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 4.6 <= gcc < 5, we implement __has_attribute
  26  * by hand.
  27  *
  28  * sparse does not support __has_attribute (yet) and defines __GNUC_MINOR__
  29  * depending on the compiler used to build it; however, these attributes have
  30  * no semantic effects for sparse, so it does not matter. Also note that,
  31  * in order to avoid sparse's warnings, even the unsupported ones must be
  32  * defined to 0.
  33  */
  34 #ifndef __has_attribute
  35 # define __has_attribute(x) __GCC4_has_attribute_##x
  36 # define __GCC4_has_attribute___assume_aligned__      (__GNUC_MINOR__ >= 9)
  37 # define __GCC4_has_attribute___copy__                0
  38 # define __GCC4_has_attribute___designated_init__     0
  39 # define __GCC4_has_attribute___externally_visible__  1
  40 # define __GCC4_has_attribute___noclone__             1
  41 # define __GCC4_has_attribute___nonstring__           0
  42 # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8)
  43 # define __GCC4_has_attribute___no_sanitize_undefined__ (__GNUC_MINOR__ >= 9)
  44 # define __GCC4_has_attribute___fallthrough__         0
  45 #endif
  46
  47 /*
  48  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute
  49  */
  50 #define __alias(symbol)                 __attribute__((__alias__(#symbol)))
  51
  52 /*
  53  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-aligned-function-attribute
  54  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-aligned-type-attribute
  55  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-aligned-variable-attribute
  56  */
  57 #define __aligned(x)                    __attribute__((__aligned__(x)))
  58 #define __aligned_largest               __attribute__((__aligned__))
  59
  60 /*
  61  * Note: users of __always_inline currently do not write "inline" themselves,
  62  * which seems to be required by gcc to apply the attribute according
  63  * to its docs (and also "warning: always_inline function might not be
  64  * inlinable [-Wattributes]" is emitted).
  65  *
  66  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-always_005finline-function-attribute
  67  * clang: mentioned
  68  */
  69 #define __always_inline                 inline __attribute__((__always_inline__))
  70
  71 /*
  72  * The second argument is optional (default 0), so we use a variadic macro
  73  * to make the shorthand.
  74  *
  75  * Beware: Do not apply this to functions which may return
  76  * ERR_PTRs. Also, it is probably unwise to apply it to functions
  77  * returning extra information in the low bits (but in that case the
  78  * compiler should see some alignment anyway, when the return value is
  79  * massaged by 'flags = ptr & 3; ptr &= ~3;').
  80  *
  81  * Optional: only supported since gcc >= 4.9
  82  * Optional: not supported by icc
  83  *
  84  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-assume_005faligned-function-attribute
  85  * clang: https://clang.llvm.org/docs/AttributeReference.html#assume-aligned
  86  */
  87 #if __has_attribute(__assume_aligned__)
  88 # define __assume_aligned(a, ...)       __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))
  89 #else
  90 # define __assume_aligned(a, ...)
  91 #endif
  92
  93 /*
  94  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-cold-function-attribute
  95  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-cold-label-attribute
  96  */
  97 #define __cold                          __attribute__((__cold__))
  98
  99 /*
 100  * Note the long name.
 101  *
 102  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-const-function-attribute
 103  */
 104 #define __attribute_const__             __attribute__((__const__))
 105
 106 /*
 107  * Optional: only supported since gcc >= 9
 108  * Optional: not supported by clang
 109  * Optional: not supported by icc
 110  *
 111  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-copy-function-attribute
 112  */
 113 #if __has_attribute(__copy__)
 114 # define __copy(symbol)                 __attribute__((__copy__(symbol)))
 115 #else
 116 # define __copy(symbol)
 117 #endif
 118
 119 /*
 120  * Don't. Just don't. See commit 771c035372a0 ("deprecate the '__deprecated'
 121  * attribute warnings entirely and for good") for more information.
