软件开发平台及语言笔记大全(超详细)

debuggerd守護進程

							<blockquote>

基於Android 6.0源碼，分析debuggerd守護進程的工作原理

/system/core/debuggerd/debuggerd.cpp /system/core/debuggerd/tombstone.cpp /system/core/debuggerd/backtrace.cpp /system/core/debuggerd/arm/Machine.cpp /system/core/debuggerd/arm64/Machine.cpp /system/core/libcutils/debugger.c /system/core/include/BacktraceMap.h /system/core/libbacktrace/BacktraceMap.cpp /system/core/libbacktrace/Backtrace.cpp

/bionic/linker/arch/arm/begin.S /bionic/linker/linker.cpp /bionic/linker/debugger.cpp

一、概述

Android系統有監控程序異常退出的機制，這便是本文要講述得debuggerd守護進程。當發生native crash或者主動調用debuggerd時，會輸出進程相關的狀態信息到文件或者控制檯。輸出的debuggerd數據保存在文件/data/tombstones/tombstone_XX，該類型文件個數上限位10個，當超過時則每次覆蓋時間最老的文件。

針對進程出現的不同的狀態，Linux kernel會發送相應的signal給異常進程，捕獲signal並對其做相應的處理（通常動作是退出異常進程）。而Android在這機制的前提下，通過攔截這些信號來dump進程信息，方便開發人員調試分析。

debuggerd守護進程會打開socket服務端，當需要調用debuggerd服務時，先通過客戶端進程向debuggerd服務端建立socket連接，然後發送不同的請求給debuggerd服務端，當服務端收到不同的請求，則會採取相應的dump操作。

接下來從源碼角度來探索debuggerd客戶端和服務端的工作原理。

二、debuggerd客戶端

   debuggerd -b <tid>
debuggerd <tid>

通過adb執行上面的命令都能觸發debuggerd進行相應的dump操作，其中參數-b表示在控制檯中輸出backtrace，參數tid表示的是需要dump的進程或者線程id。這兩個命令的輸出結果相差較大，下面來一步步分析看看這兩個命令分別能觸發哪些操作，執行上述命令都會調用debuggerd的main方法()。

2.1 main

[-> /debuggerd/debuggerd.cpp]

   int main(int argc, char** argv) {
  ...
  bool dump_backtrace = false;
  bool have_tid = false;
  pid_t tid = 0;
  //參數解析backtrace與tid信息
  for (int i = 1; i < argc; i++) {
    if (!strcmp(argv[i], "-b")) {
      dump_backtrace = true;
    } else if (!have_tid) {
      tid = atoi(argv[i]);
      have_tid = true;
    } else {
      usage();
      return 1;
    }
  }
  //沒有指定tid則直接返回
  if (!have_tid) {
    usage();
    return 1;
  }
  //【見小節2.2】
  return do_explicit_dump(tid, dump_backtrace);
}

  

對於debuggerd命令，必須指定線程tid，否則不做任何操作，直接返回。

2.2 do_explicit_dump

[-> /debuggerd/debuggerd.cpp]

static int do_explicit_dump(pid_t tid, bool dump_backtrace) {
  fprintf(stdout, "Sending request to dump task %d.\n", tid);
if (dump_backtrace) {
fflush(stdout);
//輸出到控制檯【見小節2.3】
if (dump_backtrace_to_file(tid, fileno(stdout)) < 0) {
fputs("Error dumping backtrace.\n", stderr);
return 1;
}
} else {
char tombstone_path[PATH_MAX];
//輸出到tombstone文件【見小節2.4】
if (dump_tombstone(tid, tombstone_path, sizeof(tombstone_path)) < 0) {
fputs("Error dumping tombstone.\n", stderr);
return 1;
}
fprintf(stderr, "Tombstone written to: %s\n", tombstone_path);
}
return 0;
}

dump_backtrace等於true代表的是輸出backtrace到控制檯，否則意味著輸出到tombstone文件。

2.3 dump_backtrace_to_file

[-> libcutils/debugger.c]

int dump_backtrace_to_file(pid_t tid, int fd) {
    return dump_backtrace_to_file_timeout(tid, fd, 0);
}
int dump_backtrace_to_file_timeout(pid_t tid, int fd, int timeout_secs) {
//向socket服務端發送dump backtrace的請求【見小節2.5】
int sock_fd = make_dump_request(DEBUGGER_ACTION_DUMP_BACKTRACE, tid, timeout_secs);
if (sock_fd < 0) {
return -1;
}
int result = 0;
char buffer[1024];
ssize_t n;
//阻塞等待，從sock_fd中讀取到服務端發送過來的數據，並寫入buffer
while ((n = TEMP_FAILURE_RETRY(read(sock_fd, buffer, sizeof(buffer)))) > 0) {
//再將buffer數據輸出到fd，此處是stdout文件描述符(屏幕終端)。
if (TEMP_FAILURE_RETRY(write(fd, buffer, n)) != n) {
result = -1;
break;
}
}
close(sock_fd);
return result;
}

該方法的功能：

首先，向debuggerd的socket服務端發出DEBUGGER_ACTION_DUMP_BACKTRACE請求，然後阻塞等待；
循環遍歷讀取debuggerd服務端發送過來的數據，並寫入到buffer;
再將buffer數據輸出到fd，此處是stdout文件描述符(屏幕終端)。

2.4 dump_tombstone

[-> libcutils/debugger.c]

int dump_tombstone(pid_t tid, char* pathbuf, size_t pathlen) {
  return dump_tombstone_timeout(tid, pathbuf, pathlen, 0);
}
int dump_tombstone_timeout(pid_t tid, char* pathbuf, size_t pathlen, int timeout_secs) {
//向socket服務端發送dump tombstone的請求【見小節2.5】
int sock_fd = make_dump_request(DEBUGGER_ACTION_DUMP_TOMBSTONE, tid, timeout_secs);
if (sock_fd < 0) {
return -1;
}
char buffer[100];
int result = 0; ，
//從sock_fd中讀取到服務端發送過來的tombstone文件名，並寫入buffer
ssize_t n = TEMP_FAILURE_RETRY(read(sock_fd, buffer, sizeof(buffer) - 1));
if (n <= 0) {
result = -1;
} else {
if (pathbuf && pathlen) {
if (n >= (ssize_t) pathlen) {
n = pathlen - 1;
}
buffer[n] = '\0';
//將buffer數據拷貝到pathbuf
memcpy(pathbuf, buffer, n + 1);
}
}
close(sock_fd);
return result;
}

該方法的功能：

首先，向debuggerd的socket服務端發出DEBUGGER_ACTION_DUMP_TOMBSTONE請求，然後阻塞等待；
循環遍歷讀取debuggerd服務端發送過來的tombstone文件名，並寫入到buffer;
將buffer數據拷貝到pathbuf，即拷貝tombstone文件名。

2.5 make_dump_request

[-> libcutils/debugger.c]

   static int make_dump_request(debugger_action_t action, pid_t tid, int timeout_secs) {
  debugger_msg_t msg;
  memset(&msg, 0, sizeof(msg));
  msg.tid = tid;
  msg.action = action;
  //與debuggerd服務端建立socket通信，獲取client端描述符sock_fd
  int sock_fd = socket_local_client(DEBUGGER_SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT,
      SOCK_STREAM | SOCK_CLOEXEC);
  ...
  //通過write()方法將msg信息寫入文件描述符sock_fd【見小節2.6】
  if (send_request(sock_fd, &msg, sizeof(msg)) < 0) {
    close(sock_fd);
    return -1;
  }
  return sock_fd;
}

