debugging labs fail building bpftool on Ubuntu 22.04

[lucaceresoli]

Building the debugging labs image on Ubuntu 22.04 fails under certain conditions. Superficially this looks like a Buildroot bug.

Steps to reproduce:

1. Use Ubuntu 22.04. @Tropicao said the build works on Arch. Other distros/releases might work or not.
2. Ensure the llvm package is not installed
3. Build the debugging training image according to the labs instructions (currently the debugging-training/2024.02 branch is at commit cdb4b6e)

bpftool fails building. This line is logged:

/bin/sh: 1: llvm-config: not found

Installing llvm on the host and rebuilding the build succeeds:

sudo apt install llvm
make bpftool-dirclean bpftool

Maybe just a missing dependency of the bpftool package on host-llvm?

[lucaceresoli]

Adding host-llvm to BPFTOOL_DEPENDENCIES makes the /bin/sh: 1: llvm-config: not found message disappear, and the build seems to fail a bit later, but still fails, this time ending with:

CC       struct_ops.o
CC       tracelog.o
CC       xlated_dumper.o
CC       disasm.o
LINK     bpftool
/.../buildroot/output/host/lib/libLLVM-15.so: file not recognized: file format not recognized
collect2: error: ld returned 1 exit status
make[2]: *** [Makefile:233: bpftool] Error 1
make[1]: *** [package/pkg-generic.mk:283: /.../buildroot/output/build/bpftool-v7.1.0/.stamp_built] Error 2