[RFC 2/4] Remove previous frame if we error during compute_frame_id

Andrew Burgess
2014-04-04T14:48:50Z

In get_prev_frame_if_no_cycle, if we throw an error during compute_frame_id
then we are left in a state where THIS_FRAME has a PREV_FRAME attached, but
PREV_FRAME has no frame id. This is an unexpected state that causes
internal
errors and assertions to fire.

This patch adds a cleanup that removes the previous frame created by
get_prev_frame_raw if we get an error.

OK to apply?

Thanks,
Andrew

gdb/ChangeLog:

* frame.c (remove_prev_frame): New function.
(get_prev_frame_if_no_cycle): Create / discard cleanup using
remove_prev_frame.

diff --git a/gdb/frame.c b/gdb/frame.c
index 97d54e9..5f05968 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -1733,6 +1733,22 @@ frame_register_unwind_location (struct frame_info
*this_frame, int regnum,
}
}

+/* Called during frame unwinding to remove a previous frame pointer from a
+ frame passed in ARG. */
+
+static void
+remove_prev_frame (void *arg)
+{
+ struct frame_info *this_frame, *prev_frame;
+
+ this_frame = (struct frame_info *) arg;
+ prev_frame = this_frame->prev;
+ gdb_assert (prev_frame != NULL);
+
+ prev_frame->next = NULL;
+ this_frame->prev = NULL;
+}
+
/* Get the previous raw frame, and check that it is not identical to
same other frame frame already in the chain. If it is, there is
most likely a stack cycle, so we discard it, and mark THIS_FRAME as
@@ -1745,28 +1761,36 @@ static struct frame_info *
get_prev_frame_if_no_cycle (struct frame_info *this_frame)
{
struct frame_info *prev_frame;
+ struct cleanup *prev_frame_cleanup;

prev_frame = get_prev_frame_raw (this_frame);
if (prev_frame == NULL)
return NULL;

- compute_frame_id (prev_frame);
- if (frame_stash_add (prev_frame))
- return prev_frame;
+ /* The cleanup will remove the previous frame that get_prev_frame_raw
+ linked onto THIS_FRAME. */
+ prev_frame_cleanup = make_cleanup (remove_prev_frame, this_frame);

- /* Another frame with the same id was already in the stash. We just
- detected a cycle. */
- if (frame_debug)
+ compute_frame_id (prev_frame);
+ if (!frame_stash_add (prev_frame))
{
- fprintf_unfiltered (gdb_stdlog, "-> ");
- fprint_frame (gdb_stdlog, NULL);
- fprintf_unfiltered (gdb_stdlog, " // this frame has same ID }\n");
+ /* Another frame with the same id was already in the stash. We just
+ detected a cycle. */
+ if (frame_debug)
+ {
+ fprintf_unfiltered (gdb_stdlog, "-> ");
+ fprint_frame (gdb_stdlog, NULL);
+ fprintf_unfiltered (gdb_stdlog, " // this frame has same ID }\n");
+ }
+ this_frame->stop_reason = UNWIND_SAME_ID;
+ /* Unlink. */
+ prev_frame->next = NULL;
+ this_frame->prev = NULL;
+ prev_frame = NULL;
}
- this_frame->stop_reason = UNWIND_SAME_ID;
- /* Unlink. */
- prev_frame->next = NULL;
- this_frame->prev = NULL;
- return NULL;
+
+ discard_cleanups (prev_frame_cleanup);
+ return prev_frame;
}

/* Return a "struct frame_info" corresponding to the frame that called