gen skeleton does not work on Ubuntu

[CaledoniaProject]

I'm unable to compile it on Ubuntu 20.04:

# make V=1
/usr/sbin/bpftool gen skeleton .output/pamspy.bpf.o > .output/pamspy.skel.h
Usage: /usr/lib/linux-tools/5.4.0-100-generic/bpftool [OPTIONS] OBJECT { COMMAND | help }
       /usr/lib/linux-tools/5.4.0-100-generic/bpftool batch file FILE
       /usr/lib/linux-tools/5.4.0-100-generic/bpftool version

       OBJECT := { prog | map | cgroup | perf | net | feature | btf }
       OPTIONS := { {-j|--json} [{-p|--pretty}] | {-f|--bpffs} |
	            {-m|--mapcompat} | {-n|--nomount} }
make: *** [Makefile:65: .output/pamspy.skel.h] Error 255
make: *** Deleting file '.output/pamspy.skel.h'