mirror of
https://github.com/Plexi09/Nadir-Kernel.git
synced 2026-10-20 15:07:27 +02:00
82 lines
No EOL
3.9 KiB
Markdown
82 lines
No EOL
3.9 KiB
Markdown
# Nadir Kernel
|
|
|
|
Nadir is an x86-64 kernel written from scratch.
|
|
The name Nadir comes from the Arabic word *naẓīr*. In astronomy it means the point of lowest elevation, in opposition to the zenith. The documentation assumes general knowlege about how operating systems work.
|
|
|
|
## Status of the project
|
|
|
|
The project is in its foundation phase and is not yet usable. How the boot chain works: a BIOS boot sector loads the kernel, switches through 32-bit protected mode into 64-bit long mode, and runs C code (`kmain`). The interrupt layer is live: CPU exceptions (vectors 0-31) print diagnostics, the 8259 PIC is remapped to vectors 32-47, the PIT ticks at 100 Hz on IRQ0, and PS/2 keyboard input on IRQ1 echoes to the VGA console (COM1 mirrors output at 38400 8N1). Next: memory management.
|
|
|
|
## Getting started
|
|
|
|
### Prerequisites
|
|
|
|
You need an assembler, a C toolchain, and an emulator:
|
|
|
|
- **nasm** assembles the boot sector and the long-mode entry stub.
|
|
- **gcc**, **binutils** (`ld`, `objcopy`) and **make** build the C kernel (`gcc` pulls in `binutils` on most distros).
|
|
- **qemu-system-x86_64** runs the resulting image.
|
|
|
|
Install everything from your package manager:
|
|
|
|
**Debian / Ubuntu**
|
|
```bash
|
|
sudo apt install nasm qemu-system-x86 gcc make
|
|
```
|
|
|
|
**Fedora**
|
|
```bash
|
|
sudo dnf install nasm qemu-system-x86 gcc make
|
|
```
|
|
|
|
**Arch Linux**
|
|
```bash
|
|
sudo pacman -S nasm qemu-desktop gcc make
|
|
```
|
|
|
|
**macOS (Homebrew)**
|
|
```bash
|
|
brew install nasm qemu gcc make
|
|
```
|
|
|
|
**Windows**
|
|
|
|
I can only recommend using Linux distribution, but the Windows Subsystem for Linux is a valid path if you are exclusively running Windows. Install Ubuntu from the Microsoft Store, then run the Debian command above inside its terminal (QEMU's window renders automatically through WSLg).
|
|
|
|
### Running the kernel
|
|
|
|
From the repository root:
|
|
|
|
```bash
|
|
make # builds nadir.img
|
|
make run # boots it in QEMU
|
|
```
|
|
|
|
A QEMU window opens and you should see this:
|
|
|
|
|
|
|
|
### Troubleshooting
|
|
|
|
| Symptom | Cause |
|
|
|---|---|
|
|
| `Boot failed: not a bootable disk` | The first 512 bytes of `nadir.img` are not a valid boot sector (they must end with the `0xAA55` signature). Re-run `make` and check it completes without errors. |
|
|
| Black screen / blinking cursor | The boot sector only speaks legacy BIOS (`int 0x10` text mode). This works out of the box with QEMU's default SeaBIOS firmware but will not boot under UEFI-only firmware (or UEFI-only real hardware) unless legacy/CSM boot is enabled. |
|
|
| QEMU reboots in a loop after `entering protected mode` (or before any C output) | A triple fault in the boot chain: the CPU crashed with no IDT installed and reset itself. Boot with `qemu-system-x86_64 -fda nadir.img -d int -no-reboot` and read the fault (`v=...`) plus registers from the log. |
|
|
| No window appears under WSL2 | Use the `-display curses` variant above. It should work in any terminal. |
|
|
|
|
## How booting works
|
|
|
|
1. The BIOS loads the 512-byte sector (`kernel/arch/x86_64/boot.asm`) at `0x7C00`: it enables A20, loads the kernel to `0x10000`, installs a flat GDT, and enters 32-bit protected mode.
|
|
2. The stage-2 entry (`kernel/arch/x86_64/entry.asm`) checks for long mode, identity-maps the first 1 GB with 2 MB pages, enables paging, jumps to 64-bit code, zeroes BSS, and calls `kmain`.
|
|
3. `kmain` (`kernel/core/kmain.c`) installs the exception IDT, remaps the PIC, installs IRQ gates, starts the serial log, PIT and keyboard, enables interrupts (`sti`), then loops on `hlt`: uptime prints ~1/s and keystrokes echo via the VGA text console (`kernel/arch/x86_64/console.c`, `include/console.h`).
|
|
|
|
The full memory map lives in the header comment of `kernel/arch/x86_64/boot.asm`.
|
|
|
|
## Contributing
|
|
|
|
Every contribution is welcome. Please fork and send a pull request if you wish to contribute. You will be credited at the end of this very file. Please see [CONTRIBUTING](CONTRIBUTING.md) for more information.
|
|
|
|
## License
|
|
|
|
This software is released under the MIT license. See the [LICENSE](LICENSE) file for details. |