Poccy

Poccy, whilst still a WIP, is a toy OS I've built in my spare time for a school project. More precisely, I am doing my senior's paper/thesis on operating systems and kernels, and am providing this one as an example to detail how one may go about kernel/OS development.

Goals

• Custom bootloader to obtain basic information necessary, load the kernel image and call it with passed down arguments.
• Graphics methods for plotting pixels to the screen
• Handling drawing glyphs on the screen from a font file
• GDT and IDT support (TODO: IDT impls)
• Interrupt handler
• Filesystem handler
• Memory management (pagers, vmem functions, etc.)
• Multi-threading
• Basic Bash & C support
• PS/2 Keyboard support (via interrupts)
• ACPICA implementation
• DSDT parser to expose the table in plaintext
• Basic math library (logarithms, pow(), etc.)

Building the project

First of all, you must create 2 directories: hda-contents and bootloader, as QEMU will read hda-contents as a virtual disk, and the OvmfPkg image will be placed in bootloader. In the hda-contents directory, add a new directory: EFI/BOOT.

Next, check out the bootloader project for more information on how to use the EDK2 build system and on how to compile the bootloader itself.

You're going to need Zig. This project uses Zig's drop-in replacement for GCC/Clang to cross-compile for PE+ images. I had difficulties invoking zig cc directly in CMake, as such, I simply made a bash script to circumvent this issue (although you could just prepend CC="zig cc $@" before invoking cmake), and compiled it as a binary called zigcc.

The required version of Zig (at time of writing this: August 28th, 2023) is 0.11-dev.

The rest of the dependencies are as follows:

• mingw
• LLVM
• qemu

Once you've properly set up dependencies and compiled the bootloader, execute the following commands:

cmake -S . -B <build_directory>

cd <build_directory>

cmake --build .

After that, you can just execute qemu:

qemu-system-x86_64 \
            -serial stdio \
            -bios bootloader/bios.bin \
            -drive file=fat:rw:hda-contents,format=raw,media=disk \
            -m 1024M \
            -s \
            -no-reboot -d int,cpu_reset

Additionally, if you need to use a debugger, you will need to append the -S flag when executing qemu. As per the nature of GDB, it doesn't support Microsoft's Program Database (PDB) file format, and you can only use LLDB for real-time debugging.

Kernel ABI

TODO

Credits / Resources

• UEFI.org - for providing exhaustive and detailed specifications of both UEFI and ACPI.
• OSDev Wiki - for providing me, and a plentiful of other users, with the common knowledge as an introduction for OS development.
• Tianocore - for providing UEFI utilities and abstractions.
• Mhaeuser — for providing this project with an amazing library for PE/COFF images (PeCoffLib2), which was used in the bootloader.