1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.2 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}.
55 See the Info entry for @command{gcc}, or
56 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
57 for contributors to GCC@.
62 @chapter GCC Command Options
63 @cindex GCC command options
64 @cindex command options
65 @cindex options, GCC command
67 @c man begin DESCRIPTION
68 When you invoke GCC, it normally does preprocessing, compilation,
69 assembly and linking. The ``overall options'' allow you to stop this
70 process at an intermediate stage. For example, the @option{-c} option
71 says not to run the linker. Then the output consists of object files
72 output by the assembler.
74 Other options are passed on to one stage of processing. Some options
75 control the preprocessor and others the compiler itself. Yet other
76 options control the assembler and linker; most of these are not
77 documented here, since you rarely need to use any of them.
79 @cindex C compilation options
80 Most of the command line options that you can use with GCC are useful
81 for C programs; when an option is only useful with another language
82 (usually C++), the explanation says so explicitly. If the description
83 for a particular option does not mention a source language, you can use
84 that option with all supported languages.
86 @cindex C++ compilation options
87 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
88 options for compiling C++ programs.
90 @cindex grouping options
91 @cindex options, grouping
92 The @command{gcc} program accepts options and file names as operands. Many
93 options have multi-letter names; therefore multiple single-letter options
94 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
97 @cindex order of options
98 @cindex options, order
99 You can mix options and other arguments. For the most part, the order
100 you use doesn't matter. Order does matter when you use several options
101 of the same kind; for example, if you specify @option{-L} more than once,
102 the directories are searched in the order specified.
104 Many options have long names starting with @samp{-f} or with
105 @samp{-W}---for example,
106 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
107 these have both positive and negative forms; the negative form of
108 @option{-ffoo} would be @option{-fno-foo}. This manual documents
109 only one of these two forms, whichever one is not the default.
113 @xref{Option Index}, for an index to GCC's options.
116 * Option Summary:: Brief list of all options, without explanations.
117 * Overall Options:: Controlling the kind of output:
118 an executable, object files, assembler files,
119 or preprocessed source.
120 * Invoking G++:: Compiling C++ programs.
121 * C Dialect Options:: Controlling the variant of C language compiled.
122 * C++ Dialect Options:: Variations on C++.
123 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
125 * Language Independent Options:: Controlling how diagnostics should be
127 * Warning Options:: How picky should the compiler be?
128 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
129 * Optimize Options:: How much optimization?
130 * Preprocessor Options:: Controlling header files and macro definitions.
131 Also, getting dependency information for Make.
132 * Assembler Options:: Passing options to the assembler.
133 * Link Options:: Specifying libraries and so on.
134 * Directory Options:: Where to find header files and libraries.
135 Where to find the compiler executable files.
136 * Spec Files:: How to pass switches to sub-processes.
137 * Target Options:: Running a cross-compiler, or an old version of GCC.
138 * Submodel Options:: Specifying minor hardware or convention variations,
139 such as 68010 vs 68020.
140 * Code Gen Options:: Specifying conventions for function calls, data layout
142 * Environment Variables:: Env vars that affect GCC.
143 * Precompiled Headers:: Compiling a header once, and using it many times.
144 * Running Protoize:: Automatically adding or removing function prototypes.
150 @section Option Summary
152 Here is a summary of all the options, grouped by type. Explanations are
153 in the following sections.
156 @item Overall Options
157 @xref{Overall Options,,Options Controlling the Kind of Output}.
158 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
159 -x @var{language} -v -### --help --target-help --version}
161 @item C Language Options
162 @xref{C Dialect Options,,Options Controlling C Dialect}.
163 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
164 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
165 -fhosted -ffreestanding -fms-extensions @gol
166 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
167 -fallow-single-precision -fcond-mismatch @gol
168 -fsigned-bitfields -fsigned-char @gol
169 -funsigned-bitfields -funsigned-char}
171 @item C++ Language Options
172 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
173 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
174 -fconserve-space -ffriend-injection -fno-const-strings @gol
175 -fno-elide-constructors @gol
176 -fno-enforce-eh-specs @gol
177 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
178 -fno-implicit-templates @gol
179 -fno-implicit-inline-templates @gol
180 -fno-implement-inlines -fms-extensions @gol
181 -fno-nonansi-builtins -fno-operator-names @gol
182 -fno-optional-diags -fpermissive @gol
183 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
184 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
185 -fno-default-inline -fvisibility-inlines-hidden @gol
186 -Wabi -Wctor-dtor-privacy @gol
187 -Wnon-virtual-dtor -Wreorder @gol
188 -Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol
189 -Wno-non-template-friend -Wold-style-cast @gol
190 -Woverloaded-virtual -Wno-pmf-conversions @gol
193 @item Objective-C and Objective-C++ Language Options
194 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
195 Objective-C and Objective-C++ Dialects}.
197 -fconstant-string-class=@var{class-name} @gol
198 -fgnu-runtime -fnext-runtime @gol
199 -fno-nil-receivers @gol
200 -fobjc-call-cxx-cdtors @gol
201 -fobjc-direct-dispatch @gol
202 -fobjc-exceptions @gol
204 -freplace-objc-classes @gol
207 -Wassign-intercept @gol
208 -Wno-protocol -Wselector @gol
209 -Wstrict-selector-match @gol
210 -Wundeclared-selector}
212 @item Language Independent Options
213 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
214 @gccoptlist{-fmessage-length=@var{n} @gol
215 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}} @gol
216 -fdiagnostics-show-options
218 @item Warning Options
219 @xref{Warning Options,,Options to Request or Suppress Warnings}.
220 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
221 -w -Wextra -Wall -Waggregate-return -Wno-attributes @gol
222 -Wc++-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
223 -Wconversion -Wno-deprecated-declarations @gol
224 -Wdisabled-optimization -Wno-div-by-zero -Wno-endif-labels @gol
225 -Werror -Werror-implicit-function-declaration @gol
226 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
227 -Wno-format-extra-args -Wformat-nonliteral @gol
228 -Wformat-security -Wformat-y2k @gol
229 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
230 -Wimport -Wno-import -Winit-self -Winline @gol
231 -Wno-int-to-pointer-cast @gol
232 -Wno-invalid-offsetof -Winvalid-pch @gol
233 -Wlarger-than-@var{len} -Wunsafe-loop-optimizations -Wlong-long @gol
234 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
235 -Wmissing-format-attribute -Wmissing-include-dirs @gol
236 -Wmissing-noreturn @gol
237 -Wno-multichar -Wnonnull -Wpacked -Wpadded @gol
238 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
239 -Wredundant-decls @gol
240 -Wreturn-type -Wsequence-point -Wshadow @gol
241 -Wsign-compare -Wstack-protector @gol
242 -Wstrict-aliasing -Wstrict-aliasing=2 @gol
243 -Wswitch -Wswitch-default -Wswitch-enum @gol
244 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
245 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
246 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
247 -Wunused-value -Wunused-variable -Wvariadic-macros @gol
248 -Wvolatile-register-var -Wwrite-strings}
250 @item C-only Warning Options
251 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
252 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
253 -Wstrict-prototypes -Wtraditional @gol
254 -Wdeclaration-after-statement -Wno-pointer-sign}
256 @item Debugging Options
257 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
258 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
259 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
260 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
261 -fdump-ipa-all -fdump-ipa-cgraph @gol
263 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
264 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
265 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
266 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
268 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
269 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
270 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
271 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
272 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
273 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
274 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
275 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
276 -fdump-tree-nrv -fdump-tree-vect @gol
277 -fdump-tree-sink @gol
278 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
279 -fdump-tree-salias @gol
280 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
281 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
282 -ftree-vectorizer-verbose=@var{n} @gol
283 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
284 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
285 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs @gol
286 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
287 -ftest-coverage -ftime-report -fvar-tracking @gol
288 -g -g@var{level} -gcoff -gdwarf-2 @gol
289 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
290 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
291 -print-multi-directory -print-multi-lib @gol
292 -print-prog-name=@var{program} -print-search-dirs -Q @gol
295 @item Optimization Options
296 @xref{Optimize Options,,Options that Control Optimization}.
297 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
298 -falign-labels=@var{n} -falign-loops=@var{n} @gol
299 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
300 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
301 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
302 -fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
303 -fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
304 -fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
305 -fexpensive-optimizations -ffast-math -ffloat-store @gol
306 -fforce-addr -ffunction-sections @gol
307 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
308 -floop-optimize -fcrossjumping -fif-conversion -fif-conversion2 @gol
309 -finline-functions -finline-functions-called-once @gol
310 -finline-limit=@var{n} -fkeep-inline-functions @gol
311 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
312 -fmodulo-sched -fno-branch-count-reg @gol
313 -fno-default-inline -fno-defer-pop -floop-optimize2 -fmove-loop-invariants @gol
314 -fno-function-cse -fno-guess-branch-probability @gol
315 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
316 -funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only @gol
317 -fno-trapping-math -fno-zero-initialized-in-bss @gol
318 -fomit-frame-pointer -foptimize-register-move @gol
319 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
320 -fprofile-generate -fprofile-use @gol
321 -fregmove -frename-registers @gol
322 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
323 -frerun-cse-after-loop -frerun-loop-opt @gol
324 -frounding-math -fschedule-insns -fschedule-insns2 @gol
325 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
326 -fsched-spec-load-dangerous @gol
327 -fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
328 -fsched2-use-superblocks @gol
329 -fsched2-use-traces -freschedule-modulo-scheduled-loops @gol
330 -fsignaling-nans -fsingle-precision-constant @gol
331 -fstack-protector -fstack-protector-all @gol
332 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
333 -funroll-all-loops -funroll-loops -fpeel-loops @gol
334 -fsplit-ivs-in-unroller -funswitch-loops @gol
335 -fvariable-expansion-in-unroller @gol
336 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
337 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
338 -ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
339 -ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
340 -ftree-vect-loop-version -ftree-salias -fweb @gol
341 -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
342 --param @var{name}=@var{value}
343 -O -O0 -O1 -O2 -O3 -Os}
345 @item Preprocessor Options
346 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
347 @gccoptlist{-A@var{question}=@var{answer} @gol
348 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
349 -C -dD -dI -dM -dN @gol
350 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
351 -idirafter @var{dir} @gol
352 -include @var{file} -imacros @var{file} @gol
353 -iprefix @var{file} -iwithprefix @var{dir} @gol
354 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
355 -isysroot @var{dir} @gol
356 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
357 -P -fworking-directory -remap @gol
358 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
359 -Xpreprocessor @var{option}}
361 @item Assembler Option
362 @xref{Assembler Options,,Passing Options to the Assembler}.
363 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
366 @xref{Link Options,,Options for Linking}.
367 @gccoptlist{@var{object-file-name} -l@var{library} @gol
368 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
369 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
370 -Wl,@var{option} -Xlinker @var{option} @gol
373 @item Directory Options
374 @xref{Directory Options,,Options for Directory Search}.
375 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
376 -specs=@var{file} -I- --sysroot=@var{dir}}
379 @c I wrote this xref this way to avoid overfull hbox. -- rms
380 @xref{Target Options}.
381 @gccoptlist{-V @var{version} -b @var{machine}}
383 @item Machine Dependent Options
384 @xref{Submodel Options,,Hardware Models and Configurations}.
385 @c This list is ordered alphanumerically by subsection name.
386 @c Try and put the significant identifier (CPU or system) first,
387 @c so users have a clue at guessing where the ones they want will be.
390 @gccoptlist{-EB -EL @gol
391 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
392 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
395 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
396 -mabi=@var{name} @gol
397 -mapcs-stack-check -mno-apcs-stack-check @gol
398 -mapcs-float -mno-apcs-float @gol
399 -mapcs-reentrant -mno-apcs-reentrant @gol
400 -msched-prolog -mno-sched-prolog @gol
401 -mlittle-endian -mbig-endian -mwords-little-endian @gol
402 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
403 -mthumb-interwork -mno-thumb-interwork @gol
404 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
405 -mstructure-size-boundary=@var{n} @gol
406 -mabort-on-noreturn @gol
407 -mlong-calls -mno-long-calls @gol
408 -msingle-pic-base -mno-single-pic-base @gol
409 -mpic-register=@var{reg} @gol
410 -mnop-fun-dllimport @gol
411 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
412 -mpoke-function-name @gol
414 -mtpcs-frame -mtpcs-leaf-frame @gol
415 -mcaller-super-interworking -mcallee-super-interworking @gol
419 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
420 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
422 @emph{Blackfin Options}
423 @gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
424 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
425 -mlow-64k -mno-low64k -mid-shared-library @gol
426 -mno-id-shared-library -mshared-library-id=@var{n} @gol
427 -mlong-calls -mno-long-calls}
430 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
431 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
432 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
433 -mstack-align -mdata-align -mconst-align @gol
434 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
435 -melf -maout -melinux -mlinux -sim -sim2 @gol
436 -mmul-bug-workaround -mno-mul-bug-workaround}
439 @gccoptlist{-mmac -mpush-args}
441 @emph{Darwin Options}
442 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
443 -arch_only -bind_at_load -bundle -bundle_loader @gol
444 -client_name -compatibility_version -current_version @gol
446 -dependency-file -dylib_file -dylinker_install_name @gol
447 -dynamic -dynamiclib -exported_symbols_list @gol
448 -filelist -flat_namespace -force_cpusubtype_ALL @gol
449 -force_flat_namespace -headerpad_max_install_names @gol
450 -image_base -init -install_name -keep_private_externs @gol
451 -multi_module -multiply_defined -multiply_defined_unused @gol
452 -noall_load -no_dead_strip_inits_and_terms @gol
453 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
454 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
455 -private_bundle -read_only_relocs -sectalign @gol
456 -sectobjectsymbols -whyload -seg1addr @gol
457 -sectcreate -sectobjectsymbols -sectorder @gol
458 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
459 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
460 -segprot -segs_read_only_addr -segs_read_write_addr @gol
461 -single_module -static -sub_library -sub_umbrella @gol
462 -twolevel_namespace -umbrella -undefined @gol
463 -unexported_symbols_list -weak_reference_mismatches @gol
464 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
467 @emph{DEC Alpha Options}
468 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
469 -mieee -mieee-with-inexact -mieee-conformant @gol
470 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
471 -mtrap-precision=@var{mode} -mbuild-constants @gol
472 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
473 -mbwx -mmax -mfix -mcix @gol
474 -mfloat-vax -mfloat-ieee @gol
475 -mexplicit-relocs -msmall-data -mlarge-data @gol
476 -msmall-text -mlarge-text @gol
477 -mmemory-latency=@var{time}}
479 @emph{DEC Alpha/VMS Options}
480 @gccoptlist{-mvms-return-codes}
483 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
484 -mhard-float -msoft-float @gol
485 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
486 -mdouble -mno-double @gol
487 -mmedia -mno-media -mmuladd -mno-muladd @gol
488 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
489 -mlinked-fp -mlong-calls -malign-labels @gol
490 -mlibrary-pic -macc-4 -macc-8 @gol
491 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
492 -moptimize-membar -mno-optimize-membar @gol
493 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
494 -mvliw-branch -mno-vliw-branch @gol
495 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
496 -mno-nested-cond-exec -mtomcat-stats @gol
500 @emph{H8/300 Options}
501 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
504 @gccoptlist{-march=@var{architecture-type} @gol
505 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
506 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
507 -mfixed-range=@var{register-range} @gol
508 -mjump-in-delay -mlinker-opt -mlong-calls @gol
509 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
510 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
511 -mno-jump-in-delay -mno-long-load-store @gol
512 -mno-portable-runtime -mno-soft-float @gol
513 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
514 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
515 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
516 -munix=@var{unix-std} -nolibdld -static -threads}
518 @emph{i386 and x86-64 Options}
519 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
520 -mfpmath=@var{unit} @gol
521 -masm=@var{dialect} -mno-fancy-math-387 @gol
522 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
523 -mno-wide-multiply -mrtd -malign-double @gol
524 -mpreferred-stack-boundary=@var{num} @gol
525 -mmmx -msse -msse2 -msse3 -m3dnow @gol
526 -mthreads -mno-align-stringops -minline-all-stringops @gol
527 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
528 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
529 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
530 -mcmodel=@var{code-model} @gol
531 -m32 -m64 -mlarge-data-threshold=@var{num}}
534 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
535 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
536 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
537 -minline-float-divide-max-throughput @gol
538 -minline-int-divide-min-latency @gol
539 -minline-int-divide-max-throughput @gol
540 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
541 -mno-dwarf2-asm -mearly-stop-bits @gol
542 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
543 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64}
545 @emph{M32R/D Options}
546 @gccoptlist{-m32r2 -m32rx -m32r @gol
548 -malign-loops -mno-align-loops @gol
549 -missue-rate=@var{number} @gol
550 -mbranch-cost=@var{number} @gol
551 -mmodel=@var{code-size-model-type} @gol
552 -msdata=@var{sdata-type} @gol
553 -mno-flush-func -mflush-func=@var{name} @gol
554 -mno-flush-trap -mflush-trap=@var{number} @gol
558 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
560 @emph{M680x0 Options}
561 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
562 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
563 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
564 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
565 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
567 @emph{M68hc1x Options}
568 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
569 -mauto-incdec -minmax -mlong-calls -mshort @gol
570 -msoft-reg-count=@var{count}}
573 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
574 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
575 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
576 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
577 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
580 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
581 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
582 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
583 -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
584 -mhard-float -msoft-float -msingle-float -mdouble-float @gol
585 -mdsp -mpaired-single -mips3d @gol
586 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
587 -G@var{num} -membedded-data -mno-embedded-data @gol
588 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
589 -msplit-addresses -mno-split-addresses @gol
590 -mexplicit-relocs -mno-explicit-relocs @gol
591 -mcheck-zero-division -mno-check-zero-division @gol
592 -mdivide-traps -mdivide-breaks @gol
593 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
594 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
595 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
596 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 @gol
597 -mfix-sb1 -mno-fix-sb1 @gol
598 -mflush-func=@var{func} -mno-flush-func @gol
599 -mbranch-likely -mno-branch-likely @gol
600 -mfp-exceptions -mno-fp-exceptions @gol
601 -mvr4130-align -mno-vr4130-align}
604 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
605 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
606 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
607 -mno-base-addresses -msingle-exit -mno-single-exit}
609 @emph{MN10300 Options}
610 @gccoptlist{-mmult-bug -mno-mult-bug @gol
611 -mam33 -mno-am33 @gol
612 -mam33-2 -mno-am33-2 @gol
613 -mreturn-pointer-on-d0 @gol
617 @gccoptlist{-mno-crt0 -mmul -mbacc -msim @gol
618 -march=@var{cpu-type} }
620 @emph{PDP-11 Options}
621 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
622 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
623 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
624 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
625 -mbranch-expensive -mbranch-cheap @gol
626 -msplit -mno-split -munix-asm -mdec-asm}
628 @emph{PowerPC Options}
629 See RS/6000 and PowerPC Options.
631 @emph{RS/6000 and PowerPC Options}
632 @gccoptlist{-mcpu=@var{cpu-type} @gol
633 -mtune=@var{cpu-type} @gol
634 -mpower -mno-power -mpower2 -mno-power2 @gol
635 -mpowerpc -mpowerpc64 -mno-powerpc @gol
636 -maltivec -mno-altivec @gol
637 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
638 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
639 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
640 -mnew-mnemonics -mold-mnemonics @gol
641 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
642 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
643 -malign-power -malign-natural @gol
644 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
645 -mstring -mno-string -mupdate -mno-update @gol
646 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
647 -mstrict-align -mno-strict-align -mrelocatable @gol
648 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
649 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
650 -mdynamic-no-pic -maltivec -mswdiv @gol
651 -mprioritize-restricted-insns=@var{priority} @gol
652 -msched-costly-dep=@var{dependence_type} @gol
653 -minsert-sched-nops=@var{scheme} @gol
654 -mcall-sysv -mcall-netbsd @gol
655 -maix-struct-return -msvr4-struct-return @gol
656 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
657 -misel -mno-isel @gol
658 -misel=yes -misel=no @gol
660 -mspe=yes -mspe=no @gol
661 -mvrsave -mno-vrsave @gol
662 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
663 -mprototype -mno-prototype @gol
664 -msim -mmvme -mads -myellowknife -memb -msdata @gol
665 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
667 @emph{S/390 and zSeries Options}
668 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
669 -mhard-float -msoft-float -mbackchain -mno-backchain @gol
670 -mpacked-stack -mno-packed-stack @gol
671 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
672 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
673 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
674 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
677 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
678 -m4-nofpu -m4-single-only -m4-single -m4 @gol
679 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
680 -m5-64media -m5-64media-nofpu @gol
681 -m5-32media -m5-32media-nofpu @gol
682 -m5-compact -m5-compact-nofpu @gol
683 -mb -ml -mdalign -mrelax @gol
684 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
685 -mieee -misize -mpadstruct -mspace @gol
686 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
687 -mdivsi3_libfunc=@var{name} @gol
688 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
692 @gccoptlist{-mcpu=@var{cpu-type} @gol
693 -mtune=@var{cpu-type} @gol
694 -mcmodel=@var{code-model} @gol
695 -m32 -m64 -mapp-regs -mno-app-regs @gol
696 -mfaster-structs -mno-faster-structs @gol
697 -mfpu -mno-fpu -mhard-float -msoft-float @gol
698 -mhard-quad-float -msoft-quad-float @gol
699 -mimpure-text -mno-impure-text -mlittle-endian @gol
700 -mstack-bias -mno-stack-bias @gol
701 -munaligned-doubles -mno-unaligned-doubles @gol
702 -mv8plus -mno-v8plus -mvis -mno-vis
705 @emph{System V Options}
706 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
708 @emph{TMS320C3x/C4x Options}
709 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
710 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
711 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
712 -mparallel-insns -mparallel-mpy -mpreserve-float}
715 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
716 -mprolog-function -mno-prolog-function -mspace @gol
717 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
718 -mapp-regs -mno-app-regs @gol
719 -mdisable-callt -mno-disable-callt @gol
725 @gccoptlist{-mg -mgnu -munix}
727 @emph{x86-64 Options}
728 See i386 and x86-64 Options.
730 @emph{Xstormy16 Options}
733 @emph{Xtensa Options}
734 @gccoptlist{-mconst16 -mno-const16 @gol
735 -mfused-madd -mno-fused-madd @gol
736 -mtext-section-literals -mno-text-section-literals @gol
737 -mtarget-align -mno-target-align @gol
738 -mlongcalls -mno-longcalls}
740 @emph{zSeries Options}
741 See S/390 and zSeries Options.
743 @item Code Generation Options
744 @xref{Code Gen Options,,Options for Code Generation Conventions}.
745 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
746 -ffixed-@var{reg} -fexceptions @gol
747 -fnon-call-exceptions -funwind-tables @gol
748 -fasynchronous-unwind-tables @gol
749 -finhibit-size-directive -finstrument-functions @gol
750 -fno-common -fno-ident @gol
751 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
752 -fno-jump-tables @gol
753 -freg-struct-return -fshared-data -fshort-enums @gol
754 -fshort-double -fshort-wchar @gol
755 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
756 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
757 -fargument-alias -fargument-noalias @gol
758 -fargument-noalias-global -fleading-underscore @gol
759 -ftls-model=@var{model} @gol
760 -ftrapv -fwrapv -fbounds-check @gol
765 * Overall Options:: Controlling the kind of output:
766 an executable, object files, assembler files,
767 or preprocessed source.
768 * C Dialect Options:: Controlling the variant of C language compiled.
769 * C++ Dialect Options:: Variations on C++.
770 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
772 * Language Independent Options:: Controlling how diagnostics should be
774 * Warning Options:: How picky should the compiler be?
775 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
776 * Optimize Options:: How much optimization?
777 * Preprocessor Options:: Controlling header files and macro definitions.
778 Also, getting dependency information for Make.
779 * Assembler Options:: Passing options to the assembler.
780 * Link Options:: Specifying libraries and so on.
781 * Directory Options:: Where to find header files and libraries.
782 Where to find the compiler executable files.
783 * Spec Files:: How to pass switches to sub-processes.
784 * Target Options:: Running a cross-compiler, or an old version of GCC.
787 @node Overall Options
788 @section Options Controlling the Kind of Output
790 Compilation can involve up to four stages: preprocessing, compilation
791 proper, assembly and linking, always in that order. GCC is capable of
792 preprocessing and compiling several files either into several
793 assembler input files, or into one assembler input file; then each
794 assembler input file produces an object file, and linking combines all
795 the object files (those newly compiled, and those specified as input)
796 into an executable file.
798 @cindex file name suffix
799 For any given input file, the file name suffix determines what kind of
804 C source code which must be preprocessed.
807 C source code which should not be preprocessed.
810 C++ source code which should not be preprocessed.
813 Objective-C source code. Note that you must link with the @file{libobjc}
814 library to make an Objective-C program work.
817 Objective-C source code which should not be preprocessed.
821 Objective-C++ source code. Note that you must link with the @file{libobjc}
822 library to make an Objective-C++ program work. Note that @samp{.M} refers
823 to a literal capital M@.
826 Objective-C++ source code which should not be preprocessed.
829 C, C++, Objective-C or Objective-C++ header file to be turned into a
834 @itemx @var{file}.cxx
835 @itemx @var{file}.cpp
836 @itemx @var{file}.CPP
837 @itemx @var{file}.c++
839 C++ source code which must be preprocessed. Note that in @samp{.cxx},
840 the last two letters must both be literally @samp{x}. Likewise,
841 @samp{.C} refers to a literal capital C@.
845 Objective-C++ source code which must be preprocessed.
848 Objective-C++ source code which should not be preprocessed.
852 C++ header file to be turned into a precompiled header.
855 @itemx @var{file}.for
856 @itemx @var{file}.FOR
857 Fixed form Fortran source code which should not be preprocessed.
860 @itemx @var{file}.fpp
861 @itemx @var{file}.FPP
862 Fixed form Fortran source code which must be preprocessed (with the traditional
866 @itemx @var{file}.f95
867 Free form Fortran source code which should not be preprocessed.
870 @itemx @var{file}.F95
871 Free form Fortran source code which must be preprocessed (with the
872 traditional preprocessor).
874 @c FIXME: Descriptions of Java file types.
881 Ada source code file which contains a library unit declaration (a
882 declaration of a package, subprogram, or generic, or a generic
883 instantiation), or a library unit renaming declaration (a package,
884 generic, or subprogram renaming declaration). Such files are also
887 @itemx @var{file}.adb
888 Ada source code file containing a library unit body (a subprogram or
889 package body). Such files are also called @dfn{bodies}.
891 @c GCC also knows about some suffixes for languages not yet included:
902 Assembler code which must be preprocessed.
905 An object file to be fed straight into linking.
906 Any file name with no recognized suffix is treated this way.
910 You can specify the input language explicitly with the @option{-x} option:
913 @item -x @var{language}
914 Specify explicitly the @var{language} for the following input files
915 (rather than letting the compiler choose a default based on the file
916 name suffix). This option applies to all following input files until
917 the next @option{-x} option. Possible values for @var{language} are:
919 c c-header c-cpp-output
920 c++ c++-header c++-cpp-output
921 objective-c objective-c-header objective-c-cpp-output
922 objective-c++ objective-c++-header objective-c++-cpp-output
923 assembler assembler-with-cpp
932 Turn off any specification of a language, so that subsequent files are
933 handled according to their file name suffixes (as they are if @option{-x}
934 has not been used at all).
936 @item -pass-exit-codes
937 @opindex pass-exit-codes
938 Normally the @command{gcc} program will exit with the code of 1 if any
939 phase of the compiler returns a non-success return code. If you specify
940 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
941 numerically highest error produced by any phase that returned an error
945 If you only want some of the stages of compilation, you can use
946 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
947 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
948 @command{gcc} is to stop. Note that some combinations (for example,
949 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
954 Compile or assemble the source files, but do not link. The linking
955 stage simply is not done. The ultimate output is in the form of an
956 object file for each source file.
958 By default, the object file name for a source file is made by replacing
959 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
961 Unrecognized input files, not requiring compilation or assembly, are
966 Stop after the stage of compilation proper; do not assemble. The output
967 is in the form of an assembler code file for each non-assembler input
970 By default, the assembler file name for a source file is made by
971 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
973 Input files that don't require compilation are ignored.
977 Stop after the preprocessing stage; do not run the compiler proper. The
978 output is in the form of preprocessed source code, which is sent to the
981 Input files which don't require preprocessing are ignored.
983 @cindex output file option
986 Place output in file @var{file}. This applies regardless to whatever
987 sort of output is being produced, whether it be an executable file,
988 an object file, an assembler file or preprocessed C code.
990 If @option{-o} is not specified, the default is to put an executable
991 file in @file{a.out}, the object file for
992 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
993 assembler file in @file{@var{source}.s}, a precompiled header file in
994 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
999 Print (on standard error output) the commands executed to run the stages
1000 of compilation. Also print the version number of the compiler driver
1001 program and of the preprocessor and the compiler proper.
1005 Like @option{-v} except the commands are not executed and all command
1006 arguments are quoted. This is useful for shell scripts to capture the
1007 driver-generated command lines.
1011 Use pipes rather than temporary files for communication between the
1012 various stages of compilation. This fails to work on some systems where
1013 the assembler is unable to read from a pipe; but the GNU assembler has
1018 If you are compiling multiple source files, this option tells the driver
1019 to pass all the source files to the compiler at once (for those
1020 languages for which the compiler can handle this). This will allow
1021 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1022 language for which this is supported is C@. If you pass source files for
1023 multiple languages to the driver, using this option, the driver will invoke
1024 the compiler(s) that support IMA once each, passing each compiler all the
1025 source files appropriate for it. For those languages that do not support
1026 IMA this option will be ignored, and the compiler will be invoked once for
1027 each source file in that language. If you use this option in conjunction
1028 with @option{-save-temps}, the compiler will generate multiple
1030 (one for each source file), but only one (combined) @file{.o} or
1035 Print (on the standard output) a description of the command line options
1036 understood by @command{gcc}. If the @option{-v} option is also specified
1037 then @option{--help} will also be passed on to the various processes
1038 invoked by @command{gcc}, so that they can display the command line options
1039 they accept. If the @option{-Wextra} option is also specified then command
1040 line options which have no documentation associated with them will also
1044 @opindex target-help
1045 Print (on the standard output) a description of target specific command
1046 line options for each tool.
1050 Display the version number and copyrights of the invoked GCC@.
1054 @section Compiling C++ Programs
1056 @cindex suffixes for C++ source
1057 @cindex C++ source file suffixes
1058 C++ source files conventionally use one of the suffixes @samp{.C},
1059 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1060 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1061 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1062 files with these names and compiles them as C++ programs even if you
1063 call the compiler the same way as for compiling C programs (usually
1064 with the name @command{gcc}).
1068 However, C++ programs often require class libraries as well as a
1069 compiler that understands the C++ language---and under some
1070 circumstances, you might want to compile programs or header files from
1071 standard input, or otherwise without a suffix that flags them as C++
1072 programs. You might also like to precompile a C header file with a
1073 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1074 program that calls GCC with the default language set to C++, and
1075 automatically specifies linking against the C++ library. On many
1076 systems, @command{g++} is also installed with the name @command{c++}.
1078 @cindex invoking @command{g++}
1079 When you compile C++ programs, you may specify many of the same
1080 command-line options that you use for compiling programs in any
1081 language; or command-line options meaningful for C and related
1082 languages; or options that are meaningful only for C++ programs.
1083 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1084 explanations of options for languages related to C@.
1085 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1086 explanations of options that are meaningful only for C++ programs.
1088 @node C Dialect Options
1089 @section Options Controlling C Dialect
1090 @cindex dialect options
1091 @cindex language dialect options
1092 @cindex options, dialect
1094 The following options control the dialect of C (or languages derived
1095 from C, such as C++, Objective-C and Objective-C++) that the compiler
1099 @cindex ANSI support
1103 In C mode, support all ISO C90 programs. In C++ mode,
1104 remove GNU extensions that conflict with ISO C++.
1106 This turns off certain features of GCC that are incompatible with ISO
1107 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1108 such as the @code{asm} and @code{typeof} keywords, and
1109 predefined macros such as @code{unix} and @code{vax} that identify the
1110 type of system you are using. It also enables the undesirable and
1111 rarely used ISO trigraph feature. For the C compiler,
1112 it disables recognition of C++ style @samp{//} comments as well as
1113 the @code{inline} keyword.
1115 The alternate keywords @code{__asm__}, @code{__extension__},
1116 @code{__inline__} and @code{__typeof__} continue to work despite
1117 @option{-ansi}. You would not want to use them in an ISO C program, of
1118 course, but it is useful to put them in header files that might be included
1119 in compilations done with @option{-ansi}. Alternate predefined macros
1120 such as @code{__unix__} and @code{__vax__} are also available, with or
1121 without @option{-ansi}.
1123 The @option{-ansi} option does not cause non-ISO programs to be
1124 rejected gratuitously. For that, @option{-pedantic} is required in
1125 addition to @option{-ansi}. @xref{Warning Options}.
1127 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1128 option is used. Some header files may notice this macro and refrain
1129 from declaring certain functions or defining certain macros that the
1130 ISO standard doesn't call for; this is to avoid interfering with any
1131 programs that might use these names for other things.
1133 Functions which would normally be built in but do not have semantics
1134 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1135 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1136 built-in functions provided by GCC}, for details of the functions
1141 Determine the language standard. This option is currently only
1142 supported when compiling C or C++. A value for this option must be
1143 provided; possible values are
1148 ISO C90 (same as @option{-ansi}).
1150 @item iso9899:199409
1151 ISO C90 as modified in amendment 1.
1157 ISO C99. Note that this standard is not yet fully supported; see
1158 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1159 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1162 Default, ISO C90 plus GNU extensions (including some C99 features).
1166 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1167 this will become the default. The name @samp{gnu9x} is deprecated.
1170 The 1998 ISO C++ standard plus amendments.
1173 The same as @option{-std=c++98} plus GNU extensions. This is the
1174 default for C++ code.
1177 Even when this option is not specified, you can still use some of the
1178 features of newer standards in so far as they do not conflict with
1179 previous C standards. For example, you may use @code{__restrict__} even
1180 when @option{-std=c99} is not specified.
1182 The @option{-std} options specifying some version of ISO C have the same
1183 effects as @option{-ansi}, except that features that were not in ISO C90
1184 but are in the specified version (for example, @samp{//} comments and
1185 the @code{inline} keyword in ISO C99) are not disabled.
1187 @xref{Standards,,Language Standards Supported by GCC}, for details of
1188 these standard versions.
1190 @item -aux-info @var{filename}
1192 Output to the given filename prototyped declarations for all functions
1193 declared and/or defined in a translation unit, including those in header
1194 files. This option is silently ignored in any language other than C@.
1196 Besides declarations, the file indicates, in comments, the origin of
1197 each declaration (source file and line), whether the declaration was
1198 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1199 @samp{O} for old, respectively, in the first character after the line
1200 number and the colon), and whether it came from a declaration or a
1201 definition (@samp{C} or @samp{F}, respectively, in the following
1202 character). In the case of function definitions, a K&R-style list of
1203 arguments followed by their declarations is also provided, inside
1204 comments, after the declaration.
1208 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1209 keyword, so that code can use these words as identifiers. You can use
1210 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1211 instead. @option{-ansi} implies @option{-fno-asm}.
1213 In C++, this switch only affects the @code{typeof} keyword, since
1214 @code{asm} and @code{inline} are standard keywords. You may want to
1215 use the @option{-fno-gnu-keywords} flag instead, which has the same
1216 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1217 switch only affects the @code{asm} and @code{typeof} keywords, since
1218 @code{inline} is a standard keyword in ISO C99.
1221 @itemx -fno-builtin-@var{function}
1222 @opindex fno-builtin
1223 @cindex built-in functions
1224 Don't recognize built-in functions that do not begin with
1225 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1226 functions provided by GCC}, for details of the functions affected,
1227 including those which are not built-in functions when @option{-ansi} or
1228 @option{-std} options for strict ISO C conformance are used because they
1229 do not have an ISO standard meaning.
1231 GCC normally generates special code to handle certain built-in functions
1232 more efficiently; for instance, calls to @code{alloca} may become single
1233 instructions that adjust the stack directly, and calls to @code{memcpy}
1234 may become inline copy loops. The resulting code is often both smaller
1235 and faster, but since the function calls no longer appear as such, you
1236 cannot set a breakpoint on those calls, nor can you change the behavior
1237 of the functions by linking with a different library. In addition,
1238 when a function is recognized as a built-in function, GCC may use
1239 information about that function to warn about problems with calls to
1240 that function, or to generate more efficient code, even if the
1241 resulting code still contains calls to that function. For example,
1242 warnings are given with @option{-Wformat} for bad calls to
1243 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1244 known not to modify global memory.
1246 With the @option{-fno-builtin-@var{function}} option
1247 only the built-in function @var{function} is
1248 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1249 function is named this is not built-in in this version of GCC, this
1250 option is ignored. There is no corresponding
1251 @option{-fbuiltin-@var{function}} option; if you wish to enable
1252 built-in functions selectively when using @option{-fno-builtin} or
1253 @option{-ffreestanding}, you may define macros such as:
1256 #define abs(n) __builtin_abs ((n))
1257 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1262 @cindex hosted environment
1264 Assert that compilation takes place in a hosted environment. This implies
1265 @option{-fbuiltin}. A hosted environment is one in which the
1266 entire standard library is available, and in which @code{main} has a return
1267 type of @code{int}. Examples are nearly everything except a kernel.
1268 This is equivalent to @option{-fno-freestanding}.
1270 @item -ffreestanding
1271 @opindex ffreestanding
1272 @cindex hosted environment
1274 Assert that compilation takes place in a freestanding environment. This
1275 implies @option{-fno-builtin}. A freestanding environment
1276 is one in which the standard library may not exist, and program startup may
1277 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1278 This is equivalent to @option{-fno-hosted}.
1280 @xref{Standards,,Language Standards Supported by GCC}, for details of
1281 freestanding and hosted environments.
1283 @item -fms-extensions
1284 @opindex fms-extensions
1285 Accept some non-standard constructs used in Microsoft header files.
1287 Some cases of unnamed fields in structures and unions are only
1288 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1289 fields within structs/unions}, for details.
1293 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1294 options for strict ISO C conformance) implies @option{-trigraphs}.
1296 @item -no-integrated-cpp
1297 @opindex no-integrated-cpp
1298 Performs a compilation in two passes: preprocessing and compiling. This
1299 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1300 @option{-B} option. The user supplied compilation step can then add in
1301 an additional preprocessing step after normal preprocessing but before
1302 compiling. The default is to use the integrated cpp (internal cpp)
1304 The semantics of this option will change if "cc1", "cc1plus", and
1305 "cc1obj" are merged.
1307 @cindex traditional C language
1308 @cindex C language, traditional
1310 @itemx -traditional-cpp
1311 @opindex traditional-cpp
1312 @opindex traditional
1313 Formerly, these options caused GCC to attempt to emulate a pre-standard
1314 C compiler. They are now only supported with the @option{-E} switch.
1315 The preprocessor continues to support a pre-standard mode. See the GNU
1316 CPP manual for details.
1318 @item -fcond-mismatch
1319 @opindex fcond-mismatch
1320 Allow conditional expressions with mismatched types in the second and
1321 third arguments. The value of such an expression is void. This option
1322 is not supported for C++.
1324 @item -funsigned-char
1325 @opindex funsigned-char
1326 Let the type @code{char} be unsigned, like @code{unsigned char}.
1328 Each kind of machine has a default for what @code{char} should
1329 be. It is either like @code{unsigned char} by default or like
1330 @code{signed char} by default.
1332 Ideally, a portable program should always use @code{signed char} or
1333 @code{unsigned char} when it depends on the signedness of an object.
1334 But many programs have been written to use plain @code{char} and
1335 expect it to be signed, or expect it to be unsigned, depending on the
1336 machines they were written for. This option, and its inverse, let you
1337 make such a program work with the opposite default.
1339 The type @code{char} is always a distinct type from each of
1340 @code{signed char} or @code{unsigned char}, even though its behavior
1341 is always just like one of those two.
1344 @opindex fsigned-char
1345 Let the type @code{char} be signed, like @code{signed char}.
1347 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1348 the negative form of @option{-funsigned-char}. Likewise, the option
1349 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1351 @item -fsigned-bitfields
1352 @itemx -funsigned-bitfields
1353 @itemx -fno-signed-bitfields
1354 @itemx -fno-unsigned-bitfields
1355 @opindex fsigned-bitfields
1356 @opindex funsigned-bitfields
1357 @opindex fno-signed-bitfields
1358 @opindex fno-unsigned-bitfields
1359 These options control whether a bit-field is signed or unsigned, when the
1360 declaration does not use either @code{signed} or @code{unsigned}. By
1361 default, such a bit-field is signed, because this is consistent: the
1362 basic integer types such as @code{int} are signed types.
1365 @node C++ Dialect Options
1366 @section Options Controlling C++ Dialect
1368 @cindex compiler options, C++
1369 @cindex C++ options, command line
1370 @cindex options, C++
1371 This section describes the command-line options that are only meaningful
1372 for C++ programs; but you can also use most of the GNU compiler options
1373 regardless of what language your program is in. For example, you
1374 might compile a file @code{firstClass.C} like this:
1377 g++ -g -frepo -O -c firstClass.C
1381 In this example, only @option{-frepo} is an option meant
1382 only for C++ programs; you can use the other options with any
1383 language supported by GCC@.
1385 Here is a list of options that are @emph{only} for compiling C++ programs:
1389 @item -fabi-version=@var{n}
1390 @opindex fabi-version
1391 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1392 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1393 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1394 the version that conforms most closely to the C++ ABI specification.
1395 Therefore, the ABI obtained using version 0 will change as ABI bugs
1398 The default is version 2.
1400 @item -fno-access-control
1401 @opindex fno-access-control
1402 Turn off all access checking. This switch is mainly useful for working
1403 around bugs in the access control code.
1407 Check that the pointer returned by @code{operator new} is non-null
1408 before attempting to modify the storage allocated. This check is
1409 normally unnecessary because the C++ standard specifies that
1410 @code{operator new} will only return @code{0} if it is declared
1411 @samp{throw()}, in which case the compiler will always check the
1412 return value even without this option. In all other cases, when
1413 @code{operator new} has a non-empty exception specification, memory
1414 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1415 @samp{new (nothrow)}.
1417 @item -fconserve-space
1418 @opindex fconserve-space
1419 Put uninitialized or runtime-initialized global variables into the
1420 common segment, as C does. This saves space in the executable at the
1421 cost of not diagnosing duplicate definitions. If you compile with this
1422 flag and your program mysteriously crashes after @code{main()} has
1423 completed, you may have an object that is being destroyed twice because
1424 two definitions were merged.
1426 This option is no longer useful on most targets, now that support has
1427 been added for putting variables into BSS without making them common.
1429 @item -ffriend-injection
1430 @opindex ffriend-injection
1431 Inject friend functions into the enclosing namespace, so that they are
1432 visible outside the scope of the class in which they are declared.
1433 Friend functions were documented to work this way in the old Annotated
1434 C++ Reference Manual, and versions of G++ before 4.1 always worked
1435 that way. However, in ISO C++ a friend function which is not declared
1436 in an enclosing scope can only be found using argument dependent
1437 lookup. This option causes friends to be injected as they were in
1440 This option is for compatibility, and may be removed in a future
1443 @item -fno-const-strings
1444 @opindex fno-const-strings
1445 Give string constants type @code{char *} instead of type @code{const
1446 char *}. By default, G++ uses type @code{const char *} as required by
1447 the standard. Even if you use @option{-fno-const-strings}, you cannot
1448 actually modify the value of a string constant.
1450 This option might be removed in a future release of G++. For maximum
1451 portability, you should structure your code so that it works with
1452 string constants that have type @code{const char *}.
1454 @item -fno-elide-constructors
1455 @opindex fno-elide-constructors
1456 The C++ standard allows an implementation to omit creating a temporary
1457 which is only used to initialize another object of the same type.
1458 Specifying this option disables that optimization, and forces G++ to
1459 call the copy constructor in all cases.
1461 @item -fno-enforce-eh-specs
1462 @opindex fno-enforce-eh-specs
1463 Don't generate code to check for violation of exception specifications
1464 at runtime. This option violates the C++ standard, but may be useful
1465 for reducing code size in production builds, much like defining
1466 @samp{NDEBUG}. This does not give user code permission to throw
1467 exceptions in violation of the exception specifications; the compiler
1468 will still optimize based on the specifications, so throwing an
1469 unexpected exception will result in undefined behavior.
1472 @itemx -fno-for-scope
1474 @opindex fno-for-scope
1475 If @option{-ffor-scope} is specified, the scope of variables declared in
1476 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1477 as specified by the C++ standard.
1478 If @option{-fno-for-scope} is specified, the scope of variables declared in
1479 a @i{for-init-statement} extends to the end of the enclosing scope,
1480 as was the case in old versions of G++, and other (traditional)
1481 implementations of C++.
1483 The default if neither flag is given to follow the standard,
1484 but to allow and give a warning for old-style code that would
1485 otherwise be invalid, or have different behavior.
1487 @item -fno-gnu-keywords
1488 @opindex fno-gnu-keywords
1489 Do not recognize @code{typeof} as a keyword, so that code can use this
1490 word as an identifier. You can use the keyword @code{__typeof__} instead.
1491 @option{-ansi} implies @option{-fno-gnu-keywords}.
1493 @item -fno-implicit-templates
1494 @opindex fno-implicit-templates
1495 Never emit code for non-inline templates which are instantiated
1496 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1497 @xref{Template Instantiation}, for more information.
1499 @item -fno-implicit-inline-templates
1500 @opindex fno-implicit-inline-templates
1501 Don't emit code for implicit instantiations of inline templates, either.
1502 The default is to handle inlines differently so that compiles with and
1503 without optimization will need the same set of explicit instantiations.
1505 @item -fno-implement-inlines
1506 @opindex fno-implement-inlines
1507 To save space, do not emit out-of-line copies of inline functions
1508 controlled by @samp{#pragma implementation}. This will cause linker
1509 errors if these functions are not inlined everywhere they are called.
1511 @item -fms-extensions
1512 @opindex fms-extensions
1513 Disable pedantic warnings about constructs used in MFC, such as implicit
1514 int and getting a pointer to member function via non-standard syntax.
1516 @item -fno-nonansi-builtins
1517 @opindex fno-nonansi-builtins
1518 Disable built-in declarations of functions that are not mandated by
1519 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1520 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1522 @item -fno-operator-names
1523 @opindex fno-operator-names
1524 Do not treat the operator name keywords @code{and}, @code{bitand},
1525 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1526 synonyms as keywords.
1528 @item -fno-optional-diags
1529 @opindex fno-optional-diags
1530 Disable diagnostics that the standard says a compiler does not need to
1531 issue. Currently, the only such diagnostic issued by G++ is the one for
1532 a name having multiple meanings within a class.
1535 @opindex fpermissive
1536 Downgrade some diagnostics about nonconformant code from errors to
1537 warnings. Thus, using @option{-fpermissive} will allow some
1538 nonconforming code to compile.
1542 Enable automatic template instantiation at link time. This option also
1543 implies @option{-fno-implicit-templates}. @xref{Template
1544 Instantiation}, for more information.
1548 Disable generation of information about every class with virtual
1549 functions for use by the C++ runtime type identification features
1550 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1551 of the language, you can save some space by using this flag. Note that
1552 exception handling uses the same information, but it will generate it as
1557 Emit statistics about front-end processing at the end of the compilation.
1558 This information is generally only useful to the G++ development team.
1560 @item -ftemplate-depth-@var{n}
1561 @opindex ftemplate-depth
1562 Set the maximum instantiation depth for template classes to @var{n}.
1563 A limit on the template instantiation depth is needed to detect
1564 endless recursions during template class instantiation. ANSI/ISO C++
1565 conforming programs must not rely on a maximum depth greater than 17.
1567 @item -fno-threadsafe-statics
1568 @opindex fno-threadsafe-statics
1569 Do not emit the extra code to use the routines specified in the C++
1570 ABI for thread-safe initialization of local statics. You can use this
1571 option to reduce code size slightly in code that doesn't need to be
1574 @item -fuse-cxa-atexit
1575 @opindex fuse-cxa-atexit
1576 Register destructors for objects with static storage duration with the
1577 @code{__cxa_atexit} function rather than the @code{atexit} function.
1578 This option is required for fully standards-compliant handling of static
1579 destructors, but will only work if your C library supports
1580 @code{__cxa_atexit}.
1582 @item -fvisibility-inlines-hidden
1583 @opindex fvisibility-inlines-hidden
1584 Causes all inlined methods to be marked with
1585 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1586 appear in the export table of a DSO and do not require a PLT indirection
1587 when used within the DSO@. Enabling this option can have a dramatic effect
1588 on load and link times of a DSO as it massively reduces the size of the
1589 dynamic export table when the library makes heavy use of templates. While
1590 it can cause bloating through duplication of code within each DSO where
1591 it is used, often the wastage is less than the considerable space occupied
1592 by a long symbol name in the export table which is typical when using
1593 templates and namespaces. For even more savings, combine with the
1594 @option{-fvisibility=hidden} switch.
1598 Do not use weak symbol support, even if it is provided by the linker.
1599 By default, G++ will use weak symbols if they are available. This
1600 option exists only for testing, and should not be used by end-users;
1601 it will result in inferior code and has no benefits. This option may
1602 be removed in a future release of G++.
1606 Do not search for header files in the standard directories specific to
1607 C++, but do still search the other standard directories. (This option
1608 is used when building the C++ library.)
1611 In addition, these optimization, warning, and code generation options
1612 have meanings only for C++ programs:
1615 @item -fno-default-inline
1616 @opindex fno-default-inline
1617 Do not assume @samp{inline} for functions defined inside a class scope.
1618 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1619 functions will have linkage like inline functions; they just won't be
1622 @item -Wabi @r{(C++ only)}
1624 Warn when G++ generates code that is probably not compatible with the
1625 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1626 all such cases, there are probably some cases that are not warned about,
1627 even though G++ is generating incompatible code. There may also be
1628 cases where warnings are emitted even though the code that is generated
1631 You should rewrite your code to avoid these warnings if you are
1632 concerned about the fact that code generated by G++ may not be binary
1633 compatible with code generated by other compilers.
1635 The known incompatibilities at this point include:
1640 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1641 pack data into the same byte as a base class. For example:
1644 struct A @{ virtual void f(); int f1 : 1; @};
1645 struct B : public A @{ int f2 : 1; @};
1649 In this case, G++ will place @code{B::f2} into the same byte
1650 as@code{A::f1}; other compilers will not. You can avoid this problem
1651 by explicitly padding @code{A} so that its size is a multiple of the
1652 byte size on your platform; that will cause G++ and other compilers to
1653 layout @code{B} identically.
1656 Incorrect handling of tail-padding for virtual bases. G++ does not use
1657 tail padding when laying out virtual bases. For example:
1660 struct A @{ virtual void f(); char c1; @};
1661 struct B @{ B(); char c2; @};
1662 struct C : public A, public virtual B @{@};
1666 In this case, G++ will not place @code{B} into the tail-padding for
1667 @code{A}; other compilers will. You can avoid this problem by
1668 explicitly padding @code{A} so that its size is a multiple of its
1669 alignment (ignoring virtual base classes); that will cause G++ and other
1670 compilers to layout @code{C} identically.
1673 Incorrect handling of bit-fields with declared widths greater than that
1674 of their underlying types, when the bit-fields appear in a union. For
1678 union U @{ int i : 4096; @};
1682 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1683 union too small by the number of bits in an @code{int}.
1686 Empty classes can be placed at incorrect offsets. For example:
1696 struct C : public B, public A @{@};
1700 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1701 it should be placed at offset zero. G++ mistakenly believes that the
1702 @code{A} data member of @code{B} is already at offset zero.
1705 Names of template functions whose types involve @code{typename} or
1706 template template parameters can be mangled incorrectly.
1709 template <typename Q>
1710 void f(typename Q::X) @{@}
1712 template <template <typename> class Q>
1713 void f(typename Q<int>::X) @{@}
1717 Instantiations of these templates may be mangled incorrectly.
1721 @item -Wctor-dtor-privacy @r{(C++ only)}
1722 @opindex Wctor-dtor-privacy
1723 Warn when a class seems unusable because all the constructors or
1724 destructors in that class are private, and it has neither friends nor
1725 public static member functions.
