Re: ioctl-patch for Darwin and FreeBSD

[Bruno Haible]

Eric Blake wrote:
> Maybe the real problem is that we need to ensure that our replacement
> does not do sign extension.

Yup, I think that's the point.

> Does this patch fix your issue? 
> 
> diff --git i/lib/ioctl.c w/lib/ioctl.c
> index 72f9f37..3ed4327 100644
> --- i/lib/ioctl.c
> +++ w/lib/ioctl.c
> @@ -37,7 +37,11 @@ rpl_ioctl (int fd, int request, ... /* {void *,char
> *} arg */)
>    buf = va_arg (args, void *);
>    va_end (args);
> 
> -  return ioctl (fd, request, buf);
> +  /* Generally, this replacement function is in effect when the system
> +     ioctl expects unsigned long int.  If request has the most
> +     significant bit set, then we need to make sure that
> +     sign-extension does not come into play.  */
> +  return ioctl (fd, (unsigned long) request, buf);
>  }

This is a nop, because a cast from 'int' to 'unsigned long' will sign-extend,
not zero-extend.

$ cat foo.c
#include <sys/socket.h>
#include <net/if.h>
#include <sys/sockio.h>
#include <stdio.h>

unsigned long original = SIOCSIFLLADDR;
int as_int = SIOCSIFLLADDR;
unsigned long cast_via_ulong = (unsigned long)(int)SIOCSIFLLADDR;
unsigned long cast_via_uint = (unsigned int)(int)SIOCSIFLLADDR;

int main ()
{
  printf ("original       = 0x%016lx\n", original);
  printf ("as_int         =         0x%08x\n", as_int);
  printf ("cast_via_ulong = 0x%016lx\n", cast_via_ulong);
  printf ("cast_via_uint  = 0x%016lx\n", cast_via_uint);
  return 0;
}

$ gcc -m64 -Wall foo.c
$ ./a.out 
original       = 0x000000008020693c
as_int         =         0x8020693c
cast_via_ulong = 0xffffffff8020693c
cast_via_uint  = 0x000000008020693c

Bruno
-- 
In memoriam Sophie Scholl <http://en.wikipedia.org/wiki/Sophie_Scholl>