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// Copyright (C) 2018 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#include <android-base/logging.h>
#include <atomic>
#include <iomanip>
#include <iostream>
#include <istream>
#include <jni.h>
#include <jvmti.h>
#include <memory>
#include <sstream>
#include <string.h>
#include <string>
#include <vector>
namespace fieldnull {
#define CHECK_JVMTI(x) CHECK_EQ((x), JVMTI_ERROR_NONE)
// Special art ti-version number. We will use this as a fallback if we cannot get a regular JVMTI
// env.
static constexpr jint kArtTiVersion = JVMTI_VERSION_1_2 | 0x40000000;
static JavaVM* java_vm = nullptr;
// Field is "Lclass/name/here;.field_name:Lfield/type/here;"
static std::pair<jclass, jfieldID> SplitField(JNIEnv* env, const std::string& field_id) {
CHECK_EQ(field_id[0], 'L');
env->PushLocalFrame(1);
std::istringstream is(field_id);
std::string class_name;
std::string field_name;
std::string field_type;
std::getline(is, class_name, '.');
std::getline(is, field_name, ':');
std::getline(is, field_type, '\0');
jclass klass = reinterpret_cast<jclass>(
env->NewGlobalRef(env->FindClass(class_name.substr(1, class_name.size() - 2).c_str())));
jfieldID field = env->GetFieldID(klass, field_name.c_str(), field_type.c_str());
CHECK(klass != nullptr);
CHECK(field != nullptr);
LOG(INFO) << "listing field " << field_id;
env->PopLocalFrame(nullptr);
return std::make_pair(klass, field);
}
static std::vector<std::pair<jclass, jfieldID>> GetRequestedFields(JNIEnv* env,
const std::string& args) {
std::vector<std::pair<jclass, jfieldID>> res;
std::stringstream args_stream(args);
std::string item;
while (std::getline(args_stream, item, ',')) {
if (item == "") {
continue;
}
res.push_back(SplitField(env, item));
}
return res;
}
static jint SetupJvmtiEnv(JavaVM* vm, jvmtiEnv** jvmti) {
jint res = 0;
res = vm->GetEnv(reinterpret_cast<void**>(jvmti), JVMTI_VERSION_1_1);
if (res != JNI_OK || *jvmti == nullptr) {
LOG(ERROR) << "Unable to access JVMTI, error code " << res;
return vm->GetEnv(reinterpret_cast<void**>(jvmti), kArtTiVersion);
}
return res;
}
struct RequestList {
std::vector<std::pair<jclass, jfieldID>> fields_;
};
static void DataDumpRequestCb(jvmtiEnv* jvmti) {
JNIEnv* env = nullptr;
CHECK_EQ(java_vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6), JNI_OK);
LOG(INFO) << "Dumping counts of null fields.";
LOG(INFO) << "\t" << "Field name"
<< "\t" << "null count"
<< "\t" << "total count";
RequestList* list;
CHECK_JVMTI(jvmti->GetEnvironmentLocalStorage(reinterpret_cast<void**>(&list)));
for (std::pair<jclass, jfieldID>& p : list->fields_) {
jclass klass = p.first;
jfieldID field = p.second;
// Make sure all instances of the class are tagged with the klass ptr value. Since this is a
// global ref it's guaranteed to be unique.
CHECK_JVMTI(jvmti->IterateOverInstancesOfClass(
p.first,
// We need to do this to all objects every time since we might be looking for multiple
// fields in classes that are subtypes of each other.
