1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
11 @c man begin COPYRIGHT
12 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
13 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
15 Permission is granted to copy, distribute and/or modify this document
16 under the terms of the GNU Free Documentation License, Version 1.2 or
17 any later version published by the Free Software Foundation; with the
18 Invariant Sections being ``GNU General Public License'' and ``Funding
19 Free Software'', the Front-Cover texts being (a) (see below), and with
20 the Back-Cover Texts being (b) (see below). A copy of the license is
21 included in the gfdl(7) man page.
23 (a) The FSF's Front-Cover Text is:
27 (b) The FSF's Back-Cover Text is:
29 You have freedom to copy and modify this GNU Manual, like GNU
30 software. Copies published by the Free Software Foundation raise
31 funds for GNU development.
33 @c Set file name and title for the man page.
35 @settitle GNU project C and C++ compiler
37 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
38 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
39 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
40 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
41 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
42 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
43 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
45 Only the most useful options are listed here; see below for the
46 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
49 gpl(7), gfdl(7), fsf-funding(7),
50 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
51 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
52 @file{ld}, @file{binutils} and @file{gdb}.
55 For instructions on reporting bugs, see
56 @w{@uref{http://gcc.gnu.org/bugs.html}}.
59 See the Info entry for @command{gcc}, or
60 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
61 for contributors to GCC@.
66 @chapter GCC Command Options
67 @cindex GCC command options
68 @cindex command options
69 @cindex options, GCC command
71 @c man begin DESCRIPTION
72 When you invoke GCC, it normally does preprocessing, compilation,
73 assembly and linking. The ``overall options'' allow you to stop this
74 process at an intermediate stage. For example, the @option{-c} option
75 says not to run the linker. Then the output consists of object files
76 output by the assembler.
78 Other options are passed on to one stage of processing. Some options
79 control the preprocessor and others the compiler itself. Yet other
80 options control the assembler and linker; most of these are not
81 documented here, since you rarely need to use any of them.
83 @cindex C compilation options
84 Most of the command line options that you can use with GCC are useful
85 for C programs; when an option is only useful with another language
86 (usually C++), the explanation says so explicitly. If the description
87 for a particular option does not mention a source language, you can use
88 that option with all supported languages.
90 @cindex C++ compilation options
91 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
92 options for compiling C++ programs.
94 @cindex grouping options
95 @cindex options, grouping
96 The @command{gcc} program accepts options and file names as operands. Many
97 options have multi-letter names; therefore multiple single-letter options
98 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
101 @cindex order of options
102 @cindex options, order
103 You can mix options and other arguments. For the most part, the order
104 you use doesn't matter. Order does matter when you use several options
105 of the same kind; for example, if you specify @option{-L} more than once,
106 the directories are searched in the order specified.
108 Many options have long names starting with @samp{-f} or with
109 @samp{-W}---for example,
110 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
111 these have both positive and negative forms; the negative form of
112 @option{-ffoo} would be @option{-fno-foo}. This manual documents
113 only one of these two forms, whichever one is not the default.
117 @xref{Option Index}, for an index to GCC's options.
120 * Option Summary:: Brief list of all options, without explanations.
121 * Overall Options:: Controlling the kind of output:
122 an executable, object files, assembler files,
123 or preprocessed source.
124 * Invoking G++:: Compiling C++ programs.
125 * C Dialect Options:: Controlling the variant of C language compiled.
126 * C++ Dialect Options:: Variations on C++.
127 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
129 * Language Independent Options:: Controlling how diagnostics should be
131 * Warning Options:: How picky should the compiler be?
132 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
133 * Optimize Options:: How much optimization?
134 * Preprocessor Options:: Controlling header files and macro definitions.
135 Also, getting dependency information for Make.
136 * Assembler Options:: Passing options to the assembler.
137 * Link Options:: Specifying libraries and so on.
138 * Directory Options:: Where to find header files and libraries.
139 Where to find the compiler executable files.
140 * Spec Files:: How to pass switches to sub-processes.
141 * Target Options:: Running a cross-compiler, or an old version of GCC.
142 * Submodel Options:: Specifying minor hardware or convention variations,
143 such as 68010 vs 68020.
144 * Code Gen Options:: Specifying conventions for function calls, data layout
146 * Environment Variables:: Env vars that affect GCC.
147 * Precompiled Headers:: Compiling a header once, and using it many times.
148 * Running Protoize:: Automatically adding or removing function prototypes.
154 @section Option Summary
156 Here is a summary of all the options, grouped by type. Explanations are
157 in the following sections.
160 @item Overall Options
161 @xref{Overall Options,,Options Controlling the Kind of Output}.
162 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
163 -x @var{language} -v -### --help --target-help --version @@@var{file}}
165 @item C Language Options
166 @xref{C Dialect Options,,Options Controlling C Dialect}.
167 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
168 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
169 -fhosted -ffreestanding -fms-extensions @gol
170 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
171 -fallow-single-precision -fcond-mismatch @gol
172 -fsigned-bitfields -fsigned-char @gol
173 -funsigned-bitfields -funsigned-char}
175 @item C++ Language Options
176 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
177 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
178 -fconserve-space -ffriend-injection @gol
179 -fno-elide-constructors @gol
180 -fno-enforce-eh-specs @gol
181 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
182 -fno-implicit-templates @gol
183 -fno-implicit-inline-templates @gol
184 -fno-implement-inlines -fms-extensions @gol
185 -fno-nonansi-builtins -fno-operator-names @gol
186 -fno-optional-diags -fpermissive @gol
187 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
188 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
189 -fno-default-inline -fvisibility-inlines-hidden @gol
190 -Wabi -Wctor-dtor-privacy @gol
191 -Wnon-virtual-dtor -Wreorder @gol
192 -Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol
193 -Wno-non-template-friend -Wold-style-cast @gol
194 -Woverloaded-virtual -Wno-pmf-conversions @gol
197 @item Objective-C and Objective-C++ Language Options
198 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
199 Objective-C and Objective-C++ Dialects}.
201 -fconstant-string-class=@var{class-name} @gol
202 -fgnu-runtime -fnext-runtime @gol
203 -fno-nil-receivers @gol
204 -fobjc-call-cxx-cdtors @gol
205 -fobjc-direct-dispatch @gol
206 -fobjc-exceptions @gol
208 -freplace-objc-classes @gol
211 -Wassign-intercept @gol
212 -Wno-protocol -Wselector @gol
213 -Wstrict-selector-match @gol
214 -Wundeclared-selector}
216 @item Language Independent Options
217 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
218 @gccoptlist{-fmessage-length=@var{n} @gol
219 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} @gol
220 -fdiagnostics-show-options
222 @item Warning Options
223 @xref{Warning Options,,Options to Request or Suppress Warnings}.
224 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
225 -w -Wextra -Wall -Waggregate-return -Walways-true -Wno-attributes @gol
226 -Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
227 -Wconversion -Wno-deprecated-declarations @gol
228 -Wdisabled-optimization -Wno-div-by-zero -Wno-endif-labels @gol
229 -Werror -Werror-* -Werror-implicit-function-declaration @gol
230 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
231 -Wno-format-extra-args -Wformat-nonliteral @gol
232 -Wformat-security -Wformat-y2k @gol
233 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
234 -Wimport -Wno-import -Winit-self -Winline @gol
235 -Wno-int-to-pointer-cast @gol
236 -Wno-invalid-offsetof -Winvalid-pch @gol
237 -Wlarger-than-@var{len} -Wunsafe-loop-optimizations -Wlong-long @gol
238 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
239 -Wmissing-format-attribute -Wmissing-include-dirs @gol
240 -Wmissing-noreturn @gol
241 -Wno-multichar -Wnonnull -Woverlength-strings -Wpacked -Wpadded @gol
242 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
243 -Wredundant-decls @gol
244 -Wreturn-type -Wsequence-point -Wshadow @gol
245 -Wsign-compare -Wstack-protector @gol
246 -Wstrict-aliasing -Wstrict-aliasing=2 @gol
247 -Wstring-literal-comparison @gol
248 -Wswitch -Wswitch-default -Wswitch-enum @gol
249 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
250 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
251 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
252 -Wunused-value -Wunused-variable -Wvariadic-macros @gol
253 -Wvolatile-register-var -Wwrite-strings}
255 @item C-only Warning Options
256 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
257 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
258 -Wstrict-prototypes -Wtraditional @gol
259 -Wdeclaration-after-statement -Wpointer-sign}
261 @item Debugging Options
262 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
263 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
264 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
265 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
266 -fdump-ipa-all -fdump-ipa-cgraph @gol
268 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
269 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
270 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
271 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
273 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
274 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
275 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
276 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
277 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
278 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
279 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
280 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
281 -fdump-tree-nrv -fdump-tree-vect @gol
282 -fdump-tree-sink @gol
283 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
284 -fdump-tree-salias @gol
285 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
287 -ftree-vectorizer-verbose=@var{n} @gol
288 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
289 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
290 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
291 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
292 -ftest-coverage -ftime-report -fvar-tracking @gol
293 -g -g@var{level} -gcoff -gdwarf-2 @gol
294 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
295 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
296 -print-multi-directory -print-multi-lib @gol
297 -print-prog-name=@var{program} -print-search-dirs -Q @gol
300 @item Optimization Options
301 @xref{Optimize Options,,Options that Control Optimization}.
302 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
303 -falign-labels=@var{n} -falign-loops=@var{n} @gol
304 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
305 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
306 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
307 -fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
308 -fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
309 -fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
310 -fexpensive-optimizations -ffast-math -ffloat-store @gol
311 -fforce-addr -ffunction-sections @gol
312 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
313 -fcrossjumping -fif-conversion -fif-conversion2 @gol
314 -finline-functions -finline-functions-called-once @gol
315 -finline-limit=@var{n} -fkeep-inline-functions @gol
316 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
317 -fmodulo-sched -fno-branch-count-reg @gol
318 -fno-default-inline -fno-defer-pop -fmove-loop-invariants @gol
319 -fno-function-cse -fno-guess-branch-probability @gol
320 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
321 -funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol
322 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
323 -fomit-frame-pointer -foptimize-register-move @gol
324 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
325 -fprofile-generate -fprofile-use @gol
326 -fregmove -frename-registers @gol
327 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
328 -frerun-cse-after-loop @gol
329 -frounding-math -frtl-abstract-sequences @gol
330 -fschedule-insns -fschedule-insns2 @gol
331 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
332 -fsched-spec-load-dangerous @gol
333 -fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
334 -fsched2-use-superblocks @gol
335 -fsched2-use-traces -freschedule-modulo-scheduled-loops @gol
336 -fsection-anchors -fsignaling-nans -fsingle-precision-constant @gol
337 -fstack-protector -fstack-protector-all @gol
338 -fstrict-aliasing -ftracer -fthread-jumps @gol
339 -funroll-all-loops -funroll-loops -fpeel-loops @gol
340 -fsplit-ivs-in-unroller -funswitch-loops @gol
341 -fvariable-expansion-in-unroller @gol
342 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
343 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
344 -ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
345 -ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
346 -ftree-vect-loop-version -ftree-salias -fipa-pta -fweb @gol
347 -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
348 --param @var{name}=@var{value}
349 -O -O0 -O1 -O2 -O3 -Os}
351 @item Preprocessor Options
352 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
353 @gccoptlist{-A@var{question}=@var{answer} @gol
354 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
355 -C -dD -dI -dM -dN @gol
356 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
357 -idirafter @var{dir} @gol
358 -include @var{file} -imacros @var{file} @gol
359 -iprefix @var{file} -iwithprefix @var{dir} @gol
360 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
361 -imultilib @var{dir} -isysroot @var{dir} @gol
362 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
363 -P -fworking-directory -remap @gol
364 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
365 -Xpreprocessor @var{option}}
367 @item Assembler Option
368 @xref{Assembler Options,,Passing Options to the Assembler}.
369 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
372 @xref{Link Options,,Options for Linking}.
373 @gccoptlist{@var{object-file-name} -l@var{library} @gol
374 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
375 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
376 -Wl,@var{option} -Xlinker @var{option} @gol
379 @item Directory Options
380 @xref{Directory Options,,Options for Directory Search}.
381 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
382 -specs=@var{file} -I- --sysroot=@var{dir}}
385 @c I wrote this xref this way to avoid overfull hbox. -- rms
386 @xref{Target Options}.
387 @gccoptlist{-V @var{version} -b @var{machine}}
389 @item Machine Dependent Options
390 @xref{Submodel Options,,Hardware Models and Configurations}.
391 @c This list is ordered alphanumerically by subsection name.
392 @c Try and put the significant identifier (CPU or system) first,
393 @c so users have a clue at guessing where the ones they want will be.
396 @gccoptlist{-EB -EL @gol
397 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
398 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
401 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
402 -mabi=@var{name} @gol
403 -mapcs-stack-check -mno-apcs-stack-check @gol
404 -mapcs-float -mno-apcs-float @gol
405 -mapcs-reentrant -mno-apcs-reentrant @gol
406 -msched-prolog -mno-sched-prolog @gol
407 -mlittle-endian -mbig-endian -mwords-little-endian @gol
408 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
409 -mthumb-interwork -mno-thumb-interwork @gol
410 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
411 -mstructure-size-boundary=@var{n} @gol
412 -mabort-on-noreturn @gol
413 -mlong-calls -mno-long-calls @gol
414 -msingle-pic-base -mno-single-pic-base @gol
415 -mpic-register=@var{reg} @gol
416 -mnop-fun-dllimport @gol
417 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
418 -mpoke-function-name @gol
420 -mtpcs-frame -mtpcs-leaf-frame @gol
421 -mcaller-super-interworking -mcallee-super-interworking @gol
425 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
426 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
428 @emph{Blackfin Options}
429 @gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
430 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
431 -mlow-64k -mno-low64k -mid-shared-library @gol
432 -mno-id-shared-library -mshared-library-id=@var{n} @gol
433 -mlong-calls -mno-long-calls}
436 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
437 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
438 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
439 -mstack-align -mdata-align -mconst-align @gol
440 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
441 -melf -maout -melinux -mlinux -sim -sim2 @gol
442 -mmul-bug-workaround -mno-mul-bug-workaround}
445 @gccoptlist{-mmac -mpush-args}
447 @emph{Darwin Options}
448 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
449 -arch_only -bind_at_load -bundle -bundle_loader @gol
450 -client_name -compatibility_version -current_version @gol
452 -dependency-file -dylib_file -dylinker_install_name @gol
453 -dynamic -dynamiclib -exported_symbols_list @gol
454 -filelist -flat_namespace -force_cpusubtype_ALL @gol
455 -force_flat_namespace -headerpad_max_install_names @gol
456 -image_base -init -install_name -keep_private_externs @gol
457 -multi_module -multiply_defined -multiply_defined_unused @gol
458 -noall_load -no_dead_strip_inits_and_terms @gol
459 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
460 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
461 -private_bundle -read_only_relocs -sectalign @gol
462 -sectobjectsymbols -whyload -seg1addr @gol
463 -sectcreate -sectobjectsymbols -sectorder @gol
464 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
465 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
466 -segprot -segs_read_only_addr -segs_read_write_addr @gol
467 -single_module -static -sub_library -sub_umbrella @gol
468 -twolevel_namespace -umbrella -undefined @gol
469 -unexported_symbols_list -weak_reference_mismatches @gol
470 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
473 @emph{DEC Alpha Options}
474 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
475 -mieee -mieee-with-inexact -mieee-conformant @gol
476 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
477 -mtrap-precision=@var{mode} -mbuild-constants @gol
478 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
479 -mbwx -mmax -mfix -mcix @gol
480 -mfloat-vax -mfloat-ieee @gol
481 -mexplicit-relocs -msmall-data -mlarge-data @gol
482 -msmall-text -mlarge-text @gol
483 -mmemory-latency=@var{time}}
485 @emph{DEC Alpha/VMS Options}
486 @gccoptlist{-mvms-return-codes}
489 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
490 -mhard-float -msoft-float @gol
491 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
492 -mdouble -mno-double @gol
493 -mmedia -mno-media -mmuladd -mno-muladd @gol
494 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
495 -mlinked-fp -mlong-calls -malign-labels @gol
496 -mlibrary-pic -macc-4 -macc-8 @gol
497 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
498 -moptimize-membar -mno-optimize-membar @gol
499 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
500 -mvliw-branch -mno-vliw-branch @gol
501 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
502 -mno-nested-cond-exec -mtomcat-stats @gol
506 @emph{GNU/Linux Options}
507 @gccoptlist{-muclibc}
509 @emph{H8/300 Options}
510 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
513 @gccoptlist{-march=@var{architecture-type} @gol
514 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
515 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
516 -mfixed-range=@var{register-range} @gol
517 -mjump-in-delay -mlinker-opt -mlong-calls @gol
518 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
519 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
520 -mno-jump-in-delay -mno-long-load-store @gol
521 -mno-portable-runtime -mno-soft-float @gol
522 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
523 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
524 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
525 -munix=@var{unix-std} -nolibdld -static -threads}
527 @emph{i386 and x86-64 Options}
528 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
529 -mfpmath=@var{unit} @gol
530 -masm=@var{dialect} -mno-fancy-math-387 @gol
531 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
532 -mno-wide-multiply -mrtd -malign-double @gol
533 -mpreferred-stack-boundary=@var{num} @gol
534 -mmmx -msse -msse2 -msse3 -m3dnow -msselibm @gol
535 -mthreads -mno-align-stringops -minline-all-stringops @gol
536 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
537 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
538 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
539 -mcmodel=@var{code-model} @gol
540 -m32 -m64 -mlarge-data-threshold=@var{num}}
543 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
544 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
545 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
546 -minline-float-divide-max-throughput @gol
547 -minline-int-divide-min-latency @gol
548 -minline-int-divide-max-throughput @gol
549 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
550 -mno-dwarf2-asm -mearly-stop-bits @gol
551 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
552 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64}
554 @emph{M32R/D Options}
555 @gccoptlist{-m32r2 -m32rx -m32r @gol
557 -malign-loops -mno-align-loops @gol
558 -missue-rate=@var{number} @gol
559 -mbranch-cost=@var{number} @gol
560 -mmodel=@var{code-size-model-type} @gol
561 -msdata=@var{sdata-type} @gol
562 -mno-flush-func -mflush-func=@var{name} @gol
563 -mno-flush-trap -mflush-trap=@var{number} @gol
567 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
569 @emph{M680x0 Options}
570 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
571 -m68060 -mcpu32 -m5200 -mcfv4e -m68881 -mbitfield @gol
572 -mc68000 -mc68020 @gol
573 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
574 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
575 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
577 @emph{M68hc1x Options}
578 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
579 -mauto-incdec -minmax -mlong-calls -mshort @gol
580 -msoft-reg-count=@var{count}}
583 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
584 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
585 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
586 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
587 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
590 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
591 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
592 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
593 -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
594 -mhard-float -msoft-float -msingle-float -mdouble-float @gol
595 -mdsp -mpaired-single -mips3d @gol
596 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
597 -G@var{num} -membedded-data -mno-embedded-data @gol
598 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
599 -msplit-addresses -mno-split-addresses @gol
600 -mexplicit-relocs -mno-explicit-relocs @gol
601 -mcheck-zero-division -mno-check-zero-division @gol
602 -mdivide-traps -mdivide-breaks @gol
603 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
604 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
605 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
606 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol
607 -mfix-sb1 -mno-fix-sb1 @gol
608 -mflush-func=@var{func} -mno-flush-func @gol
609 -mbranch-likely -mno-branch-likely @gol
610 -mfp-exceptions -mno-fp-exceptions @gol
611 -mvr4130-align -mno-vr4130-align}
614 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
615 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
616 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
617 -mno-base-addresses -msingle-exit -mno-single-exit}
619 @emph{MN10300 Options}
620 @gccoptlist{-mmult-bug -mno-mult-bug @gol
621 -mam33 -mno-am33 @gol
622 -mam33-2 -mno-am33-2 @gol
623 -mreturn-pointer-on-d0 @gol
627 @gccoptlist{-mno-crt0 -mbacc -msim @gol
628 -march=@var{cpu-type} }
630 @emph{PDP-11 Options}
631 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
632 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
633 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
634 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
635 -mbranch-expensive -mbranch-cheap @gol
636 -msplit -mno-split -munix-asm -mdec-asm}
638 @emph{PowerPC Options}
639 See RS/6000 and PowerPC Options.
641 @emph{RS/6000 and PowerPC Options}
642 @gccoptlist{-mcpu=@var{cpu-type} @gol
643 -mtune=@var{cpu-type} @gol
644 -mpower -mno-power -mpower2 -mno-power2 @gol
645 -mpowerpc -mpowerpc64 -mno-powerpc @gol
646 -maltivec -mno-altivec @gol
647 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
648 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
649 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
650 -mnew-mnemonics -mold-mnemonics @gol
651 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
652 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
653 -malign-power -malign-natural @gol
654 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
655 -mstring -mno-string -mupdate -mno-update @gol
656 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
657 -mstrict-align -mno-strict-align -mrelocatable @gol
658 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
659 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
660 -mdynamic-no-pic -maltivec -mswdiv @gol
661 -mprioritize-restricted-insns=@var{priority} @gol
662 -msched-costly-dep=@var{dependence_type} @gol
663 -minsert-sched-nops=@var{scheme} @gol
664 -mcall-sysv -mcall-netbsd @gol
665 -maix-struct-return -msvr4-struct-return @gol
666 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
667 -misel -mno-isel @gol
668 -misel=yes -misel=no @gol
670 -mspe=yes -mspe=no @gol
671 -mvrsave -mno-vrsave @gol
672 -mmulhw -mno-mulhw @gol
673 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
674 -mprototype -mno-prototype @gol
675 -msim -mmvme -mads -myellowknife -memb -msdata @gol
676 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
678 @emph{S/390 and zSeries Options}
679 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
680 -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
681 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
682 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
683 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
684 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
685 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
688 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
689 -m4-nofpu -m4-single-only -m4-single -m4 @gol
690 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
691 -m5-64media -m5-64media-nofpu @gol
692 -m5-32media -m5-32media-nofpu @gol
693 -m5-compact -m5-compact-nofpu @gol
694 -mb -ml -mdalign -mrelax @gol
695 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
696 -mieee -misize -mpadstruct -mspace @gol
697 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
698 -mdivsi3_libfunc=@var{name} @gol
699 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
703 @gccoptlist{-mcpu=@var{cpu-type} @gol
704 -mtune=@var{cpu-type} @gol
705 -mcmodel=@var{code-model} @gol
706 -m32 -m64 -mapp-regs -mno-app-regs @gol
707 -mfaster-structs -mno-faster-structs @gol
708 -mfpu -mno-fpu -mhard-float -msoft-float @gol
709 -mhard-quad-float -msoft-quad-float @gol
710 -mimpure-text -mno-impure-text -mlittle-endian @gol
711 -mstack-bias -mno-stack-bias @gol
712 -munaligned-doubles -mno-unaligned-doubles @gol
713 -mv8plus -mno-v8plus -mvis -mno-vis
714 -threads -pthreads -pthread}
716 @emph{System V Options}
717 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
719 @emph{TMS320C3x/C4x Options}
720 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
721 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
722 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
723 -mparallel-insns -mparallel-mpy -mpreserve-float}
726 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
727 -mprolog-function -mno-prolog-function -mspace @gol
728 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
729 -mapp-regs -mno-app-regs @gol
730 -mdisable-callt -mno-disable-callt @gol
736 @gccoptlist{-mg -mgnu -munix}
738 @emph{x86-64 Options}
739 See i386 and x86-64 Options.
741 @emph{Xstormy16 Options}
744 @emph{Xtensa Options}
745 @gccoptlist{-mconst16 -mno-const16 @gol
746 -mfused-madd -mno-fused-madd @gol
747 -mtext-section-literals -mno-text-section-literals @gol
748 -mtarget-align -mno-target-align @gol
749 -mlongcalls -mno-longcalls}
751 @emph{zSeries Options}
752 See S/390 and zSeries Options.
754 @item Code Generation Options
755 @xref{Code Gen Options,,Options for Code Generation Conventions}.
756 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
757 -ffixed-@var{reg} -fexceptions @gol
758 -fnon-call-exceptions -funwind-tables @gol
759 -fasynchronous-unwind-tables @gol
760 -finhibit-size-directive -finstrument-functions @gol
761 -fno-common -fno-ident @gol
762 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
763 -fno-jump-tables @gol
764 -freg-struct-return -fshort-enums @gol
765 -fshort-double -fshort-wchar @gol
766 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
767 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
768 -fargument-alias -fargument-noalias @gol
769 -fargument-noalias-global -fleading-underscore @gol
770 -ftls-model=@var{model} @gol
771 -ftrapv -fwrapv -fbounds-check @gol
772 -fvisibility -fopenmp}
776 * Overall Options:: Controlling the kind of output:
777 an executable, object files, assembler files,
778 or preprocessed source.
779 * C Dialect Options:: Controlling the variant of C language compiled.
780 * C++ Dialect Options:: Variations on C++.
781 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
783 * Language Independent Options:: Controlling how diagnostics should be
785 * Warning Options:: How picky should the compiler be?
786 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
787 * Optimize Options:: How much optimization?
788 * Preprocessor Options:: Controlling header files and macro definitions.
789 Also, getting dependency information for Make.
790 * Assembler Options:: Passing options to the assembler.
791 * Link Options:: Specifying libraries and so on.
792 * Directory Options:: Where to find header files and libraries.
793 Where to find the compiler executable files.
794 * Spec Files:: How to pass switches to sub-processes.
795 * Target Options:: Running a cross-compiler, or an old version of GCC.
798 @node Overall Options
799 @section Options Controlling the Kind of Output
801 Compilation can involve up to four stages: preprocessing, compilation
802 proper, assembly and linking, always in that order. GCC is capable of
803 preprocessing and compiling several files either into several
804 assembler input files, or into one assembler input file; then each
805 assembler input file produces an object file, and linking combines all
806 the object files (those newly compiled, and those specified as input)
807 into an executable file.
809 @cindex file name suffix
810 For any given input file, the file name suffix determines what kind of
815 C source code which must be preprocessed.
818 C source code which should not be preprocessed.
821 C++ source code which should not be preprocessed.
824 Objective-C source code. Note that you must link with the @file{libobjc}
825 library to make an Objective-C program work.
828 Objective-C source code which should not be preprocessed.
832 Objective-C++ source code. Note that you must link with the @file{libobjc}
833 library to make an Objective-C++ program work. Note that @samp{.M} refers
834 to a literal capital M@.
837 Objective-C++ source code which should not be preprocessed.
840 C, C++, Objective-C or Objective-C++ header file to be turned into a
845 @itemx @var{file}.cxx
846 @itemx @var{file}.cpp
847 @itemx @var{file}.CPP
848 @itemx @var{file}.c++
850 C++ source code which must be preprocessed. Note that in @samp{.cxx},
851 the last two letters must both be literally @samp{x}. Likewise,
852 @samp{.C} refers to a literal capital C@.
856 Objective-C++ source code which must be preprocessed.
859 Objective-C++ source code which should not be preprocessed.
863 C++ header file to be turned into a precompiled header.
866 @itemx @var{file}.for
867 @itemx @var{file}.FOR
868 Fixed form Fortran source code which should not be preprocessed.
871 @itemx @var{file}.fpp
872 @itemx @var{file}.FPP
873 Fixed form Fortran source code which must be preprocessed (with the traditional
877 @itemx @var{file}.f95
878 Free form Fortran source code which should not be preprocessed.
881 @itemx @var{file}.F95
882 Free form Fortran source code which must be preprocessed (with the
883 traditional preprocessor).
885 @c FIXME: Descriptions of Java file types.
892 Ada source code file which contains a library unit declaration (a
893 declaration of a package, subprogram, or generic, or a generic
894 instantiation), or a library unit renaming declaration (a package,
895 generic, or subprogram renaming declaration). Such files are also
898 @itemx @var{file}.adb
899 Ada source code file containing a library unit body (a subprogram or
900 package body). Such files are also called @dfn{bodies}.
902 @c GCC also knows about some suffixes for languages not yet included:
913 Assembler code which must be preprocessed.
916 An object file to be fed straight into linking.
917 Any file name with no recognized suffix is treated this way.
921 You can specify the input language explicitly with the @option{-x} option:
924 @item -x @var{language}
925 Specify explicitly the @var{language} for the following input files
926 (rather than letting the compiler choose a default based on the file
927 name suffix). This option applies to all following input files until
928 the next @option{-x} option. Possible values for @var{language} are:
930 c c-header c-cpp-output
931 c++ c++-header c++-cpp-output
932 objective-c objective-c-header objective-c-cpp-output
933 objective-c++ objective-c++-header objective-c++-cpp-output
934 assembler assembler-with-cpp
943 Turn off any specification of a language, so that subsequent files are
944 handled according to their file name suffixes (as they are if @option{-x}
945 has not been used at all).
947 @item -pass-exit-codes
948 @opindex pass-exit-codes
949 Normally the @command{gcc} program will exit with the code of 1 if any
950 phase of the compiler returns a non-success return code. If you specify
951 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
952 numerically highest error produced by any phase that returned an error
956 If you only want some of the stages of compilation, you can use
957 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
958 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
959 @command{gcc} is to stop. Note that some combinations (for example,
960 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
965 Compile or assemble the source files, but do not link. The linking
966 stage simply is not done. The ultimate output is in the form of an
967 object file for each source file.
969 By default, the object file name for a source file is made by replacing
970 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
972 Unrecognized input files, not requiring compilation or assembly, are
977 Stop after the stage of compilation proper; do not assemble. The output
978 is in the form of an assembler code file for each non-assembler input
981 By default, the assembler file name for a source file is made by
982 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
984 Input files that don't require compilation are ignored.
988 Stop after the preprocessing stage; do not run the compiler proper. The
989 output is in the form of preprocessed source code, which is sent to the
992 Input files which don't require preprocessing are ignored.
994 @cindex output file option
997 Place output in file @var{file}. This applies regardless to whatever
998 sort of output is being produced, whether it be an executable file,
999 an object file, an assembler file or preprocessed C code.
1001 If @option{-o} is not specified, the default is to put an executable
1002 file in @file{a.out}, the object file for
1003 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1004 assembler file in @file{@var{source}.s}, a precompiled header file in
1005 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1010 Print (on standard error output) the commands executed to run the stages
1011 of compilation. Also print the version number of the compiler driver
1012 program and of the preprocessor and the compiler proper.
1016 Like @option{-v} except the commands are not executed and all command
1017 arguments are quoted. This is useful for shell scripts to capture the
1018 driver-generated command lines.
1022 Use pipes rather than temporary files for communication between the
1023 various stages of compilation. This fails to work on some systems where
1024 the assembler is unable to read from a pipe; but the GNU assembler has
1029 If you are compiling multiple source files, this option tells the driver
1030 to pass all the source files to the compiler at once (for those
1031 languages for which the compiler can handle this). This will allow
1032 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1033 language for which this is supported is C@. If you pass source files for
1034 multiple languages to the driver, using this option, the driver will invoke
1035 the compiler(s) that support IMA once each, passing each compiler all the
1036 source files appropriate for it. For those languages that do not support
1037 IMA this option will be ignored, and the compiler will be invoked once for
1038 each source file in that language. If you use this option in conjunction
1039 with @option{-save-temps}, the compiler will generate multiple
1041 (one for each source file), but only one (combined) @file{.o} or
1046 Print (on the standard output) a description of the command line options
1047 understood by @command{gcc}. If the @option{-v} option is also specified
1048 then @option{--help} will also be passed on to the various processes
1049 invoked by @command{gcc}, so that they can display the command line options
1050 they accept. If the @option{-Wextra} option is also specified then command
1051 line options which have no documentation associated with them will also
1055 @opindex target-help
1056 Print (on the standard output) a description of target specific command
1057 line options for each tool.
1061 Display the version number and copyrights of the invoked GCC@.
1063 @include @value{srcdir}/../libiberty/at-file.texi
1067 @section Compiling C++ Programs
1069 @cindex suffixes for C++ source
1070 @cindex C++ source file suffixes
1071 C++ source files conventionally use one of the suffixes @samp{.C},
1072 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1073 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1074 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1075 files with these names and compiles them as C++ programs even if you
1076 call the compiler the same way as for compiling C programs (usually
1077 with the name @command{gcc}).
1081 However, C++ programs often require class libraries as well as a
1082 compiler that understands the C++ language---and under some
1083 circumstances, you might want to compile programs or header files from
1084 standard input, or otherwise without a suffix that flags them as C++
1085 programs. You might also like to precompile a C header file with a
1086 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1087 program that calls GCC with the default language set to C++, and
1088 automatically specifies linking against the C++ library. On many
1089 systems, @command{g++} is also installed with the name @command{c++}.
1091 @cindex invoking @command{g++}
1092 When you compile C++ programs, you may specify many of the same
1093 command-line options that you use for compiling programs in any
1094 language; or command-line options meaningful for C and related
1095 languages; or options that are meaningful only for C++ programs.
1096 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1097 explanations of options for languages related to C@.
1098 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1099 explanations of options that are meaningful only for C++ programs.
1101 @node C Dialect Options
1102 @section Options Controlling C Dialect
1103 @cindex dialect options
1104 @cindex language dialect options
1105 @cindex options, dialect
1107 The following options control the dialect of C (or languages derived
1108 from C, such as C++, Objective-C and Objective-C++) that the compiler
1112 @cindex ANSI support
1116 In C mode, support all ISO C90 programs. In C++ mode,
1117 remove GNU extensions that conflict with ISO C++.
1119 This turns off certain features of GCC that are incompatible with ISO
1120 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1121 such as the @code{asm} and @code{typeof} keywords, and
1122 predefined macros such as @code{unix} and @code{vax} that identify the
1123 type of system you are using. It also enables the undesirable and
1124 rarely used ISO trigraph feature. For the C compiler,
1125 it disables recognition of C++ style @samp{//} comments as well as
1126 the @code{inline} keyword.
1128 The alternate keywords @code{__asm__}, @code{__extension__},
1129 @code{__inline__} and @code{__typeof__} continue to work despite
1130 @option{-ansi}. You would not want to use them in an ISO C program, of
1131 course, but it is useful to put them in header files that might be included
1132 in compilations done with @option{-ansi}. Alternate predefined macros
1133 such as @code{__unix__} and @code{__vax__} are also available, with or
1134 without @option{-ansi}.
1136 The @option{-ansi} option does not cause non-ISO programs to be
1137 rejected gratuitously. For that, @option{-pedantic} is required in
1138 addition to @option{-ansi}. @xref{Warning Options}.
1140 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1141 option is used. Some header files may notice this macro and refrain
1142 from declaring certain functions or defining certain macros that the
1143 ISO standard doesn't call for; this is to avoid interfering with any
1144 programs that might use these names for other things.
1146 Functions which would normally be built in but do not have semantics
1147 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1148 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1149 built-in functions provided by GCC}, for details of the functions
1154 Determine the language standard. This option is currently only
1155 supported when compiling C or C++. A value for this option must be
1156 provided; possible values are
1161 ISO C90 (same as @option{-ansi}).
1163 @item iso9899:199409
1164 ISO C90 as modified in amendment 1.
1170 ISO C99. Note that this standard is not yet fully supported; see
1171 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1172 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1175 Default, ISO C90 plus GNU extensions (including some C99 features).
1179 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1180 this will become the default. The name @samp{gnu9x} is deprecated.
1183 The 1998 ISO C++ standard plus amendments.
1186 The same as @option{-std=c++98} plus GNU extensions. This is the
1187 default for C++ code.
1190 Even when this option is not specified, you can still use some of the
1191 features of newer standards in so far as they do not conflict with
1192 previous C standards. For example, you may use @code{__restrict__} even
1193 when @option{-std=c99} is not specified.
1195 The @option{-std} options specifying some version of ISO C have the same
1196 effects as @option{-ansi}, except that features that were not in ISO C90
1197 but are in the specified version (for example, @samp{//} comments and
1198 the @code{inline} keyword in ISO C99) are not disabled.
1200 @xref{Standards,,Language Standards Supported by GCC}, for details of
1201 these standard versions.
1203 @item -aux-info @var{filename}
1205 Output to the given filename prototyped declarations for all functions
1206 declared and/or defined in a translation unit, including those in header
1207 files. This option is silently ignored in any language other than C@.
1209 Besides declarations, the file indicates, in comments, the origin of
1210 each declaration (source file and line), whether the declaration was
1211 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1212 @samp{O} for old, respectively, in the first character after the line
1213 number and the colon), and whether it came from a declaration or a
1214 definition (@samp{C} or @samp{F}, respectively, in the following
1215 character). In the case of function definitions, a K&R-style list of
1216 arguments followed by their declarations is also provided, inside
1217 comments, after the declaration.
1221 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1222 keyword, so that code can use these words as identifiers. You can use
1223 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1224 instead. @option{-ansi} implies @option{-fno-asm}.
1226 In C++, this switch only affects the @code{typeof} keyword, since
1227 @code{asm} and @code{inline} are standard keywords. You may want to
1228 use the @option{-fno-gnu-keywords} flag instead, which has the same
1229 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1230 switch only affects the @code{asm} and @code{typeof} keywords, since
1231 @code{inline} is a standard keyword in ISO C99.
1234 @itemx -fno-builtin-@var{function}
1235 @opindex fno-builtin
1236 @cindex built-in functions
1237 Don't recognize built-in functions that do not begin with
1238 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1239 functions provided by GCC}, for details of the functions affected,
1240 including those which are not built-in functions when @option{-ansi} or
1241 @option{-std} options for strict ISO C conformance are used because they
1242 do not have an ISO standard meaning.
1244 GCC normally generates special code to handle certain built-in functions
1245 more efficiently; for instance, calls to @code{alloca} may become single
1246 instructions that adjust the stack directly, and calls to @code{memcpy}
1247 may become inline copy loops. The resulting code is often both smaller
1248 and faster, but since the function calls no longer appear as such, you
1249 cannot set a breakpoint on those calls, nor can you change the behavior
1250 of the functions by linking with a different library. In addition,
1251 when a function is recognized as a built-in function, GCC may use
1252 information about that function to warn about problems with calls to
1253 that function, or to generate more efficient code, even if the
1254 resulting code still contains calls to that function. For example,
1255 warnings are given with @option{-Wformat} for bad calls to
1256 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1257 known not to modify global memory.
1259 With the @option{-fno-builtin-@var{function}} option
1260 only the built-in function @var{function} is
1261 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1262 function is named this is not built-in in this version of GCC, this
1263 option is ignored. There is no corresponding
1264 @option{-fbuiltin-@var{function}} option; if you wish to enable
1265 built-in functions selectively when using @option{-fno-builtin} or
1266 @option{-ffreestanding}, you may define macros such as:
1269 #define abs(n) __builtin_abs ((n))
1270 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1275 @cindex hosted environment
1277 Assert that compilation takes place in a hosted environment. This implies
1278 @option{-fbuiltin}. A hosted environment is one in which the
1279 entire standard library is available, and in which @code{main} has a return
1280 type of @code{int}. Examples are nearly everything except a kernel.
1281 This is equivalent to @option{-fno-freestanding}.
1283 @item -ffreestanding
1284 @opindex ffreestanding
1285 @cindex hosted environment
1287 Assert that compilation takes place in a freestanding environment. This
1288 implies @option{-fno-builtin}. A freestanding environment
1289 is one in which the standard library may not exist, and program startup may
1290 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1291 This is equivalent to @option{-fno-hosted}.
1293 @xref{Standards,,Language Standards Supported by GCC}, for details of
1294 freestanding and hosted environments.
1296 @item -fms-extensions
1297 @opindex fms-extensions
1298 Accept some non-standard constructs used in Microsoft header files.
1300 Some cases of unnamed fields in structures and unions are only
1301 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1302 fields within structs/unions}, for details.
1306 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1307 options for strict ISO C conformance) implies @option{-trigraphs}.
1309 @item -no-integrated-cpp
1310 @opindex no-integrated-cpp
1311 Performs a compilation in two passes: preprocessing and compiling. This
1312 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1313 @option{-B} option. The user supplied compilation step can then add in
1314 an additional preprocessing step after normal preprocessing but before
1315 compiling. The default is to use the integrated cpp (internal cpp)
1317 The semantics of this option will change if "cc1", "cc1plus", and
1318 "cc1obj" are merged.
1320 @cindex traditional C language
1321 @cindex C language, traditional
1323 @itemx -traditional-cpp
1324 @opindex traditional-cpp
1325 @opindex traditional
1326 Formerly, these options caused GCC to attempt to emulate a pre-standard
1327 C compiler. They are now only supported with the @option{-E} switch.
1328 The preprocessor continues to support a pre-standard mode. See the GNU
1329 CPP manual for details.
1331 @item -fcond-mismatch
1332 @opindex fcond-mismatch
1333 Allow conditional expressions with mismatched types in the second and
1334 third arguments. The value of such an expression is void. This option
1335 is not supported for C++.
1337 @item -funsigned-char
1338 @opindex funsigned-char
1339 Let the type @code{char} be unsigned, like @code{unsigned char}.
1341 Each kind of machine has a default for what @code{char} should
1342 be. It is either like @code{unsigned char} by default or like
1343 @code{signed char} by default.
1345 Ideally, a portable program should always use @code{signed char} or
1346 @code{unsigned char} when it depends on the signedness of an object.
1347 But many programs have been written to use plain @code{char} and
1348 expect it to be signed, or expect it to be unsigned, depending on the
1349 machines they were written for. This option, and its inverse, let you
1350 make such a program work with the opposite default.
1352 The type @code{char} is always a distinct type from each of
1353 @code{signed char} or @code{unsigned char}, even though its behavior
1354 is always just like one of those two.
1357 @opindex fsigned-char
1358 Let the type @code{char} be signed, like @code{signed char}.
1360 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1361 the negative form of @option{-funsigned-char}. Likewise, the option
1362 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1364 @item -fsigned-bitfields
1365 @itemx -funsigned-bitfields
1366 @itemx -fno-signed-bitfields
1367 @itemx -fno-unsigned-bitfields
1368 @opindex fsigned-bitfields
1369 @opindex funsigned-bitfields
1370 @opindex fno-signed-bitfields
1371 @opindex fno-unsigned-bitfields
1372 These options control whether a bit-field is signed or unsigned, when the
1373 declaration does not use either @code{signed} or @code{unsigned}. By
1374 default, such a bit-field is signed, because this is consistent: the
1375 basic integer types such as @code{int} are signed types.
1378 @node C++ Dialect Options
1379 @section Options Controlling C++ Dialect
1381 @cindex compiler options, C++
1382 @cindex C++ options, command line
1383 @cindex options, C++
1384 This section describes the command-line options that are only meaningful
1385 for C++ programs; but you can also use most of the GNU compiler options
1386 regardless of what language your program is in. For example, you
1387 might compile a file @code{firstClass.C} like this:
1390 g++ -g -frepo -O -c firstClass.C
1394 In this example, only @option{-frepo} is an option meant
1395 only for C++ programs; you can use the other options with any
1396 language supported by GCC@.
1398 Here is a list of options that are @emph{only} for compiling C++ programs:
1402 @item -fabi-version=@var{n}
1403 @opindex fabi-version
1404 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1405 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1406 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1407 the version that conforms most closely to the C++ ABI specification.
1408 Therefore, the ABI obtained using version 0 will change as ABI bugs
1411 The default is version 2.
1413 @item -fno-access-control
1414 @opindex fno-access-control
1415 Turn off all access checking. This switch is mainly useful for working
1416 around bugs in the access control code.
1420 Check that the pointer returned by @code{operator new} is non-null
1421 before attempting to modify the storage allocated. This check is
1422 normally unnecessary because the C++ standard specifies that
1423 @code{operator new} will only return @code{0} if it is declared
1424 @samp{throw()}, in which case the compiler will always check the
1425 return value even without this option. In all other cases, when
1426 @code{operator new} has a non-empty exception specification, memory
1427 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1428 @samp{new (nothrow)}.
1430 @item -fconserve-space
1431 @opindex fconserve-space
1432 Put uninitialized or runtime-initialized global variables into the
1433 common segment, as C does. This saves space in the executable at the
1434 cost of not diagnosing duplicate definitions. If you compile with this
1435 flag and your program mysteriously crashes after @code{main()} has
1436 completed, you may have an object that is being destroyed twice because
1437 two definitions were merged.
1439 This option is no longer useful on most targets, now that support has
1440 been added for putting variables into BSS without making them common.
1442 @item -ffriend-injection
1443 @opindex ffriend-injection
1444 Inject friend functions into the enclosing namespace, so that they are
1445 visible outside the scope of the class in which they are declared.
1446 Friend functions were documented to work this way in the old Annotated
1447 C++ Reference Manual, and versions of G++ before 4.1 always worked
1448 that way. However, in ISO C++ a friend function which is not declared
1449 in an enclosing scope can only be found using argument dependent
1450 lookup. This option causes friends to be injected as they were in
1453 This option is for compatibility, and may be removed in a future
1456 @item -fno-elide-constructors
1457 @opindex fno-elide-constructors
1458 The C++ standard allows an implementation to omit creating a temporary
1459 which is only used to initialize another object of the same type.
1460 Specifying this option disables that optimization, and forces G++ to
1461 call the copy constructor in all cases.
1463 @item -fno-enforce-eh-specs
1464 @opindex fno-enforce-eh-specs
1465 Don't generate code to check for violation of exception specifications
1466 at runtime. This option violates the C++ standard, but may be useful
1467 for reducing code size in production builds, much like defining
1468 @samp{NDEBUG}. This does not give user code permission to throw
1469 exceptions in violation of the exception specifications; the compiler
1470 will still optimize based on the specifications, so throwing an
1471 unexpected exception will result in undefined behavior.
1474 @itemx -fno-for-scope
1476 @opindex fno-for-scope
1477 If @option{-ffor-scope} is specified, the scope of variables declared in
1478 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1479 as specified by the C++ standard.
1480 If @option{-fno-for-scope} is specified, the scope of variables declared in
1481 a @i{for-init-statement} extends to the end of the enclosing scope,
1482 as was the case in old versions of G++, and other (traditional)
1483 implementations of C++.
1485 The default if neither flag is given to follow the standard,
1486 but to allow and give a warning for old-style code that would
1487 otherwise be invalid, or have different behavior.
1489 @item -fno-gnu-keywords
1490 @opindex fno-gnu-keywords
1491 Do not recognize @code{typeof} as a keyword, so that code can use this
1492 word as an identifier. You can use the keyword @code{__typeof__} instead.
1493 @option{-ansi} implies @option{-fno-gnu-keywords}.
1495 @item -fno-implicit-templates
1496 @opindex fno-implicit-templates
1497 Never emit code for non-inline templates which are instantiated
1498 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1499 @xref{Template Instantiation}, for more information.
1501 @item -fno-implicit-inline-templates
1502 @opindex fno-implicit-inline-templates
1503 Don't emit code for implicit instantiations of inline templates, either.
1504 The default is to handle inlines differently so that compiles with and
1505 without optimization will need the same set of explicit instantiations.
1507 @item -fno-implement-inlines
1508 @opindex fno-implement-inlines
1509 To save space, do not emit out-of-line copies of inline functions
1510 controlled by @samp{#pragma implementation}. This will cause linker
1511 errors if these functions are not inlined everywhere they are called.
1513 @item -fms-extensions
1514 @opindex fms-extensions
1515 Disable pedantic warnings about constructs used in MFC, such as implicit
1516 int and getting a pointer to member function via non-standard syntax.
1518 @item -fno-nonansi-builtins
1519 @opindex fno-nonansi-builtins
1520 Disable built-in declarations of functions that are not mandated by
1521 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1522 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1524 @item -fno-operator-names
1525 @opindex fno-operator-names
1526 Do not treat the operator name keywords @code{and}, @code{bitand},
1527 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1528 synonyms as keywords.
1530 @item -fno-optional-diags
1531 @opindex fno-optional-diags
1532 Disable diagnostics that the standard says a compiler does not need to
1533 issue. Currently, the only such diagnostic issued by G++ is the one for
1534 a name having multiple meanings within a class.
1537 @opindex fpermissive
1538 Downgrade some diagnostics about nonconformant code from errors to
1539 warnings. Thus, using @option{-fpermissive} will allow some
1540 nonconforming code to compile.
1544 Enable automatic template instantiation at link time. This option also
1545 implies @option{-fno-implicit-templates}. @xref{Template
1546 Instantiation}, for more information.
1550 Disable generation of information about every class with virtual
1551 functions for use by the C++ runtime type identification features
1552 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1553 of the language, you can save some space by using this flag. Note that
1554 exception handling uses the same information, but it will generate it as
1559 Emit statistics about front-end processing at the end of the compilation.
1560 This information is generally only useful to the G++ development team.
1562 @item -ftemplate-depth-@var{n}
1563 @opindex ftemplate-depth
1564 Set the maximum instantiation depth for template classes to @var{n}.
1565 A limit on the template instantiation depth is needed to detect
1566 endless recursions during template class instantiation. ANSI/ISO C++
1567 conforming programs must not rely on a maximum depth greater than 17.
1569 @item -fno-threadsafe-statics
1570 @opindex fno-threadsafe-statics
1571 Do not emit the extra code to use the routines specified in the C++
1572 ABI for thread-safe initialization of local statics. You can use this
1573 option to reduce code size slightly in code that doesn't need to be
1576 @item -fuse-cxa-atexit
1577 @opindex fuse-cxa-atexit
1578 Register destructors for objects with static storage duration with the
1579 @code{__cxa_atexit} function rather than the @code{atexit} function.
1580 This option is required for fully standards-compliant handling of static
1581 destructors, but will only work if your C library supports
1582 @code{__cxa_atexit}.
1584 @item -fno-use-cxa-get-exception-ptr
1585 @opindex fno-use-cxa-get-exception-ptr
1586 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1587 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1588 if the runtime routine is not available.
1590 @item -fvisibility-inlines-hidden
1591 @opindex fvisibility-inlines-hidden
1592 Causes all inlined methods to be marked with
1593 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1594 appear in the export table of a DSO and do not require a PLT indirection
1595 when used within the DSO@. Enabling this option can have a dramatic effect
1596 on load and link times of a DSO as it massively reduces the size of the
1597 dynamic export table when the library makes heavy use of templates. While
1598 it can cause bloating through duplication of code within each DSO where
1599 it is used, often the wastage is less than the considerable space occupied
1600 by a long symbol name in the export table which is typical when using
1601 templates and namespaces. For even more savings, combine with the
1602 @option{-fvisibility=hidden} switch.
1606 Do not use weak symbol support, even if it is provided by the linker.
1607 By default, G++ will use weak symbols if they are available. This
1608 option exists only for testing, and should not be used by end-users;
1609 it will result in inferior code and has no benefits. This option may
1610 be removed in a future release of G++.
1614 Do not search for header files in the standard directories specific to
1615 C++, but do still search the other standard directories. (This option
1616 is used when building the C++ library.)
1619 In addition, these optimization, warning, and code generation options
1620 have meanings only for C++ programs:
1623 @item -fno-default-inline
1624 @opindex fno-default-inline
1625 Do not assume @samp{inline} for functions defined inside a class scope.
1626 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1627 functions will have linkage like inline functions; they just won't be
1630 @item -Wabi @r{(C++ only)}
1632 Warn when G++ generates code that is probably not compatible with the
1633 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1634 all such cases, there are probably some cases that are not warned about,
1635 even though G++ is generating incompatible code. There may also be
1636 cases where warnings are emitted even though the code that is generated
1639 You should rewrite your code to avoid these warnings if you are
1640 concerned about the fact that code generated by G++ may not be binary
1641 compatible with code generated by other compilers.
1643 The known incompatibilities at this point include:
1648 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1649 pack data into the same byte as a base class. For example:
1652 struct A @{ virtual void f(); int f1 : 1; @};
1653 struct B : public A @{ int f2 : 1; @};
1657 In this case, G++ will place @code{B::f2} into the same byte
1658 as@code{A::f1}; other compilers will not. You can avoid this problem
1659 by explicitly padding @code{A} so that its size is a multiple of the
1660 byte size on your platform; that will cause G++ and other compilers to
1661 layout @code{B} identically.
1664 Incorrect handling of tail-padding for virtual bases. G++ does not use
1665 tail padding when laying out virtual bases. For example:
1668 struct A @{ virtual void f(); char c1; @};
1669 struct B @{ B(); char c2; @};
1670 struct C : public A, public virtual B @{@};
1674 In this case, G++ will not place @code{B} into the tail-padding for
1675 @code{A}; other compilers will. You can avoid this problem by
1676 explicitly padding @code{A} so that its size is a multiple of its
1677 alignment (ignoring virtual base classes); that will cause G++ and other
1678 compilers to layout @code{C} identically.
1681 Incorrect handling of bit-fields with declared widths greater than that
1682 of their underlying types, when the bit-fields appear in a union. For
1686 union U @{ int i : 4096; @};
1690 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1691 union too small by the number of bits in an @code{int}.
1694 Empty classes can be placed at incorrect offsets. For example:
1704 struct C : public B, public A @{@};
1708 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1709 it should be placed at offset zero. G++ mistakenly believes that the
1710 @code{A} data member of @code{B} is already at offset zero.
