GCC enables this option by default. If you want to force the compiler to
3678 check if the variable was referenced, regardless of whether or not
3679 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3681 @item -fmerge-constants
3682 Attempt to merge identical constants (string constants and floating point
3683 constants) across compilation units.
3685 This option is the default for optimized compilation if the assembler and
3686 linker support it. Use @option{-fno-merge-constants} to inhibit this
3689 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3691 @item -fmerge-all-constants
3692 Attempt to merge identical constants and identical variables.
3694 This option implies @option{-fmerge-constants}. In addition to
3695 @option{-fmerge-constants} this considers e.g. even constant initialized
3696 arrays or initialized constant variables with integral or floating point
3697 types. Languages like C or C++ require each non-automatic variable to
3698 have distinct location, so using this option will result in non-conforming
3703 Use a graph coloring register allocator. Currently this option is meant
3704 for testing, so we are interested to hear about miscompilations with
3707 @item -fno-branch-count-reg
3708 @opindex fno-branch-count-reg
3709 Do not use ``decrement and branch'' instructions on a count register,
3710 but instead generate a sequence of instructions that decrement a
3711 register, compare it against zero, then branch based upon the result.
3712 This option is only meaningful on architectures that support such
3713 instructions, which include x86, PowerPC, IA-64 and S/390.
3715 The default is @option{-fbranch-count-reg}, enabled when
3716 @option{-fstrength-reduce} is enabled.
3718 @item -fno-function-cse
3719 @opindex fno-function-cse
3720 Do not put function addresses in registers; make each instruction that
3721 calls a constant function contain the function's address explicitly.
3723 This option results in less efficient code, but some strange hacks
3724 that alter the assembler output may be confused by the optimizations
3725 performed when this option is not used.
3727 The default is @option{-ffunction-cse}
3729 @item -fno-zero-initialized-in-bss
3730 @opindex fno-zero-initialized-in-bss
3731 If the target supports a BSS section, GCC by default puts variables that
3732 are initialized to zero into BSS@. This can save space in the resulting
3735 This option turns off this behavior because some programs explicitly
3736 rely on variables going to the data section. E.g., so that the
3737 resulting executable can find the beginning of that section and/or make
3738 assumptions based on that.
3740 The default is @option{-fzero-initialized-in-bss}.
3742 @item -fstrength-reduce
3743 @opindex fstrength-reduce
3744 Perform the optimizations of loop strength reduction and
3745 elimination of iteration variables.
3747 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3749 @item -fthread-jumps
3750 @opindex fthread-jumps
3751 Perform optimizations where we check to see if a jump branches to a
3752 location where another comparison subsumed by the first is found. If
3753 so, the first branch is redirected to either the destination of the
3754 second branch or a point immediately following it, depending on whether
3755 the condition is known to be true or false.
3757 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3759 @item -fcse-follow-jumps
3760 @opindex fcse-follow-jumps
3761 In common subexpression elimination, scan through jump instructions
3762 when the target of the jump is not reached by any other path. For
3763 example, when CSE encounters an @code{if} statement with an
3764 @code{else} clause, CSE will follow the jump when the condition
3767 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3769 @item -fcse-skip-blocks
3770 @opindex fcse-skip-blocks
3771 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3772 follow jumps which conditionally skip over blocks. When CSE
3773 encounters a simple @code{if} statement with no else clause,
3774 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3775 body of the @code{if}.
3777 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3779 @item -frerun-cse-after-loop
3780 @opindex frerun-cse-after-loop
3781 Re-run common subexpression elimination after loop optimizations has been
3784 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3786 @item -frerun-loop-opt
3787 @opindex frerun-loop-opt
3788 Run the loop optimizer twice.
3790 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3794 Perform a global common subexpression elimination pass.
3795 This pass also performs global constant and copy propagation.
3797 @emph{Note:} When compiling a program using computed gotos, a GCC
3798 extension, you may get better runtime performance if you disable
3799 the global common subexpression elimination pass by adding
3800 @option{-fno-gcse} to the command line.
3802 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3806 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3807 attempt to move loads which are only killed by stores into themselves. This
3808 allows a loop containing a load/store sequence to be changed to a load outside
3809 the loop, and a copy/store within the loop.
3811 Enabled by default when gcse is enabled.
3815 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3816 subexpression elimination. This pass will attempt to move stores out of loops.
3817 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3818 can be changed to a load before the loop and a store after the loop.
3820 Enabled by default when gcse is enabled.
3822 @item -floop-optimize
3823 @opindex floop-optimize
3824 Perform loop optimizations: move constant expressions out of loops, simplify
3825 exit test conditions and optionally do strength-reduction and loop unrolling as
3828 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3830 @item -fcrossjumping
3831 @opindex crossjumping
3832 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3833 resulting code may or may not perform better than without cross-jumping.
3835 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3837 @item -fif-conversion
3838 @opindex if-conversion
3839 Attempt to transform conditional jumps into branch-less equivalents. This
3840 include use of conditional moves, min, max, set flags and abs instructions, and
3841 some tricks doable by standard arithmetics. The use of conditional execution
3842 on chips where it is available is controlled by @code{if-conversion2}.
3844 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3846 @item -fif-conversion2
3847 @opindex if-conversion2
3848 Use conditional execution (where available) to transform conditional jumps into
3849 branch-less equivalents.
3851 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3853 @item -fdelete-null-pointer-checks
3854 @opindex fdelete-null-pointer-checks
3855 Use global dataflow analysis to identify and eliminate useless checks
3856 for null pointers. The compiler assumes that dereferencing a null
3857 pointer would have halted the program. If a pointer is checked after
3858 it has already been dereferenced, it cannot be null.
3860 In some environments, this assumption is not true, and programs can
3861 safely dereference null pointers. Use
3862 @option{-fno-delete-null-pointer-checks} to disable this optimization
3863 for programs which depend on that behavior.
3865 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3867 @item -fexpensive-optimizations
3868 @opindex fexpensive-optimizations
3869 Perform a number of minor optimizations that are relatively expensive.
3871 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3873 @item -foptimize-register-move
3875 @opindex foptimize-register-move
3877 Attempt to reassign register numbers in move instructions and as
3878 operands of other simple instructions in order to maximize the amount of
3879 register tying. This is especially helpful on machines with two-operand
3882 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3885 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3887 @item -fdelayed-branch
3888 @opindex fdelayed-branch
3889 If supported for the target machine, attempt to reorder instructions
3890 to exploit instruction slots available after delayed branch
3893 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3895 @item -fschedule-insns
3896 @opindex fschedule-insns
3897 If supported for the target machine, attempt to reorder instructions to
3898 eliminate execution stalls due to required data being unavailable. This
3899 helps machines that have slow floating point or memory load instructions
3900 by allowing other instructions to be issued until the result of the load
3901 or floating point instruction is required.
3903 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3905 @item -fschedule-insns2
3906 @opindex fschedule-insns2
3907 Similar to @option{-fschedule-insns}, but requests an additional pass of
3908 instruction scheduling after register allocation has been done. This is
3909 especially useful on machines with a relatively small number of
3910 registers and where memory load instructions take more than one cycle.
3912 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3914 @item -fno-sched-interblock
3915 @opindex fno-sched-interblock
3916 Don't schedule instructions across basic blocks. This is normally
3917 enabled by default when scheduling before register allocation, i.e.@:
3918 with @option{-fschedule-insns} or at @option{-O2} or higher.
3920 @item -fno-sched-spec
3921 @opindex fno-sched-spec
3922 Don't allow speculative motion of non-load instructions. This is normally
3923 enabled by default when scheduling before register allocation, i.e.@:
3924 with @option{-fschedule-insns} or at @option{-O2} or higher.
3926 @item -fsched-spec-load
3927 @opindex fsched-spec-load
3928 Allow speculative motion of some load instructions. This only makes
3929 sense when scheduling before register allocation, i.e.@: with
3930 @option{-fschedule-insns} or at @option{-O2} or higher.
3932 @item -fsched-spec-load-dangerous
3933 @opindex fsched-spec-load-dangerous
3934 Allow speculative motion of more load instructions. This only makes
3935 sense when scheduling before register allocation, i.e.@: with
3936 @option{-fschedule-insns} or at @option{-O2} or higher.
3938 @item -fsched2-use-superblocks
3939 @opindex fsched2-use-superblocks
3940 When schedulilng after register allocation, do use superblock scheduling
3941 algorithm. Superblock scheduling allows motion across basic block boundaries
3942 resulting on faster schedules. This option is experimental, as not all machine
3943 descriptions used by GCC model the CPU closely enough to avoid unreliable
3944 results from the algorithm.
3946 This only makes sense when scheduling after register allocation, i.e.@: with
3947 @option{-fschedule-insns2} or at @option{-O2} or higher.
3949 @item -fsched2-use-traces
3950 @opindex fsched2-use-traces
3951 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
3952 allocation and additionally perform code duplication in order to increase the
3953 size of superblocks using tracer pass. See @option{-ftracer} for details on
3956 This mode should produce faster but significantly longer programs. Also
3957 without @code{-fbranch-probabilities} the traces constructed may not match the
3958 reality and hurt the performance. This only makes
3959 sense when scheduling after register allocation, i.e.@: with
3960 @option{-fschedule-insns2} or at @option{-O2} or higher.
3962 @item -fcaller-saves
3963 @opindex fcaller-saves
3964 Enable values to be allocated in registers that will be clobbered by
3965 function calls, by emitting extra instructions to save and restore the
3966 registers around such calls. Such allocation is done only when it
3967 seems to result in better code than would otherwise be produced.
3969 This option is always enabled by default on certain machines, usually
3970 those which have no call-preserved registers to use instead.
3972 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3974 @item -fmove-all-movables
3975 @opindex fmove-all-movables
3976 Forces all invariant computations in loops to be moved
3979 @item -freduce-all-givs
3980 @opindex freduce-all-givs
3981 Forces all general-induction variables in loops to be
3984 @emph{Note:} When compiling programs written in Fortran,
3985 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
3986 by default when you use the optimizer.
3988 These options may generate better or worse code; results are highly
3989 dependent on the structure of loops within the source code.
3991 These two options are intended to be removed someday, once
3992 they have helped determine the efficacy of various
3993 approaches to improving loop optimizations.
3995 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
3996 know how use of these options affects
3997 the performance of your production code.
3998 We're very interested in code that runs @emph{slower}
3999 when these options are @emph{enabled}.
4002 @itemx -fno-peephole2
4003 @opindex fno-peephole
4004 @opindex fno-peephole2
4005 Disable any machine-specific peephole optimizations. The difference
4006 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4007 are implemented in the compiler; some targets use one, some use the
4008 other, a few use both.
4010 @option{-fpeephole} is enabled by default.
4011 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4013 @item -fno-guess-branch-probability
4014 @opindex fno-guess-branch-probability
4015 Do not guess branch probabilities using a randomized model.
4017 Sometimes gcc will opt to use a randomized model to guess branch
4018 probabilities, when none are available from either profiling feedback
4019 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4020 different runs of the compiler on the same program may produce different
4023 In a hard real-time system, people don't want different runs of the
4024 compiler to produce code that has different behavior; minimizing
4025 non-determinism is of paramount import. This switch allows users to
4026 reduce non-determinism, possibly at the expense of inferior
4029 The default is @option{-fguess-branch-probability} at levels
4030 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4032 @item -freorder-blocks
4033 @opindex freorder-blocks
4034 Reorder basic blocks in the compiled function in order to reduce number of
4035 taken branches and improve code locality.
4037 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4039 @item -freorder-functions
4040 @opindex freorder-functions
4041 Reorder basic blocks in the compiled function in order to reduce number of
4042 taken branches and improve code locality. This is implemented by using special
4043 subsections @code{text.hot} for most frequently executed functions and
4044 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4045 the linker so object file format must support named sections and linker must
4046 place them in a reasonable way.
4048 Also profile feedback must be available in to make this option effective. See
4049 @option{-fprofile-arcs} for details.
4051 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4053 @item -fstrict-aliasing
4054 @opindex fstrict-aliasing
4055 Allows the compiler to assume the strictest aliasing rules applicable to
4056 the language being compiled. For C (and C++), this activates
4057 optimizations based on the type of expressions. In particular, an
4058 object of one type is assumed never to reside at the same address as an
4059 object of a different type, unless the types are almost the same. For
4060 example, an @code{unsigned int} can alias an @code{int}, but not a
4061 @code{void*} or a @code{double}. A character type may alias any other
4064 Pay special attention to code like this:
4077 The practice of reading from a different union member than the one most
4078 recently written to (called ``type-punning'') is common. Even with
4079 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4080 is accessed through the union type. So, the code above will work as
4081 expected. However, this code might not:
4092 Every language that wishes to perform language-specific alias analysis
4093 should define a function that computes, given an @code{tree}
4094 node, an alias set for the node. Nodes in different alias sets are not
4095 allowed to alias. For an example, see the C front-end function
4096 @code{c_get_alias_set}.
4098 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4100 @item -falign-functions
4101 @itemx -falign-functions=@var{n}
4102 @opindex falign-functions
4103 Align the start of functions to the next power-of-two greater than
4104 @var{n}, skipping up to @var{n} bytes. For instance,
4105 @option{-falign-functions=32} aligns functions to the next 32-byte
4106 boundary, but @option{-falign-functions=24} would align to the next
4107 32-byte boundary only if this can be done by skipping 23 bytes or less.
4109 @option{-fno-align-functions} and @option{-falign-functions=1} are
4110 equivalent and mean that functions will not be aligned.
4112 Some assemblers only support this flag when @var{n} is a power of two;
4113 in that case, it is rounded up.
4115 If @var{n} is not specified, use a machine-dependent default.
4117 Enabled at levels @option{-O2}, @option{-O3}.
4119 @item -falign-labels
4120 @itemx -falign-labels=@var{n}
4121 @opindex falign-labels
4122 Align all branch targets to a power-of-two boundary, skipping up to
4123 @var{n} bytes like @option{-falign-functions}. This option can easily
4124 make code slower, because it must insert dummy operations for when the
4125 branch target is reached in the usual flow of the code.
4127 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4128 are greater than this value, then their values are used instead.
4130 If @var{n} is not specified, use a machine-dependent default which is
4131 very likely to be @samp{1}, meaning no alignment.
4133 Enabled at levels @option{-O2}, @option{-O3}.
4136 @itemx -falign-loops=@var{n}
4137 @opindex falign-loops
4138 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4139 like @option{-falign-functions}. The hope is that the loop will be
4140 executed many times, which will make up for any execution of the dummy
4143 If @var{n} is not specified, use a machine-dependent default.
4145 Enabled at levels @option{-O2}, @option{-O3}.
4148 @itemx -falign-jumps=@var{n}
4149 @opindex falign-jumps
4150 Align branch targets to a power-of-two boundary, for branch targets
4151 where the targets can only be reached by jumping, skipping up to @var{n}
4152 bytes like @option{-falign-functions}. In this case, no dummy operations
4155 If @var{n} is not specified, use a machine-dependent default.
4157 Enabled at levels @option{-O2}, @option{-O3}.
4159 @item -frename-registers
4160 @opindex frename-registers
4161 Attempt to avoid false dependencies in scheduled code by making use
4162 of registers left over after register allocation. This optimization
4163 will most benefit processors with lots of registers. It can, however,
4164 make debugging impossible, since variables will no longer stay in
4165 a ``home register''.
4167 Enabled at levels @option{-O3}.
4169 @item -fno-cprop-registers
4170 @opindex fno-cprop-registers
4171 After register allocation and post-register allocation instruction splitting,
4172 we perform a copy-propagation pass to try to reduce scheduling dependencies
4173 and occasionally eliminate the copy.
4175 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4179 The following options control compiler behavior regarding floating
4180 point arithmetic. These options trade off between speed and
4181 correctness. All must be specifically enabled.
4185 @opindex ffloat-store
4186 Do not store floating point variables in registers, and inhibit other
4187 options that might change whether a floating point value is taken from a
4190 @cindex floating point precision
4191 This option prevents undesirable excess precision on machines such as
4192 the 68000 where the floating registers (of the 68881) keep more
4193 precision than a @code{double} is supposed to have. Similarly for the
4194 x86 architecture. For most programs, the excess precision does only
4195 good, but a few programs rely on the precise definition of IEEE floating
4196 point. Use @option{-ffloat-store} for such programs, after modifying
4197 them to store all pertinent intermediate computations into variables.
4201 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4202 @option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
4203 @option{-fno-signaling-nans}.
4205 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4207 This option should never be turned on by any @option{-O} option since
4208 it can result in incorrect output for programs which depend on
4209 an exact implementation of IEEE or ISO rules/specifications for
4212 @item -fno-math-errno
4213 @opindex fno-math-errno
4214 Do not set ERRNO after calling math functions that are executed
4215 with a single instruction, e.g., sqrt. A program that relies on
4216 IEEE exceptions for math error handling may want to use this flag
4217 for speed while maintaining IEEE arithmetic compatibility.
4219 This option should never be turned on by any @option{-O} option since
4220 it can result in incorrect output for programs which depend on
4221 an exact implementation of IEEE or ISO rules/specifications for
4224 The default is @option{-fmath-errno}.
4226 @item -funsafe-math-optimizations
4227 @opindex funsafe-math-optimizations
4228 Allow optimizations for floating-point arithmetic that (a) assume
4229 that arguments and results are valid and (b) may violate IEEE or
4230 ANSI standards. When used at link-time, it may include libraries
4231 or startup files that change the default FPU control word or other
4232 similar optimizations.
4234 This option should never be turned on by any @option{-O} option since
4235 it can result in incorrect output for programs which depend on
4236 an exact implementation of IEEE or ISO rules/specifications for
4239 The default is @option{-fno-unsafe-math-optimizations}.
4241 @item -ffinite-math-only
4242 @opindex ffinite-math-only
4243 Allow optimizations for floating-point arithmetic that assume
4244 that arguments and results are not NaNs or +-Infs.
4246 This option should never be turned on by any @option{-O} option since
4247 it can result in incorrect output for programs which depend on
4248 an exact implementation of IEEE or ISO rules/specifications.
4250 The default is @option{-fno-finite-math-only}.
4252 @item -fno-trapping-math
4253 @opindex fno-trapping-math
4254 Compile code assuming that floating-point operations cannot generate
4255 user-visible traps. These traps include division by zero, overflow,
4256 underflow, inexact result and invalid operation. This option implies
4257 @option{-fno-signaling-nans}. Setting this option may allow faster
4258 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4260 This option should never be turned on by any @option{-O} option since
4261 it can result in incorrect output for programs which depend on
4262 an exact implementation of IEEE or ISO rules/specifications for
4265 The default is @option{-ftrapping-math}.
4267 @item -fsignaling-nans
4268 @opindex fsignaling-nans
4269 Compile code assuming that IEEE signaling NaNs may generate user-visible
4270 traps during floating-point operations. Setting this option disables
4271 optimizations that may change the number of exceptions visible with
4272 signaling NaNs. This option implies @option{-ftrapping-math}.
4274 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4277 The default is @option{-fno-signaling-nans}.
4279 This option is experimental and does not currently guarantee to
4280 disable all GCC optimizations that affect signaling NaN behavior.
4282 @item -fsingle-precision-constant
4283 @opindex fsingle-precision-constant
4284 Treat floating point constant as single precision constant instead of
4285 implicitly converting it to double precision constant.
4290 The following options control optimizations that may improve
4291 performance, but are not enabled by any @option{-O} options. This
4292 section includes experimental options that may produce broken code.
4295 @item -fbranch-probabilities
4296 @opindex fbranch-probabilities
4297 After running a program compiled with @option{-fprofile-arcs}
4298 (@pxref{Debugging Options,, Options for Debugging Your Program or
4299 @command{gcc}}), you can compile it a second time using
4300 @option{-fbranch-probabilities}, to improve optimizations based on
4301 the number of times each branch was taken. When the program
4302 compiled with @option{-fprofile-arcs} exits it saves arc execution
4303 counts to a file called @file{@var{sourcename}.da} for each source
4304 file The information in this data file is very dependent on the
4305 structure of the generated code, so you must use the same source code
4306 and the same optimization options for both compilations.
4308 With @option{-fbranch-probabilities}, GCC puts a
4309 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4310 These can be used to improve optimization. Currently, they are only
4311 used in one place: in @file{reorg.c}, instead of guessing which path a
4312 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4313 exactly determine which path is taken more often.
4317 Use a graph coloring register allocator. Currently this option is meant
4318 for testing, so we are interested to hear about miscompilations with
4323 Perform tail duplication to enlarge superblock size. This transformation
4324 simplifies the control flow of the function allowing other optimizations to do
4327 @item -funit-at-a-time
4328 @opindex funit-at-a-time
4329 Parse the whole compilation unit before starting to produce code. This allows some
4330 extra optimizations to take place but consumes more memory.
4332 @item -funroll-loops
4333 @opindex funroll-loops
4334 Unroll loops whose number of iterations can be determined at compile time or
4335 upon entry to the loop. @option{-funroll-loops} implies
4336 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4337 (i.e. complete removal of loops with small constant number of iterations).
4338 This option makes code larger, and may or may not make it run faster.
4340 @item -funroll-all-loops
4341 @opindex funroll-all-loops
4342 Unroll all loops, even if their number of iterations is uncertain when
4343 the loop is entered. This usually makes programs run more slowly.
4344 @option{-funroll-all-loops} implies the same options as
4345 @option{-funroll-loops}.
4348 @opindex fpeel-loops
4349 Peels the loops for that there is enough information that they do not
4350 roll much (from profile feedback). It also turns on complete loop peeling
4351 (i.e. complete removal of loops with small constant number of iterations).
4353 @item -funswitch-loops
4354 @opindex funswitch-loops
4355 Move branches with loop invariant conditions out of the loop, with duplicates
4356 of the loop on both branches (modified according to result of the condition).
4358 @item -fold-unroll-loops
4359 @opindex fold-unroll-loops
4360 Unroll loops whose number of iterations can be determined at compile
4361 time or upon entry to the loop, using the old loop unroller whose loop
4362 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4363 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4364 option makes code larger, and may or may not make it run faster.
4366 @item -fold-unroll-all-loops
4367 @opindex fold-unroll-all-loops
4368 Unroll all loops, even if their number of iterations is uncertain when
4369 the loop is entered. This is done using the old loop unroller whose loop
4370 recognition is based on notes from frontend. This usually makes programs run more slowly.
4371 @option{-fold-unroll-all-loops} implies the same options as
4372 @option{-fold-unroll-loops}.
4374 @item -funswitch-loops
4375 @opindex funswitch-loops
4376 Move branches with loop invariant conditions out of the loop, with duplicates
4377 of the loop on both branches (modified according to result of the condition).
4379 @item -funswitch-loops
4380 @opindex funswitch-loops
4381 Move branches with loop invariant conditions out of the loop, with duplicates
4382 of the loop on both branches (modified according to result of the condition).
4384 @item -fprefetch-loop-arrays
4385 @opindex fprefetch-loop-arrays
4386 If supported by the target machine, generate instructions to prefetch
4387 memory to improve the performance of loops that access large arrays.
4389 Disabled at level @option{-Os}.
4391 @item -ffunction-sections
4392 @itemx -fdata-sections
4393 @opindex ffunction-sections
4394 @opindex fdata-sections
4395 Place each function or data item into its own section in the output
4396 file if the target supports arbitrary sections. The name of the
4397 function or the name of the data item determines the section's name
4400 Use these options on systems where the linker can perform optimizations
4401 to improve locality of reference in the instruction space. Most systems
4402 using the ELF object format and SPARC processors running Solaris 2 have
4403 linkers with such optimizations. AIX may have these optimizations in
4406 Only use these options when there are significant benefits from doing
4407 so. When you specify these options, the assembler and linker will
4408 create larger object and executable files and will also be slower.
4409 You will not be able to use @code{gprof} on all systems if you
4410 specify this option and you may have problems with debugging if
4411 you specify both this option and @option{-g}.
4415 Perform optimizations in static single assignment form. Each function's
4416 flow graph is translated into SSA form, optimizations are performed, and
4417 the flow graph is translated back from SSA form. Users should not
4418 specify this option, since it is not yet ready for production use.
4422 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4423 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4427 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4428 Like @option{-fssa}, this is an experimental feature.
4430 @item -fbranch-target-load-optimize
4431 @opindex fbranch-target-load-optimize
4432 Perform branch target register load optimization before prologue / epilogue
4434 The use of target registers can typically be exposed only during reload,
4435 thus hoisting loads out of loops and doing inter-block scheduling needs
4436 a separate optimization pass.
4438 @item -fbranch-target-load-optimize2
4439 @opindex fbranch-target-load-optimize2
4440 Perform branch target register load optimization after prologue / epilogue
4446 @item --param @var{name}=@var{value}
4448 In some places, GCC uses various constants to control the amount of
4449 optimization that is done. For example, GCC will not inline functions
4450 that contain more that a certain number of instructions. You can
4451 control some of these constants on the command-line using the
4452 @option{--param} option.
4454 In each case, the @var{value} is an integer. The allowable choices for
4455 @var{name} are given in the following table:
4458 @item max-crossjump-edges
4459 The maximum number of incoming edges to consider for crossjumping.
4460 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4461 the number of edges incoming to each block. Increasing values mean
4462 more aggressive optimization, making the compile time increase with
4463 probably small improvement in executable size.
4465 @item max-delay-slot-insn-search
4466 The maximum number of instructions to consider when looking for an
4467 instruction to fill a delay slot. If more than this arbitrary number of
4468 instructions is searched, the time savings from filling the delay slot
4469 will be minimal so stop searching. Increasing values mean more
4470 aggressive optimization, making the compile time increase with probably
4471 small improvement in executable run time.
4473 @item max-delay-slot-live-search
4474 When trying to fill delay slots, the maximum number of instructions to
4475 consider when searching for a block with valid live register
4476 information. Increasing this arbitrarily chosen value means more
4477 aggressive optimization, increasing the compile time. This parameter
4478 should be removed when the delay slot code is rewritten to maintain the
4481 @item max-gcse-memory
4482 The approximate maximum amount of memory that will be allocated in
4483 order to perform the global common subexpression elimination
4484 optimization. If more memory than specified is required, the
4485 optimization will not be done.
4487 @item max-gcse-passes
4488 The maximum number of passes of GCSE to run.
4490 @item max-pending-list-length
4491 The maximum number of pending dependencies scheduling will allow
4492 before flushing the current state and starting over. Large functions
4493 with few branches or calls can create excessively large lists which
4494 needlessly consume memory and resources.
4496 @item max-inline-insns-single
4497 Several parameters control the tree inliner used in gcc.
4498 This number sets the maximum number of instructions (counted in gcc's
4499 internal representation) in a single function that the tree inliner
4500 will consider for inlining. This only affects functions declared
4501 inline and methods implemented in a class declaration (C++).
4502 The default value is 300.
4504 @item max-inline-insns-auto
4505 When you use @option{-finline-functions} (included in @option{-O3}),
4506 a lot of functions that would otherwise not be considered for inlining
4507 by the compiler will be investigated. To those functions, a different
4508 (more restrictive) limit compared to functions declared inline can
4510 The default value is 300.
4512 @item max-inline-insns
4513 The tree inliner does decrease the allowable size for single functions
4514 to be inlined after we already inlined the number of instructions
4515 given here by repeated inlining. This number should be a factor of
4516 two or more larger than the single function limit.
4517 Higher numbers result in better runtime performance, but incur higher
4518 compile-time resource (CPU time, memory) requirements and result in
4519 larger binaries. Very high values are not advisable, as too large
4520 binaries may adversely affect runtime performance.
4521 The default value is 600.
4523 @item max-inline-slope
4524 After exceeding the maximum number of inlined instructions by repeated
4525 inlining, a linear function is used to decrease the allowable size
4526 for single functions. The slope of that function is the negative
4527 reciprocal of the number specified here.
4528 The default value is 32.
4530 @item min-inline-insns
4531 The repeated inlining is throttled more and more by the linear function
4532 after exceeding the limit. To avoid too much throttling, a minimum for
4533 this function is specified here to allow repeated inlining for very small
4534 functions even when a lot of repeated inlining already has been done.
4535 The default value is 130.
4537 @item max-inline-insns-rtl
4538 For languages that use the RTL inliner (this happens at a later stage
4539 than tree inlining), you can set the maximum allowable size (counted
4540 in RTL instructions) for the RTL inliner with this parameter.
4541 The default value is 600.
4544 @item max-unrolled-insns
4545 The maximum number of instructions that a loop should have if that loop
4546 is unrolled, and if the loop is unrolled, it determines how many times
4547 the loop code is unrolled.
4549 @item max-average-unrolled-insns
4550 The maximum number of instructions biased by probabilities of their execution
4551 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4552 it determines how many times the loop code is unrolled.
4554 @item max-unroll-times
4555 The maximum number of unrollings of a single loop.
4557 @item max-peeled-insns
4558 The maximum number of instructions that a loop should have if that loop
4559 is peeled, and if the loop is peeled, it determines how many times
4560 the loop code is peeled.
4562 @item max-peel-times
4563 The maximum number of peelings of a single loop.
4565 @item max-completely-peeled-insns
4566 The maximum number of insns of a completely peeled loop.
4568 @item max-completely-peel-times
4569 The maximum number of iterations of a loop to be suitable for complete peeling.
4571 @item max-unswitch-insns
4572 The maximum number of insns of an unswitched loop.
4574 @item max-unswitch-level
4575 The maximum number of branches unswitched in a single loop.
4577 @item hot-bb-count-fraction
4578 Select fraction of the maximal count of repetitions of basic block in program
4579 given basic block needs to have to be considered hot.
