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

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Message-Id: <B9CF61D4-50F7-4A82-8327-86CA18450669@amacapital.net>
Date:   Wed, 1 Jul 2020 20:08:36 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 Jul 1, 2020, at 7:30 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> On Wed, Jul 1, 2020 at 5:48 PM Andy Lutomirski <luto@...nel.org> wrote:
>> 
>> You inspired me to mock it up.
> 
> Ahh, you want to just use the jump folding of gcc to avoid the problem.
> 
> I guess we could do that. Are there cases where this actually helps?
> 

I was thinking it would help avoid brain melt. For better or for worse, the kernel is written in C, and readers don’t really expect call_some_function(arg, other arg) to actually teleport elsewhere in the function.  I’m all for goto err; but at least that’s spelled “goto” and it’s really obvious what it does.