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  * __has_attribute is supported on gcc >= 5, clang >= 2.9 and icc >= 17.
  25  * In the meantime, to support gcc < 5, we implement __has_attribute
  26  * by hand.
  27  */
  28 #ifndef __has_attribute
  29 # define __has_attribute(x) __GCC4_has_attribute_##x
  30 # define __GCC4_has_attribute___assume_aligned__      1
  31 # define __GCC4_has_attribute___copy__                0
  32 # define __GCC4_has_attribute___designated_init__     0
  33 # define __GCC4_has_attribute___error__               1
  34 # define __GCC4_has_attribute___externally_visible__  1
  35 # define __GCC4_has_attribute___no_caller_saved_registers__ 0
  36 # define __GCC4_has_attribute___noclone__             1
  37 # define __GCC4_has_attribute___no_profile_instrument_function__ 0
  38 # define __GCC4_has_attribute___nonstring__           0
  39 # define __GCC4_has_attribute___no_sanitize_address__ 1
  40 # define __GCC4_has_attribute___no_sanitize_undefined__ 1
  41 # define __GCC4_has_attribute___no_sanitize_coverage__ 0
  42 # define __GCC4_has_attribute___fallthrough__         0
  43 # define __GCC4_has_attribute___warning__             1
  44 #endif
  45
  46 /*
  47  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute
  48  */
  49 #define __alias(symbol)                 __attribute__((__alias__(#symbol)))
  50
  51 /*
  52  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-aligned-function-attribute
  53  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-aligned-type-attribute
  54  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-aligned-variable-attribute
  55  */
  56 #define __aligned(x)                    __attribute__((__aligned__(x)))
  57 #define __aligned_largest               __attribute__((__aligned__))
  58
  59 /*
  60  * Note: users of __always_inline currently do not write "inline" themselves,
  61  * which seems to be required by gcc to apply the attribute according
  62  * to its docs (and also "warning: always_inline function might not be
  63  * inlinable [-Wattributes]" is emitted).
  64  *
  65  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-always_005finline-function-attribute
  66  * clang: mentioned
  67  */
  68 #define __always_inline                 inline __attribute__((__always_inline__))
  69
  70 /*
  71  * The second argument is optional (default 0), so we use a variadic macro
  72  * to make the shorthand.
  73  *
  74  * Beware: Do not apply this to functions which may return
  75  * ERR_PTRs. Also, it is probably unwise to apply it to functions
  76  * returning extra information in the low bits (but in that case the
  77  * compiler should see some alignment anyway, when the return value is
  78  * massaged by 'flags = ptr & 3; ptr &= ~3;').
  79  *
  80  * Optional: only supported since gcc >= 4.9
  81  * Optional: not supported by icc
  82  *
  83  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-assume_005faligned-function-attribute
  84  * clang: https://clang.llvm.org/docs/AttributeReference.html#assume-aligned
  85  */
  86 #if __has_attribute(__assume_aligned__)
  87 # define __assume_aligned(a, ...)       __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
  88 #else
  89 # define __assume_aligned(a, ...)
  90 #endif
  91
  92 /*
  93  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-cold-function-attribute
  94  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-cold-label-attribute
  95  */
  96 #define __cold                          __attribute__((__cold__))
  97
  98 /*
  99  * Note the long name.
 100  *
 101  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-const-function-attribute
 102  */
 103 #define __attribute_const__             __attribute__((__const__))
 104
 105 /*
 106  * Optional: only supported since gcc >= 9
 107  * Optional: not supported by clang
 108  * Optional: not supported by icc
 109  *
 110  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
 111  */
 112 #if __has_attribute(__copy__)
 113 # define __copy(symbol)                 __attribute__((__copy__(symbol)))
 114 #else
 115 # define __copy(symbol)
 116 #endif
 117
 118 /*
 119  * Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
 120  * attribute warnings entirely and for good") for more information.
