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 -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}.
197 -fconstant-string-class=@var{class-name} @gol
198 -fgnu-runtime -fnext-runtime @gol
199 -fno-nil-receivers @gol
200 -fobjc-exceptions @gol
201 -freplace-objc-classes @gol
204 -Wno-protocol -Wselector -Wundeclared-selector}
206 @item Language Independent Options
207 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
208 @gccoptlist{-fmessage-length=@var{n} @gol
209 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
211 @item Warning Options
212 @xref{Warning Options,,Options to Request or Suppress Warnings}.
213 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
214 -w -Wextra -Wall -Waggregate-return @gol
215 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
216 -Wconversion -Wno-deprecated-declarations @gol
217 -Wdisabled-optimization -Wno-div-by-zero -Wendif-labels @gol
218 -Werror -Werror-implicit-function-declaration @gol
219 -Wfloat-equal -Wformat -Wformat=2 @gol
220 -Wno-format-extra-args -Wformat-nonliteral @gol
221 -Wformat-security -Wno-format-y2k @gol
222 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
223 -Wimport -Wno-import -Winit-self -Winline @gol
224 -Wno-invalid-offsetof -Winvalid-pch @gol
225 -Wlarger-than-@var{len} -Wlong-long @gol
226 -Wmain -Wmissing-braces @gol
227 -Wmissing-format-attribute -Wmissing-noreturn @gol
228 -Wno-multichar -Wnonnull -Wpacked -Wpadded @gol
229 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
230 -Wreturn-type -Wsequence-point -Wshadow @gol
231 -Wsign-compare -Wstrict-aliasing @gol
232 -Wswitch -Wswitch-default -Wswitch-enum @gol
233 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
234 -Wunknown-pragmas -Wunreachable-code @gol
235 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
236 -Wunused-value -Wunused-variable -Wwrite-strings}
238 @item C-only Warning Options
239 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
240 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
241 -Wstrict-prototypes -Wtraditional @gol
242 -Wdeclaration-after-statement}
244 @item Debugging Options
245 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
246 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
247 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
248 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
249 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
250 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
251 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
252 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
253 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
254 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
255 -ftest-coverage -ftime-report @gol
256 -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 @gol
257 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
258 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
259 -print-multi-directory -print-multi-lib @gol
260 -print-prog-name=@var{program} -print-search-dirs -Q @gol
263 @item Optimization Options
264 @xref{Optimize Options,,Options that Control Optimization}.
265 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
266 -falign-labels=@var{n} -falign-loops=@var{n} @gol
267 -fbranch-probabilities -fprofile-values -fbranch-target-load-optimize @gol
268 -fbranch-target-load-optimize2 -fcaller-saves -fcprop-registers @gol
269 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
270 -fdelayed-branch -fdelete-null-pointer-checks @gol
271 -fexpensive-optimizations -ffast-math -ffloat-store @gol
272 -fforce-addr -fforce-mem -ffunction-sections @gol
273 -fgcse -fgcse-lm -fgcse-sm -floop-optimize -fcrossjumping @gol
274 -fif-conversion -fif-conversion2 @gol
275 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
276 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
277 -fmove-all-movables -fnew-ra -fno-branch-count-reg @gol
278 -fno-default-inline -fno-defer-pop @gol
279 -fno-function-cse -fno-guess-branch-probability @gol
280 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
281 -funsafe-math-optimizations -ffinite-math-only @gol
282 -fno-trapping-math -fno-zero-initialized-in-bss @gol
283 -fomit-frame-pointer -foptimize-register-move @gol
284 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
285 -freduce-all-givs -fregmove -frename-registers @gol
286 -freorder-blocks -freorder-functions @gol
287 -frerun-cse-after-loop -frerun-loop-opt @gol
288 -frounding-math -fschedule-insns -fschedule-insns2 @gol
289 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
290 -fsched-spec-load-dangerous -fsched2-use-superblocks @gol
291 -fsched2-use-traces -fsignaling-nans @gol
292 -fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
293 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
294 -funroll-all-loops -funroll-loops -fpeel-loops @gol
295 -funswitch-loops -fold-unroll-loops -fold-unroll-all-loops @gol
296 --param @var{name}=@var{value}
297 -O -O0 -O1 -O2 -O3 -Os}
299 @item Preprocessor Options
300 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
301 @gccoptlist{-A@var{question}=@var{answer} @gol
302 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
303 -C -dD -dI -dM -dN @gol
304 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
305 -idirafter @var{dir} @gol
306 -include @var{file} -imacros @var{file} @gol
307 -iprefix @var{file} -iwithprefix @var{dir} @gol
308 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
309 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
310 -P -fworking-directory -remap @gol
311 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
312 -Xpreprocessor @var{option}}
314 @item Assembler Option
315 @xref{Assembler Options,,Passing Options to the Assembler}.
316 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
319 @xref{Link Options,,Options for Linking}.
320 @gccoptlist{@var{object-file-name} -l@var{library} @gol
321 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
322 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
323 -Wl,@var{option} -Xlinker @var{option} @gol
326 @item Directory Options
327 @xref{Directory Options,,Options for Directory Search}.
328 @gccoptlist{-B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file}}
331 @c I wrote this xref this way to avoid overfull hbox. -- rms
332 @xref{Target Options}.
333 @gccoptlist{-V @var{version} -b @var{machine}}
335 @item Machine Dependent Options
336 @xref{Submodel Options,,Hardware Models and Configurations}.
338 @emph{M680x0 Options}
339 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
340 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
341 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
342 -malign-int -mstrict-align}
344 @emph{M68hc1x Options}
345 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
346 -mauto-incdec -minmax -mlong-calls -mshort @gol
347 -msoft-reg-count=@var{count}}
350 @gccoptlist{-mg -mgnu -munix}
353 @gccoptlist{-mcpu=@var{cpu-type} @gol
354 -mtune=@var{cpu-type} @gol
355 -mcmodel=@var{code-model} @gol
357 -mapp-regs -mbroken-saverestore -mcypress @gol
358 -mfaster-structs -mflat @gol
359 -mfpu -mhard-float -mhard-quad-float @gol
360 -mimpure-text -mlittle-endian -mlive-g0 -mno-app-regs @gol
361 -mno-faster-structs -mno-flat -mno-fpu @gol
362 -mno-impure-text -mno-stack-bias -mno-unaligned-doubles @gol
363 -msoft-float -msoft-quad-float -msparclite -mstack-bias @gol
364 -msupersparc -munaligned-doubles -mv8}
367 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
368 -mapcs-26 -mapcs-32 @gol
369 -mapcs-stack-check -mno-apcs-stack-check @gol
370 -mapcs-float -mno-apcs-float @gol
371 -mapcs-reentrant -mno-apcs-reentrant @gol
372 -msched-prolog -mno-sched-prolog @gol
373 -mlittle-endian -mbig-endian -mwords-little-endian @gol
374 -malignment-traps -mno-alignment-traps @gol
375 -msoft-float -mhard-float -mfpe @gol
376 -mthumb-interwork -mno-thumb-interwork @gol
377 -mcpu=@var{name} -march=@var{name} -mfpe=@var{name} @gol
378 -mstructure-size-boundary=@var{n} @gol
379 -mabort-on-noreturn @gol
380 -mlong-calls -mno-long-calls @gol
381 -msingle-pic-base -mno-single-pic-base @gol
382 -mpic-register=@var{reg} @gol
383 -mnop-fun-dllimport @gol
384 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
385 -mpoke-function-name @gol
387 -mtpcs-frame -mtpcs-leaf-frame @gol
388 -mcaller-super-interworking -mcallee-super-interworking}
390 @emph{MN10200 Options}
393 @emph{MN10300 Options}
394 @gccoptlist{-mmult-bug -mno-mult-bug @gol
395 -mam33 -mno-am33 @gol
396 -mam33-2 -mno-am33-2 @gol
399 @emph{M32R/D Options}
400 @gccoptlist{-m32rx -m32r -mcode-model=@var{model-type} @gol
401 -msdata=@var{sdata-type} -G @var{num}}
404 @gccoptlist{-m88000 -m88100 -m88110 -mbig-pic @gol
405 -mcheck-zero-division -mhandle-large-shift @gol
406 -midentify-revision -mno-check-zero-division @gol
407 -mno-ocs-debug-info -mno-ocs-frame-position @gol
408 -mno-optimize-arg-area -mno-serialize-volatile @gol
409 -mno-underscores -mocs-debug-info @gol
410 -mocs-frame-position -moptimize-arg-area @gol
411 -mserialize-volatile -mshort-data-@var{num} -msvr3 @gol
412 -msvr4 -mtrap-large-shift -muse-div-instruction @gol
413 -mversion-03.00 -mwarn-passed-structs}
415 @emph{RS/6000 and PowerPC Options}
416 @gccoptlist{-mcpu=@var{cpu-type} @gol
417 -mtune=@var{cpu-type} @gol
418 -mpower -mno-power -mpower2 -mno-power2 @gol
419 -mpowerpc -mpowerpc64 -mno-powerpc @gol
420 -maltivec -mno-altivec @gol
421 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
422 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
423 -mnew-mnemonics -mold-mnemonics @gol
424 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
425 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
426 -malign-power -malign-natural @gol
427 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
428 -mstring -mno-string -mupdate -mno-update @gol
429 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
430 -mstrict-align -mno-strict-align -mrelocatable @gol
431 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
432 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
433 -mdynamic-no-pic @gol
434 -mprioritize-restricted-insns=@var{priority} @gol
435 -mcall-sysv -mcall-netbsd @gol
436 -maix-struct-return -msvr4-struct-return @gol
437 -mabi=altivec -mabi=no-altivec @gol
438 -mabi=spe -mabi=no-spe @gol
439 -misel=yes -misel=no @gol
440 -mspe=yes -mspe=no @gol
441 -mfloat-gprs=yes -mfloat-gprs=no @gol
442 -mprototype -mno-prototype @gol
443 -msim -mmvme -mads -myellowknife -memb -msdata @gol
444 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
446 @emph{Darwin Options}
447 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
448 -arch_only -bind_at_load -bundle -bundle_loader @gol
449 -client_name -compatibility_version -current_version @gol
450 -dependency-file -dylib_file -dylinker_install_name @gol
451 -dynamic -dynamiclib -exported_symbols_list @gol
452 -filelist -flat_namespace -force_cpusubtype_ALL @gol
453 -force_flat_namespace -headerpad_max_install_names @gol
454 -image_base -init -install_name -keep_private_externs @gol
455 -multi_module -multiply_defined -multiply_defined_unused @gol
456 -noall_load -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
457 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
458 -private_bundle -read_only_relocs -sectalign @gol
459 -sectobjectsymbols -whyload -seg1addr @gol
460 -sectcreate -sectobjectsymbols -sectorder @gol
461 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
462 -segprot -segs_read_only_addr -segs_read_write_addr @gol
463 -single_module -static -sub_library -sub_umbrella @gol
464 -twolevel_namespace -umbrella -undefined @gol
465 -unexported_symbols_list -weak_reference_mismatches @gol
469 @gccoptlist{-mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs @gol
470 -mfull-fp-blocks -mhc-struct-return -min-line-mul @gol
471 -mminimum-fp-blocks -mnohc-struct-return}
474 @gccoptlist{-mabicalls -march=@var{cpu-type} -mtune=@var{cpu=type} @gol
475 -mcpu=@var{cpu-type} -membedded-data -muninit-const-in-rodata @gol
476 -membedded-pic -mfp32 -mfp64 -mfused-madd -mno-fused-madd @gol
477 -mgas -mgp32 -mgp64 -mhard-float -mint64 -mips1 @gol
478 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
479 -mlong64 -mlong32 -mlong-calls -mmemcpy @gol
480 -mmips-as -mmips-tfile -mno-abicalls -mxgot @gol
481 -mno-embedded-data -mno-uninit-const-in-rodata @gol
482 -mno-embedded-pic -mno-long-calls @gol
483 -mno-memcpy -mno-mips-tfile -mno-rnames @gol
484 -mrnames -msoft-float @gol
485 -m4650 -msingle-float -mmad @gol
486 -EL -EB -G @var{num} -nocpp @gol
487 -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi -mabi-fake-default @gol
488 -mfix7000 -mfix-sb1 -mno-fix-sb1 @gol
489 -mno-crt0 -mflush-func=@var{func} -mno-flush-func @gol
490 -mbranch-likely -mno-branch-likely}
492 @emph{i386 and x86-64 Options}
493 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
494 -mfpmath=@var{unit} @gol
495 -masm=@var{dialect} -mno-fancy-math-387 @gol
496 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
497 -mno-wide-multiply -mrtd -malign-double @gol
498 -mpreferred-stack-boundary=@var{num} @gol
499 -mmmx -msse -msse2 -mpni -m3dnow @gol
500 -mthreads -mno-align-stringops -minline-all-stringops @gol
501 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
502 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
503 -mno-red-zone -mno-tls-direct-seg-refs @gol
504 -mcmodel=@var{code-model} @gol
508 @gccoptlist{-march=@var{architecture-type} @gol
509 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
510 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
511 -mjump-in-delay -mlinker-opt -mlong-calls @gol
512 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
513 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
514 -mno-jump-in-delay -mno-long-load-store @gol
515 -mno-portable-runtime -mno-soft-float @gol
516 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
517 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
518 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
519 -nolibdld -static -threads}
521 @emph{Intel 960 Options}
522 @gccoptlist{-m@var{cpu-type} -masm-compat -mclean-linkage @gol
523 -mcode-align -mcomplex-addr -mleaf-procedures @gol
524 -mic-compat -mic2.0-compat -mic3.0-compat @gol
525 -mintel-asm -mno-clean-linkage -mno-code-align @gol
526 -mno-complex-addr -mno-leaf-procedures @gol
527 -mno-old-align -mno-strict-align -mno-tail-call @gol
528 -mnumerics -mold-align -msoft-float -mstrict-align @gol
531 @emph{DEC Alpha Options}
532 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
533 -mieee -mieee-with-inexact -mieee-conformant @gol
534 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
535 -mtrap-precision=@var{mode} -mbuild-constants @gol
536 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
537 -mbwx -mmax -mfix -mcix @gol
538 -mfloat-vax -mfloat-ieee @gol
539 -mexplicit-relocs -msmall-data -mlarge-data @gol
540 -msmall-text -mlarge-text @gol
541 -mmemory-latency=@var{time}}
543 @emph{DEC Alpha/VMS Options}
544 @gccoptlist{-mvms-return-codes}
546 @emph{H8/300 Options}
547 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
550 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
551 -m4-nofpu -m4-single-only -m4-single -m4 @gol
552 -m5-64media -m5-64media-nofpu @gol
553 -m5-32media -m5-32media-nofpu @gol
554 -m5-compact -m5-compact-nofpu @gol
555 -mb -ml -mdalign -mrelax @gol
556 -mbigtable -mfmovd -mhitachi -mnomacsave @gol
557 -mieee -misize -mpadstruct -mspace @gol
558 -mprefergot -musermode}
560 @emph{System V Options}
561 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
564 @gccoptlist{-EB -EL @gol
565 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
566 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
568 @emph{TMS320C3x/C4x Options}
569 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
570 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
571 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
572 -mparallel-insns -mparallel-mpy -mpreserve-float}
575 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
576 -mprolog-function -mno-prolog-function -mspace @gol
577 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
578 -mapp-regs -mno-app-regs @gol
579 -mdisable-callt -mno-disable-callt @gol
585 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
586 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
587 -mregparam -mnoregparam -msb -mnosb @gol
588 -mbitfield -mnobitfield -mhimem -mnohimem}
591 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
592 -mcall-prologues -mno-tablejump -mtiny-stack}
595 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
596 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
597 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
598 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
599 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
602 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
603 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
604 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
605 -mno-base-addresses -msingle-exit -mno-single-exit}
608 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
609 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
610 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
611 -minline-float-divide-max-throughput @gol
612 -minline-int-divide-min-latency @gol
613 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
614 -mfixed-range=@var{register-range}}
617 @gccoptlist{-mextmem -mextmemory -monchip -mno-asm-optimize @gol
618 -masm-optimize -mbranch-cost=@var{n} -mcond-exec=@var{n}}
620 @emph{S/390 and zSeries Options}
621 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
622 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
623 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
624 -m64 -m31 -mdebug -mno-debug -mesa -mzarch}
627 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
628 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
629 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
630 -mstack-align -mdata-align -mconst-align @gol
631 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
632 -melf -maout -melinux -mlinux -sim -sim2}
634 @emph{PDP-11 Options}
635 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
636 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
637 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
638 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
639 -mbranch-expensive -mbranch-cheap @gol
640 -msplit -mno-split -munix-asm -mdec-asm}
642 @emph{Xstormy16 Options}
645 @emph{Xtensa Options}
646 @gccoptlist{-mconst16 -mno-const16 @gol
647 -mfused-madd -mno-fused-madd @gol
648 -mtext-section-literals -mno-text-section-literals @gol
649 -mtarget-align -mno-target-align @gol
650 -mlongcalls -mno-longcalls}
653 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
654 -mhard-float -msoft-float @gol
655 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
656 -mdouble -mno-double @gol
657 -mmedia -mno-media -mmuladd -mno-muladd @gol
658 -mlibrary-pic -macc-4 -macc-8 @gol
659 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
660 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
661 -mvliw-branch -mno-vliw-branch @gol
662 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
663 -mno-nested-cond-exec -mtomcat-stats @gol
666 @item Code Generation Options
667 @xref{Code Gen Options,,Options for Code Generation Conventions}.
668 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
669 -ffixed-@var{reg} -fexceptions @gol
670 -fnon-call-exceptions -funwind-tables @gol
671 -fasynchronous-unwind-tables @gol
672 -finhibit-size-directive -finstrument-functions @gol
673 -fno-common -fno-ident -fno-gnu-linker @gol
674 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
675 -freg-struct-return -fshared-data -fshort-enums @gol
676 -fshort-double -fshort-wchar @gol
677 -fverbose-asm -fpack-struct -fstack-check @gol
678 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
679 -fargument-alias -fargument-noalias @gol
680 -fargument-noalias-global -fleading-underscore @gol
681 -ftls-model=@var{model} @gol
682 -ftrapv -fwrapv -fbounds-check}
686 * Overall Options:: Controlling the kind of output:
687 an executable, object files, assembler files,
688 or preprocessed source.
689 * C Dialect Options:: Controlling the variant of C language compiled.
690 * C++ Dialect Options:: Variations on C++.
691 * Objective-C Dialect Options:: Variations on Objective-C.
692 * Language Independent Options:: Controlling how diagnostics should be
694 * Warning Options:: How picky should the compiler be?
695 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
696 * Optimize Options:: How much optimization?
697 * Preprocessor Options:: Controlling header files and macro definitions.
698 Also, getting dependency information for Make.
699 * Assembler Options:: Passing options to the assembler.
700 * Link Options:: Specifying libraries and so on.
701 * Directory Options:: Where to find header files and libraries.
702 Where to find the compiler executable files.
703 * Spec Files:: How to pass switches to sub-processes.
704 * Target Options:: Running a cross-compiler, or an old version of GCC.
707 @node Overall Options
708 @section Options Controlling the Kind of Output
710 Compilation can involve up to four stages: preprocessing, compilation
711 proper, assembly and linking, always in that order. GCC is capable of
712 preprocessing and compiling several files either into several
713 assembler input files, or into one assembler input file; then each
714 assembler input file produces an object file, and linking combines all
715 the object files (those newly compiled, and those specified as input)
716 into an executable file.
718 @cindex file name suffix
719 For any given input file, the file name suffix determines what kind of
724 C source code which must be preprocessed.
727 C source code which should not be preprocessed.
730 C++ source code which should not be preprocessed.
733 Objective-C source code. Note that you must link with the library
734 @file{libobjc.a} to make an Objective-C program work.
737 Objective-C source code which should not be preprocessed.
740 C or C++ header file to be turned into a precompiled header.
744 @itemx @var{file}.cxx
745 @itemx @var{file}.cpp
746 @itemx @var{file}.CPP
747 @itemx @var{file}.c++
749 C++ source code which must be preprocessed. Note that in @samp{.cxx},
750 the last two letters must both be literally @samp{x}. Likewise,
751 @samp{.C} refers to a literal capital C@.
755 C++ header file to be turned into a precompiled header.
758 @itemx @var{file}.for
759 @itemx @var{file}.FOR
760 Fortran source code which should not be preprocessed.
763 @itemx @var{file}.fpp
764 @itemx @var{file}.FPP
765 Fortran source code which must be preprocessed (with the traditional
769 Fortran source code which must be preprocessed with a RATFOR
770 preprocessor (not included with GCC)@.
772 @xref{Overall Options,,Options Controlling the Kind of Output, g77,
773 Using and Porting GNU Fortran}, for more details of the handling of
776 @c FIXME: Descriptions of Java file types.
783 Ada source code file which contains a library unit declaration (a
784 declaration of a package, subprogram, or generic, or a generic
785 instantiation), or a library unit renaming declaration (a package,
786 generic, or subprogram renaming declaration). Such files are also
789 @itemx @var{file}.adb
790 Ada source code file containing a library unit body (a subprogram or
791 package body). Such files are also called @dfn{bodies}.
793 @c GCC also knows about some suffixes for languages not yet included:
802 Assembler code which must be preprocessed.
805 An object file to be fed straight into linking.
806 Any file name with no recognized suffix is treated this way.
810 You can specify the input language explicitly with the @option{-x} option:
813 @item -x @var{language}
814 Specify explicitly the @var{language} for the following input files
815 (rather than letting the compiler choose a default based on the file
816 name suffix). This option applies to all following input files until
817 the next @option{-x} option. Possible values for @var{language} are:
819 c c-header cpp-output
820 c++ c++-header c++-cpp-output
821 objective-c objective-c-header objc-cpp-output
822 assembler assembler-with-cpp
824 f77 f77-cpp-input ratfor
830 Turn off any specification of a language, so that subsequent files are
831 handled according to their file name suffixes (as they are if @option{-x}
832 has not been used at all).
834 @item -pass-exit-codes
835 @opindex pass-exit-codes
836 Normally the @command{gcc} program will exit with the code of 1 if any
837 phase of the compiler returns a non-success return code. If you specify
838 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
839 numerically highest error produced by any phase that returned an error
843 If you only want some of the stages of compilation, you can use
844 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
845 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
846 @command{gcc} is to stop. Note that some combinations (for example,
847 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
852 Compile or assemble the source files, but do not link. The linking
853 stage simply is not done. The ultimate output is in the form of an
854 object file for each source file.
856 By default, the object file name for a source file is made by replacing
857 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
859 Unrecognized input files, not requiring compilation or assembly, are
864 Stop after the stage of compilation proper; do not assemble. The output
865 is in the form of an assembler code file for each non-assembler input
868 By default, the assembler file name for a source file is made by
869 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
871 Input files that don't require compilation are ignored.
875 Stop after the preprocessing stage; do not run the compiler proper. The
876 output is in the form of preprocessed source code, which is sent to the
879 Input files which don't require preprocessing are ignored.
881 @cindex output file option
884 Place output in file @var{file}. This applies regardless to whatever
885 sort of output is being produced, whether it be an executable file,
886 an object file, an assembler file or preprocessed C code.
888 If you specify @option{-o} when compiling more than one input file, or
889 you are producing an executable file as output, all the source files
890 on the command line will be compiled at once.
892 If @option{-o} is not specified, the default is to put an executable file
893 in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in
894 @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and
895 all preprocessed C source on standard output.
899 Print (on standard error output) the commands executed to run the stages
900 of compilation. Also print the version number of the compiler driver
901 program and of the preprocessor and the compiler proper.
905 Like @option{-v} except the commands are not executed and all command
906 arguments are quoted. This is useful for shell scripts to capture the
907 driver-generated command lines.
911 Use pipes rather than temporary files for communication between the
912 various stages of compilation. This fails to work on some systems where
913 the assembler is unable to read from a pipe; but the GNU assembler has
918 Print (on the standard output) a description of the command line options
919 understood by @command{gcc}. If the @option{-v} option is also specified
920 then @option{--help} will also be passed on to the various processes
921 invoked by @command{gcc}, so that they can display the command line options
922 they accept. If the @option{-Wextra} option is also specified then command
923 line options which have no documentation associated with them will also
928 Print (on the standard output) a description of target specific command
929 line options for each tool.
933 Display the version number and copyrights of the invoked GCC.
937 @section Compiling C++ Programs
939 @cindex suffixes for C++ source
940 @cindex C++ source file suffixes
941 C++ source files conventionally use one of the suffixes @samp{.C},
942 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
943 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
944 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
945 files with these names and compiles them as C++ programs even if you
946 call the compiler the same way as for compiling C programs (usually
947 with the name @command{gcc}).
951 However, C++ programs often require class libraries as well as a
952 compiler that understands the C++ language---and under some
953 circumstances, you might want to compile programs or header files from
954 standard input, or otherwise without a suffix that flags them as C++
955 programs. You might also like to precompile a C header file with a
956 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
957 program that calls GCC with the default language set to C++, and
958 automatically specifies linking against the C++ library. On many
959 systems, @command{g++} is also installed with the name @command{c++}.
961 @cindex invoking @command{g++}
962 When you compile C++ programs, you may specify many of the same
963 command-line options that you use for compiling programs in any
964 language; or command-line options meaningful for C and related
965 languages; or options that are meaningful only for C++ programs.
966 @xref{C Dialect Options,,Options Controlling C Dialect}, for
967 explanations of options for languages related to C@.
968 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
969 explanations of options that are meaningful only for C++ programs.
971 @node C Dialect Options
972 @section Options Controlling C Dialect
973 @cindex dialect options
974 @cindex language dialect options
975 @cindex options, dialect
977 The following options control the dialect of C (or languages derived
978 from C, such as C++ and Objective-C) that the compiler accepts:
985 In C mode, support all ISO C90 programs. In C++ mode,
986 remove GNU extensions that conflict with ISO C++.
988 This turns off certain features of GCC that are incompatible with ISO
989 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
990 such as the @code{asm} and @code{typeof} keywords, and
991 predefined macros such as @code{unix} and @code{vax} that identify the
992 type of system you are using. It also enables the undesirable and
993 rarely used ISO trigraph feature. For the C compiler,
994 it disables recognition of C++ style @samp{//} comments as well as
995 the @code{inline} keyword.
997 The alternate keywords @code{__asm__}, @code{__extension__},
998 @code{__inline__} and @code{__typeof__} continue to work despite
999 @option{-ansi}. You would not want to use them in an ISO C program, of
1000 course, but it is useful to put them in header files that might be included
1001 in compilations done with @option{-ansi}. Alternate predefined macros
1002 such as @code{__unix__} and @code{__vax__} are also available, with or
1003 without @option{-ansi}.
1005 The @option{-ansi} option does not cause non-ISO programs to be
1006 rejected gratuitously. For that, @option{-pedantic} is required in
1007 addition to @option{-ansi}. @xref{Warning Options}.
1009 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1010 option is used. Some header files may notice this macro and refrain
1011 from declaring certain functions or defining certain macros that the
1012 ISO standard doesn't call for; this is to avoid interfering with any
1013 programs that might use these names for other things.
1015 Functions which would normally be built in but do not have semantics
1016 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1017 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1018 built-in functions provided by GCC}, for details of the functions
1023 Determine the language standard. This option is currently only
1024 supported when compiling C or C++. A value for this option must be
1025 provided; possible values are
1030 ISO C90 (same as @option{-ansi}).
1032 @item iso9899:199409
1033 ISO C90 as modified in amendment 1.
1039 ISO C99. Note that this standard is not yet fully supported; see
1040 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1041 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1044 Default, ISO C90 plus GNU extensions (including some C99 features).
1048 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1049 this will become the default. The name @samp{gnu9x} is deprecated.
1052 The 1998 ISO C++ standard plus amendments.
1055 The same as @option{-std=c++98} plus GNU extensions. This is the
1056 default for C++ code.
1059 Even when this option is not specified, you can still use some of the
1060 features of newer standards in so far as they do not conflict with
1061 previous C standards. For example, you may use @code{__restrict__} even
1062 when @option{-std=c99} is not specified.
1064 The @option{-std} options specifying some version of ISO C have the same
1065 effects as @option{-ansi}, except that features that were not in ISO C90
1066 but are in the specified version (for example, @samp{//} comments and
1067 the @code{inline} keyword in ISO C99) are not disabled.
1069 @xref{Standards,,Language Standards Supported by GCC}, for details of
1070 these standard versions.
1072 @item -aux-info @var{filename}
1074 Output to the given filename prototyped declarations for all functions
1075 declared and/or defined in a translation unit, including those in header
1076 files. This option is silently ignored in any language other than C@.
1078 Besides declarations, the file indicates, in comments, the origin of
1079 each declaration (source file and line), whether the declaration was
1080 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1081 @samp{O} for old, respectively, in the first character after the line
1082 number and the colon), and whether it came from a declaration or a
1083 definition (@samp{C} or @samp{F}, respectively, in the following
1084 character). In the case of function definitions, a K&R-style list of
1085 arguments followed by their declarations is also provided, inside
1086 comments, after the declaration.
1090 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1091 keyword, so that code can use these words as identifiers. You can use
1092 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1093 instead. @option{-ansi} implies @option{-fno-asm}.
1095 In C++, this switch only affects the @code{typeof} keyword, since
1096 @code{asm} and @code{inline} are standard keywords. You may want to
1097 use the @option{-fno-gnu-keywords} flag instead, which has the same
1098 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1099 switch only affects the @code{asm} and @code{typeof} keywords, since
1100 @code{inline} is a standard keyword in ISO C99.
1103 @itemx -fno-builtin-@var{function}
1104 @opindex fno-builtin
1105 @cindex built-in functions
1106 Don't recognize built-in functions that do not begin with
1107 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1108 functions provided by GCC}, for details of the functions affected,
1109 including those which are not built-in functions when @option{-ansi} or
1110 @option{-std} options for strict ISO C conformance are used because they
1111 do not have an ISO standard meaning.
1113 GCC normally generates special code to handle certain built-in functions
1114 more efficiently; for instance, calls to @code{alloca} may become single
1115 instructions that adjust the stack directly, and calls to @code{memcpy}
1116 may become inline copy loops. The resulting code is often both smaller
1117 and faster, but since the function calls no longer appear as such, you
1118 cannot set a breakpoint on those calls, nor can you change the behavior
1119 of the functions by linking with a different library.
1121 With the @option{-fno-builtin-@var{function}} option
1122 only the built-in function @var{function} is
1123 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1124 function is named this is not built-in in this version of GCC, this
1125 option is ignored. There is no corresponding
1126 @option{-fbuiltin-@var{function}} option; if you wish to enable
1127 built-in functions selectively when using @option{-fno-builtin} or
1128 @option{-ffreestanding}, you may define macros such as:
1131 #define abs(n) __builtin_abs ((n))
1132 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1137 @cindex hosted environment
1139 Assert that compilation takes place in a hosted environment. This implies
1140 @option{-fbuiltin}. A hosted environment is one in which the
1141 entire standard library is available, and in which @code{main} has a return
1142 type of @code{int}. Examples are nearly everything except a kernel.
1143 This is equivalent to @option{-fno-freestanding}.
1145 @item -ffreestanding
1146 @opindex ffreestanding
1147 @cindex hosted environment
1149 Assert that compilation takes place in a freestanding environment. This
1150 implies @option{-fno-builtin}. A freestanding environment
1151 is one in which the standard library may not exist, and program startup may
1152 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1153 This is equivalent to @option{-fno-hosted}.
1155 @xref{Standards,,Language Standards Supported by GCC}, for details of
1156 freestanding and hosted environments.
1158 @item -fms-extensions
1159 @opindex fms-extensions
1160 Accept some non-standard constructs used in Microsoft header files.
1164 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1165 options for strict ISO C conformance) implies @option{-trigraphs}.
1167 @item -no-integrated-cpp
1168 @opindex no-integrated-cpp
1169 Performs a compilation in two passes: preprocessing and compiling. This
1170 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1171 @option{-B} option. The user supplied compilation step can then add in
1172 an additional preprocessing step after normal preprocessing but before
1173 compiling. The default is to use the integrated cpp (internal cpp)
1175 The semantics of this option will change if "cc1", "cc1plus", and
1176 "cc1obj" are merged.
1178 @cindex traditional C language
1179 @cindex C language, traditional
1181 @itemx -traditional-cpp
1182 @opindex traditional-cpp
1183 @opindex traditional
1184 Formerly, these options caused GCC to attempt to emulate a pre-standard
1185 C compiler. They are now only supported with the @option{-E} switch.
1186 The preprocessor continues to support a pre-standard mode. See the GNU
1187 CPP manual for details.
1189 @item -fcond-mismatch
1190 @opindex fcond-mismatch
1191 Allow conditional expressions with mismatched types in the second and
1192 third arguments. The value of such an expression is void. This option
1193 is not supported for C++.
1195 @item -funsigned-char
1196 @opindex funsigned-char
1197 Let the type @code{char} be unsigned, like @code{unsigned char}.
1199 Each kind of machine has a default for what @code{char} should
1200 be. It is either like @code{unsigned char} by default or like
1201 @code{signed char} by default.
1203 Ideally, a portable program should always use @code{signed char} or
1204 @code{unsigned char} when it depends on the signedness of an object.
1205 But many programs have been written to use plain @code{char} and
1206 expect it to be signed, or expect it to be unsigned, depending on the
1207 machines they were written for. This option, and its inverse, let you
1208 make such a program work with the opposite default.
1210 The type @code{char} is always a distinct type from each of
1211 @code{signed char} or @code{unsigned char}, even though its behavior
1212 is always just like one of those two.
1215 @opindex fsigned-char
1216 Let the type @code{char} be signed, like @code{signed char}.
1218 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1219 the negative form of @option{-funsigned-char}. Likewise, the option
1220 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1222 @item -fsigned-bitfields
1223 @itemx -funsigned-bitfields
1224 @itemx -fno-signed-bitfields
1225 @itemx -fno-unsigned-bitfields
1226 @opindex fsigned-bitfields
1227 @opindex funsigned-bitfields
1228 @opindex fno-signed-bitfields
1229 @opindex fno-unsigned-bitfields
1230 These options control whether a bit-field is signed or unsigned, when the
1231 declaration does not use either @code{signed} or @code{unsigned}. By
1232 default, such a bit-field is signed, because this is consistent: the
1233 basic integer types such as @code{int} are signed types.
1235 @item -fwritable-strings
1236 @opindex fwritable-strings
1237 Store string constants in the writable data segment and don't uniquize
1238 them. This is for compatibility with old programs which assume they can
1239 write into string constants.
1241 Writing into string constants is a very bad idea; ``constants'' should
1245 @node C++ Dialect Options
1246 @section Options Controlling C++ Dialect
1248 @cindex compiler options, C++
1249 @cindex C++ options, command line
1250 @cindex options, C++
1251 This section describes the command-line options that are only meaningful
1252 for C++ programs; but you can also use most of the GNU compiler options
1253 regardless of what language your program is in. For example, you
1254 might compile a file @code{firstClass.C} like this:
1257 g++ -g -frepo -O -c firstClass.C
1261 In this example, only @option{-frepo} is an option meant
1262 only for C++ programs; you can use the other options with any
1263 language supported by GCC@.
1265 Here is a list of options that are @emph{only} for compiling C++ programs:
1269 @item -fabi-version=@var{n}
1270 @opindex fabi-version
1271 Use version @var{n} of the C++ ABI. Version 1 is the version of the C++
1272 ABI that first appeared in G++ 3.2. Version 0 will always be the
1273 version that conforms most closely to the C++ ABI specification.
1274 Therefore, the ABI obtained using version 0 will change as ABI bugs are
1277 The default is version 1.
1279 @item -fno-access-control
1280 @opindex fno-access-control
1281 Turn off all access checking. This switch is mainly useful for working
1282 around bugs in the access control code.
1286 Check that the pointer returned by @code{operator new} is non-null
1287 before attempting to modify the storage allocated. This check is
1288 normally unnecessary because the C++ standard specifies that
1289 @code{operator new} will only return @code{0} if it is declared
1290 @samp{throw()}, in which case the compiler will always check the
1291 return value even without this option. In all other cases, when
1292 @code{operator new} has a non-empty exception specification, memory
1293 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1294 @samp{new (nothrow)}.
1296 @item -fconserve-space
1297 @opindex fconserve-space
1298 Put uninitialized or runtime-initialized global variables into the
1299 common segment, as C does. This saves space in the executable at the
1300 cost of not diagnosing duplicate definitions. If you compile with this
1301 flag and your program mysteriously crashes after @code{main()} has
1302 completed, you may have an object that is being destroyed twice because
1303 two definitions were merged.
1305 This option is no longer useful on most targets, now that support has
1306 been added for putting variables into BSS without making them common.
1308 @item -fno-const-strings
1309 @opindex fno-const-strings
1310 Give string constants type @code{char *} instead of type @code{const
1311 char *}. By default, G++ uses type @code{const char *} as required by
1312 the standard. Even if you use @option{-fno-const-strings}, you cannot
1313 actually modify the value of a string constant, unless you also use
1314 @option{-fwritable-strings}.
1316 This option might be removed in a future release of G++. For maximum
1317 portability, you should structure your code so that it works with
1318 string constants that have type @code{const char *}.
1320 @item -fno-elide-constructors
1321 @opindex fno-elide-constructors
1322 The C++ standard allows an implementation to omit creating a temporary
1323 which is only used to initialize another object of the same type.
1324 Specifying this option disables that optimization, and forces G++ to
1325 call the copy constructor in all cases.
1327 @item -fno-enforce-eh-specs
1328 @opindex fno-enforce-eh-specs
1329 Don't check for violation of exception specifications at runtime. This
1330 option violates the C++ standard, but may be useful for reducing code
1331 size in production builds, much like defining @samp{NDEBUG}. The compiler
1332 will still optimize based on the exception specifications.
1334 @item -fexternal-templates
1335 @opindex fexternal-templates
1337 Cause @samp{#pragma interface} and @samp{implementation} to apply to
1338 template instantiation; template instances are emitted or not according
1339 to the location of the template definition. @xref{Template
1340 Instantiation}, for more information.
1342 This option is deprecated.
1344 @item -falt-external-templates
1345 @opindex falt-external-templates
1346 Similar to @option{-fexternal-templates}, but template instances are
1347 emitted or not according to the place where they are first instantiated.
1348 @xref{Template Instantiation}, for more information.
1350 This option is deprecated.
1353 @itemx -fno-for-scope
1355 @opindex fno-for-scope
1356 If @option{-ffor-scope} is specified, the scope of variables declared in
1357 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1358 as specified by the C++ standard.
1359 If @option{-fno-for-scope} is specified, the scope of variables declared in
1360 a @i{for-init-statement} extends to the end of the enclosing scope,
1361 as was the case in old versions of G++, and other (traditional)
1362 implementations of C++.
1364 The default if neither flag is given to follow the standard,
1365 but to allow and give a warning for old-style code that would
1366 otherwise be invalid, or have different behavior.
1368 @item -fno-gnu-keywords
1369 @opindex fno-gnu-keywords
1370 Do not recognize @code{typeof} as a keyword, so that code can use this
1371 word as an identifier. You can use the keyword @code{__typeof__} instead.
1372 @option{-ansi} implies @option{-fno-gnu-keywords}.
1374 @item -fno-implicit-templates
1375 @opindex fno-implicit-templates
1376 Never emit code for non-inline templates which are instantiated
1377 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1378 @xref{Template Instantiation}, for more information.
1380 @item -fno-implicit-inline-templates
1381 @opindex fno-implicit-inline-templates
1382 Don't emit code for implicit instantiations of inline templates, either.
1383 The default is to handle inlines differently so that compiles with and
1384 without optimization will need the same set of explicit instantiations.
1386 @item -fno-implement-inlines
1387 @opindex fno-implement-inlines
1388 To save space, do not emit out-of-line copies of inline functions
1389 controlled by @samp{#pragma implementation}. This will cause linker
1390 errors if these functions are not inlined everywhere they are called.
1392 @item -fms-extensions
1393 @opindex fms-extensions
1394 Disable pedantic warnings about constructs used in MFC, such as implicit
1395 int and getting a pointer to member function via non-standard syntax.
1397 @item -fno-nonansi-builtins
1398 @opindex fno-nonansi-builtins
1399 Disable built-in declarations of functions that are not mandated by
1400 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1401 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1403 @item -fno-operator-names
1404 @opindex fno-operator-names
1405 Do not treat the operator name keywords @code{and}, @code{bitand},
1406 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1407 synonyms as keywords.
1409 @item -fno-optional-diags
1410 @opindex fno-optional-diags
1411 Disable diagnostics that the standard says a compiler does not need to
1412 issue. Currently, the only such diagnostic issued by G++ is the one for
1413 a name having multiple meanings within a class.
1416 @opindex fpermissive
1417 Downgrade some diagnostics about nonconformant code from errors to
1418 warnings. Thus, using @option{-fpermissive} will allow some
1419 nonconforming code to compile.
1423 Enable automatic template instantiation at link time. This option also
1424 implies @option{-fno-implicit-templates}. @xref{Template
1425 Instantiation}, for more information.
1429 Disable generation of information about every class with virtual
1430 functions for use by the C++ runtime type identification features
1431 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1432 of the language, you can save some space by using this flag. Note that
1433 exception handling uses the same information, but it will generate it as
1438 Emit statistics about front-end processing at the end of the compilation.
1439 This information is generally only useful to the G++ development team.
1441 @item -ftemplate-depth-@var{n}
1442 @opindex ftemplate-depth
1443 Set the maximum instantiation depth for template classes to @var{n}.
1444 A limit on the template instantiation depth is needed to detect
1445 endless recursions during template class instantiation. ANSI/ISO C++
1446 conforming programs must not rely on a maximum depth greater than 17.
1448 @item -fuse-cxa-atexit
1449 @opindex fuse-cxa-atexit
1450 Register destructors for objects with static storage duration with the
1451 @code{__cxa_atexit} function rather than the @code{atexit} function.
1452 This option is required for fully standards-compliant handling of static
1453 destructors, but will only work if your C library supports
1454 @code{__cxa_atexit}.
1458 Do not use weak symbol support, even if it is provided by the linker.
1459 By default, G++ will use weak symbols if they are available. This
1460 option exists only for testing, and should not be used by end-users;
1461 it will result in inferior code and has no benefits. This option may
1462 be removed in a future release of G++.
1466 Do not search for header files in the standard directories specific to
1467 C++, but do still search the other standard directories. (This option
1468 is used when building the C++ library.)
1471 In addition, these optimization, warning, and code generation options
1472 have meanings only for C++ programs:
1475 @item -fno-default-inline
1476 @opindex fno-default-inline
1477 Do not assume @samp{inline} for functions defined inside a class scope.
1478 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1479 functions will have linkage like inline functions; they just won't be
1482 @item -Wabi @r{(C++ only)}
1484 Warn when G++ generates code that is probably not compatible with the
1485 vendor-neutral C++ ABI. Although an effort has been made to warn about
1486 all such cases, there are probably some cases that are not warned about,
1487 even though G++ is generating incompatible code. There may also be
1488 cases where warnings are emitted even though the code that is generated
1491 You should rewrite your code to avoid these warnings if you are
1492 concerned about the fact that code generated by G++ may not be binary
1493 compatible with code generated by other compilers.
1495 The known incompatibilities at this point include:
1500 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1501 pack data into the same byte as a base class. For example:
1504 struct A @{ virtual void f(); int f1 : 1; @};
1505 struct B : public A @{ int f2 : 1; @};
1509 In this case, G++ will place @code{B::f2} into the same byte
1510 as@code{A::f1}; other compilers will not. You can avoid this problem
1511 by explicitly padding @code{A} so that its size is a multiple of the
1512 byte size on your platform; that will cause G++ and other compilers to
1513 layout @code{B} identically.
1516 Incorrect handling of tail-padding for virtual bases. G++ does not use
1517 tail padding when laying out virtual bases. For example:
1520 struct A @{ virtual void f(); char c1; @};
1521 struct B @{ B(); char c2; @};
1522 struct C : public A, public virtual B @{@};
1526 In this case, G++ will not place @code{B} into the tail-padding for
1527 @code{A}; other compilers will. You can avoid this problem by
1528 explicitly padding @code{A} so that its size is a multiple of its
1529 alignment (ignoring virtual base classes); that will cause G++ and other
1530 compilers to layout @code{C} identically.
1533 Incorrect handling of bit-fields with declared widths greater than that
1534 of their underlying types, when the bit-fields appear in a union. For
1538 union U @{ int i : 4096; @};
1542 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1543 union too small by the number of bits in an @code{int}.
1546 Empty classes can be placed at incorrect offsets. For example:
1556 struct C : public B, public A @{@};
1560 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1561 it should be placed at offset zero. G++ mistakenly believes that the
1562 @code{A} data member of @code{B} is already at offset zero.
1565 Names of template functions whose types involve @code{typename} or
1566 template template parameters can be mangled incorrectly.
