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gh-111178: fix UBSan for example code in extending/newtypes_tutorial docs (GH-131606)

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Co-authored-by: Petr Viktorin <encukou@gmail.com>
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Bénédikt Tran 2025-03-24 17:15:32 +01:00 • committed by GitHub
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5 changed files with 120 additions and 70 deletions
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82
Doc/extending/newtypes_tutorial.rst
View file

@ -250,16 +250,17 @@ Because we now have data to manage, we have to be more careful about object
allocation and deallocation. At a minimum, we need a deallocation method::
static void
Custom_dealloc(CustomObject *self)
Custom_dealloc(PyObject *op)
{
CustomObject *self = (CustomObject *) op;
Py_XDECREF(self->first);
Py_XDECREF(self->last);
Py_TYPE(self)->tp_free((PyObject *) self);
Py_TYPE(self)->tp_free(self);
}
which is assigned to the :c:member:`~PyTypeObject.tp_dealloc` member::
.tp_dealloc = (destructor) Custom_dealloc,
.tp_dealloc = Custom_dealloc,
This method first clears the reference counts of the two Python attributes.
:c:func:`Py_XDECREF` correctly handles the case where its argument is
@ -270,11 +271,31 @@ the object's type might not be :class:`!CustomType`, because the object may
be an instance of a subclass.
.. note::
The explicit cast to ``destructor`` above is needed because we defined
``Custom_dealloc`` to take a ``CustomObject *`` argument, but the ``tp_dealloc``
function pointer expects to receive a ``PyObject *`` argument. Otherwise,
the compiler will emit a warning. This is object-oriented polymorphism,
in C!
The explicit cast to ``CustomObject *`` above is needed because we defined
``Custom_dealloc`` to take a ``PyObject *`` argument, as the ``tp_dealloc``
function pointer expects to receive a ``PyObject *`` argument.
By assigning to the the ``tp_dealloc`` slot of a type, we declare
that it can only be called with instances of our ``CustomObject``
class, so the cast to ``(CustomObject *)`` is safe.
This is object-oriented polymorphism, in C!
In existing code, or in previous versions of this tutorial,
you might see similar functions take a pointer to the subtype
object structure (``CustomObject*``) directly, like this::
Custom_dealloc(CustomObject *self)
{
Py_XDECREF(self->first);
Py_XDECREF(self->last);
Py_TYPE(self)->tp_free((PyObject *) self);
}
...
.tp_dealloc = (destructor) Custom_dealloc,
This does the same thing on all architectures that CPython
supports, but according to the C standard, it invokes
undefined behavior.
We want to make sure that the first and last names are initialized to empty
strings, so we provide a ``tp_new`` implementation::
@ -352,8 +373,9 @@ We also define an initialization function which accepts arguments to provide
initial values for our instance::
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
{
CustomObject *self = (CustomObject *) op;
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
@ -379,7 +401,7 @@ initial values for our instance::
by filling the :c:member:`~PyTypeObject.tp_init` slot. ::
.tp_init = (initproc) Custom_init,
.tp_init = Custom_init,
The :c:member:`~PyTypeObject.tp_init` slot is exposed in Python as the
:meth:`~object.__init__` method. It is used to initialize an object after it's
@ -451,8 +473,9 @@ We define a single method, :meth:`!Custom.name`, that outputs the objects name a
concatenation of the first and last names. ::
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))
{
CustomObject *self = (CustomObject *) op;
if (self->first == NULL) {
PyErr_SetString(PyExc_AttributeError, "first");
return NULL;
@ -486,7 +509,7 @@ Now that we've defined the method, we need to create an array of method
definitions::
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
{"name", Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
@ -543,15 +566,17 @@ we'll use custom getter and setter functions. Here are the functions for
getting and setting the :attr:`!first` attribute::
static PyObject *
Custom_getfirst(CustomObject *self, void *closure)
Custom_getfirst(PyObject *op, void *closure)
{
CustomObject *self = (CustomObject *) op;
Py_INCREF(self->first);
return self->first;
}
static int
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
Custom_setfirst(PyObject *op, PyObject *value, void *closure)
{
CustomObject *self = (CustomObject *) op;
PyObject *tmp;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
@ -583,9 +608,9 @@ new value is not a string.
We create an array of :c:type:`PyGetSetDef` structures::
static PyGetSetDef Custom_getsetters[] = {
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
{"first", Custom_getfirst, Custom_setfirst,
"first name", NULL},
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
{"last", Custom_getlast, Custom_setlast,
"last name", NULL},
{NULL} /* Sentinel */
};
@ -609,8 +634,9 @@ We also need to update the :c:member:`~PyTypeObject.tp_init` handler to only
allow strings [#]_ to be passed::
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
{
CustomObject *self = (CustomObject *) op;
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
@ -689,8 +715,9 @@ First, the traversal method lets the cyclic GC know about subobjects that could
participate in cycles::
static int
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
Custom_traverse(PyObject *op, visitproc visit, void *arg)
{
CustomObject *self = (CustomObject *) op;
int vret;
if (self->first) {
vret = visit(self->first, arg);
@ -716,8 +743,9 @@ functions. With :c:func:`Py_VISIT`, we can minimize the amount of boilerplate
in ``Custom_traverse``::
static int
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
Custom_traverse(PyObject *op, visitproc visit, void *arg)
{
CustomObject *self = (CustomObject *) op;
Py_VISIT(self->first);
Py_VISIT(self->last);
return 0;
@ -731,8 +759,9 @@ Second, we need to provide a method for clearing any subobjects that can
participate in cycles::
static int
Custom_clear(CustomObject *self)
Custom_clear(PyObject *op)
{
CustomObject *self = (CustomObject *) op;
Py_CLEAR(self->first);
Py_CLEAR(self->last);
return 0;
@ -765,11 +794,11 @@ Here is our reimplemented deallocator using :c:func:`PyObject_GC_UnTrack`
and ``Custom_clear``::
static void
Custom_dealloc(CustomObject *self)
Custom_dealloc(PyObject *op)
{
PyObject_GC_UnTrack(self);
Custom_clear(self);
Py_TYPE(self)->tp_free((PyObject *) self);
PyObject_GC_UnTrack(op);
(void)Custom_clear(op);
Py_TYPE(op)->tp_free(op);
}
Finally, we add the :c:macro:`Py_TPFLAGS_HAVE_GC` flag to the class flags::
@ -825,9 +854,10 @@ When a Python object is a :class:`!SubList` instance, its ``PyObject *`` pointer
can be safely cast to both ``PyListObject *`` and ``SubListObject *``::
static int
SubList_init(SubListObject *self, PyObject *args, PyObject *kwds)
SubList_init(PyObject *op, PyObject *args, PyObject *kwds)
{
if (PyList_Type.tp_init((PyObject *) self, args, kwds) < 0)
SubListObject *self = (SubListObject *) op;
if (PyList_Type.tp_init(op, args, kwds) < 0)
return -1;
self->state = 0;
return 0;

