linux-kernel - Re: [PATCH] Documentation: add minimum clang/llvm version

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Message-ID: <CA+icZUVhwqF=TT2V3XOw1RbdX4g_i5qVX-5eTkVcsgEbfGyJkw@mail.gmail.com>
Date:   Wed, 26 Aug 2020 17:53:26 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Theodore Ts'o" <tytso@....edu>, Kees Cook <keescook@...omium.org>,
        Will Deacon <will@...nel.org>, Borislav Petkov <bp@...e.de>,
        "Alexander A. Klimov" <grandmaster@...klimov.de>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        linux-kbuild@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Documentation: add minimum clang/llvm version

On Wed, Aug 26, 2020 at 12:26 AM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> Based on a vote at the LLVM BoF at Plumbers 2020, we decided to start
> small, supporting just one formal upstream release of LLVM for now.
>
> We can probably widen the support window of supported versions over
> time.  Also, note that LLVM's release process is different than GCC's.
> GCC tends to have 1 major release per year while releasing minor updates
> to the past 3 major versions.  LLVM tends to support one major release
> and one minor release every six months.
>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Note to reviewers: working remote, I'm having trouble testing/verifying
> that I have the RST links wired up correctly; I would appreciate it if
> someone is able to `make htmldocs` and check
> Documentation/output/process/changes.html properly links to
> Documentation/output/kbuild/llvm.html.
>
>  Documentation/kbuild/llvm.rst     |  2 ++
>  Documentation/process/changes.rst | 10 ++++++++++
>  2 files changed, 12 insertions(+)
>
> diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
> index 2aac50b97921..70ec6e9a183b 100644
> --- a/Documentation/kbuild/llvm.rst
> +++ b/Documentation/kbuild/llvm.rst
> @@ -1,3 +1,5 @@
> +.. _kbuild_llvm:
> +
>  ==============================
>  Building Linux with Clang/LLVM
>  ==============================
> diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
> index ee741763a3fc..6c580ef9f2a3 100644
> --- a/Documentation/process/changes.rst
> +++ b/Documentation/process/changes.rst
> @@ -30,6 +30,7 @@ you probably needn't concern yourself with pcmciautils.
>          Program        Minimal version       Command to check the version
>  ====================== ===============  ========================================
>  GNU C                  4.9              gcc --version
> +Clang/LLVM (optional)  10.0.1           clang --version
>  GNU make               3.81             make --version
>  binutils               2.23             ld -v
>  flex                   2.5.35           flex --version
> @@ -68,6 +69,15 @@ GCC
>  The gcc version requirements may vary depending on the type of CPU in your
>  computer.
>
> +Clang/LLVM (optional)
> +---------------------
> +
> +The latest formal release of clang and LLVM utils (according to
> +`releases.llvm.org <https://releases.llvm.org>`_) are supported for building
> +kernels. Older releases aren't gauranteed to work, and we may drop workarounds
> +from the kernel that were used to support older versions. Please see additional
> +docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
> +
>  Make

Thanks for the text - a first good step.

Do you plan checks in the source-code - in the future (see [1] where I
played a bit)?
Arch-specific supported LLVM toolchain versions?
Feature-specific support (like KCSAN, Clang-IAS, etc.)?
In the future we should introduce some checks for this to be user-friendly.

If you talk about "Clang/LLVM" does this include the LLD linker?
Personally, I think LLD is worth a separate item like GNU/ld (BFD) linker.

The last few days I was able to build with GCC v10.2 and LLD and even
full LLVM "bin"utils (see [2]) version 11.0.0-rc2 on Debian/unstable
AMD64.

Just some thoughts - for the future.

- Sedat -

[1] https://github.com/ClangBuiltLinux/linux/issues/941
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/kbuild/llvm.rst#n47

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