1569 template <typename Q>
1570 void f(typename Q::X) @{@}
1572 template <template <typename> class Q>
1573 void f(typename Q<int>::X) @{@}
1577 Instantiations of these templates may be mangled incorrectly.
1581 @item -Wctor-dtor-privacy @r{(C++ only)}
1582 @opindex Wctor-dtor-privacy
1583 Warn when a class seems unusable because all the constructors or
1584 destructors in that class are private, and it has neither friends nor
1585 public static member functions.
1587 @item -Wnon-virtual-dtor @r{(C++ only)}
1588 @opindex Wnon-virtual-dtor
1589 Warn when a class appears to be polymorphic, thereby requiring a virtual
1590 destructor, yet it declares a non-virtual one.
1591 This warning is enabled by @option{-Wall}.
1593 @item -Wreorder @r{(C++ only)}
1595 @cindex reordering, warning
1596 @cindex warning for reordering of member initializers
1597 Warn when the order of member initializers given in the code does not
1598 match the order in which they must be executed. For instance:
1604 A(): j (0), i (1) @{ @}
1608 The compiler will rearrange the member initializers for @samp{i}
1609 and @samp{j} to match the declaration order of the members, emitting
1610 a warning to that effect. This warning is enabled by @option{-Wall}.
1613 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1616 @item -Weffc++ @r{(C++ only)}
1618 Warn about violations of the following style guidelines from Scott Meyers'
1619 @cite{Effective C++} book:
1623 Item 11: Define a copy constructor and an assignment operator for classes
1624 with dynamically allocated memory.
1627 Item 12: Prefer initialization to assignment in constructors.
1630 Item 14: Make destructors virtual in base classes.
1633 Item 15: Have @code{operator=} return a reference to @code{*this}.
1636 Item 23: Don't try to return a reference when you must return an object.
1640 Also warn about violations of the following style guidelines from
1641 Scott Meyers' @cite{More Effective C++} book:
1645 Item 6: Distinguish between prefix and postfix forms of increment and
1646 decrement operators.
1649 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1653 When selecting this option, be aware that the standard library
1654 headers do not obey all of these guidelines; use @samp{grep -v}
1655 to filter out those warnings.
1657 @item -Wno-deprecated @r{(C++ only)}
1658 @opindex Wno-deprecated
1659 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1661 @item -Wno-non-template-friend @r{(C++ only)}
1662 @opindex Wno-non-template-friend
1663 Disable warnings when non-templatized friend functions are declared
1664 within a template. Since the advent of explicit template specification
1665 support in G++, if the name of the friend is an unqualified-id (i.e.,
1666 @samp{friend foo(int)}), the C++ language specification demands that the
1667 friend declare or define an ordinary, nontemplate function. (Section
1668 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1669 could be interpreted as a particular specialization of a templatized
1670 function. Because this non-conforming behavior is no longer the default
1671 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1672 check existing code for potential trouble spots and is on by default.
1673 This new compiler behavior can be turned off with
1674 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1675 but disables the helpful warning.
1677 @item -Wold-style-cast @r{(C++ only)}
1678 @opindex Wold-style-cast
1679 Warn if an old-style (C-style) cast to a non-void type is used within
1680 a C++ program. The new-style casts (@samp{static_cast},
1681 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1682 unintended effects and much easier to search for.
1684 @item -Woverloaded-virtual @r{(C++ only)}
1685 @opindex Woverloaded-virtual
1686 @cindex overloaded virtual fn, warning
1687 @cindex warning for overloaded virtual fn
1688 Warn when a function declaration hides virtual functions from a
1689 base class. For example, in:
1696 struct B: public A @{
1701 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1709 will fail to compile.
1711 @item -Wno-pmf-conversions @r{(C++ only)}
1712 @opindex Wno-pmf-conversions
1713 Disable the diagnostic for converting a bound pointer to member function
1716 @item -Wsign-promo @r{(C++ only)}
1717 @opindex Wsign-promo
1718 Warn when overload resolution chooses a promotion from unsigned or
1719 enumeral type to a signed type, over a conversion to an unsigned type of
1720 the same size. Previous versions of G++ would try to preserve
1721 unsignedness, but the standard mandates the current behavior.
1723 @item -Wsynth @r{(C++ only)}
1725 @cindex warning for synthesized methods
1726 @cindex synthesized methods, warning
1727 Warn when G++'s synthesis behavior does not match that of cfront. For
1733 A& operator = (int);
1743 In this example, G++ will synthesize a default @samp{A& operator =
1744 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1747 @node Objective-C Dialect Options
1748 @section Options Controlling Objective-C Dialect
1750 @cindex compiler options, Objective-C
1751 @cindex Objective-C options, command line
1752 @cindex options, Objective-C
1753 (NOTE: This manual does not describe the Objective-C language itself. See
1754 @w{@uref{http://gcc.gnu.org/readings.html}} for references.)
1756 This section describes the command-line options that are only meaningful
1757 for Objective-C programs, but you can also use most of the GNU compiler
1758 options regardless of what language your program is in. For example,
1759 you might compile a file @code{some_class.m} like this:
1762 gcc -g -fgnu-runtime -O -c some_class.m
1766 In this example, @option{-fgnu-runtime} is an option meant only for
1767 Objective-C programs; you can use the other options with any language
1770 Here is a list of options that are @emph{only} for compiling Objective-C
1774 @item -fconstant-string-class=@var{class-name}
1775 @opindex fconstant-string-class
1776 Use @var{class-name} as the name of the class to instantiate for each
1777 literal string specified with the syntax @code{@@"@dots{}"}. The default
1778 class name is @code{NXConstantString} if the GNU runtime is being used, and
1779 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1780 @option{-fconstant-cfstrings} option, if also present, will override the
1781 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1782 to be laid out as constant CoreFoundation strings.
1785 @opindex fgnu-runtime
1786 Generate object code compatible with the standard GNU Objective-C
1787 runtime. This is the default for most types of systems.
1789 @item -fnext-runtime
1790 @opindex fnext-runtime
1791 Generate output compatible with the NeXT runtime. This is the default
1792 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1793 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1796 @item -fno-nil-receivers
1797 @opindex -fno-nil-receivers
1798 Assume that all Objective-C message dispatches (e.g.,
1799 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1800 is not @code{nil}. This allows for more efficient entry points in the runtime to be
1801 used. Currently, this option is only available in conjunction with
1802 the NeXT runtime on Mac OS X 10.3 and later.
1804 @item -fobjc-exceptions
1805 @opindex -fobjc-exceptions
1806 Enable syntactic support for structured exception handling in Objective-C,
1807 similar to what is offered by C++ and Java. Currently, this option is only
1808 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1816 @@catch (AnObjCClass *exc) @{
1823 @@catch (AnotherClass *exc) @{
1826 @@catch (id allOthers) @{
1836 The @code{@@throw} statement may appear anywhere in an Objective-C or
1837 Objective-C++ program; when used inside of a @code{@@catch} block, the
1838 @code{@@throw} may appear without an argument (as shown above), in which case
1839 the object caught by the @code{@@catch} will be rethrown.
1841 Note that only (pointers to) Objective-C objects may be thrown and
1842 caught using this scheme. When an object is thrown, it will be caught
1843 by the nearest @code{@@catch} clause capable of handling objects of that type,
1844 analogously to how @code{catch} blocks work in C++ and Java. A
1845 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
1846 any and all Objective-C exceptions not caught by previous @code{@@catch}
1849 The @code{@@finally} clause, if present, will be executed upon exit from the
1850 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
1851 regardless of whether any exceptions are thrown, caught or rethrown
1852 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
1853 of the @code{finally} clause in Java.
1855 There are several caveats to using the new exception mechanism:
1859 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
1860 idioms provided by the @code{NSException} class, the new
1861 exceptions can only be used on Mac OS X 10.3 (Panther) and later
1862 systems, due to additional functionality needed in the (NeXT) Objective-C
1866 As mentioned above, the new exceptions do not support handling
1867 types other than Objective-C objects. Furthermore, when used from
1868 Objective-C++, the Objective-C exception model does not interoperate with C++
1869 exceptions at this time. This means you cannot @code{@@throw} an exception
1870 from Objective-C and @code{catch} it in C++, or vice versa
1871 (i.e., @code{throw @dots{} @@catch}).
1874 The @option{-fobjc-exceptions} switch also enables the use of synchronization
1875 blocks for thread-safe execution:
1878 @@synchronized (ObjCClass *guard) @{
1883 Upon entering the @code{@@synchronized} block, a thread of execution shall
1884 first check whether a lock has been placed on the corresponding @code{guard}
1885 object by another thread. If it has, the current thread shall wait until
1886 the other thread relinquishes its lock. Once @code{guard} becomes available,
1887 the current thread will place its own lock on it, execute the code contained in
1888 the @code{@@synchronized} block, and finally relinquish the lock (thereby
1889 making @code{guard} available to other threads).
1891 Unlike Java, Objective-C does not allow for entire methods to be marked
1892 @code{@@synchronized}. Note that throwing exceptions out of
1893 @code{@@synchronized} blocks is allowed, and will cause the guarding object
1894 to be unlocked properly.
1896 @item -freplace-objc-classes
1897 @opindex -freplace-objc-classes
1898 Emit a special marker instructing @command{ld(1)} not to statically link in
1899 the resulting object file, and allow @command{dyld(1)} to load it in at
1900 run time instead. This is used in conjunction with the Fix-and-Continue
1901 debugging mode, where the object file in question may be recompiled and
1902 dynamically reloaded in the course of program execution, without the need
1903 to restart the program itself. Currently, Fix-and-Continue functionality
1904 is only available in conjunciton withthe NeXT runtime on Mac OS X 10.3
1908 @opindex -fzero-link
1909 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
1910 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
1911 compile time) with static class references that get initialized at load time,
1912 which improves run-time performance. Specifying the @option{-fzero-link} flag
1913 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
1914 to be retained. This is useful in Zero-Link debugging mode, since it allows
1915 for individual class implementations to be modified during program execution.
1919 Dump interface declarations for all classes seen in the source file to a
1920 file named @file{@var{sourcename}.decl}.
1923 @opindex Wno-protocol
1924 If a class is declared to implement a protocol, a warning is issued for
1925 every method in the protocol that is not implemented by the class. The
1926 default behavior is to issue a warning for every method not explicitly
1927 implemented in the class, even if a method implementation is inherited
1928 from the superclass. If you use the @code{-Wno-protocol} option, then
1929 methods inherited from the superclass are considered to be implemented,
1930 and no warning is issued for them.
1934 Warn if multiple methods of different types for the same selector are
1935 found during compilation. The check is performed on the list of methods
1936 in the final stage of compilation. Additionally, a check is performed
1937 for each selector appearing in a @code{@@selector(@dots{})}
1938 expression, and a corresponding method for that selector has been found
1939 during compilation. Because these checks scan the method table only at
1940 the end of compilation, these warnings are not produced if the final
1941 stage of compilation is not reached, for example because an error is
1942 found during compilation, or because the @code{-fsyntax-only} option is
1945 @item -Wundeclared-selector
1946 @opindex Wundeclared-selector
1947 Warn if a @code{@@selector(@dots{})} expression referring to an
1948 undeclared selector is found. A selector is considered undeclared if no
1949 method with that name has been declared before the
1950 @code{@@selector(@dots{})} expression, either explicitly in an
1951 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
1952 an @code{@@implementation} section. This option always performs its
1953 checks as soon as a @code{@@selector(@dots{})} expression is found,
1954 while @code{-Wselector} only performs its checks in the final stage of
1955 compilation. This also enforces the coding style convention
1956 that methods and selectors must be declared before being used.
1958 @c not documented because only avail via -Wp
1959 @c @item -print-objc-runtime-info
1963 @node Language Independent Options
1964 @section Options to Control Diagnostic Messages Formatting
1965 @cindex options to control diagnostics formatting
1966 @cindex diagnostic messages
1967 @cindex message formatting
1969 Traditionally, diagnostic messages have been formatted irrespective of
1970 the output device's aspect (e.g.@: its width, @dots{}). The options described
1971 below can be used to control the diagnostic messages formatting
1972 algorithm, e.g.@: how many characters per line, how often source location
1973 information should be reported. Right now, only the C++ front end can
1974 honor these options. However it is expected, in the near future, that
1975 the remaining front ends would be able to digest them correctly.
1978 @item -fmessage-length=@var{n}
1979 @opindex fmessage-length
1980 Try to format error messages so that they fit on lines of about @var{n}
1981 characters. The default is 72 characters for @command{g++} and 0 for the rest of
1982 the front ends supported by GCC@. If @var{n} is zero, then no
1983 line-wrapping will be done; each error message will appear on a single
1986 @opindex fdiagnostics-show-location
1987 @item -fdiagnostics-show-location=once
1988 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
1989 reporter to emit @emph{once} source location information; that is, in
1990 case the message is too long to fit on a single physical line and has to
1991 be wrapped, the source location won't be emitted (as prefix) again,
1992 over and over, in subsequent continuation lines. This is the default
1995 @item -fdiagnostics-show-location=every-line
1996 Only meaningful in line-wrapping mode. Instructs the diagnostic
1997 messages reporter to emit the same source location information (as
1998 prefix) for physical lines that result from the process of breaking
1999 a message which is too long to fit on a single line.
2003 @node Warning Options
2004 @section Options to Request or Suppress Warnings
2005 @cindex options to control warnings
2006 @cindex warning messages
2007 @cindex messages, warning
2008 @cindex suppressing warnings
2010 Warnings are diagnostic messages that report constructions which
2011 are not inherently erroneous but which are risky or suggest there
2012 may have been an error.
2014 You can request many specific warnings with options beginning @samp{-W},
2015 for example @option{-Wimplicit} to request warnings on implicit
2016 declarations. Each of these specific warning options also has a
2017 negative form beginning @samp{-Wno-} to turn off warnings;
2018 for example, @option{-Wno-implicit}. This manual lists only one of the
2019 two forms, whichever is not the default.
2021 The following options control the amount and kinds of warnings produced
2022 by GCC; for further, language-specific options also refer to
2023 @ref{C++ Dialect Options} and @ref{Objective-C Dialect Options}.
2026 @cindex syntax checking
2028 @opindex fsyntax-only
2029 Check the code for syntax errors, but don't do anything beyond that.
2033 Issue all the warnings demanded by strict ISO C and ISO C++;
2034 reject all programs that use forbidden extensions, and some other
2035 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2036 version of the ISO C standard specified by any @option{-std} option used.
2038 Valid ISO C and ISO C++ programs should compile properly with or without
2039 this option (though a rare few will require @option{-ansi} or a
2040 @option{-std} option specifying the required version of ISO C)@. However,
2041 without this option, certain GNU extensions and traditional C and C++
2042 features are supported as well. With this option, they are rejected.
2044 @option{-pedantic} does not cause warning messages for use of the
2045 alternate keywords whose names begin and end with @samp{__}. Pedantic
2046 warnings are also disabled in the expression that follows
2047 @code{__extension__}. However, only system header files should use
2048 these escape routes; application programs should avoid them.
2049 @xref{Alternate Keywords}.
2051 Some users try to use @option{-pedantic} to check programs for strict ISO
2052 C conformance. They soon find that it does not do quite what they want:
2053 it finds some non-ISO practices, but not all---only those for which
2054 ISO C @emph{requires} a diagnostic, and some others for which
2055 diagnostics have been added.
2057 A feature to report any failure to conform to ISO C might be useful in
2058 some instances, but would require considerable additional work and would
2059 be quite different from @option{-pedantic}. We don't have plans to
2060 support such a feature in the near future.
2062 Where the standard specified with @option{-std} represents a GNU
2063 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2064 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2065 extended dialect is based. Warnings from @option{-pedantic} are given
2066 where they are required by the base standard. (It would not make sense
2067 for such warnings to be given only for features not in the specified GNU
2068 C dialect, since by definition the GNU dialects of C include all
2069 features the compiler supports with the given option, and there would be
2070 nothing to warn about.)
2072 @item -pedantic-errors
2073 @opindex pedantic-errors
2074 Like @option{-pedantic}, except that errors are produced rather than
2079 Inhibit all warning messages.
2083 Inhibit warning messages about the use of @samp{#import}.
2085 @item -Wchar-subscripts
2086 @opindex Wchar-subscripts
2087 Warn if an array subscript has type @code{char}. This is a common cause
2088 of error, as programmers often forget that this type is signed on some
2093 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2094 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2098 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2099 the arguments supplied have types appropriate to the format string
2100 specified, and that the conversions specified in the format string make
2101 sense. This includes standard functions, and others specified by format
2102 attributes (@pxref{Function Attributes}), in the @code{printf},
2103 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2104 not in the C standard) families.
2106 The formats are checked against the format features supported by GNU
2107 libc version 2.2. These include all ISO C90 and C99 features, as well
2108 as features from the Single Unix Specification and some BSD and GNU
2109 extensions. Other library implementations may not support all these
2110 features; GCC does not support warning about features that go beyond a
2111 particular library's limitations. However, if @option{-pedantic} is used
2112 with @option{-Wformat}, warnings will be given about format features not
2113 in the selected standard version (but not for @code{strfmon} formats,
2114 since those are not in any version of the C standard). @xref{C Dialect
2115 Options,,Options Controlling C Dialect}.
2117 Since @option{-Wformat} also checks for null format arguments for
2118 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2120 @option{-Wformat} is included in @option{-Wall}. For more control over some
2121 aspects of format checking, the options @option{-Wno-format-y2k},
2122 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2123 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2124 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2126 @item -Wno-format-y2k
2127 @opindex Wno-format-y2k
2128 If @option{-Wformat} is specified, do not warn about @code{strftime}
2129 formats which may yield only a two-digit year.
2131 @item -Wno-format-extra-args
2132 @opindex Wno-format-extra-args
2133 If @option{-Wformat} is specified, do not warn about excess arguments to a
2134 @code{printf} or @code{scanf} format function. The C standard specifies
2135 that such arguments are ignored.
2137 Where the unused arguments lie between used arguments that are
2138 specified with @samp{$} operand number specifications, normally
2139 warnings are still given, since the implementation could not know what
2140 type to pass to @code{va_arg} to skip the unused arguments. However,
2141 in the case of @code{scanf} formats, this option will suppress the
2142 warning if the unused arguments are all pointers, since the Single
2143 Unix Specification says that such unused arguments are allowed.
2145 @item -Wno-format-zero-length
2146 @opindex Wno-format-zero-length
2147 If @option{-Wformat} is specified, do not warn about zero-length formats.
2148 The C standard specifies that zero-length formats are allowed.
2150 @item -Wformat-nonliteral
2151 @opindex Wformat-nonliteral
2152 If @option{-Wformat} is specified, also warn if the format string is not a
2153 string literal and so cannot be checked, unless the format function
2154 takes its format arguments as a @code{va_list}.
2156 @item -Wformat-security
2157 @opindex Wformat-security
2158 If @option{-Wformat} is specified, also warn about uses of format
2159 functions that represent possible security problems. At present, this
2160 warns about calls to @code{printf} and @code{scanf} functions where the
2161 format string is not a string literal and there are no format arguments,
2162 as in @code{printf (foo);}. This may be a security hole if the format
2163 string came from untrusted input and contains @samp{%n}. (This is
2164 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2165 in future warnings may be added to @option{-Wformat-security} that are not
2166 included in @option{-Wformat-nonliteral}.)
2170 Enable @option{-Wformat} plus format checks not included in
2171 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2172 -Wformat-nonliteral -Wformat-security}.
2176 Enable warning about passing a null pointer for arguments marked as
2177 requiring a non-null value by the @code{nonnull} function attribute.
2179 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2180 can be disabled with the @option{-Wno-nonnull} option.
2182 @item -Winit-self @r{(C, C++, and Objective-C only)}
2184 Enable warning about uninitialized variables which are initalized with themselves.
2185 Note this option can only be used with the @option{-Wuninitialized} option and
2186 that only works with @option{-O}.
2188 For an example, the following code will not warn about i being uninitialized
2189 without this option:
2200 @item -Wimplicit-int
2201 @opindex Wimplicit-int
2202 Warn when a declaration does not specify a type.
2204 @item -Wimplicit-function-declaration
2205 @itemx -Werror-implicit-function-declaration
2206 @opindex Wimplicit-function-declaration
2207 @opindex Werror-implicit-function-declaration
2208 Give a warning (or error) whenever a function is used before being
2213 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2217 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2218 function with external linkage, returning int, taking either zero
2219 arguments, two, or three arguments of appropriate types.
2221 @item -Wmissing-braces
2222 @opindex Wmissing-braces
2223 Warn if an aggregate or union initializer is not fully bracketed. In
2224 the following example, the initializer for @samp{a} is not fully
2225 bracketed, but that for @samp{b} is fully bracketed.
2228 int a[2][2] = @{ 0, 1, 2, 3 @};
2229 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2233 @opindex Wparentheses
2234 Warn if parentheses are omitted in certain contexts, such
2235 as when there is an assignment in a context where a truth value
2236 is expected, or when operators are nested whose precedence people
2237 often get confused about.
2239 Also warn about constructions where there may be confusion to which
2240 @code{if} statement an @code{else} branch belongs. Here is an example of
2255 In C, every @code{else} branch belongs to the innermost possible @code{if}
2256 statement, which in this example is @code{if (b)}. This is often not
2257 what the programmer expected, as illustrated in the above example by
2258 indentation the programmer chose. When there is the potential for this
2259 confusion, GCC will issue a warning when this flag is specified.
2260 To eliminate the warning, add explicit braces around the innermost
2261 @code{if} statement so there is no way the @code{else} could belong to
2262 the enclosing @code{if}. The resulting code would look like this:
2278 @item -Wsequence-point
2279 @opindex Wsequence-point
2280 Warn about code that may have undefined semantics because of violations
2281 of sequence point rules in the C standard.
2283 The C standard defines the order in which expressions in a C program are
2284 evaluated in terms of @dfn{sequence points}, which represent a partial
2285 ordering between the execution of parts of the program: those executed
2286 before the sequence point, and those executed after it. These occur
2287 after the evaluation of a full expression (one which is not part of a
2288 larger expression), after the evaluation of the first operand of a
2289 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2290 function is called (but after the evaluation of its arguments and the
2291 expression denoting the called function), and in certain other places.
2292 Other than as expressed by the sequence point rules, the order of
2293 evaluation of subexpressions of an expression is not specified. All
2294 these rules describe only a partial order rather than a total order,
2295 since, for example, if two functions are called within one expression
2296 with no sequence point between them, the order in which the functions
2297 are called is not specified. However, the standards committee have
2298 ruled that function calls do not overlap.
2300 It is not specified when between sequence points modifications to the
2301 values of objects take effect. Programs whose behavior depends on this
2302 have undefined behavior; the C standard specifies that ``Between the
2303 previous and next sequence point an object shall have its stored value
2304 modified at most once by the evaluation of an expression. Furthermore,
2305 the prior value shall be read only to determine the value to be
2306 stored.''. If a program breaks these rules, the results on any
2307 particular implementation are entirely unpredictable.
2309 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2310 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2311 diagnosed by this option, and it may give an occasional false positive
2312 result, but in general it has been found fairly effective at detecting
2313 this sort of problem in programs.
2315 The present implementation of this option only works for C programs. A
2316 future implementation may also work for C++ programs.
2318 The C standard is worded confusingly, therefore there is some debate
2319 over the precise meaning of the sequence point rules in subtle cases.
2320 Links to discussions of the problem, including proposed formal
2321 definitions, may be found on our readings page, at
2322 @w{@uref{http://gcc.gnu.org/readings.html}}.
2325 @opindex Wreturn-type
2326 Warn whenever a function is defined with a return-type that defaults to
2327 @code{int}. Also warn about any @code{return} statement with no
2328 return-value in a function whose return-type is not @code{void}.
2330 For C++, a function without return type always produces a diagnostic
2331 message, even when @option{-Wno-return-type} is specified. The only
2332 exceptions are @samp{main} and functions defined in system headers.
2336 Warn whenever a @code{switch} statement has an index of enumeral type
2337 and lacks a @code{case} for one or more of the named codes of that
2338 enumeration. (The presence of a @code{default} label prevents this
2339 warning.) @code{case} labels outside the enumeration range also
2340 provoke warnings when this option is used.
2342 @item -Wswitch-default
2343 @opindex Wswitch-switch
2344 Warn whenever a @code{switch} statement does not have a @code{default}
2348 @opindex Wswitch-enum
2349 Warn whenever a @code{switch} statement has an index of enumeral type
2350 and lacks a @code{case} for one or more of the named codes of that
2351 enumeration. @code{case} labels outside the enumeration range also
2352 provoke warnings when this option is used.
2356 Warn if any trigraphs are encountered that might change the meaning of
2357 the program (trigraphs within comments are not warned about).
2359 @item -Wunused-function
2360 @opindex Wunused-function
2361 Warn whenever a static function is declared but not defined or a
2362 non\-inline static function is unused.
2364 @item -Wunused-label
2365 @opindex Wunused-label
2366 Warn whenever a label is declared but not used.
2368 To suppress this warning use the @samp{unused} attribute
2369 (@pxref{Variable Attributes}).
2371 @item -Wunused-parameter
2372 @opindex Wunused-parameter
2373 Warn whenever a function parameter is unused aside from its declaration.
2375 To suppress this warning use the @samp{unused} attribute
2376 (@pxref{Variable Attributes}).
2378 @item -Wunused-variable
2379 @opindex Wunused-variable
2380 Warn whenever a local variable or non-constant static variable is unused
2381 aside from its declaration
2383 To suppress this warning use the @samp{unused} attribute
2384 (@pxref{Variable Attributes}).
2386 @item -Wunused-value
2387 @opindex Wunused-value
2388 Warn whenever a statement computes a result that is explicitly not used.
2390 To suppress this warning cast the expression to @samp{void}.
2394 All the above @option{-Wunused} options combined.
2396 In order to get a warning about an unused function parameter, you must
2397 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2398 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2400 @item -Wuninitialized
2401 @opindex Wuninitialized
2402 Warn if an automatic variable is used without first being initialized or
2403 if a variable may be clobbered by a @code{setjmp} call.
2405 These warnings are possible only in optimizing compilation,
2406 because they require data flow information that is computed only
2407 when optimizing. If you don't specify @option{-O}, you simply won't
2410 If you want to warn about code which uses the uninitialized value of the
2411 variable in its own initializer, use the @option{-Winit-self} option.
2413 These warnings occur only for variables that are candidates for
2414 register allocation. Therefore, they do not occur for a variable that
2415 is declared @code{volatile}, or whose address is taken, or whose size
2416 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2417 structures, unions or arrays, even when they are in registers.
2419 Note that there may be no warning about a variable that is used only
2420 to compute a value that itself is never used, because such
2421 computations may be deleted by data flow analysis before the warnings
2424 These warnings are made optional because GCC is not smart
2425 enough to see all the reasons why the code might be correct
2426 despite appearing to have an error. Here is one example of how
2447 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2448 always initialized, but GCC doesn't know this. Here is
2449 another common case:
2454 if (change_y) save_y = y, y = new_y;
2456 if (change_y) y = save_y;
2461 This has no bug because @code{save_y} is used only if it is set.
2463 @cindex @code{longjmp} warnings
2464 This option also warns when a non-volatile automatic variable might be
2465 changed by a call to @code{longjmp}. These warnings as well are possible
2466 only in optimizing compilation.
2468 The compiler sees only the calls to @code{setjmp}. It cannot know
2469 where @code{longjmp} will be called; in fact, a signal handler could
2470 call it at any point in the code. As a result, you may get a warning
2471 even when there is in fact no problem because @code{longjmp} cannot
2472 in fact be called at the place which would cause a problem.
2474 Some spurious warnings can be avoided if you declare all the functions
2475 you use that never return as @code{noreturn}. @xref{Function
2478 @item -Wunknown-pragmas
2479 @opindex Wunknown-pragmas
2480 @cindex warning for unknown pragmas
2481 @cindex unknown pragmas, warning
2482 @cindex pragmas, warning of unknown
2483 Warn when a #pragma directive is encountered which is not understood by
2484 GCC@. If this command line option is used, warnings will even be issued
2485 for unknown pragmas in system header files. This is not the case if
2486 the warnings were only enabled by the @option{-Wall} command line option.
2488 @item -Wstrict-aliasing
2489 @opindex Wstrict-aliasing
2490 This option is only active when @option{-fstrict-aliasing} is active.
2491 It warns about code which might break the strict aliasing rules that the
2492 compiler is using for optimization. The warning does not catch all
2493 cases, but does attempt to catch the more common pitfalls. It is
2494 included in @option{-Wall}.
2498 All of the above @samp{-W} options combined. This enables all the
2499 warnings about constructions that some users consider questionable, and
2500 that are easy to avoid (or modify to prevent the warning), even in
2501 conjunction with macros. This also enables some language-specific
2502 warnings described in @ref{C++ Dialect Options} and
2503 @ref{Objective-C Dialect Options}.
2506 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2507 Some of them warn about constructions that users generally do not
2508 consider questionable, but which occasionally you might wish to check
2509 for; others warn about constructions that are necessary or hard to avoid
2510 in some cases, and there is no simple way to modify the code to suppress
2517 (This option used to be called @option{-W}. The older name is still
2518 supported, but the newer name is more descriptive.) Print extra warning
2519 messages for these events:
2523 A function can return either with or without a value. (Falling
2524 off the end of the function body is considered returning without
2525 a value.) For example, this function would evoke such a
2539 An expression-statement or the left-hand side of a comma expression
2540 contains no side effects.
2541 To suppress the warning, cast the unused expression to void.
2542 For example, an expression such as @samp{x[i,j]} will cause a warning,
2543 but @samp{x[(void)i,j]} will not.
2546 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2549 A comparison like @samp{x<=y<=z} appears; this is equivalent to
2550 @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from
2551 that of ordinary mathematical notation.
2554 Storage-class specifiers like @code{static} are not the first things in
2555 a declaration. According to the C Standard, this usage is obsolescent.
2558 The return type of a function has a type qualifier such as @code{const}.
2559 Such a type qualifier has no effect, since the value returned by a
2560 function is not an lvalue. (But don't warn about the GNU extension of
2561 @code{volatile void} return types. That extension will be warned about
2562 if @option{-pedantic} is specified.)
2565 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2569 A comparison between signed and unsigned values could produce an
2570 incorrect result when the signed value is converted to unsigned.
2571 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2574 An aggregate has an initializer which does not initialize all members.
2575 For example, the following code would cause such a warning, because
2576 @code{x.h} would be implicitly initialized to zero:
2579 struct s @{ int f, g, h; @};
2580 struct s x = @{ 3, 4 @};
2584 A function parameter is declared without a type specifier in K&R-style
2592 An empty body occurs in an @samp{if} or @samp{else} statement.
2595 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2596 @samp{>}, or @samp{>=}.
2599 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2602 Any of several floating-point events that often indicate errors, such as
2603 overflow, underflow, loss of precision, etc.
2605 @item @r{(C++ only)}
2606 An enumerator and a non-enumerator both appear in a conditional expression.
2608 @item @r{(C++ only)}
2609 A non-static reference or non-static @samp{const} member appears in a
2610 class without constructors.
2612 @item @r{(C++ only)}
2613 Ambiguous virtual bases.
2615 @item @r{(C++ only)}
2616 Subscripting an array which has been declared @samp{register}.
2618 @item @r{(C++ only)}
2619 Taking the address of a variable which has been declared @samp{register}.
2621 @item @r{(C++ only)}
2622 A base class is not initialized in a derived class' copy constructor.
2625 @item -Wno-div-by-zero
2626 @opindex Wno-div-by-zero
2627 @opindex Wdiv-by-zero
2628 Do not warn about compile-time integer division by zero. Floating point
2629 division by zero is not warned about, as it can be a legitimate way of
2630 obtaining infinities and NaNs.
2632 @item -Wsystem-headers
2633 @opindex Wsystem-headers
2634 @cindex warnings from system headers
2635 @cindex system headers, warnings from
2636 Print warning messages for constructs found in system header files.
2637 Warnings from system headers are normally suppressed, on the assumption
2638 that they usually do not indicate real problems and would only make the
2639 compiler output harder to read. Using this command line option tells
2640 GCC to emit warnings from system headers as if they occurred in user
2641 code. However, note that using @option{-Wall} in conjunction with this
2642 option will @emph{not} warn about unknown pragmas in system
2643 headers---for that, @option{-Wunknown-pragmas} must also be used.
2646 @opindex Wfloat-equal
2647 Warn if floating point values are used in equality comparisons.
2649 The idea behind this is that sometimes it is convenient (for the
2650 programmer) to consider floating-point values as approximations to
2651 infinitely precise real numbers. If you are doing this, then you need
2652 to compute (by analyzing the code, or in some other way) the maximum or
2653 likely maximum error that the computation introduces, and allow for it
2654 when performing comparisons (and when producing output, but that's a
2655 different problem). In particular, instead of testing for equality, you
2656 would check to see whether the two values have ranges that overlap; and
2657 this is done with the relational operators, so equality comparisons are
2660 @item -Wtraditional @r{(C only)}
2661 @opindex Wtraditional
2662 Warn about certain constructs that behave differently in traditional and
2663 ISO C@. Also warn about ISO C constructs that have no traditional C
2664 equivalent, and/or problematic constructs which should be avoided.
2668 Macro parameters that appear within string literals in the macro body.
2669 In traditional C macro replacement takes place within string literals,
2670 but does not in ISO C@.
2673 In traditional C, some preprocessor directives did not exist.
2674 Traditional preprocessors would only consider a line to be a directive
2675 if the @samp{#} appeared in column 1 on the line. Therefore
2676 @option{-Wtraditional} warns about directives that traditional C
2677 understands but would ignore because the @samp{#} does not appear as the
2678 first character on the line. It also suggests you hide directives like
2679 @samp{#pragma} not understood by traditional C by indenting them. Some
2680 traditional implementations would not recognize @samp{#elif}, so it
2681 suggests avoiding it altogether.
2684 A function-like macro that appears without arguments.
2687 The unary plus operator.
2690 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2691 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2692 constants.) Note, these suffixes appear in macros defined in the system
2693 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2694 Use of these macros in user code might normally lead to spurious
2695 warnings, however gcc's integrated preprocessor has enough context to
2696 avoid warning in these cases.
2699 A function declared external in one block and then used after the end of
2703 A @code{switch} statement has an operand of type @code{long}.
2706 A non-@code{static} function declaration follows a @code{static} one.
2707 This construct is not accepted by some traditional C compilers.
2710 The ISO type of an integer constant has a different width or
2711 signedness from its traditional type. This warning is only issued if
2712 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2713 typically represent bit patterns, are not warned about.
2716 Usage of ISO string concatenation is detected.
2719 Initialization of automatic aggregates.
2722 Identifier conflicts with labels. Traditional C lacks a separate
2723 namespace for labels.
2726 Initialization of unions. If the initializer is zero, the warning is
2727 omitted. This is done under the assumption that the zero initializer in
2728 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2729 initializer warnings and relies on default initialization to zero in the
2733 Conversions by prototypes between fixed/floating point values and vice
2734 versa. The absence of these prototypes when compiling with traditional
2735 C would cause serious problems. This is a subset of the possible
2736 conversion warnings, for the full set use @option{-Wconversion}.
2739 Use of ISO C style function definitions. This warning intentionally is
2740 @emph{not} issued for prototype declarations or variadic functions
2741 because these ISO C features will appear in your code when using
2742 libiberty's traditional C compatibility macros, @code{PARAMS} and
2743 @code{VPARAMS}. This warning is also bypassed for nested functions
2744 because that feature is already a gcc extension and thus not relevant to
2745 traditional C compatibility.
2748 @item -Wdeclaration-after-statement @r{(C only)}
2749 @opindex Wdeclaration-after-statement
2750 Warn when a declaration is found after a statement in a block. This
2751 construct, known from C++, was introduced with ISO C99 and is by default
2752 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2753 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2757 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2759 @item -Wendif-labels
2760 @opindex Wendif-labels
2761 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2765 Warn whenever a local variable shadows another local variable, parameter or
2766 global variable or whenever a built-in function is shadowed.
2768 @item -Wlarger-than-@var{len}
2769 @opindex Wlarger-than
2770 Warn whenever an object of larger than @var{len} bytes is defined.
2772 @item -Wpointer-arith
2773 @opindex Wpointer-arith
2774 Warn about anything that depends on the ``size of'' a function type or
2775 of @code{void}. GNU C assigns these types a size of 1, for
2776 convenience in calculations with @code{void *} pointers and pointers
2779 @item -Wbad-function-cast @r{(C only)}
2780 @opindex Wbad-function-cast
2781 Warn whenever a function call is cast to a non-matching type.
2782 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2786 Warn whenever a pointer is cast so as to remove a type qualifier from
2787 the target type. For example, warn if a @code{const char *} is cast
2788 to an ordinary @code{char *}.
2791 @opindex Wcast-align
2792 Warn whenever a pointer is cast such that the required alignment of the
2793 target is increased. For example, warn if a @code{char *} is cast to
2794 an @code{int *} on machines where integers can only be accessed at
2795 two- or four-byte boundaries.
2797 @item -Wwrite-strings
2798 @opindex Wwrite-strings
2799 When compiling C, give string constants the type @code{const
2800 char[@var{length}]} so that
2801 copying the address of one into a non-@code{const} @code{char *}
2802 pointer will get a warning; when compiling C++, warn about the
2803 deprecated conversion from string constants to @code{char *}.
2804 These warnings will help you find at
2805 compile time code that can try to write into a string constant, but
2806 only if you have been very careful about using @code{const} in
2807 declarations and prototypes. Otherwise, it will just be a nuisance;
2808 this is why we did not make @option{-Wall} request these warnings.
2811 @opindex Wconversion
2812 Warn if a prototype causes a type conversion that is different from what
2813 would happen to the same argument in the absence of a prototype. This
2814 includes conversions of fixed point to floating and vice versa, and
2815 conversions changing the width or signedness of a fixed point argument
2816 except when the same as the default promotion.
2818 Also, warn if a negative integer constant expression is implicitly
2819 converted to an unsigned type. For example, warn about the assignment
2820 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2821 casts like @code{(unsigned) -1}.
2823 @item -Wsign-compare
2824 @opindex Wsign-compare
2825 @cindex warning for comparison of signed and unsigned values
2826 @cindex comparison of signed and unsigned values, warning
2827 @cindex signed and unsigned values, comparison warning
2828 Warn when a comparison between signed and unsigned values could produce
2829 an incorrect result when the signed value is converted to unsigned.
2830 This warning is also enabled by @option{-Wextra}; to get the other warnings
2831 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2833 @item -Waggregate-return
2834 @opindex Waggregate-return
2835 Warn if any functions that return structures or unions are defined or
2836 called. (In languages where you can return an array, this also elicits
2839 @item -Wstrict-prototypes @r{(C only)}
2840 @opindex Wstrict-prototypes
2841 Warn if a function is declared or defined without specifying the
2842 argument types. (An old-style function definition is permitted without
2843 a warning if preceded by a declaration which specifies the argument
2846 @item -Wold-style-definition @r{(C only)}
2847 @opindex Wold-style-definition
2848 Warn if an old-style function definition is used. A warning is given
2849 even if there is a previous prototype.
2851 @item -Wmissing-prototypes @r{(C only)}
2852 @opindex Wmissing-prototypes
2853 Warn if a global function is defined without a previous prototype
2854 declaration. This warning is issued even if the definition itself
2855 provides a prototype. The aim is to detect global functions that fail
2856 to be declared in header files.
2858 @item -Wmissing-declarations @r{(C only)}
2859 @opindex Wmissing-declarations
2860 Warn if a global function is defined without a previous declaration.
2861 Do so even if the definition itself provides a prototype.
2862 Use this option to detect global functions that are not declared in
2865 @item -Wmissing-noreturn
2866 @opindex Wmissing-noreturn
2867 Warn about functions which might be candidates for attribute @code{noreturn}.
2868 Note these are only possible candidates, not absolute ones. Care should
2869 be taken to manually verify functions actually do not ever return before
2870 adding the @code{noreturn} attribute, otherwise subtle code generation
2871 bugs could be introduced. You will not get a warning for @code{main} in
2872 hosted C environments.
2874 @item -Wmissing-format-attribute
2875 @opindex Wmissing-format-attribute
2877 If @option{-Wformat} is enabled, also warn about functions which might be
2878 candidates for @code{format} attributes. Note these are only possible
2879 candidates, not absolute ones. GCC will guess that @code{format}
2880 attributes might be appropriate for any function that calls a function
2881 like @code{vprintf} or @code{vscanf}, but this might not always be the
2882 case, and some functions for which @code{format} attributes are
2883 appropriate may not be detected. This option has no effect unless
2884 @option{-Wformat} is enabled (possibly by @option{-Wall}).
2886 @item -Wno-multichar
2887 @opindex Wno-multichar
2889 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
2890 Usually they indicate a typo in the user's code, as they have
2891 implementation-defined values, and should not be used in portable code.
2893 @item -Wno-deprecated-declarations
2894 @opindex Wno-deprecated-declarations
2895 Do not warn about uses of functions, variables, and types marked as
2896 deprecated by using the @code{deprecated} attribute.
2897 (@pxref{Function Attributes}, @pxref{Variable Attributes},
2898 @pxref{Type Attributes}.)
2902 Warn if a structure is given the packed attribute, but the packed
2903 attribute has no effect on the layout or size of the structure.
2904 Such structures may be mis-aligned for little benefit. For
2905 instance, in this code, the variable @code{f.x} in @code{struct bar}
2906 will be misaligned even though @code{struct bar} does not itself
2907 have the packed attribute:
2914 @} __attribute__((packed));
2924 Warn if padding is included in a structure, either to align an element
2925 of the structure or to align the whole structure. Sometimes when this
2926 happens it is possible to rearrange the fields of the structure to
2927 reduce the padding and so make the structure smaller.
2929 @item -Wredundant-decls
2930 @opindex Wredundant-decls
2931 Warn if anything is declared more than once in the same scope, even in
2932 cases where multiple declaration is valid and changes nothing.
2934 @item -Wnested-externs @r{(C only)}
2935 @opindex Wnested-externs
2936 Warn if an @code{extern} declaration is encountered within a function.
2938 @item -Wunreachable-code
2939 @opindex Wunreachable-code
2940 Warn if the compiler detects that code will never be executed.
2942 This option is intended to warn when the compiler detects that at
2943 least a whole line of source code will never be executed, because
2944 some condition is never satisfied or because it is after a
2945 procedure that never returns.
2947 It is possible for this option to produce a warning even though there
2948 are circumstances under which part of the affected line can be executed,
2949 so care should be taken when removing apparently-unreachable code.
2951 For instance, when a function is inlined, a warning may mean that the
2952 line is unreachable in only one inlined copy of the function.
2954 This option is not made part of @option{-Wall} because in a debugging
2955 version of a program there is often substantial code which checks
2956 correct functioning of the program and is, hopefully, unreachable
2957 because the program does work. Another common use of unreachable
2958 code is to provide behavior which is selectable at compile-time.
2962 Warn if a function can not be inlined and it was declared as inline.
2963 Even with this option, the compiler will not warn about failures to
2964 inline functions declared in system headers.
2966 The compiler uses a variety of heuristics to determine whether or not
2967 to inline a function. For example, the compiler takes into account
2968 the size of the function being inlined and the the amount of inlining
2969 that has already been done in the current function. Therefore,
2970 seemingly insignificant changes in the source program can cause the
2971 warnings produced by @option{-Winline} to appear or disappear.
2973 @item -Wno-invalid-offsetof @r{(C++ only)}
2974 @opindex Wno-invalid-offsetof
2975 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
2976 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
2977 to a non-POD type is undefined. In existing C++ implementations,
2978 however, @samp{offsetof} typically gives meaningful results even when
2979 applied to certain kinds of non-POD types. (Such as a simple
2980 @samp{struct} that fails to be a POD type only by virtue of having a
2981 constructor.) This flag is for users who are aware that they are
2982 writing nonportable code and who have deliberately chosen to ignore the
2985 The restrictions on @samp{offsetof} may be relaxed in a future version
2986 of the C++ standard.
2989 @opindex Winvalid-pch
2990 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
2991 the search path but can't be used.
2995 @opindex Wno-long-long
2996 Warn if @samp{long long} type is used. This is default. To inhibit
2997 the warning messages, use @option{-Wno-long-long}. Flags
2998 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
2999 only when @option{-pedantic} flag is used.
3001 @item -Wdisabled-optimization
3002 @opindex Wdisabled-optimization
3003 Warn if a requested optimization pass is disabled. This warning does
3004 not generally indicate that there is anything wrong with your code; it
3005 merely indicates that GCC's optimizers were unable to handle the code
3006 effectively. Often, the problem is that your code is too big or too
3007 complex; GCC will refuse to optimize programs when the optimization
3008 itself is likely to take inordinate amounts of time.
3012 Make all warnings into errors.
3015 @node Debugging Options
3016 @section Options for Debugging Your Program or GCC
3017 @cindex options, debugging
3018 @cindex debugging information options
3020 GCC has various special options that are used for debugging
3021 either your program or GCC:
3026 Produce debugging information in the operating system's native format
3027 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
3030 On most systems that use stabs format, @option{-g} enables use of extra
3031 debugging information that only GDB can use; this extra information
3032 makes debugging work better in GDB but will probably make other debuggers
3034 refuse to read the program. If you want to control for certain whether
3035 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3036 @option{-gxcoff+}, @option{-gxcoff}, @option{-gdwarf-1+}, @option{-gdwarf-1},
3037 or @option{-gvms} (see below).