1713 Names of template functions whose types involve @code{typename} or
1714 template template parameters can be mangled incorrectly.
1717 template <typename Q>
1718 void f(typename Q::X) @{@}
1720 template <template <typename> class Q>
1721 void f(typename Q<int>::X) @{@}
1725 Instantiations of these templates may be mangled incorrectly.
1729 @item -Wctor-dtor-privacy @r{(C++ only)}
1730 @opindex Wctor-dtor-privacy
1731 Warn when a class seems unusable because all the constructors or
1732 destructors in that class are private, and it has neither friends nor
1733 public static member functions.
1735 @item -Wnon-virtual-dtor @r{(C++ only)}
1736 @opindex Wnon-virtual-dtor
1737 Warn when a class appears to be polymorphic, thereby requiring a virtual
1738 destructor, yet it declares a non-virtual one. This warning is also
1739 enabled if -Weffc++ is specified.
1741 @item -Wreorder @r{(C++ only)}
1743 @cindex reordering, warning
1744 @cindex warning for reordering of member initializers
1745 Warn when the order of member initializers given in the code does not
1746 match the order in which they must be executed. For instance:
1752 A(): j (0), i (1) @{ @}
1756 The compiler will rearrange the member initializers for @samp{i}
1757 and @samp{j} to match the declaration order of the members, emitting
1758 a warning to that effect. This warning is enabled by @option{-Wall}.
1761 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1764 @item -Weffc++ @r{(C++ only)}
1766 Warn about violations of the following style guidelines from Scott Meyers'
1767 @cite{Effective C++} book:
1771 Item 11: Define a copy constructor and an assignment operator for classes
1772 with dynamically allocated memory.
1775 Item 12: Prefer initialization to assignment in constructors.
1778 Item 14: Make destructors virtual in base classes.
1781 Item 15: Have @code{operator=} return a reference to @code{*this}.
1784 Item 23: Don't try to return a reference when you must return an object.
1788 Also warn about violations of the following style guidelines from
1789 Scott Meyers' @cite{More Effective C++} book:
1793 Item 6: Distinguish between prefix and postfix forms of increment and
1794 decrement operators.
1797 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1801 When selecting this option, be aware that the standard library
1802 headers do not obey all of these guidelines; use @samp{grep -v}
1803 to filter out those warnings.
1805 @item -Wno-deprecated @r{(C++ only)}
1806 @opindex Wno-deprecated
1807 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1809 @item -Wstrict-null-sentinel @r{(C++ only)}
1810 @opindex Wstrict-null-sentinel
1811 Warn also about the use of an uncasted @code{NULL} as sentinel. When
1812 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
1813 to @code{__null}. Although it is a null pointer constant not a null pointer,
1814 it is guaranteed to of the same size as a pointer. But this use is
1815 not portable across different compilers.
1817 @item -Wno-non-template-friend @r{(C++ only)}
1818 @opindex Wno-non-template-friend
1819 Disable warnings when non-templatized friend functions are declared
1820 within a template. Since the advent of explicit template specification
1821 support in G++, if the name of the friend is an unqualified-id (i.e.,
1822 @samp{friend foo(int)}), the C++ language specification demands that the
1823 friend declare or define an ordinary, nontemplate function. (Section
1824 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1825 could be interpreted as a particular specialization of a templatized
1826 function. Because this non-conforming behavior is no longer the default
1827 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1828 check existing code for potential trouble spots and is on by default.
1829 This new compiler behavior can be turned off with
1830 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1831 but disables the helpful warning.
1833 @item -Wold-style-cast @r{(C++ only)}
1834 @opindex Wold-style-cast
1835 Warn if an old-style (C-style) cast to a non-void type is used within
1836 a C++ program. The new-style casts (@samp{dynamic_cast},
1837 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
1838 less vulnerable to unintended effects and much easier to search for.
1840 @item -Woverloaded-virtual @r{(C++ only)}
1841 @opindex Woverloaded-virtual
1842 @cindex overloaded virtual fn, warning
1843 @cindex warning for overloaded virtual fn
1844 Warn when a function declaration hides virtual functions from a
1845 base class. For example, in:
1852 struct B: public A @{
1857 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1865 will fail to compile.
1867 @item -Wno-pmf-conversions @r{(C++ only)}
1868 @opindex Wno-pmf-conversions
1869 Disable the diagnostic for converting a bound pointer to member function
1872 @item -Wsign-promo @r{(C++ only)}
1873 @opindex Wsign-promo
1874 Warn when overload resolution chooses a promotion from unsigned or
1875 enumerated type to a signed type, over a conversion to an unsigned type of
1876 the same size. Previous versions of G++ would try to preserve
1877 unsignedness, but the standard mandates the current behavior.
1882 A& operator = (int);
1892 In this example, G++ will synthesize a default @samp{A& operator =
1893 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1896 @node Objective-C and Objective-C++ Dialect Options
1897 @section Options Controlling Objective-C and Objective-C++ Dialects
1899 @cindex compiler options, Objective-C and Objective-C++
1900 @cindex Objective-C and Objective-C++ options, command line
1901 @cindex options, Objective-C and Objective-C++
1902 (NOTE: This manual does not describe the Objective-C and Objective-C++
1903 languages themselves. See @xref{Standards,,Language Standards
1904 Supported by GCC}, for references.)
1906 This section describes the command-line options that are only meaningful
1907 for Objective-C and Objective-C++ programs, but you can also use most of
1908 the language-independent GNU compiler options.
1909 For example, you might compile a file @code{some_class.m} like this:
1912 gcc -g -fgnu-runtime -O -c some_class.m
1916 In this example, @option{-fgnu-runtime} is an option meant only for
1917 Objective-C and Objective-C++ programs; you can use the other options with
1918 any language supported by GCC@.
1920 Note that since Objective-C is an extension of the C language, Objective-C
1921 compilations may also use options specific to the C front-end (e.g.,
1922 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1923 C++-specific options (e.g., @option{-Wabi}).
1925 Here is a list of options that are @emph{only} for compiling Objective-C
1926 and Objective-C++ programs:
1929 @item -fconstant-string-class=@var{class-name}
1930 @opindex fconstant-string-class
1931 Use @var{class-name} as the name of the class to instantiate for each
1932 literal string specified with the syntax @code{@@"@dots{}"}. The default
1933 class name is @code{NXConstantString} if the GNU runtime is being used, and
1934 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1935 @option{-fconstant-cfstrings} option, if also present, will override the
1936 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1937 to be laid out as constant CoreFoundation strings.
1940 @opindex fgnu-runtime
1941 Generate object code compatible with the standard GNU Objective-C
1942 runtime. This is the default for most types of systems.
1944 @item -fnext-runtime
1945 @opindex fnext-runtime
1946 Generate output compatible with the NeXT runtime. This is the default
1947 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1948 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1951 @item -fno-nil-receivers
1952 @opindex fno-nil-receivers
1953 Assume that all Objective-C message dispatches (e.g.,
1954 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1955 is not @code{nil}. This allows for more efficient entry points in the runtime
1956 to be used. Currently, this option is only available in conjunction with
1957 the NeXT runtime on Mac OS X 10.3 and later.
1959 @item -fobjc-call-cxx-cdtors
1960 @opindex fobjc-call-cxx-cdtors
1961 For each Objective-C class, check if any of its instance variables is a
1962 C++ object with a non-trivial default constructor. If so, synthesize a
1963 special @code{- (id) .cxx_construct} instance method that will run
1964 non-trivial default constructors on any such instance variables, in order,
1965 and then return @code{self}. Similarly, check if any instance variable
1966 is a C++ object with a non-trivial destructor, and if so, synthesize a
1967 special @code{- (void) .cxx_destruct} method that will run
1968 all such default destructors, in reverse order.
1970 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
1971 thusly generated will only operate on instance variables declared in the
1972 current Objective-C class, and not those inherited from superclasses. It
1973 is the responsibility of the Objective-C runtime to invoke all such methods
1974 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
1975 will be invoked by the runtime immediately after a new object
1976 instance is allocated; the @code{- (void) .cxx_destruct} methods will
1977 be invoked immediately before the runtime deallocates an object instance.
1979 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
1980 support for invoking the @code{- (id) .cxx_construct} and
1981 @code{- (void) .cxx_destruct} methods.
1983 @item -fobjc-direct-dispatch
1984 @opindex fobjc-direct-dispatch
1985 Allow fast jumps to the message dispatcher. On Darwin this is
1986 accomplished via the comm page.
1988 @item -fobjc-exceptions
1989 @opindex fobjc-exceptions
1990 Enable syntactic support for structured exception handling in Objective-C,
1991 similar to what is offered by C++ and Java. This option is
1992 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2001 @@catch (AnObjCClass *exc) @{
2008 @@catch (AnotherClass *exc) @{
2011 @@catch (id allOthers) @{
2021 The @code{@@throw} statement may appear anywhere in an Objective-C or
2022 Objective-C++ program; when used inside of a @code{@@catch} block, the
2023 @code{@@throw} may appear without an argument (as shown above), in which case
2024 the object caught by the @code{@@catch} will be rethrown.
2026 Note that only (pointers to) Objective-C objects may be thrown and
2027 caught using this scheme. When an object is thrown, it will be caught
2028 by the nearest @code{@@catch} clause capable of handling objects of that type,
2029 analogously to how @code{catch} blocks work in C++ and Java. A
2030 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2031 any and all Objective-C exceptions not caught by previous @code{@@catch}
2034 The @code{@@finally} clause, if present, will be executed upon exit from the
2035 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2036 regardless of whether any exceptions are thrown, caught or rethrown
2037 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2038 of the @code{finally} clause in Java.
2040 There are several caveats to using the new exception mechanism:
2044 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2045 idioms provided by the @code{NSException} class, the new
2046 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2047 systems, due to additional functionality needed in the (NeXT) Objective-C
2051 As mentioned above, the new exceptions do not support handling
2052 types other than Objective-C objects. Furthermore, when used from
2053 Objective-C++, the Objective-C exception model does not interoperate with C++
2054 exceptions at this time. This means you cannot @code{@@throw} an exception
2055 from Objective-C and @code{catch} it in C++, or vice versa
2056 (i.e., @code{throw @dots{} @@catch}).
2059 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2060 blocks for thread-safe execution:
2063 @@synchronized (ObjCClass *guard) @{
2068 Upon entering the @code{@@synchronized} block, a thread of execution shall
2069 first check whether a lock has been placed on the corresponding @code{guard}
2070 object by another thread. If it has, the current thread shall wait until
2071 the other thread relinquishes its lock. Once @code{guard} becomes available,
2072 the current thread will place its own lock on it, execute the code contained in
2073 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2074 making @code{guard} available to other threads).
2076 Unlike Java, Objective-C does not allow for entire methods to be marked
2077 @code{@@synchronized}. Note that throwing exceptions out of
2078 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2079 to be unlocked properly.
2083 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2085 @item -freplace-objc-classes
2086 @opindex freplace-objc-classes
2087 Emit a special marker instructing @command{ld(1)} not to statically link in
2088 the resulting object file, and allow @command{dyld(1)} to load it in at
2089 run time instead. This is used in conjunction with the Fix-and-Continue
2090 debugging mode, where the object file in question may be recompiled and
2091 dynamically reloaded in the course of program execution, without the need
2092 to restart the program itself. Currently, Fix-and-Continue functionality
2093 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2098 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2099 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2100 compile time) with static class references that get initialized at load time,
2101 which improves run-time performance. Specifying the @option{-fzero-link} flag
2102 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2103 to be retained. This is useful in Zero-Link debugging mode, since it allows
2104 for individual class implementations to be modified during program execution.
2108 Dump interface declarations for all classes seen in the source file to a
2109 file named @file{@var{sourcename}.decl}.
2111 @item -Wassign-intercept
2112 @opindex Wassign-intercept
2113 Warn whenever an Objective-C assignment is being intercepted by the
2117 @opindex Wno-protocol
2118 If a class is declared to implement a protocol, a warning is issued for
2119 every method in the protocol that is not implemented by the class. The
2120 default behavior is to issue a warning for every method not explicitly
2121 implemented in the class, even if a method implementation is inherited
2122 from the superclass. If you use the @option{-Wno-protocol} option, then
2123 methods inherited from the superclass are considered to be implemented,
2124 and no warning is issued for them.
2128 Warn if multiple methods of different types for the same selector are
2129 found during compilation. The check is performed on the list of methods
2130 in the final stage of compilation. Additionally, a check is performed
2131 for each selector appearing in a @code{@@selector(@dots{})}
2132 expression, and a corresponding method for that selector has been found
2133 during compilation. Because these checks scan the method table only at
2134 the end of compilation, these warnings are not produced if the final
2135 stage of compilation is not reached, for example because an error is
2136 found during compilation, or because the @option{-fsyntax-only} option is
2139 @item -Wstrict-selector-match
2140 @opindex Wstrict-selector-match
2141 Warn if multiple methods with differing argument and/or return types are
2142 found for a given selector when attempting to send a message using this
2143 selector to a receiver of type @code{id} or @code{Class}. When this flag
2144 is off (which is the default behavior), the compiler will omit such warnings
2145 if any differences found are confined to types which share the same size
2148 @item -Wundeclared-selector
2149 @opindex Wundeclared-selector
2150 Warn if a @code{@@selector(@dots{})} expression referring to an
2151 undeclared selector is found. A selector is considered undeclared if no
2152 method with that name has been declared before the
2153 @code{@@selector(@dots{})} expression, either explicitly in an
2154 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2155 an @code{@@implementation} section. This option always performs its
2156 checks as soon as a @code{@@selector(@dots{})} expression is found,
2157 while @option{-Wselector} only performs its checks in the final stage of
2158 compilation. This also enforces the coding style convention
2159 that methods and selectors must be declared before being used.
2161 @item -print-objc-runtime-info
2162 @opindex print-objc-runtime-info
2163 Generate C header describing the largest structure that is passed by
2168 @node Language Independent Options
2169 @section Options to Control Diagnostic Messages Formatting
2170 @cindex options to control diagnostics formatting
2171 @cindex diagnostic messages
2172 @cindex message formatting
2174 Traditionally, diagnostic messages have been formatted irrespective of
2175 the output device's aspect (e.g.@: its width, @dots{}). The options described
2176 below can be used to control the diagnostic messages formatting
2177 algorithm, e.g.@: how many characters per line, how often source location
2178 information should be reported. Right now, only the C++ front end can
2179 honor these options. However it is expected, in the near future, that
2180 the remaining front ends would be able to digest them correctly.
2183 @item -fmessage-length=@var{n}
2184 @opindex fmessage-length
2185 Try to format error messages so that they fit on lines of about @var{n}
2186 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2187 the front ends supported by GCC@. If @var{n} is zero, then no
2188 line-wrapping will be done; each error message will appear on a single
2191 @opindex fdiagnostics-show-location
2192 @item -fdiagnostics-show-location=once
2193 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2194 reporter to emit @emph{once} source location information; that is, in
2195 case the message is too long to fit on a single physical line and has to
2196 be wrapped, the source location won't be emitted (as prefix) again,
2197 over and over, in subsequent continuation lines. This is the default
2200 @item -fdiagnostics-show-location=every-line
2201 Only meaningful in line-wrapping mode. Instructs the diagnostic
2202 messages reporter to emit the same source location information (as
2203 prefix) for physical lines that result from the process of breaking
2204 a message which is too long to fit on a single line.
2206 @item -fdiagnostics-show-options
2207 @opindex fdiagnostics-show-options
2208 This option instructs the diagnostic machinery to add text to each
2209 diagnostic emitted, which indicates which command line option directly
2210 controls that diagnostic, when such an option is known to the
2211 diagnostic machinery.
2215 @node Warning Options
2216 @section Options to Request or Suppress Warnings
2217 @cindex options to control warnings
2218 @cindex warning messages
2219 @cindex messages, warning
2220 @cindex suppressing warnings
2222 Warnings are diagnostic messages that report constructions which
2223 are not inherently erroneous but which are risky or suggest there
2224 may have been an error.
2226 You can request many specific warnings with options beginning @samp{-W},
2227 for example @option{-Wimplicit} to request warnings on implicit
2228 declarations. Each of these specific warning options also has a
2229 negative form beginning @samp{-Wno-} to turn off warnings;
2230 for example, @option{-Wno-implicit}. This manual lists only one of the
2231 two forms, whichever is not the default.
2233 The following options control the amount and kinds of warnings produced
2234 by GCC; for further, language-specific options also refer to
2235 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2239 @cindex syntax checking
2241 @opindex fsyntax-only
2242 Check the code for syntax errors, but don't do anything beyond that.
2246 Issue all the warnings demanded by strict ISO C and ISO C++;
2247 reject all programs that use forbidden extensions, and some other
2248 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2249 version of the ISO C standard specified by any @option{-std} option used.
2251 Valid ISO C and ISO C++ programs should compile properly with or without
2252 this option (though a rare few will require @option{-ansi} or a
2253 @option{-std} option specifying the required version of ISO C)@. However,
2254 without this option, certain GNU extensions and traditional C and C++
2255 features are supported as well. With this option, they are rejected.
2257 @option{-pedantic} does not cause warning messages for use of the
2258 alternate keywords whose names begin and end with @samp{__}. Pedantic
2259 warnings are also disabled in the expression that follows
2260 @code{__extension__}. However, only system header files should use
2261 these escape routes; application programs should avoid them.
2262 @xref{Alternate Keywords}.
2264 Some users try to use @option{-pedantic} to check programs for strict ISO
2265 C conformance. They soon find that it does not do quite what they want:
2266 it finds some non-ISO practices, but not all---only those for which
2267 ISO C @emph{requires} a diagnostic, and some others for which
2268 diagnostics have been added.
2270 A feature to report any failure to conform to ISO C might be useful in
2271 some instances, but would require considerable additional work and would
2272 be quite different from @option{-pedantic}. We don't have plans to
2273 support such a feature in the near future.
2275 Where the standard specified with @option{-std} represents a GNU
2276 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2277 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2278 extended dialect is based. Warnings from @option{-pedantic} are given
2279 where they are required by the base standard. (It would not make sense
2280 for such warnings to be given only for features not in the specified GNU
2281 C dialect, since by definition the GNU dialects of C include all
2282 features the compiler supports with the given option, and there would be
2283 nothing to warn about.)
2285 @item -pedantic-errors
2286 @opindex pedantic-errors
2287 Like @option{-pedantic}, except that errors are produced rather than
2292 Inhibit all warning messages.
2296 Inhibit warning messages about the use of @samp{#import}.
2298 @item -Wchar-subscripts
2299 @opindex Wchar-subscripts
2300 Warn if an array subscript has type @code{char}. This is a common cause
2301 of error, as programmers often forget that this type is signed on some
2303 This warning is enabled by @option{-Wall}.
2307 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2308 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2309 This warning is enabled by @option{-Wall}.
2311 @item -Wfatal-errors
2312 @opindex Wfatal-errors
2313 This option causes the compiler to abort compilation on the first error
2314 occurred rather than trying to keep going and printing further error
2319 @opindex ffreestanding
2320 @opindex fno-builtin
2321 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2322 the arguments supplied have types appropriate to the format string
2323 specified, and that the conversions specified in the format string make
2324 sense. This includes standard functions, and others specified by format
2325 attributes (@pxref{Function Attributes}), in the @code{printf},
2326 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2327 not in the C standard) families (or other target-specific families).
2328 Which functions are checked without format attributes having been
2329 specified depends on the standard version selected, and such checks of
2330 functions without the attribute specified are disabled by
2331 @option{-ffreestanding} or @option{-fno-builtin}.
2333 The formats are checked against the format features supported by GNU
2334 libc version 2.2. These include all ISO C90 and C99 features, as well
2335 as features from the Single Unix Specification and some BSD and GNU
2336 extensions. Other library implementations may not support all these
2337 features; GCC does not support warning about features that go beyond a
2338 particular library's limitations. However, if @option{-pedantic} is used
2339 with @option{-Wformat}, warnings will be given about format features not
2340 in the selected standard version (but not for @code{strfmon} formats,
2341 since those are not in any version of the C standard). @xref{C Dialect
2342 Options,,Options Controlling C Dialect}.
2344 Since @option{-Wformat} also checks for null format arguments for
2345 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2347 @option{-Wformat} is included in @option{-Wall}. For more control over some
2348 aspects of format checking, the options @option{-Wformat-y2k},
2349 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2350 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2351 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2354 @opindex Wformat-y2k
2355 If @option{-Wformat} is specified, also warn about @code{strftime}
2356 formats which may yield only a two-digit year.
2358 @item -Wno-format-extra-args
2359 @opindex Wno-format-extra-args
2360 If @option{-Wformat} is specified, do not warn about excess arguments to a
2361 @code{printf} or @code{scanf} format function. The C standard specifies
2362 that such arguments are ignored.
2364 Where the unused arguments lie between used arguments that are
2365 specified with @samp{$} operand number specifications, normally
2366 warnings are still given, since the implementation could not know what
2367 type to pass to @code{va_arg} to skip the unused arguments. However,
2368 in the case of @code{scanf} formats, this option will suppress the
2369 warning if the unused arguments are all pointers, since the Single
2370 Unix Specification says that such unused arguments are allowed.
2372 @item -Wno-format-zero-length
2373 @opindex Wno-format-zero-length
2374 If @option{-Wformat} is specified, do not warn about zero-length formats.
2375 The C standard specifies that zero-length formats are allowed.
2377 @item -Wformat-nonliteral
2378 @opindex Wformat-nonliteral
2379 If @option{-Wformat} is specified, also warn if the format string is not a
2380 string literal and so cannot be checked, unless the format function
2381 takes its format arguments as a @code{va_list}.
2383 @item -Wformat-security
2384 @opindex Wformat-security
2385 If @option{-Wformat} is specified, also warn about uses of format
2386 functions that represent possible security problems. At present, this
2387 warns about calls to @code{printf} and @code{scanf} functions where the
2388 format string is not a string literal and there are no format arguments,
2389 as in @code{printf (foo);}. This may be a security hole if the format
2390 string came from untrusted input and contains @samp{%n}. (This is
2391 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2392 in future warnings may be added to @option{-Wformat-security} that are not
2393 included in @option{-Wformat-nonliteral}.)
2397 Enable @option{-Wformat} plus format checks not included in
2398 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2399 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2403 Warn about passing a null pointer for arguments marked as
2404 requiring a non-null value by the @code{nonnull} function attribute.
2406 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2407 can be disabled with the @option{-Wno-nonnull} option.
2409 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2411 Warn about uninitialized variables which are initialized with themselves.
2412 Note this option can only be used with the @option{-Wuninitialized} option,
2413 which in turn only works with @option{-O1} and above.
2415 For example, GCC will warn about @code{i} being uninitialized in the
2416 following snippet only when @option{-Winit-self} has been specified:
2427 @item -Wimplicit-int
2428 @opindex Wimplicit-int
2429 Warn when a declaration does not specify a type.
2430 This warning is enabled by @option{-Wall}.
2432 @item -Wimplicit-function-declaration
2433 @itemx -Werror-implicit-function-declaration
2434 @opindex Wimplicit-function-declaration
2435 @opindex Werror-implicit-function-declaration
2436 Give a warning (or error) whenever a function is used before being
2437 declared. The form @option{-Wno-error-implicit-function-declaration}
2439 This warning is enabled by @option{-Wall} (as a warning, not an error).
2443 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2444 This warning is enabled by @option{-Wall}.
2448 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2449 function with external linkage, returning int, taking either zero
2450 arguments, two, or three arguments of appropriate types.
2451 This warning is enabled by @option{-Wall}.
2453 @item -Wmissing-braces
2454 @opindex Wmissing-braces
2455 Warn if an aggregate or union initializer is not fully bracketed. In
2456 the following example, the initializer for @samp{a} is not fully
2457 bracketed, but that for @samp{b} is fully bracketed.
2460 int a[2][2] = @{ 0, 1, 2, 3 @};
2461 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2464 This warning is enabled by @option{-Wall}.
2466 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2467 @opindex Wmissing-include-dirs
2468 Warn if a user-supplied include directory does not exist.
2471 @opindex Wparentheses
2472 Warn if parentheses are omitted in certain contexts, such
2473 as when there is an assignment in a context where a truth value
2474 is expected, or when operators are nested whose precedence people
2475 often get confused about. Only the warning for an assignment used as
2476 a truth value is supported when compiling C++; the other warnings are
2477 only supported when compiling C@.
2479 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2480 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2481 interpretation from that of ordinary mathematical notation.
2483 Also warn about constructions where there may be confusion to which
2484 @code{if} statement an @code{else} branch belongs. Here is an example of
2499 In C, every @code{else} branch belongs to the innermost possible @code{if}
2500 statement, which in this example is @code{if (b)}. This is often not
2501 what the programmer expected, as illustrated in the above example by
2502 indentation the programmer chose. When there is the potential for this
2503 confusion, GCC will issue a warning when this flag is specified.
2504 To eliminate the warning, add explicit braces around the innermost
2505 @code{if} statement so there is no way the @code{else} could belong to
2506 the enclosing @code{if}. The resulting code would look like this:
2522 This warning is enabled by @option{-Wall}.
2524 @item -Wsequence-point
2525 @opindex Wsequence-point
2526 Warn about code that may have undefined semantics because of violations
2527 of sequence point rules in the C and C++ standards.
2529 The C and C++ standards defines the order in which expressions in a C/C++
2530 program are evaluated in terms of @dfn{sequence points}, which represent
2531 a partial ordering between the execution of parts of the program: those
2532 executed before the sequence point, and those executed after it. These
2533 occur after the evaluation of a full expression (one which is not part
2534 of a larger expression), after the evaluation of the first operand of a
2535 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2536 function is called (but after the evaluation of its arguments and the
2537 expression denoting the called function), and in certain other places.
2538 Other than as expressed by the sequence point rules, the order of
2539 evaluation of subexpressions of an expression is not specified. All
2540 these rules describe only a partial order rather than a total order,
2541 since, for example, if two functions are called within one expression
2542 with no sequence point between them, the order in which the functions
2543 are called is not specified. However, the standards committee have
2544 ruled that function calls do not overlap.
2546 It is not specified when between sequence points modifications to the
2547 values of objects take effect. Programs whose behavior depends on this
2548 have undefined behavior; the C and C++ standards specify that ``Between
2549 the previous and next sequence point an object shall have its stored
2550 value modified at most once by the evaluation of an expression.
2551 Furthermore, the prior value shall be read only to determine the value
2552 to be stored.''. If a program breaks these rules, the results on any
2553 particular implementation are entirely unpredictable.
2555 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2556 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2557 diagnosed by this option, and it may give an occasional false positive
2558 result, but in general it has been found fairly effective at detecting
2559 this sort of problem in programs.
2561 The standard is worded confusingly, therefore there is some debate
2562 over the precise meaning of the sequence point rules in subtle cases.
2563 Links to discussions of the problem, including proposed formal
2564 definitions, may be found on the GCC readings page, at
2565 @w{@uref{http://gcc.gnu.org/readings.html}}.
2567 This warning is enabled by @option{-Wall} for C and C++.
2570 @opindex Wreturn-type
2571 Warn whenever a function is defined with a return-type that defaults to
2572 @code{int}. Also warn about any @code{return} statement with no
2573 return-value in a function whose return-type is not @code{void}.
2575 For C, also warn if the return type of a function has a type qualifier
2576 such as @code{const}. Such a type qualifier has no effect, since the
2577 value returned by a function is not an lvalue. ISO C prohibits
2578 qualified @code{void} return types on function definitions, so such
2579 return types always receive a warning even without this option.
2581 For C++, a function without return type always produces a diagnostic
2582 message, even when @option{-Wno-return-type} is specified. The only
2583 exceptions are @samp{main} and functions defined in system headers.
2585 This warning is enabled by @option{-Wall}.
2589 Warn whenever a @code{switch} statement has an index of enumerated type
2590 and lacks a @code{case} for one or more of the named codes of that
2591 enumeration. (The presence of a @code{default} label prevents this
2592 warning.) @code{case} labels outside the enumeration range also
2593 provoke warnings when this option is used.
2594 This warning is enabled by @option{-Wall}.
2596 @item -Wswitch-default
2597 @opindex Wswitch-switch
2598 Warn whenever a @code{switch} statement does not have a @code{default}
2602 @opindex Wswitch-enum
2603 Warn whenever a @code{switch} statement has an index of enumerated type
2604 and lacks a @code{case} for one or more of the named codes of that
2605 enumeration. @code{case} labels outside the enumeration range also
2606 provoke warnings when this option is used.
2610 Warn if any trigraphs are encountered that might change the meaning of
2611 the program (trigraphs within comments are not warned about).
2612 This warning is enabled by @option{-Wall}.
2614 @item -Wunused-function
2615 @opindex Wunused-function
2616 Warn whenever a static function is declared but not defined or a
2617 non-inline static function is unused.
2618 This warning is enabled by @option{-Wall}.
2620 @item -Wunused-label
2621 @opindex Wunused-label
2622 Warn whenever a label is declared but not used.
2623 This warning is enabled by @option{-Wall}.
2625 To suppress this warning use the @samp{unused} attribute
2626 (@pxref{Variable Attributes}).
2628 @item -Wunused-parameter
2629 @opindex Wunused-parameter
2630 Warn whenever a function parameter is unused aside from its declaration.
2632 To suppress this warning use the @samp{unused} attribute
2633 (@pxref{Variable Attributes}).
2635 @item -Wunused-variable
2636 @opindex Wunused-variable
2637 Warn whenever a local variable or non-constant static variable is unused
2638 aside from its declaration
2639 This warning is enabled by @option{-Wall}.
2641 To suppress this warning use the @samp{unused} attribute
2642 (@pxref{Variable Attributes}).
2644 @item -Wunused-value
2645 @opindex Wunused-value
2646 Warn whenever a statement computes a result that is explicitly not used.
2647 This warning is enabled by @option{-Wall}.
2649 To suppress this warning cast the expression to @samp{void}.
2653 All the above @option{-Wunused} options combined.
2655 In order to get a warning about an unused function parameter, you must
2656 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2657 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2659 @item -Wuninitialized
2660 @opindex Wuninitialized
2661 Warn if an automatic variable is used without first being initialized or
2662 if a variable may be clobbered by a @code{setjmp} call.
2664 These warnings are possible only in optimizing compilation,
2665 because they require data flow information that is computed only
2666 when optimizing. If you don't specify @option{-O}, you simply won't
2669 If you want to warn about code which uses the uninitialized value of the
2670 variable in its own initializer, use the @option{-Winit-self} option.
2672 These warnings occur for individual uninitialized or clobbered
2673 elements of structure, union or array variables as well as for
2674 variables which are uninitialized or clobbered as a whole. They do
2675 not occur for variables or elements declared @code{volatile}. Because
2676 these warnings depend on optimization, the exact variables or elements
2677 for which there are warnings will depend on the precise optimization
2678 options and version of GCC used.
2680 Note that there may be no warning about a variable that is used only
2681 to compute a value that itself is never used, because such
2682 computations may be deleted by data flow analysis before the warnings
2685 These warnings are made optional because GCC is not smart
2686 enough to see all the reasons why the code might be correct
2687 despite appearing to have an error. Here is one example of how
2708 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2709 always initialized, but GCC doesn't know this. Here is
2710 another common case:
2715 if (change_y) save_y = y, y = new_y;
2717 if (change_y) y = save_y;
2722 This has no bug because @code{save_y} is used only if it is set.
2724 @cindex @code{longjmp} warnings
2725 This option also warns when a non-volatile automatic variable might be
2726 changed by a call to @code{longjmp}. These warnings as well are possible
2727 only in optimizing compilation.
2729 The compiler sees only the calls to @code{setjmp}. It cannot know
2730 where @code{longjmp} will be called; in fact, a signal handler could
2731 call it at any point in the code. As a result, you may get a warning
2732 even when there is in fact no problem because @code{longjmp} cannot
2733 in fact be called at the place which would cause a problem.
2735 Some spurious warnings can be avoided if you declare all the functions
2736 you use that never return as @code{noreturn}. @xref{Function
2739 This warning is enabled by @option{-Wall}.
2741 @item -Wunknown-pragmas
2742 @opindex Wunknown-pragmas
2743 @cindex warning for unknown pragmas
2744 @cindex unknown pragmas, warning
2745 @cindex pragmas, warning of unknown
2746 Warn when a #pragma directive is encountered which is not understood by
2747 GCC@. If this command line option is used, warnings will even be issued
2748 for unknown pragmas in system header files. This is not the case if
2749 the warnings were only enabled by the @option{-Wall} command line option.
2752 @opindex Wno-pragmas
2754 Do not warn about misuses of pragmas, such as incorrect parameters,
2755 invalid syntax, or conflicts between pragmas. See also
2756 @samp{-Wunknown-pragmas}.
2758 @item -Wstrict-aliasing
2759 @opindex Wstrict-aliasing
2760 This option is only active when @option{-fstrict-aliasing} is active.
2761 It warns about code which might break the strict aliasing rules that the
2762 compiler is using for optimization. The warning does not catch all
2763 cases, but does attempt to catch the more common pitfalls. It is
2764 included in @option{-Wall}.
2766 @item -Wstrict-aliasing=2
2767 @opindex Wstrict-aliasing=2
2768 This option is only active when @option{-fstrict-aliasing} is active.
2769 It warns about code which might break the strict aliasing rules that the
2770 compiler is using for optimization. This warning catches more cases than
2771 @option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
2772 cases that are safe.
2776 All of the above @samp{-W} options combined. This enables all the
2777 warnings about constructions that some users consider questionable, and
2778 that are easy to avoid (or modify to prevent the warning), even in
2779 conjunction with macros. This also enables some language-specific
2780 warnings described in @ref{C++ Dialect Options} and
2781 @ref{Objective-C and Objective-C++ Dialect Options}.
2784 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2785 Some of them warn about constructions that users generally do not
2786 consider questionable, but which occasionally you might wish to check
2787 for; others warn about constructions that are necessary or hard to avoid
2788 in some cases, and there is no simple way to modify the code to suppress
2795 (This option used to be called @option{-W}. The older name is still
2796 supported, but the newer name is more descriptive.) Print extra warning
2797 messages for these events:
2801 A function can return either with or without a value. (Falling
2802 off the end of the function body is considered returning without
2803 a value.) For example, this function would evoke such a
2817 An expression-statement or the left-hand side of a comma expression
2818 contains no side effects.
2819 To suppress the warning, cast the unused expression to void.
2820 For example, an expression such as @samp{x[i,j]} will cause a warning,
2821 but @samp{x[(void)i,j]} will not.
2824 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2827 Storage-class specifiers like @code{static} are not the first things in
2828 a declaration. According to the C Standard, this usage is obsolescent.
2831 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2835 A comparison between signed and unsigned values could produce an
2836 incorrect result when the signed value is converted to unsigned.
2837 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2840 An aggregate has an initializer which does not initialize all members.
2841 This warning can be independently controlled by
2842 @option{-Wmissing-field-initializers}.
2845 A function parameter is declared without a type specifier in K&R-style
2853 An empty body occurs in an @samp{if} or @samp{else} statement.
2856 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2857 @samp{>}, or @samp{>=}.
2860 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2863 Any of several floating-point events that often indicate errors, such as
2864 overflow, underflow, loss of precision, etc.
2866 @item @r{(C++ only)}
2867 An enumerator and a non-enumerator both appear in a conditional expression.
2869 @item @r{(C++ only)}
2870 A non-static reference or non-static @samp{const} member appears in a
2871 class without constructors.
2873 @item @r{(C++ only)}
2874 Ambiguous virtual bases.
2876 @item @r{(C++ only)}
2877 Subscripting an array which has been declared @samp{register}.
2879 @item @r{(C++ only)}
2880 Taking the address of a variable which has been declared @samp{register}.
2882 @item @r{(C++ only)}
2883 A base class is not initialized in a derived class' copy constructor.
2886 @item -Wno-div-by-zero
2887 @opindex Wno-div-by-zero
2888 @opindex Wdiv-by-zero
2889 Do not warn about compile-time integer division by zero. Floating point
2890 division by zero is not warned about, as it can be a legitimate way of
2891 obtaining infinities and NaNs.
2893 @item -Wsystem-headers
2894 @opindex Wsystem-headers
2895 @cindex warnings from system headers
2896 @cindex system headers, warnings from
2897 Print warning messages for constructs found in system header files.
2898 Warnings from system headers are normally suppressed, on the assumption
2899 that they usually do not indicate real problems and would only make the
2900 compiler output harder to read. Using this command line option tells
2901 GCC to emit warnings from system headers as if they occurred in user
2902 code. However, note that using @option{-Wall} in conjunction with this
2903 option will @emph{not} warn about unknown pragmas in system
2904 headers---for that, @option{-Wunknown-pragmas} must also be used.
2907 @opindex Wfloat-equal
2908 Warn if floating point values are used in equality comparisons.
2910 The idea behind this is that sometimes it is convenient (for the
2911 programmer) to consider floating-point values as approximations to
2912 infinitely precise real numbers. If you are doing this, then you need
2913 to compute (by analyzing the code, or in some other way) the maximum or
2914 likely maximum error that the computation introduces, and allow for it
2915 when performing comparisons (and when producing output, but that's a
2916 different problem). In particular, instead of testing for equality, you
2917 would check to see whether the two values have ranges that overlap; and
2918 this is done with the relational operators, so equality comparisons are
2921 @item -Wtraditional @r{(C only)}
2922 @opindex Wtraditional
2923 Warn about certain constructs that behave differently in traditional and
2924 ISO C@. Also warn about ISO C constructs that have no traditional C
2925 equivalent, and/or problematic constructs which should be avoided.
2929 Macro parameters that appear within string literals in the macro body.
2930 In traditional C macro replacement takes place within string literals,
2931 but does not in ISO C@.
2934 In traditional C, some preprocessor directives did not exist.
2935 Traditional preprocessors would only consider a line to be a directive
2936 if the @samp{#} appeared in column 1 on the line. Therefore
2937 @option{-Wtraditional} warns about directives that traditional C
2938 understands but would ignore because the @samp{#} does not appear as the
2939 first character on the line. It also suggests you hide directives like
2940 @samp{#pragma} not understood by traditional C by indenting them. Some
2941 traditional implementations would not recognize @samp{#elif}, so it
2942 suggests avoiding it altogether.
2945 A function-like macro that appears without arguments.
2948 The unary plus operator.
2951 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2952 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2953 constants.) Note, these suffixes appear in macros defined in the system
2954 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2955 Use of these macros in user code might normally lead to spurious
2956 warnings, however GCC's integrated preprocessor has enough context to
2957 avoid warning in these cases.
2960 A function declared external in one block and then used after the end of
2964 A @code{switch} statement has an operand of type @code{long}.
2967 A non-@code{static} function declaration follows a @code{static} one.
2968 This construct is not accepted by some traditional C compilers.
2971 The ISO type of an integer constant has a different width or
2972 signedness from its traditional type. This warning is only issued if
2973 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2974 typically represent bit patterns, are not warned about.
2977 Usage of ISO string concatenation is detected.
2980 Initialization of automatic aggregates.
2983 Identifier conflicts with labels. Traditional C lacks a separate
2984 namespace for labels.
2987 Initialization of unions. If the initializer is zero, the warning is
2988 omitted. This is done under the assumption that the zero initializer in
2989 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2990 initializer warnings and relies on default initialization to zero in the
2994 Conversions by prototypes between fixed/floating point values and vice
2995 versa. The absence of these prototypes when compiling with traditional
2996 C would cause serious problems. This is a subset of the possible
2997 conversion warnings, for the full set use @option{-Wconversion}.
3000 Use of ISO C style function definitions. This warning intentionally is
3001 @emph{not} issued for prototype declarations or variadic functions
3002 because these ISO C features will appear in your code when using
3003 libiberty's traditional C compatibility macros, @code{PARAMS} and
3004 @code{VPARAMS}. This warning is also bypassed for nested functions
3005 because that feature is already a GCC extension and thus not relevant to
3006 traditional C compatibility.
3009 @item -Wdeclaration-after-statement @r{(C only)}
3010 @opindex Wdeclaration-after-statement
3011 Warn when a declaration is found after a statement in a block. This
3012 construct, known from C++, was introduced with ISO C99 and is by default
3013 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3014 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3018 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3020 @item -Wno-endif-labels
3021 @opindex Wno-endif-labels
3022 @opindex Wendif-labels
3023 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3027 Warn whenever a local variable shadows another local variable, parameter or
3028 global variable or whenever a built-in function is shadowed.
3030 @item -Wlarger-than-@var{len}
3031 @opindex Wlarger-than
3032 Warn whenever an object of larger than @var{len} bytes is defined.
3034 @item -Wunsafe-loop-optimizations
3035 @opindex Wunsafe-loop-optimizations
3036 Warn if the loop cannot be optimized because the compiler could not
3037 assume anything on the bounds of the loop indices. With
3038 @option{-funsafe-loop-optimizations} warn if the compiler made
3041 @item -Wpointer-arith
3042 @opindex Wpointer-arith
3043 Warn about anything that depends on the ``size of'' a function type or
3044 of @code{void}. GNU C assigns these types a size of 1, for
3045 convenience in calculations with @code{void *} pointers and pointers
3048 @item -Wbad-function-cast @r{(C only)}
3049 @opindex Wbad-function-cast
3050 Warn whenever a function call is cast to a non-matching type.
3051 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3054 Warn about ISO C constructs that are outside of the common subset of
3055 ISO C and ISO C++, e.g.@: request for implicit conversion from
3056 @code{void *} to a pointer to non-@code{void} type.
3060 Warn whenever a pointer is cast so as to remove a type qualifier from
3061 the target type. For example, warn if a @code{const char *} is cast
3062 to an ordinary @code{char *}.
3065 @opindex Wcast-align
3066 Warn whenever a pointer is cast such that the required alignment of the
3067 target is increased. For example, warn if a @code{char *} is cast to
3068 an @code{int *} on machines where integers can only be accessed at
3069 two- or four-byte boundaries.
3071 @item -Wwrite-strings
3072 @opindex Wwrite-strings
3073 When compiling C, give string constants the type @code{const
3074 char[@var{length}]} so that
3075 copying the address of one into a non-@code{const} @code{char *}
3076 pointer will get a warning; when compiling C++, warn about the
3077 deprecated conversion from string literals to @code{char *}. This
3078 warning, by default, is enabled for C++ programs.
3079 These warnings will help you find at
3080 compile time code that can try to write into a string constant, but
3081 only if you have been very careful about using @code{const} in
3082 declarations and prototypes. Otherwise, it will just be a nuisance;
3083 this is why we did not make @option{-Wall} request these warnings.
3086 @opindex Wconversion
3087 Warn if a prototype causes a type conversion that is different from what
3088 would happen to the same argument in the absence of a prototype. This
3089 includes conversions of fixed point to floating and vice versa, and
3090 conversions changing the width or signedness of a fixed point argument
3091 except when the same as the default promotion.
3093 Also, warn if a negative integer constant expression is implicitly
3094 converted to an unsigned type. For example, warn about the assignment
3095 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
3096 casts like @code{(unsigned) -1}.
3098 @item -Wsign-compare
3099 @opindex Wsign-compare
3100 @cindex warning for comparison of signed and unsigned values
3101 @cindex comparison of signed and unsigned values, warning
3102 @cindex signed and unsigned values, comparison warning
3103 Warn when a comparison between signed and unsigned values could produce
3104 an incorrect result when the signed value is converted to unsigned.
3105 This warning is also enabled by @option{-Wextra}; to get the other warnings
3106 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3108 @item -Waggregate-return
3109 @opindex Waggregate-return
3110 Warn if any functions that return structures or unions are defined or
3111 called. (In languages where you can return an array, this also elicits
3115 @opindex Walways-true
3116 Warn about comparisons which are always true such as testing if
3117 unsigned values are greater than or equal to zero. This warning is
3118 enabled by @option{-Wall}.
3120 @item -Wno-attributes
3121 @opindex Wno-attributes
3122 @opindex Wattributes
3123 Do not warn if an unexpected @code{__attribute__} is used, such as
3124 unrecognized attributes, function attributes applied to variables,
3125 etc. This will not stop errors for incorrect use of supported
3128 @item -Wstrict-prototypes @r{(C only)}
3129 @opindex Wstrict-prototypes
3130 Warn if a function is declared or defined without specifying the
3131 argument types. (An old-style function definition is permitted without
3132 a warning if preceded by a declaration which specifies the argument
3135 @item -Wold-style-definition @r{(C only)}
3136 @opindex Wold-style-definition
3137 Warn if an old-style function definition is used. A warning is given
3138 even if there is a previous prototype.
3140 @item -Wmissing-prototypes @r{(C only)}
3141 @opindex Wmissing-prototypes
3142 Warn if a global function is defined without a previous prototype
3143 declaration. This warning is issued even if the definition itself
3144 provides a prototype. The aim is to detect global functions that fail
3145 to be declared in header files.
3147 @item -Wmissing-declarations @r{(C only)}
3148 @opindex Wmissing-declarations
3149 Warn if a global function is defined without a previous declaration.
3150 Do so even if the definition itself provides a prototype.
3151 Use this option to detect global functions that are not declared in
3154 @item -Wmissing-field-initializers
3155 @opindex Wmissing-field-initializers
3158 Warn if a structure's initializer has some fields missing. For
3159 example, the following code would cause such a warning, because
3160 @code{x.h} is implicitly zero:
3163 struct s @{ int f, g, h; @};
3164 struct s x = @{ 3, 4 @};
3167 This option does not warn about designated initializers, so the following
3168 modification would not trigger a warning:
3171 struct s @{ int f, g, h; @};
3172 struct s x = @{ .f = 3, .g = 4 @};
3175 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3176 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3178 @item -Wmissing-noreturn
3179 @opindex Wmissing-noreturn
3180 Warn about functions which might be candidates for attribute @code{noreturn}.
3181 Note these are only possible candidates, not absolute ones. Care should
3182 be taken to manually verify functions actually do not ever return before
3183 adding the @code{noreturn} attribute, otherwise subtle code generation
3184 bugs could be introduced. You will not get a warning for @code{main} in
3185 hosted C environments.
3187 @item -Wmissing-format-attribute
3188 @opindex Wmissing-format-attribute
3190 Warn about function pointers which might be candidates for @code{format}
3191 attributes. Note these are only possible candidates, not absolute ones.
3192 GCC will guess that function pointers with @code{format} attributes that
3193 are used in assignment, initialization, parameter passing or return
3194 statements should have a corresponding @code{format} attribute in the
3195 resulting type. I.e.@: the left-hand side of the assignment or
3196 initialization, the type of the parameter variable, or the return type
3197 of the containing function respectively should also have a @code{format}
3198 attribute to avoid the warning.
3200 GCC will also warn about function definitions which might be
3201 candidates for @code{format} attributes. Again, these are only
3202 possible candidates. GCC will guess that @code{format} attributes
3203 might be appropriate for any function that calls a function like
3204 @code{vprintf} or @code{vscanf}, but this might not always be the
3205 case, and some functions for which @code{format} attributes are
3206 appropriate may not be detected.
3208 @item -Wno-multichar
3209 @opindex Wno-multichar
3211 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3212 Usually they indicate a typo in the user's code, as they have
3213 implementation-defined values, and should not be used in portable code.
3215 @item -Wnormalized=<none|id|nfc|nfkc>
3216 @opindex Wnormalized
3219 @cindex character set, input normalization
3220 In ISO C and ISO C++, two identifiers are different if they are
3221 different sequences of characters. However, sometimes when characters
3222 outside the basic ASCII character set are used, you can have two
3223 different character sequences that look the same. To avoid confusion,
3224 the ISO 10646 standard sets out some @dfn{normalization rules} which
3225 when applied ensure that two sequences that look the same are turned into
3226 the same sequence. GCC can warn you if you are using identifiers which
3227 have not been normalized; this option controls that warning.
3229 There are four levels of warning that GCC supports. The default is
3230 @option{-Wnormalized=nfc}, which warns about any identifier which is
3231 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3232 recommended form for most uses.
3234 Unfortunately, there are some characters which ISO C and ISO C++ allow
3235 in identifiers that when turned into NFC aren't allowable as
3236 identifiers. That is, there's no way to use these symbols in portable
3237 ISO C or C++ and have all your identifiers in NFC.
3238 @option{-Wnormalized=id} suppresses the warning for these characters.
3239 It is hoped that future versions of the standards involved will correct
3240 this, which is why this option is not the default.
3242 You can switch the warning off for all characters by writing
3243 @option{-Wnormalized=none}. You would only want to do this if you
3244 were using some other normalization scheme (like ``D''), because
3245 otherwise you can easily create bugs that are literally impossible to see.
3247 Some characters in ISO 10646 have distinct meanings but look identical
3248 in some fonts or display methodologies, especially once formatting has
3249 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3250 LETTER N'', will display just like a regular @code{n} which has been
3251 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3252 normalisation scheme to convert all these into a standard form as
3253 well, and GCC will warn if your code is not in NFKC if you use
3254 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3255 about every identifier that contains the letter O because it might be
3256 confused with the digit 0, and so is not the default, but may be
3257 useful as a local coding convention if the programming environment is
3258 unable to be fixed to display these characters distinctly.
3260 @item -Wno-deprecated-declarations
3261 @opindex Wno-deprecated-declarations
3262 Do not warn about uses of functions, variables, and types marked as
3263 deprecated by using the @code{deprecated} attribute.
3264 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3265 @pxref{Type Attributes}.)
3269 Warn if a structure is given the packed attribute, but the packed
3270 attribute has no effect on the layout or size of the structure.
3271 Such structures may be mis-aligned for little benefit. For
3272 instance, in this code, the variable @code{f.x} in @code{struct bar}
3273 will be misaligned even though @code{struct bar} does not itself
3274 have the packed attribute:
3281 @} __attribute__((packed));
3291 Warn if padding is included in a structure, either to align an element
3292 of the structure or to align the whole structure. Sometimes when this
3293 happens it is possible to rearrange the fields of the structure to
3294 reduce the padding and so make the structure smaller.
3296 @item -Wredundant-decls
3297 @opindex Wredundant-decls
3298 Warn if anything is declared more than once in the same scope, even in
3299 cases where multiple declaration is valid and changes nothing.
3301 @item -Wnested-externs @r{(C only)}
3302 @opindex Wnested-externs
3303 Warn if an @code{extern} declaration is encountered within a function.
3305 @item -Wunreachable-code
3306 @opindex Wunreachable-code
3307 Warn if the compiler detects that code will never be executed.
3309 This option is intended to warn when the compiler detects that at
3310 least a whole line of source code will never be executed, because
3311 some condition is never satisfied or because it is after a
3312 procedure that never returns.
3314 It is possible for this option to produce a warning even though there
3315 are circumstances under which part of the affected line can be executed,
3316 so care should be taken when removing apparently-unreachable code.
3318 For instance, when a function is inlined, a warning may mean that the
3319 line is unreachable in only one inlined copy of the function.
3321 This option is not made part of @option{-Wall} because in a debugging
3322 version of a program there is often substantial code which checks
3323 correct functioning of the program and is, hopefully, unreachable
3324 because the program does work. Another common use of unreachable
3325 code is to provide behavior which is selectable at compile-time.
3329 Warn if a function can not be inlined and it was declared as inline.
3330 Even with this option, the compiler will not warn about failures to
3331 inline functions declared in system headers.
3333 The compiler uses a variety of heuristics to determine whether or not
3334 to inline a function. For example, the compiler takes into account
3335 the size of the function being inlined and the amount of inlining
3336 that has already been done in the current function. Therefore,
3337 seemingly insignificant changes in the source program can cause the
3338 warnings produced by @option{-Winline} to appear or disappear.
3340 @item -Wno-invalid-offsetof @r{(C++ only)}
3341 @opindex Wno-invalid-offsetof
3342 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3343 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3344 to a non-POD type is undefined. In existing C++ implementations,
3345 however, @samp{offsetof} typically gives meaningful results even when
3346 applied to certain kinds of non-POD types. (Such as a simple
3347 @samp{struct} that fails to be a POD type only by virtue of having a
3348 constructor.) This flag is for users who are aware that they are
3349 writing nonportable code and who have deliberately chosen to ignore the
3352 The restrictions on @samp{offsetof} may be relaxed in a future version
3353 of the C++ standard.
3355 @item -Wno-int-to-pointer-cast @r{(C only)}
3356 @opindex Wno-int-to-pointer-cast
3357 Suppress warnings from casts to pointer type of an integer of a
3360 @item -Wno-pointer-to-int-cast @r{(C only)}
3361 @opindex Wno-pointer-to-int-cast
3362 Suppress warnings from casts from a pointer to an integer type of a
3366 @opindex Winvalid-pch
3367 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3368 the search path but can't be used.
3372 @opindex Wno-long-long
3373 Warn if @samp{long long} type is used. This is default. To inhibit
3374 the warning messages, use @option{-Wno-long-long}. Flags
3375 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3376 only when @option{-pedantic} flag is used.
3378 @item -Wvariadic-macros
3379 @opindex Wvariadic-macros
3380 @opindex Wno-variadic-macros
3381 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3382 alternate syntax when in pedantic ISO C99 mode. This is default.
