Crystal Kernel

Extending on the work started with https://github.com/ffwff/lilith/

Usage

• this kernel is designed to work with BOOTBOOT to keep the boot process simple

Building

The kernel is expected to be a standard ELF executable

• BOOTBOOT expects a single loadable segment
• Internally virtual segments are maintained and 4kb aligned - for paging protection
• the entry point takes no params and returns void
• boot and machine information is provided at a specific location by BOOTBOOT

to build run ./build.sh

Development on macOS

Install some base tools

brew install crystal
brew install qemu
brew install gdb

Download the UEFI BIOS, extract using something like 7zip to get

• OVMF-pure-efi.fd for x64
• QEMU_EFI-pflash.raw for aarch64

Running the kernel using QEMU

build the kernel

./build.sh

Can run the VM in a few different ways

• View the VM using VNC
  • qemu-system-x86_64 -cpu qemu64 -bios ../OVMF-pure-x64-efi.fd -drive file=./disk.cdr,if=ide -display vnc=127.0.0.1:0
  • connect to it using localhost (uses default port)
• With GDB debugging support:
  • qemu-system-x86_64 -cpu qemu64 -bios ../OVMF-pure-x64-efi.fd -drive file=./disk.cdr,if=ide -display vnc=127.0.0.1:0 -s -S
  • it waits for GDB to connect before starting
• Mutli-core:
  • qemu-system-x86_64 -cpu qemu64 -m 128M -bios ../OVMF-pure-x64-efi.fd -drive file=./disk.cdr,if=ide -display vnc=127.0.0.1:0 -smp "sockets=1,cores=2"

gdb
file ./bin/bootboot/X86_64
target remote tcp::1234
continue

Inspecting the ELF file output

• objdump -s bin/bootboot/X86_64
• x86_64-elf-readelf -hls bin/bootboot/X86_64
• x86_64-linux-gnu-readelf -hls bin/bootboot/X86_64
• http://www.sunshine2k.de/coding/javascript/onlineelfviewer/onlineelfviewer.html

To check for bootboot compatibility

• ./mkbootimg check bin/bootboot/X86_64