In essence, a disassembler is the exact opposite of an assembler. Where an assembler converts code written in an assembly language into binary machine code, a disassembler reverses the process and attempts to recreate the assembly code from the binary machine code.
Since most assembly languages have a one-to-one correspondence with underlying machine instructions, the process of disassembly is relatively straight-forward, and a basic disassembler can often be implemented simply by reading in bytes, and performing a table lookup. Of course, disassembly has its own problems and pitfalls, and they are covered later in this chapter.
Many disassemblers have the option to output assembly language instructions in Intel, AT&T, or (occasionally) HLA syntax. Examples in this book will use Intel and AT&T syntax interchangeably. We will typically not use HLA syntax for code examples, but that may change in the future.
Here we are going to list some commonly available disassembler tools. Notice that there are professional disassemblers (which cost money for a license) and there are freeware/shareware disassemblers. Each disassembler will have different features, so it is up to you as the reader to determine which tools you prefer to use.
ida37fw) A DOS GUI tool that behaves very much like IDA Pro, but is considerably more limited. It can disassemble code for the Z80, 6502, Intel 8051, Intel i860, and PDP-11 processors, as well as x86 instructions up to the 486.Many of the Unix disassemblers, especially the open source ones, have been ported to other platforms, like Windows (mostly using MinGW or Cygwin). Some Disassemblers like otool ([OS X) are distro-specific.
computer_intelligence_assembler_disassembler. This Forth-based tool allows to incrementally and interactively build knowledge about a code body. It is unique that all disassembled code can be re-assembled to the exact same code. Processors are 8080, 6809, 8086, 80386, Pentium I en DEC Alpha. A scripting facility aids in analyzing Elf and MSDOS headers and makes this tool extendable. The Pentium I ciasdis is available as a binary image, others are in source form, loadable onto lina Forth, available from the same site.Example usage:
