This folder contains implementation of symbolization tooling capable of extracting Android and iOS crashes from plain text comments on GitHub or from local text files and then automatically symbolize these crash reports using Flutter Engine symbols stored in the Cloud Storage.

Using this locally

$ dart pub global activate -sgit --git-path github-label-notifier/symbolizer/
$ dart pub global run symbolizer:symbolize <file-or-uri> ["overrides"]
$ dart pub global run symbolizer:symbolize --help

Symbolization overrides

Not all information might be available in the stack trace itself. In this case symbolization overrides can be used to fill in gaps. They have the following format:

[engine#<sha>|flutter#<commit>] [profile|release|debug] [x86|arm|arm64|x64]
  • engine#<sha> - use symbols for specific engine commit;
  • flutter#<commit> use symbols for specific Flutter Framework commit (this is just another way of specifiying engine commit);
  • profile|release|debug use symbols for specific build mode (iOS builds only have release symbols available though);
  • x86|arm|arm64|x64 use symbols for specific architecture.

If your backtrace comes from Crashlytics with lines that look like this:

4  Flutter                        0x106013134 (Missing)

You would need to use force ios [arm64|arm] [engine#<sha>|flutter#<commit>] overrides:

  • force ios instructs tooling to ignore native crash markers and simply look for lines that match ios backtrace format;
  • [arm64|arm] gives information about architecture, which is otherwise missing from the report;
  • engine#sha|flutter#commit gives engine version;

If your backtrace has lines that look like this:

0x0000000105340708(Flutter + 0x002b4708)

You would need to use internal [arm64|arm] [engine#<sha>|flutter#<commit>] overrides:

  • internal instructs tooling to ignore native crash markers and look for lines that match this special internal backtrace format.

Note about Relative PCs

To symbolize stack trace correctly symbolizer needs to know PC relative to binary image load base. Native crash formats usually include this information:

  • On Android pc column actually contains relative PCs rather then absolute. Though Android versions prior to Android 11 have issues with their unwinder which makes these relative PCs skewed in different ways (see this bug for more information). This package tries best to correct for these known issues;
  • On iOS crash parser is looking for lines like this Flutter + <rel-pc> which gives it necessary information.

Some crash formats (Crashlytics) do not contain neither load base nor relative PCs. In this case symbolizer will try to determine load base heuristically based on the set of return addresses available in the backtrace: it will look through Flutter Engine binary for all call sites and then iterate through potential load bases to see if one of them makes all of PCs present in the backtrace fall onto callsites. The pattern of call sites in the binary is often unique enough for the symbolizer to be able to determine a single possible load base based on 3-4 unique return addresses.



Creates .config.json with authorization tokens. It is recommended to run this script to at least configure GitHub OAuth token to ensure that you don‘t hit GitHub’s API quota limits for unauthorized users.

$ bin/configure.dart --github-token ...


$ bin/symbolize.dart <input-file|URI> 'keywords*'

Symbolize contents of the given file or GitHub comment or issue using overrides specified through keywords.



You would at minimum need GitHub OAuth token to run test - otherwise they hit GitHub API limits for unauthorized users and timeout.

Run bin/configure.dart to create .config.json.

bin/configure.dart --github-token ...

NDK tooling

To run tests or scripts locally you would need to create tools folder containing a small subset of NDK tooling. This is done by running

$ ./ <path-to-ndk>

Changing model.dart

We use freezed to define our model classes. To regenerate model.g.dart and mode.freezed.dart after editing model.dart run:

$ dart run build_runner build


$ dart test test -j1 --no-chain-stack-traces
  • -j1 is needed to avoid racy access to symbols cache from multiple tests
  • --no-chain-stack-traces needed to avoid timeouts caused by stack trace chaining overheads.

To update expectation files set REGENERATE_EXPECTATIONS environment variable to true (export REGENERATE_EXPECTATIONS=true).

SDK version

We deploy the code in form of Kernel binary - which means your local SDK needs to match the version of Dart SDK installed on crash-symbolizer. Deployment script will verify this for you.