PRIVILEGED INSTRUCTION EXECUTION CONTROLLER, PRIVILEGED INSTRUCTION EXECUTION CONTROL METHOD, AND ITS PROGRAM

摘要

PPROBLEM TO BE SOLVED: To easily judge whether or not the execution of a privileged instruction is allowable when any exceptional processing is generated due to the execution of the privileged instruction at the time of executing an application. PSOLUTION: An NOP instruction is inserted just before a privileged instruction which does not provide any means for performing access to the hardware of a DRM key, that is, the privileged instruction whose execution is permitted in a program. A CPU 40 executes the privileged instruction in a user mode, and when any exceptional processing is generated, the CPU 40 unconditionally executes the privileged instruction to recover from the exceptional processing when the address is present in a flash ROM 42 area. Also, when the NOP instruction is present just before the privileged instruction, the CPU 40 executes the privileged instruction to recover from the exceptional processing even when the address is a DRAM 43 area. On the other hand, when any NOP instruction is not present, an error is generated as privileged instruction violation. PCOPYRIGHT: (C)2003,JPO