diff --git a/compiler/compileArg.ml b/compiler/compileArg.ml
index 5556421233..82ac2f8ecc 100644
--- a/compiler/compileArg.ml
+++ b/compiler/compileArg.ml
@@ -28,7 +28,7 @@ type t =
   ; source_map : (string option * Source_map.t) option
   ; runtime_files : string list
   ; runtime_only : bool
-  ; output_file : string option
+  ; output_file : [`Name of string | `Stdout] * bool
   ; input_file : string option
   ; params : (string * string) list
   ; static_env : (string * string) list
@@ -43,7 +43,8 @@ type t =
     include_dir : string list
   ; fs_files : string list
   ; fs_output : string option
-  ; fs_external : bool }
+  ; fs_external : bool
+  ; keep_unit_names : bool }
 
 let options =
   let toplevel_section = "OPTIONS (TOPLEVEL)" in
@@ -67,6 +68,10 @@ let options =
     in
     Arg.(required & pos ~rev:true 0 (some string) None & info [] ~docv:"PROGRAM" ~doc)
   in
+  let keep_unit_names =
+    let doc = "Keep unit name" in
+    Arg.(value & flag & info ["keep-unit-names"] ~doc)
+  in
   let profile =
     let doc = "Set optimization profile : [$(docv)]." in
     let profile = List.map Driver.profiles ~f:(fun (i, p) -> string_of_int i, p) in
@@ -191,7 +196,8 @@ let options =
       sourcemap_root
       output_file
       input_file
-      js_files =
+      js_files
+      keep_unit_names =
     let chop_extension s =
       try Filename.chop_extension s with Invalid_argument _ -> s
     in
@@ -213,17 +219,21 @@ let options =
     in
     let output_file =
       match output_file with
-      | Some _ -> output_file
-      | None -> Option.map input_file ~f:(fun s -> chop_extension s ^ ".js")
+      | Some "-" -> `Stdout, true
+      | Some s -> `Name s, true
+      | None -> (
+        match input_file with
+        | Some s -> `Name (chop_extension s ^ ".js"), false
+        | None -> `Stdout, false)
     in
     let source_map =
       if ((not no_sourcemap) && sourcemap) || sourcemap_inline_in_js
       then
         let file, sm_output_file =
           match output_file with
-          | Some file when sourcemap_inline_in_js -> file, None
-          | Some file -> file, Some (chop_extension file ^ ".map")
-          | None -> "STDIN", None
+          | `Name file, _ when sourcemap_inline_in_js -> file, None
+          | `Name file, _ -> file, Some (chop_extension file ^ ".map")
+          | `Stdout, _ -> "STDIN", None
         in
         Some
           ( sm_output_file
@@ -268,7 +278,8 @@ let options =
       ; nocmis
       ; output_file
       ; input_file
-      ; source_map }
+      ; source_map
+      ; keep_unit_names }
   in
   let t =
     Term.(
@@ -296,7 +307,8 @@ let options =
       $ sourcemap_root
       $ output_file
       $ input_file
-      $ js_files)
+      $ js_files
+      $ keep_unit_names)
   in
   Term.ret t
 
diff --git a/compiler/compileArg.mli b/compiler/compileArg.mli
index 69ccd66724..06e6103711 100644
--- a/compiler/compileArg.mli
+++ b/compiler/compileArg.mli
@@ -26,7 +26,7 @@ type t =
   ; source_map : (string option * Source_map.t) option
   ; runtime_files : string list
   ; runtime_only : bool
-  ; output_file : string option
+  ; output_file : [`Name of string | `Stdout] * bool
   ; input_file : string option
   ; params : (string * string) list
   ; static_env : (string * string) list
@@ -41,7 +41,8 @@ type t =
     include_dir : string list
   ; fs_files : string list
   ; fs_output : string option
-  ; fs_external : bool }
+  ; fs_external : bool
+  ; keep_unit_names : bool }
 
