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gh-148573: correct allocation of complex types in the ctypes #148579

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gh-148573: correct allocation of complex types in the ctypes #148579

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gh-148573: correct allocation of complex types in the ctypes
skirpichev Apr 14, 2026
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Update Modules/_ctypes/_ctypes.c
skirpichev Apr 15, 2026
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Merge branch 'master' into fix-148573
skirpichev Apr 15, 2026
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skirpichev Apr 15, 2026
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5 changes: 4 additions & 1 deletion Modules/_ctypes/_ctypes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2367,7 +2367,10 @@ PyCSimpleType_init(PyObject *self, PyObject *args, PyObject *kwds)
stginfo->ffi_type_pointer = *fmt->pffi_type;
}
else {
const size_t els_size = sizeof(fmt->pffi_type->elements);
/* From primitive types - only complex types have the elements
struct field as non-NULL (two element array). */
assert(fmt->pffi_type->type == FFI_TYPE_COMPLEX);
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@encukou encukou Apr 16, 2026

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Thanks! There's one more check we can do here.

Suggested change
/* From primitive types - only complex types have the elements
struct field as non-NULL (two element array). */
assert(fmt->pffi_type->type == FFI_TYPE_COMPLEX);
/* From primitive types - only complex types have the elements struct
field as non-NULL (two element array, including final NULL). */
assert(fmt->pffi_type->type == FFI_TYPE_COMPLEX);
assert(fmt->pffi_type->elements[1] == NULL);

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@sunmy2019 sunmy2019 Apr 16, 2026 •
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If that's needed, how about using the same check in libffi, i.e.

a->elements != NULL && a->elements[0] != NULL && a->elements[1] == NULL

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@skirpichev skirpichev Apr 16, 2026

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I don't think we need this. Actual FFI-invariants are irrelevant for us. The only assumption from our side is that the possible type here is FFI_TYPE_COMPLEX.

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@sunmy2019 sunmy2019 Apr 17, 2026

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I agree it is okay without additional checks, since the behavior here is well documented.
https://github.com/libffi/libffi/blob/10056e7e6a0d40d2a21af63484b99f08898dde9e/doc/libffi.texi#L694

const size_t els_size = 2 * sizeof(ffi_type *);
stginfo->ffi_type_pointer.size = fmt->pffi_type->size;
stginfo->ffi_type_pointer.alignment = fmt->pffi_type->alignment;
stginfo->ffi_type_pointer.type = fmt->pffi_type->type;
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