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 >= 14
99 * Optional: only supported since clang >= 18
100 *
101 * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
102 * clang: https://reviews.llvm.org/D148381
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 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
338 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
339 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute
340 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute
341 * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
342 */
343#define __always_unused __attribute__((__unused__))
344#define __maybe_unused __attribute__((__unused__))
345
346/*
347 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute
348 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute
349 */
350#define __used __attribute__((__used__))
351
352/*
353 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
354 * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
355 */
356#define __must_check __attribute__((__warn_unused_result__))
357
358/*
359 * Optional: only supported since clang >= 14.0
360 *
361 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warning-function-attribute
362 */
363#if __has_attribute(__warning__)
364# define __compiletime_warning(msg) __attribute__((__warning__(msg)))
365#else
366# define __compiletime_warning(msg)
367#endif
368
369/*
370 * Optional: only supported since clang >= 14.0
371 *
372 * clang: https://clang.llvm.org/docs/AttributeReference.html#disable-sanitizer-instrumentation
373 *
374 * disable_sanitizer_instrumentation is not always similar to
375 * no_sanitize((<sanitizer-name>)): the latter may still let specific sanitizers
376 * insert code into functions to prevent false positives. Unlike that,
377 * disable_sanitizer_instrumentation prevents all kinds of instrumentation to
378 * functions with the attribute.
379 */
380#if __has_attribute(disable_sanitizer_instrumentation)
381# define __disable_sanitizer_instrumentation \
382 __attribute__((disable_sanitizer_instrumentation))
383#else
384# define __disable_sanitizer_instrumentation
385#endif
386
387/*
388 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
389 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
390 */
391#define __weak __attribute__((__weak__))
392
393/*
394 * Used by functions that use '__builtin_return_address'. These function
395 * don't want to be splited or made inline, which can make
396 * the '__builtin_return_address' get unexpected address.
397 */
398#define __fix_address noinline __noclone
399
400#endif /* __LINUX_COMPILER_ATTRIBUTES_H */
401

source code of linux/include/linux/compiler_attributes.h