how to allocate memory and access it in s-function

I allocated memory in sfunction code:

static void mdlStart(SimStruct *S)

{ uint8_T * temp = (uint8_T*)calloc(8, sizeof(uint8_T));

ssSetUserData(S, temp);

}

and free the memory in

static void mdlTerminate(SimStruct *S)

{

uint8_T *temp = ssGetUserData(S);

free(temp);

}

and used it in a output_wrapper function as

/* %%%-SFUNWIZ_wrapper_Outputs_Changes_BEGIN --- EDIT HERE TO _END */

uint8_T *temp = ssGetUserData(S);

//start message

temp = (uint8_T *)Start_Message;

Msg_ID_Package[1] = temp[0];

Msg_ID_Package[0] = temp[1];

However I am getting linker error LNK2019: unresolved external symbol in the output_wrapper file.

I am not sure what I am doing wrong.

Thank you, Khalid