// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "gin/v8_initializer.h"

#include <stddef.h>
#include <stdint.h>

#include <cstdint>
#include <memory>
#include <optional>
#include <string>
#include <string_view>
#include <utility>
#include <vector>

#include "base/bits.h"
#include "base/check.h"
#include "base/check_op.h"
#include "base/containers/span.h"
#include "base/debug/alias.h"
#include "base/debug/crash_logging.h"
#include "base/feature_list.h"
#include "base/feature_visitor.h"
#include "base/files/file.h"
#include "base/files/file_path.h"
#include "base/files/memory_mapped_file.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
#include "base/metrics/histogram_functions.h"
#include "base/metrics/histogram_macros.h"
#include "base/notreached.h"
#include "base/path_service.h"
#include "base/rand_util.h"
#include "base/strings/span_printf.h"
#include "base/strings/string_split.h"
#include "base/system/sys_info.h"
#include "base/threading/platform_thread.h"
#include "base/time/time.h"
#include "build/build_config.h"
#include "gin/array_buffer.h"
#include "gin/gin_features.h"
#include "partition_alloc/page_allocator.h"
#include "partition_alloc/partition_address_space.h"
#include "tools/v8_context_snapshot/buildflags.h"
#include "v8/include/v8-initialization.h"
#include "v8/include/v8-snapshot.h"

#if defined(V8_USE_EXTERNAL_STARTUP_DATA)
#if BUILDFLAG(IS_ANDROID)
#include "base/android/apk_assets.h"
#elif BUILDFLAG(IS_MAC)
#include "base/apple/foundation_util.h"
#endif
#endif  // V8_USE_EXTERNAL_STARTUP_DATA

namespace gin {

namespace {

// This global is never freed nor closed.
base::MemoryMappedFile* g_mapped_snapshot = nullptr;

#if defined(V8_USE_EXTERNAL_STARTUP_DATA)
std::optional<gin::V8SnapshotFileType> g_snapshot_file_type;
#endif

bool GenerateEntropy(unsigned char* buffer, size_t amount) {
  base::RandBytes(
      // SAFETY: This depends on v8 providing a valid pointer/size pair.
      //
      // TODO(crbug.com/338574383): The signature is fixed as it's a callback
      // from v8, but maybe v8 can use a span.
      UNSAFE_BUFFERS(base::span(buffer, amount)));
  return true;
}

void GetMappedFileData(base::MemoryMappedFile* mapped_file,
                       v8::StartupData* data) {
  if (mapped_file) {
    data->data = reinterpret_cast<const char*>(mapped_file->data());
    data->raw_size = static_cast<int>(mapped_file->length());
  } else {
    data->data = nullptr;
    data->raw_size = 0;
  }
}

#if defined(V8_USE_EXTERNAL_STARTUP_DATA)

#if BUILDFLAG(IS_ANDROID)
const char kV8ContextSnapshotFileName64[] = "v8_context_snapshot_64.bin";
const char kV8ContextSnapshotFileName32[] = "v8_context_snapshot_32.bin";
const char kSnapshotFileName64[] = "snapshot_blob_64.bin";
const char kSnapshotFileName32[] = "snapshot_blob_32.bin";

#if defined(__LP64__)
#define kV8ContextSnapshotFileName kV8ContextSnapshotFileName64
#define kSnapshotFileName kSnapshotFileName64
#else
#define kV8ContextSnapshotFileName kV8ContextSnapshotFileName32
#define kSnapshotFileName kSnapshotFileName32
#endif

#else  // BUILDFLAG(IS_ANDROID)
#if BUILDFLAG(USE_V8_CONTEXT_SNAPSHOT)
const char kV8ContextSnapshotFileName[] =
    BUILDFLAG(V8_CONTEXT_SNAPSHOT_FILENAME);
#endif
const char kSnapshotFileName[] = "snapshot_blob.bin";
#endif  // BUILDFLAG(IS_ANDROID)

const char* GetSnapshotFileName(const V8SnapshotFileType file_type) {
  switch (file_type) {
    case V8SnapshotFileType::kDefault:
      return kSnapshotFileName;
    case V8SnapshotFileType::kWithAdditionalContext:
#if BUILDFLAG(USE_V8_CONTEXT_SNAPSHOT)
      return kV8ContextSnapshotFileName;
#else
      NOTREACHED();
#endif
  }
  NOTREACHED();
}

void GetV8FilePath(const char* file_name, base::FilePath* path_out) {
#if BUILDFLAG(IS_ANDROID)
  // This is the path within the .apk.
  *path_out =
      base::FilePath(FILE_PATH_LITERAL("assets")).AppendASCII(file_name);
#elif BUILDFLAG(IS_MAC)
  *path_out = base::apple::PathForFrameworkBundleResource(file_name);
#else
  base::FilePath data_path;
  bool r = base::PathService::Get(base::DIR_ASSETS, &data_path);
  DCHECK(r);
  *path_out = data_path.AppendASCII(file_name);
#endif
}

bool MapV8File(base::File file,
               base::MemoryMappedFile::Region region,
               base::MemoryMappedFile** mmapped_file_out) {
  DCHECK(*mmapped_file_out == NULL);
  std::unique_ptr<base::MemoryMappedFile> mmapped_file(
      new base::MemoryMappedFile());
  if (mmapped_file->Initialize(std::move(file), region)) {
    *mmapped_file_out = mmapped_file.release();
    return true;
  }
  return false;
}

base::File OpenV8File(const char* file_name,
                      base::MemoryMappedFile::Region* region_out) {
  // Re-try logic here is motivated by http://crbug.com/479537
  // for A/V on Windows (https://support.microsoft.com/en-us/kb/316609).

  base::FilePath path;
  GetV8FilePath(file_name, &path);

#if BUILDFLAG(IS_ANDROID)
  base::File file(base::android::OpenApkAsset(path.value(), region_out));
#else
  // Re-try logic here is motivated by http://crbug.com/479537
  // for A/V on Windows (https://support.microsoft.com/en-us/kb/316609).
  const int kMaxOpenAttempts = 5;
  const int kOpenRetryDelayMillis = 250;

  int flags = base::File::FLAG_OPEN | base::File::FLAG_READ;
  base::File file;
  for (int attempt = 0; attempt < kMaxOpenAttempts; attempt++) {
    file.Initialize(path, flags);
    if (file.IsValid()) {
      *region_out = base::MemoryMappedFile::Region::kWholeFile;
      break;
    } else if (file.error_details() != base::File::FILE_ERROR_IN_USE) {
      break;
    } else if (kMaxOpenAttempts - 1 != attempt) {
      base::PlatformThread::Sleep(base::Milliseconds(kOpenRetryDelayMillis));
    }
  }
#endif  // BUILDFLAG(IS_ANDROID)
  return file;
}

#endif  // defined(V8_USE_EXTERNAL_STARTUP_DATA)

template <int LENGTH>
void SetV8Flags(const char (&flag)[LENGTH]) {
  v8::V8::SetFlagsFromString(flag, LENGTH - 1);
}

void SetV8FlagsFormatted(const char* format, ...) {
  char buffer[128];
  va_list args;
  va_start(args, format);
  int length = base::VSpanPrintf(buffer, format, args);
  if (length <= 0 || sizeof(buffer) <= static_cast<unsigned>(length)) {
    PLOG(ERROR) << "Invalid formatted V8 flag: " << format;
    return;
  }
  v8::V8::SetFlagsFromString(buffer, length);
}

template <size_t N, size_t M>
void SetV8FlagsIfOverridden(const base::Feature& feature,
                            const char (&enabling_flag)[N],
                            const char (&disabling_flag)[M]) {
  auto overridden_state = base::FeatureList::GetStateIfOverridden(feature);
  if (!overridden_state.has_value()) {
    return;
  }
  if (overridden_state.value()) {
    SetV8Flags(enabling_flag);
  } else {
    SetV8Flags(disabling_flag);
  }
}

constexpr std::string_view kV8FlagFeaturePrefix = "V8Flag_";

