linux-kernel - Re: [tip: x86/cpu] x86/cpu: Use INVPCID mnemonic in invpcid.h

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Message-ID: <20200512162845.GC6859@zn.tnic>
Date:   Tue, 12 May 2020 18:28:45 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-tip-commits@...r.kernel.org,
        "H. Peter Anvin (Intel)" <hpa@...or.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>
Subject: Re: [tip: x86/cpu] x86/cpu: Use INVPCID mnemonic in invpcid.h

On Tue, May 12, 2020 at 05:54:49PM +0200, Uros Bizjak wrote:
> Symbolic operands are agnostic to the position in the asm clause, so
> it really doesn't matter much. It just doesn't feel right, when other
> cases follow different order.
> 
> > $ diff -suprN /tmp/before /tmp/after
> > Files /tmp/before and /tmp/after are identical
> 
> Sure, otherwise assembler would complain.
> 
> > Makes sense?
> 
> Well, I don't want to bikeshed around this anymore, so any way is good.

Look at it this way: the symbolic operand names feature has made inline
assembly *orders* of magnitude more readable than what it was before.
Kernel folks, including myself, have stumbled upon the question which
operand is which, on a regular basis and having the operand names there
makes reading the inline asm almost trivial.

So while we should not convert wholesale, I think we should aim to
gradually convert those other cases to the a-lot-more readable variant
with symbolic operand names.

Thx.

-- 
Regards/Gruss,
    Boris.

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