[native_toolchain_c] Use 16 kb pages for Android by default (#1740)

Closes: #1611

pkgs/native_toolchain_c/CHANGELOG.md

@@ -1,5 +1,8 @@
 ## 0.6.1-wip
 
+- For Android, produce dylibs with page-size set to 16kb by default.
+  https://github.com/dart-lang/native/issues/1611
+
 ## 0.6.0
 
 - Address analyzer info diagnostic about multi-line if requiring a block body.

pkgs/native_toolchain_c/lib/src/cbuilder/run_cbuilder.dart

@@ -276,6 +276,9 @@ class RunCBuilder {
           cppLinkStdLib ?? defaultCppLinkStdLib[config.targetOS]!
         ],
         ...linkerOptions?.preSourcesFlags(toolInstance.tool, sourceFiles) ?? [],
+        // Support Android 15 page size by default, can be overridden by
+        // passing [flags].
+        if (config.targetOS == OS.android) '-Wl,-z,max-page-size=16384',
         ...flags,
         for (final MapEntry(key: name, :value) in defines.entries)
           if (value == null) '-D$name' else '-D$name=$value',

pkgs/native_toolchain_c/test/cbuilder/cbuilder_cross_android_test.dart

@@ -67,6 +67,9 @@ void main() {
                 .firstWhere((e) => e.contains('file format'));
             expect(machine, contains(objdumpFileFormat[target]));
           }
+          if (linkMode == DynamicLoadingBundled()) {
+            await expectPageSize(libUri, 16 * 1024);
+          }
         });
       }
     }
@@ -95,14 +98,37 @@ void main() {
     // Identical API levels should lead to an identical binary.
     expect(bytes2, bytes3);
   });
+
+  test('page size override', () async {
+    const target = Architecture.arm64;
+    final linkMode = DynamicLoadingBundled();
+    const apiLevel1 = flutterAndroidNdkVersionLowestSupported;
+    final tempUri = await tempDirForTest();
+    final outUri = tempUri.resolve('out1/');
+    await Directory.fromUri(outUri).create();
+    const pageSize = 4 * 1024;
+    final libUri = await buildLib(
+      outUri,
+      target,
+      apiLevel1,
+      linkMode,
+      flags: ['-Wl,-z,max-page-size=$pageSize'],
+    );
+    if (Platform.isMacOS || Platform.isLinux) {
+      final address = await textSectionAddress(libUri);
+      expect(address, greaterThanOrEqualTo(pageSize));
+      expect(address, isNot(greaterThanOrEqualTo(pageSize * 4)));
+    }
+  });
 }
 
 Future<Uri> buildLib(
   Uri tempUri,
   Architecture targetArchitecture,
   int androidNdkApi,
-  LinkMode linkMode,
-) async {
+  LinkMode linkMode, {
+  List<String> flags = const [],
+}) async {
   final addCUri = packageUri.resolve('test/cbuilder/testfiles/add/src/add.c');
   const name = 'add';
 
@@ -140,6 +166,7 @@ Future<Uri> buildLib(
     name: name,
     assetName: name,
     sources: [addCUri.toFilePath()],
+    flags: flags,
   );
   await cbuilder.run(
     config: buildConfig,

pkgs/native_toolchain_c/test/helpers.dart

@@ -255,3 +255,48 @@ Future<void> expectSymbols({
     throw UnimplementedError();
   }
 }
+
+Future<int> textSectionAddress(Uri dylib) async {
+  if (Platform.isMacOS) {
+    // Find the line in the objdump output that looks like:
+    //  11 .text               00000046 00000000000045a0 TEXT
+    final result = await runProcess(
+      executable: Uri.file('objdump'),
+      arguments: ['--headers', dylib.toFilePath()],
+      logger: logger,
+    );
+    expect(result.exitCode, 0);
+    final textSection =
+        result.stdout.split('\n').firstWhere((e) => e.contains('.text'));
+    final parsed = textSection.split(' ').where((e) => e.isNotEmpty).toList();
+    expect(parsed[1], '.text');
+    expect(parsed[4], 'TEXT');
+    final vma = int.parse(parsed[3], radix: 16);
+    return vma;
+  }
+  if (Platform.isLinux) {
+    // Find the line in the readelf output that looks like:
+    // [11] .text             PROGBITS   00004328 000328 000064 00  AX  0   0  4
+    final result = await readelf(dylib.toFilePath(), 'S');
+    final textSection =
+        result.split('\n').firstWhere((e) => e.contains('.text'));
+    final parsed = textSection.split(' ').where((e) => e.isNotEmpty).toList();
+    expect(parsed[1], '.text');
+    expect(parsed[2], 'PROGBITS');
+    final addr = int.parse(parsed[3], radix: 16);
+    return addr;
+  }
+  throw UnimplementedError();
+}
+
+Future<void> expectPageSize(
+  Uri dylib,
+  int pageSize,
+) async {
+  if (Platform.isMacOS || Platform.isLinux) {
+    // If page size is 16kb, the `.text` section address should be
+    // above 0x4000. With smaller page sizes it's above 0x1000.
+    final vma = await textSectionAddress(dylib);
+    expect(vma, greaterThanOrEqualTo(pageSize));
+  }
+}