Note that a really common use case for assembly files (.S files) is to expect that the file be transformed with the C preprocessor. It would be interesting to

Note that a really common use case for assembly files (.S files) is to expect that the file be transformed with the C preprocessor. It would be interesting to imagine a replacement with a rust equivalent but I can't help thinking that it's difficult or impossible to come up with an architecture / exec format independent replacement (other than m4). gas and cc1as support .macro directives - maybe that would suffice? But compatibility with existing assembly source files would suffer.