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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: not supported by gcc
99 * Optional: only supported since clang >= 14.0
100 *
101 * clang: https://clang.llvm.org/docs/AttributeReference.html#diagnose_as_builtin
102 */
103#if __has_attribute(__diagnose_as_builtin__)
104# define __diagnose_as(builtin...) __attribute__((__diagnose_as_builtin__(builtin)))
105#else
106# define __diagnose_as(builtin...)
107#endif
108
109/*
110 * Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
111 * attribute warnings entirely and for good") for more information.
112 *
113 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-deprecated-function-attribute
114 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-deprecated-type-attribute
115 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-deprecated-variable-attribute
116 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Enumerator-Attributes.html#index-deprecated-enumerator-attribute
117 * clang: https://clang.llvm.org/docs/AttributeReference.html#deprecated
118 */
119#define __deprecated
120
121/*
122 * Optional: not supported by clang
123 *
124 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-designated_005finit-type-attribute
125 */
126#if __has_attribute(__designated_init__)
127# define __designated_init __attribute__((__designated_init__))
128#else
129# define __designated_init
130#endif
131
132/*
133 * Optional: only supported since clang >= 14.0
134 *
135 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-error-function-attribute
136 */
137#if __has_attribute(__error__)
138# define __compiletime_error(msg) __attribute__((__error__(msg)))
139#else
140# define __compiletime_error(msg)
141#endif
142
143/*
144 * Optional: not supported by clang
145 *
146 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-externally_005fvisible-function-attribute
147 */
148#if __has_attribute(__externally_visible__)
149# define __visible __attribute__((__externally_visible__))
150#else
151# define __visible
152#endif
153
154/*
155 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-format-function-attribute
156 * clang: https://clang.llvm.org/docs/AttributeReference.html#format
157 */
158#define __printf(a, b) __attribute__((__format__(printf, a, b)))
159#define __scanf(a, b) __attribute__((__format__(scanf, a, b)))
160
161/*
162 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-gnu_005finline-function-attribute
163 * clang: https://clang.llvm.org/docs/AttributeReference.html#gnu-inline
164 */
165#define __gnu_inline __attribute__((__gnu_inline__))
166
167/*
168 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
169 * clang: https://clang.llvm.org/docs/AttributeReference.html#malloc
170 */
171#define __malloc __attribute__((__malloc__))
172
173/*
174 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-mode-type-attribute
175 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-mode-variable-attribute
176 */
177#define __mode(x) __attribute__((__mode__(x)))
178
179/*
180 * Optional: only supported since gcc >= 7
181 *
182 * gcc: https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html#index-no_005fcaller_005fsaved_005fregisters-function-attribute_002c-x86
183 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-caller-saved-registers
184 */
185#if __has_attribute(__no_caller_saved_registers__)
186# define __no_caller_saved_registers __attribute__((__no_caller_saved_registers__))
187#else
188# define __no_caller_saved_registers
189#endif
190
191/*
192 * Optional: not supported by clang
193 *
194 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
195 */
196#if __has_attribute(__noclone__)
197# define __noclone __attribute__((__noclone__))
198#else
199# define __noclone
200#endif
201
202/*
203 * Add the pseudo keyword 'fallthrough' so case statement blocks
204 * must end with any of these keywords:
205 * break;
206 * fallthrough;
207 * continue;
208 * goto <label>;
209 * return [expression];
210 *
211 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
212 */
213#if __has_attribute(__fallthrough__)
214# define fallthrough __attribute__((__fallthrough__))
215#else
216# define fallthrough do {} while (0) /* fallthrough */
217#endif
218
219/*
220 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
221 * clang: https://clang.llvm.org/docs/AttributeReference.html#flatten
222 */
223# define __flatten __attribute__((flatten))
224
225/*
226 * Note the missing underscores.
227 *
228 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute
229 * clang: mentioned
230 */
231#define noinline __attribute__((__noinline__))
232
233/*
234 * Optional: only supported since gcc >= 8
235 * Optional: not supported by clang
236 *
237 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute
238 */
239#if __has_attribute(__nonstring__)
240# define __nonstring __attribute__((__nonstring__))
241#else
242# define __nonstring
243#endif
244
245/*
246 * Optional: only supported since GCC >= 7.1, clang >= 13.0.
247 *
248 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fprofile_005finstrument_005ffunction-function-attribute
249 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-profile-instrument-function
250 */
251#if __has_attribute(__no_profile_instrument_function__)
252# define __no_profile __attribute__((__no_profile_instrument_function__))
253#else
254# define __no_profile
255#endif
256
257/*
258 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute
259 * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn
260 * clang: https://clang.llvm.org/docs/AttributeReference.html#id1
261 */
262#define __noreturn __attribute__((__noreturn__))
263
264/*
265 * Optional: only supported since GCC >= 11.1, clang >= 7.0.
266 *
267 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fstack_005fprotector-function-attribute
268 * clang: https://clang.llvm.org/docs/AttributeReference.html#no-stack-protector-safebuffers
269 */
270#if __has_attribute(__no_stack_protector__)
271# define __no_stack_protector __attribute__((__no_stack_protector__))
272#else
273# define __no_stack_protector
274#endif
275
276/*
277 * Optional: not supported by gcc.
278 *
279 * clang: https://clang.llvm.org/docs/AttributeReference.html#overloadable
280 */
281#if __has_attribute(__overloadable__)
282# define __overloadable __attribute__((__overloadable__))
283#else
284# define __overloadable
285#endif
286
287/*
288 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
289 * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute
290 */
291#define __packed __attribute__((__packed__))
292
293/*
294 * Note: the "type" argument should match any __builtin_object_size(p, type) usage.
295 *
296 * Optional: not supported by gcc.
297 *
298 * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size
299 */
300#if __has_attribute(__pass_dynamic_object_size__)
301# define __pass_dynamic_object_size(type) __attribute__((__pass_dynamic_object_size__(type)))
302#else
303# define __pass_dynamic_object_size(type)
304#endif
305#if __has_attribute(__pass_object_size__)
306# define __pass_object_size(type) __attribute__((__pass_object_size__(type)))
307#else
308# define __pass_object_size(type)
309#endif
310
311/*
312 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
313 */
314#define __pure __attribute__((__pure__))
315
316/*
317 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
318 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
319 * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate
320 */
321#define __section(section) __attribute__((__section__(section)))
322
323/*
324 * Optional: only supported since gcc >= 12
325 *
326 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-uninitialized-variable-attribute
327 * clang: https://clang.llvm.org/docs/AttributeReference.html#uninitialized
328 */
329#if __has_attribute(__uninitialized__)
330# define __uninitialized __attribute__((__uninitialized__))
331#else
332# define __uninitialized
333#endif
334
335/*
336 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
337 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
338 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute
339 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute
340 * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
341 */
342#define __always_unused __attribute__((__unused__))
343#define __maybe_unused __attribute__((__unused__))
344
345/*
346 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute
347 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute
348 */
349#define __used __attribute__((__used__))
350
351/*
352 * The __used attribute guarantees that the attributed variable will be
353 * always emitted by a compiler. It doesn't prevent the compiler from
354 * throwing 'unused' warnings when it can't detect how the variable is
355 * actually used. It's a compiler implementation details either emit
356 * the warning in that case or not.
357 *
358 * The combination of both 'used' and 'unused' attributes ensures that
359 * the variable would be emitted, and will not trigger 'unused' warnings.
360 * The attribute is applicable for functions, static and global variables.
361 */
362#define __always_used __used __maybe_unused
363
364/*
365 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
366 * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
367 */
368#define __must_check __attribute__((__warn_unused_result__))
369
370/*
371 * Optional: only supported since clang >= 14.0
372 *
373 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warning-function-attribute
374 */
375#if __has_attribute(__warning__)
376# define __compiletime_warning(msg) __attribute__((__warning__(msg)))
377#else
378# define __compiletime_warning(msg)
379#endif
380
381/*
382 * Optional: only supported since clang >= 14.0
383 *
384 * clang: https://clang.llvm.org/docs/AttributeReference.html#disable-sanitizer-instrumentation
385 *
386 * disable_sanitizer_instrumentation is not always similar to
387 * no_sanitize((<sanitizer-name>)): the latter may still let specific sanitizers
388 * insert code into functions to prevent false positives. Unlike that,
389 * disable_sanitizer_instrumentation prevents all kinds of instrumentation to
390 * functions with the attribute.
391 */
392#if __has_attribute(disable_sanitizer_instrumentation)
393# define __disable_sanitizer_instrumentation \
394 __attribute__((disable_sanitizer_instrumentation))
395#else
396# define __disable_sanitizer_instrumentation
397#endif
398
399/*
400 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
401 * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
402 */
403#define __weak __attribute__((__weak__))
404
405/*
406 * Used by functions that use '__builtin_return_address'. These function
407 * don't want to be splited or made inline, which can make
408 * the '__builtin_return_address' get unexpected address.
409 */
410#define __fix_address noinline __noclone
411
412#endif /* __LINUX_COMPILER_ATTRIBUTES_H */
413

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