| Message ID | 20180621232851.GA6885@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | PR libstdc++/86138 prevent implicit instantiation of COW empty rep | expand |
On 22/06/18 00:28 +0100, Jonathan Wakely wrote: >The explicit instantiation declarations for std::basic_string are >disabled for C++17 (and later) so that basic_string symbols get >implicitly instantiated in every translation unit that needs them. On >targets that don't support STB_GNU_UNIQUE this leads to multiple copies >of the empty rep symbol for COW strings. In order to detect whether a >COW string needs to deallocate its storage it compares the address with >the empty rep. When there are multiple copies of the empty rep object >the address is not unique, and so string destructors try to delete the >empty rep, which crashes. > >In order to guarantee uniqueness of the _S_empty_rep_storage symbol this >patch adds an explicit instantiation declaration for just that symbol. >This means the other symbols are still implicitly instantiated in C++17 >code, but for the empty rep the definition in the library gets used. > >Separately, there is no need for C++17 code to implicitly instantiate >the I/O functions for strings, so this also restores the explicit >instantiation declarations for those functions. > > PR libstdc++/86138 > * include/bits/basic_string.tcc: > [__cplusplus > 201402 && !_GLIBCXX_USE_CXX11_ABI] > (basic_string<char>::_Rep::_S_empty_rep_storage) > (basic_string<wchar_t>::_Rep::_S_empty_rep_storage): Add explicit > instantiation declarations. > [__cplusplus > 201402] (operator>>, operator<<, getline): Re-enable > explicit instantiation declarations. > * testsuite/21_strings/basic_string/cons/char/86138.cc: New. > * testsuite/21_strings/basic_string/cons/wchar_t/86138.cc: New. > >Tested x86_64-linux, committed to trunk. > >If this passes testing on Cygwin I'll also backport it to gcc-7 and >gcc-8, as the explicit instantiation declarations are disabled for >C++17 on those branches. The new tests are failing with _GLIBCXX_ASSERTIONS or _GLIBCXX_DEBUG defined, because enabling assertions suppresses the explicit instantiation declarations. However the COW empty reps and the I/O functions don't contain any assertions, so don't need to be implicitly instantiated. Tested x86_64-linux, committed to trunk. commit 22bd831a1bc38ba3e114c6166e96817fe03f006b Author: Jonathan Wakely <jwakely@redhat.com> Date: Tue Jun 26 22:14:29 2018 +0100 Declare some explicit instantiations for strings in Debug Mode The empty reps and the I/O functions do not need to be implicitly instantiated to enable assertions, so declare the explicit instantiations when _GLIBCXX_EXTERN_TEMPLATE == -1 (i.e. when _GLIBCXX_ASSERTIONS is defined). PR libstdc++/86138 * include/bits/basic_string.tcc: [_GLIBCXX_EXTERN_TEMPLATE < 0] Declare explicit instantiations of COW empty reps and I/O functions. diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc index 9fbea84c4af..04b68ca0202 100644 --- a/libstdc++-v3/include/bits/basic_string.tcc +++ b/libstdc++-v3/include/bits/basic_string.tcc @@ -1597,13 +1597,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // Inhibit implicit instantiations for required instantiations, // which are defined via explicit instantiations elsewhere. -#if _GLIBCXX_EXTERN_TEMPLATE > 0 +#if _GLIBCXX_EXTERN_TEMPLATE // The explicit instantiations definitions in src/c++11/string-inst.cc // are compiled as C++14, so the new C++17 members aren't instantiated. // Until those definitions are compiled as C++17 suppress the declaration, // so C++17 code will implicitly instantiate std::string and std::wstring // as needed. -# if __cplusplus <= 201402L +# if __cplusplus <= 201402L && _GLIBCXX_EXTERN_TEMPLATE > 0 extern template class basic_string<char>; # elif ! _GLIBCXX_USE_CXX11_ABI // Still need to prevent implicit instantiation of the COW empty rep, @@ -1626,7 +1626,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION getline(basic_istream<char>&, string&); #ifdef _GLIBCXX_USE_WCHAR_T -# if __cplusplus <= 201402L +# if __cplusplus <= 201402L && _GLIBCXX_EXTERN_TEMPLATE > 0 extern template class basic_string<wchar_t>; # elif ! _GLIBCXX_USE_CXX11_ABI extern template basic_string<wchar_t>::size_type @@ -1646,7 +1646,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION basic_istream<wchar_t>& getline(basic_istream<wchar_t>&, wstring&); #endif // _GLIBCXX_USE_WCHAR_T -#endif // _GLIBCXX_EXTERN_TEMPLATE > 0 +#endif // _GLIBCXX_EXTERN_TEMPLATE _GLIBCXX_END_NAMESPACE_VERSION } // namespace std
diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc index be8815c711b..9fbea84c4af 100644 --- a/libstdc++-v3/include/bits/basic_string.tcc +++ b/libstdc++-v3/include/bits/basic_string.tcc @@ -1597,8 +1597,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // Inhibit implicit instantiations for required instantiations, // which are defined via explicit instantiations elsewhere. -#if _GLIBCXX_EXTERN_TEMPLATE > 0 && __cplusplus <= 201402L +#if _GLIBCXX_EXTERN_TEMPLATE > 0 + // The explicit instantiations definitions in src/c++11/string-inst.cc + // are compiled as C++14, so the new C++17 members aren't instantiated. + // Until those definitions are compiled as C++17 suppress the declaration, + // so C++17 code will implicitly instantiate std::string and std::wstring + // as needed. +# if __cplusplus <= 201402L extern template class basic_string<char>; +# elif ! _GLIBCXX_USE_CXX11_ABI + // Still need to prevent implicit instantiation of the COW empty rep, + // to ensure the definition in libstdc++.so is unique (PR 86138). + extern template basic_string<char>::size_type + basic_string<char>::_Rep::_S_empty_rep_storage[]; +# endif + extern template basic_istream<char>& operator>>(basic_istream<char>&, string&); @@ -1613,7 +1626,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION getline(basic_istream<char>&, string&); #ifdef _GLIBCXX_USE_WCHAR_T +# if __cplusplus <= 201402L extern template class basic_string<wchar_t>; +# elif ! _GLIBCXX_USE_CXX11_ABI + extern template basic_string<wchar_t>::size_type + basic_string<wchar_t>::_Rep::_S_empty_rep_storage[]; +# endif + extern template basic_istream<wchar_t>& operator>>(basic_istream<wchar_t>&, wstring&); @@ -1626,8 +1645,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION extern template basic_istream<wchar_t>& getline(basic_istream<wchar_t>&, wstring&); -#endif -#endif +#endif // _GLIBCXX_USE_WCHAR_T +#endif // _GLIBCXX_EXTERN_TEMPLATE > 0 _GLIBCXX_END_NAMESPACE_VERSION } // namespace std diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/86138.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/86138.cc new file mode 100644 index 00000000000..224ea42a3c7 --- /dev/null +++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/86138.cc @@ -0,0 +1,30 @@ +// 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/>. + +// { dg-options "-std=gnu++17" } +// { dg-do compile { target c++17 } } +// { dg-final { scan-assembler-not "_ZNSs4_Rep20_S_empty_rep_storageE:" } } + +#undef _GLIBCXX_USE_CXX11_ABI +#define _GLIBCXX_USE_CXX11_ABI 0 +#include <string> + +void +test01(std::string* s) +{ + s->~basic_string(); +} diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/86138.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/86138.cc new file mode 100644 index 00000000000..88f136bc7bc --- /dev/null +++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/86138.cc @@ -0,0 +1,30 @@ +// 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/>. + +// { dg-options "-std=gnu++17" } +// { dg-do compile { target c++17 } } +// { dg-final { scan-assembler-not "_ZNSbIwSt11char_traitsIwESaIwEE4_Rep20_S_empty_rep_storageE:" } } + +#undef _GLIBCXX_USE_CXX11_ABI +#define _GLIBCXX_USE_CXX11_ABI 0 +#include <string> + +void +test01(std::wstring* s) +{ + s->~basic_string(); +}
The explicit instantiation declarations for std::basic_string are disabled for C++17 (and later) so that basic_string symbols get implicitly instantiated in every translation unit that needs them. On targets that don't support STB_GNU_UNIQUE this leads to multiple copies of the empty rep symbol for COW strings. In order to detect whether a COW string needs to deallocate its storage it compares the address with the empty rep. When there are multiple copies of the empty rep object the address is not unique, and so string destructors try to delete the empty rep, which crashes. In order to guarantee uniqueness of the _S_empty_rep_storage symbol this patch adds an explicit instantiation declaration for just that symbol. This means the other symbols are still implicitly instantiated in C++17 code, but for the empty rep the definition in the library gets used. Separately, there is no need for C++17 code to implicitly instantiate the I/O functions for strings, so this also restores the explicit instantiation declarations for those functions. PR libstdc++/86138 * include/bits/basic_string.tcc: [__cplusplus > 201402 && !_GLIBCXX_USE_CXX11_ABI] (basic_string<char>::_Rep::_S_empty_rep_storage) (basic_string<wchar_t>::_Rep::_S_empty_rep_storage): Add explicit instantiation declarations. [__cplusplus > 201402] (operator>>, operator<<, getline): Re-enable explicit instantiation declarations. * testsuite/21_strings/basic_string/cons/char/86138.cc: New. * testsuite/21_strings/basic_string/cons/wchar_t/86138.cc: New. Tested x86_64-linux, committed to trunk. If this passes testing on Cygwin I'll also backport it to gcc-7 and gcc-8, as the explicit instantiation declarations are disabled for C++17 on those branches. commit 798a049013ecffc0f428c0b936d3f0770471e8c6 Author: Jonathan Wakely <jwakely@redhat.com> Date: Fri Jun 22 00:10:40 2018 +0100 PR libstdc++/86138 prevent implicit instantiation of COW empty rep The explicit instantiation declarations for std::basic_string are disabled for C++17 (and later) so that basic_string symbols get implicitly instantiated in every translation unit that needs them. On targets that don't support STB_GNU_UNIQUE this leads to multiple copies of the empty rep symbol for COW strings. In order to detect whether a COW string needs to deallocate its storage it compares the address with the empty rep. When there are multiple copies of the empty rep object the address is not unique, and so string destructors try to delete the empty rep, which crashes. In order to guarantee uniqueness of the _S_empty_rep_storage symbol this patch adds an explicit instantiation declaration for just that symbol. This means the other symbols are still implicitly instantiated in C++17 code, but for the empty rep the definition in the library gets used. Separately, there is no need for C++17 code to implicitly instantiate the I/O functions for strings, so this also restores the explicit instantiation declarations for those functions. PR libstdc++/86138 * include/bits/basic_string.tcc: [__cplusplus > 201402 && !_GLIBCXX_USE_CXX11_ABI] (basic_string<char>::_Rep::_S_empty_rep_storage) (basic_string<wchar_t>::_Rep::_S_empty_rep_storage): Add explicit instantiation declarations. [__cplusplus > 201402] (operator>>, operator<<, getline): Re-enable explicit instantiation declarations. * testsuite/21_strings/basic_string/cons/char/86138.cc: New. * testsuite/21_strings/basic_string/cons/wchar_t/86138.cc: New.