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db838bb8 | 1 | @c Copyright (C) 1988, 89, 92-98, 1999 Free Software Foundation, Inc. |
74291a4b MM |
2 | @c This is part of the GCC manual. |
3 | @c For copying conditions, see the file gcc.texi. | |
4 | ||
5 | @node Invoking GCC | |
0c2d1a2a JB |
6 | @chapter GCC Command Options |
7 | @cindex GCC command options | |
74291a4b | 8 | @cindex command options |
0c2d1a2a | 9 | @cindex options, GCC command |
74291a4b | 10 | |
0c2d1a2a | 11 | When you invoke GCC, it normally does preprocessing, compilation, |
74291a4b MM |
12 | assembly and linking. The ``overall options'' allow you to stop this |
13 | process at an intermediate stage. For example, the @samp{-c} option | |
14 | says not to run the linker. Then the output consists of object files | |
15 | output by the assembler. | |
16 | ||
17 | Other options are passed on to one stage of processing. Some options | |
18 | control the preprocessor and others the compiler itself. Yet other | |
19 | options control the assembler and linker; most of these are not | |
20 | documented here, since you rarely need to use any of them. | |
21 | ||
22 | @cindex C compilation options | |
0c2d1a2a | 23 | Most of the command line options that you can use with GCC are useful |
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24 | for C programs; when an option is only useful with another language |
25 | (usually C++), the explanation says so explicitly. If the description | |
26 | for a particular option does not mention a source language, you can use | |
27 | that option with all supported languages. | |
28 | ||
29 | @cindex C++ compilation options | |
30 | @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special | |
31 | options for compiling C++ programs. | |
32 | ||
33 | @cindex grouping options | |
34 | @cindex options, grouping | |
35 | The @code{gcc} program accepts options and file names as operands. Many | |
36 | options have multiletter names; therefore multiple single-letter options | |
37 | may @emph{not} be grouped: @samp{-dr} is very different from @w{@samp{-d | |
38 | -r}}. | |
39 | ||
40 | @cindex order of options | |
41 | @cindex options, order | |
42 | You can mix options and other arguments. For the most part, the order | |
43 | you use doesn't matter. Order does matter when you use several options | |
44 | of the same kind; for example, if you specify @samp{-L} more than once, | |
45 | the directories are searched in the order specified. | |
46 | ||
47 | Many options have long names starting with @samp{-f} or with | |
48 | @samp{-W}---for example, @samp{-fforce-mem}, | |
49 | @samp{-fstrength-reduce}, @samp{-Wformat} and so on. Most of | |
50 | these have both positive and negative forms; the negative form of | |
51 | @samp{-ffoo} would be @samp{-fno-foo}. This manual documents | |
52 | only one of these two forms, whichever one is not the default. | |
53 | ||
54 | @menu | |
55 | * Option Summary:: Brief list of all options, without explanations. | |
56 | * Overall Options:: Controlling the kind of output: | |
57 | an executable, object files, assembler files, | |
58 | or preprocessed source. | |
59 | * Invoking G++:: Compiling C++ programs. | |
60 | * C Dialect Options:: Controlling the variant of C language compiled. | |
61 | * C++ Dialect Options:: Variations on C++. | |
62 | * Warning Options:: How picky should the compiler be? | |
63 | * Debugging Options:: Symbol tables, measurements, and debugging dumps. | |
64 | * Optimize Options:: How much optimization? | |
65 | * Preprocessor Options:: Controlling header files and macro definitions. | |
66 | Also, getting dependency information for Make. | |
67 | * Assembler Options:: Passing options to the assembler. | |
68 | * Link Options:: Specifying libraries and so on. | |
69 | * Directory Options:: Where to find header files and libraries. | |
70 | Where to find the compiler executable files. | |
a743d340 | 71 | * Spec Files:: How to pass switches to sub-processes. |
0c2d1a2a | 72 | * Target Options:: Running a cross-compiler, or an old version of GCC. |
74291a4b MM |
73 | * Submodel Options:: Specifying minor hardware or convention variations, |
74 | such as 68010 vs 68020. | |
75 | * Code Gen Options:: Specifying conventions for function calls, data layout | |
76 | and register usage. | |
0c2d1a2a | 77 | * Environment Variables:: Env vars that affect GCC. |
74291a4b MM |
78 | * Running Protoize:: Automatically adding or removing function prototypes. |
79 | @end menu | |
80 | ||
81 | @node Option Summary | |
82 | @section Option Summary | |
83 | ||
84 | Here is a summary of all the options, grouped by type. Explanations are | |
85 | in the following sections. | |
86 | ||
87 | @table @emph | |
88 | @item Overall Options | |
89 | @xref{Overall Options,,Options Controlling the Kind of Output}. | |
90 | @smallexample | |
844642e6 | 91 | -c -S -E -o @var{file} -pipe -v --help -x @var{language} |
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92 | @end smallexample |
93 | ||
94 | @item C Language Options | |
95 | @xref{C Dialect Options,,Options Controlling C Dialect}. | |
96 | @smallexample | |
3932261a | 97 | -ansi -flang-isoc9x -fallow-single-precision -fcond-mismatch -fno-asm |
8c81598d | 98 | -fno-builtin -ffreestanding -fhosted -fsigned-bitfields -fsigned-char |
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99 | -funsigned-bitfields -funsigned-char -fwritable-strings |
100 | -traditional -traditional-cpp -trigraphs | |
101 | @end smallexample | |
102 | ||
103 | @item C++ Language Options | |
104 | @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. | |
105 | @smallexample | |
1dc5fc4b JM |
106 | -fno-access-control -fcheck-new -fconserve-space -fdollars-in-identifiers |
107 | -fno-elide-constructors -fexternal-templates -ffor-scope | |
6eabb241 | 108 | -fno-for-scope -fno-gnu-keywords -fguiding-decls |
1dc5fc4b JM |
109 | -fhonor-std -fhuge-objects -fno-implicit-templates -finit-priority |
110 | -fno-implement-inlines -fname-mangling-version-@var{n} -fno-default-inline | |
3a6bf921 | 111 | -foperator-names -fno-optional-diags -fpermissive -frepo -fstrict-prototype |
1dc5fc4b | 112 | -fsquangle -ftemplate-depth-@var{n} -fthis-is-variable -fvtable-thunks |
2de45c06 ML |
113 | -nostdinc++ -Wctor-dtor-privacy -Wno-deprecated -Weffc++ |
114 | -Wno-non-template-friend | |
bba975d4 JM |
115 | -Wnon-virtual-dtor -Wold-style-cast -Woverloaded-virtual |
116 | -Wno-pmf-conversions -Wreorder -Wsign-promo -Wsynth | |
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117 | @end smallexample |
118 | ||
119 | @item Warning Options | |
120 | @xref{Warning Options,,Options to Request or Suppress Warnings}. | |
121 | @smallexample | |
122 | -fsyntax-only -pedantic -pedantic-errors | |
123 | -w -W -Wall -Waggregate-return -Wbad-function-cast | |
08c5b6e8 | 124 | -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment |
74291a4b | 125 | -Wconversion -Werror -Wformat |
e9a25f70 | 126 | -Wid-clash-@var{len} -Wimplicit -Wimplicit-int |
f5963e61 JL |
127 | -Wimplicit-function-declaration -Wimport |
128 | -Werror-implicit-function-declaration -Winline | |
795add94 | 129 | -Wlarger-than-@var{len} -Wlong-long |
0ca3fb0a | 130 | -Wmain -Wmissing-declarations -Wmissing-noreturn |
4a870dba | 131 | -Wmissing-prototypes -Wmultichar -Wnested-externs -Wno-import |
bba975d4 | 132 | -Wparentheses -Wpointer-arith -Wredundant-decls |
d67343c9 | 133 | -Wreturn-type -Wshadow -Wsign-compare -Wstrict-prototypes |
bba975d4 | 134 | -Wswitch -Wtraditional |
312f6255 GK |
135 | -Wtrigraphs -Wundef -Wuninitialized -Wunknown-pragmas -Wunreachable-code |
136 | -Wunused -Wwrite-strings | |
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137 | @end smallexample |
138 | ||
139 | @item Debugging Options | |
140 | @xref{Debugging Options,,Options for Debugging Your Program or GCC}. | |
141 | @smallexample | |
f71f87f9 MM |
142 | -a -ax -d@var{letters} -fdump-unnumbered -fdump-translation-unit-@var{file} |
143 | -fpretend-float -fprofile-arcs -ftest-coverage | |
8c81598d | 144 | -g -g@var{level} -gcoff -gdwarf -gdwarf-1 -gdwarf-1+ -gdwarf-2 |
74291a4b MM |
145 | -ggdb -gstabs -gstabs+ -gxcoff -gxcoff+ |
146 | -p -pg -print-file-name=@var{library} -print-libgcc-file-name | |
03c41c05 | 147 | -print-prog-name=@var{program} -print-search-dirs -save-temps -time |
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148 | @end smallexample |
149 | ||
150 | @item Optimization Options | |
151 | @xref{Optimize Options,,Options that Control Optimization}. | |
152 | @smallexample | |
efa3896a GK |
153 | -falign-functions=@var{n} -falign-labels=@var{n} -falign-loops=@var{n} |
154 | -falign-jumps=@var{n} -fbranch-probabilities | |
74291a4b MM |
155 | -fcaller-saves -fcse-follow-jumps -fcse-skip-blocks |
156 | -fdelayed-branch -fexpensive-optimizations | |
157 | -ffast-math -ffloat-store -fforce-addr -fforce-mem | |
efa3896a GK |
158 | -fdata-sections -ffunction-sections -fgcse |
159 | -finline-functions -finline-limit=@var{n} -fkeep-inline-functions | |
160 | -fmove-all-movables -fno-default-inline -fno-defer-pop | |
161 | -fno-function-cse -fno-inline -fno-peephole | |
162 | -fomit-frame-pointer -foptimize-register-moves -fregmove | |
163 | -frerun-cse-after-loop -frerun-loop-opt -freduce-all-givs | |
164 | -fschedule-insns -fschedule-insns2 -fstrength-reduce | |
165 | -fstrict-aliasing -fthread-jumps -funroll-all-loops | |
166 | -funroll-loops | |
c6aded7c | 167 | -O -O0 -O1 -O2 -O3 -Os |
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168 | @end smallexample |
169 | ||
170 | @item Preprocessor Options | |
171 | @xref{Preprocessor Options,,Options Controlling the Preprocessor}. | |
172 | @smallexample | |
173 | -A@var{question}(@var{answer}) -C -dD -dM -dN | |
174 | -D@var{macro}@r{[}=@var{defn}@r{]} -E -H | |
175 | -idirafter @var{dir} | |
176 | -include @var{file} -imacros @var{file} | |
177 | -iprefix @var{file} -iwithprefix @var{dir} | |
f5a1b0d2 | 178 | -iwithprefixbefore @var{dir} -isystem @var{dir} -isystem-c++ @var{dir} |
74291a4b MM |
179 | -M -MD -MM -MMD -MG -nostdinc -P -trigraphs |
180 | -undef -U@var{macro} -Wp,@var{option} | |
181 | @end smallexample | |
182 | ||
183 | @item Assembler Option | |
184 | @xref{Assembler Options,,Passing Options to the Assembler}. | |
185 | @smallexample | |
186 | -Wa,@var{option} | |
187 | @end smallexample | |
188 | ||
189 | @item Linker Options | |
190 | @xref{Link Options,,Options for Linking}. | |
191 | @smallexample | |
192 | @var{object-file-name} -l@var{library} | |
193 | -nostartfiles -nodefaultlibs -nostdlib | |
194 | -s -static -shared -symbolic | |
195 | -Wl,@var{option} -Xlinker @var{option} | |
196 | -u @var{symbol} | |
197 | @end smallexample | |
198 | ||
199 | @item Directory Options | |
200 | @xref{Directory Options,,Options for Directory Search}. | |
201 | @smallexample | |
8c81598d | 202 | -B@var{prefix} -I@var{dir} -I- -L@var{dir} -specs=@var{file} |
74291a4b MM |
203 | @end smallexample |
204 | ||
205 | @item Target Options | |
206 | @c I wrote this xref this way to avoid overfull hbox. -- rms | |
207 | @xref{Target Options}. | |
208 | @smallexample | |
209 | -b @var{machine} -V @var{version} | |
210 | @end smallexample | |
211 | ||
212 | @item Machine Dependent Options | |
213 | @xref{Submodel Options,,Hardware Models and Configurations}. | |
214 | @smallexample | |
215 | @emph{M680x0 Options} | |
8c81598d | 216 | -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 |
e5e809f4 | 217 | -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 |
fb868474 | 218 | -mfpa -mnobitfield -mrtd -mshort -msoft-float -mpcrel |
e5e809f4 | 219 | -malign-int |
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220 | |
221 | @emph{VAX Options} | |
222 | -mg -mgnu -munix | |
223 | ||
224 | @emph{SPARC Options} | |
ded17aad DE |
225 | -mcpu=@var{cpu type} |
226 | -mtune=@var{cpu type} | |
227 | -mcmodel=@var{code model} | |
ded17aad | 228 | -m32 -m64 |
74291a4b | 229 | -mapp-regs -mbroken-saverestore -mcypress -mepilogue |
ded17aad DE |
230 | -mflat -mfpu -mhard-float -mhard-quad-float |
231 | -mimpure-text -mlive-g0 -mno-app-regs -mno-epilogue | |
74291a4b MM |
232 | -mno-flat -mno-fpu -mno-impure-text |
233 | -mno-stack-bias -mno-unaligned-doubles | |
234 | -msoft-float -msoft-quad-float -msparclite -mstack-bias | |
235 | -msupersparc -munaligned-doubles -mv8 | |
236 | ||
237 | @emph{Convex Options} | |
238 | -mc1 -mc2 -mc32 -mc34 -mc38 | |
239 | -margcount -mnoargcount | |
240 | -mlong32 -mlong64 | |
241 | -mvolatile-cache -mvolatile-nocache | |
242 | ||
243 | @emph{AMD29K Options} | |
244 | -m29000 -m29050 -mbw -mnbw -mdw -mndw | |
245 | -mlarge -mnormal -msmall | |
246 | -mkernel-registers -mno-reuse-arg-regs | |
247 | -mno-stack-check -mno-storem-bug | |
248 | -mreuse-arg-regs -msoft-float -mstack-check | |
249 | -mstorem-bug -muser-registers | |
250 | ||
251 | @emph{ARM Options} | |
157a620e NC |
252 | -mapcs-frame -mno-apcs-frame |
253 | -mapcs-26 -mapcs-32 | |
254 | -mapcs-stack-check -mno-apcs-stack-check | |
255 | -mapcs-float -mno-apcs-float | |
256 | -mapcs-reentrant -mno-apcs-reentrant | |
257 | -msched-prolog -mno-sched-prolog | |
258 | -mlittle-endian -mbig-endian -mwords-little-endian | |
259 | -mshort-load-bytes -mno-short-load-bytes -mshort-load-words -mno-short-load-words | |
260 | -msoft-float -mhard-float -mfpe | |
261 | -mthumb-interwork -mno-thumb-interwork | |
262 | -mcpu= -march= -mfpe= | |
263 | -mstructure-size-boundary= | |
264 | -mbsd -mxopen -mno-symrename | |
f5a1b0d2 | 265 | -mabort-on-noreturn |
62b10bbc | 266 | -mnop-fun-dllimport -mno-nop-fun-dllimport |
ed0e6530 PB |
267 | -msingle-pic-base -mno-single-pic-base |
268 | -mpic-register= | |
157a620e NC |
269 | |
270 | @emph{Thumb Options} | |
271 | -mtpcs-frame -mno-tpcs-frame | |
272 | -mtpcs-leaf-frame -mno-tpcs-leaf-frame | |
273 | -mlittle-endian -mbig-endian | |
274 | -mthumb-interwork -mno-thumb-interwork | |
275 | -mstructure-size-boundary= | |
62b10bbc NC |
276 | -mnop-fun-dllimport -mno-nop-fun-dllimport |
277 | -mcallee-super-interworking -mno-callee-super-interworking | |
278 | -mcaller-super-interworking -mno-caller-super-interworking | |
4bdc1ac7 PB |
279 | -msingle-pic-base -mno-single-pic-base |
280 | -mpic-register= | |
74291a4b | 281 | |
ecff22ab JL |
282 | @emph{MN10200 Options} |
283 | -mrelax | |
284 | ||
6d6d0fa0 JL |
285 | @emph{MN10300 Options} |
286 | -mmult-bug | |
287 | -mno-mult-bug | |
ecff22ab | 288 | -mrelax |
6d6d0fa0 | 289 | |
861bb6c1 JL |
290 | @emph{M32R/D Options} |
291 | -mcode-model=@var{model type} -msdata=@var{sdata type} | |
292 | -G @var{num} | |
293 | ||
74291a4b MM |
294 | @emph{M88K Options} |
295 | -m88000 -m88100 -m88110 -mbig-pic | |
296 | -mcheck-zero-division -mhandle-large-shift | |
297 | -midentify-revision -mno-check-zero-division | |
298 | -mno-ocs-debug-info -mno-ocs-frame-position | |
299 | -mno-optimize-arg-area -mno-serialize-volatile | |
300 | -mno-underscores -mocs-debug-info | |
301 | -mocs-frame-position -moptimize-arg-area | |
302 | -mserialize-volatile -mshort-data-@var{num} -msvr3 | |
303 | -msvr4 -mtrap-large-shift -muse-div-instruction | |
304 | -mversion-03.00 -mwarn-passed-structs | |
305 | ||
306 | @emph{RS/6000 and PowerPC Options} | |
8c81598d JM |
307 | -mcpu=@var{cpu type} |
308 | -mtune=@var{cpu type} | |
74291a4b | 309 | -mpower -mno-power -mpower2 -mno-power2 |
5f59ecb7 | 310 | -mpowerpc -mpowerpc64 -mno-powerpc |
74291a4b MM |
311 | -mpowerpc-gpopt -mno-powerpc-gpopt |
312 | -mpowerpc-gfxopt -mno-powerpc-gfxopt | |
313 | -mnew-mnemonics -mno-new-mnemonics | |
314 | -mfull-toc -mminimal-toc -mno-fop-in-toc -mno-sum-in-toc | |
5f59ecb7 | 315 | -m64 -m32 -mxl-call -mno-xl-call -mthreads -mpe |
74291a4b | 316 | -msoft-float -mhard-float -mmultiple -mno-multiple |
861bb6c1 JL |
317 | -mstring -mno-string -mupdate -mno-update |
318 | -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align | |
74291a4b MM |
319 | -mstrict-align -mno-strict-align -mrelocatable |
320 | -mno-relocatable -mrelocatable-lib -mno-relocatable-lib | |
2880d0aa | 321 | -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian |
74291a4b | 322 | -mcall-aix -mcall-sysv -mprototype -mno-prototype |
2880d0aa CM |
323 | -msim -mmvme -mads -myellowknife -memb -msdata |
324 | -msdata=@var{opt} -G @var{num} | |
74291a4b MM |
325 | |
326 | @emph{RT Options} | |
327 | -mcall-lib-mul -mfp-arg-in-fpregs -mfp-arg-in-gregs | |
328 | -mfull-fp-blocks -mhc-struct-return -min-line-mul | |
329 | -mminimum-fp-blocks -mnohc-struct-return | |
330 | ||
331 | @emph{MIPS Options} | |
8c81598d | 332 | -mabicalls -mcpu=@var{cpu type} -membedded-data |
74291a4b | 333 | -membedded-pic -mfp32 -mfp64 -mgas -mgp32 -mgp64 |
8c81598d | 334 | -mgpopt -mhalf-pic -mhard-float -mint64 -mips1 |
3ce1ba83 | 335 | -mips2 -mips3 -mips4 -mlong64 -mlong32 -mlong-calls -mmemcpy |
74291a4b MM |
336 | -mmips-as -mmips-tfile -mno-abicalls |
337 | -mno-embedded-data -mno-embedded-pic | |
338 | -mno-gpopt -mno-long-calls | |
339 | -mno-memcpy -mno-mips-tfile -mno-rnames -mno-stats | |
8c81598d JM |
340 | -mrnames -msoft-float |
341 | -m4650 -msingle-float -mmad | |
74291a4b | 342 | -mstats -EL -EB -G @var{num} -nocpp |
3398f47f | 343 | -mabi=32 -mabi=n32 -mabi=64 -mabi=eabi |
74291a4b MM |
344 | |
345 | @emph{i386 Options} | |
a9f3e1a4 JL |
346 | -mcpu=@var{cpu type} |
347 | -march=@var{cpu type} | |
348 | -mieee-fp -mno-fancy-math-387 | |
74291a4b | 349 | -mno-fp-ret-in-387 -msoft-float -msvr3-shlib |
8c81598d JM |
350 | -mno-wide-multiply -mrtd -malign-double |
351 | -mreg-alloc=@var{list} -mregparm=@var{num} | |
352 | -malign-jumps=@var{num} -malign-loops=@var{num} | |
00e59549 | 353 | -malign-functions=@var{num} -mpreferred-stack-boundary=@var{num} |
74291a4b MM |
354 | |
355 | @emph{HPPA Options} | |
ea3bfbfe | 356 | -march=@var{architecture type} |
e5e809f4 JL |
357 | -mbig-switch -mdisable-fpregs -mdisable-indexing |
358 | -mfast-indirect-calls -mgas -mjump-in-delay | |
359 | -mlong-load-store -mno-big-switch -mno-disable-fpregs | |
8c81598d | 360 | -mno-disable-indexing -mno-fast-indirect-calls -mno-gas |
e5e809f4 | 361 | -mno-jump-in-delay -mno-long-load-store |
c8730d93 | 362 | -mno-portable-runtime -mno-soft-float |
e5e809f4 | 363 | -mno-space-regs -msoft-float -mpa-risc-1-0 |
ea3bfbfe | 364 | -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime |
c8730d93 | 365 | -mschedule=@var{cpu type} -mspace-regs |
74291a4b MM |
366 | |
367 | @emph{Intel 960 Options} | |
368 | -m@var{cpu type} -masm-compat -mclean-linkage | |
369 | -mcode-align -mcomplex-addr -mleaf-procedures | |
370 | -mic-compat -mic2.0-compat -mic3.0-compat | |
371 | -mintel-asm -mno-clean-linkage -mno-code-align | |
372 | -mno-complex-addr -mno-leaf-procedures | |
373 | -mno-old-align -mno-strict-align -mno-tail-call | |
374 | -mnumerics -mold-align -msoft-float -mstrict-align | |
375 | -mtail-call | |
376 | ||
377 | @emph{DEC Alpha Options} | |
956d6950 JL |
378 | -mfp-regs -mno-fp-regs -mno-soft-float -msoft-float |
379 | -malpha-as -mgas | |
8c81598d | 380 | -mieee -mieee-with-inexact -mieee-conformant |
956d6950 JL |
381 | -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} |
382 | -mtrap-precision=@var{mode} -mbuild-constants | |
383 | -mcpu=@var{cpu type} | |
384 | -mbwx -mno-bwx -mcix -mno-cix -mmax -mno-max | |
4f69985c | 385 | -mmemory-latency=@var{time} |
74291a4b MM |
386 | |
387 | @emph{Clipper Options} | |
8c81598d | 388 | -mc300 -mc400 |
74291a4b MM |
389 | |
390 | @emph{H8/300 Options} | |
dcb9d1f0 | 391 | -mrelax -mh -ms -mint32 -malign-300 |
74291a4b MM |
392 | |
393 | @emph{SH Options} | |
3d5a0820 | 394 | -m1 -m2 -m3 -m3e -mb -ml -mdalign -mrelax |
74291a4b MM |
395 | |
396 | @emph{System V Options} | |
397 | -Qy -Qn -YP,@var{paths} -Ym,@var{dir} | |
74291a4b | 398 | |
56b2d7a7 JL |
399 | @emph{ARC Options} |
400 | -EB -EL | |
401 | -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text section} | |
402 | -mdata=@var{data section} -mrodata=@var{readonly data section} | |
403 | ||
282a61e6 MH |
404 | @emph{TMS320C3x/C4x Options} |
405 | -mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm | |
406 | -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload | |
407 | -mrpts=@var{count} -mrptb -mdb -mloop-unsigned | |
408 | -mparallel-insns -mparallel-mpy -mpreserve-float | |
409 | ||
f84271d9 JL |
410 | @emph{V850 Options} |
411 | -mlong-calls -mno-long-calls -mep -mno-ep | |
412 | -mprolog-function -mno-prolog-function -mspace | |
413 | -mtda=@var{n} -msda=@var{n} -mzda=@var{n} | |
e9a25f70 | 414 | -mv850 -mbig-switch |
83575957 ID |
415 | |
416 | @emph{NS32K Options} | |
417 | -m32032 -m32332 -m32532 -m32081 -m32381 -mmult-add -mnomult-add | |
418 | -msoft-float -mrtd -mnortd -mregparam -mnoregparam -msb -mnosb | |
419 | -mbitfield -mnobitfield -mhimem -mnohimem | |
f84271d9 JL |
420 | @end smallexample |
421 | ||
74291a4b MM |
422 | @item Code Generation Options |
423 | @xref{Code Gen Options,,Options for Code Generation Conventions}. | |
424 | @smallexample | |
425 | -fcall-saved-@var{reg} -fcall-used-@var{reg} | |
f2d76545 | 426 | -fexceptions -ffixed-@var{reg} -finhibit-size-directive |
861bb6c1 | 427 | -fcheck-memory-usage -fprefix-function-name |
74291a4b MM |
428 | -fno-common -fno-ident -fno-gnu-linker |
429 | -fpcc-struct-return -fpic -fPIC | |
430 | -freg-struct-return -fshared-data -fshort-enums | |
ab87f8c8 | 431 | -fshort-double -fvolatile -fvolatile-global -fvolatile-static |
1dc5fc4b | 432 | -fverbose-asm -fpack-struct -fstack-check |
e5eb27e5 JL |
433 | -fargument-alias -fargument-noalias |
434 | -fargument-noalias-global | |
19283265 | 435 | -fleading-underscore |
74291a4b MM |
436 | @end smallexample |
437 | @end table | |
438 | ||
439 | @menu | |
440 | * Overall Options:: Controlling the kind of output: | |
441 | an executable, object files, assembler files, | |
442 | or preprocessed source. | |
443 | * C Dialect Options:: Controlling the variant of C language compiled. | |
444 | * C++ Dialect Options:: Variations on C++. | |
445 | * Warning Options:: How picky should the compiler be? | |
446 | * Debugging Options:: Symbol tables, measurements, and debugging dumps. | |
447 | * Optimize Options:: How much optimization? | |
448 | * Preprocessor Options:: Controlling header files and macro definitions. | |
449 | Also, getting dependency information for Make. | |
450 | * Assembler Options:: Passing options to the assembler. | |
451 | * Link Options:: Specifying libraries and so on. | |
452 | * Directory Options:: Where to find header files and libraries. | |
453 | Where to find the compiler executable files. | |
a743d340 | 454 | * Spec Files:: How to pass switches to sub-processes. |
0c2d1a2a | 455 | * Target Options:: Running a cross-compiler, or an old version of GCC. |
74291a4b MM |
456 | @end menu |
457 | ||
458 | @node Overall Options | |
459 | @section Options Controlling the Kind of Output | |
460 | ||
461 | Compilation can involve up to four stages: preprocessing, compilation | |
462 | proper, assembly and linking, always in that order. The first three | |
463 | stages apply to an individual source file, and end by producing an | |
464 | object file; linking combines all the object files (those newly | |
465 | compiled, and those specified as input) into an executable file. | |
466 | ||
467 | @cindex file name suffix | |
468 | For any given input file, the file name suffix determines what kind of | |
469 | compilation is done: | |
470 | ||
471 | @table @code | |
472 | @item @var{file}.c | |
473 | C source code which must be preprocessed. | |
474 | ||
475 | @item @var{file}.i | |
476 | C source code which should not be preprocessed. | |
477 | ||
478 | @item @var{file}.ii | |
479 | C++ source code which should not be preprocessed. | |
480 | ||
481 | @item @var{file}.m | |
482 | Objective-C source code. Note that you must link with the library | |
483 | @file{libobjc.a} to make an Objective-C program work. | |
484 | ||
485 | @item @var{file}.h | |
486 | C header file (not to be compiled or linked). | |
487 | ||
488 | @item @var{file}.cc | |
489 | @itemx @var{file}.cxx | |
490 | @itemx @var{file}.cpp | |
491 | @itemx @var{file}.C | |
492 | C++ source code which must be preprocessed. Note that in @samp{.cxx}, | |
493 | the last two letters must both be literally @samp{x}. Likewise, | |
494 | @samp{.C} refers to a literal capital C. | |
495 | ||
496 | @item @var{file}.s | |
497 | Assembler code. | |
498 | ||
499 | @item @var{file}.S | |
500 | Assembler code which must be preprocessed. | |
501 | ||
502 | @item @var{other} | |
503 | An object file to be fed straight into linking. | |
504 | Any file name with no recognized suffix is treated this way. | |
505 | @end table | |
506 | ||
507 | You can specify the input language explicitly with the @samp{-x} option: | |
508 | ||
509 | @table @code | |
510 | @item -x @var{language} | |
511 | Specify explicitly the @var{language} for the following input files | |
512 | (rather than letting the compiler choose a default based on the file | |
513 | name suffix). This option applies to all following input files until | |
514 | the next @samp{-x} option. Possible values for @var{language} are: | |
515 | @example | |
516 | c objective-c c++ | |
517 | c-header cpp-output c++-cpp-output | |
518 | assembler assembler-with-cpp | |
519 | @end example | |
520 | ||
521 | @item -x none | |
522 | Turn off any specification of a language, so that subsequent files are | |
523 | handled according to their file name suffixes (as they are if @samp{-x} | |
524 | has not been used at all). | |
525 | @end table | |
526 | ||
527 | If you only want some of the stages of compilation, you can use | |
528 | @samp{-x} (or filename suffixes) to tell @code{gcc} where to start, and | |
529 | one of the options @samp{-c}, @samp{-S}, or @samp{-E} to say where | |
530 | @code{gcc} is to stop. Note that some combinations (for example, | |
531 | @samp{-x cpp-output -E} instruct @code{gcc} to do nothing at all. | |
532 | ||
533 | @table @code | |
534 | @item -c | |
535 | Compile or assemble the source files, but do not link. The linking | |
536 | stage simply is not done. The ultimate output is in the form of an | |
537 | object file for each source file. | |
538 | ||
539 | By default, the object file name for a source file is made by replacing | |
540 | the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. | |
541 | ||
542 | Unrecognized input files, not requiring compilation or assembly, are | |
543 | ignored. | |
544 | ||
545 | @item -S | |
546 | Stop after the stage of compilation proper; do not assemble. The output | |
547 | is in the form of an assembler code file for each non-assembler input | |
548 | file specified. | |
549 | ||
550 | By default, the assembler file name for a source file is made by | |
551 | replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. | |
552 | ||
553 | Input files that don't require compilation are ignored. | |
554 | ||
555 | @item -E | |
556 | Stop after the preprocessing stage; do not run the compiler proper. The | |
557 | output is in the form of preprocessed source code, which is sent to the | |
558 | standard output. | |
559 | ||
560 | Input files which don't require preprocessing are ignored. | |
561 | ||
562 | @cindex output file option | |
563 | @item -o @var{file} | |
564 | Place output in file @var{file}. This applies regardless to whatever | |
565 | sort of output is being produced, whether it be an executable file, | |
566 | an object file, an assembler file or preprocessed C code. | |
567 | ||
568 | Since only one output file can be specified, it does not make sense to | |
569 | use @samp{-o} when compiling more than one input file, unless you are | |
570 | producing an executable file as output. | |
571 | ||
572 | If @samp{-o} is not specified, the default is to put an executable file | |
573 | in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in | |
574 | @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, and | |
575 | all preprocessed C source on standard output.@refill | |
576 | ||
577 | @item -v | |
578 | Print (on standard error output) the commands executed to run the stages | |
579 | of compilation. Also print the version number of the compiler driver | |
580 | program and of the preprocessor and the compiler proper. | |
581 | ||
582 | @item -pipe | |
583 | Use pipes rather than temporary files for communication between the | |
584 | various stages of compilation. This fails to work on some systems where | |
585 | the assembler is unable to read from a pipe; but the GNU assembler has | |
586 | no trouble. | |
844642e6 NC |
587 | |
588 | @item --help | |
589 | Print (on the standard output) a description of the command line options | |
590 | understood by @code{gcc}. If the @code{-v} option is also specified | |
591 | then @code{--help} will also be passed on to the various processes | |
592 | invoked by @code{gcc}, so that they can display the command line options | |
593 | they accept. If the @code{-W} option is also specified then command | |
594 | line options which have no documentation associated with them will also | |
595 | be displayed. | |
74291a4b MM |
596 | @end table |
597 | ||
598 | @node Invoking G++ | |
599 | @section Compiling C++ Programs | |
600 | ||
601 | @cindex suffixes for C++ source | |
602 | @cindex C++ source file suffixes | |
603 | C++ source files conventionally use one of the suffixes @samp{.C}, | |
bba975d4 | 604 | @samp{.cc}, @samp{.cpp}, @samp{.c++}, @samp{.cp}, or @samp{.cxx}; |
0c2d1a2a | 605 | preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes |
bba975d4 JM |
606 | files with these names and compiles them as C++ programs even if you |
607 | call the compiler the same way as for compiling C programs (usually with | |
608 | the name @code{gcc}). | |
74291a4b MM |
609 | |
610 | @findex g++ | |
611 | @findex c++ | |
612 | However, C++ programs often require class libraries as well as a | |
613 | compiler that understands the C++ language---and under some | |
614 | circumstances, you might want to compile programs from standard input, | |
615 | or otherwise without a suffix that flags them as C++ programs. | |
0c2d1a2a | 616 | @code{g++} is a program that calls GCC with the default language |
e5e809f4 | 617 | set to C++, and automatically specifies linking against the C++ |
bba975d4 | 618 | library. On many systems, the script @code{g++} is also |
74291a4b MM |
619 | installed with the name @code{c++}. |
620 | ||
621 | @cindex invoking @code{g++} | |
622 | When you compile C++ programs, you may specify many of the same | |
623 | command-line options that you use for compiling programs in any | |
624 | language; or command-line options meaningful for C and related | |
625 | languages; or options that are meaningful only for C++ programs. | |
626 | @xref{C Dialect Options,,Options Controlling C Dialect}, for | |
627 | explanations of options for languages related to C. | |
628 | @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for | |
629 | explanations of options that are meaningful only for C++ programs. | |
630 | ||
631 | @node C Dialect Options | |
632 | @section Options Controlling C Dialect | |
633 | @cindex dialect options | |
634 | @cindex language dialect options | |
635 | @cindex options, dialect | |
636 | ||
637 | The following options control the dialect of C (or languages derived | |
638 | from C, such as C++ and Objective C) that the compiler accepts: | |
639 | ||
640 | @table @code | |
641 | @cindex ANSI support | |
642 | @item -ansi | |
0c2d1a2a JB |
643 | In C mode, support all ANSI standard C programs. In C++ mode, |
644 | remove GNU extensions that conflict with ANSI C++. | |
645 | @c shouldn't we be saying "ISO"? | |
74291a4b | 646 | |
0c2d1a2a JB |
647 | This turns off certain features of GCC that are incompatible with ANSI |
648 | C (when compiling C code), or of ANSI standard C++ (when compiling C++ code), | |
649 | such as the @code{asm} and @code{typeof} keywords, and | |
74291a4b MM |
650 | predefined macros such as @code{unix} and @code{vax} that identify the |
651 | type of system you are using. It also enables the undesirable and | |
0c2d1a2a JB |
652 | rarely used ANSI trigraph feature. For the C compiler, |
653 | it disables recognition of C++ style @samp{//} comments as well as | |
654 | the @code{inline} keyword. For the C++ compiler, | |
655 | @samp{-foperator-names} is enabled as well. | |
656 | ||
74291a4b MM |
657 | |
658 | The alternate keywords @code{__asm__}, @code{__extension__}, | |
659 | @code{__inline__} and @code{__typeof__} continue to work despite | |
660 | @samp{-ansi}. You would not want to use them in an ANSI C program, of | |
661 | course, but it is useful to put them in header files that might be included | |
662 | in compilations done with @samp{-ansi}. Alternate predefined macros | |
663 | such as @code{__unix__} and @code{__vax__} are also available, with or | |
664 | without @samp{-ansi}. | |
665 | ||
666 | The @samp{-ansi} option does not cause non-ANSI programs to be | |
667 | rejected gratuitously. For that, @samp{-pedantic} is required in | |
668 | addition to @samp{-ansi}. @xref{Warning Options}. | |
669 | ||
670 | The macro @code{__STRICT_ANSI__} is predefined when the @samp{-ansi} | |
671 | option is used. Some header files may notice this macro and refrain | |
672 | from declaring certain functions or defining certain macros that the | |
673 | ANSI standard doesn't call for; this is to avoid interfering with any | |
674 | programs that might use these names for other things. | |
675 | ||
676 | The functions @code{alloca}, @code{abort}, @code{exit}, and | |
677 | @code{_exit} are not builtin functions when @samp{-ansi} is used. | |
678 | ||
3932261a MM |
679 | @item -flang-isoc9x |
680 | Enable support for features found in the C9X standard. In particular, | |
681 | enable support for the C9X @code{restrict} keyword. | |
682 | ||
683 | Even when this option is not specified, you can still use some C9X | |
684 | features in so far as they do not conflict with previous C standards. | |
685 | For example, you may use @code{__restrict__} even when -flang-isoc9x | |
686 | is not specified. | |
687 | ||
74291a4b MM |
688 | @item -fno-asm |
689 | Do not recognize @code{asm}, @code{inline} or @code{typeof} as a | |
690 | keyword, so that code can use these words as identifiers. You can use | |
691 | the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} | |
692 | instead. @samp{-ansi} implies @samp{-fno-asm}. | |
693 | ||
694 | In C++, this switch only affects the @code{typeof} keyword, since | |
695 | @code{asm} and @code{inline} are standard keywords. You may want to | |
696 | use the @samp{-fno-gnu-keywords} flag instead, as it also disables the | |
697 | other, C++-specific, extension keywords such as @code{headof}. | |
698 | ||
699 | @item -fno-builtin | |
700 | @cindex builtin functions | |
701 | @findex abort | |
702 | @findex abs | |
703 | @findex alloca | |
704 | @findex cos | |
705 | @findex exit | |
706 | @findex fabs | |
707 | @findex ffs | |
708 | @findex labs | |
709 | @findex memcmp | |
710 | @findex memcpy | |
711 | @findex sin | |
712 | @findex sqrt | |
713 | @findex strcmp | |
714 | @findex strcpy | |
715 | @findex strlen | |
ab87f8c8 | 716 | Don't recognize builtin functions that do not begin with @samp{__builtin_} |
e69fd6e5 | 717 | as prefix. Currently, the functions affected include @code{abort}, |
74291a4b MM |
718 | @code{abs}, @code{alloca}, @code{cos}, @code{exit}, @code{fabs}, |
719 | @code{ffs}, @code{labs}, @code{memcmp}, @code{memcpy}, @code{sin}, | |
720 | @code{sqrt}, @code{strcmp}, @code{strcpy}, and @code{strlen}. | |
721 | ||
722 | GCC normally generates special code to handle certain builtin functions | |
723 | more efficiently; for instance, calls to @code{alloca} may become single | |
724 | instructions that adjust the stack directly, and calls to @code{memcpy} | |
725 | may become inline copy loops. The resulting code is often both smaller | |
726 | and faster, but since the function calls no longer appear as such, you | |
727 | cannot set a breakpoint on those calls, nor can you change the behavior | |
728 | of the functions by linking with a different library. | |
729 | ||
730 | The @samp{-ansi} option prevents @code{alloca} and @code{ffs} from being | |
731 | builtin functions, since these functions do not have an ANSI standard | |
732 | meaning. | |
733 | ||
861bb6c1 JL |
734 | @item -fhosted |
735 | @cindex hosted environment | |
736 | ||
737 | Assert that compilation takes place in a hosted environment. This implies | |
738 | @samp{-fbuiltin}. A hosted environment is one in which the | |
739 | entire standard library is available, and in which @code{main} has a return | |
740 | type of @code{int}. Examples are nearly everything except a kernel. | |
741 | This is equivalent to @samp{-fno-freestanding}. | |
742 | ||
743 | @item -ffreestanding | |
744 | @cindex hosted environment | |
745 | ||
746 | Assert that compilation takes place in a freestanding environment. This | |
747 | implies @samp{-fno-builtin}. A freestanding environment | |
748 | is one in which the standard library may not exist, and program startup may | |
749 | not necessarily be at @code{main}. The most obvious example is an OS kernel. | |
750 | This is equivalent to @samp{-fno-hosted}. | |
751 | ||
74291a4b MM |
752 | @item -trigraphs |
753 | Support ANSI C trigraphs. You don't want to know about this | |
754 | brain-damage. The @samp{-ansi} option implies @samp{-trigraphs}. | |
755 | ||
756 | @cindex traditional C language | |
757 | @cindex C language, traditional | |
758 | @item -traditional | |
759 | Attempt to support some aspects of traditional C compilers. | |
760 | Specifically: | |
761 | ||
762 | @itemize @bullet | |
763 | @item | |
764 | All @code{extern} declarations take effect globally even if they | |
765 | are written inside of a function definition. This includes implicit | |
766 | declarations of functions. | |
767 | ||
768 | @item | |
769 | The newer keywords @code{typeof}, @code{inline}, @code{signed}, @code{const} | |
770 | and @code{volatile} are not recognized. (You can still use the | |
771 | alternative keywords such as @code{__typeof__}, @code{__inline__}, and | |
772 | so on.) | |
773 | ||
774 | @item | |
775 | Comparisons between pointers and integers are always allowed. | |
776 | ||
777 | @item | |
778 | Integer types @code{unsigned short} and @code{unsigned char} promote | |
779 | to @code{unsigned int}. | |
780 | ||
781 | @item | |
782 | Out-of-range floating point literals are not an error. | |
783 | ||
784 | @item | |
785 | Certain constructs which ANSI regards as a single invalid preprocessing | |
786 | number, such as @samp{0xe-0xd}, are treated as expressions instead. | |
787 | ||
788 | @item | |
789 | String ``constants'' are not necessarily constant; they are stored in | |
790 | writable space, and identical looking constants are allocated | |
791 | separately. (This is the same as the effect of | |
792 | @samp{-fwritable-strings}.) | |
793 | ||
794 | @cindex @code{longjmp} and automatic variables | |
795 | @item | |
796 | All automatic variables not declared @code{register} are preserved by | |
797 | @code{longjmp}. Ordinarily, GNU C follows ANSI C: automatic variables | |
798 | not declared @code{volatile} may be clobbered. | |
799 | ||
800 | @item | |
801 | @kindex \x | |
802 | @kindex \a | |
803 | @cindex escape sequences, traditional | |
804 | The character escape sequences @samp{\x} and @samp{\a} evaluate as the | |
805 | literal characters @samp{x} and @samp{a} respectively. Without | |
806 | @w{@samp{-traditional}}, @samp{\x} is a prefix for the hexadecimal | |
807 | representation of a character, and @samp{\a} produces a bell. | |
ad299d9b | 808 | @end itemize |
74291a4b | 809 | |
74291a4b MM |
810 | You may wish to use @samp{-fno-builtin} as well as @samp{-traditional} |
811 | if your program uses names that are normally GNU C builtin functions for | |
812 | other purposes of its own. | |
813 | ||
814 | You cannot use @samp{-traditional} if you include any header files that | |
815 | rely on ANSI C features. Some vendors are starting to ship systems with | |
816 | ANSI C header files and you cannot use @samp{-traditional} on such | |
817 | systems to compile files that include any system headers. | |
818 | ||
e5e809f4 JL |
819 | The @samp{-traditional} option also enables @samp{-traditional-cpp}, |
820 | which is described next. | |
74291a4b MM |
821 | |
822 | @item -traditional-cpp | |
823 | Attempt to support some aspects of traditional C preprocessors. | |
824 | Specifically: | |
825 | ||
826 | @itemize @bullet | |
827 | @item | |
828 | Comments convert to nothing at all, rather than to a space. This allows | |
829 | traditional token concatenation. | |
830 | ||
831 | @item | |
832 | In a preprocessing directive, the @samp{#} symbol must appear as the first | |
833 | character of a line. | |
834 | ||
835 | @item | |
836 | Macro arguments are recognized within string constants in a macro | |
837 | definition (and their values are stringified, though without additional | |
838 | quote marks, when they appear in such a context). The preprocessor | |
839 | always considers a string constant to end at a newline. | |
840 | ||
841 | @item | |
842 | @cindex detecting @w{@samp{-traditional}} | |
843 | The predefined macro @code{__STDC__} is not defined when you use | |
844 | @samp{-traditional}, but @code{__GNUC__} is (since the GNU extensions | |
845 | which @code{__GNUC__} indicates are not affected by | |
846 | @samp{-traditional}). If you need to write header files that work | |
847 | differently depending on whether @samp{-traditional} is in use, by | |
848 | testing both of these predefined macros you can distinguish four | |
849 | situations: GNU C, traditional GNU C, other ANSI C compilers, and other | |
850 | old C compilers. The predefined macro @code{__STDC_VERSION__} is also | |
851 | not defined when you use @samp{-traditional}. @xref{Standard | |
852 | Predefined,,Standard Predefined Macros,cpp.info,The C Preprocessor}, | |
853 | for more discussion of these and other predefined macros. | |
854 | ||
855 | @item | |
856 | @cindex string constants vs newline | |
857 | @cindex newline vs string constants | |
858 | The preprocessor considers a string constant to end at a newline (unless | |
859 | the newline is escaped with @samp{\}). (Without @w{@samp{-traditional}}, | |
860 | string constants can contain the newline character as typed.) | |
861 | @end itemize | |
862 | ||
863 | @item -fcond-mismatch | |
864 | Allow conditional expressions with mismatched types in the second and | |
865 | third arguments. The value of such an expression is void. | |
866 | ||
867 | @item -funsigned-char | |
868 | Let the type @code{char} be unsigned, like @code{unsigned char}. | |
869 | ||
870 | Each kind of machine has a default for what @code{char} should | |
871 | be. It is either like @code{unsigned char} by default or like | |
872 | @code{signed char} by default. | |
873 | ||
874 | Ideally, a portable program should always use @code{signed char} or | |
875 | @code{unsigned char} when it depends on the signedness of an object. | |
876 | But many programs have been written to use plain @code{char} and | |
877 | expect it to be signed, or expect it to be unsigned, depending on the | |
878 | machines they were written for. This option, and its inverse, let you | |
879 | make such a program work with the opposite default. | |
880 | ||
881 | The type @code{char} is always a distinct type from each of | |
882 | @code{signed char} or @code{unsigned char}, even though its behavior | |
883 | is always just like one of those two. | |
884 | ||
885 | @item -fsigned-char | |
886 | Let the type @code{char} be signed, like @code{signed char}. | |
887 | ||
888 | Note that this is equivalent to @samp{-fno-unsigned-char}, which is | |
889 | the negative form of @samp{-funsigned-char}. Likewise, the option | |
890 | @samp{-fno-signed-char} is equivalent to @samp{-funsigned-char}. | |
891 | ||
892 | You may wish to use @samp{-fno-builtin} as well as @samp{-traditional} | |
893 | if your program uses names that are normally GNU C builtin functions for | |
894 | other purposes of its own. | |
895 | ||
896 | You cannot use @samp{-traditional} if you include any header files that | |
897 | rely on ANSI C features. Some vendors are starting to ship systems with | |
898 | ANSI C header files and you cannot use @samp{-traditional} on such | |
899 | systems to compile files that include any system headers. | |
900 | ||
901 | @item -fsigned-bitfields | |
902 | @itemx -funsigned-bitfields | |
903 | @itemx -fno-signed-bitfields | |
904 | @itemx -fno-unsigned-bitfields | |
905 | These options control whether a bitfield is signed or unsigned, when the | |
906 | declaration does not use either @code{signed} or @code{unsigned}. By | |
907 | default, such a bitfield is signed, because this is consistent: the | |
908 | basic integer types such as @code{int} are signed types. | |
909 | ||
910 | However, when @samp{-traditional} is used, bitfields are all unsigned | |
911 | no matter what. | |
912 | ||
913 | @item -fwritable-strings | |
914 | Store string constants in the writable data segment and don't uniquize | |
915 | them. This is for compatibility with old programs which assume they can | |
916 | write into string constants. The option @samp{-traditional} also has | |
917 | this effect. | |
918 | ||
919 | Writing into string constants is a very bad idea; ``constants'' should | |
920 | be constant. | |
921 | ||
922 | @item -fallow-single-precision | |
923 | Do not promote single precision math operations to double precision, | |
924 | even when compiling with @samp{-traditional}. | |
925 | ||
926 | Traditional K&R C promotes all floating point operations to double | |
927 | precision, regardless of the sizes of the operands. On the | |
928 | architecture for which you are compiling, single precision may be faster | |
929 | than double precision. If you must use @samp{-traditional}, but want | |
930 | to use single precision operations when the operands are single | |
931 | precision, use this option. This option has no effect when compiling | |
932 | with ANSI or GNU C conventions (the default). | |
933 | ||
934 | @end table | |
935 | ||
936 | @node C++ Dialect Options | |
937 | @section Options Controlling C++ Dialect | |
938 | ||
939 | @cindex compiler options, C++ | |
940 | @cindex C++ options, command line | |
941 | @cindex options, C++ | |
942 | This section describes the command-line options that are only meaningful | |
943 | for C++ programs; but you can also use most of the GNU compiler options | |
