From: Peter Zijlstra <peterz@infradead.org>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: x86@kernel.org, llvm@lists.linux.dev,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Subject: Re: [PATCH] x86/locking: Remove semicolon from "lock" prefix
Date: Fri, 28 Feb 2025 10:15:32 +0100 [thread overview]
Message-ID: <20250228091532.GD5880@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20250228085149.2478245-1-ubizjak@gmail.com>
On Fri, Feb 28, 2025 at 09:51:15AM +0100, Uros Bizjak wrote:
> 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>
Ah, I always wondered why that ; was there.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
next prev parent reply other threads:[~2025-02-28 9:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-28 8:51 [PATCH] x86/locking: Remove semicolon from "lock" prefix Uros Bizjak
2025-02-28 9:15 ` Peter Zijlstra [this message]
2025-02-28 9:28 ` [tip: locking/core] " tip-bot2 for Uros Bizjak
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