Re: [PATCH v2] hvf: guard xgetbv call.

[Roman Bolshakov]

On Mon, Jan 11, 2021 at 09:44:40PM -0800, Hill Ma wrote:
> On Sun, Jan 10, 2021 at 8:38 PM Roman Bolshakov <r.bolshakov@yadro.com> wrote:
> > I'm not sure if eax should be modified with mask because the mask has no
> > value per se. I.e. eax &= supp_xcr0 from below should be placed inside
> > the if. It'd express clearly that eax is not modified unless xgetbv is
> > supported.
> 
> Like this?
> 
> -            uint64_t host_xcr0 = xgetbv(0);
> -            uint64_t supp_xcr0 = host_xcr0 & (XSTATE_FP_MASK |
> XSTATE_SSE_MASK |
> +            uint64_t host_xcr0;
> +            if (xgetbv(ecx, 0, &host_xcr0)) {
> +                uint64_t supp_xcr0 = host_xcr0 & (XSTATE_FP_MASK |
> XSTATE_SSE_MASK |
>                                    XSTATE_YMM_MASK | XSTATE_BNDREGS_MASK |
>                                    XSTATE_BNDCSR_MASK | XSTATE_OPMASK_MASK |
>                                    XSTATE_ZMM_Hi256_MASK |
> XSTATE_Hi16_ZMM_MASK);
> -            eax &= supp_xcr0;
> +                eax &= supp_xcr0;
> +            }

Yes.

Thanks,
Roman