feat(android): cross-build core libdb for aarch64-linux-android + CI gate

.github/workflows/android.yml

@@ -0,0 +1,91 @@
+# Android cross-build — core libdb for aarch64-linux-android (bionic libc).
+#
+# Dedicated workflow (does NOT touch ci.yml). Cross-compiles the core C
+# library with the NDK's clang against the existing root meson.build and
+# asserts that a real ARM aarch64 libdb.so is produced. This is a cross-BUILD
+# test: no emulator or device is used or needed.
+#
+# The NDK clang is just a cross-compiler; meson's HAVE_* probes are all
+# compile/link checks (which succeed cross) and sizeof/alignment resolve via
+# compile-only probes, so no target execution is required and no db_config.h
+# hand-patching is needed. As of this workflow the core library cross-builds
+# clean with zero source changes.
+#
+# continue-on-error keeps the job advisory (Android is not yet a release
+# target), but the cross-build + `file` assertion are a real signal: a
+# regression that breaks the arm64 build turns the assert step red.
+
+name: Android
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    paths:
+      - 'src/**'
+      - 'meson.build'
+      - 'meson_options.txt'
+      - 'meson/**'
+      - 'dist/android/**'
+      - '.github/workflows/android.yml'
+  schedule:
+    # Weekly (Mon 04:23 UTC): catches NDK/toolchain drift on a low cadence.
+    - cron: '23 4 * * 1'
+  workflow_dispatch:
+    inputs:
+      api:
+        description: 'Android API level'
+        default: '24'
+
+concurrency:
+  group: android-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  cross-aarch64:
+    name: cross-build aarch64-linux-android (API ${{ github.event.inputs.api || '24' }})
+    runs-on: ubuntu-latest
+    continue-on-error: true   # advisory tier — Android is not yet a release target
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install Meson + Ninja
+        run: python -m pip install --upgrade meson ninja
+
+      - name: Set up Android NDK
+        id: ndk
+        uses: nttld/setup-ndk@v1
+        with:
+          # r29 matches the nixpkgs ndk-bundle this path was validated against.
+          ndk-version: r29
+          local-cache: true
+
+      - name: Cross-build libdb.so (aarch64)
+        env:
+          ANDROID_NDK_ROOT: ${{ steps.ndk.outputs.ndk-path }}
+        run: |
+          dist/android/build_android.sh aarch64 "${{ github.event.inputs.api || 24 }}"
+
+      - name: Assert the artifact is an ARM aarch64 shared object
+        run: |
+          out=build-android/libdb.so
+          file "$out"
+          # Real gate: fail if it is not an AArch64 ELF shared object.
+          file "$out" | grep -q 'ELF 64-bit LSB shared object, ARM aarch64' \
+            || { echo "::error title=Android build::libdb.so is not aarch64"; exit 1; }
+          echo "::notice title=Android build::core libdb cross-built for aarch64-linux-android"
+
+      - name: Upload libdb.so (arm64)
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: libdb-android-aarch64
+          path: build-android/libdb.so
+          if-no-files-found: ignore

.gitignore

@@ -10,6 +10,8 @@ test/sim/TESTDIR_sim_*/
 # Meson/Ninja out-of-tree build dirs
 build-meson/
 build/
+build-android/
+build-android.cross.txt
 
