Introduction to ARM Assembly Language Programming

Jun 12, 2024

Introduction to ARM Assembly Language Programming

Overview

  • Assembly language is a low-level programming language closest to machine language, specific to computer architecture.
  • ARM (Advanced RISC Machine) assembly language is popular due to its efficiency and wide usage in over 200 billion devices.
  • Scott Cosentino, a technical instructor, teaches this course on ARM assembly programming, aiming to provide a fundamental understanding of the ARM processor and assembly programming.

Course Goals

  • Introduction to low-level programming concepts through ARM assembly language.
  • Understanding ARM processor architecture and how to interact with hardware efficiently using ARM assembly instructions.
  • Practical programming exercises using the CPULater emulator and Linux-based systems for hands-on experience.
  • Encouragement to share learned concepts with peers to enhance collaborative learning.

The CPUlater Emulator

  • Free online emulator used to follow along without needing special hardware.
  • Works with various architectures, including ARM v7 and other assembly languages like MIPS.
  • Emulating on ARM v7 D1 SOC, following similar steps to run code on actual ARM processors.

ARM Assembly Language Basics

  • Registers: Special memory locations close to the CPU for fast access and storage (R0-R7 for general purpose, R7 for system calls).
  • Special Registers: SP (Stack Pointer), LR (Link Register), PC (Program Counter), CPSR (Current Program Status Register).
  • Memory Layout: Understanding stack memory, common sizes (word, half-word, byte), and their practical uses in code.

Basic Instructions

  • Move (MOV): Moving data into registers and understanding syntax for immediate values and hexadecimal representation.
  • System Calls: Using system call numbers to interact with the operating system, e.g., terminating programs.
  • Arithmetic Operations: Add, subtract, multiply; handling larger numbers and setting condition flags (CPSR).
  • Logical Operators: AND, OR, Exclusive OR, negation (MVN for negation).

Advanced Instructions

  • Addressing Modes: Immediate, Register Direct, Register Indirect, Register Indirect with Offset, Pre and Post Increment.
  • Logical Shifts and Rotates: Left and Right shifts, rotations for manipulating bits and efficient computation.
  • Conditional Instructions: Conditional execution of instructions based on previous comparison results (like if-else in high-level languages).

Branching and Looping

  • Branches: Implementing conditional branches to create decision-making constructs, different types (branch if equal, not equal, etc.).
  • Loops: Implementing looping through branching, iterating through lists, handling list end conditions, and potential issues with uninitialized memory.

Functions and Subroutines

  • Function Calls: Creating branches with links to subroutines, using LR to return to the main program after function execution.
  • Preservation of Registers: Using push and pop to save and restore register values during function calls to avoid overwriting important values.
  • Function Flow: Detailed handling of function execution flow, return values, and managing stack memory efficiently.

Hardware Interaction

  • Emulating Devices: Using the D1 SOC emulator to interact with hardware devices like switches and LEDs.
  • Input and Output: Using memory-mapped I/O to read switch states and control LEDs, practical examples of writing and reading from hardware.

Operating System Level Programming

  • Emulating Raspbian: Setting up a Raspberry Pi environment using QEMU emulation to run ARM assembly on a Linux-based system.
  • System Calls on Linux: Using system calls through ARM assembly for tasks like printing to standard output, facilitated by the operating system (e.g., write system call).

Debugging and Memory Examination

  • GDB Debugger: Using GDB to debug assembly programs on Linux, setting breakpoints, examining register and memory states, stepping through code for detailed inspection.
  • Memory Inspection: Using GDB commands to examine memory contents in different formats (hexadecimal, decimal, character), understanding the memory layout of strings and other data.

Summary

This course provides a comprehensive introduction to ARM assembly language programming, covering essential concepts from basic instructions to complex function calls and hardware interactions, with practical tutorials using emulators and Linux environments.

Full transcript