simplex-chat/scripts/nix/README.md

Haskell builds with Nix

The compiler and all cross-compilers come from the haskell.nix input pinned in flake.lock. The ghc914-sh compiler is the stable-haskell fork, not the stock GHC 9.14 release from GHCup. Use the same source checkout and lock file for every platform; Android ARMv7 does not require a separate branch or tag.

compiler-selection.nix and compiler-cache-overlay.nix match Hydra's compiler build context, including auxiliary iserv projects, so the pinned compiler can use its existing cache. Application dependencies keep the project's current packages.

Cross projects add ghc-internal to the Cabal dependencies of the pinned composition-1.0.2.2 source. This preserves its deliberate avoidance of base while making GHC 9.14's wired-in types available in isolated target package databases. The patch runs before planning and source packaging. Native builds and the Mac-to-iOS conversion projects keep the original package metadata.

Run these commands from the repository root:

make help
make nix-list                  # list this host's existing Hydra outputs
make nix-native                # native library and CLI
make nix-android               # ARM64 + ARMv7 libraries, on x86_64-linux
make nix-windows               # Windows library and CLI, on x86_64-linux
make nix-linux-static          # x86_64, i686, and ARM64 static Linux CLIs
make nix-build                 # all existing outputs for this build host

Each command builds this checkout, without cloning another branch. Output links are placed under result-nix/<build-system>/<package>. ZIP filenames inside the outputs retain the existing Hydra names. For example, the ARMv7 client library is result-nix/x86_64-linux/armv7a-android:lib:simplex-chat/pkg-armv7a-android-libsimplex.zip. Nix includes tracked working-tree changes; add new source files to Git before building so they are included.

For a remote builder, select its build system explicitly. Nix must already have that builder configured:

make nix-ios NIX_SYSTEM=aarch64-darwin
make nix-darwin-libs NIX_SYSTEM=x86_64-darwin
make nix-build NIX_SYSTEM=aarch64-linux

nix-ios produces the Haskell static-library ZIP. It does not run Xcode, sign an iOS application, or upload to TestFlight. ARM64 device libraries and Intel simulator libraries retain their separate outputs. The existing iOS preparation scripts retag ARM64 archives with mac2ios -s when an Apple Silicon simulator is needed.

The Cabal v2 builder stores ordinary package archives in its staged store. link-mobile-library.sh relinks the selected package and its dependencies before that store is pruned. iOS ZIPs contain both the plain libHSsimplex-chat-*.a and the rolled libHSsimplex-chat-*-ghc*.a used by update-pbxproj.sh. Android and Windows clients link the threaded RTS into libsimplex.so or libsimplex.dll; Android's separate libsupport.so resolves RTS symbols from the client library. ARM64 Android libraries retain the 16 KiB linker alignment. These steps run in the derivation's build/install phases because v2 component overrides do not run the older postBuild and postInstall hooks.

Mobile builds keep the RTS's small-address-space setting. On Darwin, the final link uses ABI-checked replacement RTS registrations, plus a replacement text on ARM64. These boot libraries and all ARM64 mobile app C/C++ code target the Apple A7 instruction baseline before mac2ios retags the archives. The cached native compiler itself stays unchanged. Android applies the RTS source patch when building its boot libraries. The Android overlay also supplies GNU iconv headers and a static PIC archive to ghc-internal, including the separate iserv projects. The ghc-internal system dependency propagates GNU iconv to interpreter consumers as well. The ARM32 interpreter registers the GNU iconv function addresses for runtime object loading. Its source is patched before Cabal planning, removing false missing-function stubs that shadow real static Bionic startup routines. Android links libffi through the RTS package dependency. The minimum Android API stays at 26.

Android ARM32's QEMU wrapper preserves the guest's PER_LINUX32 execution domain when an ARM64 host kernel rejects that domain. Upper personality flags still go through the host, and queries and setters retain the previous guest value. This applies only to the Android ARM32 emulator; native compiler cache paths and the other emulator targets stay unchanged. Android's libc initializes this state again at startup after an exec.

