Try these changes instead. Untested, but it should work # String is read only. .section .rodata msg: .asciz "hello, world!\n" # Put string

Try these changes instead. Untested, but it should work # String is read only. .section .rodata msg: .asciz "hello, world!\n" # Put string length in a variable instead .set STR_SIZE, . - msg # <snip> mov rdx, STR_SIZE