6653858: dynamic languages need to be able to load anonymous classes

Low-level privileged sun.misc.Unsafe.defineAnonymousClass

Reviewed-by: kvn

hotspot/src/share/vm/prims/unsafe.cpp

@@ -837,6 +837,163 @@ UNSAFE_ENTRY(jclass, Unsafe_DefineClass1(JNIEnv *env, jobject unsafe, jstring na
   }
 UNSAFE_END
 
+#define DAC_Args CLS"[B["OBJ
+// define a class but do not make it known to the class loader or system dictionary
+// - host_class:  supplies context for linkage, access control, protection domain, and class loader
+// - data:  bytes of a class file, a raw memory address (length gives the number of bytes)
+// - cp_patches:  where non-null entries exist, they replace corresponding CP entries in data
+
+// When you load an anonymous class U, it works as if you changed its name just before loading,
+// to a name that you will never use again.  Since the name is lost, no other class can directly
+// link to any member of U.  Just after U is loaded, the only way to use it is reflectively,
+// through java.lang.Class methods like Class.newInstance.
+
+// Access checks for linkage sites within U continue to follow the same rules as for named classes.
+// The package of an anonymous class is given by the package qualifier on the name under which it was loaded.
+// An anonymous class also has special privileges to access any member of its host class.
+// This is the main reason why this loading operation is unsafe.  The purpose of this is to
+// allow language implementations to simulate "open classes"; a host class in effect gets
+// new code when an anonymous class is loaded alongside it.  A less convenient but more
+// standard way to do this is with reflection, which can also be set to ignore access
+// restrictions.
+
+// Access into an anonymous class is possible only through reflection.  Therefore, there
+// are no special access rules for calling into an anonymous class.  The relaxed access
+// rule for the host class is applied in the opposite direction:  A host class reflectively
+// access one of its anonymous classes.
+
+// If you load the same bytecodes twice, you get two different classes.  You can reload
+// the same bytecodes with or without varying CP patches.
+
+// By using the CP patching array, you can have a new anonymous class U2 refer to an older one U1.
+// The bytecodes for U2 should refer to U1 by a symbolic name (doesn't matter what the name is).
+// The CONSTANT_Class entry for that name can be patched to refer directly to U1.
+
+// This allows, for example, U2 to use U1 as a superclass or super-interface, or as
+// an outer class (so that U2 is an anonymous inner class of anonymous U1).
+// It is not possible for a named class, or an older anonymous class, to refer by
+// name (via its CP) to a newer anonymous class.
+
+// CP patching may also be used to modify (i.e., hack) the names of methods, classes,
+// or type descriptors used in the loaded anonymous class.
+
+// Finally, CP patching may be used to introduce "live" objects into the constant pool,
+// instead of "dead" strings.  A compiled statement like println((Object)"hello") can
+// be changed to println(greeting), where greeting is an arbitrary object created before
+// the anonymous class is loaded.  This is useful in dynamic languages, in which
+// various kinds of metaobjects must be introduced as constants into bytecode.
+// Note the cast (Object), which tells the verifier to expect an arbitrary object,
+// not just a literal string.  For such ldc instructions, the verifier uses the
+// type Object instead of String, if the loaded constant is not in fact a String.
+
+static oop
+Unsafe_DefineAnonymousClass_impl(JNIEnv *env,
+                                 jclass host_class, jbyteArray data, jobjectArray cp_patches_jh,
+                                 HeapWord* *temp_alloc,
+                                 TRAPS) {
+
+  if (UsePerfData) {
+    ClassLoader::unsafe_defineClassCallCounter()->inc();
+  }
+
+  if (data == NULL) {
+    THROW_0(vmSymbols::java_lang_NullPointerException());
+  }
+
+  jint length = typeArrayOop(JNIHandles::resolve_non_null(data))->length();
+  jint word_length = (length + sizeof(HeapWord)-1) / sizeof(HeapWord);
+  HeapWord* body = NEW_C_HEAP_ARRAY(HeapWord, word_length);
+  if (body == NULL) {
+    THROW_0(vmSymbols::java_lang_OutOfMemoryError());
+  }
+
+  // caller responsible to free it:
+  (*temp_alloc) = body;
+
+  {
+    jbyte* array_base = typeArrayOop(JNIHandles::resolve_non_null(data))->byte_at_addr(0);
+    Copy::conjoint_words((HeapWord*) array_base, body, word_length);
+  }
+
+  u1* class_bytes = (u1*) body;
+  int class_bytes_length = (int) length;
+  if (class_bytes_length < 0)  class_bytes_length = 0;
+  if (class_bytes == NULL
+      || host_class == NULL
+      || length != class_bytes_length)
+    THROW_0(vmSymbols::java_lang_IllegalArgumentException());
+
+  objArrayHandle cp_patches_h;
+  if (cp_patches_jh != NULL) {
+    oop p = JNIHandles::resolve_non_null(cp_patches_jh);
+    if (!p->is_objArray())
+      THROW_0(vmSymbols::java_lang_IllegalArgumentException());
+    cp_patches_h = objArrayHandle(THREAD, (objArrayOop)p);
+  }
+
+  KlassHandle host_klass(THREAD, java_lang_Class::as_klassOop(JNIHandles::resolve_non_null(host_class)));
+  const char* host_source = host_klass->external_name();
+  Handle      host_loader(THREAD, host_klass->class_loader());
+  Handle      host_domain(THREAD, host_klass->protection_domain());
+
+  GrowableArray<Handle>* cp_patches = NULL;
+  if (cp_patches_h.not_null()) {
+    int alen = cp_patches_h->length();
+    for (int i = alen-1; i >= 0; i--) {
+      oop p = cp_patches_h->obj_at(i);
+      if (p != NULL) {
+        Handle patch(THREAD, p);
+        if (cp_patches == NULL)
+          cp_patches = new GrowableArray<Handle>(i+1, i+1, Handle());
+        cp_patches->at_put(i, patch);
+      }
+    }
+  }
+
+  ClassFileStream st(class_bytes, class_bytes_length, (char*) host_source);
+
+  instanceKlassHandle anon_klass;
+  {
+    symbolHandle no_class_name;
+    klassOop anonk = SystemDictionary::parse_stream(no_class_name,
+                                                    host_loader, host_domain,
+                                                    &st, host_klass, cp_patches,
+                                                    CHECK_NULL);
+    if (anonk == NULL)  return NULL;
+    anon_klass = instanceKlassHandle(THREAD, anonk);
+  }
+
+  // let caller initialize it as needed...
+
+  return anon_klass->java_mirror();
+}
+
+UNSAFE_ENTRY(jclass, Unsafe_DefineAnonymousClass(JNIEnv *env, jobject unsafe, jclass host_class, jbyteArray data, jobjectArray cp_patches_jh))
+{
+  UnsafeWrapper("Unsafe_DefineAnonymousClass");
+  ResourceMark rm(THREAD);
+
+  HeapWord* temp_alloc = NULL;
+
+  jobject res_jh = NULL;
+
+  { oop res_oop = Unsafe_DefineAnonymousClass_impl(env,
+                                                   host_class, data, cp_patches_jh,
+                                                   &temp_alloc, THREAD);
+    if (res_oop != NULL)
+      res_jh = JNIHandles::make_local(env, res_oop);
+  }
+
+  // try/finally clause:
+  if (temp_alloc != NULL) {
+    FREE_C_HEAP_ARRAY(HeapWord, temp_alloc);
+  }
+
+  return (jclass) res_jh;
+}
+UNSAFE_END
+
+
 
