On memory error, dump the memory block traceback

Issue #26564: _PyObject_DebugDumpAddress() now dumps the traceback where a
memory block was allocated on memory block. Use the tracemalloc module to get
the traceback.

Doc/c-api/memory.rst

@@ -349,12 +349,19 @@ Customize Memory Allocators
      allocator functions of the :c:data:`PYMEM_DOMAIN_OBJ` domain (ex:
      :c:func:`PyObject_Malloc`) are called
 
+   On error, the debug hooks use the :mod:`tracemalloc` module to get the
+   traceback where a memory block was allocated. The traceback is only
+   displayed if :mod:`tracemalloc` is tracing Python memory allocations and the
+   memory block was traced.
+
    These hooks are installed by default if Python is compiled in debug
    mode. The :envvar:`PYTHONMALLOC` environment variable can be used to install
    debug hooks on a Python compiled in release mode.
 
    .. versionchanged:: 3.6
       This function now also works on Python compiled in release mode.
+      On error, the debug hooks now use :mod:`tracemalloc` to get the traceback
+      where a memory block was allocated.
 
 
 .. _pymalloc:

Doc/whatsnew/3.6.rst

@@ -129,7 +129,48 @@ the C library for all Python memory allocations using ``PYTHONMALLOC=malloc``.
 It helps to use external memory debuggers like Valgrind on a Python compiled in
 release mode.
 
-(Contributed by Victor Stinner in :issue:`26516`.)
+On error, the debug hooks on Python memory allocators now use the
+:mod:`tracemalloc` module to get the traceback where a memory block was
+allocated.
+
+Example of fatal error on buffer overflow using
+``python3.6 -X tracemalloc=5`` (store 5 frames in traces)::
+
+    Debug memory block at address p=0x7fbcd41666f8: API 'o'
+        4 bytes originally requested
+        The 7 pad bytes at p-7 are FORBIDDENBYTE, as expected.
+        The 8 pad bytes at tail=0x7fbcd41666fc are not all FORBIDDENBYTE (0xfb):
+            at tail+0: 0x02 *** OUCH
+            at tail+1: 0xfb
+            at tail+2: 0xfb
+            at tail+3: 0xfb
+            at tail+4: 0xfb
+            at tail+5: 0xfb
+            at tail+6: 0xfb
+            at tail+7: 0xfb
+        The block was made by call #1233329 to debug malloc/realloc.
+        Data at p: 1a 2b 30 00
+
+    Memory block allocated at (most recent call first):
+      File "test/test_bytes.py", line 323
+      File "unittest/case.py", line 600
+      File "unittest/case.py", line 648
+      File "unittest/suite.py", line 122
+      File "unittest/suite.py", line 84
+
+    Fatal Python error: bad trailing pad byte
+
+    Current thread 0x00007fbcdbd32700 (most recent call first):
+      File "test/test_bytes.py", line 323 in test_hex
+      File "unittest/case.py", line 600 in run
+      File "unittest/case.py", line 648 in __call__
+      File "unittest/suite.py", line 122 in run
+      File "unittest/suite.py", line 84 in __call__
+      File "unittest/suite.py", line 122 in run
+      File "unittest/suite.py", line 84 in __call__
+      ...
+
+(Contributed by Victor Stinner in :issue:`26516` and :issue:`26564`.)
 
 
 Other Language Changes

Misc/NEWS

@@ -10,6 +10,10 @@ Release date: tba
 Core and Builtins
 -----------------
 
+- Issue #26564: On error, the debug hooks on Python memory allocators now use
+  the :mod:`tracemalloc` module to get the traceback where a memory block was
+  allocated.
+
 - Issue #26558: The debug hooks on Python memory allocator
   :c:func:`PyObject_Malloc` now detect when functions are called without
   holding the GIL.

