linux-kernel - Re: [PATCH] compiler-clang: add build check for clang 10.0.1

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Message-ID: <CAKwvOdkTN4BbVvwh8MPrVXERdHjQusmp9yAo09uW=698_fi0Fg@mail.gmail.com>
Date:   Mon, 31 Aug 2020 16:32:02 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] compiler-clang: add build check for clang 10.0.1

On Wed, Aug 26, 2020 at 2:42 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Wed, Aug 26, 2020 at 01:14:19PM -0700, Nick Desaulniers wrote:
> > During Plumbers 2020, we voted to just support the latest release of
> > Clang for now.  Add a compile time check for this.
> >
> > Older clang's may work, but we will likely drop workarounds for older
> > versions.
>
> I think this part of the commit message is a little wishy-washy. If we

Yep, you're right. I'm still in denial. Let me rip that bandaid off
and send a v2, with your and Kees' suggestions.

Sorry, the docs patch already got picked up. Let's follow up with
additional patches to docs separately.

> are breaking the build for clang < 10.0.1, we are not saying "may work",
> we are saying "won't work". Because of this, we should take the
> opportunity to clean up behind us and revert/remove parts of:
>
> 87e0d4f0f37f ("kbuild: disable clang's default use of -fmerge-all-constants")
> b0fe66cf0950 ("ARM: 8905/1: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer")
> b9249cba25a5 ("arm64: bti: Require clang >= 10.0.1 for in-kernel BTI support")
> 3acf4be23528 ("arm64: vdso: Fix compilation with clang older than 8")

I'd prefer to see this land in mainline first; otherwise, I'm worried
about this patch "racing" to mainline with those patches if they go
via separate trees.  Thoughts?
-- 
Thanks,
~Nick Desaulniers