linux-kernel - Re: [PATCH 1/2] x86: Remove dynamic NOP selection

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Date: Sun, 21 Jan 2024 15:21:54 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Thorsten Glaser <tg@...ian.org>
Cc: Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, rostedt@...dmis.org,
        torvalds@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-toolchains@...r.kernel.org, jpoimboe@...hat.com,
        alexei.starovoitov@...il.com, mhiramat@...nel.org
Subject: Re: [PATCH 1/2] x86: Remove dynamic NOP selection

On 1/20/24 08:53, Thorsten Glaser wrote:
> H. Peter Anvin dixit:
> 
>> %eiz was something that binutils used to put in when disassembling
>> certain redundant encodings with SIB at some point.
> 
> Ah, fair enough. Maybe this could be added as one more line in
> the comment or something.
> 

I think "proper" gas syntax would be 0(%esi,,1), although that doesn't 
assemble either (I don't believe there is a way to get gas to actually 
generate this sequence.)

But yes, with all even remotely recent CPUs all actually handling nopl 
properly, this isn't relevant anymore.

	-hpa