atv-bootloader 1.0

Spork of atv-bootloader w/LLD build tooling. Original author's notes. Original GPLv2 license applies.

Requirements

• LLD 3.8+: LLVM's cross-platform multi-format linker

  • OSX: brew install llvm --HEAD --with-lld --with-clang
  • Debian: ask sledru to add lld to http://llvm.org/apt
    • http://anonscm.debian.org/viewvc/pkg-llvm/llvm-toolchain/branches/
    • https://packages.qa.debian.org/l/llvm-toolchain-3.8.html
    • https://packages.qa.debian.org/l/llvm-toolchain-snapshot.html

• GNU Make

• gptfdisk & mtools (to make USB images)

  • OSX: brew install gptfdisk mtools
  • Debian: #apt-get install gdisk mtools

• vmlinuz & initrd.img files in /boot or in this projects's 'boot' folder

Building

• make mach_kernel

Booting

If you are building from the AppleTV, just run make install to stage the mach_kernel to /boot,
assuming that /boot is a leading HFS partition on the drive.

You also need some files in /boot to satisfy AppleTV's EFI:

• boot.efi
  • the much maligned checksummed AppleTV-EFI bootstrap loader.
• com.apple.Boot.plist
  • config file for the EFI's Mach-O loader.
• BootLogo.png
  • Splash logo shown by the EFI loader on power up.

If you are not compiling from the Apple TV, you need to make a boot image with make stick.img.
All needed files will be put on the image's boot partitions, set up according to ATV's quirky rules.
A command will be printed that can be used to flash the image to a USB stick.

Why 1.0?

Not much has changed in the actual bootloader code from 2008, but 10 years
of LLVM development allows us to now build simple Mach-O binaries from Linux!

So the big anti-feature of 1.0 is to not ship a precompiled /mach_kernel!
Instead, lld makes it quick and easy to build one at any time from whatever kernel & initrd
your Linux distro's installer or package manager provides. That way, you can always boot
up-to-date Linux kernels with out any kexec nonsense.

Why now?

ATV1 is now in the "vintage computing" genre, but the hardware was ahead of its day.
However the OSX 10.4-lite that it shipped with is now obsolete.

The lack of hardware 1080 MPEG4 decoding makes ATV1 worse than a RasPi for home media.

I used atv-bootloader since 2009 to run Linux as a headlesss server, but even with
the "patchstick" it was not easy to get post-2009 Linux 3.0+ distributions installed and running.

Maybe Swift & its [Foundation frameworks] (https://github.com/apple/swift-corelibs-foundation) can be run on
PureDarwin to make ATV1 the first sans-ObjC Hackintosh.

What's next?

• Finish sdavilla's work on shimming vgabios so Linux will see a standard Nvidia GPU and
  control it normally without needing hacky atv-linux quirks in the mainline drivers.
  • see vgabios.patch for the gory details
• Shim up AppleTV's pre-UEFI env to natively support modern EFI-mode Linux.
• Support bootstrapping Multiboot kernels instead of vmlinuz.
  • Like Grub2's core.img -- grub-efi or grub-pc platform? BOOT ALL THE THINGS!

Code layout

• start.s
  • __start trampoline
• boot_loader.c
  • main routine to bootstrap vmlinux
• darwin_code.c
  • finds the Mach-O segments holding the linux kernel assets in /mach_kernel
• linux_code.c
  • fixes up some fake PC-BIOS memory maps to make Linux think this is a plain PC.