Index: Include/object.h

===================================================================

--- Include/object.h	(revision 87911)

+++ Include/object.h	(working copy)

@@ -914,6 +914,49 @@

 _PyObject_DebugTypeStats(FILE *out);

 #endif /* ifndef Py_LIMITED_API */

+/* 

+   Define a pair of assertion macros.

+

+   These work like the regular C assert(), in that they will abort the

+   process with a message on stderr if the given condition fails to hold,

+   but compile away to nothing if NDEBUG is defined.

+

+   However, before aborting, Python will also try to call _PyObject_Dump() on

+   the given object.  This may be of use when investigating bugs in which a

+   particular object is corrupt (e.g. buggy a tp_visit method in an extension

+   module breaking the garbage collector), to help locate the broken objects.

+

+   The WITH_MSG variant allows you to supply an additional message that Python

+   will attempt to print to stderr, after the object dump.

+*/

+#ifdef NDEBUG

+/* No debugging: compile away the assertions: */

+#define PyObject_ASSERT_WITH_MSG(obj, expr, msg) ((void)0)

+#else

+/* With debugging: generate checks: */

+#define PyObject_ASSERT_WITH_MSG(obj, expr, msg) \

+  ((expr)                                           \

+   ? (void)(0)                                      \

+   : _PyObject_AssertFailed((obj),                  \

+                            (msg),                  \

+                            (__STRING(expr)),       \

+                            (__FILE__),             \

+                            (__LINE__),             \

+                            (__PRETTY_FUNCTION__)))

+#endif

+

+#define PyObject_ASSERT(obj, expr) \

+  PyObject_ASSERT_WITH_MSG(obj, expr, NULL)

+

+/* 

+   Declare and define the entrypoint even when NDEBUG is defined, to avoid

+   causing compiler/linker errors when building extensions without NDEBUG

+   against a Python built with NDEBUG defined

+*/

+PyAPI_FUNC(void) _PyObject_AssertFailed(PyObject *,  const char *,

+                                        const char *, const char *, int,

+                                        const char *);

+

 #ifdef __cplusplus

 }

 #endif

Index: Objects/object.c

===================================================================

--- Objects/object.c	(revision 87911)

+++ Objects/object.c	(working copy)

@@ -1899,6 +1899,35 @@

     }

 }

+PyAPI_FUNC(void)

+_PyObject_AssertFailed(PyObject *obj, const char *msg, const char *expr,

+		       const char *file, int line, const char *function)

+{

+    fprintf(stderr,

+            "%s:%d: %s: Assertion \"%s\" failed.\n",

+            file, line, function, expr);

+    if (msg) {

+        fprintf(stderr, "%s\n", msg);

+    }

+

+    fflush(stderr);

+

+    if (obj) {

+        /* This might succeed or fail, but we're about to abort, so at least

+           try to provide any extra info we can: */

+        _PyObject_Dump(obj);

+    }

+    else {

+        fprintf(stderr, "NULL object\n");

+    }

+

+    fflush(stdout);

+    fflush(stderr);

+

+    /* Terminate the process: */

+    abort();

+}

+

 #ifndef Py_TRACE_REFS

 /* For Py_LIMITED_API, we need an out-of-line version of _Py_Dealloc.

    Define this here, so we can undefine the macro. */

Index: Lib/test/test_gc.py

===================================================================

--- Lib/test/test_gc.py	(revision 87911)

+++ Lib/test/test_gc.py	(working copy)

@@ -1,6 +1,6 @@

 import unittest

 from test.support import (verbose, refcount_test, run_unittest,

-                            strip_python_stderr, cpython_only)

+                            strip_python_stderr, cpython_only, import_module)

 from test.script_helper import assert_python_ok, make_script, temp_dir

 import sys

@@ -512,6 +512,48 @@

         self.assertEqual(len(gc.garbage), 0)

+    def test_refcount_errors(self):

+        self.preclean()

+        # Verify the "handling" of objects with broken refcounts

+        import_module("ctypes") #skip if not supported

+

+        import subprocess

+        code = '''if 1:

+        a = []

+        b = [a]

+

+        # Simulate the refcount of "a" being too low (compared to the

+        # references held on it by live data), but keeping it above zero

+        # (to avoid deallocating it):

+        import ctypes

+        ctypes.pythonapi.Py_DecRef(ctypes.py_object(a))

+

+        # The garbage collector should now have a fatal error when it reaches

+        # the broken object:

+        import gc

+        gc.collect()

+        '''

+        p = subprocess.Popen([sys.executable, "-c", code],

+                             stdout=subprocess.PIPE,

+                             stderr=subprocess.PIPE)

+        stdout, stderr = p.communicate()

+        p.stdout.close()

+        p.stderr.close()

+        # Verify that stderr has a useful error message:

+        self.assertRegex(stderr,

+            b'Modules/gcmodule.c:[0-9]+: visit_decref: Assertion "\(\(gc\)->gc.gc_refs >> \(1\)\) != 0" failed.')

+        self.assertRegex(stderr,

+            b'refcount was too small')

+        self.assertRegex(stderr,

+            b'object  : \[\]')

+        self.assertRegex(stderr,

+            b'type    : list')

+        self.assertRegex(stderr,

+            b'refcount: 1')

+        self.assertRegex(stderr,

+            b'address : 0x[0-9a-f]+')

+

+

 class GCTogglingTests(unittest.TestCase):

     def setUp(self):

         gc.enable()

diff -up Modules/gcmodule.c.orig2 Modules/gcmodule.c

--- Modules/gcmodule.c.orig2	2014-12-08 10:54:14.251742911 +0100

+++ Modules/gcmodule.c	2014-12-08 10:52:45.674771917 +0100

@@ -341,7 +341,8 @@ update_refs(PyGC_Head *containers)

 {

     PyGC_Head *gc = containers->gc.gc_next;

     for (; gc != containers; gc = gc->gc.gc_next) {

-        assert(_PyGCHead_REFS(gc) == GC_REACHABLE);

+        PyObject_ASSERT(FROM_GC(gc),

+                        _PyGCHead_REFS(gc) == GC_REACHABLE);

         _PyGCHead_SET_REFS(gc, Py_REFCNT(FROM_GC(gc)));

         /* Python's cyclic gc should never see an incoming refcount

          * of 0:  if something decref'ed to 0, it should have been

@@ -361,7 +362,8 @@ update_refs(PyGC_Head *containers)

          * so serious that maybe this should be a release-build

          * check instead of an assert?

          */

-        assert(_PyGCHead_REFS(gc) != 0);

+        PyObject_ASSERT(FROM_GC(gc),

+                        _PyGCHead_REFS(gc) != 0);

     }

 }

@@ -376,7 +378,9 @@ visit_decref(PyObject *op, void *data)

          * generation being collected, which can be recognized

          * because only they have positive gc_refs.

          */

-        assert(_PyGCHead_REFS(gc) != 0); /* else refcount was too small */

+        PyObject_ASSERT_WITH_MSG(FROM_GC(gc),

+                        _PyGCHead_REFS(gc) != 0,

+                        "refcount was too small"); /* else refcount was too small */

         if (_PyGCHead_REFS(gc) > 0)

             _PyGCHead_DECREF(gc);

     }

@@ -436,9 +440,10 @@ visit_reachable(PyObject *op, PyGC_Head

          * If gc_refs == GC_UNTRACKED, it must be ignored.

          */

          else {

-            assert(gc_refs > 0

-                   || gc_refs == GC_REACHABLE

-                   || gc_refs == GC_UNTRACKED);

+             PyObject_ASSERT(FROM_GC(gc),

+                             gc_refs > 0

+                             || gc_refs == GC_REACHABLE

+                             || gc_refs == GC_UNTRACKED);

          }

     }

     return 0;

@@ -480,7 +485,7 @@ move_unreachable(PyGC_Head *young, PyGC_

              */

             PyObject *op = FROM_GC(gc);

             traverseproc traverse = Py_TYPE(op)->tp_traverse;

-            assert(_PyGCHead_REFS(gc) > 0);

+            PyObject_ASSERT(op, _PyGCHead_REFS(gc) > 0);

             _PyGCHead_SET_REFS(gc, GC_REACHABLE);

             (void) traverse(op,

                             (visitproc)visit_reachable,

@@ -543,7 +548,7 @@ move_legacy_finalizers(PyGC_Head *unreac

     for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) {

         PyObject *op = FROM_GC(gc);

-        assert(IS_TENTATIVELY_UNREACHABLE(op));

+        PyObject_ASSERT(op, IS_TENTATIVELY_UNREACHABLE(op));

         next = gc->gc.gc_next;

         if (has_legacy_finalizer(op)) {

@@ -619,7 +624,7 @@ handle_weakrefs(PyGC_Head *unreachable,

         PyWeakReference **wrlist;

         op = FROM_GC(gc);

-        assert(IS_TENTATIVELY_UNREACHABLE(op));

+        PyObject_ASSERT(op, IS_TENTATIVELY_UNREACHABLE(op));

         next = gc->gc.gc_next;

         if (! PyType_SUPPORTS_WEAKREFS(Py_TYPE(op)))

@@ -640,9 +645,9 @@ handle_weakrefs(PyGC_Head *unreachable,

              * the callback pointer intact.  Obscure:  it also

              * changes *wrlist.

