Re: [RFC PATCH v5 4/4] x86/acrn: Add hypercall for ACRN guest

[Zhao, Yakui]

On 2019å04æ27æ 16:58, Borislav Petkov wrote:
> On Fri, Apr 26, 2019 at 11:18:48AM +0800, Zhao, Yakui wrote:
> > It seems that it is seldom used in kernel although the explicit register
> > variable is supported by GCC and makes the code look simpler. And it seems
> > that the explicit register variable is not suppoorted by CLAG.
>
> The more reason not to do it this way. Also, the "register" variable
> specification is not very widespread in x86 when you look at
>
> $ git grep -E "register\s.*asm" arch/x86/
>
> output.

Yes.  The explicit register variable is not very videspread for arch/x86.
So the register variable will be removed for ACRN hypercall.

> > So the explicit register variable will be removed. I will follow the asm
> > code from Borislav. Of course one minor change is that the "movq" is used
> > instead of "mov".
>
> Does that matter if your destination register is 64-bit?

Thanks for the reminder about the access width.
It is 64-bit register. What I said is the "movq", not "movl".
(I understand that movl is incorrect for 64-bit register).


Thanks
    Yakui