Generating a kernel stacktrace for every syscall error return seems like it would be needlessly wasteful on the return path (not to mention that it would change

Generating a kernel stacktrace for every syscall error return seems like it would be needlessly wasteful on the return path (not to mention that it would change between kernel releases, and wouldn't be useful to most developers). A richer error system could be as simple as giving some more information about why a syscall returned -EINVAL (because checking all possible flag bits to see which one is not supported is really not a fun exercise).