error in linking

Hi,
i am trying to add some functions to postgresql.

I created a file called "...../src/backend/executor/testing.c"
then created a file called "...../src/include/executor/testing.h"
then added "testing.o" to the OBJS in "...../src/backend/executor/Makefile"
I included "executor/testing.h" in execMain.c, and from there, I tried to
make a function call to function which is in testing.c

When I tried to gmake, i got the following error message:
********************************************************
Undefined                       first referencedsymbol                             in file
PrintPlan                           executor/SUBSYS.o
PrintQuery                          executor/SUBSYS.o
ld: fatal: Symbol referencing errors. No output written to postgres
********************************************************
this is an error during the linking.

Any idea what i am missing?

thanks,
--h