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 -feliminate-unused-debug-symbols -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 -fprofile-values -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
389 -mam33-2 -mno-am33-2 @gol
392 @emph{M32R/D Options}
393 @gccoptlist{-m32rx -m32r -mcode-model=@var{model-type} @gol
394 -msdata=@var{sdata-type} -G @var{num}}
397 @gccoptlist{-m88000 -m88100 -m88110 -mbig-pic @gol
398 -mcheck-zero-division -mhandle-large-shift @gol
399 -midentify-revision -mno-check-zero-division @gol
400 -mno-ocs-debug-info -mno-ocs-frame-position @gol
401 -mno-optimize-arg-area -mno-serialize-volatile @gol
402 -mno-underscores -mocs-debug-info @gol
403 -mocs-frame-position -moptimize-arg-area @gol
404 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
405 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
406 -mversion-03.00 -mwarn-passed-structs}
408 @emph{RS/6000 and PowerPC Options}
409 @gccoptlist{-mcpu=@var{cpu-type} @gol
410 -mtune=@var{cpu-type} @gol
411 -mpower -mno-power -mpower2 -mno-power2 @gol
412 -mpowerpc -mpowerpc64 -mno-powerpc @gol
413 -maltivec -mno-altivec @gol
414 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
415 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
416 -mnew-mnemonics -mold-mnemonics @gol
417 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
418 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
419 -malign-power -malign-natural @gol
420 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
421 -mstring -mno-string -mupdate -mno-update @gol
422 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
423 -mstrict-align -mno-strict-align -mrelocatable @gol
424 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
425 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
426 -mdynamic-no-pic @gol
427 -mcall-sysv -mcall-netbsd @gol
428 -maix-struct-return -msvr4-struct-return @gol
429 -mabi=altivec -mabi=no-altivec @gol
430 -mabi=spe -mabi=no-spe @gol
431 -misel=yes -misel=no @gol
432 -mspe=yes -mspe=no @gol
433 -mfloat-gprs=yes -mfloat-gprs=no @gol
434 -mprototype -mno-prototype @gol
435 -msim -mmvme -mads -myellowknife -memb -msdata @gol
436 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
438 @emph{Darwin Options}
439 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
440 -arch_only -bind_at_load -bundle -bundle_loader @gol
441 -client_name -compatibility_version -current_version @gol
442 -dependency-file -dylib_file -dylinker_install_name @gol
443 -dynamic -dynamiclib -exported_symbols_list @gol
444 -filelist -flat_namespace -force_cpusubtype_ALL @gol
445 -force_flat_namespace -headerpad_max_install_names @gol
446 -image_base -init -install_name -keep_private_externs @gol
447 -multi_module -multiply_defined -multiply_defined_unused @gol
448 -noall_load -nomultidefs -noprebind -noseglinkedit @gol
449 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
450 -private_bundle -read_only_relocs -sectalign @gol
451 -sectobjectsymbols -whyload -seg1addr @gol
452 -sectcreate -sectobjectsymbols -sectorder @gol
453 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
454 -segprot -segs_read_only_addr -segs_read_write_addr @gol
455 -single_module -static -sub_library -sub_umbrella @gol
456 -twolevel_namespace -umbrella -undefined @gol
457 -unexported_symbols_list -weak_reference_mismatches @gol
461 @gccoptlist{-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
462 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
463 -mminimum-fp-blocks -mnohc-struct-return}
466 @gccoptlist{-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
467 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
468 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
469 -mgas -mgp32 -mgp64 -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-long-calls @gol
475 -mno-memcpy -mno-mips-tfile -mno-rnames @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 -mpni -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. GCC is capable of
714 preprocessing and compiling several files either into several
715 assembler input files, or into one assembler input file; then each
716 assembler input file produces an object file, and linking combines all
717 the object files (those newly compiled, and those specified as input)
718 into an executable file.
720 @cindex file name suffix
721 For any given input file, the file name suffix determines what kind of
726 C source code which must be preprocessed.
729 C source code which should not be preprocessed.
732 C++ source code which should not be preprocessed.
735 Objective-C source code. Note that you must link with the library
736 @file{libobjc.a} to make an Objective-C program work.
739 Objective-C source code which should not be preprocessed.
742 C or C++ header file to be turned into a precompiled header.
746 @itemx @var{file}.cxx
747 @itemx @var{file}.cpp
748 @itemx @var{file}.CPP
749 @itemx @var{file}.c++
751 C++ source code which must be preprocessed. Note that in @samp{.cxx},
752 the last two letters must both be literally @samp{x}. Likewise,
753 @samp{.C} refers to a literal capital C@.
757 C++ header file to be turned into a precompiled header.
760 @itemx @var{file}.for
761 @itemx @var{file}.FOR
762 Fortran source code which should not be preprocessed.
765 @itemx @var{file}.fpp
766 @itemx @var{file}.FPP
767 Fortran source code which must be preprocessed (with the traditional
771 Fortran source code which must be preprocessed with a RATFOR
772 preprocessor (not included with GCC)@.
774 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
775 Using and Porting GNU Fortran}, for more details of the handling of
778 @c FIXME: Descriptions of Java file types.
785 Ada source code file which contains a library unit declaration (a
786 declaration of a package, subprogram, or generic, or a generic
787 instantiation), or a library unit renaming declaration (a package,
788 generic, or subprogram renaming declaration). Such files are also
791 @itemx @var{file}.adb
792 Ada source code file containing a library unit body (a subprogram or
793 package body). Such files are also called @dfn{bodies}.
795 @c GCC also knows about some suffixes for languages not yet included:
804 Assembler code which must be preprocessed.
807 An object file to be fed straight into linking.
808 Any file name with no recognized suffix is treated this way.
812 You can specify the input language explicitly with the @option{-x} option:
815 @item -x @var{language}
816 Specify explicitly the @var{language} for the following input files
817 (rather than letting the compiler choose a default based on the file
818 name suffix). This option applies to all following input files until
819 the next @option{-x} option. Possible values for @var{language} are:
821 c c-header cpp-output
822 c++ c++-header c++-cpp-output
823 objective-c objective-c-header objc-cpp-output
824 assembler assembler-with-cpp
826 f77 f77-cpp-input ratfor
832 Turn off any specification of a language, so that subsequent files are
833 handled according to their file name suffixes (as they are if @option{-x}
834 has not been used at all).
836 @item -pass-exit-codes
837 @opindex pass-exit-codes
838 Normally the @command{gcc} program will exit with the code of 1 if any
839 phase of the compiler returns a non-success return code. If you specify
840 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
841 numerically highest error produced by any phase that returned an error
845 If you only want some of the stages of compilation, you can use
846 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
847 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
848 @command{gcc} is to stop. Note that some combinations (for example,
849 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
854 Compile or assemble the source files, but do not link. The linking
855 stage simply is not done. The ultimate output is in the form of an
856 object file for each source file.
858 By default, the object file name for a source file is made by replacing
859 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
861 Unrecognized input files, not requiring compilation or assembly, are
866 Stop after the stage of compilation proper; do not assemble. The output
867 is in the form of an assembler code file for each non-assembler input
870 By default, the assembler file name for a source file is made by
871 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
873 Input files that don't require compilation are ignored.
877 Stop after the preprocessing stage; do not run the compiler proper. The
878 output is in the form of preprocessed source code, which is sent to the
881 Input files which don't require preprocessing are ignored.
883 @cindex output file option
886 Place output in file @var{file}. This applies regardless to whatever
887 sort of output is being produced, whether it be an executable file,
888 an object file, an assembler file or preprocessed C code.
890 If you specify @option{-o} when compiling more than one input file, or
891 you are producing an executable file as output, all the source files
892 on the command line will be compiled at once.
894 If @option{-o} is not specified, the default is to put an executable file
895 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
896 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
897 all preprocessed C source on standard output.
901 Print (on standard error output) the commands executed to run the stages
902 of compilation. Also print the version number of the compiler driver
903 program and of the preprocessor and the compiler proper.
907 Like @option{-v} except the commands are not executed and all command
908 arguments are quoted. This is useful for shell scripts to capture the
909 driver-generated command lines.
913 Use pipes rather than temporary files for communication between the
914 various stages of compilation. This fails to work on some systems where
915 the assembler is unable to read from a pipe; but the GNU assembler has
920 Print (on the standard output) a description of the command line options
921 understood by @command{gcc}. If the @option{-v} option is also specified
922 then @option{--help} will also be passed on to the various processes
923 invoked by @command{gcc}, so that they can display the command line options
924 they accept. If the @option{-Wextra} option is also specified then command
925 line options which have no documentation associated with them will also
930 Print (on the standard output) a description of target specific command
931 line options for each tool.
935 Display the version number and copyrights of the invoked GCC.
939 @section Compiling C++ Programs
941 @cindex suffixes for C++ source
942 @cindex C++ source file suffixes
943 C++ source files conventionally use one of the suffixes @samp{.C},
944 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
945 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
946 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
947 files with these names and compiles them as C++ programs even if you
948 call the compiler the same way as for compiling C programs (usually
949 with the name @command{gcc}).
953 However, C++ programs often require class libraries as well as a
954 compiler that understands the C++ language---and under some
955 circumstances, you might want to compile programs or header files from
956 standard input, or otherwise without a suffix that flags them as C++
957 programs. You might also like to precompile a C header file with a
958 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
959 program that calls GCC with the default language set to C++, and
960 automatically specifies linking against the C++ library. On many
961 systems, @command{g++} is also installed with the name @command{c++}.
963 @cindex invoking @command{g++}
964 When you compile C++ programs, you may specify many of the same
965 command-line options that you use for compiling programs in any
966 language; or command-line options meaningful for C and related
967 languages; or options that are meaningful only for C++ programs.
968 @xref{C Dialect Options,,Options Controlling C Dialect}, for
969 explanations of options for languages related to C@.
970 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
971 explanations of options that are meaningful only for C++ programs.
973 @node C Dialect Options
974 @section Options Controlling C Dialect
975 @cindex dialect options
976 @cindex language dialect options
977 @cindex options, dialect
979 The following options control the dialect of C (or languages derived
980 from C, such as C++ and Objective-C) that the compiler accepts:
987 In C mode, support all ISO C90 programs. In C++ mode,
988 remove GNU extensions that conflict with ISO C++.
990 This turns off certain features of GCC that are incompatible with ISO
991 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
992 such as the @code{asm} and @code{typeof} keywords, and
993 predefined macros such as @code{unix} and @code{vax} that identify the
994 type of system you are using. It also enables the undesirable and
995 rarely used ISO trigraph feature. For the C compiler,
996 it disables recognition of C++ style @samp{//} comments as well as
997 the @code{inline} keyword.
999 The alternate keywords @code{__asm__}, @code{__extension__},
1000 @code{__inline__} and @code{__typeof__} continue to work despite
1001 @option{-ansi}. You would not want to use them in an ISO C program, of
1002 course, but it is useful to put them in header files that might be included
1003 in compilations done with @option{-ansi}. Alternate predefined macros
1004 such as @code{__unix__} and @code{__vax__} are also available, with or
1005 without @option{-ansi}.
1007 The @option{-ansi} option does not cause non-ISO programs to be
1008 rejected gratuitously. For that, @option{-pedantic} is required in
1009 addition to @option{-ansi}. @xref{Warning Options}.
1011 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1012 option is used. Some header files may notice this macro and refrain
1013 from declaring certain functions or defining certain macros that the
1014 ISO standard doesn't call for; this is to avoid interfering with any
1015 programs that might use these names for other things.
1017 Functions which would normally be built in but do not have semantics
1018 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1019 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1020 built-in functions provided by GCC}, for details of the functions
1025 Determine the language standard. This option is currently only
1026 supported when compiling C or C++. A value for this option must be
1027 provided; possible values are
1032 ISO C90 (same as @option{-ansi}).
1034 @item iso9899:199409
1035 ISO C90 as modified in amendment 1.
1041 ISO C99. Note that this standard is not yet fully supported; see
1042 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1043 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1046 Default, ISO C90 plus GNU extensions (including some C99 features).
1050 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1051 this will become the default. The name @samp{gnu9x} is deprecated.
1054 The 1998 ISO C++ standard plus amendments.
1057 The same as @option{-std=c++98} plus GNU extensions. This is the
1058 default for C++ code.
1061 Even when this option is not specified, you can still use some of the
1062 features of newer standards in so far as they do not conflict with
1063 previous C standards. For example, you may use @code{__restrict__} even
1064 when @option{-std=c99} is not specified.
1066 The @option{-std} options specifying some version of ISO C have the same
1067 effects as @option{-ansi}, except that features that were not in ISO C90
1068 but are in the specified version (for example, @samp{//} comments and
1069 the @code{inline} keyword in ISO C99) are not disabled.
1071 @xref{Standards,,Language Standards Supported by GCC}, for details of
1072 these standard versions.
1074 @item -aux-info @var{filename}
1076 Output to the given filename prototyped declarations for all functions
1077 declared and/or defined in a translation unit, including those in header
1078 files. This option is silently ignored in any language other than C@.
1080 Besides declarations, the file indicates, in comments, the origin of
1081 each declaration (source file and line), whether the declaration was
1082 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1083 @samp{O} for old, respectively, in the first character after the line
1084 number and the colon), and whether it came from a declaration or a
1085 definition (@samp{C} or @samp{F}, respectively, in the following
1086 character). In the case of function definitions, a K&R-style list of
1087 arguments followed by their declarations is also provided, inside
1088 comments, after the declaration.
1092 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1093 keyword, so that code can use these words as identifiers. You can use
1094 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1095 instead. @option{-ansi} implies @option{-fno-asm}.
1097 In C++, this switch only affects the @code{typeof} keyword, since
1098 @code{asm} and @code{inline} are standard keywords. You may want to
1099 use the @option{-fno-gnu-keywords} flag instead, which has the same
1100 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1101 switch only affects the @code{asm} and @code{typeof} keywords, since
1102 @code{inline} is a standard keyword in ISO C99.
1105 @itemx -fno-builtin-@var{function}
1106 @opindex fno-builtin
1107 @cindex built-in functions
1108 Don't recognize built-in functions that do not begin with
1109 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1110 functions provided by GCC}, for details of the functions affected,
1111 including those which are not built-in functions when @option{-ansi} or
1112 @option{-std} options for strict ISO C conformance are used because they
1113 do not have an ISO standard meaning.
1115 GCC normally generates special code to handle certain built-in functions
1116 more efficiently; for instance, calls to @code{alloca} may become single
1117 instructions that adjust the stack directly, and calls to @code{memcpy}
1118 may become inline copy loops. The resulting code is often both smaller
1119 and faster, but since the function calls no longer appear as such, you
1120 cannot set a breakpoint on those calls, nor can you change the behavior
1121 of the functions by linking with a different library.
1123 With the @option{-fno-builtin-@var{function}} option
1124 only the built-in function @var{function} is
1125 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1126 function is named this is not built-in in this version of GCC, this
1127 option is ignored. There is no corresponding
1128 @option{-fbuiltin-@var{function}} option; if you wish to enable
1129 built-in functions selectively when using @option{-fno-builtin} or
1130 @option{-ffreestanding}, you may define macros such as:
1133 #define abs(n) __builtin_abs ((n))
1134 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1139 @cindex hosted environment
1141 Assert that compilation takes place in a hosted environment. This implies
1142 @option{-fbuiltin}. A hosted environment is one in which the
1143 entire standard library is available, and in which @code{main} has a return
1144 type of @code{int}. Examples are nearly everything except a kernel.
1145 This is equivalent to @option{-fno-freestanding}.
1147 @item -ffreestanding
1148 @opindex ffreestanding
1149 @cindex hosted environment
1151 Assert that compilation takes place in a freestanding environment. This
1152 implies @option{-fno-builtin}. A freestanding environment
1153 is one in which the standard library may not exist, and program startup may
1154 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1155 This is equivalent to @option{-fno-hosted}.
1157 @xref{Standards,,Language Standards Supported by GCC}, for details of
1158 freestanding and hosted environments.
1160 @item -fms-extensions
1161 @opindex fms-extensions
1162 Accept some non-standard constructs used in Microsoft header files.
1166 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1167 options for strict ISO C conformance) implies @option{-trigraphs}.
1169 @item -no-integrated-cpp
1170 @opindex no-integrated-cpp
1171 Performs a compilation in two passes: preprocessing and compiling. This
1172 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1173 @option{-B} option. The user supplied compilation step can then add in
1174 an additional preprocessing step after normal preprocessing but before
1175 compiling. The default is to use the integrated cpp (internal cpp)
1177 The semantics of this option will change if "cc1", "cc1plus", and
1178 "cc1obj" are merged.
1180 @cindex traditional C language
1181 @cindex C language, traditional
1183 @itemx -traditional-cpp
1184 @opindex traditional-cpp
1185 @opindex traditional
1186 Formerly, these options caused GCC to attempt to emulate a pre-standard
1187 C compiler. They are now only supported with the @option{-E} switch.
1188 The preprocessor continues to support a pre-standard mode. See the GNU
1189 CPP manual for details.
1191 @item -fcond-mismatch
1192 @opindex fcond-mismatch
1193 Allow conditional expressions with mismatched types in the second and
1194 third arguments. The value of such an expression is void. This option
1195 is not supported for C++.
1197 @item -funsigned-char
1198 @opindex funsigned-char
1199 Let the type @code{char} be unsigned, like @code{unsigned char}.
1201 Each kind of machine has a default for what @code{char} should
1202 be. It is either like @code{unsigned char} by default or like
1203 @code{signed char} by default.
1205 Ideally, a portable program should always use @code{signed char} or
1206 @code{unsigned char} when it depends on the signedness of an object.
1207 But many programs have been written to use plain @code{char} and
1208 expect it to be signed, or expect it to be unsigned, depending on the
1209 machines they were written for. This option, and its inverse, let you
1210 make such a program work with the opposite default.
1212 The type @code{char} is always a distinct type from each of
1213 @code{signed char} or @code{unsigned char}, even though its behavior
1214 is always just like one of those two.
1217 @opindex fsigned-char
1218 Let the type @code{char} be signed, like @code{signed char}.
1220 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1221 the negative form of @option{-funsigned-char}. Likewise, the option
1222 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1224 @item -fsigned-bitfields
1225 @itemx -funsigned-bitfields
1226 @itemx -fno-signed-bitfields
1227 @itemx -fno-unsigned-bitfields
1228 @opindex fsigned-bitfields
1229 @opindex funsigned-bitfields
1230 @opindex fno-signed-bitfields
1231 @opindex fno-unsigned-bitfields
1232 These options control whether a bit-field is signed or unsigned, when the
1233 declaration does not use either @code{signed} or @code{unsigned}. By
1234 default, such a bit-field is signed, because this is consistent: the
1235 basic integer types such as @code{int} are signed types.
1237 @item -fwritable-strings
1238 @opindex fwritable-strings
1239 Store string constants in the writable data segment and don't uniquize
1240 them. This is for compatibility with old programs which assume they can
1241 write into string constants.
1243 Writing into string constants is a very bad idea; ``constants'' should
1247 @node C++ Dialect Options
1248 @section Options Controlling C++ Dialect
1250 @cindex compiler options, C++
1251 @cindex C++ options, command line
1252 @cindex options, C++
1253 This section describes the command-line options that are only meaningful
1254 for C++ programs; but you can also use most of the GNU compiler options
1255 regardless of what language your program is in. For example, you
1256 might compile a file @code{firstClass.C} like this:
1259 g++ -g -frepo -O -c firstClass.C
1263 In this example, only @option{-frepo} is an option meant
1264 only for C++ programs; you can use the other options with any
1265 language supported by GCC@.
1267 Here is a list of options that are @emph{only} for compiling C++ programs:
1271 @item -fabi-version=@var{n}
1272 @opindex fabi-version
1273 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1274 ABI that first appeared in G++ 3.2. Version 0 will always be the
1275 version that conforms most closely to the C++ ABI specification.
1276 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1279 The default is version 1.
1281 @item -fno-access-control
1282 @opindex fno-access-control
1283 Turn off all access checking. This switch is mainly useful for working
1284 around bugs in the access control code.
1288 Check that the pointer returned by @code{operator new} is non-null
1289 before attempting to modify the storage allocated. This check is
1290 normally unnecessary because the C++ standard specifies that
1291 @code{operator new} will only return @code{0} if it is declared
1292 @samp{throw()}, in which case the compiler will always check the
1293 return value even without this option. In all other cases, when
1294 @code{operator new} has a non-empty exception specification, memory
1295 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1296 @samp{new (nothrow)}.
1298 @item -fconserve-space
1299 @opindex fconserve-space
1300 Put uninitialized or runtime-initialized global variables into the
1301 common segment, as C does. This saves space in the executable at the
1302 cost of not diagnosing duplicate definitions. If you compile with this
1303 flag and your program mysteriously crashes after @code{main()} has
1304 completed, you may have an object that is being destroyed twice because
1305 two definitions were merged.
1307 This option is no longer useful on most targets, now that support has
1308 been added for putting variables into BSS without making them common.
1310 @item -fno-const-strings
1311 @opindex fno-const-strings
1312 Give string constants type @code{char *} instead of type @code{const
1313 char *}. By default, G++ uses type @code{const char *} as required by
1314 the standard. Even if you use @option{-fno-const-strings}, you cannot
1315 actually modify the value of a string constant, unless you also use
1316 @option{-fwritable-strings}.
1318 This option might be removed in a future release of G++. For maximum
1319 portability, you should structure your code so that it works with
1320 string constants that have type @code{const char *}.
1322 @item -fno-elide-constructors
1323 @opindex fno-elide-constructors
1324 The C++ standard allows an implementation to omit creating a temporary
1325 which is only used to initialize another object of the same type.
1326 Specifying this option disables that optimization, and forces G++ to
1327 call the copy constructor in all cases.
1329 @item -fno-enforce-eh-specs
1330 @opindex fno-enforce-eh-specs
1331 Don't check for violation of exception specifications at runtime. This
1332 option violates the C++ standard, but may be useful for reducing code
1333 size in production builds, much like defining @samp{NDEBUG}. The compiler
1334 will still optimize based on the exception specifications.
1336 @item -fexternal-templates
1337 @opindex fexternal-templates
1339 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1340 template instantiation; template instances are emitted or not according
1341 to the location of the template definition. @xref{Template
1342 Instantiation}, for more information.
1344 This option is deprecated.
1346 @item -falt-external-templates
1347 @opindex falt-external-templates
1348 Similar to @option{-fexternal-templates}, but template instances are
1349 emitted or not according to the place where they are first instantiated.
1350 @xref{Template Instantiation}, for more information.
1352 This option is deprecated.
1355 @itemx -fno-for-scope
1357 @opindex fno-for-scope
1358 If @option{-ffor-scope} is specified, the scope of variables declared in
1359 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1360 as specified by the C++ standard.
1361 If @option{-fno-for-scope} is specified, the scope of variables declared in
1362 a @i{for-init-statement} extends to the end of the enclosing scope,
1363 as was the case in old versions of G++, and other (traditional)
1364 implementations of C++.
1366 The default if neither flag is given to follow the standard,
1367 but to allow and give a warning for old-style code that would
1368 otherwise be invalid, or have different behavior.
1370 @item -fno-gnu-keywords
1371 @opindex fno-gnu-keywords
1372 Do not recognize @code{typeof} as a keyword, so that code can use this
1373 word as an identifier. You can use the keyword @code{__typeof__} instead.
1374 @option{-ansi} implies @option{-fno-gnu-keywords}.
1376 @item -fno-implicit-templates
1377 @opindex fno-implicit-templates
1378 Never emit code for non-inline templates which are instantiated
1379 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1380 @xref{Template Instantiation}, for more information.
1382 @item -fno-implicit-inline-templates
1383 @opindex fno-implicit-inline-templates
1384 Don't emit code for implicit instantiations of inline templates, either.
1385 The default is to handle inlines differently so that compiles with and
1386 without optimization will need the same set of explicit instantiations.
1388 @item -fno-implement-inlines
1389 @opindex fno-implement-inlines
1390 To save space, do not emit out-of-line copies of inline functions
1391 controlled by @samp{#pragma implementation}. This will cause linker
1392 errors if these functions are not inlined everywhere they are called.
1394 @item -fms-extensions
1395 @opindex fms-extensions
1396 Disable pedantic warnings about constructs used in MFC, such as implicit
1397 int and getting a pointer to member function via non-standard syntax.
1399 @item -fno-nonansi-builtins
1400 @opindex fno-nonansi-builtins
1401 Disable built-in declarations of functions that are not mandated by
1402 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1403 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1405 @item -fno-operator-names
1406 @opindex fno-operator-names
1407 Do not treat the operator name keywords @code{and}, @code{bitand},
1408 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1409 synonyms as keywords.
1411 @item -fno-optional-diags
1412 @opindex fno-optional-diags
1413 Disable diagnostics that the standard says a compiler does not need to
1414 issue. Currently, the only such diagnostic issued by G++ is the one for
1415 a name having multiple meanings within a class.
1418 @opindex fpermissive
1419 Downgrade some diagnostics about nonconformant code from errors to
1420 warnings. Thus, using @option{-fpermissive} will allow some
1421 nonconforming code to compile.
1425 Enable automatic template instantiation at link time. This option also
1426 implies @option{-fno-implicit-templates}. @xref{Template
1427 Instantiation}, for more information.
1431 Disable generation of information about every class with virtual
1432 functions for use by the C++ runtime type identification features
1433 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1434 of the language, you can save some space by using this flag. Note that
1435 exception handling uses the same information, but it will generate it as
1440 Emit statistics about front-end processing at the end of the compilation.
1441 This information is generally only useful to the G++ development team.
1443 @item -ftemplate-depth-@var{n}
1444 @opindex ftemplate-depth
1445 Set the maximum instantiation depth for template classes to @var{n}.
1446 A limit on the template instantiation depth is needed to detect
1447 endless recursions during template class instantiation. ANSI/ISO C++
1448 conforming programs must not rely on a maximum depth greater than 17.
1450 @item -fuse-cxa-atexit
1451 @opindex fuse-cxa-atexit
1452 Register destructors for objects with static storage duration with the
1453 @code{__cxa_atexit} function rather than the @code{atexit} function.
1454 This option is required for fully standards-compliant handling of static
1455 destructors, but will only work if your C library supports
1456 @code{__cxa_atexit}.
1460 Emit special relocations for vtables and virtual function references
1461 so that the linker can identify unused virtual functions and zero out
1462 vtable slots that refer to them. This is most useful with
1463 @option{-ffunction-sections} and @option{-Wl,--gc-sections}, in order to
1464 also discard the functions themselves.
1466 This optimization requires GNU as and GNU ld. Not all systems support
1467 this option. @option{-Wl,--gc-sections} is ignored without @option{-static}.
1471 Do not use weak symbol support, even if it is provided by the linker.
1472 By default, G++ will use weak symbols if they are available. This
1473 option exists only for testing, and should not be used by end-users;
1474 it will result in inferior code and has no benefits. This option may
1475 be removed in a future release of G++.
1479 Do not search for header files in the standard directories specific to
1480 C++, but do still search the other standard directories. (This option
1481 is used when building the C++ library.)
1484 In addition, these optimization, warning, and code generation options
1485 have meanings only for C++ programs:
1488 @item -fno-default-inline
1489 @opindex fno-default-inline
1490 Do not assume @samp{inline} for functions defined inside a class scope.
1491 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1492 functions will have linkage like inline functions; they just won't be
1495 @item -Wabi @r{(C++ only)}
1497 Warn when G++ generates code that is probably not compatible with the
1498 vendor-neutral C++ ABI. Although an effort has been made to warn about
1499 all such cases, there are probably some cases that are not warned about,
1500 even though G++ is generating incompatible code. There may also be
1501 cases where warnings are emitted even though the code that is generated
1504 You should rewrite your code to avoid these warnings if you are
1505 concerned about the fact that code generated by G++ may not be binary
1506 compatible with code generated by other compilers.
1508 The known incompatibilities at this point include:
1513 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1514 pack data into the same byte as a base class. For example:
1517 struct A @{ virtual void f(); int f1 : 1; @};
1518 struct B : public A @{ int f2 : 1; @};
1522 In this case, G++ will place @code{B::f2} into the same byte
1523 as@code{A::f1}; other compilers will not. You can avoid this problem
1524 by explicitly padding @code{A} so that its size is a multiple of the
1525 byte size on your platform; that will cause G++ and other compilers to
1526 layout @code{B} identically.
1529 Incorrect handling of tail-padding for virtual bases. G++ does not use
1530 tail padding when laying out virtual bases. For example:
1533 struct A @{ virtual void f(); char c1; @};
1534 struct B @{ B(); char c2; @};
1535 struct C : public A, public virtual B @{@};
1539 In this case, G++ will not place @code{B} into the tail-padding for
1540 @code{A}; other compilers will. You can avoid this problem by
1541 explicitly padding @code{A} so that its size is a multiple of its
1542 alignment (ignoring virtual base classes); that will cause G++ and other
1543 compilers to layout @code{C} identically.
1546 Incorrect handling of bit-fields with declared widths greater than that
1547 of their underlying types, when the bit-fields appear in a union. For
1551 union U @{ int i : 4096; @};
1555 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1556 union too small by the number of bits in an @code{int}.
1559 Empty classes can be placed at incorrect offsets. For example:
1569 struct C : public B, public A @{@};
1573 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1574 it should be placed at offset zero. G++ mistakenly believes that the
1575 @code{A} data member of @code{B} is already at offset zero.
1578 Names of template functions whose types involve @code{typename} or
1579 template template parameters can be mangled incorrectly.
1582 template <typename Q>
1583 void f(typename Q::X) @{@}
1585 template <template <typename> class Q>
1586 void f(typename Q<int>::X) @{@}
1590 Instantiations of these templates may be mangled incorrectly.
1594 @item -Wctor-dtor-privacy @r{(C++ only)}
1595 @opindex Wctor-dtor-privacy
1596 Warn when a class seems unusable, because all the constructors or
1597 destructors in a class are private and the class has no friends or
1598 public static member functions.
1600 @item -Wnon-virtual-dtor @r{(C++ only)}
1601 @opindex Wnon-virtual-dtor
1602 Warn when a class declares a non-virtual destructor that should probably
1603 be virtual, because it looks like the class will be used polymorphically.
1604 This warning is enabled by @option{-Wall}.
1606 @item -Wreorder @r{(C++ only)}
1608 @cindex reordering, warning
1609 @cindex warning for reordering of member initializers
1610 Warn when the order of member initializers given in the code does not
1611 match the order in which they must be executed. For instance:
1617 A(): j (0), i (1) @{ @}
1621 Here the compiler will warn that the member initializers for @samp{i}
1622 and @samp{j} will be rearranged to match the declaration order of the
1623 members. This warning is enabled by @option{-Wall}.
1626 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1629 @item -Weffc++ @r{(C++ only)}
1631 Warn about violations of the following style guidelines from Scott Meyers'
1632 @cite{Effective C++} book:
1636 Item 11: Define a copy constructor and an assignment operator for classes
1637 with dynamically allocated memory.
1640 Item 12: Prefer initialization to assignment in constructors.
1643 Item 14: Make destructors virtual in base classes.
1646 Item 15: Have @code{operator=} return a reference to @code{*this}.
1649 Item 23: Don't try to return a reference when you must return an object.
1653 and about violations of the following style guidelines from Scott Meyers'
1654 @cite{More Effective C++} book:
1658 Item 6: Distinguish between prefix and postfix forms of increment and
1659 decrement operators.
1662 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1666 If you use this option, you should be aware that the standard library
1667 headers do not obey all of these guidelines; you can use @samp{grep -v}
1668 to filter out those warnings.
1670 @item -Wno-deprecated @r{(C++ only)}
1671 @opindex Wno-deprecated
1672 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1674 @item -Wno-non-template-friend @r{(C++ only)}
1675 @opindex Wno-non-template-friend
1676 Disable warnings when non-templatized friend functions are declared
1677 within a template. With the advent of explicit template specification
1678 support in G++, if the name of the friend is an unqualified-id (i.e.,
1679 @samp{friend foo(int)}), the C++ language specification demands that the
1680 friend declare or define an ordinary, nontemplate function. (Section
1681 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1682 could be interpreted as a particular specialization of a templatized
1683 function. Because this non-conforming behavior is no longer the default
1684 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1685 check existing code for potential trouble spots, and is on by default.
1686 This new compiler behavior can be turned off with
1687 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1688 but disables the helpful warning.
1690 @item -Wold-style-cast @r{(C++ only)}
1691 @opindex Wold-style-cast
1692 Warn if an old-style (C-style) cast to a non-void type is used within
1693 a C++ program. The new-style casts (@samp{static_cast},
1694 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1695 unintended effects, and much easier to grep for.
1697 @item -Woverloaded-virtual @r{(C++ only)}
1698 @opindex Woverloaded-virtual
1699 @cindex overloaded virtual fn, warning
1700 @cindex warning for overloaded virtual fn
1701 Warn when a function declaration hides virtual functions from a
1702 base class. For example, in:
1709 struct B: public A @{
1714 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1722 will fail to compile.
1724 @item -Wno-pmf-conversions @r{(C++ only)}
1725 @opindex Wno-pmf-conversions
1726 Disable the diagnostic for converting a bound pointer to member function
1729 @item -Wsign-promo @r{(C++ only)}
1730 @opindex Wsign-promo
1731 Warn when overload resolution chooses a promotion from unsigned or
1732 enumeral type to a signed type over a conversion to an unsigned type of
1733 the same size. Previous versions of G++ would try to preserve
1734 unsignedness, but the standard mandates the current behavior.
1736 @item -Wsynth @r{(C++ only)}
1738 @cindex warning for synthesized methods
1739 @cindex synthesized methods, warning
1740 Warn when G++'s synthesis behavior does not match that of cfront. For
1746 A& operator = (int);
1756 In this example, G++ will synthesize a default @samp{A& operator =
1757 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1760 @node Objective-C Dialect Options
1761 @section Options Controlling Objective-C Dialect
1763 @cindex compiler options, Objective-C
1764 @cindex Objective-C options, command line
1765 @cindex options, Objective-C
1766 This section describes the command-line options that are only meaningful
1767 for Objective-C programs; but you can also use most of the GNU compiler
1768 options regardless of what language your program is in. For example,
1769 you might compile a file @code{some_class.m} like this:
1772 gcc -g -fgnu-runtime -O -c some_class.m
1776 In this example, only @option{-fgnu-runtime} is an option meant only for
1777 Objective-C programs; you can use the other options with any language
1780 Here is a list of options that are @emph{only} for compiling Objective-C
1784 @item -fconstant-string-class=@var{class-name}
1785 @opindex fconstant-string-class
1786 Use @var{class-name} as the name of the class to instantiate for each
1787 literal string specified with the syntax @code{@@"@dots{}"}. The default
1788 class name is @code{NXConstantString}.
1791 @opindex fgnu-runtime
1792 Generate object code compatible with the standard GNU Objective-C
1793 runtime. This is the default for most types of systems.
1795 @item -fnext-runtime
1796 @opindex fnext-runtime
1797 Generate output compatible with the NeXT runtime. This is the default
1798 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1799 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1804 Dump interface declarations for all classes seen in the source file to a
1805 file named @file{@var{sourcename}.decl}.
1808 @opindex Wno-protocol
1809 If a class is declared to implement a protocol, a warning is issued for
1810 every method in the protocol that is not implemented by the class. The
1811 default behavior is to issue a warning for every method not explicitly
1812 implemented in the class, even if a method implementation is inherited
1813 from the superclass. If you use the @code{-Wno-protocol} option, then
1814 methods inherited from the superclass are considered to be implemented,
1815 and no warning is issued for them.
1819 Warn if multiple methods of different types for the same selector are
1820 found during compilation. The check is performed on the list of methods
1821 in the final stage of compilation. Additionally, a check is performed
1822 that for each selector appearing in a @code{@@selector(@dots{})}
1823 expression, a corresponding method with that selector has been found
1824 during compilation. Because these checks scan the method table only at
1825 the end of compilation, these warnings are not produced if the final
1826 stage of compilation is not reached, for example because an error is
1827 found during compilation, or because the @code{-fsyntax-only} option is
1830 @item -Wundeclared-selector
1831 @opindex Wundeclared-selector
1832 Warn if a @code{@@selector(@dots{})} expression referring to an
1833 undeclared selector is found. A selector is considered undeclared if no
1834 method with that name has been declared (explicitly, in an
1835 @code{@@interface} or @code{@@protocol} declaration, or implicitly, in
1836 an @code{@@implementation} section) before the
1837 @code{@@selector(@dots{})} expression. This option always performs its
1838 checks as soon as a @code{@@selector(@dots{})} expression is found
1839 (while @code{-Wselector} only performs its checks in the final stage of
1840 compilation), and so additionally enforces the coding style convention
1841 that methods and selectors must be declared before being used.
1843 @c not documented because only avail via -Wp
1844 @c @item -print-objc-runtime-info
1848 @node Language Independent Options
1849 @section Options to Control Diagnostic Messages Formatting
1850 @cindex options to control diagnostics formatting
1851 @cindex diagnostic messages
1852 @cindex message formatting
1854 Traditionally, diagnostic messages have been formatted irrespective of
1855 the output device's aspect (e.g.@: its width, @dots{}). The options described
1856 below can be used to control the diagnostic messages formatting
1857 algorithm, e.g.@: how many characters per line, how often source location
1858 information should be reported. Right now, only the C++ front end can
1859 honor these options. However it is expected, in the near future, that
1860 the remaining front ends would be able to digest them correctly.
1863 @item -fmessage-length=@var{n}
1864 @opindex fmessage-length
1865 Try to format error messages so that they fit on lines of about @var{n}
1866 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1867 the front ends supported by GCC@. If @var{n} is zero, then no
1868 line-wrapping will be done; each error message will appear on a single
1871 @opindex fdiagnostics-show-location
1872 @item -fdiagnostics-show-location=once
1873 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1874 reporter to emit @emph{once} source location information; that is, in
1875 case the message is too long to fit on a single physical line and has to
1876 be wrapped, the source location won't be emitted (as prefix) again,
1877 over and over, in subsequent continuation lines. This is the default
1880 @item -fdiagnostics-show-location=every-line
1881 Only meaningful in line-wrapping mode. Instructs the diagnostic
1882 messages reporter to emit the same source location information (as
1883 prefix) for physical lines that result from the process of breaking
1884 a message which is too long to fit on a single line.
1888 @node Warning Options
1889 @section Options to Request or Suppress Warnings
1890 @cindex options to control warnings
1891 @cindex warning messages
1892 @cindex messages, warning
1893 @cindex suppressing warnings
1895 Warnings are diagnostic messages that report constructions which
1896 are not inherently erroneous but which are risky or suggest there
1897 may have been an error.
1899 You can request many specific warnings with options beginning @samp{-W},
1900 for example @option{-Wimplicit} to request warnings on implicit
1901 declarations. Each of these specific warning options also has a
1902 negative form beginning @samp{-Wno-} to turn off warnings;
1903 for example, @option{-Wno-implicit}. This manual lists only one of the
1904 two forms, whichever is not the default.
1906 The following options control the amount and kinds of warnings produced
1907 by GCC; for further, language-specific options also refer to
1908 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
1911 @cindex syntax checking
1913 @opindex fsyntax-only
1914 Check the code for syntax errors, but don't do anything beyond that.
1918 Issue all the warnings demanded by strict ISO C and ISO C++;
1919 reject all programs that use forbidden extensions, and some other
1920 programs that do not follow ISO C and ISO C++. For ISO C, follows the
1921 version of the ISO C standard specified by any @option{-std} option used.
1923 Valid ISO C and ISO C++ programs should compile properly with or without
1924 this option (though a rare few will require @option{-ansi} or a
1925 @option{-std} option specifying the required version of ISO C)@. However,
1926 without this option, certain GNU extensions and traditional C and C++
1927 features are supported as well. With this option, they are rejected.
1929 @option{-pedantic} does not cause warning messages for use of the
1930 alternate keywords whose names begin and end with @samp{__}. Pedantic
1931 warnings are also disabled in the expression that follows
1932 @code{__extension__}. However, only system header files should use
1933 these escape routes; application programs should avoid them.
1934 @xref{Alternate Keywords}.
1936 Some users try to use @option{-pedantic} to check programs for strict ISO
1937 C conformance. They soon find that it does not do quite what they want:
1938 it finds some non-ISO practices, but not all---only those for which
1939 ISO C @emph{requires} a diagnostic, and some others for which
1940 diagnostics have been added.
1942 A feature to report any failure to conform to ISO C might be useful in
1943 some instances, but would require considerable additional work and would
1944 be quite different from @option{-pedantic}. We don't have plans to
1945 support such a feature in the near future.
1947 Where the standard specified with @option{-std} represents a GNU
1948 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
1949 corresponding @dfn{base standard}, the version of ISO C on which the GNU
1950 extended dialect is based. Warnings from @option{-pedantic} are given
1951 where they are required by the base standard. (It would not make sense
1952 for such warnings to be given only for features not in the specified GNU
1953 C dialect, since by definition the GNU dialects of C include all
1954 features the compiler supports with the given option, and there would be
1955 nothing to warn about.)
