libbpf: never interpret subprogs in .text as entry programs

[ Upstream commit db089c9158c1d535a36dfc010e5db37fccea2561 ]

Libbpf pre-1.0 had a legacy logic of allowing singular non-annotated
(i.e., not having explicit SEC() annotation) function to be treated as
sole entry BPF program (unless there were other explicit entry
programs).

This behavior was dropped during libbpf 1.0 transition period (unless
LIBBPF_STRICT_SEC_NAME flag was unset in libbpf_mode). When 1.0 was
released and all the legacy behavior was removed, the bug slipped
through leaving this legacy behavior around.

Fix this for good, as it actually causes very confusing behavior if BPF
object file only has subprograms, but no entry programs.

Fixes: bd054102a8c7 ("libbpf: enforce strict libbpf 1.0 behaviors")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20241010211731.4121837-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 98a6cc304bb21012210b14715f3a58afda88121d..12d99b9ddb7c1bdf59986877988b1a3073826bba 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4389,7 +4389,7 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
 
 static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog)
 {
-       return prog->sec_idx == obj->efile.text_shndx && obj->nr_programs > 1;
+       return prog->sec_idx == obj->efile.text_shndx;
 }
 
 struct bpf_program *