1. Android build
  - Download toolchain from https://releases.linaro.org/components/toolchain/binaries/6.3-2017.05/arm-eabi/
    file name : gcc-linaro-6.3.1-2017.05-x86_64_arm-eabi.tar.xz

  - Uncompress using following command at the prebuilts/gcc/linux-x86/arm/arm-eabi-6.3.1
    a) xz -d gcc-linaro-6.3.1-2017.05-x86_64_arm-eabi.tar.xz
    b) tar -xf gcc-linaro-6.3.1-2017.05-x86_64_arm-eabi.tar 
    c) mkdir prebuilts/gcc/linux-x86/arm/arm-eabi-6.3.1
    d) mv gcc-linaro-6.3.1-2017.05-x86_64_arm-eabi/* prebuilts/gcc/linux-x86/arm/arm-eabi-6.3.1

  - Download original android source code ( android-9.0.0_r37 ) from http://source.android.com
  ( $repo init -u https://android.googlesource.com/platform/manifest -b android-9.0.0_r37
    $repo sync -cdq -j12 --no-tags
    $repo start android-9.0.0_r37 --all
  )

  - And, 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

2. Kernel Build  
  - 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-3.18
    b) mkdir -p out
    c) make O=./out ARCH=arm mcv5a_lao_com_defconfig
    d) make O=./out ARCH=arm CROSS_COMPILE=$(pwd)/../prebuilts/gcc/linux-x86/arm/arm-eabi-6.3.1/bin/arm-eabi- -j4


  * "-j4" : The number, 4, is the number of multiple jobs to be invoked simultaneously. 
  - After build, you can find the build image(zImage) at out/arch/arm/boot