1957 @item -pedantic-errors
1958 @opindex pedantic-errors
1959 Like @option{-pedantic}, except that errors are produced rather than
1964 Inhibit all warning messages.
1968 Inhibit warning messages about the use of @samp{#import}.
1970 @item -Wchar-subscripts
1971 @opindex Wchar-subscripts
1972 Warn if an array subscript has type @code{char}. This is a common cause
1973 of error, as programmers often forget that this type is signed on some
1978 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
1979 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
1983 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
1984 the arguments supplied have types appropriate to the format string
1985 specified, and that the conversions specified in the format string make
1986 sense. This includes standard functions, and others specified by format
1987 attributes (@pxref{Function Attributes}), in the @code{printf},
1988 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
1989 not in the C standard) families.
1991 The formats are checked against the format features supported by GNU
1992 libc version 2.2. These include all ISO C90 and C99 features, as well
1993 as features from the Single Unix Specification and some BSD and GNU
1994 extensions. Other library implementations may not support all these
1995 features; GCC does not support warning about features that go beyond a
1996 particular library's limitations. However, if @option{-pedantic} is used
1997 with @option{-Wformat}, warnings will be given about format features not
1998 in the selected standard version (but not for @code{strfmon} formats,
1999 since those are not in any version of the C standard). @xref{C Dialect
2000 Options,,Options Controlling C Dialect}.
2002 Since @option{-Wformat} also checks for null format arguments for
2003 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2005 @option{-Wformat} is included in @option{-Wall}. For more control over some
2006 aspects of format checking, the options @option{-Wno-format-y2k},
2007 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2008 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2009 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2011 @item -Wno-format-y2k
2012 @opindex Wno-format-y2k
2013 If @option{-Wformat} is specified, do not warn about @code{strftime}
2014 formats which may yield only a two-digit year.
2016 @item -Wno-format-extra-args
2017 @opindex Wno-format-extra-args
2018 If @option{-Wformat} is specified, do not warn about excess arguments to a
2019 @code{printf} or @code{scanf} format function. The C standard specifies
2020 that such arguments are ignored.
2022 Where the unused arguments lie between used arguments that are
2023 specified with @samp{$} operand number specifications, normally
2024 warnings are still given, since the implementation could not know what
2025 type to pass to @code{va_arg} to skip the unused arguments. However,
2026 in the case of @code{scanf} formats, this option will suppress the
2027 warning if the unused arguments are all pointers, since the Single
2028 Unix Specification says that such unused arguments are allowed.
2030 @item -Wno-format-zero-length
2031 @opindex Wno-format-zero-length
2032 If @option{-Wformat} is specified, do not warn about zero-length formats.
2033 The C standard specifies that zero-length formats are allowed.
2035 @item -Wformat-nonliteral
2036 @opindex Wformat-nonliteral
2037 If @option{-Wformat} is specified, also warn if the format string is not a
2038 string literal and so cannot be checked, unless the format function
2039 takes its format arguments as a @code{va_list}.
2041 @item -Wformat-security
2042 @opindex Wformat-security
2043 If @option{-Wformat} is specified, also warn about uses of format
2044 functions that represent possible security problems. At present, this
2045 warns about calls to @code{printf} and @code{scanf} functions where the
2046 format string is not a string literal and there are no format arguments,
2047 as in @code{printf (foo);}. This may be a security hole if the format
2048 string came from untrusted input and contains @samp{%n}. (This is
2049 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2050 in future warnings may be added to @option{-Wformat-security} that are not
2051 included in @option{-Wformat-nonliteral}.)
2055 Enable @option{-Wformat} plus format checks not included in
2056 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2057 -Wformat-nonliteral -Wformat-security}.
2061 Enable warning about passing a null pointer for arguments marked as
2062 requiring a non-null value by the @code{nonnull} function attribute.
2064 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2065 can be disabled with the @option{-Wno-nonnull} option.
2067 @item -Wimplicit-int
2068 @opindex Wimplicit-int
2069 Warn when a declaration does not specify a type.
2071 @item -Wimplicit-function-declaration
2072 @itemx -Werror-implicit-function-declaration
2073 @opindex Wimplicit-function-declaration
2074 @opindex Werror-implicit-function-declaration
2075 Give a warning (or error) whenever a function is used before being
2080 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2084 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2085 function with external linkage, returning int, taking either zero
2086 arguments, two, or three arguments of appropriate types.
2088 @item -Wmissing-braces
2089 @opindex Wmissing-braces
2090 Warn if an aggregate or union initializer is not fully bracketed. In
2091 the following example, the initializer for @samp{a} is not fully
2092 bracketed, but that for @samp{b} is fully bracketed.
2095 int a[2][2] = @{ 0, 1, 2, 3 @};
2096 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2100 @opindex Wparentheses
2101 Warn if parentheses are omitted in certain contexts, such
2102 as when there is an assignment in a context where a truth value
2103 is expected, or when operators are nested whose precedence people
2104 often get confused about.
2106 Also warn about constructions where there may be confusion to which
2107 @code{if} statement an @code{else} branch belongs. Here is an example of
2122 In C, every @code{else} branch belongs to the innermost possible @code{if}
2123 statement, which in this example is @code{if (b)}. This is often not
2124 what the programmer expected, as illustrated in the above example by
2125 indentation the programmer chose. When there is the potential for this
2126 confusion, GCC will issue a warning when this flag is specified.
2127 To eliminate the warning, add explicit braces around the innermost
2128 @code{if} statement so there is no way the @code{else} could belong to
2129 the enclosing @code{if}. The resulting code would look like this:
2145 @item -Wsequence-point
2146 @opindex Wsequence-point
2147 Warn about code that may have undefined semantics because of violations
2148 of sequence point rules in the C standard.
2150 The C standard defines the order in which expressions in a C program are
2151 evaluated in terms of @dfn{sequence points}, which represent a partial
2152 ordering between the execution of parts of the program: those executed
2153 before the sequence point, and those executed after it. These occur
2154 after the evaluation of a full expression (one which is not part of a
2155 larger expression), after the evaluation of the first operand of a
2156 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2157 function is called (but after the evaluation of its arguments and the
2158 expression denoting the called function), and in certain other places.
2159 Other than as expressed by the sequence point rules, the order of
2160 evaluation of subexpressions of an expression is not specified. All
2161 these rules describe only a partial order rather than a total order,
2162 since, for example, if two functions are called within one expression
2163 with no sequence point between them, the order in which the functions
2164 are called is not specified. However, the standards committee have
2165 ruled that function calls do not overlap.
2167 It is not specified when between sequence points modifications to the
2168 values of objects take effect. Programs whose behavior depends on this
2169 have undefined behavior; the C standard specifies that ``Between the
2170 previous and next sequence point an object shall have its stored value
2171 modified at most once by the evaluation of an expression. Furthermore,
2172 the prior value shall be read only to determine the value to be
2173 stored.''. If a program breaks these rules, the results on any
2174 particular implementation are entirely unpredictable.
2176 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2177 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2178 diagnosed by this option, and it may give an occasional false positive
2179 result, but in general it has been found fairly effective at detecting
2180 this sort of problem in programs.
2182 The present implementation of this option only works for C programs. A
2183 future implementation may also work for C++ programs.
2185 The C standard is worded confusingly, therefore there is some debate
2186 over the precise meaning of the sequence point rules in subtle cases.
2187 Links to discussions of the problem, including proposed formal
2188 definitions, may be found on our readings page, at
2189 @w{@uref{http://gcc.gnu.org/readings.html}}.
2192 @opindex Wreturn-type
2193 Warn whenever a function is defined with a return-type that defaults to
2194 @code{int}. Also warn about any @code{return} statement with no
2195 return-value in a function whose return-type is not @code{void}.
2197 For C++, a function without return type always produces a diagnostic
2198 message, even when @option{-Wno-return-type} is specified. The only
2199 exceptions are @samp{main} and functions defined in system headers.
2203 Warn whenever a @code{switch} statement has an index of enumeral type
2204 and lacks a @code{case} for one or more of the named codes of that
2205 enumeration. (The presence of a @code{default} label prevents this
2206 warning.) @code{case} labels outside the enumeration range also
2207 provoke warnings when this option is used.
2209 @item -Wswitch-default
2210 @opindex Wswitch-switch
2211 Warn whenever a @code{switch} statement does not have a @code{default}
2215 @opindex Wswitch-enum
2216 Warn whenever a @code{switch} statement has an index of enumeral type
2217 and lacks a @code{case} for one or more of the named codes of that
2218 enumeration. @code{case} labels outside the enumeration range also
2219 provoke warnings when this option is used.
2223 Warn if any trigraphs are encountered that might change the meaning of
2224 the program (trigraphs within comments are not warned about).
2226 @item -Wunused-function
2227 @opindex Wunused-function
2228 Warn whenever a static function is declared but not defined or a
2229 non\-inline static function is unused.
2231 @item -Wunused-label
2232 @opindex Wunused-label
2233 Warn whenever a label is declared but not used.
2235 To suppress this warning use the @samp{unused} attribute
2236 (@pxref{Variable Attributes}).
2238 @item -Wunused-parameter
2239 @opindex Wunused-parameter
2240 Warn whenever a function parameter is unused aside from its declaration.
2242 To suppress this warning use the @samp{unused} attribute
2243 (@pxref{Variable Attributes}).
2245 @item -Wunused-variable
2246 @opindex Wunused-variable
2247 Warn whenever a local variable or non-constant static variable is unused
2248 aside from its declaration
2250 To suppress this warning use the @samp{unused} attribute
2251 (@pxref{Variable Attributes}).
2253 @item -Wunused-value
2254 @opindex Wunused-value
2255 Warn whenever a statement computes a result that is explicitly not used.
2257 To suppress this warning cast the expression to @samp{void}.
2261 All the above @option{-Wunused} options combined.
2263 In order to get a warning about an unused function parameter, you must
2264 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2265 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2267 @item -Wuninitialized
2268 @opindex Wuninitialized
2269 Warn if an automatic variable is used without first being initialized or
2270 if a variable may be clobbered by a @code{setjmp} call.
2272 These warnings are possible only in optimizing compilation,
2273 because they require data flow information that is computed only
2274 when optimizing. If you don't specify @option{-O}, you simply won't
2277 These warnings occur only for variables that are candidates for
2278 register allocation. Therefore, they do not occur for a variable that
2279 is declared @code{volatile}, or whose address is taken, or whose size
2280 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2281 structures, unions or arrays, even when they are in registers.
2283 Note that there may be no warning about a variable that is used only
2284 to compute a value that itself is never used, because such
2285 computations may be deleted by data flow analysis before the warnings
2288 These warnings are made optional because GCC is not smart
2289 enough to see all the reasons why the code might be correct
2290 despite appearing to have an error. Here is one example of how
2311 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2312 always initialized, but GCC doesn't know this. Here is
2313 another common case:
2318 if (change_y) save_y = y, y = new_y;
2320 if (change_y) y = save_y;
2325 This has no bug because @code{save_y} is used only if it is set.
2327 @cindex @code{longjmp} warnings
2328 This option also warns when a non-volatile automatic variable might be
2329 changed by a call to @code{longjmp}. These warnings as well are possible
2330 only in optimizing compilation.
2332 The compiler sees only the calls to @code{setjmp}. It cannot know
2333 where @code{longjmp} will be called; in fact, a signal handler could
2334 call it at any point in the code. As a result, you may get a warning
2335 even when there is in fact no problem because @code{longjmp} cannot
2336 in fact be called at the place which would cause a problem.
2338 Some spurious warnings can be avoided if you declare all the functions
2339 you use that never return as @code{noreturn}. @xref{Function
2342 @item -Wunknown-pragmas
2343 @opindex Wunknown-pragmas
2344 @cindex warning for unknown pragmas
2345 @cindex unknown pragmas, warning
2346 @cindex pragmas, warning of unknown
2347 Warn when a #pragma directive is encountered which is not understood by
2348 GCC@. If this command line option is used, warnings will even be issued
2349 for unknown pragmas in system header files. This is not the case if
2350 the warnings were only enabled by the @option{-Wall} command line option.
2352 @item -Wstrict-aliasing
2353 @opindex Wstrict-aliasing
2354 This option is only active when @option{-fstrict-aliasing} is active.
2355 It warns about code which might break the strict aliasing rules that the
2356 compiler is using for optimization. The warning does not catch all
2357 cases, but does attempt to catch the more common pitfalls. It is
2358 included in @option{-Wall}.
2362 All of the above @samp{-W} options combined. This enables all the
2363 warnings about constructions that some users consider questionable, and
2364 that are easy to avoid (or modify to prevent the warning), even in
2365 conjunction with macros. This also enables some language-specific
2366 warnings described in @ref{C++ Dialect Options} and
2367 @ref{Objective-C Dialect Options}.
2370 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2371 Some of them warn about constructions that users generally do not
2372 consider questionable, but which occasionally you might wish to check
2373 for; others warn about constructions that are necessary or hard to avoid
2374 in some cases, and there is no simple way to modify the code to suppress
2381 (This option used to be called @option{-W}. The older name is still
2382 supported, but the newer name is more descriptive.) Print extra warning
2383 messages for these events:
2387 A function can return either with or without a value. (Falling
2388 off the end of the function body is considered returning without
2389 a value.) For example, this function would evoke such a
2403 An expression-statement or the left-hand side of a comma expression
2404 contains no side effects.
2405 To suppress the warning, cast the unused expression to void.
2406 For example, an expression such as @samp{x[i,j]} will cause a warning,
2407 but @samp{x[(void)i,j]} will not.
2410 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2413 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2414 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2415 that of ordinary mathematical notation.
2418 Storage-class specifiers like @code{static} are not the first things in
2419 a declaration. According to the C Standard, this usage is obsolescent.
2422 The return type of a function has a type qualifier such as @code{const}.
2423 Such a type qualifier has no effect, since the value returned by a
2424 function is not an lvalue. (But don't warn about the GNU extension of
2425 @code{volatile void} return types. That extension will be warned about
2426 if @option{-pedantic} is specified.)
2429 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2433 A comparison between signed and unsigned values could produce an
2434 incorrect result when the signed value is converted to unsigned.
2435 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2438 An aggregate has an initializer which does not initialize all members.
2439 For example, the following code would cause such a warning, because
2440 @code{x.h} would be implicitly initialized to zero:
2443 struct s @{ int f, g, h; @};
2444 struct s x = @{ 3, 4 @};
2448 A function parameter is declared without a type specifier in K&R-style
2456 An empty body occurs in an @samp{if} or @samp{else} statement.
2459 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2460 @samp{>}, or @samp{>=}.
2463 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2466 Any of several floating-point events that often indicate errors, such as
2467 overflow, underflow, loss of precision, etc.
2469 @item @r{(C++ only)}
2470 An enumerator and a non-enumerator both appear in a conditional expression.
2472 @item @r{(C++ only)}
2473 A non-static reference or non-static @samp{const} member appears in a
2474 class without constructors.
2476 @item @r{(C++ only)}
2477 Ambiguous virtual bases.
2479 @item @r{(C++ only)}
2480 Subscripting an array which has been declared @samp{register}.
2482 @item @r{(C++ only)}
2483 Taking the address of a variable which has been declared @samp{register}.
2485 @item @r{(C++ only)}
2486 A base class is not initialized in a derived class' copy constructor.
2489 @item -Wno-div-by-zero
2490 @opindex Wno-div-by-zero
2491 @opindex Wdiv-by-zero
2492 Do not warn about compile-time integer division by zero. Floating point
2493 division by zero is not warned about, as it can be a legitimate way of
2494 obtaining infinities and NaNs.
2496 @item -Wsystem-headers
2497 @opindex Wsystem-headers
2498 @cindex warnings from system headers
2499 @cindex system headers, warnings from
2500 Print warning messages for constructs found in system header files.
2501 Warnings from system headers are normally suppressed, on the assumption
2502 that they usually do not indicate real problems and would only make the
2503 compiler output harder to read. Using this command line option tells
2504 GCC to emit warnings from system headers as if they occurred in user
2505 code. However, note that using @option{-Wall} in conjunction with this
2506 option will @emph{not} warn about unknown pragmas in system
2507 headers---for that, @option{-Wunknown-pragmas} must also be used.
2510 @opindex Wfloat-equal
2511 Warn if floating point values are used in equality comparisons.
2513 The idea behind this is that sometimes it is convenient (for the
2514 programmer) to consider floating-point values as approximations to
2515 infinitely precise real numbers. If you are doing this, then you need
2516 to compute (by analyzing the code, or in some other way) the maximum or
2517 likely maximum error that the computation introduces, and allow for it
2518 when performing comparisons (and when producing output, but that's a
2519 different problem). In particular, instead of testing for equality, you
2520 would check to see whether the two values have ranges that overlap; and
2521 this is done with the relational operators, so equality comparisons are
2524 @item -Wtraditional @r{(C only)}
2525 @opindex Wtraditional
2526 Warn about certain constructs that behave differently in traditional and
2527 ISO C@. Also warn about ISO C constructs that have no traditional C
2528 equivalent, and/or problematic constructs which should be avoided.
2532 Macro parameters that appear within string literals in the macro body.
2533 In traditional C macro replacement takes place within string literals,
2534 but does not in ISO C@.
2537 In traditional C, some preprocessor directives did not exist.
2538 Traditional preprocessors would only consider a line to be a directive
2539 if the @samp{#} appeared in column 1 on the line. Therefore
2540 @option{-Wtraditional} warns about directives that traditional C
2541 understands but would ignore because the @samp{#} does not appear as the
2542 first character on the line. It also suggests you hide directives like
2543 @samp{#pragma} not understood by traditional C by indenting them. Some
2544 traditional implementations would not recognize @samp{#elif}, so it
2545 suggests avoiding it altogether.
2548 A function-like macro that appears without arguments.
2551 The unary plus operator.
2554 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2555 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2556 constants.) Note, these suffixes appear in macros defined in the system
2557 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2558 Use of these macros in user code might normally lead to spurious
2559 warnings, however gcc's integrated preprocessor has enough context to
2560 avoid warning in these cases.
2563 A function declared external in one block and then used after the end of
2567 A @code{switch} statement has an operand of type @code{long}.
2570 A non-@code{static} function declaration follows a @code{static} one.
2571 This construct is not accepted by some traditional C compilers.
2574 The ISO type of an integer constant has a different width or
2575 signedness from its traditional type. This warning is only issued if
2576 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2577 typically represent bit patterns, are not warned about.
2580 Usage of ISO string concatenation is detected.
2583 Initialization of automatic aggregates.
2586 Identifier conflicts with labels. Traditional C lacks a separate
2587 namespace for labels.
2590 Initialization of unions. If the initializer is zero, the warning is
2591 omitted. This is done under the assumption that the zero initializer in
2592 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2593 initializer warnings and relies on default initialization to zero in the
2597 Conversions by prototypes between fixed/floating point values and vice
2598 versa. The absence of these prototypes when compiling with traditional
2599 C would cause serious problems. This is a subset of the possible
2600 conversion warnings, for the full set use @option{-Wconversion}.
2603 Use of ISO C style function definitions. This warning intentionally is
2604 @emph{not} issued for prototype declarations or variadic functions
2605 because these ISO C features will appear in your code when using
2606 libiberty's traditional C compatibility macros, @code{PARAMS} and
2607 @code{VPARAMS}. This warning is also bypassed for nested functions
2608 because that feature is already a gcc extension and thus not relevant to
2609 traditional C compatibility.
2614 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2616 @item -Wendif-labels
2617 @opindex Wendif-labels
2618 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2622 Warn whenever a local variable shadows another local variable, parameter or
2623 global variable or whenever a built-in function is shadowed.
2625 @item -Wlarger-than-@var{len}
2626 @opindex Wlarger-than
2627 Warn whenever an object of larger than @var{len} bytes is defined.
2629 @item -Wpointer-arith
2630 @opindex Wpointer-arith
2631 Warn about anything that depends on the ``size of'' a function type or
2632 of @code{void}. GNU C assigns these types a size of 1, for
2633 convenience in calculations with @code{void *} pointers and pointers
2636 @item -Wbad-function-cast @r{(C only)}
2637 @opindex Wbad-function-cast
2638 Warn whenever a function call is cast to a non-matching type.
2639 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2643 Warn whenever a pointer is cast so as to remove a type qualifier from
2644 the target type. For example, warn if a @code{const char *} is cast
2645 to an ordinary @code{char *}.
2648 @opindex Wcast-align
2649 Warn whenever a pointer is cast such that the required alignment of the
2650 target is increased. For example, warn if a @code{char *} is cast to
2651 an @code{int *} on machines where integers can only be accessed at
2652 two- or four-byte boundaries.
2654 @item -Wwrite-strings
2655 @opindex Wwrite-strings
2656 When compiling C, give string constants the type @code{const
2657 char[@var{length}]} so that
2658 copying the address of one into a non-@code{const} @code{char *}
2659 pointer will get a warning; when compiling C++, warn about the
2660 deprecated conversion from string constants to @code{char *}.
2661 These warnings will help you find at
2662 compile time code that can try to write into a string constant, but
2663 only if you have been very careful about using @code{const} in
2664 declarations and prototypes. Otherwise, it will just be a nuisance;
2665 this is why we did not make @option{-Wall} request these warnings.
2668 @opindex Wconversion
2669 Warn if a prototype causes a type conversion that is different from what
2670 would happen to the same argument in the absence of a prototype. This
2671 includes conversions of fixed point to floating and vice versa, and
2672 conversions changing the width or signedness of a fixed point argument
2673 except when the same as the default promotion.
2675 Also, warn if a negative integer constant expression is implicitly
2676 converted to an unsigned type. For example, warn about the assignment
2677 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2678 casts like @code{(unsigned) -1}.
2680 @item -Wsign-compare
2681 @opindex Wsign-compare
2682 @cindex warning for comparison of signed and unsigned values
2683 @cindex comparison of signed and unsigned values, warning
2684 @cindex signed and unsigned values, comparison warning
2685 Warn when a comparison between signed and unsigned values could produce
2686 an incorrect result when the signed value is converted to unsigned.
2687 This warning is also enabled by @option{-Wextra}; to get the other warnings
2688 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2690 @item -Waggregate-return
2691 @opindex Waggregate-return
2692 Warn if any functions that return structures or unions are defined or
2693 called. (In languages where you can return an array, this also elicits
2696 @item -Wstrict-prototypes @r{(C only)}
2697 @opindex Wstrict-prototypes
2698 Warn if a function is declared or defined without specifying the
2699 argument types. (An old-style function definition is permitted without
2700 a warning if preceded by a declaration which specifies the argument
2703 @item -Wmissing-prototypes @r{(C only)}
2704 @opindex Wmissing-prototypes
2705 Warn if a global function is defined without a previous prototype
2706 declaration. This warning is issued even if the definition itself
2707 provides a prototype. The aim is to detect global functions that fail
2708 to be declared in header files.
2710 @item -Wmissing-declarations @r{(C only)}
2711 @opindex Wmissing-declarations
2712 Warn if a global function is defined without a previous declaration.
2713 Do so even if the definition itself provides a prototype.
2714 Use this option to detect global functions that are not declared in
2717 @item -Wmissing-noreturn
2718 @opindex Wmissing-noreturn
2719 Warn about functions which might be candidates for attribute @code{noreturn}.
2720 Note these are only possible candidates, not absolute ones. Care should
2721 be taken to manually verify functions actually do not ever return before
2722 adding the @code{noreturn} attribute, otherwise subtle code generation
2723 bugs could be introduced. You will not get a warning for @code{main} in
2724 hosted C environments.
2726 @item -Wmissing-format-attribute
2727 @opindex Wmissing-format-attribute
2729 If @option{-Wformat} is enabled, also warn about functions which might be
2730 candidates for @code{format} attributes. Note these are only possible
2731 candidates, not absolute ones. GCC will guess that @code{format}
2732 attributes might be appropriate for any function that calls a function
2733 like @code{vprintf} or @code{vscanf}, but this might not always be the
2734 case, and some functions for which @code{format} attributes are
2735 appropriate may not be detected. This option has no effect unless
2736 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2738 @item -Wno-multichar
2739 @opindex Wno-multichar
2741 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2742 Usually they indicate a typo in the user's code, as they have
2743 implementation-defined values, and should not be used in portable code.
2745 @item -Wno-deprecated-declarations
2746 @opindex Wno-deprecated-declarations
2747 Do not warn about uses of functions, variables, and types marked as
2748 deprecated by using the @code{deprecated} attribute.
2749 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2750 @pxref{Type Attributes}.)
2754 Warn if a structure is given the packed attribute, but the packed
2755 attribute has no effect on the layout or size of the structure.
2756 Such structures may be mis-aligned for little benefit. For
2757 instance, in this code, the variable @code{f.x} in @code{struct bar}
2758 will be misaligned even though @code{struct bar} does not itself
2759 have the packed attribute:
2766 @} __attribute__((packed));
2776 Warn if padding is included in a structure, either to align an element
2777 of the structure or to align the whole structure. Sometimes when this
2778 happens it is possible to rearrange the fields of the structure to
2779 reduce the padding and so make the structure smaller.
2781 @item -Wredundant-decls
2782 @opindex Wredundant-decls
2783 Warn if anything is declared more than once in the same scope, even in
2784 cases where multiple declaration is valid and changes nothing.
2786 @item -Wnested-externs @r{(C only)}
2787 @opindex Wnested-externs
2788 Warn if an @code{extern} declaration is encountered within a function.
2790 @item -Wunreachable-code
2791 @opindex Wunreachable-code
2792 Warn if the compiler detects that code will never be executed.
2794 This option is intended to warn when the compiler detects that at
2795 least a whole line of source code will never be executed, because
2796 some condition is never satisfied or because it is after a
2797 procedure that never returns.
2799 It is possible for this option to produce a warning even though there
2800 are circumstances under which part of the affected line can be executed,
2801 so care should be taken when removing apparently-unreachable code.
2803 For instance, when a function is inlined, a warning may mean that the
2804 line is unreachable in only one inlined copy of the function.
2806 This option is not made part of @option{-Wall} because in a debugging
2807 version of a program there is often substantial code which checks
2808 correct functioning of the program and is, hopefully, unreachable
2809 because the program does work. Another common use of unreachable
2810 code is to provide behavior which is selectable at compile-time.
2814 Warn if a function can not be inlined and it was declared as inline.
2815 Even with this option, the compiler will not warn about failures to
2816 inline functions declared in system headers.
2818 The compiler uses a variety of heuristics to determine whether or not
2819 to inline a function. For example, the compiler takes into account
2820 the size of the function being inlined and the the amount of inlining
2821 that has already been done in the current function. Therefore,
2822 seemingly insignificant changes in the source program can cause the
2823 warnings produced by @option{-Winline} to appear or disappear.
2825 @item -Wno-invalid-offsetof @r{(C++ only)}
2826 @opindex Wno-invalid-offsetof
2827 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2828 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2829 to a non-POD type is undefined. In existing C++ implementations,
2830 however, @samp{offsetof} typically gives meaningful results even when
2831 applied to certain kinds of non-POD types. (Such as a simple
2832 @samp{struct} that fails to be a POD type only by virtue of having a
2833 constructor.) This flag is for users who are aware that they are
2834 writing nonportable code and who have deliberately chosen to ignore the
2837 The restrictions on @samp{offsetof} may be relaxed in a future version
2838 of the C++ standard.
2841 @opindex Winvalid-pch
2842 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2843 the search path but can't be used.
2847 @opindex Wno-long-long
2848 Warn if @samp{long long} type is used. This is default. To inhibit
2849 the warning messages, use @option{-Wno-long-long}. Flags
2850 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2851 only when @option{-pedantic} flag is used.
2853 @item -Wdisabled-optimization
2854 @opindex Wdisabled-optimization
2855 Warn if a requested optimization pass is disabled. This warning does
2856 not generally indicate that there is anything wrong with your code; it
2857 merely indicates that GCC's optimizers were unable to handle the code
2858 effectively. Often, the problem is that your code is too big or too
2859 complex; GCC will refuse to optimize programs when the optimization
2860 itself is likely to take inordinate amounts of time.
2864 Make all warnings into errors.
2867 @node Debugging Options
2868 @section Options for Debugging Your Program or GCC
2869 @cindex options, debugging
2870 @cindex debugging information options
2872 GCC has various special options that are used for debugging
2873 either your program or GCC:
2878 Produce debugging information in the operating system's native format
2879 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
2882 On most systems that use stabs format, @option{-g} enables use of extra
2883 debugging information that only GDB can use; this extra information
2884 makes debugging work better in GDB but will probably make other debuggers
2886 refuse to read the program. If you want to control for certain whether
2887 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
2888 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
2889 or @option{-gvms} (see below).
2891 Unlike most other C compilers, GCC allows you to use @option{-g} with
2892 @option{-O}. The shortcuts taken by optimized code may occasionally
2893 produce surprising results: some variables you declared may not exist
2894 at all; flow of control may briefly move where you did not expect it;
2895 some statements may not be executed because they compute constant
2896 results or their values were already at hand; some statements may
2897 execute in different places because they were moved out of loops.
2899 Nevertheless it proves possible to debug optimized output. This makes
2900 it reasonable to use the optimizer for programs that might have bugs.
2902 The following options are useful when GCC is generated with the
2903 capability for more than one debugging format.
2907 Produce debugging information for use by GDB@. This means to use the
2908 most expressive format available (DWARF 2, stabs, or the native format
2909 if neither of those are supported), including GDB extensions if at all
2914 Produce debugging information in stabs format (if that is supported),
2915 without GDB extensions. This is the format used by DBX on most BSD
2916 systems. On MIPS, Alpha and System V Release 4 systems this option
2917 produces stabs debugging output which is not understood by DBX or SDB@.
2918 On System V Release 4 systems this option requires the GNU assembler.
2920 @item -feliminate-unused-debug-symbols
2921 @opindex feliminate-unused-debug-symbols
2922 Produce debugging information in stabs format (if that is supported),
2923 for only symbols that are actually used.
2927 Produce debugging information in stabs format (if that is supported),
2928 using GNU extensions understood only by the GNU debugger (GDB)@. The
2929 use of these extensions is likely to make other debuggers crash or
2930 refuse to read the program.
2934 Produce debugging information in COFF format (if that is supported).
2935 This is the format used by SDB on most System V systems prior to
2940 Produce debugging information in XCOFF format (if that is supported).
2941 This is the format used by the DBX debugger on IBM RS/6000 systems.
2945 Produce debugging information in XCOFF format (if that is supported),
2946 using GNU extensions understood only by the GNU debugger (GDB)@. The
2947 use of these extensions is likely to make other debuggers crash or
2948 refuse to read the program, and may cause assemblers other than the GNU
2949 assembler (GAS) to fail with an error.
2953 Produce debugging information in DWARF version 1 format (if that is
2954 supported). This is the format used by SDB on most System V Release 4
2957 This option is deprecated.
2961 Produce debugging information in DWARF version 1 format (if that is
2962 supported), using GNU extensions understood only by the GNU debugger
2963 (GDB)@. The use of these extensions is likely to make other debuggers
2964 crash or refuse to read the program.
2966 This option is deprecated.
2970 Produce debugging information in DWARF version 2 format (if that is
2971 supported). This is the format used by DBX on IRIX 6.
2975 Produce debugging information in VMS debug format (if that is
2976 supported). This is the format used by DEBUG on VMS systems.
2979 @itemx -ggdb@var{level}
2980 @itemx -gstabs@var{level}
2981 @itemx -gcoff@var{level}
2982 @itemx -gxcoff@var{level}
2983 @itemx -gvms@var{level}
2984 Request debugging information and also use @var{level} to specify how
2985 much information. The default level is 2.
2987 Level 1 produces minimal information, enough for making backtraces in
2988 parts of the program that you don't plan to debug. This includes
2989 descriptions of functions and external variables, but no information
2990 about local variables and no line numbers.
2992 Level 3 includes extra information, such as all the macro definitions
2993 present in the program. Some debuggers support macro expansion when
2994 you use @option{-g3}.
2996 Note that in order to avoid confusion between DWARF1 debug level 2,
2997 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
2998 a concatenated debug level. Instead use an additional @option{-g@var{level}}
2999 option to change the debug level for DWARF1 or DWARF2.
3001 @item -feliminate-dwarf2-dups
3002 @opindex feliminate-dwarf2-dups
3003 Compress DWARF2 debugging information by eliminating duplicated
3004 information about each symbol. This option only makes sense when
3005 generating DWARF2 debugging information with @option{-gdwarf-2}.
3007 @cindex @command{prof}
3010 Generate extra code to write profile information suitable for the
3011 analysis program @command{prof}. You must use this option when compiling
3012 the source files you want data about, and you must also use it when
3015 @cindex @command{gprof}
3018 Generate extra code to write profile information suitable for the
3019 analysis program @command{gprof}. You must use this option when compiling
3020 the source files you want data about, and you must also use it when
3025 Makes the compiler print out each function name as it is compiled, and
3026 print some statistics about each pass when it finishes.
3029 @opindex ftime-report
3030 Makes the compiler print some statistics about the time consumed by each
3031 pass when it finishes.
3034 @opindex fmem-report
3035 Makes the compiler print some statistics about permanent memory
3036 allocation when it finishes.
3038 @item -fprofile-arcs
3039 @opindex fprofile-arcs
3040 Add code so that program flow @dfn{arcs} are instrumented. During
3041 execution the program records how many times each branch and call is
3042 executed and how many times it is taken or returns. When the compiled
3043 program exits it saves this data to a file called
3044 @file{@var{auxname}.da} for each source file. The data may be used for
3045 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3046 test coverage analysis (@option{-ftest-coverage}). Each object file's
3047 @var{auxname} is generated from the name of the output file, if
3048 explicitly specified and it is not the final executable, otherwise it is
3049 the basename of the source file. In both cases any suffix is removed
3050 (e.g. @file{foo.da} for input file @file{dir/foo.c}, or
3051 @file{dir/foo.da} for output file specified as @option{-o dir/foo.o}).
3056 Compile the source files with @option{-fprofile-arcs} plus optimization
3057 and code generation options. For test coverage analysis, use the
3058 additional @option{-ftest-coverage} option. You do not need to profile
3059 every source file in a program.
3062 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3063 (the latter implies the former).
3066 Run the program on a representative workload to generate the arc profile
3067 information. This may be repeated any number of times. You can run
3068 concurrent instances of your program, and provided that the file system
3069 supports locking, the data files will be correctly updated. Also
3070 @code{fork} calls are detected and correctly handled (double counting
3074 For profile-directed optimizations, compile the source files again with
3075 the same optimization and code generation options plus
3076 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3077 Control Optimization}).
3080 For test coverage analysis, use @command{gcov} to produce human readable
3081 information from the @file{.bbg} and @file{.da} files. Refer to the
3082 @command{gcov} documentation for further information.
3086 With @option{-fprofile-arcs}, for each function of your program GCC
3087 creates a program flow graph, then finds a spanning tree for the graph.
3088 Only arcs that are not on the spanning tree have to be instrumented: the
3089 compiler adds code to count the number of times that these arcs are
3090 executed. When an arc is the only exit or only entrance to a block, the
3091 instrumentation code can be added to the block; otherwise, a new basic
3092 block must be created to hold the instrumentation code.
3095 @item -ftest-coverage
3096 @opindex ftest-coverage
3097 Produce a graph file that the @command{gcov} code-coverage utility
3098 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3099 show program coverage. Each source file's data file is called
3100 @file{@var{auxname}.bbg}. Refer to the @option{-fprofile-arcs} option
3101 above for a description of @var{auxname} and instructions on how to
3102 generate test coverage data. Coverage data will match the source files
3103 more closely, if you do not optimize.
3105 @item -d@var{letters}
3107 Says to make debugging dumps during compilation at times specified by
3108 @var{letters}. This is used for debugging the compiler. The file names
3109 for most of the dumps are made by appending a pass number and a word to
3110 the @var{dumpname}. @var{dumpname} is generated from the name of the
3111 output file, if explicitly specified and it is not an executable,
3112 otherwise it is the basename of the source file. In both cases any
3113 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3114 Here are the possible letters for use in @var{letters}, and their
3120 Annotate the assembler output with miscellaneous debugging information.
3123 Dump after computing branch probabilities, to @file{@var{file}.16.bp}.
3126 Dump after block reordering, to @file{@var{file}.32.bbro}.
3129 Dump after instruction combination, to the file @file{@var{file}.22.combine}.
3132 Dump after the first if conversion, to the file @file{@var{file}.17.ce1}.
3133 Also dump after the second if conversion, to the file @file{@var{file}.23.ce2}.
3136 Dump after branch target load optimization, to to @file{@var{file}.34.btl}.
3137 Also dump after delayed branch scheduling, to @file{@var{file}.37.dbr}.
3140 Dump all macro definitions, at the end of preprocessing, in addition to
3144 Dump after SSA optimizations, to @file{@var{file}.05.ssa} and
3145 @file{@var{file}.010.ussa}.
3148 Dump after the second if conversion, to @file{@var{file}.33.ce3}.
3151 Dump after control and data flow analysis, to @file{@var{file}.15.cfg}.
3152 Also dump after life analysis, to @file{@var{file}.21.life}.
3155 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.11.addressof}.
3158 Dump after global register allocation, to @file{@var{file}.27.greg}.
3161 Dump after GCSE, to @file{@var{file}.12.gcse}.
3162 Also dump after jump bypassing and control flow optimizations, to
3163 @file{@var{file}.14.bypass}.
3166 Dump after finalization of EH handling code, to @file{@var{file}.03.eh}.
3169 Dump after sibling call optimizations, to @file{@var{file}.02.sibling}.
3172 Dump after the first jump optimization, to @file{@var{file}.04.jump}.
3175 Dump after conversion from registers to stack, to @file{@var{file}.36.stack}.
3178 Dump after local register allocation, to @file{@var{file}.26.lreg}.
3181 Dump after loop optimization passes, to @file{@var{file}.13.loop} and
3182 @file{@var{file}.19.loop2}.
3185 Dump after performing the machine dependent reorganization pass, to
3186 @file{@var{file}.37.mach}.
3189 Dump after register renumbering, to @file{@var{file}.31.rnreg}.
3192 Dump after the register move pass, to @file{@var{file}.24.regmove}.
3195 Dump after post-reload optimizations, to @file{@var{file}.28.postreload}.
3198 Dump after RTL generation, to @file{@var{file}.01.rtl}.
3201 Dump after the second scheduling pass, to @file{@var{file}.35.sched2}.
3204 Dump after CSE (including the jump optimization that sometimes follows
3205 CSE), to @file{@var{file}.019.cse}.
3208 Dump after the first scheduling pass, to @file{@var{file}.25.sched}.
3211 Dump after the second CSE pass (including the jump optimization that
3212 sometimes follows CSE), to @file{@var{file}.20.cse2}.
3215 Dump after running tracer, to @file{@var{file}.18.tracer}.
3218 Dump after null pointer elimination pass to @file{@var{file}.018.null}.
3221 Dump callgraph and unit-at-a-time optimization @file{@var{file}.00.unit}.
3224 Dump after the second flow pass, to @file{@var{file}.29.flow2}.
3227 Dump after SSA conditional constant propagation, to
3228 @file{@var{file}.06.ssaccp}.
3231 Dump after SSA dead code elimination, to @file{@var{file}.07.ssadce}.
3234 Dump after the peephole pass, to @file{@var{file}.30.peephole2}.
3237 Produce all the dumps listed above.
3240 Produce a core dump whenever an error occurs.
3243 Print statistics on memory usage, at the end of the run, to
3247 Annotate the assembler output with a comment indicating which
3248 pattern and alternative was used. The length of each instruction is
3252 Dump the RTL in the assembler output as a comment before each instruction.
3253 Also turns on @option{-dp} annotation.
3256 For each of the other indicated dump files (except for
3257 @file{@var{file}.01.rtl}), dump a representation of the control flow graph
3258 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3261 Just generate RTL for a function instead of compiling it. Usually used
3265 Dump debugging information during parsing, to standard error.
3268 @item -fdump-unnumbered
3269 @opindex fdump-unnumbered
3270 When doing debugging dumps (see @option{-d} option above), suppress instruction
3271 numbers and line number note output. This makes it more feasible to
3272 use diff on debugging dumps for compiler invocations with different
3273 options, in particular with and without @option{-g}.
3275 @item -fdump-translation-unit @r{(C and C++ only)}
3276 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3277 @opindex fdump-translation-unit
3278 Dump a representation of the tree structure for the entire translation
3279 unit to a file. The file name is made by appending @file{.tu} to the
3280 source file name. If the @samp{-@var{options}} form is used, @var{options}
3281 controls the details of the dump as described for the
3282 @option{-fdump-tree} options.
3284 @item -fdump-class-hierarchy @r{(C++ only)}
3285 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3286 @opindex fdump-class-hierarchy
3287 Dump a representation of each class's hierarchy and virtual function
3288 table layout to a file. The file name is made by appending @file{.class}
3289 to the source file name. If the @samp{-@var{options}} form is used,
3290 @var{options} controls the details of the dump as described for the
3291 @option{-fdump-tree} options.
3293 @item -fdump-tree-@var{switch} @r{(C++ only)}
3294 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3296 Control the dumping at various stages of processing the intermediate
3297 language tree to a file. The file name is generated by appending a switch
3298 specific suffix to the source file name. If the @samp{-@var{options}}
3299 form is used, @var{options} is a list of @samp{-} separated options that
3300 control the details of the dump. Not all options are applicable to all
3301 dumps, those which are not meaningful will be ignored. The following
3302 options are available
3306 Print the address of each node. Usually this is not meaningful as it
3307 changes according to the environment and source file. Its primary use
3308 is for tying up a dump file with a debug environment.
3310 Inhibit dumping of members of a scope or body of a function merely
3311 because that scope has been reached. Only dump such items when they
3312 are directly reachable by some other path.