3039 Unlike most other C compilers, GCC allows you to use @option{-g} with
3040 @option{-O}. The shortcuts taken by optimized code may occasionally
3041 produce surprising results: some variables you declared may not exist
3042 at all; flow of control may briefly move where you did not expect it;
3043 some statements may not be executed because they compute constant
3044 results or their values were already at hand; some statements may
3045 execute in different places because they were moved out of loops.
3047 Nevertheless it proves possible to debug optimized output. This makes
3048 it reasonable to use the optimizer for programs that might have bugs.
3050 The following options are useful when GCC is generated with the
3051 capability for more than one debugging format.
3055 Produce debugging information for use by GDB@. This means to use the
3056 most expressive format available (DWARF 2, stabs, or the native format
3057 if neither of those are supported), including GDB extensions if at all
3062 Produce debugging information in stabs format (if that is supported),
3063 without GDB extensions. This is the format used by DBX on most BSD
3064 systems. On MIPS, Alpha and System V Release 4 systems this option
3065 produces stabs debugging output which is not understood by DBX or SDB@.
3066 On System V Release 4 systems this option requires the GNU assembler.
3068 @item -feliminate-unused-debug-symbols
3069 @opindex feliminate-unused-debug-symbols
3070 Produce debugging information in stabs format (if that is supported),
3071 for only symbols that are actually used.
3075 Produce debugging information in stabs format (if that is supported),
3076 using GNU extensions understood only by the GNU debugger (GDB)@. The
3077 use of these extensions is likely to make other debuggers crash or
3078 refuse to read the program.
3082 Produce debugging information in COFF format (if that is supported).
3083 This is the format used by SDB on most System V systems prior to
3088 Produce debugging information in XCOFF format (if that is supported).
3089 This is the format used by the DBX debugger on IBM RS/6000 systems.
3093 Produce debugging information in XCOFF format (if that is supported),
3094 using GNU extensions understood only by the GNU debugger (GDB)@. The
3095 use of these extensions is likely to make other debuggers crash or
3096 refuse to read the program, and may cause assemblers other than the GNU
3097 assembler (GAS) to fail with an error.
3101 Produce debugging information in DWARF version 1 format (if that is
3102 supported). This is the format used by SDB on most System V Release 4
3105 This option is deprecated.
3109 Produce debugging information in DWARF version 1 format (if that is
3110 supported), using GNU extensions understood only by the GNU debugger
3111 (GDB)@. The use of these extensions is likely to make other debuggers
3112 crash or refuse to read the program.
3114 This option is deprecated.
3118 Produce debugging information in DWARF version 2 format (if that is
3119 supported). This is the format used by DBX on IRIX 6.
3123 Produce debugging information in VMS debug format (if that is
3124 supported). This is the format used by DEBUG on VMS systems.
3127 @itemx -ggdb@var{level}
3128 @itemx -gstabs@var{level}
3129 @itemx -gcoff@var{level}
3130 @itemx -gxcoff@var{level}
3131 @itemx -gvms@var{level}
3132 Request debugging information and also use @var{level} to specify how
3133 much information. The default level is 2.
3135 Level 1 produces minimal information, enough for making backtraces in
3136 parts of the program that you don't plan to debug. This includes
3137 descriptions of functions and external variables, but no information
3138 about local variables and no line numbers.
3140 Level 3 includes extra information, such as all the macro definitions
3141 present in the program. Some debuggers support macro expansion when
3142 you use @option{-g3}.
3144 Note that in order to avoid confusion between DWARF1 debug level 2,
3145 and DWARF2, neither @option{-gdwarf} nor @option{-gdwarf-2} accept
3146 a concatenated debug level. Instead use an additional @option{-g@var{level}}
3147 option to change the debug level for DWARF1 or DWARF2.
3149 @item -feliminate-dwarf2-dups
3150 @opindex feliminate-dwarf2-dups
3151 Compress DWARF2 debugging information by eliminating duplicated
3152 information about each symbol. This option only makes sense when
3153 generating DWARF2 debugging information with @option{-gdwarf-2}.
3155 @cindex @command{prof}
3158 Generate extra code to write profile information suitable for the
3159 analysis program @command{prof}. You must use this option when compiling
3160 the source files you want data about, and you must also use it when
3163 @cindex @command{gprof}
3166 Generate extra code to write profile information suitable for the
3167 analysis program @command{gprof}. You must use this option when compiling
3168 the source files you want data about, and you must also use it when
3173 Makes the compiler print out each function name as it is compiled, and
3174 print some statistics about each pass when it finishes.
3177 @opindex ftime-report
3178 Makes the compiler print some statistics about the time consumed by each
3179 pass when it finishes.
3182 @opindex fmem-report
3183 Makes the compiler print some statistics about permanent memory
3184 allocation when it finishes.
3186 @item -fprofile-arcs
3187 @opindex fprofile-arcs
3188 Add code so that program flow @dfn{arcs} are instrumented. During
3189 execution the program records how many times each branch and call is
3190 executed and how many times it is taken or returns. When the compiled
3191 program exits it saves this data to a file called
3192 @file{@var{auxname}.gcda} for each source file. The data may be used for
3193 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3194 test coverage analysis (@option{-ftest-coverage}). Each object file's
3195 @var{auxname} is generated from the name of the output file, if
3196 explicitly specified and it is not the final executable, otherwise it is
3197 the basename of the source file. In both cases any suffix is removed
3198 (e.g. @file{foo.gcda} for input file @file{dir/foo.c}, or
3199 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3204 Compile the source files with @option{-fprofile-arcs} plus optimization
3205 and code generation options. For test coverage analysis, use the
3206 additional @option{-ftest-coverage} option. You do not need to profile
3207 every source file in a program.
3210 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3211 (the latter implies the former).
3214 Run the program on a representative workload to generate the arc profile
3215 information. This may be repeated any number of times. You can run
3216 concurrent instances of your program, and provided that the file system
3217 supports locking, the data files will be correctly updated. Also
3218 @code{fork} calls are detected and correctly handled (double counting
3222 For profile-directed optimizations, compile the source files again with
3223 the same optimization and code generation options plus
3224 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3225 Control Optimization}).
3228 For test coverage analysis, use @command{gcov} to produce human readable
3229 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3230 @command{gcov} documentation for further information.
3234 With @option{-fprofile-arcs}, for each function of your program GCC
3235 creates a program flow graph, then finds a spanning tree for the graph.
3236 Only arcs that are not on the spanning tree have to be instrumented: the
3237 compiler adds code to count the number of times that these arcs are
3238 executed. When an arc is the only exit or only entrance to a block, the
3239 instrumentation code can be added to the block; otherwise, a new basic
3240 block must be created to hold the instrumentation code.
3243 @item -ftest-coverage
3244 @opindex ftest-coverage
3245 Produce a notes file that the @command{gcov} code-coverage utility
3246 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3247 show program coverage. Each source file's note file is called
3248 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3249 above for a description of @var{auxname} and instructions on how to
3250 generate test coverage data. Coverage data will match the source files
3251 more closely, if you do not optimize.
3253 @item -d@var{letters}
3255 Says to make debugging dumps during compilation at times specified by
3256 @var{letters}. This is used for debugging the compiler. The file names
3257 for most of the dumps are made by appending a pass number and a word to
3258 the @var{dumpname}. @var{dumpname} is generated from the name of the
3259 output file, if explicitly specified and it is not an executable,
3260 otherwise it is the basename of the source file. In both cases any
3261 suffix is removed (e.g. @file{foo.00.rtl} or @file{foo.01.sibling}).
3262 Here are the possible letters for use in @var{letters}, and their
3268 Annotate the assembler output with miscellaneous debugging information.
3271 Dump after computing branch probabilities, to @file{@var{file}.16.bp}.
3274 Dump after block reordering, to @file{@var{file}.32.bbro}.
3277 Dump after instruction combination, to the file @file{@var{file}.22.combine}.
3280 Dump after the first if conversion, to the file @file{@var{file}.17.ce1}.
3281 Also dump after the second if conversion, to the file @file{@var{file}.23.ce2}.
3284 Dump after branch target load optimization, to to @file{@var{file}.34.btl}.
3285 Also dump after delayed branch scheduling, to @file{@var{file}.37.dbr}.
3288 Dump all macro definitions, at the end of preprocessing, in addition to
3292 Dump after SSA optimizations, to @file{@var{file}.05.ssa} and
3293 @file{@var{file}.010.ussa}.
3296 Dump after the second if conversion, to @file{@var{file}.33.ce3}.
3299 Dump after control and data flow analysis, to @file{@var{file}.15.cfg}.
3300 Also dump after life analysis, to @file{@var{file}.21.life}.
3303 Dump after purging @code{ADDRESSOF} codes, to @file{@var{file}.11.addressof}.
3306 Dump after global register allocation, to @file{@var{file}.27.greg}.
3309 Dump after GCSE, to @file{@var{file}.12.gcse}.
3310 Also dump after jump bypassing and control flow optimizations, to
3311 @file{@var{file}.14.bypass}.
3314 Dump after finalization of EH handling code, to @file{@var{file}.03.eh}.
3317 Dump after sibling call optimizations, to @file{@var{file}.02.sibling}.
3320 Dump after the first jump optimization, to @file{@var{file}.04.jump}.
3323 Dump after conversion from registers to stack, to @file{@var{file}.36.stack}.
3326 Dump after local register allocation, to @file{@var{file}.26.lreg}.
3329 Dump after loop optimization passes, to @file{@var{file}.13.loop} and
3330 @file{@var{file}.19.loop2}.
3333 Dump after performing the machine dependent reorganization pass, to
3334 @file{@var{file}.37.mach}.
3337 Dump after register renumbering, to @file{@var{file}.31.rnreg}.
3340 Dump after the register move pass, to @file{@var{file}.24.regmove}.
3343 Dump after post-reload optimizations, to @file{@var{file}.28.postreload}.
3346 Dump after RTL generation, to @file{@var{file}.01.rtl}.
3349 Dump after the second scheduling pass, to @file{@var{file}.35.sched2}.
3352 Dump after CSE (including the jump optimization that sometimes follows
3353 CSE), to @file{@var{file}.019.cse}.
3356 Dump after the first scheduling pass, to @file{@var{file}.25.sched}.
3359 Dump after the second CSE pass (including the jump optimization that
3360 sometimes follows CSE), to @file{@var{file}.20.cse2}.
3363 Dump after running tracer, to @file{@var{file}.18.tracer}.
3366 Dump after null pointer elimination pass to @file{@var{file}.018.null}.
3369 Dump callgraph and unit-at-a-time optimization @file{@var{file}.00.unit}.
3372 Dump after the second flow pass, to @file{@var{file}.29.flow2}.
3375 Dump after SSA conditional constant propagation, to
3376 @file{@var{file}.06.ssaccp}.
3379 Dump after SSA dead code elimination, to @file{@var{file}.07.ssadce}.
3382 Dump after the peephole pass, to @file{@var{file}.30.peephole2}.
3385 Produce all the dumps listed above.
3388 Produce a core dump whenever an error occurs.
3391 Print statistics on memory usage, at the end of the run, to
3395 Annotate the assembler output with a comment indicating which
3396 pattern and alternative was used. The length of each instruction is
3400 Dump the RTL in the assembler output as a comment before each instruction.
3401 Also turns on @option{-dp} annotation.
3404 For each of the other indicated dump files (except for
3405 @file{@var{file}.01.rtl}), dump a representation of the control flow graph
3406 suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3409 Just generate RTL for a function instead of compiling it. Usually used
3413 Dump debugging information during parsing, to standard error.
3416 @item -fdump-unnumbered
3417 @opindex fdump-unnumbered
3418 When doing debugging dumps (see @option{-d} option above), suppress instruction
3419 numbers and line number note output. This makes it more feasible to
3420 use diff on debugging dumps for compiler invocations with different
3421 options, in particular with and without @option{-g}.
3423 @item -fdump-translation-unit @r{(C and C++ only)}
3424 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3425 @opindex fdump-translation-unit
3426 Dump a representation of the tree structure for the entire translation
3427 unit to a file. The file name is made by appending @file{.tu} to the
3428 source file name. If the @samp{-@var{options}} form is used, @var{options}
3429 controls the details of the dump as described for the
3430 @option{-fdump-tree} options.
3432 @item -fdump-class-hierarchy @r{(C++ only)}
3433 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3434 @opindex fdump-class-hierarchy
3435 Dump a representation of each class's hierarchy and virtual function
3436 table layout to a file. The file name is made by appending @file{.class}
3437 to the source file name. If the @samp{-@var{options}} form is used,
3438 @var{options} controls the details of the dump as described for the
3439 @option{-fdump-tree} options.
3441 @item -fdump-tree-@var{switch} @r{(C++ only)}
3442 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C++ only)}
3444 Control the dumping at various stages of processing the intermediate
3445 language tree to a file. The file name is generated by appending a switch
3446 specific suffix to the source file name. If the @samp{-@var{options}}
3447 form is used, @var{options} is a list of @samp{-} separated options that
3448 control the details of the dump. Not all options are applicable to all
3449 dumps, those which are not meaningful will be ignored. The following
3450 options are available
3454 Print the address of each node. Usually this is not meaningful as it
3455 changes according to the environment and source file. Its primary use
3456 is for tying up a dump file with a debug environment.
3458 Inhibit dumping of members of a scope or body of a function merely
3459 because that scope has been reached. Only dump such items when they
3460 are directly reachable by some other path.
3462 Turn on all options.
3465 The following tree dumps are possible:
3468 Dump before any tree based optimization, to @file{@var{file}.original}.
3470 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3472 Dump after function inlining, to @file{@var{file}.inlined}.
3475 @item -frandom-seed=@var{string}
3476 @opindex frandom-string
3477 This option provides a seed that GCC uses when it would otherwise use
3478 random numbers. It is used to generate certain symbol names
3479 that have to be different in every compiled file. It is also used to
3480 place unique stamps in coverage data files and the object files that
3481 produce them. You can use the @option{-frandom-seed} option to produce
3482 reproducibly identical object files.
3484 The @var{string} should be different for every file you compile.
3486 @item -fsched-verbose=@var{n}
3487 @opindex fsched-verbose
3488 On targets that use instruction scheduling, this option controls the
3489 amount of debugging output the scheduler prints. This information is
3490 written to standard error, unless @option{-dS} or @option{-dR} is
3491 specified, in which case it is output to the usual dump
3492 listing file, @file{.sched} or @file{.sched2} respectively. However
3493 for @var{n} greater than nine, the output is always printed to standard
3496 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3497 same information as @option{-dRS}. For @var{n} greater than one, it
3498 also output basic block probabilities, detailed ready list information
3499 and unit/insn info. For @var{n} greater than two, it includes RTL
3500 at abort point, control-flow and regions info. And for @var{n} over
3501 four, @option{-fsched-verbose} also includes dependence info.
3505 Store the usual ``temporary'' intermediate files permanently; place them
3506 in the current directory and name them based on the source file. Thus,
3507 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3508 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3509 preprocessed @file{foo.i} output file even though the compiler now
3510 normally uses an integrated preprocessor.
3514 Report the CPU time taken by each subprocess in the compilation
3515 sequence. For C source files, this is the compiler proper and assembler
3516 (plus the linker if linking is done). The output looks like this:
3523 The first number on each line is the ``user time,'' that is time spent
3524 executing the program itself. The second number is ``system time,''
3525 time spent executing operating system routines on behalf of the program.
3526 Both numbers are in seconds.
3528 @item -print-file-name=@var{library}
3529 @opindex print-file-name
3530 Print the full absolute name of the library file @var{library} that
3531 would be used when linking---and don't do anything else. With this
3532 option, GCC does not compile or link anything; it just prints the
3535 @item -print-multi-directory
3536 @opindex print-multi-directory
3537 Print the directory name corresponding to the multilib selected by any
3538 other switches present in the command line. This directory is supposed
3539 to exist in @env{GCC_EXEC_PREFIX}.
3541 @item -print-multi-lib
3542 @opindex print-multi-lib
3543 Print the mapping from multilib directory names to compiler switches
3544 that enable them. The directory name is separated from the switches by
3545 @samp{;}, and each switch starts with an @samp{@@} instead of the
3546 @samp{-}, without spaces between multiple switches. This is supposed to
3547 ease shell-processing.
3549 @item -print-prog-name=@var{program}
3550 @opindex print-prog-name
3551 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3553 @item -print-libgcc-file-name
3554 @opindex print-libgcc-file-name
3555 Same as @option{-print-file-name=libgcc.a}.
3557 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3558 but you do want to link with @file{libgcc.a}. You can do
3561 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3564 @item -print-search-dirs
3565 @opindex print-search-dirs
3566 Print the name of the configured installation directory and a list of
3567 program and library directories gcc will search---and don't do anything else.
3569 This is useful when gcc prints the error message
3570 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3571 To resolve this you either need to put @file{cpp0} and the other compiler
3572 components where gcc expects to find them, or you can set the environment
3573 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3574 Don't forget the trailing '/'.
3575 @xref{Environment Variables}.
3578 @opindex dumpmachine
3579 Print the compiler's target machine (for example,
3580 @samp{i686-pc-linux-gnu})---and don't do anything else.
3583 @opindex dumpversion
3584 Print the compiler version (for example, @samp{3.0})---and don't do
3589 Print the compiler's built-in specs---and don't do anything else. (This
3590 is used when GCC itself is being built.) @xref{Spec Files}.
3592 @item -feliminate-unused-debug-types
3593 @opindex feliminate-unused-debug-types
3594 Normally, when producing DWARF2 output, GCC will emit debugging
3595 information for all types declared in a compilation
3596 unit, regardless of whether or not they are actually used
3597 in that compilation unit. Sometimes this is useful, such as
3598 if, in the debugger, you want to cast a value to a type that is
3599 not actually used in your program (but is declared). More often,
3600 however, this results in a significant amount of wasted space.
3601 With this option, GCC will avoid producing debug symbol output
3602 for types that are nowhere used in the source file being compiled.
3605 @node Optimize Options
3606 @section Options That Control Optimization
3607 @cindex optimize options
3608 @cindex options, optimization
3610 These options control various sorts of optimizations.
3612 Without any optimization option, the compiler's goal is to reduce the
3613 cost of compilation and to make debugging produce the expected
3614 results. Statements are independent: if you stop the program with a
3615 breakpoint between statements, you can then assign a new value to any
3616 variable or change the program counter to any other statement in the
3617 function and get exactly the results you would expect from the source
3620 Turning on optimization flags makes the compiler attempt to improve
3621 the performance and/or code size at the expense of compilation time
3622 and possibly the ability to debug the program.
3624 The compiler performs optimisation based on the knowledge it has of
3625 the program. Using the @option{-funit-at-a-time} flag will allow the
3626 compiler to consider information gained from later functions in the
3627 file when compiling a function. Compiling multiple files at once to a
3628 single output file (and using @option{-funit-at-a-time}) will allow
3629 the compiler to use information gained from all of the files when
3630 compiling each of them.
3632 Not all optimizations are controlled directly by a flag. Only
3633 optimizations that have a flag are listed.
3640 Optimize. Optimizing compilation takes somewhat more time, and a lot
3641 more memory for a large function.
3643 With @option{-O}, the compiler tries to reduce code size and execution
3644 time, without performing any optimizations that take a great deal of
3647 @option{-O} turns on the following optimization flags:
3648 @gccoptlist{-fdefer-pop @gol
3649 -fmerge-constants @gol
3651 -floop-optimize @gol
3653 -fif-conversion @gol
3654 -fif-conversion2 @gol
3655 -fdelayed-branch @gol
3656 -fguess-branch-probability @gol
3659 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
3660 where doing so does not interfere with debugging.
3664 Optimize even more. GCC performs nearly all supported optimizations
3665 that do not involve a space-speed tradeoff. The compiler does not
3666 perform loop unrolling or function inlining when you specify @option{-O2}.
3667 As compared to @option{-O}, this option increases both compilation time
3668 and the performance of the generated code.
3670 @option{-O2} turns on all optimization flags specified by @option{-O}. It
3671 also turns on the following optimization flags:
3672 @gccoptlist{-fforce-mem @gol
3673 -foptimize-sibling-calls @gol
3674 -fstrength-reduce @gol
3675 -fcse-follow-jumps -fcse-skip-blocks @gol
3676 -frerun-cse-after-loop -frerun-loop-opt @gol
3677 -fgcse -fgcse-lm -fgcse-sm @gol
3678 -fdelete-null-pointer-checks @gol
3679 -fexpensive-optimizations @gol
3681 -fschedule-insns -fschedule-insns2 @gol
3682 -fsched-interblock -fsched-spec @gol
3685 -freorder-blocks -freorder-functions @gol
3686 -fstrict-aliasing @gol
3687 -falign-functions -falign-jumps @gol
3688 -falign-loops -falign-labels}
3690 Please note the warning under @option{-fgcse} about
3691 invoking @option{-O2} on programs that use computed gotos.
3695 Optimize yet more. @option{-O3} turns on all optimizations specified by
3696 @option{-O2} and also turns on the @option{-finline-functions},
3697 @option{-funit-at-a-time} and @option{-frename-registers} options.
3701 Do not optimize. This is the default.
3705 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
3706 do not typically increase code size. It also performs further
3707 optimizations designed to reduce code size.
3709 @option{-Os} disables the following optimization flags:
3710 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
3711 -falign-labels -freorder-blocks -fprefetch-loop-arrays}
3713 If you use multiple @option{-O} options, with or without level numbers,
3714 the last such option is the one that is effective.
3717 Options of the form @option{-f@var{flag}} specify machine-independent
3718 flags. Most flags have both positive and negative forms; the negative
3719 form of @option{-ffoo} would be @option{-fno-foo}. In the table
3720 below, only one of the forms is listed---the one you typically will
3721 use. You can figure out the other form by either removing @samp{no-}
3724 The following options control specific optimizations. They are either
3725 activated by @option{-O} options or are related to ones that are. You
3726 can use the following flags in the rare cases when ``fine-tuning'' of
3727 optimizations to be performed is desired.
3730 @item -fno-default-inline
3731 @opindex fno-default-inline
3732 Do not make member functions inline by default merely because they are
3733 defined inside the class scope (C++ only). Otherwise, when you specify
3734 @w{@option{-O}}, member functions defined inside class scope are compiled
3735 inline by default; i.e., you don't need to add @samp{inline} in front of
3736 the member function name.
3738 @item -fno-defer-pop
3739 @opindex fno-defer-pop
3740 Always pop the arguments to each function call as soon as that function
3741 returns. For machines which must pop arguments after a function call,
3742 the compiler normally lets arguments accumulate on the stack for several
3743 function calls and pops them all at once.
3745 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3749 Force memory operands to be copied into registers before doing
3750 arithmetic on them. This produces better code by making all memory
3751 references potential common subexpressions. When they are not common
3752 subexpressions, instruction combination should eliminate the separate
3755 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3758 @opindex fforce-addr
3759 Force memory address constants to be copied into registers before
3760 doing arithmetic on them. This may produce better code just as
3761 @option{-fforce-mem} may.
3763 @item -fomit-frame-pointer
3764 @opindex fomit-frame-pointer
3765 Don't keep the frame pointer in a register for functions that
3766 don't need one. This avoids the instructions to save, set up and
3767 restore frame pointers; it also makes an extra register available
3768 in many functions. @strong{It also makes debugging impossible on
3771 On some machines, such as the VAX, this flag has no effect, because
3772 the standard calling sequence automatically handles the frame pointer
3773 and nothing is saved by pretending it doesn't exist. The
3774 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
3775 whether a target machine supports this flag. @xref{Registers,,Register
3776 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
3778 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3780 @item -foptimize-sibling-calls
3781 @opindex foptimize-sibling-calls
3782 Optimize sibling and tail recursive calls.
3784 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3788 Don't pay attention to the @code{inline} keyword. Normally this option
3789 is used to keep the compiler from expanding any functions inline.
3790 Note that if you are not optimizing, no functions can be expanded inline.
3792 @item -finline-functions
3793 @opindex finline-functions
3794 Integrate all simple functions into their callers. The compiler
3795 heuristically decides which functions are simple enough to be worth
3796 integrating in this way.
3798 If all calls to a given function are integrated, and the function is
3799 declared @code{static}, then the function is normally not output as
3800 assembler code in its own right.
3802 Enabled at level @option{-O3}.
3804 @item -finline-limit=@var{n}
3805 @opindex finline-limit
3806 By default, gcc limits the size of functions that can be inlined. This flag
3807 allows the control of this limit for functions that are explicitly marked as
3808 inline (i.e., marked with the inline keyword or defined within the class
3809 definition in c++). @var{n} is the size of functions that can be inlined in
3810 number of pseudo instructions (not counting parameter handling). The default
3811 value of @var{n} is 600.
3812 Increasing this value can result in more inlined code at
3813 the cost of compilation time and memory consumption. Decreasing usually makes
3814 the compilation faster and less code will be inlined (which presumably
3815 means slower programs). This option is particularly useful for programs that
3816 use inlining heavily such as those based on recursive templates with C++.
3818 Inlining is actually controlled by a number of parameters, which may be
3819 specified individually by using @option{--param @var{name}=@var{value}}.
3820 The @option{-finline-limit=@var{n}} option sets some of these parameters
3824 @item max-inline-insns
3826 @item max-inline-insns-single
3827 is set to @var{n}/2.
3828 @item max-inline-insns-auto
3829 is set to @var{n}/2.
3830 @item min-inline-insns
3831 is set to 130 or @var{n}/4, whichever is smaller.
3832 @item max-inline-insns-rtl
3836 Using @option{-finline-limit=600} thus results in the default settings
3837 for these parameters. See below for a documentation of the individual
3838 parameters controlling inlining.
3840 @emph{Note:} pseudo instruction represents, in this particular context, an
3841 abstract measurement of function's size. In no way, it represents a count
3842 of assembly instructions and as such its exact meaning might change from one
3843 release to an another.
3845 @item -fkeep-inline-functions
3846 @opindex fkeep-inline-functions
3847 Even if all calls to a given function are integrated, and the function
3848 is declared @code{static}, nevertheless output a separate run-time
3849 callable version of the function. This switch does not affect
3850 @code{extern inline} functions.
3852 @item -fkeep-static-consts
3853 @opindex fkeep-static-consts
3854 Emit variables declared @code{static const} when optimization isn't turned
3855 on, even if the variables aren't referenced.
3857 GCC enables this option by default. If you want to force the compiler to
3858 check if the variable was referenced, regardless of whether or not
3859 optimization is turned on, use the @option{-fno-keep-static-consts} option.
3861 @item -fmerge-constants
3862 Attempt to merge identical constants (string constants and floating point
3863 constants) across compilation units.
3865 This option is the default for optimized compilation if the assembler and
3866 linker support it. Use @option{-fno-merge-constants} to inhibit this
3869 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3871 @item -fmerge-all-constants
3872 Attempt to merge identical constants and identical variables.
3874 This option implies @option{-fmerge-constants}. In addition to
3875 @option{-fmerge-constants} this considers e.g. even constant initialized
3876 arrays or initialized constant variables with integral or floating point
3877 types. Languages like C or C++ require each non-automatic variable to
3878 have distinct location, so using this option will result in non-conforming
3883 Use a graph coloring register allocator. Currently this option is meant
3884 for testing, so we are interested to hear about miscompilations with
3887 @item -fno-branch-count-reg
3888 @opindex fno-branch-count-reg
3889 Do not use ``decrement and branch'' instructions on a count register,
3890 but instead generate a sequence of instructions that decrement a
3891 register, compare it against zero, then branch based upon the result.
3892 This option is only meaningful on architectures that support such
3893 instructions, which include x86, PowerPC, IA-64 and S/390.
3895 The default is @option{-fbranch-count-reg}, enabled when
3896 @option{-fstrength-reduce} is enabled.
3898 @item -fno-function-cse
3899 @opindex fno-function-cse
3900 Do not put function addresses in registers; make each instruction that
3901 calls a constant function contain the function's address explicitly.
3903 This option results in less efficient code, but some strange hacks
3904 that alter the assembler output may be confused by the optimizations
3905 performed when this option is not used.
3907 The default is @option{-ffunction-cse}
3909 @item -fno-zero-initialized-in-bss
3910 @opindex fno-zero-initialized-in-bss
3911 If the target supports a BSS section, GCC by default puts variables that
3912 are initialized to zero into BSS@. This can save space in the resulting
3915 This option turns off this behavior because some programs explicitly
3916 rely on variables going to the data section. E.g., so that the
3917 resulting executable can find the beginning of that section and/or make
3918 assumptions based on that.
3920 The default is @option{-fzero-initialized-in-bss}.
3922 @item -fstrength-reduce
3923 @opindex fstrength-reduce
3924 Perform the optimizations of loop strength reduction and
3925 elimination of iteration variables.
3927 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3929 @item -fthread-jumps
3930 @opindex fthread-jumps
3931 Perform optimizations where we check to see if a jump branches to a
3932 location where another comparison subsumed by the first is found. If
3933 so, the first branch is redirected to either the destination of the
3934 second branch or a point immediately following it, depending on whether
3935 the condition is known to be true or false.
3937 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
3939 @item -fcse-follow-jumps
3940 @opindex fcse-follow-jumps
3941 In common subexpression elimination, scan through jump instructions
3942 when the target of the jump is not reached by any other path. For
3943 example, when CSE encounters an @code{if} statement with an
3944 @code{else} clause, CSE will follow the jump when the condition
3947 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3949 @item -fcse-skip-blocks
3950 @opindex fcse-skip-blocks
3951 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
3952 follow jumps which conditionally skip over blocks. When CSE
3953 encounters a simple @code{if} statement with no else clause,
3954 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
3955 body of the @code{if}.
3957 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3959 @item -frerun-cse-after-loop
3960 @opindex frerun-cse-after-loop
3961 Re-run common subexpression elimination after loop optimizations has been
3964 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3966 @item -frerun-loop-opt
3967 @opindex frerun-loop-opt
3968 Run the loop optimizer twice.
3970 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3974 Perform a global common subexpression elimination pass.
3975 This pass also performs global constant and copy propagation.
3977 @emph{Note:} When compiling a program using computed gotos, a GCC
3978 extension, you may get better runtime performance if you disable
3979 the global common subexpression elimination pass by adding
3980 @option{-fno-gcse} to the command line.
3982 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
3986 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
3987 attempt to move loads which are only killed by stores into themselves. This
3988 allows a loop containing a load/store sequence to be changed to a load outside
3989 the loop, and a copy/store within the loop.
3991 Enabled by default when gcse is enabled.
3995 When @option{-fgcse-sm} is enabled, A store motion pass is run after global common
3996 subexpression elimination. This pass will attempt to move stores out of loops.
3997 When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence
3998 can be changed to a load before the loop and a store after the loop.
4000 Enabled by default when gcse is enabled.
4002 @item -floop-optimize
4003 @opindex floop-optimize
4004 Perform loop optimizations: move constant expressions out of loops, simplify
4005 exit test conditions and optionally do strength-reduction and loop unrolling as
4008 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4010 @item -fcrossjumping
4011 @opindex crossjumping
4012 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4013 resulting code may or may not perform better than without cross-jumping.
4015 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4017 @item -fif-conversion
4018 @opindex if-conversion
4019 Attempt to transform conditional jumps into branch-less equivalents. This
4020 include use of conditional moves, min, max, set flags and abs instructions, and
4021 some tricks doable by standard arithmetics. The use of conditional execution
4022 on chips where it is available is controlled by @code{if-conversion2}.
4024 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4026 @item -fif-conversion2
4027 @opindex if-conversion2
4028 Use conditional execution (where available) to transform conditional jumps into
4029 branch-less equivalents.
4031 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4033 @item -fdelete-null-pointer-checks
4034 @opindex fdelete-null-pointer-checks
4035 Use global dataflow analysis to identify and eliminate useless checks
4036 for null pointers. The compiler assumes that dereferencing a null
4037 pointer would have halted the program. If a pointer is checked after
4038 it has already been dereferenced, it cannot be null.
4040 In some environments, this assumption is not true, and programs can
4041 safely dereference null pointers. Use
4042 @option{-fno-delete-null-pointer-checks} to disable this optimization
4043 for programs which depend on that behavior.
4045 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4047 @item -fexpensive-optimizations
4048 @opindex fexpensive-optimizations
4049 Perform a number of minor optimizations that are relatively expensive.
4051 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4053 @item -foptimize-register-move
4055 @opindex foptimize-register-move
4057 Attempt to reassign register numbers in move instructions and as
4058 operands of other simple instructions in order to maximize the amount of
4059 register tying. This is especially helpful on machines with two-operand
4062 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4065 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4067 @item -fdelayed-branch
4068 @opindex fdelayed-branch
4069 If supported for the target machine, attempt to reorder instructions
4070 to exploit instruction slots available after delayed branch
4073 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4075 @item -fschedule-insns
4076 @opindex fschedule-insns
4077 If supported for the target machine, attempt to reorder instructions to
4078 eliminate execution stalls due to required data being unavailable. This
4079 helps machines that have slow floating point or memory load instructions
4080 by allowing other instructions to be issued until the result of the load
4081 or floating point instruction is required.
4083 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4085 @item -fschedule-insns2
4086 @opindex fschedule-insns2
4087 Similar to @option{-fschedule-insns}, but requests an additional pass of
4088 instruction scheduling after register allocation has been done. This is
4089 especially useful on machines with a relatively small number of
4090 registers and where memory load instructions take more than one cycle.
4092 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4094 @item -fno-sched-interblock
4095 @opindex fno-sched-interblock
4096 Don't schedule instructions across basic blocks. This is normally
4097 enabled by default when scheduling before register allocation, i.e.@:
4098 with @option{-fschedule-insns} or at @option{-O2} or higher.
4100 @item -fno-sched-spec
4101 @opindex fno-sched-spec
4102 Don't allow speculative motion of non-load instructions. This is normally
4103 enabled by default when scheduling before register allocation, i.e.@:
4104 with @option{-fschedule-insns} or at @option{-O2} or higher.
4106 @item -fsched-spec-load
4107 @opindex fsched-spec-load
4108 Allow speculative motion of some load instructions. This only makes
4109 sense when scheduling before register allocation, i.e.@: with
4110 @option{-fschedule-insns} or at @option{-O2} or higher.
4112 @item -fsched-spec-load-dangerous
4113 @opindex fsched-spec-load-dangerous
4114 Allow speculative motion of more load instructions. This only makes
4115 sense when scheduling before register allocation, i.e.@: with
4116 @option{-fschedule-insns} or at @option{-O2} or higher.
4118 @item -fsched2-use-superblocks
4119 @opindex fsched2-use-superblocks
4120 When scheduling after register allocation, do use superblock scheduling
4121 algorithm. Superblock scheduling allows motion across basic block boundaries
4122 resulting on faster schedules. This option is experimental, as not all machine
4123 descriptions used by GCC model the CPU closely enough to avoid unreliable
4124 results from the algorithm.
4126 This only makes sense when scheduling after register allocation, i.e.@: with
4127 @option{-fschedule-insns2} or at @option{-O2} or higher.
4129 @item -fsched2-use-traces
4130 @opindex fsched2-use-traces
4131 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4132 allocation and additionally perform code duplication in order to increase the
4133 size of superblocks using tracer pass. See @option{-ftracer} for details on
4136 This mode should produce faster but significantly longer programs. Also
4137 without @code{-fbranch-probabilities} the traces constructed may not match the
4138 reality and hurt the performance. This only makes
4139 sense when scheduling after register allocation, i.e.@: with
4140 @option{-fschedule-insns2} or at @option{-O2} or higher.
4142 @item -fcaller-saves
4143 @opindex fcaller-saves
4144 Enable values to be allocated in registers that will be clobbered by
4145 function calls, by emitting extra instructions to save and restore the
4146 registers around such calls. Such allocation is done only when it
4147 seems to result in better code than would otherwise be produced.
4149 This option is always enabled by default on certain machines, usually
4150 those which have no call-preserved registers to use instead.
4152 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4154 @item -fmove-all-movables
4155 @opindex fmove-all-movables
4156 Forces all invariant computations in loops to be moved
4159 @item -freduce-all-givs
4160 @opindex freduce-all-givs
4161 Forces all general-induction variables in loops to be
4164 @emph{Note:} When compiling programs written in Fortran,
4165 @option{-fmove-all-movables} and @option{-freduce-all-givs} are enabled
4166 by default when you use the optimizer.
4168 These options may generate better or worse code; results are highly
4169 dependent on the structure of loops within the source code.
4171 These two options are intended to be removed someday, once
4172 they have helped determine the efficacy of various
4173 approaches to improving loop optimizations.
4175 Please let us (@w{@email{gcc@@gcc.gnu.org}} and @w{@email{fortran@@gnu.org}})
4176 know how use of these options affects
4177 the performance of your production code.
4178 We're very interested in code that runs @emph{slower}
4179 when these options are @emph{enabled}.
4182 @itemx -fno-peephole2
4183 @opindex fno-peephole
4184 @opindex fno-peephole2
4185 Disable any machine-specific peephole optimizations. The difference
4186 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4187 are implemented in the compiler; some targets use one, some use the
4188 other, a few use both.
4190 @option{-fpeephole} is enabled by default.
4191 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4193 @item -fno-guess-branch-probability
4194 @opindex fno-guess-branch-probability
4195 Do not guess branch probabilities using a randomized model.
4197 Sometimes gcc will opt to use a randomized model to guess branch
4198 probabilities, when none are available from either profiling feedback
4199 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4200 different runs of the compiler on the same program may produce different
4203 In a hard real-time system, people don't want different runs of the
4204 compiler to produce code that has different behavior; minimizing
4205 non-determinism is of paramount import. This switch allows users to
4206 reduce non-determinism, possibly at the expense of inferior
4209 The default is @option{-fguess-branch-probability} at levels
4210 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4212 @item -freorder-blocks
4213 @opindex freorder-blocks
4214 Reorder basic blocks in the compiled function in order to reduce number of
4215 taken branches and improve code locality.
4217 Enabled at levels @option{-O2}, @option{-O3}.
4219 @item -freorder-functions
4220 @opindex freorder-functions
4221 Reorder basic blocks in the compiled function in order to reduce number of
4222 taken branches and improve code locality. This is implemented by using special
4223 subsections @code{text.hot} for most frequently executed functions and
4224 @code{text.unlikely} for unlikely executed functions. Reordering is done by
4225 the linker so object file format must support named sections and linker must
4226 place them in a reasonable way.
4228 Also profile feedback must be available in to make this option effective. See
4229 @option{-fprofile-arcs} for details.
4231 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4233 @item -fstrict-aliasing
4234 @opindex fstrict-aliasing
4235 Allows the compiler to assume the strictest aliasing rules applicable to
4236 the language being compiled. For C (and C++), this activates
4237 optimizations based on the type of expressions. In particular, an
4238 object of one type is assumed never to reside at the same address as an
4239 object of a different type, unless the types are almost the same. For
4240 example, an @code{unsigned int} can alias an @code{int}, but not a
4241 @code{void*} or a @code{double}. A character type may alias any other
4244 Pay special attention to code like this:
4257 The practice of reading from a different union member than the one most
4258 recently written to (called ``type-punning'') is common. Even with
4259 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4260 is accessed through the union type. So, the code above will work as
4261 expected. However, this code might not:
4272 Every language that wishes to perform language-specific alias analysis
4273 should define a function that computes, given an @code{tree}
4274 node, an alias set for the node. Nodes in different alias sets are not
4275 allowed to alias. For an example, see the C front-end function
4276 @code{c_get_alias_set}.
4278 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4280 @item -falign-functions
4281 @itemx -falign-functions=@var{n}
4282 @opindex falign-functions
4283 Align the start of functions to the next power-of-two greater than
4284 @var{n}, skipping up to @var{n} bytes. For instance,
4285 @option{-falign-functions=32} aligns functions to the next 32-byte
4286 boundary, but @option{-falign-functions=24} would align to the next
4287 32-byte boundary only if this can be done by skipping 23 bytes or less.
4289 @option{-fno-align-functions} and @option{-falign-functions=1} are
4290 equivalent and mean that functions will not be aligned.
4292 Some assemblers only support this flag when @var{n} is a power of two;
4293 in that case, it is rounded up.
4295 If @var{n} is not specified or is zero, use a machine-dependent default.
4297 Enabled at levels @option{-O2}, @option{-O3}.
4299 @item -falign-labels
4300 @itemx -falign-labels=@var{n}
4301 @opindex falign-labels
4302 Align all branch targets to a power-of-two boundary, skipping up to
4303 @var{n} bytes like @option{-falign-functions}. This option can easily
4304 make code slower, because it must insert dummy operations for when the
4305 branch target is reached in the usual flow of the code.
4307 @option{-fno-align-labels} and @option{-falign-labels=1} are
4308 equivalent and mean that labels will not be aligned.
4310 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4311 are greater than this value, then their values are used instead.
4313 If @var{n} is not specified or is zero, use a machine-dependent default
4314 which is very likely to be @samp{1}, meaning no alignment.
4316 Enabled at levels @option{-O2}, @option{-O3}.
4319 @itemx -falign-loops=@var{n}
4320 @opindex falign-loops
4321 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4322 like @option{-falign-functions}. The hope is that the loop will be
4323 executed many times, which will make up for any execution of the dummy
4326 @option{-fno-align-loops} and @option{-falign-loops=1} are
4327 equivalent and mean that loops will not be aligned.
4329 If @var{n} is not specified or is zero, use a machine-dependent default.
4331 Enabled at levels @option{-O2}, @option{-O3}.
4334 @itemx -falign-jumps=@var{n}
4335 @opindex falign-jumps
4336 Align branch targets to a power-of-two boundary, for branch targets
4337 where the targets can only be reached by jumping, skipping up to @var{n}
4338 bytes like @option{-falign-functions}. In this case, no dummy operations
4341 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4342 equivalent and mean that loops will not be aligned.
4344 If @var{n} is not specified or is zero, use a machine-dependent default.
4346 Enabled at levels @option{-O2}, @option{-O3}.
4348 @item -frename-registers
4349 @opindex frename-registers
4350 Attempt to avoid false dependencies in scheduled code by making use
4351 of registers left over after register allocation. This optimization
4352 will most benefit processors with lots of registers. It can, however,
4353 make debugging impossible, since variables will no longer stay in
4354 a ``home register''.
4356 Enabled at levels @option{-O3}.
4358 @item -fno-cprop-registers
4359 @opindex fno-cprop-registers
4360 After register allocation and post-register allocation instruction splitting,
4361 we perform a copy-propagation pass to try to reduce scheduling dependencies
4362 and occasionally eliminate the copy.
4364 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4368 The following options control compiler behavior regarding floating
4369 point arithmetic. These options trade off between speed and
4370 correctness. All must be specifically enabled.
4374 @opindex ffloat-store
4375 Do not store floating point variables in registers, and inhibit other
4376 options that might change whether a floating point value is taken from a
4379 @cindex floating point precision
4380 This option prevents undesirable excess precision on machines such as
4381 the 68000 where the floating registers (of the 68881) keep more
4382 precision than a @code{double} is supposed to have. Similarly for the
4383 x86 architecture. For most programs, the excess precision does only
4384 good, but a few programs rely on the precise definition of IEEE floating
4385 point. Use @option{-ffloat-store} for such programs, after modifying
4386 them to store all pertinent intermediate computations into variables.
4390 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
4391 @option{-fno-trapping-math}, @option{-ffinite-math-only},
4392 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
4394 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
4396 This option should never be turned on by any @option{-O} option since
4397 it can result in incorrect output for programs which depend on
4398 an exact implementation of IEEE or ISO rules/specifications for
4401 @item -fno-math-errno
4402 @opindex fno-math-errno
4403 Do not set ERRNO after calling math functions that are executed
4404 with a single instruction, e.g., sqrt. A program that relies on
4405 IEEE exceptions for math error handling may want to use this flag
4406 for speed while maintaining IEEE arithmetic compatibility.
4408 This option should never be turned on by any @option{-O} option since
4409 it can result in incorrect output for programs which depend on
4410 an exact implementation of IEEE or ISO rules/specifications for
4413 The default is @option{-fmath-errno}.
4415 @item -funsafe-math-optimizations
4416 @opindex funsafe-math-optimizations
4417 Allow optimizations for floating-point arithmetic that (a) assume
4418 that arguments and results are valid and (b) may violate IEEE or
4419 ANSI standards. When used at link-time, it may include libraries
4420 or startup files that change the default FPU control word or other
4421 similar optimizations.
4423 This option should never be turned on by any @option{-O} option since
4424 it can result in incorrect output for programs which depend on
4425 an exact implementation of IEEE or ISO rules/specifications for
4428 The default is @option{-fno-unsafe-math-optimizations}.
4430 @item -ffinite-math-only
4431 @opindex ffinite-math-only
4432 Allow optimizations for floating-point arithmetic that assume
4433 that arguments and results are not NaNs or +-Infs.
4435 This option should never be turned on by any @option{-O} option since
4436 it can result in incorrect output for programs which depend on
4437 an exact implementation of IEEE or ISO rules/specifications.
