Re: Migration to Debian Bookworm and compiler updates for KernelCI

[Nathan Chancellor <nathan@kernel.org>]

Hi Denys,

On Thu, Mar 07, 2024 at 01:02:26PM +0200, Denys Fedoryshchenko wrote:
> Hello,
> 
> I'm reaching out on behalf of the KernelCI project team to discuss our
> current compiler setup and planned migration to Debian Bookworm.
> 
> As you may know, our compiler images are currently based on Debian
> Bullseye, which is approaching its end of life in July 2024. We have
> been testing using gcc-10, which has presented us with some recent
> challenges, notably a significant bug that results in false positive
> compilation errors (specifically, the -Werror memcpy issue in
> security.c). This situation has prompted us to consider an urgent
> migration to Debian Bookworm. Additionally, the migration is
> necessitated by our requirement to upgrade to a newer Python version to
> support KernelCI v2 development efforts.
> 
> However, before we proceed, we have a couple of pending questions that
> we hope to get clarity on:
> 
> 1) We've noticed that the minimal available version of clang on
> https://apt.llvm.org/bookworm/dists/ is 15, whereas our current minimal
> requirement for the Linux kernel compilation is clang-13.0.1
> (https://www.kernel.org/doc/html/next/process/changes.html). How
> critical is it to continue providing compile tests for clang-13 (and
> potentially clang-14)? This information would be vital for us in
> planning our compiler support strategy moving forward.

Coverage of the minimum version of a particular toolchain for building
the kernel is important but I would not describe it as critical.

While apt.llvm.org's Bookworm distribution does not have clang-13 and
clang-14, the Bullseye distribution of clang-13 and clang-14 does work
on Bookworm, I personally do that for my Debian development containers:

https://github.com/nathanchance/env/blob/12927502f12ec63f50a460f842c9d0a70a82c629/podman/dev/debian/setup-env.sh#L54-L64

Have you explored using the kernel.org GCC and LLVM toolchains instead
of the ones in Debian?

https://mirrors.edge.kernel.org/pub/tools/crosstool/
https://mirrors.edge.kernel.org/pub/tools/llvm/

That would potentially give you more flexibility with distribution
upgrades and stable/deterministic compiler versions around that. I
maintain the LLVM ones, which are optimized at build time to be quicker
than the Debian one's, so that would save you build minutes over time.

Cheers,
Nathan