944 | regardless of what language your program is in. For example, you | |
945 | might compile a file @code{firstClass.C} like this: | |
946 | ||
947 | @example | |
1dc5fc4b | 948 | g++ -g -frepo -O -c firstClass.C |
74291a4b MM |
949 | @end example |
950 | ||
951 | @noindent | |
1dc5fc4b | 952 | In this example, only @samp{-frepo} is an option meant |
74291a4b | 953 | only for C++ programs; you can use the other options with any |
0c2d1a2a | 954 | language supported by GCC. |
74291a4b MM |
955 | |
956 | Here is a list of options that are @emph{only} for compiling C++ programs: | |
957 | ||
958 | @table @code | |
959 | @item -fno-access-control | |
960 | Turn off all access checking. This switch is mainly useful for working | |
961 | around bugs in the access control code. | |
962 | ||
74291a4b MM |
963 | @item -fcheck-new |
964 | Check that the pointer returned by @code{operator new} is non-null | |
965 | before attempting to modify the storage allocated. The current Working | |
966 | Paper requires that @code{operator new} never return a null pointer, so | |
967 | this check is normally unnecessary. | |
968 | ||
1dc5fc4b JM |
969 | An alternative to using this option is to specify that your |
970 | @code{operator new} does not throw any exceptions; if you declare it | |
971 | @samp{throw()}, g++ will check the return value. See also @samp{new | |
972 | (nothrow)}. | |
973 | ||
74291a4b MM |
974 | @item -fconserve-space |
975 | Put uninitialized or runtime-initialized global variables into the | |
976 | common segment, as C does. This saves space in the executable at the | |
977 | cost of not diagnosing duplicate definitions. If you compile with this | |
978 | flag and your program mysteriously crashes after @code{main()} has | |
979 | completed, you may have an object that is being destroyed twice because | |
980 | two definitions were merged. | |
981 | ||
1dc5fc4b JM |
982 | This option is no longer useful on most targets, now that support has |
983 | been added for putting variables into BSS without making them common. | |
984 | ||
74291a4b MM |
985 | @item -fdollars-in-identifiers |
986 | Accept @samp{$} in identifiers. You can also explicitly prohibit use of | |
eb795509 RK |
987 | @samp{$} with the option @samp{-fno-dollars-in-identifiers}. (GNU C allows |
988 | @samp{$} by default on most target systems, but there are a few exceptions.) | |
74291a4b MM |
989 | Traditional C allowed the character @samp{$} to form part of |
990 | identifiers. However, ANSI C and C++ forbid @samp{$} in identifiers. | |
991 | ||
1dc5fc4b JM |
992 | @item -fno-elide-constructors |
993 | The C++ standard allows an implementation to omit creating a temporary | |
994 | which is only used to initialize another object of the same type. | |
995 | Specifying this option disables that optimization, and forces g++ to | |
996 | call the copy constructor in all cases. | |
74291a4b MM |
997 | |
998 | @item -fexternal-templates | |
999 | Cause template instantiations to obey @samp{#pragma interface} and | |
1000 | @samp{implementation}; template instances are emitted or not according | |
1001 | to the location of the template definition. @xref{Template | |
1002 | Instantiation}, for more information. | |
1003 | ||
37f6b6bf MM |
1004 | This option is deprecated. |
1005 | ||
74291a4b MM |
1006 | @item -falt-external-templates |
1007 | Similar to -fexternal-templates, but template instances are emitted or | |
1008 | not according to the place where they are first instantiated. | |
1009 | @xref{Template Instantiation}, for more information. | |
1010 | ||
37f6b6bf MM |
1011 | This option is deprecated. |
1012 | ||
74291a4b | 1013 | @item -ffor-scope |
8c81598d | 1014 | @itemx -fno-for-scope |
74291a4b MM |
1015 | If -ffor-scope is specified, the scope of variables declared in |
1016 | a @i{for-init-statement} is limited to the @samp{for} loop itself, | |
1017 | as specified by the draft C++ standard. | |
1018 | If -fno-for-scope is specified, the scope of variables declared in | |
1019 | a @i{for-init-statement} extends to the end of the enclosing scope, | |
1020 | as was the case in old versions of gcc, and other (traditional) | |
1021 | implementations of C++. | |
1022 | ||
1023 | The default if neither flag is given to follow the standard, | |
1024 | but to allow and give a warning for old-style code that would | |
1025 | otherwise be invalid, or have different behavior. | |
1026 | ||
1027 | @item -fno-gnu-keywords | |
6eabb241 MM |
1028 | Do not recognize @code{classof}, @code{headof}, or @code{typeof} as a |
1029 | keyword, so that code can use these words as identifiers. You can use | |
1030 | the keywords @code{__classof__}, @code{__headof__}, and | |
74291a4b MM |
1031 | @code{__typeof__} instead. @samp{-ansi} implies |
1032 | @samp{-fno-gnu-keywords}. | |
1033 | ||
37f6b6bf MM |
1034 | @item -fguiding-decls |
1035 | Treat a function declaration with the same type as a potential function | |
1036 | template instantiation as though it declares that instantiation, not a | |
1037 | normal function. If a definition is given for the function later in the | |
1038 | translation unit (or another translation unit if the target supports | |
1039 | weak symbols), that definition will be used; otherwise the template will | |
1040 | be instantiated. This behavior reflects the C++ language prior to | |
1041 | September 1996, when guiding declarations were removed. | |
1042 | ||
1043 | This option implies @samp{-fname-mangling-version-0}, and will not work | |
1dc5fc4b JM |
1044 | with other name mangling versions. Like all options that change the |
1045 | ABI, all C++ code, @emph{including libgcc.a} must be built with the same | |
1046 | setting of this option. | |
74291a4b | 1047 | |
95c81fb8 ML |
1048 | @item -fhonor-std |
1049 | Treat the @code{namespace std} as a namespace, instead of ignoring | |
1050 | it. For compatibility with earlier versions of g++, the compiler will, | |
1051 | by default, ignore @code{namespace-declarations}, | |
1052 | @code{using-declarations}, @code{using-directives}, and | |
1053 | @code{namespace-names}, if they involve @code{std}. | |
1054 | ||
74291a4b MM |
1055 | @item -fhuge-objects |
1056 | Support virtual function calls for objects that exceed the size | |
1057 | representable by a @samp{short int}. Users should not use this flag by | |
1dc5fc4b | 1058 | default; if you need to use it, the compiler will tell you so. |
74291a4b MM |
1059 | |
1060 | This flag is not useful when compiling with -fvtable-thunks. | |
1061 | ||
1dc5fc4b JM |
1062 | Like all options that change the ABI, all C++ code, @emph{including |
1063 | libgcc} must be built with the same setting of this option. | |
1064 | ||
1065 | @item -fno-implicit-templates | |
bba975d4 JM |
1066 | Never emit code for non-inline templates which are instantiated |
1067 | implicitly (i.e. by use); only emit code for explicit instantiations. | |
1068 | @xref{Template Instantiation}, for more information. | |
1069 | ||
1070 | @item -fno-implicit-inline-templates | |
1071 | Don't emit code for implicit instantiations of inline templates, either. | |
1072 | The default is to handle inlines differently so that compiles with and | |
1073 | without optimization will need the same set of explicit instantiations. | |
1dc5fc4b | 1074 | |
2ce3c6c6 JM |
1075 | @item -finit-priority |
1076 | Support @samp{__attribute__ ((init_priority (n)))} for controlling the | |
1077 | order of initialization of file-scope objects. On ELF targets, this | |
1078 | requires GNU ld 2.10 or later. | |
1079 | ||
74291a4b MM |
1080 | @item -fno-implement-inlines |
1081 | To save space, do not emit out-of-line copies of inline functions | |
1082 | controlled by @samp{#pragma implementation}. This will cause linker | |
1083 | errors if these functions are not inlined everywhere they are called. | |
1084 | ||
631cf95d JM |
1085 | @item -fms-extensions |
1086 | Disable pedwarns about constructs used in MFC, such as implicit int and | |
1087 | getting a pointer to member function via non-standard syntax. | |
1088 | ||
37f6b6bf MM |
1089 | @item -fname-mangling-version-@var{n} |
1090 | Control the way in which names are mangled. Version 0 is compatible | |
1091 | with versions of g++ before 2.8. Version 1 is the default. Version 1 | |
1092 | will allow correct mangling of function templates. For example, | |
1093 | version 0 mangling does not mangle foo<int, double> and foo<int, char> | |
1094 | given this declaration: | |
1095 | ||
1096 | @example | |
1097 | template <class T, class U> void foo(T t); | |
1098 | @end example | |
1099 | ||
bba975d4 JM |
1100 | Like all options that change the ABI, all C++ code, @emph{including |
1101 | libgcc} must be built with the same setting of this option. | |
1102 | ||
74291a4b MM |
1103 | @item -foperator-names |
1104 | Recognize the operator name keywords @code{and}, @code{bitand}, | |
1105 | @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as | |
1106 | synonyms for the symbols they refer to. @samp{-ansi} implies | |
1107 | @samp{-foperator-names}. | |
1108 | ||
4f8b4fd9 JM |
1109 | @item -fno-optional-diags |
1110 | Disable diagnostics that the standard says a compiler does not need to | |
bba975d4 JM |
1111 | issue. Currently, the only such diagnostic issued by g++ is the one for |
1112 | a name having multiple meanings within a class. | |
4f8b4fd9 | 1113 | |
8c7707b0 JM |
1114 | @item -fpermissive |
1115 | Downgrade messages about nonconformant code from errors to warnings. By | |
1116 | default, g++ effectively sets @samp{-pedantic-errors} without | |
1117 | @samp{-pedantic}; this option reverses that. This behavior and this | |
2d9f9cf1 | 1118 | option are superseded by @samp{-pedantic}, which works as it does for GNU C. |
8c7707b0 | 1119 | |
8c81598d JM |
1120 | @item -frepo |
1121 | Enable automatic template instantiation. This option also implies | |
1122 | @samp{-fno-implicit-templates}. @xref{Template Instantiation}, for more | |
1123 | information. | |
1124 | ||
8c7707b0 JM |
1125 | @item -fno-rtti |
1126 | Disable generation of the information used by C++ runtime type | |
1127 | identification features (@samp{dynamic_cast} and @samp{typeid}). If you | |
1128 | don't use those parts of the language (or exception handling, which uses | |
1129 | @samp{dynamic_cast} internally), you can save some space by using this | |
1130 | flag. | |
1131 | ||
1dc5fc4b JM |
1132 | @item -fstrict-prototype |
1133 | Within an @samp{extern "C"} linkage specification, treat a function | |
1134 | declaration with no arguments, such as @samp{int foo ();}, as declaring | |
1135 | the function to take no arguments. Normally, such a declaration means | |
1136 | that the function @code{foo} can take any combination of arguments, as | |
1137 | in C. @samp{-pedantic} implies @samp{-fstrict-prototype} unless | |
1138 | overridden with @samp{-fno-strict-prototype}. | |
1139 | ||
1140 | Specifying this option will also suppress implicit declarations of | |
1141 | functions. | |
1142 | ||
1143 | This flag no longer affects declarations with C++ linkage. | |
1144 | ||
53f23613 | 1145 | @item -fsquangle |
bd762873 | 1146 | @itemx -fno-squangle |
53f23613 BK |
1147 | @samp{-fsquangle} will enable a compressed form of name mangling for |
1148 | identifiers. In particular, it helps to shorten very long names by recognizing | |
1149 | types and class names which occur more than once, replacing them with special | |
1150 | short ID codes. This option also requires any C++ libraries being used to | |
1151 | be compiled with this option as well. The compiler has this disabled (the | |
1152 | equivalent of @samp{-fno-squangle}) by default. | |
1153 | ||
1dc5fc4b JM |
1154 | Like all options that change the ABI, all C++ code, @emph{including |
1155 | libgcc.a} must be built with the same setting of this option. | |
1156 | ||
1157 | @item -ftemplate-depth-@var{n} | |
1158 | Set the maximum instantiation depth for template classes to @var{n}. | |
1159 | A limit on the template instantiation depth is needed to detect | |
1160 | endless recursions during template class instantiation. ANSI/ISO C++ | |
1161 | conforming programs must not rely on a maximum depth greater than 17. | |
1162 | ||
74291a4b MM |
1163 | @item -fthis-is-variable |
1164 | Permit assignment to @code{this}. The incorporation of user-defined | |
1165 | free store management into C++ has made assignment to @samp{this} an | |
1166 | anachronism. Therefore, by default it is invalid to assign to | |
1167 | @code{this} within a class member function; that is, GNU C++ treats | |
1168 | @samp{this} in a member function of class @code{X} as a non-lvalue of | |
1169 | type @samp{X *}. However, for backwards compatibility, you can make it | |
1170 | valid with @samp{-fthis-is-variable}. | |
1171 | ||
1172 | @item -fvtable-thunks | |
1173 | Use @samp{thunks} to implement the virtual function dispatch table | |
1174 | (@samp{vtable}). The traditional (cfront-style) approach to | |
1175 | implementing vtables was to store a pointer to the function and two | |
1176 | offsets for adjusting the @samp{this} pointer at the call site. Newer | |
1177 | implementations store a single pointer to a @samp{thunk} function which | |
1178 | does any necessary adjustment and then calls the target function. | |
1179 | ||
f5a1b0d2 NC |
1180 | This option also enables a heuristic for controlling emission of |
1181 | vtables; if a class has any non-inline virtual functions, the vtable | |
1182 | will be emitted in the translation unit containing the first one of | |
1183 | those. | |
1184 | ||
1dc5fc4b JM |
1185 | Like all options that change the ABI, all C++ code, @emph{including |
1186 | libgcc.a} must be built with the same setting of this option. | |
861bb6c1 | 1187 | |
74291a4b MM |
1188 | @item -nostdinc++ |
1189 | Do not search for header files in the standard directories specific to | |
1190 | C++, but do still search the other standard directories. (This option | |
e5e809f4 | 1191 | is used when building the C++ library.) |
74291a4b MM |
1192 | @end table |
1193 | ||
1194 | In addition, these optimization, warning, and code generation options | |
1195 | have meanings only for C++ programs: | |
1196 | ||
1197 | @table @code | |
1198 | @item -fno-default-inline | |
1199 | Do not assume @samp{inline} for functions defined inside a class scope. | |
1dc5fc4b JM |
1200 | @xref{Optimize Options,,Options That Control Optimization}. Note that these |
1201 | functions will have linkage like inline functions; they just won't be | |
1202 | inlined by default. | |
74291a4b | 1203 | |
bba975d4 JM |
1204 | @item -Wctor-dtor-privacy (C++ only) |
1205 | Warn when a class seems unusable, because all the constructors or | |
1206 | destructors in a class are private and the class has no friends or | |
1207 | public static member functions. | |
1208 | ||
1209 | @item -Wnon-virtual-dtor (C++ only) | |
1210 | Warn when a class declares a non-virtual destructor that should probably | |
1211 | be virtual, because it looks like the class will be used polymorphically. | |
1212 | ||
1213 | @item -Wreorder (C++ only) | |
1214 | @cindex reordering, warning | |
1215 | @cindex warning for reordering of member initializers | |
1216 | Warn when the order of member initializers given in the code does not | |
1217 | match the order in which they must be executed. For instance: | |
1218 | ||
1219 | @smallexample | |
1220 | struct A @{ | |
1221 | int i; | |
1222 | int j; | |
1223 | A(): j (0), i (1) @{ @} | |
1224 | @}; | |
1225 | @end smallexample | |
1226 | ||
1227 | Here the compiler will warn that the member initializers for @samp{i} | |
1228 | and @samp{j} will be rearranged to match the declaration order of the | |
1229 | members. | |
1230 | @end table | |
1231 | ||
1232 | The following @samp{-W@dots{}} options are not affected by @samp{-Wall}. | |
1233 | ||
1234 | @table @code | |
1235 | @item -Weffc++ (C++ only) | |
1236 | Warn about violations of various style guidelines from Scott Meyers' | |
1237 | @cite{Effective C++} books. If you use this option, you should be aware | |
1238 | that the standard library headers do not obey all of these guidelines; | |
1239 | you can use @samp{grep -v} to filter out those warnings. | |
1240 | ||
2de45c06 ML |
1241 | @item -Wno-deprecated (C++ only) |
1242 | Do not warn about usage of deprecated features. @xref{Deprecated Features}. | |
1243 | ||
bba975d4 JM |
1244 | @item -Wno-non-template-friend (C++ only) |
1245 | Disable warnings when non-templatized friend functions are declared | |
1246 | within a template. With the advent of explicit template specification | |
1247 | support in g++, if the name of the friend is an unqualified-id (ie, | |
1248 | @samp{friend foo(int)}), the C++ language specification demands that the | |
1249 | friend declare or define an ordinary, nontemplate function. (Section | |
1250 | 14.5.3). Before g++ implemented explicit specification, unqualified-ids | |
1251 | could be interpreted as a particular specialization of a templatized | |
1252 | function. Because this non-conforming behavior is no longer the default | |
1253 | behavior for g++, @samp{-Wnon-template-friend} allows the compiler to | |
1254 | check existing code for potential trouble spots, and is on by default. | |
1255 | This new compiler behavior can also be turned off with the flag | |
1256 | @samp{-fguiding-decls}, which activates the older, non-specification | |
1257 | compiler code, or with @samp{-Wno-non-template-friend} which keeps the | |
1258 | conformant compiler code but disables the helpful warning. | |
1259 | ||
1260 | @item -Wold-style-cast (C++ only) | |
1261 | Warn if an old-style (C-style) cast is used within a C++ program. The | |
1262 | new-style casts (@samp{static_cast}, @samp{reinterpret_cast}, and | |
1263 | @samp{const_cast}) are less vulnerable to unintended effects. | |
1264 | ||
1265 | @item -Woverloaded-virtual (C++ only) | |
1266 | @cindex overloaded virtual fn, warning | |
1267 | @cindex warning for overloaded virtual fn | |
1268 | Warn when a derived class function declaration may be an error in | |
1269 | defining a virtual function. In a derived class, the | |
1270 | definitions of virtual functions must match the type signature of a | |
1271 | virtual function declared in the base class. With this option, the | |
1272 | compiler warns when you define a function with the same name as a | |
1273 | virtual function, but with a type signature that does not match any | |
1274 | declarations from the base class. | |
1275 | ||
1276 | @item -Wno-pmf-conversions (C++ only) | |
1277 | Disable the diagnostic for converting a bound pointer to member function | |
1278 | to a plain pointer. | |
1279 | ||
1280 | @item -Wsign-promo (C++ only) | |
1281 | Warn when overload resolution chooses a promotion from unsigned or | |
1282 | enumeral type to a signed type over a conversion to an unsigned type of | |
1283 | the same size. Previous versions of g++ would try to preserve | |
1284 | unsignedness, but the standard mandates the current behavior. | |
1285 | ||
1286 | @item -Wsynth (C++ only) | |
1287 | @cindex warning for synthesized methods | |
1288 | @cindex synthesized methods, warning | |
1289 | Warn when g++'s synthesis behavior does not match that of cfront. For | |
1290 | instance: | |
1291 | ||
1292 | @smallexample | |
1293 | struct A @{ | |
1294 | operator int (); | |
1295 | A& operator = (int); | |
1296 | @}; | |
1297 | ||
1298 | main () | |
1299 | @{ | |
1300 | A a,b; | |
1301 | a = b; | |
1302 | @} | |
1303 | @end smallexample | |
74291a4b | 1304 | |
bba975d4 JM |
1305 | In this example, g++ will synthesize a default @samp{A& operator = |
1306 | (const A&);}, while cfront will use the user-defined @samp{operator =}. | |
74291a4b MM |
1307 | @end table |
1308 | ||
1309 | @node Warning Options | |
1310 | @section Options to Request or Suppress Warnings | |
1311 | @cindex options to control warnings | |
1312 | @cindex warning messages | |
1313 | @cindex messages, warning | |
1314 | @cindex suppressing warnings | |
1315 | ||
1316 | Warnings are diagnostic messages that report constructions which | |
1317 | are not inherently erroneous but which are risky or suggest there | |
1318 | may have been an error. | |
1319 | ||
1320 | You can request many specific warnings with options beginning @samp{-W}, | |
1321 | for example @samp{-Wimplicit} to request warnings on implicit | |
1322 | declarations. Each of these specific warning options also has a | |
1323 | negative form beginning @samp{-Wno-} to turn off warnings; | |
1324 | for example, @samp{-Wno-implicit}. This manual lists only one of the | |
1325 | two forms, whichever is not the default. | |
1326 | ||
0c2d1a2a | 1327 | These options control the amount and kinds of warnings produced by GCC: |
74291a4b MM |
1328 | |
1329 | @table @code | |
1330 | @cindex syntax checking | |
1331 | @item -fsyntax-only | |
1332 | Check the code for syntax errors, but don't do anything beyond that. | |
1333 | ||
1334 | @item -pedantic | |
b1d16193 JL |
1335 | Issue all the warnings demanded by strict ANSI C and ISO C++; |
1336 | reject all programs that use forbidden extensions. | |
74291a4b | 1337 | |
b1d16193 | 1338 | Valid ANSI C and ISO C++ programs should compile properly with or without |
74291a4b | 1339 | this option (though a rare few will require @samp{-ansi}). However, |
b1d16193 JL |
1340 | without this option, certain GNU extensions and traditional C and C++ |
1341 | features are supported as well. With this option, they are rejected. | |
74291a4b MM |
1342 | |
1343 | @samp{-pedantic} does not cause warning messages for use of the | |
1344 | alternate keywords whose names begin and end with @samp{__}. Pedantic | |
1345 | warnings are also disabled in the expression that follows | |
1346 | @code{__extension__}. However, only system header files should use | |
1347 | these escape routes; application programs should avoid them. | |
1348 | @xref{Alternate Keywords}. | |
1349 | ||
1350 | This option is not intended to be @i{useful}; it exists only to satisfy | |
0c2d1a2a | 1351 | pedants who would otherwise claim that GCC fails to support the ANSI |
74291a4b MM |
1352 | standard. |
1353 | ||
1354 | Some users try to use @samp{-pedantic} to check programs for strict ANSI | |
1355 | C conformance. They soon find that it does not do quite what they want: | |
1356 | it finds some non-ANSI practices, but not all---only those for which | |
1357 | ANSI C @emph{requires} a diagnostic. | |
1358 | ||
1359 | A feature to report any failure to conform to ANSI C might be useful in | |
1360 | some instances, but would require considerable additional work and would | |
892d0a6d AO |
1361 | be quite different from @samp{-pedantic}. We don't have plans to |
1362 | support such a feature in the near future. | |
74291a4b MM |
1363 | |
1364 | @item -pedantic-errors | |
1365 | Like @samp{-pedantic}, except that errors are produced rather than | |
1366 | warnings. | |
1367 | ||
1368 | @item -w | |
1369 | Inhibit all warning messages. | |
1370 | ||
1371 | @item -Wno-import | |
1372 | Inhibit warning messages about the use of @samp{#import}. | |
1373 | ||
1374 | @item -Wchar-subscripts | |
1375 | Warn if an array subscript has type @code{char}. This is a common cause | |
1376 | of error, as programmers often forget that this type is signed on some | |
1377 | machines. | |
1378 | ||
1379 | @item -Wcomment | |
1380 | Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} | |
1381 | comment, or whenever a Backslash-Newline appears in a @samp{//} comment. | |
1382 | ||
1383 | @item -Wformat | |
1384 | Check calls to @code{printf} and @code{scanf}, etc., to make sure that | |
1385 | the arguments supplied have types appropriate to the format string | |
1386 | specified. | |
1387 | ||
e9a25f70 JL |
1388 | @item -Wimplicit-int |
1389 | Warn when a declaration does not specify a type. | |
1390 | ||
f5963e61 JL |
1391 | @item -Wimplicit-function-declaration |
1392 | @itemx -Werror-implicit-function-declaration | |
1393 | Give a warning (or error) whenever a function is used before being | |
1394 | declared. | |
e9a25f70 | 1395 | |
74291a4b | 1396 | @item -Wimplicit |
e5e809f4 JL |
1397 | Same as @samp{-Wimplicit-int} and @samp{-Wimplicit-function-}@* |
1398 | @samp{declaration}. | |
861bb6c1 JL |
1399 | |
1400 | @item -Wmain | |
1401 | Warn if the type of @samp{main} is suspicious. @samp{main} should be a | |
1402 | function with external linkage, returning int, taking either zero | |
1403 | arguments, two, or three arguments of appropriate types. | |
4a870dba JM |
1404 | |
1405 | @item -Wmultichar | |
1406 | Warn if a multicharacter constant (@samp{'FOOF'}) is used. Usually they | |
1407 | indicate a typo in the user's code, as they have implementation-defined | |
1408 | values, and should not be used in portable code. | |
861bb6c1 | 1409 | |
74291a4b MM |
1410 | @item -Wparentheses |
1411 | Warn if parentheses are omitted in certain contexts, such | |
1412 | as when there is an assignment in a context where a truth value | |
1413 | is expected, or when operators are nested whose precedence people | |
1414 | often get confused about. | |
1415 | ||
e9a25f70 JL |
1416 | Also warn about constructions where there may be confusion to which |
1417 | @code{if} statement an @code{else} branch belongs. Here is an example of | |
1418 | such a case: | |
1419 | ||
1420 | @smallexample | |
1421 | @{ | |
1422 | if (a) | |
1423 | if (b) | |
1424 | foo (); | |
1425 | else | |
1426 | bar (); | |
1427 | @} | |
1428 | @end smallexample | |
1429 | ||
1430 | In C, every @code{else} branch belongs to the innermost possible @code{if} | |
1431 | statement, which in this example is @code{if (b)}. This is often not | |
1432 | what the programmer expected, as illustrated in the above example by | |
1433 | indentation the programmer chose. When there is the potential for this | |
1434 | confusion, GNU C will issue a warning when this flag is specified. | |
1435 | To eliminate the warning, add explicit braces around the innermost | |
1436 | @code{if} statement so there is no way the @code{else} could belong to | |
1437 | the enclosing @code{if}. The resulting code would look like this: | |
1438 | ||
1439 | @smallexample | |
1440 | @{ | |
1441 | if (a) | |
1442 | @{ | |
1443 | if (b) | |
1444 | foo (); | |
1445 | else | |
1446 | bar (); | |
1447 | @} | |
1448 | @} | |
1449 | @end smallexample | |
1450 | ||
74291a4b MM |
1451 | @item -Wreturn-type |
1452 | Warn whenever a function is defined with a return-type that defaults | |
1453 | to @code{int}. Also warn about any @code{return} statement with no | |
1454 | return-value in a function whose return-type is not @code{void}. | |
1455 | ||
1456 | @item -Wswitch | |
1457 | Warn whenever a @code{switch} statement has an index of enumeral type | |
1458 | and lacks a @code{case} for one or more of the named codes of that | |
1459 | enumeration. (The presence of a @code{default} label prevents this | |
1460 | warning.) @code{case} labels outside the enumeration range also | |
1461 | provoke warnings when this option is used. | |
1462 | ||
1463 | @item -Wtrigraphs | |
1464 | Warn if any trigraphs are encountered (assuming they are enabled). | |
1465 | ||
1466 | @item -Wunused | |
1467 | Warn whenever a variable is unused aside from its declaration, | |
1468 | whenever a function is declared static but never defined, whenever a | |
1469 | label is declared but not used, and whenever a statement computes a | |
1470 | result that is explicitly not used. | |
1471 | ||
956d6950 JL |
1472 | In order to get a warning about an unused function parameter, you must |
1473 | specify both @samp{-W} and @samp{-Wunused}. | |
1474 | ||
74291a4b | 1475 | To suppress this warning for an expression, simply cast it to void. For |
736b02fd | 1476 | unused variables, parameters and labels, use the @samp{unused} attribute |
74291a4b MM |
1477 | (@pxref{Variable Attributes}). |
1478 | ||
1479 | @item -Wuninitialized | |
c5c76735 JL |
1480 | Warn if an automatic variable is used without first being initialized or |
1481 | if a variable may be clobbered by a @code{setjmp} call. | |
74291a4b MM |
1482 | |
1483 | These warnings are possible only in optimizing compilation, | |
1484 | because they require data flow information that is computed only | |
1485 | when optimizing. If you don't specify @samp{-O}, you simply won't | |
1486 | get these warnings. | |
1487 | ||
1488 | These warnings occur only for variables that are candidates for | |
1489 | register allocation. Therefore, they do not occur for a variable that | |
1490 | is declared @code{volatile}, or whose address is taken, or whose size | |
1491 | is other than 1, 2, 4 or 8 bytes. Also, they do not occur for | |
1492 | structures, unions or arrays, even when they are in registers. | |
1493 | ||
1494 | Note that there may be no warning about a variable that is used only | |
1495 | to compute a value that itself is never used, because such | |
1496 | computations may be deleted by data flow analysis before the warnings | |
1497 | are printed. | |
1498 | ||
0c2d1a2a | 1499 | These warnings are made optional because GCC is not smart |
74291a4b MM |
1500 | enough to see all the reasons why the code might be correct |
1501 | despite appearing to have an error. Here is one example of how | |
1502 | this can happen: | |
1503 | ||
1504 | @smallexample | |
1505 | @{ | |
1506 | int x; | |
1507 | switch (y) | |
1508 | @{ | |
1509 | case 1: x = 1; | |
1510 | break; | |
1511 | case 2: x = 4; | |
1512 | break; | |
1513 | case 3: x = 5; | |
1514 | @} | |
1515 | foo (x); | |
1516 | @} | |
1517 | @end smallexample | |
1518 | ||
1519 | @noindent | |
1520 | If the value of @code{y} is always 1, 2 or 3, then @code{x} is | |
0c2d1a2a | 1521 | always initialized, but GCC doesn't know this. Here is |
74291a4b MM |
1522 | another common case: |
1523 | ||
1524 | @smallexample | |
1525 | @{ | |
1526 | int save_y; | |
1527 | if (change_y) save_y = y, y = new_y; | |
1528 | @dots{} | |
1529 | if (change_y) y = save_y; | |
1530 | @} | |
1531 | @end smallexample | |
1532 | ||
1533 | @noindent | |
1534 | This has no bug because @code{save_y} is used only if it is set. | |
1535 | ||
20300b05 GK |
1536 | @cindex @code{longjmp} warnings |
1537 | This option also warns when a nonvolatile automatic variable might be | |
c5c76735 JL |
1538 | changed by a call to @code{longjmp}. These warnings as well are possible |
1539 | only in optimizing compilation. | |
20300b05 GK |
1540 | |
1541 | The compiler sees only the calls to @code{setjmp}. It cannot know | |
1542 | where @code{longjmp} will be called; in fact, a signal handler could | |
1543 | call it at any point in the code. As a result, you may get a warning | |
1544 | even when there is in fact no problem because @code{longjmp} cannot | |
1545 | in fact be called at the place which would cause a problem. | |
1546 | ||
74291a4b MM |
1547 | Some spurious warnings can be avoided if you declare all the functions |
1548 | you use that never return as @code{noreturn}. @xref{Function | |
1549 | Attributes}. | |
1550 | ||
c5c76735 JL |
1551 | @item -Wreorder (C++ only) |
1552 | @cindex reordering, warning | |
1553 | @cindex warning for reordering of member initializers | |
1554 | Warn when the order of member initializers given in the code does not | |
1555 | match the order in which they must be executed. For instance: | |
1556 | ||
d300e551 NC |
1557 | @item -Wunknown-pragmas |
1558 | @cindex warning for unknown pragmas | |
1559 | @cindex unknown pragmas, warning | |
1560 | @cindex pragmas, warning of unknown | |
1561 | Warn when a #pragma directive is encountered which is not understood by | |
1562 | GCC. If this command line option is used, warnings will even be issued | |
1563 | for unknown pragmas in system header files. This is not the case if | |
1564 | the warnings were only enabled by the @samp{-Wall} command line option. | |
1565 | ||
74291a4b MM |
1566 | @item -Wall |
1567 | All of the above @samp{-W} options combined. This enables all the | |
1568 | warnings about constructions that some users consider questionable, and | |
1569 | that are easy to avoid (or modify to prevent the warning), even in | |
1570 | conjunction with macros. | |
1571 | @end table | |
1572 | ||
1573 | The following @samp{-W@dots{}} options are not implied by @samp{-Wall}. | |
1574 | Some of them warn about constructions that users generally do not | |
1575 | consider questionable, but which occasionally you might wish to check | |
1576 | for; others warn about constructions that are necessary or hard to avoid | |
1577 | in some cases, and there is no simple way to modify the code to suppress | |
1578 | the warning. | |
1579 | ||
1580 | @table @code | |
1581 | @item -W | |
1582 | Print extra warning messages for these events: | |
1583 | ||
1584 | @itemize @bullet | |
74291a4b MM |
1585 | @item |
1586 | A function can return either with or without a value. (Falling | |
1587 | off the end of the function body is considered returning without | |
1588 | a value.) For example, this function would evoke such a | |
1589 | warning: | |
1590 | ||
1591 | @smallexample | |
1592 | @group | |
1593 | foo (a) | |
1594 | @{ | |
1595 | if (a > 0) | |
1596 | return a; | |
1597 | @} | |
1598 | @end group | |
1599 | @end smallexample | |
1600 | ||
1601 | @item | |
1602 | An expression-statement or the left-hand side of a comma expression | |
1603 | contains no side effects. | |
1604 | To suppress the warning, cast the unused expression to void. | |
1605 | For example, an expression such as @samp{x[i,j]} will cause a warning, | |
1606 | but @samp{x[(void)i,j]} will not. | |
1607 | ||
1608 | @item | |
1609 | An unsigned value is compared against zero with @samp{<} or @samp{<=}. | |
1610 | ||
1611 | @item | |
1612 | A comparison like @samp{x<=y<=z} appears; this is equivalent to | |
1613 | @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from | |
1614 | that of ordinary mathematical notation. | |
1615 | ||
1616 | @item | |
1617 | Storage-class specifiers like @code{static} are not the first things in | |
1618 | a declaration. According to the C Standard, this usage is obsolescent. | |
1619 | ||
1620 | @item | |
1621 | If @samp{-Wall} or @samp{-Wunused} is also specified, warn about unused | |
1622 | arguments. | |
1623 | ||
e9a25f70 JL |
1624 | @item |
1625 | A comparison between signed and unsigned values could produce an | |
1626 | incorrect result when the signed value is converted to unsigned. | |
e5e809f4 | 1627 | (But don't warn if @samp{-Wno-sign-compare} is also specified.) |
e9a25f70 | 1628 | |
74291a4b MM |
1629 | @item |
1630 | An aggregate has a partly bracketed initializer. | |
1631 | For example, the following code would evoke such a warning, | |
1632 | because braces are missing around the initializer for @code{x.h}: | |
1633 | ||
1634 | @smallexample | |
1635 | struct s @{ int f, g; @}; | |
1636 | struct t @{ struct s h; int i; @}; | |
1637 | struct t x = @{ 1, 2, 3 @}; | |
1638 | @end smallexample | |
dbde0d5d BH |
1639 | |
1640 | @item | |
1641 | An aggregate has an initializer which does not initialize all members. | |
1642 | For example, the following code would cause such a warning, because | |
1643 | @code{x.h} would be implicitly initialized to zero: | |
1644 | ||
1645 | @smallexample | |
1646 | struct s @{ int f, g, h; @}; | |
1647 | struct s x = @{ 3, 4 @}; | |
1648 | @end smallexample | |
74291a4b MM |
1649 | @end itemize |
1650 | ||
1651 | @item -Wtraditional | |
1652 | Warn about certain constructs that behave differently in traditional and | |
1653 | ANSI C. | |
1654 | ||
1655 | @itemize @bullet | |
1656 | @item | |
1657 | Macro arguments occurring within string constants in the macro body. | |
1658 | These would substitute the argument in traditional C, but are part of | |
1659 | the constant in ANSI C. | |
1660 | ||
1661 | @item | |
1662 | A function declared external in one block and then used after the end of | |
1663 | the block. | |
1664 | ||
1665 | @item | |
1666 | A @code{switch} statement has an operand of type @code{long}. | |
db838bb8 KG |
1667 | |
1668 | @item | |
1669 | A non-@code{static} function declaration follows a @code{static} one. | |
1670 | This construct is not accepted by some traditional C compilers. | |
74291a4b MM |
1671 | @end itemize |
1672 | ||
861bb6c1 JL |
1673 | @item -Wundef |
1674 | Warn if an undefined identifier is evaluated in an @samp{#if} directive. | |
1675 | ||
74291a4b MM |
1676 | @item -Wshadow |
1677 | Warn whenever a local variable shadows another local variable. | |
1678 | ||
1679 | @item -Wid-clash-@var{len} | |
1680 | Warn whenever two distinct identifiers match in the first @var{len} | |
1681 | characters. This may help you prepare a program that will compile | |
1682 | with certain obsolete, brain-damaged compilers. | |
1683 | ||
1684 | @item -Wlarger-than-@var{len} | |
1685 | Warn whenever an object of larger than @var{len} bytes is defined. | |
1686 | ||
1687 | @item -Wpointer-arith | |
1688 | Warn about anything that depends on the ``size of'' a function type or | |
1689 | of @code{void}. GNU C assigns these types a size of 1, for | |
1690 | convenience in calculations with @code{void *} pointers and pointers | |
1691 | to functions. | |
1692 | ||
1693 | @item -Wbad-function-cast | |
1694 | Warn whenever a function call is cast to a non-matching type. | |
1695 | For example, warn if @code{int malloc()} is cast to @code{anything *}. | |
1696 | ||
1697 | @item -Wcast-qual | |
1698 | Warn whenever a pointer is cast so as to remove a type qualifier from | |
1699 | the target type. For example, warn if a @code{const char *} is cast | |
1700 | to an ordinary @code{char *}. | |
1701 | ||
1702 | @item -Wcast-align | |
1703 | Warn whenever a pointer is cast such that the required alignment of the | |
1704 | target is increased. For example, warn if a @code{char *} is cast to | |
1705 | an @code{int *} on machines where integers can only be accessed at | |
1706 | two- or four-byte boundaries. | |
1707 | ||
1708 | @item -Wwrite-strings | |
1709 | Give string constants the type @code{const char[@var{length}]} so that | |
1710 | copying the address of one into a non-@code{const} @code{char *} | |
1711 | pointer will get a warning. These warnings will help you find at | |
1712 | compile time code that can try to write into a string constant, but | |
1713 | only if you have been very careful about using @code{const} in | |
1714 | declarations and prototypes. Otherwise, it will just be a nuisance; | |
1715 | this is why we did not make @samp{-Wall} request these warnings. | |
1716 | ||
1717 | @item -Wconversion | |
1718 | Warn if a prototype causes a type conversion that is different from what | |
1719 | would happen to the same argument in the absence of a prototype. This | |
1720 | includes conversions of fixed point to floating and vice versa, and | |
1721 | conversions changing the width or signedness of a fixed point argument | |
1722 | except when the same as the default promotion. | |
1723 | ||
1724 | Also, warn if a negative integer constant expression is implicitly | |
1725 | converted to an unsigned type. For example, warn about the assignment | |
1726 | @code{x = -1} if @code{x} is unsigned. But do not warn about explicit | |
1727 | casts like @code{(unsigned) -1}. | |
1728 | ||
e9a25f70 JL |
1729 | @item -Wsign-compare |
1730 | @cindex warning for comparison of signed and unsigned values | |
1731 | @cindex comparison of signed and unsigned values, warning | |
1732 | @cindex signed and unsigned values, comparison warning | |
1733 | Warn when a comparison between signed and unsigned values could produce | |
1734 | an incorrect result when the signed value is converted to unsigned. | |
1735 | This warning is also enabled by @samp{-W}; to get the other warnings | |
1736 | of @samp{-W} without this warning, use @samp{-W -Wno-sign-compare}. | |
1737 | ||
74291a4b MM |
1738 | @item -Waggregate-return |
1739 | Warn if any functions that return structures or unions are defined or | |
1740 | called. (In languages where you can return an array, this also elicits | |
1741 | a warning.) | |
1742 | ||
1743 | @item -Wstrict-prototypes | |
1744 | Warn if a function is declared or defined without specifying the | |
1745 | argument types. (An old-style function definition is permitted without | |
1746 | a warning if preceded by a declaration which specifies the argument | |
1747 | types.) | |
1748 | ||
1749 | @item -Wmissing-prototypes | |
1750 | Warn if a global function is defined without a previous prototype | |
1751 | declaration. This warning is issued even if the definition itself | |
1752 | provides a prototype. The aim is to detect global functions that fail | |
1753 | to be declared in header files. | |
1754 | ||
1755 | @item -Wmissing-declarations | |
1756 | Warn if a global function is defined without a previous declaration. | |
1757 | Do so even if the definition itself provides a prototype. | |
1758 | Use this option to detect global functions that are not declared in | |
1759 | header files. | |
1760 | ||
0ca3fb0a KG |
1761 | @item -Wmissing-noreturn |
1762 | Warn about functions which might be candidates for attribute @code{noreturn}. | |
1763 | Note these are only possible candidates, not absolute ones. Care should | |
1764 | be taken to manually verify functions actually do not ever return before | |
1765 | adding the @code{noreturn} attribute, otherwise subtle code generation | |
1766 | bugs could be introduced. | |
1767 | ||
74291a4b MM |
1768 | @item -Wredundant-decls |
1769 | Warn if anything is declared more than once in the same scope, even in | |
1770 | cases where multiple declaration is valid and changes nothing. | |
1771 | ||
1772 | @item -Wnested-externs | |
252215a7 | 1773 | Warn if an @code{extern} declaration is encountered within a function. |
74291a4b | 1774 | |
312f6255 GK |
1775 | @item -Wunreachable-code |
1776 | Warn if the compiler detects that code will never be executed. | |
1777 | ||
1778 | This option is intended to warn when the compiler detects that at | |
1779 | least a whole line of source code will never be executed, because | |
1780 | some condition is never satisfied or because it is after a | |
1781 | procedure that never returns. | |
1782 | ||
1783 | It is possible for this option to produce a warning even though there | |
1784 | are circumstances under which part of the affected line can be executed, | |
1785 | so care should be taken when removing apparently-unreachable code. | |
1786 | ||
1787 | For instance, when a function is inlined, a warning may mean that the | |
1788 | line is unreachable in only one inlined copy of the function. | |
1789 | ||
1790 | This option is not made part of @samp{-Wall} because in a debugging | |
1791 | version of a program there is often substantial code which checks | |
1792 | correct functioning of the program and is, hopefully, unreachable | |
1793 | because the program does work. Another common use of unreachable | |
1794 | code is to provide behaviour which is selectable at compile-time. | |
1795 | ||
74291a4b | 1796 | @item -Winline |
c5c76735 | 1797 | Warn if a function can not be inlined and it was declared as inline. |
74291a4b | 1798 | |
795add94 VM |
1799 | @item -Wlong-long |
1800 | Warn if @samp{long long} type is used. This is default. To inhibit | |
1801 | the warning messages, use @samp{-Wno-long-long}. Flags | |
1802 | @samp{-Wlong-long} and @samp{-Wno-long-long} are taken into account | |
1803 | only when @samp{-pedantic} flag is used. | |
1804 | ||
74291a4b MM |
1805 | @item -Werror |
1806 | Make all warnings into errors. | |
1807 | @end table | |
1808 | ||
1809 | @node Debugging Options | |
0c2d1a2a | 1810 | @section Options for Debugging Your Program or GCC |
74291a4b MM |
1811 | @cindex options, debugging |
1812 | @cindex debugging information options | |
1813 | ||
0c2d1a2a | 1814 | GCC has various special options that are used for debugging |
74291a4b MM |
1815 | either your program or GCC: |
1816 | ||
1817 | @table @code | |
1818 | @item -g | |
1819 | Produce debugging information in the operating system's native format | |
1820 | (stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging | |
1821 | information. | |
1822 | ||
1823 | On most systems that use stabs format, @samp{-g} enables use of extra | |
1824 | debugging information that only GDB can use; this extra information | |
1825 | makes debugging work better in GDB but will probably make other debuggers | |
1826 | crash or | |
1827 | refuse to read the program. If you want to control for certain whether | |
1828 | to generate the extra information, use @samp{-gstabs+}, @samp{-gstabs}, | |
861bb6c1 | 1829 | @samp{-gxcoff+}, @samp{-gxcoff}, @samp{-gdwarf-1+}, or @samp{-gdwarf-1} |
74291a4b MM |
1830 | (see below). |
1831 | ||
0c2d1a2a | 1832 | Unlike most other C compilers, GCC allows you to use @samp{-g} with |
74291a4b MM |
1833 | @samp{-O}. The shortcuts taken by optimized code may occasionally |
1834 | produce surprising results: some variables you declared may not exist | |
1835 | at all; flow of control may briefly move where you did not expect it; | |
1836 | some statements may not be executed because they compute constant | |
1837 | results or their values were already at hand; some statements may | |
1838 | execute in different places because they were moved out of loops. | |
1839 | ||
1840 | Nevertheless it proves possible to debug optimized output. This makes | |
1841 | it reasonable to use the optimizer for programs that might have bugs. | |
1842 | ||
0c2d1a2a | 1843 | The following options are useful when GCC is generated with the |
74291a4b MM |
1844 | capability for more than one debugging format. |
1845 | ||
1846 | @item -ggdb | |
861bb6c1 JL |
1847 | Produce debugging information for use by GDB. This means to use the |
1848 | most expressive format available (DWARF 2, stabs, or the native format | |
1849 | if neither of those are supported), including GDB extensions if at all | |
1850 | possible. | |
74291a4b MM |
1851 | |
1852 | @item -gstabs | |
1853 | Produce debugging information in stabs format (if that is supported), | |
1854 | without GDB extensions. This is the format used by DBX on most BSD | |
1855 | systems. On MIPS, Alpha and System V Release 4 systems this option | |
1856 | produces stabs debugging output which is not understood by DBX or SDB. | |
1857 | On System V Release 4 systems this option requires the GNU assembler. | |
1858 | ||
1859 | @item -gstabs+ | |
1860 | Produce debugging information in stabs format (if that is supported), | |
1861 | using GNU extensions understood only by the GNU debugger (GDB). The | |
1862 | use of these extensions is likely to make other debuggers crash or | |
