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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 13 Jan 2021 18:05:32 -0800
Message-ID: <CAKwvOdmr7RttdM25wWKiV8t+tzn8W-C_U6avwrQXQWphT8XhXQ@mail.gmail.com>
Subject: Re: [PATCH] Documentation/llvm: Add a section about supported architectures
To:     Nathan Chancellor <natechancellor@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Miguel Ojeda <ojeda@kernel.org>
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On Wed, Jan 13, 2021 at 5:19 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> Patch looks fine, but `make -j htmldocs` seems to be taking forever
> for me so I can't render it. Is this a known issue?
>
> $ make -j htmldocs

Just took a while, lots of warning spew (but not from this addition AFAICT).
Reviewed-by: Nick Desaulniers <ndesaulnier@google.com>

>
> On Wed, Jan 13, 2021 at 4:35 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > The most common question around building the Linux kernel with clang is
> > "does it work?" and the answer has always been "it depends on your
> > architecture, configuration, and LLVM version" with no hard answers for
> > users wanting to experiment. LLVM support has significantly improved
> > over the past couple of years, resulting in more architectures and
> > configurations supported, and continuous integration has made it easier
> > to see what works and what does not.
> >
> > Add a section that goes over what architectures are supported in the
> > current kernel version, how they should be built (with just clang or the
> > LLVM utilities as well), and the level of support they receive. This
> > will make it easier for people to try out building their kernel with
> > LLVM and reporting issues that come about from it.
> >
> > Suggested-by: Miguel Ojeda <ojeda@kernel.org>
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >  Documentation/kbuild/llvm.rst | 44 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> >
> > diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> > index 21c847890d03..b18401d2ba82 100644
> > --- a/Documentation/kbuild/llvm.rst
> > +++ b/Documentation/kbuild/llvm.rst
> > @@ -63,6 +63,50 @@ They can be enabled individually. The full list of the parameters: ::
> >  Currently, the integrated assembler is disabled by default. You can pass
> >  ``LLVM_IAS=1`` to enable it.
> >
> > +Supported Architectures
> > +-----------------------
> > +
> > +LLVM does not target all of the architectures that Linux supports and
> > +just because a target is supported in LLVM does not mean that the kernel
> > +will build or work without any issues. Below is a general summary of
> > +architectures that currently work with ``CC=clang`` or ``LLVM=1``. Level
> > +of support corresponds to "S" values in the MAINTAINERS files. If an
> > +architecture is not present, it either means that LLVM does not target
> > +it or there are known issues. Using the latest stable version of LLVM or
> > +even the development tree will generally yield the best results.
> > +An architecture's ``defconfig`` is generally expected to work well,
> > +certain configurations may have problems that have not been uncovered
> > +yet. Bug reports are always welcome at the issue tracker below!
> > +
> > +.. list-table::
> > +   :widths: 10 10 10
> > +   :header-rows: 1
> > +
> > +   * - Architecture
> > +     - Level of support
> > +     - ``make`` command
> > +   * - arm
> > +     - Supported
> > +     - ``LLVM=1``
> > +   * - arm64
> > +     - Supported
> > +     - ``LLVM=1``
> > +   * - mips
> > +     - Maintained
> > +     - ``CC=clang``
> > +   * - powerpc
> > +     - Maintained
> > +     - ``CC=clang``
> > +   * - riscv
> > +     - Maintained
> > +     - ``CC=clang``
> > +   * - s390
> > +     - Maintained
> > +     - ``CC=clang``
> > +   * - x86
> > +     - Supported
> > +     - ``LLVM=1``
> > +
> >  Getting Help
> >  ------------
> >
> >
> > base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837
> > --
> > 2.30.0
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers


-- 
Thanks,
~Nick Desaulniers