feat: allow custom v8 snapshots to be used in the main process and the default snapshot in the renderer process (#35695)

* feat: allow custom v8 snapshots to be used in the main process and the default snapshot in the renderer process (#35266)

* Updates to allow for using a custom v8 snapshot file name

* Allow using a custom v8 snapshot file name

* Fix up patch due to merge

* Use fuse to set up custom v8 snapshot file in browser process

* Refactor to use delegate instead of command line parameter

* Refactoring

* Update due to merge

* PR comments

* Rename patch

* Rename patch

* chore: update patches

Co-authored-by: Ryan Manuel <[email protected]>
Co-authored-by: PatchUp <73610968+patchup[bot]@users.noreply.github.com>

build/fuses/fuses.json5

@@ -7,5 +7,6 @@
   "node_options": "1",
   "node_cli_inspect": "1",
   "embedded_asar_integrity_validation": "0",
-  "only_load_app_from_asar": "0"
+  "only_load_app_from_asar": "0",
+  "load_browser_process_specific_v8_snapshot": "0"
 }

docs/tutorial/fuses.md

@@ -54,6 +54,13 @@ For more information on how to use asar integrity validation please read the [As
 
 The onlyLoadAppFromAsar fuse changes the search system that Electron uses to locate your app code.  By default Electron will search in the following order `app.asar` -> `app` -> `default_app.asar`.  When this fuse is enabled the search order becomes a single entry `app.asar` thus ensuring that when combined with the `embeddedAsarIntegrityValidation` fuse it is impossible to load non-validated code.
 
+### `loadBrowserProcessSpecificV8Snapshot`
+
+**Default:** Disabled
+**@electron/fuses:** `FuseV1Options.LoadBrowserProcessSpecificV8Snapshot`
+
+The loadBrowserProcessSpecificV8Snapshot fuse changes which V8 snapshot file is used for the browser process.  By default Electron's processes will all use the same V8 snapshot file.  When this fuse is enabled the browser process uses the file called `browser_v8_context_snapshot.bin` for its V8 snapshot. The other processes will use the V8 snapshot file that they normally do.
+
 ## How do I flip the fuses?
 
 ### The easy way

patches/chromium/.patches

@@ -122,3 +122,4 @@ fix_return_v8_value_from_localframe_requestexecutescript.patch
 disable_optimization_guide_for_preconnect_feature.patch
 fix_the_gn_gen_for_components_segmentation_platform.patch
 fix_crash_loading_non-standard_schemes_in_iframes.patch
+create_browser_v8_snapshot_file_name_fuse.patch

