Compiling ZTE OPEN kernel on Arch Linux

I need to modify kernel source codes of Firefox OS for my project. Currently I have a ZTE OPEN device (NOTE: it's different from ZTE OPEN C). ZTE have lots of kernel sources released to public, but this device is not included. After several e-mails, ZTE engineers finally release the kernel source for this device. Cheers!

After several days of trials and errors, I finally compiled and installed the kernel image. I use Arch Linux. This distribution features all softwares being latest. Here's an incomplete list of my installed softwares:

gcc-multilib 5.2.0-2
perl 5.22.0-1
python2 2.7.10-1

And here's how I've compiled the kernel:

First download the kernel source image from http://opensource.ztedevice.com/. Choose the "ZTE OPEN Icecream Sandwich Kernel(3.0.X)" one.

Extract the kernel source:

$ tar zxvf "ZTE_OPEN_Icecream_Sandwich_Kernel(3.0.X).tar.gz"

Download arm-eabi-gcc from google:

$ git clone https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6

Go into the compiler and add the \$PATH

$ pushd arm-eabi-4.6/bin
$ export PATH=$PATH:`pwd`
$ hash -r
$ popd

Go into the kernel source and check arm-eabi-gcc works
```
$ arm-eabi-gcc -v
```
You shoud find the last line like "gcc version 4.6.x-google 20120106 (prerelease) (GCC)"
Make sure the system python interpreter is python 2:
```
$ python -V
  Python 2.7.10
```
If not 2.7.x, run the following commands:
```
$ mkdir python2_dir
$ pushd python2_dir 
$ ln -s /usr/bin/python2 python
$ export PATH=`pwd`:$PATH
$ popd
```
This step is necessary on Arch Linux and a very few distributions only. On most systems the default is already python 2.
Modify script/gcc-wrapper.py and add the following lines:

Configure the kernel

$ make ARCH=arm CROSS_COMPILE=arm-eabi- msm7627a-roamer2_ath_mipi_defconfig

Build the kernel image

$ make ARCH=arm CROSS_COMPILE=arm-eabi-

Now the kernel image is in arch/arm/boot/zImage. The next step is to integrate existing initramfs with the new zImage.

Android/Firefox OS boot.img is a special format. For normal Linux distributions, zImage (vmlinuz) and initrd.gz are the two files necessary for successful booting. On Android/Firefox OS, the two files are integrated into a single file. That is boot.img. The handy tool abootimg can extract and create this file. Here's the steps to generate the new boot.img:

Get the original boot.img. This file can be found in factory images. I use "OPEN(American Standard) SD card upgrading instruction & software package(ebay)-237620B0669OPEN_US_DEV_FFOS_V1.1.0B02(for V1.1)" from http://www.ztedevice.com/support/smart_phone/b5a2981a-1714-4ac7-89e1-630e93e220f8.html

Extract boot.img:

$ unzip 2014012010173938.zip
$ cd OPEN\(American\ Standard\)\ SD\ card\ upgrading\ instruction\ \&\ software\ package\(ebay\)-237620B0669OPEN_US_DEV_FFOS_V1.1.0B02\(for\ V1.1\)
$ unzip US_DEV_FFOS_V1.1.0B06_UNFUS_SD_For_V1.1.zip boot.img

Extract initrd from boot.img:
```
$ abootimg -x boot.img
```

Generate the new boot.img:

$ abootimg --create boot_new.img -f bootimg.cfg -k ../kernel/arch/arm/boot/zImage -r initrd.img

Finally, burn the new boot.img into the device. You need adb and fastboot installed.

Enter download mode
```
$ adb reboot-bootloader
```

Burn the new boot.img

$ fastboot flash boot boot_new.img && fastboot continue

Now you can check the new kernel is written:

$ adb shell cat /proc/version
Linux version 3.0.21 (yen@PC951) (gcc version 4.6.x-google 20120106 (prerelease) (GCC) ) #1 SMP PREEMPT Wed Aug 12 03:29:06 CST 2015

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