I didn't compile the binary myself.
It has no stack protections

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

int main(int argc, char **argv)
{
  volatile int modified;
  char buffer[64];

  modified = 0;
  gets(buffer);

  if(modified != 0) {
      printf("you have changed the 'modified' variable\n");
  } else {
      printf("Try again?\n");
  }
}

The addresses of modified and buffer are printed above argv, which is nonsense.
Also their true location is different, as evidenced by what strcpy modifies. 
print &modified
$1 = (volatile int*) 0xffffcf3c
print &argv
$2 = (char***) 0xffffcf64