1727 @item -Wnon-virtual-dtor @r{(C++ only)}
1728 @opindex Wnon-virtual-dtor
1729 Warn when a class appears to be polymorphic, thereby requiring a virtual
1730 destructor, yet it declares a non-virtual one.
1731 This warning is enabled by @option{-Wall}.
1733 @item -Wreorder @r{(C++ only)}
1735 @cindex reordering, warning
1736 @cindex warning for reordering of member initializers
1737 Warn when the order of member initializers given in the code does not
1738 match the order in which they must be executed. For instance:
1744 A(): j (0), i (1) @{ @}
1748 The compiler will rearrange the member initializers for @samp{i}
1749 and @samp{j} to match the declaration order of the members, emitting
1750 a warning to that effect. This warning is enabled by @option{-Wall}.
1753 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1756 @item -Weffc++ @r{(C++ only)}
1758 Warn about violations of the following style guidelines from Scott Meyers'
1759 @cite{Effective C++} book:
1763 Item 11: Define a copy constructor and an assignment operator for classes
1764 with dynamically allocated memory.
1767 Item 12: Prefer initialization to assignment in constructors.
1770 Item 14: Make destructors virtual in base classes.
1773 Item 15: Have @code{operator=} return a reference to @code{*this}.
1776 Item 23: Don't try to return a reference when you must return an object.
1780 Also warn about violations of the following style guidelines from
1781 Scott Meyers' @cite{More Effective C++} book:
1785 Item 6: Distinguish between prefix and postfix forms of increment and
1786 decrement operators.
1789 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1793 When selecting this option, be aware that the standard library
1794 headers do not obey all of these guidelines; use @samp{grep -v}
1795 to filter out those warnings.
1797 @item -Wno-deprecated @r{(C++ only)}
1798 @opindex Wno-deprecated
1799 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1801 @item -Wstrict-null-sentinel @r{(C++ only)}
1802 @opindex Wstrict-null-sentinel
1803 Warn also about the use of an uncasted @code{NULL} as sentinel. When
1804 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
1805 to @code{__null}. Although it is a null pointer constant not a null pointer,
1806 it is guaranteed to of the same size as a pointer. But this use is
1807 not portable across different compilers.
1809 @item -Wno-non-template-friend @r{(C++ only)}
1810 @opindex Wno-non-template-friend
1811 Disable warnings when non-templatized friend functions are declared
1812 within a template. Since the advent of explicit template specification
1813 support in G++, if the name of the friend is an unqualified-id (i.e.,
1814 @samp{friend foo(int)}), the C++ language specification demands that the
1815 friend declare or define an ordinary, nontemplate function. (Section
1816 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1817 could be interpreted as a particular specialization of a templatized
1818 function. Because this non-conforming behavior is no longer the default
1819 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1820 check existing code for potential trouble spots and is on by default.
1821 This new compiler behavior can be turned off with
1822 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1823 but disables the helpful warning.
1825 @item -Wold-style-cast @r{(C++ only)}
1826 @opindex Wold-style-cast
1827 Warn if an old-style (C-style) cast to a non-void type is used within
1828 a C++ program. The new-style casts (@samp{dynamic_cast},
1829 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
1830 less vulnerable to unintended effects and much easier to search for.
1832 @item -Woverloaded-virtual @r{(C++ only)}
1833 @opindex Woverloaded-virtual
1834 @cindex overloaded virtual fn, warning
1835 @cindex warning for overloaded virtual fn
1836 Warn when a function declaration hides virtual functions from a
1837 base class. For example, in:
1844 struct B: public A @{
1849 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1857 will fail to compile.
1859 @item -Wno-pmf-conversions @r{(C++ only)}
1860 @opindex Wno-pmf-conversions
1861 Disable the diagnostic for converting a bound pointer to member function
1864 @item -Wsign-promo @r{(C++ only)}
1865 @opindex Wsign-promo
1866 Warn when overload resolution chooses a promotion from unsigned or
1867 enumerated type to a signed type, over a conversion to an unsigned type of
1868 the same size. Previous versions of G++ would try to preserve
1869 unsignedness, but the standard mandates the current behavior.
1874 A& operator = (int);
1884 In this example, G++ will synthesize a default @samp{A& operator =
1885 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1888 @node Objective-C and Objective-C++ Dialect Options
1889 @section Options Controlling Objective-C and Objective-C++ Dialects
1891 @cindex compiler options, Objective-C and Objective-C++
1892 @cindex Objective-C and Objective-C++ options, command line
1893 @cindex options, Objective-C and Objective-C++
1894 (NOTE: This manual does not describe the Objective-C and Objective-C++
1895 languages themselves. See @xref{Standards,,Language Standards
1896 Supported by GCC}, for references.)
1898 This section describes the command-line options that are only meaningful
1899 for Objective-C and Objective-C++ programs, but you can also use most of
1900 the language-independent GNU compiler options.
1901 For example, you might compile a file @code{some_class.m} like this:
1904 gcc -g -fgnu-runtime -O -c some_class.m
1908 In this example, @option{-fgnu-runtime} is an option meant only for
1909 Objective-C and Objective-C++ programs; you can use the other options with
1910 any language supported by GCC@.
1912 Note that since Objective-C is an extension of the C language, Objective-C
1913 compilations may also use options specific to the C front-end (e.g.,
1914 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1915 C++-specific options (e.g., @option{-Wabi}).
1917 Here is a list of options that are @emph{only} for compiling Objective-C
1918 and Objective-C++ programs:
1921 @item -fconstant-string-class=@var{class-name}
1922 @opindex fconstant-string-class
1923 Use @var{class-name} as the name of the class to instantiate for each
1924 literal string specified with the syntax @code{@@"@dots{}"}. The default
1925 class name is @code{NXConstantString} if the GNU runtime is being used, and
1926 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1927 @option{-fconstant-cfstrings} option, if also present, will override the
1928 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1929 to be laid out as constant CoreFoundation strings.
1932 @opindex fgnu-runtime
1933 Generate object code compatible with the standard GNU Objective-C
1934 runtime. This is the default for most types of systems.
1936 @item -fnext-runtime
1937 @opindex fnext-runtime
1938 Generate output compatible with the NeXT runtime. This is the default
1939 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1940 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1943 @item -fno-nil-receivers
1944 @opindex fno-nil-receivers
1945 Assume that all Objective-C message dispatches (e.g.,
1946 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1947 is not @code{nil}. This allows for more efficient entry points in the runtime
1948 to be used. Currently, this option is only available in conjunction with
1949 the NeXT runtime on Mac OS X 10.3 and later.
1951 @item -fobjc-call-cxx-cdtors
1952 @opindex fobjc-call-cxx-cdtors
1953 For each Objective-C class, check if any of its instance variables is a
1954 C++ object with a non-trivial default constructor. If so, synthesize a
1955 special @code{- (id) .cxx_construct} instance method that will run
1956 non-trivial default constructors on any such instance variables, in order,
1957 and then return @code{self}. Similarly, check if any instance variable
1958 is a C++ object with a non-trivial destructor, and if so, synthesize a
1959 special @code{- (void) .cxx_destruct} method that will run
1960 all such default destructors, in reverse order.
1962 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
1963 thusly generated will only operate on instance variables declared in the
1964 current Objective-C class, and not those inherited from superclasses. It
1965 is the responsibility of the Objective-C runtime to invoke all such methods
1966 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
1967 will be invoked by the runtime immediately after a new object
1968 instance is allocated; the @code{- (void) .cxx_destruct} methods will
1969 be invoked immediately before the runtime deallocates an object instance.
1971 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
1972 support for invoking the @code{- (id) .cxx_construct} and
1973 @code{- (void) .cxx_destruct} methods.
1975 @item -fobjc-direct-dispatch
1976 @opindex fobjc-direct-dispatch
1977 Allow fast jumps to the message dispatcher. On Darwin this is
1978 accomplished via the comm page.
1980 @item -fobjc-exceptions
1981 @opindex fobjc-exceptions
1982 Enable syntactic support for structured exception handling in Objective-C,
1983 similar to what is offered by C++ and Java. Currently, this option is only
1984 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1992 @@catch (AnObjCClass *exc) @{
1999 @@catch (AnotherClass *exc) @{
2002 @@catch (id allOthers) @{
2012 The @code{@@throw} statement may appear anywhere in an Objective-C or
2013 Objective-C++ program; when used inside of a @code{@@catch} block, the
2014 @code{@@throw} may appear without an argument (as shown above), in which case
2015 the object caught by the @code{@@catch} will be rethrown.
2017 Note that only (pointers to) Objective-C objects may be thrown and
2018 caught using this scheme. When an object is thrown, it will be caught
2019 by the nearest @code{@@catch} clause capable of handling objects of that type,
2020 analogously to how @code{catch} blocks work in C++ and Java. A
2021 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2022 any and all Objective-C exceptions not caught by previous @code{@@catch}
2025 The @code{@@finally} clause, if present, will be executed upon exit from the
2026 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2027 regardless of whether any exceptions are thrown, caught or rethrown
2028 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2029 of the @code{finally} clause in Java.
2031 There are several caveats to using the new exception mechanism:
2035 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2036 idioms provided by the @code{NSException} class, the new
2037 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2038 systems, due to additional functionality needed in the (NeXT) Objective-C
2042 As mentioned above, the new exceptions do not support handling
2043 types other than Objective-C objects. Furthermore, when used from
2044 Objective-C++, the Objective-C exception model does not interoperate with C++
2045 exceptions at this time. This means you cannot @code{@@throw} an exception
2046 from Objective-C and @code{catch} it in C++, or vice versa
2047 (i.e., @code{throw @dots{} @@catch}).
2050 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2051 blocks for thread-safe execution:
2054 @@synchronized (ObjCClass *guard) @{
2059 Upon entering the @code{@@synchronized} block, a thread of execution shall
2060 first check whether a lock has been placed on the corresponding @code{guard}
2061 object by another thread. If it has, the current thread shall wait until
2062 the other thread relinquishes its lock. Once @code{guard} becomes available,
2063 the current thread will place its own lock on it, execute the code contained in
2064 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2065 making @code{guard} available to other threads).
2067 Unlike Java, Objective-C does not allow for entire methods to be marked
2068 @code{@@synchronized}. Note that throwing exceptions out of
2069 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2070 to be unlocked properly.
2074 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2076 @item -freplace-objc-classes
2077 @opindex freplace-objc-classes
2078 Emit a special marker instructing @command{ld(1)} not to statically link in
2079 the resulting object file, and allow @command{dyld(1)} to load it in at
2080 run time instead. This is used in conjunction with the Fix-and-Continue
2081 debugging mode, where the object file in question may be recompiled and
2082 dynamically reloaded in the course of program execution, without the need
2083 to restart the program itself. Currently, Fix-and-Continue functionality
2084 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2089 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2090 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2091 compile time) with static class references that get initialized at load time,
2092 which improves run-time performance. Specifying the @option{-fzero-link} flag
2093 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2094 to be retained. This is useful in Zero-Link debugging mode, since it allows
2095 for individual class implementations to be modified during program execution.
2099 Dump interface declarations for all classes seen in the source file to a
2100 file named @file{@var{sourcename}.decl}.
2102 @item -Wassign-intercept
2103 @opindex Wassign-intercept
2104 Warn whenever an Objective-C assignment is being intercepted by the
2108 @opindex Wno-protocol
2109 If a class is declared to implement a protocol, a warning is issued for
2110 every method in the protocol that is not implemented by the class. The
2111 default behavior is to issue a warning for every method not explicitly
2112 implemented in the class, even if a method implementation is inherited
2113 from the superclass. If you use the @option{-Wno-protocol} option, then
2114 methods inherited from the superclass are considered to be implemented,
2115 and no warning is issued for them.
2119 Warn if multiple methods of different types for the same selector are
2120 found during compilation. The check is performed on the list of methods
2121 in the final stage of compilation. Additionally, a check is performed
2122 for each selector appearing in a @code{@@selector(@dots{})}
2123 expression, and a corresponding method for that selector has been found
2124 during compilation. Because these checks scan the method table only at
2125 the end of compilation, these warnings are not produced if the final
2126 stage of compilation is not reached, for example because an error is
2127 found during compilation, or because the @option{-fsyntax-only} option is
2130 @item -Wstrict-selector-match
2131 @opindex Wstrict-selector-match
2132 Warn if multiple methods with differing argument and/or return types are
2133 found for a given selector when attempting to send a message using this
2134 selector to a receiver of type @code{id} or @code{Class}. When this flag
2135 is off (which is the default behavior), the compiler will omit such warnings
2136 if any differences found are confined to types which share the same size
2139 @item -Wundeclared-selector
2140 @opindex Wundeclared-selector
2141 Warn if a @code{@@selector(@dots{})} expression referring to an
2142 undeclared selector is found. A selector is considered undeclared if no
2143 method with that name has been declared before the
2144 @code{@@selector(@dots{})} expression, either explicitly in an
2145 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2146 an @code{@@implementation} section. This option always performs its
2147 checks as soon as a @code{@@selector(@dots{})} expression is found,
2148 while @option{-Wselector} only performs its checks in the final stage of
2149 compilation. This also enforces the coding style convention
2150 that methods and selectors must be declared before being used.
2152 @item -print-objc-runtime-info
2153 @opindex print-objc-runtime-info
2154 Generate C header describing the largest structure that is passed by
2159 @node Language Independent Options
2160 @section Options to Control Diagnostic Messages Formatting
2161 @cindex options to control diagnostics formatting
2162 @cindex diagnostic messages
2163 @cindex message formatting
2165 Traditionally, diagnostic messages have been formatted irrespective of
2166 the output device's aspect (e.g.@: its width, @dots{}). The options described
2167 below can be used to control the diagnostic messages formatting
2168 algorithm, e.g.@: how many characters per line, how often source location
2169 information should be reported. Right now, only the C++ front end can
2170 honor these options. However it is expected, in the near future, that
2171 the remaining front ends would be able to digest them correctly.
2174 @item -fmessage-length=@var{n}
2175 @opindex fmessage-length
2176 Try to format error messages so that they fit on lines of about @var{n}
2177 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2178 the front ends supported by GCC@. If @var{n} is zero, then no
2179 line-wrapping will be done; each error message will appear on a single
2182 @opindex fdiagnostics-show-location
2183 @item -fdiagnostics-show-location=once
2184 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2185 reporter to emit @emph{once} source location information; that is, in
2186 case the message is too long to fit on a single physical line and has to
2187 be wrapped, the source location won't be emitted (as prefix) again,
2188 over and over, in subsequent continuation lines. This is the default
2191 @item -fdiagnostics-show-location=every-line
2192 Only meaningful in line-wrapping mode. Instructs the diagnostic
2193 messages reporter to emit the same source location information (as
2194 prefix) for physical lines that result from the process of breaking
2195 a message which is too long to fit on a single line.
2197 @item -fdiagnostics-show-options
2198 @opindex fdiagnostics-show-options
2199 This option instructs the diagnostic machinery to add text to each
2200 diagnostic emitted, which indicates which command line option directly
2201 controls that diagnostic, when such an option is known to the
2202 diagnostic machinery.
2206 @node Warning Options
2207 @section Options to Request or Suppress Warnings
2208 @cindex options to control warnings
2209 @cindex warning messages
2210 @cindex messages, warning
2211 @cindex suppressing warnings
2213 Warnings are diagnostic messages that report constructions which
2214 are not inherently erroneous but which are risky or suggest there
2215 may have been an error.
2217 You can request many specific warnings with options beginning @samp{-W},
2218 for example @option{-Wimplicit} to request warnings on implicit
2219 declarations. Each of these specific warning options also has a
2220 negative form beginning @samp{-Wno-} to turn off warnings;
2221 for example, @option{-Wno-implicit}. This manual lists only one of the
2222 two forms, whichever is not the default.
2224 The following options control the amount and kinds of warnings produced
2225 by GCC; for further, language-specific options also refer to
2226 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2230 @cindex syntax checking
2232 @opindex fsyntax-only
2233 Check the code for syntax errors, but don't do anything beyond that.
2237 Issue all the warnings demanded by strict ISO C and ISO C++;
2238 reject all programs that use forbidden extensions, and some other
2239 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2240 version of the ISO C standard specified by any @option{-std} option used.
2242 Valid ISO C and ISO C++ programs should compile properly with or without
2243 this option (though a rare few will require @option{-ansi} or a
2244 @option{-std} option specifying the required version of ISO C)@. However,
2245 without this option, certain GNU extensions and traditional C and C++
2246 features are supported as well. With this option, they are rejected.
2248 @option{-pedantic} does not cause warning messages for use of the
2249 alternate keywords whose names begin and end with @samp{__}. Pedantic
2250 warnings are also disabled in the expression that follows
2251 @code{__extension__}. However, only system header files should use
2252 these escape routes; application programs should avoid them.
2253 @xref{Alternate Keywords}.
2255 Some users try to use @option{-pedantic} to check programs for strict ISO
2256 C conformance. They soon find that it does not do quite what they want:
2257 it finds some non-ISO practices, but not all---only those for which
2258 ISO C @emph{requires} a diagnostic, and some others for which
2259 diagnostics have been added.
2261 A feature to report any failure to conform to ISO C might be useful in
2262 some instances, but would require considerable additional work and would
2263 be quite different from @option{-pedantic}. We don't have plans to
2264 support such a feature in the near future.
2266 Where the standard specified with @option{-std} represents a GNU
2267 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2268 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2269 extended dialect is based. Warnings from @option{-pedantic} are given
2270 where they are required by the base standard. (It would not make sense
2271 for such warnings to be given only for features not in the specified GNU
2272 C dialect, since by definition the GNU dialects of C include all
2273 features the compiler supports with the given option, and there would be
2274 nothing to warn about.)
2276 @item -pedantic-errors
2277 @opindex pedantic-errors
2278 Like @option{-pedantic}, except that errors are produced rather than
2283 Inhibit all warning messages.
2287 Inhibit warning messages about the use of @samp{#import}.
2289 @item -Wchar-subscripts
2290 @opindex Wchar-subscripts
2291 Warn if an array subscript has type @code{char}. This is a common cause
2292 of error, as programmers often forget that this type is signed on some
2294 This warning is enabled by @option{-Wall}.
2298 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2299 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2300 This warning is enabled by @option{-Wall}.
2302 @item -Wfatal-errors
2303 @opindex Wfatal-errors
2304 This option causes the compiler to abort compilation on the first error
2305 occurred rather than trying to keep going and printing further error
2310 @opindex ffreestanding
2311 @opindex fno-builtin
2312 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2313 the arguments supplied have types appropriate to the format string
2314 specified, and that the conversions specified in the format string make
2315 sense. This includes standard functions, and others specified by format
2316 attributes (@pxref{Function Attributes}), in the @code{printf},
2317 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2318 not in the C standard) families (or other target-specific families).
2319 Which functions are checked without format attributes having been
2320 specified depends on the standard version selected, and such checks of
2321 functions without the attribute specified are disabled by
2322 @option{-ffreestanding} or @option{-fno-builtin}.
2324 The formats are checked against the format features supported by GNU
2325 libc version 2.2. These include all ISO C90 and C99 features, as well
2326 as features from the Single Unix Specification and some BSD and GNU
2327 extensions. Other library implementations may not support all these
2328 features; GCC does not support warning about features that go beyond a
2329 particular library's limitations. However, if @option{-pedantic} is used
2330 with @option{-Wformat}, warnings will be given about format features not
2331 in the selected standard version (but not for @code{strfmon} formats,
2332 since those are not in any version of the C standard). @xref{C Dialect
2333 Options,,Options Controlling C Dialect}.
2335 Since @option{-Wformat} also checks for null format arguments for
2336 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2338 @option{-Wformat} is included in @option{-Wall}. For more control over some
2339 aspects of format checking, the options @option{-Wformat-y2k},
2340 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2341 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2342 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2345 @opindex Wformat-y2k
2346 If @option{-Wformat} is specified, also warn about @code{strftime}
2347 formats which may yield only a two-digit year.
2349 @item -Wno-format-extra-args
2350 @opindex Wno-format-extra-args
2351 If @option{-Wformat} is specified, do not warn about excess arguments to a
2352 @code{printf} or @code{scanf} format function. The C standard specifies
2353 that such arguments are ignored.
2355 Where the unused arguments lie between used arguments that are
2356 specified with @samp{$} operand number specifications, normally
2357 warnings are still given, since the implementation could not know what
2358 type to pass to @code{va_arg} to skip the unused arguments. However,
2359 in the case of @code{scanf} formats, this option will suppress the
2360 warning if the unused arguments are all pointers, since the Single
2361 Unix Specification says that such unused arguments are allowed.
2363 @item -Wno-format-zero-length
2364 @opindex Wno-format-zero-length
2365 If @option{-Wformat} is specified, do not warn about zero-length formats.
2366 The C standard specifies that zero-length formats are allowed.
2368 @item -Wformat-nonliteral
2369 @opindex Wformat-nonliteral
2370 If @option{-Wformat} is specified, also warn if the format string is not a
2371 string literal and so cannot be checked, unless the format function
2372 takes its format arguments as a @code{va_list}.
2374 @item -Wformat-security
2375 @opindex Wformat-security
2376 If @option{-Wformat} is specified, also warn about uses of format
2377 functions that represent possible security problems. At present, this
2378 warns about calls to @code{printf} and @code{scanf} functions where the
2379 format string is not a string literal and there are no format arguments,
2380 as in @code{printf (foo);}. This may be a security hole if the format
2381 string came from untrusted input and contains @samp{%n}. (This is
2382 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2383 in future warnings may be added to @option{-Wformat-security} that are not
2384 included in @option{-Wformat-nonliteral}.)
2388 Enable @option{-Wformat} plus format checks not included in
2389 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2390 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2394 Warn about passing a null pointer for arguments marked as
2395 requiring a non-null value by the @code{nonnull} function attribute.
2397 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2398 can be disabled with the @option{-Wno-nonnull} option.
2400 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2402 Warn about uninitialized variables which are initialized with themselves.
2403 Note this option can only be used with the @option{-Wuninitialized} option,
2404 which in turn only works with @option{-O1} and above.
2406 For example, GCC will warn about @code{i} being uninitialized in the
2407 following snippet only when @option{-Winit-self} has been specified:
2418 @item -Wimplicit-int
2419 @opindex Wimplicit-int
2420 Warn when a declaration does not specify a type.
2421 This warning is enabled by @option{-Wall}.
2423 @item -Wimplicit-function-declaration
2424 @itemx -Werror-implicit-function-declaration
2425 @opindex Wimplicit-function-declaration
2426 @opindex Werror-implicit-function-declaration
2427 Give a warning (or error) whenever a function is used before being
2428 declared. The form @option{-Wno-error-implicit-function-declaration}
2430 This warning is enabled by @option{-Wall} (as a warning, not an error).
2434 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2435 This warning is enabled by @option{-Wall}.
2439 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2440 function with external linkage, returning int, taking either zero
2441 arguments, two, or three arguments of appropriate types.
2442 This warning is enabled by @option{-Wall}.
2444 @item -Wmissing-braces
2445 @opindex Wmissing-braces
2446 Warn if an aggregate or union initializer is not fully bracketed. In
2447 the following example, the initializer for @samp{a} is not fully
2448 bracketed, but that for @samp{b} is fully bracketed.
2451 int a[2][2] = @{ 0, 1, 2, 3 @};
2452 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2455 This warning is enabled by @option{-Wall}.
2457 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2458 @opindex Wmissing-include-dirs
2459 Warn if a user-supplied include directory does not exist.
2462 @opindex Wparentheses
2463 Warn if parentheses are omitted in certain contexts, such
2464 as when there is an assignment in a context where a truth value
2465 is expected, or when operators are nested whose precedence people
2466 often get confused about. Only the warning for an assignment used as
2467 a truth value is supported when compiling C++; the other warnings are
2468 only supported when compiling C@.
2470 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2471 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2472 interpretation from that of ordinary mathematical notation.
2474 Also warn about constructions where there may be confusion to which
2475 @code{if} statement an @code{else} branch belongs. Here is an example of
2490 In C, every @code{else} branch belongs to the innermost possible @code{if}
2491 statement, which in this example is @code{if (b)}. This is often not
2492 what the programmer expected, as illustrated in the above example by
2493 indentation the programmer chose. When there is the potential for this
2494 confusion, GCC will issue a warning when this flag is specified.
2495 To eliminate the warning, add explicit braces around the innermost
2496 @code{if} statement so there is no way the @code{else} could belong to
2497 the enclosing @code{if}. The resulting code would look like this:
2513 This warning is enabled by @option{-Wall}.
2515 @item -Wsequence-point
2516 @opindex Wsequence-point
2517 Warn about code that may have undefined semantics because of violations
2518 of sequence point rules in the C standard.
2520 The C standard defines the order in which expressions in a C program are
2521 evaluated in terms of @dfn{sequence points}, which represent a partial
2522 ordering between the execution of parts of the program: those executed
2523 before the sequence point, and those executed after it. These occur
2524 after the evaluation of a full expression (one which is not part of a
2525 larger expression), after the evaluation of the first operand of a
2526 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2527 function is called (but after the evaluation of its arguments and the
2528 expression denoting the called function), and in certain other places.
2529 Other than as expressed by the sequence point rules, the order of
2530 evaluation of subexpressions of an expression is not specified. All
2531 these rules describe only a partial order rather than a total order,
2532 since, for example, if two functions are called within one expression
2533 with no sequence point between them, the order in which the functions
2534 are called is not specified. However, the standards committee have
2535 ruled that function calls do not overlap.
2537 It is not specified when between sequence points modifications to the
2538 values of objects take effect. Programs whose behavior depends on this
2539 have undefined behavior; the C standard specifies that ``Between the
2540 previous and next sequence point an object shall have its stored value
2541 modified at most once by the evaluation of an expression. Furthermore,
2542 the prior value shall be read only to determine the value to be
2543 stored.''. If a program breaks these rules, the results on any
2544 particular implementation are entirely unpredictable.
2546 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2547 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2548 diagnosed by this option, and it may give an occasional false positive
2549 result, but in general it has been found fairly effective at detecting
2550 this sort of problem in programs.
2552 The present implementation of this option only works for C programs. A
2553 future implementation may also work for C++ programs.
2555 The C standard is worded confusingly, therefore there is some debate
2556 over the precise meaning of the sequence point rules in subtle cases.
2557 Links to discussions of the problem, including proposed formal
2558 definitions, may be found on the GCC readings page, at
2559 @w{@uref{http://gcc.gnu.org/readings.html}}.
2561 This warning is enabled by @option{-Wall}.
2564 @opindex Wreturn-type
2565 Warn whenever a function is defined with a return-type that defaults to
2566 @code{int}. Also warn about any @code{return} statement with no
2567 return-value in a function whose return-type is not @code{void}.
2569 For C, also warn if the return type of a function has a type qualifier
2570 such as @code{const}. Such a type qualifier has no effect, since the
2571 value returned by a function is not an lvalue. ISO C prohibits
2572 qualified @code{void} return types on function definitions, so such
2573 return types always receive a warning even without this option.
2575 For C++, a function without return type always produces a diagnostic
2576 message, even when @option{-Wno-return-type} is specified. The only
2577 exceptions are @samp{main} and functions defined in system headers.
2579 This warning is enabled by @option{-Wall}.
2583 Warn whenever a @code{switch} statement has an index of enumerated type
2584 and lacks a @code{case} for one or more of the named codes of that
2585 enumeration. (The presence of a @code{default} label prevents this
2586 warning.) @code{case} labels outside the enumeration range also
2587 provoke warnings when this option is used.
2588 This warning is enabled by @option{-Wall}.
2590 @item -Wswitch-default
2591 @opindex Wswitch-switch
2592 Warn whenever a @code{switch} statement does not have a @code{default}
2596 @opindex Wswitch-enum
2597 Warn whenever a @code{switch} statement has an index of enumerated type
2598 and lacks a @code{case} for one or more of the named codes of that
2599 enumeration. @code{case} labels outside the enumeration range also
2600 provoke warnings when this option is used.
2604 Warn if any trigraphs are encountered that might change the meaning of
2605 the program (trigraphs within comments are not warned about).
2606 This warning is enabled by @option{-Wall}.
2608 @item -Wunused-function
2609 @opindex Wunused-function
2610 Warn whenever a static function is declared but not defined or a
2611 non-inline static function is unused.
2612 This warning is enabled by @option{-Wall}.
2614 @item -Wunused-label
2615 @opindex Wunused-label
2616 Warn whenever a label is declared but not used.
2617 This warning is enabled by @option{-Wall}.
2619 To suppress this warning use the @samp{unused} attribute
2620 (@pxref{Variable Attributes}).
2622 @item -Wunused-parameter
2623 @opindex Wunused-parameter
2624 Warn whenever a function parameter is unused aside from its declaration.
2626 To suppress this warning use the @samp{unused} attribute
2627 (@pxref{Variable Attributes}).
2629 @item -Wunused-variable
2630 @opindex Wunused-variable
2631 Warn whenever a local variable or non-constant static variable is unused
2632 aside from its declaration
2633 This warning is enabled by @option{-Wall}.
2635 To suppress this warning use the @samp{unused} attribute
2636 (@pxref{Variable Attributes}).
2638 @item -Wunused-value
2639 @opindex Wunused-value
2640 Warn whenever a statement computes a result that is explicitly not used.
2641 This warning is enabled by @option{-Wall}.
2643 To suppress this warning cast the expression to @samp{void}.
2647 All the above @option{-Wunused} options combined.
2649 In order to get a warning about an unused function parameter, you must
2650 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2651 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2653 @item -Wuninitialized
2654 @opindex Wuninitialized
2655 Warn if an automatic variable is used without first being initialized or
2656 if a variable may be clobbered by a @code{setjmp} call.
2658 These warnings are possible only in optimizing compilation,
2659 because they require data flow information that is computed only
2660 when optimizing. If you don't specify @option{-O}, you simply won't
2663 If you want to warn about code which uses the uninitialized value of the
2664 variable in its own initializer, use the @option{-Winit-self} option.
2666 These warnings occur for individual uninitialized or clobbered
2667 elements of structure, union or array variables as well as for
2668 variables which are uninitialized or clobbered as a whole. They do
2669 not occur for variables or elements declared @code{volatile}. Because
2670 these warnings depend on optimization, the exact variables or elements
2671 for which there are warnings will depend on the precise optimization
2672 options and version of GCC used.
2674 Note that there may be no warning about a variable that is used only
2675 to compute a value that itself is never used, because such
2676 computations may be deleted by data flow analysis before the warnings
2679 These warnings are made optional because GCC is not smart
2680 enough to see all the reasons why the code might be correct
2681 despite appearing to have an error. Here is one example of how
2702 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2703 always initialized, but GCC doesn't know this. Here is
2704 another common case:
2709 if (change_y) save_y = y, y = new_y;
2711 if (change_y) y = save_y;
2716 This has no bug because @code{save_y} is used only if it is set.
2718 @cindex @code{longjmp} warnings
2719 This option also warns when a non-volatile automatic variable might be
2720 changed by a call to @code{longjmp}. These warnings as well are possible
2721 only in optimizing compilation.
2723 The compiler sees only the calls to @code{setjmp}. It cannot know
2724 where @code{longjmp} will be called; in fact, a signal handler could
2725 call it at any point in the code. As a result, you may get a warning
2726 even when there is in fact no problem because @code{longjmp} cannot
2727 in fact be called at the place which would cause a problem.
2729 Some spurious warnings can be avoided if you declare all the functions
2730 you use that never return as @code{noreturn}. @xref{Function
2733 This warning is enabled by @option{-Wall}.
2735 @item -Wunknown-pragmas
2736 @opindex Wunknown-pragmas
2737 @cindex warning for unknown pragmas
2738 @cindex unknown pragmas, warning
2739 @cindex pragmas, warning of unknown
2740 Warn when a #pragma directive is encountered which is not understood by
2741 GCC@. If this command line option is used, warnings will even be issued
2742 for unknown pragmas in system header files. This is not the case if
2743 the warnings were only enabled by the @option{-Wall} command line option.
2746 @opindex Wno-pragmas
2748 Do not warn about misuses of pragmas, such as incorrect parameters,
2749 invalid syntax, or conflicts between pragmas. See also
2750 @samp{-Wunknown-pragmas}.
2752 @item -Wstrict-aliasing
2753 @opindex Wstrict-aliasing
2754 This option is only active when @option{-fstrict-aliasing} is active.
2755 It warns about code which might break the strict aliasing rules that the
2756 compiler is using for optimization. The warning does not catch all
2757 cases, but does attempt to catch the more common pitfalls. It is
2758 included in @option{-Wall}.
2760 @item -Wstrict-aliasing=2
2761 @opindex Wstrict-aliasing=2
2762 This option is only active when @option{-fstrict-aliasing} is active.
2763 It warns about code which might break the strict aliasing rules that the
2764 compiler is using for optimization. This warning catches more cases than
2765 @option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
2766 cases that are safe.
2770 All of the above @samp{-W} options combined. This enables all the
2771 warnings about constructions that some users consider questionable, and
2772 that are easy to avoid (or modify to prevent the warning), even in
2773 conjunction with macros. This also enables some language-specific
2774 warnings described in @ref{C++ Dialect Options} and
2775 @ref{Objective-C and Objective-C++ Dialect Options}.
2778 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2779 Some of them warn about constructions that users generally do not
2780 consider questionable, but which occasionally you might wish to check
2781 for; others warn about constructions that are necessary or hard to avoid
2782 in some cases, and there is no simple way to modify the code to suppress
2789 (This option used to be called @option{-W}. The older name is still
2790 supported, but the newer name is more descriptive.) Print extra warning
2791 messages for these events:
2795 A function can return either with or without a value. (Falling
2796 off the end of the function body is considered returning without
2797 a value.) For example, this function would evoke such a
2811 An expression-statement or the left-hand side of a comma expression
2812 contains no side effects.
2813 To suppress the warning, cast the unused expression to void.
2814 For example, an expression such as @samp{x[i,j]} will cause a warning,
2815 but @samp{x[(void)i,j]} will not.
2818 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2821 Storage-class specifiers like @code{static} are not the first things in
2822 a declaration. According to the C Standard, this usage is obsolescent.
2825 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2829 A comparison between signed and unsigned values could produce an
2830 incorrect result when the signed value is converted to unsigned.
2831 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2834 An aggregate has an initializer which does not initialize all members.
2835 This warning can be independently controlled by
2836 @option{-Wmissing-field-initializers}.
2839 A function parameter is declared without a type specifier in K&R-style
2847 An empty body occurs in an @samp{if} or @samp{else} statement.
2850 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2851 @samp{>}, or @samp{>=}.
2854 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2857 Any of several floating-point events that often indicate errors, such as
2858 overflow, underflow, loss of precision, etc.
2860 @item @r{(C++ only)}
2861 An enumerator and a non-enumerator both appear in a conditional expression.
2863 @item @r{(C++ only)}
2864 A non-static reference or non-static @samp{const} member appears in a
2865 class without constructors.
2867 @item @r{(C++ only)}
2868 Ambiguous virtual bases.
2870 @item @r{(C++ only)}
2871 Subscripting an array which has been declared @samp{register}.
2873 @item @r{(C++ only)}
2874 Taking the address of a variable which has been declared @samp{register}.
2876 @item @r{(C++ only)}
2877 A base class is not initialized in a derived class' copy constructor.
2880 @item -Wno-div-by-zero
2881 @opindex Wno-div-by-zero
2882 @opindex Wdiv-by-zero
2883 Do not warn about compile-time integer division by zero. Floating point
2884 division by zero is not warned about, as it can be a legitimate way of
2885 obtaining infinities and NaNs.
2887 @item -Wsystem-headers
2888 @opindex Wsystem-headers
2889 @cindex warnings from system headers
2890 @cindex system headers, warnings from
2891 Print warning messages for constructs found in system header files.
2892 Warnings from system headers are normally suppressed, on the assumption
2893 that they usually do not indicate real problems and would only make the
2894 compiler output harder to read. Using this command line option tells
2895 GCC to emit warnings from system headers as if they occurred in user
2896 code. However, note that using @option{-Wall} in conjunction with this
2897 option will @emph{not} warn about unknown pragmas in system
2898 headers---for that, @option{-Wunknown-pragmas} must also be used.
2901 @opindex Wfloat-equal
2902 Warn if floating point values are used in equality comparisons.
2904 The idea behind this is that sometimes it is convenient (for the
2905 programmer) to consider floating-point values as approximations to
2906 infinitely precise real numbers. If you are doing this, then you need
2907 to compute (by analyzing the code, or in some other way) the maximum or
2908 likely maximum error that the computation introduces, and allow for it
2909 when performing comparisons (and when producing output, but that's a
2910 different problem). In particular, instead of testing for equality, you
2911 would check to see whether the two values have ranges that overlap; and
2912 this is done with the relational operators, so equality comparisons are
2915 @item -Wtraditional @r{(C only)}
2916 @opindex Wtraditional
2917 Warn about certain constructs that behave differently in traditional and
2918 ISO C@. Also warn about ISO C constructs that have no traditional C
2919 equivalent, and/or problematic constructs which should be avoided.
2923 Macro parameters that appear within string literals in the macro body.
2924 In traditional C macro replacement takes place within string literals,
2925 but does not in ISO C@.
2928 In traditional C, some preprocessor directives did not exist.
2929 Traditional preprocessors would only consider a line to be a directive
2930 if the @samp{#} appeared in column 1 on the line. Therefore
2931 @option{-Wtraditional} warns about directives that traditional C
2932 understands but would ignore because the @samp{#} does not appear as the
2933 first character on the line. It also suggests you hide directives like
2934 @samp{#pragma} not understood by traditional C by indenting them. Some
2935 traditional implementations would not recognize @samp{#elif}, so it
2936 suggests avoiding it altogether.
2939 A function-like macro that appears without arguments.
2942 The unary plus operator.
2945 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2946 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2947 constants.) Note, these suffixes appear in macros defined in the system
2948 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2949 Use of these macros in user code might normally lead to spurious
2950 warnings, however GCC's integrated preprocessor has enough context to
2951 avoid warning in these cases.
2954 A function declared external in one block and then used after the end of
2958 A @code{switch} statement has an operand of type @code{long}.
2961 A non-@code{static} function declaration follows a @code{static} one.
2962 This construct is not accepted by some traditional C compilers.
2965 The ISO type of an integer constant has a different width or
2966 signedness from its traditional type. This warning is only issued if
2967 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2968 typically represent bit patterns, are not warned about.
2971 Usage of ISO string concatenation is detected.
2974 Initialization of automatic aggregates.
2977 Identifier conflicts with labels. Traditional C lacks a separate
2978 namespace for labels.
2981 Initialization of unions. If the initializer is zero, the warning is
2982 omitted. This is done under the assumption that the zero initializer in
2983 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2984 initializer warnings and relies on default initialization to zero in the
2988 Conversions by prototypes between fixed/floating point values and vice
2989 versa. The absence of these prototypes when compiling with traditional
2990 C would cause serious problems. This is a subset of the possible
2991 conversion warnings, for the full set use @option{-Wconversion}.
2994 Use of ISO C style function definitions. This warning intentionally is
2995 @emph{not} issued for prototype declarations or variadic functions
2996 because these ISO C features will appear in your code when using
2997 libiberty's traditional C compatibility macros, @code{PARAMS} and
2998 @code{VPARAMS}. This warning is also bypassed for nested functions
2999 because that feature is already a GCC extension and thus not relevant to
3000 traditional C compatibility.
3003 @item -Wdeclaration-after-statement @r{(C only)}
3004 @opindex Wdeclaration-after-statement
3005 Warn when a declaration is found after a statement in a block. This
3006 construct, known from C++, was introduced with ISO C99 and is by default
3007 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3008 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3012 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3014 @item -Wno-endif-labels
3015 @opindex Wno-endif-labels
3016 @opindex Wendif-labels
3017 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3021 Warn whenever a local variable shadows another local variable, parameter or
3022 global variable or whenever a built-in function is shadowed.
3024 @item -Wlarger-than-@var{len}
3025 @opindex Wlarger-than
3026 Warn whenever an object of larger than @var{len} bytes is defined.
3028 @item -Wunsafe-loop-optimizations
3029 @opindex Wunsafe-loop-optimizations
3030 Warn if the loop cannot be optimized because the compiler could not
3031 assume anything on the bounds of the loop indices. With
3032 @option{-funsafe-loop-optimizations} warn if the compiler made
3035 @item -Wpointer-arith
3036 @opindex Wpointer-arith
3037 Warn about anything that depends on the ``size of'' a function type or
3038 of @code{void}. GNU C assigns these types a size of 1, for
3039 convenience in calculations with @code{void *} pointers and pointers
3042 @item -Wbad-function-cast @r{(C only)}
3043 @opindex Wbad-function-cast
3044 Warn whenever a function call is cast to a non-matching type.
3045 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3048 Warn about ISO C constructs that are outside of the common subset of
3049 ISO C and ISO C++, e.g.@: request for implicit conversion from
3050 @code{void *} to a pointer to non-@code{void} type.
3054 Warn whenever a pointer is cast so as to remove a type qualifier from
3055 the target type. For example, warn if a @code{const char *} is cast
3056 to an ordinary @code{char *}.
3059 @opindex Wcast-align
3060 Warn whenever a pointer is cast such that the required alignment of the
3061 target is increased. For example, warn if a @code{char *} is cast to
3062 an @code{int *} on machines where integers can only be accessed at
3063 two- or four-byte boundaries.
3065 @item -Wwrite-strings
3066 @opindex Wwrite-strings
3067 When compiling C, give string constants the type @code{const
3068 char[@var{length}]} so that
3069 copying the address of one into a non-@code{const} @code{char *}
3070 pointer will get a warning; when compiling C++, warn about the
3071 deprecated conversion from string constants to @code{char *}.
3072 These warnings will help you find at
3073 compile time code that can try to write into a string constant, but
3074 only if you have been very careful about using @code{const} in
3075 declarations and prototypes. Otherwise, it will just be a nuisance;
3076 this is why we did not make @option{-Wall} request these warnings.
3079 @opindex Wconversion
3080 Warn if a prototype causes a type conversion that is different from what
3081 would happen to the same argument in the absence of a prototype. This
3082 includes conversions of fixed point to floating and vice versa, and
3083 conversions changing the width or signedness of a fixed point argument
3084 except when the same as the default promotion.
3086 Also, warn if a negative integer constant expression is implicitly
3087 converted to an unsigned type. For example, warn about the assignment
3088 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
3089 casts like @code{(unsigned) -1}.
3091 @item -Wsign-compare
3092 @opindex Wsign-compare
3093 @cindex warning for comparison of signed and unsigned values
3094 @cindex comparison of signed and unsigned values, warning
3095 @cindex signed and unsigned values, comparison warning
3096 Warn when a comparison between signed and unsigned values could produce
3097 an incorrect result when the signed value is converted to unsigned.
3098 This warning is also enabled by @option{-Wextra}; to get the other warnings
3099 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3101 @item -Waggregate-return
3102 @opindex Waggregate-return
3103 Warn if any functions that return structures or unions are defined or
3104 called. (In languages where you can return an array, this also elicits
3107 @item -Wno-attributes
3108 @opindex Wno-attributes
3109 @opindex Wattributes
3110 Do not warn if an unexpected @code{__attribute__} is used, such as
3111 unrecognized attributes, function attributes applied to variables,
3112 etc. This will not stop errors for incorrect use of supported
3115 @item -Wstrict-prototypes @r{(C only)}
3116 @opindex Wstrict-prototypes
3117 Warn if a function is declared or defined without specifying the
3118 argument types. (An old-style function definition is permitted without
3119 a warning if preceded by a declaration which specifies the argument
3122 @item -Wold-style-definition @r{(C only)}
3123 @opindex Wold-style-definition
3124 Warn if an old-style function definition is used. A warning is given
3125 even if there is a previous prototype.
3127 @item -Wmissing-prototypes @r{(C only)}
3128 @opindex Wmissing-prototypes
3129 Warn if a global function is defined without a previous prototype
3130 declaration. This warning is issued even if the definition itself
3131 provides a prototype. The aim is to detect global functions that fail
3132 to be declared in header files.
3134 @item -Wmissing-declarations @r{(C only)}
3135 @opindex Wmissing-declarations
3136 Warn if a global function is defined without a previous declaration.
3137 Do so even if the definition itself provides a prototype.
3138 Use this option to detect global functions that are not declared in
3141 @item -Wmissing-field-initializers
3142 @opindex Wmissing-field-initializers
3145 Warn if a structure's initializer has some fields missing. For
3146 example, the following code would cause such a warning, because
3147 @code{x.h} is implicitly zero:
3150 struct s @{ int f, g, h; @};
3151 struct s x = @{ 3, 4 @};
3154 This option does not warn about designated initializers, so the following
3155 modification would not trigger a warning:
3158 struct s @{ int f, g, h; @};
3159 struct s x = @{ .f = 3, .g = 4 @};
3162 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3163 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3165 @item -Wmissing-noreturn
3166 @opindex Wmissing-noreturn
3167 Warn about functions which might be candidates for attribute @code{noreturn}.
3168 Note these are only possible candidates, not absolute ones. Care should
3169 be taken to manually verify functions actually do not ever return before
3170 adding the @code{noreturn} attribute, otherwise subtle code generation
3171 bugs could be introduced. You will not get a warning for @code{main} in
3172 hosted C environments.
3174 @item -Wmissing-format-attribute
3175 @opindex Wmissing-format-attribute
3177 Warn about function pointers which might be candidates for @code{format}
3178 attributes. Note these are only possible candidates, not absolute ones.
3179 GCC will guess that function pointers with @code{format} attributes that
3180 are used in assignment, initialization, parameter passing or return
3181 statements should have a corresponding @code{format} attribute in the
3182 resulting type. I.e.@: the left-hand side of the assignment or
3183 initialization, the type of the parameter variable, or the return type
3184 of the containing function respectively should also have a @code{format}
3185 attribute to avoid the warning.
3187 GCC will also warn about function definitions which might be
3188 candidates for @code{format} attributes. Again, these are only
3189 possible candidates. GCC will guess that @code{format} attributes
3190 might be appropriate for any function that calls a function like
3191 @code{vprintf} or @code{vscanf}, but this might not always be the
3192 case, and some functions for which @code{format} attributes are
3193 appropriate may not be detected.
3195 @item -Wno-multichar
3196 @opindex Wno-multichar
3198 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3199 Usually they indicate a typo in the user's code, as they have
3200 implementation-defined values, and should not be used in portable code.
3202 @item -Wnormalized=<none|id|nfc|nfkc>
3203 @opindex Wnormalized
3206 @cindex character set, input normalization
3207 In ISO C and ISO C++, two identifiers are different if they are
3208 different sequences of characters. However, sometimes when characters
3209 outside the basic ASCII character set are used, you can have two
3210 different character sequences that look the same. To avoid confusion,
3211 the ISO 10646 standard sets out some @dfn{normalization rules} which
3212 when applied ensure that two sequences that look the same are turned into
3213 the same sequence. GCC can warn you if you are using identifiers which
3214 have not been normalized; this option controls that warning.
3216 There are four levels of warning that GCC supports. The default is
3217 @option{-Wnormalized=nfc}, which warns about any identifier which is
3218 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3219 recommended form for most uses.
3221 Unfortunately, there are some characters which ISO C and ISO C++ allow
3222 in identifiers that when turned into NFC aren't allowable as
3223 identifiers. That is, there's no way to use these symbols in portable
3224 ISO C or C++ and have all your identifiers in NFC.
3225 @option{-Wnormalized=id} suppresses the warning for these characters.
3226 It is hoped that future versions of the standards involved will correct
3227 this, which is why this option is not the default.
3229 You can switch the warning off for all characters by writing
3230 @option{-Wnormalized=none}. You would only want to do this if you
3231 were using some other normalization scheme (like ``D''), because
3232 otherwise you can easily create bugs that are literally impossible to see.
3234 Some characters in ISO 10646 have distinct meanings but look identical
3235 in some fonts or display methodologies, especially once formatting has
3236 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3237 LETTER N'', will display just like a regular @code{n} which has been
3238 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3239 normalisation scheme to convert all these into a standard form as
3240 well, and GCC will warn if your code is not in NFKC if you use
3241 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3242 about every identifier that contains the letter O because it might be
3243 confused with the digit 0, and so is not the default, but may be
3244 useful as a local coding convention if the programming environment is
3245 unable to be fixed to display these characters distinctly.
3247 @item -Wno-deprecated-declarations
3248 @opindex Wno-deprecated-declarations
3249 Do not warn about uses of functions, variables, and types marked as
3250 deprecated by using the @code{deprecated} attribute.
3251 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3252 @pxref{Type Attributes}.)
3256 Warn if a structure is given the packed attribute, but the packed
3257 attribute has no effect on the layout or size of the structure.
3258 Such structures may be mis-aligned for little benefit. For
3259 instance, in this code, the variable @code{f.x} in @code{struct bar}
3260 will be misaligned even though @code{struct bar} does not itself
3261 have the packed attribute:
3268 @} __attribute__((packed));
3278 Warn if padding is included in a structure, either to align an element
3279 of the structure or to align the whole structure. Sometimes when this
3280 happens it is possible to rearrange the fields of the structure to
3281 reduce the padding and so make the structure smaller.
3283 @item -Wredundant-decls
3284 @opindex Wredundant-decls
3285 Warn if anything is declared more than once in the same scope, even in
3286 cases where multiple declaration is valid and changes nothing.
3288 @item -Wnested-externs @r{(C only)}
3289 @opindex Wnested-externs
3290 Warn if an @code{extern} declaration is encountered within a function.
3292 @item -Wunreachable-code
3293 @opindex Wunreachable-code
3294 Warn if the compiler detects that code will never be executed.
3296 This option is intended to warn when the compiler detects that at
3297 least a whole line of source code will never be executed, because
3298 some condition is never satisfied or because it is after a
3299 procedure that never returns.
3301 It is possible for this option to produce a warning even though there
3302 are circumstances under which part of the affected line can be executed,
3303 so care should be taken when removing apparently-unreachable code.
3305 For instance, when a function is inlined, a warning may mean that the
3306 line is unreachable in only one inlined copy of the function.
3308 This option is not made part of @option{-Wall} because in a debugging
3309 version of a program there is often substantial code which checks
3310 correct functioning of the program and is, hopefully, unreachable
3311 because the program does work. Another common use of unreachable
3312 code is to provide behavior which is selectable at compile-time.
3316 Warn if a function can not be inlined and it was declared as inline.
3317 Even with this option, the compiler will not warn about failures to
3318 inline functions declared in system headers.
3320 The compiler uses a variety of heuristics to determine whether or not
3321 to inline a function. For example, the compiler takes into account
3322 the size of the function being inlined and the amount of inlining
3323 that has already been done in the current function. Therefore,
3324 seemingly insignificant changes in the source program can cause the
3325 warnings produced by @option{-Winline} to appear or disappear.
3327 @item -Wno-invalid-offsetof @r{(C++ only)}
3328 @opindex Wno-invalid-offsetof
3329 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3330 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3331 to a non-POD type is undefined. In existing C++ implementations,
3332 however, @samp{offsetof} typically gives meaningful results even when
3333 applied to certain kinds of non-POD types. (Such as a simple
3334 @samp{struct} that fails to be a POD type only by virtue of having a
3335 constructor.) This flag is for users who are aware that they are
3336 writing nonportable code and who have deliberately chosen to ignore the
3339 The restrictions on @samp{offsetof} may be relaxed in a future version
3340 of the C++ standard.
3342 @item -Wno-int-to-pointer-cast @r{(C only)}
3343 @opindex Wno-int-to-pointer-cast
3344 Suppress warnings from casts to pointer type of an integer of a
3347 @item -Wno-pointer-to-int-cast @r{(C only)}
3348 @opindex Wno-pointer-to-int-cast
3349 Suppress warnings from casts from a pointer to an integer type of a
3353 @opindex Winvalid-pch
3354 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3355 the search path but can't be used.
3359 @opindex Wno-long-long
3360 Warn if @samp{long long} type is used. This is default. To inhibit
3361 the warning messages, use @option{-Wno-long-long}. Flags
3362 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3363 only when @option{-pedantic} flag is used.