 # nix build output symlink
 /result

dist/android/build_android.sh

@@ -0,0 +1,85 @@
+#!/bin/sh
+# Cross-compile the core libdb C library for Android via the NDK's clang and
+# the existing root meson.build. Produces build-android/libdb.so (aarch64 by
+# default). No emulator/device needed -- this is a cross-BUILD test.
+#
+# The NDK clang is just a cross-compiler: meson's HAVE_* probes are all
+# compile/link checks (which work when cross-compiling) and sizeof/alignment
+# are resolved by compile-only probes, so no target execution is required.
+#
+# Usage:
+#   ANDROID_NDK_ROOT=/path/to/ndk dist/android/build_android.sh [ABI] [API]
+#
+#   ABI : android ABI          -> aarch64 (default) | arm | x86_64 | x86
+#   API : android API level    -> 24 (default)
+#
+# ANDROID_NDK_ROOT is exported by nttld/setup-ndk and android-actions/setup-android.
+# ANDROID_NDK_HOME / NDK are accepted as fallbacks.
+set -eu
+
+ABI="${1:-aarch64}"
+API="${2:-24}"
+
+NDK="${ANDROID_NDK_ROOT:-${ANDROID_NDK_HOME:-${NDK:-}}}"
+if [ -z "$NDK" ]; then
+  echo "error: set ANDROID_NDK_ROOT (or ANDROID_NDK_HOME / NDK) to the NDK root" >&2
+  exit 2
+fi
+
+# NDK layout: toolchains/llvm/prebuilt/<host>/bin/<triple><API>-clang
+# nixpkgs' ndk-bundle nests the real NDK under libexec/android-sdk/ndk/<ver>/.
+if [ ! -d "$NDK/toolchains" ]; then
+  nested=$(find "$NDK" -maxdepth 5 -type d -path '*/toolchains/llvm/prebuilt/*/bin' 2>/dev/null | head -1)
+  [ -n "$nested" ] && NDK=$(dirname "$(dirname "$(dirname "$(dirname "$(dirname "$nested")")")")")
+fi
+
+case "$(uname -s)" in
+  Linux)  HOSTTAG=linux-x86_64 ;;
+  Darwin) HOSTTAG=darwin-x86_64 ;;
+  *) echo "error: unsupported build host $(uname -s)" >&2; exit 2 ;;
+esac
+BIN="$NDK/toolchains/llvm/prebuilt/$HOSTTAG/bin"
+
+case "$ABI" in
+  aarch64) TRIPLE=aarch64-linux-android;   CPUFAM=aarch64; CPU=aarch64 ;;
+  arm)     TRIPLE=armv7a-linux-androideabi; CPUFAM=arm;     CPU=armv7a ;;
+  x86_64)  TRIPLE=x86_64-linux-android;    CPUFAM=x86_64;  CPU=x86_64 ;;
+  x86)     TRIPLE=i686-linux-android;      CPUFAM=x86;     CPU=i686 ;;
+  *) echo "error: unknown ABI '$ABI' (aarch64|arm|x86_64|x86)" >&2; exit 2 ;;
+esac
+
+CC="$BIN/${TRIPLE}${API}-clang"
+CXX="$BIN/${TRIPLE}${API}-clang++"
+[ -x "$CC" ] || { echo "error: NDK compiler not found: $CC" >&2; exit 2; }
+
+ROOT=$(cd "$(dirname "$0")/../.." && pwd)
+BUILDDIR="${BUILDDIR:-$ROOT/build-android}"
+CROSS="$BUILDDIR.cross.txt"
+mkdir -p "$BUILDDIR"
+
+cat > "$CROSS" <<EOF
+# Generated by dist/android/build_android.sh -- do not commit.
+[binaries]
+c = '$CC'
+cpp = '$CXX'
+ar = '$BIN/llvm-ar'
+strip = '$BIN/llvm-strip'
+ranlib = '$BIN/llvm-ranlib'
+
+[host_machine]
+system = 'android'
+cpu_family = '$CPUFAM'
+cpu = '$CPU'
+endian = 'little'
+EOF
+
+echo "== NDK:  $NDK"
+echo "== CC:   $CC"
+echo "== out:  $BUILDDIR/libdb.so"
+
+meson setup "$BUILDDIR" "$ROOT" --cross-file "$CROSS" --wipe 2>/dev/null \
+  || meson setup "$BUILDDIR" "$ROOT" --cross-file "$CROSS"
+ninja -C "$BUILDDIR"
+
+"$BIN/llvm-strip" -o "$BUILDDIR/libdb.so.stripped" "$BUILDDIR/libdb.so" 2>/dev/null || true
+file "$BUILDDIR/libdb.so"