Android P上Java Crash、Native Crash的异常处理流程学习

常见的应用闪退有Java Crash和Native Crash引起,基于最新的Android P源码,以下是其2者的异常处理流程学习:

一. Java Crash

Java代码中未被try catch捕获的异常发生时,虚拟机会调用Thread#dispatchUncaughtException方法来处理异常:

void Thread::HandleUncaughtExceptions(ScopedObjectAccessAlreadyRunnable& soa) {
    // ...

    // Call the Thread instance's dispatchUncaughtException(Throwable)
    tlsPtr_.jni_env->CallVoidMethod(peer.get(),
        WellKnownClasses::java_lang_Thread_dispatchUncaughtException,
        exception.get());
}

Thread#dispatchUncaughtException方法:

// libcore/ojluni/src/main/java/java/lang/Thread.java
public final void dispatchUncaughtException(Throwable e) {
    Thread.UncaughtExceptionHandler initialUeh =
        Thread.getUncaughtExceptionPreHandler();
    if (initialUeh != null) {
        try {
            initialUeh.uncaughtException(this, e);
        } catch (RuntimeException | Error ignored) {
            // Throwables thrown by the initial handler are ignored
        }
    }
    getUncaughtExceptionHandler().uncaughtException(this, e);
}

以上流程中,共有2个UncaughtExceptionHandler会参与处理,分别是PreHandler和Handler,核心是执行其各自实现的uncaughtException方法。

Android中提供了此二者的默认实现。Android系统中,应用进程由Zygote进程孵化而来,Zygote进程启动时,zygoteInit方法中会调用RuntimeInit.commonInit,代码如下:

// frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
/**
  * The main function called when started through the zygote process...
  */
public static final Runnable zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {
    // ...
    RuntimeInit.commonInit();
    ZygoteInit.nativeZygoteInit();
    return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}

RuntimeInit.commonInit方法中会设置默认的UncaughtExceptionHandler,代码如下:

// frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
protected static final void commonInit() {
    // ...
    /*
     * set handlers; these apply to all threads in the VM. Apps can replace
     * the default handler, but not the pre handler.
     */
    LoggingHandler loggingHandler = new LoggingHandler();
    Thread.setUncaughtExceptionPreHandler(loggingHandler);
    Thread.setDefaultUncaughtExceptionHandler(new KillApplicationHandler(loggingHandler));
    // ...
}

实例化2个对象,分别是LoggingHandler和KillApplicationHandler,均继承于Thread#UncaughtExceptionHandler,重写unCaughtException方法。其中:

  • LoggingHandler,打印异常信息,包括进程名,pid,Java栈信息等。
    1. 系统进程,日志以”*** FATAL EXCEPTION IN SYSTEM PROCESS: “开头
    2. 应用进程,日志以”FATAL EXCEPTION: “开头
  • KillApplicationHandler,检查日志是否已打印,通知AMS,杀死进程。代码如下:
@Override
public void uncaughtException(Thread t, Throwable e) {
    try {
        // 1. 确保LoggingHandler已打印出信息(Android 9.0新增)
        ensureLogging(t, e);

        // 2. 通知AMS处理异常,弹出闪退的对话框等
        ActivityManager.getService().handleApplicationCrash(
                   mApplicationObject, new ApplicationErrorReport.ParcelableCrashInfo(e));
    } catch (Throwable t2) {
        // ...
    } finally {
        // 3. 确保杀死进程
        Process.killProcess(Process.myPid()); // 本质上给自己发送Singal 9,杀死进程
        System.exit(10); // Java中关闭进程的方法,调用其结束Java虚拟机
    }
}

注意 1:

  • Android N及之前版本,只有一个UncaughtHandler类,继承自Thread.UncaughtExceptionHandler
  • Android O及之后版本,拆分为2个Handler类,分别是LoggingHandler和KillApplicationHandler,均继承于Thread#UncaughtExceptionHandler

通过查询change历史,Thread.java源代码中uncaughtExceptionPreHandler的添加,是来自Google的工程师Tobias Thierer,于2016年8月9日提交,change地址:https://android-review.googlesource.com/c/platform/libcore/+/249662
change comment:
Add a new @hide API to set an additional UncaughtExceptionHandler that is called before dispatching to the regular handler. The framework uses this to enforce logging.