17
Doc/includes/newtypes/custom2.c
View file

@ -10,11 +10,12 @@ typedef struct {
} CustomObject;
static void
Custom_dealloc(CustomObject *self)
Custom_dealloc(PyObject *op)
{
CustomObject *self = (CustomObject *) op;
Py_XDECREF(self->first);
Py_XDECREF(self->last);
Py_TYPE(self)->tp_free((PyObject *) self);
Py_TYPE(self)->tp_free(self);
}
static PyObject *
@ -39,8 +40,9 @@ Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
}
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
{
CustomObject *self = (CustomObject *) op;
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL;
@ -69,8 +71,9 @@ static PyMemberDef Custom_members[] = {
};
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))
{
CustomObject *self = (CustomObject *) op;
if (self->first == NULL) {
PyErr_SetString(PyExc_AttributeError, "first");
return NULL;
@ -83,7 +86,7 @@ Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
}
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
{"name", Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
@ -97,8 +100,8 @@ static PyTypeObject CustomType = {
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.tp_new = Custom_new,
.tp_init = (initproc) Custom_init,
.tp_dealloc = (destructor) Custom_dealloc,
.tp_init = Custom_init,
.tp_dealloc = Custom_dealloc,
.tp_members = Custom_members,
.tp_methods = Custom_methods,
};

33
Doc/includes/newtypes/custom3.c
View file

@ -10,11 +10,12 @@ typedef struct {
} CustomObject;
static void
Custom_dealloc(CustomObject *self)
Custom_dealloc(PyObject *op)
{
CustomObject *self = (CustomObject *) op;
Py_XDECREF(self->first);
Py_XDECREF(self->last);
Py_TYPE(self)->tp_free((PyObject *) self);
Py_TYPE(self)->tp_free(self);
}
static PyObject *
@ -39,8 +40,9 @@ Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
}
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
{
CustomObject *self = (CustomObject *) op;
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL;
@ -65,14 +67,16 @@ static PyMemberDef Custom_members[] = {
};
static PyObject *
Custom_getfirst(CustomObject *self, void *closure)
Custom_getfirst(PyObject *op, void *closure)
{
CustomObject *self = (CustomObject *) op;
return Py_NewRef(self->first);
}
static int
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
Custom_setfirst(PyObject *op, PyObject *value, void *closure)
{
CustomObject *self = (CustomObject *) op;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
@ -87,14 +91,16 @@ Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
}
static PyObject *
Custom_getlast(CustomObject *self, void *closure)
Custom_getlast(PyObject *op, void *closure)
{
CustomObject *self = (CustomObject *) op;
return Py_NewRef(self->last);
}
static int
Custom_setlast(CustomObject *self, PyObject *value, void *closure)
Custom_setlast(PyObject *op, PyObject *value, void *closure)
{
CustomObject *self = (CustomObject *) op;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
return -1;
@ -109,21 +115,22 @@ Custom_setlast(CustomObject *self, PyObject *value, void *closure)
}
static PyGetSetDef Custom_getsetters[] = {
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
{"first", Custom_getfirst, Custom_setfirst,
"first name", NULL},
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
{"last", Custom_getlast, Custom_setlast,
"last name", NULL},
{NULL} /* Sentinel */
};
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))
{
CustomObject *self = (CustomObject *) op;
return PyUnicode_FromFormat("%S %S", self->first, self->last);
}
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
{"name", Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
@ -137,8 +144,8 @@ static PyTypeObject CustomType = {
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.tp_new = Custom_new,
.tp_init = (initproc) Custom_init,
.tp_dealloc = (destructor) Custom_dealloc,
.tp_init = Custom_init,
.tp_dealloc = Custom_dealloc,
.tp_members = Custom_members,
.tp_methods = Custom_methods,
.tp_getset = Custom_getsetters,