 val options : t Cmdliner.Term.t
 
diff --git a/compiler/dune b/compiler/dune
index e19d8b5331..9b951500dc 100644
--- a/compiler/dune
+++ b/compiler/dune
@@ -5,6 +5,7 @@
   (libraries
     js_of_ocaml-compiler
     cmdliner
+    compiler-libs.common
     (select empty-findlib.ml from
      ;; Only link js_of_ocaml-compiler.findlib-support if it exists
      (js_of_ocaml-compiler.findlib-support -> empty-findlib.ml.in)
diff --git a/compiler/js_of_ocaml.ml b/compiler/js_of_ocaml.ml
index 331e992ebc..bcf62e14f0 100644
--- a/compiler/js_of_ocaml.ml
+++ b/compiler/js_of_ocaml.ml
@@ -52,6 +52,9 @@ let gen_file file f =
     Sys.remove f_tmp;
     raise exc
 
+let gen_unit_filename dir u =
+  Filename.concat dir (Printf.sprintf "%s.js" u.Cmo_format.cu_name)
+
 let f
     { CompileArg.common
     ; profile
@@ -71,7 +74,8 @@ let f
     ; fs_files
     ; fs_output
     ; fs_external
-    ; export_file } =
+    ; export_file
+    ; keep_unit_names } =
   let dynlink = dynlink || toplevel || runtime_only in
   let custom_header = common.CommonArg.custom_header in
   let global =
@@ -81,9 +85,9 @@ let f
   in
   CommonArg.eval common;
   (match output_file with
-  | None | Some "" | Some "-" -> ()
-  | Some name when debug_mem () -> Debug.start_profiling name
-  | Some _ -> ());
+  | `Stdout, _ -> ()
+  | `Name name, _ when debug_mem () -> Debug.start_profiling name
+  | `Name _, _ -> ());
   List.iter params ~f:(fun (s, v) -> Config.Param.set s v);
   List.iter static_env ~f:(fun (s, v) -> Eval.set_static_env s v);
   let t = Timer.make () in
@@ -127,7 +131,6 @@ let f
     try List.append include_dir [Findlib.find_pkg_dir "stdlib"]
     with Not_found -> include_dir
   in
-  let t1 = Timer.make () in
   if times () then Format.eprintf "Start parsing...@.";
   let need_debug =
     if source_map <> None || Config.Flag.debuginfo () || toplevel
@@ -136,39 +139,8 @@ let f
     then `Names
     else `No
   in
-  let p, cmis, d, standalone =
-    if runtime_only
-    then
-      ( Parse_bytecode.predefined_exceptions ()
-      , StringSet.empty
-      , Parse_bytecode.Debug.create ()
-      , true )
-    else
-      match input_file with
-      | None ->
-          Parse_bytecode.from_channel
-            ~includes:paths
-            ~toplevel
-            ?expunge
-            ~dynlink
-            ~debug:need_debug
-            stdin
-      | Some f ->
-          let ch = open_in_bin f in
-          let res =
-            Parse_bytecode.from_channel
-              ~includes:paths
-              ~toplevel
-              ?expunge
-              ~dynlink
-              ~debug:need_debug
-              ch
-          in
-          close_in ch;
-          res
-  in
-  let () =
-    if (not runtime_only) && source_map <> None && Parse_bytecode.Debug.is_empty d
+  let check_debug debug =
+    if (not runtime_only) && source_map <> None && Parse_bytecode.Debug.is_empty debug
     then
       warn
         "Warning: '--source-map' is enabled but the bytecode program was compiled with \
@@ -176,61 +148,156 @@ let f
          Warning: Consider passing '-g' option to ocamlc.\n\
          %!"
   in
-  let cmis = if nocmis then StringSet.empty else cmis in
-  let p =
-    let l =
-      List.map static_env ~f:(fun (k, v) ->
-          Primitive.add_external "caml_set_static_env";
-          let args = [Code.Pc (IString k); Code.Pc (IString v)] in
-          Code.(Let (Var.fresh (), Prim (Extern "caml_set_static_env", args))))
+  let pseudo_fs_instr prim debug cmis =
+    let cmis = if nocmis then StringSet.empty else cmis in
