linux-kernel - Re: [PATCH] ARM: xor-neon: Replace __GNUC__ checks with CONFIG_CC_IS

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Date:   Fri, 31 May 2019 17:28:58 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>,
        Stefan Agner <stefan@...er.ch>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] ARM: xor-neon: Replace __GNUC__ checks with
 CONFIG_CC_IS_GCC

On Fri, May 31, 2019 at 11:03:19PM +0200, Arnd Bergmann wrote:
> On Fri, May 31, 2019 at 10:06 PM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@...glegroups.com> wrote:
> >
> > On Fri, May 31, 2019 at 12:21 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > clang, I would suggest dropping your patch then, and instead adding
> >
> > I disagree.  The minimum version of gcc required to build the kernel
> > is 4.6, so the comment about older versions of gcc is irrelevant and
> > should be removed.
> 
> Sure, that's ok. It just feels wrong to remove a warning that points
> to a real problem that still exists and can be detected at the moment.
> 
> If we think that clang-9 is going to be fixed before its release,
> the warning could be changed to test for that version as a minimum,
> and point to the bugzilla entry for more details.
> 
>       Arnd

I just tested the arm64 implementation and it shows the same warnings
about cost as arm.

However, I see a warning as something that can be resolved by the user.
The GCC warning's solution is to just use a newer version of GCC
(something fairly easily attainable). This new warning currently has no
solution other than don't use clang.

It is up to you and Nick but I would say unless we are going to
prioritize fixing this, we shouldn't add a warning for it. I'd say it is
more appropriate to fix it then add a warning saying upgrade to this
version to fix it, like the GCC one (though I don't necessarily hate
adding the warning assuming that clang 9 will have it fixed).

Cheers,
Nathan