4581 @item hot-bb-frequency-fraction
4582 Select fraction of the maximal frequency of executions of basic block in
4583 function given basic block needs to have to be considered hot
4585 @item tracer-dynamic-coverage
4586 @itemx tracer-dynamic-coverage-feedback
4588 This value is used to limit superblock formation once the given percentage of
4589 executed instructions is covered. This limits unnecessary code size
4592 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4593 feedback is available. The real profiles (as opposed to statically estimated
4594 ones) are much less balanced allowing the threshold to be larger value.
4596 @item tracer-max-code-growth
4597 Stop tail duplication once code growth has reached given percentage. This is
4598 rather hokey argument, as most of the duplicates will be eliminated later in
4599 cross jumping, so it may be set to much higher values than is the desired code
4602 @item tracer-min-branch-ratio
4604 Stop reverse growth when the reverse probability of best edge is less than this
4605 threshold (in percent).
4607 @item tracer-min-branch-ratio
4608 @itemx tracer-min-branch-ratio-feedback
4610 Stop forward growth if the best edge do have probability lower than this
4613 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4614 compilation for profile feedback and one for compilation without. The value
4615 for compilation with profile feedback needs to be more conservative (higher) in
4616 order to make tracer effective.
4618 @item max-cse-path-length
4620 Maximum number of basic blocks on path that cse considers.
4622 @item ggc-min-expand
4624 GCC uses a garbage collector to manage its own memory allocation. This
4625 parameter specifies the minimum percentage by which the garbage
4626 collector's heap should be allowed to expand between collections.
4627 Tuning this may improve compilation speed; it has no effect on code
4630 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4631 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4632 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4633 GCC is not able to calculate RAM on a particular platform, the lower
4634 bound of 30% is used. Setting this parameter and
4635 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4636 every opportunity. This is extremely slow, but can be useful for
4639 @item ggc-min-heapsize
4641 Minimum size of the garbage collector's heap before it begins bothering
4642 to collect garbage. The first collection occurs after the heap expands
4643 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4644 tuning this may improve compilation speed, and has no effect on code
4647 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4648 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4649 available, the notion of "RAM" is the smallest of actual RAM,
4650 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4651 RAM on a particular platform, the lower bound is used. Setting this
4652 parameter very large effectively disables garbage collection. Setting
4653 this parameter and @option{ggc-min-expand} to zero causes a full
4654 collection to occur at every opportunity.
4656 @item reorder-blocks-duplicate
4657 @itemx reorder-blocks-duplicate-feedback
4659 Used by basic block reordering pass to decide whether to use unconditional
4660 branch or duplicate the code on it's destination. Code is duplicated when it's
4661 estimated size is smaller than this value multiplied by the estimated size of
4662 unconditional jump in the hot spots of the program.
4664 The @option{reorder-block-duplicate-feedback} is used only when profile
4665 feedback is available and may be set to higher values than
4666 @option{reorder-block-duplicate} since information about the hot spots is more
4671 @node Preprocessor Options
4672 @section Options Controlling the Preprocessor
4673 @cindex preprocessor options
4674 @cindex options, preprocessor
4676 These options control the C preprocessor, which is run on each C source
4677 file before actual compilation.
4679 If you use the @option{-E} option, nothing is done except preprocessing.
4680 Some of these options make sense only together with @option{-E} because
4681 they cause the preprocessor output to be unsuitable for actual
4686 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4687 and pass @var{option} directly through to the preprocessor. If
4688 @var{option} contains commas, it is split into multiple options at the
4689 commas. However, many options are modified, translated or interpreted
4690 by the compiler driver before being passed to the preprocessor, and
4691 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4692 interface is undocumented and subject to change, so whenever possible
4693 you should avoid using @option{-Wp} and let the driver handle the
4696 @item -Xpreprocessor @var{option}
4697 @opindex preprocessor
4698 Pass @var{option} as an option to the preprocessor. You can use this to
4699 supply system-specific preprocessor options which GCC does not know how to
4702 If you want to pass an option that takes an argument, you must use
4703 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4706 @include cppopts.texi
4708 @node Assembler Options
4709 @section Passing Options to the Assembler
4711 @c prevent bad page break with this line
4712 You can pass options to the assembler.
4715 @item -Wa,@var{option}
4717 Pass @var{option} as an option to the assembler. If @var{option}
4718 contains commas, it is split into multiple options at the commas.
4720 @item -Xassembler @var{option}
4722 Pass @var{option} as an option to the assembler. You can use this to
4723 supply system-specific assembler options which GCC does not know how to
4726 If you want to pass an option that takes an argument, you must use
4727 @option{-Xassembler} twice, once for the option and once for the argument.
4732 @section Options for Linking
4733 @cindex link options
4734 @cindex options, linking
4736 These options come into play when the compiler links object files into
4737 an executable output file. They are meaningless if the compiler is
4738 not doing a link step.
4742 @item @var{object-file-name}
4743 A file name that does not end in a special recognized suffix is
4744 considered to name an object file or library. (Object files are
4745 distinguished from libraries by the linker according to the file
4746 contents.) If linking is done, these object files are used as input
4755 If any of these options is used, then the linker is not run, and
4756 object file names should not be used as arguments. @xref{Overall
4760 @item -l@var{library}
4761 @itemx -l @var{library}
4763 Search the library named @var{library} when linking. (The second
4764 alternative with the library as a separate argument is only for
4765 POSIX compliance and is not recommended.)
4767 It makes a difference where in the command you write this option; the
4768 linker searches and processes libraries and object files in the order they
4769 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4770 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4771 to functions in @samp{z}, those functions may not be loaded.
4773 The linker searches a standard list of directories for the library,
4774 which is actually a file named @file{lib@var{library}.a}. The linker
4775 then uses this file as if it had been specified precisely by name.
4777 The directories searched include several standard system directories
4778 plus any that you specify with @option{-L}.
4780 Normally the files found this way are library files---archive files
4781 whose members are object files. The linker handles an archive file by
4782 scanning through it for members which define symbols that have so far
4783 been referenced but not defined. But if the file that is found is an
4784 ordinary object file, it is linked in the usual fashion. The only
4785 difference between using an @option{-l} option and specifying a file name
4786 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4787 and searches several directories.
4791 You need this special case of the @option{-l} option in order to
4792 link an Objective-C program.
4795 @opindex nostartfiles
4796 Do not use the standard system startup files when linking.
4797 The standard system libraries are used normally, unless @option{-nostdlib}
4798 or @option{-nodefaultlibs} is used.
4800 @item -nodefaultlibs
4801 @opindex nodefaultlibs
4802 Do not use the standard system libraries when linking.
4803 Only the libraries you specify will be passed to the linker.
4804 The standard startup files are used normally, unless @option{-nostartfiles}
4805 is used. The compiler may generate calls to memcmp, memset, and memcpy
4806 for System V (and ISO C) environments or to bcopy and bzero for
4807 BSD environments. These entries are usually resolved by entries in
4808 libc. These entry points should be supplied through some other
4809 mechanism when this option is specified.
4813 Do not use the standard system startup files or libraries when linking.
4814 No startup files and only the libraries you specify will be passed to
4815 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4816 for System V (and ISO C) environments or to bcopy and bzero for
4817 BSD environments. These entries are usually resolved by entries in
4818 libc. These entry points should be supplied through some other
4819 mechanism when this option is specified.
4821 @cindex @option{-lgcc}, use with @option{-nostdlib}
4822 @cindex @option{-nostdlib} and unresolved references
4823 @cindex unresolved references and @option{-nostdlib}
4824 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4825 @cindex @option{-nodefaultlibs} and unresolved references
4826 @cindex unresolved references and @option{-nodefaultlibs}
4827 One of the standard libraries bypassed by @option{-nostdlib} and
4828 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4829 that GCC uses to overcome shortcomings of particular machines, or special
4830 needs for some languages.
4831 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
4832 Collection (GCC) Internals},
4833 for more discussion of @file{libgcc.a}.)
4834 In most cases, you need @file{libgcc.a} even when you want to avoid
4835 other standard libraries. In other words, when you specify @option{-nostdlib}
4836 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4837 This ensures that you have no unresolved references to internal GCC
4838 library subroutines. (For example, @samp{__main}, used to ensure C++
4839 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
4840 GNU Compiler Collection (GCC) Internals}.)
4844 Produce a position independent executable on targets which support it.
4845 For predictable results, you must also specify the same set of options
4846 that were used to generate code (@option{-fpie}, @option{-fPIE},
4847 or model suboptions) when you specify this option.
4851 Remove all symbol table and relocation information from the executable.
4855 On systems that support dynamic linking, this prevents linking with the shared
4856 libraries. On other systems, this option has no effect.
4860 Produce a shared object which can then be linked with other objects to
4861 form an executable. Not all systems support this option. For predictable
4862 results, you must also specify the same set of options that were used to
4863 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4864 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4865 needs to build supplementary stub code for constructors to work. On
4866 multi-libbed systems, @samp{gcc -shared} must select the correct support
4867 libraries to link against. Failing to supply the correct flags may lead
4868 to subtle defects. Supplying them in cases where they are not necessary
4871 @item -shared-libgcc
4872 @itemx -static-libgcc
4873 @opindex shared-libgcc
4874 @opindex static-libgcc
4875 On systems that provide @file{libgcc} as a shared library, these options
4876 force the use of either the shared or static version respectively.
4877 If no shared version of @file{libgcc} was built when the compiler was
4878 configured, these options have no effect.
4880 There are several situations in which an application should use the
4881 shared @file{libgcc} instead of the static version. The most common
4882 of these is when the application wishes to throw and catch exceptions
4883 across different shared libraries. In that case, each of the libraries
4884 as well as the application itself should use the shared @file{libgcc}.
4886 Therefore, the G++ and GCJ drivers automatically add
4887 @option{-shared-libgcc} whenever you build a shared library or a main
4888 executable, because C++ and Java programs typically use exceptions, so
4889 this is the right thing to do.
4891 If, instead, you use the GCC driver to create shared libraries, you may
4892 find that they will not always be linked with the shared @file{libgcc}.
4893 If GCC finds, at its configuration time, that you have a GNU linker that
4894 does not support option @option{--eh-frame-hdr}, it will link the shared
4895 version of @file{libgcc} into shared libraries by default. Otherwise,
4896 it will take advantage of the linker and optimize away the linking with
4897 the shared version of @file{libgcc}, linking with the static version of
4898 libgcc by default. This allows exceptions to propagate through such
4899 shared libraries, without incurring relocation costs at library load
4902 However, if a library or main executable is supposed to throw or catch
4903 exceptions, you must link it using the G++ or GCJ driver, as appropriate
4904 for the languages used in the program, or using the option
4905 @option{-shared-libgcc}, such that it is linked with the shared
4910 Bind references to global symbols when building a shared object. Warn
4911 about any unresolved references (unless overridden by the link editor
4912 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4915 @item -Xlinker @var{option}
4917 Pass @var{option} as an option to the linker. You can use this to
4918 supply system-specific linker options which GCC does not know how to
4921 If you want to pass an option that takes an argument, you must use
4922 @option{-Xlinker} twice, once for the option and once for the argument.
4923 For example, to pass @option{-assert definitions}, you must write
4924 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4925 @option{-Xlinker "-assert definitions"}, because this passes the entire
4926 string as a single argument, which is not what the linker expects.
4928 @item -Wl,@var{option}
4930 Pass @var{option} as an option to the linker. If @var{option} contains
4931 commas, it is split into multiple options at the commas.
4933 @item -u @var{symbol}
4935 Pretend the symbol @var{symbol} is undefined, to force linking of
4936 library modules to define it. You can use @option{-u} multiple times with
4937 different symbols to force loading of additional library modules.
4940 @node Directory Options
4941 @section Options for Directory Search
4942 @cindex directory options
4943 @cindex options, directory search
4946 These options specify directories to search for header files, for
4947 libraries and for parts of the compiler:
4952 Add the directory @var{dir} to the head of the list of directories to be
4953 searched for header files. This can be used to override a system header
4954 file, substituting your own version, since these directories are
4955 searched before the system header file directories. However, you should
4956 not use this option to add directories that contain vendor-supplied
4957 system header files (use @option{-isystem} for that). If you use more than
4958 one @option{-I} option, the directories are scanned in left-to-right
4959 order; the standard system directories come after.
4961 If a standard system include directory, or a directory specified with
4962 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
4963 option will be ignored. The directory will still be searched but as a
4964 system directory at its normal position in the system include chain.
4965 This is to ensure that GCC's procedure to fix buggy system headers and
4966 the ordering for the include_next directive are not inadvertently changed.
4967 If you really need to change the search order for system directories,
4968 use the @option{-nostdinc} and/or @option{-isystem} options.
4972 Any directories you specify with @option{-I} options before the @option{-I-}
4973 option are searched only for the case of @samp{#include "@var{file}"};
4974 they are not searched for @samp{#include <@var{file}>}.
4976 If additional directories are specified with @option{-I} options after
4977 the @option{-I-}, these directories are searched for all @samp{#include}
4978 directives. (Ordinarily @emph{all} @option{-I} directories are used
4981 In addition, the @option{-I-} option inhibits the use of the current
4982 directory (where the current input file came from) as the first search
4983 directory for @samp{#include "@var{file}"}. There is no way to
4984 override this effect of @option{-I-}. With @option{-I.} you can specify
4985 searching the directory which was current when the compiler was
4986 invoked. That is not exactly the same as what the preprocessor does
4987 by default, but it is often satisfactory.
4989 @option{-I-} does not inhibit the use of the standard system directories
4990 for header files. Thus, @option{-I-} and @option{-nostdinc} are
4995 Add directory @var{dir} to the list of directories to be searched
4998 @item -B@var{prefix}
5000 This option specifies where to find the executables, libraries,
5001 include files, and data files of the compiler itself.
5003 The compiler driver program runs one or more of the subprograms
5004 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5005 @var{prefix} as a prefix for each program it tries to run, both with and
5006 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5008 For each subprogram to be run, the compiler driver first tries the
5009 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5010 was not specified, the driver tries two standard prefixes, which are
5011 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
5012 those results in a file name that is found, the unmodified program
5013 name is searched for using the directories specified in your
5014 @env{PATH} environment variable.
5016 The compiler will check to see if the path provided by the @option{-B}
5017 refers to a directory, and if necessary it will add a directory
5018 separator character at the end of the path.
5020 @option{-B} prefixes that effectively specify directory names also apply
5021 to libraries in the linker, because the compiler translates these
5022 options into @option{-L} options for the linker. They also apply to
5023 includes files in the preprocessor, because the compiler translates these
5024 options into @option{-isystem} options for the preprocessor. In this case,
5025 the compiler appends @samp{include} to the prefix.
5027 The run-time support file @file{libgcc.a} can also be searched for using
5028 the @option{-B} prefix, if needed. If it is not found there, the two
5029 standard prefixes above are tried, and that is all. The file is left
5030 out of the link if it is not found by those means.
5032 Another way to specify a prefix much like the @option{-B} prefix is to use
5033 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5036 As a special kludge, if the path provided by @option{-B} is
5037 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5038 9, then it will be replaced by @file{[dir/]include}. This is to help
5039 with boot-strapping the compiler.
5041 @item -specs=@var{file}
5043 Process @var{file} after the compiler reads in the standard @file{specs}
5044 file, in order to override the defaults that the @file{gcc} driver
5045 program uses when determining what switches to pass to @file{cc1},
5046 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5047 @option{-specs=@var{file}} can be specified on the command line, and they
5048 are processed in order, from left to right.
5054 @section Specifying subprocesses and the switches to pass to them
5057 @command{gcc} is a driver program. It performs its job by invoking a
5058 sequence of other programs to do the work of compiling, assembling and
5059 linking. GCC interprets its command-line parameters and uses these to
5060 deduce which programs it should invoke, and which command-line options
5061 it ought to place on their command lines. This behavior is controlled
5062 by @dfn{spec strings}. In most cases there is one spec string for each
5063 program that GCC can invoke, but a few programs have multiple spec
5064 strings to control their behavior. The spec strings built into GCC can
5065 be overridden by using the @option{-specs=} command-line switch to specify
5068 @dfn{Spec files} are plaintext files that are used to construct spec
5069 strings. They consist of a sequence of directives separated by blank
5070 lines. The type of directive is determined by the first non-whitespace
5071 character on the line and it can be one of the following:
5074 @item %@var{command}
5075 Issues a @var{command} to the spec file processor. The commands that can
5079 @item %include <@var{file}>
5081 Search for @var{file} and insert its text at the current point in the
5084 @item %include_noerr <@var{file}>
5085 @cindex %include_noerr
5086 Just like @samp{%include}, but do not generate an error message if the include
5087 file cannot be found.
5089 @item %rename @var{old_name} @var{new_name}
5091 Rename the spec string @var{old_name} to @var{new_name}.
5095 @item *[@var{spec_name}]:
5096 This tells the compiler to create, override or delete the named spec
5097 string. All lines after this directive up to the next directive or
5098 blank line are considered to be the text for the spec string. If this
5099 results in an empty string then the spec will be deleted. (Or, if the
5100 spec did not exist, then nothing will happened.) Otherwise, if the spec
5101 does not currently exist a new spec will be created. If the spec does
5102 exist then its contents will be overridden by the text of this
5103 directive, unless the first character of that text is the @samp{+}
5104 character, in which case the text will be appended to the spec.
5106 @item [@var{suffix}]:
5107 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5108 and up to the next directive or blank line are considered to make up the
5109 spec string for the indicated suffix. When the compiler encounters an
5110 input file with the named suffix, it will processes the spec string in
5111 order to work out how to compile that file. For example:
5118 This says that any input file whose name ends in @samp{.ZZ} should be
5119 passed to the program @samp{z-compile}, which should be invoked with the
5120 command-line switch @option{-input} and with the result of performing the
5121 @samp{%i} substitution. (See below.)
5123 As an alternative to providing a spec string, the text that follows a
5124 suffix directive can be one of the following:
5127 @item @@@var{language}
5128 This says that the suffix is an alias for a known @var{language}. This is
5129 similar to using the @option{-x} command-line switch to GCC to specify a
5130 language explicitly. For example:
5137 Says that .ZZ files are, in fact, C++ source files.
5140 This causes an error messages saying:
5143 @var{name} compiler not installed on this system.
5147 GCC already has an extensive list of suffixes built into it.
5148 This directive will add an entry to the end of the list of suffixes, but
5149 since the list is searched from the end backwards, it is effectively
5150 possible to override earlier entries using this technique.
5154 GCC has the following spec strings built into it. Spec files can
5155 override these strings or create their own. Note that individual
5156 targets can also add their own spec strings to this list.
5159 asm Options to pass to the assembler
5160 asm_final Options to pass to the assembler post-processor
5161 cpp Options to pass to the C preprocessor
5162 cc1 Options to pass to the C compiler
5163 cc1plus Options to pass to the C++ compiler
5164 endfile Object files to include at the end of the link
5165 link Options to pass to the linker
5166 lib Libraries to include on the command line to the linker
5167 libgcc Decides which GCC support library to pass to the linker
5168 linker Sets the name of the linker
5169 predefines Defines to be passed to the C preprocessor
5170 signed_char Defines to pass to CPP to say whether @code{char} is signed
5172 startfile Object files to include at the start of the link
5175 Here is a small example of a spec file:
5181 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5184 This example renames the spec called @samp{lib} to @samp{old_lib} and
5185 then overrides the previous definition of @samp{lib} with a new one.
5186 The new definition adds in some extra command-line options before
5187 including the text of the old definition.
5189 @dfn{Spec strings} are a list of command-line options to be passed to their
5190 corresponding program. In addition, the spec strings can contain
5191 @samp{%}-prefixed sequences to substitute variable text or to
5192 conditionally insert text into the command line. Using these constructs
5193 it is possible to generate quite complex command lines.
5195 Here is a table of all defined @samp{%}-sequences for spec
5196 strings. Note that spaces are not generated automatically around the
5197 results of expanding these sequences. Therefore you can concatenate them
5198 together or combine them with constant text in a single argument.
5202 Substitute one @samp{%} into the program name or argument.
5205 Substitute the name of the input file being processed.
5208 Substitute the basename of the input file being processed.
5209 This is the substring up to (and not including) the last period
5210 and not including the directory.
5213 This is the same as @samp{%b}, but include the file suffix (text after
5217 Marks the argument containing or following the @samp{%d} as a
5218 temporary file name, so that that file will be deleted if GCC exits
5219 successfully. Unlike @samp{%g}, this contributes no text to the
5222 @item %g@var{suffix}
5223 Substitute a file name that has suffix @var{suffix} and is chosen
5224 once per compilation, and mark the argument in the same way as
5225 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5226 name is now chosen in a way that is hard to predict even when previously
5227 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5228 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5229 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5230 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5231 was simply substituted with a file name chosen once per compilation,
5232 without regard to any appended suffix (which was therefore treated
5233 just like ordinary text), making such attacks more likely to succeed.
5235 @item %u@var{suffix}
5236 Like @samp{%g}, but generates a new temporary file name even if
5237 @samp{%u@var{suffix}} was already seen.
5239 @item %U@var{suffix}
5240 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5241 new one if there is no such last file name. In the absence of any
5242 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5243 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5244 would involve the generation of two distinct file names, one
5245 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5246 simply substituted with a file name chosen for the previous @samp{%u},
5247 without regard to any appended suffix.
5249 @item %j@var{suffix}
5250 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5251 writable, and if save-temps is off; otherwise, substitute the name
5252 of a temporary file, just like @samp{%u}. This temporary file is not
5253 meant for communication between processes, but rather as a junk
5256 @item %|@var{suffix}
5257 @itemx %m@var{suffix}
5258 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5259 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5260 all. These are the two most common ways to instruct a program that it
5261 should read from standard input or write to standard output. If you
5262 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5263 construct: see for example @file{f/lang-specs.h}.
5265 @item %.@var{SUFFIX}
5266 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5267 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5268 terminated by the next space or %.
5271 Marks the argument containing or following the @samp{%w} as the
5272 designated output file of this compilation. This puts the argument
5273 into the sequence of arguments that @samp{%o} will substitute later.
5276 Substitutes the names of all the output files, with spaces
5277 automatically placed around them. You should write spaces
5278 around the @samp{%o} as well or the results are undefined.
5279 @samp{%o} is for use in the specs for running the linker.
5280 Input files whose names have no recognized suffix are not compiled
5281 at all, but they are included among the output files, so they will
5285 Substitutes the suffix for object files. Note that this is
5286 handled specially when it immediately follows @samp{%g, %u, or %U},
5287 because of the need for those to form complete file names. The
5288 handling is such that @samp{%O} is treated exactly as if it had already
5289 been substituted, except that @samp{%g, %u, and %U} do not currently
5290 support additional @var{suffix} characters following @samp{%O} as they would
5291 following, for example, @samp{.o}.
5294 Substitutes the standard macro predefinitions for the
5295 current target machine. Use this when running @code{cpp}.
5298 Like @samp{%p}, but puts @samp{__} before and after the name of each
5299 predefined macro, except for macros that start with @samp{__} or with
5300 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5304 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5305 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5306 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5310 Current argument is the name of a library or startup file of some sort.
5311 Search for that file in a standard list of directories and substitute
5312 the full name found.
5315 Print @var{str} as an error message. @var{str} is terminated by a newline.
5316 Use this when inconsistent options are detected.
5319 Substitute the contents of spec string @var{name} at this point.
5322 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5324 @item %x@{@var{option}@}
5325 Accumulate an option for @samp{%X}.
5328 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5332 Output the accumulated assembler options specified by @option{-Wa}.
5335 Output the accumulated preprocessor options specified by @option{-Wp}.
5338 Process the @code{asm} spec. This is used to compute the
5339 switches to be passed to the assembler.
5342 Process the @code{asm_final} spec. This is a spec string for
5343 passing switches to an assembler post-processor, if such a program is
5347 Process the @code{link} spec. This is the spec for computing the
5348 command line passed to the linker. Typically it will make use of the
5349 @samp{%L %G %S %D and %E} sequences.
5352 Dump out a @option{-L} option for each directory that GCC believes might
5353 contain startup files. If the target supports multilibs then the
5354 current multilib directory will be prepended to each of these paths.
5357 Output the multilib directory with directory separators replaced with
5358 @samp{_}. If multilib directories are not set, or the multilib directory is
5359 @file{.} then this option emits nothing.
5362 Process the @code{lib} spec. This is a spec string for deciding which
5363 libraries should be included on the command line to the linker.
5366 Process the @code{libgcc} spec. This is a spec string for deciding
5367 which GCC support library should be included on the command line to the linker.
5370 Process the @code{startfile} spec. This is a spec for deciding which
5371 object files should be the first ones passed to the linker. Typically
5372 this might be a file named @file{crt0.o}.
5375 Process the @code{endfile} spec. This is a spec string that specifies
5376 the last object files that will be passed to the linker.
5379 Process the @code{cpp} spec. This is used to construct the arguments
5380 to be passed to the C preprocessor.
5383 Process the @code{signed_char} spec. This is intended to be used
5384 to tell cpp whether a char is signed. It typically has the definition:
5386 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5390 Process the @code{cc1} spec. This is used to construct the options to be
5391 passed to the actual C compiler (@samp{cc1}).
5394 Process the @code{cc1plus} spec. This is used to construct the options to be
5395 passed to the actual C++ compiler (@samp{cc1plus}).
5398 Substitute the variable part of a matched option. See below.
5399 Note that each comma in the substituted string is replaced by
5403 Remove all occurrences of @code{-S} from the command line. Note---this
5404 command is position dependent. @samp{%} commands in the spec string
5405 before this one will see @code{-S}, @samp{%} commands in the spec string
5406 after this one will not.
5408 @item %:@var{function}(@var{args})
5409 Call the named function @var{function}, passing it @var{args}.
5410 @var{args} is first processed as a nested spec string, then split
5411 into an argument vector in the usual fashion. The function returns
5412 a string which is processed as if it had appeared literally as part
5413 of the current spec.
5415 The following built-in spec functions are provided:
5418 @item @code{if-exists}
5419 The @code{if-exists} spec function takes one argument, an absolute
5420 pathname to a file. If the file exists, @code{if-exists} returns the
5421 pathname. Here is a small example of its usage:
5425 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5428 @item @code{if-exists-else}
5429 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5430 spec function, except that it takes two arguments. The first argument is
5431 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5432 returns the pathname. If it does not exist, it returns the second argument.
5433 This way, @code{if-exists-else} can be used to select one file or another,
5434 based on the existence of the first. Here is a small example of its usage:
5438 crt0%O%s %:if-exists(crti%O%s) \
5439 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5444 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5445 If that switch was not specified, this substitutes nothing. Note that
5446 the leading dash is omitted when specifying this option, and it is
5447 automatically inserted if the substitution is performed. Thus the spec
5448 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5449 and would output the command line option @option{-foo}.
5451 @item %W@{@code{S}@}
5452 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5455 @item %@{@code{S}*@}
5456 Substitutes all the switches specified to GCC whose names start
5457 with @code{-S}, but which also take an argument. This is used for
5458 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5459 GCC considers @option{-o foo} as being
5460 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5461 text, including the space. Thus two arguments would be generated.
5463 @item %@{@code{S}*&@code{T}*@}
5464 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5465 (the order of @code{S} and @code{T} in the spec is not significant).
5466 There can be any number of ampersand-separated variables; for each the
5467 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5469 @item %@{@code{S}:@code{X}@}
5470 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5472 @item %@{!@code{S}:@code{X}@}
5473 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5475 @item %@{@code{S}*:@code{X}@}
5476 Substitutes @code{X} if one or more switches whose names start with
5477 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5478 once, no matter how many such switches appeared. However, if @code{%*}
5479 appears somewhere in @code{X}, then @code{X} will be substituted once
5480 for each matching switch, with the @code{%*} replaced by the part of
5481 that switch that matched the @code{*}.
5483 @item %@{.@code{S}:@code{X}@}
5484 Substitutes @code{X}, if processing a file with suffix @code{S}.
5486 @item %@{!.@code{S}:@code{X}@}
5487 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5489 @item %@{@code{S}|@code{P}:@code{X}@}
5490 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5491 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5492 although they have a stronger binding than the @samp{|}. If @code{%*}
5493 appears in @code{X}, all of the alternatives must be starred, and only
5494 the first matching alternative is substituted.
5496 For example, a spec string like this:
5499 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5502 will output the following command-line options from the following input
5503 command-line options:
5508 -d fred.c -foo -baz -boggle
5509 -d jim.d -bar -baz -boggle
5512 @item %@{S:X; T:Y; :D@}
5514 If @code{S} was given to GCC, substitues @code{X}; else if @code{T} was
5515 given to GCC, substitues @code{Y}; else substitutes @code{D}. There can
5516 be as many clauses as you need. This may be combined with @code{.},
5517 @code{!}, @code{|}, and @code{*} as needed.
5522 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5523 construct may contain other nested @samp{%} constructs or spaces, or
5524 even newlines. They are processed as usual, as described above.
5525 Trailing white space in @code{X} is ignored. White space may also
5526 appear anywhere on the left side of the colon in these constructs,
5527 except between @code{.} or @code{*} and the corresponding word.
5529 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5530 handled specifically in these constructs. If another value of
5531 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5532 @option{-W} switch is found later in the command line, the earlier
5533 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5534 just one letter, which passes all matching options.