3314 Turn on all options.
3317 The following tree dumps are possible:
3320 Dump before any tree based optimization, to @file{@var{file}.original}.
3322 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3324 Dump after function inlining, to @file{@var{file}.inlined}.
3327 @item -frandom-seed=@var{string}
3328 @opindex frandom-string
3329 This option provides a seed that GCC uses when it would otherwise use
3330 random numbers. It is used to generate certain symbol names
3331 that have to be different in every compiled file. It is also used to
3332 place unique stamps in coverage data files and the object files that
3333 produce them. You can use the @option{-frandom-seed} option to produce
3334 reproducibly identical object files.
3336 The @var{string} should be different for every file you compile.
3338 @item -fsched-verbose=@var{n}
3339 @opindex fsched-verbose
3340 On targets that use instruction scheduling, this option controls the
3341 amount of debugging output the scheduler prints. This information is
3342 written to standard error, unless @option{-dS} or @option{-dR} is
3343 specified, in which case it is output to the usual dump
3344 listing file, @file{.sched} or @file{.sched2} respectively. However
3345 for @var{n} greater than nine, the output is always printed to standard
3348 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3349 same information as @option{-dRS}. For @var{n} greater than one, it
3350 also output basic block probabilities, detailed ready list information
3351 and unit/insn info. For @var{n} greater than two, it includes RTL
3352 at abort point, control-flow and regions info. And for @var{n} over
3353 four, @option{-fsched-verbose} also includes dependence info.
3357 Store the usual ``temporary'' intermediate files permanently; place them
3358 in the current directory and name them based on the source file. Thus,
3359 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3360 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3361 preprocessed @file{foo.i} output file even though the compiler now
3362 normally uses an integrated preprocessor.
3366 Report the CPU time taken by each subprocess in the compilation
3367 sequence. For C source files, this is the compiler proper and assembler
3368 (plus the linker if linking is done). The output looks like this:
3375 The first number on each line is the ``user time,'' that is time spent
3376 executing the program itself. The second number is ``system time,''
3377 time spent executing operating system routines on behalf of the program.
3378 Both numbers are in seconds.
3380 @item -print-file-name=@var{library}
3381 @opindex print-file-name
3382 Print the full absolute name of the library file @var{library} that
3383 would be used when linking---and don't do anything else. With this
3384 option, GCC does not compile or link anything; it just prints the
3387 @item -print-multi-directory
3388 @opindex print-multi-directory
3389 Print the directory name corresponding to the multilib selected by any
3390 other switches present in the command line. This directory is supposed
3391 to exist in @env{GCC_EXEC_PREFIX}.
3393 @item -print-multi-lib
3394 @opindex print-multi-lib
3395 Print the mapping from multilib directory names to compiler switches
3396 that enable them. The directory name is separated from the switches by
3397 @samp{;}, and each switch starts with an @samp{@@} instead of the
3398 @samp{-}, without spaces between multiple switches. This is supposed to
3399 ease shell-processing.
3401 @item -print-prog-name=@var{program}
3402 @opindex print-prog-name
3403 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3405 @item -print-libgcc-file-name
3406 @opindex print-libgcc-file-name
3407 Same as @option{-print-file-name=libgcc.a}.
3409 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3410 but you do want to link with @file{libgcc.a}. You can do
3413 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3416 @item -print-search-dirs
3417 @opindex print-search-dirs
3418 Print the name of the configured installation directory and a list of
3419 program and library directories gcc will search---and don't do anything else.
3421 This is useful when gcc prints the error message
3422 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3423 To resolve this you either need to put @file{cpp0} and the other compiler
3424 components where gcc expects to find them, or you can set the environment
3425 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3426 Don't forget the trailing '/'.
3427 @xref{Environment Variables}.
3430 @opindex dumpmachine
3431 Print the compiler's target machine (for example,
3432 @samp{i686-pc-linux-gnu})---and don't do anything else.
3435 @opindex dumpversion
3436 Print the compiler version (for example, @samp{3.0})---and don't do
3441 Print the compiler's built-in specs---and don't do anything else. (This
3442 is used when GCC itself is being built.) @xref{Spec Files}.
3444 @item -feliminate-unused-debug-types
3445 @opindex feliminate-unused-debug-types
3446 Normally, when producing DWARF2 output, GCC will emit debugging
3447 information for all types declared in a compilation
3448 unit, regardless of whether or not they are actually used
3449 in that compilation unit. Sometimes this is useful, such as
3450 if, in the debugger, you want to cast a value to a type that is
3451 not actually used in your program (but is declared). More often,
3452 however, this results in a significant amount of wasted space.
3453 With this option, GCC will avoid producing debug symbol output
3454 for types that are nowhere used in the source file being compiled.
3457 @node Optimize Options
3458 @section Options That Control Optimization
3459 @cindex optimize options
3460 @cindex options, optimization
3462 These options control various sorts of optimizations.
3464 Without any optimization option, the compiler's goal is to reduce the
3465 cost of compilation and to make debugging produce the expected
3466 results. Statements are independent: if you stop the program with a
3467 breakpoint between statements, you can then assign a new value to any
3468 variable or change the program counter to any other statement in the
3469 function and get exactly the results you would expect from the source
3472 Turning on optimization flags makes the compiler attempt to improve
3473 the performance and/or code size at the expense of compilation time
3474 and possibly the ability to debug the program.
3476 The compiler performs optimisation based on the knowledge it has of
3477 the program. Using the @option{-funit-at-a-time} flag will allow the
3478 compiler to consider information gained from later functions in the
3479 file when compiling a function. Compiling multiple files at once to a
3480 single output file (and using @option{-funit-at-a-time}) will allow
3481 the compiler to use information gained from all of the files when
3482 compiling each of them.
3484 Not all optimizations are controlled directly by a flag. Only
3485 optimizations that have a flag are listed.
3492 Optimize. Optimizing compilation takes somewhat more time, and a lot
3493 more memory for a large function.
3495 With @option{-O}, the compiler tries to reduce code size and execution
3496 time, without performing any optimizations that take a great deal of
3499 @option{-O} turns on the following optimization flags:
3500 @gccoptlist{-fdefer-pop @gol
3501 -fmerge-constants @gol
3503 -floop-optimize @gol
3505 -fif-conversion @gol
3506 -fif-conversion2 @gol
3507 -fdelayed-branch @gol
3508 -fguess-branch-probability @gol
3511 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3512 where doing so does not interfere with debugging.
3516 Optimize even more. GCC performs nearly all supported optimizations
3517 that do not involve a space-speed tradeoff. The compiler does not
3518 perform loop unrolling or function inlining when you specify @option{-O2}.
3519 As compared to @option{-O}, this option increases both compilation time
3520 and the performance of the generated code.
3522 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3523 also turns on the following optimization flags:
3524 @gccoptlist{-fforce-mem @gol
3525 -foptimize-sibling-calls @gol
3526 -fstrength-reduce @gol
3527 -fcse-follow-jumps -fcse-skip-blocks @gol
3528 -frerun-cse-after-loop -frerun-loop-opt @gol
3529 -fgcse -fgcse-lm -fgcse-sm @gol
3530 -fdelete-null-pointer-checks @gol
3531 -fexpensive-optimizations @gol
3533 -fschedule-insns -fschedule-insns2 @gol
3534 -fsched-interblock -fsched-spec @gol
3537 -freorder-blocks -freorder-functions @gol
3538 -fstrict-aliasing @gol
3539 -falign-functions -falign-jumps @gol
3540 -falign-loops -falign-labels}
3542 Please note the warning under @option{-fgcse} about
3543 invoking @option{-O2} on programs that use computed gotos.
3547 Optimize yet more. @option{-O3} turns on all optimizations specified by
3548 @option{-O2} and also turns on the @option{-finline-functions},
3549 @option{-funit-at-a-time} and @option{-frename-registers} options.
3553 Do not optimize. This is the default.
3557 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3558 do not typically increase code size. It also performs further
3559 optimizations designed to reduce code size.
3561 @option{-Os} disables the following optimization flags:
3562 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3563 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3565 If you use multiple @option{-O} options, with or without level numbers,
3566 the last such option is the one that is effective.
3569 Options of the form @option{-f@var{flag}} specify machine-independent
3570 flags. Most flags have both positive and negative forms; the negative
3571 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3572 below, only one of the forms is listed---the one you typically will
3573 use. You can figure out the other form by either removing @samp{no-}
3576 The following options control specific optimizations. They are either
3577 activated by @option{-O} options or are related to ones that are. You
3578 can use the following flags in the rare cases when ``fine-tuning'' of
3579 optimizations to be performed is desired.
3582 @item -fno-default-inline
3583 @opindex fno-default-inline
3584 Do not make member functions inline by default merely because they are
3585 defined inside the class scope (C++ only). Otherwise, when you specify
3586 @w{@option{-O}}, member functions defined inside class scope are compiled
3587 inline by default; i.e., you don't need to add @samp{inline} in front of
3588 the member function name.
3590 @item -fno-defer-pop
3591 @opindex fno-defer-pop
3592 Always pop the arguments to each function call as soon as that function
3593 returns. For machines which must pop arguments after a function call,
3594 the compiler normally lets arguments accumulate on the stack for several
3595 function calls and pops them all at once.
3597 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3601 Force memory operands to be copied into registers before doing
3602 arithmetic on them. This produces better code by making all memory
3603 references potential common subexpressions. When they are not common
3604 subexpressions, instruction combination should eliminate the separate
3607 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3610 @opindex fforce-addr
3611 Force memory address constants to be copied into registers before
3612 doing arithmetic on them. This may produce better code just as
3613 @option{-fforce-mem} may.
3615 @item -fomit-frame-pointer
3616 @opindex fomit-frame-pointer
3617 Don't keep the frame pointer in a register for functions that
3618 don't need one. This avoids the instructions to save, set up and
3619 restore frame pointers; it also makes an extra register available
3620 in many functions. @strong{It also makes debugging impossible on
3623 On some machines, such as the VAX, this flag has no effect, because
3624 the standard calling sequence automatically handles the frame pointer
3625 and nothing is saved by pretending it doesn't exist. The
3626 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3627 whether a target machine supports this flag. @xref{Registers,,Register
3628 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3630 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3632 @item -foptimize-sibling-calls
3633 @opindex foptimize-sibling-calls
3634 Optimize sibling and tail recursive calls.
3636 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3640 Don't pay attention to the @code{inline} keyword. Normally this option
3641 is used to keep the compiler from expanding any functions inline.
3642 Note that if you are not optimizing, no functions can be expanded inline.
3644 @item -finline-functions
3645 @opindex finline-functions
3646 Integrate all simple functions into their callers. The compiler
3647 heuristically decides which functions are simple enough to be worth
3648 integrating in this way.
3650 If all calls to a given function are integrated, and the function is
3651 declared @code{static}, then the function is normally not output as
3652 assembler code in its own right.
3654 Enabled at level @option{-O3}.
3656 @item -finline-limit=@var{n}
3657 @opindex finline-limit
3658 By default, gcc limits the size of functions that can be inlined. This flag
3659 allows the control of this limit for functions that are explicitly marked as
3660 inline (i.e., marked with the inline keyword or defined within the class
3661 definition in c++). @var{n} is the size of functions that can be inlined in
3662 number of pseudo instructions (not counting parameter handling). The default
3663 value of @var{n} is 600.
3664 Increasing this value can result in more inlined code at
3665 the cost of compilation time and memory consumption. Decreasing usually makes
3666 the compilation faster and less code will be inlined (which presumably
3667 means slower programs). This option is particularly useful for programs that
3668 use inlining heavily such as those based on recursive templates with C++.
3670 Inlining is actually controlled by a number of parameters, which may be
3671 specified individually by using @option{--param @var{name}=@var{value}}.
3672 The @option{-finline-limit=@var{n}} option sets some of these parameters
3676 @item max-inline-insns
3678 @item max-inline-insns-single
3679 is set to @var{n}/2.
3680 @item max-inline-insns-auto
3681 is set to @var{n}/2.
3682 @item min-inline-insns
3683 is set to 130 or @var{n}/4, whichever is smaller.
3684 @item max-inline-insns-rtl
3688 Using @option{-finline-limit=600} thus results in the default settings
3689 for these parameters. See below for a documentation of the individual
3690 parameters controlling inlining.
3692 @emph{Note:} pseudo instruction represents, in this particular context, an
3693 abstract measurement of function's size. In no way, it represents a count
3694 of assembly instructions and as such its exact meaning might change from one
3695 release to an another.
3697 @item -fkeep-inline-functions
3698 @opindex fkeep-inline-functions
3699 Even if all calls to a given function are integrated, and the function
3700 is declared @code{static}, nevertheless output a separate run-time
3701 callable version of the function. This switch does not affect
3702 @code{extern inline} functions.
3704 @item -fkeep-static-consts
3705 @opindex fkeep-static-consts
3706 Emit variables declared @code{static const} when optimization isn't turned
3707 on, even if the variables aren't referenced.
3709 GCC enables this option by default. If you want to force the compiler to
3710 check if the variable was referenced, regardless of whether or not
3711 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3713 @item -fmerge-constants
3714 Attempt to merge identical constants (string constants and floating point
3715 constants) across compilation units.
3717 This option is the default for optimized compilation if the assembler and
3718 linker support it. Use @option{-fno-merge-constants} to inhibit this
3721 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3723 @item -fmerge-all-constants
3724 Attempt to merge identical constants and identical variables.
3726 This option implies @option{-fmerge-constants}. In addition to
3727 @option{-fmerge-constants} this considers e.g. even constant initialized
3728 arrays or initialized constant variables with integral or floating point
3729 types. Languages like C or C++ require each non-automatic variable to
3730 have distinct location, so using this option will result in non-conforming
3735 Use a graph coloring register allocator. Currently this option is meant
3736 for testing, so we are interested to hear about miscompilations with
3739 @item -fno-branch-count-reg
3740 @opindex fno-branch-count-reg
3741 Do not use ``decrement and branch'' instructions on a count register,
3742 but instead generate a sequence of instructions that decrement a
3743 register, compare it against zero, then branch based upon the result.
3744 This option is only meaningful on architectures that support such
3745 instructions, which include x86, PowerPC, IA-64 and S/390.
3747 The default is @option{-fbranch-count-reg}, enabled when
3748 @option{-fstrength-reduce} is enabled.
3750 @item -fno-function-cse
3751 @opindex fno-function-cse
3752 Do not put function addresses in registers; make each instruction that
3753 calls a constant function contain the function's address explicitly.
3755 This option results in less efficient code, but some strange hacks
3756 that alter the assembler output may be confused by the optimizations
3757 performed when this option is not used.
3759 The default is @option{-ffunction-cse}
3761 @item -fno-zero-initialized-in-bss
3762 @opindex fno-zero-initialized-in-bss
3763 If the target supports a BSS section, GCC by default puts variables that
3764 are initialized to zero into BSS@. This can save space in the resulting
3767 This option turns off this behavior because some programs explicitly
3768 rely on variables going to the data section. E.g., so that the
3769 resulting executable can find the beginning of that section and/or make
3770 assumptions based on that.
3772 The default is @option{-fzero-initialized-in-bss}.
3774 @item -fstrength-reduce
3775 @opindex fstrength-reduce
3776 Perform the optimizations of loop strength reduction and
3777 elimination of iteration variables.
3779 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3781 @item -fthread-jumps
3782 @opindex fthread-jumps
3783 Perform optimizations where we check to see if a jump branches to a
3784 location where another comparison subsumed by the first is found. If
3785 so, the first branch is redirected to either the destination of the
3786 second branch or a point immediately following it, depending on whether
3787 the condition is known to be true or false.
3789 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3791 @item -fcse-follow-jumps
3792 @opindex fcse-follow-jumps
3793 In common subexpression elimination, scan through jump instructions
3794 when the target of the jump is not reached by any other path. For
3795 example, when CSE encounters an @code{if} statement with an
3796 @code{else} clause, CSE will follow the jump when the condition
3799 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3801 @item -fcse-skip-blocks
3802 @opindex fcse-skip-blocks
3803 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3804 follow jumps which conditionally skip over blocks. When CSE
3805 encounters a simple @code{if} statement with no else clause,
3806 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3807 body of the @code{if}.
3809 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3811 @item -frerun-cse-after-loop
3812 @opindex frerun-cse-after-loop
3813 Re-run common subexpression elimination after loop optimizations has been
3816 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3818 @item -frerun-loop-opt
3819 @opindex frerun-loop-opt
3820 Run the loop optimizer twice.
3822 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3826 Perform a global common subexpression elimination pass.
3827 This pass also performs global constant and copy propagation.
3829 @emph{Note:} When compiling a program using computed gotos, a GCC
3830 extension, you may get better runtime performance if you disable
3831 the global common subexpression elimination pass by adding
3832 @option{-fno-gcse} to the command line.
3834 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3838 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3839 attempt to move loads which are only killed by stores into themselves. This
3840 allows a loop containing a load/store sequence to be changed to a load outside
3841 the loop, and a copy/store within the loop.
3843 Enabled by default when gcse is enabled.
3847 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3848 subexpression elimination. This pass will attempt to move stores out of loops.
3849 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3850 can be changed to a load before the loop and a store after the loop.
3852 Enabled by default when gcse is enabled.
3854 @item -floop-optimize
3855 @opindex floop-optimize
3856 Perform loop optimizations: move constant expressions out of loops, simplify
3857 exit test conditions and optionally do strength-reduction and loop unrolling as
3860 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3862 @item -fcrossjumping
3863 @opindex crossjumping
3864 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
3865 resulting code may or may not perform better than without cross-jumping.
3867 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3869 @item -fif-conversion
3870 @opindex if-conversion
3871 Attempt to transform conditional jumps into branch-less equivalents. This
3872 include use of conditional moves, min, max, set flags and abs instructions, and
3873 some tricks doable by standard arithmetics. The use of conditional execution
3874 on chips where it is available is controlled by @code{if-conversion2}.
3876 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3878 @item -fif-conversion2
3879 @opindex if-conversion2
3880 Use conditional execution (where available) to transform conditional jumps into
3881 branch-less equivalents.
3883 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3885 @item -fdelete-null-pointer-checks
3886 @opindex fdelete-null-pointer-checks
3887 Use global dataflow analysis to identify and eliminate useless checks
3888 for null pointers. The compiler assumes that dereferencing a null
3889 pointer would have halted the program. If a pointer is checked after
3890 it has already been dereferenced, it cannot be null.
3892 In some environments, this assumption is not true, and programs can
3893 safely dereference null pointers. Use
3894 @option{-fno-delete-null-pointer-checks} to disable this optimization
3895 for programs which depend on that behavior.
3897 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3899 @item -fexpensive-optimizations
3900 @opindex fexpensive-optimizations
3901 Perform a number of minor optimizations that are relatively expensive.
3903 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3905 @item -foptimize-register-move
3907 @opindex foptimize-register-move
3909 Attempt to reassign register numbers in move instructions and as
3910 operands of other simple instructions in order to maximize the amount of
3911 register tying. This is especially helpful on machines with two-operand
3914 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
3917 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3919 @item -fdelayed-branch
3920 @opindex fdelayed-branch
3921 If supported for the target machine, attempt to reorder instructions
3922 to exploit instruction slots available after delayed branch
3925 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3927 @item -fschedule-insns
3928 @opindex fschedule-insns
3929 If supported for the target machine, attempt to reorder instructions to
3930 eliminate execution stalls due to required data being unavailable. This
3931 helps machines that have slow floating point or memory load instructions
3932 by allowing other instructions to be issued until the result of the load
3933 or floating point instruction is required.
3935 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3937 @item -fschedule-insns2
3938 @opindex fschedule-insns2
3939 Similar to @option{-fschedule-insns}, but requests an additional pass of
3940 instruction scheduling after register allocation has been done. This is
3941 especially useful on machines with a relatively small number of
3942 registers and where memory load instructions take more than one cycle.
3944 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3946 @item -fno-sched-interblock
3947 @opindex fno-sched-interblock
3948 Don't schedule instructions across basic blocks. This is normally
3949 enabled by default when scheduling before register allocation, i.e.@:
3950 with @option{-fschedule-insns} or at @option{-O2} or higher.
3952 @item -fno-sched-spec
3953 @opindex fno-sched-spec
3954 Don't allow speculative motion of non-load instructions. This is normally
3955 enabled by default when scheduling before register allocation, i.e.@:
3956 with @option{-fschedule-insns} or at @option{-O2} or higher.
3958 @item -fsched-spec-load
3959 @opindex fsched-spec-load
3960 Allow speculative motion of some load instructions. This only makes
3961 sense when scheduling before register allocation, i.e.@: with
3962 @option{-fschedule-insns} or at @option{-O2} or higher.
3964 @item -fsched-spec-load-dangerous
3965 @opindex fsched-spec-load-dangerous
3966 Allow speculative motion of more load instructions. This only makes
3967 sense when scheduling before register allocation, i.e.@: with
3968 @option{-fschedule-insns} or at @option{-O2} or higher.
3970 @item -fsched2-use-superblocks
3971 @opindex fsched2-use-superblocks
3972 When scheduling after register allocation, do use superblock scheduling
3973 algorithm. Superblock scheduling allows motion across basic block boundaries
3974 resulting on faster schedules. This option is experimental, as not all machine
3975 descriptions used by GCC model the CPU closely enough to avoid unreliable
3976 results from the algorithm.
3978 This only makes sense when scheduling after register allocation, i.e.@: with
3979 @option{-fschedule-insns2} or at @option{-O2} or higher.
3981 @item -fsched2-use-traces
3982 @opindex fsched2-use-traces
3983 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
3984 allocation and additionally perform code duplication in order to increase the
3985 size of superblocks using tracer pass. See @option{-ftracer} for details on
3988 This mode should produce faster but significantly longer programs. Also
3989 without @code{-fbranch-probabilities} the traces constructed may not match the
3990 reality and hurt the performance. This only makes
3991 sense when scheduling after register allocation, i.e.@: with
3992 @option{-fschedule-insns2} or at @option{-O2} or higher.
3994 @item -fcaller-saves
3995 @opindex fcaller-saves
3996 Enable values to be allocated in registers that will be clobbered by
3997 function calls, by emitting extra instructions to save and restore the
3998 registers around such calls. Such allocation is done only when it
3999 seems to result in better code than would otherwise be produced.
4001 This option is always enabled by default on certain machines, usually
4002 those which have no call-preserved registers to use instead.
4004 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4006 @item -fmove-all-movables
4007 @opindex fmove-all-movables
4008 Forces all invariant computations in loops to be moved
4011 @item -freduce-all-givs
4012 @opindex freduce-all-givs
4013 Forces all general-induction variables in loops to be
4016 @emph{Note:} When compiling programs written in Fortran,
4017 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
4018 by default when you use the optimizer.
4020 These options may generate better or worse code; results are highly
4021 dependent on the structure of loops within the source code.
4023 These two options are intended to be removed someday, once
4024 they have helped determine the efficacy of various
4025 approaches to improving loop optimizations.
4027 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
4028 know how use of these options affects
4029 the performance of your production code.
4030 We're very interested in code that runs @emph{slower}
4031 when these options are @emph{enabled}.
4034 @itemx -fno-peephole2
4035 @opindex fno-peephole
4036 @opindex fno-peephole2
4037 Disable any machine-specific peephole optimizations. The difference
4038 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4039 are implemented in the compiler; some targets use one, some use the
4040 other, a few use both.
4042 @option{-fpeephole} is enabled by default.
4043 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4045 @item -fno-guess-branch-probability
4046 @opindex fno-guess-branch-probability
4047 Do not guess branch probabilities using a randomized model.
4049 Sometimes gcc will opt to use a randomized model to guess branch
4050 probabilities, when none are available from either profiling feedback
4051 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4052 different runs of the compiler on the same program may produce different
4055 In a hard real-time system, people don't want different runs of the
4056 compiler to produce code that has different behavior; minimizing
4057 non-determinism is of paramount import. This switch allows users to
4058 reduce non-determinism, possibly at the expense of inferior
4061 The default is @option{-fguess-branch-probability} at levels
4062 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4064 @item -freorder-blocks
4065 @opindex freorder-blocks
4066 Reorder basic blocks in the compiled function in order to reduce number of
4067 taken branches and improve code locality.
4069 Enabled at levels @option{-O2}, @option{-O3}.
4071 @item -freorder-functions
4072 @opindex freorder-functions
4073 Reorder basic blocks in the compiled function in order to reduce number of
4074 taken branches and improve code locality. This is implemented by using special
4075 subsections @code{text.hot} for most frequently executed functions and
4076 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4077 the linker so object file format must support named sections and linker must
4078 place them in a reasonable way.
4080 Also profile feedback must be available in to make this option effective. See
4081 @option{-fprofile-arcs} for details.
4083 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4085 @item -fstrict-aliasing
4086 @opindex fstrict-aliasing
4087 Allows the compiler to assume the strictest aliasing rules applicable to
4088 the language being compiled. For C (and C++), this activates
4089 optimizations based on the type of expressions. In particular, an
4090 object of one type is assumed never to reside at the same address as an
4091 object of a different type, unless the types are almost the same. For
4092 example, an @code{unsigned int} can alias an @code{int}, but not a
4093 @code{void*} or a @code{double}. A character type may alias any other
4096 Pay special attention to code like this:
4109 The practice of reading from a different union member than the one most
4110 recently written to (called ``type-punning'') is common. Even with
4111 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4112 is accessed through the union type. So, the code above will work as
4113 expected. However, this code might not:
4124 Every language that wishes to perform language-specific alias analysis
4125 should define a function that computes, given an @code{tree}
4126 node, an alias set for the node. Nodes in different alias sets are not
4127 allowed to alias. For an example, see the C front-end function
4128 @code{c_get_alias_set}.
4130 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4132 @item -falign-functions
4133 @itemx -falign-functions=@var{n}
4134 @opindex falign-functions
4135 Align the start of functions to the next power-of-two greater than
4136 @var{n}, skipping up to @var{n} bytes. For instance,
4137 @option{-falign-functions=32} aligns functions to the next 32-byte
4138 boundary, but @option{-falign-functions=24} would align to the next
4139 32-byte boundary only if this can be done by skipping 23 bytes or less.
4141 @option{-fno-align-functions} and @option{-falign-functions=1} are
4142 equivalent and mean that functions will not be aligned.
4144 Some assemblers only support this flag when @var{n} is a power of two;
4145 in that case, it is rounded up.
4147 If @var{n} is not specified or is zero, use a machine-dependent default.
4149 Enabled at levels @option{-O2}, @option{-O3}.
4151 @item -falign-labels
4152 @itemx -falign-labels=@var{n}
4153 @opindex falign-labels
4154 Align all branch targets to a power-of-two boundary, skipping up to
4155 @var{n} bytes like @option{-falign-functions}. This option can easily
4156 make code slower, because it must insert dummy operations for when the
4157 branch target is reached in the usual flow of the code.
4159 @option{-fno-align-labels} and @option{-falign-labels=1} are
4160 equivalent and mean that labels will not be aligned.
4162 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4163 are greater than this value, then their values are used instead.
4165 If @var{n} is not specified or is zero, use a machine-dependent default
4166 which is very likely to be @samp{1}, meaning no alignment.
4168 Enabled at levels @option{-O2}, @option{-O3}.
4171 @itemx -falign-loops=@var{n}
4172 @opindex falign-loops
4173 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4174 like @option{-falign-functions}. The hope is that the loop will be
4175 executed many times, which will make up for any execution of the dummy
4178 @option{-fno-align-loops} and @option{-falign-loops=1} are
4179 equivalent and mean that loops will not be aligned.
4181 If @var{n} is not specified or is zero, use a machine-dependent default.
4183 Enabled at levels @option{-O2}, @option{-O3}.
4186 @itemx -falign-jumps=@var{n}
4187 @opindex falign-jumps
4188 Align branch targets to a power-of-two boundary, for branch targets
4189 where the targets can only be reached by jumping, skipping up to @var{n}
4190 bytes like @option{-falign-functions}. In this case, no dummy operations
4193 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4194 equivalent and mean that loops will not be aligned.
4196 If @var{n} is not specified or is zero, use a machine-dependent default.
4198 Enabled at levels @option{-O2}, @option{-O3}.
4200 @item -frename-registers
4201 @opindex frename-registers
4202 Attempt to avoid false dependencies in scheduled code by making use
4203 of registers left over after register allocation. This optimization
4204 will most benefit processors with lots of registers. It can, however,
4205 make debugging impossible, since variables will no longer stay in
4206 a ``home register''.
4208 Enabled at levels @option{-O3}.
4210 @item -fno-cprop-registers
4211 @opindex fno-cprop-registers
4212 After register allocation and post-register allocation instruction splitting,
4213 we perform a copy-propagation pass to try to reduce scheduling dependencies
4214 and occasionally eliminate the copy.
4216 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4220 The following options control compiler behavior regarding floating
4221 point arithmetic. These options trade off between speed and
4222 correctness. All must be specifically enabled.
4226 @opindex ffloat-store
4227 Do not store floating point variables in registers, and inhibit other
4228 options that might change whether a floating point value is taken from a
4231 @cindex floating point precision
4232 This option prevents undesirable excess precision on machines such as
4233 the 68000 where the floating registers (of the 68881) keep more
4234 precision than a @code{double} is supposed to have. Similarly for the
4235 x86 architecture. For most programs, the excess precision does only
4236 good, but a few programs rely on the precise definition of IEEE floating
4237 point. Use @option{-ffloat-store} for such programs, after modifying
4238 them to store all pertinent intermediate computations into variables.
4242 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4243 @option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
4244 @option{-fno-signaling-nans}.
4246 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4248 This option should never be turned on by any @option{-O} option since
4249 it can result in incorrect output for programs which depend on
4250 an exact implementation of IEEE or ISO rules/specifications for
4253 @item -fno-math-errno
4254 @opindex fno-math-errno
4255 Do not set ERRNO after calling math functions that are executed
4256 with a single instruction, e.g., sqrt. A program that relies on
4257 IEEE exceptions for math error handling may want to use this flag
4258 for speed while maintaining IEEE arithmetic compatibility.
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{-fmath-errno}.
4267 @item -funsafe-math-optimizations
4268 @opindex funsafe-math-optimizations
4269 Allow optimizations for floating-point arithmetic that (a) assume
4270 that arguments and results are valid and (b) may violate IEEE or
4271 ANSI standards. When used at link-time, it may include libraries
4272 or startup files that change the default FPU control word or other
4273 similar optimizations.
4275 This option should never be turned on by any @option{-O} option since
4276 it can result in incorrect output for programs which depend on
4277 an exact implementation of IEEE or ISO rules/specifications for
4280 The default is @option{-fno-unsafe-math-optimizations}.
4282 @item -ffinite-math-only
4283 @opindex ffinite-math-only
4284 Allow optimizations for floating-point arithmetic that assume
4285 that arguments and results are not NaNs or +-Infs.
4287 This option should never be turned on by any @option{-O} option since
4288 it can result in incorrect output for programs which depend on
4289 an exact implementation of IEEE or ISO rules/specifications.
4291 The default is @option{-fno-finite-math-only}.
4293 @item -fno-trapping-math
4294 @opindex fno-trapping-math
4295 Compile code assuming that floating-point operations cannot generate
4296 user-visible traps. These traps include division by zero, overflow,
4297 underflow, inexact result and invalid operation. This option implies
4298 @option{-fno-signaling-nans}. Setting this option may allow faster
4299 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4301 This option should never be turned on by any @option{-O} option since
4302 it can result in incorrect output for programs which depend on
4303 an exact implementation of IEEE or ISO rules/specifications for
4306 The default is @option{-ftrapping-math}.
4308 @item -fsignaling-nans
4309 @opindex fsignaling-nans
4310 Compile code assuming that IEEE signaling NaNs may generate user-visible
4311 traps during floating-point operations. Setting this option disables
4312 optimizations that may change the number of exceptions visible with
4313 signaling NaNs. This option implies @option{-ftrapping-math}.
4315 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4318 The default is @option{-fno-signaling-nans}.
4320 This option is experimental and does not currently guarantee to
4321 disable all GCC optimizations that affect signaling NaN behavior.
4323 @item -fsingle-precision-constant
4324 @opindex fsingle-precision-constant
4325 Treat floating point constant as single precision constant instead of
4326 implicitly converting it to double precision constant.
4331 The following options control optimizations that may improve
4332 performance, but are not enabled by any @option{-O} options. This
4333 section includes experimental options that may produce broken code.
4336 @item -fbranch-probabilities
4337 @opindex fbranch-probabilities
4338 After running a program compiled with @option{-fprofile-arcs}
4339 (@pxref{Debugging Options,, Options for Debugging Your Program or
4340 @command{gcc}}), you can compile it a second time using
4341 @option{-fbranch-probabilities}, to improve optimizations based on
4342 the number of times each branch was taken. When the program
4343 compiled with @option{-fprofile-arcs} exits it saves arc execution
4344 counts to a file called @file{@var{sourcename}.da} for each source
4345 file The information in this data file is very dependent on the
4346 structure of the generated code, so you must use the same source code
4347 and the same optimization options for both compilations.
4349 With @option{-fbranch-probabilities}, GCC puts a
4350 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4351 These can be used to improve optimization. Currently, they are only
4352 used in one place: in @file{reorg.c}, instead of guessing which path a
4353 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4354 exactly determine which path is taken more often.
4356 @item -fprofile-values
4357 @opindex fprofile-values
4358 If combined with @option{-fprofile-arcs}, it adds code so that some
4359 data about values of expressions in the program is gathered.
4363 Use a graph coloring register allocator. Currently this option is meant
4364 for testing, so we are interested to hear about miscompilations with
4369 Perform tail duplication to enlarge superblock size. This transformation
4370 simplifies the control flow of the function allowing other optimizations to do
4373 @item -funit-at-a-time
4374 @opindex funit-at-a-time
4375 Parse the whole compilation unit before starting to produce code.
4376 This allows some extra optimizations to take place but consumes more
4379 @item -funroll-loops
4380 @opindex funroll-loops
4381 Unroll loops whose number of iterations can be determined at compile time or
4382 upon entry to the loop. @option{-funroll-loops} implies
4383 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4384 (i.e. complete removal of loops with small constant number of iterations).
4385 This option makes code larger, and may or may not make it run faster.
4387 @item -funroll-all-loops
4388 @opindex funroll-all-loops
4389 Unroll all loops, even if their number of iterations is uncertain when
4390 the loop is entered. This usually makes programs run more slowly.
4391 @option{-funroll-all-loops} implies the same options as
4392 @option{-funroll-loops}.
4395 @opindex fpeel-loops
4396 Peels the loops for that there is enough information that they do not
4397 roll much (from profile feedback). It also turns on complete loop peeling
4398 (i.e. complete removal of loops with small constant number of iterations).
4400 @item -funswitch-loops
4401 @opindex funswitch-loops
4402 Move branches with loop invariant conditions out of the loop, with duplicates
4403 of the loop on both branches (modified according to result of the condition).
4405 @item -fold-unroll-loops
4406 @opindex fold-unroll-loops
4407 Unroll loops whose number of iterations can be determined at compile
4408 time or upon entry to the loop, using the old loop unroller whose loop
4409 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4410 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4411 option makes code larger, and may or may not make it run faster.
4413 @item -fold-unroll-all-loops
4414 @opindex fold-unroll-all-loops
4415 Unroll all loops, even if their number of iterations is uncertain when
4416 the loop is entered. This is done using the old loop unroller whose loop
4417 recognition is based on notes from frontend. This usually makes programs run more slowly.
4418 @option{-fold-unroll-all-loops} implies the same options as
4419 @option{-fold-unroll-loops}.
4421 @item -funswitch-loops
4422 @opindex funswitch-loops
4423 Move branches with loop invariant conditions out of the loop, with duplicates
4424 of the loop on both branches (modified according to result of the condition).
4426 @item -funswitch-loops
4427 @opindex funswitch-loops
4428 Move branches with loop invariant conditions out of the loop, with duplicates
4429 of the loop on both branches (modified according to result of the condition).
4431 @item -fprefetch-loop-arrays
4432 @opindex fprefetch-loop-arrays
4433 If supported by the target machine, generate instructions to prefetch
4434 memory to improve the performance of loops that access large arrays.
4436 Disabled at level @option{-Os}.
4438 @item -ffunction-sections
4439 @itemx -fdata-sections
4440 @opindex ffunction-sections
4441 @opindex fdata-sections
4442 Place each function or data item into its own section in the output
4443 file if the target supports arbitrary sections. The name of the
4444 function or the name of the data item determines the section's name
4447 Use these options on systems where the linker can perform optimizations
4448 to improve locality of reference in the instruction space. Most systems
4449 using the ELF object format and SPARC processors running Solaris 2 have
4450 linkers with such optimizations. AIX may have these optimizations in
4453 Only use these options when there are significant benefits from doing
4454 so. When you specify these options, the assembler and linker will
4455 create larger object and executable files and will also be slower.
4456 You will not be able to use @code{gprof} on all systems if you
4457 specify this option and you may have problems with debugging if
4458 you specify both this option and @option{-g}.
4462 Perform optimizations in static single assignment form. Each function's
4463 flow graph is translated into SSA form, optimizations are performed, and
4464 the flow graph is translated back from SSA form. Users should not
4465 specify this option, since it is not yet ready for production use.
4469 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4470 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4474 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4475 Like @option{-fssa}, this is an experimental feature.
4477 @item -fbranch-target-load-optimize
4478 @opindex fbranch-target-load-optimize
4479 Perform branch target register load optimization before prologue / epilogue
4481 The use of target registers can typically be exposed only during reload,
4482 thus hoisting loads out of loops and doing inter-block scheduling needs
4483 a separate optimization pass.
4485 @item -fbranch-target-load-optimize2
4486 @opindex fbranch-target-load-optimize2
4487 Perform branch target register load optimization after prologue / epilogue
4493 @item --param @var{name}=@var{value}
4495 In some places, GCC uses various constants to control the amount of
4496 optimization that is done. For example, GCC will not inline functions
4497 that contain more that a certain number of instructions. You can
4498 control some of these constants on the command-line using the
4499 @option{--param} option.
4501 In each case, the @var{value} is an integer. The allowable choices for
4502 @var{name} are given in the following table:
4505 @item max-crossjump-edges
4506 The maximum number of incoming edges to consider for crossjumping.
4507 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4508 the number of edges incoming to each block. Increasing values mean
4509 more aggressive optimization, making the compile time increase with
4510 probably small improvement in executable size.
4512 @item max-delay-slot-insn-search
4513 The maximum number of instructions to consider when looking for an
4514 instruction to fill a delay slot. If more than this arbitrary number of
4515 instructions is searched, the time savings from filling the delay slot
4516 will be minimal so stop searching. Increasing values mean more
4517 aggressive optimization, making the compile time increase with probably
4518 small improvement in executable run time.
4520 @item max-delay-slot-live-search
4521 When trying to fill delay slots, the maximum number of instructions to
4522 consider when searching for a block with valid live register
4523 information. Increasing this arbitrarily chosen value means more
4524 aggressive optimization, increasing the compile time. This parameter
4525 should be removed when the delay slot code is rewritten to maintain the
4528 @item max-gcse-memory
4529 The approximate maximum amount of memory that will be allocated in
4530 order to perform the global common subexpression elimination
4531 optimization. If more memory than specified is required, the
4532 optimization will not be done.
4534 @item max-gcse-passes
4535 The maximum number of passes of GCSE to run.
4537 @item max-pending-list-length
4538 The maximum number of pending dependencies scheduling will allow
4539 before flushing the current state and starting over. Large functions
4540 with few branches or calls can create excessively large lists which
4541 needlessly consume memory and resources.
4543 @item max-inline-insns-single
4544 Several parameters control the tree inliner used in gcc.
4545 This number sets the maximum number of instructions (counted in gcc's
4546 internal representation) in a single function that the tree inliner
4547 will consider for inlining. This only affects functions declared
4548 inline and methods implemented in a class declaration (C++).
4549 The default value is 100.
4551 @item max-inline-insns-auto
4552 When you use @option{-finline-functions} (included in @option{-O3}),
4553 a lot of functions that would otherwise not be considered for inlining
4554 by the compiler will be investigated. To those functions, a different
4555 (more restrictive) limit compared to functions declared inline can
4557 The default value is 100.
4559 @item max-inline-insns
4560 The tree inliner does decrease the allowable size for single functions
4561 to be inlined after we already inlined the number of instructions
4562 given here by repeated inlining. This number should be a factor of
4563 two or more larger than the single function limit.
4564 Higher numbers result in better runtime performance, but incur higher
4565 compile-time resource (CPU time, memory) requirements and result in
4566 larger binaries. Very high values are not advisable, as too large
4567 binaries may adversely affect runtime performance.
4568 The default value is 200.
4570 @item max-inline-slope
4571 After exceeding the maximum number of inlined instructions by repeated
4572 inlining, a linear function is used to decrease the allowable size
4573 for single functions. The slope of that function is the negative
4574 reciprocal of the number specified here.
4575 The default value is 32.
4577 @item min-inline-insns
4578 The repeated inlining is throttled more and more by the linear function
4579 after exceeding the limit. To avoid too much throttling, a minimum for
4580 this function is specified here to allow repeated inlining for very small
4581 functions even when a lot of repeated inlining already has been done.
4582 The default value is 10.
4584 @item max-inline-insns-rtl
4585 For languages that use the RTL inliner (this happens at a later stage
4586 than tree inlining), you can set the maximum allowable size (counted
4587 in RTL instructions) for the RTL inliner with this parameter.
