The gem5 repository is accessible at https://gem5.googlesource.com
Clone it with:
There is also an official read-only GitHub mirror at: https://github.com/gem5/gem5
The main method for contributing code to gem5 is via our Gerrit code review website: https://gem5-review.googlesource.com
The CONTRIBUTING file https://gem5.googlesource.com/public/gem5/+/master/CONTRIBUTING.md documents on how to contribute to gem5.
The MAINTAINERS file https://gem5.googlesource.com/public/gem5/+/master/MAINTAINERS explains who are the subsystem maintainers. You may add them to reviews that touch a given subsystem.
More general Git and Gerrit information: