I've also got the kernel source going with CAF history included (based on LA.UM.5.7.r1) at
https://github.com/jcadduono/android_kernel_razer_msm8998/tree/android-7.1
Fixed a minor bug and added some build scripts to simplify the process of configuring and building.
Added qcacld-3.0 sources into the kernel build for WiFi drivers but I appear to be missing something so it doesn't build. :/
I'm sure someone here can figure that out!
For TWRP support, essentially you'll need to build the stock kernel with additional options like f2fs and exFAT if desired. The OS and TWRP will be sharing the same kernel binaries due to the A/B setup so you *will* need to build the WiFi driver, even for recovery.
If someone is daring enough, they can simply build TWRP normally (ex. for a non-A/B device), flash it to boot_b or boot_a partition (depending what's active), boot up TWRP, and make backups of the opposite A/B partitions.
This can't actually be too hard to do, Dees_Troy has already done most of the work by supporting A/B on Pixel devices already.
I suppose I'm willing to give it a try if anyone is willing to possibly lose the ability to get into the OS until Razer releases factory images.
The chance of that happening is pretty slim, as long as we're only flashing the *active* boot partition (we'll check that in OS using mount command), we should be able to simply grab a copy of the opposite boot partition and restore it to how it was.
YOU CAN simply use fastboot to swap to the other boot partition, restoring your OS to bootable even if TWRP fails to work. (we will test this first to make sure Razer has enabled this option...)
Probably safe, but there's just that risk.
As I'm unsure exactly how to compile the WiFi drivers right now, I'll do this:
Create a normal TWRP image, which you can flash to your *active* boot partition.
Create a TWRP flashable zip that will take the ramdisk from the active boot partition and flash it to the inactive boot partition's boot image, then flash the inactive boot partition's image to your active boot partition.
Result: Both partitions contain the original stock kernel image with TWRP support and a fully working OS.
Slight issue: F2FS won't be supported because the stock kernel will have module signing enabled and TWRP won't be able to load it.
I'm also fairly certain I'll never get decryption working myself for this device...it looks like the vendor partition may be required and it is already encrypted itself? (not encrypted on the Pixel 2 so this is new)
