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assembly.md

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assembly

nasm - Netwide Assembler

yasm - Yet Another Assembler

AX - 16 bit

EAX - 32 bit

AH, AL - 8 bit each

Diagram which shows the register size

  31          16 15          8 7            0
+--------------+--------------+--------------+
|           EAX (32 bits)                    |
+--------------+--------------+--------------+
       |              |              |
       |              |              |
       |              |              +----- AL (8 bits)
       |              +-------------------- AH (8 bits)
       +------------------------------------ AX (16 bits)

working with yasm

source main.asm

section .text
  global _start
_start:
  mov rax, 60
  mov rdi, 42
  syscall

generate object file - yasm -felf64 main.asm - this will generate main.o

generate executable file - ld main.o -o main -e _start - this will generate main

generate executable file can be run as ./main

Linux system call table: https://chromium.googlesource.com/chromiumos/docs/+/master/constants/syscalls.md

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