patches/chromium/create_browser_v8_snapshot_file_name_fuse.patch

@@ -0,0 +1,156 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Ryan Manuel <[email protected]>
+Date: Thu, 4 Aug 2022 22:37:01 -0500
+Subject: Create browser v8 snapshot file name fuse
+
+By default, chromium sets up one v8 snapshot to be used in all v8 contexts. This patch allows consumers
+to have a dedicated browser process v8 snapshot defined by the file `browser_v8_context_snapshot.bin`.
+
+diff --git a/content/app/content_main_runner_impl.cc b/content/app/content_main_runner_impl.cc
+index 14ca983c91cfe495ebd2859866a7f434d0a9ab02..a3e5764a1920c8a6bf1ce21e02d0ac743b027a40 100644
+--- a/content/app/content_main_runner_impl.cc
++++ b/content/app/content_main_runner_impl.cc
+@@ -37,6 +37,7 @@
+ #include "base/process/memory.h"
+ #include "base/process/process.h"
+ #include "base/process/process_handle.h"
++#include "base/strings/string_piece.h"
+ #include "base/strings/string_number_conversions.h"
+ #include "base/strings/string_util.h"
+ #include "base/task/thread_pool/thread_pool_instance.h"
+@@ -232,8 +233,13 @@ std::string GetSnapshotDataDescriptor(const base::CommandLine& command_line) {
+ 
+ #endif
+ 
+-void LoadV8SnapshotFile(const base::CommandLine& command_line) {
++void LoadV8SnapshotFile(const raw_ptr<ContentMainDelegate> delegate, const base::CommandLine& command_line) {
+   const gin::V8SnapshotFileType snapshot_type = GetSnapshotType(command_line);
++  base::StringPiece browser_v8_snapshot_file_name = delegate->GetBrowserV8SnapshotFilename();
++  if (!browser_v8_snapshot_file_name.empty()) {
++    gin::V8Initializer::LoadV8SnapshotFromFileName(browser_v8_snapshot_file_name, snapshot_type);
++    return;
++  }
+ #if BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_MAC)
+   base::FileDescriptorStore& file_descriptor_store =
+       base::FileDescriptorStore::GetInstance();
+@@ -262,11 +268,12 @@ bool ShouldLoadV8Snapshot(const base::CommandLine& command_line,
+ 
+ #endif  // V8_USE_EXTERNAL_STARTUP_DATA
+ 
+-void LoadV8SnapshotIfNeeded(const base::CommandLine& command_line,
++void LoadV8SnapshotIfNeeded(const raw_ptr<ContentMainDelegate> delegate,
++                            const base::CommandLine& command_line,
+                             const std::string& process_type) {
+ #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
+   if (ShouldLoadV8Snapshot(command_line, process_type))
+-    LoadV8SnapshotFile(command_line);
++    LoadV8SnapshotFile(delegate, command_line);
+ #endif  // V8_USE_EXTERNAL_STARTUP_DATA
+ }
+ 
+@@ -925,7 +932,7 @@ int ContentMainRunnerImpl::Initialize(ContentMainParams params) {
+     return TerminateForFatalInitializationError();
+ #endif  // BUILDFLAG(IS_ANDROID) && (ICU_UTIL_DATA_IMPL == ICU_UTIL_DATA_FILE)
+ 
+-  LoadV8SnapshotIfNeeded(command_line, process_type);
++  LoadV8SnapshotIfNeeded(delegate_, command_line, process_type);
+ 
+   blink::TrialTokenValidator::SetOriginTrialPolicyGetter(
+       base::BindRepeating([]() -> blink::OriginTrialPolicy* {
+diff --git a/content/public/app/content_main_delegate.cc b/content/public/app/content_main_delegate.cc
+index 5450eb6ba565164953b778f861d8fc75a06b6115..3f15d5a83d6e8011da09da178a0a9dfd2dd95d30 100644
+--- a/content/public/app/content_main_delegate.cc
++++ b/content/public/app/content_main_delegate.cc
+@@ -5,6 +5,7 @@
+ #include "content/public/app/content_main_delegate.h"
+ 
+ #include "base/check.h"
++#include "base/strings/string_piece.h"
+ #include "build/build_config.h"
+ #include "content/public/browser/content_browser_client.h"
+ #include "content/public/common/content_client.h"
+@@ -83,6 +84,10 @@ absl::optional<int> ContentMainDelegate::PostEarlyInitialization(
+   return absl::nullopt;
+ }
+ 
++base::StringPiece ContentMainDelegate::GetBrowserV8SnapshotFilename() {
++  return base::StringPiece();
++}
++
+ ContentClient* ContentMainDelegate::CreateContentClient() {
+   return new ContentClient();
+ }
+diff --git a/content/public/app/content_main_delegate.h b/content/public/app/content_main_delegate.h
+index f40146c4ed20e63dd09450e43c26736171f02ed4..5e3246a1346bd0210e7b83842a17dcc1986c8647 100644
+--- a/content/public/app/content_main_delegate.h
++++ b/content/public/app/content_main_delegate.h
+@@ -9,6 +9,7 @@
+ #include <string>
+ #include <vector>
+ 
++#include "base/strings/string_piece.h"
+ #include "build/build_config.h"
+ #include "content/common/content_export.h"
+ #include "content/public/common/main_function_params.h"
+@@ -154,6 +155,8 @@ class CONTENT_EXPORT ContentMainDelegate {
+   virtual bool ShouldHandleConsoleControlEvents();
+ #endif
+ 
++  virtual base::StringPiece GetBrowserV8SnapshotFilename();
++
+  protected:
+   friend class ContentClientCreator;
+   friend class ContentClientInitializer;
+diff --git a/gin/v8_initializer.cc b/gin/v8_initializer.cc
+index 5530d975303cc96701e4b70ffbcaf6e7c02bb016..edd9959cc0fd23711e19de4aee104199a8a3599e 100644
+--- a/gin/v8_initializer.cc
++++ b/gin/v8_initializer.cc
+@@ -496,8 +496,7 @@ void V8Initializer::GetV8ExternalSnapshotData(const char** snapshot_data_out,
+ 
+ #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
+ 
+-// static
+-void V8Initializer::LoadV8Snapshot(V8SnapshotFileType snapshot_file_type) {
++void V8Initializer::LoadV8SnapshotFromFileName(base::StringPiece file_name, V8SnapshotFileType snapshot_file_type) {
+   if (g_mapped_snapshot) {
+     // TODO(crbug.com/802962): Confirm not loading different type of snapshot
+     // files in a process.
+@@ -506,10 +505,17 @@ void V8Initializer::LoadV8Snapshot(V8SnapshotFileType snapshot_file_type) {
+ 
+   base::MemoryMappedFile::Region file_region;
+   base::File file =
+-      OpenV8File(GetSnapshotFileName(snapshot_file_type), &file_region);
++      OpenV8File(file_name.data(), &file_region);
+   LoadV8SnapshotFromFile(std::move(file), &file_region, snapshot_file_type);
+ }
+ 
++// static
++void V8Initializer::LoadV8Snapshot(V8SnapshotFileType snapshot_file_type) {
++  const char* file_name = GetSnapshotFileName(snapshot_file_type);
++
++  LoadV8SnapshotFromFileName(file_name, snapshot_file_type);
++}
++
+ // static
+ void V8Initializer::LoadV8SnapshotFromFile(
+     base::File snapshot_file,
+diff --git a/gin/v8_initializer.h b/gin/v8_initializer.h
+index 13a120c7fe8e69a44793473f3124c33d572a07a3..acb294780873c1d84546eb2b9acc00f86838361d 100644
+--- a/gin/v8_initializer.h
++++ b/gin/v8_initializer.h
+@@ -9,6 +9,7 @@
+ 
+ #include "base/files/file.h"
+ #include "base/files/memory_mapped_file.h"
++#include "base/strings/string_piece.h"
+ #include "build/build_config.h"
+ #include "gin/array_buffer.h"
+ #include "gin/gin_export.h"
+@@ -42,6 +43,7 @@ class GIN_EXPORT V8Initializer {
+                                         int* snapshot_size_out);
+ 
+ #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
++  static void LoadV8SnapshotFromFileName(base::StringPiece file_name, V8SnapshotFileType snapshot_file_type);
+   // Load V8 snapshot from default resources, if they are available.
+   static void LoadV8Snapshot(
+       V8SnapshotFileType snapshot_file_type = V8SnapshotFileType::kDefault);

