Re: [PATCH] fix linuxthread debugging WRT zombies with glibc-2.2.3

[Michael Snyder <msnyder at cygnus dot com>]

Approved and checked in (I reworked the changelog entry a little).

				Michael Snyder

Ken Whaley wrote:
> 
> Problem: When debugging linuxthread programs in a glibc-2.2.3
> environment (gdb and app. built with glibc-2.2.3) with
> CVS gdb, the thread ("info threads" and "thread N") commands stop
> working as soon as any non-detached thread finishes.
> 
> Analysis: This is because when a non-detached thread terminates,
> it is in the TD_THR_ZOMBIE state.  Michael Snyder's earlier patch
> to deal with zombie threads (link below) only looks for TD_THR_UNKNOWN
> threads (terminated and detached).  In emails discussing this
> problem with Michael, he said the idea was to continue reporting
> terminated, un-detached threads to the user (since he/she may like
> to know that they're lying around and should be joined).  But a change
> in glibc-2.2.3 close to its release caused the TD_THR_ZOMBIE case
> scenario I found to fail in gdb, since the linuxthreads_db function
> td_ta_map_id2thr() now returns TD_NOTHR instead of TD_OK for
> terminated threads, which causes gdb to error().
> 
> Heres' the full flow that results in the error:
> 
> The prune_threads() call at the top of info_threads_command()
> is removing the zombie,
> because thread_alive on it returns 0,
> because thread_db_thread_alive returns 0 on it,
> because td_ta_map_id2thr_p returns TD_NOTHR
> because struct _pthread_descr_struct pds pds.p_terminated != 0
> In other words, linuxthreads says the thread is terminated,
> so gdb is removing it from its list of threads.
> Since the thread was removed in prune_threads(),
> find_new_threads is trying to add it back, and
> calls the same td_ta_map_id2thr_p function which
> returns the same TD_NOTHR value, causing the call
> to error().
> 
> This patch gets gdb thread commands functional again with glibc-2.2.3.
> Checked & cleared with Michael Snyder, who started work on
> having gdb deal with zombie linuxthreads:
> http://sources.redhat.com/ml/gdb-patches/2001-05/msg00423.html
> 
> 2001-06-29  Ken Whaley  <ken@believe.com>
> 
>         * thread-db.c: Check for TD_THR_ZOMBIE in addition to
>                  TD_THR_UNKNOWN when looking for defunct zombie threads.
>         (attach_thread)
>         (thread_db_thread_alive)
>         (find_new_threads_callback)
> 
> diff -u gdb/thread-db.c.cvs gdb/thread-db.c
> --- gdb/thread-db.c.cvs Tue May 22 17:06:15 2001
> +++ gdb/thread-db.c     Fri Jun 29 10:13:25 2001
> @@ -573,7 +573,7 @@
>    tp->private = xmalloc (sizeof (struct private_thread_info));
>    tp->private->lwpid = ti_p->ti_lid;
> 
> -  if (ti_p->ti_state == TD_THR_UNKNOWN)
> +  if ((ti_p->ti_state == TD_THR_UNKNOWN) || (ti_p->ti_state ==
> TD_THR_ZOMBIE))
>      return;/* A zombie thread that's been joined -- do not attach. */
> 
>    /* Under Linux, we have to attach to each and every thread.  */
> @@ -915,7 +915,7 @@
>        if (err != TD_OK)
>         return 0;
> 
> -      if (ti.ti_state == TD_THR_UNKNOWN)
> +      if ((ti.ti_state == TD_THR_UNKNOWN) || (ti.ti_state ==
> TD_THR_ZOMBIE))
>         return 0;       /* A zombie thread that's been joined. */
> 
>        return 1;
> @@ -938,7 +938,7 @@
>    if (err != TD_OK)
>      error ("Cannot get thread info: %s", thread_db_err_str (err));
> 
> -  if (ti.ti_state == TD_THR_UNKNOWN)
> +  if ((ti.ti_state == TD_THR_UNKNOWN) || (ti.ti_state == TD_THR_ZOMBIE))
>      return 0;  /* A zombie that's been reaped -- ignore. */
> 
>    ptid = BUILD_THREAD (ti.ti_tid, GET_PID (inferior_ptid));
> 
> --
> Ken Whaley
> ken@believe.com <mailto:ken@believe.com>