Show HN: Kakehashi – Experimental userspace to run macOS binaries on Linux ARM

Kakehashi Userspace macOS ARM64 → Linux aarch64 translation layer (CLI-first, no JIT). Load Darwin Mach-O on Linux aarch64, map a freestanding libSystem, translate BSD syscalls, and run real guests (clang probes, 7-Zip 7zz, curl, threads). Live execution Linux aarch64 (bare metal, VM, Colima/Docker) Dry-load / inspect Any host (including macOS) Design reference docs/ What works Verified on Docker/Colima and UTM (Linux aarch64). Install once: cargo install kakehashi # or from a checkout: cargo install --path crates/kh-cli --force kh bottle ensure kh install 7zip # Darwin 7zz → guest /usr/local/bin/7zz kh install curl # Darwin curl → guest /usr/local/bin/curl Relative -o / archive paths resolve against the host CWD of the kh process (create parent dirs yourself, or rely on auto-mkdir for O_CREAT). Through the bottle, /Volumes/linux/… bridges to the host root (/ → host /). 7-Zip (7zz) # Version / help kh run 7zz -- kh run 7zz -- --help # Create archive (cwd-relative) kh run 7zz -- a demo.7z README.md kh run 7zz -- t demo.7z kh run 7zz -- l demo.7z kh run 7zz -- x -o./out demo.7z # Multi-thread compress (correctness gate) kh run 7zz -- a -t7z -m0=lzma2 -mx=5 -mmt=4 mt.7z README.md kh run 7zz -- t mt.7z # expect: Everything is Ok, exit 0 Docker helpers (artifacts under host .tmp/kh-out/): ./scripts/docker-7zz.sh --help ./scripts/docker-7zz.sh a /Volumes/linux/out/demo.7z /Volumes/linux/src/README.md ls -lh .tmp/kh-out/demo.7z KAKEHASHI_HYPERCALL=1 ./scripts/docker-7zz.sh a -t7z -m0=lzma2 -mx=5 -mmt=4 \ /Volumes/linux/out/mt.7z /Volumes/linux/src/README.md ./scripts/docker-7zz.sh t /Volumes/linux/out/mt.7z curl # Banner (G1) kh run curl -- --version # HTTP GET → file (G3 / G5). Parents for -o are created when missing. kh run curl -- -sS -o .tmp/kh-out/body http://example.com/ # expect: exit 0, ~559 bytes, HTML contains "Example Domain" wc -c .tmp/kh-out/body head -c 80 .tmp/kh-out/body; echo # HTTP to stdout kh run curl -- -sS http://example.com/ | head -c 80; echo # HTTPS GET (G4) — OpenSSL + bottle CA (from host or curl.se download) kh run curl -- -sS -o .tmp/kh-out/https-body https://example.com/ wc -c .tmp/kh-out/https-body # Negative: bad / self-signed cert must fail (rc ≠ 0) kh run curl -- -sS -o /dev/null https://self-signed.badssl.com/; echo exit:$? Docker helpers: ./scripts/docker-curl.sh --version ./scripts/docker-curl.sh -sS -o /Volumes/linux/out/body http://example.com/ ./scripts/docker-curl.sh -sS -o /Volumes/linux/out/https-body https://example.com/ ls -lh .tmp/kh-out/body .tmp/kh-out/https-body # Trace-first probe logs → .tmp/kh-curl-probe/ ./scripts/docker-curl-probe.sh --version # Option matrix (large tiers) → .tmp/kh-curl-options/ ./scripts/docker-curl-options.sh tier1 ./scripts/docker-curl-options.sh tier9-10 ./scripts/docker-curl-options.sh all # tier1..10 Harmless noise on many runs: kh: open fail ENOENT(openat) path=/etc/ssl/openssl.cnf — OpenSSL optional config; HTTP/HTTPS still work via the seeded CA bundle. WARN … skip dylib … Security/CoreFoundation — Apple frameworks not in the bottle; soft stubs cover the load path. unresolved strong symbol; bound to named missing trampoline — symbols not hit on the happy path. Details and gates: docs/curl.md. Also green Surface Notes Clang / fixture probes tests/clang-probe/, tests/fixtures/ Multi-thread 7zz -mmt=4 Docker + UTM Bottle + freestanding libSystem kh bottle ensure embeds dylib Unit tests + clippy cargo test / clippy workspace (excl. kh-libsystem) Not a product claim (yet) Full curl feature set (POST bodies, proxies, HTTP/3 end-to-end, every scheme), real Apple Security.framework, git / CLT, codesign. Next product slice: git via kh install xcode-tools — see docs/git.md. Crates Crate Role kakehashi Binary kh (install this) kh-loader Mach-O parse, map, execute kh-runtime Memory, traps, BSD syscalls, bottle; embeds freestanding libSystem.B.dylib kh-libsystem Source for that dylib (aarch64-apple-darwin only; not a Linux host crate) The