* @calls: limit branch samples to calls (can be combined with @returns)
* @returns: limit branch samples to returns (can be combined with @calls)
* @callchain: add callchain to 'instructions' events
* @calls: limit branch samples to calls (can be combined with @returns)
* @returns: limit branch samples to returns (can be combined with @calls)
* @callchain: add callchain to 'instructions' events