Instruction Size

[dyn!o]

Complex question.

It depends on the sort of protection are you working on.

1. Common software.
I would suggest a disassembler source engine (you can find few on the net, as I remember also on OllyDbg page). This will deal with all offsets.

2. Crypted software.
I would suggest EIP logger since some protections use polymorphic and/or metamorphic engines, thus you will fail with disassembler engine.

3. Crypted software with virtual machine.
This is the worst assumption. In this case I would suggest to write own disassembler (for decompiling opcodes and in some fancy protections even operation types) and tracer (code flow execution control). Hard thing but the most effective.

Regards.