forked from Imagelibrary/binutils-gdb
7d18eb9983
This commit:
commit 6fe4779ac4
Date: Sat Feb 24 11:00:20 2024 +0100
[gdb/build] Fix static cast of virtual base
addressed an issue where GDB would not compile in production mode due
to a use of gdb::checked_static_cast. The problem was that we were
asking GDB to cast from a virtual base class to a sub-class, this
works fine when using dynamic_cast, but does not work with
static_cast.
The gdb::checked_static_cast actually uses dynamic_cast under the hood
in development mode in order to ensure that the cast is valid, while
in a production build we use static_cast as this is more efficient.
What this meant however, was that when gdb::checked_static_cast was
used to cast from a virtual base class, the dynamic_cast of a
non-production build worked fine, while the production build's
static_cast caused a build failure.
However, the gdb::checked_static_cast function already contains some
static_assert calls that are intended to catch any issues with invalid
type casting, the goal of these asserts was to prevent issues like
this: the build only failing in production mode. Clearly the current
asserts are not enough.
I don't think there is a std::is_virtual_base type trait check, so
what I propose instead is that in non-production mode we also make use
of static_cast. This will ensure that any errors that crop up in
production mode should also be revealed in non-production mode, and
should catch issues like this in the future.
There should be no user visible changes after this commit.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31399
Co-Authored-By: Simon Marchi <simon.marchi@polymtl.ca>
84 lines
2.9 KiB
C++
84 lines
2.9 KiB
C++
/* Copyright (C) 2022-2024 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef COMMON_GDB_CHECKED_DYNAMIC_CAST_H
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#define COMMON_GDB_CHECKED_DYNAMIC_CAST_H
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#include "gdbsupport/traits.h"
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namespace gdb
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{
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/* This function can be used in place of static_cast when casting between
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pointers of polymorphic types. The benefit of using this call is that,
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when compiling in developer mode, dynamic_cast will be used to validate
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the cast. This use of dynamic_cast is why this function will only
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work for polymorphic types.
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In non-developer (i.e. production) builds, the dynamic_cast is replaced
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with a static_cast which is usually significantly faster. */
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template<typename T, typename V>
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T
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checked_static_cast (V *v)
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{
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/* We only support casting to pointer types. */
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static_assert (std::is_pointer<T>::value, "target must be a pointer type");
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/* Check for polymorphic types explicitly in case we're in release mode. */
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static_assert (std::is_polymorphic<V>::value, "types must be polymorphic");
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/* Figure out the type that T points to. */
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using T_no_P = typename std::remove_pointer<T>::type;
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/* In developer mode this cast uses dynamic_cast to confirm at run-time
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that the cast from V* to T is valid. However, we can catch some
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mistakes at compile time, this assert prevents anything other than
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downcasts, or casts to same type. */
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static_assert (std::is_base_of<V, T_no_P>::value
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|| std::is_base_of<T_no_P, V>::value,
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"types must be related");
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#ifdef DEVELOPMENT
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gdb_assert (v == nullptr || dynamic_cast<T> (v) != nullptr);
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#endif
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/* If a base class of V is virtual then the dynamic_cast above will
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succeed, but this static_cast will fail. */
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return static_cast<T> (v);
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}
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/* Same as the above, but to cast from a reference type to another. */
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template<typename T, typename V, typename = gdb::Requires<std::is_reference<T>>>
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T
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checked_static_cast (V &v)
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{
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static_assert (std::is_reference<T>::value, "target must be a reference type");
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using T_no_R = typename std::remove_reference<T>::type;
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using T_P = typename std::add_pointer<T_no_R>::type;
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using V_no_R = typename std::remove_reference<V>::type;
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return *checked_static_cast<T_P, V_no_R> (&v);
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}
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}
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#endif /* COMMON_GDB_CHECKED_DYNAMIC_CAST_H */
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