I'm making no such assumption. I'm saying nothing should be operating on the SV. If something does play with the internals of this object, it's their own fault if they mess something up.

Ask yourself how and why a pointer value might end up in the IV slot of an SV.

The XS library is creating a handle that will later be passed back to it.

In Windows, is HANDLE signed or unsigned? The answer is that it doesn't matter.

Update: Example use of that typemap:

$ cat a.pl
use strict;
use warnings;

use Inline C => <<'__EOI__', PREFIX => 'M_';

#include <stdio.h>

typedef struct {
   int i;
   int j;
} foo_t;

foo_t* M_get() {
   foo_t* foo = (foo_t*)malloc(sizeof(foo_t));
   printf("get: %p\n", foo);
   return foo;
}

void M_free(foo_t* foo) {
   printf("free(%p)\n", foo);
   free(foo);
}

__EOI__

my $o = get();
free($o);

$ cat typemap
TYPEMAP
foo_t*  T_PTRREF

$ perl -MInline=FORCE,NOISY,NOCLEAN a.pl
...

get: 0x91ab70
free(0x91ab70)
[download]

#!/usr/bin/perl -w
use Devel::Peek;
$ptrUV = unpack('J',pack('P[12]',"Hello World"));
$ptrIV = unpack('j',pack('P[12]',"Hello World"));
print Dump($ptrUV);
print Dump($ptrIV);
$ptrUV += 2**31;
print Dump($ptrUV);
[download]

SV = IV(0x182a260) at 0x182a264
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 28545556
SV = IV(0x182a3e0) at 0x182a3e4
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 26107564
SV = IV(0x182a260) at 0x182a264
  REFCNT = 1
  FLAGS = (IOK,pIOK,IsUV)
  UV = 2176029204
[download]

There is also the possibility of performing pointer arithmetic with two pointers, one just before the 2GB boundary and one just after it. Thus mixing IV and UV math.

Whether deriving offsets in structs, or extracting or manipulating sub-strings, I'm not at all convinced that there are not places within the Perl sources themselves where such manipulations are done, that work only because most 32-bit Perls run limited to 2GB.

Certainly, when I was playing with 32-bit perl made /largeaddressaware and with /3GB set, I saw enough weirdness and crashes to give up on the idea of using that instead of a 64-bit Perl in order to get access to my full complement of ram.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

If someone changes your internals to the point of failure, it doesn't make your design bad.

Besides, if you were to fake the internals using pack and ended up with a UV, it would still work with the existing typemap.