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SubjectRe: Linux
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- 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.


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