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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