Skip to content

Commit

Permalink
Fix a long-standing bug in the handling of Python multiple inheritanc…
Browse files Browse the repository at this point in the history
…e (#30056)

* Snapshot of pybind#4762 applied to pywrapcc

* Universal `bases.size() != vhs.size()` (not as `assert()`)

* Revert "Universal `bases.size() != vhs.size()` (not as `assert()`)"

This reverts commit 4c2407d17e982e1512f43ad89bf8752c0d2c7fe0.

* Streamline implementation and avoid unsafe `reinterpret_cast<instance *>()` introduced with PR pybind#2152

The `reinterpret_cast<instance *>(self)` is unsafe if `__new__` is mocked,
which was actually found in the wild: the mock returned `None` for `self`.
This was inconsequential because `inst` is currently cast straight back to
`PyObject *` to compute `all_type_info()`, which is empty if `self` is not
a pybind11 `instance`, and then `inst` is never dereferenced. However, the
unsafe detour through `instance *` is easily avoided and the updated
implementation is less prone to accidents while debugging or refactoring.

* Fix actual undefined behavior exposed by previous changes.

It turns out the previous commit message is incorrect, the `inst` pointer is actually dereferenced, in the `value_and_holder` ctor here:

https://github.com/pybind/pybind11/blob/f3e0602802c7840992c97f4960515777cad6a5c7/include/pybind11/detail/type_caster_base.h#L262-L263

```
259     // Main constructor for a found value/holder:
260     value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index)
261         : inst{i}, index{index}, type{type},
262           vh{inst->simple_layout ? inst->simple_value_holder
263                                  : &inst->nonsimple.values_and_holders[vpos]} {}
```

* Add test_mock_new()
  • Loading branch information
Ralf W. Grosse-Kunstleve authored Sep 12, 2023
1 parent b1538fc commit dc89e50
Show file tree
Hide file tree
Showing 6 changed files with 140 additions and 12 deletions.
8 changes: 3 additions & 5 deletions include/pybind11/detail/class.h
Original file line number Diff line number Diff line change
Expand Up @@ -189,12 +189,10 @@ extern "C" inline PyObject *pybind11_meta_call(PyObject *type, PyObject *args, P
return nullptr;
}

// This must be a pybind11 instance
auto *instance = reinterpret_cast<detail::instance *>(self);

// Ensure that the base __init__ function(s) were called
for (const auto &vh : values_and_holders(instance)) {
if (!vh.holder_constructed()) {
values_and_holders vhs(self);
for (const auto &vh : vhs) {
if (!vh.holder_constructed() && !vhs.is_redundant_value_and_holder(vh)) {
PyErr_Format(PyExc_TypeError,
"%.200s.__init__() must be called when overriding __init__",
get_fully_qualified_tp_name(vh.type->type).c_str());
Expand Down
49 changes: 42 additions & 7 deletions include/pybind11/detail/type_caster_base.h
Original file line number Diff line number Diff line change
Expand Up @@ -102,8 +102,22 @@ class loader_life_support {
inline std::pair<decltype(internals::registered_types_py)::iterator, bool>
all_type_info_get_cache(PyTypeObject *type);

// Band-aid workaround to fix a subtle but serious bug in a minimalistic fashion. See PR #4762.
inline void all_type_info_add_base_most_derived_first(std::vector<type_info *> &bases,
type_info *addl_base) {
for (auto it = bases.begin(); it != bases.end(); it++) {
type_info *existing_base = *it;
if (PyType_IsSubtype(addl_base->type, existing_base->type) != 0) {
bases.insert(it, addl_base);
return;
}
}
bases.push_back(addl_base);
}

// Populates a just-created cache entry.
PYBIND11_NOINLINE void all_type_info_populate(PyTypeObject *t, std::vector<type_info *> &bases) {
assert(bases.empty());
std::vector<PyTypeObject *> check;
for (handle parent : reinterpret_borrow<tuple>(t->tp_bases)) {
check.push_back((PyTypeObject *) parent.ptr());
Expand Down Expand Up @@ -136,7 +150,7 @@ PYBIND11_NOINLINE void all_type_info_populate(PyTypeObject *t, std::vector<type_
}
}
if (!found) {
bases.push_back(tinfo);
all_type_info_add_base_most_derived_first(bases, tinfo);
}
}
} else if (type->tp_bases) {
Expand Down Expand Up @@ -322,18 +336,29 @@ struct values_and_holders {
explicit values_and_holders(instance *inst)
: inst{inst}, tinfo(all_type_info(Py_TYPE(inst))) {}

explicit values_and_holders(PyObject *obj)
: inst{nullptr}, tinfo(all_type_info(Py_TYPE(obj))) {
if (!tinfo.empty()) {
inst = reinterpret_cast<instance *>(obj);
}
}

struct iterator {
private:
instance *inst = nullptr;
const type_vec *types = nullptr;
value_and_holder curr;
friend struct values_and_holders;
iterator(instance *inst, const type_vec *tinfo)
: inst{inst}, types{tinfo},
curr(inst /* instance */,
types->empty() ? nullptr : (*types)[0] /* type info */,
0, /* vpos: (non-simple types only): the first vptr comes first */
0 /* index */) {}
iterator(instance *inst, const type_vec *tinfo) : inst{inst}, types{tinfo} {
if (inst != nullptr) {
assert(!types->empty());
curr = value_and_holder(
inst /* instance */,
(*types)[0] /* type info */,
0, /* vpos: (non-simple types only): the first vptr comes first */
0 /* index */);
}
}
// Past-the-end iterator:
explicit iterator(size_t end) : curr(end) {}

