[3.12] gh-111178: fix UBSan failures in Modules/_multiprocessing/semaphore.c (GH-129084) (#129101)

gh-111178: fix UBSan failures in `Modules/_multiprocessing/semaphore.c` (GH-129084)

fix UBSan failures for `SemLockObject`
(cherry picked from commit 5ed5572)

Co-authored-by: Bénédikt Tran <[email protected]>

Author: miss-islington

Modules/_multiprocessing/semaphore.c

@@ -23,6 +23,8 @@ typedef struct {
     char *name;
 } SemLockObject;
 
+#define _SemLockObject_CAST(op) ((SemLockObject *)(op))
+
 /*[python input]
 class SEM_HANDLE_converter(CConverter):
     type = "SEM_HANDLE"
@@ -567,8 +569,9 @@ _multiprocessing_SemLock__rebuild_impl(PyTypeObject *type, SEM_HANDLE handle,
 }
 
 static void
-semlock_dealloc(SemLockObject* self)
+semlock_dealloc(PyObject *op)
 {
+    SemLockObject *self = _SemLockObject_CAST(op);
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
     if (self->handle != SEM_FAILED)
@@ -706,7 +709,7 @@ _multiprocessing_SemLock___exit___impl(SemLockObject *self,
 }
 
 static int
-semlock_traverse(SemLockObject *s, visitproc visit, void *arg)
+semlock_traverse(PyObject *s, visitproc visit, void *arg)
 {
     Py_VISIT(Py_TYPE(s));
     return 0;