Method and apparatus for guest return address stack emulation supporting speculation

Abstract

A microprocessor implemented method of speculatively maintaining a guest return address stack (GRAS) in a fetch stage of a microprocessor pipeline. The method includes mapping instructions in a guest address space to corresponding instructions in a native address space. For each of one or more function calls made in the native address space, performing the following: (a) pushing a current entry into the GRAS responsive to the function call, where the current entry includes a guest target return address and a corresponding native target return address associated with the function call; (b) popping the current entry from the GRAS responsive to processing a return instruction; (c) comparing the current entry with an entry popped from a return address stack (RAS) maintained at a later stage of the pipeline; and (d) responsive to a mismatch, fetching instructions from the return address in the entry popped from the RAS.