Title: object.__basicsize__ is erroneously 0 on big-endian 64-bit machines (int vs Py_ssize_t)
Type: behavior Stage: patch review
Components: Versions: Python 2.7
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: Nosy List: benjamin.peterson, dmalcolm
Priority: normal Keywords: patch

Created on 2010-08-25 22:44 by dmalcolm, last changed 2010-08-25 23:13 by benjamin.peterson. This issue is now closed.

File name Uploaded Description Edit
fix-typeobject-T_INT-usage.patch dmalcolm, 2010-08-25 22:48 Patch against 2.7 branch
Messages (2)
msg114942 - (view) Author: Dave Malcolm (dmalcolm) (Python committer) Date: 2010-08-25 22:48
On 64-bit bigendian machines (ppc64 and s390x), I'm seeing:
>>> print object.__basicsize__

(Discovered via a segfault in Jinja2 tries to use ctypes to manipulate ob_refcnt of variables, and gets the wrong location, corrupting the objects instead; see )

struct _typeobject declares tp_basicsize and tp_itemsize as Py_ssize_t:
  Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */

but type_members defines them as T_INT:
 {"__basicsize__", T_INT, offsetof(PyTypeObject,tp_basicsize),READONLY},
 {"__itemsize__", T_INT, offsetof(PyTypeObject, tp_itemsize), READONLY},

Hence when accessing "object.__basicsize__", PyMember_GetOne reads it as a
T_INT, which gets it as 0 (incorrect).  Accessing it as Py_ssize_t reads it as
16 (correct)
(gdb) p *(Py_ssize_t*)addr
$9 = 16
(gdb) p *(int*)addr
$10 = 0

I'm attaching a patch which changes them to use T_PYSSIZE_T and adds a selftest.
msg114947 - (view) Author: Benjamin Peterson (benjamin.peterson) * (Python committer) Date: 2010-08-25 23:13
Date User Action Args
2010-08-25 23:13:27benjamin.petersonsetstatus: open -> closed

nosy: + benjamin.peterson
messages: + msg114947

resolution: fixed
2010-08-25 22:48:51dmalcolmsetfiles: + fix-typeobject-T_INT-usage.patch

title: object.__basicsize__ is erroneously0 -> object.__basicsize__ is erroneously 0 on big-endian 64-bit machines (int vs Py_ssize_t)
keywords: + patch
type: behavior
versions: + Python 2.7
messages: + msg114942
stage: patch review
2010-08-25 22:44:35dmalcolmcreate