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From: Andrew Burgess <aburgess@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] gdbsupport: add checked_static_cast Date: Thu, 21 Jul 2022 18:20:26 +0000 (GMT) [thread overview] Message-ID: <20220721182026.F3F48386545B@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=11da1b13b313ae46c84008ebf096ffed1701e3c1 commit 11da1b13b313ae46c84008ebf096ffed1701e3c1 Author: Andrew Burgess <aburgess@redhat.com> Date: Mon Jun 27 13:29:06 2022 +0100 gdbsupport: add checked_static_cast This commit was inspired by these mailing list posts: https://sourceware.org/pipermail/gdb-patches/2022-June/190323.html https://sourceware.org/pipermail/gdb-patches/2022-April/188098.html The idea is to add a new function gdb::checked_static_cast, which can, in some cases, be used as a drop-in replacement for static_cast. And so, if I previously wrote this: BaseClass *base = get_base_class_pointer (); DerivedClass *derived = static_cast<DerivedClass *> (base); I can now write: BaseClass *base = get_base_class_pointer (); DerivedClass *derived = gdb::checked_static_cast<DerivedClass *> (base); The requirement is that BaseClass and DerivedClass must be polymorphic. The benefit of making this change is that, when GDB is built in developer mode, a run-time check will be made to ensure that `base` really is of type DerivedClass before the cast is performed. If `base` is not of type DerivedClass then GDB will assert. In a non-developer build gdb::checked_static_cast is equivalent to a static_cast, and there should be no performance difference. This commit adds the support function, but does not make use of this function, a use will be added in the next commit. Co-Authored-By: Pedro Alves <pedro@palves.net> Co-Authored-By: Tom Tromey <tom@tromey.com> Diff: --- gdbsupport/gdb-checked-static-cast.h | 68 ++++++++++++++++++++++++++++++++++++ 1 file changed, 68 insertions(+) diff --git a/gdbsupport/gdb-checked-static-cast.h b/gdbsupport/gdb-checked-static-cast.h new file mode 100644 index 00000000000..7f281250285 --- /dev/null +++ b/gdbsupport/gdb-checked-static-cast.h @@ -0,0 +1,68 @@ +/* Copyright (C) 2022 Free Software Foundation, Inc. + + This file is part of GDB. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +#ifndef COMMON_GDB_CHECKED_DYNAMIC_CAST_H +#define COMMON_GDB_CHECKED_DYNAMIC_CAST_H + +#include "gdbsupport/traits.h" + +namespace gdb +{ + +/* This function can be used in place of static_cast when casting between + pointers of polymorphic types. The benefit of using this call is that, + when compiling in developer mode, dynamic_cast will be used to validate + the cast. This use of dynamic_cast is why this function will only + work for polymorphic types. + + In non-developer (i.e. production) builds, the dynamic_cast is replaced + with a static_cast which is usually significantly faster. */ + +template<typename T, typename V> +T +checked_static_cast (V *v) +{ + /* We only support casting to pointer types. */ + static_assert (std::is_pointer<T>::value, "target must be a pointer type"); + + /* Check for polymorphic types explicitly in case we're in release mode. */ + static_assert (std::is_polymorphic<V>::value, "types must be polymorphic"); + + /* Figure out the type that T points to. */ + using T_no_P = typename std::remove_pointer<T>::type; + + /* In developer mode this cast uses dynamic_cast to confirm at run-time + that the cast from V* to T is valid. However, we can catch some + mistakes at compile time, this assert prevents anything other than + downcasts, or casts to same type. */ + static_assert (std::is_base_of<V, T_no_P>::value + || std::is_base_of<T_no_P, V>::value, + "types must be related"); + +#ifdef DEVELOPMENT + T result = dynamic_cast<T> (v); + gdb_assert (result != nullptr); +#else + T result = static_cast<T> (v); +#endif + + return result; +} + +} + +#endif /* COMMON_GDB_CHECKED_DYNAMIC_CAST_H */
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