4439 The default is @option{-fno-finite-math-only}.
4441 @item -fno-trapping-math
4442 @opindex fno-trapping-math
4443 Compile code assuming that floating-point operations cannot generate
4444 user-visible traps. These traps include division by zero, overflow,
4445 underflow, inexact result and invalid operation. This option implies
4446 @option{-fno-signaling-nans}. Setting this option may allow faster
4447 code if one relies on ``non-stop'' IEEE arithmetic, for example.
4449 This option should never be turned on by any @option{-O} option since
4450 it can result in incorrect output for programs which depend on
4451 an exact implementation of IEEE or ISO rules/specifications for
4454 The default is @option{-ftrapping-math}.
4456 @item -frounding-math
4457 @opindex frounding-math
4458 Disable transformations and optimizations that assume default floating
4459 point rounding behavior. This is round-to-zero for all floating point
4460 to integer conversions, and round-to-nearest for all other arithmetic
4461 truncations. This option should be specified for programs that change
4462 the FP rounding mode dynamically, or that may be executed with a
4463 non-default rounding mode. This option disables constant folding of
4464 floating point expressions at compile-time (which may be affected by
4465 rounding mode) and arithmetic transformations that are unsafe in the
4466 presence of sign-dependent rounding modes.
4468 The default is @option{-fno-rounding-math}.
4470 This option is experimental and does not currently guarantee to
4471 disable all GCC optimizations that are affected by rounding mode.
4472 Future versions of gcc may provide finer control of this setting
4473 using C99's @code{FENV_ACCESS} pragma. This command line option
4474 will be used to specify the default state for @code{FENV_ACCESS}.
4476 @item -fsignaling-nans
4477 @opindex fsignaling-nans
4478 Compile code assuming that IEEE signaling NaNs may generate user-visible
4479 traps during floating-point operations. Setting this option disables
4480 optimizations that may change the number of exceptions visible with
4481 signaling NaNs. This option implies @option{-ftrapping-math}.
4483 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
4486 The default is @option{-fno-signaling-nans}.
4488 This option is experimental and does not currently guarantee to
4489 disable all GCC optimizations that affect signaling NaN behavior.
4491 @item -fsingle-precision-constant
4492 @opindex fsingle-precision-constant
4493 Treat floating point constant as single precision constant instead of
4494 implicitly converting it to double precision constant.
4499 The following options control optimizations that may improve
4500 performance, but are not enabled by any @option{-O} options. This
4501 section includes experimental options that may produce broken code.
4504 @item -fbranch-probabilities
4505 @opindex fbranch-probabilities
4506 After running a program compiled with @option{-fprofile-arcs}
4507 (@pxref{Debugging Options,, Options for Debugging Your Program or
4508 @command{gcc}}), you can compile it a second time using
4509 @option{-fbranch-probabilities}, to improve optimizations based on
4510 the number of times each branch was taken. When the program
4511 compiled with @option{-fprofile-arcs} exits it saves arc execution
4512 counts to a file called @file{@var{sourcename}.gcda} for each source
4513 file The information in this data file is very dependent on the
4514 structure of the generated code, so you must use the same source code
4515 and the same optimization options for both compilations.
4517 With @option{-fbranch-probabilities}, GCC puts a
4518 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
4519 These can be used to improve optimization. Currently, they are only
4520 used in one place: in @file{reorg.c}, instead of guessing which path a
4521 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
4522 exactly determine which path is taken more often.
4524 @item -fprofile-values
4525 @opindex fprofile-values
4526 If combined with @option{-fprofile-arcs}, it adds code so that some
4527 data about values of expressions in the program is gathered.
4529 With @option{-fbranch-probabilities}, it reads back the data gathered
4530 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
4531 notes to instructions for their later usage in optimizations.
4535 Use a graph coloring register allocator. Currently this option is meant
4536 for testing, so we are interested to hear about miscompilations with
4541 Perform tail duplication to enlarge superblock size. This transformation
4542 simplifies the control flow of the function allowing other optimizations to do
4545 @item -funit-at-a-time
4546 @opindex funit-at-a-time
4547 Parse the whole compilation unit before starting to produce code.
4548 This allows some extra optimizations to take place but consumes more
4551 @item -funroll-loops
4552 @opindex funroll-loops
4553 Unroll loops whose number of iterations can be determined at compile time or
4554 upon entry to the loop. @option{-funroll-loops} implies
4555 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
4556 (i.e. complete removal of loops with small constant number of iterations).
4557 This option makes code larger, and may or may not make it run faster.
4559 @item -funroll-all-loops
4560 @opindex funroll-all-loops
4561 Unroll all loops, even if their number of iterations is uncertain when
4562 the loop is entered. This usually makes programs run more slowly.
4563 @option{-funroll-all-loops} implies the same options as
4564 @option{-funroll-loops}.
4567 @opindex fpeel-loops
4568 Peels the loops for that there is enough information that they do not
4569 roll much (from profile feedback). It also turns on complete loop peeling
4570 (i.e. complete removal of loops with small constant number of iterations).
4572 @item -funswitch-loops
4573 @opindex funswitch-loops
4574 Move branches with loop invariant conditions out of the loop, with duplicates
4575 of the loop on both branches (modified according to result of the condition).
4577 @item -fold-unroll-loops
4578 @opindex fold-unroll-loops
4579 Unroll loops whose number of iterations can be determined at compile
4580 time or upon entry to the loop, using the old loop unroller whose loop
4581 recognition is based on notes from frontend. @option{-fold-unroll-loops} implies
4582 both @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4583 option makes code larger, and may or may not make it run faster.
4585 @item -fold-unroll-all-loops
4586 @opindex fold-unroll-all-loops
4587 Unroll all loops, even if their number of iterations is uncertain when
4588 the loop is entered. This is done using the old loop unroller whose loop
4589 recognition is based on notes from frontend. This usually makes programs run more slowly.
4590 @option{-fold-unroll-all-loops} implies the same options as
4591 @option{-fold-unroll-loops}.
4593 @item -funswitch-loops
4594 @opindex funswitch-loops
4595 Move branches with loop invariant conditions out of the loop, with duplicates
4596 of the loop on both branches (modified according to result of the condition).
4598 @item -funswitch-loops
4599 @opindex funswitch-loops
4600 Move branches with loop invariant conditions out of the loop, with duplicates
4601 of the loop on both branches (modified according to result of the condition).
4603 @item -fprefetch-loop-arrays
4604 @opindex fprefetch-loop-arrays
4605 If supported by the target machine, generate instructions to prefetch
4606 memory to improve the performance of loops that access large arrays.
4608 Disabled at level @option{-Os}.
4610 @item -ffunction-sections
4611 @itemx -fdata-sections
4612 @opindex ffunction-sections
4613 @opindex fdata-sections
4614 Place each function or data item into its own section in the output
4615 file if the target supports arbitrary sections. The name of the
4616 function or the name of the data item determines the section's name
4619 Use these options on systems where the linker can perform optimizations
4620 to improve locality of reference in the instruction space. Most systems
4621 using the ELF object format and SPARC processors running Solaris 2 have
4622 linkers with such optimizations. AIX may have these optimizations in
4625 Only use these options when there are significant benefits from doing
4626 so. When you specify these options, the assembler and linker will
4627 create larger object and executable files and will also be slower.
4628 You will not be able to use @code{gprof} on all systems if you
4629 specify this option and you may have problems with debugging if
4630 you specify both this option and @option{-g}.
4634 Perform optimizations in static single assignment form. Each function's
4635 flow graph is translated into SSA form, optimizations are performed, and
4636 the flow graph is translated back from SSA form. Users should not
4637 specify this option, since it is not yet ready for production use.
4641 Perform Sparse Conditional Constant Propagation in SSA form. Requires
4642 @option{-fssa}. Like @option{-fssa}, this is an experimental feature.
4646 Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
4647 Like @option{-fssa}, this is an experimental feature.
4649 @item -fbranch-target-load-optimize
4650 @opindex fbranch-target-load-optimize
4651 Perform branch target register load optimization before prologue / epilogue
4653 The use of target registers can typically be exposed only during reload,
4654 thus hoisting loads out of loops and doing inter-block scheduling needs
4655 a separate optimization pass.
4657 @item -fbranch-target-load-optimize2
4658 @opindex fbranch-target-load-optimize2
4659 Perform branch target register load optimization after prologue / epilogue
4665 @item --param @var{name}=@var{value}
4667 In some places, GCC uses various constants to control the amount of
4668 optimization that is done. For example, GCC will not inline functions
4669 that contain more that a certain number of instructions. You can
4670 control some of these constants on the command-line using the
4671 @option{--param} option.
4673 In each case, the @var{value} is an integer. The allowable choices for
4674 @var{name} are given in the following table:
4677 @item max-crossjump-edges
4678 The maximum number of incoming edges to consider for crossjumping.
4679 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
4680 the number of edges incoming to each block. Increasing values mean
4681 more aggressive optimization, making the compile time increase with
4682 probably small improvement in executable size.
4684 @item max-delay-slot-insn-search
4685 The maximum number of instructions to consider when looking for an
4686 instruction to fill a delay slot. If more than this arbitrary number of
4687 instructions is searched, the time savings from filling the delay slot
4688 will be minimal so stop searching. Increasing values mean more
4689 aggressive optimization, making the compile time increase with probably
4690 small improvement in executable run time.
4692 @item max-delay-slot-live-search
4693 When trying to fill delay slots, the maximum number of instructions to
4694 consider when searching for a block with valid live register
4695 information. Increasing this arbitrarily chosen value means more
4696 aggressive optimization, increasing the compile time. This parameter
4697 should be removed when the delay slot code is rewritten to maintain the
4700 @item max-gcse-memory
4701 The approximate maximum amount of memory that will be allocated in
4702 order to perform the global common subexpression elimination
4703 optimization. If more memory than specified is required, the
4704 optimization will not be done.
4706 @item max-gcse-passes
4707 The maximum number of passes of GCSE to run.
4709 @item max-pending-list-length
4710 The maximum number of pending dependencies scheduling will allow
4711 before flushing the current state and starting over. Large functions
4712 with few branches or calls can create excessively large lists which
4713 needlessly consume memory and resources.
4715 @item max-inline-insns-single
4716 Several parameters control the tree inliner used in gcc.
4717 This number sets the maximum number of instructions (counted in gcc's
4718 internal representation) in a single function that the tree inliner
4719 will consider for inlining. This only affects functions declared
4720 inline and methods implemented in a class declaration (C++).
4721 The default value is 500.
4723 @item max-inline-insns-auto
4724 When you use @option{-finline-functions} (included in @option{-O3}),
4725 a lot of functions that would otherwise not be considered for inlining
4726 by the compiler will be investigated. To those functions, a different
4727 (more restrictive) limit compared to functions declared inline can
4729 The default value is 150.
4731 @item max-inline-insns
4732 The tree inliner does decrease the allowable size for single functions
4733 to be inlined after we already inlined the number of instructions
4734 given here by repeated inlining. This number should be a factor of
4735 two or more larger than the single function limit.
4736 Higher numbers result in better runtime performance, but incur higher
4737 compile-time resource (CPU time, memory) requirements and result in
4738 larger binaries. Very high values are not advisable, as too large
4739 binaries may adversely affect runtime performance.
4740 The default value is 200.
4742 @item max-inline-slope
4743 After exceeding the maximum number of inlined instructions by repeated
4744 inlining, a linear function is used to decrease the allowable size
4745 for single functions. The slope of that function is the negative
4746 reciprocal of the number specified here.
4747 This parameter is ignored when @option{-funit-at-a-time} is used.
4748 The default value is 32.
4750 @item min-inline-insns
4751 The repeated inlining is throttled more and more by the linear function
4752 after exceeding the limit. To avoid too much throttling, a minimum for
4753 this function is specified here to allow repeated inlining for very small
4754 functions even when a lot of repeated inlining already has been done.
4755 This parameter is ignored when @option{-funit-at-a-time} is used.
4756 The default value is 10.
4758 @item large-function-insns
4759 The limit specifying really large functions. For functions greater than this
4760 limit inlining is constrained by @option{--param large-function-growth}.
4761 This parameter is useful primarily to avoid extreme compilation time caused by non-linear
4762 algorithms used by the backend.
4763 This parameter is ignored when @option{-funit-at-a-time} is not used.
4764 The default value is 30000.
4766 @item large-function-growth
4767 Specifies maximal growth of large functtion caused by inlining in percents.
4768 This parameter is ignored when @option{-funit-at-a-time} is not used.
4769 The default value is 200.
4771 @item inline-unit-growth
4772 Specifies maximal overall growth of the compilation unit caused by inlining.
4773 This parameter is ignored when @option{-funit-at-a-time} is not used.
4774 The default value is 150.
4776 @item max-inline-insns-rtl
4777 For languages that use the RTL inliner (this happens at a later stage
4778 than tree inlining), you can set the maximum allowable size (counted
4779 in RTL instructions) for the RTL inliner with this parameter.
4780 The default value is 600.
4783 @item max-unrolled-insns
4784 The maximum number of instructions that a loop should have if that loop
4785 is unrolled, and if the loop is unrolled, it determines how many times
4786 the loop code is unrolled.
4788 @item max-average-unrolled-insns
4789 The maximum number of instructions biased by probabilities of their execution
4790 that a loop should have if that loop is unrolled, and if the loop is unrolled,
4791 it determines how many times the loop code is unrolled.
4793 @item max-unroll-times
4794 The maximum number of unrollings of a single loop.
4796 @item max-peeled-insns
4797 The maximum number of instructions that a loop should have if that loop
4798 is peeled, and if the loop is peeled, it determines how many times
4799 the loop code is peeled.
4801 @item max-peel-times
4802 The maximum number of peelings of a single loop.
4804 @item max-completely-peeled-insns
4805 The maximum number of insns of a completely peeled loop.
4807 @item max-completely-peel-times
4808 The maximum number of iterations of a loop to be suitable for complete peeling.
4810 @item max-unswitch-insns
4811 The maximum number of insns of an unswitched loop.
4813 @item max-unswitch-level
4814 The maximum number of branches unswitched in a single loop.
4816 @item hot-bb-count-fraction
4817 Select fraction of the maximal count of repetitions of basic block in program
4818 given basic block needs to have to be considered hot.
4820 @item hot-bb-frequency-fraction
4821 Select fraction of the maximal frequency of executions of basic block in
4822 function given basic block needs to have to be considered hot
4824 @item tracer-dynamic-coverage
4825 @itemx tracer-dynamic-coverage-feedback
4827 This value is used to limit superblock formation once the given percentage of
4828 executed instructions is covered. This limits unnecessary code size
4831 The @option{tracer-dynamic-coverage-feedback} is used only when profile
4832 feedback is available. The real profiles (as opposed to statically estimated
4833 ones) are much less balanced allowing the threshold to be larger value.
4835 @item tracer-max-code-growth
4836 Stop tail duplication once code growth has reached given percentage. This is
4837 rather hokey argument, as most of the duplicates will be eliminated later in
4838 cross jumping, so it may be set to much higher values than is the desired code
4841 @item tracer-min-branch-ratio
4843 Stop reverse growth when the reverse probability of best edge is less than this
4844 threshold (in percent).
4846 @item tracer-min-branch-ratio
4847 @itemx tracer-min-branch-ratio-feedback
4849 Stop forward growth if the best edge do have probability lower than this
4852 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
4853 compilation for profile feedback and one for compilation without. The value
4854 for compilation with profile feedback needs to be more conservative (higher) in
4855 order to make tracer effective.
4857 @item max-cse-path-length
4859 Maximum number of basic blocks on path that cse considers.
4861 @item ggc-min-expand
4863 GCC uses a garbage collector to manage its own memory allocation. This
4864 parameter specifies the minimum percentage by which the garbage
4865 collector's heap should be allowed to expand between collections.
4866 Tuning this may improve compilation speed; it has no effect on code
4869 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
4870 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
4871 the smallest of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If
4872 GCC is not able to calculate RAM on a particular platform, the lower
4873 bound of 30% is used. Setting this parameter and
4874 @option{ggc-min-heapsize} to zero causes a full collection to occur at
4875 every opportunity. This is extremely slow, but can be useful for
4878 @item ggc-min-heapsize
4880 Minimum size of the garbage collector's heap before it begins bothering
4881 to collect garbage. The first collection occurs after the heap expands
4882 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
4883 tuning this may improve compilation speed, and has no effect on code
4886 The default is RAM/8, with a lower bound of 4096 (four megabytes) and an
4887 upper bound of 131072 (128 megabytes). If @code{getrlimit} is
4888 available, the notion of "RAM" is the smallest of actual RAM,
4889 RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS. If GCC is not able to calculate
4890 RAM on a particular platform, the lower bound is used. Setting this
4891 parameter very large effectively disables garbage collection. Setting
4892 this parameter and @option{ggc-min-expand} to zero causes a full
4893 collection to occur at every opportunity.
4895 @item reorder-blocks-duplicate
4896 @itemx reorder-blocks-duplicate-feedback
4898 Used by basic block reordering pass to decide whether to use unconditional
4899 branch or duplicate the code on its destination. Code is duplicated when its
4900 estimated size is smaller than this value multiplied by the estimated size of
4901 unconditional jump in the hot spots of the program.
4903 The @option{reorder-block-duplicate-feedback} is used only when profile
4904 feedback is available and may be set to higher values than
4905 @option{reorder-block-duplicate} since information about the hot spots is more
4910 @node Preprocessor Options
4911 @section Options Controlling the Preprocessor
4912 @cindex preprocessor options
4913 @cindex options, preprocessor
4915 These options control the C preprocessor, which is run on each C source
4916 file before actual compilation.
4918 If you use the @option{-E} option, nothing is done except preprocessing.
4919 Some of these options make sense only together with @option{-E} because
4920 they cause the preprocessor output to be unsuitable for actual
4925 You can use @option{-Wp,@var{option}} to bypass the compiler driver
4926 and pass @var{option} directly through to the preprocessor. If
4927 @var{option} contains commas, it is split into multiple options at the
4928 commas. However, many options are modified, translated or interpreted
4929 by the compiler driver before being passed to the preprocessor, and
4930 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
4931 interface is undocumented and subject to change, so whenever possible
4932 you should avoid using @option{-Wp} and let the driver handle the
4935 @item -Xpreprocessor @var{option}
4936 @opindex preprocessor
4937 Pass @var{option} as an option to the preprocessor. You can use this to
4938 supply system-specific preprocessor options which GCC does not know how to
4941 If you want to pass an option that takes an argument, you must use
4942 @option{-Xpreprocessor} twice, once for the option and once for the argument.
4945 @include cppopts.texi
4947 @node Assembler Options
4948 @section Passing Options to the Assembler
4950 @c prevent bad page break with this line
4951 You can pass options to the assembler.
4954 @item -Wa,@var{option}
4956 Pass @var{option} as an option to the assembler. If @var{option}
4957 contains commas, it is split into multiple options at the commas.
4959 @item -Xassembler @var{option}
4961 Pass @var{option} as an option to the assembler. You can use this to
4962 supply system-specific assembler options which GCC does not know how to
4965 If you want to pass an option that takes an argument, you must use
4966 @option{-Xassembler} twice, once for the option and once for the argument.
4971 @section Options for Linking
4972 @cindex link options
4973 @cindex options, linking
4975 These options come into play when the compiler links object files into
4976 an executable output file. They are meaningless if the compiler is
4977 not doing a link step.
4981 @item @var{object-file-name}
4982 A file name that does not end in a special recognized suffix is
4983 considered to name an object file or library. (Object files are
4984 distinguished from libraries by the linker according to the file
4985 contents.) If linking is done, these object files are used as input
4994 If any of these options is used, then the linker is not run, and
4995 object file names should not be used as arguments. @xref{Overall
4999 @item -l@var{library}
5000 @itemx -l @var{library}
5002 Search the library named @var{library} when linking. (The second
5003 alternative with the library as a separate argument is only for
5004 POSIX compliance and is not recommended.)
5006 It makes a difference where in the command you write this option; the
5007 linker searches and processes libraries and object files in the order they
5008 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
5009 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
5010 to functions in @samp{z}, those functions may not be loaded.
5012 The linker searches a standard list of directories for the library,
5013 which is actually a file named @file{lib@var{library}.a}. The linker
5014 then uses this file as if it had been specified precisely by name.
5016 The directories searched include several standard system directories
5017 plus any that you specify with @option{-L}.
5019 Normally the files found this way are library files---archive files
5020 whose members are object files. The linker handles an archive file by
5021 scanning through it for members which define symbols that have so far
5022 been referenced but not defined. But if the file that is found is an
5023 ordinary object file, it is linked in the usual fashion. The only
5024 difference between using an @option{-l} option and specifying a file name
5025 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
5026 and searches several directories.
5030 You need this special case of the @option{-l} option in order to
5031 link an Objective-C program.
5034 @opindex nostartfiles
5035 Do not use the standard system startup files when linking.
5036 The standard system libraries are used normally, unless @option{-nostdlib}
5037 or @option{-nodefaultlibs} is used.
5039 @item -nodefaultlibs
5040 @opindex nodefaultlibs
5041 Do not use the standard system libraries when linking.
5042 Only the libraries you specify will be passed to the linker.
5043 The standard startup files are used normally, unless @option{-nostartfiles}
5044 is used. The compiler may generate calls to memcmp, memset, and memcpy
5045 for System V (and ISO C) environments or to bcopy and bzero for
5046 BSD environments. These entries are usually resolved by entries in
5047 libc. These entry points should be supplied through some other
5048 mechanism when this option is specified.
5052 Do not use the standard system startup files or libraries when linking.
5053 No startup files and only the libraries you specify will be passed to
5054 the linker. The compiler may generate calls to memcmp, memset, and memcpy
5055 for System V (and ISO C) environments or to bcopy and bzero for
5056 BSD environments. These entries are usually resolved by entries in
5057 libc. These entry points should be supplied through some other
5058 mechanism when this option is specified.
5060 @cindex @option{-lgcc}, use with @option{-nostdlib}
5061 @cindex @option{-nostdlib} and unresolved references
5062 @cindex unresolved references and @option{-nostdlib}
5063 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
5064 @cindex @option{-nodefaultlibs} and unresolved references
5065 @cindex unresolved references and @option{-nodefaultlibs}
5066 One of the standard libraries bypassed by @option{-nostdlib} and
5067 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
5068 that GCC uses to overcome shortcomings of particular machines, or special
5069 needs for some languages.
5070 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
5071 Collection (GCC) Internals},
5072 for more discussion of @file{libgcc.a}.)
5073 In most cases, you need @file{libgcc.a} even when you want to avoid
5074 other standard libraries. In other words, when you specify @option{-nostdlib}
5075 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
5076 This ensures that you have no unresolved references to internal GCC
5077 library subroutines. (For example, @samp{__main}, used to ensure C++
5078 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
5079 GNU Compiler Collection (GCC) Internals}.)
5083 Produce a position independent executable on targets which support it.
5084 For predictable results, you must also specify the same set of options
5085 that were used to generate code (@option{-fpie}, @option{-fPIE},
5086 or model suboptions) when you specify this option.
5090 Remove all symbol table and relocation information from the executable.
5094 On systems that support dynamic linking, this prevents linking with the shared
5095 libraries. On other systems, this option has no effect.
5099 Produce a shared object which can then be linked with other objects to
5100 form an executable. Not all systems support this option. For predictable
5101 results, you must also specify the same set of options that were used to
5102 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
5103 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
5104 needs to build supplementary stub code for constructors to work. On
5105 multi-libbed systems, @samp{gcc -shared} must select the correct support
5106 libraries to link against. Failing to supply the correct flags may lead
5107 to subtle defects. Supplying them in cases where they are not necessary
5110 @item -shared-libgcc
5111 @itemx -static-libgcc
5112 @opindex shared-libgcc
5113 @opindex static-libgcc
5114 On systems that provide @file{libgcc} as a shared library, these options
5115 force the use of either the shared or static version respectively.
5116 If no shared version of @file{libgcc} was built when the compiler was
5117 configured, these options have no effect.
5119 There are several situations in which an application should use the
5120 shared @file{libgcc} instead of the static version. The most common
5121 of these is when the application wishes to throw and catch exceptions
5122 across different shared libraries. In that case, each of the libraries
5123 as well as the application itself should use the shared @file{libgcc}.
5125 Therefore, the G++ and GCJ drivers automatically add
5126 @option{-shared-libgcc} whenever you build a shared library or a main
5127 executable, because C++ and Java programs typically use exceptions, so
5128 this is the right thing to do.
5130 If, instead, you use the GCC driver to create shared libraries, you may
5131 find that they will not always be linked with the shared @file{libgcc}.
5132 If GCC finds, at its configuration time, that you have a GNU linker that
5133 does not support option @option{--eh-frame-hdr}, it will link the shared
5134 version of @file{libgcc} into shared libraries by default. Otherwise,
5135 it will take advantage of the linker and optimize away the linking with
5136 the shared version of @file{libgcc}, linking with the static version of
5137 libgcc by default. This allows exceptions to propagate through such
5138 shared libraries, without incurring relocation costs at library load
5141 However, if a library or main executable is supposed to throw or catch
5142 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5143 for the languages used in the program, or using the option
5144 @option{-shared-libgcc}, such that it is linked with the shared
5149 Bind references to global symbols when building a shared object. Warn
5150 about any unresolved references (unless overridden by the link editor
5151 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5154 @item -Xlinker @var{option}
5156 Pass @var{option} as an option to the linker. You can use this to
5157 supply system-specific linker options which GCC does not know how to
5160 If you want to pass an option that takes an argument, you must use
5161 @option{-Xlinker} twice, once for the option and once for the argument.
5162 For example, to pass @option{-assert definitions}, you must write
5163 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5164 @option{-Xlinker "-assert definitions"}, because this passes the entire
5165 string as a single argument, which is not what the linker expects.
5167 @item -Wl,@var{option}
5169 Pass @var{option} as an option to the linker. If @var{option} contains
5170 commas, it is split into multiple options at the commas.
5172 @item -u @var{symbol}
5174 Pretend the symbol @var{symbol} is undefined, to force linking of
5175 library modules to define it. You can use @option{-u} multiple times with
5176 different symbols to force loading of additional library modules.
5179 @node Directory Options
5180 @section Options for Directory Search
5181 @cindex directory options
5182 @cindex options, directory search
5185 These options specify directories to search for header files, for
5186 libraries and for parts of the compiler:
5191 Add the directory @var{dir} to the head of the list of directories to be
5192 searched for header files. This can be used to override a system header
5193 file, substituting your own version, since these directories are
5194 searched before the system header file directories. However, you should
5195 not use this option to add directories that contain vendor-supplied
5196 system header files (use @option{-isystem} for that). If you use more than
5197 one @option{-I} option, the directories are scanned in left-to-right
5198 order; the standard system directories come after.
5200 If a standard system include directory, or a directory specified with
5201 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5202 option will be ignored. The directory will still be searched but as a
5203 system directory at its normal position in the system include chain.
5204 This is to ensure that GCC's procedure to fix buggy system headers and
5205 the ordering for the include_next directive are not inadvertently changed.
5206 If you really need to change the search order for system directories,
5207 use the @option{-nostdinc} and/or @option{-isystem} options.
5211 Any directories you specify with @option{-I} options before the @option{-I-}
5212 option are searched only for the case of @samp{#include "@var{file}"};
5213 they are not searched for @samp{#include <@var{file}>}.
5215 If additional directories are specified with @option{-I} options after
5216 the @option{-I-}, these directories are searched for all @samp{#include}
5217 directives. (Ordinarily @emph{all} @option{-I} directories are used
5220 In addition, the @option{-I-} option inhibits the use of the current
5221 directory (where the current input file came from) as the first search
5222 directory for @samp{#include "@var{file}"}. There is no way to
5223 override this effect of @option{-I-}. With @option{-I.} you can specify
5224 searching the directory which was current when the compiler was
5225 invoked. That is not exactly the same as what the preprocessor does
5226 by default, but it is often satisfactory.
5228 @option{-I-} does not inhibit the use of the standard system directories
5229 for header files. Thus, @option{-I-} and @option{-nostdinc} are
5234 Add directory @var{dir} to the list of directories to be searched
5237 @item -B@var{prefix}
5239 This option specifies where to find the executables, libraries,
5240 include files, and data files of the compiler itself.
5242 The compiler driver program runs one or more of the subprograms
5243 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5244 @var{prefix} as a prefix for each program it tries to run, both with and
5245 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5247 For each subprogram to be run, the compiler driver first tries the
5248 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5249 was not specified, the driver tries two standard prefixes, which are
5250 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5251 those results in a file name that is found, the unmodified program
5252 name is searched for using the directories specified in your
5253 @env{PATH} environment variable.
5255 The compiler will check to see if the path provided by the @option{-B}
5256 refers to a directory, and if necessary it will add a directory
5257 separator character at the end of the path.
5259 @option{-B} prefixes that effectively specify directory names also apply
5260 to libraries in the linker, because the compiler translates these
5261 options into @option{-L} options for the linker. They also apply to
5262 includes files in the preprocessor, because the compiler translates these
5263 options into @option{-isystem} options for the preprocessor. In this case,
5264 the compiler appends @samp{include} to the prefix.
5266 The run-time support file @file{libgcc.a} can also be searched for using
5267 the @option{-B} prefix, if needed. If it is not found there, the two
5268 standard prefixes above are tried, and that is all. The file is left
5269 out of the link if it is not found by those means.
5271 Another way to specify a prefix much like the @option{-B} prefix is to use
5272 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5275 As a special kludge, if the path provided by @option{-B} is
5276 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5277 9, then it will be replaced by @file{[dir/]include}. This is to help
5278 with boot-strapping the compiler.
5280 @item -specs=@var{file}
5282 Process @var{file} after the compiler reads in the standard @file{specs}
5283 file, in order to override the defaults that the @file{gcc} driver
5284 program uses when determining what switches to pass to @file{cc1},
5285 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5286 @option{-specs=@var{file}} can be specified on the command line, and they
5287 are processed in order, from left to right.
5293 @section Specifying subprocesses and the switches to pass to them
5296 @command{gcc} is a driver program. It performs its job by invoking a
5297 sequence of other programs to do the work of compiling, assembling and
5298 linking. GCC interprets its command-line parameters and uses these to
5299 deduce which programs it should invoke, and which command-line options
5300 it ought to place on their command lines. This behavior is controlled
5301 by @dfn{spec strings}. In most cases there is one spec string for each
5302 program that GCC can invoke, but a few programs have multiple spec
5303 strings to control their behavior. The spec strings built into GCC can
5304 be overridden by using the @option{-specs=} command-line switch to specify
5307 @dfn{Spec files} are plaintext files that are used to construct spec
5308 strings. They consist of a sequence of directives separated by blank
5309 lines. The type of directive is determined by the first non-whitespace
5310 character on the line and it can be one of the following:
5313 @item %@var{command}
5314 Issues a @var{command} to the spec file processor. The commands that can
5318 @item %include <@var{file}>
5320 Search for @var{file} and insert its text at the current point in the
5323 @item %include_noerr <@var{file}>
5324 @cindex %include_noerr
5325 Just like @samp{%include}, but do not generate an error message if the include
5326 file cannot be found.
5328 @item %rename @var{old_name} @var{new_name}
5330 Rename the spec string @var{old_name} to @var{new_name}.
5334 @item *[@var{spec_name}]:
5335 This tells the compiler to create, override or delete the named spec
5336 string. All lines after this directive up to the next directive or
5337 blank line are considered to be the text for the spec string. If this
5338 results in an empty string then the spec will be deleted. (Or, if the
5339 spec did not exist, then nothing will happened.) Otherwise, if the spec
5340 does not currently exist a new spec will be created. If the spec does
5341 exist then its contents will be overridden by the text of this
5342 directive, unless the first character of that text is the @samp{+}
5343 character, in which case the text will be appended to the spec.
5345 @item [@var{suffix}]:
5346 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
5347 and up to the next directive or blank line are considered to make up the
5348 spec string for the indicated suffix. When the compiler encounters an
5349 input file with the named suffix, it will processes the spec string in
5350 order to work out how to compile that file. For example:
5357 This says that any input file whose name ends in @samp{.ZZ} should be
5358 passed to the program @samp{z-compile}, which should be invoked with the
5359 command-line switch @option{-input} and with the result of performing the
5360 @samp{%i} substitution. (See below.)
5362 As an alternative to providing a spec string, the text that follows a
5363 suffix directive can be one of the following:
5366 @item @@@var{language}
5367 This says that the suffix is an alias for a known @var{language}. This is
5368 similar to using the @option{-x} command-line switch to GCC to specify a
5369 language explicitly. For example:
5376 Says that .ZZ files are, in fact, C++ source files.
5379 This causes an error messages saying:
5382 @var{name} compiler not installed on this system.
5386 GCC already has an extensive list of suffixes built into it.
5387 This directive will add an entry to the end of the list of suffixes, but
5388 since the list is searched from the end backwards, it is effectively
5389 possible to override earlier entries using this technique.
5393 GCC has the following spec strings built into it. Spec files can
5394 override these strings or create their own. Note that individual
5395 targets can also add their own spec strings to this list.
5398 asm Options to pass to the assembler
5399 asm_final Options to pass to the assembler post-processor
5400 cpp Options to pass to the C preprocessor
5401 cc1 Options to pass to the C compiler
5402 cc1plus Options to pass to the C++ compiler
5403 endfile Object files to include at the end of the link
5404 link Options to pass to the linker
5405 lib Libraries to include on the command line to the linker
5406 libgcc Decides which GCC support library to pass to the linker
5407 linker Sets the name of the linker
5408 predefines Defines to be passed to the C preprocessor
5409 signed_char Defines to pass to CPP to say whether @code{char} is signed
5411 startfile Object files to include at the start of the link
5414 Here is a small example of a spec file:
5420 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
5423 This example renames the spec called @samp{lib} to @samp{old_lib} and
5424 then overrides the previous definition of @samp{lib} with a new one.
5425 The new definition adds in some extra command-line options before
5426 including the text of the old definition.
5428 @dfn{Spec strings} are a list of command-line options to be passed to their
5429 corresponding program. In addition, the spec strings can contain
5430 @samp{%}-prefixed sequences to substitute variable text or to
5431 conditionally insert text into the command line. Using these constructs
5432 it is possible to generate quite complex command lines.
5434 Here is a table of all defined @samp{%}-sequences for spec
5435 strings. Note that spaces are not generated automatically around the
5436 results of expanding these sequences. Therefore you can concatenate them
5437 together or combine them with constant text in a single argument.
5441 Substitute one @samp{%} into the program name or argument.
5444 Substitute the name of the input file being processed.
5447 Substitute the basename of the input file being processed.
5448 This is the substring up to (and not including) the last period
5449 and not including the directory.
5452 This is the same as @samp{%b}, but include the file suffix (text after
5456 Marks the argument containing or following the @samp{%d} as a
5457 temporary file name, so that that file will be deleted if GCC exits
5458 successfully. Unlike @samp{%g}, this contributes no text to the
5461 @item %g@var{suffix}
5462 Substitute a file name that has suffix @var{suffix} and is chosen
5463 once per compilation, and mark the argument in the same way as
5464 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
5465 name is now chosen in a way that is hard to predict even when previously
5466 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
5467 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
5468 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
5469 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
5470 was simply substituted with a file name chosen once per compilation,
5471 without regard to any appended suffix (which was therefore treated
5472 just like ordinary text), making such attacks more likely to succeed.
5474 @item %u@var{suffix}
5475 Like @samp{%g}, but generates a new temporary file name even if
5476 @samp{%u@var{suffix}} was already seen.
5478 @item %U@var{suffix}
5479 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
5480 new one if there is no such last file name. In the absence of any
5481 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
5482 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
5483 would involve the generation of two distinct file names, one
5484 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
5485 simply substituted with a file name chosen for the previous @samp{%u},
5486 without regard to any appended suffix.
5488 @item %j@var{suffix}
5489 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
5490 writable, and if save-temps is off; otherwise, substitute the name
5491 of a temporary file, just like @samp{%u}. This temporary file is not
5492 meant for communication between processes, but rather as a junk
5495 @item %|@var{suffix}
5496 @itemx %m@var{suffix}
5497 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
5498 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
5499 all. These are the two most common ways to instruct a program that it
5500 should read from standard input or write to standard output. If you
5501 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
5502 construct: see for example @file{f/lang-specs.h}.
5504 @item %.@var{SUFFIX}
5505 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
5506 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
5507 terminated by the next space or %.
5510 Marks the argument containing or following the @samp{%w} as the
5511 designated output file of this compilation. This puts the argument
5512 into the sequence of arguments that @samp{%o} will substitute later.
5515 Substitutes the names of all the output files, with spaces
5516 automatically placed around them. You should write spaces
5517 around the @samp{%o} as well or the results are undefined.
5518 @samp{%o} is for use in the specs for running the linker.
5519 Input files whose names have no recognized suffix are not compiled
5520 at all, but they are included among the output files, so they will
5524 Substitutes the suffix for object files. Note that this is
5525 handled specially when it immediately follows @samp{%g, %u, or %U},
5526 because of the need for those to form complete file names. The
5527 handling is such that @samp{%O} is treated exactly as if it had already
5528 been substituted, except that @samp{%g, %u, and %U} do not currently
5529 support additional @var{suffix} characters following @samp{%O} as they would
5530 following, for example, @samp{.o}.
5533 Substitutes the standard macro predefinitions for the
5534 current target machine. Use this when running @code{cpp}.
5537 Like @samp{%p}, but puts @samp{__} before and after the name of each
5538 predefined macro, except for macros that start with @samp{__} or with
5539 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
5543 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
5544 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
5545 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
5549 Current argument is the name of a library or startup file of some sort.
5550 Search for that file in a standard list of directories and substitute
5551 the full name found.
5554 Print @var{str} as an error message. @var{str} is terminated by a newline.
5555 Use this when inconsistent options are detected.
5558 Substitute the contents of spec string @var{name} at this point.
5561 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
5563 @item %x@{@var{option}@}
5564 Accumulate an option for @samp{%X}.
5567 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
5571 Output the accumulated assembler options specified by @option{-Wa}.
5574 Output the accumulated preprocessor options specified by @option{-Wp}.
5577 Process the @code{asm} spec. This is used to compute the
5578 switches to be passed to the assembler.
5581 Process the @code{asm_final} spec. This is a spec string for
5582 passing switches to an assembler post-processor, if such a program is
5586 Process the @code{link} spec. This is the spec for computing the
5587 command line passed to the linker. Typically it will make use of the
5588 @samp{%L %G %S %D and %E} sequences.
5591 Dump out a @option{-L} option for each directory that GCC believes might
5592 contain startup files. If the target supports multilibs then the
5593 current multilib directory will be prepended to each of these paths.
5596 Output the multilib directory with directory separators replaced with
5597 @samp{_}. If multilib directories are not set, or the multilib directory is
5598 @file{.} then this option emits nothing.
5601 Process the @code{lib} spec. This is a spec string for deciding which
5602 libraries should be included on the command line to the linker.
5605 Process the @code{libgcc} spec. This is a spec string for deciding
5606 which GCC support library should be included on the command line to the linker.
5609 Process the @code{startfile} spec. This is a spec for deciding which
5610 object files should be the first ones passed to the linker. Typically
5611 this might be a file named @file{crt0.o}.
5614 Process the @code{endfile} spec. This is a spec string that specifies
5615 the last object files that will be passed to the linker.
5618 Process the @code{cpp} spec. This is used to construct the arguments
5619 to be passed to the C preprocessor.
5622 Process the @code{signed_char} spec. This is intended to be used
5623 to tell cpp whether a char is signed. It typically has the definition:
5625 %@{funsigned-char:-D__CHAR_UNSIGNED__@}
5629 Process the @code{cc1} spec. This is used to construct the options to be
5630 passed to the actual C compiler (@samp{cc1}).
5633 Process the @code{cc1plus} spec. This is used to construct the options to be
5634 passed to the actual C++ compiler (@samp{cc1plus}).
5637 Substitute the variable part of a matched option. See below.
5638 Note that each comma in the substituted string is replaced by
5642 Remove all occurrences of @code{-S} from the command line. Note---this
5643 command is position dependent. @samp{%} commands in the spec string
5644 before this one will see @code{-S}, @samp{%} commands in the spec string
5645 after this one will not.
5647 @item %:@var{function}(@var{args})
5648 Call the named function @var{function}, passing it @var{args}.
5649 @var{args} is first processed as a nested spec string, then split
5650 into an argument vector in the usual fashion. The function returns
5651 a string which is processed as if it had appeared literally as part
5652 of the current spec.
5654 The following built-in spec functions are provided:
5657 @item @code{if-exists}
5658 The @code{if-exists} spec function takes one argument, an absolute
5659 pathname to a file. If the file exists, @code{if-exists} returns the
5660 pathname. Here is a small example of its usage:
5664 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
5667 @item @code{if-exists-else}
5668 The @code{if-exists-else} spec function is similar to the @code{if-exists}
5669 spec function, except that it takes two arguments. The first argument is
5670 an absolute pathname to a file. If the file exists, @code{if-exists-else}
5671 returns the pathname. If it does not exist, it returns the second argument.
5672 This way, @code{if-exists-else} can be used to select one file or another,
5673 based on the existence of the first. Here is a small example of its usage:
5677 crt0%O%s %:if-exists(crti%O%s) \
5678 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
5683 Substitutes the @code{-S} switch, if that switch was given to GCC@.
5684 If that switch was not specified, this substitutes nothing. Note that
5685 the leading dash is omitted when specifying this option, and it is
5686 automatically inserted if the substitution is performed. Thus the spec
5687 string @samp{%@{foo@}} would match the command-line option @option{-foo}
5688 and would output the command line option @option{-foo}.
5690 @item %W@{@code{S}@}
5691 Like %@{@code{S}@} but mark last argument supplied within as a file to be
5694 @item %@{@code{S}*@}
5695 Substitutes all the switches specified to GCC whose names start
5696 with @code{-S}, but which also take an argument. This is used for
5697 switches like @option{-o}, @option{-D}, @option{-I}, etc.
5698 GCC considers @option{-o foo} as being
5699 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
5700 text, including the space. Thus two arguments would be generated.
5702 @item %@{@code{S}*&@code{T}*@}
5703 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
5704 (the order of @code{S} and @code{T} in the spec is not significant).
5705 There can be any number of ampersand-separated variables; for each the
5706 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
5708 @item %@{@code{S}:@code{X}@}
5709 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
5711 @item %@{!@code{S}:@code{X}@}
5712 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
5714 @item %@{@code{S}*:@code{X}@}
5715 Substitutes @code{X} if one or more switches whose names start with
5716 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
5717 once, no matter how many such switches appeared. However, if @code{%*}
5718 appears somewhere in @code{X}, then @code{X} will be substituted once
5719 for each matching switch, with the @code{%*} replaced by the part of
5720 that switch that matched the @code{*}.
5722 @item %@{.@code{S}:@code{X}@}
5723 Substitutes @code{X}, if processing a file with suffix @code{S}.
5725 @item %@{!.@code{S}:@code{X}@}
5726 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
5728 @item %@{@code{S}|@code{P}:@code{X}@}
5729 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
5730 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
5731 although they have a stronger binding than the @samp{|}. If @code{%*}
5732 appears in @code{X}, all of the alternatives must be starred, and only
5733 the first matching alternative is substituted.
5735 For example, a spec string like this:
5738 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
5741 will output the following command-line options from the following input
5742 command-line options:
5747 -d fred.c -foo -baz -boggle
5748 -d jim.d -bar -baz -boggle
5751 @item %@{S:X; T:Y; :D@}
5753 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
5754 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
5755 be as many clauses as you need. This may be combined with @code{.},
5756 @code{!}, @code{|}, and @code{*} as needed.
5761 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
5762 construct may contain other nested @samp{%} constructs or spaces, or
5763 even newlines. They are processed as usual, as described above.
5764 Trailing white space in @code{X} is ignored. White space may also
5765 appear anywhere on the left side of the colon in these constructs,
5766 except between @code{.} or @code{*} and the corresponding word.
5768 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
5769 handled specifically in these constructs. If another value of
5770 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
5771 @option{-W} switch is found later in the command line, the earlier
5772 switch value is ignored, except with @{@code{S}*@} where @code{S} is
5773 just one letter, which passes all matching options.
5775 The character @samp{|} at the beginning of the predicate text is used to
5776 indicate that a command should be piped to the following command, but
5777 only if @option{-pipe} is specified.
5779 It is built into GCC which switches take arguments and which do not.
5780 (You might think it would be useful to generalize this to allow each
5781 compiler's spec to say which switches take arguments. But this cannot
5782 be done in a consistent fashion. GCC cannot even decide which input
5783 files have been specified without knowing which switches take arguments,
5784 and it must know which input files to compile in order to tell which
5787 GCC also knows implicitly that arguments starting in @option{-l} are to be
5788 treated as compiler output files, and passed to the linker in their
5789 proper position among the other output files.
