null pointers [LWN.net]

null pointers

Posted Mar 19, 2008 21:11 UTC (Wed) by quotemstr (subscriber, #45331)
In reply to: null pointers by nix
Parent article: Who maintains dpkg?

Can you name an example of a POSIX system for which the assumption does not hold?

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null pointers

Posted Mar 19, 2008 21:47 UTC (Wed) by nix (subscriber, #2304) [Link]

Any IA64 or PPC64-based systems. I think HPPA too but can't remember.

(On both these platforms it so happens that data pointers are all the same 
size: but function pointers are larger... and yes this has exposed bugs in 
free software.)

null pointers

Posted Mar 19, 2008 21:57 UTC (Wed) by quotemstr (subscriber, #45331) [Link]

I don't think that's true. See the downthread comments on the same topic. I'd be interested in
knowing what the specific bugs were.

null pointers

Posted Mar 19, 2008 22:18 UTC (Wed) by nix (subscriber, #2304) [Link]

If I could remember, I'd say. I'll have a dig.

null pointers

Posted Mar 28, 2008 22:33 UTC (Fri) by anton (guest, #25547) [Link]

On [PPC64 and IA64] it so happens that data pointers are all the same size: but function pointers are larger.

Not on Linux-PPC64 (and probably not on Linux-IA64, either):

#include <stdio.h>
int main()
{
  printf("%ld %ld\n", sizeof(void *), sizeof(int(*)()));
  return 0;
}

prints

8 8

null pointers

Posted Mar 29, 2008 1:08 UTC (Sat) by nix (subscriber, #2304) [Link]

Oh. My memory is failing me and I can't read simulator source code, it 
seems. (I was *sure* they were examples of arches using a descriptor 
consisting of a data pointer combined with other stuff.)