[PATCHv2 2/2] gdb: convert sentinel_frame to a frame_info_ptr

[Andrew Burgess <aburgess@redhat.com>]

The global sentinel_frame object is currently held as a raw frame_info
pointer.  In contrast, most frames are managed through a
frame_info_ptr, and the global selected_frame is itself a
frame_info_ptr.

This commit converts the sentinel_frame to a frame_info_ptr.

The frame_info_ptr constructor registers the new object in the global
frame_list, so we need to ensure that the frame_list has been
constructed before the sentinel_frame (now a frame_info_ptr) is
constructed.  This is achieved by moving the frame_list global earlier
within the frame.c file.

I chose to also move the selected_frame, selected_frame_id, and
selected_frame_level globals.  This isn't required, but keeps similar
and related objects (the frame_list, selected_frame*, and
sentinel_frame) together in the file.

In get_current_frame, when assigning to the sentinel_frame global, we
no longer need to pull the raw frame_info pointer from the result of
calling create_sentinel_frame, this means we can drop the '.get ()'
call.  I took this opportunity to move the '=' operator onto the next
line inline with GDB style.

Additionally, in get_current_frame, we no longer need to convert
sentinel_frame into a frame_info_ptr.

There should be no user visible changes after this commit.
---
 gdb/frame.c | 96 ++++++++++++++++++++++++++---------------------------
 1 file changed, 48 insertions(+), 48 deletions(-)

diff --git a/gdb/frame.c b/gdb/frame.c
index c1a7c41dc4a..22bfb95aa95 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -45,6 +45,46 @@
 #include "cli/cli-option.h"
 #include "dwarf2/loc.h"
 
+/* Number of calls to reinit_frame_cache.  */
+static unsigned int frame_cache_generation = 0;
+
+/* The "selected" stack frame is used by default for local and arg
+   access.
+
+   The "single source of truth" for the selected frame is the
+   SELECTED_FRAME_ID / SELECTED_FRAME_LEVEL pair.
+
+   Frame IDs can be saved/restored across reinitializing the frame
+   cache, while frame_info pointers can't (frame_info objects are
+   invalidated).  If we know the corresponding frame_info object, it
+   is cached in SELECTED_FRAME.
+
+   If SELECTED_FRAME_ID / SELECTED_FRAME_LEVEL are null_frame_id / -1,
+   and the target has stack and is stopped, the selected frame is the
+   current (innermost) target frame.  SELECTED_FRAME_ID is never the ID
+   of the current (innermost) target frame.  SELECTED_FRAME_LEVEL may
+   only be 0 if the selected frame is a user-created one (created and
+   selected through the "select-frame view" command), in which case
+   SELECTED_FRAME_ID is the frame id derived from the user-provided
+   addresses.
+
+   If SELECTED_FRAME_ID / SELECTED_FRAME_LEVEL are null_frame_id / -1,
+   and the target has no stack or is executing, then there's no
+   selected frame.  */
+static frame_id selected_frame_id = null_frame_id;
+static int selected_frame_level = -1;
+
+/* See frame.h.  This definition should come before any definition of a static
+   frame_info_ptr, to ensure that frame_list is destroyed after any static
+   frame_info_ptr.  This is necessary because the destructor of frame_info_ptr
+   uses frame_list.  */
+
+intrusive_list<frame_info_ptr> frame_info_ptr::frame_list;
+
+/* The cached frame_info object pointing to the selected frame.
+   Looked up on demand by get_selected_frame.  */
+static frame_info_ptr selected_frame;
+
 /* The sentinel frame terminates the innermost end of the frame chain.
    If unwound, it returns the information needed to construct an
    innermost frame.
@@ -55,10 +95,7 @@
    This is an optimization to be able to find the sentinel frame quickly,
    it could otherwise be found in the frame cache.  */
 
-static frame_info *sentinel_frame;
-
-/* Number of calls to reinit_frame_cache.  */
-static unsigned int frame_cache_generation = 0;
+static frame_info_ptr sentinel_frame;
 
 /* See frame.h.  */
 
@@ -1726,12 +1763,12 @@ get_current_frame (void)
   if (get_traceframe_number () < 0)
     validate_registers_access ();
 
-  if (sentinel_frame == NULL)
-    sentinel_frame =
-      create_sentinel_frame (current_program_space,
-			     current_inferior ()->aspace.get (),
-			     get_thread_regcache (inferior_thread ()),
-			     0, 0).get ();
+  if (sentinel_frame == nullptr)
+    sentinel_frame
+      = create_sentinel_frame (current_program_space,
+			       current_inferior ()->aspace.get (),
+			       get_thread_regcache (inferior_thread ()),
+			       0, 0);
 
   /* Set the current frame before computing the frame id, to avoid
      recursion inside compute_frame_id, in case the frame's
@@ -1744,49 +1781,12 @@ get_current_frame (void)
      want to leave with the current frame created and linked in --
      we should never end up with the sentinel frame as outermost
      frame.  */
-  current_frame = get_prev_frame_always_1 (frame_info_ptr (sentinel_frame));
+  current_frame = get_prev_frame_always_1 (sentinel_frame);
   gdb_assert (current_frame != NULL);
 
   return current_frame;
 }
 
-/* The "selected" stack frame is used by default for local and arg
-   access.
-
-   The "single source of truth" for the selected frame is the
-   SELECTED_FRAME_ID / SELECTED_FRAME_LEVEL pair.
-
-   Frame IDs can be saved/restored across reinitializing the frame
-   cache, while frame_info pointers can't (frame_info objects are
-   invalidated).  If we know the corresponding frame_info object, it
-   is cached in SELECTED_FRAME.
-
-   If SELECTED_FRAME_ID / SELECTED_FRAME_LEVEL are null_frame_id / -1,
-   and the target has stack and is stopped, the selected frame is the
-   current (innermost) target frame.  SELECTED_FRAME_ID is never the ID
-   of the current (innermost) target frame.  SELECTED_FRAME_LEVEL may
-   only be 0 if the selected frame is a user-created one (created and
-   selected through the "select-frame view" command), in which case
-   SELECTED_FRAME_ID is the frame id derived from the user-provided
-   addresses.
-
-   If SELECTED_FRAME_ID / SELECTED_FRAME_LEVEL are null_frame_id / -1,
-   and the target has no stack or is executing, then there's no
-   selected frame.  */
-static frame_id selected_frame_id = null_frame_id;
-static int selected_frame_level = -1;
-
-/* See frame.h.  This definition should come before any definition of a static
-   frame_info_ptr, to ensure that frame_list is destroyed after any static
-   frame_info_ptr.  This is necessary because the destructor of frame_info_ptr
-   uses frame_list.  */
-
-intrusive_list<frame_info_ptr> frame_info_ptr::frame_list;
-
-/* The cached frame_info object pointing to the selected frame.
-   Looked up on demand by get_selected_frame.  */
-static frame_info_ptr selected_frame;
-
 /* See frame.h.  */
 
 void
-- 
2.25.4