Build gNB with C++ 17

[HaoxinSEU]

Hi community,

We are trying to build the gNB with C++ 17. In CMakeLists.txt, the default C++ version is 14. Since we want to integrate the gNB with some external modules, which require C++ 17, we want to move to 17.

However, we noticed that building the gNB with C++ 17 generates some errors.
The problem seems to be in function_signature<Sig>::return_type. Can anyone give a hint what's the reason, and if possible, how can we fix it?

Thanks for your help!

This is the log when building the gNB with C++ 17.

[ 50%] Built target srsran_gtpu
In file included from /opt/srsRAN_Project/include/srsran/support/async/detail/../coroutine.h:26,
                 from /opt/srsRAN_Project/include/srsran/support/async/detail/base_task.h:25,
                 from /opt/srsRAN_Project/include/srsran/support/async/async_task.h:25,
                 from /opt/srsRAN_Project/include/srsran/f1ap/cu_cp/f1ap_cu.h:34,
                 from /opt/srsRAN_Project/include/srsran/cu_cp/cu_cp_f1c_handler.h:25,
                 from /opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.h:25,
                 from /opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.cpp:23:
/opt/srsRAN_Project/include/srsran/support/async/detail/function_signature.h: In substitution of 'template<class Sig> using function_return_t = typename srsran::detail::function_signature::return_type [with Sig = srsran::coro_handle<void> (srsran::async_task<srsran::srs_cu_cp::cu_cp_inter_du_handover_response>::*)(srsran::coro_handle<void>) noexcept]':
/opt/srsRAN_Project/include/srsran/support/async/detail/../coroutine.h:162:13:   required from 'bool srsran::detail::base_coro_frame<Promise>::on_await_call(Awaitable&&) [with Awaitable = srsran::async_task<srsran::srs_cu_cp::cu_cp_inter_du_handover_response>; Promise = srsran::async_task<void>::promise_type]'
/opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.cpp:95:5:   required from here
/opt/srsRAN_Project/include/srsran/support/async/detail/function_signature.h:60:7: error: invalid use of incomplete type 'struct srsran::detail::function_signature<srsran::coro_handle<void> (srsran::async_task<srsran::srs_cu_cp::cu_cp_inter_du_handover_response>::*)(srsran::coro_handle<void>) noexcept>'
   60 | using function_return_t = typename function_signature<Sig>::return_type;
      |       ^~~~~~~~~~~~~~~~~
/opt/srsRAN_Project/include/srsran/support/async/detail/function_signature.h:33:8: note: declaration of 'struct srsran::detail::function_signature<srsran::coro_handle<void> (srsran::async_task<srsran::srs_cu_cp::cu_cp_inter_du_handover_response>::*)(srsran::coro_handle<void>) noexcept>'
   33 | struct function_signature;
      |        ^~~~~~~~~~~~~~~~~~
In file included from /opt/srsRAN_Project/include/srsran/support/async/detail/base_task.h:25,
                 from /opt/srsRAN_Project/include/srsran/support/async/async_task.h:25,
                 from /opt/srsRAN_Project/include/srsran/f1ap/cu_cp/f1ap_cu.h:34,
                 from /opt/srsRAN_Project/include/srsran/cu_cp/cu_cp_f1c_handler.h:25,
                 from /opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.h:25,
                 from /opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.cpp:23:
/opt/srsRAN_Project/include/srsran/support/async/detail/../coroutine.h: In instantiation of 'bool srsran::detail::base_coro_frame<Promise>::on_await_call(Awaitable&&) [with Awaitable = srsran::async_task<srsran::srs_cu_cp::cu_cp_inter_du_handover_response>; Promise = srsran::async_task<void>::promise_type]':
/opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.cpp:95:5:   required from here
/opt/srsRAN_Project/include/srsran/support/async/detail/../coroutine.h:163:13: error: invalid use of incomplete type 'struct srsran::detail::function_signature<srsran::coro_handle<void> (srsran::async_task<srsran::srs_cu_cp::cu_cp_inter_du_handover_response>::*)(srsran::coro_handle<void>) noexcept>'
  163 |       using no_tail_resume_tag = std::is_same<void, suspend_return_t>;
      |             ^~~~~~~~~~~~~~~~~~
In file included from /opt/srsRAN_Project/include/srsran/support/async/detail/../coroutine.h:26,
                 from /opt/srsRAN_Project/include/srsran/support/async/detail/base_task.h:25,
                 from /opt/srsRAN_Project/include/srsran/support/async/async_task.h:25,
                 from /opt/srsRAN_Project/include/srsran/f1ap/cu_cp/f1ap_cu.h:34,
                 from /opt/srsRAN_Project/include/srsran/cu_cp/cu_cp_f1c_handler.h:25,
                 from /opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.h:25,
                 from /opt/srsRAN_Project/lib/cu_cp/mobility_manager/mobility_manager_impl.cpp:23:
/opt/srsRAN_Project/include/srsran/support/async/detail/function_signature.h:33:8: note: declaration of 'struct srsran::detail::function_signature<srsran::coro_handle<void> (srsran::async_task<srsran::srs_cu_cp::cu_cp_inter_du_handover_response>::*)(srsran::coro_handle<void>) noexcept>'
   33 | struct function_signature;
      |        ^~~~~~~~~~~~~~~~~~
make[3]: *** [lib/cu_cp/mobility_manager/CMakeFiles/srsran_cu_cp_mobility_manager.dir/build.make:63: lib/cu_cp/mobility_manager/CMakeFiles/srsran_cu_cp_mobility_manager.dir/mobility_manager_impl.cpp.o] Error 1
make[2]: *** [CMakeFiles/Makefile2:6839: lib/cu_cp/mobility_manager/CMakeFiles/srsran_cu_cp_mobility_manager.dir/all] Error 2

[HaoxinSEU]

Hi all,

We managed to build the gNB with C++ 17, and the UE can connect. Here are the modifications we made:

In include/srsran/support/async/detail/function_signature.h:63, add two more declaration for noexcept and const noexcept:

template <typename Ret, typename Obj, typename... Args>
struct function_signature<Ret (Obj::*)(Args...) noexcept> {
  using return_type = Ret;
  using arg_types   = type_list<Args...>;
};

template <typename Ret, typename Obj, typename... Args>
struct function_signature<Ret (Obj::*)(Args...) const noexcept> {
  using return_type = Ret;
  using arg_types   = type_list<Args...>;
};

In include/srsran/support/math_utils.h:198, add the namespace of srsran for clamp:

return srsran::clamp(value, lower_bound, upper_bound, std::less<T>());

Finally in CMakeLists.txt, change the C++ version and add linked libaray -lm:

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -lm -Wall")

The reason for the previous error: In the original file, it only defines for const. But in some places, they are called with noexcept and const noexcept, which cannot match and thus falls to the empty default one.

[pgawlowicz]

@HaoxinSEU Thank you for your investigation.
@frankist could you have a look here?

[frankist]

Thanks for the support @HaoxinSEU. There is some extra stuff we have to look into before the transition to c++17, in particular, the use of std::launder in some places in our utility libraries. I will update this discussion once we incorporate all the required changes.

[HaoxinSEU]

Thanks for the information @frankist! Yeah our goal is just to make it compile with C++ 17, so that we can integrate some submodules. Looking forward to the official updates!