[PATCH] infcmd, btrace: fix crash in 'finish' for tailcall-only frames

[Markus Metzger <markus.t.metzger@intel.com>]

Patch 7eb895307f53 Skip unwritable frames in command "finish"
skips non-writable frames in addition to tailcall frames.

If skip_tailcall_frames already returns NULL, skip_unwritable_frames
will be called with a NULL frame and crash in get_frame_arch.  This is
caught by gdb.btrace/tailcall-only.exp.

Further, if we ever end up with a mixture of tailcall and non-writable
frames, we may not skip all of them, as intended.

Loop over skip_tailcall_frames and skip_unwritable_frames as long as at least
one of them makes progress.

2016-05-31  Markus Metzger  <markus.t.metzger@intel.com>

	* infcmd.c (skip_finish_frames): New.
	(finish_command): Call skip_finish_frames.
---
 gdb/infcmd.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 14d51fd..ca8655a 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1927,6 +1927,28 @@ finish_forward (struct finish_command_fsm *sm, struct frame_info *frame)
   proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
 }
 
+/* Skip frames for "finish".  */
+
+static struct frame_info *
+skip_finish_frames (struct frame_info *frame)
+{
+  struct frame_info *start;
+
+  do {
+    start = frame;
+
+    frame = skip_tailcall_frames (frame);
+    if (frame == NULL)
+      break;
+
+    frame = skip_unwritable_frames (frame);
+    if (frame == NULL)
+      break;
+  } while (start != frame);
+
+  return frame;
+}
+
 /* "finish": Set a temporary breakpoint at the place the selected
    frame will return to, then continue.  */
 
@@ -2025,11 +2047,7 @@ finish_command (char *arg, int from_tty)
     finish_backward (sm);
   else
     {
-      /* Ignore TAILCALL_FRAME type frames, they were executed already before
-	 entering THISFRAME.  */
-      frame = skip_tailcall_frames (frame);
-
-      frame = skip_unwritable_frames (frame);
+      frame = skip_finish_frames (frame);
 
       if (frame == NULL)
 	error (_("Cannot find the caller frame."));
-- 
1.8.3.1