linux-kernel - Re: [PATCH net-next v6 07/23] zinc: ChaCha20 ARM and ARM64 implementations

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Date:   Sun, 30 Sep 2018 04:33:20 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Neves <sneves@....uc.pt>,
        Andrew Lutomirski <luto@...nel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next v6 07/23] zinc: ChaCha20 ARM and ARM64 implementations

Hi Ard,

On Sat, Sep 29, 2018 at 8:16 AM Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> > You mean to say that since these nobs are def_bool y and are
> > essentially "depends on ARM", then I should just straight up use
> > CONFIG_ARM? I had thought about this, but figured this would make it
> > easier to later make these optional or have other options block them
> > need be, or even if the dependencies and requirements for having them
> > changes (for example, with UML on x86). I think doing it this way
> > gives us some flexibility later on. So if that's a compelling enough
> > reason, I'd like to keep those.
>
> Sure. But probably better to be consistent then, and stop using
> CONFIG_ARM directly in your code.

Ack.

> > The reason it was added was indeed because of:
> > https://lists.01.org/pipermail/kbuild-all/2018-September/053114.html
> > -- exactly what you suspected, ARCH_RPC. Have a better suggestion than
> > !CPU_32v3?
>
> Yes, you could just add
>
> asflags-$(CONFIG_CPU_32v3) += -march=armv4
>
> with a comment stating that we don't actually support ARMv3 but only
> use it as a code generation target for reasons unrelated to the ISA

Alright, I'll do exactly that. Though, if the rationale for this has
to do only with codegen -- with what the C compiler does -- then
shouldn't this be set globally for CONFIG_CPU_32v3? I couldn't find
any macros that test against __LINUX_ARM_ARCH__ being 3 in the
assembly, so this shouldn't be a problem I don't think. Maybe I'll
send a patch.

Jason