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libbpf: Don't error out on CO-RE relos for overriden weak subprogs

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[ Upstream commit e89d57d938 ]

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: db2b8b0642 ("libbpf: Support CO-RE relocations for multi-prog sections")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220408181425.2287230-2-andrii@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Andrii Nakryiko 2022-04-08 11:14:23 -07:00 committed by Greg Kroah-Hartman
parent d47f85cc01
commit 049a44dfd6
1 changed files with 11 additions and 4 deletions
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15
tools/lib/bpf/libbpf.c
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@ -5238,10 +5238,17 @@ 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