Re: GDB 10.2 Release -- 2021-04-11 update

[Kevin Buettner <kevinb@redhat.com>]

On Mon, 12 Apr 2021 10:04:44 -0400
Simon Marchi <simon.marchi@polymtl.ca> wrote:

> >>     This looks like a difficult issue to solve, with both GDB *and*
> >>     GDBserver needing a fix, and no clear indication that I could see
> >>     that they would be getting a similar fix. With that in mind,
> >>     I'm wondering if we shouldn't give ourselves a deadline after which
> >>     we simply accept this as a known limitation of the 10.2 release,
> >>     and work on fixing it for the GDB 11 release instead.  
> > 
> > So... I have the beginnings of a patch for gdbserver.  I'm tracking
> > down some regressions though, so don't have anything I can share
> > quite yet.  
> 
> I didn't have time to look at GDBserver yet.  Could you share your patch
> (it could be just a link to an external git repo) even if it's not ready
> yet?

My current patch is below.  It's small, so I decided to post it in
this reply.

It no longer works for the case which originally got me interested in
this problem (which is gdb.threads/fork-plus-threads.exp w/
--target_board=native-extended-gdbserver), but it also no longer
causes regressions in gdb.threads/tls.exp.  Things are getting further
though - i.e. _rtld_global is now being found.

Things are going astray further along, but I'm not quite sure where
yet.  I'm still working on it...

diff --git a/gdbserver/thread-db.cc b/gdbserver/thread-db.cc
index 055a0fa970f..9403b419710 100644
--- a/gdbserver/thread-db.cc
+++ b/gdbserver/thread-db.cc
@@ -44,10 +44,14 @@ struct thread_db
   /* Connection to the libthread_db library.  */
   td_thragent_t *thread_agent;
 
-  /* If this flag has been set, we've already asked GDB for all
-     symbols we might need; assume symbol cache misses are
-     failures.  */
-  int all_symbols_looked_up;
+  /* This flag is set after asking GDB for symbols that we need.  It
+     does not, however, indicate that all necessary symbols have found
+     as these may be split among several shared objects.  */
+  bool initialized;
+
+  /* Flag which indicates that it's okay to ask GDB for symbols via
+     a qSymbol reply.  */
+  bool qsymbol_reply_okay;
 
 #ifndef USE_LIBTHREAD_DB_DIRECTLY
   /* Handle of the libthread_db from dlopen.  */
@@ -359,19 +363,20 @@ thread_db_look_up_symbols (void)
   const char **sym_list;
   CORE_ADDR unused;
 
+  thread_db->qsymbol_reply_okay = true;
+
   for (sym_list = thread_db->td_symbol_list_p (); *sym_list; sym_list++)
     look_up_one_symbol (*sym_list, &unused, 1);
 
-  /* We're not interested in any other libraries loaded after this
-     point, only in symbols in libpthread.so.  */
-  thread_db->all_symbols_looked_up = 1;
+  thread_db->qsymbol_reply_okay = false;
+  thread_db->initialized = true;
 }
 
 int
 thread_db_look_up_one_symbol (const char *name, CORE_ADDR *addrp)
 {
   struct thread_db *thread_db = current_process ()->priv->thread_db;
-  int may_ask_gdb = !thread_db->all_symbols_looked_up;
+  int may_ask_gdb = thread_db->qsymbol_reply_okay || !thread_db->initialized;
 
   /* If we've passed the call to thread_db_look_up_symbols, then
      anything not in the cache must not exist; we're not interested
@@ -396,7 +401,7 @@ thread_db_get_tls_address (struct thread_info *thread, CORE_ADDR offset,
   thread_db = proc->priv->thread_db;
 
   /* If the thread layer is not (yet) initialized, fail.  */
-  if (thread_db == NULL || !thread_db->all_symbols_looked_up)
+  if (thread_db == NULL || !thread_db->initialized)
     return TD_ERR;
 
   /* If td_thr_tls_get_addr is missing rather do not expect td_thr_tlsbase
@@ -888,7 +893,7 @@ thread_db_notice_clone (struct thread_info *parent_thr, ptid_t child_ptid)
 
   /* If the thread layer isn't initialized, return.  It may just
      be that the program uses clone, but does not use libthread_db.  */
-  if (thread_db == NULL || !thread_db->all_symbols_looked_up)
+  if (thread_db == NULL || !thread_db->initialized)
     return;
 
   /* find_one_thread calls into libthread_db which accesses memory via