Android 7.0系統原始碼下新增共享庫
今天的任務從早上搞到現在,才算完成,本來以為比較簡單,就是出一個Demo,將實際業務的邏輯封裝成so庫,放在系統層,對上層不暴露任何東西,中間就一層JNI呼叫,原本以為很簡單,但是由於自己的一個壞習慣,折騰了一天。將處理過程詳細記錄下來,同時吸取教訓,也希望能給大家帶來幫助。
JNI的封裝很簡單,程式碼就不上了,在Android7.0原始碼目錄下新增共享庫的過程,也有其他網友提到了,最重要的就是修改public.libraries.txt檔案。將自己的要新增的目標庫加到該檔案中,如下圖,可以看到該檔案存在三處,system目錄下兩處,vendor下一處,最終編譯成img檔案燒錄到手機上,分別是system/etc/public.libraries.txt、system/vendor/etc/public.libraries.txt、vendor/etc/public.libraries.txt,只有在這裡宣告過,應用才能呼叫,否則會因為名稱空間的問題導致應用層呼叫失敗。
自己先完成了業務邏輯的程式碼,然後編譯成so庫,push到手機上,但是發現一直停留在Android字樣的動畫開機介面,無法正常開機,於是開始抓log分析,正常和異常日誌分別如下:
1、正常開機日誌,可以看到,資料載入完成後,馬上會執行startSystemServer方法啟動system_server程序,相應的日誌都有出現,當system_server啟動成功後,介面也就快顯示出來了。
Line 1694: 01-03 22:23:11.820 361 361 D Zygote : begin preload
Line 1695: 01-03 22:23:11.820 361 361 I Zygote : Installing ICU cache reference pinning...
Line 1696: 01-03 22:23:11.820 361 361 I Zygote : Preloading ICU data...
Line 1867: 01-03 22:23:12.087 361 361 I Zygote : Preloading classes...
Line 1868: 01-03 22:23:12.094 361 361 W Zygote : Class not found for preloading: [Landroid.view.Display$ColorTransform;
Line 2304: 01-03 22:23:13.874 361 361 W Zygote : Class not found for preloading: android.view.Display$ColorTransform
Line 2305: 01-03 22:23:13.875 361 361 W Zygote : Class not found for preloading: android.view.Display$ColorTransform$1
Line 2347: 01-03 22:23:14.546 361 361 I Zygote : ...preloaded 4158 classes in 2459ms.
Line 2375: 01-03 22:23:14.734 361 361 I Zygote : Preloading resources...
Line 2423: 01-03 22:23:15.081 361 361 I Zygote : ...preloaded 114 resources in 347ms.
Line 2426: 01-03 22:23:15.097 361 361 I Zygote : ...preloaded 41 resources in 17ms.
Line 2439: 01-03 22:23:15.183 361 361 I Zygote : Preloading shared libraries...
Line 2444: 01-03 22:23:15.227 361 361 I Zygote : Uninstalled ICU cache reference pinning...
Line 2445: 01-03 22:23:15.239 361 361 I Zygote : Installed AndroidKeyStoreProvider in 12ms.
Line 2446: 01-03 22:23:15.264 361 361 I Zygote : Warmed up JCA providers in 26ms.
Line 2447: 01-03 22:23:15.265 361 361 D Zygote : end preload
Line 2462: 01-03 22:23:15.448 361 361 I Zygote : System server process 2252 has been created
Line 2463: 01-03 22:23:15.455 361 361 I Zygote : Accepting command socket connections
Line 10398: 01-03 22:25:40.307 2252 2574 I Zygote : Process: zygote socket opened, supported ABIS: armeabi-v7a,armeabi
2、異常開機日誌,從日誌中明顯可以看到,Zygote程序在載入完資料後,根據沒有成功啟動system_server,導致無法開機。
Line 1743: 01-03 22:16:43.383 347 347 D Zygote : begin preload
Line 1744: 01-03 22:16:43.383 347 347 I Zygote : Installing ICU cache reference pinning...
Line 1745: 01-03 22:16:43.384 347 347 I Zygote : Preloading ICU data...
Line 1914: 01-03 22:16:43.600 347 347 I Zygote : Preloading classes...
