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

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Date: Sun, 21 Jan 2024 18:04:42 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Thorsten Glaser <tg@...ian.org>, Steven Rostedt <rostedt@...dmis.org>
CC: 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

On January 21, 2024 5:17:36 PM PST, Thorsten Glaser <tg@...ian.org> wrote:
>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

i686 *is* Pentium Pro...