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928a5ba9 | 1 | @c Copyright (C) 1988,1989,1992,1993,1994,1996,1998,1999,2000,2001,2002,2003,2004 |
f0ddce84 | 2 | @c Free Software Foundation, Inc. |
c1f7febf RK |
3 | @c This is part of the GCC manual. |
4 | @c For copying conditions, see the file gcc.texi. | |
5 | ||
fe203faf RH |
6 | @node C Implementation |
7 | @chapter C Implementation-defined behavior | |
8 | @cindex implementation-defined behavior, C language | |
9 | ||
10 | A conforming implementation of ISO C is required to document its | |
11 | choice of behavior in each of the areas that are designated | |
12 | ``implementation defined.'' The following lists all such areas, | |
13 | along with the section number from the ISO/IEC 9899:1999 standard. | |
14 | ||
15 | @menu | |
16 | * Translation implementation:: | |
17 | * Environment implementation:: | |
18 | * Identifiers implementation:: | |
19 | * Characters implementation:: | |
20 | * Integers implementation:: | |
21 | * Floating point implementation:: | |
22 | * Arrays and pointers implementation:: | |
23 | * Hints implementation:: | |
24 | * Structures unions enumerations and bit-fields implementation:: | |
25 | * Qualifiers implementation:: | |
26 | * Preprocessing directives implementation:: | |
27 | * Library functions implementation:: | |
28 | * Architecture implementation:: | |
29 | * Locale-specific behavior implementation:: | |
30 | @end menu | |
31 | ||
32 | @node Translation implementation | |
33 | @section Translation | |
34 | ||
35 | @itemize @bullet | |
36 | @item | |
37 | @cite{How a diagnostic is identified (3.10, 5.1.1.3).} | |
38 | ||
cba57c9d GK |
39 | Diagnostics consist of all the output sent to stderr by GCC. |
40 | ||
fe203faf RH |
41 | @item |
42 | @cite{Whether each nonempty sequence of white-space characters other than | |
43 | new-line is retained or replaced by one space character in translation | |
44 | phase 3 (5.1.1.2).} | |
45 | @end itemize | |
46 | ||
47 | @node Environment implementation | |
48 | @section Environment | |
49 | ||
0c688a7d | 50 | The behavior of these points are dependent on the implementation |
fe203faf RH |
51 | of the C library, and are not defined by GCC itself. |
52 | ||
53 | @node Identifiers implementation | |
54 | @section Identifiers | |
55 | ||
56 | @itemize @bullet | |
57 | @item | |
58 | @cite{Which additional multibyte characters may appear in identifiers | |
59 | and their correspondence to universal character names (6.4.2).} | |
60 | ||
61 | @item | |
62 | @cite{The number of significant initial characters in an identifier | |
63 | (5.2.4.1, 6.4.2).} | |
cba57c9d GK |
64 | |
65 | For internal names, all characters are significant. For external names, | |
66 | the number of significant characters are defined by the linker; for | |
67 | almost all targets, all characters are significant. | |
68 | ||
fe203faf RH |
69 | @end itemize |
70 | ||
71 | @node Characters implementation | |
72 | @section Characters | |
73 | ||
74 | @itemize @bullet | |
75 | @item | |
76 | @cite{The number of bits in a byte (3.6).} | |
77 | ||
78 | @item | |
79 | @cite{The values of the members of the execution character set (5.2.1).} | |
80 | ||
81 | @item | |
82 | @cite{The unique value of the member of the execution character set produced | |
83 | for each of the standard alphabetic escape sequences (5.2.2).} | |
84 | ||
85 | @item | |
86 | @cite{The value of a @code{char} object into which has been stored any | |
87 | character other than a member of the basic execution character set (6.2.5).} | |
88 | ||
89 | @item | |
90 | @cite{Which of @code{signed char} or @code{unsigned char} has the same range, | |
39ffd3cb | 91 | representation, and behavior as ``plain'' @code{char} (6.2.5, 6.3.1.1).} |
fe203faf RH |
92 | |
93 | @item | |
94 | @cite{The mapping of members of the source character set (in character | |
95 | constants and string literals) to members of the execution character | |
96 | set (6.4.4.4, 5.1.1.2).} | |
97 | ||
98 | @item | |
99 | @cite{The value of an integer character constant containing more than one | |
100 | character or containing a character or escape sequence that does not map | |
101 | to a single-byte execution character (6.4.4.4).} | |
102 | ||
103 | @item | |
104 | @cite{The value of a wide character constant containing more than one | |
105 | multibyte character, or containing a multibyte character or escape | |
106 | sequence not represented in the extended execution character set (6.4.4.4).} | |
107 | ||
108 | @item | |
109 | @cite{The current locale used to convert a wide character constant consisting | |
110 | of a single multibyte character that maps to a member of the extended | |
111 | execution character set into a corresponding wide character code (6.4.4.4).} | |
112 | ||
113 | @item | |
114 | @cite{The current locale used to convert a wide string literal into | |
115 | corresponding wide character codes (6.4.5).} | |
116 | ||
117 | @item | |
118 | @cite{The value of a string literal containing a multibyte character or escape | |
119 | sequence not represented in the execution character set (6.4.5).} | |
120 | @end itemize | |
121 | ||
122 | @node Integers implementation | |
123 | @section Integers | |
124 | ||
125 | @itemize @bullet | |
126 | @item | |
127 | @cite{Any extended integer types that exist in the implementation (6.2.5).} | |
128 | ||
129 | @item | |
130 | @cite{Whether signed integer types are represented using sign and magnitude, | |
131 | two's complement, or one's complement, and whether the extraordinary value | |
132 | is a trap representation or an ordinary value (6.2.6.2).} | |
133 | ||
cba57c9d GK |
134 | GCC supports only two's complement integer types, and all bit patterns |
135 | are ordinary values. | |
136 | ||
fe203faf RH |
137 | @item |
138 | @cite{The rank of any extended integer type relative to another extended | |
139 | integer type with the same precision (6.3.1.1).} | |
140 | ||
141 | @item | |
142 | @cite{The result of, or the signal raised by, converting an integer to a | |
143 | signed integer type when the value cannot be represented in an object of | |
144 | that type (6.3.1.3).} | |
145 | ||
146 | @item | |
147 | @cite{The results of some bitwise operations on signed integers (6.5).} | |
148 | @end itemize | |
149 | ||
150 | @node Floating point implementation | |
151 | @section Floating point | |
152 | ||
153 | @itemize @bullet | |
154 | @item | |
155 | @cite{The accuracy of the floating-point operations and of the library | |
39ffd3cb | 156 | functions in @code{<math.h>} and @code{<complex.h>} that return floating-point |
fe203faf RH |
157 | results (5.2.4.2.2).} |
158 | ||
159 | @item | |
160 | @cite{The rounding behaviors characterized by non-standard values | |
9c34dbbf ZW |
161 | of @code{FLT_ROUNDS} @gol |
162 | (5.2.4.2.2).} | |
fe203faf RH |
163 | |
164 | @item | |
165 | @cite{The evaluation methods characterized by non-standard negative | |
166 | values of @code{FLT_EVAL_METHOD} (5.2.4.2.2).} | |
167 | ||
168 | @item | |
169 | @cite{The direction of rounding when an integer is converted to a | |
170 | floating-point number that cannot exactly represent the original | |
171 | value (6.3.1.4).} | |
172 | ||
173 | @item | |
174 | @cite{The direction of rounding when a floating-point number is | |
175 | converted to a narrower floating-point number (6.3.1.5).} | |
176 | ||
177 | @item | |
178 | @cite{How the nearest representable value or the larger or smaller | |
179 | representable value immediately adjacent to the nearest representable | |
180 | value is chosen for certain floating constants (6.4.4.2).} | |
181 | ||
182 | @item | |
183 | @cite{Whether and how floating expressions are contracted when not | |
184 | disallowed by the @code{FP_CONTRACT} pragma (6.5).} | |
185 | ||
186 | @item | |
187 | @cite{The default state for the @code{FENV_ACCESS} pragma (7.6.1).} | |
188 | ||
189 | @item | |
190 | @cite{Additional floating-point exceptions, rounding modes, environments, | |
191 | and classifications, and their macro names (7.6, 7.12).} | |
192 | ||
193 | @item | |
194 | @cite{The default state for the @code{FP_CONTRACT} pragma (7.12.2).} | |
195 | ||
196 | @item | |
197 | @cite{Whether the ``inexact'' floating-point exception can be raised | |
198 | when the rounded result actually does equal the mathematical result | |
199 | in an IEC 60559 conformant implementation (F.9).} | |
200 | ||
201 | @item | |
202 | @cite{Whether the ``underflow'' (and ``inexact'') floating-point | |
203 | exception can be raised when a result is tiny but not inexact in an | |
204 | IEC 60559 conformant implementation (F.9).} | |
205 | ||
206 | @end itemize | |
207 | ||
208 | @node Arrays and pointers implementation | |
209 | @section Arrays and pointers | |
210 | ||
211 | @itemize @bullet | |
212 | @item | |
213 | @cite{The result of converting a pointer to an integer or | |
214 | vice versa (6.3.2.3).} | |
215 | ||
cbf4c36f | 216 | A cast from pointer to integer discards most-significant bits if the |
58f4de4f RH |
217 | pointer representation is larger than the integer type, |
218 | sign-extends@footnote{Future versions of GCC may zero-extend, or use | |
219 | a target-defined @code{ptr_extend} pattern. Do not rely on sign extension.} | |
cbf4c36f RH |
220 | if the pointer representation is smaller than the integer type, otherwise |
221 | the bits are unchanged. | |
222 | @c ??? We've always claimed that pointers were unsigned entities. | |
223 | @c Shouldn't we therefore be doing zero-extension? If so, the bug | |
224 | @c is in convert_to_integer, where we call type_for_size and request | |
225 | @c a signed integral type. On the other hand, it might be most useful | |
226 | @c for the target if we extend according to POINTERS_EXTEND_UNSIGNED. | |
227 | ||
228 | A cast from integer to pointer discards most-significant bits if the | |
229 | pointer representation is smaller than the integer type, extends according | |
230 | to the signedness of the integer type if the pointer representation | |
231 | is larger than the integer type, otherwise the bits are unchanged. | |
232 | ||
233 | When casting from pointer to integer and back again, the resulting | |
234 | pointer must reference the same object as the original pointer, otherwise | |
235 | the behavior is undefined. That is, one may not use integer arithmetic to | |
236 | avoid the undefined behavior of pointer arithmetic as proscribed in 6.5.6/8. | |
237 | ||
fe203faf RH |
238 | @item |
239 | @cite{The size of the result of subtracting two pointers to elements | |
240 | of the same array (6.5.6).} | |
241 | ||
242 | @end itemize | |
243 | ||
244 | @node Hints implementation | |
245 | @section Hints | |
246 | ||
247 | @itemize @bullet | |
248 | @item | |
249 | @cite{The extent to which suggestions made by using the @code{register} | |
250 | storage-class specifier are effective (6.7.1).} | |
251 | ||
6fd14075 GK |
252 | The @code{register} specifier affects code generation only in these ways: |
253 | ||
254 | @itemize @bullet | |
255 | @item | |
daf2f129 | 256 | When used as part of the register variable extension, see |
6fd14075 GK |
257 | @ref{Explicit Reg Vars}. |
258 | ||
259 | @item | |
260 | When @option{-O0} is in use, the compiler allocates distinct stack | |
261 | memory for all variables that do not have the @code{register} | |
262 | storage-class specifier; if @code{register} is specified, the variable | |
263 | may have a shorter lifespan than the code would indicate and may never | |
264 | be placed in memory. | |
265 | ||
266 | @item | |
267 | On some rare x86 targets, @code{setjmp} doesn't save the registers in | |
268 | all circumstances. In those cases, GCC doesn't allocate any variables | |
269 | in registers unless they are marked @code{register}. | |
270 | ||
271 | @end itemize | |
272 | ||
fe203faf RH |
273 | @item |
274 | @cite{The extent to which suggestions made by using the inline function | |
275 | specifier are effective (6.7.4).} | |
276 | ||
cba57c9d GK |
277 | GCC will not inline any functions if the @option{-fno-inline} option is |
278 | used or if @option{-O0} is used. Otherwise, GCC may still be unable to | |
279 | inline a function for many reasons; the @option{-Winline} option may be | |
280 | used to determine if a function has not been inlined and why not. | |
281 | ||
fe203faf RH |
282 | @end itemize |
283 | ||
284 | @node Structures unions enumerations and bit-fields implementation | |
285 | @section Structures, unions, enumerations, and bit-fields | |
286 | ||
287 | @itemize @bullet | |
288 | @item | |
289 | @cite{Whether a ``plain'' int bit-field is treated as a @code{signed int} | |
290 | bit-field or as an @code{unsigned int} bit-field (6.7.2, 6.7.2.1).} | |
291 | ||
292 | @item | |
293 | @cite{Allowable bit-field types other than @code{_Bool}, @code{signed int}, | |
294 | and @code{unsigned int} (6.7.2.1).} | |
295 | ||
296 | @item | |
297 | @cite{Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).} | |
298 | ||
299 | @item | |
300 | @cite{The order of allocation of bit-fields within a unit (6.7.2.1).} | |
301 | ||
302 | @item | |
303 | @cite{The alignment of non-bit-field members of structures (6.7.2.1).} | |
304 | ||
305 | @item | |
306 | @cite{The integer type compatible with each enumerated type (6.7.2.2).} | |
307 | ||
308 | @end itemize | |
309 | ||
310 | @node Qualifiers implementation | |
311 | @section Qualifiers | |
312 | ||
313 | @itemize @bullet | |
314 | @item | |
315 | @cite{What constitutes an access to an object that has volatile-qualified | |
316 | type (6.7.3).} | |
317 | ||
318 | @end itemize | |
319 | ||
320 | @node Preprocessing directives implementation | |
321 | @section Preprocessing directives | |
322 | ||
323 | @itemize @bullet | |
324 | @item | |
325 | @cite{How sequences in both forms of header names are mapped to headers | |
326 | or external source file names (6.4.7).} | |
327 | ||
328 | @item | |
329 | @cite{Whether the value of a character constant in a constant expression | |
330 | that controls conditional inclusion matches the value of the same character | |
331 | constant in the execution character set (6.10.1).} | |
332 | ||
333 | @item | |
334 | @cite{Whether the value of a single-character character constant in a | |
335 | constant expression that controls conditional inclusion may have a | |
336 | negative value (6.10.1).} | |
337 | ||
338 | @item | |
339 | @cite{The places that are searched for an included @samp{<>} delimited | |
340 | header, and how the places are specified or the header is | |
341 | identified (6.10.2).} | |
342 | ||
343 | @item | |
344 | @cite{How the named source file is searched for in an included @samp{""} | |
345 | delimited header (6.10.2).} | |
346 | ||
347 | @item | |
348 | @cite{The method by which preprocessing tokens (possibly resulting from | |
349 | macro expansion) in a @code{#include} directive are combined into a header | |
350 | name (6.10.2).} | |
351 | ||
352 | @item | |
353 | @cite{The nesting limit for @code{#include} processing (6.10.2).} | |
354 | ||
cba57c9d GK |
355 | GCC imposes a limit of 200 nested @code{#include}s. |
356 | ||
fe203faf RH |
357 | @item |
358 | @cite{Whether the @samp{#} operator inserts a @samp{\} character before | |
359 | the @samp{\} character that begins a universal character name in a | |
360 | character constant or string literal (6.10.3.2).} | |
361 | ||
362 | @item | |
363 | @cite{The behavior on each recognized non-@code{STDC #pragma} | |
364 | directive (6.10.6).} | |
365 | ||
366 | @item | |
367 | @cite{The definitions for @code{__DATE__} and @code{__TIME__} when | |
368 | respectively, the date and time of translation are not available (6.10.8).} | |
369 | ||
56da7207 ZW |
370 | If the date and time are not available, @code{__DATE__} expands to |
371 | @code{@w{"??? ?? ????"}} and @code{__TIME__} expands to | |
372 | @code{"??:??:??"}. | |
cba57c9d | 373 | |
fe203faf RH |
374 | @end itemize |
375 | ||
376 | @node Library functions implementation | |
377 | @section Library functions | |
378 | ||
0c688a7d | 379 | The behavior of these points are dependent on the implementation |
fe203faf RH |
380 | of the C library, and are not defined by GCC itself. |
381 | ||
382 | @node Architecture implementation | |
383 | @section Architecture | |
384 | ||
385 | @itemize @bullet | |
386 | @item | |
387 | @cite{The values or expressions assigned to the macros specified in the | |
39ffd3cb | 388 | headers @code{<float.h>}, @code{<limits.h>}, and @code{<stdint.h>} |
fe203faf RH |
389 | (5.2.4.2, 7.18.2, 7.18.3).} |
390 | ||
391 | @item | |
392 | @cite{The number, order, and encoding of bytes in any object | |
393 | (when not explicitly specified in this International Standard) (6.2.6.1).} | |
394 | ||
395 | @item | |
396 | @cite{The value of the result of the sizeof operator (6.5.3.4).} | |
397 | ||
398 | @end itemize | |
399 | ||
400 | @node Locale-specific behavior implementation | |
401 | @section Locale-specific behavior | |
402 | ||
0c688a7d | 403 | The behavior of these points are dependent on the implementation |
fe203faf RH |
404 | of the C library, and are not defined by GCC itself. |
405 | ||
c1f7febf RK |
406 | @node C Extensions |
407 | @chapter Extensions to the C Language Family | |
408 | @cindex extensions, C language | |
409 | @cindex C language extensions | |
410 | ||
84330467 | 411 | @opindex pedantic |
161d7b59 | 412 | GNU C provides several language features not found in ISO standard C@. |
f0523f02 | 413 | (The @option{-pedantic} option directs GCC to print a warning message if |
c1f7febf RK |
414 | any of these features is used.) To test for the availability of these |
415 | features in conditional compilation, check for a predefined macro | |
161d7b59 | 416 | @code{__GNUC__}, which is always defined under GCC@. |
c1f7febf | 417 | |
161d7b59 | 418 | These extensions are available in C and Objective-C@. Most of them are |
c1f7febf RK |
419 | also available in C++. @xref{C++ Extensions,,Extensions to the |
420 | C++ Language}, for extensions that apply @emph{only} to C++. | |
421 | ||
4b404517 JM |
422 | Some features that are in ISO C99 but not C89 or C++ are also, as |
423 | extensions, accepted by GCC in C89 mode and in C++. | |
5490d604 | 424 | |
c1f7febf RK |
425 | @menu |
426 | * Statement Exprs:: Putting statements and declarations inside expressions. | |
14e33ee8 | 427 | * Local Labels:: Labels local to a block. |
c1f7febf RK |
428 | * Labels as Values:: Getting pointers to labels, and computed gotos. |
429 | * Nested Functions:: As in Algol and Pascal, lexical scoping of functions. | |
430 | * Constructing Calls:: Dispatching a call to another function. | |
c1f7febf | 431 | * Typeof:: @code{typeof}: referring to the type of an expression. |
c1f7febf RK |
432 | * Conditionals:: Omitting the middle operand of a @samp{?:} expression. |
433 | * Long Long:: Double-word integers---@code{long long int}. | |
434 | * Complex:: Data types for complex numbers. | |
6f4d7222 | 435 | * Hex Floats:: Hexadecimal floating-point constants. |
c1f7febf RK |
436 | * Zero Length:: Zero-length arrays. |
437 | * Variable Length:: Arrays whose length is computed at run time. | |
ba05abd3 | 438 | * Empty Structures:: Structures with no members. |
ccd96f0a NB |
439 | * Variadic Macros:: Macros with a variable number of arguments. |
440 | * Escaped Newlines:: Slightly looser rules for escaped newlines. | |
c1f7febf RK |
441 | * Subscripting:: Any array can be subscripted, even if not an lvalue. |
442 | * Pointer Arith:: Arithmetic on @code{void}-pointers and function pointers. | |
443 | * Initializers:: Non-constant initializers. | |
4b404517 | 444 | * Compound Literals:: Compound literals give structures, unions |
c1f7febf | 445 | or arrays as values. |
4b404517 | 446 | * Designated Inits:: Labeling elements of initializers. |
c1f7febf RK |
447 | * Cast to Union:: Casting to union type from any member of the union. |
448 | * Case Ranges:: `case 1 ... 9' and such. | |
4b404517 | 449 | * Mixed Declarations:: Mixing declarations and code. |
c1f7febf RK |
450 | * Function Attributes:: Declaring that functions have no side effects, |
451 | or that they can never return. | |
2c5e91d2 | 452 | * Attribute Syntax:: Formal syntax for attributes. |
c1f7febf RK |
453 | * Function Prototypes:: Prototype declarations and old-style definitions. |
454 | * C++ Comments:: C++ comments are recognized. | |
455 | * Dollar Signs:: Dollar sign is allowed in identifiers. | |
456 | * Character Escapes:: @samp{\e} stands for the character @key{ESC}. | |
457 | * Variable Attributes:: Specifying attributes of variables. | |
458 | * Type Attributes:: Specifying attributes of types. | |
459 | * Alignment:: Inquiring about the alignment of a type or variable. | |
460 | * Inline:: Defining inline functions (as fast as macros). | |
461 | * Extended Asm:: Assembler instructions with C expressions as operands. | |
462 | (With them you can define ``built-in'' functions.) | |
463 | * Constraints:: Constraints for asm operands | |
464 | * Asm Labels:: Specifying the assembler name to use for a C symbol. | |
465 | * Explicit Reg Vars:: Defining variables residing in specified registers. | |
466 | * Alternate Keywords:: @code{__const__}, @code{__asm__}, etc., for header files. | |
467 | * Incomplete Enums:: @code{enum foo;}, with details to follow. | |
468 | * Function Names:: Printable strings which are the name of the current | |
469 | function. | |
470 | * Return Address:: Getting the return or frame address of a function. | |
1255c85c | 471 | * Vector Extensions:: Using vector instructions through built-in functions. |
7a3ea201 | 472 | * Offsetof:: Special syntax for implementing @code{offsetof}. |
c5c76735 | 473 | * Other Builtins:: Other built-in functions. |
0975678f | 474 | * Target Builtins:: Built-in functions specific to particular targets. |
0168a849 | 475 | * Pragmas:: Pragmas accepted by GCC. |
b11cc610 | 476 | * Unnamed Fields:: Unnamed struct/union fields within structs/unions. |
3d78f2e9 | 477 | * Thread-Local:: Per-thread variables. |
c1f7febf | 478 | @end menu |
c1f7febf RK |
479 | |
480 | @node Statement Exprs | |
481 | @section Statements and Declarations in Expressions | |
482 | @cindex statements inside expressions | |
483 | @cindex declarations inside expressions | |
484 | @cindex expressions containing statements | |
485 | @cindex macros, statements in expressions | |
486 | ||
487 | @c the above section title wrapped and causes an underfull hbox.. i | |
488 | @c changed it from "within" to "in". --mew 4feb93 | |
c1f7febf | 489 | A compound statement enclosed in parentheses may appear as an expression |
161d7b59 | 490 | in GNU C@. This allows you to use loops, switches, and local variables |
c1f7febf RK |
491 | within an expression. |
492 | ||
493 | Recall that a compound statement is a sequence of statements surrounded | |
494 | by braces; in this construct, parentheses go around the braces. For | |
495 | example: | |
496 | ||
3ab51846 | 497 | @smallexample |
c1f7febf RK |
498 | (@{ int y = foo (); int z; |
499 | if (y > 0) z = y; | |
500 | else z = - y; | |
501 | z; @}) | |
3ab51846 | 502 | @end smallexample |
c1f7febf RK |
503 | |
504 | @noindent | |
505 | is a valid (though slightly more complex than necessary) expression | |
506 | for the absolute value of @code{foo ()}. | |
507 | ||
508 | The last thing in the compound statement should be an expression | |
509 | followed by a semicolon; the value of this subexpression serves as the | |
510 | value of the entire construct. (If you use some other kind of statement | |
511 | last within the braces, the construct has type @code{void}, and thus | |
512 | effectively no value.) | |
513 | ||
514 | This feature is especially useful in making macro definitions ``safe'' (so | |
515 | that they evaluate each operand exactly once). For example, the | |
516 | ``maximum'' function is commonly defined as a macro in standard C as | |
517 | follows: | |
518 | ||
3ab51846 | 519 | @smallexample |
c1f7febf | 520 | #define max(a,b) ((a) > (b) ? (a) : (b)) |
3ab51846 | 521 | @end smallexample |
c1f7febf RK |
522 | |
523 | @noindent | |
524 | @cindex side effects, macro argument | |
525 | But this definition computes either @var{a} or @var{b} twice, with bad | |
526 | results if the operand has side effects. In GNU C, if you know the | |
962e6e00 | 527 | type of the operands (here taken as @code{int}), you can define |
c1f7febf RK |
528 | the macro safely as follows: |
529 | ||
3ab51846 | 530 | @smallexample |
c1f7febf RK |
531 | #define maxint(a,b) \ |
532 | (@{int _a = (a), _b = (b); _a > _b ? _a : _b; @}) | |
3ab51846 | 533 | @end smallexample |
c1f7febf RK |
534 | |
535 | Embedded statements are not allowed in constant expressions, such as | |
c771326b | 536 | the value of an enumeration constant, the width of a bit-field, or |
c1f7febf RK |
537 | the initial value of a static variable. |
538 | ||
539 | If you don't know the type of the operand, you can still do this, but you | |
95f79357 | 540 | must use @code{typeof} (@pxref{Typeof}). |
c1f7febf | 541 | |
a5bcc582 NS |
542 | In G++, the result value of a statement expression undergoes array and |
543 | function pointer decay, and is returned by value to the enclosing | |
544 | expression. For instance, if @code{A} is a class, then | |
b98e139b | 545 | |
a5bcc582 NS |
546 | @smallexample |
547 | A a; | |
b98e139b | 548 | |
a5bcc582 NS |
549 | (@{a;@}).Foo () |
550 | @end smallexample | |
b98e139b MM |
551 | |
552 | @noindent | |
a5bcc582 NS |
553 | will construct a temporary @code{A} object to hold the result of the |
554 | statement expression, and that will be used to invoke @code{Foo}. | |
555 | Therefore the @code{this} pointer observed by @code{Foo} will not be the | |
556 | address of @code{a}. | |
557 | ||
558 | Any temporaries created within a statement within a statement expression | |
559 | will be destroyed at the statement's end. This makes statement | |
560 | expressions inside macros slightly different from function calls. In | |
561 | the latter case temporaries introduced during argument evaluation will | |
562 | be destroyed at the end of the statement that includes the function | |
563 | call. In the statement expression case they will be destroyed during | |
564 | the statement expression. For instance, | |
b98e139b | 565 | |
a5bcc582 NS |
566 | @smallexample |
567 | #define macro(a) (@{__typeof__(a) b = (a); b + 3; @}) | |
568 | template<typename T> T function(T a) @{ T b = a; return b + 3; @} | |
569 | ||
570 | void foo () | |
571 | @{ | |
572 | macro (X ()); | |
573 | function (X ()); | |
574 | @} | |
575 | @end smallexample | |
b98e139b MM |
576 | |
577 | @noindent | |
a5bcc582 NS |
578 | will have different places where temporaries are destroyed. For the |
579 | @code{macro} case, the temporary @code{X} will be destroyed just after | |
580 | the initialization of @code{b}. In the @code{function} case that | |
581 | temporary will be destroyed when the function returns. | |
b98e139b MM |
582 | |
583 | These considerations mean that it is probably a bad idea to use | |
584 | statement-expressions of this form in header files that are designed to | |
54e1d3a6 MM |
585 | work with C++. (Note that some versions of the GNU C Library contained |
586 | header files using statement-expression that lead to precisely this | |
587 | bug.) | |
b98e139b | 588 | |
c1f7febf RK |
589 | @node Local Labels |
590 | @section Locally Declared Labels | |
591 | @cindex local labels | |
592 | @cindex macros, local labels | |
593 | ||
14e33ee8 ZW |
594 | GCC allows you to declare @dfn{local labels} in any nested block |
595 | scope. A local label is just like an ordinary label, but you can | |
596 | only reference it (with a @code{goto} statement, or by taking its | |
daf2f129 | 597 | address) within the block in which it was declared. |
c1f7febf RK |
598 | |
599 | A local label declaration looks like this: | |
600 | ||
3ab51846 | 601 | @smallexample |
c1f7febf | 602 | __label__ @var{label}; |
3ab51846 | 603 | @end smallexample |
c1f7febf RK |
604 | |
605 | @noindent | |
606 | or | |
607 | ||
3ab51846 | 608 | @smallexample |
0d893a63 | 609 | __label__ @var{label1}, @var{label2}, /* @r{@dots{}} */; |
3ab51846 | 610 | @end smallexample |
c1f7febf | 611 | |
14e33ee8 ZW |
612 | Local label declarations must come at the beginning of the block, |
613 | before any ordinary declarations or statements. | |
c1f7febf RK |
614 | |
615 | The label declaration defines the label @emph{name}, but does not define | |
616 | the label itself. You must do this in the usual way, with | |
617 | @code{@var{label}:}, within the statements of the statement expression. | |
618 | ||
14e33ee8 ZW |
619 | The local label feature is useful for complex macros. If a macro |
620 | contains nested loops, a @code{goto} can be useful for breaking out of | |
621 | them. However, an ordinary label whose scope is the whole function | |
622 | cannot be used: if the macro can be expanded several times in one | |
623 | function, the label will be multiply defined in that function. A | |
624 | local label avoids this problem. For example: | |
625 | ||
3ab51846 | 626 | @smallexample |
14e33ee8 ZW |
627 | #define SEARCH(value, array, target) \ |
628 | do @{ \ | |
629 | __label__ found; \ | |
630 | typeof (target) _SEARCH_target = (target); \ | |
631 | typeof (*(array)) *_SEARCH_array = (array); \ | |
632 | int i, j; \ | |
633 | int value; \ | |
634 | for (i = 0; i < max; i++) \ | |
635 | for (j = 0; j < max; j++) \ | |
636 | if (_SEARCH_array[i][j] == _SEARCH_target) \ | |
637 | @{ (value) = i; goto found; @} \ | |
638 | (value) = -1; \ | |
639 | found:; \ | |
640 | @} while (0) | |
3ab51846 | 641 | @end smallexample |
14e33ee8 ZW |
642 | |
643 | This could also be written using a statement-expression: | |
c1f7febf | 644 | |
3ab51846 | 645 | @smallexample |
c1f7febf | 646 | #define SEARCH(array, target) \ |
310668e8 | 647 | (@{ \ |
c1f7febf RK |
648 | __label__ found; \ |
649 | typeof (target) _SEARCH_target = (target); \ | |
650 | typeof (*(array)) *_SEARCH_array = (array); \ | |
651 | int i, j; \ | |
652 | int value; \ | |
653 | for (i = 0; i < max; i++) \ | |
654 | for (j = 0; j < max; j++) \ | |
655 | if (_SEARCH_array[i][j] == _SEARCH_target) \ | |
310668e8 | 656 | @{ value = i; goto found; @} \ |
c1f7febf RK |
657 | value = -1; \ |
658 | found: \ | |
659 | value; \ | |
660 | @}) | |
3ab51846 | 661 | @end smallexample |
c1f7febf | 662 | |
14e33ee8 ZW |
663 | Local label declarations also make the labels they declare visible to |
664 | nested functions, if there are any. @xref{Nested Functions}, for details. | |
665 | ||
c1f7febf RK |
666 | @node Labels as Values |
667 | @section Labels as Values | |
668 | @cindex labels as values | |
669 | @cindex computed gotos | |
670 | @cindex goto with computed label | |
671 | @cindex address of a label | |
672 | ||
673 | You can get the address of a label defined in the current function | |
674 | (or a containing function) with the unary operator @samp{&&}. The | |
675 | value has type @code{void *}. This value is a constant and can be used | |
676 | wherever a constant of that type is valid. For example: | |
677 | ||
3ab51846 | 678 | @smallexample |
c1f7febf | 679 | void *ptr; |
0d893a63 | 680 | /* @r{@dots{}} */ |
c1f7febf | 681 | ptr = &&foo; |
3ab51846 | 682 | @end smallexample |
c1f7febf RK |
683 | |
684 | To use these values, you need to be able to jump to one. This is done | |
685 | with the computed goto statement@footnote{The analogous feature in | |
686 | Fortran is called an assigned goto, but that name seems inappropriate in | |
687 | C, where one can do more than simply store label addresses in label | |
688 | variables.}, @code{goto *@var{exp};}. For example, | |
689 | ||
3ab51846 | 690 | @smallexample |
c1f7febf | 691 | goto *ptr; |
3ab51846 | 692 | @end smallexample |
c1f7febf RK |
693 | |
694 | @noindent | |
695 | Any expression of type @code{void *} is allowed. | |
696 | ||
697 | One way of using these constants is in initializing a static array that | |
698 | will serve as a jump table: | |
699 | ||
3ab51846 | 700 | @smallexample |
c1f7febf | 701 | static void *array[] = @{ &&foo, &&bar, &&hack @}; |
3ab51846 | 702 | @end smallexample |
c1f7febf RK |
703 | |
704 | Then you can select a label with indexing, like this: | |
705 | ||
3ab51846 | 706 | @smallexample |
c1f7febf | 707 | goto *array[i]; |
3ab51846 | 708 | @end smallexample |
c1f7febf RK |
709 | |
710 | @noindent | |
711 | Note that this does not check whether the subscript is in bounds---array | |
712 | indexing in C never does that. | |
713 | ||
714 | Such an array of label values serves a purpose much like that of the | |
715 | @code{switch} statement. The @code{switch} statement is cleaner, so | |
716 | use that rather than an array unless the problem does not fit a | |
717 | @code{switch} statement very well. | |
718 | ||
719 | Another use of label values is in an interpreter for threaded code. | |
720 | The labels within the interpreter function can be stored in the | |
721 | threaded code for super-fast dispatching. | |
722 | ||
02f52e19 | 723 | You may not use this mechanism to jump to code in a different function. |
47620e09 | 724 | If you do that, totally unpredictable things will happen. The best way to |
c1f7febf RK |
725 | avoid this is to store the label address only in automatic variables and |
726 | never pass it as an argument. | |
727 | ||
47620e09 RH |
728 | An alternate way to write the above example is |
729 | ||
3ab51846 | 730 | @smallexample |
310668e8 JM |
731 | static const int array[] = @{ &&foo - &&foo, &&bar - &&foo, |
732 | &&hack - &&foo @}; | |
47620e09 | 733 | goto *(&&foo + array[i]); |
3ab51846 | 734 | @end smallexample |
47620e09 RH |
735 | |
736 | @noindent | |
737 | This is more friendly to code living in shared libraries, as it reduces | |
738 | the number of dynamic relocations that are needed, and by consequence, | |
739 | allows the data to be read-only. | |
740 | ||
c1f7febf RK |
741 | @node Nested Functions |
742 | @section Nested Functions | |
743 | @cindex nested functions | |
744 | @cindex downward funargs | |
745 | @cindex thunks | |
746 | ||
747 | A @dfn{nested function} is a function defined inside another function. | |
748 | (Nested functions are not supported for GNU C++.) The nested function's | |
749 | name is local to the block where it is defined. For example, here we | |
750 | define a nested function named @code{square}, and call it twice: | |
751 | ||
3ab51846 | 752 | @smallexample |
c1f7febf RK |
753 | @group |
754 | foo (double a, double b) | |
755 | @{ | |
756 | double square (double z) @{ return z * z; @} | |
757 | ||
758 | return square (a) + square (b); | |
759 | @} | |
760 | @end group | |
3ab51846 | 761 | @end smallexample |
c1f7febf RK |
762 | |
763 | The nested function can access all the variables of the containing | |
764 | function that are visible at the point of its definition. This is | |
765 | called @dfn{lexical scoping}. For example, here we show a nested | |
766 | function which uses an inherited variable named @code{offset}: | |
767 | ||
3ab51846 | 768 | @smallexample |
aee96fe9 | 769 | @group |
c1f7febf RK |
770 | bar (int *array, int offset, int size) |
771 | @{ | |
772 | int access (int *array, int index) | |
773 | @{ return array[index + offset]; @} | |
774 | int i; | |
0d893a63 | 775 | /* @r{@dots{}} */ |
c1f7febf | 776 | for (i = 0; i < size; i++) |
0d893a63 | 777 | /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */ |
c1f7febf | 778 | @} |
aee96fe9 | 779 | @end group |
3ab51846 | 780 | @end smallexample |
c1f7febf RK |
781 | |
782 | Nested function definitions are permitted within functions in the places | |
783 | where variable definitions are allowed; that is, in any block, before | |
784 | the first statement in the block. | |
785 | ||
786 | It is possible to call the nested function from outside the scope of its | |
787 | name by storing its address or passing the address to another function: | |
788 | ||
3ab51846 | 789 | @smallexample |
c1f7febf RK |
790 | hack (int *array, int size) |
791 | @{ | |
792 | void store (int index, int value) | |
793 | @{ array[index] = value; @} | |
794 | ||
795 | intermediate (store, size); | |
796 | @} | |
3ab51846 | 797 | @end smallexample |
c1f7febf RK |
798 | |
799 | Here, the function @code{intermediate} receives the address of | |
800 | @code{store} as an argument. If @code{intermediate} calls @code{store}, | |
801 | the arguments given to @code{store} are used to store into @code{array}. | |
802 | But this technique works only so long as the containing function | |
803 | (@code{hack}, in this example) does not exit. | |
804 | ||
805 | If you try to call the nested function through its address after the | |
806 | containing function has exited, all hell will break loose. If you try | |
807 | to call it after a containing scope level has exited, and if it refers | |
808 | to some of the variables that are no longer in scope, you may be lucky, | |
809 | but it's not wise to take the risk. If, however, the nested function | |
810 | does not refer to anything that has gone out of scope, you should be | |
811 | safe. | |
812 | ||
9c34dbbf ZW |
813 | GCC implements taking the address of a nested function using a technique |
814 | called @dfn{trampolines}. A paper describing them is available as | |
815 | ||
816 | @noindent | |
b73b1546 | 817 | @uref{http://people.debian.org/~aaronl/Usenix88-lexic.pdf}. |
c1f7febf RK |
818 | |
819 | A nested function can jump to a label inherited from a containing | |
820 | function, provided the label was explicitly declared in the containing | |
821 | function (@pxref{Local Labels}). Such a jump returns instantly to the | |
822 | containing function, exiting the nested function which did the | |
823 | @code{goto} and any intermediate functions as well. Here is an example: | |
824 | ||
3ab51846 | 825 | @smallexample |
c1f7febf RK |
826 | @group |
827 | bar (int *array, int offset, int size) | |
828 | @{ | |
829 | __label__ failure; | |
830 | int access (int *array, int index) | |
831 | @{ | |
832 | if (index > size) | |
833 | goto failure; | |
834 | return array[index + offset]; | |
835 | @} | |
836 | int i; | |
0d893a63 | 837 | /* @r{@dots{}} */ |
c1f7febf | 838 | for (i = 0; i < size; i++) |
0d893a63 MK |
839 | /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */ |
840 | /* @r{@dots{}} */ | |
c1f7febf RK |
841 | return 0; |
842 | ||
843 | /* @r{Control comes here from @code{access} | |
844 | if it detects an error.} */ | |
845 | failure: | |
846 | return -1; | |
847 | @} | |
848 | @end group | |
3ab51846 | 849 | @end smallexample |
c1f7febf RK |
850 | |
851 | A nested function always has internal linkage. Declaring one with | |
852 | @code{extern} is erroneous. If you need to declare the nested function | |
853 | before its definition, use @code{auto} (which is otherwise meaningless | |
854 | for function declarations). | |
855 | ||
3ab51846 | 856 | @smallexample |
c1f7febf RK |
857 | bar (int *array, int offset, int size) |
858 | @{ | |
859 | __label__ failure; | |
860 | auto int access (int *, int); | |
0d893a63 | 861 | /* @r{@dots{}} */ |
c1f7febf RK |
862 | int access (int *array, int index) |
863 | @{ | |
864 | if (index > size) | |
865 | goto failure; | |
866 | return array[index + offset]; | |
867 | @} | |
0d893a63 | 868 | /* @r{@dots{}} */ |
c1f7febf | 869 | @} |
3ab51846 | 870 | @end smallexample |
c1f7febf RK |
871 | |
872 | @node Constructing Calls | |
873 | @section Constructing Function Calls | |
874 | @cindex constructing calls | |
875 | @cindex forwarding calls | |
876 | ||
877 | Using the built-in functions described below, you can record | |
878 | the arguments a function received, and call another function | |
879 | with the same arguments, without knowing the number or types | |
880 | of the arguments. | |
881 | ||
882 | You can also record the return value of that function call, | |
883 | and later return that value, without knowing what data type | |
884 | the function tried to return (as long as your caller expects | |
885 | that data type). | |
886 | ||
6429bc7c EB |
887 | However, these built-in functions may interact badly with some |
888 | sophisticated features or other extensions of the language. It | |
889 | is, therefore, not recommended to use them outside very simple | |
890 | functions acting as mere forwarders for their arguments. | |
891 | ||
84330467 JM |
892 | @deftypefn {Built-in Function} {void *} __builtin_apply_args () |
893 | This built-in function returns a pointer to data | |
c1f7febf RK |
894 | describing how to perform a call with the same arguments as were passed |
895 | to the current function. | |
896 | ||
897 | The function saves the arg pointer register, structure value address, | |
898 | and all registers that might be used to pass arguments to a function | |
899 | into a block of memory allocated on the stack. Then it returns the | |
900 | address of that block. | |
84330467 | 901 | @end deftypefn |
c1f7febf | 902 | |
84330467 JM |
903 | @deftypefn {Built-in Function} {void *} __builtin_apply (void (*@var{function})(), void *@var{arguments}, size_t @var{size}) |
904 | This built-in function invokes @var{function} | |
905 | with a copy of the parameters described by @var{arguments} | |
906 | and @var{size}. | |
c1f7febf RK |
907 | |
908 | The value of @var{arguments} should be the value returned by | |
909 | @code{__builtin_apply_args}. The argument @var{size} specifies the size | |
910 | of the stack argument data, in bytes. | |
911 | ||
84330467 | 912 | This function returns a pointer to data describing |
c1f7febf RK |
913 | how to return whatever value was returned by @var{function}. The data |
914 | is saved in a block of memory allocated on the stack. | |
915 | ||
916 | It is not always simple to compute the proper value for @var{size}. The | |
917 | value is used by @code{__builtin_apply} to compute the amount of data | |
918 | that should be pushed on the stack and copied from the incoming argument | |
919 | area. | |
84330467 | 920 | @end deftypefn |
c1f7febf | 921 | |
84330467 | 922 | @deftypefn {Built-in Function} {void} __builtin_return (void *@var{result}) |
c1f7febf RK |
923 | This built-in function returns the value described by @var{result} from |
924 | the containing function. You should specify, for @var{result}, a value | |
925 | returned by @code{__builtin_apply}. | |
84330467 | 926 | @end deftypefn |
c1f7febf | 927 | |
c1f7febf RK |
928 | @node Typeof |
929 | @section Referring to a Type with @code{typeof} | |
930 | @findex typeof | |
931 | @findex sizeof | |
932 | @cindex macros, types of arguments | |
933 | ||
934 | Another way to refer to the type of an expression is with @code{typeof}. | |
935 | The syntax of using of this keyword looks like @code{sizeof}, but the | |
936 | construct acts semantically like a type name defined with @code{typedef}. | |
937 | ||
938 | There are two ways of writing the argument to @code{typeof}: with an | |
939 | expression or with a type. Here is an example with an expression: | |
940 | ||
3ab51846 | 941 | @smallexample |
c1f7febf | 942 | typeof (x[0](1)) |
3ab51846 | 943 | @end smallexample |
c1f7febf RK |
944 | |
945 | @noindent | |
89aed483 JM |
946 | This assumes that @code{x} is an array of pointers to functions; |
947 | the type described is that of the values of the functions. | |
c1f7febf RK |
948 | |
949 | Here is an example with a typename as the argument: | |
950 | ||
3ab51846 | 951 | @smallexample |
c1f7febf | 952 | typeof (int *) |
3ab51846 | 953 | @end smallexample |
c1f7febf RK |
954 | |
955 | @noindent | |
956 | Here the type described is that of pointers to @code{int}. | |
957 | ||
5490d604 | 958 | If you are writing a header file that must work when included in ISO C |
c1f7febf RK |
959 | programs, write @code{__typeof__} instead of @code{typeof}. |
960 | @xref{Alternate Keywords}. | |
961 | ||
962 | A @code{typeof}-construct can be used anywhere a typedef name could be | |
963 | used. For example, you can use it in a declaration, in a cast, or inside | |
964 | of @code{sizeof} or @code{typeof}. | |
965 | ||
95f79357 ZW |
966 | @code{typeof} is often useful in conjunction with the |
967 | statements-within-expressions feature. Here is how the two together can | |
968 | be used to define a safe ``maximum'' macro that operates on any | |
969 | arithmetic type and evaluates each of its arguments exactly once: | |
970 | ||
3ab51846 | 971 | @smallexample |
95f79357 ZW |
972 | #define max(a,b) \ |
973 | (@{ typeof (a) _a = (a); \ | |
974 | typeof (b) _b = (b); \ | |
975 | _a > _b ? _a : _b; @}) | |
3ab51846 | 976 | @end smallexample |
95f79357 | 977 | |
526278c9 VR |
978 | @cindex underscores in variables in macros |
979 | @cindex @samp{_} in variables in macros | |
980 | @cindex local variables in macros | |
981 | @cindex variables, local, in macros | |
982 | @cindex macros, local variables in | |
983 | ||
984 | The reason for using names that start with underscores for the local | |
985 | variables is to avoid conflicts with variable names that occur within the | |
986 | expressions that are substituted for @code{a} and @code{b}. Eventually we | |
987 | hope to design a new form of declaration syntax that allows you to declare | |
988 | variables whose scopes start only after their initializers; this will be a | |
989 | more reliable way to prevent such conflicts. | |
990 | ||
95f79357 ZW |
991 | @noindent |
992 | Some more examples of the use of @code{typeof}: | |
993 | ||
c1f7febf RK |
994 | @itemize @bullet |
995 | @item | |
996 | This declares @code{y} with the type of what @code{x} points to. | |
997 | ||
3ab51846 | 998 | @smallexample |
c1f7febf | 999 | typeof (*x) y; |
3ab51846 | 1000 | @end smallexample |
c1f7febf RK |
1001 | |
1002 | @item | |
1003 | This declares @code{y} as an array of such values. | |
1004 | ||
3ab51846 | 1005 | @smallexample |
c1f7febf | 1006 | typeof (*x) y[4]; |
3ab51846 | 1007 | @end smallexample |
c1f7febf RK |
1008 | |
1009 | @item | |
1010 | This declares @code{y} as an array of pointers to characters: | |
1011 | ||
3ab51846 | 1012 | @smallexample |
c1f7febf | 1013 | typeof (typeof (char *)[4]) y; |
3ab51846 | 1014 | @end smallexample |
c1f7febf RK |
1015 | |
1016 | @noindent | |
1017 | It is equivalent to the following traditional C declaration: | |
1018 | ||
3ab51846 | 1019 | @smallexample |
c1f7febf | 1020 | char *y[4]; |
3ab51846 | 1021 | @end smallexample |
c1f7febf RK |
1022 | |
1023 | To see the meaning of the declaration using @code{typeof}, and why it | |
962e6e00 | 1024 | might be a useful way to write, rewrite it with these macros: |
c1f7febf | 1025 | |
3ab51846 | 1026 | @smallexample |
c1f7febf RK |
1027 | #define pointer(T) typeof(T *) |
1028 | #define array(T, N) typeof(T [N]) | |
3ab51846 | 1029 | @end smallexample |
c1f7febf RK |
1030 | |
1031 | @noindent | |
1032 | Now the declaration can be rewritten this way: | |
1033 | ||
3ab51846 | 1034 | @smallexample |
c1f7febf | 1035 | array (pointer (char), 4) y; |
3ab51846 | 1036 | @end smallexample |
c1f7febf RK |
1037 | |
1038 | @noindent | |
1039 | Thus, @code{array (pointer (char), 4)} is the type of arrays of 4 | |
1040 | pointers to @code{char}. | |
1041 | @end itemize | |
1042 | ||
95f79357 ZW |
1043 | @emph{Compatibility Note:} In addition to @code{typeof}, GCC 2 supported |
1044 | a more limited extension which permitted one to write | |
1045 | ||
3ab51846 | 1046 | @smallexample |
95f79357 | 1047 | typedef @var{T} = @var{expr}; |
3ab51846 | 1048 | @end smallexample |
95f79357 ZW |
1049 | |
1050 | @noindent | |
1051 | with the effect of declaring @var{T} to have the type of the expression | |
1052 | @var{expr}. This extension does not work with GCC 3 (versions between | |
1053 | 3.0 and 3.2 will crash; 3.2.1 and later give an error). Code which | |
1054 | relies on it should be rewritten to use @code{typeof}: | |
1055 | ||
3ab51846 | 1056 | @smallexample |
95f79357 | 1057 | typedef typeof(@var{expr}) @var{T}; |
3ab51846 | 1058 | @end smallexample |
95f79357 ZW |
1059 | |
1060 | @noindent | |
1061 | This will work with all versions of GCC@. | |
1062 | ||
c1f7febf RK |
1063 | @node Conditionals |
1064 | @section Conditionals with Omitted Operands | |
1065 | @cindex conditional expressions, extensions | |
1066 | @cindex omitted middle-operands | |
1067 | @cindex middle-operands, omitted | |
1068 | @cindex extensions, @code{?:} | |
1069 | @cindex @code{?:} extensions | |
1070 | ||
1071 | The middle operand in a conditional expression may be omitted. Then | |
1072 | if the first operand is nonzero, its value is the value of the conditional | |
1073 | expression. | |
1074 | ||
1075 | Therefore, the expression | |
1076 | ||
3ab51846 | 1077 | @smallexample |
c1f7febf | 1078 | x ? : y |
3ab51846 | 1079 | @end smallexample |
c1f7febf RK |
1080 | |
1081 | @noindent | |
1082 | has the value of @code{x} if that is nonzero; otherwise, the value of | |
1083 | @code{y}. | |
1084 | ||
1085 | This example is perfectly equivalent to | |
1086 | ||
3ab51846 | 1087 | @smallexample |
c1f7febf | 1088 | x ? x : y |
3ab51846 | 1089 | @end smallexample |
c1f7febf RK |
1090 | |
1091 | @cindex side effect in ?: | |
1092 | @cindex ?: side effect | |
1093 | @noindent | |
1094 | In this simple case, the ability to omit the middle operand is not | |
1095 | especially useful. When it becomes useful is when the first operand does, | |
1096 | or may (if it is a macro argument), contain a side effect. Then repeating | |
1097 | the operand in the middle would perform the side effect twice. Omitting | |
1098 | the middle operand uses the value already computed without the undesirable | |
1099 | effects of recomputing it. | |
1100 | ||
1101 | @node Long Long | |
1102 | @section Double-Word Integers | |
1103 | @cindex @code{long long} data types | |
1104 | @cindex double-word arithmetic | |
1105 | @cindex multiprecision arithmetic | |
4b404517 JM |
1106 | @cindex @code{LL} integer suffix |
1107 | @cindex @code{ULL} integer suffix | |
c1f7febf | 1108 | |
4b404517 JM |
1109 | ISO C99 supports data types for integers that are at least 64 bits wide, |
1110 | and as an extension GCC supports them in C89 mode and in C++. | |
1111 | Simply write @code{long long int} for a signed integer, or | |
c1f7febf | 1112 | @code{unsigned long long int} for an unsigned integer. To make an |
84330467 | 1113 | integer constant of type @code{long long int}, add the suffix @samp{LL} |
c1f7febf | 1114 | to the integer. To make an integer constant of type @code{unsigned long |
84330467 | 1115 | long int}, add the suffix @samp{ULL} to the integer. |
c1f7febf RK |
1116 | |
1117 | You can use these types in arithmetic like any other integer types. | |
1118 | Addition, subtraction, and bitwise boolean operations on these types | |
1119 | are open-coded on all types of machines. Multiplication is open-coded | |
1120 | if the machine supports fullword-to-doubleword a widening multiply | |
1121 | instruction. Division and shifts are open-coded only on machines that | |
1122 | provide special support. The operations that are not open-coded use | |
161d7b59 | 1123 | special library routines that come with GCC@. |
c1f7febf RK |
1124 | |
1125 | There may be pitfalls when you use @code{long long} types for function | |
1126 | arguments, unless you declare function prototypes. If a function | |
1127 | expects type @code{int} for its argument, and you pass a value of type | |
1128 | @code{long long int}, confusion will result because the caller and the | |
1129 | subroutine will disagree about the number of bytes for the argument. | |
1130 | Likewise, if the function expects @code{long long int} and you pass | |
1131 | @code{int}. The best way to avoid such problems is to use prototypes. | |
1132 | ||
1133 | @node Complex | |
1134 | @section Complex Numbers | |
1135 | @cindex complex numbers | |
4b404517 JM |
1136 | @cindex @code{_Complex} keyword |
1137 | @cindex @code{__complex__} keyword | |
c1f7febf | 1138 | |
4b404517 JM |
1139 | ISO C99 supports complex floating data types, and as an extension GCC |
1140 | supports them in C89 mode and in C++, and supports complex integer data | |
1141 | types which are not part of ISO C99. You can declare complex types | |
1142 | using the keyword @code{_Complex}. As an extension, the older GNU | |
1143 | keyword @code{__complex__} is also supported. | |
c1f7febf | 1144 | |
4b404517 | 1145 | For example, @samp{_Complex double x;} declares @code{x} as a |
c1f7febf | 1146 | variable whose real part and imaginary part are both of type |
4b404517 | 1147 | @code{double}. @samp{_Complex short int y;} declares @code{y} to |
c1f7febf RK |
1148 | have real and imaginary parts of type @code{short int}; this is not |
1149 | likely to be useful, but it shows that the set of complex types is | |
1150 | complete. | |
1151 | ||
1152 | To write a constant with a complex data type, use the suffix @samp{i} or | |
1153 | @samp{j} (either one; they are equivalent). For example, @code{2.5fi} | |
4b404517 JM |
1154 | has type @code{_Complex float} and @code{3i} has type |
1155 | @code{_Complex int}. Such a constant always has a pure imaginary | |
c1f7febf | 1156 | value, but you can form any complex value you like by adding one to a |
4b404517 JM |
1157 | real constant. This is a GNU extension; if you have an ISO C99 |
1158 | conforming C library (such as GNU libc), and want to construct complex | |
1159 | constants of floating type, you should include @code{<complex.h>} and | |
1160 | use the macros @code{I} or @code{_Complex_I} instead. | |
c1f7febf | 1161 | |
4b404517 JM |
1162 | @cindex @code{__real__} keyword |
1163 | @cindex @code{__imag__} keyword | |
c1f7febf RK |
1164 | To extract the real part of a complex-valued expression @var{exp}, write |
1165 | @code{__real__ @var{exp}}. Likewise, use @code{__imag__} to | |
4b404517 JM |
1166 | extract the imaginary part. This is a GNU extension; for values of |
1167 | floating type, you should use the ISO C99 functions @code{crealf}, | |
1168 | @code{creal}, @code{creall}, @code{cimagf}, @code{cimag} and | |
1169 | @code{cimagl}, declared in @code{<complex.h>} and also provided as | |
161d7b59 | 1170 | built-in functions by GCC@. |
c1f7febf | 1171 | |
4b404517 | 1172 | @cindex complex conjugation |
c1f7febf | 1173 | The operator @samp{~} performs complex conjugation when used on a value |
4b404517 JM |
1174 | with a complex type. This is a GNU extension; for values of |
1175 | floating type, you should use the ISO C99 functions @code{conjf}, | |
1176 | @code{conj} and @code{conjl}, declared in @code{<complex.h>} and also | |
161d7b59 | 1177 | provided as built-in functions by GCC@. |
c1f7febf | 1178 | |
f0523f02 | 1179 | GCC can allocate complex automatic variables in a noncontiguous |
c1f7febf | 1180 | fashion; it's even possible for the real part to be in a register while |
580fb356 JW |
1181 | the imaginary part is on the stack (or vice-versa). Only the DWARF2 |
1182 | debug info format can represent this, so use of DWARF2 is recommended. | |
1183 | If you are using the stabs debug info format, GCC describes a noncontiguous | |
1184 | complex variable as if it were two separate variables of noncomplex type. | |
c1f7febf RK |
1185 | If the variable's actual name is @code{foo}, the two fictitious |
1186 | variables are named @code{foo$real} and @code{foo$imag}. You can | |
1187 | examine and set these two fictitious variables with your debugger. | |
1188 | ||
6f4d7222 | 1189 | @node Hex Floats |
6b42b9ea UD |
1190 | @section Hex Floats |
1191 | @cindex hex floats | |
c5c76735 | 1192 | |
4b404517 | 1193 | ISO C99 supports floating-point numbers written not only in the usual |
6f4d7222 | 1194 | decimal notation, such as @code{1.55e1}, but also numbers such as |
4b404517 JM |
1195 | @code{0x1.fp3} written in hexadecimal format. As a GNU extension, GCC |
1196 | supports this in C89 mode (except in some cases when strictly | |
1197 | conforming) and in C++. In that format the | |
84330467 | 1198 | @samp{0x} hex introducer and the @samp{p} or @samp{P} exponent field are |
6f4d7222 | 1199 | mandatory. The exponent is a decimal number that indicates the power of |
84330467 | 1200 | 2 by which the significant part will be multiplied. Thus @samp{0x1.f} is |
aee96fe9 JM |
1201 | @tex |
1202 | $1 {15\over16}$, | |
1203 | @end tex | |
1204 | @ifnottex | |
1205 | 1 15/16, | |
1206 | @end ifnottex | |
1207 | @samp{p3} multiplies it by 8, and the value of @code{0x1.fp3} | |
6f4d7222 UD |
1208 | is the same as @code{1.55e1}. |
1209 | ||
1210 | Unlike for floating-point numbers in the decimal notation the exponent | |
1211 | is always required in the hexadecimal notation. Otherwise the compiler | |
1212 | would not be able to resolve the ambiguity of, e.g., @code{0x1.f}. This | |
84330467 | 1213 | could mean @code{1.0f} or @code{1.9375} since @samp{f} is also the |
6f4d7222 UD |
1214 | extension for floating-point constants of type @code{float}. |
1215 | ||
c1f7febf RK |
1216 | @node Zero Length |
1217 | @section Arrays of Length Zero | |
1218 | @cindex arrays of length zero | |
1219 | @cindex zero-length arrays | |
1220 | @cindex length-zero arrays | |
ffc5c6a9 | 1221 | @cindex flexible array members |
c1f7febf | 1222 | |
161d7b59 | 1223 | Zero-length arrays are allowed in GNU C@. They are very useful as the |
584ef5fe | 1224 | last element of a structure which is really a header for a variable-length |
c1f7febf RK |
1225 | object: |
1226 | ||
3ab51846 | 1227 | @smallexample |
c1f7febf RK |
1228 | struct line @{ |
1229 | int length; | |
1230 | char contents[0]; | |
1231 | @}; | |
1232 | ||
584ef5fe RH |
1233 | struct line *thisline = (struct line *) |
1234 | malloc (sizeof (struct line) + this_length); | |
1235 | thisline->length = this_length; | |
3ab51846 | 1236 | @end smallexample |
c1f7febf | 1237 | |
3764f879 | 1238 | In ISO C90, you would have to give @code{contents} a length of 1, which |
c1f7febf RK |
1239 | means either you waste space or complicate the argument to @code{malloc}. |
1240 | ||
02f52e19 | 1241 | In ISO C99, you would use a @dfn{flexible array member}, which is |
584ef5fe RH |
1242 | slightly different in syntax and semantics: |
1243 | ||
1244 | @itemize @bullet | |
1245 | @item | |
1246 | Flexible array members are written as @code{contents[]} without | |
1247 | the @code{0}. | |
1248 | ||
1249 | @item | |
1250 | Flexible array members have incomplete type, and so the @code{sizeof} | |
1251 | operator may not be applied. As a quirk of the original implementation | |
1252 | of zero-length arrays, @code{sizeof} evaluates to zero. | |
1253 | ||
1254 | @item | |
1255 | Flexible array members may only appear as the last member of a | |
e7b6a0ee | 1256 | @code{struct} that is otherwise non-empty. |
2984fe64 JM |
1257 | |
1258 | @item | |
1259 | A structure containing a flexible array member, or a union containing | |
1260 | such a structure (possibly recursively), may not be a member of a | |
1261 | structure or an element of an array. (However, these uses are | |
1262 | permitted by GCC as extensions.) | |
ffc5c6a9 | 1263 | @end itemize |
a25f1211 | 1264 | |
ffc5c6a9 | 1265 | GCC versions before 3.0 allowed zero-length arrays to be statically |
e7b6a0ee DD |
1266 | initialized, as if they were flexible arrays. In addition to those |
1267 | cases that were useful, it also allowed initializations in situations | |
1268 | that would corrupt later data. Non-empty initialization of zero-length | |
1269 | arrays is now treated like any case where there are more initializer | |
1270 | elements than the array holds, in that a suitable warning about "excess | |
1271 | elements in array" is given, and the excess elements (all of them, in | |
1272 | this case) are ignored. | |
ffc5c6a9 RH |
1273 | |
1274 | Instead GCC allows static initialization of flexible array members. | |
1275 | This is equivalent to defining a new structure containing the original | |
1276 | structure followed by an array of sufficient size to contain the data. | |
e979f9e8 | 1277 | I.e.@: in the following, @code{f1} is constructed as if it were declared |
ffc5c6a9 | 1278 | like @code{f2}. |
a25f1211 | 1279 | |
3ab51846 | 1280 | @smallexample |
ffc5c6a9 RH |
1281 | struct f1 @{ |
1282 | int x; int y[]; | |
1283 | @} f1 = @{ 1, @{ 2, 3, 4 @} @}; | |
1284 | ||
1285 | struct f2 @{ | |
1286 | struct f1 f1; int data[3]; | |
1287 | @} f2 = @{ @{ 1 @}, @{ 2, 3, 4 @} @}; | |
3ab51846 | 1288 | @end smallexample |
584ef5fe | 1289 | |
ffc5c6a9 RH |
1290 | @noindent |
1291 | The convenience of this extension is that @code{f1} has the desired | |
1292 | type, eliminating the need to consistently refer to @code{f2.f1}. | |
1293 | ||
1294 | This has symmetry with normal static arrays, in that an array of | |
1295 | unknown size is also written with @code{[]}. | |
a25f1211 | 1296 | |
ffc5c6a9 RH |
1297 | Of course, this extension only makes sense if the extra data comes at |
1298 | the end of a top-level object, as otherwise we would be overwriting | |
1299 | data at subsequent offsets. To avoid undue complication and confusion | |
1300 | with initialization of deeply nested arrays, we simply disallow any | |
1301 | non-empty initialization except when the structure is the top-level | |
1302 | object. For example: | |
584ef5fe | 1303 | |
3ab51846 | 1304 | @smallexample |
ffc5c6a9 RH |
1305 | struct foo @{ int x; int y[]; @}; |
1306 | struct bar @{ struct foo z; @}; | |
1307 | ||
13ba36b4 JM |
1308 | struct foo a = @{ 1, @{ 2, 3, 4 @} @}; // @r{Valid.} |
1309 | struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @} @}; // @r{Invalid.} | |
1310 | struct bar c = @{ @{ 1, @{ @} @} @}; // @r{Valid.} | |
1311 | struct foo d[1] = @{ @{ 1 @{ 2, 3, 4 @} @} @}; // @r{Invalid.} | |
3ab51846 | 1312 | @end smallexample |
4b606faf | 1313 | |
ba05abd3 GK |
1314 | @node Empty Structures |
1315 | @section Structures With No Members | |
1316 | @cindex empty structures | |
1317 | @cindex zero-size structures | |
1318 | ||
1319 | GCC permits a C structure to have no members: | |
1320 | ||
3ab51846 | 1321 | @smallexample |
ba05abd3 GK |
1322 | struct empty @{ |
1323 | @}; | |
3ab51846 | 1324 | @end smallexample |
ba05abd3 GK |
1325 | |
1326 | The structure will have size zero. In C++, empty structures are part | |
db0b376e MM |
1327 | of the language. G++ treats empty structures as if they had a single |
1328 | member of type @code{char}. | |
ba05abd3 | 1329 | |
c1f7febf RK |
1330 | @node Variable Length |
1331 | @section Arrays of Variable Length | |
1332 | @cindex variable-length arrays | |
1333 | @cindex arrays of variable length | |
4b404517 | 1334 | @cindex VLAs |
c1f7febf | 1335 | |
4b404517 JM |
1336 | Variable-length automatic arrays are allowed in ISO C99, and as an |
1337 | extension GCC accepts them in C89 mode and in C++. (However, GCC's | |
1338 | implementation of variable-length arrays does not yet conform in detail | |
1339 | to the ISO C99 standard.) These arrays are | |
c1f7febf RK |
1340 | declared like any other automatic arrays, but with a length that is not |
1341 | a constant expression. The storage is allocated at the point of | |
1342 | declaration and deallocated when the brace-level is exited. For | |
1343 | example: | |
1344 | ||
3ab51846 | 1345 | @smallexample |
c1f7febf RK |
1346 | FILE * |
1347 | concat_fopen (char *s1, char *s2, char *mode) | |
1348 | @{ | |
1349 | char str[strlen (s1) + strlen (s2) + 1]; | |
1350 | strcpy (str, s1); | |
1351 | strcat (str, s2); | |
1352 | return fopen (str, mode); | |
1353 | @} | |
3ab51846 | 1354 | @end smallexample |
c1f7febf RK |
1355 | |
1356 | @cindex scope of a variable length array | |
1357 | @cindex variable-length array scope | |
1358 | @cindex deallocating variable length arrays | |
1359 | Jumping or breaking out of the scope of the array name deallocates the | |
1360 | storage. Jumping into the scope is not allowed; you get an error | |
1361 | message for it. | |
1362 | ||
1363 | @cindex @code{alloca} vs variable-length arrays | |
1364 | You can use the function @code{alloca} to get an effect much like | |
1365 | variable-length arrays. The function @code{alloca} is available in | |
1366 | many other C implementations (but not in all). On the other hand, | |
1367 | variable-length arrays are more elegant. | |
1368 | ||
1369 | There are other differences between these two methods. Space allocated | |
1370 | with @code{alloca} exists until the containing @emph{function} returns. | |
1371 | The space for a variable-length array is deallocated as soon as the array | |
1372 | name's scope ends. (If you use both variable-length arrays and | |
1373 | @code{alloca} in the same function, deallocation of a variable-length array | |
1374 | will also deallocate anything more recently allocated with @code{alloca}.) | |
1375 | ||
1376 | You can also use variable-length arrays as arguments to functions: | |
1377 | ||
3ab51846 | 1378 | @smallexample |
c1f7febf RK |
1379 | struct entry |
1380 | tester (int len, char data[len][len]) | |
1381 | @{ | |
0d893a63 | 1382 | /* @r{@dots{}} */ |
c1f7febf | 1383 | @} |
3ab51846 | 1384 | @end smallexample |
c1f7febf RK |
1385 | |
1386 | The length of an array is computed once when the storage is allocated | |
1387 | and is remembered for the scope of the array in case you access it with | |
1388 | @code{sizeof}. | |
1389 | ||
1390 | If you want to pass the array first and the length afterward, you can | |
1391 | use a forward declaration in the parameter list---another GNU extension. | |
1392 | ||
3ab51846 | 1393 | @smallexample |
c1f7febf RK |
1394 | struct entry |
1395 | tester (int len; char data[len][len], int len) | |
1396 | @{ | |
0d893a63 | 1397 | /* @r{@dots{}} */ |
c1f7febf | 1398 | @} |
3ab51846 | 1399 | @end smallexample |
c1f7febf RK |
1400 | |
1401 | @cindex parameter forward declaration | |
1402 | The @samp{int len} before the semicolon is a @dfn{parameter forward | |
1403 | declaration}, and it serves the purpose of making the name @code{len} | |
1404 | known when the declaration of @code{data} is parsed. | |
1405 | ||
1406 | You can write any number of such parameter forward declarations in the | |
1407 | parameter list. They can be separated by commas or semicolons, but the | |
1408 | last one must end with a semicolon, which is followed by the ``real'' | |
1409 | parameter declarations. Each forward declaration must match a ``real'' | |
4b404517 JM |
1410 | declaration in parameter name and data type. ISO C99 does not support |
1411 | parameter forward declarations. | |
c1f7febf | 1412 | |
ccd96f0a NB |
1413 | @node Variadic Macros |
1414 | @section Macros with a Variable Number of Arguments. | |
c1f7febf RK |
1415 | @cindex variable number of arguments |
1416 | @cindex macro with variable arguments | |
1417 | @cindex rest argument (in macro) | |
ccd96f0a | 1418 | @cindex variadic macros |
c1f7febf | 1419 | |
ccd96f0a NB |
1420 | In the ISO C standard of 1999, a macro can be declared to accept a |
1421 | variable number of arguments much as a function can. The syntax for | |
1422 | defining the macro is similar to that of a function. Here is an | |
1423 | example: | |
c1f7febf | 1424 | |
478c9e72 | 1425 | @smallexample |
ccd96f0a | 1426 | #define debug(format, ...) fprintf (stderr, format, __VA_ARGS__) |
478c9e72 | 1427 | @end smallexample |
c1f7febf | 1428 | |
ccd96f0a NB |
1429 | Here @samp{@dots{}} is a @dfn{variable argument}. In the invocation of |
1430 | such a macro, it represents the zero or more tokens until the closing | |
1431 | parenthesis that ends the invocation, including any commas. This set of | |
1432 | tokens replaces the identifier @code{__VA_ARGS__} in the macro body | |
1433 | wherever it appears. See the CPP manual for more information. | |
1434 | ||
1435 | GCC has long supported variadic macros, and used a different syntax that | |
1436 | allowed you to give a name to the variable arguments just like any other | |
1437 | argument. Here is an example: | |
c1f7febf | 1438 | |
3ab51846 | 1439 | @smallexample |
ccd96f0a | 1440 | #define debug(format, args...) fprintf (stderr, format, args) |
3ab51846 | 1441 | @end smallexample |
c1f7febf | 1442 | |
ccd96f0a NB |
1443 | This is in all ways equivalent to the ISO C example above, but arguably |
1444 | more readable and descriptive. | |
c1f7febf | 1445 | |
ccd96f0a NB |
1446 | GNU CPP has two further variadic macro extensions, and permits them to |
1447 | be used with either of the above forms of macro definition. | |
1448 | ||
1449 | In standard C, you are not allowed to leave the variable argument out | |
1450 | entirely; but you are allowed to pass an empty argument. For example, | |
1451 | this invocation is invalid in ISO C, because there is no comma after | |
1452 | the string: | |
c1f7febf | 1453 | |
3ab51846 | 1454 | @smallexample |
ccd96f0a | 1455 | debug ("A message") |
3ab51846 | 1456 | @end smallexample |
c1f7febf | 1457 | |
ccd96f0a NB |
1458 | GNU CPP permits you to completely omit the variable arguments in this |
1459 | way. In the above examples, the compiler would complain, though since | |
1460 | the expansion of the macro still has the extra comma after the format | |
1461 | string. | |
1462 | ||
1463 | To help solve this problem, CPP behaves specially for variable arguments | |
1464 | used with the token paste operator, @samp{##}. If instead you write | |
c1f7febf | 1465 | |
478c9e72 | 1466 | @smallexample |
ccd96f0a | 1467 | #define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__) |
478c9e72 | 1468 | @end smallexample |
c1f7febf | 1469 | |
ccd96f0a NB |
1470 | and if the variable arguments are omitted or empty, the @samp{##} |
1471 | operator causes the preprocessor to remove the comma before it. If you | |
1472 | do provide some variable arguments in your macro invocation, GNU CPP | |
1473 | does not complain about the paste operation and instead places the | |
1474 | variable arguments after the comma. Just like any other pasted macro | |
1475 | argument, these arguments are not macro expanded. | |
1476 | ||
1477 | @node Escaped Newlines | |
1478 | @section Slightly Looser Rules for Escaped Newlines | |
1479 | @cindex escaped newlines | |
1480 | @cindex newlines (escaped) | |
1481 | ||
f458d1d5 ZW |
1482 | Recently, the preprocessor has relaxed its treatment of escaped |
1483 | newlines. Previously, the newline had to immediately follow a | |
e6cc3a24 ZW |
1484 | backslash. The current implementation allows whitespace in the form |
1485 | of spaces, horizontal and vertical tabs, and form feeds between the | |
ccd96f0a NB |
1486 | backslash and the subsequent newline. The preprocessor issues a |
1487 | warning, but treats it as a valid escaped newline and combines the two | |
1488 | lines to form a single logical line. This works within comments and | |
e6cc3a24 ZW |
1489 | tokens, as well as between tokens. Comments are @emph{not} treated as |
1490 | whitespace for the purposes of this relaxation, since they have not | |
1491 | yet been replaced with spaces. | |
c1f7febf RK |
1492 | |
1493 | @node Subscripting | |
1494 | @section Non-Lvalue Arrays May Have Subscripts | |
1495 | @cindex subscripting | |
1496 | @cindex arrays, non-lvalue | |
1497 | ||
1498 | @cindex subscripting and function values | |
207bf485 JM |
1499 | In ISO C99, arrays that are not lvalues still decay to pointers, and |
1500 | may be subscripted, although they may not be modified or used after | |
1501 | the next sequence point and the unary @samp{&} operator may not be | |
1502 | applied to them. As an extension, GCC allows such arrays to be | |
1503 | subscripted in C89 mode, though otherwise they do not decay to | |
1504 | pointers outside C99 mode. For example, | |
4b404517 | 1505 | this is valid in GNU C though not valid in C89: |
c1f7febf | 1506 | |
3ab51846 | 1507 | @smallexample |
c1f7febf RK |
1508 | @group |
1509 | struct foo @{int a[4];@}; | |
1510 | ||
1511 | struct foo f(); | |
1512 | ||
1513 | bar (int index) | |
1514 | @{ | |
1515 | return f().a[index]; | |
1516 | @} | |
1517 | @end group | |
3ab51846 | 1518 | @end smallexample |
c1f7febf RK |
1519 | |
1520 | @node Pointer Arith | |
1521 | @section Arithmetic on @code{void}- and Function-Pointers | |
1522 | @cindex void pointers, arithmetic | |
1523 | @cindex void, size of pointer to | |
1524 | @cindex function pointers, arithmetic | |
1525 | @cindex function, size of pointer to | |
1526 | ||
1527 | In GNU C, addition and subtraction operations are supported on pointers to | |
1528 | @code{void} and on pointers to functions. This is done by treating the | |
1529 | size of a @code{void} or of a function as 1. | |
1530 | ||
1531 | A consequence of this is that @code{sizeof} is also allowed on @code{void} | |
1532 | and on function types, and returns 1. | |
1533 | ||
84330467 JM |
1534 | @opindex Wpointer-arith |
1535 | The option @option{-Wpointer-arith} requests a warning if these extensions | |
c1f7febf RK |
1536 | are used. |
1537 | ||
1538 | @node Initializers | |
1539 | @section Non-Constant Initializers | |
1540 | @cindex initializers, non-constant | |
1541 | @cindex non-constant initializers | |
1542 | ||
4b404517 | 1543 | As in standard C++ and ISO C99, the elements of an aggregate initializer for an |
161d7b59 | 1544 | automatic variable are not required to be constant expressions in GNU C@. |
c1f7febf RK |
1545 | Here is an example of an initializer with run-time varying elements: |
1546 | ||
3ab51846 | 1547 | @smallexample |
c1f7febf RK |
1548 | foo (float f, float g) |
1549 | @{ | |
1550 | float beat_freqs[2] = @{ f-g, f+g @}; | |
0d893a63 | 1551 | /* @r{@dots{}} */ |
c1f7febf | 1552 | @} |
3ab51846 | 1553 | @end smallexample |
c1f7febf | 1554 | |
4b404517 JM |
1555 | @node Compound Literals |
1556 | @section Compound Literals | |
c1f7febf RK |
1557 | @cindex constructor expressions |
1558 | @cindex initializations in expressions | |
1559 | @cindex structures, constructor expression | |
1560 | @cindex expressions, constructor | |
4b404517 JM |
1561 | @cindex compound literals |
1562 | @c The GNU C name for what C99 calls compound literals was "constructor expressions". | |
c1f7febf | 1563 | |
4b404517 | 1564 | ISO C99 supports compound literals. A compound literal looks like |
c1f7febf RK |
1565 | a cast containing an initializer. Its value is an object of the |
1566 | type specified in the cast, containing the elements specified in | |
db3acfa5 JM |
1567 | the initializer; it is an lvalue. As an extension, GCC supports |
1568 | compound literals in C89 mode and in C++. | |
c1f7febf RK |
1569 | |
1570 | Usually, the specified type is a structure. Assume that | |
1571 | @code{struct foo} and @code{structure} are declared as shown: | |
1572 | ||
3ab51846 | 1573 | @smallexample |
c1f7febf | 1574 | struct foo @{int a; char b[2];@} structure; |
3ab51846 | 1575 | @end smallexample |
c1f7febf RK |
1576 | |
1577 | @noindent | |
4b404517 | 1578 | Here is an example of constructing a @code{struct foo} with a compound literal: |
c1f7febf | 1579 | |
3ab51846 | 1580 | @smallexample |
c1f7febf | 1581 | structure = ((struct foo) @{x + y, 'a', 0@}); |
3ab51846 | 1582 | @end smallexample |
c1f7febf RK |
1583 | |
1584 | @noindent | |
1585 | This is equivalent to writing the following: | |
1586 | ||
3ab51846 | 1587 | @smallexample |
c1f7febf RK |
1588 | @{ |
1589 | struct foo temp = @{x + y, 'a', 0@}; | |
1590 | structure = temp; | |
1591 | @} | |
3ab51846 | 1592 | @end smallexample |
c1f7febf | 1593 | |
4b404517 | 1594 | You can also construct an array. If all the elements of the compound literal |
c1f7febf | 1595 | are (made up of) simple constant expressions, suitable for use in |
db3acfa5 JM |
1596 | initializers of objects of static storage duration, then the compound |
1597 | literal can be coerced to a pointer to its first element and used in | |
1598 | such an initializer, as shown here: | |
c1f7febf | 1599 | |
3ab51846 | 1600 | @smallexample |
c1f7febf | 1601 | char **foo = (char *[]) @{ "x", "y", "z" @}; |
3ab51846 | 1602 | @end smallexample |
c1f7febf | 1603 | |
4b404517 JM |
1604 | Compound literals for scalar types and union types are is |
1605 | also allowed, but then the compound literal is equivalent | |
c1f7febf RK |
1606 | to a cast. |
1607 | ||
59c83dbf JJ |
1608 | As a GNU extension, GCC allows initialization of objects with static storage |
1609 | duration by compound literals (which is not possible in ISO C99, because | |
1610 | the initializer is not a constant). | |
1611 | It is handled as if the object was initialized only with the bracket | |
1612 | enclosed list if compound literal's and object types match. | |
1613 | The initializer list of the compound literal must be constant. | |
1614 | If the object being initialized has array type of unknown size, the size is | |
ad47f1e5 | 1615 | determined by compound literal size. |
59c83dbf | 1616 | |
3ab51846 | 1617 | @smallexample |
59c83dbf JJ |
1618 | static struct foo x = (struct foo) @{1, 'a', 'b'@}; |
1619 | static int y[] = (int []) @{1, 2, 3@}; | |
1620 | static int z[] = (int [3]) @{1@}; | |
3ab51846 | 1621 | @end smallexample |
59c83dbf JJ |
1622 | |
1623 | @noindent | |
1624 | The above lines are equivalent to the following: | |
3ab51846 | 1625 | @smallexample |
59c83dbf JJ |
1626 | static struct foo x = @{1, 'a', 'b'@}; |
1627 | static int y[] = @{1, 2, 3@}; | |
ad47f1e5 | 1628 | static int z[] = @{1, 0, 0@}; |
3ab51846 | 1629 | @end smallexample |
59c83dbf | 1630 | |
4b404517 JM |
1631 | @node Designated Inits |
1632 | @section Designated Initializers | |
c1f7febf RK |
1633 | @cindex initializers with labeled elements |
1634 | @cindex labeled elements in initializers | |
1635 | @cindex case labels in initializers | |
4b404517 | 1636 | @cindex designated initializers |
c1f7febf | 1637 | |
26d4fec7 | 1638 | Standard C89 requires the elements of an initializer to appear in a fixed |
c1f7febf RK |
1639 | order, the same as the order of the elements in the array or structure |
1640 | being initialized. | |
1641 | ||
26d4fec7 JM |
1642 | In ISO C99 you can give the elements in any order, specifying the array |
1643 | indices or structure field names they apply to, and GNU C allows this as | |
1644 | an extension in C89 mode as well. This extension is not | |
c1f7febf RK |
1645 | implemented in GNU C++. |
1646 | ||
26d4fec7 | 1647 | To specify an array index, write |
c1f7febf RK |
1648 | @samp{[@var{index}] =} before the element value. For example, |
1649 | ||
3ab51846 | 1650 | @smallexample |
26d4fec7 | 1651 | int a[6] = @{ [4] = 29, [2] = 15 @}; |
3ab51846 | 1652 | @end smallexample |
c1f7febf RK |
1653 | |
1654 | @noindent | |
1655 | is equivalent to | |
1656 | ||
3ab51846 | 1657 | @smallexample |
c1f7febf | 1658 | int a[6] = @{ 0, 0, 15, 0, 29, 0 @}; |
3ab51846 | 1659 | @end smallexample |
c1f7febf RK |
1660 | |
1661 | @noindent | |
1662 | The index values must be constant expressions, even if the array being | |
1663 | initialized is automatic. | |
1664 | ||
26d4fec7 JM |
1665 | An alternative syntax for this which has been obsolete since GCC 2.5 but |
1666 | GCC still accepts is to write @samp{[@var{index}]} before the element | |
1667 | value, with no @samp{=}. | |
1668 | ||
c1f7febf | 1669 | To initialize a range of elements to the same value, write |
26d4fec7 JM |
1670 | @samp{[@var{first} ... @var{last}] = @var{value}}. This is a GNU |
1671 | extension. For example, | |
c1f7febf | 1672 | |
3ab51846 | 1673 | @smallexample |
c1f7febf | 1674 | int widths[] = @{ [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 @}; |
3ab51846 | 1675 | @end smallexample |
c1f7febf | 1676 | |
8b6a5902 JJ |
1677 | @noindent |
1678 | If the value in it has side-effects, the side-effects will happen only once, | |
1679 | not for each initialized field by the range initializer. | |
1680 | ||
c1f7febf RK |
1681 | @noindent |
1682 | Note that the length of the array is the highest value specified | |
1683 | plus one. | |
1684 | ||
1685 | In a structure initializer, specify the name of a field to initialize | |
26d4fec7 | 1686 | with @samp{.@var{fieldname} =} before the element value. For example, |
c1f7febf RK |
1687 | given the following structure, |
1688 | ||
3ab51846 | 1689 | @smallexample |
c1f7febf | 1690 | struct point @{ int x, y; @}; |
3ab51846 | 1691 | @end smallexample |
c1f7febf RK |
1692 | |
1693 | @noindent | |
1694 | the following initialization | |
1695 | ||
3ab51846 | 1696 | @smallexample |
26d4fec7 | 1697 | struct point p = @{ .y = yvalue, .x = xvalue @}; |
3ab51846 | 1698 | @end smallexample |
c1f7febf RK |
1699 | |
1700 | @noindent | |
1701 | is equivalent to | |
1702 | ||
3ab51846 | 1703 | @smallexample |
c1f7febf | 1704 | struct point p = @{ xvalue, yvalue @}; |
3ab51846 | 1705 | @end smallexample |
c1f7febf | 1706 | |
26d4fec7 JM |
1707 | Another syntax which has the same meaning, obsolete since GCC 2.5, is |
1708 | @samp{@var{fieldname}:}, as shown here: | |
c1f7febf | 1709 | |
3ab51846 | 1710 | @smallexample |
26d4fec7 | 1711 | struct point p = @{ y: yvalue, x: xvalue @}; |
3ab51846 | 1712 | @end smallexample |
c1f7febf | 1713 | |
4b404517 JM |
1714 | @cindex designators |
1715 | The @samp{[@var{index}]} or @samp{.@var{fieldname}} is known as a | |
1716 | @dfn{designator}. You can also use a designator (or the obsolete colon | |
1717 | syntax) when initializing a union, to specify which element of the union | |
1718 | should be used. For example, | |
c1f7febf | 1719 | |
3ab51846 | 1720 | @smallexample |
c1f7febf RK |
1721 | union foo @{ int i; double d; @}; |
1722 | ||
26d4fec7 | 1723 | union foo f = @{ .d = 4 @}; |
3ab51846 | 1724 | @end smallexample |
c1f7febf RK |
1725 | |
1726 | @noindent | |
1727 | will convert 4 to a @code{double} to store it in the union using | |
1728 | the second element. By contrast, casting 4 to type @code{union foo} | |
1729 | would store it into the union as the integer @code{i}, since it is | |
1730 | an integer. (@xref{Cast to Union}.) | |
1731 | ||
1732 | You can combine this technique of naming elements with ordinary C | |
1733 | initialization of successive elements. Each initializer element that | |
4b404517 | 1734 | does not have a designator applies to the next consecutive element of the |
c1f7febf RK |
1735 | array or structure. For example, |
1736 | ||
3ab51846 | 1737 | @smallexample |
c1f7febf | 1738 | int a[6] = @{ [1] = v1, v2, [4] = v4 @}; |
3ab51846 | 1739 | @end smallexample |
c1f7febf RK |
1740 | |
1741 | @noindent | |
1742 | is equivalent to | |
1743 | ||
3ab51846 | 1744 | @smallexample |
c1f7febf | 1745 | int a[6] = @{ 0, v1, v2, 0, v4, 0 @}; |
3ab51846 | 1746 | @end smallexample |
c1f7febf RK |
1747 | |
1748 | Labeling the elements of an array initializer is especially useful | |
1749 | when the indices are characters or belong to an @code{enum} type. | |
1750 | For example: | |
1751 | ||
3ab51846 | 1752 | @smallexample |
c1f7febf RK |
1753 | int whitespace[256] |
1754 | = @{ [' '] = 1, ['\t'] = 1, ['\h'] = 1, | |
1755 | ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 @}; | |
3ab51846 | 1756 | @end smallexample |
c1f7febf | 1757 | |
4b404517 | 1758 | @cindex designator lists |
26d4fec7 | 1759 | You can also write a series of @samp{.@var{fieldname}} and |
4b404517 | 1760 | @samp{[@var{index}]} designators before an @samp{=} to specify a |
26d4fec7 JM |
1761 | nested subobject to initialize; the list is taken relative to the |
1762 | subobject corresponding to the closest surrounding brace pair. For | |
1763 | example, with the @samp{struct point} declaration above: | |
1764 | ||
478c9e72 | 1765 | @smallexample |
26d4fec7 | 1766 | struct point ptarray[10] = @{ [2].y = yv2, [2].x = xv2, [0].x = xv0 @}; |
478c9e72 | 1767 | @end smallexample |
26d4fec7 | 1768 | |
8b6a5902 JJ |
1769 | @noindent |
1770 | If the same field is initialized multiple times, it will have value from | |
1771 | the last initialization. If any such overridden initialization has | |
1772 | side-effect, it is unspecified whether the side-effect happens or not. | |
2dd76960 | 1773 | Currently, GCC will discard them and issue a warning. |
8b6a5902 | 1774 | |
c1f7febf RK |
1775 | @node Case Ranges |
1776 | @section Case Ranges | |
1777 | @cindex case ranges | |
1778 | @cindex ranges in case statements | |
1779 | ||
1780 | You can specify a range of consecutive values in a single @code{case} label, | |
1781 | like this: | |
1782 | ||
3ab51846 | 1783 | @smallexample |
c1f7febf | 1784 | case @var{low} ... @var{high}: |
3ab51846 | 1785 | @end smallexample |
c1f7febf RK |
1786 | |
1787 | @noindent | |
1788 | This has the same effect as the proper number of individual @code{case} | |
1789 | labels, one for each integer value from @var{low} to @var{high}, inclusive. | |
1790 | ||
1791 | This feature is especially useful for ranges of ASCII character codes: | |
1792 | ||
3ab51846 | 1793 | @smallexample |
c1f7febf | 1794 | case 'A' ... 'Z': |
3ab51846 | 1795 | @end smallexample |
c1f7febf RK |
1796 | |
1797 | @strong{Be careful:} Write spaces around the @code{...}, for otherwise | |
1798 | it may be parsed wrong when you use it with integer values. For example, | |
1799 | write this: | |
1800 | ||
3ab51846 | 1801 | @smallexample |
c1f7febf | 1802 | case 1 ... 5: |
3ab51846 | 1803 | @end smallexample |
c1f7febf RK |
1804 | |
1805 | @noindent | |
1806 | rather than this: | |
1807 | ||
3ab51846 | 1808 | @smallexample |
c1f7febf | 1809 | case 1...5: |
3ab51846 | 1810 | @end smallexample |
c1f7febf RK |
1811 | |
1812 | @node Cast to Union | |
1813 | @section Cast to a Union Type | |
1814 | @cindex cast to a union | |
1815 | @cindex union, casting to a | |
1816 | ||
1817 | A cast to union type is similar to other casts, except that the type | |
1818 | specified is a union type. You can specify the type either with | |
1819 | @code{union @var{tag}} or with a typedef name. A cast to union is actually | |
1820 | a constructor though, not a cast, and hence does not yield an lvalue like | |
4b404517 | 1821 | normal casts. (@xref{Compound Literals}.) |
c1f7febf RK |
1822 | |
1823 | The types that may be cast to the union type are those of the members | |
1824 | of the union. Thus, given the following union and variables: | |
1825 | ||
3ab51846 | 1826 | @smallexample |
c1f7febf RK |
1827 | union foo @{ int i; double d; @}; |
1828 | int x; | |
1829 | double y; | |
3ab51846 | 1830 | @end smallexample |
c1f7febf RK |
1831 | |
1832 | @noindent | |
aee96fe9 | 1833 | both @code{x} and @code{y} can be cast to type @code{union foo}. |
c1f7febf RK |
1834 | |
1835 | Using the cast as the right-hand side of an assignment to a variable of | |
1836 | union type is equivalent to storing in a member of the union: | |
1837 | ||
3ab51846 | 1838 | @smallexample |
c1f7febf | 1839 | union foo u; |
0d893a63 | 1840 | /* @r{@dots{}} */ |
c1f7febf RK |
1841 | u = (union foo) x @equiv{} u.i = x |
1842 | u = (union foo) y @equiv{} u.d = y | |
3ab51846 | 1843 | @end smallexample |
c1f7febf RK |
1844 | |
1845 | You can also use the union cast as a function argument: | |
1846 | ||
3ab51846 | 1847 | @smallexample |
c1f7febf | 1848 | void hack (union foo); |
0d893a63 | 1849 | /* @r{@dots{}} */ |
c1f7febf | 1850 | hack ((union foo) x); |
3ab51846 | 1851 | @end smallexample |
c1f7febf | 1852 | |
4b404517 JM |
1853 | @node Mixed Declarations |
1854 | @section Mixed Declarations and Code | |
1855 | @cindex mixed declarations and code | |
1856 | @cindex declarations, mixed with code | |
1857 | @cindex code, mixed with declarations | |
1858 | ||
1859 | ISO C99 and ISO C++ allow declarations and code to be freely mixed | |
1860 | within compound statements. As an extension, GCC also allows this in | |
1861 | C89 mode. For example, you could do: | |
1862 | ||
3ab51846 | 1863 | @smallexample |
4b404517 | 1864 | int i; |
0d893a63 | 1865 | /* @r{@dots{}} */ |
4b404517 JM |
1866 | i++; |
1867 | int j = i + 2; | |
3ab51846 | 1868 | @end smallexample |
4b404517 JM |
1869 | |
1870 | Each identifier is visible from where it is declared until the end of | |
1871 | the enclosing block. | |
1872 | ||
c1f7febf RK |
1873 | @node Function Attributes |
1874 | @section Declaring Attributes of Functions | |
1875 | @cindex function attributes | |
1876 | @cindex declaring attributes of functions | |
1877 | @cindex functions that never return | |
1878 | @cindex functions that have no side effects | |
1879 | @cindex functions in arbitrary sections | |
2a59078d | 1880 | @cindex functions that behave like malloc |
c1f7febf RK |
1881 | @cindex @code{volatile} applied to function |
1882 | @cindex @code{const} applied to function | |
26f6672d | 1883 | @cindex functions with @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style arguments |
b34c7881 | 1884 | @cindex functions with non-null pointer arguments |
c1f7febf RK |
1885 | @cindex functions that are passed arguments in registers on the 386 |
1886 | @cindex functions that pop the argument stack on the 386 | |
1887 | @cindex functions that do not pop the argument stack on the 386 | |
1888 | ||
1889 | In GNU C, you declare certain things about functions called in your program | |
1890 | which help the compiler optimize function calls and check your code more | |
1891 | carefully. | |
1892 | ||
1893 | The keyword @code{__attribute__} allows you to specify special | |
1894 | attributes when making a declaration. This keyword is followed by an | |
9162542e | 1895 | attribute specification inside double parentheses. The following |
eacecf96 | 1896 | attributes are currently defined for functions on all targets: |
6aa77e6c | 1897 | @code{noreturn}, @code{noinline}, @code{always_inline}, |
39f2f3c8 | 1898 | @code{pure}, @code{const}, @code{nothrow}, |
9162542e AO |
1899 | @code{format}, @code{format_arg}, @code{no_instrument_function}, |
1900 | @code{section}, @code{constructor}, @code{destructor}, @code{used}, | |
b34c7881 | 1901 | @code{unused}, @code{deprecated}, @code{weak}, @code{malloc}, |
72954a4f JM |
1902 | @code{alias}, @code{warn_unused_result} and @code{nonnull}. Several other |
1903 | attributes are defined for functions on particular target systems. Other | |
1904 | attributes, including @code{section} are supported for variables declarations | |
b34c7881 | 1905 | (@pxref{Variable Attributes}) and for types (@pxref{Type Attributes}). |
c1f7febf RK |
1906 | |
1907 | You may also specify attributes with @samp{__} preceding and following | |
1908 | each keyword. This allows you to use them in header files without | |
1909 | being concerned about a possible macro of the same name. For example, | |
1910 | you may use @code{__noreturn__} instead of @code{noreturn}. | |
1911 | ||
2c5e91d2 JM |
1912 | @xref{Attribute Syntax}, for details of the exact syntax for using |
1913 | attributes. | |
1914 | ||
c1f7febf | 1915 | @table @code |
c8619b90 | 1916 | @c Keep this table alphabetized by attribute name. Treat _ as space. |
c1f7febf | 1917 | |
c8619b90 NS |
1918 | @item alias ("@var{target}") |
1919 | @cindex @code{alias} attribute | |
1920 | The @code{alias} attribute causes the declaration to be emitted as an | |
1921 | alias for another symbol, which must be specified. For instance, | |
c1f7febf RK |
1922 | |
1923 | @smallexample | |
c8619b90 NS |
1924 | void __f () @{ /* @r{Do something.} */; @} |
1925 | void f () __attribute__ ((weak, alias ("__f"))); | |
c1f7febf RK |
1926 | @end smallexample |
1927 | ||
c8619b90 NS |
1928 | declares @samp{f} to be a weak alias for @samp{__f}. In C++, the |
1929 | mangled name for the target must be used. | |
1930 | ||
1931 | Not all target machines support this attribute. | |
9162542e | 1932 | |
6aa77e6c | 1933 | @item always_inline |
c8619b90 | 1934 | @cindex @code{always_inline} function attribute |
6aa77e6c AH |
1935 | Generally, functions are not inlined unless optimization is specified. |
1936 | For functions declared inline, this attribute inlines the function even | |
1937 | if no optimization level was specified. | |
1938 | ||
c8619b90 NS |
1939 | @item cdecl |
1940 | @cindex functions that do pop the argument stack on the 386 | |
1941 | @opindex mrtd | |
1942 | On the Intel 386, the @code{cdecl} attribute causes the compiler to | |
1943 | assume that the calling function will pop off the stack space used to | |
1944 | pass arguments. This is | |
1945 | useful to override the effects of the @option{-mrtd} switch. | |
2a8f6b90 | 1946 | |
2a8f6b90 | 1947 | @item const |
c8619b90 | 1948 | @cindex @code{const} function attribute |
2a8f6b90 JH |
1949 | Many functions do not examine any values except their arguments, and |
1950 | have no effects except the return value. Basically this is just slightly | |
84330467 | 1951 | more strict class than the @code{pure} attribute above, since function is not |
2a59078d | 1952 | allowed to read global memory. |
2a8f6b90 JH |
1953 | |
1954 | @cindex pointer arguments | |
1955 | Note that a function that has pointer arguments and examines the data | |
1956 | pointed to must @emph{not} be declared @code{const}. Likewise, a | |
1957 | function that calls a non-@code{const} function usually must not be | |
1958 | @code{const}. It does not make sense for a @code{const} function to | |
1959 | return @code{void}. | |
1960 | ||
f0523f02 | 1961 | The attribute @code{const} is not implemented in GCC versions earlier |
c1f7febf RK |
1962 | than 2.5. An alternative way to declare that a function has no side |
1963 | effects, which works in the current version and in some older versions, | |
1964 | is as follows: | |
1965 | ||
1966 | @smallexample | |
1967 | typedef int intfn (); | |
1968 | ||
1969 | extern const intfn square; | |
1970 | @end smallexample | |
1971 | ||
1972 | This approach does not work in GNU C++ from 2.6.0 on, since the language | |
1973 | specifies that the @samp{const} must be attached to the return value. | |
1974 | ||
c8619b90 NS |
1975 | @item constructor |
1976 | @itemx destructor | |
1977 | @cindex @code{constructor} function attribute | |
1978 | @cindex @code{destructor} function attribute | |
1979 | The @code{constructor} attribute causes the function to be called | |
1980 | automatically before execution enters @code{main ()}. Similarly, the | |
1981 | @code{destructor} attribute causes the function to be called | |
1982 | automatically after @code{main ()} has completed or @code{exit ()} has | |
1983 | been called. Functions with these attributes are useful for | |
1984 | initializing data that will be used implicitly during the execution of | |
1985 | the program. | |
1986 | ||
1987 | These attributes are not currently implemented for Objective-C@. | |
1988 | ||
1989 | @item deprecated | |
1990 | @cindex @code{deprecated} attribute. | |
1991 | The @code{deprecated} attribute results in a warning if the function | |
1992 | is used anywhere in the source file. This is useful when identifying | |
1993 | functions that are expected to be removed in a future version of a | |
1994 | program. The warning also includes the location of the declaration | |
1995 | of the deprecated function, to enable users to easily find further | |
1996 | information about why the function is deprecated, or what they should | |
1997 | do instead. Note that the warnings only occurs for uses: | |
1998 | ||
1999 | @smallexample | |
2000 | int old_fn () __attribute__ ((deprecated)); | |
2001 | int old_fn (); | |
2002 | int (*fn_ptr)() = old_fn; | |
2003 | @end smallexample | |
2004 | ||
2005 | results in a warning on line 3 but not line 2. | |
2006 | ||
2007 | The @code{deprecated} attribute can also be used for variables and | |
2008 | types (@pxref{Variable Attributes}, @pxref{Type Attributes}.) | |
2009 | ||
2010 | @item dllexport | |
2011 | @cindex @code{__declspec(dllexport)} | |
2012 | On Microsoft Windows targets the @code{dllexport} attribute causes the | |
2013 | compiler to provide a global pointer to a pointer in a dll, so that it | |
2014 | can be referenced with the @code{dllimport} attribute. The pointer name | |
2015 | is formed by combining @code{_imp__} and the function or variable name. | |
2016 | ||
2017 | Currently, the @code{dllexport}attribute is ignored for inlined | |
2018 | functions, but export can be forced by using the | |
2019 | @option{-fkeep-inline-functions} flag. The attribute is also ignored for | |
2020 | undefined symbols. | |
2021 | ||
2022 | When applied to C++ classes. the attribute marks defined non-inlined | |
2023 | member functions and static data members as exports. Static consts | |
2024 | initialized in-class are not marked unless they are also defined | |
2025 | out-of-class. | |
2026 | ||
2027 | On cygwin, mingw and arm-pe targets, @code{__declspec(dllexport)} is | |
2028 | recognized as a synonym for @code{__attribute__ ((dllexport))} for | |
2029 | compatibility with other Microsoft Windows compilers. | |
2030 | ||
2031 | Alternative methods for including the symbol in the dll's export table | |
2032 | are to use a .def file with an @code{EXPORTS} section or, with GNU ld, | |
2033 | using the @option{--export-all} linker flag. | |
2034 | ||
2035 | @item dllimport | |
2036 | @cindex @code{__declspec(dllimport)} | |
2037 | On Microsoft Windows targets, the @code{dllimport} attribute causes the | |
2038 | compiler to reference a function or variable via a global pointer to a | |
2039 | pointer that is set up by the Microsoft Windows dll library. The pointer | |
2040 | name is formed by combining @code{_imp__} and the function or variable | |
2041 | name. The attribute implies @code{extern} storage. | |
2042 | ||
2043 | Currently, the attribute is ignored for inlined functions. If the | |
2044 | attribute is applied to a symbol @emph{definition}, an error is reported. | |
2045 | If a symbol previously declared @code{dllimport} is later defined, the | |
2046 | attribute is ignored in subsequent references, and a warning is emitted. | |
2047 | The attribute is also overridden by a subsequent declaration as | |
2048 | @code{dllexport}. | |
2049 | ||
2050 | When applied to C++ classes, the attribute marks non-inlined | |
2051 | member functions and static data members as imports. However, the | |
2052 | attribute is ignored for virtual methods to allow creation of vtables | |
2053 | using thunks. | |
2054 | ||
2055 | On cygwin, mingw and arm-pe targets, @code{__declspec(dllimport)} is | |
2056 | recognized as a synonym for @code{__attribute__ ((dllimport))} for | |
2057 | compatibility with other Microsoft Windows compilers. | |
2058 | ||
2059 | The use of the @code{dllimport} attribute on functions is not necessary, | |
2060 | but provides a small performance benefit by eliminating a thunk in the | |
2061 | dll. The use of the @code{dllimport} attribute on imported variables was | |
2062 | required on older versions of GNU ld, but can now be avoided by passing | |
2063 | the @option{--enable-auto-import} switch to ld. As with functions, using | |
2064 | the attribute for a variable eliminates a thunk in the dll. | |
2065 | ||
2066 | One drawback to using this attribute is that a pointer to a function or | |
2067 | variable marked as dllimport cannot be used as a constant address. The | |
2068 | attribute can be disabled for functions by setting the | |
2069 | @option{-mnop-fun-dllimport} flag. | |
2070 | ||
2071 | @item eightbit_data | |
2072 | @cindex eight bit data on the H8/300, H8/300H, and H8S | |
2073 | Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified | |
2074 | variable should be placed into the eight bit data section. | |
2075 | The compiler will generate more efficient code for certain operations | |
2076 | on data in the eight bit data area. Note the eight bit data area is limited to | |
2077 | 256 bytes of data. | |
2078 | ||
2079 | You must use GAS and GLD from GNU binutils version 2.7 or later for | |
2080 | this attribute to work correctly. | |
2081 | ||
2082 | @item far | |
2083 | @cindex functions which handle memory bank switching | |
2084 | On 68HC11 and 68HC12 the @code{far} attribute causes the compiler to | |
2085 | use a calling convention that takes care of switching memory banks when | |
2086 | entering and leaving a function. This calling convention is also the | |
2087 | default when using the @option{-mlong-calls} option. | |
2088 | ||
2089 | On 68HC12 the compiler will use the @code{call} and @code{rtc} instructions | |
2090 | to call and return from a function. | |
2091 | ||
2092 | On 68HC11 the compiler will generate a sequence of instructions | |
2093 | to invoke a board-specific routine to switch the memory bank and call the | |
2094 | real function. The board-specific routine simulates a @code{call}. | |
2095 | At the end of a function, it will jump to a board-specific routine | |
2096 | instead of using @code{rts}. The board-specific return routine simulates | |
2097 | the @code{rtc}. | |
2098 | ||
2099 | @item fastcall | |
2100 | @cindex functions that pop the argument stack on the 386 | |
2101 | On the Intel 386, the @code{fastcall} attribute causes the compiler to | |
2102 | pass the first two arguments in the registers ECX and EDX. Subsequent | |
2103 | arguments are passed on the stack. The called function will pop the | |
2104 | arguments off the stack. If the number of arguments is variable all | |
2105 | arguments are pushed on the stack. | |
c1f7febf RK |
2106 | |
2107 | @item format (@var{archetype}, @var{string-index}, @var{first-to-check}) | |
2108 | @cindex @code{format} function attribute | |
84330467 | 2109 | @opindex Wformat |
bb72a084 | 2110 | The @code{format} attribute specifies that a function takes @code{printf}, |
26f6672d JM |
2111 | @code{scanf}, @code{strftime} or @code{strfmon} style arguments which |
2112 | should be type-checked against a format string. For example, the | |
2113 | declaration: | |
c1f7febf RK |
2114 | |
2115 | @smallexample | |
2116 | extern int | |
2117 | my_printf (void *my_object, const char *my_format, ...) | |
2118 | __attribute__ ((format (printf, 2, 3))); | |
2119 | @end smallexample | |
2120 | ||
2121 | @noindent | |
2122 | causes the compiler to check the arguments in calls to @code{my_printf} | |
2123 | for consistency with the @code{printf} style format string argument | |
2124 | @code{my_format}. | |
2125 | ||
2126 | The parameter @var{archetype} determines how the format string is | |
26f6672d JM |
2127 | interpreted, and should be @code{printf}, @code{scanf}, @code{strftime} |
2128 | or @code{strfmon}. (You can also use @code{__printf__}, | |
2129 | @code{__scanf__}, @code{__strftime__} or @code{__strfmon__}.) The | |
c1f7febf RK |
2130 | parameter @var{string-index} specifies which argument is the format |
2131 | string argument (starting from 1), while @var{first-to-check} is the | |
2132 | number of the first argument to check against the format string. For | |
2133 | functions where the arguments are not available to be checked (such as | |
2134 | @code{vprintf}), specify the third parameter as zero. In this case the | |
b722c82c JM |
2135 | compiler only checks the format string for consistency. For |
2136 | @code{strftime} formats, the third parameter is required to be zero. | |
f57a2e3a BE |
2137 | Since non-static C++ methods have an implicit @code{this} argument, the |
2138 | arguments of such methods should be counted from two, not one, when | |
2139 | giving values for @var{string-index} and @var{first-to-check}. | |
c1f7febf RK |
2140 | |
2141 | In the example above, the format string (@code{my_format}) is the second | |
2142 | argument of the function @code{my_print}, and the arguments to check | |
2143 | start with the third argument, so the correct parameters for the format | |
2144 | attribute are 2 and 3. | |
2145 | ||
84330467 | 2146 | @opindex ffreestanding |
c1f7febf | 2147 | The @code{format} attribute allows you to identify your own functions |
f0523f02 | 2148 | which take format strings as arguments, so that GCC can check the |
b722c82c | 2149 | calls to these functions for errors. The compiler always (unless |
84330467 | 2150 | @option{-ffreestanding} is used) checks formats |
b722c82c | 2151 | for the standard library functions @code{printf}, @code{fprintf}, |
bb72a084 | 2152 | @code{sprintf}, @code{scanf}, @code{fscanf}, @code{sscanf}, @code{strftime}, |
c1f7febf | 2153 | @code{vprintf}, @code{vfprintf} and @code{vsprintf} whenever such |
84330467 | 2154 | warnings are requested (using @option{-Wformat}), so there is no need to |
b722c82c JM |
2155 | modify the header file @file{stdio.h}. In C99 mode, the functions |
2156 | @code{snprintf}, @code{vsnprintf}, @code{vscanf}, @code{vfscanf} and | |
26f6672d | 2157 | @code{vsscanf} are also checked. Except in strictly conforming C |
b4c984fb KG |
2158 | standard modes, the X/Open function @code{strfmon} is also checked as |
2159 | are @code{printf_unlocked} and @code{fprintf_unlocked}. | |
b722c82c | 2160 | @xref{C Dialect Options,,Options Controlling C Dialect}. |
c1f7febf RK |
2161 | |
2162 | @item format_arg (@var{string-index}) | |
2163 | @cindex @code{format_arg} function attribute | |
84330467 | 2164 | @opindex Wformat-nonliteral |
26f6672d JM |
2165 | The @code{format_arg} attribute specifies that a function takes a format |
2166 | string for a @code{printf}, @code{scanf}, @code{strftime} or | |
2167 | @code{strfmon} style function and modifies it (for example, to translate | |
2168 | it into another language), so the result can be passed to a | |
2169 | @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style | |
2170 | function (with the remaining arguments to the format function the same | |
2171 | as they would have been for the unmodified string). For example, the | |
2172 | declaration: | |
c1f7febf RK |
2173 | |
2174 | @smallexample | |
2175 | extern char * | |
2176 | my_dgettext (char *my_domain, const char *my_format) | |
2177 | __attribute__ ((format_arg (2))); | |
2178 | @end smallexample | |
2179 | ||
2180 | @noindent | |
26f6672d JM |
2181 | causes the compiler to check the arguments in calls to a @code{printf}, |
2182 | @code{scanf}, @code{strftime} or @code{strfmon} type function, whose | |
2183 | format string argument is a call to the @code{my_dgettext} function, for | |
2184 | consistency with the format string argument @code{my_format}. If the | |
2185 | @code{format_arg} attribute had not been specified, all the compiler | |
2186 | could tell in such calls to format functions would be that the format | |
2187 | string argument is not constant; this would generate a warning when | |
84330467 | 2188 | @option{-Wformat-nonliteral} is used, but the calls could not be checked |
26f6672d | 2189 | without the attribute. |
c1f7febf RK |
2190 | |
2191 | The parameter @var{string-index} specifies which argument is the format | |
f57a2e3a BE |
2192 | string argument (starting from one). Since non-static C++ methods have |
2193 | an implicit @code{this} argument, the arguments of such methods should | |
2194 | be counted from two. | |
c1f7febf RK |
2195 | |
2196 | The @code{format-arg} attribute allows you to identify your own | |
f0523f02 | 2197 | functions which modify format strings, so that GCC can check the |
26f6672d JM |
2198 | calls to @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} |
2199 | type function whose operands are a call to one of your own function. | |
2200 | The compiler always treats @code{gettext}, @code{dgettext}, and | |
2201 | @code{dcgettext} in this manner except when strict ISO C support is | |
84330467 JM |
2202 | requested by @option{-ansi} or an appropriate @option{-std} option, or |
2203 | @option{-ffreestanding} is used. @xref{C Dialect Options,,Options | |
26f6672d | 2204 | Controlling C Dialect}. |
c1f7febf | 2205 | |
c8619b90 NS |
2206 | @item function_vector |
2207 | @cindex calling functions through the function vector on the H8/300 processors | |
2208 | Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified | |
2209 | function should be called through the function vector. Calling a | |
2210 | function through the function vector will reduce code size, however; | |
2211 | the function vector has a limited size (maximum 128 entries on the H8/300 | |
2212 | and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector. | |
b34c7881 | 2213 | |
c8619b90 NS |
2214 | You must use GAS and GLD from GNU binutils version 2.7 or later for |
2215 | this attribute to work correctly. | |
b34c7881 | 2216 | |
c8619b90 NS |