              */

-            assert(wr->wr_object == op);

+            PyObject_ASSERT(wr->wr_object, wr->wr_object == op);

             _PyWeakref_ClearRef(wr);

-            assert(wr->wr_object == Py_None);

+            PyObject_ASSERT(wr->wr_object, wr->wr_object == Py_None);

             if (wr->wr_callback == NULL)

                 continue;                       /* no callback */

@@ -676,7 +681,7 @@ handle_weakrefs(PyGC_Head *unreachable,

      */

             if (IS_TENTATIVELY_UNREACHABLE(wr))

                 continue;

-            assert(IS_REACHABLE(wr));

+            PyObject_ASSERT(op, IS_REACHABLE(wr));

             /* Create a new reference so that wr can't go away

              * before we can process it again.

@@ -685,7 +690,8 @@ handle_weakrefs(PyGC_Head *unreachable,

             /* Move wr to wrcb_to_call, for the next pass. */

             wrasgc = AS_GC(wr);

-            assert(wrasgc != next); /* wrasgc is reachable, but

+            PyObject_ASSERT(op, wrasgc != next);

+                                    /* wrasgc is reachable, but

                                        next isn't, so they can't

                                        be the same */

             gc_list_move(wrasgc, &wrcb_to_call);

@@ -701,11 +707,11 @@ handle_weakrefs(PyGC_Head *unreachable,

         gc = wrcb_to_call.gc.gc_next;

         op = FROM_GC(gc);

-        assert(IS_REACHABLE(op));

-        assert(PyWeakref_Check(op));

+        PyObject_ASSERT(op, IS_REACHABLE(op));

+        PyObject_ASSERT(op, PyWeakref_Check(op));

         wr = (PyWeakReference *)op;

         callback = wr->wr_callback;

-        assert(callback != NULL);

+        PyObject_ASSERT(op, callback != NULL);

         /* copy-paste of weakrefobject.c's handle_callback() */

         temp = PyObject_CallFunctionObjArgs(callback, wr, NULL);

@@ -822,12 +828,14 @@ check_garbage(PyGC_Head *collectable)

     for (gc = collectable->gc.gc_next; gc != collectable;

          gc = gc->gc.gc_next) {

         _PyGCHead_SET_REFS(gc, Py_REFCNT(FROM_GC(gc)));

-        assert(_PyGCHead_REFS(gc) != 0);

+        PyObject_ASSERT(FROM_GC(gc),

+                        _PyGCHead_REFS(gc) != 0);

     }

     subtract_refs(collectable);

     for (gc = collectable->gc.gc_next; gc != collectable;

          gc = gc->gc.gc_next) {

-        assert(_PyGCHead_REFS(gc) >= 0);

+        PyObject_ASSERT(FROM_GC(gc),

+                        _PyGCHead_REFS(gc) >= 0);

         if (_PyGCHead_REFS(gc) != 0)

             return -1;

     }

diff -up Lib/test/test_gc.py.old Lib/test/test_gc.py

--- Lib/test/test_gc.py.old	2014-12-10 11:19:33.503982288 +0100

+++ Lib/test/test_gc.py	2014-12-10 11:21:13.220021364 +0100

@@ -49,6 +49,8 @@ class GC_Detector(object):

         # gc collects it.

         self.wr = weakref.ref(C1055820(666), it_happened)

+BUILD_WITH_NDEBUG = ('-DNDEBUG' in sysconfig.get_config_vars()['PY_CFLAGS'])

+

 @with_tp_del

 class Uncollectable(object):

     """Create a reference cycle with multiple __del__ methods.

@@ -854,6 +856,8 @@ class GCCallbackTests(unittest.TestCase)

         self.assertEqual(len(gc.garbage), 0)

+    @unittest.skipIf(BUILD_WITH_NDEBUG,

+                     'built with -NDEBUG')

     def test_refcount_errors(self):

         self.preclean()

         # Verify the "handling" of objects with broken refcounts

diff -up Lib/test/test_gc.py.old Lib/test/test_gc.py

--- Lib/test/test_gc.py.old	2014-12-10 12:50:58.252121318 +0100

+++ Lib/test/test_gc.py	2014-12-10 12:51:08.594266653 +0100

@@ -4,6 +4,7 @@ from test.support import (verbose, refco

 from test.script_helper import assert_python_ok, make_script, temp_dir

 import sys

+import sysconfig

 import time

 import gc

 import weakref