Can’t seem to add cores to storage/cores. The ones I tried have the *.info file already in the build.
For example, I tried to add MAME2003+ (extracted the *.so from http://raw.libretro.com/nightly/linux/armhf/latest/mame2003_plus_libretro.so.zip), it shows up in select cores, but once selected Retroarch just restarts.
Why did it not work?
Which version of Lakka are you using? I suspect that the latest Lakka is using a different kernel/libc than the one used to compile the nightly RetroArch Cores.
2.3.1 for the rpi Zero / GPi
http://le.builds.lakka.tv/RPi.GPICase.arm/Lakka-RPi.GPICase.arm-2.3.1.img.gz
If so, is there an archive for older cores? Any other MAME2003+ core I could try?
I think the only way is to compile the cores for Lakka manually.
Out of curiosity: What is wrong with the mame2003+ preinstalled in LAKKA?
Usually you don’t need to add cores manually.
[EDIT] i noticed LAKKA has only the mame2000 core installed.
From https://wiki.debian.org/RaspberryPi:
The CPU in the Raspberry Pi 1 and Zero implements the ARMv6 ISA (with VFP2) and is thus incompatible with the Debian armhf port baseline of ARMv7+VFP3 and ARM hardware-floating-point ports for other distributions, which all have the same baseline. It is compatible with Debian armel (armv4t, soft(emulated) FP), but floating-point tasks will be slow when running the Debian armel port. (This doesn’t stand for newer families)
This means you have to compile it yourself as @duduke said
Thank you, now it makes sense.