Hi George,
If I understood correctly, the module compiles correctly. When you start/run the graph it complains it can not find/'see' the function.
This could be related to default visibility of the objects. If you look at the code for your block my_adder_ff, there should be a line similar to
class TUTORIAL_API my_adder_ff { ....
The TUTORIAL_API (or whatever it is called) is a macro defined in api.h and eventually evaluates (for GNUC) to
__attribute__ ((visibility ("default")))
which ensures visibility to other modules. You can check the built library for your module using nm command, e.g.(I'm just guessing library name libTutorial.so)
$ nm -C libTutorial.so | grep -i my_add
If the function is 'qualified' with t (lower case) it will not be visible. If it is qualified with uppercase 'T', then it is visible
An easy thing to try to fix is to add to the function declaration in the header file
float TUTORIAL_API my_add(float, float)
and rebuild.
Hope that made sense
Cheers
Boris