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Subject: Re: [RFC PATCH v5 4/4] x86/acrn: Add hypercall for ACRN guest
To:     Borislav Petkov <bp@alien8.de>
Cc:     Ingo Molnar <mingo@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "Chen, Jason CJ" <jason.cj.chen@intel.com>
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 <20190425070712.GA57256@gmail.com>
 <6dd021a9-e2c0-ee84-55fd-3e6dfb4bd944@intel.com>
 <20190425110025.GA16164@zn.tnic>
 <473d145c-4bfd-4ec8-34c3-8a26a78fe40d@intel.com>
 <20190427085816.GB12360@zn.tnic>
From:   "Zhao, Yakui" <yakui.zhao@intel.com>
Message-ID: <e04c43cf-029b-d459-e9d9-1a1f5c403dab@intel.com>
Date:   Sun, 28 Apr 2019 09:56:35 +0800
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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).


Thanks
     Yakui