Build issues with LIBXDP_STATIC and BPF target includes (Arch Linux)

[Emmanuel326]

Hi! @gamemann

While trying to build this project on Arch Linux, I ran into a couple of
build-system issues that seem to be masked on Debian/Ubuntu setups.

Environment

• Distro: Arch Linux
• Compiler: clang
• Kernel: 6.x
• libconfig: 1.8.2
• libbpf/libxdp: system packages

Issue 1: libconfig detection

The loader unconditionally links against -lconfig, but there is no
early check for libconfig availability. This causes confusing linker
errors when libconfig is missing.

I added a small pkg-config check that fails early, while skipping
make clean, which seems to improve UX without changing behavior.

Issue 2: LIBXDP_STATIC=1 fails to link

When LIBXDP_STATIC=1 (default), the loader fails with unresolved symbols
(e.g. xdp_program__*, bpf_map_*). This appears to be related to how
libbpf/libxdp objects are collected and linked.

Building with LIBXDP_STATIC=0 links correctly, but then the BPF target
(-target bpf) fails due to system header usage, suggesting missing
kernel/UAPI isolation for the BPF build.

Proposed approach

• Document LIBXDP_STATIC=0 as the supported/default mode
  or
• Fix static linking by explicitly linking libbpf/libxdp (or using
  pkg-config for both)
• Isolate BPF compilation flags/headers (common pattern in libbpf-based
  projects)

I’m happy to submit a PR once direction is agreed on.

Thanks for the project — it’s been useful to study!

[gamemann]

Hey, I'm sorry for the late reply!

Thank you for digging into these issues. When I initially implemented LIBXDP_STATIC, I wanted to find a better approach since I was worried it may have issues on other Linux distros.

I believe using pkg-config would be best if possible. Would you agree in this case?

Feel free to submit a PR and I'll review/merge 😄