Raise an error when importing modules compiled for an older Python

This is a downstream workaround "implementing"
python#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.

Author: encukou

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

@@ -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

Modules/_tkinter.c

@@ -3489,6 +3489,10 @@ static struct PyModuleDef _tkintermodule = {
 PyMODINIT_FUNC
 PyInit__tkinter(void)
 {
+    if (_PyHack_CheckInternalAPIVersion("_tkinter") < 0) {
+        return NULL;
+    }
+
     PyObject *m, *uexe, *cexe;
 
     tcl_lock = PyThread_allocate_lock();

Modules/_tracemalloc.c

@@ -215,6 +215,10 @@ static struct PyModuleDef module_def = {
 PyMODINIT_FUNC
 PyInit__tracemalloc(void)
 {
+    if (_PyHack_CheckInternalAPIVersion("_tracemalloc") < 0) {
+        return NULL;
+    }
+
     PyObject *mod = PyModule_Create(&module_def);
     if (mod == NULL) {
         return NULL;

Modules/readline.c

@@ -1604,6 +1604,10 @@ static struct PyModuleDef readlinemodule = {
 PyMODINIT_FUNC
 PyInit_readline(void)
 {
+    if (_PyHack_CheckInternalAPIVersion("readline") < 0) {
+        return NULL;
+    }
+
     const char *backend = "readline";
     PyObject *m;
     readlinestate *mod_state;

Objects/moduleobject.c

@@ -50,6 +50,7 @@ _PyModule_IsExtension(PyObject *obj)
 }
 
 
+#undef PyModuleDef_Init
 PyObject*
 PyModuleDef_Init(PyModuleDef* def)
 {