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

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Message-ID: <CAHmME9rVbKCNJfVBEene0SvhBEm_g7N-XJ26ugoAab1Vj7G_ww@mail.gmail.com>
Date:   Tue, 2 Oct 2018 05:53:26 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        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 Arnd,

Apologies for the delay in getting back to you. I had some MTA issues
and stupidly assumed ARM developers were taking the day off instead...

On Tue, Oct 2, 2018 at 5:33 AM Arnd Bergmann <arnd@...db.de> wrote:
> -arch-$(CONFIG_CPU_32v3)                =-D__LINUX_ARM_ARCH__=3 -march=armv3
> +arch-$(CONFIG_CPU_32v3)                =-D__LINUX_ARM_ARCH__=3 -march=armv3m

Unfortunately this doesn't really cut it in my case, as it's not only
those multiplications:
chacha20-arm.S:402: Error: selected processor does not support `bxeq
lr' in ARM mode

I think we're going to wind up playing whack-a-mole in silly ways. The
fact of the matter is that the ARM assembly I'm adding to the tree is
for ARMv4 and up, and not for ARMv3.

I think there are three options to work around this issue:

1) Not build my assembly when CONFIG_CPU_32v3 via a Kconfig "depends".
2) Set asflags-$(CONFIG_CPU_32v3) inside my module locally to select
-march=armv4.
3) This patch.

My initial plan was (1). ArdB recommended I do (2) instead. I thought
that was a bit too nuanced and submitted (3).

It sounds like in light of the bus issues, (1) might be the best
solution after all?

Let me know, and I'll follow your direction.

Regards,
Jason