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References: <20210114003447.7363-1-natechancellor@gmail.com>
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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 13 Jan 2021 17:19:59 -0800
Message-ID: <CAKwvOdnJ0VUjTX-cyLgtHvy68DHG1VMj7s0huk_FKh1E9pH9Cg@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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Precedence: bulk

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
  SPHINX  htmldocs --> file:///android0/linux-next/Documentation/output
make[2]: Nothing to be done for 'html'.
WARNING: The kernel documentation build process
        support for Sphinx v3.0 and above is brand new. Be prepared for
        possible issues in the generated output.
        Warning: The Sphinx 'sphinx_rtd_theme' HTML theme was not
found. Make sure you have the theme installed to produce pretty HTML
output. Falling back to the default theme.
enabling CJK for LaTeX builder
./drivers/usb/dwc3/core.h:1259: warning: Function parameter or member
'gadget_max_speed' not described in 'dwc3'
./drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h:340: warning:
Incorrect use of kernel-doc format:          *
@active_vblank_irq_count
./drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h:379: warning:
Function parameter or member 'active_vblank_irq_count' not described
in 'amdgpu_display_manager'
./include/linux/rcupdate.h:884: warning: Excess function parameter
'ptr' description in 'kfree_rcu'
./include/linux/rcupdate.h:884: warning: Excess function parameter
'rhf' description in 'kfree_rcu'

<seems like no updates from here>

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