Last time I submitted a kernel patch which added some new user-visible API:

  $ grep Umask /proc/self/status
  Umask: 0002

I had to also submit a test to go along with it. I understand that these are run by CI on the main architectures, although it didn't appear to be a condition of accepting the patch that the test was correct on all arches. Also I wonder if their CI really runs on PPC601 and IA64, I guess probably not. (Obviously this minor feature doesn't depend on the arch and it's hard to see how it could go wrong even on IA64).