2217 | @item interrupt |
2218 | @cindex interrupt handler functions | |
2219 | Use this attribute on the ARM, AVR, C4x, M32R/D and Xstormy16 ports to indicate | |
2220 | that the specified function is an interrupt handler. The compiler will | |
2221 | generate function entry and exit sequences suitable for use in an | |
2222 | interrupt handler when this attribute is present. | |
b34c7881 | 2223 | |
c8619b90 NS |
2224 | Note, interrupt handlers for the m68k, H8/300, H8/300H, H8S, and SH processors |
2225 | can be specified via the @code{interrupt_handler} attribute. | |
b34c7881 | 2226 | |
c8619b90 | 2227 | Note, on the AVR, interrupts will be enabled inside the function. |
9162542e | 2228 | |
c8619b90 NS |
2229 | Note, for the ARM, you can specify the kind of interrupt to be handled by |
2230 | adding an optional parameter to the interrupt attribute like this: | |
e23bd218 IR |
2231 | |
2232 | @smallexample | |
c8619b90 | 2233 | void f () __attribute__ ((interrupt ("IRQ"))); |
e23bd218 IR |
2234 | @end smallexample |
2235 | ||
c8619b90 | 2236 | Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF@. |
e23bd218 | 2237 | |
c8619b90 NS |
2238 | @item interrupt_handler |
2239 | @cindex interrupt handler functions on the m68k, H8/300 and SH processors | |
2240 | Use this attribute on the m68k, H8/300, H8/300H, H8S, and SH to indicate that | |
2241 | the specified function is an interrupt handler. The compiler will generate | |
2242 | function entry and exit sequences suitable for use in an interrupt | |
2243 | handler when this attribute is present. | |
72954a4f | 2244 | |
c8619b90 NS |
2245 | @item long_call/short_call |
2246 | @cindex indirect calls on ARM | |
2247 | This attribute specifies how a particular function is called on | |
2248 | ARM@. Both attributes override the @option{-mlong-calls} (@pxref{ARM Options}) | |
2249 | command line switch and @code{#pragma long_calls} settings. The | |
2250 | @code{long_call} attribute causes the compiler to always call the | |
2251 | function by first loading its address into a register and then using the | |
2252 | contents of that register. The @code{short_call} attribute always places | |
2253 | the offset to the function from the call site into the @samp{BL} | |
2254 | instruction directly. | |
72954a4f | 2255 | |
c8619b90 NS |
2256 | @item longcall/shortcall |
2257 | @cindex functions called via pointer on the RS/6000 and PowerPC | |
2258 | On the RS/6000 and PowerPC, the @code{longcall} attribute causes the | |
2259 | compiler to always call this function via a pointer, just as it would if | |
2260 | the @option{-mlongcall} option had been specified. The @code{shortcall} | |
2261 | attribute causes the compiler not to do this. These attributes override | |
2262 | both the @option{-mlongcall} switch and the @code{#pragma longcall} | |
2263 | setting. | |
72954a4f | 2264 | |
c8619b90 NS |
2265 | @xref{RS/6000 and PowerPC Options}, for more information on whether long |
2266 | calls are necessary. | |
c1f7febf | 2267 | |
140592a0 AG |
2268 | @item malloc |
2269 | @cindex @code{malloc} attribute | |
2270 | The @code{malloc} attribute is used to tell the compiler that a function | |
928a5ba9 JM |
2271 | may be treated as if any non-@code{NULL} pointer it returns cannot |
2272 | alias any other pointer valid when the function returns. | |
140592a0 | 2273 | This will often improve optimization. |
928a5ba9 JM |
2274 | Standard functions with this property include @code{malloc} and |
2275 | @code{calloc}. @code{realloc}-like functions have this property as | |
2276 | long as the old pointer is never referred to (including comparing it | |
2277 | to the new pointer) after the function returns a non-@code{NULL} | |
2278 | value. | |
140592a0 | 2279 | |
c8619b90 NS |
2280 | @item model (@var{model-name}) |
2281 | @cindex function addressability on the M32R/D | |
2282 | @cindex variable addressability on the IA-64 | |
2283 | ||
2284 | On the M32R/D, use this attribute to set the addressability of an | |
2285 | object, and of the code generated for a function. The identifier | |
2286 | @var{model-name} is one of @code{small}, @code{medium}, or | |
2287 | @code{large}, representing each of the code models. | |
2288 | ||
2289 | Small model objects live in the lower 16MB of memory (so that their | |
2290 | addresses can be loaded with the @code{ld24} instruction), and are | |
2291 | callable with the @code{bl} instruction. | |
2292 | ||
2293 | Medium model objects may live anywhere in the 32-bit address space (the | |
2294 | compiler will generate @code{seth/add3} instructions to load their addresses), | |
2295 | and are callable with the @code{bl} instruction. | |
2296 | ||
2297 | Large model objects may live anywhere in the 32-bit address space (the | |
2298 | compiler will generate @code{seth/add3} instructions to load their addresses), | |
2299 | and may not be reachable with the @code{bl} instruction (the compiler will | |
2300 | generate the much slower @code{seth/add3/jl} instruction sequence). | |
2301 | ||
2302 | On IA-64, use this attribute to set the addressability of an object. | |
2303 | At present, the only supported identifier for @var{model-name} is | |
2304 | @code{small}, indicating addressability via ``small'' (22-bit) | |
2305 | addresses (so that their addresses can be loaded with the @code{addl} | |
2306 | instruction). Caveat: such addressing is by definition not position | |
2307 | independent and hence this attribute must not be used for objects | |
2308 | defined by shared libraries. | |
2309 | ||
2310 | @item naked | |
2311 | @cindex function without a prologue/epilogue code | |
2312 | Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate that the | |
2313 | specified function does not need prologue/epilogue sequences generated by | |
2314 | the compiler. It is up to the programmer to provide these sequences. | |
2315 | ||
2316 | @item near | |
2317 | @cindex functions which do not handle memory bank switching on 68HC11/68HC12 | |
2318 | On 68HC11 and 68HC12 the @code{near} attribute causes the compiler to | |
2319 | use the normal calling convention based on @code{jsr} and @code{rts}. | |
2320 | This attribute can be used to cancel the effect of the @option{-mlong-calls} | |
2321 | option. | |
2322 | ||
2323 | @item no_instrument_function | |
2324 | @cindex @code{no_instrument_function} function attribute | |
2325 | @opindex finstrument-functions | |
2326 | If @option{-finstrument-functions} is given, profiling function calls will | |
2327 | be generated at entry and exit of most user-compiled functions. | |
2328 | Functions with this attribute will not be so instrumented. | |
2329 | ||
2330 | @item noinline | |
2331 | @cindex @code{noinline} function attribute | |
2332 | This function attribute prevents a function from being considered for | |
2333 | inlining. | |
2334 | ||
2335 | @item nonnull (@var{arg-index}, @dots{}) | |
2336 | @cindex @code{nonnull} function attribute | |
2337 | The @code{nonnull} attribute specifies that some function parameters should | |
2338 | be non-null pointers. For instance, the declaration: | |
c1f7febf RK |
2339 | |
2340 | @smallexample | |
c8619b90 NS |
2341 | extern void * |
2342 | my_memcpy (void *dest, const void *src, size_t len) | |
2343 | __attribute__((nonnull (1, 2))); | |
c1f7febf RK |
2344 | @end smallexample |
2345 | ||
c8619b90 NS |
2346 | @noindent |
2347 | causes the compiler to check that, in calls to @code{my_memcpy}, | |
2348 | arguments @var{dest} and @var{src} are non-null. If the compiler | |
2349 | determines that a null pointer is passed in an argument slot marked | |
2350 | as non-null, and the @option{-Wnonnull} option is enabled, a warning | |
2351 | is issued. The compiler may also choose to make optimizations based | |
2352 | on the knowledge that certain function arguments will not be null. | |
af3e86c2 | 2353 | |
c8619b90 NS |
2354 | If no argument index list is given to the @code{nonnull} attribute, |
2355 | all pointer arguments are marked as non-null. To illustrate, the | |
2356 | following declaration is equivalent to the previous example: | |
47bd70b5 JJ |
2357 | |
2358 | @smallexample | |
c8619b90 NS |
2359 | extern void * |
2360 | my_memcpy (void *dest, const void *src, size_t len) | |
2361 | __attribute__((nonnull)); | |
47bd70b5 JJ |
2362 | @end smallexample |
2363 | ||
c8619b90 NS |
2364 | @item noreturn |
2365 | @cindex @code{noreturn} function attribute | |
2366 | A few standard library functions, such as @code{abort} and @code{exit}, | |
2367 | cannot return. GCC knows this automatically. Some programs define | |
2368 | their own functions that never return. You can declare them | |
2369 | @code{noreturn} to tell the compiler this fact. For example, | |
9e8aab55 | 2370 | |
c8619b90 NS |
2371 | @smallexample |
2372 | @group | |
2373 | void fatal () __attribute__ ((noreturn)); | |
d5c4db17 | 2374 | |
c8619b90 NS |
2375 | void |
2376 | fatal (/* @r{@dots{}} */) | |
2377 | @{ | |
2378 | /* @r{@dots{}} */ /* @r{Print error message.} */ /* @r{@dots{}} */ | |
2379 | exit (1); | |
2380 | @} | |
2381 | @end group | |
2382 | @end smallexample | |
9e8aab55 | 2383 | |
c8619b90 NS |
2384 | The @code{noreturn} keyword tells the compiler to assume that |
2385 | @code{fatal} cannot return. It can then optimize without regard to what | |
2386 | would happen if @code{fatal} ever did return. This makes slightly | |
2387 | better code. More importantly, it helps avoid spurious warnings of | |
2388 | uninitialized variables. | |
9e8aab55 | 2389 | |
c8619b90 NS |
2390 | The @code{noreturn} keyword does not affect the exceptional path when that |
2391 | applies: a @code{noreturn}-marked function may still return to the caller | |
2392 | by throwing an exception. | |
9e8aab55 | 2393 | |
c8619b90 NS |
2394 | Do not assume that registers saved by the calling function are |
2395 | restored before calling the @code{noreturn} function. | |
47bd70b5 | 2396 | |
c8619b90 NS |
2397 | It does not make sense for a @code{noreturn} function to have a return |
2398 | type other than @code{void}. | |
c1f7febf | 2399 | |
c8619b90 NS |
2400 | The attribute @code{noreturn} is not implemented in GCC versions |
2401 | earlier than 2.5. An alternative way to declare that a function does | |
2402 | not return, which works in the current version and in some older | |
2403 | versions, is as follows: | |
5d34c8e9 | 2404 | |
c8619b90 NS |
2405 | @smallexample |
2406 | typedef void voidfn (); | |
c1f7febf | 2407 | |
c8619b90 NS |
2408 | volatile voidfn fatal; |
2409 | @end smallexample | |
e91f04de | 2410 | |
c8619b90 NS |
2411 | @item nothrow |
2412 | @cindex @code{nothrow} function attribute | |
2413 | The @code{nothrow} attribute is used to inform the compiler that a | |
2414 | function cannot throw an exception. For example, most functions in | |
2415 | the standard C library can be guaranteed not to throw an exception | |
2416 | with the notable exceptions of @code{qsort} and @code{bsearch} that | |
2417 | take function pointer arguments. The @code{nothrow} attribute is not | |
2418 | implemented in GCC versions earlier than 3.2. | |
c1f7febf | 2419 | |
c8619b90 NS |
2420 | @item pure |
2421 | @cindex @code{pure} function attribute | |
2422 | Many functions have no effects except the return value and their | |
2423 | return value depends only on the parameters and/or global variables. | |
2424 | Such a function can be subject | |
2425 | to common subexpression elimination and loop optimization just as an | |
2426 | arithmetic operator would be. These functions should be declared | |
2427 | with the attribute @code{pure}. For example, | |
a5c76ee6 | 2428 | |
c8619b90 NS |
2429 | @smallexample |
2430 | int square (int) __attribute__ ((pure)); | |
2431 | @end smallexample | |
c1f7febf | 2432 | |
c8619b90 NS |
2433 | @noindent |
2434 | says that the hypothetical function @code{square} is safe to call | |
2435 | fewer times than the program says. | |
c27ba912 | 2436 | |
c8619b90 NS |
2437 | Some of common examples of pure functions are @code{strlen} or @code{memcmp}. |
2438 | Interesting non-pure functions are functions with infinite loops or those | |
2439 | depending on volatile memory or other system resource, that may change between | |
2440 | two consecutive calls (such as @code{feof} in a multithreading environment). | |
c1f7febf | 2441 | |
c8619b90 NS |
2442 | The attribute @code{pure} is not implemented in GCC versions earlier |
2443 | than 2.96. | |
c1f7febf | 2444 | |
c8619b90 NS |
2445 | @item regparm (@var{number}) |
2446 | @cindex @code{regparm} attribute | |
2447 | @cindex functions that are passed arguments in registers on the 386 | |
2448 | On the Intel 386, the @code{regparm} attribute causes the compiler to | |
2449 | pass up to @var{number} integer arguments in registers EAX, | |
2450 | EDX, and ECX instead of on the stack. Functions that take a | |
2451 | variable number of arguments will continue to be passed all of their | |
2452 | arguments on the stack. | |
6d3d9133 | 2453 | |
c8619b90 NS |
2454 | Beware that on some ELF systems this attribute is unsuitable for |
2455 | global functions in shared libraries with lazy binding (which is the | |
2456 | default). Lazy binding will send the first call via resolving code in | |
2457 | the loader, which might assume EAX, EDX and ECX can be clobbered, as | |
2458 | per the standard calling conventions. Solaris 8 is affected by this. | |
2459 | GNU systems with GLIBC 2.1 or higher, and FreeBSD, are believed to be | |
2460 | safe since the loaders there save all registers. (Lazy binding can be | |
2461 | disabled with the linker or the loader if desired, to avoid the | |
2462 | problem.) | |
6d3d9133 | 2463 | |
c8619b90 NS |
2464 | @item saveall |
2465 | @cindex save all registers on the H8/300, H8/300H, and H8S | |
2466 | Use this attribute on the H8/300, H8/300H, and H8S to indicate that | |
2467 | all registers except the stack pointer should be saved in the prologue | |
2468 | regardless of whether they are used or not. | |
6d3d9133 | 2469 | |
c8619b90 NS |
2470 | @item section ("@var{section-name}") |
2471 | @cindex @code{section} function attribute | |
2472 | Normally, the compiler places the code it generates in the @code{text} section. | |
2473 | Sometimes, however, you need additional sections, or you need certain | |
2474 | particular functions to appear in special sections. The @code{section} | |
2475 | attribute specifies that a function lives in a particular section. | |
2476 | For example, the declaration: | |
6d3d9133 NC |
2477 | |
2478 | @smallexample | |
c8619b90 | 2479 | extern void foobar (void) __attribute__ ((section ("bar"))); |
6d3d9133 NC |
2480 | @end smallexample |
2481 | ||
c8619b90 NS |
2482 | @noindent |
2483 | puts the function @code{foobar} in the @code{bar} section. | |
6d3d9133 | 2484 | |
c8619b90 NS |
2485 | Some file formats do not support arbitrary sections so the @code{section} |
2486 | attribute is not available on all platforms. | |
2487 | If you need to map the entire contents of a module to a particular | |
2488 | section, consider using the facilities of the linker instead. | |
2489 | ||
2490 | @item short_call | |
2491 | See long_call/short_call. | |
2492 | ||
2493 | @item shortcall | |
2494 | See longcall/shortcall. | |
2495 | ||
2496 | @item signal | |
2497 | @cindex signal handler functions on the AVR processors | |
2498 | Use this attribute on the AVR to indicate that the specified | |
2499 | function is a signal handler. The compiler will generate function | |
2500 | entry and exit sequences suitable for use in a signal handler when this | |
2501 | attribute is present. Interrupts will be disabled inside the function. | |
b93e3893 AO |
2502 | |
2503 | @item sp_switch | |
88ab0d1c | 2504 | Use this attribute on the SH to indicate an @code{interrupt_handler} |
b93e3893 AO |
2505 | function should switch to an alternate stack. It expects a string |
2506 | argument that names a global variable holding the address of the | |
2507 | alternate stack. | |
2508 | ||
2509 | @smallexample | |
2510 | void *alt_stack; | |
aee96fe9 JM |
2511 | void f () __attribute__ ((interrupt_handler, |
2512 | sp_switch ("alt_stack"))); | |
b93e3893 AO |
2513 | @end smallexample |
2514 | ||
c8619b90 NS |
2515 | @item stdcall |
2516 | @cindex functions that pop the argument stack on the 386 | |
2517 | On the Intel 386, the @code{stdcall} attribute causes the compiler to | |
2518 | assume that the called function will pop off the stack space used to | |
2519 | pass arguments, unless it takes a variable number of arguments. | |
c1f7febf RK |
2520 | |
2521 | @item tiny_data | |
dbacaa98 KH |
2522 | @cindex tiny data section on the H8/300H and H8S |
2523 | Use this attribute on the H8/300H and H8S to indicate that the specified | |
c1f7febf RK |
2524 | variable should be placed into the tiny data section. |
2525 | The compiler will generate more efficient code for loads and stores | |
2526 | on data in the tiny data section. Note the tiny data area is limited to | |
2527 | slightly under 32kbytes of data. | |
845da534 | 2528 | |
c8619b90 NS |
2529 | @item trap_exit |
2530 | Use this attribute on the SH for an @code{interrupt_handler} to return using | |
2531 | @code{trapa} instead of @code{rte}. This attribute expects an integer | |
2532 | argument specifying the trap number to be used. | |
845da534 | 2533 | |
c8619b90 NS |
2534 | @item unused |
2535 | @cindex @code{unused} attribute. | |
2536 | This attribute, attached to a function, means that the function is meant | |
2537 | to be possibly unused. GCC will not produce a warning for this | |
2538 | function. | |
a32767e4 | 2539 | |
c8619b90 NS |
2540 | @item used |
2541 | @cindex @code{used} attribute. | |
2542 | This attribute, attached to a function, means that code must be emitted | |
2543 | for the function even if it appears that the function is not referenced. | |
2544 | This is useful, for example, when the function is referenced only in | |
2545 | inline assembly. | |
5936c7e7 | 2546 | |
c8619b90 NS |
2547 | @item visibility ("@var{visibility_type}") |
2548 | @cindex @code{visibility} attribute | |
2549 | The @code{visibility} attribute on ELF targets causes the declaration | |
2550 | to be emitted with default, hidden, protected or internal visibility. | |
5936c7e7 | 2551 | |
c8619b90 NS |
2552 | @smallexample |
2553 | void __attribute__ ((visibility ("protected"))) | |
2554 | f () @{ /* @r{Do something.} */; @} | |
2555 | int i __attribute__ ((visibility ("hidden"))); | |
2556 | @end smallexample | |
5936c7e7 | 2557 | |
c8619b90 | 2558 | See the ELF gABI for complete details, but the short story is: |
5936c7e7 | 2559 | |
c8619b90 NS |
2560 | @table @dfn |
2561 | @c keep this list of visibilies in alphabetical order. | |
6b6cb52e | 2562 | |
c8619b90 NS |
2563 | @item default |
2564 | Default visibility is the normal case for ELF. This value is | |
2565 | available for the visibility attribute to override other options | |
2566 | that may change the assumed visibility of symbols. | |
6b6cb52e | 2567 | |
c8619b90 NS |
2568 | @item hidden |
2569 | Hidden visibility indicates that the symbol will not be placed into | |
2570 | the dynamic symbol table, so no other @dfn{module} (executable or | |
2571 | shared library) can reference it directly. | |
6b6cb52e | 2572 | |
c8619b90 NS |
2573 | @item internal |
2574 | Internal visibility is like hidden visibility, but with additional | |
2575 | processor specific semantics. Unless otherwise specified by the psABI, | |
2576 | GCC defines internal visibility to mean that the function is @emph{never} | |
2577 | called from another module. Note that hidden symbols, while they cannot | |
2578 | be referenced directly by other modules, can be referenced indirectly via | |
2579 | function pointers. By indicating that a symbol cannot be called from | |
2580 | outside the module, GCC may for instance omit the load of a PIC register | |
2581 | since it is known that the calling function loaded the correct value. | |
6b6cb52e | 2582 | |
c8619b90 NS |
2583 | @item protected |
2584 | Protected visibility indicates that the symbol will be placed in the | |
2585 | dynamic symbol table, but that references within the defining module | |
2586 | will bind to the local symbol. That is, the symbol cannot be overridden | |
2587 | by another module. | |
6b6cb52e | 2588 | |
c8619b90 | 2589 | @end table |
6b6cb52e | 2590 | |
c8619b90 | 2591 | Not all ELF targets support this attribute. |
6b6cb52e | 2592 | |
c8619b90 NS |
2593 | @item warn_unused_result |
2594 | @cindex @code{warn_unused_result} attribute | |
2595 | The @code{warn_unused_result} attribute causes a warning to be emitted | |
2596 | if a caller of the function with this attribute does not use its | |
2597 | return value. This is useful for functions where not checking | |
2598 | the result is either a security problem or always a bug, such as | |
2599 | @code{realloc}. | |
6b6cb52e | 2600 | |
c8619b90 NS |
2601 | @smallexample |
2602 | int fn () __attribute__ ((warn_unused_result)); | |
2603 | int foo () | |
2604 | @{ | |
2605 | if (fn () < 0) return -1; | |
2606 | fn (); | |
2607 | return 0; | |
2608 | @} | |
2609 | @end smallexample | |
6b6cb52e | 2610 | |
c8619b90 | 2611 | results in warning on line 5. |
6b6cb52e | 2612 | |
c8619b90 NS |
2613 | @item weak |
2614 | @cindex @code{weak} attribute | |
2615 | The @code{weak} attribute causes the declaration to be emitted as a weak | |
2616 | symbol rather than a global. This is primarily useful in defining | |
2617 | library functions which can be overridden in user code, though it can | |
2618 | also be used with non-function declarations. Weak symbols are supported | |
2619 | for ELF targets, and also for a.out targets when using the GNU assembler | |
2620 | and linker. | |
6b6cb52e | 2621 | |
c1f7febf RK |
2622 | @end table |
2623 | ||
2624 | You can specify multiple attributes in a declaration by separating them | |
2625 | by commas within the double parentheses or by immediately following an | |
2626 | attribute declaration with another attribute declaration. | |
2627 | ||
2628 | @cindex @code{#pragma}, reason for not using | |
2629 | @cindex pragma, reason for not using | |
9f1bbeaa JM |
2630 | Some people object to the @code{__attribute__} feature, suggesting that |
2631 | ISO C's @code{#pragma} should be used instead. At the time | |
2632 | @code{__attribute__} was designed, there were two reasons for not doing | |
2633 | this. | |
c1f7febf RK |
2634 | |
2635 | @enumerate | |
2636 | @item | |
2637 | It is impossible to generate @code{#pragma} commands from a macro. | |
2638 | ||
2639 | @item | |
2640 | There is no telling what the same @code{#pragma} might mean in another | |
2641 | compiler. | |
2642 | @end enumerate | |
2643 | ||
9f1bbeaa JM |
2644 | These two reasons applied to almost any application that might have been |
2645 | proposed for @code{#pragma}. It was basically a mistake to use | |
2646 | @code{#pragma} for @emph{anything}. | |
2647 | ||
2648 | The ISO C99 standard includes @code{_Pragma}, which now allows pragmas | |
2649 | to be generated from macros. In addition, a @code{#pragma GCC} | |
2650 | namespace is now in use for GCC-specific pragmas. However, it has been | |
2651 | found convenient to use @code{__attribute__} to achieve a natural | |
2652 | attachment of attributes to their corresponding declarations, whereas | |
2653 | @code{#pragma GCC} is of use for constructs that do not naturally form | |
2654 | part of the grammar. @xref{Other Directives,,Miscellaneous | |
48795525 | 2655 | Preprocessing Directives, cpp, The GNU C Preprocessor}. |
c1f7febf | 2656 | |
2c5e91d2 JM |
2657 | @node Attribute Syntax |
2658 | @section Attribute Syntax | |
2659 | @cindex attribute syntax | |
2660 | ||
2661 | This section describes the syntax with which @code{__attribute__} may be | |
2662 | used, and the constructs to which attribute specifiers bind, for the C | |
161d7b59 | 2663 | language. Some details may vary for C++ and Objective-C@. Because of |
2c5e91d2 JM |
2664 | infelicities in the grammar for attributes, some forms described here |
2665 | may not be successfully parsed in all cases. | |
2666 | ||
91d231cb JM |
2667 | There are some problems with the semantics of attributes in C++. For |
2668 | example, there are no manglings for attributes, although they may affect | |
2669 | code generation, so problems may arise when attributed types are used in | |
2670 | conjunction with templates or overloading. Similarly, @code{typeid} | |
2671 | does not distinguish between types with different attributes. Support | |
2672 | for attributes in C++ may be restricted in future to attributes on | |
2673 | declarations only, but not on nested declarators. | |
2674 | ||
2c5e91d2 JM |
2675 | @xref{Function Attributes}, for details of the semantics of attributes |
2676 | applying to functions. @xref{Variable Attributes}, for details of the | |
2677 | semantics of attributes applying to variables. @xref{Type Attributes}, | |
2678 | for details of the semantics of attributes applying to structure, union | |
2679 | and enumerated types. | |
2680 | ||
2681 | An @dfn{attribute specifier} is of the form | |
2682 | @code{__attribute__ ((@var{attribute-list}))}. An @dfn{attribute list} | |
2683 | is a possibly empty comma-separated sequence of @dfn{attributes}, where | |
2684 | each attribute is one of the following: | |
2685 | ||
2686 | @itemize @bullet | |
2687 | @item | |
2688 | Empty. Empty attributes are ignored. | |
2689 | ||
2690 | @item | |
2691 | A word (which may be an identifier such as @code{unused}, or a reserved | |
2692 | word such as @code{const}). | |
2693 | ||
2694 | @item | |
2695 | A word, followed by, in parentheses, parameters for the attribute. | |
2696 | These parameters take one of the following forms: | |
2697 | ||
2698 | @itemize @bullet | |
2699 | @item | |
2700 | An identifier. For example, @code{mode} attributes use this form. | |
2701 | ||
2702 | @item | |
2703 | An identifier followed by a comma and a non-empty comma-separated list | |
2704 | of expressions. For example, @code{format} attributes use this form. | |
2705 | ||
2706 | @item | |
2707 | A possibly empty comma-separated list of expressions. For example, | |
2708 | @code{format_arg} attributes use this form with the list being a single | |
2709 | integer constant expression, and @code{alias} attributes use this form | |
2710 | with the list being a single string constant. | |
2711 | @end itemize | |
2712 | @end itemize | |
2713 | ||
2714 | An @dfn{attribute specifier list} is a sequence of one or more attribute | |
2715 | specifiers, not separated by any other tokens. | |
2716 | ||
50fc59e7 | 2717 | In GNU C, an attribute specifier list may appear after the colon following a |
2c5e91d2 JM |
2718 | label, other than a @code{case} or @code{default} label. The only |
2719 | attribute it makes sense to use after a label is @code{unused}. This | |
2720 | feature is intended for code generated by programs which contains labels | |
2721 | that may be unused but which is compiled with @option{-Wall}. It would | |
2722 | not normally be appropriate to use in it human-written code, though it | |
2723 | could be useful in cases where the code that jumps to the label is | |
50fc59e7 NS |
2724 | contained within an @code{#ifdef} conditional. GNU C++ does not permit |
2725 | such placement of attribute lists, as it is permissible for a | |
2726 | declaration, which could begin with an attribute list, to be labelled in | |
2727 | C++. Declarations cannot be labelled in C90 or C99, so the ambiguity | |
2728 | does not arise there. | |
2c5e91d2 JM |
2729 | |
2730 | An attribute specifier list may appear as part of a @code{struct}, | |
2731 | @code{union} or @code{enum} specifier. It may go either immediately | |
2732 | after the @code{struct}, @code{union} or @code{enum} keyword, or after | |
2733 | the closing brace. It is ignored if the content of the structure, union | |
2734 | or enumerated type is not defined in the specifier in which the | |
2735 | attribute specifier list is used---that is, in usages such as | |
2736 | @code{struct __attribute__((foo)) bar} with no following opening brace. | |
2737 | Where attribute specifiers follow the closing brace, they are considered | |
2738 | to relate to the structure, union or enumerated type defined, not to any | |
2739 | enclosing declaration the type specifier appears in, and the type | |
2740 | defined is not complete until after the attribute specifiers. | |
2741 | @c Otherwise, there would be the following problems: a shift/reduce | |
4fe9b91c | 2742 | @c conflict between attributes binding the struct/union/enum and |
2c5e91d2 JM |
2743 | @c binding to the list of specifiers/qualifiers; and "aligned" |
2744 | @c attributes could use sizeof for the structure, but the size could be | |
2745 | @c changed later by "packed" attributes. | |
2746 | ||
2747 | Otherwise, an attribute specifier appears as part of a declaration, | |
2748 | counting declarations of unnamed parameters and type names, and relates | |
2749 | to that declaration (which may be nested in another declaration, for | |
91d231cb JM |
2750 | example in the case of a parameter declaration), or to a particular declarator |
2751 | within a declaration. Where an | |
ff867905 JM |
2752 | attribute specifier is applied to a parameter declared as a function or |
2753 | an array, it should apply to the function or array rather than the | |
2754 | pointer to which the parameter is implicitly converted, but this is not | |
2755 | yet correctly implemented. | |
2c5e91d2 JM |
2756 | |
2757 | Any list of specifiers and qualifiers at the start of a declaration may | |
2758 | contain attribute specifiers, whether or not such a list may in that | |
2759 | context contain storage class specifiers. (Some attributes, however, | |
2760 | are essentially in the nature of storage class specifiers, and only make | |
2761 | sense where storage class specifiers may be used; for example, | |
2762 | @code{section}.) There is one necessary limitation to this syntax: the | |
2763 | first old-style parameter declaration in a function definition cannot | |
2764 | begin with an attribute specifier, because such an attribute applies to | |
2765 | the function instead by syntax described below (which, however, is not | |
2766 | yet implemented in this case). In some other cases, attribute | |
2767 | specifiers are permitted by this grammar but not yet supported by the | |
2768 | compiler. All attribute specifiers in this place relate to the | |
c771326b | 2769 | declaration as a whole. In the obsolescent usage where a type of |
2c5e91d2 JM |
2770 | @code{int} is implied by the absence of type specifiers, such a list of |
2771 | specifiers and qualifiers may be an attribute specifier list with no | |
2772 | other specifiers or qualifiers. | |
2773 | ||
2774 | An attribute specifier list may appear immediately before a declarator | |
2775 | (other than the first) in a comma-separated list of declarators in a | |
2776 | declaration of more than one identifier using a single list of | |
4b01f8d8 | 2777 | specifiers and qualifiers. Such attribute specifiers apply |
9c34dbbf ZW |
2778 | only to the identifier before whose declarator they appear. For |
2779 | example, in | |
2780 | ||
2781 | @smallexample | |
2782 | __attribute__((noreturn)) void d0 (void), | |
2783 | __attribute__((format(printf, 1, 2))) d1 (const char *, ...), | |
2784 | d2 (void) | |
2785 | @end smallexample | |
2786 | ||
2787 | @noindent | |
2788 | the @code{noreturn} attribute applies to all the functions | |
4b01f8d8 | 2789 | declared; the @code{format} attribute only applies to @code{d1}. |
2c5e91d2 JM |
2790 | |
2791 | An attribute specifier list may appear immediately before the comma, | |
2792 | @code{=} or semicolon terminating the declaration of an identifier other | |
2793 | than a function definition. At present, such attribute specifiers apply | |
2794 | to the declared object or function, but in future they may attach to the | |
2795 | outermost adjacent declarator. In simple cases there is no difference, | |
f282ffb3 | 2796 | but, for example, in |
9c34dbbf ZW |
2797 | |
2798 | @smallexample | |
2799 | void (****f)(void) __attribute__((noreturn)); | |
2800 | @end smallexample | |
2801 | ||
2802 | @noindent | |
2803 | at present the @code{noreturn} attribute applies to @code{f}, which | |
2804 | causes a warning since @code{f} is not a function, but in future it may | |
2805 | apply to the function @code{****f}. The precise semantics of what | |
2806 | attributes in such cases will apply to are not yet specified. Where an | |
2807 | assembler name for an object or function is specified (@pxref{Asm | |
2808 | Labels}), at present the attribute must follow the @code{asm} | |
2809 | specification; in future, attributes before the @code{asm} specification | |
2810 | may apply to the adjacent declarator, and those after it to the declared | |
2811 | object or function. | |
2c5e91d2 JM |
2812 | |
2813 | An attribute specifier list may, in future, be permitted to appear after | |
2814 | the declarator in a function definition (before any old-style parameter | |
2815 | declarations or the function body). | |
2816 | ||
0e03329a JM |
2817 | Attribute specifiers may be mixed with type qualifiers appearing inside |
2818 | the @code{[]} of a parameter array declarator, in the C99 construct by | |
2819 | which such qualifiers are applied to the pointer to which the array is | |
2820 | implicitly converted. Such attribute specifiers apply to the pointer, | |
2821 | not to the array, but at present this is not implemented and they are | |
2822 | ignored. | |
2823 | ||
2c5e91d2 JM |
2824 | An attribute specifier list may appear at the start of a nested |
2825 | declarator. At present, there are some limitations in this usage: the | |
91d231cb JM |
2826 | attributes correctly apply to the declarator, but for most individual |
2827 | attributes the semantics this implies are not implemented. | |
2828 | When attribute specifiers follow the @code{*} of a pointer | |
4b01f8d8 | 2829 | declarator, they may be mixed with any type qualifiers present. |
91d231cb | 2830 | The following describes the formal semantics of this syntax. It will make the |
2c5e91d2 JM |
2831 | most sense if you are familiar with the formal specification of |
2832 | declarators in the ISO C standard. | |
2833 | ||
2834 | Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration @code{T | |
2835 | D1}, where @code{T} contains declaration specifiers that specify a type | |
2836 | @var{Type} (such as @code{int}) and @code{D1} is a declarator that | |
2837 | contains an identifier @var{ident}. The type specified for @var{ident} | |
2838 | for derived declarators whose type does not include an attribute | |
2839 | specifier is as in the ISO C standard. | |
2840 | ||
2841 | If @code{D1} has the form @code{( @var{attribute-specifier-list} D )}, | |
2842 | and the declaration @code{T D} specifies the type | |
2843 | ``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then | |
2844 | @code{T D1} specifies the type ``@var{derived-declarator-type-list} | |
2845 | @var{attribute-specifier-list} @var{Type}'' for @var{ident}. | |
2846 | ||
2847 | If @code{D1} has the form @code{* | |
2848 | @var{type-qualifier-and-attribute-specifier-list} D}, and the | |
2849 | declaration @code{T D} specifies the type | |
2850 | ``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then | |
2851 | @code{T D1} specifies the type ``@var{derived-declarator-type-list} | |
2852 | @var{type-qualifier-and-attribute-specifier-list} @var{Type}'' for | |
2853 | @var{ident}. | |
2854 | ||
f282ffb3 | 2855 | For example, |
9c34dbbf ZW |
2856 | |
2857 | @smallexample | |
2858 | void (__attribute__((noreturn)) ****f) (void); | |
2859 | @end smallexample | |
2860 | ||
2861 | @noindent | |
2862 | specifies the type ``pointer to pointer to pointer to pointer to | |
2863 | non-returning function returning @code{void}''. As another example, | |
2864 | ||
2865 | @smallexample | |
2866 | char *__attribute__((aligned(8))) *f; | |
2867 | @end smallexample | |
2868 | ||
2869 | @noindent | |
2870 | specifies the type ``pointer to 8-byte-aligned pointer to @code{char}''. | |
91d231cb JM |
2871 | Note again that this does not work with most attributes; for example, |
2872 | the usage of @samp{aligned} and @samp{noreturn} attributes given above | |
2873 | is not yet supported. | |
2874 | ||
2875 | For compatibility with existing code written for compiler versions that | |
2876 | did not implement attributes on nested declarators, some laxity is | |
2877 | allowed in the placing of attributes. If an attribute that only applies | |
2878 | to types is applied to a declaration, it will be treated as applying to | |
2879 | the type of that declaration. If an attribute that only applies to | |
2880 | declarations is applied to the type of a declaration, it will be treated | |
2881 | as applying to that declaration; and, for compatibility with code | |
2882 | placing the attributes immediately before the identifier declared, such | |
2883 | an attribute applied to a function return type will be treated as | |
2884 | applying to the function type, and such an attribute applied to an array | |
2885 | element type will be treated as applying to the array type. If an | |
2886 | attribute that only applies to function types is applied to a | |
2887 | pointer-to-function type, it will be treated as applying to the pointer | |
2888 | target type; if such an attribute is applied to a function return type | |
2889 | that is not a pointer-to-function type, it will be treated as applying | |
2890 | to the function type. | |
2c5e91d2 | 2891 | |
c1f7febf RK |
2892 | @node Function Prototypes |
2893 | @section Prototypes and Old-Style Function Definitions | |
2894 | @cindex function prototype declarations | |
2895 | @cindex old-style function definitions | |
2896 | @cindex promotion of formal parameters | |
2897 | ||
5490d604 | 2898 | GNU C extends ISO C to allow a function prototype to override a later |
c1f7febf RK |
2899 | old-style non-prototype definition. Consider the following example: |
2900 | ||
3ab51846 | 2901 | @smallexample |
c1f7febf | 2902 | /* @r{Use prototypes unless the compiler is old-fashioned.} */ |
d863830b | 2903 | #ifdef __STDC__ |
c1f7febf RK |
2904 | #define P(x) x |
2905 | #else | |
2906 | #define P(x) () | |
2907 | #endif | |
2908 | ||
2909 | /* @r{Prototype function declaration.} */ | |
2910 | int isroot P((uid_t)); | |
2911 | ||
2912 | /* @r{Old-style function definition.} */ | |
2913 | int | |
2914 | isroot (x) /* ??? lossage here ??? */ | |
2915 | uid_t x; | |
2916 | @{ | |
2917 | return x == 0; | |
2918 | @} | |
3ab51846 | 2919 | @end smallexample |
c1f7febf | 2920 | |
5490d604 | 2921 | Suppose the type @code{uid_t} happens to be @code{short}. ISO C does |
c1f7febf RK |
2922 | not allow this example, because subword arguments in old-style |
2923 | non-prototype definitions are promoted. Therefore in this example the | |
2924 | function definition's argument is really an @code{int}, which does not | |
2925 | match the prototype argument type of @code{short}. | |
2926 | ||
5490d604 | 2927 | This restriction of ISO C makes it hard to write code that is portable |
c1f7febf RK |
2928 | to traditional C compilers, because the programmer does not know |
2929 | whether the @code{uid_t} type is @code{short}, @code{int}, or | |
2930 | @code{long}. Therefore, in cases like these GNU C allows a prototype | |
2931 | to override a later old-style definition. More precisely, in GNU C, a | |
2932 | function prototype argument type overrides the argument type specified | |
2933 | by a later old-style definition if the former type is the same as the | |
2934 | latter type before promotion. Thus in GNU C the above example is | |
2935 | equivalent to the following: | |
2936 | ||
3ab51846 | 2937 | @smallexample |
c1f7febf RK |
2938 | int isroot (uid_t); |
2939 | ||
2940 | int | |
2941 | isroot (uid_t x) | |
2942 | @{ | |
2943 | return x == 0; | |
2944 | @} | |
3ab51846 | 2945 | @end smallexample |
c1f7febf | 2946 | |
9c34dbbf | 2947 | @noindent |
c1f7febf RK |
2948 | GNU C++ does not support old-style function definitions, so this |
2949 | extension is irrelevant. | |
2950 | ||
2951 | @node C++ Comments | |
2952 | @section C++ Style Comments | |
2953 | @cindex // | |
2954 | @cindex C++ comments | |
2955 | @cindex comments, C++ style | |
2956 | ||
2957 | In GNU C, you may use C++ style comments, which start with @samp{//} and | |
2958 | continue until the end of the line. Many other C implementations allow | |
f458d1d5 ZW |
2959 | such comments, and they are included in the 1999 C standard. However, |
2960 | C++ style comments are not recognized if you specify an @option{-std} | |
2961 | option specifying a version of ISO C before C99, or @option{-ansi} | |
2962 | (equivalent to @option{-std=c89}). | |
c1f7febf RK |
2963 | |
2964 | @node Dollar Signs | |
2965 | @section Dollar Signs in Identifier Names | |
2966 | @cindex $ | |
2967 | @cindex dollar signs in identifier names | |
2968 | @cindex identifier names, dollar signs in | |
2969 | ||
79188db9 RK |
2970 | In GNU C, you may normally use dollar signs in identifier names. |
2971 | This is because many traditional C implementations allow such identifiers. | |
2972 | However, dollar signs in identifiers are not supported on a few target | |
2973 | machines, typically because the target assembler does not allow them. | |
c1f7febf RK |
2974 | |
2975 | @node Character Escapes | |
2976 | @section The Character @key{ESC} in Constants | |
2977 | ||
2978 | You can use the sequence @samp{\e} in a string or character constant to | |
2979 | stand for the ASCII character @key{ESC}. | |
2980 | ||
2981 | @node Alignment | |
2982 | @section Inquiring on Alignment of Types or Variables | |
2983 | @cindex alignment | |
2984 | @cindex type alignment | |
2985 | @cindex variable alignment | |
2986 | ||
2987 | The keyword @code{__alignof__} allows you to inquire about how an object | |
2988 | is aligned, or the minimum alignment usually required by a type. Its | |
2989 | syntax is just like @code{sizeof}. | |
2990 | ||
2991 | For example, if the target machine requires a @code{double} value to be | |
2992 | aligned on an 8-byte boundary, then @code{__alignof__ (double)} is 8. | |
2993 | This is true on many RISC machines. On more traditional machine | |
2994 | designs, @code{__alignof__ (double)} is 4 or even 2. | |
2995 | ||
2996 | Some machines never actually require alignment; they allow reference to any | |
64c18e57 | 2997 | data type even at an odd address. For these machines, @code{__alignof__} |
c1f7febf RK |
2998 | reports the @emph{recommended} alignment of a type. |
2999 | ||
5372b3fb NB |
3000 | If the operand of @code{__alignof__} is an lvalue rather than a type, |
3001 | its value is the required alignment for its type, taking into account | |
3002 | any minimum alignment specified with GCC's @code{__attribute__} | |
3003 | extension (@pxref{Variable Attributes}). For example, after this | |
3004 | declaration: | |
c1f7febf | 3005 | |
3ab51846 | 3006 | @smallexample |
c1f7febf | 3007 | struct foo @{ int x; char y; @} foo1; |
3ab51846 | 3008 | @end smallexample |
c1f7febf RK |
3009 | |
3010 | @noindent | |
5372b3fb NB |
3011 | the value of @code{__alignof__ (foo1.y)} is 1, even though its actual |
3012 | alignment is probably 2 or 4, the same as @code{__alignof__ (int)}. | |
c1f7febf | 3013 | |
9d27bffe SS |
3014 | It is an error to ask for the alignment of an incomplete type. |
3015 | ||
c1f7febf RK |
3016 | @node Variable Attributes |
3017 | @section Specifying Attributes of Variables | |
3018 | @cindex attribute of variables | |
3019 | @cindex variable attributes | |
3020 | ||
3021 | The keyword @code{__attribute__} allows you to specify special | |
3022 | attributes of variables or structure fields. This keyword is followed | |
905e8651 RH |
3023 | by an attribute specification inside double parentheses. Some |
3024 | attributes are currently defined generically for variables. | |
3025 | Other attributes are defined for variables on particular target | |
3026 | systems. Other attributes are available for functions | |
3027 | (@pxref{Function Attributes}) and for types (@pxref{Type Attributes}). | |
3028 | Other front ends might define more attributes | |
3029 | (@pxref{C++ Extensions,,Extensions to the C++ Language}). | |
c1f7febf RK |
3030 | |
3031 | You may also specify attributes with @samp{__} preceding and following | |
3032 | each keyword. This allows you to use them in header files without | |
3033 | being concerned about a possible macro of the same name. For example, | |
3034 | you may use @code{__aligned__} instead of @code{aligned}. | |
3035 | ||
2c5e91d2 JM |
3036 | @xref{Attribute Syntax}, for details of the exact syntax for using |
3037 | attributes. | |
3038 | ||
c1f7febf RK |
3039 | @table @code |
3040 | @cindex @code{aligned} attribute | |
3041 | @item aligned (@var{alignment}) | |
3042 | This attribute specifies a minimum alignment for the variable or | |
3043 | structure field, measured in bytes. For example, the declaration: | |
3044 | ||
3045 | @smallexample | |
3046 | int x __attribute__ ((aligned (16))) = 0; | |
3047 | @end smallexample | |
3048 | ||
3049 | @noindent | |
3050 | causes the compiler to allocate the global variable @code{x} on a | |
3051 | 16-byte boundary. On a 68040, this could be used in conjunction with | |
3052 | an @code{asm} expression to access the @code{move16} instruction which | |
3053 | requires 16-byte aligned operands. | |
3054 | ||
3055 | You can also specify the alignment of structure fields. For example, to | |
3056 | create a double-word aligned @code{int} pair, you could write: | |
3057 | ||
3058 | @smallexample | |
3059 | struct foo @{ int x[2] __attribute__ ((aligned (8))); @}; | |
3060 | @end smallexample | |
3061 | ||
3062 | @noindent | |
3063 | This is an alternative to creating a union with a @code{double} member | |
3064 | that forces the union to be double-word aligned. | |
3065 | ||
c1f7febf RK |
3066 | As in the preceding examples, you can explicitly specify the alignment |
3067 | (in bytes) that you wish the compiler to use for a given variable or | |
3068 | structure field. Alternatively, you can leave out the alignment factor | |
3069 | and just ask the compiler to align a variable or field to the maximum | |
3070 | useful alignment for the target machine you are compiling for. For | |
3071 | example, you could write: | |
3072 | ||
3073 | @smallexample | |
3074 | short array[3] __attribute__ ((aligned)); | |
3075 | @end smallexample | |
3076 | ||
3077 | Whenever you leave out the alignment factor in an @code{aligned} attribute | |
3078 | specification, the compiler automatically sets the alignment for the declared | |
3079 | variable or field to the largest alignment which is ever used for any data | |
3080 | type on the target machine you are compiling for. Doing this can often make | |
3081 | copy operations more efficient, because the compiler can use whatever | |
3082 | instructions copy the biggest chunks of memory when performing copies to | |
3083 | or from the variables or fields that you have aligned this way. | |
3084 | ||
3085 | The @code{aligned} attribute can only increase the alignment; but you | |
3086 | can decrease it by specifying @code{packed} as well. See below. | |
3087 | ||
3088 | Note that the effectiveness of @code{aligned} attributes may be limited | |
3089 | by inherent limitations in your linker. On many systems, the linker is | |
3090 | only able to arrange for variables to be aligned up to a certain maximum | |
3091 | alignment. (For some linkers, the maximum supported alignment may | |
3092 | be very very small.) If your linker is only able to align variables | |
3093 | up to a maximum of 8 byte alignment, then specifying @code{aligned(16)} | |
3094 | in an @code{__attribute__} will still only provide you with 8 byte | |
3095 | alignment. See your linker documentation for further information. | |
3096 | ||
0bfa5f65 RH |
3097 | @item cleanup (@var{cleanup_function}) |
3098 | @cindex @code{cleanup} attribute | |
3099 | The @code{cleanup} attribute runs a function when the variable goes | |
3100 | out of scope. This attribute can only be applied to auto function | |
3101 | scope variables; it may not be applied to parameters or variables | |
3102 | with static storage duration. The function must take one parameter, | |
3103 | a pointer to a type compatible with the variable. The return value | |
3104 | of the function (if any) is ignored. | |
3105 | ||
3106 | If @option{-fexceptions} is enabled, then @var{cleanup_function} | |
3107 | will be run during the stack unwinding that happens during the | |
3108 | processing of the exception. Note that the @code{cleanup} attribute | |
3109 | does not allow the exception to be caught, only to perform an action. | |
3110 | It is undefined what happens if @var{cleanup_function} does not | |
3111 | return normally. | |
3112 | ||
905e8651 RH |
3113 | @item common |
3114 | @itemx nocommon | |
3115 | @cindex @code{common} attribute | |
3116 | @cindex @code{nocommon} attribute | |
3117 | @opindex fcommon | |
3118 | @opindex fno-common | |
3119 | The @code{common} attribute requests GCC to place a variable in | |
3120 | ``common'' storage. The @code{nocommon} attribute requests the | |
3121 | opposite -- to allocate space for it directly. | |
3122 | ||
daf2f129 | 3123 | These attributes override the default chosen by the |
905e8651 RH |
3124 | @option{-fno-common} and @option{-fcommon} flags respectively. |
3125 | ||
3126 | @item deprecated | |
3127 | @cindex @code{deprecated} attribute | |
3128 | The @code{deprecated} attribute results in a warning if the variable | |
3129 | is used anywhere in the source file. This is useful when identifying | |
3130 | variables that are expected to be removed in a future version of a | |
3131 | program. The warning also includes the location of the declaration | |
3132 | of the deprecated variable, to enable users to easily find further | |
3133 | information about why the variable is deprecated, or what they should | |
64c18e57 | 3134 | do instead. Note that the warning only occurs for uses: |
905e8651 RH |
3135 | |
3136 | @smallexample | |
3137 | extern int old_var __attribute__ ((deprecated)); | |
3138 | extern int old_var; | |
3139 | int new_fn () @{ return old_var; @} | |
3140 | @end smallexample | |
3141 | ||
3142 | results in a warning on line 3 but not line 2. | |
3143 | ||
3144 | The @code{deprecated} attribute can also be used for functions and | |
3145 | types (@pxref{Function Attributes}, @pxref{Type Attributes}.) | |
3146 | ||
c1f7febf RK |
3147 | @item mode (@var{mode}) |
3148 | @cindex @code{mode} attribute | |
3149 | This attribute specifies the data type for the declaration---whichever | |
3150 | type corresponds to the mode @var{mode}. This in effect lets you | |
3151 | request an integer or floating point type according to its width. | |
3152 | ||
3153 | You may also specify a mode of @samp{byte} or @samp{__byte__} to | |
3154 | indicate the mode corresponding to a one-byte integer, @samp{word} or | |
3155 | @samp{__word__} for the mode of a one-word integer, and @samp{pointer} | |
3156 | or @samp{__pointer__} for the mode used to represent pointers. | |
3157 | ||
c1f7febf RK |
3158 | @item packed |
3159 | @cindex @code{packed} attribute | |
3160 | The @code{packed} attribute specifies that a variable or structure field | |
3161 | should have the smallest possible alignment---one byte for a variable, | |
3162 | and one bit for a field, unless you specify a larger value with the | |
3163 | @code{aligned} attribute. | |
3164 | ||
3165 | Here is a structure in which the field @code{x} is packed, so that it | |
3166 | immediately follows @code{a}: | |
3167 | ||
3ab51846 | 3168 | @smallexample |
c1f7febf RK |
3169 | struct foo |
3170 | @{ | |
3171 | char a; | |
3172 | int x[2] __attribute__ ((packed)); | |
3173 | @}; | |
3ab51846 | 3174 | @end smallexample |
c1f7febf | 3175 | |
84330467 | 3176 | @item section ("@var{section-name}") |
c1f7febf RK |
3177 | @cindex @code{section} variable attribute |
3178 | Normally, the compiler places the objects it generates in sections like | |
3179 | @code{data} and @code{bss}. Sometimes, however, you need additional sections, | |
3180 | or you need certain particular variables to appear in special sections, | |
3181 | for example to map to special hardware. The @code{section} | |
3182 | attribute specifies that a variable (or function) lives in a particular | |
3183 | section. For example, this small program uses several specific section names: | |
3184 | ||
3185 | @smallexample | |
3186 | struct duart a __attribute__ ((section ("DUART_A"))) = @{ 0 @}; | |
3187 | struct duart b __attribute__ ((section ("DUART_B"))) = @{ 0 @}; | |
3188 | char stack[10000] __attribute__ ((section ("STACK"))) = @{ 0 @}; | |
3189 | int init_data __attribute__ ((section ("INITDATA"))) = 0; | |
3190 | ||
3191 | main() | |
3192 | @{ | |
3193 | /* Initialize stack pointer */ | |
3194 | init_sp (stack + sizeof (stack)); | |
3195 | ||
3196 | /* Initialize initialized data */ | |
3197 | memcpy (&init_data, &data, &edata - &data); | |
3198 | ||
3199 | /* Turn on the serial ports */ | |
3200 | init_duart (&a); | |
3201 | init_duart (&b); | |
3202 | @} | |
3203 | @end smallexample | |
3204 | ||
3205 | @noindent | |
3206 | Use the @code{section} attribute with an @emph{initialized} definition | |
f0523f02 | 3207 | of a @emph{global} variable, as shown in the example. GCC issues |
c1f7febf RK |
3208 | a warning and otherwise ignores the @code{section} attribute in |
3209 | uninitialized variable declarations. | |
3210 | ||
3211 | You may only use the @code{section} attribute with a fully initialized | |
3212 | global definition because of the way linkers work. The linker requires | |
3213 | each object be defined once, with the exception that uninitialized | |
