EitanOS

A 64-bit hobby operating system kernel for x86-64, built from scratch in C and NASM assembly. Boots via the Limine bootloader (UEFI/BIOS) and runs in QEMU.

Note: Some subsystems are still being migrated from the original 32-bit version and may not be fully functional.

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Images

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Features

Memory Management

• Bitmap-based Physical Memory Manager (PMM)
• 4-level paging Virtual Memory Manager (VMM), and per process page table loading
• Kernel mapped at 0xffffffff80000000, HHDM at 0xffff800000000000
• Heap allocator built on top of the VMM

Interrupts and Syscalls

• Custom 64-bit IDT with handlers for all 32 CPU exceptions and 16 hardware IRQs
• Syscall interface via int 0x80, dispatched inside the IRQ/exception handler

Process Scheduler

• Preemptive round-robin scheduler driven by the PIT timer (IRQ0)
• Per-process virtual address spaces, each with its own PML4 cloned from the kernel
• Unix-style signal definitions (SIG_KILL, SIG_TERM, SIG_SEGV, etc.)

Program Loader

• ELF32 and ELF64 loader: Loads an ELF executable and maps memory for it, then passes the program to the scheduler
• Programs are stored on disk and launched at runtime via the run syscall

Filesystem

• Custom filesystem with sector-level disk I/O
• Based on a file table
• Supports directories

Shell

• Userspace shell compiled separately and loaded as an ELF64 process
• Supports many bash commands

Display

• Limine framebuffer-based screen driver with scrollable output
• PSF font rendering (Zap font, pre-compiled into the kernel image)

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Project Structure

src/
├── memory/                   # Memory management
├── process/                  # Process scheduling, loading, etc...
├── util/                     # Utility files like stdint, string, etc...
└── compiled_programs/        # Pre-compiled userspace programs
└── compiled_fonts/           # Pre-compiled userspace programs

programs/                     # Userspace programs that will be compiled into binary data in a C file and injected into the kernel

fonts/                        # Fonts that will be loaded

linker.ld                     # Kernel linker script
build_run.sh                  # One-shot build + QEMU launch script

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Building and Running

Dependencies

• gcc (x86-64)
• nasm
• cmake
• ld (binutils)
• xorriso
• qemu-system-x86_64
• OVMF firmware (/usr/share/ovmf/OVMF.fd)

Build and run

./build_run.sh

This will compile userspace programs and fonts, build all kernel sources via CMake, link the kernel ELF, assemble a bootable ISO with Limine, and launch QEMU with UEFI firmware.

QEMU is started with -S -s (paused, GDB server on port 1234). To attach GDB:

gdb -ex "target remote :1234" build/kernel.elf

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License

Apache 2.0 — see LICENSE.