1/*
2 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24/*
25 * A simple way to test JVMTI ClassFileLoadHook. See ../testlibrary_tests/SimpleClassFileLoadHookTest.java
26 * for an example.
27 */
28#include <stdio.h>
29#include <stdarg.h>
30#include <stdlib.h>
31#include <string.h>
32
33#include <jvmti.h>
34#include <jni.h>
35
36static char* CLASS_NAME = NULL;
37static char* FROM = NULL;
38static char* TO = NULL;
39static jvmtiEnv *jvmti = NULL;
40static jvmtiEventCallbacks callbacks;
41
42/**
43 * For all classes whose name equals to CLASS_NAME, we replace all occurrence of FROM to TO
44 * in the classfile data. CLASS_NAME must be a binary class name.
45 *
46 * FROM is usually chosen as part of a UTF8 string in the class file. For example, if the
47 * original class file has
48 *    String getXXX() { return "theXXX";}
49 * You can set FROM=XXX, TO=YYY to rewrite the class to be
50 *    String getYYY() { return "theYYY";}
51 *
52 * Please note that the replacement is NOT limited just the UTF8 strings, but rather applies
53 * to all the bytes in the classfile. So if you pick a very short FROM string like X,
54 * it may override any POP2 bytecodes, which have the value 88 (ascii 'X').
55 *
56 * A good FROM string to use is 'cellphone', where the first 4 bytes represent the bytecode
57 * sequence DADD/LSUB/IDIV/IDIV, which does not appear in valid bytecode streams.
58 */
59void JNICALL
60ClassFileLoadHook(jvmtiEnv *jvmti_env, JNIEnv *env, jclass class_beeing_redefined,
61        jobject loader, const char* name, jobject protection_domain,
62        jint class_data_len, const unsigned char* class_data,
63        jint *new_class_data_len, unsigned char** new_class_data) {
64
65    if (name != NULL && (strcmp(name, CLASS_NAME) == 0)) {
66      size_t n = strlen(FROM);
67      unsigned char* new_data;
68
69      if ((*jvmti)->Allocate(jvmti, class_data_len, &new_data) == JNI_OK) {
70        const unsigned char* s = class_data;
71        unsigned char* d = new_data;
72        unsigned char* end = d + class_data_len;
73        int count = 0;
74
75        fprintf(stderr, "found class to be hooked: %s - rewriting ...\n", name);
76
77        while (d + n < end) {
78          if (memcmp(s, FROM, n) == 0) {
79            memcpy(d, TO, n);
80            s += n;
81            d += n;
82            count++;
83          } else {
84            *d++ = *s++;
85          }
86        }
87        while (d < end) {
88          *d++ = *s++;
89        }
90
91        *new_class_data_len = class_data_len;
92        *new_class_data = new_data;
93
94        fprintf(stderr, "Rewriting done. Replaced %d occurrence(s)\n", count);
95      }
96    }
97}
98
99static jint init_options(char *options) {
100  char* class_name;
101  char* from;
102  char* to;
103
104  fprintf(stderr, "Agent library loaded with options = %s\n", options);
105  if ((class_name = options) != NULL &&
106      (from = strchr(class_name, ',')) != NULL && (from[1] != 0)) {
107    *from = 0;
108    from++;
109    if ((to = strchr(from, ',')) != NULL && (to[1] != 0)) {
110      *to = 0;
111      to++;
112      if (strchr(to, ',') == NULL &&
113          strlen(to) == strlen(from) &&
114          strlen(class_name) > 0 &&
115          strlen(to) > 0) {
116        CLASS_NAME = strdup(class_name);
117        FROM = strdup(from);
118        TO = strdup(to);
119        fprintf(stderr, "CLASS_NAME = %s, FROM = %s, TO = %s\n",
120                CLASS_NAME, FROM, TO);
121        return JNI_OK;
122      }
123    }
124  }
125  fprintf(stderr,
126          "Incorrect options. You need to start the JVM with -agentlib:ClassFileLoadHook=<classname>,<from>,<to>\n"
127          "where <classname> is the class you want to hook, <from> is the string in the classfile to be replaced\n"
128          "with <to>.  <from> and <to> must have the same length. Example:\n"
129          "    @run main/native -agentlib:ClassFileLoadHook=Foo,XXX,YYY ClassFileLoadHookTest\n");
130  return JNI_ERR;
131}
132
133static jint Agent_Initialize(JavaVM *jvm, char *options, void *reserved) {
134  int rc;
135
136  if ((rc = (*jvm)->GetEnv(jvm, (void **)&jvmti, JVMTI_VERSION_1_1)) != JNI_OK) {
137    fprintf(stderr, "Unable to create jvmtiEnv, GetEnv failed, error = %d\n", rc);
138    return JNI_ERR;
139  }
140  if ((rc = init_options(options)) != JNI_OK) {
141    return JNI_ERR;
142  }
143
144  (void) memset(&callbacks, 0, sizeof(callbacks));
145  callbacks.ClassFileLoadHook = &ClassFileLoadHook;
146  if ((rc = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks))) != JNI_OK) {
147    fprintf(stderr, "SetEventCallbacks failed, error = %d\n", rc);
148    return JNI_ERR;
149  }
150
151  if ((rc = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
152                                               JVMTI_EVENT_CLASS_FILE_LOAD_HOOK, NULL)) != JNI_OK) {
153    fprintf(stderr, "SetEventNotificationMode failed, error = %d\n", rc);
154    return JNI_ERR;
155  }
156
157  return JNI_OK;
158}
159
160JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *jvm, char *options, void *reserved) {
161  return Agent_Initialize(jvm, options, reserved);
162}
163
164JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM *jvm, char *options, void *reserved) {
165  return Agent_Initialize(jvm, options, reserved);
166}
167