[Python-checkins] gh-94731: Revert to C-style casts for _Py_CAST (GH-94782) (#94849)
encukou
webhook-mailer at python.org
Fri Jul 15 03:35:34 EDT 2022
https://github.com/python/cpython/commit/d9107aa0157a2ff6741b9aa2f78759e90f522bd7
commit: d9107aa0157a2ff6741b9aa2f78759e90f522bd7
branch: 3.11
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: encukou <encukou at gmail.com>
date: 2022-07-15T09:35:23+02:00
summary:
gh-94731: Revert to C-style casts for _Py_CAST (GH-94782) (#94849)
Co-authored-by: da-woods <dw-git at d-woods.co.uk>
(cherry picked from commit 6cbb57f62d345d7a5d6aeb1b3b5d37a845344d5e)
files:
A Misc/NEWS.d/next/C API/2022-07-12-17-39-32.gh-issue-94731.9CPJNU.rst
M Include/pyport.h
M Lib/test/_testcppext.cpp
M Lib/test/setup_testcppext.py
M Lib/test/test_cppext.py
diff --git a/Include/pyport.h b/Include/pyport.h
index 59f225fc8fa5d..93250f4eb1d7a 100644
--- a/Include/pyport.h
+++ b/Include/pyport.h
@@ -14,62 +14,14 @@
#endif
-// Macro to use C++ static_cast<>, reinterpret_cast<> and const_cast<>
-// in the Python C API.
-//
-// In C++, _Py_CAST(type, expr) converts a constant expression to a
-// non constant type using const_cast<type>. For example,
-// _Py_CAST(PyObject*, op) can convert a "const PyObject*" to
-// "PyObject*".
-//
-// The type argument must not be a constant type.
+// Macro to use C++ static_cast<> in the Python C API.
#ifdef __cplusplus
-#include <cstddef>
# define _Py_STATIC_CAST(type, expr) static_cast<type>(expr)
-extern "C++" {
- namespace {
- template <typename type>
- inline type _Py_CAST_impl(long int ptr) {
- return reinterpret_cast<type>(ptr);
- }
- template <typename type>
- inline type _Py_CAST_impl(int ptr) {
- return reinterpret_cast<type>(ptr);
- }
-#if __cplusplus >= 201103
- template <typename type>
- inline type _Py_CAST_impl(std::nullptr_t) {
- return static_cast<type>(nullptr);
- }
-#endif
-
- template <typename type, typename expr_type>
- inline type _Py_CAST_impl(expr_type *expr) {
- return reinterpret_cast<type>(expr);
- }
-
- template <typename type, typename expr_type>
- inline type _Py_CAST_impl(expr_type const *expr) {
- return reinterpret_cast<type>(const_cast<expr_type *>(expr));
- }
-
- template <typename type, typename expr_type>
- inline type _Py_CAST_impl(expr_type &expr) {
- return static_cast<type>(expr);
- }
-
- template <typename type, typename expr_type>
- inline type _Py_CAST_impl(expr_type const &expr) {
- return static_cast<type>(const_cast<expr_type &>(expr));
- }
- }
-}
-# define _Py_CAST(type, expr) _Py_CAST_impl<type>(expr)
-
#else
# define _Py_STATIC_CAST(type, expr) ((type)(expr))
-# define _Py_CAST(type, expr) ((type)(expr))
#endif
+// Macro to use the more powerful/dangerous C-style cast even in C++.
+#define _Py_CAST(type, expr) ((type)(expr))
// Static inline functions should use _Py_NULL rather than using directly NULL
// to prevent C++ compiler warnings. On C++11 and newer, _Py_NULL is defined as
diff --git a/Lib/test/_testcppext.cpp b/Lib/test/_testcppext.cpp
index be7538826b6c4..0e381a78c5cee 100644
--- a/Lib/test/_testcppext.cpp
+++ b/Lib/test/_testcppext.cpp
@@ -12,6 +12,9 @@
# define NAME _testcpp03ext
#endif
+#define _STR(NAME) #NAME
+#define STR(NAME) _STR(NAME)
+
PyDoc_STRVAR(_testcppext_add_doc,
"add(x, y)\n"
"\n"
@@ -123,11 +126,77 @@ test_unicode(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
Py_RETURN_NONE;
}
+/* Test a `new`-allocated object with a virtual method.
