Add optional _align_ attribute to ctypes.Structure

Author: monkeyman192

Include/internal/pycore_global_objects_fini_generated.h

@@ -231,6 +231,7 @@ struct _Py_global_strings {
  STRUCT_FOR_ID(_abc_impl)
  STRUCT_FOR_ID(_abstract_)
  STRUCT_FOR_ID(_active)
+ STRUCT_FOR_ID(_align_)
  STRUCT_FOR_ID(_annotation)
  STRUCT_FOR_ID(_anonymous_)
  STRUCT_FOR_ID(_argtypes_)

Include/internal/pycore_global_strings.h

@@ -379,6 +379,7 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
  int bitofs;
  PyObject *tmp;
  int pack;
+ int forced_alignment = 1;
  Py_ssize_t ffi_ofs;
  int big_endian;
  int arrays_seen = 0;
@@ -419,6 +420,28 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
  pack = 0;
  }
 
+ if (PyObject_GetOptionalAttr(type, &_Py_ID(_align_), &tmp) < 0) {
+ return -1;
+ }
+ if (tmp) {
+ forced_alignment = PyLong_AsInt(tmp);
+ Py_DECREF(tmp);
+ if (forced_alignment < 0) {
+ if (!PyErr_Occurred() ||
+ PyErr_ExceptionMatches(PyExc_TypeError) ||
+ PyErr_ExceptionMatches(PyExc_OverflowError))
+ {
+ PyErr_SetString(PyExc_ValueError,
+ "_align_ must be a non-negative integer");
+ }
+ return -1;
+ }
+ }
+ else {
+ /* Setting `_align_ = 0` amounts to using the default alignment */
+ forced_alignment = 1;
+ }
+
  len = PySequence_Size(fields);
  if (len == -1) {
  if (PyErr_ExceptionMatches(PyExc_TypeError)) {
@@ -463,7 +486,7 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
  size = offset = basedict->size;
  align = basedict->align;
  union_size = 0;
- total_align = align ? align : 1;
+ total_align = align ? align : forced_alignment;
  stgdict->ffi_type_pointer.type = FFI_TYPE_STRUCT;
  stgdict->ffi_type_pointer.elements = PyMem_New(ffi_type *, basedict->length + len + 1);
  if (stgdict->ffi_type_pointer.elements == NULL) {
@@ -483,7 +506,7 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
  size = 0;
  align = 0;
  union_size = 0;
- total_align = 1;
+ total_align = forced_alignment;
  stgdict->ffi_type_pointer.type = FFI_TYPE_STRUCT;
  stgdict->ffi_type_pointer.elements = PyMem_New(ffi_type *, len + 1);
  if (stgdict->ffi_type_pointer.elements == NULL) {