Re: [PATCH test-artifacts] Build minimal images with Buildroot

[Titouan Christophe <titouan.christophe@xxxxxxx>]

On 1/10/26 14:32, Andrew Cooper wrote:
> On 01/10/2026 12:52 pm, Titouan Christophe wrote:
> > Add a way to build minimal Xen + Linux dom0 images, and their corresponding
> > cross-compilation toolchains with Buildroot [1]. This effectively provides
> > a consistent cross-architecture development environment.
> >
> > Buildroot is a project that makes it easy to build embedded system images,
> > including Linux, Xen or bootloaders. Leverage that build system to build
> > minimal images for use in the CI environment of Xen sub-projects, namely
> > Unikraft.
> >
> > This approach is based on a Buildroot External tree [2] which currently only
> > provides 2 target defconfigs (arm64 and x86_64, both running on qemu).
> > It uses a recent development version of Buildroot that integrates changes
> > to build Xen on x86_64 [3], on its latest official version 4.22.0 [4].
> > It also includes the latest kernel (linux-7.2.7 at the time of writing).
> >
> > As a byproduct, aside xen+kernel+rootfs, we also get a cross-compilation
> > toolchain (that runs on x86_64 hosts). This makes it easy to cross-compile
> > domUs for arm64, and it alleviates dynamic libraries mismatches when
> > adding userspace programs to the dom0 Linux image. As an example, one such
> > problem: Alpine linux is based on musl while your regular development
> > computer is probably based on glibc, which causes issues if you are
> > recompiling `xl` and try to use it in the Alpine image.
> >
> > [1] https://buildroot.org/
> > [2] https://buildroot.org/downloads/manual/manual.html#outside-br-custom
> > [3] 
> > https://gitlab.com/buildroot.org/buildroot/-/commit/0bf8b2ecee6b1b41746e8863b57c2c5ba3a623b1
> > [4] 
> > https://gitlab.com/buildroot.org/buildroot/-/commit/a962be2eea146e06661712159698bc7cbf3305f2
> >
> > This work is derived from this original series:
> > https://gitlab.com/xen-project/fusa/unikraft/-/merge_requests/1
> >
> > Signed-off-by: Titouan Christophe <titouan.christophe@xxxxxxx>
> Thankyou for your submission.
Hi Andrew, and thank you for having looked so quickly into this patch.

> How are you intending to use this image?  There's no consumer shown, so
> it's hard to judge the patch.
The goal is to obtain a `binaries` directory containing xen, linux and 
its rootfs; as well as the corresponding cross-compilation toolchain 
(either additional linux applications, or "bare" domUs to run with Xen).
Concretely, my next step would be to use that in Unikraft's CI in the 
following manner:
1. Download the latest binaries from test-artifacts (that should provide 
the latest Xen and a suitable linux)
2. Cross-compile a Unikraft application
3. Launch it on Xen, and assert expected output (similarly to the smoke 
tests in 
https://gitlab.com/xen-project/xen/-/tree/staging/automation/scripts)
Therefore, Xen serves as a base platform for the above, and it feels 
like a stretch to have to recompile it from scratch in Unikraft's CI. 
Perhaps there are other projects that could benefit from this ?
As far as I understand, all Xen tests are currently run on their native 
architecture (ie. arm64 runs on arm64 hosts etc...), and I had some 
trouble adding programs to the alpine images due to dynamic libraries 
mismatches (musl vs. glibc for example).
> One thing I see is that it intentionally embeds a fixed kernel and
> (commented but not actually added yet) Xen, and I'm not sure that's a
> route we want to go down.
Nit: Xen IS actually included, not sure to which commented section you 
are referring ?
> As for compiling the binary somewhere and copying it to a different
> environment, we have build containers for that, and I don't see how
> using buildroot changes the problem.
As you might guess, I'm quite new to the Xen Project :) Are these "build 
containers" the ones obtained in the test-artifacts repository ? If not, 
where are they coming from, and how are they created ?
> ~Andrew
Kind regards,
Titouan