How does one find out what file a library has been loaded from?

[Alan Mackenzie]

Hello, Emacs.

Forgive me if I've asked this before, but how does one determine what
file a library has been loaded from?  In particular, whether that file
is a source file, a byte compiled file or a native compiled file.

I've tried looking at load-history, and it tells me cc-engine was loaded
from 

  "/home/acm/emacs/emacs.git/sub-master-5/lisp/progmodes/cc-engine.elc"

..  I think that's a lie.  I suspect I'm dealing with a native compiled
cc-engine, here.  In fact, the string ".eln" doesn't occur anywhere in
load-history, and I _know_ some of the files are native compiled - my
build was configured with-native-compilation.

So, how do I find this out?

Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).