}  // namespace

class V8FeatureVisitor : public base::FeatureVisitor {
 public:
  void Visit(const std::string& feature_name,
             base::FeatureList::OverrideState override_state,
             const std::map<std::string, std::string>& params,
             const std::string& trial_name,
             const std::string& group_name) override {
    std::string_view feature_name_view(feature_name);

    // VisitFeaturesAndParams is called with kV8FlagFeaturePrefix as a filter
    // prefix, so we expect all feature names to start with "V8Flag_". Strip
    // this prefix off to get the corresponding V8 flag name.
    DCHECK(feature_name_view.starts_with(kV8FlagFeaturePrefix));
    std::string flag_name(
        feature_name_view.substr(kV8FlagFeaturePrefix.size()));

    switch (override_state) {
      case base::FeatureList::OverrideState::OVERRIDE_USE_DEFAULT:
        return;

      case base::FeatureList::OverrideState::OVERRIDE_DISABLE_FEATURE:
        SetV8FlagsFormatted("--no-%s", flag_name.c_str());
        // Do not set parameters for disabled features.
        break;

      case base::FeatureList::OverrideState::OVERRIDE_ENABLE_FEATURE:
        SetV8FlagsFormatted("--%s", flag_name.c_str());
        for (const auto& [param_name, param_value] : params) {
          SetV8FlagsFormatted("--%s=%s", param_name.c_str(),
                              param_value.c_str());
        }
        break;
    }
  }
};

namespace {

// Sets mandatory V8 flags.
void SetFlags(IsolateHolder::ScriptMode mode,
              const std::string& js_command_line_flags) {

  if (IsolateHolder::kStrictMode == mode) {
    SetV8Flags("--use_strict");
  }

  // Apply any --js-flags explicitly specified by the caller.
  if (!js_command_line_flags.empty()) {
    std::vector<std::string_view> flag_list = base::SplitStringPiece(
        js_command_line_flags, ",", base::TRIM_WHITESPACE,
        base::SPLIT_WANT_NONEMPTY);
    for (const auto& flag : flag_list) {
      v8::V8::SetFlagsFromString(std::string(flag).c_str(), flag.size());
    }
  }
}

// Sets feature flags that are default to enabled.
//
// This function must be called *before* SetFeatureFlags is called, so that
// default-enabled flags may be overridden and disabled.
//
// Usually V8 is the source of truth for the default state of feature flags.
// However, some features must be shipped from the blink side because they add
// new globals, which requires updating web tests that cannot be skipped (to
// safeguard against accidentally breaking the web).
void SetDefaultEnabledFeatureFlags() {
  SetV8Flags("--js-float16array");
  SetV8Flags("--js-explicit-resource-management");
  SetV8Flags("--js-regexp-escape");
}

// Sets feature controlled V8 flags.
void SetFeatureFlags() {
  // Chromium features prefixed with "V8Flag_" are forwarded to V8 as V8 flags,
  // with the "V8Flag_" prefix stripped off. For example, an enabled feature
  // "V8Flag_foo_bar" will be passed to V8 as the flag `--foo_bar`. Similarly,
  // if that feature is explicitly disabled, it will be passed to V8 as
  // `--no-foo_bar`. No Chromium-side declaration of a V8Flag_foo_bar feature
  // is necessary, the matching is done on strings.
  //
  // Parameters attached to features will also be passed through, with the same
  // name as the parameter and the value passed by string, to be decoded by V8's
  // flag parsing.
  //
  // Thus, running Chromium with:
  //
  //   --enable-features=V8Flag_foo,V8Flag_bar:bar_param/20
  //   --disable-features=V8Flag_baz
  //
  // will be converted, on V8 initialization, to V8 flags:
  //
  //   --foo --bar --bar_param=20 --no-baz
  V8FeatureVisitor feature_visitor;
  base::FeatureList::VisitFeaturesAndParams(feature_visitor,
                                            kV8FlagFeaturePrefix);

