diff --git a/tools/pkg/engine_build_configs/bin/run.dart b/tools/pkg/engine_build_configs/bin/run.dart
index 91e43a15ea0da..be5874b9ca55b 100644
--- a/tools/pkg/engine_build_configs/bin/run.dart
+++ b/tools/pkg/engine_build_configs/bin/run.dart
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ffi' as ffi;
 import 'dart:io' as io;
 
 import 'package:engine_build_configs/engine_build_configs.dart';
@@ -119,6 +120,7 @@ The build names are the "name" fields of the maps in the list of "builds".
   final GlobalBuildRunner buildRunner = GlobalBuildRunner(
     platform: const LocalPlatform(),
     processRunner: ProcessRunner(),
+    abi: ffi.Abi.current(),
     engineSrcDir: engine.srcDir,
     build: targetBuild,
     extraGnArgs: extraGnArgs,
diff --git a/tools/pkg/engine_build_configs/lib/src/build_config_runner.dart b/tools/pkg/engine_build_configs/lib/src/build_config_runner.dart
index 191993545c293..1bcf80c4424a9 100644
--- a/tools/pkg/engine_build_configs/lib/src/build_config_runner.dart
+++ b/tools/pkg/engine_build_configs/lib/src/build_config_runner.dart
@@ -4,7 +4,8 @@
 
 import 'dart:async';
 import 'dart:convert';
-import 'dart:io' as io show Directory, Process, ProcessResult;
+import 'dart:ffi' as ffi;
+import 'dart:io' as io show Directory, Process;
 
 import 'package:path/path.dart' as p;
 import 'package:platform/platform.dart';
@@ -111,7 +112,13 @@ typedef RunnerEventHandler = void Function(RunnerEvent);
 /// An abstract base clase for running the various tasks that a build config
 /// specifies. Derived classes implement the `run()` method.
 sealed class Runner {
-  Runner(this.platform, this.processRunner, this.engineSrcDir, this.dryRun);
+  Runner(
+    this.platform,
+    this.processRunner,
+    this.abi,
+    this.engineSrcDir,
+    this.dryRun,
+  );
 
   /// Information about the platform that hosts the runner.
   final Platform platform;
@@ -119,6 +126,9 @@ sealed class Runner {
   /// Runs the subprocesses required to run the element of the build config.
   final ProcessRunner processRunner;
 
+  /// The [Abi] of the host platform.
+  final ffi.Abi abi;
+
   /// The src/ directory of the engine checkout.
   final io.Directory engineSrcDir;
 
@@ -162,6 +172,7 @@ final class GlobalBuildRunner extends Runner {
   GlobalBuildRunner({
     Platform? platform,
     ProcessRunner? processRunner,
+    ffi.Abi? abi,
     required io.Directory engineSrcDir,
     required this.build,
     this.extraGnArgs = const <String>[],
@@ -175,6 +186,7 @@ final class GlobalBuildRunner extends Runner {
   }) : super(
     platform ?? const LocalPlatform(),
     processRunner ?? ProcessRunner(),
+    abi ?? ffi.Abi.current(),
     engineSrcDir,
     dryRun,
   );
@@ -289,22 +301,20 @@ final class GlobalBuildRunner extends Runner {
   }
 
   late final String _hostCpu = (){
-    if (platform.isWindows) {
-      return platform.environment['PROCESSOR_ARCHITECTURE'] ?? 'x64';
-    }
-    final List<String> unameCommand = <String>['uname', '-m'];
-    final io.ProcessResult unameResult = processRunner.processManager.runSync(
-      unameCommand,
-    );
-    return unameResult.exitCode == 0 ? (unameResult.stdout as String).trim() : 'x64';
+    return switch (abi) {
+      ffi.Abi.linuxArm64 || ffi.Abi.macosArm64 || ffi.Abi.windowsArm64 => 'arm64',
+      ffi.Abi.linuxX64 || ffi.Abi.macosX64 || ffi.Abi.windowsX64 => 'x64',
+      _ => throw StateError('This host platform "$abi" is not supported.'),
+    };
   }();
 