+    let paths =
+      paths @ StringSet.elements (Parse_bytecode.Debug.paths debug ~units:cmis)
     in
-    Code.prepend p l
+    PseudoFs.f ~prim ~cmis ~files:fs_files ~paths
   in
-  let p =
-    if fs_external
-    then
-      let instrs = [Code.(Let (Var.fresh (), Prim (Extern "caml_fs_init", [])))] in
-      Code.prepend p instrs
-    else p
+  let env_instr () =
+    List.map static_env ~f:(fun (k, v) ->
+        Primitive.add_external "caml_set_static_env";
+        let args = [Code.Pc (IString k); Code.Pc (IString v)] in
+        Code.(Let (Var.fresh (), Prim (Extern "caml_set_static_env", args))))
   in
-  if times () then Format.eprintf "  parsing: %a@." Timer.print t1;
-  let paths = paths @ StringSet.elements (Parse_bytecode.Debug.paths d ~units:cmis) in
-  (match output_file with
-  | None ->
-      let p = PseudoFs.f p cmis fs_files paths in
-      let fmt = Pretty_print.to_out_channel stdout in
-      Driver.f
-        ~standalone
-        ?profile
-        ~linkall
-        ~global
-        ~dynlink
-        ?source_map
-        ?custom_header
-        fmt
-        d
-        p
-  | Some file ->
-      gen_file file (fun chan ->
-          let p = if fs_output = None then PseudoFs.f p cmis fs_files paths else p in
-          let fmt = Pretty_print.to_out_channel chan in
-          Driver.f
-            ~standalone
-            ?profile
-            ~linkall
-            ~global
+  let pseudo_fs_init_instr () = if fs_external then [PseudoFs.init ()] else [] in
+  let output (one : Parse_bytecode.one) standalone output_file =
+    check_debug one.debug;
+    (match output_file with
+    | `Stdout ->
+        let instr =
+          List.concat
+            [ pseudo_fs_instr `caml_create_file one.debug one.cmis
+            ; pseudo_fs_init_instr ()
+            ; env_instr () ]
+        in
+        let code = Code.prepend one.code instr in
+        let fmt = Pretty_print.to_out_channel stdout in
+        Driver.f
+          ~standalone
+          ?profile
+          ~linkall
+          ~global
+          ~dynlink
+          ?source_map
+          ?custom_header
+          fmt
+          one.debug
+          code
+    | `Name file ->
+        let fs_instr1, fs_instr2 =
+          match fs_output with
+          | None -> pseudo_fs_instr `caml_create_file one.debug one.cmis, []
+          | Some _ -> [], pseudo_fs_instr `caml_create_file_extern one.debug one.cmis
+        in
+        gen_file file (fun chan ->
+            let instr = List.concat [fs_instr1; pseudo_fs_init_instr (); env_instr ()] in
+            let code = Code.prepend one.code instr in
+            let fmt = Pretty_print.to_out_channel chan in
+            Driver.f
+              ~standalone
+              ?profile
+              ~linkall
+              ~global
+              ~dynlink
+              ?source_map
+              ?custom_header
+              fmt
+              one.debug
+              code);
+        Option.iter fs_output ~f:(fun file ->
+            gen_file file (fun chan ->
+                let instr = fs_instr2 in
+                let code = Code.prepend Code.empty instr in
+                let pfs_fmt = Pretty_print.to_out_channel chan in
+                Driver.f
+                  ~standalone
+                  ?profile
+                  ?custom_header
+                  ~global
+                  pfs_fmt
+                  one.debug
+                  code)));
+    if times () then Format.eprintf "compilation: %a@." Timer.print t
+  in
+  (if runtime_only
+  then
+    let code : Parse_bytecode.one =
