A system comprises at least one processor, and supporting firmware for supporting at least one function of the at least one processor. The system further comprises logic operable to expand the functionality of the at least one function in a fashion that is not natively supported by the supporting firmware, and an interposer for supporting the expanded functionality of the at least one function. A method for expanding the functionality of an execution unit of a system comprises implementing an execution unit in a system, and implementing pre-existing support firmware for the execution unit in the system, wherein the pre-existing support firmware supports at least one function of the execution unit. The method further comprises implementing logic expanding the at least one function in a manner not supported by the pre-existing support firmware, and implementing an interposer to support the expansion of the at least one function.