Re: [hjl@lucon.org: Re: Does gdb 5.2 work with statically linked thread application under Linux?]

[Daniel Jacobowitz <drow at mvista dot com>]

On Fri, Mar 15, 2002 at 10:56:37PM -0500, Andrew Cagney wrote:
> >The below just feels wrong.  The hook is pulling the thread stratum off 
> >>the stack when, as far as I can tell, there is no compelling reason for 
> >>doing this.
> >>
> >>``hey'' something has happened.  At this point, nothing has happened.
> >
> >
> >What do you mean by "there is no compelling reason"?  Or how should
> >this be handled?  The issue is that we do not want thread_db to be used
> >at all for corefiles; we established that last time I touched this
> >code, I just solved the problem wrong.  Once again, it doesn't work
> >as-is, and unpushing matches the way the code was trying to behave.
> 
> I'd expect the thread stratum to be unpushed at the same time as the 
> stratum below it is also unpushed.  In the code above, nothing is being 
> unpushed so I can't see a reason to unpush the thread-db.
> 
> A few lines below the call-out is an unpush() call.  Shouldn't that 
> unpush any stratum directly dependant on it?

It unpushes only core_ops.  core_ops isn't pushed at this point, we
weren't debugging a corefile before.

> If you don't want thread-db trying to push its self on top of a core 
> stratum, why not check for core and ignore the event?
> 
> (GNU/Linux doesn't want the thread-db pushing its self on top of a CORE 
> stratum but other OS's do (with an N:M thread:lwp mapping for instance).

I can't find the precise message any more, but I believe we'd decided
thread-db and core files was a bad idea without more work on thread-db. 
In any case, Michael Snyder said to me:

>>> Umm... I had to think about this, but no.  You can't debug a corefile
>>> until you kill or detach from the process that you're already
>>> debugging.
>>> When you kill or detach, that ought to take care of the unpush.

Maybe it should, but (probably because of when thread-db gets pushed?)
it definitely does not.  Perhaps that is the real bug?

Should thread_db_detach call unpush_target?  Some targets seem to like
that model, some don't.  The way we load our target in new_objfile_hook
always struck me as somewhat gross.

> Most of GDB is almost entirely undocumented :-)  However, the user guide 
> does describe the external interface to this feature:
> http://sources.redhat.com/gdb/current/onlinedocs/gdb_16.html#SEC130

Yep, it's implementation details that worry me.

> If I understand what you're saying correctly, yes.  Unfortunatly it 
> isn't implemented that way.

It should be pretty easy, I'd think - call unpush at the appropriate
time in detach...

> Search for the words ``squashed sandwich'' in the mail archives :-)

No matches :P

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer