bpo-36389: _PyObject_CheckConsistency() available in release mode (GH-16612)

bpo-36389, bpo-38376: The _PyObject_CheckConsistency() function is
now also available in release mode. For example, it can be used to
debug a crash in the visit_decref() function of the GC.

Modify the following functions to also work in release mode:

* _PyDict_CheckConsistency()
* _PyObject_CheckConsistency()
* _PyType_CheckConsistency()
* _PyUnicode_CheckConsistency()

Other changes:

* _PyMem_IsPtrFreed(ptr) now also returns 1 if ptr is NULL
  (equals to 0).
* _PyBytesWriter_CheckConsistency() now returns 1 and is only used
  with assert().
* Reorder _PyObject_Dump() to write safe fields first, and only
  attempt to render repr() at the end.

5 files changed, 113 insertions, 111 deletions

diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index 7df9344..4223dc9 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -3206,10 +3206,10 @@ _PyBytesWriter_GetSize(_PyBytesWriter *writer, char *str)
     return str - start;
 }
 
-Py_LOCAL_INLINE(void)
+#ifndef NDEBUG
+Py_LOCAL_INLINE(int)
 _PyBytesWriter_CheckConsistency(_PyBytesWriter *writer, char *str)
 {
-#ifdef Py_DEBUG
     char *start, *end;
 
     if (writer->use_small_buffer) {
@@ -3239,15 +3239,16 @@ _PyBytesWriter_CheckConsistency(_PyBytesWriter *writer, char *str)
     end = start + writer->allocated;
     assert(str != NULL);
     assert(start <= str && str <= end);
-#endif
+    return 1;
 }
+#endif
 
 void*
 _PyBytesWriter_Resize(_PyBytesWriter *writer, void *str, Py_ssize_t size)
 {
     Py_ssize_t allocated, pos;
 
-    _PyBytesWriter_CheckConsistency(writer, str);
+    assert(_PyBytesWriter_CheckConsistency(writer, str));
     assert(writer->allocated < size);
 
     allocated = size;
@@ -3303,7 +3304,7 @@ _PyBytesWriter_Resize(_PyBytesWriter *writer, void *str, Py_ssize_t size)
     writer->allocated = allocated;
 
     str = _PyBytesWriter_AsString(writer) + pos;
-    _PyBytesWriter_CheckConsistency(writer, str);
+    assert(_PyBytesWriter_CheckConsistency(writer, str));
     return str;
 
 error:
@@ -3316,7 +3317,7 @@ _PyBytesWriter_Prepare(_PyBytesWriter *writer, void *str, Py_ssize_t size)
 {
     Py_ssize_t new_min_size;
 
-    _PyBytesWriter_CheckConsistency(writer, str);
+    assert(_PyBytesWriter_CheckConsistency(writer, str));
     assert(size >= 0);
 
     if (size == 0) {
@@ -3377,7 +3378,7 @@ _PyBytesWriter_Finish(_PyBytesWriter *writer, void *str)
     Py_ssize_t size;
     PyObject *result;
 
-    _PyBytesWriter_CheckConsistency(writer, str);
+    assert(_PyBytesWriter_CheckConsistency(writer, str));
 
     size = _PyBytesWriter_GetSize(writer, str);
     if (size == 0 && !writer->use_bytearray) {
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 164fe2a..99908a8 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -459,23 +459,26 @@ static PyObject *empty_values[1] = { NULL };
 int
 _PyDict_CheckConsistency(PyObject *op, int check_content)
 {
-#ifndef NDEBUG
-    _PyObject_ASSERT(op, PyDict_Check(op));
+#define CHECK(expr) \
+    do { if (!(expr)) { _PyObject_ASSERT_FAILED_MSG(op, Py_STRINGIFY(expr)); } } while (0)
+
+    assert(op != NULL);
+    CHECK(PyDict_Check(op));
     PyDictObject *mp = (PyDictObject *)op;
 
     PyDictKeysObject *keys = mp->ma_keys;
     int splitted = _PyDict_HasSplitTable(mp);
     Py_ssize_t usable = USABLE_FRACTION(keys->dk_size);
 
-    _PyObject_ASSERT(op, 0 <= mp->ma_used && mp->ma_used <= usable);
-    _PyObject_ASSERT(op, IS_POWER_OF_2(keys->dk_size));
-    _PyObject_ASSERT(op, 0 <= keys->dk_usable && keys->dk_usable <= usable);
-    _PyObject_ASSERT(op, 0 <= keys->dk_nentries && keys->dk_nentries <= usable);
-    _PyObject_ASSERT(op, keys->dk_usable + keys->dk_nentries <= usable);
+    CHECK(0 <= mp->ma_used && mp->ma_used <= usable);
+    CHECK(IS_POWER_OF_2(keys->dk_size));
+    CHECK(0 <= keys->dk_usable && keys->dk_usable <= usable);
+    CHECK(0 <= keys->dk_nentries && keys->dk_nentries <= usable);
+    CHECK(keys->dk_usable + keys->dk_nentries <= usable);
 
     if (!splitted) {
         /* combined table */
-        _PyObject_ASSERT(op, keys->dk_refcnt == 1);
+        CHECK(keys->dk_refcnt == 1);
     }
 
     if (check_content) {
@@ -484,7 +487,7 @@ _PyDict_CheckConsistency(PyObject *op, int check_content)
 
         for (i=0; i < keys->dk_size; i++) {
             Py_ssize_t ix = dictkeys_get_index(keys, i);
-            _PyObject_ASSERT(op, DKIX_DUMMY <= ix && ix <= usable);
+            CHECK(DKIX_DUMMY <= ix && ix <= usable);
         }
 
         for (i=0; i < usable; i++) {
@@ -494,32 +497,33 @@ _PyDict_CheckConsistency(PyObject *op, int check_content)
             if (key != NULL) {
                 if (PyUnicode_CheckExact(key)) {
                     Py_hash_t hash = ((PyASCIIObject *)key)->hash;
-                    _PyObject_ASSERT(op, hash != -1);
-                    _PyObject_ASSERT(op, entry->me_hash == hash);
+                    CHECK(hash != -1);
+                    CHECK(entry->me_hash == hash);
                 }
                 else {
                     /* test_dict fails if PyObject_Hash() is called again */
-                    _PyObject_ASSERT(op, entry->me_hash != -1);
+                    CHECK(entry->me_hash != -1);
                 }
                 if (!splitted) {
-                    _PyObject_ASSERT(op, entry->me_value != NULL);
+                    CHECK(entry->me_value != NULL);
                 }
             }
 
             if (splitted) {
-                _PyObject_ASSERT(op, entry->me_value == NULL);
+                CHECK(entry->me_value == NULL);
             }
         }
 
         if (splitted) {
             /* splitted table */
             for (i=0; i < mp->ma_used; i++) {
-                _PyObject_ASSERT(op, mp->ma_values[i] != NULL);
+                CHECK(mp->ma_values[i] != NULL);
             }
         }
     }
-#endif
     return 1;
+
+#undef CHECK
 }
 
 
diff --git a/Objects/object.c b/Objects/object.c
index 43ed4c5..e94480f 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -25,13 +25,14 @@ _Py_IDENTIFIER(__isabstractmethod__);
 int
 _PyObject_CheckConsistency(PyObject *op, int check_content)
 {
-    _PyObject_ASSERT(op, op != NULL);
-    _PyObject_ASSERT(op, !_PyObject_IsFreed(op));
-    _PyObject_ASSERT(op, Py_REFCNT(op) >= 1);
+#define CHECK(expr) \
+    do { if (!(expr)) { _PyObject_ASSERT_FAILED_MSG(op, Py_STRINGIFY(expr)); } } while (0)
 
-    PyTypeObject *type = op->ob_type;
-    _PyObject_ASSERT(op, type != NULL);
-    _PyType_CheckConsistency(type);
+    CHECK(!_PyObject_IsFreed(op));
+    CHECK(Py_REFCNT(op) >= 1);
+
+    CHECK(op->ob_type != NULL);
+    _PyType_CheckConsistency(op->ob_type);
 
     if (PyUnicode_Check(op)) {
         _PyUnicode_CheckConsistency(op, check_content);
@@ -40,6 +41,8 @@ _PyObject_CheckConsistency(PyObject *op, int check_content)
         _PyDict_CheckConsistency(op, check_content);
     }
     return 1;
+
+#undef CHECK
 }
 
