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

[Pedro Alves <palves at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1eb2dbb8d73c344e199fd04531ec3f649e2835b2

commit 1eb2dbb8d73c344e199fd04531ec3f649e2835b2
Author: Pedro Alves <palves@redhat.com>
Date:   Tue Mar 15 16:33:04 2016 +0000

    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:
---
 gdb/ChangeLog         | 10 ++++++++++
 gdb/linux-thread-db.c | 16 ++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3e72420..2e30d4a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,6 +1,16 @@
 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
 	* infrun.c (displaced_step_prepare): Also disable displaced
 	stepping on NOT_SUPPORTED_ERROR.
 	* linux-tdep.c (linux_displaced_step_location): If reading auxv
diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index 1eb457d..ce60beb 100644
--- 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
     {