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