The internal calling convention used by AngelScript in the virtual machine is quite simple.

All function arguments are pushed on the stack from last to first. All arguments are aligned to 4 byte boundaries. References are either 4 bytes or 8 bytes depending on the CPU architecture. Primitives passed by value will be pushed as-is. Objects passed by value will have a reference to the object pushed on the stack while the object itself is stored on the heap. The called function is responsible for cleaning up the object and freeing the memory. For object handles, the calling function will increase the refcount as the arguments are prepared and the handle is pushed on the stack, the ownership of the handle is then handed over to the called function that must release it before returning.

A variable argument type, ?, will have the typeid pushed on the stack before the actual argument value.

If the function is a variadic, ..., i.e. accepts any number of arguments, then the number of actual arguments is pushed on the stack after the first function argument.

If the function returns an object by value, then a hidden argument with the address where the returned object must be initialized is pushed on the stack. The returned object is owned by the called function until the control is returned to the caller, i.e. if an exception happens between the object is initialized and the control is returned to the caller, the exception handler will clean up the returned object as part of the called functions call frame.

If the function is a class method, then the address of the object instance is pushed on the stack as the last argument, thus allowing the called function to always rely on the this pointer to be on position 0 of the stack frame.