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. [...]
