gh-129502: Fix handling errors in ctypes callbacks

Unlikely errors in preparing arguments for ctypes callback are now
handled in the same way as errors raised in the callback of in converting
the result of the callback -- using sys.unraisablehook() instead of
sys.excepthook() and not setting sys.last_exc and other variables.

Author: serhiy-storchaka

Misc/NEWS.d/next/Library/2025-01-31-11-14-05.gh-issue-129502.j_ArNo.rst

@@ -0,0 +1,5 @@
+Unlikely errors in preparing arguments for :mod:`ctypes` callback are now
+handled in the same way as errors raised in the callback of in converting
+the result of the callback -- using :func:`sys.unraisablehook` instead of
+:func:`sys.excepthook` and not setting :data:`sys.last_exc` and other
+variables.

Modules/_ctypes/callbacks.c

@@ -81,22 +81,6 @@ PyType_Spec cthunk_spec = {
 
 /**************************************************************/
 
-static void
-PrintError(const char *msg, ...)
-{
-    char buf[512];
-    PyObject *f = PySys_GetObject("stderr");
-    va_list marker;
-
-    va_start(marker, msg);
-    PyOS_vsnprintf(buf, sizeof(buf), msg, marker);
-    va_end(marker);
-    if (f != NULL && f != Py_None)
-        PyFile_WriteString(buf, f);
-    PyErr_Print();
-}
-
-
 #ifdef MS_WIN32
 /*
  * We must call AddRef() on non-NULL COM pointers we receive as arguments
@@ -108,26 +92,23 @@ PrintError(const char *msg, ...)
  * after checking for PyObject_IsTrue(), but this would probably be somewhat
  * slower.
  */
-static void
+static int
 TryAddRef(PyObject *cnv, CDataObject *obj)
 {
     IUnknown *punk;
     PyObject *attrdict = _PyType_GetDict((PyTypeObject *)cnv);
     if (!attrdict) {
-        return;
+        return 0;
     }
     int r = PyDict_Contains(attrdict, &_Py_ID(_needs_com_addref_));
     if (r <= 0) {
-        if (r < 0) {
-            PrintError("getting _needs_com_addref_");
-        }
-        return;
+        return r;
     }
 
     punk = *(IUnknown **)obj->b_ptr;
     if (punk)
         punk->lpVtbl->AddRef(punk);
-    return;
+    return 0;
 }
 #endif
 
@@ -162,14 +143,13 @@ static void _CallPythonObject(ctypes_state *st,
 
         StgInfo *info;
         if (PyStgInfo_FromType(st, cnv, &info) < 0) {
-            goto Done;
+            goto Error;
         }
 
         if (info && info->getfunc && !_ctypes_simple_instance(st, cnv)) {
             PyObject *v = info->getfunc(*pArgs, info->size);
             if (!v) {
-                PrintError("create argument %zd:\n", i);
-                goto Done;
+                goto Error;
             }
             args[i] = v;
             /* XXX XXX XX
@@ -182,33 +162,39 @@ static void _CallPythonObject(ctypes_state *st,
             /* Hm, shouldn't we use PyCData_AtAddress() or something like that instead? */
             CDataObject *obj = (CDataObject *)_PyObject_CallNoArgs(cnv);
             if (!obj) {
-                PrintError("create argument %zd:\n", i);
-                goto Done;
+                goto Error;
             }
             if (!CDataObject_Check(st, obj)) {
+                PyErr_Format(PyExc_TypeError,
+                             "%R returned unexpected result of type %T", cnv, obj);
                 Py_DECREF(obj);
-                PrintError("unexpected result of create argument %zd:\n", i);
-                goto Done;
+                goto Error;
             }
             memcpy(obj->b_ptr, *pArgs, info->size);
             args[i] = (PyObject *)obj;
 #ifdef MS_WIN32
-            TryAddRef(cnv, obj);
+            if (TryAddRef(cnv, obj) < 0) {
+                goto Error;
+            }
 #endif
         } else {
-            PyErr_SetString(PyExc_TypeError,
-                            "cannot build parameter");
-            PrintError("Parsing argument %zd\n", i);
-            goto Done;
+            PyErr_Format(PyExc_TypeError,
+                         "cannot build parameter of type %R", cnv);
+            goto Error;
         }
         /* XXX error handling! */
         pArgs++;
     }
 
     if (flags & (FUNCFLAG_USE_ERRNO | FUNCFLAG_USE_LASTERROR)) {
         error_object = _ctypes_get_errobj(st, &space);
-        if (error_object == NULL)
+        if (error_object == NULL) {
+            PyErr_FormatUnraisable(
+                    "Exception ignored on setting error for "
+                    "ctypes callback function %R",
+                    callable);
             goto Done;
+        }
         if (flags & FUNCFLAG_USE_ERRNO) {
             int temp = space[0];
             space[0] = errno;
@@ -295,6 +281,14 @@ static void _CallPythonObject(ctypes_state *st,
     for (j = 0; j < i; j++) {
         Py_DECREF(args[j]);
     }
+    return;
+
+  Error:
+    PyErr_FormatUnraisable(
+            "Exception ignored on creating argument %zd for "
+            "ctypes callback function %R",
+            i, callable);
+    goto Done;
 }
 
 static void closure_fcn(ffi_cif *cif,