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#include <linux/types.h>
  88
  89/*
  90 * Following functions are taken from kernel sources and
  91 * break aliasing rules in their original form.
  92 *
  93 * While kernel is compiled with -fno-strict-aliasing,
  94 * perf uses -Wstrict-aliasing=3 which makes build fail
  95 * under gcc 4.4.
  96 *
  97 * Using extra __may_alias__ type to allow aliasing
  98 * in this case.
  99 */
 100typedef __u8  __attribute__((__may_alias__))  __u8_alias_t;
 101typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
 102typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
 103typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;
 104
 105static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
 106{
 107        switch (size) {
 108        case 1: *(__u8_alias_t  *) res = *(volatile __u8_alias_t  *) p; break;
 109        case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
 110        case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
 111        case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
 112        default:
 113                barrier();
 114                __builtin_memcpy((void *)res, (const void *)p, size);
 115                barrier();
 116        }
 117}
 118
 119static __always_inline void __write_once_size(volatile void *p, void *res, int size)
 120{
 121        switch (size) {
 122        case 1: *(volatile  __u8_alias_t *) p = *(__u8_alias_t  *) res; break;
 123        case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
 124        case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
 125        case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
 126        default:
 127                barrier();
 128                __builtin_memcpy((void *)p, (const void *)res, size);
 129                barrier();
 130        }
 131}
 132
 133/*
 134 * Prevent the compiler from merging or refetching reads or writes. The
 135 * compiler is also forbidden from reordering successive instances of
 136 * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
 137 * particular ordering. One way to make the compiler aware of ordering is to
 138 * put the two invocations of READ_ONCE or WRITE_ONCE in different C
 139 * statements.
 140 *
 141 * These two macros will also work on aggregate data types like structs or
 142 * unions. If the size of the accessed data type exceeds the word size of
 143 * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will
 144 * fall back to memcpy and print a compile-time warning.
 145 *
 146 * Their two major use cases are: (1) Mediating communication between
 147 * process-level code and irq/NMI handlers, all running on the same CPU,
 148 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
 149 * mutilate accesses that either do not require ordering or that interact
 150 * with an explicit memory barrier or atomic instruction that provides the
 151 * required ordering.
 152 */
 153
 154#define READ_ONCE(x)                                    \
 155({                                                      \
 156        union { typeof(x) __val; char __c[1]; } __u =   \
 157                { .__c = { 0 } };                       \
 158        __read_once_size(&(x), __u.__c, sizeof(x));     \
 159        __u.__val;                                      \
 160})
 161
 162#define WRITE_ONCE(x, val)                              \
 163({                                                      \
 164        union { typeof(x) __val; char __c[1]; } __u =   \
 165                { .__val = (val) };                     \
 166        __write_once_size(&(x), __u.__c, sizeof(x));    \
 167        __u.__val;                                      \
 168})
 169
 170
 171#ifndef __fallthrough
 172# define __fallthrough
 173#endif
 174
 175#endif /* _TOOLS_LINUX_COMPILER_H */
 176