Approaches for emulating an operating system. A method includes executing a first operating system (OS) on an instruction processor. The first OS includes instructions of a first instruction set that are native to the instruction processor. A second OS is emulated on the first OS and includes instructions of a second instruction set that are not native to the instruction processor. An emulated transfer-of-control instruction is determined during emulation of the second OS to target either instructions of the first set or the second set. In response to determining that instructions of the first set are targeted, control is transferred to the targeted instructions of the first set on the instruction processor. In response to determining that instructions of the second set are targeted, the targeted instructions of the second set are retrieved and emulated.