libbpf: improve BTF dedup handling of "identical" BTF types

tools/lib/bpf/btf.c

@@ -4356,59 +4356,109 @@ static inline __u16 btf_fwd_kind(struct btf_type *t)
 	return btf_kflag(t) ? BTF_KIND_UNION : BTF_KIND_STRUCT;
 }
 
-/* Check if given two types are identical ARRAY definitions */
-static bool btf_dedup_identical_arrays(struct btf_dedup *d, __u32 id1, __u32 id2)
+static bool btf_dedup_identical_types(struct btf_dedup *d, __u32 id1, __u32 id2, int depth)
 {
 	struct btf_type *t1, *t2;
+	int k1, k2;
+recur:
+	if (depth <= 0)
+		return false;
 
 	t1 = btf_type_by_id(d->btf, id1);
 	t2 = btf_type_by_id(d->btf, id2);
-	if (!btf_is_array(t1) || !btf_is_array(t2))
+
+	k1 = btf_kind(t1);
+	k2 = btf_kind(t2);
+	if (k1 != k2)
 		return false;
 
-	return btf_equal_array(t1, t2);
-}
+	switch (k1) {
+	case BTF_KIND_UNKN: /* VOID */
+		return true;
+	case BTF_KIND_INT:
+		return btf_equal_int_tag(t1, t2);
+	case BTF_KIND_ENUM:
+	case BTF_KIND_ENUM64:
+		return btf_compat_enum(t1, t2);
+	case BTF_KIND_FWD:
+	case BTF_KIND_FLOAT:
+		return btf_equal_common(t1, t2);
+	case BTF_KIND_CONST:
+	case BTF_KIND_VOLATILE:
+	case BTF_KIND_RESTRICT:
+	case BTF_KIND_PTR:
+	case BTF_KIND_TYPEDEF:
+	case BTF_KIND_FUNC:
+	case BTF_KIND_TYPE_TAG:
+		if (t1->info != t2->info || t1->name_off != t2->name_off)
+			return false;
+		id1 = t1->type;
+		id2 = t2->type;
+		goto recur;
+	case BTF_KIND_ARRAY: {
+		struct btf_array *a1, *a2;
 
-/* Check if given two types are identical STRUCT/UNION definitions */
-static bool btf_dedup_identical_structs(struct btf_dedup *d, __u32 id1, __u32 id2)
-{
-	const struct btf_member *m1, *m2;
-	struct btf_type *t1, *t2;
-	int n, i;
+		if (!btf_compat_array(t1, t2))
+			return false;
 
-	t1 = btf_type_by_id(d->btf, id1);
-	t2 = btf_type_by_id(d->btf, id2);
+		a1 = btf_array(t1);
+		a2 = btf_array(t1);
 
-	if (!btf_is_composite(t1) || btf_kind(t1) != btf_kind(t2))
-		return false;
+		if (a1->index_type != a2->index_type &&
+		    !btf_dedup_identical_types(d, a1->index_type, a2->index_type, depth - 1))
+			return false;
 
-	if (!btf_shallow_equal_struct(t1, t2))
-		return false;
+		if (a1->type != a2->type &&
+		    !btf_dedup_identical_types(d, a1->type, a2->type, depth - 1))
+			return false;
 
-	m1 = btf_members(t1);
-	m2 = btf_members(t2);
-	for (i = 0, n = btf_vlen(t1); i < n; i++, m1++, m2++) {
-		if (m1->type != m2->type &&
-		    !btf_dedup_identical_arrays(d, m1->type, m2->type) &&
-		    !btf_dedup_identical_structs(d, m1->type, m2->type))
+		return true;
+	}
+	case BTF_KIND_STRUCT:
+	case BTF_KIND_UNION: {
+		const struct btf_member *m1, *m2;
+		int i, n;
+
+		if (!btf_shallow_equal_struct(t1, t2))
 			return false;
+
+		m1 = btf_members(t1);
+		m2 = btf_members(t2);
+		for (i = 0, n = btf_vlen(t1); i < n; i++, m1++, m2++) {
+			if (m1->type == m2->type)
+				continue;
+			if (!btf_dedup_identical_types(d, m1->type, m2->type, depth - 1))
+				return false;
+		}
+		return true;
 	}
-	return true;
-}
+	case BTF_KIND_FUNC_PROTO: {
+		const struct btf_param *p1, *p2;
+		int i, n;
 
-static bool btf_dedup_identical_ptrs(struct btf_dedup *d, __u32 id1, __u32 id2)
-{
-	struct btf_type *t1, *t2;
+		if (!btf_compat_fnproto(t1, t2))
+			return false;
 
-	t1 = btf_type_by_id(d->btf, id1);
-	t2 = btf_type_by_id(d->btf, id2);
+		if (t1->type != t2->type &&
+		    !btf_dedup_identical_types(d, t1->type, t2->type, depth - 1))
+			return false;
 
-	if (!btf_is_ptr(t1) || !btf_is_ptr(t2))
+		p1 = btf_params(t1);
+		p2 = btf_params(t2);
+		for (i = 0, n = btf_vlen(t1); i < n; i++, p1++, p2++) {
+			if (p1->type == p2->type)
+				continue;
+			if (!btf_dedup_identical_types(d, p1->type, p2->type, depth - 1))
+				return false;
+		}
+		return true;
+	}
+	default:
 		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
@@ -4527,22 +4577,13 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
 		 * different fields within the *same* struct. This breaks type
 		 * equivalence check, which makes an assumption that candidate
 		 * types sub-graph has a consistent and deduped-by-compiler
-		 * types within a single CU. So work around that by explicitly
-		 * allowing identical array types here.
+		 * types within a single CU. And similar situation can happen
+		 * with struct/union sometimes, and event with pointers.
+		 * So accommodate cases like this doing a structural
+		 * comparison recursively, but avoiding being stuck in endless
+		 * loops by limiting the depth up to which we check.
 		 */
-		if (btf_dedup_identical_arrays(d, hypot_type_id, cand_id))
-			return 1;
-		/* It turns out that similar situation can happen with
-		 * struct/union sometimes, sigh... Handle the case where
-		 * structs/unions are exactly the same, down to the referenced
-		 * type IDs. Anything more complicated (e.g., if referenced
-		 * types are different, but equivalent) is *way more*
-		 * complicated and requires a many-to-many equivalence mapping.
-		 */
-		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))
+		if (btf_dedup_identical_types(d, hypot_type_id, cand_id, 16))
 			return 1;
 		return 0;
 	}