52 lines
2.8 KiB
Markdown
52 lines
2.8 KiB
Markdown
# danos documentation
|
|
|
|
Notes on how danos boots and draws, written to explain the *why* behind the code
|
|
rather than restate it. Roughly in the order things happen at runtime:
|
|
|
|
1. **[efi.md](efi.md) — EFI / the boot process.** How UEFI firmware finds and
|
|
runs the bootloader, what the loader gathers before `ExitBootServices`, how it
|
|
loads the kernel ELF, and the ABI contract for the jump into the kernel. Start
|
|
here.
|
|
2. **[gop.md](gop.md) — the Graphics Output Protocol.** How UEFI exposes graphics
|
|
modes (unlike fixed VGA modes), how we detect the monitor's native resolution
|
|
from EDID and switch to it, and the pixel formats we accept or reject.
|
|
3. **[framebuffer.md](framebuffer.md) — the framebuffer.** What the linear
|
|
framebuffer the loader hands over actually is, and what **pitch** (stride)
|
|
means versus width — the detail you have to get right to avoid a skewed image.
|
|
4. **[memory-map.md](memory-map.md) — the memory map.** How the loader learns what
|
|
physical RAM exists and hands it to the kernel in danos's own neutral format,
|
|
rather than leaking UEFI's memory descriptors across the boundary.
|
|
5. **[frame-allocator.md](frame-allocator.md) — the physical frame allocator.** The
|
|
bitmap allocator that hands out and reclaims 4 KiB physical frames from that
|
|
map — the primitive page tables and the heap will be built on.
|
|
6. **[halting.md](halting.md) — halting.** Why a kernel can't just "exit", and
|
|
how `while (true) hlt` parks the CPU safely once there's nothing left to do.
|
|
|
|
Cutting across all of these:
|
|
|
|
- **[arch.md](arch.md) — the architecture split.** How CPU-specific code is kept
|
|
behind a build-time `arch` module so the generic kernel never names x86_64,
|
|
leaving room for other systems (e.g. an AArch64 Raspberry Pi) later.
|
|
|
|
## How the pieces relate
|
|
|
|
The boot flow ties them together: UEFI runs the loader ([efi.md](efi.md)), which
|
|
queries the **GOP** to pick a graphics mode ([gop.md](gop.md)), hands the kernel a
|
|
**framebuffer** to draw into ([framebuffer.md](framebuffer.md)) and a **memory
|
|
map** of physical RAM ([memory-map.md](memory-map.md)); the kernel turns that map
|
|
into a **frame allocator** ([frame-allocator.md](frame-allocator.md)), runs — its
|
|
CPU-specific bits behind the [arch](arch.md) boundary — and when it has finished,
|
|
or panics, it **halts** ([halting.md](halting.md)).
|
|
|
|
## Source map
|
|
|
|
| Area | Code |
|
|
|------|------|
|
|
| Bootloader (UEFI app) | `src/efi.zig` → `BOOTX64.efi` |
|
|
| Kernel entry, panic, bring-up | `src/main.zig` |
|
|
| Shared loader↔kernel contract (`BootInfo`, `Framebuffer`, `MemoryMap`, ABI) | `src/root.zig` |
|
|
| Physical frame allocator | `src/pmm.zig` |
|
|
| Framebuffer text console | `src/console.zig` |
|
|
| Arch-specific kernel code (`halt`, linker script) | `src/arch/x86_64/` |
|
|
| Build + `run-efi` (QEMU/OVMF) | `build.zig` |
|