 | This software is old and outdated. It will likely never see an update again, and people may be unable to provide support if you use it. |
arm9loaderhax, also known as kernel9loaderhax, is an old exploit for the Nintendo 3DS. It was first publicizied in late 2015 at 32c3, with public versions available in early 2016. It was superceded by boot9strap in 2017.
Upgrading to boot9strap
The main guide has a page called A9LH to B9S, detailing the steps on upgrading a console from arm9loaderhax to boot9strap.
How it works
arm9loaderhax was detailed at 32c3. A video can be found at media.ccc.de (YouTube mirror). The presentation slides can be found on GitHub.