3383 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3385 @item -Wvolatile-register-var
3386 @opindex Wvolatile-register-var
3387 @opindex Wno-volatile-register-var
3388 Warn if a register variable is declared volatile. The volatile
3389 modifier does not inhibit all optimizations that may eliminate reads
3390 and/or writes to register variables.
3392 @item -Wdisabled-optimization
3393 @opindex Wdisabled-optimization
3394 Warn if a requested optimization pass is disabled. This warning does
3395 not generally indicate that there is anything wrong with your code; it
3396 merely indicates that GCC's optimizers were unable to handle the code
3397 effectively. Often, the problem is that your code is too big or too
3398 complex; GCC will refuse to optimize programs when the optimization
3399 itself is likely to take inordinate amounts of time.
3401 @item -Wpointer-sign
3402 @opindex Wpointer-sign
3403 @opindex Wno-pointer-sign
3404 Warn for pointer argument passing or assignment with different signedness.
3405 This option is only supported for C and Objective-C@. It is implied by
3406 @option{-Wall} and by @option{-pedantic}, which can be disabled with
3407 @option{-Wno-pointer-sign}.
3411 Make all warnings into errors.
3415 Make the specified warning into an errors. The specifier for a
3416 warning is appended, for example @option{-Werror=switch} turns the
3417 warnings controlled by @option{-Wswitch} into errors. This switch
3418 takes a negative form, to be used to negate @option{-Werror} for
3419 specific warnings, for example @option{-Wno-error=switch} makes
3420 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
3421 is in effect. You can use the @option{-fdiagnostics-show-option}
3422 option to have each controllable warning amended with the option which
3423 controls it, to determine what to use with this option.
3425 Note that specifying @option{-Werror=}@var{foo} automatically implies
3426 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
3429 @item -Wstack-protector
3430 @opindex Wstack-protector
3431 This option is only active when @option{-fstack-protector} is active. It
3432 warns about functions that will not be protected against stack smashing.
3434 @item -Wstring-literal-comparison
3435 @opindex Wstring-literal-comparison
3436 Warn about suspicious comparisons to string literal constants. In C,
3437 direct comparisons against the memory address of a string literal, such
3438 as @code{if (x == "abc")}, typically indicate a programmer error, and
3439 even when intentional, result in unspecified behavior and are not portable.
3440 Usually these warnings alert that the programmer intended to use
3441 @code{strcmp}. This warning is enabled by @option{-Wall}.
3443 @item -Woverlength-strings
3444 @opindex Woverlength-strings
3445 Warn about string constants which are longer than the ``minimum
3446 maximum'' length specified in the C standard. Modern compilers
3447 generally allow string constants which are much longer than the
3448 standard's minimum limit, but very portable programs should avoid
3449 using longer strings.
3451 The limit applies @emph{after} string constant concatenation, and does
3452 not count the trailing NUL@. In C89, the limit was 509 characters; in
3453 C99, it was raised to 4095. C++98 does not specify a normative
3454 minimum maximum, so we do not diagnose overlength strings in C++@.
3456 This option is implied by @option{-pedantic}, and can be disabled with
3457 @option{-Wno-overlength-strings}.
3460 @node Debugging Options
3461 @section Options for Debugging Your Program or GCC
3462 @cindex options, debugging
3463 @cindex debugging information options
3465 GCC has various special options that are used for debugging
3466 either your program or GCC:
3471 Produce debugging information in the operating system's native format
3472 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3475 On most systems that use stabs format, @option{-g} enables use of extra
3476 debugging information that only GDB can use; this extra information
3477 makes debugging work better in GDB but will probably make other debuggers
3479 refuse to read the program. If you want to control for certain whether
3480 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3481 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3483 GCC allows you to use @option{-g} with
3484 @option{-O}. The shortcuts taken by optimized code may occasionally
3485 produce surprising results: some variables you declared may not exist
3486 at all; flow of control may briefly move where you did not expect it;
3487 some statements may not be executed because they compute constant
3488 results or their values were already at hand; some statements may
3489 execute in different places because they were moved out of loops.
3491 Nevertheless it proves possible to debug optimized output. This makes
3492 it reasonable to use the optimizer for programs that might have bugs.
3494 The following options are useful when GCC is generated with the
3495 capability for more than one debugging format.
3499 Produce debugging information for use by GDB@. This means to use the
3500 most expressive format available (DWARF 2, stabs, or the native format
3501 if neither of those are supported), including GDB extensions if at all
3506 Produce debugging information in stabs format (if that is supported),
3507 without GDB extensions. This is the format used by DBX on most BSD
3508 systems. On MIPS, Alpha and System V Release 4 systems this option
3509 produces stabs debugging output which is not understood by DBX or SDB@.
3510 On System V Release 4 systems this option requires the GNU assembler.
3512 @item -feliminate-unused-debug-symbols
3513 @opindex feliminate-unused-debug-symbols
3514 Produce debugging information in stabs format (if that is supported),
3515 for only symbols that are actually used.
3519 Produce debugging information in stabs format (if that is supported),
3520 using GNU extensions understood only by the GNU debugger (GDB)@. The
3521 use of these extensions is likely to make other debuggers crash or
3522 refuse to read the program.
3526 Produce debugging information in COFF format (if that is supported).
3527 This is the format used by SDB on most System V systems prior to
3532 Produce debugging information in XCOFF format (if that is supported).
3533 This is the format used by the DBX debugger on IBM RS/6000 systems.
3537 Produce debugging information in XCOFF format (if that is supported),
3538 using GNU extensions understood only by the GNU debugger (GDB)@. The
3539 use of these extensions is likely to make other debuggers crash or
3540 refuse to read the program, and may cause assemblers other than the GNU
3541 assembler (GAS) to fail with an error.
3545 Produce debugging information in DWARF version 2 format (if that is
3546 supported). This is the format used by DBX on IRIX 6. With this
3547 option, GCC uses features of DWARF version 3 when they are useful;
3548 version 3 is upward compatible with version 2, but may still cause
3549 problems for older debuggers.
3553 Produce debugging information in VMS debug format (if that is
3554 supported). This is the format used by DEBUG on VMS systems.
3557 @itemx -ggdb@var{level}
3558 @itemx -gstabs@var{level}
3559 @itemx -gcoff@var{level}
3560 @itemx -gxcoff@var{level}
3561 @itemx -gvms@var{level}
3562 Request debugging information and also use @var{level} to specify how
3563 much information. The default level is 2.
3565 Level 1 produces minimal information, enough for making backtraces in
3566 parts of the program that you don't plan to debug. This includes
3567 descriptions of functions and external variables, but no information
3568 about local variables and no line numbers.
3570 Level 3 includes extra information, such as all the macro definitions
3571 present in the program. Some debuggers support macro expansion when
3572 you use @option{-g3}.
3574 @option{-gdwarf-2} does not accept a concatenated debug level, because
3575 GCC used to support an option @option{-gdwarf} that meant to generate
3576 debug information in version 1 of the DWARF format (which is very
3577 different from version 2), and it would have been too confusing. That
3578 debug format is long obsolete, but the option cannot be changed now.
3579 Instead use an additional @option{-g@var{level}} option to change the
3580 debug level for DWARF2.
3582 @item -feliminate-dwarf2-dups
3583 @opindex feliminate-dwarf2-dups
3584 Compress DWARF2 debugging information by eliminating duplicated
3585 information about each symbol. This option only makes sense when
3586 generating DWARF2 debugging information with @option{-gdwarf-2}.
3588 @cindex @command{prof}
3591 Generate extra code to write profile information suitable for the
3592 analysis program @command{prof}. You must use this option when compiling
3593 the source files you want data about, and you must also use it when
3596 @cindex @command{gprof}
3599 Generate extra code to write profile information suitable for the
3600 analysis program @command{gprof}. You must use this option when compiling
3601 the source files you want data about, and you must also use it when
3606 Makes the compiler print out each function name as it is compiled, and
3607 print some statistics about each pass when it finishes.
3610 @opindex ftime-report
3611 Makes the compiler print some statistics about the time consumed by each
3612 pass when it finishes.
3615 @opindex fmem-report
3616 Makes the compiler print some statistics about permanent memory
3617 allocation when it finishes.
3619 @item -fprofile-arcs
3620 @opindex fprofile-arcs
3621 Add code so that program flow @dfn{arcs} are instrumented. During
3622 execution the program records how many times each branch and call is
3623 executed and how many times it is taken or returns. When the compiled
3624 program exits it saves this data to a file called
3625 @file{@var{auxname}.gcda} for each source file. The data may be used for
3626 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3627 test coverage analysis (@option{-ftest-coverage}). Each object file's
3628 @var{auxname} is generated from the name of the output file, if
3629 explicitly specified and it is not the final executable, otherwise it is
3630 the basename of the source file. In both cases any suffix is removed
3631 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3632 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3633 @xref{Cross-profiling}.
3635 @cindex @command{gcov}
3639 This option is used to compile and link code instrumented for coverage
3640 analysis. The option is a synonym for @option{-fprofile-arcs}
3641 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
3642 linking). See the documentation for those options for more details.
3647 Compile the source files with @option{-fprofile-arcs} plus optimization
3648 and code generation options. For test coverage analysis, use the
3649 additional @option{-ftest-coverage} option. You do not need to profile
3650 every source file in a program.
3653 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3654 (the latter implies the former).
3657 Run the program on a representative workload to generate the arc profile
3658 information. This may be repeated any number of times. You can run
3659 concurrent instances of your program, and provided that the file system
3660 supports locking, the data files will be correctly updated. Also
3661 @code{fork} calls are detected and correctly handled (double counting
3665 For profile-directed optimizations, compile the source files again with
3666 the same optimization and code generation options plus
3667 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3668 Control Optimization}).
3671 For test coverage analysis, use @command{gcov} to produce human readable
3672 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3673 @command{gcov} documentation for further information.
3677 With @option{-fprofile-arcs}, for each function of your program GCC
3678 creates a program flow graph, then finds a spanning tree for the graph.
3679 Only arcs that are not on the spanning tree have to be instrumented: the
3680 compiler adds code to count the number of times that these arcs are
3681 executed. When an arc is the only exit or only entrance to a block, the
3682 instrumentation code can be added to the block; otherwise, a new basic
3683 block must be created to hold the instrumentation code.
3686 @item -ftest-coverage
3687 @opindex ftest-coverage
3688 Produce a notes file that the @command{gcov} code-coverage utility
3689 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3690 show program coverage. Each source file's note file is called
3691 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3692 above for a description of @var{auxname} and instructions on how to
3693 generate test coverage data. Coverage data will match the source files
3694 more closely, if you do not optimize.
3696 @item -d@var{letters}
3697 @item -fdump-rtl-@var{pass}
3699 Says to make debugging dumps during compilation at times specified by
3700 @var{letters}. This is used for debugging the RTL-based passes of the
3701 compiler. The file names for most of the dumps are made by appending a
3702 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3703 from the name of the output file, if explicitly specified and it is not
3704 an executable, otherwise it is the basename of the source file.
3706 Most debug dumps can be enabled either passing a letter to the @option{-d}
3707 option, or with a long @option{-fdump-rtl} switch; here are the possible
3708 letters for use in @var{letters} and @var{pass}, and their meanings:
3713 Annotate the assembler output with miscellaneous debugging information.
3716 @itemx -fdump-rtl-bbro
3718 @opindex fdump-rtl-bbro
3719 Dump after block reordering, to @file{@var{file}.30.bbro}.
3722 @itemx -fdump-rtl-combine
3724 @opindex fdump-rtl-combine
3725 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3728 @itemx -fdump-rtl-ce1
3729 @itemx -fdump-rtl-ce2
3731 @opindex fdump-rtl-ce1
3732 @opindex fdump-rtl-ce2
3733 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3734 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3735 and @option{-fdump-rtl-ce2} enable dumping after the second if
3736 conversion, to the file @file{@var{file}.18.ce2}.
3739 @itemx -fdump-rtl-btl
3740 @itemx -fdump-rtl-dbr
3742 @opindex fdump-rtl-btl
3743 @opindex fdump-rtl-dbr
3744 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3745 target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
3746 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3747 scheduling, to @file{@var{file}.36.dbr}.
3751 Dump all macro definitions, at the end of preprocessing, in addition to
3755 @itemx -fdump-rtl-ce3
3757 @opindex fdump-rtl-ce3
3758 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3761 @itemx -fdump-rtl-cfg
3762 @itemx -fdump-rtl-life
3764 @opindex fdump-rtl-cfg
3765 @opindex fdump-rtl-life
3766 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3767 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3768 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3769 to @file{@var{file}.16.life}.
3772 @itemx -fdump-rtl-greg
3774 @opindex fdump-rtl-greg
3775 Dump after global register allocation, to @file{@var{file}.23.greg}.
3778 @itemx -fdump-rtl-gcse
3779 @itemx -fdump-rtl-bypass
3781 @opindex fdump-rtl-gcse
3782 @opindex fdump-rtl-bypass
3783 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3784 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3785 enable dumping after jump bypassing and control flow optimizations, to
3786 @file{@var{file}.07.bypass}.
3789 @itemx -fdump-rtl-eh
3791 @opindex fdump-rtl-eh
3792 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3795 @itemx -fdump-rtl-sibling
3797 @opindex fdump-rtl-sibling
3798 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3801 @itemx -fdump-rtl-jump
3803 @opindex fdump-rtl-jump
3804 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3807 @itemx -fdump-rtl-stack
3809 @opindex fdump-rtl-stack
3810 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3813 @itemx -fdump-rtl-lreg
3815 @opindex fdump-rtl-lreg
3816 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3819 @itemx -fdump-rtl-loop2
3821 @opindex fdump-rtl-loop2
3822 @option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the
3823 loop optimization pass, to @file{@var{file}.119r.loop2},
3824 @file{@var{file}.120r.loop2_init},
3825 @file{@var{file}.121r.loop2_invariant},
3826 @file{@var{file}.125r.loop2_done}.
3829 @itemx -fdump-rtl-sms
3831 @opindex fdump-rtl-sms
3832 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3835 @itemx -fdump-rtl-mach
3837 @opindex fdump-rtl-mach
3838 Dump after performing the machine dependent reorganization pass, to
3839 @file{@var{file}.35.mach}.
3842 @itemx -fdump-rtl-rnreg
3844 @opindex fdump-rtl-rnreg
3845 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3848 @itemx -fdump-rtl-regmove
3850 @opindex fdump-rtl-regmove
3851 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3854 @itemx -fdump-rtl-postreload
3856 @opindex fdump-rtl-postreload
3857 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3860 @itemx -fdump-rtl-expand
3862 @opindex fdump-rtl-expand
3863 Dump after RTL generation, to @file{@var{file}.00.expand}.
3866 @itemx -fdump-rtl-sched2
3868 @opindex fdump-rtl-sched2
3869 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3872 @itemx -fdump-rtl-cse
3874 @opindex fdump-rtl-cse
3875 Dump after CSE (including the jump optimization that sometimes follows
3876 CSE), to @file{@var{file}.04.cse}.
3879 @itemx -fdump-rtl-sched
3881 @opindex fdump-rtl-sched
3882 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3885 @itemx -fdump-rtl-cse2
3887 @opindex fdump-rtl-cse2
3888 Dump after the second CSE pass (including the jump optimization that
3889 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3892 @itemx -fdump-rtl-tracer
3894 @opindex fdump-rtl-tracer
3895 Dump after running tracer, to @file{@var{file}.12.tracer}.
3898 @itemx -fdump-rtl-vpt
3899 @itemx -fdump-rtl-vartrack
3901 @opindex fdump-rtl-vpt
3902 @opindex fdump-rtl-vartrack
3903 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3904 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3905 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3906 to @file{@var{file}.34.vartrack}.
3909 @itemx -fdump-rtl-flow2
3911 @opindex fdump-rtl-flow2
3912 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3915 @itemx -fdump-rtl-peephole2
3917 @opindex fdump-rtl-peephole2
3918 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3921 @itemx -fdump-rtl-web
3923 @opindex fdump-rtl-web
3924 Dump after live range splitting, to @file{@var{file}.14.web}.
3927 @itemx -fdump-rtl-all
3929 @opindex fdump-rtl-all
3930 Produce all the dumps listed above.
3934 Produce a core dump whenever an error occurs.
3938 Print statistics on memory usage, at the end of the run, to
3943 Annotate the assembler output with a comment indicating which
3944 pattern and alternative was used. The length of each instruction is
3949 Dump the RTL in the assembler output as a comment before each instruction.
3950 Also turns on @option{-dp} annotation.
3954 For each of the other indicated dump files (either with @option{-d} or
3955 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3956 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3960 Just generate RTL for a function instead of compiling it. Usually used
3961 with @samp{r} (@option{-fdump-rtl-expand}).
3965 Dump debugging information during parsing, to standard error.
3968 @item -fdump-unnumbered
3969 @opindex fdump-unnumbered
3970 When doing debugging dumps (see @option{-d} option above), suppress instruction
3971 numbers and line number note output. This makes it more feasible to
3972 use diff on debugging dumps for compiler invocations with different
3973 options, in particular with and without @option{-g}.
3975 @item -fdump-translation-unit @r{(C++ only)}
3976 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
3977 @opindex fdump-translation-unit
3978 Dump a representation of the tree structure for the entire translation
3979 unit to a file. The file name is made by appending @file{.tu} to the
3980 source file name. If the @samp{-@var{options}} form is used, @var{options}
3981 controls the details of the dump as described for the
3982 @option{-fdump-tree} options.
3984 @item -fdump-class-hierarchy @r{(C++ only)}
3985 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3986 @opindex fdump-class-hierarchy
3987 Dump a representation of each class's hierarchy and virtual function
3988 table layout to a file. The file name is made by appending @file{.class}
3989 to the source file name. If the @samp{-@var{options}} form is used,
3990 @var{options} controls the details of the dump as described for the
3991 @option{-fdump-tree} options.
3993 @item -fdump-ipa-@var{switch}
3995 Control the dumping at various stages of inter-procedural analysis
3996 language tree to a file. The file name is generated by appending a switch
3997 specific suffix to the source file name. The following dumps are possible:
4001 Enables all inter-procedural analysis dumps; currently the only produced
4002 dump is the @samp{cgraph} dump.
4005 Dumps information about call-graph optimization, unused function removal,
4006 and inlining decisions.
4009 @item -fdump-tree-@var{switch}
4010 @itemx -fdump-tree-@var{switch}-@var{options}
4012 Control the dumping at various stages of processing the intermediate
4013 language tree to a file. The file name is generated by appending a switch
4014 specific suffix to the source file name. If the @samp{-@var{options}}
4015 form is used, @var{options} is a list of @samp{-} separated options that
4016 control the details of the dump. Not all options are applicable to all
4017 dumps, those which are not meaningful will be ignored. The following
4018 options are available
4022 Print the address of each node. Usually this is not meaningful as it
4023 changes according to the environment and source file. Its primary use
4024 is for tying up a dump file with a debug environment.
4026 Inhibit dumping of members of a scope or body of a function merely
4027 because that scope has been reached. Only dump such items when they
4028 are directly reachable by some other path. When dumping pretty-printed
4029 trees, this option inhibits dumping the bodies of control structures.
4031 Print a raw representation of the tree. By default, trees are
4032 pretty-printed into a C-like representation.
4034 Enable more detailed dumps (not honored by every dump option).
4036 Enable dumping various statistics about the pass (not honored by every dump
4039 Enable showing basic block boundaries (disabled in raw dumps).
4041 Enable showing virtual operands for every statement.
4043 Enable showing line numbers for statements.
4045 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4047 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
4050 The following tree dumps are possible:
4054 Dump before any tree based optimization, to @file{@var{file}.original}.
4057 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4060 Dump after function inlining, to @file{@var{file}.inlined}.
4063 @opindex fdump-tree-gimple
4064 Dump each function before and after the gimplification pass to a file. The
4065 file name is made by appending @file{.gimple} to the source file name.
4068 @opindex fdump-tree-cfg
4069 Dump the control flow graph of each function to a file. The file name is
4070 made by appending @file{.cfg} to the source file name.
4073 @opindex fdump-tree-vcg
4074 Dump the control flow graph of each function to a file in VCG format. The
4075 file name is made by appending @file{.vcg} to the source file name. Note
4076 that if the file contains more than one function, the generated file cannot
4077 be used directly by VCG@. You will need to cut and paste each function's
4078 graph into its own separate file first.
4081 @opindex fdump-tree-ch
4082 Dump each function after copying loop headers. The file name is made by
4083 appending @file{.ch} to the source file name.
4086 @opindex fdump-tree-ssa
4087 Dump SSA related information to a file. The file name is made by appending
4088 @file{.ssa} to the source file name.
4091 @opindex fdump-tree-salias
4092 Dump structure aliasing variable information to a file. This file name
4093 is made by appending @file{.salias} to the source file name.
4096 @opindex fdump-tree-alias
4097 Dump aliasing information for each function. The file name is made by
4098 appending @file{.alias} to the source file name.
4101 @opindex fdump-tree-ccp
4102 Dump each function after CCP@. The file name is made by appending
4103 @file{.ccp} to the source file name.
4106 @opindex fdump-tree-storeccp
4107 Dump each function after STORE-CCP. The file name is made by appending
4108 @file{.storeccp} to the source file name.
4111 @opindex fdump-tree-pre
4112 Dump trees after partial redundancy elimination. The file name is made
4113 by appending @file{.pre} to the source file name.
4116 @opindex fdump-tree-fre
4117 Dump trees after full redundancy elimination. The file name is made
4118 by appending @file{.fre} to the source file name.
4121 @opindex fdump-tree-copyprop
4122 Dump trees after copy propagation. The file name is made
4123 by appending @file{.copyprop} to the source file name.
4125 @item store_copyprop
4126 @opindex fdump-tree-store_copyprop
4127 Dump trees after store copy-propagation. The file name is made
4128 by appending @file{.store_copyprop} to the source file name.
4131 @opindex fdump-tree-dce
4132 Dump each function after dead code elimination. The file name is made by
4133 appending @file{.dce} to the source file name.
4136 @opindex fdump-tree-mudflap
4137 Dump each function after adding mudflap instrumentation. The file name is
4138 made by appending @file{.mudflap} to the source file name.
4141 @opindex fdump-tree-sra
4142 Dump each function after performing scalar replacement of aggregates. The
4143 file name is made by appending @file{.sra} to the source file name.
4146 @opindex fdump-tree-sink
4147 Dump each function after performing code sinking. The file name is made
4148 by appending @file{.sink} to the source file name.
4151 @opindex fdump-tree-dom
4152 Dump each function after applying dominator tree optimizations. The file
4153 name is made by appending @file{.dom} to the source file name.
4156 @opindex fdump-tree-dse
4157 Dump each function after applying dead store elimination. The file
4158 name is made by appending @file{.dse} to the source file name.
4161 @opindex fdump-tree-phiopt
4162 Dump each function after optimizing PHI nodes into straightline code. The file
4163 name is made by appending @file{.phiopt} to the source file name.
4166 @opindex fdump-tree-forwprop
4167 Dump each function after forward propagating single use variables. The file
4168 name is made by appending @file{.forwprop} to the source file name.
4171 @opindex fdump-tree-copyrename
4172 Dump each function after applying the copy rename optimization. The file
4173 name is made by appending @file{.copyrename} to the source file name.
4176 @opindex fdump-tree-nrv
4177 Dump each function after applying the named return value optimization on
4178 generic trees. The file name is made by appending @file{.nrv} to the source
4182 @opindex fdump-tree-vect
4183 Dump each function after applying vectorization of loops. The file name is
4184 made by appending @file{.vect} to the source file name.
4187 @opindex fdump-tree-vrp
4188 Dump each function after Value Range Propagation (VRP). The file name
4189 is made by appending @file{.vrp} to the source file name.
4192 @opindex fdump-tree-all
4193 Enable all the available tree dumps with the flags provided in this option.
4196 @item -ftree-vectorizer-verbose=@var{n}
4197 @opindex ftree-vectorizer-verbose
4198 This option controls the amount of debugging output the vectorizer prints.
4199 This information is written to standard error, unless
4200 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4201 in which case it is output to the usual dump listing file, @file{.vect}.
4202 For @var{n}=0 no diagnostic information is reported.
4203 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4204 and the total number of loops that got vectorized.
4205 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4206 the first analysis phase (vect_analyze_loop_form) - i.e. countable,
4207 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4208 level that @option{-fdump-tree-vect-stats} uses.
4209 Higher verbosity levels mean either more information dumped for each
4210 reported loop, or same amount of information reported for more loops:
4211 If @var{n}=3, alignment related information is added to the reports.
4212 If @var{n}=4, data-references related information (e.g. memory dependences,
4213 memory access-patterns) is added to the reports.
4214 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4215 that did not pass the first analysis phase (i.e. may not be countable, or
4216 may have complicated control-flow).
4217 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4218 For @var{n}=7, all the information the vectorizer generates during its
4219 analysis and transformation is reported. This is the same verbosity level
4220 that @option{-fdump-tree-vect-details} uses.
4222 @item -frandom-seed=@var{string}
4223 @opindex frandom-string
4224 This option provides a seed that GCC uses when it would otherwise use
4225 random numbers. It is used to generate certain symbol names
4226 that have to be different in every compiled file. It is also used to
4227 place unique stamps in coverage data files and the object files that
4228 produce them. You can use the @option{-frandom-seed} option to produce
4229 reproducibly identical object files.
4231 The @var{string} should be different for every file you compile.
4233 @item -fsched-verbose=@var{n}
4234 @opindex fsched-verbose
4235 On targets that use instruction scheduling, this option controls the
4236 amount of debugging output the scheduler prints. This information is
4237 written to standard error, unless @option{-dS} or @option{-dR} is
4238 specified, in which case it is output to the usual dump
4239 listing file, @file{.sched} or @file{.sched2} respectively. However
4240 for @var{n} greater than nine, the output is always printed to standard
4243 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4244 same information as @option{-dRS}. For @var{n} greater than one, it
4245 also output basic block probabilities, detailed ready list information
4246 and unit/insn info. For @var{n} greater than two, it includes RTL
4247 at abort point, control-flow and regions info. And for @var{n} over
4248 four, @option{-fsched-verbose} also includes dependence info.
4252 Store the usual ``temporary'' intermediate files permanently; place them
4253 in the current directory and name them based on the source file. Thus,
4254 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4255 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4256 preprocessed @file{foo.i} output file even though the compiler now
4257 normally uses an integrated preprocessor.
4259 When used in combination with the @option{-x} command line option,
4260 @option{-save-temps} is sensible enough to avoid over writing an
4261 input source file with the same extension as an intermediate file.
4262 The corresponding intermediate file may be obtained by renaming the
4263 source file before using @option{-save-temps}.
4267 Report the CPU time taken by each subprocess in the compilation
4268 sequence. For C source files, this is the compiler proper and assembler
4269 (plus the linker if linking is done). The output looks like this:
4276 The first number on each line is the ``user time'', that is time spent
4277 executing the program itself. The second number is ``system time'',
4278 time spent executing operating system routines on behalf of the program.
4279 Both numbers are in seconds.
4281 @item -fvar-tracking
4282 @opindex fvar-tracking
4283 Run variable tracking pass. It computes where variables are stored at each
4284 position in code. Better debugging information is then generated
4285 (if the debugging information format supports this information).
4287 It is enabled by default when compiling with optimization (@option{-Os},
4288 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
4289 the debug info format supports it.
4291 @item -print-file-name=@var{library}
4292 @opindex print-file-name
4293 Print the full absolute name of the library file @var{library} that
4294 would be used when linking---and don't do anything else. With this
4295 option, GCC does not compile or link anything; it just prints the
4298 @item -print-multi-directory
4299 @opindex print-multi-directory
4300 Print the directory name corresponding to the multilib selected by any
4301 other switches present in the command line. This directory is supposed
4302 to exist in @env{GCC_EXEC_PREFIX}.
4304 @item -print-multi-lib
4305 @opindex print-multi-lib
4306 Print the mapping from multilib directory names to compiler switches
4307 that enable them. The directory name is separated from the switches by
4308 @samp{;}, and each switch starts with an @samp{@@} instead of the
4309 @samp{-}, without spaces between multiple switches. This is supposed to
4310 ease shell-processing.
4312 @item -print-prog-name=@var{program}
4313 @opindex print-prog-name
4314 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
4316 @item -print-libgcc-file-name
4317 @opindex print-libgcc-file-name
4318 Same as @option{-print-file-name=libgcc.a}.
4320 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
4321 but you do want to link with @file{libgcc.a}. You can do
4324 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
4327 @item -print-search-dirs
4328 @opindex print-search-dirs
4329 Print the name of the configured installation directory and a list of
4330 program and library directories @command{gcc} will search---and don't do anything else.
4332 This is useful when @command{gcc} prints the error message
4333 @samp{installation problem, cannot exec cpp0: No such file or directory}.
4334 To resolve this you either need to put @file{cpp0} and the other compiler
4335 components where @command{gcc} expects to find them, or you can set the environment
4336 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
4337 Don't forget the trailing @samp{/}.
4338 @xref{Environment Variables}.
4341 @opindex dumpmachine
4342 Print the compiler's target machine (for example,
4343 @samp{i686-pc-linux-gnu})---and don't do anything else.
4346 @opindex dumpversion
4347 Print the compiler version (for example, @samp{3.0})---and don't do
4352 Print the compiler's built-in specs---and don't do anything else. (This
4353 is used when GCC itself is being built.) @xref{Spec Files}.
4355 @item -feliminate-unused-debug-types
4356 @opindex feliminate-unused-debug-types
4357 Normally, when producing DWARF2 output, GCC will emit debugging
4358 information for all types declared in a compilation
4359 unit, regardless of whether or not they are actually used
4360 in that compilation unit. Sometimes this is useful, such as
4361 if, in the debugger, you want to cast a value to a type that is
4362 not actually used in your program (but is declared). More often,
4363 however, this results in a significant amount of wasted space.
4364 With this option, GCC will avoid producing debug symbol output
4365 for types that are nowhere used in the source file being compiled.
4368 @node Optimize Options
4369 @section Options That Control Optimization
4370 @cindex optimize options
4371 @cindex options, optimization
4373 These options control various sorts of optimizations.
4375 Without any optimization option, the compiler's goal is to reduce the
4376 cost of compilation and to make debugging produce the expected
4377 results. Statements are independent: if you stop the program with a
4378 breakpoint between statements, you can then assign a new value to any
4379 variable or change the program counter to any other statement in the
4380 function and get exactly the results you would expect from the source
4383 Turning on optimization flags makes the compiler attempt to improve
4384 the performance and/or code size at the expense of compilation time
4385 and possibly the ability to debug the program.
4387 The compiler performs optimization based on the knowledge it has of
4388 the program. Optimization levels @option{-O2} and above, in
4389 particular, enable @emph{unit-at-a-time} mode, which allows the
4390 compiler to consider information gained from later functions in
4391 the file when compiling a function. Compiling multiple files at
4392 once to a single output file in @emph{unit-at-a-time} mode allows
4393 the compiler to use information gained from all of the files when
4394 compiling each of them.
4396 Not all optimizations are controlled directly by a flag. Only
4397 optimizations that have a flag are listed.
4404 Optimize. Optimizing compilation takes somewhat more time, and a lot
4405 more memory for a large function.
4407 With @option{-O}, the compiler tries to reduce code size and execution
4408 time, without performing any optimizations that take a great deal of
4411 @option{-O} turns on the following optimization flags:
4412 @gccoptlist{-fdefer-pop @gol
4413 -fdelayed-branch @gol
4414 -fguess-branch-probability @gol
4415 -fcprop-registers @gol
4416 -fif-conversion @gol
4417 -fif-conversion2 @gol
4420 -ftree-dominator-opts @gol
4425 -ftree-copyrename @gol
4430 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4431 where doing so does not interfere with debugging.
4435 Optimize even more. GCC performs nearly all supported optimizations
4436 that do not involve a space-speed tradeoff. The compiler does not
4437 perform loop unrolling or function inlining when you specify @option{-O2}.
4438 As compared to @option{-O}, this option increases both compilation time
4439 and the performance of the generated code.
4441 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4442 also turns on the following optimization flags:
4443 @gccoptlist{-fthread-jumps @gol
4445 -foptimize-sibling-calls @gol
4446 -fcse-follow-jumps -fcse-skip-blocks @gol
4447 -fgcse -fgcse-lm @gol
4448 -fexpensive-optimizations @gol
4449 -frerun-cse-after-loop @gol
4452 -fschedule-insns -fschedule-insns2 @gol
4453 -fsched-interblock -fsched-spec @gol
4455 -fstrict-aliasing @gol
4456 -fdelete-null-pointer-checks @gol
4457 -freorder-blocks -freorder-functions @gol
4458 -funit-at-a-time @gol
4459 -falign-functions -falign-jumps @gol
4460 -falign-loops -falign-labels @gol
4464 Please note the warning under @option{-fgcse} about
4465 invoking @option{-O2} on programs that use computed gotos.
4469 Optimize yet more. @option{-O3} turns on all optimizations specified by
4470 @option{-O2} and also turns on the @option{-finline-functions},
4471 @option{-funswitch-loops} and @option{-fgcse-after-reload} options.
4475 Do not optimize. This is the default.
4479 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4480 do not typically increase code size. It also performs further
4481 optimizations designed to reduce code size.
4483 @option{-Os} disables the following optimization flags:
4484 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4485 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
4486 -fprefetch-loop-arrays -ftree-vect-loop-version}
4488 If you use multiple @option{-O} options, with or without level numbers,
4489 the last such option is the one that is effective.
4492 Options of the form @option{-f@var{flag}} specify machine-independent
4493 flags. Most flags have both positive and negative forms; the negative
4494 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4495 below, only one of the forms is listed---the one you typically will
4496 use. You can figure out the other form by either removing @samp{no-}
4499 The following options control specific optimizations. They are either
4500 activated by @option{-O} options or are related to ones that are. You
4501 can use the following flags in the rare cases when ``fine-tuning'' of
4502 optimizations to be performed is desired.
4505 @item -fno-default-inline
4506 @opindex fno-default-inline
4507 Do not make member functions inline by default merely because they are
4508 defined inside the class scope (C++ only). Otherwise, when you specify
4509 @w{@option{-O}}, member functions defined inside class scope are compiled
4510 inline by default; i.e., you don't need to add @samp{inline} in front of
4511 the member function name.
4513 @item -fno-defer-pop
4514 @opindex fno-defer-pop
4515 Always pop the arguments to each function call as soon as that function
4516 returns. For machines which must pop arguments after a function call,
4517 the compiler normally lets arguments accumulate on the stack for several
4518 function calls and pops them all at once.
4520 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4524 Force memory operands to be copied into registers before doing
4525 arithmetic on them. This produces better code by making all memory
4526 references potential common subexpressions. When they are not common
4527 subexpressions, instruction combination should eliminate the separate
4528 register-load. This option is now a nop and will be removed in 4.2.
4531 @opindex fforce-addr
4532 Force memory address constants to be copied into registers before
4533 doing arithmetic on them.
4535 @item -fomit-frame-pointer
4536 @opindex fomit-frame-pointer
4537 Don't keep the frame pointer in a register for functions that
4538 don't need one. This avoids the instructions to save, set up and
4539 restore frame pointers; it also makes an extra register available
4540 in many functions. @strong{It also makes debugging impossible on
4543 On some machines, such as the VAX, this flag has no effect, because
4544 the standard calling sequence automatically handles the frame pointer
4545 and nothing is saved by pretending it doesn't exist. The
4546 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4547 whether a target machine supports this flag. @xref{Registers,,Register
4548 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4550 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4552 @item -foptimize-sibling-calls
4553 @opindex foptimize-sibling-calls
4554 Optimize sibling and tail recursive calls.
4556 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4560 Don't pay attention to the @code{inline} keyword. Normally this option
4561 is used to keep the compiler from expanding any functions inline.
4562 Note that if you are not optimizing, no functions can be expanded inline.
4564 @item -finline-functions
4565 @opindex finline-functions
4566 Integrate all simple functions into their callers. The compiler
4567 heuristically decides which functions are simple enough to be worth
4568 integrating in this way.
4570 If all calls to a given function are integrated, and the function is
4571 declared @code{static}, then the function is normally not output as
4572 assembler code in its own right.
4574 Enabled at level @option{-O3}.
4576 @item -finline-functions-called-once
4577 @opindex finline-functions-called-once
4578 Consider all @code{static} functions called once for inlining into their
4579 caller even if they are not marked @code{inline}. If a call to a given
4580 function is integrated, then the function is not output as assembler code
4583 Enabled if @option{-funit-at-a-time} is enabled.
4585 @item -fearly-inlining
4586 @opindex fearly-inlining
4587 Inline functions marked by @code{always_inline} and functions whose body seems
4588 smaller than the function call overhead early before doing
4589 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
4590 makes profiling significantly cheaper and usually inlining faster on programs
4591 having large chains of nested wrapper functions.
4595 @item -finline-limit=@var{n}
4596 @opindex finline-limit
4597 By default, GCC limits the size of functions that can be inlined. This flag
4598 allows the control of this limit for functions that are explicitly marked as
4599 inline (i.e., marked with the inline keyword or defined within the class
4600 definition in c++). @var{n} is the size of functions that can be inlined in
4601 number of pseudo instructions (not counting parameter handling). The default
4602 value of @var{n} is 600.
4603 Increasing this value can result in more inlined code at
4604 the cost of compilation time and memory consumption. Decreasing usually makes
4605 the compilation faster and less code will be inlined (which presumably
4606 means slower programs). This option is particularly useful for programs that
4607 use inlining heavily such as those based on recursive templates with C++.
4609 Inlining is actually controlled by a number of parameters, which may be
4610 specified individually by using @option{--param @var{name}=@var{value}}.
4611 The @option{-finline-limit=@var{n}} option sets some of these parameters
4615 @item max-inline-insns-single
4616 is set to @var{n}/2.
4617 @item max-inline-insns-auto
4618 is set to @var{n}/2.
4619 @item min-inline-insns
4620 is set to 130 or @var{n}/4, whichever is smaller.
4621 @item max-inline-insns-rtl
4625 See below for a documentation of the individual
4626 parameters controlling inlining.
4628 @emph{Note:} pseudo instruction represents, in this particular context, an
4629 abstract measurement of function's size. In no way does it represent a count
4630 of assembly instructions and as such its exact meaning might change from one
4631 release to an another.
4633 @item -fkeep-inline-functions
4634 @opindex fkeep-inline-functions
4635 In C, emit @code{static} functions that are declared @code{inline}
4636 into the object file, even if the function has been inlined into all
4637 of its callers. This switch does not affect functions using the
4638 @code{extern inline} extension in GNU C@. In C++, emit any and all
4639 inline functions into the object file.
4641 @item -fkeep-static-consts
4642 @opindex fkeep-static-consts
4643 Emit variables declared @code{static const} when optimization isn't turned
4644 on, even if the variables aren't referenced.
4646 GCC enables this option by default. If you want to force the compiler to
4647 check if the variable was referenced, regardless of whether or not
4648 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4650 @item -fmerge-constants
4651 Attempt to merge identical constants (string constants and floating point
4652 constants) across compilation units.
4654 This option is the default for optimized compilation if the assembler and
4655 linker support it. Use @option{-fno-merge-constants} to inhibit this
4658 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4660 @item -fmerge-all-constants
4661 Attempt to merge identical constants and identical variables.
4663 This option implies @option{-fmerge-constants}. In addition to
4664 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4665 arrays or initialized constant variables with integral or floating point
4666 types. Languages like C or C++ require each non-automatic variable to
4667 have distinct location, so using this option will result in non-conforming
4670 @item -fmodulo-sched
4671 @opindex fmodulo-sched
4672 Perform swing modulo scheduling immediately before the first scheduling
4673 pass. This pass looks at innermost loops and reorders their
4674 instructions by overlapping different iterations.
4676 @item -fno-branch-count-reg
4677 @opindex fno-branch-count-reg
4678 Do not use ``decrement and branch'' instructions on a count register,
4679 but instead generate a sequence of instructions that decrement a
4680 register, compare it against zero, then branch based upon the result.
4681 This option is only meaningful on architectures that support such
4682 instructions, which include x86, PowerPC, IA-64 and S/390.
4684 The default is @option{-fbranch-count-reg}.
4686 @item -fno-function-cse
4687 @opindex fno-function-cse
4688 Do not put function addresses in registers; make each instruction that
4689 calls a constant function contain the function's address explicitly.
4691 This option results in less efficient code, but some strange hacks
4692 that alter the assembler output may be confused by the optimizations
4693 performed when this option is not used.
4695 The default is @option{-ffunction-cse}
4697 @item -fno-zero-initialized-in-bss
4698 @opindex fno-zero-initialized-in-bss
4699 If the target supports a BSS section, GCC by default puts variables that
4700 are initialized to zero into BSS@. This can save space in the resulting
4703 This option turns off this behavior because some programs explicitly
4704 rely on variables going to the data section. E.g., so that the
4705 resulting executable can find the beginning of that section and/or make
4706 assumptions based on that.
4708 The default is @option{-fzero-initialized-in-bss}.
4710 @item -fbounds-check
4711 @opindex fbounds-check
4712 For front-ends that support it, generate additional code to check that
4713 indices used to access arrays are within the declared range. This is
4714 currently only supported by the Java and Fortran front-ends, where
4715 this option defaults to true and false respectively.
4717 @item -fmudflap -fmudflapth -fmudflapir
4721 @cindex bounds checking
4723 For front-ends that support it (C and C++), instrument all risky
4724 pointer/array dereferencing operations, some standard library
4725 string/heap functions, and some other associated constructs with
4726 range/validity tests. Modules so instrumented should be immune to
4727 buffer overflows, invalid heap use, and some other classes of C/C++
4728 programming errors. The instrumentation relies on a separate runtime
4729 library (@file{libmudflap}), which will be linked into a program if
4730 @option{-fmudflap} is given at link time. Run-time behavior of the
4731 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4732 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4735 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4736 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4737 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4738 instrumentation should ignore pointer reads. This produces less
4739 instrumentation (and therefore faster execution) and still provides
4740 some protection against outright memory corrupting writes, but allows
4741 erroneously read data to propagate within a program.
4743 @item -fthread-jumps
4744 @opindex fthread-jumps
4745 Perform optimizations where we check to see if a jump branches to a
4746 location where another comparison subsumed by the first is found. If
4747 so, the first branch is redirected to either the destination of the
4748 second branch or a point immediately following it, depending on whether
4749 the condition is known to be true or false.
4751 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4753 @item -fcse-follow-jumps
4754 @opindex fcse-follow-jumps
4755 In common subexpression elimination, scan through jump instructions
4756 when the target of the jump is not reached by any other path. For
4757 example, when CSE encounters an @code{if} statement with an
4758 @code{else} clause, CSE will follow the jump when the condition
4761 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4763 @item -fcse-skip-blocks
4764 @opindex fcse-skip-blocks
4765 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4766 follow jumps which conditionally skip over blocks. When CSE
4767 encounters a simple @code{if} statement with no else clause,
4768 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4769 body of the @code{if}.
4771 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4773 @item -frerun-cse-after-loop
4774 @opindex frerun-cse-after-loop
4775 Re-run common subexpression elimination after loop optimizations has been
4778 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4782 Perform a global common subexpression elimination pass.
4783 This pass also performs global constant and copy propagation.
4785 @emph{Note:} When compiling a program using computed gotos, a GCC
4786 extension, you may get better runtime performance if you disable
4787 the global common subexpression elimination pass by adding
4788 @option{-fno-gcse} to the command line.
4790 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4794 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4795 attempt to move loads which are only killed by stores into themselves. This
4796 allows a loop containing a load/store sequence to be changed to a load outside
4797 the loop, and a copy/store within the loop.
4799 Enabled by default when gcse is enabled.
4803 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4804 global common subexpression elimination. This pass will attempt to move
4805 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4806 loops containing a load/store sequence can be changed to a load before
4807 the loop and a store after the loop.
4809 Not enabled at any optimization level.
4813 When @option{-fgcse-las} is enabled, the global common subexpression
4814 elimination pass eliminates redundant loads that come after stores to the
4815 same memory location (both partial and full redundancies).
4817 Not enabled at any optimization level.
4819 @item -fgcse-after-reload
4820 @opindex fgcse-after-reload
4821 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4822 pass is performed after reload. The purpose of this pass is to cleanup
4825 @item -funsafe-loop-optimizations
4826 @opindex funsafe-loop-optimizations
4827 If given, the loop optimizer will assume that loop indices do not
4828 overflow, and that the loops with nontrivial exit condition are not
4829 infinite. This enables a wider range of loop optimizations even if
4830 the loop optimizer itself cannot prove that these assumptions are valid.
4831 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
4832 if it finds this kind of loop.
4834 @item -fcrossjumping
4835 @opindex crossjumping
4836 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4837 resulting code may or may not perform better than without cross-jumping.
4839 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4841 @item -fif-conversion
4842 @opindex if-conversion
4843 Attempt to transform conditional jumps into branch-less equivalents. This
4844 include use of conditional moves, min, max, set flags and abs instructions, and
4845 some tricks doable by standard arithmetics. The use of conditional execution
4846 on chips where it is available is controlled by @code{if-conversion2}.
4848 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4850 @item -fif-conversion2
4851 @opindex if-conversion2
4852 Use conditional execution (where available) to transform conditional jumps into
4853 branch-less equivalents.
4855 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4857 @item -fdelete-null-pointer-checks
4858 @opindex fdelete-null-pointer-checks
4859 Use global dataflow analysis to identify and eliminate useless checks
4860 for null pointers. The compiler assumes that dereferencing a null
4861 pointer would have halted the program. If a pointer is checked after
4862 it has already been dereferenced, it cannot be null.
4864 In some environments, this assumption is not true, and programs can
4865 safely dereference null pointers. Use
4866 @option{-fno-delete-null-pointer-checks} to disable this optimization
4867 for programs which depend on that behavior.
4869 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4871 @item -fexpensive-optimizations
4872 @opindex fexpensive-optimizations
4873 Perform a number of minor optimizations that are relatively expensive.
4875 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4877 @item -foptimize-register-move
4879 @opindex foptimize-register-move
4881 Attempt to reassign register numbers in move instructions and as
4882 operands of other simple instructions in order to maximize the amount of
4883 register tying. This is especially helpful on machines with two-operand
4886 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4889 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4891 @item -fdelayed-branch
4892 @opindex fdelayed-branch
4893 If supported for the target machine, attempt to reorder instructions
4894 to exploit instruction slots available after delayed branch
4897 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4899 @item -fschedule-insns
4900 @opindex fschedule-insns
4901 If supported for the target machine, attempt to reorder instructions to
4902 eliminate execution stalls due to required data being unavailable. This
4903 helps machines that have slow floating point or memory load instructions
4904 by allowing other instructions to be issued until the result of the load
4905 or floating point instruction is required.
4907 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4909 @item -fschedule-insns2
4910 @opindex fschedule-insns2
4911 Similar to @option{-fschedule-insns}, but requests an additional pass of
4912 instruction scheduling after register allocation has been done. This is
4913 especially useful on machines with a relatively small number of
4914 registers and where memory load instructions take more than one cycle.
4916 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4918 @item -fno-sched-interblock
4919 @opindex fno-sched-interblock
4920 Don't schedule instructions across basic blocks. This is normally
4921 enabled by default when scheduling before register allocation, i.e.@:
4922 with @option{-fschedule-insns} or at @option{-O2} or higher.
4924 @item -fno-sched-spec
4925 @opindex fno-sched-spec
4926 Don't allow speculative motion of non-load instructions. This is normally
4927 enabled by default when scheduling before register allocation, i.e.@:
4928 with @option{-fschedule-insns} or at @option{-O2} or higher.
4930 @item -fsched-spec-load
4931 @opindex fsched-spec-load
4932 Allow speculative motion of some load instructions. This only makes
4933 sense when scheduling before register allocation, i.e.@: with
4934 @option{-fschedule-insns} or at @option{-O2} or higher.
4936 @item -fsched-spec-load-dangerous
4937 @opindex fsched-spec-load-dangerous
4938 Allow speculative motion of more load instructions. This only makes
4939 sense when scheduling before register allocation, i.e.@: with
4940 @option{-fschedule-insns} or at @option{-O2} or higher.
4942 @item -fsched-stalled-insns=@var{n}
4943 @opindex fsched-stalled-insns
4944 Define how many insns (if any) can be moved prematurely from the queue
4945 of stalled insns into the ready list, during the second scheduling pass.
4947 @item -fsched-stalled-insns-dep=@var{n}
4948 @opindex fsched-stalled-insns-dep
4949 Define how many insn groups (cycles) will be examined for a dependency
4950 on a stalled insn that is candidate for premature removal from the queue
4951 of stalled insns. Has an effect only during the second scheduling pass,
4952 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4954 @item -fsched2-use-superblocks
4955 @opindex fsched2-use-superblocks
4956 When scheduling after register allocation, do use superblock scheduling
4957 algorithm. Superblock scheduling allows motion across basic block boundaries
4958 resulting on faster schedules. This option is experimental, as not all machine
4959 descriptions used by GCC model the CPU closely enough to avoid unreliable
4960 results from the algorithm.
4962 This only makes sense when scheduling after register allocation, i.e.@: with
4963 @option{-fschedule-insns2} or at @option{-O2} or higher.
4965 @item -fsched2-use-traces
4966 @opindex fsched2-use-traces
4967 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4968 allocation and additionally perform code duplication in order to increase the
4969 size of superblocks using tracer pass. See @option{-ftracer} for details on
4972 This mode should produce faster but significantly longer programs. Also
4973 without @option{-fbranch-probabilities} the traces constructed may not
4974 match the reality and hurt the performance. This only makes
4975 sense when scheduling after register allocation, i.e.@: with
4976 @option{-fschedule-insns2} or at @option{-O2} or higher.
4978 @item -freschedule-modulo-scheduled-loops
4979 @opindex fscheduling-in-modulo-scheduled-loops
4980 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4981 we may want to prevent the later scheduling passes from changing its schedule, we use this
4982 option to control that.
4984 @item -fcaller-saves
4985 @opindex fcaller-saves
4986 Enable values to be allocated in registers that will be clobbered by
4987 function calls, by emitting extra instructions to save and restore the
4988 registers around such calls. Such allocation is done only when it
4989 seems to result in better code than would otherwise be produced.
4991 This option is always enabled by default on certain machines, usually
4992 those which have no call-preserved registers to use instead.
4994 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4997 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
4998 enabled by default at @option{-O2} and @option{-O3}.
5001 Perform Full Redundancy Elimination (FRE) on trees. The difference
5002 between FRE and PRE is that FRE only considers expressions
5003 that are computed on all paths leading to the redundant computation.
5004 This analysis faster than PRE, though it exposes fewer redundancies.
5005 This flag is enabled by default at @option{-O} and higher.
5007 @item -ftree-copy-prop
5008 Perform copy propagation on trees. This pass eliminates unnecessary
5009 copy operations. This flag is enabled by default at @option{-O} and
5012 @item -ftree-store-copy-prop
5013 Perform copy propagation of memory loads and stores. This pass
5014 eliminates unnecessary copy operations in memory references
5015 (structures, global variables, arrays, etc). This flag is enabled by
5016 default at @option{-O2} and higher.
5019 Perform structural alias analysis on trees. This flag
5020 is enabled by default at @option{-O} and higher.
5023 Perform interprocedural pointer analysis.
5026 Perform forward store motion on trees. This flag is
5027 enabled by default at @option{-O} and higher.
5030 Perform sparse conditional constant propagation (CCP) on trees. This
5031 pass only operates on local scalar variables and is enabled by default
5032 at @option{-O} and higher.
5034 @item -ftree-store-ccp
5035 Perform sparse conditional constant propagation (CCP) on trees. This
5036 pass operates on both local scalar variables and memory stores and
5037 loads (global variables, structures, arrays, etc). This flag is
5038 enabled by default at @option{-O2} and higher.
5041 Perform dead code elimination (DCE) on trees. This flag is enabled by
5042 default at @option{-O} and higher.
5044 @item -ftree-dominator-opts
5045 Perform a variety of simple scalar cleanups (constant/copy
5046 propagation, redundancy elimination, range propagation and expression
5047 simplification) based on a dominator tree traversal. This also
5048 performs jump threading (to reduce jumps to jumps). This flag is
5049 enabled by default at @option{-O} and higher.
5052 Perform loop header copying on trees. This is beneficial since it increases
5053 effectiveness of code motion optimizations. It also saves one jump. This flag
5054 is enabled by default at @option{-O} and higher. It is not enabled
5055 for @option{-Os}, since it usually increases code size.
5057 @item -ftree-loop-optimize
5058 Perform loop optimizations on trees. This flag is enabled by default
5059 at @option{-O} and higher.
5061 @item -ftree-loop-linear
5062 Perform linear loop transformations on tree. This flag can improve cache
5063 performance and allow further loop optimizations to take place.
5065 @item -ftree-loop-im
5066 Perform loop invariant motion on trees. This pass moves only invariants that
5067 would be hard to handle at RTL level (function calls, operations that expand to
5068 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5069 operands of conditions that are invariant out of the loop, so that we can use
5070 just trivial invariantness analysis in loop unswitching. The pass also includes
5073 @item -ftree-loop-ivcanon
5074 Create a canonical counter for number of iterations in the loop for that
5075 determining number of iterations requires complicated analysis. Later
5076 optimizations then may determine the number easily. Useful especially
5077 in connection with unrolling.