 
@@ -463,41 +466,41 @@ _PyObject_IsFreed(PyObject *op)
 void
 _PyObject_Dump(PyObject* op)
 {
-    if (op == NULL) {
-        fprintf(stderr, "<object at NULL>\n");
-        fflush(stderr);
-        return;
-    }
-
     if (_PyObject_IsFreed(op)) {
         /* It seems like the object memory has been freed:
            don't access it to prevent a segmentation fault. */
         fprintf(stderr, "<object at %p is freed>\n", op);
+        fflush(stderr);
         return;
     }
 
-    PyGILState_STATE gil;
-    PyObject *error_type, *error_value, *error_traceback;
+    /* first, write fields which are the least likely to crash */
+    fprintf(stderr, "object address  : %p\n", (void *)op);
+    /* XXX(twouters) cast refcount to long until %zd is
+       universally available */
+    fprintf(stderr, "object refcount : %ld\n", (long)op->ob_refcnt);
+    fflush(stderr);
+
+    PyTypeObject *type = Py_TYPE(op);
+    fprintf(stderr, "object type     : %p\n", type);
+    fprintf(stderr, "object type name: %s\n",
+            type==NULL ? "NULL" : type->tp_name);
 
-    fprintf(stderr, "object  : ");
+    /* the most dangerous part */
+    fprintf(stderr, "object repr     : ");
     fflush(stderr);
-    gil = PyGILState_Ensure();
 
+    PyGILState_STATE gil = PyGILState_Ensure();
+    PyObject *error_type, *error_value, *error_traceback;
     PyErr_Fetch(&error_type, &error_value, &error_traceback);
+
     (void)PyObject_Print(op, stderr, 0);
     fflush(stderr);
-    PyErr_Restore(error_type, error_value, error_traceback);
 
+    PyErr_Restore(error_type, error_value, error_traceback);
     PyGILState_Release(gil);
-    /* XXX(twouters) cast refcount to long until %zd is
-       universally available */
-    fprintf(stderr, "\n"
-        "type    : %s\n"
-        "refcount: %ld\n"
-        "address : %p\n",
-        Py_TYPE(op)==NULL ? "NULL" : Py_TYPE(op)->tp_name,
-        (long)op->ob_refcnt,
-        (void *)op);
+
+    fprintf(stderr, "\n");
     fflush(stderr);
 }
 
@@ -2146,6 +2149,7 @@ _PyObject_AssertFailed(PyObject *obj, const char *expr, const char *msg,
         fprintf(stderr, "%s: ", function);
     }
     fflush(stderr);
+
     if (expr) {
         fprintf(stderr, "Assertion \"%s\" failed", expr);
     }
@@ -2153,26 +2157,18 @@ _PyObject_AssertFailed(PyObject *obj, const char *expr, const char *msg,
         fprintf(stderr, "Assertion failed");
     }
     fflush(stderr);
+
     if (msg) {
         fprintf(stderr, ": %s", msg);
     }
     fprintf(stderr, "\n");
     fflush(stderr);
 
-    if (obj == NULL) {
-        fprintf(stderr, "<object at NULL>\n");
-    }
-    else if (_PyObject_IsFreed(obj)) {
+    if (_PyObject_IsFreed(obj)) {
         /* It seems like the object memory has been freed:
            don't access it to prevent a segmentation fault. */
         fprintf(stderr, "<object at %p is freed>\n", obj);
-    }
-    else if (Py_TYPE(obj) == NULL) {
-        fprintf(stderr, "<object at %p: ob_type=NULL>\n", obj);
-    }
-    else if (_PyObject_IsFreed((PyObject *)Py_TYPE(obj))) {
-        fprintf(stderr, "<object at %p: type at %p is freed>\n",
-                obj, (void *)Py_TYPE(obj));
+        fflush(stderr);
     }
     else {
         /* Display the traceback where the object has been allocated.
@@ -2192,7 +2188,6 @@ _PyObject_AssertFailed(PyObject *obj, const char *expr, const char *msg,
            try to provide any extra info we can: */
         _PyObject_Dump(obj);
     }
-    fflush(stderr);
 
