linux-kernel - Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces

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Date:   Mon, 2 Nov 2020 18:19:50 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     shuo.a.liu@...el.com, linux-kernel@...r.kernel.org, x86@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yu Wang <yu1.wang@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Yakui Zhao <yakui.zhao@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fengwei Yin <fengwei.yin@...el.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Peter Zijlstra <peterz@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces

On Mon, Nov 02, 2020 at 10:09:01AM -0600, Segher Boessenkool wrote:
> I think that will work for x86_64.  But it won't matter much, most of
> the time you give an immediate number.

Yeah, my question is more along the lines of "is this constraint somehow
special, i.e., 'ir' (and not 'm') or can it be whatever, i.e., 'g'"?

> It is a tiny bit neater of course (if anyone still remembers what "g"
> is, you cannot use it much these days).

Oh I always remember what it is because it is right there in the docs:

"6.47.3.1 Simple Constraints

...

‘g’	Any register, memory or immediate integer operand is allowed,
	except for registers that are not general registers."

;-)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette