To download build environment:

docker pull ddrown/busybox-build

To build busybox binaries:

OUTPUTDIR=~/target
mkdir $OUTPUTDIR
docker run -v $OUTPUTDIR:/target ddrown/busybox-build

This will create 4 binaries in $OUTPUTDIR: busybox-x86-pie, busybox-x86-nopie, busybox-arm-pie, and busybox-arm-nopie. See the file "tests.txt" for the output of running "echo ok" with each of these binaries on various Android versions and architectures.

To build a modified busybox:

OUTPUTDIR=~/target
mkdir $OUTPUTDIR
docker run -i -t -v $OUTPUTDIR:/target ddrown/busybox-build /home/admin/shell
[make modifications]
/home/admin/build