gdb: Restore selected frame in print_frame_local_vars

PR gdb/23203 reports 'bt full' causing the currently selected frame to
change, this issue is fixed in this commit.

Add a new class scoped_restore_selected_frame that saves and restores
the selected frame.  Make use of this in print_frame_local_vars to
restore the selected frame on exit.

gdb/ChangeLog:

	PR gdb/23203
	* frame.c
	(scoped_restore_selected_frame::scoped_restore_selected_frame):
	Define.
	(scoped_restore_selected_frame::~scoped_restore_selected_frame):
	Define.
	* frame.h (class scoped_restore_selected_frame): New class.
	* stack.c (print_frame_local_vars): Remove catching and rethrowing
	of any exception, use scoped_restore_selected_frame to restore the
	frame instead.

gdb/testsuite/ChangeLog:

	PR gdb/23203
	* gdb.base/bt-selected-frame.c: New file.
	* gdb.base/bt-selected-frame.exp: New file.
	* lib/gdb.exp (get_current_frame_number): New function.

8 files changed, 182 insertions, 20 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d700d6c..503b34f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,16 @@
+2018-05-24  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	PR gdb/23203
+	* frame.c
+	(scoped_restore_selected_frame::scoped_restore_selected_frame):
+	Define.
+	(scoped_restore_selected_frame::~scoped_restore_selected_frame):
+	Define.
+	* frame.h (class scoped_restore_selected_frame): New class.
+	* stack.c (print_frame_local_vars): Remove catching and rethrowing
+	of any exception, use scoped_restore_selected_frame to restore the
+	frame instead.
+
 2018-05-24  Pedro Alves  <palves@redhat.com>
 
 	* darwin-nat.h (darwin_nat_target::create_inferior): Mark with
diff --git a/gdb/frame.c b/gdb/frame.c
index 07fa2bc..1d0eb72 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -269,6 +269,22 @@ frame_stash_invalidate (void)
   htab_empty (frame_stash);
 }
 
+/* See frame.h  */
+scoped_restore_selected_frame::scoped_restore_selected_frame ()
+{
+  m_fid = get_frame_id (get_selected_frame (NULL));
+}
+
+/* See frame.h  */
+scoped_restore_selected_frame::~scoped_restore_selected_frame ()
+{
+  frame_info *frame = frame_find_by_id (m_fid);
+  if (frame == NULL)
+    warning (_("Unable to restore previously selected frame."));
+  else
+    select_frame (frame);
+}
+
 /* Flag to control debugging.  */
 
 unsigned int frame_debug;
diff --git a/gdb/frame.h b/gdb/frame.h
index d5800b7..a6f7fd8 100644
--- a/gdb/frame.h
+++ b/gdb/frame.h
@@ -164,6 +164,25 @@ struct frame_id
   int artificial_depth;
 };
 
+/* Save and restore the currently selected frame.  */
+
+class scoped_restore_selected_frame
+{
+public:
+  /* Save the currently selected frame.  */
+  scoped_restore_selected_frame ();
+
+  /* Restore the currently selected frame.  */
+  ~scoped_restore_selected_frame ();
+
+  DISABLE_COPY_AND_ASSIGN (scoped_restore_selected_frame);
+
+private:
+
+  /* The ID of the previously selected frame.  */
+  struct frame_id m_fid;
+};
+
 /* Methods for constructing and comparing Frame IDs.  */
 
 /* For convenience.  All fields are zero.  This means "there is no frame".  */
diff --git a/gdb/stack.c b/gdb/stack.c
index 74c9253..98a2184 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -2018,7 +2018,6 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
   struct print_variable_and_value_data cb_data;
   const struct block *block;
   CORE_ADDR pc;
-  struct gdb_exception except = exception_none;
 
   if (!get_frame_pc_if_available (frame, &pc))
     {
@@ -2042,27 +2041,12 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
   /* Temporarily change the selected frame to the given FRAME.
      This allows routines that rely on the selected frame instead
      of being given a frame as parameter to use the correct frame.  */
+  scoped_restore_selected_frame restore_selected_frame;
   select_frame (frame);
 
