[Python-checkins] gh-92135: Fix _Py_reinterpret_cast() for const (#92138)
vstinner
webhook-mailer at python.org
Mon May 2 11:07:06 EDT 2022
https://github.com/python/cpython/commit/031397063e9c22711abfbf90f2617c8785cfc42c
commit: 031397063e9c22711abfbf90f2617c8785cfc42c
branch: main
author: Victor Stinner <vstinner at python.org>
committer: vstinner <vstinner at python.org>
date: 2022-05-02T17:07:00+02:00
summary:
gh-92135: Fix _Py_reinterpret_cast() for const (#92138)
Fix C++ compiler warnings on cast macros, like _PyObject_CAST(), when
casting a constant expression to a non constant type: use
const_cast<> in C++.
* In C++, Py_SAFE_DOWNCAST() now uses static_cast<> rather than
reinterpret_cast<>.
* Add tests to the _testcppext C++ extension.
* test_cppext no longer captures stdout in verbose mode.
files:
M Include/methodobject.h
M Include/objimpl.h
M Include/pyport.h
M Lib/test/_testcppext.cpp
M Lib/test/test_cppext.py
diff --git a/Include/methodobject.h b/Include/methodobject.h
index 2046ab948de05..f4be3858f2f8a 100644
--- a/Include/methodobject.h
+++ b/Include/methodobject.h
@@ -43,8 +43,7 @@ typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
// it triggers an undefined behavior when Python calls it with 2 parameters
// (bpo-33012).
#define _PyCFunction_CAST(func) \
- _Py_reinterpret_cast(PyCFunction, \
- _Py_reinterpret_cast(void(*)(void), (func)))
+ _Py_reinterpret_cast(PyCFunction, _Py_reinterpret_cast(void(*)(void), (func)))
PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);
diff --git a/Include/objimpl.h b/Include/objimpl.h
index 94e03045f882a..c8e57c9755749 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -182,9 +182,9 @@ PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
PyAPI_FUNC(void) PyObject_GC_Del(void *);
#define PyObject_GC_New(type, typeobj) \
- _Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
+ _Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
#define PyObject_GC_NewVar(type, typeobj, n) \
- _Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
+ _Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
PyAPI_FUNC(int) PyObject_GC_IsTracked(PyObject *);
PyAPI_FUNC(int) PyObject_GC_IsFinalized(PyObject *);
diff --git a/Include/pyport.h b/Include/pyport.h
index 923897305fc6b..3f5ce672bdafe 100644
--- a/Include/pyport.h
+++ b/Include/pyport.h
@@ -14,10 +14,20 @@
#endif
-// Macro to use C++ static_cast<> and reinterpret_cast<> in the Python C API
+// Macro to use C++ static_cast<>, reinterpret_cast<> and const_cast<>
+// in the Python C API.
+//
+// In C++, _Py_reinterpret_cast(type, expr) converts a constant expression to a
+// non constant type using const_cast<type>. For example,
+// _Py_reinterpret_cast(PyObject*, op) can convert a "const PyObject*" to
+// "PyObject*".
+//
+// The type argument must not be constant. For example, in C++,
+// _Py_reinterpret_cast(const PyObject*, expr) fails with a compiler error.
#ifdef __cplusplus
# define _Py_static_cast(type, expr) static_cast<type>(expr)
-# define _Py_reinterpret_cast(type, expr) reinterpret_cast<type>(expr)
+# define _Py_reinterpret_cast(type, expr) \
+ const_cast<type>(reinterpret_cast<const type>(expr))
#else
# define _Py_static_cast(type, expr) ((type)(expr))
# define _Py_reinterpret_cast(type, expr) ((type)(expr))
@@ -307,10 +317,10 @@ extern "C" {
*/
#ifdef Py_DEBUG
# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
- (assert((WIDE)(NARROW)(VALUE) == (VALUE)), (NARROW)(VALUE))
+ (assert(_Py_static_cast(WIDE, _Py_static_cast(NARROW, (VALUE))) == (VALUE)), \
+ _Py_static_cast(NARROW, (VALUE)))
#else
-# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
- _Py_reinterpret_cast(NARROW, (VALUE))
+# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) _Py_static_cast(NARROW, (VALUE))
#endif
diff --git a/Lib/test/_testcppext.cpp b/Lib/test/_testcppext.cpp
index 14cd1ddad1757..257843bfc7726 100644
--- a/Lib/test/_testcppext.cpp
+++ b/Lib/test/_testcppext.cpp
@@ -1,6 +1,9 @@
// gh-91321: Very basic C++ test extension to check that the Python C API is
// compatible with C++ and does not emit C++ compiler warnings.
+// Always enable assertions
+#undef NDEBUG
+
#include "Python.h"
PyDoc_STRVAR(_testcppext_add_doc,
@@ -20,8 +23,36 @@ _testcppext_add(PyObject *Py_UNUSED(module), PyObject *args)
}
+static PyObject *
+test_api_casts(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
+{
+ PyObject *obj = Py_BuildValue("(ii)", 1, 2);
+ if (obj == nullptr) {
+ return nullptr;
+ }
+
+ // gh-92138: For backward compatibility, functions of Python C API accepts
+ // "const PyObject*". Check that using it does not emit C++ compiler
+ // warnings.
+ const PyObject *const_obj = obj;
+ Py_INCREF(const_obj);
+ Py_DECREF(const_obj);
+ PyTypeObject *type = Py_TYPE(const_obj);
+ assert(Py_REFCNT(const_obj) >= 1);
+
+ assert(type == &PyTuple_Type);
+ assert(PyTuple_GET_SIZE(const_obj) == 2);
+ PyObject *one = PyTuple_GET_ITEM(const_obj, 0);
+ assert(PyLong_AsLong(one) == 1);
+
+ Py_DECREF(obj);
+ Py_RETURN_NONE;
+}
+
+
static PyMethodDef _testcppext_methods[] = {
{"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
+ {"test_api_casts", test_api_casts, METH_NOARGS, NULL},
{nullptr, nullptr, 0, nullptr} /* sentinel */
};
diff --git a/Lib/test/test_cppext.py b/Lib/test/test_cppext.py
index c1d02bc54b389..99f6062d79d47 100644
--- a/Lib/test/test_cppext.py
+++ b/Lib/test/test_cppext.py
@@ -1,5 +1,6 @@
# gh-91321: Build a basic C++ test extension to check that the Python C API is
# compatible with C++ and does not emit C++ compiler warnings.
+import contextlib
import os
import sys
import unittest
@@ -39,17 +40,24 @@ def build(self):
sources=[SOURCE],
language='c++',
extra_compile_args=CPPFLAGS)
+ capture_stdout = (not support.verbose)
try:
try:
- with (support.captured_stdout() as stdout,
- support.swap_attr(sys, 'argv', ['setup.py', 'build_ext'])):
+ if capture_stdout:
+ stdout = support.captured_stdout()
+ else:
+ print()
+ stdout = contextlib.nullcontext()
+ with (stdout,
+ support.swap_attr(sys, 'argv', ['setup.py', 'build_ext', '--verbose'])):
setup(name="_testcppext", ext_modules=[cpp_ext])
return
except:
- # Show output on error
- print()
- print(stdout.getvalue())
+ if capture_stdout:
+ # Show output on error
+ print()
+ print(stdout.getvalue())
raise
except SystemExit:
self.fail("Build failed")
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