From 2fe2f3aff82f41a3b7942861e29ccbd3bcc68661 Mon Sep 17 00:00:00 2001
From: Ioi Lam <iklam@openjdk.org>
Date: Wed, 17 Apr 2024 05:31:39 +0000
Subject: [PATCH] 8323900: Avoid calling os::init_random() in CDS static dump

Reviewed-by: stuefe, ccheung
---
 src/hotspot/share/cds/archiveBuilder.cpp  | 13 ++++++++++++-
 src/hotspot/share/cds/archiveBuilder.hpp  |  2 ++
 src/hotspot/share/cds/metaspaceShared.cpp |  3 ---
 src/hotspot/share/oops/symbol.cpp         |  8 +++-----
 4 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/hotspot/share/cds/archiveBuilder.cpp b/src/hotspot/share/cds/archiveBuilder.cpp
index 0fc8c29a5b7..0eee36eec21 100644
--- a/src/hotspot/share/cds/archiveBuilder.cpp
+++ b/src/hotspot/share/cds/archiveBuilder.cpp
@@ -39,6 +39,7 @@
 #include "classfile/systemDictionaryShared.hpp"
 #include "classfile/vmClasses.hpp"
 #include "interpreter/abstractInterpreter.hpp"
+#include "jvm.h"
 #include "logging/log.hpp"
 #include "logging/logStream.hpp"
 #include "memory/allStatic.hpp"
@@ -170,7 +171,7 @@ ArchiveBuilder::ArchiveBuilder() :
 {
   _klasses = new (mtClassShared) GrowableArray<Klass*>(4 * K, mtClassShared);
   _symbols = new (mtClassShared) GrowableArray<Symbol*>(256 * K, mtClassShared);
-
+  _entropy_seed = 0x12345678;
   assert(_current == nullptr, "must be");
   _current = this;
 }
@@ -190,6 +191,16 @@ ArchiveBuilder::~ArchiveBuilder() {
   }
 }
 
+// Returns a deterministic sequence of pseudo random numbers. The main purpose is NOT
+// for randomness but to get good entropy for the identity_hash() of archived Symbols,
+// while keeping the contents of static CDS archives deterministic to ensure
+// reproducibility of JDK builds.
+int ArchiveBuilder::entropy() {
+  assert(SafepointSynchronize::is_at_safepoint(), "needed to ensure deterministic sequence");
+  _entropy_seed = os::next_random(_entropy_seed);
+  return static_cast<int>(_entropy_seed);
+}
+
 class GatherKlassesAndSymbols : public UniqueMetaspaceClosure {
   ArchiveBuilder* _builder;
 
diff --git a/src/hotspot/share/cds/archiveBuilder.hpp b/src/hotspot/share/cds/archiveBuilder.hpp
index a80370d3976..e6ac2e7ac4e 100644
--- a/src/hotspot/share/cds/archiveBuilder.hpp
+++ b/src/hotspot/share/cds/archiveBuilder.hpp
@@ -219,6 +219,7 @@ private:
   ResizeableResourceHashtable<address, address, AnyObj::C_HEAP, mtClassShared> _buffered_to_src_table;
   GrowableArray<Klass*>* _klasses;
   GrowableArray<Symbol*>* _symbols;
+  unsigned int _entropy_seed;
 
   // statistics
   DumpAllocStats _alloc_stats;
@@ -341,6 +342,7 @@ public:
   ArchiveBuilder();
   ~ArchiveBuilder();
 
+  int entropy();
   void gather_klasses_and_symbols();
   void gather_source_objs();
   bool gather_klass_and_symbol(MetaspaceClosure::Ref* ref, bool read_only);
diff --git a/src/hotspot/share/cds/metaspaceShared.cpp b/src/hotspot/share/cds/metaspaceShared.cpp
index 231f69e3ab1..b13ef2101a9 100644
--- a/src/hotspot/share/cds/metaspaceShared.cpp
+++ b/src/hotspot/share/cds/metaspaceShared.cpp
@@ -513,9 +513,6 @@ void VM_PopulateDumpSharedSpace::doit() {
 
   char* cloned_vtables = CppVtables::dumptime_init(&builder);
 
-  // Initialize random for updating the hash of symbols
-  os::init_random(0x12345678);
-
   builder.dump_rw_metadata();
   builder.dump_ro_metadata();
   builder.relocate_metaspaceobj_embedded_pointers();
diff --git a/src/hotspot/share/oops/symbol.cpp b/src/hotspot/share/oops/symbol.cpp
index cbb51e1bb90..4deae372061 100644
--- a/src/hotspot/share/oops/symbol.cpp
+++ b/src/hotspot/share/oops/symbol.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -23,6 +23,7 @@
  */
 
 #include "precompiled.hpp"
+#include "cds/archiveBuilder.hpp"
 #include "cds/metaspaceShared.hpp"
 #include "classfile/altHashing.hpp"
 #include "classfile/classLoaderData.hpp"
@@ -73,11 +74,8 @@ Symbol::Symbol(const Symbol& s1) {
 
 #if INCLUDE_CDS
 void Symbol::update_identity_hash() {
-  // This is called at a safepoint during dumping of a static CDS archive. The caller should have
-  // called os::init_random() with a deterministic seed and then iterate all archived Symbols in
-  // a deterministic order.
   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
-  _hash_and_refcount =  pack_hash_and_refcount((short)os::random(), PERM_REFCOUNT);
+  _hash_and_refcount =  pack_hash_and_refcount((short)ArchiveBuilder::current()->entropy(), PERM_REFCOUNT);
 }
 
 void Symbol::set_permanent() {