From 697fef6744db851ac1613eb8eed1c91cf1f1817f Mon Sep 17 00:00:00 2001
From: Joyee Cheung <joyeec9h3@gmail.com>
Date: Wed, 12 Jul 2023 19:12:00 +0200
Subject: [PATCH] src: generate default snapshot with --predictable

To improve determinism of snapshot generation, add --predictable
to the V8 flags used to initialize a process launched to generate
snapshot. Also add a kGeneratePredictableSnapshot flag
to ProcessInitializationFlags for this and moves the configuration
of these flags into node::InitializeOncePerProcess() so that
it can be shared by embedders.
---
 src/node.cc                       | 7 +++++++
 src/node.h                        | 2 ++
 tools/snapshot/node_mksnapshot.cc | 5 ++---
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/node.cc b/src/node.cc
index f483e59dd155a8..9987d84521bd72 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -932,6 +932,13 @@ InitializeOncePerProcessInternal(const std::vector<std::string>& args,
     }
   }
 
+  if (!!(flags & ProcessInitializationFlags::kGeneratePredictableSnapshot) ||
+      per_process::cli_options->per_isolate->build_snapshot) {
+    v8::V8::SetFlagsFromString("--predictable");
+    v8::V8::SetFlagsFromString("--random_seed=42");
+    v8::V8::SetFlagsFromString("--harmony-import-assertions");
+  }
+
   if (!(flags & ProcessInitializationFlags::kNoUseLargePages) &&
       (per_process::cli_options->use_largepages == "on" ||
        per_process::cli_options->use_largepages == "silent")) {
diff --git a/src/node.h b/src/node.h
index 846ec413f8e1fc..21e8c6cdebf00e 100644
--- a/src/node.h
+++ b/src/node.h
@@ -261,6 +261,8 @@ enum Flags : uint32_t {
   kNoUseLargePages = 1 << 11,
   // Skip printing output for --help, --version, --v8-options.
   kNoPrintHelpOrVersionOutput = 1 << 12,
+  // Initialize the process for predictable snapshot generation.
+  kGeneratePredictableSnapshot = 1 << 13,
 
   // Emulate the behavior of InitializeNodeWithArgs() when passing
   // a flags argument to the InitializeOncePerProcess() replacement
diff --git a/tools/snapshot/node_mksnapshot.cc b/tools/snapshot/node_mksnapshot.cc
index ecc295acdbea32..67c48d381813c7 100644
--- a/tools/snapshot/node_mksnapshot.cc
+++ b/tools/snapshot/node_mksnapshot.cc
@@ -51,8 +51,6 @@ int main(int argc, char* argv[]) {
   setvbuf(stderr, nullptr, _IONBF, 0);
 #endif  // _WIN32
 
-  v8::V8::SetFlagsFromString("--random_seed=42");
-  v8::V8::SetFlagsFromString("--harmony-import-assertions");
   return BuildSnapshot(argc, argv);
 }
 
@@ -66,7 +64,8 @@ int BuildSnapshot(int argc, char* argv[]) {
 
   std::unique_ptr<node::InitializationResult> result =
       node::InitializeOncePerProcess(
-          std::vector<std::string>(argv, argv + argc));
+          std::vector<std::string>(argv, argv + argc),
+          node::ProcessInitializationFlags::kGeneratePredictableSnapshot);
 
   CHECK(!result->early_return());
   CHECK_EQ(result->exit_code(), 0);