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My application is built as a x64 application. After moving to VS2010 I got some problems which seems to be related to some x64/x86 mismatch in referenced dlls. Now I'm moving to target .NET4, and I get even more similar problems.
My question is: What precautions do I need to take regarding mixing x64 and x86. Can it be done at all? I thought x64 applications should be able to use x86 dlls without problems. No? What about the other way? Can a x86 application reference an x64 dll - as long as it is being run on an x64 platform? What are the pitfalls I need to be aware of?
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Yes, of course. Most programs are still 32 bit and run fine on 64-bit Windows systems. Those programs are machine language, which has a one-to-one mapping with assembly (and can be easily disassembled into x86 assembly code).
Launch depends.exe, go to File, click Open... and open the desired DLL file. In the Module section find the Module with the name of the DLL that you opened. The CPU column tells if the file was compiled for 32 bits or 64 bits.
Since x86 apps run on both x64 and x86 systems, the most compatible choice is to build x86. If you MUST build a 64 bit solution, you'll need to target x64 and use our x64 dlls.
If you're trying to check whether or not a running application is running in 32-bit or 64-bit mode, open task manager and check whether or not it has an asterisk (*32) next to the name of the process.
No, a 64-bit process can only load 64-bit DLLs and a 32-bit process can only load 32-bit DLLs. What you're probably thinking of is that a 64-bit operating system can run 32-bit processes.
The main issue with .NET is that - prior to VS2010 - executable projects defaulted to "AnyCPU" which means it would load in the "native" format of the OS it's running on (so 32-bit for 32-bit versions of Windows and 64-bit for 64-bit versions of Windows). The problem with that is that if you tested your application on 32-bit Windows (say) then it could break if you load 32-bit DLLs and tried to run on 64-bit Windows.
In VS2010, they defaulted all executable projects to be "x86" (that is, 32-bit) by default which (for the most part) mitigates the problem.
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