segmentation fault in function

I am realizing gist index and get a bug, that crashes DB. I' debugged my program as Robert(thanks !) advised me and I
knowwhich procedure crashed. <br /><br /><div style="margin-left: 40px;"><i>Datum
gist_mov_consistent(PG_FUNCTION_ARGS)</i><br/><i>{</i><br /><i>    GISTENTRY *entry = (GISTENTRY
*)PG_GETARG_POINTER(0);</i><br/><i>    BOX *query = PG_GETARG_BOX_P(1);</i><br /><i>    StrategyNumber strategy =
(StrategyNumber)PG_GETARG_UINT16(2);</i><br/><i>    </i><br /><i>    if (DatumGetMovP(entry->key) == NULL || query
==NULL)</i><br /><i>        PG_RETURN_BOOL(FALSE);</i><br /><i>    </i><br /><i>   
PG_RETURN_BOOL(obj_contains(DatumGetMovP(entry->key),query));</i><br /><i>}</i><br /><br /><i>int
obj_contains(moving_object*a, BOX *b)</i><br /><i>{</i><br /><i>    </i><br /><i>    if (b->low.x >
a->x_low)</i><br/><i>        return 0;</i><br /><i>    if (b->low.y > a->y_low)</i><br /><i>        return
0;</i><br/><i>    if (b->high.x < a->x_high)</i><br /><i>        return 0;</i><br /><i>    if (b->high.y
<a->y_high)</i><br /><i>        return 0;</i><br /><i>    return 1;</i><br /><i>}<br /></i><b><br />Do you have
anyideas ?</b><i><br /><br />Best regards,<br />Sergej Galkin<br /></i></div>