[RFC PATCH v6 5/7] libbpf: Implement BTF type sorting validation for binary search optimization

[Donglin Peng <dolinux.peng@gmail.com>]

From: Donglin Peng <pengdonglin@xiaomi.com>

This patch adds validation to verify BTF type name sorting, enabling
binary search optimization for lookups.

Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Song Liu <song@kernel.org>
Cc: Xiaoqin Zhang <zhangxiaoqin@xiaomi.com>
Signed-off-by: Donglin Peng <pengdonglin@xiaomi.com>
---
 tools/lib/bpf/btf.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index bb77e6c762cc..b29f5859c10b 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -903,6 +903,64 @@ int btf__resolve_type(const struct btf *btf, __u32 type_id)
 	return type_id;
 }
 
+/* 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;
+	struct btf_type *ta = btf_type_by_id(btf, *(__u32 *)a);
+	struct btf_type *tb = btf_type_by_id(btf, *(__u32 *)b);
+	const char *na, *nb;
+	bool anon_a, anon_b;
+
+	na = btf__str_by_offset(btf, ta->name_off);
+	nb = btf__str_by_offset(btf, tb->name_off);
+	anon_a = str_is_empty(na);
+	anon_b = str_is_empty(nb);
+
+	if (anon_a && !anon_b)
+		return 1;
+	if (!anon_a && anon_b)
+		return -1;
+	if (anon_a && anon_b)
+		return 0;
+
+	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.
+ */
+static void btf_check_sorted(struct btf *btf)
+{
+	const struct btf_type *t;
+	int i, k = 0, n, nr_sorted_types;
+
+	if (btf->nr_types < 2)
+		return;
+
+	nr_sorted_types = 0;
+	n = btf__type_cnt(btf) - 1;
+	for (i = btf->start_id; i < n; i++) {
+		k = i + 1;
+		if (btf_compare_type_names(&i, &k, btf) > 0)
+			return;
+		t = btf_type_by_id(btf, i);
+		if (!str_is_empty(btf__str_by_offset(btf, t->name_off)))
+			nr_sorted_types++;
+	}
+
+	t = btf_type_by_id(btf, k);
+	if (!str_is_empty(btf__str_by_offset(btf, t->name_off)))
+		nr_sorted_types++;
+	if (nr_sorted_types)
+		btf->nr_sorted_types = nr_sorted_types;
+}
+
 static __s32 btf_find_type_by_name_bsearch(const struct btf *btf, const char *name,
 						__s32 start_id, __s32 end_id)
 {
@@ -1148,6 +1206,7 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf, b
 	err = err ?: btf_sanity_check(btf);
 	if (err)
 		goto done;
+	btf_check_sorted(btf);
 
 done:
 	if (err) {
@@ -1332,6 +1391,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 	} else if (btf_ext) {
 		*btf_ext = NULL;
 	}
+
 done:
 	if (elf)
 		elf_end(elf);
-- 
2.34.1