187 lines
6.4 KiB
C
187 lines
6.4 KiB
C
/*
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* Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* A simple way to test JVMTI ClassFileLoadHook. See ../testlibrary_tests/jvmti/SimpleClassFileLoadHookTest.java
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* for an example.
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*/
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#include <stdio.h>
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#include <stdarg.h>
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#include <stdlib.h>
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#include <string.h>
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#include <jvmti.h>
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#include <jni.h>
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static char* CLASS_NAME = NULL;
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static char* FROM = NULL;
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static char* TO = NULL;
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static jvmtiEnv *jvmti = NULL;
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static jvmtiEventCallbacks callbacks;
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/**
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* For all classes whose name equals to CLASS_NAME, we replace all occurrence of FROM to TO
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* in the classfile data. CLASS_NAME must be a binary class name.
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*
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* FROM is usually chosen as part of a UTF8 string in the class file. For example, if the
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* original class file has
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* String getXXX() { return "theXXX";}
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* You can set FROM=XXX, TO=YYY to rewrite the class to be
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* String getYYY() { return "theYYY";}
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*
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* Please note that the replacement is NOT limited just the UTF8 strings, but rather applies
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* to all the bytes in the classfile. So if you pick a very short FROM string like X,
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* it may override any POP2 bytecodes, which have the value 88 (ascii 'X').
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*
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* A good FROM string to use is 'cellphone', where the first 4 bytes represent the bytecode
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* sequence DADD/LSUB/IDIV/IDIV, which does not appear in valid bytecode streams.
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*/
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void JNICALL
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ClassFileLoadHook(jvmtiEnv *jvmti_env, JNIEnv *env, jclass class_beeing_redefined,
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jobject loader, const char* name, jobject protection_domain,
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jint class_data_len, const unsigned char* class_data,
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jint *new_class_data_len, unsigned char** new_class_data) {
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if (name != NULL && (strcmp(name, CLASS_NAME) == 0)) {
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size_t n = strlen(FROM);
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unsigned char* new_data;
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if ((*jvmti)->Allocate(jvmti, class_data_len, &new_data) == JNI_OK) {
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const unsigned char* s = class_data;
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unsigned char* d = new_data;
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unsigned char* end = d + class_data_len;
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int count = 0;
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fprintf(stderr, "found class to be hooked: %s - rewriting ...\n", name);
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while (d + n < end) {
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if (memcmp(s, FROM, n) == 0) {
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memcpy(d, TO, n);
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s += n;
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d += n;
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count++;
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} else {
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*d++ = *s++;
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}
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}
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while (d < end) {
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*d++ = *s++;
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}
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*new_class_data_len = class_data_len;
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*new_class_data = new_data;
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fprintf(stderr, "Rewriting done. Replaced %d occurrence(s) of \"%s\" to \"%s\"\n", count, FROM, TO);
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}
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}
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}
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static int early = 0;
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static jint init_options(char *options) {
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char* class_name;
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char* from;
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char* to;
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fprintf(stderr, "Agent library loaded with options = %s\n", options);
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if (options != NULL && strncmp(options, "-early,", 7) == 0) {
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early = 1;
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options += 7;
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}
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if ((class_name = options) != NULL &&
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(from = strchr(class_name, ',')) != NULL && (from[1] != 0)) {
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*from = 0;
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from++;
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if ((to = strchr(from, ',')) != NULL && (to[1] != 0)) {
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*to = 0;
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to++;
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if (strchr(to, ',') == NULL &&
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strlen(to) == strlen(from) &&
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strlen(class_name) > 0 &&
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strlen(to) > 0) {
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CLASS_NAME = strdup(class_name);
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FROM = strdup(from);
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TO = strdup(to);
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fprintf(stderr, "CLASS_NAME = %s, FROM = %s, TO = %s\n",
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CLASS_NAME, FROM, TO);
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return JNI_OK;
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}
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}
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}
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fprintf(stderr,
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"Incorrect options. You need to start the JVM with -agentlib:ClassFileLoadHook=<classname>,<from>,<to>\n"
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"where <classname> is the class you want to hook, <from> is the string in the classfile to be replaced\n"
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"with <to>. <from> and <to> must have the same length. Example:\n"
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" @run main/native -agentlib:ClassFileLoadHook=Foo,XXX,YYY ClassFileLoadHookTest\n");
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return JNI_ERR;
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}
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static jint Agent_Initialize(JavaVM *jvm, char *options, void *reserved) {
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int rc;
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jvmtiCapabilities caps;
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if ((rc = (*jvm)->GetEnv(jvm, (void **)&jvmti, JVMTI_VERSION_1_1)) != JNI_OK) {
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fprintf(stderr, "Unable to create jvmtiEnv, GetEnv failed, error = %d\n", rc);
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return JNI_ERR;
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}
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if ((rc = init_options(options)) != JNI_OK) {
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return JNI_ERR;
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}
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memset(&caps, 0, sizeof(caps));
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caps.can_redefine_classes = 1;
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if (early) {
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fprintf(stderr, "can_generate_all_class_hook_events/can_generate_early_vmstart/can_generate_early_class_hook_events == 1\n");
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caps.can_generate_all_class_hook_events = 1;
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caps.can_generate_early_class_hook_events = 1;
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}
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if ((rc = (*jvmti)->AddCapabilities(jvmti, &caps)) != JNI_OK) {
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fprintf(stderr, "AddCapabilities failed, error = %d\n", rc);
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return JNI_ERR;
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}
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(void) memset(&callbacks, 0, sizeof(callbacks));
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callbacks.ClassFileLoadHook = &ClassFileLoadHook;
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if ((rc = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, sizeof(callbacks))) != JNI_OK) {
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fprintf(stderr, "SetEventCallbacks failed, error = %d\n", rc);
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return JNI_ERR;
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}
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if ((rc = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE,
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JVMTI_EVENT_CLASS_FILE_LOAD_HOOK, NULL)) != JNI_OK) {
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fprintf(stderr, "SetEventNotificationMode failed, error = %d\n", rc);
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return JNI_ERR;
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}
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return JNI_OK;
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}
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JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *jvm, char *options, void *reserved) {
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return Agent_Initialize(jvm, options, reserved);
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}
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JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM *jvm, char *options, void *reserved) {
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return Agent_Initialize(jvm, options, reserved);
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}
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