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.

1 files changed, 72 insertions, 0 deletions

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\."]