C Import issue Node Rs232

I have the following structure:

~/Desktop/hellonode$ ls 
build    rs232.h    testnode.js    helloworld.cc    helloworld.node    rs232.c

and in rs232.h:

int OpenComport(int, int);

But when I try to create a node native plugin and use the following code:

#include "rs232.h"

using namespace v8;

void init(Handle<Object> target) {
  int cport_nr=0;        /* /dev/ttyS0 (COM1 on windows) */

  if(OpenComport(cport_nr, bdrate))
  {
    printf("Can not open comport\n");
    return;
  }

  target->Set(String::NewSymbol("hello"),
      FunctionTemplate::New(Method)->GetFunction());
}

I build the plugin using node-waf

Everything compiles fine, however, when I try running it I get the following error:

~/Desktop/hellonode$ node testnode node: symbol lookup error: <~>/Desktop/hellonode/build/Release/helloworld.node: undefined symbol: OpenComport