a942dfca6a
The implementations of std::make_shared for -frtti and -fno-rtti are not compatible, because they pass different arguments to _Sp_counted_ptr_inplace::_M_get_deleter and so can't interoperate. Either the argument doesn't match the expected value, and so the shared_ptr::_M_ptr member is never set, or the type-punned reference is treated as a real std::type_info object and gets dereferenced. This patch removes the differences between -frtti and -fno-rtti, so that typeid is never used, and the type-punned reference is used in both cases. For backwards compatibility with existing code that passes typeid(_Sp_make_shared_tag) that still needs to be handled, but only after checking that the argument is not the type-punned reference (so it's safe to treat as a real std::type_info object). The reference is bound to an object of literal type, so that it doesn't need a guard variable to make its initialization thread-safe. This patch also fixes 87520 by ensuring that the type-punned reference is bound to "a region of storage of suitable size and alignment to contain an object of the reference's type" (as per the proposed resolution of Core DR 453). If all objects are built with the fixed version of GCC then -frtti and -fno-rtti can be mixed freely and std::make_shared will work correctly. If some objects are built with unfixed GCC versions then problems can still arise, depending on which template instantiations are kept by the linker. PR libstdc++/85930 PR libstdc++/87520 * include/bits/shared_ptr_base.h (_Sp_make_shared_tag::_S_ti) [__cpp_rtti]: Define even when RTTI is enabled. Use array of sizeof(type_info) so that type-punned reference binds to an object of the correct size as well as correct alignment. (_Sp_counted_ptr_inplace::_M_get_deleter) [__cpp_rtti]: Check for _S_ti() reference even when RTTI is enabled. (__shared_ptr(_Sp_make_shared_tag, const _Alloc&, _Args&&...)) [__cpp_rtti]: Pass _S_ti() instead of typeid(_Sp_make_shared_tag). From-SVN: r266376 |
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README
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