[wasm] Be more lenient on the names section.

R=clemensh@chromium.org,dschuff@chromium.org
BUG=v8:5632
LOG=Y

Review-Url: https://codereview.chromium.org/2501873003
Cr-Commit-Position: refs/heads/master@{#41011}

src/wasm/module-decoder.cc

@@ -623,17 +623,16 @@ class ModuleDecoder : public Decoder {
 
     // ===== Name section ====================================================
     if (section_iter.section_code() == kNameSectionCode) {
-      const byte* pos = pc_;
       uint32_t functions_count = consume_u32v("functions count");
-      if (functions_count != module->num_declared_functions) {
-        error(pos, pos, "function name count %u mismatch (%u expected)",
-              functions_count, module->num_declared_functions);
-      }
 
       for (uint32_t i = 0; ok() && i < functions_count; ++i) {
-        WasmFunction* function =
-            &module->functions[i + module->num_imported_functions];
-        function->name_offset = consume_string(&function->name_length, false);
+        uint32_t function_name_length = 0;
+        uint32_t name_offset = consume_string(&function_name_length, false);
+        uint32_t func_index = i;
+        if (func_index < module->functions.size()) {
+          module->functions[func_index].name_offset = name_offset;
+          module->functions[func_index].name_length = function_name_length;
+        }
 
         uint32_t local_names_count = consume_u32v("local names count");
         for (uint32_t j = 0; ok() && j < local_names_count; j++) {

src/wasm/wasm-module-builder.cc

@@ -509,7 +509,12 @@ void WasmModuleBuilder::WriteTo(ZoneBuffer& buffer) const {
     buffer.write_size(4);
     buffer.write(reinterpret_cast<const byte*>("name"), 4);
     // Emit the names.
-    buffer.write_size(functions_.size());
+    size_t count = functions_.size() + imports_.size();
+    buffer.write_size(count);
+    for (size_t i = 0; i < imports_.size(); i++) {
+      buffer.write_u8(0);  // empty name for import
+      buffer.write_u8(0);  // no local variables
+    }
     for (auto function : functions_) {
       buffer.write_size(function->name_.size());
       if (function->name_.size() > 0) {

test/mjsunit/wasm/wasm-module-builder.js

@@ -522,7 +522,12 @@ class WasmModuleBuilder {
       if (debug) print("emitting names @ " + binary.length);
       binary.emit_section(kUnknownSectionCode, section => {
         section.emit_string("name");
-        section.emit_u32v(wasm.functions.length);
+        var count = wasm.functions.length + wasm.num_imported_funcs;
+        section.emit_u32v(count);
+        for (var i = 0; i < wasm.num_imported_funcs; i++) {
+          section.emit_u8(0); // empty string
+          section.emit_u8(0); // local names count == 0
+        }
         for (let func of wasm.functions) {
           var name = func.name == undefined ? "" : func.name;
           section.emit_string(name);