linux-kernel - Re: [PATCH 1/2] ARM: copypage-fa: add kto and kfrom to input operands list

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Date:   Tue, 6 Nov 2018 13:16:24 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>,
        Stefan Agner <stefan@...er.ch>
Cc:     Arnd Bergmann <arnd@...db.de>, Roman Yeryomin <roman@...em.lv>,
        Linus Walleij <linus.walleij@...aro.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, Joel Stanley <joel@....id.au>,
        Hans Ulli Kroll <ulli.kroll@...glemail.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] ARM: copypage-fa: add kto and kfrom to input operands
 list

On 06/11/2018 04:49, Nicolas Pitre wrote:
[...]
>> r3 and r5 are not used above, so no need to have them in the clobber
>> list.
> 
> They are used. ldrd and strd instructions always use a pair of
> consecutive registers. So "ldrd r2, ..." loads into r2-r3 and "ldrd r4, ..."
> loads into r4-r5.

FWIW, since we should now be enabling unified syntax everywhere, I guess 
we could probably rewrite all those ldrd/strd to the UAL 3-operand form 
- i.e. "ldrd r2, r3, [...]" - if we really cared for the extra clarity.

Robin.