5536 The character @samp{|} at the beginning of the predicate text is used to
5537 indicate that a command should be piped to the following command, but
5538 only if @option{-pipe} is specified.
5540 It is built into GCC which switches take arguments and which do not.
5541 (You might think it would be useful to generalize this to allow each
5542 compiler's spec to say which switches take arguments. But this cannot
5543 be done in a consistent fashion. GCC cannot even decide which input
5544 files have been specified without knowing which switches take arguments,
5545 and it must know which input files to compile in order to tell which
5548 GCC also knows implicitly that arguments starting in @option{-l} are to be
5549 treated as compiler output files, and passed to the linker in their
5550 proper position among the other output files.
5552 @c man begin OPTIONS
5554 @node Target Options
5555 @section Specifying Target Machine and Compiler Version
5556 @cindex target options
5557 @cindex cross compiling
5558 @cindex specifying machine version
5559 @cindex specifying compiler version and target machine
5560 @cindex compiler version, specifying
5561 @cindex target machine, specifying
5563 The usual way to run GCC is to run the executable called @file{gcc}, or
5564 @file{<machine>-gcc} when cross-compiling, or
5565 @file{<machine>-gcc-<version>} to run a version other than the one that
5566 was installed last. Sometimes this is inconvenient, so GCC provides
5567 options that will switch to another cross-compiler or version.
5570 @item -b @var{machine}
5572 The argument @var{machine} specifies the target machine for compilation.
5574 The value to use for @var{machine} is the same as was specified as the
5575 machine type when configuring GCC as a cross-compiler. For
5576 example, if a cross-compiler was configured with @samp{configure
5577 i386v}, meaning to compile for an 80386 running System V, then you
5578 would specify @option{-b i386v} to run that cross compiler.
5580 @item -V @var{version}
5582 The argument @var{version} specifies which version of GCC to run.
5583 This is useful when multiple versions are installed. For example,
5584 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5587 The @option{-V} and @option{-b} options work by running the
5588 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5589 use them if you can just run that directly.
5591 @node Submodel Options
5592 @section Hardware Models and Configurations
5593 @cindex submodel options
5594 @cindex specifying hardware config
5595 @cindex hardware models and configurations, specifying
5596 @cindex machine dependent options
5598 Earlier we discussed the standard option @option{-b} which chooses among
5599 different installed compilers for completely different target
5600 machines, such as VAX vs.@: 68000 vs.@: 80386.
5602 In addition, each of these target machine types can have its own
5603 special options, starting with @samp{-m}, to choose among various
5604 hardware models or configurations---for example, 68010 vs 68020,
5605 floating coprocessor or none. A single installed version of the
5606 compiler can compile for any model or configuration, according to the
5609 Some configurations of the compiler also support additional special
5610 options, usually for compatibility with other compilers on the same
5613 These options are defined by the macro @code{TARGET_SWITCHES} in the
5614 machine description. The default for the options is also defined by
5615 that macro, which enables you to change the defaults.
5627 * RS/6000 and PowerPC Options::
5631 * i386 and x86-64 Options::
5633 * Intel 960 Options::
5634 * DEC Alpha Options::
5635 * DEC Alpha/VMS Options::
5638 * System V Options::
5639 * TMS320C3x/C4x Options::
5647 * S/390 and zSeries Options::
5651 * Xstormy16 Options::
5656 @node M680x0 Options
5657 @subsection M680x0 Options
5658 @cindex M680x0 options
5660 These are the @samp{-m} options defined for the 68000 series. The default
5661 values for these options depends on which style of 68000 was selected when
5662 the compiler was configured; the defaults for the most common choices are
5670 Generate output for a 68000. This is the default
5671 when the compiler is configured for 68000-based systems.
5673 Use this option for microcontrollers with a 68000 or EC000 core,
5674 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5680 Generate output for a 68020. This is the default
5681 when the compiler is configured for 68020-based systems.
5685 Generate output containing 68881 instructions for floating point.
5686 This is the default for most 68020 systems unless @option{--nfp} was
5687 specified when the compiler was configured.
5691 Generate output for a 68030. This is the default when the compiler is
5692 configured for 68030-based systems.
5696 Generate output for a 68040. This is the default when the compiler is
5697 configured for 68040-based systems.
5699 This option inhibits the use of 68881/68882 instructions that have to be
5700 emulated by software on the 68040. Use this option if your 68040 does not
5701 have code to emulate those instructions.
5705 Generate output for a 68060. This is the default when the compiler is
5706 configured for 68060-based systems.
5708 This option inhibits the use of 68020 and 68881/68882 instructions that
5709 have to be emulated by software on the 68060. Use this option if your 68060
5710 does not have code to emulate those instructions.
5714 Generate output for a CPU32. This is the default
5715 when the compiler is configured for CPU32-based systems.
5717 Use this option for microcontrollers with a
5718 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5719 68336, 68340, 68341, 68349 and 68360.
5723 Generate output for a 520X ``coldfire'' family cpu. This is the default
5724 when the compiler is configured for 520X-based systems.
5726 Use this option for microcontroller with a 5200 core, including
5727 the MCF5202, MCF5203, MCF5204 and MCF5202.
5732 Generate output for a 68040, without using any of the new instructions.
5733 This results in code which can run relatively efficiently on either a
5734 68020/68881 or a 68030 or a 68040. The generated code does use the
5735 68881 instructions that are emulated on the 68040.
5739 Generate output for a 68060, without using any of the new instructions.
5740 This results in code which can run relatively efficiently on either a
5741 68020/68881 or a 68030 or a 68040. The generated code does use the
5742 68881 instructions that are emulated on the 68060.
5745 @opindex msoft-float
5746 Generate output containing library calls for floating point.
5747 @strong{Warning:} the requisite libraries are not available for all m68k
5748 targets. Normally the facilities of the machine's usual C compiler are
5749 used, but this can't be done directly in cross-compilation. You must
5750 make your own arrangements to provide suitable library functions for
5751 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5752 @samp{m68k-*-coff} do provide software floating point support.
5756 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5759 @opindex mnobitfield
5760 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5761 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5765 Do use the bit-field instructions. The @option{-m68020} option implies
5766 @option{-mbitfield}. This is the default if you use a configuration
5767 designed for a 68020.
5771 Use a different function-calling convention, in which functions
5772 that take a fixed number of arguments return with the @code{rtd}
5773 instruction, which pops their arguments while returning. This
5774 saves one instruction in the caller since there is no need to pop
5775 the arguments there.
5777 This calling convention is incompatible with the one normally
5778 used on Unix, so you cannot use it if you need to call libraries
5779 compiled with the Unix compiler.
5781 Also, you must provide function prototypes for all functions that
5782 take variable numbers of arguments (including @code{printf});
5783 otherwise incorrect code will be generated for calls to those
5786 In addition, seriously incorrect code will result if you call a
5787 function with too many arguments. (Normally, extra arguments are
5788 harmlessly ignored.)
5790 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5791 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5794 @itemx -mno-align-int
5796 @opindex mno-align-int
5797 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5798 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5799 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5800 Aligning variables on 32-bit boundaries produces code that runs somewhat
5801 faster on processors with 32-bit busses at the expense of more memory.
5803 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5804 align structures containing the above types differently than
5805 most published application binary interface specifications for the m68k.
5809 Use the pc-relative addressing mode of the 68000 directly, instead of
5810 using a global offset table. At present, this option implies @option{-fpic},
5811 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5812 not presently supported with @option{-mpcrel}, though this could be supported for
5813 68020 and higher processors.
5815 @item -mno-strict-align
5816 @itemx -mstrict-align
5817 @opindex mno-strict-align
5818 @opindex mstrict-align
5819 Do not (do) assume that unaligned memory references will be handled by
5824 @node M68hc1x Options
5825 @subsection M68hc1x Options
5826 @cindex M68hc1x options
5828 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5829 microcontrollers. The default values for these options depends on
5830 which style of microcontroller was selected when the compiler was configured;
5831 the defaults for the most common choices are given below.
5838 Generate output for a 68HC11. This is the default
5839 when the compiler is configured for 68HC11-based systems.
5845 Generate output for a 68HC12. This is the default
5846 when the compiler is configured for 68HC12-based systems.
5852 Generate output for a 68HCS12.
5855 @opindex mauto-incdec
5856 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5863 Enable the use of 68HC12 min and max instructions.
5866 @itemx -mno-long-calls
5867 @opindex mlong-calls
5868 @opindex mno-long-calls
5869 Treat all calls as being far away (near). If calls are assumed to be
5870 far away, the compiler will use the @code{call} instruction to
5871 call a function and the @code{rtc} instruction for returning.
5875 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5877 @item -msoft-reg-count=@var{count}
5878 @opindex msoft-reg-count
5879 Specify the number of pseudo-soft registers which are used for the
5880 code generation. The maximum number is 32. Using more pseudo-soft
5881 register may or may not result in better code depending on the program.
5882 The default is 4 for 68HC11 and 2 for 68HC12.
5887 @subsection VAX Options
5890 These @samp{-m} options are defined for the VAX:
5895 Do not output certain jump instructions (@code{aobleq} and so on)
5896 that the Unix assembler for the VAX cannot handle across long
5901 Do output those jump instructions, on the assumption that you
5902 will assemble with the GNU assembler.
5906 Output code for g-format floating point numbers instead of d-format.
5910 @subsection SPARC Options
5911 @cindex SPARC options
5913 These @samp{-m} switches are supported on the SPARC:
5918 @opindex mno-app-regs
5920 Specify @option{-mapp-regs} to generate output using the global registers
5921 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5924 To be fully SVR4 ABI compliant at the cost of some performance loss,
5925 specify @option{-mno-app-regs}. You should compile libraries and system
5926 software with this option.
5931 @opindex mhard-float
5932 Generate output containing floating point instructions. This is the
5938 @opindex msoft-float
5939 Generate output containing library calls for floating point.
5940 @strong{Warning:} the requisite libraries are not available for all SPARC
5941 targets. Normally the facilities of the machine's usual C compiler are
5942 used, but this cannot be done directly in cross-compilation. You must make
5943 your own arrangements to provide suitable library functions for
5944 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5945 @samp{sparclite-*-*} do provide software floating point support.
5947 @option{-msoft-float} changes the calling convention in the output file;
5948 therefore, it is only useful if you compile @emph{all} of a program with
5949 this option. In particular, you need to compile @file{libgcc.a}, the
5950 library that comes with GCC, with @option{-msoft-float} in order for
5953 @item -mhard-quad-float
5954 @opindex mhard-quad-float
5955 Generate output containing quad-word (long double) floating point
5959 @opindex mimpure-text
5960 @option{-mimpure-text}, used in addition to @option{-shared}, tells
5961 the compiler to not pass @option{-z text} to the linker when linking a
5962 shared object. Using this option, you can link position-dependent
5963 code into a shared object.
5965 @option{-mimpure-text} suppresses the ``relocations remain against
5966 allocatable but non-writable sections'' linker error message.
5967 However, the necessary relocations will trigger copy-on-write, and the
5968 shared object is not actually shared across processes. Instead of
5969 using @option{-mimpure-text}, you should compile all source code with
5970 @option{-fpic} or @option{-fPIC}.
5972 This option is only available on SunOS and Solaris.
5974 @item -msoft-quad-float
5975 @opindex msoft-quad-float
5976 Generate output containing library calls for quad-word (long double)
5977 floating point instructions. The functions called are those specified
5978 in the SPARC ABI@. This is the default.
5980 As of this writing, there are no sparc implementations that have hardware
5981 support for the quad-word floating point instructions. They all invoke
5982 a trap handler for one of these instructions, and then the trap handler
5983 emulates the effect of the instruction. Because of the trap handler overhead,
5984 this is much slower than calling the ABI library routines. Thus the
5985 @option{-msoft-quad-float} option is the default.
5991 With @option{-mflat}, the compiler does not generate save/restore instructions
5992 and will use a ``flat'' or single register window calling convention.
5993 This model uses %i7 as the frame pointer and is compatible with the normal
5994 register window model. Code from either may be intermixed.
5995 The local registers and the input registers (0--5) are still treated as
5996 ``call saved'' registers and will be saved on the stack as necessary.
5998 With @option{-mno-flat} (the default), the compiler emits save/restore
5999 instructions (except for leaf functions) and is the normal mode of operation.
6001 @item -mno-unaligned-doubles
6002 @itemx -munaligned-doubles
6003 @opindex mno-unaligned-doubles
6004 @opindex munaligned-doubles
6005 Assume that doubles have 8 byte alignment. This is the default.
6007 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6008 alignment only if they are contained in another type, or if they have an
6009 absolute address. Otherwise, it assumes they have 4 byte alignment.
6010 Specifying this option avoids some rare compatibility problems with code
6011 generated by other compilers. It is not the default because it results
6012 in a performance loss, especially for floating point code.
6014 @item -mno-faster-structs
6015 @itemx -mfaster-structs
6016 @opindex mno-faster-structs
6017 @opindex mfaster-structs
6018 With @option{-mfaster-structs}, the compiler assumes that structures
6019 should have 8 byte alignment. This enables the use of pairs of
6020 @code{ldd} and @code{std} instructions for copies in structure
6021 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6022 However, the use of this changed alignment directly violates the SPARC
6023 ABI@. Thus, it's intended only for use on targets where the developer
6024 acknowledges that their resulting code will not be directly in line with
6025 the rules of the ABI@.
6031 These two options select variations on the SPARC architecture.
6033 By default (unless specifically configured for the Fujitsu SPARClite),
6034 GCC generates code for the v7 variant of the SPARC architecture.
6036 @option{-mv8} will give you SPARC v8 code. The only difference from v7
6037 code is that the compiler emits the integer multiply and integer
6038 divide instructions which exist in SPARC v8 but not in SPARC v7.
6040 @option{-msparclite} will give you SPARClite code. This adds the integer
6041 multiply, integer divide step and scan (@code{ffs}) instructions which
6042 exist in SPARClite but not in SPARC v7.
6044 These options are deprecated and will be deleted in a future GCC release.
6045 They have been replaced with @option{-mcpu=xxx}.
6050 @opindex msupersparc
6051 These two options select the processor for which the code is optimized.
6053 With @option{-mcypress} (the default), the compiler optimizes code for the
6054 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
6055 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
6057 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
6058 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
6059 of the full SPARC v8 instruction set.
6061 These options are deprecated and will be deleted in a future GCC release.
6062 They have been replaced with @option{-mcpu=xxx}.
6064 @item -mcpu=@var{cpu_type}
6066 Set the instruction set, register set, and instruction scheduling parameters
6067 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6068 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6069 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
6070 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6073 Default instruction scheduling parameters are used for values that select
6074 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6075 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6077 Here is a list of each supported architecture and their supported
6082 v8: supersparc, hypersparc
6083 sparclite: f930, f934, sparclite86x
6085 v9: ultrasparc, ultrasparc3
6088 @item -mtune=@var{cpu_type}
6090 Set the instruction scheduling parameters for machine type
6091 @var{cpu_type}, but do not set the instruction set or register set that the
6092 option @option{-mcpu=@var{cpu_type}} would.
6094 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6095 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6096 that select a particular cpu implementation. Those are @samp{cypress},
6097 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6098 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6103 These @samp{-m} switches are supported in addition to the above
6104 on the SPARCLET processor.
6107 @item -mlittle-endian
6108 @opindex mlittle-endian
6109 Generate code for a processor running in little-endian mode.
6113 Treat register @code{%g0} as a normal register.
6114 GCC will continue to clobber it as necessary but will not assume
6115 it always reads as 0.
6117 @item -mbroken-saverestore
6118 @opindex mbroken-saverestore
6119 Generate code that does not use non-trivial forms of the @code{save} and
6120 @code{restore} instructions. Early versions of the SPARCLET processor do
6121 not correctly handle @code{save} and @code{restore} instructions used with
6122 arguments. They correctly handle them used without arguments. A @code{save}
6123 instruction used without arguments increments the current window pointer
6124 but does not allocate a new stack frame. It is assumed that the window
6125 overflow trap handler will properly handle this case as will interrupt
6129 These @samp{-m} switches are supported in addition to the above
6130 on SPARC V9 processors in 64-bit environments.
6133 @item -mlittle-endian
6134 @opindex mlittle-endian
6135 Generate code for a processor running in little-endian mode.
6141 Generate code for a 32-bit or 64-bit environment.
6142 The 32-bit environment sets int, long and pointer to 32 bits.
6143 The 64-bit environment sets int to 32 bits and long and pointer
6146 @item -mcmodel=medlow
6147 @opindex mcmodel=medlow
6148 Generate code for the Medium/Low code model: the program must be linked
6149 in the low 32 bits of the address space. Pointers are 64 bits.
6150 Programs can be statically or dynamically linked.
6152 @item -mcmodel=medmid
6153 @opindex mcmodel=medmid
6154 Generate code for the Medium/Middle code model: the program must be linked
6155 in the low 44 bits of the address space, the text segment must be less than
6156 2G bytes, and data segment must be within 2G of the text segment.
6157 Pointers are 64 bits.
6159 @item -mcmodel=medany
6160 @opindex mcmodel=medany
6161 Generate code for the Medium/Anywhere code model: the program may be linked
6162 anywhere in the address space, the text segment must be less than
6163 2G bytes, and data segment must be within 2G of the text segment.
6164 Pointers are 64 bits.
6166 @item -mcmodel=embmedany
6167 @opindex mcmodel=embmedany
6168 Generate code for the Medium/Anywhere code model for embedded systems:
6169 assume a 32-bit text and a 32-bit data segment, both starting anywhere
6170 (determined at link time). Register %g4 points to the base of the
6171 data segment. Pointers are still 64 bits.
6172 Programs are statically linked, PIC is not supported.
6175 @itemx -mno-stack-bias
6176 @opindex mstack-bias
6177 @opindex mno-stack-bias
6178 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6179 frame pointer if present, are offset by @minus{}2047 which must be added back
6180 when making stack frame references.
6181 Otherwise, assume no such offset is present.
6185 @subsection ARM Options
6188 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6193 @opindex mapcs-frame
6194 Generate a stack frame that is compliant with the ARM Procedure Call
6195 Standard for all functions, even if this is not strictly necessary for
6196 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6197 with this option will cause the stack frames not to be generated for
6198 leaf functions. The default is @option{-mno-apcs-frame}.
6202 This is a synonym for @option{-mapcs-frame}.
6206 Generate code for a processor running with a 26-bit program counter,
6207 and conforming to the function calling standards for the APCS 26-bit
6208 option. This option replaces the @option{-m2} and @option{-m3} options
6209 of previous releases of the compiler.
6213 Generate code for a processor running with a 32-bit program counter,
6214 and conforming to the function calling standards for the APCS 32-bit
6215 option. This option replaces the @option{-m6} option of previous releases
6219 @c not currently implemented
6220 @item -mapcs-stack-check
6221 @opindex mapcs-stack-check
6222 Generate code to check the amount of stack space available upon entry to
6223 every function (that actually uses some stack space). If there is
6224 insufficient space available then either the function
6225 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6226 called, depending upon the amount of stack space required. The run time
6227 system is required to provide these functions. The default is
6228 @option{-mno-apcs-stack-check}, since this produces smaller code.
6230 @c not currently implemented
6232 @opindex mapcs-float
6233 Pass floating point arguments using the float point registers. This is
6234 one of the variants of the APCS@. This option is recommended if the
6235 target hardware has a floating point unit or if a lot of floating point
6236 arithmetic is going to be performed by the code. The default is
6237 @option{-mno-apcs-float}, since integer only code is slightly increased in
6238 size if @option{-mapcs-float} is used.
6240 @c not currently implemented
6241 @item -mapcs-reentrant
6242 @opindex mapcs-reentrant
6243 Generate reentrant, position independent code. The default is
6244 @option{-mno-apcs-reentrant}.
6247 @item -mthumb-interwork
6248 @opindex mthumb-interwork
6249 Generate code which supports calling between the ARM and Thumb
6250 instruction sets. Without this option the two instruction sets cannot
6251 be reliably used inside one program. The default is
6252 @option{-mno-thumb-interwork}, since slightly larger code is generated
6253 when @option{-mthumb-interwork} is specified.
6255 @item -mno-sched-prolog
6256 @opindex mno-sched-prolog
6257 Prevent the reordering of instructions in the function prolog, or the
6258 merging of those instruction with the instructions in the function's
6259 body. This means that all functions will start with a recognizable set
6260 of instructions (or in fact one of a choice from a small set of
6261 different function prologues), and this information can be used to
6262 locate the start if functions inside an executable piece of code. The
6263 default is @option{-msched-prolog}.
6266 @opindex mhard-float
6267 Generate output containing floating point instructions. This is the
6271 @opindex msoft-float
6272 Generate output containing library calls for floating point.
6273 @strong{Warning:} the requisite libraries are not available for all ARM
6274 targets. Normally the facilities of the machine's usual C compiler are
6275 used, but this cannot be done directly in cross-compilation. You must make
6276 your own arrangements to provide suitable library functions for
6279 @option{-msoft-float} changes the calling convention in the output file;
6280 therefore, it is only useful if you compile @emph{all} of a program with
6281 this option. In particular, you need to compile @file{libgcc.a}, the
6282 library that comes with GCC, with @option{-msoft-float} in order for
6285 @item -mlittle-endian
6286 @opindex mlittle-endian
6287 Generate code for a processor running in little-endian mode. This is
6288 the default for all standard configurations.
6291 @opindex mbig-endian
6292 Generate code for a processor running in big-endian mode; the default is
6293 to compile code for a little-endian processor.
6295 @item -mwords-little-endian
6296 @opindex mwords-little-endian
6297 This option only applies when generating code for big-endian processors.
6298 Generate code for a little-endian word order but a big-endian byte
6299 order. That is, a byte order of the form @samp{32107654}. Note: this
6300 option should only be used if you require compatibility with code for
6301 big-endian ARM processors generated by versions of the compiler prior to
6304 @item -malignment-traps
6305 @opindex malignment-traps
6306 Generate code that will not trap if the MMU has alignment traps enabled.
6307 On ARM architectures prior to ARMv4, there were no instructions to
6308 access half-word objects stored in memory. However, when reading from
6309 memory a feature of the ARM architecture allows a word load to be used,
6310 even if the address is unaligned, and the processor core will rotate the
6311 data as it is being loaded. This option tells the compiler that such
6312 misaligned accesses will cause a MMU trap and that it should instead
6313 synthesize the access as a series of byte accesses. The compiler can
6314 still use word accesses to load half-word data if it knows that the
6315 address is aligned to a word boundary.
6317 This option is ignored when compiling for ARM architecture 4 or later,
6318 since these processors have instructions to directly access half-word
6321 @item -mno-alignment-traps
6322 @opindex mno-alignment-traps
6323 Generate code that assumes that the MMU will not trap unaligned
6324 accesses. This produces better code when the target instruction set
6325 does not have half-word memory operations (i.e.@: implementations prior to
6328 Note that you cannot use this option to access unaligned word objects,
6329 since the processor will only fetch one 32-bit aligned object from
6332 The default setting for most targets is @option{-mno-alignment-traps}, since
6333 this produces better code when there are no half-word memory
6334 instructions available.
6336 @item -mshort-load-bytes
6337 @itemx -mno-short-load-words
6338 @opindex mshort-load-bytes
6339 @opindex mno-short-load-words
6340 These are deprecated aliases for @option{-malignment-traps}.
6342 @item -mno-short-load-bytes
6343 @itemx -mshort-load-words
6344 @opindex mno-short-load-bytes
6345 @opindex mshort-load-words
6346 This are deprecated aliases for @option{-mno-alignment-traps}.
6348 @item -mcpu=@var{name}
6350 This specifies the name of the target ARM processor. GCC uses this name
6351 to determine what kind of instructions it can emit when generating
6352 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6353 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6354 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6355 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6356 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6357 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6358 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6359 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6360 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
6361 @samp{arm1020t}, @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
6363 @itemx -mtune=@var{name}
6365 This option is very similar to the @option{-mcpu=} option, except that
6366 instead of specifying the actual target processor type, and hence
6367 restricting which instructions can be used, it specifies that GCC should
6368 tune the performance of the code as if the target were of the type
6369 specified in this option, but still choosing the instructions that it
6370 will generate based on the cpu specified by a @option{-mcpu=} option.
6371 For some ARM implementations better performance can be obtained by using
6374 @item -march=@var{name}
6376 This specifies the name of the target ARM architecture. GCC uses this
6377 name to determine what kind of instructions it can emit when generating
6378 assembly code. This option can be used in conjunction with or instead
6379 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6380 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6381 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{iwmmxt}, @samp{ep9312}.
6383 @item -mfpe=@var{number}
6384 @itemx -mfp=@var{number}
6387 This specifies the version of the floating point emulation available on
6388 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6389 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6391 @item -mstructure-size-boundary=@var{n}
6392 @opindex mstructure-size-boundary
6393 The size of all structures and unions will be rounded up to a multiple
6394 of the number of bits set by this option. Permissible values are 8 and
6395 32. The default value varies for different toolchains. For the COFF
6396 targeted toolchain the default value is 8. Specifying the larger number
6397 can produce faster, more efficient code, but can also increase the size
6398 of the program. The two values are potentially incompatible. Code
6399 compiled with one value cannot necessarily expect to work with code or
6400 libraries compiled with the other value, if they exchange information
6401 using structures or unions.
6403 @item -mabort-on-noreturn
6404 @opindex mabort-on-noreturn
6405 Generate a call to the function @code{abort} at the end of a
6406 @code{noreturn} function. It will be executed if the function tries to
6410 @itemx -mno-long-calls
6411 @opindex mlong-calls
6412 @opindex mno-long-calls
6413 Tells the compiler to perform function calls by first loading the
6414 address of the function into a register and then performing a subroutine
6415 call on this register. This switch is needed if the target function
6416 will lie outside of the 64 megabyte addressing range of the offset based
6417 version of subroutine call instruction.
6419 Even if this switch is enabled, not all function calls will be turned
6420 into long calls. The heuristic is that static functions, functions
6421 which have the @samp{short-call} attribute, functions that are inside
6422 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6423 definitions have already been compiled within the current compilation
6424 unit, will not be turned into long calls. The exception to this rule is
6425 that weak function definitions, functions with the @samp{long-call}
6426 attribute or the @samp{section} attribute, and functions that are within
6427 the scope of a @samp{#pragma long_calls} directive, will always be
6428 turned into long calls.
6430 This feature is not enabled by default. Specifying
6431 @option{-mno-long-calls} will restore the default behavior, as will
6432 placing the function calls within the scope of a @samp{#pragma
6433 long_calls_off} directive. Note these switches have no effect on how
6434 the compiler generates code to handle function calls via function
6437 @item -mnop-fun-dllimport
6438 @opindex mnop-fun-dllimport
6439 Disable support for the @code{dllimport} attribute.
6441 @item -msingle-pic-base
6442 @opindex msingle-pic-base
6443 Treat the register used for PIC addressing as read-only, rather than
6444 loading it in the prologue for each function. The run-time system is
6445 responsible for initializing this register with an appropriate value
6446 before execution begins.
6448 @item -mpic-register=@var{reg}
6449 @opindex mpic-register
6450 Specify the register to be used for PIC addressing. The default is R10
6451 unless stack-checking is enabled, when R9 is used.
6453 @item -mcirrus-fix-invalid-insns
6454 @opindex -mcirrus-fix-invalid-insns
6455 @opindex -mno-cirrus-fix-invalid-insns
6456 Insert NOPs into the instruction stream to in order to work around
6457 problems with invalid Maverick instruction combinations. This option
6458 is only valid if the @option{-mcpu=ep9312} option has been used to
6459 enable generation of instructions for the Cirrus Maverick floating
6460 point co-processor. This option is not enabled by default, since the
6461 problem is only present in older Maverick implementations. The default
6462 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6465 @item -mpoke-function-name
6466 @opindex mpoke-function-name
6467 Write the name of each function into the text section, directly
6468 preceding the function prologue. The generated code is similar to this:
6472 .ascii "arm_poke_function_name", 0
6475 .word 0xff000000 + (t1 - t0)
6476 arm_poke_function_name
6478 stmfd sp!, @{fp, ip, lr, pc@}
6482 When performing a stack backtrace, code can inspect the value of
6483 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6484 location @code{pc - 12} and the top 8 bits are set, then we know that
6485 there is a function name embedded immediately preceding this location
6486 and has length @code{((pc[-3]) & 0xff000000)}.
6490 Generate code for the 16-bit Thumb instruction set. The default is to
6491 use the 32-bit ARM instruction set.
6494 @opindex mtpcs-frame
6495 Generate a stack frame that is compliant with the Thumb Procedure Call
6496 Standard for all non-leaf functions. (A leaf function is one that does
6497 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6499 @item -mtpcs-leaf-frame
6500 @opindex mtpcs-leaf-frame
6501 Generate a stack frame that is compliant with the Thumb Procedure Call
6502 Standard for all leaf functions. (A leaf function is one that does
6503 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6505 @item -mcallee-super-interworking
6506 @opindex mcallee-super-interworking
6507 Gives all externally visible functions in the file being compiled an ARM
6508 instruction set header which switches to Thumb mode before executing the
6509 rest of the function. This allows these functions to be called from
6510 non-interworking code.
6512 @item -mcaller-super-interworking
6513 @opindex mcaller-super-interworking
6514 Allows calls via function pointers (including virtual functions) to
6515 execute correctly regardless of whether the target code has been
6516 compiled for interworking or not. There is a small overhead in the cost
6517 of executing a function pointer if this option is enabled.
6521 @node MN10200 Options
6522 @subsection MN10200 Options
6523 @cindex MN10200 options
6525 These @option{-m} options are defined for Matsushita MN10200 architectures:
6530 Indicate to the linker that it should perform a relaxation optimization pass
6531 to shorten branches, calls and absolute memory addresses. This option only
6532 has an effect when used on the command line for the final link step.
6534 This option makes symbolic debugging impossible.
6537 @node MN10300 Options
6538 @subsection MN10300 Options
6539 @cindex MN10300 options
6541 These @option{-m} options are defined for Matsushita MN10300 architectures:
6546 Generate code to avoid bugs in the multiply instructions for the MN10300
6547 processors. This is the default.
6550 @opindex mno-mult-bug
6551 Do not generate code to avoid bugs in the multiply instructions for the
6556 Generate code which uses features specific to the AM33 processor.
6560 Do not generate code which uses features specific to the AM33 processor. This
6565 Do not link in the C run-time initialization object file.
6569 Indicate to the linker that it should perform a relaxation optimization pass
6570 to shorten branches, calls and absolute memory addresses. This option only
6571 has an effect when used on the command line for the final link step.
6573 This option makes symbolic debugging impossible.
6577 @node M32R/D Options
6578 @subsection M32R/D Options
6579 @cindex M32R/D options
6581 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6586 Generate code for the M32R/X@.
6590 Generate code for the M32R@. This is the default.
6592 @item -mcode-model=small
6593 @opindex mcode-model=small
6594 Assume all objects live in the lower 16MB of memory (so that their addresses
6595 can be loaded with the @code{ld24} instruction), and assume all subroutines
6596 are reachable with the @code{bl} instruction.
6597 This is the default.
6599 The addressability of a particular object can be set with the
6600 @code{model} attribute.
6602 @item -mcode-model=medium
6603 @opindex mcode-model=medium
6604 Assume objects may be anywhere in the 32-bit address space (the compiler
6605 will generate @code{seth/add3} instructions to load their addresses), and
6606 assume all subroutines are reachable with the @code{bl} instruction.
6608 @item -mcode-model=large
6609 @opindex mcode-model=large
6610 Assume objects may be anywhere in the 32-bit address space (the compiler
6611 will generate @code{seth/add3} instructions to load their addresses), and
6612 assume subroutines may not be reachable with the @code{bl} instruction
6613 (the compiler will generate the much slower @code{seth/add3/jl}
6614 instruction sequence).
6617 @opindex msdata=none
6618 Disable use of the small data area. Variables will be put into
6619 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6620 @code{section} attribute has been specified).
6621 This is the default.
6623 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6624 Objects may be explicitly put in the small data area with the
6625 @code{section} attribute using one of these sections.
6628 @opindex msdata=sdata
6629 Put small global and static data in the small data area, but do not
6630 generate special code to reference them.
6634 Put small global and static data in the small data area, and generate
6635 special instructions to reference them.
6639 @cindex smaller data references
6640 Put global and static objects less than or equal to @var{num} bytes
6641 into the small data or bss sections instead of the normal data or bss
6642 sections. The default value of @var{num} is 8.
6643 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6644 for this option to have any effect.
6646 All modules should be compiled with the same @option{-G @var{num}} value.
6647 Compiling with different values of @var{num} may or may not work; if it
6648 doesn't the linker will give an error message---incorrect code will not be
6654 @subsection M88K Options
6655 @cindex M88k options
6657 These @samp{-m} options are defined for Motorola 88k architectures:
6662 Generate code that works well on both the m88100 and the
6667 Generate code that works best for the m88100, but that also
6672 Generate code that works best for the m88110, and may not run
6677 Obsolete option to be removed from the next revision.
6680 @item -midentify-revision
6681 @opindex midentify-revision
6682 @cindex identifying source, compiler (88k)
6683 Include an @code{ident} directive in the assembler output recording the
6684 source file name, compiler name and version, timestamp, and compilation
6687 @item -mno-underscores
6688 @opindex mno-underscores
6689 @cindex underscores, avoiding (88k)
6690 In assembler output, emit symbol names without adding an underscore
6691 character at the beginning of each name. The default is to use an
6692 underscore as prefix on each name.
6694 @item -mocs-debug-info
6695 @itemx -mno-ocs-debug-info
6696 @opindex mocs-debug-info
6697 @opindex mno-ocs-debug-info
6699 @cindex debugging, 88k OCS
6700 Include (or omit) additional debugging information (about registers used
6701 in each stack frame) as specified in the 88open Object Compatibility
6702 Standard, ``OCS''@. This extra information allows debugging of code that
6703 has had the frame pointer eliminated. The default for SVr4 and Delta 88
6704 SVr3.2 is to include this information; other 88k configurations omit this
6705 information by default.
6707 @item -mocs-frame-position
6708 @opindex mocs-frame-position
6709 @cindex register positions in frame (88k)
6710 When emitting COFF debugging information for automatic variables and
6711 parameters stored on the stack, use the offset from the canonical frame
6712 address, which is the stack pointer (register 31) on entry to the
6713 function. The SVr4 and Delta88 SVr3.2, and BCS configurations use
6714 @option{-mocs-frame-position}; other 88k configurations have the default
6715 @option{-mno-ocs-frame-position}.
6717 @item -mno-ocs-frame-position
6718 @opindex mno-ocs-frame-position
6719 @cindex register positions in frame (88k)
6720 When emitting COFF debugging information for automatic variables and
6721 parameters stored on the stack, use the offset from the frame pointer
6722 register (register 30). When this option is in effect, the frame
6723 pointer is not eliminated when debugging information is selected by the
6726 @item -moptimize-arg-area
6727 @opindex moptimize-arg-area
6728 @cindex arguments in frame (88k)
6729 Save space by reorganizing the stack frame. This option generates code
6730 that does not agree with the 88open specifications, but uses less
6733 @itemx -mno-optimize-arg-area
6734 @opindex mno-optimize-arg-area
6735 Do not reorganize the stack frame to save space. This is the default.
6736 The generated conforms to the specification, but uses more memory.
6738 @item -mshort-data-@var{num}
6739 @opindex mshort-data
6740 @cindex smaller data references (88k)
6741 @cindex r0-relative references (88k)
6742 Generate smaller data references by making them relative to @code{r0},
6743 which allows loading a value using a single instruction (rather than the
6744 usual two). You control which data references are affected by
6745 specifying @var{num} with this option. For example, if you specify
6746 @option{-mshort-data-512}, then the data references affected are those
6747 involving displacements of less than 512 bytes.
6748 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6751 @item -mserialize-volatile
6752 @opindex mserialize-volatile
6753 @itemx -mno-serialize-volatile
6754 @opindex mno-serialize-volatile
6755 @cindex sequential consistency on 88k
6756 Do, or don't, generate code to guarantee sequential consistency
6757 of volatile memory references. By default, consistency is
6760 The order of memory references made by the MC88110 processor does
6761 not always match the order of the instructions requesting those
6762 references. In particular, a load instruction may execute before
6763 a preceding store instruction. Such reordering violates
6764 sequential consistency of volatile memory references, when there
6765 are multiple processors. When consistency must be guaranteed,
6766 GCC generates special instructions, as needed, to force
6767 execution in the proper order.
6769 The MC88100 processor does not reorder memory references and so
6770 always provides sequential consistency. However, by default, GCC
6771 generates the special instructions to guarantee consistency
6772 even when you use @option{-m88100}, so that the code may be run on an
6773 MC88110 processor. If you intend to run your code only on the
6774 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6776 The extra code generated to guarantee consistency may affect the
6777 performance of your application. If you know that you can safely
6778 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6784 @cindex assembler syntax, 88k
6786 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6787 related to System V release 4 (SVr4). This controls the following:
6791 Which variant of the assembler syntax to emit.
6793 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6794 that is used on System V release 4.
6796 @option{-msvr4} makes GCC issue additional declaration directives used in
6800 @option{-msvr4} is the default for the m88k-motorola-sysv4 configuration.
6801 @option{-msvr3} is the default for all other m88k configurations.
6803 @item -mversion-03.00
6804 @opindex mversion-03.00
6805 This option is obsolete, and is ignored.
6806 @c ??? which asm syntax better for GAS? option there too?
6808 @item -mno-check-zero-division
6809 @itemx -mcheck-zero-division
6810 @opindex mno-check-zero-division
6811 @opindex mcheck-zero-division
6812 @cindex zero division on 88k
6813 Do, or don't, generate code to guarantee that integer division by
6814 zero will be detected. By default, detection is guaranteed.
6816 Some models of the MC88100 processor fail to trap upon integer
6817 division by zero under certain conditions. By default, when
6818 compiling code that might be run on such a processor, GCC
6819 generates code that explicitly checks for zero-valued divisors
6820 and traps with exception number 503 when one is detected. Use of
6821 @option{-mno-check-zero-division} suppresses such checking for code
6822 generated to run on an MC88100 processor.
6824 GCC assumes that the MC88110 processor correctly detects all instances
6825 of integer division by zero. When @option{-m88110} is specified, no
6826 explicit checks for zero-valued divisors are generated, and both
6827 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6830 @item -muse-div-instruction
6831 @opindex muse-div-instruction
6832 @cindex divide instruction, 88k
6833 Use the div instruction for signed integer division on the
6834 MC88100 processor. By default, the div instruction is not used.
6836 On the MC88100 processor the signed integer division instruction
6837 div) traps to the operating system on a negative operand. The
6838 operating system transparently completes the operation, but at a
6839 large cost in execution time. By default, when compiling code
6840 that might be run on an MC88100 processor, GCC emulates signed
6841 integer division using the unsigned integer division instruction
6842 divu), thereby avoiding the large penalty of a trap to the
6843 operating system. Such emulation has its own, smaller, execution
6844 cost in both time and space. To the extent that your code's
6845 important signed integer division operations are performed on two
6846 nonnegative operands, it may be desirable to use the div
6847 instruction directly.
6849 On the MC88110 processor the div instruction (also known as the
6850 divs instruction) processes negative operands without trapping to
6851 the operating system. When @option{-m88110} is specified,
6852 @option{-muse-div-instruction} is ignored, and the div instruction is used
6853 for signed integer division.
6855 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6856 particular, the behavior of such a division with and without
6857 @option{-muse-div-instruction} may differ.
6859 @item -mtrap-large-shift
6860 @itemx -mhandle-large-shift
6861 @opindex mtrap-large-shift
6862 @opindex mhandle-large-shift
6863 @cindex bit shift overflow (88k)
6864 @cindex large bit shifts (88k)
6865 Include code to detect bit-shifts of more than 31 bits; respectively,
6866 trap such shifts or emit code to handle them properly. By default GCC
6867 makes no special provision for large bit shifts.
6869 @item -mwarn-passed-structs
6870 @opindex mwarn-passed-structs
6871 @cindex structure passing (88k)
6872 Warn when a function passes a struct as an argument or result.
6873 Structure-passing conventions have changed during the evolution of the C
6874 language, and are often the source of portability problems. By default,
6875 GCC issues no such warning.
6878 @c break page here to avoid unsightly interparagraph stretch.
6882 @node RS/6000 and PowerPC Options
6883 @subsection IBM RS/6000 and PowerPC Options
6884 @cindex RS/6000 and PowerPC Options
6885 @cindex IBM RS/6000 and PowerPC Options
6887 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6895 @itemx -mpowerpc-gpopt
6896 @itemx -mno-powerpc-gpopt
6897 @itemx -mpowerpc-gfxopt
6898 @itemx -mno-powerpc-gfxopt
6900 @itemx -mno-powerpc64
6906 @opindex mno-powerpc
6907 @opindex mpowerpc-gpopt
6908 @opindex mno-powerpc-gpopt
6909 @opindex mpowerpc-gfxopt
6910 @opindex mno-powerpc-gfxopt
6912 @opindex mno-powerpc64
6913 GCC supports two related instruction set architectures for the
6914 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6915 instructions supported by the @samp{rios} chip set used in the original
6916 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6917 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6918 the IBM 4xx microprocessors.
6920 Neither architecture is a subset of the other. However there is a
6921 large common subset of instructions supported by both. An MQ
6922 register is included in processors supporting the POWER architecture.
6924 You use these options to specify which instructions are available on the
6925 processor you are using. The default value of these options is
6926 determined when configuring GCC@. Specifying the
6927 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6928 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6929 rather than the options listed above.
6931 The @option{-mpower} option allows GCC to generate instructions that
6932 are found only in the POWER architecture and to use the MQ register.
6933 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6934 to generate instructions that are present in the POWER2 architecture but
6935 not the original POWER architecture.
6937 The @option{-mpowerpc} option allows GCC to generate instructions that
6938 are found only in the 32-bit subset of the PowerPC architecture.
6939 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6940 GCC to use the optional PowerPC architecture instructions in the
6941 General Purpose group, including floating-point square root. Specifying
6942 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6943 use the optional PowerPC architecture instructions in the Graphics
6944 group, including floating-point select.
6946 The @option{-mpowerpc64} option allows GCC to generate the additional
6947 64-bit instructions that are found in the full PowerPC64 architecture
6948 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6949 @option{-mno-powerpc64}.
6951 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6952 will use only the instructions in the common subset of both
6953 architectures plus some special AIX common-mode calls, and will not use
6954 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
6955 permits GCC to use any instruction from either architecture and to
6956 allow use of the MQ register; specify this for the Motorola MPC601.
6958 @item -mnew-mnemonics
6959 @itemx -mold-mnemonics
6960 @opindex mnew-mnemonics
6961 @opindex mold-mnemonics
6962 Select which mnemonics to use in the generated assembler code. With
6963 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
6964 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
6965 assembler mnemonics defined for the POWER architecture. Instructions
6966 defined in only one architecture have only one mnemonic; GCC uses that
6967 mnemonic irrespective of which of these options is specified.
6969 GCC defaults to the mnemonics appropriate for the architecture in
6970 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
6971 value of these option. Unless you are building a cross-compiler, you
6972 should normally not specify either @option{-mnew-mnemonics} or
6973 @option{-mold-mnemonics}, but should instead accept the default.
6975 @item -mcpu=@var{cpu_type}
6977 Set architecture type, register usage, choice of mnemonics, and
6978 instruction scheduling parameters for machine type @var{cpu_type}.
6979 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
6980 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
6981 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
6982 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
6983 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
6984 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
6986 @option{-mcpu=common} selects a completely generic processor. Code
6987 generated under this option will run on any POWER or PowerPC processor.
6988 GCC will use only the instructions in the common subset of both
6989 architectures, and will not use the MQ register. GCC assumes a generic
6990 processor model for scheduling purposes.
6992 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
6993 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
6994 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
6995 types, with an appropriate, generic processor model assumed for
6996 scheduling purposes.
6998 The other options specify a specific processor. Code generated under
6999 those options will run best on that processor, and may not run at all on
7002 The @option{-mcpu} options automatically enable or disable other
7003 @option{-m} options as follows:
7007 @option{-mno-power}, @option{-mno-powerpc}
7014 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
7029 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7032 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7037 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
7040 @item -mtune=@var{cpu_type}
7042 Set the instruction scheduling parameters for machine type
7043 @var{cpu_type}, but do not set the architecture type, register usage, or
7044 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7045 values for @var{cpu_type} are used for @option{-mtune} as for
7046 @option{-mcpu}. If both are specified, the code generated will use the
7047 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7048 scheduling parameters set by @option{-mtune}.
7053 @opindex mno-altivec
7054 These switches enable or disable the use of built-in functions that
7055 allow access to the AltiVec instruction set. You may also need to set
7056 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7061 Extend the current ABI with SPE ABI extensions. This does not change
7062 the default ABI, instead it adds the SPE ABI extensions to the current
7066 @opindex mabi=no-spe
7067 Disable Booke SPE ABI extensions for the current ABI.
7069 @item -misel=@var{yes/no}
7072 This switch enables or disables the generation of ISEL instructions.
7074 @item -mspe=@var{yes/no}
7077 This switch enables or disables the generation of SPE simd
7080 @item -mfloat-gprs=@var{yes/no}
7082 @opindex mfloat-gprs
7083 This switch enables or disables the generation of floating point
7084 operations on the general purpose registers for architectures that
7085 support it. This option is currently only available on the MPC8540.
7088 @itemx -mno-fp-in-toc
7089 @itemx -mno-sum-in-toc
7090 @itemx -mminimal-toc
7092 @opindex mno-fp-in-toc
7093 @opindex mno-sum-in-toc
7094 @opindex mminimal-toc
7095 Modify generation of the TOC (Table Of Contents), which is created for
7096 every executable file. The @option{-mfull-toc} option is selected by
7097 default. In that case, GCC will allocate at least one TOC entry for
7098 each unique non-automatic variable reference in your program. GCC
7099 will also place floating-point constants in the TOC@. However, only
7100 16,384 entries are available in the TOC@.
7102 If you receive a linker error message that saying you have overflowed
7103 the available TOC space, you can reduce the amount of TOC space used
7104 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7105 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7106 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7107 generate code to calculate the sum of an address and a constant at
7108 run-time instead of putting that sum into the TOC@. You may specify one
7109 or both of these options. Each causes GCC to produce very slightly
7110 slower and larger code at the expense of conserving TOC space.
7112 If you still run out of space in the TOC even when you specify both of
7113 these options, specify @option{-mminimal-toc} instead. This option causes
7114 GCC to make only one TOC entry for every file. When you specify this
7115 option, GCC will produce code that is slower and larger but which
7116 uses extremely little TOC space. You may wish to use this option
7117 only on files that contain less frequently executed code.
7123 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7124 @code{long} type, and the infrastructure needed to support them.
7125 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7126 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7127 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7132 @opindex mno-xl-call
7133 On AIX, pass floating-point arguments to prototyped functions beyond the
7134 register save area (RSA) on the stack in addition to argument FPRs. The
7135 AIX calling convention was extended but not initially documented to
7136 handle an obscure K&R C case of calling a function that takes the
7137 address of its arguments with fewer arguments than declared. AIX XL
7138 compilers access floating point arguments which do not fit in the
7139 RSA from the stack when a subroutine is compiled without
7140 optimization. Because always storing floating-point arguments on the
7141 stack is inefficient and rarely needed, this option is not enabled by
7142 default and only is necessary when calling subroutines compiled by AIX
7143 XL compilers without optimization.
7147 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7148 application written to use message passing with special startup code to
7149 enable the application to run. The system must have PE installed in the
7150 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7151 must be overridden with the @option{-specs=} option to specify the
7152 appropriate directory location. The Parallel Environment does not
7153 support threads, so the @option{-mpe} option and the @option{-pthread}
7154 option are incompatible.
7156 @item -malign-natural
7157 @itemx -malign-power
7158 @opindex malign-natural
7159 @opindex malign-power
7160 On AIX, Darwin, and 64-bit PowerPC Linux, the option
7161 @option{-malign-natural} overrides the ABI-defined alignment of larger
7162 types, such as floating-point doubles, on their natural size-based boundary.
7163 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7164 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7168 @opindex msoft-float
7169 @opindex mhard-float
7170 Generate code that does not use (uses) the floating-point register set.
7171 Software floating point emulation is provided if you use the
7172 @option{-msoft-float} option, and pass the option to GCC when linking.
7175 @itemx -mno-multiple
7177 @opindex mno-multiple
7178 Generate code that uses (does not use) the load multiple word
7179 instructions and the store multiple word instructions. These
7180 instructions are generated by default on POWER systems, and not
7181 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7182 endian PowerPC systems, since those instructions do not work when the
7183 processor is in little endian mode. The exceptions are PPC740 and
7184 PPC750 which permit the instructions usage in little endian mode.
7190 Generate code that uses (does not use) the load string instructions
7191 and the store string word instructions to save multiple registers and
7192 do small block moves. These instructions are generated by default on
7193 POWER systems, and not generated on PowerPC systems. Do not use
7194 @option{-mstring} on little endian PowerPC systems, since those
7195 instructions do not work when the processor is in little endian mode.
7196 The exceptions are PPC740 and PPC750 which permit the instructions
7197 usage in little endian mode.
7203 Generate code that uses (does not use) the load or store instructions
7204 that update the base register to the address of the calculated memory
7205 location. These instructions are generated by default. If you use
7206 @option{-mno-update}, there is a small window between the time that the
7207 stack pointer is updated and the address of the previous frame is
7208 stored, which means code that walks the stack frame across interrupts or
7209 signals may get corrupted data.
7212 @itemx -mno-fused-madd
7213 @opindex mfused-madd
7214 @opindex mno-fused-madd
7215 Generate code that uses (does not use) the floating point multiply and
7216 accumulate instructions. These instructions are generated by default if
7217 hardware floating is used.
7219 @item -mno-bit-align
7221 @opindex mno-bit-align
7223 On System V.4 and embedded PowerPC systems do not (do) force structures
7224 and unions that contain bit-fields to be aligned to the base type of the
7227 For example, by default a structure containing nothing but 8
7228 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7229 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7230 the structure would be aligned to a 1 byte boundary and be one byte in
7233 @item -mno-strict-align
7234 @itemx -mstrict-align
7235 @opindex mno-strict-align
7236 @opindex mstrict-align
7237 On System V.4 and embedded PowerPC systems do not (do) assume that
7238 unaligned memory references will be handled by the system.
7241 @itemx -mno-relocatable
7242 @opindex mrelocatable
7243 @opindex mno-relocatable
7244 On embedded PowerPC systems generate code that allows (does not allow)
7245 the program to be relocated to a different address at runtime. If you
7246 use @option{-mrelocatable} on any module, all objects linked together must
7247 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7249 @item -mrelocatable-lib
7250 @itemx -mno-relocatable-lib
7251 @opindex mrelocatable-lib
7252 @opindex mno-relocatable-lib
7253 On embedded PowerPC systems generate code that allows (does not allow)
7254 the program to be relocated to a different address at runtime. Modules
7255 compiled with @option{-mrelocatable-lib} can be linked with either modules
7256 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7257 with modules compiled with the @option{-mrelocatable} options.
7263 On System V.4 and embedded PowerPC systems do not (do) assume that
7264 register 2 contains a pointer to a global area pointing to the addresses
7265 used in the program.
7268 @itemx -mlittle-endian
7270 @opindex mlittle-endian
7271 On System V.4 and embedded PowerPC systems compile code for the
7272 processor in little endian mode. The @option{-mlittle-endian} option is
7273 the same as @option{-mlittle}.
7278 @opindex mbig-endian
7279 On System V.4 and embedded PowerPC systems compile code for the
7280 processor in big endian mode. The @option{-mbig-endian} option is
7281 the same as @option{-mbig}.
7283 @item -mdynamic-no-pic
7284 @opindex mdynamic-no-pic
7285 On Darwin and Mac OS X systems, compile code so that it is not
7286 relocatable, but that its external references are relocatable. The
7287 resulting code is suitable for applications, but not shared
7292 On System V.4 and embedded PowerPC systems compile code using calling
7293 conventions that adheres to the March 1995 draft of the System V
7294 Application Binary Interface, PowerPC processor supplement. This is the
7295 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7297 @item -mcall-sysv-eabi
7298 @opindex mcall-sysv-eabi
7299 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7301 @item -mcall-sysv-noeabi
7302 @opindex mcall-sysv-noeabi
7303 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7305 @item -mcall-solaris
7306 @opindex mcall-solaris
7307 On System V.4 and embedded PowerPC systems compile code for the Solaris
7311 @opindex mcall-linux
7312 On System V.4 and embedded PowerPC systems compile code for the
7313 Linux-based GNU system.
7317 On System V.4 and embedded PowerPC systems compile code for the
7318 Hurd-based GNU system.
7321 @opindex mcall-netbsd
7322 On System V.4 and embedded PowerPC systems compile code for the
7323 NetBSD operating system.
7325 @item -maix-struct-return
7326 @opindex maix-struct-return
7327 Return all structures in memory (as specified by the AIX ABI)@.
7329 @item -msvr4-struct-return
7330 @opindex msvr4-struct-return
7331 Return structures smaller than 8 bytes in registers (as specified by the
7335 @opindex mabi=altivec
7336 Extend the current ABI with AltiVec ABI extensions. This does not
7337 change the default ABI, instead it adds the AltiVec ABI extensions to
7340 @item -mabi=no-altivec
7341 @opindex mabi=no-altivec
7342 Disable AltiVec ABI extensions for the current ABI.
7345 @itemx -mno-prototype
7347 @opindex mno-prototype
7348 On System V.4 and embedded PowerPC systems assume that all calls to
7349 variable argument functions are properly prototyped. Otherwise, the
7350 compiler must insert an instruction before every non prototyped call to
7351 set or clear bit 6 of the condition code register (@var{CR}) to
7352 indicate whether floating point values were passed in the floating point
7353 registers in case the function takes a variable arguments. With
7354 @option{-mprototype}, only calls to prototyped variable argument functions
7355 will set or clear the bit.
7359 On embedded PowerPC systems, assume that the startup module is called
7360 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7361 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7366 On embedded PowerPC systems, assume that the startup module is called
7367 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7372 On embedded PowerPC systems, assume that the startup module is called
7373 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7377 @opindex myellowknife
7378 On embedded PowerPC systems, assume that the startup module is called
7379 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7384 On System V.4 and embedded PowerPC systems, specify that you are
7385 compiling for a VxWorks system.
7389 Specify that you are compiling for the WindISS simulation environment.
7393 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7394 header to indicate that @samp{eabi} extended relocations are used.
7400 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7401 Embedded Applications Binary Interface (eabi) which is a set of
7402 modifications to the System V.4 specifications. Selecting @option{-meabi}
7403 means that the stack is aligned to an 8 byte boundary, a function
7404 @code{__eabi} is called to from @code{main} to set up the eabi
7405 environment, and the @option{-msdata} option can use both @code{r2} and
7406 @code{r13} to point to two separate small data areas. Selecting
7407 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7408 do not call an initialization function from @code{main}, and the
7409 @option{-msdata} option will only use @code{r13} to point to a single
7410 small data area. The @option{-meabi} option is on by default if you
7411 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7414 @opindex msdata=eabi
7415 On System V.4 and embedded PowerPC systems, put small initialized
7416 @code{const} global and static data in the @samp{.sdata2} section, which
7417 is pointed to by register @code{r2}. Put small initialized
7418 non-@code{const} global and static data in the @samp{.sdata} section,
7419 which is pointed to by register @code{r13}. Put small uninitialized
7420 global and static data in the @samp{.sbss} section, which is adjacent to
7421 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7422 incompatible with the @option{-mrelocatable} option. The
7423 @option{-msdata=eabi} option also sets the @option{-memb} option.
7426 @opindex msdata=sysv
7427 On System V.4 and embedded PowerPC systems, put small global and static
7428 data in the @samp{.sdata} section, which is pointed to by register
7429 @code{r13}. Put small uninitialized global and static data in the
7430 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7431 The @option{-msdata=sysv} option is incompatible with the
7432 @option{-mrelocatable} option.
7434 @item -msdata=default
7436 @opindex msdata=default
7438 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7439 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7440 same as @option{-msdata=sysv}.
7443 @opindex msdata-data
7444 On System V.4 and embedded PowerPC systems, put small global and static
7445 data in the @samp{.sdata} section. Put small uninitialized global and
7446 static data in the @samp{.sbss} section. Do not use register @code{r13}
7447 to address small data however. This is the default behavior unless
7448 other @option{-msdata} options are used.
7452 @opindex msdata=none
7454 On embedded PowerPC systems, put all initialized global and static data
7455 in the @samp{.data} section, and all uninitialized data in the
7456 @samp{.bss} section.
7460 @cindex smaller data references (PowerPC)
7461 @cindex .sdata/.sdata2 references (PowerPC)
7462 On embedded PowerPC systems, put global and static items less than or
7463 equal to @var{num} bytes into the small data or bss sections instead of
7464 the normal data or bss section. By default, @var{num} is 8. The
7465 @option{-G @var{num}} switch is also passed to the linker.
7466 All modules should be compiled with the same @option{-G @var{num}} value.
7469 @itemx -mno-regnames
7471 @opindex mno-regnames
7472 On System V.4 and embedded PowerPC systems do (do not) emit register
7473 names in the assembly language output using symbolic forms.
7476 @itemx -mno-longcall
7478 @opindex mno-longcall
7479 Default to making all function calls via pointers, so that functions
7480 which reside further than 64 megabytes (67,108,864 bytes) from the
7481 current location can be called. This setting can be overridden by the
7482 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7484 Some linkers are capable of detecting out-of-range calls and generating
7485 glue code on the fly. On these systems, long calls are unnecessary and
7486 generate slower code. As of this writing, the AIX linker can do this,
7487 as can the GNU linker for PowerPC/64. It is planned to add this feature
7488 to the GNU linker for 32-bit PowerPC systems as well.
7490 In the future, we may cause GCC to ignore all longcall specifications
7491 when the linker is known to generate glue.
7495 Adds support for multithreading with the @dfn{pthreads} library.
7496 This option sets flags for both the preprocessor and linker.
7500 @node Darwin Options
7501 @subsection Darwin Options
7502 @cindex Darwin options
7504 These options are defined for all architectures running the Darwin operating
7505 system. They are useful for compatibility with other Mac OS compilers.
7510 Loads all members of static archive libraries.
7511 See man ld(1) for more information.
7513 @item -arch_errors_fatal
7514 @opindex arch_errors_fatal
7515 Cause the errors having to do with files that have the wrong architecture
7519 @opindex bind_at_load
7520 Causes the output file to be marked such that the dynamic linker will
7521 bind all undefined references when the file is loaded or launched.
