New submission from Dave Malcolm <dmalc...@redhat.com>:
With a clean build of release27-maint (r84317), test_dbm.py fails on ppc64 with
this error:
File "test_dbm.py", line 24, in test_keys
self.assert_(k in self.d)
AssertionError
I'm building gainst gdbm-1.8.0 (specifically, on a prerelease of RHEL6, with
gdbm-devel-1.8.0-36.el6.ppc64)
All of the headers define datum as:
typedef struct {
char *dptr;
int dsize;
} datum;
Note the use of "int" for dsize.
This fragment of code in python's Modules/dbmmodule.c:dbm_contains:
if (PyString_AsStringAndSize(v, (char **)&key.dptr,
(Py_ssize_t *)&key.dsize)) {
return -1;
}
appears to assume that
sizeof(datum.dsize) == sizeof(Py_ssize_t)
which is not correct on these architectures:
(gdb) p sizeof(key.dsize)
$25 = 4
(gdb) p sizeof(Py_ssize_t)
$26 = 8
On ppc64, when PyString_AsStringAndSize writes the 0x00000000000000001 value
for the ob_size of "a" to &key.dsize, I believe the 0x00000000 part is written
to &key.size, and the 0x00000001 part is written to the 4 bytes following it,
due to the incorrect cast from (int*) to (Py_ssize_t*)
Thankfully
(gdb) p sizeof(key)
$28 = 16
so it writes this value to padding within the "datum key", rather than
corrupting the stack.
The dbm_fetch() invocation is thus passed a 0 dsize, and doesn't find the key,
hence the test fails.
The various other uses with that source file appear correct:
(i) there are various PyArg_Parse* calls using s#, with int, which is correct,
given the absence of the PY_SSIZE_T_CLEAN macro.
(ii) there are various calls of PyString_FromStringAndSize(, datum.dsize),
which I believe is correct: I believe the compiler will coerce this int to the
wider Py_ssize_t type.
I'm attaching a patch which (I hope) correctly coerces the size of the key from
Py_ssize_t to "int" within gdb_contains.
----------
components: Extension Modules
files: fix-dbm_contains-on-64bit-bigendian.patch
keywords: patch, patch
messages: 114934
nosy: dmalcolm
priority: normal
severity: normal
stage: patch review
status: open
title: dbmmodule.c:dbm_contains fails on 64bit big-endian (test_dbm.py fails)
when built against gdbm (int vs Py_ssize_t)
type: behavior
versions: Python 2.7, Python 3.1, Python 3.2
Added file:
http://bugs.python.org/file18644/fix-dbm_contains-on-64bit-bigendian.patch
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<http://bugs.python.org/issue9687>
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