root/tools/include/linux/compiler.h

INCLUDED FROM

DEFINITIONS

1. __read_once_size
2. __write_once_size

   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 */