Fix Python frame unwinder issue caught by Valgrind

Valgrind shows:

 ==17026== Invalid write of size 8
 ==17026==    at 0x54AA80: pending_frame_invalidate (py-unwind.c:477)
 ==17026==    by 0x5AB934: do_my_cleanups (cleanups.c:155)
 ==17026==    by 0x5AB9AF: do_cleanups (cleanups.c:177)
 ==17026==    by 0x54B009: pyuw_sniffer (py-unwind.c:606)
 ==17026==    by 0x755DAC: frame_unwind_try_unwinder (frame-unwind.c:105)
 ==17026==    by 0x755EEE: frame_unwind_find_by_frame (frame-unwind.c:160)
 ==17026==    by 0x750FFA: compute_frame_id (frame.c:454)
 ==17026==    by 0x753BD6: get_prev_frame_if_no_cycle (frame.c:1781)
 ==17026==    by 0x754292: get_prev_frame_always_1 (frame.c:1955)
 ==17026==    by 0x7542DA: get_prev_frame_always (frame.c:1971)
 ==17026==    by 0x7547BE: get_prev_frame (frame.c:2213)
 ==17026==    by 0x7532BD: unwind_to_current_frame (frame.c:1450)
 ==17026==  Address 0xd27b570 is 16 bytes inside a block of size 32 free'd
 ==17026==    at 0x4A07577: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
 ==17026==    by 0x54B276: gdb_Py_DECREF (python-internal.h:185)
 ==17026==    by 0x54B298: py_decref (py-utils.c:34)
 ==17026==    by 0x5AB934: do_my_cleanups (cleanups.c:155)
 ==17026==    by 0x5AB9AF: do_cleanups (cleanups.c:177)
 ==17026==    by 0x54B009: pyuw_sniffer (py-unwind.c:606)
 ==17026==    by 0x755DAC: frame_unwind_try_unwinder (frame-unwind.c:105)
 ==17026==    by 0x755EEE: frame_unwind_find_by_frame (frame-unwind.c:160)
 ==17026==    by 0x750FFA: compute_frame_id (frame.c:454)
 ==17026==    by 0x753BD6: get_prev_frame_if_no_cycle (frame.c:1781)
 ==17026==    by 0x754292: get_prev_frame_always_1 (frame.c:1955)
 ==17026==    by 0x7542DA: get_prev_frame_always (frame.c:1971)
 ==17026==

Simply invalidate the object before releasing it.

gdb/ChangeLog:
2015-08-13  Pedro Alves  <palves@redhat.com>

	* python/py-unwind.c (pyuw_sniffer): Install the invalidate
	cleanup after the decref cleanup, not before.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index f33faaabbe1948968fb20d4c33c7b71d24dccccf..7db4487b70ace470de225bc6daec288901a2d126 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-13  Pedro Alves  <palves@redhat.com>
+
+       * python/py-unwind.c (pyuw_sniffer): Install the invalidate
+       cleanup after the decref cleanup, not before.
+
 2015-08-13  Pierre-Marie de Rodat  <derodat@adacore.com>
 
        * ada-lang.c: Include namespace.h

diff --git a/gdb/python/py-unwind.c b/gdb/python/py-unwind.c
index b6e8a7531bacfaff6d589ea49c520ded56786836..18f8f4d3546b44757b0de98fa15fb1c914708683 100644 (file)
--- a/gdb/python/py-unwind.c
+++ b/gdb/python/py-unwind.c
@@ -537,8 +537,8 @@ pyuw_sniffer (const struct frame_unwind *self, struct frame_info *this_frame,
     goto error;
   ((pending_frame_object *) pyo_pending_frame)->gdbarch = gdbarch;
   ((pending_frame_object *) pyo_pending_frame)->frame_info = this_frame;
-  make_cleanup (pending_frame_invalidate, (void *) pyo_pending_frame);
   make_cleanup_py_decref (pyo_pending_frame);
+  make_cleanup (pending_frame_invalidate, (void *) pyo_pending_frame);
 
   /* Run unwinders.  */
   if (gdb_python_module == NULL