In a Kotlin Multiplatform project that is targetin...

# kotlin-native

[napperley]

In a Kotlin Multiplatform project that is targeting linuxArm32Hfp if Kotlin 1.5.0 or later is used then a boatload of undefined reference errors appear (at the linking stage), eg:

/home/napperley/.konan/dependencies/arm-unknown-linux-gnueabihf-gcc-8.3.0-glibc-2.19-kernel-4.9-2/arm-unknown-linux-gnueabihf/bin/ld.bfd: /mnt/pi_image/usr/lib/arm-linux-gnueabihf/libgdk-3.so: undefined reference to `wl_display_dispatch_pending'

However if Kotlin 1.4.31 is used then none of the errors appear, and the build is successful.

In the build output there are a boatload of warnings about missing libraries (at the linking stage) if Kotlin 1.5.0 or later is used, eg:

/home/napperley/.konan/dependencies/arm-unknown-linux-gnueabihf-gcc-8.3.0-glibc-2.19-kernel-4.9-2/arm-unknown-linux-gnueabihf/bin/ld.bfd: warning: libpcre.so.3, needed by /mnt/pi_image/usr/lib/arm-linux-gnueabihf/libglib-2.0.so, not found (try using -rpath or -rpath-link)

Are there some additional linking options that need to be passed to the linker to resolve the errors, and if so which ones?

[napperley]

Found an elegant solution (works with Kotlin 1.5.20) which involved adding the --allow-shlib-undefined flag to linkerOpts for the linuxArm32Hfp target (not the linuxX64 target) in the gtk3.def files, eg:

linkerOpts = -lgtk-3 -lgdk-3 -latk-1.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lcairo-gobject -lpango-1.0 -lcairo
linkerOpts.linux_x64 = -L/usr/lib/x86_64-linux-gnu
linkerOpts.linux_arm32_hfp = --allow-shlib-undefined -L/mnt/pi_image/usr/lib/arm-linux-gnueabihf

[napperley]

The Kotlin team will probably recoil in horror, however the solution is straightforward, and doesn't require using a custom built version of Kotlin Native, which wouldn't be straightforward and would involve too much effort with very little gain.

[napperley]

I'm not sure which version of gold (the linker) is used by the Kotlin Native linuxArm32Hfp toolchain. Found the flag in the Ubuntu 20.04 documentation for the gold linker: https://manpages.ubuntu.com/manpages/focal/man1/ld.gold.1.html

[napperley]

With the right combination of flags the new linker might behave just like the old linker 😀 , in which case it will be like Kotlin has always used the same linker even though the linker has changed 😆 .

[napperley]

I wonder if something similar can be done to resolve this issue: https://youtrack.jetbrains.com/issue/KT-43501 🤔

[napperley]

My gut feeling is that the Kotlin Native program will run just fine after applying the --allow-shlib-undefined linker option. Essential for cross compilation with the Linux ARM targets.

[napperley]

Looks like the library path for libcurl isn't correct. The library path should look similar to the following: /usr/lib/x86_64-linux-gnu

What has linkeropts been set to in the def file?

[andylamax]

there is no def file at all. Just some common code compiling to linuxX64 target. Also, using ktor-client-curl as a dependency, might the be the issue?

[napperley]

If you use a def file in the project then you can override the linker settings that are provided by the ktor-client-curl library.

[napperley]

The standard path for def files in a project is src/nativeInterop/cinterop .Below is an example of a def file:

headers = curl.h
linkerOpts = -L/usr/lib/x86_64-linux-gnu -lcurl

[napperley]

To get Kotlin's Multiplatform plugin to pick up the def file you need to create the cinterop, eg:

// ...
kotlin {
  linuxX64 {
    // ...
    cinterops.create("curl") {
      includeDirs("/usr/include/x86_64-linux-gnu/curl")
    }
  }
}
// ...

With the example above the cinterop is being created for the curl.def file.

[andylamax]

Thanks will try that. Do I have to add this, on every project that I use with ktor-client-curl?

[andylamax]

then why do I have to add the cinteropes?

[napperley]

Usually the linker settings specified in ktor-client-curl are correct. The library should just work on Linux distributions like Linux Mint 20, and Ubuntu 20.04 for example.

[napperley]

In cases where the linking fails a def file will be needed.

[andylamax]

you have been of great help to me. Let me try that when I am on laptop, will give feedback on how it goes. Much much thanks for taking your time on this

[napperley]

Linking settings do differ between Linux distributions. What works for Debian, Ubuntu, and Linux Mint won't work with Red Hat and Fedora for example.

[napperley]

Currently I am assuming that you are using Linux as the host.

[andylamax]

Yes linux as the host. Using Linux Zorin OS, a debian based distro

[andylamax]

Apparently, installing curl alone didn't install libcurl
apt-get install libcurl4-openssl-dev did the trick. Thanks alot for your help. My linux tests are passing now

[napperley]

If you remove the def file, and the Gradle build logic for creating the cinterop then the linking should still work without any issues.

[andylamax]

yes it does, thanks once again