4588 The default value is 600.
4591 @item max-unrolled-insns
4592 The maximum number of instructions that a loop should have if that loop
4593 is unrolled, and if the loop is unrolled, it determines how many times
4594 the loop code is unrolled.
4596 @item max-average-unrolled-insns
4597 The maximum number of instructions biased by probabilities of their execution
4598 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4599 it determines how many times the loop code is unrolled.
4601 @item max-unroll-times
4602 The maximum number of unrollings of a single loop.
4604 @item max-peeled-insns
4605 The maximum number of instructions that a loop should have if that loop
4606 is peeled, and if the loop is peeled, it determines how many times
4607 the loop code is peeled.
4609 @item max-peel-times
4610 The maximum number of peelings of a single loop.
4612 @item max-completely-peeled-insns
4613 The maximum number of insns of a completely peeled loop.
4615 @item max-completely-peel-times
4616 The maximum number of iterations of a loop to be suitable for complete peeling.
4618 @item max-unswitch-insns
4619 The maximum number of insns of an unswitched loop.
4621 @item max-unswitch-level
4622 The maximum number of branches unswitched in a single loop.
4624 @item hot-bb-count-fraction
4625 Select fraction of the maximal count of repetitions of basic block in program
4626 given basic block needs to have to be considered hot.
4628 @item hot-bb-frequency-fraction
4629 Select fraction of the maximal frequency of executions of basic block in
4630 function given basic block needs to have to be considered hot
4632 @item tracer-dynamic-coverage
4633 @itemx tracer-dynamic-coverage-feedback
4635 This value is used to limit superblock formation once the given percentage of
4636 executed instructions is covered. This limits unnecessary code size
4639 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4640 feedback is available. The real profiles (as opposed to statically estimated
4641 ones) are much less balanced allowing the threshold to be larger value.
4643 @item tracer-max-code-growth
4644 Stop tail duplication once code growth has reached given percentage. This is
4645 rather hokey argument, as most of the duplicates will be eliminated later in
4646 cross jumping, so it may be set to much higher values than is the desired code
4649 @item tracer-min-branch-ratio
4651 Stop reverse growth when the reverse probability of best edge is less than this
4652 threshold (in percent).
4654 @item tracer-min-branch-ratio
4655 @itemx tracer-min-branch-ratio-feedback
4657 Stop forward growth if the best edge do have probability lower than this
4660 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4661 compilation for profile feedback and one for compilation without. The value
4662 for compilation with profile feedback needs to be more conservative (higher) in
4663 order to make tracer effective.
4665 @item max-cse-path-length
4667 Maximum number of basic blocks on path that cse considers.
4669 @item ggc-min-expand
4671 GCC uses a garbage collector to manage its own memory allocation. This
4672 parameter specifies the minimum percentage by which the garbage
4673 collector's heap should be allowed to expand between collections.
4674 Tuning this may improve compilation speed; it has no effect on code
4677 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4678 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4679 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4680 GCC is not able to calculate RAM on a particular platform, the lower
4681 bound of 30% is used. Setting this parameter and
4682 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4683 every opportunity. This is extremely slow, but can be useful for
4686 @item ggc-min-heapsize
4688 Minimum size of the garbage collector's heap before it begins bothering
4689 to collect garbage. The first collection occurs after the heap expands
4690 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4691 tuning this may improve compilation speed, and has no effect on code
4694 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4695 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4696 available, the notion of "RAM" is the smallest of actual RAM,
4697 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4698 RAM on a particular platform, the lower bound is used. Setting this
4699 parameter very large effectively disables garbage collection. Setting
4700 this parameter and @option{ggc-min-expand} to zero causes a full
4701 collection to occur at every opportunity.
4703 @item reorder-blocks-duplicate
4704 @itemx reorder-blocks-duplicate-feedback
4706 Used by basic block reordering pass to decide whether to use unconditional
4707 branch or duplicate the code on it's destination. Code is duplicated when it's
4708 estimated size is smaller than this value multiplied by the estimated size of
4709 unconditional jump in the hot spots of the program.
4711 The @option{reorder-block-duplicate-feedback} is used only when profile
4712 feedback is available and may be set to higher values than
4713 @option{reorder-block-duplicate} since information about the hot spots is more
4718 @node Preprocessor Options
4719 @section Options Controlling the Preprocessor
4720 @cindex preprocessor options
4721 @cindex options, preprocessor
4723 These options control the C preprocessor, which is run on each C source
4724 file before actual compilation.
4726 If you use the @option{-E} option, nothing is done except preprocessing.
4727 Some of these options make sense only together with @option{-E} because
4728 they cause the preprocessor output to be unsuitable for actual
4733 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4734 and pass @var{option} directly through to the preprocessor. If
4735 @var{option} contains commas, it is split into multiple options at the
4736 commas. However, many options are modified, translated or interpreted
4737 by the compiler driver before being passed to the preprocessor, and
4738 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4739 interface is undocumented and subject to change, so whenever possible
4740 you should avoid using @option{-Wp} and let the driver handle the
4743 @item -Xpreprocessor @var{option}
4744 @opindex preprocessor
4745 Pass @var{option} as an option to the preprocessor. You can use this to
4746 supply system-specific preprocessor options which GCC does not know how to
4749 If you want to pass an option that takes an argument, you must use
4750 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4753 @include cppopts.texi
4755 @node Assembler Options
4756 @section Passing Options to the Assembler
4758 @c prevent bad page break with this line
4759 You can pass options to the assembler.
4762 @item -Wa,@var{option}
4764 Pass @var{option} as an option to the assembler. If @var{option}
4765 contains commas, it is split into multiple options at the commas.
4767 @item -Xassembler @var{option}
4769 Pass @var{option} as an option to the assembler. You can use this to
4770 supply system-specific assembler options which GCC does not know how to
4773 If you want to pass an option that takes an argument, you must use
4774 @option{-Xassembler} twice, once for the option and once for the argument.
4779 @section Options for Linking
4780 @cindex link options
4781 @cindex options, linking
4783 These options come into play when the compiler links object files into
4784 an executable output file. They are meaningless if the compiler is
4785 not doing a link step.
4789 @item @var{object-file-name}
4790 A file name that does not end in a special recognized suffix is
4791 considered to name an object file or library. (Object files are
4792 distinguished from libraries by the linker according to the file
4793 contents.) If linking is done, these object files are used as input
4802 If any of these options is used, then the linker is not run, and
4803 object file names should not be used as arguments. @xref{Overall
4807 @item -l@var{library}
4808 @itemx -l @var{library}
4810 Search the library named @var{library} when linking. (The second
4811 alternative with the library as a separate argument is only for
4812 POSIX compliance and is not recommended.)
4814 It makes a difference where in the command you write this option; the
4815 linker searches and processes libraries and object files in the order they
4816 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
4817 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
4818 to functions in @samp{z}, those functions may not be loaded.
4820 The linker searches a standard list of directories for the library,
4821 which is actually a file named @file{lib@var{library}.a}. The linker
4822 then uses this file as if it had been specified precisely by name.
4824 The directories searched include several standard system directories
4825 plus any that you specify with @option{-L}.
4827 Normally the files found this way are library files---archive files
4828 whose members are object files. The linker handles an archive file by
4829 scanning through it for members which define symbols that have so far
4830 been referenced but not defined. But if the file that is found is an
4831 ordinary object file, it is linked in the usual fashion. The only
4832 difference between using an @option{-l} option and specifying a file name
4833 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
4834 and searches several directories.
4838 You need this special case of the @option{-l} option in order to
4839 link an Objective-C program.
4842 @opindex nostartfiles
4843 Do not use the standard system startup files when linking.
4844 The standard system libraries are used normally, unless @option{-nostdlib}
4845 or @option{-nodefaultlibs} is used.
4847 @item -nodefaultlibs
4848 @opindex nodefaultlibs
4849 Do not use the standard system libraries when linking.
4850 Only the libraries you specify will be passed to the linker.
4851 The standard startup files are used normally, unless @option{-nostartfiles}
4852 is used. The compiler may generate calls to memcmp, memset, and memcpy
4853 for System V (and ISO C) environments or to bcopy and bzero for
4854 BSD environments. These entries are usually resolved by entries in
4855 libc. These entry points should be supplied through some other
4856 mechanism when this option is specified.
4860 Do not use the standard system startup files or libraries when linking.
4861 No startup files and only the libraries you specify will be passed to
4862 the linker. The compiler may generate calls to memcmp, memset, and memcpy
4863 for System V (and ISO C) environments or to bcopy and bzero for
4864 BSD environments. These entries are usually resolved by entries in
4865 libc. These entry points should be supplied through some other
4866 mechanism when this option is specified.
4868 @cindex @option{-lgcc}, use with @option{-nostdlib}
4869 @cindex @option{-nostdlib} and unresolved references
4870 @cindex unresolved references and @option{-nostdlib}
4871 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
4872 @cindex @option{-nodefaultlibs} and unresolved references
4873 @cindex unresolved references and @option{-nodefaultlibs}
4874 One of the standard libraries bypassed by @option{-nostdlib} and
4875 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
4876 that GCC uses to overcome shortcomings of particular machines, or special
4877 needs for some languages.
4878 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
4879 Collection (GCC) Internals},
4880 for more discussion of @file{libgcc.a}.)
4881 In most cases, you need @file{libgcc.a} even when you want to avoid
4882 other standard libraries. In other words, when you specify @option{-nostdlib}
4883 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
4884 This ensures that you have no unresolved references to internal GCC
4885 library subroutines. (For example, @samp{__main}, used to ensure C++
4886 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
4887 GNU Compiler Collection (GCC) Internals}.)
4891 Produce a position independent executable on targets which support it.
4892 For predictable results, you must also specify the same set of options
4893 that were used to generate code (@option{-fpie}, @option{-fPIE},
4894 or model suboptions) when you specify this option.
4898 Remove all symbol table and relocation information from the executable.
4902 On systems that support dynamic linking, this prevents linking with the shared
4903 libraries. On other systems, this option has no effect.
4907 Produce a shared object which can then be linked with other objects to
4908 form an executable. Not all systems support this option. For predictable
4909 results, you must also specify the same set of options that were used to
4910 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
4911 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
4912 needs to build supplementary stub code for constructors to work. On
4913 multi-libbed systems, @samp{gcc -shared} must select the correct support
4914 libraries to link against. Failing to supply the correct flags may lead
4915 to subtle defects. Supplying them in cases where they are not necessary
4918 @item -shared-libgcc
4919 @itemx -static-libgcc
4920 @opindex shared-libgcc
4921 @opindex static-libgcc
4922 On systems that provide @file{libgcc} as a shared library, these options
4923 force the use of either the shared or static version respectively.
4924 If no shared version of @file{libgcc} was built when the compiler was
4925 configured, these options have no effect.
4927 There are several situations in which an application should use the
4928 shared @file{libgcc} instead of the static version. The most common
4929 of these is when the application wishes to throw and catch exceptions
4930 across different shared libraries. In that case, each of the libraries
4931 as well as the application itself should use the shared @file{libgcc}.
4933 Therefore, the G++ and GCJ drivers automatically add
4934 @option{-shared-libgcc} whenever you build a shared library or a main
4935 executable, because C++ and Java programs typically use exceptions, so
4936 this is the right thing to do.
4938 If, instead, you use the GCC driver to create shared libraries, you may
4939 find that they will not always be linked with the shared @file{libgcc}.
4940 If GCC finds, at its configuration time, that you have a GNU linker that
4941 does not support option @option{--eh-frame-hdr}, it will link the shared
4942 version of @file{libgcc} into shared libraries by default. Otherwise,
4943 it will take advantage of the linker and optimize away the linking with
4944 the shared version of @file{libgcc}, linking with the static version of
4945 libgcc by default. This allows exceptions to propagate through such
4946 shared libraries, without incurring relocation costs at library load
4949 However, if a library or main executable is supposed to throw or catch
4950 exceptions, you must link it using the G++ or GCJ driver, as appropriate
4951 for the languages used in the program, or using the option
4952 @option{-shared-libgcc}, such that it is linked with the shared
4957 Bind references to global symbols when building a shared object. Warn
4958 about any unresolved references (unless overridden by the link editor
4959 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
4962 @item -Xlinker @var{option}
4964 Pass @var{option} as an option to the linker. You can use this to
4965 supply system-specific linker options which GCC does not know how to
4968 If you want to pass an option that takes an argument, you must use
4969 @option{-Xlinker} twice, once for the option and once for the argument.
4970 For example, to pass @option{-assert definitions}, you must write
4971 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
4972 @option{-Xlinker "-assert definitions"}, because this passes the entire
4973 string as a single argument, which is not what the linker expects.
4975 @item -Wl,@var{option}
4977 Pass @var{option} as an option to the linker. If @var{option} contains
4978 commas, it is split into multiple options at the commas.
4980 @item -u @var{symbol}
4982 Pretend the symbol @var{symbol} is undefined, to force linking of
4983 library modules to define it. You can use @option{-u} multiple times with
4984 different symbols to force loading of additional library modules.
4987 @node Directory Options
4988 @section Options for Directory Search
4989 @cindex directory options
4990 @cindex options, directory search
4993 These options specify directories to search for header files, for
4994 libraries and for parts of the compiler:
4999 Add the directory @var{dir} to the head of the list of directories to be
5000 searched for header files. This can be used to override a system header
5001 file, substituting your own version, since these directories are
5002 searched before the system header file directories. However, you should
5003 not use this option to add directories that contain vendor-supplied
5004 system header files (use @option{-isystem} for that). If you use more than
5005 one @option{-I} option, the directories are scanned in left-to-right
5006 order; the standard system directories come after.
5008 If a standard system include directory, or a directory specified with
5009 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5010 option will be ignored. The directory will still be searched but as a
5011 system directory at its normal position in the system include chain.
5012 This is to ensure that GCC's procedure to fix buggy system headers and
5013 the ordering for the include_next directive are not inadvertently changed.
5014 If you really need to change the search order for system directories,
5015 use the @option{-nostdinc} and/or @option{-isystem} options.
5019 Any directories you specify with @option{-I} options before the @option{-I-}
5020 option are searched only for the case of @samp{#include "@var{file}"};
5021 they are not searched for @samp{#include <@var{file}>}.
5023 If additional directories are specified with @option{-I} options after
5024 the @option{-I-}, these directories are searched for all @samp{#include}
5025 directives. (Ordinarily @emph{all} @option{-I} directories are used
5028 In addition, the @option{-I-} option inhibits the use of the current
5029 directory (where the current input file came from) as the first search
5030 directory for @samp{#include "@var{file}"}. There is no way to
5031 override this effect of @option{-I-}. With @option{-I.} you can specify
5032 searching the directory which was current when the compiler was
5033 invoked. That is not exactly the same as what the preprocessor does
5034 by default, but it is often satisfactory.
5036 @option{-I-} does not inhibit the use of the standard system directories
5037 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5042 Add directory @var{dir} to the list of directories to be searched
5045 @item -B@var{prefix}
5047 This option specifies where to find the executables, libraries,
5048 include files, and data files of the compiler itself.
5050 The compiler driver program runs one or more of the subprograms
5051 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5052 @var{prefix} as a prefix for each program it tries to run, both with and
5053 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5055 For each subprogram to be run, the compiler driver first tries the
5056 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5057 was not specified, the driver tries two standard prefixes, which are
5058 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of
5059 those results in a file name that is found, the unmodified program
5060 name is searched for using the directories specified in your
5061 @env{PATH} environment variable.
5063 The compiler will check to see if the path provided by the @option{-B}
5064 refers to a directory, and if necessary it will add a directory
5065 separator character at the end of the path.
5067 @option{-B} prefixes that effectively specify directory names also apply
5068 to libraries in the linker, because the compiler translates these
5069 options into @option{-L} options for the linker. They also apply to
5070 includes files in the preprocessor, because the compiler translates these
5071 options into @option{-isystem} options for the preprocessor. In this case,
5072 the compiler appends @samp{include} to the prefix.
5074 The run-time support file @file{libgcc.a} can also be searched for using
5075 the @option{-B} prefix, if needed. If it is not found there, the two
5076 standard prefixes above are tried, and that is all. The file is left
5077 out of the link if it is not found by those means.
5079 Another way to specify a prefix much like the @option{-B} prefix is to use
5080 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5083 As a special kludge, if the path provided by @option{-B} is
5084 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5085 9, then it will be replaced by @file{[dir/]include}. This is to help
5086 with boot-strapping the compiler.
5088 @item -specs=@var{file}
5090 Process @var{file} after the compiler reads in the standard @file{specs}
5091 file, in order to override the defaults that the @file{gcc} driver
5092 program uses when determining what switches to pass to @file{cc1},
5093 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5094 @option{-specs=@var{file}} can be specified on the command line, and they
5095 are processed in order, from left to right.
5101 @section Specifying subprocesses and the switches to pass to them
5104 @command{gcc} is a driver program. It performs its job by invoking a
5105 sequence of other programs to do the work of compiling, assembling and
5106 linking. GCC interprets its command-line parameters and uses these to
5107 deduce which programs it should invoke, and which command-line options
5108 it ought to place on their command lines. This behavior is controlled
5109 by @dfn{spec strings}. In most cases there is one spec string for each
5110 program that GCC can invoke, but a few programs have multiple spec
5111 strings to control their behavior. The spec strings built into GCC can
5112 be overridden by using the @option{-specs=} command-line switch to specify
5115 @dfn{Spec files} are plaintext files that are used to construct spec
5116 strings. They consist of a sequence of directives separated by blank
5117 lines. The type of directive is determined by the first non-whitespace
5118 character on the line and it can be one of the following:
5121 @item %@var{command}
5122 Issues a @var{command} to the spec file processor. The commands that can
5126 @item %include <@var{file}>
5128 Search for @var{file} and insert its text at the current point in the
5131 @item %include_noerr <@var{file}>
5132 @cindex %include_noerr
5133 Just like @samp{%include}, but do not generate an error message if the include
5134 file cannot be found.
5136 @item %rename @var{old_name} @var{new_name}
5138 Rename the spec string @var{old_name} to @var{new_name}.
5142 @item *[@var{spec_name}]:
5143 This tells the compiler to create, override or delete the named spec
5144 string. All lines after this directive up to the next directive or
5145 blank line are considered to be the text for the spec string. If this
5146 results in an empty string then the spec will be deleted. (Or, if the
5147 spec did not exist, then nothing will happened.) Otherwise, if the spec
5148 does not currently exist a new spec will be created. If the spec does
5149 exist then its contents will be overridden by the text of this
5150 directive, unless the first character of that text is the @samp{+}
5151 character, in which case the text will be appended to the spec.
5153 @item [@var{suffix}]:
5154 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5155 and up to the next directive or blank line are considered to make up the
5156 spec string for the indicated suffix. When the compiler encounters an
5157 input file with the named suffix, it will processes the spec string in
5158 order to work out how to compile that file. For example:
5165 This says that any input file whose name ends in @samp{.ZZ} should be
5166 passed to the program @samp{z-compile}, which should be invoked with the
5167 command-line switch @option{-input} and with the result of performing the
5168 @samp{%i} substitution. (See below.)
5170 As an alternative to providing a spec string, the text that follows a
5171 suffix directive can be one of the following:
5174 @item @@@var{language}
5175 This says that the suffix is an alias for a known @var{language}. This is
5176 similar to using the @option{-x} command-line switch to GCC to specify a
5177 language explicitly. For example:
5184 Says that .ZZ files are, in fact, C++ source files.
5187 This causes an error messages saying:
5190 @var{name} compiler not installed on this system.
5194 GCC already has an extensive list of suffixes built into it.
5195 This directive will add an entry to the end of the list of suffixes, but
5196 since the list is searched from the end backwards, it is effectively
5197 possible to override earlier entries using this technique.
5201 GCC has the following spec strings built into it. Spec files can
5202 override these strings or create their own. Note that individual
5203 targets can also add their own spec strings to this list.
5206 asm Options to pass to the assembler
5207 asm_final Options to pass to the assembler post-processor
5208 cpp Options to pass to the C preprocessor
5209 cc1 Options to pass to the C compiler
5210 cc1plus Options to pass to the C++ compiler
5211 endfile Object files to include at the end of the link
5212 link Options to pass to the linker
5213 lib Libraries to include on the command line to the linker
5214 libgcc Decides which GCC support library to pass to the linker
5215 linker Sets the name of the linker
5216 predefines Defines to be passed to the C preprocessor
5217 signed_char Defines to pass to CPP to say whether @code{char} is signed
5219 startfile Object files to include at the start of the link
5222 Here is a small example of a spec file:
5228 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5231 This example renames the spec called @samp{lib} to @samp{old_lib} and
5232 then overrides the previous definition of @samp{lib} with a new one.
5233 The new definition adds in some extra command-line options before
5234 including the text of the old definition.
5236 @dfn{Spec strings} are a list of command-line options to be passed to their
5237 corresponding program. In addition, the spec strings can contain
5238 @samp{%}-prefixed sequences to substitute variable text or to
5239 conditionally insert text into the command line. Using these constructs
5240 it is possible to generate quite complex command lines.
5242 Here is a table of all defined @samp{%}-sequences for spec
5243 strings. Note that spaces are not generated automatically around the
5244 results of expanding these sequences. Therefore you can concatenate them
5245 together or combine them with constant text in a single argument.
5249 Substitute one @samp{%} into the program name or argument.
5252 Substitute the name of the input file being processed.
5255 Substitute the basename of the input file being processed.
5256 This is the substring up to (and not including) the last period
5257 and not including the directory.
5260 This is the same as @samp{%b}, but include the file suffix (text after
5264 Marks the argument containing or following the @samp{%d} as a
5265 temporary file name, so that that file will be deleted if GCC exits
5266 successfully. Unlike @samp{%g}, this contributes no text to the
5269 @item %g@var{suffix}
5270 Substitute a file name that has suffix @var{suffix} and is chosen
5271 once per compilation, and mark the argument in the same way as
5272 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5273 name is now chosen in a way that is hard to predict even when previously
5274 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5275 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5276 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5277 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5278 was simply substituted with a file name chosen once per compilation,
5279 without regard to any appended suffix (which was therefore treated
5280 just like ordinary text), making such attacks more likely to succeed.
5282 @item %u@var{suffix}
5283 Like @samp{%g}, but generates a new temporary file name even if
5284 @samp{%u@var{suffix}} was already seen.
5286 @item %U@var{suffix}
5287 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5288 new one if there is no such last file name. In the absence of any
5289 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5290 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5291 would involve the generation of two distinct file names, one
5292 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5293 simply substituted with a file name chosen for the previous @samp{%u},
5294 without regard to any appended suffix.
5296 @item %j@var{suffix}
5297 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5298 writable, and if save-temps is off; otherwise, substitute the name
5299 of a temporary file, just like @samp{%u}. This temporary file is not
5300 meant for communication between processes, but rather as a junk
5303 @item %|@var{suffix}
5304 @itemx %m@var{suffix}
5305 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5306 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5307 all. These are the two most common ways to instruct a program that it
5308 should read from standard input or write to standard output. If you
5309 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5310 construct: see for example @file{f/lang-specs.h}.
5312 @item %.@var{SUFFIX}
5313 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5314 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5315 terminated by the next space or %.
5318 Marks the argument containing or following the @samp{%w} as the
5319 designated output file of this compilation. This puts the argument
5320 into the sequence of arguments that @samp{%o} will substitute later.
5323 Substitutes the names of all the output files, with spaces
5324 automatically placed around them. You should write spaces
5325 around the @samp{%o} as well or the results are undefined.
5326 @samp{%o} is for use in the specs for running the linker.
5327 Input files whose names have no recognized suffix are not compiled
5328 at all, but they are included among the output files, so they will
5332 Substitutes the suffix for object files. Note that this is
5333 handled specially when it immediately follows @samp{%g, %u, or %U},
5334 because of the need for those to form complete file names. The
5335 handling is such that @samp{%O} is treated exactly as if it had already
5336 been substituted, except that @samp{%g, %u, and %U} do not currently
5337 support additional @var{suffix} characters following @samp{%O} as they would
5338 following, for example, @samp{.o}.
5341 Substitutes the standard macro predefinitions for the
5342 current target machine. Use this when running @code{cpp}.
5345 Like @samp{%p}, but puts @samp{__} before and after the name of each
5346 predefined macro, except for macros that start with @samp{__} or with
5347 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5351 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5352 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5353 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5357 Current argument is the name of a library or startup file of some sort.
5358 Search for that file in a standard list of directories and substitute
5359 the full name found.
5362 Print @var{str} as an error message. @var{str} is terminated by a newline.
5363 Use this when inconsistent options are detected.
5366 Substitute the contents of spec string @var{name} at this point.
5369 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5371 @item %x@{@var{option}@}
5372 Accumulate an option for @samp{%X}.
5375 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5379 Output the accumulated assembler options specified by @option{-Wa}.
5382 Output the accumulated preprocessor options specified by @option{-Wp}.
5385 Process the @code{asm} spec. This is used to compute the
5386 switches to be passed to the assembler.
5389 Process the @code{asm_final} spec. This is a spec string for
5390 passing switches to an assembler post-processor, if such a program is
5394 Process the @code{link} spec. This is the spec for computing the
5395 command line passed to the linker. Typically it will make use of the
5396 @samp{%L %G %S %D and %E} sequences.
5399 Dump out a @option{-L} option for each directory that GCC believes might
5400 contain startup files. If the target supports multilibs then the
5401 current multilib directory will be prepended to each of these paths.
5404 Output the multilib directory with directory separators replaced with
5405 @samp{_}. If multilib directories are not set, or the multilib directory is
5406 @file{.} then this option emits nothing.
5409 Process the @code{lib} spec. This is a spec string for deciding which
5410 libraries should be included on the command line to the linker.
5413 Process the @code{libgcc} spec. This is a spec string for deciding
5414 which GCC support library should be included on the command line to the linker.
5417 Process the @code{startfile} spec. This is a spec for deciding which
5418 object files should be the first ones passed to the linker. Typically
5419 this might be a file named @file{crt0.o}.
5422 Process the @code{endfile} spec. This is a spec string that specifies
5423 the last object files that will be passed to the linker.
5426 Process the @code{cpp} spec. This is used to construct the arguments
5427 to be passed to the C preprocessor.
5430 Process the @code{signed_char} spec. This is intended to be used
5431 to tell cpp whether a char is signed. It typically has the definition:
5433 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5437 Process the @code{cc1} spec. This is used to construct the options to be
5438 passed to the actual C compiler (@samp{cc1}).
5441 Process the @code{cc1plus} spec. This is used to construct the options to be
5442 passed to the actual C++ compiler (@samp{cc1plus}).
5445 Substitute the variable part of a matched option. See below.
5446 Note that each comma in the substituted string is replaced by
5450 Remove all occurrences of @code{-S} from the command line. Note---this
5451 command is position dependent. @samp{%} commands in the spec string
5452 before this one will see @code{-S}, @samp{%} commands in the spec string
5453 after this one will not.
5455 @item %:@var{function}(@var{args})
5456 Call the named function @var{function}, passing it @var{args}.
5457 @var{args} is first processed as a nested spec string, then split
5458 into an argument vector in the usual fashion. The function returns
5459 a string which is processed as if it had appeared literally as part
5460 of the current spec.
5462 The following built-in spec functions are provided:
5465 @item @code{if-exists}
5466 The @code{if-exists} spec function takes one argument, an absolute
5467 pathname to a file. If the file exists, @code{if-exists} returns the
5468 pathname. Here is a small example of its usage:
5472 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5475 @item @code{if-exists-else}
5476 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5477 spec function, except that it takes two arguments. The first argument is
5478 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5479 returns the pathname. If it does not exist, it returns the second argument.
5480 This way, @code{if-exists-else} can be used to select one file or another,
5481 based on the existence of the first. Here is a small example of its usage:
5485 crt0%O%s %:if-exists(crti%O%s) \
5486 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5491 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5492 If that switch was not specified, this substitutes nothing. Note that
5493 the leading dash is omitted when specifying this option, and it is
5494 automatically inserted if the substitution is performed. Thus the spec
5495 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5496 and would output the command line option @option{-foo}.
5498 @item %W@{@code{S}@}
5499 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5502 @item %@{@code{S}*@}
5503 Substitutes all the switches specified to GCC whose names start
5504 with @code{-S}, but which also take an argument. This is used for
5505 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5506 GCC considers @option{-o foo} as being
5507 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5508 text, including the space. Thus two arguments would be generated.
5510 @item %@{@code{S}*&@code{T}*@}
5511 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5512 (the order of @code{S} and @code{T} in the spec is not significant).
5513 There can be any number of ampersand-separated variables; for each the
5514 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5516 @item %@{@code{S}:@code{X}@}
5517 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5519 @item %@{!@code{S}:@code{X}@}
5520 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5522 @item %@{@code{S}*:@code{X}@}
5523 Substitutes @code{X} if one or more switches whose names start with
5524 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5525 once, no matter how many such switches appeared. However, if @code{%*}
5526 appears somewhere in @code{X}, then @code{X} will be substituted once
5527 for each matching switch, with the @code{%*} replaced by the part of
5528 that switch that matched the @code{*}.
5530 @item %@{.@code{S}:@code{X}@}
5531 Substitutes @code{X}, if processing a file with suffix @code{S}.
5533 @item %@{!.@code{S}:@code{X}@}
5534 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5536 @item %@{@code{S}|@code{P}:@code{X}@}
5537 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5538 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5539 although they have a stronger binding than the @samp{|}. If @code{%*}
5540 appears in @code{X}, all of the alternatives must be starred, and only
5541 the first matching alternative is substituted.
5543 For example, a spec string like this:
5546 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5549 will output the following command-line options from the following input
5550 command-line options:
5555 -d fred.c -foo -baz -boggle
5556 -d jim.d -bar -baz -boggle
5559 @item %@{S:X; T:Y; :D@}
5561 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
5562 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
5563 be as many clauses as you need. This may be combined with @code{.},
5564 @code{!}, @code{|}, and @code{*} as needed.
5569 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5570 construct may contain other nested @samp{%} constructs or spaces, or
5571 even newlines. They are processed as usual, as described above.
5572 Trailing white space in @code{X} is ignored. White space may also
5573 appear anywhere on the left side of the colon in these constructs,
5574 except between @code{.} or @code{*} and the corresponding word.
5576 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5577 handled specifically in these constructs. If another value of
5578 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5579 @option{-W} switch is found later in the command line, the earlier
5580 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5581 just one letter, which passes all matching options.
5583 The character @samp{|} at the beginning of the predicate text is used to
5584 indicate that a command should be piped to the following command, but
5585 only if @option{-pipe} is specified.
5587 It is built into GCC which switches take arguments and which do not.
5588 (You might think it would be useful to generalize this to allow each
5589 compiler's spec to say which switches take arguments. But this cannot
5590 be done in a consistent fashion. GCC cannot even decide which input
5591 files have been specified without knowing which switches take arguments,
5592 and it must know which input files to compile in order to tell which
5595 GCC also knows implicitly that arguments starting in @option{-l} are to be
5596 treated as compiler output files, and passed to the linker in their
5597 proper position among the other output files.
5599 @c man begin OPTIONS
5601 @node Target Options
5602 @section Specifying Target Machine and Compiler Version
5603 @cindex target options
5604 @cindex cross compiling
5605 @cindex specifying machine version
5606 @cindex specifying compiler version and target machine
5607 @cindex compiler version, specifying
5608 @cindex target machine, specifying
5610 The usual way to run GCC is to run the executable called @file{gcc}, or
5611 @file{<machine>-gcc} when cross-compiling, or
5612 @file{<machine>-gcc-<version>} to run a version other than the one that
5613 was installed last. Sometimes this is inconvenient, so GCC provides
5614 options that will switch to another cross-compiler or version.
5617 @item -b @var{machine}
5619 The argument @var{machine} specifies the target machine for compilation.
5621 The value to use for @var{machine} is the same as was specified as the
5622 machine type when configuring GCC as a cross-compiler. For
5623 example, if a cross-compiler was configured with @samp{configure
5624 i386v}, meaning to compile for an 80386 running System V, then you
5625 would specify @option{-b i386v} to run that cross compiler.
5627 @item -V @var{version}
5629 The argument @var{version} specifies which version of GCC to run.
5630 This is useful when multiple versions are installed. For example,
5631 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5634 The @option{-V} and @option{-b} options work by running the
5635 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5636 use them if you can just run that directly.
5638 @node Submodel Options
5639 @section Hardware Models and Configurations
5640 @cindex submodel options
5641 @cindex specifying hardware config
5642 @cindex hardware models and configurations, specifying
5643 @cindex machine dependent options
5645 Earlier we discussed the standard option @option{-b} which chooses among
5646 different installed compilers for completely different target
5647 machines, such as VAX vs.@: 68000 vs.@: 80386.
5649 In addition, each of these target machine types can have its own
5650 special options, starting with @samp{-m}, to choose among various
5651 hardware models or configurations---for example, 68010 vs 68020,
5652 floating coprocessor or none. A single installed version of the
5653 compiler can compile for any model or configuration, according to the
5656 Some configurations of the compiler also support additional special
5657 options, usually for compatibility with other compilers on the same
5660 These options are defined by the macro @code{TARGET_SWITCHES} in the
5661 machine description. The default for the options is also defined by
5662 that macro, which enables you to change the defaults.
5674 * RS/6000 and PowerPC Options::
5678 * i386 and x86-64 Options::
5680 * Intel 960 Options::
5681 * DEC Alpha Options::
5682 * DEC Alpha/VMS Options::
5685 * System V Options::
5686 * TMS320C3x/C4x Options::
5694 * S/390 and zSeries Options::
5698 * Xstormy16 Options::
5703 @node M680x0 Options
5704 @subsection M680x0 Options
5705 @cindex M680x0 options
5707 These are the @samp{-m} options defined for the 68000 series. The default
5708 values for these options depends on which style of 68000 was selected when
5709 the compiler was configured; the defaults for the most common choices are
5717 Generate output for a 68000. This is the default
5718 when the compiler is configured for 68000-based systems.
5720 Use this option for microcontrollers with a 68000 or EC000 core,
5721 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5727 Generate output for a 68020. This is the default
5728 when the compiler is configured for 68020-based systems.
5732 Generate output containing 68881 instructions for floating point.
5733 This is the default for most 68020 systems unless @option{--nfp} was
5734 specified when the compiler was configured.
5738 Generate output for a 68030. This is the default when the compiler is
5739 configured for 68030-based systems.
5743 Generate output for a 68040. This is the default when the compiler is
5744 configured for 68040-based systems.
5746 This option inhibits the use of 68881/68882 instructions that have to be
5747 emulated by software on the 68040. Use this option if your 68040 does not
5748 have code to emulate those instructions.
5752 Generate output for a 68060. This is the default when the compiler is
5753 configured for 68060-based systems.
5755 This option inhibits the use of 68020 and 68881/68882 instructions that
5756 have to be emulated by software on the 68060. Use this option if your 68060
5757 does not have code to emulate those instructions.
5761 Generate output for a CPU32. This is the default
5762 when the compiler is configured for CPU32-based systems.
5764 Use this option for microcontrollers with a
5765 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5766 68336, 68340, 68341, 68349 and 68360.
5770 Generate output for a 520X ``coldfire'' family cpu. This is the default
5771 when the compiler is configured for 520X-based systems.
5773 Use this option for microcontroller with a 5200 core, including
5774 the MCF5202, MCF5203, MCF5204 and MCF5202.
5779 Generate output for a 68040, without using any of the new instructions.
5780 This results in code which can run relatively efficiently on either a
5781 68020/68881 or a 68030 or a 68040. The generated code does use the
5782 68881 instructions that are emulated on the 68040.
5786 Generate output for a 68060, without using any of the new instructions.
5787 This results in code which can run relatively efficiently on either a
5788 68020/68881 or a 68030 or a 68040. The generated code does use the
5789 68881 instructions that are emulated on the 68060.
5792 @opindex msoft-float
5793 Generate output containing library calls for floating point.
5794 @strong{Warning:} the requisite libraries are not available for all m68k
5795 targets. Normally the facilities of the machine's usual C compiler are
5796 used, but this can't be done directly in cross-compilation. You must
5797 make your own arrangements to provide suitable library functions for
5798 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5799 @samp{m68k-*-coff} do provide software floating point support.
5803 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5806 @opindex mnobitfield
5807 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
5808 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
5812 Do use the bit-field instructions. The @option{-m68020} option implies
5813 @option{-mbitfield}. This is the default if you use a configuration
5814 designed for a 68020.
5818 Use a different function-calling convention, in which functions
5819 that take a fixed number of arguments return with the @code{rtd}
5820 instruction, which pops their arguments while returning. This
5821 saves one instruction in the caller since there is no need to pop
5822 the arguments there.
5824 This calling convention is incompatible with the one normally
5825 used on Unix, so you cannot use it if you need to call libraries
5826 compiled with the Unix compiler.
5828 Also, you must provide function prototypes for all functions that
5829 take variable numbers of arguments (including @code{printf});
5830 otherwise incorrect code will be generated for calls to those
5833 In addition, seriously incorrect code will result if you call a
5834 function with too many arguments. (Normally, extra arguments are
5835 harmlessly ignored.)
5837 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
5838 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
5841 @itemx -mno-align-int
5843 @opindex mno-align-int
5844 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
5845 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
5846 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
5847 Aligning variables on 32-bit boundaries produces code that runs somewhat
5848 faster on processors with 32-bit busses at the expense of more memory.
5850 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
5851 align structures containing the above types differently than
5852 most published application binary interface specifications for the m68k.
5856 Use the pc-relative addressing mode of the 68000 directly, instead of
5857 using a global offset table. At present, this option implies @option{-fpic},
5858 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
5859 not presently supported with @option{-mpcrel}, though this could be supported for
5860 68020 and higher processors.
5862 @item -mno-strict-align
5863 @itemx -mstrict-align
5864 @opindex mno-strict-align
5865 @opindex mstrict-align
5866 Do not (do) assume that unaligned memory references will be handled by
5871 @node M68hc1x Options
5872 @subsection M68hc1x Options
5873 @cindex M68hc1x options
5875 These are the @samp{-m} options defined for the 68hc11 and 68hc12
5876 microcontrollers. The default values for these options depends on
5877 which style of microcontroller was selected when the compiler was configured;
5878 the defaults for the most common choices are given below.
5885 Generate output for a 68HC11. This is the default
5886 when the compiler is configured for 68HC11-based systems.
5892 Generate output for a 68HC12. This is the default
5893 when the compiler is configured for 68HC12-based systems.
5899 Generate output for a 68HCS12.
5902 @opindex mauto-incdec
5903 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
5910 Enable the use of 68HC12 min and max instructions.
5913 @itemx -mno-long-calls
5914 @opindex mlong-calls
5915 @opindex mno-long-calls
5916 Treat all calls as being far away (near). If calls are assumed to be
5917 far away, the compiler will use the @code{call} instruction to
5918 call a function and the @code{rtc} instruction for returning.
5922 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5924 @item -msoft-reg-count=@var{count}
5925 @opindex msoft-reg-count
5926 Specify the number of pseudo-soft registers which are used for the
5927 code generation. The maximum number is 32. Using more pseudo-soft
5928 register may or may not result in better code depending on the program.
5929 The default is 4 for 68HC11 and 2 for 68HC12.
5934 @subsection VAX Options
5937 These @samp{-m} options are defined for the VAX:
5942 Do not output certain jump instructions (@code{aobleq} and so on)
5943 that the Unix assembler for the VAX cannot handle across long
5948 Do output those jump instructions, on the assumption that you
5949 will assemble with the GNU assembler.
5953 Output code for g-format floating point numbers instead of d-format.
5957 @subsection SPARC Options
5958 @cindex SPARC options
5960 These @samp{-m} switches are supported on the SPARC:
5965 @opindex mno-app-regs
5967 Specify @option{-mapp-regs} to generate output using the global registers
5968 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
5971 To be fully SVR4 ABI compliant at the cost of some performance loss,
5972 specify @option{-mno-app-regs}. You should compile libraries and system
5973 software with this option.
5978 @opindex mhard-float
5979 Generate output containing floating point instructions. This is the
5985 @opindex msoft-float
5986 Generate output containing library calls for floating point.
5987 @strong{Warning:} the requisite libraries are not available for all SPARC
5988 targets. Normally the facilities of the machine's usual C compiler are
5989 used, but this cannot be done directly in cross-compilation. You must make
5990 your own arrangements to provide suitable library functions for
5991 cross-compilation. The embedded targets @samp{sparc-*-aout} and
5992 @samp{sparclite-*-*} do provide software floating point support.
5994 @option{-msoft-float} changes the calling convention in the output file;
5995 therefore, it is only useful if you compile @emph{all} of a program with
5996 this option. In particular, you need to compile @file{libgcc.a}, the
5997 library that comes with GCC, with @option{-msoft-float} in order for
6000 @item -mhard-quad-float
6001 @opindex mhard-quad-float
6002 Generate output containing quad-word (long double) floating point
6006 @opindex mimpure-text
6007 @option{-mimpure-text}, used in addition to @option{-shared}, tells
6008 the compiler to not pass @option{-z text} to the linker when linking a
6009 shared object. Using this option, you can link position-dependent
6010 code into a shared object.
6012 @option{-mimpure-text} suppresses the ``relocations remain against
6013 allocatable but non-writable sections'' linker error message.
6014 However, the necessary relocations will trigger copy-on-write, and the
6015 shared object is not actually shared across processes. Instead of
6016 using @option{-mimpure-text}, you should compile all source code with
6017 @option{-fpic} or @option{-fPIC}.
