[RFC bpf-next v8 5/9] 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 | 46 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 7f150c869bf6..a53d24704857 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -899,6 +899,49 @@ 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(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;
+
+	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;
+	int i, k = 0, n;
+	__u32 sorted_start_id = 0;
+
+	if (btf->nr_types < 2)
+		return;
+
+	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 (sorted_start_id == 0 &&
+			!str_is_empty(btf__str_by_offset(btf, t->name_off)))
+			sorted_start_id = i;
+	}
+
+	t = btf_type_by_id(btf, k);
+	if (sorted_start_id == 0 &&
+		!str_is_empty(btf__str_by_offset(btf, t->name_off)))
+		sorted_start_id = k;
+	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)
 {
@@ -935,7 +978,7 @@ static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,
 
 	if (start_id < btf->start_id) {
 		idx = btf_find_by_name_kind(btf->base_btf, start_id,
-			type_name, kind);
+					    type_name, kind);
 		if (idx >= 0)
 			return idx;
 		start_id = btf->start_id;
@@ -1147,6 +1190,7 @@ 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