  

該函數的功能是與debuggerd服務端建立socket通信，併發送action請求，以執行相應操作。

2.6 send_request

   static int send_request(int sock_fd, void* msg_ptr, size_t msg_len) {
  int result = 0;
  //寫入消息
  if (TEMP_FAILURE_RETRY(write(sock_fd, msg_ptr, msg_len)) != (ssize_t) msg_len) {
    result = -1;
  } else {
    char ack;
    //等待應答消息
    if (TEMP_FAILURE_RETRY(read(sock_fd, &ack, 1)) != 1) {
      result = -1;
    }
  }
  return result;
}

  

2.7 小節

通過調用debuggerd <tid>命令調用流程圖：

執行debuggerd命令最終都是調用send_request()方法，向debuggerd服務端發出DEBUGGER_ACTION_DUMP_TOMBSTONE或者DEBUGGER_ACTION_DUMP_BACKTRACE請求，那對於debuggerd服務端收到相應命令做了哪些操作呢，要想明白這個過程，接下來看看debuggerd服務端的工作。

三、debuggerd服務端

在執行debuggerd命令之前，debuggerd服務端早早就以準備就緒，時刻等待著client請求的到來。

3.1 debuggerd.rc

由init進程fork子進程來以daemon方式啟動，定義在debuggerd.rc文件（舊版本位於init.rc）

   service debuggerd /system/bin/debuggerd
    group root readproc
    writepid /dev/cpuset/system-background/tasks

  

init進程會解析上述rc文件，調用/system/bin/debuggerd文件，進入main方法，此時不帶有任何參數。接下來進入main()方法。

3.2 main

[-> /debuggerd/debuggerd.cpp]

   int main(int argc, char** argv) {
  union selinux_callback cb;
  //當參數個數為1則啟動服務
  if (argc == 1) {
    cb.func_audit = audit_callback;
    selinux_set_callback(SELINUX_CB_AUDIT, cb);
    cb.func_log = selinux_log_callback;
    selinux_set_callback(SELINUX_CB_LOG, cb);
    //【見小節3.3】
    return do_server();
  }
  ...
}

  

3.3 do_server

[-> /debuggerd/debuggerd.cpp]

static int do_server() {
  //忽略debuggerd進程自身crash的處理過程。重置所有crash handlers
  signal(SIGABRT, SIG_DFL);
  signal(SIGBUS, SIG_DFL);
  signal(SIGFPE, SIG_DFL);
  signal(SIGILL, SIG_DFL);
  signal(SIGSEGV, SIG_DFL);
#ifdef SIGSTKFLT
  signal(SIGSTKFLT, SIG_DFL);
#endif
  signal(SIGTRAP, SIG_DFL);
//忽略向已關閉socket執行寫操作失敗的信號
signal(SIGPIPE, SIG_IGN);
//阻塞SIGCHLD
sigset_t sigchld;
sigemptyset(&sigchld);
sigaddset(&sigchld, SIGCHLD);
sigprocmask(SIG_SETMASK, &sigchld, nullptr);
//建立socket通信中的服務端
int s = socket_local_server(SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT,
SOCK_STREAM | SOCK_CLOEXEC);
if (s == -1) return 1;
// Fork子進程來發送信號(同樣具有root權限)，並監聽pipe來暫停和恢復目標進程
if (!start_signal_sender()) {
ALOGE("debuggerd: failed to fork signal sender");
return 1;
}
ALOGI("debuggerd: starting\n");
for (;;) {
sockaddr_storage ss;
sockaddr* addrp = reinterpret_cast<sockaddr*>(&ss);
socklen_t alen = sizeof(ss);
//等待客戶端連接
ALOGV("waiting for connection\n");
int fd = accept4(s, addrp, &alen, SOCK_CLOEXEC);
if (fd == -1) {
ALOGE("accept failed: %s\n", strerror(errno));
continue;
}
//處理新連接的客戶端請求【見小節3.4】
handle_request(fd);
}
return 0;
}

主要功能：

忽略debuggerd進程自身crash的處理過程；
重置所有crash handlers；
建立socket通信中的服務端；
循環等待客戶端的連接，並調用handle_request處理客戶端請求。

3.4 handle_request

[-> /debuggerd/debuggerd.cpp]

static void handle_request(int fd) {
  ALOGV("handle_request(%d)\n", fd);
  android::base::unique_fd closer(fd);
  debugger_request_t request;
  memset(&request, 0, sizeof(request));
  //讀取client發送過來的請求【見小節3.5】
  int status = read_request(fd, &request);
  if (status != 0) {
    return;
  }
#if defined(LP64)
//對於32位的進程，重定向到32位debuggerd
if (is32bit(request.tid)) {
//僅僅dump backtrace和tombstone請求能重定向
if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE ||
request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
redirect_to_32(fd, &request);
}
return;
}
#endif
//fork子進程來處理其餘請求命令
pid_t fork_pid = fork();
if (fork_pid == -1) {
ALOGE("debuggerd: failed to fork: %s\n", strerror(errno));
} else if (fork_pid == 0) {
//子進程執行【見小節3.6】
worker_process(fd, request);
} else {
//父進程執行【見小節3.7】
monitor_worker_process(fork_pid, request);
}
}

3.5 read_request

[-> /debuggerd/debuggerd.cpp]

static int read_request(int fd, debugger_request_t* out_request) {
  ucred cr;
  socklen_t len = sizeof(cr);
  //從fd獲取client進程的pid,uid,gid
  int status = getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
  ...
  fcntl(fd, F_SETFL, O_NONBLOCK);
pollfd pollfds[1];
pollfds[0].fd = fd;
pollfds[0].events = POLLIN;
pollfds[0].revents = 0;
//讀取tid
status = TEMP_FAILURE_RETRY(poll(pollfds, 1, 3000));
debugger_msg_t msg;
memset(&msg, 0, sizeof(msg));
//從fd讀取數據並保存到結構體msg
status = TEMP_FAILURE_RETRY(read(fd, &msg, sizeof(msg)));
...
out_request->action = static_cast<debugger_action_t>(msg.action);
out_request->tid = msg.tid;
out_request->pid = cr.pid;
out_request->uid = cr.uid;
out_request->gid = cr.gid;
out_request->abort_msg_address = msg.abort_msg_address;
out_request->original_si_code = msg.original_si_code;
if (msg.action == DEBUGGER_ACTION_CRASH) {
// C/C++進程crash時發送過來的請求
char buf[64];
struct stat s;
snprintf(buf, sizeof buf, "/proc/%d/task/%d", out_request->pid, out_request->tid);
if (stat(buf, &s)) {
return -1;  //tid不存在，忽略該顯式dump請求
}
} else if (cr.uid == 0
|| (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
//root權限既可以可收集backtraces，又可以dump tombstones；
//system權限只允許收集backtraces;
status = get_process_info(out_request->tid, &out_request->pid,
&out_request->uid, &out_request->gid);
if (status < 0) {
return -1; //tid不存在，忽略該顯式dump請求
}
<span class="hljs-keyword">if</span> (!selinux_action_allowed(fd, out_request))
  return <span class="hljs-number">-1</span>; <span class="hljs-comment">//selinux權限不足，忽略該請求</span>

