This textbook provides a gentle introduction to assembly language programming. What makes this introduction "gentle" is that it assumes the reader is already comfortable with C or C++ coding. We use this assumed knowledge to bridge backward towards the low level ISA (Instruction Set Architecture).
We drive home a very sharp point:
Assembly language is nothing to be scared of!As mentioned, if you are already familiar with C (or languages descended from C such as C++), this book begins with what you already know.
Later chapters dive more deeply into the corners and recesses of the ARM V8 ISA and are suitable for those wishing to master the rich instruction set of the 64 bit ARM processors.
Yes, absolutely.
Assembly language programming is quite closely dependent upon the underlying hardware architecture. The host operating environment plays an outsized role in determining how assembly language programs are constructed. A "calling convention" refers to how functions are called and how parameters are passed.
Originally, this book taught only the ARM LINUX conventions. However, over time, we developed a suite of macros that make it much easier to write code for use either on MacOS or on LINUX.
This link will lead to a current copy of them as well as documentation. Macros that make programming a bit easier are also included.
This chapter provides some additional information about Apple Silicon assembly language programming.
You'll notice that we make use of the C-runtime directly rather than
make OS system calls. So, for instance, if we want to call write(),
we call write from the assembly language.
This version of the system call write is a wrapper function built into
the C-runtime (CRT) which handles the lower level details of performing
a system call. See the here on what
actually happens inside these wrapper functions.
The benefit of using the CRT wrappers is that there are differences between the distributions and architectures that are masked by using the CRT wrappers. Therefore, when you use the wrappers rather than the direct method of making system calls, your code will be more portable.
As commendable as the ARM designs are, ARM's naming conventions for their Intellectual Properties are horrid. In this book, AARCH64 and ARM V8 are taken to be synonyms for the 64 bit ARM Instruction Set Architecture (ISA).
It is very difficult to find documentation at the ARM site because they have so many versions, so many names for the same thing and so much documentation in general. It really can be maddening.
Within the text we will provide germane links as appropriate.
Here is a link to "a" main instruction set page.
Getting the tools for assembly language development is quite straight
forward - perhaps you already have them. Using apt from the Linux
terminal, say:
sudo apt update
sudo apt install build-essential gdb
On the Macintosh type:
xcode-select --install
into a terminal and follow directions. Note that gdb is replaced by
lldb with just enough differences to make you cry.
Then you'll need your favorite editor. We ourselves use vi for quick
edits and Visual Studio Code for any heavy lifting.
We use gcc, the C "compiler". g++ could also be used. On the Mac,
clang can also be used.
What sense does that make... using the "compiler" to "compile" assembly language?
Well, to answer that one must understand that the word "compiler" refers to only one step in a build sequence. What we talk about as being the "compiler" is actually an umbrella that includes:
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A preprocessor that acts on any
#preprocessor command like#include. These commands are not part of C or C++. Rather they are commands to the preprocessor.Note that
gccwill invoke the C preprocessor if your assembly language file ends in.S- capital S. It may or may not be invoked if your file ends in a lower case s or any other file extension depending upon your system. -
The actual compiler, whose job it is turn high level languages such as C and C++ into assembly language.
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The assembler, which turns assembly language into machine code which is not quite ready for execution.
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And finally, the linker, which combines potentially many intermediate machine code files (called object files), potentially many library files (statically linked .dlls on Windows and .a files on Linux). The linker is the last step in this chain.
Here is a video explaining this process.
We use gcc and g++ directly because, being umbrellas, they automate the above steps and automatically link with the CRT.
Suppose you've implemented main() in a C file (main.c) and want to
make use of an assembly language file you have written (asm.S). It can
be done in several ways.
gcc main.c asm.S
That's all you need for a minimal build. The resulting program will be
written to a.out. All the intermediate files that are generated will
be removed.
gcc -c main.c
gcc -c asm.S
gcc main.o asm.o
Used in this way, .o files are left on disk. Using the previous
method, the .o files are removed without you seeing them.
Suppose main() is implemented in assembly language and main.s is
self-contained, then simply:
gcc main.S
Often, you will want to enable the debugger gdb or lldb. Do this:
gcc -g main.S
Without the -g command line option, your debugger may not properly
operate.
To repeat, if you want gcc to run your code through the C
pre-processor (for handing #include for example), name your assembly
language source code files with a capital S. So, on Linux:
gcc main.s
Will not go through the C pre-processor but
gcc main.S
will.
To drive home the point that the "compiler" is an umbrella, using gcc to "compile" a program causes the following to be called on Ubuntu running on ARM:
/usr/bin/cpp
/usr/lib/gcc/aarch64-linux-gnu/11/cc1
/usr/bin/as
/usr/lib/gcc/aarch64-linux-gnu/11/collect2 which is...
/usr/bin/ld
cpp is the C preprocessor - it is a general tool can is used by other
languages as well (C++, for example).
cc1 is the actual compiler.
as is the assembler.
ld is the linker.
You can see why we default to using the umbrella command in this book.
