CONTROL FLOW CHECKING IN MULTITASKING SYSTEMS

Abstract

The control flow checking technique presented in our paper is based on the new watchdog- processor method SEIS1 (Signature Encoded Instruction Stream). This method is in- tended to check the still uncovered area of state-of-the-art microprocessors using on-chip caches or instruction pipelines, since the processor instruction bus needs not be monitored. The control flow is checked using assigned actual signatures and embedded reference sig- natures. Since the actual and reference signatures are embedded in the checked program, the usual reference database and the time-consuming search/ compare engine in the watch- dog can be omitted. The evaluation of the actual signature is a simple combinatorial task allowing high speed and thus the sharing of the watchdog between different tasks and processors. The checking method has been extended to higher levels of the application like simultaneous check of different processes and their synchronization in multitasking systems.