注意 2:

  • Thread#setDefaultUncaughtExceptionHandler是公开API。应用可通过调用,自定义UncaughtExceptionHandler,替换掉KillApplicationHandler,这样能自定义逻辑处理掉异常,避免闪退发生。
  • Thread#setUncaughtExceptionPreHandler是hidden API。应用无法调用,不能替换LoggingHandler。
/**
 * ......
 * @hide only for use by the Android framework (RuntimeInit) b/29624607
 */
public static void setUncaughtExceptionPreHandler(UncaughtExceptionHandler eh) {
    uncaughtExceptionPreHandler = eh;
}
....
public static void setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh) {
    defaultUncaughtExceptionHandler = eh;
}

因此常出现的情况:
App运行时抛出uncaught exception后,LoggingHandler在日志中打印出了“FATAL EXCEPTION”信息,但应用已替换KillApplicationHandler,应用进程并不会退出,AMS也不会得到通知。应用仍正常运行。

注意 3:
默认情况下,uncaught exception发生后,KillApplicationHandler的方法中会执行System.exit(10)结束进程的Java虚拟机。此时,如果进程中仍有逻辑创建新线程,会抛出错误Error:Thread starting during runtime shutdown。如下:

java.lang.InternalError: Thread starting during runtime shutdown
at java.lang.Thread.nativeCreate(Native Method)
at java.lang.Thread.start(Thread.java:733)

日志中遇见此Error,建议首先查找下引发进程异常退出的真正原因。

二. Native Crash

Native异常发生时,CPU通过异常中断的方式,触发异常处理流程。Linux kernel会将中断处理,统一为信号。应用进程可以注册接收信号。

Android P,默认注册信号处理函数的代码位置是:bionic/linker/linker_main.cpp,其中调用debuggerd_init方法注册。linker_main.cpp代码如下:

// bionic/linker/linker_main.cpp
/*
 * This code is called after the linker has linked itself and
 * fixed it's own GOT. It is safe to make references to externs
 * and other non-local data at this point.
 */
static ElfW(Addr) __linker_init_post_relocation(KernelArgumentBlock& args) {
    // ...
    debuggerd_init(&callbacks);
}

debuggerd_init方法中会执行信号处理函数的注册,代码如下:

// system/core/debuggerd/handler/debuggerd_handler.cpp
void debuggerd_init(debuggerd_callbacks_t* callbacks) {
    // ...
    struct sigaction action;
    memset(&action, 0, sizeof(action));
    sigfillset(&action.sa_mask);
    action.sa_sigaction = debuggerd_signal_handler;
    action.sa_flags = SA_RESTART | SA_SIGINFO;

    // Use the alternate signal stack if available so we can catch stack overflows.
    action.sa_flags |= SA_ONSTACK;
    debuggerd_register_handlers(&action);
}

由上看出,信号处理的默认函数是debuggerd_signal_handler,那注册接收哪些信号呢?具体看debuggerd_register_handlers方法,如下:

// system/core/debuggerd/include/debuggerd/handler.h
static void __attribute__((__unused__)) debuggerd_register_handlers(struct sigaction* action) {
    sigaction(SIGABRT, action, nullptr);
    sigaction(SIGBUS, action, nullptr);
    sigaction(SIGFPE, action, nullptr);
    sigaction(SIGILL, action, nullptr);
    sigaction(SIGSEGV, action, nullptr);
    #if defined(SIGSTKFLT)
        sigaction(SIGSTKFLT, action, nullptr);
    #endif
    sigaction(SIGSYS, action, nullptr);
    sigaction(SIGTRAP, action, nullptr);
    sigaction(DEBUGGER_SIGNAL, action, nullptr);
}

