Arch Linux s390x Port

This repository contains a complete, working s390x Arch Linux system with full root filesystem support that boots successfully on IBM mainframes and QEMU emulation.

Quick Start

# Build everything
make all

# Test initramfs-only system
make test

# Test with root filesystem
make test-rootfs

What's Working

• s390x Kernel: Linux 6.6.10 cross-compiled for IBM mainframes (11MB)
• Initramfs: Complete 5.9MB initramfs with s390x busybox
• Boot Process: Successful boot to root filesystem with busybox shell
• Root Filesystem: COMPLETE! 100MB ext4 root filesystem with Arch Linux identification
• QEMU Testing: Fully functional in s390x emulation
• Ready for Hardware: IPL configuration for real mainframes

Build Status

Core System Components

Component	Status	Details
Kernel	✅ Working	11MB bootable s390x kernel (vanilla 6.6.10)
Initramfs	✅ Working	5.9MB with native s390x binaries
Boot Process	✅ Working	IPL → kernel → initramfs → root filesystem
Root Filesystem	✅ COMPLETE	100MB ext4 with working busybox switch_root
mkinitcpio	✅ Fixed	Adapted for s390x architecture

Userspace Components

Component	Status	Details
Init System	🟨 Minimal	Busybox init (not systemd)
Shell	🟨 Minimal	Busybox sh (not bash)
Core Utilities	🟨 Minimal	Busybox applets only
Package Manager	❌ TODO	Pacman needs porting
Systemd	❌ TODO	Requires cross-compilation
Bash	❌ TODO	Needs s390x build
GNU Coreutils	❌ TODO	Replace busybox applets
Arch Kernel Patches	❌ TODO	Apply Arch-specific patches

Legend

• ✅ Complete - Fully working
• 🟨 Minimal - Working but minimal implementation
• ❌ TODO - Not yet implemented

Build System

Uses Fedora containers with Podman for cross-compilation:

# Container image:
s390x-archlinux-dev          # All-in-one development container

Build Targets:

• make all - Build complete system (kernel + initramfs)
• make kernel - Cross-compile s390x kernel only
• make initramfs - Generate initramfs with mkinitcpio
• make test - Test initramfs-only system with QEMU
• make test-rootfs - Test with root filesystem switching
• make clean - Clean build artifacts

Key Scripts:

• scripts/build-kernel-container.sh - Cross-compile kernel
• scripts/build-initramfs-final.sh - Generate initramfs
• scripts/run-qemu-initramfs-only.sh - Test initramfs-only system
• scripts/test-qemu-rootfs.sh - Test with root filesystem
• scripts/build-busybox-zvm.sh - Build static busybox on z/VM

Testing

# Install QEMU s390x
sudo pacman -S qemu-system-s390x  # Arch Linux
# or
sudo apt install qemu-system-s390x # Ubuntu/Debian

# Test initramfs-only system
make test

# Test root filesystem switching
make test-rootfs

Expected:

• make test - System boots to emergency shell in initramfs-only mode (press Ctrl-A X to exit)
• make test-rootfs - Boots completely to root filesystem with busybox shell

Output Files

After building:

• boot/vmlinuz-linux - Ready-to-use s390x kernel
• boot/initramfs-linux.img - Working initramfs
• boot/rootfs-s390x.img - Root filesystem image (created by test-rootfs)
• boot/generic.ins - IPL configuration for real hardware
• boot/arch.prm - Kernel parameters
• boot/busybox-s390x-static - Static busybox binary built on z/VM

Technical Details

s390x Adaptations:

• Big-endian architecture support
• IPL boot process (not BIOS/UEFI)
• Channel I/O subsystem drivers
• mkinitcpio modified for cross-architecture builds

Key Fixes Applied:

1. mkinitcpio adaptation - Fixed add_binary vs add_file issue for init scripts
2. Static busybox - Built natively on z/VM to eliminate dynamic linking
3. Architecture compatibility - Fixed base hook to exclude x86_64 binaries
4. Init script patching - Modified standard Arch init to use busybox switch_root

System Boot Success

The system successfully boots from initramfs to root filesystem:

[   22.867595] Run /init as init process
:: mounting '/dev/vda' on real root
[   23.131648] EXT4-fs (vda): mounted filesystem r/w with ordered data mode
/ # cat /etc/os-release
NAME="Arch Linux"
PRETTY_NAME="Arch Linux"
ID=arch

/ # uname -a
Linux arch 6.6.10 #14 SMP Mon Jun  2 14:59:34 UTC 2025 s390x GNU/Linux