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

[Andrew Cagney <cagney at gnu dot org>]

> On Mon, Oct 11, 2004 at 12:16:46PM -0400, Andrew Cagney wrote:
>
> > > > >I hadn't thought about the core issue; I'll do some pondering. However,
> > > > >I don't think your comment is quite right.  Thread_db can not be
> > > > >layered over core files, we've already decided that - it's too iffy to
> > > > >find the right thread_db, not to mention cross-debugging issues.  And
> > > > >similarly we can't use it for remote thread debugging.  Thread_db only
> > > > >makes any sense on top of local, running, native threads.
> >
> > > "we"'ve definitly not decided this.
> > >
> > > Long ago you committed a hack to stop GDB layering thread-db over core 
> > > files.  It was to stop GDB barfing on native GNU/Linux core files.  It 
> > > had the side effect of breaking threads on all other systems, namely 
> > > solaris.  What keeps being pointing out is that thread-db should be 
> > > loaded over a core file, and not doing it is broken.
> > >
> > > If we try it and it barfs, we've a bug.  But what we've not got is an 
> > > excuse for hobble native support (just because embedeed debuging is "iffy").
>
>
> Huh?  It was a change to thread-db.c which has never been used for
> Solaris, so I haven't got any idea what you are talking about.  I did
> not break Solaris threads.

Then on that front, then I'm now wrong (and not shy in admitting it ;-) 
("but" in my defence at the time the expectation was that thread-db.c 
would be used by solaris :-).

> Also, it was an approved patch.  Michael responded at the end of the
> thread saying that he agreed it was the right thing not to use
> thread_db on core files.  Yes, there was a lot of disagreement before
> that; but before the patch was committed the thread-db.c maintainer
> agreed that we should not to use thread_db in this case.  I think I'm
> justified in saying that "we" have decided this.

But here on this technical matter I'm not.

The discussion starts here (there's a bit in the next month):
http://sources.redhat.com/ml/gdb-patches/2001-12/msg00345.html
please read it.

Your position was that:

> On Thu, Dec 13, 2001 at 06:56:36PM -0500, Daniel Jacobowitz wrote:
> > Thread_db, as things stand, does not work on core files.  Is preventing
> > it from trying, and thus crashing GDB, really such a disruptive
> > suggestion?
>
> OK, that came out a little harsher than I really wanted it.  Sorry.
>
> I'd like to apply this patch and then add an entry to TODO about
> how it "should be done".  Is that better?

because:

> > Sounds like that is the bug to fix.  Enabling event reporting probably 
> > doesn't make much sense when the target is lifeless.
>
> I was about to try a patch for this when I realized that my primary
> objection still holds.
>
> This only works if you're debugging on a very similar host to the one
> the core was dumped on.  If you've got, say, a glibc 2.1.3 host and are
> looking at a glibc 2.2.3 core... well, you can provide target libraries
> and make GDB use those, but there's no way to provide a cross
> libthread_db.

Given that this was "hard" Michael approved the change (a sound 
technical decision).

Just like on Solaris and consistent with the original thread, the 
user-level thread library should be loaded over the core file as only by 
doing that can user-level thread information be displayed.

If this makes cross debugging "iffy", fix the bugs, don't cripple GDB 
for it's native users.

Andrew