Raise an error when importing modules compiled for an older Python

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

Makefile.pre.in

@@ -3153,3 +3153,6 @@ 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

Modules/_cursesmodule.c

@@ -4763,6 +4763,12 @@ curses_destructor(PyObject *op)
 PyMODINIT_FUNC
 PyInit__curses(void)
 {
+    #ifdef _PyHack_check_version_on_modinit
+        if (_PyHack_CheckInternalAPIVersion("_curses") < 0) {
+            return NULL;
+        }
+    #endif
+
     PyObject *m, *d, *v, *c_api_object;
 
     /* Initialize object type */

Modules/_tkinter.c

@@ -3431,6 +3431,12 @@ 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();

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 *m;
     m = PyModule_Create(&module_def);
     if (m == NULL)

Modules/readline.c

@@ -1540,6 +1540,12 @@ 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;

Objects/moduleobject.c

@@ -43,6 +43,7 @@ _PyModule_IsExtension(PyObject *obj)
 }
 
 
+#undef PyModuleDef_Init
 PyObject*
 PyModuleDef_Init(PyModuleDef* def)
 {