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 * Note the long name.
74 *
75 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-const-function-attribute
76 */
77#define __attribute_const__ __attribute__((__const__))
78
79/*
80 * Optional: only supported since gcc >= 9
81 * Optional: not supported by clang
82 *
83 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
84 */
85#if __has_attribute(__copy__)
86# define __copy(symbol) __attribute__((__copy__(symbol)))
87#else
88# define __copy(symbol)
89#endif
90
91/*
92 * Optional: not supported by gcc
93 * Optional: only supported since clang >= 14.0
94 *
95 * clang: https://clang.llvm.org/docs/AttributeReference.html#diagnose_as_builtin
96 */
97#if __has_attribute(__diagnose_as_builtin__)
98# define __diagnose_as(builtin...) __attribute__((__diagnose_as_builtin__(builtin)))
99#else
100# define __diagnose_as(builtin...)
101#endif
102
103/*
104 * Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
105 * attribute warnings entirely and for good") for more information.
106 *
107 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-deprecated-function-attribute
108 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-deprecated-type-attribute
109 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-deprecated-variable-attribute
110 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Enumerator-Attributes.html#index-deprecated-enumerator-attribute
111 * clang: https://clang.llvm.org/docs/AttributeReference.html#deprecated
112 */
113#define __deprecated
114
115/*
116 * Optional: not supported by clang
117 *
118 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-designated_005finit-type-attribute
119 */
120#if __has_attribute(__designated_init__)
121# define __designated_init __attribute__((__designated_init__))
122#else
123# define __designated_init
124#endif
125
126/*
127 * Optional: only supported since clang >= 14.0
128 *
129 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-error-function-attribute
130 */
131#if __has_attribute(__error__)
132# define __compiletime_error(msg) __attribute__((__error__(msg)))
133#else
134# define __compiletime_error(msg)
135#endif
136
137/*
138 * Optional: not supported by clang
139 *
140 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-externally_005fvisible-function-attribute
141 */
142#if __has_attribute(__externally_visible__)
143# define __visible __attribute__((__externally_visible__))
144#else
145# define __visible
146#endif
147
148/*
149 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-format-function-attribute
150 * clang: https://clang.llvm.org/docs/AttributeReference.html#format
151 */
152#define __printf(a, b) __attribute__((__format__(printf, a, b)))
153#define __scanf(a, b) __attribute__((__format__(scanf, a, b)))
154
155/*
156 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-gnu_005finline-function-attribute
157 * clang: https://clang.llvm.org/docs/AttributeReference.html#gnu-inline
158 */
159#define __gnu_inline __attribute__((__gnu_inline__))
160
161/*
162 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
163 * clang: https://clang.llvm.org/docs/AttributeReference.html#malloc
164 */
165#define __malloc __attribute__((__malloc__))
166
167/*
168 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-mode-type-attribute
169 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-mode-variable-attribute
170 */
171#define __mode(x) __attribute__((__mode__(x)))
172
173/*
174 * Optional: only supported since gcc >= 7
175 *
176 * gcc: https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html#index-no_005fcaller_005fsaved_005fregisters-function-attribute_002c-x86
177 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-caller-saved-registers
178 */
179#if __has_attribute(__no_caller_saved_registers__)
180# define __no_caller_saved_registers __attribute__((__no_caller_saved_registers__))
181#else
182# define __no_caller_saved_registers
183#endif
184
185/*
186 * Optional: not supported by clang
187 *
188 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
189 */
190#if __has_attribute(__noclone__)
191# define __noclone __attribute__((__noclone__))
192#else
193# define __noclone
194#endif
195
196/*
197 * Add the pseudo keyword 'fallthrough' so case statement blocks
198 * must end with any of these keywords:
199 * break;
200 * fallthrough;
201 * continue;
202 * goto <label>;
203 * return [expression];
204 *
205 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
206 */
207#if __has_attribute(__fallthrough__)
208# define fallthrough __attribute__((__fallthrough__))
209#else
210# define fallthrough do {} while (0) /* fallthrough */
211#endif
212
213/*
214 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
215 * clang: https://clang.llvm.org/docs/AttributeReference.html#flatten
216 */
217# define __flatten __attribute__((flatten))
218
219/*
220 * Note the missing underscores.
