ARMv8 Examples

The examples run on a Raspberry Pi 4 with Ubuntu 20.04.1 64 bit Server. Unfamiliar concepts are explained in source comments as they are introduced.
Examples include:
- hello.s start here if you are completely new to ARM assembly and/or linux system calls
- loop.s same as hello.s, but prints a message mutliple times in order to demonstrate a basic looping construct
- prompt.s Asks the user for a name then prints out the name with a greeting. Introduces reading input from the command line
- guess.s Generates a random number from 0 - 9 and asks the user to guess until the right answer is inputted
- collatz.s Asks the user to input a positive number and returns the number of steps for the number to converge on 1 using the Collatz Conjecture
- sort.s Demonstrates how a simple sort algorithm (insertion sort) can be implemented in assembly. Each line of the algorithm is mapped to the corresponding assembly code
- brk.s An example usage of the brk system call to dynamically allocate more memory to a program.

To Compile

$ as -g name.s -o name.o && ld name.o -o name

where "name" is replaced with the example you want to run

Examining with gdb

It's highly encouraged to step through the programs with a debugger to see what's actually going on. To do this run $ gdb name

Here are some commands you'll want to know:

start starts the program
layout asm brings up a TUI environment so you can see what assembly instructions are being executed
stepi steps one assembly instruction
i r prints out the contents of the registers
x addr prints out the contents of the given address
x/s addr prints out the contents of the given address as a string
q quit

Pressing enter at a blank prompt causes the previously executed command to run again. This can save a lot of typing.

armsim.py

This is a python3 simulator for a subset of arm64 instructions. It aims to be compatible with gnu assembler files and supports a subset of directives. Further documentation can be found in the numerous comments. Currently armsim can run hello.s, loop.s, prompt.s, guess.s, collatz.s, sort.s, and brk.s. See the guide for information on its features and what instructions are currently supported. It's advisable to use the sample programs as a starting point for understanding the supported instructions and for writing your own programs

armdb.py

A simple debugger interface for armsim. See the guide for usage instructions.

Using armsim as a Library