linux-kernel - RE: [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper for general usage

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Message-ID: <ba7e555d0dea42eb97d8b08df69b3191@AcuMS.aculab.com>
Date:   Thu, 24 Sep 2020 11:25:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Borislav Petkov' <bp@...en8.de>
CC:     Michael Matz <matz@...e.de>, 'Dave Jiang' <dave.jiang@...el.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "jing.lin@...el.com" <jing.lin@...el.com>,
        "ashok.raj@...el.com" <ashok.raj@...el.com>,
        "sanjay.k.kumar@...el.com" <sanjay.k.kumar@...el.com>,
        "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
        "kevin.tian@...el.com" <kevin.tian@...el.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5 1/5] x86/asm: Carve out a generic movdir64b() helper
 for general usage

> > No, that just says the asm uses the value of the pointer.
> > Not what it points to.
> 
> Err, no, it is *exactly* what it points to that is important here and
> you're telling the compiler that the instruction will read that much
> memory through the pointer.

You need to use an "m" constraint for that.
A 'register' constraint just requires the value of the address
to be valid.

Look at the asm output from the example code I posted.

	David

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