Line 1915: 01-03 22:16:43.607 347 347 W Zygote : Class not found for preloading: [Landroid.view.Display$ColorTransform;
Line 2347: 01-03 22:16:45.403 347 347 W Zygote : Class not found for preloading: android.view.Display$ColorTransform
Line 2348: 01-03 22:16:45.404 347 347 W Zygote : Class not found for preloading: android.view.Display$ColorTransform$1
Line 2376: 01-03 22:16:46.015 347 347 I Zygote : ...preloaded 4158 classes in 2414ms.
Line 2396: 01-03 22:16:46.191 347 347 I Zygote : Preloading resources...
Line 2438: 01-03 22:16:46.567 347 347 I Zygote : ...preloaded 114 resources in 375ms.
Line 2441: 01-03 22:16:46.583 347 347 I Zygote : ...preloaded 41 resources in 17ms.
Line 2472: 01-03 22:16:46.682 347 347 I Zygote : Preloading shared libraries...
Line 2477: 01-03 22:16:46.740 347 347 I Zygote : Uninstalled ICU cache reference pinning...
Line 2478: 01-03 22:16:46.757 347 347 I Zygote : Installed AndroidKeyStoreProvider in 16ms.
Line 2479: 01-03 22:16:46.780 347 347 I Zygote : Warmed up JCA providers in 24ms.
Line 2480: 01-03 22:16:46.781 347 347 D Zygote : end preload
啟動system_server的程式碼是從frameworks\base\cmds\app_process\app_main.cpp檔案中的main方法開始的,再往上就是init.rc角本了,main方法中組裝啟動引數,然後呼叫父類AndroidRuntime的start方法,程式碼如下:
int main(int argc, char* const argv[]) { if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0) { // Older kernels don't understand PR_SET_NO_NEW_PRIVS and return // EINVAL. Don't die on such kernels. if (errno != EINVAL) { LOG_ALWAYS_FATAL("PR_SET_NO_NEW_PRIVS failed: %s", strerror(errno)); return 12; } } AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv)); // Process command line arguments // ignore argv[0] argc--; argv++; // Everything up to '--' or first non '-' arg goes to the vm. // // The first argument after the VM args is the "parent dir", which // is currently unused. // // After the parent dir, we expect one or more the following internal // arguments : // // --zygote : Start in zygote mode // --start-system-server : Start the system server. // --application : Start in application (stand alone, non zygote) mode. // --nice-name : The nice name for this process. // // For non zygote starts, these arguments will be followed by // the main class name. All remaining arguments are passed to // the main method of this class. // // For zygote starts, all remaining arguments are passed to the zygote. // main function. // // Note that we must copy argument string values since we will rewrite the // entire argument block when we apply the nice name to argv0. int i; for (i = 0; i < argc; i++) { if (argv[i][0] != '-') { break; } if (argv[i][1] == '-' && argv[i][2] == 0) { ++i; // Skip --. break; } runtime.addOption(strdup(argv[i])); } // Parse runtime arguments. Stop at first unrecognized option. bool zygote = false; bool startSystemServer = false; bool application = false; String8 niceName; String8 className; ++i; // Skip unused "parent dir" argument. while (i < argc) { const char* arg = argv[i++]; if (strcmp(arg, "--zygote") == 0) { zygote = true; niceName = ZYGOTE_NICE_NAME; } else if (strcmp(arg, "--start-system-server") == 0) { startSystemServer = true; } else if (strcmp(arg, "--application") == 0) { application = true; } else if (strncmp(arg, "--nice-name=", 12) == 0) { niceName.setTo(arg + 12); } else if (strncmp(arg, "--", 2) != 0) { className.setTo(arg); break; } else { --i; break; } } Vector<String8> args; if (!className.isEmpty()) { // We're not in zygote mode, the only argument we need to pass // to RuntimeInit is the application argument. // // The Remainder of args get passed to startup class main(). Make // copies of them before we overwrite them with the process name. args.add(application ? String8("application") : String8("tool")); runtime.setClassNameAndArgs(className, argc - i, argv + i); } else { // We're in zygote mode. maybeCreateDalvikCache(); if (startSystemServer) { args.add(String8("start-system-server")); } char prop[PROP_VALUE_MAX]; if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) { LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.", ABI_LIST_PROPERTY); return 11; } String8 abiFlag("--abi-list="); abiFlag.append(prop); args.add(abiFlag); // In zygote mode, pass all remaining arguments to the zygote // main() method. for (; i < argc; ++i) { args.add(String8(argv[i])); } } if (!niceName.isEmpty()) { runtime.setArgv0(niceName.string()); set_process_name(niceName.string()); } if (zygote) { runtime.start("com.android.internal.os.ZygoteInit", args, zygote); } else if (className) { runtime.start("com.android.internal.os.RuntimeInit", args, zygote); } else { fprintf(stderr, "Error: no class name or --zygote supplied.