Modules/_tracemalloc.c

@@ -1161,6 +1161,25 @@ finally:
     return get_traces.list;
 }
 
+static traceback_t*
+tracemalloc_get_traceback(const void *ptr)
+{
+    trace_t trace;
+    int found;
+
+    if (!tracemalloc_config.tracing)
+        return NULL;
+
+    TABLES_LOCK();
+    found = _Py_HASHTABLE_GET(tracemalloc_traces, ptr, trace);
+    TABLES_UNLOCK();
+
+    if (!found)
+        return NULL;
+
+    return trace.traceback;
+}
+
 PyDoc_STRVAR(tracemalloc_get_object_traceback_doc,
     "_get_object_traceback(obj)\n"
     "\n"
@@ -1175,11 +1194,7 @@ py_tracemalloc_get_object_traceback(PyObject *self, PyObject *obj)
 {
     PyTypeObject *type;
     void *ptr;
-    trace_t trace;
+    traceback_t *traceback;
-    int found;
-
-    if (!tracemalloc_config.tracing)
-        Py_RETURN_NONE;
 
     type = Py_TYPE(obj);
     if (PyType_IS_GC(type))
@@ -1187,16 +1202,46 @@ py_tracemalloc_get_object_traceback(PyObject *self, PyObject *obj)
     else
         ptr = (void *)obj;
 
-    TABLES_LOCK();
+    traceback = tracemalloc_get_traceback(ptr);
-    found = _Py_HASHTABLE_GET(tracemalloc_traces, ptr, trace);
+    if (traceback == NULL)
-    TABLES_UNLOCK();
-
-    if (!found)
         Py_RETURN_NONE;
 
-    return traceback_to_pyobject(trace.traceback, NULL);
+    return traceback_to_pyobject(traceback, NULL);
 }
 
+#define PUTS(fd, str) _Py_write_noraise(fd, str, (int)strlen(str))
+
+static void
+_PyMem_DumpFrame(int fd, frame_t * frame)
+{
+    PUTS(fd, "  File \"");
+    _Py_DumpASCII(fd, frame->filename);
+    PUTS(fd, "\", line ");
+    _Py_DumpDecimal(fd, frame->lineno);
+    PUTS(fd, "\n");
+}
+
+/* Dump the traceback where a memory block was allocated into file descriptor
+   fd. The function may block on TABLES_LOCK() but it is unlikely. */
+void
+_PyMem_DumpTraceback(int fd, const void *ptr)
+{
+    traceback_t *traceback;
+    int i;
+
+    traceback = tracemalloc_get_traceback(ptr);
+    if (traceback == NULL)
+        return;
+
+    PUTS(fd, "Memory block allocated at (most recent call first):\n");
+    for (i=0; i < traceback->nframe; i++) {
+        _PyMem_DumpFrame(fd, &traceback->frames[i]);
+    }
+    PUTS(fd, "\n");
+}
+
+#undef PUTS
+
 PyDoc_STRVAR(tracemalloc_start_doc,
     "start(nframe: int=1)\n"
     "\n"

Objects/bytearrayobject.c

@@ -2820,6 +2820,7 @@ bytearray_hex(PyBytesObject *self)
 {
     char* argbuf = PyByteArray_AS_STRING(self);
     Py_ssize_t arglen = PyByteArray_GET_SIZE(self);
+    PyByteArray_AS_STRING(self)[arglen+1] = 2;
     return _Py_strhex(argbuf, arglen);
 }
 

Objects/obmalloc.c

@@ -1,5 +1,10 @@
 #include "Python.h"
 
+
+/* Defined in tracemalloc.c */
+extern void _PyMem_DumpTraceback(int fd, const void *ptr);
+
+
 /* Python's malloc wrappers (see pymem.h) */
 
 /*
@@ -2202,6 +2207,10 @@ _PyObject_DebugDumpAddress(const void *p)
         }
         fputc('\n', stderr);
     }
+    fputc('\n', stderr);
+
+    fflush(stderr);
+    _PyMem_DumpTraceback(fileno(stderr), p);
 }
 
 

Parser/pgenmain.c

@@ -38,11 +38,11 @@ Py_Exit(int sts)
 }
 
 #ifdef WITH_THREAD
-/* Needed by obmalloc.c */
+/* Functions needed by obmalloc.c */
 int PyGILState_Check(void)
-{
+{ return 1; }
-    return 1;
+void _PyMem_DumpTraceback(int fd, const void *ptr)
-}
+{}
 #endif
 
 int