+      { code = Parse_bytecode.predefined_exceptions ()
+      ; cmis = StringSet.empty
+      ; debug = Parse_bytecode.Debug.create () }
+    in
+    output code true (fst output_file)
+  else
+    let kind, ic, close_ic =
+      match input_file with
+      | None -> Parse_bytecode.from_channel stdin, stdin, fun () -> ()
+      | Some fn ->
+          let ch = open_in_bin fn in
+          let res = Parse_bytecode.from_channel ch in
+          res, ch, fun () -> close_in ch
+    in
+    (match kind with
+    | `Exe ->
+        let t1 = Timer.make () in
+        let code =
+          Parse_bytecode.from_exe
+            ~includes:paths
+            ~toplevel
+            ?expunge
             ~dynlink
-            ?source_map
-            ?custom_header
-            fmt
-            d
-            p);
-      Option.iter fs_output ~f:(fun file ->
-          gen_file file (fun chan ->
-              let pfs = PseudoFs.f_empty cmis fs_files paths in
-              let pfs_fmt = Pretty_print.to_out_channel chan in
-              Driver.f ~standalone ?profile ?custom_header ~global pfs_fmt d pfs)));
-  if times () then Format.eprintf "compilation: %a@." Timer.print t;
+            ~debug:need_debug
+            ic
+        in
+        if times () then Format.eprintf "  parsing: %a@." Timer.print t1;
+        output code true (fst output_file)
+    | `Cmo cmo ->
+        let output_file =
+          match output_file, keep_unit_names with
+          | (`Stdout, false), true -> `Name (gen_unit_filename "./" cmo)
+          | (`Name x, false), true -> `Name (gen_unit_filename (Filename.dirname x) cmo)
+          | (`Stdout, _), false -> `Stdout
+          | (`Name x, _), false -> `Name x
+          | (`Name x, true), true
+            when String.length x > 0 && x.[String.length x - 1] = '/' ->
+              `Name (gen_unit_filename x cmo)
+          | (`Name _, true), true | (`Stdout, true), true ->
+              failwith "use [-o dirname/] or remove [--keep-unit-names]"
+        in
+        let t1 = Timer.make () in
+        let code =
+          Parse_bytecode.from_cmo ~includes:paths ~toplevel ~debug:need_debug cmo ic
+        in
+        if times () then Format.eprintf "  parsing: %a@." Timer.print t1;
+        output code false output_file
+    | `Cma cma when keep_unit_names ->
+        List.iter cma.lib_units ~f:(fun cmo ->
+            let output_file =
+              match output_file with
+              | `Stdout, false -> `Name (gen_unit_filename "./" cmo)
+              | `Name x, false -> `Name (gen_unit_filename (Filename.dirname x) cmo)
+              | `Name x, true when String.length x > 0 && x.[String.length x - 1] = '/'
+                ->
+                  `Name (gen_unit_filename x cmo)
+              | `Stdout, true | `Name _, true ->
+                  failwith "use [-o dirname/] or remove [--keep-unit-names]"
+            in
+            let t1 = Timer.make () in
+            let code =
+              Parse_bytecode.from_cmo ~includes:paths ~toplevel ~debug:need_debug cmo ic
+            in
+            if times ()
+            then Format.eprintf "  parsing: %a (%s)@." Timer.print t1 cmo.cu_name;
+            output code false output_file)
+    | `Cma cma ->
+        let t1 = Timer.make () in
+        let code =
+          Parse_bytecode.from_cma ~includes:paths ~toplevel ~debug:need_debug cma ic
+        in
+        if times () then Format.eprintf "  parsing: %a@." Timer.print t1;
+        output code false (fst output_file));
+    close_ic ());
   Debug.stop_profiling ()
 
