How to get ocamlobjinfo for .cmxs files?

I’m tracking down a plugin conflict and want to inspect the checksums of the dependencies…

$ ocamlobjinfo ./ocaml/albamgr_plugin.cmxs 
File ./ocaml/albamgr_plugin.cmxs
BFD library unavailable, cannot print info on .cmxs files
Unable to read info on file ./ocaml/albamgr_plugin.cmxs

Note that BFD was available at the time opam installed my compiler switch, but it doesn’t seem to be picked up automatically.

How do I get the objinfo of this cmxs file?