Changes here work for Oreo and Nougat boot images since 8.1 final. Ensure that all changes are best applied to your boot image if you are looking to patch it.
The boot image had been unpacked by the Android Image Kitchen by @osm0sis: https://forum.xda-developers.com/showthread.php?t=2073775
Details at XDA: https://forum.xda-developers.com/nexus-6p/general/guide-tutorial-nexus-6p-bootloop-death-t3716330