I can't post photo, but it shows samsung label, yellow exclamation point with text "The tablet is not running Samsung official software..." and some other text at the top left corner of the screen that I don't understand:
Current Binary: Custom (0x30E)
FRP LOCK : OFF
OEM LOCK: ON (U)
KG STATUS: CHECKING
WARRANTY VOID : 0x1 (0x0)
RP SWREV : <some number>
QUALCOMM SECUREBOOT: ENABLE
SECURE DOWNLOAD : ENABLE
ENG MODE : DEV DEVICE
DID : <some number>
I wan't simple to build kernel (maybe rebuild stock) before try to change it.
Maybe I compiled it somehow wrong? I got sources from http://opensource.samsung.com/reception.do (search for sm-t725)
I packed kernel with mkbootimg, I also packed the original kernel to boot.img and it boots well, so there can't be mistake.
Maybe something is wrong with security, perhaps vbmeta, but I flashed vbmeta patition by instruction of installing Lineage OS for this device and think that all security mehanisms are disabled.
From recovery I can get /proc/last_kmsg but I don't know what to search for.
I can post it, and also can post kernel config file.