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

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Message-Id: <200907101659.31813.elendil@planet.nl>
Date:	Fri, 10 Jul 2009 16:59:29 +0200
From:	Frans Pop <elendil@...net.nl>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	linux-kbuild@...r.kernel.org, barryn@...ox.com,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bug 13012] 2.6.28.9 causes init to segfault on Debian etch; 2.6.28.8 OK

On Friday 10 July 2009, Frans Pop wrote:
> On Thu, 9 Apr 2009, Linus Torvalds wrote:
> > 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?

Prompted by the same suggestion from Ben Hutchings I checked this too, 
but -fno-strict-overflow was only introduced in gcc 4.2.
So using it instead of -fwrapv *would* fix the problem for gcc 4.1, but 
*only* because it would effectively do the same as the patch I proposed: 
not add an option at all for gcc 4.1.

So that change seems illogical unless there are other reasons to 
prefer -fno-strict-overflow over -fwrapv (well, it would avoid the
gcc version check).

It does however make it somewhat more logical to change the test in my 
proposed patch to also allow -fwrapv for gcc 4.2.

Cheers,
FJP
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