5080 Perform induction variable optimizations (strength reduction, induction
5081 variable merging and induction variable elimination) on trees.
5084 Perform scalar replacement of aggregates. This pass replaces structure
5085 references with scalars to prevent committing structures to memory too
5086 early. This flag is enabled by default at @option{-O} and higher.
5088 @item -ftree-copyrename
5089 Perform copy renaming on trees. This pass attempts to rename compiler
5090 temporaries to other variables at copy locations, usually resulting in
5091 variable names which more closely resemble the original variables. This flag
5092 is enabled by default at @option{-O} and higher.
5095 Perform temporary expression replacement during the SSA->normal phase. Single
5096 use/single def temporaries are replaced at their use location with their
5097 defining expression. This results in non-GIMPLE code, but gives the expanders
5098 much more complex trees to work on resulting in better RTL generation. This is
5099 enabled by default at @option{-O} and higher.
5102 Perform live range splitting during the SSA->normal phase. Distinct live
5103 ranges of a variable are split into unique variables, allowing for better
5104 optimization later. This is enabled by default at @option{-O} and higher.
5106 @item -ftree-vectorize
5107 Perform loop vectorization on trees.
5109 @item -ftree-vect-loop-version
5110 @opindex ftree-vect-loop-version
5111 Perform loop versioning when doing loop vectorization on trees. When a loop
5112 appears to be vectorizable except that data alignment or data dependence cannot
5113 be determined at compile time then vectorized and non-vectorized versions of
5114 the loop are generated along with runtime checks for alignment or dependence
5115 to control which version is executed. This option is enabled by default
5116 except at level @option{-Os} where it is disabled.
5119 Perform Value Range Propagation on trees. This is similar to the
5120 constant propagation pass, but instead of values, ranges of values are
5121 propagated. This allows the optimizers to remove unnecessary range
5122 checks like array bound checks and null pointer checks. This is
5123 enabled by default at @option{-O2} and higher. Null pointer check
5124 elimination is only done if @option{-fdelete-null-pointer-checks} is
5129 Perform tail duplication to enlarge superblock size. This transformation
5130 simplifies the control flow of the function allowing other optimizations to do
5133 @item -funroll-loops
5134 @opindex funroll-loops
5135 Unroll loops whose number of iterations can be determined at compile
5136 time or upon entry to the loop. @option{-funroll-loops} implies
5137 @option{-frerun-cse-after-loop}. This option makes code larger,
5138 and may or may not make it run faster.
5140 @item -funroll-all-loops
5141 @opindex funroll-all-loops
5142 Unroll all loops, even if their number of iterations is uncertain when
5143 the loop is entered. This usually makes programs run more slowly.
5144 @option{-funroll-all-loops} implies the same options as
5145 @option{-funroll-loops},
5147 @item -fsplit-ivs-in-unroller
5148 @opindex -fsplit-ivs-in-unroller
5149 Enables expressing of values of induction variables in later iterations
5150 of the unrolled loop using the value in the first iteration. This breaks
5151 long dependency chains, thus improving efficiency of the scheduling passes.
5153 Combination of @option{-fweb} and CSE is often sufficient to obtain the
5154 same effect. However in cases the loop body is more complicated than
5155 a single basic block, this is not reliable. It also does not work at all
5156 on some of the architectures due to restrictions in the CSE pass.
5158 This optimization is enabled by default.
5160 @item -fvariable-expansion-in-unroller
5161 @opindex -fvariable-expansion-in-unroller
5162 With this option, the compiler will create multiple copies of some
5163 local variables when unrolling a loop which can result in superior code.
5165 @item -fprefetch-loop-arrays
5166 @opindex fprefetch-loop-arrays
5167 If supported by the target machine, generate instructions to prefetch
5168 memory to improve the performance of loops that access large arrays.
5170 This option may generate better or worse code; results are highly
5171 dependent on the structure of loops within the source code.
5173 Disabled at level @option{-Os}.
5176 @itemx -fno-peephole2
5177 @opindex fno-peephole
5178 @opindex fno-peephole2
5179 Disable any machine-specific peephole optimizations. The difference
5180 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
5181 are implemented in the compiler; some targets use one, some use the
5182 other, a few use both.
5184 @option{-fpeephole} is enabled by default.
5185 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5187 @item -fno-guess-branch-probability
5188 @opindex fno-guess-branch-probability
5189 Do not guess branch probabilities using heuristics.
5191 GCC will use heuristics to guess branch probabilities if they are
5192 not provided by profiling feedback (@option{-fprofile-arcs}). These
5193 heuristics are based on the control flow graph. If some branch probabilities
5194 are specified by @samp{__builtin_expect}, then the heuristics will be
5195 used to guess branch probabilities for the rest of the control flow graph,
5196 taking the @samp{__builtin_expect} info into account. The interactions
5197 between the heuristics and @samp{__builtin_expect} can be complex, and in
5198 some cases, it may be useful to disable the heuristics so that the effects
5199 of @samp{__builtin_expect} are easier to understand.
5201 The default is @option{-fguess-branch-probability} at levels
5202 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5204 @item -freorder-blocks
5205 @opindex freorder-blocks
5206 Reorder basic blocks in the compiled function in order to reduce number of
5207 taken branches and improve code locality.
5209 Enabled at levels @option{-O2}, @option{-O3}.
5211 @item -freorder-blocks-and-partition
5212 @opindex freorder-blocks-and-partition
5213 In addition to reordering basic blocks in the compiled function, in order
5214 to reduce number of taken branches, partitions hot and cold basic blocks
5215 into separate sections of the assembly and .o files, to improve
5216 paging and cache locality performance.
5218 This optimization is automatically turned off in the presence of
5219 exception handling, for linkonce sections, for functions with a user-defined
5220 section attribute and on any architecture that does not support named
5223 @item -freorder-functions
5224 @opindex freorder-functions
5225 Reorder functions in the object file in order to
5226 improve code locality. This is implemented by using special
5227 subsections @code{.text.hot} for most frequently executed functions and
5228 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
5229 the linker so object file format must support named sections and linker must
5230 place them in a reasonable way.
5232 Also profile feedback must be available in to make this option effective. See
5233 @option{-fprofile-arcs} for details.
5235 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5237 @item -fstrict-aliasing
5238 @opindex fstrict-aliasing
5239 Allows the compiler to assume the strictest aliasing rules applicable to
5240 the language being compiled. For C (and C++), this activates
5241 optimizations based on the type of expressions. In particular, an
5242 object of one type is assumed never to reside at the same address as an
5243 object of a different type, unless the types are almost the same. For
5244 example, an @code{unsigned int} can alias an @code{int}, but not a
5245 @code{void*} or a @code{double}. A character type may alias any other
5248 Pay special attention to code like this:
5261 The practice of reading from a different union member than the one most
5262 recently written to (called ``type-punning'') is common. Even with
5263 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
5264 is accessed through the union type. So, the code above will work as
5265 expected. However, this code might not:
5276 Every language that wishes to perform language-specific alias analysis
5277 should define a function that computes, given an @code{tree}
5278 node, an alias set for the node. Nodes in different alias sets are not
5279 allowed to alias. For an example, see the C front-end function
5280 @code{c_get_alias_set}.
5282 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5284 @item -falign-functions
5285 @itemx -falign-functions=@var{n}
5286 @opindex falign-functions
5287 Align the start of functions to the next power-of-two greater than
5288 @var{n}, skipping up to @var{n} bytes. For instance,
5289 @option{-falign-functions=32} aligns functions to the next 32-byte
5290 boundary, but @option{-falign-functions=24} would align to the next
5291 32-byte boundary only if this can be done by skipping 23 bytes or less.
5293 @option{-fno-align-functions} and @option{-falign-functions=1} are
5294 equivalent and mean that functions will not be aligned.
5296 Some assemblers only support this flag when @var{n} is a power of two;
5297 in that case, it is rounded up.
5299 If @var{n} is not specified or is zero, use a machine-dependent default.
5301 Enabled at levels @option{-O2}, @option{-O3}.
5303 @item -falign-labels
5304 @itemx -falign-labels=@var{n}
5305 @opindex falign-labels
5306 Align all branch targets to a power-of-two boundary, skipping up to
5307 @var{n} bytes like @option{-falign-functions}. This option can easily
5308 make code slower, because it must insert dummy operations for when the
5309 branch target is reached in the usual flow of the code.
5311 @option{-fno-align-labels} and @option{-falign-labels=1} are
5312 equivalent and mean that labels will not be aligned.
5314 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
5315 are greater than this value, then their values are used instead.
5317 If @var{n} is not specified or is zero, use a machine-dependent default
5318 which is very likely to be @samp{1}, meaning no alignment.
5320 Enabled at levels @option{-O2}, @option{-O3}.
5323 @itemx -falign-loops=@var{n}
5324 @opindex falign-loops
5325 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
5326 like @option{-falign-functions}. The hope is that the loop will be
5327 executed many times, which will make up for any execution of the dummy
5330 @option{-fno-align-loops} and @option{-falign-loops=1} are
5331 equivalent and mean that loops will not be aligned.
5333 If @var{n} is not specified or is zero, use a machine-dependent default.
5335 Enabled at levels @option{-O2}, @option{-O3}.
5338 @itemx -falign-jumps=@var{n}
5339 @opindex falign-jumps
5340 Align branch targets to a power-of-two boundary, for branch targets
5341 where the targets can only be reached by jumping, skipping up to @var{n}
5342 bytes like @option{-falign-functions}. In this case, no dummy operations
5345 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
5346 equivalent and mean that loops will not be aligned.
5348 If @var{n} is not specified or is zero, use a machine-dependent default.
5350 Enabled at levels @option{-O2}, @option{-O3}.
5352 @item -funit-at-a-time
5353 @opindex funit-at-a-time
5354 Parse the whole compilation unit before starting to produce code.
5355 This allows some extra optimizations to take place but consumes
5356 more memory (in general). There are some compatibility issues
5357 with @emph{unit-at-a-time} mode:
5360 enabling @emph{unit-at-a-time} mode may change the order
5361 in which functions, variables, and top-level @code{asm} statements
5362 are emitted, and will likely break code relying on some particular
5363 ordering. The majority of such top-level @code{asm} statements,
5364 though, can be replaced by @code{section} attributes. The
5365 @option{fno-toplevel-reorder} option may be used to keep the ordering
5366 used in the input file, at the cost of some optimizations.
5369 @emph{unit-at-a-time} mode removes unreferenced static variables
5370 and functions. This may result in undefined references
5371 when an @code{asm} statement refers directly to variables or functions
5372 that are otherwise unused. In that case either the variable/function
5373 shall be listed as an operand of the @code{asm} statement operand or,
5374 in the case of top-level @code{asm} statements the attribute @code{used}
5375 shall be used on the declaration.
5378 Static functions now can use non-standard passing conventions that
5379 may break @code{asm} statements calling functions directly. Again,
5380 attribute @code{used} will prevent this behavior.
5383 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
5384 but this scheme may not be supported by future releases of GCC@.
5386 Enabled at levels @option{-O2}, @option{-O3}.
5388 @item -fno-toplevel-reorder
5389 Do not reorder top-level functions, variables, and @code{asm}
5390 statements. Output them in the same order that they appear in the
5391 input file. When this option is used, unreferenced static variables
5392 will not be removed. This option is intended to support existing code
5393 which relies on a particular ordering. For new code, it is better to
5398 Constructs webs as commonly used for register allocation purposes and assign
5399 each web individual pseudo register. This allows the register allocation pass
5400 to operate on pseudos directly, but also strengthens several other optimization
5401 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
5402 however, make debugging impossible, since variables will no longer stay in a
5405 Enabled by default with @option{-funroll-loops}.
5407 @item -fwhole-program
5408 @opindex fwhole-program
5409 Assume that the current compilation unit represents whole program being
5410 compiled. All public functions and variables with the exception of @code{main}
5411 and those merged by attribute @code{externally_visible} become static functions
5412 and in a affect gets more aggressively optimized by interprocedural optimizers.
5413 While this option is equivalent to proper use of @code{static} keyword for
5414 programs consisting of single file, in combination with option
5415 @option{--combine} this flag can be used to compile most of smaller scale C
5416 programs since the functions and variables become local for the whole combined
5417 compilation unit, not for the single source file itself.
5420 @item -fno-cprop-registers
5421 @opindex fno-cprop-registers
5422 After register allocation and post-register allocation instruction splitting,
5423 we perform a copy-propagation pass to try to reduce scheduling dependencies
5424 and occasionally eliminate the copy.
5426 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5428 @item -fprofile-generate
5429 @opindex fprofile-generate
5431 Enable options usually used for instrumenting application to produce
5432 profile useful for later recompilation with profile feedback based
5433 optimization. You must use @option{-fprofile-generate} both when
5434 compiling and when linking your program.
5436 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
5439 @opindex fprofile-use
5440 Enable profile feedback directed optimizations, and optimizations
5441 generally profitable only with profile feedback available.
5443 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
5444 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
5448 The following options control compiler behavior regarding floating
5449 point arithmetic. These options trade off between speed and
5450 correctness. All must be specifically enabled.
5454 @opindex ffloat-store
5455 Do not store floating point variables in registers, and inhibit other
5456 options that might change whether a floating point value is taken from a
5459 @cindex floating point precision
5460 This option prevents undesirable excess precision on machines such as
5461 the 68000 where the floating registers (of the 68881) keep more
5462 precision than a @code{double} is supposed to have. Similarly for the
5463 x86 architecture. For most programs, the excess precision does only
5464 good, but a few programs rely on the precise definition of IEEE floating
5465 point. Use @option{-ffloat-store} for such programs, after modifying
5466 them to store all pertinent intermediate computations into variables.
5470 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5471 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5472 @option{-fno-rounding-math}, @option{-fno-signaling-nans}
5473 and @option{fcx-limited-range}.
5475 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5477 This option should never be turned on by any @option{-O} option since
5478 it can result in incorrect output for programs which depend on
5479 an exact implementation of IEEE or ISO rules/specifications for
5482 @item -fno-math-errno
5483 @opindex fno-math-errno
5484 Do not set ERRNO after calling math functions that are executed
5485 with a single instruction, e.g., sqrt. A program that relies on
5486 IEEE exceptions for math error handling may want to use this flag
5487 for speed while maintaining IEEE arithmetic compatibility.
5489 This option should never be turned on by any @option{-O} option since
5490 it can result in incorrect output for programs which depend on
5491 an exact implementation of IEEE or ISO rules/specifications for
5494 The default is @option{-fmath-errno}.
5496 On Darwin systems, the math library never sets @code{errno}. There is therefore
5497 no reason for the compiler to consider the possibility that it might,
5498 and @option{-fno-math-errno} is the default.
5500 @item -funsafe-math-optimizations
5501 @opindex funsafe-math-optimizations
5502 Allow optimizations for floating-point arithmetic that (a) assume
5503 that arguments and results are valid and (b) may violate IEEE or
5504 ANSI standards. When used at link-time, it may include libraries
5505 or startup files that change the default FPU control word or other
5506 similar optimizations.
5508 This option should never be turned on by any @option{-O} option since
5509 it can result in incorrect output for programs which depend on
5510 an exact implementation of IEEE or ISO rules/specifications for
5513 The default is @option{-fno-unsafe-math-optimizations}.
5515 @item -ffinite-math-only
5516 @opindex ffinite-math-only
5517 Allow optimizations for floating-point arithmetic that assume
5518 that arguments and results are not NaNs or +-Infs.
5520 This option should never be turned on by any @option{-O} option since
5521 it can result in incorrect output for programs which depend on
5522 an exact implementation of IEEE or ISO rules/specifications.
5524 The default is @option{-fno-finite-math-only}.
5526 @item -fno-trapping-math
5527 @opindex fno-trapping-math
5528 Compile code assuming that floating-point operations cannot generate
5529 user-visible traps. These traps include division by zero, overflow,
5530 underflow, inexact result and invalid operation. This option implies
5531 @option{-fno-signaling-nans}. Setting this option may allow faster
5532 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5534 This option should never be turned on by any @option{-O} option since
5535 it can result in incorrect output for programs which depend on
5536 an exact implementation of IEEE or ISO rules/specifications for
5539 The default is @option{-ftrapping-math}.
5541 @item -frounding-math
5542 @opindex frounding-math
5543 Disable transformations and optimizations that assume default floating
5544 point rounding behavior. This is round-to-zero for all floating point
5545 to integer conversions, and round-to-nearest for all other arithmetic
5546 truncations. This option should be specified for programs that change
5547 the FP rounding mode dynamically, or that may be executed with a
5548 non-default rounding mode. This option disables constant folding of
5549 floating point expressions at compile-time (which may be affected by
5550 rounding mode) and arithmetic transformations that are unsafe in the
5551 presence of sign-dependent rounding modes.
5553 The default is @option{-fno-rounding-math}.
5555 This option is experimental and does not currently guarantee to
5556 disable all GCC optimizations that are affected by rounding mode.
5557 Future versions of GCC may provide finer control of this setting
5558 using C99's @code{FENV_ACCESS} pragma. This command line option
5559 will be used to specify the default state for @code{FENV_ACCESS}.
5561 @item -frtl-abstract-sequences
5562 @opindex frtl-abstract-sequences
5563 It is a size optimization method. This option is to find identical
5564 sequences of code, which can be turned into pseudo-procedures and
5565 then replace all occurrences with calls to the newly created
5566 subroutine. It is kind of an opposite of @option{-finline-functions}.
5567 This optimization runs at RTL level.
5569 @item -fsignaling-nans
5570 @opindex fsignaling-nans
5571 Compile code assuming that IEEE signaling NaNs may generate user-visible
5572 traps during floating-point operations. Setting this option disables
5573 optimizations that may change the number of exceptions visible with
5574 signaling NaNs. This option implies @option{-ftrapping-math}.
5576 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5579 The default is @option{-fno-signaling-nans}.
5581 This option is experimental and does not currently guarantee to
5582 disable all GCC optimizations that affect signaling NaN behavior.
5584 @item -fsingle-precision-constant
5585 @opindex fsingle-precision-constant
5586 Treat floating point constant as single precision constant instead of
5587 implicitly converting it to double precision constant.
5589 @item -fcx-limited-range
5590 @itemx -fno-cx-limited-range
5591 @opindex fcx-limited-range
5592 @opindex fno-cx-limited-range
5593 When enabled, this option states that a range reduction step is not
5594 needed when performing complex division. The default is
5595 @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
5597 This option controls the default setting of the ISO C99
5598 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
5603 The following options control optimizations that may improve
5604 performance, but are not enabled by any @option{-O} options. This
5605 section includes experimental options that may produce broken code.
5608 @item -fbranch-probabilities
5609 @opindex fbranch-probabilities
5610 After running a program compiled with @option{-fprofile-arcs}
5611 (@pxref{Debugging Options,, Options for Debugging Your Program or
5612 @command{gcc}}), you can compile it a second time using
5613 @option{-fbranch-probabilities}, to improve optimizations based on
5614 the number of times each branch was taken. When the program
5615 compiled with @option{-fprofile-arcs} exits it saves arc execution
5616 counts to a file called @file{@var{sourcename}.gcda} for each source
5617 file The information in this data file is very dependent on the
5618 structure of the generated code, so you must use the same source code
5619 and the same optimization options for both compilations.
5621 With @option{-fbranch-probabilities}, GCC puts a
5622 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5623 These can be used to improve optimization. Currently, they are only
5624 used in one place: in @file{reorg.c}, instead of guessing which path a
5625 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5626 exactly determine which path is taken more often.
5628 @item -fprofile-values
5629 @opindex fprofile-values
5630 If combined with @option{-fprofile-arcs}, it adds code so that some
5631 data about values of expressions in the program is gathered.
5633 With @option{-fbranch-probabilities}, it reads back the data gathered
5634 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5635 notes to instructions for their later usage in optimizations.
5637 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5641 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5642 a code to gather information about values of expressions.
5644 With @option{-fbranch-probabilities}, it reads back the data gathered
5645 and actually performs the optimizations based on them.
5646 Currently the optimizations include specialization of division operation
5647 using the knowledge about the value of the denominator.
5649 @item -frename-registers
5650 @opindex frename-registers
5651 Attempt to avoid false dependencies in scheduled code by making use
5652 of registers left over after register allocation. This optimization
5653 will most benefit processors with lots of registers. Depending on the
5654 debug information format adopted by the target, however, it can
5655 make debugging impossible, since variables will no longer stay in
5656 a ``home register''.
5658 Enabled by default with @option{-funroll-loops}.
5662 Perform tail duplication to enlarge superblock size. This transformation
5663 simplifies the control flow of the function allowing other optimizations to do
5666 Enabled with @option{-fprofile-use}.
5668 @item -funroll-loops
5669 @opindex funroll-loops
5670 Unroll loops whose number of iterations can be determined at compile time or
5671 upon entry to the loop. @option{-funroll-loops} implies
5672 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
5673 It also turns on complete loop peeling (i.e.@: complete removal of loops with
5674 small constant number of iterations). This option makes code larger, and may
5675 or may not make it run faster.
5677 Enabled with @option{-fprofile-use}.
5679 @item -funroll-all-loops
5680 @opindex funroll-all-loops
5681 Unroll all loops, even if their number of iterations is uncertain when
5682 the loop is entered. This usually makes programs run more slowly.
5683 @option{-funroll-all-loops} implies the same options as
5684 @option{-funroll-loops}.
5687 @opindex fpeel-loops
5688 Peels the loops for that there is enough information that they do not
5689 roll much (from profile feedback). It also turns on complete loop peeling
5690 (i.e.@: complete removal of loops with small constant number of iterations).
5692 Enabled with @option{-fprofile-use}.
5694 @item -fmove-loop-invariants
5695 @opindex fmove-loop-invariants
5696 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
5697 at level @option{-O1}
5699 @item -funswitch-loops
5700 @opindex funswitch-loops
5701 Move branches with loop invariant conditions out of the loop, with duplicates
5702 of the loop on both branches (modified according to result of the condition).
5704 @item -ffunction-sections
5705 @itemx -fdata-sections
5706 @opindex ffunction-sections
5707 @opindex fdata-sections
5708 Place each function or data item into its own section in the output
5709 file if the target supports arbitrary sections. The name of the
5710 function or the name of the data item determines the section's name
5713 Use these options on systems where the linker can perform optimizations
5714 to improve locality of reference in the instruction space. Most systems
5715 using the ELF object format and SPARC processors running Solaris 2 have
5716 linkers with such optimizations. AIX may have these optimizations in
5719 Only use these options when there are significant benefits from doing
5720 so. When you specify these options, the assembler and linker will
5721 create larger object and executable files and will also be slower.
5722 You will not be able to use @code{gprof} on all systems if you
5723 specify this option and you may have problems with debugging if
5724 you specify both this option and @option{-g}.
5726 @item -fbranch-target-load-optimize
5727 @opindex fbranch-target-load-optimize
5728 Perform branch target register load optimization before prologue / epilogue
5730 The use of target registers can typically be exposed only during reload,
5731 thus hoisting loads out of loops and doing inter-block scheduling needs
5732 a separate optimization pass.
5734 @item -fbranch-target-load-optimize2
5735 @opindex fbranch-target-load-optimize2
5736 Perform branch target register load optimization after prologue / epilogue
5739 @item -fbtr-bb-exclusive
5740 @opindex fbtr-bb-exclusive
5741 When performing branch target register load optimization, don't reuse
5742 branch target registers in within any basic block.
5744 @item -fstack-protector
5745 Emit extra code to check for buffer overflows, such as stack smashing
5746 attacks. This is done by adding a guard variable to functions with
5747 vulnerable objects. This includes functions that call alloca, and
5748 functions with buffers larger than 8 bytes. The guards are initialized
5749 when a function is entered and then checked when the function exits.
5750 If a guard check fails, an error message is printed and the program exits.
5752 @item -fstack-protector-all
5753 Like @option{-fstack-protector} except that all functions are protected.
5755 @item -fsection-anchors
5756 @opindex fsection-anchors
5757 Try to reduce the number of symbolic address calculations by using
5758 shared ``anchor'' symbols to address nearby objects. This transformation
5759 can help to reduce the number of GOT entries and GOT accesses on some
5762 For example, the implementation of the following function @code{foo}:
5766 int foo (void) @{ return a + b + c; @}
5769 would usually calculate the addresses of all three variables, but if you
5770 compile it with @option{-fsection-anchors}, it will access the variables
5771 from a common anchor point instead. The effect is similar to the
5772 following pseudocode (which isn't valid C):
5777 register int *xr = &x;
5778 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
5782 Not all targets support this option.
5784 @item --param @var{name}=@var{value}
5786 In some places, GCC uses various constants to control the amount of
5787 optimization that is done. For example, GCC will not inline functions
5788 that contain more that a certain number of instructions. You can
5789 control some of these constants on the command-line using the
5790 @option{--param} option.
5792 The names of specific parameters, and the meaning of the values, are
5793 tied to the internals of the compiler, and are subject to change
5794 without notice in future releases.
5796 In each case, the @var{value} is an integer. The allowable choices for
5797 @var{name} are given in the following table:
5800 @item salias-max-implicit-fields
5801 The maximum number of fields in a variable without direct
5802 structure accesses for which structure aliasing will consider trying
5803 to track each field. The default is 5
5805 @item salias-max-array-elements
5806 The maximum number of elements an array can have and its elements
5807 still be tracked individually by structure aliasing. The default is 4
5809 @item sra-max-structure-size
5810 The maximum structure size, in bytes, at which the scalar replacement
5811 of aggregates (SRA) optimization will perform block copies. The
5812 default value, 0, implies that GCC will select the most appropriate
5815 @item sra-field-structure-ratio
5816 The threshold ratio (as a percentage) between instantiated fields and
5817 the complete structure size. We say that if the ratio of the number
5818 of bytes in instantiated fields to the number of bytes in the complete
5819 structure exceeds this parameter, then block copies are not used. The
5822 @item max-crossjump-edges
5823 The maximum number of incoming edges to consider for crossjumping.
5824 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5825 the number of edges incoming to each block. Increasing values mean
5826 more aggressive optimization, making the compile time increase with
5827 probably small improvement in executable size.
5829 @item min-crossjump-insns
5830 The minimum number of instructions which must be matched at the end
5831 of two blocks before crossjumping will be performed on them. This
5832 value is ignored in the case where all instructions in the block being
5833 crossjumped from are matched. The default value is 5.
5835 @item max-grow-copy-bb-insns
5836 The maximum code size expansion factor when copying basic blocks
5837 instead of jumping. The expansion is relative to a jump instruction.
5838 The default value is 8.
5840 @item max-goto-duplication-insns
5841 The maximum number of instructions to duplicate to a block that jumps
5842 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
5843 passes, GCC factors computed gotos early in the compilation process,
5844 and unfactors them as late as possible. Only computed jumps at the
5845 end of a basic blocks with no more than max-goto-duplication-insns are
5846 unfactored. The default value is 8.
5848 @item max-delay-slot-insn-search
5849 The maximum number of instructions to consider when looking for an
5850 instruction to fill a delay slot. If more than this arbitrary number of
5851 instructions is searched, the time savings from filling the delay slot
5852 will be minimal so stop searching. Increasing values mean more
5853 aggressive optimization, making the compile time increase with probably
5854 small improvement in executable run time.
5856 @item max-delay-slot-live-search
5857 When trying to fill delay slots, the maximum number of instructions to
5858 consider when searching for a block with valid live register
5859 information. Increasing this arbitrarily chosen value means more
5860 aggressive optimization, increasing the compile time. This parameter
5861 should be removed when the delay slot code is rewritten to maintain the
5864 @item max-gcse-memory
5865 The approximate maximum amount of memory that will be allocated in
5866 order to perform the global common subexpression elimination
5867 optimization. If more memory than specified is required, the
5868 optimization will not be done.
5870 @item max-gcse-passes
5871 The maximum number of passes of GCSE to run. The default is 1.
5873 @item max-pending-list-length
5874 The maximum number of pending dependencies scheduling will allow
5875 before flushing the current state and starting over. Large functions
5876 with few branches or calls can create excessively large lists which
5877 needlessly consume memory and resources.
5879 @item max-inline-insns-single
5880 Several parameters control the tree inliner used in gcc.
5881 This number sets the maximum number of instructions (counted in GCC's
5882 internal representation) in a single function that the tree inliner
5883 will consider for inlining. This only affects functions declared
5884 inline and methods implemented in a class declaration (C++).
5885 The default value is 450.
5887 @item max-inline-insns-auto
5888 When you use @option{-finline-functions} (included in @option{-O3}),
5889 a lot of functions that would otherwise not be considered for inlining
5890 by the compiler will be investigated. To those functions, a different
5891 (more restrictive) limit compared to functions declared inline can
5893 The default value is 90.
5895 @item large-function-insns
5896 The limit specifying really large functions. For functions larger than this
5897 limit after inlining inlining is constrained by
5898 @option{--param large-function-growth}. This parameter is useful primarily
5899 to avoid extreme compilation time caused by non-linear algorithms used by the
5901 This parameter is ignored when @option{-funit-at-a-time} is not used.
5902 The default value is 2700.
5904 @item large-function-growth
5905 Specifies maximal growth of large function caused by inlining in percents.
5906 This parameter is ignored when @option{-funit-at-a-time} is not used.
5907 The default value is 100 which limits large function growth to 2.0 times
5910 @item large-unit-insns
5911 The limit specifying large translation unit. Growth caused by inlining of
5912 units larger than this limit is limited by @option{--param inline-unit-growth}.
5913 For small units this might be too tight (consider unit consisting of function A
5914 that is inline and B that just calls A three time. If B is small relative to
5915 A, the growth of unit is 300\% and yet such inlining is very sane. For very
5916 large units consisting of small inlininable functions however the overall unit
5917 growth limit is needed to avoid exponential explosion of code size. Thus for
5918 smaller units, the size is increased to @option{--param large-unit-insns}
5919 before applying @option{--param inline-unit-growth}. The default is 10000
5921 @item inline-unit-growth
5922 Specifies maximal overall growth of the compilation unit caused by inlining.
5923 This parameter is ignored when @option{-funit-at-a-time} is not used.
5924 The default value is 50 which limits unit growth to 1.5 times the original
5927 @item max-inline-insns-recursive
5928 @itemx max-inline-insns-recursive-auto
5929 Specifies maximum number of instructions out-of-line copy of self recursive inline
5930 function can grow into by performing recursive inlining.
5932 For functions declared inline @option{--param max-inline-insns-recursive} is
5933 taken into acount. For function not declared inline, recursive inlining
5934 happens only when @option{-finline-functions} (included in @option{-O3}) is
5935 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5936 default value is 450.
5938 @item max-inline-recursive-depth
5939 @itemx max-inline-recursive-depth-auto
5940 Specifies maximum recursion depth used by the recursive inlining.
5942 For functions declared inline @option{--param max-inline-recursive-depth} is
5943 taken into acount. For function not declared inline, recursive inlining
5944 happens only when @option{-finline-functions} (included in @option{-O3}) is
5945 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5946 default value is 450.
5948 @item min-inline-recursive-probability
5949 Recursive inlining is profitable only for function having deep recursion
5950 in average and can hurt for function having little recursion depth by
5951 increasing the prologue size or complexity of function body to other
5954 When profile feedback is available (see @option{-fprofile-generate}) the actual
5955 recursion depth can be guessed from probability that function will recurse via
5956 given call expression. This parameter limits inlining only to call expression
5957 whose probability exceeds given threshold (in percents). The default value is
5960 @item inline-call-cost
5961 Specify cost of call instruction relative to simple arithmetics operations
5962 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
5963 functions and at the same time increases size of leaf function that is believed to
5964 reduce function size by being inlined. In effect it increases amount of
5965 inlining for code having large abstraction penalty (many functions that just
5966 pass the arguments to other functions) and decrease inlining for code with low
5967 abstraction penalty. The default value is 16.
5969 @item max-unrolled-insns
5970 The maximum number of instructions that a loop should have if that loop
5971 is unrolled, and if the loop is unrolled, it determines how many times
5972 the loop code is unrolled.
5974 @item max-average-unrolled-insns
5975 The maximum number of instructions biased by probabilities of their execution
5976 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5977 it determines how many times the loop code is unrolled.
5979 @item max-unroll-times
5980 The maximum number of unrollings of a single loop.
5982 @item max-peeled-insns
5983 The maximum number of instructions that a loop should have if that loop
5984 is peeled, and if the loop is peeled, it determines how many times
5985 the loop code is peeled.
5987 @item max-peel-times
5988 The maximum number of peelings of a single loop.
5990 @item max-completely-peeled-insns
5991 The maximum number of insns of a completely peeled loop.
5993 @item max-completely-peel-times
5994 The maximum number of iterations of a loop to be suitable for complete peeling.
5996 @item max-unswitch-insns
5997 The maximum number of insns of an unswitched loop.
5999 @item max-unswitch-level
6000 The maximum number of branches unswitched in a single loop.
6003 The minimum cost of an expensive expression in the loop invariant motion.
6005 @item iv-consider-all-candidates-bound
6006 Bound on number of candidates for induction variables below that
6007 all candidates are considered for each use in induction variable
6008 optimizations. Only the most relevant candidates are considered
6009 if there are more candidates, to avoid quadratic time complexity.
6011 @item iv-max-considered-uses
6012 The induction variable optimizations give up on loops that contain more
6013 induction variable uses.
6015 @item iv-always-prune-cand-set-bound
6016 If number of candidates in the set is smaller than this value,
6017 we always try to remove unnecessary ivs from the set during its
6018 optimization when a new iv is added to the set.
6020 @item scev-max-expr-size
6021 Bound on size of expressions used in the scalar evolutions analyzer.
6022 Large expressions slow the analyzer.
6024 @item vect-max-version-checks
6025 The maximum number of runtime checks that can be performed when doing
6026 loop versioning in the vectorizer. See option ftree-vect-loop-version
6027 for more information.
6029 @item max-iterations-to-track
6031 The maximum number of iterations of a loop the brute force algorithm
6032 for analysis of # of iterations of the loop tries to evaluate.
6034 @item hot-bb-count-fraction
6035 Select fraction of the maximal count of repetitions of basic block in program
6036 given basic block needs to have to be considered hot.
6038 @item hot-bb-frequency-fraction
6039 Select fraction of the maximal frequency of executions of basic block in
6040 function given basic block needs to have to be considered hot
6042 @item max-predicted-iterations
6043 The maximum number of loop iterations we predict statically. This is useful
6044 in cases where function contain single loop with known bound and other loop
6045 with unknown. We predict the known number of iterations correctly, while
6046 the unknown number of iterations average to roughly 10. This means that the
6047 loop without bounds would appear artificially cold relative to the other one.
6049 @item tracer-dynamic-coverage
6050 @itemx tracer-dynamic-coverage-feedback
6052 This value is used to limit superblock formation once the given percentage of
6053 executed instructions is covered. This limits unnecessary code size
6056 The @option{tracer-dynamic-coverage-feedback} is used only when profile
6057 feedback is available. The real profiles (as opposed to statically estimated
6058 ones) are much less balanced allowing the threshold to be larger value.
6060 @item tracer-max-code-growth
6061 Stop tail duplication once code growth has reached given percentage. This is
6062 rather hokey argument, as most of the duplicates will be eliminated later in
6063 cross jumping, so it may be set to much higher values than is the desired code
6066 @item tracer-min-branch-ratio
6068 Stop reverse growth when the reverse probability of best edge is less than this
6069 threshold (in percent).
6071 @item tracer-min-branch-ratio
6072 @itemx tracer-min-branch-ratio-feedback
6074 Stop forward growth if the best edge do have probability lower than this
6077 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
6078 compilation for profile feedback and one for compilation without. The value
6079 for compilation with profile feedback needs to be more conservative (higher) in
6080 order to make tracer effective.
6082 @item max-cse-path-length
6084 Maximum number of basic blocks on path that cse considers. The default is 10.
6087 The maximum instructions CSE process before flushing. The default is 1000.
6089 @item global-var-threshold
6091 Counts the number of function calls (@var{n}) and the number of
6092 call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a
6093 single artificial variable will be created to represent all the
6094 call-clobbered variables at function call sites. This artificial
6095 variable will then be made to alias every call-clobbered variable.
6096 (done as @code{int * size_t} on the host machine; beware overflow).
6098 @item max-aliased-vops
6100 Maximum number of virtual operands allowed to represent aliases
6101 before triggering the alias grouping heuristic. Alias grouping
6102 reduces compile times and memory consumption needed for aliasing at
6103 the expense of precision loss in alias information.
6105 @item ggc-min-expand
6107 GCC uses a garbage collector to manage its own memory allocation. This
6108 parameter specifies the minimum percentage by which the garbage
6109 collector's heap should be allowed to expand between collections.
6110 Tuning this may improve compilation speed; it has no effect on code
6113 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
6114 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
6115 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
6116 GCC is not able to calculate RAM on a particular platform, the lower
6117 bound of 30% is used. Setting this parameter and
6118 @option{ggc-min-heapsize} to zero causes a full collection to occur at
6119 every opportunity. This is extremely slow, but can be useful for
6122 @item ggc-min-heapsize
6124 Minimum size of the garbage collector's heap before it begins bothering
6125 to collect garbage. The first collection occurs after the heap expands
6126 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
6127 tuning this may improve compilation speed, and has no effect on code
6130 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
6131 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
6132 with a lower bound of 4096 (four megabytes) and an upper bound of
6133 131072 (128 megabytes). If GCC is not able to calculate RAM on a
6134 particular platform, the lower bound is used. Setting this parameter
6135 very large effectively disables garbage collection. Setting this
6136 parameter and @option{ggc-min-expand} to zero causes a full collection
6137 to occur at every opportunity.
6139 @item max-reload-search-insns
6140 The maximum number of instruction reload should look backward for equivalent
6141 register. Increasing values mean more aggressive optimization, making the
6142 compile time increase with probably slightly better performance. The default
6145 @item max-cselib-memory-location
6146 The maximum number of memory locations cselib should take into acount.
6147 Increasing values mean more aggressive optimization, making the compile time
6148 increase with probably slightly better performance. The default value is 500.
6150 @item max-flow-memory-location
6151 Similar as @option{max-cselib-memory-location} but for dataflow liveness.
6152 The default value is 100.
6154 @item reorder-blocks-duplicate
6155 @itemx reorder-blocks-duplicate-feedback
6157 Used by basic block reordering pass to decide whether to use unconditional
6158 branch or duplicate the code on its destination. Code is duplicated when its
6159 estimated size is smaller than this value multiplied by the estimated size of
6160 unconditional jump in the hot spots of the program.
6162 The @option{reorder-block-duplicate-feedback} is used only when profile
6163 feedback is available and may be set to higher values than
6164 @option{reorder-block-duplicate} since information about the hot spots is more
6167 @item max-sched-region-blocks
6168 The maximum number of blocks in a region to be considered for
6169 interblock scheduling. The default value is 10.
6171 @item max-sched-region-insns
6172 The maximum number of insns in a region to be considered for
6173 interblock scheduling. The default value is 100.
6176 The minimum probability (in percents) of reaching a source block
6177 for interblock speculative scheduling. The default value is 40.
6179 @item max-last-value-rtl
6181 The maximum size measured as number of RTLs that can be recorded in an expression
6182 in combiner for a pseudo register as last known value of that register. The default
6185 @item integer-share-limit
6186 Small integer constants can use a shared data structure, reducing the
6187 compiler's memory usage and increasing its speed. This sets the maximum
6188 value of a shared integer constant's. The default value is 256.
6190 @item min-virtual-mappings
6191 Specifies the minimum number of virtual mappings in the incremental
6192 SSA updater that should be registered to trigger the virtual mappings
6193 heuristic defined by virtual-mappings-ratio. The default value is
6196 @item virtual-mappings-ratio
6197 If the number of virtual mappings is virtual-mappings-ratio bigger
6198 than the number of virtual symbols to be updated, then the incremental
6199 SSA updater switches to a full update for those symbols. The default
6202 @item ssp-buffer-size
6203 The minimum size of buffers (i.e. arrays) that will receive stack smashing
6204 protection when @option{-fstack-protection} is used.
6206 @item max-jump-thread-duplication-stmts
6207 Maximum number of statements allowed in a block that needs to be
6208 duplicated when threading jumps.
6210 @item max-fields-for-field-sensitive
6211 Maximum number of fields in a structure we will treat in
6212 a field sensitive manner during pointer analysis.
6217 @node Preprocessor Options
6218 @section Options Controlling the Preprocessor
6219 @cindex preprocessor options
6220 @cindex options, preprocessor
6222 These options control the C preprocessor, which is run on each C source
6223 file before actual compilation.
6225 If you use the @option{-E} option, nothing is done except preprocessing.
6226 Some of these options make sense only together with @option{-E} because
6227 they cause the preprocessor output to be unsuitable for actual
6232 You can use @option{-Wp,@var{option}} to bypass the compiler driver
6233 and pass @var{option} directly through to the preprocessor. If
6234 @var{option} contains commas, it is split into multiple options at the
6235 commas. However, many options are modified, translated or interpreted
6236 by the compiler driver before being passed to the preprocessor, and
6237 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
6238 interface is undocumented and subject to change, so whenever possible
6239 you should avoid using @option{-Wp} and let the driver handle the
6242 @item -Xpreprocessor @var{option}
6243 @opindex preprocessor
6244 Pass @var{option} as an option to the preprocessor. You can use this to
6245 supply system-specific preprocessor options which GCC does not know how to
6248 If you want to pass an option that takes an argument, you must use
6249 @option{-Xpreprocessor} twice, once for the option and once for the argument.
6252 @include cppopts.texi
6254 @node Assembler Options
6255 @section Passing Options to the Assembler
6257 @c prevent bad page break with this line
6258 You can pass options to the assembler.
6261 @item -Wa,@var{option}
6263 Pass @var{option} as an option to the assembler. If @var{option}
6264 contains commas, it is split into multiple options at the commas.
6266 @item -Xassembler @var{option}
6268 Pass @var{option} as an option to the assembler. You can use this to
6269 supply system-specific assembler options which GCC does not know how to
6272 If you want to pass an option that takes an argument, you must use
6273 @option{-Xassembler} twice, once for the option and once for the argument.
6278 @section Options for Linking
6279 @cindex link options
6280 @cindex options, linking
6282 These options come into play when the compiler links object files into
6283 an executable output file. They are meaningless if the compiler is
6284 not doing a link step.
6288 @item @var{object-file-name}
6289 A file name that does not end in a special recognized suffix is
6290 considered to name an object file or library. (Object files are
6291 distinguished from libraries by the linker according to the file
6292 contents.) If linking is done, these object files are used as input
6301 If any of these options is used, then the linker is not run, and
6302 object file names should not be used as arguments. @xref{Overall
6306 @item -l@var{library}
6307 @itemx -l @var{library}
6309 Search the library named @var{library} when linking. (The second
6310 alternative with the library as a separate argument is only for
6311 POSIX compliance and is not recommended.)
6313 It makes a difference where in the command you write this option; the
6314 linker searches and processes libraries and object files in the order they
6315 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
6316 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
6317 to functions in @samp{z}, those functions may not be loaded.
6319 The linker searches a standard list of directories for the library,
6320 which is actually a file named @file{lib@var{library}.a}. The linker
6321 then uses this file as if it had been specified precisely by name.
6323 The directories searched include several standard system directories
6324 plus any that you specify with @option{-L}.
6326 Normally the files found this way are library files---archive files
6327 whose members are object files. The linker handles an archive file by
6328 scanning through it for members which define symbols that have so far
6329 been referenced but not defined. But if the file that is found is an
6330 ordinary object file, it is linked in the usual fashion. The only
6331 difference between using an @option{-l} option and specifying a file name
6332 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
6333 and searches several directories.
6337 You need this special case of the @option{-l} option in order to
6338 link an Objective-C or Objective-C++ program.
6341 @opindex nostartfiles
6342 Do not use the standard system startup files when linking.
6343 The standard system libraries are used normally, unless @option{-nostdlib}
6344 or @option{-nodefaultlibs} is used.
6346 @item -nodefaultlibs
6347 @opindex nodefaultlibs
6348 Do not use the standard system libraries when linking.
6349 Only the libraries you specify will be passed to the linker.
6350 The standard startup files are used normally, unless @option{-nostartfiles}
6351 is used. The compiler may generate calls to @code{memcmp},
6352 @code{memset}, @code{memcpy} and @code{memmove}.
6353 These entries are usually resolved by entries in
6354 libc. These entry points should be supplied through some other
6355 mechanism when this option is specified.
6359 Do not use the standard system startup files or libraries when linking.
6360 No startup files and only the libraries you specify will be passed to
6361 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
6362 @code{memcpy} and @code{memmove}.
6363 These entries are usually resolved by entries in
6364 libc. These entry points should be supplied through some other
6365 mechanism when this option is specified.
6367 @cindex @option{-lgcc}, use with @option{-nostdlib}
6368 @cindex @option{-nostdlib} and unresolved references
6369 @cindex unresolved references and @option{-nostdlib}
6370 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
6371 @cindex @option{-nodefaultlibs} and unresolved references
6372 @cindex unresolved references and @option{-nodefaultlibs}
6373 One of the standard libraries bypassed by @option{-nostdlib} and
6374 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
6375 that GCC uses to overcome shortcomings of particular machines, or special
6376 needs for some languages.
6377 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
6378 Collection (GCC) Internals},
6379 for more discussion of @file{libgcc.a}.)
6380 In most cases, you need @file{libgcc.a} even when you want to avoid
6381 other standard libraries. In other words, when you specify @option{-nostdlib}
6382 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
6383 This ensures that you have no unresolved references to internal GCC
6384 library subroutines. (For example, @samp{__main}, used to ensure C++
6385 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
6386 GNU Compiler Collection (GCC) Internals}.)
6390 Produce a position independent executable on targets which support it.
6391 For predictable results, you must also specify the same set of options
6392 that were used to generate code (@option{-fpie}, @option{-fPIE},
6393 or model suboptions) when you specify this option.
6397 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
6398 that support it. This instructs the linker to add all symbols, not
6399 only used ones, to the dynamic symbol table. This option is needed
6400 for some uses of @code{dlopen} or to allow obtaining backtraces
6401 from within a program.
6405 Remove all symbol table and relocation information from the executable.
6409 On systems that support dynamic linking, this prevents linking with the shared
6410 libraries. On other systems, this option has no effect.
6414 Produce a shared object which can then be linked with other objects to
6415 form an executable. Not all systems support this option. For predictable
6416 results, you must also specify the same set of options that were used to
6417 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
6418 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
6419 needs to build supplementary stub code for constructors to work. On
6420 multi-libbed systems, @samp{gcc -shared} must select the correct support
6421 libraries to link against. Failing to supply the correct flags may lead
6422 to subtle defects. Supplying them in cases where they are not necessary
6425 @item -shared-libgcc
6426 @itemx -static-libgcc
6427 @opindex shared-libgcc
6428 @opindex static-libgcc
6429 On systems that provide @file{libgcc} as a shared library, these options
6430 force the use of either the shared or static version respectively.
6431 If no shared version of @file{libgcc} was built when the compiler was
6432 configured, these options have no effect.
6434 There are several situations in which an application should use the
6435 shared @file{libgcc} instead of the static version. The most common
6436 of these is when the application wishes to throw and catch exceptions
6437 across different shared libraries. In that case, each of the libraries
6438 as well as the application itself should use the shared @file{libgcc}.
6440 Therefore, the G++ and GCJ drivers automatically add
6441 @option{-shared-libgcc} whenever you build a shared library or a main
6442 executable, because C++ and Java programs typically use exceptions, so
6443 this is the right thing to do.
6445 If, instead, you use the GCC driver to create shared libraries, you may
6446 find that they will not always be linked with the shared @file{libgcc}.
6447 If GCC finds, at its configuration time, that you have a non-GNU linker
6448 or a GNU linker that does not support option @option{--eh-frame-hdr},
6449 it will link the shared version of @file{libgcc} into shared libraries
6450 by default. Otherwise, it will take advantage of the linker and optimize
6451 away the linking with the shared version of @file{libgcc}, linking with
6452 the static version of libgcc by default. This allows exceptions to
6453 propagate through such shared libraries, without incurring relocation
6454 costs at library load time.
6456 However, if a library or main executable is supposed to throw or catch
6457 exceptions, you must link it using the G++ or GCJ driver, as appropriate
6458 for the languages used in the program, or using the option
6459 @option{-shared-libgcc}, such that it is linked with the shared
6464 Bind references to global symbols when building a shared object. Warn
6465 about any unresolved references (unless overridden by the link editor
6466 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
6469 @item -Xlinker @var{option}
6471 Pass @var{option} as an option to the linker. You can use this to
6472 supply system-specific linker options which GCC does not know how to
6475 If you want to pass an option that takes an argument, you must use
6476 @option{-Xlinker} twice, once for the option and once for the argument.
6477 For example, to pass @option{-assert definitions}, you must write
6478 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
6479 @option{-Xlinker "-assert definitions"}, because this passes the entire
6480 string as a single argument, which is not what the linker expects.
6482 @item -Wl,@var{option}
6484 Pass @var{option} as an option to the linker. If @var{option} contains
6485 commas, it is split into multiple options at the commas.
6487 @item -u @var{symbol}
6489 Pretend the symbol @var{symbol} is undefined, to force linking of
6490 library modules to define it. You can use @option{-u} multiple times with
6491 different symbols to force loading of additional library modules.
6494 @node Directory Options
6495 @section Options for Directory Search
6496 @cindex directory options
6497 @cindex options, directory search
6500 These options specify directories to search for header files, for
6501 libraries and for parts of the compiler:
6506 Add the directory @var{dir} to the head of the list of directories to be
6507 searched for header files. This can be used to override a system header
6508 file, substituting your own version, since these directories are
6509 searched before the system header file directories. However, you should
6510 not use this option to add directories that contain vendor-supplied
6511 system header files (use @option{-isystem} for that). If you use more than
6512 one @option{-I} option, the directories are scanned in left-to-right
6513 order; the standard system directories come after.
6515 If a standard system include directory, or a directory specified with
6516 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
6517 option will be ignored. The directory will still be searched but as a
6518 system directory at its normal position in the system include chain.
6519 This is to ensure that GCC's procedure to fix buggy system headers and
6520 the ordering for the include_next directive are not inadvertently changed.
6521 If you really need to change the search order for system directories,
6522 use the @option{-nostdinc} and/or @option{-isystem} options.
6524 @item -iquote@var{dir}
6526 Add the directory @var{dir} to the head of the list of directories to
6527 be searched for header files only for the case of @samp{#include
6528 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
6529 otherwise just like @option{-I}.
6533 Add directory @var{dir} to the list of directories to be searched
6536 @item -B@var{prefix}
6538 This option specifies where to find the executables, libraries,
6539 include files, and data files of the compiler itself.
6541 The compiler driver program runs one or more of the subprograms
6542 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
6543 @var{prefix} as a prefix for each program it tries to run, both with and
6544 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
6546 For each subprogram to be run, the compiler driver first tries the
6547 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
6548 was not specified, the driver tries two standard prefixes, which are
6549 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
6550 those results in a file name that is found, the unmodified program
6551 name is searched for using the directories specified in your
6552 @env{PATH} environment variable.
6554 The compiler will check to see if the path provided by the @option{-B}
6555 refers to a directory, and if necessary it will add a directory
6556 separator character at the end of the path.
6558 @option{-B} prefixes that effectively specify directory names also apply
6559 to libraries in the linker, because the compiler translates these
6560 options into @option{-L} options for the linker. They also apply to
6561 includes files in the preprocessor, because the compiler translates these
6562 options into @option{-isystem} options for the preprocessor. In this case,
6563 the compiler appends @samp{include} to the prefix.
6565 The run-time support file @file{libgcc.a} can also be searched for using
6566 the @option{-B} prefix, if needed. If it is not found there, the two
6567 standard prefixes above are tried, and that is all. The file is left
6568 out of the link if it is not found by those means.
6570 Another way to specify a prefix much like the @option{-B} prefix is to use
6571 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
6574 As a special kludge, if the path provided by @option{-B} is
6575 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
6576 9, then it will be replaced by @file{[dir/]include}. This is to help
6577 with boot-strapping the compiler.
6579 @item -specs=@var{file}
6581 Process @var{file} after the compiler reads in the standard @file{specs}
6582 file, in order to override the defaults that the @file{gcc} driver
6583 program uses when determining what switches to pass to @file{cc1},
6584 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
6585 @option{-specs=@var{file}} can be specified on the command line, and they
6586 are processed in order, from left to right.
6588 @item --sysroot=@var{dir}
6590 Use @var{dir} as the logical root directory for headers and libraries.
6591 For example, if the compiler would normally search for headers in
6592 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
6593 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
6595 If you use both this option and the @option{-isysroot} option, then
6596 the @option{--sysroot} option will apply to libraries, but the
6597 @option{-isysroot} option will apply to header files.
