Re: [Xen-devel] [PATCH v6 2/5] x86/hvm: Replace architecture TSC scaling by a common function

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.02.16 at 13:54, <haozhong.zhang@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -333,6 +333,23 @@ u64 hvm_get_tsc_scaling_ratio(u32 gtsc_khz)
>      return ratio > max_ratio ? 0 : ratio;
>  }
>  
> +u64 hvm_scale_tsc(const struct domain *d, u64 tsc)
> +{
> +    u64 ratio = d->arch.hvm_domain.tsc_scaling_ratio;
> +    u64 dummy;
> +
> +    if ( ratio == hvm_default_tsc_scaling_ratio )
> +        return tsc;
> +
> +    /* tsc = (tsc * ratio) >> hvm_funcs.tsc_scaling.ratio_frac_bits */
> +    asm ( "mulq %[ratio]; shrdq %[frac],%%rdx,%[tsc]"
> +          : [tsc] "+a" (tsc), "=d" (dummy)

Is mixing named and positional asm() operands supported by all
gcc versions we care about? Also strictly speaking "=d" needs
to be switched to "=&d".

Jan


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