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1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _TOOLS_LINUX_COMPILER_H_
3 #define _TOOLS_LINUX_COMPILER_H_
6 #include <linux/compiler-gcc.h>
9 #ifndef __compiletime_error
10 # define __compiletime_error(message)
13 /* Optimization barrier */
14 /* The "volatile" is due to gcc bugs */
15 #define barrier() __asm__ __volatile__("": : :"memory")
17 #ifndef __always_inline
18 # define __always_inline inline __attribute__((always_inline))
25 /* Are two types/vars the same type (ignoring qualifiers)? */
27 # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
32 * FIXME: Big hammer to get rid of tons of:
33 * "warning: always_inline function might not be inlinable"
35 * At least on android-ndk-r12/platforms/android-24/arch-arm
37 #undef __always_inline
38 #define __always_inline inline
45 #ifndef __attribute_const__
46 # define __attribute_const__
49 #ifndef __maybe_unused
50 # define __maybe_unused __attribute__((unused))
54 # define __used __attribute__((__unused__))
58 # define __packed __attribute__((__packed__))
66 # define __weak __attribute__((weak))
70 # define likely(x) __builtin_expect(!!(x), 1)
74 # define unlikely(x) __builtin_expect(!!(x), 0)
85 #define uninitialized_var(x) x = *(&(x))
87 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
89 #include <linux/types.h>
92 * Following functions are taken from kernel sources and
93 * break aliasing rules in their original form.
95 * While kernel is compiled with -fno-strict-aliasing,
96 * perf uses -Wstrict-aliasing=3 which makes build fail
99 * Using extra __may_alias__ type to allow aliasing
102 typedef __u8
__attribute__((__may_alias__
)) __u8_alias_t
;
103 typedef __u16
__attribute__((__may_alias__
)) __u16_alias_t
;
104 typedef __u32
__attribute__((__may_alias__
)) __u32_alias_t
;
105 typedef __u64
__attribute__((__may_alias__
)) __u64_alias_t
;
107 static __always_inline
void __read_once_size(const volatile void *p
, void *res
, int size
)
110 case 1: *(__u8_alias_t
*) res
= *(volatile __u8_alias_t
*) p
; break;
111 case 2: *(__u16_alias_t
*) res
= *(volatile __u16_alias_t
*) p
; break;
112 case 4: *(__u32_alias_t
*) res
= *(volatile __u32_alias_t
*) p
; break;
113 case 8: *(__u64_alias_t
*) res
= *(volatile __u64_alias_t
*) p
; break;
116 __builtin_memcpy((void *)res
, (const void *)p
, size
);
121 static __always_inline
void __write_once_size(volatile void *p
, void *res
, int size
)
124 case 1: *(volatile __u8_alias_t
*) p
= *(__u8_alias_t
*) res
; break;
125 case 2: *(volatile __u16_alias_t
*) p
= *(__u16_alias_t
*) res
; break;
126 case 4: *(volatile __u32_alias_t
*) p
= *(__u32_alias_t
*) res
; break;
127 case 8: *(volatile __u64_alias_t
*) p
= *(__u64_alias_t
*) res
; break;
130 __builtin_memcpy((void *)p
, (const void *)res
, size
);
136 * Prevent the compiler from merging or refetching reads or writes. The
137 * compiler is also forbidden from reordering successive instances of
138 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the
139 * compiler is aware of some particular ordering. One way to make the
140 * compiler aware of ordering is to put the two invocations of READ_ONCE,
141 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
143 * In contrast to ACCESS_ONCE these two macros will also work on aggregate
144 * data types like structs or unions. If the size of the accessed data
145 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
146 * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a
147 * compile-time warning.
149 * Their two major use cases are: (1) Mediating communication between
150 * process-level code and irq/NMI handlers, all running on the same CPU,
151 * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
152 * mutilate accesses that either do not require ordering or that interact
153 * with an explicit memory barrier or atomic instruction that provides the
157 #define READ_ONCE(x) \
158 ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
160 #define WRITE_ONCE(x, val) \
161 ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
164 #ifndef __fallthrough
165 # define __fallthrough
168 #endif /* _TOOLS_LINUX_COMPILER_H */