[rfa/threads] Convert thread event descriptors to code addrs

[Andrew Cagney]

Does NPTL do anything with that address internally?  Or just pass it 
through?

> The alternative would be to modify libthread_db so that it knew that 
>> PPC64 symbol were special but I suspect that it doesn't want to know 
>> about such underlying details.
> 
> 
> It seems to me that this is really what ought to change.  ps_pglobal_lookup
> and similar symbols have always had an architecture-neutral interface (with
> the exception of our invention, ps_get_thread_area).  There is no reason
> the implementation of this function by a user of libthread_db should have
> to do anything machine-specific.  gdb already has tons of machine-specific
> knowledge, so it's not really an issue there; but if there are ever simpler
> users of libthread_db, they shouldn't have to worry about this.  It is easy
> enough to change libthread_db to request the symbols it really wants for
> the addresses it needs.  
> 
> Depending how convert_from_func_ptr_addr works, it may well be reasonable
> for gdb to use it as your patch does, to work around the existing buggy
> PPC64 libthread_db implementations.  That is, if that transformation will
> always be a no-op for a real code symbol (i.e. a ".foo" on PPC64), then you
> might as well make gdb seamlessly handle either case.  I'll leave that up
> to you, but do let me know whether you decide to take or leave it, so I
> know how urgent the glibc fix is for gdb users.
> 
>