\n"); app_usage(); LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied."); return 10; } }
這裡的runtime是一個AppRuntime型別的物件,它是AndroidRuntime的子類,start方法也是呼叫父類的,AndroidRuntime類的start方法程式碼如下:
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
ALOGD(">>>>>> START %s uid %d <<<<<<\n",
className != NULL ? className : "(unknown)", getuid());
static const String8 startSystemServer("start-system-server");
/*
* 'startSystemServer == true' means runtime is obsolete and not run from
* init.rc anymore, so we print out the boot start event here.
*/
for (size_t i = 0; i < options.size(); ++i) {
if (options[i] == startSystemServer) {
/* track our progress through the boot sequence */
const int LOG_BOOT_PROGRESS_START = 3000;
LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START, ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
}
}
const char* rootDir = getenv("ANDROID_ROOT");
if (rootDir == NULL) {
rootDir = "/system";
if (!hasDir("/system")) {
LOG_FATAL("No root directory specified, and /android does not exist.");
return;
}
setenv("ANDROID_ROOT", rootDir, 1);
}
//const char* kernelHack = getenv("LD_ASSUME_KERNEL");
//ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);
/* start the virtual machine */
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
if (startVm(&mJavaVM, &env, zygote) != 0) {
return;
}
onVmCreated(env);
/*
* Register android functions.
*/
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}
/*
* We want to call main() with a String array with arguments in it.
* At present we have two arguments, the class name and an option string.
* Create an array to hold them.
*/
jclass stringClass;
jobjectArray strArray;
jstring classNameStr;
stringClass = env->FindClass("java/lang/String");
assert(stringClass != NULL);
strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);
assert(strArray != NULL);
classNameStr = env->NewStringUTF(className);
assert(classNameStr != NULL);
env->SetObjectArrayElement(strArray, 0, classNameStr);
for (size_t i = 0; i < options.size(); ++i) {
jstring optionsStr = env->NewStringUTF(options.itemAt(i).string());
assert(optionsStr != NULL);
env->SetObjectArrayElement(strArray, i + 1, optionsStr);
}
/*
* Start VM. This thread becomes the main thread of the VM, and will
* not return until the VM exits.
*/
char* slashClassName = toSlashClassName(className);
jclass startClass = env->FindClass(slashClassName);
if (startClass == NULL) {
ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
/* keep going */
} else {
jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
"([Ljava/lang/String;)V");
if (startMeth == NULL) {
ALOGE("JavaVM unable to find main() in '%s'\n", className);
/* keep going */
} else {
env->CallStaticVoidMethod(startClass, startMeth, strArray);
#if 0
if (env->ExceptionCheck())
threadExitUncaughtException(env);
#endif
}
}
free(slashClassName);
ALOGD("Shutting down VM\n");
if (mJavaVM->DetachCurrentThread() != JNI_OK)
ALOGW("Warning: unable to detach main thread\n");
if (mJavaVM->DestroyJavaVM() != 0)
ALOGW("Warning: VM did not shut down cleanly\n");
}
這裡就是組裝引數,然後通過反射呼叫到frameworks\base\core\java\com\android\internal\os\ZygoteInit.java類的main方法,ZygoteInit類的main方法的程式碼如下:
public static void main(String argv[]) {
// Mark zygote start. This ensures that thread creation will throw
// an error.
ZygoteHooks.startZygoteNoThreadCreation();
try {
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "ZygoteInit");
RuntimeInit.enableDdms();
// Start profiling the zygote initialization.
