bionic-信号量&backtrace

Bionic 简介_zhengyad123的博客-CSDN博客_bionic linux

Bionic库是Android的基础库之一，也是连接Android系统和Linux系统内核的桥梁。

bionic/libc/platform/bionic/reserved_signals.h

33  #include
34  
35  #include "macros.h"
36  
37  // Realtime signals reserved for internal use:
38  //   32 (__SIGRTMIN + 0)        POSIX timers
39  //   33 (__SIGRTMIN + 1)        libbacktrace
40  //   34 (__SIGRTMIN + 2)        libcore
41  //   35 (__SIGRTMIN + 3)        debuggerd
42  //   36 (__SIGRTMIN + 4)        platform profilers (heapprofd, traced_perf)
43  //   37 (__SIGRTMIN + 5)        coverage (libprofile-extras)
44  //   38 (__SIGRTMIN + 6)        heapprofd ART managed heap dumps
45  //   39 (__SIGRTMIN + 7)        fdtrack
46  //   40 (__SIGRTMIN + 8)        android_run_on_all_threads (bionic/pthread_internal.cpp)
47  
48  #define BIONIC_SIGNAL_POSIX_TIMERS (__SIGRTMIN + 0)
49  #define BIONIC_SIGNAL_BACKTRACE (__SIGRTMIN + 1)
50  #define BIONIC_SIGNAL_DEBUGGER (__SIGRTMIN + 3)
51  #define BIONIC_SIGNAL_PROFILER (__SIGRTMIN + 4)
52  #define BIONIC_SIGNAL_ART_PROFILER (__SIGRTMIN + 6)
53  #define BIONIC_SIGNAL_FDTRACK (__SIGRTMIN + 7)
54  #define BIONIC_SIGNAL_RUN_ON_ALL_THREADS (__SIGRTMIN + 8)
55  

栈的回溯又分为两种：APCS(ARM Procedure Call Standard)与unwind。

arm上backtrace的分析与实现原理 - 腾讯云开发者社区-腾讯云

system/unwinding/libbacktrace/BacktraceCurrent.h
20  #include
21  #include
22  
23  #include
24  
25  // The signal used to cause a thread to dump the stack.
26  #if defined(__GLIBC__)
27  // In order to run the backtrace_tests on the host, we can't use
28  // the internal real time signals used by GLIBC. To avoid this,
29  // use SIGRTMIN for the signal to dump the stack.
30  #define THREAD_SIGNAL SIGRTMIN
31  #else
32  #define THREAD_SIGNAL (__SIGRTMIN+1)
33  #endif
34  

#define SIGRTMIN (__libc_current_sigrtmin())

int __libc_current_sigrtmin() {
34    return __SIGRTMIN + __SIGRT_RESERVED;
35  }

bionic 库中__SIGRTMIN 为32 ，预留实时信号数为 __SIGRT_RESERVED ，所以 SIGRTMIN 为41

android native 层可以通过ProcessCallStack
 ProcessCallStack pcs;
                pcs.update();
                pcs.dump(fd);

再通过 system/unwinding/libbacktrace/Backtrace.cpp    里面通过 UnwindStackCurrent 获取，是通过发送 THREAD_SIGNAL  信号给到进程获取

android java 层通过Thread.getStackTrace 获取，最终
art/runtime/thread.cc    中 Thread::CreateInternalStackTrace  获取 

art 里面进程创建：

https://www.jianshu.com/p/00793196ed37

java 层对应的是 Thread (java_peer) ，对应 native 层 thread.cc (child_thread)，最终pthread_create 创建线程，内核调用clone ，art 使用 child_thread 表示线程，java 层使用java_peer表示，内核创建对应的是 new_pthread 。

void Thread::CreateNativeThread(JNIEnv* env, jobject java_peer, size_t stack_size, bool is_daemon) {

...

Thread* child_thread = new Thread(is_daemon);

pthread_t new_pthread;
 pthread_create_result = pthread_create(&new_pthread,
                                           &attr,
                                           Thread::CreateCallback,
                                           child_thread);
  

}                   

  

linux 信号处理

线程会有自己的悬挂信号队列, 并且线程组也有一个信号悬挂队列

在内核返回用户空间前一刻，内核都会检查信号队列，有信号会发起信号队列处理，主要流程如上

核心函数do_notify_resume() -> do_signal() ->handle_signal 处理用户注册的处理函数。

当然在回到用户空间处理时，需要修改调用栈，在用户空间注册函数执行完，调用sigreturn 系统调用，需要恢复到处理信号函数之前的堆栈，从而可以

kernel-4.19/arch/arm64/kernel/signal.c 

asmlinkage void do_notify_resume(struct pt_regs *regs,
909                   unsigned long thread_flags){

...

if (thread_flags & _TIF_SIGPENDING)
934                  do_signal(regs);

...

