     alloc.allocate(stack_ctx, stack_size);
     my_context = bc::make_fcontext( stack_ctx.sp, stack_ctx.size, sf);
#elif BOOST_VERSION >= 105300
     size_t stack_size = FC_CONTEXT_STACK_SIZE;
     void*  stackptr = alloc.allocate(stack_size);
     my_context = bc::make_fcontext( stackptr, stack_size, sf);
#else
     size_t stack_size = FC_CONTEXT_STACK_SIZE;
     my_context.fc_stack.base = alloc.allocate( stack_size );
     my_context.fc_stack.limit = static_cast<char*>( my_context.fc_stack.base) - stack_size;
     make_fcontext( &my_context, sf );
#endif
    }