What is this?
A collection of scripts to {build, run, push} a Docker image to Docker Hub.
So what?
Well, this Docker image contains a Debian userland of AMD64/x86-64 architecture.
Pfft! Why should I care...
But this Debian in turn contains other Debian userlands...
Okay so you do a
chroot, been there done that.
... of differing architectures via schroot and qemu user-mode emulation -- working transparently.
Hmm, tell me more.
This permits easy testing across many architectures. E.g. the for_each_arch function which runs a command within each defined architecture's environment in turn:
$ for_each_arch file /bin/true
/bin/true: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamica
/bin/true: ELF 32-bit MSB shared object, MIPS, MIPS32 rel2 version 1 (SYSV), dyn
/bin/true: ELF 32-bit LSB shared object, MIPS, MIPS32 rel2 version 1 (SYSV), dyn
Oh that is neat. But I could also just have spun up 3 full-system QEMUs and installed 3 Linux distros.
True, but:
- This takes care of all the setup. With these scripts, moving to other {arch, debian version} is super easy.
- It would run slower since you now emulate peripherals and another Linux kernel. BTW, which boards would you pick?
- This runs under the same Linux kernel so the different programs under each architectures can interact normally; named pipes, even shared memory and IPC.
Cool! This would be great for automated {build, run-time} testing of various Linux software following a {git clone, configure, make, test}-pattern.
Yes! And when running, one could use gdb with rbreak, info variables and commands to dump scalar variables to a log. Diffing the logs between MIPS and MIPSel (with suitable magic) would reveal endianess bugs encountered. This forms the idea for an empirical endianess-bug detector.
Caveats
There is just one caveat: For now, Docker --privileged is required as binfmt must be mounted. There are ways around this though by patching QEMU user mode itself.
I just want the pre-built image
OK but this is my personal one, https://hub.docker.com/r/mpedoticon/debian_foreign/ . Disclaimer: Not production ready! I may change this image into a banana if I feel like it.
How to
Currently you do need this git cheked out first. Steps to run:
- Git clone this.
- Read through what
payload.shdoes, before you run it under a privileged Docker :) - Run:
sudo docker run --privileged -v ${PWD}:/this_dir -it mpedoticon/debian_foreign bash -x /this_dir/payload.sh