aarch64

cppkernel — aarch64

A freestanding aarch64 toy kernel written in C++ with full exceptions and RTTI enabled, running on QEMU virt. Built against unmodified libsupc++ and libgcc_eh from a stock GCC 14 install.

For the full story of why this is interesting and what it took to make it work, see the article one directory up: ../article-exceptions-rtti-aarch64.md.

What's in here

File	What it is
src/boot.S	aarch64 entry point — EL1 dispatch, FPU enable, MMU bring-up, BSS zero, .init_array, jump to C++
src/kernel.cpp	Test driver for M0 through M4 (UART, global ctors, heap, exceptions, RTTI)
src/cxxrt.cpp	Libc stub surface + __cxa_get_globals override + __register_frame caller
src/heap.hpp	512KB bump allocator
src/uart.hpp	PL011 driver at 0x09000000
src/linker.ld	Entry at 0x40080000, standard section layout + .eh_frame sentinel
src/Makefile	Build rules
Dockerfile	Reproducible build environment (Ubuntu 24.04 + g++-14)

Build

The Docker path (recommended, reproducible)

docker build -t cppkernel-aarch64 .
docker run --rm -it -v "$(pwd)/src:/src" cppkernel-aarch64 \
    bash -c "cd /src && make CXX=g++-14"

The build takes a few seconds once the image is ready. The image itself is ~3–5 minutes on first docker build (mostly apt-get update).

The native path

If you have GCC 14+ for aarch64 available directly (native on an Apple Silicon Mac, a Linux/aarch64 machine, or as a cross-compiler), you can just build in src/:

cd src
make CXX=g++-14

Anything from GCC 14 onward should work. g++-15, g++-16 trunk, etc. are all fine. g++-13 and earlier use a different FDE registration path inside libgcc and have not been tested — you might need to adjust M3's Wall 4 / Wall 5 approach.

Run

On the host (not in the container), with QEMU installed:

cd src
qemu-system-aarch64 -M virt -cpu cortex-a72 -m 128M -nographic \
    -kernel build/kernel.elf

Quit QEMU with Ctrl-A then X.

You can also run inside the Docker container via make run, which is convenient if you don't have QEMU installed on the host:

docker run --rm -it -v "$(pwd)/src:/src" cppkernel-aarch64 \
    bash -c "cd /src && make CXX=g++-14 run"

Expected output

[init] Global constructor called

========================================
  cppkernel — bare metal C++ kernel
  Toolchain: GCC 14+ / C++17
  Target:   aarch64 / QEMU virt
========================================

[M0] UART output:  OK
[M1] Global ctors: OK (banner = "cppkernel M4")
[M2] Heap allocation:
  new Device:      uart0 (id=0x1)
  new int[10]:     arr[0]=0xcafe arr[9]=0xbeef
  new RamFS:       type=ramfs
  new ProcFS:      type=procfs
  Heap used:       0x12230 / 0x80000
  PASS
[M3] Exceptions:
  caught direct: errno=0x1
  entering outer_function
  entering inner_function
  caught nested: errno=0x16 msg=EINVAL from inner
  PASS
[M4] RTTI:
  typeid(*fs1).name() = 5RamFS
  typeid(*fs2).name() = 6ProcFS
  dynamic_cast<RamFS*>(fs1):  OK
  dynamic_cast<ProcFS*>(fs1): nullptr as expected
  dynamic_cast<ProcFS*>(fs2): OK
  typeid(*fs1) != typeid(*fs2): OK
  PASS

All milestones passed. Halting.

After All milestones passed. Halting., the kernel spins in wfe and QEMU keeps running until you exit it with Ctrl-A X.