> On Jul 10, 2020, at 8:53 PM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Fri, Jul 10, 2020 at 6:30 PM Song Liu <songliubraving@xxxxxx> wrote: >> >> Calling get_perf_callchain() on perf_events from PEBS entries may cause >> unwinder errors. To fix this issue, the callchain is fetched early. Such >> perf_events are marked with __PERF_SAMPLE_CALLCHAIN_EARLY. >> >> Similarly, calling bpf_get_[stack|stackid] on perf_events from PEBS may >> also cause unwinder errors. To fix this, block bpf_get_[stack|stackid] on >> these perf_events. Unfortunately, bpf verifier cannot tell whether the >> program will be attached to perf_event with PEBS entries. Therefore, >> block such programs during ioctl(PERF_EVENT_IOC_SET_BPF). >> >> Signed-off-by: Song Liu <songliubraving@xxxxxx> >> --- > > Perhaps it's a stupid question, but why bpf_get_stack/bpf_get_stackid > can't figure out automatically that they are called from > __PERF_SAMPLE_CALLCHAIN_EARLY perf event and use different callchain, > if necessary? > > It is quite suboptimal from a user experience point of view to require > two different BPF helpers depending on PEBS or non-PEBS perf events. I am not aware of an easy way to tell the difference in bpf_get_stack. But I do agree that would be much better. Thanks, Song
