[wasm] Expose function IsSupportedVersion

- Exposes IsSupportedVersion function which compares serialized
  version to current Wasm version.
- Tweaks the comments on serialization to match the code.

Bug: chromium:719172
Change-Id: I76df9605aee16fd98cd82b54dba2e9acbd56b41b
Reviewed-on: https://chromium-review.googlesource.com/c/1265141Reviewed-by: Ben Smith <binji@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56420}

src/wasm/wasm-serialization.cc

@@ -127,14 +127,6 @@ void WriteVersion(Isolate* isolate, Writer* writer) {
   writer->Write(FlagList::Hash());
 }
 
-bool IsSupportedVersion(Isolate* isolate, const Vector<const byte> version) {
-  if (version.size() < kVersionSize) return false;
-  byte current_version[kVersionSize];
-  Writer writer({current_version, kVersionSize});
-  WriteVersion(isolate, &writer);
-  return memcmp(version.start(), current_version, kVersionSize) == 0;
-}
-
 // On Intel, call sites are encoded as a displacement. For linking and for
 // serialization/deserialization, we want to store/retrieve a tag (the function
 // index). On Intel, that means accessing the raw displacement.
@@ -537,6 +529,14 @@ bool NativeModuleDeserializer::ReadCode(uint32_t fn_index, Reader* reader) {
   return true;
 }
 
+bool IsSupportedVersion(Isolate* isolate, Vector<const byte> version) {
+  if (version.size() < kVersionSize) return false;
+  byte current_version[kVersionSize];
+  Writer writer({current_version, kVersionSize});
+  WriteVersion(isolate, &writer);
+  return memcmp(version.start(), current_version, kVersionSize) == 0;
+}
+
 MaybeHandle<WasmModuleObject> DeserializeNativeModule(
     Isolate* isolate, Vector<const byte> data, Vector<const byte> wire_bytes) {
   if (!IsWasmCodegenAllowed(isolate, isolate->native_context())) {

src/wasm/wasm-serialization.h

@@ -11,9 +11,9 @@ namespace v8 {
 namespace internal {
 namespace wasm {
 
-// Support to serialize WebAssembly {NativeModule} objects. This class intends
-// to be thread-safe in that it takes a consistent snapshot of the module state
-// at instantiation, allowing other threads to mutate the module concurrently.
+// Support for serializing WebAssembly {NativeModule} objects. This class takes
+// a snapshot of the module state at instantiation, and other code that modifies
+// the module after that won't affect the serialized result.
 class WasmSerializer {
  public:
   WasmSerializer(Isolate* isolate, NativeModule* native_module);
@@ -31,7 +31,11 @@ class WasmSerializer {
   std::vector<WasmCode*> code_table_;
 };
 
-// Support to deserialize WebAssembly {NativeModule} objects.
+// Support for deserializing WebAssembly {NativeModule} objects.
+// Checks the version header of the data against the current version.
+bool IsSupportedVersion(Isolate* isolate, Vector<const byte> data);
+
+// Deserializes the given data to create a compiled Wasm module.
 MaybeHandle<WasmModuleObject> DeserializeNativeModule(
     Isolate* isolate, Vector<const byte> data, Vector<const byte> wire_bytes);