[PATCH 1/9] x86: refine TPAUSE and UMWAIT

[H.J. Lu]

On Thu, Mar 5, 2020 at 6:51 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 05.03.2020 15:37, H.J. Lu wrote:
> > On Thu, Mar 5, 2020 at 6:08 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 haven't checked, but (a) this would be an independent change
> >> and (b) it would likely affect more than just the insns here
> >> (see e.g. other parts of the series).
> >
> > Disassembler should be adjusted when IgnoreSize is added
> > to tpause and umwait.
>
> But IgnoreSize has nothing to do with the disassembler. Right
> now all I'm after is getting the assembler to produce correct
> code. There are test cases to verify this is the case. Whether
> the disassembler deals with any of this correctly (including
> also the insns getting IgnoreSize added by "x86: add missing
> IgnoreSize", which you've already approved) is an entirely
> separate topic, which I may be willing to look into down the
> road, but not now and here.
>
> More generally, when anyone fixes one bug, why should they get
> penalized to have their bug fix accepted only when they take
> the - perhaps significant amount of - time to also fix another,
> unrelated bug? In the case here, it is definitely not my fault
> if 16-bit handling is in a bad state. And I can't afford fixing
> all issues there are in one go.
>

Then don't add IgnoreSize to tpause and umwait for now.

-- 
H.J.