Will dll be loaded as 32bit or 64bit when exe is x86(32bit) on a 64bit machine?

Question

In VS2008, for example, I have an exe built as x86(32bit) because I want it runs in 32bit even on 64bit machine. This exe will dynamically load other dlls through reflection and invoke.

Now my question is, if I build my dll as "All CPU", instead of x86, and when I run the exe host on a 64 bit machine, once my dll gets loaded, or called, the dll will be treated as 64bit or 32bit? (My test shows it is treated as 32bit, but I want to confirm with you all. I think in general, 32bit cannot access 64bit. Since the exe is 32bit, so the dlls will be always loaded as 32bit?)

Thanks

Answer 1

Yes, you are correct. Unless you jump through some serious hoops, every part of the process (at least the user code parts) will be 32-bit.

Answer 2

If the DLL to be loaded it also marked as AnyCPU then there won't be any problems.

If you have an AnyCPU EXE (for example) which is running on a 64-bit computer (so it's an x64 process) which then attempts to load an x86 DLL (which is not marked as AnyCPU) then it will fail with a runtime exception ( BadImageFormatException )