Overview

Base chroot environment for the creation of most binary packages which will be copied to the Binary Package Server.
Packages, which don't need to be built, for example Oracle's Java SE Development Kit (JDK), can be fetched from the Mirror Server.
Software stacks built upon specialized binary packages, require their own chroot environment. If possible, avoid this.
For reproducibility, Portage and Profiles are frozen with the help of version control system (git in our case). This is only done on the Mirror Server.
When building packages in a chroot environment, the portage and overlay versions need to set.

Chroot Setup

At least the following is required beforehand to ensure reproducible building:

Create a staging root and extract a stage3 or stage4 tarball
Mount proc, sys and dev (required for portage to control the tty, determine available storage space, etc.)
Copy /etc/resolv.conf
Enter the chroot

root #

stagingRoot=/var/staging/staging-base

root #

mkdir -p "${stagingRoot}"
root #

tar -xjpf /var/tmp/your-stage4.tbz2 -C "${stagingRoot}"
root #

mount -t proc none "${stagingRoot}/proc"
root #

mount --rbind /dev/ "${stagingRoot}/dev/"
root #

mount --rbind /sys/ "${stagingRoot}/sys/"
root #

cp -af /etc/resolv.conf "${stagingRoot}/etc/"
root #

chroot "${stagingRoot}" /usr/bin/env -i HOME="/root" TERM="${TERM}" /bin/bash --login

Note

We are deliberately using a special command to enter the chroot to avoid leaking environment variables