Re: [PATCH] linux-user/elfload: Add missing arm64 hwcap values

[Peter Maydell]

On Tue, 31 Oct 2023 at 09:23, Marielle Novastrider
<marielle@novastrider.com> wrote:
>
>
>
> > On 31 Oct 2023, at 00:56, Marielle Novastrider <marielle@novastrider.com> 
> > wrote:
> >
> >> On 30 Oct 2023, at 09:52, Peter Maydell <peter.maydell@linaro.org> wrote:
> >>
> >> ...but we don't implement FEAT_MTE3 yet. We would add this feature test
> >> function, and the GET_FEATURE_ID() line, when we do, but we don't
> >> need it until then.
> >
> > Understood.
> >
> > I made this patch as I noticed the discrepancy between cpuid and hwcap 
> > output.
> >
> > The following code produces the value of 3 on current master, which would 
> > be erroneous if FEAT_MT3 is unimplemented:
> >
> > #include <stdint.h>
> > #include <stdio.h>
> >
> > int main() {
> >    uint64_t aa64pfr1;
> >    __asm__("mrs %0, s3_0_c0_c4_1" : "=r"(aa64pfr1));
> >    std::printf("%lu\n", (aa64pfr1 >> 8) & 0xf);
> >    return 0;
> > }
> >
> > I can submit another patch to correct this.

> I note that commit 86f0d4c7290eb2b21ec3eb44956ec245441275db suggests that 
> FEAT_MTE3 is already implemented.

I'm sorry, you're right -- we have implemented MTE3. I was
confused by the lack of an existing feature test function for
it, but we didn't need the feature test because FEAT_MTE3 only
added behaviour to previously-reserved values of the TCF field,
so we allowed our behaviour on non-FEAT_MTE3 CPUs to be
"happens to behave like FEAT_MTE3".

Your patch as it stands is correct, and I've applied it to
target-arm.next. (There's a trivial conflict as a change has
just landed which moves all the feature test functions to
their own header, but I have fixed that up while applying.)

Thanks for the patch!

-- PMM