   late final String _buildtoolsPath = (){
-    final String platformDir = switch (platform.operatingSystem) {
+    final String os = platform.operatingSystem;
+    final String platformDir = switch (os) {
       Platform.linux => 'linux-$_hostCpu',
       Platform.macOS => 'mac-$_hostCpu',
       Platform.windows => 'windows-$_hostCpu',
-      _ => '<unknown>',
+      _ => throw StateError('This host OS "$os" is not supported.'),
     };
     return p.join(engineSrcDir.path, 'buildtools', platformDir);
   }();
@@ -317,11 +327,12 @@ final class GlobalBuildRunner extends Runner {
     final String exe = platform.isWindows ? '.exe' : '';
     final String bootstrapPath = p.join(reclientPath, 'bootstrap$exe');
     final String reproxyPath = p.join(reclientPath, 'reproxy$exe');
-    final String reclientConfigFile = switch (platform.operatingSystem) {
+    final String os = platform.operatingSystem;
+    final String reclientConfigFile = switch (os) {
       Platform.linux => 'reclient-linux.cfg',
       Platform.macOS => 'reclient-mac.cfg',
       Platform.windows => 'reclient-win.cfg',
-      _ => '<unknown>',
+      _ => throw StateError('This host OS "$os" is not supported.'),
     };
     final String reclientConfigPath = p.join(
       engineSrcDir.path, 'flutter', 'build', 'rbe', reclientConfigFile,
@@ -487,6 +498,7 @@ final class GlobalBuildRunner extends Runner {
       final BuildTaskRunner runner = BuildTaskRunner(
         processRunner: processRunner,
         platform: platform,
+        abi: abi,
         engineSrcDir: engineSrcDir,
         task: task,
         dryRun: dryRun,
@@ -503,6 +515,7 @@ final class GlobalBuildRunner extends Runner {
       final BuildTestRunner runner = BuildTestRunner(
         processRunner: processRunner,
         platform: platform,
+        abi: abi,
         engineSrcDir: engineSrcDir,
         test: test,
         extraTestArgs: extraTestArgs,
@@ -521,12 +534,14 @@ final class BuildTaskRunner extends Runner {
   BuildTaskRunner({
     Platform? platform,
     ProcessRunner? processRunner,
+    ffi.Abi? abi,
     required io.Directory engineSrcDir,
     required this.task,
     bool dryRun = false,
   }) : super(
     platform ?? const LocalPlatform(),
     processRunner ?? ProcessRunner(),
+    abi ?? ffi.Abi.current(),
     engineSrcDir,
     dryRun,
   );
@@ -571,6 +586,7 @@ final class BuildTestRunner extends Runner {
   BuildTestRunner({
     Platform? platform,
     ProcessRunner? processRunner,
+    ffi.Abi? abi,
     required io.Directory engineSrcDir,
     required this.test,
     this.extraTestArgs = const <String>[],
@@ -578,6 +594,7 @@ final class BuildTestRunner extends Runner {
   }) : super(
     platform ?? const LocalPlatform(),
     processRunner ?? ProcessRunner(),
+    abi ?? ffi.Abi.current(),
     engineSrcDir,
     dryRun,
   );
diff --git a/tools/pkg/engine_build_configs/test/build_config_runner_test.dart b/tools/pkg/engine_build_configs/test/build_config_runner_test.dart
index fa49ba23a9f51..86bc5b2cef0b9 100644
--- a/tools/pkg/engine_build_configs/test/build_config_runner_test.dart
+++ b/tools/pkg/engine_build_configs/test/build_config_runner_test.dart
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:convert' as convert;
+import 'dart:ffi' as ffi;
 import 'dart:io' as io;
 
