From 31eeef5e07c983ee8c37f63a5adeb7344d6fc5a5 Mon Sep 17 00:00:00 2001
From: Jaroslav Bachorik <j.bachorik@gmail.com>
Date: Wed, 25 Oct 2023 09:13:53 +0000
Subject: [PATCH] WIP

---
 src/hotspot/share/oops/klass.hpp        |  1 +
 src/hotspot/share/oops/klass.inline.hpp |  5 +++++
 src/hotspot/share/oops/method.cpp       | 14 +++++++++++++-
 src/hotspot/share/oops/method.hpp       | 10 ++++++++++
 4 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/hotspot/share/oops/klass.hpp b/src/hotspot/share/oops/klass.hpp
index 9d15894a4905d..b46eea59b6536 100644
--- a/src/hotspot/share/oops/klass.hpp
+++ b/src/hotspot/share/oops/klass.hpp
@@ -682,6 +682,7 @@ class Klass : public Metadata {
   virtual MetaspaceObj::Type type() const { return ClassType; }
 
   inline bool is_loader_alive() const;
+  inline bool is_loader_alive_safe() const;
 
   void clean_subklass();
 
diff --git a/src/hotspot/share/oops/klass.inline.hpp b/src/hotspot/share/oops/klass.inline.hpp
index af2480e149b45..7e4164025a959 100644
--- a/src/hotspot/share/oops/klass.inline.hpp
+++ b/src/hotspot/share/oops/klass.inline.hpp
@@ -52,6 +52,11 @@ inline bool Klass::is_loader_alive() const {
   return class_loader_data()->is_alive();
 }
 
+inline bool Klass::is_loader_alive_safe() const {
+  ClassLoaderData* cld = class_loader_data();
+  return os::is_readable_pointer(cld) ? cld->is_alive() : false;
+}
+
 inline oop Klass::java_mirror() const {
   return _java_mirror.resolve();
 }
diff --git a/src/hotspot/share/oops/method.cpp b/src/hotspot/share/oops/method.cpp
index 003f47b1e9c50..f8d21e197c4d6 100644
--- a/src/hotspot/share/oops/method.cpp
+++ b/src/hotspot/share/oops/method.cpp
@@ -125,6 +125,10 @@ Method::Method(ConstMethod* xconst, AccessFlags access_flags, Symbol* name) {
 // Release Method*.  The nmethod will be gone when we get here because
 // we've walked the code cache.
 void Method::deallocate_contents(ClassLoaderData* loader_data) {
+  // jmethodID mid = jmethod_id();
+  // if (!(mid == nullptr || *((Method**)mid) == nullptr)){
+  //   fprintf(stdout, "!!! jmethodid not cleared out\n");
+  // }
   MetadataFactory::free_metadata(loader_data, constMethod());
   set_constMethod(nullptr);
   MetadataFactory::free_metadata(loader_data, method_data());
@@ -137,6 +141,10 @@ void Method::deallocate_contents(ClassLoaderData* loader_data) {
 
 void Method::release_C_heap_structures() {
   if (method_data()) {
+    // jmethodID mid = jmethod_id();
+    // if (!(mid == nullptr || *((Method**)mid) == nullptr)){
+    //   fprintf(stdout, "!!! jmethodid not cleared out\n");
+    // }
     method_data()->release_C_heap_structures();
 
     // Destroy MethodData embedded lock
@@ -2231,12 +2239,16 @@ Method* Method::checked_resolve_jmethod_id(jmethodID mid) {
   if (o == nullptr || o == JNIMethodBlock::_free_method) {
     return nullptr;
   }
+  InstanceKlass* method_holder = o->method_holder_safe();
+  if (method_holder == nullptr || !os::is_readable_pointer(method_holder)) {
+    return nullptr;
+  }
   // Method should otherwise be valid. Assert for testing.
   assert(is_valid_method(o), "should be valid jmethodid");
   // If the method's class holder object is unreferenced, but not yet marked as
   // unloaded, we need to return null here too because after a safepoint, its memory
   // will be reclaimed.
-  return o->method_holder()->is_loader_alive() ? o : nullptr;
+  return method_holder->is_loader_alive_safe() ? o : nullptr;
 };
 
 void Method::set_on_stack(const bool value) {
diff --git a/src/hotspot/share/oops/method.hpp b/src/hotspot/share/oops/method.hpp
index 1dab585a66069..68f89732298ba 100644
--- a/src/hotspot/share/oops/method.hpp
+++ b/src/hotspot/share/oops/method.hpp
@@ -237,6 +237,11 @@ class Method : public Metadata {
 
   // constant pool for Klass* holding this method
   ConstantPool* constants() const              { return constMethod()->constants(); }
+  // constant pool for Klass* holding this method or nullptr if it can't be accessed safely
+  ConstantPool* constants_safe() const              {
+     ConstMethod* method = constMethod();
+     return os::is_readable_pointer(method) ? method->constants() : nullptr; 
+  }
   void set_constants(ConstantPool* c)          { constMethod()->set_constants(c); }
 
   // max stack
@@ -485,6 +490,11 @@ class Method : public Metadata {
 
   // method holder (the Klass* holding this method)
   InstanceKlass* method_holder() const         { return constants()->pool_holder(); }
+  // method holder (the Klass* holding this method) or nullptr if can't be accessed safely
+  InstanceKlass* method_holder_safe() const         { 
+    ConstantPool* cp = constants_safe();
+    return os::is_readable_pointer(cp) ? cp->pool_holder() : nullptr; 
+  }
 
   Symbol* klass_name() const;                    // returns the name of the method holder
   BasicType result_type() const                  { return constMethod()->result_type(); }