1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __LINUX_COMPILER_ATTRIBUTES_H
3 #define __LINUX_COMPILER_ATTRIBUTES_H
4
5 /*
6 * The attributes in this file are unconditionally defined and they directly
7 * map to compiler attribute(s), unless one of the compilers does not support
8 * the attribute. In that case, __has_attribute is used to check for support
9 * and the reason is stated in its comment ("Optional: ...").
10 *
11 * Any other "attributes" (i.e. those that depend on a configuration option,
12 * on a compiler, on an architecture, on plugins, on other attributes...)
13 * should be defined elsewhere (e.g. compiler_types.h or compiler-*.h).
14 * The intention is to keep this file as simple as possible, as well as
15 * compiler- and version-agnostic (e.g. avoiding GCC_VERSION checks).
16 *
17 * This file is meant to be sorted (by actual attribute name,
18 * not by #define identifier). Use the __attribute__((__name__)) syntax
19 * (i.e. with underscores) to avoid future collisions with other macros.
20 * Provide links to the documentation of each supported compiler, if it exists.
21 */
22
23 /*
24 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute
25 */
26 #define __alias(symbol) __attribute__((__alias__(#symbol)))
27
28 /*
29 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-aligned-function-attribute
30 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-aligned-type-attribute
31 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-aligned-variable-attribute
32 */
33 #define __aligned(x) __attribute__((__aligned__(x)))
34 #define __aligned_largest __attribute__((__aligned__))
35
36 /*
37 * Note: do not use this directly. Instead, use __alloc_size() since it is conditionally
38 * available and includes other attributes. For GCC < 9.1, __alloc_size__ gets undefined
39 * in compiler-gcc.h, due to misbehaviors.
40 *
41 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alloc_005fsize-function-attribute
42 * clang: https://clang.llvm.org/docs/AttributeReference.html#alloc-size
43 */
44 #define __alloc_size__(x, ...) __attribute__((__alloc_size__(x, ## __VA_ARGS__)))
45
46 /*
47 * Note: users of __always_inline currently do not write "inline" themselves,
48 * which seems to be required by gcc to apply the attribute according
49 * to its docs (and also "warning: always_inline function might not be
50 * inlinable [-Wattributes]" is emitted).
51 *
52 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-always_005finline-function-attribute
53 * clang: mentioned
54 */
55 #define __always_inline inline __attribute__((__always_inline__))
56
57 /*
58 * The second argument is optional (default 0), so we use a variadic macro
59 * to make the shorthand.
60 *
61 * Beware: Do not apply this to functions which may return
62 * ERR_PTRs. Also, it is probably unwise to apply it to functions
63 * returning extra information in the low bits (but in that case the
64 * compiler should see some alignment anyway, when the return value is
65 * massaged by 'flags = ptr & 3; ptr &= ~3;').
66 *
67 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-assume_005faligned-function-attribute
68 * clang: https://clang.llvm.org/docs/AttributeReference.html#assume-aligned
69 */
70 #define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
71
72 /*
73 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-cleanup-variable-attribute
74 * clang: https://clang.llvm.org/docs/AttributeReference.html#cleanup
75 */
76 #define __cleanup(func) __attribute__((__cleanup__(func)))
77
78 /*
79 * Note the long name.
80 *
81 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-const-function-attribute
82 */
83 #define __attribute_const__ __attribute__((__const__))
84
85 /*
86 * Optional: only supported since gcc >= 9
87 * Optional: not supported by clang
88 *
89 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
90 */
91 #if __has_attribute(__copy__)
92 # define __copy(symbol) __attribute__((__copy__(symbol)))
93 #else
94 # define __copy(symbol)
95 #endif
96
97 /*
98 * Optional: only supported since gcc >= 15
99 * Optional: only supported since clang >= 18
100 *
101 * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
102 * clang: https://github.com/llvm/llvm-project/pull/76348
103 */
104 #if __has_attribute(__counted_by__)
105 # define __counted_by(member) __attribute__((__counted_by__(member)))
106 #else
107 # define __counted_by(member)
108 #endif
109
110 /*
111 * Optional: not supported by gcc
112 * Optional: only supported since clang >= 14.0
113 *
114 * clang: https://clang.llvm.org/docs/AttributeReference.html#diagnose_as_builtin
115 */
116 #if __has_attribute(__diagnose_as_builtin__)
117 # define __diagnose_as(builtin...) __attribute__((__diagnose_as_builtin__(builtin)))
118 #else
119 # define __diagnose_as(builtin...)