6019 This option is only available on SunOS and Solaris.
6021 @item -msoft-quad-float
6022 @opindex msoft-quad-float
6023 Generate output containing library calls for quad-word (long double)
6024 floating point instructions. The functions called are those specified
6025 in the SPARC ABI@. This is the default.
6027 As of this writing, there are no sparc implementations that have hardware
6028 support for the quad-word floating point instructions. They all invoke
6029 a trap handler for one of these instructions, and then the trap handler
6030 emulates the effect of the instruction. Because of the trap handler overhead,
6031 this is much slower than calling the ABI library routines. Thus the
6032 @option{-msoft-quad-float} option is the default.
6038 With @option{-mflat}, the compiler does not generate save/restore instructions
6039 and will use a ``flat'' or single register window calling convention.
6040 This model uses %i7 as the frame pointer and is compatible with the normal
6041 register window model. Code from either may be intermixed.
6042 The local registers and the input registers (0--5) are still treated as
6043 ``call saved'' registers and will be saved on the stack as necessary.
6045 With @option{-mno-flat} (the default), the compiler emits save/restore
6046 instructions (except for leaf functions) and is the normal mode of operation.
6048 @item -mno-unaligned-doubles
6049 @itemx -munaligned-doubles
6050 @opindex mno-unaligned-doubles
6051 @opindex munaligned-doubles
6052 Assume that doubles have 8 byte alignment. This is the default.
6054 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6055 alignment only if they are contained in another type, or if they have an
6056 absolute address. Otherwise, it assumes they have 4 byte alignment.
6057 Specifying this option avoids some rare compatibility problems with code
6058 generated by other compilers. It is not the default because it results
6059 in a performance loss, especially for floating point code.
6061 @item -mno-faster-structs
6062 @itemx -mfaster-structs
6063 @opindex mno-faster-structs
6064 @opindex mfaster-structs
6065 With @option{-mfaster-structs}, the compiler assumes that structures
6066 should have 8 byte alignment. This enables the use of pairs of
6067 @code{ldd} and @code{std} instructions for copies in structure
6068 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6069 However, the use of this changed alignment directly violates the SPARC
6070 ABI@. Thus, it's intended only for use on targets where the developer
6071 acknowledges that their resulting code will not be directly in line with
6072 the rules of the ABI@.
6078 These two options select variations on the SPARC architecture.
6080 By default (unless specifically configured for the Fujitsu SPARClite),
6081 GCC generates code for the v7 variant of the SPARC architecture.
6083 @option{-mv8} will give you SPARC v8 code. The only difference from v7
6084 code is that the compiler emits the integer multiply and integer
6085 divide instructions which exist in SPARC v8 but not in SPARC v7.
6087 @option{-msparclite} will give you SPARClite code. This adds the integer
6088 multiply, integer divide step and scan (@code{ffs}) instructions which
6089 exist in SPARClite but not in SPARC v7.
6091 These options are deprecated and will be deleted in a future GCC release.
6092 They have been replaced with @option{-mcpu=xxx}.
6097 @opindex msupersparc
6098 These two options select the processor for which the code is optimized.
6100 With @option{-mcypress} (the default), the compiler optimizes code for the
6101 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
6102 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
6104 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
6105 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
6106 of the full SPARC v8 instruction set.
6108 These options are deprecated and will be deleted in a future GCC release.
6109 They have been replaced with @option{-mcpu=xxx}.
6111 @item -mcpu=@var{cpu_type}
6113 Set the instruction set, register set, and instruction scheduling parameters
6114 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6115 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6116 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
6117 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6120 Default instruction scheduling parameters are used for values that select
6121 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6122 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6124 Here is a list of each supported architecture and their supported
6129 v8: supersparc, hypersparc
6130 sparclite: f930, f934, sparclite86x
6132 v9: ultrasparc, ultrasparc3
6135 @item -mtune=@var{cpu_type}
6137 Set the instruction scheduling parameters for machine type
6138 @var{cpu_type}, but do not set the instruction set or register set that the
6139 option @option{-mcpu=@var{cpu_type}} would.
6141 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6142 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6143 that select a particular cpu implementation. Those are @samp{cypress},
6144 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6145 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6150 These @samp{-m} switches are supported in addition to the above
6151 on the SPARCLET processor.
6154 @item -mlittle-endian
6155 @opindex mlittle-endian
6156 Generate code for a processor running in little-endian mode.
6160 Treat register @code{%g0} as a normal register.
6161 GCC will continue to clobber it as necessary but will not assume
6162 it always reads as 0.
6164 @item -mbroken-saverestore
6165 @opindex mbroken-saverestore
6166 Generate code that does not use non-trivial forms of the @code{save} and
6167 @code{restore} instructions. Early versions of the SPARCLET processor do
6168 not correctly handle @code{save} and @code{restore} instructions used with
6169 arguments. They correctly handle them used without arguments. A @code{save}
6170 instruction used without arguments increments the current window pointer
6171 but does not allocate a new stack frame. It is assumed that the window
6172 overflow trap handler will properly handle this case as will interrupt
6176 These @samp{-m} switches are supported in addition to the above
6177 on SPARC V9 processors in 64-bit environments.
6180 @item -mlittle-endian
6181 @opindex mlittle-endian
6182 Generate code for a processor running in little-endian mode.
6188 Generate code for a 32-bit or 64-bit environment.
6189 The 32-bit environment sets int, long and pointer to 32 bits.
6190 The 64-bit environment sets int to 32 bits and long and pointer
6193 @item -mcmodel=medlow
6194 @opindex mcmodel=medlow
6195 Generate code for the Medium/Low code model: the program must be linked
6196 in the low 32 bits of the address space. Pointers are 64 bits.
6197 Programs can be statically or dynamically linked.
6199 @item -mcmodel=medmid
6200 @opindex mcmodel=medmid
6201 Generate code for the Medium/Middle code model: the program must be linked
6202 in the low 44 bits of the address space, the text segment must be less than
6203 2G bytes, and data segment must be within 2G of the text segment.
6204 Pointers are 64 bits.
6206 @item -mcmodel=medany
6207 @opindex mcmodel=medany
6208 Generate code for the Medium/Anywhere code model: the program may be linked
6209 anywhere in the address space, the text segment must be less than
6210 2G bytes, and data segment must be within 2G of the text segment.
6211 Pointers are 64 bits.
6213 @item -mcmodel=embmedany
6214 @opindex mcmodel=embmedany
6215 Generate code for the Medium/Anywhere code model for embedded systems:
6216 assume a 32-bit text and a 32-bit data segment, both starting anywhere
6217 (determined at link time). Register %g4 points to the base of the
6218 data segment. Pointers are still 64 bits.
6219 Programs are statically linked, PIC is not supported.
6222 @itemx -mno-stack-bias
6223 @opindex mstack-bias
6224 @opindex mno-stack-bias
6225 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6226 frame pointer if present, are offset by @minus{}2047 which must be added back
6227 when making stack frame references.
6228 Otherwise, assume no such offset is present.
6232 @subsection ARM Options
6235 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6240 @opindex mapcs-frame
6241 Generate a stack frame that is compliant with the ARM Procedure Call
6242 Standard for all functions, even if this is not strictly necessary for
6243 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6244 with this option will cause the stack frames not to be generated for
6245 leaf functions. The default is @option{-mno-apcs-frame}.
6249 This is a synonym for @option{-mapcs-frame}.
6253 Generate code for a processor running with a 26-bit program counter,
6254 and conforming to the function calling standards for the APCS 26-bit
6255 option. This option replaces the @option{-m2} and @option{-m3} options
6256 of previous releases of the compiler.
6260 Generate code for a processor running with a 32-bit program counter,
6261 and conforming to the function calling standards for the APCS 32-bit
6262 option. This option replaces the @option{-m6} option of previous releases
6266 @c not currently implemented
6267 @item -mapcs-stack-check
6268 @opindex mapcs-stack-check
6269 Generate code to check the amount of stack space available upon entry to
6270 every function (that actually uses some stack space). If there is
6271 insufficient space available then either the function
6272 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6273 called, depending upon the amount of stack space required. The run time
6274 system is required to provide these functions. The default is
6275 @option{-mno-apcs-stack-check}, since this produces smaller code.
6277 @c not currently implemented
6279 @opindex mapcs-float
6280 Pass floating point arguments using the float point registers. This is
6281 one of the variants of the APCS@. This option is recommended if the
6282 target hardware has a floating point unit or if a lot of floating point
6283 arithmetic is going to be performed by the code. The default is
6284 @option{-mno-apcs-float}, since integer only code is slightly increased in
6285 size if @option{-mapcs-float} is used.
6287 @c not currently implemented
6288 @item -mapcs-reentrant
6289 @opindex mapcs-reentrant
6290 Generate reentrant, position independent code. The default is
6291 @option{-mno-apcs-reentrant}.
6294 @item -mthumb-interwork
6295 @opindex mthumb-interwork
6296 Generate code which supports calling between the ARM and Thumb
6297 instruction sets. Without this option the two instruction sets cannot
6298 be reliably used inside one program. The default is
6299 @option{-mno-thumb-interwork}, since slightly larger code is generated
6300 when @option{-mthumb-interwork} is specified.
6302 @item -mno-sched-prolog
6303 @opindex mno-sched-prolog
6304 Prevent the reordering of instructions in the function prolog, or the
6305 merging of those instruction with the instructions in the function's
6306 body. This means that all functions will start with a recognizable set
6307 of instructions (or in fact one of a choice from a small set of
6308 different function prologues), and this information can be used to
6309 locate the start if functions inside an executable piece of code. The
6310 default is @option{-msched-prolog}.
6313 @opindex mhard-float
6314 Generate output containing floating point instructions. This is the
6318 @opindex msoft-float
6319 Generate output containing library calls for floating point.
6320 @strong{Warning:} the requisite libraries are not available for all ARM
6321 targets. Normally the facilities of the machine's usual C compiler are
6322 used, but this cannot be done directly in cross-compilation. You must make
6323 your own arrangements to provide suitable library functions for
6326 @option{-msoft-float} changes the calling convention in the output file;
6327 therefore, it is only useful if you compile @emph{all} of a program with
6328 this option. In particular, you need to compile @file{libgcc.a}, the
6329 library that comes with GCC, with @option{-msoft-float} in order for
6332 @item -mlittle-endian
6333 @opindex mlittle-endian
6334 Generate code for a processor running in little-endian mode. This is
6335 the default for all standard configurations.
6338 @opindex mbig-endian
6339 Generate code for a processor running in big-endian mode; the default is
6340 to compile code for a little-endian processor.
6342 @item -mwords-little-endian
6343 @opindex mwords-little-endian
6344 This option only applies when generating code for big-endian processors.
6345 Generate code for a little-endian word order but a big-endian byte
6346 order. That is, a byte order of the form @samp{32107654}. Note: this
6347 option should only be used if you require compatibility with code for
6348 big-endian ARM processors generated by versions of the compiler prior to
6351 @item -malignment-traps
6352 @opindex malignment-traps
6353 Generate code that will not trap if the MMU has alignment traps enabled.
6354 On ARM architectures prior to ARMv4, there were no instructions to
6355 access half-word objects stored in memory. However, when reading from
6356 memory a feature of the ARM architecture allows a word load to be used,
6357 even if the address is unaligned, and the processor core will rotate the
6358 data as it is being loaded. This option tells the compiler that such
6359 misaligned accesses will cause a MMU trap and that it should instead
6360 synthesize the access as a series of byte accesses. The compiler can
6361 still use word accesses to load half-word data if it knows that the
6362 address is aligned to a word boundary.
6364 This option is ignored when compiling for ARM architecture 4 or later,
6365 since these processors have instructions to directly access half-word
6368 @item -mno-alignment-traps
6369 @opindex mno-alignment-traps
6370 Generate code that assumes that the MMU will not trap unaligned
6371 accesses. This produces better code when the target instruction set
6372 does not have half-word memory operations (i.e.@: implementations prior to
6375 Note that you cannot use this option to access unaligned word objects,
6376 since the processor will only fetch one 32-bit aligned object from
6379 The default setting for most targets is @option{-mno-alignment-traps}, since
6380 this produces better code when there are no half-word memory
6381 instructions available.
6383 @item -mshort-load-bytes
6384 @itemx -mno-short-load-words
6385 @opindex mshort-load-bytes
6386 @opindex mno-short-load-words
6387 These are deprecated aliases for @option{-malignment-traps}.
6389 @item -mno-short-load-bytes
6390 @itemx -mshort-load-words
6391 @opindex mno-short-load-bytes
6392 @opindex mshort-load-words
6393 This are deprecated aliases for @option{-mno-alignment-traps}.
6395 @item -mcpu=@var{name}
6397 This specifies the name of the target ARM processor. GCC uses this name
6398 to determine what kind of instructions it can emit when generating
6399 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6400 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6401 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6402 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6403 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6404 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6405 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6406 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6407 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
6408 @samp{arm1020t}, @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
6410 @itemx -mtune=@var{name}
6412 This option is very similar to the @option{-mcpu=} option, except that
6413 instead of specifying the actual target processor type, and hence
6414 restricting which instructions can be used, it specifies that GCC should
6415 tune the performance of the code as if the target were of the type
6416 specified in this option, but still choosing the instructions that it
6417 will generate based on the cpu specified by a @option{-mcpu=} option.
6418 For some ARM implementations better performance can be obtained by using
6421 @item -march=@var{name}
6423 This specifies the name of the target ARM architecture. GCC uses this
6424 name to determine what kind of instructions it can emit when generating
6425 assembly code. This option can be used in conjunction with or instead
6426 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6427 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6428 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{iwmmxt}, @samp{ep9312}.
6430 @item -mfpe=@var{number}
6431 @itemx -mfp=@var{number}
6434 This specifies the version of the floating point emulation available on
6435 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6436 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6438 @item -mstructure-size-boundary=@var{n}
6439 @opindex mstructure-size-boundary
6440 The size of all structures and unions will be rounded up to a multiple
6441 of the number of bits set by this option. Permissible values are 8 and
6442 32. The default value varies for different toolchains. For the COFF
6443 targeted toolchain the default value is 8. Specifying the larger number
6444 can produce faster, more efficient code, but can also increase the size
6445 of the program. The two values are potentially incompatible. Code
6446 compiled with one value cannot necessarily expect to work with code or
6447 libraries compiled with the other value, if they exchange information
6448 using structures or unions.
6450 @item -mabort-on-noreturn
6451 @opindex mabort-on-noreturn
6452 Generate a call to the function @code{abort} at the end of a
6453 @code{noreturn} function. It will be executed if the function tries to
6457 @itemx -mno-long-calls
6458 @opindex mlong-calls
6459 @opindex mno-long-calls
6460 Tells the compiler to perform function calls by first loading the
6461 address of the function into a register and then performing a subroutine
6462 call on this register. This switch is needed if the target function
6463 will lie outside of the 64 megabyte addressing range of the offset based
6464 version of subroutine call instruction.
6466 Even if this switch is enabled, not all function calls will be turned
6467 into long calls. The heuristic is that static functions, functions
6468 which have the @samp{short-call} attribute, functions that are inside
6469 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6470 definitions have already been compiled within the current compilation
6471 unit, will not be turned into long calls. The exception to this rule is
6472 that weak function definitions, functions with the @samp{long-call}
6473 attribute or the @samp{section} attribute, and functions that are within
6474 the scope of a @samp{#pragma long_calls} directive, will always be
6475 turned into long calls.
6477 This feature is not enabled by default. Specifying
6478 @option{-mno-long-calls} will restore the default behavior, as will
6479 placing the function calls within the scope of a @samp{#pragma
6480 long_calls_off} directive. Note these switches have no effect on how
6481 the compiler generates code to handle function calls via function
6484 @item -mnop-fun-dllimport
6485 @opindex mnop-fun-dllimport
6486 Disable support for the @code{dllimport} attribute.
6488 @item -msingle-pic-base
6489 @opindex msingle-pic-base
6490 Treat the register used for PIC addressing as read-only, rather than
6491 loading it in the prologue for each function. The run-time system is
6492 responsible for initializing this register with an appropriate value
6493 before execution begins.
6495 @item -mpic-register=@var{reg}
6496 @opindex mpic-register
6497 Specify the register to be used for PIC addressing. The default is R10
6498 unless stack-checking is enabled, when R9 is used.
6500 @item -mcirrus-fix-invalid-insns
6501 @opindex mcirrus-fix-invalid-insns
6502 @opindex mno-cirrus-fix-invalid-insns
6503 Insert NOPs into the instruction stream to in order to work around
6504 problems with invalid Maverick instruction combinations. This option
6505 is only valid if the @option{-mcpu=ep9312} option has been used to
6506 enable generation of instructions for the Cirrus Maverick floating
6507 point co-processor. This option is not enabled by default, since the
6508 problem is only present in older Maverick implementations. The default
6509 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6512 @item -mpoke-function-name
6513 @opindex mpoke-function-name
6514 Write the name of each function into the text section, directly
6515 preceding the function prologue. The generated code is similar to this:
6519 .ascii "arm_poke_function_name", 0
6522 .word 0xff000000 + (t1 - t0)
6523 arm_poke_function_name
6525 stmfd sp!, @{fp, ip, lr, pc@}
6529 When performing a stack backtrace, code can inspect the value of
6530 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6531 location @code{pc - 12} and the top 8 bits are set, then we know that
6532 there is a function name embedded immediately preceding this location
6533 and has length @code{((pc[-3]) & 0xff000000)}.
6537 Generate code for the 16-bit Thumb instruction set. The default is to
6538 use the 32-bit ARM instruction set.
6541 @opindex mtpcs-frame
6542 Generate a stack frame that is compliant with the Thumb Procedure Call
6543 Standard for all non-leaf functions. (A leaf function is one that does
6544 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6546 @item -mtpcs-leaf-frame
6547 @opindex mtpcs-leaf-frame
6548 Generate a stack frame that is compliant with the Thumb Procedure Call
6549 Standard for all leaf functions. (A leaf function is one that does
6550 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6552 @item -mcallee-super-interworking
6553 @opindex mcallee-super-interworking
6554 Gives all externally visible functions in the file being compiled an ARM
6555 instruction set header which switches to Thumb mode before executing the
6556 rest of the function. This allows these functions to be called from
6557 non-interworking code.
6559 @item -mcaller-super-interworking
6560 @opindex mcaller-super-interworking
6561 Allows calls via function pointers (including virtual functions) to
6562 execute correctly regardless of whether the target code has been
6563 compiled for interworking or not. There is a small overhead in the cost
6564 of executing a function pointer if this option is enabled.
6568 @node MN10200 Options
6569 @subsection MN10200 Options
6570 @cindex MN10200 options
6572 These @option{-m} options are defined for Matsushita MN10200 architectures:
6577 Indicate to the linker that it should perform a relaxation optimization pass
6578 to shorten branches, calls and absolute memory addresses. This option only
6579 has an effect when used on the command line for the final link step.
6581 This option makes symbolic debugging impossible.
6584 @node MN10300 Options
6585 @subsection MN10300 Options
6586 @cindex MN10300 options
6588 These @option{-m} options are defined for Matsushita MN10300 architectures:
6593 Generate code to avoid bugs in the multiply instructions for the MN10300
6594 processors. This is the default.
6597 @opindex mno-mult-bug
6598 Do not generate code to avoid bugs in the multiply instructions for the
6603 Generate code which uses features specific to the AM33 processor.
6607 Do not generate code which uses features specific to the AM33 processor. This
6612 Do not link in the C run-time initialization object file.
6616 Indicate to the linker that it should perform a relaxation optimization pass
6617 to shorten branches, calls and absolute memory addresses. This option only
6618 has an effect when used on the command line for the final link step.
6620 This option makes symbolic debugging impossible.
6624 @node M32R/D Options
6625 @subsection M32R/D Options
6626 @cindex M32R/D options
6628 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6633 Generate code for the M32R/X@.
6637 Generate code for the M32R@. This is the default.
6639 @item -mcode-model=small
6640 @opindex mcode-model=small
6641 Assume all objects live in the lower 16MB of memory (so that their addresses
6642 can be loaded with the @code{ld24} instruction), and assume all subroutines
6643 are reachable with the @code{bl} instruction.
6644 This is the default.
6646 The addressability of a particular object can be set with the
6647 @code{model} attribute.
6649 @item -mcode-model=medium
6650 @opindex mcode-model=medium
6651 Assume objects may be anywhere in the 32-bit address space (the compiler
6652 will generate @code{seth/add3} instructions to load their addresses), and
6653 assume all subroutines are reachable with the @code{bl} instruction.
6655 @item -mcode-model=large
6656 @opindex mcode-model=large
6657 Assume objects may be anywhere in the 32-bit address space (the compiler
6658 will generate @code{seth/add3} instructions to load their addresses), and
6659 assume subroutines may not be reachable with the @code{bl} instruction
6660 (the compiler will generate the much slower @code{seth/add3/jl}
6661 instruction sequence).
6664 @opindex msdata=none
6665 Disable use of the small data area. Variables will be put into
6666 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6667 @code{section} attribute has been specified).
6668 This is the default.
6670 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6671 Objects may be explicitly put in the small data area with the
6672 @code{section} attribute using one of these sections.
6675 @opindex msdata=sdata
6676 Put small global and static data in the small data area, but do not
6677 generate special code to reference them.
6681 Put small global and static data in the small data area, and generate
6682 special instructions to reference them.
6686 @cindex smaller data references
6687 Put global and static objects less than or equal to @var{num} bytes
6688 into the small data or bss sections instead of the normal data or bss
6689 sections. The default value of @var{num} is 8.
6690 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6691 for this option to have any effect.
6693 All modules should be compiled with the same @option{-G @var{num}} value.
6694 Compiling with different values of @var{num} may or may not work; if it
6695 doesn't the linker will give an error message---incorrect code will not be
6701 @subsection M88K Options
6702 @cindex M88k options
6704 These @samp{-m} options are defined for Motorola 88k architectures:
6709 Generate code that works well on both the m88100 and the
6714 Generate code that works best for the m88100, but that also
6719 Generate code that works best for the m88110, and may not run
6724 Obsolete option to be removed from the next revision.
6727 @item -midentify-revision
6728 @opindex midentify-revision
6729 @cindex identifying source, compiler (88k)
6730 Include an @code{ident} directive in the assembler output recording the
6731 source file name, compiler name and version, timestamp, and compilation
6734 @item -mno-underscores
6735 @opindex mno-underscores
6736 @cindex underscores, avoiding (88k)
6737 In assembler output, emit symbol names without adding an underscore
6738 character at the beginning of each name. The default is to use an
6739 underscore as prefix on each name.
6741 @item -mocs-debug-info
6742 @itemx -mno-ocs-debug-info
6743 @opindex mocs-debug-info
6744 @opindex mno-ocs-debug-info
6746 @cindex debugging, 88k OCS
6747 Include (or omit) additional debugging information (about registers used
6748 in each stack frame) as specified in the 88open Object Compatibility
6749 Standard, ``OCS''@. This extra information allows debugging of code that
6750 has had the frame pointer eliminated. The default for SVr4 and Delta 88
6751 SVr3.2 is to include this information; other 88k configurations omit this
6752 information by default.
6754 @item -mocs-frame-position
6755 @opindex mocs-frame-position
6756 @cindex register positions in frame (88k)
6757 When emitting COFF debugging information for automatic variables and
6758 parameters stored on the stack, use the offset from the canonical frame
6759 address, which is the stack pointer (register 31) on entry to the
6760 function. The SVr4 and Delta88 SVr3.2, and BCS configurations use
6761 @option{-mocs-frame-position}; other 88k configurations have the default
6762 @option{-mno-ocs-frame-position}.
6764 @item -mno-ocs-frame-position
6765 @opindex mno-ocs-frame-position
6766 @cindex register positions in frame (88k)
6767 When emitting COFF debugging information for automatic variables and
6768 parameters stored on the stack, use the offset from the frame pointer
6769 register (register 30). When this option is in effect, the frame
6770 pointer is not eliminated when debugging information is selected by the
6773 @item -moptimize-arg-area
6774 @opindex moptimize-arg-area
6775 @cindex arguments in frame (88k)
6776 Save space by reorganizing the stack frame. This option generates code
6777 that does not agree with the 88open specifications, but uses less
6780 @itemx -mno-optimize-arg-area
6781 @opindex mno-optimize-arg-area
6782 Do not reorganize the stack frame to save space. This is the default.
6783 The generated conforms to the specification, but uses more memory.
6785 @item -mshort-data-@var{num}
6786 @opindex mshort-data
6787 @cindex smaller data references (88k)
6788 @cindex r0-relative references (88k)
6789 Generate smaller data references by making them relative to @code{r0},
6790 which allows loading a value using a single instruction (rather than the
6791 usual two). You control which data references are affected by
6792 specifying @var{num} with this option. For example, if you specify
6793 @option{-mshort-data-512}, then the data references affected are those
6794 involving displacements of less than 512 bytes.
6795 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6798 @item -mserialize-volatile
6799 @opindex mserialize-volatile
6800 @itemx -mno-serialize-volatile
6801 @opindex mno-serialize-volatile
6802 @cindex sequential consistency on 88k
6803 Do, or don't, generate code to guarantee sequential consistency
6804 of volatile memory references. By default, consistency is
6807 The order of memory references made by the MC88110 processor does
6808 not always match the order of the instructions requesting those
6809 references. In particular, a load instruction may execute before
6810 a preceding store instruction. Such reordering violates
6811 sequential consistency of volatile memory references, when there
6812 are multiple processors. When consistency must be guaranteed,
6813 GCC generates special instructions, as needed, to force
6814 execution in the proper order.
6816 The MC88100 processor does not reorder memory references and so
6817 always provides sequential consistency. However, by default, GCC
6818 generates the special instructions to guarantee consistency
6819 even when you use @option{-m88100}, so that the code may be run on an
6820 MC88110 processor. If you intend to run your code only on the
6821 MC88100 processor, you may use @option{-mno-serialize-volatile}.
6823 The extra code generated to guarantee consistency may affect the
6824 performance of your application. If you know that you can safely
6825 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
6831 @cindex assembler syntax, 88k
6833 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
6834 related to System V release 4 (SVr4). This controls the following:
6838 Which variant of the assembler syntax to emit.
6840 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
6841 that is used on System V release 4.
6843 @option{-msvr4} makes GCC issue additional declaration directives used in
6847 @option{-msvr4} is the default for the m88k-motorola-sysv4 configuration.
6848 @option{-msvr3} is the default for all other m88k configurations.
6850 @item -mversion-03.00
6851 @opindex mversion-03.00
6852 This option is obsolete, and is ignored.
6853 @c ??? which asm syntax better for GAS? option there too?
6855 @item -mno-check-zero-division
6856 @itemx -mcheck-zero-division
6857 @opindex mno-check-zero-division
6858 @opindex mcheck-zero-division
6859 @cindex zero division on 88k
6860 Do, or don't, generate code to guarantee that integer division by
6861 zero will be detected. By default, detection is guaranteed.
6863 Some models of the MC88100 processor fail to trap upon integer
6864 division by zero under certain conditions. By default, when
6865 compiling code that might be run on such a processor, GCC
6866 generates code that explicitly checks for zero-valued divisors
6867 and traps with exception number 503 when one is detected. Use of
6868 @option{-mno-check-zero-division} suppresses such checking for code
6869 generated to run on an MC88100 processor.
6871 GCC assumes that the MC88110 processor correctly detects all instances
6872 of integer division by zero. When @option{-m88110} is specified, no
6873 explicit checks for zero-valued divisors are generated, and both
6874 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
6877 @item -muse-div-instruction
6878 @opindex muse-div-instruction
6879 @cindex divide instruction, 88k
6880 Use the div instruction for signed integer division on the
6881 MC88100 processor. By default, the div instruction is not used.
6883 On the MC88100 processor the signed integer division instruction
6884 div) traps to the operating system on a negative operand. The
6885 operating system transparently completes the operation, but at a
6886 large cost in execution time. By default, when compiling code
6887 that might be run on an MC88100 processor, GCC emulates signed
6888 integer division using the unsigned integer division instruction
6889 divu), thereby avoiding the large penalty of a trap to the
6890 operating system. Such emulation has its own, smaller, execution
6891 cost in both time and space. To the extent that your code's
6892 important signed integer division operations are performed on two
6893 nonnegative operands, it may be desirable to use the div
6894 instruction directly.
6896 On the MC88110 processor the div instruction (also known as the
6897 divs instruction) processes negative operands without trapping to
6898 the operating system. When @option{-m88110} is specified,
6899 @option{-muse-div-instruction} is ignored, and the div instruction is used
6900 for signed integer division.
6902 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
6903 particular, the behavior of such a division with and without
6904 @option{-muse-div-instruction} may differ.
6906 @item -mtrap-large-shift
6907 @itemx -mhandle-large-shift
6908 @opindex mtrap-large-shift
6909 @opindex mhandle-large-shift
6910 @cindex bit shift overflow (88k)
6911 @cindex large bit shifts (88k)
6912 Include code to detect bit-shifts of more than 31 bits; respectively,
6913 trap such shifts or emit code to handle them properly. By default GCC
6914 makes no special provision for large bit shifts.
6916 @item -mwarn-passed-structs
6917 @opindex mwarn-passed-structs
6918 @cindex structure passing (88k)
6919 Warn when a function passes a struct as an argument or result.
6920 Structure-passing conventions have changed during the evolution of the C
6921 language, and are often the source of portability problems. By default,
6922 GCC issues no such warning.
6925 @c break page here to avoid unsightly interparagraph stretch.
6929 @node RS/6000 and PowerPC Options
6930 @subsection IBM RS/6000 and PowerPC Options
6931 @cindex RS/6000 and PowerPC Options
6932 @cindex IBM RS/6000 and PowerPC Options
6934 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
6942 @itemx -mpowerpc-gpopt
6943 @itemx -mno-powerpc-gpopt
6944 @itemx -mpowerpc-gfxopt
6945 @itemx -mno-powerpc-gfxopt
6947 @itemx -mno-powerpc64
6953 @opindex mno-powerpc
6954 @opindex mpowerpc-gpopt
6955 @opindex mno-powerpc-gpopt
6956 @opindex mpowerpc-gfxopt
6957 @opindex mno-powerpc-gfxopt
6959 @opindex mno-powerpc64
6960 GCC supports two related instruction set architectures for the
6961 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
6962 instructions supported by the @samp{rios} chip set used in the original
6963 RS/6000 systems and the @dfn{PowerPC} instruction set is the
6964 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
6965 the IBM 4xx microprocessors.
6967 Neither architecture is a subset of the other. However there is a
6968 large common subset of instructions supported by both. An MQ
6969 register is included in processors supporting the POWER architecture.
6971 You use these options to specify which instructions are available on the
6972 processor you are using. The default value of these options is
6973 determined when configuring GCC@. Specifying the
6974 @option{-mcpu=@var{cpu_type}} overrides the specification of these
6975 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
6976 rather than the options listed above.
6978 The @option{-mpower} option allows GCC to generate instructions that
6979 are found only in the POWER architecture and to use the MQ register.
6980 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
6981 to generate instructions that are present in the POWER2 architecture but
6982 not the original POWER architecture.
6984 The @option{-mpowerpc} option allows GCC to generate instructions that
6985 are found only in the 32-bit subset of the PowerPC architecture.
6986 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
6987 GCC to use the optional PowerPC architecture instructions in the
6988 General Purpose group, including floating-point square root. Specifying
6989 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
6990 use the optional PowerPC architecture instructions in the Graphics
6991 group, including floating-point select.
6993 The @option{-mpowerpc64} option allows GCC to generate the additional
6994 64-bit instructions that are found in the full PowerPC64 architecture
6995 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
6996 @option{-mno-powerpc64}.
6998 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
6999 will use only the instructions in the common subset of both
7000 architectures plus some special AIX common-mode calls, and will not use
7001 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
7002 permits GCC to use any instruction from either architecture and to
7003 allow use of the MQ register; specify this for the Motorola MPC601.
7005 @item -mnew-mnemonics
7006 @itemx -mold-mnemonics
7007 @opindex mnew-mnemonics
7008 @opindex mold-mnemonics
7009 Select which mnemonics to use in the generated assembler code. With
7010 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
7011 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
7012 assembler mnemonics defined for the POWER architecture. Instructions
7013 defined in only one architecture have only one mnemonic; GCC uses that
7014 mnemonic irrespective of which of these options is specified.
7016 GCC defaults to the mnemonics appropriate for the architecture in
7017 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
7018 value of these option. Unless you are building a cross-compiler, you
7019 should normally not specify either @option{-mnew-mnemonics} or
7020 @option{-mold-mnemonics}, but should instead accept the default.
7022 @item -mcpu=@var{cpu_type}
7024 Set architecture type, register usage, choice of mnemonics, and
7025 instruction scheduling parameters for machine type @var{cpu_type}.
7026 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
7027 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
7028 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
7029 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
7030 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
7031 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
7033 @option{-mcpu=common} selects a completely generic processor. Code
7034 generated under this option will run on any POWER or PowerPC processor.
7035 GCC will use only the instructions in the common subset of both
7036 architectures, and will not use the MQ register. GCC assumes a generic
7037 processor model for scheduling purposes.
7039 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
7040 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
7041 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
7042 types, with an appropriate, generic processor model assumed for
7043 scheduling purposes.
7045 The other options specify a specific processor. Code generated under
7046 those options will run best on that processor, and may not run at all on
7049 The @option{-mcpu} options automatically enable or disable other
7050 @option{-m} options as follows:
7054 @option{-mno-power}, @option{-mno-powerpc}
7061 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
7076 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7079 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7084 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
7087 @item -mtune=@var{cpu_type}
7089 Set the instruction scheduling parameters for machine type
7090 @var{cpu_type}, but do not set the architecture type, register usage, or
7091 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7092 values for @var{cpu_type} are used for @option{-mtune} as for
7093 @option{-mcpu}. If both are specified, the code generated will use the
7094 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7095 scheduling parameters set by @option{-mtune}.
7100 @opindex mno-altivec
7101 These switches enable or disable the use of built-in functions that
7102 allow access to the AltiVec instruction set. You may also need to set
7103 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7108 Extend the current ABI with SPE ABI extensions. This does not change
7109 the default ABI, instead it adds the SPE ABI extensions to the current
7113 @opindex mabi=no-spe
7114 Disable Booke SPE ABI extensions for the current ABI.
7116 @item -misel=@var{yes/no}
7119 This switch enables or disables the generation of ISEL instructions.
7121 @item -mspe=@var{yes/no}
7124 This switch enables or disables the generation of SPE simd
7127 @item -mfloat-gprs=@var{yes/no}
7129 @opindex mfloat-gprs
7130 This switch enables or disables the generation of floating point
7131 operations on the general purpose registers for architectures that
7132 support it. This option is currently only available on the MPC8540.
7135 @itemx -mno-fp-in-toc
7136 @itemx -mno-sum-in-toc
7137 @itemx -mminimal-toc
7139 @opindex mno-fp-in-toc
7140 @opindex mno-sum-in-toc
7141 @opindex mminimal-toc
7142 Modify generation of the TOC (Table Of Contents), which is created for
7143 every executable file. The @option{-mfull-toc} option is selected by
7144 default. In that case, GCC will allocate at least one TOC entry for
7145 each unique non-automatic variable reference in your program. GCC
7146 will also place floating-point constants in the TOC@. However, only
7147 16,384 entries are available in the TOC@.
7149 If you receive a linker error message that saying you have overflowed
7150 the available TOC space, you can reduce the amount of TOC space used
7151 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7152 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7153 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7154 generate code to calculate the sum of an address and a constant at
7155 run-time instead of putting that sum into the TOC@. You may specify one
7156 or both of these options. Each causes GCC to produce very slightly
7157 slower and larger code at the expense of conserving TOC space.
7159 If you still run out of space in the TOC even when you specify both of
7160 these options, specify @option{-mminimal-toc} instead. This option causes
7161 GCC to make only one TOC entry for every file. When you specify this
7162 option, GCC will produce code that is slower and larger but which
7163 uses extremely little TOC space. You may wish to use this option
7164 only on files that contain less frequently executed code.
7170 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7171 @code{long} type, and the infrastructure needed to support them.
7172 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7173 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7174 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7179 @opindex mno-xl-call
7180 On AIX, pass floating-point arguments to prototyped functions beyond the
7181 register save area (RSA) on the stack in addition to argument FPRs. The
7182 AIX calling convention was extended but not initially documented to
7183 handle an obscure K&R C case of calling a function that takes the
7184 address of its arguments with fewer arguments than declared. AIX XL
7185 compilers access floating point arguments which do not fit in the
7186 RSA from the stack when a subroutine is compiled without
7187 optimization. Because always storing floating-point arguments on the
7188 stack is inefficient and rarely needed, this option is not enabled by
7189 default and only is necessary when calling subroutines compiled by AIX
7190 XL compilers without optimization.
7194 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7195 application written to use message passing with special startup code to
7196 enable the application to run. The system must have PE installed in the
7197 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7198 must be overridden with the @option{-specs=} option to specify the
7199 appropriate directory location. The Parallel Environment does not
7200 support threads, so the @option{-mpe} option and the @option{-pthread}
7201 option are incompatible.
7203 @item -malign-natural
7204 @itemx -malign-power
7205 @opindex malign-natural
7206 @opindex malign-power
7207 On AIX, Darwin, and 64-bit PowerPC Linux, the option
7208 @option{-malign-natural} overrides the ABI-defined alignment of larger
7209 types, such as floating-point doubles, on their natural size-based boundary.
7210 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7211 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7215 @opindex msoft-float
7216 @opindex mhard-float
7217 Generate code that does not use (uses) the floating-point register set.
7218 Software floating point emulation is provided if you use the
7219 @option{-msoft-float} option, and pass the option to GCC when linking.
7222 @itemx -mno-multiple
7224 @opindex mno-multiple
7225 Generate code that uses (does not use) the load multiple word
7226 instructions and the store multiple word instructions. These
7227 instructions are generated by default on POWER systems, and not
7228 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7229 endian PowerPC systems, since those instructions do not work when the
7230 processor is in little endian mode. The exceptions are PPC740 and
7231 PPC750 which permit the instructions usage in little endian mode.
7237 Generate code that uses (does not use) the load string instructions
7238 and the store string word instructions to save multiple registers and
7239 do small block moves. These instructions are generated by default on
7240 POWER systems, and not generated on PowerPC systems. Do not use
7241 @option{-mstring} on little endian PowerPC systems, since those
7242 instructions do not work when the processor is in little endian mode.
7243 The exceptions are PPC740 and PPC750 which permit the instructions
7244 usage in little endian mode.
7250 Generate code that uses (does not use) the load or store instructions
7251 that update the base register to the address of the calculated memory
7252 location. These instructions are generated by default. If you use
7253 @option{-mno-update}, there is a small window between the time that the
7254 stack pointer is updated and the address of the previous frame is
7255 stored, which means code that walks the stack frame across interrupts or
7256 signals may get corrupted data.
7259 @itemx -mno-fused-madd
7260 @opindex mfused-madd
7261 @opindex mno-fused-madd
7262 Generate code that uses (does not use) the floating point multiply and
7263 accumulate instructions. These instructions are generated by default if
7264 hardware floating is used.
7266 @item -mno-bit-align
7268 @opindex mno-bit-align
7270 On System V.4 and embedded PowerPC systems do not (do) force structures
7271 and unions that contain bit-fields to be aligned to the base type of the
7274 For example, by default a structure containing nothing but 8
7275 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7276 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7277 the structure would be aligned to a 1 byte boundary and be one byte in
7280 @item -mno-strict-align
7281 @itemx -mstrict-align
7282 @opindex mno-strict-align
7283 @opindex mstrict-align
7284 On System V.4 and embedded PowerPC systems do not (do) assume that
7285 unaligned memory references will be handled by the system.
7288 @itemx -mno-relocatable
7289 @opindex mrelocatable
7290 @opindex mno-relocatable
7291 On embedded PowerPC systems generate code that allows (does not allow)
7292 the program to be relocated to a different address at runtime. If you
7293 use @option{-mrelocatable} on any module, all objects linked together must
7294 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7296 @item -mrelocatable-lib
7297 @itemx -mno-relocatable-lib
7298 @opindex mrelocatable-lib
7299 @opindex mno-relocatable-lib
7300 On embedded PowerPC systems generate code that allows (does not allow)
7301 the program to be relocated to a different address at runtime. Modules
7302 compiled with @option{-mrelocatable-lib} can be linked with either modules
7303 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7304 with modules compiled with the @option{-mrelocatable} options.
7310 On System V.4 and embedded PowerPC systems do not (do) assume that
7311 register 2 contains a pointer to a global area pointing to the addresses
7312 used in the program.
7315 @itemx -mlittle-endian
7317 @opindex mlittle-endian
7318 On System V.4 and embedded PowerPC systems compile code for the
7319 processor in little endian mode. The @option{-mlittle-endian} option is
7320 the same as @option{-mlittle}.
7325 @opindex mbig-endian
7326 On System V.4 and embedded PowerPC systems compile code for the
7327 processor in big endian mode. The @option{-mbig-endian} option is
7328 the same as @option{-mbig}.
