Building

PureDarwin is built with Nix. Every artifact the project produces, from a single library to a bootable disk image, is a flake output: components, kernel collections, disk images, and the QEMU runners that boot them. The short version, on a Linux host:

nix-store --add-fixed sha256 /path/to/MacOSX11.3.sdk.tar.xz
nix build .#image-minimal
nix run .#vm

Under the Nix layer, the Darwin sources themselves are compiled by CMake. That CMake tree exists because Apple’s Xcode projects had to be ported to it, and it is driven by Nix rather than used on its own; configuring it by hand is not a supported path. Both layers rely on a cross toolchain the project builds for itself, and there is one proprietary prerequisite that has not yet been designed out. Those four topics get a page each:

• The Nix flake - the outputs, how they are organised, and the dev shell.
• The CMake tree - what CMake does here, and why it is not a supported entry point on its own.
• Host tools and toolchains - the cross compilers, the real ld64, and the bootstrap sequence that produces them.
• The Apple SDK requirement - the one file you have to supply yourself.

Two traps

Untracked files are invisible. The flake is evaluated from a git+file:// source, so a file you have not git added does not exist as far as the build is concerned. The failure mode is not an error: the build quietly uses the old state, and your change appears to do nothing. Stage before you build.

CMake is not an entry point. It is driven by Nix. The dev shell is for iterating on a single component, not for producing a system, so read The CMake tree before reaching for it.