Why am I getting "Undefined Symbol" warning for using S-Function in Simulink?

I created an S-Function and copied it in my simulink model. Now getting software build warning " Undefined Symbol: SFunction_output_wrapper" in object file. Can anyone help me with this?

Is there any way to embed SFunction.c & SFunction_wrapper.c code in S function block or Similiar block?

[Raghunandan V]

Are those C files in the same path as the model?

[TH]

Yes, they all are in same folder/path. After copying S function into my model, I did a code gen. In that code, only an external Sfunction-_output_wrapper is called. I expected my custom S function code in the generated code file from my model.