6599 The GNU linker (beginning with version 2.16) has the necessary support
6600 for this option. If your linker does not support this option, the
6601 header file aspect of @option{--sysroot} will still work, but the
6602 library aspect will not.
6606 This option has been deprecated. Please use @option{-iquote} instead for
6607 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
6608 Any directories you specify with @option{-I} options before the @option{-I-}
6609 option are searched only for the case of @samp{#include "@var{file}"};
6610 they are not searched for @samp{#include <@var{file}>}.
6612 If additional directories are specified with @option{-I} options after
6613 the @option{-I-}, these directories are searched for all @samp{#include}
6614 directives. (Ordinarily @emph{all} @option{-I} directories are used
6617 In addition, the @option{-I-} option inhibits the use of the current
6618 directory (where the current input file came from) as the first search
6619 directory for @samp{#include "@var{file}"}. There is no way to
6620 override this effect of @option{-I-}. With @option{-I.} you can specify
6621 searching the directory which was current when the compiler was
6622 invoked. That is not exactly the same as what the preprocessor does
6623 by default, but it is often satisfactory.
6625 @option{-I-} does not inhibit the use of the standard system directories
6626 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6633 @section Specifying subprocesses and the switches to pass to them
6636 @command{gcc} is a driver program. It performs its job by invoking a
6637 sequence of other programs to do the work of compiling, assembling and
6638 linking. GCC interprets its command-line parameters and uses these to
6639 deduce which programs it should invoke, and which command-line options
6640 it ought to place on their command lines. This behavior is controlled
6641 by @dfn{spec strings}. In most cases there is one spec string for each
6642 program that GCC can invoke, but a few programs have multiple spec
6643 strings to control their behavior. The spec strings built into GCC can
6644 be overridden by using the @option{-specs=} command-line switch to specify
6647 @dfn{Spec files} are plaintext files that are used to construct spec
6648 strings. They consist of a sequence of directives separated by blank
6649 lines. The type of directive is determined by the first non-whitespace
6650 character on the line and it can be one of the following:
6653 @item %@var{command}
6654 Issues a @var{command} to the spec file processor. The commands that can
6658 @item %include <@var{file}>
6660 Search for @var{file} and insert its text at the current point in the
6663 @item %include_noerr <@var{file}>
6664 @cindex %include_noerr
6665 Just like @samp{%include}, but do not generate an error message if the include
6666 file cannot be found.
6668 @item %rename @var{old_name} @var{new_name}
6670 Rename the spec string @var{old_name} to @var{new_name}.
6674 @item *[@var{spec_name}]:
6675 This tells the compiler to create, override or delete the named spec
6676 string. All lines after this directive up to the next directive or
6677 blank line are considered to be the text for the spec string. If this
6678 results in an empty string then the spec will be deleted. (Or, if the
6679 spec did not exist, then nothing will happened.) Otherwise, if the spec
6680 does not currently exist a new spec will be created. If the spec does
6681 exist then its contents will be overridden by the text of this
6682 directive, unless the first character of that text is the @samp{+}
6683 character, in which case the text will be appended to the spec.
6685 @item [@var{suffix}]:
6686 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6687 and up to the next directive or blank line are considered to make up the
6688 spec string for the indicated suffix. When the compiler encounters an
6689 input file with the named suffix, it will processes the spec string in
6690 order to work out how to compile that file. For example:
6697 This says that any input file whose name ends in @samp{.ZZ} should be
6698 passed to the program @samp{z-compile}, which should be invoked with the
6699 command-line switch @option{-input} and with the result of performing the
6700 @samp{%i} substitution. (See below.)
6702 As an alternative to providing a spec string, the text that follows a
6703 suffix directive can be one of the following:
6706 @item @@@var{language}
6707 This says that the suffix is an alias for a known @var{language}. This is
6708 similar to using the @option{-x} command-line switch to GCC to specify a
6709 language explicitly. For example:
6716 Says that .ZZ files are, in fact, C++ source files.
6719 This causes an error messages saying:
6722 @var{name} compiler not installed on this system.
6726 GCC already has an extensive list of suffixes built into it.
6727 This directive will add an entry to the end of the list of suffixes, but
6728 since the list is searched from the end backwards, it is effectively
6729 possible to override earlier entries using this technique.
6733 GCC has the following spec strings built into it. Spec files can
6734 override these strings or create their own. Note that individual
6735 targets can also add their own spec strings to this list.
6738 asm Options to pass to the assembler
6739 asm_final Options to pass to the assembler post-processor
6740 cpp Options to pass to the C preprocessor
6741 cc1 Options to pass to the C compiler
6742 cc1plus Options to pass to the C++ compiler
6743 endfile Object files to include at the end of the link
6744 link Options to pass to the linker
6745 lib Libraries to include on the command line to the linker
6746 libgcc Decides which GCC support library to pass to the linker
6747 linker Sets the name of the linker
6748 predefines Defines to be passed to the C preprocessor
6749 signed_char Defines to pass to CPP to say whether @code{char} is signed
6751 startfile Object files to include at the start of the link
6754 Here is a small example of a spec file:
6760 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6763 This example renames the spec called @samp{lib} to @samp{old_lib} and
6764 then overrides the previous definition of @samp{lib} with a new one.
6765 The new definition adds in some extra command-line options before
6766 including the text of the old definition.
6768 @dfn{Spec strings} are a list of command-line options to be passed to their
6769 corresponding program. In addition, the spec strings can contain
6770 @samp{%}-prefixed sequences to substitute variable text or to
6771 conditionally insert text into the command line. Using these constructs
6772 it is possible to generate quite complex command lines.
6774 Here is a table of all defined @samp{%}-sequences for spec
6775 strings. Note that spaces are not generated automatically around the
6776 results of expanding these sequences. Therefore you can concatenate them
6777 together or combine them with constant text in a single argument.
6781 Substitute one @samp{%} into the program name or argument.
6784 Substitute the name of the input file being processed.
6787 Substitute the basename of the input file being processed.
6788 This is the substring up to (and not including) the last period
6789 and not including the directory.
6792 This is the same as @samp{%b}, but include the file suffix (text after
6796 Marks the argument containing or following the @samp{%d} as a
6797 temporary file name, so that that file will be deleted if GCC exits
6798 successfully. Unlike @samp{%g}, this contributes no text to the
6801 @item %g@var{suffix}
6802 Substitute a file name that has suffix @var{suffix} and is chosen
6803 once per compilation, and mark the argument in the same way as
6804 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6805 name is now chosen in a way that is hard to predict even when previously
6806 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6807 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6808 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6809 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6810 was simply substituted with a file name chosen once per compilation,
6811 without regard to any appended suffix (which was therefore treated
6812 just like ordinary text), making such attacks more likely to succeed.
6814 @item %u@var{suffix}
6815 Like @samp{%g}, but generates a new temporary file name even if
6816 @samp{%u@var{suffix}} was already seen.
6818 @item %U@var{suffix}
6819 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6820 new one if there is no such last file name. In the absence of any
6821 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6822 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6823 would involve the generation of two distinct file names, one
6824 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6825 simply substituted with a file name chosen for the previous @samp{%u},
6826 without regard to any appended suffix.
6828 @item %j@var{suffix}
6829 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6830 writable, and if save-temps is off; otherwise, substitute the name
6831 of a temporary file, just like @samp{%u}. This temporary file is not
6832 meant for communication between processes, but rather as a junk
6835 @item %|@var{suffix}
6836 @itemx %m@var{suffix}
6837 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6838 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6839 all. These are the two most common ways to instruct a program that it
6840 should read from standard input or write to standard output. If you
6841 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6842 construct: see for example @file{f/lang-specs.h}.
6844 @item %.@var{SUFFIX}
6845 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6846 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6847 terminated by the next space or %.
6850 Marks the argument containing or following the @samp{%w} as the
6851 designated output file of this compilation. This puts the argument
6852 into the sequence of arguments that @samp{%o} will substitute later.
6855 Substitutes the names of all the output files, with spaces
6856 automatically placed around them. You should write spaces
6857 around the @samp{%o} as well or the results are undefined.
6858 @samp{%o} is for use in the specs for running the linker.
6859 Input files whose names have no recognized suffix are not compiled
6860 at all, but they are included among the output files, so they will
6864 Substitutes the suffix for object files. Note that this is
6865 handled specially when it immediately follows @samp{%g, %u, or %U},
6866 because of the need for those to form complete file names. The
6867 handling is such that @samp{%O} is treated exactly as if it had already
6868 been substituted, except that @samp{%g, %u, and %U} do not currently
6869 support additional @var{suffix} characters following @samp{%O} as they would
6870 following, for example, @samp{.o}.
6873 Substitutes the standard macro predefinitions for the
6874 current target machine. Use this when running @code{cpp}.
6877 Like @samp{%p}, but puts @samp{__} before and after the name of each
6878 predefined macro, except for macros that start with @samp{__} or with
6879 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6883 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6884 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
6885 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6886 and @option{-imultilib} as necessary.
6889 Current argument is the name of a library or startup file of some sort.
6890 Search for that file in a standard list of directories and substitute
6891 the full name found.
6894 Print @var{str} as an error message. @var{str} is terminated by a newline.
6895 Use this when inconsistent options are detected.
6898 Substitute the contents of spec string @var{name} at this point.
6901 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6903 @item %x@{@var{option}@}
6904 Accumulate an option for @samp{%X}.
6907 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6911 Output the accumulated assembler options specified by @option{-Wa}.
6914 Output the accumulated preprocessor options specified by @option{-Wp}.
6917 Process the @code{asm} spec. This is used to compute the
6918 switches to be passed to the assembler.
6921 Process the @code{asm_final} spec. This is a spec string for
6922 passing switches to an assembler post-processor, if such a program is
6926 Process the @code{link} spec. This is the spec for computing the
6927 command line passed to the linker. Typically it will make use of the
6928 @samp{%L %G %S %D and %E} sequences.
6931 Dump out a @option{-L} option for each directory that GCC believes might
6932 contain startup files. If the target supports multilibs then the
6933 current multilib directory will be prepended to each of these paths.
6936 Process the @code{lib} spec. This is a spec string for deciding which
6937 libraries should be included on the command line to the linker.
6940 Process the @code{libgcc} spec. This is a spec string for deciding
6941 which GCC support library should be included on the command line to the linker.
6944 Process the @code{startfile} spec. This is a spec for deciding which
6945 object files should be the first ones passed to the linker. Typically
6946 this might be a file named @file{crt0.o}.
6949 Process the @code{endfile} spec. This is a spec string that specifies
6950 the last object files that will be passed to the linker.
6953 Process the @code{cpp} spec. This is used to construct the arguments
6954 to be passed to the C preprocessor.
6957 Process the @code{cc1} spec. This is used to construct the options to be
6958 passed to the actual C compiler (@samp{cc1}).
6961 Process the @code{cc1plus} spec. This is used to construct the options to be
6962 passed to the actual C++ compiler (@samp{cc1plus}).
6965 Substitute the variable part of a matched option. See below.
6966 Note that each comma in the substituted string is replaced by
6970 Remove all occurrences of @code{-S} from the command line. Note---this
6971 command is position dependent. @samp{%} commands in the spec string
6972 before this one will see @code{-S}, @samp{%} commands in the spec string
6973 after this one will not.
6975 @item %:@var{function}(@var{args})
6976 Call the named function @var{function}, passing it @var{args}.
6977 @var{args} is first processed as a nested spec string, then split
6978 into an argument vector in the usual fashion. The function returns
6979 a string which is processed as if it had appeared literally as part
6980 of the current spec.
6982 The following built-in spec functions are provided:
6985 @item @code{if-exists}
6986 The @code{if-exists} spec function takes one argument, an absolute
6987 pathname to a file. If the file exists, @code{if-exists} returns the
6988 pathname. Here is a small example of its usage:
6992 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6995 @item @code{if-exists-else}
6996 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6997 spec function, except that it takes two arguments. The first argument is
6998 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6999 returns the pathname. If it does not exist, it returns the second argument.
7000 This way, @code{if-exists-else} can be used to select one file or another,
7001 based on the existence of the first. Here is a small example of its usage:
7005 crt0%O%s %:if-exists(crti%O%s) \
7006 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
7009 @item @code{replace-outfile}
7010 The @code{replace-outfile} spec function takes two arguments. It looks for the
7011 first argument in the outfiles array and replaces it with the second argument. Here
7012 is a small example of its usage:
7015 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
7021 Substitutes the @code{-S} switch, if that switch was given to GCC@.
7022 If that switch was not specified, this substitutes nothing. Note that
7023 the leading dash is omitted when specifying this option, and it is
7024 automatically inserted if the substitution is performed. Thus the spec
7025 string @samp{%@{foo@}} would match the command-line option @option{-foo}
7026 and would output the command line option @option{-foo}.
7028 @item %W@{@code{S}@}
7029 Like %@{@code{S}@} but mark last argument supplied within as a file to be
7032 @item %@{@code{S}*@}
7033 Substitutes all the switches specified to GCC whose names start
7034 with @code{-S}, but which also take an argument. This is used for
7035 switches like @option{-o}, @option{-D}, @option{-I}, etc.
7036 GCC considers @option{-o foo} as being
7037 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
7038 text, including the space. Thus two arguments would be generated.
7040 @item %@{@code{S}*&@code{T}*@}
7041 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
7042 (the order of @code{S} and @code{T} in the spec is not significant).
7043 There can be any number of ampersand-separated variables; for each the
7044 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
7046 @item %@{@code{S}:@code{X}@}
7047 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
7049 @item %@{!@code{S}:@code{X}@}
7050 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
7052 @item %@{@code{S}*:@code{X}@}
7053 Substitutes @code{X} if one or more switches whose names start with
7054 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
7055 once, no matter how many such switches appeared. However, if @code{%*}
7056 appears somewhere in @code{X}, then @code{X} will be substituted once
7057 for each matching switch, with the @code{%*} replaced by the part of
7058 that switch that matched the @code{*}.
7060 @item %@{.@code{S}:@code{X}@}
7061 Substitutes @code{X}, if processing a file with suffix @code{S}.
7063 @item %@{!.@code{S}:@code{X}@}
7064 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
7066 @item %@{@code{S}|@code{P}:@code{X}@}
7067 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
7068 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
7069 although they have a stronger binding than the @samp{|}. If @code{%*}
7070 appears in @code{X}, all of the alternatives must be starred, and only
7071 the first matching alternative is substituted.
7073 For example, a spec string like this:
7076 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
7079 will output the following command-line options from the following input
7080 command-line options:
7085 -d fred.c -foo -baz -boggle
7086 -d jim.d -bar -baz -boggle
7089 @item %@{S:X; T:Y; :D@}
7091 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
7092 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
7093 be as many clauses as you need. This may be combined with @code{.},
7094 @code{!}, @code{|}, and @code{*} as needed.
7099 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
7100 construct may contain other nested @samp{%} constructs or spaces, or
7101 even newlines. They are processed as usual, as described above.
7102 Trailing white space in @code{X} is ignored. White space may also
7103 appear anywhere on the left side of the colon in these constructs,
7104 except between @code{.} or @code{*} and the corresponding word.
7106 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
7107 handled specifically in these constructs. If another value of
7108 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
7109 @option{-W} switch is found later in the command line, the earlier
7110 switch value is ignored, except with @{@code{S}*@} where @code{S} is
7111 just one letter, which passes all matching options.
7113 The character @samp{|} at the beginning of the predicate text is used to
7114 indicate that a command should be piped to the following command, but
7115 only if @option{-pipe} is specified.
7117 It is built into GCC which switches take arguments and which do not.
7118 (You might think it would be useful to generalize this to allow each
7119 compiler's spec to say which switches take arguments. But this cannot
7120 be done in a consistent fashion. GCC cannot even decide which input
7121 files have been specified without knowing which switches take arguments,
7122 and it must know which input files to compile in order to tell which
7125 GCC also knows implicitly that arguments starting in @option{-l} are to be
7126 treated as compiler output files, and passed to the linker in their
7127 proper position among the other output files.
7129 @c man begin OPTIONS
7131 @node Target Options
7132 @section Specifying Target Machine and Compiler Version
7133 @cindex target options
7134 @cindex cross compiling
7135 @cindex specifying machine version
7136 @cindex specifying compiler version and target machine
7137 @cindex compiler version, specifying
7138 @cindex target machine, specifying
7140 The usual way to run GCC is to run the executable called @file{gcc}, or
7141 @file{<machine>-gcc} when cross-compiling, or
7142 @file{<machine>-gcc-<version>} to run a version other than the one that
7143 was installed last. Sometimes this is inconvenient, so GCC provides
7144 options that will switch to another cross-compiler or version.
7147 @item -b @var{machine}
7149 The argument @var{machine} specifies the target machine for compilation.
7151 The value to use for @var{machine} is the same as was specified as the
7152 machine type when configuring GCC as a cross-compiler. For
7153 example, if a cross-compiler was configured with @samp{configure
7154 arm-elf}, meaning to compile for an arm processor with elf binaries,
7155 then you would specify @option{-b arm-elf} to run that cross compiler.
7156 Because there are other options beginning with @option{-b}, the
7157 configuration must contain a hyphen.
7159 @item -V @var{version}
7161 The argument @var{version} specifies which version of GCC to run.
7162 This is useful when multiple versions are installed. For example,
7163 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
7166 The @option{-V} and @option{-b} options work by running the
7167 @file{<machine>-gcc-<version>} executable, so there's no real reason to
7168 use them if you can just run that directly.
7170 @node Submodel Options
7171 @section Hardware Models and Configurations
7172 @cindex submodel options
7173 @cindex specifying hardware config
7174 @cindex hardware models and configurations, specifying
7175 @cindex machine dependent options
7177 Earlier we discussed the standard option @option{-b} which chooses among
7178 different installed compilers for completely different target
7179 machines, such as VAX vs.@: 68000 vs.@: 80386.
7181 In addition, each of these target machine types can have its own
7182 special options, starting with @samp{-m}, to choose among various
7183 hardware models or configurations---for example, 68010 vs 68020,
7184 floating coprocessor or none. A single installed version of the
7185 compiler can compile for any model or configuration, according to the
7188 Some configurations of the compiler also support additional special
7189 options, usually for compatibility with other compilers on the same
7192 @c This list is ordered alphanumerically by subsection name.
7193 @c It should be the same order and spelling as these options are listed
7194 @c in Machine Dependent Options
7200 * Blackfin Options::
7204 * DEC Alpha Options::
7205 * DEC Alpha/VMS Options::
7207 * GNU/Linux Options::
7210 * i386 and x86-64 Options::
7223 * RS/6000 and PowerPC Options::
7224 * S/390 and zSeries Options::
7227 * System V Options::
7228 * TMS320C3x/C4x Options::
7232 * Xstormy16 Options::
7238 @subsection ARC Options
7241 These options are defined for ARC implementations:
7246 Compile code for little endian mode. This is the default.
7250 Compile code for big endian mode.
7253 @opindex mmangle-cpu
7254 Prepend the name of the cpu to all public symbol names.
7255 In multiple-processor systems, there are many ARC variants with different
7256 instruction and register set characteristics. This flag prevents code
7257 compiled for one cpu to be linked with code compiled for another.
7258 No facility exists for handling variants that are ``almost identical''.
7259 This is an all or nothing option.
7261 @item -mcpu=@var{cpu}
7263 Compile code for ARC variant @var{cpu}.
7264 Which variants are supported depend on the configuration.
7265 All variants support @option{-mcpu=base}, this is the default.
7267 @item -mtext=@var{text-section}
7268 @itemx -mdata=@var{data-section}
7269 @itemx -mrodata=@var{readonly-data-section}
7273 Put functions, data, and readonly data in @var{text-section},
7274 @var{data-section}, and @var{readonly-data-section} respectively
7275 by default. This can be overridden with the @code{section} attribute.
7276 @xref{Variable Attributes}.
7281 @subsection ARM Options
7284 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
7288 @item -mabi=@var{name}
7290 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
7291 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
7294 @opindex mapcs-frame
7295 Generate a stack frame that is compliant with the ARM Procedure Call
7296 Standard for all functions, even if this is not strictly necessary for
7297 correct execution of the code. Specifying @option{-fomit-frame-pointer}
7298 with this option will cause the stack frames not to be generated for
7299 leaf functions. The default is @option{-mno-apcs-frame}.
7303 This is a synonym for @option{-mapcs-frame}.
7306 @c not currently implemented
7307 @item -mapcs-stack-check
7308 @opindex mapcs-stack-check
7309 Generate code to check the amount of stack space available upon entry to
7310 every function (that actually uses some stack space). If there is
7311 insufficient space available then either the function
7312 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
7313 called, depending upon the amount of stack space required. The run time
7314 system is required to provide these functions. The default is
7315 @option{-mno-apcs-stack-check}, since this produces smaller code.
7317 @c not currently implemented
7319 @opindex mapcs-float
7320 Pass floating point arguments using the float point registers. This is
7321 one of the variants of the APCS@. This option is recommended if the
7322 target hardware has a floating point unit or if a lot of floating point
7323 arithmetic is going to be performed by the code. The default is
7324 @option{-mno-apcs-float}, since integer only code is slightly increased in
7325 size if @option{-mapcs-float} is used.
7327 @c not currently implemented
7328 @item -mapcs-reentrant
7329 @opindex mapcs-reentrant
7330 Generate reentrant, position independent code. The default is
7331 @option{-mno-apcs-reentrant}.
7334 @item -mthumb-interwork
7335 @opindex mthumb-interwork
7336 Generate code which supports calling between the ARM and Thumb
7337 instruction sets. Without this option the two instruction sets cannot
7338 be reliably used inside one program. The default is
7339 @option{-mno-thumb-interwork}, since slightly larger code is generated
7340 when @option{-mthumb-interwork} is specified.
7342 @item -mno-sched-prolog
7343 @opindex mno-sched-prolog
7344 Prevent the reordering of instructions in the function prolog, or the
7345 merging of those instruction with the instructions in the function's
7346 body. This means that all functions will start with a recognizable set
7347 of instructions (or in fact one of a choice from a small set of
7348 different function prologues), and this information can be used to
7349 locate the start if functions inside an executable piece of code. The
7350 default is @option{-msched-prolog}.
7353 @opindex mhard-float
7354 Generate output containing floating point instructions. This is the
7358 @opindex msoft-float
7359 Generate output containing library calls for floating point.
7360 @strong{Warning:} the requisite libraries are not available for all ARM
7361 targets. Normally the facilities of the machine's usual C compiler are
7362 used, but this cannot be done directly in cross-compilation. You must make
7363 your own arrangements to provide suitable library functions for
7366 @option{-msoft-float} changes the calling convention in the output file;
7367 therefore, it is only useful if you compile @emph{all} of a program with
7368 this option. In particular, you need to compile @file{libgcc.a}, the
7369 library that comes with GCC, with @option{-msoft-float} in order for
7372 @item -mfloat-abi=@var{name}
7374 Specifies which ABI to use for floating point values. Permissible values
7375 are: @samp{soft}, @samp{softfp} and @samp{hard}.
7377 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
7378 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
7379 of floating point instructions, but still uses the soft-float calling
7382 @item -mlittle-endian
7383 @opindex mlittle-endian
7384 Generate code for a processor running in little-endian mode. This is
7385 the default for all standard configurations.
7388 @opindex mbig-endian
7389 Generate code for a processor running in big-endian mode; the default is
7390 to compile code for a little-endian processor.
7392 @item -mwords-little-endian
7393 @opindex mwords-little-endian
7394 This option only applies when generating code for big-endian processors.
7395 Generate code for a little-endian word order but a big-endian byte
7396 order. That is, a byte order of the form @samp{32107654}. Note: this
7397 option should only be used if you require compatibility with code for
7398 big-endian ARM processors generated by versions of the compiler prior to
7401 @item -mcpu=@var{name}
7403 This specifies the name of the target ARM processor. GCC uses this name
7404 to determine what kind of instructions it can emit when generating
7405 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
7406 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
7407 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
7408 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
7409 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
7410 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
7411 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
7412 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
7413 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
7414 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
7415 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
7416 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
7417 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
7418 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
7421 @itemx -mtune=@var{name}
7423 This option is very similar to the @option{-mcpu=} option, except that
7424 instead of specifying the actual target processor type, and hence
7425 restricting which instructions can be used, it specifies that GCC should
7426 tune the performance of the code as if the target were of the type
7427 specified in this option, but still choosing the instructions that it
7428 will generate based on the cpu specified by a @option{-mcpu=} option.
7429 For some ARM implementations better performance can be obtained by using
7432 @item -march=@var{name}
7434 This specifies the name of the target ARM architecture. GCC uses this
7435 name to determine what kind of instructions it can emit when generating
7436 assembly code. This option can be used in conjunction with or instead
7437 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
7438 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
7439 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
7440 @samp{iwmmxt}, @samp{ep9312}.
7442 @item -mfpu=@var{name}
7443 @itemx -mfpe=@var{number}
7444 @itemx -mfp=@var{number}
7448 This specifies what floating point hardware (or hardware emulation) is
7449 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
7450 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
7451 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
7452 with older versions of GCC@.
7454 If @option{-msoft-float} is specified this specifies the format of
7455 floating point values.
7457 @item -mstructure-size-boundary=@var{n}
7458 @opindex mstructure-size-boundary
7459 The size of all structures and unions will be rounded up to a multiple
7460 of the number of bits set by this option. Permissible values are 8, 32
7461 and 64. The default value varies for different toolchains. For the COFF
7462 targeted toolchain the default value is 8. A value of 64 is only allowed
7463 if the underlying ABI supports it.
7465 Specifying the larger number can produce faster, more efficient code, but
7466 can also increase the size of the program. Different values are potentially
7467 incompatible. Code compiled with one value cannot necessarily expect to
7468 work with code or libraries compiled with another value, if they exchange
7469 information using structures or unions.
7471 @item -mabort-on-noreturn
7472 @opindex mabort-on-noreturn
7473 Generate a call to the function @code{abort} at the end of a
7474 @code{noreturn} function. It will be executed if the function tries to
7478 @itemx -mno-long-calls
7479 @opindex mlong-calls
7480 @opindex mno-long-calls
7481 Tells the compiler to perform function calls by first loading the
7482 address of the function into a register and then performing a subroutine
7483 call on this register. This switch is needed if the target function
7484 will lie outside of the 64 megabyte addressing range of the offset based
7485 version of subroutine call instruction.
7487 Even if this switch is enabled, not all function calls will be turned
7488 into long calls. The heuristic is that static functions, functions
7489 which have the @samp{short-call} attribute, functions that are inside
7490 the scope of a @samp{#pragma no_long_calls} directive and functions whose
7491 definitions have already been compiled within the current compilation
7492 unit, will not be turned into long calls. The exception to this rule is
7493 that weak function definitions, functions with the @samp{long-call}
7494 attribute or the @samp{section} attribute, and functions that are within
7495 the scope of a @samp{#pragma long_calls} directive, will always be
7496 turned into long calls.
7498 This feature is not enabled by default. Specifying
7499 @option{-mno-long-calls} will restore the default behavior, as will
7500 placing the function calls within the scope of a @samp{#pragma
7501 long_calls_off} directive. Note these switches have no effect on how
7502 the compiler generates code to handle function calls via function
7505 @item -mnop-fun-dllimport
7506 @opindex mnop-fun-dllimport
7507 Disable support for the @code{dllimport} attribute.
7509 @item -msingle-pic-base
7510 @opindex msingle-pic-base
7511 Treat the register used for PIC addressing as read-only, rather than
7512 loading it in the prologue for each function. The run-time system is
7513 responsible for initializing this register with an appropriate value
7514 before execution begins.
7516 @item -mpic-register=@var{reg}
7517 @opindex mpic-register
7518 Specify the register to be used for PIC addressing. The default is R10
7519 unless stack-checking is enabled, when R9 is used.
7521 @item -mcirrus-fix-invalid-insns
7522 @opindex mcirrus-fix-invalid-insns
7523 @opindex mno-cirrus-fix-invalid-insns
7524 Insert NOPs into the instruction stream to in order to work around
7525 problems with invalid Maverick instruction combinations. This option
7526 is only valid if the @option{-mcpu=ep9312} option has been used to
7527 enable generation of instructions for the Cirrus Maverick floating
7528 point co-processor. This option is not enabled by default, since the
7529 problem is only present in older Maverick implementations. The default
7530 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
7533 @item -mpoke-function-name
7534 @opindex mpoke-function-name
7535 Write the name of each function into the text section, directly
7536 preceding the function prologue. The generated code is similar to this:
7540 .ascii "arm_poke_function_name", 0
7543 .word 0xff000000 + (t1 - t0)
7544 arm_poke_function_name
7546 stmfd sp!, @{fp, ip, lr, pc@}
7550 When performing a stack backtrace, code can inspect the value of
7551 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
7552 location @code{pc - 12} and the top 8 bits are set, then we know that
7553 there is a function name embedded immediately preceding this location
7554 and has length @code{((pc[-3]) & 0xff000000)}.
7558 Generate code for the 16-bit Thumb instruction set. The default is to
7559 use the 32-bit ARM instruction set.
7562 @opindex mtpcs-frame
7563 Generate a stack frame that is compliant with the Thumb Procedure Call
7564 Standard for all non-leaf functions. (A leaf function is one that does
7565 not call any other functions.) The default is @option{-mno-tpcs-frame}.
7567 @item -mtpcs-leaf-frame
7568 @opindex mtpcs-leaf-frame
7569 Generate a stack frame that is compliant with the Thumb Procedure Call
7570 Standard for all leaf functions. (A leaf function is one that does
7571 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
7573 @item -mcallee-super-interworking
7574 @opindex mcallee-super-interworking
7575 Gives all externally visible functions in the file being compiled an ARM
7576 instruction set header which switches to Thumb mode before executing the
7577 rest of the function. This allows these functions to be called from
7578 non-interworking code.
7580 @item -mcaller-super-interworking
7581 @opindex mcaller-super-interworking
7582 Allows calls via function pointers (including virtual functions) to
7583 execute correctly regardless of whether the target code has been
7584 compiled for interworking or not. There is a small overhead in the cost
7585 of executing a function pointer if this option is enabled.
7587 @item -mtp=@var{name}
7589 Specify the access model for the thread local storage pointer. The valid
7590 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
7591 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
7592 (supported in the arm6k architecture), and @option{auto}, which uses the
7593 best available method for the selected processor. The default setting is
7599 @subsection AVR Options
7602 These options are defined for AVR implementations:
7605 @item -mmcu=@var{mcu}
7607 Specify ATMEL AVR instruction set or MCU type.
7609 Instruction set avr1 is for the minimal AVR core, not supported by the C
7610 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
7611 attiny11, attiny12, attiny15, attiny28).
7613 Instruction set avr2 (default) is for the classic AVR core with up to
7614 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
7615 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
7616 at90c8534, at90s8535).
7618 Instruction set avr3 is for the classic AVR core with up to 128K program
7619 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
7621 Instruction set avr4 is for the enhanced AVR core with up to 8K program
7622 memory space (MCU types: atmega8, atmega83, atmega85).
7624 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7625 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7626 atmega64, atmega128, at43usb355, at94k).
7630 Output instruction sizes to the asm file.
7632 @item -minit-stack=@var{N}
7633 @opindex minit-stack
7634 Specify the initial stack address, which may be a symbol or numeric value,
7635 @samp{__stack} is the default.
7637 @item -mno-interrupts
7638 @opindex mno-interrupts
7639 Generated code is not compatible with hardware interrupts.
7640 Code size will be smaller.
7642 @item -mcall-prologues
7643 @opindex mcall-prologues
7644 Functions prologues/epilogues expanded as call to appropriate
7645 subroutines. Code size will be smaller.
7647 @item -mno-tablejump
7648 @opindex mno-tablejump
7649 Do not generate tablejump insns which sometimes increase code size.
7652 @opindex mtiny-stack
7653 Change only the low 8 bits of the stack pointer.
7657 Assume int to be 8 bit integer. This affects the sizes of all types: A
7658 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7659 and long long will be 4 bytes. Please note that this option does not
7660 comply to the C standards, but it will provide you with smaller code
7664 @node Blackfin Options
7665 @subsection Blackfin Options
7666 @cindex Blackfin Options
7669 @item -momit-leaf-frame-pointer
7670 @opindex momit-leaf-frame-pointer
7671 Don't keep the frame pointer in a register for leaf functions. This
7672 avoids the instructions to save, set up and restore frame pointers and
7673 makes an extra register available in leaf functions. The option
7674 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7675 which might make debugging harder.
7677 @item -mspecld-anomaly
7678 @opindex mspecld-anomaly
7679 When enabled, the compiler will ensure that the generated code does not
7680 contain speculative loads after jump instructions. This option is enabled
7683 @item -mno-specld-anomaly
7684 @opindex mno-specld-anomaly
7685 Don't generate extra code to prevent speculative loads from occurring.
7687 @item -mcsync-anomaly
7688 @opindex mcsync-anomaly
7689 When enabled, the compiler will ensure that the generated code does not
7690 contain CSYNC or SSYNC instructions too soon after conditional branches.
7691 This option is enabled by default.
7693 @item -mno-csync-anomaly
7694 @opindex mno-csync-anomaly
7695 Don't generate extra code to prevent CSYNC or SSYNC instructions from
7696 occurring too soon after a conditional branch.
7700 When enabled, the compiler is free to take advantage of the knowledge that
7701 the entire program fits into the low 64k of memory.
7704 @opindex mno-low-64k
7705 Assume that the program is arbitrarily large. This is the default.
7707 @item -mid-shared-library
7708 @opindex mid-shared-library
7709 Generate code that supports shared libraries via the library ID method.
7710 This allows for execute in place and shared libraries in an environment
7711 without virtual memory management. This option implies @option{-fPIC}.
7713 @item -mno-id-shared-library
7714 @opindex mno-id-shared-library
7715 Generate code that doesn't assume ID based shared libraries are being used.
7716 This is the default.
7718 @item -mshared-library-id=n
7719 @opindex mshared-library-id
7720 Specified the identification number of the ID based shared library being
7721 compiled. Specifying a value of 0 will generate more compact code, specifying
7722 other values will force the allocation of that number to the current
7723 library but is no more space or time efficient than omitting this option.
7726 @itemx -mno-long-calls
7727 @opindex mlong-calls
7728 @opindex mno-long-calls
7729 Tells the compiler to perform function calls by first loading the
7730 address of the function into a register and then performing a subroutine
7731 call on this register. This switch is needed if the target function
7732 will lie outside of the 24 bit addressing range of the offset based
7733 version of subroutine call instruction.
7735 This feature is not enabled by default. Specifying
7736 @option{-mno-long-calls} will restore the default behavior. Note these
7737 switches have no effect on how the compiler generates code to handle
7738 function calls via function pointers.
7742 @subsection CRIS Options
7743 @cindex CRIS Options
7745 These options are defined specifically for the CRIS ports.
7748 @item -march=@var{architecture-type}
7749 @itemx -mcpu=@var{architecture-type}
7752 Generate code for the specified architecture. The choices for
7753 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7754 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
7755 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7758 @item -mtune=@var{architecture-type}
7760 Tune to @var{architecture-type} everything applicable about the generated
7761 code, except for the ABI and the set of available instructions. The
7762 choices for @var{architecture-type} are the same as for
7763 @option{-march=@var{architecture-type}}.
7765 @item -mmax-stack-frame=@var{n}
7766 @opindex mmax-stack-frame
7767 Warn when the stack frame of a function exceeds @var{n} bytes.
7769 @item -melinux-stacksize=@var{n}
7770 @opindex melinux-stacksize
7771 Only available with the @samp{cris-axis-aout} target. Arranges for
7772 indications in the program to the kernel loader that the stack of the
7773 program should be set to @var{n} bytes.
7779 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7780 @option{-march=v3} and @option{-march=v8} respectively.
7782 @item -mmul-bug-workaround
7783 @itemx -mno-mul-bug-workaround
7784 @opindex mmul-bug-workaround
7785 @opindex mno-mul-bug-workaround
7786 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7787 models where it applies. This option is active by default.
7791 Enable CRIS-specific verbose debug-related information in the assembly
7792 code. This option also has the effect to turn off the @samp{#NO_APP}
7793 formatted-code indicator to the assembler at the beginning of the
7798 Do not use condition-code results from previous instruction; always emit
7799 compare and test instructions before use of condition codes.
7801 @item -mno-side-effects
7802 @opindex mno-side-effects
7803 Do not emit instructions with side-effects in addressing modes other than
7807 @itemx -mno-stack-align
7809 @itemx -mno-data-align
7810 @itemx -mconst-align
7811 @itemx -mno-const-align
7812 @opindex mstack-align
7813 @opindex mno-stack-align
7814 @opindex mdata-align
7815 @opindex mno-data-align
7816 @opindex mconst-align
7817 @opindex mno-const-align
7818 These options (no-options) arranges (eliminate arrangements) for the
7819 stack-frame, individual data and constants to be aligned for the maximum
7820 single data access size for the chosen CPU model. The default is to
7821 arrange for 32-bit alignment. ABI details such as structure layout are
7822 not affected by these options.
7830 Similar to the stack- data- and const-align options above, these options
7831 arrange for stack-frame, writable data and constants to all be 32-bit,
7832 16-bit or 8-bit aligned. The default is 32-bit alignment.
7834 @item -mno-prologue-epilogue
7835 @itemx -mprologue-epilogue
7836 @opindex mno-prologue-epilogue
7837 @opindex mprologue-epilogue
7838 With @option{-mno-prologue-epilogue}, the normal function prologue and
7839 epilogue that sets up the stack-frame are omitted and no return
7840 instructions or return sequences are generated in the code. Use this
7841 option only together with visual inspection of the compiled code: no
7842 warnings or errors are generated when call-saved registers must be saved,
7843 or storage for local variable needs to be allocated.
7849 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7850 instruction sequences that load addresses for functions from the PLT part
7851 of the GOT rather than (traditional on other architectures) calls to the
7852 PLT@. The default is @option{-mgotplt}.
7856 Legacy no-op option only recognized with the cris-axis-aout target.
7860 Legacy no-op option only recognized with the cris-axis-elf and
7861 cris-axis-linux-gnu targets.
7865 Only recognized with the cris-axis-aout target, where it selects a
7866 GNU/linux-like multilib, include files and instruction set for
7871 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7875 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7876 to link with input-output functions from a simulator library. Code,
7877 initialized data and zero-initialized data are allocated consecutively.
7881 Like @option{-sim}, but pass linker options to locate initialized data at
7882 0x40000000 and zero-initialized data at 0x80000000.
7886 @subsection CRX Options
7889 These options are defined specifically for the CRX ports.
7895 Enable the use of multiply-accumulate instructions. Disabled by default.
7899 Push instructions will be used to pass outgoing arguments when functions
7900 are called. Enabled by default.
7903 @node Darwin Options
7904 @subsection Darwin Options
7905 @cindex Darwin options
7907 These options are defined for all architectures running the Darwin operating
7910 FSF GCC on Darwin does not create ``fat'' object files; it will create
7911 an object file for the single architecture that it was built to
7912 target. Apple's GCC on Darwin does create ``fat'' files if multiple
7913 @option{-arch} options are used; it does so by running the compiler or
7914 linker multiple times and joining the results together with
7917 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
7918 @samp{i686}) is determined by the flags that specify the ISA
7919 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
7920 @option{-force_cpusubtype_ALL} option can be used to override this.
7922 The Darwin tools vary in their behavior when presented with an ISA
7923 mismatch. The assembler, @file{as}, will only permit instructions to
7924 be used that are valid for the subtype of the file it is generating,
7925 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
7926 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
7927 and print an error if asked to create a shared library with a less
7928 restrictive subtype than its input files (for instance, trying to put
7929 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
7930 for executables, @file{ld}, will quietly give the executable the most
7931 restrictive subtype of any of its input files.
7936 Add the framework directory @var{dir} to the head of the list of
7937 directories to be searched for header files. These directories are
7938 interleaved with those specified by @option{-I} options and are
7939 scanned in a left-to-right order.
7941 A framework directory is a directory with frameworks in it. A
7942 framework is a directory with a @samp{"Headers"} and/or
7943 @samp{"PrivateHeaders"} directory contained directly in it that ends
7944 in @samp{".framework"}. The name of a framework is the name of this
7945 directory excluding the @samp{".framework"}. Headers associated with
7946 the framework are found in one of those two directories, with
7947 @samp{"Headers"} being searched first. A subframework is a framework
7948 directory that is in a framework's @samp{"Frameworks"} directory.
7949 Includes of subframework headers can only appear in a header of a
7950 framework that contains the subframework, or in a sibling subframework
7951 header. Two subframeworks are siblings if they occur in the same
7952 framework. A subframework should not have the same name as a
7953 framework, a warning will be issued if this is violated. Currently a
7954 subframework cannot have subframeworks, in the future, the mechanism
7955 may be extended to support this. The standard frameworks can be found
7956 in @samp{"/System/Library/Frameworks"} and
7957 @samp{"/Library/Frameworks"}. An example include looks like
7958 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7959 the name of the framework and header.h is found in the
7960 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7964 Emit debugging information for symbols that are used. For STABS
7965 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7966 This is by default ON@.
7970 Emit debugging information for all symbols and types.
7972 @item -mmacosx-version-min=@var{version}
7973 The earliest version of MacOS X that this executable will run on
7974 is @var{version}. Typical values of @var{version} include @code{10.1},
7975 @code{10.2}, and @code{10.3.9}.
7977 The default for this option is to make choices that seem to be most
7980 @item -mone-byte-bool
7981 @opindex -mone-byte-bool
7982 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7983 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7984 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7985 option has no effect on x86.
7987 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7988 to generate code that is not binary compatible with code generated
7989 without that switch. Using this switch may require recompiling all
7990 other modules in a program, including system libraries. Use this
7991 switch to conform to a non-default data model.
7993 @item -mfix-and-continue
7994 @itemx -ffix-and-continue
7995 @itemx -findirect-data
7996 @opindex mfix-and-continue
7997 @opindex ffix-and-continue
7998 @opindex findirect-data
7999 Generate code suitable for fast turn around development. Needed to
8000 enable gdb to dynamically load @code{.o} files into already running
8001 programs. @option{-findirect-data} and @option{-ffix-and-continue}
8002 are provided for backwards compatibility.
8006 Loads all members of static archive libraries.
8007 See man ld(1) for more information.
8009 @item -arch_errors_fatal
8010 @opindex arch_errors_fatal
8011 Cause the errors having to do with files that have the wrong architecture
8015 @opindex bind_at_load
8016 Causes the output file to be marked such that the dynamic linker will
8017 bind all undefined references when the file is loaded or launched.
8021 Produce a Mach-o bundle format file.
8022 See man ld(1) for more information.
8024 @item -bundle_loader @var{executable}
8025 @opindex bundle_loader
8026 This option specifies the @var{executable} that will be loading the build
8027 output file being linked. See man ld(1) for more information.
8030 @opindex -dynamiclib
8031 When passed this option, GCC will produce a dynamic library instead of
8032 an executable when linking, using the Darwin @file{libtool} command.
8034 @item -force_cpusubtype_ALL
8035 @opindex -force_cpusubtype_ALL
8036 This causes GCC's output file to have the @var{ALL} subtype, instead of
8037 one controlled by the @option{-mcpu} or @option{-march} option.
8039 @item -allowable_client @var{client_name}
8041 @itemx -compatibility_version
8042 @itemx -current_version
8044 @itemx -dependency-file
8046 @itemx -dylinker_install_name
8048 @itemx -exported_symbols_list
8050 @itemx -flat_namespace
8051 @itemx -force_flat_namespace
8052 @itemx -headerpad_max_install_names
8055 @itemx -install_name
8056 @itemx -keep_private_externs
8057 @itemx -multi_module
8058 @itemx -multiply_defined
8059 @itemx -multiply_defined_unused
8061 @itemx -no_dead_strip_inits_and_terms
8062 @itemx -nofixprebinding
8065 @itemx -noseglinkedit
8066 @itemx -pagezero_size
8068 @itemx -prebind_all_twolevel_modules
8069 @itemx -private_bundle
8070 @itemx -read_only_relocs
8072 @itemx -sectobjectsymbols
8076 @itemx -sectobjectsymbols
8079 @itemx -segs_read_only_addr
8080 @itemx -segs_read_write_addr
8081 @itemx -seg_addr_table
8082 @itemx -seg_addr_table_filename
8085 @itemx -segs_read_only_addr
8086 @itemx -segs_read_write_addr
8087 @itemx -single_module
8090 @itemx -sub_umbrella
8091 @itemx -twolevel_namespace
8094 @itemx -unexported_symbols_list
8095 @itemx -weak_reference_mismatches
8098 @opindex allowable_client
8099 @opindex client_name
8100 @opindex compatibility_version
8101 @opindex current_version
8103 @opindex dependency-file
8105 @opindex dylinker_install_name
8107 @opindex exported_symbols_list
8109 @opindex flat_namespace
8110 @opindex force_flat_namespace
8111 @opindex headerpad_max_install_names
8114 @opindex install_name
8115 @opindex keep_private_externs
8116 @opindex multi_module
8117 @opindex multiply_defined
8118 @opindex multiply_defined_unused
8120 @opindex no_dead_strip_inits_and_terms
8121 @opindex nofixprebinding
8122 @opindex nomultidefs
8124 @opindex noseglinkedit
8125 @opindex pagezero_size
8127 @opindex prebind_all_twolevel_modules
8128 @opindex private_bundle
8129 @opindex read_only_relocs
8131 @opindex sectobjectsymbols
8135 @opindex sectobjectsymbols
8138 @opindex segs_read_only_addr
8139 @opindex segs_read_write_addr
8140 @opindex seg_addr_table
8141 @opindex seg_addr_table_filename
8142 @opindex seglinkedit
8144 @opindex segs_read_only_addr
8145 @opindex segs_read_write_addr
8146 @opindex single_module
8148 @opindex sub_library
8149 @opindex sub_umbrella
8150 @opindex twolevel_namespace
8153 @opindex unexported_symbols_list
8154 @opindex weak_reference_mismatches
8155 @opindex whatsloaded
8157 These options are passed to the Darwin linker. The Darwin linker man page
8158 describes them in detail.
8161 @node DEC Alpha Options
8162 @subsection DEC Alpha Options
8164 These @samp{-m} options are defined for the DEC Alpha implementations:
8167 @item -mno-soft-float
8169 @opindex mno-soft-float
8170 @opindex msoft-float
8171 Use (do not use) the hardware floating-point instructions for
8172 floating-point operations. When @option{-msoft-float} is specified,
8173 functions in @file{libgcc.a} will be used to perform floating-point
8174 operations. Unless they are replaced by routines that emulate the
8175 floating-point operations, or compiled in such a way as to call such
8176 emulations routines, these routines will issue floating-point
8177 operations. If you are compiling for an Alpha without floating-point
8178 operations, you must ensure that the library is built so as not to call
8181 Note that Alpha implementations without floating-point operations are
8182 required to have floating-point registers.
8187 @opindex mno-fp-regs
8188 Generate code that uses (does not use) the floating-point register set.
8189 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8190 register set is not used, floating point operands are passed in integer
8191 registers as if they were integers and floating-point results are passed
8192 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8193 so any function with a floating-point argument or return value called by code
8194 compiled with @option{-mno-fp-regs} must also be compiled with that
8197 A typical use of this option is building a kernel that does not use,
8198 and hence need not save and restore, any floating-point registers.
8202 The Alpha architecture implements floating-point hardware optimized for
8203 maximum performance. It is mostly compliant with the IEEE floating
8204 point standard. However, for full compliance, software assistance is
8205 required. This option generates code fully IEEE compliant code
8206 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8207 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8208 defined during compilation. The resulting code is less efficient but is
8209 able to correctly support denormalized numbers and exceptional IEEE
8210 values such as not-a-number and plus/minus infinity. Other Alpha
8211 compilers call this option @option{-ieee_with_no_inexact}.
8213 @item -mieee-with-inexact
8214 @opindex mieee-with-inexact
8215 This is like @option{-mieee} except the generated code also maintains
8216 the IEEE @var{inexact-flag}. Turning on this option causes the
8217 generated code to implement fully-compliant IEEE math. In addition to
8218 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8219 macro. On some Alpha implementations the resulting code may execute
8220 significantly slower than the code generated by default. Since there is
8221 very little code that depends on the @var{inexact-flag}, you should
8222 normally not specify this option. Other Alpha compilers call this
8223 option @option{-ieee_with_inexact}.
8225 @item -mfp-trap-mode=@var{trap-mode}
8226 @opindex mfp-trap-mode
8227 This option controls what floating-point related traps are enabled.
8228 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8229 The trap mode can be set to one of four values:
8233 This is the default (normal) setting. The only traps that are enabled
8234 are the ones that cannot be disabled in software (e.g., division by zero
8238 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8242 Like @samp{su}, but the instructions are marked to be safe for software
8243 completion (see Alpha architecture manual for details).
8246 Like @samp{su}, but inexact traps are enabled as well.
8249 @item -mfp-rounding-mode=@var{rounding-mode}
8250 @opindex mfp-rounding-mode
8251 Selects the IEEE rounding mode. Other Alpha compilers call this option
8252 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8257 Normal IEEE rounding mode. Floating point numbers are rounded towards
8258 the nearest machine number or towards the even machine number in case
8262 Round towards minus infinity.
8265 Chopped rounding mode. Floating point numbers are rounded towards zero.
8268 Dynamic rounding mode. A field in the floating point control register
8269 (@var{fpcr}, see Alpha architecture reference manual) controls the
8270 rounding mode in effect. The C library initializes this register for
8271 rounding towards plus infinity. Thus, unless your program modifies the
8272 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8275 @item -mtrap-precision=@var{trap-precision}
8276 @opindex mtrap-precision
8277 In the Alpha architecture, floating point traps are imprecise. This
8278 means without software assistance it is impossible to recover from a
8279 floating trap and program execution normally needs to be terminated.
8280 GCC can generate code that can assist operating system trap handlers
8281 in determining the exact location that caused a floating point trap.
8282 Depending on the requirements of an application, different levels of
8283 precisions can be selected:
8287 Program precision. This option is the default and means a trap handler
8288 can only identify which program caused a floating point exception.
8291 Function precision. The trap handler can determine the function that
8292 caused a floating point exception.
8295 Instruction precision. The trap handler can determine the exact
8296 instruction that caused a floating point exception.
8299 Other Alpha compilers provide the equivalent options called
8300 @option{-scope_safe} and @option{-resumption_safe}.
8302 @item -mieee-conformant
8303 @opindex mieee-conformant
8304 This option marks the generated code as IEEE conformant. You must not
8305 use this option unless you also specify @option{-mtrap-precision=i} and either
8306 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8307 is to emit the line @samp{.eflag 48} in the function prologue of the
8308 generated assembly file. Under DEC Unix, this has the effect that
8309 IEEE-conformant math library routines will be linked in.
8311 @item -mbuild-constants
8312 @opindex mbuild-constants
8313 Normally GCC examines a 32- or 64-bit integer constant to
8314 see if it can construct it from smaller constants in two or three
8315 instructions. If it cannot, it will output the constant as a literal and
8316 generate code to load it from the data segment at runtime.
8318 Use this option to require GCC to construct @emph{all} integer constants
8319 using code, even if it takes more instructions (the maximum is six).
8321 You would typically use this option to build a shared library dynamic
8322 loader. Itself a shared library, it must relocate itself in memory
8323 before it can find the variables and constants in its own data segment.
8329 Select whether to generate code to be assembled by the vendor-supplied
8330 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8348 Indicate whether GCC should generate code to use the optional BWX,
8349 CIX, FIX and MAX instruction sets. The default is to use the instruction
8350 sets supported by the CPU type specified via @option{-mcpu=} option or that
8351 of the CPU on which GCC was built if none was specified.
8356 @opindex mfloat-ieee
8357 Generate code that uses (does not use) VAX F and G floating point
8358 arithmetic instead of IEEE single and double precision.
8360 @item -mexplicit-relocs
8361 @itemx -mno-explicit-relocs
8362 @opindex mexplicit-relocs
8363 @opindex mno-explicit-relocs
8364 Older Alpha assemblers provided no way to generate symbol relocations
8365 except via assembler macros. Use of these macros does not allow
8366 optimal instruction scheduling. GNU binutils as of version 2.12
8367 supports a new syntax that allows the compiler to explicitly mark
8368 which relocations should apply to which instructions. This option
8369 is mostly useful for debugging, as GCC detects the capabilities of
8370 the assembler when it is built and sets the default accordingly.
8374 @opindex msmall-data
8375 @opindex mlarge-data
8376 When @option{-mexplicit-relocs} is in effect, static data is
8377 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8378 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8379 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8380 16-bit relocations off of the @code{$gp} register. This limits the
8381 size of the small data area to 64KB, but allows the variables to be
8382 directly accessed via a single instruction.
8384 The default is @option{-mlarge-data}. With this option the data area
8385 is limited to just below 2GB@. Programs that require more than 2GB of
8386 data must use @code{malloc} or @code{mmap} to allocate the data in the
8387 heap instead of in the program's data segment.
