# Sylva OS — Agent Guide

x86_64 UEFI hobby OS. C17 boot (`.c`) → C++17 kernel (`.cpp`), ELF64 → PE32+ via objcopy.

## Build & Run

| Command | What |
|---------|------|
| `make` | Build `build/BOOTX64.EFI` |
| `make run` | QEMU + OVMF, serial port 1 → `serial.log`, serial port 2 → stdio, paused for GDB (`-s -S`) |
| `make clean` | **Always before commit** — gnu-efi build produces untracked files outside `build/` |

## Architecture

- `boot.c` — UEFI entrypoint (`efi_main` → `kernel_main()`)
- `kernel/main.cpp` — `extern "C" kernel_main()`: init GOP → serial → PMM → heap → idle (`hlt`)
- `kernel/serial.cpp` — UEFI serial protocol wrapper
- `kernel/memory/pmm.cpp` — bitmap + free-list physical page allocator
- `kernel/memory/heap.cpp` — kmalloc/kfree/kcalloc/krealloc (first-fit, coalescing)
- `graphics/` — GOP framebuffer pixel drawing, `fonts/` — Hankaku 8×16 font renderer
- `efi/` — bundled gnu-efi source; `gnu-efi/` is an unregistered submodule reference

## Quirks

- **`uefi_call_wrapper` required for all UEFI protocol calls** — omitting it causes page-faults (see `kernel/main.cpp:49`)
- `kernel_main` must be `extern "C"` (C→C++ linkage)
- QEMU starts paused — connect GDB to `:1234` to proceed
- Compiler standards: C17 (`boot.c`), C++17 (`kernel/`), `-ffreestanding -fno-stack-protector -fshort-wchar -mno-red-zone`
- `#define ASM asm volatile` in `include/common.h`
- `BUILD_INFOS.h` — placeholder for CI; `.github/` is empty
- No tests, no CI, no lint/formatter config