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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/x86/lib/cmpxchg16b_emu.S
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/* SPDX-License-Identifier: GPL-2.0-only */

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#include <linux/linkage.h>

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#include <asm/percpu.h>

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#include <asm/processor-flags.h>

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.text

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/*

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 * Emulate 'cmpxchg16b %gs:(%rsi)'

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 *

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 * Inputs:

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 * %rsi : memory location to compare

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 * %rax : low 64 bits of old value

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 * %rdx : high 64 bits of old value

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 * %rbx : low 64 bits of new value

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 * %rcx : high 64 bits of new value

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 *

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 * Notably this is not LOCK prefixed and is not safe against NMIs

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 */

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SYM_FUNC_START(this_cpu_cmpxchg16b_emu)

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	pushfq

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	cli

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	/* if (*ptr == old) */

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	cmpq	__percpu (%rsi), %rax

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	jne	.Lnot_same

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	cmpq	__percpu 8(%rsi), %rdx

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	jne	.Lnot_same

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	/* *ptr = new */

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	movq	%rbx, __percpu (%rsi)

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	movq	%rcx, __percpu 8(%rsi)

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	/* set ZF in EFLAGS to indicate success */

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	orl	$X86_EFLAGS_ZF, (%rsp)

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	popfq

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	RET

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.Lnot_same:

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	/* *ptr != old */

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	/* old = *ptr */

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	movq	__percpu (%rsi), %rax

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	movq	__percpu 8(%rsi), %rdx

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	/* clear ZF in EFLAGS to indicate failure */

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	andl	$(~X86_EFLAGS_ZF), (%rsp)

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	popfq

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	RET

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SYM_FUNC_END(this_cpu_cmpxchg16b_emu)

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