[PATCH] Don't try to unwind the PC in frame.c:get_prev_frame()

Mark Kettenis
2004-01-05T20:33:40Z

As suggested by Andrew, this removes the attempt to unwind the PC in
frame.c:get_prev_frame(). This bit of code shouldn't be necessary and
made it impossible to backtrace from a sentinel frame with PC == 0,
which would aroise from calling a null function pointer.

Andrew, I saw no use for retaining some of the commentd, so I delete
the thing completely.

Committed,

Mark

Index: ChangeLog
from Mark Kettenis <kettenis@gnu.org>

* frame.c (get_prev_frame): Don't try to unwind the PC. This
fixes PR backtrace/1476.

Index: frame.c
===================================================================
RCS file: /cvs/src/src/gdb/frame.c,v
retrieving revision 1.153
diff -u -p -r1.153 frame.c
--- frame.c 10 Dec 2003 17:40:42 -0000 1.153
+++ frame.c 5 Jan 2004 20:27:20 -0000
@@ -1943,37 +1943,6 @@ get_prev_frame (struct frame_info *this_
prev_frame = FRAME_OBSTACK_ZALLOC (struct frame_info);
prev_frame->level = this_frame->level + 1;

- /* Try to unwind the PC. If that doesn't work, assume we've reached
- the oldest frame and simply return. Is there a better sentinal
- value? The unwound PC value is then used to initialize the new
- previous frame's type.
-
- Note that the pc-unwind is intentionally performed before the
- frame chain. This is ok since, for old targets, both
- frame_pc_unwind (nee, FRAME_SAVED_PC) and
- DEPRECATED_FRAME_CHAIN()) assume THIS_FRAME's data structures
- have already been initialized (using
- DEPRECATED_INIT_EXTRA_FRAME_INFO) and hence the call order
- doesn't matter.
-
- By unwinding the PC first, it becomes possible to, in the case of
- a dummy frame, avoid also unwinding the frame ID. This is
- because (well ignoring the PPC) a dummy frame can be located
- using THIS_FRAME's frame ID. */
-
- if (frame_pc_unwind (this_frame) == 0)
- {
- /* The allocated PREV_FRAME will be reclaimed when the frame
- obstack is next purged. */
- if (frame_debug)
- {
- fprintf_unfiltered (gdb_stdlog, "-> ");
- fprint_frame (gdb_stdlog, NULL);
- fprintf_unfiltered (gdb_stdlog, " // unwound PC zero }\n");
- }
- return NULL;
- }
-
/* Don't yet compute ->unwind (and hence ->type). It is computed
on-demand in get_frame_type, frame_register_unwind, and
get_frame_id. */