Re: Debugging threaded processes

[Tobias Nygren <tnn%NetBSD.org@localhost>]

On Wed, 17 Mar 2010 17:34:58 -0400
"Paul Koning" <Paul_Koning%Dell.com@localhost> wrote:

> I'm working on adding thread debug support to gdb to handle the
> kernel-based pthreads support that showed up in 5.0.
> 
> The basics are easy enough and I have that working.  (This will be
> submitted to the FSF GDB team.)

Great! I could really use this functionality ASAP for analyzing PR
pkg/42988 if you need an early beta tester.

> So what happens, if I correctly interpreted my debug sessions, is that
> one thread hits the breakpoint, sets p_xstat to 5, calls sigswitch() to
> get some other LWP scheduled.  However, the LWP that's picked is one of
> the other threads for the same process.  It's continuing from a break,
> so it calls sigchecktrace() to see if gdb gave it a signal.
> sigchecktrace returns what's in p_xstat, which is 5, so a break is
> delivered to the process, which kills it.

Doh! I think this is exactly the issue I'm seeing with firefox dying
after stopping on my breakpoint. Don't know what the right fix is,
though.

Cheers,
-Tobias