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  *   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 */