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Date: Tue, 02 Sep 2014 09:07:22 +0200
From: Christian Borntraeger <borntraeger@de.ibm.com>
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Subject: Re: [Qemu-devel] [PATCH 1/5] s390x/gdb: don't touch the cc if tcg
	is not enabled
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To: Alexander Graf <agraf@suse.de>, Jens Freimann <jfrei@linux.vnet.ibm.com>, Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: David Hildenbrand <dahi@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On 02/09/14 00:39, Alexander Graf wrote:
> 
> 
> On 29.08.14 15:52, Jens Freimann wrote:
>> From: David Hildenbrand <dahi@linux.vnet.ibm.com>
>>
>> When reading/writing the psw mask, the condition code may only be touched if
>> running on tcg.
> 
> Why? Shouldn't we be able to set CC from gdb as well?
> 

You can. What this patch does (and the patch description is a bit vague here) is to not modify the PSW it gets from KVM when passing it to gdb:
The qemu core gets the PSW from KVM. Without this patch, we use cc_op to calculate the current CC of the PSW (No idea of TCG, I guess its evaluated lazy - at least this is how valgrind works). This is wrong for the KVM case, as cc_op does not contain any useful data for the KVM case. With this patch we simply pass the psw from KVM to gdb and back.

The symptom was that the cc was always shown as zero.

Christian