--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/testlibrary/jvmti/libSimpleClassFileLoadHook.c	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,166 @@
+/*
+ * Copyright (c) 2016, 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.
+ */
+
+/*
+ * A simple way to test JVMTI ClassFileLoadHook. See ../testlibrary_tests/SimpleClassFileLoadHookTest.java
+ * for an example.
+ */
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <jvmti.h>
+#include <jni.h>
+
+static char* CLASS_NAME = NULL;
+static char* FROM = NULL;
+static char* TO = NULL;
+static jvmtiEnv *jvmti = NULL;
+static jvmtiEventCallbacks callbacks;
+
+/**
+ * For all classes whose name equals to CLASS_NAME, we replace all occurrence of FROM to TO
+ * in the classfile data. CLASS_NAME must be a binary class name.
+ *
+ * FROM is usually chosen as part of a UTF8 string in the class file. For example, if the
+ * original class file has
+ *    String getXXX() { return "theXXX";}
+ * You can set FROM=XXX, TO=YYY to rewrite the class to be
+ *    String getYYY() { return "theYYY";}
+ *
+ * Please note that the replacement is NOT limited just the UTF8 strings, but rather applies
+ * to all the bytes in the classfile. So if you pick a very short FROM string like X,
+ * it may override any POP2 bytecodes, which have the value 88 (ascii 'X').
+ *
+ * A good FROM string to use is 'cellphone', where the first 4 bytes represent the bytecode
+ * sequence DADD/LSUB/IDIV/IDIV, which does not appear in valid bytecode streams.
+ */
+void JNICALL
+ClassFileLoadHook(jvmtiEnv *jvmti_env, JNIEnv *env, jclass class_beeing_redefined,
+        jobject loader, const char* name, jobject protection_domain,
+        jint class_data_len, const unsigned char* class_data,
+        jint *new_class_data_len, unsigned char** new_class_data) {
+
+    if (name != NULL && (strcmp(name, CLASS_NAME) == 0)) {
+      size_t n = strlen(FROM);
+      unsigned char* new_data;
+
+      if ((*jvmti)->Allocate(jvmti, class_data_len, &new_data) == JNI_OK) {
+        const unsigned char* s = class_data;
+        unsigned char* d = new_data;
+        unsigned char* end = d + class_data_len;
+        int count = 0;
+
+        fprintf(stderr, "found class to be hooked: %s - rewriting ...\n", name);
+
+        while (d + n < end) {
+          if (memcmp(s, FROM, n) == 0) {
+            memcpy(d, TO, n);
+            s += n;
+            d += n;
+            count++;
+          } else {
+            *d++ = *s++;
+          }
+        }
+        while (d < end) {
+          *d++ = *s++;
+        }
+
+        *new_class_data_len = class_data_len;
+        *new_class_data = new_data;
+
+        fprintf(stderr, "Rewriting done. Replaced %d occurrence(s)\n", count);
+      }
+    }
+}
+
+static jint init_options(char *options) {
+  char* class_name;
+  char* from;
+  char* to;
+
+  fprintf(stderr, "Agent library loaded with options = %s\n", options);
+  if ((class_name = options) != NULL &&
+      (from = strchr(class_name, ',')) != NULL && (from[1] != 0)) {
+    *from = 0;
+    from++;
+    if ((to = strchr(from, ',')) != NULL && (to[1] != 0)) {
+      *to = 0;
+      to++;
+      if (strchr(to, ',') == NULL &&
+          strlen(to) == strlen(from) &&
+          strlen(class_name) > 0 &&
+          strlen(to) > 0) {
+        CLASS_NAME = strdup(class_name);
+        FROM = strdup(from);
+        TO = strdup(to);
+        fprintf(stderr, "CLASS_NAME = %s, FROM = %s, TO = %s\n",
+                CLASS_NAME, FROM, TO);
+        return JNI_OK;
+      }
+    }
+  }
+  fprintf(stderr,
+          "Incorrect options. You need to start the JVM with -agentlib:ClassFileLoadHook=<classname>,<from>,<to>\n"
+          "where <classname> is the class you want to hook, <from> is the string in the classfile to be replaced\n"
+          "with <to>.  <from> and <to> must have the same length. Example:\n"
+          "    @run main/native -agentlib:ClassFileLoadHook=Foo,XXX,YYY ClassFileLoadHookTest\n");
+  return JNI_ERR;
+}
+
+static jint Agent_Initialize(JavaVM *jvm, char *options, void *reserved) {
+  int rc;
+
+  if ((rc = (*jvm)->GetEnv(jvm, (void **)&jvmti, JVMTI_VERSION_1_1)) != JNI_OK) {
+    fprintf(stderr, "Unable to create jvmtiEnv, GetEnv failed, error = %d\n", rc);
+    return JNI_ERR;
+  }
+  if ((rc = init_options(options)) != JNI_OK) {
+    return JNI_ERR;
+  }
+
+  (void) memset(&callbacks, 0, sizeof(callbacks));
+  callbacks.ClassFileLoadHook = &ClassFileLoadHook;
+  if ((rc = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks))) != JNI_OK) {
+    fprintf(stderr, "SetEventCallbacks failed, error = %d\n", rc);
+    return JNI_ERR;
+  }
+
+  if ((rc = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
+                                               JVMTI_EVENT_CLASS_FILE_LOAD_HOOK, NULL)) != JNI_OK) {
+    fprintf(stderr, "SetEventNotificationMode failed, error = %d\n", rc);
+    return JNI_ERR;
+  }
+
+  return JNI_OK;
+}
+
+JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *jvm, char *options, void *reserved) {
+  return Agent_Initialize(jvm, options, reserved);
+}
+
+JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM *jvm, char *options, void *reserved) {
+  return Agent_Initialize(jvm, options, reserved);
+}