| Message ID | 20181031123119.GA17297@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | PR libstdc++/87822 fix layout change for nested std::pair | expand |
On 31/10/18 12:31 +0000, Jonathan Wakely wrote: >The introduction of the empty __pair_base base class for PR 86751 >changed the layout of std::pair<std::pair<...>, ...>. The outer pair and >its first member both have a base class of the same type, which cannot >exist at the same address. This causes the first member to be at a >non-zero offset. > >The solution is to make the base class depend on the template >parameters, so that each pair type has a different base class type, >which allows the base classes of the outer pair and its first member to >have the same address. > > PR libstdc++/87822 > * include/bits/stl_pair.h (__pair_base): Change to class template. > (pair): Make base class type depend on template parameters. > * testsuite/20_util/pair/87822.cc: New test. Jakub suggested some more testing, as attached. Tested powerpc64le-linux and x86_64-linux, committed to trunk. I'll include this in the backports too. commit 75efd61131798bd9001b15b551bd6f1cbfc2bc33 Author: Jonathan Wakely <jwakely@redhat.com> Date: Wed Oct 31 12:57:07 2018 +0000 More testing for std::pair layout change * testsuite/20_util/pair/87822.cc: Test deeper nesting. diff --git a/libstdc++-v3/testsuite/20_util/pair/87822.cc b/libstdc++-v3/testsuite/20_util/pair/87822.cc index cd099d6f9f9..523d583f08a 100644 --- a/libstdc++-v3/testsuite/20_util/pair/87822.cc +++ b/libstdc++-v3/testsuite/20_util/pair/87822.cc @@ -26,6 +26,7 @@ test01() static_assert(sizeof(p) == (3 * sizeof(int)), "PR libstdc++/87822"); #endif VERIFY( (void*)&p == (void*)&p.first ); + VERIFY( (void*)&p == (void*)&p.first.first ); } struct empty { }; @@ -40,8 +41,24 @@ test02() VERIFY( (void*)&p == (void*)&p.first ); } +void +test03() +{ + typedef std::pair<int, int> int_pair; + typedef std::pair<int_pair, int_pair> int_pair_pair; + std::pair<int_pair_pair, int_pair_pair> p; +#if __cplusplus >= 201103L + static_assert(sizeof(int_pair_pair) == (2 * sizeof(int_pair)), "nested"); + static_assert(sizeof(p) == (2 * sizeof(int_pair_pair)), "nested again"); +#endif + VERIFY( (void*)&p == (void*)&p.first ); + VERIFY( (void*)&p == (void*)&p.first.first ); + VERIFY( (void*)&p == (void*)&p.first.first.first ); +} + int main() { test01(); test02(); + test03(); }
diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h index ea8bd981559..48af2b02ef9 100644 --- a/libstdc++-v3/include/bits/stl_pair.h +++ b/libstdc++-v3/include/bits/stl_pair.h @@ -187,7 +187,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION }; #endif // C++11 - class __pair_base + template<typename _U1, typename _U2> class __pair_base { #if __cplusplus >= 201103L template<typename _T1, typename _T2> friend struct pair; @@ -206,7 +206,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION */ template<typename _T1, typename _T2> struct pair - : private __pair_base + : private __pair_base<_T1, _T2> { typedef _T1 first_type; /// @c first_type is the first bound type typedef _T2 second_type; /// @c second_type is the second bound type diff --git a/libstdc++-v3/testsuite/20_util/pair/87822.cc b/libstdc++-v3/testsuite/20_util/pair/87822.cc new file mode 100644 index 00000000000..cd099d6f9f9 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/pair/87822.cc @@ -0,0 +1,47 @@ +// Copyright (C) 2018 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/>. + +#include <utility> +#include <testsuite_hooks.h> + +void +test01() +{ + std::pair<std::pair<int, int>, int> p; +#if __cplusplus >= 201103L + static_assert(sizeof(p) == (3 * sizeof(int)), "PR libstdc++/87822"); +#endif + VERIFY( (void*)&p == (void*)&p.first ); +} + +struct empty { }; + +void +test02() +{ + std::pair<std::pair<empty, empty>, empty> p; +#if __cplusplus >= 201103L + static_assert(sizeof(p) == (3 * sizeof(empty)), "PR libstdc++/87822"); +#endif + VERIFY( (void*)&p == (void*)&p.first ); +} + +int main() +{ + test01(); + test02(); +}
The introduction of the empty __pair_base base class for PR 86751 changed the layout of std::pair<std::pair<...>, ...>. The outer pair and its first member both have a base class of the same type, which cannot exist at the same address. This causes the first member to be at a non-zero offset. The solution is to make the base class depend on the template parameters, so that each pair type has a different base class type, which allows the base classes of the outer pair and its first member to have the same address. PR libstdc++/87822 * include/bits/stl_pair.h (__pair_base): Change to class template. (pair): Make base class type depend on template parameters. * testsuite/20_util/pair/87822.cc: New test. Tested powerpc64le-linux and x86_64-linux, committed to trunk. Backports to gcc-7 and gcc-8 branches coming ASAP. This layout change is unfortunately in gcc 6.5 and that branch is now closed. I'm very sorry :-( commit 581b5447f18f4758a55b1fda4f8bf597e9466d40 Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4> Date: Wed Oct 31 12:29:02 2018 +0000 PR libstdc++/87822 fix layout change for nested std::pair The introduction of the empty __pair_base base class for PR 86751 changed the layout of std::pair<std::pair<...>, ...>. The outer pair and its first member both have a base class of the same type, which cannot exist at the same address. This causes the first member to be at a non-zero offset. The solution is to make the base class depend on the template parameters, so that each pair type has a different base class type, which allows the base classes of the outer pair and its first member to have the same address. PR libstdc++/87822 * include/bits/stl_pair.h (__pair_base): Change to class template. (pair): Make base class type depend on template parameters. * testsuite/20_util/pair/87822.cc: New test. git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@265678 138bc75d-0d04-0410-961f-82ee72b054a4