120 #endif
121
122 /*
123 * Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
124 * attribute warnings entirely and for good") for more information.
125 *
126 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-deprecated-function-attribute
127 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-deprecated-type-attribute
128 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-deprecated-variable-attribute
129 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Enumerator-Attributes.html#index-deprecated-enumerator-attribute
130 * clang: https://clang.llvm.org/docs/AttributeReference.html#deprecated
131 */
132 #define __deprecated
133
134 /*
135 * Optional: not supported by clang
136 *
137 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-designated_005finit-type-attribute
138 */
139 #if __has_attribute(__designated_init__)
140 # define __designated_init __attribute__((__designated_init__))
141 #else
142 # define __designated_init
143 #endif
144
145 /*
146 * Optional: only supported since clang >= 14.0
147 *
148 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-error-function-attribute
149 */
150 #if __has_attribute(__error__)
151 # define __compiletime_error(msg) __attribute__((__error__(msg)))
152 #else
153 # define __compiletime_error(msg)
154 #endif
155
156 /*
157 * Optional: not supported by clang
158 *
159 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-externally_005fvisible-function-attribute
160 */
161 #if __has_attribute(__externally_visible__)
162 # define __visible __attribute__((__externally_visible__))
163 #else
164 # define __visible
165 #endif
166
167 /*
168 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-format-function-attribute
169 * clang: https://clang.llvm.org/docs/AttributeReference.html#format
170 */
171 #define __printf(a, b) __attribute__((__format__(printf, a, b)))
172 #define __scanf(a, b) __attribute__((__format__(scanf, a, b)))
173
174 /*
175 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-gnu_005finline-function-attribute
176 * clang: https://clang.llvm.org/docs/AttributeReference.html#gnu-inline
177 */
178 #define __gnu_inline __attribute__((__gnu_inline__))
179
180 /*
181 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
182 * clang: https://clang.llvm.org/docs/AttributeReference.html#malloc
183 */
184 #define __malloc __attribute__((__malloc__))
185
186 /*
187 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-mode-type-attribute
188 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-mode-variable-attribute
189 */
190 #define __mode(x) __attribute__((__mode__(x)))
191
192 /*
193 * Optional: only supported since gcc >= 7
194 *
195 * gcc: https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html#index-no_005fcaller_005fsaved_005fregisters-function-attribute_002c-x86
196 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-caller-saved-registers
197 */
198 #if __has_attribute(__no_caller_saved_registers__)
199 # define __no_caller_saved_registers __attribute__((__no_caller_saved_registers__))
200 #else
201 # define __no_caller_saved_registers
202 #endif
203
204 /*
205 * Optional: not supported by clang
206 *
207 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
208 */
209 #if __has_attribute(__noclone__)
210 # define __noclone __attribute__((__noclone__))
211 #else
212 # define __noclone
213 #endif
214
215 /*
216 * Add the pseudo keyword 'fallthrough' so case statement blocks
217 * must end with any of these keywords:
218 * break;
219 * fallthrough;
220 * continue;
221 * goto <label>;
222 * return [expression];
223 *
224 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
225 */
226 #if __has_attribute(__fallthrough__)
227 # define fallthrough __attribute__((__fallthrough__))
228 #else
229 # define fallthrough do {} while (0) /* fallthrough */
230 #endif
231
232 /*
233 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
234 * clang: https://clang.llvm.org/docs/AttributeReference.html#flatten
235 */
236 # define __flatten __attribute__((flatten))
237
238 /*
239 * Note the missing underscores.
240 *
241 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute
242 * clang: mentioned
243 */
244 #define noinline __attribute__((__noinline__))
245
246 /*
247 * Optional: only supported since gcc >= 8
248 * Optional: not supported by clang
249 *
250 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute
251 */
252 #if __has_attribute(__nonstring__)
253 # define __nonstring __attribute__((__nonstring__))
254 #else
255 # define __nonstring
256 #endif
257
258 /*
259 * Optional: only supported since GCC >= 7.1, clang >= 13.0.
260 *
261 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fprofile_005finstrument_005ffunction-function-attribute
262 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-profile-instrument-function
263 */
264 #if __has_attribute(__no_profile_instrument_function__)
265 # define __no_profile __attribute__((__no_profile_instrument_function__))
266 #else
267 # define __no_profile
268 #endif
269
270 /*
271 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute
272 * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn
273 * clang: https://clang.llvm.org/docs/AttributeReference.html#id1
274 */
275 #define __noreturn __attribute__((__noreturn__))
276
277 /*
278 * Optional: only supported since GCC >= 11.1, clang >= 7.0.
