Fábio Coutada bafa872415 refactor(kernel): rewrite Stage 1 kernel in C++

- Rename kernel.c -> kernel.cpp and uart.c -> uart.cpp
- Add universalisos::uart namespace with constexpr register definitions
- Use extern "C" linkage for kernel_main() called from boot.S
- Compile with arm-none-eabi-g++ using C++17 freestanding flags
  (-fno-exceptions, -fno-rtti, -fno-threadsafe-statics, -fno-use-cxa-atexit)
- Update Makefile to use g++ and .cpp build rules

2026-07-06 22:53:50 +01:00

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Universalisos Kernel — Stage 1 Bare-Metal Skeleton (C++)

This is the first bootable type-1 hypervisor milestone for Universalisos: a minimal bare-metal kernel written in C++ that runs on QEMU's ARM virt machine and prints to the PL011 UART.

Building

Requires arm-none-eabi-gcc and qemu-system-arm.

cd kernel
make

Outputs:

kernel.elf — ELF image for debugging
kernel.bin — raw binary for QEMU -kernel

Running in QEMU

make run

This runs qemu-system-arm with the ELF image so that QEMU loads the kernel at the address specified in the linker script.

Expected output:

Universalisos type-1 hypervisor booted.
Stage 1: bare-metal C++ skeleton running on QEMU ARM virt.

Press Ctrl+A then X to exit QEMU.

Inspecting the binary

make dump

Layout

File	Purpose
`arch/arm/boot.S`	Assembly entry point, stack/BSS setup
`arch/arm/linker.ld`	Memory layout for QEMU virt (load at 0x40000000)
`arch/arm/uart.cpp`	PL011 UART driver
`arch/arm/uart.h`	UART interface
`kernel.cpp`	`kernel_main()` entry point

Design notes

The kernel is loaded by QEMU at RAM base 0x40000000.
A 64 KiB stack is reserved immediately after the BSS section.
Interrupts are disabled in the boot stub; the kernel idles with wfi.

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