Abstract: In a data processing system implementing Dynamic Object Code Translation (DOCT) for emulating Target system instructions on a Host system, each Target system instruction has an associated index/offset field and an associated code tag that identifies whether the Target instruction has been translated into Host code, and if already translated, whether it is an entry point, middle, or last instruction in a block of code. When an emulator encounters a code tag indicating an entry point into a block of code, execution control is transferred to the corresponding Host code. Upon completion of the Host code block, execution control is returned to the emulator, with an indication of the next Target system instruction to execute. One code tag value is utilized to identify self-modified code. Another code tag value is utilized to indicate how often untranslated Target instructions have been interpreted in order to determine when to perform DOCT.

Abstract: In a data processing system implementing Dynamic Object Code Translation (DOCT) for emulating Target system instructions on a Host system, each Target system instruction has an associated index/offset field and an associated code tag that identifies whether the Target instruction has been translated into Host code, and if already translated, whether it is an entry point, middle, or last instruction in a block of code. When an emulator encounters a code tag indicating an entry point into a block of code, execution control is transferred to the corresponding Host code. Upon completion of the Host code block, execution control is returned to the emulator, with an indication of the next Target system instruction to execute. One code tag value is utilized to identify self-modified code. Another code tag value is utilized to indicate how often untranslated Target instructions have been interpreted in order to determine when to perform DOCT.

Abstract: In a data processing system implementing Dynamic Object Code Translation (DOCT) for emulating Target system instructions on a Host system, each Target system instruction has an associated index/offset field and an associated code tag that identifies whether the Target instruction has been translated into Host code, and if already translated, whether it is an entry point, middle, or last instruction in a block of code. When an emulator encounters a code tag indicating an entry point into a block of code, execution control is transferred to the corresponding Host code. Upon completion of the Host code block, execution control is returned to the emulator, with an indication of the next Target system instruction to execute. One code tag value is utilized to identify self-modified code. Another code tag value is utilized to indicate how often untranslated Target instructions have been interpreted in order to determine when to perform DOCT.

Abstract: When emulating a Target architecture on a Host system having a different architecture, virtual-to-real address translation is typically expensive in terms of computer cycles. The cost for translating addresses for instruction fetches can be significantly reduced by maintaining both a virtual and a real memory address instruction counter. Both are incremented on each instruction fetch. Virtual to real address translation is eliminated as long as execution continues on the same real memory page of instructions. Alternatively, only a real memory address instruction counter is incremented, while maintaining a delta instruction counter value to efficiently translate back and forth to and from the corresponding virtual memory address.