1863 | refuse to read the program. | |
1864 | ||
1865 | @item -gcoff | |
1866 | Produce debugging information in COFF format (if that is supported). | |
1867 | This is the format used by SDB on most System V systems prior to | |
1868 | System V Release 4. | |
1869 | ||
1870 | @item -gxcoff | |
1871 | Produce debugging information in XCOFF format (if that is supported). | |
1872 | This is the format used by the DBX debugger on IBM RS/6000 systems. | |
1873 | ||
1874 | @item -gxcoff+ | |
1875 | Produce debugging information in XCOFF format (if that is supported), | |
1876 | using GNU extensions understood only by the GNU debugger (GDB). The | |
1877 | use of these extensions is likely to make other debuggers crash or | |
1878 | refuse to read the program, and may cause assemblers other than the GNU | |
1879 | assembler (GAS) to fail with an error. | |
1880 | ||
1881 | @item -gdwarf | |
861bb6c1 JL |
1882 | Produce debugging information in DWARF version 1 format (if that is |
1883 | supported). This is the format used by SDB on most System V Release 4 | |
1884 | systems. | |
74291a4b MM |
1885 | |
1886 | @item -gdwarf+ | |
861bb6c1 JL |
1887 | Produce debugging information in DWARF version 1 format (if that is |
1888 | supported), using GNU extensions understood only by the GNU debugger | |
1889 | (GDB). The use of these extensions is likely to make other debuggers | |
1890 | crash or refuse to read the program. | |
1891 | ||
1892 | @item -gdwarf-2 | |
1893 | Produce debugging information in DWARF version 2 format (if that is | |
1894 | supported). This is the format used by DBX on IRIX 6. | |
74291a4b MM |
1895 | |
1896 | @item -g@var{level} | |
1897 | @itemx -ggdb@var{level} | |
1898 | @itemx -gstabs@var{level} | |
1899 | @itemx -gcoff@var{level} | |
1900 | @itemx -gxcoff@var{level} | |
1901 | @itemx -gdwarf@var{level} | |
861bb6c1 | 1902 | @itemx -gdwarf-2@var{level} |
74291a4b MM |
1903 | Request debugging information and also use @var{level} to specify how |
1904 | much information. The default level is 2. | |
1905 | ||
1906 | Level 1 produces minimal information, enough for making backtraces in | |
1907 | parts of the program that you don't plan to debug. This includes | |
1908 | descriptions of functions and external variables, but no information | |
1909 | about local variables and no line numbers. | |
1910 | ||
1911 | Level 3 includes extra information, such as all the macro definitions | |
1912 | present in the program. Some debuggers support macro expansion when | |
1913 | you use @samp{-g3}. | |
1914 | ||
1915 | @cindex @code{prof} | |
1916 | @item -p | |
1917 | Generate extra code to write profile information suitable for the | |
1918 | analysis program @code{prof}. You must use this option when compiling | |
1919 | the source files you want data about, and you must also use it when | |
1920 | linking. | |
1921 | ||
1922 | @cindex @code{gprof} | |
1923 | @item -pg | |
1924 | Generate extra code to write profile information suitable for the | |
1925 | analysis program @code{gprof}. You must use this option when compiling | |
1926 | the source files you want data about, and you must also use it when | |
1927 | linking. | |
1928 | ||
1929 | @cindex @code{tcov} | |
1930 | @item -a | |
1931 | Generate extra code to write profile information for basic blocks, which will | |
1932 | record the number of times each basic block is executed, the basic block start | |
1933 | address, and the function name containing the basic block. If @samp{-g} is | |
1934 | used, the line number and filename of the start of the basic block will also be | |
1935 | recorded. If not overridden by the machine description, the default action is | |
1936 | to append to the text file @file{bb.out}. | |
1937 | ||
1938 | This data could be analyzed by a program like @code{tcov}. Note, | |
1939 | however, that the format of the data is not what @code{tcov} expects. | |
1940 | Eventually GNU @code{gprof} should be extended to process this data. | |
1941 | ||
898f531b JL |
1942 | @item -Q |
1943 | Makes the compiler print out each function name as it is compiled, and | |
1944 | print some statistics about each pass when it finishes. | |
1945 | ||
74291a4b MM |
1946 | @item -ax |
1947 | Generate extra code to profile basic blocks. Your executable will | |
1948 | produce output that is a superset of that produced when @samp{-a} is | |
1949 | used. Additional output is the source and target address of the basic | |
1950 | blocks where a jump takes place, the number of times a jump is executed, | |
1951 | and (optionally) the complete sequence of basic blocks being executed. | |
1952 | The output is appended to file @file{bb.out}. | |
1953 | ||
1954 | You can examine different profiling aspects without recompilation. Your | |
956d6950 | 1955 | executable will read a list of function names from file @file{bb.in}. |
74291a4b MM |
1956 | Profiling starts when a function on the list is entered and stops when |
1957 | that invocation is exited. To exclude a function from profiling, prefix | |
1958 | its name with `-'. If a function name is not unique, you can | |
1959 | disambiguate it by writing it in the form | |
1960 | @samp{/path/filename.d:functionname}. Your executable will write the | |
1961 | available paths and filenames in file @file{bb.out}. | |
1962 | ||
1963 | Several function names have a special meaning: | |
1964 | @table @code | |
1965 | @item __bb_jumps__ | |
1966 | Write source, target and frequency of jumps to file @file{bb.out}. | |
1967 | @item __bb_hidecall__ | |
1968 | Exclude function calls from frequency count. | |
1969 | @item __bb_showret__ | |
1970 | Include function returns in frequency count. | |
1971 | @item __bb_trace__ | |
1972 | Write the sequence of basic blocks executed to file @file{bbtrace.gz}. | |
1973 | The file will be compressed using the program @samp{gzip}, which must | |
1974 | exist in your @code{PATH}. On systems without the @samp{popen} | |
1975 | function, the file will be named @file{bbtrace} and will not be | |
1976 | compressed. @strong{Profiling for even a few seconds on these systems | |
1977 | will produce a very large file.} Note: @code{__bb_hidecall__} and | |
1978 | @code{__bb_showret__} will not affect the sequence written to | |
1979 | @file{bbtrace.gz}. | |
1980 | @end table | |
1981 | ||
1982 | Here's a short example using different profiling parameters | |
1983 | in file @file{bb.in}. Assume function @code{foo} consists of basic blocks | |
1984 | 1 and 2 and is called twice from block 3 of function @code{main}. After | |
1985 | the calls, block 3 transfers control to block 4 of @code{main}. | |
1986 | ||
1987 | With @code{__bb_trace__} and @code{main} contained in file @file{bb.in}, | |
1988 | the following sequence of blocks is written to file @file{bbtrace.gz}: | |
1989 | 0 3 1 2 1 2 4. The return from block 2 to block 3 is not shown, because | |
1990 | the return is to a point inside the block and not to the top. The | |
1991 | block address 0 always indicates, that control is transferred | |
1992 | to the trace from somewhere outside the observed functions. With | |
1993 | @samp{-foo} added to @file{bb.in}, the blocks of function | |
1994 | @code{foo} are removed from the trace, so only 0 3 4 remains. | |
1995 | ||
1996 | With @code{__bb_jumps__} and @code{main} contained in file @file{bb.in}, | |
1997 | jump frequencies will be written to file @file{bb.out}. The | |
1998 | frequencies are obtained by constructing a trace of blocks | |
1999 | and incrementing a counter for every neighbouring pair of blocks | |
2000 | in the trace. The trace 0 3 1 2 1 2 4 displays the following | |
2001 | frequencies: | |
2002 | ||
2003 | @example | |
2004 | Jump from block 0x0 to block 0x3 executed 1 time(s) | |
2005 | Jump from block 0x3 to block 0x1 executed 1 time(s) | |
2006 | Jump from block 0x1 to block 0x2 executed 2 time(s) | |
2007 | Jump from block 0x2 to block 0x1 executed 1 time(s) | |
2008 | Jump from block 0x2 to block 0x4 executed 1 time(s) | |
2009 | @end example | |
2010 | ||
2011 | With @code{__bb_hidecall__}, control transfer due to call instructions | |
2012 | is removed from the trace, that is the trace is cut into three parts: 0 | |
2013 | 3 4, 0 1 2 and 0 1 2. With @code{__bb_showret__}, control transfer due | |
2014 | to return instructions is added to the trace. The trace becomes: 0 3 1 | |
2015 | 2 3 1 2 3 4. Note, that this trace is not the same, as the sequence | |
2016 | written to @file{bbtrace.gz}. It is solely used for counting jump | |
2017 | frequencies. | |
2018 | ||
861bb6c1 JL |
2019 | @item -fprofile-arcs |
2020 | Instrument @dfn{arcs} during compilation. For each function of your | |
0c2d1a2a | 2021 | program, GCC creates a program flow graph, then finds a spanning tree |
861bb6c1 JL |
2022 | for the graph. Only arcs that are not on the spanning tree have to be |
2023 | instrumented: the compiler adds code to count the number of times that these | |
2024 | arcs are executed. When an arc is the only exit or only entrance to a | |
2025 | block, the instrumentation code can be added to the block; otherwise, a | |
2026 | new basic block must be created to hold the instrumentation code. | |
2027 | ||
2028 | Since not every arc in the program must be instrumented, programs | |
2029 | compiled with this option run faster than programs compiled with | |
2030 | @samp{-a}, which adds instrumentation code to every basic block in the | |
2031 | program. The tradeoff: since @code{gcov} does not have | |
2032 | execution counts for all branches, it must start with the execution | |
2033 | counts for the instrumented branches, and then iterate over the program | |
2034 | flow graph until the entire graph has been solved. Hence, @code{gcov} | |
2035 | runs a little more slowly than a program which uses information from | |
2036 | @samp{-a}. | |
2037 | ||
2038 | @samp{-fprofile-arcs} also makes it possible to estimate branch | |
2039 | probabilities, and to calculate basic block execution counts. In | |
2040 | general, basic block execution counts do not give enough information to | |
2041 | estimate all branch probabilities. When the compiled program exits, it | |
2042 | saves the arc execution counts to a file called | |
2043 | @file{@var{sourcename}.da}. Use the compiler option | |
2044 | @samp{-fbranch-probabilities} (@pxref{Optimize Options,,Options that | |
2045 | Control Optimization}) when recompiling, to optimize using estimated | |
2046 | branch probabilities. | |
2047 | ||
2048 | @need 2000 | |
2049 | @item -ftest-coverage | |
2050 | Create data files for the @code{gcov} code-coverage utility | |
0c2d1a2a | 2051 | (@pxref{Gcov,, @code{gcov}: a GCC Test Coverage Program}). |
861bb6c1 JL |
2052 | The data file names begin with the name of your source file: |
2053 | ||
2054 | @table @code | |
2055 | @item @var{sourcename}.bb | |
2056 | A mapping from basic blocks to line numbers, which @code{gcov} uses to | |
2057 | associate basic block execution counts with line numbers. | |
2058 | ||
2059 | @item @var{sourcename}.bbg | |
2060 | A list of all arcs in the program flow graph. This allows @code{gcov} | |
2061 | to reconstruct the program flow graph, so that it can compute all basic | |
2062 | block and arc execution counts from the information in the | |
2063 | @code{@var{sourcename}.da} file (this last file is the output from | |
2064 | @samp{-fprofile-arcs}). | |
2065 | @end table | |
2066 | ||
956d6950 JL |
2067 | @item -Q |
2068 | Makes the compiler print out each function name as it is compiled, and | |
2069 | print some statistics about each pass when it finishes. | |
2070 | ||
74291a4b MM |
2071 | @item -d@var{letters} |
2072 | Says to make debugging dumps during compilation at times specified by | |
2073 | @var{letters}. This is used for debugging the compiler. The file names | |
2074 | for most of the dumps are made by appending a word to the source file | |
2075 | name (e.g. @file{foo.c.rtl} or @file{foo.c.jump}). Here are the | |
2076 | possible letters for use in @var{letters}, and their meanings: | |
2077 | ||
2078 | @table @samp | |
956d6950 JL |
2079 | @item b |
2080 | Dump after computing branch probabilities, to @file{@var{file}.bp}. | |
032713aa NC |
2081 | @item c |
2082 | Dump after instruction combination, to the file @file{@var{file}.combine}. | |
2083 | @item d | |
2084 | Dump after delayed branch scheduling, to @file{@var{file}.dbr}. | |
2085 | @item D | |
f5963e61 JL |
2086 | Dump all macro definitions, at the end of preprocessing, in addition to |
2087 | normal output. | |
f5963e61 JL |
2088 | @item r |
2089 | Dump after RTL generation, to @file{@var{file}.rtl}. | |
f5963e61 JL |
2090 | @item j |
2091 | Dump after first jump optimization, to @file{@var{file}.jump}. | |
f5963e61 | 2092 | @item F |
032713aa | 2093 | Dump after purging ADDRESSOF, to @file{@var{file}.addressof}. |
74291a4b MM |
2094 | @item f |
2095 | Dump after flow analysis, to @file{@var{file}.flow}. | |
74291a4b | 2096 | @item g |
032713aa | 2097 | Dump after global register allocation, to @file{@var{file}.greg}. |
7506f491 DE |
2098 | @item G |
2099 | Dump after GCSE, to @file{@var{file}.gcse}. | |
032713aa NC |
2100 | @item j |
2101 | Dump after first jump optimization, to @file{@var{file}.jump}. | |
74291a4b MM |
2102 | @item J |
2103 | Dump after last jump optimization, to @file{@var{file}.jump2}. | |
74291a4b MM |
2104 | @item k |
2105 | Dump after conversion from registers to stack, to @file{@var{file}.stack}. | |
032713aa NC |
2106 | @item l |
2107 | Dump after local register allocation, to @file{@var{file}.lreg}. | |
2108 | @item L | |
2109 | Dump after loop optimization, to @file{@var{file}.loop}. | |
2110 | @item M | |
2111 | Dump after performing the machine dependent reorganisation pass, to | |
2112 | @file{@var{file}.mach}. | |
2113 | @item N | |
2114 | Dump after the register move pass, to @file{@var{file}.regmove}. | |
2115 | @item r | |
2116 | Dump after RTL generation, to @file{@var{file}.rtl}. | |
2117 | @item R | |
2118 | Dump after the second instruction scheduling pass, to @file{@var{file}.sched2}. | |
2119 | @item s | |
2120 | Dump after CSE (including the jump optimization that sometimes follows | |
2121 | CSE), to @file{@var{file}.cse}. | |
2122 | @item S | |
2123 | Dump after the first instruction scheduling pass, to @file{@var{file}.sched}. | |
2124 | @item t | |
2125 | Dump after the second CSE pass (including the jump optimization that | |
2126 | sometimes follows CSE), to @file{@var{file}.cse2}. | |
74291a4b MM |
2127 | @item a |
2128 | Produce all the dumps listed above. | |
2129 | @item m | |
2130 | Print statistics on memory usage, at the end of the run, to | |
2131 | standard error. | |
2132 | @item p | |
2133 | Annotate the assembler output with a comment indicating which | |
f20b5577 MM |
2134 | pattern and alternative was used. The length of each instruction is |
2135 | also printed. | |
62a1403d AS |
2136 | @item x |
2137 | Just generate RTL for a function instead of compiling it. Usually used | |
2138 | with @samp{r}. | |
032713aa NC |
2139 | @item y |
2140 | Dump debugging information during parsing, to standard error. | |
74291a4b MM |
2141 | @item A |
2142 | Annotate the assembler output with miscellaneous debugging information. | |
2143 | @end table | |
2144 | ||
b707b450 R |
2145 | @item -fdump-unnumbered |
2146 | When doing debugging dumps (see -d option above), suppress instruction | |
2147 | numbers and line number note output. This makes it more feasible to | |
2148 | use diff on debugging dumps for compiler invokations with different | |
2149 | options, in particular with and without -g. | |
2150 | ||
f71f87f9 MM |
2151 | @item -fdump-translation-unit-@var{file} (C++ only) |
2152 | Dump a representation of the tree structure for the entire translation | |
2153 | unit to @var{file}. | |
2154 | ||
74291a4b MM |
2155 | @item -fpretend-float |
2156 | When running a cross-compiler, pretend that the target machine uses the | |
2157 | same floating point format as the host machine. This causes incorrect | |
2158 | output of the actual floating constants, but the actual instruction | |
0c2d1a2a | 2159 | sequence will probably be the same as GCC would make when running on |
74291a4b MM |
2160 | the target machine. |
2161 | ||
2162 | @item -save-temps | |
2163 | Store the usual ``temporary'' intermediate files permanently; place them | |
2164 | in the current directory and name them based on the source file. Thus, | |
2165 | compiling @file{foo.c} with @samp{-c -save-temps} would produce files | |
2166 | @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. | |
2167 | ||
03c41c05 ZW |
2168 | @item -time |
2169 | Report the CPU time taken by each subprocess in the compilation | |
2170 | sequence. For C source files, this is the preprocessor, compiler | |
2171 | proper, and assembler. The output looks like this: | |
2172 | ||
2173 | @smallexample | |
2174 | # cpp 0.04 0.04 | |
2175 | # cc1 0.12 0.01 | |
2176 | # as 0.00 0.01 | |
2177 | @end smallexample | |
2178 | ||
2179 | The first number on each line is the ``user time,'' that is time spent | |
2180 | executing the program itself. The second number is ``system time,'' | |
2181 | time spent executing operating system routines on behalf of the program. | |
2182 | Both numbers are in seconds. | |
2183 | ||
74291a4b MM |
2184 | @item -print-file-name=@var{library} |
2185 | Print the full absolute name of the library file @var{library} that | |
2186 | would be used when linking---and don't do anything else. With this | |
0c2d1a2a | 2187 | option, GCC does not compile or link anything; it just prints the |
74291a4b MM |
2188 | file name. |
2189 | ||
2190 | @item -print-prog-name=@var{program} | |
2191 | Like @samp{-print-file-name}, but searches for a program such as @samp{cpp}. | |
2192 | ||
2193 | @item -print-libgcc-file-name | |
2194 | Same as @samp{-print-file-name=libgcc.a}. | |
2195 | ||
2196 | This is useful when you use @samp{-nostdlib} or @samp{-nodefaultlibs} | |
2197 | but you do want to link with @file{libgcc.a}. You can do | |
2198 | ||
2199 | @example | |
2200 | gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` | |
2201 | @end example | |
2202 | ||
2203 | @item -print-search-dirs | |
2204 | Print the name of the configured installation directory and a list of | |
2205 | program and library directories gcc will search---and don't do anything else. | |
2206 | ||
2207 | This is useful when gcc prints the error message | |
2208 | @samp{installation problem, cannot exec cpp: No such file or directory}. | |
2209 | To resolve this you either need to put @file{cpp} and the other compiler | |
2210 | components where gcc expects to find them, or you can set the environment | |
2211 | variable @code{GCC_EXEC_PREFIX} to the directory where you installed them. | |
2212 | Don't forget the trailing '/'. | |
2213 | @xref{Environment Variables}. | |
2214 | @end table | |
2215 | ||
2216 | @node Optimize Options | |
2217 | @section Options That Control Optimization | |
2218 | @cindex optimize options | |
2219 | @cindex options, optimization | |
2220 | ||
2221 | These options control various sorts of optimizations: | |
2222 | ||
2223 | @table @code | |
2224 | @item -O | |
2225 | @itemx -O1 | |
2226 | Optimize. Optimizing compilation takes somewhat more time, and a lot | |
2227 | more memory for a large function. | |
2228 | ||
2229 | Without @samp{-O}, the compiler's goal is to reduce the cost of | |
2230 | compilation and to make debugging produce the expected results. | |
2231 | Statements are independent: if you stop the program with a breakpoint | |
2232 | between statements, you can then assign a new value to any variable or | |
2233 | change the program counter to any other statement in the function and | |
2234 | get exactly the results you would expect from the source code. | |
2235 | ||
2236 | Without @samp{-O}, the compiler only allocates variables declared | |
2237 | @code{register} in registers. The resulting compiled code is a little | |
2238 | worse than produced by PCC without @samp{-O}. | |
2239 | ||
2240 | With @samp{-O}, the compiler tries to reduce code size and execution | |
2241 | time. | |
2242 | ||
2243 | When you specify @samp{-O}, the compiler turns on @samp{-fthread-jumps} | |
2244 | and @samp{-fdefer-pop} on all machines. The compiler turns on | |
2245 | @samp{-fdelayed-branch} on machines that have delay slots, and | |
2246 | @samp{-fomit-frame-pointer} on machines that can support debugging even | |
2247 | without a frame pointer. On some machines the compiler also turns | |
2248 | on other flags.@refill | |
2249 | ||
2250 | @item -O2 | |
0c2d1a2a | 2251 | Optimize even more. GCC performs nearly all supported optimizations |
74291a4b MM |
2252 | that do not involve a space-speed tradeoff. The compiler does not |
2253 | perform loop unrolling or function inlining when you specify @samp{-O2}. | |
2254 | As compared to @samp{-O}, this option increases both compilation time | |
2255 | and the performance of the generated code. | |
2256 | ||
2257 | @samp{-O2} turns on all optional optimizations except for loop unrolling | |
2258 | and function inlining. It also turns on the @samp{-fforce-mem} option | |
2259 | on all machines and frame pointer elimination on machines where doing so | |
2260 | does not interfere with debugging. | |
2261 | ||
2262 | @item -O3 | |
2263 | Optimize yet more. @samp{-O3} turns on all optimizations specified by | |
2264 | @samp{-O2} and also turns on the @samp{inline-functions} option. | |
2265 | ||
2266 | @item -O0 | |
2267 | Do not optimize. | |
2268 | ||
c6aded7c AG |
2269 | @item -Os |
2270 | Optimize for size. @samp{-Os} enables all @samp{-O2} optimizations that | |
2271 | do not typically increase code size. It also performs further | |
2272 | optimizations designed to reduce code size. | |
2273 | ||
74291a4b MM |
2274 | If you use multiple @samp{-O} options, with or without level numbers, |
2275 | the last such option is the one that is effective. | |
2276 | @end table | |
2277 | ||
2278 | Options of the form @samp{-f@var{flag}} specify machine-independent | |
2279 | flags. Most flags have both positive and negative forms; the negative | |
2280 | form of @samp{-ffoo} would be @samp{-fno-foo}. In the table below, | |
2281 | only one of the forms is listed---the one which is not the default. | |
2282 | You can figure out the other form by either removing @samp{no-} or | |
2283 | adding it. | |
2284 | ||
2285 | @table @code | |
2286 | @item -ffloat-store | |
2287 | Do not store floating point variables in registers, and inhibit other | |
2288 | options that might change whether a floating point value is taken from a | |
2289 | register or memory. | |
2290 | ||
2291 | @cindex floating point precision | |
2292 | This option prevents undesirable excess precision on machines such as | |
2293 | the 68000 where the floating registers (of the 68881) keep more | |
2294 | precision than a @code{double} is supposed to have. Similarly for the | |
2295 | x86 architecture. For most programs, the excess precision does only | |
2296 | good, but a few programs rely on the precise definition of IEEE floating | |
6fd74494 CB |
2297 | point. Use @samp{-ffloat-store} for such programs, after modifying |
2298 | them to store all pertinent intermediate computations into variables. | |
74291a4b MM |
2299 | |
2300 | @item -fno-default-inline | |
2301 | Do not make member functions inline by default merely because they are | |
2302 | defined inside the class scope (C++ only). Otherwise, when you specify | |
2303 | @w{@samp{-O}}, member functions defined inside class scope are compiled | |
2304 | inline by default; i.e., you don't need to add @samp{inline} in front of | |
2305 | the member function name. | |
2306 | ||
2307 | @item -fno-defer-pop | |
2308 | Always pop the arguments to each function call as soon as that function | |
2309 | returns. For machines which must pop arguments after a function call, | |
2310 | the compiler normally lets arguments accumulate on the stack for several | |
2311 | function calls and pops them all at once. | |
2312 | ||
2313 | @item -fforce-mem | |
2314 | Force memory operands to be copied into registers before doing | |
2315 | arithmetic on them. This produces better code by making all memory | |
2316 | references potential common subexpressions. When they are not common | |
2317 | subexpressions, instruction combination should eliminate the separate | |
2318 | register-load. The @samp{-O2} option turns on this option. | |
2319 | ||
2320 | @item -fforce-addr | |
2321 | Force memory address constants to be copied into registers before | |
2322 | doing arithmetic on them. This may produce better code just as | |
2323 | @samp{-fforce-mem} may. | |
2324 | ||
2325 | @item -fomit-frame-pointer | |
2326 | Don't keep the frame pointer in a register for functions that | |
2327 | don't need one. This avoids the instructions to save, set up and | |
2328 | restore frame pointers; it also makes an extra register available | |
2329 | in many functions. @strong{It also makes debugging impossible on | |
2330 | some machines.} | |
2331 | ||
2332 | @ifset INTERNALS | |
2333 | On some machines, such as the Vax, this flag has no effect, because | |
2334 | the standard calling sequence automatically handles the frame pointer | |
2335 | and nothing is saved by pretending it doesn't exist. The | |
2336 | machine-description macro @code{FRAME_POINTER_REQUIRED} controls | |
2337 | whether a target machine supports this flag. @xref{Registers}.@refill | |
2338 | @end ifset | |
2339 | @ifclear INTERNALS | |
2340 | On some machines, such as the Vax, this flag has no effect, because | |
2341 | the standard calling sequence automatically handles the frame pointer | |
2342 | and nothing is saved by pretending it doesn't exist. The | |
2343 | machine-description macro @code{FRAME_POINTER_REQUIRED} controls | |
2344 | whether a target machine supports this flag. @xref{Registers,,Register | |
2345 | Usage, gcc.info, Using and Porting GCC}.@refill | |
2346 | @end ifclear | |
2347 | ||
2348 | @item -fno-inline | |
2349 | Don't pay attention to the @code{inline} keyword. Normally this option | |
2350 | is used to keep the compiler from expanding any functions inline. | |
2351 | Note that if you are not optimizing, no functions can be expanded inline. | |
2352 | ||
2353 | @item -finline-functions | |
2354 | Integrate all simple functions into their callers. The compiler | |
2355 | heuristically decides which functions are simple enough to be worth | |
2356 | integrating in this way. | |
2357 | ||
2358 | If all calls to a given function are integrated, and the function is | |
2359 | declared @code{static}, then the function is normally not output as | |
2360 | assembler code in its own right. | |
2361 | ||
efa3896a | 2362 | @item -finline-limit=@var{n} |
f9e814f1 TP |
2363 | By default, gcc limits the size of functions that can be inlined. This flag |
2364 | allows the control of this limit for functions that are explicitly marked as | |
2365 | inline (ie marked with the inline keyword or defined within the class | |
2366 | definition in c++). @var{n} is the size of functions that can be inlined in | |
2367 | number of pseudo instructions (not counting parameter handling). The default | |
2368 | value of n is 10000. Increasing this value can result in more inlined code at | |
2369 | the cost of compilation time and memory consumption. Decreasing usually makes | |
2370 | the compilation faster and less code will be inlined (which presumably | |
2371 | means slower programs). This option is particularly useful for programs that | |
2372 | use inlining heavily such as those based on recursive templates with c++. | |
2373 | ||
2374 | @emph{Note:} pseudo instruction represents, in this particular context, an | |
2375 | abstract measurement of function's size. In no way, it represents a count | |
2376 | of assembly instructions and as such its exact meaning might change from one | |
2377 | release to an another. | |
2378 | ||
74291a4b MM |
2379 | @item -fkeep-inline-functions |
2380 | Even if all calls to a given function are integrated, and the function | |
2381 | is declared @code{static}, nevertheless output a separate run-time | |
2382 | callable version of the function. This switch does not affect | |
2383 | @code{extern inline} functions. | |
2384 | ||
2385 | @item -fkeep-static-consts | |
2386 | Emit variables declared @code{static const} when optimization isn't turned | |
2387 | on, even if the variables aren't referenced. | |
2388 | ||
0c2d1a2a | 2389 | GCC enables this option by default. If you want to force the compiler to |
74291a4b MM |
2390 | check if the variable was referenced, regardless of whether or not |
2391 | optimization is turned on, use the @samp{-fno-keep-static-consts} option. | |
2392 | ||
2393 | @item -fno-function-cse | |
2394 | Do not put function addresses in registers; make each instruction that | |
2395 | calls a constant function contain the function's address explicitly. | |
2396 | ||
2397 | This option results in less efficient code, but some strange hacks | |
2398 | that alter the assembler output may be confused by the optimizations | |
2399 | performed when this option is not used. | |
2400 | ||
2401 | @item -ffast-math | |
2402 | This option allows GCC to violate some ANSI or IEEE rules and/or | |
2403 | specifications in the interest of optimizing code for speed. For | |
2404 | example, it allows the compiler to assume arguments to the @code{sqrt} | |
2405 | function are non-negative numbers and that no floating-point values | |
2406 | are NaNs. | |
2407 | ||
2408 | This option should never be turned on by any @samp{-O} option since | |
2409 | it can result in incorrect output for programs which depend on | |
2410 | an exact implementation of IEEE or ANSI rules/specifications for | |
2411 | math functions. | |
2412 | @end table | |
2413 | ||
2414 | @c following causes underfulls.. they don't look great, but we deal. | |
2415 | @c --mew 26jan93 | |
2416 | The following options control specific optimizations. The @samp{-O2} | |
2417 | option turns on all of these optimizations except @samp{-funroll-loops} | |
2418 | and @samp{-funroll-all-loops}. On most machines, the @samp{-O} option | |
2419 | turns on the @samp{-fthread-jumps} and @samp{-fdelayed-branch} options, | |
2420 | but specific machines may handle it differently. | |
2421 | ||
2422 | You can use the following flags in the rare cases when ``fine-tuning'' | |
2423 | of optimizations to be performed is desired. | |
2424 | ||
2425 | @table @code | |
2426 | @item -fstrength-reduce | |
2427 | Perform the optimizations of loop strength reduction and | |
2428 | elimination of iteration variables. | |
2429 | ||
2430 | @item -fthread-jumps | |
2431 | Perform optimizations where we check to see if a jump branches to a | |
2432 | location where another comparison subsumed by the first is found. If | |
2433 | so, the first branch is redirected to either the destination of the | |
2434 | second branch or a point immediately following it, depending on whether | |
2435 | the condition is known to be true or false. | |
2436 | ||
2437 | @item -fcse-follow-jumps | |
2438 | In common subexpression elimination, scan through jump instructions | |
2439 | when the target of the jump is not reached by any other path. For | |
2440 | example, when CSE encounters an @code{if} statement with an | |
2441 | @code{else} clause, CSE will follow the jump when the condition | |
2442 | tested is false. | |
2443 | ||
2444 | @item -fcse-skip-blocks | |
2445 | This is similar to @samp{-fcse-follow-jumps}, but causes CSE to | |
2446 | follow jumps which conditionally skip over blocks. When CSE | |
2447 | encounters a simple @code{if} statement with no else clause, | |
2448 | @samp{-fcse-skip-blocks} causes CSE to follow the jump around the | |
2449 | body of the @code{if}. | |
2450 | ||
2451 | @item -frerun-cse-after-loop | |
2452 | Re-run common subexpression elimination after loop optimizations has been | |
2453 | performed. | |
2454 | ||
6d6d0fa0 JL |
2455 | @item -frerun-loop-opt |
2456 | Run the loop optimizer twice. | |
2457 | ||
7506f491 DE |
2458 | @item -fgcse |
2459 | Perform a global common subexpression elimination pass. | |
2460 | This pass also performs global constant and copy propagation. | |
2461 | ||
74291a4b MM |
2462 | @item -fexpensive-optimizations |
2463 | Perform a number of minor optimizations that are relatively expensive. | |
2464 | ||
9ec36da5 | 2465 | @item -foptimize-register-moves |
59d40964 | 2466 | @itemx -fregmove |
9ec36da5 JL |
2467 | Attempt to reassign register numbers in move instructions and as |
2468 | operands of other simple instructions in order to maximize the amount of | |
56159047 | 2469 | register tying. This is especially helpful on machines with two-operand |
0c2d1a2a | 2470 | instructions. GCC enables this optimization by default with @samp{-O2} |
9ec36da5 JL |
2471 | or higher. |
2472 | ||
2473 | Note @code{-fregmove} and @code{-foptimize-register-moves} are the same | |
2474 | optimization. | |
2475 | ||
74291a4b MM |
2476 | @item -fdelayed-branch |
2477 | If supported for the target machine, attempt to reorder instructions | |
2478 | to exploit instruction slots available after delayed branch | |
2479 | instructions. | |
2480 | ||
2481 | @item -fschedule-insns | |
2482 | If supported for the target machine, attempt to reorder instructions to | |
2483 | eliminate execution stalls due to required data being unavailable. This | |
2484 | helps machines that have slow floating point or memory load instructions | |
2485 | by allowing other instructions to be issued until the result of the load | |
2486 | or floating point instruction is required. | |
2487 | ||
2488 | @item -fschedule-insns2 | |
2489 | Similar to @samp{-fschedule-insns}, but requests an additional pass of | |
2490 | instruction scheduling after register allocation has been done. This is | |
2491 | especially useful on machines with a relatively small number of | |
2492 | registers and where memory load instructions take more than one cycle. | |
2493 | ||
2494 | @item -ffunction-sections | |
59d40964 | 2495 | @itemx -fdata-sections |
7d0756fb CM |
2496 | Place each function or data item into its own section in the output |
2497 | file if the target supports arbitrary sections. The name of the | |
2498 | function or the name of the data item determines the section's name | |
2499 | in the output file. | |
74291a4b | 2500 | |
7d0756fb | 2501 | Use these options on systems where the linker can perform optimizations |
74291a4b MM |
2502 | to improve locality of reference in the instruction space. HPPA |
2503 | processors running HP-UX and Sparc processors running Solaris 2 have | |
2504 | linkers with such optimizations. Other systems using the ELF object format | |
2505 | as well as AIX may have these optimizations in the future. | |
2506 | ||
7d0756fb CM |
2507 | Only use these options when there are significant benefits from doing |
2508 | so. When you specify these options, the assembler and linker will | |
74291a4b MM |
2509 | create larger object and executable files and will also be slower. |
2510 | You will not be able to use @code{gprof} on all systems if you | |
2511 | specify this option and you may have problems with debugging if | |
2512 | you specify both this option and @samp{-g}. | |
2513 | ||
2514 | @item -fcaller-saves | |
2515 | Enable values to be allocated in registers that will be clobbered by | |
2516 | function calls, by emitting extra instructions to save and restore the | |
2517 | registers around such calls. Such allocation is done only when it | |
2518 | seems to result in better code than would otherwise be produced. | |
2519 | ||
81610a0d HPN |
2520 | This option is always enabled by default on certain machines, usually |
2521 | those which have no call-preserved registers to use instead. | |
2522 | ||
2523 | For all machines, optimization level 2 and higher enables this flag by | |
2524 | default. | |
74291a4b MM |
2525 | |
2526 | @item -funroll-loops | |
2527 | Perform the optimization of loop unrolling. This is only done for loops | |
2528 | whose number of iterations can be determined at compile time or run time. | |
1bd31d56 | 2529 | @samp{-funroll-loops} implies both @samp{-fstrength-reduce} and |
74291a4b MM |
2530 | @samp{-frerun-cse-after-loop}. |
2531 | ||
2532 | @item -funroll-all-loops | |
2533 | Perform the optimization of loop unrolling. This is done for all loops | |
2534 | and usually makes programs run more slowly. @samp{-funroll-all-loops} | |
2535 | implies @samp{-fstrength-reduce} as well as @samp{-frerun-cse-after-loop}. | |
2536 | ||
e5eb27e5 JL |
2537 | @item -fmove-all-movables |
2538 | Forces all invariant computations in loops to be moved | |
2539 | outside the loop. | |
2540 | ||
2541 | @item -freduce-all-givs | |
2542 | Forces all general-induction variables in loops to be | |
2543 | strength-reduced. | |
2544 | ||
2545 | @emph{Note:} When compiling programs written in Fortran, | |
1bd31d56 | 2546 | @samp{-fmove-all-movables} and @samp{-freduce-all-givs} are enabled |
e5eb27e5 JL |
2547 | by default when you use the optimizer. |
2548 | ||
2549 | These options may generate better or worse code; results are highly | |
2550 | dependent on the structure of loops within the source code. | |
2551 | ||
2552 | These two options are intended to be removed someday, once | |
2553 | they have helped determine the efficacy of various | |
2554 | approaches to improving loop optimizations. | |
2555 | ||
1e1ec633 | 2556 | Please let us (@code{gcc@@gcc.gnu.org} and @code{fortran@@gnu.org}) |
e5eb27e5 JL |
2557 | know how use of these options affects |
2558 | the performance of your production code. | |
2559 | We're very interested in code that runs @emph{slower} | |
2560 | when these options are @emph{enabled}. | |
2561 | ||
74291a4b MM |
2562 | @item -fno-peephole |
2563 | Disable any machine-specific peephole optimizations. | |
861bb6c1 JL |
2564 | |
2565 | @item -fbranch-probabilities | |
2566 | After running a program compiled with @samp{-fprofile-arcs} | |
2567 | (@pxref{Debugging Options,, Options for Debugging Your Program or | |
2568 | @code{gcc}}), you can compile it a second time using | |
2569 | @samp{-fbranch-probabilities}, to improve optimizations based on | |
2570 | guessing the path a branch might take. | |
2571 | ||
2572 | @ifset INTERNALS | |
e5e809f4 | 2573 | With @samp{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT} |
861bb6c1 JL |
2574 | note on the first instruction of each basic block, and a |
2575 | @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. | |
2576 | These can be used to improve optimization. Currently, they are only | |
2577 | used in one place: in @file{reorg.c}, instead of guessing which path a | |
2578 | branch is mostly to take, the @samp{REG_BR_PROB} values are used to | |
2579 | exactly determine which path is taken more often. | |
2580 | @end ifset | |
8c660648 | 2581 | |
41472af8 MM |
2582 | @item -fstrict-aliasing |
2583 | Allows the compiler to assume the strictest aliasing rules applicable to | |
2584 | the language being compiled. For C (and C++), this activates | |
2585 | optimizations based on the type of expressions. In particular, an | |
2586 | object of one type is assumed never to reside at the same address as an | |
2587 | object of a different type, unless the types are almost the same. For | |
2588 | example, an @code{unsigned int} can alias an @code{int}, but not a | |
2589 | @code{void*} or a @code{double}. A character type may alias any other | |
2590 | type. | |
2591 | ||
2592 | Pay special attention to code like this: | |
2593 | @example | |
2594 | union a_union @{ | |
2595 | int i; | |
2596 | double d; | |
2597 | @}; | |
2598 | ||
2599 | int f() @{ | |
2600 | a_union t; | |
2601 | t.d = 3.0; | |
2602 | return t.i; | |
2603 | @} | |
2604 | @end example | |
2605 | The practice of reading from a different union member than the one most | |
2606 | recently written to (called ``type-punning'') is common. Even with | |
2607 | @samp{-fstrict-aliasing}, type-punning is allowed, provided the memory | |
2608 | is accessed through the union type. So, the code above will work as | |
2609 | expected. However, this code might not: | |
2610 | @example | |
2611 | int f() @{ | |
2612 | a_union t; | |
2613 | int* ip; | |
2614 | t.d = 3.0; | |
2615 | ip = &t.i; | |
2616 | return *ip; | |
2617 | @} | |
2618 | @end example | |
2619 | ||
41472af8 MM |
2620 | @ifset INTERNALS |
2621 | Every language that wishes to perform language-specific alias analysis | |
2622 | should define a function that computes, given an @code{tree} | |
2623 | node, an alias set for the node. Nodes in different alias sets are not | |
2624 | allowed to alias. For an example, see the C front-end function | |
2625 | @code{c_get_alias_set}. | |
2626 | @end ifset | |
2627 | ||
efa3896a GK |
2628 | @item -falign-functions |
2629 | @itemx -falign-functions=@var{n} | |
2630 | Align the start of functions to the next power-of-two greater than | |
2631 | @var{n}, skipping up to @var{n} bytes. For instance, | |
2632 | @samp{-falign-functions=32} aligns functions to the next 32-byte | |
2633 | boundary, but @samp{-falign-functions=24} would align to the next | |
2634 | 32-byte boundary only if this can be done by skipping 23 bytes or less. | |
2635 | ||
2636 | @samp{-fno-align-functions} and @samp{-falign-functions=1} are | |
2637 | equivalent and mean that functions will not be aligned. | |
2638 | ||
2639 | Some assemblers only support this flag when @var{n} is a power of two; | |
2640 | in that case, it is rounded up. | |
2641 | ||
2642 | If @var{n} is not specified, use a machine-dependent default. | |
2643 | ||
2644 | @item -falign-labels | |
2645 | @itemx -falign-labels=@var{n} | |
2646 | Align all branch targets to a power-of-two boundary, skipping up to | |
2647 | @var{n} bytes like @samp{-falign-functions}. This option can easily | |
2648 | make code slower, because it must insert dummy operations for when the | |
2649 | branch target is reached in the usual flow of the code. | |
2650 | ||
2651 | If @samp{-falign-loops} or @samp{-falign-jumps} are applicable and | |
2652 | are greater than this value, then their values are used instead. | |
2653 | ||
2654 | If @var{n} is not specified, use a machine-dependent default which is | |
2655 | very likely to be @samp{1}, meaning no alignment. | |
2656 | ||
2657 | @item -falign-loops | |
2658 | @itemx -falign-loops=@var{n} | |
2659 | Align loops to a power-of-two boundary, skipping up to @var{n} bytes | |
2660 | like @samp{-falign-functions}. The hope is that the loop will be | |
2661 | executed many times, which will make up for any execution of the dummy | |
2662 | operations. | |
2663 | ||
2664 | If @var{n} is not specified, use a machine-dependent default. | |
2665 | ||
2666 | @item -falign-jumps | |
2667 | @itemx -falign-jumps=@var{n} | |
2668 | Align branch targets to a power-of-two boundary, for branch targets | |
2669 | where the targets can only be reached by jumping, skipping up to @var{n} | |
2670 | bytes like @samp{-falign-functions}. In this case, no dummy operations | |
2671 | need be executed. | |
2672 | ||
2673 | If @var{n} is not specified, use a machine-dependent default. | |
2674 | ||
74291a4b MM |
2675 | @end table |
2676 | ||
2677 | @node Preprocessor Options | |
2678 | @section Options Controlling the Preprocessor | |
2679 | @cindex preprocessor options | |
2680 | @cindex options, preprocessor | |
2681 | ||
2682 | These options control the C preprocessor, which is run on each C source | |
2683 | file before actual compilation. | |
2684 | ||
2685 | If you use the @samp{-E} option, nothing is done except preprocessing. | |
2686 | Some of these options make sense only together with @samp{-E} because | |
2687 | they cause the preprocessor output to be unsuitable for actual | |
2688 | compilation. | |
2689 | ||
2690 | @table @code | |
2691 | @item -include @var{file} | |
2692 | Process @var{file} as input before processing the regular input file. | |
2693 | In effect, the contents of @var{file} are compiled first. Any @samp{-D} | |
2694 | and @samp{-U} options on the command line are always processed before | |
2695 | @samp{-include @var{file}}, regardless of the order in which they are | |
2696 | written. All the @samp{-include} and @samp{-imacros} options are | |
2697 | processed in the order in which they are written. | |
2698 | ||
2699 | @item -imacros @var{file} | |
2700 | Process @var{file} as input, discarding the resulting output, before | |
2701 | processing the regular input file. Because the output generated from | |
2702 | @var{file} is discarded, the only effect of @samp{-imacros @var{file}} | |
2703 | is to make the macros defined in @var{file} available for use in the | |
2704 | main input. | |
2705 | ||
2706 | Any @samp{-D} and @samp{-U} options on the command line are always | |
2707 | processed before @samp{-imacros @var{file}}, regardless of the order in | |
2708 | which they are written. All the @samp{-include} and @samp{-imacros} | |
2709 | options are processed in the order in which they are written. | |
2710 | ||
2711 | @item -idirafter @var{dir} | |
2712 | @cindex second include path | |
2713 | Add the directory @var{dir} to the second include path. The directories | |
2714 | on the second include path are searched when a header file is not found | |
2715 | in any of the directories in the main include path (the one that | |
2716 | @samp{-I} adds to). | |
2717 | ||
2718 | @item -iprefix @var{prefix} | |
2719 | Specify @var{prefix} as the prefix for subsequent @samp{-iwithprefix} | |
2720 | options. | |
2721 | ||
2722 | @item -iwithprefix @var{dir} | |
2723 | Add a directory to the second include path. The directory's name is | |
2724 | made by concatenating @var{prefix} and @var{dir}, where @var{prefix} was | |
2725 | specified previously with @samp{-iprefix}. If you have not specified a | |
2726 | prefix yet, the directory containing the installed passes of the | |
2727 | compiler is used as the default. | |
2728 | ||
2729 | @item -iwithprefixbefore @var{dir} | |
2730 | Add a directory to the main include path. The directory's name is made | |
2731 | by concatenating @var{prefix} and @var{dir}, as in the case of | |
2732 | @samp{-iwithprefix}. | |
2733 | ||
2734 | @item -isystem @var{dir} | |
2735 | Add a directory to the beginning of the second include path, marking it | |
2736 | as a system directory, so that it gets the same special treatment as | |
2737 | is applied to the standard system directories. | |
2738 | ||
