Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > 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. Right, makes sense. I'll just wait for your follow-up series for the dynamic re-linking, then. Thanks for the explanation :) -Toke
