64-bit Assembly Language

Assembly on x86_64 and AArch64 architectures

Introduction

First of all, Computer Architecture mainly refers to a central computing unit(CPU) design, including its memory and input-output (IO) subsystems. It also includes some elements such as  RAM and memory reserved and mapped for external devices. Currently, the most common architecture families are:

• x86    - Intel/AMD architecture, mainly used in most desktop machines 
• ARM - the dominant mobile and embedded architecture created by Acorn

A CPU can only understand byte code generated assembly language by an assembler. Assembly language and the number of instructions may vary for each architecture and assembler. So I have created a repository on my GitHub which contains an example code written for x86_64 and AArch64 to demonstrate the architecture differences and assembly language. Feel free to check it out!

• 64-bit assembly

I placed the code for each architecture in a dedicated folder containing a Makefile to build and create executables for each program. Each folder also includes a challenging program that prints times table for numbers from 1 to 12 with nice formating. That challenge especially demonstrates the differences in Assembly instructions, structure and design between x86_64 and AArch64.

Comparison

The most notable differences in the mentioned architectures are:

• Different instruction sets, syntax and usage
• Different number of registers, their usages and names
• The x86_64 has 16 registers: rax, rbx, rcx, rdx, rbp, rsp, rsi, rdi and r8-r15 
• The AArch64 has 31 registers named r0-r30 and one more named rzr/rsp
• Different numbers for syscalls
• AArch64 uses the fixed-length instructions in contrast to variable-length for x86_64

Conclusion

I have learned the basic operations and techniques used in modern assembly while working on the code for each architecture. But I have also encountered some problems I have managed to debug and solve using breakpoints and the "objdump" command. Overall, it was a great experience and a fascinating topic to explore, and it was fun to compare it with simple 6502 Assembly. Not to mention the process of exploring assembly generated by the C and C++ compilers. But it is hard to argue that high-level languages are much easier to write with.

Author: Iurii Kondrakov 

Email: deezzir@gmail.com

GitHub: github.com

P.S this blog post is created for the SPO600 Lab 4