2739 | @item -nostdinc | |
2740 | Do not search the standard system directories for header files. Only | |
2741 | the directories you have specified with @samp{-I} options (and the | |
2742 | current directory, if appropriate) are searched. @xref{Directory | |
2743 | Options}, for information on @samp{-I}. | |
2744 | ||
2745 | By using both @samp{-nostdinc} and @samp{-I-}, you can limit the include-file | |
2746 | search path to only those directories you specify explicitly. | |
2747 | ||
2748 | @item -undef | |
2749 | Do not predefine any nonstandard macros. (Including architecture flags). | |
2750 | ||
2751 | @item -E | |
2752 | Run only the C preprocessor. Preprocess all the C source files | |
2753 | specified and output the results to standard output or to the | |
2754 | specified output file. | |
2755 | ||
2756 | @item -C | |
2757 | Tell the preprocessor not to discard comments. Used with the | |
2758 | @samp{-E} option. | |
2759 | ||
2760 | @item -P | |
2761 | Tell the preprocessor not to generate @samp{#line} directives. | |
2762 | Used with the @samp{-E} option. | |
2763 | ||
2764 | @cindex make | |
2765 | @cindex dependencies, make | |
2766 | @item -M | |
2767 | Tell the preprocessor to output a rule suitable for @code{make} | |
2768 | describing the dependencies of each object file. For each source file, | |
2769 | the preprocessor outputs one @code{make}-rule whose target is the object | |
2770 | file name for that source file and whose dependencies are all the | |
2771 | @code{#include} header files it uses. This rule may be a single line or | |
2772 | may be continued with @samp{\}-newline if it is long. The list of rules | |
2773 | is printed on standard output instead of the preprocessed C program. | |
2774 | ||
2775 | @samp{-M} implies @samp{-E}. | |
2776 | ||
2777 | Another way to specify output of a @code{make} rule is by setting | |
2778 | the environment variable @code{DEPENDENCIES_OUTPUT} (@pxref{Environment | |
2779 | Variables}). | |
2780 | ||
2781 | @item -MM | |
2782 | Like @samp{-M} but the output mentions only the user header files | |
2783 | included with @samp{#include "@var{file}"}. System header files | |
2784 | included with @samp{#include <@var{file}>} are omitted. | |
2785 | ||
2786 | @item -MD | |
2787 | Like @samp{-M} but the dependency information is written to a file made by | |
2788 | replacing ".c" with ".d" at the end of the input file names. | |
2789 | This is in addition to compiling the file as specified---@samp{-MD} does | |
2790 | not inhibit ordinary compilation the way @samp{-M} does. | |
2791 | ||
2792 | In Mach, you can use the utility @code{md} to merge multiple dependency | |
2793 | files into a single dependency file suitable for using with the @samp{make} | |
2794 | command. | |
2795 | ||
2796 | @item -MMD | |
2797 | Like @samp{-MD} except mention only user header files, not system | |
2798 | header files. | |
2799 | ||
2800 | @item -MG | |
2801 | Treat missing header files as generated files and assume they live in the | |
2802 | same directory as the source file. If you specify @samp{-MG}, you | |
2803 | must also specify either @samp{-M} or @samp{-MM}. @samp{-MG} is not | |
2804 | supported with @samp{-MD} or @samp{-MMD}. | |
2805 | ||
2806 | @item -H | |
2807 | Print the name of each header file used, in addition to other normal | |
2808 | activities. | |
2809 | ||
2810 | @item -A@var{question}(@var{answer}) | |
2811 | Assert the answer @var{answer} for @var{question}, in case it is tested | |
2812 | with a preprocessing conditional such as @samp{#if | |
2813 | #@var{question}(@var{answer})}. @samp{-A-} disables the standard | |
2814 | assertions that normally describe the target machine. | |
2815 | ||
2816 | @item -D@var{macro} | |
2817 | Define macro @var{macro} with the string @samp{1} as its definition. | |
2818 | ||
2819 | @item -D@var{macro}=@var{defn} | |
2820 | Define macro @var{macro} as @var{defn}. All instances of @samp{-D} on | |
2821 | the command line are processed before any @samp{-U} options. | |
2822 | ||
2823 | @item -U@var{macro} | |
2824 | Undefine macro @var{macro}. @samp{-U} options are evaluated after all | |
2825 | @samp{-D} options, but before any @samp{-include} and @samp{-imacros} | |
2826 | options. | |
2827 | ||
2828 | @item -dM | |
2829 | Tell the preprocessor to output only a list of the macro definitions | |
2830 | that are in effect at the end of preprocessing. Used with the @samp{-E} | |
2831 | option. | |
2832 | ||
2833 | @item -dD | |
2834 | Tell the preprocessing to pass all macro definitions into the output, in | |
2835 | their proper sequence in the rest of the output. | |
2836 | ||
2837 | @item -dN | |
2838 | Like @samp{-dD} except that the macro arguments and contents are omitted. | |
2839 | Only @samp{#define @var{name}} is included in the output. | |
2840 | ||
2841 | @item -trigraphs | |
2842 | Support ANSI C trigraphs. The @samp{-ansi} option also has this effect. | |
2843 | ||
2844 | @item -Wp,@var{option} | |
2845 | Pass @var{option} as an option to the preprocessor. If @var{option} | |
2846 | contains commas, it is split into multiple options at the commas. | |
2847 | @end table | |
2848 | ||
2849 | @node Assembler Options | |
2850 | @section Passing Options to the Assembler | |
2851 | ||
2852 | @c prevent bad page break with this line | |
2853 | You can pass options to the assembler. | |
2854 | ||
2855 | @table @code | |
2856 | @item -Wa,@var{option} | |
2857 | Pass @var{option} as an option to the assembler. If @var{option} | |
2858 | contains commas, it is split into multiple options at the commas. | |
2859 | @end table | |
2860 | ||
2861 | @node Link Options | |
2862 | @section Options for Linking | |
2863 | @cindex link options | |
2864 | @cindex options, linking | |
2865 | ||
2866 | These options come into play when the compiler links object files into | |
2867 | an executable output file. They are meaningless if the compiler is | |
2868 | not doing a link step. | |
2869 | ||
2870 | @table @code | |
2871 | @cindex file names | |
2872 | @item @var{object-file-name} | |
2873 | A file name that does not end in a special recognized suffix is | |
2874 | considered to name an object file or library. (Object files are | |
2875 | distinguished from libraries by the linker according to the file | |
2876 | contents.) If linking is done, these object files are used as input | |
2877 | to the linker. | |
2878 | ||
2879 | @item -c | |
2880 | @itemx -S | |
2881 | @itemx -E | |
2882 | If any of these options is used, then the linker is not run, and | |
2883 | object file names should not be used as arguments. @xref{Overall | |
2884 | Options}. | |
2885 | ||
2886 | @cindex Libraries | |
2887 | @item -l@var{library} | |
2888 | Search the library named @var{library} when linking. | |
2889 | ||
2890 | It makes a difference where in the command you write this option; the | |
2891 | linker searches processes libraries and object files in the order they | |
2892 | are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} | |
2893 | after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers | |
2894 | to functions in @samp{z}, those functions may not be loaded. | |
2895 | ||
2896 | The linker searches a standard list of directories for the library, | |
2897 | which is actually a file named @file{lib@var{library}.a}. The linker | |
2898 | then uses this file as if it had been specified precisely by name. | |
2899 | ||
2900 | The directories searched include several standard system directories | |
2901 | plus any that you specify with @samp{-L}. | |
2902 | ||
2903 | Normally the files found this way are library files---archive files | |
2904 | whose members are object files. The linker handles an archive file by | |
2905 | scanning through it for members which define symbols that have so far | |
2906 | been referenced but not defined. But if the file that is found is an | |
2907 | ordinary object file, it is linked in the usual fashion. The only | |
2908 | difference between using an @samp{-l} option and specifying a file name | |
2909 | is that @samp{-l} surrounds @var{library} with @samp{lib} and @samp{.a} | |
2910 | and searches several directories. | |
2911 | ||
2912 | @item -lobjc | |
2913 | You need this special case of the @samp{-l} option in order to | |
2914 | link an Objective C program. | |
2915 | ||
2916 | @item -nostartfiles | |
2917 | Do not use the standard system startup files when linking. | |
2918 | The standard system libraries are used normally, unless @code{-nostdlib} | |
2919 | or @code{-nodefaultlibs} is used. | |
2920 | ||
2921 | @item -nodefaultlibs | |
2922 | Do not use the standard system libraries when linking. | |
2923 | Only the libraries you specify will be passed to the linker. | |
2924 | The standard startup files are used normally, unless @code{-nostartfiles} | |
4754172c | 2925 | is used. The compiler may generate calls to memcmp, memset, and memcpy |
8dd8e764 | 2926 | for System V (and ANSI C) environments or to bcopy and bzero for |
4754172c CM |
2927 | BSD environments. These entries are usually resolved by entries in |
2928 | libc. These entry points should be supplied through some other | |
2929 | mechanism when this option is specified. | |
74291a4b MM |
2930 | |
2931 | @item -nostdlib | |
2932 | Do not use the standard system startup files or libraries when linking. | |
2933 | No startup files and only the libraries you specify will be passed to | |
4754172c | 2934 | the linker. The compiler may generate calls to memcmp, memset, and memcpy |
8dd8e764 | 2935 | for System V (and ANSI C) environments or to bcopy and bzero for |
4754172c CM |
2936 | BSD environments. These entries are usually resolved by entries in |
2937 | libc. These entry points should be supplied through some other | |
2938 | mechanism when this option is specified. | |
74291a4b MM |
2939 | |
2940 | @cindex @code{-lgcc}, use with @code{-nostdlib} | |
2941 | @cindex @code{-nostdlib} and unresolved references | |
2942 | @cindex unresolved references and @code{-nostdlib} | |
2943 | @cindex @code{-lgcc}, use with @code{-nodefaultlibs} | |
2944 | @cindex @code{-nodefaultlibs} and unresolved references | |
2945 | @cindex unresolved references and @code{-nodefaultlibs} | |
2946 | One of the standard libraries bypassed by @samp{-nostdlib} and | |
2947 | @samp{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines | |
0c2d1a2a | 2948 | that GCC uses to overcome shortcomings of particular machines, or special |
74291a4b MM |
2949 | needs for some languages. |
2950 | @ifset INTERNALS | |
0c2d1a2a | 2951 | (@xref{Interface,,Interfacing to GCC Output}, for more discussion of |
74291a4b MM |
2952 | @file{libgcc.a}.) |
2953 | @end ifset | |
2954 | @ifclear INTERNALS | |
0c2d1a2a | 2955 | (@xref{Interface,,Interfacing to GCC Output,gcc.info,Porting GCC}, |
74291a4b MM |
2956 | for more discussion of @file{libgcc.a}.) |
2957 | @end ifclear | |
2958 | In most cases, you need @file{libgcc.a} even when you want to avoid | |
2959 | other standard libraries. In other words, when you specify @samp{-nostdlib} | |
2960 | or @samp{-nodefaultlibs} you should usually specify @samp{-lgcc} as well. | |
0c2d1a2a | 2961 | This ensures that you have no unresolved references to internal GCC |
74291a4b MM |
2962 | library subroutines. (For example, @samp{__main}, used to ensure C++ |
2963 | constructors will be called; @pxref{Collect2,,@code{collect2}}.) | |
2964 | ||
2965 | @item -s | |
2966 | Remove all symbol table and relocation information from the executable. | |
2967 | ||
2968 | @item -static | |
2969 | On systems that support dynamic linking, this prevents linking with the shared | |
2970 | libraries. On other systems, this option has no effect. | |
2971 | ||
2972 | @item -shared | |
2973 | Produce a shared object which can then be linked with other objects to | |
2974 | form an executable. Not all systems support this option. You must | |
2975 | also specify @samp{-fpic} or @samp{-fPIC} on some systems when | |
2976 | you specify this option. | |
2977 | ||
2978 | @item -symbolic | |
2979 | Bind references to global symbols when building a shared object. Warn | |
2980 | about any unresolved references (unless overridden by the link editor | |
2981 | option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support | |
2982 | this option. | |
2983 | ||
2984 | @item -Xlinker @var{option} | |
2985 | Pass @var{option} as an option to the linker. You can use this to | |
0c2d1a2a | 2986 | supply system-specific linker options which GCC does not know how to |
74291a4b MM |
2987 | recognize. |
2988 | ||
2989 | If you want to pass an option that takes an argument, you must use | |
2990 | @samp{-Xlinker} twice, once for the option and once for the argument. | |
2991 | For example, to pass @samp{-assert definitions}, you must write | |
2992 | @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write | |
2993 | @samp{-Xlinker "-assert definitions"}, because this passes the entire | |
2994 | string as a single argument, which is not what the linker expects. | |
2995 | ||
2996 | @item -Wl,@var{option} | |
2997 | Pass @var{option} as an option to the linker. If @var{option} contains | |
2998 | commas, it is split into multiple options at the commas. | |
2999 | ||
3000 | @item -u @var{symbol} | |
3001 | Pretend the symbol @var{symbol} is undefined, to force linking of | |
3002 | library modules to define it. You can use @samp{-u} multiple times with | |
3003 | different symbols to force loading of additional library modules. | |
3004 | @end table | |
3005 | ||
3006 | @node Directory Options | |
3007 | @section Options for Directory Search | |
3008 | @cindex directory options | |
3009 | @cindex options, directory search | |
3010 | @cindex search path | |
3011 | ||
3012 | These options specify directories to search for header files, for | |
3013 | libraries and for parts of the compiler: | |
3014 | ||
3015 | @table @code | |
3016 | @item -I@var{dir} | |
861bb6c1 JL |
3017 | Add the directory @var{dir} to the head of the list of directories to be |
3018 | searched for header files. This can be used to override a system header | |
3019 | file, substituting your own version, since these directories are | |
74291a4b MM |
3020 | searched before the system header file directories. If you use more |
3021 | than one @samp{-I} option, the directories are scanned in left-to-right | |
3022 | order; the standard system directories come after. | |
3023 | ||
3024 | @item -I- | |
3025 | Any directories you specify with @samp{-I} options before the @samp{-I-} | |
3026 | option are searched only for the case of @samp{#include "@var{file}"}; | |
3027 | they are not searched for @samp{#include <@var{file}>}. | |
3028 | ||
3029 | If additional directories are specified with @samp{-I} options after | |
3030 | the @samp{-I-}, these directories are searched for all @samp{#include} | |
3031 | directives. (Ordinarily @emph{all} @samp{-I} directories are used | |
3032 | this way.) | |
3033 | ||
3034 | In addition, the @samp{-I-} option inhibits the use of the current | |
3035 | directory (where the current input file came from) as the first search | |
3036 | directory for @samp{#include "@var{file}"}. There is no way to | |
3037 | override this effect of @samp{-I-}. With @samp{-I.} you can specify | |
3038 | searching the directory which was current when the compiler was | |
3039 | invoked. That is not exactly the same as what the preprocessor does | |
3040 | by default, but it is often satisfactory. | |
3041 | ||
3042 | @samp{-I-} does not inhibit the use of the standard system directories | |
3043 | for header files. Thus, @samp{-I-} and @samp{-nostdinc} are | |
3044 | independent. | |
3045 | ||
3046 | @item -L@var{dir} | |
3047 | Add directory @var{dir} to the list of directories to be searched | |
3048 | for @samp{-l}. | |
3049 | ||
3050 | @item -B@var{prefix} | |
3051 | This option specifies where to find the executables, libraries, | |
3052 | include files, and data files of the compiler itself. | |
3053 | ||
3054 | The compiler driver program runs one or more of the subprograms | |
3055 | @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries | |
3056 | @var{prefix} as a prefix for each program it tries to run, both with and | |
3057 | without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). | |
3058 | ||
3059 | For each subprogram to be run, the compiler driver first tries the | |
3060 | @samp{-B} prefix, if any. If that name is not found, or if @samp{-B} | |
3061 | was not specified, the driver tries two standard prefixes, which are | |
3062 | @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc-lib/}. If neither of | |
3063 | those results in a file name that is found, the unmodified program | |
3064 | name is searched for using the directories specified in your | |
3065 | @samp{PATH} environment variable. | |
3066 | ||
3067 | @samp{-B} prefixes that effectively specify directory names also apply | |
3068 | to libraries in the linker, because the compiler translates these | |
3069 | options into @samp{-L} options for the linker. They also apply to | |
3070 | includes files in the preprocessor, because the compiler translates these | |
3071 | options into @samp{-isystem} options for the preprocessor. In this case, | |
3072 | the compiler appends @samp{include} to the prefix. | |
3073 | ||
3074 | The run-time support file @file{libgcc.a} can also be searched for using | |
3075 | the @samp{-B} prefix, if needed. If it is not found there, the two | |
3076 | standard prefixes above are tried, and that is all. The file is left | |
3077 | out of the link if it is not found by those means. | |
3078 | ||
3079 | Another way to specify a prefix much like the @samp{-B} prefix is to use | |
3080 | the environment variable @code{GCC_EXEC_PREFIX}. @xref{Environment | |
3081 | Variables}. | |
861bb6c1 JL |
3082 | |
3083 | @item -specs=@var{file} | |
3084 | Process @var{file} after the compiler reads in the standard @file{specs} | |
3085 | file, in order to override the defaults that the @file{gcc} driver | |
3086 | program uses when determining what switches to pass to @file{cc1}, | |
3087 | @file{cc1plus}, @file{as}, @file{ld}, etc. More than one | |
3088 | @samp{-specs=}@var{file} can be specified on the command line, and they | |
3089 | are processed in order, from left to right. | |
74291a4b MM |
3090 | @end table |
3091 | ||
a743d340 NC |
3092 | @node Spec Files |
3093 | @section Specifying subprocesses and the switches to pass to them | |
3094 | @cindex Spec Files | |
3095 | @code{GCC} is a driver program. It performs its job by invoking a | |
3096 | sequence of other programs to do the work of compiling, assembling and | |
3097 | linking. GCC interprets its command-line parameters and uses these to | |
3098 | deduce which programs it should invoke, and which command-line options | |
3099 | it ought to place on their command lines. This behaviour is controlled | |
3100 | by @dfn{spec strings}. In most cases there is one spec string for each | |
3101 | program that GCC can invoke, but a few programs have multiple spec | |
3102 | strings to control their behaviour. The spec strings built into GCC can | |
3103 | be overridden by using the @samp{-specs=} command-line switch to specify | |
3104 | a spec file. | |
3105 | ||
3106 | @dfn{Spec files} are plaintext files that are used to construct spec | |
3107 | strings. They consist of a sequence of directives separated by blank | |
3108 | lines. The type of directive is determined by the first non-whitespace | |
3109 | character on the line and it can be one of the following: | |
3110 | ||
3111 | @table @code | |
3112 | @item %@var{command} | |
3113 | Issues a @var{command} to the spec file processor. The commands that can | |
3114 | appear here are: | |
3115 | ||
3116 | @table @code | |
3117 | @item %include <@var{file}> | |
3118 | @cindex %include | |
3119 | Search for @var{file} and insert its text at the current point in the | |
3120 | specs file. | |
3121 | ||
3122 | @item %include_noerr <@var{file}> | |
3123 | @cindex %include_noerr | |
3124 | Just like @samp{%include}, but do not generate an error message if the include | |
3125 | file cannot be found. | |
3126 | ||
3127 | @item %rename @var{old_name} @var{new_name} | |
3128 | @cindex %rename | |
3129 | Rename the spec string @var{old_name} to @var{new_name}. | |
3130 | ||
3131 | @end table | |
3132 | ||
3133 | @item *[@var{spec_name}]: | |
3134 | This tells the compiler to create, override or delete the named spec | |
3135 | string. All lines after this directive up to the next directive or | |
3136 | blank line are considered to be the text for the spec string. If this | |
3137 | results in an empty string then the spec will be deleted. (Or, if the | |
3138 | spec did not exist, then nothing will happened.) Otherwise, if the spec | |
3139 | does not currently exist a new spec will be created. If the spec does | |
3140 | exist then its contents will be overridden by the text of this | |
3141 | directive, unless the first character of that text is the @samp{+} | |
3142 | character, in which case the text will be appended to the spec. | |
3143 | ||
3144 | @item [@var{suffix}]: | |
3145 | Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive | |
3146 | and up to the next directive or blank line are considered to make up the | |
3147 | spec string for the indicated suffix. When the compiler encounters an | |
3148 | input file with the named suffix, it will processes the spec string in | |
3149 | order to work out how to compile that file. For example: | |
3150 | ||
3151 | @smallexample | |
3152 | .ZZ: | |
3153 | z-compile -input %i | |
3154 | @end smallexample | |
3155 | ||
3156 | This says that any input file whose name ends in @samp{.ZZ} should be | |
3157 | passed to the program @samp{z-compile}, which should be invoked with the | |
3158 | command-line switch @samp{-input} and with the result of performing the | |
3159 | @samp{%i} substitution. (See below.) | |
3160 | ||
3161 | As an alternative to providing a spec string, the text that follows a | |
3162 | suffix directive can be one of the following: | |
3163 | ||
3164 | @table @code | |
3165 | @item @@@var{language} | |
3166 | This says that the suffix is an alias for a known @var{language}. This is | |
3167 | similar to using the @code{-x} command-line switch to GCC to specify a | |
3168 | language explicitly. For example: | |
3169 | ||
3170 | @smallexample | |
3171 | .ZZ: | |
3172 | @@c++ | |
3173 | @end smallexample | |
3174 | ||
3175 | Says that .ZZ files are, in fact, C++ source files. | |
3176 | ||
3177 | @item #@var{name} | |
3178 | This causes an error messages saying: | |
3179 | ||
3180 | @smallexample | |
3181 | @var{name} compiler not installed on this system. | |
3182 | @end smallexample | |
3183 | @end table | |
3184 | ||
3185 | GCC already has an extensive list of suffixes built into it. | |
3186 | This directive will add an entry to the end of the list of suffixes, but | |
3187 | since the list is searched from the end backwards, it is effectively | |
3188 | possible to override earlier entries using this technique. | |
3189 | ||
3190 | @end table | |
3191 | ||
3192 | GCC has the following spec strings built into it. Spec files can | |
3193 | override these strings or create their own. Note that individual | |
3194 | targets can also add their own spec strings to this list. | |
3195 | ||
3196 | @smallexample | |
3197 | asm Options to pass to the assembler | |
3198 | asm_final Options to pass to the assembler post-processor | |
3199 | cpp Options to pass to the C preprocessor | |
3200 | cc1 Options to pass to the C compiler | |
3201 | cc1plus Options to pass to the C++ compiler | |
3202 | endfile Object files to include at the end of the link | |
3203 | link Options to pass to the linker | |
3204 | lib Libraries to include on the command line to the linker | |
3205 | libgcc Decides which GCC support library to pass to the linker | |
3206 | linker Sets the name of the linker | |
3207 | predefines Defines to be passed to the C preprocessor | |
3208 | signed_char Defines to pass to CPP to say whether @code{char} is signed by default | |
3209 | startfile Object files to include at the start of the link | |
3210 | @end smallexample | |
3211 | ||
3212 | Here is a small example of a spec file: | |
3213 | ||
3214 | @smallexample | |
3215 | %rename lib old_lib | |
3216 | ||
3217 | *lib: | |
3218 | --start-group -lgcc -lc -leval1 --end-group %(old_lib) | |
3219 | @end smallexample | |
3220 | ||
3221 | This example renames the spec called @samp{lib} to @samp{old_lib} and | |
3222 | then overrides the previous definition of @samp{lib} with a new one. | |
3223 | The new definition adds in some extra command-line options before | |
3224 | including the text of the old definition. | |
3225 | ||
3226 | @dfn{Spec strings} are a list of command-line options to be passed to their | |
3227 | corresponding program. In addition, the spec strings can contain | |
3228 | @samp{%}-prefixed sequences to substitute variable text or to | |
3229 | conditionally insert text into the command line. Using these constructs | |
3230 | it is possible to generate quite complex command lines. | |
3231 | ||
3232 | Here is a table of all defined @samp{%}-sequences for spec | |
3233 | strings. Note that spaces are not generated automatically around the | |
3234 | results of expanding these sequences. Therefore you can concatenate them | |
3235 | together or combine them with constant text in a single argument. | |
3236 | ||
3237 | @table @code | |
3238 | @item %% | |
3239 | Substitute one @samp{%} into the program name or argument. | |
3240 | ||
3241 | @item %i | |
3242 | Substitute the name of the input file being processed. | |
3243 | ||
3244 | @item %b | |
3245 | Substitute the basename of the input file being processed. | |
3246 | This is the substring up to (and not including) the last period | |
3247 | and not including the directory. | |
3248 | ||
3249 | @item %d | |
3250 | Marks the argument containing or following the @samp{%d} as a | |
3251 | temporary file name, so that that file will be deleted if GCC exits | |
3252 | successfully. Unlike @samp{%g}, this contributes no text to the | |
3253 | argument. | |
3254 | ||
3255 | @item %g@var{suffix} | |
3256 | Substitute a file name that has suffix @var{suffix} and is chosen | |
3257 | once per compilation, and mark the argument in the same way as | |
3258 | @samp{%d}. To reduce exposure to denial-of-service attacks, the file | |
3259 | name is now chosen in a way that is hard to predict even when previously | |
3260 | chosen file names are known. For example, @samp{%g.s ... %g.o ... %g.s} | |
3261 | might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches | |
3262 | the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is | |
3263 | treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} | |
3264 | was simply substituted with a file name chosen once per compilation, | |
3265 | without regard to any appended suffix (which was therefore treated | |
3266 | just like ordinary text), making such attacks more likely to succeed. | |
3267 | ||
3268 | @item %u@var{suffix} | |
3269 | Like @samp{%g}, but generates a new temporary file name even if | |
3270 | @samp{%u@var{suffix}} was already seen. | |
3271 | ||
3272 | @item %U@var{suffix} | |
3273 | Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a | |
3274 | new one if there is no such last file name. In the absence of any | |
3275 | @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share | |
3276 | the same suffix @emph{space}, so @samp{%g.s ... %U.s ... %g.s ... %U.s} | |
3277 | would involve the generation of two distinct file names, one | |
3278 | for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was | |
3279 | simply substituted with a file name chosen for the previous @samp{%u}, | |
3280 | without regard to any appended suffix. | |
3281 | ||
3282 | @item %w | |
3283 | Marks the argument containing or following the @samp{%w} as the | |
3284 | designated output file of this compilation. This puts the argument | |
3285 | into the sequence of arguments that @samp{%o} will substitute later. | |
3286 | ||
3287 | @item %o | |
3288 | Substitutes the names of all the output files, with spaces | |
3289 | automatically placed around them. You should write spaces | |
3290 | around the @samp{%o} as well or the results are undefined. | |
3291 | @samp{%o} is for use in the specs for running the linker. | |
3292 | Input files whose names have no recognized suffix are not compiled | |
3293 | at all, but they are included among the output files, so they will | |
3294 | be linked. | |
3295 | ||
3296 | @item %O | |
3297 | Substitutes the suffix for object files. Note that this is | |
3298 | handled specially when it immediately follows @samp{%g, %u, or %U}, | |
3299 | because of the need for those to form complete file names. The | |
3300 | handling is such that @samp{%O} is treated exactly as if it had already | |
3301 | been substituted, except that @samp{%g, %u, and %U} do not currently | |
3302 | support additional @var{suffix} characters following @samp{%O} as they would | |
3303 | following, for example, @samp{.o}. | |
3304 | ||
3305 | @item %p | |
3306 | Substitutes the standard macro predefinitions for the | |
3307 | current target machine. Use this when running @code{cpp}. | |
3308 | ||
3309 | @item %P | |
3310 | Like @samp{%p}, but puts @samp{__} before and after the name of each | |
3311 | predefined macro, except for macros that start with @samp{__} or with | |
3312 | @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ANSI | |
3313 | C. | |
3314 | ||
3315 | @item %I | |
3316 | Substitute a @samp{-iprefix} option made from GCC_EXEC_PREFIX. | |
3317 | ||
3318 | @item %s | |
3319 | Current argument is the name of a library or startup file of some sort. | |
3320 | Search for that file in a standard list of directories and substitute | |
3321 | the full name found. | |
3322 | ||
3323 | @item %e@var{str} | |
3324 | Print @var{str} as an error message. @var{str} is terminated by a newline. | |
3325 | Use this when inconsistent options are detected. | |
3326 | ||
3327 | @item %| | |
3328 | Output @samp{-} if the input for the current command is coming from a pipe. | |
3329 | ||
3330 | @item %(@var{name}) | |
3331 | Substitute the contents of spec string @var{name} at this point. | |
3332 | ||
3333 | @item %[@var{name}] | |
3334 | Like @samp{%(...)} but put @samp{__} around @samp{-D} arguments. | |
3335 | ||
3336 | @item %x@{@var{option}@} | |
3337 | Accumulate an option for @samp{%X}. | |
3338 | ||
3339 | @item %X | |
3340 | Output the accumulated linker options specified by @samp{-Wl} or a @samp{%x} | |
3341 | spec string. | |
3342 | ||
3343 | @item %Y | |
3344 | Output the accumulated assembler options specified by @samp{-Wa}. | |
3345 | ||
3346 | @item %Z | |
3347 | Output the accumulated preprocessor options specified by @samp{-Wp}. | |
3348 | ||
3349 | @item %v1 | |
3350 | Substitute the major version number of GCC. | |
3351 | (For version 2.9.5, this is 2.) | |
3352 | ||
3353 | @item %v2 | |
3354 | Substitute the minor version number of GCC. | |
3355 | (For version 2.9.5, this is 9.) | |
3356 | ||
3357 | @item %a | |
3358 | Process the @code{asm} spec. This is used to compute the | |
3359 | switches to be passed to the assembler. | |
3360 | ||
3361 | @item %A | |
3362 | Process the @code{asm_final} spec. This is a spec string for | |
3363 | passing switches to an assembler post-processor, if such a program is | |
3364 | needed. | |
3365 | ||
3366 | @item %l | |
3367 | Process the @code{link} spec. This is the spec for computing the | |
3368 | command line passed to the linker. Typically it will make use of the | |
3369 | @samp{%L %G %S %D and %E} sequences. | |
3370 | ||
3371 | @item %D | |
3372 | Dump out a @samp{-L} option for each directory that GCC believes might | |
3373 | contain startup files. If the target supports multilibs then the | |
3374 | current multilib directory will be prepended to each of these paths. | |
3375 | ||
3376 | @item %L | |
3377 | Process the @code{lib} spec. This is a spec string for deciding which | |
3378 | libraries should be included on the command line to the linker. | |
3379 | ||
3380 | @item %G | |
3381 | Process the @code{libgcc} spec. This is a spec string for deciding | |
3382 | which GCC support library should be included on the command line to the linker. | |
3383 | ||
3384 | @item %S | |
3385 | Process the @code{startfile} spec. This is a spec for deciding which | |
3386 | object files should be the first ones passed to the linker. Typically | |
3387 | this might be a file named @file{crt0.o}. | |
3388 | ||
3389 | @item %E | |
3390 | Process the @code{endfile} spec. This is a spec string that specifies | |
3391 | the last object files that will be passed to the linker. | |
3392 | ||
3393 | @item %C | |
3394 | Process the @code{cpp} spec. This is used to construct the arguments | |
3395 | to be passed to the C preprocessor. | |
3396 | ||
3397 | @item %c | |
3398 | Process the @code{signed_char} spec. This is intended to be used | |
3399 | to tell cpp whether a char is signed. It typically has the definition: | |
3400 | @smallexample | |
3401 | %@{funsigned-char:-D__CHAR_UNSIGNED__@} | |
3402 | @end smallexample | |
3403 | ||
3404 | @item %1 | |
3405 | Process the @code{cc1} spec. This is used to construct the options to be | |
3406 | passed to the actual C compiler (@samp{cc1}). | |
3407 | ||
3408 | @item %2 | |
3409 | Process the @code{cc1plus} spec. This is used to construct the options to be | |
3410 | passed to the actual C++ compiler (@samp{cc1plus}). | |
3411 | ||
3412 | @item %* | |
3413 | Substitute the variable part of a matched option. See below. | |
3414 | Note that each comma in the substituted string is replaced by | |
3415 | a single space. | |
3416 | ||
3417 | @item %@{@code{S}@} | |
3418 | Substitutes the @code{-S} switch, if that switch was given to GCC. | |
3419 | If that switch was not specified, this substitutes nothing. Note that | |
3420 | the leading dash is omitted when specifying this option, and it is | |
3421 | automatically inserted if the substitution is performed. Thus the spec | |
3422 | string @samp{%@{foo@}} would match the command-line option @samp{-foo} | |
3423 | and would output the command line option @samp{-foo}. | |
3424 | ||
3425 | @item %W@{@code{S}@} | |
3426 | Like %@{@code{S}@} but mark last argument supplied within as a file to be | |
3427 | deleted on failure. | |
3428 | ||
3429 | @item %@{@code{S}*@} | |
3430 | Substitutes all the switches specified to GCC whose names start | |
3431 | with @code{-S}, but which also take an argument. This is used for | |
3432 | switches like @samp{-o, -D, -I}, etc. GCC considers @samp{-o foo} as being | |
3433 | one switch whose names starts with @samp{o}. %@{o*@} would substitute this | |
3434 | text, including the space. Thus two arguments would be generated. | |
3435 | ||
3436 | @item %@{^@code{S}*@} | |
3437 | Like %@{@code{S}*@}, but don't put a blank between a switch and its | |
3438 | argument. Thus %@{^o*@} would only generate one argument, not two. | |
3439 | ||
3440 | @item %@{@code{S}*:@code{X}@} | |
3441 | Substitutes @code{X} if one or more switches whose names start with | |
3442 | @code{-S} are specified to GCC. Note that the tail part of the | |
3443 | @code{-S} option (i.e. the part matched by the @samp{*}) will be substituted | |
3444 | for each occurrence of @samp{%*} within @code{X}. | |
3445 | ||
3446 | @item %@{@code{S}:@code{X}@} | |
3447 | Substitutes @code{X}, but only if the @samp{-S} switch was given to GCC. | |
3448 | ||
3449 | @item %@{!@code{S}:@code{X}@} | |
3450 | Substitutes @code{X}, but only if the @samp{-S} switch was @emph{not} given to GCC. | |
3451 | ||
3452 | @item %@{|@code{S}:@code{X}@} | |
3453 | Like %@{@code{S}:@code{X}@}, but if no @code{S} switch, substitute @samp{-}. | |
3454 | ||
3455 | @item %@{|!@code{S}:@code{X}@} | |
3456 | Like %@{!@code{S}:@code{X}@}, but if there is an @code{S} switch, substitute @samp{-}. | |
3457 | ||
3458 | @item %@{.@code{S}:@code{X}@} | |
3459 | Substitutes @code{X}, but only if processing a file with suffix @code{S}. | |
3460 | ||
3461 | @item %@{!.@code{S}:@code{X}@} | |
3462 | Substitutes @code{X}, but only if @emph{not} processing a file with suffix @code{S}. | |
3463 | ||
3464 | @item %@{@code{S}|@code{P}:@code{X}@} | |
3465 | Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC. This may be | |
3466 | combined with @samp{!} and @samp{.} sequences as well, although they | |
3467 | have a stronger binding than the @samp{|}. For example a spec string | |
3468 | like this: | |
3469 | ||
3470 | @smallexample | |
3471 | %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} | |
3472 | @end smallexample | |
3473 | ||
3474 | will output the following command-line options from the following input | |
3475 | command-line options: | |
3476 | ||
3477 | @smallexample | |
3478 | fred.c -foo -baz | |
3479 | jim.d -bar -boggle | |
3480 | -d fred.c -foo -baz -boggle | |
3481 | -d jim.d -bar -baz -boggle | |
3482 | @end smallexample | |
3483 | ||
3484 | @end table | |
3485 | ||
3486 | The conditional text @code{X} in a %@{@code{S}:@code{X}@} or | |
3487 | %@{!@code{S}:@code{X}@} construct may contain other nested @samp{%} constructs | |
3488 | or spaces, or even newlines. They are processed as usual, as described | |
3489 | above. | |
3490 | ||
3491 | The @samp{-O, -f, -m, and -W} switches are handled specifically in these | |
3492 | constructs. If another value of @samp{-O} or the negated form of a @samp{-f, -m, or | |
3493 | -W} switch is found later in the command line, the earlier switch | |
3494 | value is ignored, except with @{@code{S}*@} where @code{S} is just one | |
3495 | letter, which passes all matching options. | |
3496 | ||
3497 | The character @samp{|} at the beginning of the predicate text is used to indicate | |
3498 | that a command should be piped to the following command, but only if @samp{-pipe} | |
3499 | is specified. | |
3500 | ||
3501 | It is built into GCC which switches take arguments and which do not. | |
3502 | (You might think it would be useful to generalize this to allow each | |
3503 | compiler's spec to say which switches take arguments. But this cannot | |
3504 | be done in a consistent fashion. GCC cannot even decide which input | |
3505 | files have been specified without knowing which switches take arguments, | |
3506 | and it must know which input files to compile in order to tell which | |
3507 | compilers to run). | |
3508 | ||
3509 | GCC also knows implicitly that arguments starting in @samp{-l} are to be | |
3510 | treated as compiler output files, and passed to the linker in their | |
3511 | proper position among the other output files. | |
3512 | ||
74291a4b MM |
3513 | @node Target Options |
3514 | @section Specifying Target Machine and Compiler Version | |
3515 | @cindex target options | |
3516 | @cindex cross compiling | |
3517 | @cindex specifying machine version | |
3518 | @cindex specifying compiler version and target machine | |
3519 | @cindex compiler version, specifying | |
3520 | @cindex target machine, specifying | |
3521 | ||
0c2d1a2a | 3522 | By default, GCC compiles code for the same type of machine that you |
74291a4b MM |
3523 | are using. However, it can also be installed as a cross-compiler, to |
3524 | compile for some other type of machine. In fact, several different | |
0c2d1a2a | 3525 | configurations of GCC, for different target machines, can be |
74291a4b MM |
3526 | installed side by side. Then you specify which one to use with the |
3527 | @samp{-b} option. | |
3528 | ||
0c2d1a2a | 3529 | In addition, older and newer versions of GCC can be installed side |
74291a4b MM |
3530 | by side. One of them (probably the newest) will be the default, but |
3531 | you may sometimes wish to use another. | |
3532 | ||
3533 | @table @code | |
3534 | @item -b @var{machine} | |
3535 | The argument @var{machine} specifies the target machine for compilation. | |
0c2d1a2a | 3536 | This is useful when you have installed GCC as a cross-compiler. |
74291a4b MM |
3537 | |
3538 | The value to use for @var{machine} is the same as was specified as the | |
0c2d1a2a | 3539 | machine type when configuring GCC as a cross-compiler. For |
74291a4b MM |
3540 | example, if a cross-compiler was configured with @samp{configure |
3541 | i386v}, meaning to compile for an 80386 running System V, then you | |
3542 | would specify @samp{-b i386v} to run that cross compiler. | |
3543 | ||
3544 | When you do not specify @samp{-b}, it normally means to compile for | |
3545 | the same type of machine that you are using. | |
3546 | ||
3547 | @item -V @var{version} | |
0c2d1a2a | 3548 | The argument @var{version} specifies which version of GCC to run. |
74291a4b | 3549 | This is useful when multiple versions are installed. For example, |
0c2d1a2a | 3550 | @var{version} might be @samp{2.0}, meaning to run GCC version 2.0. |
74291a4b MM |
3551 | |
3552 | The default version, when you do not specify @samp{-V}, is the last | |
0c2d1a2a | 3553 | version of GCC that you installed. |
74291a4b MM |
3554 | @end table |
3555 | ||
3556 | The @samp{-b} and @samp{-V} options actually work by controlling part of | |
3557 | the file name used for the executable files and libraries used for | |
0c2d1a2a | 3558 | compilation. A given version of GCC, for a given target machine, is |
74291a4b MM |
3559 | normally kept in the directory @file{/usr/local/lib/gcc-lib/@var{machine}/@var{version}}.@refill |
3560 | ||
3561 | Thus, sites can customize the effect of @samp{-b} or @samp{-V} either by | |
3562 | changing the names of these directories or adding alternate names (or | |
3563 | symbolic links). If in directory @file{/usr/local/lib/gcc-lib/} the | |
3564 | file @file{80386} is a link to the file @file{i386v}, then @samp{-b | |
3565 | 80386} becomes an alias for @samp{-b i386v}. | |
3566 | ||
3567 | In one respect, the @samp{-b} or @samp{-V} do not completely change | |
3568 | to a different compiler: the top-level driver program @code{gcc} | |
3569 | that you originally invoked continues to run and invoke the other | |
3570 | executables (preprocessor, compiler per se, assembler and linker) | |
3571 | that do the real work. However, since no real work is done in the | |
3572 | driver program, it usually does not matter that the driver program | |
3573 | in use is not the one for the specified target and version. | |
3574 | ||
3575 | The only way that the driver program depends on the target machine is | |
3576 | in the parsing and handling of special machine-specific options. | |
3577 | However, this is controlled by a file which is found, along with the | |
3578 | other executables, in the directory for the specified version and | |
3579 | target machine. As a result, a single installed driver program adapts | |
3580 | to any specified target machine and compiler version. | |
3581 | ||
3582 | The driver program executable does control one significant thing, | |
3583 | however: the default version and target machine. Therefore, you can | |
3584 | install different instances of the driver program, compiled for | |
3585 | different targets or versions, under different names. | |
3586 | ||
3587 | For example, if the driver for version 2.0 is installed as @code{ogcc} | |
3588 | and that for version 2.1 is installed as @code{gcc}, then the command | |
3589 | @code{gcc} will use version 2.1 by default, while @code{ogcc} will use | |
3590 | 2.0 by default. However, you can choose either version with either | |
3591 | command with the @samp{-V} option. | |
3592 | ||
3593 | @node Submodel Options | |
3594 | @section Hardware Models and Configurations | |
3595 | @cindex submodel options | |
3596 | @cindex specifying hardware config | |
3597 | @cindex hardware models and configurations, specifying | |
3598 | @cindex machine dependent options | |
3599 | ||
3600 | Earlier we discussed the standard option @samp{-b} which chooses among | |
3601 | different installed compilers for completely different target | |
3602 | machines, such as Vax vs. 68000 vs. 80386. | |
3603 | ||
3604 | In addition, each of these target machine types can have its own | |
3605 | special options, starting with @samp{-m}, to choose among various | |
3606 | hardware models or configurations---for example, 68010 vs 68020, | |
3607 | floating coprocessor or none. A single installed version of the | |
3608 | compiler can compile for any model or configuration, according to the | |
3609 | options specified. | |
3610 | ||
3611 | Some configurations of the compiler also support additional special | |
3612 | options, usually for compatibility with other compilers on the same | |
3613 | platform. | |
3614 | ||
3615 | @ifset INTERNALS | |
3616 | These options are defined by the macro @code{TARGET_SWITCHES} in the | |
3617 | machine description. The default for the options is also defined by | |
3618 | that macro, which enables you to change the defaults. | |
3619 | @end ifset | |
3620 | ||
3621 | @menu | |
3622 | * M680x0 Options:: | |
3623 | * VAX Options:: | |
3624 | * SPARC Options:: | |
3625 | * Convex Options:: | |
3626 | * AMD29K Options:: | |
3627 | * ARM Options:: | |
157a620e | 3628 | * Thumb Options:: |
ecff22ab | 3629 | * MN10200 Options:: |
6d6d0fa0 | 3630 | * MN10300 Options:: |
861bb6c1 | 3631 | * M32R/D Options:: |
74291a4b MM |
3632 | * M88K Options:: |
3633 | * RS/6000 and PowerPC Options:: | |
3634 | * RT Options:: | |
3635 | * MIPS Options:: | |
3636 | * i386 Options:: | |
3637 | * HPPA Options:: | |
3638 | * Intel 960 Options:: | |
3639 | * DEC Alpha Options:: | |
3640 | * Clipper Options:: | |
3641 | * H8/300 Options:: | |
3642 | * SH Options:: | |
3643 | * System V Options:: | |
282a61e6 | 3644 | * TMS320C3x/C4x Options:: |
f84271d9 | 3645 | * V850 Options:: |
56b2d7a7 | 3646 | * ARC Options:: |
83575957 | 3647 | * NS32K Options:: |
74291a4b MM |
3648 | @end menu |
3649 | ||
3650 | @node M680x0 Options | |
3651 | @subsection M680x0 Options | |
3652 | @cindex M680x0 options | |
3653 | ||
3654 | These are the @samp{-m} options defined for the 68000 series. The default | |
3655 | values for these options depends on which style of 68000 was selected when | |
3656 | the compiler was configured; the defaults for the most common choices are | |
3657 | given below. | |
3658 | ||
3659 | @table @code | |
3660 | @item -m68000 | |
3661 | @itemx -mc68000 | |
3662 | Generate output for a 68000. This is the default | |
3663 | when the compiler is configured for 68000-based systems. | |
3664 | ||
74cf1c6d RK |
3665 | Use this option for microcontrollers with a 68000 or EC000 core, |
