Messages in this thread | | | Subject | Re: [PATCH v2 4/5] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter | From | Alexei Starovoitov <> | Date | Wed, 22 Jul 2015 19:22:35 -0700 |
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On 7/22/15 7:12 PM, xiakaixu wrote: > So you mean like this? > > u64 bpf_perf_event_read(u64 r1, u64 index,...) > { > struct bpf_perf_event_array *array = (void *) (long) r1; > struct perf_event *event; > ... > event = array->events[index]; > ... > }
yes. the only thing needed is to add: if (index >= array->map.max_entries) return -E2BIG; before accessing array->events[index];
>> > >>> >>+const struct bpf_func_proto bpf_perf_event_read_proto = { >>> >>+ .func = bpf_perf_event_read, >>> >>+ .gpl_only = false, >>> >>+ .ret_type = RET_INTEGER, >>> >>+ .arg1_type = ARG_CONST_MAP_PTR, >>> >>+ .arg2_type = ARG_PTR_TO_MAP_KEY, >> > >> >make it arg2_type = ARG_ANYTHING then you'll just index >> >into array the way prog_array does and similar to bpf_tail_call.
> ARG_ANYTHING means any (initialized) argument is ok, but we here
correct.
> really want is map key. So I'm not sure ARG_ANYTHING is suitable. > You know ARG_ANYTHING is not checked enough in verifier.
why? during perf_event_array creation time we check that key_size == u32 so we can accept any integer. ARG_PTR_TO_MAP_KEY forces program author to use stack instead of passing index directly. Direct index is obviously faster.
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