Re: [kvm-unit-tests PATCH v2 5/5] powerpc: Check lswx in little-endian mode.

[Laurent Vivier <lvivier@redhat.com>]

On 22/03/2016 09:12, Thomas Huth wrote:
> On 22.03.2016 00:56, David Gibson wrote:
>> On Mon, 21 Mar 2016 12:33:34 +0100
>> Laurent Vivier <lvivier@redhat.com> wrote:
>>
>>> For lswx in little-endian mode, an alignment interrupt occurs.
>>>
>>> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
>>> Reviewed-by: Thomas Huth <thuth@redhat.com>
>>
>> I'm not entirely clear here; will the test fail if the alignment
>> exception doesn't occur in little endian mode?
> 
> I think so, yes.
> 
>> The general trend in Power has been for less and less things to trigger
>> alignment exceptions, so failing to cause an alignment exception
>> shouldn't cause a test failure (as long as the unaligned case is
>> correctly processed, of course).
> 
> According to the PowerISA 2.07, chapter 6.5.8, lswx should always
> trigger an alignment exception in little endian mode. So that's
> architected behavior and the test should be OK, as far as I can see...
> In case this gets changed with a future CPU, I think the test could be
> adapted later, too?

Exactly.

Then in the kernel, the instruction is emulated. It's why I didn't
understand why this test case fails with kvm in little endian mode,
while is was working on a real host or in a guest.

Laurent