Re: Read corruption on ARM

[Dave Chinner <david@fromorbit.com>]

On Thu, Feb 28, 2013 at 03:38:51PM -0600, Jason Detring wrote:
> On 2/27/13, Eric Sandeen <sandeen@sandeen.net> wrote:
> > On 2/27/13 10:50 PM, Eric Sandeen wrote:
> >> On 2/27/13 10:38 PM, Eric Sandeen wrote:
> >>
> >> ...
> >>
> >>> re-cc'ing xfs list
> >>>
> >>> So I used pahole to look at all structs, objdump -d to disassemble,
> >>> and md5sum'd the results to see what's different.
> >>>
> >>> pi@raspberrypi ~ $ md5sum cross/*.dis cross/*.pahole native/*.dis
> >>> native/*.pahole
> >>>
> >>> <manual sort>
> >>>
> >>> c0abd80c3bf049db5e1909fd851261cc  cross/xfs-O1-g.ko.pahole
> >>> c0abd80c3bf049db5e1909fd851261cc  cross/xfs-O2-g.ko.pahole
> >>> c0abd80c3bf049db5e1909fd851261cc  cross/xfs-Os-g.ko.pahole
> >>> c0abd80c3bf049db5e1909fd851261cc  native/xfs-O1-g.ko.pahole
> >>> c0abd80c3bf049db5e1909fd851261cc  native/xfs-O2-g.ko.pahole
> >>> c0abd80c3bf049db5e1909fd851261cc  native/xfs-Os-g.ko.pahole
> >>>
> >>> so all structures look identical, good - but:
> >>>
> >>> while disassembly of these two modules match:
> >>>
> >>> d76f6ebf4d8a1b9f786facefbcf16f69  cross/xfs-O1-g.ko.dis
> >>> d76f6ebf4d8a1b9f786facefbcf16f69  native/xfs-O1-g.ko.dis
> >>>
> >>> do you see the problem w/ the cross-compiled xfs-O1-g.ko as well?
> 
> No, I didn't.  The problem has only shown itself on the -O2 builds,
> both native and cross-compiled.  Lower optimization levels don't show
> any of the symptoms.
> 
> Perhaps a better comparison would be-O2 builds among working and
> non-working compilers?   You'd asked for these before, but I just
> finished them today.  The modules, build logs, and fs/xfs/ build trees
> are up at
>   <http://www.splack.org/~jason/projects/xfs-arm-corruption/3.6.11-g89caf39/>
> A quick rundown:
>   -cross-gcc4.4:  OK
>   -cross-gcc4.5:  OK
>   -cross-gcc4.6:  BAD
>   -cross-gcc4.7:  BAD
>   -cross-gcc4.8:  OK
> Some of these don't seem to want to rmmod after they've been inserted.
>  Argh reboots.

Do we really need to go any further than this to say conclusively
that this is a compiler problem? It's clearly not a problem with the
C code in that some compilers produce working code....

i.e. what steps do we need to take to get -cross-gcc4.[67]
blacklisted when it comes to building ARM kernels?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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