7525 Produce a Mach-o bundle format file.
7526 See man ld(1) for more information.
7528 @item -bundle_loader @var{executable}
7529 @opindex bundle_loader
7530 This specifies the @var{executable} that will be loading the build
7531 output file being linked. See man ld(1) for more information.
7533 @item -allowable_client @var{client_name}
7537 @item -compatibility_version
7538 @item -current_version
7539 @item -dependency-file
7541 @item -dylinker_install_name
7544 @item -exported_symbols_list
7546 @item -flat_namespace
7547 @item -force_cpusubtype_ALL
7548 @item -force_flat_namespace
7549 @item -headerpad_max_install_names
7553 @item -keep_private_externs
7555 @item -multiply_defined
7556 @item -multiply_defined_unused
7560 @item -noseglinkedit
7561 @item -pagezero_size
7563 @item -prebind_all_twolevel_modules
7564 @item -private_bundle
7565 @item -read_only_relocs
7567 @item -sectobjectsymbols
7571 @item -sectobjectsymbols
7573 @item -seg_addr_table
7574 @item -seg_addr_table_filename
7577 @item -segs_read_only_addr
7578 @item -segs_read_write_addr
7579 @item -single_module
7583 @item -twolevel_namespace
7586 @item -unexported_symbols_list
7587 @item -weak_reference_mismatches
7590 @opindex allowable_client
7592 @opindex client_name
7593 @opindex compatibility_version
7594 @opindex current_version
7595 @opindex dependency-file
7597 @opindex dylinker_install_name
7600 @opindex exported_symbols_list
7602 @opindex flat_namespace
7603 @opindex force_cpusubtype_ALL
7604 @opindex force_flat_namespace
7605 @opindex headerpad_max_install_names
7608 @opindex install_name
7609 @opindex keep_private_externs
7610 @opindex multi_module
7611 @opindex multiply_defined
7612 @opindex multiply_defined_unused
7614 @opindex nomultidefs
7616 @opindex noseglinkedit
7617 @opindex pagezero_size
7619 @opindex prebind_all_twolevel_modules
7620 @opindex private_bundle
7621 @opindex read_only_relocs
7623 @opindex sectobjectsymbols
7627 @opindex sectobjectsymbols
7629 @opindex seg_addr_table
7630 @opindex seg_addr_table_filename
7631 @opindex seglinkedit
7633 @opindex segs_read_only_addr
7634 @opindex segs_read_write_addr
7635 @opindex single_module
7637 @opindex sub_library
7638 @opindex sub_umbrella
7639 @opindex twolevel_namespace
7642 @opindex unexported_symbols_list
7643 @opindex weak_reference_mismatches
7644 @opindex whatsloaded
7646 This options are available for Darwin linker. Darwin linker man page
7647 describes them in detail.
7652 @subsection IBM RT Options
7654 @cindex IBM RT options
7656 These @samp{-m} options are defined for the IBM RT PC:
7660 @opindex min-line-mul
7661 Use an in-line code sequence for integer multiplies. This is the
7664 @item -mcall-lib-mul
7665 @opindex mcall-lib-mul
7666 Call @code{lmul$$} for integer multiples.
7668 @item -mfull-fp-blocks
7669 @opindex mfull-fp-blocks
7670 Generate full-size floating point data blocks, including the minimum
7671 amount of scratch space recommended by IBM@. This is the default.
7673 @item -mminimum-fp-blocks
7674 @opindex mminimum-fp-blocks
7675 Do not include extra scratch space in floating point data blocks. This
7676 results in smaller code, but slower execution, since scratch space must
7677 be allocated dynamically.
7679 @cindex @file{stdarg.h} and RT PC
7680 @item -mfp-arg-in-fpregs
7681 @opindex mfp-arg-in-fpregs
7682 Use a calling sequence incompatible with the IBM calling convention in
7683 which floating point arguments are passed in floating point registers.
7684 Note that @code{stdarg.h} will not work with floating point operands
7685 if this option is specified.
7687 @item -mfp-arg-in-gregs
7688 @opindex mfp-arg-in-gregs
7689 Use the normal calling convention for floating point arguments. This is
7692 @item -mhc-struct-return
7693 @opindex mhc-struct-return
7694 Return structures of more than one word in memory, rather than in a
7695 register. This provides compatibility with the MetaWare HighC (hc)
7696 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7697 with the Portable C Compiler (pcc).
7699 @item -mnohc-struct-return
7700 @opindex mnohc-struct-return
7701 Return some structures of more than one word in registers, when
7702 convenient. This is the default. For compatibility with the
7703 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7704 option @option{-mhc-struct-return}.
7708 @subsection MIPS Options
7709 @cindex MIPS options
7711 These @samp{-m} options are defined for the MIPS family of computers:
7715 @item -march=@var{arch}
7717 Generate code that will run on @var{arch}, which can be the name of a
7718 generic MIPS ISA, or the name of a particular processor.
7720 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
7721 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
7722 The processor names are:
7723 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7725 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
7726 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
7729 @samp{vr4100}, @samp{vr4300}, and @samp{vr5000}.
7730 The special value @samp{from-abi} selects the
7731 most compatible architecture for the selected ABI (that is,
7732 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7734 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7735 (for example, @samp{-march=r2k}). Prefixes are optional, and
7736 @samp{vr} may be written @samp{r}.
7738 GCC defines two macros based on the value of this option. The first
7739 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7740 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7741 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
7742 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7743 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7745 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7746 above. In other words, it will have the full prefix and will not
7747 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7748 the macro names the resolved architecture (either @samp{"mips1"} or
7749 @samp{"mips3"}). It names the default architecture when no
7750 @option{-march} option is given.
7752 @item -mtune=@var{arch}
7754 Optimize for @var{arch}. Among other things, this option controls
7755 the way instructions are scheduled, and the perceived cost of arithmetic
7756 operations. The list of @var{arch} values is the same as for
7759 When this option is not used, GCC will optimize for the processor
7760 specified by @option{-march}. By using @option{-march} and
7761 @option{-mtune} together, it is possible to generate code that will
7762 run on a family of processors, but optimize the code for one
7763 particular member of that family.
7765 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7766 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7767 @samp{-march} ones described above.
7771 Equivalent to @samp{-march=mips1}.
7775 Equivalent to @samp{-march=mips2}.
7779 Equivalent to @samp{-march=mips3}.
7783 Equivalent to @samp{-march=mips4}.
7787 Equivalent to @samp{-march=mips32}.
7791 Equivalent to @samp{-march=mips32r2}.
7795 Equivalent to @samp{-march=mips64}.
7798 @itemx -mno-fused-madd
7799 @opindex mfused-madd
7800 @opindex mno-fused-madd
7801 Generate code that uses (does not use) the floating point multiply and
7802 accumulate instructions, when they are available. These instructions
7803 are generated by default if they are available, but this may be
7804 undesirable if the extra precision causes problems or on certain chips
7805 in the mode where denormals are rounded to zero where denormals
7806 generated by multiply and accumulate instructions cause exceptions
7811 Assume that floating point registers are 32 bits wide.
7815 Assume that floating point registers are 64 bits wide.
7819 Assume that general purpose registers are 32 bits wide.
7823 Assume that general purpose registers are 64 bits wide.
7827 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7828 explanation of the default, and the width of pointers.
7832 Force long types to be 64 bits wide. See @option{-mlong32} for an
7833 explanation of the default, and the width of pointers.
7837 Force long, int, and pointer types to be 32 bits wide.
7839 The default size of ints, longs and pointers depends on the ABI@. All
7840 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
7841 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
7842 are the same size as longs, or the same size as integer registers,
7843 whichever is smaller.
7857 Generate code for the given ABI@.
7859 Note that there are two embedded ABIs: @option{-mabi=eabi}
7860 selects the one defined by Cygnus while @option{-meabi=meabi}
7861 selects the one defined by MIPS@. Both these ABIs have
7862 32-bit and 64-bit variants. Normally, GCC will generate
7863 64-bit code when you select a 64-bit architecture, but you
7864 can use @option{-mgp32} to get 32-bit code instead.
7866 @item -mabi-fake-default
7867 @opindex mabi-fake-default
7868 You don't want to know what this option does. No, really. I mean
7869 it. Move on to the next option.
7871 What? You're still here? Oh, well@enddots{} Ok, here's the deal. GCC
7872 wants the default set of options to get the root of the multilib tree,
7873 and the shared library SONAMEs without any multilib-indicating
7874 suffixes. This is not convenience for @samp{mips64-linux-gnu}, since
7875 we want to default to the N32 ABI, while still being binary-compatible
7876 with @samp{mips-linux-gnu} if you stick to the O32 ABI@. Being
7877 binary-compatible means shared libraries should have the same SONAMEs,
7878 and libraries should live in the same location. Having O32 libraries
7879 in a sub-directory named say @file{o32} is not acceptable.
7881 So we trick GCC into believing that O32 is the default ABI, except
7882 that we override the default with some internal command-line
7883 processing magic. Problem is, if we stopped at that, and you then
7884 created a multilib-aware package that used the output of @command{gcc
7885 -print-multi-lib} to decide which multilibs to build, and how, and
7886 you'd find yourself in an awkward situation when you found out that
7887 some of the options listed ended up mapping to the same multilib, and
7888 none of your libraries was actually built for the multilib that
7889 @option{-print-multi-lib} claims to be the default. So we added this
7890 option that disables the default switcher, falling back to GCC's
7891 original notion of the default library. Confused yet?
7893 For short: don't ever use this option, unless you find it in the list
7894 of additional options to be used when building for multilibs, in the
7895 output of @option{gcc -print-multi-lib}.
7899 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7900 add normal debug information. This is the default for all
7901 platforms except for the OSF/1 reference platform, using the OSF/rose
7902 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7903 switches are used, the @file{mips-tfile} program will encapsulate the
7904 stabs within MIPS ECOFF@.
7908 Generate code for the GNU assembler. This is the default on the OSF/1
7909 reference platform, using the OSF/rose object format. Also, this is
7910 the default if the configure option @option{--with-gnu-as} is used.
7912 @item -msplit-addresses
7913 @itemx -mno-split-addresses
7914 @opindex msplit-addresses
7915 @opindex mno-split-addresses
7916 Generate code to load the high and low parts of address constants separately.
7917 This allows GCC to optimize away redundant loads of the high order
7918 bits of addresses. This optimization requires GNU as and GNU ld.
7919 This optimization is enabled by default for some embedded targets where
7920 GNU as and GNU ld are standard.
7926 The @option{-mrnames} switch says to output code using the MIPS software
7927 names for the registers, instead of the hardware names (ie, @var{a0}
7928 instead of @var{$4}). The only known assembler that supports this option
7929 is the Algorithmics assembler.
7935 The @option{-mgpopt} switch says to write all of the data declarations
7936 before the instructions in the text section, this allows the MIPS
7937 assembler to generate one word memory references instead of using two
7938 words for short global or static data items. This is on by default if
7939 optimization is selected.
7945 The @option{-mmemcpy} switch makes all block moves call the appropriate
7946 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7947 generating inline code.
7950 @itemx -mno-mips-tfile
7951 @opindex mmips-tfile
7952 @opindex mno-mips-tfile
7953 The @option{-mno-mips-tfile} switch causes the compiler not
7954 postprocess the object file with the @file{mips-tfile} program,
7955 after the MIPS assembler has generated it to add debug support. If
7956 @file{mips-tfile} is not run, then no local variables will be
7957 available to the debugger. In addition, @file{stage2} and
7958 @file{stage3} objects will have the temporary file names passed to the
7959 assembler embedded in the object file, which means the objects will
7960 not compare the same. The @option{-mno-mips-tfile} switch should only
7961 be used when there are bugs in the @file{mips-tfile} program that
7962 prevents compilation.
7965 @opindex msoft-float
7966 Generate output containing library calls for floating point.
7967 @strong{Warning:} the requisite libraries are not part of GCC@.
7968 Normally the facilities of the machine's usual C compiler are used, but
7969 this can't be done directly in cross-compilation. You must make your
7970 own arrangements to provide suitable library functions for
7974 @opindex mhard-float
7975 Generate output containing floating point instructions. This is the
7976 default if you use the unmodified sources.
7979 @itemx -mno-abicalls
7981 @opindex mno-abicalls
7982 Emit (or do not emit) the pseudo operations @samp{.abicalls},
7983 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
7984 position independent code.
7987 @itemx -mno-long-calls
7988 @opindex mlong-calls
7989 @opindex mno-long-calls
7990 Do all calls with the @samp{JALR} instruction, which requires
7991 loading up a function's address into a register before the call.
7992 You need to use this switch, if you call outside of the current
7993 512 megabyte segment to functions that are not through pointers.
7996 @itemx -mno-half-pic
7998 @opindex mno-half-pic
7999 Put pointers to extern references into the data section and load them
8000 up, rather than put the references in the text section.
8002 @item -membedded-pic
8003 @itemx -mno-embedded-pic
8004 @opindex membedded-pic
8005 @opindex mno-embedded-pic
8006 Generate PIC code suitable for some embedded systems. All calls are
8007 made using PC relative address, and all data is addressed using the $gp
8008 register. No more than 65536 bytes of global data may be used. This
8009 requires GNU as and GNU ld which do most of the work. This currently
8010 only works on targets which use ECOFF; it does not work with ELF@.
8012 @item -membedded-data
8013 @itemx -mno-embedded-data
8014 @opindex membedded-data
8015 @opindex mno-embedded-data
8016 Allocate variables to the read-only data section first if possible, then
8017 next in the small data section if possible, otherwise in data. This gives
8018 slightly slower code than the default, but reduces the amount of RAM required
8019 when executing, and thus may be preferred for some embedded systems.
8021 @item -muninit-const-in-rodata
8022 @itemx -mno-uninit-const-in-rodata
8023 @opindex muninit-const-in-rodata
8024 @opindex mno-uninit-const-in-rodata
8025 When used together with @option{-membedded-data}, it will always store uninitialized
8026 const variables in the read-only data section.
8028 @item -msingle-float
8029 @itemx -mdouble-float
8030 @opindex msingle-float
8031 @opindex mdouble-float
8032 The @option{-msingle-float} switch tells gcc to assume that the floating
8033 point coprocessor only supports single precision operations, as on the
8034 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
8035 double precision operations. This is the default.
8041 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
8042 as on the @samp{r4650} chip.
8046 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
8047 @option{-mcpu=r4650}.
8053 Enable 16-bit instructions.
8057 Use the entry and exit pseudo ops. This option can only be used with
8062 Compile code for the processor in little endian mode.
8063 The requisite libraries are assumed to exist.
8067 Compile code for the processor in big endian mode.
8068 The requisite libraries are assumed to exist.
8072 @cindex smaller data references (MIPS)
8073 @cindex gp-relative references (MIPS)
8074 Put global and static items less than or equal to @var{num} bytes into
8075 the small data or bss sections instead of the normal data or bss
8076 section. This allows the assembler to emit one word memory reference
8077 instructions based on the global pointer (@var{gp} or @var{$28}),
8078 instead of the normal two words used. By default, @var{num} is 8 when
8079 the MIPS assembler is used, and 0 when the GNU assembler is used. The
8080 @option{-G @var{num}} switch is also passed to the assembler and linker.
8081 All modules should be compiled with the same @option{-G @var{num}}
8086 Tell the MIPS assembler to not run its preprocessor over user
8087 assembler files (with a @samp{.s} suffix) when assembling them.
8091 Pass an option to gas which will cause nops to be inserted if
8092 the read of the destination register of an mfhi or mflo instruction
8093 occurs in the following two instructions.
8097 Do not include the default crt0.
8099 @item -mflush-func=@var{func}
8100 @itemx -mno-flush-func
8101 @opindex mflush-func
8102 Specifies the function to call to flush the I and D caches, or to not
8103 call any such function. If called, the function must take the same
8104 arguments as the common @code{_flush_func()}, that is, the address of the
8105 memory range for which the cache is being flushed, the size of the
8106 memory range, and the number 3 (to flush both caches). The default
8107 depends on the target gcc was configured for, but commonly is either
8108 @samp{_flush_func} or @samp{__cpu_flush}.
8110 @item -mbranch-likely
8111 @itemx -mno-branch-likely
8112 @opindex mbranch-likely
8113 @opindex mno-branch-likely
8114 Enable or disable use of Branch Likely instructions, regardless of the
8115 default for the selected architecture. By default, Branch Likely
8116 instructions may be generated if they are supported by the selected
8117 architecture. An exception is for the MIPS32 and MIPS64 architectures
8118 and processors which implement those architectures; for those, Branch
8119 Likely instructions will not be generated by default because the MIPS32
8120 and MIPS64 architectures specifically deprecate their use.
8123 @node i386 and x86-64 Options
8124 @subsection Intel 386 and AMD x86-64 Options
8125 @cindex i386 Options
8126 @cindex x86-64 Options
8127 @cindex Intel 386 Options
8128 @cindex AMD x86-64 Options
8130 These @samp{-m} options are defined for the i386 and x86-64 family of
8134 @item -mtune=@var{cpu-type}
8136 Tune to @var{cpu-type} everything applicable about the generated code, except
8137 for the ABI and the set of available instructions. The choices for
8138 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
8139 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
8140 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
8141 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
8142 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2}, @samp{k8}, @samp{c3}
8145 While picking a specific @var{cpu-type} will schedule things appropriately
8146 for that particular chip, the compiler will not generate any code that
8147 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8148 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
8149 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
8150 AMD chips as opposed to the Intel ones.
8152 @item -march=@var{cpu-type}
8154 Generate instructions for the machine type @var{cpu-type}. The choices
8155 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8156 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8158 @item -mcpu=@var{cpu-type}
8160 A deprecated synonym for @option{-mtune}.
8169 @opindex mpentiumpro
8170 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8171 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8172 These synonyms are deprecated.
8174 @item -mfpmath=@var{unit}
8176 generate floating point arithmetics for selected unit @var{unit}. the choices
8181 Use the standard 387 floating point coprocessor present majority of chips and
8182 emulated otherwise. Code compiled with this option will run almost everywhere.
8183 The temporary results are computed in 80bit precision instead of precision
8184 specified by the type resulting in slightly different results compared to most
8185 of other chips. See @option{-ffloat-store} for more detailed description.
8187 This is the default choice for i386 compiler.
8190 Use scalar floating point instructions present in the SSE instruction set.
8191 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8192 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8193 instruction set supports only single precision arithmetics, thus the double and
8194 extended precision arithmetics is still done using 387. Later version, present
8195 only in Pentium4 and the future AMD x86-64 chips supports double precision
8198 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8199 @option{-msse2} switches to enable SSE extensions and make this option
8200 effective. For x86-64 compiler, these extensions are enabled by default.
8202 The resulting code should be considerably faster in majority of cases and avoid
8203 the numerical instability problems of 387 code, but may break some existing
8204 code that expects temporaries to be 80bit.
8206 This is the default choice for x86-64 compiler.
8209 Attempt to utilize both instruction sets at once. This effectively double the
8210 amount of available registers and on chips with separate execution units for
8211 387 and SSE the execution resources too. Use this option with care, as it is
8212 still experimental, because gcc register allocator does not model separate
8213 functional units well resulting in instable performance.
8216 @item -masm=@var{dialect}
8217 @opindex masm=@var{dialect}
8218 Output asm instructions using selected @var{dialect}. Supported choices are
8219 @samp{intel} or @samp{att} (the default one).
8224 @opindex mno-ieee-fp
8225 Control whether or not the compiler uses IEEE floating point
8226 comparisons. These handle correctly the case where the result of a
8227 comparison is unordered.
8230 @opindex msoft-float
8231 Generate output containing library calls for floating point.
8232 @strong{Warning:} the requisite libraries are not part of GCC@.
8233 Normally the facilities of the machine's usual C compiler are used, but
8234 this can't be done directly in cross-compilation. You must make your
8235 own arrangements to provide suitable library functions for
8238 On machines where a function returns floating point results in the 80387
8239 register stack, some floating point opcodes may be emitted even if
8240 @option{-msoft-float} is used.
8242 @item -mno-fp-ret-in-387
8243 @opindex mno-fp-ret-in-387
8244 Do not use the FPU registers for return values of functions.
8246 The usual calling convention has functions return values of types
8247 @code{float} and @code{double} in an FPU register, even if there
8248 is no FPU@. The idea is that the operating system should emulate
8251 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8252 in ordinary CPU registers instead.
8254 @item -mno-fancy-math-387
8255 @opindex mno-fancy-math-387
8256 Some 387 emulators do not support the @code{sin}, @code{cos} and
8257 @code{sqrt} instructions for the 387. Specify this option to avoid
8258 generating those instructions. This option is the default on FreeBSD,
8259 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8260 indicates that the target cpu will always have an FPU and so the
8261 instruction will not need emulation. As of revision 2.6.1, these
8262 instructions are not generated unless you also use the
8263 @option{-funsafe-math-optimizations} switch.
8265 @item -malign-double
8266 @itemx -mno-align-double
8267 @opindex malign-double
8268 @opindex mno-align-double
8269 Control whether GCC aligns @code{double}, @code{long double}, and
8270 @code{long long} variables on a two word boundary or a one word
8271 boundary. Aligning @code{double} variables on a two word boundary will
8272 produce code that runs somewhat faster on a @samp{Pentium} at the
8273 expense of more memory.
8275 @strong{Warning:} if you use the @option{-malign-double} switch,
8276 structures containing the above types will be aligned differently than
8277 the published application binary interface specifications for the 386
8278 and will not be binary compatible with structures in code compiled
8279 without that switch.
8281 @item -m96bit-long-double
8282 @item -m128bit-long-double
8283 @opindex m96bit-long-double
8284 @opindex m128bit-long-double
8285 These switches control the size of @code{long double} type. The i386
8286 application binary interface specifies the size to be 96 bits,
8287 so @option{-m96bit-long-double} is the default in 32 bit mode.
8289 Modern architectures (Pentium and newer) would prefer @code{long double}
8290 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8291 conforming to the ABI, this would not be possible. So specifying a
8292 @option{-m128bit-long-double} will align @code{long double}
8293 to a 16 byte boundary by padding the @code{long double} with an additional
8296 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8297 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8299 Notice that neither of these options enable any extra precision over the x87
8300 standard of 80 bits for a @code{long double}.
8302 @strong{Warning:} if you override the default value for your target ABI, the
8303 structures and arrays containing @code{long double} will change their size as
8304 well as function calling convention for function taking @code{long double}
8305 will be modified. Hence they will not be binary compatible with arrays or
8306 structures in code compiled without that switch.
8310 @itemx -mno-svr3-shlib
8311 @opindex msvr3-shlib
8312 @opindex mno-svr3-shlib
8313 Control whether GCC places uninitialized local variables into the
8314 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8315 into @code{bss}. These options are meaningful only on System V Release 3.
8319 Use a different function-calling convention, in which functions that
8320 take a fixed number of arguments return with the @code{ret} @var{num}
8321 instruction, which pops their arguments while returning. This saves one
8322 instruction in the caller since there is no need to pop the arguments
8325 You can specify that an individual function is called with this calling
8326 sequence with the function attribute @samp{stdcall}. You can also
8327 override the @option{-mrtd} option by using the function attribute
8328 @samp{cdecl}. @xref{Function Attributes}.
8330 @strong{Warning:} this calling convention is incompatible with the one
8331 normally used on Unix, so you cannot use it if you need to call
8332 libraries compiled with the Unix compiler.
8334 Also, you must provide function prototypes for all functions that
8335 take variable numbers of arguments (including @code{printf});
8336 otherwise incorrect code will be generated for calls to those
8339 In addition, seriously incorrect code will result if you call a
8340 function with too many arguments. (Normally, extra arguments are
8341 harmlessly ignored.)
8343 @item -mregparm=@var{num}
8345 Control how many registers are used to pass integer arguments. By
8346 default, no registers are used to pass arguments, and at most 3
8347 registers can be used. You can control this behavior for a specific
8348 function by using the function attribute @samp{regparm}.
8349 @xref{Function Attributes}.
8351 @strong{Warning:} if you use this switch, and
8352 @var{num} is nonzero, then you must build all modules with the same
8353 value, including any libraries. This includes the system libraries and
8356 @item -mpreferred-stack-boundary=@var{num}
8357 @opindex mpreferred-stack-boundary
8358 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8359 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8360 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8361 size (@option{-Os}), in which case the default is the minimum correct
8362 alignment (4 bytes for x86, and 8 bytes for x86-64).
8364 On Pentium and PentiumPro, @code{double} and @code{long double} values
8365 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8366 suffer significant run time performance penalties. On Pentium III, the
8367 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8368 penalties if it is not 16 byte aligned.
8370 To ensure proper alignment of this values on the stack, the stack boundary
8371 must be as aligned as that required by any value stored on the stack.
8372 Further, every function must be generated such that it keeps the stack
8373 aligned. Thus calling a function compiled with a higher preferred
8374 stack boundary from a function compiled with a lower preferred stack
8375 boundary will most likely misalign the stack. It is recommended that
8376 libraries that use callbacks always use the default setting.
8378 This extra alignment does consume extra stack space, and generally
8379 increases code size. Code that is sensitive to stack space usage, such
8380 as embedded systems and operating system kernels, may want to reduce the
8381 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8397 These switches enable or disable the use of built-in functions that allow
8398 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
8400 @xref{X86 Built-in Functions}, for details of the functions enabled
8401 and disabled by these switches.
8403 To have SSE/SSE2 instructions generated automatically from floating-point
8404 code, see @option{-mfpmath=sse}.
8407 @itemx -mno-push-args
8409 @opindex mno-push-args
8410 Use PUSH operations to store outgoing parameters. This method is shorter
8411 and usually equally fast as method using SUB/MOV operations and is enabled
8412 by default. In some cases disabling it may improve performance because of
8413 improved scheduling and reduced dependencies.
8415 @item -maccumulate-outgoing-args
8416 @opindex maccumulate-outgoing-args
8417 If enabled, the maximum amount of space required for outgoing arguments will be
8418 computed in the function prologue. This is faster on most modern CPUs
8419 because of reduced dependencies, improved scheduling and reduced stack usage
8420 when preferred stack boundary is not equal to 2. The drawback is a notable
8421 increase in code size. This switch implies @option{-mno-push-args}.
8425 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8426 on thread-safe exception handling must compile and link all code with the
8427 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8428 @option{-D_MT}; when linking, it links in a special thread helper library
8429 @option{-lmingwthrd} which cleans up per thread exception handling data.
8431 @item -mno-align-stringops
8432 @opindex mno-align-stringops
8433 Do not align destination of inlined string operations. This switch reduces
8434 code size and improves performance in case the destination is already aligned,
8435 but gcc don't know about it.
8437 @item -minline-all-stringops
8438 @opindex minline-all-stringops
8439 By default GCC inlines string operations only when destination is known to be
8440 aligned at least to 4 byte boundary. This enables more inlining, increase code
8441 size, but may improve performance of code that depends on fast memcpy, strlen
8442 and memset for short lengths.
8444 @item -momit-leaf-frame-pointer
8445 @opindex momit-leaf-frame-pointer
8446 Don't keep the frame pointer in a register for leaf functions. This
8447 avoids the instructions to save, set up and restore frame pointers and
8448 makes an extra register available in leaf functions. The option
8449 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8450 which might make debugging harder.
8452 @item -mtls-direct-seg-refs
8453 @itemx -mno-tls-direct-seg-refs
8454 @opindex mtls-direct-seg-refs
8455 Controls whether TLS variables may be accessed with offsets from the
8456 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8457 or whether the thread base pointer must be added. Whether or not this
8458 is legal depends on the operating system, and whether it maps the
8459 segment to cover the entire TLS area.
8461 For systems that use GNU libc, the default is on.
8464 These @samp{-m} switches are supported in addition to the above
8465 on AMD x86-64 processors in 64-bit environments.
8472 Generate code for a 32-bit or 64-bit environment.
8473 The 32-bit environment sets int, long and pointer to 32 bits and
8474 generates code that runs on any i386 system.
8475 The 64-bit environment sets int to 32 bits and long and pointer
8476 to 64 bits and generates code for AMD's x86-64 architecture.
8479 @opindex no-red-zone
8480 Do not use a so called red zone for x86-64 code. The red zone is mandated
8481 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8482 stack pointer that will not be modified by signal or interrupt handlers
8483 and therefore can be used for temporary data without adjusting the stack
8484 pointer. The flag @option{-mno-red-zone} disables this red zone.
8486 @item -mcmodel=small
8487 @opindex mcmodel=small
8488 Generate code for the small code model: the program and its symbols must
8489 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8490 Programs can be statically or dynamically linked. This is the default
8493 @item -mcmodel=kernel
8494 @opindex mcmodel=kernel
8495 Generate code for the kernel code model. The kernel runs in the
8496 negative 2 GB of the address space.
8497 This model has to be used for Linux kernel code.
8499 @item -mcmodel=medium
8500 @opindex mcmodel=medium
8501 Generate code for the medium model: The program is linked in the lower 2
8502 GB of the address space but symbols can be located anywhere in the
8503 address space. Programs can be statically or dynamically linked, but
8504 building of shared libraries are not supported with the medium model.