A standalone C regression checks startup, full personality values, the host's UNAME26 effect, and independent thread/fork state. Run it from this checkout with configured Linux builders; Nix supplies the pinned Android API26 NDK and patched QEMU. The NDK compiles the tiny payload on x86_64 Linux; QEMU then runs on the selected Linux architecture. For example, on an Apple Silicon Mac whose Linux builder supports both x86_64 and ARM64:

nix build --impure --file scripts/nix/check-android-personality.nix \
  --argstr system aarch64-linux --max-jobs 1 --cores 1 --print-build-logs

Use --argstr system x86_64-linux for an x86_64 Linux builder. This optional check does not add a Hydra output. It checks C startup and personality handling; it does not qualify GHC/base under Rosetta, cross-TH, or Android device behavior. The static C fixture supplies the ARM TLS alignment input added to newer Android CRTs; its minimum API stays at 26. On 2026-10-15 this regression passed on native ARM64 Linux, native x86_64 Linux, and x86_64 Linux through Rosetta on an Apple Silicon Mac.

NIX_ARGS passes additional options to nix build, and NIX_OUT_DIR changes the output-link directory. Each derivation has a two-hour timeout by default; set NIX_BUILD_TIMEOUT in seconds to change it. For a wall-clock limit on a local batch, use timeout from GNU coreutils to include environment setup in the limit:

timeout 6h nix develop -c make nix-build
make nix-native NIX_ARGS=--dry-run

.github/workflows/nix.yml runs these same outputs on Linux ARM64/x86_64 and Darwin ARM64/x86_64, with a six-hour limit per job. Its seven jobs cover all 21 outputs once: x86_64 Linux runs native, android, windows, and linux-static separately; ARM64 Linux runs native; both Darwin hosts run all. A failed native Linux build therefore leaves the cross-build jobs running. Each job uploads its existing library ZIPs and CLIs under an artifact named for the build host, target group, and source SHA. Each native CLI also runs the encrypted-store and profile-password smoke test, which can be repeated with python3 scripts/nix/smoke-cli.py result-nix/BUILD_SYSTEM/exe:simplex-chat/bin/simplex-chat.

After a failed native x86_64 Linux library build, CI tries a separate derivation with -v2 -ddump-timings and GDB on compile calls and uploads native-linux-ghc-phase-trace.log, including when that trace fails. Compiler queries and the original source, plan, dependency units and GHC arguments stay unchanged. GDB follows the compiler's shell wrapper into the actual ELF program, preserving its injected package DB and -B arguments. On a stopped fault it records up to 80 frames per thread, registers, the PC symbol and disassembly, shared libraries and memory mappings. It does not dump the environment or a core file. Normal compiler exit codes propagate; faults and debugger errors fail the diagnostic. The canonical build remains failed. The trace runs one derivation at a time and inherits the canonical Nix core setting, preserving Setup's job count and the compiler job arguments. It has a two-hour wall-clock/per-derivation bound, including cache-only debugger setup; a debugger cache miss fails visibly without compiling GDB locally or remotely. The job's six-hour limit stays in place. A local --cores override also changes those job arguments and must be reported when comparing diagnostics. trace-native-ghc.nix accepts the original component via --arg original and an optional pinned GDB derivation via --arg debugger. Omitting debugger retains the phase-only trace. GDB leaves ASLR enabled; its host/runtime effects must be reported when comparing diagnostics.

Hydra continues to consume the same hydraJobs attributes. The older application release workflow still uses its existing GHCup/Docker compiler settings; migrating that packaging and release path is separate from this Nix build lane.

Hydra needs builders advertising aarch64-darwin and x86_64-darwin to run the corresponding Mac/iOS jobs. Check its builder pool when jobs remain queued. For cross builds, the pinned haskell.nix uses recursive-nix as a scheduling marker; these builds do not need recursive Nix operations. This checkout opts ghc914-sh Android ARM32 out of that restriction on Linux with patched QEMU 9.1–11, after passing normal target TH under emulation. Other target/compiler package sets retain the upstream guard, which also covers cross-compiler stalls without QEMU. Advertise the marker on a native x86_64 Linux builder for those jobs; keep it off Rosetta slots. Nix also requires the recursive-nix experimental feature when building derivations with this reserved marker. Enable both extra-experimental-features = recursive-nix and extra-system-features = recursive-nix on that builder. The GitHub workflow sets both only for its native x86_64 Linux runner. The upstream fixes and regression jobs are in haskell.nix PR #2585.

