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 */ 76 typedef __u8 __attribute__((__may_alias__)) __u8_alias_t; 77 typedef __u16 __attribute__((__may_alias__)) __u16_alias_t; 78 typedef __u32 __attribute__((__may_alias__)) __u32_alias_t; 79 typedef __u64 __attribute__((__may_alias__)) __u64_alias_t; 80 81 static __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 95 static __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 */ 143