 121  *
 122  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-deprecated-function-attribute
 123  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-deprecated-type-attribute
 124  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-deprecated-variable-attribute
 125  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Enumerator-Attributes.html#index-deprecated-enumerator-attribute
 126  * clang: https://clang.llvm.org/docs/AttributeReference.html#deprecated
 127  */
 128 #define __deprecated
 129
 130 /*
 131  * Optional: only supported since gcc >= 5.1
 132  * Optional: not supported by clang
 133  * Optional: not supported by icc
 134  *
 135  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-designated_005finit-type-attribute
 136  */
 137 #if __has_attribute(__designated_init__)
 138 # define __designated_init              __attribute__((__designated_init__))
 139 #else
 140 # define __designated_init
 141 #endif
 142
 143 /*
 144  * Optional: only supported since clang >= 14.0
 145  *
 146  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-error-function-attribute
 147  */
 148 #if __has_attribute(__error__)
 149 # define __compiletime_error(msg)       __attribute__((__error__(msg)))
 150 #else
 151 # define __compiletime_error(msg)
 152 #endif
 153
 154 /*
 155  * Optional: not supported by clang
 156  *
 157  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-externally_005fvisible-function-attribute
 158  */
 159 #if __has_attribute(__externally_visible__)
 160 # define __visible                      __attribute__((__externally_visible__))
 161 #else
 162 # define __visible
 163 #endif
 164
 165 /*
 166  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-format-function-attribute
 167  * clang: https://clang.llvm.org/docs/AttributeReference.html#format
 168  */
 169 #define __printf(a, b)                  __attribute__((__format__(printf, a, b)))
 170 #define __scanf(a, b)                   __attribute__((__format__(scanf, a, b)))
 171
 172 /*
 173  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-gnu_005finline-function-attribute
 174  * clang: https://clang.llvm.org/docs/AttributeReference.html#gnu-inline
 175  */
 176 #define __gnu_inline                    __attribute__((__gnu_inline__))
 177
 178 /*
 179  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
 180  */
 181 #define __malloc                        __attribute__((__malloc__))
 182
 183 /*
 184  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-mode-type-attribute
 185  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-mode-variable-attribute
 186  */
 187 #define __mode(x)                       __attribute__((__mode__(x)))
 188
 189 /*
 190  * Optional: only supported since gcc >= 7
 191  *
 192  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/x86-Function-Attributes.html#index-no_005fcaller_005fsaved_005fregisters-function-attribute_002c-x86
 193  * clang: https://clang.llvm.org/docs/AttributeReference.html#no-caller-saved-registers
 194  */
 195 #if __has_attribute(__no_caller_saved_registers__)
 196 # define __no_caller_saved_registers    __attribute__((__no_caller_saved_registers__))
 197 #else
 198 # define __no_caller_saved_registers
 199 #endif
 200
 201 /*
 202  * Optional: not supported by clang
 203  *
 204  *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
 205  */
 206 #if __has_attribute(__noclone__)
 207 # define __noclone                      __attribute__((__noclone__))
 208 #else
 209 # define __noclone
 210 #endif
 211
 212 /*
 213  * Add the pseudo keyword 'fallthrough' so case statement blocks
 214  * must end with any of these keywords:
 215  *   break;
 216  *   fallthrough;
 217  *   continue;
 218  *   goto <label>;
 219  *   return [expression];
 220  *
 221  *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
 222  */
 223 #if __has_attribute(__fallthrough__)
 224 # define fallthrough                    __attribute__((__fallthrough__))
 225 #else
 226 # define fallthrough                    do {} while (0)  /* fallthrough */
 227 #endif
 228
 229 /*
 230  * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
 231  * clang: https://clang.llvm.org/docs/AttributeReference.html#flatten
 232  */
 233 # define __flatten                      __attribute__((flatten))
 234
 235 /*
 236  * Note the missing underscores.
 237  *
 238  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute
 239  * clang: mentioned
 240  */
 241 #define   noinline                      __attribute__((__noinline__))
 242
 243 /*
 244  * Optional: only supported since gcc >= 8
 245  * Optional: not supported by clang
 246  * Optional: not supported by icc
 247  *
 248  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute
 249  */
 250 #if __has_attribute(__nonstring__)
 251 # define __nonstring                    __attribute__((__nonstring__))
 252 #else
 253 # define __nonstring
 254 #endif
 255
 256 /*
 257  * Optional: only supported since GCC >= 7.1, clang >= 13.0.
 258  *
 259  *      gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fprofile_005finstrument_005ffunction-function-attribute
 260  *    clang: https://clang.llvm.org/docs/AttributeReference.html#no-profile-instrument-function
 261  */
 262 #if __has_attribute(__no_profile_instrument_function__)
 263 # define __no_profile                  __attribute__((__no_profile_instrument_function__))
 264 #else
 265 # define __no_profile
 266 #endif
 267
 268 /*
 269  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute
 270  * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn
 271  * clang: https://clang.llvm.org/docs/AttributeReference.html#id1
 272  */
 273 #define __noreturn                      __attribute__((__noreturn__))
 274
 275 /*
 276  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
 277  * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute
 278  */
 279 #define __packed                        __attribute__((__packed__))
 280
 281 /*
 282  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
 283  */
 284 #define __pure                          __attribute__((__pure__))
 285
 286 /*
 287  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
 288  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
 289  * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate
 290  */
 291 #define __section(section)              __attribute__((__section__(section)))
 292
 293 /*
 294  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
 295  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
 296  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute
 297  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute
 298  * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
 299  */
 300 #define __always_unused                 __attribute__((__unused__))
 301 #define __maybe_unused                  __attribute__((__unused__))
 302
 303 /*
 304  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute
 305  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute
 306  */
 307 #define __used                          __attribute__((__used__))
 308
 309 /*
 310  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
 311  * clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
 312  */
 313 #define __must_check                    __attribute__((__warn_unused_result__))
 314
 315 /*
 316  * Optional: only supported since clang >= 14.0
 317  *
 318  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warning-function-attribute
 319  */
 320 #if __has_attribute(__warning__)
 321 # define __compiletime_warning(msg)     __attribute__((__warning__(msg)))
 322 #else
 323 # define __compiletime_warning(msg)
 324 #endif
 325
 326 /*
 327  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
 328  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
 329  */
 330 #define __weak                          __attribute__((__weak__))
 331
 332 #endif /* __LINUX_COMPILER_ATTRIBUTES_H */