engine/runtime/dart_snapshot.cc

// Copyright 2013 The Flutter 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 "flutter/runtime/dart_snapshot.h"

#include <sstream>

#include "flutter/fml/native_library.h"
#include "flutter/fml/paths.h"
#include "flutter/fml/trace_event.h"
#include "flutter/lib/snapshot/snapshot.h"
#include "flutter/runtime/dart_vm.h"

namespace flutter {

const char* DartSnapshot::kVMDataSymbol = "kDartVmSnapshotData";
const char* DartSnapshot::kVMInstructionsSymbol = "kDartVmSnapshotInstructions";
const char* DartSnapshot::kIsolateDataSymbol = "kDartIsolateSnapshotData";
const char* DartSnapshot::kIsolateInstructionsSymbol =
    "kDartIsolateSnapshotInstructions";

// On Windows and Android (in debug mode) the engine finds the Dart snapshot
// data through symbols that are statically linked into the executable.
// On other platforms this data is obtained by a dynamic symbol lookup.
#define DART_SNAPSHOT_STATIC_LINK \
  (OS_WIN || (OS_ANDROID && FLUTTER_JIT_RUNTIME))

#if !DART_SNAPSHOT_STATIC_LINK

static std::unique_ptr<const fml::Mapping> GetFileMapping(
    const std::string& path,
    bool executable) {
  if (executable) {
    return fml::FileMapping::CreateReadExecute(path);
  } else {
    return fml::FileMapping::CreateReadOnly(path);
  }
}

// The first party embedders don't yet use the stable embedder API and depend on
// the engine figuring out the locations of the various heap and instructions
// buffers. Consequently, the engine had baked in opinions about where these
// buffers would reside and how they would be packaged (examples, in an external
// dylib, in the same dylib, at a path, at a path relative to and FD, etc..). As
// the needs of the platforms changed, the lack of an API meant that the engine
// had to be patched to look for new fields in the settings object. This grew
// untenable and with the addition of the new Fuchsia embedder and the generic C
// embedder API, embedders could specify the mapping directly. Once everyone
// moves to the embedder API, this method can effectively be reduced to just
// invoking the embedder_mapping_callback directly.
static std::shared_ptr<const fml::Mapping> SearchMapping(
    MappingCallback embedder_mapping_callback,
    const std::string& file_path,
    const std::vector<std::string>& native_library_path,
    const char* native_library_symbol_name,
    bool is_executable) {
  // Ask the embedder. There is no fallback as we expect the embedders (via
  // their embedding APIs) to just specify the mappings directly.
  if (embedder_mapping_callback) {
    return embedder_mapping_callback();
  }

  // Attempt to open file at path specified.
  if (file_path.size() > 0) {
    if (auto file_mapping = GetFileMapping(file_path, is_executable)) {
      return file_mapping;
    }
  }

  // Look in application specified native library if specified.
  for (const std::string& path : native_library_path) {
    auto native_library = fml::NativeLibrary::Create(path.c_str());
    auto symbol_mapping = std::make_unique<const fml::SymbolMapping>(
        native_library, native_library_symbol_name);
    if (symbol_mapping->GetMapping() != nullptr) {
      return symbol_mapping;
    }
  }

  // Look inside the currently loaded process.
  {
    auto loaded_process = fml::NativeLibrary::CreateForCurrentProcess();
    auto symbol_mapping = std::make_unique<const fml::SymbolMapping>(
        loaded_process, native_library_symbol_name);
    if (symbol_mapping->GetMapping() != nullptr) {
      return symbol_mapping;
    }
  }

  return nullptr;
}

#endif  // !DART_SNAPSHOT_STATIC_LINK

static std::shared_ptr<const fml::Mapping> ResolveVMData(
    const Settings& settings) {
#if DART_SNAPSHOT_STATIC_LINK
  return std::make_unique<fml::NonOwnedMapping>(kDartVmSnapshotData, 0);
#else   // DART_SNAPSHOT_STATIC_LINK
  return SearchMapping(
      settings.vm_snapshot_data,          // embedder_mapping_callback
      settings.vm_snapshot_data_path,     // file_path
      settings.application_library_path,  // native_library_path
      DartSnapshot::kVMDataSymbol,        // native_library_symbol_name
      false                               // is_executable
  );
#endif  // DART_SNAPSHOT_STATIC_LINK
}