} else {
//其他情況，則直接忽略
return -1;
}
return 0;
}

該方法的功能是首先從socket獲取client進程的pid,uid,gid用於權限控制，能處理以下三種情況：

C/C++進程crash時發送過來的請求；
root權限既可以可收集backtraces，又可以dump tombstones；
system權限只允許收集backtraces。

針對這些情況若相應的tid不存在或selinux權限不滿足，則都忽略該顯式dump請求。read_request執行完成後，則從socket通道中讀取到request信息。

3.6 worker_process

處於client發送過來的請求，server端通過子進程來處理

[-> /debuggerd/debuggerd.cpp]

static void worker_process(int fd, debugger_request_t& request) {
  std::string tombstone_path;
  int tombstone_fd = -1;
  switch (request.action) {
    case DEBUGGER_ACTION_DUMP_TOMBSTONE: //case1:輸出tombstone文件
    case DEBUGGER_ACTION_CRASH: //case2:出現native crash
      //打開tombstone文件【見小節3.6.1】
      tombstone_fd = open_tombstone(&tombstone_path);
      if (tombstone_fd == -1) {
        exit(1); //無法打開tombstone文件，則退出該進程
      }
      break;
<span class="hljs-keyword">case</span> DEBUGGER_ACTION_DUMP_BACKTRACE: <span class="hljs-comment">//case3:輸出backtrace</span>
  <span class="hljs-keyword">break</span>;

<span class="hljs-keyword">default</span>:
  <span class="hljs-built_in">exit</span>(<span class="hljs-number">1</span>); <span class="hljs-comment">//其他case則直接結束進程</span>

}
// Attach到目標進程
if (ptrace(PTRACE_ATTACH, request.tid, 0, 0) != 0) {
exit(1); //attach失敗則退出該進程
}
bool attach_gdb = should_attach_gdb(request);
if (attach_gdb) {
// 在特權模式降級之前，打開所有需要監聽的input設備
if (init_getevent() != 0) {
attach_gdb = false; //初始化input設備失敗，不再等待gdb
}
}
...
//生成backtrace【見小節3.6.2】
std::unique_ptr<BacktraceMap> backtrace_map(BacktraceMap::Create(request.pid));
int amfd = -1;
std::unique_ptr<std::string> amfd_data;
if (request.action == DEBUGGER_ACTION_CRASH) {
//當發生native crash，則連接到AMS【見小節3.6.3】
amfd = activity_manager_connect();
amfd_data.reset(new std::string);
}
bool succeeded = false;
//取消特權模式
if (!drop_privileges()) {
_exit(1); //操作失敗，則退出
}
int crash_signal = SIGKILL;
//執行dump操作，【見小節3.6.4】
succeeded = perform_dump(request, fd, tombstone_fd, backtrace_map.get(), siblings,
&crash_signal, amfd_data.get());
if (succeeded) {
if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
if (!tombstone_path.empty()) {
android::base::WriteFully(fd, tombstone_path.c_str(), tombstone_path.length());
}
}
}
if (attach_gdb) {
//向目標進程發送SIGSTOP信號
if (!send_signal(request.pid, 0, SIGSTOP)) {
attach_gdb = false; //無法停止通過gdb attach的進程
}
}
if (!attach_gdb) {
//將進程crash情況告知AMS【見小節3.6.5】
activity_manager_write(request.pid, crash_signal, amfd, *amfd_data.get());
}
//detach目標進程
ptrace(PTRACE_DETACH, request.tid, 0, 0);
for (pid_t sibling : siblings) {
ptrace(PTRACE_DETACH, sibling, 0, 0);
}
if (!attach_gdb && request.action == DEBUGGER_ACTION_CRASH) {
//發送信號SIGKILL給目標進程
if (!send_signal(request.pid, request.tid, crash_signal)) {
ALOGE("debuggerd: failed to kill process %d: %s", request.pid, strerror(errno));
}
}
//如果需要則等待gdb
if (attach_gdb) {
wait_for_user_action(request);
//將進程crash情況告知AMS
activity_manager_write(request.pid, crash_signal, amfd, *amfd_data.get());
<span class="hljs-comment">//發送信號SIGCONT給目標進程</span>
<span class="hljs-keyword">if</span> (!send_signal(request.pid, <span class="hljs-number">0</span>, SIGCONT)) {
  ALOGE(<span class="hljs-string">"debuggerd: failed to resume process %d: %s"</span>, request.pid, strerror(errno));
}

uninit_getevent();

}
close(amfd);
exit(!succeeded);
}

這個流程比較長，這裡介紹attach_gdb=false的執行流程

3.6.1 open_tombstone

[-> tombstone.cpp]

int open_tombstone(std::string* out_path) {
  char path[128];
  int fd = -1;
  int oldest = -1;
  struct stat oldest_sb;
  //遍歷查找
  for (int i = 0; i < MAX_TOMBSTONES; i++) {
    snprintf(path, sizeof(path), TOMBSTONE_TEMPLATE, i);
    struct stat sb;
    if (stat(path, &sb) == 0) {
      //記錄修改時間最老的tombstone文件
      if (oldest < 0 || sb.st_mtime < oldest_sb.st_mtime) {
        oldest = i;
        oldest_sb.st_mtime = sb.st_mtime;
      }
      continue;
    }
    //存在沒有使用的tombstone文件，則打開並賦給out_path，然後直接返回
    fd = open(path, O_CREAT | O_EXCL | O_WRONLY | O_NOFOLLOW | O_CLOEXEC, 0600);
<span class="hljs-keyword">if</span> (out_path) {
  *out_path = path;
}
fchown(fd, AID_SYSTEM, AID_SYSTEM);
<span class="hljs-keyword">return</span> fd;

}
//找不到最老的可用tombstone文件，則默認使用tombstone 0
if (oldest < 0) {
oldest = 0;
}
snprintf(path, sizeof(path), TOMBSTONE_TEMPLATE, oldest);
//打開最老的tombstone文件
fd = open(path, O_CREAT | O_TRUNC | O_WRONLY | O_NOFOLLOW | O_CLOEXEC, 0600);
...
if (out_path) {
*out_path = path;
}
fchown(fd, AID_SYSTEM, AID_SYSTEM);
return fd;
}

其中TOMBSTONE_TEMPLATE為data/tombstones/tombstone_%02d，文件個數上限MAX_TOMBSTONES=10

打開tombstone文件規則：

當已使用的tombstone文件個數小於10時，則創建新的tombstone文件；否則執行2；
獲取修改時間最老的tombstone文件，並覆寫該文件；
如果最老文件不存在，則默認使用文件data/tombstones/tombstone_00

3.6.2 BacktraceMap::Create

[-> BacktraceMap.cpp]

   BacktraceMap* BacktraceMap::Create(pid_t pid, bool /*uncached*/) {
  BacktraceMap* map = new BacktraceMap(pid);
  if (!map->Build()) {
    delete map;
    return nullptr;
  }
  return map;
}

  

解析/proc/[pid]/maps, 生成BacktraceMap.

