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