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EXTENDROM_PREROOT_BOOT (legacy)

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steadfasterX edited this page Oct 4, 2023 · 1 revision

EXTENDROM_PREROOT_BOOT

WARNING

This method is deprecated as of now and replaced by this

WARNING

State

State Branch Supported Android version(s) Tested on Howto Guide
DEPRECATED any magisk_xx A9, A10, A11, A12, A13 A9, A10, A11, A12, A13 see here

Flags

flag values meaning where to configure
EXTENDROM_PREROOT_BOOT can be unset or true must be true to activate patching a boot.img with MAGISK device/<vendor>/<model>/vendorsetup.sh or device/<vendor>/<model>/<any>.mk

Pre-rooting with MAGISK seemingless within the AOSP build process while keeping AVB / DM-VERITY intact !

Important: This has been tested on the A/B device OnePlus 7T pro (hotdog) only! No idea what happens on devices without a dedicated recovery partition / boot image without ramdisk. I guess it just means adding INSTALLED_RECOVERYIMAGE_TARGET to mkbootimg.mk as it all uses the internal magisk functions for patching.

Technical background (how does it work)

  1. when executing vendor/extendrom/er.sh the specified Magisk version will be downloaded, extracted and all necessary components moved to a temporary patch dir (out/.magisk)
  2. When building your ROM a completely unmodified magisk boot_patch.sh will be executed (also a completely unmodified utils_functions.sh gets included) which actually does the patching of your boot.img like the Magisk App would do.

Choose the right extendrom branch

You might noticed that extendrom has several branches:

  • main -> usually the greatest and latest but sometimes Magisk had caused issues in the past on new releases
  • magisk_vXX -> always kept up2date with main with the only diff of the given specific Magisk (Major) release

so choose e.g. magisk_v24 to get the latest v24 magisk release or magisk_v20 for the latest v20 etc.

Required flags (device/<vendor>/<model>/vendorsetup.sh)

  • EXTENDROM_PREROOT_BOOT = true
  • EXTENDROM_PACKAGES = Magisk | SignMagisk
  • MAGISK_TARGET_ARCH=arm -> OPTIONAL: when using 32bit devices (ONLY then)*

(*)note: MAGISK_TARGET_ARCH will be parsed when set in your vendorsetup.sh or specified as env variable. It can be arm or arm64 which will copy the correct libs according to whats specified. If unset the default is expecting arm64 - so ensure you set it for 32bit devices (see above)!

Required mkbootimg.mk

When you enable this flag you HAVE to use a custom mkbootimg.mk in order to make use of it. That means you have to set this in your BoardConfig.mk:

BOARD_CUSTOM_BOOTIMG_MK := $(DEVICE_PATH)/mkbootimg.mk

A fully working example configuration for a mkbootimg.mk can be found here. Note: that can differ from what you need, especially Samsung devices are different / having often one which need to be adapted accordingly.

not all devices can / will use the same mkbootimg.mk. You need to check build/core/Makefile -> $(INSTALLED_BOOTIMAGE_TARGET): to identify if you need to adapt this or not. Here are the most important things you need to do:

  1. add: ROOTBOOT := $(shell echo $$EXTENDROM_PREROOT_BOOT) at the top / first line
  2. add: ROOT_BOOT_BIN := $(OUT_DIR)/.magisk/boot_patch.sh at the top / second line
  3. copy the whole (matching to your device..) $(INSTALLED_BOOTIMAGE_TARGET): block from build/core/Makefile
  4. add: @/bin/bash $(ROOT_BOOT_BIN) $$PWD/$@ in the block of $(INSTALLED_BOOTIMAGE_TARGET): , AFTER the MKBOOTIMG line and BEFORE any AVB line
  5. add: @cp -v $(OUT_DIR)/.magisk/new-boot.img $(PRODUCT_OUT)/boot.img after that

some notes:

  • ROOT_BOOT_BIN is the script coming with vendor/extendrom which does the pre-rooting and $$PWD is needed as it expects an absolute path
  • Notice: When using AVB / dm-verity this path --image $(OUT_DIR)/.magisk/IMAGES/boot.img is important exactly like that as well
  • Even though you might not want to use the recovery coming with the ROM you are building -> when specifying a custom mkbootimg.mk you also might have to set INSTALLED_RECOVERYIMAGE_TARGET here as well!
  • When it comes to AVB / dm-verity it is important to set the pre-root script BEFORE adding the hash footer (obviously). The result is a boot image accepted by a locked bootloader (when your bootloader supports custom ROMs / keys) which means you can use a custom ROM + MAGISK and all that on a fully locked device..
  • The given mkbookimg.mk example also contains a block for using a prebuilt recovery which is not in scope of this documentation so you likely need to change that block completely (check your build/core/Makefile again)
  • last but not least the example file handles rooting or not rooting automatically depending if the flag EXTENDROM_PREROOT_BOOT = true has been set or not. If you always wanna root you can leave out that part ofc (but the flag needs to be set always).
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