[PATCH bpf-next v10 05/13] libbpf: Verify BTF Sorting

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

From: pengdonglin <pengdonglin@xiaomi.com>

This patch checks whether the BTF is sorted by name in ascending
order. If sorted, binary search will be used when looking up types.

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: Ihor Solodrai <ihor.solodrai@linux.dev>
Cc: Xiaoqin Zhang <zhangxiaoqin@xiaomi.com>
Signed-off-by: pengdonglin <pengdonglin@xiaomi.com>
---
 tools/lib/bpf/btf.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 2facb57d7e5f..c63d46b7d74b 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -899,6 +899,46 @@ int btf__resolve_type(const struct btf *btf, __u32 type_id)
 	return type_id;
 }
 
+/*
+ * Assuming that types are sorted by name in ascending order.
+ */
+static int btf_compare_type_names(__u32 *a, __u32 *b, const struct btf *btf)
+{
+	struct btf_type *ta = btf_type_by_id(btf, *a);
+	struct btf_type *tb = btf_type_by_id(btf, *b);
+	const char *na, *nb;
+
+	na = btf__str_by_offset(btf, ta->name_off);
+	nb = btf__str_by_offset(btf, tb->name_off);
+	return strcmp(na, nb);
+}
+
+static void btf_check_sorted(struct btf *btf)
+{
+	const struct btf_type *t;
+	__u32 i, k, n;
+	__u32 sorted_start_id;
+
+	if (btf->nr_types < 2)
+		return;
+
+	sorted_start_id = 0;
+	n = btf__type_cnt(btf);
+	for (i = btf->start_id; i < n; i++) {
+		k = i + 1;
+		if (k < n && btf_compare_type_names(&i, &k, btf) > 0)
+			return;
+		if (sorted_start_id == 0) {
+			t = btf_type_by_id(btf, i);
+			if (t->name_off)
+				sorted_start_id = i;
+		}
+	}
+
+	if (sorted_start_id)
+		btf->sorted_start_id = sorted_start_id;
+}
+
 static __s32 btf_find_by_name_bsearch(const struct btf *btf, const char *name,
 						__s32 start_id, __s32 end_id)
 {
@@ -1147,6 +1187,7 @@ 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) {
-- 
2.34.1