https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88782
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> --- Author: redi Date: Mon Jan 21 13:16:25 2019 New Revision: 268114 URL: https://gcc.gnu.org/viewcvs?rev=268114&root=gcc&view=rev Log: PR libstdc++/88782 avoid ODR problems in std::make_shared The old version of _Sp_counted_ptr_inplace::_M_get_deleter (up to GCC 8.2.0) expects to be passed a real std::typeinfo object, so mixing that with the new definition of the __shared_ptr constructor (which always passes the fake tag) leads to accessing the fake object as a real std::typeinfo. Instead of trying to make it safe to mix the old and new definitions, just stop using that function. By passing a reference to __shared_ptr::_M_ptr to the __shared_count constructor it can be set directly, without needing to obtain the pointer via the _M_get_deleter back-channel. This avoids a virtual dispatch (which fixes PR 87514). This means that code built against new libstdc++ headers doesn't use _M_get_deleter at all, and so make_shared works the same whether RTTI is enabled or not. Unlike on trunk, where _M_get_deleter calls a new library function that can detect the real type_info object even when RTTI is disabled, this commit for gcc-8-branch cannot add a new symbol to the shared library. That means _M_get_deleter still returns null if compiled without RTTI and it gets called from a translation unit that was compiled with RTTI. If linking to objects built against older versions of libstdc++ then if all objects use -frtti or all use -fno-rtti, then the caller of _M_get_deleter and the definition of _M_get_deleter will be consistent and it will work. If mixing -frtti with -fno-rtti it can still fail if the linker picks an old definition of _M_get_deleter and an old __shared_ptr constructor that are incompatible. In that case some or all objects might need to be recompiled (or just relinked in a different order). Backport from mainline 2019-01-18 Jonathan Wakely <jwak...@redhat.com> PR libstdc++/87514 PR libstdc++/87520 PR libstdc++/88782 * config/abi/pre/gnu.ver (GLIBCXX_3.4.26): Export new symbol. * include/bits/shared_ptr.h (shared_ptr(_Sp_make_shared_tag, const Alloc&, Args&&...)) (allocate_shared): Change to use new tag type. * include/bits/shared_ptr_base.h (_Sp_make_shared_tag::_S_eq): Declare new member function. (_Sp_alloc_shared_tag): Define new type. (_Sp_counted_ptr_inplace): Declare __shared_count<_Lp> as a friend. (_Sp_counted_ptr_inplace::_M_get_deleter) [!__cpp_rtti]: Use _Sp_make_shared_tag::_S_eq to check type_info. (__shared_count(Ptr, Deleter),__shared_count(Ptr, Deleter, Alloc)): Constrain to prevent being called with _Sp_alloc_shared_tag. (__shared_count(_Sp_make_shared_tag, const _Alloc&, Args&&...)): Replace constructor with ... (__shared_count(Tp*&, _Sp_alloc_shared_tag<_Alloc>, Args&&...)): Use reference parameter so address of the new object can be returned to the caller. Obtain the allocator from the tag type. (__shared_ptr(_Sp_make_shared_tag, const Alloc&, Args&&...)): Replace constructor with ... (__shared_ptr(_Sp_alloc_shared_tag<Alloc>, Args&&...)): Pass _M_ptr to the __shared_count constructor. (__allocate_shared): Change to use new tag type. * src/c++11/shared_ptr.cc (_Sp_make_shared_tag::_S_eq): Define. Modified: branches/gcc-8-branch/libstdc++-v3/ChangeLog branches/gcc-8-branch/libstdc++-v3/include/bits/shared_ptr.h branches/gcc-8-branch/libstdc++-v3/include/bits/shared_ptr_base.h
