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

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Message-ID: <20190427085816.GB12360@zn.tnic>
Date:   Sat, 27 Apr 2019 10:58:16 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Zhao, Yakui" <yakui.zhao@...el.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Chen, Jason CJ" <jason.cj.chen@...el.com>
Subject: Re: [RFC PATCH v5 4/4] x86/acrn: Add hypercall for ACRN guest

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.

> 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?

-- 
Regards/Gruss,
    Boris.

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