[Interpreter] Decode/encode the data count section (#59)

Author: binji

interpreter/binary/decode.ml

@@ -485,6 +485,7 @@ let id s =
     | 9 -> `ElemSection
     | 10 -> `CodeSection
     | 11 -> `DataSection
+    | 12 -> `DataCountSection
     | _ -> error s (pos s) "invalid section id"
     ) bo
 
@@ -639,6 +640,12 @@ let data_section s =
   section `DataSection (vec (at memory_segment)) [] s
 
 
+(* DataCount section *)
+
+let data_count_section s =
+  section `DataCountSection (opt vu32 true) None s
+
+
 (* Custom section *)
 
 let custom size s =
@@ -679,13 +686,18 @@ let module_ s =
   iterate custom_section s;
   let elems = elem_section s in
   iterate custom_section s;
+  let data_count = data_count_section s in
+  iterate custom_section s;
   let func_bodies = code_section s in
   iterate custom_section s;
   let data = data_section s in
   iterate custom_section s;
   require (pos s = len s) s (len s) "junk after last section";
   require (List.length func_types = List.length func_bodies)
     s (len s) "function and code section have inconsistent lengths";
+  require
+    (data_count = None || data_count = Some (Int32.of_int (List.length data)))
+    s (len s) "data count and data section have inconsistent lengths";
   let funcs =
     List.map2 Source.(fun t f -> {f.it with ftype = t} @@ f.at)
       func_types func_bodies

interpreter/binary/encode.ml

@@ -503,6 +503,11 @@ let encode m =
     let data_section data =
       section 11 (vec memory_segment) data (data <> [])
 
+    (* DataCount section *)
+
+    let data_count_section data =
+      section 12 len (List.length data) (data <> [])
+
     (* Module *)
 
     let module_ m =
@@ -517,6 +522,7 @@ let encode m =
       export_section m.it.exports;
       start_section m.it.start;
       elem_section m.it.elems;
+      data_count_section m.it.data;
       code_section m.it.funcs;
       data_section m.it.data
   end

test/core/custom.wast

@@ -118,3 +118,13 @@
   )
   "length out of bounds"
 )
+
+(assert_malformed
+  (module binary
+    "\00asm" "\01\00\00\00"
+    "\05\03\01\00\01"                         ;; memory section
+    "\0c\01\02"                               ;; data count section (2 segments)
+    "\0b\06\01\00\41\00\0b\00"                ;; data section (1 segment)
+  )
+  "data count and data section have inconsistent lengths"
+)