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