Read the class name from the bytecode if the class name is null during class definition.

Make ClassLoader#findLoadedClass0 compatible with JDK implementation.

Author: jovanstevanovic

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/hub/registry/ClassRegistries.java

@@ -300,13 +300,17 @@ public static Class<?> defineClass(ClassLoader loader, String name, byte[] b, in
             // The defineClass path usually can't throw ClassNotFoundException
             throw sneakyThrow(new ClassNotFoundException(name));
         }
-        ByteSequence typeBytes = ByteSequence.createTypeFromName(name);
-        Symbol<Type> type = SymbolsSupport.getTypes().getOrCreateValidType(typeBytes);
-        if (type == null) {
-            throw new NoClassDefFoundError(name);
-        }
         AbstractRuntimeClassRegistry registry = (AbstractRuntimeClassRegistry) singleton().getRegistry(loader);
-        return registry.defineClass(type, b, off, len, info);
+        if (name != null) {
+            ByteSequence typeBytes = ByteSequence.createTypeFromName(name);
+            Symbol<Type> type = SymbolsSupport.getTypes().getOrCreateValidType(typeBytes);
+            if (type == null) {
+                throw new NoClassDefFoundError(name);
+            }
+            return registry.defineClass(type, b, off, len, info);
+        } else {
+            return registry.defineClass(null, b, off, len, info);
+        }
     }
 
     @SuppressWarnings("unchecked")

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/Target_java_lang_ClassLoader.java

@@ -199,6 +199,10 @@ Class<?> loadClass(Module module, String name) {
     @BasedOnJDKFile("https://github.com/openjdk/jdk/blob/jdk-25+16/src/hotspot/share/prims/jvm.cpp#L1056-L1096")
     @SuppressWarnings({"unused"}) //
     private Class<?> findLoadedClass0(String name) {
+        if (name == null) {
+            return null;
+        }
+
         /*
          * HotSpot supports both dot- and slash-names here as well as array types The only caller
          * (findLoadedClass) errors out on slash-names and array types so we assume dot-names