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author | Andrew Burgess <aburgess@redhat.com> | 2022-06-27 13:29:06 +0100 |
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committer | Andrew Burgess <aburgess@redhat.com> | 2022-07-21 15:19:43 +0100 |
commit | 11da1b13b313ae46c84008ebf096ffed1701e3c1 (patch) | |
tree | e33bbfa15ff289c9ee5b486cc420940917bf8e16 /gdbsupport/gdb-checked-static-cast.h | |
parent | 08106042d9f5fdff60c129bf33190639f1a98b2a (diff) | |
download | binutils-11da1b13b313ae46c84008ebf096ffed1701e3c1.zip binutils-11da1b13b313ae46c84008ebf096ffed1701e3c1.tar.gz binutils-11da1b13b313ae46c84008ebf096ffed1701e3c1.tar.bz2 |
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>
Diffstat (limited to 'gdbsupport/gdb-checked-static-cast.h')
-rw-r--r-- | gdbsupport/gdb-checked-static-cast.h | 68 |
1 files changed, 68 insertions, 0 deletions
diff --git a/gdbsupport/gdb-checked-static-cast.h b/gdbsupport/gdb-checked-static-cast.h new file mode 100644 index 0000000..7f28125 --- /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 */ |