[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH] target-ppc: Multiple/String Word alignment exce

From: Laurent Vivier
Subject: Re: [Qemu-devel] [PATCH] target-ppc: Multiple/String Word alignment exception
Date: Thu, 31 Mar 2016 09:39:41 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1

On 31/03/2016 09:15, Alexander Graf wrote:
> On 31.03.16 09:06, Laurent Vivier wrote:
>> On 31/03/2016 08:54, Alexander Graf wrote:
>>> On 31.03.16 01:29, David Gibson wrote:
>>>> On Wed, 30 Mar 2016 19:13:00 +0200
>>>> Laurent Vivier <address@hidden> wrote:
>>>>> If the processor is in little-endian mode, an alignment interrupt must
>>>>> occur for the following instructions: lmw, stmw, lswi, lswx, stswi or 
>>>>> stswx.
>>>>> This is what happens with KVM, so change TCG to do the same.
>>>>> As the instruction can be emulated by the kernel, enable the change
>>>>> only in softmmu mode.
>>>>> Signed-off-by: Laurent Vivier <address@hidden>
>>>> I guess this makes sense given the existing hardware behaviour, even
>>>> though it seems a bit perverse to me to make the emulator strictly less
>>>> functional.
>>>> Alex, what do you think?
>>> In general we only implement strict checks if it breaks guests not to
>>> have them. Are you aware of any such case?
>> No, it does not break anything. The idea was to have the same behavior
>> with TCG as with a real CPU (or kvm). But if it is not the rule, we can
>> drop this patch.
> I guess if you really care about same behavior, we'd need to have risu
> ported to ppc. However, that's a huge can of worms. Once we start that,
> we'd have to verify risu against every single CPU type we support
> because they all interpret certain corner cases differently.

I didn't know risu: it seems to be a wonderful tool!
> That's basically what David was trying to say with POWER9. How do you
> know that POWER9 still requires strong alignment checks for indexed LE
> instructions? If it doesn't, we'd have to add a case in TCG to not the
> the checks again. These multiply very quickly :).

I understand. So just forget this patch :)


reply via email to

[Prev in Thread] Current Thread [Next in Thread]