Re: [PATCH] hvf: guard xgetbv call.

[Richard Henderson]

On 1/9/21 3:46 PM, Roman Bolshakov wrote:
> +static int xgetbv(uint32_t cpuid_ecx, uint32_t idx, uint64_t *xcr)
>  {
> -    uint32_t eax, edx;
> +    uint32_t xcrl, xcrh;
> 
> -    __asm__ volatile ("xgetbv"
> -                      : "=a" (eax), "=d" (edx)
> -                      : "c" (xcr));
> +    if (cpuid_ecx && CPUID_EXT_OSXSAVE) {
> +        /* The xgetbv instruction is not available to older versions of
> +         * the assembler, so we encode the instruction manually.
> +         */
> +        asm(".byte 0x0f, 0x01, 0xd0" : "=a" (xcrl), "=d" (xcrh) : "c" (idx));
> 
> -    return (((uint64_t)edx) << 32) | eax;
> +        *xcr = (((uint64_t)xcrh) << 32) | xcrl;
> +        return 0;
> +    }
> +
> +    return 1;
>  }

Not to bikeshed too much, but this looks like it should return bool, and true
on success, not the other way around.


r~