Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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linux
1#ifndef _TOOLS_LINUX_COMPILER_H_
2#define _TOOLS_LINUX_COMPILER_H_
3
4/* Optimization barrier */
5/* The "volatile" is due to gcc bugs */
6#define barrier() __asm__ __volatile__("": : :"memory")
7
8#ifndef __always_inline
9# define __always_inline inline __attribute__((always_inline))
10#endif
11
12#define __user
13
14#ifndef __attribute_const__
15# define __attribute_const__
16#endif
17
18#ifndef __maybe_unused
19# define __maybe_unused __attribute__((unused))
20#endif
21
22#ifndef __packed
23# define __packed __attribute__((__packed__))
24#endif
25
26#ifndef __force
27# define __force
28#endif
29
30#ifndef __weak
31# define __weak __attribute__((weak))
32#endif
33
34#ifndef likely
35# define likely(x) __builtin_expect(!!(x), 1)
36#endif
37
38#ifndef unlikely
39# define unlikely(x) __builtin_expect(!!(x), 0)
40#endif
41
42#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
43
44#include <linux/types.h>
45
46static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
47{
48 switch (size) {
49 case 1: *(__u8 *)res = *(volatile __u8 *)p; break;
50 case 2: *(__u16 *)res = *(volatile __u16 *)p; break;
51 case 4: *(__u32 *)res = *(volatile __u32 *)p; break;
52 case 8: *(__u64 *)res = *(volatile __u64 *)p; break;
53 default:
54 barrier();
55 __builtin_memcpy((void *)res, (const void *)p, size);
56 barrier();
57 }
58}
59
60static __always_inline void __write_once_size(volatile void *p, void *res, int size)
61{
62 switch (size) {
63 case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
64 case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
65 case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
66 case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
67 default:
68 barrier();
69 __builtin_memcpy((void *)p, (const void *)res, size);
70 barrier();
71 }
72}
73
74/*
75 * Prevent the compiler from merging or refetching reads or writes. The
76 * compiler is also forbidden from reordering successive instances of
77 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
78 * compiler is aware of some particular ordering. One way to make the
79 * compiler aware of ordering is to put the two invocations of READ_ONCE,
80 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
81 *
82 * In contrast to ACCESS_ONCE these two macros will also work on aggregate
83 * data types like structs or unions. If the size of the accessed data
84 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
85 * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
86 * compile-time warning.
87 *
88 * Their two major use cases are: (1) Mediating communication between
89 * process-level code and irq/NMI handlers, all running on the same CPU,
90 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
91 * mutilate accesses that either do not require ordering or that interact
92 * with an explicit memory barrier or atomic instruction that provides the
93 * required ordering.
94 */
95
96#define READ_ONCE(x) \
97 ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
98
99#define WRITE_ONCE(x, val) \
100 ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
101
102#endif /* _TOOLS_LINUX_COMPILER_H */