Re: [Qemu-devel] [Qemu-ppc] [PATCH v2 5/6] target-ppc: implement xxextractuw instruction

[Nikunj A Dadhania]

David Gibson <address@hidden> writes:

> [ Unknown signature status ]
> On Mon, Dec 12, 2016 at 09:31:11AM +0530, Nikunj Dadhania wrote:
>> On 12 December 2016 at 06:00, David Gibson <address@hidden> wrote:
>> > On Fri, Dec 09, 2016 at 05:47:24PM +0530, Nikunj A Dadhania wrote:
>> >> xxextractuw: VSX Vector Extract Unsigned Word
>> >>
>> >> Signed-off-by: Nikunj A Dadhania <address@hidden>
>> >> +        tcg_gen_movi_i64(cpu_vsrh(xT(ctx->opcode)), 0);         \
>> >> +        tcg_gen_movi_i64(cpu_vsrl(xT(ctx->opcode)), 0);         \
>> >> +        return;                                                 \
>> >
>> > So, I know the architecture says it is undefined.  But since you're
>> > testing for the bogus case anyway, why not turn this into an
>> > exception. That seems like it would be more helpful for debugging the
>> > guest than just setting the result to zero.  Or is this done to match
>> > actual hardware behaviour?
>> 
>> I havent had a change to run on the real hardware, but on the system
>> simulator, it happily
>> returns extracted content even if UIMM > 12.
>
> Hm.  Returns what exactly?

So for LE case extracting from 15 returns following, basically its
rounding up to 0.

xxextractuw: 15 - ooTSET a si sihT
                  ________ihTo____

Regards,
Nikunj