IXLandSystem

IXLandSystem is the Linux-shaped runtime substrate for IXLand on iOS. It is a virtual kernel/runtime inside one iOS app sandbox whose job is to present Linux-oriented source and runtime semantics while keeping iOS host mediation private.

Status

This repository is under active virtualization and proof work. It is not public drop-in compatibility proof for arbitrary Linux userspace yet. Current proof in this repo is limited to:

• internal runtime semantic tests for selected subsystems
• Linux UAPI / ABI compile smoke tests for vendored headers
• canonical iOS Simulator builds and XCTest execution through XcodeGen + Xcodebuild

Build Truth

XcodeGen and the generated Xcode project are the only build truth.

Canonical flow:

xcodegen generate --project .
xcodebuild -list -project IXLandSystem.xcodeproj
xcodebuild -project IXLandSystem.xcodeproj -scheme IXLandSystem-6.12-arm64 -sdk iphonesimulator -arch arm64 -configuration Debug build
xcodebuild test -project IXLandSystem.xcodeproj -scheme IXLandSystem-6.12-arm64 -sdk iphonesimulator -configuration Debug -destination 'platform=iOS Simulator,name=iPhone 17'

Canonical project surface:

• Targets:
  • IXLandSystem
  • IXLandSystemTests
• Scheme:
  • IXLandSystem-6.12-arm64

swift build, CMake, Make, package manifests, and ad hoc build flows are not authoritative for this repo.

Repository Layout

Current top-level ownership is organized around the implemented subsystems in this tree:

• kernel/ — process/task, signal, pid, wait, cred, time, sync, init, resource, random, sys, network ownership
• fs/ — VFS, fdtable, open/read/write, stat, fcntl, ioctl, exec, path, mount, inode, readdir, eventpoll ownership
• runtime/native/ — native command registry surface
• arch/darwin/ — private host bridges only
• IXLandSystemTests/ — XCTest-based internal semantic tests and Linux UAPI compile smoke
• third_party/linux-uapi/6.12/arm64/include/ — vendored Linux UAPI truth
• project.yml — authoritative XcodeGen project specification

Architecture Direction

IXLandSystem does not define its Linux-facing contract by delegating host semantics directly. Its direction is a Linux-shaped virtual runtime with private iOS mediation. That includes:

• virtual task/process identity
• virtual process groups and sessions
• virtual credentials
• Linux-shaped signal ownership and semantics
• Linux-shaped VFS, fdtable, and exec ownership
• virtualization of unsupported host behavior where possible inside IXLand boundaries

Darwin and iOS APIs are private implementation details and must not define the Linux-facing contract.

Linux ABI and Header Policy

Vendored Linux 6.12 arm64 exported UAPI is the only Linux ABI truth in this repo.

Location:

• third_party/linux-uapi/6.12/arm64/include

Allowed include forms:

• #include <linux/...>
• #include <asm/...>
• #include <asm-generic/...>

Forbidden include forms:

• path traversal into vendored headers
• includes containing third_party/linux-uapi
• includes containing 6.12
• includes containing arm64

Test Layering

This XCTest tranche contains two kinds of proof only:

1. INTERNAL RUNTIME SEMANTIC TEST

   • uses private internal headers and _impl()/owner entry points
   • verifies IXLandSystem runtime behavior inside this repo
   • does not prove public drop-in compatibility

2. LINUX UAPI / ABI COMPILE TEST

   • uses vendored Linux UAPI headers through canonical include paths
   • proves header/constants/types resolution only
   • does not prove runtime behavior

Current files:

• IXLandSystemTests/SignalTests.m — INTERNAL RUNTIME SEMANTIC TEST
• IXLandSystemTests/TaskGroupTests.m — INTERNAL RUNTIME SEMANTIC TEST
• IXLandSystemTests/CredentialTests.m — INTERNAL RUNTIME SEMANTIC TEST
• IXLandSystemTests/LinuxUAPICompileSmoke.c — LINUX UAPI / ABI COMPILE TEST

True public drop-in Linux userspace compatibility proof is not part of this XCTest tranche.

Current Constraints

IXLandSystem runs inside one iOS app sandbox. Host limitations must be virtualized where possible rather than leaked into the Linux-facing contract. Some subsystems remain incomplete or partial; incomplete behavior should be treated as implementation work in progress, not as proof of finished Linux compatibility.

Primary References

• AGENTS.md — development rules for syscall ownership, _impl() usage, build proof, and error handling
• BUILD.md — canonical build and test commands
• docs/SUBSTRATE_CONTRACT.md — current architecture and ownership contract