3666 | including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. | |
3667 | ||
74291a4b MM |
3668 | @item -m68020 |
3669 | @itemx -mc68020 | |
3670 | Generate output for a 68020. This is the default | |
3671 | when the compiler is configured for 68020-based systems. | |
3672 | ||
3673 | @item -m68881 | |
3674 | Generate output containing 68881 instructions for floating point. | |
3675 | This is the default for most 68020 systems unless @samp{-nfp} was | |
3676 | specified when the compiler was configured. | |
3677 | ||
3678 | @item -m68030 | |
3679 | Generate output for a 68030. This is the default when the compiler is | |
3680 | configured for 68030-based systems. | |
3681 | ||
3682 | @item -m68040 | |
3683 | Generate output for a 68040. This is the default when the compiler is | |
3684 | configured for 68040-based systems. | |
3685 | ||
3686 | This option inhibits the use of 68881/68882 instructions that have to be | |
74cf1c6d RK |
3687 | emulated by software on the 68040. Use this option if your 68040 does not |
3688 | have code to emulate those instructions. | |
74291a4b MM |
3689 | |
3690 | @item -m68060 | |
3691 | Generate output for a 68060. This is the default when the compiler is | |
3692 | configured for 68060-based systems. | |
3693 | ||
3694 | This option inhibits the use of 68020 and 68881/68882 instructions that | |
74cf1c6d RK |
3695 | have to be emulated by software on the 68060. Use this option if your 68060 |
3696 | does not have code to emulate those instructions. | |
3697 | ||
3698 | @item -mcpu32 | |
3699 | Generate output for a CPU32. This is the default | |
3700 | when the compiler is configured for CPU32-based systems. | |
3701 | ||
3702 | Use this option for microcontrollers with a | |
3703 | CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, | |
3704 | 68336, 68340, 68341, 68349 and 68360. | |
74291a4b MM |
3705 | |
3706 | @item -m5200 | |
3707 | Generate output for a 520X "coldfire" family cpu. This is the default | |
3708 | when the compiler is configured for 520X-based systems. | |
3709 | ||
74cf1c6d RK |
3710 | Use this option for microcontroller with a 5200 core, including |
3711 | the MCF5202, MCF5203, MCF5204 and MCF5202. | |
3712 | ||
74291a4b MM |
3713 | |
3714 | @item -m68020-40 | |
3715 | Generate output for a 68040, without using any of the new instructions. | |
3716 | This results in code which can run relatively efficiently on either a | |
3717 | 68020/68881 or a 68030 or a 68040. The generated code does use the | |
3718 | 68881 instructions that are emulated on the 68040. | |
3719 | ||
861bb6c1 JL |
3720 | @item -m68020-60 |
3721 | Generate output for a 68060, without using any of the new instructions. | |
3722 | This results in code which can run relatively efficiently on either a | |
3723 | 68020/68881 or a 68030 or a 68040. The generated code does use the | |
3724 | 68881 instructions that are emulated on the 68060. | |
3725 | ||
74291a4b MM |
3726 | @item -mfpa |
3727 | Generate output containing Sun FPA instructions for floating point. | |
3728 | ||
3729 | @item -msoft-float | |
3730 | Generate output containing library calls for floating point. | |
3731 | @strong{Warning:} the requisite libraries are not available for all m68k | |
3732 | targets. Normally the facilities of the machine's usual C compiler are | |
3733 | used, but this can't be done directly in cross-compilation. You must | |
3734 | make your own arrangements to provide suitable library functions for | |
3735 | cross-compilation. The embedded targets @samp{m68k-*-aout} and | |
3736 | @samp{m68k-*-coff} do provide software floating point support. | |
3737 | ||
3738 | @item -mshort | |
3739 | Consider type @code{int} to be 16 bits wide, like @code{short int}. | |
3740 | ||
3741 | @item -mnobitfield | |
74cf1c6d RK |
3742 | Do not use the bit-field instructions. The @samp{-m68000}, @samp{-mcpu32} |
3743 | and @samp{-m5200} options imply @w{@samp{-mnobitfield}}. | |
74291a4b MM |
3744 | |
3745 | @item -mbitfield | |
3746 | Do use the bit-field instructions. The @samp{-m68020} option implies | |
3747 | @samp{-mbitfield}. This is the default if you use a configuration | |
3748 | designed for a 68020. | |
3749 | ||
3750 | @item -mrtd | |
3751 | Use a different function-calling convention, in which functions | |
3752 | that take a fixed number of arguments return with the @code{rtd} | |
3753 | instruction, which pops their arguments while returning. This | |
3754 | saves one instruction in the caller since there is no need to pop | |
3755 | the arguments there. | |
3756 | ||
3757 | This calling convention is incompatible with the one normally | |
3758 | used on Unix, so you cannot use it if you need to call libraries | |
3759 | compiled with the Unix compiler. | |
3760 | ||
3761 | Also, you must provide function prototypes for all functions that | |
3762 | take variable numbers of arguments (including @code{printf}); | |
3763 | otherwise incorrect code will be generated for calls to those | |
3764 | functions. | |
3765 | ||
3766 | In addition, seriously incorrect code will result if you call a | |
3767 | function with too many arguments. (Normally, extra arguments are | |
3768 | harmlessly ignored.) | |
3769 | ||
3770 | The @code{rtd} instruction is supported by the 68010, 68020, 68030, | |
74cf1c6d | 3771 | 68040, 68060 and CPU32 processors, but not by the 68000 or 5200. |
861bb6c1 JL |
3772 | |
3773 | @item -malign-int | |
3774 | @itemx -mno-align-int | |
0c2d1a2a | 3775 | Control whether GCC aligns @code{int}, @code{long}, @code{long long}, |
861bb6c1 JL |
3776 | @code{float}, @code{double}, and @code{long double} variables on a 32-bit |
3777 | boundary (@samp{-malign-int}) or a 16-bit boundary (@samp{-mno-align-int}). | |
3778 | Aligning variables on 32-bit boundaries produces code that runs somewhat | |
3779 | faster on processors with 32-bit busses at the expense of more memory. | |
3780 | ||
0c2d1a2a | 3781 | @strong{Warning:} if you use the @samp{-malign-int} switch, GCC will |
861bb6c1 JL |
3782 | align structures containing the above types differently than |
3783 | most published application binary interface specifications for the m68k. | |
3784 | ||
fb868474 DL |
3785 | @item -mpcrel |
3786 | Use the pc-relative addressing mode of the 68000 directly, instead of | |
3787 | using a global offset table. At present, this option implies -fpic, | |
3788 | allowing at most a 16-bit offset for pc-relative addressing. -fPIC is | |
3789 | not presently supported with -mpcrel, though this could be supported for | |
3790 | 68020 and higher processors. | |
3791 | ||
74291a4b MM |
3792 | @end table |
3793 | ||
3794 | @node VAX Options | |
3795 | @subsection VAX Options | |
3796 | @cindex VAX options | |
3797 | ||
3798 | These @samp{-m} options are defined for the Vax: | |
3799 | ||
3800 | @table @code | |
3801 | @item -munix | |
3802 | Do not output certain jump instructions (@code{aobleq} and so on) | |
3803 | that the Unix assembler for the Vax cannot handle across long | |
3804 | ranges. | |
3805 | ||
3806 | @item -mgnu | |
3807 | Do output those jump instructions, on the assumption that you | |
3808 | will assemble with the GNU assembler. | |
3809 | ||
3810 | @item -mg | |
3811 | Output code for g-format floating point numbers instead of d-format. | |
3812 | @end table | |
3813 | ||
3814 | @node SPARC Options | |
3815 | @subsection SPARC Options | |
3816 | @cindex SPARC options | |
3817 | ||
3818 | These @samp{-m} switches are supported on the SPARC: | |
3819 | ||
3820 | @table @code | |
3821 | @item -mno-app-regs | |
3822 | @itemx -mapp-regs | |
3823 | Specify @samp{-mapp-regs} to generate output using the global registers | |
3824 | 2 through 4, which the SPARC SVR4 ABI reserves for applications. This | |
3825 | is the default. | |
3826 | ||
3827 | To be fully SVR4 ABI compliant at the cost of some performance loss, | |
3828 | specify @samp{-mno-app-regs}. You should compile libraries and system | |
3829 | software with this option. | |
3830 | ||
3831 | @item -mfpu | |
3832 | @itemx -mhard-float | |
3833 | Generate output containing floating point instructions. This is the | |
3834 | default. | |
3835 | ||
3836 | @item -mno-fpu | |
3837 | @itemx -msoft-float | |
3838 | Generate output containing library calls for floating point. | |
3839 | @strong{Warning:} the requisite libraries are not available for all SPARC | |
3840 | targets. Normally the facilities of the machine's usual C compiler are | |
3841 | used, but this cannot be done directly in cross-compilation. You must make | |
3842 | your own arrangements to provide suitable library functions for | |
3843 | cross-compilation. The embedded targets @samp{sparc-*-aout} and | |
3844 | @samp{sparclite-*-*} do provide software floating point support. | |
3845 | ||
3846 | @samp{-msoft-float} changes the calling convention in the output file; | |
3847 | therefore, it is only useful if you compile @emph{all} of a program with | |
3848 | this option. In particular, you need to compile @file{libgcc.a}, the | |
0c2d1a2a | 3849 | library that comes with GCC, with @samp{-msoft-float} in order for |
74291a4b MM |
3850 | this to work. |
3851 | ||
3852 | @item -mhard-quad-float | |
3853 | Generate output containing quad-word (long double) floating point | |
3854 | instructions. | |
3855 | ||
3856 | @item -msoft-quad-float | |
3857 | Generate output containing library calls for quad-word (long double) | |
3858 | floating point instructions. The functions called are those specified | |
3859 | in the SPARC ABI. This is the default. | |
3860 | ||
3861 | As of this writing, there are no sparc implementations that have hardware | |
3862 | support for the quad-word floating point instructions. They all invoke | |
3863 | a trap handler for one of these instructions, and then the trap handler | |
3864 | emulates the effect of the instruction. Because of the trap handler overhead, | |
3865 | this is much slower than calling the ABI library routines. Thus the | |
3866 | @samp{-msoft-quad-float} option is the default. | |
3867 | ||
3868 | @item -mno-epilogue | |
3869 | @itemx -mepilogue | |
3870 | With @samp{-mepilogue} (the default), the compiler always emits code for | |
3871 | function exit at the end of each function. Any function exit in | |
3872 | the middle of the function (such as a return statement in C) will | |
3873 | generate a jump to the exit code at the end of the function. | |
3874 | ||
3875 | With @samp{-mno-epilogue}, the compiler tries to emit exit code inline | |
3876 | at every function exit. | |
3877 | ||
3878 | @item -mno-flat | |
3879 | @itemx -mflat | |
3880 | With @samp{-mflat}, the compiler does not generate save/restore instructions | |
3881 | and will use a "flat" or single register window calling convention. | |
3882 | This model uses %i7 as the frame pointer and is compatible with the normal | |
3883 | register window model. Code from either may be intermixed. | |
3884 | The local registers and the input registers (0-5) are still treated as | |
3885 | "call saved" registers and will be saved on the stack as necessary. | |
3886 | ||
3887 | With @samp{-mno-flat} (the default), the compiler emits save/restore | |
3888 | instructions (except for leaf functions) and is the normal mode of operation. | |
3889 | ||
3890 | @item -mno-unaligned-doubles | |
3891 | @itemx -munaligned-doubles | |
3892 | Assume that doubles have 8 byte alignment. This is the default. | |
3893 | ||
0c2d1a2a | 3894 | With @samp{-munaligned-doubles}, GCC assumes that doubles have 8 byte |
74291a4b MM |
3895 | alignment only if they are contained in another type, or if they have an |
3896 | absolute address. Otherwise, it assumes they have 4 byte alignment. | |
3897 | Specifying this option avoids some rare compatibility problems with code | |
3898 | generated by other compilers. It is not the default because it results | |
3899 | in a performance loss, especially for floating point code. | |
3900 | ||
3901 | @item -mv8 | |
3902 | @itemx -msparclite | |
3903 | These two options select variations on the SPARC architecture. | |
3904 | ||
3905 | By default (unless specifically configured for the Fujitsu SPARClite), | |
3906 | GCC generates code for the v7 variant of the SPARC architecture. | |
3907 | ||
3908 | @samp{-mv8} will give you SPARC v8 code. The only difference from v7 | |
3909 | code is that the compiler emits the integer multiply and integer | |
3910 | divide instructions which exist in SPARC v8 but not in SPARC v7. | |
3911 | ||
3912 | @samp{-msparclite} will give you SPARClite code. This adds the integer | |
3913 | multiply, integer divide step and scan (@code{ffs}) instructions which | |
3914 | exist in SPARClite but not in SPARC v7. | |
3915 | ||
0c2d1a2a | 3916 | These options are deprecated and will be deleted in a future GCC release. |
74291a4b MM |
3917 | They have been replaced with @samp{-mcpu=xxx}. |
3918 | ||
3919 | @item -mcypress | |
3920 | @itemx -msupersparc | |
3921 | These two options select the processor for which the code is optimised. | |
3922 | ||
3923 | With @samp{-mcypress} (the default), the compiler optimizes code for the | |
3924 | Cypress CY7C602 chip, as used in the SparcStation/SparcServer 3xx series. | |
3925 | This is also appropriate for the older SparcStation 1, 2, IPX etc. | |
3926 | ||
3927 | With @samp{-msupersparc} the compiler optimizes code for the SuperSparc cpu, as | |
3928 | used in the SparcStation 10, 1000 and 2000 series. This flag also enables use | |
3929 | of the full SPARC v8 instruction set. | |
3930 | ||
0c2d1a2a | 3931 | These options are deprecated and will be deleted in a future GCC release. |
74291a4b MM |
3932 | They have been replaced with @samp{-mcpu=xxx}. |
3933 | ||
3934 | @item -mcpu=@var{cpu_type} | |
c0498f43 DE |
3935 | Set the instruction set, register set, and instruction scheduling parameters |
3936 | for machine type @var{cpu_type}. Supported values for @var{cpu_type} are | |
3937 | @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite}, | |
ad6843d7 RH |
3938 | @samp{hypersparc}, @samp{sparclite86x}, @samp{f930}, @samp{f934}, |
3939 | @samp{sparclet}, @samp{tsc701}, @samp{v9}, and @samp{ultrasparc}. | |
c0498f43 DE |
3940 | |
3941 | Default instruction scheduling parameters are used for values that select | |
3942 | an architecture and not an implementation. These are @samp{v7}, @samp{v8}, | |
3943 | @samp{sparclite}, @samp{sparclet}, @samp{v9}. | |
3944 | ||
3945 | Here is a list of each supported architecture and their supported | |
3946 | implementations. | |
3947 | ||
3948 | @smallexample | |
3949 | v7: cypress | |
ad6843d7 RH |
3950 | v8: supersparc, hypersparc |
3951 | sparclite: f930, f934, sparclite86x | |
c0498f43 DE |
3952 | sparclet: tsc701 |
3953 | v9: ultrasparc | |
3954 | @end smallexample | |
74291a4b MM |
3955 | |
3956 | @item -mtune=@var{cpu_type} | |
3957 | Set the instruction scheduling parameters for machine type | |
c0498f43 DE |
3958 | @var{cpu_type}, but do not set the instruction set or register set that the |
3959 | option @samp{-mcpu=}@var{cpu_type} would. | |
3960 | ||
3961 | The same values for @samp{-mcpu=}@var{cpu_type} are used for | |
e5e809f4 | 3962 | @samp{-mtune=}@*@var{cpu_type}, though the only useful values are those that |
c0498f43 | 3963 | select a particular cpu implementation: @samp{cypress}, @samp{supersparc}, |
ad6843d7 RH |
3964 | @samp{hypersparc}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, |
3965 | @samp{tsc701}, @samp{ultrasparc}. | |
74291a4b MM |
3966 | |
3967 | @end table | |
3968 | ||
3969 | These @samp{-m} switches are supported in addition to the above | |
3970 | on the SPARCLET processor. | |
3971 | ||
3972 | @table @code | |
3973 | @item -mlittle-endian | |
3974 | Generate code for a processor running in little-endian mode. | |
3975 | ||
3976 | @item -mlive-g0 | |
3977 | Treat register @code{%g0} as a normal register. | |
3978 | GCC will continue to clobber it as necessary but will not assume | |
3979 | it always reads as 0. | |
3980 | ||
3981 | @item -mbroken-saverestore | |
3982 | Generate code that does not use non-trivial forms of the @code{save} and | |
3983 | @code{restore} instructions. Early versions of the SPARCLET processor do | |
3984 | not correctly handle @code{save} and @code{restore} instructions used with | |
3985 | arguments. They correctly handle them used without arguments. A @code{save} | |
3986 | instruction used without arguments increments the current window pointer | |
3987 | but does not allocate a new stack frame. It is assumed that the window | |
3988 | overflow trap handler will properly handle this case as will interrupt | |
3989 | handlers. | |
3990 | @end table | |
3991 | ||
3992 | These @samp{-m} switches are supported in addition to the above | |
3993 | on SPARC V9 processors in 64 bit environments. | |
3994 | ||
3995 | @table @code | |
3996 | @item -mlittle-endian | |
3997 | Generate code for a processor running in little-endian mode. | |
3998 | ||
ded17aad DE |
3999 | @item -m32 |
4000 | @itemx -m64 | |
4001 | Generate code for a 32 bit or 64 bit environment. | |
4002 | The 32 bit environment sets int, long and pointer to 32 bits. | |
4003 | The 64 bit environment sets int to 32 bits and long and pointer | |
4004 | to 64 bits. | |
4005 | ||
4006 | @item -mcmodel=medlow | |
4007 | Generate code for the Medium/Low code model: the program must be linked | |
4008 | in the low 32 bits of the address space. Pointers are 64 bits. | |
4009 | Programs can be statically or dynamically linked. | |
4010 | ||
4011 | @item -mcmodel=medmid | |
4012 | Generate code for the Medium/Middle code model: the program must be linked | |
4013 | in the low 44 bits of the address space, the text segment must be less than | |
4014 | 2G bytes, and data segment must be within 2G of the text segment. | |
4015 | Pointers are 64 bits. | |
4016 | ||
4017 | @item -mcmodel=medany | |
4018 | Generate code for the Medium/Anywhere code model: the program may be linked | |
4019 | anywhere in the address space, the text segment must be less than | |
4020 | 2G bytes, and data segment must be within 2G of the text segment. | |
4021 | Pointers are 64 bits. | |
4022 | ||
4023 | @item -mcmodel=embmedany | |
4024 | Generate code for the Medium/Anywhere code model for embedded systems: | |
4025 | assume a 32 bit text and a 32 bit data segment, both starting anywhere | |
4026 | (determined at link time). Register %g4 points to the base of the | |
4027 | data segment. Pointers still 64 bits. | |
4028 | Programs are statically linked, PIC is not supported. | |
74291a4b MM |
4029 | |
4030 | @item -mstack-bias | |
4031 | @itemx -mno-stack-bias | |
0c2d1a2a | 4032 | With @samp{-mstack-bias}, GCC assumes that the stack pointer, and |
74291a4b MM |
4033 | frame pointer if present, are offset by -2047 which must be added back |
4034 | when making stack frame references. | |
4035 | Otherwise, assume no such offset is present. | |
4036 | @end table | |
4037 | ||
4038 | @node Convex Options | |
4039 | @subsection Convex Options | |
4040 | @cindex Convex options | |
4041 | ||
4042 | These @samp{-m} options are defined for Convex: | |
4043 | ||
4044 | @table @code | |
4045 | @item -mc1 | |
4046 | Generate output for C1. The code will run on any Convex machine. | |
4047 | The preprocessor symbol @code{__convex__c1__} is defined. | |
4048 | ||
4049 | @item -mc2 | |
4050 | Generate output for C2. Uses instructions not available on C1. | |
4051 | Scheduling and other optimizations are chosen for max performance on C2. | |
4052 | The preprocessor symbol @code{__convex_c2__} is defined. | |
4053 | ||
4054 | @item -mc32 | |
4055 | Generate output for C32xx. Uses instructions not available on C1. | |
4056 | Scheduling and other optimizations are chosen for max performance on C32. | |
4057 | The preprocessor symbol @code{__convex_c32__} is defined. | |
4058 | ||
4059 | @item -mc34 | |
4060 | Generate output for C34xx. Uses instructions not available on C1. | |
4061 | Scheduling and other optimizations are chosen for max performance on C34. | |
4062 | The preprocessor symbol @code{__convex_c34__} is defined. | |
4063 | ||
4064 | @item -mc38 | |
4065 | Generate output for C38xx. Uses instructions not available on C1. | |
4066 | Scheduling and other optimizations are chosen for max performance on C38. | |
4067 | The preprocessor symbol @code{__convex_c38__} is defined. | |
4068 | ||
4069 | @item -margcount | |
4070 | Generate code which puts an argument count in the word preceding each | |
4071 | argument list. This is compatible with regular CC, and a few programs | |
4072 | may need the argument count word. GDB and other source-level debuggers | |
4073 | do not need it; this info is in the symbol table. | |
4074 | ||
4075 | @item -mnoargcount | |
4076 | Omit the argument count word. This is the default. | |
4077 | ||
4078 | @item -mvolatile-cache | |
4079 | Allow volatile references to be cached. This is the default. | |
4080 | ||
4081 | @item -mvolatile-nocache | |
4082 | Volatile references bypass the data cache, going all the way to memory. | |
4083 | This is only needed for multi-processor code that does not use standard | |
4084 | synchronization instructions. Making non-volatile references to volatile | |
4085 | locations will not necessarily work. | |
4086 | ||
4087 | @item -mlong32 | |
4088 | Type long is 32 bits, the same as type int. This is the default. | |
4089 | ||
4090 | @item -mlong64 | |
4091 | Type long is 64 bits, the same as type long long. This option is useless, | |
4092 | because no library support exists for it. | |
4093 | @end table | |
4094 | ||
4095 | @node AMD29K Options | |
4096 | @subsection AMD29K Options | |
4097 | @cindex AMD29K options | |
4098 | ||
4099 | These @samp{-m} options are defined for the AMD Am29000: | |
4100 | ||
4101 | @table @code | |
4102 | @item -mdw | |
4103 | @kindex -mdw | |
4104 | @cindex DW bit (29k) | |
4105 | Generate code that assumes the @code{DW} bit is set, i.e., that byte and | |
4106 | halfword operations are directly supported by the hardware. This is the | |
4107 | default. | |
4108 | ||
4109 | @item -mndw | |
4110 | @kindex -mndw | |
4111 | Generate code that assumes the @code{DW} bit is not set. | |
4112 | ||
4113 | @item -mbw | |
4114 | @kindex -mbw | |
4115 | @cindex byte writes (29k) | |
4116 | Generate code that assumes the system supports byte and halfword write | |
4117 | operations. This is the default. | |
4118 | ||
4119 | @item -mnbw | |
4120 | @kindex -mnbw | |
4121 | Generate code that assumes the systems does not support byte and | |
4122 | halfword write operations. @samp{-mnbw} implies @samp{-mndw}. | |
4123 | ||
4124 | @item -msmall | |
4125 | @kindex -msmall | |
4126 | @cindex memory model (29k) | |
4127 | Use a small memory model that assumes that all function addresses are | |
4128 | either within a single 256 KB segment or at an absolute address of less | |
4129 | than 256k. This allows the @code{call} instruction to be used instead | |
4130 | of a @code{const}, @code{consth}, @code{calli} sequence. | |
4131 | ||
4132 | @item -mnormal | |
4133 | @kindex -mnormal | |
4134 | Use the normal memory model: Generate @code{call} instructions only when | |
4135 | calling functions in the same file and @code{calli} instructions | |
4136 | otherwise. This works if each file occupies less than 256 KB but allows | |
4137 | the entire executable to be larger than 256 KB. This is the default. | |
4138 | ||
4139 | @item -mlarge | |
4140 | Always use @code{calli} instructions. Specify this option if you expect | |
4141 | a single file to compile into more than 256 KB of code. | |
4142 | ||
4143 | @item -m29050 | |
4144 | @kindex -m29050 | |
4145 | @cindex processor selection (29k) | |
4146 | Generate code for the Am29050. | |
4147 | ||
4148 | @item -m29000 | |
4149 | @kindex -m29000 | |
4150 | Generate code for the Am29000. This is the default. | |
4151 | ||
4152 | @item -mkernel-registers | |
4153 | @kindex -mkernel-registers | |
4154 | @cindex kernel and user registers (29k) | |
4155 | Generate references to registers @code{gr64-gr95} instead of to | |
4156 | registers @code{gr96-gr127}. This option can be used when compiling | |
4157 | kernel code that wants a set of global registers disjoint from that used | |
4158 | by user-mode code. | |
4159 | ||
4160 | Note that when this option is used, register names in @samp{-f} flags | |
4161 | must use the normal, user-mode, names. | |
4162 | ||
4163 | @item -muser-registers | |
4164 | @kindex -muser-registers | |
4165 | Use the normal set of global registers, @code{gr96-gr127}. This is the | |
4166 | default. | |
4167 | ||
4168 | @item -mstack-check | |
4169 | @itemx -mno-stack-check | |
4170 | @kindex -mstack-check | |
4171 | @cindex stack checks (29k) | |
4172 | Insert (or do not insert) a call to @code{__msp_check} after each stack | |
4173 | adjustment. This is often used for kernel code. | |
4174 | ||
4175 | @item -mstorem-bug | |
4176 | @itemx -mno-storem-bug | |
4177 | @kindex -mstorem-bug | |
4178 | @cindex storem bug (29k) | |
4179 | @samp{-mstorem-bug} handles 29k processors which cannot handle the | |
4180 | separation of a mtsrim insn and a storem instruction (most 29000 chips | |
4181 | to date, but not the 29050). | |
4182 | ||
4183 | @item -mno-reuse-arg-regs | |
4184 | @itemx -mreuse-arg-regs | |
4185 | @kindex -mreuse-arg-regs | |
4186 | @samp{-mno-reuse-arg-regs} tells the compiler to only use incoming argument | |
4187 | registers for copying out arguments. This helps detect calling a function | |
4188 | with fewer arguments than it was declared with. | |
4189 | ||
861bb6c1 JL |
4190 | @item -mno-impure-text |
4191 | @itemx -mimpure-text | |
4192 | @kindex -mimpure-text | |
4193 | @samp{-mimpure-text}, used in addition to @samp{-shared}, tells the compiler to | |
4194 | not pass @samp{-assert pure-text} to the linker when linking a shared object. | |
4195 | ||
74291a4b MM |
4196 | @item -msoft-float |
4197 | @kindex -msoft-float | |
4198 | Generate output containing library calls for floating point. | |
0c2d1a2a | 4199 | @strong{Warning:} the requisite libraries are not part of GCC. |
74291a4b MM |
4200 | Normally the facilities of the machine's usual C compiler are used, but |
4201 | this can't be done directly in cross-compilation. You must make your | |
4202 | own arrangements to provide suitable library functions for | |
4203 | cross-compilation. | |
4e8d7ddc JW |
4204 | |
4205 | @item -mno-multm | |
4206 | @kindex -mno-multm | |
4207 | Do not generate multm or multmu instructions. This is useful for some embedded | |
4208 | systems which do not have trap handlers for these instructions. | |
74291a4b MM |
4209 | @end table |
4210 | ||
4211 | @node ARM Options | |
4212 | @subsection ARM Options | |
4213 | @cindex ARM options | |
4214 | ||
4215 | These @samp{-m} options are defined for Advanced RISC Machines (ARM) | |
4216 | architectures: | |
4217 | ||
4218 | @table @code | |
4219 | @item -mapcs-frame | |
4220 | @kindex -mapcs-frame | |
4221 | Generate a stack frame that is compliant with the ARM Procedure Call | |
4222 | Standard for all functions, even if this is not strictly necessary for | |
157a620e NC |
4223 | correct execution of the code. Specifying @samp{-fomit-frame-pointer} |
4224 | with this option will cause the stack frames not to be generated for | |
4225 | leaf functions. The default is @samp{-mno-apcs-frame}. | |
4226 | ||
4227 | @item -mapcs | |
4228 | @kindex -mapcs | |
4229 | This is a synonym for @samp{-mapcs-frame}. | |
74291a4b MM |
4230 | |
4231 | @item -mapcs-26 | |
4232 | @kindex -mapcs-26 | |
4233 | Generate code for a processor running with a 26-bit program counter, | |
4234 | and conforming to the function calling standards for the APCS 26-bit | |
4235 | option. This option replaces the @samp{-m2} and @samp{-m3} options | |
4236 | of previous releases of the compiler. | |
4237 | ||
4238 | @item -mapcs-32 | |
4239 | @kindex -mapcs-32 | |
4240 | Generate code for a processor running with a 32-bit program counter, | |
4241 | and conforming to the function calling standards for the APCS 32-bit | |
4242 | option. This option replaces the @samp{-m6} option of previous releases | |
4243 | of the compiler. | |
4244 | ||
157a620e NC |
4245 | @item -mapcs-stack-check |
4246 | @kindex -mapcs-stack-check | |
4247 | @kindex -mno-apcs-stack-check | |
4248 | Generate code to check the amount of stack space available upon entry to | |
4249 | every function (that actually uses some stack space). If there is | |
4250 | insufficient space available then either the function | |
4251 | @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be | |
4252 | called, depending upon the amount of stack space required. The run time | |
4253 | system is required to provide these functions. The default is | |
4254 | @samp{-mno-apcs-stack-check}, since this produces smaller code. | |
4255 | ||
4256 | @item -mapcs-float | |
4257 | @kindex -mapcs-float | |
4258 | @kindex -mno-apcs-float | |
4259 | Pass floating point arguments using the float point registers. This is | |
ed0e6530 | 4260 | one of the variants of the APCS. This option is recommended if the |
157a620e NC |
4261 | target hardware has a floating point unit or if a lot of floating point |
4262 | arithmetic is going to be performed by the code. The default is | |
4263 | @samp{-mno-apcs-float}, since integer only code is slightly increased in | |
4264 | size if @samp{-mapcs-float} is used. | |
4265 | ||
4266 | @item -mapcs-reentrant | |
4267 | @kindex -mapcs-reentrant | |
4268 | @kindex -mno-apcs-reentrant | |
4269 | Generate reentrant, position independent code. This is the equivalent | |
4270 | to specifying the @samp{-fpic} option. The default is | |
4271 | @samp{-mno-apcs-reentrant}. | |
4272 | ||
4273 | @item -mthumb-interwork | |
4274 | @kindex -mthumb-interwork | |
4275 | @kindex -mno-thumb-interwork | |
4276 | Generate code which supports calling between the ARM and THUMB | |
4277 | instruction sets. Without this option the two instruction sets cannot | |
4278 | be reliably used inside one program. The default is | |
4279 | @samp{-mno-thumb-interwork}, since slightly larger code is generated | |
4280 | when @samp{-mthumb-interwork} is specified. | |
4281 | ||
4282 | @item -mno-sched-prolog | |
4283 | @kindex -mno-sched-prolog | |
4284 | @kindex -msched-prolog | |
4285 | Prevent the reordering of instructions in the function prolog, or the | |
4286 | merging of those instruction with the instructions in the function's | |
ed0e6530 PB |
4287 | body. This means that all functions will start with a recognizable set |
4288 | of instructions (or in fact one of a choice from a small set of | |
157a620e NC |
4289 | different function prologues), and this information can be used to |
4290 | locate the start if functions inside an executable piece of code. The | |
4291 | default is @samp{-msched-prolog}. | |
4292 | ||
74291a4b MM |
4293 | @item -mhard-float |
4294 | Generate output containing floating point instructions. This is the | |
4295 | default. | |
4296 | ||
4297 | @item -msoft-float | |
4298 | Generate output containing library calls for floating point. | |
4299 | @strong{Warning:} the requisite libraries are not available for all ARM | |
4300 | targets. Normally the facilities of the machine's usual C compiler are | |
4301 | used, but this cannot be done directly in cross-compilation. You must make | |
4302 | your own arrangements to provide suitable library functions for | |
4303 | cross-compilation. | |
4304 | ||
4305 | @samp{-msoft-float} changes the calling convention in the output file; | |
4306 | therefore, it is only useful if you compile @emph{all} of a program with | |
4307 | this option. In particular, you need to compile @file{libgcc.a}, the | |
0c2d1a2a | 4308 | library that comes with GCC, with @samp{-msoft-float} in order for |
74291a4b MM |
4309 | this to work. |
4310 | ||
4311 | @item -mlittle-endian | |
4312 | Generate code for a processor running in little-endian mode. This is | |
4313 | the default for all standard configurations. | |
4314 | ||
4315 | @item -mbig-endian | |
4316 | Generate code for a processor running in big-endian mode; the default is | |
4317 | to compile code for a little-endian processor. | |
4318 | ||
4319 | @item -mwords-little-endian | |
4320 | This option only applies when generating code for big-endian processors. | |
4321 | Generate code for a little-endian word order but a big-endian byte | |
4322 | order. That is, a byte order of the form @samp{32107654}. Note: this | |
4323 | option should only be used if you require compatibility with code for | |
4324 | big-endian ARM processors generated by versions of the compiler prior to | |
4325 | 2.8. | |
4326 | ||
4327 | @item -mshort-load-bytes | |
4328 | @kindex -mshort-load-bytes | |
4329 | Do not try to load half-words (eg @samp{short}s) by loading a word from | |
4330 | an unaligned address. For some targets the MMU is configured to trap | |
4331 | unaligned loads; use this option to generate code that is safe in these | |
4332 | environments. | |
4333 | ||
4334 | @item -mno-short-load-bytes | |
4335 | @kindex -mno-short-load-bytes | |
4336 | Use unaligned word loads to load half-words (eg @samp{short}s). This | |
4337 | option produces more efficient code, but the MMU is sometimes configured | |
4338 | to trap these instructions. | |
4339 | ||
157a620e NC |
4340 | @item -mshort-load-words |
4341 | @kindex -mshort-load-words | |
ed0e6530 | 4342 | This is a synonym for @samp{-mno-short-load-bytes}. |
157a620e NC |
4343 | |
4344 | @item -mno-short-load-words | |
4345 | @kindex -mno-short-load-words | |
ed0e6530 | 4346 | This is a synonym for @samp{-mshort-load-bytes}. |
157a620e | 4347 | |
74291a4b MM |
4348 | @item -mbsd |
4349 | @kindex -mbsd | |
4350 | This option only applies to RISC iX. Emulate the native BSD-mode | |
4351 | compiler. This is the default if @samp{-ansi} is not specified. | |
4352 | ||
4353 | @item -mxopen | |
4354 | @kindex -mxopen | |
4355 | This option only applies to RISC iX. Emulate the native X/Open-mode | |
4356 | compiler. | |
4357 | ||
4358 | @item -mno-symrename | |
4359 | @kindex -mno-symrename | |
4360 | This option only applies to RISC iX. Do not run the assembler | |
4361 | post-processor, @samp{symrename}, after code has been assembled. | |
4362 | Normally it is necessary to modify some of the standard symbols in | |
4363 | preparation for linking with the RISC iX C library; this option | |
4364 | suppresses this pass. The post-processor is never run when the | |
4365 | compiler is built for cross-compilation. | |
157a620e NC |
4366 | |
4367 | @item -mcpu=<name> | |
4368 | @kindex -mcpu= | |
4369 | This specifies the name of the target ARM processor. GCC uses this name | |
4370 | to determine what kind of instructions it can use when generating | |
ed0e6530 | 4371 | assembly code. Permissible names are: arm2, arm250, arm3, arm6, arm60, |
157a620e NC |
4372 | arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi, |
4373 | arm70, arm700, arm700i, arm710, arm710c, arm7100, arm7500, arm7500fe, | |
f5a1b0d2 | 4374 | arm7tdmi, arm8, strongarm, strongarm110, strongarm1100, arm8, arm810, |
62b10bbc NC |
4375 | arm9, arm920, arm920t, arm9tdmi. |
4376 | ||
4377 | @itemx -mtune=<name> | |
4378 | @kindex -mtune= | |
4379 | This option is very similar to the @samp{-mcpu=} option, except that | |
4380 | instead of specifying the actual target processor type, and hence | |
4381 | restricting which instructions can be used, it specifies that GCC should | |
4382 | tune the performance of the code as if the target were of the type | |
4383 | specified in this option, but still choosing the instructions that it | |
4384 | will generate based on the cpu specified by a @samp{-mcpu=} option. | |
4385 | For some arm implementations better performance can be obtained by using | |
4386 | this option. | |
157a620e NC |
4387 | |
4388 | @item -march=<name> | |
4389 | @kindex -march= | |
4390 | This specifies the name of the target ARM architecture. GCC uses this | |
4391 | name to determine what kind of instructions it can use when generating | |
4392 | assembly code. This option can be used in conjunction with or instead | |
ed0e6530 | 4393 | of the @samp{-mcpu=} option. Permissible names are: armv2, armv2a, |
62b10bbc | 4394 | armv3, armv3m, armv4, armv4t, armv5. |
157a620e NC |
4395 | |
4396 | @item -mfpe=<number> | |
59d40964 | 4397 | @itemx -mfp=<number> |
157a620e | 4398 | @kindex -mfpe= |
f5a1b0d2 | 4399 | @kindex -mfp= |
157a620e | 4400 | This specifes the version of the floating point emulation available on |
ed0e6530 | 4401 | the target. Permissible values are 2 and 3. @samp{-mfp=} is a synonym |
f5a1b0d2 | 4402 | for @samp{-mfpe=} to support older versions of GCC. |
157a620e NC |
4403 | |
4404 | @item -mstructure-size-boundary=<n> | |
4405 | @kindex -mstructure-size-boundary | |
4406 | The size of all structures and unions will be rounded up to a multiple | |
ed0e6530 | 4407 | of the number of bits set by this option. Permissible values are 8 and |
157a620e NC |
4408 | 32. The default value varies for different toolchains. For the COFF |
4409 | targeted toolchain the default value is 8. Specifying the larger number | |
ed0e6530 | 4410 | can produce faster, more efficient code, but can also increase the size |
157a620e NC |
4411 | of the program. The two values are potentially incompatible. Code |
4412 | compiled with one value cannot necessarily expect to work with code or | |
4413 | libraries compiled with the other value, if they exchange information | |
4414 | using structures or unions. Programmers are encouraged to use the 32 | |
4415 | value as future versions of the toolchain may default to this value. | |
4416 | ||
f5a1b0d2 NC |
4417 | @item -mabort-on-noreturn |
4418 | @kindex -mabort-on-noreturn | |
4419 | @kindex -mnoabort-on-noreturn | |
4420 | Generate a call to the function abort at the end of a noreturn function. | |
4421 | It will be executed if the function tries to return. | |
4422 | ||
62b10bbc NC |
4423 | @item -mnop-fun-dllimport |
4424 | @kindex -mnop-fun-dllimport | |
4425 | Disable the support for the @emph{dllimport} attribute. | |
4426 | ||
ed0e6530 PB |
4427 | @item -msingle-pic-base |
4428 | @kindex -msingle-pic-base | |
4429 | Treat the register used for PIC addressing as read-only, rather than | |
4430 | loading it in the prologue for each function. The run-time system is | |
4431 | responsible for initialising this register with an appropriate value | |
4432 | before execution begins. | |
4433 | ||
4434 | @item -mpic-register=<reg> | |
4435 | @kindex -mpic-register= | |
4436 | Specify the register to be used for PIC addressing. The default is R10 | |
4437 | unless stack-checking is enabled, when R9 is used. | |
4438 | ||
74291a4b MM |
4439 | @end table |
4440 | ||
157a620e NC |
4441 | @node Thumb Options |
4442 | @subsection Thumb Options | |
4443 | @cindex Thumb Options | |
4444 | ||
4445 | @table @code | |
4446 | ||
4447 | @item -mthumb-interwork | |
4448 | @kindex -mthumb-interwork | |
4449 | @kindex -mno-thumb-interwork | |
4450 | Generate code which supports calling between the THUMB and ARM | |
4451 | instruction sets. Without this option the two instruction sets cannot | |
4452 | be reliably used inside one program. The default is | |
4453 | @samp{-mno-thumb-interwork}, since slightly smaller code is generated | |
4454 | with this option. | |
4455 | ||
4456 | @item -mtpcs-frame | |
4457 | @kindex -mtpcs-frame | |
4458 | @kindex -mno-tpcs-frame | |
4459 | Generate a stack frame that is compliant with the Thumb Procedure Call | |
4460 | Standard for all non-leaf functions. (A leaf function is one that does | |
4461 | not call any other functions). The default is @samp{-mno-apcs-frame}. | |
4462 | ||
4463 | @item -mtpcs-leaf-frame | |
4464 | @kindex -mtpcs-leaf-frame | |
4465 | @kindex -mno-tpcs-leaf-frame | |
4466 | Generate a stack frame that is compliant with the Thumb Procedure Call | |
4467 | Standard for all leaf functions. (A leaf function is one that does | |
4468 | not call any other functions). The default is @samp{-mno-apcs-leaf-frame}. | |
4469 | ||
4470 | @item -mlittle-endian | |
4471 | @kindex -mlittle-endian | |
4472 | Generate code for a processor running in little-endian mode. This is | |
4473 | the default for all standard configurations. | |
4474 | ||
4475 | @item -mbig-endian | |
4476 | @kindex -mbig-endian | |
4477 | Generate code for a processor running in big-endian mode. | |
4478 | ||
4479 | @item -mstructure-size-boundary=<n> | |
4480 | @kindex -mstructure-size-boundary | |
4481 | The size of all structures and unions will be rounded up to a multiple | |
4bdc1ac7 | 4482 | of the number of bits set by this option. Permissible values are 8 and |
157a620e NC |
4483 | 32. The default value varies for different toolchains. For the COFF |
4484 | targeted toolchain the default value is 8. Specifying the larger number | |
4485 | can produced faster, more efficient code, but can also increase the size | |
4486 | of the program. The two values are potentially incompatible. Code | |
4487 | compiled with one value cannot necessarily expect to work with code or | |
4488 | libraries compiled with the other value, if they exchange information | |
4489 | using structures or unions. Programmers are encouraged to use the 32 | |
4490 | value as future versions of the toolchain may default to this value. | |
4491 | ||
62b10bbc NC |
4492 | @item -mnop-fun-dllimport |
4493 | @kindex -mnop-fun-dllimport | |
4494 | Disable the support for the @emph{dllimport} attribute. | |
4495 | ||
4496 | @item -mcallee-super-interworking | |
4497 | @kindex -mcallee-super-interworking | |
4498 | Gives all externally visible functions in the file being compiled an ARM | |
4499 | instruction set header which switches to Thumb mode before executing the | |
4500 | rest of the function. This allows these functions to be called from | |
4501 | non-interworking code. | |
4502 | ||
4503 | @item -mcaller-super-interworking | |
4504 | @kindex -mcaller-super-interworking | |
4505 | Allows calls via function pointers (including virtual functions) to | |
4506 | execute correctly regardless of whether the target code has been | |
4507 | compiled for interworking or not. There is a small overhead in the cost | |
4bdc1ac7 PB |
4508 | of executing a function pointer if this option is enabled. |
4509 | ||
4510 | @item -msingle-pic-base | |
4511 | @kindex -msingle-pic-base | |
4512 | Treat the register used for PIC addressing as read-only, rather than | |
4513 | loading it in the prologue for each function. The run-time system is | |
4514 | responsible for initialising this register with an appropriate value | |
4515 | before execution begins. | |
4516 | ||
4517 | @item -mpic-register=<reg> | |
4518 | @kindex -mpic-register= | |
4519 | Specify the register to be used for PIC addressing. The default is R10. | |
62b10bbc | 4520 | |
157a620e NC |
4521 | @end table |
4522 | ||
ecff22ab JL |
4523 | @node MN10200 Options |
4524 | @subsection MN10200 Options | |
4525 | @cindex MN10200 options | |
4526 | These @samp{-m} options are defined for Matsushita MN10200 architectures: | |
4527 | @table @code | |
4528 | ||
4529 | @item -mrelax | |
4530 | Indicate to the linker that it should perform a relaxation optimization pass | |
4531 | to shorten branches, calls and absolute memory addresses. This option only | |
4532 | has an effect when used on the command line for the final link step. | |
4533 | ||
4534 | This option makes symbolic debugging impossible. | |
4535 | @end table | |
157a620e | 4536 | |
6d6d0fa0 JL |
4537 | @node MN10300 Options |
4538 | @subsection MN10300 Options | |
4539 | @cindex MN10300 options | |
4540 | These @samp{-m} options are defined for Matsushita MN10300 architectures: | |
4541 | ||
4542 | @table @code | |
4543 | @item -mmult-bug | |
4544 | Generate code to avoid bugs in the multiply instructions for the MN10300 | |
4545 | processors. This is the default. | |
4546 | ||
4547 | @item -mno-mult-bug | |
4548 | Do not generate code to avoid bugs in the multiply instructions for the | |
4549 | MN10300 processors. | |
ecff22ab JL |
4550 | |
4551 | @item -mrelax | |
4552 | Indicate to the linker that it should perform a relaxation optimization pass | |
4553 | to shorten branches, calls and absolute memory addresses. This option only | |
4554 | has an effect when used on the command line for the final link step. | |
4555 | ||
4556 | This option makes symbolic debugging impossible. | |
6d6d0fa0 JL |
4557 | @end table |
4558 | ||
ecff22ab | 4559 | |
861bb6c1 JL |
4560 | @node M32R/D Options |
4561 | @subsection M32R/D Options | |
4562 | @cindex M32R/D options | |
4563 | ||
4564 | These @samp{-m} options are defined for Mitsubishi M32R/D architectures: | |
4565 | ||
4566 | @table @code | |
4567 | @item -mcode-model=small | |
4568 | Assume all objects live in the lower 16MB of memory (so that their addresses | |
4569 | can be loaded with the @code{ld24} instruction), and assume all subroutines | |
4570 | are reachable with the @code{bl} instruction. | |
4571 | This is the default. | |
4572 | ||
4573 | The addressability of a particular object can be set with the | |
4574 | @code{model} attribute. | |
4575 | ||
4576 | @item -mcode-model=medium | |
4577 | Assume objects may be anywhere in the 32 bit address space (the compiler | |
4578 | will generate @code{seth/add3} instructions to load their addresses), and | |
4579 | assume all subroutines are reachable with the @code{bl} instruction. | |
4580 | ||
4581 | @item -mcode-model=large | |
4582 | Assume objects may be anywhere in the 32 bit address space (the compiler | |
4583 | will generate @code{seth/add3} instructions to load their addresses), and | |
4584 | assume subroutines may not be reachable with the @code{bl} instruction | |
4585 | (the compiler will generate the much slower @code{seth/add3/jl} | |
4586 | instruction sequence). | |
4587 | ||
4588 | @item -msdata=none | |
4589 | Disable use of the small data area. Variables will be put into | |
4590 | one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the | |
4591 | @code{section} attribute has been specified). | |
4592 | This is the default. | |
4593 | ||
4594 | The small data area consists of sections @samp{.sdata} and @samp{.sbss}. | |
4595 | Objects may be explicitly put in the small data area with the | |
4596 | @code{section} attribute using one of these sections. | |
4597 | ||
4598 | @item -msdata=sdata | |
4599 | Put small global and static data in the small data area, but do not | |
4600 | generate special code to reference them. | |
4601 | ||
4602 | @item -msdata=use | |