  // Otherwise, feature flags explicitly defined in Chromium are translated
  // to V8 flags as follows. We ignore feature flag default values, instead
  // using the corresponding V8 flags default values if there is no explicit
  // feature override.
  SetV8FlagsIfOverridden(features::kV8CompactCodeSpaceWithStack,
                         "--compact-code-space-with-stack",
                         "--no-compact-code-space-with-stack");
  SetV8FlagsIfOverridden(features::kV8CompactWithStack, "--compact-with-stack",
                         "--no-compact-with-stack");
  SetV8FlagsIfOverridden(features::kV8OptimizeJavascript, "--opt", "--no-opt");
  SetV8FlagsIfOverridden(features::kV8FlushBytecode, "--flush-bytecode",
                         "--no-flush-bytecode");
  SetV8FlagsIfOverridden(features::kV8FlushBaselineCode,
                         "--flush-baseline-code", "--no-flush-baseline-code");
  SetV8FlagsIfOverridden(features::kV8FlushCodeBasedOnTabVisibility,
                         "--flush-code-based-on-tab-visibility",
                         "--no-flush-code-based-on-tab-visibility");
  SetV8FlagsIfOverridden(features::kV8FlushCodeBasedOnTime,
                         "--flush-code-based-on-time",
                         "--no-flush-code-based-on-time");
  SetV8FlagsIfOverridden(features::kV8OffThreadFinalization,
                         "--finalize-streaming-on-background",
                         "--no-finalize-streaming-on-background");
  if (base::FeatureList::IsEnabled(features::kV8DelayMemoryReducer)) {
    SetV8FlagsFormatted(
        "--gc-memory-reducer-start-delay-ms=%i",
        static_cast<int>(
            features::kV8MemoryReducerStartDelay.Get().InMilliseconds()));
  }
  SetV8FlagsIfOverridden(features::kV8ConcurrentMarkingHighPriorityThreads,
                         "--concurrent-marking-high-priority-threads",
                         "--no-concurrent-marking-high-priority-threads");
  SetV8FlagsIfOverridden(features::kV8LazyFeedbackAllocation,
                         "--lazy-feedback-allocation",
                         "--no-lazy-feedback-allocation");
  SetV8FlagsIfOverridden(features::kV8PerContextMarkingWorklist,
                         "--stress-per-context-marking-worklist",
                         "--no-stress-per-context-marking-worklist");
  SetV8FlagsIfOverridden(features::kV8FlushEmbeddedBlobICache,
                         "--experimental-flush-embedded-blob-icache",
                         "--no-experimental-flush-embedded-blob-icache");
  SetV8FlagsIfOverridden(features::kV8ReduceConcurrentMarkingTasks,
                         "--gc-experiment-reduce-concurrent-marking-tasks",
                         "--no-gc-experiment-reduce-concurrent-marking-tasks");
  SetV8FlagsIfOverridden(features::kV8NoReclaimUnmodifiedWrappers,
                         "--no-reclaim-unmodified-wrappers",
                         "--reclaim-unmodified-wrappers");
  SetV8FlagsIfOverridden(
      features::kV8ExperimentalRegexpEngine,
      "--enable-experimental-regexp-engine-on-excessive-backtracks",
      "--no-enable-experimental-regexp-engine-on-excessive-backtracks");
  SetV8FlagsIfOverridden(features::kV8ExternalMemoryAccountedInGlobalLimit,
                         "--external-memory-accounted-in-global-limit",
                         "--no-external-memory-accounted-in-global-limit");
  SetV8FlagsIfOverridden(features::kV8TurboFastApiCalls,
                         "--turbo-fast-api-calls", "--no-turbo-fast-api-calls");
  SetV8FlagsIfOverridden(features::kV8MegaDomIC, "--mega-dom-ic",
                         "--no-mega-dom-ic");
  SetV8FlagsIfOverridden(features::kV8Maglev, "--maglev", "--no-maglev");