 122  *
 123  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-deprecated-function-attribute
 124  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-deprecated-type-attribute
 125  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-deprecated-variable-attribute
 126  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Enumerator-Attributes.html#index-deprecated-enumerator-attribute
 127  * clang: https://clang.llvm.org/docs/AttributeReference.html#deprecated
 128  */
 129 #define __deprecated
 130
 131 /*
 132  * Optional: only supported since gcc >= 5.1
 133  * Optional: not supported by clang
 134  * Optional: not supported by icc
 135  *
 136  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-designated_005finit-type-attribute
 137  */
 138 #if __has_attribute(__designated_init__)
 139 # define __designated_init              __attribute__((__designated_init__))
 140 #else
 141 # define __designated_init
 142 #endif
 143
 144 /*
 145  * Optional: not supported by clang
 146  *
 147  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-externally_005fvisible-function-attribute
 148  */
 149 #if __has_attribute(__externally_visible__)
 150 # define __visible                      __attribute__((__externally_visible__))
 151 #else
 152 # define __visible
 153 #endif
 154
 155 /*
 156  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-format-function-attribute
 157  * clang: https://clang.llvm.org/docs/AttributeReference.html#format
 158  */
 159 #define __printf(a, b)                  __attribute__((__format__(printf, a, b)))
 160 #define __scanf(a, b)                   __attribute__((__format__(scanf, a, b)))
 161
 162 /*
 163  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-gnu_005finline-function-attribute
 164  * clang: https://clang.llvm.org/docs/AttributeReference.html#gnu-inline
 165  */
 166 #define __gnu_inline                    __attribute__((__gnu_inline__))
 167
 168 /*
 169  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute
 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: not supported by clang
 181  *
 182  *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noclone-function-attribute
 183  */
 184 #if __has_attribute(__noclone__)
 185 # define __noclone                      __attribute__((__noclone__))
 186 #else
 187 # define __noclone
 188 #endif
 189
 190 /*
 191  * Add the pseudo keyword 'fallthrough' so case statement blocks
 192  * must end with any of these keywords:
 193  *   break;
 194  *   fallthrough;
 195  *   goto <label>;
 196  *   return [expression];
 197  *
 198  *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
 199  */
 200 #if __has_attribute(__fallthrough__)
 201 # define fallthrough                    __attribute__((__fallthrough__))
 202 #else
 203 # define fallthrough                    do {} while (0)  /* fallthrough */
 204 #endif
 205
 206 /*
 207  * Note the missing underscores.
 208  *
 209  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute
 210  * clang: mentioned
 211  */
 212 #define   noinline                      __attribute__((__noinline__))
 213
 214 /*
 215  * Optional: only supported since gcc >= 8
 216  * Optional: not supported by clang
 217  * Optional: not supported by icc
 218  *
 219  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-nonstring-variable-attribute
 220  */
 221 #if __has_attribute(__nonstring__)
 222 # define __nonstring                    __attribute__((__nonstring__))
 223 #else
 224 # define __nonstring
 225 #endif
 226
 227 /*
 228  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute
 229  * clang: https://clang.llvm.org/docs/AttributeReference.html#noreturn
 230  * clang: https://clang.llvm.org/docs/AttributeReference.html#id1
 231  */
 232 #define __noreturn                      __attribute__((__noreturn__))
 233
 234 /*
 235  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-packed-type-attribute
 236  * clang: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-packed-variable-attribute
 237  */
 238 #define __packed                        __attribute__((__packed__))
 239
 240 /*
 241  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
 242  */
 243 #define __pure                          __attribute__((__pure__))
 244
 245 /*
 246  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-section-function-attribute
 247  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-section-variable-attribute
 248  * clang: https://clang.llvm.org/docs/AttributeReference.html#section-declspec-allocate
 249  */
 250 #define __section(S)                    __attribute__((__section__(#S)))
 251
 252 /*
 253  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-unused-function-attribute
 254  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html#index-unused-type-attribute
 255  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-unused-variable-attribute
 256  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Label-Attributes.html#index-unused-label-attribute
 257  * clang: https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
 258  */
 259 #define __always_unused                 __attribute__((__unused__))
 260 #define __maybe_unused                  __attribute__((__unused__))
 261
 262 /*
 263  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-used-function-attribute
 264  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-used-variable-attribute
 265  */
 266 #define __used                          __attribute__((__used__))
 267
 268 /*
 269  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
 270  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
 271  */
 272 #define __weak                          __attribute__((__weak__))
 273
 274 #endif /* __LINUX_COMPILER_ATTRIBUTES_H */