JVMTI_HEAP_OBJECT_EITHER,
/* class_tag, size, tag_ptr, user_data*/
[](jlong, jlong, jlong* tag_ptr, void* klass) -> jvmtiIterationControl {
*tag_ptr = static_cast<jlong>(reinterpret_cast<intptr_t>(klass));
return JVMTI_ITERATION_CONTINUE;
},
klass));
jobject* obj_list;
jint obj_len;
jlong tag = static_cast<jlong>(reinterpret_cast<intptr_t>(klass));
CHECK_JVMTI(jvmti->GetObjectsWithTags(1, &tag, &obj_len, &obj_list, nullptr));
uint64_t null_cnt = 0;
for (jint i = 0; i < obj_len; i++) {
if (env->GetObjectField(obj_list[i], field) == nullptr) {
null_cnt++;
}
}
char* field_name;
char* field_sig;
char* class_name;
CHECK_JVMTI(jvmti->GetFieldName(klass, field, &field_name, &field_sig, nullptr));
CHECK_JVMTI(jvmti->GetClassSignature(klass, &class_name, nullptr));
LOG(INFO) << "\t" << class_name << "." << field_name << ":" << field_sig
<< "\t" << null_cnt
<< "\t" << obj_len;
CHECK_JVMTI(jvmti->Deallocate(reinterpret_cast<unsigned char*>(field_name)));
CHECK_JVMTI(jvmti->Deallocate(reinterpret_cast<unsigned char*>(field_sig)));
CHECK_JVMTI(jvmti->Deallocate(reinterpret_cast<unsigned char*>(class_name)));
}
}
static void VMDeathCb(jvmtiEnv* jvmti, JNIEnv* env ATTRIBUTE_UNUSED) {
DataDumpRequestCb(jvmti);
RequestList* list = nullptr;
CHECK_JVMTI(jvmti->GetEnvironmentLocalStorage(reinterpret_cast<void**>(&list)));
delete list;
}
static void CreateFieldList(jvmtiEnv* jvmti, JNIEnv* env, const std::string& args) {
RequestList* list = nullptr;
CHECK_JVMTI(jvmti->Allocate(sizeof(*list), reinterpret_cast<unsigned char**>(&list)));
new (list) RequestList { .fields_ = GetRequestedFields(env, args), };
CHECK_JVMTI(jvmti->SetEnvironmentLocalStorage(list));
}
static void VMInitCb(jvmtiEnv* jvmti, JNIEnv* env, jobject thr ATTRIBUTE_UNUSED) {
char* args = nullptr;
CHECK_JVMTI(jvmti->GetEnvironmentLocalStorage(reinterpret_cast<void**>(&args)));
CHECK_JVMTI(jvmti->SetEnvironmentLocalStorage(nullptr));
CreateFieldList(jvmti, env, args);
CHECK_JVMTI(jvmti->SetEventNotificationMode(JVMTI_ENABLE, JVMTI_EVENT_VM_DEATH, nullptr));
CHECK_JVMTI(jvmti->SetEventNotificationMode(JVMTI_ENABLE,
JVMTI_EVENT_DATA_DUMP_REQUEST,
nullptr));
CHECK_JVMTI(jvmti->Deallocate(reinterpret_cast<unsigned char*>(args)));
}
static jint AgentStart(JavaVM* vm, char* options, bool is_onload) {
android::base::InitLogging(/* argv= */nullptr);
java_vm = vm;
jvmtiEnv* jvmti = nullptr;
if (SetupJvmtiEnv(vm, &jvmti) != JNI_OK) {
LOG(ERROR) << "Could not get JVMTI env or ArtTiEnv!";
return JNI_ERR;
}
jvmtiCapabilities caps { .can_tag_objects = 1, };
CHECK_JVMTI(jvmti->AddCapabilities(&caps));
jvmtiEventCallbacks cb {
.VMInit = VMInitCb,
.VMDeath = VMDeathCb,
.DataDumpRequest = DataDumpRequestCb,
};
CHECK_JVMTI(jvmti->SetEventCallbacks(&cb, sizeof(cb)));
if (is_onload) {
unsigned char* ptr = nullptr;
CHECK_JVMTI(jvmti->Allocate(strlen(options) + 1, &ptr));
strcpy(reinterpret_cast<char*>(ptr), options);
CHECK_JVMTI(jvmti->SetEnvironmentLocalStorage(ptr));
CHECK_JVMTI(jvmti->SetEventNotificationMode(JVMTI_ENABLE, JVMTI_EVENT_VM_INIT, nullptr));
} else {
JNIEnv* env = nullptr;
CHECK_EQ(vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6), JNI_OK);
CreateFieldList(jvmti, env, options);
CHECK_JVMTI(jvmti->SetEventNotificationMode(JVMTI_ENABLE, JVMTI_EVENT_VM_DEATH, nullptr));
CHECK_JVMTI(jvmti->SetEventNotificationMode(JVMTI_ENABLE,
JVMTI_EVENT_DATA_DUMP_REQUEST,
nullptr));
}
return JNI_OK;
}
// Late attachment (e.g. 'am attach-agent').
extern "C" JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM *vm,
char* options,
void* reserved ATTRIBUTE_UNUSED) {
return AgentStart(vm, options, /*is_onload=*/false);
}
// Early attachment
extern "C" JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM* jvm,
char* options,
void* reserved ATTRIBUTE_UNUSED) {
return AgentStart(jvm, options, /*is_onload=*/true);
}
} // namespace fieldnull
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