3365 @item -Wvariadic-macros
3366 @opindex Wvariadic-macros
3367 @opindex Wno-variadic-macros
3368 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3369 alternate syntax when in pedantic ISO C99 mode. This is default.
3370 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3372 @item -Wvolatile-register-var
3373 @opindex Wvolatile-register-var
3374 @opindex Wno-volatile-register-var
3375 Warn if a register variable is declared volatile. The volatile
3376 modifier does not inhibit all optimizations that may eliminate reads
3377 and/or writes to register variables.
3379 @item -Wdisabled-optimization
3380 @opindex Wdisabled-optimization
3381 Warn if a requested optimization pass is disabled. This warning does
3382 not generally indicate that there is anything wrong with your code; it
3383 merely indicates that GCC's optimizers were unable to handle the code
3384 effectively. Often, the problem is that your code is too big or too
3385 complex; GCC will refuse to optimize programs when the optimization
3386 itself is likely to take inordinate amounts of time.
3388 @item -Wno-pointer-sign
3389 @opindex Wno-pointer-sign
3390 Don't warn for pointer argument passing or assignment with different signedness.
3391 Only useful in the negative form since this warning is enabled by default.
3392 This option is only supported for C and Objective-C@.
3396 Make all warnings into errors.
3398 @item -Wstack-protector
3399 This option is only active when @option{-fstack-protector} is active. It
3400 warns about functions that will not be protected against stack smashing.
3404 @node Debugging Options
3405 @section Options for Debugging Your Program or GCC
3406 @cindex options, debugging
3407 @cindex debugging information options
3409 GCC has various special options that are used for debugging
3410 either your program or GCC:
3415 Produce debugging information in the operating system's native format
3416 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3419 On most systems that use stabs format, @option{-g} enables use of extra
3420 debugging information that only GDB can use; this extra information
3421 makes debugging work better in GDB but will probably make other debuggers
3423 refuse to read the program. If you want to control for certain whether
3424 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3425 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3427 GCC allows you to use @option{-g} with
3428 @option{-O}. The shortcuts taken by optimized code may occasionally
3429 produce surprising results: some variables you declared may not exist
3430 at all; flow of control may briefly move where you did not expect it;
3431 some statements may not be executed because they compute constant
3432 results or their values were already at hand; some statements may
3433 execute in different places because they were moved out of loops.
3435 Nevertheless it proves possible to debug optimized output. This makes
3436 it reasonable to use the optimizer for programs that might have bugs.
3438 The following options are useful when GCC is generated with the
3439 capability for more than one debugging format.
3443 Produce debugging information for use by GDB@. This means to use the
3444 most expressive format available (DWARF 2, stabs, or the native format
3445 if neither of those are supported), including GDB extensions if at all
3450 Produce debugging information in stabs format (if that is supported),
3451 without GDB extensions. This is the format used by DBX on most BSD
3452 systems. On MIPS, Alpha and System V Release 4 systems this option
3453 produces stabs debugging output which is not understood by DBX or SDB@.
3454 On System V Release 4 systems this option requires the GNU assembler.
3456 @item -feliminate-unused-debug-symbols
3457 @opindex feliminate-unused-debug-symbols
3458 Produce debugging information in stabs format (if that is supported),
3459 for only symbols that are actually used.
3463 Produce debugging information in stabs format (if that is supported),
3464 using GNU extensions understood only by the GNU debugger (GDB)@. The
3465 use of these extensions is likely to make other debuggers crash or
3466 refuse to read the program.
3470 Produce debugging information in COFF format (if that is supported).
3471 This is the format used by SDB on most System V systems prior to
3476 Produce debugging information in XCOFF format (if that is supported).
3477 This is the format used by the DBX debugger on IBM RS/6000 systems.
3481 Produce debugging information in XCOFF format (if that is supported),
3482 using GNU extensions understood only by the GNU debugger (GDB)@. The
3483 use of these extensions is likely to make other debuggers crash or
3484 refuse to read the program, and may cause assemblers other than the GNU
3485 assembler (GAS) to fail with an error.
3489 Produce debugging information in DWARF version 2 format (if that is
3490 supported). This is the format used by DBX on IRIX 6. With this
3491 option, GCC uses features of DWARF version 3 when they are useful;
3492 version 3 is upward compatible with version 2, but may still cause
3493 problems for older debuggers.
3497 Produce debugging information in VMS debug format (if that is
3498 supported). This is the format used by DEBUG on VMS systems.
3501 @itemx -ggdb@var{level}
3502 @itemx -gstabs@var{level}
3503 @itemx -gcoff@var{level}
3504 @itemx -gxcoff@var{level}
3505 @itemx -gvms@var{level}
3506 Request debugging information and also use @var{level} to specify how
3507 much information. The default level is 2.
3509 Level 1 produces minimal information, enough for making backtraces in
3510 parts of the program that you don't plan to debug. This includes
3511 descriptions of functions and external variables, but no information
3512 about local variables and no line numbers.
3514 Level 3 includes extra information, such as all the macro definitions
3515 present in the program. Some debuggers support macro expansion when
3516 you use @option{-g3}.
3518 @option{-gdwarf-2} does not accept a concatenated debug level, because
3519 GCC used to support an option @option{-gdwarf} that meant to generate
3520 debug information in version 1 of the DWARF format (which is very
3521 different from version 2), and it would have been too confusing. That
3522 debug format is long obsolete, but the option cannot be changed now.
3523 Instead use an additional @option{-g@var{level}} option to change the
3524 debug level for DWARF2.
3526 @item -feliminate-dwarf2-dups
3527 @opindex feliminate-dwarf2-dups
3528 Compress DWARF2 debugging information by eliminating duplicated
3529 information about each symbol. This option only makes sense when
3530 generating DWARF2 debugging information with @option{-gdwarf-2}.
3532 @cindex @command{prof}
3535 Generate extra code to write profile information suitable for the
3536 analysis program @command{prof}. You must use this option when compiling
3537 the source files you want data about, and you must also use it when
3540 @cindex @command{gprof}
3543 Generate extra code to write profile information suitable for the
3544 analysis program @command{gprof}. You must use this option when compiling
3545 the source files you want data about, and you must also use it when
3550 Makes the compiler print out each function name as it is compiled, and
3551 print some statistics about each pass when it finishes.
3554 @opindex ftime-report
3555 Makes the compiler print some statistics about the time consumed by each
3556 pass when it finishes.
3559 @opindex fmem-report
3560 Makes the compiler print some statistics about permanent memory
3561 allocation when it finishes.
3563 @item -fprofile-arcs
3564 @opindex fprofile-arcs
3565 Add code so that program flow @dfn{arcs} are instrumented. During
3566 execution the program records how many times each branch and call is
3567 executed and how many times it is taken or returns. When the compiled
3568 program exits it saves this data to a file called
3569 @file{@var{auxname}.gcda} for each source file. The data may be used for
3570 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3571 test coverage analysis (@option{-ftest-coverage}). Each object file's
3572 @var{auxname} is generated from the name of the output file, if
3573 explicitly specified and it is not the final executable, otherwise it is
3574 the basename of the source file. In both cases any suffix is removed
3575 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3576 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3577 @xref{Cross-profiling}.
3579 @cindex @command{gcov}
3583 This option is used to compile and link code instrumented for coverage
3584 analysis. The option is a synonym for @option{-fprofile-arcs}
3585 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
3586 linking). See the documentation for those options for more details.
3591 Compile the source files with @option{-fprofile-arcs} plus optimization
3592 and code generation options. For test coverage analysis, use the
3593 additional @option{-ftest-coverage} option. You do not need to profile
3594 every source file in a program.
3597 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3598 (the latter implies the former).
3601 Run the program on a representative workload to generate the arc profile
3602 information. This may be repeated any number of times. You can run
3603 concurrent instances of your program, and provided that the file system
3604 supports locking, the data files will be correctly updated. Also
3605 @code{fork} calls are detected and correctly handled (double counting
3609 For profile-directed optimizations, compile the source files again with
3610 the same optimization and code generation options plus
3611 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3612 Control Optimization}).
3615 For test coverage analysis, use @command{gcov} to produce human readable
3616 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3617 @command{gcov} documentation for further information.
3621 With @option{-fprofile-arcs}, for each function of your program GCC
3622 creates a program flow graph, then finds a spanning tree for the graph.
3623 Only arcs that are not on the spanning tree have to be instrumented: the
3624 compiler adds code to count the number of times that these arcs are
3625 executed. When an arc is the only exit or only entrance to a block, the
3626 instrumentation code can be added to the block; otherwise, a new basic
3627 block must be created to hold the instrumentation code.
3630 @item -ftest-coverage
3631 @opindex ftest-coverage
3632 Produce a notes file that the @command{gcov} code-coverage utility
3633 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3634 show program coverage. Each source file's note file is called
3635 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3636 above for a description of @var{auxname} and instructions on how to
3637 generate test coverage data. Coverage data will match the source files
3638 more closely, if you do not optimize.
3640 @item -d@var{letters}
3641 @item -fdump-rtl-@var{pass}
3643 Says to make debugging dumps during compilation at times specified by
3644 @var{letters}. This is used for debugging the RTL-based passes of the
3645 compiler. The file names for most of the dumps are made by appending a
3646 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3647 from the name of the output file, if explicitly specified and it is not
3648 an executable, otherwise it is the basename of the source file.
3650 Most debug dumps can be enabled either passing a letter to the @option{-d}
3651 option, or with a long @option{-fdump-rtl} switch; here are the possible
3652 letters for use in @var{letters} and @var{pass}, and their meanings:
3657 Annotate the assembler output with miscellaneous debugging information.
3660 @itemx -fdump-rtl-bp
3662 @opindex fdump-rtl-bp
3663 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3666 @itemx -fdump-rtl-bbro
3668 @opindex fdump-rtl-bbro
3669 Dump after block reordering, to @file{@var{file}.30.bbro}.
3672 @itemx -fdump-rtl-combine
3674 @opindex fdump-rtl-combine
3675 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3678 @itemx -fdump-rtl-ce1
3679 @itemx -fdump-rtl-ce2
3681 @opindex fdump-rtl-ce1
3682 @opindex fdump-rtl-ce2
3683 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3684 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3685 and @option{-fdump-rtl-ce2} enable dumping after the second if
3686 conversion, to the file @file{@var{file}.18.ce2}.
3689 @itemx -fdump-rtl-btl
3690 @itemx -fdump-rtl-dbr
3692 @opindex fdump-rtl-btl
3693 @opindex fdump-rtl-dbr
3694 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3695 target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
3696 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3697 scheduling, to @file{@var{file}.36.dbr}.
3701 Dump all macro definitions, at the end of preprocessing, in addition to
3705 @itemx -fdump-rtl-ce3
3707 @opindex fdump-rtl-ce3
3708 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3711 @itemx -fdump-rtl-cfg
3712 @itemx -fdump-rtl-life
3714 @opindex fdump-rtl-cfg
3715 @opindex fdump-rtl-life
3716 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3717 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3718 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3719 to @file{@var{file}.16.life}.
3722 @itemx -fdump-rtl-greg
3724 @opindex fdump-rtl-greg
3725 Dump after global register allocation, to @file{@var{file}.23.greg}.
3728 @itemx -fdump-rtl-gcse
3729 @itemx -fdump-rtl-bypass
3731 @opindex fdump-rtl-gcse
3732 @opindex fdump-rtl-bypass
3733 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3734 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3735 enable dumping after jump bypassing and control flow optimizations, to
3736 @file{@var{file}.07.bypass}.
3739 @itemx -fdump-rtl-eh
3741 @opindex fdump-rtl-eh
3742 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3745 @itemx -fdump-rtl-sibling
3747 @opindex fdump-rtl-sibling
3748 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3751 @itemx -fdump-rtl-jump
3753 @opindex fdump-rtl-jump
3754 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3757 @itemx -fdump-rtl-stack
3759 @opindex fdump-rtl-stack
3760 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3763 @itemx -fdump-rtl-lreg
3765 @opindex fdump-rtl-lreg
3766 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3769 @itemx -fdump-rtl-loop
3770 @itemx -fdump-rtl-loop2
3772 @opindex fdump-rtl-loop
3773 @opindex fdump-rtl-loop2
3774 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3775 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3776 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3777 @file{@var{file}.13.loop2}.
3780 @itemx -fdump-rtl-sms
3782 @opindex fdump-rtl-sms
3783 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3786 @itemx -fdump-rtl-mach
3788 @opindex fdump-rtl-mach
3789 Dump after performing the machine dependent reorganization pass, to
3790 @file{@var{file}.35.mach}.
3793 @itemx -fdump-rtl-rnreg
3795 @opindex fdump-rtl-rnreg
3796 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3799 @itemx -fdump-rtl-regmove
3801 @opindex fdump-rtl-regmove
3802 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3805 @itemx -fdump-rtl-postreload
3807 @opindex fdump-rtl-postreload
3808 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3811 @itemx -fdump-rtl-expand
3813 @opindex fdump-rtl-expand
3814 Dump after RTL generation, to @file{@var{file}.00.expand}.
3817 @itemx -fdump-rtl-sched2
3819 @opindex fdump-rtl-sched2
3820 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3823 @itemx -fdump-rtl-cse
3825 @opindex fdump-rtl-cse
3826 Dump after CSE (including the jump optimization that sometimes follows
3827 CSE), to @file{@var{file}.04.cse}.
3830 @itemx -fdump-rtl-sched
3832 @opindex fdump-rtl-sched
3833 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3836 @itemx -fdump-rtl-cse2
3838 @opindex fdump-rtl-cse2
3839 Dump after the second CSE pass (including the jump optimization that
3840 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3843 @itemx -fdump-rtl-tracer
3845 @opindex fdump-rtl-tracer
3846 Dump after running tracer, to @file{@var{file}.12.tracer}.
3849 @itemx -fdump-rtl-vpt
3850 @itemx -fdump-rtl-vartrack
3852 @opindex fdump-rtl-vpt
3853 @opindex fdump-rtl-vartrack
3854 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3855 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3856 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3857 to @file{@var{file}.34.vartrack}.
3860 @itemx -fdump-rtl-flow2
3862 @opindex fdump-rtl-flow2
3863 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3866 @itemx -fdump-rtl-peephole2
3868 @opindex fdump-rtl-peephole2
3869 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3872 @itemx -fdump-rtl-web
3874 @opindex fdump-rtl-web
3875 Dump after live range splitting, to @file{@var{file}.14.web}.
3878 @itemx -fdump-rtl-all
3880 @opindex fdump-rtl-all
3881 Produce all the dumps listed above.
3885 Produce a core dump whenever an error occurs.
3889 Print statistics on memory usage, at the end of the run, to
3894 Annotate the assembler output with a comment indicating which
3895 pattern and alternative was used. The length of each instruction is
3900 Dump the RTL in the assembler output as a comment before each instruction.
3901 Also turns on @option{-dp} annotation.
3905 For each of the other indicated dump files (either with @option{-d} or
3906 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3907 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3911 Just generate RTL for a function instead of compiling it. Usually used
3912 with @samp{r} (@option{-fdump-rtl-expand}).
3916 Dump debugging information during parsing, to standard error.
3919 @item -fdump-unnumbered
3920 @opindex fdump-unnumbered
3921 When doing debugging dumps (see @option{-d} option above), suppress instruction
3922 numbers and line number note output. This makes it more feasible to
3923 use diff on debugging dumps for compiler invocations with different
3924 options, in particular with and without @option{-g}.
3926 @item -fdump-translation-unit @r{(C++ only)}
3927 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
3928 @opindex fdump-translation-unit
3929 Dump a representation of the tree structure for the entire translation
3930 unit to a file. The file name is made by appending @file{.tu} to the
3931 source file name. If the @samp{-@var{options}} form is used, @var{options}
3932 controls the details of the dump as described for the
3933 @option{-fdump-tree} options.
3935 @item -fdump-class-hierarchy @r{(C++ only)}
3936 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3937 @opindex fdump-class-hierarchy
3938 Dump a representation of each class's hierarchy and virtual function
3939 table layout to a file. The file name is made by appending @file{.class}
3940 to the source file name. If the @samp{-@var{options}} form is used,
3941 @var{options} controls the details of the dump as described for the
3942 @option{-fdump-tree} options.
3944 @item -fdump-ipa-@var{switch}
3946 Control the dumping at various stages of inter-procedural analysis
3947 language tree to a file. The file name is generated by appending a switch
3948 specific suffix to the source file name. The following dumps are possible:
3952 Enables all inter-procedural analysis dumps; currently the only produced
3953 dump is the @samp{cgraph} dump.
3956 Dumps information about call-graph optimization, unused function removal,
3957 and inlining decisions.
3960 @item -fdump-tree-@var{switch} @r{(C and C++ only)}
3961 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C and C++ only)}
3963 Control the dumping at various stages of processing the intermediate
3964 language tree to a file. The file name is generated by appending a switch
3965 specific suffix to the source file name. If the @samp{-@var{options}}
3966 form is used, @var{options} is a list of @samp{-} separated options that
3967 control the details of the dump. Not all options are applicable to all
3968 dumps, those which are not meaningful will be ignored. The following
3969 options are available
3973 Print the address of each node. Usually this is not meaningful as it
3974 changes according to the environment and source file. Its primary use
3975 is for tying up a dump file with a debug environment.
3977 Inhibit dumping of members of a scope or body of a function merely
3978 because that scope has been reached. Only dump such items when they
3979 are directly reachable by some other path. When dumping pretty-printed
3980 trees, this option inhibits dumping the bodies of control structures.
3982 Print a raw representation of the tree. By default, trees are
3983 pretty-printed into a C-like representation.
3985 Enable more detailed dumps (not honored by every dump option).
3987 Enable dumping various statistics about the pass (not honored by every dump
3990 Enable showing basic block boundaries (disabled in raw dumps).
3992 Enable showing virtual operands for every statement.
3994 Enable showing line numbers for statements.
3996 Enable showing the unique ID (@code{DECL_UID}) for each variable.
3998 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
4001 The following tree dumps are possible:
4005 Dump before any tree based optimization, to @file{@var{file}.original}.
4008 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4011 Dump after function inlining, to @file{@var{file}.inlined}.
4014 @opindex fdump-tree-gimple
4015 Dump each function before and after the gimplification pass to a file. The
4016 file name is made by appending @file{.gimple} to the source file name.
4019 @opindex fdump-tree-cfg
4020 Dump the control flow graph of each function to a file. The file name is
4021 made by appending @file{.cfg} to the source file name.
4024 @opindex fdump-tree-vcg
4025 Dump the control flow graph of each function to a file in VCG format. The
4026 file name is made by appending @file{.vcg} to the source file name. Note
4027 that if the file contains more than one function, the generated file cannot
4028 be used directly by VCG@. You will need to cut and paste each function's
4029 graph into its own separate file first.
4032 @opindex fdump-tree-ch
4033 Dump each function after copying loop headers. The file name is made by
4034 appending @file{.ch} to the source file name.
4037 @opindex fdump-tree-ssa
4038 Dump SSA related information to a file. The file name is made by appending
4039 @file{.ssa} to the source file name.
4042 @opindex fdump-tree-salias
4043 Dump structure aliasing variable information to a file. This file name
4044 is made by appending @file{.salias} to the source file name.
4047 @opindex fdump-tree-alias
4048 Dump aliasing information for each function. The file name is made by
4049 appending @file{.alias} to the source file name.
4052 @opindex fdump-tree-ccp
4053 Dump each function after CCP@. The file name is made by appending
4054 @file{.ccp} to the source file name.
4057 @opindex fdump-tree-storeccp
4058 Dump each function after STORE-CCP. The file name is made by appending
4059 @file{.storeccp} to the source file name.
4062 @opindex fdump-tree-pre
4063 Dump trees after partial redundancy elimination. The file name is made
4064 by appending @file{.pre} to the source file name.
4067 @opindex fdump-tree-fre
4068 Dump trees after full redundancy elimination. The file name is made
4069 by appending @file{.fre} to the source file name.
4072 @opindex fdump-tree-copyprop
4073 Dump trees after copy propagation. The file name is made
4074 by appending @file{.copyprop} to the source file name.
4076 @item store_copyprop
4077 @opindex fdump-tree-store_copyprop
4078 Dump trees after store copy-propagation. The file name is made
4079 by appending @file{.store_copyprop} to the source file name.
4082 @opindex fdump-tree-dce
4083 Dump each function after dead code elimination. The file name is made by
4084 appending @file{.dce} to the source file name.
4087 @opindex fdump-tree-mudflap
4088 Dump each function after adding mudflap instrumentation. The file name is
4089 made by appending @file{.mudflap} to the source file name.
4092 @opindex fdump-tree-sra
4093 Dump each function after performing scalar replacement of aggregates. The
4094 file name is made by appending @file{.sra} to the source file name.
4097 @opindex fdump-tree-sink
4098 Dump each function after performing code sinking. The file name is made
4099 by appending @file{.sink} to the source file name.
4102 @opindex fdump-tree-dom
4103 Dump each function after applying dominator tree optimizations. The file
4104 name is made by appending @file{.dom} to the source file name.
4107 @opindex fdump-tree-dse
4108 Dump each function after applying dead store elimination. The file
4109 name is made by appending @file{.dse} to the source file name.
4112 @opindex fdump-tree-phiopt
4113 Dump each function after optimizing PHI nodes into straightline code. The file
4114 name is made by appending @file{.phiopt} to the source file name.
4117 @opindex fdump-tree-forwprop
4118 Dump each function after forward propagating single use variables. The file
4119 name is made by appending @file{.forwprop} to the source file name.
4122 @opindex fdump-tree-copyrename
4123 Dump each function after applying the copy rename optimization. The file
4124 name is made by appending @file{.copyrename} to the source file name.
4127 @opindex fdump-tree-nrv
4128 Dump each function after applying the named return value optimization on
4129 generic trees. The file name is made by appending @file{.nrv} to the source
4133 @opindex fdump-tree-vect
4134 Dump each function after applying vectorization of loops. The file name is
4135 made by appending @file{.vect} to the source file name.
4138 @opindex fdump-tree-vrp
4139 Dump each function after Value Range Propagation (VRP). The file name
4140 is made by appending @file{.vrp} to the source file name.
4143 @opindex fdump-tree-all
4144 Enable all the available tree dumps with the flags provided in this option.
4147 @item -ftree-vectorizer-verbose=@var{n}
4148 @opindex ftree-vectorizer-verbose
4149 This option controls the amount of debugging output the vectorizer prints.
4150 This information is written to standard error, unless @option{-fdump-tree-all}
4151 or @option{-fdump-tree-vect} is specified, in which case it is output to the
4152 usual dump listing file, @file{.vect}.
4154 @item -frandom-seed=@var{string}
4155 @opindex frandom-string
4156 This option provides a seed that GCC uses when it would otherwise use
4157 random numbers. It is used to generate certain symbol names
4158 that have to be different in every compiled file. It is also used to
4159 place unique stamps in coverage data files and the object files that
4160 produce them. You can use the @option{-frandom-seed} option to produce
4161 reproducibly identical object files.
4163 The @var{string} should be different for every file you compile.
4165 @item -fsched-verbose=@var{n}
4166 @opindex fsched-verbose
4167 On targets that use instruction scheduling, this option controls the
4168 amount of debugging output the scheduler prints. This information is
4169 written to standard error, unless @option{-dS} or @option{-dR} is
4170 specified, in which case it is output to the usual dump
4171 listing file, @file{.sched} or @file{.sched2} respectively. However
4172 for @var{n} greater than nine, the output is always printed to standard
4175 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4176 same information as @option{-dRS}. For @var{n} greater than one, it
4177 also output basic block probabilities, detailed ready list information
4178 and unit/insn info. For @var{n} greater than two, it includes RTL
4179 at abort point, control-flow and regions info. And for @var{n} over
4180 four, @option{-fsched-verbose} also includes dependence info.
4184 Store the usual ``temporary'' intermediate files permanently; place them
4185 in the current directory and name them based on the source file. Thus,
4186 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4187 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4188 preprocessed @file{foo.i} output file even though the compiler now
4189 normally uses an integrated preprocessor.
4191 When used in combination with the @option{-x} command line option,
4192 @option{-save-temps} is sensible enough to avoid over writing an
4193 input source file with the same extension as an intermediate file.
4194 The corresponding intermediate file may be obtained by renaming the
4195 source file before using @option{-save-temps}.
4199 Report the CPU time taken by each subprocess in the compilation
4200 sequence. For C source files, this is the compiler proper and assembler
4201 (plus the linker if linking is done). The output looks like this:
4208 The first number on each line is the ``user time'', that is time spent
4209 executing the program itself. The second number is ``system time'',
4210 time spent executing operating system routines on behalf of the program.
4211 Both numbers are in seconds.
4213 @item -fvar-tracking
4214 @opindex fvar-tracking
4215 Run variable tracking pass. It computes where variables are stored at each
4216 position in code. Better debugging information is then generated
4217 (if the debugging information format supports this information).
4219 It is enabled by default when compiling with optimization (@option{-Os},
4220 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
4221 the debug info format supports it.
4223 @item -print-file-name=@var{library}
4224 @opindex print-file-name
4225 Print the full absolute name of the library file @var{library} that
4226 would be used when linking---and don't do anything else. With this
4227 option, GCC does not compile or link anything; it just prints the
4230 @item -print-multi-directory
4231 @opindex print-multi-directory
4232 Print the directory name corresponding to the multilib selected by any
4233 other switches present in the command line. This directory is supposed
4234 to exist in @env{GCC_EXEC_PREFIX}.
4236 @item -print-multi-lib
4237 @opindex print-multi-lib
4238 Print the mapping from multilib directory names to compiler switches
4239 that enable them. The directory name is separated from the switches by
4240 @samp{;}, and each switch starts with an @samp{@@} instead of the
4241 @samp{-}, without spaces between multiple switches. This is supposed to
4242 ease shell-processing.
4244 @item -print-prog-name=@var{program}
4245 @opindex print-prog-name
4246 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
4248 @item -print-libgcc-file-name
4249 @opindex print-libgcc-file-name
4250 Same as @option{-print-file-name=libgcc.a}.
4252 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
4253 but you do want to link with @file{libgcc.a}. You can do
4256 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
4259 @item -print-search-dirs
4260 @opindex print-search-dirs
4261 Print the name of the configured installation directory and a list of
4262 program and library directories @command{gcc} will search---and don't do anything else.
4264 This is useful when @command{gcc} prints the error message
4265 @samp{installation problem, cannot exec cpp0: No such file or directory}.
4266 To resolve this you either need to put @file{cpp0} and the other compiler
4267 components where @command{gcc} expects to find them, or you can set the environment
4268 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
4269 Don't forget the trailing @samp{/}.
4270 @xref{Environment Variables}.
4273 @opindex dumpmachine
4274 Print the compiler's target machine (for example,
4275 @samp{i686-pc-linux-gnu})---and don't do anything else.
4278 @opindex dumpversion
4279 Print the compiler version (for example, @samp{3.0})---and don't do
4284 Print the compiler's built-in specs---and don't do anything else. (This
4285 is used when GCC itself is being built.) @xref{Spec Files}.
4287 @item -feliminate-unused-debug-types
4288 @opindex feliminate-unused-debug-types
4289 Normally, when producing DWARF2 output, GCC will emit debugging
4290 information for all types declared in a compilation
4291 unit, regardless of whether or not they are actually used
4292 in that compilation unit. Sometimes this is useful, such as
4293 if, in the debugger, you want to cast a value to a type that is
4294 not actually used in your program (but is declared). More often,
4295 however, this results in a significant amount of wasted space.
4296 With this option, GCC will avoid producing debug symbol output
4297 for types that are nowhere used in the source file being compiled.
4300 @node Optimize Options
4301 @section Options That Control Optimization
4302 @cindex optimize options
4303 @cindex options, optimization
4305 These options control various sorts of optimizations.
4307 Without any optimization option, the compiler's goal is to reduce the
4308 cost of compilation and to make debugging produce the expected
4309 results. Statements are independent: if you stop the program with a
4310 breakpoint between statements, you can then assign a new value to any
4311 variable or change the program counter to any other statement in the
4312 function and get exactly the results you would expect from the source
4315 Turning on optimization flags makes the compiler attempt to improve
4316 the performance and/or code size at the expense of compilation time
4317 and possibly the ability to debug the program.
4319 The compiler performs optimization based on the knowledge it has of
4320 the program. Optimization levels @option{-O2} and above, in
4321 particular, enable @emph{unit-at-a-time} mode, which allows the
4322 compiler to consider information gained from later functions in
4323 the file when compiling a function. Compiling multiple files at
4324 once to a single output file in @emph{unit-at-a-time} mode allows
4325 the compiler to use information gained from all of the files when
4326 compiling each of them.
4328 Not all optimizations are controlled directly by a flag. Only
4329 optimizations that have a flag are listed.
4336 Optimize. Optimizing compilation takes somewhat more time, and a lot
4337 more memory for a large function.
4339 With @option{-O}, the compiler tries to reduce code size and execution
4340 time, without performing any optimizations that take a great deal of
4343 @option{-O} turns on the following optimization flags:
4344 @gccoptlist{-fdefer-pop @gol
4345 -fdelayed-branch @gol
4346 -fguess-branch-probability @gol
4347 -fcprop-registers @gol
4348 -floop-optimize @gol
4349 -fif-conversion @gol
4350 -fif-conversion2 @gol
4353 -ftree-dominator-opts @gol
4358 -ftree-copyrename @gol
4363 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4364 where doing so does not interfere with debugging.
4368 Optimize even more. GCC performs nearly all supported optimizations
4369 that do not involve a space-speed tradeoff. The compiler does not
4370 perform loop unrolling or function inlining when you specify @option{-O2}.
4371 As compared to @option{-O}, this option increases both compilation time
4372 and the performance of the generated code.
4374 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4375 also turns on the following optimization flags:
4376 @gccoptlist{-fthread-jumps @gol
4378 -foptimize-sibling-calls @gol
4379 -fcse-follow-jumps -fcse-skip-blocks @gol
4380 -fgcse -fgcse-lm @gol
4381 -fexpensive-optimizations @gol
4382 -fstrength-reduce @gol
4383 -frerun-cse-after-loop -frerun-loop-opt @gol
4386 -fschedule-insns -fschedule-insns2 @gol
4387 -fsched-interblock -fsched-spec @gol
4389 -fstrict-aliasing @gol
4390 -fdelete-null-pointer-checks @gol
4391 -freorder-blocks -freorder-functions @gol
4392 -funit-at-a-time @gol
4393 -falign-functions -falign-jumps @gol
4394 -falign-loops -falign-labels @gol
4398 Please note the warning under @option{-fgcse} about
4399 invoking @option{-O2} on programs that use computed gotos.
4403 Optimize yet more. @option{-O3} turns on all optimizations specified by
4404 @option{-O2} and also turns on the @option{-finline-functions},
4405 @option{-funswitch-loops} and @option{-fgcse-after-reload} options.
4409 Do not optimize. This is the default.
4413 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4414 do not typically increase code size. It also performs further
4415 optimizations designed to reduce code size.
4417 @option{-Os} disables the following optimization flags:
4418 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4419 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
4420 -fprefetch-loop-arrays -ftree-vect-loop-version}
4422 If you use multiple @option{-O} options, with or without level numbers,
4423 the last such option is the one that is effective.
4426 Options of the form @option{-f@var{flag}} specify machine-independent
4427 flags. Most flags have both positive and negative forms; the negative
4428 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4429 below, only one of the forms is listed---the one you typically will
4430 use. You can figure out the other form by either removing @samp{no-}
4433 The following options control specific optimizations. They are either
4434 activated by @option{-O} options or are related to ones that are. You
4435 can use the following flags in the rare cases when ``fine-tuning'' of
4436 optimizations to be performed is desired.
4439 @item -fno-default-inline
4440 @opindex fno-default-inline
4441 Do not make member functions inline by default merely because they are
4442 defined inside the class scope (C++ only). Otherwise, when you specify
4443 @w{@option{-O}}, member functions defined inside class scope are compiled
4444 inline by default; i.e., you don't need to add @samp{inline} in front of
4445 the member function name.
4447 @item -fno-defer-pop
4448 @opindex fno-defer-pop
4449 Always pop the arguments to each function call as soon as that function
4450 returns. For machines which must pop arguments after a function call,
4451 the compiler normally lets arguments accumulate on the stack for several
4452 function calls and pops them all at once.
4454 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4458 Force memory operands to be copied into registers before doing
4459 arithmetic on them. This produces better code by making all memory
4460 references potential common subexpressions. When they are not common
4461 subexpressions, instruction combination should eliminate the separate
4462 register-load. This option is now a nop and will be removed in 4.2.
4465 @opindex fforce-addr
4466 Force memory address constants to be copied into registers before
4467 doing arithmetic on them.
4469 @item -fomit-frame-pointer
4470 @opindex fomit-frame-pointer
4471 Don't keep the frame pointer in a register for functions that
4472 don't need one. This avoids the instructions to save, set up and
4473 restore frame pointers; it also makes an extra register available
4474 in many functions. @strong{It also makes debugging impossible on
4477 On some machines, such as the VAX, this flag has no effect, because
4478 the standard calling sequence automatically handles the frame pointer
4479 and nothing is saved by pretending it doesn't exist. The
4480 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4481 whether a target machine supports this flag. @xref{Registers,,Register
4482 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4484 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4486 @item -foptimize-sibling-calls
4487 @opindex foptimize-sibling-calls
4488 Optimize sibling and tail recursive calls.
4490 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4494 Don't pay attention to the @code{inline} keyword. Normally this option
4495 is used to keep the compiler from expanding any functions inline.
4496 Note that if you are not optimizing, no functions can be expanded inline.
4498 @item -finline-functions
4499 @opindex finline-functions
4500 Integrate all simple functions into their callers. The compiler
4501 heuristically decides which functions are simple enough to be worth
4502 integrating in this way.
4504 If all calls to a given function are integrated, and the function is
4505 declared @code{static}, then the function is normally not output as
4506 assembler code in its own right.
4508 Enabled at level @option{-O3}.
4510 @item -finline-functions-called-once
4511 @opindex finline-functions-called-once
4512 Consider all @code{static} functions called once for inlining into their
4513 caller even if they are not marked @code{inline}. If a call to a given
4514 function is integrated, then the function is not output as assembler code
4517 Enabled if @option{-funit-at-a-time} is enabled.
4519 @item -fearly-inlining
4520 @opindex fearly-inlining
4521 Inline functions marked by @code{always_inline} and functions whose body seems
4522 smaller than the function call overhead early before doing
4523 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
4524 makes profiling significantly cheaper and usually inlining faster on programs
4525 having large chains of nested wrapper functions.
4529 @item -finline-limit=@var{n}
4530 @opindex finline-limit
4531 By default, GCC limits the size of functions that can be inlined. This flag
4532 allows the control of this limit for functions that are explicitly marked as
4533 inline (i.e., marked with the inline keyword or defined within the class
4534 definition in c++). @var{n} is the size of functions that can be inlined in
4535 number of pseudo instructions (not counting parameter handling). The default
4536 value of @var{n} is 600.
4537 Increasing this value can result in more inlined code at
4538 the cost of compilation time and memory consumption. Decreasing usually makes
4539 the compilation faster and less code will be inlined (which presumably
4540 means slower programs). This option is particularly useful for programs that
4541 use inlining heavily such as those based on recursive templates with C++.
4543 Inlining is actually controlled by a number of parameters, which may be
4544 specified individually by using @option{--param @var{name}=@var{value}}.
4545 The @option{-finline-limit=@var{n}} option sets some of these parameters
4549 @item max-inline-insns-single
4550 is set to @var{n}/2.
4551 @item max-inline-insns-auto
4552 is set to @var{n}/2.
4553 @item min-inline-insns
4554 is set to 130 or @var{n}/4, whichever is smaller.
4555 @item max-inline-insns-rtl
4559 See below for a documentation of the individual
4560 parameters controlling inlining.
4562 @emph{Note:} pseudo instruction represents, in this particular context, an
4563 abstract measurement of function's size. In no way does it represent a count
4564 of assembly instructions and as such its exact meaning might change from one
4565 release to an another.
4567 @item -fkeep-inline-functions
4568 @opindex fkeep-inline-functions
4569 In C, emit @code{static} functions that are declared @code{inline}
4570 into the object file, even if the function has been inlined into all
4571 of its callers. This switch does not affect functions using the
4572 @code{extern inline} extension in GNU C@. In C++, emit any and all
4573 inline functions into the object file.
4575 @item -fkeep-static-consts
4576 @opindex fkeep-static-consts
4577 Emit variables declared @code{static const} when optimization isn't turned
4578 on, even if the variables aren't referenced.
4580 GCC enables this option by default. If you want to force the compiler to
4581 check if the variable was referenced, regardless of whether or not
4582 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4584 @item -fmerge-constants
4585 Attempt to merge identical constants (string constants and floating point
4586 constants) across compilation units.
4588 This option is the default for optimized compilation if the assembler and
4589 linker support it. Use @option{-fno-merge-constants} to inhibit this
4592 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4594 @item -fmerge-all-constants
4595 Attempt to merge identical constants and identical variables.
4597 This option implies @option{-fmerge-constants}. In addition to
4598 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4599 arrays or initialized constant variables with integral or floating point
4600 types. Languages like C or C++ require each non-automatic variable to
4601 have distinct location, so using this option will result in non-conforming
4604 @item -fmodulo-sched
4605 @opindex fmodulo-sched
4606 Perform swing modulo scheduling immediately before the first scheduling
4607 pass. This pass looks at innermost loops and reorders their
4608 instructions by overlapping different iterations.
4610 @item -fno-branch-count-reg
4611 @opindex fno-branch-count-reg
4612 Do not use ``decrement and branch'' instructions on a count register,
4613 but instead generate a sequence of instructions that decrement a
4614 register, compare it against zero, then branch based upon the result.
4615 This option is only meaningful on architectures that support such
4616 instructions, which include x86, PowerPC, IA-64 and S/390.
4618 The default is @option{-fbranch-count-reg}, enabled when
4619 @option{-fstrength-reduce} is enabled.
4621 @item -fno-function-cse
4622 @opindex fno-function-cse
4623 Do not put function addresses in registers; make each instruction that
4624 calls a constant function contain the function's address explicitly.
4626 This option results in less efficient code, but some strange hacks
4627 that alter the assembler output may be confused by the optimizations
4628 performed when this option is not used.
4630 The default is @option{-ffunction-cse}
4632 @item -fno-zero-initialized-in-bss
4633 @opindex fno-zero-initialized-in-bss
4634 If the target supports a BSS section, GCC by default puts variables that
4635 are initialized to zero into BSS@. This can save space in the resulting
4638 This option turns off this behavior because some programs explicitly
4639 rely on variables going to the data section. E.g., so that the
4640 resulting executable can find the beginning of that section and/or make
4641 assumptions based on that.
4643 The default is @option{-fzero-initialized-in-bss}.
4645 @item -fbounds-check
4646 @opindex fbounds-check
4647 For front-ends that support it, generate additional code to check that
4648 indices used to access arrays are within the declared range. This is
4649 currently only supported by the Java and Fortran front-ends, where
4650 this option defaults to true and false respectively.
4652 @item -fmudflap -fmudflapth -fmudflapir
4656 @cindex bounds checking
4658 For front-ends that support it (C and C++), instrument all risky
4659 pointer/array dereferencing operations, some standard library
4660 string/heap functions, and some other associated constructs with
4661 range/validity tests. Modules so instrumented should be immune to
4662 buffer overflows, invalid heap use, and some other classes of C/C++
4663 programming errors. The instrumentation relies on a separate runtime
4664 library (@file{libmudflap}), which will be linked into a program if
4665 @option{-fmudflap} is given at link time. Run-time behavior of the
4666 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4667 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4670 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4671 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4672 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4673 instrumentation should ignore pointer reads. This produces less
4674 instrumentation (and therefore faster execution) and still provides
4675 some protection against outright memory corrupting writes, but allows
4676 erroneously read data to propagate within a program.
4678 @item -fstrength-reduce
4679 @opindex fstrength-reduce
4680 Perform the optimizations of loop strength reduction and
4681 elimination of iteration variables.
4683 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4685 @item -fthread-jumps
4686 @opindex fthread-jumps
4687 Perform optimizations where we check to see if a jump branches to a
4688 location where another comparison subsumed by the first is found. If
4689 so, the first branch is redirected to either the destination of the
4690 second branch or a point immediately following it, depending on whether
4691 the condition is known to be true or false.
4693 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4695 @item -fcse-follow-jumps
4696 @opindex fcse-follow-jumps
4697 In common subexpression elimination, scan through jump instructions
4698 when the target of the jump is not reached by any other path. For
4699 example, when CSE encounters an @code{if} statement with an
4700 @code{else} clause, CSE will follow the jump when the condition
4703 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4705 @item -fcse-skip-blocks
4706 @opindex fcse-skip-blocks
4707 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4708 follow jumps which conditionally skip over blocks. When CSE
4709 encounters a simple @code{if} statement with no else clause,
4710 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4711 body of the @code{if}.
4713 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4715 @item -frerun-cse-after-loop
4716 @opindex frerun-cse-after-loop
4717 Re-run common subexpression elimination after loop optimizations has been
4720 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4722 @item -frerun-loop-opt
4723 @opindex frerun-loop-opt
4724 Run the loop optimizer twice.
4726 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4730 Perform a global common subexpression elimination pass.
4731 This pass also performs global constant and copy propagation.
4733 @emph{Note:} When compiling a program using computed gotos, a GCC
4734 extension, you may get better runtime performance if you disable
4735 the global common subexpression elimination pass by adding
4736 @option{-fno-gcse} to the command line.
4738 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4742 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4743 attempt to move loads which are only killed by stores into themselves. This
4744 allows a loop containing a load/store sequence to be changed to a load outside
4745 the loop, and a copy/store within the loop.
4747 Enabled by default when gcse is enabled.
4751 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4752 global common subexpression elimination. This pass will attempt to move
4753 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4754 loops containing a load/store sequence can be changed to a load before
4755 the loop and a store after the loop.
4757 Not enabled at any optimization level.
4761 When @option{-fgcse-las} is enabled, the global common subexpression
4762 elimination pass eliminates redundant loads that come after stores to the
4763 same memory location (both partial and full redundancies).
4765 Not enabled at any optimization level.
4767 @item -fgcse-after-reload
4768 @opindex fgcse-after-reload
4769 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4770 pass is performed after reload. The purpose of this pass is to cleanup
4773 @item -floop-optimize
4774 @opindex floop-optimize
4775 Perform loop optimizations: move constant expressions out of loops, simplify
4776 exit test conditions and optionally do strength-reduction as well.
4778 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4780 @item -floop-optimize2
4781 @opindex floop-optimize2
4782 Perform loop optimizations using the new loop optimizer. The optimizations
4783 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4786 @item -funsafe-loop-optimizations
4787 @opindex funsafe-loop-optimizations
4788 If given, the loop optimizer will assume that loop indices do not
4789 overflow, and that the loops with nontrivial exit condition are not
4790 infinite. This enables a wider range of loop optimizations even if
4791 the loop optimizer itself cannot prove that these assumptions are valid.
4792 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
4793 if it finds this kind of loop.
4795 @item -fcrossjumping
4796 @opindex crossjumping
4797 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4798 resulting code may or may not perform better than without cross-jumping.
4800 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4802 @item -fif-conversion
4803 @opindex if-conversion
4804 Attempt to transform conditional jumps into branch-less equivalents. This
4805 include use of conditional moves, min, max, set flags and abs instructions, and
4806 some tricks doable by standard arithmetics. The use of conditional execution
4807 on chips where it is available is controlled by @code{if-conversion2}.
4809 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4811 @item -fif-conversion2
4812 @opindex if-conversion2
4813 Use conditional execution (where available) to transform conditional jumps into
4814 branch-less equivalents.
4816 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4818 @item -fdelete-null-pointer-checks
4819 @opindex fdelete-null-pointer-checks
4820 Use global dataflow analysis to identify and eliminate useless checks
4821 for null pointers. The compiler assumes that dereferencing a null
4822 pointer would have halted the program. If a pointer is checked after
4823 it has already been dereferenced, it cannot be null.
4825 In some environments, this assumption is not true, and programs can
4826 safely dereference null pointers. Use
4827 @option{-fno-delete-null-pointer-checks} to disable this optimization
4828 for programs which depend on that behavior.
4830 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4832 @item -fexpensive-optimizations
4833 @opindex fexpensive-optimizations
4834 Perform a number of minor optimizations that are relatively expensive.
4836 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4838 @item -foptimize-register-move
4840 @opindex foptimize-register-move
4842 Attempt to reassign register numbers in move instructions and as
4843 operands of other simple instructions in order to maximize the amount of
4844 register tying. This is especially helpful on machines with two-operand
4847 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4850 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4852 @item -fdelayed-branch
4853 @opindex fdelayed-branch
4854 If supported for the target machine, attempt to reorder instructions
4855 to exploit instruction slots available after delayed branch
4858 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4860 @item -fschedule-insns
4861 @opindex fschedule-insns
4862 If supported for the target machine, attempt to reorder instructions to
4863 eliminate execution stalls due to required data being unavailable. This
4864 helps machines that have slow floating point or memory load instructions
4865 by allowing other instructions to be issued until the result of the load
4866 or floating point instruction is required.
4868 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4870 @item -fschedule-insns2
4871 @opindex fschedule-insns2
4872 Similar to @option{-fschedule-insns}, but requests an additional pass of
4873 instruction scheduling after register allocation has been done. This is
4874 especially useful on machines with a relatively small number of
4875 registers and where memory load instructions take more than one cycle.
4877 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4879 @item -fno-sched-interblock
4880 @opindex fno-sched-interblock
4881 Don't schedule instructions across basic blocks. This is normally
4882 enabled by default when scheduling before register allocation, i.e.@:
4883 with @option{-fschedule-insns} or at @option{-O2} or higher.
4885 @item -fno-sched-spec
4886 @opindex fno-sched-spec
4887 Don't allow speculative motion of non-load instructions. This is normally
4888 enabled by default when scheduling before register allocation, i.e.@:
4889 with @option{-fschedule-insns} or at @option{-O2} or higher.
4891 @item -fsched-spec-load
4892 @opindex fsched-spec-load
4893 Allow speculative motion of some load instructions. This only makes
4894 sense when scheduling before register allocation, i.e.@: with
4895 @option{-fschedule-insns} or at @option{-O2} or higher.
4897 @item -fsched-spec-load-dangerous
4898 @opindex fsched-spec-load-dangerous
4899 Allow speculative motion of more load instructions. This only makes
4900 sense when scheduling before register allocation, i.e.@: with
4901 @option{-fschedule-insns} or at @option{-O2} or higher.
4903 @item -fsched-stalled-insns=@var{n}
4904 @opindex fsched-stalled-insns
4905 Define how many insns (if any) can be moved prematurely from the queue
4906 of stalled insns into the ready list, during the second scheduling pass.
4908 @item -fsched-stalled-insns-dep=@var{n}
4909 @opindex fsched-stalled-insns-dep
4910 Define how many insn groups (cycles) will be examined for a dependency
4911 on a stalled insn that is candidate for premature removal from the queue
4912 of stalled insns. Has an effect only during the second scheduling pass,
4913 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4915 @item -fsched2-use-superblocks
4916 @opindex fsched2-use-superblocks
4917 When scheduling after register allocation, do use superblock scheduling
4918 algorithm. Superblock scheduling allows motion across basic block boundaries
4919 resulting on faster schedules. This option is experimental, as not all machine
4920 descriptions used by GCC model the CPU closely enough to avoid unreliable
4921 results from the algorithm.
4923 This only makes sense when scheduling after register allocation, i.e.@: with
4924 @option{-fschedule-insns2} or at @option{-O2} or higher.
4926 @item -fsched2-use-traces
4927 @opindex fsched2-use-traces
4928 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4929 allocation and additionally perform code duplication in order to increase the
4930 size of superblocks using tracer pass. See @option{-ftracer} for details on
4933 This mode should produce faster but significantly longer programs. Also
4934 without @option{-fbranch-probabilities} the traces constructed may not
4935 match the reality and hurt the performance. This only makes
4936 sense when scheduling after register allocation, i.e.@: with
4937 @option{-fschedule-insns2} or at @option{-O2} or higher.
4939 @item -freschedule-modulo-scheduled-loops
4940 @opindex fscheduling-in-modulo-scheduled-loops
4941 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4942 we may want to prevent the later scheduling passes from changing its schedule, we use this
4943 option to control that.
4945 @item -fcaller-saves
4946 @opindex fcaller-saves
4947 Enable values to be allocated in registers that will be clobbered by
4948 function calls, by emitting extra instructions to save and restore the
4949 registers around such calls. Such allocation is done only when it
4950 seems to result in better code than would otherwise be produced.
4952 This option is always enabled by default on certain machines, usually
4953 those which have no call-preserved registers to use instead.
4955 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4958 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
4959 enabled by default at @option{-O2} and @option{-O3}.
4962 Perform Full Redundancy Elimination (FRE) on trees. The difference
4963 between FRE and PRE is that FRE only considers expressions
4964 that are computed on all paths leading to the redundant computation.
4965 This analysis faster than PRE, though it exposes fewer redundancies.
4966 This flag is enabled by default at @option{-O} and higher.
4968 @item -ftree-copy-prop
4969 Perform copy propagation on trees. This pass eliminates unnecessary
4970 copy operations. This flag is enabled by default at @option{-O} and
4973 @item -ftree-store-copy-prop
4974 Perform copy propagation of memory loads and stores. This pass
4975 eliminates unnecessary copy operations in memory references
4976 (structures, global variables, arrays, etc). This flag is enabled by
4977 default at @option{-O2} and higher.
4980 Perform structural alias analysis on trees. This flag
4981 is enabled by default at @option{-O} and higher.
4984 Perform forward store motion on trees. This flag is
4985 enabled by default at @option{-O} and higher.
4988 Perform sparse conditional constant propagation (CCP) on trees. This
4989 pass only operates on local scalar variables and is enabled by default
4990 at @option{-O} and higher.
4992 @item -ftree-store-ccp
4993 Perform sparse conditional constant propagation (CCP) on trees. This
4994 pass operates on both local scalar variables and memory stores and
4995 loads (global variables, structures, arrays, etc). This flag is
4996 enabled by default at @option{-O2} and higher.
4999 Perform dead code elimination (DCE) on trees. This flag is enabled by
5000 default at @option{-O} and higher.
5002 @item -ftree-dominator-opts
5003 Perform a variety of simple scalar cleanups (constant/copy
5004 propagation, redundancy elimination, range propagation and expression
5005 simplification) based on a dominator tree traversal. This also
5006 performs jump threading (to reduce jumps to jumps). This flag is
5007 enabled by default at @option{-O} and higher.
5010 Perform loop header copying on trees. This is beneficial since it increases
5011 effectiveness of code motion optimizations. It also saves one jump. This flag
5012 is enabled by default at @option{-O} and higher. It is not enabled
5013 for @option{-Os}, since it usually increases code size.
5015 @item -ftree-loop-optimize
5016 Perform loop optimizations on trees. This flag is enabled by default
5017 at @option{-O} and higher.
5019 @item -ftree-loop-linear
5020 Perform linear loop transformations on tree. This flag can improve cache
5021 performance and allow further loop optimizations to take place.
5023 @item -ftree-loop-im
5024 Perform loop invariant motion on trees. This pass moves only invariants that
5025 would be hard to handle at RTL level (function calls, operations that expand to
5026 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5027 operands of conditions that are invariant out of the loop, so that we can use
5028 just trivial invariantness analysis in loop unswitching. The pass also includes
5031 @item -ftree-loop-ivcanon
5032 Create a canonical counter for number of iterations in the loop for that
5033 determining number of iterations requires complicated analysis. Later
5034 optimizations then may determine the number easily. Useful especially
5035 in connection with unrolling.
5038 Perform induction variable optimizations (strength reduction, induction
5039 variable merging and induction variable elimination) on trees.
5042 Perform scalar replacement of aggregates. This pass replaces structure
5043 references with scalars to prevent committing structures to memory too
5044 early. This flag is enabled by default at @option{-O} and higher.
