generate and ship vmlinux.h to allow packages to build BPF CO-RE

[Luca Boccassi]

A vmlinux.h header generated from a kernel build with bpftool is needed to build and ship BPF CO-RE programs. We are looking to ship these in the next version of systemd.
vmlinux.h being generated depends on the kernel version, architecture and kconfig. There are some vague promises of backward compatibility, but it is hard to gauge.

We definitely do not want this file to be generated from the kernel running the build machine when building a package though, as very often these are very old and stable kernels building packages for the bleeding edge.

In Fedora and now Debian we generate vmlinux.h at kernel package build time, and ship it with the other kernel headers (_not_ UAPI, the internal headers): https://salsa.debian.org/kernel-team/linux/-/commit/ac6f7eda4c3e8b0d0db20ad4bb8236371cf8d38e

Please consider doing the same in Ubuntu's linux-headers.

[Luca Boccassi (bluca)]

We have now moved it in Debian:

https://salsa.debian.org/kernel-team/linux/-/commit/f52d006f3915ac4358dc8c98aa417477ebee026e

New binary package 'linux-bpf-dev' that installs /usr/include/${DEB_HOST_MULTIARCH}/linux/bpf/vmlinux.h - it would be great to have the same setup in Ubuntu so that we don't have to ifdef in debian/rules. It would greatly simplify things. Thanks!

[Luca Boccassi (bluca)]

I have sent a patch to kernel-team adding this new package, tested a local build on oracular amd64 and it seems to work:

https://lists.ubuntu.com/archives/kernel-team/2024-July/152477.html