Reporting Problems

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Many of the people on the gem5-users mailing list are happy to help when someone has a problem or something doesn't work. However, please keep in mind that it's not our job to help. We all have other commitments, so before we spend time helping someone we like to see that they have put some effort into solving the problem themselves.

  1. Before posting a question to the list, please check if the question is already answered. The wiki provides answers to the most common questions (check both Documentation and the Frequently Asked Questions), and the mailing list archive at is easily searchable.
  2. If your problem is with your configuration script, look at the config.ini output. This is the final configuration that's getting built in textual form. Make sure this reflects the configuration you think you're building.
  3. Make sure you're running with gem5.opt or gem5.debug and not The binary compiles out assertion checking for speed, so a problem that causes a crash or mysterious error on may result in a more informative assertion failure with gem5.opt or gem5.debug.
  4. Try running your code on the latest version from the gem5 repository, if you're not doing that already. Your problem may have been fixed since you last updated your local version.
  5. Take a few minutes to look at the source code and see if you can identify your problem. If you're running into a specific error message, the file and line number where the error message is printed should be displayed along with the error message, so start there. Even if you don't get a specific error message, look at the module that's giving you trouble and see if you can figure it out. Use cscope or another tool to find where relevant functions/variables are used. gem5 is not like other open-source software packages where end users would never be expected to look at the source code when problems occur. gem5 is as much of a framework as an application. We don't (and you shouldn't) expect to have it do everything you want without touching the source code.
  6. If it seems appropriate, enable some debug flags (--debug-flags=Foo) and see if the resulting information helps. Your examination of the source in step 3 should show you which trace flags might be relevant (they're the first argument to the DPRINTF calls). If your problem is occurring on the C++ side, don't be afraid to run under gdb to see what's really happening. See Debugging for more details.
  7. If you still need help, use the information you've gathered in steps 1-4 to ask the most specific and informative question possible on the gem5-users list. Include the command line you used, specific error messages, program outputs, stack traces, relevant trace snippets, etc. (Don't post huge traces in their entirety though... just the relevant bits.) If you've written your own scripts, try and find the shortest script (or the minimum modification to one of the supplied example scripts) that exhibits the same problem and post that. If you found something on the wiki but it didn't quite apply or didn't work, mention that so we can update the wiki appropriately. If you have a theory about what the problem might be, please let us know, but include enough basic information so others can decide whether your theory is correct.
  8. If you have solved a problem that you reported on the list and the answer may be of general interest, post it to the list as a follow-up to the original thread so others can benefit from the solution.

Finally, please don't e-mail or call any list member directly unless explicitly invited to do so. If we haven't responded we are either busy, don't know the answer or some combination of the two. Pestering will not get your question answered faster, and it may get it never answered at all.