3.6.3 activity_manager_connect

[-> debuggerd.cpp]

static int activity_manager_connect() {
  android::base::unique_fd amfd(socket(PF_UNIX, SOCK_STREAM, 0));
  if (amfd.get() < -1) {
    return -1; ///無法連接到ActivityManager(socket失敗)
  }
struct sockaddr_un address;
memset(&address, 0, sizeof(address));
address.sun_family = AF_UNIX;
//該路徑必須匹配NativeCrashListener.java中的定義
strncpy(address.sun_path, "/data/system/ndebugsocket", sizeof(address.sun_path));
if (TEMP_FAILURE_RETRY(connect(amfd.get(), reinterpret_cast<struct sockaddr*>(&address),
sizeof(address))) == -1) {
return -1;  //無法連接到ActivityManager(connect失敗)
}
struct timeval tv;
memset(&tv, 0, sizeof(tv));
tv.tv_sec = 1;
if (setsockopt(amfd.get(), SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv)) == -1) {
ALOGE("debuggerd: Unable to connect to activity manager (setsockopt SO_SNDTIMEO failed: %s)",
strerror(errno));
return -1; //無法連接到ActivityManager(setsockopt SO_SNDTIMEO失敗)
}
tv.tv_sec = 3;
if (setsockopt(amfd.get(), SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)) == -1) {
ALOGE("debuggerd: Unable to connect to activity manager (setsockopt SO_RCVTIMEO failed: %s)",
strerror(errno));
return -1; //無法連接到ActivityManager(setsockopt SO_RCVTIMEO失敗)
}
return amfd.release();
}

該方法的功能是建立與ActivityManager的socket連接。

3.6.4 perform_dump

根據接收到不同的signal採取相應的操作

[-> debuggerd.cpp]

static bool perform_dump(const debugger_request_t& request, int fd, int tombstone_fd,
                         BacktraceMap* backtrace_map, const std::set<pid_t>& siblings,
                         int* crash_signal, std::string* amfd_data) {
  if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
    ALOGE("debuggerd: failed to respond to client: %s\n", strerror(errno));
    return false; //無法響應client端請求
  }
int total_sleep_time_usec = 0;
while (true) {
//等待信號到來
int signal = wait_for_signal(request.tid, &total_sleep_time_usec);
switch (signal) {
case -1:
ALOGE("debuggerd: timed out waiting for signal");
return false; //等待超時
  <span class="hljs-keyword">case</span> SIGSTOP:
    <span class="hljs-keyword">if</span> (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
      ALOGV(<span class="hljs-string">"debuggerd: stopped -- dumping to tombstone"</span>);
      <span class="hljs-comment">//【見小節4.1】</span>
      engrave_tombstone(tombstone_fd, backtrace_map, request.pid, request.tid, siblings, signal,
                        request.original_si_code, request.abort_msg_address, amfd_data);
    } <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE) {
      ALOGV(<span class="hljs-string">"debuggerd: stopped -- dumping to fd"</span>);
      <span class="hljs-comment">//【見小節4.4】</span>
      dump_backtrace(fd, backtrace_map, request.pid, request.tid, siblings, <span class="hljs-literal">nullptr</span>);
    } <span class="hljs-keyword">else</span> {
      ALOGV(<span class="hljs-string">"debuggerd: stopped -- continuing"</span>);
      <span class="hljs-keyword">if</span> (ptrace(PTRACE_CONT, request.tid, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>) != <span class="hljs-number">0</span>) {
        ALOGE(<span class="hljs-string">"debuggerd: ptrace continue failed: %s"</span>, strerror(errno));
        return <span class="hljs-literal">false</span>;
      }
      <span class="hljs-keyword">continue</span>;  <span class="hljs-comment">//再次循環</span>
    }
    <span class="hljs-keyword">break</span>;

  <span class="hljs-keyword">case</span> SIGABRT:
  <span class="hljs-keyword">case</span> SIGBUS:
  <span class="hljs-keyword">case</span> SIGFPE:
  <span class="hljs-keyword">case</span> SIGILL:
  <span class="hljs-keyword">case</span> SIGSEGV:

#ifdef SIGSTKFLT
case SIGSTKFLT:
#endif
case SIGTRAP:
ALOGV("stopped -- fatal signal\n");
*crash_signal = signal;
//【見小節4.1】
engrave_tombstone(tombstone_fd, backtrace_map, request.pid, request.tid, siblings, signal,
request.original_si_code, request.abort_msg_address, amfd_data);
break;
  <span class="hljs-keyword">default</span>:
    ALOGE(<span class="hljs-string">"debuggerd: process stopped due to unexpected signal %d\n"</span>, signal);
    <span class="hljs-keyword">break</span>;
}
<span class="hljs-keyword">break</span>;

}
return true;
}

致命信號有SIGABRT，SIGBUS，SIGFPE，SIGILL，SIGSEGV，SIGSTKFLT，SIGTRAP共7個信息，能造成native crash。

3.6.5 activity_manager_write

[-> debuggerd.cpp]

static void activity_manager_write(int pid, int signal, int amfd, const std::string& amfd_data) {
  if (amfd == -1) {
    return;
  }
//寫入32-bit pid和signal，以及原始dump信息，最後添加0以標記結束
uint32_t datum = htonl(pid);
if (!android::base::WriteFully(amfd, &datum, 4)) {
return; //AM pid寫入失敗
}
datum = htonl(signal);
if (!android::base::WriteFully(amfd, &datum, 4)) {
return;//AM signal寫入失敗
}
if (!android::base::WriteFully(amfd, amfd_data.c_str(), amfd_data.size())) {
return;//AM data寫入失敗
}
uint8_t eodMarker = 0;
if (!android::base::WriteFully(amfd, &eodMarker, 1)) {
return; //AM eod 寫入失敗
}
//讀取應答消息，如果3s超時未收到則讀取失敗
android::base::ReadFully(amfd, &eodMarker, 1);
}

3.7 monitor_worker_process

父進程處理

[-> debuggerd.cpp]

static void monitor_worker_process(int child_pid, const debugger_request_t& request) {
  struct timespec timeout = {.tv_sec = 10, .tv_nsec = 0 };
  if (should_attach_gdb(request)) {
    timeout.tv_sec = INT_MAX;
  }
sigset_t signal_set;
sigemptyset(&signal_set);
sigaddset(&signal_set, SIGCHLD);
bool kill_worker = false;
bool kill_target = false;
bool kill_self = false;
int status;
siginfo_t siginfo;
int signal = TEMP_FAILURE_RETRY(sigtimedwait(&signal_set, &siginfo, &timeout));
if (signal == SIGCHLD) {
pid_t rc = waitpid(-1, &status, WNOHANG | WUNTRACED);
if (rc != child_pid) {
ALOGE("debuggerd: waitpid returned unexpected pid (%d), committing murder-suicide", rc);
  <span class="hljs-keyword">if</span> (WIFEXITED(status)) {
    ALOGW(<span class="hljs-string">"debuggerd: pid %d exited with status %d"</span>, rc, WEXITSTATUS(status));
  } <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (WIFSIGNALED(status)) {
    ALOGW(<span class="hljs-string">"debuggerd: pid %d received signal %d"</span>, rc, WTERMSIG(status));
  } <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (WIFSTOPPED(status)) {
    ALOGW(<span class="hljs-string">"debuggerd: pid %d stopped by signal %d"</span>, rc, WSTOPSIG(status));
  } <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (WIFCONTINUED(status)) {
    ALOGW(<span class="hljs-string">"debuggerd: pid %d continued"</span>, rc);
  }

  <span class="hljs-built_in">kill</span>_worker = <span class="hljs-literal">true</span>;
  <span class="hljs-built_in">kill</span>_target = <span class="hljs-literal">true</span>;
  <span class="hljs-built_in">kill</span>_self = <span class="hljs-literal">true</span>;
} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (WIFSIGNALED(status)) {
  ALOGE(<span class="hljs-string">"debuggerd: worker process %d terminated due to signal %d"</span>, child_pid, WTERMSIG(status));
  <span class="hljs-built_in">kill</span>_worker = <span class="hljs-literal">false</span>;
  <span class="hljs-built_in">kill</span>_target = <span class="hljs-literal">true</span>;
} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (WIFSTOPPED(status)) {
  ALOGE(<span class="hljs-string">"debuggerd: worker process %d stopped due to signal %d"</span>, child_pid, WSTOPSIG(status));
  <span class="hljs-built_in">kill</span>_worker = <span class="hljs-literal">true</span>;
  <span class="hljs-built_in">kill</span>_target = <span class="hljs-literal">true</span>;
}

} else {
ALOGE("debuggerd: worker process %d timed out", child_pid);
kill_worker = true;
kill_target = true;
}
if (kill_worker) {
// Something bad happened, kill the worker.
if (kill(child_pid, SIGKILL) != 0) {
ALOGE("debuggerd: failed to kill worker process %d: %s", child_pid, strerror(errno));
} else {
waitpid(child_pid, &status, 0);
}
}
int exit_signal = SIGCONT;
if (kill_target && request.action == DEBUGGER_ACTION_CRASH) {
ALOGE("debuggerd: killing target %d", request.pid);
exit_signal = SIGKILL;
} else {
ALOGW("debuggerd: resuming target %d", request.pid);
}
if (kill(request.pid, exit_signal) != 0) {
ALOGE("debuggerd: failed to send signal %d to target: %s", exit_signal, strerror(errno));
}
if (kill_self) {
stop_signal_sender();
_exit(1);
}
}

3.8 小節

調用流程：

   debuggerd.main
    do_server
        handle_request
            read_request
                worker_process(子進程)
                monitor_worker_process(父進程)

  

整個過程的核心方法為worker_process()，其流程如下：

根據請worker_process()求中的不同action採取相應操作，除此之外則立即結束進程
- DEBUGGER_ACTION_DUMP_TOMBSTONE，則調用open_tombstone並繼續執行；
- DEBUGGER_ACTION_CRASH ，則調用open_tombstone並繼續執行；
- DEBUGGER_ACTION_DUMP_BACKTRACE，則直接繼續執行；
調用ptrace方法attach到目標進程;
調用BacktraceMap::Create來生成backtrace;
當Action=DEBUGGER_ACTION_CRASH，則執行activity_manager_connect；
調用drop_privileges來取消特權模式；
通過perform_dump執行dump操作：【見小節3.6.4】
- SIGSTOP && DEBUGGER_ACTION_DUMP_BACKTRACE，則dump_backtrace()
- SIGSTOP && DEBUGGER_ACTION_DUMP_TOMBSTONE，則engrave_tombstone()
- SIGBUS等致命信號，則engrave_tombstone()
當Action=DEBUGGER_ACTION_DUMP_TOMBSTONE，則將向client端寫入tombstone數據；
調用activity_manager_write，將進程crash情況告知AMS；
調用ptrace方法detach到目標進程;
當Action=DEBUGGER_ACTION_CRASH，發送信號SIGKILL給目標進程tid
調用exit來結束進程。

整個過程中，【見小節3.6.4】perform_dump是核心過程：對於DEBUGGER_ACTION_DUMP_BACKTRACE命令，則執行dump_backtrace；否則執行engrave_tombstone。接下來分別說說這兩個過程

四、tombstone

4.1 engrave_tombstone

[-> debuggerd/tombstone.cpp]

void engrave_tombstone(int tombstone_fd, BacktraceMap* map, pid_t pid, pid_t tid,
                       const std::set<pid_t>& siblings, int signal, int original_si_code,
                       uintptr_t abort_msg_address, std::string* amfd_data) {
  log_t log;
  log.current_tid = tid;
  log.crashed_tid = tid;
if (tombstone_fd < 0) {
ALOGE("debuggerd: skipping tombstone write, nothing to do.\n");
return;
}
log.tfd = tombstone_fd;
log.amfd_data = amfd_data;
//【見小節4.2】
dump_crash(&log, map, pid, tid, siblings, signal, original_si_code, abort_msg_address);
}

4.2 dump_crash

[-> debuggerd/tombstone.cpp]

// Dump該pid所對應進程的所有tombstone信息
static void dump_crash(log_t* log, BacktraceMap* map, pid_t pid, pid_t tid,
                       const std::set<pid_t>& siblings, int signal, int si_code,
                       uintptr_t abort_msg_address) {
  char value[PROPERTY_VALUE_MAX];
  //當ro.debuggable =1，則輸出log信息
  property_get("ro.debuggable", value, "0");
  bool want_logs = (value[0] == '1');
_LOG(log, logtype::HEADER,
"*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***\n");
//tombstone頭部信息【見小節4.3】
dump_header_info(log);
//tombstone線程信息【見小節4.4】
dump_thread(log, pid, tid, map, signal, si_code, abort_msg_address, true);
if (want_logs) {
//輸出log信息【見小節4.5】
dump_logs(log, pid, 5);
}
if (!siblings.empty()) {
for (pid_t sibling : siblings) {
//tombstone兄弟線程信息【見小節4.4】
dump_thread(log, pid, sibling, map, 0, 0, 0, false);
}
}
if (want_logs) {
dump_logs(log, pid, 0);
}
}

主要輸出信息：

dump_header_info
主線程dump_thread
dump_logs (ro.debuggable=1 才輸出此項)
兄弟線程dump_thread
dump_logs (ro.debuggable=1 才輸出此項)

4.3 dump_header_info

[-> debuggerd/tombstone.cpp]

static void dump_header_info(log_t* log) {
  char fingerprint[PROPERTY_VALUE_MAX];
  char revision[PROPERTY_VALUE_MAX];
property_get("ro.build.fingerprint", fingerprint, "unknown");
property_get("ro.revision", revision, "unknown");
_LOG(log, logtype::HEADER, "Build fingerprint: '%s'\n", fingerprint);
_LOG(log, logtype::HEADER, "Revision: '%s'\n", revision);
_LOG(log, logtype::HEADER, "ABI: '%s'\n", ABI_STRING);
}

例如：

   Build fingerprint: 'xxx/xxx/MMB29M/gityuan06080845:userdebug/test-keys'
Revision: '0'
ABI: 'arm'

  

4.4 dump_thread(主)

調用方法dump_thread(log, pid, tid, map, signal, si_code, abort_msg_address, true);

[-> debuggerd/tombstone.cpp]

static void dump_thread(log_t* log, pid_t pid, pid_t tid, BacktraceMap* map, int signal,
                        int si_code, uintptr_t abort_msg_address, bool primary_thread) {
  log->current_tid = tid;
  //【見小節4.4.1】
  dump_thread_info(log, pid, tid);
if (signal) {
//【見小節4.4.2】
dump_signal_info(log, tid, signal, si_code);
}
//【見小節3.6.2】
std::unique_ptr<Backtrace> backtrace(Backtrace::Create(pid, tid, map));
if (primary_thread) {
//【見小節4.4.3】
dump_abort_message(backtrace.get(), log, abort_msg_address);
}
//【見小節4.4.4】
dump_registers(log, tid);
if (backtrace->Unwind(0)) {
//【見小節4.4.5】
dump_backtrace_and_stack(backtrace.get(), log);
} else {
ALOGE("Unwind failed: pid = %d, tid = %d", pid, tid);
}
if (primary_thread) {
//【見小節4.4.6】
dump_memory_and_code(log, backtrace.get());
if (map) {
//【見小節4.4.7】
dump_all_maps(backtrace.get(), map, log, tid);
}
}
log->current_tid = log->crashed_tid;
}

