Re: [PATCH RFA] lin-lwp.c: Block SIGCHLD events when attaching

[Kevin Buettner <kevinb@cygnus.com>]

On Nov 19,  5:42pm, Kevin Buettner wrote:

> > # gcc -g ex11.c -lpthread -lrt -D_GNU_SOURCE -static
> > # a.out
> > # gdb a.out
> > ...
> > (gdb) att 14226
> > Attaching to program: /home/hjl/bugs/gdb/thread/a.out, process 14226
> > ...
> > lin-lwp.c:620: gdb-internal-error: stop_wait_callback: Assertion `pid == GET_LWP (lp->ptid)' failed.
> > An internal GDB error was detected.  This may make further
> > 
> > ex11.c is from glibc and 14226 is the first thread. Your patch may fix
> > it also.
> 
> I think this might be a different problem.  I haven't been able to
> reproduce the exact problem that you mentioned above, either with
> or without my patch.
> 
> I do occassionally see "Cannot find new threads: generic error".  I'm
> going to try to figure this one out...

The "Cannot find new threads:  generic error" that I'm seeing in this
program is happening because td_ta_thr_iter() in libthread_db.so is
requesting that gdb read the memory associated with a struct
_pthread_descr_struct (which has size 1056).  It turns out that gdb
is able to read 1024 bytes of this struct, but no more.  (ptrace()
returns EIO when attempting to read more.)

I'm not sure why this is happening.  Could it be that the manager thread
is in the midst of updating the descriptor data structures?

Kevin