Chapter 11. x86 Assembly Language Programming

Chapter 11. x86 Assembly Language Programming
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Table of Contents

11.1. Synopsis
11.2. The Tools
11.3. System Calls
11.4. Return Values
11.5. Creating Portable Code
11.6. Our First Program
11.7. Writing UNIX® Filters
11.8. Buffered Input and Output
11.9. Command Line Arguments
11.10. UNIX® Environment
11.11. Working with Files
11.12. One-Pointed Mind
11.13. Using the FPU
11.14. Caveats
11.15. Acknowledgements

This chapter was written by G. Adam Stanislav <adam@redprince.net>.

11.1. Synopsis

Assembly language programming under UNIX® is highly undocumented. It is generally assumed that no one would ever want to use it because various UNIX® systems run on different microprocessors, so everything should be written in C for portability.

In reality, C portability is quite a myth. Even C programs need to be modified when ported from one UNIX® to another, regardless of what processor each runs on. Typically, such a program is full of conditional statements depending on the system it is compiled for.

Even if we believe that all of UNIX® software should be written in C, or some other high-level language, we still need assembly language programmers: Who else would write the section of C library that accesses the kernel?

In this chapter I will attempt to show you how you can use assembly language writing UNIX® programs, specifically under FreeBSD.

This chapter does not explain the basics of assembly language. There are enough resources about that (for a complete online course in assembly language, see Randall Hyde's Art of Assembly Language; or if you prefer a printed book, take a look at Jeff Duntemann's Assembly Language Step-by-Step (ISBN: 0471375233). However, once the chapter is finished, any assembly language programmer will be able to write programs for FreeBSD quickly and efficiently.