ARM Assembly

Preface

I recently designed a course on the subject of ARM assembly programming, which I am now teaching.  During the design of the course, I spent a great deal of time struggling to find information on certain topics within the subject.  I found a distinct lack of good resources on many things.  The biggest problem was finding information about the interface between assembly level code and the operating system.  On one occasion I even taught my students something totally wrong, because I had been forced to learn it myself through reverse engineering, and it turns out that the operating system and the debugger don't behave the same way.  Of course, I corrected myself two days later, and I used the incident as a teaching opportunity.  What I learned from all of this is that assembly programming, especially for the ARM architecture, is very poorly documented at the interface between OS and user space programs.  I am writing this series with an aim to fix this problem.

Introduction

This series will teach ARM assembly programming, using ARMv7 assembly running on the Raspberry Pi 2.  The Pi 3 should also work fine for a vast majority of this, however some parts will not work for the original Pis.  I will do my best to identify these where I am aware of them.

This series assumes that if you have a Raspberry Pi, you either already have everything you need to use it, or you can figure out what you need and obtain it.  The essential things you will need are internet access for your Pi, at least briefly for the first chapter, and some way to input text and view text output.  This can be a USB keyboard and a monitor that will work with the Pi, it can be an SSH connection to the Pi over a network, or it can be a serial to USB adapter that gives you direct terminal access through the GPIO pins (Adafruit sells these).  There are plenty of resources online for each of these methods.

The operating system used for this series is Raspbian.  At least one of my students is using Arch Linux successfully, so this may also be a viable option.  Raspbian can either be installed using the NOOBs installer that comes on most SD cards sold specifically for the Pi, or you can download a Raspbian image and install it directly.  The second option is recommended, as it will give you the most recent version of Raspbian.  In addition, you may be able to avoid certain issues some of my students have run into with Raspbian installed through NOOBs for another assembly project you might be interested in that is currently outside the scope of this series.

Additionally, this series expects you to already have a basic understanding of the concepts of processor registers and assembly instructions.  I am sure many people will be able to figure these things out as they go along, but if you start this without that understanding and find yourself struggling to understand even the basic concepts, perhaps you should take a break and spend a little bit of time learning about modern processor architectures and how they work.  (I will probably write a short article on this in the future, but right now this series takes higher priority.)

Table of Contents

This will be populated with links to each chapter as they are published, in order of publication.

1. Setup
2. The ARM Architecture
3. Basic Math
4. Math with Small Data Types
5. Type Casting
6. Advanced Integer Math
7. Memory Architecture
8. Integer Division
9. Ditching GCC
10. The Stack
11. Pointers and Global Memory Access
12. Function Pointers
13. Branches
14. Conditional Branching
15. Loops
16. Indexing Modes
17. Arrays and Structs

Index

This will be populated with links to the chapters sorted by topic.