221 *
222 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute
223 * clang: mentioned
224 */
225#define noinline __attribute__((__noinline__))
226
227/*
228 * Optional: only supported since gcc >= 8
229 * Optional: not supported by clang
230 *
231 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute
232 */
233#if __has_attribute(__nonstring__)
234# define __nonstring __attribute__((__nonstring__))
235#else
236# define __nonstring
237#endif
238
239/*
240 * Optional: only supported since GCC >= 7.1, clang >= 13.0.
241 *
242 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fprofile_005finstrument_005ffunction-function-attribute
243 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-profile-instrument-function
244 */
245#if __has_attribute(__no_profile_instrument_function__)
246# define __no_profile __attribute__((__no_profile_instrument_function__))
247#else
248# define __no_profile
249#endif
250
251/*
252 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute
253 * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn
254 * clang: https://clang.llvm.org/docs/AttributeReference.html#id1
255 */
256#define __noreturn __attribute__((__noreturn__))
257
258/*
259 * Optional: not supported by gcc.
260 *
261 * clang: https://clang.llvm.org/docs/AttributeReference.html#overloadable
262 */
263#if __has_attribute(__overloadable__)
264# define __overloadable __attribute__((__overloadable__))
265#else
266# define __overloadable
267#endif
268
269/*
270 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
271 * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute
272 */
273#define __packed __attribute__((__packed__))
274
275/*
276 * Note: the "type" argument should match any __builtin_object_size(p, type) usage.
277 *
278 * Optional: not supported by gcc.
279 *
280 * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size
281 */
282#if __has_attribute(__pass_dynamic_object_size__)
283# define __pass_dynamic_object_size(type) __attribute__((__pass_dynamic_object_size__(type)))
284#else
285# define __pass_dynamic_object_size(type)
286#endif
287#if __has_attribute(__pass_object_size__)
288# define __pass_object_size(type) __attribute__((__pass_object_size__(type)))
289#else
290# define __pass_object_size(type)
291#endif
292
293/*
294 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
295 */
296#define __pure __attribute__((__pure__))
297
298/*
299 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
300 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
301 * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate
302 */
303#define __section(section) __attribute__((__section__(section)))
304
305/*
306 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
307 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
308 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute
309 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute
310 * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
311 */
312#define __always_unused __attribute__((__unused__))
313#define __maybe_unused __attribute__((__unused__))
314
315/*
316 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute
317 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute
318 */
319#define __used __attribute__((__used__))
320
321/*
322 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
323 * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
324 */
325#define __must_check __attribute__((__warn_unused_result__))
326
327/*
328 * Optional: only supported since clang >= 14.0
329 *
330 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warning-function-attribute
331 */
332#if __has_attribute(__warning__)
333# define __compiletime_warning(msg) __attribute__((__warning__(msg)))
334#else
335# define __compiletime_warning(msg)
336#endif
337
338/*
339 * Optional: only supported since clang >= 14.0
340 *
341 * clang: https://clang.llvm.org/docs/AttributeReference.html#disable-sanitizer-instrumentation
342 *
343 * disable_sanitizer_instrumentation is not always similar to
344 * no_sanitize((<sanitizer-name>)): the latter may still let specific sanitizers
345 * insert code into functions to prevent false positives. Unlike that,
346 * disable_sanitizer_instrumentation prevents all kinds of instrumentation to
347 * functions with the attribute.
348 */
349#if __has_attribute(disable_sanitizer_instrumentation)
350# define __disable_sanitizer_instrumentation \
351 __attribute__((disable_sanitizer_instrumentation))
352#else
353# define __disable_sanitizer_instrumentation
354#endif
355
356/*
357 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
358 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
359 */
360#define __weak __attribute__((__weak__))
361
362/*
363 * Used by functions that use '__builtin_return_address'. These function
364 * don't want to be splited or made inline, which can make
365 * the '__builtin_return_address' get unexpected address.
366 */
367#define __fix_address noinline __noclone
368
369#endif /* __LINUX_COMPILER_ATTRIBUTES_H */
370

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