linux-kernel - Re: objtool clac/stac handling change..

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Message-ID: <20200701205108.wtgfnijav7lgfiqe@treble>
Date:   Wed, 1 Jul 2020 15:51:08 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: objtool clac/stac handling change..

On Wed, Jul 01, 2020 at 01:36:22PM -0700, Andy Lutomirski wrote:
> If we do this extable change, we end up with a different mess: some
> exception handlers will clear AC and some won’t.  I’m sure objtool can
> deal with this with some effort, but I’m not convinced it’s worth it.

Yeah.  Peter's more of the expert here, but I think we'd at least need
to annotate the code which expects an implicit CLAC so objtool knows
what to expect.  It's not trivial, but it might be doable.

-- 
Josh