bpo-40217: Ensure Py_VISIT(Py_TYPE(self)) is always called for PyType_FromSpec types (GH-19414)
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@ -1021,6 +1021,38 @@ type_call(PyTypeObject *type, PyObject *args, PyObject *kwds)
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return obj;
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}
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PyObject *
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PyType_FromSpec_Alloc(PyTypeObject *type, Py_ssize_t nitems)
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{
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PyObject *obj;
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const size_t size = _Py_SIZE_ROUND_UP(
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_PyObject_VAR_SIZE(type, nitems+1) + sizeof(traverseproc),
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SIZEOF_VOID_P);
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/* note that we need to add one, for the sentinel and space for the
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provided tp-traverse: See bpo-40217 for more details */
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if (PyType_IS_GC(type))
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obj = _PyObject_GC_Malloc(size);
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else
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obj = (PyObject *)PyObject_MALLOC(size);
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if (obj == NULL)
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return PyErr_NoMemory();
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obj = obj;
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memset(obj, '\0', size);
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if (type->tp_itemsize == 0)
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(void)PyObject_INIT(obj, type);
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else
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(void) PyObject_INIT_VAR((PyVarObject *)obj, type, nitems);
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if (PyType_IS_GC(type))
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_PyObject_GC_TRACK(obj);
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return obj;
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}
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PyObject *
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PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)
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{
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@ -2853,6 +2885,36 @@ static const short slotoffsets[] = {
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#include "typeslots.inc"
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};
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static int
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PyType_FromSpec_tp_traverse(PyObject *self, visitproc visit, void *arg)
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{
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PyTypeObject *parent = Py_TYPE(self);
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// Only a instance of a type that is directly created by
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// PyType_FromSpec (not subclasses) must visit its parent.
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if (parent->tp_traverse == PyType_FromSpec_tp_traverse) {
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Py_VISIT(parent);
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}
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// Search for the original type that was created using PyType_FromSpec
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PyTypeObject *base;
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base = parent;
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while (base->tp_traverse != PyType_FromSpec_tp_traverse) {
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base = base->tp_base;
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assert(base);
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}
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// Extract the user defined traverse function that we placed at the end
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// of the type and call it.
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size_t size = Py_SIZE(base);
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size_t _offset = _PyObject_VAR_SIZE(&PyType_Type, size+1);
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traverseproc fun = *(traverseproc*)((char*)base + _offset);
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if (fun == NULL) {
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return 0;
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}
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return fun(self, visit, arg);
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}
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PyObject *
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PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
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{
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@ -2886,7 +2948,7 @@ PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
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}
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}
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res = (PyHeapTypeObject*)PyType_GenericAlloc(&PyType_Type, nmembers);
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res = (PyHeapTypeObject*)PyType_FromSpec_Alloc(&PyType_Type, nmembers);
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if (res == NULL)
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return NULL;
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res_start = (char*)res;
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@ -2991,6 +3053,26 @@ PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
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memcpy(PyHeapType_GET_MEMBERS(res), slot->pfunc, len);
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type->tp_members = PyHeapType_GET_MEMBERS(res);
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}
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else if (slot->slot == Py_tp_traverse) {
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/* Types created by PyType_FromSpec own a strong reference to their
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* type, but this was added in Python 3.8. The tp_traverse function
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* needs to call Py_VISIT on the type but all existing traverse
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* functions cannot be updated (especially the ones from existing user
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* functions) so we need to provide a tp_traverse that manually calls
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* Py_VISIT(Py_TYPE(self)) and then call the provided tp_traverse. In
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* this way, user functions do not need to be updated, preserve
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* backwards compatibility.
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*
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* We store the user-provided traverse function at the end of the type
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* (we have allocated space for it) so we can call it from our
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* PyType_FromSpec_tp_traverse wrapper. */
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type->tp_traverse = PyType_FromSpec_tp_traverse;
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size_t _offset = _PyObject_VAR_SIZE(&PyType_Type, nmembers+1);
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traverseproc *user_traverse = (traverseproc*)((char*)type + _offset);
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*user_traverse = slot->pfunc;
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}
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else {
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/* Copy other slots directly */
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*(void**)(res_start + slotoffsets[slot->slot]) = slot->pfunc;
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