 let main = Cmdliner.Term.(pure f $ CompileArg.options), CompileArg.info
diff --git a/compiler/lib/parse_bytecode.ml b/compiler/lib/parse_bytecode.ml
index 5c1556b18e..a23239e76f 100644
--- a/compiler/lib/parse_bytecode.ml
+++ b/compiler/lib/parse_bytecode.ml
@@ -26,7 +26,7 @@ let debug_parser = Debug.find "parser"
 
 let debug_sourcemap = Debug.find "sourcemap"
 
-type code = string
+type bytecode = string
 
 let predefined_exceptions =
   [ 0, "Out_of_memory"
@@ -236,7 +236,7 @@ end
 module Blocks : sig
   type t
 
-  val analyse : Debug.data -> code -> t
+  val analyse : Debug.data -> bytecode -> t
 
   val add : t -> int -> t
 
@@ -1955,6 +1955,11 @@ let match_exn_traps (blocks : 'a Addr.Map.t) =
 
 (****)
 
+type one =
+  { code : Code.program
+  ; cmis : StringSet.t
+  ; debug : Debug.data }
+
 let parse_bytecode ~debug code globals debug_data =
   let state = State.initial globals in
   Code.Var.reset ();
@@ -2028,14 +2033,14 @@ let read_toc ic =
   done;
   !section_table
 
-let exe_from_channel
-    ~includes
+let from_exe
+    ?(includes = [])
     ?(toplevel = false)
     ?(expunge = fun _ -> `Keep)
     ?(dynlink = false)
-    ~debug
-    ~debug_data
+    ?(debug = `No)
     ic =
+  let debug_data = Debug.create () in
   let toc = read_toc ic in
   let prim_size = seek_section toc ic "PRIM" in
   let prim = really_input_string ic prim_size in
@@ -2184,12 +2189,14 @@ let exe_from_channel
         StringSet.empty
     else StringSet.empty
   in
-  prepend p body, cmis, debug_data
+  let code = prepend p body in
+  Code.invariant code;
+  {code; cmis; debug = debug_data}
 
 (* As input: list of primitives + size of global table *)
-let from_bytes primitives (code : code) =
-  let globals = make_globals 0 [||] primitives in
+let from_bytes primitives (code : bytecode) =
   let debug_data = Debug.create () in
+  let globals = make_globals 0 [||] primitives in
   let p = parse_bytecode ~debug:`No code globals debug_data in
   let gdata = Var.fresh () in
   let body =
@@ -2213,6 +2220,7 @@ module Reloc = struct
   type t =
     { mutable pos : int
     ; mutable constants : Obj.t list
+    ; mutable step2_started : bool
     ; names : (string, int) Hashtbl.t
     ; primitives : (string, int) Hashtbl.t }
 
@@ -2220,10 +2228,13 @@ module Reloc = struct
     let constants = [] in
     { pos = List.length constants
     ; constants
+    ; step2_started = false
     ; names = Hashtbl.create 17
     ; primitives = Hashtbl.create 17 }
 
+  (* We currently rely on constants to be relocated before globals. *)
   let step1 t compunit code =
+    if t.step2_started then assert false;
     let open Cmo_format in
     List.iter compunit.cu_primitives ~f:(fun name ->
         Hashtbl.add t.primitives name (Hashtbl.length t.primitives));
@@ -2246,15 +2257,16 @@ module Reloc = struct
         | _ -> ())
 
   let step2 t compunit code =
+    t.step2_started <- true;
     let open Cmo_format in
     let next id =
       let name = Ident.name id in
       try Hashtbl.find t.names name
       with Not_found ->
-        let x = t.pos in
+        let pos = t.pos in
         t.pos <- succ t.pos;
-        Hashtbl.add t.names name x;
-        x
+        Hashtbl.add t.names name pos;
+        pos
     in
     let slot_for_getglobal id = next id in
     let slot_for_setglobal id = next id in
@@ -2331,16 +2343,53 @@ let from_compilation_units ~includes:_ ~toplevel ~debug ~debug_data l =
           StringSet.add compunit.Cmo_format.cu_name acc)
     else StringSet.empty
   in
-  prepend prog body, cmis, debug_data
+  {code = prepend prog body; cmis; debug = debug_data}
 