3214 | variables tentatively go in the @code{common} (or @code{bss}) section | |
84330467 JM |
3215 | and can be multiply ``defined''. You can force a variable to be |
3216 | initialized with the @option{-fno-common} flag or the @code{nocommon} | |
c1f7febf RK |
3217 | attribute. |
3218 | ||
3219 | Some file formats do not support arbitrary sections so the @code{section} | |
3220 | attribute is not available on all platforms. | |
3221 | If you need to map the entire contents of a module to a particular | |
3222 | section, consider using the facilities of the linker instead. | |
3223 | ||
593d3a34 MK |
3224 | @item shared |
3225 | @cindex @code{shared} variable attribute | |
95fef11f | 3226 | On Microsoft Windows, in addition to putting variable definitions in a named |
02f52e19 | 3227 | section, the section can also be shared among all running copies of an |
161d7b59 | 3228 | executable or DLL@. For example, this small program defines shared data |
84330467 | 3229 | by putting it in a named section @code{shared} and marking the section |
593d3a34 MK |
3230 | shareable: |
3231 | ||
3232 | @smallexample | |
3233 | int foo __attribute__((section ("shared"), shared)) = 0; | |
3234 | ||
3235 | int | |
3236 | main() | |
3237 | @{ | |
310668e8 JM |
3238 | /* Read and write foo. All running |
3239 | copies see the same value. */ | |
593d3a34 MK |
3240 | return 0; |
3241 | @} | |
3242 | @end smallexample | |
3243 | ||
3244 | @noindent | |
3245 | You may only use the @code{shared} attribute along with @code{section} | |
02f52e19 | 3246 | attribute with a fully initialized global definition because of the way |
593d3a34 MK |
3247 | linkers work. See @code{section} attribute for more information. |
3248 | ||
95fef11f | 3249 | The @code{shared} attribute is only available on Microsoft Windows@. |
593d3a34 | 3250 | |
905e8651 RH |
3251 | @item tls_model ("@var{tls_model}") |
3252 | @cindex @code{tls_model} attribute | |
3253 | The @code{tls_model} attribute sets thread-local storage model | |
3254 | (@pxref{Thread-Local}) of a particular @code{__thread} variable, | |
3255 | overriding @code{-ftls-model=} command line switch on a per-variable | |
3256 | basis. | |
3257 | The @var{tls_model} argument should be one of @code{global-dynamic}, | |
3258 | @code{local-dynamic}, @code{initial-exec} or @code{local-exec}. | |
3259 | ||
3260 | Not all targets support this attribute. | |
3261 | ||
c1f7febf RK |
3262 | @item transparent_union |
3263 | This attribute, attached to a function parameter which is a union, means | |
3264 | that the corresponding argument may have the type of any union member, | |
3265 | but the argument is passed as if its type were that of the first union | |
3266 | member. For more details see @xref{Type Attributes}. You can also use | |
3267 | this attribute on a @code{typedef} for a union data type; then it | |
3268 | applies to all function parameters with that type. | |
3269 | ||
3270 | @item unused | |
3271 | This attribute, attached to a variable, means that the variable is meant | |
f0523f02 | 3272 | to be possibly unused. GCC will not produce a warning for this |
c1f7febf RK |
3273 | variable. |
3274 | ||
1b9191d2 AH |
3275 | @item vector_size (@var{bytes}) |
3276 | This attribute specifies the vector size for the variable, measured in | |
3277 | bytes. For example, the declaration: | |
3278 | ||
3279 | @smallexample | |
3280 | int foo __attribute__ ((vector_size (16))); | |
3281 | @end smallexample | |
3282 | ||
3283 | @noindent | |
3284 | causes the compiler to set the mode for @code{foo}, to be 16 bytes, | |
3285 | divided into @code{int} sized units. Assuming a 32-bit int (a vector of | |
3286 | 4 units of 4 bytes), the corresponding mode of @code{foo} will be V4SI@. | |
3287 | ||
3288 | This attribute is only applicable to integral and float scalars, | |
3289 | although arrays, pointers, and function return values are allowed in | |
3290 | conjunction with this construct. | |
3291 | ||
3292 | Aggregates with this attribute are invalid, even if they are of the same | |
3293 | size as a corresponding scalar. For example, the declaration: | |
3294 | ||
3295 | @smallexample | |
ad706f54 | 3296 | struct S @{ int a; @}; |
1b9191d2 AH |
3297 | struct S __attribute__ ((vector_size (16))) foo; |
3298 | @end smallexample | |
3299 | ||
3300 | @noindent | |
3301 | is invalid even if the size of the structure is the same as the size of | |
3302 | the @code{int}. | |
3303 | ||
c1f7febf RK |
3304 | @item weak |
3305 | The @code{weak} attribute is described in @xref{Function Attributes}. | |
6b6cb52e DS |
3306 | |
3307 | @item dllimport | |
3308 | The @code{dllimport} attribute is described in @xref{Function Attributes}. | |
3309 | ||
3310 | @item dlexport | |
3311 | The @code{dllexport} attribute is described in @xref{Function Attributes}. | |
3312 | ||
905e8651 RH |
3313 | @end table |
3314 | ||
3315 | @subsection M32R/D Variable Attributes | |
845da534 | 3316 | |
905e8651 RH |
3317 | One attribute is currently defined for the M32R/D. |
3318 | ||
3319 | @table @code | |
845da534 DE |
3320 | @item model (@var{model-name}) |
3321 | @cindex variable addressability on the M32R/D | |
3322 | Use this attribute on the M32R/D to set the addressability of an object. | |
3323 | The identifier @var{model-name} is one of @code{small}, @code{medium}, | |
3324 | or @code{large}, representing each of the code models. | |
3325 | ||
3326 | Small model objects live in the lower 16MB of memory (so that their | |
3327 | addresses can be loaded with the @code{ld24} instruction). | |
3328 | ||
02f52e19 | 3329 | Medium and large model objects may live anywhere in the 32-bit address space |
845da534 DE |
3330 | (the compiler will generate @code{seth/add3} instructions to load their |
3331 | addresses). | |
905e8651 | 3332 | @end table |
845da534 | 3333 | |
fe77449a DR |
3334 | @subsection i386 Variable Attributes |
3335 | ||
3336 | Two attributes are currently defined for i386 configurations: | |
3337 | @code{ms_struct} and @code{gcc_struct} | |
3338 | ||
905e8651 | 3339 | @table @code |
fe77449a DR |
3340 | @item ms_struct |
3341 | @itemx gcc_struct | |
905e8651 RH |
3342 | @cindex @code{ms_struct} attribute |
3343 | @cindex @code{gcc_struct} attribute | |
fe77449a DR |
3344 | |
3345 | If @code{packed} is used on a structure, or if bit-fields are used | |
3346 | it may be that the Microsoft ABI packs them differently | |
3347 | than GCC would normally pack them. Particularly when moving packed | |
3348 | data between functions compiled with GCC and the native Microsoft compiler | |
3349 | (either via function call or as data in a file), it may be necessary to access | |
3350 | either format. | |
3351 | ||
95fef11f | 3352 | Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86 |
fe77449a | 3353 | compilers to match the native Microsoft compiler. |
c1f7febf RK |
3354 | @end table |
3355 | ||
c1f7febf RK |
3356 | @node Type Attributes |
3357 | @section Specifying Attributes of Types | |
3358 | @cindex attribute of types | |
3359 | @cindex type attributes | |
3360 | ||
3361 | The keyword @code{__attribute__} allows you to specify special | |
3362 | attributes of @code{struct} and @code{union} types when you define such | |
3363 | types. This keyword is followed by an attribute specification inside | |
d18b1ed8 | 3364 | double parentheses. Six attributes are currently defined for types: |
e23bd218 | 3365 | @code{aligned}, @code{packed}, @code{transparent_union}, @code{unused}, |
d18b1ed8 OS |
3366 | @code{deprecated} and @code{may_alias}. Other attributes are defined for |
3367 | functions (@pxref{Function Attributes}) and for variables | |
3368 | (@pxref{Variable Attributes}). | |
c1f7febf RK |
3369 | |
3370 | You may also specify any one of these attributes with @samp{__} | |
3371 | preceding and following its keyword. This allows you to use these | |
3372 | attributes in header files without being concerned about a possible | |
3373 | macro of the same name. For example, you may use @code{__aligned__} | |
3374 | instead of @code{aligned}. | |
3375 | ||
3376 | You may specify the @code{aligned} and @code{transparent_union} | |
3377 | attributes either in a @code{typedef} declaration or just past the | |
3378 | closing curly brace of a complete enum, struct or union type | |
3379 | @emph{definition} and the @code{packed} attribute only past the closing | |
3380 | brace of a definition. | |
3381 | ||
4051959b JM |
3382 | You may also specify attributes between the enum, struct or union |
3383 | tag and the name of the type rather than after the closing brace. | |
3384 | ||
2c5e91d2 JM |
3385 | @xref{Attribute Syntax}, for details of the exact syntax for using |
3386 | attributes. | |
3387 | ||
c1f7febf RK |
3388 | @table @code |
3389 | @cindex @code{aligned} attribute | |
3390 | @item aligned (@var{alignment}) | |
3391 | This attribute specifies a minimum alignment (in bytes) for variables | |
3392 | of the specified type. For example, the declarations: | |
3393 | ||
3394 | @smallexample | |
f69eecfb JL |
3395 | struct S @{ short f[3]; @} __attribute__ ((aligned (8))); |
3396 | typedef int more_aligned_int __attribute__ ((aligned (8))); | |
c1f7febf RK |
3397 | @end smallexample |
3398 | ||
3399 | @noindent | |
d863830b | 3400 | force the compiler to insure (as far as it can) that each variable whose |
c1f7febf | 3401 | type is @code{struct S} or @code{more_aligned_int} will be allocated and |
981f6289 | 3402 | aligned @emph{at least} on a 8-byte boundary. On a SPARC, having all |
c1f7febf RK |
3403 | variables of type @code{struct S} aligned to 8-byte boundaries allows |
3404 | the compiler to use the @code{ldd} and @code{std} (doubleword load and | |
3405 | store) instructions when copying one variable of type @code{struct S} to | |
3406 | another, thus improving run-time efficiency. | |
3407 | ||
3408 | Note that the alignment of any given @code{struct} or @code{union} type | |
5490d604 | 3409 | is required by the ISO C standard to be at least a perfect multiple of |
c1f7febf RK |
3410 | the lowest common multiple of the alignments of all of the members of |
3411 | the @code{struct} or @code{union} in question. This means that you @emph{can} | |
3412 | effectively adjust the alignment of a @code{struct} or @code{union} | |
3413 | type by attaching an @code{aligned} attribute to any one of the members | |
3414 | of such a type, but the notation illustrated in the example above is a | |
3415 | more obvious, intuitive, and readable way to request the compiler to | |
3416 | adjust the alignment of an entire @code{struct} or @code{union} type. | |
3417 | ||
3418 | As in the preceding example, you can explicitly specify the alignment | |
3419 | (in bytes) that you wish the compiler to use for a given @code{struct} | |
3420 | or @code{union} type. Alternatively, you can leave out the alignment factor | |
3421 | and just ask the compiler to align a type to the maximum | |
3422 | useful alignment for the target machine you are compiling for. For | |
3423 | example, you could write: | |
3424 | ||
3425 | @smallexample | |
3426 | struct S @{ short f[3]; @} __attribute__ ((aligned)); | |
3427 | @end smallexample | |
3428 | ||
3429 | Whenever you leave out the alignment factor in an @code{aligned} | |
3430 | attribute specification, the compiler automatically sets the alignment | |
3431 | for the type to the largest alignment which is ever used for any data | |
3432 | type on the target machine you are compiling for. Doing this can often | |
3433 | make copy operations more efficient, because the compiler can use | |
3434 | whatever instructions copy the biggest chunks of memory when performing | |
3435 | copies to or from the variables which have types that you have aligned | |
3436 | this way. | |
3437 | ||
3438 | In the example above, if the size of each @code{short} is 2 bytes, then | |
3439 | the size of the entire @code{struct S} type is 6 bytes. The smallest | |
3440 | power of two which is greater than or equal to that is 8, so the | |
3441 | compiler sets the alignment for the entire @code{struct S} type to 8 | |
3442 | bytes. | |
3443 | ||
3444 | Note that although you can ask the compiler to select a time-efficient | |
3445 | alignment for a given type and then declare only individual stand-alone | |
3446 | objects of that type, the compiler's ability to select a time-efficient | |
3447 | alignment is primarily useful only when you plan to create arrays of | |
3448 | variables having the relevant (efficiently aligned) type. If you | |
3449 | declare or use arrays of variables of an efficiently-aligned type, then | |
3450 | it is likely that your program will also be doing pointer arithmetic (or | |
3451 | subscripting, which amounts to the same thing) on pointers to the | |
3452 | relevant type, and the code that the compiler generates for these | |
3453 | pointer arithmetic operations will often be more efficient for | |
3454 | efficiently-aligned types than for other types. | |
3455 | ||
3456 | The @code{aligned} attribute can only increase the alignment; but you | |
3457 | can decrease it by specifying @code{packed} as well. See below. | |
3458 | ||
3459 | Note that the effectiveness of @code{aligned} attributes may be limited | |
3460 | by inherent limitations in your linker. On many systems, the linker is | |
3461 | only able to arrange for variables to be aligned up to a certain maximum | |
3462 | alignment. (For some linkers, the maximum supported alignment may | |
3463 | be very very small.) If your linker is only able to align variables | |
3464 | up to a maximum of 8 byte alignment, then specifying @code{aligned(16)} | |
3465 | in an @code{__attribute__} will still only provide you with 8 byte | |
3466 | alignment. See your linker documentation for further information. | |
3467 | ||
3468 | @item packed | |
a5bcc582 NS |
3469 | This attribute, attached to @code{struct} or @code{union} type |
3470 | definition, specifies that each member of the structure or union is | |
3471 | placed to minimize the memory required. When attached to an @code{enum} | |
3472 | definition, it indicates that the smallest integral type should be used. | |
c1f7febf | 3473 | |
84330467 | 3474 | @opindex fshort-enums |
c1f7febf RK |
3475 | Specifying this attribute for @code{struct} and @code{union} types is |
3476 | equivalent to specifying the @code{packed} attribute on each of the | |
84330467 | 3477 | structure or union members. Specifying the @option{-fshort-enums} |
c1f7febf RK |
3478 | flag on the line is equivalent to specifying the @code{packed} |
3479 | attribute on all @code{enum} definitions. | |
3480 | ||
a5bcc582 NS |
3481 | In the following example @code{struct my_packed_struct}'s members are |
3482 | packed closely together, but the internal layout of its @code{s} member | |
3483 | is not packed -- to do that, @code{struct my_unpacked_struct} would need to | |
3484 | be packed too. | |
3485 | ||
3486 | @smallexample | |
3487 | struct my_unpacked_struct | |
3488 | @{ | |
3489 | char c; | |
3490 | int i; | |
3491 | @}; | |
3492 | ||
3493 | struct my_packed_struct __attribute__ ((__packed__)) | |
3494 | @{ | |
3495 | char c; | |
3496 | int i; | |
3497 | struct my_unpacked_struct s; | |
3498 | @}; | |
3499 | @end smallexample | |
3500 | ||
3501 | You may only specify this attribute on the definition of a @code{enum}, | |
3502 | @code{struct} or @code{union}, not on a @code{typedef} which does not | |
3503 | also define the enumerated type, structure or union. | |
c1f7febf RK |
3504 | |
3505 | @item transparent_union | |
3506 | This attribute, attached to a @code{union} type definition, indicates | |
3507 | that any function parameter having that union type causes calls to that | |
3508 | function to be treated in a special way. | |
3509 | ||
3510 | First, the argument corresponding to a transparent union type can be of | |
3511 | any type in the union; no cast is required. Also, if the union contains | |
3512 | a pointer type, the corresponding argument can be a null pointer | |
3513 | constant or a void pointer expression; and if the union contains a void | |
3514 | pointer type, the corresponding argument can be any pointer expression. | |
3515 | If the union member type is a pointer, qualifiers like @code{const} on | |
3516 | the referenced type must be respected, just as with normal pointer | |
3517 | conversions. | |
3518 | ||
3519 | Second, the argument is passed to the function using the calling | |
64c18e57 | 3520 | conventions of the first member of the transparent union, not the calling |
c1f7febf RK |
3521 | conventions of the union itself. All members of the union must have the |
3522 | same machine representation; this is necessary for this argument passing | |
3523 | to work properly. | |
3524 | ||
3525 | Transparent unions are designed for library functions that have multiple | |
3526 | interfaces for compatibility reasons. For example, suppose the | |
3527 | @code{wait} function must accept either a value of type @code{int *} to | |
3528 | comply with Posix, or a value of type @code{union wait *} to comply with | |
3529 | the 4.1BSD interface. If @code{wait}'s parameter were @code{void *}, | |
3530 | @code{wait} would accept both kinds of arguments, but it would also | |
3531 | accept any other pointer type and this would make argument type checking | |
3532 | less useful. Instead, @code{<sys/wait.h>} might define the interface | |
3533 | as follows: | |
3534 | ||
3535 | @smallexample | |
3536 | typedef union | |
3537 | @{ | |
3538 | int *__ip; | |
3539 | union wait *__up; | |
3540 | @} wait_status_ptr_t __attribute__ ((__transparent_union__)); | |
3541 | ||
3542 | pid_t wait (wait_status_ptr_t); | |
3543 | @end smallexample | |
3544 | ||
3545 | This interface allows either @code{int *} or @code{union wait *} | |
3546 | arguments to be passed, using the @code{int *} calling convention. | |
3547 | The program can call @code{wait} with arguments of either type: | |
3548 | ||
3ab51846 | 3549 | @smallexample |
c1f7febf RK |
3550 | int w1 () @{ int w; return wait (&w); @} |
3551 | int w2 () @{ union wait w; return wait (&w); @} | |
3ab51846 | 3552 | @end smallexample |
c1f7febf RK |
3553 | |
3554 | With this interface, @code{wait}'s implementation might look like this: | |
3555 | ||
3ab51846 | 3556 | @smallexample |
c1f7febf RK |
3557 | pid_t wait (wait_status_ptr_t p) |
3558 | @{ | |
3559 | return waitpid (-1, p.__ip, 0); | |
3560 | @} | |
3ab51846 | 3561 | @end smallexample |
d863830b JL |
3562 | |
3563 | @item unused | |
3564 | When attached to a type (including a @code{union} or a @code{struct}), | |
3565 | this attribute means that variables of that type are meant to appear | |
f0523f02 | 3566 | possibly unused. GCC will not produce a warning for any variables of |
d863830b JL |
3567 | that type, even if the variable appears to do nothing. This is often |
3568 | the case with lock or thread classes, which are usually defined and then | |
3569 | not referenced, but contain constructors and destructors that have | |
956d6950 | 3570 | nontrivial bookkeeping functions. |
d863830b | 3571 | |
e23bd218 IR |
3572 | @item deprecated |
3573 | The @code{deprecated} attribute results in a warning if the type | |
3574 | is used anywhere in the source file. This is useful when identifying | |
3575 | types that are expected to be removed in a future version of a program. | |
3576 | If possible, the warning also includes the location of the declaration | |
3577 | of the deprecated type, to enable users to easily find further | |
3578 | information about why the type is deprecated, or what they should do | |
3579 | instead. Note that the warnings only occur for uses and then only | |
adc9fe67 | 3580 | if the type is being applied to an identifier that itself is not being |
e23bd218 IR |
3581 | declared as deprecated. |
3582 | ||
3583 | @smallexample | |
3584 | typedef int T1 __attribute__ ((deprecated)); | |
3585 | T1 x; | |
3586 | typedef T1 T2; | |
3587 | T2 y; | |
3588 | typedef T1 T3 __attribute__ ((deprecated)); | |
3589 | T3 z __attribute__ ((deprecated)); | |
3590 | @end smallexample | |
3591 | ||
3592 | results in a warning on line 2 and 3 but not lines 4, 5, or 6. No | |
3593 | warning is issued for line 4 because T2 is not explicitly | |
3594 | deprecated. Line 5 has no warning because T3 is explicitly | |
3595 | deprecated. Similarly for line 6. | |
3596 | ||
3597 | The @code{deprecated} attribute can also be used for functions and | |
3598 | variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.) | |
3599 | ||
d18b1ed8 OS |
3600 | @item may_alias |
3601 | Accesses to objects with types with this attribute are not subjected to | |
3602 | type-based alias analysis, but are instead assumed to be able to alias | |
3603 | any other type of objects, just like the @code{char} type. See | |
3604 | @option{-fstrict-aliasing} for more information on aliasing issues. | |
3605 | ||
3606 | Example of use: | |
3607 | ||
478c9e72 | 3608 | @smallexample |
d18b1ed8 OS |
3609 | typedef short __attribute__((__may_alias__)) short_a; |
3610 | ||
3611 | int | |
3612 | main (void) | |
3613 | @{ | |
3614 | int a = 0x12345678; | |
3615 | short_a *b = (short_a *) &a; | |
3616 | ||
3617 | b[1] = 0; | |
3618 | ||
3619 | if (a == 0x12345678) | |
3620 | abort(); | |
3621 | ||
3622 | exit(0); | |
3623 | @} | |
478c9e72 | 3624 | @end smallexample |
d18b1ed8 OS |
3625 | |
3626 | If you replaced @code{short_a} with @code{short} in the variable | |
3627 | declaration, the above program would abort when compiled with | |
3628 | @option{-fstrict-aliasing}, which is on by default at @option{-O2} or | |
3629 | above in recent GCC versions. | |
fe77449a DR |
3630 | |
3631 | @subsection i386 Type Attributes | |
3632 | ||
3633 | Two attributes are currently defined for i386 configurations: | |
3634 | @code{ms_struct} and @code{gcc_struct} | |
3635 | ||
3636 | @item ms_struct | |
3637 | @itemx gcc_struct | |
3638 | @cindex @code{ms_struct} | |
3639 | @cindex @code{gcc_struct} | |
3640 | ||
3641 | If @code{packed} is used on a structure, or if bit-fields are used | |
3642 | it may be that the Microsoft ABI packs them differently | |
3643 | than GCC would normally pack them. Particularly when moving packed | |
3644 | data between functions compiled with GCC and the native Microsoft compiler | |
3645 | (either via function call or as data in a file), it may be necessary to access | |
3646 | either format. | |
3647 | ||
95fef11f | 3648 | Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86 |
fe77449a | 3649 | compilers to match the native Microsoft compiler. |
c1f7febf RK |
3650 | @end table |
3651 | ||
3652 | To specify multiple attributes, separate them by commas within the | |
3653 | double parentheses: for example, @samp{__attribute__ ((aligned (16), | |
3654 | packed))}. | |
3655 | ||
3656 | @node Inline | |
3657 | @section An Inline Function is As Fast As a Macro | |
3658 | @cindex inline functions | |
3659 | @cindex integrating function code | |
3660 | @cindex open coding | |
3661 | @cindex macros, inline alternative | |
3662 | ||
f0523f02 | 3663 | By declaring a function @code{inline}, you can direct GCC to |
c1f7febf RK |
3664 | integrate that function's code into the code for its callers. This |
3665 | makes execution faster by eliminating the function-call overhead; in | |
3666 | addition, if any of the actual argument values are constant, their known | |
3667 | values may permit simplifications at compile time so that not all of the | |
3668 | inline function's code needs to be included. The effect on code size is | |
3669 | less predictable; object code may be larger or smaller with function | |
3670 | inlining, depending on the particular case. Inlining of functions is an | |
3671 | optimization and it really ``works'' only in optimizing compilation. If | |
84330467 | 3672 | you don't use @option{-O}, no function is really inline. |
c1f7febf | 3673 | |
4b404517 JM |
3674 | Inline functions are included in the ISO C99 standard, but there are |
3675 | currently substantial differences between what GCC implements and what | |
3676 | the ISO C99 standard requires. | |
3677 | ||
c1f7febf RK |
3678 | To declare a function inline, use the @code{inline} keyword in its |
3679 | declaration, like this: | |
3680 | ||
3ab51846 | 3681 | @smallexample |
c1f7febf RK |
3682 | inline int |
3683 | inc (int *a) | |
3684 | @{ | |
3685 | (*a)++; | |
3686 | @} | |
3ab51846 | 3687 | @end smallexample |
c1f7febf | 3688 | |
5490d604 | 3689 | (If you are writing a header file to be included in ISO C programs, write |
c1f7febf | 3690 | @code{__inline__} instead of @code{inline}. @xref{Alternate Keywords}.) |
c1f7febf | 3691 | You can also make all ``simple enough'' functions inline with the option |
84330467 | 3692 | @option{-finline-functions}. |
247b14bd | 3693 | |
84330467 | 3694 | @opindex Winline |
247b14bd RH |
3695 | Note that certain usages in a function definition can make it unsuitable |
3696 | for inline substitution. Among these usages are: use of varargs, use of | |
3697 | alloca, use of variable sized data types (@pxref{Variable Length}), | |
3698 | use of computed goto (@pxref{Labels as Values}), use of nonlocal goto, | |
84330467 | 3699 | and nested functions (@pxref{Nested Functions}). Using @option{-Winline} |
247b14bd RH |
3700 | will warn when a function marked @code{inline} could not be substituted, |
3701 | and will give the reason for the failure. | |
c1f7febf | 3702 | |
2147b154 | 3703 | Note that in C and Objective-C, unlike C++, the @code{inline} keyword |
c1f7febf RK |
3704 | does not affect the linkage of the function. |
3705 | ||
3706 | @cindex automatic @code{inline} for C++ member fns | |
3707 | @cindex @code{inline} automatic for C++ member fns | |
3708 | @cindex member fns, automatically @code{inline} | |
3709 | @cindex C++ member fns, automatically @code{inline} | |
84330467 | 3710 | @opindex fno-default-inline |
f0523f02 | 3711 | GCC automatically inlines member functions defined within the class |
c1f7febf | 3712 | body of C++ programs even if they are not explicitly declared |
84330467 | 3713 | @code{inline}. (You can override this with @option{-fno-default-inline}; |
c1f7febf RK |
3714 | @pxref{C++ Dialect Options,,Options Controlling C++ Dialect}.) |
3715 | ||
3716 | @cindex inline functions, omission of | |
84330467 | 3717 | @opindex fkeep-inline-functions |
c1f7febf RK |
3718 | When a function is both inline and @code{static}, if all calls to the |
3719 | function are integrated into the caller, and the function's address is | |
3720 | never used, then the function's own assembler code is never referenced. | |
f0523f02 | 3721 | In this case, GCC does not actually output assembler code for the |
84330467 | 3722 | function, unless you specify the option @option{-fkeep-inline-functions}. |
c1f7febf RK |
3723 | Some calls cannot be integrated for various reasons (in particular, |
3724 | calls that precede the function's definition cannot be integrated, and | |
3725 | neither can recursive calls within the definition). If there is a | |
3726 | nonintegrated call, then the function is compiled to assembler code as | |
3727 | usual. The function must also be compiled as usual if the program | |
3728 | refers to its address, because that can't be inlined. | |
3729 | ||
3730 | @cindex non-static inline function | |
3731 | When an inline function is not @code{static}, then the compiler must assume | |
3732 | that there may be calls from other source files; since a global symbol can | |
3733 | be defined only once in any program, the function must not be defined in | |
3734 | the other source files, so the calls therein cannot be integrated. | |
3735 | Therefore, a non-@code{static} inline function is always compiled on its | |
3736 | own in the usual fashion. | |
3737 | ||
3738 | If you specify both @code{inline} and @code{extern} in the function | |
3739 | definition, then the definition is used only for inlining. In no case | |
3740 | is the function compiled on its own, not even if you refer to its | |
3741 | address explicitly. Such an address becomes an external reference, as | |
3742 | if you had only declared the function, and had not defined it. | |
3743 | ||
3744 | This combination of @code{inline} and @code{extern} has almost the | |
3745 | effect of a macro. The way to use it is to put a function definition in | |
3746 | a header file with these keywords, and put another copy of the | |
3747 | definition (lacking @code{inline} and @code{extern}) in a library file. | |
3748 | The definition in the header file will cause most calls to the function | |
3749 | to be inlined. If any uses of the function remain, they will refer to | |
3750 | the single copy in the library. | |
3751 | ||
64c18e57 DF |
3752 | Since GCC eventually will implement ISO C99 semantics for |
3753 | inline functions, it is best to use @code{static inline} only | |
9c2d4260 | 3754 | to guarantee compatibility. (The |
4b404517 JM |
3755 | existing semantics will remain available when @option{-std=gnu89} is |
3756 | specified, but eventually the default will be @option{-std=gnu99} and | |
3757 | that will implement the C99 semantics, though it does not do so yet.) | |
3758 | ||
6aa77e6c AH |
3759 | GCC does not inline any functions when not optimizing unless you specify |
3760 | the @samp{always_inline} attribute for the function, like this: | |
3761 | ||
3ab51846 | 3762 | @smallexample |
6aa77e6c AH |
3763 | /* Prototype. */ |
3764 | inline void foo (const char) __attribute__((always_inline)); | |
3ab51846 | 3765 | @end smallexample |
c1f7febf RK |
3766 | |
3767 | @node Extended Asm | |
3768 | @section Assembler Instructions with C Expression Operands | |
3769 | @cindex extended @code{asm} | |
3770 | @cindex @code{asm} expressions | |
3771 | @cindex assembler instructions | |
3772 | @cindex registers | |
3773 | ||
c85f7c16 JL |
3774 | In an assembler instruction using @code{asm}, you can specify the |
3775 | operands of the instruction using C expressions. This means you need not | |
3776 | guess which registers or memory locations will contain the data you want | |
c1f7febf RK |
3777 | to use. |
3778 | ||
c85f7c16 JL |
3779 | You must specify an assembler instruction template much like what |
3780 | appears in a machine description, plus an operand constraint string for | |
3781 | each operand. | |
c1f7febf RK |
3782 | |
3783 | For example, here is how to use the 68881's @code{fsinx} instruction: | |
3784 | ||
3ab51846 | 3785 | @smallexample |
c1f7febf | 3786 | asm ("fsinx %1,%0" : "=f" (result) : "f" (angle)); |
3ab51846 | 3787 | @end smallexample |
c1f7febf RK |
3788 | |
3789 | @noindent | |
3790 | Here @code{angle} is the C expression for the input operand while | |
3791 | @code{result} is that of the output operand. Each has @samp{"f"} as its | |
c85f7c16 JL |
3792 | operand constraint, saying that a floating point register is required. |
3793 | The @samp{=} in @samp{=f} indicates that the operand is an output; all | |
3794 | output operands' constraints must use @samp{=}. The constraints use the | |
3795 | same language used in the machine description (@pxref{Constraints}). | |
3796 | ||
3797 | Each operand is described by an operand-constraint string followed by | |
3798 | the C expression in parentheses. A colon separates the assembler | |
3799 | template from the first output operand and another separates the last | |
3800 | output operand from the first input, if any. Commas separate the | |
84b72302 RH |
3801 | operands within each group. The total number of operands is currently |
3802 | limited to 30; this limitation may be lifted in some future version of | |
3803 | GCC. | |
c85f7c16 JL |
3804 | |
3805 | If there are no output operands but there are input operands, you must | |
3806 | place two consecutive colons surrounding the place where the output | |
c1f7febf RK |
3807 | operands would go. |
3808 | ||
84b72302 RH |
3809 | As of GCC version 3.1, it is also possible to specify input and output |
3810 | operands using symbolic names which can be referenced within the | |
3811 | assembler code. These names are specified inside square brackets | |
3812 | preceding the constraint string, and can be referenced inside the | |
3813 | assembler code using @code{%[@var{name}]} instead of a percentage sign | |
3814 | followed by the operand number. Using named operands the above example | |
3815 | could look like: | |
3816 | ||
3ab51846 | 3817 | @smallexample |
84b72302 RH |
3818 | asm ("fsinx %[angle],%[output]" |
3819 | : [output] "=f" (result) | |
3820 | : [angle] "f" (angle)); | |
3ab51846 | 3821 | @end smallexample |
84b72302 RH |
3822 | |
3823 | @noindent | |
3824 | Note that the symbolic operand names have no relation whatsoever to | |
3825 | other C identifiers. You may use any name you like, even those of | |
64c18e57 | 3826 | existing C symbols, but you must ensure that no two operands within the same |
84b72302 RH |
3827 | assembler construct use the same symbolic name. |
3828 | ||
c1f7febf | 3829 | Output operand expressions must be lvalues; the compiler can check this. |
c85f7c16 JL |
3830 | The input operands need not be lvalues. The compiler cannot check |
3831 | whether the operands have data types that are reasonable for the | |
3832 | instruction being executed. It does not parse the assembler instruction | |
3833 | template and does not know what it means or even whether it is valid | |
3834 | assembler input. The extended @code{asm} feature is most often used for | |
3835 | machine instructions the compiler itself does not know exist. If | |
3836 | the output expression cannot be directly addressed (for example, it is a | |
f0523f02 | 3837 | bit-field), your constraint must allow a register. In that case, GCC |
c85f7c16 JL |
3838 | will use the register as the output of the @code{asm}, and then store |
3839 | that register into the output. | |
3840 | ||
f0523f02 | 3841 | The ordinary output operands must be write-only; GCC will assume that |
c85f7c16 JL |
3842 | the values in these operands before the instruction are dead and need |
3843 | not be generated. Extended asm supports input-output or read-write | |
3844 | operands. Use the constraint character @samp{+} to indicate such an | |
373a04f1 JM |
3845 | operand and list it with the output operands. You should only use |
3846 | read-write operands when the constraints for the operand (or the | |
3847 | operand in which only some of the bits are to be changed) allow a | |
3848 | register. | |
3849 | ||
3850 | You may, as an alternative, logically split its function into two | |
3851 | separate operands, one input operand and one write-only output | |
3852 | operand. The connection between them is expressed by constraints | |
3853 | which say they need to be in the same location when the instruction | |
3854 | executes. You can use the same C expression for both operands, or | |
3855 | different expressions. For example, here we write the (fictitious) | |
3856 | @samp{combine} instruction with @code{bar} as its read-only source | |
3857 | operand and @code{foo} as its read-write destination: | |
c1f7febf | 3858 | |
3ab51846 | 3859 | @smallexample |
c1f7febf | 3860 | asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar)); |
3ab51846 | 3861 | @end smallexample |
c1f7febf RK |
3862 | |
3863 | @noindent | |
c85f7c16 | 3864 | The constraint @samp{"0"} for operand 1 says that it must occupy the |
84b72302 RH |
3865 | same location as operand 0. A number in constraint is allowed only in |
3866 | an input operand and it must refer to an output operand. | |
c1f7febf | 3867 | |
84b72302 | 3868 | Only a number in the constraint can guarantee that one operand will be in |
c85f7c16 JL |
3869 | the same place as another. The mere fact that @code{foo} is the value |
3870 | of both operands is not enough to guarantee that they will be in the | |
3871 | same place in the generated assembler code. The following would not | |
3872 | work reliably: | |
c1f7febf | 3873 | |
3ab51846 | 3874 | @smallexample |
c1f7febf | 3875 | asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar)); |
3ab51846 | 3876 | @end smallexample |
c1f7febf RK |
3877 | |
3878 | Various optimizations or reloading could cause operands 0 and 1 to be in | |
f0523f02 | 3879 | different registers; GCC knows no reason not to do so. For example, the |
c1f7febf RK |
3880 | compiler might find a copy of the value of @code{foo} in one register and |
3881 | use it for operand 1, but generate the output operand 0 in a different | |
3882 | register (copying it afterward to @code{foo}'s own address). Of course, | |
3883 | since the register for operand 1 is not even mentioned in the assembler | |
f0523f02 | 3884 | code, the result will not work, but GCC can't tell that. |
c1f7febf | 3885 | |
84b72302 RH |
3886 | As of GCC version 3.1, one may write @code{[@var{name}]} instead of |
3887 | the operand number for a matching constraint. For example: | |
3888 | ||
3ab51846 | 3889 | @smallexample |
84b72302 RH |
3890 | asm ("cmoveq %1,%2,%[result]" |
3891 | : [result] "=r"(result) | |
3892 | : "r" (test), "r"(new), "[result]"(old)); | |
3ab51846 | 3893 | @end smallexample |
84b72302 | 3894 | |
c85f7c16 JL |
3895 | Some instructions clobber specific hard registers. To describe this, |
3896 | write a third colon after the input operands, followed by the names of | |
3897 | the clobbered hard registers (given as strings). Here is a realistic | |
3898 | example for the VAX: | |
c1f7febf | 3899 | |
3ab51846 | 3900 | @smallexample |
c1f7febf RK |
3901 | asm volatile ("movc3 %0,%1,%2" |
3902 | : /* no outputs */ | |
3903 | : "g" (from), "g" (to), "g" (count) | |
3904 | : "r0", "r1", "r2", "r3", "r4", "r5"); | |
3ab51846 | 3905 | @end smallexample |
c1f7febf | 3906 | |
c5c76735 JL |
3907 | You may not write a clobber description in a way that overlaps with an |
3908 | input or output operand. For example, you may not have an operand | |
3909 | describing a register class with one member if you mention that register | |
acb5d088 HPN |
3910 | in the clobber list. Variables declared to live in specific registers |
3911 | (@pxref{Explicit Reg Vars}), and used as asm input or output operands must | |
3912 | have no part mentioned in the clobber description. | |
3913 | There is no way for you to specify that an input | |
c5c76735 JL |
3914 | operand is modified without also specifying it as an output |
3915 | operand. Note that if all the output operands you specify are for this | |
3916 | purpose (and hence unused), you will then also need to specify | |
3917 | @code{volatile} for the @code{asm} construct, as described below, to | |
f0523f02 | 3918 | prevent GCC from deleting the @code{asm} statement as unused. |
8fe1938e | 3919 | |
c1f7febf | 3920 | If you refer to a particular hardware register from the assembler code, |
c85f7c16 JL |
3921 | you will probably have to list the register after the third colon to |
3922 | tell the compiler the register's value is modified. In some assemblers, | |
3923 | the register names begin with @samp{%}; to produce one @samp{%} in the | |
3924 | assembler code, you must write @samp{%%} in the input. | |
3925 | ||
3926 | If your assembler instruction can alter the condition code register, add | |
f0523f02 | 3927 | @samp{cc} to the list of clobbered registers. GCC on some machines |
c85f7c16 JL |
3928 | represents the condition codes as a specific hardware register; |
3929 | @samp{cc} serves to name this register. On other machines, the | |
3930 | condition code is handled differently, and specifying @samp{cc} has no | |
3931 | effect. But it is valid no matter what the machine. | |
c1f7febf | 3932 | |
bbf5a54d | 3933 | If your assembler instructions access memory in an unpredictable |
c85f7c16 | 3934 | fashion, add @samp{memory} to the list of clobbered registers. This |
bbf5a54d AJ |
3935 | will cause GCC to not keep memory values cached in registers across the |
3936 | assembler instruction and not optimize stores or loads to that memory. | |
3937 | You will also want to add the @code{volatile} keyword if the memory | |
3938 | affected is not listed in the inputs or outputs of the @code{asm}, as | |
3939 | the @samp{memory} clobber does not count as a side-effect of the | |
3940 | @code{asm}. If you know how large the accessed memory is, you can add | |
3941 | it as input or output but if this is not known, you should add | |
3942 | @samp{memory}. As an example, if you access ten bytes of a string, you | |
3943 | can use a memory input like: | |
3944 | ||
3945 | @example | |
3946 | @{"m"( (@{ struct @{ char x[10]; @} *p = (void *)ptr ; *p; @}) )@}. | |
3947 | @end example | |
3948 | ||
3949 | Note that in the following example the memory input is necessary, | |
3950 | otherwise GCC might optimize the store to @code{x} away: | |
3951 | @example | |
3952 | int foo () | |
3953 | @{ | |
3954 | int x = 42; | |
3955 | int *y = &x; | |
3956 | int result; | |
3957 | asm ("magic stuff accessing an 'int' pointed to by '%1'" | |
3958 | "=&d" (r) : "a" (y), "m" (*y)); | |
3959 | return result; | |
3960 | @} | |
3961 | @end example | |
c1f7febf | 3962 | |
c85f7c16 | 3963 | You can put multiple assembler instructions together in a single |
8720914b HPN |
3964 | @code{asm} template, separated by the characters normally used in assembly |
3965 | code for the system. A combination that works in most places is a newline | |
3966 | to break the line, plus a tab character to move to the instruction field | |
3967 | (written as @samp{\n\t}). Sometimes semicolons can be used, if the | |
3968 | assembler allows semicolons as a line-breaking character. Note that some | |
3969 | assembler dialects use semicolons to start a comment. | |
3970 | The input operands are guaranteed not to use any of the clobbered | |
c85f7c16 JL |
3971 | registers, and neither will the output operands' addresses, so you can |
3972 | read and write the clobbered registers as many times as you like. Here | |
3973 | is an example of multiple instructions in a template; it assumes the | |
3974 | subroutine @code{_foo} accepts arguments in registers 9 and 10: | |
c1f7febf | 3975 | |
3ab51846 | 3976 | @smallexample |
8720914b | 3977 | asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo" |
c1f7febf RK |
3978 | : /* no outputs */ |
3979 | : "g" (from), "g" (to) | |
3980 | : "r9", "r10"); | |
3ab51846 | 3981 | @end smallexample |
c1f7febf | 3982 | |
f0523f02 | 3983 | Unless an output operand has the @samp{&} constraint modifier, GCC |
c85f7c16 JL |
3984 | may allocate it in the same register as an unrelated input operand, on |
3985 | the assumption the inputs are consumed before the outputs are produced. | |
c1f7febf RK |
3986 | This assumption may be false if the assembler code actually consists of |
3987 | more than one instruction. In such a case, use @samp{&} for each output | |
c85f7c16 | 3988 | operand that may not overlap an input. @xref{Modifiers}. |
c1f7febf | 3989 | |
c85f7c16 JL |
3990 | If you want to test the condition code produced by an assembler |
3991 | instruction, you must include a branch and a label in the @code{asm} | |
3992 | construct, as follows: | |
c1f7febf | 3993 | |
3ab51846 | 3994 | @smallexample |
8720914b | 3995 | asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:" |
c1f7febf RK |
3996 | : "g" (result) |
3997 | : "g" (input)); | |
3ab51846 | 3998 | @end smallexample |
c1f7febf RK |
3999 | |
4000 | @noindent | |
4001 | This assumes your assembler supports local labels, as the GNU assembler | |
4002 | and most Unix assemblers do. | |
4003 | ||
4004 | Speaking of labels, jumps from one @code{asm} to another are not | |
c85f7c16 JL |
4005 | supported. The compiler's optimizers do not know about these jumps, and |
4006 | therefore they cannot take account of them when deciding how to | |
c1f7febf RK |
4007 | optimize. |
4008 | ||
4009 | @cindex macros containing @code{asm} | |
4010 | Usually the most convenient way to use these @code{asm} instructions is to | |
4011 | encapsulate them in macros that look like functions. For example, | |
4012 | ||
3ab51846 | 4013 | @smallexample |
c1f7febf RK |
4014 | #define sin(x) \ |
4015 | (@{ double __value, __arg = (x); \ | |
4016 | asm ("fsinx %1,%0": "=f" (__value): "f" (__arg)); \ | |
4017 | __value; @}) | |
3ab51846 | 4018 | @end smallexample |
c1f7febf RK |
4019 | |
4020 | @noindent | |
4021 | Here the variable @code{__arg} is used to make sure that the instruction | |
4022 | operates on a proper @code{double} value, and to accept only those | |
4023 | arguments @code{x} which can convert automatically to a @code{double}. | |
4024 | ||
c85f7c16 JL |
4025 | Another way to make sure the instruction operates on the correct data |
4026 | type is to use a cast in the @code{asm}. This is different from using a | |
c1f7febf RK |
4027 | variable @code{__arg} in that it converts more different types. For |
4028 | example, if the desired type were @code{int}, casting the argument to | |
4029 | @code{int} would accept a pointer with no complaint, while assigning the | |
4030 | argument to an @code{int} variable named @code{__arg} would warn about | |
4031 | using a pointer unless the caller explicitly casts it. | |
4032 | ||
f0523f02 | 4033 | If an @code{asm} has output operands, GCC assumes for optimization |
c85f7c16 JL |
4034 | purposes the instruction has no side effects except to change the output |
4035 | operands. This does not mean instructions with a side effect cannot be | |
4036 | used, but you must be careful, because the compiler may eliminate them | |
4037 | if the output operands aren't used, or move them out of loops, or | |
4038 | replace two with one if they constitute a common subexpression. Also, | |
4039 | if your instruction does have a side effect on a variable that otherwise | |
4040 | appears not to change, the old value of the variable may be reused later | |
4041 | if it happens to be found in a register. | |
c1f7febf RK |
4042 | |
4043 | You can prevent an @code{asm} instruction from being deleted, moved | |
4044 | significantly, or combined, by writing the keyword @code{volatile} after | |
4045 | the @code{asm}. For example: | |
4046 | ||
3ab51846 | 4047 | @smallexample |
310668e8 JM |
4048 | #define get_and_set_priority(new) \ |
4049 | (@{ int __old; \ | |
4050 | asm volatile ("get_and_set_priority %0, %1" \ | |
4051 | : "=g" (__old) : "g" (new)); \ | |
c85f7c16 | 4052 | __old; @}) |
3ab51846 | 4053 | @end smallexample |
c1f7febf RK |
4054 | |
4055 | @noindent | |
f0523f02 | 4056 | If you write an @code{asm} instruction with no outputs, GCC will know |
c85f7c16 | 4057 | the instruction has side-effects and will not delete the instruction or |
e71b34aa | 4058 | move it outside of loops. |
c85f7c16 | 4059 | |
e71b34aa MM |
4060 | The @code{volatile} keyword indicates that the instruction has |
4061 | important side-effects. GCC will not delete a volatile @code{asm} if | |
4062 | it is reachable. (The instruction can still be deleted if GCC can | |
4063 | prove that control-flow will never reach the location of the | |
4064 | instruction.) In addition, GCC will not reschedule instructions | |
4065 | across a volatile @code{asm} instruction. For example: | |
4066 | ||
3ab51846 | 4067 | @smallexample |
bd78000b | 4068 | *(volatile int *)addr = foo; |
e71b34aa | 4069 | asm volatile ("eieio" : : ); |
3ab51846 | 4070 | @end smallexample |
e71b34aa | 4071 | |
ebb48a4d | 4072 | @noindent |
e71b34aa MM |
4073 | Assume @code{addr} contains the address of a memory mapped device |
4074 | register. The PowerPC @code{eieio} instruction (Enforce In-order | |
aee96fe9 | 4075 | Execution of I/O) tells the CPU to make sure that the store to that |
161d7b59 | 4076 | device register happens before it issues any other I/O@. |
c1f7febf RK |
4077 | |
4078 | Note that even a volatile @code{asm} instruction can be moved in ways | |
4079 | that appear insignificant to the compiler, such as across jump | |
4080 | instructions. You can't expect a sequence of volatile @code{asm} | |
4081 | instructions to remain perfectly consecutive. If you want consecutive | |
e71b34aa MM |
4082 | output, use a single @code{asm}. Also, GCC will perform some |
4083 | optimizations across a volatile @code{asm} instruction; GCC does not | |
4084 | ``forget everything'' when it encounters a volatile @code{asm} | |
4085 | instruction the way some other compilers do. | |
4086 | ||
4087 | An @code{asm} instruction without any operands or clobbers (an ``old | |
4088 | style'' @code{asm}) will be treated identically to a volatile | |
4089 | @code{asm} instruction. | |
c1f7febf RK |
4090 | |
4091 | It is a natural idea to look for a way to give access to the condition | |
4092 | code left by the assembler instruction. However, when we attempted to | |
4093 | implement this, we found no way to make it work reliably. The problem | |
4094 | is that output operands might need reloading, which would result in | |
4095 | additional following ``store'' instructions. On most machines, these | |
4096 | instructions would alter the condition code before there was time to | |
4097 | test it. This problem doesn't arise for ordinary ``test'' and | |
4098 | ``compare'' instructions because they don't have any output operands. | |
4099 | ||
eda3fbbe GB |
4100 | For reasons similar to those described above, it is not possible to give |
4101 | an assembler instruction access to the condition code left by previous | |
4102 | instructions. | |
4103 | ||
5490d604 | 4104 | If you are writing a header file that should be includable in ISO C |
c1f7febf RK |
4105 | programs, write @code{__asm__} instead of @code{asm}. @xref{Alternate |
4106 | Keywords}. | |
4107 | ||
ece7fc1c RE |
4108 | @subsection Size of an @code{asm} |
4109 | ||
4110 | Some targets require that GCC track the size of each instruction used in | |
4111 | order to generate correct code. Because the final length of an | |
4112 | @code{asm} is only known by the assembler, GCC must make an estimate as | |
4113 | to how big it will be. The estimate is formed by counting the number of | |
4114 | statements in the pattern of the @code{asm} and multiplying that by the | |
4115 | length of the longest instruction on that processor. Statements in the | |
4116 | @code{asm} are identified by newline characters and whatever statement | |
4117 | separator characters are supported by the assembler; on most processors | |
4118 | this is the `@code{;}' character. | |
4119 | ||
4120 | Normally, GCC's estimate is perfectly adequate to ensure that correct | |
4121 | code is generated, but it is possible to confuse the compiler if you use | |
4122 | pseudo instructions or assembler macros that expand into multiple real | |
4123 | instructions or if you use assembler directives that expand to more | |
4124 | space in the object file than would be needed for a single instruction. | |
4125 | If this happens then the assembler will produce a diagnostic saying that | |
4126 | a label is unreachable. | |
4127 | ||
fe0ce426 JH |
4128 | @subsection i386 floating point asm operands |
4129 | ||
4130 | There are several rules on the usage of stack-like regs in | |
4131 | asm_operands insns. These rules apply only to the operands that are | |
4132 | stack-like regs: | |
4133 | ||
4134 | @enumerate | |
4135 | @item | |
4136 | Given a set of input regs that die in an asm_operands, it is | |
4137 | necessary to know which are implicitly popped by the asm, and | |
4138 | which must be explicitly popped by gcc. | |
4139 | ||
4140 | An input reg that is implicitly popped by the asm must be | |
4141 | explicitly clobbered, unless it is constrained to match an | |
4142 | output operand. | |
4143 | ||
4144 | @item | |
4145 | For any input reg that is implicitly popped by an asm, it is | |
4146 | necessary to know how to adjust the stack to compensate for the pop. | |
4147 | If any non-popped input is closer to the top of the reg-stack than | |
4148 | the implicitly popped reg, it would not be possible to know what the | |
84330467 | 4149 | stack looked like---it's not clear how the rest of the stack ``slides |
fe0ce426 JH |
4150 | up''. |
4151 | ||
4152 | All implicitly popped input regs must be closer to the top of | |
4153 | the reg-stack than any input that is not implicitly popped. | |
4154 | ||
4155 | It is possible that if an input dies in an insn, reload might | |
4156 | use the input reg for an output reload. Consider this example: | |
4157 | ||
3ab51846 | 4158 | @smallexample |
fe0ce426 | 4159 | asm ("foo" : "=t" (a) : "f" (b)); |
3ab51846 | 4160 | @end smallexample |
fe0ce426 JH |
4161 | |
4162 | This asm says that input B is not popped by the asm, and that | |
c771326b | 4163 | the asm pushes a result onto the reg-stack, i.e., the stack is one |
fe0ce426 JH |
4164 | deeper after the asm than it was before. But, it is possible that |
4165 | reload will think that it can use the same reg for both the input and | |
4166 | the output, if input B dies in this insn. | |
4167 | ||
4168 | If any input operand uses the @code{f} constraint, all output reg | |
4169 | constraints must use the @code{&} earlyclobber. | |
4170 | ||
4171 | The asm above would be written as | |
4172 | ||
3ab51846 | 4173 | @smallexample |
fe0ce426 | 4174 | asm ("foo" : "=&t" (a) : "f" (b)); |
3ab51846 | 4175 | @end smallexample |
fe0ce426 JH |
4176 | |
4177 | @item | |
4178 | Some operands need to be in particular places on the stack. All | |
84330467 | 4179 | output operands fall in this category---there is no other way to |
fe0ce426 JH |
4180 | know which regs the outputs appear in unless the user indicates |
4181 | this in the constraints. | |
4182 | ||
4183 | Output operands must specifically indicate which reg an output | |
4184 | appears in after an asm. @code{=f} is not allowed: the operand | |
4185 | constraints must select a class with a single reg. | |
4186 | ||
4187 | @item | |
4188 | Output operands may not be ``inserted'' between existing stack regs. | |
4189 | Since no 387 opcode uses a read/write operand, all output operands | |
4190 | are dead before the asm_operands, and are pushed by the asm_operands. | |
4191 | It makes no sense to push anywhere but the top of the reg-stack. | |
