include/linux/compiler_attributes.h

   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 gcc >= 14
 128  * Optional: only supported since clang >= 17
 129  *
 130  *   gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
 131  * clang: https://reviews.llvm.org/D148381
 132  */
 133 #if __has_attribute(__element_count__)
 134 # define __counted_by(member)           __attribute__((__element_count__(#member)))
 135 #else
 136 # define __counted_by(member)
 137 #endif
 138
 139 /*
 140  * Optional: only supported since clang >= 14.0
 141  *
 142  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-error-function-attribute
 143  */
 144 #if __has_attribute(__error__)
 145 # define __compiletime_error(msg)       __attribute__((__error__(msg)))
 146 #else
 147 # define __compiletime_error(msg)
 148 #endif
 149
 150 /*
 151  * Optional: not supported by clang
 152  *
 153  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-externally_005fvisible-function-attribute
 154  */
 155 #if __has_attribute(__externally_visible__)
 156 # define __visible                      __attribute__((__externally_visible__))
 157 #else
 158 # define __visible
 159 #endif
 160
 161 /*
 162  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-format-function-attribute
 163  * clang: https://clang.llvm.org/docs/AttributeReference.html#format
 164  */
 165 #define __printf(a, b)                  __attribute__((__format__(printf, a, b)))
 166 #define __scanf(a, b)                   __attribute__((__format__(scanf, a, b)))
 167
 168 /*
 169  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-gnu_005finline-function-attribute
 170  * clang: https://clang.llvm.org/docs/AttributeReference.html#gnu-inline
 171  */
 172 #define __gnu_inline                    __attribute__((__gnu_inline__))
 173
 174 /*
 175  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
 176  * clang: https://clang.llvm.org/docs/AttributeReference.html#malloc
 177  */
 178 #define __malloc                        __attribute__((__malloc__))
 179
 180 /*
 181  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-mode-type-attribute
 182  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-mode-variable-attribute
 183  */
 184 #define __mode(x)                       __attribute__((__mode__(x)))
 185
 186 /*
 187  * Optional: only supported since gcc >= 7
 188  *
 189  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html#index-no_005fcaller_005fsaved_005fregisters-function-attribute_002c-x86
 190  * clang: https://clang.llvm.org/docs/AttributeReference.html#no-caller-saved-registers
 191  */
 192 #if __has_attribute(__no_caller_saved_registers__)
 193 # define __no_caller_saved_registers    __attribute__((__no_caller_saved_registers__))
 194 #else
 195 # define __no_caller_saved_registers
 196 #endif
 197
 198 /*
 199  * Optional: not supported by clang
 200  *
 201  *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
 202  */
 203 #if __has_attribute(__noclone__)
 204 # define __noclone                      __attribute__((__noclone__))
 205 #else
 206 # define __noclone
 207 #endif
 208
 209 /*
 210  * Add the pseudo keyword 'fallthrough' so case statement blocks
 211  * must end with any of these keywords:
 212  *   break;
 213  *   fallthrough;
 214  *   continue;
 215  *   goto <label>;
 216  *   return [expression];
 217  *
 218  *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
 219  */
 220 #if __has_attribute(__fallthrough__)
 221 # define fallthrough                    __attribute__((__fallthrough__))
 222 #else
 223 # define fallthrough                    do {} while (0)  /* fallthrough */
 224 #endif
 225
 226 /*
 227  * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
 228  * clang: https://clang.llvm.org/docs/AttributeReference.html#flatten
 229  */
 230 # define __flatten                      __attribute__((flatten))
 231
 232 /*
 233  * Note the missing underscores.
 234  *
 235  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute
 236  * clang: mentioned
 237  */
 238 #define   noinline                      __attribute__((__noinline__))
 239
 240 /*
 241  * Optional: only supported since gcc >= 8
 242  * Optional: not supported by clang
 243  *
 244  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute
 245  */
 246 #if __has_attribute(__nonstring__)
 247 # define __nonstring                    __attribute__((__nonstring__))
 248 #else
 249 # define __nonstring
 250 #endif
 251
 252 /*
 253  * Optional: only supported since GCC >= 7.1, clang >= 13.0.
