linux-kernel - Re: [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f

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Message-ID: <20180208101348.GF25201@hirez.programming.kicks-ass.net>
Date:   Thu, 8 Feb 2018 11:13:48 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        kbuild test robot <fengguang.wu@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [linus:master] BUILD REGRESSION
 a2e5790d841658485d642196dbb0927303d6c22f

On Thu, Feb 08, 2018 at 09:47:53AM +0000, David Laight wrote:
> From: Peter Zijlstra

> > I went through the register opcodes and matched it against the ModR/M
> > encoding, and the best option I've found so far is using 0xd6 as the
> > next byte.
> 
> Wouldn't 0xc3 work as well.
> A retq is probably better than an extra (bad).

I explicity did not use c3 because that generates spurious "retq" in the
code flow which is mighty confusing when you read the stuff.