Nasm's syntax and AT&T syntax differ quite a bit. Nasm syntax:
global _start
section .text
_start
mov eax,4
mov ebx,1
mov ecx, msg
mov edx,msg_len
int 80h
mov eax,1
int 80h
section .data
msg db 'Hello, world',0Ah
msg_len equ $-msg
(G)as syntax (AT&T):
.global _start
.text
_start:
movl $4, %eax
movl $1, %ebx
movl $msg, %ecx
movl $msg_len, %edx
int $0x80
movl %eax, %ebx
movl $1, %eax
int $0x80
.data
msg: .ascii "Hello World!\n"
msg_len = . - msg
As you can see, they look quite different, but recognizably do the same thing.
Best,
Frank