libbpf: never interpret subprogs in .text as entry programs

JIRA: https://issues.redhat.com/browse/RHEL-85485

commit db089c9
Author: Andrii Nakryiko <andrii@kernel.org>
Date:   Thu Oct 10 14:17:30 2024 -0700

    libbpf: never interpret subprogs in .text as entry programs

    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: bd05410 ("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: Viktor Malik <vmalik@redhat.com>

Author: viktormalik

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 *