/* * 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/SimpleClassFileLoadHookTest.java * for an example. */ #include #include #include #include #include #include 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=,,\n" "where is the class you want to hook, is the string in the classfile to be replaced\n" "with . and 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); }