 import 'package:engine_build_configs/src/build_config.dart';
@@ -39,6 +40,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       task: generator,
       dryRun: true,
@@ -65,6 +67,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       test: test,
       dryRun: true,
@@ -93,6 +96,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       dryRun: true,
@@ -154,6 +158,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       extraGnArgs: <String>['--extra-gn-arg'],
@@ -193,6 +198,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       extraGnArgs: <String>['--goma'],
@@ -218,10 +224,9 @@ void main() {
     final GlobalBuildRunner buildRunner = GlobalBuildRunner(
       platform: FakePlatform(operatingSystem: Platform.linux),
       processRunner: ProcessRunner(
-        processManager: _fakeProcessManager(
-          unameResult: io.ProcessResult(1, 0, 'arm64', ''),
-        ),
+        processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       extraGnArgs: <String>['--rbe'],
@@ -263,6 +268,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       runGn: false,
@@ -297,6 +303,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       runNinja: false,
@@ -338,6 +345,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       runGenerators: false,
@@ -381,6 +389,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       runTests: false,
@@ -409,10 +418,9 @@ void main() {
     final GlobalBuildRunner buildRunner = GlobalBuildRunner(
       platform: FakePlatform(operatingSystem: Platform.linux),
       processRunner: ProcessRunner(
-        processManager: _fakeProcessManager(
-          unameResult: io.ProcessResult(1, 0, 'arm64', ''),
-        ),
+        processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       extraGnArgs: <String>['--no-lto', '--no-goma', '--rbe'],
@@ -448,6 +456,7 @@ void main() {
         // dryRun should not try to spawn any processes.
         processManager: _fakeProcessManager(),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       dryRun: true,
@@ -469,6 +478,7 @@ void main() {
           gnResult: io.ProcessResult(1, 1, '', ''),
         ),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
     );
@@ -495,6 +505,7 @@ void main() {
           ninjaResult: io.ProcessResult(1, 1, '', ''),
         ),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
     );
@@ -518,10 +529,10 @@ void main() {
       platform: FakePlatform(operatingSystem: Platform.linux),
       processRunner: ProcessRunner(
         processManager: _fakeProcessManager(
-          unameResult: io.ProcessResult(1, 0, 'arm64', ''),
           bootstrapResult: io.ProcessResult(1, 1, '', ''),
         ),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       extraGnArgs: <String>['--rbe'],
@@ -547,7 +558,6 @@ void main() {
       platform: FakePlatform(operatingSystem: Platform.linux),
       processRunner: ProcessRunner(
         processManager: _fakeProcessManager(
-          unameResult: io.ProcessResult(1, 0, 'arm64', ''),
           canRun: (Object? exe, {String? workingDirectory}) {
             if (exe is String? && exe != null && exe.endsWith('bootstrap')) {
               return false;
@@ -556,6 +566,7 @@ void main() {
           },
         ),
       ),
+      abi: ffi.Abi.linuxX64,
       engineSrcDir: engine.srcDir,
       build: targetBuild,
       extraGnArgs: <String>['--rbe'],
@@ -568,10 +579,31 @@ void main() {
 
     expect(events[2] is RunnerError, isTrue);
   });
+
+  test('GlobalBuildRunner throws a StateError on an unsupported host cpu', () async {
+    final GlobalBuild targetBuild = buildConfig.builds[0];
+    final GlobalBuildRunner buildRunner = GlobalBuildRunner(
+      platform: FakePlatform(operatingSystem: Platform.linux),
+      processRunner: ProcessRunner(
+        processManager: _fakeProcessManager(),
+      ),
+      abi: ffi.Abi.linuxRiscv32,
+      engineSrcDir: engine.srcDir,
+      build: targetBuild,
+      extraGnArgs: <String>['--rbe'],
+    );
+
+    bool caughtError = false;
+    try {
+      await buildRunner.run((RunnerEvent event) {});
+    } on StateError catch (_) {
+      caughtError = true;
+    }
+    expect(caughtError, isTrue);
+  });
 }
 
 FakeProcessManager _fakeProcessManager({
-  io.ProcessResult? unameResult,
   io.ProcessResult? bootstrapResult,
   io.ProcessResult? gnResult,
   io.ProcessResult? ninjaResult,
@@ -587,7 +619,6 @@ FakeProcessManager _fakeProcessManager({
   return FakeProcessManager(
     canRun: canRun ?? (Object? exe, {String? workingDirectory}) => true,
     onRun: (List<String> cmd) => switch (cmd) {
-      ['uname', ...] => unameResult ?? success,
       _ => failUnknown ? io.ProcessResult(1, 1, '', '') : success,
     },
     onStart: (List<String> cmd) => switch (cmd) {