7330 @item -mdynamic-no-pic
7331 @opindex mdynamic-no-pic
7332 On Darwin and Mac OS X systems, compile code so that it is not
7333 relocatable, but that its external references are relocatable. The
7334 resulting code is suitable for applications, but not shared
7339 On System V.4 and embedded PowerPC systems compile code using calling
7340 conventions that adheres to the March 1995 draft of the System V
7341 Application Binary Interface, PowerPC processor supplement. This is the
7342 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7344 @item -mcall-sysv-eabi
7345 @opindex mcall-sysv-eabi
7346 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7348 @item -mcall-sysv-noeabi
7349 @opindex mcall-sysv-noeabi
7350 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7352 @item -mcall-solaris
7353 @opindex mcall-solaris
7354 On System V.4 and embedded PowerPC systems compile code for the Solaris
7358 @opindex mcall-linux
7359 On System V.4 and embedded PowerPC systems compile code for the
7360 Linux-based GNU system.
7364 On System V.4 and embedded PowerPC systems compile code for the
7365 Hurd-based GNU system.
7368 @opindex mcall-netbsd
7369 On System V.4 and embedded PowerPC systems compile code for the
7370 NetBSD operating system.
7372 @item -maix-struct-return
7373 @opindex maix-struct-return
7374 Return all structures in memory (as specified by the AIX ABI)@.
7376 @item -msvr4-struct-return
7377 @opindex msvr4-struct-return
7378 Return structures smaller than 8 bytes in registers (as specified by the
7382 @opindex mabi=altivec
7383 Extend the current ABI with AltiVec ABI extensions. This does not
7384 change the default ABI, instead it adds the AltiVec ABI extensions to
7387 @item -mabi=no-altivec
7388 @opindex mabi=no-altivec
7389 Disable AltiVec ABI extensions for the current ABI.
7392 @itemx -mno-prototype
7394 @opindex mno-prototype
7395 On System V.4 and embedded PowerPC systems assume that all calls to
7396 variable argument functions are properly prototyped. Otherwise, the
7397 compiler must insert an instruction before every non prototyped call to
7398 set or clear bit 6 of the condition code register (@var{CR}) to
7399 indicate whether floating point values were passed in the floating point
7400 registers in case the function takes a variable arguments. With
7401 @option{-mprototype}, only calls to prototyped variable argument functions
7402 will set or clear the bit.
7406 On embedded PowerPC systems, assume that the startup module is called
7407 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7408 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7413 On embedded PowerPC systems, assume that the startup module is called
7414 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7419 On embedded PowerPC systems, assume that the startup module is called
7420 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7424 @opindex myellowknife
7425 On embedded PowerPC systems, assume that the startup module is called
7426 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7431 On System V.4 and embedded PowerPC systems, specify that you are
7432 compiling for a VxWorks system.
7436 Specify that you are compiling for the WindISS simulation environment.
7440 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7441 header to indicate that @samp{eabi} extended relocations are used.
7447 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7448 Embedded Applications Binary Interface (eabi) which is a set of
7449 modifications to the System V.4 specifications. Selecting @option{-meabi}
7450 means that the stack is aligned to an 8 byte boundary, a function
7451 @code{__eabi} is called to from @code{main} to set up the eabi
7452 environment, and the @option{-msdata} option can use both @code{r2} and
7453 @code{r13} to point to two separate small data areas. Selecting
7454 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7455 do not call an initialization function from @code{main}, and the
7456 @option{-msdata} option will only use @code{r13} to point to a single
7457 small data area. The @option{-meabi} option is on by default if you
7458 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7461 @opindex msdata=eabi
7462 On System V.4 and embedded PowerPC systems, put small initialized
7463 @code{const} global and static data in the @samp{.sdata2} section, which
7464 is pointed to by register @code{r2}. Put small initialized
7465 non-@code{const} global and static data in the @samp{.sdata} section,
7466 which is pointed to by register @code{r13}. Put small uninitialized
7467 global and static data in the @samp{.sbss} section, which is adjacent to
7468 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7469 incompatible with the @option{-mrelocatable} option. The
7470 @option{-msdata=eabi} option also sets the @option{-memb} option.
7473 @opindex msdata=sysv
7474 On System V.4 and embedded PowerPC systems, put small global and static
7475 data in the @samp{.sdata} section, which is pointed to by register
7476 @code{r13}. Put small uninitialized global and static data in the
7477 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7478 The @option{-msdata=sysv} option is incompatible with the
7479 @option{-mrelocatable} option.
7481 @item -msdata=default
7483 @opindex msdata=default
7485 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7486 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7487 same as @option{-msdata=sysv}.
7490 @opindex msdata-data
7491 On System V.4 and embedded PowerPC systems, put small global and static
7492 data in the @samp{.sdata} section. Put small uninitialized global and
7493 static data in the @samp{.sbss} section. Do not use register @code{r13}
7494 to address small data however. This is the default behavior unless
7495 other @option{-msdata} options are used.
7499 @opindex msdata=none
7501 On embedded PowerPC systems, put all initialized global and static data
7502 in the @samp{.data} section, and all uninitialized data in the
7503 @samp{.bss} section.
7507 @cindex smaller data references (PowerPC)
7508 @cindex .sdata/.sdata2 references (PowerPC)
7509 On embedded PowerPC systems, put global and static items less than or
7510 equal to @var{num} bytes into the small data or bss sections instead of
7511 the normal data or bss section. By default, @var{num} is 8. The
7512 @option{-G @var{num}} switch is also passed to the linker.
7513 All modules should be compiled with the same @option{-G @var{num}} value.
7516 @itemx -mno-regnames
7518 @opindex mno-regnames
7519 On System V.4 and embedded PowerPC systems do (do not) emit register
7520 names in the assembly language output using symbolic forms.
7523 @itemx -mno-longcall
7525 @opindex mno-longcall
7526 Default to making all function calls via pointers, so that functions
7527 which reside further than 64 megabytes (67,108,864 bytes) from the
7528 current location can be called. This setting can be overridden by the
7529 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7531 Some linkers are capable of detecting out-of-range calls and generating
7532 glue code on the fly. On these systems, long calls are unnecessary and
7533 generate slower code. As of this writing, the AIX linker can do this,
7534 as can the GNU linker for PowerPC/64. It is planned to add this feature
7535 to the GNU linker for 32-bit PowerPC systems as well.
7537 In the future, we may cause GCC to ignore all longcall specifications
7538 when the linker is known to generate glue.
7542 Adds support for multithreading with the @dfn{pthreads} library.
7543 This option sets flags for both the preprocessor and linker.
7547 @node Darwin Options
7548 @subsection Darwin Options
7549 @cindex Darwin options
7551 These options are defined for all architectures running the Darwin operating
7552 system. They are useful for compatibility with other Mac OS compilers.
7557 Loads all members of static archive libraries.
7558 See man ld(1) for more information.
7560 @item -arch_errors_fatal
7561 @opindex arch_errors_fatal
7562 Cause the errors having to do with files that have the wrong architecture
7566 @opindex bind_at_load
7567 Causes the output file to be marked such that the dynamic linker will
7568 bind all undefined references when the file is loaded or launched.
7572 Produce a Mach-o bundle format file.
7573 See man ld(1) for more information.
7575 @item -bundle_loader @var{executable}
7576 @opindex bundle_loader
7577 This specifies the @var{executable} that will be loading the build
7578 output file being linked. See man ld(1) for more information.
7580 @item -allowable_client @var{client_name}
7584 @item -compatibility_version
7585 @item -current_version
7586 @item -dependency-file
7588 @item -dylinker_install_name
7591 @item -exported_symbols_list
7593 @item -flat_namespace
7594 @item -force_cpusubtype_ALL
7595 @item -force_flat_namespace
7596 @item -headerpad_max_install_names
7600 @item -keep_private_externs
7602 @item -multiply_defined
7603 @item -multiply_defined_unused
7607 @item -noseglinkedit
7608 @item -pagezero_size
7610 @item -prebind_all_twolevel_modules
7611 @item -private_bundle
7612 @item -read_only_relocs
7614 @item -sectobjectsymbols
7618 @item -sectobjectsymbols
7620 @item -seg_addr_table
7621 @item -seg_addr_table_filename
7624 @item -segs_read_only_addr
7625 @item -segs_read_write_addr
7626 @item -single_module
7630 @item -twolevel_namespace
7633 @item -unexported_symbols_list
7634 @item -weak_reference_mismatches
7637 @opindex allowable_client
7639 @opindex client_name
7640 @opindex compatibility_version
7641 @opindex current_version
7642 @opindex dependency-file
7644 @opindex dylinker_install_name
7647 @opindex exported_symbols_list
7649 @opindex flat_namespace
7650 @opindex force_cpusubtype_ALL
7651 @opindex force_flat_namespace
7652 @opindex headerpad_max_install_names
7655 @opindex install_name
7656 @opindex keep_private_externs
7657 @opindex multi_module
7658 @opindex multiply_defined
7659 @opindex multiply_defined_unused
7661 @opindex nomultidefs
7663 @opindex noseglinkedit
7664 @opindex pagezero_size
7666 @opindex prebind_all_twolevel_modules
7667 @opindex private_bundle
7668 @opindex read_only_relocs
7670 @opindex sectobjectsymbols
7674 @opindex sectobjectsymbols
7676 @opindex seg_addr_table
7677 @opindex seg_addr_table_filename
7678 @opindex seglinkedit
7680 @opindex segs_read_only_addr
7681 @opindex segs_read_write_addr
7682 @opindex single_module
7684 @opindex sub_library
7685 @opindex sub_umbrella
7686 @opindex twolevel_namespace
7689 @opindex unexported_symbols_list
7690 @opindex weak_reference_mismatches
7691 @opindex whatsloaded
7693 This options are available for Darwin linker. Darwin linker man page
7694 describes them in detail.
7699 @subsection IBM RT Options
7701 @cindex IBM RT options
7703 These @samp{-m} options are defined for the IBM RT PC:
7707 @opindex min-line-mul
7708 Use an in-line code sequence for integer multiplies. This is the
7711 @item -mcall-lib-mul
7712 @opindex mcall-lib-mul
7713 Call @code{lmul$$} for integer multiples.
7715 @item -mfull-fp-blocks
7716 @opindex mfull-fp-blocks
7717 Generate full-size floating point data blocks, including the minimum
7718 amount of scratch space recommended by IBM@. This is the default.
7720 @item -mminimum-fp-blocks
7721 @opindex mminimum-fp-blocks
7722 Do not include extra scratch space in floating point data blocks. This
7723 results in smaller code, but slower execution, since scratch space must
7724 be allocated dynamically.
7726 @cindex @file{stdarg.h} and RT PC
7727 @item -mfp-arg-in-fpregs
7728 @opindex mfp-arg-in-fpregs
7729 Use a calling sequence incompatible with the IBM calling convention in
7730 which floating point arguments are passed in floating point registers.
7731 Note that @code{stdarg.h} will not work with floating point operands
7732 if this option is specified.
7734 @item -mfp-arg-in-gregs
7735 @opindex mfp-arg-in-gregs
7736 Use the normal calling convention for floating point arguments. This is
7739 @item -mhc-struct-return
7740 @opindex mhc-struct-return
7741 Return structures of more than one word in memory, rather than in a
7742 register. This provides compatibility with the MetaWare HighC (hc)
7743 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7744 with the Portable C Compiler (pcc).
7746 @item -mnohc-struct-return
7747 @opindex mnohc-struct-return
7748 Return some structures of more than one word in registers, when
7749 convenient. This is the default. For compatibility with the
7750 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7751 option @option{-mhc-struct-return}.
7755 @subsection MIPS Options
7756 @cindex MIPS options
7758 These @samp{-m} options are defined for the MIPS family of computers:
7762 @item -march=@var{arch}
7764 Generate code that will run on @var{arch}, which can be the name of a
7765 generic MIPS ISA, or the name of a particular processor.
7767 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
7768 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
7769 The processor names are:
7770 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7772 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
7773 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
7776 @samp{vr4100}, @samp{vr4300}, and @samp{vr5000}.
7777 The special value @samp{from-abi} selects the
7778 most compatible architecture for the selected ABI (that is,
7779 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7781 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7782 (for example, @samp{-march=r2k}). Prefixes are optional, and
7783 @samp{vr} may be written @samp{r}.
7785 GCC defines two macros based on the value of this option. The first
7786 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7787 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7788 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
7789 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7790 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7792 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7793 above. In other words, it will have the full prefix and will not
7794 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
7795 the macro names the resolved architecture (either @samp{"mips1"} or
7796 @samp{"mips3"}). It names the default architecture when no
7797 @option{-march} option is given.
7799 @item -mtune=@var{arch}
7801 Optimize for @var{arch}. Among other things, this option controls
7802 the way instructions are scheduled, and the perceived cost of arithmetic
7803 operations. The list of @var{arch} values is the same as for
7806 When this option is not used, GCC will optimize for the processor
7807 specified by @option{-march}. By using @option{-march} and
7808 @option{-mtune} together, it is possible to generate code that will
7809 run on a family of processors, but optimize the code for one
7810 particular member of that family.
7812 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
7813 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
7814 @samp{-march} ones described above.
7818 Equivalent to @samp{-march=mips1}.
7822 Equivalent to @samp{-march=mips2}.
7826 Equivalent to @samp{-march=mips3}.
7830 Equivalent to @samp{-march=mips4}.
7834 Equivalent to @samp{-march=mips32}.
7838 Equivalent to @samp{-march=mips32r2}.
7842 Equivalent to @samp{-march=mips64}.
7845 @itemx -mno-fused-madd
7846 @opindex mfused-madd
7847 @opindex mno-fused-madd
7848 Generate code that uses (does not use) the floating point multiply and
7849 accumulate instructions, when they are available. These instructions
7850 are generated by default if they are available, but this may be
7851 undesirable if the extra precision causes problems or on certain chips
7852 in the mode where denormals are rounded to zero where denormals
7853 generated by multiply and accumulate instructions cause exceptions
7858 Assume that floating point registers are 32 bits wide.
7862 Assume that floating point registers are 64 bits wide.
7866 Assume that general purpose registers are 32 bits wide.
7870 Assume that general purpose registers are 64 bits wide.
7874 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
7875 explanation of the default, and the width of pointers.
7879 Force long types to be 64 bits wide. See @option{-mlong32} for an
7880 explanation of the default, and the width of pointers.
7884 Force long, int, and pointer types to be 32 bits wide.
7886 The default size of ints, longs and pointers depends on the ABI@. All
7887 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
7888 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
7889 are the same size as longs, or the same size as integer registers,
7890 whichever is smaller.
7904 Generate code for the given ABI@.
7906 Note that there are two embedded ABIs: @option{-mabi=eabi}
7907 selects the one defined by Cygnus while @option{-meabi=meabi}
7908 selects the one defined by MIPS@. Both these ABIs have
7909 32-bit and 64-bit variants. Normally, GCC will generate
7910 64-bit code when you select a 64-bit architecture, but you
7911 can use @option{-mgp32} to get 32-bit code instead.
7913 @item -mabi-fake-default
7914 @opindex mabi-fake-default
7915 You don't want to know what this option does. No, really. I mean
7916 it. Move on to the next option.
7918 What? You're still here? Oh, well@enddots{} Ok, here's the deal. GCC
7919 wants the default set of options to get the root of the multilib tree,
7920 and the shared library SONAMEs without any multilib-indicating
7921 suffixes. This is not convenience for @samp{mips64-linux-gnu}, since
7922 we want to default to the N32 ABI, while still being binary-compatible
7923 with @samp{mips-linux-gnu} if you stick to the O32 ABI@. Being
7924 binary-compatible means shared libraries should have the same SONAMEs,
7925 and libraries should live in the same location. Having O32 libraries
7926 in a sub-directory named say @file{o32} is not acceptable.
7928 So we trick GCC into believing that O32 is the default ABI, except
7929 that we override the default with some internal command-line
7930 processing magic. Problem is, if we stopped at that, and you then
7931 created a multilib-aware package that used the output of @command{gcc
7932 -print-multi-lib} to decide which multilibs to build, and how, and
7933 you'd find yourself in an awkward situation when you found out that
7934 some of the options listed ended up mapping to the same multilib, and
7935 none of your libraries was actually built for the multilib that
7936 @option{-print-multi-lib} claims to be the default. So we added this
7937 option that disables the default switcher, falling back to GCC's
7938 original notion of the default library. Confused yet?
7940 For short: don't ever use this option, unless you find it in the list
7941 of additional options to be used when building for multilibs, in the
7942 output of @option{gcc -print-multi-lib}.
7946 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
7947 add normal debug information. This is the default for all
7948 platforms except for the OSF/1 reference platform, using the OSF/rose
7949 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
7950 switches are used, the @file{mips-tfile} program will encapsulate the
7951 stabs within MIPS ECOFF@.
7955 Generate code for the GNU assembler. This is the default on the OSF/1
7956 reference platform, using the OSF/rose object format. Also, this is
7957 the default if the configure option @option{--with-gnu-as} is used.
7959 @item -msplit-addresses
7960 @itemx -mno-split-addresses
7961 @opindex msplit-addresses
7962 @opindex mno-split-addresses
7963 Generate code to load the high and low parts of address constants separately.
7964 This allows GCC to optimize away redundant loads of the high order
7965 bits of addresses. This optimization requires GNU as and GNU ld.
7966 This optimization is enabled by default for some embedded targets where
7967 GNU as and GNU ld are standard.
7973 The @option{-mrnames} switch says to output code using the MIPS software
7974 names for the registers, instead of the hardware names (ie, @var{a0}
7975 instead of @var{$4}). The only known assembler that supports this option
7976 is the Algorithmics assembler.
7982 The @option{-mmemcpy} switch makes all block moves call the appropriate
7983 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
7984 generating inline code.
7987 @itemx -mno-mips-tfile
7988 @opindex mmips-tfile
7989 @opindex mno-mips-tfile
7990 The @option{-mno-mips-tfile} switch causes the compiler not
7991 postprocess the object file with the @file{mips-tfile} program,
7992 after the MIPS assembler has generated it to add debug support. If
7993 @file{mips-tfile} is not run, then no local variables will be
7994 available to the debugger. In addition, @file{stage2} and
7995 @file{stage3} objects will have the temporary file names passed to the
7996 assembler embedded in the object file, which means the objects will
7997 not compare the same. The @option{-mno-mips-tfile} switch should only
7998 be used when there are bugs in the @file{mips-tfile} program that
7999 prevents compilation.
8002 @opindex msoft-float
8003 Generate output containing library calls for floating point.
8004 @strong{Warning:} the requisite libraries are not part of GCC@.
8005 Normally the facilities of the machine's usual C compiler are used, but
8006 this can't be done directly in cross-compilation. You must make your
8007 own arrangements to provide suitable library functions for
8011 @opindex mhard-float
8012 Generate output containing floating point instructions. This is the
8013 default if you use the unmodified sources.
8016 @itemx -mno-abicalls
8018 @opindex mno-abicalls
8019 Emit (or do not emit) the pseudo operations @samp{.abicalls},
8020 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
8021 position independent code.
8024 @itemx -mno-long-calls
8025 @opindex mlong-calls
8026 @opindex mno-long-calls
8027 Do all calls with the @samp{JALR} instruction, which requires
8028 loading up a function's address into a register before the call.
8029 You need to use this switch, if you call outside of the current
8030 512 megabyte segment to functions that are not through pointers.
8032 @item -membedded-pic
8033 @itemx -mno-embedded-pic
8034 @opindex membedded-pic
8035 @opindex mno-embedded-pic
8036 Generate PIC code suitable for some embedded systems. All calls are
8037 made using PC relative address, and all data is addressed using the $gp
8038 register. No more than 65536 bytes of global data may be used. This
8039 requires GNU as and GNU ld which do most of the work. This currently
8040 only works on targets which use ECOFF; it does not work with ELF@.
8042 @item -membedded-data
8043 @itemx -mno-embedded-data
8044 @opindex membedded-data
8045 @opindex mno-embedded-data
8046 Allocate variables to the read-only data section first if possible, then
8047 next in the small data section if possible, otherwise in data. This gives
8048 slightly slower code than the default, but reduces the amount of RAM required
8049 when executing, and thus may be preferred for some embedded systems.
8051 @item -muninit-const-in-rodata
8052 @itemx -mno-uninit-const-in-rodata
8053 @opindex muninit-const-in-rodata
8054 @opindex mno-uninit-const-in-rodata
8055 When used together with @option{-membedded-data}, it will always store uninitialized
8056 const variables in the read-only data section.
8058 @item -msingle-float
8059 @itemx -mdouble-float
8060 @opindex msingle-float
8061 @opindex mdouble-float
8062 The @option{-msingle-float} switch tells gcc to assume that the floating
8063 point coprocessor only supports single precision operations, as on the
8064 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
8065 double precision operations. This is the default.
8071 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
8072 as on the @samp{r4650} chip.
8076 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
8077 @option{-mcpu=r4650}.
8083 Enable 16-bit instructions.
8087 Use the entry and exit pseudo ops. This option can only be used with
8092 Compile code for the processor in little endian mode.
8093 The requisite libraries are assumed to exist.
8097 Compile code for the processor in big endian mode.
8098 The requisite libraries are assumed to exist.
8102 @cindex smaller data references (MIPS)
8103 @cindex gp-relative references (MIPS)
8104 Put global and static items less than or equal to @var{num} bytes into
8105 the small data or bss sections instead of the normal data or bss
8106 section. This allows the assembler to emit one word memory reference
8107 instructions based on the global pointer (@var{gp} or @var{$28}),
8108 instead of the normal two words used. By default, @var{num} is 8 when
8109 the MIPS assembler is used, and 0 when the GNU assembler is used. The
8110 @option{-G @var{num}} switch is also passed to the assembler and linker.
8111 All modules should be compiled with the same @option{-G @var{num}}
8116 Tell the MIPS assembler to not run its preprocessor over user
8117 assembler files (with a @samp{.s} suffix) when assembling them.
8121 Pass an option to gas which will cause nops to be inserted if
8122 the read of the destination register of an mfhi or mflo instruction
8123 occurs in the following two instructions.
8127 Do not include the default crt0.
8129 @item -mflush-func=@var{func}
8130 @itemx -mno-flush-func
8131 @opindex mflush-func
8132 Specifies the function to call to flush the I and D caches, or to not
8133 call any such function. If called, the function must take the same
8134 arguments as the common @code{_flush_func()}, that is, the address of the
8135 memory range for which the cache is being flushed, the size of the
8136 memory range, and the number 3 (to flush both caches). The default
8137 depends on the target gcc was configured for, but commonly is either
8138 @samp{_flush_func} or @samp{__cpu_flush}.
8140 @item -mbranch-likely
8141 @itemx -mno-branch-likely
8142 @opindex mbranch-likely
8143 @opindex mno-branch-likely
8144 Enable or disable use of Branch Likely instructions, regardless of the
8145 default for the selected architecture. By default, Branch Likely
8146 instructions may be generated if they are supported by the selected
8147 architecture. An exception is for the MIPS32 and MIPS64 architectures
8148 and processors which implement those architectures; for those, Branch
8149 Likely instructions will not be generated by default because the MIPS32
8150 and MIPS64 architectures specifically deprecate their use.
8153 @node i386 and x86-64 Options
8154 @subsection Intel 386 and AMD x86-64 Options
8155 @cindex i386 Options
8156 @cindex x86-64 Options
8157 @cindex Intel 386 Options
8158 @cindex AMD x86-64 Options
8160 These @samp{-m} options are defined for the i386 and x86-64 family of
8164 @item -mtune=@var{cpu-type}
8166 Tune to @var{cpu-type} everything applicable about the generated code, except
8167 for the ABI and the set of available instructions. The choices for
8168 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
8169 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
8170 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
8171 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
8172 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2}, @samp{k8}, @samp{c3}
8175 While picking a specific @var{cpu-type} will schedule things appropriately
8176 for that particular chip, the compiler will not generate any code that
8177 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8178 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
8179 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
8180 AMD chips as opposed to the Intel ones.
8182 @item -march=@var{cpu-type}
8184 Generate instructions for the machine type @var{cpu-type}. The choices
8185 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8186 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8188 @item -mcpu=@var{cpu-type}
8190 A deprecated synonym for @option{-mtune}.
8199 @opindex mpentiumpro
8200 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8201 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8202 These synonyms are deprecated.
8204 @item -mfpmath=@var{unit}
8206 generate floating point arithmetics for selected unit @var{unit}. the choices
8211 Use the standard 387 floating point coprocessor present majority of chips and
8212 emulated otherwise. Code compiled with this option will run almost everywhere.
8213 The temporary results are computed in 80bit precision instead of precision
8214 specified by the type resulting in slightly different results compared to most
8215 of other chips. See @option{-ffloat-store} for more detailed description.
8217 This is the default choice for i386 compiler.
8220 Use scalar floating point instructions present in the SSE instruction set.
8221 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8222 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8223 instruction set supports only single precision arithmetics, thus the double and
8224 extended precision arithmetics is still done using 387. Later version, present
8225 only in Pentium4 and the future AMD x86-64 chips supports double precision
8228 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8229 @option{-msse2} switches to enable SSE extensions and make this option
8230 effective. For x86-64 compiler, these extensions are enabled by default.
8232 The resulting code should be considerably faster in majority of cases and avoid
8233 the numerical instability problems of 387 code, but may break some existing
8234 code that expects temporaries to be 80bit.
8236 This is the default choice for x86-64 compiler.
8239 Use all SSE extensions enabled by @option{-msse2} as well as the new
8240 SSE extensions in Prescott New Instructions. @option{-mpni} also
8241 enables 2 builtin functions, @code{__builtin_ia32_monitor} and
8242 @code{__builtin_ia32_mwait}, for new instructions @code{monitor} and
8246 Attempt to utilize both instruction sets at once. This effectively double the
8247 amount of available registers and on chips with separate execution units for
8248 387 and SSE the execution resources too. Use this option with care, as it is
8249 still experimental, because gcc register allocator does not model separate
8250 functional units well resulting in instable performance.
8253 @item -masm=@var{dialect}
8254 @opindex masm=@var{dialect}
8255 Output asm instructions using selected @var{dialect}. Supported choices are
8256 @samp{intel} or @samp{att} (the default one).
8261 @opindex mno-ieee-fp
8262 Control whether or not the compiler uses IEEE floating point
8263 comparisons. These handle correctly the case where the result of a
8264 comparison is unordered.
8267 @opindex msoft-float
8268 Generate output containing library calls for floating point.
8269 @strong{Warning:} the requisite libraries are not part of GCC@.
8270 Normally the facilities of the machine's usual C compiler are used, but
8271 this can't be done directly in cross-compilation. You must make your
8272 own arrangements to provide suitable library functions for
8275 On machines where a function returns floating point results in the 80387
8276 register stack, some floating point opcodes may be emitted even if
8277 @option{-msoft-float} is used.
8279 @item -mno-fp-ret-in-387
8280 @opindex mno-fp-ret-in-387
8281 Do not use the FPU registers for return values of functions.
8283 The usual calling convention has functions return values of types
8284 @code{float} and @code{double} in an FPU register, even if there
8285 is no FPU@. The idea is that the operating system should emulate
8288 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8289 in ordinary CPU registers instead.
8291 @item -mno-fancy-math-387
8292 @opindex mno-fancy-math-387
8293 Some 387 emulators do not support the @code{sin}, @code{cos} and
8294 @code{sqrt} instructions for the 387. Specify this option to avoid
8295 generating those instructions. This option is the default on FreeBSD,
8296 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8297 indicates that the target cpu will always have an FPU and so the
8298 instruction will not need emulation. As of revision 2.6.1, these
8299 instructions are not generated unless you also use the
8300 @option{-funsafe-math-optimizations} switch.
8302 @item -malign-double
8303 @itemx -mno-align-double
8304 @opindex malign-double
8305 @opindex mno-align-double
8306 Control whether GCC aligns @code{double}, @code{long double}, and
8307 @code{long long} variables on a two word boundary or a one word
8308 boundary. Aligning @code{double} variables on a two word boundary will
8309 produce code that runs somewhat faster on a @samp{Pentium} at the
8310 expense of more memory.
8312 @strong{Warning:} if you use the @option{-malign-double} switch,
8313 structures containing the above types will be aligned differently than
8314 the published application binary interface specifications for the 386
8315 and will not be binary compatible with structures in code compiled
8316 without that switch.
8318 @item -m96bit-long-double
8319 @item -m128bit-long-double
8320 @opindex m96bit-long-double
8321 @opindex m128bit-long-double
8322 These switches control the size of @code{long double} type. The i386
8323 application binary interface specifies the size to be 96 bits,
8324 so @option{-m96bit-long-double} is the default in 32 bit mode.
8326 Modern architectures (Pentium and newer) would prefer @code{long double}
8327 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8328 conforming to the ABI, this would not be possible. So specifying a
8329 @option{-m128bit-long-double} will align @code{long double}
8330 to a 16 byte boundary by padding the @code{long double} with an additional
8333 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8334 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8336 Notice that neither of these options enable any extra precision over the x87
8337 standard of 80 bits for a @code{long double}.
8339 @strong{Warning:} if you override the default value for your target ABI, the
8340 structures and arrays containing @code{long double} will change their size as
8341 well as function calling convention for function taking @code{long double}
8342 will be modified. Hence they will not be binary compatible with arrays or
8343 structures in code compiled without that switch.
8347 @itemx -mno-svr3-shlib
8348 @opindex msvr3-shlib
8349 @opindex mno-svr3-shlib
8350 Control whether GCC places uninitialized local variables into the
8351 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8352 into @code{bss}. These options are meaningful only on System V Release 3.
8356 Use a different function-calling convention, in which functions that
8357 take a fixed number of arguments return with the @code{ret} @var{num}
8358 instruction, which pops their arguments while returning. This saves one
8359 instruction in the caller since there is no need to pop the arguments
8362 You can specify that an individual function is called with this calling
8363 sequence with the function attribute @samp{stdcall}. You can also
8364 override the @option{-mrtd} option by using the function attribute
8365 @samp{cdecl}. @xref{Function Attributes}.
8367 @strong{Warning:} this calling convention is incompatible with the one
8368 normally used on Unix, so you cannot use it if you need to call
8369 libraries compiled with the Unix compiler.
8371 Also, you must provide function prototypes for all functions that
8372 take variable numbers of arguments (including @code{printf});
8373 otherwise incorrect code will be generated for calls to those
8376 In addition, seriously incorrect code will result if you call a
8377 function with too many arguments. (Normally, extra arguments are
8378 harmlessly ignored.)
8380 @item -mregparm=@var{num}
8382 Control how many registers are used to pass integer arguments. By
8383 default, no registers are used to pass arguments, and at most 3
8384 registers can be used. You can control this behavior for a specific
8385 function by using the function attribute @samp{regparm}.
8386 @xref{Function Attributes}.
8388 @strong{Warning:} if you use this switch, and
8389 @var{num} is nonzero, then you must build all modules with the same
8390 value, including any libraries. This includes the system libraries and
8393 @item -mpreferred-stack-boundary=@var{num}
8394 @opindex mpreferred-stack-boundary
8395 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8396 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8397 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8398 size (@option{-Os}), in which case the default is the minimum correct
8399 alignment (4 bytes for x86, and 8 bytes for x86-64).
8401 On Pentium and PentiumPro, @code{double} and @code{long double} values
8402 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8403 suffer significant run time performance penalties. On Pentium III, the
8404 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8405 penalties if it is not 16 byte aligned.
8407 To ensure proper alignment of this values on the stack, the stack boundary
8408 must be as aligned as that required by any value stored on the stack.
8409 Further, every function must be generated such that it keeps the stack
8410 aligned. Thus calling a function compiled with a higher preferred
8411 stack boundary from a function compiled with a lower preferred stack
8412 boundary will most likely misalign the stack. It is recommended that
8413 libraries that use callbacks always use the default setting.
8415 This extra alignment does consume extra stack space, and generally
8416 increases code size. Code that is sensitive to stack space usage, such
8417 as embedded systems and operating system kernels, may want to reduce the
8418 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8436 These switches enable or disable the use of built-in functions that allow
8437 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
8439 @xref{X86 Built-in Functions}, for details of the functions enabled
8440 and disabled by these switches.
8442 To have SSE/SSE2 instructions generated automatically from floating-point
8443 code, see @option{-mfpmath=sse}.
8446 @itemx -mno-push-args
8448 @opindex mno-push-args
8449 Use PUSH operations to store outgoing parameters. This method is shorter
8450 and usually equally fast as method using SUB/MOV operations and is enabled
8451 by default. In some cases disabling it may improve performance because of
8452 improved scheduling and reduced dependencies.
8454 @item -maccumulate-outgoing-args
8455 @opindex maccumulate-outgoing-args
8456 If enabled, the maximum amount of space required for outgoing arguments will be
8457 computed in the function prologue. This is faster on most modern CPUs
8458 because of reduced dependencies, improved scheduling and reduced stack usage
8459 when preferred stack boundary is not equal to 2. The drawback is a notable
8460 increase in code size. This switch implies @option{-mno-push-args}.
8464 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8465 on thread-safe exception handling must compile and link all code with the
8466 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8467 @option{-D_MT}; when linking, it links in a special thread helper library
8468 @option{-lmingwthrd} which cleans up per thread exception handling data.
8470 @item -mno-align-stringops
8471 @opindex mno-align-stringops
8472 Do not align destination of inlined string operations. This switch reduces
8473 code size and improves performance in case the destination is already aligned,
8474 but gcc don't know about it.
8476 @item -minline-all-stringops
8477 @opindex minline-all-stringops
8478 By default GCC inlines string operations only when destination is known to be
8479 aligned at least to 4 byte boundary. This enables more inlining, increase code
8480 size, but may improve performance of code that depends on fast memcpy, strlen
8481 and memset for short lengths.
8483 @item -momit-leaf-frame-pointer
8484 @opindex momit-leaf-frame-pointer
8485 Don't keep the frame pointer in a register for leaf functions. This
8486 avoids the instructions to save, set up and restore frame pointers and
8487 makes an extra register available in leaf functions. The option
8488 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8489 which might make debugging harder.
8491 @item -mtls-direct-seg-refs
8492 @itemx -mno-tls-direct-seg-refs
8493 @opindex mtls-direct-seg-refs
8494 Controls whether TLS variables may be accessed with offsets from the
8495 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8496 or whether the thread base pointer must be added. Whether or not this
8497 is legal depends on the operating system, and whether it maps the
8498 segment to cover the entire TLS area.
8500 For systems that use GNU libc, the default is on.
8503 These @samp{-m} switches are supported in addition to the above
8504 on AMD x86-64 processors in 64-bit environments.
8511 Generate code for a 32-bit or 64-bit environment.
8512 The 32-bit environment sets int, long and pointer to 32 bits and
8513 generates code that runs on any i386 system.
8514 The 64-bit environment sets int to 32 bits and long and pointer
8515 to 64 bits and generates code for AMD's x86-64 architecture.
8518 @opindex no-red-zone
8519 Do not use a so called red zone for x86-64 code. The red zone is mandated
8520 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8521 stack pointer that will not be modified by signal or interrupt handlers
8522 and therefore can be used for temporary data without adjusting the stack
8523 pointer. The flag @option{-mno-red-zone} disables this red zone.
8525 @item -mcmodel=small
8526 @opindex mcmodel=small
8527 Generate code for the small code model: the program and its symbols must
8528 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8529 Programs can be statically or dynamically linked. This is the default
8532 @item -mcmodel=kernel
8533 @opindex mcmodel=kernel
8534 Generate code for the kernel code model. The kernel runs in the
8535 negative 2 GB of the address space.
8536 This model has to be used for Linux kernel code.
8538 @item -mcmodel=medium
8539 @opindex mcmodel=medium
8540 Generate code for the medium model: The program is linked in the lower 2
8541 GB of the address space but symbols can be located anywhere in the
8542 address space. Programs can be statically or dynamically linked, but
8543 building of shared libraries are not supported with the medium model.
8545 @item -mcmodel=large
8546 @opindex mcmodel=large
8547 Generate code for the large model: This model makes no assumptions
8548 about addresses and sizes of sections. Currently GCC does not implement
8553 @subsection HPPA Options
8554 @cindex HPPA Options
8556 These @samp{-m} options are defined for the HPPA family of computers:
8559 @item -march=@var{architecture-type}
8561 Generate code for the specified architecture. The choices for
8562 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8563 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8564 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8565 architecture option for your machine. Code compiled for lower numbered
8566 architectures will run on higher numbered architectures, but not the
8569 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8570 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8574 @itemx -mpa-risc-1-1
8575 @itemx -mpa-risc-2-0
8576 @opindex mpa-risc-1-0
8577 @opindex mpa-risc-1-1
8578 @opindex mpa-risc-2-0
8579 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8582 @opindex mbig-switch
8583 Generate code suitable for big switch tables. Use this option only if
8584 the assembler/linker complain about out of range branches within a switch
8587 @item -mjump-in-delay
8588 @opindex mjump-in-delay
8589 Fill delay slots of function calls with unconditional jump instructions
8590 by modifying the return pointer for the function call to be the target
8591 of the conditional jump.
8593 @item -mdisable-fpregs
8594 @opindex mdisable-fpregs
8595 Prevent floating point registers from being used in any manner. This is
8596 necessary for compiling kernels which perform lazy context switching of
8597 floating point registers. If you use this option and attempt to perform
8598 floating point operations, the compiler will abort.
8600 @item -mdisable-indexing
8601 @opindex mdisable-indexing
8602 Prevent the compiler from using indexing address modes. This avoids some
8603 rather obscure problems when compiling MIG generated code under MACH@.
8605 @item -mno-space-regs
8606 @opindex mno-space-regs
8607 Generate code that assumes the target has no space registers. This allows
8608 GCC to generate faster indirect calls and use unscaled index address modes.
8610 Such code is suitable for level 0 PA systems and kernels.
8612 @item -mfast-indirect-calls
8613 @opindex mfast-indirect-calls
8614 Generate code that assumes calls never cross space boundaries. This
8615 allows GCC to emit code which performs faster indirect calls.
8617 This option will not work in the presence of shared libraries or nested
8620 @item -mlong-load-store
8621 @opindex mlong-load-store
8622 Generate 3-instruction load and store sequences as sometimes required by
8623 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8626 @item -mportable-runtime
8627 @opindex mportable-runtime
8628 Use the portable calling conventions proposed by HP for ELF systems.
8632 Enable the use of assembler directives only GAS understands.
8634 @item -mschedule=@var{cpu-type}
8636 Schedule code according to the constraints for the machine type
8637 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8638 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8639 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8640 proper scheduling option for your machine. The default scheduling is
8644 @opindex mlinker-opt
8645 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8646 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8647 linkers in which they give bogus error messages when linking some programs.
8650 @opindex msoft-float
8651 Generate output containing library calls for floating point.
8652 @strong{Warning:} the requisite libraries are not available for all HPPA
8653 targets. Normally the facilities of the machine's usual C compiler are
8654 used, but this cannot be done directly in cross-compilation. You must make
8655 your own arrangements to provide suitable library functions for
8656 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8657 does provide software floating point support.
8659 @option{-msoft-float} changes the calling convention in the output file;
8660 therefore, it is only useful if you compile @emph{all} of a program with
8661 this option. In particular, you need to compile @file{libgcc.a}, the
8662 library that comes with GCC, with @option{-msoft-float} in order for
8667 Generate the predefine, @code{_SIO}, for server IO. The default is
8668 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8669 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8670 options are available under HP-UX and HI-UX.
8674 Use GNU ld specific options. This passes @option{-shared} to ld when
8675 building a shared library. It is the default when GCC is configured,
8676 explicitly or implicitly, with the GNU linker. This option does not
8677 have any affect on which ld is called, it only changes what parameters
8678 are passed to that ld. The ld that is called is determined by the
8679 @option{--with-ld} configure option, gcc's program search path, and
8680 finally by the user's @env{PATH}. The linker used by GCC can be printed
8681 using @samp{which `gcc -print-prog-name=ld`}.
8685 Use HP ld specific options. This passes @option{-b} to ld when building
8686 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8687 links. It is the default when GCC is configured, explicitly or
8688 implicitly, with the HP linker. This option does not have any affect on
8689 which ld is called, it only changes what parameters are passed to that
8690 ld. The ld that is called is determined by the @option{--with-ld}
8691 configure option, gcc's program search path, and finally by the user's
8692 @env{PATH}. The linker used by GCC can be printed using @samp{which
8693 `gcc -print-prog-name=ld`}.
8696 @opindex mno-long-calls
8697 Generate code that uses long call sequences. This ensures that a call
8698 is always able to reach linker generated stubs. The default is to generate
8699 long calls only when the distance from the call site to the beginning
8700 of the function or translation unit, as the case may be, exceeds a
8701 predefined limit set by the branch type being used. The limits for
8702 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8703 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8706 Distances are measured from the beginning of functions when using the
8707 @option{-ffunction-sections} option, or when using the @option{-mgas}
8708 and @option{-mno-portable-runtime} options together under HP-UX with
8711 It is normally not desirable to use this option as it will degrade
8712 performance. However, it may be useful in large applications,
8713 particularly when partial linking is used to build the application.
8715 The types of long calls used depends on the capabilities of the
8716 assembler and linker, and the type of code being generated. The
8717 impact on systems that support long absolute calls, and long pic
8718 symbol-difference or pc-relative calls should be relatively small.
8719 However, an indirect call is used on 32-bit ELF systems in pic code
8720 and it is quite long.
8724 Suppress the generation of link options to search libdld.sl when the
8725 @option{-static} option is specified on HP-UX 10 and later.
8729 The HP-UX implementation of setlocale in libc has a dependency on
8730 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8731 when the @option{-static} option is specified, special link options
8732 are needed to resolve this dependency.
8734 On HP-UX 10 and later, the GCC driver adds the necessary options to
8735 link with libdld.sl when the @option{-static} option is specified.