8506 @item -mcmodel=large
8507 @opindex mcmodel=large
8508 Generate code for the large model: This model makes no assumptions
8509 about addresses and sizes of sections. Currently GCC does not implement
8514 @subsection HPPA Options
8515 @cindex HPPA Options
8517 These @samp{-m} options are defined for the HPPA family of computers:
8520 @item -march=@var{architecture-type}
8522 Generate code for the specified architecture. The choices for
8523 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8524 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8525 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8526 architecture option for your machine. Code compiled for lower numbered
8527 architectures will run on higher numbered architectures, but not the
8530 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8531 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8535 @itemx -mpa-risc-1-1
8536 @itemx -mpa-risc-2-0
8537 @opindex mpa-risc-1-0
8538 @opindex mpa-risc-1-1
8539 @opindex mpa-risc-2-0
8540 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8543 @opindex mbig-switch
8544 Generate code suitable for big switch tables. Use this option only if
8545 the assembler/linker complain about out of range branches within a switch
8548 @item -mjump-in-delay
8549 @opindex mjump-in-delay
8550 Fill delay slots of function calls with unconditional jump instructions
8551 by modifying the return pointer for the function call to be the target
8552 of the conditional jump.
8554 @item -mdisable-fpregs
8555 @opindex mdisable-fpregs
8556 Prevent floating point registers from being used in any manner. This is
8557 necessary for compiling kernels which perform lazy context switching of
8558 floating point registers. If you use this option and attempt to perform
8559 floating point operations, the compiler will abort.
8561 @item -mdisable-indexing
8562 @opindex mdisable-indexing
8563 Prevent the compiler from using indexing address modes. This avoids some
8564 rather obscure problems when compiling MIG generated code under MACH@.
8566 @item -mno-space-regs
8567 @opindex mno-space-regs
8568 Generate code that assumes the target has no space registers. This allows
8569 GCC to generate faster indirect calls and use unscaled index address modes.
8571 Such code is suitable for level 0 PA systems and kernels.
8573 @item -mfast-indirect-calls
8574 @opindex mfast-indirect-calls
8575 Generate code that assumes calls never cross space boundaries. This
8576 allows GCC to emit code which performs faster indirect calls.
8578 This option will not work in the presence of shared libraries or nested
8581 @item -mlong-load-store
8582 @opindex mlong-load-store
8583 Generate 3-instruction load and store sequences as sometimes required by
8584 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8587 @item -mportable-runtime
8588 @opindex mportable-runtime
8589 Use the portable calling conventions proposed by HP for ELF systems.
8593 Enable the use of assembler directives only GAS understands.
8595 @item -mschedule=@var{cpu-type}
8597 Schedule code according to the constraints for the machine type
8598 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8599 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8600 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8601 proper scheduling option for your machine. The default scheduling is
8605 @opindex mlinker-opt
8606 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8607 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8608 linkers in which they give bogus error messages when linking some programs.
8611 @opindex msoft-float
8612 Generate output containing library calls for floating point.
8613 @strong{Warning:} the requisite libraries are not available for all HPPA
8614 targets. Normally the facilities of the machine's usual C compiler are
8615 used, but this cannot be done directly in cross-compilation. You must make
8616 your own arrangements to provide suitable library functions for
8617 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8618 does provide software floating point support.
8620 @option{-msoft-float} changes the calling convention in the output file;
8621 therefore, it is only useful if you compile @emph{all} of a program with
8622 this option. In particular, you need to compile @file{libgcc.a}, the
8623 library that comes with GCC, with @option{-msoft-float} in order for
8628 Generate the predefine, @code{_SIO}, for server IO. The default is
8629 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8630 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8631 options are available under HP-UX and HI-UX.
8635 Use GNU ld specific options. This passes @option{-shared} to ld when
8636 building a shared library. It is the default when GCC is configured,
8637 explicitly or implicitly, with the GNU linker. This option does not
8638 have any affect on which ld is called, it only changes what parameters
8639 are passed to that ld. The ld that is called is determined by the
8640 @option{--with-ld} configure option, gcc's program search path, and
8641 finally by the user's @env{PATH}. The linker used by GCC can be printed
8642 using @samp{which `gcc -print-prog-name=ld`}.
8646 Use HP ld specific options. This passes @option{-b} to ld when building
8647 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8648 links. It is the default when GCC is configured, explicitly or
8649 implicitly, with the HP linker. This option does not have any affect on
8650 which ld is called, it only changes what parameters are passed to that
8651 ld. The ld that is called is determined by the @option{--with-ld}
8652 configure option, gcc's program search path, and finally by the user's
8653 @env{PATH}. The linker used by GCC can be printed using @samp{which
8654 `gcc -print-prog-name=ld`}.
8657 @opindex mno-long-calls
8658 Generate code that uses long call sequences. This ensures that a call
8659 is always able to reach linker generated stubs. The default is to generate
8660 long calls only when the distance from the call site to the beginning
8661 of the function or translation unit, as the case may be, exceeds a
8662 predefined limit set by the branch type being used. The limits for
8663 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8664 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8667 Distances are measured from the beginning of functions when using the
8668 @option{-ffunction-sections} option, or when using the @option{-mgas}
8669 and @option{-mno-portable-runtime} options together under HP-UX with
8672 It is normally not desirable to use this option as it will degrade
8673 performance. However, it may be useful in large applications,
8674 particularly when partial linking is used to build the application.
8676 The types of long calls used depends on the capabilities of the
8677 assembler and linker, and the type of code being generated. The
8678 impact on systems that support long absolute calls, and long pic
8679 symbol-difference or pc-relative calls should be relatively small.
8680 However, an indirect call is used on 32-bit ELF systems in pic code
8681 and it is quite long.
8685 Suppress the generation of link options to search libdld.sl when the
8686 @option{-static} option is specified on HP-UX 10 and later.
8690 The HP-UX implementation of setlocale in libc has a dependency on
8691 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8692 when the @option{-static} option is specified, special link options
8693 are needed to resolve this dependency.
8695 On HP-UX 10 and later, the GCC driver adds the necessary options to
8696 link with libdld.sl when the @option{-static} option is specified.
8697 This causes the resulting binary to be dynamic. On the 64-bit port,
8698 the linkers generate dynamic binaries by default in any case. The
8699 @option{-nolibdld} option can be used to prevent the GCC driver from
8700 adding these link options.
8704 Add support for multithreading with the @dfn{dce thread} library
8705 under HP-UX. This option sets flags for both the preprocessor and
8709 @node Intel 960 Options
8710 @subsection Intel 960 Options
8712 These @samp{-m} options are defined for the Intel 960 implementations:
8715 @item -m@var{cpu-type}
8723 Assume the defaults for the machine type @var{cpu-type} for some of
8724 the other options, including instruction scheduling, floating point
8725 support, and addressing modes. The choices for @var{cpu-type} are
8726 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8727 @samp{sa}, and @samp{sb}.
8734 @opindex msoft-float
8735 The @option{-mnumerics} option indicates that the processor does support
8736 floating-point instructions. The @option{-msoft-float} option indicates
8737 that floating-point support should not be assumed.
8739 @item -mleaf-procedures
8740 @itemx -mno-leaf-procedures
8741 @opindex mleaf-procedures
8742 @opindex mno-leaf-procedures
8743 Do (or do not) attempt to alter leaf procedures to be callable with the
8744 @code{bal} instruction as well as @code{call}. This will result in more
8745 efficient code for explicit calls when the @code{bal} instruction can be
8746 substituted by the assembler or linker, but less efficient code in other
8747 cases, such as calls via function pointers, or using a linker that doesn't
8748 support this optimization.
8751 @itemx -mno-tail-call
8753 @opindex mno-tail-call
8754 Do (or do not) make additional attempts (beyond those of the
8755 machine-independent portions of the compiler) to optimize tail-recursive
8756 calls into branches. You may not want to do this because the detection of
8757 cases where this is not valid is not totally complete. The default is
8758 @option{-mno-tail-call}.
8760 @item -mcomplex-addr
8761 @itemx -mno-complex-addr
8762 @opindex mcomplex-addr
8763 @opindex mno-complex-addr
8764 Assume (or do not assume) that the use of a complex addressing mode is a
8765 win on this implementation of the i960. Complex addressing modes may not
8766 be worthwhile on the K-series, but they definitely are on the C-series.
8767 The default is currently @option{-mcomplex-addr} for all processors except
8771 @itemx -mno-code-align
8772 @opindex mcode-align
8773 @opindex mno-code-align
8774 Align code to 8-byte boundaries for faster fetching (or don't bother).
8775 Currently turned on by default for C-series implementations only.
8778 @item -mclean-linkage
8779 @itemx -mno-clean-linkage
8780 @opindex mclean-linkage
8781 @opindex mno-clean-linkage
8782 These options are not fully implemented.
8786 @itemx -mic2.0-compat
8787 @itemx -mic3.0-compat
8789 @opindex mic2.0-compat
8790 @opindex mic3.0-compat
8791 Enable compatibility with iC960 v2.0 or v3.0.
8795 @opindex masm-compat
8797 Enable compatibility with the iC960 assembler.
8799 @item -mstrict-align
8800 @itemx -mno-strict-align
8801 @opindex mstrict-align
8802 @opindex mno-strict-align
8803 Do not permit (do permit) unaligned accesses.
8807 Enable structure-alignment compatibility with Intel's gcc release version
8808 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8810 @item -mlong-double-64
8811 @opindex mlong-double-64
8812 Implement type @samp{long double} as 64-bit floating point numbers.
8813 Without the option @samp{long double} is implemented by 80-bit
8814 floating point numbers. The only reason we have it because there is
8815 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8816 is only useful for people using soft-float targets. Otherwise, we
8817 should recommend against use of it.
8821 @node DEC Alpha Options
8822 @subsection DEC Alpha Options
8824 These @samp{-m} options are defined for the DEC Alpha implementations:
8827 @item -mno-soft-float
8829 @opindex mno-soft-float
8830 @opindex msoft-float
8831 Use (do not use) the hardware floating-point instructions for
8832 floating-point operations. When @option{-msoft-float} is specified,
8833 functions in @file{libgcc.a} will be used to perform floating-point
8834 operations. Unless they are replaced by routines that emulate the
8835 floating-point operations, or compiled in such a way as to call such
8836 emulations routines, these routines will issue floating-point
8837 operations. If you are compiling for an Alpha without floating-point
8838 operations, you must ensure that the library is built so as not to call
8841 Note that Alpha implementations without floating-point operations are
8842 required to have floating-point registers.
8847 @opindex mno-fp-regs
8848 Generate code that uses (does not use) the floating-point register set.
8849 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8850 register set is not used, floating point operands are passed in integer
8851 registers as if they were integers and floating-point results are passed
8852 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8853 so any function with a floating-point argument or return value called by code
8854 compiled with @option{-mno-fp-regs} must also be compiled with that
8857 A typical use of this option is building a kernel that does not use,
8858 and hence need not save and restore, any floating-point registers.
8862 The Alpha architecture implements floating-point hardware optimized for
8863 maximum performance. It is mostly compliant with the IEEE floating
8864 point standard. However, for full compliance, software assistance is
8865 required. This option generates code fully IEEE compliant code
8866 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8867 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8868 defined during compilation. The resulting code is less efficient but is
8869 able to correctly support denormalized numbers and exceptional IEEE
8870 values such as not-a-number and plus/minus infinity. Other Alpha
8871 compilers call this option @option{-ieee_with_no_inexact}.
8873 @item -mieee-with-inexact
8874 @opindex mieee-with-inexact
8875 This is like @option{-mieee} except the generated code also maintains
8876 the IEEE @var{inexact-flag}. Turning on this option causes the
8877 generated code to implement fully-compliant IEEE math. In addition to
8878 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8879 macro. On some Alpha implementations the resulting code may execute
8880 significantly slower than the code generated by default. Since there is
8881 very little code that depends on the @var{inexact-flag}, you should
8882 normally not specify this option. Other Alpha compilers call this
8883 option @option{-ieee_with_inexact}.
8885 @item -mfp-trap-mode=@var{trap-mode}
8886 @opindex mfp-trap-mode
8887 This option controls what floating-point related traps are enabled.
8888 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8889 The trap mode can be set to one of four values:
8893 This is the default (normal) setting. The only traps that are enabled
8894 are the ones that cannot be disabled in software (e.g., division by zero
8898 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8902 Like @samp{su}, but the instructions are marked to be safe for software
8903 completion (see Alpha architecture manual for details).
8906 Like @samp{su}, but inexact traps are enabled as well.
8909 @item -mfp-rounding-mode=@var{rounding-mode}
8910 @opindex mfp-rounding-mode
8911 Selects the IEEE rounding mode. Other Alpha compilers call this option
8912 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8917 Normal IEEE rounding mode. Floating point numbers are rounded towards
8918 the nearest machine number or towards the even machine number in case
8922 Round towards minus infinity.
8925 Chopped rounding mode. Floating point numbers are rounded towards zero.
8928 Dynamic rounding mode. A field in the floating point control register
8929 (@var{fpcr}, see Alpha architecture reference manual) controls the
8930 rounding mode in effect. The C library initializes this register for
8931 rounding towards plus infinity. Thus, unless your program modifies the
8932 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8935 @item -mtrap-precision=@var{trap-precision}
8936 @opindex mtrap-precision
8937 In the Alpha architecture, floating point traps are imprecise. This
8938 means without software assistance it is impossible to recover from a
8939 floating trap and program execution normally needs to be terminated.
8940 GCC can generate code that can assist operating system trap handlers
8941 in determining the exact location that caused a floating point trap.
8942 Depending on the requirements of an application, different levels of
8943 precisions can be selected:
8947 Program precision. This option is the default and means a trap handler
8948 can only identify which program caused a floating point exception.
8951 Function precision. The trap handler can determine the function that
8952 caused a floating point exception.
8955 Instruction precision. The trap handler can determine the exact
8956 instruction that caused a floating point exception.
8959 Other Alpha compilers provide the equivalent options called
8960 @option{-scope_safe} and @option{-resumption_safe}.
8962 @item -mieee-conformant
8963 @opindex mieee-conformant
8964 This option marks the generated code as IEEE conformant. You must not
8965 use this option unless you also specify @option{-mtrap-precision=i} and either
8966 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8967 is to emit the line @samp{.eflag 48} in the function prologue of the
8968 generated assembly file. Under DEC Unix, this has the effect that
8969 IEEE-conformant math library routines will be linked in.
8971 @item -mbuild-constants
8972 @opindex mbuild-constants
8973 Normally GCC examines a 32- or 64-bit integer constant to
8974 see if it can construct it from smaller constants in two or three
8975 instructions. If it cannot, it will output the constant as a literal and
8976 generate code to load it from the data segment at runtime.
8978 Use this option to require GCC to construct @emph{all} integer constants
8979 using code, even if it takes more instructions (the maximum is six).
8981 You would typically use this option to build a shared library dynamic
8982 loader. Itself a shared library, it must relocate itself in memory
8983 before it can find the variables and constants in its own data segment.
8989 Select whether to generate code to be assembled by the vendor-supplied
8990 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9008 Indicate whether GCC should generate code to use the optional BWX,
9009 CIX, FIX and MAX instruction sets. The default is to use the instruction
9010 sets supported by the CPU type specified via @option{-mcpu=} option or that
9011 of the CPU on which GCC was built if none was specified.
9016 @opindex mfloat-ieee
9017 Generate code that uses (does not use) VAX F and G floating point
9018 arithmetic instead of IEEE single and double precision.
9020 @item -mexplicit-relocs
9021 @itemx -mno-explicit-relocs
9022 @opindex mexplicit-relocs
9023 @opindex mno-explicit-relocs
9024 Older Alpha assemblers provided no way to generate symbol relocations
9025 except via assembler macros. Use of these macros does not allow
9026 optimal instruction scheduling. GNU binutils as of version 2.12
9027 supports a new syntax that allows the compiler to explicitly mark
9028 which relocations should apply to which instructions. This option
9029 is mostly useful for debugging, as GCC detects the capabilities of
9030 the assembler when it is built and sets the default accordingly.
9034 @opindex msmall-data
9035 @opindex mlarge-data
9036 When @option{-mexplicit-relocs} is in effect, static data is
9037 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9038 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9039 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9040 16-bit relocations off of the @code{$gp} register. This limits the
9041 size of the small data area to 64KB, but allows the variables to be
9042 directly accessed via a single instruction.
9044 The default is @option{-mlarge-data}. With this option the data area
9045 is limited to just below 2GB. Programs that require more than 2GB of
9046 data must use @code{malloc} or @code{mmap} to allocate the data in the
9047 heap instead of in the program's data segment.
9049 When generating code for shared libraries, @option{-fpic} implies
9050 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9054 @opindex msmall-text
9055 @opindex mlarge-text
9056 When @option{-msmall-text} is used, the compiler assumes that the
9057 code of the entire program (or shared library) fits in 4MB, and is
9058 thus reachable with a branch instruction. When @option{-msmall-data}
9059 is used, the compiler can assume that all local symbols share the
9060 same @code{$gp} value, and thus reduce the number of instructions
9061 required for a function call from 4 to 1.
9063 The default is @option{-mlarge-text}.
9065 @item -mcpu=@var{cpu_type}
9067 Set the instruction set and instruction scheduling parameters for
9068 machine type @var{cpu_type}. You can specify either the @samp{EV}
9069 style name or the corresponding chip number. GCC supports scheduling
9070 parameters for the EV4, EV5 and EV6 family of processors and will
9071 choose the default values for the instruction set from the processor
9072 you specify. If you do not specify a processor type, GCC will default
9073 to the processor on which the compiler was built.
9075 Supported values for @var{cpu_type} are
9081 Schedules as an EV4 and has no instruction set extensions.
9085 Schedules as an EV5 and has no instruction set extensions.
9089 Schedules as an EV5 and supports the BWX extension.
9094 Schedules as an EV5 and supports the BWX and MAX extensions.
9098 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9102 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9105 @item -mtune=@var{cpu_type}
9107 Set only the instruction scheduling parameters for machine type
9108 @var{cpu_type}. The instruction set is not changed.
9110 @item -mmemory-latency=@var{time}
9111 @opindex mmemory-latency
9112 Sets the latency the scheduler should assume for typical memory
9113 references as seen by the application. This number is highly
9114 dependent on the memory access patterns used by the application
9115 and the size of the external cache on the machine.
9117 Valid options for @var{time} are
9121 A decimal number representing clock cycles.
9127 The compiler contains estimates of the number of clock cycles for
9128 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9129 (also called Dcache, Scache, and Bcache), as well as to main memory.
9130 Note that L3 is only valid for EV5.
9135 @node DEC Alpha/VMS Options
9136 @subsection DEC Alpha/VMS Options
9138 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9141 @item -mvms-return-codes
9142 @opindex mvms-return-codes
9143 Return VMS condition codes from main. The default is to return POSIX
9144 style condition (e.g.@ error) codes.
9147 @node H8/300 Options
9148 @subsection H8/300 Options
9150 These @samp{-m} options are defined for the H8/300 implementations:
9155 Shorten some address references at link time, when possible; uses the
9156 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9157 ld.info, Using ld}, for a fuller description.
9161 Generate code for the H8/300H@.
9165 Generate code for the H8S@.
9169 Generate code for the H8S and H8/300H in the normal mode. This switch
9170 must be used either with -mh or -ms.
9174 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9178 Make @code{int} data 32 bits by default.
9182 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9183 The default for the H8/300H and H8S is to align longs and floats on 4
9185 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9186 This option has no effect on the H8/300.
9190 @subsection SH Options
9192 These @samp{-m} options are defined for the SH implementations:
9197 Generate code for the SH1.
9201 Generate code for the SH2.
9204 Generate code for the SH2e.
9208 Generate code for the SH3.
9212 Generate code for the SH3e.
9216 Generate code for the SH4 without a floating-point unit.
9218 @item -m4-single-only
9219 @opindex m4-single-only
9220 Generate code for the SH4 with a floating-point unit that only
9221 supports single-precision arithmetic.
9225 Generate code for the SH4 assuming the floating-point unit is in
9226 single-precision mode by default.
9230 Generate code for the SH4.
9234 Compile code for the processor in big endian mode.
9238 Compile code for the processor in little endian mode.
9242 Align doubles at 64-bit boundaries. Note that this changes the calling
9243 conventions, and thus some functions from the standard C library will
9244 not work unless you recompile it first with @option{-mdalign}.
9248 Shorten some address references at link time, when possible; uses the
9249 linker option @option{-relax}.
9253 Use 32-bit offsets in @code{switch} tables. The default is to use
9258 Enable the use of the instruction @code{fmovd}.
9262 Comply with the calling conventions defined by Renesas.
9266 Mark the @code{MAC} register as call-clobbered, even if
9267 @option{-mhitachi} is given.
9271 Increase IEEE-compliance of floating-point code.
9275 Dump instruction size and location in the assembly code.
9279 This option is deprecated. It pads structures to multiple of 4 bytes,
9280 which is incompatible with the SH ABI@.
9284 Optimize for space instead of speed. Implied by @option{-Os}.
9288 When generating position-independent code, emit function calls using
9289 the Global Offset Table instead of the Procedure Linkage Table.
9293 Generate a library function call to invalidate instruction cache
9294 entries, after fixing up a trampoline. This library function call
9295 doesn't assume it can write to the whole memory address space. This
9296 is the default when the target is @code{sh-*-linux*}.
9299 @node System V Options
9300 @subsection Options for System V
9302 These additional options are available on System V Release 4 for
9303 compatibility with other compilers on those systems:
9308 Create a shared object.
9309 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9313 Identify the versions of each tool used by the compiler, in a
9314 @code{.ident} assembler directive in the output.
9318 Refrain from adding @code{.ident} directives to the output file (this is
9321 @item -YP,@var{dirs}
9323 Search the directories @var{dirs}, and no others, for libraries
9324 specified with @option{-l}.
9328 Look in the directory @var{dir} to find the M4 preprocessor.
9329 The assembler uses this option.
9330 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9331 @c the generic assembler that comes with Solaris takes just -Ym.
9334 @node TMS320C3x/C4x Options
9335 @subsection TMS320C3x/C4x Options
9336 @cindex TMS320C3x/C4x Options
9338 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9342 @item -mcpu=@var{cpu_type}
9344 Set the instruction set, register set, and instruction scheduling
9345 parameters for machine type @var{cpu_type}. Supported values for
9346 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9347 @samp{c44}. The default is @samp{c40} to generate code for the
9352 @itemx -msmall-memory
9354 @opindex mbig-memory
9356 @opindex msmall-memory
9358 Generates code for the big or small memory model. The small memory
9359 model assumed that all data fits into one 64K word page. At run-time
9360 the data page (DP) register must be set to point to the 64K page
9361 containing the .bss and .data program sections. The big memory model is
9362 the default and requires reloading of the DP register for every direct
9369 Allow (disallow) allocation of general integer operands into the block
9376 Enable (disable) generation of code using decrement and branch,
9377 DBcond(D), instructions. This is enabled by default for the C4x. To be
9378 on the safe side, this is disabled for the C3x, since the maximum
9379 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9380 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9381 that it can utilize the decrement and branch instruction, but will give
9382 up if there is more than one memory reference in the loop. Thus a loop
9383 where the loop counter is decremented can generate slightly more
9384 efficient code, in cases where the RPTB instruction cannot be utilized.
9386 @item -mdp-isr-reload
9388 @opindex mdp-isr-reload
9390 Force the DP register to be saved on entry to an interrupt service
9391 routine (ISR), reloaded to point to the data section, and restored on
9392 exit from the ISR@. This should not be required unless someone has
9393 violated the small memory model by modifying the DP register, say within
9400 For the C3x use the 24-bit MPYI instruction for integer multiplies
9401 instead of a library call to guarantee 32-bit results. Note that if one
9402 of the operands is a constant, then the multiplication will be performed
9403 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9404 then squaring operations are performed inline instead of a library call.
9407 @itemx -mno-fast-fix
9409 @opindex mno-fast-fix
9410 The C3x/C4x FIX instruction to convert a floating point value to an
9411 integer value chooses the nearest integer less than or equal to the
9412 floating point value rather than to the nearest integer. Thus if the
9413 floating point number is negative, the result will be incorrectly
9414 truncated an additional code is necessary to detect and correct this
9415 case. This option can be used to disable generation of the additional
9416 code required to correct the result.
9422 Enable (disable) generation of repeat block sequences using the RPTB
9423 instruction for zero overhead looping. The RPTB construct is only used
9424 for innermost loops that do not call functions or jump across the loop
9425 boundaries. There is no advantage having nested RPTB loops due to the
9426 overhead required to save and restore the RC, RS, and RE registers.
9427 This is enabled by default with @option{-O2}.
9429 @item -mrpts=@var{count}
9433 Enable (disable) the use of the single instruction repeat instruction
9434 RPTS@. If a repeat block contains a single instruction, and the loop
9435 count can be guaranteed to be less than the value @var{count}, GCC will
9436 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9437 then a RPTS will be emitted even if the loop count cannot be determined
9438 at compile time. Note that the repeated instruction following RPTS does
9439 not have to be reloaded from memory each iteration, thus freeing up the
9440 CPU buses for operands. However, since interrupts are blocked by this
9441 instruction, it is disabled by default.
9443 @item -mloop-unsigned
9444 @itemx -mno-loop-unsigned
9445 @opindex mloop-unsigned
9446 @opindex mno-loop-unsigned
9447 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9448 is @math{2^{31} + 1} since these instructions test if the iteration count is
9449 negative to terminate the loop. If the iteration count is unsigned
9450 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9451 exceeded. This switch allows an unsigned iteration count.
9455 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9456 with. This also enforces compatibility with the API employed by the TI
9457 C3x C compiler. For example, long doubles are passed as structures
9458 rather than in floating point registers.
9464 Generate code that uses registers (stack) for passing arguments to functions.
9465 By default, arguments are passed in registers where possible rather
9466 than by pushing arguments on to the stack.
9468 @item -mparallel-insns
9469 @itemx -mno-parallel-insns
9470 @opindex mparallel-insns
9471 @opindex mno-parallel-insns
9472 Allow the generation of parallel instructions. This is enabled by
9473 default with @option{-O2}.
9475 @item -mparallel-mpy
9476 @itemx -mno-parallel-mpy
9477 @opindex mparallel-mpy
9478 @opindex mno-parallel-mpy
9479 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9480 provided @option{-mparallel-insns} is also specified. These instructions have
9481 tight register constraints which can pessimize the code generation
9487 @subsection V850 Options
9488 @cindex V850 Options
9490 These @samp{-m} options are defined for V850 implementations:
9494 @itemx -mno-long-calls
9495 @opindex mlong-calls
9496 @opindex mno-long-calls
9497 Treat all calls as being far away (near). If calls are assumed to be
9498 far away, the compiler will always load the functions address up into a
9499 register, and call indirect through the pointer.
9505 Do not optimize (do optimize) basic blocks that use the same index
9506 pointer 4 or more times to copy pointer into the @code{ep} register, and
9507 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9508 option is on by default if you optimize.
9510 @item -mno-prolog-function
9511 @itemx -mprolog-function
9512 @opindex mno-prolog-function
9513 @opindex mprolog-function
9514 Do not use (do use) external functions to save and restore registers at
9515 the prolog and epilog of a function. The external functions are slower,
9516 but use less code space if more than one function saves the same number
9517 of registers. The @option{-mprolog-function} option is on by default if
9522 Try to make the code as small as possible. At present, this just turns
9523 on the @option{-mep} and @option{-mprolog-function} options.
9527 Put static or global variables whose size is @var{n} bytes or less into
9528 the tiny data area that register @code{ep} points to. The tiny data
9529 area can hold up to 256 bytes in total (128 bytes for byte references).
9533 Put static or global variables whose size is @var{n} bytes or less into
9534 the small data area that register @code{gp} points to. The small data
9535 area can hold up to 64 kilobytes.
9539 Put static or global variables whose size is @var{n} bytes or less into
9540 the first 32 kilobytes of memory.
9544 Specify that the target processor is the V850.
9547 @opindex mbig-switch
9548 Generate code suitable for big switch tables. Use this option only if
9549 the assembler/linker complain about out of range branches within a switch
9554 This option will cause r2 and r5 to be used in the code generated by
9555 the compiler. This setting is the default.
9558 @opindex -mno-app-regs
9559 This option will cause r2 and r5 to be treated as fixed registers.
9563 Specify that the target processor is the V850E. The preprocessor
9564 constant @samp{__v850e__} will be defined if this option is used.
9566 If neither @option{-mv850} nor @option{-mv850e} are defined
9567 then a default target processor will be chosen and the relevant
9568 @samp{__v850*__} preprocessor constant will be defined.
9570 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9571 defined, regardless of which processor variant is the target.
9573 @item -mdisable-callt
9574 @opindex -mdisable-callt
9575 This option will suppress generation of the CALLT instruction for the
9576 v850e flavors of the v850 architecture. The default is
9577 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9582 @subsection ARC Options
9585 These options are defined for ARC implementations:
9590 Compile code for little endian mode. This is the default.
9594 Compile code for big endian mode.
9597 @opindex mmangle-cpu
9598 Prepend the name of the cpu to all public symbol names.
9599 In multiple-processor systems, there are many ARC variants with different
9600 instruction and register set characteristics. This flag prevents code
9601 compiled for one cpu to be linked with code compiled for another.
9602 No facility exists for handling variants that are ``almost identical''.
9603 This is an all or nothing option.
9605 @item -mcpu=@var{cpu}
9607 Compile code for ARC variant @var{cpu}.
9608 Which variants are supported depend on the configuration.
9609 All variants support @option{-mcpu=base}, this is the default.
9611 @item -mtext=@var{text-section}
9612 @itemx -mdata=@var{data-section}
9613 @itemx -mrodata=@var{readonly-data-section}
9617 Put functions, data, and readonly data in @var{text-section},
9618 @var{data-section}, and @var{readonly-data-section} respectively
9619 by default. This can be overridden with the @code{section} attribute.
