From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-479702-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 55507 invoked by alias); 8 Mar 2015 18:09:04 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 55463 invoked by uid 48); 8 Mar 2015 18:09:00 -0000
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/65352] array<T,0>::begin()/end() etc. forms a null reference and breaks on clang+ubsan
Date: Sun, 08 Mar 2015 18:09:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 4.9.2
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: bug_status cf_reconfirmed_on everconfirmed
Message-ID: <bug-65352-4-WbV5uaiVWv@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-65352-4@http.gcc.gnu.org/bugzilla/>
References: <bug-65352-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-03/txt/msg00846.txt.bz2

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65352

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-03-08
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Or just (untested):

--- a/libstdc++-v3/include/std/array
+++ b/libstdc++-v3/include/std/array
@@ -58,9 +58,9 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    {
      struct _Type { };

-     static constexpr _Tp&
+     static _Tp&
      _S_ref(const _Type&, std::size_t) noexcept
-     { return *static_cast<_Tp*>(nullptr); }
+     { return reinterpret_cast<_Tp&>(const_cast<_Type&>(t)); }
    };

   /**

It's undefined to refer to the element in the zero-size case, so casting to an
incompatible reference type shouldn't matter as noone will ever access anything
through that reference.