1. A data processing system for executing a program of virtual machine instructions with a processor core that is arranged to execute native instructions comprising the processor core; a memory; a virtual machine interpreter for receiving virtual machine instructions selected dependent on program flow during execution of the program, the virtual machine interpreter being coupled to the processor core to generate native machine instructions that implement the virtual machine instructions for execution by the processor core, the virtual machine interpreter being arranged to identify an initial virtual machine instruction from a body of successive ones of the selected virtual machine instructions, where the body is expected to be executed repeatedly; to record a correspondence between the initial virtual machine instruction in the body and a memory location in the memory; to write native instructions for the body into the memory from said memory location, the native instructions for the body being generated for virtual machine instructions starting from the initial virtual machine instruction; to cause the processor core to execute the native instructions for the body and to repeat execution of the native instructions for the body by executing the written native machine instructions for the body from memory starting from said memory location.