9620 @xref{Variable Attributes}.
9625 @subsection NS32K Options
9626 @cindex NS32K options
9628 These are the @samp{-m} options defined for the 32000 series. The default
9629 values for these options depends on which style of 32000 was selected when
9630 the compiler was configured; the defaults for the most common choices are
9638 Generate output for a 32032. This is the default
9639 when the compiler is configured for 32032 and 32016 based systems.
9645 Generate output for a 32332. This is the default
9646 when the compiler is configured for 32332-based systems.
9652 Generate output for a 32532. This is the default
9653 when the compiler is configured for 32532-based systems.
9657 Generate output containing 32081 instructions for floating point.
9658 This is the default for all systems.
9662 Generate output containing 32381 instructions for floating point. This
9663 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9664 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9668 Try and generate multiply-add floating point instructions @code{polyF}
9669 and @code{dotF}. This option is only available if the @option{-m32381}
9670 option is in effect. Using these instructions requires changes to
9671 register allocation which generally has a negative impact on
9672 performance. This option should only be enabled when compiling code
9673 particularly likely to make heavy use of multiply-add instructions.
9676 @opindex mnomulti-add
9677 Do not try and generate multiply-add floating point instructions
9678 @code{polyF} and @code{dotF}. This is the default on all platforms.
9681 @opindex msoft-float
9682 Generate output containing library calls for floating point.
9683 @strong{Warning:} the requisite libraries may not be available.
9685 @item -mieee-compare
9686 @itemx -mno-ieee-compare
9687 @opindex mieee-compare
9688 @opindex mno-ieee-compare
9689 Control whether or not the compiler uses IEEE floating point
9690 comparisons. These handle correctly the case where the result of a
9691 comparison is unordered.
9692 @strong{Warning:} the requisite kernel support may not be available.
9695 @opindex mnobitfield
9696 Do not use the bit-field instructions. On some machines it is faster to
9697 use shifting and masking operations. This is the default for the pc532.
9701 Do use the bit-field instructions. This is the default for all platforms
9706 Use a different function-calling convention, in which functions
9707 that take a fixed number of arguments return pop their
9708 arguments on return with the @code{ret} instruction.
9710 This calling convention is incompatible with the one normally
9711 used on Unix, so you cannot use it if you need to call libraries
9712 compiled with the Unix compiler.
9714 Also, you must provide function prototypes for all functions that
9715 take variable numbers of arguments (including @code{printf});
9716 otherwise incorrect code will be generated for calls to those
9719 In addition, seriously incorrect code will result if you call a
9720 function with too many arguments. (Normally, extra arguments are
9721 harmlessly ignored.)
9723 This option takes its name from the 680x0 @code{rtd} instruction.
9728 Use a different function-calling convention where the first two arguments
9729 are passed in registers.
9731 This calling convention is incompatible with the one normally
9732 used on Unix, so you cannot use it if you need to call libraries
9733 compiled with the Unix compiler.
9736 @opindex mnoregparam
9737 Do not pass any arguments in registers. This is the default for all
9742 It is OK to use the sb as an index register which is always loaded with
9743 zero. This is the default for the pc532-netbsd target.
9747 The sb register is not available for use or has not been initialized to
9748 zero by the run time system. This is the default for all targets except
9749 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9750 @option{-fpic} is set.
9754 Many ns32000 series addressing modes use displacements of up to 512MB@.
9755 If an address is above 512MB then displacements from zero can not be used.
9756 This option causes code to be generated which can be loaded above 512MB@.
9757 This may be useful for operating systems or ROM code.
9761 Assume code will be loaded in the first 512MB of virtual address space.
9762 This is the default for all platforms.
9768 @subsection AVR Options
9771 These options are defined for AVR implementations:
9774 @item -mmcu=@var{mcu}
9776 Specify ATMEL AVR instruction set or MCU type.
9778 Instruction set avr1 is for the minimal AVR core, not supported by the C
9779 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9780 attiny11, attiny12, attiny15, attiny28).
9782 Instruction set avr2 (default) is for the classic AVR core with up to
9783 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9784 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9785 at90c8534, at90s8535).
9787 Instruction set avr3 is for the classic AVR core with up to 128K program
9788 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9790 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9791 memory space (MCU types: atmega8, atmega83, atmega85).
9793 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9794 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9795 atmega64, atmega128, at43usb355, at94k).
9799 Output instruction sizes to the asm file.
9801 @item -minit-stack=@var{N}
9802 @opindex minit-stack
9803 Specify the initial stack address, which may be a symbol or numeric value,
9804 @samp{__stack} is the default.
9806 @item -mno-interrupts
9807 @opindex mno-interrupts
9808 Generated code is not compatible with hardware interrupts.
9809 Code size will be smaller.
9811 @item -mcall-prologues
9812 @opindex mcall-prologues
9813 Functions prologues/epilogues expanded as call to appropriate
9814 subroutines. Code size will be smaller.
9816 @item -mno-tablejump
9817 @opindex mno-tablejump
9818 Do not generate tablejump insns which sometimes increase code size.
9821 @opindex mtiny-stack
9822 Change only the low 8 bits of the stack pointer.
9826 @subsection MCore Options
9827 @cindex MCore options
9829 These are the @samp{-m} options defined for the Motorola M*Core
9837 @opindex mno-hardlit
9838 Inline constants into the code stream if it can be done in two
9839 instructions or less.
9845 Use the divide instruction. (Enabled by default).
9847 @item -mrelax-immediate
9848 @itemx -mno-relax-immediate
9849 @opindex mrelax-immediate
9850 @opindex mno-relax-immediate
9851 Allow arbitrary sized immediates in bit operations.
9853 @item -mwide-bitfields
9854 @itemx -mno-wide-bitfields
9855 @opindex mwide-bitfields
9856 @opindex mno-wide-bitfields
9857 Always treat bit-fields as int-sized.
9859 @item -m4byte-functions
9860 @itemx -mno-4byte-functions
9861 @opindex m4byte-functions
9862 @opindex mno-4byte-functions
9863 Force all functions to be aligned to a four byte boundary.
9865 @item -mcallgraph-data
9866 @itemx -mno-callgraph-data
9867 @opindex mcallgraph-data
9868 @opindex mno-callgraph-data
9869 Emit callgraph information.
9872 @itemx -mno-slow-bytes
9873 @opindex mslow-bytes
9874 @opindex mno-slow-bytes
9875 Prefer word access when reading byte quantities.
9877 @item -mlittle-endian
9879 @opindex mlittle-endian
9880 @opindex mbig-endian
9881 Generate code for a little endian target.
9887 Generate code for the 210 processor.
9891 @subsection IA-64 Options
9892 @cindex IA-64 Options
9894 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9898 @opindex mbig-endian
9899 Generate code for a big endian target. This is the default for HP-UX@.
9901 @item -mlittle-endian
9902 @opindex mlittle-endian
9903 Generate code for a little endian target. This is the default for AIX5
9910 Generate (or don't) code for the GNU assembler. This is the default.
9911 @c Also, this is the default if the configure option @option{--with-gnu-as}
9918 Generate (or don't) code for the GNU linker. This is the default.
9919 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9924 Generate code that does not use a global pointer register. The result
9925 is not position independent code, and violates the IA-64 ABI@.
9927 @item -mvolatile-asm-stop
9928 @itemx -mno-volatile-asm-stop
9929 @opindex mvolatile-asm-stop
9930 @opindex mno-volatile-asm-stop
9931 Generate (or don't) a stop bit immediately before and after volatile asm
9936 Generate code that works around Itanium B step errata.
9938 @item -mregister-names
9939 @itemx -mno-register-names
9940 @opindex mregister-names
9941 @opindex mno-register-names
9942 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9943 the stacked registers. This may make assembler output more readable.
9949 Disable (or enable) optimizations that use the small data section. This may
9950 be useful for working around optimizer bugs.
9953 @opindex mconstant-gp
9954 Generate code that uses a single constant global pointer value. This is
9955 useful when compiling kernel code.
9959 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9960 This is useful when compiling firmware code.
9962 @item -minline-float-divide-min-latency
9963 @opindex minline-float-divide-min-latency
9964 Generate code for inline divides of floating point values
9965 using the minimum latency algorithm.
9967 @item -minline-float-divide-max-throughput
9968 @opindex minline-float-divide-max-throughput
9969 Generate code for inline divides of floating point values
9970 using the maximum throughput algorithm.
9972 @item -minline-int-divide-min-latency
9973 @opindex minline-int-divide-min-latency
9974 Generate code for inline divides of integer values
9975 using the minimum latency algorithm.
9977 @item -minline-int-divide-max-throughput
9978 @opindex minline-int-divide-max-throughput
9979 Generate code for inline divides of integer values
9980 using the maximum throughput algorithm.
9982 @item -mno-dwarf2-asm
9984 @opindex mno-dwarf2-asm
9985 @opindex mdwarf2-asm
9986 Don't (or do) generate assembler code for the DWARF2 line number debugging
9987 info. This may be useful when not using the GNU assembler.
9989 @item -mfixed-range=@var{register-range}
9990 @opindex mfixed-range
9991 Generate code treating the given register range as fixed registers.
9992 A fixed register is one that the register allocator can not use. This is
9993 useful when compiling kernel code. A register range is specified as
9994 two registers separated by a dash. Multiple register ranges can be
9995 specified separated by a comma.
9997 @item -mearly-stop-bits
9998 @itemx -mno-early-stop-bits
9999 @opindex mearly-stop-bits
10000 @opindex mno-early-stop-bits
10001 Allow stop bits to be placed earlier than immediately preceding the
10002 instruction that triggered the stop bit. This can improve instruction
10003 scheduling, but does not always do so.
10007 @subsection D30V Options
10008 @cindex D30V Options
10010 These @samp{-m} options are defined for D30V implementations:
10015 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10016 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10017 memory, which starts at location @code{0x80000000}.
10020 @opindex mextmemory
10021 Same as the @option{-mextmem} switch.
10025 Link the @samp{.text} section into onchip text memory, which starts at
10026 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10027 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10028 into onchip data memory, which starts at location @code{0x20000000}.
10030 @item -mno-asm-optimize
10031 @itemx -masm-optimize
10032 @opindex mno-asm-optimize
10033 @opindex masm-optimize
10034 Disable (enable) passing @option{-O} to the assembler when optimizing.
10035 The assembler uses the @option{-O} option to automatically parallelize
10036 adjacent short instructions where possible.
10038 @item -mbranch-cost=@var{n}
10039 @opindex mbranch-cost
10040 Increase the internal costs of branches to @var{n}. Higher costs means
10041 that the compiler will issue more instructions to avoid doing a branch.
10044 @item -mcond-exec=@var{n}
10045 @opindex mcond-exec
10046 Specify the maximum number of conditionally executed instructions that
10047 replace a branch. The default is 4.
10050 @node S/390 and zSeries Options
10051 @subsection S/390 and zSeries Options
10052 @cindex S/390 and zSeries Options
10054 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10058 @itemx -msoft-float
10059 @opindex mhard-float
10060 @opindex msoft-float
10061 Use (do not use) the hardware floating-point instructions and registers
10062 for floating-point operations. When @option{-msoft-float} is specified,
10063 functions in @file{libgcc.a} will be used to perform floating-point
10064 operations. When @option{-mhard-float} is specified, the compiler
10065 generates IEEE floating-point instructions. This is the default.
10068 @itemx -mno-backchain
10069 @opindex mbackchain
10070 @opindex mno-backchain
10071 Generate (or do not generate) code which maintains an explicit
10072 backchain within the stack frame that points to the caller's frame.
10073 This is currently needed to allow debugging. The default is to
10074 generate the backchain.
10077 @itemx -mno-small-exec
10078 @opindex msmall-exec
10079 @opindex mno-small-exec
10080 Generate (or do not generate) code using the @code{bras} instruction
10081 to do subroutine calls.
10082 This only works reliably if the total executable size does not
10083 exceed 64k. The default is to use the @code{basr} instruction instead,
10084 which does not have this limitation.
10090 When @option{-m31} is specified, generate code compliant to the
10091 Linux for S/390 ABI@. When @option{-m64} is specified, generate
10092 code compliant to the Linux for zSeries ABI@. This allows GCC in
10093 particular to generate 64-bit instructions. For the @samp{s390}
10094 targets, the default is @option{-m31}, while the @samp{s390x}
10095 targets default to @option{-m64}.
10101 When @option{-mzarch} is specified, generate code using the
10102 instructions available on z/Architecture.
10103 When @option{-mesa} is specified, generate code using the
10104 instructions available on ESA/390. Note that @option{-mesa} is
10105 not possible with @option{-m64}.
10106 For the @samp{s390} targets, the default is @option{-mesa},
10107 while the @samp{s390x} targets default to @option{-mzarch}.
10113 Generate (or do not generate) code using the @code{mvcle} instruction
10114 to perform block moves. When @option{-mno-mvcle} is specified,
10115 use a @code{mvc} loop instead. This is the default.
10121 Print (or do not print) additional debug information when compiling.
10122 The default is to not print debug information.
10124 @item -march=@var{arch}
10126 Generate code that will run on @var{arch}, which is the name of system
10127 representing a certain processor type. Possible values for
10128 @var{cpu-type} are @samp{g5}, @samp{g6} and @samp{z900}.
10130 @item -mtune=@var{arch}
10132 Tune to @var{cpu-type} everything applicable about the generated code,
10133 except for the ABI and the set of available instructions.
10134 The list of @var{arch} values is the same as for @option{-march}.
10139 @subsection CRIS Options
10140 @cindex CRIS Options
10142 These options are defined specifically for the CRIS ports.
10145 @item -march=@var{architecture-type}
10146 @itemx -mcpu=@var{architecture-type}
10149 Generate code for the specified architecture. The choices for
10150 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10151 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10152 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10155 @item -mtune=@var{architecture-type}
10157 Tune to @var{architecture-type} everything applicable about the generated
10158 code, except for the ABI and the set of available instructions. The
10159 choices for @var{architecture-type} are the same as for
10160 @option{-march=@var{architecture-type}}.
10162 @item -mmax-stack-frame=@var{n}
10163 @opindex mmax-stack-frame
10164 Warn when the stack frame of a function exceeds @var{n} bytes.
10166 @item -melinux-stacksize=@var{n}
10167 @opindex melinux-stacksize
10168 Only available with the @samp{cris-axis-aout} target. Arranges for
10169 indications in the program to the kernel loader that the stack of the
10170 program should be set to @var{n} bytes.
10176 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10177 @option{-march=v3} and @option{-march=v8} respectively.
10181 Enable CRIS-specific verbose debug-related information in the assembly
10182 code. This option also has the effect to turn off the @samp{#NO_APP}
10183 formatted-code indicator to the assembler at the beginning of the
10188 Do not use condition-code results from previous instruction; always emit
10189 compare and test instructions before use of condition codes.
10191 @item -mno-side-effects
10192 @opindex mno-side-effects
10193 Do not emit instructions with side-effects in addressing modes other than
10196 @item -mstack-align
10197 @itemx -mno-stack-align
10198 @itemx -mdata-align
10199 @itemx -mno-data-align
10200 @itemx -mconst-align
10201 @itemx -mno-const-align
10202 @opindex mstack-align
10203 @opindex mno-stack-align
10204 @opindex mdata-align
10205 @opindex mno-data-align
10206 @opindex mconst-align
10207 @opindex mno-const-align
10208 These options (no-options) arranges (eliminate arrangements) for the
10209 stack-frame, individual data and constants to be aligned for the maximum
10210 single data access size for the chosen CPU model. The default is to
10211 arrange for 32-bit alignment. ABI details such as structure layout are
10212 not affected by these options.
10220 Similar to the stack- data- and const-align options above, these options
10221 arrange for stack-frame, writable data and constants to all be 32-bit,
10222 16-bit or 8-bit aligned. The default is 32-bit alignment.
10224 @item -mno-prologue-epilogue
10225 @itemx -mprologue-epilogue
10226 @opindex mno-prologue-epilogue
10227 @opindex mprologue-epilogue
10228 With @option{-mno-prologue-epilogue}, the normal function prologue and
10229 epilogue that sets up the stack-frame are omitted and no return
10230 instructions or return sequences are generated in the code. Use this
10231 option only together with visual inspection of the compiled code: no
10232 warnings or errors are generated when call-saved registers must be saved,
10233 or storage for local variable needs to be allocated.
10237 @opindex mno-gotplt
10239 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10240 instruction sequences that load addresses for functions from the PLT part
10241 of the GOT rather than (traditional on other architectures) calls to the
10242 PLT. The default is @option{-mgotplt}.
10246 Legacy no-op option only recognized with the cris-axis-aout target.
10250 Legacy no-op option only recognized with the cris-axis-elf and
10251 cris-axis-linux-gnu targets.
10255 Only recognized with the cris-axis-aout target, where it selects a
10256 GNU/linux-like multilib, include files and instruction set for
10257 @option{-march=v8}.
10261 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10265 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10266 to link with input-output functions from a simulator library. Code,
10267 initialized data and zero-initialized data are allocated consecutively.
10271 Like @option{-sim}, but pass linker options to locate initialized data at
10272 0x40000000 and zero-initialized data at 0x80000000.
10276 @subsection MMIX Options
10277 @cindex MMIX Options
10279 These options are defined for the MMIX:
10283 @itemx -mno-libfuncs
10285 @opindex mno-libfuncs
10286 Specify that intrinsic library functions are being compiled, passing all
10287 values in registers, no matter the size.
10290 @itemx -mno-epsilon
10292 @opindex mno-epsilon
10293 Generate floating-point comparison instructions that compare with respect
10294 to the @code{rE} epsilon register.
10296 @item -mabi=mmixware
10298 @opindex mabi-mmixware
10300 Generate code that passes function parameters and return values that (in
10301 the called function) are seen as registers @code{$0} and up, as opposed to
10302 the GNU ABI which uses global registers @code{$231} and up.
10304 @item -mzero-extend
10305 @itemx -mno-zero-extend
10306 @opindex mzero-extend
10307 @opindex mno-zero-extend
10308 When reading data from memory in sizes shorter than 64 bits, use (do not
10309 use) zero-extending load instructions by default, rather than
10310 sign-extending ones.
10313 @itemx -mno-knuthdiv
10315 @opindex mno-knuthdiv
10316 Make the result of a division yielding a remainder have the same sign as
10317 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10318 remainder follows the sign of the dividend. Both methods are
10319 arithmetically valid, the latter being almost exclusively used.
10321 @item -mtoplevel-symbols
10322 @itemx -mno-toplevel-symbols
10323 @opindex mtoplevel-symbols
10324 @opindex mno-toplevel-symbols
10325 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10326 code can be used with the @code{PREFIX} assembly directive.
10330 Generate an executable in the ELF format, rather than the default
10331 @samp{mmo} format used by the @command{mmix} simulator.
10333 @item -mbranch-predict
10334 @itemx -mno-branch-predict
10335 @opindex mbranch-predict
10336 @opindex mno-branch-predict
10337 Use (do not use) the probable-branch instructions, when static branch
10338 prediction indicates a probable branch.
10340 @item -mbase-addresses
10341 @itemx -mno-base-addresses
10342 @opindex mbase-addresses
10343 @opindex mno-base-addresses
10344 Generate (do not generate) code that uses @emph{base addresses}. Using a
10345 base address automatically generates a request (handled by the assembler
10346 and the linker) for a constant to be set up in a global register. The
10347 register is used for one or more base address requests within the range 0
10348 to 255 from the value held in the register. The generally leads to short
10349 and fast code, but the number of different data items that can be
10350 addressed is limited. This means that a program that uses lots of static
10351 data may require @option{-mno-base-addresses}.
10353 @item -msingle-exit
10354 @itemx -mno-single-exit
10355 @opindex msingle-exit
10356 @opindex mno-single-exit
10357 Force (do not force) generated code to have a single exit point in each
10361 @node PDP-11 Options
10362 @subsection PDP-11 Options
10363 @cindex PDP-11 Options
10365 These options are defined for the PDP-11:
10370 Use hardware FPP floating point. This is the default. (FIS floating
10371 point on the PDP-11/40 is not supported.)
10374 @opindex msoft-float
10375 Do not use hardware floating point.
10379 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10383 Return floating-point results in memory. This is the default.
10387 Generate code for a PDP-11/40.
10391 Generate code for a PDP-11/45. This is the default.
10395 Generate code for a PDP-11/10.
10397 @item -mbcopy-builtin
10398 @opindex bcopy-builtin
10399 Use inline @code{movstrhi} patterns for copying memory. This is the
10404 Do not use inline @code{movstrhi} patterns for copying memory.
10410 Use 16-bit @code{int}. This is the default.
10416 Use 32-bit @code{int}.
10419 @itemx -mno-float32
10421 @opindex mno-float32
10422 Use 64-bit @code{float}. This is the default.
10427 @opindex mno-float64
10428 Use 32-bit @code{float}.
10432 Use @code{abshi2} pattern. This is the default.
10436 Do not use @code{abshi2} pattern.
10438 @item -mbranch-expensive
10439 @opindex mbranch-expensive
10440 Pretend that branches are expensive. This is for experimenting with
10441 code generation only.
10443 @item -mbranch-cheap
10444 @opindex mbranch-cheap
10445 Do not pretend that branches are expensive. This is the default.
10449 Generate code for a system with split I&D.
10453 Generate code for a system without split I&D. This is the default.
10457 Use Unix assembler syntax. This is the default when configured for
10458 @samp{pdp11-*-bsd}.
10462 Use DEC assembler syntax. This is the default when configured for any
10463 PDP-11 target other than @samp{pdp11-*-bsd}.
10466 @node Xstormy16 Options
10467 @subsection Xstormy16 Options
10468 @cindex Xstormy16 Options
10470 These options are defined for Xstormy16:
10475 Choose startup files and linker script suitable for the simulator.
10479 @subsection FRV Options
10480 @cindex FRV Options
10486 Only use the first 32 general purpose registers.
10491 Use all 64 general purpose registers.
10496 Use only the first 32 floating point registers.
10501 Use all 64 floating point registers
10504 @opindex mhard-float
10506 Use hardware instructions for floating point operations.
10509 @opindex msoft-float
10511 Use library routines for floating point operations.
10516 Dynamically allocate condition code registers.
10521 Do not try to dynamically allocate condition code registers, only
10522 use @code{icc0} and @code{fcc0}.
10527 Change ABI to use double word insns.
10532 Do not use double word instructions.
10537 Use floating point double instructions.
10540 @opindex mno-double
10542 Do not use floating point double instructions.
10547 Use media instructions.
10552 Do not use media instructions.
10557 Use multiply and add/subtract instructions.
10560 @opindex mno-muladd
10562 Do not use multiply and add/subtract instructions.
10564 @item -mlibrary-pic
10565 @opindex mlibrary-pic
10567 Enable PIC support for building libraries
10572 Use only the first four media accumulator registers.
10577 Use all eight media accumulator registers.
10582 Pack VLIW instructions.
10587 Do not pack VLIW instructions.
10590 @opindex mno-eflags
10592 Do not mark ABI switches in e_flags.
10595 @opindex mcond-move
10597 Enable the use of conditional-move instructions (default).
10599 This switch is mainly for debugging the compiler and will likely be removed
10600 in a future version.
10602 @item -mno-cond-move
10603 @opindex mno-cond-move
10605 Disable the use of conditional-move instructions.
10607 This switch is mainly for debugging the compiler and will likely be removed
10608 in a future version.
10613 Enable the use of conditional set instructions (default).
10615 This switch is mainly for debugging the compiler and will likely be removed
10616 in a future version.
10621 Disable the use of conditional set instructions.
10623 This switch is mainly for debugging the compiler and will likely be removed
10624 in a future version.
10627 @opindex mcond-exec
10629 Enable the use of conditional execution (default).
10631 This switch is mainly for debugging the compiler and will likely be removed
10632 in a future version.
10634 @item -mno-cond-exec
10635 @opindex mno-cond-exec
10637 Disable the use of conditional execution.
10639 This switch is mainly for debugging the compiler and will likely be removed
10640 in a future version.
10642 @item -mvliw-branch
10643 @opindex mvliw-branch
10645 Run a pass to pack branches into VLIW instructions (default).
10647 This switch is mainly for debugging the compiler and will likely be removed
10648 in a future version.
10650 @item -mno-vliw-branch
10651 @opindex mno-vliw-branch
10653 Do not run a pass to pack branches into VLIW instructions.
10655 This switch is mainly for debugging the compiler and will likely be removed
10656 in a future version.
10658 @item -mmulti-cond-exec
10659 @opindex mmulti-cond-exec
10661 Enable optimization of @code{&&} and @code{||} in conditional execution
10664 This switch is mainly for debugging the compiler and will likely be removed
10665 in a future version.
10667 @item -mno-multi-cond-exec
10668 @opindex mno-multi-cond-exec
10670 Disable optimization of @code{&&} and @code{||} in conditional execution.
10672 This switch is mainly for debugging the compiler and will likely be removed
10673 in a future version.
10675 @item -mnested-cond-exec
10676 @opindex mnested-cond-exec
10678 Enable nested conditional execution optimizations (default).
10680 This switch is mainly for debugging the compiler and will likely be removed
10681 in a future version.
10683 @item -mno-nested-cond-exec
10684 @opindex mno-nested-cond-exec
10686 Disable nested conditional execution optimizations.
10688 This switch is mainly for debugging the compiler and will likely be removed
10689 in a future version.
10691 @item -mtomcat-stats
10692 @opindex mtomcat-stats
10694 Cause gas to print out tomcat statistics.
10696 @item -mcpu=@var{cpu}
10699 Select the processor type for which to generate code. Possible values are
10700 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
10705 @node Xtensa Options
10706 @subsection Xtensa Options
10707 @cindex Xtensa Options
10709 The Xtensa architecture is designed to support many different
10710 configurations. The compiler's default options can be set to match a
10711 particular Xtensa configuration by copying a configuration file into the
10712 GCC sources when building GCC@. The options below may be used to
10713 override the default options.
10717 @itemx -mlittle-endian
10718 @opindex mbig-endian
10719 @opindex mlittle-endian
10720 Specify big-endian or little-endian byte ordering for the target Xtensa
10724 @itemx -mno-density
10726 @opindex mno-density
10727 Enable or disable use of the optional Xtensa code density instructions.
10730 @itemx -mno-const16
10732 @opindex mno-const16
10733 Enable or disable use of @code{CONST16} instructions for loading
10734 constant values. The @code{CONST16} instruction is currently not a
10735 standard option from Tensilica. When enabled, @code{CONST16}
10736 instructions are always used in place of the standard @code{L32R}
10737 instructions. The use of @code{CONST16} is enabled by default only if
10738 the @code{L32R} instruction is not available.
10744 Enable or disable use of the Xtensa @code{ABS} instruction for absolute
10751 Enable or disable use of the Xtensa @code{ADDX} and @code{SUBX}
10758 Enable or disable use of the Xtensa MAC16 option. When enabled, GCC
10759 will generate MAC16 instructions from standard C code, with the
10760 limitation that it will use neither the MR register file nor any
10761 instruction that operates on the MR registers. When this option is
10762 disabled, GCC will translate 16-bit multiply/accumulate operations to a
10763 combination of core instructions and library calls, depending on whether
10764 any other multiplier options are enabled.
10770 Enable or disable use of the 16-bit integer multiplier option. When
10771 enabled, the compiler will generate 16-bit multiply instructions for
10772 multiplications of 16 bits or smaller in standard C code. When this
10773 option is disabled, the compiler will either use 32-bit multiply or
10774 MAC16 instructions if they are available or generate library calls to
10775 perform the multiply operations using shifts and adds.
10781 Enable or disable use of the 32-bit integer multiplier option. When
10782 enabled, the compiler will generate 32-bit multiply instructions for
10783 multiplications of 32 bits or smaller in standard C code. When this
10784 option is disabled, the compiler will generate library calls to perform
10785 the multiply operations using either shifts and adds or 16-bit multiply
10786 instructions if they are available.
10792 Enable or disable use of the optional normalization shift amount
10793 (@code{NSA}) instructions to implement the built-in @code{ffs} function.
10798 @opindex mno-minmax
10799 Enable or disable use of the optional minimum and maximum value
10806 Enable or disable use of the optional sign extend (@code{SEXT})
10810 @itemx -mno-booleans
10812 @opindex mno-booleans
10813 Enable or disable support for the boolean register file used by Xtensa
10814 coprocessors. This is not typically useful by itself but may be
10815 required for other options that make use of the boolean registers (e.g.,
10816 the floating-point option).
10819 @itemx -msoft-float
10820 @opindex mhard-float
10821 @opindex msoft-float
10822 Enable or disable use of the floating-point option. When enabled, GCC
10823 generates floating-point instructions for 32-bit @code{float}
10824 operations. When this option is disabled, GCC generates library calls
10825 to emulate 32-bit floating-point operations using integer instructions.
10826 Regardless of this option, 64-bit @code{double} operations are always
10827 emulated with calls to library functions.
