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

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Message-ID: <CAHmME9ocfHx2BxCqor-hg0ida6mS7x9M3RU2rZdoaxk=s9bHTQ@mail.gmail.com>
Date:   Tue, 2 Oct 2018 05:56:47 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>, arm@...nel.org
Subject: Re: [PATCH] ARM: makefile: pass -march=armv4 to assembler even on CPU32v3

Hi Ard,

On Tue, Oct 2, 2018 at 5:54 AM Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
> So Arnd's suggestion to switch to armv3-m would actually be feasible
> then? The code in question does not use ldrh only umull, and so it
> should build with armv3m as well. And we will even generate some
> better code for RiscPC if we apply it to both the cflags and the
> asflags.

It turns out armv3m isn't a solution for the crypto code, since it
does other armv4-isms. So we'll need to find another solution for
that; I'm partial to my initial Kconfig one just doing "depends
!CPU_32V3".

With regards to RiscPC though, given that armv3 codegen might be
better, it sounds like it's a good idea to set -march=armv3m anyway
for the platform, irrespective of fixing the problem at hand here.

Regards,
Jason