Linker errors are produced when compiling a minimal example with GNU ld or GNU gold linkers

[arun5309]

Linker errors are produced when compiling a minimal example with GNU ld or GNU gold linkers both on my local machine and on godbolt.org (https://godbolt.org/z/fhGME8f6Y). It builds without any issues and runs as expected when using lld or mold linker. I have tested with gcc 12.2 and clang 15 (using libstdc++) on Void Linux (kernel version 6.6.10) on my local machine.

Also, refer to the issue opened by me here https://github.com/compiler-explorer/compiler-explorer/issues/5960.

[klemens-morgenstern]

I wonder why it works on ld and gold, when you don't actually link against the cobalt lib.

[klemens-morgenstern]

Can you please provide the linking command on your local machine? Because you're not linking against boost_cobalt on the compiler explorer.

[arun5309]

I wonder why it works on ld and gold, when you don't actually link against the cobalt lib.

It actually doesn't work with ld or gold but works with mold or lld. I should have also clearly stated that the examples provided build fine when using cmake with the provided cmake files (even with ld) but results in linker errors when I manually invoke the compiler with a command such as:-

g++ ../cobalt/build/libboost_cobalt.a basic.cpp -o basic -I../cobalt/include -std=c++20 -lboost_system -fuse-ld=gold

'libboost_cobalt.a' is getting linked here. I checked out into tags/boost-1.84.0 before building cobalt in Release mode. I also have boost 1.83 on my system from the void repository. Also, I don't need the -lboost_system flag to build the minimal example when using mold or lld.

Also, ld and gold are producing similar errors locally as the godbolt.org link above. I am copy pasting the errors I got locally here as well.

/tmp/ccOHnbJV.o:basic.cpp:function co_main(co_main(int, char**)::_Z7co_mainiPPc.Frame*) [clone .actor]: error: undefined reference to 'boost::cobalt::detail::main_promise::final_suspend()'
/tmp/ccOHnbJV.o:basic.cpp:function main::reset_res::operator()(std::pmr::memory_resource*): error: undefined reference to 'boost::cobalt::this_thread::set_default_resource(std::pmr::memory_resource*)'
/tmp/ccOHnbJV.o:basic.cpp:function main: error: undefined reference to 'boost::cobalt::this_thread::set_default_resource(std::pmr::memory_resource*)'
/tmp/ccOHnbJV.o:basic.cpp:function main: error: undefined reference to 'boost::cobalt::detail::main_promise::run_main(boost::cobalt::main)'
/tmp/ccOHnbJV.o:basic.cpp:function bool boost::cobalt::detail::promise_receiver<void>::awaitable::await_suspend<boost::cobalt::detail::fork::promise_type>(std::__n4861::coroutine_handle<boost::cobalt::detail::fork::promise_type>): error: undefined reference to 'boost::cobalt::detail::already_awaited()'
/tmp/ccOHnbJV.o:basic.cpp:function boost::cobalt::detail::promise_receiver<void>::awaitable::interrupt_await() &: error: undefined reference to 'boost::cobalt::detail::detached_exception()'
collect2: error: ld returned 1 exit status

The linker versions used locally are ld 2.39 (binutils 2.39), gold 1.16 (binutils 2.39), lld 15.0.7 and mold 2.4.0.

[arun5309]

Can you please provide the linking command on your local machine? Because you're not linking against boost_cobalt on the compiler explorer.

I have provided the compile command on the above comment. I haven't linked against boost_cobalt explicitly on the compiler explorer code as usually selecting the library links it automatically (so no need for option like -lboost_cobalt). Also, I am still getting errors on compiler explorer passing the -lboost_cobalt option explicitly.

[arun5309]

It works with gold and ld if the order of libboost_cobalt.a and basic.cpp is swapped. The following command works:-

g++ basic.cpp ../cobalt/build/libboost_cobalt.a -o basic -I../cobalt/include -std=c++20 -lboost_system -fuse-ld=gold

Not sure if this is a bug but it causes issues like when trying to use it in tools like compiler explorer.

[klemens-morgenstern]

It might be because the boost_cobalt target is conditional. I.e. it's not available if you're building with a standard below C++20.

[mitsubishirgb]

@klemens-morgenstern how do i obtain the libboost_cobalt.lib i am kinda new to cpp so i don't know how to get it, i tried to run cmake i got openssl unrecognized errors with correct paths but idk ????

[mitsubishirgb]

cmake -G "Visual Studio 17 2022" .. -DBOOST_ROOT="C:/libs/boost_1_86_0" -DBoost_NO_SYSTEM_PATHS=ON -DBoost_INCLUDE_DIR="C:/libs/boost_1_86_0" -DBoost_LIBRARY_DIR="C:/libs/boost_1_86_0/stage/lib" -DBoost_SYSTEM_LIBRARY="/libs/boost_1_86_0/stage/lib/libboost_system-vc143-mt-x64-1_86.lib" -DOPENSSL_ROOT_DIR="C:/libs/OpenSSL-Win64" -DOPENSSL_INCLUDE_DIR="C:/libs/OpenSSL-Win64/include" -DOPENSSL_SSL_LIBRARY="C:/libs/OpenSSL-Win64/lib/VC/x64/MT/libssl.lib" -DOPENSSL_CRYPTO_LIBRARY="C:/libs/OpenSSL-Win64/lib/VC/x64/MT/libcrypto.lib"

CMake Error at example/CMakeLists.txt:44 (target_link_libraries): Target "boost_cobalt_example_channel" links to:

OpenSSL::SSL

but the target was not found. Possible reasons include:

* There is a typo in the target name.
* A find_package call is missing for an IMPORTED target.
* An ALIAS target is missing.

[klemens-morgenstern]

You should build cobalt as part of boost. The above looks like you're doing something different.

Here are more details on how to build boost. https://www.boost.io/doc/user-guide/getting-started.html

[mitsubishirgb]

You should build cobalt as part of boost. The above looks like you're doing something different.

Here are more details on how to build boost. https://www.boost.io/doc/user-guide/getting-started.html

i replaced the libssl and crypto on the lib directoy of openssl and the code above worked successfully appreantly i attained the libboost_cobalt.lib and it compiles with no errors