The scripts contained within are a small set of tools that reliably build a disk that can boot Zircon systems from a GPT EFI System Partition on the same machine. This is a convenience for booting Zircon/Fuchsia on BIOS based systems, while still using a GPT layouts.
fx full-build ./scripts/grubdisk/build-all.sh
The output will be out/grub.raw, which may be installed as a disk to any BIOS based computer, such as a compute VM. The configuration will search for a GPT ESP partition on the system containing zircon.bin and bootdata.bin and boot it.
In your Fuchsia checkout:
fx full-build ./third_party/grubdisk/build-grub.sh
# Linux: fallocate -l 1m out/grub.raw # OSX: mkfile -nv 1m out/grub.raw # POSIX: head -c 1048576 /dev/zero > out/grub.raw # Physical disk: sudo chown $USER /dev/target_disk_device
./third_party/grubdisk/build-core.sh
Substitute grub.raw for your disk device if you are targeting a real disk.
./third_party/grubdisk/embed.sh out/grub.raw
The tools contained here simply drive grub and implement a pure-userspace host-ignorant equivalent to grub-install(1). The standard grub tools have a challenging propensity of reading information from the host system in order to detect how to install grub. While this is convenient for your average GNU/Linux user, it is a pain for embedded/alternative use cases. If you read documentation on how people normally do the kind of work these tools do, they end up with loopback mounts, chroots and so on.
This tool creates a protective MBR, a GPT, and a single BIOS partition. It installs the grub boot.img into the PMBR Boot Code, and then installs the core.img into the BIOS partition it created.
The core.img that is created contains an embedded grub.cfg that searches the system GPTs for a partition containing zircon.bin. Once it finds that, it will multiboot zircon.bin with bootdata.bin.