[PATCH] Fix overflow handling in std::align

[Jonathan Wakely]

On 21/09/20 10:42 -0400, Glen Fernandes via Libstdc++ wrote:
>On Mon, Sep 14, 2020 at 5:44 PM Thomas Rodgers  wrote:
>> > On Sep 14, 2020, at 7:30 AM, Ville Voutilainen  wrote:
>> >
>> > On Mon, 14 Sep 2020 at 15:49, Glen Fernandes  wrote:
>> >> Sounds like a good idea. Updated patch attached.
>> >
>> > Looks good to me.
>>
>> Agree.
>
>Rebased patch on latest changes to bits/align.h.

Oh nice, I was about to do that myself.

I'll get the patch committed today, thanks!


>Fix overflow handling in align
>
>2020-09-20  Glen Joseph Fernandes  <glenjofe@gmail.com>
>
>        * include/bits/align.h (align): Fix overflow handling.
>        * testsuite/20_util/align/3.cc: New tests.
>
>Glen

>commit f18840a2b03e927e296adef8b1a13fdf255e1828
>Author: Glen Joseph Fernandes <glenjofe@gmail.com>
>Date:   Mon Sep 14 01:21:27 2020 -0400
>
>    Fix overflow handling in align
>
>    2020-09-20  Glen Joseph Fernandes  <glenjofe@gmail.com>
>
>            * include/bits/align.h (align): Fix overflow handling.
>            * testsuite/20_util/align/3.cc: New tests.
>
>diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
>index 28b66ccca7a..a26faef547e 100644
>--- a/libstdc++-v3/ChangeLog
>+++ b/libstdc++-v3/ChangeLog
>@@ -1,3 +1,8 @@
>+2020-09-20  Glen Joseph Fernandes  <glenjofe@gmail.com>
>+
>+    * include/bits/align.h (align): Fix overflow handling.
>+    * testsuite/20_util/align/3.cc: New tests.
>+
> 2020-09-20  Jonathan Wakely  <jwakely@redhat.com>
>
> 	PR libstdc++/97101
>diff --git a/libstdc++-v3/include/bits/align.h b/libstdc++-v3/include/bits/align.h
>index faa92bec2f8..597b4103ed8 100644
>--- a/libstdc++-v3/include/bits/align.h
>+++ b/libstdc++-v3/include/bits/align.h
>@@ -60,10 +60,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> inline void*
> align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
> {
>+  if (__space < __size)
>+    return nullptr;
>   const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
>   const auto __aligned = (__intptr - 1u + __align) & -__align;
>   const auto __diff = __aligned - __intptr;
>-  if ((__size + __diff) > __space)
>+  if (__diff > (__space - __size))
>     return nullptr;
>   else
>     {
>diff --git a/libstdc++-v3/testsuite/20_util/align/3.cc b/libstdc++-v3/testsuite/20_util/align/3.cc
>new file mode 100644
>index 00000000000..74116a59867
>--- /dev/null
>+++ b/libstdc++-v3/testsuite/20_util/align/3.cc
>@@ -0,0 +1,53 @@
>+// { dg-do run { target c++11 } }
>+
>+// 2020-09-20 Glen Joseph Fernandes <glenjofe@gmail.com>
>+
>+// Copyright (C) 2020 Free Software Foundation, Inc.
>+//
>+// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option) any later
>+// version.
>+
>+// This library 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 library; see the file COPYING3.  If not see
>+// <http://www.gnu.org/licenses/>.
>+
>+// C++11 [ptr.align] (20.6.5): std::align
>+
>+#include <memory>
>+#include <testsuite_hooks.h>
>+
>+void test01()
>+{
>+  void* p1 = reinterpret_cast<void*>(5);
>+  void* p2 = p1;
>+  std::size_t s1 = 3072;
>+  std::size_t s2 = s1;
>+  VERIFY(std::align(1024, static_cast<std::size_t>(-1), p1, s1) == nullptr);
>+  VERIFY(p1 == p2);
>+  VERIFY(s1 == s2);
>+}
>+
>+void test02()
>+{
>+  void* p1 = reinterpret_cast<void*>(1);
>+  void* p2 = p1;
>+  std::size_t s1 = -1;
>+  std::size_t s2 = s1;
>+  VERIFY(std::align(2, static_cast<std::size_t>(-1), p1, s1) == nullptr);
>+  VERIFY(p1 == p2);
>+  VERIFY(s1 == s2);
>+}
>+
>+int main()
>+{
>+  test01();
>+  test02();
>+}