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Re: [PATCH 1/9] x86: refine TPAUSE and UMWAIT
On 05.03.2020 16:37, H.J. Lu wrote:
> On Thu, Mar 5, 2020 at 7:22 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 05.03.2020 15:04, H.J. Lu wrote:
>>> On Thu, Mar 5, 2020 at 12:08 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>
>>>> On 04.03.2020 12:44, H.J. Lu wrote:
>>>>> On Wed, Mar 4, 2020 at 3:40 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>>> On 04.03.2020 12:36, H.J. Lu wrote:
>>>>>>> On Wed, Mar 4, 2020 at 1:37 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>>>>> Allowing 64-bit registers is misleading here: Elsewhere these get allowed
>>>>>>>> when there's no difference between either variant, because of 32-bit
>>>>>>>> destination registers having their upper halves zeroed in 64-bit mode.
>>>>>>>> Here, however, they're source registers, and hence specifying 64-bit
>>>>>>>> registers would lead to the ambiguity of whether the upper 32 bits
>>>>>>>> actually matter.
>>>>>>>>
>>>>>>>> Additionally, for proper code generation in 16-bit mode, IgnoreSize is
>>>>>>>> needed on both.
>>>>>>>
>>>>>>> Are there testcases to show IgnoreSize is needed on them?
>>>>>>
>>>>>> The situation with 16-bit test cases is rather poor anyway. I didn't
>>>>>> consider it reasonable to add such very special ones when far more
>>>>>> general ones don't exist. But if your question is to mean you demand
>>>>>
>>>>> Let's start from somewhere.
>>>>>
>>>>>> such to be added, then I'll (somewhat hesitantly) add/extend some.
>>>>>> Please clarify.
>>>>>
>>>>> Please add testcases.
>>>>
>>>> Actually they were there, in patch 2. I've moved them to this patch
>>>> and have just sent v1.1 for just this one patch.
>>>
>>> Do we need to adjust disassembler for 16-bit mode?
>>
>> I've checked now - no, we don't.
>>
>
> So disassembler has been correct. Is the bug only in assembler?
> What is the difference in encoding before and after your change?
UMWAIT gets a stray 66 prefix emitted, and TPAUSE fails to
assemble ("same type of prefix used twice").
Jan