Kexec-Hardboot based bootloader/boot menu for booting modern Linux kernels on ASUS TF300T

supports device trees (DTB). This repo contains the frontend. The kernel with the actual hardboot patch is found here.

Installation

Requirements

• ASUS TF300T tablet, or TF700T, TF201 (untested)
• PC with adb and fastboot installed
• boot.blob and android-bootfiles.zip (available from releases page of this repo)
• microSD or USB drive with an image of your favorite linux distribution for ARM

Setup Android Dual-Booting (optional)

This loader will be installed to the tablet's boot partition. The Android kernel and initrd, which would normally be there, need to be moved to a different place.

extract the android bootfiles and upload the directory using adb as /sdcard/boot:

unzip android-bootfiles.zip
adb push android-bootfiles /sdcard/boot

Now you should have the following files in /sdcard/boot:

• zImage-android: Kernel image for Android
• initrd-android: Ramdisk image for Android
• android.dtbootmenu: Loader entry for this loader.

Important: The zImage and initrd files are dependent on the Android ROM you use. The ones provided in this repo are from KatKiss version #039. If you use another ROM you have to extract them from your ROMs boot.blob using blobunpack and abootimg.

Prepare the Linux disk

In the /boot directory, where the kernels and initrds are, add your zImage (we assume here you want to use a custom kernel from the Grate poject, which includes drivers needed for our device that are not yet upstreamed).

Now, add a file called mylinux.dtboomenu with the following contents:

kernel: <name of your zImage file>
initrd: <name of initrd file that comes with distro>
title: <title the entry should have in the menu>
cmdline: console=tty0 root=<root device> rw

The root drive is the typical Linux block device path your Linux installation is on, for example /dev/mmcblk1p1 for first partition of the microSD, or /dev/sda1 for first partition of USB drive.

Complete example:

kernel: zImage-grate
initrd: initrd.img
title: Debian
cmdline: console=tty0 root=/dev/mmcblk1p1 rw

Flash the loader

Put the tablet into fastboot mode by holding the Volume Down key while starting. Run the following to flash:

fastboot flash boot boot.blob
fastboot reboot

Building from Sources

boot.blob

Requirements

• GCC Cross-compiler targeting armv7 Linux with C++ support. In this example the target is called arm-unknown-linux-uclibcgnueabi. Change accordingly if yours calls the target differently.
• blobtools, abootimg, adb, fastboot
• everything required to compile a Linux kernel

Building the Kexec-Hardboot kernel

git clone https://github.com/zagto/tf300t-dtboot-kernel
cd tf300t-dtboot-kernel
export ARCH=arm
export CROSS_COMPILE=arm-unknown-linux-uclibcgnueabi-
make tf300t_dtbootloader_defconfig
make zImage -j16

Building the user-space kexec binary

git clone git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
cd kexec-tools
./bootstrap
LDFLAGS=-static ./configure --host=arm-unknown-linux-uclibcgnueabi
make -j16

Building the menu binary from this repo

cd src
make CXX=arm-unknown-linux-uclibcgnueabi-g++ CXXFLAGS=-static

Combining it all together

./create-boot-blob.sh tf300t-dtboot-kernel/arch/arm/boot/zImage kexec-tools/build/sbin/kexec src/dtbootmenu

DTBs

git clone https://github.com/grate-driver/linux.git
cd linux
export ARCH=arm
make tegra30-asus-tf201.dtb
make tegra30-asus-tf300t.dtb
make tegra30-asus-tf700t.dtb