1// SPDX-License-Identifier: GPL-2.0
2/* Copyright Leon Hwang */
3
4#include <linux/bpf.h>
5#include <bpf/bpf_helpers.h>
6
7#define ERRMSG_LEN 64
8
9struct xdp_errmsg {
10	char msg[ERRMSG_LEN];
11};
12
13struct {
14	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
15	__type(key, int);
16	__type(value, int);
17} xdp_errmsg_pb SEC(".maps");
18
19struct xdp_attach_error_ctx {
20	unsigned long unused;
21
22	/*
23	 * bpf does not support tracepoint __data_loc directly.
24	 *
25	 * Actually, this field is a 32 bit integer whose value encodes
26	 * information on where to find the actual data. The first 2 bytes is
27	 * the size of the data. The last 2 bytes is the offset from the start
28	 * of the tracepoint struct where the data begins.
29	 * -- https://github.com/iovisor/bpftrace/pull/1542
30	 */
31	__u32 msg; // __data_loc char[] msg;
32};
33
34/*
35 * Catch the error message at the tracepoint.
36 */
37
38SEC("tp/xdp/bpf_xdp_link_attach_failed")
39int tp__xdp__bpf_xdp_link_attach_failed(struct xdp_attach_error_ctx *ctx)
40{
41	char *msg = (void *)(__u64) ((void *) ctx + (__u16) ctx->msg);
42	struct xdp_errmsg errmsg = {};
43
44	bpf_probe_read_kernel_str(&errmsg.msg, ERRMSG_LEN, msg);
45	bpf_perf_event_output(ctx, &xdp_errmsg_pb, BPF_F_CURRENT_CPU, &errmsg,
46			      ERRMSG_LEN);
47	return 0;
48}
49
50/*
51 * Reuse the XDP program in xdp_dummy.c.
52 */
53
54char LICENSE[] SEC("license") = "GPL";
55