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To: freebsd-amd64@freebsd.org
Date: Sat, 28 Feb 2009 13:06:41 +0000
From: Dieter <freebsd@sopwith.solgatos.com>
Subject: Re: 32-bit truncation of 64-bit values
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> Having just tracked down an issue caused by a pointer-to-int truncation,

Was this in C?  Didn't the compiler complain?

cat demo_ptr_into_int.c ; gcc -O3 -o demo_ptr_into_int demo_ptr_into_int.c ; ./demo_ptr_into_int
/* demo_ptr_into_int.c
 *
 * Verify that compiler complains about truncation when
 * attempting to stuff a 64 bit pointer into a 32 bit int.
 */

#include <stdio.h>   /* for printf(3) */

int
main(int argc, char **argv)
{
  int i;
  int *p;

  p = &i;
  i = p;
  printf("i = 0x%x p = 0x%p\n", i, p);
  return(0);
}
demo_ptr_into_int.c: In function 'main':
demo_ptr_into_int.c:16: warning: assignment makes integer from pointer without a cast
i = 0xffffebc4 p = 0x0x7fffffffebc4


Adding a cast still yields a complaint:

i = (int) p;

demo_ptr_into_int.c: In function 'main':
demo_ptr_into_int.c:16: warning: cast from pointer to integer of different size