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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 16:44:30 +0000
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To: qemu-devel@nongnu.org
Cc: blauwirbel@gmail.com, Alexander Graf <alex@csgraf.de>, Alexander Graf <agraf@suse.de>

> If anyone knows how to really fix this, please step forward and do
> so. This only makes things work at all for me :-).

I bet lwsync being a nop is a clue.

When an MMU exception occurs, qemu figures out the guest location from the 
location of the MMU access in guest code (see cpu_restore_state). My guess is 
that this breaks when two guest instructions have the same location. I'm not 
entirely sure what the correct fix is, or where the bug lies 
(cpu_restore_state,  gen_intermediate_code_pc, or tcg_gen_code_search_pc) but 
hopefully this will point you in the right direction.

One thing to try (to confirm this theory) is make lwsync do domething (write 
to a dummy register or call a helper function) and see if the problem goes 
away.

Paul