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

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Message-ID: <Pine.BSM.4.64L.2401220106590.999@herc.mirbsd.org>
Date: Mon, 22 Jan 2024 01:17:36 +0000 (UTC)
From: Thorsten Glaser <tg@...ian.org>
To: Steven Rostedt <rostedt@...dmis.org>
cc: "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
        x86@...nel.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

Steven Rostedt dixit:

>> >This was, incidentally, triggered by looking into a problem report that
>> >something did *not* work on a Geode LX system.
>
>What problem happened?

It turned out to be a compiler issue (GCC thinks i686 means PPro,
not 686-class CPUs, and -fcf-protection causes long NOPs, which
not all 686-class CPUs support, to be inserted). This turned out
to break a large part of Debian stable on OLPCs and other systems,
and the kernel’s changes in nopl handling were tabled as arguments.

https://www.jookia.org/wiki/Nopl has a longer writeup on the nopl
history.

bye,
//mirabilos
-- 
<igli> exceptions: a truly awful implementation of quite a nice idea.
<igli> just about the worst way you could do something like that, afaic.
<igli> it's like anti-design.  <mirabilos> that too… may I quote you on that?
<igli> sure, tho i doubt anyone will listen ;)