pythongh-91353: Fix void return type handling in ctypes (pythonGH-32246)

Author: hoodmane

Misc/NEWS.d/next/Core and Builtins/2022-04-03-17-21-04.bpo-47197.Ji_c30.rst

@@ -0,0 +1,5 @@
+ctypes used to mishandle ``void`` return types, so that for instance a
+function declared like ``ctypes.CFUNCTYPE(None, ctypes.c_int)`` would be
+called with signature ``int f(int)`` instead of ``void f(int)``. Wasm
+targets require function pointers to be called with the correct signatures
+so this led to crashes. The problem is now fixed.

Modules/_ctypes/callbacks.c

@@ -399,7 +399,7 @@ CThunkObject *_ctypes_alloc_callback(PyObject *callable,
 #endif
     result = ffi_prep_cif(&p->cif, cc,
                           Py_SAFE_DOWNCAST(nargs, Py_ssize_t, int),
-                          _ctypes_get_ffi_type(restype),
+                          p->ffi_restype,
                           &p->atypes[0]);
     if (result != FFI_OK) {
         PyErr_Format(PyExc_RuntimeError,

Modules/_ctypes/callproc.c

@@ -1209,7 +1209,12 @@ PyObject *_ctypes_callproc(PPROC pProc,
         }
     }
 
-    rtype = _ctypes_get_ffi_type(restype);
+    if (restype == Py_None) {
+        rtype = &ffi_type_void;
+    } else {
+        rtype = _ctypes_get_ffi_type(restype);
+    }
+
     resbuf = alloca(max(rtype->size, sizeof(ffi_arg)));
 
 #ifdef _Py_MEMORY_SANITIZER