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