I'd like to compile a C++ library (Jolt) so that I can use it in a Kotlin/Native application. Howeve...

# kotlin-native

[Adam S]

I'd like to compile a C++ library (Jolt) so that I can use it in a Kotlin/Native application. However, while I can compile Jolt using its own build scripts, this produces a library that's incompatible with Kotlin/Native (see this similar issue: https://youtrack.jetbrains.com/issue/KT-52275). I've tried compiling with a GCC installed with MSYS2, but this also produces an incompatible library.

I'm trying to use the g++.exe that Kotlin/Native seems to use, ~\.konan\dependencies\msys2-mingw-w64-x86_64-2\bin\g++.exe, but then I get this error:

cpp.exe: fatal error: cannot execute 'cc1plus': CreateProcess: No such file or directory

I was able to compile and use this library on a Mac using Gradle's C++ plugin, but now when I try on a Windows machine I get these errors, which is pretty disappointing. I was hoping to be able to use the library on all platforms.

[Oleg Yukhnevich]

you could try to use K/N toolchain to compile it via run_conan
more info here: https://github.com/JetBrains/kotlin/blob/master/kotlin-native/HACKING.md#running-clang-the-same-way-kotlinnative-compiler-does

[Adam S]

thanks @Oleg Yukhnevich, that sounds useful, I'll take a look!

[Adam S]

I managed to compile Jolt to .o object files! 🎉 Thanks for the tip @Oleg Yukhnevich. Next step is compiling them into a .a library...

[Oleg Yukhnevich]

it’s not compiling really 🙂 .a file is just specific achieve AFAIK
You could look into how skiko builds .a files (but there are a lot of logic there, and I don’t really remember where it happens)
you can also use run_konan for this: ./run_konan llvm llvm-ar macos_x64 - llvm-ar is used to create .a library - but Im not fully sure if it will work regarding cross compiling

[Adam S]

ahh okay, cool

[Adam S]

it doesn't look like skiko uses llvm-ar

[Oleg Yukhnevich]

Yeah, I’ve found what they use: https://github.com/JetBrains/skiko/blob/75555658e1735315df02a7b72d9b8b74ee031713/skiko/build.gradle.kts#L558
though, may be Im wrong and llvm-ar can not be used 🙂

[Adam S]

ah cool, thanks

[Adam S]

I'm on Windows, so it looks like that would trigger the error "Unexpected OS for native bridges linking"

[Oleg Yukhnevich]

yeah… I don’t use windows for a long time now, so it will be hard for me to help here…

[Adam S]

hmmm when I run run_konan llvm llvm-ar mingw_x64 it doesn't seem to recognise the args I've provided and just prints usage instructions

D:\Users\Adam\.konan\dependencies\llvm-11.1.0-windows-x64-essentials/bin/llvm-ar mingw_x64 @args
OVERVIEW: LLVM Archiver

USAGE: llvm-ar [options] [-]<operation>[modifiers] [relpos] [count] <archive> [files]
       llvm-ar -M [<mri-script]

OPTIONS:
  --format              - archive format to create
    =default            -   default
...

[Adam S]

I don’t use windows for a long time now

me neither! I was able to compile Jolt on Mac and Linux a few weeks ago.

[Adam S]

ah, it looks like adding the Kotlin target doesn't work for llvm, so it should just be ./run_konan llvm llvm-ar (not ./run_konan llvm llvm-ar mingw_x64)

[Oleg Yukhnevich]

last resort - you can look on how K/N compiler do the linking here https://github.com/JetBrains/kotlin/blob/52d6ac5ed0fe29bde09b24bdde41950811afcebb/native/utils/src/org/jetbrains/kotlin/konan/target/Linker.kt#L29
Overall, looks rather strait-forward, but I haven’t tried, so can’t help further here
Good luck!

[Adam S]

it's working it's working I got it working!!!!!

[Oleg Yukhnevich]

Nice!
BTW, is it open-sourced, or at least will be?
I would like to look on setup (for improving ffi-kotlin)

[Adam S]

yes, I plan to open source the project eventually

[Oleg Yukhnevich]

Nice! Will wait for it!

[Adam S]

https://gist.github.com/aSemy/0ec58b89f79702ea9822f198ccef0dc3

[Adam S]

that's a rough overview of the Gradle code I've got to compile the sources

[Adam S]

and here's the demo! https://i.imgur.com/sQ7mhW3.mp4

[Adam S]

sQ7mhW3.mp4

sQ7mhW3.mp4

[Oleg Yukhnevich]

Nice looking demo! and bit thanks for code snippet !