bpo-41073: PyType_GetSlot() can now accept static types. (pythonGH-21931

)

PyType_GetSlot() can now accept static types.

Co-Authored-By: Petr Viktorin <encukou@gmail.com>

Automerge-Triggered-By: GH:encukou

Doc/c-api/type.rst

@@ -105,10 +105,12 @@ Type Objects
 
    See :c:member:`PyType_Slot.slot` for possible values of the *slot* argument.
 
-   An exception is raised if *type* is not a heap type.
-
    .. versionadded:: 3.4
 
+   .. versionchanged:: 3.10
+      :c:func:`PyType_GetSlot` can now accept all types.
+      Previously, it was limited to heap types.
+
 .. c:function:: PyObject* PyType_GetModule(PyTypeObject *type)
 
    Return the module object associated with the given type when the type was

Doc/whatsnew/3.10.rst

@@ -436,6 +436,9 @@ New Features
   slot.
   (Contributed by Hai Shi in :issue:`41832`.)
 
+* The :c:func:`PyType_GetSlot` function can accept static types.
+  (Contributed by Hai Shi and Petr Viktorin in :issue:`41073`.)
+
 
 Porting to Python 3.10
 ----------------------

Misc/NEWS.d/next/C API/2020-07-08-21-01-49.bpo-41073.VqQZON.rst

@@ -0,0 +1 @@
+:c:func:`PyType_GetSlot()` can now accept static types.

Modules/_testcapimodule.c

@@ -1018,6 +1018,62 @@ test_buildvalue_N(PyObject *self, PyObject *Py_UNUSED(ignored))
 }
 
 
+static PyObject *
+test_get_statictype_slots(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    newfunc tp_new = PyType_GetSlot(&PyLong_Type, Py_tp_new);
+    if (PyLong_Type.tp_new != tp_new) {
+        PyErr_SetString(PyExc_AssertionError, "mismatch: tp_new of long");
+        return NULL;
+    }
+
+    reprfunc tp_repr = PyType_GetSlot(&PyLong_Type, Py_tp_repr);
+    if (PyLong_Type.tp_repr != tp_repr) {
+        PyErr_SetString(PyExc_AssertionError, "mismatch: tp_repr of long");
+        return NULL;
+    }
+
+    ternaryfunc tp_call = PyType_GetSlot(&PyLong_Type, Py_tp_call);
+    if (tp_call != NULL) {
+        PyErr_SetString(PyExc_AssertionError, "mismatch: tp_call of long");
+        return NULL;
+    }
+
+    binaryfunc nb_add = PyType_GetSlot(&PyLong_Type, Py_nb_add);
+    if (PyLong_Type.tp_as_number->nb_add != nb_add) {
+        PyErr_SetString(PyExc_AssertionError, "mismatch: nb_add of long");
+        return NULL;
+    }
+
+    lenfunc mp_length = PyType_GetSlot(&PyLong_Type, Py_mp_length);
+    if (mp_length != NULL) {
+        PyErr_SetString(PyExc_AssertionError, "mismatch: mp_length of long");
+        return NULL;
+    }
+
+    void *over_value = PyType_GetSlot(&PyLong_Type, Py_bf_releasebuffer + 1);
+    if (over_value != NULL) {
+        PyErr_SetString(PyExc_AssertionError, "mismatch: max+1 of long");
+        return NULL;
+    }
+
+    tp_new = PyType_GetSlot(&PyLong_Type, 0);
+    if (tp_new != NULL) {
+        PyErr_SetString(PyExc_AssertionError, "mismatch: slot 0 of long");
+        return NULL;
+    }
+    if (PyErr_ExceptionMatches(PyExc_SystemError)) {
+        // This is the right exception
+        PyErr_Clear();
+    }
+    else {
+        return NULL;
+    }
+
+    Py_RETURN_NONE;
+}
+
+
 static PyObject *
 get_args(PyObject *self, PyObject *args)
 {
@@ -5627,8 +5683,10 @@ static PyMethodDef TestMethods[] = {
     {"PyBuffer_SizeFromFormat",  test_PyBuffer_SizeFromFormat, METH_VARARGS},
     {"test_buildvalue_N",       test_buildvalue_N,               METH_NOARGS},
     {"test_buildvalue_issue38913", test_buildvalue_issue38913,   METH_NOARGS},
-    {"get_args", get_args, METH_VARARGS},
-    {"get_kwargs", (PyCFunction)(void(*)(void))get_kwargs, METH_VARARGS|METH_KEYWORDS},
+    {"get_args",                get_args,                        METH_VARARGS},
+    {"test_get_statictype_slots", test_get_statictype_slots,     METH_NOARGS},
+    {"get_kwargs", (PyCFunction)(void(*)(void))get_kwargs,
+      METH_VARARGS|METH_KEYWORDS},
     {"getargs_tuple",           getargs_tuple,                   METH_VARARGS},
     {"getargs_keywords", (PyCFunction)(void(*)(void))getargs_keywords,
       METH_VARARGS|METH_KEYWORDS},