+ * (https://github.com/python/cpython/issues/94731) */
+
+class VirtualPyObject : public PyObject {
+public:
+ VirtualPyObject();
+ virtual ~VirtualPyObject() {
+ delete [] internal_data;
+ --instance_count;
+ }
+ virtual void set_internal_data() {
+ internal_data[0] = 1;
+ }
+ static void dealloc(PyObject* o) {
+ delete static_cast<VirtualPyObject*>(o);
+ }
+
+ // Number of "living" instances
+ static int instance_count;
+private:
+ // buffer that can get corrupted
+ int* internal_data;
+};
+
+int VirtualPyObject::instance_count = 0;
+
+PyType_Slot VirtualPyObject_Slots[] = {
+ {Py_tp_free, (void*)VirtualPyObject::dealloc},
+ {0, _Py_NULL},
+};
+
+PyType_Spec VirtualPyObject_Spec = {
+ /* .name */ STR(NAME) ".VirtualPyObject",
+ /* .basicsize */ sizeof(VirtualPyObject),
+ /* .itemsize */ 0,
+ /* .flags */ Py_TPFLAGS_DEFAULT,
+ /* .slots */ VirtualPyObject_Slots,
+};
+
+VirtualPyObject::VirtualPyObject() {
+ // Create a temporary type (just so we don't need to store it)
+ PyObject *type = PyType_FromSpec(&VirtualPyObject_Spec);
+ // no good way to signal failure from a C++ constructor, so use assert
+ // for error handling
+ assert(type);
+ assert(PyObject_Init(this, (PyTypeObject *)type));
+ Py_DECREF(type);
+ internal_data = new int[50];
+ ++instance_count;
+}
+
+static PyObject *
+test_virtual_object(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
+{
+ VirtualPyObject* obj = new VirtualPyObject();
+ obj->set_internal_data();
+ Py_DECREF(obj);
+ if (VirtualPyObject::instance_count != 0) {
+ return PyErr_Format(
+ PyExc_AssertionError,
+ "instance_count should be 0, got %d",
+ VirtualPyObject::instance_count);
+ }
+ Py_RETURN_NONE;
+}
static PyMethodDef _testcppext_methods[] = {
{"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
{"test_api_casts", test_api_casts, METH_NOARGS, _Py_NULL},
{"test_unicode", test_unicode, METH_NOARGS, _Py_NULL},
+ {"test_virtual_object", test_virtual_object, METH_NOARGS, _Py_NULL},
// Note: _testcppext_exec currently runs all test functions directly.
// When adding a new one, add a call there.
@@ -152,6 +221,10 @@ _testcppext_exec(PyObject *module)
if (!result) return -1;
Py_DECREF(result);
+ result = PyObject_CallMethod(module, "test_virtual_object", "");
+ if (!result) return -1;
+ Py_DECREF(result);
+
return 0;
}
@@ -163,9 +236,6 @@ static PyModuleDef_Slot _testcppext_slots[] = {
PyDoc_STRVAR(_testcppext_doc, "C++ test extension.");
-#define _STR(NAME) #NAME
-#define STR(NAME) _STR(NAME)
-
static struct PyModuleDef _testcppext_module = {
PyModuleDef_HEAD_INIT, // m_base
STR(NAME), // m_name
diff --git a/Lib/test/setup_testcppext.py b/Lib/test/setup_testcppext.py
index ae81e33e23b6b..c6b68104d1333 100644
--- a/Lib/test/setup_testcppext.py
+++ b/Lib/test/setup_testcppext.py
@@ -17,8 +17,6 @@
# a C++ extension using the Python C API does not emit C++ compiler
# warnings
'-Werror',
- # Warn on old-style cast (C cast) like: (PyObject*)op
- '-Wold-style-cast',
]
else:
# Don't pass any compiler flag to MSVC
@@ -37,9 +35,6 @@ def main():
name = '_testcpp11ext'
cppflags = [*CPPFLAGS, f'-std={std}']
- if std == 'c++11':
- # Warn when using NULL rather than _Py_NULL in static inline functions
- cppflags.append('-Wzero-as-null-pointer-constant')
cpp_ext = Extension(
name,
diff --git a/Lib/test/test_cppext.py b/Lib/test/test_cppext.py
index 2c54d33711691..465894d24e7df 100644
--- a/Lib/test/test_cppext.py
+++ b/Lib/test/test_cppext.py
@@ -4,6 +4,7 @@
import sys
import unittest
import subprocess
+import sysconfig
from test import support
from test.support import os_helper
@@ -25,6 +26,11 @@ def test_build_cpp03(self):
# With MSVC, the linker fails with: cannot open file 'python311.lib'
# https://github.com/python/cpython/pull/32175#issuecomment-1111175897
@unittest.skipIf(MS_WINDOWS, 'test fails on Windows')
+ # Building and running an extension in clang sanitizing mode is not
+ # straightforward
+ @unittest.skipIf(
+ '-fsanitize' in (sysconfig.get_config_var('PY_CFLAGS') or ''),
+ 'test does not work with analyzing builds')
# the test uses venv+pip: skip if it's not available
@support.requires_venv_with_pip()
def check_build(self, std_cpp03, extension_name):
diff --git a/Misc/NEWS.d/next/C API/2022-07-12-17-39-32.gh-issue-94731.9CPJNU.rst b/Misc/NEWS.d/next/C API/2022-07-12-17-39-32.gh-issue-94731.9CPJNU.rst
new file mode 100644
index 0000000000000..b7816d28215e7
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2022-07-12-17-39-32.gh-issue-94731.9CPJNU.rst
@@ -0,0 +1,3 @@
+Python again uses C-style casts for most casting operations when compiled
+with C++. This may trigger compiler warnings, if they are enabled with e.g.
+``-Wold-style-cast `` or ``-Wzero-as-null-pointer-constant`` options for ``g++``.
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