}
 

 static void do_signal(struct pt_regs *regs){

if (get_signal(&ksig)) {   //说明用户注册的信号出路函数信号
877          /*
878           * Depending on the signal settings, we may need to revert the
879           * decision to restart the system call, but skip this if a
880           * debugger has chosen to restart at a different PC.
881           */
882          if (regs->pc == restart_addr &&
883              (retval == -ERESTARTNOHAND ||
884               retval == -ERESTART_RESTARTBLOCK ||
885               (retval == -ERESTARTSYS &&
886                !(ksig.ka.sa.sa_flags & SA_RESTART)))) {
887              regs->regs[0] = -EINTR;
888              regs->pc = continue_addr;
889          }
890  
891          handle_signal(&ksig, regs); 
892          return;
893      }

....

}

init 忽略掉SIGKILL and SIGSTOP

89  static bool sig_task_ignored(struct task_struct *t, int sig, bool force)
90  {
91      void __user *handler;
92  
93      handler = sig_handler(t, sig);
94  
95      /* SIGKILL and SIGSTOP may not be sent to the global init */
96      if (unlikely(is_global_init(t) && sig_kernel_only(sig)))      
97          return true;
98  
99      if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
100          handler == SIG_DFL && !(force && sig_kernel_only(sig)))
101          return true;
102  
103      /* Only allow kernel generated signals to this kthread */
104      if (unlikely((t->flags & PF_KTHREAD) &&
105               (handler == SIG_KTHREAD_KERNEL) && !force))
106          return true;
107  
108      return sig_handler_ignored(handler, sig);
109  }

在do_signal函数中，会去判断每个被挂起的信号，如果这个信号在用户态没有设置处理函数，那么内核会按照信号的默认处理行为处理信号，如果这个信号在用户态设置了处理函数，那么需要返回用户态去调用这个函数，在内核中会在用户态的栈中插入一个调用那个处理函数的栈针，调用完用户态处理函数后返回内核态，继续do_signal函数的处理。

linux 发送信号

kernel-4.19/kernel/signal.c

# sig就是信号代码。

#  info就是发送信号的时候附加信息

#  t目标进程task_struct

#  pid_type是接受信号对象的类型 

1232  static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
1233              enum pid_type type)
1234  {
1235      int from_ancestor_ns = 0;
1236  
1237  #ifdef CONFIG_PID_NS
1238      from_ancestor_ns = si_fromuser(info) &&
1239                 !task_pid_nr_ns(current, task_active_pid_ns(t));
1240  #endif
1241  
1242      return __send_signal(sig, info, t, type, from_ancestor_ns);
1243  }

__send_signal(){

1115      if(1) {
1116  
1117          if((sig == SIGHUP || sig == 33 || sig == SIGKILL || sig == SIGSTOP || sig == SIGABRT || sig == SIGTERM || sig == SIGCONT) && is_key_process(t)) {
1118              printk("Some other process %d:%s want to send sig:%d to pid:%d tgid:%d comm:%s\n", current->pid, current->comm,sig, t->pid, t->tgid, t->comm);
1119          }
1120      }

q = __sigqueue_alloc(sig, t, GFP_ATOMIC, override_rlimit);
1160      if (q) {
1161          list_add_tail(&q->list, &pending->list);
1162          switch ((unsigned long) info) {
1163          case (unsigned long) SEND_SIG_NOINFO:   //用户空间发生的信号
1164              clear_siginfo(&q->info);
1165              q->info.si_signo = sig;
1166              q->info.si_errno = 0;
1167              q->info.si_code = SI_USER;
1168              q->info.si_pid = task_tgid_nr_ns(current,
1169                              task_active_pid_ns(t));
1170              q->info.si_uid = from_kuid_munged(current_user_ns(), current_uid());
1171              break;
1172          case (unsigned long) SEND_SIG_PRIV:
1173              clear_siginfo(&q->info);
1174              q->info.si_signo = sig;
1175              q->info.si_errno = 0;
1176              q->info.si_code = SI_KERNEL;   //内核空间发生的信号
1177              q->info.si_pid = 0;
1178              q->info.si_uid = 0;
1179              break;
1180          default:
1181              copy_siginfo(&q->info, info);
1182              if (from_ancestor_ns)
1183                  q->info.si_pid = 0;
1184              break;
1185          }
1186  
1187          userns_fixup_signal_uid(&q->info, t);
1188  
1189      }

1209      signalfd_notify(t, sig);
1210      sigaddset(&pending->signal, sig);

complete_signal(sig, t, type);

}
 

Signal Catcher

Signal Catcher线程接受到kernel系统底层的消息进行dump当前虚拟机的信息并且设置每个线程的标志位(check_point)和请求线程状态为挂起，当线程运行过程中进行上下文切换时会检查该标记。等到线程都挂起后，开始遍历Dump每个线程的堆栈和线程数据后再唤醒线程