4603 | Put small global and static data in the small data area, and generate | |
4604 | special instructions to reference them. | |
4605 | ||
4606 | @item -G @var{num} | |
4607 | @cindex smaller data references | |
4608 | Put global and static objects less than or equal to @var{num} bytes | |
4609 | into the small data or bss sections instead of the normal data or bss | |
4610 | sections. The default value of @var{num} is 8. | |
4611 | The @samp{-msdata} option must be set to one of @samp{sdata} or @samp{use} | |
4612 | for this option to have any effect. | |
4613 | ||
4614 | All modules should be compiled with the same @samp{-G @var{num}} value. | |
4615 | Compiling with different values of @var{num} may or may not work; if it | |
4616 | doesn't the linker will give an error message - incorrect code will not be | |
4617 | generated. | |
4618 | ||
4619 | @end table | |
4620 | ||
74291a4b MM |
4621 | @node M88K Options |
4622 | @subsection M88K Options | |
4623 | @cindex M88k options | |
4624 | ||
4625 | These @samp{-m} options are defined for Motorola 88k architectures: | |
4626 | ||
4627 | @table @code | |
4628 | @item -m88000 | |
4629 | @kindex -m88000 | |
4630 | Generate code that works well on both the m88100 and the | |
4631 | m88110. | |
4632 | ||
4633 | @item -m88100 | |
4634 | @kindex -m88100 | |
4635 | Generate code that works best for the m88100, but that also | |
4636 | runs on the m88110. | |
4637 | ||
4638 | @item -m88110 | |
4639 | @kindex -m88110 | |
4640 | Generate code that works best for the m88110, and may not run | |
4641 | on the m88100. | |
4642 | ||
4643 | @item -mbig-pic | |
4644 | @kindex -mbig-pic | |
4645 | Obsolete option to be removed from the next revision. | |
4646 | Use @samp{-fPIC}. | |
4647 | ||
4648 | @item -midentify-revision | |
4649 | @kindex -midentify-revision | |
4650 | @kindex ident | |
4651 | @cindex identifying source, compiler (88k) | |
4652 | Include an @code{ident} directive in the assembler output recording the | |
4653 | source file name, compiler name and version, timestamp, and compilation | |
4654 | flags used. | |
4655 | ||
4656 | @item -mno-underscores | |
4657 | @kindex -mno-underscores | |
4658 | @cindex underscores, avoiding (88k) | |
4659 | In assembler output, emit symbol names without adding an underscore | |
4660 | character at the beginning of each name. The default is to use an | |
4661 | underscore as prefix on each name. | |
4662 | ||
4663 | @item -mocs-debug-info | |
4664 | @itemx -mno-ocs-debug-info | |
4665 | @kindex -mocs-debug-info | |
4666 | @kindex -mno-ocs-debug-info | |
4667 | @cindex OCS (88k) | |
4668 | @cindex debugging, 88k OCS | |
4669 | Include (or omit) additional debugging information (about registers used | |
4670 | in each stack frame) as specified in the 88open Object Compatibility | |
4671 | Standard, ``OCS''. This extra information allows debugging of code that | |
4672 | has had the frame pointer eliminated. The default for DG/UX, SVr4, and | |
4673 | Delta 88 SVr3.2 is to include this information; other 88k configurations | |
4674 | omit this information by default. | |
4675 | ||
4676 | @item -mocs-frame-position | |
4677 | @kindex -mocs-frame-position | |
4678 | @cindex register positions in frame (88k) | |
4679 | When emitting COFF debugging information for automatic variables and | |
4680 | parameters stored on the stack, use the offset from the canonical frame | |
4681 | address, which is the stack pointer (register 31) on entry to the | |
4682 | function. The DG/UX, SVr4, Delta88 SVr3.2, and BCS configurations use | |
4683 | @samp{-mocs-frame-position}; other 88k configurations have the default | |
4684 | @samp{-mno-ocs-frame-position}. | |
4685 | ||
4686 | @item -mno-ocs-frame-position | |
4687 | @kindex -mno-ocs-frame-position | |
4688 | @cindex register positions in frame (88k) | |
4689 | When emitting COFF debugging information for automatic variables and | |
4690 | parameters stored on the stack, use the offset from the frame pointer | |
4691 | register (register 30). When this option is in effect, the frame | |
4692 | pointer is not eliminated when debugging information is selected by the | |
4693 | -g switch. | |
4694 | ||
4695 | @item -moptimize-arg-area | |
4696 | @itemx -mno-optimize-arg-area | |
4697 | @kindex -moptimize-arg-area | |
4698 | @kindex -mno-optimize-arg-area | |
4699 | @cindex arguments in frame (88k) | |
4700 | Control how function arguments are stored in stack frames. | |
4701 | @samp{-moptimize-arg-area} saves space by optimizing them, but this | |
4702 | conflicts with the 88open specifications. The opposite alternative, | |
4703 | @samp{-mno-optimize-arg-area}, agrees with 88open standards. By default | |
0c2d1a2a | 4704 | GCC does not optimize the argument area. |
74291a4b MM |
4705 | |
4706 | @item -mshort-data-@var{num} | |
4707 | @kindex -mshort-data-@var{num} | |
4708 | @cindex smaller data references (88k) | |
4709 | @cindex r0-relative references (88k) | |
4710 | Generate smaller data references by making them relative to @code{r0}, | |
4711 | which allows loading a value using a single instruction (rather than the | |
4712 | usual two). You control which data references are affected by | |
4713 | specifying @var{num} with this option. For example, if you specify | |
4714 | @samp{-mshort-data-512}, then the data references affected are those | |
4715 | involving displacements of less than 512 bytes. | |
4716 | @samp{-mshort-data-@var{num}} is not effective for @var{num} greater | |
4717 | than 64k. | |
4718 | ||
4719 | @item -mserialize-volatile | |
4720 | @kindex -mserialize-volatile | |
4721 | @itemx -mno-serialize-volatile | |
4722 | @kindex -mno-serialize-volatile | |
4723 | @cindex sequential consistency on 88k | |
4724 | Do, or don't, generate code to guarantee sequential consistency | |
4725 | of volatile memory references. By default, consistency is | |
4726 | guaranteed. | |
4727 | ||
4728 | The order of memory references made by the MC88110 processor does | |
4729 | not always match the order of the instructions requesting those | |
4730 | references. In particular, a load instruction may execute before | |
4731 | a preceding store instruction. Such reordering violates | |
4732 | sequential consistency of volatile memory references, when there | |
4733 | are multiple processors. When consistency must be guaranteed, | |
4734 | GNU C generates special instructions, as needed, to force | |
4735 | execution in the proper order. | |
4736 | ||
4737 | The MC88100 processor does not reorder memory references and so | |
4738 | always provides sequential consistency. However, by default, GNU | |
4739 | C generates the special instructions to guarantee consistency | |
4740 | even when you use @samp{-m88100}, so that the code may be run on an | |
4741 | MC88110 processor. If you intend to run your code only on the | |
4742 | MC88100 processor, you may use @samp{-mno-serialize-volatile}. | |
4743 | ||
4744 | The extra code generated to guarantee consistency may affect the | |
4745 | performance of your application. If you know that you can safely | |
4746 | forgo this guarantee, you may use @samp{-mno-serialize-volatile}. | |
4747 | ||
4748 | @item -msvr4 | |
4749 | @itemx -msvr3 | |
4750 | @kindex -msvr4 | |
4751 | @kindex -msvr3 | |
4752 | @cindex assembler syntax, 88k | |
4753 | @cindex SVr4 | |
4754 | Turn on (@samp{-msvr4}) or off (@samp{-msvr3}) compiler extensions | |
4755 | related to System V release 4 (SVr4). This controls the following: | |
4756 | ||
4757 | @enumerate | |
4758 | @item | |
4759 | Which variant of the assembler syntax to emit. | |
4760 | @item | |
4761 | @samp{-msvr4} makes the C preprocessor recognize @samp{#pragma weak} | |
4762 | that is used on System V release 4. | |
4763 | @item | |
0c2d1a2a | 4764 | @samp{-msvr4} makes GCC issue additional declaration directives used in |
74291a4b MM |
4765 | SVr4. |
4766 | @end enumerate | |
4767 | ||
4768 | @samp{-msvr4} is the default for the m88k-motorola-sysv4 and | |
4769 | m88k-dg-dgux m88k configurations. @samp{-msvr3} is the default for all | |
4770 | other m88k configurations. | |
4771 | ||
4772 | @item -mversion-03.00 | |
4773 | @kindex -mversion-03.00 | |
4774 | This option is obsolete, and is ignored. | |
4775 | @c ??? which asm syntax better for GAS? option there too? | |
4776 | ||
4777 | @item -mno-check-zero-division | |
4778 | @itemx -mcheck-zero-division | |
4779 | @kindex -mno-check-zero-division | |
4780 | @kindex -mcheck-zero-division | |
4781 | @cindex zero division on 88k | |
4782 | Do, or don't, generate code to guarantee that integer division by | |
4783 | zero will be detected. By default, detection is guaranteed. | |
4784 | ||
4785 | Some models of the MC88100 processor fail to trap upon integer | |
4786 | division by zero under certain conditions. By default, when | |
4787 | compiling code that might be run on such a processor, GNU C | |
4788 | generates code that explicitly checks for zero-valued divisors | |
4789 | and traps with exception number 503 when one is detected. Use of | |
4790 | mno-check-zero-division suppresses such checking for code | |
4791 | generated to run on an MC88100 processor. | |
4792 | ||
4793 | GNU C assumes that the MC88110 processor correctly detects all | |
4794 | instances of integer division by zero. When @samp{-m88110} is | |
4795 | specified, both @samp{-mcheck-zero-division} and | |
4796 | @samp{-mno-check-zero-division} are ignored, and no explicit checks for | |
4797 | zero-valued divisors are generated. | |
4798 | ||
4799 | @item -muse-div-instruction | |
4800 | @kindex -muse-div-instruction | |
4801 | @cindex divide instruction, 88k | |
4802 | Use the div instruction for signed integer division on the | |
4803 | MC88100 processor. By default, the div instruction is not used. | |
4804 | ||
4805 | On the MC88100 processor the signed integer division instruction | |
4806 | div) traps to the operating system on a negative operand. The | |
4807 | operating system transparently completes the operation, but at a | |
4808 | large cost in execution time. By default, when compiling code | |
4809 | that might be run on an MC88100 processor, GNU C emulates signed | |
4810 | integer division using the unsigned integer division instruction | |
4811 | divu), thereby avoiding the large penalty of a trap to the | |
4812 | operating system. Such emulation has its own, smaller, execution | |
4813 | cost in both time and space. To the extent that your code's | |
4814 | important signed integer division operations are performed on two | |
4815 | nonnegative operands, it may be desirable to use the div | |
4816 | instruction directly. | |
4817 | ||
4818 | On the MC88110 processor the div instruction (also known as the | |
4819 | divs instruction) processes negative operands without trapping to | |
4820 | the operating system. When @samp{-m88110} is specified, | |
4821 | @samp{-muse-div-instruction} is ignored, and the div instruction is used | |
4822 | for signed integer division. | |
4823 | ||
4824 | Note that the result of dividing INT_MIN by -1 is undefined. In | |
4825 | particular, the behavior of such a division with and without | |
4826 | @samp{-muse-div-instruction} may differ. | |
4827 | ||
4828 | @item -mtrap-large-shift | |
4829 | @itemx -mhandle-large-shift | |
4830 | @kindex -mtrap-large-shift | |
4831 | @kindex -mhandle-large-shift | |
4832 | @cindex bit shift overflow (88k) | |
4833 | @cindex large bit shifts (88k) | |
4834 | Include code to detect bit-shifts of more than 31 bits; respectively, | |
0c2d1a2a | 4835 | trap such shifts or emit code to handle them properly. By default GCC |
74291a4b MM |
4836 | makes no special provision for large bit shifts. |
4837 | ||
4838 | @item -mwarn-passed-structs | |
4839 | @kindex -mwarn-passed-structs | |
4840 | @cindex structure passing (88k) | |
4841 | Warn when a function passes a struct as an argument or result. | |
4842 | Structure-passing conventions have changed during the evolution of the C | |
4843 | language, and are often the source of portability problems. By default, | |
0c2d1a2a | 4844 | GCC issues no such warning. |
74291a4b MM |
4845 | @end table |
4846 | ||
4847 | @node RS/6000 and PowerPC Options | |
4848 | @subsection IBM RS/6000 and PowerPC Options | |
4849 | @cindex RS/6000 and PowerPC Options | |
4850 | @cindex IBM RS/6000 and PowerPC Options | |
4851 | ||
4852 | These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: | |
4853 | @table @code | |
4854 | @item -mpower | |
4855 | @itemx -mno-power | |
4856 | @itemx -mpower2 | |
4857 | @itemx -mno-power2 | |
4858 | @itemx -mpowerpc | |
4859 | @itemx -mno-powerpc | |
4860 | @itemx -mpowerpc-gpopt | |
4861 | @itemx -mno-powerpc-gpopt | |
4862 | @itemx -mpowerpc-gfxopt | |
4863 | @itemx -mno-powerpc-gfxopt | |
7fe90e7b DE |
4864 | @itemx -mpowerpc64 |
4865 | @itemx -mno-powerpc64 | |
74291a4b MM |
4866 | @kindex -mpower |
4867 | @kindex -mpower2 | |
4868 | @kindex -mpowerpc | |
4869 | @kindex -mpowerpc-gpopt | |
4870 | @kindex -mpowerpc-gfxopt | |
7fe90e7b | 4871 | @kindex -mpowerpc64 |
0c2d1a2a | 4872 | GCC supports two related instruction set architectures for the |
74291a4b MM |
4873 | RS/6000 and PowerPC. The @dfn{POWER} instruction set are those |
4874 | instructions supported by the @samp{rios} chip set used in the original | |
4875 | RS/6000 systems and the @dfn{PowerPC} instruction set is the | |
4876 | architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and | |
861bb6c1 | 4877 | the IBM 4xx microprocessors. |
74291a4b MM |
4878 | |
4879 | Neither architecture is a subset of the other. However there is a | |
4880 | large common subset of instructions supported by both. An MQ | |
4881 | register is included in processors supporting the POWER architecture. | |
4882 | ||
4883 | You use these options to specify which instructions are available on the | |
4884 | processor you are using. The default value of these options is | |
0c2d1a2a | 4885 | determined when configuring GCC. Specifying the |
74291a4b MM |
4886 | @samp{-mcpu=@var{cpu_type}} overrides the specification of these |
4887 | options. We recommend you use the @samp{-mcpu=@var{cpu_type}} option | |
4888 | rather than the options listed above. | |
4889 | ||
0c2d1a2a | 4890 | The @samp{-mpower} option allows GCC to generate instructions that |
74291a4b | 4891 | are found only in the POWER architecture and to use the MQ register. |
0c2d1a2a | 4892 | Specifying @samp{-mpower2} implies @samp{-power} and also allows GCC |
74291a4b MM |
4893 | to generate instructions that are present in the POWER2 architecture but |
4894 | not the original POWER architecture. | |
4895 | ||
0c2d1a2a | 4896 | The @samp{-mpowerpc} option allows GCC to generate instructions that |
74291a4b MM |
4897 | are found only in the 32-bit subset of the PowerPC architecture. |
4898 | Specifying @samp{-mpowerpc-gpopt} implies @samp{-mpowerpc} and also allows | |
0c2d1a2a | 4899 | GCC to use the optional PowerPC architecture instructions in the |
74291a4b | 4900 | General Purpose group, including floating-point square root. Specifying |
0c2d1a2a | 4901 | @samp{-mpowerpc-gfxopt} implies @samp{-mpowerpc} and also allows GCC to |
74291a4b MM |
4902 | use the optional PowerPC architecture instructions in the Graphics |
4903 | group, including floating-point select. | |
4904 | ||
0c2d1a2a | 4905 | The @samp{-mpowerpc64} option allows GCC to generate the additional |
7fe90e7b | 4906 | 64-bit instructions that are found in the full PowerPC64 architecture |
0c2d1a2a | 4907 | and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to |
7fe90e7b DE |
4908 | @samp{-mno-powerpc64}. |
4909 | ||
0c2d1a2a | 4910 | If you specify both @samp{-mno-power} and @samp{-mno-powerpc}, GCC |
74291a4b MM |
4911 | will use only the instructions in the common subset of both |
4912 | architectures plus some special AIX common-mode calls, and will not use | |
4913 | the MQ register. Specifying both @samp{-mpower} and @samp{-mpowerpc} | |
0c2d1a2a | 4914 | permits GCC to use any instruction from either architecture and to |
74291a4b MM |
4915 | allow use of the MQ register; specify this for the Motorola MPC601. |
4916 | ||
4917 | @item -mnew-mnemonics | |
4918 | @itemx -mold-mnemonics | |
4919 | @kindex -mnew-mnemonics | |
4920 | @kindex -mold-mnemonics | |
4921 | Select which mnemonics to use in the generated assembler code. | |
4922 | @samp{-mnew-mnemonics} requests output that uses the assembler mnemonics | |
4923 | defined for the PowerPC architecture, while @samp{-mold-mnemonics} | |
4924 | requests the assembler mnemonics defined for the POWER architecture. | |
4925 | Instructions defined in only one architecture have only one mnemonic; | |
0c2d1a2a | 4926 | GCC uses that mnemonic irrespective of which of these options is |
74291a4b MM |
4927 | specified. |
4928 | ||
0c2d1a2a | 4929 | GCC defaults to the mnemonics appropriate for the architecture in |
7fe90e7b DE |
4930 | use. Specifying @samp{-mcpu=@var{cpu_type}} sometimes overrides the |
4931 | value of these option. Unless you are building a cross-compiler, you | |
4932 | should normally not specify either @samp{-mnew-mnemonics} or | |
74291a4b MM |
4933 | @samp{-mold-mnemonics}, but should instead accept the default. |
4934 | ||
4935 | @item -mcpu=@var{cpu_type} | |
7fe90e7b | 4936 | @kindex -mcpu |
74291a4b MM |
4937 | Set architecture type, register usage, choice of mnemonics, and |
4938 | instruction scheduling parameters for machine type @var{cpu_type}. | |
5f59ecb7 DE |
4939 | Supported values for @var{cpu_type} are @samp{rios}, @samp{rios1}, |
4940 | @samp{rsc}, @samp{rios2}, @samp{rs64a}, @samp{601}, @samp{602}, | |
4941 | @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, | |
4942 | @samp{630}, @samp{740}, @samp{750}, @samp{power}, @samp{power2}, | |
4943 | @samp{powerpc}, @samp{403}, @samp{505}, @samp{801}, @samp{821}, | |
4944 | @samp{823}, and @samp{860} and @samp{common}. @samp{-mcpu=power}, | |
4945 | @samp{-mcpu=power2}, @samp{-mcpu=powerpc}, and @samp{-mcpu=powerpc64} | |
4946 | specify generic POWER, POWER2, pure 32-bit PowerPC (i.e., not MPC601), | |
4947 | and 64-bit PowerPC architecture machine types, with an appropriate, | |
bef84347 | 4948 | generic processor model assumed for scheduling purposes.@refill |
74291a4b | 4949 | |
74291a4b MM |
4950 | Specifying any of the following options: |
4951 | @samp{-mcpu=rios1}, @samp{-mcpu=rios2}, @samp{-mcpu=rsc}, | |
4952 | @samp{-mcpu=power}, or @samp{-mcpu=power2} | |
4953 | enables the @samp{-mpower} option and disables the @samp{-mpowerpc} option; | |
4954 | @samp{-mcpu=601} enables both the @samp{-mpower} and @samp{-mpowerpc} options. | |
5f59ecb7 DE |
4955 | All of @samp{-mcpu=rs64a}, @samp{-mcpu=602}, @samp{-mcpu=603}, |
4956 | @samp{-mcpu=603e}, @samp{-mcpu=604}, @samp{-mcpu=620}, @samp{-mcpu=630}, | |
4957 | @samp{-mcpu=740}, and @samp{-mcpu=750} | |
74291a4b MM |
4958 | enable the @samp{-mpowerpc} option and disable the @samp{-mpower} option. |
4959 | Exactly similarly, all of @samp{-mcpu=403}, | |
4960 | @samp{-mcpu=505}, @samp{-mcpu=821}, @samp{-mcpu=860} and @samp{-mcpu=powerpc} | |
4961 | enable the @samp{-mpowerpc} option and disable the @samp{-mpower} option. | |
4962 | @samp{-mcpu=common} disables both the | |
4963 | @samp{-mpower} and @samp{-mpowerpc} options.@refill | |
74291a4b MM |
4964 | |
4965 | AIX versions 4 or greater selects @samp{-mcpu=common} by default, so | |
5f59ecb7 | 4966 | that code will operate on all members of the RS/6000 POWER and PowerPC |
0c2d1a2a | 4967 | families. In that case, GCC will use only the instructions in the |
74291a4b | 4968 | common subset of both architectures plus some special AIX common-mode |
0c2d1a2a | 4969 | calls, and will not use the MQ register. GCC assumes a generic |
74291a4b MM |
4970 | processor model for scheduling purposes. |
4971 | ||
4972 | Specifying any of the options @samp{-mcpu=rios1}, @samp{-mcpu=rios2}, | |
4973 | @samp{-mcpu=rsc}, @samp{-mcpu=power}, or @samp{-mcpu=power2} also | |
4974 | disables the @samp{new-mnemonics} option. Specifying @samp{-mcpu=601}, | |
4975 | @samp{-mcpu=602}, @samp{-mcpu=603}, @samp{-mcpu=603e}, @samp{-mcpu=604}, | |
5f59ecb7 DE |
4976 | @samp{-mcpu=620}, @samp{-mcpu=630}, @samp{-mcpu=403}, @samp{-mcpu=505}, |
4977 | @samp{-mcpu=821}, @samp{-mcpu=860} or @samp{-mcpu=powerpc} also enables | |
4978 | the @samp{new-mnemonics} option.@refill | |
74291a4b MM |
4979 | |
4980 | Specifying @samp{-mcpu=403}, @samp{-mcpu=821}, or @samp{-mcpu=860} also | |
4981 | enables the @samp{-msoft-float} option. | |
4982 | ||
4983 | @item -mtune=@var{cpu_type} | |
4984 | Set the instruction scheduling parameters for machine type | |
4985 | @var{cpu_type}, but do not set the architecture type, register usage, | |
4986 | choice of mnemonics like @samp{-mcpu=}@var{cpu_type} would. The same | |
4987 | values for @var{cpu_type} are used for @samp{-mtune=}@var{cpu_type} as | |
4988 | for @samp{-mcpu=}@var{cpu_type}. The @samp{-mtune=}@var{cpu_type} | |
4989 | option overrides the @samp{-mcpu=}@var{cpu_type} option in terms of | |
4990 | instruction scheduling parameters. | |
4991 | ||
4992 | @item -mfull-toc | |
4993 | @itemx -mno-fp-in-toc | |
4994 | @itemx -mno-sum-in-toc | |
4995 | @itemx -mminimal-toc | |
7fe90e7b | 4996 | @kindex -mminimal-toc |
74291a4b MM |
4997 | Modify generation of the TOC (Table Of Contents), which is created for |
4998 | every executable file. The @samp{-mfull-toc} option is selected by | |
0c2d1a2a JB |
4999 | default. In that case, GCC will allocate at least one TOC entry for |
5000 | each unique non-automatic variable reference in your program. GCC | |
74291a4b MM |
5001 | will also place floating-point constants in the TOC. However, only |
5002 | 16,384 entries are available in the TOC. | |
5003 | ||
5004 | If you receive a linker error message that saying you have overflowed | |
5005 | the available TOC space, you can reduce the amount of TOC space used | |
5006 | with the @samp{-mno-fp-in-toc} and @samp{-mno-sum-in-toc} options. | |
0c2d1a2a JB |
5007 | @samp{-mno-fp-in-toc} prevents GCC from putting floating-point |
5008 | constants in the TOC and @samp{-mno-sum-in-toc} forces GCC to | |
74291a4b MM |
5009 | generate code to calculate the sum of an address and a constant at |
5010 | run-time instead of putting that sum into the TOC. You may specify one | |
0c2d1a2a | 5011 | or both of these options. Each causes GCC to produce very slightly |
74291a4b MM |
5012 | slower and larger code at the expense of conserving TOC space. |
5013 | ||
5014 | If you still run out of space in the TOC even when you specify both of | |
5015 | these options, specify @samp{-mminimal-toc} instead. This option causes | |
0c2d1a2a JB |
5016 | GCC to make only one TOC entry for every file. When you specify this |
5017 | option, GCC will produce code that is slower and larger but which | |
74291a4b MM |
5018 | uses extremely little TOC space. You may wish to use this option |
5019 | only on files that contain less frequently executed code. @refill | |
5020 | ||
5f59ecb7 DE |
5021 | @item -m64 |
5022 | @itemx -m32 | |
5023 | @kindex -m64 | |
5024 | @kindex -m32 | |
5025 | Enable 64-bit PowerPC ABI and calling convention: 64-bit pointers, 64-bit | |
7fe90e7b | 5026 | @code{long} type, and the infrastructure needed to support them. |
5f59ecb7 DE |
5027 | Specifying @samp{-m64} implies @samp{-mpowerpc64} and |
5028 | @samp{-mpowerpc}, while @samp{-m32} disables the 64-bit ABI and | |
0c2d1a2a | 5029 | implies @samp{-mno-powerpc64}. GCC defaults to @samp{-m32}. |
7fe90e7b | 5030 | |
74291a4b MM |
5031 | @item -mxl-call |
5032 | @itemx -mno-xl-call | |
7fe90e7b | 5033 | @kindex -mxl-call |
74291a4b MM |
5034 | On AIX, pass floating-point arguments to prototyped functions beyond the |
5035 | register save area (RSA) on the stack in addition to argument FPRs. The | |
5036 | AIX calling convention was extended but not initially documented to | |
5037 | handle an obscure K&R C case of calling a function that takes the | |
5038 | address of its arguments with fewer arguments than declared. AIX XL | |
7fe90e7b DE |
5039 | compilers access floating point arguments which do not fit in the |
5040 | RSA from the stack when a subroutine is compiled without | |
74291a4b MM |
5041 | optimization. Because always storing floating-point arguments on the |
5042 | stack is inefficient and rarely needed, this option is not enabled by | |
5043 | default and only is necessary when calling subroutines compiled by AIX | |
5044 | XL compilers without optimization. | |
5045 | ||
861bb6c1 | 5046 | @item -mthreads |
7fe90e7b | 5047 | @kindex -mthreads |
861bb6c1 JL |
5048 | Support @dfn{AIX Threads}. Link an application written to use |
5049 | @dfn{pthreads} with special libraries and startup code to enable the | |
5050 | application to run. | |
5051 | ||
5052 | @item -mpe | |
7fe90e7b | 5053 | @kindex -mpe |
861bb6c1 JL |
5054 | Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE). Link an |
5055 | application written to use message passing with special startup code to | |
5056 | enable the application to run. The system must have PE installed in the | |
5057 | standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file | |
5058 | must be overridden with the @samp{-specs=} option to specify the | |
5059 | appropriate directory location. The Parallel Environment does not | |
5060 | support threads, so the @samp{-mpe} option and the @samp{-mthreads} | |
5061 | option are incompatible. | |
5062 | ||
74291a4b MM |
5063 | @item -msoft-float |
5064 | @itemx -mhard-float | |
7fe90e7b | 5065 | @kindex -msoft-float |
74291a4b MM |
5066 | Generate code that does not use (uses) the floating-point register set. |
5067 | Software floating point emulation is provided if you use the | |
0c2d1a2a | 5068 | @samp{-msoft-float} option, and pass the option to GCC when linking. |
74291a4b MM |
5069 | |
5070 | @item -mmultiple | |
5071 | @itemx -mno-multiple | |
5072 | Generate code that uses (does not use) the load multiple word | |
5073 | instructions and the store multiple word instructions. These | |
5074 | instructions are generated by default on POWER systems, and not | |
5075 | generated on PowerPC systems. Do not use @samp{-mmultiple} on little | |
5076 | endian PowerPC systems, since those instructions do not work when the | |
bef84347 VM |
5077 | processor is in little endian mode. The exceptions are PPC740 and |
5078 | PPC750 which permit the instructions usage in little endian mode. | |
74291a4b MM |
5079 | |
5080 | @item -mstring | |
5081 | @itemx -mno-string | |
7fe90e7b | 5082 | @kindex -mstring |
bef84347 VM |
5083 | Generate code that uses (does not use) the load string instructions |
5084 | and the store string word instructions to save multiple registers and | |
5085 | do small block moves. These instructions are generated by default on | |
5086 | POWER systems, and not generated on PowerPC systems. Do not use | |
5087 | @samp{-mstring} on little endian PowerPC systems, since those | |
5088 | instructions do not work when the processor is in little endian mode. | |
5089 | The exceptions are PPC740 and PPC750 which permit the instructions | |
5090 | usage in little endian mode. | |
74291a4b | 5091 | |
861bb6c1 JL |
5092 | @item -mupdate |
5093 | @itemx -mno-update | |
7fe90e7b | 5094 | @kindex -mupdate |
861bb6c1 JL |
5095 | Generate code that uses (does not use) the load or store instructions |
5096 | that update the base register to the address of the calculated memory | |
5097 | location. These instructions are generated by default. If you use | |
5098 | @samp{-mno-update}, there is a small window between the time that the | |
5099 | stack pointer is updated and the address of the previous frame is | |
5100 | stored, which means code that walks the stack frame across interrupts or | |
5101 | signals may get corrupted data. | |
5102 | ||
5103 | @item -mfused-madd | |
5104 | @itemx -mno-fused-madd | |
7fe90e7b | 5105 | @kindex -mfused-madd |
861bb6c1 JL |
5106 | Generate code that uses (does not use) the floating point multiply and |
5107 | accumulate instructions. These instructions are generated by default if | |
5108 | hardware floating is used. | |
5109 | ||
74291a4b MM |
5110 | @item -mno-bit-align |
5111 | @itemx -mbit-align | |
7fe90e7b | 5112 | @kindex -mbit-align |
74291a4b MM |
5113 | On System V.4 and embedded PowerPC systems do not (do) force structures |
5114 | and unions that contain bit fields to be aligned to the base type of the | |
5115 | bit field. | |
5116 | ||
5117 | For example, by default a structure containing nothing but 8 | |
5118 | @code{unsigned} bitfields of length 1 would be aligned to a 4 byte | |
5119 | boundary and have a size of 4 bytes. By using @samp{-mno-bit-align}, | |
5120 | the structure would be aligned to a 1 byte boundary and be one byte in | |
5121 | size. | |
5122 | ||
5123 | @item -mno-strict-align | |
5124 | @itemx -mstrict-align | |
7fe90e7b | 5125 | @kindex -mstrict-align |
74291a4b MM |
5126 | On System V.4 and embedded PowerPC systems do not (do) assume that |
5127 | unaligned memory references will be handled by the system. | |
5128 | ||
5129 | @item -mrelocatable | |
5130 | @itemx -mno-relocatable | |
7fe90e7b | 5131 | @kindex -mrelocatable |
74291a4b MM |
5132 | On embedded PowerPC systems generate code that allows (does not allow) |
5133 | the program to be relocated to a different address at runtime. If you | |
5134 | use @samp{-mrelocatable} on any module, all objects linked together must | |
5135 | be compiled with @samp{-mrelocatable} or @samp{-mrelocatable-lib}. | |
5136 | ||
5137 | @item -mrelocatable-lib | |
5138 | @itemx -mno-relocatable-lib | |
5139 | On embedded PowerPC systems generate code that allows (does not allow) | |
5140 | the program to be relocated to a different address at runtime. Modules | |
956d6950 | 5141 | compiled with @samp{-mrelocatable-lib} can be linked with either modules |
74291a4b MM |
5142 | compiled without @samp{-mrelocatable} and @samp{-mrelocatable-lib} or |
5143 | with modules compiled with the @samp{-mrelocatable} options. | |
5144 | ||
5145 | @item -mno-toc | |
5146 | @itemx -mtoc | |
5147 | On System V.4 and embedded PowerPC systems do not (do) assume that | |
5148 | register 2 contains a pointer to a global area pointing to the addresses | |
5149 | used in the program. | |
5150 | ||
74291a4b MM |
5151 | @item -mlittle |
5152 | @itemx -mlittle-endian | |
5153 | On System V.4 and embedded PowerPC systems compile code for the | |
5154 | processor in little endian mode. The @samp{-mlittle-endian} option is | |
5155 | the same as @samp{-mlittle}. | |
5156 | ||
5157 | @item -mbig | |
5158 | @itemx -mbig-endian | |
5159 | On System V.4 and embedded PowerPC systems compile code for the | |
5160 | processor in big endian mode. The @samp{-mbig-endian} option is | |
5161 | the same as @samp{-mbig}. | |
5162 | ||
5163 | @item -mcall-sysv | |
5164 | On System V.4 and embedded PowerPC systems compile code using calling | |
5165 | conventions that adheres to the March 1995 draft of the System V | |
5166 | Application Binary Interface, PowerPC processor supplement. This is the | |
5167 | default unless you configured GCC using @samp{powerpc-*-eabiaix}. | |
5168 | ||
5169 | @item -mcall-sysv-eabi | |
5170 | Specify both @samp{-mcall-sysv} and @samp{-meabi} options. | |
5171 | ||
5172 | @item -mcall-sysv-noeabi | |
5173 | Specify both @samp{-mcall-sysv} and @samp{-mno-eabi} options. | |
5174 | ||
5175 | @item -mcall-aix | |
5176 | On System V.4 and embedded PowerPC systems compile code using calling | |
5177 | conventions that are similar to those used on AIX. This is the | |
5178 | default if you configured GCC using @samp{powerpc-*-eabiaix}. | |
5179 | ||
5180 | @item -mcall-solaris | |
5181 | On System V.4 and embedded PowerPC systems compile code for the Solaris | |
5182 | operating system. | |
5183 | ||
5184 | @item -mcall-linux | |
861bb6c1 JL |
5185 | On System V.4 and embedded PowerPC systems compile code for the |
5186 | Linux-based GNU system. | |
74291a4b MM |
5187 | |
5188 | @item -mprototype | |
e9a25f70 | 5189 | @itemx -mno-prototype |
74291a4b MM |
5190 | On System V.4 and embedded PowerPC systems assume that all calls to |
5191 | variable argument functions are properly prototyped. Otherwise, the | |
5192 | compiler must insert an instruction before every non prototyped call to | |
5193 | set or clear bit 6 of the condition code register (@var{CR}) to | |
5194 | indicate whether floating point values were passed in the floating point | |
5195 | registers in case the function takes a variable arguments. With | |
5196 | @samp{-mprototype}, only calls to prototyped variable argument functions | |
5197 | will set or clear the bit. | |
5198 | ||
5199 | @item -msim | |
5200 | On embedded PowerPC systems, assume that the startup module is called | |
5201 | @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and | |
5202 | @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}. | |
5203 | configurations. | |
5204 | ||
5205 | @item -mmvme | |
5206 | On embedded PowerPC systems, assume that the startup module is called | |
e9a25f70 JL |
5207 | @file{crt0.o} and the standard C libraries are @file{libmvme.a} and |
5208 | @file{libc.a}. | |
5209 | ||
5210 | @item -mads | |
5211 | On embedded PowerPC systems, assume that the startup module is called | |
5212 | @file{crt0.o} and the standard C libraries are @file{libads.a} and | |
5213 | @file{libc.a}. | |
5214 | ||
5215 | @item -myellowknife | |
5216 | On embedded PowerPC systems, assume that the startup module is called | |
5217 | @file{crt0.o} and the standard C libraries are @file{libyk.a} and | |
74291a4b MM |
5218 | @file{libc.a}. |
5219 | ||
5220 | @item -memb | |
5221 | On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags | |
5222 | header to indicate that @samp{eabi} extended relocations are used. | |
5223 | ||
5224 | @item -meabi | |
5225 | @itemx -mno-eabi | |
5226 | On System V.4 and embedded PowerPC systems do (do not) adhere to the | |
5227 | Embedded Applications Binary Interface (eabi) which is a set of | |
5228 | modifications to the System V.4 specifications. Selecting @code{-meabi} | |
5229 | means that the stack is aligned to an 8 byte boundary, a function | |
5230 | @code{__eabi} is called to from @code{main} to set up the eabi | |
5231 | environment, and the @samp{-msdata} option can use both @code{r2} and | |
5232 | @code{r13} to point to two separate small data areas. Selecting | |
5233 | @code{-mno-eabi} means that the stack is aligned to a 16 byte boundary, | |
5234 | do not call an initialization function from @code{main}, and the | |
5235 | @samp{-msdata} option will only use @code{r13} to point to a single | |
5236 | small data area. The @samp{-meabi} option is on by default if you | |
5237 | configured GCC using one of the @samp{powerpc*-*-eabi*} options. | |
5238 | ||
5239 | @item -msdata=eabi | |
5240 | On System V.4 and embedded PowerPC systems, put small initialized | |
5241 | @code{const} global and static data in the @samp{.sdata2} section, which | |
5242 | is pointed to by register @code{r2}. Put small initialized | |
5243 | non-@code{const} global and static data in the @samp{.sdata} section, | |
5244 | which is pointed to by register @code{r13}. Put small uninitialized | |
5245 | global and static data in the @samp{.sbss} section, which is adjacent to | |
5246 | the @samp{.sdata} section. The @samp{-msdata=eabi} option is | |
5247 | incompatible with the @samp{-mrelocatable} option. The | |
5248 | @samp{-msdata=eabi} option also sets the @samp{-memb} option. | |
5249 | ||
5250 | @item -msdata=sysv | |
5251 | On System V.4 and embedded PowerPC systems, put small global and static | |
5252 | data in the @samp{.sdata} section, which is pointed to by register | |
5253 | @code{r13}. Put small uninitialized global and static data in the | |
5254 | @samp{.sbss} section, which is adjacent to the @samp{.sdata} section. | |
5255 | The @samp{-msdata=sysv} option is incompatible with the | |
5256 | @samp{-mrelocatable} option. | |
5257 | ||
5258 | @item -msdata=default | |
5259 | @itemx -msdata | |
5260 | On System V.4 and embedded PowerPC systems, if @samp{-meabi} is used, | |
5261 | compile code the same as @samp{-msdata=eabi}, otherwise compile code the | |
5262 | same as @samp{-msdata=sysv}. | |
5263 | ||
5264 | @item -msdata-data | |
5265 | On System V.4 and embedded PowerPC systems, put small global and static | |
5266 | data in the @samp{.sdata} section. Put small uninitialized global and | |
5267 | static data in the @samp{.sbss} section. Do not use register @code{r13} | |
5268 | to address small data however. This is the default behavior unless | |
5269 | other @samp{-msdata} options are used. | |
5270 | ||
5271 | @item -msdata=none | |
5272 | @itemx -mno-sdata | |
5273 | On embedded PowerPC systems, put all initialized global and static data | |
5274 | in the @samp{.data} section, and all uninitialized data in the | |
5275 | @samp{.bss} section. | |
5276 | ||
5277 | @item -G @var{num} | |
5278 | @cindex smaller data references (PowerPC) | |
5279 | @cindex .sdata/.sdata2 references (PowerPC) | |
956d6950 | 5280 | On embedded PowerPC systems, put global and static items less than or |
74291a4b MM |
5281 | equal to @var{num} bytes into the small data or bss sections instead of |
5282 | the normal data or bss section. By default, @var{num} is 8. The | |
5283 | @samp{-G @var{num}} switch is also passed to the linker. | |
5284 | All modules should be compiled with the same @samp{-G @var{num}} value. | |
5285 | ||
5286 | @item -mregnames | |
5287 | @itemx -mno-regnames | |
5288 | On System V.4 and embedded PowerPC systems do (do not) emit register | |
5289 | names in the assembly language output using symbolic forms. | |
f5a1b0d2 | 5290 | |
74291a4b | 5291 | @end table |
f5a1b0d2 | 5292 | |
74291a4b MM |
5293 | @node RT Options |
5294 | @subsection IBM RT Options | |
5295 | @cindex RT options | |
5296 | @cindex IBM RT options | |
5297 | ||
5298 | These @samp{-m} options are defined for the IBM RT PC: | |
5299 | ||
5300 | @table @code | |
5301 | @item -min-line-mul | |
5302 | Use an in-line code sequence for integer multiplies. This is the | |
5303 | default. | |
5304 | ||
5305 | @item -mcall-lib-mul | |
5306 | Call @code{lmul$$} for integer multiples. | |
5307 | ||
5308 | @item -mfull-fp-blocks | |
5309 | Generate full-size floating point data blocks, including the minimum | |
5310 | amount of scratch space recommended by IBM. This is the default. | |
5311 | ||
5312 | @item -mminimum-fp-blocks | |
5313 | Do not include extra scratch space in floating point data blocks. This | |
5314 | results in smaller code, but slower execution, since scratch space must | |
5315 | be allocated dynamically. | |
5316 | ||
5317 | @cindex @file{varargs.h} and RT PC | |
5318 | @cindex @file{stdarg.h} and RT PC | |
5319 | @item -mfp-arg-in-fpregs | |
5320 | Use a calling sequence incompatible with the IBM calling convention in | |
5321 | which floating point arguments are passed in floating point registers. | |
5322 | Note that @code{varargs.h} and @code{stdargs.h} will not work with | |
5323 | floating point operands if this option is specified. | |
5324 | ||
5325 | @item -mfp-arg-in-gregs | |
5326 | Use the normal calling convention for floating point arguments. This is | |
5327 | the default. | |
5328 | ||
5329 | @item -mhc-struct-return | |
5330 | Return structures of more than one word in memory, rather than in a | |
5331 | register. This provides compatibility with the MetaWare HighC (hc) | |
5332 | compiler. Use the option @samp{-fpcc-struct-return} for compatibility | |
5333 | with the Portable C Compiler (pcc). | |
5334 | ||
5335 | @item -mnohc-struct-return | |
5336 | Return some structures of more than one word in registers, when | |
5337 | convenient. This is the default. For compatibility with the | |
5338 | IBM-supplied compilers, use the option @samp{-fpcc-struct-return} or the | |
5339 | option @samp{-mhc-struct-return}. | |
5340 | @end table | |
5341 | ||
5342 | @node MIPS Options | |
5343 | @subsection MIPS Options | |
5344 | @cindex MIPS options | |
5345 | ||
5346 | These @samp{-m} options are defined for the MIPS family of computers: | |
5347 | ||
5348 | @table @code | |
5349 | @item -mcpu=@var{cpu type} | |
5350 | Assume the defaults for the machine type @var{cpu type} when scheduling | |
5351 | instructions. The choices for @var{cpu type} are @samp{r2000}, @samp{r3000}, | |
8b9243df JJ |
5352 | @samp{r3900}, @samp{r4000}, @samp{r4100}, @samp{r4300}, @samp{r4400}, |
5353 | @samp{r4600}, @samp{r4650}, @samp{r5000}, @samp{r6000}, @samp{r8000}, | |
5354 | and @samp{orion}. Additionally, the @samp{r2000}, @samp{r3000}, | |
5355 | @samp{r4000}, @samp{r5000}, and @samp{r6000} can be abbreviated as | |
5356 | @samp{r2k} (or @samp{r2K}), @samp{r3k}, etc. While picking a specific | |
5357 | @var{cpu type} will schedule things appropriately for that particular | |
5358 | chip, the compiler will not generate any code that does not meet level 1 | |
5359 | of the MIPS ISA (instruction set architecture) without a @samp{-mipsX} | |
5360 | or @samp{-mabi} switch being used. | |
74291a4b MM |
5361 | |
5362 | @item -mips1 | |
5363 | Issue instructions from level 1 of the MIPS ISA. This is the default. | |
5364 | @samp{r3000} is the default @var{cpu type} at this ISA level. | |
5365 | ||
5366 | @item -mips2 | |
5367 | Issue instructions from level 2 of the MIPS ISA (branch likely, square | |
5368 | root instructions). @samp{r6000} is the default @var{cpu type} at this | |
5369 | ISA level. | |
5370 | ||
5371 | @item -mips3 | |
5372 | Issue instructions from level 3 of the MIPS ISA (64 bit instructions). | |
5373 | @samp{r4000} is the default @var{cpu type} at this ISA level. | |
74291a4b | 5374 | |
3398f47f | 5375 | @item -mips4 |
8b9243df JJ |
5376 | Issue instructions from level 4 of the MIPS ISA (conditional move, |
5377 | prefetch, enhanced FPU instructions). @samp{r8000} is the default | |
5378 | @var{cpu type} at this ISA level. | |
3398f47f | 5379 | |
74291a4b MM |
5380 | @item -mfp32 |
5381 | Assume that 32 32-bit floating point registers are available. This is | |
5382 | the default. | |
5383 | ||
5384 | @item -mfp64 | |
5385 | Assume that 32 64-bit floating point registers are available. This is | |
5386 | the default when the @samp{-mips3} option is used. | |
5387 | ||
5388 | @item -mgp32 | |
5389 | Assume that 32 32-bit general purpose registers are available. This is | |
5390 | the default. | |
5391 | ||
5392 | @item -mgp64 | |
5393 | Assume that 32 64-bit general purpose registers are available. This is | |
5394 | the default when the @samp{-mips3} option is used. | |
5395 | ||
5396 | @item -mint64 | |
3ce1ba83 GRK |
5397 | Force int and long types to be 64 bits wide. See @samp{-mlong32} for an |
5398 | explanation of the default, and the width of pointers. | |
74291a4b MM |
5399 | |
5400 | @item -mlong64 | |
3ce1ba83 GRK |
5401 | Force long types to be 64 bits wide. See @samp{-mlong32} for an |
5402 | explanation of the default, and the width of pointers. | |
fb1bf66d | 5403 | |
3ce1ba83 GRK |
5404 | @item -mlong32 |
5405 | Force long, int, and pointer types to be 32 bits wide. | |
5406 | ||
5407 | If none of @samp{-mlong32}, @samp{-mlong64}, or @samp{-mint64} are set, | |
5408 | the size of ints, longs, and pointers depends on the ABI and ISA choosen. | |
5409 | For @samp{-mabi=32}, and @samp{-mabi=n32}, ints and longs are 32 bits | |
5410 | wide. For @samp{-mabi=64}, ints are 32 bits, and longs are 64 bits wide. | |
5411 | For @samp{-mabi=eabi} and either @samp{-mips1} or @samp{-mips2}, ints | |
5412 | and longs are 32 bits wide. For @samp{-mabi=eabi} and higher ISAs, ints | |
5413 | are 32 bits, and longs are 64 bits wide. The width of pointer types is | |
5414 | the smaller of the width of longs or the width of general purpose | |
5415 | registers (which in turn depends on the ISA). | |
74291a4b | 5416 | |
62a1403d | 5417 | @item -mabi=32 |
8b9243df | 5418 | @itemx -mabi=o64 |
3398f47f MM |
5419 | @itemx -mabi=n32 |
5420 | @itemx -mabi=64 | |
5421 | @itemx -mabi=eabi | |
8b9243df JJ |
5422 | Generate code for the indicated ABI. The default instruction level is |
5423 | @samp{-mips1} for @samp{32}, @samp{-mips3} for @samp{n32}, and | |
5424 | @samp{-mips4} otherwise. Conversely, with @samp{-mips1} or | |
5425 | @samp{-mips2}, the default ABI is @samp{32}; otherwise, the default ABI | |
5426 | is @samp{64}. | |
3398f47f | 5427 | |
74291a4b MM |
5428 | @item -mmips-as |
5429 | Generate code for the MIPS assembler, and invoke @file{mips-tfile} to | |
5430 | add normal debug information. This is the default for all | |
5431 | platforms except for the OSF/1 reference platform, using the OSF/rose | |
5432 | object format. If the either of the @samp{-gstabs} or @samp{-gstabs+} | |
5433 | switches are used, the @file{mips-tfile} program will encapsulate the | |
5434 | stabs within MIPS ECOFF. | |
5435 | ||
5436 | @item -mgas | |
5437 | Generate code for the GNU assembler. This is the default on the OSF/1 | |
861bb6c1 JL |
5438 | reference platform, using the OSF/rose object format. Also, this is |
5439 | the default if the configure option @samp{--with-gnu-as} is used. | |
5440 | ||
5441 | @item -msplit-addresses | |
5442 | @itemx -mno-split-addresses | |
5443 | Generate code to load the high and low parts of address constants separately. | |
5444 | This allows @code{gcc} to optimize away redundant loads of the high order | |
5445 | bits of addresses. This optimization requires GNU as and GNU ld. | |
5446 | This optimization is enabled by default for some embedded targets where | |
5447 | GNU as and GNU ld are standard. | |
74291a4b MM |
5448 | |
5449 | @item -mrnames | |
5450 | @itemx -mno-rnames | |
5451 | The @samp{-mrnames} switch says to output code using the MIPS software | |
5452 | names for the registers, instead of the hardware names (ie, @var{a0} | |
5453 | instead of @var{$4}). The only known assembler that supports this option | |
5454 | is the Algorithmics assembler. | |
5455 | ||
5456 | @item -mgpopt | |
5457 | @itemx -mno-gpopt | |
5458 | The @samp{-mgpopt} switch says to write all of the data declarations | |
5459 | before the instructions in the text section, this allows the MIPS | |
5460 | assembler to generate one word memory references instead of using two | |
5461 | words for short global or static data items. This is on by default if | |
5462 | optimization is selected. | |
5463 | ||
5464 | @item -mstats | |
5465 | @itemx -mno-stats | |
5466 | For each non-inline function processed, the @samp{-mstats} switch | |
5467 | causes the compiler to emit one line to the standard error file to | |