  SetV8FlagsIfOverridden(features::kV8ConcurrentMaglevHighPriorityThreads,
                         "--concurrent-maglev-high-priority-threads",
                         "--no-concurrent-maglev-high-priority-threads");
  if (base::FeatureList::IsEnabled(features::kV8MemoryReducer)) {
    SetV8FlagsFormatted("--memory-reducer-gc-count=%i",
                        features::kV8MemoryReducerGCCount.Get());
  }
  if (base::FeatureList::IsEnabled(features::kV8PreconfigureOldGen)) {
    SetV8FlagsFormatted("--preconfigured-old-space-size=%i",
                        features::kV8PreconfigureOldGenSize.Get());
  }
  SetV8FlagsIfOverridden(features::kV8IncrementalMarkingStartUserVisible,
                         "--incremental-marking-start-user-visible",
                         "--no-incremental-marking-start-user-visible");
  SetV8FlagsIfOverridden(features::kV8IdleGcOnContextDisposal,
                         "--idle-gc-on-context-disposal",
                         "--no-idle-gc-on-context-disposal");
  SetV8FlagsIfOverridden(features::kV8MinorMS, "--minor-ms", "--no-minor-ms");
  if (base::FeatureList::IsEnabled(features::kV8ScavengerHigherCapacity)) {
    SetV8FlagsFormatted("--scavenger-max-new-space-capacity-mb=%i",
                        features::kV8ScavengerMaxCapacity.Get());
  }
  SetV8FlagsIfOverridden(features::kV8Sparkplug, "--sparkplug",
                         "--no-sparkplug");
  SetV8FlagsIfOverridden(features::kV8Turbofan, "--turbofan", "--no-turbofan");
  SetV8FlagsIfOverridden(features::kV8Turboshaft, "--turboshaft",
                         "--no-turboshaft");
  SetV8FlagsIfOverridden(features::kV8TurboshaftInstructionSelection,
                         "--turboshaft-instruction-selection",
                         "--no-turboshaft-instruction-selection");
  SetV8FlagsIfOverridden(features::kV8ConcurrentSparkplug,
                         "--concurrent-sparkplug", "--no-concurrent-sparkplug");
  SetV8FlagsIfOverridden(features::kV8SparkplugNeedsShortBuiltinCalls,
                         "--sparkplug-needs-short-builtins",
                         "--no-sparkplug-needs-short-builtins");
  SetV8FlagsIfOverridden(features::kV8BaselineBatchCompilation,
                         "--baseline-batch-compilation",
                         "--no-baseline-batch-compilation");
  SetV8FlagsIfOverridden(features::kV8ShortBuiltinCalls,
                         "--short-builtin-calls", "--no-short-builtin-calls");
  SetV8FlagsIfOverridden(features::kV8CodeMemoryWriteProtection,
                         "--write-protect-code-memory",
                         "--no-write-protect-code-memory");
  SetV8FlagsIfOverridden(features::kV8SlowHistograms, "--slow-histograms",
                         "--no-slow-histograms");
  SetV8FlagsIfOverridden(features::kV8SideStepTransitions,
                         "--clone_object_sidestep_transitions",
                         "--noclone_object_sidestep_transitions");
  SetV8FlagsIfOverridden(features::kV8SingleThreadedGCInBackground,
                         "--single-threaded-gc-in-background",
                         "--no-single-threaded-gc-in-background");
  SetV8FlagsIfOverridden(features::kV8SingleThreadedGCInBackgroundParallelPause,
                         "--parallel-pause-for-gc-in-background",
                         "--no-parallel-pause-for-gc-in-background");
  SetV8FlagsIfOverridden(
      features::kV8SingleThreadedGCInBackgroundNoIncrementalMarking,
      "--no-incremental-marking-for-gc-in-background",
      "--incremental-marking-for-gc-in-background");
  SetV8FlagsIfOverridden(features::kV8DecommitPooledPages,
                         "--decommit-pooled-pages",
                         "--no-decommit-pooled-pages");