guest dylib is vendored at crates/kh-runtime/resources/libSystem.B.dylib and compiled into the runtime with include_bytes!. Publishing kh-runtime ships the dylib; end users do not need a separate download. Requirements Rust 1.88+ Linux aarch64 for live kh run / kh trace Page sizes: 4 KiB (containers) and 16 KiB (Asahi-class) Optional: curl/wget + tar for kh install 7zip / kh install curl Install cargo install kakehashi # or from a checkout: cargo install --path crates/kh-cli kh bottle ensure kh install 7zip kh install curl Bottle layout Default root: ~/.local/share/kakehashi/bottle/ (override with KAKEHASHI_DATA_DIR / KAKEHASHI_ROOT). Host Guest …/bottle/ / …/usr/local/bin/7zz …/usr/local/bin/7zz …/bottle/ / …/usr/local/bin/curl …/usr/local/bin/curl …/bottle/ / …/usr/lib/libSystem.B.dylib …/usr/lib/libSystem.B.dylib …/private/etc/ssl/cert.pem /etc/ssl/cert.pem (host CA or downloaded Mozilla) …/Volumes/linux/… /Volumes/linux/… → host FS Performance (honest) Kakehashi runs guest code natively on the CPU. The tax is the syscall boundary (TLS switch, alt stack, NEON save/restore, Rust dispatch) × how chatty the guest is — not an instruction emulator. Measured gap On Ubuntu aarch64 bare-metal (UTM), multi-file 7zz archive (-t7z -m0=lzma2 -mx=5 -mmt=4, ~8k files / ~240 MiB tree): native Linux 7zz Darwin 7zz under kh ratio wall ~22.5 s ~118 s ~×5.2 On compression-heavy, few-file samples the gap is often much smaller (~×1.1–1.2). The large multi-file gap is dominated by path walk + per-syscall boundary, not “wrong LZMA”. Hypercall is on by default for all guest threads. Opt out with KAKEHASHI_HYPERCALL=0 only for debug (residual svc→brk / SIGTRAP). Why ~×5 is still useful in CI The product goal for CI is not “as fast as native macOS,” but run Darwin CLI/tools on cheap Linux aarch64 runners instead of scarce, expensive macOS capacity. GitHub Actions hosted runners (private-repo overage rates, USD per minute; see Actions runner pricing): Runner Per-minute rate Linux 2-core arm64 $0.005 Linux 2-core x64 $0.006 macOS 3–4 core (M1/Intel) $0.062 macOS larger (e.g. 12-core / M2 Pro) $0.077–$0.102 macOS standard is roughly ×10–×12 the Linux arm64 minute rate before any wall-time difference. Even if a job runs ×5 slower under kh on Linux arm64 than the same work on a macOS runner, billable cost can still be lower because the macOS minute is an order of magnitude more expensive (illustrative: 5 × $0.005 ≈ $0.025 vs 1 × $0.062). Public-repo free minutes and self-hosted Linux amplify that further; macOS hosted capacity also tends to queue longer and (on GitLab SaaS) is Premium/Ultimate / beta-gated. When macOS runners still win: GUI, codesign/notarization, Xcode UI tests, or any workload that is not a pure CLI Darwin binary under freestanding libSystem. Gates, not benches: CI correctness is cargo test / smoke / 7zz -mmt=4, not “match native wall clock.” Perf work is tracked in docs/roadmap.md. Quick start (Docker / Colima on Apple Silicon) docker build -t kakehashi:dev -f Dockerfile.dev . docker run --rm -v "$PWD":/src -w /src kakehashi:dev \ cargo test --workspace --exclude kh-libsystem # Full smoke (build + clippy + test + micro run) ./scripts/docker-smoke.sh Build cargo build -p kakehashi --release cargo test --workspace --exclude kh-libsystem cargo clippy --workspace --exclude kh-libsystem --all-targets -- -D warnings # Maintainers: refresh embed after freestanding ABI changes cargo build -p kh-libsystem --release --target aarch64-apple-darwin ./scripts/stage-libsystem.sh # → crates/kh-runtime/resources/libSystem.B.dylib libSystem discovery: --libsystem → KAKEHASHI_LIBSYSTEM → paths next to kh → crate resources/ → embedded bytes in kh-runtime. Testing map Goal Command Artifacts Unit tests cargo test --workspace --exclude kh-libsystem terminal Docker smoke ./scripts/docker-smoke.sh ends with smoke ok Fixtures kh run --expect-code … tests/fixtures/… see tests/fixtures/README.md Clang probes kh run --root tests/fixtures/bottle tests/clang-probe/puts_hello stdout hello Real Darwin 7zz ./scripts/