/* swap.c  ... based on CMU system's course lecture 4
 *
 *   $ gcc -O1 -m32 swap.c -o swap
 *
 *   $ gdb swap
 *   (gdb) start
 *   (gdb) disass swap
 *   Dump of assembler code for function swap:
 *      0x08048394 <+0>:        push   %ebp
 *      0x08048395 <+1>:        mov    %esp,%ebp
 *      0x08048397 <+3>:        push   %ebx
 *      0x08048398 <+4>:        mov    0x8(%ebp),%edx
 *      0x0804839b <+7>:        mov    0xc(%ebp),%eax
 *      0x0804839e <+10>:       mov    (%edx),%ecx
 *      0x080483a0 <+12>:       mov    (%eax),%ebx
 *      0x080483a2 <+14>:       mov    %ebx,(%edx)
 *      0x080483a4 <+16>:       mov    %ecx,(%eax)
 *      0x080483a6 <+18>:       pop    %ebx
 *      0x080483a7 <+19>:       pop    %ebp
 *      0x080483a8 <+20>:       ret    
 *   (gdb) break *(swap +4)
 *   (gdb) continue
 *   (gdb) info stack
 *   #0  0x08048398 in swap ()
 *   #1  0x080483cf in doit ()
 *   #2  0x080483df in main ()
 *   (gdb) info frame
 *   Stack level 0, frame at 0xbffff608:
 *     eip = 0x8048398 in swap; saved eip 0x80483cf
 *     called by frame at 0xbffff628
 *     Arglist at 0xbffff600, args: 
 *    Locals at 0xbffff600, Previous frame's sp is 0xbffff608
 *    Saved registers:
 *     ebx at 0xbffff5fc, ebp at 0xbffff600, eip at 0xbffff604
 *   (gdb) print $eip
 *   $1 = (void (*)()) 0x8048398 <swap+4>
 *   (gdb) x/32x $esp
 *   0xbffff5fc:        0xb7fceff4      0xbffff620      0x080483cf      0xbffff61c
 *   0xbffff60c:        0xbffff618      0xb7e9ad35      0xb7ff0a70      0x000001c8
 *   0xbffff61c:        0x0000007b      0xbffff628      0x080483df      0xbffff6a8
 *   0xbffff62c:        0xb7e81e37      0x00000001      0xbffff6d4      0xbffff6dc
 *   0xbffff63c:        0xf57fe414      0xffffffff      0xb7ffeff4      0x08048215
 *   0xbffff64c:        0x00000001      0xbffff690      0xb7fefa51      0xb7fffad0
 *   0xbffff65c:        0xb7fe09d0      0x00000001      0xb7fceff4      0x00000000
 *   0xbffff66c:        0x00000000      0xbffff6a8      0x58a166bb      0x7776feab
 *   (gdb) x/32d $esp
 *   0xbffff5fc:        -1208160268     -1073744352     134513615       -1073744356
 *   0xbffff60c:        -1073744360     -1209422539     -1208022416     456
 *   0xbffff61c:        123     -1073744344     134513631       -1073744216
 *   0xbffff62c:        -1209524681     1       -1073744172     -1073744164
 *   0xbffff63c:        -176167916      -1      -1207963660     134513173
 *   0xbffff64c:        1       -1073744240     -1208026543     -1207960880
 *   0xbffff65c:        -1208088112     1       -1208160268     0
 *   0xbffff66c:        0       -1073744216     1486972603      2004287147
 *  (gdb) quit
 */

void swap(int *xp, int *yp){
  int t0 = *xp;
  int t1 = *yp;
  *xp = t1;
  *yp = t0;
}

int doit(){
  int x = 123;
  int y = 456;
  swap(&x, &y);
  return x + y;
}

int main(){
  int z = doit();
  return 0;
}