From: Andrii Nakryiko Date: Fri, 8 Apr 2022 18:14:23 +0000 (-0700) Subject: libbpf: Don't error out on CO-RE relos for overriden weak subprogs X-Git-Tag: v6.6.17~7459^2~363^2~4 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=e89d57d938c8fa80c457982154ed6110804814fe;p=platform%2Fkernel%2Flinux-rpi.git libbpf: Don't error out on CO-RE relos for overriden weak subprogs During BPF static linking, all the ELF relocations and .BTF.ext information (including CO-RE relocations) are preserved for __weak subprograms that were logically overriden by either previous weak subprogram instance or by corresponding "strong" (non-weak) subprogram. This is just how native user-space linkers work, nothing new. But libbpf is over-zealous when processing CO-RE relocation to error out when CO-RE relocation belonging to such eliminated weak subprogram is encountered. Instead of erroring out on this expected situation, log debug-level message and skip the relocation. Fixes: db2b8b06423c ("libbpf: Support CO-RE relocations for multi-prog sections") Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20220408181425.2287230-2-andrii@kernel.org --- diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 9deb1fc..465b7c0 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -5687,10 +5687,17 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path) insn_idx = rec->insn_off / BPF_INSN_SZ; prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx); if (!prog) { - pr_warn("sec '%s': failed to find program at insn #%d for CO-RE offset relocation #%d\n", - sec_name, insn_idx, i); - err = -EINVAL; - goto out; + /* When __weak subprog is "overridden" by another instance + * of the subprog from a different object file, linker still + * appends all the .BTF.ext info that used to belong to that + * eliminated subprogram. + * This is similar to what x86-64 linker does for relocations. + * So just ignore such relocations just like we ignore + * subprog instructions when discovering subprograms. + */ + pr_debug("sec '%s': skipping CO-RE relocation #%d for insn #%d belonging to eliminated weak subprogram\n", + sec_name, i, insn_idx); + continue; } /* no need to apply CO-RE relocation if the program is * not going to be loaded