  if (base::FeatureList::IsEnabled(features::kV8ConcurrentSparkplug)) {
    if (int max_threads = features::kV8ConcurrentSparkplugMaxThreads.Get()) {
      SetV8FlagsFormatted("--concurrent-sparkplug-max-threads=%i", max_threads);
    }
    SetV8FlagsIfOverridden(features::kV8ConcurrentSparkplugHighPriorityThreads,
                           "--concurrent-sparkplug-high-priority-threads",
                           "--no-concurrent-sparkplug-high-priority-threads");
  }

  if (base::FeatureList::IsEnabled(features::kV8FlushBytecode)) {
    if (int old_age = features::kV8FlushBytecodeOldAge.Get()) {
      SetV8FlagsFormatted("--bytecode-old-age=%i", old_age);
    }
  }

  if (base::FeatureList::IsEnabled(features::kV8FlushCodeBasedOnTime)) {
    if (int old_time = features::kV8FlushCodeOldTime.Get()) {
      SetV8FlagsFormatted("--bytecode-old-time=%i", old_time);
    }
  }

  if (base::FeatureList::IsEnabled(features::kV8EfficiencyModeTiering)) {
    int delay = features::kV8EfficiencyModeTieringDelayTurbofan.Get();
    if (delay == 0) {
      SetV8FlagsFormatted(
          "--efficiency-mode-for-tiering-heuristics "
          "--efficiency-mode-disable-turbofan");
    } else {
      SetV8FlagsFormatted(
          "--efficiency-mode-for-tiering-heuristics "
          "--noefficiency-mode-disable-turbofan "
          "--efficiency-mode-delay-turbofan=%i",
          delay);
    }
  } else {
    SetV8FlagsFormatted("--no-efficiency-mode-for-tiering-heuristics");
  }

  // Make sure aliases of kV8SlowHistograms only enable the feature to
  // avoid contradicting settings between multiple finch experiments.
  bool any_slow_histograms_alias =
      base::FeatureList::IsEnabled(
          features::kV8SlowHistogramsCodeMemoryWriteProtection) ||
      base::FeatureList::IsEnabled(
          features::kV8SlowHistogramsIntelJCCErratumMitigation) ||
      base::FeatureList::IsEnabled(features::kV8SlowHistogramsSparkplug) ||
      base::FeatureList::IsEnabled(
          features::kV8SlowHistogramsSparkplugAndroid) ||
      base::FeatureList::IsEnabled(features::kV8SlowHistogramsNoTurbofan);
  if (any_slow_histograms_alias) {
    SetV8Flags("--slow-histograms");
  } else {
    SetV8FlagsIfOverridden(features::kV8SlowHistograms, "--slow-histograms",
                           "--no-slow-histograms");
  }

  SetV8FlagsIfOverridden(features::kV8IgnitionElideRedundantTdzChecks,
                         "--ignition-elide-redundant-tdz-checks",
                         "--no-ignition-elide-redundant-tdz-checks");

  SetV8FlagsIfOverridden(features::kV8IntelJCCErratumMitigation,
                         "--intel-jcc-erratum-mitigation",
                         "--no-intel-jcc-erratum-mitigation");

  SetV8FlagsIfOverridden(features::kV8UseLibmTrigFunctions,
                         "--use-libm-trig-functions",
                         "--no-use-libm-trig-functions");

  SetV8FlagsIfOverridden(features::kV8UseOriginalMessageForStackTrace,
                         "--use-original-message-for-stack-trace",
                         "--no-use-original-message-for-stack-trace");

  // JavaScript language features.
  SetV8FlagsIfOverridden(features::kJavaScriptRegExpModifiers,
                         "--js-regexp-modifiers", "--no-js-regexp-modifiers");
  SetV8FlagsIfOverridden(features::kJavaScriptImportAttributes,
                         "--harmony-import-attributes",
                         "--no-harmony-import-attributes");
  SetV8FlagsIfOverridden(features::kJavaScriptRegExpDuplicateNamedGroups,
                         "--js-regexp-duplicate-named-groups",
                         "--no-js-duplicate-named-groups");
  SetV8FlagsIfOverridden(features::kJavaScriptPromiseTry, "--js-promise-try",
                         "--no-js-promise-try");

  // WebAssembly features.

