rimage is a DSP firmware image creation and signing tool targeting the DSP on certain Intel System-on-Chip (SoC). This is used by the Sound Open Firmware (SOF) to generate binary image files.

Most users don't build rimage directly but as an ExternalProject defined by CMake in SOF. This being said, rimage can be built with the usual CMake commands:

$ cmake -B build/
$ make  -C build/ help # lists all targets
$ make  -C build/
$ sudo make -C build/ install # optional

This section is about leveraging SOF validation to test rimage changes before submitting them to the rimage repository.

Nothing here is actually specific to SOF and rimage; you can apply the same test logic to any submodule and parent on Github. In fact the same logic applies to submodule alternatives. Github is the only requirement.

This is unfortunately not optional for SOF and rimage.

For various reasons submodules seem to confuse many git users. Maybe because the versions of the submodules are not directly visible in some configuration file like with most alternatives? Either way, an unfortunate prerequisite before doing any rimage work is to get familiar with git submodules in general. As submodules are built-in there are many resources about them on the Internet. One possible starting point is https://git-scm.com/book/en/v2/Git-Tools-Submodules but feel free to use any other good tutorial instead. Make sure you actually practice a tutorial; don't just read it. Practicing on a temporary and throw-away copy of SOF + rimage is a great idea.

Obviously, you also need to be familiar with regular Github pull requests.

First, push the rimage commits you want to be tested to any branch of your rimage fork on Github. Do not submit an rimage pull request yet.

Note your rimage fork must have been created using the actual "fork" button on Github so Github is aware of the connection with the upstream rimage repo. In the top-left corner you should see forked from thesofproject/rimage under the name of your fork. If not then search the Internet for "re-attach detached github fork".

Then, pretend these rimage commits have already been accepted and merged (they have been neither) and submit to SOF a draft pull request that updates the main SOF branch with your brand new rimage commits to test. The only SOF commit in this SOF TEST pull request is an SOF commit that updates the rimage pointer to the SHA of your last rimage commit. If you're not sure how to do this then you must go back to the previous section and practice submodules more.

Submit this SOF pull request as a Github draft so reviewers are not notified. Starting every pull request as a draft is always a good idea but in this case this particular SOF pull request can be especially confusing because it points at commits in a different repo and commits that are not merged yet. So you really don't want to bother busy reviewers (here's a secret: some of the reviewers don't like submodules either). You can freely switch back and forth between draft and ready status and should indeed switch to draft if you forgot at submission time but you can never "un-notify" reviewers.

Github has very good support for submodules and will display your SOF TEST pull request better than what the git command line can show. For instance Github will list your rimage changes directly in the SOF Pull Request. So if something looks unexpected on Github then it means you did something wrong. Stop immediately (except for switching to draft if you forgot) and ask the closest git guru for help.

Search for "Submodule" in the build logs and make sure the last of your new rimage commits has been checked out.

Iterate and force-push your rimage branch and your SOF TEST pull request until all the SOF tests pass. Then you can submit your rimage pull request as usual. In the comments section of the rimage pull request, point at your test results on the SOF side to impress the rimage reviewers and get your rimage changes merged faster.

Finally, after your rimage changes have been merged, you can if you want submit one final SOF pull request that points to the final rimage SHA. Or, if your rimage change is not urgently needed, you can just wait for someone else to do it later. If you do it, copy the rimage git log --oneline in the SOF commit message. Find some good (and less good) rimage commit message examples at https://github.com/thesofproject/sof/commits/main/rimage