Generating Decision Trees for Decoding Binaries

Tools reading binary code, like analysers, debuggers, disassemblers, etc., need to decode the target's machine code. A decision tree is often used to represent the decoding function. Manually writing a decoder is a lengthy and error-prone task. It is desirable to be able to use the vendor's instruction code manual and to easily transform the documentation into a specification that a tool can use to generate a decoder. This paper presents a novel algorithm that computes a decision tree from machine code bit patterns alone. Neither the bit fields of the machine code, nor the width of the machine command, nor the order in which the bits should be decoded need to be specified. The decoding algorithm accesses any significant bit exactly once during decoding.