 254  *
 255  *      gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fprofile_005finstrument_005ffunction-function-attribute
 256  *    clang: https://clang.llvm.org/docs/AttributeReference.html#no-profile-instrument-function
 257  */
 258 #if __has_attribute(__no_profile_instrument_function__)
 259 # define __no_profile                  __attribute__((__no_profile_instrument_function__))
 260 #else
 261 # define __no_profile
 262 #endif
 263
 264 /*
 265  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute
 266  * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn
 267  * clang: https://clang.llvm.org/docs/AttributeReference.html#id1
 268  */
 269 #define __noreturn                      __attribute__((__noreturn__))
 270
 271 /*
 272  * Optional: only supported since GCC >= 11.1, clang >= 7.0.
 273  *
 274  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fstack_005fprotector-function-attribute
 275  *   clang: https://clang.llvm.org/docs/AttributeReference.html#no-stack-protector-safebuffers
 276  */
 277 #if __has_attribute(__no_stack_protector__)
 278 # define __no_stack_protector           __attribute__((__no_stack_protector__))
 279 #else
 280 # define __no_stack_protector
 281 #endif
 282
 283 /*
 284  * Optional: not supported by gcc.
 285  *
 286  * clang: https://clang.llvm.org/docs/AttributeReference.html#overloadable
 287  */
 288 #if __has_attribute(__overloadable__)
 289 # define __overloadable                 __attribute__((__overloadable__))
 290 #else
 291 # define __overloadable
 292 #endif
 293
 294 /*
 295  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
 296  * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute
 297  */
 298 #define __packed                        __attribute__((__packed__))
 299
 300 /*
 301  * Note: the "type" argument should match any __builtin_object_size(p, type) usage.
 302  *
 303  * Optional: not supported by gcc.
 304  *
 305  * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size
 306  */
 307 #if __has_attribute(__pass_dynamic_object_size__)
 308 # define __pass_dynamic_object_size(type)       __attribute__((__pass_dynamic_object_size__(type)))
 309 #else
 310 # define __pass_dynamic_object_size(type)
 311 #endif
 312 #if __has_attribute(__pass_object_size__)
 313 # define __pass_object_size(type)       __attribute__((__pass_object_size__(type)))
 314 #else
 315 # define __pass_object_size(type)
 316 #endif
 317
 318 /*
 319  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
 320  */
 321 #define __pure                          __attribute__((__pure__))
 322
 323 /*
 324  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
 325  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
 326  * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate
 327  */
 328 #define __section(section)              __attribute__((__section__(section)))
 329
 330 /*
 331  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
 332  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
 333  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute
 334  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute
 335  * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
 336  */
 337 #define __always_unused                 __attribute__((__unused__))
 338 #define __maybe_unused                  __attribute__((__unused__))
 339
 340 /*
 341  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute
 342  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute
 343  */
 344 #define __used                          __attribute__((__used__))
 345
 346 /*
 347  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
 348  * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
 349  */
 350 #define __must_check                    __attribute__((__warn_unused_result__))
 351
 352 /*
 353  * Optional: only supported since clang >= 14.0
 354  *
 355  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warning-function-attribute
 356  */
 357 #if __has_attribute(__warning__)
 358 # define __compiletime_warning(msg)     __attribute__((__warning__(msg)))
 359 #else
 360 # define __compiletime_warning(msg)
 361 #endif
 362
 363 /*
 364  * Optional: only supported since clang >= 14.0
 365  *
 366  * clang: https://clang.llvm.org/docs/AttributeReference.html#disable-sanitizer-instrumentation
 367  *
 368  * disable_sanitizer_instrumentation is not always similar to
 369  * no_sanitize((<sanitizer-name>)): the latter may still let specific sanitizers
 370  * insert code into functions to prevent false positives. Unlike that,
 371  * disable_sanitizer_instrumentation prevents all kinds of instrumentation to
 372  * functions with the attribute.
 373  */
 374 #if __has_attribute(disable_sanitizer_instrumentation)
 375 # define __disable_sanitizer_instrumentation \
 376          __attribute__((disable_sanitizer_instrumentation))
 377 #else
 378 # define __disable_sanitizer_instrumentation
 379 #endif
 380
 381 /*
 382  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
 383  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
 384  */
 385 #define __weak                          __attribute__((__weak__))
 386
 387 /*
 388  * Used by functions that use '__builtin_return_address'. These function
 389  * don't want to be splited or made inline, which can make
 390  * the '__builtin_return_address' get unexpected address.
 391  */
 392 #define __fix_address noinline __noclone
 393
 394 #endif /* __LINUX_COMPILER_ATTRIBUTES_H */