This is achieved by tracking the observers on the run_time_cache (with a fixed amount of slots, 2 for each observer).
That way round, if the run_time_cache is freed all associated observer data is as well.
This approach has been chosen, as to avoid any ABI or API breakage.
Future versions may for example choose to provide a hookable API for run_time_cache freeing or similar.
The motivation for this change is to prevent extensions from having to check executor globals for the current execute_data during function call init. A previous implementation of the observer API initialized the function call from runtime cache initialization before execute_data was allocated which is why zend_function was passed in.
But now that the observer API is implemented via opcode specialization, it makes sense to pass in the execute_data. This also keeps the API a bit more consistent for existing extensions that already hook zend_execute_ex.
Closes GH-6209
Bob Weinand