Reversing: Secrets of Reverse Engineering

Appendix A. Deciphering Code Structures

This appendix discusses the most common logical and control flow constructs used in high-level languages and demonstrates how they are implemented in IA-32 assembly language. The idea is to provide a sort of dictionary for typical assembly language sequences you are likely to run into while reversing IA-32 assembly language code.

This appendix starts off with a detailed explanation of how logic is implemented in IA-32, including how operands are compared and the various conditional codes used by the conditional branch instructions. This is followed by a detailed examination of every popular control flow construct and how it is implemented in assembly language, including loops and a variety of conditional blocks. The next section discusses branchless logic, and demonstrates the most common branchless logic sequences. Finally, I've included a brief discussion on the impact of working-set tuning on the reversing process for Windows applications.

Understanding Low-Level Logic

The most basic element in software that distinguishes your average pocket calculator from a full-blown computer is the ability to execute a sequence of logical and conditional instructions. The following sections demonstrate the most common types of low-level logical constructs frequently encountered while reversing, and explain their exact meanings. I begin by going over the process of comparing two operands in assembly language, which is a significant building block used in ...