linux-kernel - Re: [Bugme-new] [Bug 13012] New: 2.6.28.9 causes init to segfault on Debian etch; 2.6.28.8 OK

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Date:	Thu, 9 Apr 2009 14:52:54 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	bugzilla-daemon@...zilla.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Barry K. Nathan" <barryn@...ox.com>, stable@...nel.org
Subject: Re: [Bugme-new] [Bug 13012] New: 2.6.28.9 causes init to segfault
 on Debian etch; 2.6.28.8 OK



On Thu, 9 Apr 2009, Andrew Morton wrote:
> 
> -fwrapv killed Barry's gcc-4.1.2-compiled kernel in 2.6.27.x, 2.6.28.x
> and presumably 2.6.29, 2.6.30.

Auughh. I hate compiler bugs. They're horrible to debug.

I _think_ 'fwrapv' only really matters with gcc-4.3, so maybe we could 
just enable it for new versions.

HOWEVER, I also wonder if we could instead of "-fwrapv" use 
"-fno-strict-overflow". They are apparently subtly different, and maybe 
the bug literally only happens with -fwrapv.

Barry, can you see if that simple "replace -fwrapv with 
-fno-strict-overflow" works for you?

Or just go with Barry's helpful debugging:

> > I also noticed that the problem only happens with some gcc's:
> > 
> > Problem occurs:
> > gcc (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
> > gcc-4.1 (GCC) 4.1.3 20080704 (prerelease) (Debian 4.1.2-25)
> > 
> > Problem does not occur (i.e. 2.6.28.9 works and I don't have to revert
> > anything):
> > gcc-4.2 (GCC) 4.2.4 (Debian 4.2.4-6)
> > gcc (Debian 4.3.2-1.1) 4.3.2

and consider 4.2 to be the point where it's ok.

Do we have some gcc developer who 
 (a) knows what the rules are
and
 (b) might even help us figure out where the bug occurs?

		Linus
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