4192 | ||
4193 | Output operands must start at the top of the reg-stack: output | |
4194 | operands may not ``skip'' a reg. | |
4195 | ||
4196 | @item | |
4197 | Some asm statements may need extra stack space for internal | |
4198 | calculations. This can be guaranteed by clobbering stack registers | |
4199 | unrelated to the inputs and outputs. | |
4200 | ||
4201 | @end enumerate | |
4202 | ||
4203 | Here are a couple of reasonable asms to want to write. This asm | |
4204 | takes one input, which is internally popped, and produces two outputs. | |
4205 | ||
3ab51846 | 4206 | @smallexample |
fe0ce426 | 4207 | asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp)); |
3ab51846 | 4208 | @end smallexample |
fe0ce426 JH |
4209 | |
4210 | This asm takes two inputs, which are popped by the @code{fyl2xp1} opcode, | |
4211 | and replaces them with one output. The user must code the @code{st(1)} | |
4212 | clobber for reg-stack.c to know that @code{fyl2xp1} pops both inputs. | |
4213 | ||
3ab51846 | 4214 | @smallexample |
fe0ce426 | 4215 | asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)"); |
3ab51846 | 4216 | @end smallexample |
fe0ce426 | 4217 | |
c1f7febf | 4218 | @include md.texi |
c1f7febf RK |
4219 | |
4220 | @node Asm Labels | |
4221 | @section Controlling Names Used in Assembler Code | |
4222 | @cindex assembler names for identifiers | |
4223 | @cindex names used in assembler code | |
4224 | @cindex identifiers, names in assembler code | |
4225 | ||
4226 | You can specify the name to be used in the assembler code for a C | |
4227 | function or variable by writing the @code{asm} (or @code{__asm__}) | |
4228 | keyword after the declarator as follows: | |
4229 | ||
3ab51846 | 4230 | @smallexample |
c1f7febf | 4231 | int foo asm ("myfoo") = 2; |
3ab51846 | 4232 | @end smallexample |
c1f7febf RK |
4233 | |
4234 | @noindent | |
4235 | This specifies that the name to be used for the variable @code{foo} in | |
4236 | the assembler code should be @samp{myfoo} rather than the usual | |
4237 | @samp{_foo}. | |
4238 | ||
4239 | On systems where an underscore is normally prepended to the name of a C | |
4240 | function or variable, this feature allows you to define names for the | |
4241 | linker that do not start with an underscore. | |
4242 | ||
0adc3c19 MM |
4243 | It does not make sense to use this feature with a non-static local |
4244 | variable since such variables do not have assembler names. If you are | |
4245 | trying to put the variable in a particular register, see @ref{Explicit | |
4246 | Reg Vars}. GCC presently accepts such code with a warning, but will | |
4247 | probably be changed to issue an error, rather than a warning, in the | |
4248 | future. | |
4249 | ||
c1f7febf RK |
4250 | You cannot use @code{asm} in this way in a function @emph{definition}; but |
4251 | you can get the same effect by writing a declaration for the function | |
4252 | before its definition and putting @code{asm} there, like this: | |
4253 | ||
3ab51846 | 4254 | @smallexample |
c1f7febf RK |
4255 | extern func () asm ("FUNC"); |
4256 | ||
4257 | func (x, y) | |
4258 | int x, y; | |
0d893a63 | 4259 | /* @r{@dots{}} */ |
3ab51846 | 4260 | @end smallexample |
c1f7febf RK |
4261 | |
4262 | It is up to you to make sure that the assembler names you choose do not | |
4263 | conflict with any other assembler symbols. Also, you must not use a | |
f0523f02 JM |
4264 | register name; that would produce completely invalid assembler code. GCC |
4265 | does not as yet have the ability to store static variables in registers. | |
c1f7febf RK |
4266 | Perhaps that will be added. |
4267 | ||
4268 | @node Explicit Reg Vars | |
4269 | @section Variables in Specified Registers | |
4270 | @cindex explicit register variables | |
4271 | @cindex variables in specified registers | |
4272 | @cindex specified registers | |
4273 | @cindex registers, global allocation | |
4274 | ||
4275 | GNU C allows you to put a few global variables into specified hardware | |
4276 | registers. You can also specify the register in which an ordinary | |
4277 | register variable should be allocated. | |
4278 | ||
4279 | @itemize @bullet | |
4280 | @item | |
4281 | Global register variables reserve registers throughout the program. | |
4282 | This may be useful in programs such as programming language | |
4283 | interpreters which have a couple of global variables that are accessed | |
4284 | very often. | |
4285 | ||
4286 | @item | |
4287 | Local register variables in specific registers do not reserve the | |
4288 | registers. The compiler's data flow analysis is capable of determining | |
4289 | where the specified registers contain live values, and where they are | |
8d344fbc | 4290 | available for other uses. Stores into local register variables may be deleted |
0deaf590 JL |
4291 | when they appear to be dead according to dataflow analysis. References |
4292 | to local register variables may be deleted or moved or simplified. | |
c1f7febf RK |
4293 | |
4294 | These local variables are sometimes convenient for use with the extended | |
4295 | @code{asm} feature (@pxref{Extended Asm}), if you want to write one | |
4296 | output of the assembler instruction directly into a particular register. | |
4297 | (This will work provided the register you specify fits the constraints | |
4298 | specified for that operand in the @code{asm}.) | |
4299 | @end itemize | |
4300 | ||
4301 | @menu | |
4302 | * Global Reg Vars:: | |
4303 | * Local Reg Vars:: | |
4304 | @end menu | |
4305 | ||
4306 | @node Global Reg Vars | |
4307 | @subsection Defining Global Register Variables | |
4308 | @cindex global register variables | |
4309 | @cindex registers, global variables in | |
4310 | ||
4311 | You can define a global register variable in GNU C like this: | |
4312 | ||
3ab51846 | 4313 | @smallexample |
c1f7febf | 4314 | register int *foo asm ("a5"); |
3ab51846 | 4315 | @end smallexample |
c1f7febf RK |
4316 | |
4317 | @noindent | |
4318 | Here @code{a5} is the name of the register which should be used. Choose a | |
4319 | register which is normally saved and restored by function calls on your | |
4320 | machine, so that library routines will not clobber it. | |
4321 | ||
4322 | Naturally the register name is cpu-dependent, so you would need to | |
4323 | conditionalize your program according to cpu type. The register | |
4324 | @code{a5} would be a good choice on a 68000 for a variable of pointer | |
4325 | type. On machines with register windows, be sure to choose a ``global'' | |
4326 | register that is not affected magically by the function call mechanism. | |
4327 | ||
4328 | In addition, operating systems on one type of cpu may differ in how they | |
4329 | name the registers; then you would need additional conditionals. For | |
4330 | example, some 68000 operating systems call this register @code{%a5}. | |
4331 | ||
4332 | Eventually there may be a way of asking the compiler to choose a register | |
4333 | automatically, but first we need to figure out how it should choose and | |
4334 | how to enable you to guide the choice. No solution is evident. | |
4335 | ||
4336 | Defining a global register variable in a certain register reserves that | |
4337 | register entirely for this use, at least within the current compilation. | |
4338 | The register will not be allocated for any other purpose in the functions | |
4339 | in the current compilation. The register will not be saved and restored by | |
4340 | these functions. Stores into this register are never deleted even if they | |
4341 | would appear to be dead, but references may be deleted or moved or | |
4342 | simplified. | |
4343 | ||
4344 | It is not safe to access the global register variables from signal | |
4345 | handlers, or from more than one thread of control, because the system | |
4346 | library routines may temporarily use the register for other things (unless | |
4347 | you recompile them specially for the task at hand). | |
4348 | ||
4349 | @cindex @code{qsort}, and global register variables | |
4350 | It is not safe for one function that uses a global register variable to | |
4351 | call another such function @code{foo} by way of a third function | |
e979f9e8 | 4352 | @code{lose} that was compiled without knowledge of this variable (i.e.@: in a |
c1f7febf RK |
4353 | different source file in which the variable wasn't declared). This is |
4354 | because @code{lose} might save the register and put some other value there. | |
4355 | For example, you can't expect a global register variable to be available in | |
4356 | the comparison-function that you pass to @code{qsort}, since @code{qsort} | |
4357 | might have put something else in that register. (If you are prepared to | |
4358 | recompile @code{qsort} with the same global register variable, you can | |
4359 | solve this problem.) | |
4360 | ||
4361 | If you want to recompile @code{qsort} or other source files which do not | |
4362 | actually use your global register variable, so that they will not use that | |
4363 | register for any other purpose, then it suffices to specify the compiler | |
84330467 | 4364 | option @option{-ffixed-@var{reg}}. You need not actually add a global |
c1f7febf RK |
4365 | register declaration to their source code. |
4366 | ||
4367 | A function which can alter the value of a global register variable cannot | |
4368 | safely be called from a function compiled without this variable, because it | |
4369 | could clobber the value the caller expects to find there on return. | |
4370 | Therefore, the function which is the entry point into the part of the | |
4371 | program that uses the global register variable must explicitly save and | |
4372 | restore the value which belongs to its caller. | |
4373 | ||
4374 | @cindex register variable after @code{longjmp} | |
4375 | @cindex global register after @code{longjmp} | |
4376 | @cindex value after @code{longjmp} | |
4377 | @findex longjmp | |
4378 | @findex setjmp | |
4379 | On most machines, @code{longjmp} will restore to each global register | |
4380 | variable the value it had at the time of the @code{setjmp}. On some | |
4381 | machines, however, @code{longjmp} will not change the value of global | |
4382 | register variables. To be portable, the function that called @code{setjmp} | |
4383 | should make other arrangements to save the values of the global register | |
4384 | variables, and to restore them in a @code{longjmp}. This way, the same | |
4385 | thing will happen regardless of what @code{longjmp} does. | |
4386 | ||
4387 | All global register variable declarations must precede all function | |
4388 | definitions. If such a declaration could appear after function | |
4389 | definitions, the declaration would be too late to prevent the register from | |
4390 | being used for other purposes in the preceding functions. | |
4391 | ||
4392 | Global register variables may not have initial values, because an | |
4393 | executable file has no means to supply initial contents for a register. | |
4394 | ||
981f6289 | 4395 | On the SPARC, there are reports that g3 @dots{} g7 are suitable |
c1f7febf RK |
4396 | registers, but certain library functions, such as @code{getwd}, as well |
4397 | as the subroutines for division and remainder, modify g3 and g4. g1 and | |
4398 | g2 are local temporaries. | |
4399 | ||
4400 | On the 68000, a2 @dots{} a5 should be suitable, as should d2 @dots{} d7. | |
4401 | Of course, it will not do to use more than a few of those. | |
4402 | ||
4403 | @node Local Reg Vars | |
4404 | @subsection Specifying Registers for Local Variables | |
4405 | @cindex local variables, specifying registers | |
4406 | @cindex specifying registers for local variables | |
4407 | @cindex registers for local variables | |
4408 | ||
4409 | You can define a local register variable with a specified register | |
4410 | like this: | |
4411 | ||
3ab51846 | 4412 | @smallexample |
c1f7febf | 4413 | register int *foo asm ("a5"); |
3ab51846 | 4414 | @end smallexample |
c1f7febf RK |
4415 | |
4416 | @noindent | |
4417 | Here @code{a5} is the name of the register which should be used. Note | |
4418 | that this is the same syntax used for defining global register | |
4419 | variables, but for a local variable it would appear within a function. | |
4420 | ||
4421 | Naturally the register name is cpu-dependent, but this is not a | |
4422 | problem, since specific registers are most often useful with explicit | |
4423 | assembler instructions (@pxref{Extended Asm}). Both of these things | |
4424 | generally require that you conditionalize your program according to | |
4425 | cpu type. | |
4426 | ||
4427 | In addition, operating systems on one type of cpu may differ in how they | |
4428 | name the registers; then you would need additional conditionals. For | |
4429 | example, some 68000 operating systems call this register @code{%a5}. | |
4430 | ||
c1f7febf RK |
4431 | Defining such a register variable does not reserve the register; it |
4432 | remains available for other uses in places where flow control determines | |
d754127f | 4433 | the variable's value is not live. |
e5e809f4 | 4434 | |
f0523f02 | 4435 | This option does not guarantee that GCC will generate code that has |
e5e809f4 JL |
4436 | this variable in the register you specify at all times. You may not |
4437 | code an explicit reference to this register in an @code{asm} statement | |
4438 | and assume it will always refer to this variable. | |
c1f7febf | 4439 | |
8d344fbc | 4440 | Stores into local register variables may be deleted when they appear to be dead |
0deaf590 JL |
4441 | according to dataflow analysis. References to local register variables may |
4442 | be deleted or moved or simplified. | |
4443 | ||
c1f7febf RK |
4444 | @node Alternate Keywords |
4445 | @section Alternate Keywords | |
4446 | @cindex alternate keywords | |
4447 | @cindex keywords, alternate | |
4448 | ||
5490d604 | 4449 | @option{-ansi} and the various @option{-std} options disable certain |
f458d1d5 ZW |
4450 | keywords. This causes trouble when you want to use GNU C extensions, or |
4451 | a general-purpose header file that should be usable by all programs, | |
4452 | including ISO C programs. The keywords @code{asm}, @code{typeof} and | |
4453 | @code{inline} are not available in programs compiled with | |
4454 | @option{-ansi} or @option{-std} (although @code{inline} can be used in a | |
4455 | program compiled with @option{-std=c99}). The ISO C99 keyword | |
5490d604 JM |
4456 | @code{restrict} is only available when @option{-std=gnu99} (which will |
4457 | eventually be the default) or @option{-std=c99} (or the equivalent | |
bd819a4a | 4458 | @option{-std=iso9899:1999}) is used. |
c1f7febf RK |
4459 | |
4460 | The way to solve these problems is to put @samp{__} at the beginning and | |
4461 | end of each problematical keyword. For example, use @code{__asm__} | |
f458d1d5 | 4462 | instead of @code{asm}, and @code{__inline__} instead of @code{inline}. |
c1f7febf RK |
4463 | |
4464 | Other C compilers won't accept these alternative keywords; if you want to | |
4465 | compile with another compiler, you can define the alternate keywords as | |
4466 | macros to replace them with the customary keywords. It looks like this: | |
4467 | ||
3ab51846 | 4468 | @smallexample |
c1f7febf RK |
4469 | #ifndef __GNUC__ |
4470 | #define __asm__ asm | |
4471 | #endif | |
3ab51846 | 4472 | @end smallexample |
c1f7febf | 4473 | |
6e6b0525 | 4474 | @findex __extension__ |
84330467 JM |
4475 | @opindex pedantic |
4476 | @option{-pedantic} and other options cause warnings for many GNU C extensions. | |
dbe519e0 | 4477 | You can |
c1f7febf RK |
4478 | prevent such warnings within one expression by writing |
4479 | @code{__extension__} before the expression. @code{__extension__} has no | |
4480 | effect aside from this. | |
4481 | ||
4482 | @node Incomplete Enums | |
4483 | @section Incomplete @code{enum} Types | |
4484 | ||
4485 | You can define an @code{enum} tag without specifying its possible values. | |
4486 | This results in an incomplete type, much like what you get if you write | |
4487 | @code{struct foo} without describing the elements. A later declaration | |
4488 | which does specify the possible values completes the type. | |
4489 | ||
4490 | You can't allocate variables or storage using the type while it is | |
4491 | incomplete. However, you can work with pointers to that type. | |
4492 | ||
4493 | This extension may not be very useful, but it makes the handling of | |
4494 | @code{enum} more consistent with the way @code{struct} and @code{union} | |
4495 | are handled. | |
4496 | ||
4497 | This extension is not supported by GNU C++. | |
4498 | ||
4499 | @node Function Names | |
4500 | @section Function Names as Strings | |
e6cc3a24 | 4501 | @cindex @code{__func__} identifier |
4b404517 JM |
4502 | @cindex @code{__FUNCTION__} identifier |
4503 | @cindex @code{__PRETTY_FUNCTION__} identifier | |
c1f7febf | 4504 | |
e6cc3a24 ZW |
4505 | GCC provides three magic variables which hold the name of the current |
4506 | function, as a string. The first of these is @code{__func__}, which | |
4507 | is part of the C99 standard: | |
4508 | ||
4509 | @display | |
4510 | The identifier @code{__func__} is implicitly declared by the translator | |
4511 | as if, immediately following the opening brace of each function | |
4512 | definition, the declaration | |
4513 | ||
4514 | @smallexample | |
4515 | static const char __func__[] = "function-name"; | |
4516 | @end smallexample | |
c1f7febf | 4517 | |
e6cc3a24 ZW |
4518 | appeared, where function-name is the name of the lexically-enclosing |
4519 | function. This name is the unadorned name of the function. | |
4520 | @end display | |
4521 | ||
4522 | @code{__FUNCTION__} is another name for @code{__func__}. Older | |
4523 | versions of GCC recognize only this name. However, it is not | |
4524 | standardized. For maximum portability, we recommend you use | |
4525 | @code{__func__}, but provide a fallback definition with the | |
4526 | preprocessor: | |
4527 | ||
4528 | @smallexample | |
4529 | #if __STDC_VERSION__ < 199901L | |
4530 | # if __GNUC__ >= 2 | |
4531 | # define __func__ __FUNCTION__ | |
4532 | # else | |
4533 | # define __func__ "<unknown>" | |
4534 | # endif | |
4535 | #endif | |
4536 | @end smallexample | |
4537 | ||
4538 | In C, @code{__PRETTY_FUNCTION__} is yet another name for | |
4539 | @code{__func__}. However, in C++, @code{__PRETTY_FUNCTION__} contains | |
4540 | the type signature of the function as well as its bare name. For | |
4541 | example, this program: | |
c1f7febf RK |
4542 | |
4543 | @smallexample | |
4544 | extern "C" @{ | |
4545 | extern int printf (char *, ...); | |
4546 | @} | |
4547 | ||
4548 | class a @{ | |
4549 | public: | |
a721a601 | 4550 | void sub (int i) |
c1f7febf RK |
4551 | @{ |
4552 | printf ("__FUNCTION__ = %s\n", __FUNCTION__); | |
4553 | printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__); | |
4554 | @} | |
4555 | @}; | |
4556 | ||
4557 | int | |
4558 | main (void) | |
4559 | @{ | |
4560 | a ax; | |
4561 | ax.sub (0); | |
4562 | return 0; | |
4563 | @} | |
4564 | @end smallexample | |
4565 | ||
4566 | @noindent | |
4567 | gives this output: | |
4568 | ||
4569 | @smallexample | |
4570 | __FUNCTION__ = sub | |
e6cc3a24 | 4571 | __PRETTY_FUNCTION__ = void a::sub(int) |
22acfb79 NM |
4572 | @end smallexample |
4573 | ||
e6cc3a24 ZW |
4574 | These identifiers are not preprocessor macros. In GCC 3.3 and |
4575 | earlier, in C only, @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__} | |
4576 | were treated as string literals; they could be used to initialize | |
4577 | @code{char} arrays, and they could be concatenated with other string | |
4578 | literals. GCC 3.4 and later treat them as variables, like | |
4579 | @code{__func__}. In C++, @code{__FUNCTION__} and | |
4580 | @code{__PRETTY_FUNCTION__} have always been variables. | |
22acfb79 | 4581 | |
c1f7febf RK |
4582 | @node Return Address |
4583 | @section Getting the Return or Frame Address of a Function | |
4584 | ||
4585 | These functions may be used to get information about the callers of a | |
4586 | function. | |
4587 | ||
84330467 | 4588 | @deftypefn {Built-in Function} {void *} __builtin_return_address (unsigned int @var{level}) |
c1f7febf RK |
4589 | This function returns the return address of the current function, or of |
4590 | one of its callers. The @var{level} argument is number of frames to | |
4591 | scan up the call stack. A value of @code{0} yields the return address | |
4592 | of the current function, a value of @code{1} yields the return address | |
95b1627e EC |
4593 | of the caller of the current function, and so forth. When inlining |
4594 | the expected behavior is that the function will return the address of | |
4595 | the function that will be returned to. To work around this behavior use | |
4596 | the @code{noinline} function attribute. | |
c1f7febf RK |
4597 | |
4598 | The @var{level} argument must be a constant integer. | |
4599 | ||
4600 | On some machines it may be impossible to determine the return address of | |
4601 | any function other than the current one; in such cases, or when the top | |
dd96fbc5 L |
4602 | of the stack has been reached, this function will return @code{0} or a |
4603 | random value. In addition, @code{__builtin_frame_address} may be used | |
4604 | to determine if the top of the stack has been reached. | |
c1f7febf | 4605 | |
df2a54e9 | 4606 | This function should only be used with a nonzero argument for debugging |
c1f7febf | 4607 | purposes. |
84330467 | 4608 | @end deftypefn |
c1f7febf | 4609 | |
84330467 | 4610 | @deftypefn {Built-in Function} {void *} __builtin_frame_address (unsigned int @var{level}) |
c1f7febf RK |
4611 | This function is similar to @code{__builtin_return_address}, but it |
4612 | returns the address of the function frame rather than the return address | |
4613 | of the function. Calling @code{__builtin_frame_address} with a value of | |
4614 | @code{0} yields the frame address of the current function, a value of | |
4615 | @code{1} yields the frame address of the caller of the current function, | |
4616 | and so forth. | |
4617 | ||
4618 | The frame is the area on the stack which holds local variables and saved | |
4619 | registers. The frame address is normally the address of the first word | |
4620 | pushed on to the stack by the function. However, the exact definition | |
4621 | depends upon the processor and the calling convention. If the processor | |
4622 | has a dedicated frame pointer register, and the function has a frame, | |
4623 | then @code{__builtin_frame_address} will return the value of the frame | |
4624 | pointer register. | |
4625 | ||
dd96fbc5 L |
4626 | On some machines it may be impossible to determine the frame address of |
4627 | any function other than the current one; in such cases, or when the top | |
4628 | of the stack has been reached, this function will return @code{0} if | |
4629 | the first frame pointer is properly initialized by the startup code. | |
4630 | ||
df2a54e9 | 4631 | This function should only be used with a nonzero argument for debugging |
dd96fbc5 | 4632 | purposes. |
84330467 | 4633 | @end deftypefn |
c1f7febf | 4634 | |
1255c85c BS |
4635 | @node Vector Extensions |
4636 | @section Using vector instructions through built-in functions | |
4637 | ||
4638 | On some targets, the instruction set contains SIMD vector instructions that | |
4639 | operate on multiple values contained in one large register at the same time. | |
4640 | For example, on the i386 the MMX, 3Dnow! and SSE extensions can be used | |
4641 | this way. | |
4642 | ||
4643 | The first step in using these extensions is to provide the necessary data | |
4644 | types. This should be done using an appropriate @code{typedef}: | |
4645 | ||
3ab51846 | 4646 | @smallexample |
4a5eab38 | 4647 | typedef int v4si __attribute__ ((vector_size (16))); |
3ab51846 | 4648 | @end smallexample |
1255c85c | 4649 | |
4a5eab38 PB |
4650 | The @code{int} type specifies the base type, while the attribute specifies |
4651 | the vector size for the variable, measured in bytes. For example, the | |
4652 | declaration above causes the compiler to set the mode for the @code{v4si} | |
4653 | type to be 16 bytes wide and divided into @code{int} sized units. For | |
4654 | a 32-bit @code{int} this means a vector of 4 units of 4 bytes, and the | |
4655 | corresponding mode of @code{foo} will be @acronym{V4SI}. | |
1255c85c | 4656 | |
4a5eab38 PB |
4657 | The @code{vector_size} attribute is only applicable to integral and |
4658 | float scalars, although arrays, pointers, and function return values | |
4659 | are allowed in conjunction with this construct. | |
4660 | ||
4661 | All the basic integer types can be used as base types, both as signed | |
4662 | and as unsigned: @code{char}, @code{short}, @code{int}, @code{long}, | |
4663 | @code{long long}. In addition, @code{float} and @code{double} can be | |
4664 | used to build floating-point vector types. | |
1255c85c | 4665 | |
cb2a532e | 4666 | Specifying a combination that is not valid for the current architecture |
2dd76960 | 4667 | will cause GCC to synthesize the instructions using a narrower mode. |
cb2a532e | 4668 | For example, if you specify a variable of type @code{V4SI} and your |
2dd76960 | 4669 | architecture does not allow for this specific SIMD type, GCC will |
cb2a532e AH |
4670 | produce code that uses 4 @code{SIs}. |
4671 | ||
4672 | The types defined in this manner can be used with a subset of normal C | |
2dd76960 | 4673 | operations. Currently, GCC will allow using the following operators |
3a3e1600 | 4674 | on these types: @code{+, -, *, /, unary minus, ^, |, &, ~}@. |
cb2a532e AH |
4675 | |
4676 | The operations behave like C++ @code{valarrays}. Addition is defined as | |
4677 | the addition of the corresponding elements of the operands. For | |
4678 | example, in the code below, each of the 4 elements in @var{a} will be | |
4679 | added to the corresponding 4 elements in @var{b} and the resulting | |
4680 | vector will be stored in @var{c}. | |
4681 | ||
3ab51846 | 4682 | @smallexample |
4a5eab38 | 4683 | typedef int v4si __attribute__ ((vector_size (16))); |
cb2a532e AH |
4684 | |
4685 | v4si a, b, c; | |
4686 | ||
4687 | c = a + b; | |
3ab51846 | 4688 | @end smallexample |
cb2a532e | 4689 | |
3a3e1600 GK |
4690 | Subtraction, multiplication, division, and the logical operations |
4691 | operate in a similar manner. Likewise, the result of using the unary | |
4692 | minus or complement operators on a vector type is a vector whose | |
4693 | elements are the negative or complemented values of the corresponding | |
cb2a532e AH |
4694 | elements in the operand. |
4695 | ||
4696 | You can declare variables and use them in function calls and returns, as | |
4697 | well as in assignments and some casts. You can specify a vector type as | |
4698 | a return type for a function. Vector types can also be used as function | |
4699 | arguments. It is possible to cast from one vector type to another, | |
4700 | provided they are of the same size (in fact, you can also cast vectors | |
4701 | to and from other datatypes of the same size). | |
4702 | ||
4703 | You cannot operate between vectors of different lengths or different | |
90a21764 | 4704 | signedness without a cast. |
cb2a532e AH |
4705 | |
4706 | A port that supports hardware vector operations, usually provides a set | |
4707 | of built-in functions that can be used to operate on vectors. For | |
4708 | example, a function to add two vectors and multiply the result by a | |
4709 | third could look like this: | |
1255c85c | 4710 | |
3ab51846 | 4711 | @smallexample |
1255c85c BS |
4712 | v4si f (v4si a, v4si b, v4si c) |
4713 | @{ | |
4714 | v4si tmp = __builtin_addv4si (a, b); | |
4715 | return __builtin_mulv4si (tmp, c); | |
4716 | @} | |
4717 | ||
3ab51846 | 4718 | @end smallexample |
1255c85c | 4719 | |
7a3ea201 RH |
4720 | @node Offsetof |
4721 | @section Offsetof | |
4722 | @findex __builtin_offsetof | |
4723 | ||
4724 | GCC implements for both C and C++ a syntactic extension to implement | |
4725 | the @code{offsetof} macro. | |
4726 | ||
4727 | @smallexample | |
4728 | primary: | |
4729 | "__builtin_offsetof" "(" @code{typename} "," offsetof_member_designator ")" | |
4730 | ||
4731 | offsetof_member_designator: | |
4732 | @code{identifier} | |
4733 | | offsetof_member_designator "." @code{identifier} | |
4734 | | offsetof_member_designator "[" @code{expr} "]" | |
4735 | @end smallexample | |
4736 | ||
4737 | This extension is sufficient such that | |
4738 | ||
4739 | @smallexample | |
4740 | #define offsetof(@var{type}, @var{member}) __builtin_offsetof (@var{type}, @var{member}) | |
4741 | @end smallexample | |
4742 | ||
4743 | is a suitable definition of the @code{offsetof} macro. In C++, @var{type} | |
4744 | may be dependent. In either case, @var{member} may consist of a single | |
4745 | identifier, or a sequence of member accesses and array references. | |
4746 | ||
185ebd6c | 4747 | @node Other Builtins |
f0523f02 | 4748 | @section Other built-in functions provided by GCC |
c771326b | 4749 | @cindex built-in functions |
01702459 JM |
4750 | @findex __builtin_isgreater |
4751 | @findex __builtin_isgreaterequal | |
4752 | @findex __builtin_isless | |
4753 | @findex __builtin_islessequal | |
4754 | @findex __builtin_islessgreater | |
4755 | @findex __builtin_isunordered | |
98ff7c4d KG |
4756 | @findex _Exit |
4757 | @findex _exit | |
01702459 JM |
4758 | @findex abort |
4759 | @findex abs | |
98ff7c4d KG |
4760 | @findex acos |
4761 | @findex acosf | |
4762 | @findex acosh | |
4763 | @findex acoshf | |
4764 | @findex acoshl | |
4765 | @findex acosl | |
01702459 | 4766 | @findex alloca |
98ff7c4d KG |
4767 | @findex asin |
4768 | @findex asinf | |
4769 | @findex asinh | |
4770 | @findex asinhf | |
4771 | @findex asinhl | |
4772 | @findex asinl | |
29f523be | 4773 | @findex atan |
46847aa6 RS |
4774 | @findex atan2 |
4775 | @findex atan2f | |
4776 | @findex atan2l | |
29f523be | 4777 | @findex atanf |
98ff7c4d KG |
4778 | @findex atanh |
4779 | @findex atanhf | |
4780 | @findex atanhl | |
29f523be | 4781 | @findex atanl |
01702459 JM |
4782 | @findex bcmp |
4783 | @findex bzero | |
075ec276 RS |
4784 | @findex cabs |
4785 | @findex cabsf | |
4786 | @findex cabsl | |
11bf0eb0 KG |
4787 | @findex cacos |
4788 | @findex cacosf | |
4789 | @findex cacosh | |
4790 | @findex cacoshf | |
4791 | @findex cacoshl | |
4792 | @findex cacosl | |
1331d16f | 4793 | @findex calloc |
11bf0eb0 KG |
4794 | @findex carg |
4795 | @findex cargf | |
4796 | @findex cargl | |
4797 | @findex casin | |
4798 | @findex casinf | |
4799 | @findex casinh | |
4800 | @findex casinhf | |
4801 | @findex casinhl | |
4802 | @findex casinl | |
4803 | @findex catan | |
4804 | @findex catanf | |
4805 | @findex catanh | |
4806 | @findex catanhf | |
4807 | @findex catanhl | |
4808 | @findex catanl | |
98ff7c4d KG |
4809 | @findex cbrt |
4810 | @findex cbrtf | |
4811 | @findex cbrtl | |
11bf0eb0 KG |
4812 | @findex ccos |
4813 | @findex ccosf | |
4814 | @findex ccosh | |
4815 | @findex ccoshf | |
4816 | @findex ccoshl | |
4817 | @findex ccosl | |
b052d8ee RS |
4818 | @findex ceil |
4819 | @findex ceilf | |
4820 | @findex ceill | |
11bf0eb0 KG |
4821 | @findex cexp |
4822 | @findex cexpf | |
4823 | @findex cexpl | |
341e3d11 JM |
4824 | @findex cimag |
4825 | @findex cimagf | |
4826 | @findex cimagl | |
4827 | @findex conj | |
4828 | @findex conjf | |
4829 | @findex conjl | |
98ff7c4d KG |
4830 | @findex copysign |
4831 | @findex copysignf | |
4832 | @findex copysignl | |
01702459 JM |
4833 | @findex cos |
4834 | @findex cosf | |
98ff7c4d KG |
4835 | @findex cosh |
4836 | @findex coshf | |
4837 | @findex coshl | |
01702459 | 4838 | @findex cosl |
11bf0eb0 KG |
4839 | @findex cpow |
4840 | @findex cpowf | |
4841 | @findex cpowl | |
4842 | @findex cproj | |
4843 | @findex cprojf | |
4844 | @findex cprojl | |
341e3d11 JM |
4845 | @findex creal |
4846 | @findex crealf | |
4847 | @findex creall | |
11bf0eb0 KG |
4848 | @findex csin |
4849 | @findex csinf | |
4850 | @findex csinh | |
4851 | @findex csinhf | |
4852 | @findex csinhl | |
4853 | @findex csinl | |
4854 | @findex csqrt | |
4855 | @findex csqrtf | |
4856 | @findex csqrtl | |
4857 | @findex ctan | |
4858 | @findex ctanf | |
4859 | @findex ctanh | |
4860 | @findex ctanhf | |
4861 | @findex ctanhl | |
4862 | @findex ctanl | |
178b2b9f RS |
4863 | @findex dcgettext |
4864 | @findex dgettext | |
98ff7c4d KG |
4865 | @findex drem |
4866 | @findex dremf | |
4867 | @findex dreml | |
488f17e1 KG |
4868 | @findex erf |
4869 | @findex erfc | |
4870 | @findex erfcf | |
4871 | @findex erfcl | |
4872 | @findex erff | |
4873 | @findex erfl | |
01702459 | 4874 | @findex exit |
e7b489c8 | 4875 | @findex exp |
98ff7c4d KG |
4876 | @findex exp10 |
4877 | @findex exp10f | |
4878 | @findex exp10l | |
4879 | @findex exp2 | |
4880 | @findex exp2f | |
4881 | @findex exp2l | |
e7b489c8 RS |
4882 | @findex expf |
4883 | @findex expl | |
98ff7c4d KG |
4884 | @findex expm1 |
4885 | @findex expm1f | |
4886 | @findex expm1l | |
01702459 JM |
4887 | @findex fabs |
4888 | @findex fabsf | |
4889 | @findex fabsl | |
98ff7c4d KG |
4890 | @findex fdim |
4891 | @findex fdimf | |
4892 | @findex fdiml | |
01702459 | 4893 | @findex ffs |
b052d8ee RS |
4894 | @findex floor |
4895 | @findex floorf | |
4896 | @findex floorl | |
98ff7c4d KG |
4897 | @findex fma |
4898 | @findex fmaf | |
4899 | @findex fmal | |
4900 | @findex fmax | |
4901 | @findex fmaxf | |
4902 | @findex fmaxl | |
4903 | @findex fmin | |
4904 | @findex fminf | |
4905 | @findex fminl | |
b052d8ee RS |
4906 | @findex fmod |
4907 | @findex fmodf | |
4908 | @findex fmodl | |
18f988a0 | 4909 | @findex fprintf |
b4c984fb | 4910 | @findex fprintf_unlocked |
01702459 | 4911 | @findex fputs |
b4c984fb | 4912 | @findex fputs_unlocked |
a2a919aa KG |
4913 | @findex frexp |
4914 | @findex frexpf | |
4915 | @findex frexpl | |
178b2b9f | 4916 | @findex fscanf |
488f17e1 KG |
4917 | @findex gamma |
4918 | @findex gammaf | |
4919 | @findex gammal | |
178b2b9f | 4920 | @findex gettext |
98ff7c4d KG |
4921 | @findex hypot |
4922 | @findex hypotf | |
4923 | @findex hypotl | |
4924 | @findex ilogb | |
4925 | @findex ilogbf | |
4926 | @findex ilogbl | |
e78f4a97 | 4927 | @findex imaxabs |
c7b6c6cd | 4928 | @findex index |
740e5b6f KG |
4929 | @findex isalnum |
4930 | @findex isalpha | |
4931 | @findex isascii | |
4932 | @findex isblank | |
4933 | @findex iscntrl | |
4934 | @findex isdigit | |
4935 | @findex isgraph | |
4936 | @findex islower | |
4937 | @findex isprint | |
4938 | @findex ispunct | |
4939 | @findex isspace | |
4940 | @findex isupper | |
ca4944e1 KG |
4941 | @findex iswalnum |
4942 | @findex iswalpha | |
4943 | @findex iswblank | |
4944 | @findex iswcntrl | |
4945 | @findex iswdigit | |
4946 | @findex iswgraph | |
4947 | @findex iswlower | |
4948 | @findex iswprint | |
4949 | @findex iswpunct | |
4950 | @findex iswspace | |
4951 | @findex iswupper | |
4952 | @findex iswxdigit | |
740e5b6f | 4953 | @findex isxdigit |
488f17e1 KG |
4954 | @findex j0 |
4955 | @findex j0f | |
4956 | @findex j0l | |
4957 | @findex j1 | |
4958 | @findex j1f | |
4959 | @findex j1l | |
4960 | @findex jn | |
4961 | @findex jnf | |
4962 | @findex jnl | |
01702459 | 4963 | @findex labs |
98ff7c4d KG |
4964 | @findex ldexp |
4965 | @findex ldexpf | |
4966 | @findex ldexpl | |
488f17e1 KG |
4967 | @findex lgamma |
4968 | @findex lgammaf | |
4969 | @findex lgammal | |
01702459 | 4970 | @findex llabs |
98ff7c4d KG |
4971 | @findex llrint |
4972 | @findex llrintf | |
4973 | @findex llrintl | |
4974 | @findex llround | |
4975 | @findex llroundf | |
4976 | @findex llroundl | |
e7b489c8 | 4977 | @findex log |
98ff7c4d KG |
4978 | @findex log10 |
4979 | @findex log10f | |
4980 | @findex log10l | |
4981 | @findex log1p | |
4982 | @findex log1pf | |
4983 | @findex log1pl | |
4984 | @findex log2 | |
4985 | @findex log2f | |
4986 | @findex log2l | |
4987 | @findex logb | |
4988 | @findex logbf | |
4989 | @findex logbl | |
e7b489c8 RS |
4990 | @findex logf |
4991 | @findex logl | |
98ff7c4d KG |
4992 | @findex lrint |
4993 | @findex lrintf | |
4994 | @findex lrintl | |
4995 | @findex lround | |
4996 | @findex lroundf | |
4997 | @findex lroundl | |
1331d16f | 4998 | @findex malloc |
01702459 JM |
4999 | @findex memcmp |
5000 | @findex memcpy | |
9cb65f92 | 5001 | @findex mempcpy |
01702459 | 5002 | @findex memset |
a2a919aa KG |
5003 | @findex modf |
5004 | @findex modff | |
5005 | @findex modfl | |
b052d8ee RS |
5006 | @findex nearbyint |
5007 | @findex nearbyintf | |
5008 | @findex nearbyintl | |
98ff7c4d KG |
5009 | @findex nextafter |
5010 | @findex nextafterf | |
5011 | @findex nextafterl | |
5012 | @findex nexttoward | |
5013 | @findex nexttowardf | |
5014 | @findex nexttowardl | |
46847aa6 | 5015 | @findex pow |
98ff7c4d KG |
5016 | @findex pow10 |
5017 | @findex pow10f | |
5018 | @findex pow10l | |
46847aa6 RS |
5019 | @findex powf |
5020 | @findex powl | |
01702459 | 5021 | @findex printf |
b4c984fb | 5022 | @findex printf_unlocked |
08291658 RS |
5023 | @findex putchar |
5024 | @findex puts | |
98ff7c4d KG |
5025 | @findex remainder |
5026 | @findex remainderf | |
5027 | @findex remainderl | |
a2a919aa KG |
5028 | @findex remquo |
5029 | @findex remquof | |
5030 | @findex remquol | |
c7b6c6cd | 5031 | @findex rindex |
98ff7c4d KG |
5032 | @findex rint |
5033 | @findex rintf | |
5034 | @findex rintl | |
b052d8ee RS |
5035 | @findex round |
5036 | @findex roundf | |
5037 | @findex roundl | |
98ff7c4d KG |
5038 | @findex scalb |
5039 | @findex scalbf | |
5040 | @findex scalbl | |
5041 | @findex scalbln | |
5042 | @findex scalblnf | |
5043 | @findex scalblnf | |
5044 | @findex scalbn | |
5045 | @findex scalbnf | |
5046 | @findex scanfnl | |
ef79730c RS |
5047 | @findex signbit |
5048 | @findex signbitf | |
5049 | @findex signbitl | |
488f17e1 KG |
5050 | @findex significand |
5051 | @findex significandf | |
5052 | @findex significandl | |
01702459 | 5053 | @findex sin |
a2a919aa KG |
5054 | @findex sincos |
5055 | @findex sincosf | |
5056 | @findex sincosl | |
01702459 | 5057 | @findex sinf |
98ff7c4d KG |
5058 | @findex sinh |
5059 | @findex sinhf | |
5060 | @findex sinhl | |
01702459 | 5061 | @findex sinl |
08291658 RS |
5062 | @findex snprintf |
5063 | @findex sprintf | |
01702459 JM |
5064 | @findex sqrt |
5065 | @findex sqrtf | |
5066 | @findex sqrtl | |
08291658 | 5067 | @findex sscanf |
9cb65f92 | 5068 | @findex stpcpy |
d118937d | 5069 | @findex strcat |
01702459 JM |
5070 | @findex strchr |
5071 | @findex strcmp | |
5072 | @findex strcpy | |
d118937d | 5073 | @findex strcspn |
1331d16f | 5074 | @findex strdup |
178b2b9f RS |
5075 | @findex strfmon |
5076 | @findex strftime | |
01702459 | 5077 | @findex strlen |
d118937d | 5078 | @findex strncat |
da9e9f08 KG |
5079 | @findex strncmp |
5080 | @findex strncpy | |
01702459 JM |
5081 | @findex strpbrk |
5082 | @findex strrchr | |
d118937d | 5083 | @findex strspn |
01702459 | 5084 | @findex strstr |
29f523be RS |
5085 | @findex tan |
5086 | @findex tanf | |
98ff7c4d KG |
5087 | @findex tanh |
5088 | @findex tanhf | |
5089 | @findex tanhl | |
29f523be | 5090 | @findex tanl |
488f17e1 KG |
5091 | @findex tgamma |
5092 | @findex tgammaf | |
5093 | @findex tgammal | |
740e5b6f KG |
5094 | @findex toascii |
5095 | @findex tolower | |
5096 | @findex toupper | |
ca4944e1 KG |
5097 | @findex towlower |
5098 | @findex towupper | |
4977bab6 ZW |
5099 | @findex trunc |
5100 | @findex truncf | |
5101 | @findex truncl | |
178b2b9f RS |
5102 | @findex vfprintf |
5103 | @findex vfscanf | |
08291658 RS |
5104 | @findex vprintf |
5105 | @findex vscanf | |
5106 | @findex vsnprintf | |
5107 | @findex vsprintf | |
5108 | @findex vsscanf | |
488f17e1 KG |
5109 | @findex y0 |
5110 | @findex y0f | |
5111 | @findex y0l | |
5112 | @findex y1 | |
5113 | @findex y1f | |
5114 | @findex y1l | |
5115 | @findex yn | |
5116 | @findex ynf | |
5117 | @findex ynl | |
185ebd6c | 5118 | |
f0523f02 | 5119 | GCC provides a large number of built-in functions other than the ones |
185ebd6c RH |
5120 | mentioned above. Some of these are for internal use in the processing |
5121 | of exceptions or variable-length argument lists and will not be | |
5122 | documented here because they may change from time to time; we do not | |
5123 | recommend general use of these functions. | |
5124 | ||
5125 | The remaining functions are provided for optimization purposes. | |
5126 | ||
84330467 | 5127 | @opindex fno-builtin |
9c34dbbf ZW |
5128 | GCC includes built-in versions of many of the functions in the standard |
5129 | C library. The versions prefixed with @code{__builtin_} will always be | |
5130 | treated as having the same meaning as the C library function even if you | |
5131 | specify the @option{-fno-builtin} option. (@pxref{C Dialect Options}) | |
5132 | Many of these functions are only optimized in certain cases; if they are | |
01702459 JM |
5133 | not optimized in a particular case, a call to the library function will |
5134 | be emitted. | |
5135 | ||
84330467 JM |
5136 | @opindex ansi |
5137 | @opindex std | |
b052d8ee | 5138 | Outside strict ISO C mode (@option{-ansi}, @option{-std=c89} or |
98ff7c4d KG |
5139 | @option{-std=c99}), the functions |
5140 | @code{_exit}, @code{alloca}, @code{bcmp}, @code{bzero}, | |
5141 | @code{dcgettext}, @code{dgettext}, @code{dremf}, @code{dreml}, | |
5142 | @code{drem}, @code{exp10f}, @code{exp10l}, @code{exp10}, @code{ffsll}, | |
5143 | @code{ffsl}, @code{ffs}, @code{fprintf_unlocked}, @code{fputs_unlocked}, | |
488f17e1 | 5144 | @code{gammaf}, @code{gammal}, @code{gamma}, @code{gettext}, |
740e5b6f KG |
5145 | @code{index}, @code{isascii}, @code{j0f}, @code{j0l}, @code{j0}, |
5146 | @code{j1f}, @code{j1l}, @code{j1}, @code{jnf}, @code{jnl}, @code{jn}, | |
5147 | @code{mempcpy}, @code{pow10f}, @code{pow10l}, @code{pow10}, | |
5148 | @code{printf_unlocked}, @code{rindex}, @code{scalbf}, @code{scalbl}, | |
5149 | @code{scalb}, @code{signbit}, @code{signbitf}, @code{signbitl}, | |
488f17e1 | 5150 | @code{significandf}, @code{significandl}, @code{significand}, |
a2a919aa | 5151 | @code{sincosf}, @code{sincosl}, @code{sincos}, @code{stpcpy}, |
740e5b6f KG |
5152 | @code{strdup}, @code{strfmon}, @code{toascii}, @code{y0f}, @code{y0l}, |
5153 | @code{y0}, @code{y1f}, @code{y1l}, @code{y1}, @code{ynf}, @code{ynl} and | |
5154 | @code{yn} | |
1331d16f | 5155 | may be handled as built-in functions. |
b052d8ee | 5156 | All these functions have corresponding versions |
9c34dbbf ZW |
5157 | prefixed with @code{__builtin_}, which may be used even in strict C89 |
5158 | mode. | |
01702459 | 5159 | |
075ec276 | 5160 | The ISO C99 functions |
98ff7c4d KG |
5161 | @code{_Exit}, @code{acoshf}, @code{acoshl}, @code{acosh}, @code{asinhf}, |
5162 | @code{asinhl}, @code{asinh}, @code{atanhf}, @code{atanhl}, @code{atanh}, | |
11bf0eb0 KG |
5163 | @code{cabsf}, @code{cabsl}, @code{cabs}, @code{cacosf}, @code{cacoshf}, |
5164 | @code{cacoshl}, @code{cacosh}, @code{cacosl}, @code{cacos}, | |
5165 | @code{cargf}, @code{cargl}, @code{carg}, @code{casinf}, @code{casinhf}, | |
5166 | @code{casinhl}, @code{casinh}, @code{casinl}, @code{casin}, | |
5167 | @code{catanf}, @code{catanhf}, @code{catanhl}, @code{catanh}, | |
5168 | @code{catanl}, @code{catan}, @code{cbrtf}, @code{cbrtl}, @code{cbrt}, | |
5169 | @code{ccosf}, @code{ccoshf}, @code{ccoshl}, @code{ccosh}, @code{ccosl}, | |
5170 | @code{ccos}, @code{cexpf}, @code{cexpl}, @code{cexp}, @code{cimagf}, | |
740e5b6f KG |
5171 | @code{cimagl}, @code{cimag}, @code{conjf}, @code{conjl}, @code{conj}, |
5172 | @code{copysignf}, @code{copysignl}, @code{copysign}, @code{cpowf}, | |
5173 | @code{cpowl}, @code{cpow}, @code{cprojf}, @code{cprojl}, @code{cproj}, | |
5174 | @code{crealf}, @code{creall}, @code{creal}, @code{csinf}, @code{csinhf}, | |
5175 | @code{csinhl}, @code{csinh}, @code{csinl}, @code{csin}, @code{csqrtf}, | |
5176 | @code{csqrtl}, @code{csqrt}, @code{ctanf}, @code{ctanhf}, @code{ctanhl}, | |
5177 | @code{ctanh}, @code{ctanl}, @code{ctan}, @code{erfcf}, @code{erfcl}, | |
5178 | @code{erfc}, @code{erff}, @code{erfl}, @code{erf}, @code{exp2f}, | |
5179 | @code{exp2l}, @code{exp2}, @code{expm1f}, @code{expm1l}, @code{expm1}, | |
5180 | @code{fdimf}, @code{fdiml}, @code{fdim}, @code{fmaf}, @code{fmal}, | |
5181 | @code{fmaxf}, @code{fmaxl}, @code{fmax}, @code{fma}, @code{fminf}, | |
5182 | @code{fminl}, @code{fmin}, @code{hypotf}, @code{hypotl}, @code{hypot}, | |
5183 | @code{ilogbf}, @code{ilogbl}, @code{ilogb}, @code{imaxabs}, | |
ca4944e1 KG |
5184 | @code{isblank}, @code{iswblank}, @code{lgammaf}, @code{lgammal}, |
5185 | @code{lgamma}, @code{llabs}, @code{llrintf}, @code{llrintl}, | |
5186 | @code{llrint}, @code{llroundf}, @code{llroundl}, @code{llround}, | |
5187 | @code{log1pf}, @code{log1pl}, @code{log1p}, @code{log2f}, @code{log2l}, | |
5188 | @code{log2}, @code{logbf}, @code{logbl}, @code{logb}, @code{lrintf}, | |
5189 | @code{lrintl}, @code{lrint}, @code{lroundf}, @code{lroundl}, | |
5190 | @code{lround}, @code{nearbyintf}, @code{nearbyintl}, @code{nearbyint}, | |
740e5b6f KG |
5191 | @code{nextafterf}, @code{nextafterl}, @code{nextafter}, |
5192 | @code{nexttowardf}, @code{nexttowardl}, @code{nexttoward}, | |
5193 | @code{remainderf}, @code{remainderl}, @code{remainder}, @code{remquof}, | |
5194 | @code{remquol}, @code{remquo}, @code{rintf}, @code{rintl}, @code{rint}, | |
5195 | @code{roundf}, @code{roundl}, @code{round}, @code{scalblnf}, | |
5196 | @code{scalblnl}, @code{scalbln}, @code{scalbnf}, @code{scalbnl}, | |
5197 | @code{scalbn}, @code{snprintf}, @code{tgammaf}, @code{tgammal}, | |
5198 | @code{tgamma}, @code{truncf}, @code{truncl}, @code{trunc}, | |
5199 | @code{vfscanf}, @code{vscanf}, @code{vsnprintf} and @code{vsscanf} | |
08291658 | 5200 | are handled as built-in functions |
b052d8ee | 5201 | except in strict ISO C90 mode (@option{-ansi} or @option{-std=c89}). |
46847aa6 | 5202 | |
98ff7c4d KG |
5203 | There are also built-in versions of the ISO C99 functions |
5204 | @code{acosf}, @code{acosl}, @code{asinf}, @code{asinl}, @code{atan2f}, | |
29f523be | 5205 | @code{atan2l}, @code{atanf}, @code{atanl}, @code{ceilf}, @code{ceill}, |
98ff7c4d KG |
5206 | @code{cosf}, @code{coshf}, @code{coshl}, @code{cosl}, @code{expf}, |
5207 | @code{expl}, @code{fabsf}, @code{fabsl}, @code{floorf}, @code{floorl}, | |
a2a919aa KG |
5208 | @code{fmodf}, @code{fmodl}, @code{frexpf}, @code{frexpl}, @code{ldexpf}, |
5209 | @code{ldexpl}, @code{log10f}, @code{log10l}, @code{logf}, @code{logl}, | |
5210 | @code{modfl}, @code{modf}, @code{powf}, @code{powl}, @code{sinf}, | |
5211 | @code{sinhf}, @code{sinhl}, @code{sinl}, @code{sqrtf}, @code{sqrtl}, | |
5212 | @code{tanf}, @code{tanhf}, @code{tanhl} and @code{tanl} | |
46847aa6 RS |
5213 | that are recognized in any mode since ISO C90 reserves these names for |
5214 | the purpose to which ISO C99 puts them. All these functions have | |
5215 | corresponding versions prefixed with @code{__builtin_}. | |
5216 | ||
ca4944e1 KG |
5217 | The ISO C94 functions |
5218 | @code{iswalnum}, @code{iswalpha}, @code{iswcntrl}, @code{iswdigit}, | |
5219 | @code{iswgraph}, @code{iswlower}, @code{iswprint}, @code{iswpunct}, | |
5220 | @code{iswspace}, @code{iswupper}, @code{iswxdigit}, @code{towlower} and | |
5221 | @code{towupper} | |
5222 | are handled as built-in functions | |
5223 | except in strict ISO C90 mode (@option{-ansi} or @option{-std=c89}). | |
5224 | ||
98ff7c4d KG |
5225 | The ISO C90 functions |
5226 | @code{abort}, @code{abs}, @code{acos}, @code{asin}, @code{atan2}, | |
5227 | @code{atan}, @code{calloc}, @code{ceil}, @code{cosh}, @code{cos}, | |
5228 | @code{exit}, @code{exp}, @code{fabs}, @code{floor}, @code{fmod}, | |
740e5b6f KG |
5229 | @code{fprintf}, @code{fputs}, @code{frexp}, @code{fscanf}, |
5230 | @code{isalnum}, @code{isalpha}, @code{iscntrl}, @code{isdigit}, | |
5231 | @code{isgraph}, @code{islower}, @code{isprint}, @code{ispunct}, | |
5232 | @code{isspace}, @code{isupper}, @code{isxdigit}, @code{tolower}, | |
5233 | @code{toupper}, @code{labs}, @code{ldexp}, @code{log10}, @code{log}, | |
5234 | @code{malloc}, @code{memcmp}, @code{memcpy}, @code{memset}, @code{modf}, | |
5235 | @code{pow}, @code{printf}, @code{putchar}, @code{puts}, @code{scanf}, | |
5236 | @code{sinh}, @code{sin}, @code{snprintf}, @code{sprintf}, @code{sqrt}, | |
5237 | @code{sscanf}, @code{strcat}, @code{strchr}, @code{strcmp}, | |
5238 | @code{strcpy}, @code{strcspn}, @code{strlen}, @code{strncat}, | |
5239 | @code{strncmp}, @code{strncpy}, @code{strpbrk}, @code{strrchr}, | |
5240 | @code{strspn}, @code{strstr}, @code{tanh}, @code{tan}, @code{vfprintf}, | |
5241 | @code{vprintf} and @code{vsprintf} | |
08291658 | 5242 | are all recognized as built-in functions unless |
46847aa6 RS |
5243 | @option{-fno-builtin} is specified (or @option{-fno-builtin-@var{function}} |
5244 | is specified for an individual function). All of these functions have | |
4977bab6 | 5245 | corresponding versions prefixed with @code{__builtin_}. |
9c34dbbf ZW |
5246 | |
5247 | GCC provides built-in versions of the ISO C99 floating point comparison | |
5248 | macros that avoid raising exceptions for unordered operands. They have | |
5249 | the same names as the standard macros ( @code{isgreater}, | |
5250 | @code{isgreaterequal}, @code{isless}, @code{islessequal}, | |
5251 | @code{islessgreater}, and @code{isunordered}) , with @code{__builtin_} | |
5252 | prefixed. We intend for a library implementor to be able to simply | |
5253 | @code{#define} each standard macro to its built-in equivalent. | |
185ebd6c | 5254 | |
ecbcf7b3 AH |
5255 | @deftypefn {Built-in Function} int __builtin_types_compatible_p (@var{type1}, @var{type2}) |
5256 | ||
5257 | You can use the built-in function @code{__builtin_types_compatible_p} to | |
5258 | determine whether two types are the same. | |
5259 | ||
5260 | This built-in function returns 1 if the unqualified versions of the | |
5261 | types @var{type1} and @var{type2} (which are types, not expressions) are | |
5262 | compatible, 0 otherwise. The result of this built-in function can be | |
5263 | used in integer constant expressions. | |
5264 | ||
5265 | This built-in function ignores top level qualifiers (e.g., @code{const}, | |
5266 | @code{volatile}). For example, @code{int} is equivalent to @code{const | |
5267 | int}. | |
5268 | ||
5269 | The type @code{int[]} and @code{int[5]} are compatible. On the other | |
5270 | hand, @code{int} and @code{char *} are not compatible, even if the size | |
5271 | of their types, on the particular architecture are the same. Also, the | |
5272 | amount of pointer indirection is taken into account when determining | |
5273 | similarity. Consequently, @code{short *} is not similar to | |
5274 | @code{short **}. Furthermore, two types that are typedefed are | |
5275 | considered compatible if their underlying types are compatible. | |
5276 | ||
bca63328 JM |
5277 | An @code{enum} type is not considered to be compatible with another |
5278 | @code{enum} type even if both are compatible with the same integer | |
5279 | type; this is what the C standard specifies. | |
5280 | For example, @code{enum @{foo, bar@}} is not similar to | |
ecbcf7b3 AH |
5281 | @code{enum @{hot, dog@}}. |
5282 | ||
5283 | You would typically use this function in code whose execution varies | |
5284 | depending on the arguments' types. For example: | |
5285 | ||
5286 | @smallexample | |
6e5bb5ad JM |
5287 | #define foo(x) \ |
5288 | (@{ \ | |
5289 | typeof (x) tmp; \ | |
5290 | if (__builtin_types_compatible_p (typeof (x), long double)) \ | |
5291 | tmp = foo_long_double (tmp); \ | |
5292 | else if (__builtin_types_compatible_p (typeof (x), double)) \ | |
5293 | tmp = foo_double (tmp); \ | |
5294 | else if (__builtin_types_compatible_p (typeof (x), float)) \ | |
5295 | tmp = foo_float (tmp); \ | |
5296 | else \ | |
5297 | abort (); \ | |
5298 | tmp; \ | |
ecbcf7b3 AH |
5299 | @}) |
5300 | @end smallexample | |
5301 | ||
5302 | @emph{Note:} This construct is only available for C. | |
5303 | ||
5304 | @end deftypefn | |
5305 | ||
5306 | @deftypefn {Built-in Function} @var{type} __builtin_choose_expr (@var{const_exp}, @var{exp1}, @var{exp2}) | |
5307 | ||
5308 | You can use the built-in function @code{__builtin_choose_expr} to | |
5309 | evaluate code depending on the value of a constant expression. This | |
5310 | built-in function returns @var{exp1} if @var{const_exp}, which is a | |
5311 | constant expression that must be able to be determined at compile time, | |
5312 | is nonzero. Otherwise it returns 0. | |
5313 | ||
5314 | This built-in function is analogous to the @samp{? :} operator in C, | |
5315 | except that the expression returned has its type unaltered by promotion | |
5316 | rules. Also, the built-in function does not evaluate the expression | |
5317 | that was not chosen. For example, if @var{const_exp} evaluates to true, | |
5318 | @var{exp2} is not evaluated even if it has side-effects. | |
5319 | ||
5320 | This built-in function can return an lvalue if the chosen argument is an | |
5321 | lvalue. | |
5322 | ||
5323 | If @var{exp1} is returned, the return type is the same as @var{exp1}'s | |
5324 | type. Similarly, if @var{exp2} is returned, its return type is the same | |
5325 | as @var{exp2}. | |
5326 | ||
5327 | Example: | |
5328 | ||
5329 | @smallexample | |
478c9e72 JJ |
5330 | #define foo(x) \ |
5331 | __builtin_choose_expr ( \ | |
5332 | __builtin_types_compatible_p (typeof (x), double), \ | |
5333 | foo_double (x), \ | |
5334 | __builtin_choose_expr ( \ | |
5335 | __builtin_types_compatible_p (typeof (x), float), \ | |
5336 | foo_float (x), \ | |
5337 | /* @r{The void expression results in a compile-time error} \ | |
5338 | @r{when assigning the result to something.} */ \ | |
ecbcf7b3 AH |
5339 | (void)0)) |
5340 | @end smallexample | |
5341 | ||
5342 | @emph{Note:} This construct is only available for C. Furthermore, the | |
5343 | unused expression (@var{exp1} or @var{exp2} depending on the value of | |
