g++ -Wall -pedantic -ansi -O3   -c -o boost_serialize_protected_bug_minimal.o boost_serialize_protected_bug_minimal.cc
/usr/include/boost/serialization/base_object.hpp: In function ‘typename boost::serialization::detail::base_cast<B, D>::type& boost::serialization::base_object(Derived&) [with Base = Base2, Derived = Derived]’:
boost_serialize_protected_bug_minimal.cc:46:   instantiated from ‘void Derived::serialize(Archive&, unsigned int) [with Archive = boost::archive::text_iarchive]’
/usr/include/boost/serialization/access.hpp:109:   instantiated from ‘static void boost::serialization::access::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_iarchive, T = Derived]’
/usr/include/boost/serialization/serialization.hpp:74:   instantiated from ‘void boost::serialization::serialize(Archive&, T&, unsigned int) [with Archive = boost::archive::text_iarchive, T = Derived]’
/usr/include/boost/serialization/serialization.hpp:133:   instantiated from ‘void boost::serialization::serialize_adl(Archive&, T&, unsigned int) [with Archive = boost::archive::text_iarchive, T = Derived]’
/usr/include/boost/archive/detail/iserializer.hpp:152:   instantiated from ‘void boost::archive::detail::iserializer<Archive, T>::load_object_data(boost::archive::detail::basic_iarchive&, void*, unsigned int) const [with Archive = boost::archive::text_iarchive, T = Derived]’
boost_serialize_protected_bug_minimal.cc:59:   instantiated from here
/usr/include/boost/serialization/base_object.hpp:103: error: ‘Base2’ is an inaccessible base of ‘Derived’
/usr/include/boost/serialization/smart_cast.hpp: In static member function ‘static T boost::serialization::smart_cast_impl::pointer<T>::polymorphic::cast(U*) [with U = const Derived, T = const Base2*]’:
/usr/include/boost/serialization/smart_cast.hpp:232:   instantiated from ‘static T boost::serialization::smart_cast_impl::pointer<T>::cast(U*) [with U = const Derived, T = const Base2*]’
/usr/include/boost/serialization/smart_cast.hpp:288:   instantiated from ‘T boost::serialization::smart_cast(U) [with T = const Base2*, U = const Derived*]’
/usr/include/boost/serialization/void_cast.hpp:140:   instantiated from ‘const void* boost::serialization::void_cast_detail::void_caster_primitive<Derived, Base>::upcast(const void*) const [with Derived = Derived, Base = Base2]’
boost_serialize_protected_bug_minimal.cc:59:   instantiated from here
/usr/include/boost/serialization/smart_cast.hpp:202: error: ‘Base2’ is an inaccessible base of ‘Derived’
make: *** [boost_serialize_protected_bug_minimal.o] Error 1