type-punning?

Hi all

I have a program which, with inessential details removed,
looks like this:

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

static int punme(void** dat,size_t newsize)
{
  void *newdat = realloc(*dat,newsize);

  if (! newdat) return 1;

  *dat = newdat;

  return 0;
}

int main (void)
{
  char *dat = malloc(30);

  int ret = punme((void**)&dat,40);

  printf("punme returns %i\n",ret);

  return 0;
}
--

My compiler (gcc -Wall -O3) tells me that "typepun.c:19:
warning: dereferencing type-punned pointer will break
strict-aliasing rules".  The code works as expected, ie,
prints that punme returns 0.

Who is the idiot? Me or the compiler?

Many thanks!

Jim