linux-kernel - Re: [PATCH] ARM: makefile: pass -march=armv4 to assembler even on CPU32v3

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Message-ID: <CAHmME9q96VvYVkUUvq8CCihhs24AdJRRn_JMnJ42k2tyLK1WAQ@mail.gmail.com>
Date:   Tue, 2 Oct 2018 06:08:07 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>, arm@...nel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH] ARM: makefile: pass -march=armv4 to assembler even on CPU32v3

Hi Russell,

> On 1 October 2018 at 19:56, Russell King - ARM Linux <linux@...linux.org.uk> wrote:
> We could argue that the ARMv3 assembly files are now stable, so the
> chances of ldrh/strh being introduced is low, which would make this
> change tolerable, but the commit message needs to spell out that
> we lose this protection.

Actually I don't think that argument really holds too well. We very
well could introduce some new ARMv4 assembly -- an optimized crypto
routine, for example -- and it could use ldrh/strh. That isn't the
case now, but it might be the case later. For that reason, I suspect
the proper solution is just not building new cryptography assembly
that's written for ARMv4 in mind on CPU_32v3 systems. This way there's
never a mismatch of expectations.

Jason