multiple calls don't work

[phanen]

when calling function, only the first will work

void test_print() {
  put_str("call put_str in kernel\n");
}

int main() {

  test_print(); // work and return from here ?

  // all the followinng lines don't print
  test_print();
  test_print();
  test_print();
  test_print();
  put_str("call put_str in kernel\n");

  while(1);
}

but when write as declaration + definition, it works...

void test_print();
int main() {

  test_print();
  test_print();
  test_print();
  test_print();
  test_print();

  while(1);
}

void test_print() {
  put_str("call put_str in kernel\n");
}