8389 When generating code for shared libraries, @option{-fpic} implies
8390 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8394 @opindex msmall-text
8395 @opindex mlarge-text
8396 When @option{-msmall-text} is used, the compiler assumes that the
8397 code of the entire program (or shared library) fits in 4MB, and is
8398 thus reachable with a branch instruction. When @option{-msmall-data}
8399 is used, the compiler can assume that all local symbols share the
8400 same @code{$gp} value, and thus reduce the number of instructions
8401 required for a function call from 4 to 1.
8403 The default is @option{-mlarge-text}.
8405 @item -mcpu=@var{cpu_type}
8407 Set the instruction set and instruction scheduling parameters for
8408 machine type @var{cpu_type}. You can specify either the @samp{EV}
8409 style name or the corresponding chip number. GCC supports scheduling
8410 parameters for the EV4, EV5 and EV6 family of processors and will
8411 choose the default values for the instruction set from the processor
8412 you specify. If you do not specify a processor type, GCC will default
8413 to the processor on which the compiler was built.
8415 Supported values for @var{cpu_type} are
8421 Schedules as an EV4 and has no instruction set extensions.
8425 Schedules as an EV5 and has no instruction set extensions.
8429 Schedules as an EV5 and supports the BWX extension.
8434 Schedules as an EV5 and supports the BWX and MAX extensions.
8438 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8442 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8445 @item -mtune=@var{cpu_type}
8447 Set only the instruction scheduling parameters for machine type
8448 @var{cpu_type}. The instruction set is not changed.
8450 @item -mmemory-latency=@var{time}
8451 @opindex mmemory-latency
8452 Sets the latency the scheduler should assume for typical memory
8453 references as seen by the application. This number is highly
8454 dependent on the memory access patterns used by the application
8455 and the size of the external cache on the machine.
8457 Valid options for @var{time} are
8461 A decimal number representing clock cycles.
8467 The compiler contains estimates of the number of clock cycles for
8468 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8469 (also called Dcache, Scache, and Bcache), as well as to main memory.
8470 Note that L3 is only valid for EV5.
8475 @node DEC Alpha/VMS Options
8476 @subsection DEC Alpha/VMS Options
8478 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8481 @item -mvms-return-codes
8482 @opindex mvms-return-codes
8483 Return VMS condition codes from main. The default is to return POSIX
8484 style condition (e.g.@ error) codes.
8488 @subsection FRV Options
8495 Only use the first 32 general purpose registers.
8500 Use all 64 general purpose registers.
8505 Use only the first 32 floating point registers.
8510 Use all 64 floating point registers
8513 @opindex mhard-float
8515 Use hardware instructions for floating point operations.
8518 @opindex msoft-float
8520 Use library routines for floating point operations.
8525 Dynamically allocate condition code registers.
8530 Do not try to dynamically allocate condition code registers, only
8531 use @code{icc0} and @code{fcc0}.
8536 Change ABI to use double word insns.
8541 Do not use double word instructions.
8546 Use floating point double instructions.
8551 Do not use floating point double instructions.
8556 Use media instructions.
8561 Do not use media instructions.
8566 Use multiply and add/subtract instructions.
8571 Do not use multiply and add/subtract instructions.
8576 Select the FDPIC ABI, that uses function descriptors to represent
8577 pointers to functions. Without any PIC/PIE-related options, it
8578 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
8579 assumes GOT entries and small data are within a 12-bit range from the
8580 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
8581 are computed with 32 bits.
8584 @opindex minline-plt
8586 Enable inlining of PLT entries in function calls to functions that are
8587 not known to bind locally. It has no effect without @option{-mfdpic}.
8588 It's enabled by default if optimizing for speed and compiling for
8589 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
8590 optimization option such as @option{-O3} or above is present in the
8596 Assume a large TLS segment when generating thread-local code.
8601 Do not assume a large TLS segment when generating thread-local code.
8606 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
8607 that is known to be in read-only sections. It's enabled by default,
8608 except for @option{-fpic} or @option{-fpie}: even though it may help
8609 make the global offset table smaller, it trades 1 instruction for 4.
8610 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
8611 one of which may be shared by multiple symbols, and it avoids the need
8612 for a GOT entry for the referenced symbol, so it's more likely to be a
8613 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
8615 @item -multilib-library-pic
8616 @opindex multilib-library-pic
8618 Link with the (library, not FD) pic libraries. It's implied by
8619 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
8620 @option{-fpic} without @option{-mfdpic}. You should never have to use
8626 Follow the EABI requirement of always creating a frame pointer whenever
8627 a stack frame is allocated. This option is enabled by default and can
8628 be disabled with @option{-mno-linked-fp}.
8631 @opindex mlong-calls
8633 Use indirect addressing to call functions outside the current
8634 compilation unit. This allows the functions to be placed anywhere
8635 within the 32-bit address space.
8637 @item -malign-labels
8638 @opindex malign-labels
8640 Try to align labels to an 8-byte boundary by inserting nops into the
8641 previous packet. This option only has an effect when VLIW packing
8642 is enabled. It doesn't create new packets; it merely adds nops to
8646 @opindex mlibrary-pic
8648 Generate position-independent EABI code.
8653 Use only the first four media accumulator registers.
8658 Use all eight media accumulator registers.
8663 Pack VLIW instructions.
8668 Do not pack VLIW instructions.
8673 Do not mark ABI switches in e_flags.
8678 Enable the use of conditional-move instructions (default).
8680 This switch is mainly for debugging the compiler and will likely be removed
8681 in a future version.
8683 @item -mno-cond-move
8684 @opindex mno-cond-move
8686 Disable the use of conditional-move instructions.
8688 This switch is mainly for debugging the compiler and will likely be removed
8689 in a future version.
8694 Enable the use of conditional set instructions (default).
8696 This switch is mainly for debugging the compiler and will likely be removed
8697 in a future version.
8702 Disable the use of conditional set instructions.
8704 This switch is mainly for debugging the compiler and will likely be removed
8705 in a future version.
8710 Enable the use of conditional execution (default).
8712 This switch is mainly for debugging the compiler and will likely be removed
8713 in a future version.
8715 @item -mno-cond-exec
8716 @opindex mno-cond-exec
8718 Disable the use of conditional execution.
8720 This switch is mainly for debugging the compiler and will likely be removed
8721 in a future version.
8724 @opindex mvliw-branch
8726 Run a pass to pack branches into VLIW instructions (default).
8728 This switch is mainly for debugging the compiler and will likely be removed
8729 in a future version.
8731 @item -mno-vliw-branch
8732 @opindex mno-vliw-branch
8734 Do not run a pass to pack branches into VLIW instructions.
8736 This switch is mainly for debugging the compiler and will likely be removed
8737 in a future version.
8739 @item -mmulti-cond-exec
8740 @opindex mmulti-cond-exec
8742 Enable optimization of @code{&&} and @code{||} in conditional execution
8745 This switch is mainly for debugging the compiler and will likely be removed
8746 in a future version.
8748 @item -mno-multi-cond-exec
8749 @opindex mno-multi-cond-exec
8751 Disable optimization of @code{&&} and @code{||} in conditional execution.
8753 This switch is mainly for debugging the compiler and will likely be removed
8754 in a future version.
8756 @item -mnested-cond-exec
8757 @opindex mnested-cond-exec
8759 Enable nested conditional execution optimizations (default).
8761 This switch is mainly for debugging the compiler and will likely be removed
8762 in a future version.
8764 @item -mno-nested-cond-exec
8765 @opindex mno-nested-cond-exec
8767 Disable nested conditional execution optimizations.
8769 This switch is mainly for debugging the compiler and will likely be removed
8770 in a future version.
8772 @item -moptimize-membar
8773 @opindex moptimize-membar
8775 This switch removes redundant @code{membar} instructions from the
8776 compiler generated code. It is enabled by default.
8778 @item -mno-optimize-membar
8779 @opindex mno-optimize-membar
8781 This switch disables the automatic removal of redundant @code{membar}
8782 instructions from the generated code.
8784 @item -mtomcat-stats
8785 @opindex mtomcat-stats
8787 Cause gas to print out tomcat statistics.
8789 @item -mcpu=@var{cpu}
8792 Select the processor type for which to generate code. Possible values are
8793 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8794 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8798 @node GNU/Linux Options
8799 @subsection GNU/Linux Options
8801 These @samp{-m} options are defined for GNU/Linux targets:
8806 Use the GNU C library instead of uClibc. This is the default except
8807 on @samp{*-*-linux-*uclibc*} targets.
8811 Use uClibc instead of the GNU C library. This is the default on
8812 @samp{*-*-linux-*uclibc*} targets.
8815 @node H8/300 Options
8816 @subsection H8/300 Options
8818 These @samp{-m} options are defined for the H8/300 implementations:
8823 Shorten some address references at link time, when possible; uses the
8824 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8825 ld, Using ld}, for a fuller description.
8829 Generate code for the H8/300H@.
8833 Generate code for the H8S@.
8837 Generate code for the H8S and H8/300H in the normal mode. This switch
8838 must be used either with @option{-mh} or @option{-ms}.
8842 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8846 Make @code{int} data 32 bits by default.
8850 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8851 The default for the H8/300H and H8S is to align longs and floats on 4
8853 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8854 This option has no effect on the H8/300.
8858 @subsection HPPA Options
8859 @cindex HPPA Options
8861 These @samp{-m} options are defined for the HPPA family of computers:
8864 @item -march=@var{architecture-type}
8866 Generate code for the specified architecture. The choices for
8867 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8868 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8869 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8870 architecture option for your machine. Code compiled for lower numbered
8871 architectures will run on higher numbered architectures, but not the
8875 @itemx -mpa-risc-1-1
8876 @itemx -mpa-risc-2-0
8877 @opindex mpa-risc-1-0
8878 @opindex mpa-risc-1-1
8879 @opindex mpa-risc-2-0
8880 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8883 @opindex mbig-switch
8884 Generate code suitable for big switch tables. Use this option only if
8885 the assembler/linker complain about out of range branches within a switch
8888 @item -mjump-in-delay
8889 @opindex mjump-in-delay
8890 Fill delay slots of function calls with unconditional jump instructions
8891 by modifying the return pointer for the function call to be the target
8892 of the conditional jump.
8894 @item -mdisable-fpregs
8895 @opindex mdisable-fpregs
8896 Prevent floating point registers from being used in any manner. This is
8897 necessary for compiling kernels which perform lazy context switching of
8898 floating point registers. If you use this option and attempt to perform
8899 floating point operations, the compiler will abort.
8901 @item -mdisable-indexing
8902 @opindex mdisable-indexing
8903 Prevent the compiler from using indexing address modes. This avoids some
8904 rather obscure problems when compiling MIG generated code under MACH@.
8906 @item -mno-space-regs
8907 @opindex mno-space-regs
8908 Generate code that assumes the target has no space registers. This allows
8909 GCC to generate faster indirect calls and use unscaled index address modes.
8911 Such code is suitable for level 0 PA systems and kernels.
8913 @item -mfast-indirect-calls
8914 @opindex mfast-indirect-calls
8915 Generate code that assumes calls never cross space boundaries. This
8916 allows GCC to emit code which performs faster indirect calls.
8918 This option will not work in the presence of shared libraries or nested
8921 @item -mfixed-range=@var{register-range}
8922 @opindex mfixed-range
8923 Generate code treating the given register range as fixed registers.
8924 A fixed register is one that the register allocator can not use. This is
8925 useful when compiling kernel code. A register range is specified as
8926 two registers separated by a dash. Multiple register ranges can be
8927 specified separated by a comma.
8929 @item -mlong-load-store
8930 @opindex mlong-load-store
8931 Generate 3-instruction load and store sequences as sometimes required by
8932 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8935 @item -mportable-runtime
8936 @opindex mportable-runtime
8937 Use the portable calling conventions proposed by HP for ELF systems.
8941 Enable the use of assembler directives only GAS understands.
8943 @item -mschedule=@var{cpu-type}
8945 Schedule code according to the constraints for the machine type
8946 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8947 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8948 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8949 proper scheduling option for your machine. The default scheduling is
8953 @opindex mlinker-opt
8954 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8955 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8956 linkers in which they give bogus error messages when linking some programs.
8959 @opindex msoft-float
8960 Generate output containing library calls for floating point.
8961 @strong{Warning:} the requisite libraries are not available for all HPPA
8962 targets. Normally the facilities of the machine's usual C compiler are
8963 used, but this cannot be done directly in cross-compilation. You must make
8964 your own arrangements to provide suitable library functions for
8965 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8966 does provide software floating point support.
8968 @option{-msoft-float} changes the calling convention in the output file;
8969 therefore, it is only useful if you compile @emph{all} of a program with
8970 this option. In particular, you need to compile @file{libgcc.a}, the
8971 library that comes with GCC, with @option{-msoft-float} in order for
8976 Generate the predefine, @code{_SIO}, for server IO@. The default is
8977 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8978 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
8979 options are available under HP-UX and HI-UX@.
8983 Use GNU ld specific options. This passes @option{-shared} to ld when
8984 building a shared library. It is the default when GCC is configured,
8985 explicitly or implicitly, with the GNU linker. This option does not
8986 have any affect on which ld is called, it only changes what parameters
8987 are passed to that ld. The ld that is called is determined by the
8988 @option{--with-ld} configure option, GCC's program search path, and
8989 finally by the user's @env{PATH}. The linker used by GCC can be printed
8990 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
8991 on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8995 Use HP ld specific options. This passes @option{-b} to ld when building
8996 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8997 links. It is the default when GCC is configured, explicitly or
8998 implicitly, with the HP linker. This option does not have any affect on
8999 which ld is called, it only changes what parameters are passed to that
9000 ld. The ld that is called is determined by the @option{--with-ld}
9001 configure option, GCC's program search path, and finally by the user's
9002 @env{PATH}. The linker used by GCC can be printed using @samp{which
9003 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
9004 HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
9007 @opindex mno-long-calls
9008 Generate code that uses long call sequences. This ensures that a call
9009 is always able to reach linker generated stubs. The default is to generate
9010 long calls only when the distance from the call site to the beginning
9011 of the function or translation unit, as the case may be, exceeds a
9012 predefined limit set by the branch type being used. The limits for
9013 normal calls are 7,600,000 and 240,000 bytes, respectively for the
9014 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
9017 Distances are measured from the beginning of functions when using the
9018 @option{-ffunction-sections} option, or when using the @option{-mgas}
9019 and @option{-mno-portable-runtime} options together under HP-UX with
9022 It is normally not desirable to use this option as it will degrade
9023 performance. However, it may be useful in large applications,
9024 particularly when partial linking is used to build the application.
9026 The types of long calls used depends on the capabilities of the
9027 assembler and linker, and the type of code being generated. The
9028 impact on systems that support long absolute calls, and long pic
9029 symbol-difference or pc-relative calls should be relatively small.
9030 However, an indirect call is used on 32-bit ELF systems in pic code
9031 and it is quite long.
9033 @item -munix=@var{unix-std}
9035 Generate compiler predefines and select a startfile for the specified
9036 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
9037 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
9038 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
9039 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
9040 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
9043 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
9044 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
9045 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
9046 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
9047 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
9048 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
9050 It is @emph{important} to note that this option changes the interfaces
9051 for various library routines. It also affects the operational behavior
9052 of the C library. Thus, @emph{extreme} care is needed in using this
9055 Library code that is intended to operate with more than one UNIX
9056 standard must test, set and restore the variable @var{__xpg4_extended_mask}
9057 as appropriate. Most GNU software doesn't provide this capability.
9061 Suppress the generation of link options to search libdld.sl when the
9062 @option{-static} option is specified on HP-UX 10 and later.
9066 The HP-UX implementation of setlocale in libc has a dependency on
9067 libdld.sl. There isn't an archive version of libdld.sl. Thus,
9068 when the @option{-static} option is specified, special link options
9069 are needed to resolve this dependency.
9071 On HP-UX 10 and later, the GCC driver adds the necessary options to
9072 link with libdld.sl when the @option{-static} option is specified.
9073 This causes the resulting binary to be dynamic. On the 64-bit port,
9074 the linkers generate dynamic binaries by default in any case. The
9075 @option{-nolibdld} option can be used to prevent the GCC driver from
9076 adding these link options.
9080 Add support for multithreading with the @dfn{dce thread} library
9081 under HP-UX@. This option sets flags for both the preprocessor and
9085 @node i386 and x86-64 Options
9086 @subsection Intel 386 and AMD x86-64 Options
9087 @cindex i386 Options
9088 @cindex x86-64 Options
9089 @cindex Intel 386 Options
9090 @cindex AMD x86-64 Options
9092 These @samp{-m} options are defined for the i386 and x86-64 family of
9096 @item -mtune=@var{cpu-type}
9098 Tune to @var{cpu-type} everything applicable about the generated code, except
9099 for the ABI and the set of available instructions. The choices for
9103 Produce code optimized for the most common IA32/AMD64/EM64T processors.
9104 If you know the CPU on which your code will run, then you should use
9105 the corresponding @option{-mtune} option instead of
9106 @option{-mtune=generic}. But, if you do not know exactly what CPU users
9107 of your application will have, then you should use this option.
9109 As new processors are deployed in the marketplace, the behavior of this
9110 option will change. Therefore, if you upgrade to a newer version of
9111 GCC, the code generated option will change to reflect the processors
9112 that were most common when that version of GCC was released.
9114 There is no @option{-march=generic} option because @option{-march}
9115 indicates the instruction set the compiler can use, and there is no
9116 generic instruction set applicable to all processors. In contrast,
9117 @option{-mtune} indicates the processor (or, in this case, collection of
9118 processors) for which the code is optimized.
9120 Original Intel's i386 CPU@.
9122 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
9124 Intel Pentium CPU with no MMX support.
9126 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
9128 Intel PentiumPro CPU@.
9130 Same as @code{generic}, but when used as @code{march} option, PentiumPro
9131 instruction set will be used, so the code will run on all i686 familly chips.
9133 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
9134 @item pentium3, pentium3m
9135 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
9138 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
9139 support. Used by Centrino notebooks.
9140 @item pentium4, pentium4m
9141 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
9143 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
9146 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
9147 SSE2 and SSE3 instruction set support.
9149 AMD K6 CPU with MMX instruction set support.
9151 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
9152 @item athlon, athlon-tbird
9153 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
9155 @item athlon-4, athlon-xp, athlon-mp
9156 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
9157 instruction set support.
9158 @item k8, opteron, athlon64, athlon-fx
9159 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
9160 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
9162 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
9165 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
9166 instruction set support.
9168 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
9169 implemented for this chip.)
9171 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
9172 implemented for this chip.)
9175 While picking a specific @var{cpu-type} will schedule things appropriately
9176 for that particular chip, the compiler will not generate any code that
9177 does not run on the i386 without the @option{-march=@var{cpu-type}} option
9180 @item -march=@var{cpu-type}
9182 Generate instructions for the machine type @var{cpu-type}. The choices
9183 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
9184 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
9186 @item -mcpu=@var{cpu-type}
9188 A deprecated synonym for @option{-mtune}.
9197 @opindex mpentiumpro
9198 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
9199 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
9200 These synonyms are deprecated.
9202 @item -mfpmath=@var{unit}
9204 Generate floating point arithmetics for selected unit @var{unit}. The choices
9209 Use the standard 387 floating point coprocessor present majority of chips and
9210 emulated otherwise. Code compiled with this option will run almost everywhere.
9211 The temporary results are computed in 80bit precision instead of precision
9212 specified by the type resulting in slightly different results compared to most
9213 of other chips. See @option{-ffloat-store} for more detailed description.
9215 This is the default choice for i386 compiler.
9218 Use scalar floating point instructions present in the SSE instruction set.
9219 This instruction set is supported by Pentium3 and newer chips, in the AMD line
9220 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
9221 instruction set supports only single precision arithmetics, thus the double and
9222 extended precision arithmetics is still done using 387. Later version, present
9223 only in Pentium4 and the future AMD x86-64 chips supports double precision
9226 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
9227 or @option{-msse2} switches to enable SSE extensions and make this option
9228 effective. For the x86-64 compiler, these extensions are enabled by default.
9230 The resulting code should be considerably faster in the majority of cases and avoid
9231 the numerical instability problems of 387 code, but may break some existing
9232 code that expects temporaries to be 80bit.
9234 This is the default choice for the x86-64 compiler.
9237 Attempt to utilize both instruction sets at once. This effectively double the
9238 amount of available registers and on chips with separate execution units for
9239 387 and SSE the execution resources too. Use this option with care, as it is
9240 still experimental, because the GCC register allocator does not model separate
9241 functional units well resulting in instable performance.
9244 @item -masm=@var{dialect}
9245 @opindex masm=@var{dialect}
9246 Output asm instructions using selected @var{dialect}. Supported
9247 choices are @samp{intel} or @samp{att} (the default one). Darwin does
9248 not support @samp{intel}.
9253 @opindex mno-ieee-fp
9254 Control whether or not the compiler uses IEEE floating point
9255 comparisons. These handle correctly the case where the result of a
9256 comparison is unordered.
9259 @opindex msoft-float
9260 Generate output containing library calls for floating point.
9261 @strong{Warning:} the requisite libraries are not part of GCC@.
9262 Normally the facilities of the machine's usual C compiler are used, but
9263 this can't be done directly in cross-compilation. You must make your
9264 own arrangements to provide suitable library functions for
9267 On machines where a function returns floating point results in the 80387
9268 register stack, some floating point opcodes may be emitted even if
9269 @option{-msoft-float} is used.
9271 @item -mno-fp-ret-in-387
9272 @opindex mno-fp-ret-in-387
9273 Do not use the FPU registers for return values of functions.
9275 The usual calling convention has functions return values of types
9276 @code{float} and @code{double} in an FPU register, even if there
9277 is no FPU@. The idea is that the operating system should emulate
9280 The option @option{-mno-fp-ret-in-387} causes such values to be returned
9281 in ordinary CPU registers instead.
9283 @item -mno-fancy-math-387
9284 @opindex mno-fancy-math-387
9285 Some 387 emulators do not support the @code{sin}, @code{cos} and
9286 @code{sqrt} instructions for the 387. Specify this option to avoid
9287 generating those instructions. This option is the default on FreeBSD,
9288 OpenBSD and NetBSD@. This option is overridden when @option{-march}
9289 indicates that the target cpu will always have an FPU and so the
9290 instruction will not need emulation. As of revision 2.6.1, these
9291 instructions are not generated unless you also use the
9292 @option{-funsafe-math-optimizations} switch.
9294 @item -malign-double
9295 @itemx -mno-align-double
9296 @opindex malign-double
9297 @opindex mno-align-double
9298 Control whether GCC aligns @code{double}, @code{long double}, and
9299 @code{long long} variables on a two word boundary or a one word
9300 boundary. Aligning @code{double} variables on a two word boundary will
9301 produce code that runs somewhat faster on a @samp{Pentium} at the
9302 expense of more memory.
9304 @strong{Warning:} if you use the @option{-malign-double} switch,
9305 structures containing the above types will be aligned differently than
9306 the published application binary interface specifications for the 386
9307 and will not be binary compatible with structures in code compiled
9308 without that switch.
9310 @item -m96bit-long-double
9311 @itemx -m128bit-long-double
9312 @opindex m96bit-long-double
9313 @opindex m128bit-long-double
9314 These switches control the size of @code{long double} type. The i386
9315 application binary interface specifies the size to be 96 bits,
9316 so @option{-m96bit-long-double} is the default in 32 bit mode.
9318 Modern architectures (Pentium and newer) would prefer @code{long double}
9319 to be aligned to an 8 or 16 byte boundary. In arrays or structures
9320 conforming to the ABI, this would not be possible. So specifying a
9321 @option{-m128bit-long-double} will align @code{long double}
9322 to a 16 byte boundary by padding the @code{long double} with an additional
9325 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
9326 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
9328 Notice that neither of these options enable any extra precision over the x87
9329 standard of 80 bits for a @code{long double}.
9331 @strong{Warning:} if you override the default value for your target ABI, the
9332 structures and arrays containing @code{long double} variables will change
9333 their size as well as function calling convention for function taking
9334 @code{long double} will be modified. Hence they will not be binary
9335 compatible with arrays or structures in code compiled without that switch.
9337 @item -mmlarge-data-threshold=@var{number}
9338 @opindex mlarge-data-threshold=@var{number}
9339 When @option{-mcmodel=medium} is specified, the data greater than
9340 @var{threshold} are placed in large data section. This value must be the
9341 same across all object linked into the binary and defaults to 65535.
9344 @itemx -mno-svr3-shlib
9345 @opindex msvr3-shlib
9346 @opindex mno-svr3-shlib
9347 Control whether GCC places uninitialized local variables into the
9348 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
9349 into @code{bss}. These options are meaningful only on System V Release 3.
9353 Use a different function-calling convention, in which functions that
9354 take a fixed number of arguments return with the @code{ret} @var{num}
9355 instruction, which pops their arguments while returning. This saves one
9356 instruction in the caller since there is no need to pop the arguments
9359 You can specify that an individual function is called with this calling
9360 sequence with the function attribute @samp{stdcall}. You can also
9361 override the @option{-mrtd} option by using the function attribute
9362 @samp{cdecl}. @xref{Function Attributes}.
9364 @strong{Warning:} this calling convention is incompatible with the one
9365 normally used on Unix, so you cannot use it if you need to call
9366 libraries compiled with the Unix compiler.
9368 Also, you must provide function prototypes for all functions that
9369 take variable numbers of arguments (including @code{printf});
9370 otherwise incorrect code will be generated for calls to those
9373 In addition, seriously incorrect code will result if you call a
9374 function with too many arguments. (Normally, extra arguments are
9375 harmlessly ignored.)
9377 @item -mregparm=@var{num}
9379 Control how many registers are used to pass integer arguments. By
9380 default, no registers are used to pass arguments, and at most 3
9381 registers can be used. You can control this behavior for a specific
9382 function by using the function attribute @samp{regparm}.
9383 @xref{Function Attributes}.
9385 @strong{Warning:} if you use this switch, and
9386 @var{num} is nonzero, then you must build all modules with the same
9387 value, including any libraries. This includes the system libraries and
9391 @opindex msseregparm
9392 Use SSE register passing conventions for float and double arguments
9393 and return values. You can control this behavior for a specific
9394 function by using the function attribute @samp{sseregparm}.
9395 @xref{Function Attributes}.
9397 @strong{Warning:} if you use this switch then you must build all
9398 modules with the same value, including any libraries. This includes
9399 the system libraries and startup modules.
9401 @item -mpreferred-stack-boundary=@var{num}
9402 @opindex mpreferred-stack-boundary
9403 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
9404 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
9405 the default is 4 (16 bytes or 128 bits), except when optimizing for code
9406 size (@option{-Os}), in which case the default is the minimum correct
9407 alignment (4 bytes for x86, and 8 bytes for x86-64).
9409 On Pentium and PentiumPro, @code{double} and @code{long double} values
9410 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
9411 suffer significant run time performance penalties. On Pentium III, the
9412 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
9413 penalties if it is not 16 byte aligned.
9415 To ensure proper alignment of this values on the stack, the stack boundary
9416 must be as aligned as that required by any value stored on the stack.
9417 Further, every function must be generated such that it keeps the stack
9418 aligned. Thus calling a function compiled with a higher preferred
9419 stack boundary from a function compiled with a lower preferred stack
9420 boundary will most likely misalign the stack. It is recommended that
9421 libraries that use callbacks always use the default setting.
9423 This extra alignment does consume extra stack space, and generally
9424 increases code size. Code that is sensitive to stack space usage, such
9425 as embedded systems and operating system kernels, may want to reduce the
9426 preferred alignment to @option{-mpreferred-stack-boundary=2}.
9444 These switches enable or disable the use of instructions in the MMX,
9445 SSE, SSE2 or 3DNow! extended instruction sets. These extensions are
9446 also available as built-in functions: see @ref{X86 Built-in Functions},
9447 for details of the functions enabled and disabled by these switches.
9449 To have SSE/SSE2 instructions generated automatically from floating-point
9450 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
9452 These options will enable GCC to use these extended instructions in
9453 generated code, even without @option{-mfpmath=sse}. Applications which
9454 perform runtime CPU detection must compile separate files for each
9455 supported architecture, using the appropriate flags. In particular,
9456 the file containing the CPU detection code should be compiled without
9461 Use special versions of certain libm routines that come with an SSE
9462 ABI and an SSE implementation. Useful together with @option{-mfpmath=sse}
9463 to avoid moving values between SSE registers and the x87 FP stack.
9466 @itemx -mno-push-args
9468 @opindex mno-push-args
9469 Use PUSH operations to store outgoing parameters. This method is shorter
9470 and usually equally fast as method using SUB/MOV operations and is enabled
9471 by default. In some cases disabling it may improve performance because of
9472 improved scheduling and reduced dependencies.
9474 @item -maccumulate-outgoing-args
9475 @opindex maccumulate-outgoing-args
9476 If enabled, the maximum amount of space required for outgoing arguments will be
9477 computed in the function prologue. This is faster on most modern CPUs
9478 because of reduced dependencies, improved scheduling and reduced stack usage
9479 when preferred stack boundary is not equal to 2. The drawback is a notable
9480 increase in code size. This switch implies @option{-mno-push-args}.
9484 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
9485 on thread-safe exception handling must compile and link all code with the
9486 @option{-mthreads} option. When compiling, @option{-mthreads} defines
9487 @option{-D_MT}; when linking, it links in a special thread helper library
9488 @option{-lmingwthrd} which cleans up per thread exception handling data.
9490 @item -mno-align-stringops
9491 @opindex mno-align-stringops
9492 Do not align destination of inlined string operations. This switch reduces
9493 code size and improves performance in case the destination is already aligned,
9494 but GCC doesn't know about it.
9496 @item -minline-all-stringops
9497 @opindex minline-all-stringops
9498 By default GCC inlines string operations only when destination is known to be
9499 aligned at least to 4 byte boundary. This enables more inlining, increase code
9500 size, but may improve performance of code that depends on fast memcpy, strlen
9501 and memset for short lengths.
9503 @item -momit-leaf-frame-pointer
9504 @opindex momit-leaf-frame-pointer
9505 Don't keep the frame pointer in a register for leaf functions. This
9506 avoids the instructions to save, set up and restore frame pointers and
9507 makes an extra register available in leaf functions. The option
9508 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9509 which might make debugging harder.
9511 @item -mtls-direct-seg-refs
9512 @itemx -mno-tls-direct-seg-refs
9513 @opindex mtls-direct-seg-refs
9514 Controls whether TLS variables may be accessed with offsets from the
9515 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
9516 or whether the thread base pointer must be added. Whether or not this
9517 is legal depends on the operating system, and whether it maps the
9518 segment to cover the entire TLS area.
9520 For systems that use GNU libc, the default is on.
9523 These @samp{-m} switches are supported in addition to the above
9524 on AMD x86-64 processors in 64-bit environments.
9531 Generate code for a 32-bit or 64-bit environment.
9532 The 32-bit environment sets int, long and pointer to 32 bits and
9533 generates code that runs on any i386 system.
9534 The 64-bit environment sets int to 32 bits and long and pointer
9535 to 64 bits and generates code for AMD's x86-64 architecture.
9538 @opindex no-red-zone
9539 Do not use a so called red zone for x86-64 code. The red zone is mandated
9540 by the x86-64 ABI, it is a 128-byte area beyond the location of the
9541 stack pointer that will not be modified by signal or interrupt handlers
9542 and therefore can be used for temporary data without adjusting the stack
9543 pointer. The flag @option{-mno-red-zone} disables this red zone.
9545 @item -mcmodel=small
9546 @opindex mcmodel=small
9547 Generate code for the small code model: the program and its symbols must
9548 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
9549 Programs can be statically or dynamically linked. This is the default
9552 @item -mcmodel=kernel
9553 @opindex mcmodel=kernel
9554 Generate code for the kernel code model. The kernel runs in the
9555 negative 2 GB of the address space.
9556 This model has to be used for Linux kernel code.
9558 @item -mcmodel=medium
9559 @opindex mcmodel=medium
9560 Generate code for the medium model: The program is linked in the lower 2
9561 GB of the address space but symbols can be located anywhere in the
9562 address space. Programs can be statically or dynamically linked, but
9563 building of shared libraries are not supported with the medium model.
9565 @item -mcmodel=large
9566 @opindex mcmodel=large
9567 Generate code for the large model: This model makes no assumptions
9568 about addresses and sizes of sections. Currently GCC does not implement
9573 @subsection IA-64 Options
9574 @cindex IA-64 Options
9576 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9580 @opindex mbig-endian
9581 Generate code for a big endian target. This is the default for HP-UX@.
9583 @item -mlittle-endian
9584 @opindex mlittle-endian
9585 Generate code for a little endian target. This is the default for AIX5
9592 Generate (or don't) code for the GNU assembler. This is the default.
9593 @c Also, this is the default if the configure option @option{--with-gnu-as}
9600 Generate (or don't) code for the GNU linker. This is the default.
9601 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9606 Generate code that does not use a global pointer register. The result
9607 is not position independent code, and violates the IA-64 ABI@.
9609 @item -mvolatile-asm-stop
9610 @itemx -mno-volatile-asm-stop
9611 @opindex mvolatile-asm-stop
9612 @opindex mno-volatile-asm-stop
9613 Generate (or don't) a stop bit immediately before and after volatile asm
9616 @item -mregister-names
9617 @itemx -mno-register-names
9618 @opindex mregister-names
9619 @opindex mno-register-names
9620 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9621 the stacked registers. This may make assembler output more readable.
9627 Disable (or enable) optimizations that use the small data section. This may
9628 be useful for working around optimizer bugs.
9631 @opindex mconstant-gp
9632 Generate code that uses a single constant global pointer value. This is
9633 useful when compiling kernel code.
9637 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9638 This is useful when compiling firmware code.
9640 @item -minline-float-divide-min-latency
9641 @opindex minline-float-divide-min-latency
9642 Generate code for inline divides of floating point values
9643 using the minimum latency algorithm.
9645 @item -minline-float-divide-max-throughput
9646 @opindex minline-float-divide-max-throughput
9647 Generate code for inline divides of floating point values
9648 using the maximum throughput algorithm.
9650 @item -minline-int-divide-min-latency
9651 @opindex minline-int-divide-min-latency
9652 Generate code for inline divides of integer values
9653 using the minimum latency algorithm.
9655 @item -minline-int-divide-max-throughput
9656 @opindex minline-int-divide-max-throughput
9657 Generate code for inline divides of integer values
9658 using the maximum throughput algorithm.
9660 @item -minline-sqrt-min-latency
9661 @opindex minline-sqrt-min-latency
9662 Generate code for inline square roots
9663 using the minimum latency algorithm.
9665 @item -minline-sqrt-max-throughput
9666 @opindex minline-sqrt-max-throughput
9667 Generate code for inline square roots
9668 using the maximum throughput algorithm.
9670 @item -mno-dwarf2-asm
9672 @opindex mno-dwarf2-asm
9673 @opindex mdwarf2-asm
9674 Don't (or do) generate assembler code for the DWARF2 line number debugging
9675 info. This may be useful when not using the GNU assembler.
9677 @item -mearly-stop-bits
9678 @itemx -mno-early-stop-bits
9679 @opindex mearly-stop-bits
9680 @opindex mno-early-stop-bits
9681 Allow stop bits to be placed earlier than immediately preceding the
9682 instruction that triggered the stop bit. This can improve instruction
9683 scheduling, but does not always do so.
9685 @item -mfixed-range=@var{register-range}
9686 @opindex mfixed-range
9687 Generate code treating the given register range as fixed registers.
9688 A fixed register is one that the register allocator can not use. This is
9689 useful when compiling kernel code. A register range is specified as
9690 two registers separated by a dash. Multiple register ranges can be
9691 specified separated by a comma.
9693 @item -mtls-size=@var{tls-size}
9695 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
9698 @item -mtune=@var{cpu-type}
9700 Tune the instruction scheduling for a particular CPU, Valid values are
9701 itanium, itanium1, merced, itanium2, and mckinley.
9707 Add support for multithreading using the POSIX threads library. This
9708 option sets flags for both the preprocessor and linker. It does
9709 not affect the thread safety of object code produced by the compiler or
9710 that of libraries supplied with it. These are HP-UX specific flags.
9716 Generate code for a 32-bit or 64-bit environment.
9717 The 32-bit environment sets int, long and pointer to 32 bits.
9718 The 64-bit environment sets int to 32 bits and long and pointer
9719 to 64 bits. These are HP-UX specific flags.
9724 @subsection M32C Options
9725 @cindex M32C options
9728 @item -mcpu=@var{name}
9730 Select the CPU for which code is generated. @var{name} may be one of
9731 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
9732 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
9737 Specifies that the program will be run on the simulator. This causes
9738 an alternate runtime library to be linked in which supports, for
9739 example, file I/O. You must not use this option when generating
9740 programs that will run on real hardware; you must provide your own
9741 runtime library for whatever I/O functions are needed.
9743 @item -memregs=@var{number}
9745 Specifies the number of memory-based pseudo-registers GCC will use
9746 during code generation. These pseudo-registers will be used like real
9747 registers, so there is a tradeoff between GCC's ability to fit the
9748 code into available registers, and the performance penalty of using
9749 memory instead of registers. Note that all modules in a program must
9750 be compiled with the same value for this option. Because of that, you
9751 must not use this option with the default runtime libraries gcc
9756 @node M32R/D Options
9757 @subsection M32R/D Options
9758 @cindex M32R/D options
9760 These @option{-m} options are defined for Renesas M32R/D architectures:
9765 Generate code for the M32R/2@.
9769 Generate code for the M32R/X@.
9773 Generate code for the M32R@. This is the default.
9776 @opindex mmodel=small
9777 Assume all objects live in the lower 16MB of memory (so that their addresses
9778 can be loaded with the @code{ld24} instruction), and assume all subroutines
9779 are reachable with the @code{bl} instruction.
9780 This is the default.
9782 The addressability of a particular object can be set with the
9783 @code{model} attribute.
9785 @item -mmodel=medium
9786 @opindex mmodel=medium
9787 Assume objects may be anywhere in the 32-bit address space (the compiler
9788 will generate @code{seth/add3} instructions to load their addresses), and
9789 assume all subroutines are reachable with the @code{bl} instruction.
9792 @opindex mmodel=large
9793 Assume objects may be anywhere in the 32-bit address space (the compiler
9794 will generate @code{seth/add3} instructions to load their addresses), and
9795 assume subroutines may not be reachable with the @code{bl} instruction
9796 (the compiler will generate the much slower @code{seth/add3/jl}
9797 instruction sequence).
9800 @opindex msdata=none
9801 Disable use of the small data area. Variables will be put into
9802 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
9803 @code{section} attribute has been specified).
9804 This is the default.
9806 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
9807 Objects may be explicitly put in the small data area with the
9808 @code{section} attribute using one of these sections.
9811 @opindex msdata=sdata
9812 Put small global and static data in the small data area, but do not
9813 generate special code to reference them.
9817 Put small global and static data in the small data area, and generate
9818 special instructions to reference them.
9822 @cindex smaller data references
9823 Put global and static objects less than or equal to @var{num} bytes
9824 into the small data or bss sections instead of the normal data or bss
9825 sections. The default value of @var{num} is 8.
9826 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
9827 for this option to have any effect.
9829 All modules should be compiled with the same @option{-G @var{num}} value.
9830 Compiling with different values of @var{num} may or may not work; if it
9831 doesn't the linker will give an error message---incorrect code will not be
9836 Makes the M32R specific code in the compiler display some statistics
9837 that might help in debugging programs.
9840 @opindex malign-loops
9841 Align all loops to a 32-byte boundary.
9843 @item -mno-align-loops
9844 @opindex mno-align-loops
9845 Do not enforce a 32-byte alignment for loops. This is the default.
9847 @item -missue-rate=@var{number}
9848 @opindex missue-rate=@var{number}
9849 Issue @var{number} instructions per cycle. @var{number} can only be 1
9852 @item -mbranch-cost=@var{number}
9853 @opindex mbranch-cost=@var{number}
9854 @var{number} can only be 1 or 2. If it is 1 then branches will be
9855 preferred over conditional code, if it is 2, then the opposite will
9858 @item -mflush-trap=@var{number}
9859 @opindex mflush-trap=@var{number}
9860 Specifies the trap number to use to flush the cache. The default is
9861 12. Valid numbers are between 0 and 15 inclusive.
9863 @item -mno-flush-trap
9864 @opindex mno-flush-trap
9865 Specifies that the cache cannot be flushed by using a trap.
9867 @item -mflush-func=@var{name}
9868 @opindex mflush-func=@var{name}
9869 Specifies the name of the operating system function to call to flush
9870 the cache. The default is @emph{_flush_cache}, but a function call
9871 will only be used if a trap is not available.
9873 @item -mno-flush-func
9874 @opindex mno-flush-func
9875 Indicates that there is no OS function for flushing the cache.
9879 @node M680x0 Options
9880 @subsection M680x0 Options
9881 @cindex M680x0 options
9883 These are the @samp{-m} options defined for the 68000 series. The default
9884 values for these options depends on which style of 68000 was selected when
9885 the compiler was configured; the defaults for the most common choices are
9893 Generate output for a 68000. This is the default
9894 when the compiler is configured for 68000-based systems.
9896 Use this option for microcontrollers with a 68000 or EC000 core,
9897 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
9903 Generate output for a 68020. This is the default
9904 when the compiler is configured for 68020-based systems.
9908 Generate output containing 68881 instructions for floating point.
9909 This is the default for most 68020 systems unless @option{--nfp} was
9910 specified when the compiler was configured.
9914 Generate output for a 68030. This is the default when the compiler is
9915 configured for 68030-based systems.
9919 Generate output for a 68040. This is the default when the compiler is
9920 configured for 68040-based systems.
9922 This option inhibits the use of 68881/68882 instructions that have to be
9923 emulated by software on the 68040. Use this option if your 68040 does not
9924 have code to emulate those instructions.
9928 Generate output for a 68060. This is the default when the compiler is
9929 configured for 68060-based systems.
9931 This option inhibits the use of 68020 and 68881/68882 instructions that
9932 have to be emulated by software on the 68060. Use this option if your 68060
9933 does not have code to emulate those instructions.
9937 Generate output for a CPU32. This is the default
9938 when the compiler is configured for CPU32-based systems.
9940 Use this option for microcontrollers with a
9941 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9942 68336, 68340, 68341, 68349 and 68360.
9946 Generate output for a 520X ``coldfire'' family cpu. This is the default
9947 when the compiler is configured for 520X-based systems.
9949 Use this option for microcontroller with a 5200 core, including
9950 the MCF5202, MCF5203, MCF5204 and MCF5202.
9954 Generate output for a ColdFire V4e family cpu (e.g.@: 547x/548x).
9955 This includes use of hardware floating point instructions.
9959 Generate output for a 68040, without using any of the new instructions.
9960 This results in code which can run relatively efficiently on either a
9961 68020/68881 or a 68030 or a 68040. The generated code does use the
9962 68881 instructions that are emulated on the 68040.
9966 Generate output for a 68060, without using any of the new instructions.
9967 This results in code which can run relatively efficiently on either a
9968 68020/68881 or a 68030 or a 68040. The generated code does use the
9969 68881 instructions that are emulated on the 68060.
9972 @opindex msoft-float
9973 Generate output containing library calls for floating point.
9974 @strong{Warning:} the requisite libraries are not available for all m68k
9975 targets. Normally the facilities of the machine's usual C compiler are
9976 used, but this can't be done directly in cross-compilation. You must
9977 make your own arrangements to provide suitable library functions for
9978 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9979 @samp{m68k-*-coff} do provide software floating point support.
9983 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9984 Additionally, parameters passed on the stack are also aligned to a
9985 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9988 @opindex mnobitfield
9989 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9990 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9994 Do use the bit-field instructions. The @option{-m68020} option implies
9995 @option{-mbitfield}. This is the default if you use a configuration
9996 designed for a 68020.
10000 Use a different function-calling convention, in which functions
10001 that take a fixed number of arguments return with the @code{rtd}
10002 instruction, which pops their arguments while returning. This
10003 saves one instruction in the caller since there is no need to pop
10004 the arguments there.
10006 This calling convention is incompatible with the one normally
10007 used on Unix, so you cannot use it if you need to call libraries
10008 compiled with the Unix compiler.
10010 Also, you must provide function prototypes for all functions that
10011 take variable numbers of arguments (including @code{printf});
10012 otherwise incorrect code will be generated for calls to those
10015 In addition, seriously incorrect code will result if you call a
10016 function with too many arguments. (Normally, extra arguments are
10017 harmlessly ignored.)
10019 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
10020 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
10023 @itemx -mno-align-int
10024 @opindex malign-int
10025 @opindex mno-align-int
10026 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
10027 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
10028 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
10029 Aligning variables on 32-bit boundaries produces code that runs somewhat
10030 faster on processors with 32-bit busses at the expense of more memory.
10032 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
10033 align structures containing the above types differently than
10034 most published application binary interface specifications for the m68k.
10038 Use the pc-relative addressing mode of the 68000 directly, instead of
10039 using a global offset table. At present, this option implies @option{-fpic},
10040 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
10041 not presently supported with @option{-mpcrel}, though this could be supported for
10042 68020 and higher processors.
10044 @item -mno-strict-align
10045 @itemx -mstrict-align
10046 @opindex mno-strict-align
10047 @opindex mstrict-align
10048 Do not (do) assume that unaligned memory references will be handled by
10052 Generate code that allows the data segment to be located in a different
10053 area of memory from the text segment. This allows for execute in place in
10054 an environment without virtual memory management. This option implies
10057 @item -mno-sep-data
10058 Generate code that assumes that the data segment follows the text segment.
10059 This is the default.
10061 @item -mid-shared-library
10062 Generate code that supports shared libraries via the library ID method.
10063 This allows for execute in place and shared libraries in an environment
10064 without virtual memory management. This option implies @option{-fPIC}.
10066 @item -mno-id-shared-library
10067 Generate code that doesn't assume ID based shared libraries are being used.
10068 This is the default.
10070 @item -mshared-library-id=n
10071 Specified the identification number of the ID based shared library being
10072 compiled. Specifying a value of 0 will generate more compact code, specifying
10073 other values will force the allocation of that number to the current
10074 library but is no more space or time efficient than omitting this option.
10078 @node M68hc1x Options
10079 @subsection M68hc1x Options
10080 @cindex M68hc1x options
10082 These are the @samp{-m} options defined for the 68hc11 and 68hc12
10083 microcontrollers. The default values for these options depends on
10084 which style of microcontroller was selected when the compiler was configured;
10085 the defaults for the most common choices are given below.
10092 Generate output for a 68HC11. This is the default
10093 when the compiler is configured for 68HC11-based systems.
10099 Generate output for a 68HC12. This is the default
10100 when the compiler is configured for 68HC12-based systems.
10106 Generate output for a 68HCS12.
10108 @item -mauto-incdec
10109 @opindex mauto-incdec
10110 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
10117 Enable the use of 68HC12 min and max instructions.
10120 @itemx -mno-long-calls
10121 @opindex mlong-calls
10122 @opindex mno-long-calls
10123 Treat all calls as being far away (near). If calls are assumed to be
10124 far away, the compiler will use the @code{call} instruction to
10125 call a function and the @code{rtc} instruction for returning.
10129 Consider type @code{int} to be 16 bits wide, like @code{short int}.
10131 @item -msoft-reg-count=@var{count}
10132 @opindex msoft-reg-count
10133 Specify the number of pseudo-soft registers which are used for the
10134 code generation. The maximum number is 32. Using more pseudo-soft
10135 register may or may not result in better code depending on the program.
10136 The default is 4 for 68HC11 and 2 for 68HC12.
10140 @node MCore Options
10141 @subsection MCore Options
10142 @cindex MCore options
10144 These are the @samp{-m} options defined for the Motorola M*Core
10150 @itemx -mno-hardlit
10152 @opindex mno-hardlit
10153 Inline constants into the code stream if it can be done in two
10154 instructions or less.
10160 Use the divide instruction. (Enabled by default).
10162 @item -mrelax-immediate
10163 @itemx -mno-relax-immediate
10164 @opindex mrelax-immediate
10165 @opindex mno-relax-immediate
10166 Allow arbitrary sized immediates in bit operations.
10168 @item -mwide-bitfields
10169 @itemx -mno-wide-bitfields
10170 @opindex mwide-bitfields
10171 @opindex mno-wide-bitfields
10172 Always treat bit-fields as int-sized.
10174 @item -m4byte-functions
10175 @itemx -mno-4byte-functions
10176 @opindex m4byte-functions
10177 @opindex mno-4byte-functions
10178 Force all functions to be aligned to a four byte boundary.
10180 @item -mcallgraph-data
10181 @itemx -mno-callgraph-data
10182 @opindex mcallgraph-data
10183 @opindex mno-callgraph-data
10184 Emit callgraph information.
10187 @itemx -mno-slow-bytes
10188 @opindex mslow-bytes
10189 @opindex mno-slow-bytes
10190 Prefer word access when reading byte quantities.
10192 @item -mlittle-endian
10193 @itemx -mbig-endian
10194 @opindex mlittle-endian
10195 @opindex mbig-endian
10196 Generate code for a little endian target.
10202 Generate code for the 210 processor.
10206 @subsection MIPS Options
10207 @cindex MIPS options
10213 Generate big-endian code.
10217 Generate little-endian code. This is the default for @samp{mips*el-*-*}
10220 @item -march=@var{arch}
10222 Generate code that will run on @var{arch}, which can be the name of a
10223 generic MIPS ISA, or the name of a particular processor.
10225 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
10226 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
10227 The processor names are:
10228 @samp{4kc}, @samp{4km}, @samp{4kp},
10229 @samp{5kc}, @samp{5kf},
10231 @samp{24k}, @samp{24kc}, @samp{24kf}, @samp{24kx},
10234 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
10235 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
10236 @samp{rm7000}, @samp{rm9000},
10239 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
10240 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
10241 The special value @samp{from-abi} selects the
10242 most compatible architecture for the selected ABI (that is,
10243 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
10245 In processor names, a final @samp{000} can be abbreviated as @samp{k}
10246 (for example, @samp{-march=r2k}). Prefixes are optional, and
10247 @samp{vr} may be written @samp{r}.
10249 GCC defines two macros based on the value of this option. The first
10250 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
10251 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
10252 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
10253 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
10254 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
10256 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
10257 above. In other words, it will have the full prefix and will not
10258 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
10259 the macro names the resolved architecture (either @samp{"mips1"} or
10260 @samp{"mips3"}). It names the default architecture when no
10261 @option{-march} option is given.
10263 @item -mtune=@var{arch}
10265 Optimize for @var{arch}. Among other things, this option controls
10266 the way instructions are scheduled, and the perceived cost of arithmetic
10267 operations. The list of @var{arch} values is the same as for
10270 When this option is not used, GCC will optimize for the processor
10271 specified by @option{-march}. By using @option{-march} and
10272 @option{-mtune} together, it is possible to generate code that will
10273 run on a family of processors, but optimize the code for one
10274 particular member of that family.
10276 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
10277 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
10278 @samp{-march} ones described above.
10282 Equivalent to @samp{-march=mips1}.
10286 Equivalent to @samp{-march=mips2}.
10290 Equivalent to @samp{-march=mips3}.
10294 Equivalent to @samp{-march=mips4}.
10298 Equivalent to @samp{-march=mips32}.
10302 Equivalent to @samp{-march=mips32r2}.
10306 Equivalent to @samp{-march=mips64}.
10311 @opindex mno-mips16
10312 Generate (do not generate) MIPS16 code. If GCC is targetting a
10313 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
10325 Generate code for the given ABI@.
10327 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
10328 generates 64-bit code when you select a 64-bit architecture, but you
10329 can use @option{-mgp32} to get 32-bit code instead.
10331 For information about the O64 ABI, see
10332 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
10335 @itemx -mno-abicalls
10337 @opindex mno-abicalls
10338 Generate (do not generate) SVR4-style position-independent code.
10339 @option{-mabicalls} is the default for SVR4-based systems.
10345 Lift (do not lift) the usual restrictions on the size of the global
10348 GCC normally uses a single instruction to load values from the GOT@.
10349 While this is relatively efficient, it will only work if the GOT
10350 is smaller than about 64k. Anything larger will cause the linker
10351 to report an error such as:
10353 @cindex relocation truncated to fit (MIPS)
10355 relocation truncated to fit: R_MIPS_GOT16 foobar
10358 If this happens, you should recompile your code with @option{-mxgot}.
10359 It should then work with very large GOTs, although it will also be
10360 less efficient, since it will take three instructions to fetch the
10361 value of a global symbol.
10363 Note that some linkers can create multiple GOTs. If you have such a
10364 linker, you should only need to use @option{-mxgot} when a single object
10365 file accesses more than 64k's worth of GOT entries. Very few do.
10367 These options have no effect unless GCC is generating position
10372 Assume that general-purpose registers are 32 bits wide.
10376 Assume that general-purpose registers are 64 bits wide.
10380 Assume that floating-point registers are 32 bits wide.
10384 Assume that floating-point registers are 64 bits wide.
10387 @opindex mhard-float
10388 Use floating-point coprocessor instructions.
10391 @opindex msoft-float
10392 Do not use floating-point coprocessor instructions. Implement
10393 floating-point calculations using library calls instead.