shell/app/electron_main_delegate.cc

@@ -23,6 +23,7 @@
 #include "components/content_settings/core/common/content_settings_pattern.h"
 #include "content/public/common/content_switches.h"
 #include "electron/buildflags/buildflags.h"
+#include "electron/fuses.h"
 #include "extensions/common/constants.h"
 #include "ipc/ipc_buildflags.h"
 #include "sandbox/policy/switches.h"
@@ -422,6 +423,20 @@ absl::optional<int> ElectronMainDelegate::PreBrowserMain() {
   return absl::nullopt;
 }
 
+base::StringPiece ElectronMainDelegate::GetBrowserV8SnapshotFilename() {
+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  std::string process_type =
+      command_line->GetSwitchValueASCII(::switches::kProcessType);
+  bool load_browser_process_specific_v8_snapshot =
+      process_type.empty() &&
+      electron::fuses::IsLoadBrowserProcessSpecificV8SnapshotEnabled();
+  if (load_browser_process_specific_v8_snapshot) {
+    return "browser_v8_context_snapshot.bin";
+  }
+  return ContentMainDelegate::GetBrowserV8SnapshotFilename();
+}
+
 content::ContentBrowserClient*
 ElectronMainDelegate::CreateContentBrowserClient() {
   browser_client_ = std::make_unique<ElectronBrowserClient>();

shell/app/electron_main_delegate.h

@@ -30,6 +30,8 @@ class ElectronMainDelegate : public content::ContentMainDelegate {
   ElectronMainDelegate(const ElectronMainDelegate&) = delete;
   ElectronMainDelegate& operator=(const ElectronMainDelegate&) = delete;
 
+  base::StringPiece GetBrowserV8SnapshotFilename() override;
+
  protected:
   // content::ContentMainDelegate:
   absl::optional<int> BasicStartupComplete() override;