-let from_channel
-    ?(includes = [])
-    ?(toplevel = false)
-    ?expunge
-    ?(dynlink = false)
-    ?(debug = `No)
-    ic =
+let from_cmo ?(includes = [])
+             ?(toplevel = false)
+             ?(debug = `No)
+             compunit
+             ic =
   let debug_data = Debug.create () in
+  seek_in ic compunit.Cmo_format.cu_pos;
+  let code = Bytes.create compunit.Cmo_format.cu_codesize in
+  really_input ic code 0 compunit.Cmo_format.cu_codesize;
+  if debug = `No || compunit.Cmo_format.cu_debug = 0
+  then ()
+  else (
+    seek_in ic compunit.Cmo_format.cu_debug;
+    Debug.read_event_list debug_data ~crcs:[] ~includes ~orig:0 ic);
+  let p =
+    from_compilation_units ~toplevel ~includes ~debug ~debug_data [compunit, code]
+  in
+  Code.invariant p.code;
+  p
+
+let from_cma ?(includes = [])
+             ?(toplevel = false)
+             ?(debug = `No)
+             lib
+             ic =
+  let debug_data = Debug.create () in
+  let orig = ref 0 in
+  let units =
+    List.map lib.Cmo_format.lib_units ~f:(fun compunit ->
+        seek_in ic compunit.Cmo_format.cu_pos;
+        let code = Bytes.create compunit.Cmo_format.cu_codesize in
+        really_input ic code 0 compunit.Cmo_format.cu_codesize;
+        if debug = `No || compunit.Cmo_format.cu_debug = 0
+        then ()
+        else (
+          seek_in ic compunit.Cmo_format.cu_debug;
+          Debug.read_event_list debug_data ~crcs:[] ~includes ~orig:!orig ic);
+        orig := !orig + compunit.Cmo_format.cu_codesize;
+        compunit, code)
+  in
+  let p = from_compilation_units ~toplevel ~includes ~debug ~debug_data units in
+  Code.invariant p.code;
+  p
+
+let from_channel ic =
   let format =
     try
       let header = really_input_string ic Magic_number.size in
@@ -2360,18 +2409,7 @@ let from_channel
         let compunit_pos = input_binary_int ic in
         seek_in ic compunit_pos;
         let compunit : Cmo_format.compilation_unit = input_value ic in
-        seek_in ic compunit.Cmo_format.cu_pos;
-        let code = Bytes.create compunit.Cmo_format.cu_codesize in
-        really_input ic code 0 compunit.Cmo_format.cu_codesize;
-        if debug = `No || compunit.Cmo_format.cu_debug = 0
-        then ()
-        else (
-          seek_in ic compunit.Cmo_format.cu_debug;
-          Debug.read_event_list debug_data ~crcs:[] ~includes ~orig:0 ic);
-        let a, b, c =
-          from_compilation_units ~toplevel ~includes ~debug ~debug_data [compunit, code]
-        in
-        a, b, c, false
+        `Cmo compunit
     | `Cma ->
         if Config.Flag.check_magic () && magic <> Magic_number.current_cma
         then raise Magic_number.(Bad_magic_version magic);
@@ -2379,35 +2417,14 @@ let from_channel
         (* Go to table of contents *)
         seek_in ic pos_toc;
         let lib : Cmo_format.library = input_value ic in
-        let orig = ref 0 in
-        let units =
-          List.map lib.Cmo_format.lib_units ~f:(fun compunit ->
-              seek_in ic compunit.Cmo_format.cu_pos;
-              let code = Bytes.create compunit.Cmo_format.cu_codesize in
-              really_input ic code 0 compunit.Cmo_format.cu_codesize;
-              if debug = `No || compunit.Cmo_format.cu_debug = 0
-              then ()
-              else (
-                seek_in ic compunit.Cmo_format.cu_debug;
-                Debug.read_event_list debug_data ~crcs:[] ~includes ~orig:!orig ic);
-              orig := !orig + compunit.Cmo_format.cu_codesize;
-              compunit, code)
-        in
-        let a, b, c =
-          from_compilation_units ~toplevel ~includes ~debug ~debug_data units
-        in
-        a, b, c, false
+        `Cma lib
     | _ -> raise Magic_number.(Bad_magic_number (to_string magic)))
   | `Post magic -> (
     match Magic_number.kind magic with
     | `Exe ->
         if Config.Flag.check_magic () && magic <> Magic_number.current_exe
         then raise Magic_number.(Bad_magic_version magic);
-        let a, b, c =
-          exe_from_channel ~includes ~toplevel ?expunge ~dynlink ~debug ~debug_data ic
-        in
-        Code.invariant a;
-        a, b, c, true
+        `Exe
     | _ -> raise Magic_number.(Bad_magic_number (to_string magic)))
 
 let predefined_exceptions () =
diff --git a/compiler/lib/parse_bytecode.mli b/compiler/lib/parse_bytecode.mli
index 2cf3ec342c..9cdd43468e 100644
--- a/compiler/lib/parse_bytecode.mli
+++ b/compiler/lib/parse_bytecode.mli
@@ -32,14 +32,38 @@ module Debug : sig
   val paths : data -> units:StringSet.t -> StringSet.t
 end
 
