Re: [Qemu-devel] [Qemu-ppc] [PATCH 47/58] Implement POWER7's CFAR in TCG

[Alexander Graf]

Am 19.09.2011 um 08:00 schrieb David Gibson <address@hidden>:

> On Sat, Sep 17, 2011 at 05:08:29PM +0000, Blue Swirl wrote:
>> On Wed, Sep 14, 2011 at 8:43 AM, Alexander Graf <address@hidden> wrote:
>>> From: David Gibson <address@hidden>
>>> 
>>> This patch implements support for the CFAR SPR on POWER7 (Come From
>>> Address Register), which snapshots the PC value at the time of a branch or
>>> an rfid.  The latest powerpc-next kernel also catches it and can show it in
>>> xmon or in the signal frames.
>>> 
>>> This works well enough to let recent kernels boot (which otherwise oops
>>> on the CFAR access).  It hasn't been tested enough to be confident that the
>>> CFAR values are actually accurate, but one thing at a time.
>> 
>> This looks accurate at least for the cases covered.
>> 
>> A higher performance implementation could be to only update the
>> register lazily when the SPR is read, in most other times CFAR would
>> be only stored to DisasContext.
> 
> Uh, yeah.  I think I'll leave that to someone who actually understands
> TCG, rather than just bluffing it.

CFAR is only written on branches at which point we'd have to flush everything 
from disascontext to env anyways :). So putting it there doesn't buy us 
anything.

Alex