1 #ifndef _TOOLS_LINUX_COMPILER_H_
2 #define _TOOLS_LINUX_COMPILER_H_
5 #include <linux/compiler-gcc.h>
8 #ifndef __compiletime_error
9 # define __compiletime_error(message)
12 /* Optimization barrier */
13 /* The "volatile" is due to gcc bugs */
14 #define barrier() __asm__ __volatile__("": : :"memory")
16 #ifndef __always_inline
17 # define __always_inline inline __attribute__((always_inline))
22 * FIXME: Big hammer to get rid of tons of:
23 * "warning: always_inline function might not be inlinable"
25 * At least on android-ndk-r12/platforms/android-24/arch-arm
27 #undef __always_inline
28 #define __always_inline inline
35 #ifndef __attribute_const__
36 # define __attribute_const__
39 #ifndef __maybe_unused
40 # define __maybe_unused __attribute__((unused))
44 # define __packed __attribute__((__packed__))
52 # define __weak __attribute__((weak))
56 # define likely(x) __builtin_expect(!!(x), 1)
60 # define unlikely(x) __builtin_expect(!!(x), 0)
63 #define uninitialized_var(x) x = *(&(x))
65 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
67 #include <linux/types.h>
70 * Following functions are taken from kernel sources and
71 * break aliasing rules in their original form.
73 * While kernel is compiled with -fno-strict-aliasing,
74 * perf uses -Wstrict-aliasing=3 which makes build fail
77 * Using extra __may_alias__ type to allow aliasing
80 typedef __u8 __attribute__((__may_alias__)) __u8_alias_t;
81 typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
82 typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
83 typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;
85 static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
88 case 1: *(__u8_alias_t *) res = *(volatile __u8_alias_t *) p; break;
89 case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
90 case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
91 case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
94 __builtin_memcpy((void *)res, (const void *)p, size);
99 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
102 case 1: *(volatile __u8_alias_t *) p = *(__u8_alias_t *) res; break;
103 case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
104 case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
105 case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
108 __builtin_memcpy((void *)p, (const void *)res, size);
114 * Prevent the compiler from merging or refetching reads or writes. The
115 * compiler is also forbidden from reordering successive instances of
116 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
117 * compiler is aware of some particular ordering. One way to make the
118 * compiler aware of ordering is to put the two invocations of READ_ONCE,
119 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
121 * In contrast to ACCESS_ONCE these two macros will also work on aggregate
122 * data types like structs or unions. If the size of the accessed data
123 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
124 * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
125 * compile-time warning.
127 * Their two major use cases are: (1) Mediating communication between
128 * process-level code and irq/NMI handlers, all running on the same CPU,
129 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
130 * mutilate accesses that either do not require ordering or that interact
131 * with an explicit memory barrier or atomic instruction that provides the
135 #define READ_ONCE(x) \
136 ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
138 #define WRITE_ONCE(x, val) \
139 ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
142 #ifndef __fallthrough
143 # define __fallthrough
146 #endif /* _TOOLS_LINUX_COMPILER_H */