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

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Message-ID: <20170309211234.GA11875@amd>
Date:   Thu, 9 Mar 2017 22:12:34 +0100
From:   Pavel Machek <pavel@....cz>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        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>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: v4.10: kernel stack frame pointer .. has bad value (null)

On Thu 2017-03-09 16:29:10, Peter Zijlstra wrote:
> On Wed, Mar 08, 2017 at 10:22:53PM +0100, Pavel Machek wrote:
> > 
> > Well, I have fast CPUs, but most of the time they just compile
> > stuff. Especially bisect is compile-heavy. I suspect going back to
> > gcc-3.2 would bring me bigger advantages than CPU upgrade...
> > 
> 
> But note that 3.2 compiles a distinctly different kernel from something
> new and shiny. The kernel uses a lot of GCC features optimistically to
> generate different code.
> 
> So if by some chance your error depends on one of the new features,
> bisecting with some ancient compiler will not work.

Well, yes, obviously different compilers generate different code.

OTOH for drivers (where most errors are) the difference should not be
significant.

And actually.. if you realize it bug is gcc version dependend, you'll
know where to look for the bug.

(Anyway, it looks like gcc-3.3 is not usable for kernel on x86, and it
is actually slower, too. So -- bad idea. gcc -O1 looks promising.)

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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