8225093: Special property jdk.boot.class.path.append should not default to empty string

Reviewed-by: dholmes, sspitsyn, alanb

src/hotspot/share/runtime/arguments.cpp

@@ -412,7 +412,7 @@ void Arguments::init_system_properties() {
   // It can only be set by either:
   //    - -Xbootclasspath/a:
   //    - AddToBootstrapClassLoaderSearch during JVMTI OnLoad phase
-  _jdk_boot_class_path_append = new SystemProperty("jdk.boot.class.path.append", "", false, true);
+  _jdk_boot_class_path_append = new SystemProperty("jdk.boot.class.path.append", NULL, false, true);
 
   // Add to System Property list.
   PropertyList_add(&_system_properties, _sun_boot_library_path);

src/hotspot/share/runtime/arguments.hpp

@@ -109,7 +109,8 @@ class SystemProperty : public PathString {
   void set_next(SystemProperty* next) { _next = next; }
 
   bool is_readable() const {
-    return !_internal || strcmp(_key, "jdk.boot.class.path.append") == 0;
+    return !_internal || (strcmp(_key, "jdk.boot.class.path.append") == 0 &&
+                          value() != NULL);
   }
 
   // A system property should only have its value set

test/hotspot/jtreg/runtime/BootClassAppendProp/GetBootClassPathAppendProp.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2021, 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 8225093
+ * @summary Check that JVMTI GetSystemProperty API returns the right values for
+ *          property jdk.boot.class.path.append.
+ * @requires vm.jvmti
+ * @library /test/lib
+ * @run main/othervm/native -agentlib:GetBootClassPathAppendProp GetBootClassPathAppendProp
+ * @run main/othervm/native -Xbootclasspath/a:blah -agentlib:GetBootClassPathAppendProp GetBootClassPathAppendProp one_arg
+ *
+ */
+
+public class GetBootClassPathAppendProp {
+    private static native String getSystemProperty();
+
+    public static void main(String[] args) throws Exception {
+        String path = getSystemProperty();
+        if (args.length > 0) {
+            if (!path.equals("blah")) {
+                throw new RuntimeException("Wrong value returned for jdk.boot.class.path.append: " +
+                                           path);
+           }
+        } else {
+            if (path != null) {
+                throw new RuntimeException("Null value expected for jdk.boot.class.path.append: " +
+                                           path);
+            }
+        }
+    }
+}

test/hotspot/jtreg/runtime/BootClassAppendProp/libGetBootClassPathAppendProp.c

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2021, 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.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <jvmti.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static jvmtiEnv *jvmti = NULL;
+
+JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *jvm, char *options, void *reserved) {
+  int err = (*jvm)->GetEnv(jvm, (void**) &jvmti, JVMTI_VERSION_9);
+  if (err != JNI_OK) {
+    return JNI_ERR;
+  }
+  return JNI_OK;
+}
+
+JNIEXPORT jstring JNICALL
+Java_GetBootClassPathAppendProp_getSystemProperty(JNIEnv *env, jclass cls) {
+  jvmtiError err;
+  char* prop_value;
+
+  err = (*jvmti)->GetSystemProperty(jvmti, "jdk.boot.class.path.append", &prop_value);
+  if (err == JVMTI_ERROR_NOT_AVAILABLE) {
+    return NULL;
+  }
+  if (err != JVMTI_ERROR_NONE) {
+    char err_msg[50];
+    snprintf(err_msg, 50, "Wrong JVM TI error code: %d", err);
+    return (*env)->NewStringUTF(env, err_msg);
+  }
+
+  return (*env)->NewStringUTF(env, prop_value);
+}
+
+#ifdef __cplusplus
+}
+#endif