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Date:   Tue, 1 Dec 2020 09:20:27 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Naresh Kamboju <naresh.kamboju@linaro.org>,
        linux-stable <stable@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        lkft-triage@lists.linaro.org, Sasha Levin <sashal@kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        x86@vger.kernel.org, Matthias Kaehlcke <mka@chromium.org>
Subject: Re: [stable 4.9] PANIC: double fault, error_code: 0x0 - clang boot
 failed on x86_64
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On Mon, Nov 30, 2020 at 12:12:39PM -0800, Nick Desaulniers wrote:
> On Wed, Nov 25, 2020 at 10:38 PM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > Is the mainline 4.9 tree supposed to work with clang?  I didn't think
> > that upstream effort started until 4.19 or so.
> 
> (For historical records, separate from the initial bug report that
> started this thread)
> 
> I consider 785f11aa595b ("kbuild: Add better clang cross build
> support") to be the starting point of a renewed effort to upstream
> clang support. 785f11aa595b landed in v4.12-rc1.  I think most patches
> landed between there and 4.15 (would have been my guess).  From there,
> support was backported to 4.14, 4.9, and 4.4 for x86_64 and aarch64.
> We still have CI coverage of those branches+arches with Clang today.
> Pixel 2 shipped with 4.4+clang, Pixel 3 and 3a with 4.9+clang, Pixel 4
> and 4a with 4.14+clang.  CrOS has also shipped clang built kernels
> since 4.4+.

Thanks for the info.  Naresh, does this help explain why maybe testing
these kernel branches with clang might not be the best thing to do?

greg k-h