[3.11] GH-91742: Fix pdb crash after jump (GH-94171) (#94176)

Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>

Author: miss-islington

Lib/test/test_pdb.py

@@ -1363,7 +1363,50 @@ def test_pdb_issue_43318():
     4
     """
 
+def test_pdb_issue_gh_91742():
+    """See GH-91742
 
+    >>> def test_function():
+    ...    __author__ = "pi"
+    ...    __version__ = "3.14"
+    ...
+    ...    def about():
+    ...        '''About'''
+    ...        print(f"Author: {__author__!r}",
+    ...            f"Version: {__version__!r}",
+    ...            sep=" ")
+    ...
+    ...    import pdb; pdb.Pdb(nosigint=True, readrc=False).set_trace()
+    ...    about()
+
+
+    >>> reset_Breakpoint()
+    >>> with PdbTestInput([  # doctest: +NORMALIZE_WHITESPACE
+    ...     'step',
+    ...     'next',
+    ...     'next',
+    ...     'jump 5',
+    ...     'continue'
+    ... ]):
+    ...     test_function()
+    > <doctest test.test_pdb.test_pdb_issue_gh_91742[0]>(12)test_function()
+    -> about()
+    (Pdb) step
+    --Call--
+    > <doctest test.test_pdb.test_pdb_issue_gh_91742[0]>(5)about()
+    -> def about():
+    (Pdb) next
+    > <doctest test.test_pdb.test_pdb_issue_gh_91742[0]>(7)about()
+    -> print(f"Author: {__author__!r}",
+    (Pdb) next
+    > <doctest test.test_pdb.test_pdb_issue_gh_91742[0]>(8)about()
+    -> f"Version: {__version__!r}",
+    (Pdb) jump 5
+    > <doctest test.test_pdb.test_pdb_issue_gh_91742[0]>(5)about()
+    -> def about():
+    (Pdb) continue
+    Author: 'pi' Version: '3.14'
+    """
 @support.requires_subprocess()
 class PdbTestCase(unittest.TestCase):
     def tearDown(self):

Misc/NEWS.d/next/Library/2022-06-23-13-12-05.gh-issue-91742.sNytVX.rst

@@ -0,0 +1 @@
+Fix :mod:`pdb` crash after jump caused by a null pointer dereference. Patch by Kumar Aditya.

Objects/frameobject.c

@@ -418,7 +418,7 @@ static void
 frame_stack_pop(PyFrameObject *f)
 {
     PyObject *v = _PyFrame_StackPop(f->f_frame);
-    Py_DECREF(v);
+    Py_XDECREF(v);
 }
 
 static PyFrameState