gh-126937: ctypes: fix TypeError when a field's size is >65535 bytes

.pre-commit-config.yaml

@@ -29,12 +29,12 @@ repos:
       - id: black
         name: Run Black on Tools/build/check_warnings.py
         files: ^Tools/build/check_warnings.py
-        language_version: python3.12
+        language_version: python3
         args: [--line-length=79]
       - id: black
         name: Run Black on Tools/jit/
         files: ^Tools/jit/
-        language_version: python3.12
+        language_version: python3
 
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v5.0.0

Lib/test/test_ctypes/test_struct_fields.py

@@ -75,6 +75,13 @@ def __init_subclass__(cls, **kwargs):
                                     'ctypes state is not initialized'):
             class Subclass(BrokenStructure): ...
 
+    def test_gh126937(self):
+        class X(self.cls):
+            _fields_ = [('char', c_char),]
+        class Y(self.cls):
+            # (2^31 - 1) is the largest size that can fit into a signed 32 bit int
+            _fields_ = [('largeField', X * (2 ** 31 - 1))]
+
     # __set__ and __get__ should raise a TypeError in case their self
     # argument is not a ctype instance.
     def test___set__(self):

Misc/NEWS.d/next/Core_and_Builtins/2024-11-17-21-35-55.gh-issue-126937.qluVM0.rst

@@ -0,0 +1 @@
+Fixed TypeError when a Structure's field's size is >65535 bytes

Modules/_ctypes/cfield.c

@@ -110,8 +110,20 @@
         goto error;
     }
 
-    Py_ssize_t bit_size = NUM_BITS(size);
-    if (bit_size) {
+    if (bit_size_obj != Py_None) {
+
+        Py_ssize_t bit_size;
+
+        if (PyLong_Check(bit_size_obj)) {
+            bit_size = PyLong_AsSsize_t(bit_size_obj);
+        } else {
+            PyErr_Format(
+                PyExc_ValueError,
+                "bit size of field %R must be an integer size for bit fields",
+                self->name
+            );
+            goto error;
+        }
         assert(bit_size > 0);
         assert(bit_size <= info->size * 8);
         switch(info->ffi_type_pointer.type) {