Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
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
46/*
47 * Following functions are taken from kernel sources and
48 * break aliasing rules in their original form.
49 *
50 * While kernel is compiled with -fno-strict-aliasing,
51 * perf uses -Wstrict-aliasing=3 which makes build fail
52 * under gcc 4.4.
53 *
54 * Using extra __may_alias__ type to allow aliasing
55 * in this case.
56 */
57typedef __u8 __attribute__((__may_alias__)) __u8_alias_t;
58typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
59typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
60typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;
61
62static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
63{
64 switch (size) {
65 case 1: *(__u8_alias_t *) res = *(volatile __u8_alias_t *) p; break;
66 case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
67 case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
68 case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
69 default:
70 barrier();
71 __builtin_memcpy((void *)res, (const void *)p, size);
72 barrier();
73 }
74}
75
76static __always_inline void __write_once_size(volatile void *p, void *res, int size)
77{
78 switch (size) {
79 case 1: *(volatile __u8_alias_t *) p = *(__u8_alias_t *) res; break;
80 case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
81 case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
82 case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
83 default:
84 barrier();
85 __builtin_memcpy((void *)p, (const void *)res, size);
86 barrier();
87 }
88}
89
90/*
91 * Prevent the compiler from merging or refetching reads or writes. The
92 * compiler is also forbidden from reordering successive instances of
93 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
94 * compiler is aware of some particular ordering. One way to make the
95 * compiler aware of ordering is to put the two invocations of READ_ONCE,
96 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
97 *
98 * In contrast to ACCESS_ONCE these two macros will also work on aggregate
99 * data types like structs or unions. If the size of the accessed data
100 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
101 * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
102 * compile-time warning.
103 *
104 * Their two major use cases are: (1) Mediating communication between
105 * process-level code and irq/NMI handlers, all running on the same CPU,
106 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
107 * mutilate accesses that either do not require ordering or that interact
108 * with an explicit memory barrier or atomic instruction that provides the
109 * required ordering.
110 */
111
112#define READ_ONCE(x) \
113 ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
114
115#define WRITE_ONCE(x, val) \
116 ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
117
118#endif /* _TOOLS_LINUX_COMPILER_H */