     Py_FatalError("_PyObject_AssertFailed");
 }
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 94a4da2..890246e 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -137,22 +137,24 @@ skip_signature(const char *doc)
 int
 _PyType_CheckConsistency(PyTypeObject *type)
 {
-#define ASSERT(expr) _PyObject_ASSERT((PyObject *)type, (expr))
+#define CHECK(expr) \
+    do { if (!(expr)) { _PyObject_ASSERT_FAILED_MSG((PyObject *)type, Py_STRINGIFY(expr)); } } while (0)
+
+    CHECK(!_PyObject_IsFreed((PyObject *)type));
 
     if (!(type->tp_flags & Py_TPFLAGS_READY)) {
-        /* don't check types before PyType_Ready() */
+        /* don't check static types before PyType_Ready() */
         return 1;
     }
 
-    ASSERT(!_PyObject_IsFreed((PyObject *)type));
-    ASSERT(Py_REFCNT(type) >= 1);
-    ASSERT(PyType_Check(type));
+    CHECK(Py_REFCNT(type) >= 1);
+    CHECK(PyType_Check(type));
 
-    ASSERT(!(type->tp_flags & Py_TPFLAGS_READYING));
-    ASSERT(type->tp_dict != NULL);
+    CHECK(!(type->tp_flags & Py_TPFLAGS_READYING));
+    CHECK(type->tp_dict != NULL);
 
     return 1;
-#undef ASSERT
+#undef CHECK
 }
 
 static const char *
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 0526225..8d442fb 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -487,65 +487,63 @@ PyUnicode_GetMax(void)
 int
 _PyUnicode_CheckConsistency(PyObject *op, int check_content)
 {
+#define CHECK(expr) \
+    do { if (!(expr)) { _PyObject_ASSERT_FAILED_MSG(op, Py_STRINGIFY(expr)); } } while (0)
+
     PyASCIIObject *ascii;
     unsigned int kind;
 
-    _PyObject_ASSERT(op, PyUnicode_Check(op));
+    assert(op != NULL);
+    CHECK(PyUnicode_Check(op));
 
     ascii = (PyASCIIObject *)op;
     kind = ascii->state.kind;
 
     if (ascii->state.ascii == 1 && ascii->state.compact == 1) {
-        _PyObject_ASSERT(op, kind == PyUnicode_1BYTE_KIND);
-        _PyObject_ASSERT(op, ascii->state.ready == 1);
+        CHECK(kind == PyUnicode_1BYTE_KIND);
+        CHECK(ascii->state.ready == 1);
     }
     else {
         PyCompactUnicodeObject *compact = (PyCompactUnicodeObject *)op;
-#ifndef NDEBUG
         void *data;
-#endif
 
         if (ascii->state.compact == 1) {
-#ifndef NDEBUG
             data = compact + 1;
-#endif
-            _PyObject_ASSERT(op, kind == PyUnicode_1BYTE_KIND
+            CHECK(kind == PyUnicode_1BYTE_KIND
                                  || kind == PyUnicode_2BYTE_KIND
                                  || kind == PyUnicode_4BYTE_KIND);
-            _PyObject_ASSERT(op, ascii->state.ascii == 0);
-            _PyObject_ASSERT(op, ascii->state.ready == 1);
-            _PyObject_ASSERT(op, compact->utf8 != data);
+            CHECK(ascii->state.ascii == 0);
+            CHECK(ascii->state.ready == 1);
+            CHECK(compact->utf8 != data);
         }
         else {
-#ifndef NDEBUG
             PyUnicodeObject *unicode = (PyUnicodeObject *)op;
 
