# quick & dirty asm tut for x86_64.
#
# Uses a syscall of write() and exit()
#
# Compile and execute like:
# as -o write.o write.s
# ld -o write write.o
# ./write
# Hi Mom!
#
# Tested on a x86_64 Gentoo System 2017.03.10.
#
# Found to be very helpful:
# http://blog.rchapman.org/posts/Linux_System_Call_Table_for_x86_64

.data # data section

msg:    .asciz "Hi Mom!\n"  # Our string to write
        len = . - msg - 1   # Length of our string to write

.text
.global _start

_start:                  # Program entry point
       movq  $1,%rax     # Write(); move the syscall number into %rax
       movq  $len,%rdx   # Arg 3 of write(); move length of string msg into %rdx
       movq  $msg,%rsi   # Arg 2 of write(); move pointer to string msg into %rsi
       movq  $1,%rdi     # Arg 1 of write(); move file descriptor (STDOUT) into %rdi
       syscall           # Call the Kernel
       movq  $60,%rax    # Exit(); move the syscall number into %rax
       xor   %rdi,%rdi   # Clear %rdi
       syscall           # Call the Kernel