5344 | @var{const_exp}) may still generate syntax errors. This may change in | |
5345 | future revisions. | |
5346 | ||
5347 | @end deftypefn | |
5348 | ||
84330467 JM |
5349 | @deftypefn {Built-in Function} int __builtin_constant_p (@var{exp}) |
5350 | You can use the built-in function @code{__builtin_constant_p} to | |
185ebd6c | 5351 | determine if a value is known to be constant at compile-time and hence |
f0523f02 | 5352 | that GCC can perform constant-folding on expressions involving that |
185ebd6c RH |
5353 | value. The argument of the function is the value to test. The function |
5354 | returns the integer 1 if the argument is known to be a compile-time | |
5355 | constant and 0 if it is not known to be a compile-time constant. A | |
5356 | return of 0 does not indicate that the value is @emph{not} a constant, | |
f0523f02 | 5357 | but merely that GCC cannot prove it is a constant with the specified |
84330467 | 5358 | value of the @option{-O} option. |
185ebd6c RH |
5359 | |
5360 | You would typically use this function in an embedded application where | |
5361 | memory was a critical resource. If you have some complex calculation, | |
5362 | you may want it to be folded if it involves constants, but need to call | |
5363 | a function if it does not. For example: | |
5364 | ||
4d390518 | 5365 | @smallexample |
310668e8 JM |
5366 | #define Scale_Value(X) \ |
5367 | (__builtin_constant_p (X) \ | |
5368 | ? ((X) * SCALE + OFFSET) : Scale (X)) | |
185ebd6c RH |
5369 | @end smallexample |
5370 | ||
84330467 | 5371 | You may use this built-in function in either a macro or an inline |
185ebd6c | 5372 | function. However, if you use it in an inlined function and pass an |
f0523f02 | 5373 | argument of the function as the argument to the built-in, GCC will |
185ebd6c | 5374 | never return 1 when you call the inline function with a string constant |
4b404517 | 5375 | or compound literal (@pxref{Compound Literals}) and will not return 1 |
185ebd6c | 5376 | when you pass a constant numeric value to the inline function unless you |
84330467 | 5377 | specify the @option{-O} option. |
13104975 ZW |
5378 | |
5379 | You may also use @code{__builtin_constant_p} in initializers for static | |
5380 | data. For instance, you can write | |
5381 | ||
5382 | @smallexample | |
79323c50 | 5383 | static const int table[] = @{ |
13104975 | 5384 | __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1, |
0d893a63 | 5385 | /* @r{@dots{}} */ |
79323c50 | 5386 | @}; |
13104975 ZW |
5387 | @end smallexample |
5388 | ||
5389 | @noindent | |
5390 | This is an acceptable initializer even if @var{EXPRESSION} is not a | |
5391 | constant expression. GCC must be more conservative about evaluating the | |
5392 | built-in in this case, because it has no opportunity to perform | |
5393 | optimization. | |
5394 | ||
5395 | Previous versions of GCC did not accept this built-in in data | |
5396 | initializers. The earliest version where it is completely safe is | |
5397 | 3.0.1. | |
84330467 | 5398 | @end deftypefn |
185ebd6c | 5399 | |
84330467 JM |
5400 | @deftypefn {Built-in Function} long __builtin_expect (long @var{exp}, long @var{c}) |
5401 | @opindex fprofile-arcs | |
02f52e19 | 5402 | You may use @code{__builtin_expect} to provide the compiler with |
994a57cd | 5403 | branch prediction information. In general, you should prefer to |
84330467 | 5404 | use actual profile feedback for this (@option{-fprofile-arcs}), as |
994a57cd | 5405 | programmers are notoriously bad at predicting how their programs |
60b6e1f5 | 5406 | actually perform. However, there are applications in which this |
994a57cd RH |
5407 | data is hard to collect. |
5408 | ||
5409 | The return value is the value of @var{exp}, which should be an | |
5410 | integral expression. The value of @var{c} must be a compile-time | |
84330467 | 5411 | constant. The semantics of the built-in are that it is expected |
994a57cd RH |
5412 | that @var{exp} == @var{c}. For example: |
5413 | ||
5414 | @smallexample | |
5415 | if (__builtin_expect (x, 0)) | |
5416 | foo (); | |
5417 | @end smallexample | |
5418 | ||
5419 | @noindent | |
5420 | would indicate that we do not expect to call @code{foo}, since | |
5421 | we expect @code{x} to be zero. Since you are limited to integral | |
5422 | expressions for @var{exp}, you should use constructions such as | |
5423 | ||
5424 | @smallexample | |
5425 | if (__builtin_expect (ptr != NULL, 1)) | |
5426 | error (); | |
5427 | @end smallexample | |
5428 | ||
5429 | @noindent | |
5430 | when testing pointer or floating-point values. | |
84330467 | 5431 | @end deftypefn |
994a57cd | 5432 | |
3bca17dd | 5433 | @deftypefn {Built-in Function} void __builtin_prefetch (const void *@var{addr}, ...) |
a9ccbb60 JJ |
5434 | This function is used to minimize cache-miss latency by moving data into |
5435 | a cache before it is accessed. | |
5436 | You can insert calls to @code{__builtin_prefetch} into code for which | |
5437 | you know addresses of data in memory that is likely to be accessed soon. | |
5438 | If the target supports them, data prefetch instructions will be generated. | |
5439 | If the prefetch is done early enough before the access then the data will | |
5440 | be in the cache by the time it is accessed. | |
5441 | ||
5442 | The value of @var{addr} is the address of the memory to prefetch. | |
e83d297b | 5443 | There are two optional arguments, @var{rw} and @var{locality}. |
a9ccbb60 | 5444 | The value of @var{rw} is a compile-time constant one or zero; one |
e83d297b JJ |
5445 | means that the prefetch is preparing for a write to the memory address |
5446 | and zero, the default, means that the prefetch is preparing for a read. | |
a9ccbb60 JJ |
5447 | The value @var{locality} must be a compile-time constant integer between |
5448 | zero and three. A value of zero means that the data has no temporal | |
5449 | locality, so it need not be left in the cache after the access. A value | |
5450 | of three means that the data has a high degree of temporal locality and | |
5451 | should be left in all levels of cache possible. Values of one and two | |
e83d297b JJ |
5452 | mean, respectively, a low or moderate degree of temporal locality. The |
5453 | default is three. | |
a9ccbb60 JJ |
5454 | |
5455 | @smallexample | |
5456 | for (i = 0; i < n; i++) | |
5457 | @{ | |
5458 | a[i] = a[i] + b[i]; | |
5459 | __builtin_prefetch (&a[i+j], 1, 1); | |
5460 | __builtin_prefetch (&b[i+j], 0, 1); | |
0d893a63 | 5461 | /* @r{@dots{}} */ |
a9ccbb60 JJ |
5462 | @} |
5463 | @end smallexample | |
5464 | ||
f282ffb3 | 5465 | Data prefetch does not generate faults if @var{addr} is invalid, but |
a9ccbb60 JJ |
5466 | the address expression itself must be valid. For example, a prefetch |
5467 | of @code{p->next} will not fault if @code{p->next} is not a valid | |
5468 | address, but evaluation will fault if @code{p} is not a valid address. | |
5469 | ||
5470 | If the target does not support data prefetch, the address expression | |
5471 | is evaluated if it includes side effects but no other code is generated | |
5472 | and GCC does not issue a warning. | |
5473 | @end deftypefn | |
5474 | ||
ab5e2615 RH |
5475 | @deftypefn {Built-in Function} double __builtin_huge_val (void) |
5476 | Returns a positive infinity, if supported by the floating-point format, | |
5477 | else @code{DBL_MAX}. This function is suitable for implementing the | |
5478 | ISO C macro @code{HUGE_VAL}. | |
5479 | @end deftypefn | |
5480 | ||
5481 | @deftypefn {Built-in Function} float __builtin_huge_valf (void) | |
5482 | Similar to @code{__builtin_huge_val}, except the return type is @code{float}. | |
5483 | @end deftypefn | |
5484 | ||
dad78426 | 5485 | @deftypefn {Built-in Function} {long double} __builtin_huge_vall (void) |
ab5e2615 RH |
5486 | Similar to @code{__builtin_huge_val}, except the return |
5487 | type is @code{long double}. | |
5488 | @end deftypefn | |
5489 | ||
5490 | @deftypefn {Built-in Function} double __builtin_inf (void) | |
5491 | Similar to @code{__builtin_huge_val}, except a warning is generated | |
5492 | if the target floating-point format does not support infinities. | |
5493 | This function is suitable for implementing the ISO C99 macro @code{INFINITY}. | |
5494 | @end deftypefn | |
5495 | ||
5496 | @deftypefn {Built-in Function} float __builtin_inff (void) | |
5497 | Similar to @code{__builtin_inf}, except the return type is @code{float}. | |
5498 | @end deftypefn | |
5499 | ||
dad78426 | 5500 | @deftypefn {Built-in Function} {long double} __builtin_infl (void) |
ab5e2615 RH |
5501 | Similar to @code{__builtin_inf}, except the return |
5502 | type is @code{long double}. | |
5503 | @end deftypefn | |
5504 | ||
1472e41c RH |
5505 | @deftypefn {Built-in Function} double __builtin_nan (const char *str) |
5506 | This is an implementation of the ISO C99 function @code{nan}. | |
5507 | ||
5508 | Since ISO C99 defines this function in terms of @code{strtod}, which we | |
c0478a66 | 5509 | do not implement, a description of the parsing is in order. The string |
1472e41c RH |
5510 | is parsed as by @code{strtol}; that is, the base is recognized by |
5511 | leading @samp{0} or @samp{0x} prefixes. The number parsed is placed | |
5512 | in the significand such that the least significant bit of the number | |
daf2f129 | 5513 | is at the least significant bit of the significand. The number is |
1472e41c RH |
5514 | truncated to fit the significand field provided. The significand is |
5515 | forced to be a quiet NaN. | |
5516 | ||
5517 | This function, if given a string literal, is evaluated early enough | |
5518 | that it is considered a compile-time constant. | |
5519 | @end deftypefn | |
5520 | ||
5521 | @deftypefn {Built-in Function} float __builtin_nanf (const char *str) | |
5522 | Similar to @code{__builtin_nan}, except the return type is @code{float}. | |
5523 | @end deftypefn | |
5524 | ||
dad78426 | 5525 | @deftypefn {Built-in Function} {long double} __builtin_nanl (const char *str) |
1472e41c RH |
5526 | Similar to @code{__builtin_nan}, except the return type is @code{long double}. |
5527 | @end deftypefn | |
5528 | ||
5529 | @deftypefn {Built-in Function} double __builtin_nans (const char *str) | |
daf2f129 | 5530 | Similar to @code{__builtin_nan}, except the significand is forced |
1472e41c | 5531 | to be a signaling NaN. The @code{nans} function is proposed by |
aaa67502 | 5532 | @uref{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm,,WG14 N965}. |
1472e41c RH |
5533 | @end deftypefn |
5534 | ||
5535 | @deftypefn {Built-in Function} float __builtin_nansf (const char *str) | |
5536 | Similar to @code{__builtin_nans}, except the return type is @code{float}. | |
5537 | @end deftypefn | |
5538 | ||
dad78426 | 5539 | @deftypefn {Built-in Function} {long double} __builtin_nansl (const char *str) |
1472e41c RH |
5540 | Similar to @code{__builtin_nans}, except the return type is @code{long double}. |
5541 | @end deftypefn | |
5542 | ||
2928cd7a RH |
5543 | @deftypefn {Built-in Function} int __builtin_ffs (unsigned int x) |
5544 | Returns one plus the index of the least significant 1-bit of @var{x}, or | |
5545 | if @var{x} is zero, returns zero. | |
5546 | @end deftypefn | |
5547 | ||
5548 | @deftypefn {Built-in Function} int __builtin_clz (unsigned int x) | |
5549 | Returns the number of leading 0-bits in @var{x}, starting at the most | |
5550 | significant bit position. If @var{x} is 0, the result is undefined. | |
5551 | @end deftypefn | |
5552 | ||
5553 | @deftypefn {Built-in Function} int __builtin_ctz (unsigned int x) | |
5554 | Returns the number of trailing 0-bits in @var{x}, starting at the least | |
5555 | significant bit position. If @var{x} is 0, the result is undefined. | |
5556 | @end deftypefn | |
5557 | ||
5558 | @deftypefn {Built-in Function} int __builtin_popcount (unsigned int x) | |
5559 | Returns the number of 1-bits in @var{x}. | |
5560 | @end deftypefn | |
5561 | ||
5562 | @deftypefn {Built-in Function} int __builtin_parity (unsigned int x) | |
5563 | Returns the parity of @var{x}, i.@:e. the number of 1-bits in @var{x} | |
5564 | modulo 2. | |
5565 | @end deftypefn | |
5566 | ||
5567 | @deftypefn {Built-in Function} int __builtin_ffsl (unsigned long) | |
5568 | Similar to @code{__builtin_ffs}, except the argument type is | |
5569 | @code{unsigned long}. | |
5570 | @end deftypefn | |
5571 | ||
5572 | @deftypefn {Built-in Function} int __builtin_clzl (unsigned long) | |
5573 | Similar to @code{__builtin_clz}, except the argument type is | |
5574 | @code{unsigned long}. | |
5575 | @end deftypefn | |
5576 | ||
5577 | @deftypefn {Built-in Function} int __builtin_ctzl (unsigned long) | |
5578 | Similar to @code{__builtin_ctz}, except the argument type is | |
5579 | @code{unsigned long}. | |
5580 | @end deftypefn | |
5581 | ||
5582 | @deftypefn {Built-in Function} int __builtin_popcountl (unsigned long) | |
5583 | Similar to @code{__builtin_popcount}, except the argument type is | |
5584 | @code{unsigned long}. | |
5585 | @end deftypefn | |
5586 | ||
5587 | @deftypefn {Built-in Function} int __builtin_parityl (unsigned long) | |
5588 | Similar to @code{__builtin_parity}, except the argument type is | |
5589 | @code{unsigned long}. | |
5590 | @end deftypefn | |
5591 | ||
5592 | @deftypefn {Built-in Function} int __builtin_ffsll (unsigned long long) | |
5593 | Similar to @code{__builtin_ffs}, except the argument type is | |
5594 | @code{unsigned long long}. | |
5595 | @end deftypefn | |
5596 | ||
5597 | @deftypefn {Built-in Function} int __builtin_clzll (unsigned long long) | |
5598 | Similar to @code{__builtin_clz}, except the argument type is | |
5599 | @code{unsigned long long}. | |
5600 | @end deftypefn | |
5601 | ||
5602 | @deftypefn {Built-in Function} int __builtin_ctzll (unsigned long long) | |
5603 | Similar to @code{__builtin_ctz}, except the argument type is | |
5604 | @code{unsigned long long}. | |
5605 | @end deftypefn | |
5606 | ||
5607 | @deftypefn {Built-in Function} int __builtin_popcountll (unsigned long long) | |
5608 | Similar to @code{__builtin_popcount}, except the argument type is | |
5609 | @code{unsigned long long}. | |
5610 | @end deftypefn | |
5611 | ||
5612 | @deftypefn {Built-in Function} int __builtin_parityll (unsigned long long) | |
5613 | Similar to @code{__builtin_parity}, except the argument type is | |
5614 | @code{unsigned long long}. | |
5615 | @end deftypefn | |
5616 | ||
5617 | ||
0975678f JM |
5618 | @node Target Builtins |
5619 | @section Built-in Functions Specific to Particular Target Machines | |
5620 | ||
5621 | On some target machines, GCC supports many built-in functions specific | |
5622 | to those machines. Generally these generate calls to specific machine | |
5623 | instructions, but allow the compiler to schedule those calls. | |
5624 | ||
5625 | @menu | |
6d8fd7bb | 5626 | * Alpha Built-in Functions:: |
4bc73018 | 5627 | * ARM Built-in Functions:: |
0975678f | 5628 | * X86 Built-in Functions:: |
333c8841 | 5629 | * PowerPC AltiVec Built-in Functions:: |
0975678f JM |
5630 | @end menu |
5631 | ||
6d8fd7bb RH |
5632 | @node Alpha Built-in Functions |
5633 | @subsection Alpha Built-in Functions | |
5634 | ||
5635 | These built-in functions are available for the Alpha family of | |
5636 | processors, depending on the command-line switches used. | |
5637 | ||
95b1627e | 5638 | The following built-in functions are always available. They |
6d8fd7bb RH |
5639 | all generate the machine instruction that is part of the name. |
5640 | ||
3ab51846 | 5641 | @smallexample |
6d8fd7bb RH |
5642 | long __builtin_alpha_implver (void) |
5643 | long __builtin_alpha_rpcc (void) | |
5644 | long __builtin_alpha_amask (long) | |
5645 | long __builtin_alpha_cmpbge (long, long) | |
c4b50f1a RH |
5646 | long __builtin_alpha_extbl (long, long) |
5647 | long __builtin_alpha_extwl (long, long) | |
5648 | long __builtin_alpha_extll (long, long) | |
6d8fd7bb | 5649 | long __builtin_alpha_extql (long, long) |
c4b50f1a RH |
5650 | long __builtin_alpha_extwh (long, long) |
5651 | long __builtin_alpha_extlh (long, long) | |
6d8fd7bb | 5652 | long __builtin_alpha_extqh (long, long) |
c4b50f1a RH |
5653 | long __builtin_alpha_insbl (long, long) |
5654 | long __builtin_alpha_inswl (long, long) | |
5655 | long __builtin_alpha_insll (long, long) | |
5656 | long __builtin_alpha_insql (long, long) | |
5657 | long __builtin_alpha_inswh (long, long) | |
5658 | long __builtin_alpha_inslh (long, long) | |
5659 | long __builtin_alpha_insqh (long, long) | |
5660 | long __builtin_alpha_mskbl (long, long) | |
5661 | long __builtin_alpha_mskwl (long, long) | |
5662 | long __builtin_alpha_mskll (long, long) | |
5663 | long __builtin_alpha_mskql (long, long) | |
5664 | long __builtin_alpha_mskwh (long, long) | |
5665 | long __builtin_alpha_msklh (long, long) | |
5666 | long __builtin_alpha_mskqh (long, long) | |
5667 | long __builtin_alpha_umulh (long, long) | |
6d8fd7bb RH |
5668 | long __builtin_alpha_zap (long, long) |
5669 | long __builtin_alpha_zapnot (long, long) | |
3ab51846 | 5670 | @end smallexample |
6d8fd7bb RH |
5671 | |
5672 | The following built-in functions are always with @option{-mmax} | |
5673 | or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{pca56} or | |
5674 | later. They all generate the machine instruction that is part | |
5675 | of the name. | |
5676 | ||
3ab51846 | 5677 | @smallexample |
6d8fd7bb RH |
5678 | long __builtin_alpha_pklb (long) |
5679 | long __builtin_alpha_pkwb (long) | |
5680 | long __builtin_alpha_unpkbl (long) | |
5681 | long __builtin_alpha_unpkbw (long) | |
5682 | long __builtin_alpha_minub8 (long, long) | |
5683 | long __builtin_alpha_minsb8 (long, long) | |
5684 | long __builtin_alpha_minuw4 (long, long) | |
5685 | long __builtin_alpha_minsw4 (long, long) | |
5686 | long __builtin_alpha_maxub8 (long, long) | |
5687 | long __builtin_alpha_maxsb8 (long, long) | |
5688 | long __builtin_alpha_maxuw4 (long, long) | |
5689 | long __builtin_alpha_maxsw4 (long, long) | |
5690 | long __builtin_alpha_perr (long, long) | |
3ab51846 | 5691 | @end smallexample |
6d8fd7bb | 5692 | |
c4b50f1a RH |
5693 | The following built-in functions are always with @option{-mcix} |
5694 | or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{ev67} or | |
5695 | later. They all generate the machine instruction that is part | |
5696 | of the name. | |
5697 | ||
3ab51846 | 5698 | @smallexample |
c4b50f1a RH |
5699 | long __builtin_alpha_cttz (long) |
5700 | long __builtin_alpha_ctlz (long) | |
5701 | long __builtin_alpha_ctpop (long) | |
3ab51846 | 5702 | @end smallexample |
c4b50f1a | 5703 | |
116b7a5e RH |
5704 | The following builtins are available on systems that use the OSF/1 |
5705 | PALcode. Normally they invoke the @code{rduniq} and @code{wruniq} | |
5706 | PAL calls, but when invoked with @option{-mtls-kernel}, they invoke | |
5707 | @code{rdval} and @code{wrval}. | |
5708 | ||
3ab51846 | 5709 | @smallexample |
116b7a5e RH |
5710 | void *__builtin_thread_pointer (void) |
5711 | void __builtin_set_thread_pointer (void *) | |
3ab51846 | 5712 | @end smallexample |
116b7a5e | 5713 | |
4bc73018 NC |
5714 | @node ARM Built-in Functions |
5715 | @subsection ARM Built-in Functions | |
5716 | ||
5717 | These built-in functions are available for the ARM family of | |
5718 | processors, when the @option{-mcpu=iwmmxt} switch is used: | |
5719 | ||
3ab51846 | 5720 | @smallexample |
d63851eb ILT |
5721 | typedef int v2si __attribute__ ((vector_size (8))); |
5722 | typedef short v4hi __attribute__ ((vector_size (8))); | |
5723 | typedef char v8qi __attribute__ ((vector_size (8))); | |
5724 | ||
5725 | int __builtin_arm_getwcx (int) | |
5726 | void __builtin_arm_setwcx (int, int) | |
5727 | int __builtin_arm_textrmsb (v8qi, int) | |
5728 | int __builtin_arm_textrmsh (v4hi, int) | |
5729 | int __builtin_arm_textrmsw (v2si, int) | |
5730 | int __builtin_arm_textrmub (v8qi, int) | |
5731 | int __builtin_arm_textrmuh (v4hi, int) | |
5732 | int __builtin_arm_textrmuw (v2si, int) | |
5733 | v8qi __builtin_arm_tinsrb (v8qi, int) | |
5734 | v4hi __builtin_arm_tinsrh (v4hi, int) | |
5735 | v2si __builtin_arm_tinsrw (v2si, int) | |
5736 | long long __builtin_arm_tmia (long long, int, int) | |
5737 | long long __builtin_arm_tmiabb (long long, int, int) | |
5738 | long long __builtin_arm_tmiabt (long long, int, int) | |
5739 | long long __builtin_arm_tmiaph (long long, int, int) | |
5740 | long long __builtin_arm_tmiatb (long long, int, int) | |
5741 | long long __builtin_arm_tmiatt (long long, int, int) | |
5742 | int __builtin_arm_tmovmskb (v8qi) | |
5743 | int __builtin_arm_tmovmskh (v4hi) | |
5744 | int __builtin_arm_tmovmskw (v2si) | |
5745 | long long __builtin_arm_waccb (v8qi) | |
5746 | long long __builtin_arm_wacch (v4hi) | |
5747 | long long __builtin_arm_waccw (v2si) | |
5748 | v8qi __builtin_arm_waddb (v8qi, v8qi) | |
5749 | v8qi __builtin_arm_waddbss (v8qi, v8qi) | |
5750 | v8qi __builtin_arm_waddbus (v8qi, v8qi) | |
5751 | v4hi __builtin_arm_waddh (v4hi, v4hi) | |
5752 | v4hi __builtin_arm_waddhss (v4hi, v4hi) | |
5753 | v4hi __builtin_arm_waddhus (v4hi, v4hi) | |
4bc73018 | 5754 | v2si __builtin_arm_waddw (v2si, v2si) |
4bc73018 | 5755 | v2si __builtin_arm_waddwss (v2si, v2si) |
4bc73018 | 5756 | v2si __builtin_arm_waddwus (v2si, v2si) |
d63851eb ILT |
5757 | v8qi __builtin_arm_walign (v8qi, v8qi, int) |
5758 | long long __builtin_arm_wand(long long, long long) | |
5759 | long long __builtin_arm_wandn (long long, long long) | |
5760 | v8qi __builtin_arm_wavg2b (v8qi, v8qi) | |
5761 | v8qi __builtin_arm_wavg2br (v8qi, v8qi) | |
5762 | v4hi __builtin_arm_wavg2h (v4hi, v4hi) | |
5763 | v4hi __builtin_arm_wavg2hr (v4hi, v4hi) | |
5764 | v8qi __builtin_arm_wcmpeqb (v8qi, v8qi) | |
5765 | v4hi __builtin_arm_wcmpeqh (v4hi, v4hi) | |
4bc73018 | 5766 | v2si __builtin_arm_wcmpeqw (v2si, v2si) |
d63851eb ILT |
5767 | v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi) |
5768 | v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi) | |
4bc73018 | 5769 | v2si __builtin_arm_wcmpgtsw (v2si, v2si) |
d63851eb ILT |
5770 | v8qi __builtin_arm_wcmpgtub (v8qi, v8qi) |
5771 | v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi) | |
5772 | v2si __builtin_arm_wcmpgtuw (v2si, v2si) | |
5773 | long long __builtin_arm_wmacs (long long, v4hi, v4hi) | |
5774 | long long __builtin_arm_wmacsz (v4hi, v4hi) | |
5775 | long long __builtin_arm_wmacu (long long, v4hi, v4hi) | |
5776 | long long __builtin_arm_wmacuz (v4hi, v4hi) | |
5777 | v4hi __builtin_arm_wmadds (v4hi, v4hi) | |
5778 | v4hi __builtin_arm_wmaddu (v4hi, v4hi) | |
5779 | v8qi __builtin_arm_wmaxsb (v8qi, v8qi) | |
5780 | v4hi __builtin_arm_wmaxsh (v4hi, v4hi) | |
4bc73018 | 5781 | v2si __builtin_arm_wmaxsw (v2si, v2si) |
d63851eb ILT |
5782 | v8qi __builtin_arm_wmaxub (v8qi, v8qi) |
5783 | v4hi __builtin_arm_wmaxuh (v4hi, v4hi) | |
4bc73018 | 5784 | v2si __builtin_arm_wmaxuw (v2si, v2si) |
d63851eb ILT |
5785 | v8qi __builtin_arm_wminsb (v8qi, v8qi) |
5786 | v4hi __builtin_arm_wminsh (v4hi, v4hi) | |
4bc73018 | 5787 | v2si __builtin_arm_wminsw (v2si, v2si) |
d63851eb ILT |
5788 | v8qi __builtin_arm_wminub (v8qi, v8qi) |
5789 | v4hi __builtin_arm_wminuh (v4hi, v4hi) | |
4bc73018 | 5790 | v2si __builtin_arm_wminuw (v2si, v2si) |
d63851eb ILT |
5791 | v4hi __builtin_arm_wmulsm (v4hi, v4hi) |
5792 | v4hi __builtin_arm_wmulul (v4hi, v4hi) | |
5793 | v4hi __builtin_arm_wmulum (v4hi, v4hi) | |
5794 | long long __builtin_arm_wor (long long, long long) | |
5795 | v2si __builtin_arm_wpackdss (long long, long long) | |
5796 | v2si __builtin_arm_wpackdus (long long, long long) | |
5797 | v8qi __builtin_arm_wpackhss (v4hi, v4hi) | |
5798 | v8qi __builtin_arm_wpackhus (v4hi, v4hi) | |
5799 | v4hi __builtin_arm_wpackwss (v2si, v2si) | |
5800 | v4hi __builtin_arm_wpackwus (v2si, v2si) | |
5801 | long long __builtin_arm_wrord (long long, long long) | |
5802 | long long __builtin_arm_wrordi (long long, int) | |
5803 | v4hi __builtin_arm_wrorh (v4hi, long long) | |
5804 | v4hi __builtin_arm_wrorhi (v4hi, int) | |
5805 | v2si __builtin_arm_wrorw (v2si, long long) | |
5806 | v2si __builtin_arm_wrorwi (v2si, int) | |
5807 | v2si __builtin_arm_wsadb (v8qi, v8qi) | |
5808 | v2si __builtin_arm_wsadbz (v8qi, v8qi) | |
5809 | v2si __builtin_arm_wsadh (v4hi, v4hi) | |
5810 | v2si __builtin_arm_wsadhz (v4hi, v4hi) | |
5811 | v4hi __builtin_arm_wshufh (v4hi, int) | |
5812 | long long __builtin_arm_wslld (long long, long long) | |
5813 | long long __builtin_arm_wslldi (long long, int) | |
5814 | v4hi __builtin_arm_wsllh (v4hi, long long) | |
5815 | v4hi __builtin_arm_wsllhi (v4hi, int) | |
5816 | v2si __builtin_arm_wsllw (v2si, long long) | |
4bc73018 | 5817 | v2si __builtin_arm_wsllwi (v2si, int) |
d63851eb ILT |
5818 | long long __builtin_arm_wsrad (long long, long long) |
5819 | long long __builtin_arm_wsradi (long long, int) | |
5820 | v4hi __builtin_arm_wsrah (v4hi, long long) | |
5821 | v4hi __builtin_arm_wsrahi (v4hi, int) | |
5822 | v2si __builtin_arm_wsraw (v2si, long long) | |
4bc73018 | 5823 | v2si __builtin_arm_wsrawi (v2si, int) |
d63851eb ILT |
5824 | long long __builtin_arm_wsrld (long long, long long) |
5825 | long long __builtin_arm_wsrldi (long long, int) | |
5826 | v4hi __builtin_arm_wsrlh (v4hi, long long) | |
5827 | v4hi __builtin_arm_wsrlhi (v4hi, int) | |
5828 | v2si __builtin_arm_wsrlw (v2si, long long) | |
4bc73018 | 5829 | v2si __builtin_arm_wsrlwi (v2si, int) |
d63851eb ILT |
5830 | v8qi __builtin_arm_wsubb (v8qi, v8qi) |
5831 | v8qi __builtin_arm_wsubbss (v8qi, v8qi) | |
5832 | v8qi __builtin_arm_wsubbus (v8qi, v8qi) | |
5833 | v4hi __builtin_arm_wsubh (v4hi, v4hi) | |
5834 | v4hi __builtin_arm_wsubhss (v4hi, v4hi) | |
5835 | v4hi __builtin_arm_wsubhus (v4hi, v4hi) | |
5836 | v2si __builtin_arm_wsubw (v2si, v2si) | |
5837 | v2si __builtin_arm_wsubwss (v2si, v2si) | |
5838 | v2si __builtin_arm_wsubwus (v2si, v2si) | |
5839 | v4hi __builtin_arm_wunpckehsb (v8qi) | |
5840 | v2si __builtin_arm_wunpckehsh (v4hi) | |
5841 | long long __builtin_arm_wunpckehsw (v2si) | |
5842 | v4hi __builtin_arm_wunpckehub (v8qi) | |
5843 | v2si __builtin_arm_wunpckehuh (v4hi) | |
5844 | long long __builtin_arm_wunpckehuw (v2si) | |
5845 | v4hi __builtin_arm_wunpckelsb (v8qi) | |
5846 | v2si __builtin_arm_wunpckelsh (v4hi) | |
5847 | long long __builtin_arm_wunpckelsw (v2si) | |
5848 | v4hi __builtin_arm_wunpckelub (v8qi) | |
5849 | v2si __builtin_arm_wunpckeluh (v4hi) | |
5850 | long long __builtin_arm_wunpckeluw (v2si) | |
5851 | v8qi __builtin_arm_wunpckihb (v8qi, v8qi) | |
5852 | v4hi __builtin_arm_wunpckihh (v4hi, v4hi) | |
4bc73018 | 5853 | v2si __builtin_arm_wunpckihw (v2si, v2si) |
d63851eb ILT |
5854 | v8qi __builtin_arm_wunpckilb (v8qi, v8qi) |
5855 | v4hi __builtin_arm_wunpckilh (v4hi, v4hi) | |
4bc73018 | 5856 | v2si __builtin_arm_wunpckilw (v2si, v2si) |
d63851eb ILT |
5857 | long long __builtin_arm_wxor (long long, long long) |
5858 | long long __builtin_arm_wzero () | |
3ab51846 | 5859 | @end smallexample |
4bc73018 | 5860 | |
0975678f JM |
5861 | @node X86 Built-in Functions |
5862 | @subsection X86 Built-in Functions | |
5863 | ||
5864 | These built-in functions are available for the i386 and x86-64 family | |
5865 | of computers, depending on the command-line switches used. | |
5866 | ||
5867 | The following machine modes are available for use with MMX built-in functions | |
333c8841 AH |
5868 | (@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32-bit integers, |
5869 | @code{V4HI} for a vector of four 16-bit integers, and @code{V8QI} for a | |
5870 | vector of eight 8-bit integers. Some of the built-in functions operate on | |
5871 | MMX registers as a whole 64-bit entity, these use @code{DI} as their mode. | |
0975678f JM |
5872 | |
5873 | If 3Dnow extensions are enabled, @code{V2SF} is used as a mode for a vector | |
333c8841 | 5874 | of two 32-bit floating point values. |
0975678f | 5875 | |
333c8841 AH |
5876 | If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32-bit |
5877 | floating point values. Some instructions use a vector of four 32-bit | |
0975678f | 5878 | integers, these use @code{V4SI}. Finally, some instructions operate on an |
333c8841 | 5879 | entire vector register, interpreting it as a 128-bit integer, these use mode |
0975678f JM |
5880 | @code{TI}. |
5881 | ||
5882 | The following built-in functions are made available by @option{-mmmx}. | |
5883 | All of them generate the machine instruction that is part of the name. | |
5884 | ||
3ab51846 | 5885 | @smallexample |
0975678f JM |
5886 | v8qi __builtin_ia32_paddb (v8qi, v8qi) |
5887 | v4hi __builtin_ia32_paddw (v4hi, v4hi) | |
5888 | v2si __builtin_ia32_paddd (v2si, v2si) | |
5889 | v8qi __builtin_ia32_psubb (v8qi, v8qi) | |
5890 | v4hi __builtin_ia32_psubw (v4hi, v4hi) | |
5891 | v2si __builtin_ia32_psubd (v2si, v2si) | |
5892 | v8qi __builtin_ia32_paddsb (v8qi, v8qi) | |
5893 | v4hi __builtin_ia32_paddsw (v4hi, v4hi) | |
5894 | v8qi __builtin_ia32_psubsb (v8qi, v8qi) | |
5895 | v4hi __builtin_ia32_psubsw (v4hi, v4hi) | |
5896 | v8qi __builtin_ia32_paddusb (v8qi, v8qi) | |
5897 | v4hi __builtin_ia32_paddusw (v4hi, v4hi) | |
5898 | v8qi __builtin_ia32_psubusb (v8qi, v8qi) | |
5899 | v4hi __builtin_ia32_psubusw (v4hi, v4hi) | |
5900 | v4hi __builtin_ia32_pmullw (v4hi, v4hi) | |
5901 | v4hi __builtin_ia32_pmulhw (v4hi, v4hi) | |
5902 | di __builtin_ia32_pand (di, di) | |
5903 | di __builtin_ia32_pandn (di,di) | |
5904 | di __builtin_ia32_por (di, di) | |
5905 | di __builtin_ia32_pxor (di, di) | |
5906 | v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi) | |
5907 | v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi) | |
5908 | v2si __builtin_ia32_pcmpeqd (v2si, v2si) | |
5909 | v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi) | |
5910 | v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi) | |
5911 | v2si __builtin_ia32_pcmpgtd (v2si, v2si) | |
5912 | v8qi __builtin_ia32_punpckhbw (v8qi, v8qi) | |
5913 | v4hi __builtin_ia32_punpckhwd (v4hi, v4hi) | |
5914 | v2si __builtin_ia32_punpckhdq (v2si, v2si) | |
5915 | v8qi __builtin_ia32_punpcklbw (v8qi, v8qi) | |
5916 | v4hi __builtin_ia32_punpcklwd (v4hi, v4hi) | |
5917 | v2si __builtin_ia32_punpckldq (v2si, v2si) | |
5918 | v8qi __builtin_ia32_packsswb (v4hi, v4hi) | |
5919 | v4hi __builtin_ia32_packssdw (v2si, v2si) | |
5920 | v8qi __builtin_ia32_packuswb (v4hi, v4hi) | |
3ab51846 | 5921 | @end smallexample |
0975678f JM |
5922 | |
5923 | The following built-in functions are made available either with | |
5924 | @option{-msse}, or with a combination of @option{-m3dnow} and | |
5925 | @option{-march=athlon}. All of them generate the machine | |
5926 | instruction that is part of the name. | |
5927 | ||
3ab51846 | 5928 | @smallexample |
0975678f JM |
5929 | v4hi __builtin_ia32_pmulhuw (v4hi, v4hi) |
5930 | v8qi __builtin_ia32_pavgb (v8qi, v8qi) | |
5931 | v4hi __builtin_ia32_pavgw (v4hi, v4hi) | |
5932 | v4hi __builtin_ia32_psadbw (v8qi, v8qi) | |
5933 | v8qi __builtin_ia32_pmaxub (v8qi, v8qi) | |
5934 | v4hi __builtin_ia32_pmaxsw (v4hi, v4hi) | |
5935 | v8qi __builtin_ia32_pminub (v8qi, v8qi) | |
5936 | v4hi __builtin_ia32_pminsw (v4hi, v4hi) | |
5937 | int __builtin_ia32_pextrw (v4hi, int) | |
5938 | v4hi __builtin_ia32_pinsrw (v4hi, int, int) | |
5939 | int __builtin_ia32_pmovmskb (v8qi) | |
5940 | void __builtin_ia32_maskmovq (v8qi, v8qi, char *) | |
5941 | void __builtin_ia32_movntq (di *, di) | |
5942 | void __builtin_ia32_sfence (void) | |
3ab51846 | 5943 | @end smallexample |
0975678f JM |
5944 | |
5945 | The following built-in functions are available when @option{-msse} is used. | |
5946 | All of them generate the machine instruction that is part of the name. | |
5947 | ||
3ab51846 | 5948 | @smallexample |
0975678f JM |
5949 | int __builtin_ia32_comieq (v4sf, v4sf) |
5950 | int __builtin_ia32_comineq (v4sf, v4sf) | |
5951 | int __builtin_ia32_comilt (v4sf, v4sf) | |
5952 | int __builtin_ia32_comile (v4sf, v4sf) | |
5953 | int __builtin_ia32_comigt (v4sf, v4sf) | |
5954 | int __builtin_ia32_comige (v4sf, v4sf) | |
5955 | int __builtin_ia32_ucomieq (v4sf, v4sf) | |
5956 | int __builtin_ia32_ucomineq (v4sf, v4sf) | |
5957 | int __builtin_ia32_ucomilt (v4sf, v4sf) | |
5958 | int __builtin_ia32_ucomile (v4sf, v4sf) | |
5959 | int __builtin_ia32_ucomigt (v4sf, v4sf) | |
5960 | int __builtin_ia32_ucomige (v4sf, v4sf) | |
5961 | v4sf __builtin_ia32_addps (v4sf, v4sf) | |
5962 | v4sf __builtin_ia32_subps (v4sf, v4sf) | |
5963 | v4sf __builtin_ia32_mulps (v4sf, v4sf) | |
5964 | v4sf __builtin_ia32_divps (v4sf, v4sf) | |
5965 | v4sf __builtin_ia32_addss (v4sf, v4sf) | |
5966 | v4sf __builtin_ia32_subss (v4sf, v4sf) | |
5967 | v4sf __builtin_ia32_mulss (v4sf, v4sf) | |
5968 | v4sf __builtin_ia32_divss (v4sf, v4sf) | |
5969 | v4si __builtin_ia32_cmpeqps (v4sf, v4sf) | |
5970 | v4si __builtin_ia32_cmpltps (v4sf, v4sf) | |
5971 | v4si __builtin_ia32_cmpleps (v4sf, v4sf) | |
5972 | v4si __builtin_ia32_cmpgtps (v4sf, v4sf) | |
5973 | v4si __builtin_ia32_cmpgeps (v4sf, v4sf) | |
5974 | v4si __builtin_ia32_cmpunordps (v4sf, v4sf) | |
5975 | v4si __builtin_ia32_cmpneqps (v4sf, v4sf) | |
5976 | v4si __builtin_ia32_cmpnltps (v4sf, v4sf) | |
5977 | v4si __builtin_ia32_cmpnleps (v4sf, v4sf) | |
5978 | v4si __builtin_ia32_cmpngtps (v4sf, v4sf) | |
5979 | v4si __builtin_ia32_cmpngeps (v4sf, v4sf) | |
5980 | v4si __builtin_ia32_cmpordps (v4sf, v4sf) | |
5981 | v4si __builtin_ia32_cmpeqss (v4sf, v4sf) | |
5982 | v4si __builtin_ia32_cmpltss (v4sf, v4sf) | |
5983 | v4si __builtin_ia32_cmpless (v4sf, v4sf) | |
0975678f JM |
5984 | v4si __builtin_ia32_cmpunordss (v4sf, v4sf) |
5985 | v4si __builtin_ia32_cmpneqss (v4sf, v4sf) | |
5986 | v4si __builtin_ia32_cmpnlts (v4sf, v4sf) | |
5987 | v4si __builtin_ia32_cmpnless (v4sf, v4sf) | |
0975678f JM |
5988 | v4si __builtin_ia32_cmpordss (v4sf, v4sf) |
5989 | v4sf __builtin_ia32_maxps (v4sf, v4sf) | |
5990 | v4sf __builtin_ia32_maxss (v4sf, v4sf) | |
5991 | v4sf __builtin_ia32_minps (v4sf, v4sf) | |
5992 | v4sf __builtin_ia32_minss (v4sf, v4sf) | |
5993 | v4sf __builtin_ia32_andps (v4sf, v4sf) | |
5994 | v4sf __builtin_ia32_andnps (v4sf, v4sf) | |
5995 | v4sf __builtin_ia32_orps (v4sf, v4sf) | |
5996 | v4sf __builtin_ia32_xorps (v4sf, v4sf) | |
5997 | v4sf __builtin_ia32_movss (v4sf, v4sf) | |
5998 | v4sf __builtin_ia32_movhlps (v4sf, v4sf) | |
5999 | v4sf __builtin_ia32_movlhps (v4sf, v4sf) | |
6000 | v4sf __builtin_ia32_unpckhps (v4sf, v4sf) | |
6001 | v4sf __builtin_ia32_unpcklps (v4sf, v4sf) | |
6002 | v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si) | |
6003 | v4sf __builtin_ia32_cvtsi2ss (v4sf, int) | |
6004 | v2si __builtin_ia32_cvtps2pi (v4sf) | |
6005 | int __builtin_ia32_cvtss2si (v4sf) | |
6006 | v2si __builtin_ia32_cvttps2pi (v4sf) | |
6007 | int __builtin_ia32_cvttss2si (v4sf) | |
6008 | v4sf __builtin_ia32_rcpps (v4sf) | |
6009 | v4sf __builtin_ia32_rsqrtps (v4sf) | |
6010 | v4sf __builtin_ia32_sqrtps (v4sf) | |
6011 | v4sf __builtin_ia32_rcpss (v4sf) | |
6012 | v4sf __builtin_ia32_rsqrtss (v4sf) | |
6013 | v4sf __builtin_ia32_sqrtss (v4sf) | |
6014 | v4sf __builtin_ia32_shufps (v4sf, v4sf, int) | |
6015 | void __builtin_ia32_movntps (float *, v4sf) | |
6016 | int __builtin_ia32_movmskps (v4sf) | |
3ab51846 | 6017 | @end smallexample |
0975678f JM |
6018 | |
6019 | The following built-in functions are available when @option{-msse} is used. | |
6020 | ||
6021 | @table @code | |
6022 | @item v4sf __builtin_ia32_loadaps (float *) | |
6023 | Generates the @code{movaps} machine instruction as a load from memory. | |
6024 | @item void __builtin_ia32_storeaps (float *, v4sf) | |
6025 | Generates the @code{movaps} machine instruction as a store to memory. | |
6026 | @item v4sf __builtin_ia32_loadups (float *) | |
6027 | Generates the @code{movups} machine instruction as a load from memory. | |
6028 | @item void __builtin_ia32_storeups (float *, v4sf) | |
6029 | Generates the @code{movups} machine instruction as a store to memory. | |
6030 | @item v4sf __builtin_ia32_loadsss (float *) | |
6031 | Generates the @code{movss} machine instruction as a load from memory. | |
6032 | @item void __builtin_ia32_storess (float *, v4sf) | |
6033 | Generates the @code{movss} machine instruction as a store to memory. | |
6034 | @item v4sf __builtin_ia32_loadhps (v4sf, v2si *) | |
6035 | Generates the @code{movhps} machine instruction as a load from memory. | |
6036 | @item v4sf __builtin_ia32_loadlps (v4sf, v2si *) | |
6037 | Generates the @code{movlps} machine instruction as a load from memory | |
6038 | @item void __builtin_ia32_storehps (v4sf, v2si *) | |
6039 | Generates the @code{movhps} machine instruction as a store to memory. | |
6040 | @item void __builtin_ia32_storelps (v4sf, v2si *) | |
6041 | Generates the @code{movlps} machine instruction as a store to memory. | |
6042 | @end table | |
6043 | ||
9e200aaf | 6044 | The following built-in functions are available when @option{-msse3} is used. |
22c7c85e L |
6045 | All of them generate the machine instruction that is part of the name. |
6046 | ||
3ab51846 | 6047 | @smallexample |
22c7c85e L |
6048 | v2df __builtin_ia32_addsubpd (v2df, v2df) |
6049 | v2df __builtin_ia32_addsubps (v2df, v2df) | |
6050 | v2df __builtin_ia32_haddpd (v2df, v2df) | |
6051 | v2df __builtin_ia32_haddps (v2df, v2df) | |
6052 | v2df __builtin_ia32_hsubpd (v2df, v2df) | |
6053 | v2df __builtin_ia32_hsubps (v2df, v2df) | |
6054 | v16qi __builtin_ia32_lddqu (char const *) | |
6055 | void __builtin_ia32_monitor (void *, unsigned int, unsigned int) | |
6056 | v2df __builtin_ia32_movddup (v2df) | |
6057 | v4sf __builtin_ia32_movshdup (v4sf) | |
6058 | v4sf __builtin_ia32_movsldup (v4sf) | |
6059 | void __builtin_ia32_mwait (unsigned int, unsigned int) | |
3ab51846 | 6060 | @end smallexample |
22c7c85e | 6061 | |
9e200aaf | 6062 | The following built-in functions are available when @option{-msse3} is used. |
22c7c85e L |
6063 | |
6064 | @table @code | |
6065 | @item v2df __builtin_ia32_loadddup (double const *) | |
6066 | Generates the @code{movddup} machine instruction as a load from memory. | |
6067 | @end table | |
6068 | ||
0975678f JM |
6069 | The following built-in functions are available when @option{-m3dnow} is used. |
6070 | All of them generate the machine instruction that is part of the name. | |
6071 | ||
3ab51846 | 6072 | @smallexample |
0975678f JM |
6073 | void __builtin_ia32_femms (void) |
6074 | v8qi __builtin_ia32_pavgusb (v8qi, v8qi) | |
6075 | v2si __builtin_ia32_pf2id (v2sf) | |
6076 | v2sf __builtin_ia32_pfacc (v2sf, v2sf) | |
6077 | v2sf __builtin_ia32_pfadd (v2sf, v2sf) | |
6078 | v2si __builtin_ia32_pfcmpeq (v2sf, v2sf) | |
6079 | v2si __builtin_ia32_pfcmpge (v2sf, v2sf) | |
6080 | v2si __builtin_ia32_pfcmpgt (v2sf, v2sf) | |
6081 | v2sf __builtin_ia32_pfmax (v2sf, v2sf) | |
6082 | v2sf __builtin_ia32_pfmin (v2sf, v2sf) | |
6083 | v2sf __builtin_ia32_pfmul (v2sf, v2sf) | |
6084 | v2sf __builtin_ia32_pfrcp (v2sf) | |
6085 | v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf) | |
6086 | v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf) | |
6087 | v2sf __builtin_ia32_pfrsqrt (v2sf) | |
6088 | v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf) | |
6089 | v2sf __builtin_ia32_pfsub (v2sf, v2sf) | |
6090 | v2sf __builtin_ia32_pfsubr (v2sf, v2sf) | |
6091 | v2sf __builtin_ia32_pi2fd (v2si) | |
6092 | v4hi __builtin_ia32_pmulhrw (v4hi, v4hi) | |
3ab51846 | 6093 | @end smallexample |
0975678f JM |
6094 | |
6095 | The following built-in functions are available when both @option{-m3dnow} | |
6096 | and @option{-march=athlon} are used. All of them generate the machine | |
6097 | instruction that is part of the name. | |
6098 | ||
3ab51846 | 6099 | @smallexample |
0975678f JM |
6100 | v2si __builtin_ia32_pf2iw (v2sf) |
6101 | v2sf __builtin_ia32_pfnacc (v2sf, v2sf) | |
6102 | v2sf __builtin_ia32_pfpnacc (v2sf, v2sf) | |
6103 | v2sf __builtin_ia32_pi2fw (v2si) | |
6104 | v2sf __builtin_ia32_pswapdsf (v2sf) | |
6105 | v2si __builtin_ia32_pswapdsi (v2si) | |
3ab51846 | 6106 | @end smallexample |
0975678f | 6107 | |
333c8841 AH |
6108 | @node PowerPC AltiVec Built-in Functions |
6109 | @subsection PowerPC AltiVec Built-in Functions | |
6110 | ||
6111 | These built-in functions are available for the PowerPC family | |
6112 | of computers, depending on the command-line switches used. | |
6113 | ||
6114 | The following machine modes are available for use with AltiVec built-in | |
6115 | functions (@pxref{Vector Extensions}): @code{V4SI} for a vector of four | |
6116 | 32-bit integers, @code{V4SF} for a vector of four 32-bit floating point | |
6117 | numbers, @code{V8HI} for a vector of eight 16-bit integers, and | |
6118 | @code{V16QI} for a vector of sixteen 8-bit integers. | |
6119 | ||
6120 | The following functions are made available by including | |
6121 | @code{<altivec.h>} and using @option{-maltivec} and | |
6122 | @option{-mabi=altivec}. The functions implement the functionality | |
6123 | described in Motorola's AltiVec Programming Interface Manual. | |
6124 | ||
90989b26 AH |
6125 | There are a few differences from Motorola's documentation and GCC's |
6126 | implementation. Vector constants are done with curly braces (not | |
6127 | parentheses). Vector initializers require no casts if the vector | |
6128 | constant is of the same type as the variable it is initializing. The | |
6129 | @code{vector bool} type is deprecated and will be discontinued in | |
6130 | further revisions. Use @code{vector signed} instead. If @code{signed} | |
6131 | or @code{unsigned} is omitted, the vector type will default to | |
8254cb45 | 6132 | @code{signed}. Lastly, all overloaded functions are implemented with macros |
90989b26 AH |
6133 | for the C implementation. So code the following example will not work: |
6134 | ||
6135 | @smallexample | |
8254cb45 | 6136 | vec_add ((vector signed int)@{1, 2, 3, 4@}, foo); |
90989b26 AH |
6137 | @end smallexample |
6138 | ||
6139 | Since vec_add is a macro, the vector constant in the above example will | |
6140 | be treated as four different arguments. Wrap the entire argument in | |
6141 | parentheses for this to work. The C++ implementation does not use | |
6142 | macros. | |
6143 | ||
ae4b4a02 AH |
6144 | @emph{Note:} Only the @code{<altivec.h>} interface is supported. |
6145 | Internally, GCC uses built-in functions to achieve the functionality in | |
6146 | the aforementioned header file, but they are not supported and are | |
6147 | subject to change without notice. | |
6148 | ||
333c8841 AH |
6149 | @smallexample |
6150 | vector signed char vec_abs (vector signed char, vector signed char); | |
6151 | vector signed short vec_abs (vector signed short, vector signed short); | |
6152 | vector signed int vec_abs (vector signed int, vector signed int); | |
6153 | vector signed float vec_abs (vector signed float, vector signed float); | |
6154 | ||
6155 | vector signed char vec_abss (vector signed char, vector signed char); | |
6156 | vector signed short vec_abss (vector signed short, vector signed short); | |
6157 | ||
6158 | vector signed char vec_add (vector signed char, vector signed char); | |
6159 | vector unsigned char vec_add (vector signed char, vector unsigned char); | |
6160 | ||
6161 | vector unsigned char vec_add (vector unsigned char, vector signed char); | |
6162 | ||
924fcc4e JM |
6163 | vector unsigned char vec_add (vector unsigned char, |
6164 | vector unsigned char); | |
333c8841 | 6165 | vector signed short vec_add (vector signed short, vector signed short); |
924fcc4e JM |
6166 | vector unsigned short vec_add (vector signed short, |
6167 | vector unsigned short); | |
6168 | vector unsigned short vec_add (vector unsigned short, | |
6169 | vector signed short); | |
6e5bb5ad JM |
6170 | vector unsigned short vec_add (vector unsigned short, |
6171 | vector unsigned short); | |
333c8841 AH |
6172 | vector signed int vec_add (vector signed int, vector signed int); |
6173 | vector unsigned int vec_add (vector signed int, vector unsigned int); | |
6174 | vector unsigned int vec_add (vector unsigned int, vector signed int); | |
6175 | vector unsigned int vec_add (vector unsigned int, vector unsigned int); | |
6176 | vector float vec_add (vector float, vector float); | |
6177 | ||
6178 | vector unsigned int vec_addc (vector unsigned int, vector unsigned int); | |
6179 | ||
924fcc4e JM |
6180 | vector unsigned char vec_adds (vector signed char, |
6181 | vector unsigned char); | |
6182 | vector unsigned char vec_adds (vector unsigned char, | |
6183 | vector signed char); | |
6184 | vector unsigned char vec_adds (vector unsigned char, | |
6185 | vector unsigned char); | |
333c8841 | 6186 | vector signed char vec_adds (vector signed char, vector signed char); |
924fcc4e JM |
6187 | vector unsigned short vec_adds (vector signed short, |
6188 | vector unsigned short); | |
6189 | vector unsigned short vec_adds (vector unsigned short, | |
6190 | vector signed short); | |
6e5bb5ad JM |
6191 | vector unsigned short vec_adds (vector unsigned short, |
6192 | vector unsigned short); | |
333c8841 AH |
6193 | vector signed short vec_adds (vector signed short, vector signed short); |
6194 | ||
6195 | vector unsigned int vec_adds (vector signed int, vector unsigned int); | |
6196 | vector unsigned int vec_adds (vector unsigned int, vector signed int); | |
6197 | vector unsigned int vec_adds (vector unsigned int, vector unsigned int); | |
6198 | ||
6199 | vector signed int vec_adds (vector signed int, vector signed int); | |
6200 | ||
6201 | vector float vec_and (vector float, vector float); | |
6202 | vector float vec_and (vector float, vector signed int); | |
6203 | vector float vec_and (vector signed int, vector float); | |
6204 | vector signed int vec_and (vector signed int, vector signed int); | |
6205 | vector unsigned int vec_and (vector signed int, vector unsigned int); | |
6206 | vector unsigned int vec_and (vector unsigned int, vector signed int); | |
6207 | vector unsigned int vec_and (vector unsigned int, vector unsigned int); | |
6208 | vector signed short vec_and (vector signed short, vector signed short); | |
924fcc4e JM |
6209 | vector unsigned short vec_and (vector signed short, |
6210 | vector unsigned short); | |
6211 | vector unsigned short vec_and (vector unsigned short, | |
6212 | vector signed short); | |
6e5bb5ad JM |
6213 | vector unsigned short vec_and (vector unsigned short, |
6214 | vector unsigned short); | |
333c8841 AH |
6215 | vector signed char vec_and (vector signed char, vector signed char); |
6216 | vector unsigned char vec_and (vector signed char, vector unsigned char); | |
6217 | ||
6218 | vector unsigned char vec_and (vector unsigned char, vector signed char); | |
6219 | ||
924fcc4e JM |
6220 | vector unsigned char vec_and (vector unsigned char, |
6221 | vector unsigned char); | |
333c8841 AH |
6222 | |
6223 | vector float vec_andc (vector float, vector float); | |
6224 | vector float vec_andc (vector float, vector signed int); | |
6225 | vector float vec_andc (vector signed int, vector float); | |
6226 | vector signed int vec_andc (vector signed int, vector signed int); | |
6227 | vector unsigned int vec_andc (vector signed int, vector unsigned int); | |
6228 | vector unsigned int vec_andc (vector unsigned int, vector signed int); | |
6229 | vector unsigned int vec_andc (vector unsigned int, vector unsigned int); | |
6230 | ||
6231 | vector signed short vec_andc (vector signed short, vector signed short); | |
6232 | ||
924fcc4e JM |
6233 | vector unsigned short vec_andc (vector signed short, |
6234 | vector unsigned short); | |
6235 | vector unsigned short vec_andc (vector unsigned short, | |
6236 | vector signed short); | |
6e5bb5ad JM |
6237 | vector unsigned short vec_andc (vector unsigned short, |
6238 | vector unsigned short); | |
333c8841 | 6239 | vector signed char vec_andc (vector signed char, vector signed char); |
924fcc4e JM |
6240 | vector unsigned char vec_andc (vector signed char, |
6241 | vector unsigned char); | |
6242 | vector unsigned char vec_andc (vector unsigned char, | |
6243 | vector signed char); | |
6244 | vector unsigned char vec_andc (vector unsigned char, | |
6245 | vector unsigned char); | |
333c8841 | 6246 | |
924fcc4e JM |
6247 | vector unsigned char vec_avg (vector unsigned char, |
6248 | vector unsigned char); | |
333c8841 | 6249 | vector signed char vec_avg (vector signed char, vector signed char); |
6e5bb5ad JM |
6250 | vector unsigned short vec_avg (vector unsigned short, |
6251 | vector unsigned short); | |
333c8841 AH |
6252 | vector signed short vec_avg (vector signed short, vector signed short); |
6253 | vector unsigned int vec_avg (vector unsigned int, vector unsigned int); | |
6254 | vector signed int vec_avg (vector signed int, vector signed int); | |
6255 | ||
6256 | vector float vec_ceil (vector float); | |
6257 | ||
6258 | vector signed int vec_cmpb (vector float, vector float); | |
6259 | ||
6260 | vector signed char vec_cmpeq (vector signed char, vector signed char); | |
924fcc4e JM |
6261 | vector signed char vec_cmpeq (vector unsigned char, |
6262 | vector unsigned char); | |
6263 | vector signed short vec_cmpeq (vector signed short, | |
6264 | vector signed short); | |
6e5bb5ad JM |
6265 | vector signed short vec_cmpeq (vector unsigned short, |
6266 | vector unsigned short); | |
333c8841 AH |
6267 | vector signed int vec_cmpeq (vector signed int, vector signed int); |
6268 | vector signed int vec_cmpeq (vector unsigned int, vector unsigned int); | |
6269 | vector signed int vec_cmpeq (vector float, vector float); | |
6270 | ||
6271 | vector signed int vec_cmpge (vector float, vector float); | |
6272 | ||
924fcc4e JM |
6273 | vector signed char vec_cmpgt (vector unsigned char, |
6274 | vector unsigned char); | |
333c8841 | 6275 | vector signed char vec_cmpgt (vector signed char, vector signed char); |
6e5bb5ad JM |
6276 | vector signed short vec_cmpgt (vector unsigned short, |
6277 | vector unsigned short); | |
924fcc4e JM |
6278 | vector signed short vec_cmpgt (vector signed short, |
6279 | vector signed short); | |
333c8841 AH |
6280 | vector signed int vec_cmpgt (vector unsigned int, vector unsigned int); |
6281 | vector signed int vec_cmpgt (vector signed int, vector signed int); | |
6282 | vector signed int vec_cmpgt (vector float, vector float); | |
6283 | ||
6284 | vector signed int vec_cmple (vector float, vector float); | |
6285 | ||
924fcc4e JM |
6286 | vector signed char vec_cmplt (vector unsigned char, |
6287 | vector unsigned char); | |
333c8841 | 6288 | vector signed char vec_cmplt (vector signed char, vector signed char); |
6e5bb5ad JM |
6289 | vector signed short vec_cmplt (vector unsigned short, |
6290 | vector unsigned short); | |
924fcc4e JM |
6291 | vector signed short vec_cmplt (vector signed short, |
6292 | vector signed short); | |
333c8841 AH |
6293 | vector signed int vec_cmplt (vector unsigned int, vector unsigned int); |
6294 | vector signed int vec_cmplt (vector signed int, vector signed int); | |
6295 | vector signed int vec_cmplt (vector float, vector float); | |
6296 | ||
6297 | vector float vec_ctf (vector unsigned int, const char); | |
6298 | vector float vec_ctf (vector signed int, const char); | |
6299 | ||
6300 | vector signed int vec_cts (vector float, const char); | |
6301 | ||
6302 | vector unsigned int vec_ctu (vector float, const char); | |
6303 | ||
6304 | void vec_dss (const char); | |
6305 | ||
6306 | void vec_dssall (void); | |
6307 | ||
6308 | void vec_dst (void *, int, const char); | |
6309 | ||
6310 | void vec_dstst (void *, int, const char); | |
6311 | ||
6312 | void vec_dststt (void *, int, const char); | |
6313 | ||
6314 | void vec_dstt (void *, int, const char); | |
6315 | ||
6316 | vector float vec_expte (vector float, vector float); | |
6317 | ||
6318 | vector float vec_floor (vector float, vector float); | |
6319 | ||
6320 | vector float vec_ld (int, vector float *); | |
6321 | vector float vec_ld (int, float *): | |
6322 | vector signed int vec_ld (int, int *); | |
6323 | vector signed int vec_ld (int, vector signed int *); | |
6324 | vector unsigned int vec_ld (int, vector unsigned int *); | |
6325 | vector unsigned int vec_ld (int, unsigned int *); | |
6326 | vector signed short vec_ld (int, short *, vector signed short *); | |
6e5bb5ad JM |
6327 | vector unsigned short vec_ld (int, unsigned short *, |
6328 | vector unsigned short *); | |
333c8841 AH |
6329 | vector signed char vec_ld (int, signed char *); |
6330 | vector signed char vec_ld (int, vector signed char *); | |
6331 | vector unsigned char vec_ld (int, unsigned char *); | |
6332 | vector unsigned char vec_ld (int, vector unsigned char *); | |
6333 | ||
6334 | vector signed char vec_lde (int, signed char *); | |
6335 | vector unsigned char vec_lde (int, unsigned char *); | |
6336 | vector signed short vec_lde (int, short *); | |
6337 | vector unsigned short vec_lde (int, unsigned short *); | |
6338 | vector float vec_lde (int, float *); | |
6339 | vector signed int vec_lde (int, int *); | |
6340 | vector unsigned int vec_lde (int, unsigned int *); | |
6341 | ||
6342 | void float vec_ldl (int, float *); | |
6343 | void float vec_ldl (int, vector float *); | |
6344 | void signed int vec_ldl (int, vector signed int *); | |
6345 | void signed int vec_ldl (int, int *); | |
6346 | void unsigned int vec_ldl (int, unsigned int *); | |
6347 | void unsigned int vec_ldl (int, vector unsigned int *); | |
6348 | void signed short vec_ldl (int, vector signed short *); | |
6349 | void signed short vec_ldl (int, short *); | |
6350 | void unsigned short vec_ldl (int, vector unsigned short *); | |
6351 | void unsigned short vec_ldl (int, unsigned short *); | |
6352 | void signed char vec_ldl (int, vector signed char *); | |
6353 | void signed char vec_ldl (int, signed char *); | |
6354 | void unsigned char vec_ldl (int, vector unsigned char *); | |
6355 | void unsigned char vec_ldl (int, unsigned char *); | |
6356 | ||
6357 | vector float vec_loge (vector float); | |
6358 | ||
6359 | vector unsigned char vec_lvsl (int, void *, int *); | |
6360 | ||
6361 | vector unsigned char vec_lvsr (int, void *, int *); | |
6362 | ||
