System, method and computer program product for on-the-fly patching of executable code

A system for on-the-fly patching of executable code comprising:

• a processor;
• a memory operatively coupled to the processor;
• computer code loaded into the memory for implementing the functionality of:
• means for copying original instructions to be changed to a storage location while the original instructions are being executed;
• means for adding a hook with a first jump instruction for transferring control to the copied instructions;
• means for using a second jump instruction in the copied instructions to transfer control to an unpatched instruction in a location where the instructions are being patched;
• means for replacing the original instructions with mark instructions by using atomic writes that guarantee that a result of the operation can be observed as completed or not observed at all;
• using the mark instructions, means for storing, in a stack, a number representing how many instructions have been patched;
• means for calling the hook;
• and
• using the hook, means for activating the second jump instruction to transfer control to a location just after one of the original instructions from which the hook was called,
• wherein a number of times the mark instructions have been executed is counted to determine where, in the patched instructions, execution should resume, and
• wherein instructions, at a location of the original instructions Cede, are used to determine a number of the instructions that had already been executed based on the number representing how many instructions have been patched and the number of times the mark instructions have been executed.