[luke@YavinIV LOR]$ cat test.s            
# AT&T syntax
# Add 3 and 2
.global _start

.text

_start: movq  $0x0123456789abcdef,%rax
        movl  $0x0000ffff,%eax
        movq  $0x0123456789abcdef,%rax
        movw  $0x00ff,%ax
        movq  $0x0123456789abcdef,%rax
        movb  $0x0f,%ah
        movq  $0x0123456789abcdef,%rax
        movb  $0x0f,%al

        movq  $1,%rax #halt programm
        int   $0x80 #call linux

[luke@YavinIV LOR]$ as test.s -g -o test.o
[luke@YavinIV LOR]$ ld test.o -g -o test  
[luke@YavinIV LOR]$ gdb ./test  
          
...

(gdb) b _start
Breakpoint 1 at 0x400078: file test.s, line 7.
(gdb) r
Starting program: /home/luke/asm/LOR/test 

Breakpoint 1, _start () at test.s:7
7	_start: movq  $0x0123456789abcdef,%rax
(gdb) si
8	        movl  $0x0000ffff,%eax
(gdb) p/x $rax
$1 = 0x123456789abcdef
(gdb) si
9	        movq  $0x0123456789abcdef,%rax
(gdb) p/x $rax
$2 = 0xffff
(gdb) si
10	        movw  $0x00ff,%ax
(gdb) p/x $rax
$3 = 0x123456789abcdef
(gdb) si
11	        movq  $0x0123456789abcdef,%rax
(gdb) p/x $rax
$4 = 0x123456789ab00ff
(gdb) si
12	        movb  $0x0f,%ah
(gdb) p/x $rax
$5 = 0x123456789abcdef
(gdb) si
13	        movq  $0x0123456789abcdef,%rax
(gdb) p/x $rax
$6 = 0x123456789ab0fef
(gdb) si
14	        movb  $0x0f,%al
(gdb) p/x $rax
$7 = 0x123456789abcdef
(gdb) si
16	        movq  $1,%rax #halt programm
(gdb) p/x $rax
$8 = 0x123456789abcd0f
(gdb) quit
A debugging session is active.

	Inferior 1 [process 21303] will be killed.

Quit anyway? (y or n) y