From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Petr Viktorin <encukou@gmail.com>
Date: Fri, 6 Feb 2026 10:51:02 +0100
Subject: 00477: Raise an error when importing stdlib modules compiled for a
 different Python version

This is a downstream workaround "implementing"
https://github.com/python/cpython/pull/137212 -
the mechanism for the check exists in Python 3.15+, where it needs to be
added to the standard library modules.
In Fedora, we need it also in previous Python versions, as we experience
segmentation fault when importing stdlib modules after update while
Python is running.

_tkinter, _tracemalloc and readline are not calling PyModuleDef_Init,
which is modified with this patch, hence they need a
direct call to the check function.

Co-Authored-By: Karolina Surma <ksurma@redhat.com>
---
 Include/moduleobject.h | 43 ++++++++++++++++++++++++++++++++++++++++++
 Makefile.pre.in        |  3 +++
 Modules/_tkinter.c     |  6 ++++++
 Modules/_tracemalloc.c |  6 ++++++
 Modules/readline.c     |  6 ++++++
 Objects/moduleobject.c |  1 +
 6 files changed, 65 insertions(+)

diff --git a/Include/moduleobject.h b/Include/moduleobject.h
index 2a17c891dd..64017c666c 100644
--- a/Include/moduleobject.h
+++ b/Include/moduleobject.h
@@ -116,6 +116,49 @@ struct PyModuleDef {
   freefunc m_free;
 };
 
+#if defined(_PyHack_check_version_on_modinit) && defined(Py_BUILD_CORE)
+/* The mechanism for the check has been implemented on Python 3.15+:
+ * https://github.com/python/cpython/pull/137212.
+ * In Fedora, we need this in older Pythons too:
+ * if somebody attempts to import a module compiled for a different Python version,
+ * instead of segmentation fault a meaningful error is raised.
+ */
+PyAPI_DATA(const unsigned long) Py_Version;
+
+static inline int
+_PyHack_CheckInternalAPIVersion(const char *mod_name)
+{
+    if (PY_VERSION_HEX != Py_Version) {
+        PyErr_Format(
+            PyExc_ImportError,
+            "internal Python C API version mismatch: "
+            "module %s compiled with %lu.%lu.%lu; "
+            "runtime version is %lu.%lu.%lu",
+            mod_name,
+            (const unsigned long)((PY_VERSION_HEX >> 24) & 0xFF),
+            (const unsigned long)((PY_VERSION_HEX >> 16) & 0xFF),
+            (const unsigned long)((PY_VERSION_HEX >> 8) & 0xFF),
+            (const unsigned long)((Py_Version >> 24) & 0xFF),
+            (const unsigned long)((Py_Version >> 16) & 0xFF),
+            (const unsigned long)((Py_Version >> 8) & 0xFF)
+        );
+        return -1;
+    }
+    return 0;
+}
+
+static inline PyObject *
+PyModuleDef_Init_with_check(PyModuleDef *def)
+{
+    if (_PyHack_CheckInternalAPIVersion(def->m_name) < 0) {
+        return NULL;
+    }
+    return PyModuleDef_Init(def);
+}
+
+#define PyModuleDef_Init PyModuleDef_Init_with_check
+#endif
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 38a355a23f..67c19c329e 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -3415,3 +3415,6 @@ MODULE__MULTIBYTECODEC_DEPS=$(srcdir)/Modules/cjkcodecs/multibytecodec.h
 # Local Variables:
 # mode: makefile
 # End:
+
+# Fedora-specific, downstream only
+PY_STDMODULE_CFLAGS += -D_PyHack_check_version_on_modinit=1
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index 2216de509e..a640496f7f 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -3489,6 +3489,12 @@ static struct PyModuleDef _tkintermodule = {
 PyMODINIT_FUNC
 PyInit__tkinter(void)
 {
+    #ifdef _PyHack_check_version_on_modinit
+        if (_PyHack_CheckInternalAPIVersion("_tkinter") < 0) {
+            return NULL;
+        }
+    #endif
+
     PyObject *m, *uexe, *cexe;
 
     tcl_lock = PyThread_allocate_lock();
diff --git a/Modules/_tracemalloc.c b/Modules/_tracemalloc.c
index be71fc9fc9..67922098b2 100644
--- a/Modules/_tracemalloc.c
+++ b/Modules/_tracemalloc.c
@@ -215,6 +215,12 @@ static struct PyModuleDef module_def = {
 PyMODINIT_FUNC
 PyInit__tracemalloc(void)
 {
+    #ifdef _PyHack_check_version_on_modinit
+        if (_PyHack_CheckInternalAPIVersion("_tracemalloc") < 0) {
+            return NULL;
+        }
+    #endif
+
     PyObject *mod = PyModule_Create(&module_def);
     if (mod == NULL) {
         return NULL;
diff --git a/Modules/readline.c b/Modules/readline.c
index 8475846eef..b3f5eb3a1f 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -1604,6 +1604,12 @@ static struct PyModuleDef readlinemodule = {
 PyMODINIT_FUNC
 PyInit_readline(void)
 {
+    #ifdef _PyHack_check_version_on_modinit
+        if (_PyHack_CheckInternalAPIVersion("readline") < 0) {
+            return NULL;
+        }
+    #endif
+
     const char *backend = "readline";
     PyObject *m;
     readlinestate *mod_state;
diff --git a/Objects/moduleobject.c b/Objects/moduleobject.c
index b68584b5dd..cbf95dc92a 100644
--- a/Objects/moduleobject.c
+++ b/Objects/moduleobject.c
@@ -50,6 +50,7 @@ _PyModule_IsExtension(PyObject *obj)
 }
 
 
+#undef PyModuleDef_Init
 PyObject*
 PyModuleDef_Init(PyModuleDef* def)
 {