How to build TWRP for the TB-8504X/F

I recently started a project to build LineageOS for the Lenovo TB-8504X/F. Part of the journey typically involves building a custom recovery. TWRP is now the defacto so I started there.

Prerequisites:

1. An Android build environment: https://source.android.com/setup/build/initializing or something like https://github.com/jfloff/docker-lineageos
2. Repo Installed: https://source.android.com/setup/build/downloading

Steps:

1. Create a working directory and cd into it
   • mkdir twrp && cd twrp
2. Check out limited manifest for building TWRP
   • repo init -u git://github.com/minimal-manifest-twrp/platform_manifest_twrp_omni.git -b twrp-7.1
3. Sync
   • repo sync
4. Make a directory for the tb_8504x device inside the repository directory and cd into it
   • mkdir -p device/lenovo/tb_8504x && cd device/lenovo/tb_8504x
5. Clone the recovery source into the tb_85004x directory
   • git clone git@github.com:Matshias/twrp_android_device_tb_8504x.git
6. Go back to the top level directory and lets start to build
   • source build/envsetup.sh
lunch omni_tb_8504x-userdebug
mka recoveryimage

If everything goes well you should have a recovery image available in out/target/product/tb_8504x/

Big thanks to https://github.com/Matshias

You can find the final output and a continuing thread here: https://forum.xda-developers.com/thinkpad-tablet/general/twrp-root-tab-4-plus-tb-x704l-f-tb-t3664407