swift

A Swift runtime built from source for OS X 10.9 "Mavericks" (Intel x86_64).

Modern Swift (6.3.x) assumes an Objective-C runtime and Swift ABI machinery that first shipped in macOS 10.14.4. mavericks-swift builds libswiftCore from unmodified swiftlang/swift sources with a 10.9 deployment target, plus a small set of source patches that make Swift's class-realization path work on 10.9's objc4-532 runtime. The result is memory-safe on real hardware: the validation test runs 510/510 consecutive clean on macOS 10.9.5, verified under Guard Malloc and MallocScribble.

This is Increment 0 (the core runtime) of a larger roadmap.

What works

A memory-safe Swift core runtime: strings, arrays, dictionaries, sets, closures, generics, existentials/protocol witnesses, ARC (incl. weak/unowned), class hierarchies, NSObject subclasses, runtime-instantiated generic classes (the storage behind Dictionary/Set/String), and if #available. Enough for command-line / computational Swift.

Scope / bounds — read before using

• Intel x86_64, OS X 10.9 only.
• Core runtime only. Ships libswiftCore (+ libswiftSwiftOnoneSupport for -Onone). The Foundation / AppKit overlays — needed for most apps, and for GUI — are later roadmap increments.
• Framework ceiling untouched. Swift running does not bring back APIs absent from 10.9 (modern WKWebView, CryptoKit, Network.framework, …). Those are separate work.
• Compilation happens on a modern host cross-targeting x86_64-apple-macosx10.9. This is a runtime, not a native toolchain.
• Running on an OS with no security updates is your own risk.

Install

sudo installer -pkg mavericks-swift-<version>.pkg -target /

Installs libswiftCore.dylib into /usr/lib/swift/. Build consumers for x86_64-apple-macosx10.9 with an absolute rpath of /usr/lib/swift (10.9's dyld does not honor @loader_path):

swiftc -target x86_64-apple-macosx10.9 -O -Xlinker -rpath -Xlinker /usr/lib/swift hello.swift -o hello
./hello

How it's built

./build.sh on a modern macOS: fetch the pinned swift.org toolchain, check out pinned Swift + llvm-project sources, apply patches/, build the standard library only (no full LLVM), and self-check with the compat guard. CI does the same on a macos-26 runner and attaches the .pkg to a GitHub Release (see .github/workflows/release.yml).

The fix stack (all confirmed on real 10.9.5)

1. Threading — SWIFT_THREADING_PACKAGE="OSX:pthreads" removes os_unfair_lock (10.12).
2. -fno-sized-deallocation — 10.9's libc++ lacks the C++14 sized operator delete.
3. os_system_version guard — guarded + CoreFoundation SystemVersion.plist fallback, so if #available works on 10.9.
4. objc_readClassPair guard + minimal in-place realization — 10.9's objc lacks the 10.11 SPI; the runtime realizes runtime-instantiated generic classes itself, in objc4-532's layout.
5. Realization-aware getROData — follow rw->ro when RW_REALIZED (objc-532 realizes eagerly at image load, so the class's Data word is the rw, not the ro).
6. objc-super instance-size fix — size subclasses from class_getInstanceSize(super) on 10.9, where objc-532 drops the Swift is-swift bit and the normal path under-sizes them.

All gated to the pre-objc_readClassPair (10.9/10.10) runtime; the modern-OS code path is byte-unchanged.

Validation

The gate is on real 10.9.5 (a modern host is structurally blind to these bugs): the test binary must pass 100× consecutive exit 0 + Guard Malloc + MallocScribble clean, with no DYLD environment variables. See tests/thorough_test.swift.

Licensing

Swift is Apache License 2.0 with the Runtime Library Exception (see LICENSE). mavericks-swift builds that source and redistributes the resulting binary under those terms — it does not redistribute any Apple prebuilt runtime, SDK, or framework. See NOTICE for attribution and the list of local patches. This repo's own glue (scripts, packaging) is under the same license.

Provenance

Every release ships a MANIFEST with the exact Swift version, source commit SHAs, build flags, and per-file sha256. No Apple bytes are committed here.