Fix PR gdb/19676: Internal error in linux-thread.db.c if /proc not mounted

If /proc is not mounted, GDB fails an assertion in find_new_threads_once:

 Continuing.
 .../src/gdb/linux-thread-db.c:1249: internal-error: find_new_threads_once: Assertion `!target_has_execution' failed.
 A problem internal to GDB has been detected,
 further debugging may prove unreliable.
 Quit this debugging session? (y or n)

That was supposed to catch misuses of td_ta_thr_iter, which is unsafe
for live debugging.  However, if /proc is not mounted, we still
fallback to using it.

I didn't bother with a warning, because GDB already prints several
others related to failing to open /proc files.

gdb/ChangeLog:
2016-03-15  Pedro Alves  <palves@redhat.com>

	PR gdb/19676
	* linux-thread-db.c (try_thread_db_load_1): Leave
	info->td_ta_thr_iter_p NULL iff debugging a live process and we
	have /proc access.
	(find_new_threads_once): Assert that we have a non-NULL
	info->td_ta_thr_iter_p instead of checking whether the target has
	execution.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3e72420282f0310ab3a76b58a00da1d0b1d07733..2e30d4acef3c4dc9afebbb6170236d5510cb6112 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,13 @@
+2016-03-15  Pedro Alves  <palves@redhat.com>
+
+       PR gdb/19676
+       * linux-thread-db.c (try_thread_db_load_1): Leave
+       info->td_ta_thr_iter_p NULL iff debugging a live process and we
+       have /proc access.
+       (find_new_threads_once): Assert that we have a non-NULL
+       info->td_ta_thr_iter_p instead of checking whether the target has
+       execution.
+
 2016-03-15  Pedro Alves  <palves@redhat.com>
 
        PR gdb/19676

diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index 1eb457de105823df829f6013ff3d01d5932fe938..ce60bebe3c9c092cf3fec068bf0b586e95985db0 100644 (file)
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -564,7 +564,6 @@ try_thread_db_load_1 (struct thread_db_info *info)
 
   /* These are essential.  */
   CHK (TDB_VERBOSE_DLSYM (info, td_ta_map_lwp2thr));
-  CHK (TDB_VERBOSE_DLSYM (info, td_ta_thr_iter));
   CHK (TDB_VERBOSE_DLSYM (info, td_thr_validate));
   CHK (TDB_VERBOSE_DLSYM (info, td_thr_get_info));
 
@@ -572,10 +571,6 @@ try_thread_db_load_1 (struct thread_db_info *info)
   TDB_DLSYM (info, td_thr_tls_get_addr);
   TDB_DLSYM (info, td_thr_tlsbase);
 
-#undef TDB_VERBOSE_DLSYM
-#undef TDB_DLSYM
-#undef CHK
-
   /* It's best to avoid td_ta_thr_iter if possible.  That walks data
      structures in the inferior's address space that may be corrupted,
      or, if the target is running, may change while we walk them.  If
@@ -587,6 +582,15 @@ try_thread_db_load_1 (struct thread_db_info *info)
      currently on core targets, as it uses ptrace directly.  */
   if (target_has_execution
       && linux_proc_task_list_dir_exists (ptid_get_pid (inferior_ptid)))
+    info->td_ta_thr_iter_p = NULL;
+  else
+    CHK (TDB_VERBOSE_DLSYM (info, td_ta_thr_iter));
+
+#undef TDB_VERBOSE_DLSYM
+#undef TDB_DLSYM
+#undef CHK
+
+  if (info->td_ta_thr_iter_p == NULL)
     {
       struct lwp_info *lp;
       int pid = ptid_get_pid (inferior_ptid);
@@ -1246,7 +1250,7 @@ find_new_threads_once (struct thread_db_info *info, int iteration,
   data.new_threads = 0;
 
   /* See comment in thread_db_update_thread_list.  */
-  gdb_assert (!target_has_execution);
+  gdb_assert (info->td_ta_thr_iter_p != NULL);
 
   TRY
     {