linux-kernel - Re: Linux 2.6.27.27

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Date:	Mon, 20 Jul 2009 19:47:37 -0400
From:	Marc Dionne <marc.c.dionne@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Krzysztof Oledzki <olel@....pl>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, stable@...nel.org,
	lwn@....net
Subject: Re: Linux 2.6.27.27

On 07/20/2009 06:08 PM, Linus Torvalds wrote:
>
> On Mon, 20 Jul 2009, Krzysztof Oledzki wrote:
>> No problem. Please let me know what should I do to help tracking this issue.
>
> Can you build two kernels: one with -fwrapv, and one with
> -fno-strict-overflow, and then verify that
>
>   - they are otherwise identical (ie exact same source code, same compiler
>     etc)
>
>   - verify that yes, the -fwrapv kernel works, the other does not. Just to
>     avoid the confusion that obviously exists with Debian/sid binutils
>     upgrades that _also_ happens result in nonbootable kernels.
>
>   - upload the 'vmlinux' images somewhere (I'm not sure what the limits for
>     binary attachments are at the kernel bugzilla, but that would be the
>     logical place)
>
> In fact, it would be nice to have a third "identical" kernel build, except
> with neither -fwrapv/-fno-strict-overflow.
>
> 			Linus

I might be seeing a slightly different bug, but in case it's helpful, 
the behaviour here on Fedora rawhide with gcc-4.4.0-14.x86_64 and 
binutils-2.19.51.0.11-27.fc12.x86_64 is that I get various .o files that 
come out as completely empty files (or in one case as a precisely 64K 
sized file that gives a "File format not recognized" error"), and the 
latest 2.6.31-rc git can't be built at all.

If I replace -fno-strict-overflow with -fwrapv in Makefile everything 
builds and runs fine.

Interestingly though, "-fno-strict-overflow -v" also gives me a good 
kernel, and comparing the assembly for one of the affected files doesn't 
show any difference between -fwrapv and -fno-strict-overflow.

Marc
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