cregit-Linux how code gets into the kernel

Release 4.14 tools/include/linux/compiler.h

/* SPDX-License-Identifier: GPL-2.0 */


#ifdef __GNUC__
#include <linux/compiler-gcc.h>

#ifndef __compiletime_error

# define __compiletime_error(message)

/* Optimization barrier */
/* The "volatile" is due to gcc bugs */

#define barrier() __asm__ __volatile__("": : :"memory")

#ifndef __always_inline

# define __always_inline	inline __attribute__((always_inline))

#ifndef noinline

#define noinline

/* Are two types/vars the same type (ignoring qualifiers)? */
#ifndef __same_type

# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))

#ifdef __ANDROID__
 * FIXME: Big hammer to get rid of tons of:
 *   "warning: always_inline function might not be inlinable"
 * At least on android-ndk-r12/platforms/android-24/arch-arm

#undef __always_inline

#define __always_inline	inline

#define __user

#define __rcu

#define __read_mostly

#ifndef __attribute_const__

# define __attribute_const__

#ifndef __maybe_unused

# define __maybe_unused		__attribute__((unused))

#ifndef __used

# define __used		__attribute__((__unused__))

#ifndef __packed

# define __packed		__attribute__((__packed__))

#ifndef __force

# define __force

#ifndef __weak

# define __weak			__attribute__((weak))

#ifndef likely

# define likely(x)		__builtin_expect(!!(x), 1)

#ifndef unlikely

# define unlikely(x)		__builtin_expect(!!(x), 0)

#ifndef __init

# define __init

#ifndef noinline

# define noinline

#define uninitialized_var(x) x = *(&(x))

#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))

#include <linux/types.h>

 * Following functions are taken from kernel sources and
 * break aliasing rules in their original form.
 * While kernel is compiled with -fno-strict-aliasing,
 * perf uses -Wstrict-aliasing=3 which makes build fail
 * under gcc 4.4.
 * Using extra __may_alias__ type to allow aliasing
 * in this case.

typedef __u8  __attribute__((__may_alias__))  __u8_alias_t;

typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;

typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;

typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;

static __always_inline void __read_once_size(const volatile void *p, void *res, int size) { switch (size) { case 1: *(__u8_alias_t *) res = *(volatile __u8_alias_t *) p; break; case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break; case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break; case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break; default: barrier(); __builtin_memcpy((void *)res, (const void *)p, size); barrier(); } }


Arnaldo Carvalho de Melo11993.70%150.00%
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static __always_inline void __write_once_size(volatile void *p, void *res, int size) { switch (size) { case 1: *(volatile __u8_alias_t *) p = *(__u8_alias_t *) res; break; case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break; case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break; case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break; default: barrier(); __builtin_memcpy((void *)p, (const void *)res, size); barrier(); } }


Arnaldo Carvalho de Melo11893.65%150.00%
Jiri Olsa86.35%150.00%

/* * Prevent the compiler from merging or refetching reads or writes. The * compiler is also forbidden from reordering successive instances of * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), but only when the * compiler is aware of some particular ordering. One way to make the * compiler aware of ordering is to put the two invocations of READ_ONCE, * WRITE_ONCE or ACCESS_ONCE() in different C statements. * * In contrast to ACCESS_ONCE these two macros will also work on aggregate * data types like structs or unions. If the size of the accessed data * type exceeds the word size of the machine (e.g., 32 bits or 64 bits) * READ_ONCE() and WRITE_ONCE() will fall back to memcpy and print a * compile-time warning. * * Their two major use cases are: (1) Mediating communication between * process-level code and irq/NMI handlers, all running on the same CPU, * and (2) Ensuring that the compiler does not fold, spindle, or otherwise * mutilate accesses that either do not require ordering or that interact * with an explicit memory barrier or atomic instruction that provides the * required ordering. */ #define READ_ONCE(x) \ ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) #define WRITE_ONCE(x, val) \ ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) #ifndef __fallthrough # define __fallthrough #endif #endif /* _TOOLS_LINUX_COMPILER_H */

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Namhyung Kim275.19%28.70%
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Frédéric Weisbecker203.85%14.35%
Irina Tirdea152.88%28.70%
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