ZBC Semihosting

The Zero Board Computer is the hardware equivalent of Hello World. It’s the minimum viable computer – just enough to prove your CPU and toolchain work.

The Zero Board Computer <https://www.zeroboardcomputer.com> is an idealized computer architecture, designed for bringing up new toolchains, new CPUs, and new compilers, quickly and easily. Its design is simple and clean; it’s easy to emulate, debug, and understand.

Functionally, the ZBC just your favorite CPU, a whole bunch of RAM, a super simple (optional) video display, and a semihosting device.

This ZBC semihosting device provides an ARM-like standardized interface, so that guest programs can request host services such as file I/O and timekeeping. This repository is a reference implementation of that semihosting device, which you can use to add semihosting support to your favorite emulator or toolchain.

Whether you’re building a bare-metal toolchain for a new CPU, writing an emulator, or compiling an operating system, ZBC semihosting makes it easy for you to get standard C library features like file I/O, console output, and time services up and running quickly, without having to muck around writing device drivers.

Full documentation: https://johnwbyrd.github.io/semihost/

Who Is This For?

  • Bare-metal developers – filesystem, console, and time services on a new (or old) architecture, without writing device drivers

  • Toolchain and SDK developers – run compiler test suites on emulated hardware

  • Emulator authors – add semihosting so guest programs can access host files

  • libc porters – implement fopen/fread/fwrite without real device drivers

Features

  • Works on any CPU from 8-bit to 64-bit (architecture-agnostic RIFF protocol)

  • ARM semihosting compatible syscall numbers

  • C90 compliant to be friendly with ancient compilers

  • Extremely portable

  • Does zero heap allocation – you allocate all your own buffers

  • Secure (sandboxed) and insecure backends

  • GitHub test suite for Ubuntu, macOS, and Windows

  • Automatic fuzzing of RIFF parser

Documentation

User Guides

API Reference

# Basic build + host tests
cmake -B build && cmake --build build && ctest --test-dir build

# With on-target tests (requires MAME + cross-compilers)
cmake -B build -DZBC_TARGET_TESTS=ON

# With seccomp sandbox (Linux)
cmake -B build -DZBC_USE_SECCOMP=ON

# With fuzzing (requires Clang)
cmake -B build-fuzz -DENABLE_FUZZING=ON

Testing

Tests run on Linux, macOS, and Windows. CI includes AddressSanitizer, UndefinedBehaviorSanitizer, and continuous fuzzing via ClusterFuzzLite.