% gdb tryaddone 
GNU gdb Red Hat Linux (5.2.1-4)
Copyright 2002 Free Software Foundation, Inc.
...
(gdb) b main
Breakpoint 1 at 0x804836c: file TryAddOne.c, line 15.
(gdb) r
Starting program: /www/matloff/public_html/50/PLN/tryaddone 

Breakpoint 1, main () at TryAddOne.c:15
15	{  x = 7;
(gdb) n
16	   addone(&x);
(gdb) p/x $esp
$1 = 0xbfffdcf0
(gdb) p/x &x
$2 = 0x8049524
(gdb) s
addone () at AddOne.s:26
26	   push %ebx
Current language:  auto; currently asm
(gdb) p/x $esp
$3 = 0xbfffdcdc
(gdb) p/x $ebx
$4 = 0x4213820c
(gdb) x/2w $esp
0xbfffdcdc:	0x08048383	0x08049524
(gdb) si
31	   movl 8(%esp), %ebx  
(gdb) p/x $esp
$5 = 0xbfffdcd8
(gdb) x/3w $esp
0xbfffdcd8:	0x4213820c	0x08048383	0x08049524
(gdb) si
33	   incl (%ebx)  # need the (), since the argument was an address
(gdb) si
36	   pop %ebx
(gdb) si
38	   ret
(gdb) p/x $esp
$6 = 0xbfffdcdc
(gdb) p/x $ebx
$7 = 0x4213820c
(gdb) x/2w $esp
0xbfffdcdc:	0x08048383	0x08049524
(gdb) si
0x08048383 in main () at TryAddOne.c:16
16	   addone(&x);
Current language:  auto; currently c
(gdb) p/x $esp
$8 = 0xbfffdce0