gh-156204: report recursion overflow as unraisable

Author: BHUVANSH855

Lib/test/test_exceptions.py

@@ -2827,8 +2827,10 @@ def test_given_exception_matches_deeply_nested_tuple(self):
         for _ in range(500_000):
             tup = (tup,)
 
-        with self.assertRaises(RecursionError):
-            _testcapi.err_givenexceptionmatches(TypeError(), tup)
+        with support.catch_unraisable_exception() as cm:
+            self.assertFalse(
+                _testcapi.err_givenexceptionmatches(ValueError(), tup))
+            self.assertIsInstance(cm.unraisable.exc_value, RecursionError)
 
 
 class PEP626Tests(unittest.TestCase):

Misc/NEWS.d/next/Core_and_Builtins/2026-08-21-18-49-12.gh-issue-156204.ZusA7e.rst

@@ -1,3 +1,3 @@
-Fix unhandled recursion error in :c:func:`PyErr_GivenExceptionMatches` when
-evaluating deeply nested exception tuples, preventing crashes caused by
-stack exhaustion.
+Fix a crash in :c:func:`PyErr_GivenExceptionMatches` when evaluating deeply
+nested exception tuples. The recursion is now bounded, and exceeding the
+limit is reported as an unraisable exception.

Modules/_testcapi/exceptions.c

@@ -70,9 +70,7 @@ _testcapi_err_givenexceptionmatches_impl(PyObject *module, PyObject *err,
 {
     assert(!PyErr_Occurred());
     int res = PyErr_GivenExceptionMatches(err, exc);
-    if (res == 0 && PyErr_Occurred()) {
-        return NULL;
-    }
+    assert(!PyErr_Occurred());
     return PyBool_FromLong(res);
 }
 

Python/errors.c

@@ -4,6 +4,7 @@
 #include "Python.h"
 #include "pycore_audit.h"         // _PySys_Audit()
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
+#include "pycore_ceval.h"         // _Py_ReachedRecursionLimitWithMargin()
 #include "pycore_fileutils.h"     // _PyFile_Flush
 #include "pycore_initconfig.h"    // _PyStatus_ERR()
 #include "pycore_pyerrors.h"      // _PyErr_Format()
@@ -337,7 +338,15 @@ PyErr_GivenExceptionMatches(PyObject *err, PyObject *exc)
         return 0;
     }
     if (PyTuple_Check(exc)) {
-        if (Py_EnterRecursiveCall(" in PyErr_GivenExceptionMatches")) {
+        PyThreadState *tstate = _PyThreadState_GET();
+        if (_Py_ReachedRecursionLimitWithMargin(tstate, 2)) {
+            PyObject *exc_value = _PyErr_GetRaisedException(tstate);
+            _PyErr_SetString(tstate, PyExc_RecursionError,
+                             "maximum recursion depth exceeded while "
+                             "checking exception tuple");
+            PyErr_FormatUnraisable("Exception ignored while "
+                                   "checking exception tuple");
+            _PyErr_SetRaisedException(tstate, exc_value);
             return 0;
         }
         int res = 0;
@@ -349,7 +358,6 @@ PyErr_GivenExceptionMatches(PyObject *err, PyObject *exc)
                 break;
             }
         }
-        Py_LeaveRecursiveCall();
         return res;
     }
     /* err might be an instance, so check its class. */