10830 @itemx -mno-fused-madd
10831 @opindex mfused-madd
10832 @opindex mno-fused-madd
10833 Enable or disable use of fused multiply/add and multiply/subtract
10834 instructions in the floating-point option. This has no effect if the
10835 floating-point option is not also enabled. Disabling fused multiply/add
10836 and multiply/subtract instructions forces the compiler to use separate
10837 instructions for the multiply and add/subtract operations. This may be
10838 desirable in some cases where strict IEEE 754-compliant results are
10839 required: the fused multiply add/subtract instructions do not round the
10840 intermediate result, thereby producing results with @emph{more} bits of
10841 precision than specified by the IEEE standard. Disabling fused multiply
10842 add/subtract instructions also ensures that the program output is not
10843 sensitive to the compiler's ability to combine multiply and add/subtract
10846 @item -mtext-section-literals
10847 @itemx -mno-text-section-literals
10848 @opindex mtext-section-literals
10849 @opindex mno-text-section-literals
10850 Control the treatment of literal pools. The default is
10851 @option{-mno-text-section-literals}, which places literals in a separate
10852 section in the output file. This allows the literal pool to be placed
10853 in a data RAM/ROM, and it also allows the linker to combine literal
10854 pools from separate object files to remove redundant literals and
10855 improve code size. With @option{-mtext-section-literals}, the literals
10856 are interspersed in the text section in order to keep them as close as
10857 possible to their references. This may be necessary for large assembly
10860 @item -mtarget-align
10861 @itemx -mno-target-align
10862 @opindex mtarget-align
10863 @opindex mno-target-align
10864 When this option is enabled, GCC instructs the assembler to
10865 automatically align instructions to reduce branch penalties at the
10866 expense of some code density. The assembler attempts to widen density
10867 instructions to align branch targets and the instructions following call
10868 instructions. If there are not enough preceding safe density
10869 instructions to align a target, no widening will be performed. The
10870 default is @option{-mtarget-align}. These options do not affect the
10871 treatment of auto-aligned instructions like @code{LOOP}, which the
10872 assembler will always align, either by widening density instructions or
10873 by inserting no-op instructions.
10876 @itemx -mno-longcalls
10877 @opindex mlongcalls
10878 @opindex mno-longcalls
10879 When this option is enabled, GCC instructs the assembler to translate
10880 direct calls to indirect calls unless it can determine that the target
10881 of a direct call is in the range allowed by the call instruction. This
10882 translation typically occurs for calls to functions in other source
10883 files. Specifically, the assembler translates a direct @code{CALL}
10884 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
10885 The default is @option{-mno-longcalls}. This option should be used in
10886 programs where the call target can potentially be out of range. This
10887 option is implemented in the assembler, not the compiler, so the
10888 assembly code generated by GCC will still show direct call
10889 instructions---look at the disassembled object code to see the actual
10890 instructions. Note that the assembler will use an indirect call for
10891 every cross-file call, not just those that really will be out of range.
10894 @node Code Gen Options
10895 @section Options for Code Generation Conventions
10896 @cindex code generation conventions
10897 @cindex options, code generation
10898 @cindex run-time options
10900 These machine-independent options control the interface conventions
10901 used in code generation.
10903 Most of them have both positive and negative forms; the negative form
10904 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
10905 one of the forms is listed---the one which is not the default. You
10906 can figure out the other form by either removing @samp{no-} or adding
10910 @item -fbounds-check
10911 @opindex fbounds-check
10912 For front-ends that support it, generate additional code to check that
10913 indices used to access arrays are within the declared range. This is
10914 currently only supported by the Java and Fortran 77 front-ends, where
10915 this option defaults to true and false respectively.
10919 This option generates traps for signed overflow on addition, subtraction,
10920 multiplication operations.
10924 This option instructs the compiler to assume that signed arithmetic
10925 overflow of addition, subtraction and multiplication wraps around
10926 using twos-complement representation. This flag enables some optimzations
10927 and disables other. This option is enabled by default for the Java
10928 front-end, as required by the Java language specification.
10931 @opindex fexceptions
10932 Enable exception handling. Generates extra code needed to propagate
10933 exceptions. For some targets, this implies GCC will generate frame
10934 unwind information for all functions, which can produce significant data
10935 size overhead, although it does not affect execution. If you do not
10936 specify this option, GCC will enable it by default for languages like
10937 C++ which normally require exception handling, and disable it for
10938 languages like C that do not normally require it. However, you may need
10939 to enable this option when compiling C code that needs to interoperate
10940 properly with exception handlers written in C++. You may also wish to
10941 disable this option if you are compiling older C++ programs that don't
10942 use exception handling.
10944 @item -fnon-call-exceptions
10945 @opindex fnon-call-exceptions
10946 Generate code that allows trapping instructions to throw exceptions.
10947 Note that this requires platform-specific runtime support that does
10948 not exist everywhere. Moreover, it only allows @emph{trapping}
10949 instructions to throw exceptions, i.e.@: memory references or floating
10950 point instructions. It does not allow exceptions to be thrown from
10951 arbitrary signal handlers such as @code{SIGALRM}.
10953 @item -funwind-tables
10954 @opindex funwind-tables
10955 Similar to @option{-fexceptions}, except that it will just generate any needed
10956 static data, but will not affect the generated code in any other way.
10957 You will normally not enable this option; instead, a language processor
10958 that needs this handling would enable it on your behalf.
10960 @item -fasynchronous-unwind-tables
10961 @opindex funwind-tables
10962 Generate unwind table in dwarf2 format, if supported by target machine. The
10963 table is exact at each instruction boundary, so it can be used for stack
10964 unwinding from asynchronous events (such as debugger or garbage collector).
10966 @item -fpcc-struct-return
10967 @opindex fpcc-struct-return
10968 Return ``short'' @code{struct} and @code{union} values in memory like
10969 longer ones, rather than in registers. This convention is less
10970 efficient, but it has the advantage of allowing intercallability between
10971 GCC-compiled files and files compiled with other compilers, particularly
10972 the Portable C Compiler (pcc).
10974 The precise convention for returning structures in memory depends
10975 on the target configuration macros.
10977 Short structures and unions are those whose size and alignment match
10978 that of some integer type.
10980 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
10981 switch is not binary compatible with code compiled with the
10982 @option{-freg-struct-return} switch.
10983 Use it to conform to a non-default application binary interface.
10985 @item -freg-struct-return
10986 @opindex freg-struct-return
10987 Return @code{struct} and @code{union} values in registers when possible.
10988 This is more efficient for small structures than
10989 @option{-fpcc-struct-return}.
10991 If you specify neither @option{-fpcc-struct-return} nor
10992 @option{-freg-struct-return}, GCC defaults to whichever convention is
10993 standard for the target. If there is no standard convention, GCC
10994 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
10995 the principal compiler. In those cases, we can choose the standard, and
10996 we chose the more efficient register return alternative.
10998 @strong{Warning:} code compiled with the @option{-freg-struct-return}
10999 switch is not binary compatible with code compiled with the
11000 @option{-fpcc-struct-return} switch.
11001 Use it to conform to a non-default application binary interface.
11003 @item -fshort-enums
11004 @opindex fshort-enums
11005 Allocate to an @code{enum} type only as many bytes as it needs for the
11006 declared range of possible values. Specifically, the @code{enum} type
11007 will be equivalent to the smallest integer type which has enough room.
11009 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11010 code that is not binary compatible with code generated without that switch.
11011 Use it to conform to a non-default application binary interface.
11013 @item -fshort-double
11014 @opindex fshort-double
11015 Use the same size for @code{double} as for @code{float}.
11017 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11018 code that is not binary compatible with code generated without that switch.
11019 Use it to conform to a non-default application binary interface.
11021 @item -fshort-wchar
11022 @opindex fshort-wchar
11023 Override the underlying type for @samp{wchar_t} to be @samp{short
11024 unsigned int} instead of the default for the target. This option is
11025 useful for building programs to run under WINE@.
11027 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11028 code that is not binary compatible with code generated without that switch.
11029 Use it to conform to a non-default application binary interface.
11031 @item -fshared-data
11032 @opindex fshared-data
11033 Requests that the data and non-@code{const} variables of this
11034 compilation be shared data rather than private data. The distinction
11035 makes sense only on certain operating systems, where shared data is
11036 shared between processes running the same program, while private data
11037 exists in one copy per process.
11040 @opindex fno-common
11041 In C, allocate even uninitialized global variables in the data section of the
11042 object file, rather than generating them as common blocks. This has the
11043 effect that if the same variable is declared (without @code{extern}) in
11044 two different compilations, you will get an error when you link them.
11045 The only reason this might be useful is if you wish to verify that the
11046 program will work on other systems which always work this way.
11050 Ignore the @samp{#ident} directive.
11052 @item -fno-gnu-linker
11053 @opindex fno-gnu-linker
11054 Do not output global initializations (such as C++ constructors and
11055 destructors) in the form used by the GNU linker (on systems where the GNU
11056 linker is the standard method of handling them). Use this option when
11057 you want to use a non-GNU linker, which also requires using the
11058 @command{collect2} program to make sure the system linker includes
11059 constructors and destructors. (@command{collect2} is included in the GCC
11060 distribution.) For systems which @emph{must} use @command{collect2}, the
11061 compiler driver @command{gcc} is configured to do this automatically.
11063 @item -finhibit-size-directive
11064 @opindex finhibit-size-directive
11065 Don't output a @code{.size} assembler directive, or anything else that
11066 would cause trouble if the function is split in the middle, and the
11067 two halves are placed at locations far apart in memory. This option is
11068 used when compiling @file{crtstuff.c}; you should not need to use it
11071 @item -fverbose-asm
11072 @opindex fverbose-asm
11073 Put extra commentary information in the generated assembly code to
11074 make it more readable. This option is generally only of use to those
11075 who actually need to read the generated assembly code (perhaps while
11076 debugging the compiler itself).
11078 @option{-fno-verbose-asm}, the default, causes the
11079 extra information to be omitted and is useful when comparing two assembler
11084 @cindex global offset table
11086 Generate position-independent code (PIC) suitable for use in a shared
11087 library, if supported for the target machine. Such code accesses all
11088 constant addresses through a global offset table (GOT)@. The dynamic
11089 loader resolves the GOT entries when the program starts (the dynamic
11090 loader is not part of GCC; it is part of the operating system). If
11091 the GOT size for the linked executable exceeds a machine-specific
11092 maximum size, you get an error message from the linker indicating that
11093 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11094 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
11095 on the m68k and RS/6000. The 386 has no such limit.)
11097 Position-independent code requires special support, and therefore works
11098 only on certain machines. For the 386, GCC supports PIC for System V
11099 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11100 position-independent.
11104 If supported for the target machine, emit position-independent code,
11105 suitable for dynamic linking and avoiding any limit on the size of the
11106 global offset table. This option makes a difference on the m68k, m88k,
11109 Position-independent code requires special support, and therefore works
11110 only on certain machines.
11116 These options are similar to @option{-fpic} and @option{-fPIC}, but
11117 generated position independent code can be only linked into executables.
11118 Usually these options are used when @option{-pie} GCC option will be
11119 used during linking.
11121 @item -ffixed-@var{reg}
11123 Treat the register named @var{reg} as a fixed register; generated code
11124 should never refer to it (except perhaps as a stack pointer, frame
11125 pointer or in some other fixed role).
11127 @var{reg} must be the name of a register. The register names accepted
11128 are machine-specific and are defined in the @code{REGISTER_NAMES}
11129 macro in the machine description macro file.
11131 This flag does not have a negative form, because it specifies a
11134 @item -fcall-used-@var{reg}
11135 @opindex fcall-used
11136 Treat the register named @var{reg} as an allocable register that is
11137 clobbered by function calls. It may be allocated for temporaries or
11138 variables that do not live across a call. Functions compiled this way
11139 will not save and restore the register @var{reg}.
11141 It is an error to used this flag with the frame pointer or stack pointer.
11142 Use of this flag for other registers that have fixed pervasive roles in
11143 the machine's execution model will produce disastrous results.
11145 This flag does not have a negative form, because it specifies a
11148 @item -fcall-saved-@var{reg}
11149 @opindex fcall-saved
11150 Treat the register named @var{reg} as an allocable register saved by
11151 functions. It may be allocated even for temporaries or variables that
11152 live across a call. Functions compiled this way will save and restore
11153 the register @var{reg} if they use it.
11155 It is an error to used this flag with the frame pointer or stack pointer.
11156 Use of this flag for other registers that have fixed pervasive roles in
11157 the machine's execution model will produce disastrous results.
11159 A different sort of disaster will result from the use of this flag for
11160 a register in which function values may be returned.
11162 This flag does not have a negative form, because it specifies a
11165 @item -fpack-struct
11166 @opindex fpack-struct
11167 Pack all structure members together without holes.
11169 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11170 code that is not binary compatible with code generated without that switch.
11171 Additionally, it makes the code suboptimal.
11172 Use it to conform to a non-default application binary interface.
11174 @item -finstrument-functions
11175 @opindex finstrument-functions
11176 Generate instrumentation calls for entry and exit to functions. Just
11177 after function entry and just before function exit, the following
11178 profiling functions will be called with the address of the current
11179 function and its call site. (On some platforms,
11180 @code{__builtin_return_address} does not work beyond the current
11181 function, so the call site information may not be available to the
11182 profiling functions otherwise.)
11185 void __cyg_profile_func_enter (void *this_fn,
11187 void __cyg_profile_func_exit (void *this_fn,
11191 The first argument is the address of the start of the current function,
11192 which may be looked up exactly in the symbol table.
11194 This instrumentation is also done for functions expanded inline in other
11195 functions. The profiling calls will indicate where, conceptually, the
11196 inline function is entered and exited. This means that addressable
11197 versions of such functions must be available. If all your uses of a
11198 function are expanded inline, this may mean an additional expansion of
11199 code size. If you use @samp{extern inline} in your C code, an
11200 addressable version of such functions must be provided. (This is
11201 normally the case anyways, but if you get lucky and the optimizer always
11202 expands the functions inline, you might have gotten away without
11203 providing static copies.)
11205 A function may be given the attribute @code{no_instrument_function}, in
11206 which case this instrumentation will not be done. This can be used, for
11207 example, for the profiling functions listed above, high-priority
11208 interrupt routines, and any functions from which the profiling functions
11209 cannot safely be called (perhaps signal handlers, if the profiling
11210 routines generate output or allocate memory).
11212 @item -fstack-check
11213 @opindex fstack-check
11214 Generate code to verify that you do not go beyond the boundary of the
11215 stack. You should specify this flag if you are running in an
11216 environment with multiple threads, but only rarely need to specify it in
11217 a single-threaded environment since stack overflow is automatically
11218 detected on nearly all systems if there is only one stack.
11220 Note that this switch does not actually cause checking to be done; the
11221 operating system must do that. The switch causes generation of code
11222 to ensure that the operating system sees the stack being extended.
11224 @item -fstack-limit-register=@var{reg}
11225 @itemx -fstack-limit-symbol=@var{sym}
11226 @itemx -fno-stack-limit
11227 @opindex fstack-limit-register
11228 @opindex fstack-limit-symbol
11229 @opindex fno-stack-limit
11230 Generate code to ensure that the stack does not grow beyond a certain value,
11231 either the value of a register or the address of a symbol. If the stack
11232 would grow beyond the value, a signal is raised. For most targets,
11233 the signal is raised before the stack overruns the boundary, so
11234 it is possible to catch the signal without taking special precautions.
11236 For instance, if the stack starts at absolute address @samp{0x80000000}
11237 and grows downwards, you can use the flags
11238 @option{-fstack-limit-symbol=__stack_limit} and
11239 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11240 of 128KB@. Note that this may only work with the GNU linker.
11242 @cindex aliasing of parameters
11243 @cindex parameters, aliased
11244 @item -fargument-alias
11245 @itemx -fargument-noalias
11246 @itemx -fargument-noalias-global
11247 @opindex fargument-alias
11248 @opindex fargument-noalias
11249 @opindex fargument-noalias-global
11250 Specify the possible relationships among parameters and between
11251 parameters and global data.
11253 @option{-fargument-alias} specifies that arguments (parameters) may
11254 alias each other and may alias global storage.@*
11255 @option{-fargument-noalias} specifies that arguments do not alias
11256 each other, but may alias global storage.@*
11257 @option{-fargument-noalias-global} specifies that arguments do not
11258 alias each other and do not alias global storage.
11260 Each language will automatically use whatever option is required by
11261 the language standard. You should not need to use these options yourself.
11263 @item -fleading-underscore
11264 @opindex fleading-underscore
11265 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11266 change the way C symbols are represented in the object file. One use
11267 is to help link with legacy assembly code.
11269 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11270 generate code that is not binary compatible with code generated without that
11271 switch. Use it to conform to a non-default application binary interface.
11272 Not all targets provide complete support for this switch.
11274 @item -ftls-model=@var{model}
11275 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11276 The @var{model} argument should be one of @code{global-dynamic},
11277 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11279 The default without @option{-fpic} is @code{initial-exec}; with
11280 @option{-fpic} the default is @code{global-dynamic}.
11285 @node Environment Variables
11286 @section Environment Variables Affecting GCC
11287 @cindex environment variables
11289 @c man begin ENVIRONMENT
11290 This section describes several environment variables that affect how GCC
11291 operates. Some of them work by specifying directories or prefixes to use
11292 when searching for various kinds of files. Some are used to specify other
11293 aspects of the compilation environment.
11295 Note that you can also specify places to search using options such as
11296 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11297 take precedence over places specified using environment variables, which
11298 in turn take precedence over those specified by the configuration of GCC@.
11299 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11300 GNU Compiler Collection (GCC) Internals}.
11305 @c @itemx LC_COLLATE
11307 @c @itemx LC_MONETARY
11308 @c @itemx LC_NUMERIC
11313 @c @findex LC_COLLATE
11314 @findex LC_MESSAGES
11315 @c @findex LC_MONETARY
11316 @c @findex LC_NUMERIC
11320 These environment variables control the way that GCC uses
11321 localization information that allow GCC to work with different
11322 national conventions. GCC inspects the locale categories
11323 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11324 so. These locale categories can be set to any value supported by your
11325 installation. A typical value is @samp{en_UK} for English in the United
11328 The @env{LC_CTYPE} environment variable specifies character
11329 classification. GCC uses it to determine the character boundaries in
11330 a string; this is needed for some multibyte encodings that contain quote
11331 and escape characters that would otherwise be interpreted as a string
11334 The @env{LC_MESSAGES} environment variable specifies the language to
11335 use in diagnostic messages.
11337 If the @env{LC_ALL} environment variable is set, it overrides the value
11338 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11339 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11340 environment variable. If none of these variables are set, GCC
11341 defaults to traditional C English behavior.
11345 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11346 files. GCC uses temporary files to hold the output of one stage of
11347 compilation which is to be used as input to the next stage: for example,
11348 the output of the preprocessor, which is the input to the compiler
11351 @item GCC_EXEC_PREFIX
11352 @findex GCC_EXEC_PREFIX
11353 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11354 names of the subprograms executed by the compiler. No slash is added
11355 when this prefix is combined with the name of a subprogram, but you can
11356 specify a prefix that ends with a slash if you wish.
11358 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11359 an appropriate prefix to use based on the pathname it was invoked with.
11361 If GCC cannot find the subprogram using the specified prefix, it
11362 tries looking in the usual places for the subprogram.
11364 The default value of @env{GCC_EXEC_PREFIX} is
11365 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
11366 of @code{prefix} when you ran the @file{configure} script.
11368 Other prefixes specified with @option{-B} take precedence over this prefix.
11370 This prefix is also used for finding files such as @file{crt0.o} that are
11373 In addition, the prefix is used in an unusual way in finding the
11374 directories to search for header files. For each of the standard
11375 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
11376 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11377 replacing that beginning with the specified prefix to produce an
11378 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11379 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11380 These alternate directories are searched first; the standard directories
11383 @item COMPILER_PATH
11384 @findex COMPILER_PATH
11385 The value of @env{COMPILER_PATH} is a colon-separated list of
11386 directories, much like @env{PATH}. GCC tries the directories thus
11387 specified when searching for subprograms, if it can't find the
11388 subprograms using @env{GCC_EXEC_PREFIX}.
11391 @findex LIBRARY_PATH
11392 The value of @env{LIBRARY_PATH} is a colon-separated list of
11393 directories, much like @env{PATH}. When configured as a native compiler,
11394 GCC tries the directories thus specified when searching for special
11395 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11396 using GCC also uses these directories when searching for ordinary
11397 libraries for the @option{-l} option (but directories specified with
11398 @option{-L} come first).
11402 @cindex locale definition
11403 This variable is used to pass locale information to the compiler. One way in
11404 which this information is used is to determine the character set to be used
11405 when character literals, string literals and comments are parsed in C and C++.
11406 When the compiler is configured to allow multibyte characters,
11407 the following values for @env{LANG} are recognized:
11411 Recognize JIS characters.
11413 Recognize SJIS characters.
11415 Recognize EUCJP characters.
11418 If @env{LANG} is not defined, or if it has some other value, then the
11419 compiler will use mblen and mbtowc as defined by the default locale to
11420 recognize and translate multibyte characters.
11424 Some additional environments variables affect the behavior of the
11427 @include cppenv.texi
11431 @node Precompiled Headers
11432 @section Using Precompiled Headers
11433 @cindex precompiled headers
11434 @cindex speed of compilation
11436 Often large projects have many header files that are included in every
11437 source file. The time the compiler takes to process these header files
11438 over and over again can account for nearly all of the time required to
11439 build the project. To make builds faster, GCC allows users to
11440 `precompile' a header file; then, if builds can use the precompiled
11441 header file they will be much faster.
11443 To create a precompiled header file, simply compile it as you would any
11444 other file, if necessary using the @option{-x} option to make the driver
11445 treat it as a C or C++ header file. You will probably want to use a
11446 tool like @command{make} to keep the precompiled header up-to-date when
11447 the headers it contains change.
11449 A precompiled header file will be searched for when @code{#include} is
11450 seen in the compilation. As it searches for the included file
11451 (@pxref{Search Path,,Search Path,cpp.info,The C Preprocessor}) the
11452 compiler looks for a precompiled header in each directory just before it
11453 looks for the include file in that directory. The name searched for is
11454 the name specified in the @code{#include} with @samp{.gch} appended. If
11455 the precompiled header file can't be used, it is ignored.
11457 For instance, if you have @code{#include "all.h"}, and you have
11458 @file{all.h.gch} in the same directory as @file{all.h}, then the
11459 precompiled header file will be used if possible, and the original
11460 header will be used otherwise.
11462 Alternatively, you might decide to put the precompiled header file in a
11463 directory and use @option{-I} to ensure that directory is searched
11464 before (or instead of) the directory containing the original header.
11465 Then, if you want to check that the precompiled header file is always
11466 used, you can put a file of the same name as the original header in this
11467 directory containing an @code{#error} command.
11469 This also works with @option{-include}. So yet another way to use
11470 precompiled headers, good for projects not designed with precompiled
11471 header files in mind, is to simply take most of the header files used by
11472 a project, include them from another header file, precompile that header
11473 file, and @option{-include} the precompiled header. If the header files
11474 have guards against multiple inclusion, they will be skipped because
11475 they've already been included (in the precompiled header).
11477 If you need to precompile the same header file for different
11478 languages, targets, or compiler options, you can instead make a
11479 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11480 header in the directory. (It doesn't matter what you call the files
11481 in the directory, every precompiled header in the directory will be
11482 considered.) The first precompiled header encountered in the
11483 directory that is valid for this compilation will be used; they're
11484 searched in no particular order.
11486 There are many other possibilities, limited only by your imagination,
11487 good sense, and the constraints of your build system.
11489 A precompiled header file can be used only when these conditions apply:
11493 Only one precompiled header can be used in a particular compilation.
11495 A precompiled header can't be used once the first C token is seen. You
11496 can have preprocessor directives before a precompiled header; you can
11497 even include a precompiled header from inside another header, so long as
11498 there are no C tokens before the @code{#include}.
11500 The precompiled header file must be produced for the same language as
11501 the current compilation. You can't use a C precompiled header for a C++
11504 The precompiled header file must be produced by the same compiler
11505 version and configuration as the current compilation is using.
11506 The easiest way to guarantee this is to use the same compiler binary
11507 for creating and using precompiled headers.
11509 Any macros defined before the precompiled header (including with
11510 @option{-D}) must either be defined in the same way as when the
11511 precompiled header was generated, or must not affect the precompiled
11512 header, which usually means that the they don't appear in the
11513 precompiled header at all.
11515 Certain command-line options must be defined in the same way as when the
11516 precompiled header was generated. At present, it's not clear which
11517 options are safe to change and which are not; the safest choice is to
11518 use exactly the same options when generating and using the precompiled
11522 For all of these but the last, the compiler will automatically ignore
11523 the precompiled header if the conditions aren't met. For the last item,
11524 some option changes will cause the precompiled header to be rejected,
11525 but not all incompatible option combinations have yet been found. If
11526 you find a new incompatible combination, please consider filing a bug
11527 report, see @ref{Bugs}.
11529 @node Running Protoize
11530 @section Running Protoize
11532 The program @code{protoize} is an optional part of GCC@. You can use
11533 it to add prototypes to a program, thus converting the program to ISO
11534 C in one respect. The companion program @code{unprotoize} does the
11535 reverse: it removes argument types from any prototypes that are found.
11537 When you run these programs, you must specify a set of source files as
11538 command line arguments. The conversion programs start out by compiling
11539 these files to see what functions they define. The information gathered
11540 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11542 After scanning comes actual conversion. The specified files are all
11543 eligible to be converted; any files they include (whether sources or
11544 just headers) are eligible as well.
11546 But not all the eligible files are converted. By default,
11547 @code{protoize} and @code{unprotoize} convert only source and header
11548 files in the current directory. You can specify additional directories
11549 whose files should be converted with the @option{-d @var{directory}}
11550 option. You can also specify particular files to exclude with the
11551 @option{-x @var{file}} option. A file is converted if it is eligible, its
11552 directory name matches one of the specified directory names, and its
11553 name within the directory has not been excluded.
11555 Basic conversion with @code{protoize} consists of rewriting most
11556 function definitions and function declarations to specify the types of
11557 the arguments. The only ones not rewritten are those for varargs
11560 @code{protoize} optionally inserts prototype declarations at the
11561 beginning of the source file, to make them available for any calls that
11562 precede the function's definition. Or it can insert prototype
11563 declarations with block scope in the blocks where undeclared functions
11566 Basic conversion with @code{unprotoize} consists of rewriting most
11567 function declarations to remove any argument types, and rewriting
11568 function definitions to the old-style pre-ISO form.
11570 Both conversion programs print a warning for any function declaration or
11571 definition that they can't convert. You can suppress these warnings
11574 The output from @code{protoize} or @code{unprotoize} replaces the
11575 original source file. The original file is renamed to a name ending
11576 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11577 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11578 for DOS) file already exists, then the source file is simply discarded.
11580 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11581 scan the program and collect information about the functions it uses.
11582 So neither of these programs will work until GCC is installed.
11584 Here is a table of the options you can use with @code{protoize} and
11585 @code{unprotoize}. Each option works with both programs unless
11589 @item -B @var{directory}
11590 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11591 usual directory (normally @file{/usr/local/lib}). This file contains
11592 prototype information about standard system functions. This option
11593 applies only to @code{protoize}.
11595 @item -c @var{compilation-options}
11596 Use @var{compilation-options} as the options when running @command{gcc} to
11597 produce the @samp{.X} files. The special option @option{-aux-info} is
11598 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11600 Note that the compilation options must be given as a single argument to
11601 @code{protoize} or @code{unprotoize}. If you want to specify several
11602 @command{gcc} options, you must quote the entire set of compilation options
11603 to make them a single word in the shell.
11605 There are certain @command{gcc} arguments that you cannot use, because they
11606 would produce the wrong kind of output. These include @option{-g},
11607 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11608 the @var{compilation-options}, they are ignored.
11611 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11612 systems) instead of @samp{.c}. This is convenient if you are converting
11613 a C program to C++. This option applies only to @code{protoize}.
11616 Add explicit global declarations. This means inserting explicit
11617 declarations at the beginning of each source file for each function
11618 that is called in the file and was not declared. These declarations
11619 precede the first function definition that contains a call to an
11620 undeclared function. This option applies only to @code{protoize}.
11622 @item -i @var{string}
11623 Indent old-style parameter declarations with the string @var{string}.
11624 This option applies only to @code{protoize}.
11626 @code{unprotoize} converts prototyped function definitions to old-style
11627 function definitions, where the arguments are declared between the
11628 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11629 uses five spaces as the indentation. If you want to indent with just
11630 one space instead, use @option{-i " "}.
11633 Keep the @samp{.X} files. Normally, they are deleted after conversion
11637 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11638 a prototype declaration for each function in each block which calls the
11639 function without any declaration. This option applies only to
11643 Make no real changes. This mode just prints information about the conversions
11644 that would have been done without @option{-n}.
11647 Make no @samp{.save} files. The original files are simply deleted.
11648 Use this option with caution.
11650 @item -p @var{program}
11651 Use the program @var{program} as the compiler. Normally, the name
11652 @file{gcc} is used.
11655 Work quietly. Most warnings are suppressed.
11658 Print the version number, just like @option{-v} for @command{gcc}.
11661 If you need special compiler options to compile one of your program's
11662 source files, then you should generate that file's @samp{.X} file
11663 specially, by running @command{gcc} on that source file with the
11664 appropriate options and the option @option{-aux-info}. Then run
11665 @code{protoize} on the entire set of files. @code{protoize} will use
11666 the existing @samp{.X} file because it is newer than the source file.
11670 gcc -Dfoo=bar file1.c -aux-info file1.X
11675 You need to include the special files along with the rest in the
11676 @code{protoize} command, even though their @samp{.X} files already
11677 exist, because otherwise they won't get converted.
11679 @xref{Protoize Caveats}, for more information on how to use
11680 @code{protoize} successfully.