Re: [Qemu-devel] [PULL 5/8] target-sparc: Use global registers for the register window

From: Richard Henderson <rth@twiddle.net>
To: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PULL 5/8] target-sparc: Use global registers for the register window
Date: Thu, 23 Jun 2016 20:57:39 -0700	[thread overview]
Message-ID: <65a57d82-174f-cc1c-d613-984bffce13d3@twiddle.net> (raw)
In-Reply-To: <57631FC9.1040303@ilande.co.uk>

On 06/16/2016 02:53 PM, Mark Cave-Ayland wrote:
> On 16/06/16 21:26, Richard Henderson wrote:
>
>> On 06/14/2016 02:52 PM, Mark Cave-Ayland wrote:
>>> Following up the bug report at
>>> https://bugs.launchpad.net/qemu/+bug/1588328, I bisected the regression
>>> down to this particular commit. I can't see anything obvious here, so
>>> perhaps this is exposing another bug somewhere else?
>>>
>>
>> Probably.  I'm downloading the solaris image now.
>>
>>
>> r~
>
> Thanks for taking a look - otherwise I won't be able to get to this
> until next week. My thinking was that since the code makes access to
> regwptr direct instead of copied into a temporary, something is
> accidentally clobbering a destination register...

I've been unable to find this.

Whatever happens, it happens after 10GB of logs, which is simply too much to 
sift through.  I've tried to narrow it down, but the lack of a hardware tlb 
refill means that we get hundreds of thousands of Data Access Faults that are 
simply TLB misses and not the actual Segmentation Fault in question.

It doesn't seem to affect other OSes, so I can't imagine what quirk is being 
exercised in this case.

As loath as I am to suggest it, we may have to revert the sparc indirect 
register patch for the release.

I do now ping the rest of my sparc improvements patchset.  It's completely 
independent of the use of indirect registers.

r~