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Fix ctypes function pointer casts on Python 3.14 by youknowdot · Pull Request #8965 · RustPython/RustPython · GitHub
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Fix ctypes function pointer casts on Python 3.14 #8965

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Merged
youknowone merged 1 commit into from
Oct 5, 2026
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Fix ctypes function pointer casts on Python 3.14 #8965

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Preserve callable addresses in ctypes function pointer casts 
Read the stored executable address when casting a function pointer and accept function pointer types as cast destinations. The existing ownership dictionary retains the original callback through a cast roundtrip.

Extracted independently on the unchanged Python 3.14 target, without typed callback argument or broader py_object transport changes. One unique callback-address/ownership regression extends the existing ctypes snippet; canonical coverage was checked for duplicates.

Assisted-by: Codex:model-version-unavailable
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@youknowdot
youknowdot committed Oct 4, 2026
commit e8bd96dc6c32c259c53a43ddbf4ba2c13ff65c64
8 changes: 7 additions & 1 deletion crates/vm/src/stdlib/_ctypes/function.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -509,7 +509,10 @@ fn cast_check_pointertype(ctype: &PyObject, vm: &VirtualMachine) -> bool {
return true;
}

// PyCFuncPtrTypeObject_Check - TODO
// PyCFuncPtrTypeObject_Check
if ctype.class().fast_issubclass(PyCFuncPtrType::static_type()) {
return true;
}

// simple pointer types via StgInfo.proto (c_void_p, c_char_p, etc.)
if let Ok(type_attr) = ctype.get_attr("_type_", vm)
Expand Down Expand Up @@ -562,6 +565,9 @@ pub(super) fn cast_impl(
// Simple type (c_void_p, c_char_p, etc.) → value from buffer
let buffer = simple.0.buffer.read();
rustpython_host_env::ctypes::read_pointer_from_buffer(&buffer)
} else if let Some(funcptr) = obj.downcast_ref::<PyCFuncPtr>() {
// A function pointer stores the executable address in its buffer.
funcptr.get_func_ptr()
} else if let Some(cdata) = obj.downcast_ref::<PyCData>() {
// Array, Structure, Union → buffer address (b_ptr)
cdata.buffer.read().as_ptr() as usize
Expand Down
11 changes: 11 additions & 0 deletions extra_tests/snippets/stdlib_ctypes.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import ctypes
import gc
import itertools
import os as _os
import sys as _sys
Expand Down Expand Up @@ -458,4 +459,14 @@ def get_win_folder_via_ctypes(csidl_name: str) -> str:
else:
raise AssertionError("an unallocatable array was created")

# A function-pointer cast retains the callback and its executable address.
Unary = ctypes.CFUNCTYPE(ctypes.c_int, ctypes.c_int)
callback = Unary(lambda value: value + 1)
address = ctypes.cast(callback, ctypes.c_void_p)
roundtrip = ctypes.cast(address, Unary)
assert roundtrip._objects[id(callback)] is callback
del callback, address
gc.collect()
assert roundtrip(41) == 42

print("done")
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