The libbpf directory is a git submodule for repository
  https://github.com/libbpf/libbpf

If you have any change in libbpf directory, please upstream to linux
first as libbpf repo is a mirror of linux/tools/lib/bpf directory.

If any top-commit update of libbpf submodule contains a uapi header
change, the following are necessary steps to sync properly with
rest of bcc:
  1. sync compat/linux/virtual_bpf.h with libbpf/include/uapi/linux/bpf.h
     as virtual_bpf.h has an extra string wrapper for bpf.h.
  2. if new bpf.h has new helpers, add corresponding helper func define
     in bcc:src/cc/export/helpers.h and helper entry for error reporting
     in bcc:src/cc/libbpf.c.
  3. if new bpf.h has new map types, program types, update
     bcc:introspection/bps.c for these new map/program types.