Expand Down Expand Up @@ -364,6 +389,16 @@ struct values_and_holders {
}

size_t size() { return tinfo.size(); }

// Band-aid workaround to fix a subtle but serious bug in a minimalistic fashion. See PR #4762.
bool is_redundant_value_and_holder(const value_and_holder &vh) {
for (size_t i = 0; i < vh.index; i++) {
if (PyType_IsSubtype(tinfo[i]->type, tinfo[vh.index]->type) != 0) {
return true;
}
}
return false;
}
};

/**
Expand Down
1 change: 1 addition & 0 deletions tests/CMakeLists.txt
Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,7 @@ set(PYBIND11_TEST_FILES
test_opaque_types
test_operator_overloading
test_pickling
test_python_multiple_inheritance
test_pytypes
test_return_value_policy_override
test_return_value_policy_pack
Expand Down
14 changes: 14 additions & 0 deletions tests/test_class.py
Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
from unittest import mock

import pytest

import env
Expand Down Expand Up @@ -203,6 +205,18 @@ def __init__(self):
assert msg(exc_info.value) == expected


@pytest.mark.parametrize(
"mock_return_value", [None, (1, 2, 3), m.Pet("Polly", "parrot"), m.Dog("Molly")]
)
def test_mock_new(mock_return_value):
with mock.patch.object(
m.Pet, "__new__", return_value=mock_return_value
) as mock_new:
obj = m.Pet("Noname", "Nospecies")
assert obj is mock_return_value
mock_new.assert_called_once_with(m.Pet, "Noname", "Nospecies")


def test_automatic_upcasting():
assert type(m.return_class_1()).__name__ == "DerivedClass1"
assert type(m.return_class_2()).__name__ == "DerivedClass2"
Expand Down
45 changes: 45 additions & 0 deletions tests/test_python_multiple_inheritance.cpp
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
#include "pybind11_tests.h"

namespace test_python_multiple_inheritance {

// Copied from:
// https://github.com/google/clif/blob/5718e4d0807fd3b6a8187dde140069120b81ecef/clif/testing/python_multiple_inheritance.h

struct CppBase {
explicit CppBase(int value) : base_value(value) {}
int get_base_value() const { return base_value; }
void reset_base_value(int new_value) { base_value = new_value; }

private:
int base_value;
};

struct CppDrvd : CppBase {
explicit CppDrvd(int value) : CppBase(value), drvd_value(value * 3) {}
int get_drvd_value() const { return drvd_value; }
void reset_drvd_value(int new_value) { drvd_value = new_value; }

int get_base_value_from_drvd() const { return get_base_value(); }
void reset_base_value_from_drvd(int new_value) { reset_base_value(new_value); }

private:
int drvd_value;
};

} // namespace test_python_multiple_inheritance

TEST_SUBMODULE(python_multiple_inheritance, m) {
using namespace test_python_multiple_inheritance;

py::class_<CppBase>(m, "CppBase")
.def(py::init<int>())
.def("get_base_value", &CppBase::get_base_value)
.def("reset_base_value", &CppBase::reset_base_value);

py::class_<CppDrvd, CppBase>(m, "CppDrvd")
.def(py::init<int>())
.def("get_drvd_value", &CppDrvd::get_drvd_value)
.def("reset_drvd_value", &CppDrvd::reset_drvd_value)
.def("get_base_value_from_drvd", &CppDrvd::get_base_value_from_drvd)
.def("reset_base_value_from_drvd", &CppDrvd::reset_base_value_from_drvd);
}
35 changes: 35 additions & 0 deletions tests/test_python_multiple_inheritance.py
Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
# Adapted from:
# https://github.com/google/clif/blob/5718e4d0807fd3b6a8187dde140069120b81ecef/clif/testing/python/python_multiple_inheritance_test.py

from pybind11_tests import python_multiple_inheritance as m


class PC(m.CppBase):
pass


class PPCC(PC, m.CppDrvd):
pass


def test_PC():
d = PC(11)
assert d.get_base_value() == 11
d.reset_base_value(13)
assert d.get_base_value() == 13


def test_PPCC():
d = PPCC(11)
assert d.get_drvd_value() == 33
d.reset_drvd_value(55)
assert d.get_drvd_value() == 55

assert d.get_base_value() == 11
assert d.get_base_value_from_drvd() == 11
d.reset_base_value(20)
assert d.get_base_value() == 20
assert d.get_base_value_from_drvd() == 20
d.reset_base_value_from_drvd(30)
assert d.get_base_value() == 30
assert d.get_base_value_from_drvd() == 30

0 comments on commit dc89e50

Please sign in to comment.