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

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Message-Id: <20211023120452.212885-3-jolsa@kernel.org>
Date:   Sat, 23 Oct 2021 14:04:52 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: [PATCH bpf-next 2/2] bpf: Add support to detect and dedup instances of same structs

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@...nel.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