5046 @item -ftree-copyrename
5047 Perform copy renaming on trees. This pass attempts to rename compiler
5048 temporaries to other variables at copy locations, usually resulting in
5049 variable names which more closely resemble the original variables. This flag
5050 is enabled by default at @option{-O} and higher.
5053 Perform temporary expression replacement during the SSA->normal phase. Single
5054 use/single def temporaries are replaced at their use location with their
5055 defining expression. This results in non-GIMPLE code, but gives the expanders
5056 much more complex trees to work on resulting in better RTL generation. This is
5057 enabled by default at @option{-O} and higher.
5060 Perform live range splitting during the SSA->normal phase. Distinct live
5061 ranges of a variable are split into unique variables, allowing for better
5062 optimization later. This is enabled by default at @option{-O} and higher.
5064 @item -ftree-vectorize
5065 Perform loop vectorization on trees.
5067 @item -ftree-vect-loop-version
5068 @opindex ftree-vect-loop-version
5069 Perform loop versioning when doing loop vectorization on trees. When a loop
5070 appears to be vectorizable except that data alignment or data dependence cannot
5071 be determined at compile time then vectorized and non-vectorized versions of
5072 the loop are generated along with runtime checks for alignment or dependence
5073 to control which version is executed. This option is enabled by default
5074 except at level @option{-Os} where it is disabled.
5077 Perform Value Range Propagation on trees. This is similar to the
5078 constant propagation pass, but instead of values, ranges of values are
5079 propagated. This allows the optimizers to remove unnecessary range
5080 checks like array bound checks and null pointer checks. This is
5081 enabled by default at @option{-O2} and higher. Null pointer check
5082 elimination is only done if @option{-fdelete-null-pointer-checks} is
5087 Perform tail duplication to enlarge superblock size. This transformation
5088 simplifies the control flow of the function allowing other optimizations to do
5091 @item -funroll-loops
5092 @opindex funroll-loops
5093 Unroll loops whose number of iterations can be determined at compile
5094 time or upon entry to the loop. @option{-funroll-loops} implies both
5095 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
5096 option makes code larger, and may or may not make it run faster.
5098 @item -funroll-all-loops
5099 @opindex funroll-all-loops
5100 Unroll all loops, even if their number of iterations is uncertain when
5101 the loop is entered. This usually makes programs run more slowly.
5102 @option{-funroll-all-loops} implies the same options as
5103 @option{-funroll-loops},
5105 @item -fsplit-ivs-in-unroller
5106 @opindex -fsplit-ivs-in-unroller
5107 Enables expressing of values of induction variables in later iterations
5108 of the unrolled loop using the value in the first iteration. This breaks
5109 long dependency chains, thus improving efficiency of the scheduling passes.
5111 Combination of @option{-fweb} and CSE is often sufficient to obtain the
5112 same effect. However in cases the loop body is more complicated than
5113 a single basic block, this is not reliable. It also does not work at all
5114 on some of the architectures due to restrictions in the CSE pass.
5116 This optimization is enabled by default.
5118 @item -fvariable-expansion-in-unroller
5119 @opindex -fvariable-expansion-in-unroller
5120 With this option, the compiler will create multiple copies of some
5121 local variables when unrolling a loop which can result in superior code.
5123 @item -fprefetch-loop-arrays
5124 @opindex fprefetch-loop-arrays
5125 If supported by the target machine, generate instructions to prefetch
5126 memory to improve the performance of loops that access large arrays.
5128 These options may generate better or worse code; results are highly
5129 dependent on the structure of loops within the source code.
5132 @itemx -fno-peephole2
5133 @opindex fno-peephole
5134 @opindex fno-peephole2
5135 Disable any machine-specific peephole optimizations. The difference
5136 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
5137 are implemented in the compiler; some targets use one, some use the
5138 other, a few use both.
5140 @option{-fpeephole} is enabled by default.
5141 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5143 @item -fno-guess-branch-probability
5144 @opindex fno-guess-branch-probability
5145 Do not guess branch probabilities using heuristics.
5147 GCC will use heuristics to guess branch probabilities if they are
5148 not provided by profiling feedback (@option{-fprofile-arcs}). These
5149 heuristics are based on the control flow graph. If some branch probabilities
5150 are specified by @samp{__builtin_expect}, then the heuristics will be
5151 used to guess branch probabilities for the rest of the control flow graph,
5152 taking the @samp{__builtin_expect} info into account. The interactions
5153 between the heuristics and @samp{__builtin_expect} can be complex, and in
5154 some cases, it may be useful to disable the heuristics so that the effects
5155 of @samp{__builtin_expect} are easier to understand.
5157 The default is @option{-fguess-branch-probability} at levels
5158 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5160 @item -freorder-blocks
5161 @opindex freorder-blocks
5162 Reorder basic blocks in the compiled function in order to reduce number of
5163 taken branches and improve code locality.
5165 Enabled at levels @option{-O2}, @option{-O3}.
5167 @item -freorder-blocks-and-partition
5168 @opindex freorder-blocks-and-partition
5169 In addition to reordering basic blocks in the compiled function, in order
5170 to reduce number of taken branches, partitions hot and cold basic blocks
5171 into separate sections of the assembly and .o files, to improve
5172 paging and cache locality performance.
5174 This optimization is automatically turned off in the presence of
5175 exception handling, for linkonce sections, for functions with a user-defined
5176 section attribute and on any architecture that does not support named
5179 @item -freorder-functions
5180 @opindex freorder-functions
5181 Reorder functions in the object file in order to
5182 improve code locality. This is implemented by using special
5183 subsections @code{.text.hot} for most frequently executed functions and
5184 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
5185 the linker so object file format must support named sections and linker must
5186 place them in a reasonable way.
5188 Also profile feedback must be available in to make this option effective. See
5189 @option{-fprofile-arcs} for details.
5191 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5193 @item -fstrict-aliasing
5194 @opindex fstrict-aliasing
5195 Allows the compiler to assume the strictest aliasing rules applicable to
5196 the language being compiled. For C (and C++), this activates
5197 optimizations based on the type of expressions. In particular, an
5198 object of one type is assumed never to reside at the same address as an
5199 object of a different type, unless the types are almost the same. For
5200 example, an @code{unsigned int} can alias an @code{int}, but not a
5201 @code{void*} or a @code{double}. A character type may alias any other
5204 Pay special attention to code like this:
5217 The practice of reading from a different union member than the one most
5218 recently written to (called ``type-punning'') is common. Even with
5219 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
5220 is accessed through the union type. So, the code above will work as
5221 expected. However, this code might not:
5232 Every language that wishes to perform language-specific alias analysis
5233 should define a function that computes, given an @code{tree}
5234 node, an alias set for the node. Nodes in different alias sets are not
5235 allowed to alias. For an example, see the C front-end function
5236 @code{c_get_alias_set}.
5238 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5240 @item -falign-functions
5241 @itemx -falign-functions=@var{n}
5242 @opindex falign-functions
5243 Align the start of functions to the next power-of-two greater than
5244 @var{n}, skipping up to @var{n} bytes. For instance,
5245 @option{-falign-functions=32} aligns functions to the next 32-byte
5246 boundary, but @option{-falign-functions=24} would align to the next
5247 32-byte boundary only if this can be done by skipping 23 bytes or less.
5249 @option{-fno-align-functions} and @option{-falign-functions=1} are
5250 equivalent and mean that functions will not be aligned.
5252 Some assemblers only support this flag when @var{n} is a power of two;
5253 in that case, it is rounded up.
5255 If @var{n} is not specified or is zero, use a machine-dependent default.
5257 Enabled at levels @option{-O2}, @option{-O3}.
5259 @item -falign-labels
5260 @itemx -falign-labels=@var{n}
5261 @opindex falign-labels
5262 Align all branch targets to a power-of-two boundary, skipping up to
5263 @var{n} bytes like @option{-falign-functions}. This option can easily
5264 make code slower, because it must insert dummy operations for when the
5265 branch target is reached in the usual flow of the code.
5267 @option{-fno-align-labels} and @option{-falign-labels=1} are
5268 equivalent and mean that labels will not be aligned.
5270 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
5271 are greater than this value, then their values are used instead.
5273 If @var{n} is not specified or is zero, use a machine-dependent default
5274 which is very likely to be @samp{1}, meaning no alignment.
5276 Enabled at levels @option{-O2}, @option{-O3}.
5279 @itemx -falign-loops=@var{n}
5280 @opindex falign-loops
5281 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
5282 like @option{-falign-functions}. The hope is that the loop will be
5283 executed many times, which will make up for any execution of the dummy
5286 @option{-fno-align-loops} and @option{-falign-loops=1} are
5287 equivalent and mean that loops will not be aligned.
5289 If @var{n} is not specified or is zero, use a machine-dependent default.
5291 Enabled at levels @option{-O2}, @option{-O3}.
5294 @itemx -falign-jumps=@var{n}
5295 @opindex falign-jumps
5296 Align branch targets to a power-of-two boundary, for branch targets
5297 where the targets can only be reached by jumping, skipping up to @var{n}
5298 bytes like @option{-falign-functions}. In this case, no dummy operations
5301 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
5302 equivalent and mean that loops will not be aligned.
5304 If @var{n} is not specified or is zero, use a machine-dependent default.
5306 Enabled at levels @option{-O2}, @option{-O3}.
5308 @item -funit-at-a-time
5309 @opindex funit-at-a-time
5310 Parse the whole compilation unit before starting to produce code.
5311 This allows some extra optimizations to take place but consumes
5312 more memory (in general). There are some compatibility issues
5313 with @emph{unit-at-at-time} mode:
5316 enabling @emph{unit-at-a-time} mode may change the order
5317 in which functions, variables, and top-level @code{asm} statements
5318 are emitted, and will likely break code relying on some particular
5319 ordering. The majority of such top-level @code{asm} statements,
5320 though, can be replaced by @code{section} attributes.
5323 @emph{unit-at-a-time} mode removes unreferenced static variables
5324 and functions. This may result in undefined references
5325 when an @code{asm} statement refers directly to variables or functions
5326 that are otherwise unused. In that case either the variable/function
5327 shall be listed as an operand of the @code{asm} statement operand or,
5328 in the case of top-level @code{asm} statements the attribute @code{used}
5329 shall be used on the declaration.
5332 Static functions now can use non-standard passing conventions that
5333 may break @code{asm} statements calling functions directly. Again,
5334 attribute @code{used} will prevent this behavior.
5337 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
5338 but this scheme may not be supported by future releases of GCC@.
5340 Enabled at levels @option{-O2}, @option{-O3}.
5344 Constructs webs as commonly used for register allocation purposes and assign
5345 each web individual pseudo register. This allows the register allocation pass
5346 to operate on pseudos directly, but also strengthens several other optimization
5347 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
5348 however, make debugging impossible, since variables will no longer stay in a
5351 Enabled by default with @option{-funroll-loops}.
5353 @item -fwhole-program
5354 @opindex fwhole-program
5355 Assume that the current compilation unit represents whole program being
5356 compiled. All public functions and variables with the exception of @code{main}
5357 and those merged by attribute @code{externally_visible} become static functions
5358 and in a affect gets more aggressively optimized by interprocedural optimizers.
5359 While this option is equivalent to proper use of @code{static} keyword for
5360 programs consisting of single file, in combination with option
5361 @option{--combine} this flag can be used to compile most of smaller scale C
5362 programs since the functions and variables become local for the whole combined
5363 compilation unit, not for the single source file itself.
5366 @item -fno-cprop-registers
5367 @opindex fno-cprop-registers
5368 After register allocation and post-register allocation instruction splitting,
5369 we perform a copy-propagation pass to try to reduce scheduling dependencies
5370 and occasionally eliminate the copy.
5372 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5374 @item -fprofile-generate
5375 @opindex fprofile-generate
5377 Enable options usually used for instrumenting application to produce
5378 profile useful for later recompilation with profile feedback based
5379 optimization. You must use @option{-fprofile-generate} both when
5380 compiling and when linking your program.
5382 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
5385 @opindex fprofile-use
5386 Enable profile feedback directed optimizations, and optimizations
5387 generally profitable only with profile feedback available.
5389 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
5390 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer},
5391 @code{-fno-loop-optimize}.
5395 The following options control compiler behavior regarding floating
5396 point arithmetic. These options trade off between speed and
5397 correctness. All must be specifically enabled.
5401 @opindex ffloat-store
5402 Do not store floating point variables in registers, and inhibit other
5403 options that might change whether a floating point value is taken from a
5406 @cindex floating point precision
5407 This option prevents undesirable excess precision on machines such as
5408 the 68000 where the floating registers (of the 68881) keep more
5409 precision than a @code{double} is supposed to have. Similarly for the
5410 x86 architecture. For most programs, the excess precision does only
5411 good, but a few programs rely on the precise definition of IEEE floating
5412 point. Use @option{-ffloat-store} for such programs, after modifying
5413 them to store all pertinent intermediate computations into variables.
5417 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5418 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5419 @option{-fno-rounding-math}, @option{-fno-signaling-nans}
5420 and @option{fcx-limited-range}.
5422 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5424 This option should never be turned on by any @option{-O} option since
5425 it can result in incorrect output for programs which depend on
5426 an exact implementation of IEEE or ISO rules/specifications for
5429 @item -fno-math-errno
5430 @opindex fno-math-errno
5431 Do not set ERRNO after calling math functions that are executed
5432 with a single instruction, e.g., sqrt. A program that relies on
5433 IEEE exceptions for math error handling may want to use this flag
5434 for speed while maintaining IEEE arithmetic compatibility.
5436 This option should never be turned on by any @option{-O} option since
5437 it can result in incorrect output for programs which depend on
5438 an exact implementation of IEEE or ISO rules/specifications for
5441 The default is @option{-fmath-errno}.
5443 On Darwin systems, the math library never sets @code{errno}. There is therefore
5444 no reason for the compiler to consider the possibility that it might,
5445 and @option{-fno-math-errno} is the default.
5447 @item -funsafe-math-optimizations
5448 @opindex funsafe-math-optimizations
5449 Allow optimizations for floating-point arithmetic that (a) assume
5450 that arguments and results are valid and (b) may violate IEEE or
5451 ANSI standards. When used at link-time, it may include libraries
5452 or startup files that change the default FPU control word or other
5453 similar optimizations.
5455 This option should never be turned on by any @option{-O} option since
5456 it can result in incorrect output for programs which depend on
5457 an exact implementation of IEEE or ISO rules/specifications for
5460 The default is @option{-fno-unsafe-math-optimizations}.
5462 @item -ffinite-math-only
5463 @opindex ffinite-math-only
5464 Allow optimizations for floating-point arithmetic that assume
5465 that arguments and results are not NaNs or +-Infs.
5467 This option should never be turned on by any @option{-O} option since
5468 it can result in incorrect output for programs which depend on
5469 an exact implementation of IEEE or ISO rules/specifications.
5471 The default is @option{-fno-finite-math-only}.
5473 @item -fno-trapping-math
5474 @opindex fno-trapping-math
5475 Compile code assuming that floating-point operations cannot generate
5476 user-visible traps. These traps include division by zero, overflow,
5477 underflow, inexact result and invalid operation. This option implies
5478 @option{-fno-signaling-nans}. Setting this option may allow faster
5479 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5481 This option should never be turned on by any @option{-O} option since
5482 it can result in incorrect output for programs which depend on
5483 an exact implementation of IEEE or ISO rules/specifications for
5486 The default is @option{-ftrapping-math}.
5488 @item -frounding-math
5489 @opindex frounding-math
5490 Disable transformations and optimizations that assume default floating
5491 point rounding behavior. This is round-to-zero for all floating point
5492 to integer conversions, and round-to-nearest for all other arithmetic
5493 truncations. This option should be specified for programs that change
5494 the FP rounding mode dynamically, or that may be executed with a
5495 non-default rounding mode. This option disables constant folding of
5496 floating point expressions at compile-time (which may be affected by
5497 rounding mode) and arithmetic transformations that are unsafe in the
5498 presence of sign-dependent rounding modes.
5500 The default is @option{-fno-rounding-math}.
5502 This option is experimental and does not currently guarantee to
5503 disable all GCC optimizations that are affected by rounding mode.
5504 Future versions of GCC may provide finer control of this setting
5505 using C99's @code{FENV_ACCESS} pragma. This command line option
5506 will be used to specify the default state for @code{FENV_ACCESS}.
5508 @item -fsignaling-nans
5509 @opindex fsignaling-nans
5510 Compile code assuming that IEEE signaling NaNs may generate user-visible
5511 traps during floating-point operations. Setting this option disables
5512 optimizations that may change the number of exceptions visible with
5513 signaling NaNs. This option implies @option{-ftrapping-math}.
5515 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5518 The default is @option{-fno-signaling-nans}.
5520 This option is experimental and does not currently guarantee to
5521 disable all GCC optimizations that affect signaling NaN behavior.
5523 @item -fsingle-precision-constant
5524 @opindex fsingle-precision-constant
5525 Treat floating point constant as single precision constant instead of
5526 implicitly converting it to double precision constant.
5528 @item -fcx-limited-range
5529 @itemx -fno-cx-limited-range
5530 @opindex fcx-limited-range
5531 @opindex fno-cx-limited-range
5532 When enabled, this option states that a range reduction step is not
5533 needed when performing complex division. The default is
5534 @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
5536 This option controls the default setting of the ISO C99
5537 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
5542 The following options control optimizations that may improve
5543 performance, but are not enabled by any @option{-O} options. This
5544 section includes experimental options that may produce broken code.
5547 @item -fbranch-probabilities
5548 @opindex fbranch-probabilities
5549 After running a program compiled with @option{-fprofile-arcs}
5550 (@pxref{Debugging Options,, Options for Debugging Your Program or
5551 @command{gcc}}), you can compile it a second time using
5552 @option{-fbranch-probabilities}, to improve optimizations based on
5553 the number of times each branch was taken. When the program
5554 compiled with @option{-fprofile-arcs} exits it saves arc execution
5555 counts to a file called @file{@var{sourcename}.gcda} for each source
5556 file The information in this data file is very dependent on the
5557 structure of the generated code, so you must use the same source code
5558 and the same optimization options for both compilations.
5560 With @option{-fbranch-probabilities}, GCC puts a
5561 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5562 These can be used to improve optimization. Currently, they are only
5563 used in one place: in @file{reorg.c}, instead of guessing which path a
5564 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5565 exactly determine which path is taken more often.
5567 @item -fprofile-values
5568 @opindex fprofile-values
5569 If combined with @option{-fprofile-arcs}, it adds code so that some
5570 data about values of expressions in the program is gathered.
5572 With @option{-fbranch-probabilities}, it reads back the data gathered
5573 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5574 notes to instructions for their later usage in optimizations.
5576 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5580 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5581 a code to gather information about values of expressions.
5583 With @option{-fbranch-probabilities}, it reads back the data gathered
5584 and actually performs the optimizations based on them.
5585 Currently the optimizations include specialization of division operation
5586 using the knowledge about the value of the denominator.
5588 @item -frename-registers
5589 @opindex frename-registers
5590 Attempt to avoid false dependencies in scheduled code by making use
5591 of registers left over after register allocation. This optimization
5592 will most benefit processors with lots of registers. Depending on the
5593 debug information format adopted by the target, however, it can
5594 make debugging impossible, since variables will no longer stay in
5595 a ``home register''.
5597 Enabled by default with @option{-funroll-loops}.
5601 Perform tail duplication to enlarge superblock size. This transformation
5602 simplifies the control flow of the function allowing other optimizations to do
5605 Enabled with @option{-fprofile-use}.
5607 @item -funroll-loops
5608 @opindex funroll-loops
5609 Unroll loops whose number of iterations can be determined at compile time or
5610 upon entry to the loop. @option{-funroll-loops} implies
5611 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
5612 It also turns on complete loop peeling (i.e.@: complete removal of loops with
5613 small constant number of iterations). This option makes code larger, and may
5614 or may not make it run faster.
5616 Enabled with @option{-fprofile-use}.
5618 @item -funroll-all-loops
5619 @opindex funroll-all-loops
5620 Unroll all loops, even if their number of iterations is uncertain when
5621 the loop is entered. This usually makes programs run more slowly.
5622 @option{-funroll-all-loops} implies the same options as
5623 @option{-funroll-loops}.
5626 @opindex fpeel-loops
5627 Peels the loops for that there is enough information that they do not
5628 roll much (from profile feedback). It also turns on complete loop peeling
5629 (i.e.@: complete removal of loops with small constant number of iterations).
5631 Enabled with @option{-fprofile-use}.
5633 @item -fmove-loop-invariants
5634 @opindex fmove-loop-invariants
5635 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5636 at level @option{-O1}
5638 @item -funswitch-loops
5639 @opindex funswitch-loops
5640 Move branches with loop invariant conditions out of the loop, with duplicates
5641 of the loop on both branches (modified according to result of the condition).
5643 @item -fprefetch-loop-arrays
5644 @opindex fprefetch-loop-arrays
5645 If supported by the target machine, generate instructions to prefetch
5646 memory to improve the performance of loops that access large arrays.
5648 Disabled at level @option{-Os}.
5650 @item -ffunction-sections
5651 @itemx -fdata-sections
5652 @opindex ffunction-sections
5653 @opindex fdata-sections
5654 Place each function or data item into its own section in the output
5655 file if the target supports arbitrary sections. The name of the
5656 function or the name of the data item determines the section's name
5659 Use these options on systems where the linker can perform optimizations
5660 to improve locality of reference in the instruction space. Most systems
5661 using the ELF object format and SPARC processors running Solaris 2 have
5662 linkers with such optimizations. AIX may have these optimizations in
5665 Only use these options when there are significant benefits from doing
5666 so. When you specify these options, the assembler and linker will
5667 create larger object and executable files and will also be slower.
5668 You will not be able to use @code{gprof} on all systems if you
5669 specify this option and you may have problems with debugging if
5670 you specify both this option and @option{-g}.
5672 @item -fbranch-target-load-optimize
5673 @opindex fbranch-target-load-optimize
5674 Perform branch target register load optimization before prologue / epilogue
5676 The use of target registers can typically be exposed only during reload,
5677 thus hoisting loads out of loops and doing inter-block scheduling needs
5678 a separate optimization pass.
5680 @item -fbranch-target-load-optimize2
5681 @opindex fbranch-target-load-optimize2
5682 Perform branch target register load optimization after prologue / epilogue
5685 @item -fbtr-bb-exclusive
5686 @opindex fbtr-bb-exclusive
5687 When performing branch target register load optimization, don't reuse
5688 branch target registers in within any basic block.
5690 @item -fstack-protector
5691 Emit extra code to check for buffer overflows, such as stack smashing
5692 attacks. This is done by adding a guard variable to functions with
5693 vulnerable objects. This includes functions that call alloca, and
5694 functions with buffers larger than 8 bytes. The guards are initialized
5695 when a function is entered and then checked when the function exits.
5696 If a guard check fails, an error message is printed and the program exits.
5698 @item -fstack-protector-all
5699 Like @option{-fstack-protector} except that all functions are protected.
5701 @item --param @var{name}=@var{value}
5703 In some places, GCC uses various constants to control the amount of
5704 optimization that is done. For example, GCC will not inline functions
5705 that contain more that a certain number of instructions. You can
5706 control some of these constants on the command-line using the
5707 @option{--param} option.
5709 The names of specific parameters, and the meaning of the values, are
5710 tied to the internals of the compiler, and are subject to change
5711 without notice in future releases.
5713 In each case, the @var{value} is an integer. The allowable choices for
5714 @var{name} are given in the following table:
5717 @item salias-max-implicit-fields
5718 The maximum number of fields in a variable without direct
5719 structure accesses for which structure aliasing will consider trying
5720 to track each field. The default is 5
5722 @item sra-max-structure-size
5723 The maximum structure size, in bytes, at which the scalar replacement
5724 of aggregates (SRA) optimization will perform block copies. The
5725 default value, 0, implies that GCC will select the most appropriate
5728 @item sra-field-structure-ratio
5729 The threshold ratio (as a percentage) between instantiated fields and
5730 the complete structure size. We say that if the ratio of the number
5731 of bytes in instantiated fields to the number of bytes in the complete
5732 structure exceeds this parameter, then block copies are not used. The
5735 @item max-crossjump-edges
5736 The maximum number of incoming edges to consider for crossjumping.
5737 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5738 the number of edges incoming to each block. Increasing values mean
5739 more aggressive optimization, making the compile time increase with
5740 probably small improvement in executable size.
5742 @item min-crossjump-insns
5743 The minimum number of instructions which must be matched at the end
5744 of two blocks before crossjumping will be performed on them. This
5745 value is ignored in the case where all instructions in the block being
5746 crossjumped from are matched. The default value is 5.
5748 @item max-grow-copy-bb-insns
5749 The maximum code size expansion factor when copying basic blocks
5750 instead of jumping. The expansion is relative to a jump instruction.
5751 The default value is 8.
5753 @item max-goto-duplication-insns
5754 The maximum number of instructions to duplicate to a block that jumps
5755 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
5756 passes, GCC factors computed gotos early in the compilation process,
5757 and unfactors them as late as possible. Only computed jumps at the
5758 end of a basic blocks with no more than max-goto-duplication-insns are
5759 unfactored. The default value is 8.
5761 @item max-delay-slot-insn-search
5762 The maximum number of instructions to consider when looking for an
5763 instruction to fill a delay slot. If more than this arbitrary number of
5764 instructions is searched, the time savings from filling the delay slot
5765 will be minimal so stop searching. Increasing values mean more
5766 aggressive optimization, making the compile time increase with probably
5767 small improvement in executable run time.
5769 @item max-delay-slot-live-search
5770 When trying to fill delay slots, the maximum number of instructions to
5771 consider when searching for a block with valid live register
5772 information. Increasing this arbitrarily chosen value means more
5773 aggressive optimization, increasing the compile time. This parameter
5774 should be removed when the delay slot code is rewritten to maintain the
5777 @item max-gcse-memory
5778 The approximate maximum amount of memory that will be allocated in
5779 order to perform the global common subexpression elimination
5780 optimization. If more memory than specified is required, the
5781 optimization will not be done.
5783 @item max-gcse-passes
5784 The maximum number of passes of GCSE to run. The default is 1.
5786 @item max-pending-list-length
5787 The maximum number of pending dependencies scheduling will allow
5788 before flushing the current state and starting over. Large functions
5789 with few branches or calls can create excessively large lists which
5790 needlessly consume memory and resources.
5792 @item max-inline-insns-single
5793 Several parameters control the tree inliner used in gcc.
5794 This number sets the maximum number of instructions (counted in GCC's
5795 internal representation) in a single function that the tree inliner
5796 will consider for inlining. This only affects functions declared
5797 inline and methods implemented in a class declaration (C++).
5798 The default value is 450.
5800 @item max-inline-insns-auto
5801 When you use @option{-finline-functions} (included in @option{-O3}),
5802 a lot of functions that would otherwise not be considered for inlining
5803 by the compiler will be investigated. To those functions, a different
5804 (more restrictive) limit compared to functions declared inline can
5806 The default value is 90.
5808 @item large-function-insns
5809 The limit specifying really large functions. For functions larger than this
5810 limit after inlining inlining is constrained by
5811 @option{--param large-function-growth}. This parameter is useful primarily
5812 to avoid extreme compilation time caused by non-linear algorithms used by the
5814 This parameter is ignored when @option{-funit-at-a-time} is not used.
5815 The default value is 2700.
5817 @item large-function-growth
5818 Specifies maximal growth of large function caused by inlining in percents.
5819 This parameter is ignored when @option{-funit-at-a-time} is not used.
5820 The default value is 100 which limits large function growth to 2.0 times
5823 @item large-unit-insns
5824 The limit specifying large translation unit. Growth caused by inlining of
5825 units larger than this limit is limited by @option{--param inline-unit-growth}.
5826 For small units this might be too tight (consider unit consisting of function A
5827 that is inline and B that just calls A three time. If B is small relative to
5828 A, the growth of unit is 300\% and yet such inlining is very sane. For very
5829 large units consisting of small inlininable functions however the overall unit
5830 growth limit is needed to avoid exponential explosion of code size. Thus for
5831 smaller units, the size is increased to @option{--param large-unit-insns}
5832 before aplying @option{--param inline-unit-growth}. The default is 10000
5834 @item inline-unit-growth
5835 Specifies maximal overall growth of the compilation unit caused by inlining.
5836 This parameter is ignored when @option{-funit-at-a-time} is not used.
5837 The default value is 50 which limits unit growth to 1.5 times the original
5840 @item max-inline-insns-recursive
5841 @itemx max-inline-insns-recursive-auto
5842 Specifies maximum number of instructions out-of-line copy of self recursive inline
5843 function can grow into by performing recursive inlining.
5845 For functions declared inline @option{--param max-inline-insns-recursive} is
5846 taken into acount. For function not declared inline, recursive inlining
5847 happens only when @option{-finline-functions} (included in @option{-O3}) is
5848 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5849 default value is 450.
5851 @item max-inline-recursive-depth
5852 @itemx max-inline-recursive-depth-auto
5853 Specifies maximum recursion depth used by the recursive inlining.
5855 For functions declared inline @option{--param max-inline-recursive-depth} is
5856 taken into acount. For function not declared inline, recursive inlining
5857 happens only when @option{-finline-functions} (included in @option{-O3}) is
5858 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5859 default value is 450.
5861 @item min-inline-recursive-probability
5862 Recursive inlining is profitable only for function having deep recursion
5863 in average and can hurt for function having little recursion depth by
5864 increasing the prologue size or complexity of function body to other
5867 When profile feedback is available (see @option{-fprofile-generate}) the actual
5868 recursion depth can be guessed from probability that function will recurse via
5869 given call expression. This parameter limits inlining only to call expression
5870 whose probability exceeds given threshold (in percents). The default value is
5873 @item inline-call-cost
5874 Specify cost of call instruction relative to simple arithmetics operations
5875 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
5876 functions and at the same time increases size of leaf function that is believed to
5877 reduce function size by being inlined. In effect it increases amount of
5878 inlining for code having large abstraction penalty (many functions that just
5879 pass the arguments to other functions) and decrease inlining for code with low
5880 abstraction penalty. The default value is 16.
5882 @item max-unrolled-insns
5883 The maximum number of instructions that a loop should have if that loop
5884 is unrolled, and if the loop is unrolled, it determines how many times
5885 the loop code is unrolled.
5887 @item max-average-unrolled-insns
5888 The maximum number of instructions biased by probabilities of their execution
5889 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5890 it determines how many times the loop code is unrolled.
5892 @item max-unroll-times
5893 The maximum number of unrollings of a single loop.
5895 @item max-peeled-insns
5896 The maximum number of instructions that a loop should have if that loop
5897 is peeled, and if the loop is peeled, it determines how many times
5898 the loop code is peeled.
5900 @item max-peel-times
5901 The maximum number of peelings of a single loop.
5903 @item max-completely-peeled-insns
5904 The maximum number of insns of a completely peeled loop.
5906 @item max-completely-peel-times
5907 The maximum number of iterations of a loop to be suitable for complete peeling.
5909 @item max-unswitch-insns
5910 The maximum number of insns of an unswitched loop.
5912 @item max-unswitch-level
5913 The maximum number of branches unswitched in a single loop.
5916 The minimum cost of an expensive expression in the loop invariant motion.
5918 @item iv-consider-all-candidates-bound
5919 Bound on number of candidates for induction variables below that
5920 all candidates are considered for each use in induction variable
5921 optimizations. Only the most relevant candidates are considered
5922 if there are more candidates, to avoid quadratic time complexity.
5924 @item iv-max-considered-uses
5925 The induction variable optimizations give up on loops that contain more
5926 induction variable uses.
5928 @item iv-always-prune-cand-set-bound
5929 If number of candidates in the set is smaller than this value,
5930 we always try to remove unnecessary ivs from the set during its
5931 optimization when a new iv is added to the set.
5933 @item scev-max-expr-size
5934 Bound on size of expressions used in the scalar evolutions analyzer.
5935 Large expressions slow the analyzer.
5937 @item vect-max-version-checks
5938 The maximum number of runtime checks that can be performed when doing
5939 loop versioning in the vectorizer. See option ftree-vect-loop-version
5940 for more information.
5942 @item max-iterations-to-track
5944 The maximum number of iterations of a loop the brute force algorithm
5945 for analysis of # of iterations of the loop tries to evaluate.
5947 @item hot-bb-count-fraction
5948 Select fraction of the maximal count of repetitions of basic block in program
5949 given basic block needs to have to be considered hot.
5951 @item hot-bb-frequency-fraction
5952 Select fraction of the maximal frequency of executions of basic block in
5953 function given basic block needs to have to be considered hot
5955 @item max-predicted-iterations
5956 The maximum number of loop iterations we predict statically. This is useful
5957 in cases where function contain single loop with known bound and other loop
5958 with unknown. We predict the known number of iterations correctly, while
5959 the unknown number of iterations average to roughly 10. This means that the
5960 loop without bounds would appear artificially cold relative to the other one.
5962 @item tracer-dynamic-coverage
5963 @itemx tracer-dynamic-coverage-feedback
5965 This value is used to limit superblock formation once the given percentage of
5966 executed instructions is covered. This limits unnecessary code size
5969 The @option{tracer-dynamic-coverage-feedback} is used only when profile
5970 feedback is available. The real profiles (as opposed to statically estimated
5971 ones) are much less balanced allowing the threshold to be larger value.
5973 @item tracer-max-code-growth
5974 Stop tail duplication once code growth has reached given percentage. This is
5975 rather hokey argument, as most of the duplicates will be eliminated later in
5976 cross jumping, so it may be set to much higher values than is the desired code
5979 @item tracer-min-branch-ratio
5981 Stop reverse growth when the reverse probability of best edge is less than this
5982 threshold (in percent).
5984 @item tracer-min-branch-ratio
5985 @itemx tracer-min-branch-ratio-feedback
5987 Stop forward growth if the best edge do have probability lower than this
5990 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
5991 compilation for profile feedback and one for compilation without. The value
5992 for compilation with profile feedback needs to be more conservative (higher) in
5993 order to make tracer effective.
5995 @item max-cse-path-length
5997 Maximum number of basic blocks on path that cse considers. The default is 10.
6000 The maximum instructions CSE process before flushing. The default is 1000.
6002 @item global-var-threshold
6004 Counts the number of function calls (@var{n}) and the number of
6005 call-clobbered variables (@var{v}). If @var{n}x@var{v} is larger than this limit, a
6006 single artificial variable will be created to represent all the
6007 call-clobbered variables at function call sites. This artificial
6008 variable will then be made to alias every call-clobbered variable.
6009 (done as @code{int * size_t} on the host machine; beware overflow).
6011 @item max-aliased-vops
6013 Maximum number of virtual operands allowed to represent aliases
6014 before triggering the alias grouping heuristic. Alias grouping
6015 reduces compile times and memory consumption needed for aliasing at
6016 the expense of precision loss in alias information.
6018 @item ggc-min-expand
6020 GCC uses a garbage collector to manage its own memory allocation. This
6021 parameter specifies the minimum percentage by which the garbage
6022 collector's heap should be allowed to expand between collections.
6023 Tuning this may improve compilation speed; it has no effect on code
6026 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
6027 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
6028 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
6029 GCC is not able to calculate RAM on a particular platform, the lower
6030 bound of 30% is used. Setting this parameter and
6031 @option{ggc-min-heapsize} to zero causes a full collection to occur at
6032 every opportunity. This is extremely slow, but can be useful for
6035 @item ggc-min-heapsize
6037 Minimum size of the garbage collector's heap before it begins bothering
6038 to collect garbage. The first collection occurs after the heap expands
6039 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
6040 tuning this may improve compilation speed, and has no effect on code
6043 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
6044 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
6045 with a lower bound of 4096 (four megabytes) and an upper bound of
6046 131072 (128 megabytes). If GCC is not able to calculate RAM on a
6047 particular platform, the lower bound is used. Setting this parameter
6048 very large effectively disables garbage collection. Setting this
6049 parameter and @option{ggc-min-expand} to zero causes a full collection
6050 to occur at every opportunity.
6052 @item max-reload-search-insns
6053 The maximum number of instruction reload should look backward for equivalent
6054 register. Increasing values mean more aggressive optimization, making the
6055 compile time increase with probably slightly better performance. The default
6058 @item max-cselib-memory-location
6059 The maximum number of memory locations cselib should take into acount.
6060 Increasing values mean more aggressive optimization, making the compile time
6061 increase with probably slightly better performance. The default value is 500.
6063 @item max-flow-memory-location
6064 Similar as @option{max-cselib-memory-location} but for dataflow liveness.
6065 The default value is 100.
6067 @item reorder-blocks-duplicate
6068 @itemx reorder-blocks-duplicate-feedback
6070 Used by basic block reordering pass to decide whether to use unconditional
6071 branch or duplicate the code on its destination. Code is duplicated when its
6072 estimated size is smaller than this value multiplied by the estimated size of
6073 unconditional jump in the hot spots of the program.
6075 The @option{reorder-block-duplicate-feedback} is used only when profile
6076 feedback is available and may be set to higher values than
6077 @option{reorder-block-duplicate} since information about the hot spots is more
6080 @item max-sched-region-blocks
6081 The maximum number of blocks in a region to be considered for
6082 interblock scheduling. The default value is 10.
6084 @item max-sched-region-insns
6085 The maximum number of insns in a region to be considered for
6086 interblock scheduling. The default value is 100.
6088 @item min-sched-prob
6089 The minimum probability of reaching a source block for interblock
6090 speculative scheduling. The default value is 40.
6092 @item max-last-value-rtl
6094 The maximum size measured as number of RTLs that can be recorded in an expression
6095 in combiner for a pseudo register as last known value of that register. The default
6098 @item integer-share-limit
6099 Small integer constants can use a shared data structure, reducing the
6100 compiler's memory usage and increasing its speed. This sets the maximum
6101 value of a shared integer constant's. The default value is 256.
6103 @item min-virtual-mappings
6104 Specifies the minimum number of virtual mappings in the incremental
6105 SSA updater that should be registered to trigger the virtual mappings
6106 heuristic defined by virtual-mappings-ratio. The default value is
6109 @item virtual-mappings-ratio
6110 If the number of virtual mappings is virtual-mappings-ratio bigger
6111 than the number of virtual symbols to be updated, then the incremental
6112 SSA updater switches to a full update for those symbols. The default
6115 @item ssp-buffer-size
6116 The minimum size of buffers (i.e. arrays) that will receive stack smashing
6117 protection when @option{-fstack-protection} is used.
6119 @item max-jump-thread-duplication-stmts
6120 Maximum number of statements allowed in a block that needs to be
6121 duplicated when threading jumps.
6125 @node Preprocessor Options
6126 @section Options Controlling the Preprocessor
6127 @cindex preprocessor options
6128 @cindex options, preprocessor
6130 These options control the C preprocessor, which is run on each C source
6131 file before actual compilation.
6133 If you use the @option{-E} option, nothing is done except preprocessing.
6134 Some of these options make sense only together with @option{-E} because
6135 they cause the preprocessor output to be unsuitable for actual
6140 You can use @option{-Wp,@var{option}} to bypass the compiler driver
6141 and pass @var{option} directly through to the preprocessor. If
6142 @var{option} contains commas, it is split into multiple options at the
6143 commas. However, many options are modified, translated or interpreted
6144 by the compiler driver before being passed to the preprocessor, and
6145 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
6146 interface is undocumented and subject to change, so whenever possible
6147 you should avoid using @option{-Wp} and let the driver handle the
6150 @item -Xpreprocessor @var{option}
6151 @opindex preprocessor
6152 Pass @var{option} as an option to the preprocessor. You can use this to
6153 supply system-specific preprocessor options which GCC does not know how to
6156 If you want to pass an option that takes an argument, you must use
6157 @option{-Xpreprocessor} twice, once for the option and once for the argument.
6160 @include cppopts.texi
6162 @node Assembler Options
6163 @section Passing Options to the Assembler
6165 @c prevent bad page break with this line
6166 You can pass options to the assembler.
6169 @item -Wa,@var{option}
6171 Pass @var{option} as an option to the assembler. If @var{option}
6172 contains commas, it is split into multiple options at the commas.
6174 @item -Xassembler @var{option}
6176 Pass @var{option} as an option to the assembler. You can use this to
6177 supply system-specific assembler options which GCC does not know how to
6180 If you want to pass an option that takes an argument, you must use
6181 @option{-Xassembler} twice, once for the option and once for the argument.
6186 @section Options for Linking
6187 @cindex link options
6188 @cindex options, linking
6190 These options come into play when the compiler links object files into
6191 an executable output file. They are meaningless if the compiler is
6192 not doing a link step.
6196 @item @var{object-file-name}
6197 A file name that does not end in a special recognized suffix is
6198 considered to name an object file or library. (Object files are
6199 distinguished from libraries by the linker according to the file
6200 contents.) If linking is done, these object files are used as input
6209 If any of these options is used, then the linker is not run, and
6210 object file names should not be used as arguments. @xref{Overall
6214 @item -l@var{library}
6215 @itemx -l @var{library}
6217 Search the library named @var{library} when linking. (The second
6218 alternative with the library as a separate argument is only for
6219 POSIX compliance and is not recommended.)
6221 It makes a difference where in the command you write this option; the
6222 linker searches and processes libraries and object files in the order they
6223 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
6224 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
6225 to functions in @samp{z}, those functions may not be loaded.
6227 The linker searches a standard list of directories for the library,
6228 which is actually a file named @file{lib@var{library}.a}. The linker
6229 then uses this file as if it had been specified precisely by name.
6231 The directories searched include several standard system directories
6232 plus any that you specify with @option{-L}.
6234 Normally the files found this way are library files---archive files
6235 whose members are object files. The linker handles an archive file by
6236 scanning through it for members which define symbols that have so far
6237 been referenced but not defined. But if the file that is found is an
6238 ordinary object file, it is linked in the usual fashion. The only
6239 difference between using an @option{-l} option and specifying a file name
6240 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
6241 and searches several directories.
6245 You need this special case of the @option{-l} option in order to
6246 link an Objective-C or Objective-C++ program.
6249 @opindex nostartfiles
6250 Do not use the standard system startup files when linking.
6251 The standard system libraries are used normally, unless @option{-nostdlib}
6252 or @option{-nodefaultlibs} is used.
6254 @item -nodefaultlibs
6255 @opindex nodefaultlibs
6256 Do not use the standard system libraries when linking.
6257 Only the libraries you specify will be passed to the linker.
6258 The standard startup files are used normally, unless @option{-nostartfiles}
6259 is used. The compiler may generate calls to @code{memcmp},
6260 @code{memset}, @code{memcpy} and @code{memmove}.
6261 These entries are usually resolved by entries in
6262 libc. These entry points should be supplied through some other
6263 mechanism when this option is specified.
6267 Do not use the standard system startup files or libraries when linking.
6268 No startup files and only the libraries you specify will be passed to
6269 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
6270 @code{memcpy} and @code{memmove}.
6271 These entries are usually resolved by entries in
6272 libc. These entry points should be supplied through some other
6273 mechanism when this option is specified.
6275 @cindex @option{-lgcc}, use with @option{-nostdlib}
6276 @cindex @option{-nostdlib} and unresolved references
6277 @cindex unresolved references and @option{-nostdlib}
6278 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
6279 @cindex @option{-nodefaultlibs} and unresolved references
6280 @cindex unresolved references and @option{-nodefaultlibs}
6281 One of the standard libraries bypassed by @option{-nostdlib} and
6282 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
6283 that GCC uses to overcome shortcomings of particular machines, or special
6284 needs for some languages.
6285 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
6286 Collection (GCC) Internals},
6287 for more discussion of @file{libgcc.a}.)
6288 In most cases, you need @file{libgcc.a} even when you want to avoid
6289 other standard libraries. In other words, when you specify @option{-nostdlib}
6290 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
6291 This ensures that you have no unresolved references to internal GCC
6292 library subroutines. (For example, @samp{__main}, used to ensure C++
6293 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
6294 GNU Compiler Collection (GCC) Internals}.)
6298 Produce a position independent executable on targets which support it.
6299 For predictable results, you must also specify the same set of options
6300 that were used to generate code (@option{-fpie}, @option{-fPIE},
6301 or model suboptions) when you specify this option.
6305 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
6306 that support it. This instructs the linker to add all symbols, not
6307 only used ones, to the dynamic symbol table. This option is needed
6308 for some uses of @code{dlopen} or to allow obtaining backtraces
6309 from within a program.
6313 Remove all symbol table and relocation information from the executable.
6317 On systems that support dynamic linking, this prevents linking with the shared
6318 libraries. On other systems, this option has no effect.
6322 Produce a shared object which can then be linked with other objects to
6323 form an executable. Not all systems support this option. For predictable
6324 results, you must also specify the same set of options that were used to
6325 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
6326 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
6327 needs to build supplementary stub code for constructors to work. On
6328 multi-libbed systems, @samp{gcc -shared} must select the correct support
6329 libraries to link against. Failing to supply the correct flags may lead
6330 to subtle defects. Supplying them in cases where they are not necessary
6333 @item -shared-libgcc
6334 @itemx -static-libgcc
6335 @opindex shared-libgcc
6336 @opindex static-libgcc
6337 On systems that provide @file{libgcc} as a shared library, these options
6338 force the use of either the shared or static version respectively.
6339 If no shared version of @file{libgcc} was built when the compiler was
6340 configured, these options have no effect.
6342 There are several situations in which an application should use the
6343 shared @file{libgcc} instead of the static version. The most common
6344 of these is when the application wishes to throw and catch exceptions
6345 across different shared libraries. In that case, each of the libraries
6346 as well as the application itself should use the shared @file{libgcc}.
6348 Therefore, the G++ and GCJ drivers automatically add
6349 @option{-shared-libgcc} whenever you build a shared library or a main
6350 executable, because C++ and Java programs typically use exceptions, so
6351 this is the right thing to do.
6353 If, instead, you use the GCC driver to create shared libraries, you may
6354 find that they will not always be linked with the shared @file{libgcc}.
6355 If GCC finds, at its configuration time, that you have a non-GNU linker
6356 or a GNU linker that does not support option @option{--eh-frame-hdr},
6357 it will link the shared version of @file{libgcc} into shared libraries
6358 by default. Otherwise, it will take advantage of the linker and optimize
6359 away the linking with the shared version of @file{libgcc}, linking with
6360 the static version of libgcc by default. This allows exceptions to
6361 propagate through such shared libraries, without incurring relocation
6362 costs at library load time.
6364 However, if a library or main executable is supposed to throw or catch
6365 exceptions, you must link it using the G++ or GCJ driver, as appropriate
6366 for the languages used in the program, or using the option
6367 @option{-shared-libgcc}, such that it is linked with the shared
6372 Bind references to global symbols when building a shared object. Warn
6373 about any unresolved references (unless overridden by the link editor
6374 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
6377 @item -Xlinker @var{option}
6379 Pass @var{option} as an option to the linker. You can use this to
6380 supply system-specific linker options which GCC does not know how to
6383 If you want to pass an option that takes an argument, you must use
6384 @option{-Xlinker} twice, once for the option and once for the argument.
6385 For example, to pass @option{-assert definitions}, you must write
6386 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
6387 @option{-Xlinker "-assert definitions"}, because this passes the entire
6388 string as a single argument, which is not what the linker expects.
6390 @item -Wl,@var{option}
6392 Pass @var{option} as an option to the linker. If @var{option} contains
6393 commas, it is split into multiple options at the commas.
6395 @item -u @var{symbol}
6397 Pretend the symbol @var{symbol} is undefined, to force linking of
6398 library modules to define it. You can use @option{-u} multiple times with
6399 different symbols to force loading of additional library modules.
6402 @node Directory Options
6403 @section Options for Directory Search
6404 @cindex directory options
6405 @cindex options, directory search
6408 These options specify directories to search for header files, for
6409 libraries and for parts of the compiler:
6414 Add the directory @var{dir} to the head of the list of directories to be
6415 searched for header files. This can be used to override a system header
6416 file, substituting your own version, since these directories are
6417 searched before the system header file directories. However, you should
6418 not use this option to add directories that contain vendor-supplied
6419 system header files (use @option{-isystem} for that). If you use more than
6420 one @option{-I} option, the directories are scanned in left-to-right
6421 order; the standard system directories come after.
6423 If a standard system include directory, or a directory specified with
6424 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
6425 option will be ignored. The directory will still be searched but as a
6426 system directory at its normal position in the system include chain.
6427 This is to ensure that GCC's procedure to fix buggy system headers and
6428 the ordering for the include_next directive are not inadvertently changed.
6429 If you really need to change the search order for system directories,
6430 use the @option{-nostdinc} and/or @option{-isystem} options.
6432 @item -iquote@var{dir}
6434 Add the directory @var{dir} to the head of the list of directories to
6435 be searched for header files only for the case of @samp{#include
6436 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
6437 otherwise just like @option{-I}.
6441 Add directory @var{dir} to the list of directories to be searched
6444 @item -B@var{prefix}
6446 This option specifies where to find the executables, libraries,
6447 include files, and data files of the compiler itself.
6449 The compiler driver program runs one or more of the subprograms
6450 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
6451 @var{prefix} as a prefix for each program it tries to run, both with and
6452 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
6454 For each subprogram to be run, the compiler driver first tries the
6455 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
6456 was not specified, the driver tries two standard prefixes, which are
6457 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
6458 those results in a file name that is found, the unmodified program
6459 name is searched for using the directories specified in your
6460 @env{PATH} environment variable.
6462 The compiler will check to see if the path provided by the @option{-B}
6463 refers to a directory, and if necessary it will add a directory
6464 separator character at the end of the path.
6466 @option{-B} prefixes that effectively specify directory names also apply
6467 to libraries in the linker, because the compiler translates these
6468 options into @option{-L} options for the linker. They also apply to
6469 includes files in the preprocessor, because the compiler translates these
6470 options into @option{-isystem} options for the preprocessor. In this case,
6471 the compiler appends @samp{include} to the prefix.
6473 The run-time support file @file{libgcc.a} can also be searched for using
6474 the @option{-B} prefix, if needed. If it is not found there, the two
6475 standard prefixes above are tried, and that is all. The file is left
6476 out of the link if it is not found by those means.
6478 Another way to specify a prefix much like the @option{-B} prefix is to use
6479 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
6482 As a special kludge, if the path provided by @option{-B} is
6483 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
6484 9, then it will be replaced by @file{[dir/]include}. This is to help
6485 with boot-strapping the compiler.
6487 @item -specs=@var{file}
6489 Process @var{file} after the compiler reads in the standard @file{specs}
6490 file, in order to override the defaults that the @file{gcc} driver
6491 program uses when determining what switches to pass to @file{cc1},
6492 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
6493 @option{-specs=@var{file}} can be specified on the command line, and they
6494 are processed in order, from left to right.
6496 @item --sysroot=@var{dir}
6498 Use @var{dir} as the logical root directory for headers and libraries.
6499 For example, if the compiler would normally search for headers in
6500 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
6501 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
6503 If you use both this option and the @option{-isysroot} option, then
6504 the @option{--sysroot} option will apply to libraries, but the
6505 @option{-isysroot} option will apply to header files.
6507 The GNU linker (beginning with version 2.16) has the necessary support
6508 for this option. If your linker does not support this option, the
6509 header file aspect of @option{--sysroot} will still work, but the
6510 library aspect will not.
6514 This option has been deprecated. Please use @option{-iquote} instead for
6515 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
6516 Any directories you specify with @option{-I} options before the @option{-I-}
6517 option are searched only for the case of @samp{#include "@var{file}"};
6518 they are not searched for @samp{#include <@var{file}>}.
6520 If additional directories are specified with @option{-I} options after
6521 the @option{-I-}, these directories are searched for all @samp{#include}
6522 directives. (Ordinarily @emph{all} @option{-I} directories are used
6525 In addition, the @option{-I-} option inhibits the use of the current
6526 directory (where the current input file came from) as the first search
6527 directory for @samp{#include "@var{file}"}. There is no way to
6528 override this effect of @option{-I-}. With @option{-I.} you can specify
6529 searching the directory which was current when the compiler was
6530 invoked. That is not exactly the same as what the preprocessor does
6531 by default, but it is often satisfactory.
