[WIP] Enable bpf-next tree build and test

[yurinnick]

I'd like to enable bpf-next tree build and testing on KernelCI.

BPF subsystem requires cutting edge llvm (comes with clang) and pahole (added) to maximize passing tests. I added most of the parts required for build, not sure if I tie them together correctly though.

Progress

• Configure bpf-next tree checkout
• Add llvm + pahole build image
• Add bpf-next build config
• Test bpf-next build configuration with kci_build
• Configure bpf-next kselftest
• Test bpf-next kselftest configuration with kci_test

Testing

1. Build clang-17 + pahole image

$ ./kci docker build clang-17 pahole kselftest kernelci --prefix=yurinnick/
$ docker images
REPOSITORY                       TAG                         IMAGE ID       CREATED              SIZE
yurinnick/clang-17               pahole-kselftest-kernelci   50697711d09e   36 seconds ago       1.4GB

2. Add kernelci.toml config

$ cat kernelci.toml
...
[kci_build]
mirror = "bpf-next.git"
kdir = "linux-bpf"
output = "linux-bpf/build-x86"
build_env = "gcc-10"
build_config = "bpf-next"
arch = "x86_64"
j = 13
install = true
...

3. Following kci_build docs build bpf-next kernel

$ ./kci_build update_mirrot
$ ./kci_build update_repo
$ ./kci_build generate_fragments
$ ./kci_build init_bmeta
$ docker run -it -v $PWD:/home/kernelci yurinnick/clang-17:pahole-kselftest-kernelci /bin/bash
./kci_build make_config --defconfig=x86_64_defconfig+bpf
./kci_build fetch_firmware
./kci_build make_kernel
./kci_build make_modules

[gctucker]

I believe we're going to face practical issues with this due to the LLVM version requirements. Does the bpf fragment already require this or can we use a standard LLVM 17 toolchain?

[gctucker]

It might be better to directly declare the variants here rather than elsewhere in the file with an anchor as it's only used with the BPF tree.

[gctucker]

I don't think we can actually do this because, like you mentioned, BPF requires an unreasonably cutting-edge toolchain. It's actually one of the reasons why it got disabled by default:

commit 7a6eb7c34a78498742b5f82543b7a68c1c443329 (tag: linux-kselftest-fixes-5.11-rc4)
Author: Mark Brown <broonie@kernel.org>
Date:   Thu Dec 10 18:52:33 2020 +0000

    selftests: Skip BPF seftests by default

So a prerequisite before being able to run this test automatically would be to have a dedicated job to build a custom toolchain Docker image. This sounds like something to do with the new API, at some point in 2024 I guess.