LXR linux/tools/include/linux/compiler.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _TOOLS_LINUX_COMPILER_H_
   3#define _TOOLS_LINUX_COMPILER_H_
   4
   5#include <linux/compiler_types.h>
   6
   7#ifndef __compiletime_error
   8# define __compiletime_error(message)
   9#endif
  10
  11#ifdef __OPTIMIZE__
  12# define __compiletime_assert(condition, msg, prefix, suffix)           \
  13        do {                                                            \
  14                extern void prefix ## suffix(void) __compiletime_error(msg); \
  15                if (!(condition))                                       \
  16                        prefix ## suffix();                             \
  17        } while (0)
  18#else
  19# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
  20#endif
  21
  22#define _compiletime_assert(condition, msg, prefix, suffix) \
  23        __compiletime_assert(condition, msg, prefix, suffix)
  24
  25/**
  26 * compiletime_assert - break build and emit msg if condition is false
  27 * @condition: a compile-time constant condition to check
  28 * @msg:       a message to emit if condition is false
  29 *
  30 * In tradition of POSIX assert, this macro will break the build if the
  31 * supplied condition is *false*, emitting the supplied error message if the
  32 * compiler has support to do so.
  33 */
  34#define compiletime_assert(condition, msg) \
  35        _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
  36
  37/* Optimization barrier */
  38/* The "volatile" is due to gcc bugs */
  39#define barrier() __asm__ __volatile__("": : :"memory")
  40
  41#ifndef __always_inline
  42# define __always_inline        inline __attribute__((always_inline))
  43#endif
  44
  45#ifndef noinline
  46#define noinline
  47#endif
  48
  49/* Are two types/vars the same type (ignoring qualifiers)? */
  50#ifndef __same_type
  51# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
  52#endif
  53
  54#ifdef __ANDROID__
  55/*
  56 * FIXME: Big hammer to get rid of tons of:
  57 *   "warning: always_inline function might not be inlinable"
  58 *
  59 * At least on android-ndk-r12/platforms/android-24/arch-arm
  60 */
  61#undef __always_inline
  62#define __always_inline inline
  63#endif
  64
  65#define __user
  66#define __rcu
  67#define __read_mostly
  68
  69#ifndef __attribute_const__
  70# define __attribute_const__
  71#endif
  72
  73#ifndef __maybe_unused
  74# define __maybe_unused         __attribute__((unused))
  75#endif
  76
  77#ifndef __used
  78# define __used         __attribute__((__unused__))
  79#endif
  80
  81#ifndef __packed
  82# define __packed               __attribute__((__packed__))
  83#endif
  84
  85#ifndef __force
  86# define __force
  87#endif
  88
  89#ifndef __weak
  90# define __weak                 __attribute__((weak))
  91#endif
  92
  93#ifndef likely
  94# define likely(x)              __builtin_expect(!!(x), 1)
  95#endif
  96
  97#ifndef unlikely
  98# define unlikely(x)            __builtin_expect(!!(x), 0)
  99#endif
 100
 101#ifndef __init
 102# define __init
 103#endif
 104
 105#include <linux/types.h>
 106
 107/*
 108 * Following functions are taken from kernel sources and
 109 * break aliasing rules in their original form.
 110 *
 111 * While kernel is compiled with -fno-strict-aliasing,
 112 * perf uses -Wstrict-aliasing=3 which makes build fail
 113 * under gcc 4.4.
 114 *
 115 * Using extra __may_alias__ type to allow aliasing
 116 * in this case.
 117 */
 118typedef __u8  __attribute__((__may_alias__))  __u8_alias_t;
 119typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
 120typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
 121typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;
 122
 123static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
 124{
 125        switch (size) {
 126        case 1: *(__u8_alias_t  *) res = *(volatile __u8_alias_t  *) p; break;
 127        case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
 128        case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
 129        case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
 130        default:
 131                barrier();
 132                __builtin_memcpy((void *)res, (const void *)p, size);
 133                barrier();
 134        }
 135}
 136
 137static __always_inline void __write_once_size(volatile void *p, void *res, int size)
 138{
 139        switch (size) {
 140        case 1: *(volatile  __u8_alias_t *) p = *(__u8_alias_t  *) res; break;
 141        case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
 142        case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
 143        case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
 144        default:
 145                barrier();
 146                __builtin_memcpy((void *)p, (const void *)res, size);
 147                barrier();
 148        }
 149}
 150
 151/*
 152 * Prevent the compiler from merging or refetching reads or writes. The
 153 * compiler is also forbidden from reordering successive instances of
 154 * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
 155 * particular ordering. One way to make the compiler aware of ordering is to
 156 * put the two invocations of READ_ONCE or WRITE_ONCE in different C
 157 * statements.
 158 *
 159 * These two macros will also work on aggregate data types like structs or
 160 * unions. If the size of the accessed data type exceeds the word size of
 161 * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
 162 * fall back to memcpy and print a compile-time warning.
 163 *
 164 * Their two major use cases are: (1) Mediating communication between
 165 * process-level code and irq/NMI handlers, all running on the same CPU,
 166 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
 167 * mutilate accesses that either do not require ordering or that interact
 168 * with an explicit memory barrier or atomic instruction that provides the
 169 * required ordering.
 170 */
 171
 172#define READ_ONCE(x)                                    \
 173({                                                      \
 174        union { typeof(x) __val; char __c[1]; } __u =   \
 175                { .__c = { 0 } };                       \
 176        __read_once_size(&(x), __u.__c, sizeof(x));     \
 177        __u.__val;                                      \
 178})
 179
 180#define WRITE_ONCE(x, val)                              \
 181({                                                      \
 182        union { typeof(x) __val; char __c[1]; } __u =   \
 183                { .__val = (val) };                     \
 184        __write_once_size(&(x), __u.__c, sizeof(x));    \
 185        __u.__val;                                      \
 186})
 187
 188
 189#ifndef __fallthrough
 190# define __fallthrough
 191#endif
 192
 193/* Indirect macros required for expanded argument pasting, eg. __LINE__. */
 194#define ___PASTE(a, b) a##b
 195#define __PASTE(a, b) ___PASTE(a, b)
 196
 197#endif /* _TOOLS_LINUX_COMPILER_H */
 198