4.4.1 dump_thread_info

static void dump_thread_info(log_t* log, pid_t pid, pid_t tid) {
  char path[64];
  char threadnamebuf[1024];
  char* threadname = nullptr;
  FILE *fp;
  //獲取/proc/<tid>/comm節點的線程名
  snprintf(path, sizeof(path), "/proc/%d/comm", tid);
  if ((fp = fopen(path, "r"))) {
    threadname = fgets(threadnamebuf, sizeof(threadnamebuf), fp);
    fclose(fp);
    if (threadname) {
      size_t len = strlen(threadname);
      if (len && threadname[len - 1] == '\n') {
        threadname[len - 1] = '\0';
      }
    }
  }
  // Blacklist logd, logd.reader, logd.writer, logd.auditd, logd.control ...
  static const char logd[] = "logd";
  if (threadname != nullptr && !strncmp(threadname, logd, sizeof(logd) - 1)
      && (!threadname[sizeof(logd) - 1] || (threadname[sizeof(logd) - 1] == '.'))) {
    log->should_retrieve_logcat = false;
  }
char procnamebuf[1024];
char* procname = nullptr;
//獲取/proc/<pid>/cmdline節點的進程名
snprintf(path, sizeof(path), "/proc/%d/cmdline", pid);
if ((fp = fopen(path, "r"))) {
procname = fgets(procnamebuf, sizeof(procnamebuf), fp);
fclose(fp);
}
_LOG(log, logtype::HEADER, "pid: %d, tid: %d, name: %s  >>> %s <<<\n", pid, tid,
threadname ? threadname : "UNKNOWN", procname ? procname : "UNKNOWN");
}

獲取進程名：/proc/<pid>/cmdline
獲取線程名：/proc/<tid>/comm

例如：

   //代表system_server進程的主線程system_server
pid: 1789, tid: 1789, name: system_server  >>> system_server <<<
//代表system_server進程的子線程ActivityManager
pid: 1789, tid: 1827, name: ActivityManager  >>> system_server <<<

  

4.4.2 dump_signal_info

static void dump_signal_info(log_t* log, pid_t tid, int signal, int si_code) {
  siginfo_t si;
  memset(&si, 0, sizeof(si));
  if (ptrace(PTRACE_GETSIGINFO, tid, 0, &si) == -1) {
    ALOGE("cannot get siginfo: %s\n", strerror(errno));
    return;
  }
si.si_code = si_code;
char addr_desc[32];
if (signal_has_si_addr(signal)) {
snprintf(addr_desc, sizeof(addr_desc), "%p", si.si_addr);
} else {
snprintf(addr_desc, sizeof(addr_desc), "--------");
}
_LOG(log, logtype::HEADER, "signal %d (%s), code %d (%s), fault addr %s\n",
signal, get_signame(signal), si.si_code, get_sigcode(signal, si.si_code), addr_desc);
}

對於SIGBUS，SIGFPE，SIGILL，SIGSEGV，SIGTRAP時觸發的dump,則會輸出fault addr的具體地址，
對於SIGSTOP時,則輸出fault addr為”——–”

例如：

   signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0xd140109c
signal 19 (SIGSTOP), code 0 (SI_USER), fault addr --------

此處get_sigcode函數功能負責根據signal以及si_code來獲取相應信息，下面來列舉每種signal所包含的信息種類：

signal	get_sigcode
SIGILL	ILL_ILLOPC
SIGILL	ILL_ILLOPN
SIGILL	ILL_ILLADR
SIGILL	ILL_ILLTRP
SIGILL	ILL_PRVOPC
SIGILL	ILL_PRVREG
SIGILL	ILL_COPROC
SIGILL	ILL_BADSTK

signal	get_sigcode
SIGBUS	BUS_ADRALN
SIGBUS	BUS_ADRERR
SIGBUS	BUS_OBJERR
SIGBUS	BUS_MCEERR_AR
SIGBUS	BUS_MCEERR_AO

signal	get_sigcode
SIGFPE	FPE_INTDIV
SIGFPE	FPE_INTOVF
SIGFPE	FPE_FLTDIV
SIGFPE	FPE_FLTOVF
SIGFPE	FPE_FLTUND
SIGFPE	FPE_FLTRES
SIGFPE	FPE_FLTINV
SIGFPE	FPE_FLTSUB

signal	get_sigcode
SIGSEGV	SEGV_MAPERR
SIGSEGV	SEGV_ACCERR
SIGSEGV	SEGV_BNDERR
SIGSEGV	SEGV_MAPERR

signal	get_sigcode
SIGTRAP	TRAP_BRKPT
SIGTRAP	TRAP_TRACE
SIGTRAP	TRAP_BRANCH
SIGTRAP	TRAP_HWBKPT

4.4.3 dump_abort_message

static void dump_abort_message(Backtrace* backtrace, log_t* log, uintptr_t address) {
  if (address == 0) {
    return;
  }
address += sizeof(size_t);  // Skip the buffer length.
char msg[512];
memset(msg, 0, sizeof(msg));
char* p = &msg[0];
while (p < &msg[sizeof(msg)]) {
word_t data;
size_t len = sizeof(word_t);
if (!backtrace->ReadWord(address, &data)) {
break;
}
address += sizeof(word_t);
<span class="hljs-keyword">while</span> (len &gt; <span class="hljs-number">0</span> &amp;&amp; (*p++ = (data &gt;&gt; (sizeof(<span class="hljs-keyword">word_t</span>) - len) * <span class="hljs-number">8</span>) &amp; <span class="hljs-number">0xff</span>) != <span class="hljs-number">0</span>) {
  len--;
}

}
msg[sizeof(msg) - 1] = '\0';
_LOG(log, logtype::HEADER, "Abort message: '%s'\n", msg);
}

4.4.4 dump_registers

輸出系統寄存器信息，這裡以arm為例來說明

[-> debuggerd/arm/Machine.cpp]