279 *
280 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fstack_005fprotector-function-attribute
281 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-stack-protector-safebuffers
282 */
283 #if __has_attribute(__no_stack_protector__)
284 # define __no_stack_protector __attribute__((__no_stack_protector__))
285 #else
286 # define __no_stack_protector
287 #endif
288
289 /*
290 * Optional: not supported by gcc.
291 *
292 * clang: https://clang.llvm.org/docs/AttributeReference.html#overloadable
293 */
294 #if __has_attribute(__overloadable__)
295 # define __overloadable __attribute__((__overloadable__))
296 #else
297 # define __overloadable
298 #endif
299
300 /*
301 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
302 * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute
303 */
304 #define __packed __attribute__((__packed__))
305
306 /*
307 * Note: the "type" argument should match any __builtin_object_size(p, type) usage.
308 *
309 * Optional: not supported by gcc.
310 *
311 * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size
312 */
313 #if __has_attribute(__pass_dynamic_object_size__)
314 # define __pass_dynamic_object_size(type) __attribute__((__pass_dynamic_object_size__(type)))
315 #else
316 # define __pass_dynamic_object_size(type)
317 #endif
318 #if __has_attribute(__pass_object_size__)
319 # define __pass_object_size(type) __attribute__((__pass_object_size__(type)))
320 #else
321 # define __pass_object_size(type)
322 #endif
323
324 /*
325 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
326 */
327 #define __pure __attribute__((__pure__))
328
329 /*
330 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
331 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
332 * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate
333 */
334 #define __section(section) __attribute__((__section__(section)))
335
336 /*
337 * Optional: only supported since gcc >= 12
338 *
339 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-uninitialized-variable-attribute
340 * clang: https://clang.llvm.org/docs/AttributeReference.html#uninitialized
341 */
342 #if __has_attribute(__uninitialized__)
343 # define __uninitialized __attribute__((__uninitialized__))
344 #else
345 # define __uninitialized
346 #endif
347
348 /*
349 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
350 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
351 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute
352 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute
353 * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
354 */
355 #define __always_unused __attribute__((__unused__))
356 #define __maybe_unused __attribute__((__unused__))
357
358 /*
359 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute
360 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute
361 */
362 #define __used __attribute__((__used__))
363
364 /*
365 * The __used attribute guarantees that the attributed variable will be
366 * always emitted by a compiler. It doesn't prevent the compiler from
367 * throwing 'unused' warnings when it can't detect how the variable is
368 * actually used. It's a compiler implementation details either emit
369 * the warning in that case or not.
370 *
371 * The combination of both 'used' and 'unused' attributes ensures that
372 * the variable would be emitted, and will not trigger 'unused' warnings.
373 * The attribute is applicable for functions, static and global variables.
374 */
375 #define __always_used __used __maybe_unused
376
377 /*
378 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
379 * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
380 */
381 #define __must_check __attribute__((__warn_unused_result__))
382
383 /*
384 * Optional: only supported since clang >= 14.0
385 *
386 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warning-function-attribute
387 */
388 #if __has_attribute(__warning__)
389 # define __compiletime_warning(msg) __attribute__((__warning__(msg)))
390 #else
391 # define __compiletime_warning(msg)
392 #endif
393
394 /*
395 * Optional: only supported since clang >= 14.0
396 *
397 * clang: https://clang.llvm.org/docs/AttributeReference.html#disable-sanitizer-instrumentation
398 *
399 * disable_sanitizer_instrumentation is not always similar to
400 * no_sanitize((<sanitizer-name>)): the latter may still let specific sanitizers
401 * insert code into functions to prevent false positives. Unlike that,
402 * disable_sanitizer_instrumentation prevents all kinds of instrumentation to
403 * functions with the attribute.
404 */
405 #if __has_attribute(disable_sanitizer_instrumentation)
406 # define __disable_sanitizer_instrumentation \
407 __attribute__((disable_sanitizer_instrumentation))
408 #else
409 # define __disable_sanitizer_instrumentation
410 #endif
411
412 /*
413 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
414 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
415 */
416 #define __weak __attribute__((__weak__))
417
418 /*
419 * Used by functions that use '__builtin_return_address'. These function
420 * don't want to be splited or made inline, which can make
421 * the '__builtin_return_address' get unexpected address.
422 */
423 #define __fix_address noinline __noclone
424
425 #endif /* __LINUX_COMPILER_ATTRIBUTES_H */
426
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