v8dasm.cpp

#include <libplatform/libplatform.h>
#include <v8.h>

#include <string>

using namespace v8;

static Isolate* isolate = nullptr;

static v8::ScriptCompiler::CachedData* compileCode(const char* data) {
  auto str = String::NewFromUtf8(isolate, data).ToLocalChecked();
  auto script =
      Script::Compile(isolate->GetCurrentContext(), str).ToLocalChecked();
  auto unboundScript = script->GetUnboundScript();

  return ScriptCompiler::CreateCodeCache(unboundScript);
}

static void fixBytecode(uint8_t* bytecodeBuffer, const char* code) {
  auto dummyBytecode = compileCode(code);
  // Copy version hash, source hash and flag hash from dummy bytecode to source
  // bytecode. Offsets of these value may differ in different version of V8.
  // Refer V8 src/snapshot/code-serializer.h for details.
  for (int i = 4; i < 16; i++) {
    bytecodeBuffer[i] = dummyBytecode->data[i];
  }
  delete dummyBytecode;
}

static void runBytecode(uint8_t* bytecodeBuffer, int len) {
  // Compile some dummy code to get version hash, source hash and flag hash.
  const char* code = "console.log('hello');";
  fixBytecode(bytecodeBuffer, code);

  // Load code into code cache.
  auto cached_data = new ScriptCompiler::CachedData(bytecodeBuffer, len);

  // Create dummy source.
  ScriptOrigin origin(isolate, String::NewFromUtf8Literal(isolate, "code.jsc"));
  ScriptCompiler::Source source(
      String::NewFromUtf8(isolate, code).ToLocalChecked(), origin, cached_data);

  // Compile code from code cache to print disassembly.
  MaybeLocal<UnboundScript> v8_script = ScriptCompiler::CompileUnboundScript(
      isolate, &source, ScriptCompiler::kConsumeCodeCache);
}

static void readAllBytes(const std::string& file, std::vector<char>& buffer) {
  std::ifstream infile(file, std::ifstream::binary);

  infile.seekg(0, infile.end);
  size_t length = infile.tellg();
  infile.seekg(0, infile.beg);

  if (length > 0) {
    buffer.resize(length);
    infile.read(&buffer[0], length);
  }
}

int main(int argc, char* argv[]) {
  // Set flags here, flags that affects code generation and seririalzation
  // should be same as the target program. You can add other flags freely
  // because flag hash will be overrided in fixBytecode().
  v8::V8::SetFlagsFromString("--no-lazy --no-flush-bytecode --log-all");

  v8::V8::InitializeICUDefaultLocation(argv[0]);
  v8::V8::InitializeExternalStartupData(argv[0]);
  auto plat = v8::platform::NewDefaultPlatform();
  v8::V8::InitializePlatform(plat.get());
  v8::V8::Initialize();

  Isolate::CreateParams p = {};
  p.array_buffer_allocator = v8::ArrayBuffer::Allocator::NewDefaultAllocator();

  isolate = Isolate::New(p);
  {
    v8::Isolate::Scope isolate_scope(isolate);
    v8::HandleScope scope(isolate);
    auto ctx = v8::Context::New(isolate);
    Context::Scope context_scope(ctx);

    std::vector<char> data;
    readAllBytes(argv[1], data);
    runBytecode((uint8_t*)data.data(), data.size());
  }
}