8. 32-bit x86 Assembly (IA32)

In this chapter, we cover the Intel Architecture 32-bit (IA32) instruction set architecture. Recall that an instruction set architecture (or ISA) defines the set of instructions and binary encodings of a machine-level program. To run the examples in this chapter, you will need access to a machine with an x86 processor or a compiler that can create 32-bit executables. The term "x86" is often used synonymously with the IA32 architecture. The x86 (and its 64-bit variant x86-64) are ubiquitous in modern computers, including Apple, Windows and Linux machines.

Very few modern machines have 32-bit processors; most Intel and AMD systems produced since 2007 have 64-bit processors. To check what type of process you have, use the uname -p command:

$ uname -p

If typing uname -p returns either i686 or i386, your system has a 32-bit processor. However, if the uname -p command returns x86_64, your system has a newer 64-bit processor. Please note that since x86-64 is an extension of the older IA32 ISA, virtually all 64-bit systems contain a 32-bit subsystem that allows the execution of 32-bit executables.

If you have a 64-bit Linux system, additional packages are sometimes required to allow users to create 32-bit executables, like we will be doing in this chapter. For example, on an Ubuntu machine you will need to install 32-bit development libraries and additional packages to augment GCC with crosscompiling features:

sudo apt-get install libc6-dev-i386 gcc-multilib
x86 Syntax Branches

x86 architectures typically follow one of two different syntax branches. UNIX machines commonly use the AT&T syntax, since UNIX was developed at AT&T Bell labs. The corresponding assembler is GNU Assembler (GAS). Since we use GCC for most examples in this book, we cover AT&T syntax in this chapter. Windows machines commonly use Intel syntax, which is used by Microsoft’s Macro Assembler (MASM). The Netwide Assembler (NASM) is an example of a Linux assembler that uses Intel syntax. The argument on the superiority of one syntax over the other is one of the "holy wars" of the discipline. However, there is value in being familiar with both syntaxes, as a programmer may encounter either in various circumstances.