1 #ifndef _TOOLS_LINUX_COMPILER_H_
2 #define _TOOLS_LINUX_COMPILER_H_
5 #include <linux/compiler-gcc.h>
8 /* Optimization barrier */
9 /* The "volatile" is due to gcc bugs */
10 #define barrier() __asm__ __volatile__("": : :"memory")
12 #ifndef __always_inline
13 # define __always_inline inline __attribute__((always_inline))
18 * FIXME: Big hammer to get rid of tons of:
19 * "warning: always_inline function might not be inlinable"
21 * At least on android-ndk-r12/platforms/android-24/arch-arm
23 #undef __always_inline
24 #define __always_inline inline
29 #ifndef __attribute_const__
30 # define __attribute_const__
33 #ifndef __maybe_unused
34 # define __maybe_unused __attribute__((unused))
38 # define __packed __attribute__((__packed__))
46 # define __weak __attribute__((weak))
50 # define likely(x) __builtin_expect(!!(x), 1)
54 # define unlikely(x) __builtin_expect(!!(x), 0)
57 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
59 #include <linux/types.h>
62 * Following functions are taken from kernel sources and
63 * break aliasing rules in their original form.
65 * While kernel is compiled with -fno-strict-aliasing,
66 * perf uses -Wstrict-aliasing=3 which makes build fail
69 * Using extra __may_alias__ type to allow aliasing
72 typedef __u8 __attribute__((__may_alias__)) __u8_alias_t;
73 typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
74 typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
75 typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;
77 static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
80 case 1: *(__u8_alias_t *) res = *(volatile __u8_alias_t *) p; break;
81 case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
82 case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
83 case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
86 __builtin_memcpy((void *)res, (const void *)p, size);
91 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
94 case 1: *(volatile __u8_alias_t *) p = *(__u8_alias_t *) res; break;
95 case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
96 case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
97 case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
100 __builtin_memcpy((void *)p, (const void *)res, size);
106 * Prevent the compiler from merging or refetching reads or writes. The
107 * compiler is also forbidden from reordering successive instances of
108 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
109 * compiler is aware of some particular ordering. One way to make the
110 * compiler aware of ordering is to put the two invocations of READ_ONCE,
111 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
113 * In contrast to ACCESS_ONCE these two macros will also work on aggregate
114 * data types like structs or unions. If the size of the accessed data
115 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
116 * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
117 * compile-time warning.
119 * Their two major use cases are: (1) Mediating communication between
120 * process-level code and irq/NMI handlers, all running on the same CPU,
121 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
122 * mutilate accesses that either do not require ordering or that interact
123 * with an explicit memory barrier or atomic instruction that provides the
127 #define READ_ONCE(x) \
128 ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
130 #define WRITE_ONCE(x, val) \
131 ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
134 #ifndef __fallthrough
135 # define __fallthrough
138 #endif /* _TOOLS_LINUX_COMPILER_H */