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089db01ea7
Minimum version of binutils required to compile the kernel is 2.25. This version correctly handles the "lock" prefix, so it is possible to remove the semicolon, which was used to support ancient versions of GNU as. Due to the semicolon, the compiler considers "lock; insn" as two separate instructions. Removing the semicolon makes asm length calculations more accurate, consequently making scheduling and inlining decisions of the compiler more accurate. Removing the semicolon also enables assembler checks involving lock prefix. Trying to assemble e.g. "lock andl %eax, %ebx" results in: Error: expecting lockable instruction after `lock' Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Richard Weinberger <richard@nod.at> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: Johannes Berg <johannes@sipsolutions.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Link: https://patch.msgid.link/20250228090058.2499163-1-ubizjak@gmail.com Signed-off-by: Johannes Berg <johannes.berg@intel.com>
29 lines
773 B
C
29 lines
773 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_UM_BARRIER_H_
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#define _ASM_UM_BARRIER_H_
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#include <asm/cpufeatures.h>
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#include <asm/alternative.h>
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/*
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* Force strict CPU ordering.
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* And yes, this is required on UP too when we're talking
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* to devices.
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*/
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#ifdef CONFIG_X86_32
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#define mb() alternative("lock addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
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#define rmb() alternative("lock addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)
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#define wmb() alternative("lock addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)
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#else /* CONFIG_X86_32 */
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#define mb() asm volatile("mfence" : : : "memory")
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#define rmb() asm volatile("lfence" : : : "memory")
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#define wmb() asm volatile("sfence" : : : "memory")
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#endif /* CONFIG_X86_32 */
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#include <asm-generic/barrier.h>
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#endif
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