FUNCTIONS

td_ta_map_lwp2thr:
 - always needs to call ps_getpid (currently passed as an argument)
 - needs to access inferior memory (done)
 - generally needs to call ps_get_thread_area (SYSTEM FUNC CALLS)
 - returns multiple values

td_ta_thr_iter:
 - walks linked lists in inferior
 - calls a user-supplied function:   (SYSTEM FUNC CALLS VIA ARG)
   Args:
     - (supposedly) opaque (to caller) thread handle
     - opaque to libthread_db void *callback_data (just passed in)
   Returns:
     - just some int to indicate an error
 - also calls ps_getpid (could easily be passed as an argument)

td_thr_get_info:
 - writes into a structure passed as an argument
   (probably no portable way to do this -- sizes, offsets different)
   maybe just return a lot of values
 - also calls ps_getpid (less obvious as an argument but why not?)

td_thr_tls_get_addr:
 - accesses link map (which is not in the same solib... need an
   INFINTY_EXPORT there)
 - basically a wrapper for td_thr_tlsbase (I8FUNC-I8FUNC FUNC CALLS)

td_thr_tlsbase:
 - Calls __td_ta_lookup_th_unique (part of map_lwp2thr!)
 - dtv_slotinfo???

Basically need to have functions as first class objects.
All the function calls could be rolled into DW_OP_GNU_i8call

Need some (convention? enforcement?) to say "these functions
are internal"

I think it has to be convention, there's no way to group functions
together other than by provider (no cross-provider calling of internal
functions? but we're allowing cross-provider symbol reference so...)

Thread handles from td_ta_map_lwp2thr/td_ta_thr_iter and to
td_thr_get_info will likely be just the th_unique member of
td_thrhandle_t.