5791 @c man begin OPTIONS
5793 @node Target Options
5794 @section Specifying Target Machine and Compiler Version
5795 @cindex target options
5796 @cindex cross compiling
5797 @cindex specifying machine version
5798 @cindex specifying compiler version and target machine
5799 @cindex compiler version, specifying
5800 @cindex target machine, specifying
5802 The usual way to run GCC is to run the executable called @file{gcc}, or
5803 @file{<machine>-gcc} when cross-compiling, or
5804 @file{<machine>-gcc-<version>} to run a version other than the one that
5805 was installed last. Sometimes this is inconvenient, so GCC provides
5806 options that will switch to another cross-compiler or version.
5809 @item -b @var{machine}
5811 The argument @var{machine} specifies the target machine for compilation.
5813 The value to use for @var{machine} is the same as was specified as the
5814 machine type when configuring GCC as a cross-compiler. For
5815 example, if a cross-compiler was configured with @samp{configure
5816 i386v}, meaning to compile for an 80386 running System V, then you
5817 would specify @option{-b i386v} to run that cross compiler.
5819 @item -V @var{version}
5821 The argument @var{version} specifies which version of GCC to run.
5822 This is useful when multiple versions are installed. For example,
5823 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
5826 The @option{-V} and @option{-b} options work by running the
5827 @file{<machine>-gcc-<version>} executable, so there's no real reason to
5828 use them if you can just run that directly.
5830 @node Submodel Options
5831 @section Hardware Models and Configurations
5832 @cindex submodel options
5833 @cindex specifying hardware config
5834 @cindex hardware models and configurations, specifying
5835 @cindex machine dependent options
5837 Earlier we discussed the standard option @option{-b} which chooses among
5838 different installed compilers for completely different target
5839 machines, such as VAX vs.@: 68000 vs.@: 80386.
5841 In addition, each of these target machine types can have its own
5842 special options, starting with @samp{-m}, to choose among various
5843 hardware models or configurations---for example, 68010 vs 68020,
5844 floating coprocessor or none. A single installed version of the
5845 compiler can compile for any model or configuration, according to the
5848 Some configurations of the compiler also support additional special
5849 options, usually for compatibility with other compilers on the same
5852 These options are defined by the macro @code{TARGET_SWITCHES} in the
5853 machine description. The default for the options is also defined by
5854 that macro, which enables you to change the defaults.
5866 * RS/6000 and PowerPC Options::
5870 * i386 and x86-64 Options::
5872 * Intel 960 Options::
5873 * DEC Alpha Options::
5874 * DEC Alpha/VMS Options::
5877 * System V Options::
5878 * TMS320C3x/C4x Options::
5886 * S/390 and zSeries Options::
5890 * Xstormy16 Options::
5895 @node M680x0 Options
5896 @subsection M680x0 Options
5897 @cindex M680x0 options
5899 These are the @samp{-m} options defined for the 68000 series. The default
5900 values for these options depends on which style of 68000 was selected when
5901 the compiler was configured; the defaults for the most common choices are
5909 Generate output for a 68000. This is the default
5910 when the compiler is configured for 68000-based systems.
5912 Use this option for microcontrollers with a 68000 or EC000 core,
5913 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
5919 Generate output for a 68020. This is the default
5920 when the compiler is configured for 68020-based systems.
5924 Generate output containing 68881 instructions for floating point.
5925 This is the default for most 68020 systems unless @option{--nfp} was
5926 specified when the compiler was configured.
5930 Generate output for a 68030. This is the default when the compiler is
5931 configured for 68030-based systems.
5935 Generate output for a 68040. This is the default when the compiler is
5936 configured for 68040-based systems.
5938 This option inhibits the use of 68881/68882 instructions that have to be
5939 emulated by software on the 68040. Use this option if your 68040 does not
5940 have code to emulate those instructions.
5944 Generate output for a 68060. This is the default when the compiler is
5945 configured for 68060-based systems.
5947 This option inhibits the use of 68020 and 68881/68882 instructions that
5948 have to be emulated by software on the 68060. Use this option if your 68060
5949 does not have code to emulate those instructions.
5953 Generate output for a CPU32. This is the default
5954 when the compiler is configured for CPU32-based systems.
5956 Use this option for microcontrollers with a
5957 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
5958 68336, 68340, 68341, 68349 and 68360.
5962 Generate output for a 520X ``coldfire'' family cpu. This is the default
5963 when the compiler is configured for 520X-based systems.
5965 Use this option for microcontroller with a 5200 core, including
5966 the MCF5202, MCF5203, MCF5204 and MCF5202.
5971 Generate output for a 68040, without using any of the new instructions.
5972 This results in code which can run relatively efficiently on either a
5973 68020/68881 or a 68030 or a 68040. The generated code does use the
5974 68881 instructions that are emulated on the 68040.
5978 Generate output for a 68060, without using any of the new instructions.
5979 This results in code which can run relatively efficiently on either a
5980 68020/68881 or a 68030 or a 68040. The generated code does use the
5981 68881 instructions that are emulated on the 68060.
5984 @opindex msoft-float
5985 Generate output containing library calls for floating point.
5986 @strong{Warning:} the requisite libraries are not available for all m68k
5987 targets. Normally the facilities of the machine's usual C compiler are
5988 used, but this can't be done directly in cross-compilation. You must
5989 make your own arrangements to provide suitable library functions for
5990 cross-compilation. The embedded targets @samp{m68k-*-aout} and
5991 @samp{m68k-*-coff} do provide software floating point support.
5995 Consider type @code{int} to be 16 bits wide, like @code{short int}.
5998 @opindex mnobitfield
5999 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
6000 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
6004 Do use the bit-field instructions. The @option{-m68020} option implies
6005 @option{-mbitfield}. This is the default if you use a configuration
6006 designed for a 68020.
6010 Use a different function-calling convention, in which functions
6011 that take a fixed number of arguments return with the @code{rtd}
6012 instruction, which pops their arguments while returning. This
6013 saves one instruction in the caller since there is no need to pop
6014 the arguments there.
6016 This calling convention is incompatible with the one normally
6017 used on Unix, so you cannot use it if you need to call libraries
6018 compiled with the Unix compiler.
6020 Also, you must provide function prototypes for all functions that
6021 take variable numbers of arguments (including @code{printf});
6022 otherwise incorrect code will be generated for calls to those
6025 In addition, seriously incorrect code will result if you call a
6026 function with too many arguments. (Normally, extra arguments are
6027 harmlessly ignored.)
6029 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
6030 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
6033 @itemx -mno-align-int
6035 @opindex mno-align-int
6036 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
6037 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
6038 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
6039 Aligning variables on 32-bit boundaries produces code that runs somewhat
6040 faster on processors with 32-bit busses at the expense of more memory.
6042 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
6043 align structures containing the above types differently than
6044 most published application binary interface specifications for the m68k.
6048 Use the pc-relative addressing mode of the 68000 directly, instead of
6049 using a global offset table. At present, this option implies @option{-fpic},
6050 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
6051 not presently supported with @option{-mpcrel}, though this could be supported for
6052 68020 and higher processors.
6054 @item -mno-strict-align
6055 @itemx -mstrict-align
6056 @opindex mno-strict-align
6057 @opindex mstrict-align
6058 Do not (do) assume that unaligned memory references will be handled by
6063 @node M68hc1x Options
6064 @subsection M68hc1x Options
6065 @cindex M68hc1x options
6067 These are the @samp{-m} options defined for the 68hc11 and 68hc12
6068 microcontrollers. The default values for these options depends on
6069 which style of microcontroller was selected when the compiler was configured;
6070 the defaults for the most common choices are given below.
6077 Generate output for a 68HC11. This is the default
6078 when the compiler is configured for 68HC11-based systems.
6084 Generate output for a 68HC12. This is the default
6085 when the compiler is configured for 68HC12-based systems.
6091 Generate output for a 68HCS12.
6094 @opindex mauto-incdec
6095 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
6102 Enable the use of 68HC12 min and max instructions.
6105 @itemx -mno-long-calls
6106 @opindex mlong-calls
6107 @opindex mno-long-calls
6108 Treat all calls as being far away (near). If calls are assumed to be
6109 far away, the compiler will use the @code{call} instruction to
6110 call a function and the @code{rtc} instruction for returning.
6114 Consider type @code{int} to be 16 bits wide, like @code{short int}.
6116 @item -msoft-reg-count=@var{count}
6117 @opindex msoft-reg-count
6118 Specify the number of pseudo-soft registers which are used for the
6119 code generation. The maximum number is 32. Using more pseudo-soft
6120 register may or may not result in better code depending on the program.
6121 The default is 4 for 68HC11 and 2 for 68HC12.
6126 @subsection VAX Options
6129 These @samp{-m} options are defined for the VAX:
6134 Do not output certain jump instructions (@code{aobleq} and so on)
6135 that the Unix assembler for the VAX cannot handle across long
6140 Do output those jump instructions, on the assumption that you
6141 will assemble with the GNU assembler.
6145 Output code for g-format floating point numbers instead of d-format.
6149 @subsection SPARC Options
6150 @cindex SPARC options
6152 These @samp{-m} switches are supported on the SPARC:
6157 @opindex mno-app-regs
6159 Specify @option{-mapp-regs} to generate output using the global registers
6160 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
6163 To be fully SVR4 ABI compliant at the cost of some performance loss,
6164 specify @option{-mno-app-regs}. You should compile libraries and system
6165 software with this option.
6170 @opindex mhard-float
6171 Generate output containing floating point instructions. This is the
6177 @opindex msoft-float
6178 Generate output containing library calls for floating point.
6179 @strong{Warning:} the requisite libraries are not available for all SPARC
6180 targets. Normally the facilities of the machine's usual C compiler are
6181 used, but this cannot be done directly in cross-compilation. You must make
6182 your own arrangements to provide suitable library functions for
6183 cross-compilation. The embedded targets @samp{sparc-*-aout} and
6184 @samp{sparclite-*-*} do provide software floating point support.
6186 @option{-msoft-float} changes the calling convention in the output file;
6187 therefore, it is only useful if you compile @emph{all} of a program with
6188 this option. In particular, you need to compile @file{libgcc.a}, the
6189 library that comes with GCC, with @option{-msoft-float} in order for
6192 @item -mhard-quad-float
6193 @opindex mhard-quad-float
6194 Generate output containing quad-word (long double) floating point
6197 @item -msoft-quad-float
6198 @opindex msoft-quad-float
6199 Generate output containing library calls for quad-word (long double)
6200 floating point instructions. The functions called are those specified
6201 in the SPARC ABI@. This is the default.
6203 As of this writing, there are no sparc implementations that have hardware
6204 support for the quad-word floating point instructions. They all invoke
6205 a trap handler for one of these instructions, and then the trap handler
6206 emulates the effect of the instruction. Because of the trap handler overhead,
6207 this is much slower than calling the ABI library routines. Thus the
6208 @option{-msoft-quad-float} option is the default.
6214 With @option{-mflat}, the compiler does not generate save/restore instructions
6215 and will use a ``flat'' or single register window calling convention.
6216 This model uses %i7 as the frame pointer and is compatible with the normal
6217 register window model. Code from either may be intermixed.
6218 The local registers and the input registers (0--5) are still treated as
6219 ``call saved'' registers and will be saved on the stack as necessary.
6221 With @option{-mno-flat} (the default), the compiler emits save/restore
6222 instructions (except for leaf functions) and is the normal mode of operation.
6224 @item -mno-unaligned-doubles
6225 @itemx -munaligned-doubles
6226 @opindex mno-unaligned-doubles
6227 @opindex munaligned-doubles
6228 Assume that doubles have 8 byte alignment. This is the default.
6230 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
6231 alignment only if they are contained in another type, or if they have an
6232 absolute address. Otherwise, it assumes they have 4 byte alignment.
6233 Specifying this option avoids some rare compatibility problems with code
6234 generated by other compilers. It is not the default because it results
6235 in a performance loss, especially for floating point code.
6237 @item -mno-faster-structs
6238 @itemx -mfaster-structs
6239 @opindex mno-faster-structs
6240 @opindex mfaster-structs
6241 With @option{-mfaster-structs}, the compiler assumes that structures
6242 should have 8 byte alignment. This enables the use of pairs of
6243 @code{ldd} and @code{std} instructions for copies in structure
6244 assignment, in place of twice as many @code{ld} and @code{st} pairs.
6245 However, the use of this changed alignment directly violates the SPARC
6246 ABI@. Thus, it's intended only for use on targets where the developer
6247 acknowledges that their resulting code will not be directly in line with
6248 the rules of the ABI@.
6251 @opindex mimpure-text
6252 @option{-mimpure-text}, used in addition to @option{-shared}, tells
6253 the compiler to not pass @option{-z text} to the linker when linking a
6254 shared object. Using this option, you can link position-dependent
6255 code into a shared object.
6257 @option{-mimpure-text} suppresses the ``relocations remain against
6258 allocatable but non-writable sections'' linker error message.
6259 However, the necessary relocations will trigger copy-on-write, and the
6260 shared object is not actually shared across processes. Instead of
6261 using @option{-mimpure-text}, you should compile all source code with
6262 @option{-fpic} or @option{-fPIC}.
6264 This option is only available on SunOS and Solaris.
6270 These two options select variations on the SPARC architecture.
6272 By default (unless specifically configured for the Fujitsu SPARClite),
6273 GCC generates code for the v7 variant of the SPARC architecture.
6275 @option{-mv8} will give you SPARC v8 code. The only difference from v7
6276 code is that the compiler emits the integer multiply and integer
6277 divide instructions which exist in SPARC v8 but not in SPARC v7.
6279 @option{-msparclite} will give you SPARClite code. This adds the integer
6280 multiply, integer divide step and scan (@code{ffs}) instructions which
6281 exist in SPARClite but not in SPARC v7.
6283 These options are deprecated and will be deleted in a future GCC release.
6284 They have been replaced with @option{-mcpu=xxx}.
6289 @opindex msupersparc
6290 These two options select the processor for which the code is optimized.
6292 With @option{-mcypress} (the default), the compiler optimizes code for the
6293 Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series.
6294 This is also appropriate for the older SPARCStation 1, 2, IPX etc.
6296 With @option{-msupersparc} the compiler optimizes code for the SuperSPARC cpu, as
6297 used in the SPARCStation 10, 1000 and 2000 series. This flag also enables use
6298 of the full SPARC v8 instruction set.
6300 These options are deprecated and will be deleted in a future GCC release.
6301 They have been replaced with @option{-mcpu=xxx}.
6303 @item -mcpu=@var{cpu_type}
6305 Set the instruction set, register set, and instruction scheduling parameters
6306 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
6307 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
6308 @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934},
6309 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
6312 Default instruction scheduling parameters are used for values that select
6313 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
6314 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
6316 Here is a list of each supported architecture and their supported
6321 v8: supersparc, hypersparc
6322 sparclite: f930, f934, sparclite86x
6324 v9: ultrasparc, ultrasparc3
6327 @item -mtune=@var{cpu_type}
6329 Set the instruction scheduling parameters for machine type
6330 @var{cpu_type}, but do not set the instruction set or register set that the
6331 option @option{-mcpu=@var{cpu_type}} would.
6333 The same values for @option{-mcpu=@var{cpu_type}} can be used for
6334 @option{-mtune=@var{cpu_type}}, but the only useful values are those
6335 that select a particular cpu implementation. Those are @samp{cypress},
6336 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
6337 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
6342 These @samp{-m} switches are supported in addition to the above
6343 on the SPARCLET processor.
6346 @item -mlittle-endian
6347 @opindex mlittle-endian
6348 Generate code for a processor running in little-endian mode.
6352 Treat register @code{%g0} as a normal register.
6353 GCC will continue to clobber it as necessary but will not assume
6354 it always reads as 0.
6356 @item -mbroken-saverestore
6357 @opindex mbroken-saverestore
6358 Generate code that does not use non-trivial forms of the @code{save} and
6359 @code{restore} instructions. Early versions of the SPARCLET processor do
6360 not correctly handle @code{save} and @code{restore} instructions used with
6361 arguments. They correctly handle them used without arguments. A @code{save}
6362 instruction used without arguments increments the current window pointer
6363 but does not allocate a new stack frame. It is assumed that the window
6364 overflow trap handler will properly handle this case as will interrupt
6368 These @samp{-m} switches are supported in addition to the above
6369 on SPARC V9 processors in 64-bit environments.
6372 @item -mlittle-endian
6373 @opindex mlittle-endian
6374 Generate code for a processor running in little-endian mode. It is only
6375 available for a few configurations and most notably not on Solaris.
6381 Generate code for a 32-bit or 64-bit environment.
6382 The 32-bit environment sets int, long and pointer to 32 bits.
6383 The 64-bit environment sets int to 32 bits and long and pointer
6386 @item -mcmodel=medlow
6387 @opindex mcmodel=medlow
6388 Generate code for the Medium/Low code model: the program must be linked
6389 in the low 32 bits of the address space. Pointers are 64 bits.
6390 Programs can be statically or dynamically linked.
6392 @item -mcmodel=medmid
6393 @opindex mcmodel=medmid
6394 Generate code for the Medium/Middle code model: the program must be linked
6395 in the low 44 bits of the address space, the text segment must be less than
6396 2G bytes, and data segment must be within 2G of the text segment.
6397 Pointers are 64 bits.
6399 @item -mcmodel=medany
6400 @opindex mcmodel=medany
6401 Generate code for the Medium/Anywhere code model: the program may be linked
6402 anywhere in the address space, the text segment must be less than
6403 2G bytes, and data segment must be within 2G of the text segment.
6404 Pointers are 64 bits.
6406 @item -mcmodel=embmedany
6407 @opindex mcmodel=embmedany
6408 Generate code for the Medium/Anywhere code model for embedded systems:
6409 assume a 32-bit text and a 32-bit data segment, both starting anywhere
6410 (determined at link time). Register %g4 points to the base of the
6411 data segment. Pointers are still 64 bits.
6412 Programs are statically linked, PIC is not supported.
6415 @itemx -mno-stack-bias
6416 @opindex mstack-bias
6417 @opindex mno-stack-bias
6418 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
6419 frame pointer if present, are offset by @minus{}2047 which must be added back
6420 when making stack frame references.
6421 Otherwise, assume no such offset is present.
6425 @subsection ARM Options
6428 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6433 @opindex mapcs-frame
6434 Generate a stack frame that is compliant with the ARM Procedure Call
6435 Standard for all functions, even if this is not strictly necessary for
6436 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6437 with this option will cause the stack frames not to be generated for
6438 leaf functions. The default is @option{-mno-apcs-frame}.
6442 This is a synonym for @option{-mapcs-frame}.
6446 Generate code for a processor running with a 26-bit program counter,
6447 and conforming to the function calling standards for the APCS 26-bit
6448 option. This option replaces the @option{-m2} and @option{-m3} options
6449 of previous releases of the compiler.
6453 Generate code for a processor running with a 32-bit program counter,
6454 and conforming to the function calling standards for the APCS 32-bit
6455 option. This option replaces the @option{-m6} option of previous releases
6459 @c not currently implemented
6460 @item -mapcs-stack-check
6461 @opindex mapcs-stack-check
6462 Generate code to check the amount of stack space available upon entry to
6463 every function (that actually uses some stack space). If there is
6464 insufficient space available then either the function
6465 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6466 called, depending upon the amount of stack space required. The run time
6467 system is required to provide these functions. The default is
6468 @option{-mno-apcs-stack-check}, since this produces smaller code.
6470 @c not currently implemented
6472 @opindex mapcs-float
6473 Pass floating point arguments using the float point registers. This is
6474 one of the variants of the APCS@. This option is recommended if the
6475 target hardware has a floating point unit or if a lot of floating point
6476 arithmetic is going to be performed by the code. The default is
6477 @option{-mno-apcs-float}, since integer only code is slightly increased in
6478 size if @option{-mapcs-float} is used.
6480 @c not currently implemented
6481 @item -mapcs-reentrant
6482 @opindex mapcs-reentrant
6483 Generate reentrant, position independent code. The default is
6484 @option{-mno-apcs-reentrant}.
6487 @item -mthumb-interwork
6488 @opindex mthumb-interwork
6489 Generate code which supports calling between the ARM and Thumb
6490 instruction sets. Without this option the two instruction sets cannot
6491 be reliably used inside one program. The default is
6492 @option{-mno-thumb-interwork}, since slightly larger code is generated
6493 when @option{-mthumb-interwork} is specified.
6495 @item -mno-sched-prolog
6496 @opindex mno-sched-prolog
6497 Prevent the reordering of instructions in the function prolog, or the
6498 merging of those instruction with the instructions in the function's
6499 body. This means that all functions will start with a recognizable set
6500 of instructions (or in fact one of a choice from a small set of
6501 different function prologues), and this information can be used to
6502 locate the start if functions inside an executable piece of code. The
6503 default is @option{-msched-prolog}.
6506 @opindex mhard-float
6507 Generate output containing floating point instructions. This is the
6511 @opindex msoft-float
6512 Generate output containing library calls for floating point.
6513 @strong{Warning:} the requisite libraries are not available for all ARM
6514 targets. Normally the facilities of the machine's usual C compiler are
6515 used, but this cannot be done directly in cross-compilation. You must make
6516 your own arrangements to provide suitable library functions for
6519 @option{-msoft-float} changes the calling convention in the output file;
6520 therefore, it is only useful if you compile @emph{all} of a program with
6521 this option. In particular, you need to compile @file{libgcc.a}, the
6522 library that comes with GCC, with @option{-msoft-float} in order for
6525 @item -mlittle-endian
6526 @opindex mlittle-endian
6527 Generate code for a processor running in little-endian mode. This is
6528 the default for all standard configurations.
6531 @opindex mbig-endian
6532 Generate code for a processor running in big-endian mode; the default is
6533 to compile code for a little-endian processor.
6535 @item -mwords-little-endian
6536 @opindex mwords-little-endian
6537 This option only applies when generating code for big-endian processors.
6538 Generate code for a little-endian word order but a big-endian byte
6539 order. That is, a byte order of the form @samp{32107654}. Note: this
6540 option should only be used if you require compatibility with code for
6541 big-endian ARM processors generated by versions of the compiler prior to
6544 @item -malignment-traps
6545 @opindex malignment-traps
6546 Generate code that will not trap if the MMU has alignment traps enabled.
6547 On ARM architectures prior to ARMv4, there were no instructions to
6548 access half-word objects stored in memory. However, when reading from
6549 memory a feature of the ARM architecture allows a word load to be used,
6550 even if the address is unaligned, and the processor core will rotate the
6551 data as it is being loaded. This option tells the compiler that such
6552 misaligned accesses will cause a MMU trap and that it should instead
6553 synthesize the access as a series of byte accesses. The compiler can
6554 still use word accesses to load half-word data if it knows that the
6555 address is aligned to a word boundary.
6557 This option is ignored when compiling for ARM architecture 4 or later,
6558 since these processors have instructions to directly access half-word
6561 @item -mno-alignment-traps
6562 @opindex mno-alignment-traps
6563 Generate code that assumes that the MMU will not trap unaligned
6564 accesses. This produces better code when the target instruction set
6565 does not have half-word memory operations (i.e.@: implementations prior to
6568 Note that you cannot use this option to access unaligned word objects,
6569 since the processor will only fetch one 32-bit aligned object from
6572 The default setting for most targets is @option{-mno-alignment-traps}, since
6573 this produces better code when there are no half-word memory
6574 instructions available.
6576 @item -mshort-load-bytes
6577 @itemx -mno-short-load-words
6578 @opindex mshort-load-bytes
6579 @opindex mno-short-load-words
6580 These are deprecated aliases for @option{-malignment-traps}.
6582 @item -mno-short-load-bytes
6583 @itemx -mshort-load-words
6584 @opindex mno-short-load-bytes
6585 @opindex mshort-load-words
6586 This are deprecated aliases for @option{-mno-alignment-traps}.
6588 @item -mcpu=@var{name}
6590 This specifies the name of the target ARM processor. GCC uses this name
6591 to determine what kind of instructions it can emit when generating
6592 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6593 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6594 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6595 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6596 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6597 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm8},
6598 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6599 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6600 @samp{arm920t}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi},
6601 @samp{arm1020t}, @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
6603 @itemx -mtune=@var{name}
6605 This option is very similar to the @option{-mcpu=} option, except that
6606 instead of specifying the actual target processor type, and hence
6607 restricting which instructions can be used, it specifies that GCC should
6608 tune the performance of the code as if the target were of the type
6609 specified in this option, but still choosing the instructions that it
6610 will generate based on the cpu specified by a @option{-mcpu=} option.
6611 For some ARM implementations better performance can be obtained by using
6614 @item -march=@var{name}
6616 This specifies the name of the target ARM architecture. GCC uses this
6617 name to determine what kind of instructions it can emit when generating
6618 assembly code. This option can be used in conjunction with or instead
6619 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6620 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6621 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{iwmmxt}, @samp{ep9312}.
6623 @item -mfpe=@var{number}
6624 @itemx -mfp=@var{number}
6627 This specifies the version of the floating point emulation available on
6628 the target. Permissible values are 2 and 3. @option{-mfp=} is a synonym
6629 for @option{-mfpe=}, for compatibility with older versions of GCC@.
6631 @item -mstructure-size-boundary=@var{n}
6632 @opindex mstructure-size-boundary
6633 The size of all structures and unions will be rounded up to a multiple
6634 of the number of bits set by this option. Permissible values are 8 and
6635 32. The default value varies for different toolchains. For the COFF
6636 targeted toolchain the default value is 8. Specifying the larger number
6637 can produce faster, more efficient code, but can also increase the size
6638 of the program. The two values are potentially incompatible. Code
6639 compiled with one value cannot necessarily expect to work with code or
6640 libraries compiled with the other value, if they exchange information
6641 using structures or unions.
6643 @item -mabort-on-noreturn
6644 @opindex mabort-on-noreturn
6645 Generate a call to the function @code{abort} at the end of a
6646 @code{noreturn} function. It will be executed if the function tries to
6650 @itemx -mno-long-calls
6651 @opindex mlong-calls
6652 @opindex mno-long-calls
6653 Tells the compiler to perform function calls by first loading the
6654 address of the function into a register and then performing a subroutine
6655 call on this register. This switch is needed if the target function
6656 will lie outside of the 64 megabyte addressing range of the offset based
6657 version of subroutine call instruction.
6659 Even if this switch is enabled, not all function calls will be turned
6660 into long calls. The heuristic is that static functions, functions
6661 which have the @samp{short-call} attribute, functions that are inside
6662 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6663 definitions have already been compiled within the current compilation
6664 unit, will not be turned into long calls. The exception to this rule is
6665 that weak function definitions, functions with the @samp{long-call}
6666 attribute or the @samp{section} attribute, and functions that are within
6667 the scope of a @samp{#pragma long_calls} directive, will always be
6668 turned into long calls.
6670 This feature is not enabled by default. Specifying
6671 @option{-mno-long-calls} will restore the default behavior, as will
6672 placing the function calls within the scope of a @samp{#pragma
6673 long_calls_off} directive. Note these switches have no effect on how
6674 the compiler generates code to handle function calls via function
6677 @item -mnop-fun-dllimport
6678 @opindex mnop-fun-dllimport
6679 Disable support for the @code{dllimport} attribute.
6681 @item -msingle-pic-base
6682 @opindex msingle-pic-base
6683 Treat the register used for PIC addressing as read-only, rather than
6684 loading it in the prologue for each function. The run-time system is
6685 responsible for initializing this register with an appropriate value
6686 before execution begins.
6688 @item -mpic-register=@var{reg}
6689 @opindex mpic-register
6690 Specify the register to be used for PIC addressing. The default is R10
6691 unless stack-checking is enabled, when R9 is used.
6693 @item -mcirrus-fix-invalid-insns
6694 @opindex mcirrus-fix-invalid-insns
6695 @opindex mno-cirrus-fix-invalid-insns
6696 Insert NOPs into the instruction stream to in order to work around
6697 problems with invalid Maverick instruction combinations. This option
6698 is only valid if the @option{-mcpu=ep9312} option has been used to
6699 enable generation of instructions for the Cirrus Maverick floating
6700 point co-processor. This option is not enabled by default, since the
6701 problem is only present in older Maverick implementations. The default
6702 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6705 @item -mpoke-function-name
6706 @opindex mpoke-function-name
6707 Write the name of each function into the text section, directly
6708 preceding the function prologue. The generated code is similar to this:
6712 .ascii "arm_poke_function_name", 0
6715 .word 0xff000000 + (t1 - t0)
6716 arm_poke_function_name
6718 stmfd sp!, @{fp, ip, lr, pc@}
6722 When performing a stack backtrace, code can inspect the value of
6723 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6724 location @code{pc - 12} and the top 8 bits are set, then we know that
6725 there is a function name embedded immediately preceding this location
6726 and has length @code{((pc[-3]) & 0xff000000)}.
6730 Generate code for the 16-bit Thumb instruction set. The default is to
6731 use the 32-bit ARM instruction set.
6734 @opindex mtpcs-frame
6735 Generate a stack frame that is compliant with the Thumb Procedure Call
6736 Standard for all non-leaf functions. (A leaf function is one that does
6737 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6739 @item -mtpcs-leaf-frame
6740 @opindex mtpcs-leaf-frame
6741 Generate a stack frame that is compliant with the Thumb Procedure Call
6742 Standard for all leaf functions. (A leaf function is one that does
6743 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6745 @item -mcallee-super-interworking
6746 @opindex mcallee-super-interworking
6747 Gives all externally visible functions in the file being compiled an ARM
6748 instruction set header which switches to Thumb mode before executing the
6749 rest of the function. This allows these functions to be called from
6750 non-interworking code.
6752 @item -mcaller-super-interworking
6753 @opindex mcaller-super-interworking
6754 Allows calls via function pointers (including virtual functions) to
6755 execute correctly regardless of whether the target code has been
6756 compiled for interworking or not. There is a small overhead in the cost
6757 of executing a function pointer if this option is enabled.
6761 @node MN10200 Options
6762 @subsection MN10200 Options
6763 @cindex MN10200 options
6765 These @option{-m} options are defined for Matsushita MN10200 architectures:
6770 Indicate to the linker that it should perform a relaxation optimization pass
6771 to shorten branches, calls and absolute memory addresses. This option only
6772 has an effect when used on the command line for the final link step.
6774 This option makes symbolic debugging impossible.
6777 @node MN10300 Options
6778 @subsection MN10300 Options
6779 @cindex MN10300 options
6781 These @option{-m} options are defined for Matsushita MN10300 architectures:
6786 Generate code to avoid bugs in the multiply instructions for the MN10300
6787 processors. This is the default.
6790 @opindex mno-mult-bug
6791 Do not generate code to avoid bugs in the multiply instructions for the
6796 Generate code which uses features specific to the AM33 processor.
6800 Do not generate code which uses features specific to the AM33 processor. This
6805 Do not link in the C run-time initialization object file.
6809 Indicate to the linker that it should perform a relaxation optimization pass
6810 to shorten branches, calls and absolute memory addresses. This option only
6811 has an effect when used on the command line for the final link step.
6813 This option makes symbolic debugging impossible.
6817 @node M32R/D Options
6818 @subsection M32R/D Options
6819 @cindex M32R/D options
6821 These @option{-m} options are defined for Mitsubishi M32R/D architectures:
6826 Generate code for the M32R/X@.
6830 Generate code for the M32R@. This is the default.
6832 @item -mcode-model=small
6833 @opindex mcode-model=small
6834 Assume all objects live in the lower 16MB of memory (so that their addresses
6835 can be loaded with the @code{ld24} instruction), and assume all subroutines
6836 are reachable with the @code{bl} instruction.
6837 This is the default.
6839 The addressability of a particular object can be set with the
6840 @code{model} attribute.
6842 @item -mcode-model=medium
6843 @opindex mcode-model=medium
6844 Assume objects may be anywhere in the 32-bit address space (the compiler
6845 will generate @code{seth/add3} instructions to load their addresses), and
6846 assume all subroutines are reachable with the @code{bl} instruction.
6848 @item -mcode-model=large
6849 @opindex mcode-model=large
6850 Assume objects may be anywhere in the 32-bit address space (the compiler
6851 will generate @code{seth/add3} instructions to load their addresses), and
6852 assume subroutines may not be reachable with the @code{bl} instruction
6853 (the compiler will generate the much slower @code{seth/add3/jl}
6854 instruction sequence).
6857 @opindex msdata=none
6858 Disable use of the small data area. Variables will be put into
6859 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
6860 @code{section} attribute has been specified).
6861 This is the default.
6863 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
6864 Objects may be explicitly put in the small data area with the
6865 @code{section} attribute using one of these sections.
6868 @opindex msdata=sdata
6869 Put small global and static data in the small data area, but do not
6870 generate special code to reference them.
6874 Put small global and static data in the small data area, and generate
6875 special instructions to reference them.
6879 @cindex smaller data references
6880 Put global and static objects less than or equal to @var{num} bytes
6881 into the small data or bss sections instead of the normal data or bss
6882 sections. The default value of @var{num} is 8.
6883 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
6884 for this option to have any effect.
6886 All modules should be compiled with the same @option{-G @var{num}} value.
6887 Compiling with different values of @var{num} may or may not work; if it
6888 doesn't the linker will give an error message---incorrect code will not be
6894 @subsection M88K Options
6895 @cindex M88k options
6897 These @samp{-m} options are defined for Motorola 88k architectures:
6902 Generate code that works well on both the m88100 and the
6907 Generate code that works best for the m88100, but that also
6912 Generate code that works best for the m88110, and may not run
6917 Obsolete option to be removed from the next revision.
6920 @item -midentify-revision
6921 @opindex midentify-revision
6922 @cindex identifying source, compiler (88k)
6923 Include an @code{ident} directive in the assembler output recording the
6924 source file name, compiler name and version, timestamp, and compilation
6927 @item -mno-underscores
6928 @opindex mno-underscores
6929 @cindex underscores, avoiding (88k)
6930 In assembler output, emit symbol names without adding an underscore
6931 character at the beginning of each name. The default is to use an
6932 underscore as prefix on each name.
6934 @item -mocs-debug-info
6935 @itemx -mno-ocs-debug-info
6936 @opindex mocs-debug-info
6937 @opindex mno-ocs-debug-info
6939 @cindex debugging, 88k OCS
6940 Include (or omit) additional debugging information (about registers used
6941 in each stack frame) as specified in the 88open Object Compatibility
6942 Standard, ``OCS''@. This extra information allows debugging of code that
6943 has had the frame pointer eliminated. The default for SVr4 and Delta 88
6944 SVr3.2 is to include this information; other 88k configurations omit this
6945 information by default.
6947 @item -mocs-frame-position
6948 @opindex mocs-frame-position
6949 @cindex register positions in frame (88k)
6950 When emitting COFF debugging information for automatic variables and
6951 parameters stored on the stack, use the offset from the canonical frame
6952 address, which is the stack pointer (register 31) on entry to the
6953 function. The SVr4 and Delta88 SVr3.2, and BCS configurations use
6954 @option{-mocs-frame-position}; other 88k configurations have the default
6955 @option{-mno-ocs-frame-position}.
6957 @item -mno-ocs-frame-position
6958 @opindex mno-ocs-frame-position
6959 @cindex register positions in frame (88k)
6960 When emitting COFF debugging information for automatic variables and
6961 parameters stored on the stack, use the offset from the frame pointer
6962 register (register 30). When this option is in effect, the frame
6963 pointer is not eliminated when debugging information is selected by the
6966 @item -moptimize-arg-area
6967 @opindex moptimize-arg-area
6968 @cindex arguments in frame (88k)
6969 Save space by reorganizing the stack frame. This option generates code
6970 that does not agree with the 88open specifications, but uses less
6973 @itemx -mno-optimize-arg-area
6974 @opindex mno-optimize-arg-area
6975 Do not reorganize the stack frame to save space. This is the default.
6976 The generated conforms to the specification, but uses more memory.
6978 @item -mshort-data-@var{num}
6979 @opindex mshort-data
6980 @cindex smaller data references (88k)
6981 @cindex r0-relative references (88k)
6982 Generate smaller data references by making them relative to @code{r0},
6983 which allows loading a value using a single instruction (rather than the
6984 usual two). You control which data references are affected by
6985 specifying @var{num} with this option. For example, if you specify
6986 @option{-mshort-data-512}, then the data references affected are those
6987 involving displacements of less than 512 bytes.
6988 @option{-mshort-data-@var{num}} is not effective for @var{num} greater
6991 @item -mserialize-volatile
6992 @opindex mserialize-volatile
6993 @itemx -mno-serialize-volatile
6994 @opindex mno-serialize-volatile
6995 @cindex sequential consistency on 88k
6996 Do, or don't, generate code to guarantee sequential consistency
6997 of volatile memory references. By default, consistency is
7000 The order of memory references made by the MC88110 processor does
7001 not always match the order of the instructions requesting those
7002 references. In particular, a load instruction may execute before
7003 a preceding store instruction. Such reordering violates
7004 sequential consistency of volatile memory references, when there
7005 are multiple processors. When consistency must be guaranteed,
7006 GCC generates special instructions, as needed, to force
7007 execution in the proper order.
7009 The MC88100 processor does not reorder memory references and so
7010 always provides sequential consistency. However, by default, GCC
7011 generates the special instructions to guarantee consistency
7012 even when you use @option{-m88100}, so that the code may be run on an
7013 MC88110 processor. If you intend to run your code only on the
7014 MC88100 processor, you may use @option{-mno-serialize-volatile}.
7016 The extra code generated to guarantee consistency may affect the
7017 performance of your application. If you know that you can safely
7018 forgo this guarantee, you may use @option{-mno-serialize-volatile}.
7024 @cindex assembler syntax, 88k
7026 Turn on (@option{-msvr4}) or off (@option{-msvr3}) compiler extensions
7027 related to System V release 4 (SVr4). This controls the following:
7031 Which variant of the assembler syntax to emit.
7033 @option{-msvr4} makes the C preprocessor recognize @samp{#pragma weak}
7034 that is used on System V release 4.
7036 @option{-msvr4} makes GCC issue additional declaration directives used in
7040 @option{-msvr4} is the default for the m88k-motorola-sysv4 configuration.
7041 @option{-msvr3} is the default for all other m88k configurations.
7043 @item -mversion-03.00
7044 @opindex mversion-03.00
7045 This option is obsolete, and is ignored.
7046 @c ??? which asm syntax better for GAS? option there too?
7048 @item -mno-check-zero-division
7049 @itemx -mcheck-zero-division
7050 @opindex mno-check-zero-division
7051 @opindex mcheck-zero-division
7052 @cindex zero division on 88k
7053 Do, or don't, generate code to guarantee that integer division by
7054 zero will be detected. By default, detection is guaranteed.
7056 Some models of the MC88100 processor fail to trap upon integer
7057 division by zero under certain conditions. By default, when
7058 compiling code that might be run on such a processor, GCC
7059 generates code that explicitly checks for zero-valued divisors
7060 and traps with exception number 503 when one is detected. Use of
7061 @option{-mno-check-zero-division} suppresses such checking for code
7062 generated to run on an MC88100 processor.
7064 GCC assumes that the MC88110 processor correctly detects all instances
7065 of integer division by zero. When @option{-m88110} is specified, no
7066 explicit checks for zero-valued divisors are generated, and both
7067 @option{-mcheck-zero-division} and @option{-mno-check-zero-division} are
7070 @item -muse-div-instruction
7071 @opindex muse-div-instruction
7072 @cindex divide instruction, 88k
7073 Use the div instruction for signed integer division on the
7074 MC88100 processor. By default, the div instruction is not used.
7076 On the MC88100 processor the signed integer division instruction
7077 div) traps to the operating system on a negative operand. The
7078 operating system transparently completes the operation, but at a
7079 large cost in execution time. By default, when compiling code
7080 that might be run on an MC88100 processor, GCC emulates signed
7081 integer division using the unsigned integer division instruction
7082 divu), thereby avoiding the large penalty of a trap to the
7083 operating system. Such emulation has its own, smaller, execution
7084 cost in both time and space. To the extent that your code's
7085 important signed integer division operations are performed on two
7086 nonnegative operands, it may be desirable to use the div
7087 instruction directly.
7089 On the MC88110 processor the div instruction (also known as the
7090 divs instruction) processes negative operands without trapping to
7091 the operating system. When @option{-m88110} is specified,
7092 @option{-muse-div-instruction} is ignored, and the div instruction is used
7093 for signed integer division.
7095 Note that the result of dividing @code{INT_MIN} by @minus{}1 is undefined. In
7096 particular, the behavior of such a division with and without
7097 @option{-muse-div-instruction} may differ.
7099 @item -mtrap-large-shift
7100 @itemx -mhandle-large-shift
7101 @opindex mtrap-large-shift
7102 @opindex mhandle-large-shift
7103 @cindex bit shift overflow (88k)
7104 @cindex large bit shifts (88k)
7105 Include code to detect bit-shifts of more than 31 bits; respectively,
7106 trap such shifts or emit code to handle them properly. By default GCC
7107 makes no special provision for large bit shifts.
7109 @item -mwarn-passed-structs
7110 @opindex mwarn-passed-structs
7111 @cindex structure passing (88k)
7112 Warn when a function passes a struct as an argument or result.
7113 Structure-passing conventions have changed during the evolution of the C
7114 language, and are often the source of portability problems. By default,
7115 GCC issues no such warning.
7118 @c break page here to avoid unsightly interparagraph stretch.
7122 @node RS/6000 and PowerPC Options
7123 @subsection IBM RS/6000 and PowerPC Options
7124 @cindex RS/6000 and PowerPC Options
7125 @cindex IBM RS/6000 and PowerPC Options
7127 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
7135 @itemx -mpowerpc-gpopt
7136 @itemx -mno-powerpc-gpopt
7137 @itemx -mpowerpc-gfxopt
7138 @itemx -mno-powerpc-gfxopt
7140 @itemx -mno-powerpc64
7146 @opindex mno-powerpc
7147 @opindex mpowerpc-gpopt
7148 @opindex mno-powerpc-gpopt
7149 @opindex mpowerpc-gfxopt
7150 @opindex mno-powerpc-gfxopt
7152 @opindex mno-powerpc64
7153 GCC supports two related instruction set architectures for the
7154 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
7155 instructions supported by the @samp{rios} chip set used in the original
7156 RS/6000 systems and the @dfn{PowerPC} instruction set is the
7157 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
7158 the IBM 4xx microprocessors.
7160 Neither architecture is a subset of the other. However there is a
7161 large common subset of instructions supported by both. An MQ
7162 register is included in processors supporting the POWER architecture.
7164 You use these options to specify which instructions are available on the
7165 processor you are using. The default value of these options is
7166 determined when configuring GCC@. Specifying the
7167 @option{-mcpu=@var{cpu_type}} overrides the specification of these
7168 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
7169 rather than the options listed above.
7171 The @option{-mpower} option allows GCC to generate instructions that
7172 are found only in the POWER architecture and to use the MQ register.
7173 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
7174 to generate instructions that are present in the POWER2 architecture but
7175 not the original POWER architecture.
7177 The @option{-mpowerpc} option allows GCC to generate instructions that
7178 are found only in the 32-bit subset of the PowerPC architecture.
7179 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
7180 GCC to use the optional PowerPC architecture instructions in the
7181 General Purpose group, including floating-point square root. Specifying
7182 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
7183 use the optional PowerPC architecture instructions in the Graphics
7184 group, including floating-point select.
7186 The @option{-mpowerpc64} option allows GCC to generate the additional
7187 64-bit instructions that are found in the full PowerPC64 architecture
7188 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
7189 @option{-mno-powerpc64}.
7191 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
7192 will use only the instructions in the common subset of both
7193 architectures plus some special AIX common-mode calls, and will not use
7194 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
7195 permits GCC to use any instruction from either architecture and to
7196 allow use of the MQ register; specify this for the Motorola MPC601.
7198 @item -mnew-mnemonics
7199 @itemx -mold-mnemonics
7200 @opindex mnew-mnemonics
7201 @opindex mold-mnemonics
7202 Select which mnemonics to use in the generated assembler code. With
7203 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
7204 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
7205 assembler mnemonics defined for the POWER architecture. Instructions
7206 defined in only one architecture have only one mnemonic; GCC uses that
7207 mnemonic irrespective of which of these options is specified.
7209 GCC defaults to the mnemonics appropriate for the architecture in
7210 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
7211 value of these option. Unless you are building a cross-compiler, you
7212 should normally not specify either @option{-mnew-mnemonics} or
7213 @option{-mold-mnemonics}, but should instead accept the default.
7215 @item -mcpu=@var{cpu_type}
7217 Set architecture type, register usage, choice of mnemonics, and
7218 instruction scheduling parameters for machine type @var{cpu_type}.
7219 Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1},
7220 @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602},
7221 @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620},
7222 @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750},
7223 @samp{power}, @samp{power2}, @samp{powerpc}, @samp{403}, @samp{505},
7224 @samp{801}, @samp{821}, @samp{823}, and @samp{860} and @samp{common}.
7226 @option{-mcpu=common} selects a completely generic processor. Code
7227 generated under this option will run on any POWER or PowerPC processor.
7228 GCC will use only the instructions in the common subset of both
7229 architectures, and will not use the MQ register. GCC assumes a generic
7230 processor model for scheduling purposes.
7232 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
7233 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
7234 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
7235 types, with an appropriate, generic processor model assumed for
7236 scheduling purposes.
