On Thu, Jan 09, 2020 at 09:57:50AM +0100, Toke Høiland-Jørgensen wrote: > > > As far as future plans when libbpf sees FUNC_EXTERN it will do the linking the > > way we discussed in the other thread. The kernel will support FUNC_EXTERN when > > we introduce dynamic libraries. A collection of bpf functions will be loaded > > into the kernel first (like libc.so) and later programs will have FUNC_EXTERN > > as part of their BTF to be resolved while loading. The func name to btf_id > > resolution will be done by libbpf. The kernel verifier will do the type > > checking on BTFs. > > Right, FUNC_EXTERN will be rejected by the kernel unless it's patched up > with "target" btf_ids by libbpf before load? So it'll be > FUNC_GLOBAL-linked functions that will be replaceable after the fact > with the "dynamic re-linking" feature? Right. When libbpf statically links two .o it will need to produce a combined BTF out of these two .o. That new BTF will not have FUNC_EXTERN anymore if they are resolved. When the kernel sees FUNC_EXTERN it's a directive for the kernel to resolve it. BPF program with FUNC_EXTERN references would be loadable, but not executable. Anyhow the extern work is not immediate. I don't think any of that is necessary for dynamic re-linking.
