I built boot.img as described on Build & Update Linux kernel on hikey970 - 96Boards.
But boot fail due to calling init failure.
I checked if there was init file. It was.
android$ ls -l out/target/product/hikey970/system/bin/init
-rwxrwxr-x 1 jole jole 640768 Oct 2 15:28 out/target/product/hikey970/system/bin/init
[ 5.618658] init: init first stage started!
[ 5.622934] init: Using Android DT directory /proc/device-tree/firmware/android/
[ 5.630411] init: [libfs_mgr]fs_mgr_read_fstab_dt(): failed to read fstab from dt
[ 5.637965] init: Failed to read fstab from device tree
[ 5.643279] init: [libfs_mgr]fs_mgr_read_fstab_default(): failed to find device default fstab
[ 5.651818] init: [libfs_mgr]fs_mgr_read_fstab_dt(): failed to read fstab from dt
[ 5.659329] init: First stage mount skipped (missing/incompatible/empty fstab in device tree)
[ 5.667884] init: Skipped setting INIT_AVB_VERSION (not in recovery mode)
[ 5.674687] init: execv("/system/bin/init") failed: No such file or directory
[ 5.681825] init: Reboot ending, jumping to kernel
[ 5.686622] kvm: exiting hardware virtualization
[ 5.691494] hifi_misc [I][360334]:hifi_reboot_notifier:1378: reboot +.
[ 5.698024] hifi_misc [I][360548]:hifi_reboot_notifier:1387: reboot -.
[ 5.705749] sd 0:0:0:3: [sdd] Synchronizing SCSI cache
[ 5.711189] sd 0:0:0:2: [sdc] Synchronizing SCSI cache
[ 5.716590] sd 0:0:0:1: [sdb] Synchronizing SCSI cache
[ 5.721989] sd 0:0:0:0: [sda] Synchronizing SCSI cache
[ 5.797919] (stk) : timed out waiting for ldisc to be un-installed[ 5.910948] (stk) :ldisc_install = 1
[ 5.921942] reboot: Restarting system with command ‘bootloader’