"Signal Catcher" daemon prio=10 tid=2 Runnable
  | group="system" sCount=0 ucsCount=0 flags=0 obj=0x12d80180 self=0xb40000791080f000
  | sysTid=1678 nice=-20 cgrp=default sched=0/0 handle=0x790f7fbcb0
  | state=R schedstat=( 7676736981 897590846 13817 ) utm=496 stm=270 core=6 HZ=100
  | stack=0x790f704000-0x790f706000 stackSize=991KB
  | held mutexes= "mutator lock"(shared held)
  native: #00 pc 00000000005374cc  /apex/com.android.art/lib64/libart.so (art::DumpNativeStack(std::__1::basic_ostream >&, int, BacktraceMap*, char const*, art::ArtMethod*, void*, bool)+128) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #01 pc 00000000006f0d94  /apex/com.android.art/lib64/libart.so (art::Thread::DumpStack(std::__1::basic_ostream >&, bool, BacktraceMap*, bool) const+236) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #02 pc 00000000006fe620  /apex/com.android.art/lib64/libart.so (art::DumpCheckpoint::Run(art::Thread*)+208) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #03 pc 00000000003641d4  /apex/com.android.art/lib64/libart.so (art::ThreadList::RunCheckpoint(art::Closure*, art::Closure*)+440) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #04 pc 00000000006fcdc0  /apex/com.android.art/lib64/libart.so (art::ThreadList::Dump(std::__1::basic_ostream >&, bool)+280) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #05 pc 00000000006fc7b4  /apex/com.android.art/lib64/libart.so (art::ThreadList::DumpForSigQuit(std::__1::basic_ostream >&)+292) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #06 pc 00000000006d57e4  /apex/com.android.art/lib64/libart.so (art::Runtime::DumpForSigQuit(std::__1::basic_ostream >&)+184) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #07 pc 00000000006e1928  /apex/com.android.art/lib64/libart.so (art::SignalCatcher::HandleSigQuit()+468) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #08 pc 0000000000573c40  /apex/com.android.art/lib64/libart.so (art::SignalCatcher::Run(void*)+264) (BuildId: 97fdb979efb7d2b596fa4fceabaad95b)
  native: #09 pc 00000000000eb630  /apex/com.android.runtime/lib64/bionic/libc.so (__pthread_start(void*)+208) (BuildId: 6940bde3287fe65faab4354aae30b200)
  native: #10 pc 000000000007e210  /apex/com.android.runtime/lib64/bionic/libc.so (__start_thread+64) (BuildId: 6940bde3287fe65faab4354aae30b200)
  (no managed stack frames)

<4>[53270.460373] -(7)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1666 tgid:1666 comm:system_server
<4>[53270.472326] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1679 tgid:1666 comm:perfetto_hprof_
<4>[53270.482760] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1680 tgid:1666 comm:ADB-JDWP Connec
<4>[53270.484789] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1681 tgid:1666 comm:Jit thread pool
<4>[53270.485597] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1682 tgid:1666 comm:HeapTaskDaemon
<4>[53270.487248] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1686 tgid:1666 comm:binder:1666_1
<4>[53270.490018] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1687 tgid:1666 comm:binder:1666_2
<4>[53270.490620] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1696 tgid:1666 comm:Verification th
<4>[53270.491026] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1698 tgid:1666 comm:State
<4>[53270.491692] -(6)[1678:Signal Catcher]Some other process 1678:Signal Catcher want to send sig:33 to pid:1699 tgid:1666 comm:android.fg

art/runtime/native_stack_dump.cc

318  void DumpNativeStack(std::ostream& os,
319                       pid_t tid,
320                       BacktraceMap* existing_map,
321                       const char* prefix,
322                       ArtMethod* current_method,
323                       void* ucontext_ptr,
324                       bool skip_frames) {
325    // Historical note: This was disabled when running under Valgrind (b/18119146).
326  
327    BacktraceMap* map = existing_map;
328    std::unique_ptr tmp_map;
329    if (map == nullptr) {
330      tmp_map.reset(BacktraceMap::Create(getpid()));  ###创建UnwindStackCurrent
331      map = tmp_map.get();
332    }
333    std::unique_ptr backtrace(Backtrace::Create(BACKTRACE_CURRENT_PROCESS, tid, map));
334    backtrace->SetSkipFrames(skip_frames);
335    if (!backtrace->Unwind(0, reinterpret_cast(ucontext_ptr))) {
336      os << prefix << "(backtrace::Unwind failed for thread " << tid
337         << ": " <<  backtrace->GetErrorString(backtrace->GetError()) << ")" << std::endl;
338      return;
339    } else if (backtrace->NumFrames() == 0) {
340      os << prefix << "(no native stack frames for thread " << tid << ")" << std::endl;
341      return;
342    }

