Re: Isn't HANDLE 64 bits on Win64?

On Tue, Nov 16, 2010 at 16:23, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Magnus Hagander <magnus(at)hagander(dot)net> writes:
>> Do you still have a reference to the page that said they will never be
>> assigned that high?
>
> http://msdn.microsoft.com/en-us/library/ms810720.aspx
>
> which says
>
>    USER and GDI handles are sign extended 32b values
>
>    To facilitate the porting, a decision has been made that these system
>    handles should stay as 32b values, sign extended to 64b on the 64b
>    platform. That is, the individual handle types are still based on the
>    HANDLE type, which maps to void *, and so the size of the handle is the
>    size of the pointer, i.e. 4 bytes on 32b and 8 bytes on 64b. However,
>    the actual value of the handle on the 64b platform, (i.e. the meaningful
>    bits), fits within the lower 32b, while the upper bits just carry the
>    sign.
>
>    This should make it easy to port the majority of the application
>    code. Handling of the special values, like -1, should be fairly
>    transparent. It also should agree nicely with all the cases where the
>    handles had been remoted with the help of the IDL definitions from the
>    public file wtypes.idl. However, care needs to be taken when remoting
>    the handles was done via a DWORD, as the upper long should be properly
>    sign extended on the 64b side. The app should use HandleToLong() and
>    LongToHandle() macros (inline functions) to do the casting right.
>
> What's not clear to me is whether the section title means that only
> certain handles have this guarantee, and if so whether we have to worry
> about running into ones that don't.

I think it is pretty clear it does - the section has a list of
different handles at the bottom. What we're using is a File Mapping
Object, which is not on that list. And which is, AFAICT, not a user or
gdi handle.

That doesn't mean it's not guaranteed to be in the 32-bit space, but
I'm pretty sure that specific page doesn't guarantee it.

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/