[Samsung Gear S3] tids2k:
THIS IS WHAT I KNOW SO FAR

1. There was a port done on the Gear S2 forums by biktor_bj

Partition layout he used :

Partition layout

bota0 -> ../../mmcblk0p1
bota1 -> ../../mmcblk0p2
csa -> ../../mmcblk0p3 --> ext4 -> /csa
boot -> ../../mmcblk0p5 --> Main Kernel
csc -> ../../mmcblk0p12 --> ext4 -> /system/csc
fota -> ../../mmcblk0p10 --> seems empty
ramdisk-recovery -> mmcblk0p8 -> ext4 -> Unused in tizen --> USED AS BOOT PARTITION IN ANDROID
module -> ../../mmcblk0p9 --> ext4 -> /lib/modules --> USED FOR TWRP IN ANDROID
rootfs -> ../../mmcblk0p15 ext4 "/" --> Root file system, recovery works from here too. If you break it it will only boot to download mode. --> USED AS SYSTEM PARTITION IN ANDROID
system -> ../../mmcblk0p11 EMPTY --> Did samsung start with Android on this thing then changed their minds?
system-data -> ../../mmcblk0p13 --> ext4, /opt --> If you erase this partition, your watch won't boot back into Tizen. Do not touch it unless you have a backup and know your way into restoring it.
user -> ../../mmcblk0p14 EXT4, /opt/usr --> all user data, including the MTP available part (/opt/usr/media) --> USED AS DATA & SDCARD IN ANDROID

Partition table on our device:

sh-3.2# ls -l /dev/disk/by-partlabel
total 0
lrwxrwxrwx 1 root root 15 Apr 6 09:52 boot -> ../../mmcblk0p8
lrwxrwxrwx 1 root root 15 Apr 6 09:52 cm -> ../../mmcblk0p7
lrwxrwxrwx 1 root root 15 Apr 6 09:52 cpnvcore -> ../../mmcblk0p3
lrwxrwxrwx 1 root root 15 Apr 6 09:52 csa -> ../../mmcblk0p2
lrwxrwxrwx 1 root root 16 Apr 6 09:52 csc -> ../../mmcblk0p11
lrwxrwxrwx 1 root root 16 Apr 6 09:52 module -> ../../mmcblk0p10
lrwxrwxrwx 1 root root 15 Apr 6 09:52 param -> ../../mmcblk0p6
lrwxrwxrwx 1 root root 15 Apr 6 09:52 ramdisk1 -> ../../mmcblk0p5
lrwxrwxrwx 1 root root 15 Apr 6 09:52 ramdisk2 -> ../../mmcblk0p4
lrwxrwxrwx 1 root root 15 Apr 6 09:52 recovery -> ../../mmcblk0p9
lrwxrwxrwx 1 root root 16 Apr 6 09:52 rootfs -> ../../mmcblk0p14
lrwxrwxrwx 1 root root 16 Apr 6 09:52 steady -> ../../mmcblk0p15
lrwxrwxrwx 1 root root 16 Apr 6 09:52 system-data -> ../../mmcblk0p12
lrwxrwxrwx 1 root root 15 Apr 6 09:52 tup -> ../../mmcblk0p1
lrwxrwxrwx 1 root root 16 Apr 6 09:52 user -> ../../mmcblk0p13

His GITHUB commits to kernel and device tree are here:

https://github.com/Biktorgj/Android_b2_Kernel
https://www.mediafire.com/folder/092gaz7gudh0f/Gear2#092gaz7gudh0f

2. Now the Google's android wear does support Exynos platform which is here:

https://android.googlesource.com/kernel/exynos/+/android-exynos-3.4
https://android.googlesource.com/kernel/msm/+/android-8.1.0_r0.27

3. This is the kernel tree from an exynos watch ( sorry forgot the name of the watch maybe casio wd-1000)

https://android.googlesource.com/kernel/exynos/+/android-exynos-koi-3.18-nougat-mr1-wear-release

4. LG Urbane 2 LTEAndroid Wear 2.0 Image

http://storage.googleapis.com/androiddevelopers/shareables/wear-preview/nemo-mnc40x-factory-fa528bec.tgz

5. Huawie Android Wear 2.0 Image

http://storage.googleapis.com/androiddevelopers/shareables/wear-preview/sturgeon-mec23l-factory-48003078.tgz

5. Official Samsung source code for SM-R7XX devices

https://opensource.samsung.com/reception/receptionSub.do?method=sub&sub=F&searchValue=SM-R760

No one is an expert here who can build a kernel for the device. I hope this info helps.

If you can teach me to how to build a kernel, I can definately help :)

Vulnerbaility which can be used for the bootloader:

https://alephsecurity.com/2018/01/22/qualcomm-edl-1/

SBoot - Samsung Bootloader Dissection

https://blog.quarkslab.com/reverse-engineering-samsung-s6-sboot-part-ii.html
http://hexdetective.blogspot.com.au/2017/02/exploiting-android-s-boot-getting.html

Tizen Boot Process

https://docs.tizen.org/docs/open-source-tizen/porting/kernel.page

Also looked at your thread "Fastboot for ARM/ARM64" :)

I will update more I can remember.