/usr/lib/ocaml/camlp4/Camlp4/Struct/ is in camlp4 3.12.1-2ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ocaml/camlp4/Camlp4/Struct/Camlp4Ast2OCamlAst.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/CommentFilter.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/DynLoader.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/EmptyError.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/EmptyPrinter.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/FreeVars.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/Grammar/
/usr/lib/ocaml/camlp4/Camlp4/Struct/Grammar/Fold.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/Grammar/Parser.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/Grammar/Print.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/Loc.mli
/usr/lib/ocaml/camlp4/Camlp4/Struct/Token.mli