linux-kernel - Re: [PATCH] arm64/neon: Disable -Wincompatible-pointer-types when building with Clang

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Date:   Tue, 19 Feb 2019 12:35:16 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Will Deacon <will.deacon@....com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Brown <broonie@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kevin Hilman <khilman@...libre.com>,
        Sandeep Patil <sspatil@...gle.com>
Subject: Re: [PATCH] arm64/neon: Disable -Wincompatible-pointer-types when
 building with Clang

On Tue, 19 Feb 2019 at 12:19, Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Tue, Feb 19, 2019 at 11:35:12AM +0100, Ard Biesheuvel wrote:
> > On Fri, 15 Feb 2019 at 20:45, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
> > >
> > > On Fri, 15 Feb 2019 at 20:43, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> > > >
> > > > On Fri, Feb 15, 2019 at 11:28 AM Ard Biesheuvel
> > > > <ard.biesheuvel@...aro.org> wrote:
> > > > >
> > > > > On Fri, 15 Feb 2019 at 20:25, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> > > > > >
> > > > > > On Fri, Feb 15, 2019 at 11:20 AM Ard Biesheuvel
> > > > > > <ard.biesheuvel@...aro.org> wrote:
> > > > > > > Provided that we stop sending Clang enablement patches to -stable:
> > > > > >
> > > > > > What does that mean?  We're trying to provide clang support back to
> > > > > > 4.4 LTS branches. (so 4.4, 4.9, 4.14, 4.19).
> > > > >
> > > > > I understand that is what you are attempting, but that does not mean
> > > > > it /belongs/ in -stable.
> > > > >
> > > > > There are rules for stable, and people that track stable kernels (such
> > > > > as the distros) should be able to rely on us to only backport bug
> > > > > fixes, not linker script changes and other updates that fix issues
> > > > > that did not exist when those kernels were released.
> > > > >
> > > > > It is unclear to me how these clang changes benefit those users.
> > > >
> > > > If you're referring to
> > > > https://www.spinics.net/lists/stable/msg278381.html, that's fair (I
> > > > think those were helpful for LLD support on arm64).
> > > >
> > > > Why didn't you speak up then?  Why is this coming up now?
> > >
> > > That is just one example, and I failed to realise it at the time.
> > >
> > > I think the Clang/LLVM work you are doing is very important, but I
> > > simply don't think any of it belongs in -stable kernels.
> >
> > OK, to clarify my position:
> >
> > I have no problem whatsoever with taking this patch into v5.x, so
> >
> > Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> >
> > but going forward, I will push back on -stable backports for
> > Clang/LLVM specific changes, since they are obviously in violation of
> > the stable kernel rules.
>
> Getting older kernels to build/run properly on newer compilers is just a
> part of life for the stable trees.  If you note, we have done a lot of
> gcc7, then gcc8, and clang patches backported over the years in order to
> make it possible for people (like me and my testing infrastructure at
> the least) to keep building these old kernels on newer systems.
>
> So while it's not part of the "documented" rules, I do take this type of
> change, as it does help out a huge population of users and testers.
>

That doesn't make a lot of sense to me, but that is the common
practice, then I won't object any longer.