[PATCH v5 bpf-next 3/5] libbpf: print hint when PERF_EVENT_IOC_SET_BPF returns -EPROTO

[Song Liu]

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: Song Liu <songliubrav...@fb.com>
---
 tools/lib/bpf/libbpf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 846164c79df1c..484e50d49a4cf 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -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) {
-- 
2.24.1