Introduction
Welcome to Assembly x86_64! If you're here, you probably fall in to one of these categories: being forced to learn this for school/a job, or being genuinely interested in learning this. Or maybe you just stumbled across this and you thought "Why not? It can't be that hard."
Well, it is that hard. I'll give you the code, and then explain it after.
The Code
section .data ; this is where variables are initialized
msg db "Hello, World!", 0xa ; 0xa is a newline
msglen equ $ - msg
section .text ; this is the code section
global _start ; declare entry point
_start: ; define entry point
mov rax, 1 ; sys_write(
mov rdi, 1 ; STDOUT_FILENO,
mov rsi, msg ; msg,
mov rdx, msglen ; sizeof(msg)
syscall ; );
; exit
mov rax, 60 ; exit
mov rdi, 0 ; exit_status
syscall ; );
I'm hoping you're still here. Although probably not 😁.
Anyway, here's the line-by-line:
- This is the section where variables are declared
- Declare the
msg
variable to the sizedata byte
, or 8 bits.;
starts a comment. - Set the
msglen
variable to asizeof(msg)
- This is the code section.
- This line declares the entry point, called
_start
- This line starts the definition of the
_start
function -
rax
is the system call id. So exit is 60, stdout is 1, 2 is stderr, etc. - This line sets the file descriptor (fd) to 1, which is stdout.
- "Invoke" the message
- "Invoke the message length
-
syscall
means "execute the stuff that I just made." - Set
rax
to 60, which issys_exit
- This line is the exit status
- Call the code.
I'm still learning though, so if I'm wrong, please correct me.
By the way, it's a fantastic idea to align Assembly code to maintain the nearly non-existent readability. Please also use comments (I didn't because I described it afterword).
There are plenty of great books and videos on how to learn Assembly. If you still want to learn it, find one! I recommend this YouTube playlist.
(Also, if you know how to add syntax highlighting for this code block, please tell me in the comments 🙂)
Top comments (3)
Thanks for this reminder! And very happy to see people still try to "struggle" with assembly. 🙂 It is a dive into the unknown, all that registers and shifting ...
How to run/compile this code? This is my first time using assembly lol.
You need the NASM compiler. After installing it, run this:
Then link the object file:
Then run the file:
Sorry, I forgot to put this in the article!