46
Doc/includes/newtypes/custom4.c
View file

@ -10,27 +10,29 @@ typedef struct {
} CustomObject;
static int
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
Custom_traverse(PyObject *op, visitproc visit, void *arg)
{
CustomObject *self = (CustomObject *) op;
Py_VISIT(self->first);
Py_VISIT(self->last);
return 0;
}
static int
Custom_clear(CustomObject *self)
Custom_clear(PyObject *op)
{
CustomObject *self = (CustomObject *) op;
Py_CLEAR(self->first);
Py_CLEAR(self->last);
return 0;
}
static void
Custom_dealloc(CustomObject *self)
Custom_dealloc(PyObject *op)
{
PyObject_GC_UnTrack(self);
Custom_clear(self);
Py_TYPE(self)->tp_free((PyObject *) self);
PyObject_GC_UnTrack(op);
(void)Custom_clear(op);
Py_TYPE(op)->tp_free(op);
}
static PyObject *
@ -55,8 +57,9 @@ Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
}
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
{
CustomObject *self = (CustomObject *) op;
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL;
@ -81,14 +84,16 @@ static PyMemberDef Custom_members[] = {
};
static PyObject *
Custom_getfirst(CustomObject *self, void *closure)
Custom_getfirst(PyObject *op, void *closure)
{
CustomObject *self = (CustomObject *) op;
return Py_NewRef(self->first);
}
static int
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
Custom_setfirst(PyObject *op, PyObject *value, void *closure)
{
CustomObject *self = (CustomObject *) op;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
@ -103,14 +108,16 @@ Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
}
static PyObject *
Custom_getlast(CustomObject *self, void *closure)
Custom_getlast(PyObject *op, void *closure)
{
CustomObject *self = (CustomObject *) op;
return Py_NewRef(self->last);
}
static int
Custom_setlast(CustomObject *self, PyObject *value, void *closure)
Custom_setlast(PyObject *op, PyObject *value, void *closure)
{
CustomObject *self = (CustomObject *) op;
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
return -1;
@ -125,21 +132,22 @@ Custom_setlast(CustomObject *self, PyObject *value, void *closure)
}
static PyGetSetDef Custom_getsetters[] = {
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
{"first", Custom_getfirst, Custom_setfirst,
"first name", NULL},
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
{"last", Custom_getlast, Custom_setlast,
"last name", NULL},
{NULL} /* Sentinel */
};
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))
{
CustomObject *self = (CustomObject *) op;
return PyUnicode_FromFormat("%S %S", self->first, self->last);
}
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
{"name", Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
@ -153,10 +161,10 @@ static PyTypeObject CustomType = {
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
.tp_new = Custom_new,
.tp_init = (initproc) Custom_init,
.tp_dealloc = (destructor) Custom_dealloc,
.tp_traverse = (traverseproc) Custom_traverse,
.tp_clear = (inquiry) Custom_clear,
.tp_init = Custom_init,
.tp_dealloc = Custom_dealloc,
.tp_traverse = Custom_traverse,
.tp_clear = Custom_clear,
.tp_members = Custom_members,
.tp_methods = Custom_methods,
.tp_getset = Custom_getsetters,

12
Doc/includes/newtypes/sublist.c
View file

@ -7,22 +7,24 @@ typedef struct {
} SubListObject;
static PyObject *
SubList_increment(SubListObject *self, PyObject *unused)
SubList_increment(PyObject *op, PyObject *Py_UNUSED(dummy))
{
SubListObject *self = (SubListObject *) op;
self->state++;
return PyLong_FromLong(self->state);
}
static PyMethodDef SubList_methods[] = {
{"increment", (PyCFunction) SubList_increment, METH_NOARGS,
{"increment", SubList_increment, METH_NOARGS,
PyDoc_STR("increment state counter")},
{NULL},
};
static int
SubList_init(SubListObject *self, PyObject *args, PyObject *kwds)
SubList_init(PyObject *op, PyObject *args, PyObject *kwds)
{
if (PyList_Type.tp_init((PyObject *) self, args, kwds) < 0)
SubListObject *self = (SubListObject *) op;
if (PyList_Type.tp_init(op, args, kwds) < 0)
return -1;
self->state = 0;
return 0;
@ -35,7 +37,7 @@ static PyTypeObject SubListType = {
.tp_basicsize = sizeof(SubListObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.tp_init = (initproc) SubList_init,
.tp_init = SubList_init,
.tp_methods = SubList_methods,
};