#!/bin/sh
# Build one or more .subx files into an ELF binary, and package it up into a
# bootable ISO image with a Linux kernel.
#
# Must be run on Linux.
#
# Dependencies:
#   apt install build-essential flex bison wget libelf-dev libssl-dev xorriso
#
# Based on http://minimal.linux-bg.org (GPLv3)

set -e

if [ $# -eq 0 ]
then
  echo "Usage: `basename $0` file.subx ..."
  exit 1
fi

echo "=== building SubX binary"
./ntranslate $*
mv a.elf init
chmod +x init

echo "=== constructing initramfs out of SubX binary"
rm -rf tmp/isoimage
mkdir -p tmp/isoimage/boot
echo init | cpio -R root:root -H newc -o | xz -9 --check=none > tmp/isoimage/boot/rootfs.xz

if [ ! -d kernel.linux ]
then
  echo "=== cloning linux kernel"
  git clone https://github.com/akkartik/kernel kernel.linux
fi

echo "=== building linux kernel"
( cd kernel.linux
  make bzImage -j $(grep ^processor /proc/cpuinfo | wc -l)
)
cp *.linux/arch/x86/boot/bzImage tmp/isoimage/boot/kernel.xz

echo "=== downloading syslinux"
test -f tmp/syslinux-6.03.tar.xz  ||  wget https://kernel.org/pub/linux/utils/boot/syslinux/syslinux-6.03.tar.xz -P tmp
echo "=== unpacking syslinux"
tar xf tmp/syslinux-*.tar.xz -C tmp

mkdir -p tmp/isoimage/boot/syslinux
cp syslinux.cfg \
   tmp/syslinux-*/bios/core/isolinux.bin \
   tmp/syslinux-*/bios/com32/elflink/ldlinux/ldlinux.c32 \
   tmp/isoimage/boot/syslinux

echo "=== generating mu-linux.iso"
# 'hybrid' ISO can also be used on non-optical media such as a disk or USB stick
xorriso -as mkisofs \
  -isohybrid-mbr tmp/syslinux-*/bios/mbr/isohdpfx.bin \
  -c boot/syslinux/boot.cat \
  -b boot/syslinux/isolinux.bin \
    -no-emul-boot \
    -boot-load-size 4 \
    -boot-info-table \
  tmp/isoimage -o mu_linux.iso