How to build your own linux kernel for your android device
Requirements
- A rooted android device
- An Android-SDK [5]
- A running android debugging server ("adb devices" oder "adb start-server" - both need to be executed as root)
ATTENTION
If you have a custom recovery manager installed on your device, you should create a backup! If you have none, have a look at Clockworkmod. 
Build your own kernel for your android device
1. You need the kernelsources matching the currently running kernel. For information how do determine your kernel version have a look at Figure out correct kernel version.
- How do you get the sources for a official google device is described in [3].
2. You need the config for currently running kernel
Custom images like CyanogenMod have enabled config export through the proc-filesystem. You could obtain it by:
adb pull /proc/config.gz .
gunzip config.gz
cp config /path/to/your/kernel/.config
b. If you run a stock image, have a look at documentation/kernel-tree.txt. It lists a set of Android device their kernel trees and the matching default config.
3. Set the CROSS_COMPILE variable.
- export CROSS_COMPILE=/path/to/your/toolchain/`
For the Android prebuilt toolchain this step may look like:
export CROSS_COMPILE=/<path>/prebuilt/linux-x86/toolchain/arm-eabi-4.4.0/bin/arm-eabi-
4. First, clearify your configuration is up-to-date
- make ARCH=arm oldconfig
Set all needed options for SystemTap descriped in [7]
- make ARCH=arm menuconfig
5. Don't forget to build the kernel itself
- make ARCH=arm [-j X]
The compiled kernel image is located in arch/arm/boot/.
6. Now you need the current boot image, because it contains the initialramdisk which we will recylce. First, determine the boot partition.
Newer devices place symlinks with human readable names in /dev/, e.g. the Samsung Galaxy Nexus /dev/block/platform/omap/omap_hsmmc.0/by-name/boot
Otherwise you have to determine the kind of flashdriver used and print the partitiontable. Two examples are given below:
- HTC Dream (aka T-Mobile G1): cat /proc/mtd
- #cat /proc/mtd
- dev: size erasesize name
- mtd0: 00040000 00020000 "misc"
- mtd1: 00500000 00020000 "recovery"
- mtd2: 00280000 00020000 "boot"
- mtd3: 04380000 00020000 "system"
- mtd4: 04380000 00020000 "cache"
- mtd5: 04ac0000 00020000 "userdata"
- HTC Desire Z: cat /proc/emmc
- # cat /proc/emmc
- dev: size erasesize name
- mmcblk0p17: 00040000 00000200 "misc"
- mmcblk0p21: 0087f400 00000200 "recovery"
- mmcblk0p22: 00400000 00000200 "boot"
- mmcblk0p25: 22dffe00 00000200 "system"
- mmcblk0p27: 12bffe00 00000200 "cache"
- mmcblk0p26: 442ffe00 00000200 "userdata"
- mmcblk0p28: 014bfe00 00000200 "devlog"
- mmcblk0p29: 00040000 00000200 "pdata"
If you have determined the correct boot partition, dump it and copy the dump to your computer:
adb shell dd if=/dev/<path> of=/sdcard/boot.img adb pull /sdcard/boot.img
7. Unpack the boot image with the tool unpackbootimg. Its sourcecode is located in tools/bootimg.
- unpackbootimg boot.img
The output may look like this:
- $ unpackbootimg ./boot.img
- Magic value:ANDROID!
- Kernel: size:3691628 addr:0x80008000
- Ramdisk: size:223281 addr:0x81000000
- Second: size:0 addr:0x80f00000
- Page size: 2048
- Name:
- Cmd:
- Calc file size:3919872 stat size:3919872
- Extracting kernel (3691628 bytes)...
- Extracting ramdisk (223281 bytes)...
- No secondary image found.
Pay attention on the kernel loadaddress. Here it is 0x80008000, which means the baseaddress is 0x80000000. Keep that in mind! You have to copy the displayed commandline arguments as well.
8. To create the new boot image just run one command and push it to the device:
mkbootimg --kernel /path/to/kernel/arch/arm/boot/zImage --ramdisk ramdisk.img --cmdline "<look at output of unpackbootimg>" -o new_boot.img adb push new_boot.img /sdcard/
9. Finally, you have to flash the new boot image. On some firmware images the tool flash_kernel, not on aosp images, is available. I prefer to use this tool. Otherwise you must do it with dd.
- Someone may argue to reset the flash with zeros before flashing it:
dd if=/dev/zero of=/dev/<path> flash_kernel boot /sdcard/new_boot.img or
dd if=/sdcard/new_boot.img of=/dev/<path>