6533 @option{-I-} does not inhibit the use of the standard system directories
6534 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6541 @section Specifying subprocesses and the switches to pass to them
6544 @command{gcc} is a driver program. It performs its job by invoking a
6545 sequence of other programs to do the work of compiling, assembling and
6546 linking. GCC interprets its command-line parameters and uses these to
6547 deduce which programs it should invoke, and which command-line options
6548 it ought to place on their command lines. This behavior is controlled
6549 by @dfn{spec strings}. In most cases there is one spec string for each
6550 program that GCC can invoke, but a few programs have multiple spec
6551 strings to control their behavior. The spec strings built into GCC can
6552 be overridden by using the @option{-specs=} command-line switch to specify
6555 @dfn{Spec files} are plaintext files that are used to construct spec
6556 strings. They consist of a sequence of directives separated by blank
6557 lines. The type of directive is determined by the first non-whitespace
6558 character on the line and it can be one of the following:
6561 @item %@var{command}
6562 Issues a @var{command} to the spec file processor. The commands that can
6566 @item %include <@var{file}>
6568 Search for @var{file} and insert its text at the current point in the
6571 @item %include_noerr <@var{file}>
6572 @cindex %include_noerr
6573 Just like @samp{%include}, but do not generate an error message if the include
6574 file cannot be found.
6576 @item %rename @var{old_name} @var{new_name}
6578 Rename the spec string @var{old_name} to @var{new_name}.
6582 @item *[@var{spec_name}]:
6583 This tells the compiler to create, override or delete the named spec
6584 string. All lines after this directive up to the next directive or
6585 blank line are considered to be the text for the spec string. If this
6586 results in an empty string then the spec will be deleted. (Or, if the
6587 spec did not exist, then nothing will happened.) Otherwise, if the spec
6588 does not currently exist a new spec will be created. If the spec does
6589 exist then its contents will be overridden by the text of this
6590 directive, unless the first character of that text is the @samp{+}
6591 character, in which case the text will be appended to the spec.
6593 @item [@var{suffix}]:
6594 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6595 and up to the next directive or blank line are considered to make up the
6596 spec string for the indicated suffix. When the compiler encounters an
6597 input file with the named suffix, it will processes the spec string in
6598 order to work out how to compile that file. For example:
6605 This says that any input file whose name ends in @samp{.ZZ} should be
6606 passed to the program @samp{z-compile}, which should be invoked with the
6607 command-line switch @option{-input} and with the result of performing the
6608 @samp{%i} substitution. (See below.)
6610 As an alternative to providing a spec string, the text that follows a
6611 suffix directive can be one of the following:
6614 @item @@@var{language}
6615 This says that the suffix is an alias for a known @var{language}. This is
6616 similar to using the @option{-x} command-line switch to GCC to specify a
6617 language explicitly. For example:
6624 Says that .ZZ files are, in fact, C++ source files.
6627 This causes an error messages saying:
6630 @var{name} compiler not installed on this system.
6634 GCC already has an extensive list of suffixes built into it.
6635 This directive will add an entry to the end of the list of suffixes, but
6636 since the list is searched from the end backwards, it is effectively
6637 possible to override earlier entries using this technique.
6641 GCC has the following spec strings built into it. Spec files can
6642 override these strings or create their own. Note that individual
6643 targets can also add their own spec strings to this list.
6646 asm Options to pass to the assembler
6647 asm_final Options to pass to the assembler post-processor
6648 cpp Options to pass to the C preprocessor
6649 cc1 Options to pass to the C compiler
6650 cc1plus Options to pass to the C++ compiler
6651 endfile Object files to include at the end of the link
6652 link Options to pass to the linker
6653 lib Libraries to include on the command line to the linker
6654 libgcc Decides which GCC support library to pass to the linker
6655 linker Sets the name of the linker
6656 predefines Defines to be passed to the C preprocessor
6657 signed_char Defines to pass to CPP to say whether @code{char} is signed
6659 startfile Object files to include at the start of the link
6662 Here is a small example of a spec file:
6668 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6671 This example renames the spec called @samp{lib} to @samp{old_lib} and
6672 then overrides the previous definition of @samp{lib} with a new one.
6673 The new definition adds in some extra command-line options before
6674 including the text of the old definition.
6676 @dfn{Spec strings} are a list of command-line options to be passed to their
6677 corresponding program. In addition, the spec strings can contain
6678 @samp{%}-prefixed sequences to substitute variable text or to
6679 conditionally insert text into the command line. Using these constructs
6680 it is possible to generate quite complex command lines.
6682 Here is a table of all defined @samp{%}-sequences for spec
6683 strings. Note that spaces are not generated automatically around the
6684 results of expanding these sequences. Therefore you can concatenate them
6685 together or combine them with constant text in a single argument.
6689 Substitute one @samp{%} into the program name or argument.
6692 Substitute the name of the input file being processed.
6695 Substitute the basename of the input file being processed.
6696 This is the substring up to (and not including) the last period
6697 and not including the directory.
6700 This is the same as @samp{%b}, but include the file suffix (text after
6704 Marks the argument containing or following the @samp{%d} as a
6705 temporary file name, so that that file will be deleted if GCC exits
6706 successfully. Unlike @samp{%g}, this contributes no text to the
6709 @item %g@var{suffix}
6710 Substitute a file name that has suffix @var{suffix} and is chosen
6711 once per compilation, and mark the argument in the same way as
6712 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6713 name is now chosen in a way that is hard to predict even when previously
6714 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6715 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6716 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6717 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6718 was simply substituted with a file name chosen once per compilation,
6719 without regard to any appended suffix (which was therefore treated
6720 just like ordinary text), making such attacks more likely to succeed.
6722 @item %u@var{suffix}
6723 Like @samp{%g}, but generates a new temporary file name even if
6724 @samp{%u@var{suffix}} was already seen.
6726 @item %U@var{suffix}
6727 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6728 new one if there is no such last file name. In the absence of any
6729 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6730 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6731 would involve the generation of two distinct file names, one
6732 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6733 simply substituted with a file name chosen for the previous @samp{%u},
6734 without regard to any appended suffix.
6736 @item %j@var{suffix}
6737 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6738 writable, and if save-temps is off; otherwise, substitute the name
6739 of a temporary file, just like @samp{%u}. This temporary file is not
6740 meant for communication between processes, but rather as a junk
6743 @item %|@var{suffix}
6744 @itemx %m@var{suffix}
6745 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6746 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6747 all. These are the two most common ways to instruct a program that it
6748 should read from standard input or write to standard output. If you
6749 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6750 construct: see for example @file{f/lang-specs.h}.
6752 @item %.@var{SUFFIX}
6753 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6754 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6755 terminated by the next space or %.
6758 Marks the argument containing or following the @samp{%w} as the
6759 designated output file of this compilation. This puts the argument
6760 into the sequence of arguments that @samp{%o} will substitute later.
6763 Substitutes the names of all the output files, with spaces
6764 automatically placed around them. You should write spaces
6765 around the @samp{%o} as well or the results are undefined.
6766 @samp{%o} is for use in the specs for running the linker.
6767 Input files whose names have no recognized suffix are not compiled
6768 at all, but they are included among the output files, so they will
6772 Substitutes the suffix for object files. Note that this is
6773 handled specially when it immediately follows @samp{%g, %u, or %U},
6774 because of the need for those to form complete file names. The
6775 handling is such that @samp{%O} is treated exactly as if it had already
6776 been substituted, except that @samp{%g, %u, and %U} do not currently
6777 support additional @var{suffix} characters following @samp{%O} as they would
6778 following, for example, @samp{.o}.
6781 Substitutes the standard macro predefinitions for the
6782 current target machine. Use this when running @code{cpp}.
6785 Like @samp{%p}, but puts @samp{__} before and after the name of each
6786 predefined macro, except for macros that start with @samp{__} or with
6787 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6791 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6792 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
6793 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6797 Current argument is the name of a library or startup file of some sort.
6798 Search for that file in a standard list of directories and substitute
6799 the full name found.
6802 Print @var{str} as an error message. @var{str} is terminated by a newline.
6803 Use this when inconsistent options are detected.
6806 Substitute the contents of spec string @var{name} at this point.
6809 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6811 @item %x@{@var{option}@}
6812 Accumulate an option for @samp{%X}.
6815 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6819 Output the accumulated assembler options specified by @option{-Wa}.
6822 Output the accumulated preprocessor options specified by @option{-Wp}.
6825 Process the @code{asm} spec. This is used to compute the
6826 switches to be passed to the assembler.
6829 Process the @code{asm_final} spec. This is a spec string for
6830 passing switches to an assembler post-processor, if such a program is
6834 Process the @code{link} spec. This is the spec for computing the
6835 command line passed to the linker. Typically it will make use of the
6836 @samp{%L %G %S %D and %E} sequences.
6839 Dump out a @option{-L} option for each directory that GCC believes might
6840 contain startup files. If the target supports multilibs then the
6841 current multilib directory will be prepended to each of these paths.
6844 Process the @code{lib} spec. This is a spec string for deciding which
6845 libraries should be included on the command line to the linker.
6848 Process the @code{libgcc} spec. This is a spec string for deciding
6849 which GCC support library should be included on the command line to the linker.
6852 Process the @code{startfile} spec. This is a spec for deciding which
6853 object files should be the first ones passed to the linker. Typically
6854 this might be a file named @file{crt0.o}.
6857 Process the @code{endfile} spec. This is a spec string that specifies
6858 the last object files that will be passed to the linker.
6861 Process the @code{cpp} spec. This is used to construct the arguments
6862 to be passed to the C preprocessor.
6865 Process the @code{cc1} spec. This is used to construct the options to be
6866 passed to the actual C compiler (@samp{cc1}).
6869 Process the @code{cc1plus} spec. This is used to construct the options to be
6870 passed to the actual C++ compiler (@samp{cc1plus}).
6873 Substitute the variable part of a matched option. See below.
6874 Note that each comma in the substituted string is replaced by
6878 Remove all occurrences of @code{-S} from the command line. Note---this
6879 command is position dependent. @samp{%} commands in the spec string
6880 before this one will see @code{-S}, @samp{%} commands in the spec string
6881 after this one will not.
6883 @item %:@var{function}(@var{args})
6884 Call the named function @var{function}, passing it @var{args}.
6885 @var{args} is first processed as a nested spec string, then split
6886 into an argument vector in the usual fashion. The function returns
6887 a string which is processed as if it had appeared literally as part
6888 of the current spec.
6890 The following built-in spec functions are provided:
6893 @item @code{if-exists}
6894 The @code{if-exists} spec function takes one argument, an absolute
6895 pathname to a file. If the file exists, @code{if-exists} returns the
6896 pathname. Here is a small example of its usage:
6900 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6903 @item @code{if-exists-else}
6904 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6905 spec function, except that it takes two arguments. The first argument is
6906 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6907 returns the pathname. If it does not exist, it returns the second argument.
6908 This way, @code{if-exists-else} can be used to select one file or another,
6909 based on the existence of the first. Here is a small example of its usage:
6913 crt0%O%s %:if-exists(crti%O%s) \
6914 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
6917 @item @code{replace-outfile}
6918 The @code{replace-outfile} spec function takes two arguments. It looks for the
6919 first argument in the outfiles array and replaces it with the second argument. Here
6920 is a small example of its usage:
6923 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
6929 Substitutes the @code{-S} switch, if that switch was given to GCC@.
6930 If that switch was not specified, this substitutes nothing. Note that
6931 the leading dash is omitted when specifying this option, and it is
6932 automatically inserted if the substitution is performed. Thus the spec
6933 string @samp{%@{foo@}} would match the command-line option @option{-foo}
6934 and would output the command line option @option{-foo}.
6936 @item %W@{@code{S}@}
6937 Like %@{@code{S}@} but mark last argument supplied within as a file to be
6940 @item %@{@code{S}*@}
6941 Substitutes all the switches specified to GCC whose names start
6942 with @code{-S}, but which also take an argument. This is used for
6943 switches like @option{-o}, @option{-D}, @option{-I}, etc.
6944 GCC considers @option{-o foo} as being
6945 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
6946 text, including the space. Thus two arguments would be generated.
6948 @item %@{@code{S}*&@code{T}*@}
6949 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
6950 (the order of @code{S} and @code{T} in the spec is not significant).
6951 There can be any number of ampersand-separated variables; for each the
6952 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
6954 @item %@{@code{S}:@code{X}@}
6955 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
6957 @item %@{!@code{S}:@code{X}@}
6958 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
6960 @item %@{@code{S}*:@code{X}@}
6961 Substitutes @code{X} if one or more switches whose names start with
6962 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
6963 once, no matter how many such switches appeared. However, if @code{%*}
6964 appears somewhere in @code{X}, then @code{X} will be substituted once
6965 for each matching switch, with the @code{%*} replaced by the part of
6966 that switch that matched the @code{*}.
6968 @item %@{.@code{S}:@code{X}@}
6969 Substitutes @code{X}, if processing a file with suffix @code{S}.
6971 @item %@{!.@code{S}:@code{X}@}
6972 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
6974 @item %@{@code{S}|@code{P}:@code{X}@}
6975 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
6976 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
6977 although they have a stronger binding than the @samp{|}. If @code{%*}
6978 appears in @code{X}, all of the alternatives must be starred, and only
6979 the first matching alternative is substituted.
6981 For example, a spec string like this:
6984 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
6987 will output the following command-line options from the following input
6988 command-line options:
6993 -d fred.c -foo -baz -boggle
6994 -d jim.d -bar -baz -boggle
6997 @item %@{S:X; T:Y; :D@}
6999 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
7000 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
7001 be as many clauses as you need. This may be combined with @code{.},
7002 @code{!}, @code{|}, and @code{*} as needed.
7007 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
7008 construct may contain other nested @samp{%} constructs or spaces, or
7009 even newlines. They are processed as usual, as described above.
7010 Trailing white space in @code{X} is ignored. White space may also
7011 appear anywhere on the left side of the colon in these constructs,
7012 except between @code{.} or @code{*} and the corresponding word.
7014 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
7015 handled specifically in these constructs. If another value of
7016 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
7017 @option{-W} switch is found later in the command line, the earlier
7018 switch value is ignored, except with @{@code{S}*@} where @code{S} is
7019 just one letter, which passes all matching options.
7021 The character @samp{|} at the beginning of the predicate text is used to
7022 indicate that a command should be piped to the following command, but
7023 only if @option{-pipe} is specified.
7025 It is built into GCC which switches take arguments and which do not.
7026 (You might think it would be useful to generalize this to allow each
7027 compiler's spec to say which switches take arguments. But this cannot
7028 be done in a consistent fashion. GCC cannot even decide which input
7029 files have been specified without knowing which switches take arguments,
7030 and it must know which input files to compile in order to tell which
7033 GCC also knows implicitly that arguments starting in @option{-l} are to be
7034 treated as compiler output files, and passed to the linker in their
7035 proper position among the other output files.
7037 @c man begin OPTIONS
7039 @node Target Options
7040 @section Specifying Target Machine and Compiler Version
7041 @cindex target options
7042 @cindex cross compiling
7043 @cindex specifying machine version
7044 @cindex specifying compiler version and target machine
7045 @cindex compiler version, specifying
7046 @cindex target machine, specifying
7048 The usual way to run GCC is to run the executable called @file{gcc}, or
7049 @file{<machine>-gcc} when cross-compiling, or
7050 @file{<machine>-gcc-<version>} to run a version other than the one that
7051 was installed last. Sometimes this is inconvenient, so GCC provides
7052 options that will switch to another cross-compiler or version.
7055 @item -b @var{machine}
7057 The argument @var{machine} specifies the target machine for compilation.
7059 The value to use for @var{machine} is the same as was specified as the
7060 machine type when configuring GCC as a cross-compiler. For
7061 example, if a cross-compiler was configured with @samp{configure
7062 arm-elf}, meaning to compile for an arm processor with elf binaries,
7063 then you would specify @option{-b arm-elf} to run that cross compiler.
7064 Because there are other options beginning with @option{-b}, the
7065 configuration must contain a hyphen.
7067 @item -V @var{version}
7069 The argument @var{version} specifies which version of GCC to run.
7070 This is useful when multiple versions are installed. For example,
7071 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
7074 The @option{-V} and @option{-b} options work by running the
7075 @file{<machine>-gcc-<version>} executable, so there's no real reason to
7076 use them if you can just run that directly.
7078 @node Submodel Options
7079 @section Hardware Models and Configurations
7080 @cindex submodel options
7081 @cindex specifying hardware config
7082 @cindex hardware models and configurations, specifying
7083 @cindex machine dependent options
7085 Earlier we discussed the standard option @option{-b} which chooses among
7086 different installed compilers for completely different target
7087 machines, such as VAX vs.@: 68000 vs.@: 80386.
7089 In addition, each of these target machine types can have its own
7090 special options, starting with @samp{-m}, to choose among various
7091 hardware models or configurations---for example, 68010 vs 68020,
7092 floating coprocessor or none. A single installed version of the
7093 compiler can compile for any model or configuration, according to the
7096 Some configurations of the compiler also support additional special
7097 options, usually for compatibility with other compilers on the same
7100 @c This list is ordered alphanumerically by subsection name.
7101 @c It should be the same order and spelling as these options are listed
7102 @c in Machine Dependent Options
7108 * Blackfin Options::
7112 * DEC Alpha Options::
7113 * DEC Alpha/VMS Options::
7117 * i386 and x86-64 Options::
7130 * RS/6000 and PowerPC Options::
7131 * S/390 and zSeries Options::
7134 * System V Options::
7135 * TMS320C3x/C4x Options::
7139 * Xstormy16 Options::
7145 @subsection ARC Options
7148 These options are defined for ARC implementations:
7153 Compile code for little endian mode. This is the default.
7157 Compile code for big endian mode.
7160 @opindex mmangle-cpu
7161 Prepend the name of the cpu to all public symbol names.
7162 In multiple-processor systems, there are many ARC variants with different
7163 instruction and register set characteristics. This flag prevents code
7164 compiled for one cpu to be linked with code compiled for another.
7165 No facility exists for handling variants that are ``almost identical''.
7166 This is an all or nothing option.
7168 @item -mcpu=@var{cpu}
7170 Compile code for ARC variant @var{cpu}.
7171 Which variants are supported depend on the configuration.
7172 All variants support @option{-mcpu=base}, this is the default.
7174 @item -mtext=@var{text-section}
7175 @itemx -mdata=@var{data-section}
7176 @itemx -mrodata=@var{readonly-data-section}
7180 Put functions, data, and readonly data in @var{text-section},
7181 @var{data-section}, and @var{readonly-data-section} respectively
7182 by default. This can be overridden with the @code{section} attribute.
7183 @xref{Variable Attributes}.
7188 @subsection ARM Options
7191 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
7195 @item -mabi=@var{name}
7197 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
7198 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
7201 @opindex mapcs-frame
7202 Generate a stack frame that is compliant with the ARM Procedure Call
7203 Standard for all functions, even if this is not strictly necessary for
7204 correct execution of the code. Specifying @option{-fomit-frame-pointer}
7205 with this option will cause the stack frames not to be generated for
7206 leaf functions. The default is @option{-mno-apcs-frame}.
7210 This is a synonym for @option{-mapcs-frame}.
7213 @c not currently implemented
7214 @item -mapcs-stack-check
7215 @opindex mapcs-stack-check
7216 Generate code to check the amount of stack space available upon entry to
7217 every function (that actually uses some stack space). If there is
7218 insufficient space available then either the function
7219 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
7220 called, depending upon the amount of stack space required. The run time
7221 system is required to provide these functions. The default is
7222 @option{-mno-apcs-stack-check}, since this produces smaller code.
7224 @c not currently implemented
7226 @opindex mapcs-float
7227 Pass floating point arguments using the float point registers. This is
7228 one of the variants of the APCS@. This option is recommended if the
7229 target hardware has a floating point unit or if a lot of floating point
7230 arithmetic is going to be performed by the code. The default is
7231 @option{-mno-apcs-float}, since integer only code is slightly increased in
7232 size if @option{-mapcs-float} is used.
7234 @c not currently implemented
7235 @item -mapcs-reentrant
7236 @opindex mapcs-reentrant
7237 Generate reentrant, position independent code. The default is
7238 @option{-mno-apcs-reentrant}.
7241 @item -mthumb-interwork
7242 @opindex mthumb-interwork
7243 Generate code which supports calling between the ARM and Thumb
7244 instruction sets. Without this option the two instruction sets cannot
7245 be reliably used inside one program. The default is
7246 @option{-mno-thumb-interwork}, since slightly larger code is generated
7247 when @option{-mthumb-interwork} is specified.
7249 @item -mno-sched-prolog
7250 @opindex mno-sched-prolog
7251 Prevent the reordering of instructions in the function prolog, or the
7252 merging of those instruction with the instructions in the function's
7253 body. This means that all functions will start with a recognizable set
7254 of instructions (or in fact one of a choice from a small set of
7255 different function prologues), and this information can be used to
7256 locate the start if functions inside an executable piece of code. The
7257 default is @option{-msched-prolog}.
7260 @opindex mhard-float
7261 Generate output containing floating point instructions. This is the
7265 @opindex msoft-float
7266 Generate output containing library calls for floating point.
7267 @strong{Warning:} the requisite libraries are not available for all ARM
7268 targets. Normally the facilities of the machine's usual C compiler are
7269 used, but this cannot be done directly in cross-compilation. You must make
7270 your own arrangements to provide suitable library functions for
7273 @option{-msoft-float} changes the calling convention in the output file;
7274 therefore, it is only useful if you compile @emph{all} of a program with
7275 this option. In particular, you need to compile @file{libgcc.a}, the
7276 library that comes with GCC, with @option{-msoft-float} in order for
7279 @item -mfloat-abi=@var{name}
7281 Specifies which ABI to use for floating point values. Permissible values
7282 are: @samp{soft}, @samp{softfp} and @samp{hard}.
7284 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
7285 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
7286 of floating point instructions, but still uses the soft-float calling
7289 @item -mlittle-endian
7290 @opindex mlittle-endian
7291 Generate code for a processor running in little-endian mode. This is
7292 the default for all standard configurations.
7295 @opindex mbig-endian
7296 Generate code for a processor running in big-endian mode; the default is
7297 to compile code for a little-endian processor.
7299 @item -mwords-little-endian
7300 @opindex mwords-little-endian
7301 This option only applies when generating code for big-endian processors.
7302 Generate code for a little-endian word order but a big-endian byte
7303 order. That is, a byte order of the form @samp{32107654}. Note: this
7304 option should only be used if you require compatibility with code for
7305 big-endian ARM processors generated by versions of the compiler prior to
7308 @item -mcpu=@var{name}
7310 This specifies the name of the target ARM processor. GCC uses this name
7311 to determine what kind of instructions it can emit when generating
7312 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
7313 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
7314 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
7315 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
7316 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
7317 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
7318 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
7319 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
7320 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
7321 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
7322 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
7323 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
7324 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
7325 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
7328 @itemx -mtune=@var{name}
7330 This option is very similar to the @option{-mcpu=} option, except that
7331 instead of specifying the actual target processor type, and hence
7332 restricting which instructions can be used, it specifies that GCC should
7333 tune the performance of the code as if the target were of the type
7334 specified in this option, but still choosing the instructions that it
7335 will generate based on the cpu specified by a @option{-mcpu=} option.
7336 For some ARM implementations better performance can be obtained by using
7339 @item -march=@var{name}
7341 This specifies the name of the target ARM architecture. GCC uses this
7342 name to determine what kind of instructions it can emit when generating
7343 assembly code. This option can be used in conjunction with or instead
7344 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
7345 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
7346 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
7347 @samp{iwmmxt}, @samp{ep9312}.
7349 @item -mfpu=@var{name}
7350 @itemx -mfpe=@var{number}
7351 @itemx -mfp=@var{number}
7355 This specifies what floating point hardware (or hardware emulation) is
7356 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
7357 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
7358 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
7359 with older versions of GCC@.
7361 If @option{-msoft-float} is specified this specifies the format of
7362 floating point values.
7364 @item -mstructure-size-boundary=@var{n}
7365 @opindex mstructure-size-boundary
7366 The size of all structures and unions will be rounded up to a multiple
7367 of the number of bits set by this option. Permissible values are 8, 32
7368 and 64. The default value varies for different toolchains. For the COFF
7369 targeted toolchain the default value is 8. A value of 64 is only allowed
7370 if the underlying ABI supports it.
7372 Specifying the larger number can produce faster, more efficient code, but
7373 can also increase the size of the program. Different values are potentially
7374 incompatible. Code compiled with one value cannot necessarily expect to
7375 work with code or libraries compiled with another value, if they exchange
7376 information using structures or unions.
7378 @item -mabort-on-noreturn
7379 @opindex mabort-on-noreturn
7380 Generate a call to the function @code{abort} at the end of a
7381 @code{noreturn} function. It will be executed if the function tries to
7385 @itemx -mno-long-calls
7386 @opindex mlong-calls
7387 @opindex mno-long-calls
7388 Tells the compiler to perform function calls by first loading the
7389 address of the function into a register and then performing a subroutine
7390 call on this register. This switch is needed if the target function
7391 will lie outside of the 64 megabyte addressing range of the offset based
7392 version of subroutine call instruction.
7394 Even if this switch is enabled, not all function calls will be turned
7395 into long calls. The heuristic is that static functions, functions
7396 which have the @samp{short-call} attribute, functions that are inside
7397 the scope of a @samp{#pragma no_long_calls} directive and functions whose
7398 definitions have already been compiled within the current compilation
7399 unit, will not be turned into long calls. The exception to this rule is
7400 that weak function definitions, functions with the @samp{long-call}
7401 attribute or the @samp{section} attribute, and functions that are within
7402 the scope of a @samp{#pragma long_calls} directive, will always be
7403 turned into long calls.
7405 This feature is not enabled by default. Specifying
7406 @option{-mno-long-calls} will restore the default behavior, as will
7407 placing the function calls within the scope of a @samp{#pragma
7408 long_calls_off} directive. Note these switches have no effect on how
7409 the compiler generates code to handle function calls via function
7412 @item -mnop-fun-dllimport
7413 @opindex mnop-fun-dllimport
7414 Disable support for the @code{dllimport} attribute.
7416 @item -msingle-pic-base
7417 @opindex msingle-pic-base
7418 Treat the register used for PIC addressing as read-only, rather than
7419 loading it in the prologue for each function. The run-time system is
7420 responsible for initializing this register with an appropriate value
7421 before execution begins.
7423 @item -mpic-register=@var{reg}
7424 @opindex mpic-register
7425 Specify the register to be used for PIC addressing. The default is R10
7426 unless stack-checking is enabled, when R9 is used.
7428 @item -mcirrus-fix-invalid-insns
7429 @opindex mcirrus-fix-invalid-insns
7430 @opindex mno-cirrus-fix-invalid-insns
7431 Insert NOPs into the instruction stream to in order to work around
7432 problems with invalid Maverick instruction combinations. This option
7433 is only valid if the @option{-mcpu=ep9312} option has been used to
7434 enable generation of instructions for the Cirrus Maverick floating
7435 point co-processor. This option is not enabled by default, since the
7436 problem is only present in older Maverick implementations. The default
7437 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
7440 @item -mpoke-function-name
7441 @opindex mpoke-function-name
7442 Write the name of each function into the text section, directly
7443 preceding the function prologue. The generated code is similar to this:
7447 .ascii "arm_poke_function_name", 0
7450 .word 0xff000000 + (t1 - t0)
7451 arm_poke_function_name
7453 stmfd sp!, @{fp, ip, lr, pc@}
7457 When performing a stack backtrace, code can inspect the value of
7458 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
7459 location @code{pc - 12} and the top 8 bits are set, then we know that
7460 there is a function name embedded immediately preceding this location
7461 and has length @code{((pc[-3]) & 0xff000000)}.
7465 Generate code for the 16-bit Thumb instruction set. The default is to
7466 use the 32-bit ARM instruction set.
7469 @opindex mtpcs-frame
7470 Generate a stack frame that is compliant with the Thumb Procedure Call
7471 Standard for all non-leaf functions. (A leaf function is one that does
7472 not call any other functions.) The default is @option{-mno-tpcs-frame}.
7474 @item -mtpcs-leaf-frame
7475 @opindex mtpcs-leaf-frame
7476 Generate a stack frame that is compliant with the Thumb Procedure Call
7477 Standard for all leaf functions. (A leaf function is one that does
7478 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
7480 @item -mcallee-super-interworking
7481 @opindex mcallee-super-interworking
7482 Gives all externally visible functions in the file being compiled an ARM
7483 instruction set header which switches to Thumb mode before executing the
7484 rest of the function. This allows these functions to be called from
7485 non-interworking code.
7487 @item -mcaller-super-interworking
7488 @opindex mcaller-super-interworking
7489 Allows calls via function pointers (including virtual functions) to
7490 execute correctly regardless of whether the target code has been
7491 compiled for interworking or not. There is a small overhead in the cost
7492 of executing a function pointer if this option is enabled.
7494 @item -mtp=@var{name}
7496 Specify the access model for the thread local storage pointer. The valid
7497 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
7498 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
7499 (supported in the arm6k architecture), and @option{auto}, which uses the
7500 best available method for the selected processor. The default setting is
7506 @subsection AVR Options
7509 These options are defined for AVR implementations:
7512 @item -mmcu=@var{mcu}
7514 Specify ATMEL AVR instruction set or MCU type.
7516 Instruction set avr1 is for the minimal AVR core, not supported by the C
7517 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
7518 attiny11, attiny12, attiny15, attiny28).
7520 Instruction set avr2 (default) is for the classic AVR core with up to
7521 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
7522 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
7523 at90c8534, at90s8535).
7525 Instruction set avr3 is for the classic AVR core with up to 128K program
7526 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
7528 Instruction set avr4 is for the enhanced AVR core with up to 8K program
7529 memory space (MCU types: atmega8, atmega83, atmega85).
7531 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7532 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7533 atmega64, atmega128, at43usb355, at94k).
7537 Output instruction sizes to the asm file.
7539 @item -minit-stack=@var{N}
7540 @opindex minit-stack
7541 Specify the initial stack address, which may be a symbol or numeric value,
7542 @samp{__stack} is the default.
7544 @item -mno-interrupts
7545 @opindex mno-interrupts
7546 Generated code is not compatible with hardware interrupts.
7547 Code size will be smaller.
7549 @item -mcall-prologues
7550 @opindex mcall-prologues
7551 Functions prologues/epilogues expanded as call to appropriate
7552 subroutines. Code size will be smaller.
7554 @item -mno-tablejump
7555 @opindex mno-tablejump
7556 Do not generate tablejump insns which sometimes increase code size.
7559 @opindex mtiny-stack
7560 Change only the low 8 bits of the stack pointer.
7564 Assume int to be 8 bit integer. This affects the sizes of all types: A
7565 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7566 and long long will be 4 bytes. Please note that this option does not
7567 comply to the C standards, but it will provide you with smaller code
7571 @node Blackfin Options
7572 @subsection Blackfin Options
7573 @cindex Blackfin Options
7576 @item -momit-leaf-frame-pointer
7577 @opindex momit-leaf-frame-pointer
7578 Don't keep the frame pointer in a register for leaf functions. This
7579 avoids the instructions to save, set up and restore frame pointers and
7580 makes an extra register available in leaf functions. The option
7581 @option{-fomit-frame-pointer} removes the frame pointer for all functions
7582 which might make debugging harder.
7584 @item -mspecld-anomaly
7585 @opindex mspecld-anomaly
7586 When enabled, the compiler will ensure that the generated code does not
7587 contain speculative loads after jump instructions. This option is enabled
7590 @item -mno-specld-anomaly
7591 @opindex mno-specld-anomaly
7592 Don't generate extra code to prevent speculative loads from occurring.
7594 @item -mcsync-anomaly
7595 @opindex mcsync-anomaly
7596 When enabled, the compiler will ensure that the generated code does not
7597 contain CSYNC or SSYNC instructions too soon after conditional branches.
7598 This option is enabled by default.
7600 @item -mno-csync-anomaly
7601 @opindex mno-csync-anomaly
7602 Don't generate extra code to prevent CSYNC or SSYNC instructions from
7603 occurring too soon after a conditional branch.
7607 When enabled, the compiler is free to take advantage of the knowledge that
7608 the entire program fits into the low 64k of memory.
7611 @opindex mno-low-64k
7612 Assume that the program is arbitrarily large. This is the default.
7614 @item -mid-shared-library
7615 @opindex mid-shared-library
7616 Generate code that supports shared libraries via the library ID method.
7617 This allows for execute in place and shared libraries in an environment
7618 without virtual memory management. This option implies @option{-fPIC}.
7620 @item -mno-id-shared-library
7621 @opindex mno-id-shared-library
7622 Generate code that doesn't assume ID based shared libraries are being used.
7623 This is the default.
7625 @item -mshared-library-id=n
7626 @opindex mshared-library-id
7627 Specified the identification number of the ID based shared library being
7628 compiled. Specifying a value of 0 will generate more compact code, specifying
7629 other values will force the allocation of that number to the current
7630 library but is no more space or time efficient than omitting this option.
7633 @itemx -mno-long-calls
7634 @opindex mlong-calls
7635 @opindex mno-long-calls
7636 Tells the compiler to perform function calls by first loading the
7637 address of the function into a register and then performing a subroutine
7638 call on this register. This switch is needed if the target function
7639 will lie outside of the 24 bit addressing range of the offset based
7640 version of subroutine call instruction.
7642 This feature is not enabled by default. Specifying
7643 @option{-mno-long-calls} will restore the default behavior. Note these
7644 switches have no effect on how the compiler generates code to handle
7645 function calls via function pointers.
7649 @subsection CRIS Options
7650 @cindex CRIS Options
7652 These options are defined specifically for the CRIS ports.
7655 @item -march=@var{architecture-type}
7656 @itemx -mcpu=@var{architecture-type}
7659 Generate code for the specified architecture. The choices for
7660 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7661 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
7662 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7665 @item -mtune=@var{architecture-type}
7667 Tune to @var{architecture-type} everything applicable about the generated
7668 code, except for the ABI and the set of available instructions. The
7669 choices for @var{architecture-type} are the same as for
7670 @option{-march=@var{architecture-type}}.
7672 @item -mmax-stack-frame=@var{n}
7673 @opindex mmax-stack-frame
7674 Warn when the stack frame of a function exceeds @var{n} bytes.
7676 @item -melinux-stacksize=@var{n}
7677 @opindex melinux-stacksize
7678 Only available with the @samp{cris-axis-aout} target. Arranges for
7679 indications in the program to the kernel loader that the stack of the
7680 program should be set to @var{n} bytes.
7686 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7687 @option{-march=v3} and @option{-march=v8} respectively.
7689 @item -mmul-bug-workaround
7690 @itemx -mno-mul-bug-workaround
7691 @opindex mmul-bug-workaround
7692 @opindex mno-mul-bug-workaround
7693 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7694 models where it applies. This option is active by default.
7698 Enable CRIS-specific verbose debug-related information in the assembly
7699 code. This option also has the effect to turn off the @samp{#NO_APP}
7700 formatted-code indicator to the assembler at the beginning of the
7705 Do not use condition-code results from previous instruction; always emit
7706 compare and test instructions before use of condition codes.
7708 @item -mno-side-effects
7709 @opindex mno-side-effects
7710 Do not emit instructions with side-effects in addressing modes other than
7714 @itemx -mno-stack-align
7716 @itemx -mno-data-align
7717 @itemx -mconst-align
7718 @itemx -mno-const-align
7719 @opindex mstack-align
7720 @opindex mno-stack-align
7721 @opindex mdata-align
7722 @opindex mno-data-align
7723 @opindex mconst-align
7724 @opindex mno-const-align
7725 These options (no-options) arranges (eliminate arrangements) for the
7726 stack-frame, individual data and constants to be aligned for the maximum
7727 single data access size for the chosen CPU model. The default is to
7728 arrange for 32-bit alignment. ABI details such as structure layout are
7729 not affected by these options.
7737 Similar to the stack- data- and const-align options above, these options
7738 arrange for stack-frame, writable data and constants to all be 32-bit,
7739 16-bit or 8-bit aligned. The default is 32-bit alignment.
7741 @item -mno-prologue-epilogue
7742 @itemx -mprologue-epilogue
7743 @opindex mno-prologue-epilogue
7744 @opindex mprologue-epilogue
7745 With @option{-mno-prologue-epilogue}, the normal function prologue and
7746 epilogue that sets up the stack-frame are omitted and no return
7747 instructions or return sequences are generated in the code. Use this
7748 option only together with visual inspection of the compiled code: no
7749 warnings or errors are generated when call-saved registers must be saved,
7750 or storage for local variable needs to be allocated.
7756 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7757 instruction sequences that load addresses for functions from the PLT part
7758 of the GOT rather than (traditional on other architectures) calls to the
7759 PLT@. The default is @option{-mgotplt}.
7763 Legacy no-op option only recognized with the cris-axis-aout target.
7767 Legacy no-op option only recognized with the cris-axis-elf and
7768 cris-axis-linux-gnu targets.
7772 Only recognized with the cris-axis-aout target, where it selects a
7773 GNU/linux-like multilib, include files and instruction set for
7778 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7782 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7783 to link with input-output functions from a simulator library. Code,
7784 initialized data and zero-initialized data are allocated consecutively.
7788 Like @option{-sim}, but pass linker options to locate initialized data at
7789 0x40000000 and zero-initialized data at 0x80000000.
7793 @subsection CRX Options
7796 These options are defined specifically for the CRX ports.
7802 Enable the use of multiply-accumulate instructions. Disabled by default.
7806 Push instructions will be used to pass outgoing arguments when functions
7807 are called. Enabled by default.
7810 @node Darwin Options
7811 @subsection Darwin Options
7812 @cindex Darwin options
7814 These options are defined for all architectures running the Darwin operating
7817 FSF GCC on Darwin does not create ``fat'' object files; it will create
7818 an object file for the single architecture that it was built to
7819 target. Apple's GCC on Darwin does create ``fat'' files if multiple
7820 @option{-arch} options are used; it does so by running the compiler or
7821 linker multiple times and joining the results together with
7824 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
7825 @samp{i686}) is determined by the flags that specify the ISA
7826 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
7827 @option{-force_cpusubtype_ALL} option can be used to override this.
7829 The Darwin tools vary in their behavior when presented with an ISA
7830 mismatch. The assembler, @file{as}, will only permit instructions to
7831 be used that are valid for the subtype of the file it is generating,
7832 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
7833 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
7834 and print an error if asked to create a shared library with a less
7835 restrictive subtype than its input files (for instance, trying to put
7836 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
7837 for executables, @file{ld}, will quietly give the executable the most
7838 restrictive subtype of any of its input files.
7843 Add the framework directory @var{dir} to the head of the list of
7844 directories to be searched for header files. These directories are
7845 interleaved with those specified by @option{-I} options and are
7846 scanned in a left-to-right order.
7848 A framework directory is a directory with frameworks in it. A
7849 framework is a directory with a @samp{"Headers"} and/or
7850 @samp{"PrivateHeaders"} directory contained directly in it that ends
7851 in @samp{".framework"}. The name of a framework is the name of this
7852 directory excluding the @samp{".framework"}. Headers associated with
7853 the framework are found in one of those two directories, with
7854 @samp{"Headers"} being searched first. A subframework is a framework
7855 directory that is in a framework's @samp{"Frameworks"} directory.
7856 Includes of subframework headers can only appear in a header of a
7857 framework that contains the subframework, or in a sibling subframework
7858 header. Two subframeworks are siblings if they occur in the same
7859 framework. A subframework should not have the same name as a
7860 framework, a warning will be issued if this is violated. Currently a
7861 subframework cannot have subframeworks, in the future, the mechanism
7862 may be extended to support this. The standard frameworks can be found
7863 in @samp{"/System/Library/Frameworks"} and
7864 @samp{"/Library/Frameworks"}. An example include looks like
7865 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7866 the name of the framework and header.h is found in the
7867 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7871 Emit debugging information for symbols that are used. For STABS
7872 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7873 This is by default ON@.
7877 Emit debugging information for all symbols and types.
7879 @item -mmacosx-version-min=@var{version}
7880 The earliest version of MacOS X that this executable will run on
7881 is @var{version}. Typical values of @var{version} include @code{10.1},
7882 @code{10.2}, and @code{10.3.9}.
7884 The default for this option is to make choices that seem to be most
7887 @item -mone-byte-bool
7888 @opindex -mone-byte-bool
7889 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7890 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7891 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7892 option has no effect on x86.
7894 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7895 to generate code that is not binary compatible with code generated
7896 without that switch. Using this switch may require recompiling all
7897 other modules in a program, including system libraries. Use this
7898 switch to conform to a non-default data model.
7900 @item -mfix-and-continue
7901 @itemx -ffix-and-continue
7902 @itemx -findirect-data
7903 @opindex mfix-and-continue
7904 @opindex ffix-and-continue
7905 @opindex findirect-data
7906 Generate code suitable for fast turn around development. Needed to
7907 enable gdb to dynamically load @code{.o} files into already running
7908 programs. @option{-findirect-data} and @option{-ffix-and-continue}
7909 are provided for backwards compatibility.
7913 Loads all members of static archive libraries.
7914 See man ld(1) for more information.
7916 @item -arch_errors_fatal
7917 @opindex arch_errors_fatal
7918 Cause the errors having to do with files that have the wrong architecture
7922 @opindex bind_at_load
7923 Causes the output file to be marked such that the dynamic linker will
7924 bind all undefined references when the file is loaded or launched.
7928 Produce a Mach-o bundle format file.
7929 See man ld(1) for more information.
7931 @item -bundle_loader @var{executable}
7932 @opindex bundle_loader
7933 This option specifies the @var{executable} that will be loading the build
7934 output file being linked. See man ld(1) for more information.
7937 @opindex -dynamiclib
7938 When passed this option, GCC will produce a dynamic library instead of
7939 an executable when linking, using the Darwin @file{libtool} command.
7941 @item -force_cpusubtype_ALL
7942 @opindex -force_cpusubtype_ALL
7943 This causes GCC's output file to have the @var{ALL} subtype, instead of
7944 one controlled by the @option{-mcpu} or @option{-march} option.
7946 @item -allowable_client @var{client_name}
7948 @itemx -compatibility_version
7949 @itemx -current_version
7951 @itemx -dependency-file
7953 @itemx -dylinker_install_name
7955 @itemx -exported_symbols_list
7957 @itemx -flat_namespace
7958 @itemx -force_flat_namespace
7959 @itemx -headerpad_max_install_names
7962 @itemx -install_name
7963 @itemx -keep_private_externs
7964 @itemx -multi_module
7965 @itemx -multiply_defined
7966 @itemx -multiply_defined_unused
7968 @itemx -no_dead_strip_inits_and_terms
7969 @itemx -nofixprebinding
7972 @itemx -noseglinkedit
7973 @itemx -pagezero_size
7975 @itemx -prebind_all_twolevel_modules
7976 @itemx -private_bundle
7977 @itemx -read_only_relocs
7979 @itemx -sectobjectsymbols
7983 @itemx -sectobjectsymbols
7986 @itemx -segs_read_only_addr
7987 @itemx -segs_read_write_addr
7988 @itemx -seg_addr_table
7989 @itemx -seg_addr_table_filename
7992 @itemx -segs_read_only_addr
7993 @itemx -segs_read_write_addr
7994 @itemx -single_module
7997 @itemx -sub_umbrella
7998 @itemx -twolevel_namespace
8001 @itemx -unexported_symbols_list
8002 @itemx -weak_reference_mismatches
8005 @opindex allowable_client
8006 @opindex client_name
8007 @opindex compatibility_version
8008 @opindex current_version
8010 @opindex dependency-file
8012 @opindex dylinker_install_name
8014 @opindex exported_symbols_list
8016 @opindex flat_namespace
8017 @opindex force_flat_namespace
8018 @opindex headerpad_max_install_names
8021 @opindex install_name
8022 @opindex keep_private_externs
8023 @opindex multi_module
8024 @opindex multiply_defined
8025 @opindex multiply_defined_unused
8027 @opindex no_dead_strip_inits_and_terms
8028 @opindex nofixprebinding
8029 @opindex nomultidefs
8031 @opindex noseglinkedit
8032 @opindex pagezero_size
8034 @opindex prebind_all_twolevel_modules
8035 @opindex private_bundle
8036 @opindex read_only_relocs
8038 @opindex sectobjectsymbols
8042 @opindex sectobjectsymbols
8045 @opindex segs_read_only_addr
8046 @opindex segs_read_write_addr
8047 @opindex seg_addr_table
8048 @opindex seg_addr_table_filename
8049 @opindex seglinkedit
8051 @opindex segs_read_only_addr
8052 @opindex segs_read_write_addr
8053 @opindex single_module
8055 @opindex sub_library
8056 @opindex sub_umbrella
8057 @opindex twolevel_namespace
8060 @opindex unexported_symbols_list
8061 @opindex weak_reference_mismatches
8062 @opindex whatsloaded
8064 These options are passed to the Darwin linker. The Darwin linker man page
8065 describes them in detail.
8068 @node DEC Alpha Options
8069 @subsection DEC Alpha Options
8071 These @samp{-m} options are defined for the DEC Alpha implementations:
8074 @item -mno-soft-float
8076 @opindex mno-soft-float
8077 @opindex msoft-float
8078 Use (do not use) the hardware floating-point instructions for
8079 floating-point operations. When @option{-msoft-float} is specified,
8080 functions in @file{libgcc.a} will be used to perform floating-point
8081 operations. Unless they are replaced by routines that emulate the
8082 floating-point operations, or compiled in such a way as to call such
8083 emulations routines, these routines will issue floating-point
8084 operations. If you are compiling for an Alpha without floating-point
8085 operations, you must ensure that the library is built so as not to call
8088 Note that Alpha implementations without floating-point operations are
8089 required to have floating-point registers.
8094 @opindex mno-fp-regs
8095 Generate code that uses (does not use) the floating-point register set.
8096 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
8097 register set is not used, floating point operands are passed in integer
8098 registers as if they were integers and floating-point results are passed
8099 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
8100 so any function with a floating-point argument or return value called by code
8101 compiled with @option{-mno-fp-regs} must also be compiled with that
8104 A typical use of this option is building a kernel that does not use,
8105 and hence need not save and restore, any floating-point registers.
8109 The Alpha architecture implements floating-point hardware optimized for
8110 maximum performance. It is mostly compliant with the IEEE floating
8111 point standard. However, for full compliance, software assistance is
8112 required. This option generates code fully IEEE compliant code
8113 @emph{except} that the @var{inexact-flag} is not maintained (see below).
8114 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
8115 defined during compilation. The resulting code is less efficient but is
8116 able to correctly support denormalized numbers and exceptional IEEE
8117 values such as not-a-number and plus/minus infinity. Other Alpha
8118 compilers call this option @option{-ieee_with_no_inexact}.
8120 @item -mieee-with-inexact
8121 @opindex mieee-with-inexact
8122 This is like @option{-mieee} except the generated code also maintains
8123 the IEEE @var{inexact-flag}. Turning on this option causes the
8124 generated code to implement fully-compliant IEEE math. In addition to
8125 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
8126 macro. On some Alpha implementations the resulting code may execute
8127 significantly slower than the code generated by default. Since there is
8128 very little code that depends on the @var{inexact-flag}, you should
8129 normally not specify this option. Other Alpha compilers call this
8130 option @option{-ieee_with_inexact}.
8132 @item -mfp-trap-mode=@var{trap-mode}
8133 @opindex mfp-trap-mode
8134 This option controls what floating-point related traps are enabled.
8135 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
8136 The trap mode can be set to one of four values:
8140 This is the default (normal) setting. The only traps that are enabled
8141 are the ones that cannot be disabled in software (e.g., division by zero
8145 In addition to the traps enabled by @samp{n}, underflow traps are enabled
8149 Like @samp{su}, but the instructions are marked to be safe for software
8150 completion (see Alpha architecture manual for details).
8153 Like @samp{su}, but inexact traps are enabled as well.
8156 @item -mfp-rounding-mode=@var{rounding-mode}
8157 @opindex mfp-rounding-mode
8158 Selects the IEEE rounding mode. Other Alpha compilers call this option
8159 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
8164 Normal IEEE rounding mode. Floating point numbers are rounded towards
8165 the nearest machine number or towards the even machine number in case
8169 Round towards minus infinity.
8172 Chopped rounding mode. Floating point numbers are rounded towards zero.
8175 Dynamic rounding mode. A field in the floating point control register
8176 (@var{fpcr}, see Alpha architecture reference manual) controls the
8177 rounding mode in effect. The C library initializes this register for
8178 rounding towards plus infinity. Thus, unless your program modifies the
8179 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
8182 @item -mtrap-precision=@var{trap-precision}
8183 @opindex mtrap-precision
8184 In the Alpha architecture, floating point traps are imprecise. This
8185 means without software assistance it is impossible to recover from a
8186 floating trap and program execution normally needs to be terminated.
8187 GCC can generate code that can assist operating system trap handlers
8188 in determining the exact location that caused a floating point trap.
8189 Depending on the requirements of an application, different levels of
8190 precisions can be selected:
8194 Program precision. This option is the default and means a trap handler
8195 can only identify which program caused a floating point exception.
8198 Function precision. The trap handler can determine the function that
8199 caused a floating point exception.
8202 Instruction precision. The trap handler can determine the exact
8203 instruction that caused a floating point exception.
8206 Other Alpha compilers provide the equivalent options called
8207 @option{-scope_safe} and @option{-resumption_safe}.
8209 @item -mieee-conformant
8210 @opindex mieee-conformant
8211 This option marks the generated code as IEEE conformant. You must not
8212 use this option unless you also specify @option{-mtrap-precision=i} and either
8213 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
8214 is to emit the line @samp{.eflag 48} in the function prologue of the
8215 generated assembly file. Under DEC Unix, this has the effect that
8216 IEEE-conformant math library routines will be linked in.
8218 @item -mbuild-constants
8219 @opindex mbuild-constants
8220 Normally GCC examines a 32- or 64-bit integer constant to
8221 see if it can construct it from smaller constants in two or three
8222 instructions. If it cannot, it will output the constant as a literal and
8223 generate code to load it from the data segment at runtime.
8225 Use this option to require GCC to construct @emph{all} integer constants
8226 using code, even if it takes more instructions (the maximum is six).
8228 You would typically use this option to build a shared library dynamic
8229 loader. Itself a shared library, it must relocate itself in memory
8230 before it can find the variables and constants in its own data segment.
8236 Select whether to generate code to be assembled by the vendor-supplied
8237 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
8255 Indicate whether GCC should generate code to use the optional BWX,
8256 CIX, FIX and MAX instruction sets. The default is to use the instruction
8257 sets supported by the CPU type specified via @option{-mcpu=} option or that
8258 of the CPU on which GCC was built if none was specified.
8263 @opindex mfloat-ieee
8264 Generate code that uses (does not use) VAX F and G floating point
8265 arithmetic instead of IEEE single and double precision.
8267 @item -mexplicit-relocs
8268 @itemx -mno-explicit-relocs
8269 @opindex mexplicit-relocs
8270 @opindex mno-explicit-relocs
8271 Older Alpha assemblers provided no way to generate symbol relocations
8272 except via assembler macros. Use of these macros does not allow
8273 optimal instruction scheduling. GNU binutils as of version 2.12
8274 supports a new syntax that allows the compiler to explicitly mark
8275 which relocations should apply to which instructions. This option
8276 is mostly useful for debugging, as GCC detects the capabilities of
8277 the assembler when it is built and sets the default accordingly.
8281 @opindex msmall-data
8282 @opindex mlarge-data
8283 When @option{-mexplicit-relocs} is in effect, static data is
8284 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
8285 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
8286 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
8287 16-bit relocations off of the @code{$gp} register. This limits the
8288 size of the small data area to 64KB, but allows the variables to be
8289 directly accessed via a single instruction.
8291 The default is @option{-mlarge-data}. With this option the data area
8292 is limited to just below 2GB@. Programs that require more than 2GB of
8293 data must use @code{malloc} or @code{mmap} to allocate the data in the
8294 heap instead of in the program's data segment.
