Re: [PATCH v3] x86/emulate: Remove HAVE_AS_RDRAND and HAVE_AS_RDSEED

[Denis Mukhin <dmkhn@xxxxxxxxx>]

On Monday, April 7th, 2025 at 2:17 AM, Andrew Cooper 
<andrew.cooper3@xxxxxxxxxx> wrote:

> 
> 
> On 05/04/2025 2:25 am, dmkhn@xxxxxxxxx wrote:
> 
> > From: Denis Mukhin dmukhin@xxxxxxxx
> > 
> > The new toolchain baseline knows the rdrand/rdseed instructions,
> > no need to carry the workaround in the code.
> 
> 
> A few minor notes. Instructions in CAPITALS please to make them easier
> to parse in context. The comma ought to be a semi-colon.
> 
> You should note that arch_get_random() is adjusted too.
> 
> Also, it's useful to state "No functional change." to help reviewers.
> (Or to help archaeologies figure out the intent of the patch if they
> subsequently find a bug in it.)

Noted, thanks for the feedback

> 
> > diff --git a/xen/arch/x86/include/asm/random.h 
> > b/xen/arch/x86/include/asm/random.h
> > index 9e1fe0bc1d..e1c1c765e1 100644
> > --- a/xen/arch/x86/include/asm/random.h
> > +++ b/xen/arch/x86/include/asm/random.h
> > @@ -8,7 +8,7 @@ static inline unsigned int arch_get_random(void)
> > unsigned int val = 0;
> > 
> > if ( cpu_has(&current_cpu_data, X86_FEATURE_RDRAND) )
> > - asm volatile ( ".byte 0x0f,0xc7,0xf0" : "+a" (val) );
> > + asm volatile ( "rdrand %0" : "=a" (val) );
> 
> 
> This was only tied to "a" because 0xf0 is the ModRM byte. Now that we
> can use the mnemonic, it can become "=r".
> 
> I've fixed all on commit.

Thank you!

> 
> ~Andrew