void dump_registers(log_t* log, pid_t tid) {
  pt_regs r;
  if (ptrace(PTRACE_GETREGS, tid, 0, &r)) {
    ALOGE("cannot get registers: %s\n", strerror(errno));
    return;
  }
_LOG(log, logtype::REGISTERS, "    r0 %08x  r1 %08x  r2 %08x  r3 %08x\n",
static_cast<uint32_t>(r.ARM_r0), static_cast<uint32_t>(r.ARM_r1),
static_cast<uint32_t>(r.ARM_r2), static_cast<uint32_t>(r.ARM_r3));
_LOG(log, logtype::REGISTERS, "    r4 %08x  r5 %08x  r6 %08x  r7 %08x\n",
static_cast<uint32_t>(r.ARM_r4), static_cast<uint32_t>(r.ARM_r5),
static_cast<uint32_t>(r.ARM_r6), static_cast<uint32_t>(r.ARM_r7));
_LOG(log, logtype::REGISTERS, "    r8 %08x  r9 %08x  sl %08x  fp %08x\n",
static_cast<uint32_t>(r.ARM_r8), static_cast<uint32_t>(r.ARM_r9),
static_cast<uint32_t>(r.ARM_r10), static_cast<uint32_t>(r.ARM_fp));
_LOG(log, logtype::REGISTERS, "    ip %08x  sp %08x  lr %08x  pc %08x  cpsr %08x\n",
static_cast<uint32_t>(r.ARM_ip), static_cast<uint32_t>(r.ARM_sp),
static_cast<uint32_t>(r.ARM_lr), static_cast<uint32_t>(r.ARM_pc),
static_cast<uint32_t>(r.ARM_cpsr));
user_vfp vfp_regs;
if (ptrace(PTRACE_GETVFPREGS, tid, 0, &vfp_regs)) {
ALOGE("cannot get FP registers: %s\n", strerror(errno));
return;
}
for (size_t i = 0; i < 32; i += 2) {
_LOG(log, logtype::FP_REGISTERS, "    d%-2d %016llx  d%-2d %016llx\n",
i, vfp_regs.fpregs[i], i+1, vfp_regs.fpregs[i+1]);
}
_LOG(log, logtype::FP_REGISTERS, "    scr %08lx\n", vfp_regs.fpscr);
}

通過ptrace獲取寄存器狀態信息，這裡輸出r0-r9,sl,fp,ip,sp,lr,pc,cpsr 以及32個fpregs和一個fpscr.

4.4.5 dump_backtrace_and_stack

[-> debuggerd/tombstone.cpp]

static void dump_backtrace_and_stack(Backtrace* backtrace, log_t* log) {
  if (backtrace->NumFrames()) {
    _LOG(log, logtype::BACKTRACE, "\nbacktrace:\n");
    //【見小節4.4.5.1】
    dump_backtrace_to_log(backtrace, log, "    ");
_LOG(<span class="hljs-built_in">log</span>, logtype::STACK, <span class="hljs-string">"\nstack:\n"</span>);
<span class="hljs-comment">//【見小節4.4.5.2】</span>
dump_stack(backtrace, <span class="hljs-built_in">log</span>);

}
}

4.4.5.1 輸出backtrace信息

[-> debuggerd/Backtrace.cpp]

   void dump_backtrace_to_log(Backtrace* backtrace, log_t* log, const char* prefix) {
  for (size_t i = 0; i < backtrace->NumFrames(); i++) {
    _LOG(log, logtype::BACKTRACE, "%s%s\n", prefix, backtrace->FormatFrameData(i).c_str());
  }
}

  

4.4.5.2 輸出stack信息

[-> debuggerd/tombstone.cpp]

static void dump_stack(Backtrace* backtrace, log_t* log) {
  size_t first = 0, last;
  for (size_t i = 0; i < backtrace->NumFrames(); i++) {
    const backtrace_frame_data_t* frame = backtrace->GetFrame(i);
    if (frame->sp) {
      if (!first) {
        first = i+1;
      }
      last = i;
    }
  }
  if (!first) {
    return;
  }
  first--;
// Dump a few words before the first frame.
word_t sp = backtrace->GetFrame(first)->sp - STACK_WORDS * sizeof(word_t);
dump_stack_segment(backtrace, log, &sp, STACK_WORDS, -1);
// Dump a few words from all successive frames.
// Only log the first 3 frames, put the rest in the tombstone.
for (size_t i = first; i <= last; i++) {
const backtrace_frame_data_t* frame = backtrace->GetFrame(i);
if (sp != frame->sp) {
_LOG(log, logtype::STACK, "         ........  ........\n");
sp = frame->sp;
}
if (i == last) {
dump_stack_segment(backtrace, log, &sp, STACK_WORDS, i);
if (sp < frame->sp + frame->stack_size) {
_LOG(log, logtype::STACK, "         ........  ........\n");
}
} else {
size_t words = frame->stack_size / sizeof(word_t);
if (words == 0) {
words = 1;
} else if (words > STACK_WORDS) {
words = STACK_WORDS;
}
dump_stack_segment(backtrace, log, &sp, words, i);
}
}
}

4.4.6 dump_memory_and_code

[-> debuggerd/arm/Machine.cpp]

void dump_memory_and_code(log_t* log, Backtrace* backtrace) {
  pt_regs regs;
  if (ptrace(PTRACE_GETREGS, backtrace->Tid(), 0, &regs)) {
    ALOGE("cannot get registers: %s\n", strerror(errno));
    return;
  }
static const char reg_names[] = "r0r1r2r3r4r5r6r7r8r9slfpipsp";
for (int reg = 0; reg < 14; reg++) {
dump_memory(log, backtrace, regs.uregs[reg], "memory near %.2s:", &reg_names[reg * 2]);
}
dump_memory(log, backtrace, static_cast<uintptr_t>(regs.ARM_pc), "code around pc:");
if (regs.ARM_pc != regs.ARM_lr) {
dump_memory(log, backtrace, static_cast<uintptr_t>(regs.ARM_lr), "code around lr:");
}
}

4.4.7 dump_all_maps

[-> debuggerd/tombstone.cpp]

static void dump_all_maps(Backtrace* backtrace, BacktraceMap* map, log_t* log, pid_t tid) {
  bool print_fault_address_marker = false;
  uintptr_t addr = 0;
  siginfo_t si;
  memset(&si, 0, sizeof(si));
  if (ptrace(PTRACE_GETSIGINFO, tid, 0, &si) != -1) {
    print_fault_address_marker = signal_has_si_addr(si.si_signo);
    addr = reinterpret_cast<uintptr_t>(si.si_addr);
  } else {
    ALOGE("Cannot get siginfo for %d: %s\n", tid, strerror(errno));
  }
_LOG(log, logtype::MAPS, "\n");
if (!print_fault_address_marker) {
_LOG(log, logtype::MAPS, "memory map:\n");
} else {
_LOG(log, logtype::MAPS, "memory map: (fault address prefixed with --->)\n");
if (map->begin() != map->end() && addr < map->begin()->start) {
_LOG(log, logtype::MAPS, "--->Fault address falls at %s before any mapped regions\n",
get_addr_string(addr).c_str());
print_fault_address_marker = false;
}
}
std::string line;
for (BacktraceMap::const_iterator it = map->begin(); it != map->end(); ++it) {
line = "    ";
if (print_fault_address_marker) {
if (addr < it->start) {
_LOG(log, logtype::MAPS, "--->Fault address falls at %s between mapped regions\n",
get_addr_string(addr).c_str());
print_fault_address_marker = false;
} else if (addr >= it->start && addr < it->end) {
line = "--->";
print_fault_address_marker = false;
}
}
line += get_addr_string(it->start) + '-' + get_addr_string(it->end - 1) + ' ';
if (it->flags & PROT_READ) {
line += 'r';
} else {
line += '-';
}
if (it->flags & PROT_WRITE) {
line += 'w';
} else {
line += '-';
}
if (it->flags & PROT_EXEC) {
line += 'x';
} else {
line += '-';
}
line += android::base::StringPrintf("  %8" PRIxPTR "  %8" PRIxPTR,
it->offset, it->end - it->start);
bool space_needed = true;
if (it->name.length() > 0) {
space_needed = false;
line += "  " + it->name;
std::string build_id;
if ((it->flags & PROT_READ) && elf_get_build_id(backtrace, it->start, &build_id)) {
line += " (BuildId: " + build_id + ")";
}
}
if (it->load_base != 0) {
if (space_needed) {
line += ' ';
}
line += android::base::StringPrintf(" (load base 0x%" PRIxPTR ")", it->load_base);
}
_LOG(log, logtype::MAPS, "%s\n", line.c_str());
}
if (print_fault_address_marker) {
_LOG(log, logtype::MAPS, "--->Fault address falls at %s after any mapped regions\n",
get_addr_string(addr).c_str());
}
}

