8318563: GetClassFields should not use random access to field

Reviewed-by: sspitsyn, cjplummer, fparain

src/hotspot/share/prims/jvmtiEnv.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 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
@@ -2896,26 +2896,20 @@ JvmtiEnv::GetClassFields(oop k_mirror, jint* field_count_ptr, jfieldID** fields_
     return JVMTI_ERROR_NONE;
   }
 
-
   InstanceKlass* ik = InstanceKlass::cast(k);
 
-  int result_count = 0;
+  FilteredJavaFieldStream flds(ik);
-  // First, count the fields.
-  FilteredFieldStream flds(ik, true, true);
-  result_count = flds.field_count();
 
-  // Allocate the result and fill it in
+  int result_count = flds.field_count();
-  jfieldID* result_list = (jfieldID*) jvmtiMalloc(result_count * sizeof(jfieldID));
-  // The JVMTI spec requires fields in the order they occur in the class file,
-  // this is the reverse order of what FieldStream hands out.
-  int id_index = (result_count - 1);
 
-  for (FilteredFieldStream src_st(ik, true, true); !src_st.eos(); src_st.next()) {
+  // Allocate the result and fill it in.
-    result_list[id_index--] = jfieldIDWorkaround::to_jfieldID(
+  jfieldID* result_list = (jfieldID*)jvmtiMalloc(result_count * sizeof(jfieldID));
-                                            ik, src_st.offset(),
+  for (int i = 0; i < result_count; i++, flds.next()) {
-                                            src_st.access_flags().is_static());
+    result_list[i] = jfieldIDWorkaround::to_jfieldID(ik, flds.offset(),
+                                                     flds.access_flags().is_static());
   }
-  assert(id_index == -1, "just checking");
+  assert(flds.done(), "just checking");
+
   // Fill in the results
   *field_count_ptr = result_count;
   *fields_ptr = result_list;

src/hotspot/share/runtime/reflectionUtils.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1999, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1999, 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
@@ -26,6 +26,7 @@
 #define SHARE_RUNTIME_REFLECTIONUTILS_HPP
 
 #include "memory/allStatic.hpp"
+#include "oops/fieldStreams.inline.hpp"
 #include "oops/instanceKlass.hpp"
 #include "oops/objArrayOop.hpp"
 #include "oops/oopsHierarchy.hpp"
@@ -237,4 +238,36 @@ class FilteredFieldStream : public FieldStream {
   }
 };
 
+// Iterate over Java fields filtering fields like reflection does.
+class FilteredJavaFieldStream : public JavaFieldStream {
+private:
+  InstanceKlass* _klass;
+  int  _filtered_fields_count;
+  bool has_filtered_field() const { return (_filtered_fields_count > 0); }
+  void skip_filtered_fields() {
+    if (has_filtered_field()) {
+      while (!done() && FilteredFieldsMap::is_filtered_field((Klass*)_klass, offset())) {
+        JavaFieldStream::next();
+      }
+    }
+  }
+
+public:
+  FilteredJavaFieldStream(InstanceKlass* klass)
+    : JavaFieldStream(klass),
+      _klass(klass),
+      _filtered_fields_count(FilteredFieldsMap::filtered_fields_count(klass, true))
+  {
+    // skip filtered fields at the beginning
+    skip_filtered_fields();
+  }
+  int field_count() const {
+    return _klass->java_fields_count() - _filtered_fields_count;
+  }
+  void next() {
+    JavaFieldStream::next();
+    skip_filtered_fields();
+  }
+};
+
 #endif // SHARE_RUNTIME_REFLECTIONUTILS_HPP