linux-kernel - Re: [PATCH] Documentation/llvm: Add a section about supported architectures

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Date:   Thu, 14 Jan 2021 08:39:11 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Jonathan Corbet <corbet@....net>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        linux-kbuild@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>
Subject: Re: [PATCH] Documentation/llvm: Add a section about supported architectures

On Thu, Jan 14, 2021 at 1:35 AM Nathan Chancellor
<natechancellor@...il.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.
>

Thanks, this was overdue and is definitely helpful for users and developers.

For x86 64bit:

   Reviewed-by: Sedat Dilek <sedat.dilek@...il.com>

Together with "[PATCH] kbuild: check the minimum compiler version in
Kconfig" this looks very good to me.

/o\
- Sedat -

[1] https://marc.info/?t=161059811000001&r=1&w=2

> Suggested-by: Miguel Ojeda <ojeda@...nel.org>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.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
>
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