Re: COM dll server registration on Windows 64 bits

"Willy Denoyette [MVP]" <>
Thu, 28 Feb 2008 11:06:25 +0100
"Olivier" <> wrote in message

Hello Willy,

"Willy Denoyette [MVP]" <> a ?crit dans le
message de news: OO2AWQXeIHA.5900@TK2MSFTNGP02.phx.gbl...

"Olivier" <> wrote in message


We have another question related to this problem:

Can a 64 bits process (or dll) is able to access a TypeLib embedded in a
32 bits dll (or the opposite)?

Using ProcessExplorer, we saw a 64 bits dll listed in our 32 bits
process (and, yes, we are sure that this dll is 64 bits).

Best regards,


Are you sure that the 64-bit DLL was a COM DLL?
For instance, a 32-bit process loads the 32-bit and the 64-bit of the
ntdll.dll, part of each 32-bit process contains 64-bit code which is used
when calling into the kernel. Besides ntdll.dll there are other dll's
loaded that are 64-bit (wow64.dll, wow64cpu.dll etc..).

Yes, we are sure because this is one of our COM dlls compiled in 64 bits
ProcessExplorer and DependencyWalker tell us that this dll is 64 bits

This is weird, 32-bit COM should not have an idea about the location of this
64-bit DLL, nor should DependencyWalker show this DLL, are you sure you
don't statically link?.
I would suggest you to forget about these tools and load the application in
the Windbg (or similar) debugger, set a breakpoint on library load (sxe ld

Nevertheless, I will check this again.

Maybe a typelib resource can be accessed using RPC? I mean if a 32 bits
process requires this typelib (only) stored in a 64 bits module, then COM
may use RPC to access it (or a specific Win32 API that is only interested
by the resource)

I would be very surprised if the 32-bit COM library would (could) load a
64-bit COM DLL into a process just to get at the embedded typelib info,
which is already present in the 32-bit COM dll.

Does COM exist as 32 bits and 64 bits on Windows64?

I think so.

Sure, the COM library (OLE32, oleaut32 etc..) is user mode code, only
libraries with the same bit-ness can/will be loaded in a user mode process
(except the ones I mentioned before).


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