Method and apparatus for runtime remediation of object-code instructions in a computer program

Abstract

A method and apparatus for runtime remediation of object-code instructions (such as date instructions that are not year 2000 compliant) in a computer program. Before runtime, a setup function of a program monitor locates each instruction to be remediated in a load module of a user program and overlays the instruction with a trap instruction. The address of the overlaid instruction is stored in a scan slot of a window control table (WCT). The text of the overlaid instruction is stored in a corresponding operand slot of the WCT along with control information including a set of flags and windowing and cycling parameters. At runtime, upon decoding a trap instruction, the CPU transfers control to an instruction simulation function of the program monitor, which searches the scan slots of the WCT for the one containing the address of the overlaid instruction. Upon finding the scan slot, the instruction simulation function performs an instruction simulation operation in accordance with the control information in the corresponding operand slot, then returns control to the user program. If an execute flag is not set, the instruction simulation function invokes a specified user routine without executing the overlaid instruction. If the execute flag is set, the instruction simulation function executes the overlaid instruction in a mode of operation determined by the remaining flags. In a windowing mode, one or both instruction operands are compared with a specified delimiter, and the instruction is executed as though a specified increment were added to the operand before performing the operation of the instruction if the operand is less than the delimiter. In a cycling mode, a specified increment is added to the result the instruction would otherwise produce if that result is less than zero.