通过sigaction方法,注册接收的信号有:SIGABRT,SIGBUS,SIGFPE,SIGILL,SIGSEGV,SIGSTKFLT,SIGSYS,SIGTRAP,DEBUGGER_SIGNAL,共计9个。

接下来,如果Native异常发生,处理流程如下:

  1. 应用的默认信号处理函数debuggerd_signal_handler被调用,执行线程是出问题的当前线程。其主要作用有2个,1是调用log_signal_summary方法,打印一条基本的异常信息;2是执行clone方法,创建子进程,然后debuggerd_dispatch_pseudothread方法会被调用(注意:debuggerd_dispatch_pseudothread方法执行时pid,tid不变。以下面日志为例,pid:8745,tid:8783)。如下:
// system/core/debuggerd/handler/debuggerd_handler.cpp

// Handler that does crash dumping by forking and doing the processing in the child.
// Do this by ptracing the relevant thread, and then execing debuggerd to do the actual dump.
static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void* context) {
    // ...
    // 1. 打印一条Fatal signal日志,包含基本的异常信息
    log_signal_summary(info); 
    
    // 2. clone子进程
    pid_t child_pid = 
        clone(debuggerd_dispatch_pseudothread, pseudothread_stack,
              CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID,
              &thread_info, nullptr, nullptr, &thread_info.pseudothread_tid);
    
    // Wait for the child to start...
    futex_wait(&thread_info.pseudothread_tid, -1);
    // and then wait for it to terminate.
    futex_wait(&thread_info.pseudothread_tid, child_pid);
    // ...
}

log_signal_summary方法会在日志中打印一条“Fatal signal”的异常信息。通过注释大致了解,如果后续过程失败,至少先保留一条基本的Native异常信息。例如:
03-04 17:54:46.444 10168 8745 8783 F libc : Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x74 in tid 8783 (test), pid 8745 (com.kevin.test)

内容包括:

  • 信号:如signal 11 (SIGSEGV) ——> 来自siginfo_t->si_signo,SIGSEGV字符串是由si_signo转换得到
  • 错误码:如code 1 (SEGV_MAPERR) ——> 来自siginfo_t->si_code,SEGV_MAPERR字符串是由si_signo+si_code转换得到
  • 错误地址:如fault addr 0x74 ——> 来自siginfo_t→si_addr
  • 出错的tid,线程名称:如8783 (test) ——> 通过系统调用:syscall(__NR_gettid);线程名称:通过prctl(PR_GET_NAME, reinterpret_cast<unsigned long>(thread_name), 0, 0, 0);
  • 出错的pid,主线程名称:如pid 8745 (com.kevin.test) ——> 通过系统调用:syscall(__NR_getpid);主线程名称:/proc/self/comm,通过当前进程读取此路径获取

另外clone方法执行时:

  • 参数1:debuggerd_dispatch_pseudothread ——> 子进程执行的函数
  • 参数2:pseudothread_stack ——> 为子进程分配系统堆栈的指针
  • 参数3:CLONE_THREAD ——> Linux 2.4中增加以支持POSIX线程标准,子进程与父进程共享相同的线程群
  • 参数3:CLONE_SIGHAND ——> 子进程与父进程共享相同的信号处理(signal handler)表
  • 参数3:CLONE_VM ——> 子进程与父进程运行于相同的内存空间
  • 参数3:CLONE_CHILD_SETTID ——> Writes the PID of the child into the User Mode variable of the child pointed to by thectid parameter
  • 参数3:CLONE_CHILD_CLEARTID ——> When set, the kernel sets up a mechanism to be triggered when the child process will exit or when it will start executing a new program. In these cases, the kernel will clear the User Mode variable pointed to by the ctid parameter and will awaken any process waiting for this event
  • 参数4:thread_info ——> 传递给debuggerd_dispatch_pseudothread方法的参数Args