8736 This causes the resulting binary to be dynamic. On the 64-bit port,
8737 the linkers generate dynamic binaries by default in any case. The
8738 @option{-nolibdld} option can be used to prevent the GCC driver from
8739 adding these link options.
8743 Add support for multithreading with the @dfn{dce thread} library
8744 under HP-UX. This option sets flags for both the preprocessor and
8748 @node Intel 960 Options
8749 @subsection Intel 960 Options
8751 These @samp{-m} options are defined for the Intel 960 implementations:
8754 @item -m@var{cpu-type}
8762 Assume the defaults for the machine type @var{cpu-type} for some of
8763 the other options, including instruction scheduling, floating point
8764 support, and addressing modes. The choices for @var{cpu-type} are
8765 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
8766 @samp{sa}, and @samp{sb}.
8773 @opindex msoft-float
8774 The @option{-mnumerics} option indicates that the processor does support
8775 floating-point instructions. The @option{-msoft-float} option indicates
8776 that floating-point support should not be assumed.
8778 @item -mleaf-procedures
8779 @itemx -mno-leaf-procedures
8780 @opindex mleaf-procedures
8781 @opindex mno-leaf-procedures
8782 Do (or do not) attempt to alter leaf procedures to be callable with the
8783 @code{bal} instruction as well as @code{call}. This will result in more
8784 efficient code for explicit calls when the @code{bal} instruction can be
8785 substituted by the assembler or linker, but less efficient code in other
8786 cases, such as calls via function pointers, or using a linker that doesn't
8787 support this optimization.
8790 @itemx -mno-tail-call
8792 @opindex mno-tail-call
8793 Do (or do not) make additional attempts (beyond those of the
8794 machine-independent portions of the compiler) to optimize tail-recursive
8795 calls into branches. You may not want to do this because the detection of
8796 cases where this is not valid is not totally complete. The default is
8797 @option{-mno-tail-call}.
8799 @item -mcomplex-addr
8800 @itemx -mno-complex-addr
8801 @opindex mcomplex-addr
8802 @opindex mno-complex-addr
8803 Assume (or do not assume) that the use of a complex addressing mode is a
8804 win on this implementation of the i960. Complex addressing modes may not
8805 be worthwhile on the K-series, but they definitely are on the C-series.
8806 The default is currently @option{-mcomplex-addr} for all processors except
8810 @itemx -mno-code-align
8811 @opindex mcode-align
8812 @opindex mno-code-align
8813 Align code to 8-byte boundaries for faster fetching (or don't bother).
8814 Currently turned on by default for C-series implementations only.
8817 @item -mclean-linkage
8818 @itemx -mno-clean-linkage
8819 @opindex mclean-linkage
8820 @opindex mno-clean-linkage
8821 These options are not fully implemented.
8825 @itemx -mic2.0-compat
8826 @itemx -mic3.0-compat
8828 @opindex mic2.0-compat
8829 @opindex mic3.0-compat
8830 Enable compatibility with iC960 v2.0 or v3.0.
8834 @opindex masm-compat
8836 Enable compatibility with the iC960 assembler.
8838 @item -mstrict-align
8839 @itemx -mno-strict-align
8840 @opindex mstrict-align
8841 @opindex mno-strict-align
8842 Do not permit (do permit) unaligned accesses.
8846 Enable structure-alignment compatibility with Intel's gcc release version
8847 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
8849 @item -mlong-double-64
8850 @opindex mlong-double-64
8851 Implement type @samp{long double} as 64-bit floating point numbers.
8852 Without the option @samp{long double} is implemented by 80-bit
8853 floating point numbers. The only reason we have it because there is
8854 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
8855 is only useful for people using soft-float targets. Otherwise, we
8856 should recommend against use of it.
8860 @node DEC Alpha Options
8861 @subsection DEC Alpha Options
8863 These @samp{-m} options are defined for the DEC Alpha implementations:
8866 @item -mno-soft-float
8868 @opindex mno-soft-float
8869 @opindex msoft-float
8870 Use (do not use) the hardware floating-point instructions for
8871 floating-point operations. When @option{-msoft-float} is specified,
8872 functions in @file{libgcc.a} will be used to perform floating-point
8873 operations. Unless they are replaced by routines that emulate the
8874 floating-point operations, or compiled in such a way as to call such
8875 emulations routines, these routines will issue floating-point
8876 operations. If you are compiling for an Alpha without floating-point
8877 operations, you must ensure that the library is built so as not to call
8880 Note that Alpha implementations without floating-point operations are
8881 required to have floating-point registers.
8886 @opindex mno-fp-regs
8887 Generate code that uses (does not use) the floating-point register set.
8888 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8889 register set is not used, floating point operands are passed in integer
8890 registers as if they were integers and floating-point results are passed
8891 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8892 so any function with a floating-point argument or return value called by code
8893 compiled with @option{-mno-fp-regs} must also be compiled with that
8896 A typical use of this option is building a kernel that does not use,
8897 and hence need not save and restore, any floating-point registers.
8901 The Alpha architecture implements floating-point hardware optimized for
8902 maximum performance. It is mostly compliant with the IEEE floating
8903 point standard. However, for full compliance, software assistance is
8904 required. This option generates code fully IEEE compliant code
8905 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8906 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8907 defined during compilation. The resulting code is less efficient but is
8908 able to correctly support denormalized numbers and exceptional IEEE
8909 values such as not-a-number and plus/minus infinity. Other Alpha
8910 compilers call this option @option{-ieee_with_no_inexact}.
8912 @item -mieee-with-inexact
8913 @opindex mieee-with-inexact
8914 This is like @option{-mieee} except the generated code also maintains
8915 the IEEE @var{inexact-flag}. Turning on this option causes the
8916 generated code to implement fully-compliant IEEE math. In addition to
8917 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8918 macro. On some Alpha implementations the resulting code may execute
8919 significantly slower than the code generated by default. Since there is
8920 very little code that depends on the @var{inexact-flag}, you should
8921 normally not specify this option. Other Alpha compilers call this
8922 option @option{-ieee_with_inexact}.
8924 @item -mfp-trap-mode=@var{trap-mode}
8925 @opindex mfp-trap-mode
8926 This option controls what floating-point related traps are enabled.
8927 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8928 The trap mode can be set to one of four values:
8932 This is the default (normal) setting. The only traps that are enabled
8933 are the ones that cannot be disabled in software (e.g., division by zero
8937 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8941 Like @samp{su}, but the instructions are marked to be safe for software
8942 completion (see Alpha architecture manual for details).
8945 Like @samp{su}, but inexact traps are enabled as well.
8948 @item -mfp-rounding-mode=@var{rounding-mode}
8949 @opindex mfp-rounding-mode
8950 Selects the IEEE rounding mode. Other Alpha compilers call this option
8951 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8956 Normal IEEE rounding mode. Floating point numbers are rounded towards
8957 the nearest machine number or towards the even machine number in case
8961 Round towards minus infinity.
8964 Chopped rounding mode. Floating point numbers are rounded towards zero.
8967 Dynamic rounding mode. A field in the floating point control register
8968 (@var{fpcr}, see Alpha architecture reference manual) controls the
8969 rounding mode in effect. The C library initializes this register for
8970 rounding towards plus infinity. Thus, unless your program modifies the
8971 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8974 @item -mtrap-precision=@var{trap-precision}
8975 @opindex mtrap-precision
8976 In the Alpha architecture, floating point traps are imprecise. This
8977 means without software assistance it is impossible to recover from a
8978 floating trap and program execution normally needs to be terminated.
8979 GCC can generate code that can assist operating system trap handlers
8980 in determining the exact location that caused a floating point trap.
8981 Depending on the requirements of an application, different levels of
8982 precisions can be selected:
8986 Program precision. This option is the default and means a trap handler
8987 can only identify which program caused a floating point exception.
8990 Function precision. The trap handler can determine the function that
8991 caused a floating point exception.
8994 Instruction precision. The trap handler can determine the exact
8995 instruction that caused a floating point exception.
8998 Other Alpha compilers provide the equivalent options called
8999 @option{-scope_safe} and @option{-resumption_safe}.
9001 @item -mieee-conformant
9002 @opindex mieee-conformant
9003 This option marks the generated code as IEEE conformant. You must not
9004 use this option unless you also specify @option{-mtrap-precision=i} and either
9005 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9006 is to emit the line @samp{.eflag 48} in the function prologue of the
9007 generated assembly file. Under DEC Unix, this has the effect that
9008 IEEE-conformant math library routines will be linked in.
9010 @item -mbuild-constants
9011 @opindex mbuild-constants
9012 Normally GCC examines a 32- or 64-bit integer constant to
9013 see if it can construct it from smaller constants in two or three
9014 instructions. If it cannot, it will output the constant as a literal and
9015 generate code to load it from the data segment at runtime.
9017 Use this option to require GCC to construct @emph{all} integer constants
9018 using code, even if it takes more instructions (the maximum is six).
9020 You would typically use this option to build a shared library dynamic
9021 loader. Itself a shared library, it must relocate itself in memory
9022 before it can find the variables and constants in its own data segment.
9028 Select whether to generate code to be assembled by the vendor-supplied
9029 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9047 Indicate whether GCC should generate code to use the optional BWX,
9048 CIX, FIX and MAX instruction sets. The default is to use the instruction
9049 sets supported by the CPU type specified via @option{-mcpu=} option or that
9050 of the CPU on which GCC was built if none was specified.
9055 @opindex mfloat-ieee
9056 Generate code that uses (does not use) VAX F and G floating point
9057 arithmetic instead of IEEE single and double precision.
9059 @item -mexplicit-relocs
9060 @itemx -mno-explicit-relocs
9061 @opindex mexplicit-relocs
9062 @opindex mno-explicit-relocs
9063 Older Alpha assemblers provided no way to generate symbol relocations
9064 except via assembler macros. Use of these macros does not allow
9065 optimal instruction scheduling. GNU binutils as of version 2.12
9066 supports a new syntax that allows the compiler to explicitly mark
9067 which relocations should apply to which instructions. This option
9068 is mostly useful for debugging, as GCC detects the capabilities of
9069 the assembler when it is built and sets the default accordingly.
9073 @opindex msmall-data
9074 @opindex mlarge-data
9075 When @option{-mexplicit-relocs} is in effect, static data is
9076 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9077 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9078 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9079 16-bit relocations off of the @code{$gp} register. This limits the
9080 size of the small data area to 64KB, but allows the variables to be
9081 directly accessed via a single instruction.
9083 The default is @option{-mlarge-data}. With this option the data area
9084 is limited to just below 2GB. Programs that require more than 2GB of
9085 data must use @code{malloc} or @code{mmap} to allocate the data in the
9086 heap instead of in the program's data segment.
9088 When generating code for shared libraries, @option{-fpic} implies
9089 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9093 @opindex msmall-text
9094 @opindex mlarge-text
9095 When @option{-msmall-text} is used, the compiler assumes that the
9096 code of the entire program (or shared library) fits in 4MB, and is
9097 thus reachable with a branch instruction. When @option{-msmall-data}
9098 is used, the compiler can assume that all local symbols share the
9099 same @code{$gp} value, and thus reduce the number of instructions
9100 required for a function call from 4 to 1.
9102 The default is @option{-mlarge-text}.
9104 @item -mcpu=@var{cpu_type}
9106 Set the instruction set and instruction scheduling parameters for
9107 machine type @var{cpu_type}. You can specify either the @samp{EV}
9108 style name or the corresponding chip number. GCC supports scheduling
9109 parameters for the EV4, EV5 and EV6 family of processors and will
9110 choose the default values for the instruction set from the processor
9111 you specify. If you do not specify a processor type, GCC will default
9112 to the processor on which the compiler was built.
9114 Supported values for @var{cpu_type} are
9120 Schedules as an EV4 and has no instruction set extensions.
9124 Schedules as an EV5 and has no instruction set extensions.
9128 Schedules as an EV5 and supports the BWX extension.
9133 Schedules as an EV5 and supports the BWX and MAX extensions.
9137 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9141 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9144 @item -mtune=@var{cpu_type}
9146 Set only the instruction scheduling parameters for machine type
9147 @var{cpu_type}. The instruction set is not changed.
9149 @item -mmemory-latency=@var{time}
9150 @opindex mmemory-latency
9151 Sets the latency the scheduler should assume for typical memory
9152 references as seen by the application. This number is highly
9153 dependent on the memory access patterns used by the application
9154 and the size of the external cache on the machine.
9156 Valid options for @var{time} are
9160 A decimal number representing clock cycles.
9166 The compiler contains estimates of the number of clock cycles for
9167 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9168 (also called Dcache, Scache, and Bcache), as well as to main memory.
9169 Note that L3 is only valid for EV5.
9174 @node DEC Alpha/VMS Options
9175 @subsection DEC Alpha/VMS Options
9177 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9180 @item -mvms-return-codes
9181 @opindex mvms-return-codes
9182 Return VMS condition codes from main. The default is to return POSIX
9183 style condition (e.g.@ error) codes.
9186 @node H8/300 Options
9187 @subsection H8/300 Options
9189 These @samp{-m} options are defined for the H8/300 implementations:
9194 Shorten some address references at link time, when possible; uses the
9195 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9196 ld.info, Using ld}, for a fuller description.
9200 Generate code for the H8/300H@.
9204 Generate code for the H8S@.
9208 Generate code for the H8S and H8/300H in the normal mode. This switch
9209 must be used either with -mh or -ms.
9213 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9217 Make @code{int} data 32 bits by default.
9221 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9222 The default for the H8/300H and H8S is to align longs and floats on 4
9224 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9225 This option has no effect on the H8/300.
9229 @subsection SH Options
9231 These @samp{-m} options are defined for the SH implementations:
9236 Generate code for the SH1.
9240 Generate code for the SH2.
9243 Generate code for the SH2e.
9247 Generate code for the SH3.
9251 Generate code for the SH3e.
9255 Generate code for the SH4 without a floating-point unit.
9257 @item -m4-single-only
9258 @opindex m4-single-only
9259 Generate code for the SH4 with a floating-point unit that only
9260 supports single-precision arithmetic.
9264 Generate code for the SH4 assuming the floating-point unit is in
9265 single-precision mode by default.
9269 Generate code for the SH4.
9273 Compile code for the processor in big endian mode.
9277 Compile code for the processor in little endian mode.
9281 Align doubles at 64-bit boundaries. Note that this changes the calling
9282 conventions, and thus some functions from the standard C library will
9283 not work unless you recompile it first with @option{-mdalign}.
9287 Shorten some address references at link time, when possible; uses the
9288 linker option @option{-relax}.
9292 Use 32-bit offsets in @code{switch} tables. The default is to use
9297 Enable the use of the instruction @code{fmovd}.
9301 Comply with the calling conventions defined by Renesas.
9305 Mark the @code{MAC} register as call-clobbered, even if
9306 @option{-mhitachi} is given.
9310 Increase IEEE-compliance of floating-point code.
9314 Dump instruction size and location in the assembly code.
9318 This option is deprecated. It pads structures to multiple of 4 bytes,
9319 which is incompatible with the SH ABI@.
9323 Optimize for space instead of speed. Implied by @option{-Os}.
9327 When generating position-independent code, emit function calls using
9328 the Global Offset Table instead of the Procedure Linkage Table.
9332 Generate a library function call to invalidate instruction cache
9333 entries, after fixing up a trampoline. This library function call
9334 doesn't assume it can write to the whole memory address space. This
9335 is the default when the target is @code{sh-*-linux*}.
9338 @node System V Options
9339 @subsection Options for System V
9341 These additional options are available on System V Release 4 for
9342 compatibility with other compilers on those systems:
9347 Create a shared object.
9348 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9352 Identify the versions of each tool used by the compiler, in a
9353 @code{.ident} assembler directive in the output.
9357 Refrain from adding @code{.ident} directives to the output file (this is
9360 @item -YP,@var{dirs}
9362 Search the directories @var{dirs}, and no others, for libraries
9363 specified with @option{-l}.
9367 Look in the directory @var{dir} to find the M4 preprocessor.
9368 The assembler uses this option.
9369 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9370 @c the generic assembler that comes with Solaris takes just -Ym.
9373 @node TMS320C3x/C4x Options
9374 @subsection TMS320C3x/C4x Options
9375 @cindex TMS320C3x/C4x Options
9377 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9381 @item -mcpu=@var{cpu_type}
9383 Set the instruction set, register set, and instruction scheduling
9384 parameters for machine type @var{cpu_type}. Supported values for
9385 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9386 @samp{c44}. The default is @samp{c40} to generate code for the
9391 @itemx -msmall-memory
9393 @opindex mbig-memory
9395 @opindex msmall-memory
9397 Generates code for the big or small memory model. The small memory
9398 model assumed that all data fits into one 64K word page. At run-time
9399 the data page (DP) register must be set to point to the 64K page
9400 containing the .bss and .data program sections. The big memory model is
9401 the default and requires reloading of the DP register for every direct
9408 Allow (disallow) allocation of general integer operands into the block
9415 Enable (disable) generation of code using decrement and branch,
9416 DBcond(D), instructions. This is enabled by default for the C4x. To be
9417 on the safe side, this is disabled for the C3x, since the maximum
9418 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9419 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9420 that it can utilize the decrement and branch instruction, but will give
9421 up if there is more than one memory reference in the loop. Thus a loop
9422 where the loop counter is decremented can generate slightly more
9423 efficient code, in cases where the RPTB instruction cannot be utilized.
9425 @item -mdp-isr-reload
9427 @opindex mdp-isr-reload
9429 Force the DP register to be saved on entry to an interrupt service
9430 routine (ISR), reloaded to point to the data section, and restored on
9431 exit from the ISR@. This should not be required unless someone has
9432 violated the small memory model by modifying the DP register, say within
9439 For the C3x use the 24-bit MPYI instruction for integer multiplies
9440 instead of a library call to guarantee 32-bit results. Note that if one
9441 of the operands is a constant, then the multiplication will be performed
9442 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9443 then squaring operations are performed inline instead of a library call.
9446 @itemx -mno-fast-fix
9448 @opindex mno-fast-fix
9449 The C3x/C4x FIX instruction to convert a floating point value to an
9450 integer value chooses the nearest integer less than or equal to the
9451 floating point value rather than to the nearest integer. Thus if the
9452 floating point number is negative, the result will be incorrectly
9453 truncated an additional code is necessary to detect and correct this
9454 case. This option can be used to disable generation of the additional
9455 code required to correct the result.
9461 Enable (disable) generation of repeat block sequences using the RPTB
9462 instruction for zero overhead looping. The RPTB construct is only used
9463 for innermost loops that do not call functions or jump across the loop
9464 boundaries. There is no advantage having nested RPTB loops due to the
9465 overhead required to save and restore the RC, RS, and RE registers.
9466 This is enabled by default with @option{-O2}.
9468 @item -mrpts=@var{count}
9472 Enable (disable) the use of the single instruction repeat instruction
9473 RPTS@. If a repeat block contains a single instruction, and the loop
9474 count can be guaranteed to be less than the value @var{count}, GCC will
9475 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9476 then a RPTS will be emitted even if the loop count cannot be determined
9477 at compile time. Note that the repeated instruction following RPTS does
9478 not have to be reloaded from memory each iteration, thus freeing up the
9479 CPU buses for operands. However, since interrupts are blocked by this
9480 instruction, it is disabled by default.
9482 @item -mloop-unsigned
9483 @itemx -mno-loop-unsigned
9484 @opindex mloop-unsigned
9485 @opindex mno-loop-unsigned
9486 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9487 is @math{2^{31} + 1} since these instructions test if the iteration count is
9488 negative to terminate the loop. If the iteration count is unsigned
9489 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9490 exceeded. This switch allows an unsigned iteration count.
9494 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9495 with. This also enforces compatibility with the API employed by the TI
9496 C3x C compiler. For example, long doubles are passed as structures
9497 rather than in floating point registers.
9503 Generate code that uses registers (stack) for passing arguments to functions.
9504 By default, arguments are passed in registers where possible rather
9505 than by pushing arguments on to the stack.
9507 @item -mparallel-insns
9508 @itemx -mno-parallel-insns
9509 @opindex mparallel-insns
9510 @opindex mno-parallel-insns
9511 Allow the generation of parallel instructions. This is enabled by
9512 default with @option{-O2}.
9514 @item -mparallel-mpy
9515 @itemx -mno-parallel-mpy
9516 @opindex mparallel-mpy
9517 @opindex mno-parallel-mpy
9518 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9519 provided @option{-mparallel-insns} is also specified. These instructions have
9520 tight register constraints which can pessimize the code generation
9526 @subsection V850 Options
9527 @cindex V850 Options
9529 These @samp{-m} options are defined for V850 implementations:
9533 @itemx -mno-long-calls
9534 @opindex mlong-calls
9535 @opindex mno-long-calls
9536 Treat all calls as being far away (near). If calls are assumed to be
9537 far away, the compiler will always load the functions address up into a
9538 register, and call indirect through the pointer.
9544 Do not optimize (do optimize) basic blocks that use the same index
9545 pointer 4 or more times to copy pointer into the @code{ep} register, and
9546 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9547 option is on by default if you optimize.
9549 @item -mno-prolog-function
9550 @itemx -mprolog-function
9551 @opindex mno-prolog-function
9552 @opindex mprolog-function
9553 Do not use (do use) external functions to save and restore registers at
9554 the prolog and epilog of a function. The external functions are slower,
9555 but use less code space if more than one function saves the same number
9556 of registers. The @option{-mprolog-function} option is on by default if
9561 Try to make the code as small as possible. At present, this just turns
9562 on the @option{-mep} and @option{-mprolog-function} options.
9566 Put static or global variables whose size is @var{n} bytes or less into
9567 the tiny data area that register @code{ep} points to. The tiny data
9568 area can hold up to 256 bytes in total (128 bytes for byte references).
9572 Put static or global variables whose size is @var{n} bytes or less into
9573 the small data area that register @code{gp} points to. The small data
9574 area can hold up to 64 kilobytes.
9578 Put static or global variables whose size is @var{n} bytes or less into
9579 the first 32 kilobytes of memory.
9583 Specify that the target processor is the V850.
9586 @opindex mbig-switch
9587 Generate code suitable for big switch tables. Use this option only if
9588 the assembler/linker complain about out of range branches within a switch
9593 This option will cause r2 and r5 to be used in the code generated by
9594 the compiler. This setting is the default.
9597 @opindex mno-app-regs
9598 This option will cause r2 and r5 to be treated as fixed registers.
9602 Specify that the target processor is the V850E. The preprocessor
9603 constant @samp{__v850e__} will be defined if this option is used.
9605 If neither @option{-mv850} nor @option{-mv850e} are defined
9606 then a default target processor will be chosen and the relevant
9607 @samp{__v850*__} preprocessor constant will be defined.
9609 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9610 defined, regardless of which processor variant is the target.
9612 @item -mdisable-callt
9613 @opindex mdisable-callt
9614 This option will suppress generation of the CALLT instruction for the
9615 v850e flavors of the v850 architecture. The default is
9616 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9621 @subsection ARC Options
9624 These options are defined for ARC implementations:
9629 Compile code for little endian mode. This is the default.
9633 Compile code for big endian mode.
9636 @opindex mmangle-cpu
9637 Prepend the name of the cpu to all public symbol names.
9638 In multiple-processor systems, there are many ARC variants with different
9639 instruction and register set characteristics. This flag prevents code
9640 compiled for one cpu to be linked with code compiled for another.
9641 No facility exists for handling variants that are ``almost identical''.
9642 This is an all or nothing option.
9644 @item -mcpu=@var{cpu}
9646 Compile code for ARC variant @var{cpu}.
9647 Which variants are supported depend on the configuration.
9648 All variants support @option{-mcpu=base}, this is the default.
9650 @item -mtext=@var{text-section}
9651 @itemx -mdata=@var{data-section}
9652 @itemx -mrodata=@var{readonly-data-section}
9656 Put functions, data, and readonly data in @var{text-section},
9657 @var{data-section}, and @var{readonly-data-section} respectively
9658 by default. This can be overridden with the @code{section} attribute.
9659 @xref{Variable Attributes}.
9664 @subsection NS32K Options
9665 @cindex NS32K options
9667 These are the @samp{-m} options defined for the 32000 series. The default
9668 values for these options depends on which style of 32000 was selected when
9669 the compiler was configured; the defaults for the most common choices are
9677 Generate output for a 32032. This is the default
9678 when the compiler is configured for 32032 and 32016 based systems.
9684 Generate output for a 32332. This is the default
9685 when the compiler is configured for 32332-based systems.
9691 Generate output for a 32532. This is the default
9692 when the compiler is configured for 32532-based systems.
9696 Generate output containing 32081 instructions for floating point.
9697 This is the default for all systems.
9701 Generate output containing 32381 instructions for floating point. This
9702 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9703 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9707 Try and generate multiply-add floating point instructions @code{polyF}
9708 and @code{dotF}. This option is only available if the @option{-m32381}
9709 option is in effect. Using these instructions requires changes to
9710 register allocation which generally has a negative impact on
9711 performance. This option should only be enabled when compiling code
9712 particularly likely to make heavy use of multiply-add instructions.
9715 @opindex mnomulti-add
9716 Do not try and generate multiply-add floating point instructions
9717 @code{polyF} and @code{dotF}. This is the default on all platforms.
9720 @opindex msoft-float
9721 Generate output containing library calls for floating point.
9722 @strong{Warning:} the requisite libraries may not be available.
9724 @item -mieee-compare
9725 @itemx -mno-ieee-compare
9726 @opindex mieee-compare
9727 @opindex mno-ieee-compare
9728 Control whether or not the compiler uses IEEE floating point
9729 comparisons. These handle correctly the case where the result of a
9730 comparison is unordered.
9731 @strong{Warning:} the requisite kernel support may not be available.
9734 @opindex mnobitfield
9735 Do not use the bit-field instructions. On some machines it is faster to
9736 use shifting and masking operations. This is the default for the pc532.
9740 Do use the bit-field instructions. This is the default for all platforms
9745 Use a different function-calling convention, in which functions
9746 that take a fixed number of arguments return pop their
9747 arguments on return with the @code{ret} instruction.
9749 This calling convention is incompatible with the one normally
9750 used on Unix, so you cannot use it if you need to call libraries
9751 compiled with the Unix compiler.
9753 Also, you must provide function prototypes for all functions that
9754 take variable numbers of arguments (including @code{printf});
9755 otherwise incorrect code will be generated for calls to those
9758 In addition, seriously incorrect code will result if you call a
9759 function with too many arguments. (Normally, extra arguments are
9760 harmlessly ignored.)
9762 This option takes its name from the 680x0 @code{rtd} instruction.
9767 Use a different function-calling convention where the first two arguments
9768 are passed in registers.
9770 This calling convention is incompatible with the one normally
9771 used on Unix, so you cannot use it if you need to call libraries
9772 compiled with the Unix compiler.
9775 @opindex mnoregparam
9776 Do not pass any arguments in registers. This is the default for all
9781 It is OK to use the sb as an index register which is always loaded with
9782 zero. This is the default for the pc532-netbsd target.
9786 The sb register is not available for use or has not been initialized to
9787 zero by the run time system. This is the default for all targets except
9788 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9789 @option{-fpic} is set.
9793 Many ns32000 series addressing modes use displacements of up to 512MB@.
9794 If an address is above 512MB then displacements from zero can not be used.
9795 This option causes code to be generated which can be loaded above 512MB@.
9796 This may be useful for operating systems or ROM code.
9800 Assume code will be loaded in the first 512MB of virtual address space.
9801 This is the default for all platforms.
9807 @subsection AVR Options
9810 These options are defined for AVR implementations:
9813 @item -mmcu=@var{mcu}
9815 Specify ATMEL AVR instruction set or MCU type.
9817 Instruction set avr1 is for the minimal AVR core, not supported by the C
9818 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9819 attiny11, attiny12, attiny15, attiny28).
9821 Instruction set avr2 (default) is for the classic AVR core with up to
9822 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9823 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9824 at90c8534, at90s8535).
9826 Instruction set avr3 is for the classic AVR core with up to 128K program
9827 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9829 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9830 memory space (MCU types: atmega8, atmega83, atmega85).
9832 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9833 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9834 atmega64, atmega128, at43usb355, at94k).
9838 Output instruction sizes to the asm file.
9840 @item -minit-stack=@var{N}
9841 @opindex minit-stack
9842 Specify the initial stack address, which may be a symbol or numeric value,
9843 @samp{__stack} is the default.
9845 @item -mno-interrupts
9846 @opindex mno-interrupts
9847 Generated code is not compatible with hardware interrupts.
9848 Code size will be smaller.
9850 @item -mcall-prologues
9851 @opindex mcall-prologues
9852 Functions prologues/epilogues expanded as call to appropriate
9853 subroutines. Code size will be smaller.
9855 @item -mno-tablejump
9856 @opindex mno-tablejump
9857 Do not generate tablejump insns which sometimes increase code size.
9860 @opindex mtiny-stack
9861 Change only the low 8 bits of the stack pointer.
9865 @subsection MCore Options
9866 @cindex MCore options
9868 These are the @samp{-m} options defined for the Motorola M*Core
9876 @opindex mno-hardlit
9877 Inline constants into the code stream if it can be done in two
9878 instructions or less.
9884 Use the divide instruction. (Enabled by default).
9886 @item -mrelax-immediate
9887 @itemx -mno-relax-immediate
9888 @opindex mrelax-immediate
9889 @opindex mno-relax-immediate
9890 Allow arbitrary sized immediates in bit operations.
9892 @item -mwide-bitfields
9893 @itemx -mno-wide-bitfields
9894 @opindex mwide-bitfields
9895 @opindex mno-wide-bitfields
9896 Always treat bit-fields as int-sized.
9898 @item -m4byte-functions
9899 @itemx -mno-4byte-functions
9900 @opindex m4byte-functions
9901 @opindex mno-4byte-functions
9902 Force all functions to be aligned to a four byte boundary.
9904 @item -mcallgraph-data
9905 @itemx -mno-callgraph-data
9906 @opindex mcallgraph-data
9907 @opindex mno-callgraph-data
9908 Emit callgraph information.
9911 @itemx -mno-slow-bytes
9912 @opindex mslow-bytes
9913 @opindex mno-slow-bytes
9914 Prefer word access when reading byte quantities.
9916 @item -mlittle-endian
9918 @opindex mlittle-endian
9919 @opindex mbig-endian
9920 Generate code for a little endian target.
9926 Generate code for the 210 processor.
9930 @subsection IA-64 Options
9931 @cindex IA-64 Options
9933 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9937 @opindex mbig-endian
9938 Generate code for a big endian target. This is the default for HP-UX@.
9940 @item -mlittle-endian
9941 @opindex mlittle-endian
9942 Generate code for a little endian target. This is the default for AIX5
9949 Generate (or don't) code for the GNU assembler. This is the default.
9950 @c Also, this is the default if the configure option @option{--with-gnu-as}
9957 Generate (or don't) code for the GNU linker. This is the default.
9958 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9963 Generate code that does not use a global pointer register. The result
9964 is not position independent code, and violates the IA-64 ABI@.
9966 @item -mvolatile-asm-stop
9967 @itemx -mno-volatile-asm-stop
9968 @opindex mvolatile-asm-stop
9969 @opindex mno-volatile-asm-stop
9970 Generate (or don't) a stop bit immediately before and after volatile asm
9975 Generate code that works around Itanium B step errata.
9977 @item -mregister-names
9978 @itemx -mno-register-names
9979 @opindex mregister-names
9980 @opindex mno-register-names
9981 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9982 the stacked registers. This may make assembler output more readable.
9988 Disable (or enable) optimizations that use the small data section. This may
9989 be useful for working around optimizer bugs.
9992 @opindex mconstant-gp
9993 Generate code that uses a single constant global pointer value. This is
9994 useful when compiling kernel code.
9998 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9999 This is useful when compiling firmware code.
10001 @item -minline-float-divide-min-latency
10002 @opindex minline-float-divide-min-latency
10003 Generate code for inline divides of floating point values
10004 using the minimum latency algorithm.
10006 @item -minline-float-divide-max-throughput
10007 @opindex minline-float-divide-max-throughput
10008 Generate code for inline divides of floating point values
10009 using the maximum throughput algorithm.
10011 @item -minline-int-divide-min-latency
10012 @opindex minline-int-divide-min-latency
10013 Generate code for inline divides of integer values
10014 using the minimum latency algorithm.
10016 @item -minline-int-divide-max-throughput
10017 @opindex minline-int-divide-max-throughput
10018 Generate code for inline divides of integer values
10019 using the maximum throughput algorithm.
10021 @item -mno-dwarf2-asm
10022 @itemx -mdwarf2-asm
10023 @opindex mno-dwarf2-asm
10024 @opindex mdwarf2-asm
10025 Don't (or do) generate assembler code for the DWARF2 line number debugging
10026 info. This may be useful when not using the GNU assembler.
10028 @item -mfixed-range=@var{register-range}
10029 @opindex mfixed-range
10030 Generate code treating the given register range as fixed registers.
10031 A fixed register is one that the register allocator can not use. This is
10032 useful when compiling kernel code. A register range is specified as
10033 two registers separated by a dash. Multiple register ranges can be
10034 specified separated by a comma.
10036 @item -mearly-stop-bits
10037 @itemx -mno-early-stop-bits
10038 @opindex mearly-stop-bits
10039 @opindex mno-early-stop-bits
10040 Allow stop bits to be placed earlier than immediately preceding the
10041 instruction that triggered the stop bit. This can improve instruction
10042 scheduling, but does not always do so.
10046 @subsection D30V Options
10047 @cindex D30V Options
10049 These @samp{-m} options are defined for D30V implementations:
10054 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10055 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10056 memory, which starts at location @code{0x80000000}.
10059 @opindex mextmemory
10060 Same as the @option{-mextmem} switch.
10064 Link the @samp{.text} section into onchip text memory, which starts at
10065 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10066 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10067 into onchip data memory, which starts at location @code{0x20000000}.
10069 @item -mno-asm-optimize
10070 @itemx -masm-optimize
10071 @opindex mno-asm-optimize
10072 @opindex masm-optimize
10073 Disable (enable) passing @option{-O} to the assembler when optimizing.
10074 The assembler uses the @option{-O} option to automatically parallelize
10075 adjacent short instructions where possible.
10077 @item -mbranch-cost=@var{n}
10078 @opindex mbranch-cost
10079 Increase the internal costs of branches to @var{n}. Higher costs means
10080 that the compiler will issue more instructions to avoid doing a branch.
10083 @item -mcond-exec=@var{n}
10084 @opindex mcond-exec
10085 Specify the maximum number of conditionally executed instructions that
10086 replace a branch. The default is 4.
10089 @node S/390 and zSeries Options
10090 @subsection S/390 and zSeries Options
10091 @cindex S/390 and zSeries Options
10093 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10097 @itemx -msoft-float
10098 @opindex mhard-float
10099 @opindex msoft-float
10100 Use (do not use) the hardware floating-point instructions and registers
10101 for floating-point operations. When @option{-msoft-float} is specified,
10102 functions in @file{libgcc.a} will be used to perform floating-point
10103 operations. When @option{-mhard-float} is specified, the compiler
10104 generates IEEE floating-point instructions. This is the default.
10107 @itemx -mno-backchain
10108 @opindex mbackchain
10109 @opindex mno-backchain
10110 Generate (or do not generate) code which maintains an explicit
10111 backchain within the stack frame that points to the caller's frame.
10112 This is currently needed to allow debugging. The default is to
10113 generate the backchain.
10116 @itemx -mno-small-exec
10117 @opindex msmall-exec
10118 @opindex mno-small-exec
10119 Generate (or do not generate) code using the @code{bras} instruction
10120 to do subroutine calls.
10121 This only works reliably if the total executable size does not
10122 exceed 64k. The default is to use the @code{basr} instruction instead,
10123 which does not have this limitation.
10129 When @option{-m31} is specified, generate code compliant to the
10130 Linux for S/390 ABI@. When @option{-m64} is specified, generate
10131 code compliant to the Linux for zSeries ABI@. This allows GCC in
10132 particular to generate 64-bit instructions. For the @samp{s390}
10133 targets, the default is @option{-m31}, while the @samp{s390x}
10134 targets default to @option{-m64}.
10140 When @option{-mzarch} is specified, generate code using the
10141 instructions available on z/Architecture.
10142 When @option{-mesa} is specified, generate code using the
10143 instructions available on ESA/390. Note that @option{-mesa} is
10144 not possible with @option{-m64}.
10145 When generating code compliant to the Linux for S/390 ABI,
10146 the default is @option{-mesa}. When generating code compliant
10147 to the Linux for zSeries ABI, the default is @option{-mzarch}.
10153 Generate (or do not generate) code using the @code{mvcle} instruction
10154 to perform block moves. When @option{-mno-mvcle} is specified,
10155 use a @code{mvc} loop instead. This is the default.
10161 Print (or do not print) additional debug information when compiling.
10162 The default is to not print debug information.
10164 @item -march=@var{cpu-type}
10166 Generate code that will run on @var{cpu-type}, which is the name of a system
10167 representing a certain processor type. Possible values for
10168 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10169 When generating code using the instructions available on z/Architecture,
10170 the default is @option{-march=z900}. Otherwise, the default is
10171 @option{-march=g5}.
10173 @item -mtune=@var{cpu-type}
10175 Tune to @var{cpu-type} everything applicable about the generated code,
10176 except for the ABI and the set of available instructions.
10177 The list of @var{cpu-type} values is the same as for @option{-march}.
10178 The default is the value used for @option{-march}.
10183 @subsection CRIS Options
10184 @cindex CRIS Options
10186 These options are defined specifically for the CRIS ports.
10189 @item -march=@var{architecture-type}
10190 @itemx -mcpu=@var{architecture-type}
10193 Generate code for the specified architecture. The choices for
10194 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10195 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10196 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10199 @item -mtune=@var{architecture-type}
10201 Tune to @var{architecture-type} everything applicable about the generated
10202 code, except for the ABI and the set of available instructions. The
10203 choices for @var{architecture-type} are the same as for
10204 @option{-march=@var{architecture-type}}.
10206 @item -mmax-stack-frame=@var{n}
10207 @opindex mmax-stack-frame
10208 Warn when the stack frame of a function exceeds @var{n} bytes.
10210 @item -melinux-stacksize=@var{n}
10211 @opindex melinux-stacksize
10212 Only available with the @samp{cris-axis-aout} target. Arranges for
10213 indications in the program to the kernel loader that the stack of the
10214 program should be set to @var{n} bytes.
10220 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10221 @option{-march=v3} and @option{-march=v8} respectively.
10225 Enable CRIS-specific verbose debug-related information in the assembly
10226 code. This option also has the effect to turn off the @samp{#NO_APP}
10227 formatted-code indicator to the assembler at the beginning of the
10232 Do not use condition-code results from previous instruction; always emit
10233 compare and test instructions before use of condition codes.
10235 @item -mno-side-effects
10236 @opindex mno-side-effects
10237 Do not emit instructions with side-effects in addressing modes other than
10240 @item -mstack-align
10241 @itemx -mno-stack-align
10242 @itemx -mdata-align
10243 @itemx -mno-data-align
10244 @itemx -mconst-align
10245 @itemx -mno-const-align
10246 @opindex mstack-align
10247 @opindex mno-stack-align
10248 @opindex mdata-align
10249 @opindex mno-data-align
10250 @opindex mconst-align
10251 @opindex mno-const-align
10252 These options (no-options) arranges (eliminate arrangements) for the
10253 stack-frame, individual data and constants to be aligned for the maximum
10254 single data access size for the chosen CPU model. The default is to
10255 arrange for 32-bit alignment. ABI details such as structure layout are
10256 not affected by these options.
10264 Similar to the stack- data- and const-align options above, these options
10265 arrange for stack-frame, writable data and constants to all be 32-bit,
10266 16-bit or 8-bit aligned. The default is 32-bit alignment.
10268 @item -mno-prologue-epilogue
10269 @itemx -mprologue-epilogue
10270 @opindex mno-prologue-epilogue
10271 @opindex mprologue-epilogue
10272 With @option{-mno-prologue-epilogue}, the normal function prologue and
10273 epilogue that sets up the stack-frame are omitted and no return
10274 instructions or return sequences are generated in the code. Use this
10275 option only together with visual inspection of the compiled code: no
10276 warnings or errors are generated when call-saved registers must be saved,
10277 or storage for local variable needs to be allocated.
10281 @opindex mno-gotplt
10283 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10284 instruction sequences that load addresses for functions from the PLT part
10285 of the GOT rather than (traditional on other architectures) calls to the
10286 PLT. The default is @option{-mgotplt}.
10290 Legacy no-op option only recognized with the cris-axis-aout target.
10294 Legacy no-op option only recognized with the cris-axis-elf and
10295 cris-axis-linux-gnu targets.
10299 Only recognized with the cris-axis-aout target, where it selects a
10300 GNU/linux-like multilib, include files and instruction set for
10301 @option{-march=v8}.
10305 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10309 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10310 to link with input-output functions from a simulator library. Code,
10311 initialized data and zero-initialized data are allocated consecutively.
10315 Like @option{-sim}, but pass linker options to locate initialized data at
10316 0x40000000 and zero-initialized data at 0x80000000.
10320 @subsection MMIX Options
10321 @cindex MMIX Options
10323 These options are defined for the MMIX:
10327 @itemx -mno-libfuncs
10329 @opindex mno-libfuncs
10330 Specify that intrinsic library functions are being compiled, passing all
10331 values in registers, no matter the size.
