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, 19 insertions, 0 deletions

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".  */