SamplingProfilerIntegration.start();
boolean startSystemServer = false;
String socketName = "zygote";
String abiList = null;
for (int i = 1; i < argv.length; i++) {
if ("start-system-server".equals(argv[i])) {
startSystemServer = true;
} else if (argv[i].startsWith(ABI_LIST_ARG)) {
abiList = argv[i].substring(ABI_LIST_ARG.length());
} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
socketName = argv[i].substring(SOCKET_NAME_ARG.length());
} else {
throw new RuntimeException("Unknown command line argument: " + argv[i]);
}
}
if (abiList == null) {
throw new RuntimeException("No ABI list supplied.");
}
registerZygoteSocket(socketName);
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "ZygotePreload");
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
preload();
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
SystemClock.uptimeMillis());
Trace.traceEnd(Trace.TRACE_TAG_DALVIK);
// Finish profiling the zygote initialization.
SamplingProfilerIntegration.writeZygoteSnapshot();
// Do an initial gc to clean up after startup
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "PostZygoteInitGC");
gcAndFinalize();
Trace.traceEnd(Trace.TRACE_TAG_DALVIK);
Trace.traceEnd(Trace.TRACE_TAG_DALVIK);
// Disable tracing so that forked processes do not inherit stale tracing tags from
// Zygote.
Trace.setTracingEnabled(false);
// Zygote process unmounts root storage spaces.
Zygote.nativeUnmountStorageOnInit();
ZygoteHooks.stopZygoteNoThreadCreation();
if (startSystemServer) {
startSystemServer(abiList, socketName);
}
Log.i(TAG, "Accepting command socket connections");
runSelectLoop(abiList);
closeServerSocket();
} catch (MethodAndArgsCaller caller) {
caller.run();
} catch (Throwable ex) {
Log.e(TAG, "Zygote died with exception", ex);
closeServerSocket();
throw ex;
}
}
這裡和日誌上對應的就是呼叫preload()方法,它會去載入所有的類、資源、動態庫,日誌也都有列印,載入完成後,因為在app_main.cpp檔案中有封裝start-system-server引數,所以startSystemServer值為true,繼續呼叫startSystemServer(abiList, socketName)去啟動system_server,我的問題也就是在這裡產生的,於是,在這裡加日誌,發現這裡的邏輯是正常的,於是繼續往下查,到Zygote類中的forkSystemServer方法的呼叫也都是正常,但是for的方法沒有返回,fork真正的邏輯是在frameworks\base\core\jni\com_android_internal_os_Zygote.cpp檔案中的ForkAndSpecializeCommon方法中呼叫完成的,我之前的部落格中也都有提及,但是這裡往上沒辦法加日誌了,加了日誌編譯不通過,沒辦法只能往回找。
開始將自己cpp檔案中的邏輯全部刪掉,但是編譯後仍然無法正常啟動,因為我就是搞簡單Demo,所以就兩個檔案,一個cpp,一個mk,於是繼續排查mk,最終在這裡找到了答案,原來我的mk中依賴了另一個so庫,而那個so庫cpp檔案中定義了一個全域性變數,該變數在so加載入時就會構造,而構造方法中寫了部分和串列埠通訊的邏輯,然而問題出現的場景中,系統還未啟動,而且我的裝置根本沒有串列埠,導致fork無返回,部分程式碼截圖如下:
註釋掉和串列埠通訊的那行邏輯,就可以正常啟動了。看到下面Zygote已經開始fork其他程序,說明我們已經成功了,馬上鬆口氣。
問題解決了,得到什麼教訓呢?就是我們以後要實現一個功能,如果有依賴時,先從最簡單的開始,什麼都不要依賴,條件超少越好,最簡單的能實現,然後再往上加邏輯,這樣即使出問題,也比較容易排查。如果我們一開始就把業務邏輯加上去,依賴的東西比較多,那麼此時出問題的話, 排查起來方向也很多,難度就大了很多,像我這樣,如果按照前面的思路去查Zygote,估計這問題肯定把我折騰死了。
非常深刻的教訓,希望大家能有所啟發。夜深了,該休息了!!