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

From: Zhao, Yakui
Date: Sat Apr 27 2019 - 22:00:41 EST

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/


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).