linux_kernel/tools/arch/x86/include/asm/cmpxchg.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef TOOLS_ASM_X86_CMPXCHG_H
#define TOOLS_ASM_X86_CMPXCHG_H

#include <linux/compiler.h>

/*
 * Non-existant functions to indicate usage errors at link time
 * (or compile-time if the compiler implements __compiletime_error().
 */
extern void __cmpxchg_wrong_size(void)
	__compiletime_error("Bad argument size for cmpxchg");

/*
 * Constants for operation sizes. On 32-bit, the 64-bit size it set to
 * -1 because sizeof will never return -1, thereby making those switch
 * case statements guaranteeed dead code which the compiler will
 * eliminate, and allowing the "missing symbol in the default case" to
 * indicate a usage error.
 */
#define __X86_CASE_B	1
#define __X86_CASE_W	2
#define __X86_CASE_L	4
#ifdef __x86_64__
#define __X86_CASE_Q	8
#else
#define	__X86_CASE_Q	-1		/* sizeof will never return -1 */
#endif

/*
 * Atomic compare and exchange.  Compare OLD with MEM, if identical,
 * store NEW in MEM.  Return the initial value in MEM.  Success is
 * indicated by comparing RETURN with OLD.
 */
#define __raw_cmpxchg(ptr, old, new, size, lock)			\
({									\
	__typeof__(*(ptr)) __ret;					\
	__typeof__(*(ptr)) __old = (old);				\
	__typeof__(*(ptr)) __new = (new);				\
	switch (size) {							\
	case __X86_CASE_B:						\
	{								\
		volatile u8 *__ptr = (volatile u8 *)(ptr);		\
		asm volatile(lock "cmpxchgb %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "q" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	case __X86_CASE_W:						\
	{								\
		volatile u16 *__ptr = (volatile u16 *)(ptr);		\
		asm volatile(lock "cmpxchgw %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "r" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	case __X86_CASE_L:						\
	{								\
		volatile u32 *__ptr = (volatile u32 *)(ptr);		\
		asm volatile(lock "cmpxchgl %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "r" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	case __X86_CASE_Q:						\
	{								\
		volatile u64 *__ptr = (volatile u64 *)(ptr);		\
		asm volatile(lock "cmpxchgq %2,%1"			\
			     : "=a" (__ret), "+m" (*__ptr)		\
			     : "r" (__new), "0" (__old)			\
			     : "memory");				\
		break;							\
	}								\
	default:							\
		__cmpxchg_wrong_size();					\
	}								\
	__ret;								\
})

#define __cmpxchg(ptr, old, new, size)					\
	__raw_cmpxchg((ptr), (old), (new), (size), LOCK_PREFIX)

#define cmpxchg(ptr, old, new)						\
	__cmpxchg(ptr, old, new, sizeof(*(ptr)))


#endif	/* TOOLS_ASM_X86_CMPXCHG_H */