1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _TOOLS_LINUX_COMPILER_H_ 3 #define _TOOLS_LINUX_COMPILER_H_ 4 5 #ifdef __GNUC__ 6 #include <linux/compiler-gcc.h> 7 #endif 8 9 #ifndef __compiletime_error 10 # define __compiletime_error(message) 11 #endif 12 13 /* Optimization barrier */ 14 /* The "volatile" is due to gcc bugs */ 15 #define barrier() __asm__ __volatile__("": : :"memory") 16 17 #ifndef __always_inline 18 # define __always_inline inline __attribute__((always_inline)) 19 #endif 20 21 #ifndef noinline 22 #define noinline 23 #endif 24 25 /* Are two types/vars the same type (ignoring qualifiers)? */ 26 #ifndef __same_type 27 # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b)) 28 #endif 29 30 #ifdef __ANDROID__ 31 /* 32 * FIXME: Big hammer to get rid of tons of: 33 * "warning: always_inline function might not be inlinable" 34 * 35 * At least on android-ndk-r12/platforms/android-24/arch-arm 36 */ 37 #undef __always_inline 38 #define __always_inline inline 39 #endif 40 41 #define __user 42 #define __rcu 43 #define __read_mostly 44 45 #ifndef __attribute_const__ 46 # define __attribute_const__ 47 #endif 48 49 #ifndef __maybe_unused 50 # define __maybe_unused __attribute__((unused)) 51 #endif 52 53 #ifndef __used 54 # define __used __attribute__((__unused__)) 55 #endif 56 57 #ifndef __packed 58 # define __packed __attribute__((__packed__)) 59 #endif 60 61 #ifndef __force 62 # define __force 63 #endif 64 65 #ifndef __weak 66 # define __weak __attribute__((weak)) 67 #endif 68 69 #ifndef likely 70 # define likely(x) __builtin_expect(!!(x), 1) 71 #endif 72 73 #ifndef unlikely 74 # define unlikely(x) __builtin_expect(!!(x), 0) 75 #endif 76 77 #ifndef __init 78 # define __init 79 #endif 80 81 #ifndef noinline 82 # define noinline 83 #endif 84 85 #define uninitialized_var(x) x = *(&(x)) 86 87 #include <linux/types.h> 88 89 /* 90 * Following functions are taken from kernel sources and 91 * break aliasing rules in their original form. 92 * 93 * While kernel is compiled with -fno-strict-aliasing, 94 * perf uses -Wstrict-aliasing=3 which makes build fail 95 * under gcc 4.4. 96 * 97 * Using extra __may_alias__ type to allow aliasing 98 * in this case. 99 */ 100 typedef __u8 __attribute__((__may_alias__)) __u8_alias_t; 101 typedef __u16 __attribute__((__may_alias__)) __u16_alias_t; 102 typedef __u32 __attribute__((__may_alias__)) __u32_alias_t; 103 typedef __u64 __attribute__((__may_alias__)) __u64_alias_t; 104 105 static __always_inline void __read_once_size(const volatile void *p, void *res, int size) 106 { 107 switch (size) { 108 case 1: *(__u8_alias_t *) res = *(volatile __u8_alias_t *) p; break; 109 case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break; 110 case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break; 111 case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break; 112 default: 113 barrier(); 114 __builtin_memcpy((void *)res, (const void *)p, size); 115 barrier(); 116 } 117 } 118 119 static __always_inline void __write_once_size(volatile void *p, void *res, int size) 120 { 121 switch (size) { 122 case 1: *(volatile __u8_alias_t *) p = *(__u8_alias_t *) res; break; 123 case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break; 124 case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break; 125 case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break; 126 default: 127 barrier(); 128 __builtin_memcpy((void *)p, (const void *)res, size); 129 barrier(); 130 } 131 } 132 133 /* 134 * Prevent the compiler from merging or refetching reads or writes. The 135 * compiler is also forbidden from reordering successive instances of 136 * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some 137 * particular ordering. One way to make the compiler aware of ordering is to 138 * put the two invocations of READ_ONCE or WRITE_ONCE in different C 139 * statements. 140 * 141 * These two macros will also work on aggregate data types like structs or 142 * unions. If the size of the accessed data type exceeds the word size of 143 * the machine (e.g., 32 bits or 64 bits) READ_ONCE() and WRITE_ONCE() will 144 * fall back to memcpy and print a compile-time warning. 145 * 146 * Their two major use cases are: (1) Mediating communication between 147 * process-level code and irq/NMI handlers, all running on the same CPU, 148 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise 149 * mutilate accesses that either do not require ordering or that interact 150 * with an explicit memory barrier or atomic instruction that provides the 151 * required ordering. 152 */ 153 154 #define READ_ONCE(x) \ 155 ({ \ 156 union { typeof(x) __val; char __c[1]; } __u = \ 157 { .__c = { 0 } }; \ 158 __read_once_size(&(x), __u.__c, sizeof(x)); \ 159 __u.__val; \ 160 }) 161 162 #define WRITE_ONCE(x, val) \ 163 ({ \ 164 union { typeof(x) __val; char __c[1]; } __u = \ 165 { .__val = (val) }; \ 166 __write_once_size(&(x), __u.__c, sizeof(x)); \ 167 __u.__val; \ 168 }) 169 170 171 #ifndef __fallthrough 172 # define __fallthrough 173 #endif 174 175 #endif /* _TOOLS_LINUX_COMPILER_H */ 176