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

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Message-ID: <CA+55aFyjEuRLN6PMZZqi6k0rA6=AsTTZeN37eyyJM5ig-mnM4w@mail.gmail.com>
Date:   Tue, 7 Mar 2017 10:40:14 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Andy Lutomirski <luto@...capital.net>, 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 10:28 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> Also, the gcc documentation says -maccumulate-outgoing-args is
> "generally beneficial for performance and size."

Hmm. I wonder how true that is. I'm pretty sure it generates bigger
code, although it's probably less noticeable in the kernel (as opposed
to the traditional x86 "push everything" model) due to having the
three register arguments.

And the "it's faster" is almost certainly garbage. It's true on P4 and
some older AMD cores that couldn't do push/pops quickly.

> Not to mention the fact that -maccumulate-outgoing-args seems to already
> be enabled in most cases anyway.

Yeah, that's the main argument for this patch, I think - just remove
the (unusual) special case.

                 Linus