Internal PG functions, how to pass proper parameters?

Hi all

I need a bit assistance. In  ../src/backend/utils/adt/tsginidx.c there
is a function called gin_extract_tsquery.

It recieves 5 parameters and I would like to execute it from C code
using my own function. The gin_extract_tsquery relevant part:

Datum
gin_extract_tsquery(PG_FUNCTION_ARGS)
{
        TSQuery                query = PG_GETARG_TSQUERY(0);
        int32           *nentries = (int32 *) PG_GETARG_POINTER(1);
        /* StrategyNumber strategy = PG_GETARG_UINT16(2); */
        bool          **ptr_partialmatch = (bool **) PG_GETARG_POINTER(3);
        Pointer   **extra_data = (Pointer **) PG_GETARG_POINTER(4);
        Datum           *entries = NULL;
        bool           *partialmatch;
        elog(NOTICE,"[%s,%d]","step: ",03);
        *nentries = 0;
        elog(NOTICE,"[%s,%d]","step: ",04);
.....
}

I created my own simple wrapper function, so I can control the
gin_extract_tsquery directly. Here's the code:

Datum
test(PG_FUNCTION_ARGS)
{
    //arguments
    HStore<----><------>*hs = PG_GETARG_HS(0);
    TSQuery<---><------>tq = PG_GETARG_TSQUERY(1);
    Datum<-----><------>*dats;

    elog(NOTICE,"[%s,%d]","step: ",01);

    //variables
    char<------><------>*nentries;
    elog(NOTICE,"[%s,%d]","step: ",02);

    //operations
    nentries = DirectFunctionCall2(gin_extract_tsquery_ljd,
TSQueryGetDatum(tq), dats);
....
}

The above function call is incompleate (only 2 params instead of 5)
but it's not relevant at this point. The issue is that no matter what
I pass (Datum, pointer to Datum, pointer to char, pointer to int32, PG
macros to variables and pointers, etc...) as a 2nd parameter I get an
error when I call my wrapper function from Postgres. It goes well
right until the line before "step: 04" notice in gin_extract_tsquery.
Namely the "*nentries = 0;" line.

What do I need to pass in my wrapper function so it works properly? An
example and short explanation (I just started learning C & PG) would
be greatly appreciated.

Also a related question: Is it possible to launch a function like
gin_extract_query directly from Postgres? I'ts decralation is:

CREATE OR REPLACE FUNCTION gin_extract_tsquery(tsquery, internal,
smallint, internal, internal)
  RETURNS internal AS ....

I've tried to find something about "internal" parameters in functions
in manual but failed. If it's possible, what would be a working
example?

Thanks in advance.