8296 When generating code for shared libraries, @option{-fpic} implies
8297 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
8301 @opindex msmall-text
8302 @opindex mlarge-text
8303 When @option{-msmall-text} is used, the compiler assumes that the
8304 code of the entire program (or shared library) fits in 4MB, and is
8305 thus reachable with a branch instruction. When @option{-msmall-data}
8306 is used, the compiler can assume that all local symbols share the
8307 same @code{$gp} value, and thus reduce the number of instructions
8308 required for a function call from 4 to 1.
8310 The default is @option{-mlarge-text}.
8312 @item -mcpu=@var{cpu_type}
8314 Set the instruction set and instruction scheduling parameters for
8315 machine type @var{cpu_type}. You can specify either the @samp{EV}
8316 style name or the corresponding chip number. GCC supports scheduling
8317 parameters for the EV4, EV5 and EV6 family of processors and will
8318 choose the default values for the instruction set from the processor
8319 you specify. If you do not specify a processor type, GCC will default
8320 to the processor on which the compiler was built.
8322 Supported values for @var{cpu_type} are
8328 Schedules as an EV4 and has no instruction set extensions.
8332 Schedules as an EV5 and has no instruction set extensions.
8336 Schedules as an EV5 and supports the BWX extension.
8341 Schedules as an EV5 and supports the BWX and MAX extensions.
8345 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
8349 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
8352 @item -mtune=@var{cpu_type}
8354 Set only the instruction scheduling parameters for machine type
8355 @var{cpu_type}. The instruction set is not changed.
8357 @item -mmemory-latency=@var{time}
8358 @opindex mmemory-latency
8359 Sets the latency the scheduler should assume for typical memory
8360 references as seen by the application. This number is highly
8361 dependent on the memory access patterns used by the application
8362 and the size of the external cache on the machine.
8364 Valid options for @var{time} are
8368 A decimal number representing clock cycles.
8374 The compiler contains estimates of the number of clock cycles for
8375 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
8376 (also called Dcache, Scache, and Bcache), as well as to main memory.
8377 Note that L3 is only valid for EV5.
8382 @node DEC Alpha/VMS Options
8383 @subsection DEC Alpha/VMS Options
8385 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
8388 @item -mvms-return-codes
8389 @opindex mvms-return-codes
8390 Return VMS condition codes from main. The default is to return POSIX
8391 style condition (e.g.@ error) codes.
8395 @subsection FRV Options
8402 Only use the first 32 general purpose registers.
8407 Use all 64 general purpose registers.
8412 Use only the first 32 floating point registers.
8417 Use all 64 floating point registers
8420 @opindex mhard-float
8422 Use hardware instructions for floating point operations.
8425 @opindex msoft-float
8427 Use library routines for floating point operations.
8432 Dynamically allocate condition code registers.
8437 Do not try to dynamically allocate condition code registers, only
8438 use @code{icc0} and @code{fcc0}.
8443 Change ABI to use double word insns.
8448 Do not use double word instructions.
8453 Use floating point double instructions.
8458 Do not use floating point double instructions.
8463 Use media instructions.
8468 Do not use media instructions.
8473 Use multiply and add/subtract instructions.
8478 Do not use multiply and add/subtract instructions.
8483 Select the FDPIC ABI, that uses function descriptors to represent
8484 pointers to functions. Without any PIC/PIE-related options, it
8485 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
8486 assumes GOT entries and small data are within a 12-bit range from the
8487 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
8488 are computed with 32 bits.
8491 @opindex minline-plt
8493 Enable inlining of PLT entries in function calls to functions that are
8494 not known to bind locally. It has no effect without @option{-mfdpic}.
8495 It's enabled by default if optimizing for speed and compiling for
8496 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
8497 optimization option such as @option{-O3} or above is present in the
8503 Assume a large TLS segment when generating thread-local code.
8508 Do not assume a large TLS segment when generating thread-local code.
8513 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
8514 that is known to be in read-only sections. It's enabled by default,
8515 except for @option{-fpic} or @option{-fpie}: even though it may help
8516 make the global offset table smaller, it trades 1 instruction for 4.
8517 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
8518 one of which may be shared by multiple symbols, and it avoids the need
8519 for a GOT entry for the referenced symbol, so it's more likely to be a
8520 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
8522 @item -multilib-library-pic
8523 @opindex multilib-library-pic
8525 Link with the (library, not FD) pic libraries. It's implied by
8526 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
8527 @option{-fpic} without @option{-mfdpic}. You should never have to use
8533 Follow the EABI requirement of always creating a frame pointer whenever
8534 a stack frame is allocated. This option is enabled by default and can
8535 be disabled with @option{-mno-linked-fp}.
8538 @opindex mlong-calls
8540 Use indirect addressing to call functions outside the current
8541 compilation unit. This allows the functions to be placed anywhere
8542 within the 32-bit address space.
8544 @item -malign-labels
8545 @opindex malign-labels
8547 Try to align labels to an 8-byte boundary by inserting nops into the
8548 previous packet. This option only has an effect when VLIW packing
8549 is enabled. It doesn't create new packets; it merely adds nops to
8553 @opindex mlibrary-pic
8555 Generate position-independent EABI code.
8560 Use only the first four media accumulator registers.
8565 Use all eight media accumulator registers.
8570 Pack VLIW instructions.
8575 Do not pack VLIW instructions.
8580 Do not mark ABI switches in e_flags.
8585 Enable the use of conditional-move instructions (default).
8587 This switch is mainly for debugging the compiler and will likely be removed
8588 in a future version.
8590 @item -mno-cond-move
8591 @opindex mno-cond-move
8593 Disable the use of conditional-move instructions.
8595 This switch is mainly for debugging the compiler and will likely be removed
8596 in a future version.
8601 Enable the use of conditional set instructions (default).
8603 This switch is mainly for debugging the compiler and will likely be removed
8604 in a future version.
8609 Disable the use of conditional set instructions.
8611 This switch is mainly for debugging the compiler and will likely be removed
8612 in a future version.
8617 Enable the use of conditional execution (default).
8619 This switch is mainly for debugging the compiler and will likely be removed
8620 in a future version.
8622 @item -mno-cond-exec
8623 @opindex mno-cond-exec
8625 Disable the use of conditional execution.
8627 This switch is mainly for debugging the compiler and will likely be removed
8628 in a future version.
8631 @opindex mvliw-branch
8633 Run a pass to pack branches into VLIW instructions (default).
8635 This switch is mainly for debugging the compiler and will likely be removed
8636 in a future version.
8638 @item -mno-vliw-branch
8639 @opindex mno-vliw-branch
8641 Do not run a pass to pack branches into VLIW instructions.
8643 This switch is mainly for debugging the compiler and will likely be removed
8644 in a future version.
8646 @item -mmulti-cond-exec
8647 @opindex mmulti-cond-exec
8649 Enable optimization of @code{&&} and @code{||} in conditional execution
8652 This switch is mainly for debugging the compiler and will likely be removed
8653 in a future version.
8655 @item -mno-multi-cond-exec
8656 @opindex mno-multi-cond-exec
8658 Disable optimization of @code{&&} and @code{||} in conditional execution.
8660 This switch is mainly for debugging the compiler and will likely be removed
8661 in a future version.
8663 @item -mnested-cond-exec
8664 @opindex mnested-cond-exec
8666 Enable nested conditional execution optimizations (default).
8668 This switch is mainly for debugging the compiler and will likely be removed
8669 in a future version.
8671 @item -mno-nested-cond-exec
8672 @opindex mno-nested-cond-exec
8674 Disable nested conditional execution optimizations.
8676 This switch is mainly for debugging the compiler and will likely be removed
8677 in a future version.
8679 @item -moptimize-membar
8680 @opindex moptimize-membar
8682 This switch removes redundant @code{membar} instructions from the
8683 compiler generated code. It is enabled by default.
8685 @item -mno-optimize-membar
8686 @opindex mno-optimize-membar
8688 This switch disables the automatic removal of redundant @code{membar}
8689 instructions from the generated code.
8691 @item -mtomcat-stats
8692 @opindex mtomcat-stats
8694 Cause gas to print out tomcat statistics.
8696 @item -mcpu=@var{cpu}
8699 Select the processor type for which to generate code. Possible values are
8700 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8701 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8705 @node H8/300 Options
8706 @subsection H8/300 Options
8708 These @samp{-m} options are defined for the H8/300 implementations:
8713 Shorten some address references at link time, when possible; uses the
8714 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8715 ld, Using ld}, for a fuller description.
8719 Generate code for the H8/300H@.
8723 Generate code for the H8S@.
8727 Generate code for the H8S and H8/300H in the normal mode. This switch
8728 must be used either with @option{-mh} or @option{-ms}.
8732 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8736 Make @code{int} data 32 bits by default.
8740 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8741 The default for the H8/300H and H8S is to align longs and floats on 4
8743 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8744 This option has no effect on the H8/300.
8748 @subsection HPPA Options
8749 @cindex HPPA Options
8751 These @samp{-m} options are defined for the HPPA family of computers:
8754 @item -march=@var{architecture-type}
8756 Generate code for the specified architecture. The choices for
8757 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8758 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8759 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8760 architecture option for your machine. Code compiled for lower numbered
8761 architectures will run on higher numbered architectures, but not the
8765 @itemx -mpa-risc-1-1
8766 @itemx -mpa-risc-2-0
8767 @opindex mpa-risc-1-0
8768 @opindex mpa-risc-1-1
8769 @opindex mpa-risc-2-0
8770 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8773 @opindex mbig-switch
8774 Generate code suitable for big switch tables. Use this option only if
8775 the assembler/linker complain about out of range branches within a switch
8778 @item -mjump-in-delay
8779 @opindex mjump-in-delay
8780 Fill delay slots of function calls with unconditional jump instructions
8781 by modifying the return pointer for the function call to be the target
8782 of the conditional jump.
8784 @item -mdisable-fpregs
8785 @opindex mdisable-fpregs
8786 Prevent floating point registers from being used in any manner. This is
8787 necessary for compiling kernels which perform lazy context switching of
8788 floating point registers. If you use this option and attempt to perform
8789 floating point operations, the compiler will abort.
8791 @item -mdisable-indexing
8792 @opindex mdisable-indexing
8793 Prevent the compiler from using indexing address modes. This avoids some
8794 rather obscure problems when compiling MIG generated code under MACH@.
8796 @item -mno-space-regs
8797 @opindex mno-space-regs
8798 Generate code that assumes the target has no space registers. This allows
8799 GCC to generate faster indirect calls and use unscaled index address modes.
8801 Such code is suitable for level 0 PA systems and kernels.
8803 @item -mfast-indirect-calls
8804 @opindex mfast-indirect-calls
8805 Generate code that assumes calls never cross space boundaries. This
8806 allows GCC to emit code which performs faster indirect calls.
8808 This option will not work in the presence of shared libraries or nested
8811 @item -mfixed-range=@var{register-range}
8812 @opindex mfixed-range
8813 Generate code treating the given register range as fixed registers.
8814 A fixed register is one that the register allocator can not use. This is
8815 useful when compiling kernel code. A register range is specified as
8816 two registers separated by a dash. Multiple register ranges can be
8817 specified separated by a comma.
8819 @item -mlong-load-store
8820 @opindex mlong-load-store
8821 Generate 3-instruction load and store sequences as sometimes required by
8822 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8825 @item -mportable-runtime
8826 @opindex mportable-runtime
8827 Use the portable calling conventions proposed by HP for ELF systems.
8831 Enable the use of assembler directives only GAS understands.
8833 @item -mschedule=@var{cpu-type}
8835 Schedule code according to the constraints for the machine type
8836 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8837 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8838 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8839 proper scheduling option for your machine. The default scheduling is
8843 @opindex mlinker-opt
8844 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8845 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8846 linkers in which they give bogus error messages when linking some programs.
8849 @opindex msoft-float
8850 Generate output containing library calls for floating point.
8851 @strong{Warning:} the requisite libraries are not available for all HPPA
8852 targets. Normally the facilities of the machine's usual C compiler are
8853 used, but this cannot be done directly in cross-compilation. You must make
8854 your own arrangements to provide suitable library functions for
8855 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8856 does provide software floating point support.
8858 @option{-msoft-float} changes the calling convention in the output file;
8859 therefore, it is only useful if you compile @emph{all} of a program with
8860 this option. In particular, you need to compile @file{libgcc.a}, the
8861 library that comes with GCC, with @option{-msoft-float} in order for
8866 Generate the predefine, @code{_SIO}, for server IO@. The default is
8867 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8868 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
8869 options are available under HP-UX and HI-UX@.
8873 Use GNU ld specific options. This passes @option{-shared} to ld when
8874 building a shared library. It is the default when GCC is configured,
8875 explicitly or implicitly, with the GNU linker. This option does not
8876 have any affect on which ld is called, it only changes what parameters
8877 are passed to that ld. The ld that is called is determined by the
8878 @option{--with-ld} configure option, GCC's program search path, and
8879 finally by the user's @env{PATH}. The linker used by GCC can be printed
8880 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
8881 on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8885 Use HP ld specific options. This passes @option{-b} to ld when building
8886 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8887 links. It is the default when GCC is configured, explicitly or
8888 implicitly, with the HP linker. This option does not have any affect on
8889 which ld is called, it only changes what parameters are passed to that
8890 ld. The ld that is called is determined by the @option{--with-ld}
8891 configure option, GCC's program search path, and finally by the user's
8892 @env{PATH}. The linker used by GCC can be printed using @samp{which
8893 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
8894 HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
8897 @opindex mno-long-calls
8898 Generate code that uses long call sequences. This ensures that a call
8899 is always able to reach linker generated stubs. The default is to generate
8900 long calls only when the distance from the call site to the beginning
8901 of the function or translation unit, as the case may be, exceeds a
8902 predefined limit set by the branch type being used. The limits for
8903 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8904 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8907 Distances are measured from the beginning of functions when using the
8908 @option{-ffunction-sections} option, or when using the @option{-mgas}
8909 and @option{-mno-portable-runtime} options together under HP-UX with
8912 It is normally not desirable to use this option as it will degrade
8913 performance. However, it may be useful in large applications,
8914 particularly when partial linking is used to build the application.
8916 The types of long calls used depends on the capabilities of the
8917 assembler and linker, and the type of code being generated. The
8918 impact on systems that support long absolute calls, and long pic
8919 symbol-difference or pc-relative calls should be relatively small.
8920 However, an indirect call is used on 32-bit ELF systems in pic code
8921 and it is quite long.
8923 @item -munix=@var{unix-std}
8925 Generate compiler predefines and select a startfile for the specified
8926 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
8927 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
8928 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
8929 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
8930 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
8933 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
8934 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
8935 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
8936 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
8937 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
8938 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
8940 It is @emph{important} to note that this option changes the interfaces
8941 for various library routines. It also affects the operational behavior
8942 of the C library. Thus, @emph{extreme} care is needed in using this
8945 Library code that is intended to operate with more than one UNIX
8946 standard must test, set and restore the variable @var{__xpg4_extended_mask}
8947 as appropriate. Most GNU software doesn't provide this capability.
8951 Suppress the generation of link options to search libdld.sl when the
8952 @option{-static} option is specified on HP-UX 10 and later.
8956 The HP-UX implementation of setlocale in libc has a dependency on
8957 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8958 when the @option{-static} option is specified, special link options
8959 are needed to resolve this dependency.
8961 On HP-UX 10 and later, the GCC driver adds the necessary options to
8962 link with libdld.sl when the @option{-static} option is specified.
8963 This causes the resulting binary to be dynamic. On the 64-bit port,
8964 the linkers generate dynamic binaries by default in any case. The
8965 @option{-nolibdld} option can be used to prevent the GCC driver from
8966 adding these link options.
8970 Add support for multithreading with the @dfn{dce thread} library
8971 under HP-UX@. This option sets flags for both the preprocessor and
8975 @node i386 and x86-64 Options
8976 @subsection Intel 386 and AMD x86-64 Options
8977 @cindex i386 Options
8978 @cindex x86-64 Options
8979 @cindex Intel 386 Options
8980 @cindex AMD x86-64 Options
8982 These @samp{-m} options are defined for the i386 and x86-64 family of
8986 @item -mtune=@var{cpu-type}
8988 Tune to @var{cpu-type} everything applicable about the generated code, except
8989 for the ABI and the set of available instructions. The choices for
8993 Original Intel's i386 CPU@.
8995 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
8997 Intel Pentium CPU with no MMX support.
8999 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
9000 @item i686, pentiumpro
9001 Intel PentiumPro CPU@.
9003 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
9004 @item pentium3, pentium3m
9005 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
9008 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
9009 support. Used by Centrino notebooks.
9010 @item pentium4, pentium4m
9011 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
9013 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
9016 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
9017 SSE2 and SSE3 instruction set support.
9019 AMD K6 CPU with MMX instruction set support.
9021 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
9022 @item athlon, athlon-tbird
9023 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
9025 @item athlon-4, athlon-xp, athlon-mp
9026 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
9027 instruction set support.
9028 @item k8, opteron, athlon64, athlon-fx
9029 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
9030 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
9032 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
9035 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
9036 instruction set support.
9038 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
9039 implemented for this chip.)
9041 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
9042 implemented for this chip.)
9045 While picking a specific @var{cpu-type} will schedule things appropriately
9046 for that particular chip, the compiler will not generate any code that
9047 does not run on the i386 without the @option{-march=@var{cpu-type}} option
9050 @item -march=@var{cpu-type}
9052 Generate instructions for the machine type @var{cpu-type}. The choices
9053 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
9054 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
9056 @item -mcpu=@var{cpu-type}
9058 A deprecated synonym for @option{-mtune}.
9067 @opindex mpentiumpro
9068 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
9069 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
9070 These synonyms are deprecated.
9072 @item -mfpmath=@var{unit}
9074 Generate floating point arithmetics for selected unit @var{unit}. The choices
9079 Use the standard 387 floating point coprocessor present majority of chips and
9080 emulated otherwise. Code compiled with this option will run almost everywhere.
9081 The temporary results are computed in 80bit precision instead of precision
9082 specified by the type resulting in slightly different results compared to most
9083 of other chips. See @option{-ffloat-store} for more detailed description.
9085 This is the default choice for i386 compiler.
9088 Use scalar floating point instructions present in the SSE instruction set.
9089 This instruction set is supported by Pentium3 and newer chips, in the AMD line
9090 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
9091 instruction set supports only single precision arithmetics, thus the double and
9092 extended precision arithmetics is still done using 387. Later version, present
9093 only in Pentium4 and the future AMD x86-64 chips supports double precision
9096 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
9097 or @option{-msse2} switches to enable SSE extensions and make this option
9098 effective. For the x86-64 compiler, these extensions are enabled by default.
9100 The resulting code should be considerably faster in the majority of cases and avoid
9101 the numerical instability problems of 387 code, but may break some existing
9102 code that expects temporaries to be 80bit.
9104 This is the default choice for the x86-64 compiler.
9107 Attempt to utilize both instruction sets at once. This effectively double the
9108 amount of available registers and on chips with separate execution units for
9109 387 and SSE the execution resources too. Use this option with care, as it is
9110 still experimental, because the GCC register allocator does not model separate
9111 functional units well resulting in instable performance.
9114 @item -masm=@var{dialect}
9115 @opindex masm=@var{dialect}
9116 Output asm instructions using selected @var{dialect}. Supported
9117 choices are @samp{intel} or @samp{att} (the default one). Darwin does
9118 not support @samp{intel}.
9123 @opindex mno-ieee-fp
9124 Control whether or not the compiler uses IEEE floating point
9125 comparisons. These handle correctly the case where the result of a
9126 comparison is unordered.
9129 @opindex msoft-float
9130 Generate output containing library calls for floating point.
9131 @strong{Warning:} the requisite libraries are not part of GCC@.
9132 Normally the facilities of the machine's usual C compiler are used, but
9133 this can't be done directly in cross-compilation. You must make your
9134 own arrangements to provide suitable library functions for
9137 On machines where a function returns floating point results in the 80387
9138 register stack, some floating point opcodes may be emitted even if
9139 @option{-msoft-float} is used.
9141 @item -mno-fp-ret-in-387
9142 @opindex mno-fp-ret-in-387
9143 Do not use the FPU registers for return values of functions.
9145 The usual calling convention has functions return values of types
9146 @code{float} and @code{double} in an FPU register, even if there
9147 is no FPU@. The idea is that the operating system should emulate
9150 The option @option{-mno-fp-ret-in-387} causes such values to be returned
9151 in ordinary CPU registers instead.
9153 @item -mno-fancy-math-387
9154 @opindex mno-fancy-math-387
9155 Some 387 emulators do not support the @code{sin}, @code{cos} and
9156 @code{sqrt} instructions for the 387. Specify this option to avoid
9157 generating those instructions. This option is the default on FreeBSD,
9158 OpenBSD and NetBSD@. This option is overridden when @option{-march}
9159 indicates that the target cpu will always have an FPU and so the
9160 instruction will not need emulation. As of revision 2.6.1, these
9161 instructions are not generated unless you also use the
9162 @option{-funsafe-math-optimizations} switch.
9164 @item -malign-double
9165 @itemx -mno-align-double
9166 @opindex malign-double
9167 @opindex mno-align-double
9168 Control whether GCC aligns @code{double}, @code{long double}, and
9169 @code{long long} variables on a two word boundary or a one word
9170 boundary. Aligning @code{double} variables on a two word boundary will
9171 produce code that runs somewhat faster on a @samp{Pentium} at the
9172 expense of more memory.
9174 @strong{Warning:} if you use the @option{-malign-double} switch,
9175 structures containing the above types will be aligned differently than
9176 the published application binary interface specifications for the 386
9177 and will not be binary compatible with structures in code compiled
9178 without that switch.
9180 @item -m96bit-long-double
9181 @itemx -m128bit-long-double
9182 @opindex m96bit-long-double
9183 @opindex m128bit-long-double
9184 These switches control the size of @code{long double} type. The i386
9185 application binary interface specifies the size to be 96 bits,
9186 so @option{-m96bit-long-double} is the default in 32 bit mode.
9188 Modern architectures (Pentium and newer) would prefer @code{long double}
9189 to be aligned to an 8 or 16 byte boundary. In arrays or structures
9190 conforming to the ABI, this would not be possible. So specifying a
9191 @option{-m128bit-long-double} will align @code{long double}
9192 to a 16 byte boundary by padding the @code{long double} with an additional
9195 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
9196 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
9198 Notice that neither of these options enable any extra precision over the x87
9199 standard of 80 bits for a @code{long double}.
9201 @strong{Warning:} if you override the default value for your target ABI, the
9202 structures and arrays containing @code{long double} variables will change
9203 their size as well as function calling convention for function taking
9204 @code{long double} will be modified. Hence they will not be binary
9205 compatible with arrays or structures in code compiled without that switch.
9207 @item -mmlarge-data-threshold=@var{number}
9208 @opindex mlarge-data-threshold=@var{number}
9209 When @option{-mcmodel=medium} is specified, the data greater than
9210 @var{threshold} are placed in large data section. This value must be the
9211 same across all object linked into the binary and defaults to 65535.
9214 @itemx -mno-svr3-shlib
9215 @opindex msvr3-shlib
9216 @opindex mno-svr3-shlib
9217 Control whether GCC places uninitialized local variables into the
9218 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
9219 into @code{bss}. These options are meaningful only on System V Release 3.
9223 Use a different function-calling convention, in which functions that
9224 take a fixed number of arguments return with the @code{ret} @var{num}
9225 instruction, which pops their arguments while returning. This saves one
9226 instruction in the caller since there is no need to pop the arguments
9229 You can specify that an individual function is called with this calling
9230 sequence with the function attribute @samp{stdcall}. You can also
9231 override the @option{-mrtd} option by using the function attribute
9232 @samp{cdecl}. @xref{Function Attributes}.
9234 @strong{Warning:} this calling convention is incompatible with the one
9235 normally used on Unix, so you cannot use it if you need to call
9236 libraries compiled with the Unix compiler.
9238 Also, you must provide function prototypes for all functions that
9239 take variable numbers of arguments (including @code{printf});
9240 otherwise incorrect code will be generated for calls to those
9243 In addition, seriously incorrect code will result if you call a
9244 function with too many arguments. (Normally, extra arguments are
9245 harmlessly ignored.)
9247 @item -mregparm=@var{num}
9249 Control how many registers are used to pass integer arguments. By
9250 default, no registers are used to pass arguments, and at most 3
9251 registers can be used. You can control this behavior for a specific
9252 function by using the function attribute @samp{regparm}.
9253 @xref{Function Attributes}.
9255 @strong{Warning:} if you use this switch, and
9256 @var{num} is nonzero, then you must build all modules with the same
9257 value, including any libraries. This includes the system libraries and
9261 @opindex msseregparm
9262 Use SSE register passing conventions for float and double arguments
9263 and return values. You can control this behavior for a specific
9264 function by using the function attribute @samp{sseregparm}.
9265 @xref{Function Attributes}.
9267 @strong{Warning:} if you use this switch then you must build all
9268 modules with the same value, including any libraries. This includes
9269 the system libraries and startup modules.
9271 @item -mpreferred-stack-boundary=@var{num}
9272 @opindex mpreferred-stack-boundary
9273 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
9274 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
9275 the default is 4 (16 bytes or 128 bits), except when optimizing for code
9276 size (@option{-Os}), in which case the default is the minimum correct
9277 alignment (4 bytes for x86, and 8 bytes for x86-64).
9279 On Pentium and PentiumPro, @code{double} and @code{long double} values
9280 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
9281 suffer significant run time performance penalties. On Pentium III, the
9282 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
9283 penalties if it is not 16 byte aligned.
9285 To ensure proper alignment of this values on the stack, the stack boundary
9286 must be as aligned as that required by any value stored on the stack.
9287 Further, every function must be generated such that it keeps the stack
9288 aligned. Thus calling a function compiled with a higher preferred
9289 stack boundary from a function compiled with a lower preferred stack
9290 boundary will most likely misalign the stack. It is recommended that
9291 libraries that use callbacks always use the default setting.
9293 This extra alignment does consume extra stack space, and generally
9294 increases code size. Code that is sensitive to stack space usage, such
9295 as embedded systems and operating system kernels, may want to reduce the
9296 preferred alignment to @option{-mpreferred-stack-boundary=2}.
9314 These switches enable or disable the use of instructions in the MMX,
9315 SSE, SSE2 or 3DNow! extended instruction sets. These extensions are
9316 also available as built-in functions: see @ref{X86 Built-in Functions},
9317 for details of the functions enabled and disabled by these switches.
9319 To have SSE/SSE2 instructions generated automatically from floating-point
9320 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
9322 These options will enable GCC to use these extended instructions in
9323 generated code, even without @option{-mfpmath=sse}. Applications which
9324 perform runtime CPU detection must compile separate files for each
9325 supported architecture, using the appropriate flags. In particular,
9326 the file containing the CPU detection code should be compiled without
9330 @itemx -mno-push-args
9332 @opindex mno-push-args
9333 Use PUSH operations to store outgoing parameters. This method is shorter
9334 and usually equally fast as method using SUB/MOV operations and is enabled
9335 by default. In some cases disabling it may improve performance because of
9336 improved scheduling and reduced dependencies.
9338 @item -maccumulate-outgoing-args
9339 @opindex maccumulate-outgoing-args
9340 If enabled, the maximum amount of space required for outgoing arguments will be
9341 computed in the function prologue. This is faster on most modern CPUs
9342 because of reduced dependencies, improved scheduling and reduced stack usage
9343 when preferred stack boundary is not equal to 2. The drawback is a notable
9344 increase in code size. This switch implies @option{-mno-push-args}.
9348 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
9349 on thread-safe exception handling must compile and link all code with the
9350 @option{-mthreads} option. When compiling, @option{-mthreads} defines
9351 @option{-D_MT}; when linking, it links in a special thread helper library
9352 @option{-lmingwthrd} which cleans up per thread exception handling data.
9354 @item -mno-align-stringops
9355 @opindex mno-align-stringops
9356 Do not align destination of inlined string operations. This switch reduces
9357 code size and improves performance in case the destination is already aligned,
9358 but GCC doesn't know about it.
9360 @item -minline-all-stringops
9361 @opindex minline-all-stringops
9362 By default GCC inlines string operations only when destination is known to be
9363 aligned at least to 4 byte boundary. This enables more inlining, increase code
9364 size, but may improve performance of code that depends on fast memcpy, strlen
9365 and memset for short lengths.
9367 @item -momit-leaf-frame-pointer
9368 @opindex momit-leaf-frame-pointer
9369 Don't keep the frame pointer in a register for leaf functions. This
9370 avoids the instructions to save, set up and restore frame pointers and
9371 makes an extra register available in leaf functions. The option
9372 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9373 which might make debugging harder.
9375 @item -mtls-direct-seg-refs
9376 @itemx -mno-tls-direct-seg-refs
9377 @opindex mtls-direct-seg-refs
9378 Controls whether TLS variables may be accessed with offsets from the
9379 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
9380 or whether the thread base pointer must be added. Whether or not this
9381 is legal depends on the operating system, and whether it maps the
9382 segment to cover the entire TLS area.
9384 For systems that use GNU libc, the default is on.
9387 These @samp{-m} switches are supported in addition to the above
9388 on AMD x86-64 processors in 64-bit environments.
9395 Generate code for a 32-bit or 64-bit environment.
9396 The 32-bit environment sets int, long and pointer to 32 bits and
9397 generates code that runs on any i386 system.
9398 The 64-bit environment sets int to 32 bits and long and pointer
9399 to 64 bits and generates code for AMD's x86-64 architecture.
9402 @opindex no-red-zone
9403 Do not use a so called red zone for x86-64 code. The red zone is mandated
9404 by the x86-64 ABI, it is a 128-byte area beyond the location of the
9405 stack pointer that will not be modified by signal or interrupt handlers
9406 and therefore can be used for temporary data without adjusting the stack
9407 pointer. The flag @option{-mno-red-zone} disables this red zone.
9409 @item -mcmodel=small
9410 @opindex mcmodel=small
9411 Generate code for the small code model: the program and its symbols must
9412 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
9413 Programs can be statically or dynamically linked. This is the default
9416 @item -mcmodel=kernel
9417 @opindex mcmodel=kernel
9418 Generate code for the kernel code model. The kernel runs in the
9419 negative 2 GB of the address space.
9420 This model has to be used for Linux kernel code.
9422 @item -mcmodel=medium
9423 @opindex mcmodel=medium
9424 Generate code for the medium model: The program is linked in the lower 2
9425 GB of the address space but symbols can be located anywhere in the
9426 address space. Programs can be statically or dynamically linked, but
9427 building of shared libraries are not supported with the medium model.
9429 @item -mcmodel=large
9430 @opindex mcmodel=large
9431 Generate code for the large model: This model makes no assumptions
9432 about addresses and sizes of sections. Currently GCC does not implement
9437 @subsection IA-64 Options
9438 @cindex IA-64 Options
9440 These are the @samp{-m} options defined for the Intel IA-64 architecture.
9444 @opindex mbig-endian
9445 Generate code for a big endian target. This is the default for HP-UX@.
9447 @item -mlittle-endian
9448 @opindex mlittle-endian
9449 Generate code for a little endian target. This is the default for AIX5
9456 Generate (or don't) code for the GNU assembler. This is the default.
9457 @c Also, this is the default if the configure option @option{--with-gnu-as}
9464 Generate (or don't) code for the GNU linker. This is the default.
9465 @c Also, this is the default if the configure option @option{--with-gnu-ld}
9470 Generate code that does not use a global pointer register. The result
9471 is not position independent code, and violates the IA-64 ABI@.
9473 @item -mvolatile-asm-stop
9474 @itemx -mno-volatile-asm-stop
9475 @opindex mvolatile-asm-stop
9476 @opindex mno-volatile-asm-stop
9477 Generate (or don't) a stop bit immediately before and after volatile asm
9480 @item -mregister-names
9481 @itemx -mno-register-names
9482 @opindex mregister-names
9483 @opindex mno-register-names
9484 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
9485 the stacked registers. This may make assembler output more readable.
9491 Disable (or enable) optimizations that use the small data section. This may
9492 be useful for working around optimizer bugs.
9495 @opindex mconstant-gp
9496 Generate code that uses a single constant global pointer value. This is
9497 useful when compiling kernel code.
9501 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
9502 This is useful when compiling firmware code.
9504 @item -minline-float-divide-min-latency
9505 @opindex minline-float-divide-min-latency
9506 Generate code for inline divides of floating point values
9507 using the minimum latency algorithm.
9509 @item -minline-float-divide-max-throughput
9510 @opindex minline-float-divide-max-throughput
9511 Generate code for inline divides of floating point values
9512 using the maximum throughput algorithm.
9514 @item -minline-int-divide-min-latency
9515 @opindex minline-int-divide-min-latency
9516 Generate code for inline divides of integer values
9517 using the minimum latency algorithm.
9519 @item -minline-int-divide-max-throughput
9520 @opindex minline-int-divide-max-throughput
9521 Generate code for inline divides of integer values
9522 using the maximum throughput algorithm.
9524 @item -minline-sqrt-min-latency
9525 @opindex minline-sqrt-min-latency
9526 Generate code for inline square roots
9527 using the minimum latency algorithm.
9529 @item -minline-sqrt-max-throughput
9530 @opindex minline-sqrt-max-throughput
9531 Generate code for inline square roots
9532 using the maximum throughput algorithm.
9534 @item -mno-dwarf2-asm
9536 @opindex mno-dwarf2-asm
9537 @opindex mdwarf2-asm
9538 Don't (or do) generate assembler code for the DWARF2 line number debugging
9539 info. This may be useful when not using the GNU assembler.
9541 @item -mearly-stop-bits
9542 @itemx -mno-early-stop-bits
9543 @opindex mearly-stop-bits
9544 @opindex mno-early-stop-bits
9545 Allow stop bits to be placed earlier than immediately preceding the
9546 instruction that triggered the stop bit. This can improve instruction
9547 scheduling, but does not always do so.
9549 @item -mfixed-range=@var{register-range}
9550 @opindex mfixed-range
9551 Generate code treating the given register range as fixed registers.
9552 A fixed register is one that the register allocator can not use. This is
9553 useful when compiling kernel code. A register range is specified as
9554 two registers separated by a dash. Multiple register ranges can be
9555 specified separated by a comma.
9557 @item -mtls-size=@var{tls-size}
9559 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
9562 @item -mtune=@var{cpu-type}
9564 Tune the instruction scheduling for a particular CPU, Valid values are
9565 itanium, itanium1, merced, itanium2, and mckinley.
9571 Add support for multithreading using the POSIX threads library. This
9572 option sets flags for both the preprocessor and linker. It does
9573 not affect the thread safety of object code produced by the compiler or
9574 that of libraries supplied with it. These are HP-UX specific flags.
9580 Generate code for a 32-bit or 64-bit environment.
9581 The 32-bit environment sets int, long and pointer to 32 bits.
9582 The 64-bit environment sets int to 32 bits and long and pointer
9583 to 64 bits. These are HP-UX specific flags.
9588 @subsection M32C Options
9589 @cindex M32C options
9592 @item -mcpu=@var{name}
9594 Select the CPU for which code is generated. @var{name} may be one of
9595 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
9596 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
9601 Specifies that the program will be run on the simulator. This causes
9602 an alternate runtime library to be linked in which supports, for
9603 example, file I/O. You must not use this option when generating
9604 programs that will run on real hardware; you must provide your own
9605 runtime library for whatever I/O functions are needed.
9607 @item -memregs=@var{number}
9609 Specifies the number of memory-based pseudo-registers GCC will use
9610 during code generation. These pseudo-registers will be used like real
9611 registers, so there is a tradeoff between GCC's ability to fit the
9612 code into available registers, and the performance penalty of using
9613 memory instead of registers. Note that all modules in a program must
9614 be compiled with the same value for this option. Because of that, you
9615 must not use this option with the default runtime libraries gcc
9620 @node M32R/D Options
9621 @subsection M32R/D Options
9622 @cindex M32R/D options
9624 These @option{-m} options are defined for Renesas M32R/D architectures:
9629 Generate code for the M32R/2@.
9633 Generate code for the M32R/X@.
9637 Generate code for the M32R@. This is the default.
9640 @opindex mmodel=small
9641 Assume all objects live in the lower 16MB of memory (so that their addresses
9642 can be loaded with the @code{ld24} instruction), and assume all subroutines
9643 are reachable with the @code{bl} instruction.
9644 This is the default.
9646 The addressability of a particular object can be set with the
9647 @code{model} attribute.
9649 @item -mmodel=medium
9650 @opindex mmodel=medium
9651 Assume objects may be anywhere in the 32-bit address space (the compiler
9652 will generate @code{seth/add3} instructions to load their addresses), and
9653 assume all subroutines are reachable with the @code{bl} instruction.
9656 @opindex mmodel=large
9657 Assume objects may be anywhere in the 32-bit address space (the compiler
9658 will generate @code{seth/add3} instructions to load their addresses), and
9659 assume subroutines may not be reachable with the @code{bl} instruction
9660 (the compiler will generate the much slower @code{seth/add3/jl}
9661 instruction sequence).
9664 @opindex msdata=none
9665 Disable use of the small data area. Variables will be put into
9666 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
9667 @code{section} attribute has been specified).
9668 This is the default.
9670 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
9671 Objects may be explicitly put in the small data area with the
9672 @code{section} attribute using one of these sections.
9675 @opindex msdata=sdata
9676 Put small global and static data in the small data area, but do not
9677 generate special code to reference them.
9681 Put small global and static data in the small data area, and generate
9682 special instructions to reference them.
9686 @cindex smaller data references
9687 Put global and static objects less than or equal to @var{num} bytes
9688 into the small data or bss sections instead of the normal data or bss
9689 sections. The default value of @var{num} is 8.
9690 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
9691 for this option to have any effect.
9693 All modules should be compiled with the same @option{-G @var{num}} value.
9694 Compiling with different values of @var{num} may or may not work; if it
9695 doesn't the linker will give an error message---incorrect code will not be
9700 Makes the M32R specific code in the compiler display some statistics
9701 that might help in debugging programs.
9704 @opindex malign-loops
9705 Align all loops to a 32-byte boundary.
9707 @item -mno-align-loops
9708 @opindex mno-align-loops
9709 Do not enforce a 32-byte alignment for loops. This is the default.
9711 @item -missue-rate=@var{number}
9712 @opindex missue-rate=@var{number}
9713 Issue @var{number} instructions per cycle. @var{number} can only be 1
9716 @item -mbranch-cost=@var{number}
9717 @opindex mbranch-cost=@var{number}
9718 @var{number} can only be 1 or 2. If it is 1 then branches will be
9719 preferred over conditional code, if it is 2, then the opposite will
9722 @item -mflush-trap=@var{number}
9723 @opindex mflush-trap=@var{number}
9724 Specifies the trap number to use to flush the cache. The default is
9725 12. Valid numbers are between 0 and 15 inclusive.
9727 @item -mno-flush-trap
9728 @opindex mno-flush-trap
9729 Specifies that the cache cannot be flushed by using a trap.
9731 @item -mflush-func=@var{name}
9732 @opindex mflush-func=@var{name}
9733 Specifies the name of the operating system function to call to flush
9734 the cache. The default is @emph{_flush_cache}, but a function call
9735 will only be used if a trap is not available.
9737 @item -mno-flush-func
9738 @opindex mno-flush-func
9739 Indicates that there is no OS function for flushing the cache.
9743 @node M680x0 Options
9744 @subsection M680x0 Options
9745 @cindex M680x0 options
9747 These are the @samp{-m} options defined for the 68000 series. The default
9748 values for these options depends on which style of 68000 was selected when
9749 the compiler was configured; the defaults for the most common choices are
9757 Generate output for a 68000. This is the default
9758 when the compiler is configured for 68000-based systems.
9760 Use this option for microcontrollers with a 68000 or EC000 core,
9761 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
9767 Generate output for a 68020. This is the default
9768 when the compiler is configured for 68020-based systems.
9772 Generate output containing 68881 instructions for floating point.
9773 This is the default for most 68020 systems unless @option{--nfp} was
9774 specified when the compiler was configured.
9778 Generate output for a 68030. This is the default when the compiler is
9779 configured for 68030-based systems.
9783 Generate output for a 68040. This is the default when the compiler is
9784 configured for 68040-based systems.
9786 This option inhibits the use of 68881/68882 instructions that have to be
9787 emulated by software on the 68040. Use this option if your 68040 does not
9788 have code to emulate those instructions.
9792 Generate output for a 68060. This is the default when the compiler is
9793 configured for 68060-based systems.
9795 This option inhibits the use of 68020 and 68881/68882 instructions that
9796 have to be emulated by software on the 68060. Use this option if your 68060
9797 does not have code to emulate those instructions.
9801 Generate output for a CPU32. This is the default
9802 when the compiler is configured for CPU32-based systems.
9804 Use this option for microcontrollers with a
9805 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9806 68336, 68340, 68341, 68349 and 68360.
9810 Generate output for a 520X ``coldfire'' family cpu. This is the default
9811 when the compiler is configured for 520X-based systems.
9813 Use this option for microcontroller with a 5200 core, including
9814 the MCF5202, MCF5203, MCF5204 and MCF5202.
9819 Generate output for a 68040, without using any of the new instructions.
9820 This results in code which can run relatively efficiently on either a
9821 68020/68881 or a 68030 or a 68040. The generated code does use the
9822 68881 instructions that are emulated on the 68040.
9826 Generate output for a 68060, without using any of the new instructions.
9827 This results in code which can run relatively efficiently on either a
9828 68020/68881 or a 68030 or a 68040. The generated code does use the
9829 68881 instructions that are emulated on the 68060.
9832 @opindex msoft-float
9833 Generate output containing library calls for floating point.
9834 @strong{Warning:} the requisite libraries are not available for all m68k
9835 targets. Normally the facilities of the machine's usual C compiler are
9836 used, but this can't be done directly in cross-compilation. You must
9837 make your own arrangements to provide suitable library functions for
9838 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9839 @samp{m68k-*-coff} do provide software floating point support.
9843 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9844 Additionally, parameters passed on the stack are also aligned to a
9845 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9848 @opindex mnobitfield
9849 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9850 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9854 Do use the bit-field instructions. The @option{-m68020} option implies
9855 @option{-mbitfield}. This is the default if you use a configuration
9856 designed for a 68020.
9860 Use a different function-calling convention, in which functions
9861 that take a fixed number of arguments return with the @code{rtd}
9862 instruction, which pops their arguments while returning. This
9863 saves one instruction in the caller since there is no need to pop
9864 the arguments there.
9866 This calling convention is incompatible with the one normally
9867 used on Unix, so you cannot use it if you need to call libraries
9868 compiled with the Unix compiler.
9870 Also, you must provide function prototypes for all functions that
9871 take variable numbers of arguments (including @code{printf});
9872 otherwise incorrect code will be generated for calls to those
9875 In addition, seriously incorrect code will result if you call a
9876 function with too many arguments. (Normally, extra arguments are
9877 harmlessly ignored.)
9879 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
9880 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
9883 @itemx -mno-align-int
9885 @opindex mno-align-int
9886 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
9887 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
9888 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
9889 Aligning variables on 32-bit boundaries produces code that runs somewhat
9890 faster on processors with 32-bit busses at the expense of more memory.
9892 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
9893 align structures containing the above types differently than
9894 most published application binary interface specifications for the m68k.
9898 Use the pc-relative addressing mode of the 68000 directly, instead of
9899 using a global offset table. At present, this option implies @option{-fpic},
9900 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
9901 not presently supported with @option{-mpcrel}, though this could be supported for
9902 68020 and higher processors.
9904 @item -mno-strict-align
9905 @itemx -mstrict-align
9906 @opindex mno-strict-align
9907 @opindex mstrict-align
9908 Do not (do) assume that unaligned memory references will be handled by
9912 Generate code that allows the data segment to be located in a different
9913 area of memory from the text segment. This allows for execute in place in
9914 an environment without virtual memory management. This option implies
9918 Generate code that assumes that the data segment follows the text segment.
9919 This is the default.
9921 @item -mid-shared-library
9922 Generate code that supports shared libraries via the library ID method.
9923 This allows for execute in place and shared libraries in an environment
9924 without virtual memory management. This option implies @option{-fPIC}.
9926 @item -mno-id-shared-library
9927 Generate code that doesn't assume ID based shared libraries are being used.
9928 This is the default.
9930 @item -mshared-library-id=n
9931 Specified the identification number of the ID based shared library being
9932 compiled. Specifying a value of 0 will generate more compact code, specifying
9933 other values will force the allocation of that number to the current
9934 library but is no more space or time efficient than omitting this option.
9938 @node M68hc1x Options
9939 @subsection M68hc1x Options
9940 @cindex M68hc1x options
9942 These are the @samp{-m} options defined for the 68hc11 and 68hc12
9943 microcontrollers. The default values for these options depends on
9944 which style of microcontroller was selected when the compiler was configured;
9945 the defaults for the most common choices are given below.
9952 Generate output for a 68HC11. This is the default
9953 when the compiler is configured for 68HC11-based systems.
9959 Generate output for a 68HC12. This is the default
9960 when the compiler is configured for 68HC12-based systems.
9966 Generate output for a 68HCS12.
9969 @opindex mauto-incdec
9970 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
9977 Enable the use of 68HC12 min and max instructions.
9980 @itemx -mno-long-calls
9981 @opindex mlong-calls
9982 @opindex mno-long-calls
9983 Treat all calls as being far away (near). If calls are assumed to be
9984 far away, the compiler will use the @code{call} instruction to
9985 call a function and the @code{rtc} instruction for returning.
9989 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9991 @item -msoft-reg-count=@var{count}
9992 @opindex msoft-reg-count
9993 Specify the number of pseudo-soft registers which are used for the
9994 code generation. The maximum number is 32. Using more pseudo-soft
9995 register may or may not result in better code depending on the program.
9996 The default is 4 for 68HC11 and 2 for 68HC12.
10000 @node MCore Options
10001 @subsection MCore Options
10002 @cindex MCore options
10004 These are the @samp{-m} options defined for the Motorola M*Core
10010 @itemx -mno-hardlit
10012 @opindex mno-hardlit
10013 Inline constants into the code stream if it can be done in two
10014 instructions or less.
10020 Use the divide instruction. (Enabled by default).
10022 @item -mrelax-immediate
10023 @itemx -mno-relax-immediate
10024 @opindex mrelax-immediate
10025 @opindex mno-relax-immediate
10026 Allow arbitrary sized immediates in bit operations.
10028 @item -mwide-bitfields
10029 @itemx -mno-wide-bitfields
10030 @opindex mwide-bitfields
10031 @opindex mno-wide-bitfields
10032 Always treat bit-fields as int-sized.
10034 @item -m4byte-functions
10035 @itemx -mno-4byte-functions
10036 @opindex m4byte-functions
10037 @opindex mno-4byte-functions
10038 Force all functions to be aligned to a four byte boundary.
10040 @item -mcallgraph-data
10041 @itemx -mno-callgraph-data
10042 @opindex mcallgraph-data
10043 @opindex mno-callgraph-data
10044 Emit callgraph information.
10047 @itemx -mno-slow-bytes
10048 @opindex mslow-bytes
10049 @opindex mno-slow-bytes
10050 Prefer word access when reading byte quantities.
10052 @item -mlittle-endian
10053 @itemx -mbig-endian
10054 @opindex mlittle-endian
10055 @opindex mbig-endian
10056 Generate code for a little endian target.
10062 Generate code for the 210 processor.
10066 @subsection MIPS Options
10067 @cindex MIPS options
10073 Generate big-endian code.
10077 Generate little-endian code. This is the default for @samp{mips*el-*-*}
10080 @item -march=@var{arch}
10082 Generate code that will run on @var{arch}, which can be the name of a
10083 generic MIPS ISA, or the name of a particular processor.
10085 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
10086 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
10087 The processor names are:
10088 @samp{4kc}, @samp{4km}, @samp{4kp},
10089 @samp{5kc}, @samp{5kf},
10091 @samp{24k}, @samp{24kc}, @samp{24kf}, @samp{24kx},
10094 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
10095 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
10096 @samp{rm7000}, @samp{rm9000},
10099 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
10100 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
10101 The special value @samp{from-abi} selects the
10102 most compatible architecture for the selected ABI (that is,
10103 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
10105 In processor names, a final @samp{000} can be abbreviated as @samp{k}
10106 (for example, @samp{-march=r2k}). Prefixes are optional, and
10107 @samp{vr} may be written @samp{r}.
10109 GCC defines two macros based on the value of this option. The first
10110 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
10111 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
10112 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
10113 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
10114 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
10116 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
10117 above. In other words, it will have the full prefix and will not
10118 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
10119 the macro names the resolved architecture (either @samp{"mips1"} or
10120 @samp{"mips3"}). It names the default architecture when no
10121 @option{-march} option is given.
10123 @item -mtune=@var{arch}
10125 Optimize for @var{arch}. Among other things, this option controls
10126 the way instructions are scheduled, and the perceived cost of arithmetic
10127 operations. The list of @var{arch} values is the same as for
10130 When this option is not used, GCC will optimize for the processor
10131 specified by @option{-march}. By using @option{-march} and
10132 @option{-mtune} together, it is possible to generate code that will
10133 run on a family of processors, but optimize the code for one
10134 particular member of that family.
10136 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
10137 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
10138 @samp{-march} ones described above.
10142 Equivalent to @samp{-march=mips1}.
10146 Equivalent to @samp{-march=mips2}.
10150 Equivalent to @samp{-march=mips3}.
10154 Equivalent to @samp{-march=mips4}.
10158 Equivalent to @samp{-march=mips32}.
10162 Equivalent to @samp{-march=mips32r2}.
10166 Equivalent to @samp{-march=mips64}.
10171 @opindex mno-mips16
10172 Generate (do not generate) MIPS16 code. If GCC is targetting a
10173 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
10185 Generate code for the given ABI@.
10187 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
10188 generates 64-bit code when you select a 64-bit architecture, but you
10189 can use @option{-mgp32} to get 32-bit code instead.
10191 For information about the O64 ABI, see
10192 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
10195 @itemx -mno-abicalls
10197 @opindex mno-abicalls
10198 Generate (do not generate) SVR4-style position-independent code.
10199 @option{-mabicalls} is the default for SVR4-based systems.
10205 Lift (do not lift) the usual restrictions on the size of the global
10208 GCC normally uses a single instruction to load values from the GOT@.
10209 While this is relatively efficient, it will only work if the GOT
10210 is smaller than about 64k. Anything larger will cause the linker
10211 to report an error such as:
10213 @cindex relocation truncated to fit (MIPS)
10215 relocation truncated to fit: R_MIPS_GOT16 foobar
10218 If this happens, you should recompile your code with @option{-mxgot}.
10219 It should then work with very large GOTs, although it will also be
10220 less efficient, since it will take three instructions to fetch the
10221 value of a global symbol.
10223 Note that some linkers can create multiple GOTs. If you have such a
10224 linker, you should only need to use @option{-mxgot} when a single object
10225 file accesses more than 64k's worth of GOT entries. Very few do.
10227 These options have no effect unless GCC is generating position
10232 Assume that general-purpose registers are 32 bits wide.
10236 Assume that general-purpose registers are 64 bits wide.
10240 Assume that floating-point registers are 32 bits wide.
10244 Assume that floating-point registers are 64 bits wide.
10247 @opindex mhard-float
10248 Use floating-point coprocessor instructions.
10251 @opindex msoft-float
10252 Do not use floating-point coprocessor instructions. Implement
10253 floating-point calculations using library calls instead.
10255 @item -msingle-float
10256 @opindex msingle-float
10257 Assume that the floating-point coprocessor only supports single-precision
10260 @itemx -mdouble-float
10261 @opindex mdouble-float
10262 Assume that the floating-point coprocessor supports double-precision
10263 operations. This is the default.
10269 Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
10271 @itemx -mpaired-single
10272 @itemx -mno-paired-single
10273 @opindex mpaired-single
10274 @opindex mno-paired-single
10275 Use (do not use) paired-single floating-point instructions.
10276 @xref{MIPS Paired-Single Support}. This option can only be used
10277 when generating 64-bit code and requires hardware floating-point
10278 support to be enabled.
10283 @opindex mno-mips3d
10284 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
10285 The option @option{-mips3d} implies @option{-mpaired-single}.
10289 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
10290 an explanation of the default and the way that the pointer size is
10295 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
10297 The default size of @code{int}s, @code{long}s and pointers depends on
10298 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
10299 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
10300 32-bit @code{long}s. Pointers are the same size as @code{long}s,
10301 or the same size as integer registers, whichever is smaller.