We start by providing what we're calling "bridging" from C and C++ to assembly language. We use the knowledge you already have to learn new knowledge - how cool is that!
| Chapter | Markdown | |
|---|---|---|
| 0 | Kickstart | Link |
| 1 | Hello World | Link |
| 2 | If Statements | Link |
| 3 | Loops | |
| 3a | While Loops | Link |
| 3b | For Loops | Link |
| 3c | Implementing Continue | Link |
| 3d | Implementing Break | Link |
| 4 | Interludes | |
| 4a | Registers | Link |
| 4b | Load and Store | Link |
| 4c | More About ldr |
Link |
| 4d | Register Sizes | Link |
| 4e | Hexadecimal | Link |
| 5 | switch |
Link |
| 6 | Functions | |
| 6a | Calling and Returning | Link |
| 6b | Passing Parameters | Link |
| 6c | Example of calling some common C runtime functions | Link |
| 7 | FizzBuzz - a Complete Program | Link |
| 8 | Structs | |
| 8a | Alignment | Link |
| 8b | Defining | Link |
| 8c | Using | Link |
| 8d | What is "this" | Link |
| 9 | const |
Link |
Floating point operations use their own instructions and their own set of registers. Therefore, floating point operations are covered in their own section:
| Chapter | Markdown | |
|---|---|---|
| 0 | Chapter Overview | Link |
| 1 | What Are Floating Point Numbers? | Link |
| 2 | Registers | Link |
| 3 | Truncation and Rounding | Link |
| 4 | Literals | Link |
| 5 | fmov |
Link |
| 6 | Half Precision Floats | Link |
| 7 | NEON SIMD Not Yet Written | Link |
What would a book about assembly language be without bit bashing?
| Chapter | Markdown | |
|---|---|---|
| 1 | Bit Fields | |
| 1a | Without Bit Fields | Link |
| 1b | With Bit Fields | Link |
| 1c | Review of Newly Described Instructions | Link |
| 2 | Endianness | Link |
In this section, we present miscellaneous material including our "world famous lecture" on debugging. This lecture has been invited at several colleges and universities. It is intended for audiences working with languages like C, C++ and assembly language but some of the lessons contained therein are applicable to all languages.
| Chapter | Markdown | |
|---|---|---|
| 1 | Apple Silicon | Link |
| 2 | Apple / Linux Convergence | Link |
| 3 | Variadic Functions | Link |
| 4 | Under the hood: System Calls | Link |
| 5 | Determining string literal lengths for C functions | Link |
| 6 | Calling Assembly Language From Python | Link |
| 7 | Atomic Operations | Link |
| 8 | Jump Tables | Link |
| 9 | argv | ASM CODE |
| 10 | spin-locks | Link |
| - | Debugging Lecture | PPTX |
As indicated immediately above, the macro suite can be found here.
Here are some project specifications to offer a challenge to your growing mastery. Here are very brief descriptions presented in alphabetical order.
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Perhaps before you tackle these, check out the fully described FIZZBUZZ program first.
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Then try this as your very first project. With some blank lines and comments it weighs in at 35 lines.
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The DIRENT project demonstrates how a complex
structcan be used in assembly language. -
The PI project demonstrates floating point instructions. The program will "throw darts at a target," calculating an approximation of PI by tracking how many darts "hit the target" versus the total number of darts "thrown".
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The SINE project stresses floating point math and functions.
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The SNOW project uses 1970's era tech to animate a simple particle system. This project demonstrates a reasonable design process of breaking down complex problems into simpler parts.
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The WALKIES presents a cute little animation demonstrating looping with some pointer dereferencing.
Perry Kivolowitz's career in the Computer Sciences spans just under five decades. He launched more than 5 companies, mostly relating to hardware, image processing and visual effects (for motion pictures and television). Perry received Emmy recognition for his work on the The Gathering, the pilot episode of Babylon 5. Later he received an Emmy Award for Engineering along with his colleagues at SilhouetteFX, LLC. SilhouetteFX is used in almost every significant motion picture for rotoscoping, paint, tracking, 2D to 3D reconstruction, compositing and more.
In 1996 Perry received an Academy Award for Scientific and Technical Achievement for his invention of Shape Driven Warping and Morphing. This is the technique responsible for many of the famous effects in Forrest Gump, Titanic and Stargate.
Twenty twenty three marks Perry's 19th year teaching Computer Science at the college level, ten years at the UW Madison and now 8+ at Carthage College.
Assembly language is a passion for Perry having worked in the following ISAs (in chronological order):
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Univac 1100
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Digital Equipment Corporation PDP-11
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Digital Equipment Corporation VAX-11
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Motorola 68000
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ARM beginning with AARCH64
This work is dedicated to my wife Sara and sons Ian and Evan.
Perry has created a library of about 200 programming projects suitable for CS 1, CS 2, Data Structures, Networking, Operating Systems and Computer Organization classes. If a publisher of CS text books (or other CS related content) would be interested in purchasing the library, please reach out.
Also, check out Get Off My L@wn, a Zombie novel for coders.
You read that right... elite programmer Doug Handsman retires to his wife Ruth Ann's native northern Wisconsin. And then, well, the apocalypse happens. Bummer.
Rated 4.3 out of 5 with more than 70 reviews, it's a fun read and costs next to nothing.