Add optional _align_ attribute to ctypes.Structure

monkeyman192 · Nov 17, 2023 · e3ad227 · e3ad227
1 parent 0ee2d77
commit e3ad227
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Showing 5 changed files with 31 additions and 2 deletions.
diff --git a/Include/internal/pycore_global_objects_fini_generated.h b/Include/internal/pycore_global_objects_fini_generated.h
diff --git a/Include/internal/pycore_global_strings.h b/Include/internal/pycore_global_strings.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_)

diff --git a/Include/internal/pycore_runtime_init_generated.h b/Include/internal/pycore_runtime_init_generated.h
diff --git a/Include/internal/pycore_unicodeobject_generated.h b/Include/internal/pycore_unicodeobject_generated.h
diff --git a/Modules/_ctypes/stgdict.c b/Modules/_ctypes/stgdict.c
@@ -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) {