Fast interpreter using gcc's computed goto

0x1 - takes following byte in insn stream and prints "first <byte>"
0x2 - prints "second"
0x3 - terminates program

#include <stdio.h>

void interp(char* start) {
  void* table[4] = {NULL, &&inst1, &&inst2, &&inst3};
#define DISPATCH(n) start += n; goto *(table[*start]);
  DISPATCH(0);
  do {    
    inst1:
      printf("first %d\n", *(start+1));
      DISPATCH(2);
    inst2:
      printf("second\n");
      DISPATCH(1);
    inst3:
      break;
  } while (1);
}

int main() {
  char test[] = {0x1, 0x5, 0x1, 0x2, 0x2, 0x3};
  interp(test);
  return;
}

 80483c6:       0f be 03                movsbl (%ebx),%eax
 80483c9:       8b 04 84                mov    (%esp,%eax,4),%eax
 80483cc:       ff e0                   jmp    *%eax
 80483ce:       89 f6                   mov    %esi,%esi
 80483d0:       83 ec 08                sub    $0x8,%esp
 80483d3:       0f be 43 01             movsbl 0x1(%ebx),%eax
 80483d7:       50                      push   %eax
 80483d8:       68 0c 85 04 08          push   $0x804850c
 80483dd:       e8 0a ff ff ff          call   80482ec 
 80483e2:       83 c3 02                add    $0x2,%ebx
 80483e5:       0f be 03                movsbl (%ebx),%eax
 80483e8:       8b 44 84 10             mov    0x10(%esp,%eax,4),%eax
 80483ec:       83 c4 10                add    $0x10,%esp
 80483ef:       ff e0                   jmp    *%eax
 80483f1:       8d 76 00                lea    0x0(%esi),%esi
 80483f4:       83 ec 0c                sub    $0xc,%esp
 80483f7:       68 16 85 04 08          push   $0x8048516
 80483fc:       e8 cb fe ff ff          call   80482cc 
 8048401:       43                      inc    %ebx
 8048402:       0f be 03                movsbl (%ebx),%eax
 8048405:       8b 44 84 10             mov    0x10(%esp,%eax,4),%eax
 8048409:       83 c4 10                add    $0x10,%esp
 804840c:       ff e0                   jmp    *%eax
 804840e:       89 f6                   mov    %esi,%esi
 8048410:       83 c4 10                add    $0x10,%esp
 8048413:       5b                      pop    %ebx
 8048414:       5e                      pop    %esi
 8048415:       5f                      pop    %edi
 8048416:       c3                      ret    
 8048417:       90                      nop    

Posted at 03:33PM Jun 07, 2007 by nike in Sun  |  Comments[12]