7238 The other options specify a specific processor. Code generated under
7239 those options will run best on that processor, and may not run at all on
7242 The @option{-mcpu} options automatically enable or disable other
7243 @option{-m} options as follows:
7247 @option{-mno-power}, @option{-mno-powerpc}
7254 @option{-mpower}, @option{-mno-powerpc}, @option{-mno-new-mnemonics}
7269 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7272 @option{-mpower}, @option{-mpowerpc}, @option{-mnew-mnemonics}
7277 @option{-mno-power}, @option{-mpowerpc}, @option{-mnew-mnemonics}, @option{-msoft-float}
7280 @item -mtune=@var{cpu_type}
7282 Set the instruction scheduling parameters for machine type
7283 @var{cpu_type}, but do not set the architecture type, register usage, or
7284 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
7285 values for @var{cpu_type} are used for @option{-mtune} as for
7286 @option{-mcpu}. If both are specified, the code generated will use the
7287 architecture, registers, and mnemonics set by @option{-mcpu}, but the
7288 scheduling parameters set by @option{-mtune}.
7293 @opindex mno-altivec
7294 These switches enable or disable the use of built-in functions that
7295 allow access to the AltiVec instruction set. You may also need to set
7296 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
7301 Extend the current ABI with SPE ABI extensions. This does not change
7302 the default ABI, instead it adds the SPE ABI extensions to the current
7306 @opindex mabi=no-spe
7307 Disable Booke SPE ABI extensions for the current ABI.
7309 @item -misel=@var{yes/no}
7312 This switch enables or disables the generation of ISEL instructions.
7314 @item -mspe=@var{yes/no}
7317 This switch enables or disables the generation of SPE simd
7320 @item -mfloat-gprs=@var{yes/no}
7322 @opindex mfloat-gprs
7323 This switch enables or disables the generation of floating point
7324 operations on the general purpose registers for architectures that
7325 support it. This option is currently only available on the MPC8540.
7328 @itemx -mno-fp-in-toc
7329 @itemx -mno-sum-in-toc
7330 @itemx -mminimal-toc
7332 @opindex mno-fp-in-toc
7333 @opindex mno-sum-in-toc
7334 @opindex mminimal-toc
7335 Modify generation of the TOC (Table Of Contents), which is created for
7336 every executable file. The @option{-mfull-toc} option is selected by
7337 default. In that case, GCC will allocate at least one TOC entry for
7338 each unique non-automatic variable reference in your program. GCC
7339 will also place floating-point constants in the TOC@. However, only
7340 16,384 entries are available in the TOC@.
7342 If you receive a linker error message that saying you have overflowed
7343 the available TOC space, you can reduce the amount of TOC space used
7344 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
7345 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
7346 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
7347 generate code to calculate the sum of an address and a constant at
7348 run-time instead of putting that sum into the TOC@. You may specify one
7349 or both of these options. Each causes GCC to produce very slightly
7350 slower and larger code at the expense of conserving TOC space.
7352 If you still run out of space in the TOC even when you specify both of
7353 these options, specify @option{-mminimal-toc} instead. This option causes
7354 GCC to make only one TOC entry for every file. When you specify this
7355 option, GCC will produce code that is slower and larger but which
7356 uses extremely little TOC space. You may wish to use this option
7357 only on files that contain less frequently executed code.
7363 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
7364 @code{long} type, and the infrastructure needed to support them.
7365 Specifying @option{-maix64} implies @option{-mpowerpc64} and
7366 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
7367 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
7372 @opindex mno-xl-call
7373 On AIX, pass floating-point arguments to prototyped functions beyond the
7374 register save area (RSA) on the stack in addition to argument FPRs. The
7375 AIX calling convention was extended but not initially documented to
7376 handle an obscure K&R C case of calling a function that takes the
7377 address of its arguments with fewer arguments than declared. AIX XL
7378 compilers access floating point arguments which do not fit in the
7379 RSA from the stack when a subroutine is compiled without
7380 optimization. Because always storing floating-point arguments on the
7381 stack is inefficient and rarely needed, this option is not enabled by
7382 default and only is necessary when calling subroutines compiled by AIX
7383 XL compilers without optimization.
7387 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
7388 application written to use message passing with special startup code to
7389 enable the application to run. The system must have PE installed in the
7390 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
7391 must be overridden with the @option{-specs=} option to specify the
7392 appropriate directory location. The Parallel Environment does not
7393 support threads, so the @option{-mpe} option and the @option{-pthread}
7394 option are incompatible.
7396 @item -malign-natural
7397 @itemx -malign-power
7398 @opindex malign-natural
7399 @opindex malign-power
7400 On AIX, Darwin, and 64-bit PowerPC Linux, the option
7401 @option{-malign-natural} overrides the ABI-defined alignment of larger
7402 types, such as floating-point doubles, on their natural size-based boundary.
7403 The option @option{-malign-power} instructs GCC to follow the ABI-specified
7404 alignment rules. GCC defaults to the standard alignment defined in the ABI.
7408 @opindex msoft-float
7409 @opindex mhard-float
7410 Generate code that does not use (uses) the floating-point register set.
7411 Software floating point emulation is provided if you use the
7412 @option{-msoft-float} option, and pass the option to GCC when linking.
7415 @itemx -mno-multiple
7417 @opindex mno-multiple
7418 Generate code that uses (does not use) the load multiple word
7419 instructions and the store multiple word instructions. These
7420 instructions are generated by default on POWER systems, and not
7421 generated on PowerPC systems. Do not use @option{-mmultiple} on little
7422 endian PowerPC systems, since those instructions do not work when the
7423 processor is in little endian mode. The exceptions are PPC740 and
7424 PPC750 which permit the instructions usage in little endian mode.
7430 Generate code that uses (does not use) the load string instructions
7431 and the store string word instructions to save multiple registers and
7432 do small block moves. These instructions are generated by default on
7433 POWER systems, and not generated on PowerPC systems. Do not use
7434 @option{-mstring} on little endian PowerPC systems, since those
7435 instructions do not work when the processor is in little endian mode.
7436 The exceptions are PPC740 and PPC750 which permit the instructions
7437 usage in little endian mode.
7443 Generate code that uses (does not use) the load or store instructions
7444 that update the base register to the address of the calculated memory
7445 location. These instructions are generated by default. If you use
7446 @option{-mno-update}, there is a small window between the time that the
7447 stack pointer is updated and the address of the previous frame is
7448 stored, which means code that walks the stack frame across interrupts or
7449 signals may get corrupted data.
7452 @itemx -mno-fused-madd
7453 @opindex mfused-madd
7454 @opindex mno-fused-madd
7455 Generate code that uses (does not use) the floating point multiply and
7456 accumulate instructions. These instructions are generated by default if
7457 hardware floating is used.
7459 @item -mno-bit-align
7461 @opindex mno-bit-align
7463 On System V.4 and embedded PowerPC systems do not (do) force structures
7464 and unions that contain bit-fields to be aligned to the base type of the
7467 For example, by default a structure containing nothing but 8
7468 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
7469 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
7470 the structure would be aligned to a 1 byte boundary and be one byte in
7473 @item -mno-strict-align
7474 @itemx -mstrict-align
7475 @opindex mno-strict-align
7476 @opindex mstrict-align
7477 On System V.4 and embedded PowerPC systems do not (do) assume that
7478 unaligned memory references will be handled by the system.
7481 @itemx -mno-relocatable
7482 @opindex mrelocatable
7483 @opindex mno-relocatable
7484 On embedded PowerPC systems generate code that allows (does not allow)
7485 the program to be relocated to a different address at runtime. If you
7486 use @option{-mrelocatable} on any module, all objects linked together must
7487 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
7489 @item -mrelocatable-lib
7490 @itemx -mno-relocatable-lib
7491 @opindex mrelocatable-lib
7492 @opindex mno-relocatable-lib
7493 On embedded PowerPC systems generate code that allows (does not allow)
7494 the program to be relocated to a different address at runtime. Modules
7495 compiled with @option{-mrelocatable-lib} can be linked with either modules
7496 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
7497 with modules compiled with the @option{-mrelocatable} options.
7503 On System V.4 and embedded PowerPC systems do not (do) assume that
7504 register 2 contains a pointer to a global area pointing to the addresses
7505 used in the program.
7508 @itemx -mlittle-endian
7510 @opindex mlittle-endian
7511 On System V.4 and embedded PowerPC systems compile code for the
7512 processor in little endian mode. The @option{-mlittle-endian} option is
7513 the same as @option{-mlittle}.
7518 @opindex mbig-endian
7519 On System V.4 and embedded PowerPC systems compile code for the
7520 processor in big endian mode. The @option{-mbig-endian} option is
7521 the same as @option{-mbig}.
7523 @item -mdynamic-no-pic
7524 @opindex mdynamic-no-pic
7525 On Darwin and Mac OS X systems, compile code so that it is not
7526 relocatable, but that its external references are relocatable. The
7527 resulting code is suitable for applications, but not shared
7530 @item -mprioritize-restricted-insns=@var{priority}
7531 @opindex mprioritize-restricted-insns
7532 This option controls the priority that is assigned to
7533 dispatch-slot restricted instructions during the second scheduling
7534 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
7535 @var{no/highest/second-highest} priority to dispatch slot restricted
7540 On System V.4 and embedded PowerPC systems compile code using calling
7541 conventions that adheres to the March 1995 draft of the System V
7542 Application Binary Interface, PowerPC processor supplement. This is the
7543 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
7545 @item -mcall-sysv-eabi
7546 @opindex mcall-sysv-eabi
7547 Specify both @option{-mcall-sysv} and @option{-meabi} options.
7549 @item -mcall-sysv-noeabi
7550 @opindex mcall-sysv-noeabi
7551 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
7553 @item -mcall-solaris
7554 @opindex mcall-solaris
7555 On System V.4 and embedded PowerPC systems compile code for the Solaris
7559 @opindex mcall-linux
7560 On System V.4 and embedded PowerPC systems compile code for the
7561 Linux-based GNU system.
7565 On System V.4 and embedded PowerPC systems compile code for the
7566 Hurd-based GNU system.
7569 @opindex mcall-netbsd
7570 On System V.4 and embedded PowerPC systems compile code for the
7571 NetBSD operating system.
7573 @item -maix-struct-return
7574 @opindex maix-struct-return
7575 Return all structures in memory (as specified by the AIX ABI)@.
7577 @item -msvr4-struct-return
7578 @opindex msvr4-struct-return
7579 Return structures smaller than 8 bytes in registers (as specified by the
7583 @opindex mabi=altivec
7584 Extend the current ABI with AltiVec ABI extensions. This does not
7585 change the default ABI, instead it adds the AltiVec ABI extensions to
7588 @item -mabi=no-altivec
7589 @opindex mabi=no-altivec
7590 Disable AltiVec ABI extensions for the current ABI.
7593 @itemx -mno-prototype
7595 @opindex mno-prototype
7596 On System V.4 and embedded PowerPC systems assume that all calls to
7597 variable argument functions are properly prototyped. Otherwise, the
7598 compiler must insert an instruction before every non prototyped call to
7599 set or clear bit 6 of the condition code register (@var{CR}) to
7600 indicate whether floating point values were passed in the floating point
7601 registers in case the function takes a variable arguments. With
7602 @option{-mprototype}, only calls to prototyped variable argument functions
7603 will set or clear the bit.
7607 On embedded PowerPC systems, assume that the startup module is called
7608 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
7609 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
7614 On embedded PowerPC systems, assume that the startup module is called
7615 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
7620 On embedded PowerPC systems, assume that the startup module is called
7621 @file{crt0.o} and the standard C libraries are @file{libads.a} and
7625 @opindex myellowknife
7626 On embedded PowerPC systems, assume that the startup module is called
7627 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
7632 On System V.4 and embedded PowerPC systems, specify that you are
7633 compiling for a VxWorks system.
7637 Specify that you are compiling for the WindISS simulation environment.
7641 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
7642 header to indicate that @samp{eabi} extended relocations are used.
7648 On System V.4 and embedded PowerPC systems do (do not) adhere to the
7649 Embedded Applications Binary Interface (eabi) which is a set of
7650 modifications to the System V.4 specifications. Selecting @option{-meabi}
7651 means that the stack is aligned to an 8 byte boundary, a function
7652 @code{__eabi} is called to from @code{main} to set up the eabi
7653 environment, and the @option{-msdata} option can use both @code{r2} and
7654 @code{r13} to point to two separate small data areas. Selecting
7655 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
7656 do not call an initialization function from @code{main}, and the
7657 @option{-msdata} option will only use @code{r13} to point to a single
7658 small data area. The @option{-meabi} option is on by default if you
7659 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
7662 @opindex msdata=eabi
7663 On System V.4 and embedded PowerPC systems, put small initialized
7664 @code{const} global and static data in the @samp{.sdata2} section, which
7665 is pointed to by register @code{r2}. Put small initialized
7666 non-@code{const} global and static data in the @samp{.sdata} section,
7667 which is pointed to by register @code{r13}. Put small uninitialized
7668 global and static data in the @samp{.sbss} section, which is adjacent to
7669 the @samp{.sdata} section. The @option{-msdata=eabi} option is
7670 incompatible with the @option{-mrelocatable} option. The
7671 @option{-msdata=eabi} option also sets the @option{-memb} option.
7674 @opindex msdata=sysv
7675 On System V.4 and embedded PowerPC systems, put small global and static
7676 data in the @samp{.sdata} section, which is pointed to by register
7677 @code{r13}. Put small uninitialized global and static data in the
7678 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
7679 The @option{-msdata=sysv} option is incompatible with the
7680 @option{-mrelocatable} option.
7682 @item -msdata=default
7684 @opindex msdata=default
7686 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
7687 compile code the same as @option{-msdata=eabi}, otherwise compile code the
7688 same as @option{-msdata=sysv}.
7691 @opindex msdata-data
7692 On System V.4 and embedded PowerPC systems, put small global and static
7693 data in the @samp{.sdata} section. Put small uninitialized global and
7694 static data in the @samp{.sbss} section. Do not use register @code{r13}
7695 to address small data however. This is the default behavior unless
7696 other @option{-msdata} options are used.
7700 @opindex msdata=none
7702 On embedded PowerPC systems, put all initialized global and static data
7703 in the @samp{.data} section, and all uninitialized data in the
7704 @samp{.bss} section.
7708 @cindex smaller data references (PowerPC)
7709 @cindex .sdata/.sdata2 references (PowerPC)
7710 On embedded PowerPC systems, put global and static items less than or
7711 equal to @var{num} bytes into the small data or bss sections instead of
7712 the normal data or bss section. By default, @var{num} is 8. The
7713 @option{-G @var{num}} switch is also passed to the linker.
7714 All modules should be compiled with the same @option{-G @var{num}} value.
7717 @itemx -mno-regnames
7719 @opindex mno-regnames
7720 On System V.4 and embedded PowerPC systems do (do not) emit register
7721 names in the assembly language output using symbolic forms.
7724 @itemx -mno-longcall
7726 @opindex mno-longcall
7727 Default to making all function calls via pointers, so that functions
7728 which reside further than 64 megabytes (67,108,864 bytes) from the
7729 current location can be called. This setting can be overridden by the
7730 @code{shortcall} function attribute, or by @code{#pragma longcall(0)}.
7732 Some linkers are capable of detecting out-of-range calls and generating
7733 glue code on the fly. On these systems, long calls are unnecessary and
7734 generate slower code. As of this writing, the AIX linker can do this,
7735 as can the GNU linker for PowerPC/64. It is planned to add this feature
7736 to the GNU linker for 32-bit PowerPC systems as well.
7738 In the future, we may cause GCC to ignore all longcall specifications
7739 when the linker is known to generate glue.
7743 Adds support for multithreading with the @dfn{pthreads} library.
7744 This option sets flags for both the preprocessor and linker.
7748 @node Darwin Options
7749 @subsection Darwin Options
7750 @cindex Darwin options
7752 These options are defined for all architectures running the Darwin operating
7753 system. They are useful for compatibility with other Mac OS compilers.
7758 Loads all members of static archive libraries.
7759 See man ld(1) for more information.
7761 @item -arch_errors_fatal
7762 @opindex arch_errors_fatal
7763 Cause the errors having to do with files that have the wrong architecture
7767 @opindex bind_at_load
7768 Causes the output file to be marked such that the dynamic linker will
7769 bind all undefined references when the file is loaded or launched.
7773 Produce a Mach-o bundle format file.
7774 See man ld(1) for more information.
7776 @item -bundle_loader @var{executable}
7777 @opindex bundle_loader
7778 This specifies the @var{executable} that will be loading the build
7779 output file being linked. See man ld(1) for more information.
7781 @item -allowable_client @var{client_name}
7785 @item -compatibility_version
7786 @item -current_version
7787 @item -dependency-file
7789 @item -dylinker_install_name
7792 @item -exported_symbols_list
7794 @item -flat_namespace
7795 @item -force_cpusubtype_ALL
7796 @item -force_flat_namespace
7797 @item -headerpad_max_install_names
7801 @item -keep_private_externs
7803 @item -multiply_defined
7804 @item -multiply_defined_unused
7806 @item -nofixprebinding
7809 @item -noseglinkedit
7810 @item -pagezero_size
7812 @item -prebind_all_twolevel_modules
7813 @item -private_bundle
7814 @item -read_only_relocs
7816 @item -sectobjectsymbols
7820 @item -sectobjectsymbols
7822 @item -seg_addr_table
7823 @item -seg_addr_table_filename
7826 @item -segs_read_only_addr
7827 @item -segs_read_write_addr
7828 @item -single_module
7832 @item -twolevel_namespace
7835 @item -unexported_symbols_list
7836 @item -weak_reference_mismatches
7839 @opindex allowable_client
7841 @opindex client_name
7842 @opindex compatibility_version
7843 @opindex current_version
7844 @opindex dependency-file
7846 @opindex dylinker_install_name
7849 @opindex exported_symbols_list
7851 @opindex flat_namespace
7852 @opindex force_cpusubtype_ALL
7853 @opindex force_flat_namespace
7854 @opindex headerpad_max_install_names
7857 @opindex install_name
7858 @opindex keep_private_externs
7859 @opindex multi_module
7860 @opindex multiply_defined
7861 @opindex multiply_defined_unused
7863 @opindex nofixprebinding
7864 @opindex nomultidefs
7866 @opindex noseglinkedit
7867 @opindex pagezero_size
7869 @opindex prebind_all_twolevel_modules
7870 @opindex private_bundle
7871 @opindex read_only_relocs
7873 @opindex sectobjectsymbols
7877 @opindex sectobjectsymbols
7879 @opindex seg_addr_table
7880 @opindex seg_addr_table_filename
7881 @opindex seglinkedit
7883 @opindex segs_read_only_addr
7884 @opindex segs_read_write_addr
7885 @opindex single_module
7887 @opindex sub_library
7888 @opindex sub_umbrella
7889 @opindex twolevel_namespace
7892 @opindex unexported_symbols_list
7893 @opindex weak_reference_mismatches
7894 @opindex whatsloaded
7896 This options are available for Darwin linker. Darwin linker man page
7897 describes them in detail.
7902 @subsection IBM RT Options
7904 @cindex IBM RT options
7906 These @samp{-m} options are defined for the IBM RT PC:
7910 @opindex min-line-mul
7911 Use an in-line code sequence for integer multiplies. This is the
7914 @item -mcall-lib-mul
7915 @opindex mcall-lib-mul
7916 Call @code{lmul$$} for integer multiples.
7918 @item -mfull-fp-blocks
7919 @opindex mfull-fp-blocks
7920 Generate full-size floating point data blocks, including the minimum
7921 amount of scratch space recommended by IBM@. This is the default.
7923 @item -mminimum-fp-blocks
7924 @opindex mminimum-fp-blocks
7925 Do not include extra scratch space in floating point data blocks. This
7926 results in smaller code, but slower execution, since scratch space must
7927 be allocated dynamically.
7929 @cindex @file{stdarg.h} and RT PC
7930 @item -mfp-arg-in-fpregs
7931 @opindex mfp-arg-in-fpregs
7932 Use a calling sequence incompatible with the IBM calling convention in
7933 which floating point arguments are passed in floating point registers.
7934 Note that @code{stdarg.h} will not work with floating point operands
7935 if this option is specified.
7937 @item -mfp-arg-in-gregs
7938 @opindex mfp-arg-in-gregs
7939 Use the normal calling convention for floating point arguments. This is
7942 @item -mhc-struct-return
7943 @opindex mhc-struct-return
7944 Return structures of more than one word in memory, rather than in a
7945 register. This provides compatibility with the MetaWare HighC (hc)
7946 compiler. Use the option @option{-fpcc-struct-return} for compatibility
7947 with the Portable C Compiler (pcc).
7949 @item -mnohc-struct-return
7950 @opindex mnohc-struct-return
7951 Return some structures of more than one word in registers, when
7952 convenient. This is the default. For compatibility with the
7953 IBM-supplied compilers, use the option @option{-fpcc-struct-return} or the
7954 option @option{-mhc-struct-return}.
7958 @subsection MIPS Options
7959 @cindex MIPS options
7961 These @samp{-m} options are defined for the MIPS family of computers:
7965 @item -march=@var{arch}
7967 Generate code that will run on @var{arch}, which can be the name of a
7968 generic MIPS ISA, or the name of a particular processor.
7970 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
7971 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
7972 The processor names are:
7973 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
7975 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
7976 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
7980 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4300},
7981 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
7982 The special value @samp{from-abi} selects the
7983 most compatible architecture for the selected ABI (that is,
7984 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
7986 In processor names, a final @samp{000} can be abbreviated as @samp{k}
7987 (for example, @samp{-march=r2k}). Prefixes are optional, and
7988 @samp{vr} may be written @samp{r}.
7990 GCC defines two macros based on the value of this option. The first
7991 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
7992 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
7993 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
7994 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
7995 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
7997 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
7998 above. In other words, it will have the full prefix and will not
7999 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
8000 the macro names the resolved architecture (either @samp{"mips1"} or
8001 @samp{"mips3"}). It names the default architecture when no
8002 @option{-march} option is given.
8004 @item -mtune=@var{arch}
8006 Optimize for @var{arch}. Among other things, this option controls
8007 the way instructions are scheduled, and the perceived cost of arithmetic
8008 operations. The list of @var{arch} values is the same as for
8011 When this option is not used, GCC will optimize for the processor
8012 specified by @option{-march}. By using @option{-march} and
8013 @option{-mtune} together, it is possible to generate code that will
8014 run on a family of processors, but optimize the code for one
8015 particular member of that family.
8017 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
8018 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
8019 @samp{-march} ones described above.
8023 Equivalent to @samp{-march=mips1}.
8027 Equivalent to @samp{-march=mips2}.
8031 Equivalent to @samp{-march=mips3}.
8035 Equivalent to @samp{-march=mips4}.
8039 Equivalent to @samp{-march=mips32}.
8043 Equivalent to @samp{-march=mips32r2}.
8047 Equivalent to @samp{-march=mips64}.
8050 @itemx -mno-fused-madd
8051 @opindex mfused-madd
8052 @opindex mno-fused-madd
8053 Generate code that uses (does not use) the floating point multiply and
8054 accumulate instructions, when they are available. These instructions
8055 are generated by default if they are available, but this may be
8056 undesirable if the extra precision causes problems or on certain chips
8057 in the mode where denormals are rounded to zero where denormals
8058 generated by multiply and accumulate instructions cause exceptions
8063 Assume that floating point registers are 32 bits wide.
8067 Assume that floating point registers are 64 bits wide.
8071 Assume that general purpose registers are 32 bits wide.
8075 Assume that general purpose registers are 64 bits wide.
8079 Force int and long types to be 64 bits wide. See @option{-mlong32} for an
8080 explanation of the default, and the width of pointers.
8084 Force long types to be 64 bits wide. See @option{-mlong32} for an
8085 explanation of the default, and the width of pointers.
8089 Force long, int, and pointer types to be 32 bits wide.
8091 The default size of ints, longs and pointers depends on the ABI@. All
8092 the supported ABIs use 32-bit ints. The n64 ABI uses 64-bit longs, as
8093 does the 64-bit Cygnus EABI; the others use 32-bit longs. Pointers
8094 are the same size as longs, or the same size as integer registers,
8095 whichever is smaller.
8109 Generate code for the given ABI@.
8111 Note that there are two embedded ABIs: @option{-mabi=eabi}
8112 selects the one defined by Cygnus while @option{-meabi=meabi}
8113 selects the one defined by MIPS@. Both these ABIs have
8114 32-bit and 64-bit variants. Normally, GCC will generate
8115 64-bit code when you select a 64-bit architecture, but you
8116 can use @option{-mgp32} to get 32-bit code instead.
8118 @item -mabi-fake-default
8119 @opindex mabi-fake-default
8120 You don't want to know what this option does. No, really. I mean
8121 it. Move on to the next option.
8123 What? You're still here? Oh, well@enddots{} Ok, here's the deal. GCC
8124 wants the default set of options to get the root of the multilib tree,
8125 and the shared library SONAMEs without any multilib-indicating
8126 suffixes. This is not convenience for @samp{mips64-linux-gnu}, since
8127 we want to default to the N32 ABI, while still being binary-compatible
8128 with @samp{mips-linux-gnu} if you stick to the O32 ABI@. Being
8129 binary-compatible means shared libraries should have the same SONAMEs,
8130 and libraries should live in the same location. Having O32 libraries
8131 in a sub-directory named say @file{o32} is not acceptable.
8133 So we trick GCC into believing that O32 is the default ABI, except
8134 that we override the default with some internal command-line
8135 processing magic. Problem is, if we stopped at that, and you then
8136 created a multilib-aware package that used the output of @command{gcc
8137 -print-multi-lib} to decide which multilibs to build, and how, and
8138 you'd find yourself in an awkward situation when you found out that
8139 some of the options listed ended up mapping to the same multilib, and
8140 none of your libraries was actually built for the multilib that
8141 @option{-print-multi-lib} claims to be the default. So we added this
8142 option that disables the default switcher, falling back to GCC's
8143 original notion of the default library. Confused yet?
8145 For short: don't ever use this option, unless you find it in the list
8146 of additional options to be used when building for multilibs, in the
8147 output of @option{gcc -print-multi-lib}.
8151 Generate code for the MIPS assembler, and invoke @file{mips-tfile} to
8152 add normal debug information. This is the default for all
8153 platforms except for the OSF/1 reference platform, using the OSF/rose
8154 object format. If the either of the @option{-gstabs} or @option{-gstabs+}
8155 switches are used, the @file{mips-tfile} program will encapsulate the
8156 stabs within MIPS ECOFF@.
8160 Generate code for the GNU assembler. This is the default on the OSF/1
8161 reference platform, using the OSF/rose object format. Also, this is
8162 the default if the configure option @option{--with-gnu-as} is used.
8164 @item -msplit-addresses
8165 @itemx -mno-split-addresses
8166 @opindex msplit-addresses
8167 @opindex mno-split-addresses
8168 Generate code to load the high and low parts of address constants separately.
8169 This allows GCC to optimize away redundant loads of the high order
8170 bits of addresses. This optimization requires GNU as and GNU ld.
8171 This optimization is enabled by default for some embedded targets where
8172 GNU as and GNU ld are standard.
8178 The @option{-mrnames} switch says to output code using the MIPS software
8179 names for the registers, instead of the hardware names (ie, @var{a0}
8180 instead of @var{$4}). The only known assembler that supports this option
8181 is the Algorithmics assembler.
8187 The @option{-mmemcpy} switch makes all block moves call the appropriate
8188 string function (@samp{memcpy} or @samp{bcopy}) instead of possibly
8189 generating inline code.
8192 @itemx -mno-mips-tfile
8193 @opindex mmips-tfile
8194 @opindex mno-mips-tfile
8195 The @option{-mno-mips-tfile} switch causes the compiler not
8196 postprocess the object file with the @file{mips-tfile} program,
8197 after the MIPS assembler has generated it to add debug support. If
8198 @file{mips-tfile} is not run, then no local variables will be
8199 available to the debugger. In addition, @file{stage2} and
8200 @file{stage3} objects will have the temporary file names passed to the
8201 assembler embedded in the object file, which means the objects will
8202 not compare the same. The @option{-mno-mips-tfile} switch should only
8203 be used when there are bugs in the @file{mips-tfile} program that
8204 prevents compilation.
8207 @opindex msoft-float
8208 Generate output containing library calls for floating point.
8209 @strong{Warning:} the requisite libraries are not part of GCC@.
8210 Normally the facilities of the machine's usual C compiler are used, but
8211 this can't be done directly in cross-compilation. You must make your
8212 own arrangements to provide suitable library functions for
8216 @opindex mhard-float
8217 Generate output containing floating point instructions. This is the
8218 default if you use the unmodified sources.
8221 @itemx -mno-abicalls
8223 @opindex mno-abicalls
8224 Emit (or do not emit) the pseudo operations @samp{.abicalls},
8225 @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for
8226 position independent code.
8232 Lift (or do not lift) the usual restrictions on the size of the global
8235 GCC normally uses a single instruction to load values from the GOT.
8236 While this is relatively efficient, it will only work if the GOT
8237 is smaller than about 64k. Anything larger will cause the linker
8238 to report an error such as:
8240 @cindex relocation truncated to fit (MIPS)
8242 relocation truncated to fit: R_MIPS_GOT16 foobar
8245 If this happens, you should recompile your code with @option{-mxgot}.
8246 It should then work with very large GOTs, although it will also be
8247 less efficient, since it will take three instructions to fetch the
8248 value of a global symbol.
8250 Note that some linkers can create multiple GOTs. If you have such a
8251 linker, you should only need to use @option{-mxgot} when a single object
8252 file accesses more than 64k's worth of GOT entries. Very few do.
8254 These options have no effect unless GCC is generating position
8258 @itemx -mno-long-calls
8259 @opindex mlong-calls
8260 @opindex mno-long-calls
8261 Do all calls with the @samp{JALR} instruction, which requires
8262 loading up a function's address into a register before the call.
8263 You need to use this switch, if you call outside of the current
8264 512 megabyte segment to functions that are not through pointers.
8266 @item -membedded-pic
8267 @itemx -mno-embedded-pic
8268 @opindex membedded-pic
8269 @opindex mno-embedded-pic
8270 Generate PIC code suitable for some embedded systems. All calls are
8271 made using PC relative address, and all data is addressed using the $gp
8272 register. No more than 65536 bytes of global data may be used. This
8273 requires GNU as and GNU ld which do most of the work. This currently
8274 only works on targets which use ECOFF; it does not work with ELF@.
8276 @item -membedded-data
8277 @itemx -mno-embedded-data
8278 @opindex membedded-data
8279 @opindex mno-embedded-data
8280 Allocate variables to the read-only data section first if possible, then
8281 next in the small data section if possible, otherwise in data. This gives
8282 slightly slower code than the default, but reduces the amount of RAM required
8283 when executing, and thus may be preferred for some embedded systems.
8285 @item -muninit-const-in-rodata
8286 @itemx -mno-uninit-const-in-rodata
8287 @opindex muninit-const-in-rodata
8288 @opindex mno-uninit-const-in-rodata
8289 When used together with @option{-membedded-data}, it will always store uninitialized
8290 const variables in the read-only data section.
8292 @item -msingle-float
8293 @itemx -mdouble-float
8294 @opindex msingle-float
8295 @opindex mdouble-float
8296 The @option{-msingle-float} switch tells gcc to assume that the floating
8297 point coprocessor only supports single precision operations, as on the
8298 @samp{r4650} chip. The @option{-mdouble-float} switch permits gcc to use
8299 double precision operations. This is the default.
8305 Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions,
8306 as on the @samp{r4650} chip.
8310 Turns on @option{-msingle-float}, @option{-mmad}, and, at least for now,
8311 @option{-mcpu=r4650}.
8317 Enable 16-bit instructions.
8321 Compile code for the processor in little endian mode.
8322 The requisite libraries are assumed to exist.
8326 Compile code for the processor in big endian mode.
8327 The requisite libraries are assumed to exist.
8331 @cindex smaller data references (MIPS)
8332 @cindex gp-relative references (MIPS)
8333 Put global and static items less than or equal to @var{num} bytes into
8334 the small data or bss sections instead of the normal data or bss
8335 section. This allows the assembler to emit one word memory reference
8336 instructions based on the global pointer (@var{gp} or @var{$28}),
8337 instead of the normal two words used. By default, @var{num} is 8 when
8338 the MIPS assembler is used, and 0 when the GNU assembler is used. The
8339 @option{-G @var{num}} switch is also passed to the assembler and linker.
8340 All modules should be compiled with the same @option{-G @var{num}}
8345 Tell the MIPS assembler to not run its preprocessor over user
8346 assembler files (with a @samp{.s} suffix) when assembling them.
8350 Pass an option to gas which will cause nops to be inserted if
8351 the read of the destination register of an mfhi or mflo instruction
8352 occurs in the following two instructions.
8357 Work around certain SB-1 CPU core errata.
8358 (This flag currently works around the SB-1 revision 2
8359 ``F1'' and ``F2'' floating point errata.)
8363 Do not include the default crt0.
8365 @item -mflush-func=@var{func}
8366 @itemx -mno-flush-func
8367 @opindex mflush-func
8368 Specifies the function to call to flush the I and D caches, or to not
8369 call any such function. If called, the function must take the same
8370 arguments as the common @code{_flush_func()}, that is, the address of the
8371 memory range for which the cache is being flushed, the size of the
8372 memory range, and the number 3 (to flush both caches). The default
8373 depends on the target gcc was configured for, but commonly is either
8374 @samp{_flush_func} or @samp{__cpu_flush}.
8376 @item -mbranch-likely
8377 @itemx -mno-branch-likely
8378 @opindex mbranch-likely
8379 @opindex mno-branch-likely
8380 Enable or disable use of Branch Likely instructions, regardless of the
8381 default for the selected architecture. By default, Branch Likely
8382 instructions may be generated if they are supported by the selected
8383 architecture. An exception is for the MIPS32 and MIPS64 architectures
8384 and processors which implement those architectures; for those, Branch
8385 Likely instructions will not be generated by default because the MIPS32
8386 and MIPS64 architectures specifically deprecate their use.
8389 @node i386 and x86-64 Options
8390 @subsection Intel 386 and AMD x86-64 Options
8391 @cindex i386 Options
8392 @cindex x86-64 Options
8393 @cindex Intel 386 Options
8394 @cindex AMD x86-64 Options
8396 These @samp{-m} options are defined for the i386 and x86-64 family of
8400 @item -mtune=@var{cpu-type}
8402 Tune to @var{cpu-type} everything applicable about the generated code, except
8403 for the ABI and the set of available instructions. The choices for
8404 @var{cpu-type} are @samp{i386}, @samp{i486}, @samp{i586}, @samp{i686},
8405 @samp{pentium}, @samp{pentium-mmx}, @samp{pentiumpro}, @samp{pentium2},
8406 @samp{pentium3}, @samp{pentium4}, @samp{k6}, @samp{k6-2}, @samp{k6-3},
8407 @samp{athlon}, @samp{athlon-tbird}, @samp{athlon-4}, @samp{athlon-xp},
8408 @samp{athlon-mp}, @samp{winchip-c6}, @samp{winchip2}, @samp{k8}, @samp{c3}
8411 While picking a specific @var{cpu-type} will schedule things appropriately
8412 for that particular chip, the compiler will not generate any code that
8413 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8414 being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686}
8415 is equivalent to @samp{pentiumpro}. @samp{k6} and @samp{athlon} are the
8416 AMD chips as opposed to the Intel ones.
8418 @item -march=@var{cpu-type}
8420 Generate instructions for the machine type @var{cpu-type}. The choices
8421 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8422 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8424 @item -mcpu=@var{cpu-type}
8426 A deprecated synonym for @option{-mtune}.
8435 @opindex mpentiumpro
8436 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8437 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8438 These synonyms are deprecated.
8440 @item -mfpmath=@var{unit}
8442 generate floating point arithmetics for selected unit @var{unit}. the choices
8447 Use the standard 387 floating point coprocessor present majority of chips and
8448 emulated otherwise. Code compiled with this option will run almost everywhere.
8449 The temporary results are computed in 80bit precision instead of precision
8450 specified by the type resulting in slightly different results compared to most
8451 of other chips. See @option{-ffloat-store} for more detailed description.
8453 This is the default choice for i386 compiler.
8456 Use scalar floating point instructions present in the SSE instruction set.
8457 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8458 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8459 instruction set supports only single precision arithmetics, thus the double and
8460 extended precision arithmetics is still done using 387. Later version, present
8461 only in Pentium4 and the future AMD x86-64 chips supports double precision
8464 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8465 @option{-msse2} switches to enable SSE extensions and make this option
8466 effective. For x86-64 compiler, these extensions are enabled by default.
8468 The resulting code should be considerably faster in majority of cases and avoid
8469 the numerical instability problems of 387 code, but may break some existing
8470 code that expects temporaries to be 80bit.
8472 This is the default choice for x86-64 compiler.
8475 Use all SSE extensions enabled by @option{-msse2} as well as the new
8476 SSE extensions in Prescott New Instructions. @option{-mpni} also
8477 enables 2 builtin functions, @code{__builtin_ia32_monitor} and
8478 @code{__builtin_ia32_mwait}, for new instructions @code{monitor} and
8482 Attempt to utilize both instruction sets at once. This effectively double the
8483 amount of available registers and on chips with separate execution units for
8484 387 and SSE the execution resources too. Use this option with care, as it is
8485 still experimental, because gcc register allocator does not model separate
8486 functional units well resulting in instable performance.
8489 @item -masm=@var{dialect}
8490 @opindex masm=@var{dialect}
8491 Output asm instructions using selected @var{dialect}. Supported choices are
8492 @samp{intel} or @samp{att} (the default one).
8497 @opindex mno-ieee-fp
8498 Control whether or not the compiler uses IEEE floating point
8499 comparisons. These handle correctly the case where the result of a
8500 comparison is unordered.
8503 @opindex msoft-float
8504 Generate output containing library calls for floating point.
8505 @strong{Warning:} the requisite libraries are not part of GCC@.
8506 Normally the facilities of the machine's usual C compiler are used, but
8507 this can't be done directly in cross-compilation. You must make your
8508 own arrangements to provide suitable library functions for
8511 On machines where a function returns floating point results in the 80387
8512 register stack, some floating point opcodes may be emitted even if
8513 @option{-msoft-float} is used.
8515 @item -mno-fp-ret-in-387
8516 @opindex mno-fp-ret-in-387
8517 Do not use the FPU registers for return values of functions.
8519 The usual calling convention has functions return values of types
8520 @code{float} and @code{double} in an FPU register, even if there
8521 is no FPU@. The idea is that the operating system should emulate
8524 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8525 in ordinary CPU registers instead.
8527 @item -mno-fancy-math-387
8528 @opindex mno-fancy-math-387
8529 Some 387 emulators do not support the @code{sin}, @code{cos} and
8530 @code{sqrt} instructions for the 387. Specify this option to avoid
8531 generating those instructions. This option is the default on FreeBSD,
8532 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8533 indicates that the target cpu will always have an FPU and so the
8534 instruction will not need emulation. As of revision 2.6.1, these
8535 instructions are not generated unless you also use the
8536 @option{-funsafe-math-optimizations} switch.
8538 @item -malign-double
8539 @itemx -mno-align-double
8540 @opindex malign-double
8541 @opindex mno-align-double
8542 Control whether GCC aligns @code{double}, @code{long double}, and
8543 @code{long long} variables on a two word boundary or a one word
8544 boundary. Aligning @code{double} variables on a two word boundary will
8545 produce code that runs somewhat faster on a @samp{Pentium} at the
8546 expense of more memory.
8548 @strong{Warning:} if you use the @option{-malign-double} switch,
8549 structures containing the above types will be aligned differently than
8550 the published application binary interface specifications for the 386
8551 and will not be binary compatible with structures in code compiled
8552 without that switch.
8554 @item -m96bit-long-double
8555 @item -m128bit-long-double
8556 @opindex m96bit-long-double
8557 @opindex m128bit-long-double
8558 These switches control the size of @code{long double} type. The i386
8559 application binary interface specifies the size to be 96 bits,
8560 so @option{-m96bit-long-double} is the default in 32 bit mode.
8562 Modern architectures (Pentium and newer) would prefer @code{long double}
8563 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8564 conforming to the ABI, this would not be possible. So specifying a
8565 @option{-m128bit-long-double} will align @code{long double}
8566 to a 16 byte boundary by padding the @code{long double} with an additional
8569 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8570 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8572 Notice that neither of these options enable any extra precision over the x87
8573 standard of 80 bits for a @code{long double}.
8575 @strong{Warning:} if you override the default value for your target ABI, the
8576 structures and arrays containing @code{long double} will change their size as
8577 well as function calling convention for function taking @code{long double}
8578 will be modified. Hence they will not be binary compatible with arrays or
8579 structures in code compiled without that switch.
8583 @itemx -mno-svr3-shlib
8584 @opindex msvr3-shlib
8585 @opindex mno-svr3-shlib
8586 Control whether GCC places uninitialized local variables into the
8587 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8588 into @code{bss}. These options are meaningful only on System V Release 3.
8592 Use a different function-calling convention, in which functions that
8593 take a fixed number of arguments return with the @code{ret} @var{num}
8594 instruction, which pops their arguments while returning. This saves one
8595 instruction in the caller since there is no need to pop the arguments
8598 You can specify that an individual function is called with this calling
8599 sequence with the function attribute @samp{stdcall}. You can also
8600 override the @option{-mrtd} option by using the function attribute
8601 @samp{cdecl}. @xref{Function Attributes}.
8603 @strong{Warning:} this calling convention is incompatible with the one
8604 normally used on Unix, so you cannot use it if you need to call
8605 libraries compiled with the Unix compiler.
8607 Also, you must provide function prototypes for all functions that
8608 take variable numbers of arguments (including @code{printf});
8609 otherwise incorrect code will be generated for calls to those
8612 In addition, seriously incorrect code will result if you call a
8613 function with too many arguments. (Normally, extra arguments are
8614 harmlessly ignored.)
8616 @item -mregparm=@var{num}
8618 Control how many registers are used to pass integer arguments. By
8619 default, no registers are used to pass arguments, and at most 3
8620 registers can be used. You can control this behavior for a specific
8621 function by using the function attribute @samp{regparm}.
8622 @xref{Function Attributes}.
8624 @strong{Warning:} if you use this switch, and
8625 @var{num} is nonzero, then you must build all modules with the same
8626 value, including any libraries. This includes the system libraries and
8629 @item -mpreferred-stack-boundary=@var{num}
8630 @opindex mpreferred-stack-boundary
8631 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8632 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8633 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8634 size (@option{-Os}), in which case the default is the minimum correct
8635 alignment (4 bytes for x86, and 8 bytes for x86-64).
8637 On Pentium and PentiumPro, @code{double} and @code{long double} values
8638 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8639 suffer significant run time performance penalties. On Pentium III, the
8640 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8641 penalties if it is not 16 byte aligned.
8643 To ensure proper alignment of this values on the stack, the stack boundary
8644 must be as aligned as that required by any value stored on the stack.
8645 Further, every function must be generated such that it keeps the stack
8646 aligned. Thus calling a function compiled with a higher preferred
8647 stack boundary from a function compiled with a lower preferred stack
8648 boundary will most likely misalign the stack. It is recommended that
8649 libraries that use callbacks always use the default setting.
8651 This extra alignment does consume extra stack space, and generally
8652 increases code size. Code that is sensitive to stack space usage, such
8653 as embedded systems and operating system kernels, may want to reduce the
8654 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8672 These switches enable or disable the use of built-in functions that allow
8673 direct access to the MMX, SSE and 3Dnow extensions of the instruction set.
8675 @xref{X86 Built-in Functions}, for details of the functions enabled
8676 and disabled by these switches.
8678 To have SSE/SSE2 instructions generated automatically from floating-point
8679 code, see @option{-mfpmath=sse}.
8682 @itemx -mno-push-args
8684 @opindex mno-push-args
8685 Use PUSH operations to store outgoing parameters. This method is shorter
8686 and usually equally fast as method using SUB/MOV operations and is enabled
8687 by default. In some cases disabling it may improve performance because of
8688 improved scheduling and reduced dependencies.
8690 @item -maccumulate-outgoing-args
8691 @opindex maccumulate-outgoing-args
8692 If enabled, the maximum amount of space required for outgoing arguments will be
8693 computed in the function prologue. This is faster on most modern CPUs
8694 because of reduced dependencies, improved scheduling and reduced stack usage
8695 when preferred stack boundary is not equal to 2. The drawback is a notable
8696 increase in code size. This switch implies @option{-mno-push-args}.
8700 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8701 on thread-safe exception handling must compile and link all code with the
8702 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8703 @option{-D_MT}; when linking, it links in a special thread helper library
8704 @option{-lmingwthrd} which cleans up per thread exception handling data.
8706 @item -mno-align-stringops
8707 @opindex mno-align-stringops
8708 Do not align destination of inlined string operations. This switch reduces
8709 code size and improves performance in case the destination is already aligned,
8710 but gcc don't know about it.
8712 @item -minline-all-stringops
8713 @opindex minline-all-stringops
8714 By default GCC inlines string operations only when destination is known to be
8715 aligned at least to 4 byte boundary. This enables more inlining, increase code
8716 size, but may improve performance of code that depends on fast memcpy, strlen
8717 and memset for short lengths.