10395 @item -msingle-float
10396 @opindex msingle-float
10397 Assume that the floating-point coprocessor only supports single-precision
10400 @itemx -mdouble-float
10401 @opindex mdouble-float
10402 Assume that the floating-point coprocessor supports double-precision
10403 operations. This is the default.
10409 Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
10411 @itemx -mpaired-single
10412 @itemx -mno-paired-single
10413 @opindex mpaired-single
10414 @opindex mno-paired-single
10415 Use (do not use) paired-single floating-point instructions.
10416 @xref{MIPS Paired-Single Support}. This option can only be used
10417 when generating 64-bit code and requires hardware floating-point
10418 support to be enabled.
10423 @opindex mno-mips3d
10424 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
10425 The option @option{-mips3d} implies @option{-mpaired-single}.
10429 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
10430 an explanation of the default and the way that the pointer size is
10435 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
10437 The default size of @code{int}s, @code{long}s and pointers depends on
10438 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
10439 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
10440 32-bit @code{long}s. Pointers are the same size as @code{long}s,
10441 or the same size as integer registers, whichever is smaller.
10447 Assume (do not assume) that all symbols have 32-bit values, regardless
10448 of the selected ABI@. This option is useful in combination with
10449 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
10450 to generate shorter and faster references to symbolic addresses.
10454 @cindex smaller data references (MIPS)
10455 @cindex gp-relative references (MIPS)
10456 Put global and static items less than or equal to @var{num} bytes into
10457 the small data or bss section instead of the normal data or bss section.
10458 This allows the data to be accessed using a single instruction.
10460 All modules should be compiled with the same @option{-G @var{num}}
10463 @item -membedded-data
10464 @itemx -mno-embedded-data
10465 @opindex membedded-data
10466 @opindex mno-embedded-data
10467 Allocate variables to the read-only data section first if possible, then
10468 next in the small data section if possible, otherwise in data. This gives
10469 slightly slower code than the default, but reduces the amount of RAM required
10470 when executing, and thus may be preferred for some embedded systems.
10472 @item -muninit-const-in-rodata
10473 @itemx -mno-uninit-const-in-rodata
10474 @opindex muninit-const-in-rodata
10475 @opindex mno-uninit-const-in-rodata
10476 Put uninitialized @code{const} variables in the read-only data section.
10477 This option is only meaningful in conjunction with @option{-membedded-data}.
10479 @item -msplit-addresses
10480 @itemx -mno-split-addresses
10481 @opindex msplit-addresses
10482 @opindex mno-split-addresses
10483 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
10484 relocation operators. This option has been superseded by
10485 @option{-mexplicit-relocs} but is retained for backwards compatibility.
10487 @item -mexplicit-relocs
10488 @itemx -mno-explicit-relocs
10489 @opindex mexplicit-relocs
10490 @opindex mno-explicit-relocs
10491 Use (do not use) assembler relocation operators when dealing with symbolic
10492 addresses. The alternative, selected by @option{-mno-explicit-relocs},
10493 is to use assembler macros instead.
10495 @option{-mexplicit-relocs} is the default if GCC was configured
10496 to use an assembler that supports relocation operators.
10498 @item -mcheck-zero-division
10499 @itemx -mno-check-zero-division
10500 @opindex mcheck-zero-division
10501 @opindex mno-check-zero-division
10502 Trap (do not trap) on integer division by zero. The default is
10503 @option{-mcheck-zero-division}.
10505 @item -mdivide-traps
10506 @itemx -mdivide-breaks
10507 @opindex mdivide-traps
10508 @opindex mdivide-breaks
10509 MIPS systems check for division by zero by generating either a
10510 conditional trap or a break instruction. Using traps results in
10511 smaller code, but is only supported on MIPS II and later. Also, some
10512 versions of the Linux kernel have a bug that prevents trap from
10513 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
10514 allow conditional traps on architectures that support them and
10515 @option{-mdivide-breaks} to force the use of breaks.
10517 The default is usually @option{-mdivide-traps}, but this can be
10518 overridden at configure time using @option{--with-divide=breaks}.
10519 Divide-by-zero checks can be completely disabled using
10520 @option{-mno-check-zero-division}.
10525 @opindex mno-memcpy
10526 Force (do not force) the use of @code{memcpy()} for non-trivial block
10527 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
10528 most constant-sized copies.
10531 @itemx -mno-long-calls
10532 @opindex mlong-calls
10533 @opindex mno-long-calls
10534 Disable (do not disable) use of the @code{jal} instruction. Calling
10535 functions using @code{jal} is more efficient but requires the caller
10536 and callee to be in the same 256 megabyte segment.
10538 This option has no effect on abicalls code. The default is
10539 @option{-mno-long-calls}.
10545 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
10546 instructions, as provided by the R4650 ISA@.
10549 @itemx -mno-fused-madd
10550 @opindex mfused-madd
10551 @opindex mno-fused-madd
10552 Enable (disable) use of the floating point multiply-accumulate
10553 instructions, when they are available. The default is
10554 @option{-mfused-madd}.
10556 When multiply-accumulate instructions are used, the intermediate
10557 product is calculated to infinite precision and is not subject to
10558 the FCSR Flush to Zero bit. This may be undesirable in some
10563 Tell the MIPS assembler to not run its preprocessor over user
10564 assembler files (with a @samp{.s} suffix) when assembling them.
10567 @itemx -mno-fix-r4000
10568 @opindex mfix-r4000
10569 @opindex mno-fix-r4000
10570 Work around certain R4000 CPU errata:
10573 A double-word or a variable shift may give an incorrect result if executed
10574 immediately after starting an integer division.
10576 A double-word or a variable shift may give an incorrect result if executed
10577 while an integer multiplication is in progress.
10579 An integer division may give an incorrect result if started in a delay slot
10580 of a taken branch or a jump.
10584 @itemx -mno-fix-r4400
10585 @opindex mfix-r4400
10586 @opindex mno-fix-r4400
10587 Work around certain R4400 CPU errata:
10590 A double-word or a variable shift may give an incorrect result if executed
10591 immediately after starting an integer division.
10595 @itemx -mno-fix-vr4120
10596 @opindex mfix-vr4120
10597 Work around certain VR4120 errata:
10600 @code{dmultu} does not always produce the correct result.
10602 @code{div} and @code{ddiv} do not always produce the correct result if one
10603 of the operands is negative.
10605 The workarounds for the division errata rely on special functions in
10606 @file{libgcc.a}. At present, these functions are only provided by
10607 the @code{mips64vr*-elf} configurations.
10609 Other VR4120 errata require a nop to be inserted between certain pairs of
10610 instructions. These errata are handled by the assembler, not by GCC itself.
10613 @opindex mfix-vr4130
10614 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
10615 workarounds are implemented by the assembler rather than by GCC,
10616 although GCC will avoid using @code{mflo} and @code{mfhi} if the
10617 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
10618 instructions are available instead.
10621 @itemx -mno-fix-sb1
10623 Work around certain SB-1 CPU core errata.
10624 (This flag currently works around the SB-1 revision 2
10625 ``F1'' and ``F2'' floating point errata.)
10627 @item -mflush-func=@var{func}
10628 @itemx -mno-flush-func
10629 @opindex mflush-func
10630 Specifies the function to call to flush the I and D caches, or to not
10631 call any such function. If called, the function must take the same
10632 arguments as the common @code{_flush_func()}, that is, the address of the
10633 memory range for which the cache is being flushed, the size of the
10634 memory range, and the number 3 (to flush both caches). The default
10635 depends on the target GCC was configured for, but commonly is either
10636 @samp{_flush_func} or @samp{__cpu_flush}.
10638 @item -mbranch-likely
10639 @itemx -mno-branch-likely
10640 @opindex mbranch-likely
10641 @opindex mno-branch-likely
10642 Enable or disable use of Branch Likely instructions, regardless of the
10643 default for the selected architecture. By default, Branch Likely
10644 instructions may be generated if they are supported by the selected
10645 architecture. An exception is for the MIPS32 and MIPS64 architectures
10646 and processors which implement those architectures; for those, Branch
10647 Likely instructions will not be generated by default because the MIPS32
10648 and MIPS64 architectures specifically deprecate their use.
10650 @item -mfp-exceptions
10651 @itemx -mno-fp-exceptions
10652 @opindex mfp-exceptions
10653 Specifies whether FP exceptions are enabled. This affects how we schedule
10654 FP instructions for some processors. The default is that FP exceptions are
10657 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
10658 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
10661 @item -mvr4130-align
10662 @itemx -mno-vr4130-align
10663 @opindex mvr4130-align
10664 The VR4130 pipeline is two-way superscalar, but can only issue two
10665 instructions together if the first one is 8-byte aligned. When this
10666 option is enabled, GCC will align pairs of instructions that it
10667 thinks should execute in parallel.
10669 This option only has an effect when optimizing for the VR4130.
10670 It normally makes code faster, but at the expense of making it bigger.
10671 It is enabled by default at optimization level @option{-O3}.
10675 @subsection MMIX Options
10676 @cindex MMIX Options
10678 These options are defined for the MMIX:
10682 @itemx -mno-libfuncs
10684 @opindex mno-libfuncs
10685 Specify that intrinsic library functions are being compiled, passing all
10686 values in registers, no matter the size.
10689 @itemx -mno-epsilon
10691 @opindex mno-epsilon
10692 Generate floating-point comparison instructions that compare with respect
10693 to the @code{rE} epsilon register.
10695 @item -mabi=mmixware
10697 @opindex mabi-mmixware
10699 Generate code that passes function parameters and return values that (in
10700 the called function) are seen as registers @code{$0} and up, as opposed to
10701 the GNU ABI which uses global registers @code{$231} and up.
10703 @item -mzero-extend
10704 @itemx -mno-zero-extend
10705 @opindex mzero-extend
10706 @opindex mno-zero-extend
10707 When reading data from memory in sizes shorter than 64 bits, use (do not
10708 use) zero-extending load instructions by default, rather than
10709 sign-extending ones.
10712 @itemx -mno-knuthdiv
10714 @opindex mno-knuthdiv
10715 Make the result of a division yielding a remainder have the same sign as
10716 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10717 remainder follows the sign of the dividend. Both methods are
10718 arithmetically valid, the latter being almost exclusively used.
10720 @item -mtoplevel-symbols
10721 @itemx -mno-toplevel-symbols
10722 @opindex mtoplevel-symbols
10723 @opindex mno-toplevel-symbols
10724 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10725 code can be used with the @code{PREFIX} assembly directive.
10729 Generate an executable in the ELF format, rather than the default
10730 @samp{mmo} format used by the @command{mmix} simulator.
10732 @item -mbranch-predict
10733 @itemx -mno-branch-predict
10734 @opindex mbranch-predict
10735 @opindex mno-branch-predict
10736 Use (do not use) the probable-branch instructions, when static branch
10737 prediction indicates a probable branch.
10739 @item -mbase-addresses
10740 @itemx -mno-base-addresses
10741 @opindex mbase-addresses
10742 @opindex mno-base-addresses
10743 Generate (do not generate) code that uses @emph{base addresses}. Using a
10744 base address automatically generates a request (handled by the assembler
10745 and the linker) for a constant to be set up in a global register. The
10746 register is used for one or more base address requests within the range 0
10747 to 255 from the value held in the register. The generally leads to short
10748 and fast code, but the number of different data items that can be
10749 addressed is limited. This means that a program that uses lots of static
10750 data may require @option{-mno-base-addresses}.
10752 @item -msingle-exit
10753 @itemx -mno-single-exit
10754 @opindex msingle-exit
10755 @opindex mno-single-exit
10756 Force (do not force) generated code to have a single exit point in each
10760 @node MN10300 Options
10761 @subsection MN10300 Options
10762 @cindex MN10300 options
10764 These @option{-m} options are defined for Matsushita MN10300 architectures:
10769 Generate code to avoid bugs in the multiply instructions for the MN10300
10770 processors. This is the default.
10772 @item -mno-mult-bug
10773 @opindex mno-mult-bug
10774 Do not generate code to avoid bugs in the multiply instructions for the
10775 MN10300 processors.
10779 Generate code which uses features specific to the AM33 processor.
10783 Do not generate code which uses features specific to the AM33 processor. This
10786 @item -mreturn-pointer-on-d0
10787 @opindex mreturn-pointer-on-d0
10788 When generating a function which returns a pointer, return the pointer
10789 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
10790 only in a0, and attempts to call such functions without a prototype
10791 would result in errors. Note that this option is on by default; use
10792 @option{-mno-return-pointer-on-d0} to disable it.
10796 Do not link in the C run-time initialization object file.
10800 Indicate to the linker that it should perform a relaxation optimization pass
10801 to shorten branches, calls and absolute memory addresses. This option only
10802 has an effect when used on the command line for the final link step.
10804 This option makes symbolic debugging impossible.
10808 @subsection MT Options
10811 These @option{-m} options are defined for Morpho MT architectures:
10815 @item -march=@var{cpu-type}
10817 Generate code that will run on @var{cpu-type}, which is the name of a system
10818 representing a certain processor type. Possible values for
10819 @var{cpu-type} are @samp{ms1-64-001}, @samp{ms1-16-002},
10820 @samp{ms1-16-003} and @samp{ms2}.
10822 When this option is not used, the default is @option{-march=ms1-16-002}.
10826 Use byte loads and stores when generating code.
10830 Do not use byte loads and stores when generating code.
10834 Use simulator runtime
10838 Do not link in the C run-time initialization object file
10839 @file{crti.o}. Other run-time initialization and termination files
10840 such as @file{startup.o} and @file{exit.o} are still included on the
10841 linker command line.
10845 @node PDP-11 Options
10846 @subsection PDP-11 Options
10847 @cindex PDP-11 Options
10849 These options are defined for the PDP-11:
10854 Use hardware FPP floating point. This is the default. (FIS floating
10855 point on the PDP-11/40 is not supported.)
10858 @opindex msoft-float
10859 Do not use hardware floating point.
10863 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10867 Return floating-point results in memory. This is the default.
10871 Generate code for a PDP-11/40.
10875 Generate code for a PDP-11/45. This is the default.
10879 Generate code for a PDP-11/10.
10881 @item -mbcopy-builtin
10882 @opindex bcopy-builtin
10883 Use inline @code{movmemhi} patterns for copying memory. This is the
10888 Do not use inline @code{movmemhi} patterns for copying memory.
10894 Use 16-bit @code{int}. This is the default.
10900 Use 32-bit @code{int}.
10903 @itemx -mno-float32
10905 @opindex mno-float32
10906 Use 64-bit @code{float}. This is the default.
10909 @itemx -mno-float64
10911 @opindex mno-float64
10912 Use 32-bit @code{float}.
10916 Use @code{abshi2} pattern. This is the default.
10920 Do not use @code{abshi2} pattern.
10922 @item -mbranch-expensive
10923 @opindex mbranch-expensive
10924 Pretend that branches are expensive. This is for experimenting with
10925 code generation only.
10927 @item -mbranch-cheap
10928 @opindex mbranch-cheap
10929 Do not pretend that branches are expensive. This is the default.
10933 Generate code for a system with split I&D@.
10937 Generate code for a system without split I&D@. This is the default.
10941 Use Unix assembler syntax. This is the default when configured for
10942 @samp{pdp11-*-bsd}.
10946 Use DEC assembler syntax. This is the default when configured for any
10947 PDP-11 target other than @samp{pdp11-*-bsd}.
10950 @node PowerPC Options
10951 @subsection PowerPC Options
10952 @cindex PowerPC options
10954 These are listed under @xref{RS/6000 and PowerPC Options}.
10956 @node RS/6000 and PowerPC Options
10957 @subsection IBM RS/6000 and PowerPC Options
10958 @cindex RS/6000 and PowerPC Options
10959 @cindex IBM RS/6000 and PowerPC Options
10961 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10968 @itemx -mno-powerpc
10969 @itemx -mpowerpc-gpopt
10970 @itemx -mno-powerpc-gpopt
10971 @itemx -mpowerpc-gfxopt
10972 @itemx -mno-powerpc-gfxopt
10974 @itemx -mno-powerpc64
10978 @itemx -mno-popcntb
10984 @opindex mno-power2
10986 @opindex mno-powerpc
10987 @opindex mpowerpc-gpopt
10988 @opindex mno-powerpc-gpopt
10989 @opindex mpowerpc-gfxopt
10990 @opindex mno-powerpc-gfxopt
10991 @opindex mpowerpc64
10992 @opindex mno-powerpc64
10996 @opindex mno-popcntb
10999 GCC supports two related instruction set architectures for the
11000 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
11001 instructions supported by the @samp{rios} chip set used in the original
11002 RS/6000 systems and the @dfn{PowerPC} instruction set is the
11003 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
11004 the IBM 4xx, 6xx, and follow-on microprocessors.
11006 Neither architecture is a subset of the other. However there is a
11007 large common subset of instructions supported by both. An MQ
11008 register is included in processors supporting the POWER architecture.
11010 You use these options to specify which instructions are available on the
11011 processor you are using. The default value of these options is
11012 determined when configuring GCC@. Specifying the
11013 @option{-mcpu=@var{cpu_type}} overrides the specification of these
11014 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
11015 rather than the options listed above.
11017 The @option{-mpower} option allows GCC to generate instructions that
11018 are found only in the POWER architecture and to use the MQ register.
11019 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
11020 to generate instructions that are present in the POWER2 architecture but
11021 not the original POWER architecture.
11023 The @option{-mpowerpc} option allows GCC to generate instructions that
11024 are found only in the 32-bit subset of the PowerPC architecture.
11025 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
11026 GCC to use the optional PowerPC architecture instructions in the
11027 General Purpose group, including floating-point square root. Specifying
11028 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
11029 use the optional PowerPC architecture instructions in the Graphics
11030 group, including floating-point select.
11032 The @option{-mmfcrf} option allows GCC to generate the move from
11033 condition register field instruction implemented on the POWER4
11034 processor and other processors that support the PowerPC V2.01
11036 The @option{-mpopcntb} option allows GCC to generate the popcount and
11037 double precision FP reciprocal estimate instruction implemented on the
11038 POWER5 processor and other processors that support the PowerPC V2.02
11040 The @option{-mfprnd} option allows GCC to generate the FP round to
11041 integer instructions implemented on the POWER5+ processor and other
11042 processors that support the PowerPC V2.03 architecture.
11044 The @option{-mpowerpc64} option allows GCC to generate the additional
11045 64-bit instructions that are found in the full PowerPC64 architecture
11046 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
11047 @option{-mno-powerpc64}.
11049 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
11050 will use only the instructions in the common subset of both
11051 architectures plus some special AIX common-mode calls, and will not use
11052 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
11053 permits GCC to use any instruction from either architecture and to
11054 allow use of the MQ register; specify this for the Motorola MPC601.
11056 @item -mnew-mnemonics
11057 @itemx -mold-mnemonics
11058 @opindex mnew-mnemonics
11059 @opindex mold-mnemonics
11060 Select which mnemonics to use in the generated assembler code. With
11061 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
11062 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
11063 assembler mnemonics defined for the POWER architecture. Instructions
11064 defined in only one architecture have only one mnemonic; GCC uses that
11065 mnemonic irrespective of which of these options is specified.
11067 GCC defaults to the mnemonics appropriate for the architecture in
11068 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
11069 value of these option. Unless you are building a cross-compiler, you
11070 should normally not specify either @option{-mnew-mnemonics} or
11071 @option{-mold-mnemonics}, but should instead accept the default.
11073 @item -mcpu=@var{cpu_type}
11075 Set architecture type, register usage, choice of mnemonics, and
11076 instruction scheduling parameters for machine type @var{cpu_type}.
11077 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
11078 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
11079 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
11080 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
11081 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
11082 @samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
11083 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
11084 @samp{power4}, @samp{power5}, @samp{power5+},
11085 @samp{common}, @samp{powerpc}, @samp{powerpc64},
11086 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
11088 @option{-mcpu=common} selects a completely generic processor. Code
11089 generated under this option will run on any POWER or PowerPC processor.
11090 GCC will use only the instructions in the common subset of both
11091 architectures, and will not use the MQ register. GCC assumes a generic
11092 processor model for scheduling purposes.
11094 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
11095 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
11096 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
11097 types, with an appropriate, generic processor model assumed for
11098 scheduling purposes.
11100 The other options specify a specific processor. Code generated under
11101 those options will run best on that processor, and may not run at all on
11104 The @option{-mcpu} options automatically enable or disable the
11105 following options: @option{-maltivec}, @option{-mfprnd},
11106 @option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple},
11107 @option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower},
11108 @option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt},
11109 @option{-mpowerpc-gfxopt}, @option{-mstring}, @option{-mmulhw}.
11110 The particular options
11111 set for any particular CPU will vary between compiler versions,
11112 depending on what setting seems to produce optimal code for that CPU;
11113 it doesn't necessarily reflect the actual hardware's capabilities. If
11114 you wish to set an individual option to a particular value, you may
11115 specify it after the @option{-mcpu} option, like @samp{-mcpu=970
11118 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
11119 not enabled or disabled by the @option{-mcpu} option at present because
11120 AIX does not have full support for these options. You may still
11121 enable or disable them individually if you're sure it'll work in your
11124 @item -mtune=@var{cpu_type}
11126 Set the instruction scheduling parameters for machine type
11127 @var{cpu_type}, but do not set the architecture type, register usage, or
11128 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
11129 values for @var{cpu_type} are used for @option{-mtune} as for
11130 @option{-mcpu}. If both are specified, the code generated will use the
11131 architecture, registers, and mnemonics set by @option{-mcpu}, but the
11132 scheduling parameters set by @option{-mtune}.
11138 Generate code to compute division as reciprocal estimate and iterative
11139 refinement, creating opportunities for increased throughput. This
11140 feature requires: optional PowerPC Graphics instruction set for single
11141 precision and FRE instruction for double precision, assuming divides
11142 cannot generate user-visible traps, and the domain values not include
11143 Infinities, denormals or zero denominator.
11146 @itemx -mno-altivec
11148 @opindex mno-altivec
11149 Generate code that uses (does not use) AltiVec instructions, and also
11150 enable the use of built-in functions that allow more direct access to
11151 the AltiVec instruction set. You may also need to set
11152 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
11158 @opindex mno-vrsave
11159 Generate VRSAVE instructions when generating AltiVec code.
11162 @opindex msecure-plt
11163 Generate code that allows ld and ld.so to build executables and shared
11164 libraries with non-exec .plt and .got sections. This is a PowerPC
11165 32-bit SYSV ABI option.
11169 Generate code that uses a BSS .plt section that ld.so fills in, and
11170 requires .plt and .got sections that are both writable and executable.
11171 This is a PowerPC 32-bit SYSV ABI option.
11177 This switch enables or disables the generation of ISEL instructions.
11179 @item -misel=@var{yes/no}
11180 This switch has been deprecated. Use @option{-misel} and
11181 @option{-mno-isel} instead.
11187 This switch enables or disables the generation of SPE simd
11190 @item -mspe=@var{yes/no}
11191 This option has been deprecated. Use @option{-mspe} and
11192 @option{-mno-spe} instead.
11194 @item -mfloat-gprs=@var{yes/single/double/no}
11195 @itemx -mfloat-gprs
11196 @opindex mfloat-gprs
11197 This switch enables or disables the generation of floating point
11198 operations on the general purpose registers for architectures that
11201 The argument @var{yes} or @var{single} enables the use of
11202 single-precision floating point operations.
11204 The argument @var{double} enables the use of single and
11205 double-precision floating point operations.
11207 The argument @var{no} disables floating point operations on the
11208 general purpose registers.
11210 This option is currently only available on the MPC854x.
11216 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
11217 targets (including GNU/Linux). The 32-bit environment sets int, long
11218 and pointer to 32 bits and generates code that runs on any PowerPC
11219 variant. The 64-bit environment sets int to 32 bits and long and
11220 pointer to 64 bits, and generates code for PowerPC64, as for
11221 @option{-mpowerpc64}.
11224 @itemx -mno-fp-in-toc
11225 @itemx -mno-sum-in-toc
11226 @itemx -mminimal-toc
11228 @opindex mno-fp-in-toc
11229 @opindex mno-sum-in-toc
11230 @opindex mminimal-toc
11231 Modify generation of the TOC (Table Of Contents), which is created for
11232 every executable file. The @option{-mfull-toc} option is selected by
11233 default. In that case, GCC will allocate at least one TOC entry for
11234 each unique non-automatic variable reference in your program. GCC
11235 will also place floating-point constants in the TOC@. However, only
11236 16,384 entries are available in the TOC@.
11238 If you receive a linker error message that saying you have overflowed
11239 the available TOC space, you can reduce the amount of TOC space used
11240 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
11241 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
11242 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
11243 generate code to calculate the sum of an address and a constant at
11244 run-time instead of putting that sum into the TOC@. You may specify one
11245 or both of these options. Each causes GCC to produce very slightly
11246 slower and larger code at the expense of conserving TOC space.
11248 If you still run out of space in the TOC even when you specify both of
11249 these options, specify @option{-mminimal-toc} instead. This option causes
11250 GCC to make only one TOC entry for every file. When you specify this
11251 option, GCC will produce code that is slower and larger but which
11252 uses extremely little TOC space. You may wish to use this option
11253 only on files that contain less frequently executed code.
11259 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
11260 @code{long} type, and the infrastructure needed to support them.
11261 Specifying @option{-maix64} implies @option{-mpowerpc64} and
11262 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
11263 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
11266 @itemx -mno-xl-compat
11267 @opindex mxl-compat
11268 @opindex mno-xl-compat
11269 Produce code that conforms more closely to IBM XL compiler semantics
11270 when using AIX-compatible ABI. Pass floating-point arguments to
11271 prototyped functions beyond the register save area (RSA) on the stack
11272 in addition to argument FPRs. Do not assume that most significant
11273 double in 128-bit long double value is properly rounded when comparing
11274 values and converting to double. Use XL symbol names for long double
11277 The AIX calling convention was extended but not initially documented to
11278 handle an obscure K&R C case of calling a function that takes the
11279 address of its arguments with fewer arguments than declared. IBM XL
11280 compilers access floating point arguments which do not fit in the
11281 RSA from the stack when a subroutine is compiled without
11282 optimization. Because always storing floating-point arguments on the
11283 stack is inefficient and rarely needed, this option is not enabled by
11284 default and only is necessary when calling subroutines compiled by IBM
11285 XL compilers without optimization.
11289 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
11290 application written to use message passing with special startup code to
11291 enable the application to run. The system must have PE installed in the
11292 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
11293 must be overridden with the @option{-specs=} option to specify the
11294 appropriate directory location. The Parallel Environment does not
11295 support threads, so the @option{-mpe} option and the @option{-pthread}
11296 option are incompatible.
11298 @item -malign-natural
11299 @itemx -malign-power
11300 @opindex malign-natural
11301 @opindex malign-power
11302 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
11303 @option{-malign-natural} overrides the ABI-defined alignment of larger
11304 types, such as floating-point doubles, on their natural size-based boundary.
11305 The option @option{-malign-power} instructs GCC to follow the ABI-specified
11306 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
11308 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
11312 @itemx -mhard-float
11313 @opindex msoft-float
11314 @opindex mhard-float
11315 Generate code that does not use (uses) the floating-point register set.
11316 Software floating point emulation is provided if you use the
11317 @option{-msoft-float} option, and pass the option to GCC when linking.
11320 @itemx -mno-multiple
11322 @opindex mno-multiple
11323 Generate code that uses (does not use) the load multiple word
11324 instructions and the store multiple word instructions. These
11325 instructions are generated by default on POWER systems, and not
11326 generated on PowerPC systems. Do not use @option{-mmultiple} on little
11327 endian PowerPC systems, since those instructions do not work when the
11328 processor is in little endian mode. The exceptions are PPC740 and
11329 PPC750 which permit the instructions usage in little endian mode.
11334 @opindex mno-string
11335 Generate code that uses (does not use) the load string instructions
11336 and the store string word instructions to save multiple registers and
11337 do small block moves. These instructions are generated by default on
11338 POWER systems, and not generated on PowerPC systems. Do not use
11339 @option{-mstring} on little endian PowerPC systems, since those
11340 instructions do not work when the processor is in little endian mode.
11341 The exceptions are PPC740 and PPC750 which permit the instructions
11342 usage in little endian mode.
11347 @opindex mno-update
11348 Generate code that uses (does not use) the load or store instructions
11349 that update the base register to the address of the calculated memory
11350 location. These instructions are generated by default. If you use
11351 @option{-mno-update}, there is a small window between the time that the
11352 stack pointer is updated and the address of the previous frame is
11353 stored, which means code that walks the stack frame across interrupts or
11354 signals may get corrupted data.
11357 @itemx -mno-fused-madd
11358 @opindex mfused-madd
11359 @opindex mno-fused-madd
11360 Generate code that uses (does not use) the floating point multiply and
11361 accumulate instructions. These instructions are generated by default if
11362 hardware floating is used.
11368 Generate code that uses (does not use) the half-word multiply and
11369 multiply-accumulate instructions on the IBM 405 and 440 processors.
11370 These instructions are generated by default when targetting those
11373 @item -mno-bit-align
11375 @opindex mno-bit-align
11376 @opindex mbit-align
11377 On System V.4 and embedded PowerPC systems do not (do) force structures
11378 and unions that contain bit-fields to be aligned to the base type of the
11381 For example, by default a structure containing nothing but 8
11382 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
11383 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
11384 the structure would be aligned to a 1 byte boundary and be one byte in
11387 @item -mno-strict-align
11388 @itemx -mstrict-align
11389 @opindex mno-strict-align
11390 @opindex mstrict-align
11391 On System V.4 and embedded PowerPC systems do not (do) assume that
11392 unaligned memory references will be handled by the system.
11394 @item -mrelocatable
11395 @itemx -mno-relocatable
11396 @opindex mrelocatable
11397 @opindex mno-relocatable
11398 On embedded PowerPC systems generate code that allows (does not allow)
11399 the program to be relocated to a different address at runtime. If you
11400 use @option{-mrelocatable} on any module, all objects linked together must
11401 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
11403 @item -mrelocatable-lib
11404 @itemx -mno-relocatable-lib
11405 @opindex mrelocatable-lib
11406 @opindex mno-relocatable-lib
11407 On embedded PowerPC systems generate code that allows (does not allow)
11408 the program to be relocated to a different address at runtime. Modules
11409 compiled with @option{-mrelocatable-lib} can be linked with either modules
11410 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
11411 with modules compiled with the @option{-mrelocatable} options.
11417 On System V.4 and embedded PowerPC systems do not (do) assume that
11418 register 2 contains a pointer to a global area pointing to the addresses
11419 used in the program.
11422 @itemx -mlittle-endian
11424 @opindex mlittle-endian
11425 On System V.4 and embedded PowerPC systems compile code for the
11426 processor in little endian mode. The @option{-mlittle-endian} option is
11427 the same as @option{-mlittle}.
11430 @itemx -mbig-endian
11432 @opindex mbig-endian
11433 On System V.4 and embedded PowerPC systems compile code for the
11434 processor in big endian mode. The @option{-mbig-endian} option is
11435 the same as @option{-mbig}.
11437 @item -mdynamic-no-pic
11438 @opindex mdynamic-no-pic
11439 On Darwin and Mac OS X systems, compile code so that it is not
11440 relocatable, but that its external references are relocatable. The
11441 resulting code is suitable for applications, but not shared
11444 @item -mprioritize-restricted-insns=@var{priority}
11445 @opindex mprioritize-restricted-insns
11446 This option controls the priority that is assigned to
11447 dispatch-slot restricted instructions during the second scheduling
11448 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
11449 @var{no/highest/second-highest} priority to dispatch slot restricted
11452 @item -msched-costly-dep=@var{dependence_type}
11453 @opindex msched-costly-dep
11454 This option controls which dependences are considered costly
11455 by the target during instruction scheduling. The argument
11456 @var{dependence_type} takes one of the following values:
11457 @var{no}: no dependence is costly,
11458 @var{all}: all dependences are costly,
11459 @var{true_store_to_load}: a true dependence from store to load is costly,
11460 @var{store_to_load}: any dependence from store to load is costly,
11461 @var{number}: any dependence which latency >= @var{number} is costly.
11463 @item -minsert-sched-nops=@var{scheme}
11464 @opindex minsert-sched-nops
11465 This option controls which nop insertion scheme will be used during
11466 the second scheduling pass. The argument @var{scheme} takes one of the
11468 @var{no}: Don't insert nops.
11469 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
11470 according to the scheduler's grouping.
11471 @var{regroup_exact}: Insert nops to force costly dependent insns into
11472 separate groups. Insert exactly as many nops as needed to force an insn
11473 to a new group, according to the estimated processor grouping.
11474 @var{number}: Insert nops to force costly dependent insns into
11475 separate groups. Insert @var{number} nops to force an insn to a new group.
11478 @opindex mcall-sysv
11479 On System V.4 and embedded PowerPC systems compile code using calling
11480 conventions that adheres to the March 1995 draft of the System V
11481 Application Binary Interface, PowerPC processor supplement. This is the
11482 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
11484 @item -mcall-sysv-eabi
11485 @opindex mcall-sysv-eabi
11486 Specify both @option{-mcall-sysv} and @option{-meabi} options.
11488 @item -mcall-sysv-noeabi
11489 @opindex mcall-sysv-noeabi
11490 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
11492 @item -mcall-solaris
11493 @opindex mcall-solaris
11494 On System V.4 and embedded PowerPC systems compile code for the Solaris
11498 @opindex mcall-linux
11499 On System V.4 and embedded PowerPC systems compile code for the
11500 Linux-based GNU system.
11504 On System V.4 and embedded PowerPC systems compile code for the
11505 Hurd-based GNU system.
11507 @item -mcall-netbsd
11508 @opindex mcall-netbsd
11509 On System V.4 and embedded PowerPC systems compile code for the
11510 NetBSD operating system.
11512 @item -maix-struct-return
11513 @opindex maix-struct-return
11514 Return all structures in memory (as specified by the AIX ABI)@.
11516 @item -msvr4-struct-return
11517 @opindex msvr4-struct-return
11518 Return structures smaller than 8 bytes in registers (as specified by the
11521 @item -mabi=@var{abi-type}
11523 Extend the current ABI with a particular extension, or remove such extension.
11524 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
11525 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
11529 Extend the current ABI with SPE ABI extensions. This does not change
11530 the default ABI, instead it adds the SPE ABI extensions to the current
11534 @opindex mabi=no-spe
11535 Disable Booke SPE ABI extensions for the current ABI@.
11537 @item -mabi=ibmlongdouble
11538 @opindex mabi=ibmlongdouble
11539 Change the current ABI to use IBM extended precision long double.
11540 This is a PowerPC 32-bit SYSV ABI option.
11542 @item -mabi=ieeelongdouble
11543 @opindex mabi=ieeelongdouble
11544 Change the current ABI to use IEEE extended precision long double.
11545 This is a PowerPC 32-bit Linux ABI option.
11548 @itemx -mno-prototype
11549 @opindex mprototype
11550 @opindex mno-prototype
11551 On System V.4 and embedded PowerPC systems assume that all calls to
11552 variable argument functions are properly prototyped. Otherwise, the
11553 compiler must insert an instruction before every non prototyped call to
11554 set or clear bit 6 of the condition code register (@var{CR}) to
11555 indicate whether floating point values were passed in the floating point
11556 registers in case the function takes a variable arguments. With
11557 @option{-mprototype}, only calls to prototyped variable argument functions
11558 will set or clear the bit.
11562 On embedded PowerPC systems, assume that the startup module is called
11563 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
11564 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
11569 On embedded PowerPC systems, assume that the startup module is called
11570 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
11575 On embedded PowerPC systems, assume that the startup module is called
11576 @file{crt0.o} and the standard C libraries are @file{libads.a} and
11579 @item -myellowknife
11580 @opindex myellowknife
11581 On embedded PowerPC systems, assume that the startup module is called
11582 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
11587 On System V.4 and embedded PowerPC systems, specify that you are
11588 compiling for a VxWorks system.
11592 Specify that you are compiling for the WindISS simulation environment.
11596 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
11597 header to indicate that @samp{eabi} extended relocations are used.
11603 On System V.4 and embedded PowerPC systems do (do not) adhere to the
11604 Embedded Applications Binary Interface (eabi) which is a set of
11605 modifications to the System V.4 specifications. Selecting @option{-meabi}
11606 means that the stack is aligned to an 8 byte boundary, a function
11607 @code{__eabi} is called to from @code{main} to set up the eabi
11608 environment, and the @option{-msdata} option can use both @code{r2} and
11609 @code{r13} to point to two separate small data areas. Selecting
11610 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
11611 do not call an initialization function from @code{main}, and the
11612 @option{-msdata} option will only use @code{r13} to point to a single
11613 small data area. The @option{-meabi} option is on by default if you
11614 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
11617 @opindex msdata=eabi
11618 On System V.4 and embedded PowerPC systems, put small initialized
11619 @code{const} global and static data in the @samp{.sdata2} section, which
11620 is pointed to by register @code{r2}. Put small initialized
11621 non-@code{const} global and static data in the @samp{.sdata} section,
11622 which is pointed to by register @code{r13}. Put small uninitialized
11623 global and static data in the @samp{.sbss} section, which is adjacent to
11624 the @samp{.sdata} section. The @option{-msdata=eabi} option is
11625 incompatible with the @option{-mrelocatable} option. The
11626 @option{-msdata=eabi} option also sets the @option{-memb} option.
11629 @opindex msdata=sysv
11630 On System V.4 and embedded PowerPC systems, put small global and static
11631 data in the @samp{.sdata} section, which is pointed to by register
11632 @code{r13}. Put small uninitialized global and static data in the
11633 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
11634 The @option{-msdata=sysv} option is incompatible with the
11635 @option{-mrelocatable} option.
11637 @item -msdata=default
11639 @opindex msdata=default
11641 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
11642 compile code the same as @option{-msdata=eabi}, otherwise compile code the
11643 same as @option{-msdata=sysv}.
11646 @opindex msdata-data
11647 On System V.4 and embedded PowerPC systems, put small global
11648 data in the @samp{.sdata} section. Put small uninitialized global
11649 data in the @samp{.sbss} section. Do not use register @code{r13}
11650 to address small data however. This is the default behavior unless
11651 other @option{-msdata} options are used.
11655 @opindex msdata=none
11657 On embedded PowerPC systems, put all initialized global and static data
11658 in the @samp{.data} section, and all uninitialized data in the
11659 @samp{.bss} section.
11663 @cindex smaller data references (PowerPC)
11664 @cindex .sdata/.sdata2 references (PowerPC)
11665 On embedded PowerPC systems, put global and static items less than or
11666 equal to @var{num} bytes into the small data or bss sections instead of
11667 the normal data or bss section. By default, @var{num} is 8. The
11668 @option{-G @var{num}} switch is also passed to the linker.
11669 All modules should be compiled with the same @option{-G @var{num}} value.
11672 @itemx -mno-regnames
11674 @opindex mno-regnames
11675 On System V.4 and embedded PowerPC systems do (do not) emit register
11676 names in the assembly language output using symbolic forms.
11679 @itemx -mno-longcall
11681 @opindex mno-longcall
11682 Default to making all function calls indirectly, using a register, so
11683 that functions which reside further than 32 megabytes (33,554,432
11684 bytes) from the current location can be called. This setting can be
11685 overridden by the @code{shortcall} function attribute, or by
11686 @code{#pragma longcall(0)}.
11688 Some linkers are capable of detecting out-of-range calls and generating
11689 glue code on the fly. On these systems, long calls are unnecessary and
11690 generate slower code. As of this writing, the AIX linker can do this,
11691 as can the GNU linker for PowerPC/64. It is planned to add this feature
11692 to the GNU linker for 32-bit PowerPC systems as well.
11694 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
11695 callee, L42'', plus a ``branch island'' (glue code). The two target
11696 addresses represent the callee and the ``branch island''. The
11697 Darwin/PPC linker will prefer the first address and generate a ``bl
11698 callee'' if the PPC ``bl'' instruction will reach the callee directly;
11699 otherwise, the linker will generate ``bl L42'' to call the ``branch
11700 island''. The ``branch island'' is appended to the body of the
11701 calling function; it computes the full 32-bit address of the callee
11704 On Mach-O (Darwin) systems, this option directs the compiler emit to
11705 the glue for every direct call, and the Darwin linker decides whether
11706 to use or discard it.
11708 In the future, we may cause GCC to ignore all longcall specifications
11709 when the linker is known to generate glue.
11713 Adds support for multithreading with the @dfn{pthreads} library.
11714 This option sets flags for both the preprocessor and linker.
11718 @node S/390 and zSeries Options
11719 @subsection S/390 and zSeries Options
11720 @cindex S/390 and zSeries Options
11722 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
11726 @itemx -msoft-float
11727 @opindex mhard-float
11728 @opindex msoft-float
11729 Use (do not use) the hardware floating-point instructions and registers
11730 for floating-point operations. When @option{-msoft-float} is specified,
11731 functions in @file{libgcc.a} will be used to perform floating-point
11732 operations. When @option{-mhard-float} is specified, the compiler
11733 generates IEEE floating-point instructions. This is the default.
11735 @item -mlong-double-64
11736 @itemx -mlong-double-128
11737 @opindex mlong-double-64
11738 @opindex mlong-double-128
11739 These switches control the size of @code{long double} type. A size
11740 of 64bit makes the @code{long double} type equivalent to the @code{double}
11741 type. This is the default.
11744 @itemx -mno-backchain
11745 @opindex mbackchain
11746 @opindex mno-backchain
11747 Store (do not store) the address of the caller's frame as backchain pointer
11748 into the callee's stack frame.
11749 A backchain may be needed to allow debugging using tools that do not understand
11750 DWARF-2 call frame information.
11751 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
11752 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
11753 the backchain is placed into the topmost word of the 96/160 byte register
11756 In general, code compiled with @option{-mbackchain} is call-compatible with
11757 code compiled with @option{-mmo-backchain}; however, use of the backchain
11758 for debugging purposes usually requires that the whole binary is built with
11759 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
11760 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11761 to build a linux kernel use @option{-msoft-float}.
11763 The default is to not maintain the backchain.
11765 @item -mpacked-stack
11766 @item -mno-packed-stack
11767 @opindex mpacked-stack
11768 @opindex mno-packed-stack
11769 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
11770 specified, the compiler uses the all fields of the 96/160 byte register save
11771 area only for their default purpose; unused fields still take up stack space.
11772 When @option{-mpacked-stack} is specified, register save slots are densely
11773 packed at the top of the register save area; unused space is reused for other
11774 purposes, allowing for more efficient use of the available stack space.
11775 However, when @option{-mbackchain} is also in effect, the topmost word of
11776 the save area is always used to store the backchain, and the return address
11777 register is always saved two words below the backchain.
11779 As long as the stack frame backchain is not used, code generated with
11780 @option{-mpacked-stack} is call-compatible with code generated with
11781 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
11782 S/390 or zSeries generated code that uses the stack frame backchain at run
11783 time, not just for debugging purposes. Such code is not call-compatible
11784 with code compiled with @option{-mpacked-stack}. Also, note that the
11785 combination of @option{-mbackchain},
11786 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11787 to build a linux kernel use @option{-msoft-float}.
11789 The default is to not use the packed stack layout.
11792 @itemx -mno-small-exec
11793 @opindex msmall-exec
11794 @opindex mno-small-exec
11795 Generate (or do not generate) code using the @code{bras} instruction
11796 to do subroutine calls.
11797 This only works reliably if the total executable size does not
11798 exceed 64k. The default is to use the @code{basr} instruction instead,
11799 which does not have this limitation.
11805 When @option{-m31} is specified, generate code compliant to the
11806 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
11807 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
11808 particular to generate 64-bit instructions. For the @samp{s390}
11809 targets, the default is @option{-m31}, while the @samp{s390x}
11810 targets default to @option{-m64}.
11816 When @option{-mzarch} is specified, generate code using the
11817 instructions available on z/Architecture.
11818 When @option{-mesa} is specified, generate code using the
11819 instructions available on ESA/390. Note that @option{-mesa} is
11820 not possible with @option{-m64}.
11821 When generating code compliant to the GNU/Linux for S/390 ABI,
11822 the default is @option{-mesa}. When generating code compliant
11823 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
11829 Generate (or do not generate) code using the @code{mvcle} instruction
11830 to perform block moves. When @option{-mno-mvcle} is specified,
11831 use a @code{mvc} loop instead. This is the default unless optimizing for
11838 Print (or do not print) additional debug information when compiling.
11839 The default is to not print debug information.
11841 @item -march=@var{cpu-type}
11843 Generate code that will run on @var{cpu-type}, which is the name of a system
11844 representing a certain processor type. Possible values for
11845 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
11846 When generating code using the instructions available on z/Architecture,
11847 the default is @option{-march=z900}. Otherwise, the default is
11848 @option{-march=g5}.
11850 @item -mtune=@var{cpu-type}
11852 Tune to @var{cpu-type} everything applicable about the generated code,
11853 except for the ABI and the set of available instructions.
11854 The list of @var{cpu-type} values is the same as for @option{-march}.
11855 The default is the value used for @option{-march}.
11858 @itemx -mno-tpf-trace
11859 @opindex mtpf-trace
11860 @opindex mno-tpf-trace
11861 Generate code that adds (does not add) in TPF OS specific branches to trace
11862 routines in the operating system. This option is off by default, even
11863 when compiling for the TPF OS@.
11866 @itemx -mno-fused-madd
11867 @opindex mfused-madd
11868 @opindex mno-fused-madd
11869 Generate code that uses (does not use) the floating point multiply and
11870 accumulate instructions. These instructions are generated by default if
11871 hardware floating point is used.
11873 @item -mwarn-framesize=@var{framesize}
11874 @opindex mwarn-framesize
11875 Emit a warning if the current function exceeds the given frame size. Because
11876 this is a compile time check it doesn't need to be a real problem when the program
11877 runs. It is intended to identify functions which most probably cause
11878 a stack overflow. It is useful to be used in an environment with limited stack
11879 size e.g.@: the linux kernel.
11881 @item -mwarn-dynamicstack
11882 @opindex mwarn-dynamicstack
11883 Emit a warning if the function calls alloca or uses dynamically
11884 sized arrays. This is generally a bad idea with a limited stack size.
11886 @item -mstack-guard=@var{stack-guard}
11887 @item -mstack-size=@var{stack-size}
11888 @opindex mstack-guard
11889 @opindex mstack-size
11890 These arguments always have to be used in conjunction. If they are present the s390
11891 back end emits additional instructions in the function prologue which trigger a trap
11892 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
11893 (remember that the stack on s390 grows downward). These options are intended to
11894 be used to help debugging stack overflow problems. The additionally emitted code
11895 causes only little overhead and hence can also be used in production like systems
11896 without greater performance degradation. The given values have to be exact
11897 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without
11899 In order to be efficient the extra code makes the assumption that the stack starts
11900 at an address aligned to the value given by @var{stack-size}.
11904 @subsection SH Options
11906 These @samp{-m} options are defined for the SH implementations:
11911 Generate code for the SH1.
11915 Generate code for the SH2.
11918 Generate code for the SH2e.
11922 Generate code for the SH3.
11926 Generate code for the SH3e.
11930 Generate code for the SH4 without a floating-point unit.
11932 @item -m4-single-only
11933 @opindex m4-single-only
11934 Generate code for the SH4 with a floating-point unit that only
11935 supports single-precision arithmetic.
11939 Generate code for the SH4 assuming the floating-point unit is in
11940 single-precision mode by default.
11944 Generate code for the SH4.
11948 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
11949 floating-point unit is not used.
11951 @item -m4a-single-only
11952 @opindex m4a-single-only
11953 Generate code for the SH4a, in such a way that no double-precision
11954 floating point operations are used.
11957 @opindex m4a-single
11958 Generate code for the SH4a assuming the floating-point unit is in
11959 single-precision mode by default.
11963 Generate code for the SH4a.
11967 Same as @option{-m4a-nofpu}, except that it implicitly passes
11968 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11969 instructions at the moment.
11973 Compile code for the processor in big endian mode.
11977 Compile code for the processor in little endian mode.
11981 Align doubles at 64-bit boundaries. Note that this changes the calling
11982 conventions, and thus some functions from the standard C library will
11983 not work unless you recompile it first with @option{-mdalign}.
11987 Shorten some address references at link time, when possible; uses the
11988 linker option @option{-relax}.
11992 Use 32-bit offsets in @code{switch} tables. The default is to use
11997 Enable the use of the instruction @code{fmovd}.
12001 Comply with the calling conventions defined by Renesas.
12005 Comply with the calling conventions defined by Renesas.
12009 Comply with the calling conventions defined for GCC before the Renesas
12010 conventions were available. This option is the default for all
12011 targets of the SH toolchain except for @samp{sh-symbianelf}.
12014 @opindex mnomacsave
12015 Mark the @code{MAC} register as call-clobbered, even if
12016 @option{-mhitachi} is given.
12020 Increase IEEE-compliance of floating-point code.
12021 At the moment, this is equivalent to @option{-fno-finite-math-only}.
12022 When generating 16 bit SH opcodes, getting IEEE-conforming results for
12023 comparisons of NANs / infinities incurs extra overhead in every
12024 floating point comparison, therefore the default is set to
12025 @option{-ffinite-math-only}.
12029 Dump instruction size and location in the assembly code.
12032 @opindex mpadstruct
12033 This option is deprecated. It pads structures to multiple of 4 bytes,
12034 which is incompatible with the SH ABI@.
12038 Optimize for space instead of speed. Implied by @option{-Os}.
12041 @opindex mprefergot
12042 When generating position-independent code, emit function calls using
12043 the Global Offset Table instead of the Procedure Linkage Table.
12047 Generate a library function call to invalidate instruction cache
12048 entries, after fixing up a trampoline. This library function call
12049 doesn't assume it can write to the whole memory address space. This
12050 is the default when the target is @code{sh-*-linux*}.
12052 @item -multcost=@var{number}
12053 @opindex multcost=@var{number}
12054 Set the cost to assume for a multiply insn.
12056 @item -mdiv=@var{strategy}
12057 @opindex mdiv=@var{strategy}
12058 Set the division strategy to use for SHmedia code. @var{strategy} must be
12059 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
12060 inv:call2, inv:fp .
12061 "fp" performs the operation in floating point. This has a very high latency,
12062 but needs only a few instructions, so it might be a good choice if
12063 your code has enough easily exploitable ILP to allow the compiler to
12064 schedule the floating point instructions together with other instructions.
12065 Division by zero causes a floating point exception.
12066 "inv" uses integer operations to calculate the inverse of the divisor,
12067 and then multiplies the dividend with the inverse. This strategy allows
12068 cse and hoisting of the inverse calculation. Division by zero calculates
12069 an unspecified result, but does not trap.
12070 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
12071 have been found, or if the entire operation has been hoisted to the same
12072 place, the last stages of the inverse calculation are intertwined with the
12073 final multiply to reduce the overall latency, at the expense of using a few
12074 more instructions, and thus offering fewer scheduling opportunities with
12076 "call" calls a library function that usually implements the inv:minlat
12078 This gives high code density for m5-*media-nofpu compilations.
12079 "call2" uses a different entry point of the same library function, where it
12080 assumes that a pointer to a lookup table has already been set up, which
12081 exposes the pointer load to cse / code hoisting optimizations.
12082 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
12083 code generation, but if the code stays unoptimized, revert to the "call",
12084 "call2", or "fp" strategies, respectively. Note that the
12085 potentially-trapping side effect of division by zero is carried by a
12086 separate instruction, so it is possible that all the integer instructions
12087 are hoisted out, but the marker for the side effect stays where it is.
12088 A recombination to fp operations or a call is not possible in that case.
12089 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
12090 that the inverse calculation was nor separated from the multiply, they speed
12091 up division where the dividend fits into 20 bits (plus sign where applicable),
12092 by inserting a test to skip a number of operations in this case; this test
12093 slows down the case of larger dividends. inv20u assumes the case of a such
12094 a small dividend to be unlikely, and inv20l assumes it to be likely.
12096 @item -mdivsi3_libfunc=@var{name}
12097 @opindex mdivsi3_libfunc=@var{name}
12098 Set the name of the library function used for 32 bit signed division to
12099 @var{name}. This only affect the name used in the call and inv:call
12100 division strategies, and the compiler will still expect the same
12101 sets of input/output/clobbered registers as if this option was not present.
12103 @item -madjust-unroll
12104 @opindex madjust-unroll
12105 Throttle unrolling to avoid thrashing target registers.
12106 This option only has an effect if the gcc code base supports the
12107 TARGET_ADJUST_UNROLL_MAX target hook.
12109 @item -mindexed-addressing
12110 @opindex mindexed-addressing
12111 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
12112 This is only safe if the hardware and/or OS implement 32 bit wrap-around
12113 semantics for the indexed addressing mode. The architecture allows the
12114 implementation of processors with 64 bit MMU, which the OS could use to
12115 get 32 bit addressing, but since no current hardware implementation supports
12116 this or any other way to make the indexed addressing mode safe to use in
12117 the 32 bit ABI, the default is -mno-indexed-addressing.
