Linking errors with auto-generated model code containing non-inlined s-functions

I am trying to compile the autogenerated code from a R2017a Simulink model for real time execution on a linux target. The model contains 2 non-inlined S functions that were written a very long time ago. An equivalent simulink model made in R14a is able to auto generate and compile on the target with no issues. I have updated the model to Matlab 2017a's simulink version, and added some features.

When auto-coding, I got an error which told me I needed to manually enable support for non-inlined s-functions, so I did that, and the code generated successfuly with a few innocuous warnings. We will assume that the name of the s-functions are "foo" and "bar". When attempting to compile on the target I get the following linking errors in the top level c file i.e. "Model_that_implements_foo_and_bar.c":

undefined reference to 'foo(SimStruct_tag*)'

undefined reference to 'bar(SimStruct_tag)*'

Any help to get me past this linking error would be greatly appreciated.

The definition of the functions looks like this:

Model_that_implements_foo_and_bar_private.h:

extern void foo(SimStruct *rts);
extern void bar(SimStruct *rts);

The code surrounding each implementation of the functions looks like this:

Model_that_implements_foo_and_bar.c:

        /* RWORK */
        ssSetDWorkWidth(rts, 0, 2012);
        ssSetDWorkDataType(rts, 0,SS_DOUBLE);
        ssSetDWorkComplexSignal(rts, 0, 0);
        ssSetDWork(rts, 0, &rtDWork.fooSFunction_RWORK[0]);
        /* DSTATE */
        ssSetDWorkWidth(rts, 1, 802);
        ssSetDWorkDataType(rts, 1,SS_DOUBLE);
        ssSetDWorkComplexSignal(rts, 1, 0);
        ssSetDWorkUsedAsDState(rts, 1, 1);
        ssSetDWork(rts, 1, &rtDWork.fooSFunction_DSTATE[0]);
      }
      /* registration */
      foo(rts);                        % ** this line throws the error **
      sfcnInitializeSizes(rts);
      sfcnInitializeSampleTimes(rts);

      /* adjust sample time */
      ssSetSampleTime(rts, 0, 0.002);
      ssSetOffsetTime(rts, 0, 0.0);
      sfcnTsMap[0] = 0;

     
     

Additionally there are some very suspicious warnings that are saying many of the lines of code with calls to ssSet functions have no effect, for example:

statement has no effect 'ssSetDWork(rts, 0, &rtDWork.SFunctionfoo_RWORK[0])'

statement has no effect 'ssSetInputPortBufferDstPort(rts, 0, -1)'