Please also especially look at link collection. There is tons in stuff in forums (like archived se-developers).
RTFM: See elflib wiki on mobilefree with function descriptions.
#TODO: link to english translated mobilefree-wiki
The old-school way is to use iAR Embedded Workbench 4.0 for compiling elf and dyn.
Use elf2vkpex to convert elf for vkp patch creation.
See srcs in mobilefree forum threads and
See source code snippets in se-developers.net archive and
https://github.com/justdanpo/elfpack-se
https://archive.perk11.info/svn/
https://github.com/farid1991/patch-se?tab=readme-ov-file
https://github.com/farid1991/new-patch-se
https://github.com/Rescor/SE_ELFS (also mirrored by scanlab49406)
https://github.com/NKolyanich/elfs_se
https://github.com/davicdsalves/accuweather-widget
https://github.com/davicdsalves/anoying-alarm
⚠️Info:
Please look first if you can find what you need in a repository which is still maintained.
Following is only old stuff which I have archived from vanishing www around ~2015. It may have been mirrored or forked.
deskbridge_developers_guide.pdf
google code
https://code.google.com/archive/p/centrumse/
https://code.google.com/archive/p/seelf/
https://code.google.com/archive/p/blacklizard/
source-archive_blacklizard.zip
source-archive_centrumse.zip
source-archive_developer-se.zip
source-archive_fmse.zip
source-archive_se-patch.googlecode.zip
source-archive_seelf.zip