注意:debuggerd_signal_handler方法中执行到clone后,调用futex_wait等待debuggerd_dispatch_pseudothread方法执行完成后,继续跑完剩余逻辑。然后针对这次Native Crash,debuggerd完成使命。

  1. 子进程clone出后,会执行debuggerd_dispatch_pseudothread方法,其主要作用是通过execle函数,执行/system/bin/crash_dump32或/system/bin/crash_dump64程序,并传入相关参数,包括:
    • main_tid:发生Native Crash的线程id(目标进程)
    • pseudothread_tid:初步从代码看,与获取backtrace有关,后续更多调研
    • debuggerd_dump_type:共有4种dump类型,发生Native Crash时的类型是kDebuggerdTombstone
static int debuggerd_dispatch_pseudothread(void* arg) {
    // 注意:会先执行一次clone,__fork函数这里的实现是:clone(nullptr, nullptr, 0, nullptr);
    // 这句执行完后,一个新进程会继续执行,新的pid(未来crash_dump的执行进程)
    pid_t crash_dump_pid = __fork();   

    execle(CRASH_DUMP_PATH, CRASH_DUMP_NAME, main_tid, pseudothread_tid, debuggerd_dump_type, nullptr, nullptr);
    // ...
}

一直等到crash_dump应用执行完成后,debuggerd_dispatch_pseudothread的原流程会继续执行(如上面日志例子,pid:8745,tid:8783),然后如上面所说:debuggerd_signal_handler继续执行完成。

  1. /system/bin/crash_dump64的main方法会执行,代码位置:system/core/debuggerd/crash_dump.cpp,这里可以说是Native Crash异常处理的核心代码,其主要作用是:
    • main方法执行时,先调用DefuseSignalHandlers方法,其本质是调用debuggerd_register_handlers方法,给crash_dump64进程注册空signal action,避免自己发生Native异常时,dump自己
      注意:crash_dump64进程的main方法执行前,该进程的debuggerd_init方法会先被调用,完成一系列signal的注册,因此需要解除注册

    • 调用一次fork函数,fork crash_dump64的当前进程,然后新进程会在main方法里从fork调用处继续执行下去。以下逻辑是新crash_dump64进程所做的事

    • 解析传入的参数,包括发生Native Crash的目标线程id,目标进程名等。并调用GetProcessTids方法获取目标进程的所有线程id集合

    • 通过ptrace attach到应用(看源码这里循环ptrace到应用的每条子线程,针对发生Native Crash的线程会调用ReadCrashInfo方法),读取应用的寄存器等信息,最终汇总所有异常信息,包括机型版本,ABI,信号,寄存器,backtrace等,在日志中输出
      注意:

      • a. 循环目标进程的线程集合时,针对每一个线程,先调用ptrace_seize_thread方法(本质是ptrace到线程,即ptrace(PTRACE_SEIZE, tid, 0, flags),并同时验证此线程,是否还所属于目标进程),再调用ptrace(PTRACE_INTERRUPT, tid, 0, 0),接着针对目标线程,会调用ReadCrashInfo方法读取异常信息,其他子线程,会获取其寄存器信息
      • b. 目标进程的所有线程,调用ptrace(PTRACE_DETACH, tid, 0, resume_signal),以便detach
    • 通过Socket通知tombstoned进程(系统常驻进程),传输异常信息,由tombstoned进程将所有异常信息输出到/data/tombstones/tombstone_xx文件中
      注意:

      • a. tombstoned进程共计监听3个端口,socket name分别是:tombstoned_crash,tombstoned_java_trace,tombstoned_intercept。用于不同的功能,这里我们crash_dump64进程与tombstoned进程用到的socket name是:tombstoned_crash。相关代码位置:system/core/debuggerd/tombstoned/tombstoned.cpp。如下图: 《Android P上Java Crash、Native Crash的异常处理流程学习》

