SchOS/docs/building.md

Building SchOS

Supported hosts: Linux, macOS, FreeBSD/OpenBSD/NetBSD, and Windows (under Git Bash or MSYS2). The build is developed from both Windows and Linux, so a change that only works on one of them is a bug.

make          # kernel + bootloader + root filesystem -> schos.img
make qemu     # build and boot it

Prerequisites

Need	Why	Windows	Linux	macOS	BSD
clang, ld.lld, llvm-objcopy, llvm-objdump	cross-compiles the kernel, the 16/32-bit boot code, and musl userland	LLVM installer	clang lld llvm	brew install llvm	pkg install llvm
make	—	Git Bash	make	Xcode CLT	gmake
perl	generates the interrupt vector table	Git Bash	usually present	present	pkg install perl5
python3	boot logo, crash-screen QR	python.org (python)	python3	brew install python	pkg install python3
qemu-system-x86_64	running and testing	scoop install qemu	qemu-system-x86	brew install qemu	pkg install qemu
curl, tar	fetching ports	Git Bash	present	present	present
xorriso or mkisofs	make iso only	scoop install cdrtools	xorriso	brew install xorriso	pkg install xorriso

A host C compiler (cc) is also needed, for the tools that build the disk images. On Windows that must be mingw-w64's gcc, not clang: clang defaults to an MSVC target there, and tools/mkfs.c needs <unistd.h> and <dirent.h>, which the Windows SDK does not have.

Why clang rather than a cross-gcc

clang is a cross-compiler by construction, so one ordinary LLVM install targets everything this tree needs — bare-metal ELF, code linked below one megabyte, and Linux/musl userland — from any host. A cross binutils+gcc would be a day of setup per platform that then rots, and on macOS it means brewing x86_64-elf-gcc before anything builds at all.

The Makefile selects clang+lld whenever both are on PATH. To force the GNU toolchain instead:

make USE_GNU=1                    # needs a cross toolchain that emits x86_64 ELF
make USE_GNU=1 TOOLPREFIX=x86_64-elf-

Testing

tools/bootcheck.ps1               # boots, drives the shell, asserts on output
tools/bootcheck.ps1 -Tty -Ps      # plus terminal behaviour and process listing
make schfs-check                  # SchFS unit, object and image suites

bootcheck is PowerShell, and PowerShell 7 (pwsh) runs on Linux, macOS and the BSDs as well as Windows — brew install powershell, or your distribution's powershell package. It finds QEMU on PATH.

Booting to a prompt proves nothing on its own: a filesystem can mount and still fail the first real command, which has happened here. bootcheck types commands at the serial console and greps the transcript for the answers they should produce.

Ports

musl, toybox and mksh are built from source into sysroot/. This does not work on a Windows host — make prints ports: skipped and uses whatever is already staged in sysroot/. Building them needs a Linux host (or any other Unix); do it once and the staged result serves the Windows builds.

Known host differences, already handled

Listed because they are the shape of the next such bug, not because anything is outstanding:

• <sys/sysmacros.h> is glibc/musl only. macOS and the BSDs take major() and minor() from <sys/types.h>.
• sha256sum exists on Linux and Git Bash; macOS has shasum -a 256, FreeBSD/NetBSD sha256, OpenBSD cksum -a sha256. tools/sha256check.sh finds whichever is present.
• nproc is coreutils, so absent on macOS and BSD, where it is sysctl -n hw.ncpu.
• In the PowerShell tools, path literals must use forward slashes: Join-Path $root 'build\x' produces a filename containing a backslash on a Unix host.

Working on two machines

Claude Code's project memory is kept in the repo and moved with:

tools/memory-sync.sh status
tools/memory-sync.sh export   # after a session that learned something; then commit
tools/memory-sync.sh import   # after cloning or pulling elsewhere