Preface

To run LXC, we need a kernel that has the options required by LXC on. This article shows how to build an Android kernel that has the required options on, built by Gentoo's latest stable cross-compile toolchain built by crossdev.

Install Cross-Compile Toolchain

We'll use crossdev, a set of wrapper scripts that provides cross-compilation capability to Portage. The following instructions assume that the workstation is a Gentoo machine.

First, install sys-devel/crossdev:

emerge -av sys-devel/crossdev

Install the latest stable toolchain:

crossdev --stable -t aarch64-unknown-linux-gnu

Clone the kernel sources and compile

The kernel source repository for Nexus 6P with my patches for compiling with GCC 6 as well as LXC-enabled config is at KireinaHoro/android_kernel_huawei_angler. Clone this repository and compile the kernel:

git clone https://github.com/KireinaHoro/android_kernel_huawei_angler
cd android_kernel_huawei_angler
make sharkbait_angler_defconfig
make -j8

The target kernel image will be available at arch/arm64/Image.gz-dtb. Copy this to the preinit repository to continue following Starting Android in LXC to build the preinit boot.img.

Notes

Linux kernel's make savedefconfig doesn't really save a working defconfig, at least it's not the case for Android kernels. When changes are made to .config (via make menuconfig or so), copy .config back to arch/arm64/configs instead of relying on the savedefconfig target, otherwise you may encounter problems such as missing drivers or things that should be built-in turned out to be built as a module.

GCC 6 support was accomplished by introducing compiler-gcc6.h from SaberMod/android-kernel-lge-hammerhead on GitLab. A few fixes regarding the static inline behavior change since GCC 6 has been made to make the source compile without problem. Warning checks in gcc-wrapper.py was disabled as well.