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/*
* Copyright (c) 2016, 2018, 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/jvmti/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) of \"%s\" to \"%s\"\n", count, FROM, TO);
}
}
}
static int early = 0;
static jint init_options(char *options) {
char* class_name;
char* from;
char* to;
fprintf(stderr, "Agent library loaded with options = %s\n", options);
if (options != NULL && strncmp(options, "-early,", 7) == 0) {
early = 1;
options += 7;
}
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;
jvmtiCapabilities caps;
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;
}
memset(&caps, 0, sizeof(caps));
caps.can_redefine_classes = 1;
if (early) {
fprintf(stderr, "can_generate_all_class_hook_events/can_generate_early_vmstart/can_generate_early_class_hook_events == 1\n");
caps.can_generate_all_class_hook_events = 1;
caps.can_generate_early_class_hook_events = 1;
}
if ((rc = (*jvmti)->AddCapabilities(jvmti, &caps)) != JNI_OK) {
fprintf(stderr, "AddCapabilities failed, error = %d\n", rc);
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);
}
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