VSOS is a really-basic, portable, hobby operating system written in C.

• bootstrap with qemu-system-aarch -M virt(arm64)
• return from interrupt at EL1 context (arm64)
• console driver (PL011 UART)
• printk (arm64)
• cooperative multitasking (arm64)
• system-timer driver (arm64)
• virtual memory at EL1 context (arm64)
• interruptible process sleep (arm64)
• bitmap based allocator
• SYS_read (arm64)
• SYS_write (arm64)
• initial shell (arm64)
• ELF loader (arm64)
• virtual memory at EL0 context (arm64)
• zygote user process (arm64)
• O_NONBLOCK and SYS_select (arm64)
• block device driver (arm64)
• file system (arm64)

• ARCHITECTURE.md - System architecture
• DESIGN.md - System design
• Build and usage instructions - See sections below

On Ubuntu 25.04, we need these dependencies:

sudo apt install build-essential clang clangd lld llvm ninja-build qemu-system-arm

We use ninja for building. To build the kernel and the shell, type:

ninja

This process produces kernel.elf, the kernel. The build process (see ninja.build) embeds the shell ELF binary inside the kernel itself.

To remove all built artifacts, use:

ninja -t clean

We use qemu-system-aarch64 -M virt for testing.

This is the only system supported by VSOS.

qemu-system-aarch64 \
  -M virt \
  -cpu cortex-a53 \
  -nographic \
  -kernel kernel.elf

To investigate errors, obtain more detailed logs using:

qemu-system-aarch64 \
  -M virt \
  -cpu cortex-a53 \
  -d in_asm,cpu,int,guest_errors -D qemu.log \
  -nographic \
  -kernel kernel.elf

This invocation will produce extensive logs inside the qemu.log file.

You will frequently need to correlate the logs with the kernel disassembly.

To obtain the kernel disassembly, use:

llvm-objdump -d --no-show-raw-insn -M no-aliases kernel.elf

or:

readelf -a kernel.elf

SPDX-License-Identifier: MIT

Portions of this code derive from nuta/operating-system-in-1000-lines.