[wasm] Start function must not have a return value.

src/wasm/module-decoder.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/wasm/module-decoder.h"
 
 #include "src/base/functional.h"
 #include "src/base/platform/platform.h"
 #include "src/flags.h"
 #include "src/macro-assembler.h"
@@ skipping 494 matching lines @@
         }
       }
       section_iter.advance();
     }
 
     // ===== Start section ===================================================
     if (section_iter.section_code() == kStartSectionCode) {
       WasmFunction* func;
       const byte* pos = pc_;
       module->start_function_index = consume_func_index(module, &func);
-      if (func && func->sig->parameter_count() > 0) {
-        error(pos, "invalid start function: non-zero parameter count");
+      if (func &&
+          (func->sig->parameter_count() > 0 || func->sig->return_count() > 0)) {
+        error(pos,
+              "invalid start function: non-zero parameter or return count");
       }
       section_iter.advance();
     }
 
     // ===== Elements section ================================================
     if (section_iter.section_code() == kElementSectionCode) {
       uint32_t element_count = consume_u32v("element count");
       for (uint32_t i = 0; ok() && i < element_count; ++i) {
         const byte* pos = pc();
         uint32_t table_index = consume_u32v("table index");
@@ skipping 685 matching lines @@
     table.push_back(std::move(func_asm_offsets));
   }
   if (decoder.more()) decoder.error("unexpected additional bytes");
 
   return decoder.toResult(std::move(table));
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8