COM calling convention on x64

Question

I am trying to get a definitive answer regarding the way COM behaves on a x64 machine. Does Windows use the normal x64 calling convention when dispatching calls to COM interfaces on x64 machines (assuming the COM implementation is 64 bits)? Specifically, I dynamically generate my vtbl entries to point to a chunk of assembly that's dynamically loaded during runtime. This assembly needs to know how to get parameters correctly from whomever is calling it. Thus, I'd like to know if COM sets up the call to my assembly using the standard x64 calling convention (pretty much fastcall).

Answer 1

The COM calling convention is whatever the STDMETHOD/STDMETHODIMP macros (and their variants) defines it to be. On IA-32, it's stdcall for most of them; I do not know what is used on x86-64 (I only have the 32-bit mingw cross-compiler installed).