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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH 7/7] PPC64: Don't fault at lwsync
Date: Thu, 5 Mar 2009 16:29:13 +0000
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To: Alexander Graf <agraf@suse.de>
Cc: blauwirbel@gmail.com, Alexander Graf <alex@csgraf.de>, qemu-devel@nongnu.org

> > 0xc0000000000ba524:  lwsync
> > 0xc0000000000ba528:  lwarx   r0,0,r3
> > 0xc0000000000ba52c:  cmpw    r0,r4
> > 0xc0000000000ba530:  bne-    0xc0000000000ba540
> >
> >
> > And I seriously have trouble understanding how a data storage exception
> > could happen on the lwsync opcode. It looks like R3 became 0 from the
> > guest's point of view after lwsync though - hum.
>
> Ah I remember that one now :-). The futex_init function tests if cmpxchg
> works with NULL values and that's why R3 is 0. It's actually _supposed_
> to fault here. But something gets messed up when the fault happens on
> IP=lwsync instead of IP=lwarx and I haven't really researched into why.

That's what you need to fix then :-)

I'm pretty sure that terminating the TB after the lwsync is not the correct 
solution, and is just hiding the real bug.

Paul