System and Method for Debugging of Computer

A backwards debugger configured to implement a method of returning to a state in the history of execution of a computer program, said state comprising a set of values of one or more of registers of a processor on which the program is running, working memory space to which the program has access and operating system resources allocated to the program, the method comprising:

• identifying in machine code representing said program, instances of machine code instructions associated with substantially non-deterministic events;
• modifying said program machine code to execute a program instrumentation set of machine code instructions to handle said substantially non-deterministic events;
• executing said modified program machine code, storing a time series of said states during said executing;
• restoring a said stored state;
• and
• executing said modified program machine code forward in time starting at said restored state to return to said state in said program history of execution.

A backwards debugger, the debugger comprising:

• code to record data identifying a state of a program for backwards debugging whilst said program is running in a forwards direction;
• and
• code to provide an effective backwards debugging function by running said program forward from a said state;
• and
• wherein said debugger further comprises:
• code to handle non-deterministic events in said program, said non-deterministic events comprising one or more events selected from the group consisting of:
• a thread switch event;
• an asynchronous event;
• and a data read from memory shared with a second program, process or device.

A backwards debugger configured to implement a method of going to an arbitrary point in computer program code execution of a processor connected to a memory, said arbitrary point being determined by a selection criterion, the backwards debugger, in operation:

• partitioning the computer program code into first portions of code comprising instructions for linear computer program code execution and second portions of code comprising instructions for non-linear computer program code execution;
• executing said computer program code by executing a said first portion of code and by evaluating to which point in the computer program code a said second portion of code following said executed first portion of code would, if executed, transfer execution, and continuing execution of said computer program code at that point;
• storing at least one snapshot of computer program code execution during said executing, said snapshot comprising at least one of register values of the processor and memory values of the memory;
• and
• selecting a said snapshot, restoring register values of the processor and memory values of the memory to those in the snapshot and continuing execution from that point until the selection criterion has been met, to go to said arbitrary point;
• and
• handling non-deterministic thread switch events by:
• modifying code of said computer program code to add mutex drop followed by mutex take instructions to each thread of said program;
• logging data identifying a new thread to take said mutex following a said mutex drop;
• and
• recreating said thread switch events during backwards debugging using said logged data.