Interesting! I didn't realize the extent to which an ELF is a little database. It does seem worthwhile reexamine our formats from time to time. And yeah, since Nix relies on patching ELFs maybe a better tool for that would avoid some headaches.

I'm a little unclear of the idea of SELF executables as closures. If we want to avoid duplication of libraries on disk, would that require the one-userland idea? How would a NixOS setup work with all binaries packed into one SELF file?