linux-kernel - Re: [GIT PULL] x86/asm changes for v5.6

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Date:   Thu, 30 Jan 2020 18:39:10 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Luck, Tony" <tony.luck@...el.com>, Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86/asm changes for v5.6

On Thu, Jan 30, 2020 at 07:27:28AM -0800, Linus Torvalds wrote:
> Fair enough. Let's not complicate things just to avoid a few nops.

Yeah, judging by the frequency this keeps popping up, we might end up
doing proper insn parsing for the alternatives soon. :)

> That does make me wonder about RIP-relative addressing in alternatives
> too. Particularly anything where we let gcc pick addressing modes. I
> guess we don't have any, but maybe this branch issue and possible RIP
> addressing is something that objtool could be taught to warn about?

Yeah, makes sense. It would help if one slaps a relative JMP as *not*
the first insn in an alternatives replacement and the build to warn that
it can't work. Lemme go stare at objtool.

-- 
Regards/Gruss,
    Boris.

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