Android

The thing is, "building a kernel" for Linux is NOTHING compared to a custom ROM. Linux Kernel:

• one repo, just clone it
• tooling to easily build it, just set some flags
• a huge monokernel, not including the entire OS and all the SOC stuff

Android is different. It doesnt use a huge monokernel. They use mostly the upstream kernel, but the drivers are not in there afaik. There are many proprietary parts also in the firmware. And those come from the hardware suppliers, signed by them, you cant replace it. This totally sucks.

If you look at it the Laptop market is equally bad as firmwares are often not updated at all. But every system simply continues to run, so nobody cares.

On Android its all one thing. A distro / custom OS (ROM is not correct, the OS is not read only otherwise you cant change it, lol) deals with all of that.

Look at the GrapheneOS information articles. They explain very well what they all do to make AOSP

• secure with monthly updates
• hardened in maaany areas
• functional (removing Vendor app dependency, integrating some Pixel and even Samsung components, Sandboxed Play services, ...)

Its a on of work to REALLY support a device, its simply a real OS. LineageOS or even worse PostmarketOS are just random projects often. Using some generic software with missing firmware updates and timely security patches.

It works, somehow. But it is nothing worth investing a lot of time in really, if the phone is not super special.

Just get a used Google Pixel ≥ 6a and install GrapheneOS. Contribute Code to healthy upstream projects.

The work for supporting a single device is insane. And samsung is especially shit, security features would be close to Pixels but they block lots of features for alternative OSses and different software everywhere. Also completely anti-repairable.

My answer is not going to be complete in any way, but your biggest problem is going to be getting your hands on kernel sources that build and that actually work for your hardware.

To complicate the matter, not any kernel will do. The kernel you use must support the Android userspace you want. You cannot arbitrarily pair your kernel version with your Android version. Further, the state of open source kernels on Android is quite poor. Many vendors--Samsung for example release kernel sources but they're not actually in a buildable, usable state. If you're just starting out, I would recommend starting with a Pixel where you know you will have sufficient sources to produce a compatible kernel, else you have the unenviable task of patching together something that works from the bits and pieces that get released that comply with the letter of the GPL but not the spirit of it.

Whether or not you can even build a custom ROM for a device is largely a matter of opportunity and whether the resources you need actually exist to begin building one.

if there are no custom roms for your device you should just give up. it requires so much resources that it's almost tiring. If you really want to build lineage for your phone though, there's a guide on lineage wiki to port the rom. It's really easy, you just have to download the source code of the rom, add the source code of your phone with its proprietary blobs, then build. The hard part is wether you have the hardware to build or no. You need: 64gb of ram, ccache and zram enabled, 300gbs of storage, and an 8 cores cpu

I'm a beginner as well and I found Alaska Linux user channel on yt a good source for explanations. First videos are a bit outdated... some new tech like Soong was introduced - which is a new, google developed, build system for Android.

https://www.youtube.com/channel/UCnGqG_jyyXmTzdamBpKfeHA

Go to the playlist section. It groups videos per topic, e.g. building a device tree from scratch.

S8 is a not a good choice If I remember correctly, no custom roms exist for that phone. Reasons might be due to exynos of that era...