8000 gh-111178: fix UBSan for example code in `extending/newtypes_tutorial… · python/cpython@1d6a2e6 · GitHub
[go: up one dir, main page]
Skip to content

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly
Appearance settings

Commit 1d6a2e6

Browse files
picnixzencukou
picnixz
and
encukou
authored
gh-111178: fix UBSan for example code in extending/newtypes_tutorial docs (GH-131606)
Co-authored-by: Petr Viktorin <encukou@gmail.com>
1 parent d372472 commit 1d6a2e6

File tree

5 files changed

+120
-70
lines changed

5 files changed

+120
-70
lines changed

‎Doc/extending/newtypes_tutorial.rst

Lines changed: 56 additions & 26 deletions
Original file line numberDiff line numberDiff line change
@@ -250,16 +250,17 @@ Because we now have data to manage, we have to be more careful about object
250250
allocation and deallocation. At a minimum, we need a deallocation method::
251251

252252
static void
253-
Custom_dealloc(CustomObject *self)
253+
Custom_dealloc(PyObject *op)
254254
{
255+
CustomObject *self = (CustomObject *) op;
255256
Py_XDECREF(self->first);
256257
Py_XDECREF(self->last);
257-
Py_TYPE(self)->tp_free((PyObject *) self);
258+
Py_TYPE(self)->tp_free(self);
258259
}
259260

260261
which is assigned to the :c:member:`~PyTypeObject.tp_dealloc` member::
261262

262-
.tp_dealloc = (destructor) Custom_dealloc,
263+
.tp_dealloc = Custom_dealloc,
263264

264265
This method first clears the reference counts of the two Python attributes.
265266
: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
270271
be an instance of a subclass.
271272

272273
.. note::
273-
The explicit cast to ``destructor`` above is needed because we defined
274-
``Custom_dealloc`` to take a ``CustomObject *`` argument, but the ``tp_dealloc``
275-
function pointer expects to receive a ``PyObject *`` argument. Otherwise,
276-
the compiler will emit a warning. This is object-oriented polymorphism,
277-
in C!
274+
275+
The explicit cast to ``CustomObject *`` above is needed because we defined
276+
``Custom_dealloc`` to take a ``PyObject *`` argument, as the ``tp_dealloc``
277+
function pointer expects to receive a ``PyObject *`` argument.
278+
By assigning to the the ``tp_dealloc`` slot of a type, we declare
279+
that it can only be called with instances of our ``CustomObject``
280+
class, so the cast to ``(CustomObject *)`` is safe.
281+
This is object-oriented polymorphism, in C!
282+
283+
In existing code, or in previous versions of this tutorial,
284+
you might see similar functions take a pointer to the subtype
285+
object structure (``CustomObject*``) directly, like this::
286+
287+
Custom_dealloc(CustomObject *self)
288+
{
289+
Py_XDECREF(self->first);
290+
Py_XDECREF(self->last);
291+
Py_TYPE(self)->tp_free((PyObject *) self);
292+
}
293+
...
294+
.tp_dealloc = (destructor) Custom_dealloc,
295+
296+
This does the same thing on all architectures that CPython
297+
supports, but according to the C standard, it invokes
298+
undefined behavior.
278299

279300
We want to make sure that the first and last names are initialized to empty
280301
strings, so we provide a ``tp_new`` implementation::
@@ -352,8 +373,9 @@ We also define an initialization function which accepts arguments to provide
352373
initial values for our instance::
353374

354375
static int
355-
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
376+
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
356377
{
378+
CustomObject *self = (CustomObject *) op;
357379
static char *kwlist[] = {"first", "last", "number", NULL};
358380
PyObject *first = NULL, *last = NULL, *tmp;
359381

@@ -379,7 +401,7 @@ initial values for our instance::
379401

380402
by filling the :c:member:`~PyTypeObject.tp_init` slot. ::
381403

382-
.tp_init = (initproc) Custom_init,
404+
.tp_init = Custom_init,
383405

384406
The :c:member:`~PyTypeObject.tp_init` slot is exposed in Python as the
385407
: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
451473< F438 /code>
concatenation of the first and last names. ::
452474

453475
static PyObject *
454-
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
476+
Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))
455477
{
478+
CustomObject *self = (CustomObject *) op;
456479
if (self->first == NULL) {
457480
PyErr_SetString(PyExc_AttributeError, "first");
458481
return NULL;
@@ -486,7 +509,7 @@ Now that we've defined the method, we need to create an array of method
486509
definitions::
487510

488511
static PyMethodDef Custom_methods[] = {
489-
{"name", (PyCFunction) Custom_name, METH_NOARGS,
512+
{"name", Custom_name, METH_NOARGS,
490513
"Return the name, combining the first and last name"
491514
},
492515
{NULL} /* Sentinel */
@@ -543,15 +566,17 @@ we'll use custom getter and setter functions. Here are the functions for
543566
getting and setting the :attr:`!first` attribute::
544567

545568
static PyObject *
546-
Custom_getfirst(CustomObject *self, void *closure)
569+
Custom_getfirst(PyObject *op, void *closure)
547570
{
571+
CustomObject *self = (CustomObject *) op;
548572
Py_INCREF(self->first);
549573
return self->first;
550574
}
551575

552576
static int
553-
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
577+
Custom_setfirst(PyObject *op, PyObject *value, void *closure)
554578
{
579+
CustomObject *self = (CustomObject *) op;
555580
PyObject *tmp;
556581
if (value == NULL) {
557582
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
@@ -583,9 +608,9 @@ new value is not a string.
583608
We create an array of :c:type:`PyGetSetDef` structures::
584609

585610
static PyGetSetDef Custom_getsetters[] = {
586-
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
611+
{"first", Custom_getfirst, Custom_setfirst,
587612
"first name", NULL},
588-
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
613+
{"last", Custom_getlast, Custom_setlast,
589614
"last name", NULL},
590615
{NULL} /* Sentinel */
591616
};
@@ -609,8 +634,9 @@ We also need to update the :c:member:`~PyTypeObject.tp_init` handler to only
609634
allow strings [#]_ to be passed::
610635

611636
static int
612-
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
637+
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
613638
{
639+
CustomObject *self = (CustomObject *) op;
614640
static char *kwlist[] = {"first", "last", "number", NULL};
615641
PyObject *first = NULL, *last = NULL, *tmp;
616642

@@ -689,8 +715,9 @@ First, the traversal method lets the cyclic GC know about subobjects that could
689715
participate in cycles::
690716

691717
static int
692-
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
718+
Custom_traverse(PyObject *op, visitproc visit, void *arg)
693719
{
720+
CustomObject *self = (CustomObject *) op;
694721
int vret;
695722
if (self->first) {
696723
vret = visit(self->first, arg);
@@ -716,8 +743,9 @@ functions. With :c:func:`Py_VISIT`, we can minimize the amount of boilerplate
716743
in ``Custom_traverse``::
717744

718745
static int
719-
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
746+
Custom_traverse(PyObject *op, visitproc visit, void *arg)
720747
{
748+
CustomObject *self = (CustomObject *) op;
721749
Py_VISIT(self->first);
722750
Py_VISIT(self->last);
723751
return 0;
@@ -731,8 +759,9 @@ Second, we need to provide a method for clearing any subobjects that can
731759
participate in cycles::
732760

733761
static int
734-
Custom_clear(CustomObject *self)
762+
Custom_clear(PyObject *op)
735763
{
764+
CustomObject *self = (CustomObject *) op;
736765
Py_CLEAR(self->first);
737766
Py_CLEAR(self->last);
738767
return 0;
@@ -765,11 +794,11 @@ Here is our reimplemented deallocator using :c:func:`PyObject_GC_UnTrack`
765794
and ``Custom_clear``::
766795

767796
static void
768-
Custom_dealloc(CustomObject *self)
797+
Custom_dealloc(PyObject *op)
769798
{
770-
PyObject_GC_UnTrack(self);
771-
Custom_clear(self);
772-
Py_TYPE(self)->tp_free((PyObject *) self);
799+
PyObject_GC_UnTrack(op);
800+
(void)Custom_clear(op);
801+
Py_TYPE(op)->tp_free(op);
773802
}
774803

775804
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
825854
can be safely cast to both ``PyListObject *`` and ``SubListObject *``::
826855

827856
static int
828-
SubList_init(SubListObject *self, PyObject *args, PyObject *kwds)
857+
SubList_init(PyObject *op, PyObject *args, PyObject *kwds)
829858
{
830-
if (PyList_Type.tp_init((PyObject *) self, args, kwds) < 0)
859+
SubListObject *self = (SubListObject *) op;
860+
if (PyList_Type.tp_init(op, args, kwds) < 0)
831861
return -1;
832862
self->state = 0;
833863
return 0;

‎Doc/includes/newtypes/custom2.c

Lines changed: 10 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -10,11 +10,12 @@ typedef struct {
1010
} CustomObject;
1111

1212
static void
13-
Custom_dealloc(CustomObject *self)
13+
Custom_dealloc(PyObject *op)
1414
{
15+
CustomObject *self = (CustomObject *) op;
1516
Py_XDECREF(self->first);
1617
Py_XDECREF(self->last);
17-
Py_TYPE(self)->tp_free((PyObject *) self);
18+
Py_TYPE(self)->tp_free(self);
1819
}
1920

2021
static PyObject *
@@ -39,8 +40,9 @@ Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
3940
}
4041

4142
static int
42-
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
43+
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
4344
{
45+
CustomObject *self = (CustomObject *) op;
4446
static char *kwlist[] = {"first", "last", "number", NULL};
4547
PyObject *first = NULL, *last = NULL;
4648

