Re: Amusing problem in current libthread_db

[Daniel Jacobowitz <drow@mvista.com>]

On Tue, Jun 03, 2003 at 03:30:47PM -0700, Roland McGrath wrote:
> The reason that code is needed for linuxthreads is that the thread
> descriptor might be uninitialized.  The main thread and the manager thread
> are always reported by td_ta_thr_iter.  However, early on their descriptors
> are all zeros and so td_thr_get_info et al need to be able to cope with
> that.  It might make more sense not to report any threads at all before
> they are initialized enough to report useful information.  But I think that
> was deemed a more risky change (vs possible presumptions of old gdbs, etc)
> than faking the all-zeros responses in the early stages.  
> 
> The reason this wasn't an issue before and got changed was that the array
> of thread descriptors used to be in initialized data, where the first two
> elements were initialized nonzero to set up the the main and manager threads.
> Now the whole array is in uninitialized so it can go in bss and not take up
> space on disk; thus the main and manager threads' elements start out zero too.
> 
> td_thr_get_info does a somewhat more convincing job of faking info when
> dealing with an uninitialized descriptor in the inferior, i.e. always just
> use the main thread in that case.  td_thr_getgregs et al could be made to
> do that.

Will the manager thread be reported as created only after its thread
descriptor is initialized?  I'm guessing "yes".  In that case, using
the main thread is sufficient.

Here's a patch to fix the problem, since it turned out to be more than
theoretical on ARM targets.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

2003-08-18  Daniel Jacobowitz  <drow@mvista.com>

	* td_thr_getfpregs.c (td_thr_getfpregs): Use the main thread if
	the descriptor is uninitialized.
	* td_thr_getgregs.c (td_thr_getgregs): Likewise.

diff -urp -x '*~' glibc-2.3.2/linuxthreads_db.orig/td_thr_getfpregs.c glibc-2.3.2/linuxthreads_db/td_thr_getfpregs.c
--- glibc-2.3.2/linuxthreads_db.orig/td_thr_getfpregs.c	2002-07-15 23:25:16.000000000 -0400
+++ glibc-2.3.2/linuxthreads_db/td_thr_getfpregs.c	2003-08-18 14:44:11.000000000 -0400
@@ -1,5 +1,5 @@
 /* Get a thread's floating-point register set.
-   Copyright (C) 1999, 2001 Free Software Foundation, Inc.
+   Copyright (C) 1999, 2001, 2003 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1999.
 
@@ -30,7 +30,10 @@ td_thr_getfpregs (const td_thrhandle_t *
 
   if (th->th_unique == NULL)
     {
-      memset (regset, '\0', sizeof (*regset));
+      /* No data yet.  Use the main thread.  */
+      pid_t pid = ps_getpid (th->th_ta_p->ph);
+      if (ps_lgetfpregs (th->th_ta_p->ph, pid, regset) != PS_OK)
+	return TD_ERR;
       return TD_OK;
     }
 
diff -urp -x '*~' glibc-2.3.2/linuxthreads_db.orig/td_thr_getgregs.c glibc-2.3.2/linuxthreads_db/td_thr_getgregs.c
--- glibc-2.3.2/linuxthreads_db.orig/td_thr_getgregs.c	2002-07-15 23:24:27.000000000 -0400
+++ glibc-2.3.2/linuxthreads_db/td_thr_getgregs.c	2003-08-18 14:43:08.000000000 -0400
@@ -1,5 +1,5 @@
 /* Get a thread's general register set.
-   Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
+   Copyright (C) 1999, 2000, 2001, 2003 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1999.
 
@@ -30,8 +30,10 @@ td_thr_getgregs (const td_thrhandle_t *t
 
   if (th->th_unique == NULL)
     {
-      /* No data yet.  */
-      memset (gregs, '\0', sizeof (prgregset_t));
+      /* No data yet.  Use the main thread.  */
+      pid_t pid = ps_getpid (th->th_ta_p->ph);
+      if (ps_lgetregs (th->th_ta_p->ph, pid, gregs) != PS_OK)
+	return TD_ERR;
       return TD_OK;
     }