8719 @item -momit-leaf-frame-pointer
8720 @opindex momit-leaf-frame-pointer
8721 Don't keep the frame pointer in a register for leaf functions. This
8722 avoids the instructions to save, set up and restore frame pointers and
8723 makes an extra register available in leaf functions. The option
8724 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8725 which might make debugging harder.
8727 @item -mtls-direct-seg-refs
8728 @itemx -mno-tls-direct-seg-refs
8729 @opindex mtls-direct-seg-refs
8730 Controls whether TLS variables may be accessed with offsets from the
8731 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8732 or whether the thread base pointer must be added. Whether or not this
8733 is legal depends on the operating system, and whether it maps the
8734 segment to cover the entire TLS area.
8736 For systems that use GNU libc, the default is on.
8739 These @samp{-m} switches are supported in addition to the above
8740 on AMD x86-64 processors in 64-bit environments.
8747 Generate code for a 32-bit or 64-bit environment.
8748 The 32-bit environment sets int, long and pointer to 32 bits and
8749 generates code that runs on any i386 system.
8750 The 64-bit environment sets int to 32 bits and long and pointer
8751 to 64 bits and generates code for AMD's x86-64 architecture.
8754 @opindex no-red-zone
8755 Do not use a so called red zone for x86-64 code. The red zone is mandated
8756 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8757 stack pointer that will not be modified by signal or interrupt handlers
8758 and therefore can be used for temporary data without adjusting the stack
8759 pointer. The flag @option{-mno-red-zone} disables this red zone.
8761 @item -mcmodel=small
8762 @opindex mcmodel=small
8763 Generate code for the small code model: the program and its symbols must
8764 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8765 Programs can be statically or dynamically linked. This is the default
8768 @item -mcmodel=kernel
8769 @opindex mcmodel=kernel
8770 Generate code for the kernel code model. The kernel runs in the
8771 negative 2 GB of the address space.
8772 This model has to be used for Linux kernel code.
8774 @item -mcmodel=medium
8775 @opindex mcmodel=medium
8776 Generate code for the medium model: The program is linked in the lower 2
8777 GB of the address space but symbols can be located anywhere in the
8778 address space. Programs can be statically or dynamically linked, but
8779 building of shared libraries are not supported with the medium model.
8781 @item -mcmodel=large
8782 @opindex mcmodel=large
8783 Generate code for the large model: This model makes no assumptions
8784 about addresses and sizes of sections. Currently GCC does not implement
8789 @subsection HPPA Options
8790 @cindex HPPA Options
8792 These @samp{-m} options are defined for the HPPA family of computers:
8795 @item -march=@var{architecture-type}
8797 Generate code for the specified architecture. The choices for
8798 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8799 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8800 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8801 architecture option for your machine. Code compiled for lower numbered
8802 architectures will run on higher numbered architectures, but not the
8805 PA 2.0 support currently requires gas snapshot 19990413 or later. The
8806 next release of binutils (current is 2.9.1) will probably contain PA 2.0
8810 @itemx -mpa-risc-1-1
8811 @itemx -mpa-risc-2-0
8812 @opindex mpa-risc-1-0
8813 @opindex mpa-risc-1-1
8814 @opindex mpa-risc-2-0
8815 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8818 @opindex mbig-switch
8819 Generate code suitable for big switch tables. Use this option only if
8820 the assembler/linker complain about out of range branches within a switch
8823 @item -mjump-in-delay
8824 @opindex mjump-in-delay
8825 Fill delay slots of function calls with unconditional jump instructions
8826 by modifying the return pointer for the function call to be the target
8827 of the conditional jump.
8829 @item -mdisable-fpregs
8830 @opindex mdisable-fpregs
8831 Prevent floating point registers from being used in any manner. This is
8832 necessary for compiling kernels which perform lazy context switching of
8833 floating point registers. If you use this option and attempt to perform
8834 floating point operations, the compiler will abort.
8836 @item -mdisable-indexing
8837 @opindex mdisable-indexing
8838 Prevent the compiler from using indexing address modes. This avoids some
8839 rather obscure problems when compiling MIG generated code under MACH@.
8841 @item -mno-space-regs
8842 @opindex mno-space-regs
8843 Generate code that assumes the target has no space registers. This allows
8844 GCC to generate faster indirect calls and use unscaled index address modes.
8846 Such code is suitable for level 0 PA systems and kernels.
8848 @item -mfast-indirect-calls
8849 @opindex mfast-indirect-calls
8850 Generate code that assumes calls never cross space boundaries. This
8851 allows GCC to emit code which performs faster indirect calls.
8853 This option will not work in the presence of shared libraries or nested
8856 @item -mlong-load-store
8857 @opindex mlong-load-store
8858 Generate 3-instruction load and store sequences as sometimes required by
8859 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8862 @item -mportable-runtime
8863 @opindex mportable-runtime
8864 Use the portable calling conventions proposed by HP for ELF systems.
8868 Enable the use of assembler directives only GAS understands.
8870 @item -mschedule=@var{cpu-type}
8872 Schedule code according to the constraints for the machine type
8873 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8874 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8875 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8876 proper scheduling option for your machine. The default scheduling is
8880 @opindex mlinker-opt
8881 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8882 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8883 linkers in which they give bogus error messages when linking some programs.
8886 @opindex msoft-float
8887 Generate output containing library calls for floating point.
8888 @strong{Warning:} the requisite libraries are not available for all HPPA
8889 targets. Normally the facilities of the machine's usual C compiler are
8890 used, but this cannot be done directly in cross-compilation. You must make
8891 your own arrangements to provide suitable library functions for
8892 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8893 does provide software floating point support.
8895 @option{-msoft-float} changes the calling convention in the output file;
8896 therefore, it is only useful if you compile @emph{all} of a program with
8897 this option. In particular, you need to compile @file{libgcc.a}, the
8898 library that comes with GCC, with @option{-msoft-float} in order for
8903 Generate the predefine, @code{_SIO}, for server IO. The default is
8904 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8905 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8906 options are available under HP-UX and HI-UX.
8910 Use GNU ld specific options. This passes @option{-shared} to ld when
8911 building a shared library. It is the default when GCC is configured,
8912 explicitly or implicitly, with the GNU linker. This option does not
8913 have any affect on which ld is called, it only changes what parameters
8914 are passed to that ld. The ld that is called is determined by the
8915 @option{--with-ld} configure option, gcc's program search path, and
8916 finally by the user's @env{PATH}. The linker used by GCC can be printed
8917 using @samp{which `gcc -print-prog-name=ld`}.
8921 Use HP ld specific options. This passes @option{-b} to ld when building
8922 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8923 links. It is the default when GCC is configured, explicitly or
8924 implicitly, with the HP linker. This option does not have any affect on
8925 which ld is called, it only changes what parameters are passed to that
8926 ld. The ld that is called is determined by the @option{--with-ld}
8927 configure option, gcc's program search path, and finally by the user's
8928 @env{PATH}. The linker used by GCC can be printed using @samp{which
8929 `gcc -print-prog-name=ld`}.
8932 @opindex mno-long-calls
8933 Generate code that uses long call sequences. This ensures that a call
8934 is always able to reach linker generated stubs. The default is to generate
8935 long calls only when the distance from the call site to the beginning
8936 of the function or translation unit, as the case may be, exceeds a
8937 predefined limit set by the branch type being used. The limits for
8938 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8939 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8942 Distances are measured from the beginning of functions when using the
8943 @option{-ffunction-sections} option, or when using the @option{-mgas}
8944 and @option{-mno-portable-runtime} options together under HP-UX with
8947 It is normally not desirable to use this option as it will degrade
8948 performance. However, it may be useful in large applications,
8949 particularly when partial linking is used to build the application.
8951 The types of long calls used depends on the capabilities of the
8952 assembler and linker, and the type of code being generated. The
8953 impact on systems that support long absolute calls, and long pic
8954 symbol-difference or pc-relative calls should be relatively small.
8955 However, an indirect call is used on 32-bit ELF systems in pic code
8956 and it is quite long.
8960 Suppress the generation of link options to search libdld.sl when the
8961 @option{-static} option is specified on HP-UX 10 and later.
8965 The HP-UX implementation of setlocale in libc has a dependency on
8966 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8967 when the @option{-static} option is specified, special link options
8968 are needed to resolve this dependency.
8970 On HP-UX 10 and later, the GCC driver adds the necessary options to
8971 link with libdld.sl when the @option{-static} option is specified.
8972 This causes the resulting binary to be dynamic. On the 64-bit port,
8973 the linkers generate dynamic binaries by default in any case. The
8974 @option{-nolibdld} option can be used to prevent the GCC driver from
8975 adding these link options.
8979 Add support for multithreading with the @dfn{dce thread} library
8980 under HP-UX. This option sets flags for both the preprocessor and
8984 @node Intel 960 Options
8985 @subsection Intel 960 Options
8987 These @samp{-m} options are defined for the Intel 960 implementations:
8990 @item -m@var{cpu-type}
8998 Assume the defaults for the machine type @var{cpu-type} for some of
8999 the other options, including instruction scheduling, floating point
9000 support, and addressing modes. The choices for @var{cpu-type} are
9001 @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf},
9002 @samp{sa}, and @samp{sb}.
9009 @opindex msoft-float
9010 The @option{-mnumerics} option indicates that the processor does support
9011 floating-point instructions. The @option{-msoft-float} option indicates
9012 that floating-point support should not be assumed.
9014 @item -mleaf-procedures
9015 @itemx -mno-leaf-procedures
9016 @opindex mleaf-procedures
9017 @opindex mno-leaf-procedures
9018 Do (or do not) attempt to alter leaf procedures to be callable with the
9019 @code{bal} instruction as well as @code{call}. This will result in more
9020 efficient code for explicit calls when the @code{bal} instruction can be
9021 substituted by the assembler or linker, but less efficient code in other
9022 cases, such as calls via function pointers, or using a linker that doesn't
9023 support this optimization.
9026 @itemx -mno-tail-call
9028 @opindex mno-tail-call
9029 Do (or do not) make additional attempts (beyond those of the
9030 machine-independent portions of the compiler) to optimize tail-recursive
9031 calls into branches. You may not want to do this because the detection of
9032 cases where this is not valid is not totally complete. The default is
9033 @option{-mno-tail-call}.
9035 @item -mcomplex-addr
9036 @itemx -mno-complex-addr
9037 @opindex mcomplex-addr
9038 @opindex mno-complex-addr
9039 Assume (or do not assume) that the use of a complex addressing mode is a
9040 win on this implementation of the i960. Complex addressing modes may not
9041 be worthwhile on the K-series, but they definitely are on the C-series.
9042 The default is currently @option{-mcomplex-addr} for all processors except
9046 @itemx -mno-code-align
9047 @opindex mcode-align
9048 @opindex mno-code-align
9049 Align code to 8-byte boundaries for faster fetching (or don't bother).
9050 Currently turned on by default for C-series implementations only.
9053 @item -mclean-linkage
9054 @itemx -mno-clean-linkage
9055 @opindex mclean-linkage
9056 @opindex mno-clean-linkage
9057 These options are not fully implemented.
9061 @itemx -mic2.0-compat
9062 @itemx -mic3.0-compat
9064 @opindex mic2.0-compat
9065 @opindex mic3.0-compat
9066 Enable compatibility with iC960 v2.0 or v3.0.
9070 @opindex masm-compat
9072 Enable compatibility with the iC960 assembler.
9074 @item -mstrict-align
9075 @itemx -mno-strict-align
9076 @opindex mstrict-align
9077 @opindex mno-strict-align
9078 Do not permit (do permit) unaligned accesses.
9082 Enable structure-alignment compatibility with Intel's gcc release version
9083 1.3 (based on gcc 1.37). This option implies @option{-mstrict-align}.
9085 @item -mlong-double-64
9086 @opindex mlong-double-64
9087 Implement type @samp{long double} as 64-bit floating point numbers.
9088 Without the option @samp{long double} is implemented by 80-bit
9089 floating point numbers. The only reason we have it because there is
9090 no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it
9091 is only useful for people using soft-float targets. Otherwise, we
9092 should recommend against use of it.
9096 @node DEC Alpha Options
9097 @subsection DEC Alpha Options
9099 These @samp{-m} options are defined for the DEC Alpha implementations:
9102 @item -mno-soft-float
9104 @opindex mno-soft-float
9105 @opindex msoft-float
9106 Use (do not use) the hardware floating-point instructions for
9107 floating-point operations. When @option{-msoft-float} is specified,
9108 functions in @file{libgcc.a} will be used to perform floating-point
9109 operations. Unless they are replaced by routines that emulate the
9110 floating-point operations, or compiled in such a way as to call such
9111 emulations routines, these routines will issue floating-point
9112 operations. If you are compiling for an Alpha without floating-point
9113 operations, you must ensure that the library is built so as not to call
9116 Note that Alpha implementations without floating-point operations are
9117 required to have floating-point registers.
9122 @opindex mno-fp-regs
9123 Generate code that uses (does not use) the floating-point register set.
9124 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9125 register set is not used, floating point operands are passed in integer
9126 registers as if they were integers and floating-point results are passed
9127 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9128 so any function with a floating-point argument or return value called by code
9129 compiled with @option{-mno-fp-regs} must also be compiled with that
9132 A typical use of this option is building a kernel that does not use,
9133 and hence need not save and restore, any floating-point registers.
9137 The Alpha architecture implements floating-point hardware optimized for
9138 maximum performance. It is mostly compliant with the IEEE floating
9139 point standard. However, for full compliance, software assistance is
9140 required. This option generates code fully IEEE compliant code
9141 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9142 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9143 defined during compilation. The resulting code is less efficient but is
9144 able to correctly support denormalized numbers and exceptional IEEE
9145 values such as not-a-number and plus/minus infinity. Other Alpha
9146 compilers call this option @option{-ieee_with_no_inexact}.
9148 @item -mieee-with-inexact
9149 @opindex mieee-with-inexact
9150 This is like @option{-mieee} except the generated code also maintains
9151 the IEEE @var{inexact-flag}. Turning on this option causes the
9152 generated code to implement fully-compliant IEEE math. In addition to
9153 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9154 macro. On some Alpha implementations the resulting code may execute
9155 significantly slower than the code generated by default. Since there is
9156 very little code that depends on the @var{inexact-flag}, you should
9157 normally not specify this option. Other Alpha compilers call this
9158 option @option{-ieee_with_inexact}.
9160 @item -mfp-trap-mode=@var{trap-mode}
9161 @opindex mfp-trap-mode
9162 This option controls what floating-point related traps are enabled.
9163 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9164 The trap mode can be set to one of four values:
9168 This is the default (normal) setting. The only traps that are enabled
9169 are the ones that cannot be disabled in software (e.g., division by zero
9173 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9177 Like @samp{su}, but the instructions are marked to be safe for software
9178 completion (see Alpha architecture manual for details).
9181 Like @samp{su}, but inexact traps are enabled as well.
9184 @item -mfp-rounding-mode=@var{rounding-mode}
9185 @opindex mfp-rounding-mode
9186 Selects the IEEE rounding mode. Other Alpha compilers call this option
9187 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9192 Normal IEEE rounding mode. Floating point numbers are rounded towards
9193 the nearest machine number or towards the even machine number in case
9197 Round towards minus infinity.
9200 Chopped rounding mode. Floating point numbers are rounded towards zero.
9203 Dynamic rounding mode. A field in the floating point control register
9204 (@var{fpcr}, see Alpha architecture reference manual) controls the
9205 rounding mode in effect. The C library initializes this register for
9206 rounding towards plus infinity. Thus, unless your program modifies the
9207 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9210 @item -mtrap-precision=@var{trap-precision}
9211 @opindex mtrap-precision
9212 In the Alpha architecture, floating point traps are imprecise. This
9213 means without software assistance it is impossible to recover from a
9214 floating trap and program execution normally needs to be terminated.
9215 GCC can generate code that can assist operating system trap handlers
9216 in determining the exact location that caused a floating point trap.
9217 Depending on the requirements of an application, different levels of
9218 precisions can be selected:
9222 Program precision. This option is the default and means a trap handler
9223 can only identify which program caused a floating point exception.
9226 Function precision. The trap handler can determine the function that
9227 caused a floating point exception.
9230 Instruction precision. The trap handler can determine the exact
9231 instruction that caused a floating point exception.
9234 Other Alpha compilers provide the equivalent options called
9235 @option{-scope_safe} and @option{-resumption_safe}.
9237 @item -mieee-conformant
9238 @opindex mieee-conformant
9239 This option marks the generated code as IEEE conformant. You must not
9240 use this option unless you also specify @option{-mtrap-precision=i} and either
9241 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9242 is to emit the line @samp{.eflag 48} in the function prologue of the
9243 generated assembly file. Under DEC Unix, this has the effect that
9244 IEEE-conformant math library routines will be linked in.
9246 @item -mbuild-constants
9247 @opindex mbuild-constants
9248 Normally GCC examines a 32- or 64-bit integer constant to
9249 see if it can construct it from smaller constants in two or three
9250 instructions. If it cannot, it will output the constant as a literal and
9251 generate code to load it from the data segment at runtime.
9253 Use this option to require GCC to construct @emph{all} integer constants
9254 using code, even if it takes more instructions (the maximum is six).
9256 You would typically use this option to build a shared library dynamic
9257 loader. Itself a shared library, it must relocate itself in memory
9258 before it can find the variables and constants in its own data segment.
9264 Select whether to generate code to be assembled by the vendor-supplied
9265 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9283 Indicate whether GCC should generate code to use the optional BWX,
9284 CIX, FIX and MAX instruction sets. The default is to use the instruction
9285 sets supported by the CPU type specified via @option{-mcpu=} option or that
9286 of the CPU on which GCC was built if none was specified.
9291 @opindex mfloat-ieee
9292 Generate code that uses (does not use) VAX F and G floating point
9293 arithmetic instead of IEEE single and double precision.
9295 @item -mexplicit-relocs
9296 @itemx -mno-explicit-relocs
9297 @opindex mexplicit-relocs
9298 @opindex mno-explicit-relocs
9299 Older Alpha assemblers provided no way to generate symbol relocations
9300 except via assembler macros. Use of these macros does not allow
9301 optimal instruction scheduling. GNU binutils as of version 2.12
9302 supports a new syntax that allows the compiler to explicitly mark
9303 which relocations should apply to which instructions. This option
9304 is mostly useful for debugging, as GCC detects the capabilities of
9305 the assembler when it is built and sets the default accordingly.
9309 @opindex msmall-data
9310 @opindex mlarge-data
9311 When @option{-mexplicit-relocs} is in effect, static data is
9312 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9313 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9314 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9315 16-bit relocations off of the @code{$gp} register. This limits the
9316 size of the small data area to 64KB, but allows the variables to be
9317 directly accessed via a single instruction.
9319 The default is @option{-mlarge-data}. With this option the data area
9320 is limited to just below 2GB. Programs that require more than 2GB of
9321 data must use @code{malloc} or @code{mmap} to allocate the data in the
9322 heap instead of in the program's data segment.
9324 When generating code for shared libraries, @option{-fpic} implies
9325 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9329 @opindex msmall-text
9330 @opindex mlarge-text
9331 When @option{-msmall-text} is used, the compiler assumes that the
9332 code of the entire program (or shared library) fits in 4MB, and is
9333 thus reachable with a branch instruction. When @option{-msmall-data}
9334 is used, the compiler can assume that all local symbols share the
9335 same @code{$gp} value, and thus reduce the number of instructions
9336 required for a function call from 4 to 1.
9338 The default is @option{-mlarge-text}.
9340 @item -mcpu=@var{cpu_type}
9342 Set the instruction set and instruction scheduling parameters for
9343 machine type @var{cpu_type}. You can specify either the @samp{EV}
9344 style name or the corresponding chip number. GCC supports scheduling
9345 parameters for the EV4, EV5 and EV6 family of processors and will
9346 choose the default values for the instruction set from the processor
9347 you specify. If you do not specify a processor type, GCC will default
9348 to the processor on which the compiler was built.
9350 Supported values for @var{cpu_type} are
9356 Schedules as an EV4 and has no instruction set extensions.
9360 Schedules as an EV5 and has no instruction set extensions.
9364 Schedules as an EV5 and supports the BWX extension.
9369 Schedules as an EV5 and supports the BWX and MAX extensions.
9373 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9377 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9380 @item -mtune=@var{cpu_type}
9382 Set only the instruction scheduling parameters for machine type
9383 @var{cpu_type}. The instruction set is not changed.
9385 @item -mmemory-latency=@var{time}
9386 @opindex mmemory-latency
9387 Sets the latency the scheduler should assume for typical memory
9388 references as seen by the application. This number is highly
9389 dependent on the memory access patterns used by the application
9390 and the size of the external cache on the machine.
9392 Valid options for @var{time} are
9396 A decimal number representing clock cycles.
9402 The compiler contains estimates of the number of clock cycles for
9403 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9404 (also called Dcache, Scache, and Bcache), as well as to main memory.
9405 Note that L3 is only valid for EV5.
9410 @node DEC Alpha/VMS Options
9411 @subsection DEC Alpha/VMS Options
9413 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9416 @item -mvms-return-codes
9417 @opindex mvms-return-codes
9418 Return VMS condition codes from main. The default is to return POSIX
9419 style condition (e.g.@ error) codes.
9422 @node H8/300 Options
9423 @subsection H8/300 Options
9425 These @samp{-m} options are defined for the H8/300 implementations:
9430 Shorten some address references at link time, when possible; uses the
9431 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9432 ld.info, Using ld}, for a fuller description.
9436 Generate code for the H8/300H@.
9440 Generate code for the H8S@.
9444 Generate code for the H8S and H8/300H in the normal mode. This switch
9445 must be used either with -mh or -ms.
9449 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9453 Make @code{int} data 32 bits by default.
9457 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9458 The default for the H8/300H and H8S is to align longs and floats on 4
9460 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9461 This option has no effect on the H8/300.
9465 @subsection SH Options
9467 These @samp{-m} options are defined for the SH implementations:
9472 Generate code for the SH1.
9476 Generate code for the SH2.
9479 Generate code for the SH2e.
9483 Generate code for the SH3.
9487 Generate code for the SH3e.
9491 Generate code for the SH4 without a floating-point unit.
9493 @item -m4-single-only
9494 @opindex m4-single-only
9495 Generate code for the SH4 with a floating-point unit that only
9496 supports single-precision arithmetic.
9500 Generate code for the SH4 assuming the floating-point unit is in
9501 single-precision mode by default.
9505 Generate code for the SH4.
9509 Compile code for the processor in big endian mode.
9513 Compile code for the processor in little endian mode.
9517 Align doubles at 64-bit boundaries. Note that this changes the calling
9518 conventions, and thus some functions from the standard C library will
9519 not work unless you recompile it first with @option{-mdalign}.
9523 Shorten some address references at link time, when possible; uses the
9524 linker option @option{-relax}.
9528 Use 32-bit offsets in @code{switch} tables. The default is to use
9533 Enable the use of the instruction @code{fmovd}.
9537 Comply with the calling conventions defined by Renesas.
9541 Mark the @code{MAC} register as call-clobbered, even if
9542 @option{-mhitachi} is given.
9546 Increase IEEE-compliance of floating-point code.
9550 Dump instruction size and location in the assembly code.
9554 This option is deprecated. It pads structures to multiple of 4 bytes,
9555 which is incompatible with the SH ABI@.
9559 Optimize for space instead of speed. Implied by @option{-Os}.
9563 When generating position-independent code, emit function calls using
9564 the Global Offset Table instead of the Procedure Linkage Table.
9568 Generate a library function call to invalidate instruction cache
9569 entries, after fixing up a trampoline. This library function call
9570 doesn't assume it can write to the whole memory address space. This
9571 is the default when the target is @code{sh-*-linux*}.
9574 @node System V Options
9575 @subsection Options for System V
9577 These additional options are available on System V Release 4 for
9578 compatibility with other compilers on those systems:
9583 Create a shared object.
9584 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
9588 Identify the versions of each tool used by the compiler, in a
9589 @code{.ident} assembler directive in the output.
9593 Refrain from adding @code{.ident} directives to the output file (this is
9596 @item -YP,@var{dirs}
9598 Search the directories @var{dirs}, and no others, for libraries
9599 specified with @option{-l}.
9603 Look in the directory @var{dir} to find the M4 preprocessor.
9604 The assembler uses this option.
9605 @c This is supposed to go with a -Yd for predefined M4 macro files, but
9606 @c the generic assembler that comes with Solaris takes just -Ym.
9609 @node TMS320C3x/C4x Options
9610 @subsection TMS320C3x/C4x Options
9611 @cindex TMS320C3x/C4x Options
9613 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
9617 @item -mcpu=@var{cpu_type}
9619 Set the instruction set, register set, and instruction scheduling
9620 parameters for machine type @var{cpu_type}. Supported values for
9621 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
9622 @samp{c44}. The default is @samp{c40} to generate code for the
9627 @itemx -msmall-memory
9629 @opindex mbig-memory
9631 @opindex msmall-memory
9633 Generates code for the big or small memory model. The small memory
9634 model assumed that all data fits into one 64K word page. At run-time
9635 the data page (DP) register must be set to point to the 64K page
9636 containing the .bss and .data program sections. The big memory model is
9637 the default and requires reloading of the DP register for every direct
9644 Allow (disallow) allocation of general integer operands into the block
9651 Enable (disable) generation of code using decrement and branch,
9652 DBcond(D), instructions. This is enabled by default for the C4x. To be
9653 on the safe side, this is disabled for the C3x, since the maximum
9654 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
9655 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
9656 that it can utilize the decrement and branch instruction, but will give
9657 up if there is more than one memory reference in the loop. Thus a loop
9658 where the loop counter is decremented can generate slightly more
9659 efficient code, in cases where the RPTB instruction cannot be utilized.
9661 @item -mdp-isr-reload
9663 @opindex mdp-isr-reload
9665 Force the DP register to be saved on entry to an interrupt service
9666 routine (ISR), reloaded to point to the data section, and restored on
9667 exit from the ISR@. This should not be required unless someone has
9668 violated the small memory model by modifying the DP register, say within
9675 For the C3x use the 24-bit MPYI instruction for integer multiplies
9676 instead of a library call to guarantee 32-bit results. Note that if one
9677 of the operands is a constant, then the multiplication will be performed
9678 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
9679 then squaring operations are performed inline instead of a library call.
9682 @itemx -mno-fast-fix
9684 @opindex mno-fast-fix
9685 The C3x/C4x FIX instruction to convert a floating point value to an
9686 integer value chooses the nearest integer less than or equal to the
9687 floating point value rather than to the nearest integer. Thus if the
9688 floating point number is negative, the result will be incorrectly
9689 truncated an additional code is necessary to detect and correct this
9690 case. This option can be used to disable generation of the additional
9691 code required to correct the result.
9697 Enable (disable) generation of repeat block sequences using the RPTB
9698 instruction for zero overhead looping. The RPTB construct is only used
9699 for innermost loops that do not call functions or jump across the loop
9700 boundaries. There is no advantage having nested RPTB loops due to the
9701 overhead required to save and restore the RC, RS, and RE registers.
9702 This is enabled by default with @option{-O2}.
9704 @item -mrpts=@var{count}
9708 Enable (disable) the use of the single instruction repeat instruction
9709 RPTS@. If a repeat block contains a single instruction, and the loop
9710 count can be guaranteed to be less than the value @var{count}, GCC will
9711 emit a RPTS instruction instead of a RPTB@. If no value is specified,
9712 then a RPTS will be emitted even if the loop count cannot be determined
9713 at compile time. Note that the repeated instruction following RPTS does
9714 not have to be reloaded from memory each iteration, thus freeing up the
9715 CPU buses for operands. However, since interrupts are blocked by this
9716 instruction, it is disabled by default.
9718 @item -mloop-unsigned
9719 @itemx -mno-loop-unsigned
9720 @opindex mloop-unsigned
9721 @opindex mno-loop-unsigned
9722 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
9723 is @math{2^{31} + 1} since these instructions test if the iteration count is
9724 negative to terminate the loop. If the iteration count is unsigned
9725 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
9726 exceeded. This switch allows an unsigned iteration count.
9730 Try to emit an assembler syntax that the TI assembler (asm30) is happy
9731 with. This also enforces compatibility with the API employed by the TI
9732 C3x C compiler. For example, long doubles are passed as structures
9733 rather than in floating point registers.
9739 Generate code that uses registers (stack) for passing arguments to functions.
9740 By default, arguments are passed in registers where possible rather
9741 than by pushing arguments on to the stack.
9743 @item -mparallel-insns
9744 @itemx -mno-parallel-insns
9745 @opindex mparallel-insns
9746 @opindex mno-parallel-insns
9747 Allow the generation of parallel instructions. This is enabled by
9748 default with @option{-O2}.
9750 @item -mparallel-mpy
9751 @itemx -mno-parallel-mpy
9752 @opindex mparallel-mpy
9753 @opindex mno-parallel-mpy
9754 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
9755 provided @option{-mparallel-insns} is also specified. These instructions have
9756 tight register constraints which can pessimize the code generation
9762 @subsection V850 Options
9763 @cindex V850 Options
9765 These @samp{-m} options are defined for V850 implementations:
9769 @itemx -mno-long-calls
9770 @opindex mlong-calls
9771 @opindex mno-long-calls
9772 Treat all calls as being far away (near). If calls are assumed to be
9773 far away, the compiler will always load the functions address up into a
9774 register, and call indirect through the pointer.
9780 Do not optimize (do optimize) basic blocks that use the same index
9781 pointer 4 or more times to copy pointer into the @code{ep} register, and
9782 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
9783 option is on by default if you optimize.
9785 @item -mno-prolog-function
9786 @itemx -mprolog-function
9787 @opindex mno-prolog-function
9788 @opindex mprolog-function
9789 Do not use (do use) external functions to save and restore registers
9790 at the prologue and epilogue of a function. The external functions
9791 are slower, but use less code space if more than one function saves
9792 the same number of registers. The @option{-mprolog-function} option
9793 is on by default if you optimize.
9797 Try to make the code as small as possible. At present, this just turns
9798 on the @option{-mep} and @option{-mprolog-function} options.
9802 Put static or global variables whose size is @var{n} bytes or less into
9803 the tiny data area that register @code{ep} points to. The tiny data
9804 area can hold up to 256 bytes in total (128 bytes for byte references).
9808 Put static or global variables whose size is @var{n} bytes or less into
9809 the small data area that register @code{gp} points to. The small data
9810 area can hold up to 64 kilobytes.
9814 Put static or global variables whose size is @var{n} bytes or less into
9815 the first 32 kilobytes of memory.
9819 Specify that the target processor is the V850.
9822 @opindex mbig-switch
9823 Generate code suitable for big switch tables. Use this option only if
9824 the assembler/linker complain about out of range branches within a switch
9829 This option will cause r2 and r5 to be used in the code generated by
9830 the compiler. This setting is the default.
9833 @opindex mno-app-regs
9834 This option will cause r2 and r5 to be treated as fixed registers.
9838 Specify that the target processor is the V850E1. The preprocessor
9839 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
9840 this option is used.
9844 Specify that the target processor is the V850E. The preprocessor
9845 constant @samp{__v850e__} will be defined if this option is used.
9847 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
9848 are defined then a default target processor will be chosen and the
9849 relevant @samp{__v850*__} preprocessor constant will be defined.
9851 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
9852 defined, regardless of which processor variant is the target.
9854 @item -mdisable-callt
9855 @opindex mdisable-callt
9856 This option will suppress generation of the CALLT instruction for the
9857 v850e and v850e1 flavors of the v850 architecture. The default is
9858 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
9863 @subsection ARC Options
9866 These options are defined for ARC implementations:
9871 Compile code for little endian mode. This is the default.
9875 Compile code for big endian mode.
9878 @opindex mmangle-cpu
9879 Prepend the name of the cpu to all public symbol names.
9880 In multiple-processor systems, there are many ARC variants with different
9881 instruction and register set characteristics. This flag prevents code
9882 compiled for one cpu to be linked with code compiled for another.
9883 No facility exists for handling variants that are ``almost identical''.
9884 This is an all or nothing option.
9886 @item -mcpu=@var{cpu}
9888 Compile code for ARC variant @var{cpu}.
9889 Which variants are supported depend on the configuration.
9890 All variants support @option{-mcpu=base}, this is the default.
9892 @item -mtext=@var{text-section}
9893 @itemx -mdata=@var{data-section}
9894 @itemx -mrodata=@var{readonly-data-section}
9898 Put functions, data, and readonly data in @var{text-section},
9899 @var{data-section}, and @var{readonly-data-section} respectively
9900 by default. This can be overridden with the @code{section} attribute.
9901 @xref{Variable Attributes}.
9906 @subsection NS32K Options
9907 @cindex NS32K options
9909 These are the @samp{-m} options defined for the 32000 series. The default
9910 values for these options depends on which style of 32000 was selected when
9911 the compiler was configured; the defaults for the most common choices are
9919 Generate output for a 32032. This is the default
9920 when the compiler is configured for 32032 and 32016 based systems.
9926 Generate output for a 32332. This is the default
9927 when the compiler is configured for 32332-based systems.
9933 Generate output for a 32532. This is the default
9934 when the compiler is configured for 32532-based systems.
9938 Generate output containing 32081 instructions for floating point.
9939 This is the default for all systems.
9943 Generate output containing 32381 instructions for floating point. This
9944 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9945 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9949 Try and generate multiply-add floating point instructions @code{polyF}
9950 and @code{dotF}. This option is only available if the @option{-m32381}
9951 option is in effect. Using these instructions requires changes to
9952 register allocation which generally has a negative impact on
9953 performance. This option should only be enabled when compiling code
9954 particularly likely to make heavy use of multiply-add instructions.
9957 @opindex mnomulti-add
9958 Do not try and generate multiply-add floating point instructions
9959 @code{polyF} and @code{dotF}. This is the default on all platforms.
9962 @opindex msoft-float
9963 Generate output containing library calls for floating point.
9964 @strong{Warning:} the requisite libraries may not be available.
9966 @item -mieee-compare
9967 @itemx -mno-ieee-compare
9968 @opindex mieee-compare
9969 @opindex mno-ieee-compare
9970 Control whether or not the compiler uses IEEE floating point
9971 comparisons. These handle correctly the case where the result of a
9972 comparison is unordered.
9973 @strong{Warning:} the requisite kernel support may not be available.
9976 @opindex mnobitfield
9977 Do not use the bit-field instructions. On some machines it is faster to
9978 use shifting and masking operations. This is the default for the pc532.
9982 Do use the bit-field instructions. This is the default for all platforms
9987 Use a different function-calling convention, in which functions
9988 that take a fixed number of arguments return pop their
9989 arguments on return with the @code{ret} instruction.
9991 This calling convention is incompatible with the one normally
9992 used on Unix, so you cannot use it if you need to call libraries
9993 compiled with the Unix compiler.
9995 Also, you must provide function prototypes for all functions that
9996 take variable numbers of arguments (including @code{printf});
9997 otherwise incorrect code will be generated for calls to those
10000 In addition, seriously incorrect code will result if you call a
10001 function with too many arguments. (Normally, extra arguments are
10002 harmlessly ignored.)
10004 This option takes its name from the 680x0 @code{rtd} instruction.
10009 Use a different function-calling convention where the first two arguments
10010 are passed in registers.
10012 This calling convention is incompatible with the one normally
10013 used on Unix, so you cannot use it if you need to call libraries
10014 compiled with the Unix compiler.
10017 @opindex mnoregparam
10018 Do not pass any arguments in registers. This is the default for all
10023 It is OK to use the sb as an index register which is always loaded with
10024 zero. This is the default for the pc532-netbsd target.
10028 The sb register is not available for use or has not been initialized to
10029 zero by the run time system. This is the default for all targets except
10030 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
10031 @option{-fpic} is set.
10035 Many ns32000 series addressing modes use displacements of up to 512MB@.
10036 If an address is above 512MB then displacements from zero can not be used.
10037 This option causes code to be generated which can be loaded above 512MB@.
10038 This may be useful for operating systems or ROM code.
10042 Assume code will be loaded in the first 512MB of virtual address space.
10043 This is the default for all platforms.
10049 @subsection AVR Options
10050 @cindex AVR Options
10052 These options are defined for AVR implementations:
10055 @item -mmcu=@var{mcu}
10057 Specify ATMEL AVR instruction set or MCU type.
10059 Instruction set avr1 is for the minimal AVR core, not supported by the C
10060 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
10061 attiny11, attiny12, attiny15, attiny28).
10063 Instruction set avr2 (default) is for the classic AVR core with up to
10064 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
10065 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
10066 at90c8534, at90s8535).
10068 Instruction set avr3 is for the classic AVR core with up to 128K program
10069 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
10071 Instruction set avr4 is for the enhanced AVR core with up to 8K program
10072 memory space (MCU types: atmega8, atmega83, atmega85).
10074 Instruction set avr5 is for the enhanced AVR core with up to 128K program
10075 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
10076 atmega64, atmega128, at43usb355, at94k).
10080 Output instruction sizes to the asm file.
10082 @item -minit-stack=@var{N}
10083 @opindex minit-stack
10084 Specify the initial stack address, which may be a symbol or numeric value,
10085 @samp{__stack} is the default.
10087 @item -mno-interrupts
10088 @opindex mno-interrupts
10089 Generated code is not compatible with hardware interrupts.
10090 Code size will be smaller.
10092 @item -mcall-prologues
10093 @opindex mcall-prologues
10094 Functions prologues/epilogues expanded as call to appropriate
10095 subroutines. Code size will be smaller.
10097 @item -mno-tablejump
10098 @opindex mno-tablejump
10099 Do not generate tablejump insns which sometimes increase code size.
10102 @opindex mtiny-stack
10103 Change only the low 8 bits of the stack pointer.
10106 @node MCore Options
10107 @subsection MCore Options
10108 @cindex MCore options
10110 These are the @samp{-m} options defined for the Motorola M*Core
10116 @itemx -mno-hardlit
10118 @opindex mno-hardlit
10119 Inline constants into the code stream if it can be done in two
10120 instructions or less.
10126 Use the divide instruction. (Enabled by default).
10128 @item -mrelax-immediate
10129 @itemx -mno-relax-immediate
10130 @opindex mrelax-immediate
10131 @opindex mno-relax-immediate
10132 Allow arbitrary sized immediates in bit operations.
10134 @item -mwide-bitfields
10135 @itemx -mno-wide-bitfields
10136 @opindex mwide-bitfields
10137 @opindex mno-wide-bitfields
10138 Always treat bit-fields as int-sized.
10140 @item -m4byte-functions
10141 @itemx -mno-4byte-functions
10142 @opindex m4byte-functions
10143 @opindex mno-4byte-functions
10144 Force all functions to be aligned to a four byte boundary.
10146 @item -mcallgraph-data
10147 @itemx -mno-callgraph-data
10148 @opindex mcallgraph-data
10149 @opindex mno-callgraph-data
10150 Emit callgraph information.
10153 @itemx -mno-slow-bytes
10154 @opindex mslow-bytes
10155 @opindex mno-slow-bytes
10156 Prefer word access when reading byte quantities.
10158 @item -mlittle-endian
10159 @itemx -mbig-endian
10160 @opindex mlittle-endian
10161 @opindex mbig-endian
10162 Generate code for a little endian target.
10168 Generate code for the 210 processor.
10171 @node IA-64 Options
10172 @subsection IA-64 Options
10173 @cindex IA-64 Options
10175 These are the @samp{-m} options defined for the Intel IA-64 architecture.
10179 @opindex mbig-endian
10180 Generate code for a big endian target. This is the default for HP-UX@.
10182 @item -mlittle-endian
10183 @opindex mlittle-endian
10184 Generate code for a little endian target. This is the default for AIX5
10190 @opindex mno-gnu-as
10191 Generate (or don't) code for the GNU assembler. This is the default.
10192 @c Also, this is the default if the configure option @option{--with-gnu-as}
10198 @opindex mno-gnu-ld
10199 Generate (or don't) code for the GNU linker. This is the default.
10200 @c Also, this is the default if the configure option @option{--with-gnu-ld}
10205 Generate code that does not use a global pointer register. The result
10206 is not position independent code, and violates the IA-64 ABI@.
10208 @item -mvolatile-asm-stop
10209 @itemx -mno-volatile-asm-stop
10210 @opindex mvolatile-asm-stop
10211 @opindex mno-volatile-asm-stop
10212 Generate (or don't) a stop bit immediately before and after volatile asm
10217 Generate code that works around Itanium B step errata.
10219 @item -mregister-names
10220 @itemx -mno-register-names
10221 @opindex mregister-names
10222 @opindex mno-register-names
10223 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
10224 the stacked registers. This may make assembler output more readable.
10230 Disable (or enable) optimizations that use the small data section. This may
10231 be useful for working around optimizer bugs.
10233 @item -mconstant-gp
10234 @opindex mconstant-gp
10235 Generate code that uses a single constant global pointer value. This is
10236 useful when compiling kernel code.
10240 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
10241 This is useful when compiling firmware code.
10243 @item -minline-float-divide-min-latency
10244 @opindex minline-float-divide-min-latency
10245 Generate code for inline divides of floating point values
10246 using the minimum latency algorithm.
10248 @item -minline-float-divide-max-throughput
10249 @opindex minline-float-divide-max-throughput
10250 Generate code for inline divides of floating point values
10251 using the maximum throughput algorithm.
10253 @item -minline-int-divide-min-latency
10254 @opindex minline-int-divide-min-latency
10255 Generate code for inline divides of integer values
10256 using the minimum latency algorithm.
10258 @item -minline-int-divide-max-throughput
10259 @opindex minline-int-divide-max-throughput
10260 Generate code for inline divides of integer values
10261 using the maximum throughput algorithm.
10263 @item -mno-dwarf2-asm
10264 @itemx -mdwarf2-asm
10265 @opindex mno-dwarf2-asm
10266 @opindex mdwarf2-asm
10267 Don't (or do) generate assembler code for the DWARF2 line number debugging
10268 info. This may be useful when not using the GNU assembler.
10270 @item -mfixed-range=@var{register-range}
10271 @opindex mfixed-range
10272 Generate code treating the given register range as fixed registers.
10273 A fixed register is one that the register allocator can not use. This is
10274 useful when compiling kernel code. A register range is specified as
10275 two registers separated by a dash. Multiple register ranges can be
10276 specified separated by a comma.
10278 @item -mearly-stop-bits
10279 @itemx -mno-early-stop-bits
10280 @opindex mearly-stop-bits
10281 @opindex mno-early-stop-bits
10282 Allow stop bits to be placed earlier than immediately preceding the
10283 instruction that triggered the stop bit. This can improve instruction
10284 scheduling, but does not always do so.
10288 @subsection D30V Options
10289 @cindex D30V Options
10291 These @samp{-m} options are defined for D30V implementations:
10296 Link the @samp{.text}, @samp{.data}, @samp{.bss}, @samp{.strings},
10297 @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections into external
10298 memory, which starts at location @code{0x80000000}.
10301 @opindex mextmemory
10302 Same as the @option{-mextmem} switch.
10306 Link the @samp{.text} section into onchip text memory, which starts at
10307 location @code{0x0}. Also link @samp{.data}, @samp{.bss},
10308 @samp{.strings}, @samp{.rodata}, @samp{.rodata1}, @samp{.data1} sections
10309 into onchip data memory, which starts at location @code{0x20000000}.
10311 @item -mno-asm-optimize
10312 @itemx -masm-optimize
10313 @opindex mno-asm-optimize
10314 @opindex masm-optimize
10315 Disable (enable) passing @option{-O} to the assembler when optimizing.
10316 The assembler uses the @option{-O} option to automatically parallelize
10317 adjacent short instructions where possible.
10319 @item -mbranch-cost=@var{n}
10320 @opindex mbranch-cost
10321 Increase the internal costs of branches to @var{n}. Higher costs means
10322 that the compiler will issue more instructions to avoid doing a branch.
10325 @item -mcond-exec=@var{n}
10326 @opindex mcond-exec
10327 Specify the maximum number of conditionally executed instructions that
10328 replace a branch. The default is 4.
10331 @node S/390 and zSeries Options
10332 @subsection S/390 and zSeries Options
10333 @cindex S/390 and zSeries Options
10335 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10339 @itemx -msoft-float
10340 @opindex mhard-float
10341 @opindex msoft-float
10342 Use (do not use) the hardware floating-point instructions and registers
10343 for floating-point operations. When @option{-msoft-float} is specified,
10344 functions in @file{libgcc.a} will be used to perform floating-point
10345 operations. When @option{-mhard-float} is specified, the compiler
10346 generates IEEE floating-point instructions. This is the default.
10349 @itemx -mno-backchain
10350 @opindex mbackchain
10351 @opindex mno-backchain
10352 Generate (or do not generate) code which maintains an explicit
10353 backchain within the stack frame that points to the caller's frame.
10354 This is currently needed to allow debugging. The default is to
10355 generate the backchain.
10358 @itemx -mno-small-exec
10359 @opindex msmall-exec
10360 @opindex mno-small-exec
10361 Generate (or do not generate) code using the @code{bras} instruction
10362 to do subroutine calls.