5468 | print statistics about the program (number of registers saved, stack | |
5469 | size, etc.). | |
5470 | ||
5471 | @item -mmemcpy | |
5472 | @itemx -mno-memcpy | |
5473 | The @samp{-mmemcpy} switch makes all block moves call the appropriate | |
5474 | string function (@samp{memcpy} or @samp{bcopy}) instead of possibly | |
5475 | generating inline code. | |
5476 | ||
5477 | @item -mmips-tfile | |
5478 | @itemx -mno-mips-tfile | |
5479 | The @samp{-mno-mips-tfile} switch causes the compiler not | |
5480 | postprocess the object file with the @file{mips-tfile} program, | |
5481 | after the MIPS assembler has generated it to add debug support. If | |
5482 | @file{mips-tfile} is not run, then no local variables will be | |
5483 | available to the debugger. In addition, @file{stage2} and | |
5484 | @file{stage3} objects will have the temporary file names passed to the | |
5485 | assembler embedded in the object file, which means the objects will | |
5486 | not compare the same. The @samp{-mno-mips-tfile} switch should only | |
5487 | be used when there are bugs in the @file{mips-tfile} program that | |
5488 | prevents compilation. | |
5489 | ||
5490 | @item -msoft-float | |
5491 | Generate output containing library calls for floating point. | |
0c2d1a2a | 5492 | @strong{Warning:} the requisite libraries are not part of GCC. |
74291a4b MM |
5493 | Normally the facilities of the machine's usual C compiler are used, but |
5494 | this can't be done directly in cross-compilation. You must make your | |
5495 | own arrangements to provide suitable library functions for | |
5496 | cross-compilation. | |
5497 | ||
5498 | @item -mhard-float | |
5499 | Generate output containing floating point instructions. This is the | |
5500 | default if you use the unmodified sources. | |
5501 | ||
5502 | @item -mabicalls | |
5503 | @itemx -mno-abicalls | |
5504 | Emit (or do not emit) the pseudo operations @samp{.abicalls}, | |
5505 | @samp{.cpload}, and @samp{.cprestore} that some System V.4 ports use for | |
5506 | position independent code. | |
5507 | ||
5508 | @item -mlong-calls | |
5509 | @itemx -mno-long-calls | |
5510 | Do all calls with the @samp{JALR} instruction, which requires | |
5511 | loading up a function's address into a register before the call. | |
5512 | You need to use this switch, if you call outside of the current | |
5513 | 512 megabyte segment to functions that are not through pointers. | |
5514 | ||
5515 | @item -mhalf-pic | |
5516 | @itemx -mno-half-pic | |
5517 | Put pointers to extern references into the data section and load them | |
5518 | up, rather than put the references in the text section. | |
5519 | ||
5520 | @item -membedded-pic | |
5521 | @itemx -mno-embedded-pic | |
69fa83cf JW |
5522 | Generate PIC code suitable for some embedded systems. All calls are |
5523 | made using PC relative address, and all data is addressed using the $gp | |
5524 | register. No more than 65536 bytes of global data may be used. This | |
5525 | requires GNU as and GNU ld which do most of the work. This currently | |
5526 | only works on targets which use ECOFF; it does not work with ELF. | |
74291a4b MM |
5527 | |
5528 | @item -membedded-data | |
5529 | @itemx -mno-embedded-data | |
5530 | Allocate variables to the read-only data section first if possible, then | |
5531 | next in the small data section if possible, otherwise in data. This gives | |
5532 | slightly slower code than the default, but reduces the amount of RAM required | |
5533 | when executing, and thus may be preferred for some embedded systems. | |
5534 | ||
5535 | @item -msingle-float | |
5536 | @itemx -mdouble-float | |
5537 | The @samp{-msingle-float} switch tells gcc to assume that the floating | |
5538 | point coprocessor only supports single precision operations, as on the | |
5539 | @samp{r4650} chip. The @samp{-mdouble-float} switch permits gcc to use | |
5540 | double precision operations. This is the default. | |
5541 | ||
5542 | @item -mmad | |
5543 | @itemx -mno-mad | |
5544 | Permit use of the @samp{mad}, @samp{madu} and @samp{mul} instructions, | |
5545 | as on the @samp{r4650} chip. | |
5546 | ||
5547 | @item -m4650 | |
5548 | Turns on @samp{-msingle-float}, @samp{-mmad}, and, at least for now, | |
5549 | @samp{-mcpu=r4650}. | |
5550 | ||
8b9243df JJ |
5551 | @item -mips16 |
5552 | @itemx -mno-mips16 | |
5553 | Enable 16-bit instructions. | |
5554 | ||
5555 | @item -mentry | |
5556 | Use the entry and exit pseudo ops. This option can only be used with | |
5557 | @samp{-mips16}. | |
5558 | ||
74291a4b MM |
5559 | @item -EL |
5560 | Compile code for the processor in little endian mode. | |
5561 | The requisite libraries are assumed to exist. | |
5562 | ||
5563 | @item -EB | |
5564 | Compile code for the processor in big endian mode. | |
5565 | The requisite libraries are assumed to exist. | |
5566 | ||
5567 | @item -G @var{num} | |
5568 | @cindex smaller data references (MIPS) | |
5569 | @cindex gp-relative references (MIPS) | |
5570 | Put global and static items less than or equal to @var{num} bytes into | |
5571 | the small data or bss sections instead of the normal data or bss | |
5572 | section. This allows the assembler to emit one word memory reference | |
5573 | instructions based on the global pointer (@var{gp} or @var{$28}), | |
5574 | instead of the normal two words used. By default, @var{num} is 8 when | |
5575 | the MIPS assembler is used, and 0 when the GNU assembler is used. The | |
5576 | @samp{-G @var{num}} switch is also passed to the assembler and linker. | |
5577 | All modules should be compiled with the same @samp{-G @var{num}} | |
5578 | value. | |
5579 | ||
5580 | @item -nocpp | |
9ec36da5 | 5581 | Tell the MIPS assembler to not run its preprocessor over user |
74291a4b MM |
5582 | assembler files (with a @samp{.s} suffix) when assembling them. |
5583 | @end table | |
5584 | ||
5585 | @ifset INTERNALS | |
5586 | These options are defined by the macro | |
5587 | @code{TARGET_SWITCHES} in the machine description. The default for the | |
5588 | options is also defined by that macro, which enables you to change the | |
5589 | defaults. | |
5590 | @end ifset | |
5591 | ||
5592 | @node i386 Options | |
5593 | @subsection Intel 386 Options | |
5594 | @cindex i386 Options | |
5595 | @cindex Intel 386 Options | |
5596 | ||
5597 | These @samp{-m} options are defined for the i386 family of computers: | |
5598 | ||
f45ebe47 | 5599 | @table @code |
a9f3e1a4 JL |
5600 | @item -mcpu=@var{cpu type} |
5601 | Assume the defaults for the machine type @var{cpu type} when scheduling | |
6f670fde RH |
5602 | instructions. The choices for @var{cpu type} are: |
5603 | ||
5604 | @multitable @columnfractions .20 .20 .20 .20 | |
5605 | @item @samp{i386} @tab @samp{i486} @tab @samp{i586} @tab @samp{i686} | |
5606 | @item @samp{pentium} @tab @samp{pentiumpro} @tab @samp{k6} | |
5607 | @end multitable | |
5608 | ||
5609 | While picking a specific @var{cpu type} will schedule things appropriately | |
5610 | for that particular chip, the compiler will not generate any code that | |
5611 | does not run on the i386 without the @samp{-march=@var{cpu type}} option | |
7001ee2d CB |
5612 | being used. @samp{i586} is equivalent to @samp{pentium} and @samp{i686} |
5613 | is equivalent to @samp{pentiumpro}. @samp{k6} is the AMD chip as | |
5614 | opposed to the Intel ones. | |
a9f3e1a4 JL |
5615 | |
5616 | @item -march=@var{cpu type} | |
5617 | Generate instructions for the machine type @var{cpu type}. The choices | |
6f670fde RH |
5618 | for @var{cpu type} are the same as for @samp{-mcpu}. Moreover, |
5619 | specifying @samp{-march=@var{cpu type}} implies @samp{-mcpu=@var{cpu type}}. | |
a9f3e1a4 JL |
5620 | |
5621 | @item -m386 | |
5622 | @itemx -m486 | |
5623 | @itemx -mpentium | |
5624 | @itemx -mpentiumpro | |
5625 | Synonyms for -mcpu=i386, -mcpu=i486, -mcpu=pentium, and -mcpu=pentiumpro | |
7001ee2d | 5626 | respectively. These synonyms are deprecated. |
74291a4b MM |
5627 | |
5628 | @item -mieee-fp | |
5629 | @itemx -mno-ieee-fp | |
5630 | Control whether or not the compiler uses IEEE floating point | |
5631 | comparisons. These handle correctly the case where the result of a | |
5632 | comparison is unordered. | |
5633 | ||
5634 | @item -msoft-float | |
5635 | Generate output containing library calls for floating point. | |
0c2d1a2a | 5636 | @strong{Warning:} the requisite libraries are not part of GCC. |
74291a4b MM |
5637 | Normally the facilities of the machine's usual C compiler are used, but |
5638 | this can't be done directly in cross-compilation. You must make your | |
5639 | own arrangements to provide suitable library functions for | |
5640 | cross-compilation. | |
5641 | ||
5642 | On machines where a function returns floating point results in the 80387 | |
5643 | register stack, some floating point opcodes may be emitted even if | |
5644 | @samp{-msoft-float} is used. | |
5645 | ||
5646 | @item -mno-fp-ret-in-387 | |
5647 | Do not use the FPU registers for return values of functions. | |
5648 | ||
5649 | The usual calling convention has functions return values of types | |
5650 | @code{float} and @code{double} in an FPU register, even if there | |
5651 | is no FPU. The idea is that the operating system should emulate | |
5652 | an FPU. | |
5653 | ||
5654 | The option @samp{-mno-fp-ret-in-387} causes such values to be returned | |
5655 | in ordinary CPU registers instead. | |
5656 | ||
5657 | @item -mno-fancy-math-387 | |
5658 | Some 387 emulators do not support the @code{sin}, @code{cos} and | |
5659 | @code{sqrt} instructions for the 387. Specify this option to avoid | |
5660 | generating those instructions. This option is the default on FreeBSD. | |
5661 | As of revision 2.6.1, these instructions are not generated unless you | |
5662 | also use the @samp{-ffast-math} switch. | |
5663 | ||
5664 | @item -malign-double | |
5665 | @itemx -mno-align-double | |
0c2d1a2a | 5666 | Control whether GCC aligns @code{double}, @code{long double}, and |
74291a4b MM |
5667 | @code{long long} variables on a two word boundary or a one word |
5668 | boundary. Aligning @code{double} variables on a two word boundary will | |
5669 | produce code that runs somewhat faster on a @samp{Pentium} at the | |
5670 | expense of more memory. | |
5671 | ||
5672 | @strong{Warning:} if you use the @samp{-malign-double} switch, | |
5673 | structures containing the above types will be aligned differently than | |
5674 | the published application binary interface specifications for the 386. | |
5675 | ||
5676 | @item -msvr3-shlib | |
5677 | @itemx -mno-svr3-shlib | |
0c2d1a2a | 5678 | Control whether GCC places uninitialized locals into @code{bss} or |
74291a4b MM |
5679 | @code{data}. @samp{-msvr3-shlib} places these locals into @code{bss}. |
5680 | These options are meaningful only on System V Release 3. | |
5681 | ||
5682 | @item -mno-wide-multiply | |
5683 | @itemx -mwide-multiply | |
0c2d1a2a | 5684 | Control whether GCC uses the @code{mul} and @code{imul} that produce |
74291a4b MM |
5685 | 64 bit results in @code{eax:edx} from 32 bit operands to do @code{long |
5686 | long} multiplies and 32-bit division by constants. | |
5687 | ||
5688 | @item -mrtd | |
5689 | Use a different function-calling convention, in which functions that | |
5690 | take a fixed number of arguments return with the @code{ret} @var{num} | |
5691 | instruction, which pops their arguments while returning. This saves one | |
5692 | instruction in the caller since there is no need to pop the arguments | |
5693 | there. | |
5694 | ||
5695 | You can specify that an individual function is called with this calling | |
5696 | sequence with the function attribute @samp{stdcall}. You can also | |
5697 | override the @samp{-mrtd} option by using the function attribute | |
0b433de6 | 5698 | @samp{cdecl}. @xref{Function Attributes}. |
74291a4b MM |
5699 | |
5700 | @strong{Warning:} this calling convention is incompatible with the one | |
5701 | normally used on Unix, so you cannot use it if you need to call | |
5702 | libraries compiled with the Unix compiler. | |
5703 | ||
5704 | Also, you must provide function prototypes for all functions that | |
5705 | take variable numbers of arguments (including @code{printf}); | |
5706 | otherwise incorrect code will be generated for calls to those | |
5707 | functions. | |
5708 | ||
5709 | In addition, seriously incorrect code will result if you call a | |
5710 | function with too many arguments. (Normally, extra arguments are | |
5711 | harmlessly ignored.) | |
5712 | ||
5713 | @item -mreg-alloc=@var{regs} | |
5714 | Control the default allocation order of integer registers. The | |
5715 | string @var{regs} is a series of letters specifying a register. The | |
5716 | supported letters are: @code{a} allocate EAX; @code{b} allocate EBX; | |
5717 | @code{c} allocate ECX; @code{d} allocate EDX; @code{S} allocate ESI; | |
5718 | @code{D} allocate EDI; @code{B} allocate EBP. | |
5719 | ||
5720 | @item -mregparm=@var{num} | |
5721 | Control how many registers are used to pass integer arguments. By | |
5722 | default, no registers are used to pass arguments, and at most 3 | |
5723 | registers can be used. You can control this behavior for a specific | |
0b433de6 JL |
5724 | function by using the function attribute @samp{regparm}. |
5725 | @xref{Function Attributes}. | |
74291a4b MM |
5726 | |
5727 | @strong{Warning:} if you use this switch, and | |
5728 | @var{num} is nonzero, then you must build all modules with the same | |
5729 | value, including any libraries. This includes the system libraries and | |
5730 | startup modules. | |
5731 | ||
5732 | @item -malign-loops=@var{num} | |
5733 | Align loops to a 2 raised to a @var{num} byte boundary. If | |
9e423e6d JW |
5734 | @samp{-malign-loops} is not specified, the default is 2 unless |
5735 | gas 2.8 (or later) is being used in which case the default is | |
5736 | to align the loop on a 16 byte boundary if it is less than 8 | |
5737 | bytes away. | |
74291a4b MM |
5738 | |
5739 | @item -malign-jumps=@var{num} | |
5740 | Align instructions that are only jumped to to a 2 raised to a @var{num} | |
5741 | byte boundary. If @samp{-malign-jumps} is not specified, the default is | |
9e423e6d JW |
5742 | 2 if optimizing for a 386, and 4 if optimizing for a 486 unless |
5743 | gas 2.8 (or later) is being used in which case the default is | |
5744 | to align the instruction on a 16 byte boundary if it is less | |
5745 | than 8 bytes away. | |
74291a4b MM |
5746 | |
5747 | @item -malign-functions=@var{num} | |
5748 | Align the start of functions to a 2 raised to @var{num} byte boundary. | |
6d4312dd | 5749 | If @samp{-malign-functions} is not specified, the default is 2 if optimizing |
74291a4b | 5750 | for a 386, and 4 if optimizing for a 486. |
74291a4b | 5751 | |
3af4bd89 JH |
5752 | @item -mpreferred-stack-boundary=@var{num} |
5753 | Attempt to keep the stack boundary aligned to a 2 raised to @var{num} | |
5754 | byte boundary. If @samp{-mpreferred-stack-boundary} is not specified, | |
5755 | the default is 4 (16 bytes or 128 bits). | |
5756 | ||
5757 | The stack is required to be aligned on a 4 byte boundary. On Pentium | |
5758 | and PentiumPro, @code{double} and @code{long double} values should be | |
5759 | aligned to an 8 byte boundary (see @samp{-malign-double}) or suffer | |
5760 | significant run time performance penalties. On Pentium III, the | |
5761 | Streaming SIMD Extention (SSE) data type @code{__m128} suffers similar | |
5762 | penalties if it is not 16 byte aligned. | |
5763 | ||
5764 | To ensure proper alignment of this values on the stack, the stack boundary | |
5765 | must be as aligned as that required by any value stored on the stack. | |
5766 | Further, every function must be generated such that it keeps the stack | |
5767 | aligned. Thus calling a function compiled with a higher preferred | |
5768 | stack boundary from a function compiled with a lower preferred stack | |
5769 | boundary will most likely misalign the stack. It is recommended that | |
5770 | libraries that use callbacks always use the default setting. | |
5771 | ||
5772 | This extra alignment does consume extra stack space. Code that is sensitive | |
5773 | to stack space usage, such as embedded systems and operating system kernels, | |
5774 | may want to reduce the preferred alignment to | |
5775 | @samp{-mpreferred-stack-boundary=2}. | |
5776 | @end table | |
5777 | ||
74291a4b MM |
5778 | @node HPPA Options |
5779 | @subsection HPPA Options | |
5780 | @cindex HPPA Options | |
5781 | ||
5782 | These @samp{-m} options are defined for the HPPA family of computers: | |
5783 | ||
5784 | @table @code | |
ea3bfbfe JQ |
5785 | @item -march=@var{architecture type} |
5786 | Generate code for the specified architecture. The choices for | |
5787 | @var{architecture type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA | |
5788 | 1.1, and @samp{2.0} for PA 2.0 processors. Refer to | |
5789 | @file{/usr/lib/sched.models} on an HP-UX system to determine the proper | |
5790 | architecture option for your machine. Code compiled for lower numbered | |
5791 | architectures will run on higher numbered architectures, but not the | |
5792 | other way around. | |
5793 | ||
5794 | PA 2.0 support currently requires gas snapshot 19990413 or later. The | |
5795 | next release of binutils (current is 2.9.1) will probably contain PA 2.0 | |
5796 | support. | |
74291a4b | 5797 | |
ea3bfbfe | 5798 | @item -mpa-risc-1-0 |
62a1403d AS |
5799 | @itemx -mpa-risc-1-1 |
5800 | @itemx -mpa-risc-2-0 | |
ea3bfbfe | 5801 | Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively. |
74291a4b | 5802 | |
861bb6c1 JL |
5803 | @item -mbig-switch |
5804 | Generate code suitable for big switch tables. Use this option only if | |
5805 | the assembler/linker complain about out of range branches within a switch | |
5806 | table. | |
5807 | ||
74291a4b MM |
5808 | @item -mjump-in-delay |
5809 | Fill delay slots of function calls with unconditional jump instructions | |
5810 | by modifying the return pointer for the function call to be the target | |
5811 | of the conditional jump. | |
5812 | ||
5813 | @item -mdisable-fpregs | |
5814 | Prevent floating point registers from being used in any manner. This is | |
5815 | necessary for compiling kernels which perform lazy context switching of | |
5816 | floating point registers. If you use this option and attempt to perform | |
5817 | floating point operations, the compiler will abort. | |
5818 | ||
5819 | @item -mdisable-indexing | |
5820 | Prevent the compiler from using indexing address modes. This avoids some | |
5821 | rather obscure problems when compiling MIG generated code under MACH. | |
5822 | ||
5823 | @item -mno-space-regs | |
5824 | Generate code that assumes the target has no space registers. This allows | |
5825 | GCC to generate faster indirect calls and use unscaled index address modes. | |
5826 | ||
5827 | Such code is suitable for level 0 PA systems and kernels. | |
5828 | ||
5829 | @item -mfast-indirect-calls | |
5830 | Generate code that assumes calls never cross space boundaries. This | |
5831 | allows GCC to emit code which performs faster indirect calls. | |
5832 | ||
5833 | This option will not work in the presense of shared libraries or nested | |
5834 | functions. | |
5835 | ||
74291a4b MM |
5836 | @item -mlong-load-store |
5837 | Generate 3-instruction load and store sequences as sometimes required by | |
5838 | the HP-UX 10 linker. This is equivalent to the @samp{+k} option to | |
5839 | the HP compilers. | |
5840 | ||
5841 | @item -mportable-runtime | |
5842 | Use the portable calling conventions proposed by HP for ELF systems. | |
5843 | ||
5844 | @item -mgas | |
5845 | Enable the use of assembler directives only GAS understands. | |
5846 | ||
5847 | @item -mschedule=@var{cpu type} | |
5848 | Schedule code according to the constraints for the machine type | |
732135bf | 5849 | @var{cpu type}. The choices for @var{cpu type} are @samp{700} |
e14b50ce | 5850 | @samp{7100}, @samp{7100LC}, @samp{7200}, and @samp{8000}. Refer to |
732135bf JL |
5851 | @file{/usr/lib/sched.models} on an HP-UX system to determine the |
5852 | proper scheduling option for your machine. | |
74291a4b MM |
5853 | |
5854 | @item -mlinker-opt | |
5855 | Enable the optimization pass in the HPUX linker. Note this makes symbolic | |
5856 | debugging impossible. It also triggers a bug in the HPUX 8 and HPUX 9 linkers | |
5857 | in which they give bogus error messages when linking some programs. | |
5858 | ||
5859 | @item -msoft-float | |
5860 | Generate output containing library calls for floating point. | |
5861 | @strong{Warning:} the requisite libraries are not available for all HPPA | |
5862 | targets. Normally the facilities of the machine's usual C compiler are | |
5863 | used, but this cannot be done directly in cross-compilation. You must make | |
5864 | your own arrangements to provide suitable library functions for | |
5865 | cross-compilation. The embedded target @samp{hppa1.1-*-pro} | |
5866 | does provide software floating point support. | |
5867 | ||
5868 | @samp{-msoft-float} changes the calling convention in the output file; | |
5869 | therefore, it is only useful if you compile @emph{all} of a program with | |
5870 | this option. In particular, you need to compile @file{libgcc.a}, the | |
0c2d1a2a | 5871 | library that comes with GCC, with @samp{-msoft-float} in order for |
74291a4b MM |
5872 | this to work. |
5873 | @end table | |
5874 | ||
5875 | @node Intel 960 Options | |
5876 | @subsection Intel 960 Options | |
5877 | ||
5878 | These @samp{-m} options are defined for the Intel 960 implementations: | |
5879 | ||
5880 | @table @code | |
5881 | @item -m@var{cpu type} | |
5882 | Assume the defaults for the machine type @var{cpu type} for some of | |
5883 | the other options, including instruction scheduling, floating point | |
5884 | support, and addressing modes. The choices for @var{cpu type} are | |
5885 | @samp{ka}, @samp{kb}, @samp{mc}, @samp{ca}, @samp{cf}, | |
5886 | @samp{sa}, and @samp{sb}. | |
5887 | The default is | |
5888 | @samp{kb}. | |
5889 | ||
5890 | @item -mnumerics | |
5891 | @itemx -msoft-float | |
5892 | The @samp{-mnumerics} option indicates that the processor does support | |
5893 | floating-point instructions. The @samp{-msoft-float} option indicates | |
5894 | that floating-point support should not be assumed. | |
5895 | ||
5896 | @item -mleaf-procedures | |
5897 | @itemx -mno-leaf-procedures | |
5898 | Do (or do not) attempt to alter leaf procedures to be callable with the | |
5899 | @code{bal} instruction as well as @code{call}. This will result in more | |
5900 | efficient code for explicit calls when the @code{bal} instruction can be | |
5901 | substituted by the assembler or linker, but less efficient code in other | |
5902 | cases, such as calls via function pointers, or using a linker that doesn't | |
5903 | support this optimization. | |
5904 | ||
5905 | @item -mtail-call | |
5906 | @itemx -mno-tail-call | |
5907 | Do (or do not) make additional attempts (beyond those of the | |
5908 | machine-independent portions of the compiler) to optimize tail-recursive | |
5909 | calls into branches. You may not want to do this because the detection of | |
5910 | cases where this is not valid is not totally complete. The default is | |
5911 | @samp{-mno-tail-call}. | |
5912 | ||
5913 | @item -mcomplex-addr | |
5914 | @itemx -mno-complex-addr | |
5915 | Assume (or do not assume) that the use of a complex addressing mode is a | |
5916 | win on this implementation of the i960. Complex addressing modes may not | |
5917 | be worthwhile on the K-series, but they definitely are on the C-series. | |
5918 | The default is currently @samp{-mcomplex-addr} for all processors except | |
5919 | the CB and CC. | |
5920 | ||
5921 | @item -mcode-align | |
5922 | @itemx -mno-code-align | |
5923 | Align code to 8-byte boundaries for faster fetching (or don't bother). | |
5924 | Currently turned on by default for C-series implementations only. | |
5925 | ||
5926 | @ignore | |
5927 | @item -mclean-linkage | |
5928 | @itemx -mno-clean-linkage | |
5929 | These options are not fully implemented. | |
5930 | @end ignore | |
5931 | ||
5932 | @item -mic-compat | |
5933 | @itemx -mic2.0-compat | |
5934 | @itemx -mic3.0-compat | |
5935 | Enable compatibility with iC960 v2.0 or v3.0. | |
5936 | ||
5937 | @item -masm-compat | |
5938 | @itemx -mintel-asm | |
5939 | Enable compatibility with the iC960 assembler. | |
5940 | ||
5941 | @item -mstrict-align | |
5942 | @itemx -mno-strict-align | |
5943 | Do not permit (do permit) unaligned accesses. | |
5944 | ||
5945 | @item -mold-align | |
5946 | Enable structure-alignment compatibility with Intel's gcc release version | |
861bb6c1 | 5947 | 1.3 (based on gcc 1.37). This option implies @samp{-mstrict-align}. |
eaa4b44c VM |
5948 | |
5949 | @item -mlong-double-64 | |
5950 | Implement type @samp{long double} as 64-bit floating point numbers. | |
5951 | Without the option @samp{long double} is implemented by 80-bit | |
5952 | floating point numbers. The only reason we have it because there is | |
5953 | no 128-bit @samp{long double} support in @samp{fp-bit.c} yet. So it | |
5954 | is only useful for people using soft-float targets. Otherwise, we | |
5955 | should recommend against use of it. | |
5956 | ||
74291a4b MM |
5957 | @end table |
5958 | ||
5959 | @node DEC Alpha Options | |
5960 | @subsection DEC Alpha Options | |
5961 | ||
5962 | These @samp{-m} options are defined for the DEC Alpha implementations: | |
5963 | ||
5964 | @table @code | |
5965 | @item -mno-soft-float | |
5966 | @itemx -msoft-float | |
5967 | Use (do not use) the hardware floating-point instructions for | |
5968 | floating-point operations. When @code{-msoft-float} is specified, | |
5969 | functions in @file{libgcc1.c} will be used to perform floating-point | |
5970 | operations. Unless they are replaced by routines that emulate the | |
5971 | floating-point operations, or compiled in such a way as to call such | |
5972 | emulations routines, these routines will issue floating-point | |
5973 | operations. If you are compiling for an Alpha without floating-point | |
5974 | operations, you must ensure that the library is built so as not to call | |
5975 | them. | |
5976 | ||
5977 | Note that Alpha implementations without floating-point operations are | |
5978 | required to have floating-point registers. | |
5979 | ||
5980 | @item -mfp-reg | |
5981 | @itemx -mno-fp-regs | |
5982 | Generate code that uses (does not use) the floating-point register set. | |
5983 | @code{-mno-fp-regs} implies @code{-msoft-float}. If the floating-point | |
5984 | register set is not used, floating point operands are passed in integer | |
5985 | registers as if they were integers and floating-point results are passed | |
5986 | in $0 instead of $f0. This is a non-standard calling sequence, so any | |
5987 | function with a floating-point argument or return value called by code | |
5988 | compiled with @code{-mno-fp-regs} must also be compiled with that | |
5989 | option. | |
5990 | ||
5991 | A typical use of this option is building a kernel that does not use, | |
5992 | and hence need not save and restore, any floating-point registers. | |
5993 | ||
5994 | @item -mieee | |
5995 | The Alpha architecture implements floating-point hardware optimized for | |
5996 | maximum performance. It is mostly compliant with the IEEE floating | |
5997 | point standard. However, for full compliance, software assistance is | |
5998 | required. This option generates code fully IEEE compliant code | |
5999 | @emph{except} that the @var{inexact flag} is not maintained (see below). | |
6000 | If this option is turned on, the CPP macro @code{_IEEE_FP} is defined | |
6001 | during compilation. The option is a shorthand for: @samp{-D_IEEE_FP | |
6002 | -mfp-trap-mode=su -mtrap-precision=i -mieee-conformant}. The resulting | |
6003 | code is less efficient but is able to correctly support denormalized | |
6004 | numbers and exceptional IEEE values such as not-a-number and plus/minus | |
6005 | infinity. Other Alpha compilers call this option | |
6006 | @code{-ieee_with_no_inexact}. | |
6007 | ||
6008 | @item -mieee-with-inexact | |
6009 | @c overfull hbox here --bob 22 jul96 | |
6010 | @c original text between ignore ... end ignore | |
6011 | @ignore | |
6012 | This is like @samp{-mieee} except the generated code also maintains the | |
6013 | IEEE @var{inexact flag}. Turning on this option causes the generated | |
6014 | code to implement fully-compliant IEEE math. The option is a shorthand | |
6015 | for @samp{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus @samp{-mieee-conformant}, | |
6016 | @samp{-mfp-trap-mode=sui}, and @samp{-mtrap-precision=i}. On some Alpha | |
6017 | implementations the resulting code may execute significantly slower than | |
6018 | the code generated by default. Since there is very little code that | |
6019 | depends on the @var{inexact flag}, you should normally not specify this | |
6020 | option. Other Alpha compilers call this option | |
6021 | @samp{-ieee_with_inexact}. | |
6022 | @end ignore | |
6023 | @c changed paragraph | |
6024 | This is like @samp{-mieee} except the generated code also maintains the | |
6025 | IEEE @var{inexact flag}. Turning on this option causes the generated | |
6026 | code to implement fully-compliant IEEE math. The option is a shorthand | |
6027 | for @samp{-D_IEEE_FP -D_IEEE_FP_INEXACT} plus the three following: | |
6028 | @samp{-mieee-conformant}, | |
6029 | @samp{-mfp-trap-mode=sui}, | |
6030 | and @samp{-mtrap-precision=i}. | |
6031 | On some Alpha implementations the resulting code may execute | |
6032 | significantly slower than the code generated by default. Since there | |
6033 | is very little code that depends on the @var{inexact flag}, you should | |
6034 | normally not specify this option. Other Alpha compilers call this | |
6035 | option @samp{-ieee_with_inexact}. | |
6036 | @c end changes to prevent overfull hboxes | |
6037 | ||
6038 | @item -mfp-trap-mode=@var{trap mode} | |
6039 | This option controls what floating-point related traps are enabled. | |
6040 | Other Alpha compilers call this option @samp{-fptm }@var{trap mode}. | |
6041 | The trap mode can be set to one of four values: | |
6042 | ||
6043 | @table @samp | |
6044 | @item n | |
6045 | This is the default (normal) setting. The only traps that are enabled | |
6046 | are the ones that cannot be disabled in software (e.g., division by zero | |
6047 | trap). | |
6048 | ||
6049 | @item u | |
6050 | In addition to the traps enabled by @samp{n}, underflow traps are enabled | |
6051 | as well. | |
6052 | ||
6053 | @item su | |
6054 | Like @samp{su}, but the instructions are marked to be safe for software | |
6055 | completion (see Alpha architecture manual for details). | |
6056 | ||
6057 | @item sui | |
6058 | Like @samp{su}, but inexact traps are enabled as well. | |
6059 | @end table | |
6060 | ||
6061 | @item -mfp-rounding-mode=@var{rounding mode} | |
6062 | Selects the IEEE rounding mode. Other Alpha compilers call this option | |
6063 | @samp{-fprm }@var{rounding mode}. The @var{rounding mode} can be one | |
6064 | of: | |
6065 | ||
6066 | @table @samp | |
6067 | @item n | |
6068 | Normal IEEE rounding mode. Floating point numbers are rounded towards | |
6069 | the nearest machine number or towards the even machine number in case | |
6070 | of a tie. | |
6071 | ||
6072 | @item m | |
6073 | Round towards minus infinity. | |
6074 | ||
6075 | @item c | |
6076 | Chopped rounding mode. Floating point numbers are rounded towards zero. | |
6077 | ||
6078 | @item d | |
6079 | Dynamic rounding mode. A field in the floating point control register | |
6080 | (@var{fpcr}, see Alpha architecture reference manual) controls the | |
6081 | rounding mode in effect. The C library initializes this register for | |
6082 | rounding towards plus infinity. Thus, unless your program modifies the | |
ec4b2ecb CB |
6083 | @var{fpcr}, @samp{d} corresponds to round towards plus infinity. |
6084 | @end table | |
74291a4b MM |
6085 | |
6086 | @item -mtrap-precision=@var{trap precision} | |
6087 | In the Alpha architecture, floating point traps are imprecise. This | |
6088 | means without software assistance it is impossible to recover from a | |
6089 | floating trap and program execution normally needs to be terminated. | |
0c2d1a2a | 6090 | GCC can generate code that can assist operating system trap handlers |
74291a4b MM |
6091 | in determining the exact location that caused a floating point trap. |
6092 | Depending on the requirements of an application, different levels of | |
6093 | precisions can be selected: | |
6094 | ||
6095 | @table @samp | |
6096 | @item p | |
6097 | Program precision. This option is the default and means a trap handler | |
6098 | can only identify which program caused a floating point exception. | |
6099 | ||
6100 | @item f | |
6101 | Function precision. The trap handler can determine the function that | |
6102 | caused a floating point exception. | |
6103 | ||
6104 | @item i | |
6105 | Instruction precision. The trap handler can determine the exact | |
6106 | instruction that caused a floating point exception. | |
6107 | @end table | |
6108 | ||
6109 | Other Alpha compilers provide the equivalent options called | |
6110 | @samp{-scope_safe} and @samp{-resumption_safe}. | |
6111 | ||
6112 | @item -mieee-conformant | |
6113 | This option marks the generated code as IEEE conformant. You must not | |
6114 | use this option unless you also specify @samp{-mtrap-precision=i} and either | |
6115 | @samp{-mfp-trap-mode=su} or @samp{-mfp-trap-mode=sui}. Its only effect | |
6116 | is to emit the line @samp{.eflag 48} in the function prologue of the | |
6117 | generated assembly file. Under DEC Unix, this has the effect that | |
6118 | IEEE-conformant math library routines will be linked in. | |
6119 | ||
6120 | @item -mbuild-constants | |
0c2d1a2a | 6121 | Normally GCC examines a 32- or 64-bit integer constant to |
74291a4b MM |
6122 | see if it can construct it from smaller constants in two or three |
6123 | instructions. If it cannot, it will output the constant as a literal and | |
956d6950 | 6124 | generate code to load it from the data segment at runtime. |
74291a4b | 6125 | |
0c2d1a2a | 6126 | Use this option to require GCC to construct @emph{all} integer constants |
74291a4b MM |
6127 | using code, even if it takes more instructions (the maximum is six). |
6128 | ||
6129 | You would typically use this option to build a shared library dynamic | |
6130 | loader. Itself a shared library, it must relocate itself in memory | |
6131 | before it can find the variables and constants in its own data segment. | |
956d6950 JL |
6132 | |
6133 | @item -malpha-as | |
6134 | @itemx -mgas | |
6135 | Select whether to generate code to be assembled by the vendor-supplied | |
6136 | assembler (@samp{-malpha-as}) or by the GNU assembler @samp{-mgas}. | |
6137 | ||
6138 | @item -mbwx | |
6139 | @itemx -mno-bwx | |
6140 | @itemx -mcix | |
6141 | @itemx -mno-cix | |
6142 | @itemx -mmax | |
6143 | @itemx -mno-max | |
0c2d1a2a | 6144 | Indicate whether GCC should generate code to use the optional BWX, |
956d6950 JL |
6145 | CIX, and MAX instruction sets. The default is to use the instruction sets |
6146 | supported by the CPU type specified via @samp{-mcpu=} option or that | |
0c2d1a2a | 6147 | of the CPU on which GCC was built if none was specified. |
956d6950 | 6148 | |
956d6950 JL |
6149 | @item -mcpu=@var{cpu_type} |
6150 | Set the instruction set, register set, and instruction scheduling | |
6151 | parameters for machine type @var{cpu_type}. You can specify either the | |
0c2d1a2a | 6152 | @samp{EV} style name or the corresponding chip number. GCC |
956d6950 JL |
6153 | supports scheduling parameters for the EV4 and EV5 family of processors |
6154 | and will choose the default values for the instruction set from | |
6155 | the processor you specify. If you do not specify a processor type, | |
0c2d1a2a | 6156 | GCC will default to the processor on which the compiler was built. |
956d6950 JL |
6157 | |
6158 | Supported values for @var{cpu_type} are | |
6159 | ||
6160 | @table @samp | |
6161 | @item ev4 | |
6162 | @itemx 21064 | |
6163 | Schedules as an EV4 and has no instruction set extensions. | |
6164 | ||
6165 | @item ev5 | |
6166 | @itemx 21164 | |
6167 | Schedules as an EV5 and has no instruction set extensions. | |
6168 | ||
6169 | @item ev56 | |
6170 | @itemx 21164a | |
6171 | Schedules as an EV5 and supports the BWX extension. | |
6172 | ||
6173 | @item pca56 | |
4f69985c | 6174 | @itemx 21164pc |
956d6950 JL |
6175 | @itemx 21164PC |
6176 | Schedules as an EV5 and supports the BWX and MAX extensions. | |
6177 | ||
6178 | @item ev6 | |
6179 | @itemx 21264 | |
6180 | Schedules as an EV5 (until Digital releases the scheduling parameters | |
6181 | for the EV6) and supports the BWX, CIX, and MAX extensions. | |
4f69985c RH |
6182 | @end table |
6183 | ||
6184 | @item -mmemory-latency=@var{time} | |
6185 | Sets the latency the scheduler should assume for typical memory | |
6186 | references as seen by the application. This number is highly | |
6187 | dependant on the memory access patterns used by the application | |
6188 | and the size of the external cache on the machine. | |
6189 | ||
6190 | Valid options for @var{time} are | |
6191 | ||
6192 | @table @samp | |
6193 | @item @var{number} | |
6194 | A decimal number representing clock cycles. | |
6195 | ||
6196 | @item L1 | |
6197 | @itemx L2 | |
6198 | @itemx L3 | |
6199 | @itemx main | |
6200 | The compiler contains estimates of the number of clock cycles for | |
6201 | ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches | |
6202 | (also called Dcache, Scache, and Bcache), as well as to main memory. | |
6203 | Note that L3 is only valid for EV5. | |
6204 | ||
956d6950 | 6205 | @end table |
74291a4b MM |
6206 | @end table |
6207 | ||
6208 | @node Clipper Options | |
6209 | @subsection Clipper Options | |
6210 | ||
6211 | These @samp{-m} options are defined for the Clipper implementations: | |
6212 | ||
6213 | @table @code | |
6214 | @item -mc300 | |
6215 | Produce code for a C300 Clipper processor. This is the default. | |
6216 | ||
62a1403d | 6217 | @item -mc400 |
74291a4b MM |
6218 | Produce code for a C400 Clipper processor i.e. use floating point |
6219 | registers f8..f15. | |
6220 | @end table | |
6221 | ||
6222 | @node H8/300 Options | |
6223 | @subsection H8/300 Options | |
6224 | ||
6225 | These @samp{-m} options are defined for the H8/300 implementations: | |
6226 | ||
6227 | @table @code | |
6228 | @item -mrelax | |
6229 | Shorten some address references at link time, when possible; uses the | |
6230 | linker option @samp{-relax}. @xref{H8/300,, @code{ld} and the H8/300, | |
6231 | ld.info, Using ld}, for a fuller description. | |
6232 | ||
6233 | @item -mh | |
6234 | Generate code for the H8/300H. | |
6235 | ||
dcb9d1f0 JL |
6236 | @item -ms |
6237 | Generate code for the H8/S. | |
6238 | ||
74291a4b MM |
6239 | @item -mint32 |
6240 | Make @code{int} data 32 bits by default. | |
6241 | ||
6242 | @item -malign-300 | |
6243 | On the h8/300h, use the same alignment rules as for the h8/300. | |
6244 | The default for the h8/300h is to align longs and floats on 4 byte boundaries. | |
6245 | @samp{-malign-300} causes them to be aligned on 2 byte boundaries. | |
6246 | This option has no effect on the h8/300. | |
6247 | @end table | |
6248 | ||
6249 | @node SH Options | |
6250 | @subsection SH Options | |
6251 | ||
6252 | These @samp{-m} options are defined for the SH implementations: | |
6253 | ||
6254 | @table @code | |
6255 | @item -m1 | |
6256 | Generate code for the SH1. | |
6257 | ||
6258 | @item -m2 | |
6259 | Generate code for the SH2. | |
6260 | ||
6261 | @item -m3 | |
6262 | Generate code for the SH3. | |
6263 | ||
6264 | @item -m3e | |
6265 | Generate code for the SH3e. | |
6266 | ||
6267 | @item -mb | |
6268 | Compile code for the processor in big endian mode. | |
6269 | ||
6270 | @item -ml | |
6271 | Compile code for the processor in little endian mode. | |
6272 | ||
3d5a0820 R |
6273 | @item -mdalign |
6274 | Align doubles at 64 bit boundaries. Note that this changes the calling | |
6275 | conventions, and thus some functions from the standard C library will | |
6276 | not work unless you recompile it first with -mdalign. | |
6277 | ||
74291a4b MM |
6278 | @item -mrelax |
6279 | Shorten some address references at link time, when possible; uses the | |
6280 | linker option @samp{-relax}. | |
6281 | @end table | |
6282 | ||
6283 | @node System V Options | |
6284 | @subsection Options for System V | |
6285 | ||
6286 | These additional options are available on System V Release 4 for | |
6287 | compatibility with other compilers on those systems: | |
6288 | ||
6289 | @table @code | |
6290 | @item -G | |
6291 | Create a shared object. | |
6292 | It is recommended that @samp{-symbolic} or @samp{-shared} be used instead. | |
6293 | ||
6294 | @item -Qy | |
6295 | Identify the versions of each tool used by the compiler, in a | |
6296 | @code{.ident} assembler directive in the output. | |
6297 | ||
6298 | @item -Qn | |
6299 | Refrain from adding @code{.ident} directives to the output file (this is | |
6300 | the default). | |
6301 | ||
6302 | @item -YP,@var{dirs} | |
6303 | Search the directories @var{dirs}, and no others, for libraries | |
6304 | specified with @samp{-l}. | |
6305 | ||
6306 | @item -Ym,@var{dir} | |
6307 | Look in the directory @var{dir} to find the M4 preprocessor. | |
6308 | The assembler uses this option. | |
6309 | @c This is supposed to go with a -Yd for predefined M4 macro files, but | |
6310 | @c the generic assembler that comes with Solaris takes just -Ym. | |
6311 | @end table | |
6312 | ||
282a61e6 MH |
6313 | @node TMS320C3x/C4x Options |
6314 | @subsection TMS320C3x/C4x Options | |
6315 | @cindex TMS320C3x/C4x Options | |
6316 | ||
6317 | These @samp{-m} options are defined for TMS320C3x/C4x implementations: | |
6318 | ||
6319 | @table @code | |
6320 | ||
6321 | @item -mcpu=@var{cpu_type} | |
6322 | Set the instruction set, register set, and instruction scheduling | |
6323 | parameters for machine type @var{cpu_type}. Supported values for | |
6324 | @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and | |
6325 | @samp{c44}. The default is @samp{c40} to generate code for the | |
6326 | TMS320C40. | |
6327 | ||
6328 | @item -mbig-memory | |
6329 | @item -mbig | |
6330 | @itemx -msmall-memory | |
6331 | @itemx -msmall | |
6332 | Generates code for the big or small memory model. The small memory | |
6333 | model assumed that all data fits into one 64K word page. At run-time | |
6334 | the data page (DP) register must be set to point to the 64K page | |
6335 | containing the .bss and .data program sections. The big memory model is | |
6336 | the default and requires reloading of the DP register for every direct | |
6337 | memory access. | |
6338 | ||
6339 | @item -mbk | |
6340 | @itemx -mno-bk | |
6341 | Allow (disallow) allocation of general integer operands into the block | |
6342 | count register BK. | |
6343 | ||
6344 | @item -mdb | |
6345 | @itemx -mno-db | |
6346 | Enable (disable) generation of code using decrement and branch, | |
6347 | DBcond(D), instructions. This is enabled by default for the C4x. To be | |
6348 | on the safe side, this is disabled for the C3x, since the maximum | |
6349 | iteration count on the C3x is 2^23 + 1 (but who iterates loops more than | |
6350 | 2^23 times on the C3x?). Note that GCC will try to reverse a loop so | |
6351 | that it can utilise the decrement and branch instruction, but will give | |
6352 | up if there is more than one memory reference in the loop. Thus a loop | |
6353 | where the loop counter is decremented can generate slightly more | |
6354 | efficient code, in cases where the RPTB instruction cannot be utilised. | |
6355 | ||
6356 | @item -mdp-isr-reload | |
6357 | @itemx -mparanoid | |
6358 | Force the DP register to be saved on entry to an interrupt service | |
6359 | routine (ISR), reloaded to point to the data section, and restored on | |
6360 | exit from the ISR. This should not be required unless someone has | |
6361 | violated the small memory model by modifying the DP register, say within | |
6362 | an object library. | |
6363 | ||
6364 | @item -mmpyi | |
6365 | @itemx -mno-mpyi | |
6366 | For the C3x use the 24-bit MPYI instruction for integer multiplies | |
6367 | instead of a library call to guarantee 32-bit results. Note that if one | |
6368 | of the operands is a constant, then the multiplication will be performed | |
6369 | using shifts and adds. If the -mmpyi option is not specified for the C3x, | |
6370 | then squaring operations are performed inline instead of a library call. | |
6371 | ||
6372 | @item -mfast-fix | |
6373 | @itemx -mno-fast-fix | |
6374 | The C3x/C4x FIX instruction to convert a floating point value to an | |
6375 | integer value chooses the nearest integer less than or equal to the | |
6376 | floating point value rather than to the nearest integer. Thus if the | |
6377 | floating point number is negative, the result will be incorrectly | |
6378 | truncated an additional code is necessary to detect and correct this | |
6379 | case. This option can be used to disable generation of the additional | |
6380 | code required to correct the result. | |
6381 | ||
6382 | @item -mrptb | |
6383 | @itemx -mno-rptb | |
6384 | Enable (disable) generation of repeat block sequences using the RPTB | |
6385 | instruction for zero overhead looping. The RPTB construct is only used | |
6386 | for innermost loops that do not call functions or jump across the loop | |
6387 | boundaries. There is no advantage having nested RPTB loops due to the | |
6388 | overhead required to save and restore the RC, RS, and RE registers. | |
6389 | This is enabled by default with -O2. | |
6390 | ||
6391 | @item -mrpts=@var{count} | |
6392 | @itemx -mno-rpts | |
6393 | Enable (disable) the use of the single instruction repeat instruction | |
6394 | RPTS. If a repeat block contains a single instruction, and the loop | |
6395 | count can be guaranteed to be less than the value @var{count}, GCC will | |
6396 | emit a RPTS instruction instead of a RPTB. If no value is specified, | |
6397 | then a RPTS will be emitted even if the loop count cannot be determined | |
6398 | at compile time. Note that the repeated instruction following RPTS does | |
6399 | not have to be reloaded from memory each iteration, thus freeing up the | |
6400 | CPU buses for oeprands. However, since interrupts are blocked by this | |
