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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: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200723180648.1429892-4-songliubraving@fb.com
This commit is contained in:
Song Liu 2020-07-23 11:06:46 -07:00 committed by Alexei Starovoitov
parent 5d99cb2c86
commit d4b4dd6ce7
1 changed files with 3 additions and 0 deletions
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3
tools/lib/bpf/libbpf.c
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@ -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", pr_warn("program '%s': failed to attach to pfd %d: %s\n",
bpf_program__title(prog, false), pfd, bpf_program__title(prog, false), pfd,
libbpf_strerror_r(err, errmsg, sizeof(errmsg))); 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); return ERR_PTR(err);
} }
if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) { if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {