8291360: Create entry points to expose low-level class file information

Reviewed-by: dholmes, rriggs

make/data/hotspot-symbols/symbols-unix

@@ -81,6 +81,7 @@ JVM_GetClassDeclaredConstructors
 JVM_GetClassDeclaredFields
 JVM_GetClassDeclaredMethods
 JVM_GetClassFieldsCount
+JVM_GetClassFileVersion
 JVM_GetClassInterfaces
 JVM_GetClassMethodsCount
 JVM_GetClassModifiers

src/hotspot/share/include/jvm.h

@@ -1159,6 +1159,12 @@ JVM_VirtualThreadUnmountBegin(JNIEnv* env, jobject vthread, jboolean last_unmoun
 JNIEXPORT void JNICALL
 JVM_VirtualThreadUnmountEnd(JNIEnv* env, jobject vthread, jboolean last_unmount);
 
+/*
+ * Core reflection support.
+ */
+JNIEXPORT jint JNICALL
+JVM_GetClassFileVersion(JNIEnv *env, jclass current);
+
 /*
  * This structure is used by the launcher to get the default thread
  * stack size from the VM using JNI_GetDefaultJavaVMInitArgs() with a

src/hotspot/share/prims/jvm.cpp

@@ -4044,3 +4044,22 @@ JVM_ENTRY(void, JVM_VirtualThreadUnmountEnd(JNIEnv* env, jobject vthread, jboole
   fatal("Should only be called with JVMTI enabled");
 #endif
 JVM_END
+
+/*
+ * Return the current class's class file version.  The low order 16 bits of the
+ * returned jint contain the class's major version.  The high order 16 bits
+ * contain the class's minor version.
+ */
+JVM_ENTRY(jint, JVM_GetClassFileVersion(JNIEnv* env, jclass current))
+  oop mirror = JNIHandles::resolve_non_null(current);
+  if (java_lang_Class::is_primitive(mirror)) {
+    // return latest major version and minor version of 0.
+    return JVM_CLASSFILE_MAJOR_VERSION;
+  }
+  assert(!java_lang_Class::as_Klass(mirror)->is_array_klass(), "unexpected array class");
+
+  Klass* c = java_lang_Class::as_Klass(mirror);
+  assert(c->is_instance_klass(), "must be");
+  InstanceKlass* ik = InstanceKlass::cast(c);
+  return (ik->minor_version() << 16) | ik->major_version();
+JVM_END

src/java.base/share/classes/java/lang/Class.java

@@ -4668,4 +4668,34 @@ public boolean isSealed() {
     }
 
     private native Class<?>[] getPermittedSubclasses0();
+
+    /*
+     * Return the class's major and minor class file version packed into an int.
+     * The high order 16 bits contain the class's minor version.  The low order
+     * 16 bits contain the class's major version.
+     *
+     * If the class is an array type then the class file version of its element
+     * type is returned.  If the class is a primitive type then the latest class
+     * file major version is returned and zero is returned for the minor version.
+     */
+    private int getClassFileVersion() {
+        Class<?> c = isArray() ? elementType() : this;
+        return c.getClassFileVersion0();
+    }
+
+    private native int getClassFileVersion0();
+
+    /*
+     * Return the access flags as they were in the class's bytecode, including
+     * the original setting of ACC_SUPER.
+     *
+     * If the class is an array type then the access flags of the element type is
+     * returned.  If the class is a primitive then ACC_ABSTRACT | ACC_FINAL | ACC_PUBLIC.
+     */
+    private int getClassAccessFlagsRaw() {
+        Class<?> c = isArray() ? elementType() : this;
+        return c.getClassAccessFlagsRaw0();
+    }
+
+    private native int getClassAccessFlagsRaw0();
 }

src/java.base/share/native/libjava/Class.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1994, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 2022, 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
@@ -82,6 +82,8 @@ static JNINativeMethod methods[] = {
     {"getRecordComponents0", "()[" RC,      (void *)&JVM_GetRecordComponents},
     {"isRecord0",            "()Z",         (void *)&JVM_IsRecord},
     {"getPermittedSubclasses0", "()[" CLS,  (void *)&JVM_GetPermittedSubclasses},
+    {"getClassFileVersion0", "()I",         (void *)&JVM_GetClassFileVersion},
+    {"getClassAccessFlagsRaw0", "()I",      (void *)&JVM_GetClassAccessFlags},
 };
 
 #undef OBJ

test/hotspot/jtreg/runtime/ClassFile/ClassAccessFlagsRawTest.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2022, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+/**
+ * @test
+ * @bug 8291360
+ * @summary Test getting a class's raw access flags using java.lang.Class API
+ * @modules java.base/java.lang:open
+ * @compile classAccessFlagsRaw.jcod
+ * @run main/othervm ClassAccessFlagsRawTest
+ */
+
+import java.lang.reflect.*;
+
+public class ClassAccessFlagsRawTest {
+
+    static Method m;
+
+    public static void testIt(String className, int expectedResult) throws Exception {
+        Class<?> testClass = Class.forName(className);
+        int flags = (int)m.invoke(testClass);
+        if (flags != expectedResult) {
+            throw new RuntimeException(
+                "expected 0x" + Integer.toHexString(expectedResult) + ", got 0x" + Integer.toHexString(flags) + " for class " + className);
+        }
+    }
+
+    public static void main(String argv[]) throws Throwable {
+        Class<?> cl = java.lang.Class.class;
+        m = cl.getDeclaredMethod("getClassAccessFlagsRaw", new Class[0]);
+        m.setAccessible(true);
+
+        testIt("SUPERset", 0x21);  // ACC_SUPER 0x20 + ACC_PUBLIC 0x1
+        testIt("SUPERnotset", Modifier.PUBLIC);
+
+        // test primitive array.  should return ACC_ABSTRACT | ACC_FINAL | ACC_PUBLIC.
+        int flags = (int)m.invoke((new int[3]).getClass());
+        if (flags != (Modifier.ABSTRACT | Modifier.FINAL | Modifier.PUBLIC)) {
+            throw new RuntimeException(
+                "expected 0x411, got 0x" + Integer.toHexString(flags) + " for primitive array");
+        }
+
+        // test object array.  should return flags of component.
+        flags = (int)m.invoke((new SUPERnotset[2]).getClass());
+        if (flags != Modifier.PUBLIC) {
+            throw new RuntimeException(
+                "expected 0x1, got 0x" + Integer.toHexString(flags) + " for object array");
+        }
+
+        // test multi-dimensional object array.  should return flags of component.
+        flags = (int)m.invoke((new SUPERnotset[4][2]).getClass());
+        if (flags != Modifier.PUBLIC) {
+            throw new RuntimeException(
+                "expected 0x1, got 0x" + Integer.toHexString(flags) + " for object array");
+        }
+    }
+}

test/hotspot/jtreg/runtime/ClassFile/ClassFileVersionTest.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2022, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+/**
+ * @test
+ * @bug 8291360
+ * @summary Test getting the class file version for java.lang.Class API
+ * @modules java.base/java.lang:open
+ * @compile classFileVersions.jcod
+ * @run main/othervm --enable-preview ClassFileVersionTest
+ */
+
+import java.lang.reflect.*;
+
+public class ClassFileVersionTest {
+
+    static Method m;
+
+    public static void testIt(String className, int expectedResult) throws Exception {
+        Class<?> testClass = Class.forName(className);
+        int ver = (int)m.invoke(testClass);
+        if (ver != expectedResult) {
+            int exp_minor = (expectedResult >> 16) & 0x0000FFFF;
+            int exp_major = expectedResult & 0x0000FFFF;
+            int got_minor = (ver >> 16) & 0x0000FFFF;
+            int got_major = ver & 0x0000FFFF;
+            throw new RuntimeException(
+                "Expected " + exp_minor + ":" + exp_major + " but got " + got_minor + ":" + got_major);
+        }
+    }
+
+    public static void main(String argv[]) throws Throwable {
+        Class<?> cl = java.lang.Class.class;
+        m = cl.getDeclaredMethod("getClassFileVersion", new Class[0]);
+        m.setAccessible(true);
+
+        testIt("Version64", 64);
+        testIt("Version59", 59);
+        testIt("Version45_3", 0x3002D);  // 3:45
+        // test minor version of 65535.
+        testIt("Version64_65535", 0xFFFF0040);  // 0xFFFF0040 = 65535:64
+
+        // test primitive array.  should return latest version.
+        int ver = (int)m.invoke((new int[3]).getClass());
+        if (ver != 64) {
+            int got_minor = (ver >> 16) & 0x0000FFFF;
+            int got_major = ver & 0x0000FFFF;
+            throw new RuntimeException(
+                "Expected 0:64, but got " + got_minor + ":" + got_major + " for primitive array");
+        }
+
+        // test object array.  should return class file version of component.
+        ver = (int)m.invoke((new Version59[2]).getClass());
+        if (ver != 59) {
+            int got_minor = (ver >> 16) & 0x0000FFFF;
+            int got_major = ver & 0x0000FFFF;
+            throw new RuntimeException(
+                "Expected 0:59, but got " + got_minor + ":" + got_major + " for object array");
+        }
+
+        // test multi-dimensional object array.  should return class file version of component.
+        ver = (int)m.invoke((new Version59[3][2]).getClass());
+        if (ver != 59) {
+            int got_minor = (ver >> 16) & 0x0000FFFF;
+            int got_major = ver & 0x0000FFFF;
+            throw new RuntimeException(
+                "Expected 0:59, but got " + got_minor + ":" + got_major + " for object array");
+        }
+    }
+}