-  TRY
-    {
-      iterate_over_block_local_vars (block,
-				     do_print_variable_and_value,
-				     &cb_data);
-    }
-  CATCH (ex, RETURN_MASK_ALL)
-    {
-      except = ex;
-    }
-  END_CATCH
-
-  /* Restore the selected frame, and then rethrow if there was a problem.  */
-  select_frame (frame_find_by_id (cb_data.frame_id));
-  if (except.reason < 0)
-    throw_exception (except);
-
-  /* do_print_variable_and_value invalidates FRAME.  */
-  frame = NULL;
+  iterate_over_block_local_vars (block,
+				 do_print_variable_and_value,
+				 &cb_data);
 
   if (!cb_data.values_printed)
     fprintf_filtered (stream, _("No locals.\n"));
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 426b438..b2938b1 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2018-05-24  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	PR gdb/23203
+	* gdb.base/bt-selected-frame.c: New file.
+	* gdb.base/bt-selected-frame.exp: New file.
+	* lib/gdb.exp (get_current_frame_number): New function.
+
 2018-05-24  Maciej W. Rozycki  <macro@mips.com>
 	    Pedro Alves  <palves@redhat.com>
 
diff --git a/gdb/testsuite/gdb.base/bt-selected-frame.c b/gdb/testsuite/gdb.base/bt-selected-frame.c
new file mode 100644
index 0000000..708dc69
--- /dev/null
+++ b/gdb/testsuite/gdb.base/bt-selected-frame.c
@@ -0,0 +1,35 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+void
+breakpt ()
+{
+  asm ("" ::: "memory");
+}
+
+void
+func ()
+{
+  breakpt ();
+}
+
+int
+main ()
+{
+  func ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/bt-selected-frame.exp b/gdb/testsuite/gdb.base/bt-selected-frame.exp
new file mode 100644
index 0000000..a60962f
--- /dev/null
+++ b/gdb/testsuite/gdb.base/bt-selected-frame.exp
@@ -0,0 +1,72 @@
+# Copyright 2018 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check that the selected stack frame doesn't change after a backtrace.
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } {
+    return -1
+}
+
+proc check_selected_frame_after_bt { bt_cmd stack_pattern } {
+    global binfile
+
+    clean_restart $binfile
+
+    with_test_prefix $bt_cmd {
+
+	if ![runto_main] then {
+	    fail "can't run to main"
+	    return 0
+	}
+
+	gdb_breakpoint "breakpt"
+	gdb_continue_to_breakpoint "breakpt"
+
+	# Visit each frame in the stack and ensure that the selected
+	# frame doesn't change after executing the backtrace command
+	# in BT_CMD.
+	foreach_with_prefix frame {0 1 2} {
+	    if { $frame == 0 } {
+		gdb_assert {[get_current_frame_number] == $frame} \
+		    "check frame"
+	    } else {
+		gdb_test "frame $frame" "#$frame .*" "select frame"
+	    }
+
+	    gdb_test "$bt_cmd" $stack_pattern \
+		"perform backtrace command"
+
+	    gdb_assert {[get_current_frame_number] == $frame} \
+		"check frame is still selected"
+	}
+    }
+}
+
+check_selected_frame_after_bt "bt" \
+    [multi_line          \
+	 "#0 \[^\n\r\]+" \
+	 "#1 \[^\n\r\]+" \
+	 "#2 \[^\n\r\]+"]
+
+check_selected_frame_after_bt "bt full" \
+    [multi_line          \
+	 "#0 \[^\n\r\]+" \
+	 "No locals\."   \
+	 "#1 \[^\n\r\]+" \
+	 "No locals\."   \
+	 "#2 \[^\n\r\]+" \
+	 "No locals\."]
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 0f05d04..ee66a38 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5805,6 +5805,22 @@ proc get_var_address { var } {
     return ""
 }
 
+# Return the frame number for the currently selected frame
+proc get_current_frame_number {{test_name ""}} {
+    global gdb_prompt
+
+    if { $test_name == "" } {
+	set test_name "get current frame number"
+    }
+    set frame_num -1
+    gdb_test_multiple "frame" $test_name {
+	-re "#(\[0-9\]+) .*$gdb_prompt $" {
+	    set frame_num $expect_out(1,string)
+	}
+    }
+    return $frame_num
+}
+
 # Get the current value for remotetimeout and return it.
 proc get_remotetimeout { } {
     global gdb_prompt