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Re: [Qemu-ppc] [PATCH 20/22] ppc: move load and store helpers, switch to

From: Blue Swirl
Subject: Re: [Qemu-ppc] [PATCH 20/22] ppc: move load and store helpers, switch to AREG0 free mode
Date: Tue, 1 May 2012 16:58:50 +0000

On Tue, May 1, 2012 at 14:25, Alexander Graf <address@hidden> wrote:
> On 01.05.2012, at 11:15, Blue Swirl <address@hidden> wrote:
>> On Mon, Apr 30, 2012 at 11:51, Alexander Graf <address@hidden> wrote:
>>> On 30.04.2012, at 12:45, Alexander Graf wrote:
>>>> On 22.04.2012, at 15:26, Blue Swirl wrote:
>>>>> Add an explicit CPUPPCState parameter instead of relying on AREG0
>>>>> and rename op_helper.c (which only contains load and store helpers)
>>>>> to mem_helper.c. Remove AREG0 swapping in
>>>>> tlb_fill().
>>>>> Switch to AREG0 free mode. Use cpu_ld{l,uw}_code in translation
>>>>> and interrupt handling, cpu_{ld,st}{l,uw}_data in loads and stores.
>>>> This patch breaks qemu-system-ppc64 on ppc32 host user space for me. I'm 
>>>> trying to debug it down, but worst case I'll omit this patch set for 1.1.
>>> Ok, so apparently nobody ever tested TCG_AREG0 mode with the ppc tcg 
>>> target. It looks as if the 64-bit-guest-registers-in-32-bit-host-registers 
>>> code path is missing completely.
>>> This actually makes me less confident that this is a change we want for 
>>> 1.1. I'll remove the patches from the queue.
>> Meh. It should be perfectly OK to apply all patches except the last
>> one which enables the AREG0 free mode.
> Yeah, that's what I did at first, but that still didn't get me into usable 
> user space inside a ppc64 guest. Right now I don't have the time to track 
> down if it's due to your patches and if so, why.

On second thought, I probably tested the set too lightly, so
'perfectly OK' was way too bold a claim.

>> Also the problem with last
>> patch is not in the patch itself but PPC TCG host support, which by
>> the way is probably also broken for AREG0 free Sparc and Alpha, so I'd
>> really like to see them in 1.1.
> I do agree on the first part. We need to make sure to test sparc and alpha 
> targets on unusual host platforms and fix them there. But why do we need to 
> also break ppc along the way?
>> There should be plenty of time to fix
>> bugs in PPC TCG support during the freeze.
> Since this is a non user visible feature (in fact, looking at the emitted asm 
> code it'll be more of a slowdown than anything), I'd rather like to keep 1.1 
> stable and get this into git right after the release split.
> It's really not going against your patches. In fact, I really do like them - 
> especially the cleanups. But this feature is pretty invasive and at least I 
> do run ppc-on-ppc tcg, so we should be able to hammer out all bugs until the 
> next release :). The whole AREG0 thing could also use some optimization 
> love...


> Alex

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