10334 @itemx -mno-epsilon
10336 @opindex mno-epsilon
10337 Generate floating-point comparison instructions that compare with respect
10338 to the @code{rE} epsilon register.
10340 @item -mabi=mmixware
10342 @opindex mabi-mmixware
10344 Generate code that passes function parameters and return values that (in
10345 the called function) are seen as registers @code{$0} and up, as opposed to
10346 the GNU ABI which uses global registers @code{$231} and up.
10348 @item -mzero-extend
10349 @itemx -mno-zero-extend
10350 @opindex mzero-extend
10351 @opindex mno-zero-extend
10352 When reading data from memory in sizes shorter than 64 bits, use (do not
10353 use) zero-extending load instructions by default, rather than
10354 sign-extending ones.
10357 @itemx -mno-knuthdiv
10359 @opindex mno-knuthdiv
10360 Make the result of a division yielding a remainder have the same sign as
10361 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10362 remainder follows the sign of the dividend. Both methods are
10363 arithmetically valid, the latter being almost exclusively used.
10365 @item -mtoplevel-symbols
10366 @itemx -mno-toplevel-symbols
10367 @opindex mtoplevel-symbols
10368 @opindex mno-toplevel-symbols
10369 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10370 code can be used with the @code{PREFIX} assembly directive.
10374 Generate an executable in the ELF format, rather than the default
10375 @samp{mmo} format used by the @command{mmix} simulator.
10377 @item -mbranch-predict
10378 @itemx -mno-branch-predict
10379 @opindex mbranch-predict
10380 @opindex mno-branch-predict
10381 Use (do not use) the probable-branch instructions, when static branch
10382 prediction indicates a probable branch.
10384 @item -mbase-addresses
10385 @itemx -mno-base-addresses
10386 @opindex mbase-addresses
10387 @opindex mno-base-addresses
10388 Generate (do not generate) code that uses @emph{base addresses}. Using a
10389 base address automatically generates a request (handled by the assembler
10390 and the linker) for a constant to be set up in a global register. The
10391 register is used for one or more base address requests within the range 0
10392 to 255 from the value held in the register. The generally leads to short
10393 and fast code, but the number of different data items that can be
10394 addressed is limited. This means that a program that uses lots of static
10395 data may require @option{-mno-base-addresses}.
10397 @item -msingle-exit
10398 @itemx -mno-single-exit
10399 @opindex msingle-exit
10400 @opindex mno-single-exit
10401 Force (do not force) generated code to have a single exit point in each
10405 @node PDP-11 Options
10406 @subsection PDP-11 Options
10407 @cindex PDP-11 Options
10409 These options are defined for the PDP-11:
10414 Use hardware FPP floating point. This is the default. (FIS floating
10415 point on the PDP-11/40 is not supported.)
10418 @opindex msoft-float
10419 Do not use hardware floating point.
10423 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10427 Return floating-point results in memory. This is the default.
10431 Generate code for a PDP-11/40.
10435 Generate code for a PDP-11/45. This is the default.
10439 Generate code for a PDP-11/10.
10441 @item -mbcopy-builtin
10442 @opindex bcopy-builtin
10443 Use inline @code{movstrhi} patterns for copying memory. This is the
10448 Do not use inline @code{movstrhi} patterns for copying memory.
10454 Use 16-bit @code{int}. This is the default.
10460 Use 32-bit @code{int}.
10463 @itemx -mno-float32
10465 @opindex mno-float32
10466 Use 64-bit @code{float}. This is the default.
10471 @opindex mno-float64
10472 Use 32-bit @code{float}.
10476 Use @code{abshi2} pattern. This is the default.
10480 Do not use @code{abshi2} pattern.
10482 @item -mbranch-expensive
10483 @opindex mbranch-expensive
10484 Pretend that branches are expensive. This is for experimenting with
10485 code generation only.
10487 @item -mbranch-cheap
10488 @opindex mbranch-cheap
10489 Do not pretend that branches are expensive. This is the default.
10493 Generate code for a system with split I&D.
10497 Generate code for a system without split I&D. This is the default.
10501 Use Unix assembler syntax. This is the default when configured for
10502 @samp{pdp11-*-bsd}.
10506 Use DEC assembler syntax. This is the default when configured for any
10507 PDP-11 target other than @samp{pdp11-*-bsd}.
10510 @node Xstormy16 Options
10511 @subsection Xstormy16 Options
10512 @cindex Xstormy16 Options
10514 These options are defined for Xstormy16:
10519 Choose startup files and linker script suitable for the simulator.
10523 @subsection FRV Options
10524 @cindex FRV Options
10530 Only use the first 32 general purpose registers.
10535 Use all 64 general purpose registers.
10540 Use only the first 32 floating point registers.
10545 Use all 64 floating point registers
10548 @opindex mhard-float
10550 Use hardware instructions for floating point operations.
10553 @opindex msoft-float
10555 Use library routines for floating point operations.
10560 Dynamically allocate condition code registers.
10565 Do not try to dynamically allocate condition code registers, only
10566 use @code{icc0} and @code{fcc0}.
10571 Change ABI to use double word insns.
10576 Do not use double word instructions.
10581 Use floating point double instructions.
10584 @opindex mno-double
10586 Do not use floating point double instructions.
10591 Use media instructions.
10596 Do not use media instructions.
10601 Use multiply and add/subtract instructions.
10604 @opindex mno-muladd
10606 Do not use multiply and add/subtract instructions.
10608 @item -mlibrary-pic
10609 @opindex mlibrary-pic
10611 Enable PIC support for building libraries
10616 Use only the first four media accumulator registers.
10621 Use all eight media accumulator registers.
10626 Pack VLIW instructions.
10631 Do not pack VLIW instructions.
10634 @opindex mno-eflags
10636 Do not mark ABI switches in e_flags.
10639 @opindex mcond-move
10641 Enable the use of conditional-move instructions (default).
10643 This switch is mainly for debugging the compiler and will likely be removed
10644 in a future version.
10646 @item -mno-cond-move
10647 @opindex mno-cond-move
10649 Disable the use of conditional-move instructions.
10651 This switch is mainly for debugging the compiler and will likely be removed
10652 in a future version.
10657 Enable the use of conditional set instructions (default).
10659 This switch is mainly for debugging the compiler and will likely be removed
10660 in a future version.
10665 Disable the use of conditional set instructions.
10667 This switch is mainly for debugging the compiler and will likely be removed
10668 in a future version.
10671 @opindex mcond-exec
10673 Enable the use of conditional execution (default).
10675 This switch is mainly for debugging the compiler and will likely be removed
10676 in a future version.
10678 @item -mno-cond-exec
10679 @opindex mno-cond-exec
10681 Disable the use of conditional execution.
10683 This switch is mainly for debugging the compiler and will likely be removed
10684 in a future version.
10686 @item -mvliw-branch
10687 @opindex mvliw-branch
10689 Run a pass to pack branches into VLIW instructions (default).
10691 This switch is mainly for debugging the compiler and will likely be removed
10692 in a future version.
10694 @item -mno-vliw-branch
10695 @opindex mno-vliw-branch
10697 Do not run a pass to pack branches into VLIW instructions.
10699 This switch is mainly for debugging the compiler and will likely be removed
10700 in a future version.
10702 @item -mmulti-cond-exec
10703 @opindex mmulti-cond-exec
10705 Enable optimization of @code{&&} and @code{||} in conditional execution
10708 This switch is mainly for debugging the compiler and will likely be removed
10709 in a future version.
10711 @item -mno-multi-cond-exec
10712 @opindex mno-multi-cond-exec
10714 Disable optimization of @code{&&} and @code{||} in conditional execution.
10716 This switch is mainly for debugging the compiler and will likely be removed
10717 in a future version.
10719 @item -mnested-cond-exec
10720 @opindex mnested-cond-exec
10722 Enable nested conditional execution optimizations (default).
10724 This switch is mainly for debugging the compiler and will likely be removed
10725 in a future version.
10727 @item -mno-nested-cond-exec
10728 @opindex mno-nested-cond-exec
10730 Disable nested conditional execution optimizations.
10732 This switch is mainly for debugging the compiler and will likely be removed
10733 in a future version.
10735 @item -mtomcat-stats
10736 @opindex mtomcat-stats
10738 Cause gas to print out tomcat statistics.
10740 @item -mcpu=@var{cpu}
10743 Select the processor type for which to generate code. Possible values are
10744 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
10749 @node Xtensa Options
10750 @subsection Xtensa Options
10751 @cindex Xtensa Options
10753 The Xtensa architecture is designed to support many different
10754 configurations. The compiler's default options can be set to match a
10755 particular Xtensa configuration by copying a configuration file into the
10756 GCC sources when building GCC@. The options below may be used to
10757 override the default options.
10761 @itemx -mlittle-endian
10762 @opindex mbig-endian
10763 @opindex mlittle-endian
10764 Specify big-endian or little-endian byte ordering for the target Xtensa
10768 @itemx -mno-density
10770 @opindex mno-density
10771 Enable or disable use of the optional Xtensa code density instructions.
10774 @itemx -mno-const16
10776 @opindex mno-const16
10777 Enable or disable use of @code{CONST16} instructions for loading
10778 constant values. The @code{CONST16} instruction is currently not a
10779 standard option from Tensilica. When enabled, @code{CONST16}
10780 instructions are always used in place of the standard @code{L32R}
10781 instructions. The use of @code{CONST16} is enabled by default only if
10782 the @code{L32R} instruction is not available.
10788 Enable or disable use of the Xtensa @code{ABS} instruction for absolute
10795 Enable or disable use of the Xtensa @code{ADDX} and @code{SUBX}
10802 Enable or disable use of the Xtensa MAC16 option. When enabled, GCC
10803 will generate MAC16 instructions from standard C code, with the
10804 limitation that it will use neither the MR register file nor any
10805 instruction that operates on the MR registers. When this option is
10806 disabled, GCC will translate 16-bit multiply/accumulate operations to a
10807 combination of core instructions and library calls, depending on whether
10808 any other multiplier options are enabled.
10814 Enable or disable use of the 16-bit integer multiplier option. When
10815 enabled, the compiler will generate 16-bit multiply instructions for
10816 multiplications of 16 bits or smaller in standard C code. When this
10817 option is disabled, the compiler will either use 32-bit multiply or
10818 MAC16 instructions if they are available or generate library calls to
10819 perform the multiply operations using shifts and adds.
10825 Enable or disable use of the 32-bit integer multiplier option. When
10826 enabled, the compiler will generate 32-bit multiply instructions for
10827 multiplications of 32 bits or smaller in standard C code. When this
10828 option is disabled, the compiler will generate library calls to perform
10829 the multiply operations using either shifts and adds or 16-bit multiply
10830 instructions if they are available.
10836 Enable or disable use of the optional normalization shift amount
10837 (@code{NSA}) instructions to implement the built-in @code{ffs} function.
10842 @opindex mno-minmax
10843 Enable or disable use of the optional minimum and maximum value
10850 Enable or disable use of the optional sign extend (@code{SEXT})
10854 @itemx -mno-booleans
10856 @opindex mno-booleans
10857 Enable or disable support for the boolean register file used by Xtensa
10858 coprocessors. This is not typically useful by itself but may be
10859 required for other options that make use of the boolean registers (e.g.,
10860 the floating-point option).
10863 @itemx -msoft-float
10864 @opindex mhard-float
10865 @opindex msoft-float
10866 Enable or disable use of the floating-point option. When enabled, GCC
10867 generates floating-point instructions for 32-bit @code{float}
10868 operations. When this option is disabled, GCC generates library calls
10869 to emulate 32-bit floating-point operations using integer instructions.
10870 Regardless of this option, 64-bit @code{double} operations are always
10871 emulated with calls to library functions.
10874 @itemx -mno-fused-madd
10875 @opindex mfused-madd
10876 @opindex mno-fused-madd
10877 Enable or disable use of fused multiply/add and multiply/subtract
10878 instructions in the floating-point option. This has no effect if the
10879 floating-point option is not also enabled. Disabling fused multiply/add
10880 and multiply/subtract instructions forces the compiler to use separate
10881 instructions for the multiply and add/subtract operations. This may be
10882 desirable in some cases where strict IEEE 754-compliant results are
10883 required: the fused multiply add/subtract instructions do not round the
10884 intermediate result, thereby producing results with @emph{more} bits of
10885 precision than specified by the IEEE standard. Disabling fused multiply
10886 add/subtract instructions also ensures that the program output is not
10887 sensitive to the compiler's ability to combine multiply and add/subtract
10890 @item -mtext-section-literals
10891 @itemx -mno-text-section-literals
10892 @opindex mtext-section-literals
10893 @opindex mno-text-section-literals
10894 Control the treatment of literal pools. The default is
10895 @option{-mno-text-section-literals}, which places literals in a separate
10896 section in the output file. This allows the literal pool to be placed
10897 in a data RAM/ROM, and it also allows the linker to combine literal
10898 pools from separate object files to remove redundant literals and
10899 improve code size. With @option{-mtext-section-literals}, the literals
10900 are interspersed in the text section in order to keep them as close as
10901 possible to their references. This may be necessary for large assembly
10904 @item -mtarget-align
10905 @itemx -mno-target-align
10906 @opindex mtarget-align
10907 @opindex mno-target-align
10908 When this option is enabled, GCC instructs the assembler to
10909 automatically align instructions to reduce branch penalties at the
10910 expense of some code density. The assembler attempts to widen density
10911 instructions to align branch targets and the instructions following call
10912 instructions. If there are not enough preceding safe density
10913 instructions to align a target, no widening will be performed. The
10914 default is @option{-mtarget-align}. These options do not affect the
10915 treatment of auto-aligned instructions like @code{LOOP}, which the
10916 assembler will always align, either by widening density instructions or
10917 by inserting no-op instructions.
10920 @itemx -mno-longcalls
10921 @opindex mlongcalls
10922 @opindex mno-longcalls
10923 When this option is enabled, GCC instructs the assembler to translate
10924 direct calls to indirect calls unless it can determine that the target
10925 of a direct call is in the range allowed by the call instruction. This
10926 translation typically occurs for calls to functions in other source
10927 files. Specifically, the assembler translates a direct @code{CALL}
10928 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
10929 The default is @option{-mno-longcalls}. This option should be used in
10930 programs where the call target can potentially be out of range. This
10931 option is implemented in the assembler, not the compiler, so the
10932 assembly code generated by GCC will still show direct call
10933 instructions---look at the disassembled object code to see the actual
10934 instructions. Note that the assembler will use an indirect call for
10935 every cross-file call, not just those that really will be out of range.
10938 @node Code Gen Options
10939 @section Options for Code Generation Conventions
10940 @cindex code generation conventions
10941 @cindex options, code generation
10942 @cindex run-time options
10944 These machine-independent options control the interface conventions
10945 used in code generation.
10947 Most of them have both positive and negative forms; the negative form
10948 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
10949 one of the forms is listed---the one which is not the default. You
10950 can figure out the other form by either removing @samp{no-} or adding
10954 @item -fbounds-check
10955 @opindex fbounds-check
10956 For front-ends that support it, generate additional code to check that
10957 indices used to access arrays are within the declared range. This is
10958 currently only supported by the Java and Fortran 77 front-ends, where
10959 this option defaults to true and false respectively.
10963 This option generates traps for signed overflow on addition, subtraction,
10964 multiplication operations.
10968 This option instructs the compiler to assume that signed arithmetic
10969 overflow of addition, subtraction and multiplication wraps around
10970 using twos-complement representation. This flag enables some optimizations
10971 and disables other. This option is enabled by default for the Java
10972 front-end, as required by the Java language specification.
10975 @opindex fexceptions
10976 Enable exception handling. Generates extra code needed to propagate
10977 exceptions. For some targets, this implies GCC will generate frame
10978 unwind information for all functions, which can produce significant data
10979 size overhead, although it does not affect execution. If you do not
10980 specify this option, GCC will enable it by default for languages like
10981 C++ which normally require exception handling, and disable it for
10982 languages like C that do not normally require it. However, you may need
10983 to enable this option when compiling C code that needs to interoperate
10984 properly with exception handlers written in C++. You may also wish to
10985 disable this option if you are compiling older C++ programs that don't
10986 use exception handling.
10988 @item -fnon-call-exceptions
10989 @opindex fnon-call-exceptions
10990 Generate code that allows trapping instructions to throw exceptions.
10991 Note that this requires platform-specific runtime support that does
10992 not exist everywhere. Moreover, it only allows @emph{trapping}
10993 instructions to throw exceptions, i.e.@: memory references or floating
10994 point instructions. It does not allow exceptions to be thrown from
10995 arbitrary signal handlers such as @code{SIGALRM}.
10997 @item -funwind-tables
10998 @opindex funwind-tables
10999 Similar to @option{-fexceptions}, except that it will just generate any needed
11000 static data, but will not affect the generated code in any other way.
11001 You will normally not enable this option; instead, a language processor
11002 that needs this handling would enable it on your behalf.
11004 @item -fasynchronous-unwind-tables
11005 @opindex funwind-tables
11006 Generate unwind table in dwarf2 format, if supported by target machine. The
11007 table is exact at each instruction boundary, so it can be used for stack
11008 unwinding from asynchronous events (such as debugger or garbage collector).
11010 @item -fpcc-struct-return
11011 @opindex fpcc-struct-return
11012 Return ``short'' @code{struct} and @code{union} values in memory like
11013 longer ones, rather than in registers. This convention is less
11014 efficient, but it has the advantage of allowing intercallability between
11015 GCC-compiled files and files compiled with other compilers, particularly
11016 the Portable C Compiler (pcc).
11018 The precise convention for returning structures in memory depends
11019 on the target configuration macros.
11021 Short structures and unions are those whose size and alignment match
11022 that of some integer type.
11024 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11025 switch is not binary compatible with code compiled with the
11026 @option{-freg-struct-return} switch.
11027 Use it to conform to a non-default application binary interface.
11029 @item -freg-struct-return
11030 @opindex freg-struct-return
11031 Return @code{struct} and @code{union} values in registers when possible.
11032 This is more efficient for small structures than
11033 @option{-fpcc-struct-return}.
11035 If you specify neither @option{-fpcc-struct-return} nor
11036 @option{-freg-struct-return}, GCC defaults to whichever convention is
11037 standard for the target. If there is no standard convention, GCC
11038 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11039 the principal compiler. In those cases, we can choose the standard, and
11040 we chose the more efficient register return alternative.
11042 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11043 switch is not binary compatible with code compiled with the
11044 @option{-fpcc-struct-return} switch.
11045 Use it to conform to a non-default application binary interface.
11047 @item -fshort-enums
11048 @opindex fshort-enums
11049 Allocate to an @code{enum} type only as many bytes as it needs for the
11050 declared range of possible values. Specifically, the @code{enum} type
11051 will be equivalent to the smallest integer type which has enough room.
11053 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11054 code that is not binary compatible with code generated without that switch.
11055 Use it to conform to a non-default application binary interface.
11057 @item -fshort-double
11058 @opindex fshort-double
11059 Use the same size for @code{double} as for @code{float}.
11061 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11062 code that is not binary compatible with code generated without that switch.
11063 Use it to conform to a non-default application binary interface.
11065 @item -fshort-wchar
11066 @opindex fshort-wchar
11067 Override the underlying type for @samp{wchar_t} to be @samp{short
11068 unsigned int} instead of the default for the target. This option is
11069 useful for building programs to run under WINE@.
11071 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11072 code that is not binary compatible with code generated without that switch.
11073 Use it to conform to a non-default application binary interface.
11075 @item -fshared-data
11076 @opindex fshared-data
11077 Requests that the data and non-@code{const} variables of this
11078 compilation be shared data rather than private data. The distinction
11079 makes sense only on certain operating systems, where shared data is
11080 shared between processes running the same program, while private data
11081 exists in one copy per process.
11084 @opindex fno-common
11085 In C, allocate even uninitialized global variables in the data section of the
11086 object file, rather than generating them as common blocks. This has the
11087 effect that if the same variable is declared (without @code{extern}) in
11088 two different compilations, you will get an error when you link them.
11089 The only reason this might be useful is if you wish to verify that the
11090 program will work on other systems which always work this way.
11094 Ignore the @samp{#ident} directive.
11096 @item -fno-gnu-linker
11097 @opindex fno-gnu-linker
11098 Do not output global initializations (such as C++ constructors and
11099 destructors) in the form used by the GNU linker (on systems where the GNU
11100 linker is the standard method of handling them). Use this option when
11101 you want to use a non-GNU linker, which also requires using the
11102 @command{collect2} program to make sure the system linker includes
11103 constructors and destructors. (@command{collect2} is included in the GCC
11104 distribution.) For systems which @emph{must} use @command{collect2}, the
11105 compiler driver @command{gcc} is configured to do this automatically.
11107 @item -finhibit-size-directive
11108 @opindex finhibit-size-directive
11109 Don't output a @code{.size} assembler directive, or anything else that
11110 would cause trouble if the function is split in the middle, and the
11111 two halves are placed at locations far apart in memory. This option is
11112 used when compiling @file{crtstuff.c}; you should not need to use it
11115 @item -fverbose-asm
11116 @opindex fverbose-asm
11117 Put extra commentary information in the generated assembly code to
11118 make it more readable. This option is generally only of use to those
11119 who actually need to read the generated assembly code (perhaps while
11120 debugging the compiler itself).
11122 @option{-fno-verbose-asm}, the default, causes the
11123 extra information to be omitted and is useful when comparing two assembler
11128 @cindex global offset table
11130 Generate position-independent code (PIC) suitable for use in a shared
11131 library, if supported for the target machine. Such code accesses all
11132 constant addresses through a global offset table (GOT)@. The dynamic
11133 loader resolves the GOT entries when the program starts (the dynamic
11134 loader is not part of GCC; it is part of the operating system). If
11135 the GOT size for the linked executable exceeds a machine-specific
11136 maximum size, you get an error message from the linker indicating that
11137 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11138 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
11139 on the m68k and RS/6000. The 386 has no such limit.)
11141 Position-independent code requires special support, and therefore works
11142 only on certain machines. For the 386, GCC supports PIC for System V
11143 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11144 position-independent.
11148 If supported for the target machine, emit position-independent code,
11149 suitable for dynamic linking and avoiding any limit on the size of the
11150 global offset table. This option makes a difference on the m68k, m88k,
11153 Position-independent code requires special support, and therefore works
11154 only on certain machines.
11160 These options are similar to @option{-fpic} and @option{-fPIC}, but
11161 generated position independent code can be only linked into executables.
11162 Usually these options are used when @option{-pie} GCC option will be
11163 used during linking.
11165 @item -ffixed-@var{reg}
11167 Treat the register named @var{reg} as a fixed register; generated code
11168 should never refer to it (except perhaps as a stack pointer, frame
11169 pointer or in some other fixed role).
11171 @var{reg} must be the name of a register. The register names accepted
11172 are machine-specific and are defined in the @code{REGISTER_NAMES}
11173 macro in the machine description macro file.
11175 This flag does not have a negative form, because it specifies a
11178 @item -fcall-used-@var{reg}
11179 @opindex fcall-used
11180 Treat the register named @var{reg} as an allocable register that is
11181 clobbered by function calls. It may be allocated for temporaries or
11182 variables that do not live across a call. Functions compiled this way
11183 will not save and restore the register @var{reg}.
11185 It is an error to used this flag with the frame pointer or stack pointer.
11186 Use of this flag for other registers that have fixed pervasive roles in
11187 the machine's execution model will produce disastrous results.
11189 This flag does not have a negative form, because it specifies a
11192 @item -fcall-saved-@var{reg}
11193 @opindex fcall-saved
11194 Treat the register named @var{reg} as an allocable register saved by
11195 functions. It may be allocated even for temporaries or variables that
11196 live across a call. Functions compiled this way will save and restore
11197 the register @var{reg} if they use it.
11199 It is an error to used this flag with the frame pointer or stack pointer.
11200 Use of this flag for other registers that have fixed pervasive roles in
11201 the machine's execution model will produce disastrous results.
11203 A different sort of disaster will result from the use of this flag for
11204 a register in which function values may be returned.
11206 This flag does not have a negative form, because it specifies a
11209 @item -fpack-struct
11210 @opindex fpack-struct
11211 Pack all structure members together without holes.
11213 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11214 code that is not binary compatible with code generated without that switch.
11215 Additionally, it makes the code suboptimal.
11216 Use it to conform to a non-default application binary interface.
11218 @item -finstrument-functions
11219 @opindex finstrument-functions
11220 Generate instrumentation calls for entry and exit to functions. Just
11221 after function entry and just before function exit, the following
11222 profiling functions will be called with the address of the current
11223 function and its call site. (On some platforms,
11224 @code{__builtin_return_address} does not work beyond the current
11225 function, so the call site information may not be available to the
11226 profiling functions otherwise.)
11229 void __cyg_profile_func_enter (void *this_fn,
11231 void __cyg_profile_func_exit (void *this_fn,
11235 The first argument is the address of the start of the current function,
11236 which may be looked up exactly in the symbol table.
11238 This instrumentation is also done for functions expanded inline in other
11239 functions. The profiling calls will indicate where, conceptually, the
11240 inline function is entered and exited. This means that addressable
11241 versions of such functions must be available. If all your uses of a
11242 function are expanded inline, this may mean an additional expansion of
11243 code size. If you use @samp{extern inline} in your C code, an
11244 addressable version of such functions must be provided. (This is
11245 normally the case anyways, but if you get lucky and the optimizer always
11246 expands the functions inline, you might have gotten away without
11247 providing static copies.)
11249 A function may be given the attribute @code{no_instrument_function}, in
11250 which case this instrumentation will not be done. This can be used, for
11251 example, for the profiling functions listed above, high-priority
11252 interrupt routines, and any functions from which the profiling functions
11253 cannot safely be called (perhaps signal handlers, if the profiling
11254 routines generate output or allocate memory).
11256 @item -fstack-check
11257 @opindex fstack-check
11258 Generate code to verify that you do not go beyond the boundary of the
11259 stack. You should specify this flag if you are running in an
11260 environment with multiple threads, but only rarely need to specify it in
11261 a single-threaded environment since stack overflow is automatically
11262 detected on nearly all systems if there is only one stack.
11264 Note that this switch does not actually cause checking to be done; the
11265 operating system must do that. The switch causes generation of code
11266 to ensure that the operating system sees the stack being extended.
11268 @item -fstack-limit-register=@var{reg}
11269 @itemx -fstack-limit-symbol=@var{sym}
11270 @itemx -fno-stack-limit
11271 @opindex fstack-limit-register
11272 @opindex fstack-limit-symbol
11273 @opindex fno-stack-limit
11274 Generate code to ensure that the stack does not grow beyond a certain value,
11275 either the value of a register or the address of a symbol. If the stack
11276 would grow beyond the value, a signal is raised. For most targets,
11277 the signal is raised before the stack overruns the boundary, so
11278 it is possible to catch the signal without taking special precautions.
11280 For instance, if the stack starts at absolute address @samp{0x80000000}
11281 and grows downwards, you can use the flags
11282 @option{-fstack-limit-symbol=__stack_limit} and
11283 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11284 of 128KB@. Note that this may only work with the GNU linker.
11286 @cindex aliasing of parameters
11287 @cindex parameters, aliased
11288 @item -fargument-alias
11289 @itemx -fargument-noalias
11290 @itemx -fargument-noalias-global
11291 @opindex fargument-alias
11292 @opindex fargument-noalias
11293 @opindex fargument-noalias-global
11294 Specify the possible relationships among parameters and between
11295 parameters and global data.
11297 @option{-fargument-alias} specifies that arguments (parameters) may
11298 alias each other and may alias global storage.@*
11299 @option{-fargument-noalias} specifies that arguments do not alias
11300 each other, but may alias global storage.@*
11301 @option{-fargument-noalias-global} specifies that arguments do not
11302 alias each other and do not alias global storage.
11304 Each language will automatically use whatever option is required by
11305 the language standard. You should not need to use these options yourself.
11307 @item -fleading-underscore
11308 @opindex fleading-underscore
11309 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11310 change the way C symbols are represented in the object file. One use
11311 is to help link with legacy assembly code.
11313 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11314 generate code that is not binary compatible with code generated without that
11315 switch. Use it to conform to a non-default application binary interface.
11316 Not all targets provide complete support for this switch.
11318 @item -ftls-model=@var{model}
11319 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11320 The @var{model} argument should be one of @code{global-dynamic},
11321 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11323 The default without @option{-fpic} is @code{initial-exec}; with
11324 @option{-fpic} the default is @code{global-dynamic}.
11329 @node Environment Variables
11330 @section Environment Variables Affecting GCC
11331 @cindex environment variables
11333 @c man begin ENVIRONMENT
11334 This section describes several environment variables that affect how GCC
11335 operates. Some of them work by specifying directories or prefixes to use
11336 when searching for various kinds of files. Some are used to specify other
11337 aspects of the compilation environment.
11339 Note that you can also specify places to search using options such as
11340 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11341 take precedence over places specified using environment variables, which
11342 in turn take precedence over those specified by the configuration of GCC@.
11343 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11344 GNU Compiler Collection (GCC) Internals}.
11349 @c @itemx LC_COLLATE
11351 @c @itemx LC_MONETARY
11352 @c @itemx LC_NUMERIC
11357 @c @findex LC_COLLATE
11358 @findex LC_MESSAGES
11359 @c @findex LC_MONETARY
11360 @c @findex LC_NUMERIC
11364 These environment variables control the way that GCC uses
11365 localization information that allow GCC to work with different
11366 national conventions. GCC inspects the locale categories
11367 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11368 so. These locale categories can be set to any value supported by your
11369 installation. A typical value is @samp{en_UK} for English in the United
11372 The @env{LC_CTYPE} environment variable specifies character
11373 classification. GCC uses it to determine the character boundaries in
11374 a string; this is needed for some multibyte encodings that contain quote
11375 and escape characters that would otherwise be interpreted as a string
11378 The @env{LC_MESSAGES} environment variable specifies the language to
11379 use in diagnostic messages.
11381 If the @env{LC_ALL} environment variable is set, it overrides the value
11382 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11383 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11384 environment variable. If none of these variables are set, GCC
11385 defaults to traditional C English behavior.
11389 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11390 files. GCC uses temporary files to hold the output of one stage of
11391 compilation which is to be used as input to the next stage: for example,
11392 the output of the preprocessor, which is the input to the compiler
11395 @item GCC_EXEC_PREFIX
11396 @findex GCC_EXEC_PREFIX
11397 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11398 names of the subprograms executed by the compiler. No slash is added
11399 when this prefix is combined with the name of a subprogram, but you can
11400 specify a prefix that ends with a slash if you wish.
11402 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11403 an appropriate prefix to use based on the pathname it was invoked with.
11405 If GCC cannot find the subprogram using the specified prefix, it
11406 tries looking in the usual places for the subprogram.
11408 The default value of @env{GCC_EXEC_PREFIX} is
11409 @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value
11410 of @code{prefix} when you ran the @file{configure} script.
11412 Other prefixes specified with @option{-B} take precedence over this prefix.
11414 This prefix is also used for finding files such as @file{crt0.o} that are
11417 In addition, the prefix is used in an unusual way in finding the
11418 directories to search for header files. For each of the standard
11419 directories whose name normally begins with @samp{/usr/local/lib/gcc-lib}
11420 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11421 replacing that beginning with the specified prefix to produce an
11422 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11423 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11424 These alternate directories are searched first; the standard directories
11427 @item COMPILER_PATH
11428 @findex COMPILER_PATH
11429 The value of @env{COMPILER_PATH} is a colon-separated list of
11430 directories, much like @env{PATH}. GCC tries the directories thus
11431 specified when searching for subprograms, if it can't find the
11432 subprograms using @env{GCC_EXEC_PREFIX}.
11435 @findex LIBRARY_PATH
11436 The value of @env{LIBRARY_PATH} is a colon-separated list of
11437 directories, much like @env{PATH}. When configured as a native compiler,
11438 GCC tries the directories thus specified when searching for special
11439 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11440 using GCC also uses these directories when searching for ordinary
11441 libraries for the @option{-l} option (but directories specified with
11442 @option{-L} come first).
11446 @cindex locale definition
11447 This variable is used to pass locale information to the compiler. One way in
11448 which this information is used is to determine the character set to be used
11449 when character literals, string literals and comments are parsed in C and C++.
11450 When the compiler is configured to allow multibyte characters,
11451 the following values for @env{LANG} are recognized:
11455 Recognize JIS characters.
11457 Recognize SJIS characters.
11459 Recognize EUCJP characters.
11462 If @env{LANG} is not defined, or if it has some other value, then the
11463 compiler will use mblen and mbtowc as defined by the default locale to
11464 recognize and translate multibyte characters.
11468 Some additional environments variables affect the behavior of the
11471 @include cppenv.texi
11475 @node Precompiled Headers
11476 @section Using Precompiled Headers
11477 @cindex precompiled headers
11478 @cindex speed of compilation
11480 Often large projects have many header files that are included in every
11481 source file. The time the compiler takes to process these header files
11482 over and over again can account for nearly all of the time required to
11483 build the project. To make builds faster, GCC allows users to
11484 `precompile' a header file; then, if builds can use the precompiled
11485 header file they will be much faster.
11487 To create a precompiled header file, simply compile it as you would any
11488 other file, if necessary using the @option{-x} option to make the driver
11489 treat it as a C or C++ header file. You will probably want to use a
11490 tool like @command{make} to keep the precompiled header up-to-date when
11491 the headers it contains change.
11493 A precompiled header file will be searched for when @code{#include} is
11494 seen in the compilation. As it searches for the included file
11495 (@pxref{Search Path,,Search Path,cpp.info,The C Preprocessor}) the
11496 compiler looks for a precompiled header in each directory just before it
11497 looks for the include file in that directory. The name searched for is
11498 the name specified in the @code{#include} with @samp{.gch} appended. If
11499 the precompiled header file can't be used, it is ignored.
11501 For instance, if you have @code{#include "all.h"}, and you have
11502 @file{all.h.gch} in the same directory as @file{all.h}, then the
11503 precompiled header file will be used if possible, and the original
11504 header will be used otherwise.
11506 Alternatively, you might decide to put the precompiled header file in a
11507 directory and use @option{-I} to ensure that directory is searched
11508 before (or instead of) the directory containing the original header.
11509 Then, if you want to check that the precompiled header file is always
11510 used, you can put a file of the same name as the original header in this
11511 directory containing an @code{#error} command.
11513 This also works with @option{-include}. So yet another way to use
11514 precompiled headers, good for projects not designed with precompiled
11515 header files in mind, is to simply take most of the header files used by
11516 a project, include them from another header file, precompile that header
11517 file, and @option{-include} the precompiled header. If the header files
11518 have guards against multiple inclusion, they will be skipped because
11519 they've already been included (in the precompiled header).
11521 If you need to precompile the same header file for different
11522 languages, targets, or compiler options, you can instead make a
11523 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11524 header in the directory. (It doesn't matter what you call the files
11525 in the directory, every precompiled header in the directory will be
11526 considered.) The first precompiled header encountered in the
11527 directory that is valid for this compilation will be used; they're
11528 searched in no particular order.
11530 There are many other possibilities, limited only by your imagination,
11531 good sense, and the constraints of your build system.
11533 A precompiled header file can be used only when these conditions apply:
11537 Only one precompiled header can be used in a particular compilation.
11539 A precompiled header can't be used once the first C token is seen. You
11540 can have preprocessor directives before a precompiled header; you can
11541 even include a precompiled header from inside another header, so long as
11542 there are no C tokens before the @code{#include}.
11544 The precompiled header file must be produced for the same language as
11545 the current compilation. You can't use a C precompiled header for a C++
11548 The precompiled header file must be produced by the same compiler
11549 version and configuration as the current compilation is using.
11550 The easiest way to guarantee this is to use the same compiler binary
11551 for creating and using precompiled headers.
11553 Any macros defined before the precompiled header (including with
11554 @option{-D}) must either be defined in the same way as when the
11555 precompiled header was generated, or must not affect the precompiled
11556 header, which usually means that the they don't appear in the
11557 precompiled header at all.
11559 Certain command-line options must be defined in the same way as when the
11560 precompiled header was generated. At present, it's not clear which
11561 options are safe to change and which are not; the safest choice is to
11562 use exactly the same options when generating and using the precompiled
11566 For all of these but the last, the compiler will automatically ignore
11567 the precompiled header if the conditions aren't met. For the last item,
11568 some option changes will cause the precompiled header to be rejected,
11569 but not all incompatible option combinations have yet been found. If
11570 you find a new incompatible combination, please consider filing a bug
11571 report, see @ref{Bugs}.
11573 @node Running Protoize
11574 @section Running Protoize
11576 The program @code{protoize} is an optional part of GCC@. You can use
11577 it to add prototypes to a program, thus converting the program to ISO
11578 C in one respect. The companion program @code{unprotoize} does the
11579 reverse: it removes argument types from any prototypes that are found.
11581 When you run these programs, you must specify a set of source files as
11582 command line arguments. The conversion programs start out by compiling
11583 these files to see what functions they define. The information gathered
11584 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11586 After scanning comes actual conversion. The specified files are all
11587 eligible to be converted; any files they include (whether sources or
11588 just headers) are eligible as well.
11590 But not all the eligible files are converted. By default,
11591 @code{protoize} and @code{unprotoize} convert only source and header
11592 files in the current directory. You can specify additional directories
11593 whose files should be converted with the @option{-d @var{directory}}
11594 option. You can also specify particular files to exclude with the
11595 @option{-x @var{file}} option. A file is converted if it is eligible, its
11596 directory name matches one of the specified directory names, and its
11597 name within the directory has not been excluded.
11599 Basic conversion with @code{protoize} consists of rewriting most
11600 function definitions and function declarations to specify the types of
11601 the arguments. The only ones not rewritten are those for varargs
11604 @code{protoize} optionally inserts prototype declarations at the
11605 beginning of the source file, to make them available for any calls that
11606 precede the function's definition. Or it can insert prototype
11607 declarations with block scope in the blocks where undeclared functions
11610 Basic conversion with @code{unprotoize} consists of rewriting most
11611 function declarations to remove any argument types, and rewriting
11612 function definitions to the old-style pre-ISO form.
11614 Both conversion programs print a warning for any function declaration or
11615 definition that they can't convert. You can suppress these warnings
11618 The output from @code{protoize} or @code{unprotoize} replaces the
11619 original source file. The original file is renamed to a name ending
11620 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11621 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11622 for DOS) file already exists, then the source file is simply discarded.
11624 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11625 scan the program and collect information about the functions it uses.
11626 So neither of these programs will work until GCC is installed.
11628 Here is a table of the options you can use with @code{protoize} and
11629 @code{unprotoize}. Each option works with both programs unless
11633 @item -B @var{directory}
11634 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11635 usual directory (normally @file{/usr/local/lib}). This file contains
11636 prototype information about standard system functions. This option
11637 applies only to @code{protoize}.
11639 @item -c @var{compilation-options}
11640 Use @var{compilation-options} as the options when running @command{gcc} to
11641 produce the @samp{.X} files. The special option @option{-aux-info} is
11642 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11644 Note that the compilation options must be given as a single argument to
11645 @code{protoize} or @code{unprotoize}. If you want to specify several
11646 @command{gcc} options, you must quote the entire set of compilation options
11647 to make them a single word in the shell.
11649 There are certain @command{gcc} arguments that you cannot use, because they
11650 would produce the wrong kind of output. These include @option{-g},
11651 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11652 the @var{compilation-options}, they are ignored.
11655 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11656 systems) instead of @samp{.c}. This is convenient if you are converting
11657 a C program to C++. This option applies only to @code{protoize}.
11660 Add explicit global declarations. This means inserting explicit
11661 declarations at the beginning of each source file for each function
11662 that is called in the file and was not declared. These declarations
11663 precede the first function definition that contains a call to an
11664 undeclared function. This option applies only to @code{protoize}.
11666 @item -i @var{string}
11667 Indent old-style parameter declarations with the string @var{string}.
11668 This option applies only to @code{protoize}.
11670 @code{unprotoize} converts prototyped function definitions to old-style
11671 function definitions, where the arguments are declared between the
11672 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11673 uses five spaces as the indentation. If you want to indent with just
11674 one space instead, use @option{-i " "}.
11677 Keep the @samp{.X} files. Normally, they are deleted after conversion
11681 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11682 a prototype declaration for each function in each block which calls the
11683 function without any declaration. This option applies only to
11687 Make no real changes. This mode just prints information about the conversions
11688 that would have been done without @option{-n}.
11691 Make no @samp{.save} files. The original files are simply deleted.
11692 Use this option with caution.
11694 @item -p @var{program}
11695 Use the program @var{program} as the compiler. Normally, the name
11696 @file{gcc} is used.
11699 Work quietly. Most warnings are suppressed.
11702 Print the version number, just like @option{-v} for @command{gcc}.
11705 If you need special compiler options to compile one of your program's
11706 source files, then you should generate that file's @samp{.X} file
11707 specially, by running @command{gcc} on that source file with the
11708 appropriate options and the option @option{-aux-info}. Then run
11709 @code{protoize} on the entire set of files. @code{protoize} will use
11710 the existing @samp{.X} file because it is newer than the source file.
11714 gcc -Dfoo=bar file1.c -aux-info file1.X
11719 You need to include the special files along with the rest in the
11720 @code{protoize} command, even though their @samp{.X} files already
11721 exist, because otherwise they won't get converted.
11723 @xref{Protoize Caveats}, for more information on how to use
11724 @code{protoize} successfully.