C++ STL Library on Android does not support `exception_ptr`

[mrousavy]

Description

For some reason, std::exception_ptr is broken in react-native.

I have added this code to react-native/ReactAndroid/src/main/jni/react/jni/OnLoad.cpp:

__android_log_print(ANDROID_LOG_ERROR, "EXCEPTION", "Running exception test...");
try {
  throw std::runtime_error("Test exception");
} catch (...) {
  auto eptr = std::current_exception();
  try {
    std::rethrow_exception(eptr);
  } catch (const std::exception& e) {
    __android_log_print(ANDROID_LOG_ERROR, "EXCEPTION", "Caught std::exception: %s", e.what());
  } catch (...) {
    __android_log_print(ANDROID_LOG_ERROR, "EXCEPTION", "Caught unknown exception!!");
  }
}

And it logs

11-29 17:50:54.049 31176 31176 E EXCEPTION: Running exception test...
11-29 17:50:54.054 31176 31176 E EXCEPTION: Caught unknown exception!!

If you run the same code on iOS (replace log with NSLog), it works as expected:

11-29 17:50:54.049 31176 31176 E EXCEPTION: Running exception test...
11-29 17:50:54.054 31176 31176 E EXCEPTION: Caught std::exception: Test exception

So for some reason, the Android C++ lib fails to properly rethrow std::exception_ptr. ❌

iOS uses libc++ since ever.

Android uses libc++ since 2015, and apparently used libstdc++ (from GNU) before 2015 - could it be that libstdc++ is still used today somehow?
From what I'm seeing in RN's build.gradle, it correctly uses libc++: https://github.com/facebook/react-native/blob/91e217ff54e3bffb49454a723594d11669783e87/packages/react-native/ReactAndroid/build.gradle.kts#L535

Anyways... The code above does not work as expected. I think I read somewhere that exception_ptr does not work on ARMv5 since it needs some compare instruction that isn't available there, but afaik my device is ARMv8.

I have confirmed that;

• ✅ It works in a blank Android C++ app
• ✅ It works on iOS
• ❌ It fails in a blank react-native Android app

Steps to reproduce

1. Create a clean new app (npx create-expo-app@latest)
2. Run npx expo prebuild
3. Enable "build react-native from source" (by following these instructions)
4. Add the above code to OnLoad.cpp
5. Run npx expo android
6. In adb, see exception_ptr not properly being castable

React Native Version

0.76.2

Affected Platforms

Runtime - Android

Output of npx react-native info

info Fetching system and libraries information...
System:
  OS: macOS 15.0.1
  CPU: (12) arm64 Apple M2 Pro
  Memory: 240.17 MB / 32.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 18.18.0
    path: ~/.nvm/versions/node/v18.18.0/bin/node
  Yarn:
    version: 1.22.19
    path: ~/.nvm/versions/node/v18.18.0/bin/yarn
  npm:
    version: 10.8.1
    path: ~/.nvm/versions/node/v18.18.0/bin/npm
  Watchman:
    version: 2024.11.11.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.1
      - iOS 18.1
      - macOS 15.1
      - tvOS 18.1
      - visionOS 2.1
      - watchOS 11.1
  Android SDK:
    API Levels:
      - "28"
      - "30"
      - "31"
      - "33"
      - "33"
      - "34"
      - "35"
    Build Tools:
      - 30.0.3
      - 31.0.0
      - 33.0.0
      - 33.0.1
      - 33.0.2
      - 34.0.0
      - 34.0.0
      - 35.0.0
    System Images:
      - android-33 | Google APIs ARM 64 v8a
      - android-34 | Google Play ARM 64 v8a
    Android NDK: 25.2.9519653
IDEs:
  Android Studio: 2024.2 AI-242.23339.11.2421.12550806
  Xcode:
    version: 16.1/16B40
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /opt/homebrew/opt/openjdk@17/bin/javac
  Ruby:
    version: 2.7.6
    path: /Users/mrousavy/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 15.1.2
    wanted: ^15.1.2
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.76.3
    wanted: 0.76.3
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

11-29 17:50:54.049 31176 31176 E EXCEPTION: Running exception test...
11-29 17:50:54.054 31176 31176 E EXCEPTION: Caught unknown exception!!

Reproducer

https://github.com/mrousavy/react-native-exception_ptr-bug

Screenshots and Videos

No response

[react-native-bot]

Warning

Could not parse version: We could not find or parse the version number of React Native in your issue report. Please use the template, and report your version including major, minor, and patch numbers - e.g. 0.76.2.

[react-native-bot]

Warning

Could not parse version: We could not find or parse the version number of React Native in your issue report. Please use the template, and report your version including major, minor, and patch numbers - e.g. 0.76.2.

[mrousavy]

The CMakeLists.txt of the project where I added the code to OnLoad.cpp to also enables exceptions: https://github.com/facebook/react-native/blob/91e217ff54e3bffb49454a723594d11669783e87/packages/react-native/ReactAndroid/src/main/jni/react/jni/CMakeLists.txt#L11-L14

I also added -frtti to those options and rebuilt the app, but it still doesn't work.

[NickGerleman]

could it be that libstdc++ is still used today somehow?

Nope. We are using libc++. When we bumped to NDK 26, this got bumped to LLVM 17. IIRC latest beta NDK uses libc++ based on LLVM 19.

All of the build logic we control should also have RTTI enabled I think. I could imagine weirdness happening if a library is using static STL, and RN is using shared STL (so we have different copies of exception types/ODR issues), or if NDK is setting some special flags that XCode isn't. IIRC libc++ had some different ways of being able to implement RTTI, which we do not fuss with ourselves.

[mrousavy]

hm, I can't seem to pinpoint it. It's definitely broken in a blank app created with the expo 52 template bootstrapper.

[cortinico]

@mrousavy have you tried on a vanilla Android App without React Native?

[mrousavy]

@cortinico Yep, in a blank new Android C++ template it works: