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Date:   Sun, 28 Apr 2019 09:56:35 +0800
From:   "Zhao, Yakui" <>
To:     Borislav Petkov <>
Cc:     Ingo Molnar <>,
        "" <>,
        "" <>,
        "" <>,
        "Chen, Jason CJ" <>
Subject: Re: [RFC PATCH v5 4/4] x86/acrn: Add hypercall for ACRN guest

On 2019年04月27日 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).


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