btf: Add lazy sorting validation for binary search

Implement lazy validation of BTF type ordering to enable efficient
binary search for sorted BTF while maintaining linear search fallback
for unsorted cases.

Cc: Eduard Zingerman <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Alan Maguire <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Xiaoqin Zhang <[email protected]>
Signed-off-by: Donglin Peng <[email protected]>
Signed-off-by: Donglin Peng <[email protected]>

Author: Donglin Peng

kernel/bpf/btf.c

@@ -552,6 +552,70 @@ u32 btf_nr_types(const struct btf *btf)
 	return total;
 }
 
+/* Anonymous types (with empty names) are considered greater than named types
+ * and are sorted after them. Two anonymous types are considered equal. Named
+ * types are compared lexicographically.
+ */
+static int btf_compare_type_names(const void *a, const void *b, void *priv)
+{
+	struct btf *btf = (struct btf *)priv;
+	const struct btf_type *ta = btf_type_by_id(btf, *(__u32 *)a);
+	const struct btf_type *tb = btf_type_by_id(btf, *(__u32 *)b);
+	const char *na, *nb;
+
+	if (!ta->name_off && tb->name_off)
+		return 1;
+	if (ta->name_off && !tb->name_off)
+		return -1;
+	if (!ta->name_off && !tb->name_off)
+		return 0;
+
+	na = btf_name_by_offset(btf, ta->name_off);
+	nb = btf_name_by_offset(btf, tb->name_off);
+	return strcmp(na, nb);
+}
+
+/* Verifies that BTF types are sorted in ascending order according to their
+ * names, with named types appearing before anonymous types. If the ordering
+ * is correct, counts the number of named types and updates the BTF object's
+ * nr_sorted_types field.
+ *
+ * Return: true if types are properly sorted, false otherwise
+ */
+static bool btf_check_sorted(struct btf *btf)
+{
+	const struct btf_type *t;
+	int i, n, k = 0, nr_sorted_types;
+
+	if (likely(btf->nr_sorted_types != BTF_NEED_SORT_CHECK))
+		goto out;
+	btf->nr_sorted_types = 0;
+
+	if (btf->nr_types < 2)
+		goto out;
+
+	nr_sorted_types = 0;
+	n = btf_nr_types(btf) - 1;
+	for (i = btf_start_id(btf); i < n; i++) {
+		k = i + 1;
+		if (btf_compare_type_names(&i, &k, btf) > 0)
+			goto out;
+
+		t = btf_type_by_id(btf, i);
+		if (t->name_off)
+			nr_sorted_types++;
+	}
+
+	t = btf_type_by_id(btf, k);
+	if (t->name_off)
+		nr_sorted_types++;
+	if (nr_sorted_types)
+		btf->nr_sorted_types = nr_sorted_types;
+
+out:
+	return btf->nr_sorted_types > 0;
+}
+
 /* Performs binary search within specified type ID range to find the leftmost
  * BTF type matching the given name. The search assumes types are sorted by
  * name in lexicographical order within the specified range.
@@ -610,7 +674,7 @@ s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind)
 			goto out;
 	}
 
-	if (btf->nr_sorted_types != BTF_NEED_SORT_CHECK) {
+	if (btf_check_sorted((struct btf *)btf)) {
 		/* binary search */
 		bool skip_first;
 		s32 start_id, end_id;;