RebornOS

A small, serious Unix-like operating system, built from scratch.

Not a Linux clone. Not a microkernel research project. Not a desktop OS. RebornOS is a UEFI x86_64 OS written primarily in C, with a monolithic but modular kernel, a small native userspace, and a design that grows toward POSIX-like behavior over time, starting from a kernel that boots, logs, and doesn't lie to you when it crashes.

Features

• From-scratch UEFI bootloader -- no gnu-efi, no EDK2. Loads and parses the kernel's own ELF64 image directly off the EFI System Partition.
• Real memory management -- a physical page allocator, the kernel's own page tables, a heap, per-process address spaces, and page-fault-driven stack growth.
• Preemptive multitasking -- a round-robin scheduler, ring 0/ring 3 privilege separation, and a real int $0x80 syscall boundary.
• Process isolation -- every process gets its own page tables, with real per-process pointer validation instead of a heuristic.
• A real filesystem and disk driver -- FAT16 with subdirectories, arguments, and write support, served by a polled AHCI driver (no RAM-loaded disk images).
• An interactive shell -- PS/2 keyboard and mouse drivers, disk-loaded ELF programs, and a real shell to launch them.
• Networking -- a polled Intel e1000 driver plus Ethernet/ARP/ICMP, proven with a real ping round-trip through QEMU's NAT.
• SMP -- every CPU core discovered via ACPI and brought up through a real-mode trampoline into 64-bit long mode.
• Fault isolation -- a crashing user process is killed and reported, not the whole kernel.
• Graphics primitives -- framebuffer mapping, mouse input, and a heap-growth syscall for userland, laying the groundwork for a GUI.

Not yet: a windowing system, UDP/TCP, piping, package management, or Linux binary compatibility. GUI and userland ergonomics are deliberately on hold until the kernel itself is rock solid.

Building

Everything here runs inside WSL2 (or native Linux) -- the toolchains (cross-compiler, mingw, QEMU+OVMF) are far more consistent there than on native Windows.

# one-time: build our own x86_64-elf-gcc cross-compiler into ~/opt/cross
make toolchain

# boot it interactively (serial on stdio, Ctrl-A X to quit QEMU)
make run

# scriptable pass/fail smoke test (no human watching QEMU)
make test

# boot paused with a GDB stub on :1234
make debug

Required host packages (Ubuntu/Debian):

sudo apt-get install -y bison flex libgmp-dev libmpc-dev libmpfr-dev \
    texinfo libisl-dev qemu-system-x86 ovmf gcc-mingw-w64-x86-64

Layout

boot/      UEFI bootloader (PE32+, built with mingw)
kernel/    the kernel (ELF64, built with our own cross-compiler)
common/    code shared by both (serial driver, boot_info.h, freestanding libc bits)
userland/  RebornOS's own user programs (ELF64, no libc, loaded off disk at boot)
tools/     ESP staging, QEMU run/test/debug scripts, panic symbolizer
toolchain/ builds the x86_64-elf-gcc cross-compiler from source

Philosophy

The kernel provides sharp primitives; userspace builds the actual world. GUI, package managers, and Linux binary compatibility are deliberately out of scope until there's a command-line system that boots reliably, manages memory correctly, runs isolated programs, and touches files.

License

MIT -- see LICENSE.