6363 | vector float vec_madd (vector float, vector float, vector float); | |
6364 | ||
6e5bb5ad JM |
6365 | vector signed short vec_madds (vector signed short, vector signed short, |
6366 | vector signed short); | |
333c8841 AH |
6367 | |
6368 | vector unsigned char vec_max (vector signed char, vector unsigned char); | |
6369 | ||
6370 | vector unsigned char vec_max (vector unsigned char, vector signed char); | |
6371 | ||
924fcc4e JM |
6372 | vector unsigned char vec_max (vector unsigned char, |
6373 | vector unsigned char); | |
333c8841 | 6374 | vector signed char vec_max (vector signed char, vector signed char); |
924fcc4e JM |
6375 | vector unsigned short vec_max (vector signed short, |
6376 | vector unsigned short); | |
6377 | vector unsigned short vec_max (vector unsigned short, | |
6378 | vector signed short); | |
6e5bb5ad JM |
6379 | vector unsigned short vec_max (vector unsigned short, |
6380 | vector unsigned short); | |
333c8841 AH |
6381 | vector signed short vec_max (vector signed short, vector signed short); |
6382 | vector unsigned int vec_max (vector signed int, vector unsigned int); | |
6383 | vector unsigned int vec_max (vector unsigned int, vector signed int); | |
6384 | vector unsigned int vec_max (vector unsigned int, vector unsigned int); | |
6385 | vector signed int vec_max (vector signed int, vector signed int); | |
6386 | vector float vec_max (vector float, vector float); | |
6387 | ||
6388 | vector signed char vec_mergeh (vector signed char, vector signed char); | |
6e5bb5ad JM |
6389 | vector unsigned char vec_mergeh (vector unsigned char, |
6390 | vector unsigned char); | |
924fcc4e JM |
6391 | vector signed short vec_mergeh (vector signed short, |
6392 | vector signed short); | |
6e5bb5ad JM |
6393 | vector unsigned short vec_mergeh (vector unsigned short, |
6394 | vector unsigned short); | |
333c8841 AH |
6395 | vector float vec_mergeh (vector float, vector float); |
6396 | vector signed int vec_mergeh (vector signed int, vector signed int); | |
924fcc4e JM |
6397 | vector unsigned int vec_mergeh (vector unsigned int, |
6398 | vector unsigned int); | |
333c8841 AH |
6399 | |
6400 | vector signed char vec_mergel (vector signed char, vector signed char); | |
6e5bb5ad JM |
6401 | vector unsigned char vec_mergel (vector unsigned char, |
6402 | vector unsigned char); | |
924fcc4e JM |
6403 | vector signed short vec_mergel (vector signed short, |
6404 | vector signed short); | |
6e5bb5ad JM |
6405 | vector unsigned short vec_mergel (vector unsigned short, |
6406 | vector unsigned short); | |
333c8841 AH |
6407 | vector float vec_mergel (vector float, vector float); |
6408 | vector signed int vec_mergel (vector signed int, vector signed int); | |
924fcc4e JM |
6409 | vector unsigned int vec_mergel (vector unsigned int, |
6410 | vector unsigned int); | |
333c8841 AH |
6411 | |
6412 | vector unsigned short vec_mfvscr (void); | |
6413 | ||
6414 | vector unsigned char vec_min (vector signed char, vector unsigned char); | |
6415 | ||
6416 | vector unsigned char vec_min (vector unsigned char, vector signed char); | |
6417 | ||
924fcc4e JM |
6418 | vector unsigned char vec_min (vector unsigned char, |
6419 | vector unsigned char); | |
333c8841 | 6420 | vector signed char vec_min (vector signed char, vector signed char); |
924fcc4e JM |
6421 | vector unsigned short vec_min (vector signed short, |
6422 | vector unsigned short); | |
6423 | vector unsigned short vec_min (vector unsigned short, | |
6424 | vector signed short); | |
6e5bb5ad JM |
6425 | vector unsigned short vec_min (vector unsigned short, |
6426 | vector unsigned short); | |
333c8841 AH |
6427 | vector signed short vec_min (vector signed short, vector signed short); |
6428 | vector unsigned int vec_min (vector signed int, vector unsigned int); | |
6429 | vector unsigned int vec_min (vector unsigned int, vector signed int); | |
6430 | vector unsigned int vec_min (vector unsigned int, vector unsigned int); | |
6431 | vector signed int vec_min (vector signed int, vector signed int); | |
6432 | vector float vec_min (vector float, vector float); | |
6433 | ||
6e5bb5ad JM |
6434 | vector signed short vec_mladd (vector signed short, vector signed short, |
6435 | vector signed short); | |
924fcc4e JM |
6436 | vector signed short vec_mladd (vector signed short, |
6437 | vector unsigned short, | |
6e5bb5ad | 6438 | vector unsigned short); |
924fcc4e JM |
6439 | vector signed short vec_mladd (vector unsigned short, |
6440 | vector signed short, | |
6e5bb5ad JM |
6441 | vector signed short); |
6442 | vector unsigned short vec_mladd (vector unsigned short, | |
6443 | vector unsigned short, | |
6444 | vector unsigned short); | |
6445 | ||
924fcc4e JM |
6446 | vector signed short vec_mradds (vector signed short, |
6447 | vector signed short, | |
6e5bb5ad JM |
6448 | vector signed short); |
6449 | ||
924fcc4e JM |
6450 | vector unsigned int vec_msum (vector unsigned char, |
6451 | vector unsigned char, | |
6e5bb5ad JM |
6452 | vector unsigned int); |
6453 | vector signed int vec_msum (vector signed char, vector unsigned char, | |
6454 | vector signed int); | |
924fcc4e JM |
6455 | vector unsigned int vec_msum (vector unsigned short, |
6456 | vector unsigned short, | |
6e5bb5ad JM |
6457 | vector unsigned int); |
6458 | vector signed int vec_msum (vector signed short, vector signed short, | |
6459 | vector signed int); | |
6460 | ||
6461 | vector unsigned int vec_msums (vector unsigned short, | |
924fcc4e JM |
6462 | vector unsigned short, |
6463 | vector unsigned int); | |
6e5bb5ad JM |
6464 | vector signed int vec_msums (vector signed short, vector signed short, |
6465 | vector signed int); | |
333c8841 AH |
6466 | |
6467 | void vec_mtvscr (vector signed int); | |
6468 | void vec_mtvscr (vector unsigned int); | |
6469 | void vec_mtvscr (vector signed short); | |
6470 | void vec_mtvscr (vector unsigned short); | |
6471 | void vec_mtvscr (vector signed char); | |
6472 | void vec_mtvscr (vector unsigned char); | |
6473 | ||
924fcc4e JM |
6474 | vector unsigned short vec_mule (vector unsigned char, |
6475 | vector unsigned char); | |
333c8841 | 6476 | vector signed short vec_mule (vector signed char, vector signed char); |
924fcc4e JM |
6477 | vector unsigned int vec_mule (vector unsigned short, |
6478 | vector unsigned short); | |
333c8841 AH |
6479 | vector signed int vec_mule (vector signed short, vector signed short); |
6480 | ||
924fcc4e JM |
6481 | vector unsigned short vec_mulo (vector unsigned char, |
6482 | vector unsigned char); | |
333c8841 | 6483 | vector signed short vec_mulo (vector signed char, vector signed char); |
924fcc4e JM |
6484 | vector unsigned int vec_mulo (vector unsigned short, |
6485 | vector unsigned short); | |
333c8841 AH |
6486 | vector signed int vec_mulo (vector signed short, vector signed short); |
6487 | ||
6488 | vector float vec_nmsub (vector float, vector float, vector float); | |
6489 | ||
6490 | vector float vec_nor (vector float, vector float); | |
6491 | vector signed int vec_nor (vector signed int, vector signed int); | |
6492 | vector unsigned int vec_nor (vector unsigned int, vector unsigned int); | |
6493 | vector signed short vec_nor (vector signed short, vector signed short); | |
6e5bb5ad JM |
6494 | vector unsigned short vec_nor (vector unsigned short, |
6495 | vector unsigned short); | |
333c8841 | 6496 | vector signed char vec_nor (vector signed char, vector signed char); |
924fcc4e JM |
6497 | vector unsigned char vec_nor (vector unsigned char, |
6498 | vector unsigned char); | |
333c8841 AH |
6499 | |
6500 | vector float vec_or (vector float, vector float); | |
6501 | vector float vec_or (vector float, vector signed int); | |
6502 | vector float vec_or (vector signed int, vector float); | |
6503 | vector signed int vec_or (vector signed int, vector signed int); | |
6504 | vector unsigned int vec_or (vector signed int, vector unsigned int); | |
6505 | vector unsigned int vec_or (vector unsigned int, vector signed int); | |
6506 | vector unsigned int vec_or (vector unsigned int, vector unsigned int); | |
6507 | vector signed short vec_or (vector signed short, vector signed short); | |
924fcc4e JM |
6508 | vector unsigned short vec_or (vector signed short, |
6509 | vector unsigned short); | |
6510 | vector unsigned short vec_or (vector unsigned short, | |
6511 | vector signed short); | |
6512 | vector unsigned short vec_or (vector unsigned short, | |
6513 | vector unsigned short); | |
333c8841 AH |
6514 | vector signed char vec_or (vector signed char, vector signed char); |
6515 | vector unsigned char vec_or (vector signed char, vector unsigned char); | |
6516 | vector unsigned char vec_or (vector unsigned char, vector signed char); | |
924fcc4e JM |
6517 | vector unsigned char vec_or (vector unsigned char, |
6518 | vector unsigned char); | |
333c8841 AH |
6519 | |
6520 | vector signed char vec_pack (vector signed short, vector signed short); | |
6e5bb5ad JM |
6521 | vector unsigned char vec_pack (vector unsigned short, |
6522 | vector unsigned short); | |
333c8841 | 6523 | vector signed short vec_pack (vector signed int, vector signed int); |
924fcc4e JM |
6524 | vector unsigned short vec_pack (vector unsigned int, |
6525 | vector unsigned int); | |
333c8841 | 6526 | |
924fcc4e JM |
6527 | vector signed short vec_packpx (vector unsigned int, |
6528 | vector unsigned int); | |
333c8841 | 6529 | |
6e5bb5ad JM |
6530 | vector unsigned char vec_packs (vector unsigned short, |
6531 | vector unsigned short); | |
333c8841 AH |
6532 | vector signed char vec_packs (vector signed short, vector signed short); |
6533 | ||
924fcc4e JM |
6534 | vector unsigned short vec_packs (vector unsigned int, |
6535 | vector unsigned int); | |
333c8841 AH |
6536 | vector signed short vec_packs (vector signed int, vector signed int); |
6537 | ||
6e5bb5ad JM |
6538 | vector unsigned char vec_packsu (vector unsigned short, |
6539 | vector unsigned short); | |
924fcc4e JM |
6540 | vector unsigned char vec_packsu (vector signed short, |
6541 | vector signed short); | |
6542 | vector unsigned short vec_packsu (vector unsigned int, | |
6543 | vector unsigned int); | |
333c8841 AH |
6544 | vector unsigned short vec_packsu (vector signed int, vector signed int); |
6545 | ||
924fcc4e JM |
6546 | vector float vec_perm (vector float, vector float, |
6547 | vector unsigned char); | |
6e5bb5ad JM |
6548 | vector signed int vec_perm (vector signed int, vector signed int, |
6549 | vector unsigned char); | |
6550 | vector unsigned int vec_perm (vector unsigned int, vector unsigned int, | |
6551 | vector unsigned char); | |
6552 | vector signed short vec_perm (vector signed short, vector signed short, | |
6553 | vector unsigned char); | |
6554 | vector unsigned short vec_perm (vector unsigned short, | |
6555 | vector unsigned short, | |
6556 | vector unsigned char); | |
6557 | vector signed char vec_perm (vector signed char, vector signed char, | |
6558 | vector unsigned char); | |
924fcc4e JM |
6559 | vector unsigned char vec_perm (vector unsigned char, |
6560 | vector unsigned char, | |
6e5bb5ad | 6561 | vector unsigned char); |
333c8841 AH |
6562 | |
6563 | vector float vec_re (vector float); | |
6564 | ||
6565 | vector signed char vec_rl (vector signed char, vector unsigned char); | |
924fcc4e JM |
6566 | vector unsigned char vec_rl (vector unsigned char, |
6567 | vector unsigned char); | |
333c8841 AH |
6568 | vector signed short vec_rl (vector signed short, vector unsigned short); |
6569 | ||
924fcc4e JM |
6570 | vector unsigned short vec_rl (vector unsigned short, |
6571 | vector unsigned short); | |
333c8841 AH |
6572 | vector signed int vec_rl (vector signed int, vector unsigned int); |
6573 | vector unsigned int vec_rl (vector unsigned int, vector unsigned int); | |
6574 | ||
6575 | vector float vec_round (vector float); | |
6576 | ||
6577 | vector float vec_rsqrte (vector float); | |
6578 | ||
6579 | vector float vec_sel (vector float, vector float, vector signed int); | |
6580 | vector float vec_sel (vector float, vector float, vector unsigned int); | |
6e5bb5ad JM |
6581 | vector signed int vec_sel (vector signed int, vector signed int, |
6582 | vector signed int); | |
6583 | vector signed int vec_sel (vector signed int, vector signed int, | |
6584 | vector unsigned int); | |
6585 | vector unsigned int vec_sel (vector unsigned int, vector unsigned int, | |
6586 | vector signed int); | |
6587 | vector unsigned int vec_sel (vector unsigned int, vector unsigned int, | |
6588 | vector unsigned int); | |
6589 | vector signed short vec_sel (vector signed short, vector signed short, | |
6590 | vector signed short); | |
6591 | vector signed short vec_sel (vector signed short, vector signed short, | |
6592 | vector unsigned short); | |
6593 | vector unsigned short vec_sel (vector unsigned short, | |
924fcc4e JM |
6594 | vector unsigned short, |
6595 | vector signed short); | |
6e5bb5ad JM |
6596 | vector unsigned short vec_sel (vector unsigned short, |
6597 | vector unsigned short, | |
6598 | vector unsigned short); | |
6599 | vector signed char vec_sel (vector signed char, vector signed char, | |
6600 | vector signed char); | |
6601 | vector signed char vec_sel (vector signed char, vector signed char, | |
6602 | vector unsigned char); | |
924fcc4e JM |
6603 | vector unsigned char vec_sel (vector unsigned char, |
6604 | vector unsigned char, | |
6e5bb5ad | 6605 | vector signed char); |
924fcc4e JM |
6606 | vector unsigned char vec_sel (vector unsigned char, |
6607 | vector unsigned char, | |
6e5bb5ad | 6608 | vector unsigned char); |
333c8841 AH |
6609 | |
6610 | vector signed char vec_sl (vector signed char, vector unsigned char); | |
924fcc4e JM |
6611 | vector unsigned char vec_sl (vector unsigned char, |
6612 | vector unsigned char); | |
333c8841 AH |
6613 | vector signed short vec_sl (vector signed short, vector unsigned short); |
6614 | ||
924fcc4e JM |
6615 | vector unsigned short vec_sl (vector unsigned short, |
6616 | vector unsigned short); | |
333c8841 AH |
6617 | vector signed int vec_sl (vector signed int, vector unsigned int); |
6618 | vector unsigned int vec_sl (vector unsigned int, vector unsigned int); | |
6619 | ||
6620 | vector float vec_sld (vector float, vector float, const char); | |
6e5bb5ad JM |
6621 | vector signed int vec_sld (vector signed int, vector signed int, |
6622 | const char); | |
6623 | vector unsigned int vec_sld (vector unsigned int, vector unsigned int, | |
6624 | const char); | |
6625 | vector signed short vec_sld (vector signed short, vector signed short, | |
6626 | const char); | |
6627 | vector unsigned short vec_sld (vector unsigned short, | |
6628 | vector unsigned short, const char); | |
6629 | vector signed char vec_sld (vector signed char, vector signed char, | |
6630 | const char); | |
924fcc4e JM |
6631 | vector unsigned char vec_sld (vector unsigned char, |
6632 | vector unsigned char, | |
6e5bb5ad | 6633 | const char); |
333c8841 AH |
6634 | |
6635 | vector signed int vec_sll (vector signed int, vector unsigned int); | |
6636 | vector signed int vec_sll (vector signed int, vector unsigned short); | |
6637 | vector signed int vec_sll (vector signed int, vector unsigned char); | |
6638 | vector unsigned int vec_sll (vector unsigned int, vector unsigned int); | |
924fcc4e JM |
6639 | vector unsigned int vec_sll (vector unsigned int, |
6640 | vector unsigned short); | |
333c8841 AH |
6641 | vector unsigned int vec_sll (vector unsigned int, vector unsigned char); |
6642 | ||
6643 | vector signed short vec_sll (vector signed short, vector unsigned int); | |
924fcc4e JM |
6644 | vector signed short vec_sll (vector signed short, |
6645 | vector unsigned short); | |
333c8841 AH |
6646 | vector signed short vec_sll (vector signed short, vector unsigned char); |
6647 | ||
924fcc4e JM |
6648 | vector unsigned short vec_sll (vector unsigned short, |
6649 | vector unsigned int); | |
6e5bb5ad JM |
6650 | vector unsigned short vec_sll (vector unsigned short, |
6651 | vector unsigned short); | |
924fcc4e JM |
6652 | vector unsigned short vec_sll (vector unsigned short, |
6653 | vector unsigned char); | |
333c8841 AH |
6654 | vector signed char vec_sll (vector signed char, vector unsigned int); |
6655 | vector signed char vec_sll (vector signed char, vector unsigned short); | |
6656 | vector signed char vec_sll (vector signed char, vector unsigned char); | |
924fcc4e JM |
6657 | vector unsigned char vec_sll (vector unsigned char, |
6658 | vector unsigned int); | |
6659 | vector unsigned char vec_sll (vector unsigned char, | |
6660 | vector unsigned short); | |
6661 | vector unsigned char vec_sll (vector unsigned char, | |
6662 | vector unsigned char); | |
333c8841 AH |
6663 | |
6664 | vector float vec_slo (vector float, vector signed char); | |
6665 | vector float vec_slo (vector float, vector unsigned char); | |
6666 | vector signed int vec_slo (vector signed int, vector signed char); | |
6667 | vector signed int vec_slo (vector signed int, vector unsigned char); | |
6668 | vector unsigned int vec_slo (vector unsigned int, vector signed char); | |
6669 | vector unsigned int vec_slo (vector unsigned int, vector unsigned char); | |
6670 | ||
6671 | vector signed short vec_slo (vector signed short, vector signed char); | |
6672 | vector signed short vec_slo (vector signed short, vector unsigned char); | |
6673 | ||
924fcc4e JM |
6674 | vector unsigned short vec_slo (vector unsigned short, |
6675 | vector signed char); | |
6676 | vector unsigned short vec_slo (vector unsigned short, | |
6677 | vector unsigned char); | |
333c8841 AH |
6678 | vector signed char vec_slo (vector signed char, vector signed char); |
6679 | vector signed char vec_slo (vector signed char, vector unsigned char); | |
6680 | vector unsigned char vec_slo (vector unsigned char, vector signed char); | |
6681 | ||
924fcc4e JM |
6682 | vector unsigned char vec_slo (vector unsigned char, |
6683 | vector unsigned char); | |
333c8841 AH |
6684 | |
6685 | vector signed char vec_splat (vector signed char, const char); | |
6686 | vector unsigned char vec_splat (vector unsigned char, const char); | |
6687 | vector signed short vec_splat (vector signed short, const char); | |
6688 | vector unsigned short vec_splat (vector unsigned short, const char); | |
6689 | vector float vec_splat (vector float, const char); | |
6690 | vector signed int vec_splat (vector signed int, const char); | |
6691 | vector unsigned int vec_splat (vector unsigned int, const char); | |
6692 | ||
6693 | vector signed char vec_splat_s8 (const char); | |
6694 | ||
6695 | vector signed short vec_splat_s16 (const char); | |
6696 | ||
6697 | vector signed int vec_splat_s32 (const char); | |
6698 | ||
6699 | vector unsigned char vec_splat_u8 (const char); | |
6700 | ||
6701 | vector unsigned short vec_splat_u16 (const char); | |
6702 | ||
6703 | vector unsigned int vec_splat_u32 (const char); | |
6704 | ||
6705 | vector signed char vec_sr (vector signed char, vector unsigned char); | |
924fcc4e JM |
6706 | vector unsigned char vec_sr (vector unsigned char, |
6707 | vector unsigned char); | |
333c8841 AH |
6708 | vector signed short vec_sr (vector signed short, vector unsigned short); |
6709 | ||
924fcc4e JM |
6710 | vector unsigned short vec_sr (vector unsigned short, |
6711 | vector unsigned short); | |
333c8841 AH |
6712 | vector signed int vec_sr (vector signed int, vector unsigned int); |
6713 | vector unsigned int vec_sr (vector unsigned int, vector unsigned int); | |
6714 | ||
6715 | vector signed char vec_sra (vector signed char, vector unsigned char); | |
924fcc4e JM |
6716 | vector unsigned char vec_sra (vector unsigned char, |
6717 | vector unsigned char); | |
6718 | vector signed short vec_sra (vector signed short, | |
6719 | vector unsigned short); | |
6e5bb5ad JM |
6720 | vector unsigned short vec_sra (vector unsigned short, |
6721 | vector unsigned short); | |
333c8841 AH |
6722 | vector signed int vec_sra (vector signed int, vector unsigned int); |
6723 | vector unsigned int vec_sra (vector unsigned int, vector unsigned int); | |
6724 | ||
6725 | vector signed int vec_srl (vector signed int, vector unsigned int); | |
6726 | vector signed int vec_srl (vector signed int, vector unsigned short); | |
6727 | vector signed int vec_srl (vector signed int, vector unsigned char); | |
6728 | vector unsigned int vec_srl (vector unsigned int, vector unsigned int); | |
924fcc4e JM |
6729 | vector unsigned int vec_srl (vector unsigned int, |
6730 | vector unsigned short); | |
333c8841 AH |
6731 | vector unsigned int vec_srl (vector unsigned int, vector unsigned char); |
6732 | ||
6733 | vector signed short vec_srl (vector signed short, vector unsigned int); | |
924fcc4e JM |
6734 | vector signed short vec_srl (vector signed short, |
6735 | vector unsigned short); | |
333c8841 AH |
6736 | vector signed short vec_srl (vector signed short, vector unsigned char); |
6737 | ||
924fcc4e JM |
6738 | vector unsigned short vec_srl (vector unsigned short, |
6739 | vector unsigned int); | |
6e5bb5ad JM |
6740 | vector unsigned short vec_srl (vector unsigned short, |
6741 | vector unsigned short); | |
924fcc4e JM |
6742 | vector unsigned short vec_srl (vector unsigned short, |
6743 | vector unsigned char); | |
333c8841 AH |
6744 | vector signed char vec_srl (vector signed char, vector unsigned int); |
6745 | vector signed char vec_srl (vector signed char, vector unsigned short); | |
6746 | vector signed char vec_srl (vector signed char, vector unsigned char); | |
924fcc4e JM |
6747 | vector unsigned char vec_srl (vector unsigned char, |
6748 | vector unsigned int); | |
6749 | vector unsigned char vec_srl (vector unsigned char, | |
6750 | vector unsigned short); | |
6751 | vector unsigned char vec_srl (vector unsigned char, | |
6752 | vector unsigned char); | |
333c8841 AH |
6753 | |
6754 | vector float vec_sro (vector float, vector signed char); | |
6755 | vector float vec_sro (vector float, vector unsigned char); | |
6756 | vector signed int vec_sro (vector signed int, vector signed char); | |
6757 | vector signed int vec_sro (vector signed int, vector unsigned char); | |
6758 | vector unsigned int vec_sro (vector unsigned int, vector signed char); | |
6759 | vector unsigned int vec_sro (vector unsigned int, vector unsigned char); | |
6760 | ||
6761 | vector signed short vec_sro (vector signed short, vector signed char); | |
6762 | vector signed short vec_sro (vector signed short, vector unsigned char); | |
6763 | ||
924fcc4e JM |
6764 | vector unsigned short vec_sro (vector unsigned short, |
6765 | vector signed char); | |
6766 | vector unsigned short vec_sro (vector unsigned short, | |
6767 | vector unsigned char); | |
333c8841 AH |
6768 | vector signed char vec_sro (vector signed char, vector signed char); |
6769 | vector signed char vec_sro (vector signed char, vector unsigned char); | |
6770 | vector unsigned char vec_sro (vector unsigned char, vector signed char); | |
6771 | ||
924fcc4e JM |
6772 | vector unsigned char vec_sro (vector unsigned char, |
6773 | vector unsigned char); | |
333c8841 AH |
6774 | |
6775 | void vec_st (vector float, int, float *); | |
6776 | void vec_st (vector float, int, vector float *); | |
6777 | void vec_st (vector signed int, int, int *); | |
6778 | void vec_st (vector signed int, int, unsigned int *); | |
6779 | void vec_st (vector unsigned int, int, unsigned int *); | |
6780 | void vec_st (vector unsigned int, int, vector unsigned int *); | |
6781 | void vec_st (vector signed short, int, short *); | |
6782 | void vec_st (vector signed short, int, vector unsigned short *); | |
6783 | void vec_st (vector signed short, int, vector signed short *); | |
6784 | void vec_st (vector unsigned short, int, unsigned short *); | |
6785 | void vec_st (vector unsigned short, int, vector unsigned short *); | |
6786 | void vec_st (vector signed char, int, signed char *); | |
6787 | void vec_st (vector signed char, int, unsigned char *); | |
6788 | void vec_st (vector signed char, int, vector signed char *); | |
6789 | void vec_st (vector unsigned char, int, unsigned char *); | |
6790 | void vec_st (vector unsigned char, int, vector unsigned char *); | |
6791 | ||
6792 | void vec_ste (vector signed char, int, unsigned char *); | |
6793 | void vec_ste (vector signed char, int, signed char *); | |
6794 | void vec_ste (vector unsigned char, int, unsigned char *); | |
6795 | void vec_ste (vector signed short, int, short *); | |
6796 | void vec_ste (vector signed short, int, unsigned short *); | |
6797 | void vec_ste (vector unsigned short, int, void *); | |
6798 | void vec_ste (vector signed int, int, unsigned int *); | |
6799 | void vec_ste (vector signed int, int, int *); | |
6800 | void vec_ste (vector unsigned int, int, unsigned int *); | |
6801 | void vec_ste (vector float, int, float *); | |
6802 | ||
6803 | void vec_stl (vector float, int, vector float *); | |
6804 | void vec_stl (vector float, int, float *); | |
6805 | void vec_stl (vector signed int, int, vector signed int *); | |
6806 | void vec_stl (vector signed int, int, int *); | |
6807 | void vec_stl (vector signed int, int, unsigned int *); | |
6808 | void vec_stl (vector unsigned int, int, vector unsigned int *); | |
6809 | void vec_stl (vector unsigned int, int, unsigned int *); | |
6810 | void vec_stl (vector signed short, int, short *); | |
6811 | void vec_stl (vector signed short, int, unsigned short *); | |
6812 | void vec_stl (vector signed short, int, vector signed short *); | |
6813 | void vec_stl (vector unsigned short, int, unsigned short *); | |
6814 | void vec_stl (vector unsigned short, int, vector signed short *); | |
6815 | void vec_stl (vector signed char, int, signed char *); | |
6816 | void vec_stl (vector signed char, int, unsigned char *); | |
6817 | void vec_stl (vector signed char, int, vector signed char *); | |
6818 | void vec_stl (vector unsigned char, int, unsigned char *); | |
6819 | void vec_stl (vector unsigned char, int, vector unsigned char *); | |
6820 | ||
6821 | vector signed char vec_sub (vector signed char, vector signed char); | |
6822 | vector unsigned char vec_sub (vector signed char, vector unsigned char); | |
6823 | ||
6824 | vector unsigned char vec_sub (vector unsigned char, vector signed char); | |
6825 | ||
924fcc4e JM |
6826 | vector unsigned char vec_sub (vector unsigned char, |
6827 | vector unsigned char); | |
333c8841 | 6828 | vector signed short vec_sub (vector signed short, vector signed short); |
924fcc4e JM |
6829 | vector unsigned short vec_sub (vector signed short, |
6830 | vector unsigned short); | |
6831 | vector unsigned short vec_sub (vector unsigned short, | |
6832 | vector signed short); | |
6e5bb5ad JM |
6833 | vector unsigned short vec_sub (vector unsigned short, |
6834 | vector unsigned short); | |
333c8841 AH |
6835 | vector signed int vec_sub (vector signed int, vector signed int); |
6836 | vector unsigned int vec_sub (vector signed int, vector unsigned int); | |
6837 | vector unsigned int vec_sub (vector unsigned int, vector signed int); | |
6838 | vector unsigned int vec_sub (vector unsigned int, vector unsigned int); | |
6839 | vector float vec_sub (vector float, vector float); | |
6840 | ||
6841 | vector unsigned int vec_subc (vector unsigned int, vector unsigned int); | |
6842 | ||
924fcc4e JM |
6843 | vector unsigned char vec_subs (vector signed char, |
6844 | vector unsigned char); | |
6845 | vector unsigned char vec_subs (vector unsigned char, | |
6846 | vector signed char); | |
6847 | vector unsigned char vec_subs (vector unsigned char, | |
6848 | vector unsigned char); | |
333c8841 | 6849 | vector signed char vec_subs (vector signed char, vector signed char); |
924fcc4e JM |
6850 | vector unsigned short vec_subs (vector signed short, |
6851 | vector unsigned short); | |
6852 | vector unsigned short vec_subs (vector unsigned short, | |
6853 | vector signed short); | |
6e5bb5ad JM |
6854 | vector unsigned short vec_subs (vector unsigned short, |
6855 | vector unsigned short); | |
333c8841 AH |
6856 | vector signed short vec_subs (vector signed short, vector signed short); |
6857 | ||
6858 | vector unsigned int vec_subs (vector signed int, vector unsigned int); | |
6859 | vector unsigned int vec_subs (vector unsigned int, vector signed int); | |
6860 | vector unsigned int vec_subs (vector unsigned int, vector unsigned int); | |
6861 | ||
6862 | vector signed int vec_subs (vector signed int, vector signed int); | |
6863 | ||
924fcc4e JM |
6864 | vector unsigned int vec_sum4s (vector unsigned char, |
6865 | vector unsigned int); | |
333c8841 AH |
6866 | vector signed int vec_sum4s (vector signed char, vector signed int); |
6867 | vector signed int vec_sum4s (vector signed short, vector signed int); | |
6868 | ||
6869 | vector signed int vec_sum2s (vector signed int, vector signed int); | |
6870 | ||
6871 | vector signed int vec_sums (vector signed int, vector signed int); | |
6872 | ||
6873 | vector float vec_trunc (vector float); | |
6874 | ||
6875 | vector signed short vec_unpackh (vector signed char); | |
6876 | vector unsigned int vec_unpackh (vector signed short); | |
6877 | vector signed int vec_unpackh (vector signed short); | |
6878 | ||
6879 | vector signed short vec_unpackl (vector signed char); | |
6880 | vector unsigned int vec_unpackl (vector signed short); | |
6881 | vector signed int vec_unpackl (vector signed short); | |
6882 | ||
6883 | vector float vec_xor (vector float, vector float); | |
6884 | vector float vec_xor (vector float, vector signed int); | |
6885 | vector float vec_xor (vector signed int, vector float); | |
6886 | vector signed int vec_xor (vector signed int, vector signed int); | |
6887 | vector unsigned int vec_xor (vector signed int, vector unsigned int); | |
6888 | vector unsigned int vec_xor (vector unsigned int, vector signed int); | |
6889 | vector unsigned int vec_xor (vector unsigned int, vector unsigned int); | |
6890 | vector signed short vec_xor (vector signed short, vector signed short); | |
924fcc4e JM |
6891 | vector unsigned short vec_xor (vector signed short, |
6892 | vector unsigned short); | |
6893 | vector unsigned short vec_xor (vector unsigned short, | |
6894 | vector signed short); | |
6e5bb5ad JM |
6895 | vector unsigned short vec_xor (vector unsigned short, |
6896 | vector unsigned short); | |
333c8841 AH |
6897 | vector signed char vec_xor (vector signed char, vector signed char); |
6898 | vector unsigned char vec_xor (vector signed char, vector unsigned char); | |
6899 | ||
6900 | vector unsigned char vec_xor (vector unsigned char, vector signed char); | |
6901 | ||
924fcc4e JM |
6902 | vector unsigned char vec_xor (vector unsigned char, |
6903 | vector unsigned char); | |
333c8841 AH |
6904 | |
6905 | vector signed int vec_all_eq (vector signed char, vector unsigned char); | |
6906 | ||
6907 | vector signed int vec_all_eq (vector signed char, vector signed char); | |
6908 | vector signed int vec_all_eq (vector unsigned char, vector signed char); | |
6909 | ||
924fcc4e JM |
6910 | vector signed int vec_all_eq (vector unsigned char, |
6911 | vector unsigned char); | |
6912 | vector signed int vec_all_eq (vector signed short, | |
6913 | vector unsigned short); | |
333c8841 AH |
6914 | vector signed int vec_all_eq (vector signed short, vector signed short); |
6915 | ||
924fcc4e JM |
6916 | vector signed int vec_all_eq (vector unsigned short, |
6917 | vector signed short); | |
6918 | vector signed int vec_all_eq (vector unsigned short, | |
6919 | vector unsigned short); | |
333c8841 AH |
6920 | vector signed int vec_all_eq (vector signed int, vector unsigned int); |
6921 | vector signed int vec_all_eq (vector signed int, vector signed int); | |
6922 | vector signed int vec_all_eq (vector unsigned int, vector signed int); | |
6923 | vector signed int vec_all_eq (vector unsigned int, vector unsigned int); | |
6924 | ||
6925 | vector signed int vec_all_eq (vector float, vector float); | |
6926 | ||
6927 | vector signed int vec_all_ge (vector signed char, vector unsigned char); | |
6928 | ||
6929 | vector signed int vec_all_ge (vector unsigned char, vector signed char); | |
6930 | ||
924fcc4e JM |
6931 | vector signed int vec_all_ge (vector unsigned char, |
6932 | vector unsigned char); | |
333c8841 | 6933 | vector signed int vec_all_ge (vector signed char, vector signed char); |
924fcc4e JM |
6934 | vector signed int vec_all_ge (vector signed short, |
6935 | vector unsigned short); | |
6936 | vector signed int vec_all_ge (vector unsigned short, | |
6937 | vector signed short); | |
6938 | vector signed int vec_all_ge (vector unsigned short, | |
6939 | vector unsigned short); | |
333c8841 AH |
6940 | vector signed int vec_all_ge (vector signed short, vector signed short); |
6941 | ||
6942 | vector signed int vec_all_ge (vector signed int, vector unsigned int); | |
6943 | vector signed int vec_all_ge (vector unsigned int, vector signed int); | |
6944 | vector signed int vec_all_ge (vector unsigned int, vector unsigned int); | |
6945 | ||
6946 | vector signed int vec_all_ge (vector signed int, vector signed int); | |
6947 | vector signed int vec_all_ge (vector float, vector float); | |
6948 | ||
6949 | vector signed int vec_all_gt (vector signed char, vector unsigned char); | |
6950 | ||
6951 | vector signed int vec_all_gt (vector unsigned char, vector signed char); | |
6952 | ||
924fcc4e JM |
6953 | vector signed int vec_all_gt (vector unsigned char, |
6954 | vector unsigned char); | |
333c8841 | 6955 | vector signed int vec_all_gt (vector signed char, vector signed char); |
924fcc4e JM |
6956 | vector signed int vec_all_gt (vector signed short, |
6957 | vector unsigned short); | |
f282ffb3 | 6958 | vector signed int vec_all_gt (vector unsigned short, |
924fcc4e JM |
6959 | vector signed short); |
6960 | vector signed int vec_all_gt (vector unsigned short, | |
6961 | vector unsigned short); | |
333c8841 AH |
6962 | vector signed int vec_all_gt (vector signed short, vector signed short); |
6963 | ||
6964 | vector signed int vec_all_gt (vector signed int, vector unsigned int); | |
6965 | vector signed int vec_all_gt (vector unsigned int, vector signed int); | |
6966 | vector signed int vec_all_gt (vector unsigned int, vector unsigned int); | |
6967 | ||
6968 | vector signed int vec_all_gt (vector signed int, vector signed int); | |
6969 | vector signed int vec_all_gt (vector float, vector float); | |
6970 | ||
6971 | vector signed int vec_all_in (vector float, vector float); | |
6972 | ||
6973 | vector signed int vec_all_le (vector signed char, vector unsigned char); | |
6974 | ||
6975 | vector signed int vec_all_le (vector unsigned char, vector signed char); | |
6976 | ||
924fcc4e JM |
6977 | vector signed int vec_all_le (vector unsigned char, |
6978 | vector unsigned char); | |
333c8841 | 6979 | vector signed int vec_all_le (vector signed char, vector signed char); |
924fcc4e JM |
6980 | vector signed int vec_all_le (vector signed short, |
6981 | vector unsigned short); | |
6982 | vector signed int vec_all_le (vector unsigned short, | |
6983 | vector signed short); | |
6984 | vector signed int vec_all_le (vector unsigned short, | |
6985 | vector unsigned short); | |
333c8841 AH |
6986 | vector signed int vec_all_le (vector signed short, vector signed short); |
6987 | ||
6988 | vector signed int vec_all_le (vector signed int, vector unsigned int); | |
6989 | vector signed int vec_all_le (vector unsigned int, vector signed int); | |
6990 | vector signed int vec_all_le (vector unsigned int, vector unsigned int); | |
6991 | ||
6992 | vector signed int vec_all_le (vector signed int, vector signed int); | |
6993 | vector signed int vec_all_le (vector float, vector float); | |
6994 | ||
6995 | vector signed int vec_all_lt (vector signed char, vector unsigned char); | |
6996 | ||
6997 | vector signed int vec_all_lt (vector unsigned char, vector signed char); | |
6998 | ||
924fcc4e JM |
6999 | vector signed int vec_all_lt (vector unsigned char, |
7000 | vector unsigned char); | |
333c8841 | 7001 | vector signed int vec_all_lt (vector signed char, vector signed char); |
924fcc4e JM |
7002 | vector signed int vec_all_lt (vector signed short, |
7003 | vector unsigned short); | |
7004 | vector signed int vec_all_lt (vector unsigned short, | |
7005 | vector signed short); | |
7006 | vector signed int vec_all_lt (vector unsigned short, | |
7007 | vector unsigned short); | |
333c8841 AH |
7008 | vector signed int vec_all_lt (vector signed short, vector signed short); |
7009 | ||
7010 | vector signed int vec_all_lt (vector signed int, vector unsigned int); | |
7011 | vector signed int vec_all_lt (vector unsigned int, vector signed int); | |
7012 | vector signed int vec_all_lt (vector unsigned int, vector unsigned int); | |
7013 | ||
7014 | vector signed int vec_all_lt (vector signed int, vector signed int); | |
7015 | vector signed int vec_all_lt (vector float, vector float); | |
7016 | ||
7017 | vector signed int vec_all_nan (vector float); | |
7018 | ||
7019 | vector signed int vec_all_ne (vector signed char, vector unsigned char); | |
7020 | ||
7021 | vector signed int vec_all_ne (vector signed char, vector signed char); | |
7022 | vector signed int vec_all_ne (vector unsigned char, vector signed char); | |
7023 | ||
924fcc4e JM |
7024 | vector signed int vec_all_ne (vector unsigned char, |
7025 | vector unsigned char); | |
7026 | vector signed int vec_all_ne (vector signed short, | |
7027 | vector unsigned short); | |
333c8841 AH |
7028 | vector signed int vec_all_ne (vector signed short, vector signed short); |
7029 | ||
924fcc4e JM |
7030 | vector signed int vec_all_ne (vector unsigned short, |
7031 | vector signed short); | |
7032 | vector signed int vec_all_ne (vector unsigned short, | |
7033 | vector unsigned short); | |
333c8841 AH |
7034 | vector signed int vec_all_ne (vector signed int, vector unsigned int); |
7035 | vector signed int vec_all_ne (vector signed int, vector signed int); | |
7036 | vector signed int vec_all_ne (vector unsigned int, vector signed int); | |
7037 | vector signed int vec_all_ne (vector unsigned int, vector unsigned int); | |
7038 | ||
7039 | vector signed int vec_all_ne (vector float, vector float); | |
7040 | ||
7041 | vector signed int vec_all_nge (vector float, vector float); | |
7042 | ||
7043 | vector signed int vec_all_ngt (vector float, vector float); | |
7044 | ||
7045 | vector signed int vec_all_nle (vector float, vector float); | |
7046 | ||
7047 | vector signed int vec_all_nlt (vector float, vector float); | |
7048 | ||
7049 | vector signed int vec_all_numeric (vector float); | |
7050 | ||
7051 | vector signed int vec_any_eq (vector signed char, vector unsigned char); | |
7052 | ||
7053 | vector signed int vec_any_eq (vector signed char, vector signed char); | |
7054 | vector signed int vec_any_eq (vector unsigned char, vector signed char); | |
7055 | ||
924fcc4e JM |
7056 | vector signed int vec_any_eq (vector unsigned char, |
7057 | vector unsigned char); | |
7058 | vector signed int vec_any_eq (vector signed short, | |
7059 | vector unsigned short); | |
333c8841 AH |
7060 | vector signed int vec_any_eq (vector signed short, vector signed short); |
7061 | ||
924fcc4e JM |
7062 | vector signed int vec_any_eq (vector unsigned short, |
7063 | vector signed short); | |
7064 | vector signed int vec_any_eq (vector unsigned short, | |
7065 | vector unsigned short); | |
333c8841 AH |
7066 | vector signed int vec_any_eq (vector signed int, vector unsigned int); |
7067 | vector signed int vec_any_eq (vector signed int, vector signed int); | |
7068 | vector signed int vec_any_eq (vector unsigned int, vector signed int); | |
7069 | vector signed int vec_any_eq (vector unsigned int, vector unsigned int); | |
7070 | ||
7071 | vector signed int vec_any_eq (vector float, vector float); | |
7072 | ||
7073 | vector signed int vec_any_ge (vector signed char, vector unsigned char); | |
7074 | ||
7075 | vector signed int vec_any_ge (vector unsigned char, vector signed char); | |
7076 | ||
924fcc4e JM |
7077 | vector signed int vec_any_ge (vector unsigned char, |
7078 | vector unsigned char); | |
333c8841 | 7079 | vector signed int vec_any_ge (vector signed char, vector signed char); |
924fcc4e JM |
7080 | vector signed int vec_any_ge (vector signed short, |
7081 | vector unsigned short); | |
7082 | vector signed int vec_any_ge (vector unsigned short, | |
7083 | vector signed short); | |
7084 | vector signed int vec_any_ge (vector unsigned short, | |
7085 | vector unsigned short); | |
333c8841 AH |
7086 | vector signed int vec_any_ge (vector signed short, vector signed short); |
7087 | ||
7088 | vector signed int vec_any_ge (vector signed int, vector unsigned int); | |
7089 | vector signed int vec_any_ge (vector unsigned int, vector signed int); | |
7090 | vector signed int vec_any_ge (vector unsigned int, vector unsigned int); | |
7091 | ||
7092 | vector signed int vec_any_ge (vector signed int, vector signed int); | |
7093 | vector signed int vec_any_ge (vector float, vector float); | |
7094 | ||
7095 | vector signed int vec_any_gt (vector signed char, vector unsigned char); | |
7096 | ||
7097 | vector signed int vec_any_gt (vector unsigned char, vector signed char); | |
7098 | ||
924fcc4e JM |
7099 | vector signed int vec_any_gt (vector unsigned char, |
7100 | vector unsigned char); | |
333c8841 | 7101 | vector signed int vec_any_gt (vector signed char, vector signed char); |
924fcc4e JM |
7102 | vector signed int vec_any_gt (vector signed short, |
7103 | vector unsigned short); | |
7104 | vector signed int vec_any_gt (vector unsigned short, | |
7105 | vector signed short); | |
7106 | vector signed int vec_any_gt (vector unsigned short, | |
7107 | vector unsigned short); | |
333c8841 AH |
7108 | vector signed int vec_any_gt (vector signed short, vector signed short); |
7109 | ||
7110 | vector signed int vec_any_gt (vector signed int, vector unsigned int); | |
7111 | vector signed int vec_any_gt (vector unsigned int, vector signed int); | |
7112 | vector signed int vec_any_gt (vector unsigned int, vector unsigned int); | |
7113 | ||
7114 | vector signed int vec_any_gt (vector signed int, vector signed int); | |
7115 | vector signed int vec_any_gt (vector float, vector float); | |
7116 | ||
7117 | vector signed int vec_any_le (vector signed char, vector unsigned char); | |
7118 | ||
7119 | vector signed int vec_any_le (vector unsigned char, vector signed char); | |
7120 | ||
924fcc4e JM |
7121 | vector signed int vec_any_le (vector unsigned char, |
7122 | vector unsigned char); | |
333c8841 | 7123 | vector signed int vec_any_le (vector signed char, vector signed char); |
924fcc4e JM |
7124 | vector signed int vec_any_le (vector signed short, |
7125 | vector unsigned short); | |
7126 | vector signed int vec_any_le (vector unsigned short, | |
7127 | vector signed short); | |
7128 | vector signed int vec_any_le (vector unsigned short, | |
7129 | vector unsigned short); | |
333c8841 AH |
7130 | vector signed int vec_any_le (vector signed short, vector signed short); |
7131 | ||
7132 | vector signed int vec_any_le (vector signed int, vector unsigned int); | |
7133 | vector signed int vec_any_le (vector unsigned int, vector signed int); | |
7134 | vector signed int vec_any_le (vector unsigned int, vector unsigned int); | |
7135 | ||
7136 | vector signed int vec_any_le (vector signed int, vector signed int); | |
7137 | vector signed int vec_any_le (vector float, vector float); | |
7138 | ||
7139 | vector signed int vec_any_lt (vector signed char, vector unsigned char); | |
7140 | ||
7141 | vector signed int vec_any_lt (vector unsigned char, vector signed char); | |
7142 | ||
924fcc4e JM |
7143 | vector signed int vec_any_lt (vector unsigned char, |
7144 | vector unsigned char); | |
333c8841 | 7145 | vector signed int vec_any_lt (vector signed char, vector signed char); |
924fcc4e JM |
7146 | vector signed int vec_any_lt (vector signed short, |
7147 | vector unsigned short); | |
7148 | vector signed int vec_any_lt (vector unsigned short, | |
7149 | vector signed short); | |
7150 | vector signed int vec_any_lt (vector unsigned short, | |
7151 | vector unsigned short); | |
333c8841 AH |
7152 | vector signed int vec_any_lt (vector signed short, vector signed short); |
7153 | ||
7154 | vector signed int vec_any_lt (vector signed int, vector unsigned int); | |
7155 | vector signed int vec_any_lt (vector unsigned int, vector signed int); | |
7156 | vector signed int vec_any_lt (vector unsigned int, vector unsigned int); | |
7157 | ||
7158 | vector signed int vec_any_lt (vector signed int, vector signed int); | |
7159 | vector signed int vec_any_lt (vector float, vector float); | |
7160 | ||
7161 | vector signed int vec_any_nan (vector float); | |
7162 | ||
7163 | vector signed int vec_any_ne (vector signed char, vector unsigned char); | |
7164 | ||
7165 | vector signed int vec_any_ne (vector signed char, vector signed char); | |
7166 | vector signed int vec_any_ne (vector unsigned char, vector signed char); | |
7167 | ||
924fcc4e JM |
7168 | vector signed int vec_any_ne (vector unsigned char, |
7169 | vector unsigned char); | |
7170 | vector signed int vec_any_ne (vector signed short, | |
7171 | vector unsigned short); | |
333c8841 AH |
7172 | vector signed int vec_any_ne (vector signed short, vector signed short); |
7173 | ||
924fcc4e JM |
7174 | vector signed int vec_any_ne (vector unsigned short, |
7175 | vector signed short); | |
7176 | vector signed int vec_any_ne (vector unsigned short, | |
7177 | vector unsigned short); | |
333c8841 AH |
7178 | vector signed int vec_any_ne (vector signed int, vector unsigned int); |
7179 | vector signed int vec_any_ne (vector signed int, vector signed int); | |
7180 | vector signed int vec_any_ne (vector unsigned int, vector signed int); | |
7181 | vector signed int vec_any_ne (vector unsigned int, vector unsigned int); | |
7182 | ||
7183 | vector signed int vec_any_ne (vector float, vector float); | |
7184 | ||
7185 | vector signed int vec_any_nge (vector float, vector float); | |
7186 | ||
7187 | vector signed int vec_any_ngt (vector float, vector float); | |
7188 | ||
7189 | vector signed int vec_any_nle (vector float, vector float); | |
7190 | ||
7191 | vector signed int vec_any_nlt (vector float, vector float); | |
7192 | ||
7193 | vector signed int vec_any_numeric (vector float); | |
7194 | ||
7195 | vector signed int vec_any_out (vector float, vector float); | |
7196 | @end smallexample | |
7197 | ||
0168a849 SS |
7198 | @node Pragmas |
7199 | @section Pragmas Accepted by GCC | |
7200 | @cindex pragmas | |
7201 | @cindex #pragma | |
7202 | ||
7203 | GCC supports several types of pragmas, primarily in order to compile | |
7204 | code originally written for other compilers. Note that in general | |
7205 | we do not recommend the use of pragmas; @xref{Function Attributes}, | |
7206 | for further explanation. | |
7207 | ||
7208 | @menu | |
7209 | * ARM Pragmas:: | |
a5c76ee6 | 7210 | * RS/6000 and PowerPC Pragmas:: |
0168a849 | 7211 | * Darwin Pragmas:: |
84b8b0e0 | 7212 | * Symbol-Renaming Pragmas:: |
0168a849 SS |
7213 | @end menu |
7214 | ||
7215 | @node ARM Pragmas | |
7216 | @subsection ARM Pragmas | |
7217 | ||
7218 | The ARM target defines pragmas for controlling the default addition of | |
7219 | @code{long_call} and @code{short_call} attributes to functions. | |
7220 | @xref{Function Attributes}, for information about the effects of these | |
7221 | attributes. | |
7222 | ||
7223 | @table @code | |
7224 | @item long_calls | |
7225 | @cindex pragma, long_calls | |
7226 | Set all subsequent functions to have the @code{long_call} attribute. | |
7227 | ||
7228 | @item no_long_calls | |
7229 | @cindex pragma, no_long_calls | |
7230 | Set all subsequent functions to have the @code{short_call} attribute. | |
7231 | ||
7232 | @item long_calls_off | |
7233 | @cindex pragma, long_calls_off | |
7234 | Do not affect the @code{long_call} or @code{short_call} attributes of | |
7235 | subsequent functions. | |
7236 | @end table | |
7237 | ||
a5c76ee6 ZW |
7238 | @node RS/6000 and PowerPC Pragmas |
7239 | @subsection RS/6000 and PowerPC Pragmas | |
7240 | ||
7241 | The RS/6000 and PowerPC targets define one pragma for controlling | |
7242 | whether or not the @code{longcall} attribute is added to function | |
7243 | declarations by default. This pragma overrides the @option{-mlongcall} | |
95b1627e | 7244 | option, but not the @code{longcall} and @code{shortcall} attributes. |
a5c76ee6 ZW |
7245 | @xref{RS/6000 and PowerPC Options}, for more information about when long |
7246 | calls are and are not necessary. | |
7247 | ||
7248 | @table @code | |
7249 | @item longcall (1) | |
7250 | @cindex pragma, longcall | |
7251 | Apply the @code{longcall} attribute to all subsequent function | |
7252 | declarations. | |
7253 | ||
7254 | @item longcall (0) | |
7255 | Do not apply the @code{longcall} attribute to subsequent function | |
7256 | declarations. | |
7257 | @end table | |
7258 | ||
0168a849 SS |
7259 | @c Describe c4x pragmas here. |
7260 | @c Describe h8300 pragmas here. | |
0168a849 SS |
7261 | @c Describe sh pragmas here. |
7262 | @c Describe v850 pragmas here. | |
7263 | ||
7264 | @node Darwin Pragmas | |
7265 | @subsection Darwin Pragmas | |
7266 | ||
7267 | The following pragmas are available for all architectures running the | |
7268 | Darwin operating system. These are useful for compatibility with other | |
85ebf0c6 | 7269 | Mac OS compilers. |
0168a849 SS |
7270 | |
7271 | @table @code | |
7272 | @item mark @var{tokens}@dots{} | |
7273 | @cindex pragma, mark | |
7274 | This pragma is accepted, but has no effect. | |
7275 | ||
7276 | @item options align=@var{alignment} | |
7277 | @cindex pragma, options align | |
7278 | This pragma sets the alignment of fields in structures. The values of | |
7279 | @var{alignment} may be @code{mac68k}, to emulate m68k alignment, or | |
7280 | @code{power}, to emulate PowerPC alignment. Uses of this pragma nest | |
7281 | properly; to restore the previous setting, use @code{reset} for the | |
7282 | @var{alignment}. | |
7283 | ||
7284 | @item segment @var{tokens}@dots{} | |
7285 | @cindex pragma, segment | |
7286 | This pragma is accepted, but has no effect. | |
7287 | ||
7288 | @item unused (@var{var} [, @var{var}]@dots{}) | |
7289 | @cindex pragma, unused | |
7290 | This pragma declares variables to be possibly unused. GCC will not | |
7291 | produce warnings for the listed variables. The effect is similar to | |
7292 | that of the @code{unused} attribute, except that this pragma may appear | |
7293 | anywhere within the variables' scopes. | |
7294 | @end table | |
7295 | ||
84b8b0e0 ZW |
7296 | @node Symbol-Renaming Pragmas |
7297 | @subsection Symbol-Renaming Pragmas | |
41c64394 | 7298 | |
84b8b0e0 ZW |
7299 | For compatibility with the Solaris and Tru64 UNIX system headers, GCC |
7300 | supports two @code{#pragma} directives which change the name used in | |
7301 | assembly for a given declaration. These pragmas are only available on | |
7302 | platforms whose system headers need them. To get this effect on all | |
7303 | platforms supported by GCC, use the asm labels extension (@pxref{Asm | |
7304 | Labels}). | |
41c64394 RH |
7305 | |
7306 | @table @code | |
7307 | @item redefine_extname @var{oldname} @var{newname} | |
7308 | @cindex pragma, redefine_extname | |
7309 | ||
84b8b0e0 ZW |
7310 | This pragma gives the C function @var{oldname} the assembly symbol |
7311 | @var{newname}. The preprocessor macro @code{__PRAGMA_REDEFINE_EXTNAME} | |
7312 | will be defined if this pragma is available (currently only on | |
7313 | Solaris). | |
41c64394 | 7314 | |
41c64394 RH |
7315 | @item extern_prefix @var{string} |
7316 | @cindex pragma, extern_prefix | |
7317 | ||
84b8b0e0 ZW |
7318 | This pragma causes all subsequent external function and variable |
7319 | declarations to have @var{string} prepended to their assembly symbols. | |
7320 | This effect may be terminated with another @code{extern_prefix} pragma | |
7321 | whose argument is an empty string. The preprocessor macro | |
7322 | @code{__PRAGMA_EXTERN_PREFIX} will be defined if this pragma is | |
7323 | available (currently only on Tru64 UNIX). | |
41c64394 RH |
7324 | @end table |
7325 | ||
84b8b0e0 ZW |
7326 | These pragmas and the asm labels extension interact in a complicated |
7327 | manner. Here are some corner cases you may want to be aware of. | |
7328 | ||
7329 | @enumerate | |
7330 | @item Both pragmas silently apply only to declarations with external | |
7331 | linkage. Asm labels do not have this restriction. | |
7332 | ||
7333 | @item In C++, both pragmas silently apply only to declarations with | |
7334 | ``C'' linkage. Again, asm labels do not have this restriction. | |
7335 | ||
7336 | @item If any of the three ways of changing the assembly name of a | |
7337 | declaration is applied to a declaration whose assembly name has | |
7338 | already been determined (either by a previous use of one of these | |
7339 | features, or because the compiler needed the assembly name in order to | |
7340 | generate code), and the new name is different, a warning issues and | |
7341 | the name does not change. | |
7342 | ||
7343 | @item The @var{oldname} used by @code{#pragma redefine_extname} is | |
7344 | always the C-language name. | |
7345 | ||
7346 | @item If @code{#pragma extern_prefix} is in effect, and a declaration | |
7347 | occurs with an asm label attached, the prefix is silently ignored for | |
7348 | that declaration. | |
7349 | ||
7350 | @item If @code{#pragma extern_prefix} and @code{#pragma redefine_extname} | |
7351 | apply to the same declaration, whichever triggered first wins, and a | |
7352 | warning issues if they contradict each other. (We would like to have | |
7353 | @code{#pragma redefine_extname} always win, for consistency with asm | |
7354 | labels, but if @code{#pragma extern_prefix} triggers first we have no | |
7355 | way of knowing that that happened.) | |
7356 | @end enumerate | |
7357 | ||
3e96a2fd DD |
7358 | @node Unnamed Fields |
7359 | @section Unnamed struct/union fields within structs/unions. | |
7360 | @cindex struct | |
7361 | @cindex union | |
7362 | ||
7363 | For compatibility with other compilers, GCC allows you to define | |
