[wasm] Add a flag to generate an mjsunit test out of a wasm-code fuzzer test case.

test/fuzzer/wasm-code.cc

 // Copyright 2016 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 <stddef.h>
 #include <stdint.h>
 
 #include "include/v8.h"
 #include "src/isolate.h"
 #include "src/objects.h"
+#include "src/ostreams.h"
 #include "src/wasm/wasm-interpreter.h"
 #include "src/wasm/wasm-module-builder.h"
 #include "src/wasm/wasm-module.h"
 #include "test/common/wasm/test-signatures.h"
 #include "test/common/wasm/wasm-module-runner.h"
 #include "test/fuzzer/fuzzer-support.h"
 
 #define WASM_CODE_FUZZER_HASH_SEED 83
 
 using namespace v8::internal::wasm;
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  // Save the flag so that we can change it and restore it later.
+  bool generate_test = v8::internal::FLAG_wasm_code_generate_test;
+  if (generate_test) {
+    v8::internal::OFStream os(stdout);
+
+    os << "// Copyright 2016 the V8 project authors. All rights reserved."
+       << std::endl;
+    os << "// Use of this source code is governed by a BSD-style license that "
+          "can be"
+       << std::endl;
+    os << "// found in the LICENSE file." << std::endl;
+    os << std::endl;
+    os << "// Flags: --expose-wasm" << std::endl;
+    os << std::endl;
+    os << "load(\"test/mjsunit/wasm/wasm-constants.js\");" << std::endl;
+    os << "load(\"test/mjsunit/wasm/wasm-module-builder.js\");" << std::endl;
+    os << std::endl;
+    os << "(function() {" << std::endl;
+    os << "  var builder = new WasmModuleBuilder();" << std::endl;
+    os << "  builder.addFunction(\"test\", kSig_i_iii)" << std::endl;
+    os << "    .addBody([" << std::endl;
+  }
   v8_fuzzer::FuzzerSupport* support = v8_fuzzer::FuzzerSupport::Get();
   v8::Isolate* isolate = support->GetIsolate();
   v8::internal::Isolate* i_isolate =
       reinterpret_cast<v8::internal::Isolate*>(isolate);
 
   // Clear any pending exceptions from a prior run.
   if (i_isolate->has_pending_exception()) {
     i_isolate->clear_pending_exception();
   }
 
@@ skipping 19 matching lines @@
 
   v8::internal::wasm::testing::SetupIsolateForWasmModule(i_isolate);
 
   v8::internal::HandleScope scope(i_isolate);
 
   ErrorThrower interpreter_thrower(i_isolate, "Interpreter");
   std::unique_ptr<const WasmModule> module(testing::DecodeWasmModuleForTesting(
       i_isolate, &interpreter_thrower, buffer.begin(), buffer.end(),
       v8::internal::wasm::ModuleOrigin::kWasmOrigin, true));
 
+  // Clear the flag so that the WebAssembly code is not printed twice.
+  v8::internal::FLAG_wasm_code_generate_test = false;
   if (module == nullptr) {
+    if (generate_test) {
+      v8::internal::OFStream os(stdout);
+      os << "            ])" << std::endl;
+      os << "            .exportFunc();" << std::endl;
+      os << "  assertThrows(function() { builder.instantiate(); });"
+         << std::endl;
+      os << "})();" << std::endl;
+    }
     return 0;
   }
+  if (generate_test) {
+    v8::internal::OFStream os(stdout);
+    os << "            ])" << std::endl;
+    os << "            .exportFunc();" << std::endl;
+    os << "  var module = builder.instantiate();" << std::endl;
+    os << "  module.exports.test(1, 2, 3);" << std::endl;
+    os << "})();" << std::endl;
+  }
+
   int32_t result_interpreted;
   bool possible_nondeterminism = false;
   {
     WasmVal args[] = {WasmVal(1), WasmVal(2), WasmVal(3)};
     result_interpreted = testing::InterpretWasmModule(
         i_isolate, &interpreter_thrower, module.get(), 0, args,
         &possible_nondeterminism);
   }
 
   ErrorThrower compiler_thrower(i_isolate, "Compiler");
   v8::internal::Handle<v8::internal::JSObject> instance =
       testing::InstantiateModuleForTesting(i_isolate, &compiler_thrower,
                                            module.get());
-
+  // Restore the flag.
+  v8::internal::FLAG_wasm_code_generate_test = generate_test;
   if (!interpreter_thrower.error()) {
     CHECK(!instance.is_null());
   } else {
     return 0;
   }
   int32_t result_compiled;
   {
     v8::internal::Handle<v8::internal::Object> arguments[] = {
         v8::internal::handle(v8::internal::Smi::FromInt(1), i_isolate),
         v8::internal::handle(v8::internal::Smi::FromInt(2), i_isolate),
@@ skipping 11 matching lines @@
     // result_compiled. Therefore we do not check the equality of the results
     // if the execution may have produced a NaN at some point.
     if (!possible_nondeterminism && (result_interpreted != result_compiled)) {
       V8_Fatal(__FILE__, __LINE__, "WasmCodeFuzzerHash=%x",
                v8::internal::StringHasher::HashSequentialString(
                    data, static_cast<int>(size), WASM_CODE_FUZZER_HASH_SEED));
     }
   }
   return 0;
 }