  SetV8FlagsIfOverridden(features::kWebAssemblyDeopt, "--wasm-deopt",
                         "--no-wasm-deopt");
  SetV8FlagsIfOverridden(features::kWebAssemblyInliningCallIndirect,
                         "--wasm-inlining-call-indirect",
                         "--no-wasm-inlining-call-indirect");
}

}  // namespace

// static
void V8Initializer::Initialize(IsolateHolder::ScriptMode mode,
                               const std::string& js_command_line_flags,
                               bool disallow_v8_feature_flag_overrides,
                               v8::OOMErrorCallback oom_error_callback) {
  static bool v8_is_initialized = false;
  if (v8_is_initialized)
    return;

  // Flags need to be set before InitializePlatform as they are used for system
  // instrumentation initialization, see https://crbug.com/v8/11043. --js-flags
  // and other mandatory flags in `SetFlags` must be ordered after feature flag
  // overrides.
  SetDefaultEnabledFeatureFlags();
  if (!disallow_v8_feature_flag_overrides) {
    SetFeatureFlags();
  }
  SetFlags(mode, js_command_line_flags);

  v8::V8::InitializePlatform(V8Platform::Get());

  // Set this as early as possible in order to ensure OOM errors are reported
  // correctly.
  v8::V8::SetFatalMemoryErrorCallback(oom_error_callback);

  // Set this early on as some initialization steps, such as the initialization
  // of the virtual memory cage, already use V8's random number generator.
  v8::V8::SetEntropySource(&GenerateEntropy);

#if defined(V8_USE_EXTERNAL_STARTUP_DATA)
  if (g_mapped_snapshot) {
    v8::StartupData snapshot;
    GetMappedFileData(g_mapped_snapshot, &snapshot);
    v8::V8::SetSnapshotDataBlob(&snapshot);
  }
#endif  // V8_USE_EXTERNAL_STARTUP_DATA

  v8::V8::Initialize();

  v8_is_initialized = true;

#if defined(V8_ENABLE_SANDBOX)
  // Record some sandbox statistics into UMA.
  // The main reason for capturing these histograms here instead of having V8
  // do it is that there are no Isolates available yet, which are required
  // for recording histograms in V8.

  // Record the mode of the sandbox.
  // These values are persisted to logs. Entries should not be renumbered and
  // numeric values should never be reused. This should match enum
  // V8SandboxMode in tools/metrics/histograms/enums.xml.
  enum class V8SandboxMode {
    kSecure = 0,
    kInsecure = 1,
    kMaxValue = kInsecure,
  };
  base::UmaHistogramEnumeration("V8.SandboxMode",
                                v8::V8::IsSandboxConfiguredSecurely()
                                    ? V8SandboxMode::kSecure
                                    : V8SandboxMode::kInsecure);

  // Record the size of the address space reservation backing the sandbox.
  // The size will always be one of a handful of values, so use a sparse
  // histogram to capture it.
  size_t size = v8::V8::GetSandboxReservationSizeInBytes();
  DCHECK_GT(size, 0U);
  size_t sizeInGB = size >> 30;
  DCHECK_EQ(sizeInGB << 30, size);
  base::UmaHistogramSparse("V8.SandboxReservationSizeGB", sizeInGB);

