[PATCH bpf-next 2/2] bpf: Add support to detect and dedup instances of same structs

[Jiri Olsa <jolsa@redhat.com>]

The s390x compiler generates multiple definitions of the same struct
and dedup algorithm does not seem to handle this at the moment.

I found code in dedup that seems to handle such situation for arrays,
and added btf_dedup_is_equiv call for structs.

With this change I can no longer see vmlinux's structs in kernel
module BTF data, but I have no idea if that breaks anything else.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/bpf/btf.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 3a01c4b7f36a..ec164d0cee30 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -3920,8 +3920,16 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
 		 * types within a single CU. So work around that by explicitly
 		 * allowing identical array types here.
 		 */
-		return hypot_type_id == cand_id ||
-		       btf_dedup_identical_arrays(d, hypot_type_id, cand_id);
+		struct btf_type *t;
+
+		if (hypot_type_id == cand_id)
+			return 1;
+		t = btf_type_by_id(d->btf, hypot_type_id);
+		if (btf_is_array(t))
+			return btf_dedup_identical_arrays(d, hypot_type_id, cand_id);
+		if (btf_is_struct(t))
+			return btf_dedup_is_equiv(d, hypot_type_id, cand_id);
+		return 0;
 	}
 
 	if (btf_dedup_hypot_map_add(d, canon_id, cand_id))
-- 
2.31.1