1. Android build
  - Download original android source code ( android-9.0.0_r51 ) from http://source.android.com
  ( $repo init -u https://android.googlesource.com/platform/manifest -b android-9.0.0_r51
    $repo sync -cdq -j12 --no-tags
    $repo start android-9.0.0_r51 --all
  )
	   
  - Then, merge the source into the android source code
  - Run following scripts to build android
    a) source build/envsetup.sh
    b) lunch 1
    c) make -j4
	
  - When you compile the android source code, you have to add google original prebuilt source(toolchain) into the android directory.
  - After build, you can find output at out/target/product/generic

2. Kernel Build  
  - Uncompress using following command at the android directory

    a) tar -xvzf *_Kernel_Pie.tar.gz

  - When you compile the kernel source code, you have to add google original "prebuilt" source(toolchain) into the android directory.
  - Run following scripts to build kernel
  
    a) cd kernel/msm-4.9
    b) mkdir -p ../out_kernel
    c) make -j9 O=../out_kernel ARCH=arm CROSS_COMPILE=../../prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9/bin/arm-linux-androideabi- mh5lm-perf_defconfig headers_install zImage


	* "-j9" : The number, 9, is the number of multiple jobs to be invoked simultaneously. 
  - After build, you can find the build image(zImage) at kernel/out_kernel/arch/arm/boot



