#!/bin/sh
# Build one or more .subx files into an ELF binary, and package it up into a
# bootable ISO image.
#
# Must be run on Linux.
#
# Dependencies:
#   apt install build-essential flex bison 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 "=== constructing initramfs out of SubX binary"
./ntranslate $*
mv a.elf init
chmod +x init
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 ]
then
  echo "=== downloading kernel"
  test -f tmp/linux-4.14.12.tar.xz  ||  wget https://kernel.org/pub/linux/kernel/v4.x/linux-4.14.12.tar.xz -P tmp
  echo "=== unpacking kernel"
  tar xf tmp/linux-4.14.12.tar.xz
  mv linux-4.14.12 kernel
fi

echo "=== building kernel"
( cd kernel

  make mrproper -j $NUM_JOBS
  make defconfig -j $NUM_JOBS
  sed -i "s/.*CONFIG_DEFAULT_HOSTNAME.*/CONFIG_DEFAULT_HOSTNAME=\"mu\"/" .config
  # enable overlay support, e.g. merge ro and rw directories (3.18+).
  sed -i "s/.*CONFIG_OVERLAY_FS.*/CONFIG_OVERLAY_FS=y/" .config
  # enable overlayfs redirection (4.10+).
  echo "CONFIG_OVERLAY_FS_REDIRECT_DIR=y" >> .config
  # turn on inodes index feature (4.13+).
  echo "CONFIG_OVERLAY_FS_INDEX=y" >> .config
  # disable all kernel compression options
  sed -i "s/.*\\(CONFIG_KERNEL_.*\\)=y/\\#\\ \\1 is not set/" .config
  # enable the VESA framebuffer for graphics support
  sed -i "s/.*CONFIG_FB_VESA.*/CONFIG_FB_VESA=y/" .config
  # disable boot logo
  sed -i "s/.*CONFIG_LOGO_LINUX_CLUT224.*/\\# CONFIG_LOGO_LINUX_CLUT224 is not set/" .config
  sed -i "s/.*CONFIG_EFI_STUB.*/CONFIG_EFI_STUB=y/" .config
  # request that the firmware clear the contents of RAM after reboot (4.14+)
  echo "CONFIG_RESET_ATTACK_MITIGATION=y" >> .config
  echo "CONFIG_APPLE_PROPERTIES=n" >> .config

  if [ "`grep "CONFIG_X86_64=y" .config`" = "CONFIG_X86_64=y" ]
  then
    echo "CONFIG_EFI_MIXED=y" >> .config
  fi

  make bzImage -j $(grep ^processor /proc/cpuinfo | wc -l)
)
cp kernel/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 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.iso