  // When the sandbox is enabled, ArrayBuffers must be allocated inside of
  // it. To achieve that, PA's ConfigurablePool is created inside the sandbox
  // and Blink then creates the ArrayBuffer partition in that Pool.
  v8::VirtualAddressSpace* sandbox_address_space =
      v8::V8::GetSandboxAddressSpace();
  const size_t max_pool_size = partition_alloc::internal::
      PartitionAddressSpace::ConfigurablePoolMaxSize();
  const size_t min_pool_size = partition_alloc::internal::
      PartitionAddressSpace::ConfigurablePoolMinSize();
  size_t pool_size = max_pool_size;
  // Try to reserve the maximum size of the pool at first, then keep halving
  // the size on failure until it succeeds.
  uintptr_t pool_base = 0;
  while (!pool_base && pool_size >= min_pool_size) {
    pool_base = sandbox_address_space->AllocatePages(
        0, pool_size, pool_size, v8::PagePermissions::kNoAccess);
    if (!pool_base) {
      pool_size /= 2;
    }
  }
  // The V8 sandbox is guaranteed to be large enough to host the pool.
  CHECK(pool_base);
  partition_alloc::internal::PartitionAddressSpace::InitConfigurablePool(
      pool_base, pool_size);
  // TODO(saelo) maybe record the size of the Pool into UMA.
#endif  // V8_ENABLE_SANDBOX

  // Initialize the partition used by gin::ArrayBufferAllocator instances. This
  // needs to happen now, after the V8 sandbox has been initialized, so that
  // the partition is placed inside the configurable pool initialized above.
  ArrayBufferAllocator::InitializePartition();
}

// static
void V8Initializer::GetV8ExternalSnapshotData(v8::StartupData* snapshot) {
  GetMappedFileData(g_mapped_snapshot, snapshot);
}

// static
void V8Initializer::GetV8ExternalSnapshotData(const char** snapshot_data_out,
                                              int* snapshot_size_out) {
  v8::StartupData snapshot;
  GetV8ExternalSnapshotData(&snapshot);
  *snapshot_data_out = snapshot.data;
  *snapshot_size_out = snapshot.raw_size;
}

#if defined(V8_USE_EXTERNAL_STARTUP_DATA)

// static
void V8Initializer::LoadV8Snapshot(V8SnapshotFileType snapshot_file_type) {
  if (g_mapped_snapshot) {
    // TODO(crbug.com/40558459): Confirm not loading different type of snapshot
    // files in a process.
    return;
  }

  base::MemoryMappedFile::Region file_region;
  base::File file =
      OpenV8File(GetSnapshotFileName(snapshot_file_type), &file_region);
  LoadV8SnapshotFromFile(std::move(file), &file_region, snapshot_file_type);
}

// static
void V8Initializer::LoadV8SnapshotFromFile(
    base::File snapshot_file,
    base::MemoryMappedFile::Region* snapshot_file_region,
    V8SnapshotFileType snapshot_file_type) {
  if (g_mapped_snapshot)
    return;

  if (!snapshot_file.IsValid()) {
    LOG(FATAL) << "Error loading V8 startup snapshot file";
  }

  g_snapshot_file_type = snapshot_file_type;
  base::MemoryMappedFile::Region region =
      base::MemoryMappedFile::Region::kWholeFile;
  if (snapshot_file_region) {
    region = *snapshot_file_region;
  }

  if (!MapV8File(std::move(snapshot_file), region, &g_mapped_snapshot)) {
    LOG(FATAL) << "Error mapping V8 startup snapshot file";
  }
}

#if BUILDFLAG(IS_ANDROID)
// static
base::FilePath V8Initializer::GetSnapshotFilePath(
    bool abi_32_bit,
    V8SnapshotFileType snapshot_file_type) {
  base::FilePath path;
  const char* filename = nullptr;
  switch (snapshot_file_type) {
    case V8SnapshotFileType::kDefault:
      filename = abi_32_bit ? kSnapshotFileName32 : kSnapshotFileName64;
      break;
    case V8SnapshotFileType::kWithAdditionalContext:
      filename = abi_32_bit ? kV8ContextSnapshotFileName32
                            : kV8ContextSnapshotFileName64;
      break;
  }
  CHECK(filename);

  GetV8FilePath(filename, &path);
  return path;
}
#endif  // BUILDFLAG(IS_ANDROID)

V8SnapshotFileType GetLoadedSnapshotFileType() {
  DCHECK(g_snapshot_file_type.has_value());
  return *g_snapshot_file_type;
}

#endif  // defined(V8_USE_EXTERNAL_STARTUP_DATA)

}  // namespace gin