-val from_channel :
+type one =
+  { code : Code.program
+  ; cmis : StringSet.t
+  ; debug : Debug.data }
+
+val from_exe :
      ?includes:string list
   -> ?toplevel:bool
   -> ?expunge:(string -> [`Keep | `Skip])
   -> ?dynlink:bool
   -> ?debug:[`Full | `Names | `No]
   -> in_channel
-  -> Code.program * StringSet.t * Debug.data * bool
+  -> one
+
+val from_cmo :
+     ?includes:string list
+  -> ?toplevel:bool
+  -> ?debug:[`Full | `Names | `No]
+  -> Cmo_format.compilation_unit
+  -> in_channel
+  -> one
+
+val from_cma :
+     ?includes:string list
+  -> ?toplevel:bool
+  -> ?debug:[`Full | `Names | `No]
+  -> Cmo_format.library
+  -> in_channel
+  -> one
+
+val from_channel :
+  in_channel -> [`Cmo of Cmo_format.compilation_unit | `Cma of Cmo_format.library | `Exe]
 
 val from_string : string array -> string -> Code.program * Debug.data
 
diff --git a/compiler/lib/pseudoFs.ml b/compiler/lib/pseudoFs.ml
index cac4d266e4..b423b00793 100644
--- a/compiler/lib/pseudoFs.ml
+++ b/compiler/lib/pseudoFs.ml
@@ -70,77 +70,53 @@ let list_files name paths =
   in
   expand_path exts file virtname
 
-let cmi_dir = "/static/cmis"
-
 let find_cmi paths base =
-  try
-    let name = String.uncapitalize_ascii base ^ ".cmi" in
-    Filename.concat cmi_dir name, Findlib.find_in_findlib_paths paths name
-  with Not_found ->
-    let name = String.capitalize_ascii base ^ ".cmi" in
-    Filename.concat cmi_dir name, Findlib.find_in_findlib_paths paths name
+  let name, filename =
+    try
+      let name = String.uncapitalize_ascii base ^ ".cmi" in
+      name, Findlib.find_in_findlib_paths paths name
+    with Not_found ->
+      let name = String.capitalize_ascii base ^ ".cmi" in
+      name, Findlib.find_in_findlib_paths paths name
+  in
+  Filename.concat "/static/cmis" name, filename
 
-open Code
+let instr_of_name_content prim ~name ~content =
+  let open Code in
+  Let (Var.fresh (), Prim (Extern prim, [Pc (IString name); Pc (IString content)]))
 
-let read name filename =
-  let content = Fs.read_file filename in
-  Pc (IString name), Pc (IString content)
+let embed_file ~name ~filename =
+  instr_of_name_content "caml_create_file_extern" ~name ~content:(Fs.read_file filename)
 
-let program_of_files l =
-  let fs = List.map l ~f:(fun (name, filename) -> read name filename) in
-  let body =
-    List.map fs ~f:(fun (n, c) ->
-        Let (Var.fresh (), Prim (Extern "caml_create_file_extern", [n; c])))
-  in
-  let pc = 0 in
-  let blocks =
-    Addr.Map.add
-      pc
-      {params = []; handler = None; body = []; branch = Stop}
-      Addr.Map.empty
-  in
-  let p = pc, blocks, pc + 1 in
-  Code.prepend p body
+let init () = Code.(Let (Var.fresh (), Prim (Extern "caml_fs_init", [])))
 
