Bug Reporting

All bugs should be filed in the GitHub main Emscripten repository Issue Tracker.

Please supply as much relevant information as possible, including:

  • Original source code.
  • Generated bitcode (.bc, .o or .ll)
  • Environment information — including emcc and clang versions (as reported by emcc -v).
  • Error symptoms.
  • Proposed solutions, ideally with a pull request.


Compile with EMCC_DEBUG=1 and grab the /tmp/emscripten_temp/emcc-* files (these include the bitcode and JavaScript in several stages). Note that the emscripten_temp directory should be emptied manually first, so it only contains new content!

Fastcomp LLVM-Backend and Clang bugs

LLVM Backend bugs may instead be posted to the appropriate Emscripten LLVM fork or Emscripten Clang fork if you are certain that the bug is specific to these repositories. If uncertain, bugs must be posted to the main repository.

Pull requests must (of course) go to the proper repository.

Site and documentation bugs

Documentation (site) bugs should be filed in the same Issue Tracker.

Include relevant information including:

  • The URL and title of the affected page(s).
  • A description of the problem.
  • Suggestions for a possible solution.


The Page bug link on the bottom-right of every page opens the Issue Tracker pre-seeded with the current page URL and title.