12119 @item -mgettrcost=@var{number}
12120 @opindex mgettrcost=@var{number}
12121 Set the cost assumed for the gettr instruction to @var{number}.
12122 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
12126 Assume pt* instructions won't trap. This will generally generate better
12127 scheduled code, but is unsafe on current hardware. The current architecture
12128 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
12129 This has the unintentional effect of making it unsafe to schedule ptabs /
12130 ptrel before a branch, or hoist it out of a loop. For example,
12131 __do_global_ctors, a part of libgcc that runs constructors at program
12132 startup, calls functions in a list which is delimited by -1. With the
12133 -mpt-fixed option, the ptabs will be done before testing against -1.
12134 That means that all the constructors will be run a bit quicker, but when
12135 the loop comes to the end of the list, the program crashes because ptabs
12136 loads -1 into a target register. Since this option is unsafe for any
12137 hardware implementing the current architecture specification, the default
12138 is -mno-pt-fixed. Unless the user specifies a specific cost with
12139 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
12140 this deters register allocation using target registers for storing
12143 @item -minvalid-symbols
12144 @opindex minvalid-symbols
12145 Assume symbols might be invalid. Ordinary function symbols generated by
12146 the compiler will always be valid to load with movi/shori/ptabs or
12147 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
12148 to generate symbols that will cause ptabs / ptrel to trap.
12149 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
12150 It will then prevent cross-basic-block cse, hoisting and most scheduling
12151 of symbol loads. The default is @option{-mno-invalid-symbols}.
12154 @node SPARC Options
12155 @subsection SPARC Options
12156 @cindex SPARC options
12158 These @samp{-m} options are supported on the SPARC:
12161 @item -mno-app-regs
12163 @opindex mno-app-regs
12165 Specify @option{-mapp-regs} to generate output using the global registers
12166 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
12169 To be fully SVR4 ABI compliant at the cost of some performance loss,
12170 specify @option{-mno-app-regs}. You should compile libraries and system
12171 software with this option.
12174 @itemx -mhard-float
12176 @opindex mhard-float
12177 Generate output containing floating point instructions. This is the
12181 @itemx -msoft-float
12183 @opindex msoft-float
12184 Generate output containing library calls for floating point.
12185 @strong{Warning:} the requisite libraries are not available for all SPARC
12186 targets. Normally the facilities of the machine's usual C compiler are
12187 used, but this cannot be done directly in cross-compilation. You must make
12188 your own arrangements to provide suitable library functions for
12189 cross-compilation. The embedded targets @samp{sparc-*-aout} and
12190 @samp{sparclite-*-*} do provide software floating point support.
12192 @option{-msoft-float} changes the calling convention in the output file;
12193 therefore, it is only useful if you compile @emph{all} of a program with
12194 this option. In particular, you need to compile @file{libgcc.a}, the
12195 library that comes with GCC, with @option{-msoft-float} in order for
12198 @item -mhard-quad-float
12199 @opindex mhard-quad-float
12200 Generate output containing quad-word (long double) floating point
12203 @item -msoft-quad-float
12204 @opindex msoft-quad-float
12205 Generate output containing library calls for quad-word (long double)
12206 floating point instructions. The functions called are those specified
12207 in the SPARC ABI@. This is the default.
12209 As of this writing, there are no SPARC implementations that have hardware
12210 support for the quad-word floating point instructions. They all invoke
12211 a trap handler for one of these instructions, and then the trap handler
12212 emulates the effect of the instruction. Because of the trap handler overhead,
12213 this is much slower than calling the ABI library routines. Thus the
12214 @option{-msoft-quad-float} option is the default.
12216 @item -mno-unaligned-doubles
12217 @itemx -munaligned-doubles
12218 @opindex mno-unaligned-doubles
12219 @opindex munaligned-doubles
12220 Assume that doubles have 8 byte alignment. This is the default.
12222 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
12223 alignment only if they are contained in another type, or if they have an
12224 absolute address. Otherwise, it assumes they have 4 byte alignment.
12225 Specifying this option avoids some rare compatibility problems with code
12226 generated by other compilers. It is not the default because it results
12227 in a performance loss, especially for floating point code.
12229 @item -mno-faster-structs
12230 @itemx -mfaster-structs
12231 @opindex mno-faster-structs
12232 @opindex mfaster-structs
12233 With @option{-mfaster-structs}, the compiler assumes that structures
12234 should have 8 byte alignment. This enables the use of pairs of
12235 @code{ldd} and @code{std} instructions for copies in structure
12236 assignment, in place of twice as many @code{ld} and @code{st} pairs.
12237 However, the use of this changed alignment directly violates the SPARC
12238 ABI@. Thus, it's intended only for use on targets where the developer
12239 acknowledges that their resulting code will not be directly in line with
12240 the rules of the ABI@.
12242 @item -mimpure-text
12243 @opindex mimpure-text
12244 @option{-mimpure-text}, used in addition to @option{-shared}, tells
12245 the compiler to not pass @option{-z text} to the linker when linking a
12246 shared object. Using this option, you can link position-dependent
12247 code into a shared object.
12249 @option{-mimpure-text} suppresses the ``relocations remain against
12250 allocatable but non-writable sections'' linker error message.
12251 However, the necessary relocations will trigger copy-on-write, and the
12252 shared object is not actually shared across processes. Instead of
12253 using @option{-mimpure-text}, you should compile all source code with
12254 @option{-fpic} or @option{-fPIC}.
12256 This option is only available on SunOS and Solaris.
12258 @item -mcpu=@var{cpu_type}
12260 Set the instruction set, register set, and instruction scheduling parameters
12261 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
12262 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
12263 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
12264 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
12265 @samp{ultrasparc3}, and @samp{niagara}.
12267 Default instruction scheduling parameters are used for values that select
12268 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
12269 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
12271 Here is a list of each supported architecture and their supported
12276 v8: supersparc, hypersparc
12277 sparclite: f930, f934, sparclite86x
12279 v9: ultrasparc, ultrasparc3, niagara
12282 By default (unless configured otherwise), GCC generates code for the V7
12283 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
12284 additionally optimizes it for the Cypress CY7C602 chip, as used in the
12285 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
12286 SPARCStation 1, 2, IPX etc.
12288 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
12289 architecture. The only difference from V7 code is that the compiler emits
12290 the integer multiply and integer divide instructions which exist in SPARC-V8
12291 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
12292 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
12295 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
12296 the SPARC architecture. This adds the integer multiply, integer divide step
12297 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
12298 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
12299 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
12300 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
12301 MB86934 chip, which is the more recent SPARClite with FPU@.
12303 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
12304 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
12305 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
12306 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
12307 optimizes it for the TEMIC SPARClet chip.
12309 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
12310 architecture. This adds 64-bit integer and floating-point move instructions,
12311 3 additional floating-point condition code registers and conditional move
12312 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
12313 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
12314 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
12315 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
12316 @option{-mcpu=niagara}, the compiler additionally optimizes it for
12317 Sun UltraSPARC T1 chips.
12319 @item -mtune=@var{cpu_type}
12321 Set the instruction scheduling parameters for machine type
12322 @var{cpu_type}, but do not set the instruction set or register set that the
12323 option @option{-mcpu=@var{cpu_type}} would.
12325 The same values for @option{-mcpu=@var{cpu_type}} can be used for
12326 @option{-mtune=@var{cpu_type}}, but the only useful values are those
12327 that select a particular cpu implementation. Those are @samp{cypress},
12328 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
12329 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
12330 @samp{ultrasparc3}, and @samp{niagara}.
12335 @opindex mno-v8plus
12336 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
12337 difference from the V8 ABI is that the global and out registers are
12338 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
12339 mode for all SPARC-V9 processors.
12345 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
12346 Visual Instruction Set extensions. The default is @option{-mno-vis}.
12349 These @samp{-m} options are supported in addition to the above
12350 on SPARC-V9 processors in 64-bit environments:
12353 @item -mlittle-endian
12354 @opindex mlittle-endian
12355 Generate code for a processor running in little-endian mode. It is only
12356 available for a few configurations and most notably not on Solaris and Linux.
12362 Generate code for a 32-bit or 64-bit environment.
12363 The 32-bit environment sets int, long and pointer to 32 bits.
12364 The 64-bit environment sets int to 32 bits and long and pointer
12367 @item -mcmodel=medlow
12368 @opindex mcmodel=medlow
12369 Generate code for the Medium/Low code model: 64-bit addresses, programs
12370 must be linked in the low 32 bits of memory. Programs can be statically
12371 or dynamically linked.
12373 @item -mcmodel=medmid
12374 @opindex mcmodel=medmid
12375 Generate code for the Medium/Middle code model: 64-bit addresses, programs
12376 must be linked in the low 44 bits of memory, the text and data segments must
12377 be less than 2GB in size and the data segment must be located within 2GB of
12380 @item -mcmodel=medany
12381 @opindex mcmodel=medany
12382 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
12383 may be linked anywhere in memory, the text and data segments must be less
12384 than 2GB in size and the data segment must be located within 2GB of the
12387 @item -mcmodel=embmedany
12388 @opindex mcmodel=embmedany
12389 Generate code for the Medium/Anywhere code model for embedded systems:
12390 64-bit addresses, the text and data segments must be less than 2GB in
12391 size, both starting anywhere in memory (determined at link time). The
12392 global register %g4 points to the base of the data segment. Programs
12393 are statically linked and PIC is not supported.
12396 @itemx -mno-stack-bias
12397 @opindex mstack-bias
12398 @opindex mno-stack-bias
12399 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
12400 frame pointer if present, are offset by @minus{}2047 which must be added back
12401 when making stack frame references. This is the default in 64-bit mode.
12402 Otherwise, assume no such offset is present.
12405 These switches are supported in addition to the above on Solaris:
12410 Add support for multithreading using the Solaris threads library. This
12411 option sets flags for both the preprocessor and linker. This option does
12412 not affect the thread safety of object code produced by the compiler or
12413 that of libraries supplied with it.
12417 Add support for multithreading using the POSIX threads library. This
12418 option sets flags for both the preprocessor and linker. This option does
12419 not affect the thread safety of object code produced by the compiler or
12420 that of libraries supplied with it.
12424 This is a synonym for @option{-pthreads}.
12427 @node System V Options
12428 @subsection Options for System V
12430 These additional options are available on System V Release 4 for
12431 compatibility with other compilers on those systems:
12436 Create a shared object.
12437 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
12441 Identify the versions of each tool used by the compiler, in a
12442 @code{.ident} assembler directive in the output.
12446 Refrain from adding @code{.ident} directives to the output file (this is
12449 @item -YP,@var{dirs}
12451 Search the directories @var{dirs}, and no others, for libraries
12452 specified with @option{-l}.
12454 @item -Ym,@var{dir}
12456 Look in the directory @var{dir} to find the M4 preprocessor.
12457 The assembler uses this option.
12458 @c This is supposed to go with a -Yd for predefined M4 macro files, but
12459 @c the generic assembler that comes with Solaris takes just -Ym.
12462 @node TMS320C3x/C4x Options
12463 @subsection TMS320C3x/C4x Options
12464 @cindex TMS320C3x/C4x Options
12466 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
12470 @item -mcpu=@var{cpu_type}
12472 Set the instruction set, register set, and instruction scheduling
12473 parameters for machine type @var{cpu_type}. Supported values for
12474 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
12475 @samp{c44}. The default is @samp{c40} to generate code for the
12480 @itemx -msmall-memory
12482 @opindex mbig-memory
12484 @opindex msmall-memory
12486 Generates code for the big or small memory model. The small memory
12487 model assumed that all data fits into one 64K word page. At run-time
12488 the data page (DP) register must be set to point to the 64K page
12489 containing the .bss and .data program sections. The big memory model is
12490 the default and requires reloading of the DP register for every direct
12497 Allow (disallow) allocation of general integer operands into the block
12498 count register BK@.
12504 Enable (disable) generation of code using decrement and branch,
12505 DBcond(D), instructions. This is enabled by default for the C4x. To be
12506 on the safe side, this is disabled for the C3x, since the maximum
12507 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
12508 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
12509 that it can utilize the decrement and branch instruction, but will give
12510 up if there is more than one memory reference in the loop. Thus a loop
12511 where the loop counter is decremented can generate slightly more
12512 efficient code, in cases where the RPTB instruction cannot be utilized.
12514 @item -mdp-isr-reload
12516 @opindex mdp-isr-reload
12518 Force the DP register to be saved on entry to an interrupt service
12519 routine (ISR), reloaded to point to the data section, and restored on
12520 exit from the ISR@. This should not be required unless someone has
12521 violated the small memory model by modifying the DP register, say within
12528 For the C3x use the 24-bit MPYI instruction for integer multiplies
12529 instead of a library call to guarantee 32-bit results. Note that if one
12530 of the operands is a constant, then the multiplication will be performed
12531 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
12532 then squaring operations are performed inline instead of a library call.
12535 @itemx -mno-fast-fix
12537 @opindex mno-fast-fix
12538 The C3x/C4x FIX instruction to convert a floating point value to an
12539 integer value chooses the nearest integer less than or equal to the
12540 floating point value rather than to the nearest integer. Thus if the
12541 floating point number is negative, the result will be incorrectly
12542 truncated an additional code is necessary to detect and correct this
12543 case. This option can be used to disable generation of the additional
12544 code required to correct the result.
12550 Enable (disable) generation of repeat block sequences using the RPTB
12551 instruction for zero overhead looping. The RPTB construct is only used
12552 for innermost loops that do not call functions or jump across the loop
12553 boundaries. There is no advantage having nested RPTB loops due to the
12554 overhead required to save and restore the RC, RS, and RE registers.
12555 This is enabled by default with @option{-O2}.
12557 @item -mrpts=@var{count}
12561 Enable (disable) the use of the single instruction repeat instruction
12562 RPTS@. If a repeat block contains a single instruction, and the loop
12563 count can be guaranteed to be less than the value @var{count}, GCC will
12564 emit a RPTS instruction instead of a RPTB@. If no value is specified,
12565 then a RPTS will be emitted even if the loop count cannot be determined
12566 at compile time. Note that the repeated instruction following RPTS does
12567 not have to be reloaded from memory each iteration, thus freeing up the
12568 CPU buses for operands. However, since interrupts are blocked by this
12569 instruction, it is disabled by default.
12571 @item -mloop-unsigned
12572 @itemx -mno-loop-unsigned
12573 @opindex mloop-unsigned
12574 @opindex mno-loop-unsigned
12575 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
12576 is @math{2^{31} + 1} since these instructions test if the iteration count is
12577 negative to terminate the loop. If the iteration count is unsigned
12578 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
12579 exceeded. This switch allows an unsigned iteration count.
12583 Try to emit an assembler syntax that the TI assembler (asm30) is happy
12584 with. This also enforces compatibility with the API employed by the TI
12585 C3x C compiler. For example, long doubles are passed as structures
12586 rather than in floating point registers.
12592 Generate code that uses registers (stack) for passing arguments to functions.
12593 By default, arguments are passed in registers where possible rather
12594 than by pushing arguments on to the stack.
12596 @item -mparallel-insns
12597 @itemx -mno-parallel-insns
12598 @opindex mparallel-insns
12599 @opindex mno-parallel-insns
12600 Allow the generation of parallel instructions. This is enabled by
12601 default with @option{-O2}.
12603 @item -mparallel-mpy
12604 @itemx -mno-parallel-mpy
12605 @opindex mparallel-mpy
12606 @opindex mno-parallel-mpy
12607 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
12608 provided @option{-mparallel-insns} is also specified. These instructions have
12609 tight register constraints which can pessimize the code generation
12610 of large functions.
12615 @subsection V850 Options
12616 @cindex V850 Options
12618 These @samp{-m} options are defined for V850 implementations:
12622 @itemx -mno-long-calls
12623 @opindex mlong-calls
12624 @opindex mno-long-calls
12625 Treat all calls as being far away (near). If calls are assumed to be
12626 far away, the compiler will always load the functions address up into a
12627 register, and call indirect through the pointer.
12633 Do not optimize (do optimize) basic blocks that use the same index
12634 pointer 4 or more times to copy pointer into the @code{ep} register, and
12635 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
12636 option is on by default if you optimize.
12638 @item -mno-prolog-function
12639 @itemx -mprolog-function
12640 @opindex mno-prolog-function
12641 @opindex mprolog-function
12642 Do not use (do use) external functions to save and restore registers
12643 at the prologue and epilogue of a function. The external functions
12644 are slower, but use less code space if more than one function saves
12645 the same number of registers. The @option{-mprolog-function} option
12646 is on by default if you optimize.
12650 Try to make the code as small as possible. At present, this just turns
12651 on the @option{-mep} and @option{-mprolog-function} options.
12653 @item -mtda=@var{n}
12655 Put static or global variables whose size is @var{n} bytes or less into
12656 the tiny data area that register @code{ep} points to. The tiny data
12657 area can hold up to 256 bytes in total (128 bytes for byte references).
12659 @item -msda=@var{n}
12661 Put static or global variables whose size is @var{n} bytes or less into
12662 the small data area that register @code{gp} points to. The small data
12663 area can hold up to 64 kilobytes.
12665 @item -mzda=@var{n}
12667 Put static or global variables whose size is @var{n} bytes or less into
12668 the first 32 kilobytes of memory.
12672 Specify that the target processor is the V850.
12675 @opindex mbig-switch
12676 Generate code suitable for big switch tables. Use this option only if
12677 the assembler/linker complain about out of range branches within a switch
12682 This option will cause r2 and r5 to be used in the code generated by
12683 the compiler. This setting is the default.
12685 @item -mno-app-regs
12686 @opindex mno-app-regs
12687 This option will cause r2 and r5 to be treated as fixed registers.
12691 Specify that the target processor is the V850E1. The preprocessor
12692 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
12693 this option is used.
12697 Specify that the target processor is the V850E@. The preprocessor
12698 constant @samp{__v850e__} will be defined if this option is used.
12700 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
12701 are defined then a default target processor will be chosen and the
12702 relevant @samp{__v850*__} preprocessor constant will be defined.
12704 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
12705 defined, regardless of which processor variant is the target.
12707 @item -mdisable-callt
12708 @opindex mdisable-callt
12709 This option will suppress generation of the CALLT instruction for the
12710 v850e and v850e1 flavors of the v850 architecture. The default is
12711 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
12716 @subsection VAX Options
12717 @cindex VAX options
12719 These @samp{-m} options are defined for the VAX:
12724 Do not output certain jump instructions (@code{aobleq} and so on)
12725 that the Unix assembler for the VAX cannot handle across long
12730 Do output those jump instructions, on the assumption that you
12731 will assemble with the GNU assembler.
12735 Output code for g-format floating point numbers instead of d-format.
12738 @node x86-64 Options
12739 @subsection x86-64 Options
12740 @cindex x86-64 options
12742 These are listed under @xref{i386 and x86-64 Options}.
12744 @node Xstormy16 Options
12745 @subsection Xstormy16 Options
12746 @cindex Xstormy16 Options
12748 These options are defined for Xstormy16:
12753 Choose startup files and linker script suitable for the simulator.
12756 @node Xtensa Options
12757 @subsection Xtensa Options
12758 @cindex Xtensa Options
12760 These options are supported for Xtensa targets:
12764 @itemx -mno-const16
12766 @opindex mno-const16
12767 Enable or disable use of @code{CONST16} instructions for loading
12768 constant values. The @code{CONST16} instruction is currently not a
12769 standard option from Tensilica. When enabled, @code{CONST16}
12770 instructions are always used in place of the standard @code{L32R}
12771 instructions. The use of @code{CONST16} is enabled by default only if
12772 the @code{L32R} instruction is not available.
12775 @itemx -mno-fused-madd
12776 @opindex mfused-madd
12777 @opindex mno-fused-madd
12778 Enable or disable use of fused multiply/add and multiply/subtract
12779 instructions in the floating-point option. This has no effect if the
12780 floating-point option is not also enabled. Disabling fused multiply/add
12781 and multiply/subtract instructions forces the compiler to use separate
12782 instructions for the multiply and add/subtract operations. This may be
12783 desirable in some cases where strict IEEE 754-compliant results are
12784 required: the fused multiply add/subtract instructions do not round the
12785 intermediate result, thereby producing results with @emph{more} bits of
12786 precision than specified by the IEEE standard. Disabling fused multiply
12787 add/subtract instructions also ensures that the program output is not
12788 sensitive to the compiler's ability to combine multiply and add/subtract
12791 @item -mtext-section-literals
12792 @itemx -mno-text-section-literals
12793 @opindex mtext-section-literals
12794 @opindex mno-text-section-literals
12795 Control the treatment of literal pools. The default is
12796 @option{-mno-text-section-literals}, which places literals in a separate
12797 section in the output file. This allows the literal pool to be placed
12798 in a data RAM/ROM, and it also allows the linker to combine literal
12799 pools from separate object files to remove redundant literals and
12800 improve code size. With @option{-mtext-section-literals}, the literals
12801 are interspersed in the text section in order to keep them as close as
12802 possible to their references. This may be necessary for large assembly
12805 @item -mtarget-align
12806 @itemx -mno-target-align
12807 @opindex mtarget-align
12808 @opindex mno-target-align
12809 When this option is enabled, GCC instructs the assembler to
12810 automatically align instructions to reduce branch penalties at the
12811 expense of some code density. The assembler attempts to widen density
12812 instructions to align branch targets and the instructions following call
12813 instructions. If there are not enough preceding safe density
12814 instructions to align a target, no widening will be performed. The
12815 default is @option{-mtarget-align}. These options do not affect the
12816 treatment of auto-aligned instructions like @code{LOOP}, which the
12817 assembler will always align, either by widening density instructions or
12818 by inserting no-op instructions.
12821 @itemx -mno-longcalls
12822 @opindex mlongcalls
12823 @opindex mno-longcalls
12824 When this option is enabled, GCC instructs the assembler to translate
12825 direct calls to indirect calls unless it can determine that the target
12826 of a direct call is in the range allowed by the call instruction. This
12827 translation typically occurs for calls to functions in other source
12828 files. Specifically, the assembler translates a direct @code{CALL}
12829 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
12830 The default is @option{-mno-longcalls}. This option should be used in
12831 programs where the call target can potentially be out of range. This
12832 option is implemented in the assembler, not the compiler, so the
12833 assembly code generated by GCC will still show direct call
12834 instructions---look at the disassembled object code to see the actual
12835 instructions. Note that the assembler will use an indirect call for
12836 every cross-file call, not just those that really will be out of range.
12839 @node zSeries Options
12840 @subsection zSeries Options
12841 @cindex zSeries options
12843 These are listed under @xref{S/390 and zSeries Options}.
12845 @node Code Gen Options
12846 @section Options for Code Generation Conventions
12847 @cindex code generation conventions
12848 @cindex options, code generation
12849 @cindex run-time options
12851 These machine-independent options control the interface conventions
12852 used in code generation.
12854 Most of them have both positive and negative forms; the negative form
12855 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
12856 one of the forms is listed---the one which is not the default. You
12857 can figure out the other form by either removing @samp{no-} or adding
12861 @item -fbounds-check
12862 @opindex fbounds-check
12863 For front-ends that support it, generate additional code to check that
12864 indices used to access arrays are within the declared range. This is
12865 currently only supported by the Java and Fortran 77 front-ends, where
12866 this option defaults to true and false respectively.
12870 This option generates traps for signed overflow on addition, subtraction,
12871 multiplication operations.
12875 This option instructs the compiler to assume that signed arithmetic
12876 overflow of addition, subtraction and multiplication wraps around
12877 using twos-complement representation. This flag enables some optimizations
12878 and disables others. This option is enabled by default for the Java
12879 front-end, as required by the Java language specification.
12882 @opindex fexceptions
12883 Enable exception handling. Generates extra code needed to propagate
12884 exceptions. For some targets, this implies GCC will generate frame
12885 unwind information for all functions, which can produce significant data
12886 size overhead, although it does not affect execution. If you do not
12887 specify this option, GCC will enable it by default for languages like
12888 C++ which normally require exception handling, and disable it for
12889 languages like C that do not normally require it. However, you may need
12890 to enable this option when compiling C code that needs to interoperate
12891 properly with exception handlers written in C++. You may also wish to
12892 disable this option if you are compiling older C++ programs that don't
12893 use exception handling.
12895 @item -fnon-call-exceptions
12896 @opindex fnon-call-exceptions
12897 Generate code that allows trapping instructions to throw exceptions.
12898 Note that this requires platform-specific runtime support that does
12899 not exist everywhere. Moreover, it only allows @emph{trapping}
12900 instructions to throw exceptions, i.e.@: memory references or floating
12901 point instructions. It does not allow exceptions to be thrown from
12902 arbitrary signal handlers such as @code{SIGALRM}.
12904 @item -funwind-tables
12905 @opindex funwind-tables
12906 Similar to @option{-fexceptions}, except that it will just generate any needed
12907 static data, but will not affect the generated code in any other way.
12908 You will normally not enable this option; instead, a language processor
12909 that needs this handling would enable it on your behalf.
12911 @item -fasynchronous-unwind-tables
12912 @opindex fasynchronous-unwind-tables
12913 Generate unwind table in dwarf2 format, if supported by target machine. The
12914 table is exact at each instruction boundary, so it can be used for stack
12915 unwinding from asynchronous events (such as debugger or garbage collector).
12917 @item -fpcc-struct-return
12918 @opindex fpcc-struct-return
12919 Return ``short'' @code{struct} and @code{union} values in memory like
12920 longer ones, rather than in registers. This convention is less
12921 efficient, but it has the advantage of allowing intercallability between
12922 GCC-compiled files and files compiled with other compilers, particularly
12923 the Portable C Compiler (pcc).
12925 The precise convention for returning structures in memory depends
12926 on the target configuration macros.
12928 Short structures and unions are those whose size and alignment match
12929 that of some integer type.
12931 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
12932 switch is not binary compatible with code compiled with the
12933 @option{-freg-struct-return} switch.
12934 Use it to conform to a non-default application binary interface.
12936 @item -freg-struct-return
12937 @opindex freg-struct-return
12938 Return @code{struct} and @code{union} values in registers when possible.
12939 This is more efficient for small structures than
12940 @option{-fpcc-struct-return}.
12942 If you specify neither @option{-fpcc-struct-return} nor
12943 @option{-freg-struct-return}, GCC defaults to whichever convention is
12944 standard for the target. If there is no standard convention, GCC
12945 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
12946 the principal compiler. In those cases, we can choose the standard, and
12947 we chose the more efficient register return alternative.
12949 @strong{Warning:} code compiled with the @option{-freg-struct-return}
12950 switch is not binary compatible with code compiled with the
12951 @option{-fpcc-struct-return} switch.
12952 Use it to conform to a non-default application binary interface.
12954 @item -fshort-enums
12955 @opindex fshort-enums
12956 Allocate to an @code{enum} type only as many bytes as it needs for the
12957 declared range of possible values. Specifically, the @code{enum} type
12958 will be equivalent to the smallest integer type which has enough room.
12960 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
12961 code that is not binary compatible with code generated without that switch.
12962 Use it to conform to a non-default application binary interface.
12964 @item -fshort-double
12965 @opindex fshort-double
12966 Use the same size for @code{double} as for @code{float}.
12968 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
12969 code that is not binary compatible with code generated without that switch.
12970 Use it to conform to a non-default application binary interface.
12972 @item -fshort-wchar
12973 @opindex fshort-wchar
12974 Override the underlying type for @samp{wchar_t} to be @samp{short
12975 unsigned int} instead of the default for the target. This option is
12976 useful for building programs to run under WINE@.
12978 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
12979 code that is not binary compatible with code generated without that switch.
12980 Use it to conform to a non-default application binary interface.
12983 @opindex fno-common
12984 In C, allocate even uninitialized global variables in the data section of the
12985 object file, rather than generating them as common blocks. This has the
12986 effect that if the same variable is declared (without @code{extern}) in
12987 two different compilations, you will get an error when you link them.
12988 The only reason this might be useful is if you wish to verify that the
12989 program will work on other systems which always work this way.
12993 Ignore the @samp{#ident} directive.
12995 @item -finhibit-size-directive
12996 @opindex finhibit-size-directive
12997 Don't output a @code{.size} assembler directive, or anything else that
12998 would cause trouble if the function is split in the middle, and the
12999 two halves are placed at locations far apart in memory. This option is
13000 used when compiling @file{crtstuff.c}; you should not need to use it
13003 @item -fverbose-asm
13004 @opindex fverbose-asm
13005 Put extra commentary information in the generated assembly code to
13006 make it more readable. This option is generally only of use to those
13007 who actually need to read the generated assembly code (perhaps while
13008 debugging the compiler itself).
13010 @option{-fno-verbose-asm}, the default, causes the
13011 extra information to be omitted and is useful when comparing two assembler
13016 @cindex global offset table
13018 Generate position-independent code (PIC) suitable for use in a shared
13019 library, if supported for the target machine. Such code accesses all
13020 constant addresses through a global offset table (GOT)@. The dynamic
13021 loader resolves the GOT entries when the program starts (the dynamic
13022 loader is not part of GCC; it is part of the operating system). If
13023 the GOT size for the linked executable exceeds a machine-specific
13024 maximum size, you get an error message from the linker indicating that
13025 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
13026 instead. (These maximums are 8k on the SPARC and 32k
13027 on the m68k and RS/6000. The 386 has no such limit.)
13029 Position-independent code requires special support, and therefore works
13030 only on certain machines. For the 386, GCC supports PIC for System V
13031 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
13032 position-independent.
13034 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13039 If supported for the target machine, emit position-independent code,
13040 suitable for dynamic linking and avoiding any limit on the size of the
13041 global offset table. This option makes a difference on the m68k,
13042 PowerPC and SPARC@.
13044 Position-independent code requires special support, and therefore works
13045 only on certain machines.
13047 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13054 These options are similar to @option{-fpic} and @option{-fPIC}, but
13055 generated position independent code can be only linked into executables.
13056 Usually these options are used when @option{-pie} GCC option will be
13057 used during linking.
13059 @item -fno-jump-tables
13060 @opindex fno-jump-tables
13061 Do not use jump tables for switch statements even where it would be
13062 more efficient than other code generation strategies. This option is
13063 of use in conjunction with @option{-fpic} or @option{-fPIC} for
13064 building code which forms part of a dynamic linker and cannot
13065 reference the address of a jump table. On some targets, jump tables
13066 do not require a GOT and this option is not needed.
13068 @item -ffixed-@var{reg}
13070 Treat the register named @var{reg} as a fixed register; generated code
13071 should never refer to it (except perhaps as a stack pointer, frame
13072 pointer or in some other fixed role).
13074 @var{reg} must be the name of a register. The register names accepted
13075 are machine-specific and are defined in the @code{REGISTER_NAMES}
13076 macro in the machine description macro file.
13078 This flag does not have a negative form, because it specifies a
13081 @item -fcall-used-@var{reg}
13082 @opindex fcall-used
13083 Treat the register named @var{reg} as an allocable register that is
13084 clobbered by function calls. It may be allocated for temporaries or
13085 variables that do not live across a call. Functions compiled this way
13086 will not save and restore the register @var{reg}.
13088 It is an error to used this flag with the frame pointer or stack pointer.
13089 Use of this flag for other registers that have fixed pervasive roles in
13090 the machine's execution model will produce disastrous results.
13092 This flag does not have a negative form, because it specifies a
13095 @item -fcall-saved-@var{reg}
13096 @opindex fcall-saved
13097 Treat the register named @var{reg} as an allocable register saved by
13098 functions. It may be allocated even for temporaries or variables that
13099 live across a call. Functions compiled this way will save and restore
13100 the register @var{reg} if they use it.
13102 It is an error to used this flag with the frame pointer or stack pointer.
13103 Use of this flag for other registers that have fixed pervasive roles in
13104 the machine's execution model will produce disastrous results.
13106 A different sort of disaster will result from the use of this flag for
13107 a register in which function values may be returned.
13109 This flag does not have a negative form, because it specifies a
13112 @item -fpack-struct[=@var{n}]
13113 @opindex fpack-struct
13114 Without a value specified, pack all structure members together without
13115 holes. When a value is specified (which must be a small power of two), pack
13116 structure members according to this value, representing the maximum
13117 alignment (that is, objects with default alignment requirements larger than
13118 this will be output potentially unaligned at the next fitting location.
13120 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
13121 code that is not binary compatible with code generated without that switch.
13122 Additionally, it makes the code suboptimal.
13123 Use it to conform to a non-default application binary interface.
13125 @item -finstrument-functions
13126 @opindex finstrument-functions
13127 Generate instrumentation calls for entry and exit to functions. Just
13128 after function entry and just before function exit, the following
13129 profiling functions will be called with the address of the current
13130 function and its call site. (On some platforms,
13131 @code{__builtin_return_address} does not work beyond the current
13132 function, so the call site information may not be available to the
13133 profiling functions otherwise.)
13136 void __cyg_profile_func_enter (void *this_fn,
13138 void __cyg_profile_func_exit (void *this_fn,
13142 The first argument is the address of the start of the current function,
13143 which may be looked up exactly in the symbol table.
13145 This instrumentation is also done for functions expanded inline in other
13146 functions. The profiling calls will indicate where, conceptually, the
13147 inline function is entered and exited. This means that addressable
13148 versions of such functions must be available. If all your uses of a
13149 function are expanded inline, this may mean an additional expansion of
13150 code size. If you use @samp{extern inline} in your C code, an
13151 addressable version of such functions must be provided. (This is
13152 normally the case anyways, but if you get lucky and the optimizer always
13153 expands the functions inline, you might have gotten away without
13154 providing static copies.)
13156 A function may be given the attribute @code{no_instrument_function}, in
13157 which case this instrumentation will not be done. This can be used, for
13158 example, for the profiling functions listed above, high-priority
13159 interrupt routines, and any functions from which the profiling functions
13160 cannot safely be called (perhaps signal handlers, if the profiling
13161 routines generate output or allocate memory).
13163 @item -fstack-check
13164 @opindex fstack-check
13165 Generate code to verify that you do not go beyond the boundary of the
13166 stack. You should specify this flag if you are running in an
13167 environment with multiple threads, but only rarely need to specify it in
13168 a single-threaded environment since stack overflow is automatically
13169 detected on nearly all systems if there is only one stack.
13171 Note that this switch does not actually cause checking to be done; the
13172 operating system must do that. The switch causes generation of code
13173 to ensure that the operating system sees the stack being extended.
13175 @item -fstack-limit-register=@var{reg}
13176 @itemx -fstack-limit-symbol=@var{sym}
13177 @itemx -fno-stack-limit
13178 @opindex fstack-limit-register
13179 @opindex fstack-limit-symbol
13180 @opindex fno-stack-limit
13181 Generate code to ensure that the stack does not grow beyond a certain value,
13182 either the value of a register or the address of a symbol. If the stack
13183 would grow beyond the value, a signal is raised. For most targets,
13184 the signal is raised before the stack overruns the boundary, so
13185 it is possible to catch the signal without taking special precautions.
13187 For instance, if the stack starts at absolute address @samp{0x80000000}
13188 and grows downwards, you can use the flags
13189 @option{-fstack-limit-symbol=__stack_limit} and
13190 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
13191 of 128KB@. Note that this may only work with the GNU linker.
13193 @cindex aliasing of parameters
13194 @cindex parameters, aliased
13195 @item -fargument-alias
13196 @itemx -fargument-noalias
13197 @itemx -fargument-noalias-global
13198 @opindex fargument-alias
13199 @opindex fargument-noalias
13200 @opindex fargument-noalias-global
13201 Specify the possible relationships among parameters and between
13202 parameters and global data.
13204 @option{-fargument-alias} specifies that arguments (parameters) may
13205 alias each other and may alias global storage.@*
13206 @option{-fargument-noalias} specifies that arguments do not alias
13207 each other, but may alias global storage.@*
13208 @option{-fargument-noalias-global} specifies that arguments do not
13209 alias each other and do not alias global storage.
13211 Each language will automatically use whatever option is required by
13212 the language standard. You should not need to use these options yourself.
13214 @item -fleading-underscore
13215 @opindex fleading-underscore
13216 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
13217 change the way C symbols are represented in the object file. One use
13218 is to help link with legacy assembly code.
13220 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
13221 generate code that is not binary compatible with code generated without that
13222 switch. Use it to conform to a non-default application binary interface.
13223 Not all targets provide complete support for this switch.
13225 @item -ftls-model=@var{model}
13226 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
13227 The @var{model} argument should be one of @code{global-dynamic},
13228 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
13230 The default without @option{-fpic} is @code{initial-exec}; with
13231 @option{-fpic} the default is @code{global-dynamic}.
13233 @item -fvisibility=@var{default|internal|hidden|protected}
13234 @opindex fvisibility
13235 Set the default ELF image symbol visibility to the specified option---all
13236 symbols will be marked with this unless overridden within the code.
13237 Using this feature can very substantially improve linking and
13238 load times of shared object libraries, produce more optimized
13239 code, provide near-perfect API export and prevent symbol clashes.
13240 It is @strong{strongly} recommended that you use this in any shared objects
13243 Despite the nomenclature, @code{default} always means public ie;
13244 available to be linked against from outside the shared object.
13245 @code{protected} and @code{internal} are pretty useless in real-world
13246 usage so the only other commonly used option will be @code{hidden}.
13247 The default if @option{-fvisibility} isn't specified is
13248 @code{default}, i.e., make every
13249 symbol public---this causes the same behavior as previous versions of
13252 A good explanation of the benefits offered by ensuring ELF
13253 symbols have the correct visibility is given by ``How To Write
13254 Shared Libraries'' by Ulrich Drepper (which can be found at
13255 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
13256 solution made possible by this option to marking things hidden when
13257 the default is public is to make the default hidden and mark things
13258 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
13259 and @code{__attribute__ ((visibility("default")))} instead of
13260 @code{__declspec(dllexport)} you get almost identical semantics with
13261 identical syntax. This is a great boon to those working with
13262 cross-platform projects.
13264 For those adding visibility support to existing code, you may find
13265 @samp{#pragma GCC visibility} of use. This works by you enclosing
13266 the declarations you wish to set visibility for with (for example)
13267 @samp{#pragma GCC visibility push(hidden)} and
13268 @samp{#pragma GCC visibility pop}.
13269 Bear in mind that symbol visibility should be viewed @strong{as
13270 part of the API interface contract} and thus all new code should
13271 always specify visibility when it is not the default ie; declarations
13272 only for use within the local DSO should @strong{always} be marked explicitly
13273 as hidden as so to avoid PLT indirection overheads---making this
13274 abundantly clear also aids readability and self-documentation of the code.
13275 Note that due to ISO C++ specification requirements, operator new and
13276 operator delete must always be of default visibility.
13278 An overview of these techniques, their benefits and how to use them
13279 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
13283 @cindex openmp parallel
13284 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
13285 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
13286 compiler generates parallel code according to the OpenMP Application
13287 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}.
13293 @node Environment Variables
13294 @section Environment Variables Affecting GCC
13295 @cindex environment variables
13297 @c man begin ENVIRONMENT
13298 This section describes several environment variables that affect how GCC
13299 operates. Some of them work by specifying directories or prefixes to use
13300 when searching for various kinds of files. Some are used to specify other
13301 aspects of the compilation environment.
13303 Note that you can also specify places to search using options such as
13304 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
13305 take precedence over places specified using environment variables, which
13306 in turn take precedence over those specified by the configuration of GCC@.
13307 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
13308 GNU Compiler Collection (GCC) Internals}.
13313 @c @itemx LC_COLLATE
13315 @c @itemx LC_MONETARY
13316 @c @itemx LC_NUMERIC
13321 @c @findex LC_COLLATE
13322 @findex LC_MESSAGES
13323 @c @findex LC_MONETARY
13324 @c @findex LC_NUMERIC
13328 These environment variables control the way that GCC uses
13329 localization information that allow GCC to work with different
13330 national conventions. GCC inspects the locale categories
13331 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
13332 so. These locale categories can be set to any value supported by your
13333 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
13334 Kingdom encoded in UTF-8.
13336 The @env{LC_CTYPE} environment variable specifies character
13337 classification. GCC uses it to determine the character boundaries in
13338 a string; this is needed for some multibyte encodings that contain quote
13339 and escape characters that would otherwise be interpreted as a string
13342 The @env{LC_MESSAGES} environment variable specifies the language to
13343 use in diagnostic messages.
13345 If the @env{LC_ALL} environment variable is set, it overrides the value
13346 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
13347 and @env{LC_MESSAGES} default to the value of the @env{LANG}
13348 environment variable. If none of these variables are set, GCC
13349 defaults to traditional C English behavior.
13353 If @env{TMPDIR} is set, it specifies the directory to use for temporary
13354 files. GCC uses temporary files to hold the output of one stage of
13355 compilation which is to be used as input to the next stage: for example,
13356 the output of the preprocessor, which is the input to the compiler
13359 @item GCC_EXEC_PREFIX
13360 @findex GCC_EXEC_PREFIX
13361 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
13362 names of the subprograms executed by the compiler. No slash is added
13363 when this prefix is combined with the name of a subprogram, but you can
13364 specify a prefix that ends with a slash if you wish.
13366 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
13367 an appropriate prefix to use based on the pathname it was invoked with.
13369 If GCC cannot find the subprogram using the specified prefix, it
13370 tries looking in the usual places for the subprogram.
13372 The default value of @env{GCC_EXEC_PREFIX} is
13373 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
13374 of @code{prefix} when you ran the @file{configure} script.
13376 Other prefixes specified with @option{-B} take precedence over this prefix.
13378 This prefix is also used for finding files such as @file{crt0.o} that are
13381 In addition, the prefix is used in an unusual way in finding the
13382 directories to search for header files. For each of the standard
13383 directories whose name normally begins with @samp{/usr/local/lib/gcc}
13384 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
13385 replacing that beginning with the specified prefix to produce an
13386 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
13387 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
13388 These alternate directories are searched first; the standard directories
13391 @item COMPILER_PATH
13392 @findex COMPILER_PATH
13393 The value of @env{COMPILER_PATH} is a colon-separated list of
13394 directories, much like @env{PATH}. GCC tries the directories thus
13395 specified when searching for subprograms, if it can't find the
13396 subprograms using @env{GCC_EXEC_PREFIX}.
13399 @findex LIBRARY_PATH
13400 The value of @env{LIBRARY_PATH} is a colon-separated list of
13401 directories, much like @env{PATH}. When configured as a native compiler,
13402 GCC tries the directories thus specified when searching for special
13403 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
13404 using GCC also uses these directories when searching for ordinary
13405 libraries for the @option{-l} option (but directories specified with
13406 @option{-L} come first).
13410 @cindex locale definition
13411 This variable is used to pass locale information to the compiler. One way in
13412 which this information is used is to determine the character set to be used
13413 when character literals, string literals and comments are parsed in C and C++.
13414 When the compiler is configured to allow multibyte characters,
13415 the following values for @env{LANG} are recognized:
13419 Recognize JIS characters.
13421 Recognize SJIS characters.
13423 Recognize EUCJP characters.
13426 If @env{LANG} is not defined, or if it has some other value, then the
13427 compiler will use mblen and mbtowc as defined by the default locale to
13428 recognize and translate multibyte characters.
13432 Some additional environments variables affect the behavior of the
13435 @include cppenv.texi
13439 @node Precompiled Headers
13440 @section Using Precompiled Headers
13441 @cindex precompiled headers
13442 @cindex speed of compilation
13444 Often large projects have many header files that are included in every
13445 source file. The time the compiler takes to process these header files
13446 over and over again can account for nearly all of the time required to
13447 build the project. To make builds faster, GCC allows users to
13448 `precompile' a header file; then, if builds can use the precompiled
13449 header file they will be much faster.
13451 To create a precompiled header file, simply compile it as you would any
13452 other file, if necessary using the @option{-x} option to make the driver
13453 treat it as a C or C++ header file. You will probably want to use a
13454 tool like @command{make} to keep the precompiled header up-to-date when
13455 the headers it contains change.
13457 A precompiled header file will be searched for when @code{#include} is
13458 seen in the compilation. As it searches for the included file
13459 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
13460 compiler looks for a precompiled header in each directory just before it
13461 looks for the include file in that directory. The name searched for is
13462 the name specified in the @code{#include} with @samp{.gch} appended. If
13463 the precompiled header file can't be used, it is ignored.
13465 For instance, if you have @code{#include "all.h"}, and you have
13466 @file{all.h.gch} in the same directory as @file{all.h}, then the
13467 precompiled header file will be used if possible, and the original
13468 header will be used otherwise.
13470 Alternatively, you might decide to put the precompiled header file in a
13471 directory and use @option{-I} to ensure that directory is searched
13472 before (or instead of) the directory containing the original header.
13473 Then, if you want to check that the precompiled header file is always
13474 used, you can put a file of the same name as the original header in this
13475 directory containing an @code{#error} command.
13477 This also works with @option{-include}. So yet another way to use
13478 precompiled headers, good for projects not designed with precompiled
13479 header files in mind, is to simply take most of the header files used by
13480 a project, include them from another header file, precompile that header
13481 file, and @option{-include} the precompiled header. If the header files
13482 have guards against multiple inclusion, they will be skipped because
13483 they've already been included (in the precompiled header).
13485 If you need to precompile the same header file for different
13486 languages, targets, or compiler options, you can instead make a
13487 @emph{directory} named like @file{all.h.gch}, and put each precompiled
13488 header in the directory, perhaps using @option{-o}. It doesn't matter
13489 what you call the files in the directory, every precompiled header in
13490 the directory will be considered. The first precompiled header
13491 encountered in the directory that is valid for this compilation will
13492 be used; they're searched in no particular order.
13494 There are many other possibilities, limited only by your imagination,
13495 good sense, and the constraints of your build system.
13497 A precompiled header file can be used only when these conditions apply:
13501 Only one precompiled header can be used in a particular compilation.
13504 A precompiled header can't be used once the first C token is seen. You
13505 can have preprocessor directives before a precompiled header; you can
13506 even include a precompiled header from inside another header, so long as
13507 there are no C tokens before the @code{#include}.
13510 The precompiled header file must be produced for the same language as
13511 the current compilation. You can't use a C precompiled header for a C++
13515 The precompiled header file must have been produced by the same compiler
13516 binary as the current compilation is using.
13519 Any macros defined before the precompiled header is included must
13520 either be defined in the same way as when the precompiled header was
13521 generated, or must not affect the precompiled header, which usually
13522 means that they don't appear in the precompiled header at all.
13524 The @option{-D} option is one way to define a macro before a
13525 precompiled header is included; using a @code{#define} can also do it.
13526 There are also some options that define macros implicitly, like
13527 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
13530 @item If debugging information is output when using the precompiled
13531 header, using @option{-g} or similar, the same kind of debugging information
13532 must have been output when building the precompiled header. However,
13533 a precompiled header built using @option{-g} can be used in a compilation
13534 when no debugging information is being output.
13536 @item The same @option{-m} options must generally be used when building
13537 and using the precompiled header. @xref{Submodel Options},
13538 for any cases where this rule is relaxed.
13540 @item Each of the following options must be the same when building and using
13541 the precompiled header:
13543 @gccoptlist{-fexceptions -funit-at-a-time}
13546 Some other command-line options starting with @option{-f},
13547 @option{-p}, or @option{-O} must be defined in the same way as when
13548 the precompiled header was generated. At present, it's not clear
13549 which options are safe to change and which are not; the safest choice
13550 is to use exactly the same options when generating and using the
13551 precompiled header. The following are known to be safe:
13553 @gccoptlist{-fmessage-length= -fpreprocessed
13554 -fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
13555 -fsched-verbose=<number> -fschedule-insns -fvisibility=
13560 For all of these except the last, the compiler will automatically
13561 ignore the precompiled header if the conditions aren't met. If you
13562 find an option combination that doesn't work and doesn't cause the
13563 precompiled header to be ignored, please consider filing a bug report,
13566 If you do use differing options when generating and using the
13567 precompiled header, the actual behavior will be a mixture of the
13568 behavior for the options. For instance, if you use @option{-g} to
13569 generate the precompiled header but not when using it, you may or may
13570 not get debugging information for routines in the precompiled header.
13572 @node Running Protoize
13573 @section Running Protoize
13575 The program @code{protoize} is an optional part of GCC@. You can use
13576 it to add prototypes to a program, thus converting the program to ISO
13577 C in one respect. The companion program @code{unprotoize} does the
13578 reverse: it removes argument types from any prototypes that are found.
13580 When you run these programs, you must specify a set of source files as
13581 command line arguments. The conversion programs start out by compiling
13582 these files to see what functions they define. The information gathered
13583 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
13585 After scanning comes actual conversion. The specified files are all
13586 eligible to be converted; any files they include (whether sources or
13587 just headers) are eligible as well.
13589 But not all the eligible files are converted. By default,
13590 @code{protoize} and @code{unprotoize} convert only source and header
13591 files in the current directory. You can specify additional directories
13592 whose files should be converted with the @option{-d @var{directory}}
13593 option. You can also specify particular files to exclude with the
13594 @option{-x @var{file}} option. A file is converted if it is eligible, its
13595 directory name matches one of the specified directory names, and its
13596 name within the directory has not been excluded.
13598 Basic conversion with @code{protoize} consists of rewriting most
13599 function definitions and function declarations to specify the types of
13600 the arguments. The only ones not rewritten are those for varargs
13603 @code{protoize} optionally inserts prototype declarations at the
13604 beginning of the source file, to make them available for any calls that
13605 precede the function's definition. Or it can insert prototype
13606 declarations with block scope in the blocks where undeclared functions
13609 Basic conversion with @code{unprotoize} consists of rewriting most
13610 function declarations to remove any argument types, and rewriting
13611 function definitions to the old-style pre-ISO form.
13613 Both conversion programs print a warning for any function declaration or
13614 definition that they can't convert. You can suppress these warnings
13617 The output from @code{protoize} or @code{unprotoize} replaces the
13618 original source file. The original file is renamed to a name ending
13619 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
13620 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
13621 for DOS) file already exists, then the source file is simply discarded.
13623 @code{protoize} and @code{unprotoize} both depend on GCC itself to
13624 scan the program and collect information about the functions it uses.
13625 So neither of these programs will work until GCC is installed.
13627 Here is a table of the options you can use with @code{protoize} and
13628 @code{unprotoize}. Each option works with both programs unless
13632 @item -B @var{directory}
13633 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
13634 usual directory (normally @file{/usr/local/lib}). This file contains
13635 prototype information about standard system functions. This option
13636 applies only to @code{protoize}.
13638 @item -c @var{compilation-options}
13639 Use @var{compilation-options} as the options when running @command{gcc} to
13640 produce the @samp{.X} files. The special option @option{-aux-info} is
13641 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
13643 Note that the compilation options must be given as a single argument to
13644 @code{protoize} or @code{unprotoize}. If you want to specify several
13645 @command{gcc} options, you must quote the entire set of compilation options
13646 to make them a single word in the shell.
13648 There are certain @command{gcc} arguments that you cannot use, because they
13649 would produce the wrong kind of output. These include @option{-g},
13650 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
13651 the @var{compilation-options}, they are ignored.
13654 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
13655 systems) instead of @samp{.c}. This is convenient if you are converting
13656 a C program to C++. This option applies only to @code{protoize}.
13659 Add explicit global declarations. This means inserting explicit
13660 declarations at the beginning of each source file for each function
13661 that is called in the file and was not declared. These declarations
13662 precede the first function definition that contains a call to an
13663 undeclared function. This option applies only to @code{protoize}.
13665 @item -i @var{string}
13666 Indent old-style parameter declarations with the string @var{string}.
13667 This option applies only to @code{protoize}.
13669 @code{unprotoize} converts prototyped function definitions to old-style
13670 function definitions, where the arguments are declared between the
13671 argument list and the initial @samp{@{}. By default, @code{unprotoize}
13672 uses five spaces as the indentation. If you want to indent with just
13673 one space instead, use @option{-i " "}.
13676 Keep the @samp{.X} files. Normally, they are deleted after conversion
13680 Add explicit local declarations. @code{protoize} with @option{-l} inserts
13681 a prototype declaration for each function in each block which calls the
13682 function without any declaration. This option applies only to
13686 Make no real changes. This mode just prints information about the conversions
13687 that would have been done without @option{-n}.
13690 Make no @samp{.save} files. The original files are simply deleted.
13691 Use this option with caution.
13693 @item -p @var{program}
13694 Use the program @var{program} as the compiler. Normally, the name
13695 @file{gcc} is used.
13698 Work quietly. Most warnings are suppressed.
13701 Print the version number, just like @option{-v} for @command{gcc}.
13704 If you need special compiler options to compile one of your program's
13705 source files, then you should generate that file's @samp{.X} file
13706 specially, by running @command{gcc} on that source file with the
13707 appropriate options and the option @option{-aux-info}. Then run
13708 @code{protoize} on the entire set of files. @code{protoize} will use
13709 the existing @samp{.X} file because it is newer than the source file.
13713 gcc -Dfoo=bar file1.c -aux-info file1.X
13718 You need to include the special files along with the rest in the
13719 @code{protoize} command, even though their @samp{.X} files already
13720 exist, because otherwise they won't get converted.
13722 @xref{Protoize Caveats}, for more information on how to use
13723 @code{protoize} successfully.