PAPI_event_code_to_name potential memory risk

[anustuvicl]

For native events PAPI_event_code_to_name(int EventCode, char *out) calls _papi_hwi_native_code_to_name( EventCode, out, PAPI_MAX_STR_LEN). Thus, it assumes that the event name could be max 128 characters. There are several potential problems with this,

• CUDA Perfworks has event names that can go up to 133 characters, thus calling this function returns PAPI_ENOMEM which is not documented behavior. These long cuda events are all multipass (and cannot be measured) but PAPI event name<->code API should work for them too.
• If the user has a string defined as char evt_name[64] and calls PAPI_event_code_to_name(EventCode, evt_name) then it's a buffer overflow. The example in docs shows char EventCodeStr[PAPI_MAX_STR_LEN] but this is not mentioned as a requirement.

PAPI API needs to account for possibly longer event names, and properly truncate at user string length. The function should be defined as PAPI_event_code_to_name(int EventCode, char *out, int len).

Alternatively, we can have a function that returns a pointer to a dynamically allocated string that the user needs to free.