Write a 64-bit program in assembly that prints Hello, world in .asm

section .data
    hello db 'Hello, world!',0

section .text
    global _start

_start:
    ; write Hello, world! to stdout
    mov eax, 4            ; system call number (sys_write)
    mov ebx, 1            ; file descriptor (stdout)
    mov ecx, hello        ; pointer to the message
    mov edx, 13           ; message length
    int 0x80              ; interrupt to invoke syscall

    ; exit the program
    mov eax, 1            ; system call number (sys_exit)
    xor ebx, ebx          ; exit code 0
    int 0x80              ; interrupt to invoke syscall

This assembly program uses the Linux system call interface to print "Hello, world!" to the standard output and then exits. The explanation for each step is provided as comments in the code:

  1. Section .data: Declare a data section to store constants.

assembly section .data hello db 'Hello, world!',0

  • hello is a null-terminated string containing the message to be printed.

  • Section .text: Declare a text section where the main code resides.

assembly section .text global _start

  • _start is the entry point for the program.

  • Start of the code (_start):

assembly _start:

  1. Write to stdout (sys_write):

assembly mov eax, 4 ; system call number (sys_write) mov ebx, 1 ; file descriptor (stdout) mov ecx, hello ; pointer to the message mov edx, 13 ; message length int 0x80 ; interrupt to invoke syscall

  • Set up registers for the write system call:

    • eax contains the system call number (4 for write).
    • ebx contains the file descriptor (1 for stdout).
    • ecx contains the pointer to the message (hello).
    • edx contains the message length (13 characters).
    • Trigger the system call using interrupt 0x80.

  • Exit the program (sys_exit):

assembly mov eax, 1 ; system call number (sys_exit) xor ebx, ebx ; exit code 0 int 0x80 ; interrupt to invoke syscall

  • Set up registers for the exit system call:
    • eax contains the system call number (1 for exit).
    • ebx contains the exit code (0).
    • Trigger the system call using interrupt 0x80.