當內存出現故障時，可搜索關鍵詞：

memory map: (fault address prefixed with --->)

4.5 dump_logs

[-> debuggerd/tombstone.cpp]

   static void dump_logs(log_t* log, pid_t pid, unsigned int tail) {
  dump_log_file(log, pid, "system", tail); //輸出system log
  dump_log_file(log, pid, "main", tail); //輸出main log
}

  

4.6 dump_thread(兄弟)

dump_thread(log, pid, sibling, map, 0, 0, 0, false);

[-> debuggerd/tombstone.cpp]

static void dump_thread(log_t* log, pid_t pid, pid_t tid, BacktraceMap* map, int signal,
                        int si_code, uintptr_t abort_msg_address, bool primary_thread) {
  log->current_tid = tid;
if (!primary_thread) {
_LOG(log, logtype::THREAD, "--- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---\n");
}
//【見小節4.4.1】
dump_thread_info(log, pid, tid);
std::unique_ptr<Backtrace> backtrace(Backtrace::Create(pid, tid, map));
//【見小節4.4.4】
dump_registers(log, tid);
if (backtrace->Unwind(0)) {
//【見小節4.4.5】
dump_backtrace_and_stack(backtrace.get(), log);
}
log->current_tid = log->crashed_tid;
}

兄弟線程dump_thread的輸出內容：

線程相關信息，包含pid/tid以及相應name
寄存器狀態
backtrace以及stack

4.7 小節

engrave_tombstone主要輸出信息：

dump_header_info
主線程dump_thread 【見小節4.7.1】
dump_logs (ro.debuggable=1 才輸出此項)
兄弟線程dump_thread 見小節4.7.2】
dump_logs (ro.debuggable=1 才輸出此項)

4.7.1 主線程dump_thread

build相關頭信息；
線程相關信息，包含pid/tid以及相應name
signal相關信息，包含fault address
寄存器狀態
backtrace
stack
memory near
code around
memory map

4.7.2 兄弟線程dump_thread

線程相關信息，包含pid/tid以及相應name
寄存器狀態
backtrace
stack

兄弟線程調用dump_thread也會輸出的內容其實是主線程dump的第2，4，5，6項目。

五、實例

這裡是dump_tombstone文件內容的組成：

5.1 文件頭信息

   *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
//【見小節4.3】dump_header_info
Build fingerprint: 'xxx/xxx/MMB29M/gityuan06080845:userdebug/test-keys'
Revision: '0'
ABI: 'arm'

  

5.2 主線程dump_thread

//【見小節4.4.1】dump_thread_info pid: 1789, tid: 1789, name: system_server >>> system_server <<< //【見小節4.4.2】dump_signal_info signal 19 (SIGSTOP), code 0 (SI_USER), fault addr -------- //【見小節4.4.4】dump_registers r0 fffffffc r1 bed67e68 r2 00000010 r3 0000ea60 r4 00000000 r5 00000008 r6 00000000 r7 0000015a ... //【見小節4.4.5】dump_backtrace_and_stack backtrace: #00 pc 00000000004489bc /data/dalvik-cache/arm64/system@framework@boot.oat (offset 0x3e2e000) #01 pc 00000000003e8a74 /data/dalvik-cache/arm64/system@framework@boot.oat (offset 0x3e2e000) stack: 0000007ff47b26b0 0000000012cf05e0 /dev/ashmem/dalvik-main space (deleted) 0000007ff47b26b8 0000000000000000 0000007ff47b26c0 0000000012cf05e0 /dev/ashmem/dalvik-main space (deleted) //【見小節4.4.6】dump_memory_and_code memory near r1: ... code around pc: code around lr:

//【見小節4.4.7】dump_all_maps memory map: //【見小節4.5】dump_logs

5.3 兄弟線程dump_thread

--- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
//【見小節4.4.1】dump_thread_info
pid: 1789, tid: 1803, name: Binder_1  >>> system_server <<<
//【見小節4.4.4】dump_registers
    r0 0000000b  r1 c0186201  r2 b3589868  r3 b3589860
//【見小節4.4.5】dump_backtrace_and_stack
backtrace:
    #00 pc 00040aac  /system/lib/libc.so (__ioctl+8)
    #01 pc 00047529  /system/lib/libc.so (ioctl+14)
    #02 pc 0001e909  /system/lib/libbinder.so (_ZN7android14IPCThreadState14talkWithDriverEb+132)
stack:
b3589810  00000000
b3589814  00000000
b3589818  b6ebf07c  /system/lib/libcutils.so
b358981c  b6eb4405  /system/lib/libcutils.so

所有兄弟線程是以一系列---作為開頭的分割符。

六. 總結

這裡主要以源碼角度來分析debuggerd的原理，整個過程中最重要的產物便是tombstone文件，先留坑，後續再進一步講述如何分析tombstone文件。

debuggerd -b <tid>:
發送請求的action為DEBUGGER_ACTION_DUMP_BACKTRACE，則調用dump_backtrace();Native進程之Trace原理
debuggerd <tid>: 發送請求的action為DEBUGGER_ACTION_DUMP_TOMBSTONE，則調用engrave_tombstone();
native crash: 發送請求的action為DEBUGGER_ACTION_CRASH，且發送信號為SIGBUS等致命信號，則調用engrave_tombstone()。

软件开发平台及语言笔记大全(超详细)

debuggerd守護進程

一、概述

二、debuggerd客戶端

2.1 main

2.2 do_explicit_dump

2.3 dump_backtrace_to_file

2.4 dump_tombstone

2.5 make_dump_request

2.6 send_request

2.7 小節

三、debuggerd服務端

3.1 debuggerd.rc

3.2 main

3.3 do_server

3.4 handle_request

3.5 read_request

3.6 worker_process

3.6.1 open_tombstone

3.6.2 BacktraceMap::Create

3.6.3 activity_manager_connect

3.6.4 perform_dump

3.6.5 activity_manager_write

3.7 monitor_worker_process

3.8 小節

四、tombstone

4.1 engrave_tombstone

4.2 dump_crash

4.3 dump_header_info

4.4 dump_thread(主)

4.4.1 dump_thread_info

4.4.2 dump_signal_info

4.4.3 dump_abort_message

4.4.4 dump_registers

4.4.5 dump_backtrace_and_stack

4.4.6 dump_memory_and_code

4.4.7 dump_all_maps

4.5 dump_logs

4.6 dump_thread(兄弟)

4.7 小節

4.7.1 主線程dump_thread

4.7.2 兄弟線程dump_thread

五、實例

5.1 文件頭信息

5.2 主線程dump_thread

5.3 兄弟線程dump_thread

六. 總結

雪城大学计算机与网络安全讲义

Linux命令大全搜索工具

Linux秘传心法

Redux 中文文档

Spring Framework 4.x 参考文档中文版

各种程序开发相关的Awesome开源项目清单