-let make_body prim cmis files paths =
-  let fs, missing =
+let f ~prim ~cmis ~files ~paths =
+  let prim =
+    match prim with
+    | `caml_create_file -> "caml_create_file"
+    | `caml_create_file_extern -> "caml_create_file_extern"
+  in
+  let cmi_files, missing_cmis =
     StringSet.fold
       (fun s (acc, missing) ->
         try
           let name, filename = find_cmi paths s in
-          read name filename :: acc, missing
+          (name, Fs.read_file filename) :: acc, missing
         with Not_found -> acc, s :: missing)
       cmis
       ([], [])
   in
-  if missing <> []
+  if missing_cmis <> []
   then (
     warn "Some OCaml interface files were not found.@.";
     warn "Use [-I dir_of_cmis] option to bring them into scope@.";
     (* [`ocamlc -where`/expunge in.byte out.byte moduleA moduleB ... moduleN] *)
-    List.iter missing ~f:(fun nm -> warn "  %s@." nm));
-  let fs =
-    List.fold_left files ~init:fs ~f:(fun acc f ->
-        let l = list_files f paths in
-        List.fold_left l ~init:acc ~f:(fun acc (n, fn) -> read n fn :: acc))
-  in
-  let body =
-    List.map fs ~f:(fun (n, c) -> Let (Var.fresh (), Prim (Extern prim, [n; c])))
-  in
-  body
-
-let f p cmis files paths =
-  let body = make_body "caml_create_file" cmis files paths in
-  Code.prepend p body
-
-let f_empty cmis files paths =
-  let body = make_body "caml_create_file_extern" cmis files paths in
-  let pc = 0 in
-  let blocks =
-    Addr.Map.add
-      pc
-      {params = []; handler = None; body = []; branch = Stop}
-      Addr.Map.empty
+    List.iter missing_cmis ~f:(fun nm -> warn "  %s@." nm));
+  let other_files =
+    List.map files ~f:(fun f ->
+        List.map (list_files f paths) ~f:(fun (name, filename) ->
+            name, Fs.read_file filename))
+    |> List.concat
   in
-  let p = pc, blocks, pc + 1 in
-  Code.prepend p body
+  List.map (other_files @ cmi_files) ~f:(fun (name, content) ->
+      instr_of_name_content prim ~name ~content)
diff --git a/compiler/lib/pseudoFs.mli b/compiler/lib/pseudoFs.mli
index 243d54e697..006737c015 100644
--- a/compiler/lib/pseudoFs.mli
+++ b/compiler/lib/pseudoFs.mli
@@ -19,8 +19,13 @@
 
 open Stdlib
 
-val f : Code.program -> StringSet.t -> string list -> string list -> Code.program
+val f :
+     prim:[`caml_create_file | `caml_create_file_extern]
+  -> cmis:StringSet.t
+  -> files:string list
+  -> paths:string list
+  -> Code.instr list
 
-val f_empty : StringSet.t -> string list -> string list -> Code.program
+val embed_file : name:string -> filename:string -> Code.instr
 
-val program_of_files : (string * string) list -> Code.program
+val init : unit -> Code.instr
diff --git a/toplevel/bin/jsoo_mkcmis.ml b/toplevel/bin/jsoo_mkcmis.ml
index f8fa8086ff..1a0eaefeab 100644
--- a/toplevel/bin/jsoo_mkcmis.ml
+++ b/toplevel/bin/jsoo_mkcmis.ml
@@ -61,8 +61,16 @@ let args =
   let js, args = List.partition (fun s -> Filename.check_suffix s ".js") args in
   let js = if !runtime then "+runtime.js" :: js else js in
   let all = Jsoo_common.cmis args in
-  let all = List.map (fun x -> Filename.(concat !prefix (basename x)), x) all in
-  let program = Js_of_ocaml_compiler.PseudoFs.program_of_files all in
+  let instr =
+    List.map
+      (fun filename ->
+        let name = Filename.(concat !prefix (basename filename)) in
+        Js_of_ocaml_compiler.PseudoFs.embed_file ~name ~filename)
+      all
+  in
+  let program =
+    Js_of_ocaml_compiler.Code.prepend Js_of_ocaml_compiler.Code.empty instr
+  in
   let oc =
     match !output, args with
     | Some x, _ -> open_out x