android crash 二 Android端线上NativeCrash收集的两种方法(下)

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上文中介绍了基于google-breakpad的NativeCrash日志收集方法的全过程，但其有个缺陷就是生成的通用SO和dmp日志比较大，对sdk大小有严格要求的APP不是很方便，且不利于收集线上用户的NativeCrash数据(需要在wifi情况下收集)。本文介绍另外一种基于linux信号处理的轻量级方法。

实现原理

基于linux信号异常处理的NativeCrash收集实现原理

上图给出了基于linux信号异常处理的Native崩溃捕获的实现原理，即当Native层代码发生崩溃崩溃时，会发送异常signal(主要有SIGILL/SIGSEGV/SIGBUS/SIGABRT/SIGSTKFLT等)，系统捕获到异常signal后，回调信号异常处理函数(需事先注册)，在异常处理函数中获取C层崩溃堆栈数据，通过JNI回调至JAVA层，进行解析、上传等操作。

注册信号处理函数如下：

int sigaction(int signum,const struct sigaction *act,struct sigaction *oldact);struct sigaction {    void (*sa_handler)(int);    void (*sa_sigaction)(int,siginfo_t *,void *);    sigset_t sa_mask;    int sa_flag;    void (*sa_restorer)(void);}

此方案的难点在于如何在信号异常处理函数中获取native崩溃堆栈数据。网上提的比较多的方法是利用libcorkscrew.so来获取，但是libcorkscrew.so在Android4.4之后废弃了。当Android版本号大于4.4时，可以采用libbacktrace.so来获取崩溃数据。
如下给出信号异常处理函数的具体实现。

void _handleNativeCrash(const char *reason, struct siginfo *siginfo,        void *sigcontext) {    LOGD("_handleNativeCrash");    JNIEnv *env = 0;    int result = javaVM->GetEnv((void **) &env, JNI_VERSION_1_6);    if (result == JNI_EDETACHED) {        LOGW("Native crash occured in a non jvm-attached thread");        result = javaVM->AttachCurrentThread(&env, NULL);    }    if (result != JNI_OK) {        LOGE("Could not attach thread to Java VM for crash reporting.\n Crash was: %s", reason);    } else if (androidversion < 21) {       init();        char lines[MAX_BACKTRACE_LINES_LENGTH] = { 0, };        if (unwind_backtrace_signal_arch != NULL && siginfo != NULL) {            LOGI("libcorkscrew.so start");            map_info_t *map_info = acquire_my_map_info_list();            backtrace_frame_t frames[256] = { 0, };            backtrace_symbol_t symbols[256] = { 0, };            const ssize_t size = unwind_backtrace_signal_arch(siginfo,                    sigcontext, map_info, frames, 0, 255);            get_backtrace_symbols(frames, size, symbols);            for (int i = 0; i < size; ++i) {                char line[MAX_BACKTRACE_LINE_LENGTH];                const char *method = symbols[i].demangled_name;                if (!method) {                    method = symbols[i].symbol_name;                }                const char *file = symbols[i].map_name;                if (!file) {                    file = "<unknown>";                }                size_t fieldWidth = (MAX_BACKTRACE_LINE_LENGTH - 80) / 2;                if (method) {                    uintptr_t pc_offset = symbols[i].relative_pc                            - symbols[i].relative_symbol_addr;                    if (pc_offset) {                        snprintf(line, MAX_BACKTRACE_LINE_LENGTH,                                "#%02d  pc %08x  %.*s (%.*s+%u)", i,                                symbols[i].relative_pc, fieldWidth, file,                                fieldWidth, method, pc_offset);                    } else {                        snprintf(line, MAX_BACKTRACE_LINE_LENGTH,                                "#%02d  pc %08x  %.*s (%.*s)", i,                                symbols[i].relative_pc, fieldWidth, file,                                fieldWidth, method);                    }                } else {                    method = "<unknown>";                    snprintf(line, MAX_BACKTRACE_LINE_LENGTH,                            "#%02d  pc %08x  %.*s", i, symbols[i].relative_pc,                            fieldWidth, file);                }                snprintf(lines, sizeof(lines), "%s \n%s", lines, line);            }            free_backtrace_symbols(symbols, size);            release_my_map_info_list(map_info);            LOGI("before call makeCrashReportMethod");            env->CallStaticVoidMethod(applicationClass, makeCrashReportMethod,            env->NewStringUTF(reason), env->NewStringUTF(lines), (jint) gettid());            LOGI("after call makeCrashReportMethod");        }    }else if(android version >= 21){      if(captureNativeCrashForAndroid5(sigcontext,reason) == -1){                    LOGI("--libbacktrace fail");       }                       }}void init(){    void * libcorkscrew = dlopen("libcorkscrew.so", RTLD_LAZY | RTLD_LOCAL);    if (libcorkscrew) {        unwind_backtrace_signal_arch = (t_unwind_backtrace_signal_arch) dlsym(                libcorkscrew, "unwind_backtrace_signal_arch");        acquire_my_map_info_list = (t_acquire_my_map_info_list) dlsym(                libcorkscrew, "acquire_my_map_info_list");        release_my_map_info_list = (t_release_my_map_info_list) dlsym(                libcorkscrew, "release_my_map_info_list");        get_backtrace_symbols = (t_get_backtrace_symbols) dlsym(libcorkscrew,                "get_backtrace_symbols");        free_backtrace_symbols = (t_free_backtrace_symbols) dlsym(libcorkscrew,                "free_backtrace_symbols");    }}int captureNativeCrashForAndroid5(const void* ctx, const char* reason){    char lines[MAX_BACKTRACE_LINES_LENGTH] = { 0, };    void* libbacktrace = dlopen( "libbacktrace.so", RTLD_LAZY |RTLD_LOCAL );    if ( !libbacktrace ){        return -1;    }    Backtrace* (*create)(int,int,void*);    *(void**)&create = dlsym( libbacktrace, "_ZN9Backtrace6CreateEiiP12BacktraceMap" );    if ( !create ){        return -1;    }    Backtrace* t = create(getpid(), 0, NULL );    if ( !t ){        return -1;    }    int ret = t->Unwind(0, (ucontext*)ctx);    if ( !ret ) {        return -1;    }    size_t count = t->NumFrames();    for ( size_t i=0; i < MAX_BACKTRACE_LINE_LENGTH; i++ ) {        std::string line = t->FormatFrameData(i);        if(line == ""){            break;        }        snprintf(lines, sizeof(lines), "%s \n%s", lines, line.c_str());    }    dumpFile(reason,lines);    return 0;}

Android.mk代码如下

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE    := nativecrashLOCAL_SRC_FILES := NativeCrashHandler.cpp LOCAL_CPPFLAGS :=  -Os -fvisibility=hidden LOCAL_CFLAGS :=  -Os -fvisibility=hidden LOCAL_CFLAGS += -Wno-psabiLOCAL_CFLAGS += -funwind-tables -gLOCAL_LDLIBS += -llog -ldl -landroid

Application.mk代码如下

APP_ABI := armeabi-v7a armeabi mips x86 APP_STL := stlport_staticAPP_OPTIM := releaseAPP_CPPFLAGS += -Wno-error=format-security

至此两种NativeCrash收集的方法介绍完毕，两种方法各有优缺点，基于google-breakpad的方法体量较大，但获取的信息较全面。基于异常信号处理方法体量小，但信息不全面，只有崩溃线程的堆栈信息，不利于定位多线程崩溃的问题。

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