Hey guys. How do I say Kotlin/Native to link my cI...

# kotlin-native

[salomonbrys]

Hey guys.
How do I say Kotlin/Native to link my cInterop library to link against the C++11 standard library ?
I'm having a whole lot of undefined symbol: std::__cxx11::basic_string... error at linkage.
My library is a C interface to some OpenCV features. I have libopencv-dev installed on my computer.
Because my C wrapper transforms const char* into std::string , I can't compile my it with -D_GLIBCXX_USE_CXX11_ABI=0 (then I get undefined symbol errors on all OpenCV method I use that takes a std::string because the ABI is different).
The only solution I see is to download and re-compile OpenCV and all its dependencies with -D_GLIBCXX_USE_CXX11_ABI=0 , which is an enormous hassle.
Is there a way to instruct the Kotlin/Native linker to link against the C++11 standard library ?

[natario1]

If I remember correctly there is a cinterop flag that tells Kotlin to not transform const chars into Strings. Not sure if that helps

[salomonbrys]

Nope. Sorry. This is about c-interop generated API.
This is about C++11 ABI.

[natario1]

Oh I read it wrong. I thought cinterop was the one transforming chars into Strings

[Markus Böck]

Shouldn't libopencv-dev be compiled with your system compiler and therefore with your system stdlibc++ and its ABI? Also simply setting that flag won't change the ABI. You'd actually have to recompile GCC and libstdc++ to do that since libstdc++.so would also have to change. I think there is something else going on. Maybe you need to explicitly specify -lstdc++ in the linker flags? I don't know if kotlin does that for you

[salomonbrys]

-lstdc++ doesn't change anything.

[salomonbrys]

I'm able to compile a demo C++ command line app from the static library, no problems there.

[salomonbrys]

The problem only arises when K/N compiler tries to link its C-Interop lib with my static lib.

[Markus Böck]

Does Kotlin native even use the system compiler actually?

[salomonbrys]

Nope 😉
It uses its own compiler toolchain

[Markus Böck]

Yeah that's probably where the problem lies

[Markus Böck]

If you know what the path to the compiler toolchain is that it downloads you can run ./gcc -v and it'll show you with what config it was compiled with and compare it to your system compiler

[Markus Böck]

Might want to raise an issue on Github. On Linux they have to use the system compiler I am pretty sure. Although that makes shipping their own runtime a pain possibly

[napperley]

On the Linux side Kotlin Native uses its own compiler. Below are some of the contents from the toolchain for the linuxX64 target:

target-gcc-toolchain-3-linux-x86-64/bin
├── x86_64-unknown-linux-gnu-addr2line
├── x86_64-unknown-linux-gnu-ar
├── x86_64-unknown-linux-gnu-as
├── x86_64-unknown-linux-gnu-c++
├── x86_64-unknown-linux-gnu-cc -> x86_64-unknown-linux-gnu-gcc
├── x86_64-unknown-linux-gnu-c++filt
├── x86_64-unknown-linux-gnu-cpp
├── x86_64-unknown-linux-gnu-ct-ng.config
├── x86_64-unknown-linux-gnu-dwp
├── x86_64-unknown-linux-gnu-elfedit
├── x86_64-unknown-linux-gnu-g++
├── x86_64-unknown-linux-gnu-gcc
├── x86_64-unknown-linux-gnu-gcc-4.8.5
├── x86_64-unknown-linux-gnu-gcc-ar
├── x86_64-unknown-linux-gnu-gcc-nm
├── x86_64-unknown-linux-gnu-gcc-ranlib
├── x86_64-unknown-linux-gnu-gcov
├── x86_64-unknown-linux-gnu-gdb
├── x86_64-unknown-linux-gnu-gprof
├── x86_64-unknown-linux-gnu-ld
├── x86_64-unknown-linux-gnu-ld.bfd
├── x86_64-unknown-linux-gnu-ldd
├── x86_64-unknown-linux-gnu-ld.gold
├── x86_64-unknown-linux-gnu-nm
├── x86_64-unknown-linux-gnu-objcopy
├── x86_64-unknown-linux-gnu-objdump
├── x86_64-unknown-linux-gnu-populate
├── x86_64-unknown-linux-gnu-ranlib
├── x86_64-unknown-linux-gnu-readelf
├── x86_64-unknown-linux-gnu-size
├── x86_64-unknown-linux-gnu-strings
└── x86_64-unknown-linux-gnu-strip

All of this comes from the ~/.konan/dependencies directory.

[Markus Böck]

Yeah that's an "ancient" version of GCC that doesn't use C++11 ABI. Any Linux distro that uses GCC 5 or higher will basically not be able to link its system libraries with Kotlin native I believe. Seems to be quite the huge oversight.

[napperley]

One of the big advantages with Kotlin Native having it own toolchain is that setting up the toolchain is quick and easy. Its all automated by Kotlin Native for you 😁 .

[Markus Böck]

Better to be functional than beautiful