verilog / iverilog return value from vpi

gistfile1.txt

# include  <vpi_user.h>

static int rnginit_compiletf(char*user_data __attribute__((unused)))
{
      return 0;
}

static int rnginit_calltf(char*user_data __attribute__((unused)))
{
      vpiHandle callh;
      s_vpi_value val;
      callh = vpi_handle(vpiSysTfCall, 0);
      vpi_printf("Hello, World!\n");
      val.format = vpiIntVal;
      val.value.integer = 0xffffffff;
      vpi_put_value(callh, &val, 0, vpiNoDelay);
      return 0;
}

void rnginit_register(void)
{
      s_vpi_systf_data tf_data;

      tf_data.type        = vpiSysFunc;
      tf_data.sysfunctype = vpiSysFuncInt;
      tf_data.tfname      = "$rnginit";
      tf_data.calltf      = rnginit_calltf;
      tf_data.compiletf   = rnginit_compiletf;
      tf_data.sizetf      = 0;
      tf_data.user_data   = 0;
      vpi_register_systf(&tf_data);
}

void (*vlog_startup_routines[])(void) = {
    rnginit_register,
    0
};