Make RTS data segment passive

src/linking/linkModule.ml

@@ -866,6 +866,22 @@ let link (em1 : extended_module) libname (em2 : extended_module) =
     add_or_get_ty fun_ty.it
   in
 
+  (* Check that the first module generated by the compiler backend does not use 
+     active data segments. *)
+  let is_active data_segment = match data_segment.it.dmode.it with
+  | Active _ -> true
+  | _ -> false
+  in
+  let em1_active_data_segments = List.filter is_active em1.module_.datas in
+  assert ((List.length em1_active_data_segments) = 0);
+
+  let is_passive data_segment = match data_segment.it.dmode.it with 
+  | Passive -> true
+  | _ -> false
+  in
+  let em1_passive_data_segments = List.filter is_passive em1.module_.datas in
+  let dm2_data_segment_offset = List.length em1_passive_data_segments in
+
   (* Rename types in first module *)
   let em1_tys =
     map_module (fun m -> { (rename_types (ty_renamer m.types) m) with types = [] }) em1
@@ -895,6 +911,63 @@ let link (em1 : extended_module) libname (em2 : extended_module) =
     Int32.add (Int32.add lib_table_start dylink.table_size) (Int32.of_int (List.length got_func_imports))
   in
 
+  (* Rust generates active data segments for the runtime system code that are not supported with orthogonal persistence.
+     Therefore, make the data segments passive and load them on initialization to their reserved static space. 
+     Note: If Rust would also use passive data segments in future, the segment load indices need to be renumbered. *)
+  let make_rts_data_segments_passive : module_' -> module_' = fun m ->
+    let segment_mode' (dmode : segment_mode') = 
+      match dmode with 
+        | Active _ -> Passive
+        | _ -> raise (LinkError "Passive data segments are not yet supported in the RTS module")
+    in
+    let segment_mode = phrase (segment_mode') in
+    let data_segment' (s : data_segment') = { s with dmode = segment_mode s.dmode; } in
+    let data_segment = phrase (data_segment') in
+    let data_segments = List.map data_segment in
+    { m with datas = data_segments m.datas; }
+  in
+
+  let load_rts_data_segments numbering_offset data_segments : module_' -> module_' = fun m ->
+      let imported_functions = Int32.to_int (count_imports is_fun_import m) in
+      let start_index = Int32.to_int (match m.start with
+      | Some index -> index.it
+      | None -> raise (LinkError "The module has no start function to inject"))
+      in
+      let local_start_function = Int.sub start_index imported_functions in
+      if local_start_function < 0 then
+        raise (LinkError "The module start refers to an imported function that cannot be injected");
+      assert (local_start_function < (List.length m.funcs));
+
+      let load_passive_segment index data_segment =
+        let segment_index = Int32.of_int (Int.add index numbering_offset) in
+        let compile_const_i32 value = Const (Wasm.Values.I32 value @@ no_region) @@ no_region in
+        let data_target = match data_segment.it.dmode.it with
+          | Active { offset; _ } -> offset.it
+          | _ -> raise (LinkError "Passive data segments are not yet supported in the RTS module")
+        in
+        let data_length = Int32.of_int (String.length data_segment.it.dinit) in
+        let memory_init = MemoryInit (segment_index @@ no_region) @@ no_region in
+        data_target @
+        [ 
+          compile_const_i32 0l; (* data offset *)
+          compile_const_i32 data_length; 
+          memory_init 
+        ]
+      in
+      let load_passive_segments = List.concat (List.mapi load_passive_segment data_segments) in
+
+      let inject_in_func' code f = { f with body = code @ f.body } in
+      let inject_in_func code = phrase (inject_in_func' code) in
+      let patch_functions functions = 
+        List.mapi (fun index func -> 
+          if index = local_start_function then 
+            inject_in_func load_passive_segments func
+          else func
+        ) functions
+      in
+      { m with funcs = patch_functions m.funcs; }
+    in
+
   let merged = join_modules
     ( em1_tys
     |> map_module (fun m -> { m with types = type_indices_sorted })
@@ -908,6 +981,7 @@ let link (em1 : extended_module) libname (em2 : extended_module) =
     |> map_module (set_table_size new_table_size)
     )
     ( dm2
+    |> make_rts_data_segments_passive
     |> remove_imports is_fun_import fun_resolved21
     |> remove_imports is_global_import global_resolved21
     |> remove_imports is_memory_import [0l, 0l]
@@ -923,6 +997,7 @@ let link (em1 : extended_module) libname (em2 : extended_module) =
     type_indices
   |> add_call_ctors
   |> remove_non_ic_exports (* only sane if no additional files get linked in *)
+  |> map_module (load_rts_data_segments dm2_data_segment_offset dm2.datas)
   in
 
   (* Rename global and function indices in GOT.func stuff *)