Lets say a 64 bit program that wants to use a third party dll in which you have no code only header, lib and dll.

I suppose that by creating a 32 bit executable, linked with a dll, and then use it to relay the calls from the 64 bit program to the 32 bit dll and vice-versa, it would work. The question is what is the most efficient way to do this?

Also, Is there a way to create a shared block of memory between a 64 bit process and a 32 bit process?

Does anybody has any links that explains how to do this 2 things?

Yes, it is possible.

How often the 32- and 64-bit code will call each other? If you really need a 64-bit app then ok, but otherwise verify that you will really get something of this, because the performance hit to implement this is not small.

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No, you are mixing concepts here. A 64-bit process CAN'T call a 32-bit DLL directly, even if you manage to load a 32-bit executable image into a 64-bit process the processors will misinterpret the 32-bit code as a 64-bit one. What it is true is that the processor provides the so called "compatibility mode" inside long mode, that one allows to run 32-bit processes on a 64-bit environment (like Win95 allows to execute 16-bit code on a 32-bit environment).

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nop, long mode:


And talking about real mode, when the processor is in long mode it does not provide support for V86 mode. Executing DOS programs requires using DOSBox or any other emulator since the "compatibility mode" sub-mode does not provide support for this.

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Must 32-bit code run on another core than 64-bit, or how does the OS switch between them when running different processes?

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