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 #define __rcu 25 #define __read_mostly 26 27 #ifndef __attribute_const__ 28 # define __attribute_const__ 29 #endif 30 31 #ifndef __maybe_unused 32 # define __maybe_unused __attribute__((unused)) 33 #endif 34 35 #ifndef __packed 36 # define __packed __attribute__((__packed__)) 37 #endif 38 39 #ifndef __force 40 # define __force 41 #endif 42 43 #ifndef __weak 44 # define __weak __attribute__((weak)) 45 #endif 46 47 #ifndef likely 48 # define likely(x) __builtin_expect(!!(x), 1) 49 #endif 50 51 #ifndef unlikely 52 # define unlikely(x) __builtin_expect(!!(x), 0) 53 #endif 54 55 #define uninitialized_var(x) x = *(&(x)) 56 57 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) 58 59 #include <linux/types.h> 60 61 /* 62 * Following functions are taken from kernel sources and 63 * break aliasing rules in their original form. 64 * 65 * While kernel is compiled with -fno-strict-aliasing, 66 * perf uses -Wstrict-aliasing=3 which makes build fail 67 * under gcc 4.4. 68 * 69 * Using extra __may_alias__ type to allow aliasing 70 * in this case. 71 */ 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; 76 77 static __always_inline void __read_once_size(const volatile void *p, void *res, int size) 78 { 79 switch (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; 84 default: 85 barrier(); 86 __builtin_memcpy((void *)res, (const void *)p, size); 87 barrier(); 88 } 89 } 90 91 static __always_inline void __write_once_size(volatile void *p, void *res, int size) 92 { 93 switch (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; 98 default: 99 barrier(); 100 __builtin_memcpy((void *)p, (const void *)res, size); 101 barrier(); 102 } 103 } 104 105 /* 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. 112 * 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. 118 * 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 124 * required ordering. 125 */ 126 127 #define READ_ONCE(x) \ 128 ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) 129 130 #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; }) 132 133 #endif /* _TOOLS_LINUX_COMPILER_H */ 134