Commit d4b4dd6c authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

libbpf: Print hint when PERF_EVENT_IOC_SET_BPF returns -EPROTO 



The kernel prevents potential unwinder warnings and crashes by blocking
BPF program with bpf_get_[stack|stackid] on perf_event without
PERF_SAMPLE_CALLCHAIN, or with exclude_callchain_[kernel|user]. Print a
hint message in libbpf to help the user debug such issues.

Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200723180648.1429892-4-songliubraving@fb.com
parent 5d99cb2c

tools/lib/bpf/libbpf.c

+3 −0
Original line number Diff line number Diff line
@@ -7833,6 +7833,9 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, 
		pr_warn("program '%s': failed to attach to pfd %d: %s\n",

			bpf_program__title(prog, false), pfd,

			   libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		if (err == -EPROTO)

			pr_warn("program '%s': try add PERF_SAMPLE_CALLCHAIN to or remove exclude_callchain_[kernel|user] from pfd %d\n",

				bpf_program__title(prog, false), pfd);

		return ERR_PTR(err);

	}

	if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {