linux-kernel - Re: v4.10: kernel stack frame pointer .. has bad value (null)

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Message-ID: <CA+55aFw+WVjwPBPKpnKcZUkqX=mYWv7A6M44uJpmWuzGU0zpqw@mail.gmail.com>
Date:   Tue, 7 Mar 2017 09:52:21 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Pavel Machek <pavel@....cz>,
        kernel list <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Peter Anvin <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: v4.10: kernel stack frame pointer .. has bad value (null)

On Tue, Mar 7, 2017 at 9:38 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> So I'm thinking we should have -maccumulate-outgoing-args always enabled
> on x86_32 just like we already do on x86_64.

Ugh. I realize we have workarounds for bugs, but I think
-maccumulate-outgoing-args is nasty. It just generates worse code by
avoiding the much nicer push/pop sequences, afaik.

On x86-64 it's not such a big deal, because we pass the first six
arguments in registers anyway, so the arguments on the stack is a
fairly unusual special case.

But on x86-32, we only have three argument registers, so this
braindamage is potentially worse.

I guess we already do this in most situations due to the gcc bugs, but
I do think it's sad that we would do it for our _own_ bugs too.

                   Linus