Supported and Unsupported Calling Conventions

The thunk compiler supports thunk functions that follow these guidelines for calling convention and parameters:

• Use the __stdcall calling convention on the 32-bit side of the thunk
• Use the __pascal calling convention on the 16-bit side of the thunk
• Contain 14 or fewer parameters

If you try to build a thunk that uses an unsupported calling convention, the linker will return the error "unresolved external" because the function names produced by the C/C++ compiler will not match the names produced by the thunk compiler. Although the thunk must use the __pascal and __stdcall calling conventions, the thunk may call or be called by functions that use other calling conventions.

To thunk to a function that uses the __cdecl or __fastcall calling convention, you must create the thunk function with a supported calling convention. Then make the thunk function call the target function.