linux/arch/x86/kernel/cpu/cmpxchg.c

/*
 * cmpxchg*() fallbacks for CPU not supporting these instructions
 */

#include <linux/kernel.h>
#include <linux/smp.h>
#include <linux/module.h>

#ifndef CONFIG_X86_CMPXCHG
unsigned long cmpxchg_386_u8(volatile void *ptr, u8 old, u8 new)
{
	u8 prev;
	unsigned long flags;

	/* Poor man's cmpxchg for 386. Unsuitable for SMP */
	local_irq_save(flags);
	prev = *(u8 *)ptr;
	if (prev == old)
		*(u8 *)ptr = new;
	local_irq_restore(flags);
	return prev;
}
EXPORT_SYMBOL(cmpxchg_386_u8);

unsigned long cmpxchg_386_u16(volatile void *ptr, u16 old, u16 new)
{
	u16 prev;
	unsigned long flags;

	/* Poor man's cmpxchg for 386. Unsuitable for SMP */
	local_irq_save(flags);
	prev = *(u16 *)ptr;
	if (prev == old)
		*(u16 *)ptr = new;
	local_irq_restore(flags);
	return prev;
}
EXPORT_SYMBOL(cmpxchg_386_u16);

unsigned long cmpxchg_386_u32(volatile void *ptr, u32 old, u32 new)
{
	u32 prev;
	unsigned long flags;

	/* Poor man's cmpxchg for 386. Unsuitable for SMP */
	local_irq_save(flags);
	prev = *(u32 *)ptr;
	if (prev == old)
		*(u32 *)ptr = new;
	local_irq_restore(flags);
	return prev;
}
EXPORT_SYMBOL(cmpxchg_386_u32);
#endif

#ifndef CONFIG_X86_CMPXCHG64
unsigned long long cmpxchg_486_u64(volatile void *ptr, u64 old, u64 new)
{
	u64 prev;
	unsigned long flags;

	/* Poor man's cmpxchg8b for 386 and 486. Unsuitable for SMP */
	local_irq_save(flags);
	prev = *(u64 *)ptr;
	if (prev == old)
		*(u64 *)ptr = new;
	local_irq_restore(flags);
	return prev;
}
EXPORT_SYMBOL(cmpxchg_486_u64);
#endif