Objects/typeobject.c

@@ -56,6 +56,11 @@ static struct method_cache_entry method_cache[1 << MCACHE_SIZE_EXP];
 static unsigned int next_version_tag = 0;
 #endif
 
+typedef struct PySlot_Offset {
+    short subslot_offset;
+    short slot_offset;
+} PySlot_Offset;
+
 #define MCACHE_STATS 0
 
 #if MCACHE_STATS
@@ -2870,8 +2875,18 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
     return NULL;
 }
 
-static const short slotoffsets[] = {
-    -1, /* invalid slot */
+/* An array of type slot offsets corresponding to Py_tp_* constants,
+  * for use in e.g. PyType_Spec and PyType_GetSlot.
+  * Each entry has two offsets: "slot_offset" and "subslot_offset".
+  * If is subslot_offset is -1, slot_offset is an offset within the
+  * PyTypeObject struct.
+  * Otherwise slot_offset is an offset to a pointer to a sub-slots struct
+  * (such as "tp_as_number"), and subslot_offset is the offset within
+  * that struct.
+  * The actual table is generated by a script.
+  */
+static const PySlot_Offset pyslot_offsets[] = {
+    {0, 0},
 #include "typeslots.inc"
 };
 
@@ -2892,6 +2907,7 @@ PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
     const PyType_Slot *slot;
     Py_ssize_t nmembers, weaklistoffset, dictoffset, vectorcalloffset;
     char *res_start;
+    short slot_offset, subslot_offset;
 
     nmembers = weaklistoffset = dictoffset = vectorcalloffset = 0;
     for (slot = spec->slots; slot->slot; slot++) {
@@ -3001,7 +3017,7 @@ PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
 
     for (slot = spec->slots; slot->slot; slot++) {
         if (slot->slot < 0
-            || (size_t)slot->slot >= Py_ARRAY_LENGTH(slotoffsets)) {
+            || (size_t)slot->slot >= Py_ARRAY_LENGTH(pyslot_offsets)) {
             PyErr_SetString(PyExc_RuntimeError, "invalid slot offset");
             goto fail;
         }
@@ -3034,7 +3050,15 @@ PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
         }
         else {
             /* Copy other slots directly */
-            *(void**)(res_start + slotoffsets[slot->slot]) = slot->pfunc;
+            PySlot_Offset slotoffsets = pyslot_offsets[slot->slot];
+            slot_offset = slotoffsets.slot_offset;
+            if (slotoffsets.subslot_offset == -1) {
+                *(void**)((char*)res_start + slot_offset) = slot->pfunc;
+            } else {
+                void *parent_slot = *(void**)((char*)res_start + slot_offset);
+                subslot_offset = slotoffsets.subslot_offset;
+                *(void**)((char*)parent_slot + subslot_offset) = slot->pfunc;
+            }
         }
     }
     if (type->tp_dealloc == NULL) {
@@ -3117,15 +3141,23 @@ PyType_FromSpec(PyType_Spec *spec)
 void *
 PyType_GetSlot(PyTypeObject *type, int slot)
 {
-    if (!_PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE) || slot < 0) {
+    void *parent_slot;
+    int slots_len = Py_ARRAY_LENGTH(pyslot_offsets);
+
+    if (slot <= 0 || slot >= slots_len) {
         PyErr_BadInternalCall();
         return NULL;
     }
-    if ((size_t)slot >= Py_ARRAY_LENGTH(slotoffsets)) {
-        /* Extension module requesting slot from a future version */
+
+    parent_slot = *(void**)((char*)type + pyslot_offsets[slot].slot_offset);
+    if (parent_slot == NULL) {
         return NULL;
     }
-    return  *(void**)(((char*)type) + slotoffsets[slot]);
+    /* Return slot directly if we have no sub slot. */
+    if (pyslot_offsets[slot].subslot_offset == -1) {
+        return parent_slot;
+    }
+    return *(void**)((char*)parent_slot + pyslot_offsets[slot].subslot_offset);
 }
 
 PyObject *