Static builds with newer libelf require -l zstd

[bobrik]

Ubuntu 24.04 links libelf.so against libzstd.so. This doesn't matter at all for dynamically linked builds, but if you want a link a fully static binary, you need -l zstd in CGO_LDFLAGS. Currently libbpfgo only has:

#cgo LDFLAGS: -lelf -lz

I worked around this in ebpf_exporter:

• https://github.com/cloudflare/ebpf_exporter/blob/b908d3ba7/Makefile#L34-L37

# If libelf is new and it links to zstd, then zstd needs to be manually linked in.
ifneq ($(shell ldd $(shell /sbin/ldconfig -n -p | grep libelf.so.1 | awk '{ print $$NF }') | grep zstd),)
CGO_LDFLAGS := $(CGO_LDFLAGS) -l zstd
endif

Perhaps there's a better way in libbpfgo itself.

[geyslan]

@bobrik thanks for reporting this.

@trvll is it the same that you facing? Could you test it?

[bobrik]

I think you can replicate this in Github actions by bumping Ubuntu 22.04 to 24.04.

[geyslan]

Thanks @bobrik. zstd is indeed a requirement depending on the environment when a static build is the target. I'll be bumping this repo as soon as possible and tackling that.