@@ -69,8 +71,9 @@ static PyMemberDef Custom_members[] = {
6971
};
7072

7173
static PyObject *
72-
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
74+
Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))
7375
{
76+
CustomObject *self = (CustomObject *) op;
7477
if (self->first == NULL) {
7578
PyErr_SetString(PyExc_AttributeError, "first");
7679
return NULL;
@@ -83,7 +86,7 @@ Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
8386
}
8487

8588
static PyMethodDef Custom_methods[] = {
86-
{"name", (PyCFunction) Custom_name, METH_NOARGS,
89+
{"name", Custom_name, METH_NOARGS,
8790
"Return the name, combining the first and last name"
8891
},
8992
{NULL} /* Sentinel */
@@ -97,8 +100,8 @@ static PyTypeObject CustomType = {
97100
.tp_itemsize = 0,
98101
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
99102
.tp_new = Custom_new,
100-
.tp_init = (initproc) Custom_init,
101-
.tp_dealloc = (destructor) Custom_dealloc,
103+
.tp_init = Custom_init,
104+
.tp_dealloc = Custom_dealloc,
102105
.tp_members = Custom_members,
103106
.tp_methods = Custom_methods,
104107
};

‎Doc/includes/newtypes/custom3.c

Lines changed: 20 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -10,11 +10,12 @@ typedef struct {
1010
} CustomObject;
1111

1212
static void
13-
Custom_dealloc(CustomObject *self)
13+
Custom_dealloc(PyObject *op)
1414
{
15+
CustomObject *self = (CustomObject *) op;
1516
Py_XDECREF(self->first);
1617
Py_XDECREF(self->last);
17-
Py_TYPE(self)->tp_free((PyObject *) self);
18+
Py_TYPE(self)->tp_free(self);
1819
}
1920

2021
static PyObject *
@@ -39,8 +40,9 @@ Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
3940
}
4041

4142
static int
42-
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
43+
Custom_init(PyObject *op, PyObject *args, PyObject *kwds)
4344
{
45+
CustomObject *self = (CustomObject *) op;
4446
static char *kwlist[] = {"first", "last", "number", NULL};
4547
PyObject *first = NULL, *last = NULL;
4648

@@ -65,14 +67,16 @@ static PyMemberDef Custom_members[] = {
6567
};
6668

6769
static PyObject *
68-
Custom_getfirst(CustomObject *self, void *closure)
70+
Custom_getfirst(PyObject *op, void *closure)
6971
{
72+
CustomObject *self = (CustomObject *) op;
7073
return Py_NewRef(self->first);
7174
}
7275

7376
static int
74-
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
77+
Custom_setfirst(PyObject *op, PyObject *value, void *closure)
7578
{
79+
CustomObject *self = (CustomObject *) op;
7680
if (value == NULL) {
7781
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
7882
return -1;
@@ -87,14 +91,16 @@ Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
8791
}
8892

8993
static PyObject *
90-
Custom_getlast(CustomObject *self, void *closure)
94+
Custom_getlast(PyObject *op, void *closure)
9195
{
96+
CustomObject *self = (CustomObject *) op;
9297
return Py_NewRef(self->last);
9398
}
9499

95100
static int
96-
Custom_setlast(CustomObject *self, PyObject *value, void *closure)
101+
Custom_setlast(PyObject *op, PyObject *value, void *closure)
97102
{
103+
CustomObject *self = (CustomObject *) op;
98104
if (value == NULL) {
99105
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
100106
return -1;
@@ -109,21 +115,22 @@ Custom_setlast(CustomObject *self, PyObject *value, void *closure)
109115
}
110116

111117
static PyGetSetDef Custom_getsetters[] = {
112-
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
118+
{"first", Custom_getfirst, Custom_setfirst,
113119
"first name", NULL},
114-
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
120+
{"last", Custom_getlast, Custom_setlast,
115121
"last name", NULL},
116122
{NULL} /* Sentinel */
117123
};
118124

119125
static PyObject *
120-
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
126+
Custom_name(PyObject *op, PyObject *Py_UNUSED(dummy))
121127
{
128+
CustomObject *self = (CustomObject *) op;
122129
return PyUnicode_FromFormat("%S %S", self->first, self->last);
123130
}
124131

125132
static PyMethodDef Custom_methods[] = {
126-
{"name", (PyCFunction) Custom_name, METH_NOARGS,
133+
{"name", Custom_name, METH_NOARGS,
127134
"Return the name, combining the first and last name"
128135
},
129136
{NULL} /* Sentinel */
@@ -137,8 +144,8 @@ static PyTypeObject CustomType = {
137144
.tp_itemsize = 0,
138145
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
139146
.tp_new = Custom_new,
140-
.tp_init = (initproc) Custom_init,
141-
.tp_dealloc = (destructor) Custom_dealloc,
147+
.tp_init = Custom_init,
148+
.tp_dealloc = Custom_dealloc,
142149
.tp_members = Custom_members,
143150
.tp_methods = Custom_methods,
144151
.tp_getset = Custom_getsetters,

0 commit comments

Comments
 (0)
0