[llvm-bugs] [Bug 45953] New: Code for virtual function not generated

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45953

            Bug ID: 45953
           Summary: Code for virtual function not generated
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++17
          Assignee: unassignedclangbugs at nondot.org
          Reporter: profclonk at gmail.com
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

Created attachment 23496
  --> https://bugs.llvm.org/attachment.cgi?id=23496&action=edit
Test code

For the attached C++17 code involving Boost.Beast, clang++ gives an "undefined
symbol" error (full message below). It appears that the code for the function
"boost::beast::stable_async_base<...>::before_invoke_hook()" is not generated,
leading to the error. It works with g++.

The error occurs with the LLVM 10.0.0 prebuilt binary for Ubuntu x86_64 and
using the Boost library version 1.73.0, on Linux Mint 19.3. It happens with
both LD and LLD. The Boost libraries were compiled with clang as well, but I
think this is not really relevant as the missing function is a template and
should be generated when compiling the application.

The code is compiled with "clang++ test.cpp -fuse-ld=lld -lboost_system
-pthread -lssl -lcrypto".

This is the missing function:
https://github.com/boostorg/beast/blob/boost-1.73.0/include/boost/beast/core/async_base.hpp#L193

The attached code of course makes zero sense, but appears to be the minimal
amount that reproduces the problem. It is unnecessarily contrived and I have
since been pointed to a better (and working) solution, but there may still be a
bug in Clang/LLVM that could be worth fixing.

The full linker error is:

ld.lld: error: undefined symbol: boost::beast::stable_async_base<void
LoaderConnection::onResolve<int>(int&&, boost::system::error_code const&,
boost::asio::ip::basic_resolver_results<boost::asio::ip::tcp>
const&)::'lambda'(boost::system::error_code const&, unsigned long),
boost::asio::executor, std::allocator<void> >::before_invoke_hook()
>>> referenced by test.cpp
>>>               /tmp/test-223f2a.o:(vtable for boost::beast::http::detail::write_msg_op<void LoaderConnection::onResolve<int>(int&&, boost::system::error_code const&, boost::asio::ip::basic_resolver_results<boost::asio::ip::tcp> const&)::'lambda'(boost::system::error_code const&, unsigned long), boost::beast::ssl_stream<boost::beast::basic_stream<boost::asio::ip::tcp, boost::asio::executor, boost::beast::unlimited_rate_policy> >, true, boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >)
>>> referenced by test.cpp
>>>               /tmp/test-223f2a.o:(vtable for boost::beast::stable_async_base<void LoaderConnection::onResolve<int>(int&&, boost::system::error_code const&, boost::asio::ip::basic_resolver_results<boost::asio::ip::tcp> const&)::'lambda'(boost::system::error_code const&, unsigned long), boost::asio::executor, std::allocator<void> >)

ld.lld: error: undefined symbol:
boost::beast::detail::allocate_stable_state<boost::beast::http::serializer<true,
boost::beast::http::empty_body,
boost::beast::http::basic_fields<std::allocator<char> > >, std::allocator<void>
>::~allocate_stable_state()
>>> referenced by test.cpp
>>>               /tmp/test-223f2a.o:(vtable for boost::beast::detail::allocate_stable_state<boost::beast::http::serializer<true, boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >, std::allocator<void> >)

ld.lld: error: undefined symbol:
boost::beast::detail::allocate_stable_state<boost::beast::http::serializer<true,
boost::beast::http::empty_body,
boost::beast::http::basic_fields<std::allocator<char> > >, std::allocator<void>
>::~allocate_stable_state()
>>> referenced by test.cpp
>>>               /tmp/test-223f2a.o:(vtable for boost::beast::detail::allocate_stable_state<boost::beast::http::serializer<true, boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >, std::allocator<void> >)

ld.lld: error: undefined symbol:
boost::beast::detail::allocate_stable_state<boost::beast::http::serializer<true,
boost::beast::http::empty_body,
boost::beast::http::basic_fields<std::allocator<char> > >, std::allocator<void>
>::destroy()
>>> referenced by test.cpp
>>>               /tmp/test-223f2a.o:(vtable for boost::beast::detail::allocate_stable_state<boost::beast::http::serializer<true, boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >, std::allocator<void> >)
clang-10: error: linker command failed with exit code 1 (use -v to see
invocation)

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