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