      • b. crash_dump64进程与tombstoned进程建立Socket通信后,crash_dump64进程调用核心的engrave_tombstone方法,来汇总与格式化所有异常信息,打印在日志中,并通过Socket传输给tombstoned进程。所有异常信息包括(备注:不包括输出至tombstone文件的信息,其信息会更多,涉及其他子线程,内存等):

        • Header信息,分别从ro.build.fingerprint,ro.revision,ABI_STRING中读取,如下:

        03-04 17:54:46.581 10168 8792 8792 F DEBUG : Build fingerprint: ‘Xiaomi/perseus/perseus:9/PKQ1.180729.001/1.1.1:userdebug/test-keys’
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : Revision: ‘0’
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : ABI: ‘arm64’

        • 线程信息,信息前面已获得,如下:

        03-04 17:54:46.581 10168 8792 8792 F DEBUG : pid: 8745, tid: 8783, name: test >>> com.kevin.test <<<

        • Signal异常信息,包括信号,错误码,错误地址,可能的错误原因(根据信号+错误地址匹配得到,详见方法:dump_probable_cause),如下:

        03-04 17:54:46.581 10168 8792 8792 F DEBUG : signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x74
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : Cause: null pointer dereference

        • 异常线程的寄存器信息,前面通过ptrace获取,保存在数据结构std::map<pid_t, ThreadInfo> thread_info中,如下:

        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x0 0000000000000074 x1 0000006ffd44976c x2 000000709a531212 x3 0000000000000010
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x4 0000000000000074 x5 000000007fffffff x6 0000000000000002 x7 0000000000000030
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x8 0101010101010101 x9 000000709a4f1d7f x10 0000000000000002 x11 0000006ffd59b90d
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x12 0000006ffd59bea8 x13 0000000000000006 x14 0000000000000000 x15 0000006ffd59be98
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x16 000000709a52f0f8 x17 000000709a45e4d0 x18 0000000000000001 x19 0000006ffd59bec0
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x20 000000008000002f x21 000000709a531212 x22 0000000000000006 x23 0000006ffd59be90
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x24 0000000000000000 x25 0000006ffd59d588 x26 000000000ccccccc x27 0000006ffd59bea8
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : x28 0000006ffd449774 x29 0000006ffd59be80
        03-04 17:54:46.581 10168 8792 8792 F DEBUG : sp 0000006ffd59b700 lr 000000709a49f37c pc 000000709a45e4e0

        • backtrace信息,获取过程稍有点复杂,与debuggerd_signal_handler方法中第一次clone时返回的child_pid有关,经过crash_dump.cpp中wait_for_vm_process方法,获取vim_pid,传递给system/core/libbacktrace/BacktraceMap.cpp类处理,获取backtrace等信息。如下:

