WARNING: I'm not responsible for any damage to your device. Backup your data, do this at your own risk.
1. Download new firmware for your phone following the steps from this section: https://harrytang.xyz/blog/download-xperia-firmware-flashtool
2. Open the downloaded .ftf firmware using a zip application (7z, WinZip) and extract kernel.sin.
3. Run Flashtool, open Tools -> SIN Editor, select extracted kernel.sin from step 2 then click Extract data, you will end up with kernel.elf.
4. Download rootkernel (v5.20) and extract it (credit to tobias.waldvogel).
5. Go to the extracted rootkernel folder, create boot.img by running this command:
rootkernel kernel.elf boot.img
You will see the output like below:
- Unpacking kernel
Found elf boot image
Kernel version: 3.10.84-perf-gda8446f
Found appended DTB
- Detected vendor: somc (Sony), device: ivy (Xperia Z3+/Z4), variant: dsds
- Unpacking initramfs
- Detected platform: 64-bit
- Detected Android version: 7.0
- dm-verity is enabled. Disable? (Say yes if you modify /system) [Y/n] Y
Disabling dm-verity
- Sony RIC is enabled. Disable? [Y/n] Y
Disabling Sony RIC
- Install TWRP recovery? [Y/n] Y
Installing TWRP
Compressing TWRP image
- Found SuperSU-v2.79-201612051815.zip. Install? [Y/n] Y
Adding service entry for SuperSU
- Install DRM fix? [Y/n] Y
- Install busybox? [Y/n] Y
- Creating new initramfs
- Creating boot image
- Cleaning up
Done
6. Flash the download .ftf firmware using Flashtool, ensure that no option in the “Wipe” pane is ticked:
7. Enter fastboot mode (Poweroff, hold volume up and insert USB cable) to flash the boot.img from step 5:
fastboot flash boot boot.img
Reboot your phone and enejoy new software without losing root :)