 UNSAFE_ENTRY(void, Unsafe_MonitorEnter(JNIEnv *env, jobject unsafe, jobject jobj))
   UnsafeWrapper("Unsafe_MonitorEnter");
@@ -1292,6 +1449,9 @@ JNINativeMethod memcopy_methods_15[] = {
     {CC"copyMemory",         CC"("ADR ADR"J)V",          FN_PTR(Unsafe_CopyMemory)}
 };
 
+JNINativeMethod anonk_methods[] = {
+    {CC"defineAnonymousClass", CC"("DAC_Args")"CLS,      FN_PTR(Unsafe_DefineAnonymousClass)},
+};
 
 #undef CC
 #undef FN_PTR
@@ -1354,6 +1514,15 @@ JVM_ENTRY(void, JVM_RegisterUnsafeMethods(JNIEnv *env, jclass unsafecls))
         }
       }
     }
+    if (AnonymousClasses) {
+      env->RegisterNatives(unsafecls, anonk_methods, sizeof(anonk_methods)/sizeof(JNINativeMethod));
+      if (env->ExceptionOccurred()) {
+        if (PrintMiscellaneous && (Verbose || WizardMode)) {
+          tty->print_cr("Warning:  SDK 1.7 Unsafe.defineClass (anonymous version) not found.");
+        }
+        env->ExceptionClear();
+      }
+    }
     int status = env->RegisterNatives(unsafecls, methods, sizeof(methods)/sizeof(JNINativeMethod));
     if (env->ExceptionOccurred()) {
       if (PrintMiscellaneous && (Verbose || WizardMode)) {