From 031397063e9c22711abfbf90f2617c8785cfc42c Mon Sep 17 00:00:00 2001 From: Victor Stinner Date: Mon, 2 May 2022 17:07:00 +0200 Subject: 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. --- Include/methodobject.h | 3 +-- Include/objimpl.h | 4 ++-- Include/pyport.h | 20 +++++++++++++++----- Lib/test/_testcppext.cpp | 31 +++++++++++++++++++++++++++++++ Lib/test/test_cppext.py | 18 +++++++++++++----- 5 files changed, 62 insertions(+), 14 deletions(-) diff --git a/Include/methodobject.h b/Include/methodobject.h index 2046ab9..f4be385 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 94e0304..c8e57c9 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 9238973..3f5ce67 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. 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(expr) -# define _Py_reinterpret_cast(type, expr) reinterpret_cast(expr) +# define _Py_reinterpret_cast(type, expr) \ + const_cast(reinterpret_cast(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 14cd1dd..257843b 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 c1d02bc..99f6062 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 @@ class TestCPPExt(unittest.TestCase): 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") -- cgit v0.12