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* [binutils-gdb] gdbsupport: add checked_static_cast
@ 2022-07-21 18:20 Andrew Burgess
  0 siblings, 0 replies; only message in thread
From: Andrew Burgess @ 2022-07-21 18:20 UTC (permalink / raw)
  To: gdb-cvs;h=11da1b13b313ae46c84008ebf096ffed1701e3c1

commit 11da1b13b313ae46c84008ebf096ffed1701e3c1
Author: Andrew Burgess <>
Date:   Mon Jun 27 13:29:06 2022 +0100

    gdbsupport: add checked_static_cast
    This commit was inspired by these mailing list posts:
    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
    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 <>
    Co-Authored-By: Tom Tromey <>

 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
+   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 <>.  */
+#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>
+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");
+  T result = dynamic_cast<T> (v);
+  gdb_assert (result != nullptr);
+  T result = static_cast<T> (v);
+  return result;

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