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Assembly code (NASM) for mac - hello world

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  1. ; Hello World in assembly for mac
  2. ; nasm -f macho hello.asm
  3. ; ld -e _start -o hello hello.o
  4. ;
  5. section     .text
  6.  global _start                       ;must be declared for linker (ld)
  7.  
  8. _syscall:           
  9.      int     0x80            ;system call
  10.      ret
  11.  
  12. _start:                         ;tell linker entry point
  13.  
  14.      push    dword len       ;message length
  15.      push    dword msg       ;message to write
  16.      push    dword 1         ;file descriptor (stdout)
  17.      mov     eax,0x4         ;system call number (sys_write)
  18.      call    _syscall        ;call kernel
  19.  
  20.                              ;the alternate way to call kernel:
  21.                              ;push   eax
  22.                              ;call   7:0
  23.  
  24.      add     esp,12          ;clean stack (3 arguments * 4)
  25.  
  26.      push    dword 0         ;exit code
  27.      mov     eax,0x1         ;system call number (sys_exit)
  28.      call    _syscall        ;call kernel
  29.  
  30.                              ;we do not return from sys_exit,
  31.                              ;there's no need to clean stack
  32. section .data
  33.  
  34. msg     db      "Hello, world!",0xa     ;our dear string
  35. len     equ     $ - msg                 ;length of our dear string

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