File 0001-libbpf-Add-identical-pointer-detection-to-btf_dedup_.patch of Package libbpf

From 1f7c2f78d74e239ee4fce03f9a858062ae3d5512 Mon Sep 17 00:00:00 2001
From: Alan Maguire <alan.maguire@oracle.com>
Date: Tue, 29 Apr 2025 17:10:42 +0100
Subject: [PATCH 1/1] libbpf: Add identical pointer detection to
 btf_dedup_is_equiv()

Recently as a side-effect of

commit ac053946f5c4 ("compiler.h: introduce TYPEOF_UNQUAL() macro")

issues were observed in deduplication between modules and kernel BTF
such that a large number of kernel types were not deduplicated so
were found in module BTF (task_struct, bpf_prog etc).  The root cause
appeared to be a failure to dedup struct types, specifically those
with members that were pointers with __percpu annotations.

The issue in dedup is at the point that we are deduplicating structures,
we have not yet deduplicated reference types like pointers.  If multiple
copies of a pointer point at the same (deduplicated) integer as in this
case, we do not see them as identical.  Special handling already exists
to deal with structures and arrays, so add pointer handling here too.

Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250429161042.2069678-1-alan.maguire@oracle.com
---
 src/btf.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/btf.c b/src/btf.c
index e9673c0..c7df63d 100644
--- a/src/btf.c
+++ b/src/btf.c
@@ -4337,6 +4337,19 @@ static bool btf_dedup_identical_structs(struct btf_dedup *d, __u32 id1, __u32 id
 	return true;
 }
 
+static bool btf_dedup_identical_ptrs(struct btf_dedup *d, __u32 id1, __u32 id2)
+{
+	struct btf_type *t1, *t2;
+
+	t1 = btf_type_by_id(d->btf, id1);
+	t2 = btf_type_by_id(d->btf, id2);
+
+	if (!btf_is_ptr(t1) || !btf_is_ptr(t2))
+		return false;
+
+	return t1->type == t2->type;
+}
+
 /*
  * Check equivalence of BTF type graph formed by candidate struct/union (we'll
  * call it "candidate graph" in this description for brevity) to a type graph
@@ -4469,6 +4482,9 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
 		 */
 		if (btf_dedup_identical_structs(d, hypot_type_id, cand_id))
 			return 1;
+		/* A similar case is again observed for PTRs. */
+		if (btf_dedup_identical_ptrs(d, hypot_type_id, cand_id))
+			return 1;
 		return 0;
 	}
 
-- 
2.49.0