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Crashes

Ian Hickson edited this page Nov 5, 2018 · 2 revisions

Symbolicating stack traces for engine crashes

Android

Get the symbols

  1. Get the Flutter Framework or Flutter Engine revision from the report. If you have the Engine revision, skip to step 3.

  2. Get the Engine revision from the Framework (this could be automated). https://github.com/flutter/flutter/blob/master/bin/internal/engine.version is the file which contains the information. Substitute the framework hash for master in that url.

  3. With the full engine revision (e.g. cea5ed2b9be42a981eac762af3664e4a17d0a53f), you can now get the proper symbol files:

    To view the available artifacts for a build, visit this URL in a browser (replacing the engine hash with your hash): https://console.cloud.google.com/storage/browser/flutter_infra/flutter/cea5ed2b9be42a981eac762af3664e4a17d0a53f

    To download the symbols for android-arm, download this URL using your browser (replacing the hash again, and noting that this URL is on a different host, "storage", compared to the one above, which uses "console"): https://storage.cloud.google.com/flutter_infra/flutter/cea5ed2b9be42a981eac762af3664e4a17d0a53f/android-arm/symbols.zip.

    You have to use your browser because it does authentication.

Symbolicate

Once you have the symbols unzipped, you can use ndk-stack from your Android NDK. Suppose stack.txt contains the stack (including the leading *** *** *** line from the crash):

.../ndk/prebuilt/linux-x86_64/bin/ndk-stack -sym .../path/to/downloaded/symbols < stack.txt

Expanding Git Revisions

Go to a commit page with the short commit as the last fragment of the URL: (e.g. https://github.com/flutter/flutter/commit/9cb914df1 or https://github.com/flutter/engine/commit/2a13567) and then find the full revision on the page.

Symbolicating local builds

If you have made your own builds, you can use ndk-stack directly:

# dev/engine is where your engine's .gclient file is
# android_debug_unopt is whatever build of your engine you are using
adb logcat | ~/dev/engine/src/third_party/android_tools/ndk/prebuilt/linux-x86_64/bin/ndk-stack -sym ~/dev/engine/src/out/android_debug_unopt

iOS

The dSYM file for App.framework (which contains the app-specific code) can be located in the directory of your app under build/dSYMs.noindex/App.framework.dSYM for release and profile builds created with flutter build ios.

The dSYM file for Flutter.framework (which is the Flutter Engine) for ios-release builds can be downloaded from Google Cloud Storage. Follow the steps from the Android section in this guide, but in the last step use a download url following this schema: https://storage.cloud.google.com/flutter_infra/flutter/38a646e14cc25f5a56a989c6a5787bf74e0ea386/ios-release/Flutter.dSYM.zip (replace the engine hash with your hash).

Crashes in Dart AOT code

If the crash is in AOT Dart code (in --release or --profile builds) on iOS, and you can build your own engine, these steps will be helpful for the VM team to fix the bug:

  • Prepare a reduced test case.
  • Compile the engine in profile mode and disable optimizations for symbolicated traces.
    • sky/tools/gn --ios --unopt --runtime-mode profile; ninja -C out/ios_profile_unopt -j800.
  • Launch the application via the Xcode project and make it crash in the debugger.
  • File a bug on dart-lang/sdk.
  • Dump the register state and paste it into the bug.
    • In lldb, register read.
  • Copy the backtrace and paste it into the bug.
    • In lldb, thread backtrace. Assumes you are on the thread that crashed. If not, thread select n.
  • Disassemble the last frame and paste it into the bug.
    • In lldb, frame select 0 then disassemble --frame.
  • Disassemble using the gen_snapshot and paste the function into the bug for more detailed information.
    • In the backtrace, look for the name of the precompiled function that caused the crash.
    • Open SnapshotterInvoke from Xcode and to the RunCommand ... Snapshotter call, add the --disassemble flags.
    • Modify the RunCommand function to dump to a file.
    • Build again. The results should end up in the file.
    • Look for the function name (by substring match) in this file and copy out that information to the bug.
  • Ping someone on dart-lang/sdk.

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