International Business Machines Corporation

Transitive Limited

Transitive Limted

John H Sandham

Geraint M North

Alasdair Rawsthorne

Jason Souloglou

Paul Knowles

An emulator allows subject code written for a subject processor having subject processor registers and condition code flags to run in a non-compatible computing environment. The emulator identifies and records parameters of instructions in the subject code that affect status of the subject condition code flags. Then, when an instruction in the subject code is encountered, such as a branch or jump, that uses the flag status to make a decision, the flag status is resolved from the recorded instruction parameters. Advantageously, emulation overhead is substantially reduced.

Condition code flag emulation for program code conversion

A method and apparatus for verifying program code conversion performed by an emulator. A first emulator configured in a same-to-same (X-X) mode converts subject code into target code for execution by a subject processor. Execution of the subject code natively by the subject processor is compared against execution through the first emulator, to verify that program code conversion. Optionally, the first emulator is then used to incrementally validate program code conversion (i.e. optimisation and/or translation) performed by a second emulator, such as a this-to-that (X-Y) mode emulator running on a target processor.

Method and apparatus for performing incremental validation of program code conversion

A method of handling exceptions for use in an emulator () performing program code conversion. Registers (X) of a subject machine () being emulated () are represented by a pair of abstract registers (X,X) on the target machine (), suitably using memory locations of the target machine and/or any available target registers. One of the pair (e.g., Reg X) holds a definitive value at entry into a section () of subject code () while the other (e.g., Reg X) holds a speculative value which is updated during translation and execution of that section of code. Exceptions are handled by recovering the conditions of the virtual subject machine () upon entry into the section of subject code () using the definitive version of each abstract register (i.e., Reg X). Advantageously, the function of the pair of registers (X,X) is alternated upon successful completion of each section of subject code () such that a definitive version of each register is always available for exception handling while avoiding time consuming copy and storing operations.

Exception handling method and apparatus for use in program code conversion

An emulator () allows subject code () written for a subject processor () having subject processor registers () and condition code flags () to run in a non-compatible computing environment (). The emulator () identifies and records parameters of instructions in the subject code () that affect status of the subject condition code flags (). Then, when an instruction in the subject code () is encountered, such as a branch or jump, that uses the flag status to make a decision, the flag status is resolved from the recorded instruction parameters. Advantageously, emulation overhead is substantially reduced.

A method for emulating a processor of a first endian type on a processor of a second endian type, wherein each memory access address B of string length L is transformed to the address A&#x2212;B&#x2212;L+S, wherein A is the total number of bytes allocated to a program, and S is the start address of the program.

Growing community of inventors

Manchester, United Kingdom

John H Sandham