             data = unicode->data.any;
-#endif
             if (kind == PyUnicode_WCHAR_KIND) {
-                _PyObject_ASSERT(op, ascii->length == 0);
-                _PyObject_ASSERT(op, ascii->hash == -1);
-                _PyObject_ASSERT(op, ascii->state.compact == 0);
-                _PyObject_ASSERT(op, ascii->state.ascii == 0);
-                _PyObject_ASSERT(op, ascii->state.ready == 0);
-                _PyObject_ASSERT(op, ascii->state.interned == SSTATE_NOT_INTERNED);
-                _PyObject_ASSERT(op, ascii->wstr != NULL);
-                _PyObject_ASSERT(op, data == NULL);
-                _PyObject_ASSERT(op, compact->utf8 == NULL);
+                CHECK(ascii->length == 0);
+                CHECK(ascii->hash == -1);
+                CHECK(ascii->state.compact == 0);
+                CHECK(ascii->state.ascii == 0);
+                CHECK(ascii->state.ready == 0);
+                CHECK(ascii->state.interned == SSTATE_NOT_INTERNED);
+                CHECK(ascii->wstr != NULL);
+                CHECK(data == NULL);
+                CHECK(compact->utf8 == NULL);
             }
             else {
-                _PyObject_ASSERT(op, kind == PyUnicode_1BYTE_KIND
+                CHECK(kind == PyUnicode_1BYTE_KIND
                                      || kind == PyUnicode_2BYTE_KIND
                                      || kind == PyUnicode_4BYTE_KIND);
-                _PyObject_ASSERT(op, ascii->state.compact == 0);
-                _PyObject_ASSERT(op, ascii->state.ready == 1);
-                _PyObject_ASSERT(op, data != NULL);
+                CHECK(ascii->state.compact == 0);
+                CHECK(ascii->state.ready == 1);
+                CHECK(data != NULL);
                 if (ascii->state.ascii) {
-                    _PyObject_ASSERT(op, compact->utf8 == data);
-                    _PyObject_ASSERT(op, compact->utf8_length == ascii->length);
+                    CHECK(compact->utf8 == data);
+                    CHECK(compact->utf8_length == ascii->length);
                 }
                 else
-                    _PyObject_ASSERT(op, compact->utf8 != data);
+                    CHECK(compact->utf8 != data);
             }
         }
         if (kind != PyUnicode_WCHAR_KIND) {
@@ -557,16 +555,16 @@ _PyUnicode_CheckConsistency(PyObject *op, int check_content)
 #endif
                )
             {
-                _PyObject_ASSERT(op, ascii->wstr == data);
-                _PyObject_ASSERT(op, compact->wstr_length == ascii->length);
+                CHECK(ascii->wstr == data);
+                CHECK(compact->wstr_length == ascii->length);
             } else
-                _PyObject_ASSERT(op, ascii->wstr != data);
+                CHECK(ascii->wstr != data);
         }
 
         if (compact->utf8 == NULL)
-            _PyObject_ASSERT(op, compact->utf8_length == 0);
+            CHECK(compact->utf8_length == 0);
         if (ascii->wstr == NULL)
-            _PyObject_ASSERT(op, compact->wstr_length == 0);
+            CHECK(compact->wstr_length == 0);
     }
 
     /* check that the best kind is used: O(n) operation */
@@ -585,23 +583,25 @@ _PyUnicode_CheckConsistency(PyObject *op, int check_content)
         }
         if (kind == PyUnicode_1BYTE_KIND) {
             if (ascii->state.ascii == 0) {
-                _PyObject_ASSERT(op, maxchar >= 128);
-                _PyObject_ASSERT(op, maxchar <= 255);
+                CHECK(maxchar >= 128);
+                CHECK(maxchar <= 255);
             }
             else
-                _PyObject_ASSERT(op, maxchar < 128);
+                CHECK(maxchar < 128);
         }
         else if (kind == PyUnicode_2BYTE_KIND) {
-            _PyObject_ASSERT(op, maxchar >= 0x100);
-            _PyObject_ASSERT(op, maxchar <= 0xFFFF);
+            CHECK(maxchar >= 0x100);
+            CHECK(maxchar <= 0xFFFF);
         }
         else {
-            _PyObject_ASSERT(op, maxchar >= 0x10000);
-            _PyObject_ASSERT(op, maxchar <= MAX_UNICODE);
+            CHECK(maxchar >= 0x10000);
+            CHECK(maxchar <= MAX_UNICODE);
         }
-        _PyObject_ASSERT(op, PyUnicode_READ(kind, data, ascii->length) == 0);
+        CHECK(PyUnicode_READ(kind, data, ascii->length) == 0);
     }
     return 1;
+
+#undef CHECK
 }