        03-04 17:54:46.611 10168 8792 8792 F DEBUG : backtrace:
        03-04 17:54:46.611 10168 8792 8792 F DEBUG : #00 pc 000000000001e4e0 /system/lib64/libc.so (strlen+16)
        03-04 17:54:46.611 10168 8792 8792 F DEBUG : #01 pc 000000000005f378 /system/lib64/libc.so (__vfprintf+6004)
        03-04 17:54:46.611 10168 8792 8792 F DEBUG : #02 pc 000000000007d3c4 /system/lib64/libc.so (vsnprintf+164)
        03-04 17:54:46.611 10168 8792 8792 F DEBUG : #03 pc 00000000000474bc /system/lib64/libc.so (__vsnprintf_chk+72)
        03-04 17:54:46.611 10168 8792 8792 F DEBUG : #04 pc 0000000000007e38 /system/lib64/liblog.so (__android_log_print+144)
        03-04 17:54:46.611 10168 8792 8792 F DEBUG : #05 pc 00000000000006e8 /data/app/com.kevin.test-8raHGHng-dnI7-DiURmk1w==/lib/arm64/libtest-jni.so (Java_com_kevin_test_TestJni_getStringFromNativeMethod+124)
        03-04 17:54:46.611 10168 8792 8792 F DEBUG : #06 pc 00000000005659e0 /system/lib64/libart.so (art_quick_generic_jni_trampoline+144)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #07 pc 000000000055cc4c /system/lib64/libart.so (art_quick_invoke_static_stub+604)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #08 pc 00000000000d0540 /system/lib64/libart.so (art::ArtMethod::Invoke(art::Thread, unsigned int, unsigned int, art::JValue, char const)+232)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #09 pc 0000000000280b90 /system/lib64/libart.so (art::interpreter::ArtInterpreterToCompiledCodeBridge(art::Thread, art::ArtMethod, art::ShadowFrame, unsigned short, art::JValue)+344)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #10 pc 000000000027aba4 /system/lib64/libart.so (bool art::interpreter::DoCall<false, false>(art::ArtMethod, art::Thread, art::ShadowFrame&, art::Instruction const, unsigned short, art::JValue)+968)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #11 pc 000000000052d7e0 /system/lib64/libart.so (MterpInvokeStatic+204)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #12 pc 000000000054f194 /system/lib64/libart.so (ExecuteMterpImpl+14612)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #13 pc 0000000000112514 /dev/ashmem/dalvik-classes.dex extracted in memory from /data/app/com.kevin.test-8raHGHng-dnI7-DiURmk1w==/base.apk (deleted) (com.kevin.test.MainActivity$TestRunnable.run)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #14 pc 00000000002548a8 /system/lib64/libart.so (_ZN3art11interpreterL7ExecuteEPNS_6ThreadERKNS_20CodeItemDataAccessorERNS_11ShadowFrameENS_6JValueEb.llvm.223931584+488)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #15 pc 000000000025a39c /system/lib64/libart.so (art::interpreter::ArtInterpreterToInterpreterBridge(art::Thread, art::CodeItemDataAccessor const&, art::ShadowFrame, art::JValue)+216)
        03-04 17:54:46.612 10168 8792 8792 F DEBUG : #16 pc 000000000027ab88 /system/lib64/libart.so (bool art::interpreter::DoCall<false, false>(art::ArtMethod
        , art::Thread, art::ShadowFrame&, art::Instruction const, unsigned short, art::JValue*)+940)

        以上所有信息,在engrave_tombstone中格式化处理,组织在一起时,会同时保存在字符串amfd_data中,它会被传递给system_server进程

      • c. crash_dump64进程与tombstoned进程Socket通信时,tombstoned进程会打印2条日志记录,大家会常见到,如下:

      03-04 17:54:46.567 1058 1089 1089 I /system/bin/tombstoned: received crash request for pid 8783
      ……
      03-04 17:54:46.924 1058 1089 1089 E /system/bin/tombstoned: Tombstone written to: /data/tombstones/tombstone_01

    • 通过Socket通知System_server进程,(NativeCrashListener线程会监听socket通信),并最终调用到AMS#handleApplicationCrashInner方法(逻辑同Java Crash的处理此时保持一致)

以上逻辑,主要代码如下:

// system/core/debuggerd/crash_dump.cpp
int main(int argc, char** argv) {
    // 1. 本质是调用debuggerd_register_handlers方法,给crash_dump64进程注册空signal action,避免自己发生Native异常时,dump自己
    DefuseSignalHandlers();
 
     // 2. 调用fork
    pid_t forkpid = fork();
 
    // 3. 解析传入参数,获取目标进程所有线程等
    Initialize(argv);
    ParseArgs(argc, argv, &pseudothread_tid, &dump_type);
     
    // In order to reduce the duration that we pause the process for, we ptrace
    // the threads, fetch their registers and associated information, and then
    // fork a separate process as a snapshot of the process's address space.
    std::set<pid_t> threads;
 
