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[3.13] gh-132673: Fix crash with zero-alignment in a ctypes.Structure #132695

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Merged
merged 5 commits into from
Apr 19, 2025
Merged

[3.13] gh-132673: Fix crash with zero-alignment in a ctypes.Structure #132695

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c46aa6c
Fix zero-alignment with ctypes
ZeroIntensity Apr 18, 2025
e80b023
Add blurb.
ZeroIntensity Apr 18, 2025
18d8d93
Update 2025-04-18-12-45-18.gh-issue-132673.P7Z3F1.rst
ZeroIntensity Apr 19, 2025
e5e7b26
Update stgdict.c
ZeroIntensity Apr 19, 2025
9a06987
Merge branch '3.13' into ctypes-align-zero
ZeroIntensity Apr 19, 2025
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37 changes: 36 additions & 1 deletion Lib/test/test_ctypes/test_aligned_structures.py
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
from ctypes import (
c_char, c_uint32, c_uint16, c_ubyte, c_byte, alignment, sizeof,
BigEndianStructure, LittleEndianStructure,
BigEndianUnion, LittleEndianUnion,
BigEndianUnion, LittleEndianUnion, Structure
)
import struct
import unittest
Expand Down Expand Up @@ -281,6 +281,41 @@ class Main(sbase):
self.assertEqual(main.b.y, 3)
self.assertEqual(main.c, 4)

def test_negative_align(self):
for base in (Structure, LittleEndianStructure, BigEndianStructure):
with (
self.subTest(base=base),
self.assertRaisesRegex(
ValueError,
'_align_ must be a non-negative integer',
)
):
class MyStructure(base):
_align_ = -1
_fields_ = []

def test_zero_align_no_fields(self):
for base in (Structure, LittleEndianStructure, BigEndianStructure):
with self.subTest(base=base):
class MyStructure(base):
_align_ = 0
_fields_ = []

self.assertEqual(alignment(MyStructure), 1)
self.assertEqual(alignment(MyStructure()), 1)

def test_zero_align_with_fields(self):
for base in (Structure, LittleEndianStructure, BigEndianStructure):
with self.subTest(base=base):
class MyStructure(base):
_align_ = 0
_fields_ = [
("x", c_ubyte),
]

self.assertEqual(alignment(MyStructure), 1)
self.assertEqual(alignment(MyStructure()), 1)


if __name__ == '__main__':
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2025-04-18-12-45-18.gh-issue-132673.P7Z3F1.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a crash when using ``_align_ = 0`` and ``_fields_ = []`` in a
:class:`ctypes.Structure`.
3 changes: 2 additions & 1 deletion Modules/_ctypes/stgdict.c
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Original file line number Diff line number Diff line change
Expand Up @@ -383,7 +383,7 @@ PyCStructUnionType_update_stginfo(PyObject *type, PyObject *fields, int isStruct
size = 0;
align = 0;
union_size = 0;
total_align = forced_alignment;
total_align = forced_alignment == 0 ? 1 : forced_alignment;
stginfo->ffi_type_pointer.type = FFI_TYPE_STRUCT;
stginfo->ffi_type_pointer.elements = PyMem_New(ffi_type *, len + 1);
if (stginfo->ffi_type_pointer.elements == NULL) {
Expand Down Expand Up @@ -570,6 +570,7 @@ PyCStructUnionType_update_stginfo(PyObject *type, PyObject *fields, int isStruct
}

/* Adjust the size according to the alignment requirements */
assert(total_align != 0);
aligned_size = ((size + total_align - 1) / total_align) * total_align;

if (isStruct) {
Expand Down
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