343  
344    // Check whether we have and should use addr2line.
345    bool use_addr2line;
346    if (kUseAddr2line) {
347      // Try to run it to see whether we have it. Push an argument so that it doesn't assume a.out
348      // and print to stderr.
349      use_addr2line = (gAborting > 0) && RunCommand(FindAddr2line() + " -h");
350    } else {
351      use_addr2line = false;
352    }
....

system/unwinding/libbacktrace/Backtrace.cpp
130  Backtrace* Backtrace::Create(pid_t pid, pid_t tid, BacktraceMap* map) {
131    if (pid == BACKTRACE_CURRENT_PROCESS) {
132      pid = getpid();
133      if (tid == BACKTRACE_CURRENT_THREAD) {
134        tid = android::base::GetThreadId();
135      }
136    } else if (tid == BACKTRACE_CURRENT_THREAD) {
137      tid = pid;
138    }
139  
140    if (pid == getpid()) {
141      return new UnwindStackCurrent(pid, tid, map);
142    } else {
143      return new UnwindStackPtrace(pid, tid, map);
144    }
145  }
 

UnwindStackCurrent  里面会发生 THREAD_SIGNAL  ，即信号33 

接受到底层发生的 SIGQUIT ，接着发生 THREAD_SIGNAL  获取堆栈

SignalCatcher::Run
signal_catcher.cc

void* SignalCatcher::Run(void* arg) {
  SignalCatcher* signal_catcher = reinterpret_cast(arg);
  CHECK(signal_catcher != nullptr);

  Runtime* runtime = Runtime::Current();
  // 将当前线程 attach 到当前的 JavaVM
  CHECK(runtime->AttachCurrentThread("Signal Catcher", true, runtime->GetSystemThreadGroup(),
                                     !runtime->IsAotCompiler()));

  Thread* self = Thread::Current();
  DCHECK_NE(self->GetState(), kRunnable);
  {
    MutexLock mu(self, signal_catcher->lock_);
    signal_catcher->thread_ = self;
    signal_catcher->cond_.Broadcast(self);
  }

  // Set up mask with signals we want to handle.
  SignalSet signals;
  signals.Add(SIGQUIT);
  signals.Add(SIGUSR1);

  while (true) {
    // 见 1.2.3
    int signal_number = signal_catcher->WaitForSignal(self, signals);
    if (signal_catcher->ShouldHalt()) {
      runtime->DetachCurrentThread();
      return nullptr;
    }

    switch (signal_number) {
    case SIGQUIT:
      signal_catcher->HandleSigQuit();
      break;
    case SIGUSR1:
      signal_catcher->HandleSigUsr1();
      break;
    default:
      LOG(ERROR) << "Unexpected signal %d" << signal_number;
      break;
    }
  }
}

PaletteWriteCrashThreadStacks  会连接tombstoned 
106  void SignalCatcher::Output(const std::string& s) {
107    ScopedThreadStateChange tsc(Thread::Current(), kWaitingForSignalCatcherOutput);
108    palette_status_t status = PaletteWriteCrashThreadStacks(s.data(), s.size());
109    if (status == PALETTE_STATUS_OK) {
110      LOG(INFO) << "Wrote stack traces to tombstoned";
111    } else {
112      CHECK(status == PALETTE_STATUS_FAILED_CHECK_LOG);
113      LOG(ERROR) << "Failed to write stack traces to tombstoned";
114    }
115  }
116  
117  void SignalCatcher::HandleSigQuit() {
118    Runtime* runtime = Runtime::Current();
119    std::ostringstream os;
120    os << "\n"
121        << "----- pid " << getpid() << " at " << GetIsoDate() << " -----\n";
122  
123    DumpCmdLine(os);
124  
125    // Note: The strings "Build fingerprint:" and "ABI:" are chosen to match the format used by
126    // debuggerd. This allows, for example, the stack tool to work.
127    std::string fingerprint = runtime->GetFingerprint();
128    os << "Build fingerprint: '" << (fingerprint.empty() ? "unknown" : fingerprint) << "'\n";
129    os << "ABI: '" << GetInstructionSetString(runtime->GetInstructionSet()) << "'\n";
130  
131    os << "Build type: " << (kIsDebugBuild ? "debug" : "optimized") << "\n";
132  
133    runtime->DumpForSigQuit(os);
134  
135    if ((false)) {
136      std::string maps;
137      if (android::base::ReadFileToString("/proc/self/maps", &maps)) {
138        os << "/proc/self/maps:\n" << maps;
139      }
140    }
141    os << "----- end " << getpid() << " -----\n";
142    Output(os.str());
143  }

android SIGQUIT 

「ANR」Android SIGQUIT(3) 信号拦截与处理_阿里巴巴终端技术的博客-CSDN博客_signal 拦截

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