Exception handling method and apparatus for use in program code conversion

An emulator apparatus, comprising:

• an emulator for mapping an abstract register representing a subject register of a subject machine to either a first location or to a second location within a target machine, the emulator for alternating mapping of the abstract register between the first and second locations such that the content of one of the first or second locations represents a definitive version of the abstract register for use by the emulator during exception handling, whilst the other of the first or second locations represents a speculative version of the abstract register.

An emulator apparatus for performing program code conversion between subject code suitable for a subject processor and target codes suitable for a target processor, the emulator apparatus comprising:

• at least one abstract register each representing a register of the subject processor;
• and
• an emulator for mapping the or each abstract register to a corresponding pair of locations within the target processor, and for alternating mapping of the or each abstract register between a first of the pair of locations and a second of the pair of locations, such that for a predetermined section of subject code, one of the first or second locations holds a definitive value of the abstract register at entry into that section for use by the emulator during exception handling, whilst the other of the first or second locations holds a speculative current value of the abstract register for updating by the emulator during that section.

A computer program product containing computer readable instructions for performing a method of representing a subject register in an emulator, the method comprising the steps of:

• (a) mapping an abstract register representing a subject register of a subject machine to either a first location or to a second location within a target machine;
• and
• (b) alternating mapping of the abstract register between the first and second locations such that one of the first or second locations represents a definitive version of the abstract register for use by the emulator during exception handling, whilst the other of the first or second locations represents a speculative version of the abstract register.