6401 | instruction, it is disabled by default. | |
6402 | ||
6403 | @item -mloop-unsigned | |
6404 | @itemx -mno-loop-unsigned | |
6405 | The maximum iteration count when using RPTS and RPTB (and DB on the C40) | |
6406 | is 2^31 + 1 since these instructions test if the iteration count is | |
6407 | negative to terminate the loop. If the iteration count is unsigned | |
6408 | there is a possibility than the 2^31 + 1 maximum iteration count may be | |
6409 | exceeded. This switch allows an unsigned iteration count. | |
6410 | ||
6411 | @item -mti | |
6412 | Try to emit an assembler syntax that the TI assembler (asm30) is happy | |
6413 | with. This also enforces compatibility with the API employed by the TI | |
6414 | C3x C compiler. For example, long doubles are passed as structures | |
6415 | rather than in floating point registers. | |
6416 | ||
6417 | @item -mregparm | |
6418 | @itemx -mmemparm | |
6419 | Generate code that uses registers (stack) for passing arguments to functions. | |
6420 | By default, arguments are passed in registers where possible rather | |
6421 | than by pushing arguments on to the stack. | |
6422 | ||
6423 | @item -mparallel-insns | |
6424 | @itemx -mno-parallel-insns | |
6425 | Allow the generation of parallel instructions. This is enabled by | |
6426 | default with -O2. | |
6427 | ||
6428 | @item -mparallel-mpy | |
6429 | @itemx -mno-parallel-mpy | |
6430 | Allow the generation of MPY||ADD and MPY||SUB parallel instructions, | |
6431 | provided -mparallel-insns is also specified. These instructions have | |
6432 | tight register constraints which can pessimize the code generation | |
6433 | of large functions. | |
6434 | ||
6435 | @end table | |
6436 | ||
f84271d9 JL |
6437 | @node V850 Options |
6438 | @subsection V850 Options | |
6439 | @cindex V850 Options | |
6440 | ||
6441 | These @samp{-m} options are defined for V850 implementations: | |
6442 | ||
6443 | @table @code | |
6444 | @item -mlong-calls | |
6445 | @itemx -mno-long-calls | |
6446 | Treat all calls as being far away (near). If calls are assumed to be | |
6447 | far away, the compiler will always load the functions address up into a | |
6448 | register, and call indirect through the pointer. | |
6449 | ||
6450 | @item -mno-ep | |
bd762873 | 6451 | @itemx -mep |
f84271d9 JL |
6452 | Do not optimize (do optimize) basic blocks that use the same index |
6453 | pointer 4 or more times to copy pointer into the @code{ep} register, and | |
6454 | use the shorter @code{sld} and @code{sst} instructions. The @samp{-mep} | |
6455 | option is on by default if you optimize. | |
6456 | ||
6457 | @item -mno-prolog-function | |
6458 | @itemx -mprolog-function | |
6459 | Do not use (do use) external functions to save and restore registers at | |
6460 | the prolog and epilog of a function. The external functions are slower, | |
6461 | but use less code space if more than one function saves the same number | |
6462 | of registers. The @samp{-mprolog-function} option is on by default if | |
6463 | you optimize. | |
6464 | ||
6465 | @item -mspace | |
6466 | Try to make the code as small as possible. At present, this just turns | |
6467 | on the @samp{-mep} and @samp{-mprolog-function} options. | |
6468 | ||
6469 | @item -mtda=@var{n} | |
6470 | Put static or global variables whose size is @var{n} bytes or less into | |
6471 | the tiny data area that register @code{ep} points to. The tiny data | |
6472 | area can hold up to 256 bytes in total (128 bytes for byte references). | |
6473 | ||
6474 | @item -msda=@var{n} | |
6475 | Put static or global variables whose size is @var{n} bytes or less into | |
6476 | the small data area that register @code{gp} points to. The small data | |
6477 | area can hold up to 64 kilobytes. | |
6478 | ||
6479 | @item -mzda=@var{n} | |
6480 | Put static or global variables whose size is @var{n} bytes or less into | |
6481 | the first 32 kilobytes of memory. | |
e9a25f70 | 6482 | |
48f0be1b SC |
6483 | @item -mv850 |
6484 | Specify that the target processor is the V850. | |
6485 | ||
e9a25f70 JL |
6486 | @item -mbig-switch |
6487 | Generate code suitable for big switch tables. Use this option only if | |
6488 | the assembler/linker complain about out of range branches within a switch | |
6489 | table. | |
f84271d9 JL |
6490 | @end table |
6491 | ||
56b2d7a7 JL |
6492 | @node ARC Options |
6493 | @subsection ARC Options | |
6494 | @cindex ARC Options | |
6495 | ||
6496 | These options are defined for ARC implementations: | |
6497 | ||
6498 | @table @code | |
6499 | @item -EL | |
6500 | Compile code for little endian mode. This is the default. | |
6501 | ||
6502 | @item -EB | |
6503 | Compile code for big endian mode. | |
6504 | ||
6505 | @item -mmangle-cpu | |
6506 | Prepend the name of the cpu to all public symbol names. | |
6507 | In multiple-processor systems, there are many ARC variants with different | |
6508 | instruction and register set characteristics. This flag prevents code | |
6509 | compiled for one cpu to be linked with code compiled for another. | |
6510 | No facility exists for handling variants that are "almost identical". | |
6511 | This is an all or nothing option. | |
6512 | ||
6513 | @item -mcpu=@var{cpu} | |
6514 | Compile code for ARC variant @var{cpu}. | |
6515 | Which variants are supported depend on the configuration. | |
6516 | All variants support @samp{-mcpu=base}, this is the default. | |
6517 | ||
6518 | @item -mtext=@var{text section} | |
59d40964 AS |
6519 | @itemx -mdata=@var{data section} |
6520 | @itemx -mrodata=@var{readonly data section} | |
56b2d7a7 JL |
6521 | Put functions, data, and readonly data in @var{text section}, |
6522 | @var{data section}, and @var{readonly data section} respectively | |
6523 | by default. This can be overridden with the @code{section} attribute. | |
0b433de6 | 6524 | @xref{Variable Attributes}. |
56b2d7a7 JL |
6525 | |
6526 | @end table | |
6527 | ||
83575957 ID |
6528 | @node NS32K Options |
6529 | @subsection NS32K Options | |
6530 | @cindex NS32K options | |
6531 | ||
6532 | These are the @samp{-m} options defined for the 32000 series. The default | |
6533 | values for these options depends on which style of 32000 was selected when | |
6534 | the compiler was configured; the defaults for the most common choices are | |
6535 | given below. | |
6536 | ||
6537 | @table @code | |
6538 | @item -m32032 | |
6539 | @itemx -m32032 | |
6540 | Generate output for a 32032. This is the default | |
6541 | when the compiler is configured for 32032 and 32016 based systems. | |
6542 | ||
6543 | @item -m32332 | |
6544 | @itemx -m32332 | |
6545 | Generate output for a 32332. This is the default | |
6546 | when the compiler is configured for 32332-based systems. | |
6547 | ||
6548 | @item -m32532 | |
6549 | @itemx -m32532 | |
6550 | Generate output for a 32532. This is the default | |
6551 | when the compiler is configured for 32532-based systems. | |
6552 | ||
6553 | @item -m32081 | |
6554 | Generate output containing 32081 instructions for floating point. | |
6555 | This is the default for all systems. | |
6556 | ||
6557 | @item -m32381 | |
6558 | Generate output containing 32381 instructions for floating point. This | |
6559 | also implies @samp{-m32081}. The 32381 is only compatible with the 32332 | |
6560 | and 32532 cpus. This is the default for the pc532-netbsd configuration. | |
6561 | ||
6562 | @item -mmulti-add | |
6563 | Try and generate multiply-add floating point instructions @code{polyF} | |
6564 | and @code{dotF}. This option is only available if the @samp{-m32381} | |
6565 | option is in effect. Using these instructions requires changes to to | |
6566 | register allocation which generally has a negative impact on | |
6567 | performance. This option should only be enabled when compiling code | |
6568 | particularly likely to make heavy use of multiply-add instructions. | |
6569 | ||
6570 | @item -mnomulti-add | |
6571 | Do not try and generate multiply-add floating point instructions | |
6572 | @code{polyF} and @code{dotF}. This is the default on all platforms. | |
6573 | ||
6574 | @item -msoft-float | |
6575 | Generate output containing library calls for floating point. | |
6576 | @strong{Warning:} the requisite libraries may not be available. | |
6577 | ||
6578 | @item -mnobitfield | |
6579 | Do not use the bit-field instructions. On some machines it is faster to | |
6580 | use shifting and masking operations. This is the default for the pc532. | |
6581 | ||
6582 | @item -mbitfield | |
6583 | Do use the bit-field instructions. This is the default for all platforms | |
6584 | except the pc532. | |
6585 | ||
6586 | @item -mrtd | |
6587 | Use a different function-calling convention, in which functions | |
6588 | that take a fixed number of arguments return pop their | |
6589 | arguments on return with the @code{ret} instruction. | |
6590 | ||
6591 | This calling convention is incompatible with the one normally | |
6592 | used on Unix, so you cannot use it if you need to call libraries | |
6593 | compiled with the Unix compiler. | |
6594 | ||
6595 | Also, you must provide function prototypes for all functions that | |
6596 | take variable numbers of arguments (including @code{printf}); | |
6597 | otherwise incorrect code will be generated for calls to those | |
6598 | functions. | |
6599 | ||
6600 | In addition, seriously incorrect code will result if you call a | |
6601 | function with too many arguments. (Normally, extra arguments are | |
6602 | harmlessly ignored.) | |
6603 | ||
6604 | This option takes its name from the 680x0 @code{rtd} instruction. | |
6605 | ||
6606 | ||
6607 | @item -mregparam | |
6608 | Use a different function-calling convention where the first two arguments | |
6609 | are passed in registers. | |
6610 | ||
6611 | This calling convention is incompatible with the one normally | |
6612 | used on Unix, so you cannot use it if you need to call libraries | |
6613 | compiled with the Unix compiler. | |
6614 | ||
6615 | @item -mnoregparam | |
6616 | Do not pass any arguments in registers. This is the default for all | |
6617 | targets. | |
6618 | ||
6619 | @item -msb | |
6620 | It is OK to use the sb as an index register which is always loaded with | |
6621 | zero. This is the default for the pc532-netbsd target. | |
6622 | ||
6623 | @item -mnosb | |
6624 | The sb register is not available for use or has not been initialized to | |
6625 | zero by the run time system. This is the default for all targets except | |
6626 | the pc532-netbsd. It is also implied whenever @samp{-mhimem} or | |
6627 | @samp{-fpic} is set. | |
6628 | ||
6629 | @item -mhimem | |
6630 | Many ns32000 series addressing modes use displacements of up to 512MB. | |
6631 | If an address is above 512MB then displacements from zero can not be used. | |
6632 | This option causes code to be generated which can be loaded above 512MB. | |
6633 | This may be useful for operating systems or ROM code. | |
6634 | ||
6635 | @item -mnohimem | |
6636 | Assume code will be loaded in the first 512MB of virtual address space. | |
6637 | This is the default for all platforms. | |
6638 | ||
6639 | ||
6640 | @end table | |
6641 | ||
6642 | ||
56b2d7a7 | 6643 | |
74291a4b MM |
6644 | @node Code Gen Options |
6645 | @section Options for Code Generation Conventions | |
6646 | @cindex code generation conventions | |
6647 | @cindex options, code generation | |
6648 | @cindex run-time options | |
6649 | ||
6650 | These machine-independent options control the interface conventions | |
6651 | used in code generation. | |
6652 | ||
6653 | Most of them have both positive and negative forms; the negative form | |
6654 | of @samp{-ffoo} would be @samp{-fno-foo}. In the table below, only | |
6655 | one of the forms is listed---the one which is not the default. You | |
6656 | can figure out the other form by either removing @samp{no-} or adding | |
6657 | it. | |
6658 | ||
6659 | @table @code | |
956d6950 | 6660 | @item -fexceptions |
89ed4e9d | 6661 | Enable exception handling. Generates extra code needed to propagate |
c5c76735 JL |
6662 | exceptions. For some targets, this implies GNU CC will generate frame |
6663 | unwind information for all functions, which can produce significant data | |
6664 | size overhead, although it does not affect execution. If you do not | |
6665 | specify this option, GNU CC will enable it by default for languages like | |
6666 | C++ which normally require exception handling, and disable itfor | |
6667 | languages like C that do not normally require it. However, you may need | |
6668 | to enable this option when compiling C code that needs to interoperate | |
6669 | properly with exception handlers written in C++. You may also wish to | |
6670 | disable this option if you are compiling older C++ programs that don't | |
6671 | use exception handling. | |
956d6950 | 6672 | |
74291a4b MM |
6673 | @item -fpcc-struct-return |
6674 | Return ``short'' @code{struct} and @code{union} values in memory like | |
6675 | longer ones, rather than in registers. This convention is less | |
6676 | efficient, but it has the advantage of allowing intercallability between | |
0c2d1a2a | 6677 | GCC-compiled files and files compiled with other compilers. |
74291a4b MM |
6678 | |
6679 | The precise convention for returning structures in memory depends | |
6680 | on the target configuration macros. | |
6681 | ||
6682 | Short structures and unions are those whose size and alignment match | |
6683 | that of some integer type. | |
6684 | ||
6685 | @item -freg-struct-return | |
6686 | Use the convention that @code{struct} and @code{union} values are | |
6687 | returned in registers when possible. This is more efficient for small | |
6688 | structures than @samp{-fpcc-struct-return}. | |
6689 | ||
6690 | If you specify neither @samp{-fpcc-struct-return} nor its contrary | |
0c2d1a2a JB |
6691 | @samp{-freg-struct-return}, GCC defaults to whichever convention is |
6692 | standard for the target. If there is no standard convention, GCC | |
6693 | defaults to @samp{-fpcc-struct-return}, except on targets where GCC | |
74291a4b MM |
6694 | is the principal compiler. In those cases, we can choose the standard, |
6695 | and we chose the more efficient register return alternative. | |
6696 | ||
6697 | @item -fshort-enums | |
6698 | Allocate to an @code{enum} type only as many bytes as it needs for the | |
6699 | declared range of possible values. Specifically, the @code{enum} type | |
6700 | will be equivalent to the smallest integer type which has enough room. | |
6701 | ||
6702 | @item -fshort-double | |
6703 | Use the same size for @code{double} as for @code{float}. | |
6704 | ||
6705 | @item -fshared-data | |
6706 | Requests that the data and non-@code{const} variables of this | |
6707 | compilation be shared data rather than private data. The distinction | |
6708 | makes sense only on certain operating systems, where shared data is | |
6709 | shared between processes running the same program, while private data | |
6710 | exists in one copy per process. | |
6711 | ||
6712 | @item -fno-common | |
c5c76735 | 6713 | Allocate even uninitialized global variables in the data section of the |
74291a4b MM |
6714 | object file, rather than generating them as common blocks. This has the |
6715 | effect that if the same variable is declared (without @code{extern}) in | |
6716 | two different compilations, you will get an error when you link them. | |
6717 | The only reason this might be useful is if you wish to verify that the | |
6718 | program will work on other systems which always work this way. | |
6719 | ||
6720 | @item -fno-ident | |
6721 | Ignore the @samp{#ident} directive. | |
6722 | ||
6723 | @item -fno-gnu-linker | |
6724 | Do not output global initializations (such as C++ constructors and | |
6725 | destructors) in the form used by the GNU linker (on systems where the GNU | |
6726 | linker is the standard method of handling them). Use this option when | |
6727 | you want to use a non-GNU linker, which also requires using the | |
6728 | @code{collect2} program to make sure the system linker includes | |
0c2d1a2a | 6729 | constructors and destructors. (@code{collect2} is included in the GCC |
74291a4b MM |
6730 | distribution.) For systems which @emph{must} use @code{collect2}, the |
6731 | compiler driver @code{gcc} is configured to do this automatically. | |
6732 | ||
6733 | @item -finhibit-size-directive | |
6734 | Don't output a @code{.size} assembler directive, or anything else that | |
6735 | would cause trouble if the function is split in the middle, and the | |
6736 | two halves are placed at locations far apart in memory. This option is | |
6737 | used when compiling @file{crtstuff.c}; you should not need to use it | |
6738 | for anything else. | |
6739 | ||
6740 | @item -fverbose-asm | |
6741 | Put extra commentary information in the generated assembly code to | |
6742 | make it more readable. This option is generally only of use to those | |
6743 | who actually need to read the generated assembly code (perhaps while | |
6744 | debugging the compiler itself). | |
6745 | ||
c85f7c16 | 6746 | @samp{-fno-verbose-asm}, the default, causes the |
74291a4b MM |
6747 | extra information to be omitted and is useful when comparing two assembler |
6748 | files. | |
6749 | ||
6750 | @item -fvolatile | |
6751 | Consider all memory references through pointers to be volatile. | |
6752 | ||
6753 | @item -fvolatile-global | |
6754 | Consider all memory references to extern and global data items to | |
0c2d1a2a | 6755 | be volatile. GCC does not consider static data items to be volatile |
ab87f8c8 JL |
6756 | because of this switch. |
6757 | ||
6758 | @item -fvolatile-static | |
6759 | Consider all memory references to static data to be volatile. | |
74291a4b MM |
6760 | |
6761 | @item -fpic | |
6762 | @cindex global offset table | |
6763 | @cindex PIC | |
6764 | Generate position-independent code (PIC) suitable for use in a shared | |
6765 | library, if supported for the target machine. Such code accesses all | |
861bb6c1 JL |
6766 | constant addresses through a global offset table (GOT). The dynamic |
6767 | loader resolves the GOT entries when the program starts (the dynamic | |
0c2d1a2a | 6768 | loader is not part of GCC; it is part of the operating system). If |
861bb6c1 JL |
6769 | the GOT size for the linked executable exceeds a machine-specific |
6770 | maximum size, you get an error message from the linker indicating that | |
6771 | @samp{-fpic} does not work; in that case, recompile with @samp{-fPIC} | |
6772 | instead. (These maximums are 16k on the m88k, 8k on the Sparc, and 32k | |
6773 | on the m68k and RS/6000. The 386 has no such limit.) | |
74291a4b MM |
6774 | |
6775 | Position-independent code requires special support, and therefore works | |
0c2d1a2a | 6776 | only on certain machines. For the 386, GCC supports PIC for System V |
74291a4b MM |
6777 | but not for the Sun 386i. Code generated for the IBM RS/6000 is always |
6778 | position-independent. | |
6779 | ||
74291a4b MM |
6780 | @item -fPIC |
6781 | If supported for the target machine, emit position-independent code, | |
6782 | suitable for dynamic linking and avoiding any limit on the size of the | |
6783 | global offset table. This option makes a difference on the m68k, m88k, | |
6784 | and the Sparc. | |
6785 | ||
6786 | Position-independent code requires special support, and therefore works | |
6787 | only on certain machines. | |
6788 | ||
6789 | @item -ffixed-@var{reg} | |
6790 | Treat the register named @var{reg} as a fixed register; generated code | |
6791 | should never refer to it (except perhaps as a stack pointer, frame | |
6792 | pointer or in some other fixed role). | |
6793 | ||
6794 | @var{reg} must be the name of a register. The register names accepted | |
6795 | are machine-specific and are defined in the @code{REGISTER_NAMES} | |
6796 | macro in the machine description macro file. | |
6797 | ||
6798 | This flag does not have a negative form, because it specifies a | |
6799 | three-way choice. | |
6800 | ||
6801 | @item -fcall-used-@var{reg} | |
956d6950 | 6802 | Treat the register named @var{reg} as an allocable register that is |
74291a4b MM |
6803 | clobbered by function calls. It may be allocated for temporaries or |
6804 | variables that do not live across a call. Functions compiled this way | |
6805 | will not save and restore the register @var{reg}. | |
6806 | ||
cb2fdc84 GRK |
6807 | It is an error to used this flag with the frame pointer or stack pointer. |
6808 | Use of this flag for other registers that have fixed pervasive roles in | |
6809 | the machine's execution model will produce disastrous results. | |
74291a4b MM |
6810 | |
6811 | This flag does not have a negative form, because it specifies a | |
6812 | three-way choice. | |
6813 | ||
6814 | @item -fcall-saved-@var{reg} | |
956d6950 | 6815 | Treat the register named @var{reg} as an allocable register saved by |
74291a4b MM |
6816 | functions. It may be allocated even for temporaries or variables that |
6817 | live across a call. Functions compiled this way will save and restore | |
6818 | the register @var{reg} if they use it. | |
6819 | ||
cb2fdc84 GRK |
6820 | It is an error to used this flag with the frame pointer or stack pointer. |
6821 | Use of this flag for other registers that have fixed pervasive roles in | |
6822 | the machine's execution model will produce disastrous results. | |
74291a4b MM |
6823 | |
6824 | A different sort of disaster will result from the use of this flag for | |
6825 | a register in which function values may be returned. | |
6826 | ||
6827 | This flag does not have a negative form, because it specifies a | |
6828 | three-way choice. | |
6829 | ||
6830 | @item -fpack-struct | |
6831 | Pack all structure members together without holes. Usually you would | |
6832 | not want to use this option, since it makes the code suboptimal, and | |
6833 | the offsets of structure members won't agree with system libraries. | |
6834 | ||
861bb6c1 | 6835 | @item -fcheck-memory-usage |
0c2d1a2a | 6836 | Generate extra code to check each memory access. GCC will generate |
861bb6c1 | 6837 | code that is suitable for a detector of bad memory accesses such as |
7d384cc0 | 6838 | @file{Checker}. |
861bb6c1 | 6839 | |
d3111037 CB |
6840 | Normally, you should compile all, or none, of your code with this option. |
6841 | ||
6842 | If you do mix code compiled with and without this option, | |
6843 | you must ensure that all code that has side effects | |
6844 | and that is called by code compiled with this option | |
6845 | is, itself, compiled with this option. | |
6846 | If you do not, you might get erroneous messages from the detector. | |
6847 | ||
861bb6c1 | 6848 | If you use functions from a library that have side-effects (such as |
d3111037 | 6849 | @code{read}), you might not be able to recompile the library and |
861bb6c1 | 6850 | specify this option. In that case, you can enable the |
0c2d1a2a | 6851 | @samp{-fprefix-function-name} option, which requests GCC to encapsulate |
861bb6c1 JL |
6852 | your code and make other functions look as if they were compiled with |
6853 | @samp{-fcheck-memory-usage}. This is done by calling ``stubs'', | |
6854 | which are provided by the detector. If you cannot find or build | |
d3111037 | 6855 | stubs for every function you call, you might have to specify |
861bb6c1 JL |
6856 | @samp{-fcheck-memory-usage} without @samp{-fprefix-function-name}. |
6857 | ||
7d384cc0 | 6858 | If you specify this option, you can not use the @code{asm} or |
c5c76735 JL |
6859 | @code{__asm__} keywords in functions with memory checking enabled. GNU |
6860 | CC cannot understand what the @code{asm} statement may do, and therefore | |
6861 | cannot generate the appropriate code, so it will reject it. However, if | |
6862 | you specify the function attribute @code{no_check_memory_usage} (see | |
6863 | @pxref{Function Attributes}, GNU CC will disable memory checking within a | |
6864 | function; you may use @code{asm} statements inside such functions. You | |
6865 | may have an inline expansion of a non-checked function within a checked | |
6866 | function; in that case GNU CC will not generate checks for the inlined | |
6867 | function's memory accesses. | |
6868 | ||
6869 | If you move your @code{asm} statements to non-checked inline functions | |
6870 | and they do access memory, you can add calls to the support code in your | |
7d384cc0 KR |
6871 | inline function, to indicate any reads, writes, or copies being done. |
6872 | These calls would be similar to those done in the stubs described above. | |
6873 | ||
861bb6c1 | 6874 | @item -fprefix-function-name |
0c2d1a2a JB |
6875 | Request GCC to add a prefix to the symbols generated for function names. |
6876 | GCC adds a prefix to the names of functions defined as well as | |
861bb6c1 | 6877 | functions called. Code compiled with this option and code compiled |
d3111037 | 6878 | without the option can't be linked together, unless stubs are used. |
861bb6c1 JL |
6879 | |
6880 | If you compile the following code with @samp{-fprefix-function-name} | |
6881 | @example | |
6882 | extern void bar (int); | |
6883 | void | |
6884 | foo (int a) | |
6885 | @{ | |
6886 | return bar (a + 5); | |
861bb6c1 JL |
6887 | @} |
6888 | @end example | |
6889 | ||
6890 | @noindent | |
0c2d1a2a | 6891 | GCC will compile the code as if it was written: |
861bb6c1 JL |
6892 | @example |
6893 | extern void prefix_bar (int); | |
6894 | void | |
6895 | prefix_foo (int a) | |
6896 | @{ | |
6897 | return prefix_bar (a + 5); | |
6898 | @} | |
6899 | @end example | |
6900 | This option is designed to be used with @samp{-fcheck-memory-usage}. | |
6901 | ||
07417085 KR |
6902 | @item -finstrument-functions |
6903 | Generate instrumentation calls for entry and exit to functions. Just | |
6904 | after function entry and just before function exit, the following | |
6905 | profiling functions will be called with the address of the current | |
6906 | function and its call site. (On some platforms, | |
6907 | @code{__builtin_return_address} does not work beyond the current | |
6908 | function, so the call site information may not be available to the | |
6909 | profiling functions otherwise.) | |
6910 | ||
6911 | @example | |
6912 | void __cyg_profile_func_enter (void *this_fn, void *call_site); | |
6913 | void __cyg_profile_func_exit (void *this_fn, void *call_site); | |
6914 | @end example | |
6915 | ||
6916 | The first argument is the address of the start of the current function, | |
6917 | which may be looked up exactly in the symbol table. | |
6918 | ||
6919 | This instrumentation is also done for functions expanded inline in other | |
6920 | functions. The profiling calls will indicate where, conceptually, the | |
6921 | inline function is entered and exited. This means that addressable | |
6922 | versions of such functions must be available. If all your uses of a | |
6923 | function are expanded inline, this may mean an additional expansion of | |
6924 | code size. If you use @samp{extern inline} in your C code, an | |
6925 | addressable version of such functions must be provided. (This is | |
6926 | normally the case anyways, but if you get lucky and the optimizer always | |
6927 | expands the functions inline, you might have gotten away without | |
6928 | providing static copies.) | |
6929 | ||
6930 | A function may be given the attribute @code{no_instrument_function}, in | |
6931 | which case this instrumentation will not be done. This can be used, for | |
6932 | example, for the profiling functions listed above, high-priority | |
6933 | interrupt routines, and any functions from which the profiling functions | |
6934 | cannot safely be called (perhaps signal handlers, if the profiling | |
6935 | routines generate output or allocate memory). | |
6936 | ||
861bb6c1 JL |
6937 | @item -fstack-check |
6938 | Generate code to verify that you do not go beyond the boundary of the | |
6939 | stack. You should specify this flag if you are running in an | |
6940 | environment with multiple threads, but only rarely need to specify it in | |
6941 | a single-threaded environment since stack overflow is automatically | |
6942 | detected on nearly all systems if there is only one stack. | |
6943 | ||
e5eb27e5 JL |
6944 | @cindex aliasing of parameters |
6945 | @cindex parameters, aliased | |
6946 | @item -fargument-alias | |
04afd9d6 JL |
6947 | @itemx -fargument-noalias |
6948 | @itemx -fargument-noalias-global | |
e5eb27e5 JL |
6949 | Specify the possible relationships among parameters and between |
6950 | parameters and global data. | |
6951 | ||
6952 | @samp{-fargument-alias} specifies that arguments (parameters) may | |
6953 | alias each other and may alias global storage. | |
6954 | @samp{-fargument-noalias} specifies that arguments do not alias | |
6955 | each other, but may alias global storage. | |
6956 | @samp{-fargument-noalias-global} specifies that arguments do not | |
6957 | alias each other and do not alias global storage. | |
6958 | ||
6959 | Each language will automatically use whatever option is required by | |
6960 | the language standard. You should not need to use these options yourself. | |
19283265 RH |
6961 | |
6962 | @item -fleading-underscore | |
6963 | This option and its counterpart, -fno-leading-underscore, forcibly | |
6964 | change the way C symbols are represented in the object file. One use | |
6965 | is to help link with legacy assembly code. | |
6966 | ||
6967 | Be warned that you should know what you are doing when invoking this | |
6968 | option, and that not all targets provide complete support for it. | |
74291a4b MM |
6969 | @end table |
6970 | ||
6971 | @node Environment Variables | |
0c2d1a2a | 6972 | @section Environment Variables Affecting GCC |
74291a4b MM |
6973 | @cindex environment variables |
6974 | ||
0c2d1a2a JB |
6975 | This section describes several environment variables that affect how GCC |
6976 | operates. Some of them work by specifying directories or prefixes to use | |
56f48ce9 | 6977 | when searching for various kinds of files. Some are used to specify other |
46103ab4 | 6978 | aspects of the compilation environment. |
74291a4b MM |
6979 | |
6980 | @ifclear INTERNALS | |
6981 | Note that you can also specify places to search using options such as | |
6982 | @samp{-B}, @samp{-I} and @samp{-L} (@pxref{Directory Options}). These | |
6983 | take precedence over places specified using environment variables, which | |
0c2d1a2a JB |
6984 | in turn take precedence over those specified by the configuration of GCC. |
6985 | ||
74291a4b MM |
6986 | @end ifclear |
6987 | @ifset INTERNALS | |
6988 | Note that you can also specify places to search using options such as | |
6989 | @samp{-B}, @samp{-I} and @samp{-L} (@pxref{Directory Options}). These | |
6990 | take precedence over places specified using environment variables, which | |
0c2d1a2a JB |
6991 | in turn take precedence over those specified by the configuration of GCC. |
6992 | @xref{Driver}. | |
74291a4b MM |
6993 | @end ifset |
6994 | ||
6995 | @table @code | |
ab87f8c8 JL |
6996 | @item LANG |
6997 | @itemx LC_CTYPE | |
6998 | @c @itemx LC_COLLATE | |
6999 | @itemx LC_MESSAGES | |
7000 | @c @itemx LC_MONETARY | |
7001 | @c @itemx LC_NUMERIC | |
7002 | @c @itemx LC_TIME | |
7003 | @itemx LC_ALL | |
7004 | @findex LANG | |
7005 | @findex LC_CTYPE | |
7006 | @c @findex LC_COLLATE | |
7007 | @findex LC_MESSAGES | |
7008 | @c @findex LC_MONETARY | |
7009 | @c @findex LC_NUMERIC | |
7010 | @c @findex LC_TIME | |
7011 | @findex LC_ALL | |
7012 | @cindex locale | |
0c2d1a2a JB |
7013 | These environment variables control the way that GCC uses |
7014 | localization information that allow GCC to work with different | |
7015 | national conventions. GCC inspects the locale categories | |
ab87f8c8 JL |
7016 | @code{LC_CTYPE} and @code{LC_MESSAGES} if it has been configured to do |
7017 | so. These locale categories can be set to any value supported by your | |
7018 | installation. A typical value is @samp{en_UK} for English in the United | |
7019 | Kingdom. | |
7020 | ||
7021 | The @code{LC_CTYPE} environment variable specifies character | |
0c2d1a2a | 7022 | classification. GCC uses it to determine the character boundaries in |
ab87f8c8 JL |
7023 | a string; this is needed for some multibyte encodings that contain quote |
7024 | and escape characters that would otherwise be interpreted as a string | |
7025 | end or escape. | |
7026 | ||
7027 | The @code{LC_MESSAGES} environment variable specifies the language to | |
7028 | use in diagnostic messages. | |
7029 | ||
7030 | If the @code{LC_ALL} environment variable is set, it overrides the value | |
7031 | of @code{LC_CTYPE} and @code{LC_MESSAGES}; otherwise, @code{LC_CTYPE} | |
7032 | and @code{LC_MESSAGES} default to the value of the @code{LANG} | |
0c2d1a2a | 7033 | environment variable. If none of these variables are set, GCC |
ab87f8c8 JL |
7034 | defaults to traditional C English behavior. |
7035 | ||
74291a4b MM |
7036 | @item TMPDIR |
7037 | @findex TMPDIR | |
7038 | If @code{TMPDIR} is set, it specifies the directory to use for temporary | |
0c2d1a2a | 7039 | files. GCC uses temporary files to hold the output of one stage of |
74291a4b MM |
7040 | compilation which is to be used as input to the next stage: for example, |
7041 | the output of the preprocessor, which is the input to the compiler | |
7042 | proper. | |
7043 | ||
7044 | @item GCC_EXEC_PREFIX | |
7045 | @findex GCC_EXEC_PREFIX | |
7046 | If @code{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the | |
7047 | names of the subprograms executed by the compiler. No slash is added | |
7048 | when this prefix is combined with the name of a subprogram, but you can | |
7049 | specify a prefix that ends with a slash if you wish. | |
7050 | ||
0c2d1a2a | 7051 | If GCC cannot find the subprogram using the specified prefix, it |
74291a4b MM |
7052 | tries looking in the usual places for the subprogram. |
7053 | ||
7054 | The default value of @code{GCC_EXEC_PREFIX} is | |
7055 | @file{@var{prefix}/lib/gcc-lib/} where @var{prefix} is the value | |
7056 | of @code{prefix} when you ran the @file{configure} script. | |
7057 | ||
7058 | Other prefixes specified with @samp{-B} take precedence over this prefix. | |
7059 | ||
7060 | This prefix is also used for finding files such as @file{crt0.o} that are | |
7061 | used for linking. | |
7062 | ||
7063 | In addition, the prefix is used in an unusual way in finding the | |
7064 | directories to search for header files. For each of the standard | |
7065 | directories whose name normally begins with @samp{/usr/local/lib/gcc-lib} | |
0c2d1a2a | 7066 | (more precisely, with the value of @code{GCC_INCLUDE_DIR}), GCC tries |
74291a4b | 7067 | replacing that beginning with the specified prefix to produce an |
0c2d1a2a | 7068 | alternate directory name. Thus, with @samp{-Bfoo/}, GCC will search |
74291a4b MM |
7069 | @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}. |
7070 | These alternate directories are searched first; the standard directories | |
7071 | come next. | |
7072 | ||
7073 | @item COMPILER_PATH | |
7074 | @findex COMPILER_PATH | |
7075 | The value of @code{COMPILER_PATH} is a colon-separated list of | |
0c2d1a2a | 7076 | directories, much like @code{PATH}. GCC tries the directories thus |
74291a4b MM |
7077 | specified when searching for subprograms, if it can't find the |
7078 | subprograms using @code{GCC_EXEC_PREFIX}. | |
7079 | ||
7080 | @item LIBRARY_PATH | |
7081 | @findex LIBRARY_PATH | |
7082 | The value of @code{LIBRARY_PATH} is a colon-separated list of | |
7083 | directories, much like @code{PATH}. When configured as a native compiler, | |
0c2d1a2a | 7084 | GCC tries the directories thus specified when searching for special |
74291a4b | 7085 | linker files, if it can't find them using @code{GCC_EXEC_PREFIX}. Linking |
0c2d1a2a | 7086 | using GCC also uses these directories when searching for ordinary |
74291a4b MM |
7087 | libraries for the @samp{-l} option (but directories specified with |
7088 | @samp{-L} come first). | |
7089 | ||
7090 | @item C_INCLUDE_PATH | |
7091 | @itemx CPLUS_INCLUDE_PATH | |
7092 | @itemx OBJC_INCLUDE_PATH | |
7093 | @findex C_INCLUDE_PATH | |
7094 | @findex CPLUS_INCLUDE_PATH | |
7095 | @findex OBJC_INCLUDE_PATH | |
7096 | @c @itemx OBJCPLUS_INCLUDE_PATH | |
7097 | These environment variables pertain to particular languages. Each | |
7098 | variable's value is a colon-separated list of directories, much like | |
0c2d1a2a | 7099 | @code{PATH}. When GCC searches for header files, it tries the |
74291a4b MM |
7100 | directories listed in the variable for the language you are using, after |
7101 | the directories specified with @samp{-I} but before the standard header | |
7102 | file directories. | |
7103 | ||
7104 | @item DEPENDENCIES_OUTPUT | |
7105 | @findex DEPENDENCIES_OUTPUT | |
7106 | @cindex dependencies for make as output | |
7107 | If this variable is set, its value specifies how to output dependencies | |
7108 | for Make based on the header files processed by the compiler. This | |
7109 | output looks much like the output from the @samp{-M} option | |
7110 | (@pxref{Preprocessor Options}), but it goes to a separate file, and is | |
7111 | in addition to the usual results of compilation. | |
7112 | ||
7113 | The value of @code{DEPENDENCIES_OUTPUT} can be just a file name, in | |
7114 | which case the Make rules are written to that file, guessing the target | |
7115 | name from the source file name. Or the value can have the form | |
7116 | @samp{@var{file} @var{target}}, in which case the rules are written to | |
7117 | file @var{file} using @var{target} as the target name. | |
56f48ce9 DB |
7118 | |
7119 | @item LANG | |
7120 | @findex LANG | |
7121 | @cindex locale definition | |
7122 | This variable is used to pass locale information to the compiler. One way in | |
7123 | which this information is used is to determine the character set to be used | |
7124 | when character literals, string literals and comments are parsed in C and C++. | |
7125 | When the compiler is configured to allow multibyte characters, | |
7126 | the following values for @code{LANG} are recognized: | |
7127 | ||
7128 | @table @code | |
7129 | @item C-JIS | |
7130 | Recognize JIS characters. | |
7131 | @item C-SJIS | |
7132 | Recognize SJIS characters. | |
7133 | @item C-EUCJP | |
7134 | Recognize EUCJP characters. | |
7135 | @end table | |
7136 | ||
46103ab4 | 7137 | If @code{LANG} is not defined, or if it has some other value, then the |
56f48ce9 DB |
7138 | compiler will use mblen and mbtowc as defined by the default locale to |
7139 | recognize and translate multibyte characters. | |
74291a4b MM |
7140 | @end table |
7141 | ||
7142 | @node Running Protoize | |
7143 | @section Running Protoize | |
7144 | ||
7145 | The program @code{protoize} is an optional part of GNU C. You can use | |
7146 | it to add prototypes to a program, thus converting the program to ANSI | |
7147 | C in one respect. The companion program @code{unprotoize} does the | |
7148 | reverse: it removes argument types from any prototypes that are found. | |
7149 | ||
7150 | When you run these programs, you must specify a set of source files as | |
7151 | command line arguments. The conversion programs start out by compiling | |
7152 | these files to see what functions they define. The information gathered | |
7153 | about a file @var{foo} is saved in a file named @file{@var{foo}.X}. | |
7154 | ||
7155 | After scanning comes actual conversion. The specified files are all | |
7156 | eligible to be converted; any files they include (whether sources or | |
7157 | just headers) are eligible as well. | |
7158 | ||
7159 | But not all the eligible files are converted. By default, | |
7160 | @code{protoize} and @code{unprotoize} convert only source and header | |
7161 | files in the current directory. You can specify additional directories | |
7162 | whose files should be converted with the @samp{-d @var{directory}} | |
7163 | option. You can also specify particular files to exclude with the | |
7164 | @samp{-x @var{file}} option. A file is converted if it is eligible, its | |
7165 | directory name matches one of the specified directory names, and its | |
7166 | name within the directory has not been excluded. | |
7167 | ||
7168 | Basic conversion with @code{protoize} consists of rewriting most | |
7169 | function definitions and function declarations to specify the types of | |
7170 | the arguments. The only ones not rewritten are those for varargs | |
7171 | functions. | |
7172 | ||
7173 | @code{protoize} optionally inserts prototype declarations at the | |
7174 | beginning of the source file, to make them available for any calls that | |
7175 | precede the function's definition. Or it can insert prototype | |
7176 | declarations with block scope in the blocks where undeclared functions | |
7177 | are called. | |
7178 | ||
7179 | Basic conversion with @code{unprotoize} consists of rewriting most | |
7180 | function declarations to remove any argument types, and rewriting | |
7181 | function definitions to the old-style pre-ANSI form. | |
7182 | ||
7183 | Both conversion programs print a warning for any function declaration or | |
7184 | definition that they can't convert. You can suppress these warnings | |
7185 | with @samp{-q}. | |
7186 | ||
7187 | The output from @code{protoize} or @code{unprotoize} replaces the | |
7188 | original source file. The original file is renamed to a name ending | |
7189 | with @samp{.save}. If the @samp{.save} file already exists, then | |
7190 | the source file is simply discarded. | |
7191 | ||
0c2d1a2a | 7192 | @code{protoize} and @code{unprotoize} both depend on GCC itself to |
74291a4b | 7193 | scan the program and collect information about the functions it uses. |
0c2d1a2a | 7194 | So neither of these programs will work until GCC is installed. |
74291a4b MM |
7195 | |
7196 | Here is a table of the options you can use with @code{protoize} and | |
7197 | @code{unprotoize}. Each option works with both programs unless | |
7198 | otherwise stated. | |
7199 | ||
7200 | @table @code | |
7201 | @item -B @var{directory} | |
7202 | Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the | |
7203 | usual directory (normally @file{/usr/local/lib}). This file contains | |
7204 | prototype information about standard system functions. This option | |
7205 | applies only to @code{protoize}. | |
7206 | ||
7207 | @item -c @var{compilation-options} | |
7208 | Use @var{compilation-options} as the options when running @code{gcc} to | |
7209 | produce the @samp{.X} files. The special option @samp{-aux-info} is | |
7210 | always passed in addition, to tell @code{gcc} to write a @samp{.X} file. | |
7211 | ||
7212 | Note that the compilation options must be given as a single argument to | |
7213 | @code{protoize} or @code{unprotoize}. If you want to specify several | |
7214 | @code{gcc} options, you must quote the entire set of compilation options | |
7215 | to make them a single word in the shell. | |
7216 | ||
7217 | There are certain @code{gcc} arguments that you cannot use, because they | |
7218 | would produce the wrong kind of output. These include @samp{-g}, | |
7219 | @samp{-O}, @samp{-c}, @samp{-S}, and @samp{-o} If you include these in | |
7220 | the @var{compilation-options}, they are ignored. | |
7221 | ||
7222 | @item -C | |
7223 | Rename files to end in @samp{.C} instead of @samp{.c}. | |
7224 | This is convenient if you are converting a C program to C++. | |
7225 | This option applies only to @code{protoize}. | |
7226 | ||
7227 | @item -g | |
7228 | Add explicit global declarations. This means inserting explicit | |
7229 | declarations at the beginning of each source file for each function | |
7230 | that is called in the file and was not declared. These declarations | |
7231 | precede the first function definition that contains a call to an | |
7232 | undeclared function. This option applies only to @code{protoize}. | |
7233 | ||
7234 | @item -i @var{string} | |
7235 | Indent old-style parameter declarations with the string @var{string}. | |
7236 | This option applies only to @code{protoize}. | |
7237 | ||
7238 | @code{unprotoize} converts prototyped function definitions to old-style | |
7239 | function definitions, where the arguments are declared between the | |
7240 | argument list and the initial @samp{@{}. By default, @code{unprotoize} | |
7241 | uses five spaces as the indentation. If you want to indent with just | |
7242 | one space instead, use @samp{-i " "}. | |
7243 | ||
7244 | @item -k | |
7245 | Keep the @samp{.X} files. Normally, they are deleted after conversion | |
7246 | is finished. | |
7247 | ||
7248 | @item -l | |
7249 | Add explicit local declarations. @code{protoize} with @samp{-l} inserts | |
7250 | a prototype declaration for each function in each block which calls the | |
7251 | function without any declaration. This option applies only to | |
7252 | @code{protoize}. | |
7253 | ||
7254 | @item -n | |
7255 | Make no real changes. This mode just prints information about the conversions | |
7256 | that would have been done without @samp{-n}. | |
7257 | ||
7258 | @item -N | |
7259 | Make no @samp{.save} files. The original files are simply deleted. | |
7260 | Use this option with caution. | |
7261 | ||
7262 | @item -p @var{program} | |
7263 | Use the program @var{program} as the compiler. Normally, the name | |
7264 | @file{gcc} is used. | |
7265 | ||
7266 | @item -q | |
7267 | Work quietly. Most warnings are suppressed. | |
7268 | ||
7269 | @item -v | |
7270 | Print the version number, just like @samp{-v} for @code{gcc}. | |
7271 | @end table | |
7272 | ||
7273 | If you need special compiler options to compile one of your program's | |
7274 | source files, then you should generate that file's @samp{.X} file | |
7275 | specially, by running @code{gcc} on that source file with the | |
7276 | appropriate options and the option @samp{-aux-info}. Then run | |
7277 | @code{protoize} on the entire set of files. @code{protoize} will use | |
7278 | the existing @samp{.X} file because it is newer than the source file. | |
7279 | For example: | |
7280 | ||
7281 | @example | |
7282 | gcc -Dfoo=bar file1.c -aux-info | |
7283 | protoize *.c | |
7284 | @end example | |
7285 | ||
7286 | @noindent | |
7287 | You need to include the special files along with the rest in the | |
7288 | @code{protoize} command, even though their @samp{.X} files already | |
7289 | exist, because otherwise they won't get converted. | |
7290 | ||
7291 | @xref{Protoize Caveats}, for more information on how to use | |
7292 | @code{protoize} successfully. | |
7293 |