Overview

There is a helper script to aid bootstrapping Gentoo Prefix on different platforms. Please browse this wiki page to get this script. This bootstrap-prefix.sh works for arm64 platform with some manual tuning, due to the absent of arm64/prefix profile. After this commit, it shall work smoothly. This script divides the whole process into three stages, namely stage1, stage2, and stage3. Stage1 and stage2 will bring you a tool chain in ${EPREFIX}/tmp, as well as a portage and its dependencies. Stage3 will using the tool chain in ${EPREFIX}/tmp to bootstrap a complete system.

Preparation

You need an native tool chain as well as other programs like bash to run the script. There are ways to achieve these requirements.

Method 0: Using an aarch64 Gentoo prefix

Yes, Gentoo prefix on Linux(RAP) could bootstrap itself to a different prefix path. This method is less time consuming than the following two, since you could directly go to stage3 without doing stage1 & 2 with an existing Gentoo prefix installed.

Method 1: Using a native GNU/Linux environment

You could choose any Linux Distro that support aarch64 and install it on some device(Raspberry Pi 3 is a option).

The problem with this method is that it is hard to find powerful aarch64 machine running GNU/Linux. Using chroot with an Android device, or qemu-chroot with an amd64 GNU/Linux are acceptable workaround. After chroot into an aarch64 GNU/Linux, you could easily obtain a working tool chain with the package manager. Note that, qemu-chroot’s performance is not so good, though still acceptable. Generally speaking, a normal laptop’s performance under qemu-chroot is worse than a recent Android phone. What’s more, qemu-chroot doesn’t support all system calls, I encountered some errors when trying to bootstrap a stage3 Gentoo prefix with qemu-chroot, while stage1 & stage2 compiles happily with qemu-chroot, and you could copy stage2 to you Android device and doing stage3 there.

Method 2: Cross compile an aarch64 tool chain

There is an outdated wiki. Note that, current cross emerge command ignores EPREFIX in its environment, but offers an command line options --prefix for it. I haven’t succeeded with this method.

Stage1 & 2

Before compiling everything, you might want to read this wiki page.

According to this wiki page(It worths reading):

$ export EPREFIX="/data/gentoo-arm64"
$ export PATH="${EPREFIX}/usr/bin:${EPREFIX}/bin"
$ export PATH="${PATH}:${EPREFIX}/tmp/usr/bin:${EPREFIX}/tmp/bin:/usr/bin:/bin"
$ ./bootstrap-prefix.sh "${EPREFIX}" setup
$ ./bootstrap-prefix.sh "${EPREFIX}" stage1
$ ./bootstrap-prefix.sh "${EPREFIX}" stage2

If you are lucky enough, you shall run these commands without any errors. If you encounter some errors, try to fix it by reading build logs. You don’t need to delete all files between two trail, the script will handle it correctly. You might want to do a snapshot between commands as checkpoint or change portage configuration during the process.

Some of the problems I encountered are:

  1. Wrong gid for /dev/pts on Android and glibc refuse to compile, to fix it:

    $ /system/bin/mount -t devpts -o remount,gid=5 devpts /dev/pts

  2. /bin/bash not found on Android(or something like that), you could fix it by doing a simple soft linking.

  3. Some package failed to merge since trying to installed files outside of $EPREFIX/. I encountered this problem when forcing a stable keywords by adding ACCEPT_KEYWORDS="arm64 -~arm64" to make.conf. To fix it:

    $ echo "sys-devel/gcc-config ~arm64" >> "${EPREFIX}/etc/portage/package.accept_keywords"

    Or you could just stick to the default unstable keywords which works fine.

  4. groupadd and useradd not found, to workaround it:

    $ touch "${EPREFIX}/bin/groupadd" && chmod +x "${EPREFIX}/bin/groupadd"
$ touch "${EPREFIX}/bin/useradd" && chmod +x "${EPREFIX}/bin/useradd"

    Then manually editing /etc/{shadow,group} if necessary.

  5. emerge failed to download distfiles(e.g. due to wget not found), just download it else where and put it under portage’s distfile/ directory.

Stage3

If you use Method 0 and you still want to use the helper script to do stage3, you need to manually do necessary soft links under /bin and ${EPREFIX}/{bin,usr/bin} for bash, python, etc. Then soft link the usr/portage directory in previous Gentoo prefix to the new one. Don’t forget to include the previous Gentoo prefix in PATH:

$ export PATH="${EPREFIX}/usr/bin:${EPREFIX}/bin"
$ export PATH="${PATH}:${EPREFIX}/tmp/usr/bin:${EPREFIX}/tmp/bin"
$ export PATH="${PATH}:${PREVIOUS_EPREFIX}/usr/bin:${PREVIOUS_EPREFIX}/bin"

Note that, the sequence matters.

After copying stage2 to your Android device, you could use the helper script to bootstrap stage3:

$ ./bootstrap-prefix.sh "${EPREFIX}" stage3

You might encounter errors similar to what I listed in previous section, and the solutions are similar, too. Other than already listed errors, problems I encountered in this stage are:

  1. Failed to build gmp due to some C++ errors. Simply disable the cxx use flag for gmp, this use flag is not needed to build gcc.
  2. Wrong shebang, fix it by manual editing the shebang or doing soft linking.

Finishing

You shall do a emerge -e @system after finishing doing stage3. You could use distcc to make it less time consuming. And since you might encounter errors, while emerge -e will not remember which package you have already rebuild:

$ emerge -e -pv @system > pkgs

Then edit ./pkgs to get a package list. Do not delete packages’ version! Then:

$ cat ./pkgs|while read pkg; do
	emerge --oneshot --nodeps "${pkg}" || exit 1
done

Using the prefix

Script to start prefix

You might want to use a script to start the prefix. It is a bit more tricky for Android. Please refer to this wiki page for more information.

SSH

The etc/init.d/sshd script doesn’t work well with prefix. You might want to run sshd manually.

HOME=/data/gentoo-arm64/root /data/gentoo-arm64/usr/sbin/sshd -E sshd.log -p 22222

Put your public key in /data/gentoo-arm64/root/.ssh/authorized_key and change sshd’s configuration so that root user could login. If you are still not able to do ssh, try adding StrictModes No to the configuration file and restart the daemon.

Distcc

Distcc is a tool to distribute C family language compilation to speed things up. A general guide could be found here. For this scenery, cross Distcc is needed. This is a guide for cross Distcc. I encountered some problems with the cross Distcc. The ${EPREFIX}/usr/lib/distcc/bin} folder shall be ${EPREFIX}/usr/lib64/distcc/bin for aarch64 devices.

Distcc’s plain mode would run the preprocessing on the local machine and the pump mode would try to run preprocessing remotely. Sometimes distcc pump mode might failed to build some package(because pump mode assumes headers will not change during the compilation, but for some package, e.g. llvm, this is not true), try using Distcc’s plain mode instead. You could still enable the lzo option with plain mode, which would reduce the the networking load.