Assembly

Assembly

Low-level language with a very strong correspondence between the instruction in the language and the architecture's machine code instructions.

When to Use

• Operating System Kernels
• Embedded Systems / Microcontrollers
• Reverse Engineering
• Extreme optimization (rarely needed today)

Quick Start (x86_64 Linux)

section .data
    msg db "Hello, World!", 0xa
    len equ $ - msg

section .text
    global _start

_start:
    mov rax, 1      ; write syscall
    mov rdi, 1      ; stdout
    mov rsi, msg    ; buffer
    mov rdx, len    ; length
    syscall

    mov rax, 60     ; exit syscall
    xor rdi, rdi    ; exit code 0
    syscall

Core Concepts

Registers

Small, fast storage locations directly in the CPU (e.g., RAX, RBX, RIP).

Instructions

Commands executed by the CPU (MOV, ADD, SUB, JMP).

Stack

Region of memory for storing local variables and return addresses (USH, POP).

Best Practices

Do:

• Use comments liberally (assembly is hard to read)
• Follow calling conventions (e.g., System V AMD64 ABI)
• Use descriptive labels

Don't:

• Hand-optimize unless you beat the compiler (unlikely)
• Ignore alignment requirements

References

• x86 Assembly Guide