10307 Assume (do not assume) that all symbols have 32-bit values, regardless
10308 of the selected ABI@. This option is useful in combination with
10309 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
10310 to generate shorter and faster references to symbolic addresses.
10314 @cindex smaller data references (MIPS)
10315 @cindex gp-relative references (MIPS)
10316 Put global and static items less than or equal to @var{num} bytes into
10317 the small data or bss section instead of the normal data or bss section.
10318 This allows the data to be accessed using a single instruction.
10320 All modules should be compiled with the same @option{-G @var{num}}
10323 @item -membedded-data
10324 @itemx -mno-embedded-data
10325 @opindex membedded-data
10326 @opindex mno-embedded-data
10327 Allocate variables to the read-only data section first if possible, then
10328 next in the small data section if possible, otherwise in data. This gives
10329 slightly slower code than the default, but reduces the amount of RAM required
10330 when executing, and thus may be preferred for some embedded systems.
10332 @item -muninit-const-in-rodata
10333 @itemx -mno-uninit-const-in-rodata
10334 @opindex muninit-const-in-rodata
10335 @opindex mno-uninit-const-in-rodata
10336 Put uninitialized @code{const} variables in the read-only data section.
10337 This option is only meaningful in conjunction with @option{-membedded-data}.
10339 @item -msplit-addresses
10340 @itemx -mno-split-addresses
10341 @opindex msplit-addresses
10342 @opindex mno-split-addresses
10343 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
10344 relocation operators. This option has been superseded by
10345 @option{-mexplicit-relocs} but is retained for backwards compatibility.
10347 @item -mexplicit-relocs
10348 @itemx -mno-explicit-relocs
10349 @opindex mexplicit-relocs
10350 @opindex mno-explicit-relocs
10351 Use (do not use) assembler relocation operators when dealing with symbolic
10352 addresses. The alternative, selected by @option{-mno-explicit-relocs},
10353 is to use assembler macros instead.
10355 @option{-mexplicit-relocs} is the default if GCC was configured
10356 to use an assembler that supports relocation operators.
10358 @item -mcheck-zero-division
10359 @itemx -mno-check-zero-division
10360 @opindex mcheck-zero-division
10361 @opindex mno-check-zero-division
10362 Trap (do not trap) on integer division by zero. The default is
10363 @option{-mcheck-zero-division}.
10365 @item -mdivide-traps
10366 @itemx -mdivide-breaks
10367 @opindex mdivide-traps
10368 @opindex mdivide-breaks
10369 MIPS systems check for division by zero by generating either a
10370 conditional trap or a break instruction. Using traps results in
10371 smaller code, but is only supported on MIPS II and later. Also, some
10372 versions of the Linux kernel have a bug that prevents trap from
10373 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
10374 allow conditional traps on architectures that support them and
10375 @option{-mdivide-breaks} to force the use of breaks.
10377 The default is usually @option{-mdivide-traps}, but this can be
10378 overridden at configure time using @option{--with-divide=breaks}.
10379 Divide-by-zero checks can be completely disabled using
10380 @option{-mno-check-zero-division}.
10385 @opindex mno-memcpy
10386 Force (do not force) the use of @code{memcpy()} for non-trivial block
10387 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
10388 most constant-sized copies.
10391 @itemx -mno-long-calls
10392 @opindex mlong-calls
10393 @opindex mno-long-calls
10394 Disable (do not disable) use of the @code{jal} instruction. Calling
10395 functions using @code{jal} is more efficient but requires the caller
10396 and callee to be in the same 256 megabyte segment.
10398 This option has no effect on abicalls code. The default is
10399 @option{-mno-long-calls}.
10405 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
10406 instructions, as provided by the R4650 ISA@.
10409 @itemx -mno-fused-madd
10410 @opindex mfused-madd
10411 @opindex mno-fused-madd
10412 Enable (disable) use of the floating point multiply-accumulate
10413 instructions, when they are available. The default is
10414 @option{-mfused-madd}.
10416 When multiply-accumulate instructions are used, the intermediate
10417 product is calculated to infinite precision and is not subject to
10418 the FCSR Flush to Zero bit. This may be undesirable in some
10423 Tell the MIPS assembler to not run its preprocessor over user
10424 assembler files (with a @samp{.s} suffix) when assembling them.
10427 @itemx -mno-fix-r4000
10428 @opindex mfix-r4000
10429 @opindex mno-fix-r4000
10430 Work around certain R4000 CPU errata:
10433 A double-word or a variable shift may give an incorrect result if executed
10434 immediately after starting an integer division.
10436 A double-word or a variable shift may give an incorrect result if executed
10437 while an integer multiplication is in progress.
10439 An integer division may give an incorrect result if started in a delay slot
10440 of a taken branch or a jump.
10444 @itemx -mno-fix-r4400
10445 @opindex mfix-r4400
10446 @opindex mno-fix-r4400
10447 Work around certain R4400 CPU errata:
10450 A double-word or a variable shift may give an incorrect result if executed
10451 immediately after starting an integer division.
10455 @itemx -mno-fix-vr4120
10456 @opindex mfix-vr4120
10457 Work around certain VR4120 errata:
10460 @code{dmultu} does not always produce the correct result.
10462 @code{div} and @code{ddiv} do not always produce the correct result if one
10463 of the operands is negative.
10465 The workarounds for the division errata rely on special functions in
10466 @file{libgcc.a}. At present, these functions are only provided by
10467 the @code{mips64vr*-elf} configurations.
10469 Other VR4120 errata require a nop to be inserted between certain pairs of
10470 instructions. These errata are handled by the assembler, not by GCC itself.
10473 @opindex mfix-vr4130
10474 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
10475 workarounds are implemented by the assembler rather than by GCC,
10476 although GCC will avoid using @code{mflo} and @code{mfhi} if the
10477 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
10478 instructions are available instead.
10481 @itemx -mno-fix-sb1
10483 Work around certain SB-1 CPU core errata.
10484 (This flag currently works around the SB-1 revision 2
10485 ``F1'' and ``F2'' floating point errata.)
10487 @item -mflush-func=@var{func}
10488 @itemx -mno-flush-func
10489 @opindex mflush-func
10490 Specifies the function to call to flush the I and D caches, or to not
10491 call any such function. If called, the function must take the same
10492 arguments as the common @code{_flush_func()}, that is, the address of the
10493 memory range for which the cache is being flushed, the size of the
10494 memory range, and the number 3 (to flush both caches). The default
10495 depends on the target GCC was configured for, but commonly is either
10496 @samp{_flush_func} or @samp{__cpu_flush}.
10498 @item -mbranch-likely
10499 @itemx -mno-branch-likely
10500 @opindex mbranch-likely
10501 @opindex mno-branch-likely
10502 Enable or disable use of Branch Likely instructions, regardless of the
10503 default for the selected architecture. By default, Branch Likely
10504 instructions may be generated if they are supported by the selected
10505 architecture. An exception is for the MIPS32 and MIPS64 architectures
10506 and processors which implement those architectures; for those, Branch
10507 Likely instructions will not be generated by default because the MIPS32
10508 and MIPS64 architectures specifically deprecate their use.
10510 @item -mfp-exceptions
10511 @itemx -mno-fp-exceptions
10512 @opindex mfp-exceptions
10513 Specifies whether FP exceptions are enabled. This affects how we schedule
10514 FP instructions for some processors. The default is that FP exceptions are
10517 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
10518 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
10521 @item -mvr4130-align
10522 @itemx -mno-vr4130-align
10523 @opindex mvr4130-align
10524 The VR4130 pipeline is two-way superscalar, but can only issue two
10525 instructions together if the first one is 8-byte aligned. When this
10526 option is enabled, GCC will align pairs of instructions that it
10527 thinks should execute in parallel.
10529 This option only has an effect when optimizing for the VR4130.
10530 It normally makes code faster, but at the expense of making it bigger.
10531 It is enabled by default at optimization level @option{-O3}.
10535 @subsection MMIX Options
10536 @cindex MMIX Options
10538 These options are defined for the MMIX:
10542 @itemx -mno-libfuncs
10544 @opindex mno-libfuncs
10545 Specify that intrinsic library functions are being compiled, passing all
10546 values in registers, no matter the size.
10549 @itemx -mno-epsilon
10551 @opindex mno-epsilon
10552 Generate floating-point comparison instructions that compare with respect
10553 to the @code{rE} epsilon register.
10555 @item -mabi=mmixware
10557 @opindex mabi-mmixware
10559 Generate code that passes function parameters and return values that (in
10560 the called function) are seen as registers @code{$0} and up, as opposed to
10561 the GNU ABI which uses global registers @code{$231} and up.
10563 @item -mzero-extend
10564 @itemx -mno-zero-extend
10565 @opindex mzero-extend
10566 @opindex mno-zero-extend
10567 When reading data from memory in sizes shorter than 64 bits, use (do not
10568 use) zero-extending load instructions by default, rather than
10569 sign-extending ones.
10572 @itemx -mno-knuthdiv
10574 @opindex mno-knuthdiv
10575 Make the result of a division yielding a remainder have the same sign as
10576 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
10577 remainder follows the sign of the dividend. Both methods are
10578 arithmetically valid, the latter being almost exclusively used.
10580 @item -mtoplevel-symbols
10581 @itemx -mno-toplevel-symbols
10582 @opindex mtoplevel-symbols
10583 @opindex mno-toplevel-symbols
10584 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
10585 code can be used with the @code{PREFIX} assembly directive.
10589 Generate an executable in the ELF format, rather than the default
10590 @samp{mmo} format used by the @command{mmix} simulator.
10592 @item -mbranch-predict
10593 @itemx -mno-branch-predict
10594 @opindex mbranch-predict
10595 @opindex mno-branch-predict
10596 Use (do not use) the probable-branch instructions, when static branch
10597 prediction indicates a probable branch.
10599 @item -mbase-addresses
10600 @itemx -mno-base-addresses
10601 @opindex mbase-addresses
10602 @opindex mno-base-addresses
10603 Generate (do not generate) code that uses @emph{base addresses}. Using a
10604 base address automatically generates a request (handled by the assembler
10605 and the linker) for a constant to be set up in a global register. The
10606 register is used for one or more base address requests within the range 0
10607 to 255 from the value held in the register. The generally leads to short
10608 and fast code, but the number of different data items that can be
10609 addressed is limited. This means that a program that uses lots of static
10610 data may require @option{-mno-base-addresses}.
10612 @item -msingle-exit
10613 @itemx -mno-single-exit
10614 @opindex msingle-exit
10615 @opindex mno-single-exit
10616 Force (do not force) generated code to have a single exit point in each
10620 @node MN10300 Options
10621 @subsection MN10300 Options
10622 @cindex MN10300 options
10624 These @option{-m} options are defined for Matsushita MN10300 architectures:
10629 Generate code to avoid bugs in the multiply instructions for the MN10300
10630 processors. This is the default.
10632 @item -mno-mult-bug
10633 @opindex mno-mult-bug
10634 Do not generate code to avoid bugs in the multiply instructions for the
10635 MN10300 processors.
10639 Generate code which uses features specific to the AM33 processor.
10643 Do not generate code which uses features specific to the AM33 processor. This
10646 @item -mreturn-pointer-on-d0
10647 @opindex mreturn-pointer-on-d0
10648 When generating a function which returns a pointer, return the pointer
10649 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
10650 only in a0, and attempts to call such functions without a prototype
10651 would result in errors. Note that this option is on by default; use
10652 @option{-mno-return-pointer-on-d0} to disable it.
10656 Do not link in the C run-time initialization object file.
10660 Indicate to the linker that it should perform a relaxation optimization pass
10661 to shorten branches, calls and absolute memory addresses. This option only
10662 has an effect when used on the command line for the final link step.
10664 This option makes symbolic debugging impossible.
10668 @subsection MS1 Options
10669 @cindex MS1 options
10671 These @option{-m} options are defined for Morpho MS1 architectures:
10675 @item -march=@var{cpu-type}
10677 Generate code that will run on @var{cpu-type}, which is the name of a system
10678 representing a certain processor type. Possible values for
10679 @var{cpu-type} are @samp{MS1-64-001}, @samp{MS1-16-002}, and
10682 When this option is not used, the default is @option{-march=MS1-16-003}.
10686 Generate multiply instructions.
10690 Do not generate multiply instructions.
10694 Use byte loads and stores when generating code.
10698 Do not use byte loads and stores when generating code.
10702 Use simulator runtime
10706 Do not link in the C run-time initialization object file
10707 @file{crti.o}. Other run-time initialization and termination files
10708 such as @file{startup.o} and @file{exit.o} are still included on the
10709 linker command line.
10713 @node PDP-11 Options
10714 @subsection PDP-11 Options
10715 @cindex PDP-11 Options
10717 These options are defined for the PDP-11:
10722 Use hardware FPP floating point. This is the default. (FIS floating
10723 point on the PDP-11/40 is not supported.)
10726 @opindex msoft-float
10727 Do not use hardware floating point.
10731 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10735 Return floating-point results in memory. This is the default.
10739 Generate code for a PDP-11/40.
10743 Generate code for a PDP-11/45. This is the default.
10747 Generate code for a PDP-11/10.
10749 @item -mbcopy-builtin
10750 @opindex bcopy-builtin
10751 Use inline @code{movmemhi} patterns for copying memory. This is the
10756 Do not use inline @code{movmemhi} patterns for copying memory.
10762 Use 16-bit @code{int}. This is the default.
10768 Use 32-bit @code{int}.
10771 @itemx -mno-float32
10773 @opindex mno-float32
10774 Use 64-bit @code{float}. This is the default.
10777 @itemx -mno-float64
10779 @opindex mno-float64
10780 Use 32-bit @code{float}.
10784 Use @code{abshi2} pattern. This is the default.
10788 Do not use @code{abshi2} pattern.
10790 @item -mbranch-expensive
10791 @opindex mbranch-expensive
10792 Pretend that branches are expensive. This is for experimenting with
10793 code generation only.
10795 @item -mbranch-cheap
10796 @opindex mbranch-cheap
10797 Do not pretend that branches are expensive. This is the default.
10801 Generate code for a system with split I&D@.
10805 Generate code for a system without split I&D@. This is the default.
10809 Use Unix assembler syntax. This is the default when configured for
10810 @samp{pdp11-*-bsd}.
10814 Use DEC assembler syntax. This is the default when configured for any
10815 PDP-11 target other than @samp{pdp11-*-bsd}.
10818 @node PowerPC Options
10819 @subsection PowerPC Options
10820 @cindex PowerPC options
10822 These are listed under @xref{RS/6000 and PowerPC Options}.
10824 @node RS/6000 and PowerPC Options
10825 @subsection IBM RS/6000 and PowerPC Options
10826 @cindex RS/6000 and PowerPC Options
10827 @cindex IBM RS/6000 and PowerPC Options
10829 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10836 @itemx -mno-powerpc
10837 @itemx -mpowerpc-gpopt
10838 @itemx -mno-powerpc-gpopt
10839 @itemx -mpowerpc-gfxopt
10840 @itemx -mno-powerpc-gfxopt
10842 @itemx -mno-powerpc64
10846 @itemx -mno-popcntb
10852 @opindex mno-power2
10854 @opindex mno-powerpc
10855 @opindex mpowerpc-gpopt
10856 @opindex mno-powerpc-gpopt
10857 @opindex mpowerpc-gfxopt
10858 @opindex mno-powerpc-gfxopt
10859 @opindex mpowerpc64
10860 @opindex mno-powerpc64
10864 @opindex mno-popcntb
10867 GCC supports two related instruction set architectures for the
10868 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10869 instructions supported by the @samp{rios} chip set used in the original
10870 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10871 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
10872 the IBM 4xx, 6xx, and follow-on microprocessors.
10874 Neither architecture is a subset of the other. However there is a
10875 large common subset of instructions supported by both. An MQ
10876 register is included in processors supporting the POWER architecture.
10878 You use these options to specify which instructions are available on the
10879 processor you are using. The default value of these options is
10880 determined when configuring GCC@. Specifying the
10881 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10882 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10883 rather than the options listed above.
10885 The @option{-mpower} option allows GCC to generate instructions that
10886 are found only in the POWER architecture and to use the MQ register.
10887 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
10888 to generate instructions that are present in the POWER2 architecture but
10889 not the original POWER architecture.
10891 The @option{-mpowerpc} option allows GCC to generate instructions that
10892 are found only in the 32-bit subset of the PowerPC architecture.
10893 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
10894 GCC to use the optional PowerPC architecture instructions in the
10895 General Purpose group, including floating-point square root. Specifying
10896 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
10897 use the optional PowerPC architecture instructions in the Graphics
10898 group, including floating-point select.
10900 The @option{-mmfcrf} option allows GCC to generate the move from
10901 condition register field instruction implemented on the POWER4
10902 processor and other processors that support the PowerPC V2.01
10904 The @option{-mpopcntb} option allows GCC to generate the popcount and
10905 double precision FP reciprocal estimate instruction implemented on the
10906 POWER5 processor and other processors that support the PowerPC V2.02
10908 The @option{-mfprnd} option allows GCC to generate the FP round to
10909 integer instructions implemented on the POWER5+ processor and other
10910 processors that support the PowerPC V2.03 architecture.
10912 The @option{-mpowerpc64} option allows GCC to generate the additional
10913 64-bit instructions that are found in the full PowerPC64 architecture
10914 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
10915 @option{-mno-powerpc64}.
10917 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
10918 will use only the instructions in the common subset of both
10919 architectures plus some special AIX common-mode calls, and will not use
10920 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
10921 permits GCC to use any instruction from either architecture and to
10922 allow use of the MQ register; specify this for the Motorola MPC601.
10924 @item -mnew-mnemonics
10925 @itemx -mold-mnemonics
10926 @opindex mnew-mnemonics
10927 @opindex mold-mnemonics
10928 Select which mnemonics to use in the generated assembler code. With
10929 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
10930 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
10931 assembler mnemonics defined for the POWER architecture. Instructions
10932 defined in only one architecture have only one mnemonic; GCC uses that
10933 mnemonic irrespective of which of these options is specified.
10935 GCC defaults to the mnemonics appropriate for the architecture in
10936 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
10937 value of these option. Unless you are building a cross-compiler, you
10938 should normally not specify either @option{-mnew-mnemonics} or
10939 @option{-mold-mnemonics}, but should instead accept the default.
10941 @item -mcpu=@var{cpu_type}
10943 Set architecture type, register usage, choice of mnemonics, and
10944 instruction scheduling parameters for machine type @var{cpu_type}.
10945 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
10946 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
10947 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
10948 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
10949 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
10950 @samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
10951 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
10952 @samp{power4}, @samp{power5}, @samp{power5+},
10953 @samp{common}, @samp{powerpc}, @samp{powerpc64},
10954 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
10956 @option{-mcpu=common} selects a completely generic processor. Code
10957 generated under this option will run on any POWER or PowerPC processor.
10958 GCC will use only the instructions in the common subset of both
10959 architectures, and will not use the MQ register. GCC assumes a generic
10960 processor model for scheduling purposes.
10962 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
10963 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
10964 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
10965 types, with an appropriate, generic processor model assumed for
10966 scheduling purposes.
10968 The other options specify a specific processor. Code generated under
10969 those options will run best on that processor, and may not run at all on
10972 The @option{-mcpu} options automatically enable or disable the
10973 following options: @option{-maltivec}, @option{-mfprnd},
10974 @option{-mhard-float}, @option{-mmfcrf}, @option{-mmultiple},
10975 @option{-mnew-mnemonics}, @option{-mpopcntb}, @option{-mpower},
10976 @option{-mpower2}, @option{-mpowerpc64}, @option{-mpowerpc-gpopt},
10977 @option{-mpowerpc-gfxopt}, @option{-mstring}. The particular options
10978 set for any particular CPU will vary between compiler versions,
10979 depending on what setting seems to produce optimal code for that CPU;
10980 it doesn't necessarily reflect the actual hardware's capabilities. If
10981 you wish to set an individual option to a particular value, you may
10982 specify it after the @option{-mcpu} option, like @samp{-mcpu=970
10985 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
10986 not enabled or disabled by the @option{-mcpu} option at present because
10987 AIX does not have full support for these options. You may still
10988 enable or disable them individually if you're sure it'll work in your
10991 @item -mtune=@var{cpu_type}
10993 Set the instruction scheduling parameters for machine type
10994 @var{cpu_type}, but do not set the architecture type, register usage, or
10995 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
10996 values for @var{cpu_type} are used for @option{-mtune} as for
10997 @option{-mcpu}. If both are specified, the code generated will use the
10998 architecture, registers, and mnemonics set by @option{-mcpu}, but the
10999 scheduling parameters set by @option{-mtune}.
11005 Generate code to compute division as reciprocal estimate and iterative
11006 refinement, creating opportunities for increased throughput. This
11007 feature requires: optional PowerPC Graphics instruction set for single
11008 precision and FRE instruction for double precision, assuming divides
11009 cannot generate user-visible traps, and the domain values not include
11010 Infinities, denormals or zero denominator.
11013 @itemx -mno-altivec
11015 @opindex mno-altivec
11016 Generate code that uses (does not use) AltiVec instructions, and also
11017 enable the use of built-in functions that allow more direct access to
11018 the AltiVec instruction set. You may also need to set
11019 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
11025 @opindex mno-vrsave
11026 Generate VRSAVE instructions when generating AltiVec code.
11030 Extend the current ABI with SPE ABI extensions. This does not change
11031 the default ABI, instead it adds the SPE ABI extensions to the current
11035 @opindex mabi=no-spe
11036 Disable Booke SPE ABI extensions for the current ABI@.
11039 @opindex msecure-plt
11040 Generate code that allows ld and ld.so to build executables and shared
11041 libraries with non-exec .plt and .got sections. This is a PowerPC
11042 32-bit SYSV ABI option.
11046 Generate code that uses a BSS .plt section that ld.so fills in, and
11047 requires .plt and .got sections that are both writable and executable.
11048 This is a PowerPC 32-bit SYSV ABI option.
11054 This switch enables or disables the generation of ISEL instructions.
11056 @item -misel=@var{yes/no}
11057 This switch has been deprecated. Use @option{-misel} and
11058 @option{-mno-isel} instead.
11064 This switch enables or disables the generation of SPE simd
11067 @item -mspe=@var{yes/no}
11068 This option has been deprecated. Use @option{-mspe} and
11069 @option{-mno-spe} instead.
11071 @item -mfloat-gprs=@var{yes/single/double/no}
11072 @itemx -mfloat-gprs
11073 @opindex mfloat-gprs
11074 This switch enables or disables the generation of floating point
11075 operations on the general purpose registers for architectures that
11078 The argument @var{yes} or @var{single} enables the use of
11079 single-precision floating point operations.
11081 The argument @var{double} enables the use of single and
11082 double-precision floating point operations.
11084 The argument @var{no} disables floating point operations on the
11085 general purpose registers.
11087 This option is currently only available on the MPC854x.
11093 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
11094 targets (including GNU/Linux). The 32-bit environment sets int, long
11095 and pointer to 32 bits and generates code that runs on any PowerPC
11096 variant. The 64-bit environment sets int to 32 bits and long and
11097 pointer to 64 bits, and generates code for PowerPC64, as for
11098 @option{-mpowerpc64}.
11101 @itemx -mno-fp-in-toc
11102 @itemx -mno-sum-in-toc
11103 @itemx -mminimal-toc
11105 @opindex mno-fp-in-toc
11106 @opindex mno-sum-in-toc
11107 @opindex mminimal-toc
11108 Modify generation of the TOC (Table Of Contents), which is created for
11109 every executable file. The @option{-mfull-toc} option is selected by
11110 default. In that case, GCC will allocate at least one TOC entry for
11111 each unique non-automatic variable reference in your program. GCC
11112 will also place floating-point constants in the TOC@. However, only
11113 16,384 entries are available in the TOC@.
11115 If you receive a linker error message that saying you have overflowed
11116 the available TOC space, you can reduce the amount of TOC space used
11117 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
11118 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
11119 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
11120 generate code to calculate the sum of an address and a constant at
11121 run-time instead of putting that sum into the TOC@. You may specify one
11122 or both of these options. Each causes GCC to produce very slightly
11123 slower and larger code at the expense of conserving TOC space.
11125 If you still run out of space in the TOC even when you specify both of
11126 these options, specify @option{-mminimal-toc} instead. This option causes
11127 GCC to make only one TOC entry for every file. When you specify this
11128 option, GCC will produce code that is slower and larger but which
11129 uses extremely little TOC space. You may wish to use this option
11130 only on files that contain less frequently executed code.
11136 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
11137 @code{long} type, and the infrastructure needed to support them.
11138 Specifying @option{-maix64} implies @option{-mpowerpc64} and
11139 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
11140 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
11143 @itemx -mno-xl-compat
11144 @opindex mxl-compat
11145 @opindex mno-xl-compat
11146 Produce code that conforms more closely to IBM XLC semantics when using
11147 AIX-compatible ABI. Pass floating-point arguments to prototyped
11148 functions beyond the register save area (RSA) on the stack in addition
11149 to argument FPRs. Do not assume that most significant double in 128
11150 bit long double value is properly rounded when comparing values.
11152 The AIX calling convention was extended but not initially documented to
11153 handle an obscure K&R C case of calling a function that takes the
11154 address of its arguments with fewer arguments than declared. AIX XL
11155 compilers access floating point arguments which do not fit in the
11156 RSA from the stack when a subroutine is compiled without
11157 optimization. Because always storing floating-point arguments on the
11158 stack is inefficient and rarely needed, this option is not enabled by
11159 default and only is necessary when calling subroutines compiled by AIX
11160 XL compilers without optimization.
11164 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
11165 application written to use message passing with special startup code to
11166 enable the application to run. The system must have PE installed in the
11167 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
11168 must be overridden with the @option{-specs=} option to specify the
11169 appropriate directory location. The Parallel Environment does not
11170 support threads, so the @option{-mpe} option and the @option{-pthread}
11171 option are incompatible.
11173 @item -malign-natural
11174 @itemx -malign-power
11175 @opindex malign-natural
11176 @opindex malign-power
11177 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
11178 @option{-malign-natural} overrides the ABI-defined alignment of larger
11179 types, such as floating-point doubles, on their natural size-based boundary.
11180 The option @option{-malign-power} instructs GCC to follow the ABI-specified
11181 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
11183 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
11187 @itemx -mhard-float
11188 @opindex msoft-float
11189 @opindex mhard-float
11190 Generate code that does not use (uses) the floating-point register set.
11191 Software floating point emulation is provided if you use the
11192 @option{-msoft-float} option, and pass the option to GCC when linking.
11195 @itemx -mno-multiple
11197 @opindex mno-multiple
11198 Generate code that uses (does not use) the load multiple word
11199 instructions and the store multiple word instructions. These
11200 instructions are generated by default on POWER systems, and not
11201 generated on PowerPC systems. Do not use @option{-mmultiple} on little
11202 endian PowerPC systems, since those instructions do not work when the
11203 processor is in little endian mode. The exceptions are PPC740 and
11204 PPC750 which permit the instructions usage in little endian mode.
11209 @opindex mno-string
11210 Generate code that uses (does not use) the load string instructions
11211 and the store string word instructions to save multiple registers and
11212 do small block moves. These instructions are generated by default on
11213 POWER systems, and not generated on PowerPC systems. Do not use
11214 @option{-mstring} on little endian PowerPC systems, since those
11215 instructions do not work when the processor is in little endian mode.
11216 The exceptions are PPC740 and PPC750 which permit the instructions
11217 usage in little endian mode.
11222 @opindex mno-update
11223 Generate code that uses (does not use) the load or store instructions
11224 that update the base register to the address of the calculated memory
11225 location. These instructions are generated by default. If you use
11226 @option{-mno-update}, there is a small window between the time that the
11227 stack pointer is updated and the address of the previous frame is
11228 stored, which means code that walks the stack frame across interrupts or
11229 signals may get corrupted data.
11232 @itemx -mno-fused-madd
11233 @opindex mfused-madd
11234 @opindex mno-fused-madd
11235 Generate code that uses (does not use) the floating point multiply and
11236 accumulate instructions. These instructions are generated by default if
11237 hardware floating is used.
11239 @item -mno-bit-align
11241 @opindex mno-bit-align
11242 @opindex mbit-align
11243 On System V.4 and embedded PowerPC systems do not (do) force structures
11244 and unions that contain bit-fields to be aligned to the base type of the
11247 For example, by default a structure containing nothing but 8
11248 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
11249 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
11250 the structure would be aligned to a 1 byte boundary and be one byte in
11253 @item -mno-strict-align
11254 @itemx -mstrict-align
11255 @opindex mno-strict-align
11256 @opindex mstrict-align
11257 On System V.4 and embedded PowerPC systems do not (do) assume that
11258 unaligned memory references will be handled by the system.
11260 @item -mrelocatable
11261 @itemx -mno-relocatable
11262 @opindex mrelocatable
11263 @opindex mno-relocatable
11264 On embedded PowerPC systems generate code that allows (does not allow)
11265 the program to be relocated to a different address at runtime. If you
11266 use @option{-mrelocatable} on any module, all objects linked together must
11267 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
11269 @item -mrelocatable-lib
11270 @itemx -mno-relocatable-lib
11271 @opindex mrelocatable-lib
11272 @opindex mno-relocatable-lib
11273 On embedded PowerPC systems generate code that allows (does not allow)
11274 the program to be relocated to a different address at runtime. Modules
11275 compiled with @option{-mrelocatable-lib} can be linked with either modules
11276 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
11277 with modules compiled with the @option{-mrelocatable} options.
11283 On System V.4 and embedded PowerPC systems do not (do) assume that
11284 register 2 contains a pointer to a global area pointing to the addresses
11285 used in the program.
11288 @itemx -mlittle-endian
11290 @opindex mlittle-endian
11291 On System V.4 and embedded PowerPC systems compile code for the
11292 processor in little endian mode. The @option{-mlittle-endian} option is
11293 the same as @option{-mlittle}.
11296 @itemx -mbig-endian
11298 @opindex mbig-endian
11299 On System V.4 and embedded PowerPC systems compile code for the
11300 processor in big endian mode. The @option{-mbig-endian} option is
11301 the same as @option{-mbig}.
11303 @item -mdynamic-no-pic
11304 @opindex mdynamic-no-pic
11305 On Darwin and Mac OS X systems, compile code so that it is not
11306 relocatable, but that its external references are relocatable. The
11307 resulting code is suitable for applications, but not shared
11310 @item -mprioritize-restricted-insns=@var{priority}
11311 @opindex mprioritize-restricted-insns
11312 This option controls the priority that is assigned to
11313 dispatch-slot restricted instructions during the second scheduling
11314 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
11315 @var{no/highest/second-highest} priority to dispatch slot restricted
11318 @item -msched-costly-dep=@var{dependence_type}
11319 @opindex msched-costly-dep
11320 This option controls which dependences are considered costly
11321 by the target during instruction scheduling. The argument
11322 @var{dependence_type} takes one of the following values:
11323 @var{no}: no dependence is costly,
11324 @var{all}: all dependences are costly,
11325 @var{true_store_to_load}: a true dependence from store to load is costly,
11326 @var{store_to_load}: any dependence from store to load is costly,
11327 @var{number}: any dependence which latency >= @var{number} is costly.
11329 @item -minsert-sched-nops=@var{scheme}
11330 @opindex minsert-sched-nops
11331 This option controls which nop insertion scheme will be used during
11332 the second scheduling pass. The argument @var{scheme} takes one of the
11334 @var{no}: Don't insert nops.
11335 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
11336 according to the scheduler's grouping.
11337 @var{regroup_exact}: Insert nops to force costly dependent insns into
11338 separate groups. Insert exactly as many nops as needed to force an insn
11339 to a new group, according to the estimated processor grouping.
11340 @var{number}: Insert nops to force costly dependent insns into
11341 separate groups. Insert @var{number} nops to force an insn to a new group.
11344 @opindex mcall-sysv
11345 On System V.4 and embedded PowerPC systems compile code using calling
11346 conventions that adheres to the March 1995 draft of the System V
11347 Application Binary Interface, PowerPC processor supplement. This is the
11348 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
11350 @item -mcall-sysv-eabi
11351 @opindex mcall-sysv-eabi
11352 Specify both @option{-mcall-sysv} and @option{-meabi} options.
11354 @item -mcall-sysv-noeabi
11355 @opindex mcall-sysv-noeabi
11356 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
11358 @item -mcall-solaris
11359 @opindex mcall-solaris
11360 On System V.4 and embedded PowerPC systems compile code for the Solaris
11364 @opindex mcall-linux
11365 On System V.4 and embedded PowerPC systems compile code for the
11366 Linux-based GNU system.
11370 On System V.4 and embedded PowerPC systems compile code for the
11371 Hurd-based GNU system.
11373 @item -mcall-netbsd
11374 @opindex mcall-netbsd
11375 On System V.4 and embedded PowerPC systems compile code for the
11376 NetBSD operating system.
11378 @item -maix-struct-return
11379 @opindex maix-struct-return
11380 Return all structures in memory (as specified by the AIX ABI)@.
11382 @item -msvr4-struct-return
11383 @opindex msvr4-struct-return
11384 Return structures smaller than 8 bytes in registers (as specified by the
11387 @item -mabi=@var{abi-type}
11389 Extend the current ABI with a particular extension, or remove such extension.
11390 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
11394 @itemx -mno-prototype
11395 @opindex mprototype
11396 @opindex mno-prototype
11397 On System V.4 and embedded PowerPC systems assume that all calls to
11398 variable argument functions are properly prototyped. Otherwise, the
11399 compiler must insert an instruction before every non prototyped call to
11400 set or clear bit 6 of the condition code register (@var{CR}) to
11401 indicate whether floating point values were passed in the floating point
11402 registers in case the function takes a variable arguments. With
11403 @option{-mprototype}, only calls to prototyped variable argument functions
11404 will set or clear the bit.
11408 On embedded PowerPC systems, assume that the startup module is called
11409 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
11410 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
11415 On embedded PowerPC systems, assume that the startup module is called
11416 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
11421 On embedded PowerPC systems, assume that the startup module is called
11422 @file{crt0.o} and the standard C libraries are @file{libads.a} and
11425 @item -myellowknife
11426 @opindex myellowknife
11427 On embedded PowerPC systems, assume that the startup module is called
11428 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
11433 On System V.4 and embedded PowerPC systems, specify that you are
11434 compiling for a VxWorks system.
11438 Specify that you are compiling for the WindISS simulation environment.
11442 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
11443 header to indicate that @samp{eabi} extended relocations are used.
11449 On System V.4 and embedded PowerPC systems do (do not) adhere to the
11450 Embedded Applications Binary Interface (eabi) which is a set of
11451 modifications to the System V.4 specifications. Selecting @option{-meabi}
11452 means that the stack is aligned to an 8 byte boundary, a function
11453 @code{__eabi} is called to from @code{main} to set up the eabi
11454 environment, and the @option{-msdata} option can use both @code{r2} and
11455 @code{r13} to point to two separate small data areas. Selecting
11456 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
11457 do not call an initialization function from @code{main}, and the
11458 @option{-msdata} option will only use @code{r13} to point to a single
11459 small data area. The @option{-meabi} option is on by default if you
11460 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
11463 @opindex msdata=eabi
11464 On System V.4 and embedded PowerPC systems, put small initialized
11465 @code{const} global and static data in the @samp{.sdata2} section, which
11466 is pointed to by register @code{r2}. Put small initialized
11467 non-@code{const} global and static data in the @samp{.sdata} section,
11468 which is pointed to by register @code{r13}. Put small uninitialized
11469 global and static data in the @samp{.sbss} section, which is adjacent to
11470 the @samp{.sdata} section. The @option{-msdata=eabi} option is
11471 incompatible with the @option{-mrelocatable} option. The
11472 @option{-msdata=eabi} option also sets the @option{-memb} option.
11475 @opindex msdata=sysv
11476 On System V.4 and embedded PowerPC systems, put small global and static
11477 data in the @samp{.sdata} section, which is pointed to by register
11478 @code{r13}. Put small uninitialized global and static data in the
11479 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
11480 The @option{-msdata=sysv} option is incompatible with the
11481 @option{-mrelocatable} option.
11483 @item -msdata=default
11485 @opindex msdata=default
11487 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
11488 compile code the same as @option{-msdata=eabi}, otherwise compile code the
11489 same as @option{-msdata=sysv}.
11492 @opindex msdata-data
11493 On System V.4 and embedded PowerPC systems, put small global and static
11494 data in the @samp{.sdata} section. Put small uninitialized global and
11495 static data in the @samp{.sbss} section. Do not use register @code{r13}
11496 to address small data however. This is the default behavior unless
11497 other @option{-msdata} options are used.
11501 @opindex msdata=none
11503 On embedded PowerPC systems, put all initialized global and static data
11504 in the @samp{.data} section, and all uninitialized data in the
11505 @samp{.bss} section.
11509 @cindex smaller data references (PowerPC)
11510 @cindex .sdata/.sdata2 references (PowerPC)
11511 On embedded PowerPC systems, put global and static items less than or
11512 equal to @var{num} bytes into the small data or bss sections instead of
11513 the normal data or bss section. By default, @var{num} is 8. The
11514 @option{-G @var{num}} switch is also passed to the linker.
11515 All modules should be compiled with the same @option{-G @var{num}} value.
11518 @itemx -mno-regnames
11520 @opindex mno-regnames
11521 On System V.4 and embedded PowerPC systems do (do not) emit register
11522 names in the assembly language output using symbolic forms.
11525 @itemx -mno-longcall
11527 @opindex mno-longcall
11528 Default to making all function calls indirectly, using a register, so
11529 that functions which reside further than 32 megabytes (33,554,432
11530 bytes) from the current location can be called. This setting can be
11531 overridden by the @code{shortcall} function attribute, or by
11532 @code{#pragma longcall(0)}.
11534 Some linkers are capable of detecting out-of-range calls and generating
11535 glue code on the fly. On these systems, long calls are unnecessary and
11536 generate slower code. As of this writing, the AIX linker can do this,
11537 as can the GNU linker for PowerPC/64. It is planned to add this feature
11538 to the GNU linker for 32-bit PowerPC systems as well.
11540 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
11541 callee, L42'', plus a ``branch island'' (glue code). The two target
11542 addresses represent the callee and the ``branch island''. The
11543 Darwin/PPC linker will prefer the first address and generate a ``bl
11544 callee'' if the PPC ``bl'' instruction will reach the callee directly;
11545 otherwise, the linker will generate ``bl L42'' to call the ``branch
11546 island''. The ``branch island'' is appended to the body of the
11547 calling function; it computes the full 32-bit address of the callee
11550 On Mach-O (Darwin) systems, this option directs the compiler emit to
11551 the glue for every direct call, and the Darwin linker decides whether
11552 to use or discard it.
11554 In the future, we may cause GCC to ignore all longcall specifications
11555 when the linker is known to generate glue.
11559 Adds support for multithreading with the @dfn{pthreads} library.
11560 This option sets flags for both the preprocessor and linker.
11564 @node S/390 and zSeries Options
11565 @subsection S/390 and zSeries Options
11566 @cindex S/390 and zSeries Options
11568 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
11572 @itemx -msoft-float
11573 @opindex mhard-float
11574 @opindex msoft-float
11575 Use (do not use) the hardware floating-point instructions and registers
11576 for floating-point operations. When @option{-msoft-float} is specified,
11577 functions in @file{libgcc.a} will be used to perform floating-point
11578 operations. When @option{-mhard-float} is specified, the compiler
11579 generates IEEE floating-point instructions. This is the default.
11582 @itemx -mno-backchain
11583 @opindex mbackchain
11584 @opindex mno-backchain
11585 Store (do not store) the address of the caller's frame as backchain pointer
11586 into the callee's stack frame.
11587 A backchain may be needed to allow debugging using tools that do not understand
11588 DWARF-2 call frame information.
11589 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
11590 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
11591 the backchain is placed into the topmost word of the 96/160 byte register
11594 In general, code compiled with @option{-mbackchain} is call-compatible with
11595 code compiled with @option{-mmo-backchain}; however, use of the backchain
11596 for debugging purposes usually requires that the whole binary is built with
11597 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
11598 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11599 to build a linux kernel use @option{-msoft-float}.
11601 The default is to not maintain the backchain.
11603 @item -mpacked-stack
11604 @item -mno-packed-stack
11605 @opindex mpacked-stack
11606 @opindex mno-packed-stack
11607 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
11608 specified, the compiler uses the all fields of the 96/160 byte register save
11609 area only for their default purpose; unused fields still take up stack space.
11610 When @option{-mpacked-stack} is specified, register save slots are densely
11611 packed at the top of the register save area; unused space is reused for other
11612 purposes, allowing for more efficient use of the available stack space.
11613 However, when @option{-mbackchain} is also in effect, the topmost word of
11614 the save area is always used to store the backchain, and the return address
11615 register is always saved two words below the backchain.
11617 As long as the stack frame backchain is not used, code generated with
11618 @option{-mpacked-stack} is call-compatible with code generated with
11619 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
11620 S/390 or zSeries generated code that uses the stack frame backchain at run
11621 time, not just for debugging purposes. Such code is not call-compatible
11622 with code compiled with @option{-mpacked-stack}. Also, note that the
11623 combination of @option{-mbackchain},
11624 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
11625 to build a linux kernel use @option{-msoft-float}.
11627 The default is to not use the packed stack layout.
11630 @itemx -mno-small-exec
11631 @opindex msmall-exec
11632 @opindex mno-small-exec
11633 Generate (or do not generate) code using the @code{bras} instruction
11634 to do subroutine calls.
11635 This only works reliably if the total executable size does not
11636 exceed 64k. The default is to use the @code{basr} instruction instead,
11637 which does not have this limitation.
11643 When @option{-m31} is specified, generate code compliant to the
11644 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
11645 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
11646 particular to generate 64-bit instructions. For the @samp{s390}
11647 targets, the default is @option{-m31}, while the @samp{s390x}
11648 targets default to @option{-m64}.
11654 When @option{-mzarch} is specified, generate code using the
11655 instructions available on z/Architecture.
11656 When @option{-mesa} is specified, generate code using the
11657 instructions available on ESA/390. Note that @option{-mesa} is
11658 not possible with @option{-m64}.
11659 When generating code compliant to the GNU/Linux for S/390 ABI,
11660 the default is @option{-mesa}. When generating code compliant
11661 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
11667 Generate (or do not generate) code using the @code{mvcle} instruction
11668 to perform block moves. When @option{-mno-mvcle} is specified,
11669 use a @code{mvc} loop instead. This is the default unless optimizing for
11676 Print (or do not print) additional debug information when compiling.
11677 The default is to not print debug information.
11679 @item -march=@var{cpu-type}
11681 Generate code that will run on @var{cpu-type}, which is the name of a system
11682 representing a certain processor type. Possible values for
11683 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
11684 When generating code using the instructions available on z/Architecture,
11685 the default is @option{-march=z900}. Otherwise, the default is
11686 @option{-march=g5}.
11688 @item -mtune=@var{cpu-type}
11690 Tune to @var{cpu-type} everything applicable about the generated code,
11691 except for the ABI and the set of available instructions.
11692 The list of @var{cpu-type} values is the same as for @option{-march}.
11693 The default is the value used for @option{-march}.
11696 @itemx -mno-tpf-trace
11697 @opindex mtpf-trace
11698 @opindex mno-tpf-trace
11699 Generate code that adds (does not add) in TPF OS specific branches to trace
11700 routines in the operating system. This option is off by default, even
11701 when compiling for the TPF OS@.
11704 @itemx -mno-fused-madd
11705 @opindex mfused-madd
11706 @opindex mno-fused-madd
11707 Generate code that uses (does not use) the floating point multiply and
11708 accumulate instructions. These instructions are generated by default if
11709 hardware floating point is used.
11711 @item -mwarn-framesize=@var{framesize}
11712 @opindex mwarn-framesize
11713 Emit a warning if the current function exceeds the given frame size. Because
11714 this is a compile time check it doesn't need to be a real problem when the program
11715 runs. It is intended to identify functions which most probably cause
11716 a stack overflow. It is useful to be used in an environment with limited stack
11717 size e.g.@: the linux kernel.
11719 @item -mwarn-dynamicstack
11720 @opindex mwarn-dynamicstack
11721 Emit a warning if the function calls alloca or uses dynamically
11722 sized arrays. This is generally a bad idea with a limited stack size.
11724 @item -mstack-guard=@var{stack-guard}
11725 @item -mstack-size=@var{stack-size}
11726 @opindex mstack-guard
11727 @opindex mstack-size
11728 These arguments always have to be used in conjunction. If they are present the s390
11729 back end emits additional instructions in the function prologue which trigger a trap
11730 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
11731 (remember that the stack on s390 grows downward). These options are intended to
11732 be used to help debugging stack overflow problems. The additionally emitted code
11733 causes only little overhead and hence can also be used in production like systems
11734 without greater performance degradation. The given values have to be exact
11735 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without
11737 In order to be efficient the extra code makes the assumption that the stack starts
11738 at an address aligned to the value given by @var{stack-size}.
11742 @subsection SH Options
11744 These @samp{-m} options are defined for the SH implementations:
11749 Generate code for the SH1.
11753 Generate code for the SH2.
11756 Generate code for the SH2e.
11760 Generate code for the SH3.
11764 Generate code for the SH3e.
11768 Generate code for the SH4 without a floating-point unit.
11770 @item -m4-single-only
11771 @opindex m4-single-only
11772 Generate code for the SH4 with a floating-point unit that only
11773 supports single-precision arithmetic.
11777 Generate code for the SH4 assuming the floating-point unit is in
11778 single-precision mode by default.
11782 Generate code for the SH4.
11786 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
11787 floating-point unit is not used.
11789 @item -m4a-single-only
11790 @opindex m4a-single-only
11791 Generate code for the SH4a, in such a way that no double-precision
11792 floating point operations are used.
11795 @opindex m4a-single
11796 Generate code for the SH4a assuming the floating-point unit is in
11797 single-precision mode by default.
11801 Generate code for the SH4a.
11805 Same as @option{-m4a-nofpu}, except that it implicitly passes
11806 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11807 instructions at the moment.
11811 Compile code for the processor in big endian mode.
11815 Compile code for the processor in little endian mode.
11819 Align doubles at 64-bit boundaries. Note that this changes the calling
11820 conventions, and thus some functions from the standard C library will
11821 not work unless you recompile it first with @option{-mdalign}.
11825 Shorten some address references at link time, when possible; uses the
11826 linker option @option{-relax}.
11830 Use 32-bit offsets in @code{switch} tables. The default is to use
11835 Enable the use of the instruction @code{fmovd}.
11839 Comply with the calling conventions defined by Renesas.
11843 Comply with the calling conventions defined by Renesas.
11847 Comply with the calling conventions defined for GCC before the Renesas
11848 conventions were available. This option is the default for all
11849 targets of the SH toolchain except for @samp{sh-symbianelf}.
11852 @opindex mnomacsave
11853 Mark the @code{MAC} register as call-clobbered, even if
11854 @option{-mhitachi} is given.
11858 Increase IEEE-compliance of floating-point code.
11859 At the moment, this is equivalent to @option{-fno-finite-math-only}.
11860 When generating 16 bit SH opcodes, getting IEEE-conforming results for
11861 comparisons of NANs / infinities incurs extra overhead in every
11862 floating point comparison, therefore the default is set to
11863 @option{-ffinite-math-only}.
11867 Dump instruction size and location in the assembly code.
11870 @opindex mpadstruct
11871 This option is deprecated. It pads structures to multiple of 4 bytes,
11872 which is incompatible with the SH ABI@.
11876 Optimize for space instead of speed. Implied by @option{-Os}.
11879 @opindex mprefergot
11880 When generating position-independent code, emit function calls using
11881 the Global Offset Table instead of the Procedure Linkage Table.
11885 Generate a library function call to invalidate instruction cache
11886 entries, after fixing up a trampoline. This library function call
11887 doesn't assume it can write to the whole memory address space. This
11888 is the default when the target is @code{sh-*-linux*}.
11890 @item -multcost=@var{number}
11891 @opindex multcost=@var{number}
11892 Set the cost to assume for a multiply insn.
11894 @item -mdiv=@var{strategy}
11895 @opindex mdiv=@var{strategy}
11896 Set the division strategy to use for SHmedia code. @var{strategy} must be
11897 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
11898 inv:call2, inv:fp .
11899 "fp" performs the operation in floating point. This has a very high latency,
11900 but needs only a few instructions, so it might be a good choice if
11901 your code has enough easily exploitable ILP to allow the compiler to
11902 schedule the floating point instructions together with other instructions.
11903 Division by zero causes a floating point exception.
11904 "inv" uses integer operations to calculate the inverse of the divisor,
11905 and then multiplies the dividend with the inverse. This strategy allows
11906 cse and hoisting of the inverse calculation. Division by zero calculates
11907 an unspecified result, but does not trap.
11908 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
11909 have been found, or if the entire operation has been hoisted to the same
11910 place, the last stages of the inverse calculation are intertwined with the
11911 final multiply to reduce the overall latency, at the expense of using a few
11912 more instructions, and thus offering fewer scheduling opportunities with
11914 "call" calls a library function that usually implements the inv:minlat
11916 This gives high code density for m5-*media-nofpu compilations.
11917 "call2" uses a different entry point of the same library function, where it
11918 assumes that a pointer to a lookup table has already been set up, which
11919 exposes the pointer load to cse / code hoisting optimizations.
11920 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
11921 code generation, but if the code stays unoptimized, revert to the "call",
11922 "call2", or "fp" strategies, respectively. Note that the
11923 potentially-trapping side effect of division by zero is carried by a
11924 separate instruction, so it is possible that all the integer instructions
11925 are hoisted out, but the marker for the side effect stays where it is.
11926 A recombination to fp operations or a call is not possible in that case.
11927 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
11928 that the inverse calculation was nor separated from the multiply, they speed
11929 up division where the dividend fits into 20 bits (plus sign where applicable),
11930 by inserting a test to skip a number of operations in this case; this test
11931 slows down the case of larger dividends. inv20u assumes the case of a such
11932 a small dividend to be unlikely, and inv20l assumes it to be likely.
11934 @item -mdivsi3_libfunc=@var{name}
11935 @opindex mdivsi3_libfunc=@var{name}
11936 Set the name of the library function used for 32 bit signed division to
11937 @var{name}. This only affect the name used in the call and inv:call
11938 division strategies, and the compiler will still expect the same
11939 sets of input/output/clobbered registers as if this option was not present.
11941 @item -madjust-unroll
11942 @opindex madjust-unroll
11943 Throttle unrolling to avoid thrashing target registers.
11944 This option only has an effect if the gcc code base supports the
11945 TARGET_ADJUST_UNROLL_MAX target hook.
11947 @item -mindexed-addressing
11948 @opindex mindexed-addressing
11949 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
11950 This is only safe if the hardware and/or OS implement 32 bit wrap-around
11951 semantics for the indexed addressing mode. The architecture allows the
11952 implementation of processors with 64 bit MMU, which the OS could use to
11953 get 32 bit addressing, but since no current hardware implementation supports
11954 this or any other way to make the indexed addressing mode safe to use in
11955 the 32 bit ABI, the default is -mno-indexed-addressing.
11957 @item -mgettrcost=@var{number}
11958 @opindex mgettrcost=@var{number}
11959 Set the cost assumed for the gettr instruction to @var{number}.
11960 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
11964 Assume pt* instructions won't trap. This will generally generate better
11965 scheduled code, but is unsafe on current hardware. The current architecture
11966 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
11967 This has the unintentional effect of making it unsafe to schedule ptabs /
11968 ptrel before a branch, or hoist it out of a loop. For example,
11969 __do_global_ctors, a part of libgcc that runs constructors at program
11970 startup, calls functions in a list which is delimited by -1. With the
11971 -mpt-fixed option, the ptabs will be done before testing against -1.