To build both Android APK ABIs from the current checkout, preserving the same compiler and source, use the existing builder's source/skip-checkout flags:

scripts/android/build-android.sh -sg VERSION_CODE

This command also needs the Android SDK, Gradle, and its other existing tools. The APK reproduction script now checks out the supplied tag for both ABIs. Historical releases that used a separate -armv7a tag must be reproduced with their historical build scripts.

Migration validation

On 2026-10-16, all 21 existing Hydra derivations evaluated successfully at f26dbbc0d93a5c359427307b4c57f7f5e2123d69: 11 on x86_64 Linux, two on ARM64 Linux, and four on each Darwin architecture. This includes both Android ABIs, Windows, and all three static Linux targets. This establishes derivation evaluation; the completed artifact builds are listed below.

The native ARM64 Darwin library and CLI built with Nix at f26dbbc0d and passed python3 scripts/nix/smoke-cli.py /path/to/simplex-chat, covering encrypted stores and profile passwords. Their actual outputs contain ARM64 macOS objects and the expected library registration or CLI executable. Earlier native BBS checks also passed; the relevant native source, compiler, flags, and dependencies remain unchanged.

A native build with the iOS Swift/CommonCrypto flags passed mobile C API checks using the rolled archive produced by link-mobile-library.sh: Swift JSON, encrypted stores, UTF-8, reopen behavior, and wrong-key errors with copying and nonmoving GC. This ran on macOS before archive retagging. The CommonCrypto SQLCipher component also built with Nix and registered both Apple frameworks. The replacement RTS and text built with Nix and passed ABI, instruction-baseline, UTF-8, and GC checks.

Both full Nix ARM64 iOS library ZIPs, Swift JSON and tagged JSON, built at f26dbbc0d93a5c359427307b4c57f7f5e2123d69. Each ZIP contained its five expected archive entries with valid CRCs and 3,630 Mach-O members tagged ARM64/iOS. Their Hydra product markers pointed to the actual ZIPs. The production FFI archive previously passed an instruction-baseline check with unchanged inputs. The package uses the full Cabal v2 unit ID in its archive filenames; the existing Xcode project updater accepts those names. This verifies the packaged library, not execution after retagging.

The Android API26 ARMv7 ghc-internal built with all 292 Haskell modules and C sources. Its unit ID and ABI match the earlier build, and GNU iconv is retained in installed paths and consumer dependencies. Canonical base and the complete normal interpreter dependency closure also built under Rosetta.

On 2026-10-16, the normal ARM32 TH trial passed with the production compiler, interpreter, and all 40 target-library outputs. A target-side splice asserted System.Info.arch == "arm" and a 32-bit Int, then emitted 42. The resulting shared ELF32 ARM library exported the test function; a static C caller initialized the Haskell RTS and received 42 from the same compiled object. This inspects the shared library and executes a static caller, rather than loading the shared library on an Android device. The byte-identical upstream annotation test also compiled through the target interpreter.

The identical production interpreter reached Haskell main with both x86_64 QEMU under Rosetta and native ARM64 Linux QEMU. It has no PT_TLS segment and needed no TLS adjustment. The separate C caller retains the API26 CRT alignment fixture used by the C regression. The final QEMU version guard preserves the exact compiler, core, base, interpreter, and wrapper identities from this trial. These functional changes are integrated at 748becda3eac5173bdbf34ef4eec476a9215326f.

The trial used a normal-only diagnostic wrapper around the real production vanilla interpreter. The full mobile wrapper also references a profiling interpreter, so normal application builds can still compile profiling dependencies. Profiling execution, final Linux/Windows and Intel Darwin outputs, complete Android libraries/applications, device tests, and an Xcode application build remain unverified. Derivation evaluation and the normal trial do not establish that those builds and runtime checks pass.

Updating package hashes

1. Install nix, gawk and jq.

2. Start nix-shell from repo root:

nix-shell -p nix-prefetch-git

3. Run in nix shell:

gawk -f ./scripts/nix/update-sha256.awk cabal.project > ./scripts/nix/sha256map.nix