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