10363 This only works reliably if the total executable size does not
10364 exceed 64k. The default is to use the @code{basr} instruction instead,
10365 which does not have this limitation.
10371 When @option{-m31} is specified, generate code compliant to the
10372 Linux for S/390 ABI@. When @option{-m64} is specified, generate
10373 code compliant to the Linux for zSeries ABI@. This allows GCC in
10374 particular to generate 64-bit instructions. For the @samp{s390}
10375 targets, the default is @option{-m31}, while the @samp{s390x}
10376 targets default to @option{-m64}.
10382 When @option{-mzarch} is specified, generate code using the
10383 instructions available on z/Architecture.
10384 When @option{-mesa} is specified, generate code using the
10385 instructions available on ESA/390. Note that @option{-mesa} is
10386 not possible with @option{-m64}.
10387 When generating code compliant to the Linux for S/390 ABI,
10388 the default is @option{-mesa}. When generating code compliant
10389 to the Linux for zSeries ABI, the default is @option{-mzarch}.
10395 Generate (or do not generate) code using the @code{mvcle} instruction
10396 to perform block moves. When @option{-mno-mvcle} is specified,
10397 use a @code{mvc} loop instead. This is the default.
10403 Print (or do not print) additional debug information when compiling.
10404 The default is to not print debug information.
10406 @item -march=@var{cpu-type}
10408 Generate code that will run on @var{cpu-type}, which is the name of a system
10409 representing a certain processor type. Possible values for
10410 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10411 When generating code using the instructions available on z/Architecture,
10412 the default is @option{-march=z900}. Otherwise, the default is
10413 @option{-march=g5}.
10415 @item -mtune=@var{cpu-type}
10417 Tune to @var{cpu-type} everything applicable about the generated code,
10418 except for the ABI and the set of available instructions.
10419 The list of @var{cpu-type} values is the same as for @option{-march}.
10420 The default is the value used for @option{-march}.
10425 @subsection CRIS Options
10426 @cindex CRIS Options
10428 These options are defined specifically for the CRIS ports.
10431 @item -march=@var{architecture-type}
10432 @itemx -mcpu=@var{architecture-type}
10435 Generate code for the specified architecture. The choices for
10436 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10437 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
10438 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10441 @item -mtune=@var{architecture-type}
10443 Tune to @var{architecture-type} everything applicable about the generated
10444 code, except for the ABI and the set of available instructions. The
10445 choices for @var{architecture-type} are the same as for
10446 @option{-march=@var{architecture-type}}.
10448 @item -mmax-stack-frame=@var{n}
10449 @opindex mmax-stack-frame
10450 Warn when the stack frame of a function exceeds @var{n} bytes.
10452 @item -melinux-stacksize=@var{n}
10453 @opindex melinux-stacksize
10454 Only available with the @samp{cris-axis-aout} target. Arranges for
10455 indications in the program to the kernel loader that the stack of the
10456 program should be set to @var{n} bytes.
10462 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10463 @option{-march=v3} and @option{-march=v8} respectively.
10467 Enable CRIS-specific verbose debug-related information in the assembly
10468 code. This option also has the effect to turn off the @samp{#NO_APP}
10469 formatted-code indicator to the assembler at the beginning of the
10474 Do not use condition-code results from previous instruction; always emit
10475 compare and test instructions before use of condition codes.
10477 @item -mno-side-effects
10478 @opindex mno-side-effects
10479 Do not emit instructions with side-effects in addressing modes other than
10482 @item -mstack-align
10483 @itemx -mno-stack-align
10484 @itemx -mdata-align
10485 @itemx -mno-data-align
10486 @itemx -mconst-align
10487 @itemx -mno-const-align
10488 @opindex mstack-align
10489 @opindex mno-stack-align
10490 @opindex mdata-align
10491 @opindex mno-data-align
10492 @opindex mconst-align
10493 @opindex mno-const-align
10494 These options (no-options) arranges (eliminate arrangements) for the
10495 stack-frame, individual data and constants to be aligned for the maximum
10496 single data access size for the chosen CPU model. The default is to
10497 arrange for 32-bit alignment. ABI details such as structure layout are
10498 not affected by these options.
10506 Similar to the stack- data- and const-align options above, these options
10507 arrange for stack-frame, writable data and constants to all be 32-bit,
10508 16-bit or 8-bit aligned. The default is 32-bit alignment.
10510 @item -mno-prologue-epilogue
10511 @itemx -mprologue-epilogue
10512 @opindex mno-prologue-epilogue
10513 @opindex mprologue-epilogue
10514 With @option{-mno-prologue-epilogue}, the normal function prologue and
10515 epilogue that sets up the stack-frame are omitted and no return
10516 instructions or return sequences are generated in the code. Use this
10517 option only together with visual inspection of the compiled code: no
10518 warnings or errors are generated when call-saved registers must be saved,
10519 or storage for local variable needs to be allocated.
10523 @opindex mno-gotplt
10525 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10526 instruction sequences that load addresses for functions from the PLT part
10527 of the GOT rather than (traditional on other architectures) calls to the
10528 PLT. The default is @option{-mgotplt}.
10532 Legacy no-op option only recognized with the cris-axis-aout target.
10536 Legacy no-op option only recognized with the cris-axis-elf and
10537 cris-axis-linux-gnu targets.
10541 Only recognized with the cris-axis-aout target, where it selects a
10542 GNU/linux-like multilib, include files and instruction set for
10543 @option{-march=v8}.
10547 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10551 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
10552 to link with input-output functions from a simulator library. Code,
10553 initialized data and zero-initialized data are allocated consecutively.
10557 Like @option{-sim}, but pass linker options to locate initialized data at
10558 0x40000000 and zero-initialized data at 0x80000000.
10562 @subsection MMIX Options
10563 @cindex MMIX Options
10565 These options are defined for the MMIX:
10569 @itemx -mno-libfuncs
10571 @opindex mno-libfuncs
10572 Specify that intrinsic library functions are being compiled, passing all
10573 values in registers, no matter the size.
10576 @itemx -mno-epsilon
10578 @opindex mno-epsilon
10579 Generate floating-point comparison instructions that compare with respect
10580 to the @code{rE} epsilon register.
10582 @item -mabi=mmixware
10584 @opindex mabi-mmixware
10586 Generate code that passes function parameters and return values that (in
10587 the called function) are seen as registers @code{$0} and up, as opposed to
10588 the GNU ABI which uses global registers @code{$231} and up.
10590 @item -mzero-extend
10591 @itemx -mno-zero-extend
10592 @opindex mzero-extend
10593 @opindex mno-zero-extend
10594 When reading data from memory in sizes shorter than 64 bits, use (do not
10595 use) zero-extending load instructions by default, rather than
10596 sign-extending ones.
10599 @itemx -mno-knuthdiv
10601 @opindex mno-knuthdiv
10602 Make the result of a division yielding a remainder have the same sign as
10603 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10604 remainder follows the sign of the dividend. Both methods are
10605 arithmetically valid, the latter being almost exclusively used.
10607 @item -mtoplevel-symbols
10608 @itemx -mno-toplevel-symbols
10609 @opindex mtoplevel-symbols
10610 @opindex mno-toplevel-symbols
10611 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10612 code can be used with the @code{PREFIX} assembly directive.
10616 Generate an executable in the ELF format, rather than the default
10617 @samp{mmo} format used by the @command{mmix} simulator.
10619 @item -mbranch-predict
10620 @itemx -mno-branch-predict
10621 @opindex mbranch-predict
10622 @opindex mno-branch-predict
10623 Use (do not use) the probable-branch instructions, when static branch
10624 prediction indicates a probable branch.
10626 @item -mbase-addresses
10627 @itemx -mno-base-addresses
10628 @opindex mbase-addresses
10629 @opindex mno-base-addresses
10630 Generate (do not generate) code that uses @emph{base addresses}. Using a
10631 base address automatically generates a request (handled by the assembler
10632 and the linker) for a constant to be set up in a global register. The
10633 register is used for one or more base address requests within the range 0
10634 to 255 from the value held in the register. The generally leads to short
10635 and fast code, but the number of different data items that can be
10636 addressed is limited. This means that a program that uses lots of static
10637 data may require @option{-mno-base-addresses}.
10639 @item -msingle-exit
10640 @itemx -mno-single-exit
10641 @opindex msingle-exit
10642 @opindex mno-single-exit
10643 Force (do not force) generated code to have a single exit point in each
10647 @node PDP-11 Options
10648 @subsection PDP-11 Options
10649 @cindex PDP-11 Options
10651 These options are defined for the PDP-11:
10656 Use hardware FPP floating point. This is the default. (FIS floating
10657 point on the PDP-11/40 is not supported.)
10660 @opindex msoft-float
10661 Do not use hardware floating point.
10665 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10669 Return floating-point results in memory. This is the default.
10673 Generate code for a PDP-11/40.
10677 Generate code for a PDP-11/45. This is the default.
10681 Generate code for a PDP-11/10.
10683 @item -mbcopy-builtin
10684 @opindex bcopy-builtin
10685 Use inline @code{movstrhi} patterns for copying memory. This is the
10690 Do not use inline @code{movstrhi} patterns for copying memory.
10696 Use 16-bit @code{int}. This is the default.
10702 Use 32-bit @code{int}.
10705 @itemx -mno-float32
10707 @opindex mno-float32
10708 Use 64-bit @code{float}. This is the default.
10713 @opindex mno-float64
10714 Use 32-bit @code{float}.
10718 Use @code{abshi2} pattern. This is the default.
10722 Do not use @code{abshi2} pattern.
10724 @item -mbranch-expensive
10725 @opindex mbranch-expensive
10726 Pretend that branches are expensive. This is for experimenting with
10727 code generation only.
10729 @item -mbranch-cheap
10730 @opindex mbranch-cheap
10731 Do not pretend that branches are expensive. This is the default.
10735 Generate code for a system with split I&D.
10739 Generate code for a system without split I&D. This is the default.
10743 Use Unix assembler syntax. This is the default when configured for
10744 @samp{pdp11-*-bsd}.
10748 Use DEC assembler syntax. This is the default when configured for any
10749 PDP-11 target other than @samp{pdp11-*-bsd}.
10752 @node Xstormy16 Options
10753 @subsection Xstormy16 Options
10754 @cindex Xstormy16 Options
10756 These options are defined for Xstormy16:
10761 Choose startup files and linker script suitable for the simulator.
10765 @subsection FRV Options
10766 @cindex FRV Options
10772 Only use the first 32 general purpose registers.
10777 Use all 64 general purpose registers.
10782 Use only the first 32 floating point registers.
10787 Use all 64 floating point registers
10790 @opindex mhard-float
10792 Use hardware instructions for floating point operations.
10795 @opindex msoft-float
10797 Use library routines for floating point operations.
10802 Dynamically allocate condition code registers.
10807 Do not try to dynamically allocate condition code registers, only
10808 use @code{icc0} and @code{fcc0}.
10813 Change ABI to use double word insns.
10818 Do not use double word instructions.
10823 Use floating point double instructions.
10826 @opindex mno-double
10828 Do not use floating point double instructions.
10833 Use media instructions.
10838 Do not use media instructions.
10843 Use multiply and add/subtract instructions.
10846 @opindex mno-muladd
10848 Do not use multiply and add/subtract instructions.
10850 @item -mlibrary-pic
10851 @opindex mlibrary-pic
10853 Enable PIC support for building libraries
10858 Use only the first four media accumulator registers.
10863 Use all eight media accumulator registers.
10868 Pack VLIW instructions.
10873 Do not pack VLIW instructions.
10876 @opindex mno-eflags
10878 Do not mark ABI switches in e_flags.
10881 @opindex mcond-move
10883 Enable the use of conditional-move instructions (default).
10885 This switch is mainly for debugging the compiler and will likely be removed
10886 in a future version.
10888 @item -mno-cond-move
10889 @opindex mno-cond-move
10891 Disable the use of conditional-move instructions.
10893 This switch is mainly for debugging the compiler and will likely be removed
10894 in a future version.
10899 Enable the use of conditional set instructions (default).
10901 This switch is mainly for debugging the compiler and will likely be removed
10902 in a future version.
10907 Disable the use of conditional set instructions.
10909 This switch is mainly for debugging the compiler and will likely be removed
10910 in a future version.
10913 @opindex mcond-exec
10915 Enable the use of conditional execution (default).
10917 This switch is mainly for debugging the compiler and will likely be removed
10918 in a future version.
10920 @item -mno-cond-exec
10921 @opindex mno-cond-exec
10923 Disable the use of conditional execution.
10925 This switch is mainly for debugging the compiler and will likely be removed
10926 in a future version.
10928 @item -mvliw-branch
10929 @opindex mvliw-branch
10931 Run a pass to pack branches into VLIW instructions (default).
10933 This switch is mainly for debugging the compiler and will likely be removed
10934 in a future version.
10936 @item -mno-vliw-branch
10937 @opindex mno-vliw-branch
10939 Do not run a pass to pack branches into VLIW instructions.
10941 This switch is mainly for debugging the compiler and will likely be removed
10942 in a future version.
10944 @item -mmulti-cond-exec
10945 @opindex mmulti-cond-exec
10947 Enable optimization of @code{&&} and @code{||} in conditional execution
10950 This switch is mainly for debugging the compiler and will likely be removed
10951 in a future version.
10953 @item -mno-multi-cond-exec
10954 @opindex mno-multi-cond-exec
10956 Disable optimization of @code{&&} and @code{||} in conditional execution.
10958 This switch is mainly for debugging the compiler and will likely be removed
10959 in a future version.
10961 @item -mnested-cond-exec
10962 @opindex mnested-cond-exec
10964 Enable nested conditional execution optimizations (default).
10966 This switch is mainly for debugging the compiler and will likely be removed
10967 in a future version.
10969 @item -mno-nested-cond-exec
10970 @opindex mno-nested-cond-exec
10972 Disable nested conditional execution optimizations.
10974 This switch is mainly for debugging the compiler and will likely be removed
10975 in a future version.
10977 @item -mtomcat-stats
10978 @opindex mtomcat-stats
10980 Cause gas to print out tomcat statistics.
10982 @item -mcpu=@var{cpu}
10985 Select the processor type for which to generate code. Possible values are
10986 @samp{simple}, @samp{tomcat}, @samp{fr500}, @samp{fr400}, @samp{fr300},
10991 @node Xtensa Options
10992 @subsection Xtensa Options
10993 @cindex Xtensa Options
10995 These options are supported for Xtensa targets:
10999 @itemx -mno-const16
11001 @opindex mno-const16
11002 Enable or disable use of @code{CONST16} instructions for loading
11003 constant values. The @code{CONST16} instruction is currently not a
11004 standard option from Tensilica. When enabled, @code{CONST16}
11005 instructions are always used in place of the standard @code{L32R}
11006 instructions. The use of @code{CONST16} is enabled by default only if
11007 the @code{L32R} instruction is not available.
11010 @itemx -mno-fused-madd
11011 @opindex mfused-madd
11012 @opindex mno-fused-madd
11013 Enable or disable use of fused multiply/add and multiply/subtract
11014 instructions in the floating-point option. This has no effect if the
11015 floating-point option is not also enabled. Disabling fused multiply/add
11016 and multiply/subtract instructions forces the compiler to use separate
11017 instructions for the multiply and add/subtract operations. This may be
11018 desirable in some cases where strict IEEE 754-compliant results are
11019 required: the fused multiply add/subtract instructions do not round the
11020 intermediate result, thereby producing results with @emph{more} bits of
11021 precision than specified by the IEEE standard. Disabling fused multiply
11022 add/subtract instructions also ensures that the program output is not
11023 sensitive to the compiler's ability to combine multiply and add/subtract
11026 @item -mtext-section-literals
11027 @itemx -mno-text-section-literals
11028 @opindex mtext-section-literals
11029 @opindex mno-text-section-literals
11030 Control the treatment of literal pools. The default is
11031 @option{-mno-text-section-literals}, which places literals in a separate
11032 section in the output file. This allows the literal pool to be placed
11033 in a data RAM/ROM, and it also allows the linker to combine literal
11034 pools from separate object files to remove redundant literals and
11035 improve code size. With @option{-mtext-section-literals}, the literals
11036 are interspersed in the text section in order to keep them as close as
11037 possible to their references. This may be necessary for large assembly
11040 @item -mtarget-align
11041 @itemx -mno-target-align
11042 @opindex mtarget-align
11043 @opindex mno-target-align
11044 When this option is enabled, GCC instructs the assembler to
11045 automatically align instructions to reduce branch penalties at the
11046 expense of some code density. The assembler attempts to widen density
11047 instructions to align branch targets and the instructions following call
11048 instructions. If there are not enough preceding safe density
11049 instructions to align a target, no widening will be performed. The
11050 default is @option{-mtarget-align}. These options do not affect the
11051 treatment of auto-aligned instructions like @code{LOOP}, which the
11052 assembler will always align, either by widening density instructions or
11053 by inserting no-op instructions.
11056 @itemx -mno-longcalls
11057 @opindex mlongcalls
11058 @opindex mno-longcalls
11059 When this option is enabled, GCC instructs the assembler to translate
11060 direct calls to indirect calls unless it can determine that the target
11061 of a direct call is in the range allowed by the call instruction. This
11062 translation typically occurs for calls to functions in other source
11063 files. Specifically, the assembler translates a direct @code{CALL}
11064 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
11065 The default is @option{-mno-longcalls}. This option should be used in
11066 programs where the call target can potentially be out of range. This
11067 option is implemented in the assembler, not the compiler, so the
11068 assembly code generated by GCC will still show direct call
11069 instructions---look at the disassembled object code to see the actual
11070 instructions. Note that the assembler will use an indirect call for
11071 every cross-file call, not just those that really will be out of range.
11074 @node Code Gen Options
11075 @section Options for Code Generation Conventions
11076 @cindex code generation conventions
11077 @cindex options, code generation
11078 @cindex run-time options
11080 These machine-independent options control the interface conventions
11081 used in code generation.
11083 Most of them have both positive and negative forms; the negative form
11084 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
11085 one of the forms is listed---the one which is not the default. You
11086 can figure out the other form by either removing @samp{no-} or adding
11090 @item -fbounds-check
11091 @opindex fbounds-check
11092 For front-ends that support it, generate additional code to check that
11093 indices used to access arrays are within the declared range. This is
11094 currently only supported by the Java and Fortran 77 front-ends, where
11095 this option defaults to true and false respectively.
11099 This option generates traps for signed overflow on addition, subtraction,
11100 multiplication operations.
11104 This option instructs the compiler to assume that signed arithmetic
11105 overflow of addition, subtraction and multiplication wraps around
11106 using twos-complement representation. This flag enables some optimizations
11107 and disables other. This option is enabled by default for the Java
11108 front-end, as required by the Java language specification.
11111 @opindex fexceptions
11112 Enable exception handling. Generates extra code needed to propagate
11113 exceptions. For some targets, this implies GCC will generate frame
11114 unwind information for all functions, which can produce significant data
11115 size overhead, although it does not affect execution. If you do not
11116 specify this option, GCC will enable it by default for languages like
11117 C++ which normally require exception handling, and disable it for
11118 languages like C that do not normally require it. However, you may need
11119 to enable this option when compiling C code that needs to interoperate
11120 properly with exception handlers written in C++. You may also wish to
11121 disable this option if you are compiling older C++ programs that don't
11122 use exception handling.
11124 @item -fnon-call-exceptions
11125 @opindex fnon-call-exceptions
11126 Generate code that allows trapping instructions to throw exceptions.
11127 Note that this requires platform-specific runtime support that does
11128 not exist everywhere. Moreover, it only allows @emph{trapping}
11129 instructions to throw exceptions, i.e.@: memory references or floating
11130 point instructions. It does not allow exceptions to be thrown from
11131 arbitrary signal handlers such as @code{SIGALRM}.
11133 @item -funwind-tables
11134 @opindex funwind-tables
11135 Similar to @option{-fexceptions}, except that it will just generate any needed
11136 static data, but will not affect the generated code in any other way.
11137 You will normally not enable this option; instead, a language processor
11138 that needs this handling would enable it on your behalf.
11140 @item -fasynchronous-unwind-tables
11141 @opindex funwind-tables
11142 Generate unwind table in dwarf2 format, if supported by target machine. The
11143 table is exact at each instruction boundary, so it can be used for stack
11144 unwinding from asynchronous events (such as debugger or garbage collector).
11146 @item -fpcc-struct-return
11147 @opindex fpcc-struct-return
11148 Return ``short'' @code{struct} and @code{union} values in memory like
11149 longer ones, rather than in registers. This convention is less
11150 efficient, but it has the advantage of allowing intercallability between
11151 GCC-compiled files and files compiled with other compilers, particularly
11152 the Portable C Compiler (pcc).
11154 The precise convention for returning structures in memory depends
11155 on the target configuration macros.
11157 Short structures and unions are those whose size and alignment match
11158 that of some integer type.
11160 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11161 switch is not binary compatible with code compiled with the
11162 @option{-freg-struct-return} switch.
11163 Use it to conform to a non-default application binary interface.
11165 @item -freg-struct-return
11166 @opindex freg-struct-return
11167 Return @code{struct} and @code{union} values in registers when possible.
11168 This is more efficient for small structures than
11169 @option{-fpcc-struct-return}.
11171 If you specify neither @option{-fpcc-struct-return} nor
11172 @option{-freg-struct-return}, GCC defaults to whichever convention is
11173 standard for the target. If there is no standard convention, GCC
11174 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11175 the principal compiler. In those cases, we can choose the standard, and
11176 we chose the more efficient register return alternative.
11178 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11179 switch is not binary compatible with code compiled with the
11180 @option{-fpcc-struct-return} switch.
11181 Use it to conform to a non-default application binary interface.
11183 @item -fshort-enums
11184 @opindex fshort-enums
11185 Allocate to an @code{enum} type only as many bytes as it needs for the
11186 declared range of possible values. Specifically, the @code{enum} type
11187 will be equivalent to the smallest integer type which has enough room.
11189 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11190 code that is not binary compatible with code generated without that switch.
11191 Use it to conform to a non-default application binary interface.
11193 @item -fshort-double
11194 @opindex fshort-double
11195 Use the same size for @code{double} as for @code{float}.
11197 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11198 code that is not binary compatible with code generated without that switch.
11199 Use it to conform to a non-default application binary interface.
11201 @item -fshort-wchar
11202 @opindex fshort-wchar
11203 Override the underlying type for @samp{wchar_t} to be @samp{short
11204 unsigned int} instead of the default for the target. This option is
11205 useful for building programs to run under WINE@.
11207 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11208 code that is not binary compatible with code generated without that switch.
11209 Use it to conform to a non-default application binary interface.
11211 @item -fshared-data
11212 @opindex fshared-data
11213 Requests that the data and non-@code{const} variables of this
11214 compilation be shared data rather than private data. The distinction
11215 makes sense only on certain operating systems, where shared data is
11216 shared between processes running the same program, while private data
11217 exists in one copy per process.
11220 @opindex fno-common
11221 In C, allocate even uninitialized global variables in the data section of the
11222 object file, rather than generating them as common blocks. This has the
11223 effect that if the same variable is declared (without @code{extern}) in
11224 two different compilations, you will get an error when you link them.
11225 The only reason this might be useful is if you wish to verify that the
11226 program will work on other systems which always work this way.
11230 Ignore the @samp{#ident} directive.
11232 @item -fno-gnu-linker
11233 @opindex fno-gnu-linker
11234 Do not output global initializations (such as C++ constructors and
11235 destructors) in the form used by the GNU linker (on systems where the GNU
11236 linker is the standard method of handling them). Use this option when
11237 you want to use a non-GNU linker, which also requires using the
11238 @command{collect2} program to make sure the system linker includes
11239 constructors and destructors. (@command{collect2} is included in the GCC
11240 distribution.) For systems which @emph{must} use @command{collect2}, the
11241 compiler driver @command{gcc} is configured to do this automatically.
11243 @item -finhibit-size-directive
11244 @opindex finhibit-size-directive
11245 Don't output a @code{.size} assembler directive, or anything else that
11246 would cause trouble if the function is split in the middle, and the
11247 two halves are placed at locations far apart in memory. This option is
11248 used when compiling @file{crtstuff.c}; you should not need to use it
11251 @item -fverbose-asm
11252 @opindex fverbose-asm
11253 Put extra commentary information in the generated assembly code to
11254 make it more readable. This option is generally only of use to those
11255 who actually need to read the generated assembly code (perhaps while
11256 debugging the compiler itself).
11258 @option{-fno-verbose-asm}, the default, causes the
11259 extra information to be omitted and is useful when comparing two assembler
11264 @cindex global offset table
11266 Generate position-independent code (PIC) suitable for use in a shared
11267 library, if supported for the target machine. Such code accesses all
11268 constant addresses through a global offset table (GOT)@. The dynamic
11269 loader resolves the GOT entries when the program starts (the dynamic
11270 loader is not part of GCC; it is part of the operating system). If
11271 the GOT size for the linked executable exceeds a machine-specific
11272 maximum size, you get an error message from the linker indicating that
11273 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11274 instead. (These maximums are 16k on the m88k, 8k on the SPARC, and 32k
11275 on the m68k and RS/6000. The 386 has no such limit.)
11277 Position-independent code requires special support, and therefore works
11278 only on certain machines. For the 386, GCC supports PIC for System V
11279 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11280 position-independent.
11284 If supported for the target machine, emit position-independent code,
11285 suitable for dynamic linking and avoiding any limit on the size of the
11286 global offset table. This option makes a difference on the m68k, m88k,
11289 Position-independent code requires special support, and therefore works
11290 only on certain machines.
11296 These options are similar to @option{-fpic} and @option{-fPIC}, but
11297 generated position independent code can be only linked into executables.
11298 Usually these options are used when @option{-pie} GCC option will be
11299 used during linking.
11301 @item -ffixed-@var{reg}
11303 Treat the register named @var{reg} as a fixed register; generated code
11304 should never refer to it (except perhaps as a stack pointer, frame
11305 pointer or in some other fixed role).
11307 @var{reg} must be the name of a register. The register names accepted
11308 are machine-specific and are defined in the @code{REGISTER_NAMES}
11309 macro in the machine description macro file.
11311 This flag does not have a negative form, because it specifies a
11314 @item -fcall-used-@var{reg}
11315 @opindex fcall-used
11316 Treat the register named @var{reg} as an allocable register that is
11317 clobbered by function calls. It may be allocated for temporaries or
11318 variables that do not live across a call. Functions compiled this way
11319 will not save and restore the register @var{reg}.
11321 It is an error to used this flag with the frame pointer or stack pointer.
11322 Use of this flag for other registers that have fixed pervasive roles in
11323 the machine's execution model will produce disastrous results.
11325 This flag does not have a negative form, because it specifies a
11328 @item -fcall-saved-@var{reg}
11329 @opindex fcall-saved
11330 Treat the register named @var{reg} as an allocable register saved by
11331 functions. It may be allocated even for temporaries or variables that
11332 live across a call. Functions compiled this way will save and restore
11333 the register @var{reg} if they use it.
11335 It is an error to used this flag with the frame pointer or stack pointer.
11336 Use of this flag for other registers that have fixed pervasive roles in
11337 the machine's execution model will produce disastrous results.
11339 A different sort of disaster will result from the use of this flag for
11340 a register in which function values may be returned.
11342 This flag does not have a negative form, because it specifies a
11345 @item -fpack-struct
11346 @opindex fpack-struct
11347 Pack all structure members together without holes.
11349 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
11350 code that is not binary compatible with code generated without that switch.
11351 Additionally, it makes the code suboptimal.
11352 Use it to conform to a non-default application binary interface.
11354 @item -finstrument-functions
11355 @opindex finstrument-functions
11356 Generate instrumentation calls for entry and exit to functions. Just
11357 after function entry and just before function exit, the following
11358 profiling functions will be called with the address of the current
11359 function and its call site. (On some platforms,
11360 @code{__builtin_return_address} does not work beyond the current
11361 function, so the call site information may not be available to the
11362 profiling functions otherwise.)
11365 void __cyg_profile_func_enter (void *this_fn,
11367 void __cyg_profile_func_exit (void *this_fn,
11371 The first argument is the address of the start of the current function,
11372 which may be looked up exactly in the symbol table.
11374 This instrumentation is also done for functions expanded inline in other
11375 functions. The profiling calls will indicate where, conceptually, the
11376 inline function is entered and exited. This means that addressable
11377 versions of such functions must be available. If all your uses of a
11378 function are expanded inline, this may mean an additional expansion of
11379 code size. If you use @samp{extern inline} in your C code, an
11380 addressable version of such functions must be provided. (This is
11381 normally the case anyways, but if you get lucky and the optimizer always
11382 expands the functions inline, you might have gotten away without
11383 providing static copies.)
11385 A function may be given the attribute @code{no_instrument_function}, in
11386 which case this instrumentation will not be done. This can be used, for
11387 example, for the profiling functions listed above, high-priority
11388 interrupt routines, and any functions from which the profiling functions
11389 cannot safely be called (perhaps signal handlers, if the profiling
11390 routines generate output or allocate memory).
11392 @item -fstack-check
11393 @opindex fstack-check
11394 Generate code to verify that you do not go beyond the boundary of the
11395 stack. You should specify this flag if you are running in an
11396 environment with multiple threads, but only rarely need to specify it in
11397 a single-threaded environment since stack overflow is automatically
11398 detected on nearly all systems if there is only one stack.
11400 Note that this switch does not actually cause checking to be done; the
11401 operating system must do that. The switch causes generation of code
11402 to ensure that the operating system sees the stack being extended.
11404 @item -fstack-limit-register=@var{reg}
11405 @itemx -fstack-limit-symbol=@var{sym}
11406 @itemx -fno-stack-limit
11407 @opindex fstack-limit-register
11408 @opindex fstack-limit-symbol
11409 @opindex fno-stack-limit
11410 Generate code to ensure that the stack does not grow beyond a certain value,
11411 either the value of a register or the address of a symbol. If the stack
11412 would grow beyond the value, a signal is raised. For most targets,
11413 the signal is raised before the stack overruns the boundary, so
11414 it is possible to catch the signal without taking special precautions.
11416 For instance, if the stack starts at absolute address @samp{0x80000000}
11417 and grows downwards, you can use the flags
11418 @option{-fstack-limit-symbol=__stack_limit} and
11419 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11420 of 128KB@. Note that this may only work with the GNU linker.
11422 @cindex aliasing of parameters
11423 @cindex parameters, aliased
11424 @item -fargument-alias
11425 @itemx -fargument-noalias
11426 @itemx -fargument-noalias-global
11427 @opindex fargument-alias
11428 @opindex fargument-noalias
11429 @opindex fargument-noalias-global
11430 Specify the possible relationships among parameters and between
11431 parameters and global data.
11433 @option{-fargument-alias} specifies that arguments (parameters) may
11434 alias each other and may alias global storage.@*
11435 @option{-fargument-noalias} specifies that arguments do not alias
11436 each other, but may alias global storage.@*
11437 @option{-fargument-noalias-global} specifies that arguments do not
11438 alias each other and do not alias global storage.
11440 Each language will automatically use whatever option is required by
11441 the language standard. You should not need to use these options yourself.
11443 @item -fleading-underscore
11444 @opindex fleading-underscore
11445 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
11446 change the way C symbols are represented in the object file. One use
11447 is to help link with legacy assembly code.
11449 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
11450 generate code that is not binary compatible with code generated without that
11451 switch. Use it to conform to a non-default application binary interface.
11452 Not all targets provide complete support for this switch.
11454 @item -ftls-model=@var{model}
11455 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
11456 The @var{model} argument should be one of @code{global-dynamic},
11457 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
11459 The default without @option{-fpic} is @code{initial-exec}; with
11460 @option{-fpic} the default is @code{global-dynamic}.
11465 @node Environment Variables
11466 @section Environment Variables Affecting GCC
11467 @cindex environment variables
11469 @c man begin ENVIRONMENT
11470 This section describes several environment variables that affect how GCC
11471 operates. Some of them work by specifying directories or prefixes to use
11472 when searching for various kinds of files. Some are used to specify other
11473 aspects of the compilation environment.
11475 Note that you can also specify places to search using options such as
11476 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
11477 take precedence over places specified using environment variables, which
11478 in turn take precedence over those specified by the configuration of GCC@.
11479 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
11480 GNU Compiler Collection (GCC) Internals}.
11485 @c @itemx LC_COLLATE
11487 @c @itemx LC_MONETARY
11488 @c @itemx LC_NUMERIC
11493 @c @findex LC_COLLATE
11494 @findex LC_MESSAGES
11495 @c @findex LC_MONETARY
11496 @c @findex LC_NUMERIC
11500 These environment variables control the way that GCC uses
11501 localization information that allow GCC to work with different
11502 national conventions. GCC inspects the locale categories
11503 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
11504 so. These locale categories can be set to any value supported by your
11505 installation. A typical value is @samp{en_UK} for English in the United
11508 The @env{LC_CTYPE} environment variable specifies character
11509 classification. GCC uses it to determine the character boundaries in
11510 a string; this is needed for some multibyte encodings that contain quote
11511 and escape characters that would otherwise be interpreted as a string
11514 The @env{LC_MESSAGES} environment variable specifies the language to
11515 use in diagnostic messages.
11517 If the @env{LC_ALL} environment variable is set, it overrides the value
11518 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
11519 and @env{LC_MESSAGES} default to the value of the @env{LANG}
11520 environment variable. If none of these variables are set, GCC
11521 defaults to traditional C English behavior.
11525 If @env{TMPDIR} is set, it specifies the directory to use for temporary
11526 files. GCC uses temporary files to hold the output of one stage of
11527 compilation which is to be used as input to the next stage: for example,
11528 the output of the preprocessor, which is the input to the compiler
11531 @item GCC_EXEC_PREFIX
11532 @findex GCC_EXEC_PREFIX
11533 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
11534 names of the subprograms executed by the compiler. No slash is added
11535 when this prefix is combined with the name of a subprogram, but you can
11536 specify a prefix that ends with a slash if you wish.
11538 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
11539 an appropriate prefix to use based on the pathname it was invoked with.
11541 If GCC cannot find the subprogram using the specified prefix, it
11542 tries looking in the usual places for the subprogram.
11544 The default value of @env{GCC_EXEC_PREFIX} is
11545 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
11546 of @code{prefix} when you ran the @file{configure} script.
11548 Other prefixes specified with @option{-B} take precedence over this prefix.
11550 This prefix is also used for finding files such as @file{crt0.o} that are
11553 In addition, the prefix is used in an unusual way in finding the
11554 directories to search for header files. For each of the standard
11555 directories whose name normally begins with @samp{/usr/local/lib/gcc}
11556 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
11557 replacing that beginning with the specified prefix to produce an
11558 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
11559 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
11560 These alternate directories are searched first; the standard directories
11563 @item COMPILER_PATH
11564 @findex COMPILER_PATH
11565 The value of @env{COMPILER_PATH} is a colon-separated list of
11566 directories, much like @env{PATH}. GCC tries the directories thus
11567 specified when searching for subprograms, if it can't find the
11568 subprograms using @env{GCC_EXEC_PREFIX}.
11571 @findex LIBRARY_PATH
11572 The value of @env{LIBRARY_PATH} is a colon-separated list of
11573 directories, much like @env{PATH}. When configured as a native compiler,
11574 GCC tries the directories thus specified when searching for special
11575 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
11576 using GCC also uses these directories when searching for ordinary
11577 libraries for the @option{-l} option (but directories specified with
11578 @option{-L} come first).
11582 @cindex locale definition
11583 This variable is used to pass locale information to the compiler. One way in
11584 which this information is used is to determine the character set to be used
11585 when character literals, string literals and comments are parsed in C and C++.
11586 When the compiler is configured to allow multibyte characters,
11587 the following values for @env{LANG} are recognized:
11591 Recognize JIS characters.
11593 Recognize SJIS characters.
11595 Recognize EUCJP characters.
11598 If @env{LANG} is not defined, or if it has some other value, then the
11599 compiler will use mblen and mbtowc as defined by the default locale to
11600 recognize and translate multibyte characters.
11604 Some additional environments variables affect the behavior of the
11607 @include cppenv.texi
11611 @node Precompiled Headers
11612 @section Using Precompiled Headers
11613 @cindex precompiled headers
11614 @cindex speed of compilation
11616 Often large projects have many header files that are included in every
11617 source file. The time the compiler takes to process these header files
11618 over and over again can account for nearly all of the time required to
11619 build the project. To make builds faster, GCC allows users to
11620 `precompile' a header file; then, if builds can use the precompiled
11621 header file they will be much faster.
11623 To create a precompiled header file, simply compile it as you would any
11624 other file, if necessary using the @option{-x} option to make the driver
11625 treat it as a C or C++ header file. You will probably want to use a
11626 tool like @command{make} to keep the precompiled header up-to-date when
11627 the headers it contains change.
11629 A precompiled header file will be searched for when @code{#include} is
11630 seen in the compilation. As it searches for the included file
11631 (@pxref{Search Path,,Search Path,cpp.info,The C Preprocessor}) the
11632 compiler looks for a precompiled header in each directory just before it
11633 looks for the include file in that directory. The name searched for is
11634 the name specified in the @code{#include} with @samp{.gch} appended. If
11635 the precompiled header file can't be used, it is ignored.
11637 For instance, if you have @code{#include "all.h"}, and you have
11638 @file{all.h.gch} in the same directory as @file{all.h}, then the
11639 precompiled header file will be used if possible, and the original
11640 header will be used otherwise.
11642 Alternatively, you might decide to put the precompiled header file in a
11643 directory and use @option{-I} to ensure that directory is searched
11644 before (or instead of) the directory containing the original header.
11645 Then, if you want to check that the precompiled header file is always
11646 used, you can put a file of the same name as the original header in this
11647 directory containing an @code{#error} command.
11649 This also works with @option{-include}. So yet another way to use
11650 precompiled headers, good for projects not designed with precompiled
11651 header files in mind, is to simply take most of the header files used by
11652 a project, include them from another header file, precompile that header
11653 file, and @option{-include} the precompiled header. If the header files
11654 have guards against multiple inclusion, they will be skipped because
11655 they've already been included (in the precompiled header).
11657 If you need to precompile the same header file for different
11658 languages, targets, or compiler options, you can instead make a
11659 @emph{directory} named like @file{all.h.gch}, and put each precompiled
11660 header in the directory. (It doesn't matter what you call the files
11661 in the directory, every precompiled header in the directory will be
11662 considered.) The first precompiled header encountered in the
11663 directory that is valid for this compilation will be used; they're
11664 searched in no particular order.
11666 There are many other possibilities, limited only by your imagination,
11667 good sense, and the constraints of your build system.
11669 A precompiled header file can be used only when these conditions apply:
11673 Only one precompiled header can be used in a particular compilation.
11675 A precompiled header can't be used once the first C token is seen. You
11676 can have preprocessor directives before a precompiled header; you can
11677 even include a precompiled header from inside another header, so long as
11678 there are no C tokens before the @code{#include}.
11680 The precompiled header file must be produced for the same language as
11681 the current compilation. You can't use a C precompiled header for a C++
11684 The precompiled header file must be produced by the same compiler
11685 version and configuration as the current compilation is using.
11686 The easiest way to guarantee this is to use the same compiler binary
11687 for creating and using precompiled headers.
11689 Any macros defined before the precompiled header (including with
11690 @option{-D}) must either be defined in the same way as when the
11691 precompiled header was generated, or must not affect the precompiled
11692 header, which usually means that the they don't appear in the
11693 precompiled header at all.
11695 Certain command-line options must be defined in the same way as when the
11696 precompiled header was generated. At present, it's not clear which
11697 options are safe to change and which are not; the safest choice is to
11698 use exactly the same options when generating and using the precompiled
11702 For all of these but the last, the compiler will automatically ignore
11703 the precompiled header if the conditions aren't met. For the last item,
11704 some option changes will cause the precompiled header to be rejected,
11705 but not all incompatible option combinations have yet been found. If
11706 you find a new incompatible combination, please consider filing a bug
11707 report, see @ref{Bugs}.
11709 @node Running Protoize
11710 @section Running Protoize
11712 The program @code{protoize} is an optional part of GCC@. You can use
11713 it to add prototypes to a program, thus converting the program to ISO
11714 C in one respect. The companion program @code{unprotoize} does the
11715 reverse: it removes argument types from any prototypes that are found.
11717 When you run these programs, you must specify a set of source files as
11718 command line arguments. The conversion programs start out by compiling
11719 these files to see what functions they define. The information gathered
11720 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
11722 After scanning comes actual conversion. The specified files are all
11723 eligible to be converted; any files they include (whether sources or
11724 just headers) are eligible as well.
11726 But not all the eligible files are converted. By default,
11727 @code{protoize} and @code{unprotoize} convert only source and header
11728 files in the current directory. You can specify additional directories
11729 whose files should be converted with the @option{-d @var{directory}}
11730 option. You can also specify particular files to exclude with the
11731 @option{-x @var{file}} option. A file is converted if it is eligible, its
11732 directory name matches one of the specified directory names, and its
11733 name within the directory has not been excluded.
11735 Basic conversion with @code{protoize} consists of rewriting most
11736 function definitions and function declarations to specify the types of
11737 the arguments. The only ones not rewritten are those for varargs
11740 @code{protoize} optionally inserts prototype declarations at the
11741 beginning of the source file, to make them available for any calls that
11742 precede the function's definition. Or it can insert prototype
11743 declarations with block scope in the blocks where undeclared functions
11746 Basic conversion with @code{unprotoize} consists of rewriting most
11747 function declarations to remove any argument types, and rewriting
11748 function definitions to the old-style pre-ISO form.
11750 Both conversion programs print a warning for any function declaration or
11751 definition that they can't convert. You can suppress these warnings
11754 The output from @code{protoize} or @code{unprotoize} replaces the
11755 original source file. The original file is renamed to a name ending
11756 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
11757 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
11758 for DOS) file already exists, then the source file is simply discarded.
11760 @code{protoize} and @code{unprotoize} both depend on GCC itself to
11761 scan the program and collect information about the functions it uses.
11762 So neither of these programs will work until GCC is installed.
11764 Here is a table of the options you can use with @code{protoize} and
11765 @code{unprotoize}. Each option works with both programs unless
11769 @item -B @var{directory}
11770 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
11771 usual directory (normally @file{/usr/local/lib}). This file contains
11772 prototype information about standard system functions. This option
11773 applies only to @code{protoize}.
11775 @item -c @var{compilation-options}
11776 Use @var{compilation-options} as the options when running @command{gcc} to
11777 produce the @samp{.X} files. The special option @option{-aux-info} is
11778 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
11780 Note that the compilation options must be given as a single argument to
11781 @code{protoize} or @code{unprotoize}. If you want to specify several
11782 @command{gcc} options, you must quote the entire set of compilation options
11783 to make them a single word in the shell.
11785 There are certain @command{gcc} arguments that you cannot use, because they
11786 would produce the wrong kind of output. These include @option{-g},
11787 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
11788 the @var{compilation-options}, they are ignored.
11791 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
11792 systems) instead of @samp{.c}. This is convenient if you are converting
11793 a C program to C++. This option applies only to @code{protoize}.
11796 Add explicit global declarations. This means inserting explicit
11797 declarations at the beginning of each source file for each function
11798 that is called in the file and was not declared. These declarations
11799 precede the first function definition that contains a call to an
11800 undeclared function. This option applies only to @code{protoize}.
11802 @item -i @var{string}
11803 Indent old-style parameter declarations with the string @var{string}.
11804 This option applies only to @code{protoize}.
11806 @code{unprotoize} converts prototyped function definitions to old-style
11807 function definitions, where the arguments are declared between the
11808 argument list and the initial @samp{@{}. By default, @code{unprotoize}
11809 uses five spaces as the indentation. If you want to indent with just
11810 one space instead, use @option{-i " "}.
11813 Keep the @samp{.X} files. Normally, they are deleted after conversion
11817 Add explicit local declarations. @code{protoize} with @option{-l} inserts
11818 a prototype declaration for each function in each block which calls the
11819 function without any declaration. This option applies only to
11823 Make no real changes. This mode just prints information about the conversions
11824 that would have been done without @option{-n}.
11827 Make no @samp{.save} files. The original files are simply deleted.
11828 Use this option with caution.
11830 @item -p @var{program}
11831 Use the program @var{program} as the compiler. Normally, the name
11832 @file{gcc} is used.
11835 Work quietly. Most warnings are suppressed.
11838 Print the version number, just like @option{-v} for @command{gcc}.
11841 If you need special compiler options to compile one of your program's
11842 source files, then you should generate that file's @samp{.X} file
11843 specially, by running @command{gcc} on that source file with the
11844 appropriate options and the option @option{-aux-info}. Then run
11845 @code{protoize} on the entire set of files. @code{protoize} will use
11846 the existing @samp{.X} file because it is newer than the source file.
11850 gcc -Dfoo=bar file1.c -aux-info file1.X
11855 You need to include the special files along with the rest in the
11856 @code{protoize} command, even though their @samp{.X} files already
11857 exist, because otherwise they won't get converted.
11859 @xref{Protoize Caveats}, for more information on how to use
11860 @code{protoize} successfully.