11972 That means that all the constructors will be run a bit quicker, but when
11973 the loop comes to the end of the list, the program crashes because ptabs
11974 loads -1 into a target register. Since this option is unsafe for any
11975 hardware implementing the current architecture specification, the default
11976 is -mno-pt-fixed. Unless the user specifies a specific cost with
11977 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
11978 this deters register allocation using target registers for storing
11981 @item -minvalid-symbols
11982 @opindex minvalid-symbols
11983 Assume symbols might be invalid. Ordinary function symbols generated by
11984 the compiler will always be valid to load with movi/shori/ptabs or
11985 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
11986 to generate symbols that will cause ptabs / ptrel to trap.
11987 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
11988 It will then prevent cross-basic-block cse, hoisting and most scheduling
11989 of symbol loads. The default is @option{-mno-invalid-symbols}.
11992 @node SPARC Options
11993 @subsection SPARC Options
11994 @cindex SPARC options
11996 These @samp{-m} options are supported on the SPARC:
11999 @item -mno-app-regs
12001 @opindex mno-app-regs
12003 Specify @option{-mapp-regs} to generate output using the global registers
12004 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
12007 To be fully SVR4 ABI compliant at the cost of some performance loss,
12008 specify @option{-mno-app-regs}. You should compile libraries and system
12009 software with this option.
12012 @itemx -mhard-float
12014 @opindex mhard-float
12015 Generate output containing floating point instructions. This is the
12019 @itemx -msoft-float
12021 @opindex msoft-float
12022 Generate output containing library calls for floating point.
12023 @strong{Warning:} the requisite libraries are not available for all SPARC
12024 targets. Normally the facilities of the machine's usual C compiler are
12025 used, but this cannot be done directly in cross-compilation. You must make
12026 your own arrangements to provide suitable library functions for
12027 cross-compilation. The embedded targets @samp{sparc-*-aout} and
12028 @samp{sparclite-*-*} do provide software floating point support.
12030 @option{-msoft-float} changes the calling convention in the output file;
12031 therefore, it is only useful if you compile @emph{all} of a program with
12032 this option. In particular, you need to compile @file{libgcc.a}, the
12033 library that comes with GCC, with @option{-msoft-float} in order for
12036 @item -mhard-quad-float
12037 @opindex mhard-quad-float
12038 Generate output containing quad-word (long double) floating point
12041 @item -msoft-quad-float
12042 @opindex msoft-quad-float
12043 Generate output containing library calls for quad-word (long double)
12044 floating point instructions. The functions called are those specified
12045 in the SPARC ABI@. This is the default.
12047 As of this writing, there are no SPARC implementations that have hardware
12048 support for the quad-word floating point instructions. They all invoke
12049 a trap handler for one of these instructions, and then the trap handler
12050 emulates the effect of the instruction. Because of the trap handler overhead,
12051 this is much slower than calling the ABI library routines. Thus the
12052 @option{-msoft-quad-float} option is the default.
12054 @item -mno-unaligned-doubles
12055 @itemx -munaligned-doubles
12056 @opindex mno-unaligned-doubles
12057 @opindex munaligned-doubles
12058 Assume that doubles have 8 byte alignment. This is the default.
12060 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
12061 alignment only if they are contained in another type, or if they have an
12062 absolute address. Otherwise, it assumes they have 4 byte alignment.
12063 Specifying this option avoids some rare compatibility problems with code
12064 generated by other compilers. It is not the default because it results
12065 in a performance loss, especially for floating point code.
12067 @item -mno-faster-structs
12068 @itemx -mfaster-structs
12069 @opindex mno-faster-structs
12070 @opindex mfaster-structs
12071 With @option{-mfaster-structs}, the compiler assumes that structures
12072 should have 8 byte alignment. This enables the use of pairs of
12073 @code{ldd} and @code{std} instructions for copies in structure
12074 assignment, in place of twice as many @code{ld} and @code{st} pairs.
12075 However, the use of this changed alignment directly violates the SPARC
12076 ABI@. Thus, it's intended only for use on targets where the developer
12077 acknowledges that their resulting code will not be directly in line with
12078 the rules of the ABI@.
12080 @item -mimpure-text
12081 @opindex mimpure-text
12082 @option{-mimpure-text}, used in addition to @option{-shared}, tells
12083 the compiler to not pass @option{-z text} to the linker when linking a
12084 shared object. Using this option, you can link position-dependent
12085 code into a shared object.
12087 @option{-mimpure-text} suppresses the ``relocations remain against
12088 allocatable but non-writable sections'' linker error message.
12089 However, the necessary relocations will trigger copy-on-write, and the
12090 shared object is not actually shared across processes. Instead of
12091 using @option{-mimpure-text}, you should compile all source code with
12092 @option{-fpic} or @option{-fPIC}.
12094 This option is only available on SunOS and Solaris.
12096 @item -mcpu=@var{cpu_type}
12098 Set the instruction set, register set, and instruction scheduling parameters
12099 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
12100 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
12101 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
12102 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
12103 @samp{ultrasparc3}.
12105 Default instruction scheduling parameters are used for values that select
12106 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
12107 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
12109 Here is a list of each supported architecture and their supported
12114 v8: supersparc, hypersparc
12115 sparclite: f930, f934, sparclite86x
12117 v9: ultrasparc, ultrasparc3
12120 By default (unless configured otherwise), GCC generates code for the V7
12121 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
12122 additionally optimizes it for the Cypress CY7C602 chip, as used in the
12123 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
12124 SPARCStation 1, 2, IPX etc.
12126 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
12127 architecture. The only difference from V7 code is that the compiler emits
12128 the integer multiply and integer divide instructions which exist in SPARC-V8
12129 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
12130 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
12133 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
12134 the SPARC architecture. This adds the integer multiply, integer divide step
12135 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
12136 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
12137 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
12138 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
12139 MB86934 chip, which is the more recent SPARClite with FPU@.
12141 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
12142 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
12143 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
12144 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
12145 optimizes it for the TEMIC SPARClet chip.
12147 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
12148 architecture. This adds 64-bit integer and floating-point move instructions,
12149 3 additional floating-point condition code registers and conditional move
12150 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
12151 optimizes it for the Sun UltraSPARC I/II chips. With
12152 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
12153 Sun UltraSPARC III chip.
12155 @item -mtune=@var{cpu_type}
12157 Set the instruction scheduling parameters for machine type
12158 @var{cpu_type}, but do not set the instruction set or register set that the
12159 option @option{-mcpu=@var{cpu_type}} would.
12161 The same values for @option{-mcpu=@var{cpu_type}} can be used for
12162 @option{-mtune=@var{cpu_type}}, but the only useful values are those
12163 that select a particular cpu implementation. Those are @samp{cypress},
12164 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
12165 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
12166 @samp{ultrasparc3}.
12171 @opindex mno-v8plus
12172 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
12173 difference from the V8 ABI is that the global and out registers are
12174 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
12175 mode for all SPARC-V9 processors.
12181 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
12182 Visual Instruction Set extensions. The default is @option{-mno-vis}.
12185 These @samp{-m} options are supported in addition to the above
12186 on SPARC-V9 processors in 64-bit environments:
12189 @item -mlittle-endian
12190 @opindex mlittle-endian
12191 Generate code for a processor running in little-endian mode. It is only
12192 available for a few configurations and most notably not on Solaris and Linux.
12198 Generate code for a 32-bit or 64-bit environment.
12199 The 32-bit environment sets int, long and pointer to 32 bits.
12200 The 64-bit environment sets int to 32 bits and long and pointer
12203 @item -mcmodel=medlow
12204 @opindex mcmodel=medlow
12205 Generate code for the Medium/Low code model: 64-bit addresses, programs
12206 must be linked in the low 32 bits of memory. Programs can be statically
12207 or dynamically linked.
12209 @item -mcmodel=medmid
12210 @opindex mcmodel=medmid
12211 Generate code for the Medium/Middle code model: 64-bit addresses, programs
12212 must be linked in the low 44 bits of memory, the text and data segments must
12213 be less than 2GB in size and the data segment must be located within 2GB of
12216 @item -mcmodel=medany
12217 @opindex mcmodel=medany
12218 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
12219 may be linked anywhere in memory, the text and data segments must be less
12220 than 2GB in size and the data segment must be located within 2GB of the
12223 @item -mcmodel=embmedany
12224 @opindex mcmodel=embmedany
12225 Generate code for the Medium/Anywhere code model for embedded systems:
12226 64-bit addresses, the text and data segments must be less than 2GB in
12227 size, both starting anywhere in memory (determined at link time). The
12228 global register %g4 points to the base of the data segment. Programs
12229 are statically linked and PIC is not supported.
12232 @itemx -mno-stack-bias
12233 @opindex mstack-bias
12234 @opindex mno-stack-bias
12235 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
12236 frame pointer if present, are offset by @minus{}2047 which must be added back
12237 when making stack frame references. This is the default in 64-bit mode.
12238 Otherwise, assume no such offset is present.
12241 These switches are supported in addition to the above on Solaris:
12246 Add support for multithreading using the Solaris threads library. This
12247 option sets flags for both the preprocessor and linker. This option does
12248 not affect the thread safety of object code produced by the compiler or
12249 that of libraries supplied with it.
12253 Add support for multithreading using the POSIX threads library. This
12254 option sets flags for both the preprocessor and linker. This option does
12255 not affect the thread safety of object code produced by the compiler or
12256 that of libraries supplied with it.
12259 @node System V Options
12260 @subsection Options for System V
12262 These additional options are available on System V Release 4 for
12263 compatibility with other compilers on those systems:
12268 Create a shared object.
12269 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
12273 Identify the versions of each tool used by the compiler, in a
12274 @code{.ident} assembler directive in the output.
12278 Refrain from adding @code{.ident} directives to the output file (this is
12281 @item -YP,@var{dirs}
12283 Search the directories @var{dirs}, and no others, for libraries
12284 specified with @option{-l}.
12286 @item -Ym,@var{dir}
12288 Look in the directory @var{dir} to find the M4 preprocessor.
12289 The assembler uses this option.
12290 @c This is supposed to go with a -Yd for predefined M4 macro files, but
12291 @c the generic assembler that comes with Solaris takes just -Ym.
12294 @node TMS320C3x/C4x Options
12295 @subsection TMS320C3x/C4x Options
12296 @cindex TMS320C3x/C4x Options
12298 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
12302 @item -mcpu=@var{cpu_type}
12304 Set the instruction set, register set, and instruction scheduling
12305 parameters for machine type @var{cpu_type}. Supported values for
12306 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
12307 @samp{c44}. The default is @samp{c40} to generate code for the
12312 @itemx -msmall-memory
12314 @opindex mbig-memory
12316 @opindex msmall-memory
12318 Generates code for the big or small memory model. The small memory
12319 model assumed that all data fits into one 64K word page. At run-time
12320 the data page (DP) register must be set to point to the 64K page
12321 containing the .bss and .data program sections. The big memory model is
12322 the default and requires reloading of the DP register for every direct
12329 Allow (disallow) allocation of general integer operands into the block
12330 count register BK@.
12336 Enable (disable) generation of code using decrement and branch,
12337 DBcond(D), instructions. This is enabled by default for the C4x. To be
12338 on the safe side, this is disabled for the C3x, since the maximum
12339 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
12340 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
12341 that it can utilize the decrement and branch instruction, but will give
12342 up if there is more than one memory reference in the loop. Thus a loop
12343 where the loop counter is decremented can generate slightly more
12344 efficient code, in cases where the RPTB instruction cannot be utilized.
12346 @item -mdp-isr-reload
12348 @opindex mdp-isr-reload
12350 Force the DP register to be saved on entry to an interrupt service
12351 routine (ISR), reloaded to point to the data section, and restored on
12352 exit from the ISR@. This should not be required unless someone has
12353 violated the small memory model by modifying the DP register, say within
12360 For the C3x use the 24-bit MPYI instruction for integer multiplies
12361 instead of a library call to guarantee 32-bit results. Note that if one
12362 of the operands is a constant, then the multiplication will be performed
12363 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
12364 then squaring operations are performed inline instead of a library call.
12367 @itemx -mno-fast-fix
12369 @opindex mno-fast-fix
12370 The C3x/C4x FIX instruction to convert a floating point value to an
12371 integer value chooses the nearest integer less than or equal to the
12372 floating point value rather than to the nearest integer. Thus if the
12373 floating point number is negative, the result will be incorrectly
12374 truncated an additional code is necessary to detect and correct this
12375 case. This option can be used to disable generation of the additional
12376 code required to correct the result.
12382 Enable (disable) generation of repeat block sequences using the RPTB
12383 instruction for zero overhead looping. The RPTB construct is only used
12384 for innermost loops that do not call functions or jump across the loop
12385 boundaries. There is no advantage having nested RPTB loops due to the
12386 overhead required to save and restore the RC, RS, and RE registers.
12387 This is enabled by default with @option{-O2}.
12389 @item -mrpts=@var{count}
12393 Enable (disable) the use of the single instruction repeat instruction
12394 RPTS@. If a repeat block contains a single instruction, and the loop
12395 count can be guaranteed to be less than the value @var{count}, GCC will
12396 emit a RPTS instruction instead of a RPTB@. If no value is specified,
12397 then a RPTS will be emitted even if the loop count cannot be determined
12398 at compile time. Note that the repeated instruction following RPTS does
12399 not have to be reloaded from memory each iteration, thus freeing up the
12400 CPU buses for operands. However, since interrupts are blocked by this
12401 instruction, it is disabled by default.
12403 @item -mloop-unsigned
12404 @itemx -mno-loop-unsigned
12405 @opindex mloop-unsigned
12406 @opindex mno-loop-unsigned
12407 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
12408 is @math{2^{31} + 1} since these instructions test if the iteration count is
12409 negative to terminate the loop. If the iteration count is unsigned
12410 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
12411 exceeded. This switch allows an unsigned iteration count.
12415 Try to emit an assembler syntax that the TI assembler (asm30) is happy
12416 with. This also enforces compatibility with the API employed by the TI
12417 C3x C compiler. For example, long doubles are passed as structures
12418 rather than in floating point registers.
12424 Generate code that uses registers (stack) for passing arguments to functions.
12425 By default, arguments are passed in registers where possible rather
12426 than by pushing arguments on to the stack.
12428 @item -mparallel-insns
12429 @itemx -mno-parallel-insns
12430 @opindex mparallel-insns
12431 @opindex mno-parallel-insns
12432 Allow the generation of parallel instructions. This is enabled by
12433 default with @option{-O2}.
12435 @item -mparallel-mpy
12436 @itemx -mno-parallel-mpy
12437 @opindex mparallel-mpy
12438 @opindex mno-parallel-mpy
12439 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
12440 provided @option{-mparallel-insns} is also specified. These instructions have
12441 tight register constraints which can pessimize the code generation
12442 of large functions.
12447 @subsection V850 Options
12448 @cindex V850 Options
12450 These @samp{-m} options are defined for V850 implementations:
12454 @itemx -mno-long-calls
12455 @opindex mlong-calls
12456 @opindex mno-long-calls
12457 Treat all calls as being far away (near). If calls are assumed to be
12458 far away, the compiler will always load the functions address up into a
12459 register, and call indirect through the pointer.
12465 Do not optimize (do optimize) basic blocks that use the same index
12466 pointer 4 or more times to copy pointer into the @code{ep} register, and
12467 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
12468 option is on by default if you optimize.
12470 @item -mno-prolog-function
12471 @itemx -mprolog-function
12472 @opindex mno-prolog-function
12473 @opindex mprolog-function
12474 Do not use (do use) external functions to save and restore registers
12475 at the prologue and epilogue of a function. The external functions
12476 are slower, but use less code space if more than one function saves
12477 the same number of registers. The @option{-mprolog-function} option
12478 is on by default if you optimize.
12482 Try to make the code as small as possible. At present, this just turns
12483 on the @option{-mep} and @option{-mprolog-function} options.
12485 @item -mtda=@var{n}
12487 Put static or global variables whose size is @var{n} bytes or less into
12488 the tiny data area that register @code{ep} points to. The tiny data
12489 area can hold up to 256 bytes in total (128 bytes for byte references).
12491 @item -msda=@var{n}
12493 Put static or global variables whose size is @var{n} bytes or less into
12494 the small data area that register @code{gp} points to. The small data
12495 area can hold up to 64 kilobytes.
12497 @item -mzda=@var{n}
12499 Put static or global variables whose size is @var{n} bytes or less into
12500 the first 32 kilobytes of memory.
12504 Specify that the target processor is the V850.
12507 @opindex mbig-switch
12508 Generate code suitable for big switch tables. Use this option only if
12509 the assembler/linker complain about out of range branches within a switch
12514 This option will cause r2 and r5 to be used in the code generated by
12515 the compiler. This setting is the default.
12517 @item -mno-app-regs
12518 @opindex mno-app-regs
12519 This option will cause r2 and r5 to be treated as fixed registers.
12523 Specify that the target processor is the V850E1. The preprocessor
12524 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
12525 this option is used.
12529 Specify that the target processor is the V850E@. The preprocessor
12530 constant @samp{__v850e__} will be defined if this option is used.
12532 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
12533 are defined then a default target processor will be chosen and the
12534 relevant @samp{__v850*__} preprocessor constant will be defined.
12536 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
12537 defined, regardless of which processor variant is the target.
12539 @item -mdisable-callt
12540 @opindex mdisable-callt
12541 This option will suppress generation of the CALLT instruction for the
12542 v850e and v850e1 flavors of the v850 architecture. The default is
12543 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
12548 @subsection VAX Options
12549 @cindex VAX options
12551 These @samp{-m} options are defined for the VAX:
12556 Do not output certain jump instructions (@code{aobleq} and so on)
12557 that the Unix assembler for the VAX cannot handle across long
12562 Do output those jump instructions, on the assumption that you
12563 will assemble with the GNU assembler.
12567 Output code for g-format floating point numbers instead of d-format.
12570 @node x86-64 Options
12571 @subsection x86-64 Options
12572 @cindex x86-64 options
12574 These are listed under @xref{i386 and x86-64 Options}.
12576 @node Xstormy16 Options
12577 @subsection Xstormy16 Options
12578 @cindex Xstormy16 Options
12580 These options are defined for Xstormy16:
12585 Choose startup files and linker script suitable for the simulator.
12588 @node Xtensa Options
12589 @subsection Xtensa Options
12590 @cindex Xtensa Options
12592 These options are supported for Xtensa targets:
12596 @itemx -mno-const16
12598 @opindex mno-const16
12599 Enable or disable use of @code{CONST16} instructions for loading
12600 constant values. The @code{CONST16} instruction is currently not a
12601 standard option from Tensilica. When enabled, @code{CONST16}
12602 instructions are always used in place of the standard @code{L32R}
12603 instructions. The use of @code{CONST16} is enabled by default only if
12604 the @code{L32R} instruction is not available.
12607 @itemx -mno-fused-madd
12608 @opindex mfused-madd
12609 @opindex mno-fused-madd
12610 Enable or disable use of fused multiply/add and multiply/subtract
12611 instructions in the floating-point option. This has no effect if the
12612 floating-point option is not also enabled. Disabling fused multiply/add
12613 and multiply/subtract instructions forces the compiler to use separate
12614 instructions for the multiply and add/subtract operations. This may be
12615 desirable in some cases where strict IEEE 754-compliant results are
12616 required: the fused multiply add/subtract instructions do not round the
12617 intermediate result, thereby producing results with @emph{more} bits of
12618 precision than specified by the IEEE standard. Disabling fused multiply
12619 add/subtract instructions also ensures that the program output is not
12620 sensitive to the compiler's ability to combine multiply and add/subtract
12623 @item -mtext-section-literals
12624 @itemx -mno-text-section-literals
12625 @opindex mtext-section-literals
12626 @opindex mno-text-section-literals
12627 Control the treatment of literal pools. The default is
12628 @option{-mno-text-section-literals}, which places literals in a separate
12629 section in the output file. This allows the literal pool to be placed
12630 in a data RAM/ROM, and it also allows the linker to combine literal
12631 pools from separate object files to remove redundant literals and
12632 improve code size. With @option{-mtext-section-literals}, the literals
12633 are interspersed in the text section in order to keep them as close as
12634 possible to their references. This may be necessary for large assembly
12637 @item -mtarget-align
12638 @itemx -mno-target-align
12639 @opindex mtarget-align
12640 @opindex mno-target-align
12641 When this option is enabled, GCC instructs the assembler to
12642 automatically align instructions to reduce branch penalties at the
12643 expense of some code density. The assembler attempts to widen density
12644 instructions to align branch targets and the instructions following call
12645 instructions. If there are not enough preceding safe density
12646 instructions to align a target, no widening will be performed. The
12647 default is @option{-mtarget-align}. These options do not affect the
12648 treatment of auto-aligned instructions like @code{LOOP}, which the
12649 assembler will always align, either by widening density instructions or
12650 by inserting no-op instructions.
12653 @itemx -mno-longcalls
12654 @opindex mlongcalls
12655 @opindex mno-longcalls
12656 When this option is enabled, GCC instructs the assembler to translate
12657 direct calls to indirect calls unless it can determine that the target
12658 of a direct call is in the range allowed by the call instruction. This
12659 translation typically occurs for calls to functions in other source
12660 files. Specifically, the assembler translates a direct @code{CALL}
12661 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
12662 The default is @option{-mno-longcalls}. This option should be used in
12663 programs where the call target can potentially be out of range. This
12664 option is implemented in the assembler, not the compiler, so the
12665 assembly code generated by GCC will still show direct call
12666 instructions---look at the disassembled object code to see the actual
12667 instructions. Note that the assembler will use an indirect call for
12668 every cross-file call, not just those that really will be out of range.
12671 @node zSeries Options
12672 @subsection zSeries Options
12673 @cindex zSeries options
12675 These are listed under @xref{S/390 and zSeries Options}.
12677 @node Code Gen Options
12678 @section Options for Code Generation Conventions
12679 @cindex code generation conventions
12680 @cindex options, code generation
12681 @cindex run-time options
12683 These machine-independent options control the interface conventions
12684 used in code generation.
12686 Most of them have both positive and negative forms; the negative form
12687 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
12688 one of the forms is listed---the one which is not the default. You
12689 can figure out the other form by either removing @samp{no-} or adding
12693 @item -fbounds-check
12694 @opindex fbounds-check
12695 For front-ends that support it, generate additional code to check that
12696 indices used to access arrays are within the declared range. This is
12697 currently only supported by the Java and Fortran 77 front-ends, where
12698 this option defaults to true and false respectively.
12702 This option generates traps for signed overflow on addition, subtraction,
12703 multiplication operations.
12707 This option instructs the compiler to assume that signed arithmetic
12708 overflow of addition, subtraction and multiplication wraps around
12709 using twos-complement representation. This flag enables some optimizations
12710 and disables others. This option is enabled by default for the Java
12711 front-end, as required by the Java language specification.
12714 @opindex fexceptions
12715 Enable exception handling. Generates extra code needed to propagate
12716 exceptions. For some targets, this implies GCC will generate frame
12717 unwind information for all functions, which can produce significant data
12718 size overhead, although it does not affect execution. If you do not
12719 specify this option, GCC will enable it by default for languages like
12720 C++ which normally require exception handling, and disable it for
12721 languages like C that do not normally require it. However, you may need
12722 to enable this option when compiling C code that needs to interoperate
12723 properly with exception handlers written in C++. You may also wish to
12724 disable this option if you are compiling older C++ programs that don't
12725 use exception handling.
12727 @item -fnon-call-exceptions
12728 @opindex fnon-call-exceptions
12729 Generate code that allows trapping instructions to throw exceptions.
12730 Note that this requires platform-specific runtime support that does
12731 not exist everywhere. Moreover, it only allows @emph{trapping}
12732 instructions to throw exceptions, i.e.@: memory references or floating
12733 point instructions. It does not allow exceptions to be thrown from
12734 arbitrary signal handlers such as @code{SIGALRM}.
12736 @item -funwind-tables
12737 @opindex funwind-tables
12738 Similar to @option{-fexceptions}, except that it will just generate any needed
12739 static data, but will not affect the generated code in any other way.
12740 You will normally not enable this option; instead, a language processor
12741 that needs this handling would enable it on your behalf.
12743 @item -fasynchronous-unwind-tables
12744 @opindex fasynchronous-unwind-tables
12745 Generate unwind table in dwarf2 format, if supported by target machine. The
12746 table is exact at each instruction boundary, so it can be used for stack
12747 unwinding from asynchronous events (such as debugger or garbage collector).
12749 @item -fpcc-struct-return
12750 @opindex fpcc-struct-return
12751 Return ``short'' @code{struct} and @code{union} values in memory like
12752 longer ones, rather than in registers. This convention is less
12753 efficient, but it has the advantage of allowing intercallability between
12754 GCC-compiled files and files compiled with other compilers, particularly
12755 the Portable C Compiler (pcc).
12757 The precise convention for returning structures in memory depends
12758 on the target configuration macros.
12760 Short structures and unions are those whose size and alignment match
12761 that of some integer type.
12763 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
12764 switch is not binary compatible with code compiled with the
12765 @option{-freg-struct-return} switch.
12766 Use it to conform to a non-default application binary interface.
12768 @item -freg-struct-return
12769 @opindex freg-struct-return
12770 Return @code{struct} and @code{union} values in registers when possible.
12771 This is more efficient for small structures than
12772 @option{-fpcc-struct-return}.
12774 If you specify neither @option{-fpcc-struct-return} nor
12775 @option{-freg-struct-return}, GCC defaults to whichever convention is
12776 standard for the target. If there is no standard convention, GCC
12777 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
12778 the principal compiler. In those cases, we can choose the standard, and
12779 we chose the more efficient register return alternative.
12781 @strong{Warning:} code compiled with the @option{-freg-struct-return}
12782 switch is not binary compatible with code compiled with the
12783 @option{-fpcc-struct-return} switch.
12784 Use it to conform to a non-default application binary interface.
12786 @item -fshort-enums
12787 @opindex fshort-enums
12788 Allocate to an @code{enum} type only as many bytes as it needs for the
12789 declared range of possible values. Specifically, the @code{enum} type
12790 will be equivalent to the smallest integer type which has enough room.
12792 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
12793 code that is not binary compatible with code generated without that switch.
12794 Use it to conform to a non-default application binary interface.
12796 @item -fshort-double
12797 @opindex fshort-double
12798 Use the same size for @code{double} as for @code{float}.
12800 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
12801 code that is not binary compatible with code generated without that switch.
12802 Use it to conform to a non-default application binary interface.
12804 @item -fshort-wchar
12805 @opindex fshort-wchar
12806 Override the underlying type for @samp{wchar_t} to be @samp{short
12807 unsigned int} instead of the default for the target. This option is
12808 useful for building programs to run under WINE@.
12810 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
12811 code that is not binary compatible with code generated without that switch.
12812 Use it to conform to a non-default application binary interface.
12814 @item -fshared-data
12815 @opindex fshared-data
12816 Requests that the data and non-@code{const} variables of this
12817 compilation be shared data rather than private data. The distinction
12818 makes sense only on certain operating systems, where shared data is
12819 shared between processes running the same program, while private data
12820 exists in one copy per process.
12823 @opindex fno-common
12824 In C, allocate even uninitialized global variables in the data section of the
12825 object file, rather than generating them as common blocks. This has the
12826 effect that if the same variable is declared (without @code{extern}) in
12827 two different compilations, you will get an error when you link them.
12828 The only reason this might be useful is if you wish to verify that the
12829 program will work on other systems which always work this way.
12833 Ignore the @samp{#ident} directive.
12835 @item -finhibit-size-directive
12836 @opindex finhibit-size-directive
12837 Don't output a @code{.size} assembler directive, or anything else that
12838 would cause trouble if the function is split in the middle, and the
12839 two halves are placed at locations far apart in memory. This option is
12840 used when compiling @file{crtstuff.c}; you should not need to use it
12843 @item -fverbose-asm
12844 @opindex fverbose-asm
12845 Put extra commentary information in the generated assembly code to
12846 make it more readable. This option is generally only of use to those
12847 who actually need to read the generated assembly code (perhaps while
12848 debugging the compiler itself).
12850 @option{-fno-verbose-asm}, the default, causes the
12851 extra information to be omitted and is useful when comparing two assembler
12856 @cindex global offset table
12858 Generate position-independent code (PIC) suitable for use in a shared
12859 library, if supported for the target machine. Such code accesses all
12860 constant addresses through a global offset table (GOT)@. The dynamic
12861 loader resolves the GOT entries when the program starts (the dynamic
12862 loader is not part of GCC; it is part of the operating system). If
12863 the GOT size for the linked executable exceeds a machine-specific
12864 maximum size, you get an error message from the linker indicating that
12865 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
12866 instead. (These maximums are 8k on the SPARC and 32k
12867 on the m68k and RS/6000. The 386 has no such limit.)
12869 Position-independent code requires special support, and therefore works
12870 only on certain machines. For the 386, GCC supports PIC for System V
12871 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
12872 position-independent.
12876 If supported for the target machine, emit position-independent code,
12877 suitable for dynamic linking and avoiding any limit on the size of the
12878 global offset table. This option makes a difference on the m68k,
12879 PowerPC and SPARC@.
12881 Position-independent code requires special support, and therefore works
12882 only on certain machines.
12888 These options are similar to @option{-fpic} and @option{-fPIC}, but
12889 generated position independent code can be only linked into executables.
12890 Usually these options are used when @option{-pie} GCC option will be
12891 used during linking.
12893 @item -fno-jump-tables
12894 @opindex fno-jump-tables
12895 Do not use jump tables for switch statements even where it would be
12896 more efficient than other code generation strategies. This option is
12897 of use in conjunction with @option{-fpic} or @option{-fPIC} for
12898 building code which forms part of a dynamic linker and cannot
12899 reference the address of a jump table. On some targets, jump tables
12900 do not require a GOT and this option is not needed.
12902 @item -ffixed-@var{reg}
12904 Treat the register named @var{reg} as a fixed register; generated code
12905 should never refer to it (except perhaps as a stack pointer, frame
12906 pointer or in some other fixed role).
12908 @var{reg} must be the name of a register. The register names accepted
12909 are machine-specific and are defined in the @code{REGISTER_NAMES}
12910 macro in the machine description macro file.
12912 This flag does not have a negative form, because it specifies a
12915 @item -fcall-used-@var{reg}
12916 @opindex fcall-used
12917 Treat the register named @var{reg} as an allocable register that is
12918 clobbered by function calls. It may be allocated for temporaries or
12919 variables that do not live across a call. Functions compiled this way
12920 will not save and restore the register @var{reg}.
12922 It is an error to used this flag with the frame pointer or stack pointer.
12923 Use of this flag for other registers that have fixed pervasive roles in
12924 the machine's execution model will produce disastrous results.
12926 This flag does not have a negative form, because it specifies a
12929 @item -fcall-saved-@var{reg}
12930 @opindex fcall-saved
12931 Treat the register named @var{reg} as an allocable register saved by
12932 functions. It may be allocated even for temporaries or variables that
12933 live across a call. Functions compiled this way will save and restore
12934 the register @var{reg} if they use it.
12936 It is an error to used this flag with the frame pointer or stack pointer.
12937 Use of this flag for other registers that have fixed pervasive roles in
12938 the machine's execution model will produce disastrous results.
12940 A different sort of disaster will result from the use of this flag for
12941 a register in which function values may be returned.
12943 This flag does not have a negative form, because it specifies a
12946 @item -fpack-struct[=@var{n}]
12947 @opindex fpack-struct
12948 Without a value specified, pack all structure members together without
12949 holes. When a value is specified (which must be a small power of two), pack
12950 structure members according to this value, representing the maximum
12951 alignment (that is, objects with default alignment requirements larger than
12952 this will be output potentially unaligned at the next fitting location.
12954 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
12955 code that is not binary compatible with code generated without that switch.
12956 Additionally, it makes the code suboptimal.
12957 Use it to conform to a non-default application binary interface.
12959 @item -finstrument-functions
12960 @opindex finstrument-functions
12961 Generate instrumentation calls for entry and exit to functions. Just
12962 after function entry and just before function exit, the following
12963 profiling functions will be called with the address of the current
12964 function and its call site. (On some platforms,
12965 @code{__builtin_return_address} does not work beyond the current
12966 function, so the call site information may not be available to the
12967 profiling functions otherwise.)
12970 void __cyg_profile_func_enter (void *this_fn,
12972 void __cyg_profile_func_exit (void *this_fn,
12976 The first argument is the address of the start of the current function,
12977 which may be looked up exactly in the symbol table.
12979 This instrumentation is also done for functions expanded inline in other
12980 functions. The profiling calls will indicate where, conceptually, the
12981 inline function is entered and exited. This means that addressable
12982 versions of such functions must be available. If all your uses of a
12983 function are expanded inline, this may mean an additional expansion of
12984 code size. If you use @samp{extern inline} in your C code, an
12985 addressable version of such functions must be provided. (This is
12986 normally the case anyways, but if you get lucky and the optimizer always
12987 expands the functions inline, you might have gotten away without
12988 providing static copies.)
12990 A function may be given the attribute @code{no_instrument_function}, in
12991 which case this instrumentation will not be done. This can be used, for
12992 example, for the profiling functions listed above, high-priority
12993 interrupt routines, and any functions from which the profiling functions
12994 cannot safely be called (perhaps signal handlers, if the profiling
12995 routines generate output or allocate memory).
12997 @item -fstack-check
12998 @opindex fstack-check
12999 Generate code to verify that you do not go beyond the boundary of the
13000 stack. You should specify this flag if you are running in an
13001 environment with multiple threads, but only rarely need to specify it in
13002 a single-threaded environment since stack overflow is automatically
13003 detected on nearly all systems if there is only one stack.
13005 Note that this switch does not actually cause checking to be done; the
13006 operating system must do that. The switch causes generation of code
13007 to ensure that the operating system sees the stack being extended.
13009 @item -fstack-limit-register=@var{reg}
13010 @itemx -fstack-limit-symbol=@var{sym}
13011 @itemx -fno-stack-limit
13012 @opindex fstack-limit-register
13013 @opindex fstack-limit-symbol
13014 @opindex fno-stack-limit
13015 Generate code to ensure that the stack does not grow beyond a certain value,
13016 either the value of a register or the address of a symbol. If the stack
13017 would grow beyond the value, a signal is raised. For most targets,
13018 the signal is raised before the stack overruns the boundary, so
13019 it is possible to catch the signal without taking special precautions.
13021 For instance, if the stack starts at absolute address @samp{0x80000000}
13022 and grows downwards, you can use the flags
13023 @option{-fstack-limit-symbol=__stack_limit} and
13024 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
13025 of 128KB@. Note that this may only work with the GNU linker.
13027 @cindex aliasing of parameters
13028 @cindex parameters, aliased
13029 @item -fargument-alias
13030 @itemx -fargument-noalias
13031 @itemx -fargument-noalias-global
13032 @opindex fargument-alias
13033 @opindex fargument-noalias
13034 @opindex fargument-noalias-global
13035 Specify the possible relationships among parameters and between
13036 parameters and global data.
13038 @option{-fargument-alias} specifies that arguments (parameters) may
13039 alias each other and may alias global storage.@*
13040 @option{-fargument-noalias} specifies that arguments do not alias
13041 each other, but may alias global storage.@*
13042 @option{-fargument-noalias-global} specifies that arguments do not
13043 alias each other and do not alias global storage.
13045 Each language will automatically use whatever option is required by
13046 the language standard. You should not need to use these options yourself.
13048 @item -fleading-underscore
13049 @opindex fleading-underscore
13050 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
13051 change the way C symbols are represented in the object file. One use
13052 is to help link with legacy assembly code.
13054 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
13055 generate code that is not binary compatible with code generated without that
13056 switch. Use it to conform to a non-default application binary interface.
13057 Not all targets provide complete support for this switch.
13059 @item -ftls-model=@var{model}
13060 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
13061 The @var{model} argument should be one of @code{global-dynamic},
13062 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
13064 The default without @option{-fpic} is @code{initial-exec}; with
13065 @option{-fpic} the default is @code{global-dynamic}.
13067 @item -fvisibility=@var{default|internal|hidden|protected}
13068 @opindex fvisibility
13069 Set the default ELF image symbol visibility to the specified option---all
13070 symbols will be marked with this unless overridden within the code.
13071 Using this feature can very substantially improve linking and
13072 load times of shared object libraries, produce more optimized
13073 code, provide near-perfect API export and prevent symbol clashes.
13074 It is @strong{strongly} recommended that you use this in any shared objects
13077 Despite the nomenclature, @code{default} always means public ie;
13078 available to be linked against from outside the shared object.
13079 @code{protected} and @code{internal} are pretty useless in real-world
13080 usage so the only other commonly used option will be @code{hidden}.
13081 The default if @option{-fvisibility} isn't specified is
13082 @code{default}, i.e., make every
13083 symbol public---this causes the same behavior as previous versions of
13086 A good explanation of the benefits offered by ensuring ELF
13087 symbols have the correct visibility is given by ``How To Write
13088 Shared Libraries'' by Ulrich Drepper (which can be found at
13089 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
13090 solution made possible by this option to marking things hidden when
13091 the default is public is to make the default hidden and mark things
13092 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
13093 and @code{__attribute__ ((visibility("default")))} instead of
13094 @code{__declspec(dllexport)} you get almost identical semantics with
13095 identical syntax. This is a great boon to those working with
13096 cross-platform projects.
13098 For those adding visibility support to existing code, you may find
13099 @samp{#pragma GCC visibility} of use. This works by you enclosing
13100 the declarations you wish to set visibility for with (for example)
13101 @samp{#pragma GCC visibility push(hidden)} and
13102 @samp{#pragma GCC visibility pop}.
13103 Bear in mind that symbol visibility should be viewed @strong{as
13104 part of the API interface contract} and thus all new code should
13105 always specify visibility when it is not the default ie; declarations
13106 only for use within the local DSO should @strong{always} be marked explicitly
13107 as hidden as so to avoid PLT indirection overheads---making this
13108 abundantly clear also aids readability and self-documentation of the code.
13109 Note that due to ISO C++ specification requirements, operator new and
13110 operator delete must always be of default visibility.
13112 An overview of these techniques, their benefits and how to use them
13113 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
13119 @node Environment Variables
13120 @section Environment Variables Affecting GCC
13121 @cindex environment variables
13123 @c man begin ENVIRONMENT
13124 This section describes several environment variables that affect how GCC
13125 operates. Some of them work by specifying directories or prefixes to use
13126 when searching for various kinds of files. Some are used to specify other
13127 aspects of the compilation environment.
13129 Note that you can also specify places to search using options such as
13130 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
13131 take precedence over places specified using environment variables, which
13132 in turn take precedence over those specified by the configuration of GCC@.
13133 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
13134 GNU Compiler Collection (GCC) Internals}.
13139 @c @itemx LC_COLLATE
13141 @c @itemx LC_MONETARY
13142 @c @itemx LC_NUMERIC
13147 @c @findex LC_COLLATE
13148 @findex LC_MESSAGES
13149 @c @findex LC_MONETARY
13150 @c @findex LC_NUMERIC
13154 These environment variables control the way that GCC uses
13155 localization information that allow GCC to work with different
13156 national conventions. GCC inspects the locale categories
13157 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
13158 so. These locale categories can be set to any value supported by your
13159 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
13160 Kingdom encoded in UTF-8.
13162 The @env{LC_CTYPE} environment variable specifies character
13163 classification. GCC uses it to determine the character boundaries in
13164 a string; this is needed for some multibyte encodings that contain quote
13165 and escape characters that would otherwise be interpreted as a string
13168 The @env{LC_MESSAGES} environment variable specifies the language to
13169 use in diagnostic messages.
13171 If the @env{LC_ALL} environment variable is set, it overrides the value
13172 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
13173 and @env{LC_MESSAGES} default to the value of the @env{LANG}
13174 environment variable. If none of these variables are set, GCC
13175 defaults to traditional C English behavior.
13179 If @env{TMPDIR} is set, it specifies the directory to use for temporary
13180 files. GCC uses temporary files to hold the output of one stage of
13181 compilation which is to be used as input to the next stage: for example,
13182 the output of the preprocessor, which is the input to the compiler
13185 @item GCC_EXEC_PREFIX
13186 @findex GCC_EXEC_PREFIX
13187 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
13188 names of the subprograms executed by the compiler. No slash is added
13189 when this prefix is combined with the name of a subprogram, but you can
13190 specify a prefix that ends with a slash if you wish.
13192 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
13193 an appropriate prefix to use based on the pathname it was invoked with.
13195 If GCC cannot find the subprogram using the specified prefix, it
13196 tries looking in the usual places for the subprogram.
13198 The default value of @env{GCC_EXEC_PREFIX} is
13199 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
13200 of @code{prefix} when you ran the @file{configure} script.
13202 Other prefixes specified with @option{-B} take precedence over this prefix.
13204 This prefix is also used for finding files such as @file{crt0.o} that are
13207 In addition, the prefix is used in an unusual way in finding the
13208 directories to search for header files. For each of the standard
13209 directories whose name normally begins with @samp{/usr/local/lib/gcc}
13210 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
13211 replacing that beginning with the specified prefix to produce an
13212 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
13213 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
13214 These alternate directories are searched first; the standard directories
13217 @item COMPILER_PATH
13218 @findex COMPILER_PATH
13219 The value of @env{COMPILER_PATH} is a colon-separated list of
13220 directories, much like @env{PATH}. GCC tries the directories thus
13221 specified when searching for subprograms, if it can't find the
13222 subprograms using @env{GCC_EXEC_PREFIX}.
13225 @findex LIBRARY_PATH
13226 The value of @env{LIBRARY_PATH} is a colon-separated list of
13227 directories, much like @env{PATH}. When configured as a native compiler,
13228 GCC tries the directories thus specified when searching for special
13229 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
13230 using GCC also uses these directories when searching for ordinary
13231 libraries for the @option{-l} option (but directories specified with
13232 @option{-L} come first).
13236 @cindex locale definition
13237 This variable is used to pass locale information to the compiler. One way in
13238 which this information is used is to determine the character set to be used
13239 when character literals, string literals and comments are parsed in C and C++.
13240 When the compiler is configured to allow multibyte characters,
13241 the following values for @env{LANG} are recognized:
13245 Recognize JIS characters.
13247 Recognize SJIS characters.
13249 Recognize EUCJP characters.
13252 If @env{LANG} is not defined, or if it has some other value, then the
13253 compiler will use mblen and mbtowc as defined by the default locale to
13254 recognize and translate multibyte characters.
13258 Some additional environments variables affect the behavior of the
13261 @include cppenv.texi
13265 @node Precompiled Headers
13266 @section Using Precompiled Headers
13267 @cindex precompiled headers
13268 @cindex speed of compilation
13270 Often large projects have many header files that are included in every
13271 source file. The time the compiler takes to process these header files
13272 over and over again can account for nearly all of the time required to
13273 build the project. To make builds faster, GCC allows users to
13274 `precompile' a header file; then, if builds can use the precompiled
13275 header file they will be much faster.
13277 To create a precompiled header file, simply compile it as you would any
13278 other file, if necessary using the @option{-x} option to make the driver
13279 treat it as a C or C++ header file. You will probably want to use a
13280 tool like @command{make} to keep the precompiled header up-to-date when
13281 the headers it contains change.
13283 A precompiled header file will be searched for when @code{#include} is
13284 seen in the compilation. As it searches for the included file
13285 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
13286 compiler looks for a precompiled header in each directory just before it
13287 looks for the include file in that directory. The name searched for is
13288 the name specified in the @code{#include} with @samp{.gch} appended. If
13289 the precompiled header file can't be used, it is ignored.
13291 For instance, if you have @code{#include "all.h"}, and you have
13292 @file{all.h.gch} in the same directory as @file{all.h}, then the
13293 precompiled header file will be used if possible, and the original
13294 header will be used otherwise.
13296 Alternatively, you might decide to put the precompiled header file in a
13297 directory and use @option{-I} to ensure that directory is searched
13298 before (or instead of) the directory containing the original header.
13299 Then, if you want to check that the precompiled header file is always
13300 used, you can put a file of the same name as the original header in this
13301 directory containing an @code{#error} command.
13303 This also works with @option{-include}. So yet another way to use
13304 precompiled headers, good for projects not designed with precompiled
13305 header files in mind, is to simply take most of the header files used by
13306 a project, include them from another header file, precompile that header
13307 file, and @option{-include} the precompiled header. If the header files
13308 have guards against multiple inclusion, they will be skipped because
13309 they've already been included (in the precompiled header).
13311 If you need to precompile the same header file for different
13312 languages, targets, or compiler options, you can instead make a
13313 @emph{directory} named like @file{all.h.gch}, and put each precompiled
13314 header in the directory, perhaps using @option{-o}. It doesn't matter
13315 what you call the files in the directory, every precompiled header in
13316 the directory will be considered. The first precompiled header
13317 encountered in the directory that is valid for this compilation will
13318 be used; they're searched in no particular order.
13320 There are many other possibilities, limited only by your imagination,
13321 good sense, and the constraints of your build system.
13323 A precompiled header file can be used only when these conditions apply:
13327 Only one precompiled header can be used in a particular compilation.
13330 A precompiled header can't be used once the first C token is seen. You
13331 can have preprocessor directives before a precompiled header; you can
13332 even include a precompiled header from inside another header, so long as
13333 there are no C tokens before the @code{#include}.
13336 The precompiled header file must be produced for the same language as
13337 the current compilation. You can't use a C precompiled header for a C++
13341 The precompiled header file must have been produced by the same compiler
13342 binary as the current compilation is using.
13345 Any macros defined before the precompiled header is included must
13346 either be defined in the same way as when the precompiled header was
13347 generated, or must not affect the precompiled header, which usually
13348 means that they don't appear in the precompiled header at all.
13350 The @option{-D} option is one way to define a macro before a
13351 precompiled header is included; using a @code{#define} can also do it.
13352 There are also some options that define macros implicitly, like
13353 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
13356 @item If debugging information is output when using the precompiled
13357 header, using @option{-g} or similar, the same kind of debugging information
13358 must have been output when building the precompiled header. However,
13359 a precompiled header built using @option{-g} can be used in a compilation
13360 when no debugging information is being output.
13362 @item The same @option{-m} options must generally be used when building
13363 and using the precompiled header. @xref{Submodel Options},
13364 for any cases where this rule is relaxed.
13366 @item Each of the following options must be the same when building and using
13367 the precompiled header:
13369 @gccoptlist{-fexceptions -funit-at-a-time}
13372 Some other command-line options starting with @option{-f},
13373 @option{-p}, or @option{-O} must be defined in the same way as when
13374 the precompiled header was generated. At present, it's not clear
13375 which options are safe to change and which are not; the safest choice
13376 is to use exactly the same options when generating and using the
13377 precompiled header. The following are known to be safe:
13379 @gccoptlist{-fmessage-length= -fpreprocessed
13380 -fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous
13381 -fsched-verbose=<number> -fschedule-insns -fvisibility=
13386 For all of these except the last, the compiler will automatically
13387 ignore the precompiled header if the conditions aren't met. If you
13388 find an option combination that doesn't work and doesn't cause the
13389 precompiled header to be ignored, please consider filing a bug report,
13392 If you do use differing options when generating and using the
13393 precompiled header, the actual behavior will be a mixture of the
13394 behavior for the options. For instance, if you use @option{-g} to
13395 generate the precompiled header but not when using it, you may or may
13396 not get debugging information for routines in the precompiled header.
13398 @node Running Protoize
13399 @section Running Protoize
13401 The program @code{protoize} is an optional part of GCC@. You can use
13402 it to add prototypes to a program, thus converting the program to ISO
13403 C in one respect. The companion program @code{unprotoize} does the
13404 reverse: it removes argument types from any prototypes that are found.
13406 When you run these programs, you must specify a set of source files as
13407 command line arguments. The conversion programs start out by compiling
13408 these files to see what functions they define. The information gathered
13409 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
13411 After scanning comes actual conversion. The specified files are all
13412 eligible to be converted; any files they include (whether sources or
13413 just headers) are eligible as well.
13415 But not all the eligible files are converted. By default,
13416 @code{protoize} and @code{unprotoize} convert only source and header
13417 files in the current directory. You can specify additional directories
13418 whose files should be converted with the @option{-d @var{directory}}
13419 option. You can also specify particular files to exclude with the
13420 @option{-x @var{file}} option. A file is converted if it is eligible, its
13421 directory name matches one of the specified directory names, and its
13422 name within the directory has not been excluded.
13424 Basic conversion with @code{protoize} consists of rewriting most
13425 function definitions and function declarations to specify the types of
13426 the arguments. The only ones not rewritten are those for varargs
13429 @code{protoize} optionally inserts prototype declarations at the
13430 beginning of the source file, to make them available for any calls that
13431 precede the function's definition. Or it can insert prototype
13432 declarations with block scope in the blocks where undeclared functions
13435 Basic conversion with @code{unprotoize} consists of rewriting most
13436 function declarations to remove any argument types, and rewriting
13437 function definitions to the old-style pre-ISO form.
13439 Both conversion programs print a warning for any function declaration or
13440 definition that they can't convert. You can suppress these warnings
13443 The output from @code{protoize} or @code{unprotoize} replaces the
13444 original source file. The original file is renamed to a name ending
13445 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
13446 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
13447 for DOS) file already exists, then the source file is simply discarded.
13449 @code{protoize} and @code{unprotoize} both depend on GCC itself to
13450 scan the program and collect information about the functions it uses.
13451 So neither of these programs will work until GCC is installed.
13453 Here is a table of the options you can use with @code{protoize} and
13454 @code{unprotoize}. Each option works with both programs unless
13458 @item -B @var{directory}
13459 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
13460 usual directory (normally @file{/usr/local/lib}). This file contains
13461 prototype information about standard system functions. This option
13462 applies only to @code{protoize}.
13464 @item -c @var{compilation-options}
13465 Use @var{compilation-options} as the options when running @command{gcc} to
13466 produce the @samp{.X} files. The special option @option{-aux-info} is
13467 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
13469 Note that the compilation options must be given as a single argument to
13470 @code{protoize} or @code{unprotoize}. If you want to specify several
13471 @command{gcc} options, you must quote the entire set of compilation options
13472 to make them a single word in the shell.
13474 There are certain @command{gcc} arguments that you cannot use, because they
13475 would produce the wrong kind of output. These include @option{-g},
13476 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
13477 the @var{compilation-options}, they are ignored.
13480 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
13481 systems) instead of @samp{.c}. This is convenient if you are converting
13482 a C program to C++. This option applies only to @code{protoize}.
13485 Add explicit global declarations. This means inserting explicit
13486 declarations at the beginning of each source file for each function
13487 that is called in the file and was not declared. These declarations
13488 precede the first function definition that contains a call to an
13489 undeclared function. This option applies only to @code{protoize}.
13491 @item -i @var{string}
13492 Indent old-style parameter declarations with the string @var{string}.
13493 This option applies only to @code{protoize}.
13495 @code{unprotoize} converts prototyped function definitions to old-style
13496 function definitions, where the arguments are declared between the
13497 argument list and the initial @samp{@{}. By default, @code{unprotoize}
13498 uses five spaces as the indentation. If you want to indent with just
13499 one space instead, use @option{-i " "}.
13502 Keep the @samp{.X} files. Normally, they are deleted after conversion
13506 Add explicit local declarations. @code{protoize} with @option{-l} inserts
13507 a prototype declaration for each function in each block which calls the
13508 function without any declaration. This option applies only to
13512 Make no real changes. This mode just prints information about the conversions
13513 that would have been done without @option{-n}.
13516 Make no @samp{.save} files. The original files are simply deleted.
13517 Use this option with caution.
13519 @item -p @var{program}
13520 Use the program @var{program} as the compiler. Normally, the name
13521 @file{gcc} is used.
13524 Work quietly. Most warnings are suppressed.
13527 Print the version number, just like @option{-v} for @command{gcc}.
13530 If you need special compiler options to compile one of your program's
13531 source files, then you should generate that file's @samp{.X} file
13532 specially, by running @command{gcc} on that source file with the
13533 appropriate options and the option @option{-aux-info}. Then run
13534 @code{protoize} on the entire set of files. @code{protoize} will use
13535 the existing @samp{.X} file because it is newer than the source file.
13539 gcc -Dfoo=bar file1.c -aux-info file1.X
13544 You need to include the special files along with the rest in the
13545 @code{protoize} command, even though their @samp{.X} files already
13546 exist, because otherwise they won't get converted.
13548 @xref{Protoize Caveats}, for more information on how to use
13549 @code{protoize} successfully.