8255578: [JVMCI] be more careful about reflective reads of Class.componentType.

Reviewed-by: kvn, dlong

src/hotspot/share/classfile/javaClasses.hpp

@@ -322,6 +322,8 @@ class java_lang_Class : AllStatic {
   static oop  class_data(oop java_class);
   static void set_class_data(oop java_class, oop classData);
 
+  static int component_mirror_offset() { return _component_mirror_offset; }
+
   static oop class_loader(oop java_class);
   static void set_module(oop java_class, oop module);
   static oop module(oop java_class);

src/hotspot/share/jvmci/jvmciCompilerToVM.cpp

@@ -1995,6 +1995,14 @@ C2V_VMENTRY_NULL(jobject, readFieldValue, (JNIEnv* env, jobject, jobject object,
     JVMCI_THROW_MSG_NULL(IllegalArgumentException,
                          err_msg("Unexpected type: %s", JVMCIENV->klass_name(base)));
   }
+
+  if (displacement == java_lang_Class::component_mirror_offset() && java_lang_Class::is_instance(obj()) &&
+      !java_lang_Class::as_Klass(obj())->is_array_klass()) {
+    // Class.componentType for non-array classes can transiently contain an int[] that's
+    // used for locking so always return null to mimic Class.getComponentType()
+    return JVMCIENV->get_jobject(JVMCIENV->get_JavaConstant_NULL_POINTER());
+  }
+
   jlong value = 0;
   JVMCIObject kind;
   switch (constant_type) {
@@ -2220,6 +2228,13 @@ C2V_VMENTRY_NULL(jobject, getObject, (JNIEnv* env, jobject, jobject x, long disp
     JVMCI_THROW_0(NullPointerException);
   }
   Handle xobj = JVMCIENV->asConstant(JVMCIENV->wrap(x), JVMCI_CHECK_0);
+  if (displacement == java_lang_Class::component_mirror_offset() && java_lang_Class::is_instance(xobj()) &&
+      !java_lang_Class::as_Klass(xobj())->is_array_klass()) {
+    // Class.componentType for non-array classes can transiently contain an int[] that's
+    // used for locking so always return null to mimic Class.getComponentType()
+    return JVMCIENV->get_jobject(JVMCIENV->get_JavaConstant_NULL_POINTER());
+  }
+
   oop res = xobj->obj_field(displacement);
   JVMCIObject result = JVMCIENV->get_object_constant(res);
   return JVMCIENV->get_jobject(result);

src/jdk.internal.vm.ci/share/classes/jdk.vm.ci.hotspot/src/jdk/vm/ci/hotspot/HotSpotJDKReflection.java

@@ -404,6 +404,14 @@ final class HotSpotJDKReflection extends HotSpotJVMCIReflection {
         assert obj != null;
         assert !field.isStatic() || obj instanceof Class;
         long displacement = field.getOffset();
+        if (obj instanceof Class && field.getName().equals("componentType")) {
+            Class<?> clazz = (Class<?>) obj;
+            if (!clazz.isArray()) {
+                // Class.componentType for non-array classes can transiently contain an int[] that's
+                // used for locking so always return null to mimic Class.getComponentType()
+                return JavaConstant.NULL_POINTER;
+            }
+        }
 
         assert checkRead(field.getJavaKind(), displacement,
                         (HotSpotResolvedObjectType) runtime().getHostJVMCIBackend().getMetaAccess().lookupJavaType(field.isStatic() ? (Class<?>) obj : obj.getClass()),