Commit 0cc114dc authored by D. Wythe's avatar D. Wythe Committed by Andrii Nakryiko
Browse files

libbpf: Fix error when st-prefix_ops and ops from differ btf 



When a module registers a struct_ops, the struct_ops type and its
corresponding map_value type ("bpf_struct_ops_") may reside in different
btf objects, here are four possible case:

+--------+---------------+-------------+---------------------------------+
|        |bpf_struct_ops_| xxx_ops     |                                 |
+--------+---------------+-------------+---------------------------------+
| case 0 | btf_vmlinux   | btf_vmlinux | be used and reg only in vmlinux |
+--------+---------------+-------------+---------------------------------+
| case 1 | btf_vmlinux   | mod_btf     | INVALID                         |
+--------+---------------+-------------+---------------------------------+
| case 2 | mod_btf       | btf_vmlinux | reg in mod but be used both in  |
|        |               |             | vmlinux and mod.                |
+--------+---------------+-------------+---------------------------------+
| case 3 | mod_btf       | mod_btf     | be used and reg only in mod     |
+--------+---------------+-------------+---------------------------------+

Currently we figure out the mod_btf by searching with the struct_ops type,
which makes it impossible to figure out the mod_btf when the struct_ops
type is in btf_vmlinux while it's corresponding map_value type is in
mod_btf (case 2).

The fix is to use the corresponding map_value type ("bpf_struct_ops_")
as the lookup anchor instead of the struct_ops type to figure out the
`btf` and `mod_btf` via find_ksym_btf_id(), and then we can locate
the kern_type_id via btf__find_by_name_kind() with the `btf` we just
obtained from find_ksym_btf_id().

With this change the lookup obtains the correct btf and mod_btf for case 2,
preserves correct behavior for other valid cases, and still fails as
expected for the invalid scenario (case 1).

Fixes: 590a0088 ("bpf: libbpf: Add STRUCT_OPS support")
Signed-off-by: default avatarD. Wythe <alibuda@linux.alibaba.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/bpf/20250926071751.108293-1-alibuda@linux.alibaba.com
parent 991e555e

tools/lib/bpf/libbpf.c

+17 −19
Original line number Diff line number Diff line
@@ -1018,35 +1018,33 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname_raw, 
	const struct btf_member *kern_data_member;

	struct btf *btf = NULL;

	__s32 kern_vtype_id, kern_type_id;

	char tname[256];

	char tname[192], stname[256];

	__u32 i;



	snprintf(tname, sizeof(tname), "%.*s",

		 (int)bpf_core_essential_name_len(tname_raw), tname_raw);



	kern_type_id = find_ksym_btf_id(obj, tname, BTF_KIND_STRUCT,

					&btf, mod_btf);

	if (kern_type_id < 0) {

		pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n",

			tname);

		return kern_type_id;

	}

	kern_type = btf__type_by_id(btf, kern_type_id);

	snprintf(stname, sizeof(stname), "%s%s", STRUCT_OPS_VALUE_PREFIX, tname);



	/* Find the corresponding "map_value" type that will be used

	 * in map_update(BPF_MAP_TYPE_STRUCT_OPS).  For example,

	 * find "struct bpf_struct_ops_tcp_congestion_ops" from the

	 * btf_vmlinux.

	/* Look for the corresponding "map_value" type that will be used

	 * in map_update(BPF_MAP_TYPE_STRUCT_OPS) first, figure out the btf

	 * and the mod_btf.

	 * For example, find "struct bpf_struct_ops_tcp_congestion_ops".

	 */

	kern_vtype_id = find_btf_by_prefix_kind(btf, STRUCT_OPS_VALUE_PREFIX,

						tname, BTF_KIND_STRUCT);

	kern_vtype_id = find_ksym_btf_id(obj, stname, BTF_KIND_STRUCT, &btf, mod_btf);

	if (kern_vtype_id < 0) {

		pr_warn("struct_ops init_kern: struct %s%s is not found in kernel BTF\n",

			STRUCT_OPS_VALUE_PREFIX, tname);

		pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n", stname);

		return kern_vtype_id;

	}

	kern_vtype = btf__type_by_id(btf, kern_vtype_id);



	kern_type_id = btf__find_by_name_kind(btf, tname, BTF_KIND_STRUCT);

	if (kern_type_id < 0) {

		pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n", tname);

		return kern_type_id;

	}

	kern_type = btf__type_by_id(btf, kern_type_id);



	/* Find "struct tcp_congestion_ops" from

	 * struct bpf_struct_ops_tcp_congestion_ops {

	 *	[ ... ]
@@ -1059,8 +1057,8 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname_raw, 
			break;

	}

	if (i == btf_vlen(kern_vtype)) {

		pr_warn("struct_ops init_kern: struct %s data is not found in struct %s%s\n",

			tname, STRUCT_OPS_VALUE_PREFIX, tname);

		pr_warn("struct_ops init_kern: struct %s data is not found in struct %s\n",

			tname, stname);

		return -EINVAL;

	}