    // 4. 通过ptrach attach到应用,获取异常信息
    ATRACE_NAME("ptrace");
    for (pid_t thread : threads) {
        // ...
        ThreadInfo info;
        info.pid = target_process;
        info.tid = thread;
        info.process_name = process_name;
        info.thread_name = get_thread_name(thread);
 
        if (!ptrace_interrupt(thread, &info.signo)) {
            PLOG(WARNING) << "failed to ptrace interrupt thread " << thread;
            ptrace(PTRACE_DETACH, thread, 0, 0);
            continue;
        }
 
        if (thread == g_target_thread) {
            // Read the thread's registers along with the rest of the crash info out of the pipe.kDebuggerdTombstone,
            ReadCrashInfo(input_pipe, &siginfo, &info.registers, &abort_address);
            info.siginfo = &siginfo;
            info.signo = info.siginfo->si_signo;
        } else {
            info.registers.reset(Regs::RemoteGet(thread));
            if (!info.registers) {
                PLOG(WARNING) << "failed to fetch registers for thread " << thread;
                ptrace(PTRACE_DETACH, thread, 0, 0);
                continue;
            }
        }
        // ...
    }
 
    // 5. 与tombstoned进程建立Socket通信,目的由tombstoned进程输出异常信息至/data/tombstones/tombstone_xx文件
    {
        ATRACE_NAME("tombstoned_connect");
        LOG(INFO) << "obtaining output fd from tombstoned, type: " << dump_type;
        g_tombstoned_connected =
            tombstoned_connect(g_target_thread, &g_tombstoned_socket, &g_output_fd, dump_type);
    }
 
    engrave_tombstone(std::move(g_output_fd), map.get(), process_memory.get(), thread_info, g_target_thread, abort_address, &open_files, &amfd_data);
 
 
    // 6. 通过Socket通知System_server进程,amfd_data是一个字符串类型,包含着所有已格式化的异常信息
    activity_manager_notify(target_process, signo, amfd_data);
    // ...
}

  1. 最后介绍下AMS端的处理。system_server进程中,AMS启动时,会先调用startObservingNativeCrashes方法,启动1个新线程NativeCrashListener,其作用是循环监听Socket端口(Socket Path:/data/system/ndebugsocket),接收来自debuggerd端的Native异常信息(如上面分析,对端是执行crash_dump程序的进程)。主要代码如下:
// frameworks/base/services/core/java/com/android/server/am/NativeCrashListener.java
final class NativeCrashListener extends Thread {
    // ...
    @Override
    public void run() {
        // ...
        try {
            FileDescriptor serverFd = Os.socket(AF_UNIX, SOCK_STREAM, 0);
            final UnixSocketAddress sockAddr = UnixSocketAddress.createFileSystem(
                    DEBUGGERD_SOCKET_PATH);
            Os.bind(serverFd, sockAddr);
            Os.listen(serverFd, 1);
            Os.chmod(DEBUGGERD_SOCKET_PATH, 0777);

            while (true) {
                FileDescriptor peerFd = null;
                try {
                    if (MORE_DEBUG) Slog.v(TAG, "Waiting for debuggerd connection");
                    peerFd = Os.accept(serverFd, null /* peerAddress */);
                    if (MORE_DEBUG) Slog.v(TAG, "Got debuggerd socket " + peerFd);
                    if (peerFd != null) {
                        // 
                        consumeNativeCrashData(peerFd);
                    }
             // ...
        }

每接收到一次Native异常信息后,通过consumeNativeCrashData方法,启动1个新线程,调用AcitivityManagerService#handleApplicationCrashInner方法,至此处理逻辑将与Java Crash保持一致。通知AMS,有Native Crash发生,打印日志,弹出FC闪退对话框等。

欢迎点个喜欢支持下~文中如有不正确或需完善的地方,欢迎指正,一起学习,谢谢:-)

作者:kevin song,南京市建邺区

文章历史:
2018.12.18 第一版
2019.03.08 第二版:校正,补充完善更多信息,包括Native Crash等

    原文作者:kevinsong0810
    原文地址: https://www.jianshu.com/p/f39e9265ea66
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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