7364 | a structure or union that contains, as fields, structures and unions | |
7365 | without names. For example: | |
7366 | ||
3ab51846 | 7367 | @smallexample |
3e96a2fd DD |
7368 | struct @{ |
7369 | int a; | |
7370 | union @{ | |
7371 | int b; | |
7372 | float c; | |
7373 | @}; | |
7374 | int d; | |
7375 | @} foo; | |
3ab51846 | 7376 | @end smallexample |
3e96a2fd DD |
7377 | |
7378 | In this example, the user would be able to access members of the unnamed | |
7379 | union with code like @samp{foo.b}. Note that only unnamed structs and | |
7380 | unions are allowed, you may not have, for example, an unnamed | |
7381 | @code{int}. | |
7382 | ||
7383 | You must never create such structures that cause ambiguous field definitions. | |
7384 | For example, this structure: | |
7385 | ||
3ab51846 | 7386 | @smallexample |
3e96a2fd DD |
7387 | struct @{ |
7388 | int a; | |
7389 | struct @{ | |
7390 | int a; | |
7391 | @}; | |
7392 | @} foo; | |
3ab51846 | 7393 | @end smallexample |
3e96a2fd DD |
7394 | |
7395 | It is ambiguous which @code{a} is being referred to with @samp{foo.a}. | |
7396 | Such constructs are not supported and must be avoided. In the future, | |
7397 | such constructs may be detected and treated as compilation errors. | |
7398 | ||
3d78f2e9 RH |
7399 | @node Thread-Local |
7400 | @section Thread-Local Storage | |
7401 | @cindex Thread-Local Storage | |
9217ef40 | 7402 | @cindex @acronym{TLS} |
3d78f2e9 RH |
7403 | @cindex __thread |
7404 | ||
9217ef40 RH |
7405 | Thread-local storage (@acronym{TLS}) is a mechanism by which variables |
7406 | are allocated such that there is one instance of the variable per extant | |
3d78f2e9 RH |
7407 | thread. The run-time model GCC uses to implement this originates |
7408 | in the IA-64 processor-specific ABI, but has since been migrated | |
7409 | to other processors as well. It requires significant support from | |
7410 | the linker (@command{ld}), dynamic linker (@command{ld.so}), and | |
7411 | system libraries (@file{libc.so} and @file{libpthread.so}), so it | |
9217ef40 | 7412 | is not available everywhere. |
3d78f2e9 RH |
7413 | |
7414 | At the user level, the extension is visible with a new storage | |
7415 | class keyword: @code{__thread}. For example: | |
7416 | ||
3ab51846 | 7417 | @smallexample |
3d78f2e9 RH |
7418 | __thread int i; |
7419 | extern __thread struct state s; | |
7420 | static __thread char *p; | |
3ab51846 | 7421 | @end smallexample |
3d78f2e9 RH |
7422 | |
7423 | The @code{__thread} specifier may be used alone, with the @code{extern} | |
7424 | or @code{static} specifiers, but with no other storage class specifier. | |
7425 | When used with @code{extern} or @code{static}, @code{__thread} must appear | |
7426 | immediately after the other storage class specifier. | |
7427 | ||
7428 | The @code{__thread} specifier may be applied to any global, file-scoped | |
244c2241 RH |
7429 | static, function-scoped static, or static data member of a class. It may |
7430 | not be applied to block-scoped automatic or non-static data member. | |
3d78f2e9 RH |
7431 | |
7432 | When the address-of operator is applied to a thread-local variable, it is | |
7433 | evaluated at run-time and returns the address of the current thread's | |
7434 | instance of that variable. An address so obtained may be used by any | |
7435 | thread. When a thread terminates, any pointers to thread-local variables | |
7436 | in that thread become invalid. | |
7437 | ||
7438 | No static initialization may refer to the address of a thread-local variable. | |
7439 | ||
244c2241 RH |
7440 | In C++, if an initializer is present for a thread-local variable, it must |
7441 | be a @var{constant-expression}, as defined in 5.19.2 of the ANSI/ISO C++ | |
7442 | standard. | |
3d78f2e9 RH |
7443 | |
7444 | See @uref{http://people.redhat.com/drepper/tls.pdf, | |
7445 | ELF Handling For Thread-Local Storage} for a detailed explanation of | |
7446 | the four thread-local storage addressing models, and how the run-time | |
7447 | is expected to function. | |
7448 | ||
9217ef40 RH |
7449 | @menu |
7450 | * C99 Thread-Local Edits:: | |
7451 | * C++98 Thread-Local Edits:: | |
7452 | @end menu | |
7453 | ||
7454 | @node C99 Thread-Local Edits | |
7455 | @subsection ISO/IEC 9899:1999 Edits for Thread-Local Storage | |
7456 | ||
7457 | The following are a set of changes to ISO/IEC 9899:1999 (aka C99) | |
7458 | that document the exact semantics of the language extension. | |
7459 | ||
7460 | @itemize @bullet | |
7461 | @item | |
7462 | @cite{5.1.2 Execution environments} | |
7463 | ||
7464 | Add new text after paragraph 1 | |
7465 | ||
7466 | @quotation | |
7467 | Within either execution environment, a @dfn{thread} is a flow of | |
7468 | control within a program. It is implementation defined whether | |
7469 | or not there may be more than one thread associated with a program. | |
7470 | It is implementation defined how threads beyond the first are | |
7471 | created, the name and type of the function called at thread | |
7472 | startup, and how threads may be terminated. However, objects | |
7473 | with thread storage duration shall be initialized before thread | |
7474 | startup. | |
7475 | @end quotation | |
7476 | ||
7477 | @item | |
7478 | @cite{6.2.4 Storage durations of objects} | |
7479 | ||
7480 | Add new text before paragraph 3 | |
7481 | ||
7482 | @quotation | |
7483 | An object whose identifier is declared with the storage-class | |
7484 | specifier @w{@code{__thread}} has @dfn{thread storage duration}. | |
7485 | Its lifetime is the entire execution of the thread, and its | |
7486 | stored value is initialized only once, prior to thread startup. | |
7487 | @end quotation | |
7488 | ||
7489 | @item | |
7490 | @cite{6.4.1 Keywords} | |
7491 | ||
7492 | Add @code{__thread}. | |
7493 | ||
7494 | @item | |
7495 | @cite{6.7.1 Storage-class specifiers} | |
7496 | ||
7497 | Add @code{__thread} to the list of storage class specifiers in | |
7498 | paragraph 1. | |
7499 | ||
7500 | Change paragraph 2 to | |
7501 | ||
7502 | @quotation | |
7503 | With the exception of @code{__thread}, at most one storage-class | |
7504 | specifier may be given [@dots{}]. The @code{__thread} specifier may | |
7505 | be used alone, or immediately following @code{extern} or | |
7506 | @code{static}. | |
7507 | @end quotation | |
7508 | ||
7509 | Add new text after paragraph 6 | |
7510 | ||
7511 | @quotation | |
7512 | The declaration of an identifier for a variable that has | |
7513 | block scope that specifies @code{__thread} shall also | |
7514 | specify either @code{extern} or @code{static}. | |
7515 | ||
7516 | The @code{__thread} specifier shall be used only with | |
7517 | variables. | |
7518 | @end quotation | |
7519 | @end itemize | |
7520 | ||
7521 | @node C++98 Thread-Local Edits | |
7522 | @subsection ISO/IEC 14882:1998 Edits for Thread-Local Storage | |
7523 | ||
7524 | The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) | |
7525 | that document the exact semantics of the language extension. | |
7526 | ||
7527 | @itemize @bullet | |
8d23a2c8 | 7528 | @item |
9217ef40 RH |
7529 | @b{[intro.execution]} |
7530 | ||
7531 | New text after paragraph 4 | |
7532 | ||
7533 | @quotation | |
7534 | A @dfn{thread} is a flow of control within the abstract machine. | |
7535 | It is implementation defined whether or not there may be more than | |
7536 | one thread. | |
7537 | @end quotation | |
7538 | ||
7539 | New text after paragraph 7 | |
7540 | ||
7541 | @quotation | |
95b1627e | 7542 | It is unspecified whether additional action must be taken to |
9217ef40 RH |
7543 | ensure when and whether side effects are visible to other threads. |
7544 | @end quotation | |
7545 | ||
7546 | @item | |
7547 | @b{[lex.key]} | |
7548 | ||
7549 | Add @code{__thread}. | |
7550 | ||
7551 | @item | |
7552 | @b{[basic.start.main]} | |
7553 | ||
7554 | Add after paragraph 5 | |
7555 | ||
7556 | @quotation | |
7557 | The thread that begins execution at the @code{main} function is called | |
95b1627e | 7558 | the @dfn{main thread}. It is implementation defined how functions |
9217ef40 RH |
7559 | beginning threads other than the main thread are designated or typed. |
7560 | A function so designated, as well as the @code{main} function, is called | |
7561 | a @dfn{thread startup function}. It is implementation defined what | |
7562 | happens if a thread startup function returns. It is implementation | |
7563 | defined what happens to other threads when any thread calls @code{exit}. | |
7564 | @end quotation | |
7565 | ||
7566 | @item | |
7567 | @b{[basic.start.init]} | |
7568 | ||
7569 | Add after paragraph 4 | |
7570 | ||
7571 | @quotation | |
7572 | The storage for an object of thread storage duration shall be | |
c0478a66 | 7573 | statically initialized before the first statement of the thread startup |
9217ef40 RH |
7574 | function. An object of thread storage duration shall not require |
7575 | dynamic initialization. | |
7576 | @end quotation | |
7577 | ||
7578 | @item | |
7579 | @b{[basic.start.term]} | |
7580 | ||
7581 | Add after paragraph 3 | |
7582 | ||
7583 | @quotation | |
244c2241 RH |
7584 | The type of an object with thread storage duration shall not have a |
7585 | non-trivial destructor, nor shall it be an array type whose elements | |
7586 | (directly or indirectly) have non-trivial destructors. | |
9217ef40 RH |
7587 | @end quotation |
7588 | ||
7589 | @item | |
7590 | @b{[basic.stc]} | |
7591 | ||
7592 | Add ``thread storage duration'' to the list in paragraph 1. | |
7593 | ||
7594 | Change paragraph 2 | |
7595 | ||
7596 | @quotation | |
7597 | Thread, static, and automatic storage durations are associated with | |
7598 | objects introduced by declarations [@dots{}]. | |
7599 | @end quotation | |
7600 | ||
7601 | Add @code{__thread} to the list of specifiers in paragraph 3. | |
7602 | ||
7603 | @item | |
7604 | @b{[basic.stc.thread]} | |
7605 | ||
7606 | New section before @b{[basic.stc.static]} | |
7607 | ||
7608 | @quotation | |
63519d23 | 7609 | The keyword @code{__thread} applied to a non-local object gives the |
9217ef40 RH |
7610 | object thread storage duration. |
7611 | ||
7612 | A local variable or class data member declared both @code{static} | |
7613 | and @code{__thread} gives the variable or member thread storage | |
7614 | duration. | |
7615 | @end quotation | |
7616 | ||
7617 | @item | |
7618 | @b{[basic.stc.static]} | |
7619 | ||
7620 | Change paragraph 1 | |
7621 | ||
7622 | @quotation | |
7623 | All objects which have neither thread storage duration, dynamic | |
7624 | storage duration nor are local [@dots{}]. | |
7625 | @end quotation | |
7626 | ||
7627 | @item | |
7628 | @b{[dcl.stc]} | |
7629 | ||
7630 | Add @code{__thread} to the list in paragraph 1. | |
7631 | ||
7632 | Change paragraph 1 | |
7633 | ||
7634 | @quotation | |
7635 | With the exception of @code{__thread}, at most one | |
7636 | @var{storage-class-specifier} shall appear in a given | |
7637 | @var{decl-specifier-seq}. The @code{__thread} specifier may | |
7638 | be used alone, or immediately following the @code{extern} or | |
7639 | @code{static} specifiers. [@dots{}] | |
7640 | @end quotation | |
7641 | ||
7642 | Add after paragraph 5 | |
7643 | ||
7644 | @quotation | |
7645 | The @code{__thread} specifier can be applied only to the names of objects | |
7646 | and to anonymous unions. | |
7647 | @end quotation | |
7648 | ||
7649 | @item | |
7650 | @b{[class.mem]} | |
7651 | ||
7652 | Add after paragraph 6 | |
7653 | ||
7654 | @quotation | |
7655 | Non-@code{static} members shall not be @code{__thread}. | |
7656 | @end quotation | |
7657 | @end itemize | |
7658 | ||
c1f7febf RK |
7659 | @node C++ Extensions |
7660 | @chapter Extensions to the C++ Language | |
7661 | @cindex extensions, C++ language | |
7662 | @cindex C++ language extensions | |
7663 | ||
7664 | The GNU compiler provides these extensions to the C++ language (and you | |
7665 | can also use most of the C language extensions in your C++ programs). If you | |
7666 | want to write code that checks whether these features are available, you can | |
7667 | test for the GNU compiler the same way as for C programs: check for a | |
7668 | predefined macro @code{__GNUC__}. You can also use @code{__GNUG__} to | |
48795525 GP |
7669 | test specifically for GNU C++ (@pxref{Common Predefined Macros,, |
7670 | Predefined Macros,cpp,The GNU C Preprocessor}). | |
c1f7febf RK |
7671 | |
7672 | @menu | |
c1f7febf | 7673 | * Min and Max:: C++ Minimum and maximum operators. |
02cac427 | 7674 | * Volatiles:: What constitutes an access to a volatile object. |
49419c8f | 7675 | * Restricted Pointers:: C99 restricted pointers and references. |
7a81cf7f | 7676 | * Vague Linkage:: Where G++ puts inlines, vtables and such. |
c1f7febf | 7677 | * C++ Interface:: You can use a single C++ header file for both |
e6f3b89d | 7678 | declarations and definitions. |
c1f7febf | 7679 | * Template Instantiation:: Methods for ensuring that exactly one copy of |
e6f3b89d | 7680 | each needed template instantiation is emitted. |
0ded1f18 JM |
7681 | * Bound member functions:: You can extract a function pointer to the |
7682 | method denoted by a @samp{->*} or @samp{.*} expression. | |
e6f3b89d | 7683 | * C++ Attributes:: Variable, function, and type attributes for C++ only. |
86098eb8 | 7684 | * Strong Using:: Strong using-directives for namespace composition. |
1f730ff7 | 7685 | * Java Exceptions:: Tweaking exception handling to work with Java. |
90ea7324 | 7686 | * Deprecated Features:: Things will disappear from g++. |
e6f3b89d | 7687 | * Backwards Compatibility:: Compatibilities with earlier definitions of C++. |
c1f7febf RK |
7688 | @end menu |
7689 | ||
c1f7febf RK |
7690 | @node Min and Max |
7691 | @section Minimum and Maximum Operators in C++ | |
7692 | ||
7693 | It is very convenient to have operators which return the ``minimum'' or the | |
7694 | ``maximum'' of two arguments. In GNU C++ (but not in GNU C), | |
7695 | ||
7696 | @table @code | |
7697 | @item @var{a} <? @var{b} | |
7698 | @findex <? | |
7699 | @cindex minimum operator | |
7700 | is the @dfn{minimum}, returning the smaller of the numeric values | |
7701 | @var{a} and @var{b}; | |
7702 | ||
7703 | @item @var{a} >? @var{b} | |
7704 | @findex >? | |
7705 | @cindex maximum operator | |
7706 | is the @dfn{maximum}, returning the larger of the numeric values @var{a} | |
7707 | and @var{b}. | |
7708 | @end table | |
7709 | ||
7710 | These operations are not primitive in ordinary C++, since you can | |
7711 | use a macro to return the minimum of two things in C++, as in the | |
7712 | following example. | |
7713 | ||
3ab51846 | 7714 | @smallexample |
c1f7febf | 7715 | #define MIN(X,Y) ((X) < (Y) ? : (X) : (Y)) |
3ab51846 | 7716 | @end smallexample |
c1f7febf RK |
7717 | |
7718 | @noindent | |
7719 | You might then use @w{@samp{int min = MIN (i, j);}} to set @var{min} to | |
7720 | the minimum value of variables @var{i} and @var{j}. | |
7721 | ||
7722 | However, side effects in @code{X} or @code{Y} may cause unintended | |
7723 | behavior. For example, @code{MIN (i++, j++)} will fail, incrementing | |
95f79357 ZW |
7724 | the smaller counter twice. The GNU C @code{typeof} extension allows you |
7725 | to write safe macros that avoid this kind of problem (@pxref{Typeof}). | |
7726 | However, writing @code{MIN} and @code{MAX} as macros also forces you to | |
7727 | use function-call notation for a fundamental arithmetic operation. | |
7728 | Using GNU C++ extensions, you can write @w{@samp{int min = i <? j;}} | |
7729 | instead. | |
c1f7febf RK |
7730 | |
7731 | Since @code{<?} and @code{>?} are built into the compiler, they properly | |
7732 | handle expressions with side-effects; @w{@samp{int min = i++ <? j++;}} | |
7733 | works correctly. | |
7734 | ||
02cac427 NS |
7735 | @node Volatiles |
7736 | @section When is a Volatile Object Accessed? | |
7737 | @cindex accessing volatiles | |
7738 | @cindex volatile read | |
7739 | @cindex volatile write | |
7740 | @cindex volatile access | |
7741 | ||
767094dd JM |
7742 | Both the C and C++ standard have the concept of volatile objects. These |
7743 | are normally accessed by pointers and used for accessing hardware. The | |
8117da65 | 7744 | standards encourage compilers to refrain from optimizations |
02cac427 | 7745 | concerning accesses to volatile objects that it might perform on |
767094dd JM |
7746 | non-volatile objects. The C standard leaves it implementation defined |
7747 | as to what constitutes a volatile access. The C++ standard omits to | |
02cac427 | 7748 | specify this, except to say that C++ should behave in a similar manner |
767094dd | 7749 | to C with respect to volatiles, where possible. The minimum either |
8117da65 | 7750 | standard specifies is that at a sequence point all previous accesses to |
02cac427 | 7751 | volatile objects have stabilized and no subsequent accesses have |
767094dd | 7752 | occurred. Thus an implementation is free to reorder and combine |
02cac427 | 7753 | volatile accesses which occur between sequence points, but cannot do so |
767094dd | 7754 | for accesses across a sequence point. The use of volatiles does not |
02cac427 NS |
7755 | allow you to violate the restriction on updating objects multiple times |
7756 | within a sequence point. | |
7757 | ||
7758 | In most expressions, it is intuitively obvious what is a read and what is | |
767094dd | 7759 | a write. For instance |
02cac427 | 7760 | |
3ab51846 | 7761 | @smallexample |
c771326b JM |
7762 | volatile int *dst = @var{somevalue}; |
7763 | volatile int *src = @var{someothervalue}; | |
02cac427 | 7764 | *dst = *src; |
3ab51846 | 7765 | @end smallexample |
02cac427 NS |
7766 | |
7767 | @noindent | |
7768 | will cause a read of the volatile object pointed to by @var{src} and stores the | |
767094dd | 7769 | value into the volatile object pointed to by @var{dst}. There is no |
02cac427 NS |
7770 | guarantee that these reads and writes are atomic, especially for objects |
7771 | larger than @code{int}. | |
7772 | ||
7773 | Less obvious expressions are where something which looks like an access | |
767094dd | 7774 | is used in a void context. An example would be, |
02cac427 | 7775 | |
3ab51846 | 7776 | @smallexample |
c771326b | 7777 | volatile int *src = @var{somevalue}; |
02cac427 | 7778 | *src; |
3ab51846 | 7779 | @end smallexample |
02cac427 NS |
7780 | |
7781 | With C, such expressions are rvalues, and as rvalues cause a read of | |
f0523f02 | 7782 | the object, GCC interprets this as a read of the volatile being pointed |
767094dd | 7783 | to. The C++ standard specifies that such expressions do not undergo |
02cac427 | 7784 | lvalue to rvalue conversion, and that the type of the dereferenced |
767094dd | 7785 | object may be incomplete. The C++ standard does not specify explicitly |
02cac427 | 7786 | that it is this lvalue to rvalue conversion which is responsible for |
767094dd JM |
7787 | causing an access. However, there is reason to believe that it is, |
7788 | because otherwise certain simple expressions become undefined. However, | |
f0523f02 | 7789 | because it would surprise most programmers, G++ treats dereferencing a |
02cac427 | 7790 | pointer to volatile object of complete type in a void context as a read |
767094dd | 7791 | of the object. When the object has incomplete type, G++ issues a |
02cac427 NS |
7792 | warning. |
7793 | ||
3ab51846 | 7794 | @smallexample |
02cac427 NS |
7795 | struct S; |
7796 | struct T @{int m;@}; | |
c771326b JM |
7797 | volatile S *ptr1 = @var{somevalue}; |
7798 | volatile T *ptr2 = @var{somevalue}; | |
02cac427 NS |
7799 | *ptr1; |
7800 | *ptr2; | |
3ab51846 | 7801 | @end smallexample |
02cac427 NS |
7802 | |
7803 | In this example, a warning is issued for @code{*ptr1}, and @code{*ptr2} | |
767094dd | 7804 | causes a read of the object pointed to. If you wish to force an error on |
02cac427 NS |
7805 | the first case, you must force a conversion to rvalue with, for instance |
7806 | a static cast, @code{static_cast<S>(*ptr1)}. | |
7807 | ||
f0523f02 | 7808 | When using a reference to volatile, G++ does not treat equivalent |
02cac427 | 7809 | expressions as accesses to volatiles, but instead issues a warning that |
767094dd | 7810 | no volatile is accessed. The rationale for this is that otherwise it |
02cac427 NS |
7811 | becomes difficult to determine where volatile access occur, and not |
7812 | possible to ignore the return value from functions returning volatile | |
767094dd | 7813 | references. Again, if you wish to force a read, cast the reference to |
02cac427 NS |
7814 | an rvalue. |
7815 | ||
535233a8 NS |
7816 | @node Restricted Pointers |
7817 | @section Restricting Pointer Aliasing | |
7818 | @cindex restricted pointers | |
7819 | @cindex restricted references | |
7820 | @cindex restricted this pointer | |
7821 | ||
2dd76960 | 7822 | As with the C front end, G++ understands the C99 feature of restricted pointers, |
535233a8 | 7823 | specified with the @code{__restrict__}, or @code{__restrict} type |
767094dd | 7824 | qualifier. Because you cannot compile C++ by specifying the @option{-std=c99} |
535233a8 NS |
7825 | language flag, @code{restrict} is not a keyword in C++. |
7826 | ||
7827 | In addition to allowing restricted pointers, you can specify restricted | |
7828 | references, which indicate that the reference is not aliased in the local | |
7829 | context. | |
7830 | ||
3ab51846 | 7831 | @smallexample |
535233a8 NS |
7832 | void fn (int *__restrict__ rptr, int &__restrict__ rref) |
7833 | @{ | |
0d893a63 | 7834 | /* @r{@dots{}} */ |
535233a8 | 7835 | @} |
3ab51846 | 7836 | @end smallexample |
535233a8 NS |
7837 | |
7838 | @noindent | |
7839 | In the body of @code{fn}, @var{rptr} points to an unaliased integer and | |
7840 | @var{rref} refers to a (different) unaliased integer. | |
7841 | ||
7842 | You may also specify whether a member function's @var{this} pointer is | |
7843 | unaliased by using @code{__restrict__} as a member function qualifier. | |
7844 | ||
3ab51846 | 7845 | @smallexample |
535233a8 NS |
7846 | void T::fn () __restrict__ |
7847 | @{ | |
0d893a63 | 7848 | /* @r{@dots{}} */ |
535233a8 | 7849 | @} |
3ab51846 | 7850 | @end smallexample |
535233a8 NS |
7851 | |
7852 | @noindent | |
7853 | Within the body of @code{T::fn}, @var{this} will have the effective | |
767094dd | 7854 | definition @code{T *__restrict__ const this}. Notice that the |
535233a8 NS |
7855 | interpretation of a @code{__restrict__} member function qualifier is |
7856 | different to that of @code{const} or @code{volatile} qualifier, in that it | |
767094dd | 7857 | is applied to the pointer rather than the object. This is consistent with |
535233a8 NS |
7858 | other compilers which implement restricted pointers. |
7859 | ||
7860 | As with all outermost parameter qualifiers, @code{__restrict__} is | |
767094dd | 7861 | ignored in function definition matching. This means you only need to |
535233a8 NS |
7862 | specify @code{__restrict__} in a function definition, rather than |
7863 | in a function prototype as well. | |
7864 | ||
7a81cf7f JM |
7865 | @node Vague Linkage |
7866 | @section Vague Linkage | |
7867 | @cindex vague linkage | |
7868 | ||
7869 | There are several constructs in C++ which require space in the object | |
7870 | file but are not clearly tied to a single translation unit. We say that | |
7871 | these constructs have ``vague linkage''. Typically such constructs are | |
7872 | emitted wherever they are needed, though sometimes we can be more | |
7873 | clever. | |
7874 | ||
7875 | @table @asis | |
7876 | @item Inline Functions | |
7877 | Inline functions are typically defined in a header file which can be | |
7878 | included in many different compilations. Hopefully they can usually be | |
7879 | inlined, but sometimes an out-of-line copy is necessary, if the address | |
7880 | of the function is taken or if inlining fails. In general, we emit an | |
7881 | out-of-line copy in all translation units where one is needed. As an | |
7882 | exception, we only emit inline virtual functions with the vtable, since | |
7883 | it will always require a copy. | |
7884 | ||
7885 | Local static variables and string constants used in an inline function | |
7886 | are also considered to have vague linkage, since they must be shared | |
7887 | between all inlined and out-of-line instances of the function. | |
7888 | ||
7889 | @item VTables | |
7890 | @cindex vtable | |
7891 | C++ virtual functions are implemented in most compilers using a lookup | |
7892 | table, known as a vtable. The vtable contains pointers to the virtual | |
7893 | functions provided by a class, and each object of the class contains a | |
7894 | pointer to its vtable (or vtables, in some multiple-inheritance | |
7895 | situations). If the class declares any non-inline, non-pure virtual | |
7896 | functions, the first one is chosen as the ``key method'' for the class, | |
7897 | and the vtable is only emitted in the translation unit where the key | |
7898 | method is defined. | |
7899 | ||
7900 | @emph{Note:} If the chosen key method is later defined as inline, the | |
7901 | vtable will still be emitted in every translation unit which defines it. | |
7902 | Make sure that any inline virtuals are declared inline in the class | |
7903 | body, even if they are not defined there. | |
7904 | ||
7905 | @item type_info objects | |
7906 | @cindex type_info | |
7907 | @cindex RTTI | |
7908 | C++ requires information about types to be written out in order to | |
7909 | implement @samp{dynamic_cast}, @samp{typeid} and exception handling. | |
7910 | For polymorphic classes (classes with virtual functions), the type_info | |
7911 | object is written out along with the vtable so that @samp{dynamic_cast} | |
7912 | can determine the dynamic type of a class object at runtime. For all | |
7913 | other types, we write out the type_info object when it is used: when | |
7914 | applying @samp{typeid} to an expression, throwing an object, or | |
7915 | referring to a type in a catch clause or exception specification. | |
7916 | ||
7917 | @item Template Instantiations | |
7918 | Most everything in this section also applies to template instantiations, | |
7919 | but there are other options as well. | |
7920 | @xref{Template Instantiation,,Where's the Template?}. | |
7921 | ||
7922 | @end table | |
7923 | ||
7924 | When used with GNU ld version 2.8 or later on an ELF system such as | |
95fef11f | 7925 | GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of |
7a81cf7f JM |
7926 | these constructs will be discarded at link time. This is known as |
7927 | COMDAT support. | |
7928 | ||
7929 | On targets that don't support COMDAT, but do support weak symbols, GCC | |
7930 | will use them. This way one copy will override all the others, but | |
7931 | the unused copies will still take up space in the executable. | |
7932 | ||
7933 | For targets which do not support either COMDAT or weak symbols, | |
7934 | most entities with vague linkage will be emitted as local symbols to | |
7935 | avoid duplicate definition errors from the linker. This will not happen | |
7936 | for local statics in inlines, however, as having multiple copies will | |
7937 | almost certainly break things. | |
7938 | ||
7939 | @xref{C++ Interface,,Declarations and Definitions in One Header}, for | |
7940 | another way to control placement of these constructs. | |
7941 | ||
c1f7febf | 7942 | @node C++ Interface |
fc72b380 | 7943 | @section #pragma interface and implementation |
c1f7febf RK |
7944 | |
7945 | @cindex interface and implementation headers, C++ | |
7946 | @cindex C++ interface and implementation headers | |
c1f7febf | 7947 | @cindex pragmas, interface and implementation |
c1f7febf | 7948 | |
fc72b380 JM |
7949 | @code{#pragma interface} and @code{#pragma implementation} provide the |
7950 | user with a way of explicitly directing the compiler to emit entities | |
7951 | with vague linkage (and debugging information) in a particular | |
7952 | translation unit. | |
c1f7febf | 7953 | |
fc72b380 JM |
7954 | @emph{Note:} As of GCC 2.7.2, these @code{#pragma}s are not useful in |
7955 | most cases, because of COMDAT support and the ``key method'' heuristic | |
7956 | mentioned in @ref{Vague Linkage}. Using them can actually cause your | |
7957 | program to grow due to unnecesary out-of-line copies of inline | |
7958 | functions. Currently (3.4) the only benefit of these | |
7959 | @code{#pragma}s is reduced duplication of debugging information, and | |
7960 | that should be addressed soon on DWARF 2 targets with the use of | |
7961 | COMDAT groups. | |
c1f7febf RK |
7962 | |
7963 | @table @code | |
7964 | @item #pragma interface | |
7965 | @itemx #pragma interface "@var{subdir}/@var{objects}.h" | |
7966 | @kindex #pragma interface | |
7967 | Use this directive in @emph{header files} that define object classes, to save | |
7968 | space in most of the object files that use those classes. Normally, | |
7969 | local copies of certain information (backup copies of inline member | |
7970 | functions, debugging information, and the internal tables that implement | |
7971 | virtual functions) must be kept in each object file that includes class | |
7972 | definitions. You can use this pragma to avoid such duplication. When a | |
7973 | header file containing @samp{#pragma interface} is included in a | |
7974 | compilation, this auxiliary information will not be generated (unless | |
7975 | the main input source file itself uses @samp{#pragma implementation}). | |
7976 | Instead, the object files will contain references to be resolved at link | |
7977 | time. | |
7978 | ||
7979 | The second form of this directive is useful for the case where you have | |
7980 | multiple headers with the same name in different directories. If you | |
7981 | use this form, you must specify the same string to @samp{#pragma | |
7982 | implementation}. | |
7983 | ||
7984 | @item #pragma implementation | |
7985 | @itemx #pragma implementation "@var{objects}.h" | |
7986 | @kindex #pragma implementation | |
7987 | Use this pragma in a @emph{main input file}, when you want full output from | |
7988 | included header files to be generated (and made globally visible). The | |
7989 | included header file, in turn, should use @samp{#pragma interface}. | |
7990 | Backup copies of inline member functions, debugging information, and the | |
7991 | internal tables used to implement virtual functions are all generated in | |
7992 | implementation files. | |
7993 | ||
7994 | @cindex implied @code{#pragma implementation} | |
7995 | @cindex @code{#pragma implementation}, implied | |
7996 | @cindex naming convention, implementation headers | |
7997 | If you use @samp{#pragma implementation} with no argument, it applies to | |
7998 | an include file with the same basename@footnote{A file's @dfn{basename} | |
7999 | was the name stripped of all leading path information and of trailing | |
8000 | suffixes, such as @samp{.h} or @samp{.C} or @samp{.cc}.} as your source | |
8001 | file. For example, in @file{allclass.cc}, giving just | |
8002 | @samp{#pragma implementation} | |
8003 | by itself is equivalent to @samp{#pragma implementation "allclass.h"}. | |
8004 | ||
8005 | In versions of GNU C++ prior to 2.6.0 @file{allclass.h} was treated as | |
8006 | an implementation file whenever you would include it from | |
8007 | @file{allclass.cc} even if you never specified @samp{#pragma | |
8008 | implementation}. This was deemed to be more trouble than it was worth, | |
8009 | however, and disabled. | |
8010 | ||
c1f7febf RK |
8011 | Use the string argument if you want a single implementation file to |
8012 | include code from multiple header files. (You must also use | |
8013 | @samp{#include} to include the header file; @samp{#pragma | |
8014 | implementation} only specifies how to use the file---it doesn't actually | |
8015 | include it.) | |
8016 | ||
8017 | There is no way to split up the contents of a single header file into | |
8018 | multiple implementation files. | |
8019 | @end table | |
8020 | ||
8021 | @cindex inlining and C++ pragmas | |
8022 | @cindex C++ pragmas, effect on inlining | |
8023 | @cindex pragmas in C++, effect on inlining | |
8024 | @samp{#pragma implementation} and @samp{#pragma interface} also have an | |
8025 | effect on function inlining. | |
8026 | ||
8027 | If you define a class in a header file marked with @samp{#pragma | |
fc72b380 JM |
8028 | interface}, the effect on an inline function defined in that class is |
8029 | similar to an explicit @code{extern} declaration---the compiler emits | |
8030 | no code at all to define an independent version of the function. Its | |
8031 | definition is used only for inlining with its callers. | |
c1f7febf | 8032 | |
84330467 | 8033 | @opindex fno-implement-inlines |
c1f7febf RK |
8034 | Conversely, when you include the same header file in a main source file |
8035 | that declares it as @samp{#pragma implementation}, the compiler emits | |
8036 | code for the function itself; this defines a version of the function | |
8037 | that can be found via pointers (or by callers compiled without | |
8038 | inlining). If all calls to the function can be inlined, you can avoid | |
84330467 | 8039 | emitting the function by compiling with @option{-fno-implement-inlines}. |
c1f7febf RK |
8040 | If any calls were not inlined, you will get linker errors. |
8041 | ||
8042 | @node Template Instantiation | |
8043 | @section Where's the Template? | |
c1f7febf RK |
8044 | @cindex template instantiation |
8045 | ||
8046 | C++ templates are the first language feature to require more | |
8047 | intelligence from the environment than one usually finds on a UNIX | |
8048 | system. Somehow the compiler and linker have to make sure that each | |
8049 | template instance occurs exactly once in the executable if it is needed, | |
8050 | and not at all otherwise. There are two basic approaches to this | |
962e6e00 | 8051 | problem, which are referred to as the Borland model and the Cfront model. |
c1f7febf RK |
8052 | |
8053 | @table @asis | |
8054 | @item Borland model | |
8055 | Borland C++ solved the template instantiation problem by adding the code | |
469b759e JM |
8056 | equivalent of common blocks to their linker; the compiler emits template |
8057 | instances in each translation unit that uses them, and the linker | |
8058 | collapses them together. The advantage of this model is that the linker | |
8059 | only has to consider the object files themselves; there is no external | |
8060 | complexity to worry about. This disadvantage is that compilation time | |
8061 | is increased because the template code is being compiled repeatedly. | |
8062 | Code written for this model tends to include definitions of all | |
8063 | templates in the header file, since they must be seen to be | |
8064 | instantiated. | |
c1f7febf RK |
8065 | |
8066 | @item Cfront model | |
8067 | The AT&T C++ translator, Cfront, solved the template instantiation | |
8068 | problem by creating the notion of a template repository, an | |
469b759e JM |
8069 | automatically maintained place where template instances are stored. A |
8070 | more modern version of the repository works as follows: As individual | |
8071 | object files are built, the compiler places any template definitions and | |
8072 | instantiations encountered in the repository. At link time, the link | |
8073 | wrapper adds in the objects in the repository and compiles any needed | |
8074 | instances that were not previously emitted. The advantages of this | |
8075 | model are more optimal compilation speed and the ability to use the | |
8076 | system linker; to implement the Borland model a compiler vendor also | |
c1f7febf | 8077 | needs to replace the linker. The disadvantages are vastly increased |
469b759e JM |
8078 | complexity, and thus potential for error; for some code this can be |
8079 | just as transparent, but in practice it can been very difficult to build | |
c1f7febf | 8080 | multiple programs in one directory and one program in multiple |
469b759e JM |
8081 | directories. Code written for this model tends to separate definitions |
8082 | of non-inline member templates into a separate file, which should be | |
8083 | compiled separately. | |
c1f7febf RK |
8084 | @end table |
8085 | ||
469b759e | 8086 | When used with GNU ld version 2.8 or later on an ELF system such as |
2dd76960 JM |
8087 | GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the |
8088 | Borland model. On other systems, G++ implements neither automatic | |
a4b3b54a | 8089 | model. |
469b759e | 8090 | |
2dd76960 | 8091 | A future version of G++ will support a hybrid model whereby the compiler |
469b759e JM |
8092 | will emit any instantiations for which the template definition is |
8093 | included in the compile, and store template definitions and | |
8094 | instantiation context information into the object file for the rest. | |
8095 | The link wrapper will extract that information as necessary and invoke | |
8096 | the compiler to produce the remaining instantiations. The linker will | |
8097 | then combine duplicate instantiations. | |
8098 | ||
8099 | In the mean time, you have the following options for dealing with | |
8100 | template instantiations: | |
c1f7febf RK |
8101 | |
8102 | @enumerate | |
d863830b | 8103 | @item |
84330467 JM |
8104 | @opindex frepo |
8105 | Compile your template-using code with @option{-frepo}. The compiler will | |
d863830b JL |
8106 | generate files with the extension @samp{.rpo} listing all of the |
8107 | template instantiations used in the corresponding object files which | |
8108 | could be instantiated there; the link wrapper, @samp{collect2}, will | |
8109 | then update the @samp{.rpo} files to tell the compiler where to place | |
8110 | those instantiations and rebuild any affected object files. The | |
8111 | link-time overhead is negligible after the first pass, as the compiler | |
8112 | will continue to place the instantiations in the same files. | |
8113 | ||
8114 | This is your best option for application code written for the Borland | |
8115 | model, as it will just work. Code written for the Cfront model will | |
8116 | need to be modified so that the template definitions are available at | |
8117 | one or more points of instantiation; usually this is as simple as adding | |
8118 | @code{#include <tmethods.cc>} to the end of each template header. | |
8119 | ||
8120 | For library code, if you want the library to provide all of the template | |
8121 | instantiations it needs, just try to link all of its object files | |
8122 | together; the link will fail, but cause the instantiations to be | |
8123 | generated as a side effect. Be warned, however, that this may cause | |
8124 | conflicts if multiple libraries try to provide the same instantiations. | |
8125 | For greater control, use explicit instantiation as described in the next | |
8126 | option. | |
8127 | ||
c1f7febf | 8128 | @item |
84330467 JM |
8129 | @opindex fno-implicit-templates |
8130 | Compile your code with @option{-fno-implicit-templates} to disable the | |
c1f7febf RK |
8131 | implicit generation of template instances, and explicitly instantiate |
8132 | all the ones you use. This approach requires more knowledge of exactly | |
8133 | which instances you need than do the others, but it's less | |
8134 | mysterious and allows greater control. You can scatter the explicit | |
8135 | instantiations throughout your program, perhaps putting them in the | |
8136 | translation units where the instances are used or the translation units | |
8137 | that define the templates themselves; you can put all of the explicit | |
8138 | instantiations you need into one big file; or you can create small files | |
8139 | like | |
8140 | ||
3ab51846 | 8141 | @smallexample |
c1f7febf RK |
8142 | #include "Foo.h" |
8143 | #include "Foo.cc" | |
8144 | ||
8145 | template class Foo<int>; | |
8146 | template ostream& operator << | |
8147 | (ostream&, const Foo<int>&); | |
3ab51846 | 8148 | @end smallexample |
c1f7febf RK |
8149 | |
8150 | for each of the instances you need, and create a template instantiation | |
8151 | library from those. | |
8152 | ||
8153 | If you are using Cfront-model code, you can probably get away with not | |
84330467 | 8154 | using @option{-fno-implicit-templates} when compiling files that don't |
c1f7febf RK |
8155 | @samp{#include} the member template definitions. |
8156 | ||
8157 | If you use one big file to do the instantiations, you may want to | |
84330467 | 8158 | compile it without @option{-fno-implicit-templates} so you get all of the |
c1f7febf RK |
8159 | instances required by your explicit instantiations (but not by any |
8160 | other files) without having to specify them as well. | |
8161 | ||
2dd76960 | 8162 | G++ has extended the template instantiation syntax given in the ISO |
6d9c4c83 | 8163 | standard to allow forward declaration of explicit instantiations |
4003d7f9 | 8164 | (with @code{extern}), instantiation of the compiler support data for a |
e979f9e8 | 8165 | template class (i.e.@: the vtable) without instantiating any of its |
4003d7f9 JM |
8166 | members (with @code{inline}), and instantiation of only the static data |
8167 | members of a template class, without the support data or member | |
8168 | functions (with (@code{static}): | |
c1f7febf | 8169 | |
3ab51846 | 8170 | @smallexample |
c1f7febf | 8171 | extern template int max (int, int); |
c1f7febf | 8172 | inline template class Foo<int>; |
4003d7f9 | 8173 | static template class Foo<int>; |
3ab51846 | 8174 | @end smallexample |
c1f7febf RK |
8175 | |
8176 | @item | |
2dd76960 | 8177 | Do nothing. Pretend G++ does implement automatic instantiation |
c1f7febf RK |
8178 | management. Code written for the Borland model will work fine, but |
8179 | each translation unit will contain instances of each of the templates it | |
8180 | uses. In a large program, this can lead to an unacceptable amount of code | |
8181 | duplication. | |
c1f7febf RK |
8182 | @end enumerate |
8183 | ||
0ded1f18 JM |
8184 | @node Bound member functions |
8185 | @section Extracting the function pointer from a bound pointer to member function | |
0ded1f18 JM |
8186 | @cindex pmf |
8187 | @cindex pointer to member function | |
8188 | @cindex bound pointer to member function | |
8189 | ||
8190 | In C++, pointer to member functions (PMFs) are implemented using a wide | |
8191 | pointer of sorts to handle all the possible call mechanisms; the PMF | |
8192 | needs to store information about how to adjust the @samp{this} pointer, | |
8193 | and if the function pointed to is virtual, where to find the vtable, and | |
8194 | where in the vtable to look for the member function. If you are using | |
8195 | PMFs in an inner loop, you should really reconsider that decision. If | |
8196 | that is not an option, you can extract the pointer to the function that | |
8197 | would be called for a given object/PMF pair and call it directly inside | |
8198 | the inner loop, to save a bit of time. | |
8199 | ||
8200 | Note that you will still be paying the penalty for the call through a | |
8201 | function pointer; on most modern architectures, such a call defeats the | |
161d7b59 | 8202 | branch prediction features of the CPU@. This is also true of normal |
0ded1f18 JM |
8203 | virtual function calls. |
8204 | ||
8205 | The syntax for this extension is | |
8206 | ||
3ab51846 | 8207 | @smallexample |
0ded1f18 JM |
8208 | extern A a; |
8209 | extern int (A::*fp)(); | |
8210 | typedef int (*fptr)(A *); | |
8211 | ||
8212 | fptr p = (fptr)(a.*fp); | |
3ab51846 | 8213 | @end smallexample |
0ded1f18 | 8214 | |
e979f9e8 | 8215 | For PMF constants (i.e.@: expressions of the form @samp{&Klasse::Member}), |
767094dd | 8216 | no object is needed to obtain the address of the function. They can be |
0fb6bbf5 ML |
8217 | converted to function pointers directly: |
8218 | ||
3ab51846 | 8219 | @smallexample |
0fb6bbf5 | 8220 | fptr p1 = (fptr)(&A::foo); |
3ab51846 | 8221 | @end smallexample |
0fb6bbf5 | 8222 | |
84330467 JM |
8223 | @opindex Wno-pmf-conversions |
8224 | You must specify @option{-Wno-pmf-conversions} to use this extension. | |
0ded1f18 | 8225 | |
5c25e11d PE |
8226 | @node C++ Attributes |
8227 | @section C++-Specific Variable, Function, and Type Attributes | |
8228 | ||
8229 | Some attributes only make sense for C++ programs. | |
8230 | ||
8231 | @table @code | |
8232 | @item init_priority (@var{priority}) | |
8233 | @cindex init_priority attribute | |
8234 | ||
8235 | ||
8236 | In Standard C++, objects defined at namespace scope are guaranteed to be | |
8237 | initialized in an order in strict accordance with that of their definitions | |
8238 | @emph{in a given translation unit}. No guarantee is made for initializations | |
8239 | across translation units. However, GNU C++ allows users to control the | |
3844cd2e | 8240 | order of initialization of objects defined at namespace scope with the |
5c25e11d PE |
8241 | @code{init_priority} attribute by specifying a relative @var{priority}, |
8242 | a constant integral expression currently bounded between 101 and 65535 | |
8243 | inclusive. Lower numbers indicate a higher priority. | |
8244 | ||
8245 | In the following example, @code{A} would normally be created before | |
8246 | @code{B}, but the @code{init_priority} attribute has reversed that order: | |
8247 | ||
478c9e72 | 8248 | @smallexample |
5c25e11d PE |
8249 | Some_Class A __attribute__ ((init_priority (2000))); |
8250 | Some_Class B __attribute__ ((init_priority (543))); | |
478c9e72 | 8251 | @end smallexample |
5c25e11d PE |
8252 | |
8253 | @noindent | |
8254 | Note that the particular values of @var{priority} do not matter; only their | |
8255 | relative ordering. | |
8256 | ||
60c87482 BM |
8257 | @item java_interface |
8258 | @cindex java_interface attribute | |
8259 | ||
02f52e19 | 8260 | This type attribute informs C++ that the class is a Java interface. It may |
60c87482 | 8261 | only be applied to classes declared within an @code{extern "Java"} block. |
02f52e19 AJ |
8262 | Calls to methods declared in this interface will be dispatched using GCJ's |
8263 | interface table mechanism, instead of regular virtual table dispatch. | |
60c87482 | 8264 | |
5c25e11d PE |
8265 | @end table |
8266 | ||
86098eb8 JM |
8267 | See also @xref{Strong Using}. |
8268 | ||
8269 | @node Strong Using | |
8270 | @section Strong Using | |
8271 | ||
fea77ed9 MM |
8272 | @strong{Caution:} The semantics of this extension are not fully |
8273 | defined. Users should refrain from using this extension as its | |
8274 | semantics may change subtly over time. It is possible that this | |
8275 | extension wil be removed in future versions of G++. | |
8276 | ||
86098eb8 JM |
8277 | A using-directive with @code{__attribute ((strong))} is stronger |
8278 | than a normal using-directive in two ways: | |
8279 | ||
8280 | @itemize @bullet | |
8281 | @item | |
8282 | Templates from the used namespace can be specialized as though they were members of the using namespace. | |
8283 | ||
8284 | @item | |
8285 | The using namespace is considered an associated namespace of all | |
8286 | templates in the used namespace for purposes of argument-dependent | |
8287 | name lookup. | |
8288 | @end itemize | |
8289 | ||
8290 | This is useful for composing a namespace transparently from | |
8291 | implementation namespaces. For example: | |
8292 | ||
8293 | @smallexample | |
8294 | namespace std @{ | |
8295 | namespace debug @{ | |
8296 | template <class T> struct A @{ @}; | |
8297 | @} | |
8298 | using namespace debug __attribute ((__strong__)); | |
8299 | template <> struct A<int> @{ @}; // ok to specialize | |
8300 | ||
8301 | template <class T> void f (A<T>); | |
8302 | @} | |
8303 | ||
8304 | int main() | |
8305 | @{ | |
8306 | f (std::A<float>()); // lookup finds std::f | |
8307 | f (std::A<int>()); | |
8308 | @} | |
8309 | @end smallexample | |
8310 | ||
1f730ff7 ZW |
8311 | @node Java Exceptions |
8312 | @section Java Exceptions | |
8313 | ||
8314 | The Java language uses a slightly different exception handling model | |
8315 | from C++. Normally, GNU C++ will automatically detect when you are | |
8316 | writing C++ code that uses Java exceptions, and handle them | |
8317 | appropriately. However, if C++ code only needs to execute destructors | |
8318 | when Java exceptions are thrown through it, GCC will guess incorrectly. | |
9c34dbbf | 8319 | Sample problematic code is: |
1f730ff7 | 8320 | |
478c9e72 | 8321 | @smallexample |
1f730ff7 | 8322 | struct S @{ ~S(); @}; |
9c34dbbf | 8323 | extern void bar(); // is written in Java, and may throw exceptions |
1f730ff7 ZW |
8324 | void foo() |
8325 | @{ | |
8326 | S s; | |
8327 | bar(); | |
8328 | @} | |
478c9e72 | 8329 | @end smallexample |
1f730ff7 ZW |
8330 | |
8331 | @noindent | |
8332 | The usual effect of an incorrect guess is a link failure, complaining of | |
8333 | a missing routine called @samp{__gxx_personality_v0}. | |
8334 | ||
8335 | You can inform the compiler that Java exceptions are to be used in a | |
8336 | translation unit, irrespective of what it might think, by writing | |
8337 | @samp{@w{#pragma GCC java_exceptions}} at the head of the file. This | |
8338 | @samp{#pragma} must appear before any functions that throw or catch | |
8339 | exceptions, or run destructors when exceptions are thrown through them. | |
8340 | ||
8341 | You cannot mix Java and C++ exceptions in the same translation unit. It | |
8342 | is believed to be safe to throw a C++ exception from one file through | |
9c34dbbf ZW |
8343 | another file compiled for the Java exception model, or vice versa, but |
8344 | there may be bugs in this area. | |
1f730ff7 | 8345 | |
e6f3b89d PE |
8346 | @node Deprecated Features |
8347 | @section Deprecated Features | |
8348 | ||
8349 | In the past, the GNU C++ compiler was extended to experiment with new | |
767094dd | 8350 | features, at a time when the C++ language was still evolving. Now that |
e6f3b89d | 8351 | the C++ standard is complete, some of those features are superseded by |
767094dd JM |
8352 | superior alternatives. Using the old features might cause a warning in |
8353 | some cases that the feature will be dropped in the future. In other | |
e6f3b89d PE |
8354 | cases, the feature might be gone already. |
8355 | ||
8356 | While the list below is not exhaustive, it documents some of the options | |
8357 | that are now deprecated: | |
8358 | ||
8359 | @table @code | |
8360 | @item -fexternal-templates | |
8361 | @itemx -falt-external-templates | |
2dd76960 | 8362 | These are two of the many ways for G++ to implement template |
767094dd | 8363 | instantiation. @xref{Template Instantiation}. The C++ standard clearly |
e6f3b89d | 8364 | defines how template definitions have to be organized across |
2dd76960 | 8365 | implementation units. G++ has an implicit instantiation mechanism that |
e6f3b89d PE |
8366 | should work just fine for standard-conforming code. |
8367 | ||
8368 | @item -fstrict-prototype | |
8369 | @itemx -fno-strict-prototype | |
8370 | Previously it was possible to use an empty prototype parameter list to | |
8371 | indicate an unspecified number of parameters (like C), rather than no | |
767094dd | 8372 | parameters, as C++ demands. This feature has been removed, except where |
e6f3b89d PE |
8373 | it is required for backwards compatibility @xref{Backwards Compatibility}. |
8374 | @end table | |
8375 | ||
ad1a6d45 | 8376 | The named return value extension has been deprecated, and is now |
2dd76960 | 8377 | removed from G++. |
e6f3b89d | 8378 | |
82c18d5c | 8379 | The use of initializer lists with new expressions has been deprecated, |
2dd76960 | 8380 | and is now removed from G++. |
ad1a6d45 NS |
8381 | |
8382 | Floating and complex non-type template parameters have been deprecated, | |
2dd76960 | 8383 | and are now removed from G++. |
ad1a6d45 | 8384 | |
90ea7324 | 8385 | The implicit typename extension has been deprecated and is now |
2dd76960 | 8386 | removed from G++. |
90ea7324 NS |
8387 | |
8388 | The use of default arguments in function pointers, function typedefs and | |
8389 | and other places where they are not permitted by the standard is | |
2dd76960 | 8390 | deprecated and will be removed from a future version of G++. |
82c18d5c | 8391 | |
e6f3b89d PE |
8392 | @node Backwards Compatibility |
8393 | @section Backwards Compatibility | |
8394 | @cindex Backwards Compatibility | |
8395 | @cindex ARM [Annotated C++ Reference Manual] | |
8396 | ||
aee96fe9 | 8397 | Now that there is a definitive ISO standard C++, G++ has a specification |
767094dd | 8398 | to adhere to. The C++ language evolved over time, and features that |
e6f3b89d | 8399 | used to be acceptable in previous drafts of the standard, such as the ARM |
767094dd | 8400 | [Annotated C++ Reference Manual], are no longer accepted. In order to allow |
aee96fe9 | 8401 | compilation of C++ written to such drafts, G++ contains some backwards |
767094dd | 8402 | compatibilities. @emph{All such backwards compatibility features are |
aee96fe9 | 8403 | liable to disappear in future versions of G++.} They should be considered |
e6f3b89d PE |
8404 | deprecated @xref{Deprecated Features}. |
8405 | ||
8406 | @table @code | |
8407 | @item For scope | |
8408 | If a variable is declared at for scope, it used to remain in scope until | |
8409 | the end of the scope which contained the for statement (rather than just | |
aee96fe9 | 8410 | within the for scope). G++ retains this, but issues a warning, if such a |
e6f3b89d PE |
8411 | variable is accessed outside the for scope. |
8412 | ||
ad1a6d45 | 8413 | @item Implicit C language |
630d3d5a | 8414 | Old C system header files did not contain an @code{extern "C" @{@dots{}@}} |
767094dd JM |
8415 | scope to set the language. On such systems, all header files are |
8416 | implicitly scoped inside a C language scope. Also, an empty prototype | |
e6f3b89d PE |
8417 | @code{()} will be treated as an unspecified number of arguments, rather |
8418 | than no arguments, as C++ demands. | |
8419 | @end table |