[native_toolchain_c] Fix page size assertions in tests (#2838)

Fixes #2837

The tests that asserted on the page size started failing on macOS (see #2837). According to Gemini they weren't asserting on the right thing: The virtual memory address within a section (this is what the test was asserting) is not the same thing as the alignment of the ELF load segment (this is what the test supposedly wanted to test to verify that the page size setting was honored).

Author: goderbauer

pkgs/native_toolchain_c/test/cbuilder/cbuilder_cross_android_test.dart

@@ -91,11 +91,7 @@ void main() {
       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)));
-    }
+    await expectPageSize(libUri, pageSize);
   });
 }
 

pkgs/native_toolchain_c/test/helpers.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:ffi';
 import 'dart:io';
+import 'dart:math' as math;
 
 import 'package:code_assets/code_assets.dart';
 import 'package:logging/logging.dart';
@@ -245,47 +246,45 @@ Future<RunProcessResult?> _runDumpbin(
   );
 }
 
-Future<int> textSectionAddress(Uri dylib) async {
+Future<void> expectPageSize(Uri dylib, int pageSize) async {
   if (Platform.isMacOS) {
     // Find the line in the objdump output that looks like:
-    //  11 .text               00000046 00000000000045a0 TEXT
+    //   LOAD off    0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**14
     final result = await runProcess(
       executable: Uri.file('objdump'),
-      arguments: ['--headers', dylib.toFilePath()],
+      arguments: ['-p', dylib.toFilePath()],
       logger: logger,
     );
     expect(result.exitCode, 0);
-    final textSection = result.stdout
+    final loadHeader = 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;
+        .firstWhere((e) => e.contains('LOAD'));
+    final parsed = loadHeader.split(' ').where((e) => e.isNotEmpty).toList();
+    expect(parsed[7], 'align');
+    expect(parsed[8], startsWith('2**'));
+    final alignment = math.pow(2, int.parse(parsed[8].substring('2**'.length)));
+    expect(alignment, pageSize);
   }
   if (Platform.isLinux) {
+    // The readelf output has the following structure:
+    //   Type           Offset             VirtAddr           PhysAddr
+    //                  FileSiz            MemSiz              Flags  Align
     // 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));
+    //   LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
+    //                  0x0000000000000528 0x0000000000000528  R      0x1000
+    final result = await readelf(dylib.toFilePath(), 'l');
+    // Capture the line after the line that contains "LOAD".
+    final regExp = RegExp('LOAD.*\n(.*)');
+    final loadSegment = regExp.firstMatch(result)!.group(1)!;
+    final alignment = int.parse(
+      loadSegment
+          .split(' ')
+          .where((e) => e.isNotEmpty)
+          .last
+          .substring('0x'.length),
+      radix: 16,
+    );
+    expect(alignment, pageSize);
   }
 }