A processor includes an execution unit and a processing logic operatively coupled to the execution unit, the processing logic to: enter a first execution state; responsive to executing a control transfer instruction having a pre-defined subcode, remain in the first execution state; responsive to executing a control transfer instruction not having the pre-defined subcode, transition into a second execution state; and responsive to determining, in the second execution state, that a next instruction to be executed differs from an ENDBRANCH instruction, raise an execution exception.