Re: [rfa] Include the LWP in thread-db's PTIDs

[Mark Kettenis <kettenis@gnu.org>]

   Date: Mon, 11 Oct 2004 11:26:27 -0400
   From: Andrew Cagney <cagney@gnu.org>

   > At one time, I believe that thread-db.c was planned to support
   > the full range of features supported by the libthread_db
   > interface, presumably as defined by Sun's implementation.  That
   > never panned out, and while non-1:1 support did work at one
   > point, I don't think it has in a long while.  If it was wanted, I
   > wouldn't re-implement it the same way.  So this patch begins the
   > process of removing unneeded generality from thread-db.  In
   > particular, while thread-db will still compute the TID, the
   > mapping of threads to LWPs will be considered fixed.

I think assuming 1:1 threads is fair enough.  But Daniel, if you're
going to do that, I'd like to ask you to rename thread-db.c into
linux-thread.c or something like that.

Anyway, in that case I think linux-thread.c should be a fairly
lightweight layer around the normal Linux LWP-aware
inf-ptrace.c-derived target vector.  Only use it to provide an LWP <->
TID mapping, and perhaps an initial list of LWPs to attach, but
nothing else.  The normal Linux target vector should in no way be
dependent on it, such that it allows alternative threads strata on top
of it.  Something else just would be a bad design.

Hmm, I guess I'm just re-stating Andrew's points here.

   JeffJ's been in a constant fight with that one.

That's because we try to support every combination of a broken glibc
and a broken kernel that we can find out there.  Well, perhaps not
every possible combination, but certainly some broken combinations.
Reliable threads-debugging requires reliable reporting of thread/LWP
exits.  Otherwise we keep having problems with threads disappearing
from beneath us, leaving us poking at nonexistent memory and
registers.

I think we should ditch most of the buggy combinations and state that
Linux threads debugging will only work reliably on Linux x.y.z or
later with glibc a.b.c or later.

Mark