static std::shared_ptr<const fml::Mapping> ResolveVMInstructions(
    const Settings& settings) {
#if DART_SNAPSHOT_STATIC_LINK
  return std::make_unique<fml::NonOwnedMapping>(kDartVmSnapshotInstructions, 0);
#else   // DART_SNAPSHOT_STATIC_LINK
  return SearchMapping(
      settings.vm_snapshot_instr,           // embedder_mapping_callback
      settings.vm_snapshot_instr_path,      // file_path
      settings.application_library_path,    // native_library_path
      DartSnapshot::kVMInstructionsSymbol,  // native_library_symbol_name
      true                                  // is_executable
  );
#endif  // DART_SNAPSHOT_STATIC_LINK
}

static std::shared_ptr<const fml::Mapping> ResolveIsolateData(
    const Settings& settings) {
#if DART_SNAPSHOT_STATIC_LINK
  return std::make_unique<fml::NonOwnedMapping>(kDartIsolateSnapshotData, 0);
#else   // DART_SNAPSHOT_STATIC_LINK
  return SearchMapping(
      settings.isolate_snapshot_data,       // embedder_mapping_callback
      settings.isolate_snapshot_data_path,  // file_path
      settings.application_library_path,    // native_library_path
      DartSnapshot::kIsolateDataSymbol,     // native_library_symbol_name
      false                                 // is_executable
  );
#endif  // DART_SNAPSHOT_STATIC_LINK
}

static std::shared_ptr<const fml::Mapping> ResolveIsolateInstructions(
    const Settings& settings) {
#if DART_SNAPSHOT_STATIC_LINK
  return std::make_unique<fml::NonOwnedMapping>(
      kDartIsolateSnapshotInstructions, 0);
#else   // DART_SNAPSHOT_STATIC_LINK
  return SearchMapping(
      settings.isolate_snapshot_instr,           // embedder_mapping_callback
      settings.isolate_snapshot_instr_path,      // file_path
      settings.application_library_path,         // native_library_path
      DartSnapshot::kIsolateInstructionsSymbol,  // native_library_symbol_name
      true                                       // is_executable
  );
#endif  // DART_SNAPSHOT_STATIC_LINK
}

fml::RefPtr<DartSnapshot> DartSnapshot::VMSnapshotFromSettings(
    const Settings& settings) {
  TRACE_EVENT0("flutter", "DartSnapshot::VMSnapshotFromSettings");
  auto snapshot =
      fml::MakeRefCounted<DartSnapshot>(ResolveVMData(settings),         //
                                        ResolveVMInstructions(settings)  //
      );
  if (snapshot->IsValid()) {
    return snapshot;
  }
  return nullptr;
}

fml::RefPtr<DartSnapshot> DartSnapshot::IsolateSnapshotFromSettings(
    const Settings& settings) {
  TRACE_EVENT0("flutter", "DartSnapshot::IsolateSnapshotFromSettings");
  auto snapshot =
      fml::MakeRefCounted<DartSnapshot>(ResolveIsolateData(settings),         //
                                        ResolveIsolateInstructions(settings)  //
      );
  if (snapshot->IsValid()) {
    return snapshot;
  }
  return nullptr;
}

DartSnapshot::DartSnapshot(std::shared_ptr<const fml::Mapping> data,
                           std::shared_ptr<const fml::Mapping> instructions)
    : data_(std::move(data)), instructions_(std::move(instructions)) {}

DartSnapshot::~DartSnapshot() = default;

bool DartSnapshot::IsValid() const {
  return static_cast<bool>(data_);
}

bool DartSnapshot::IsValidForAOT() const {
  return data_ && instructions_;
}

const uint8_t* DartSnapshot::GetDataMapping() const {
  return data_ ? data_->GetMapping() : nullptr;
}

const uint8_t* DartSnapshot::GetInstructionsMapping() const {
  return instructions_ ? instructions_->GetMapping() : nullptr;
}

}  // namespace flutter