https://kotlinlang.org logo
#kotlin-native
Title
# kotlin-native
n

napperley

10/26/2021, 1:42 AM
I have completely forgotten how to setup a Kotlin Native project (for a Kotlin Native program) to use a dreaded C header only library 😱. The library being used in this case is LVGL ( https://lvgl.io/ ) via its Linux Frame Buffer ( https://kevinboone.me/linuxfbc.html?i=1 ) backend. At one point I had a Kotlin Native project that successfully used a C header only library (the third party library provided some GTK Chart widgets) but can't find it 😦. @Artyom Degtyarev [JB] - Can someone please advise on how to use a C header only library in a Kotlin Native project that will generate a Linux program (an ELF binary).
Have found the magic incantation I was looking for. In the def file a linker option ( https://www.commandlinux.com/man-page/man1/gold.1.html ) needs to be passed through in order to get the linker to shutup on undefined symbols, eg:
Copy code
linkerOpts = --warn-unresolved-symbols
After applying the incantation the linking process now works 😂. What could possibly go wrong? 😆
a

Artyom Degtyarev [JB]

10/26/2021, 8:28 AM
n

napperley

10/26/2021, 9:58 PM
The Kotlin program initially started on the Raspberry Pi with printing a message (Starting LVGL Test...), but abruptly exited with the following symbol lookup error:
Copy code
undefined symbol: lv_init
Here is the project: https://gitlab.com/napperley/lvgl-hello Something is missing for including the definitions from the header files into the binary itself. I did look at the Stackoverflow link but found there was a lack of details for using a C header only library in a Kotlin Native project.
@Artyom Degtyarev [JB] - The definition for lv_init is in the lv_obj.c file, how is the definition included from that file (incl its corresponding header file) into the binary file?
a

Artyom Degtyarev [JB]

10/27/2021, 10:22 AM
So, that’s not a header-only library, correct?
👌 1
n

napperley

10/27/2021, 10:09 PM
Eventually managed to get the library working by generating static library files for both LVGL and its required LV Drivers library (provides the Linux Frame Buffer backend support - https://github.com/lvgl/lv_drivers ), however the build process is convoluted and until recently LV Drivers didn't use a build system (eg CMake).
Hopefully the LVGL team start to realise that Embedded Linux developers expect C libraries to be distributed in a form where both the header and static/dynamic library files are available or can be easily generated on the fly via a standard build system (Make or CMake).
Unfortunately I had to hard code the static library paths since the Kotlin Multiplatform Gradle plugin doesn't have the option to change the paths dynamically.
Since LLGL originated from the uC (Micro Controller) side there are some strange things done with reusable C code that would look very weird to Embedded Linux developers.
2 Views