DO NOT MERGE: adb: reenable (and fix) Windows build.

[android-x86/system-core.git] / libbacktrace / BacktraceCurrent.cpp

diff --git a/libbacktrace/BacktraceCurrent.cpp b/libbacktrace/BacktraceCurrent.cpp
index fd1f4da..d339550 100644 (file)
--- a/libbacktrace/BacktraceCurrent.cpp
+++ b/libbacktrace/BacktraceCurrent.cpp
@@ -29,6 +29,8 @@
 #include <backtrace/Backtrace.h>
 #include <backtrace/BacktraceMap.h>
 
+#include <cutils/threads.h>
+
 #include "BacktraceCurrent.h"
 #include "BacktraceLog.h"
 #include "ThreadEntry.h"
@@ -63,6 +65,11 @@ size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
 }
 
 bool BacktraceCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
+  if (GetMap() == nullptr) {
+    // Without a map object, we can't do anything.
+    return false;
+  }
+
   if (ucontext) {
     return UnwindFromContext(num_ignore_frames, ucontext);
   }
@@ -86,10 +93,14 @@ bool BacktraceCurrent::DiscardFrame(const backtrace_frame_data_t& frame) {
 
 static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;
 
+static void SignalLogOnly(int, siginfo_t*, void*) {
+  BACK_LOGE("pid %d, tid %d: Received a spurious signal %d\n", getpid(), gettid(), THREAD_SIGNAL);
+}
+
 static void SignalHandler(int, siginfo_t*, void* sigcontext) {
   ThreadEntry* entry = ThreadEntry::Get(getpid(), gettid(), false);
   if (!entry) {
-    BACK_LOGW("Unable to find pid %d tid %d information", getpid(), gettid());
+    BACK_LOGE("pid %d, tid %d entry not found", getpid(), gettid());
     return;
   }
 
@@ -102,9 +113,14 @@ static void SignalHandler(int, siginfo_t*, void* sigcontext) {
   // the thread run ahead causing problems.
   // The number indicates that we are waiting for the second Wake() call
   // overall which is made by the thread requesting an unwind.
-  entry->Wait(2);
-
-  ThreadEntry::Remove(entry);
+  if (entry->Wait(2)) {
+    // Do not remove the entry here because that can result in a deadlock
+    // if the code cannot properly send a signal to the thread under test.
+    entry->Wake();
+  } else {
+    // At this point, it is possible that entry has been freed, so just exit.
+    BACK_LOGE("Timed out waiting for unwind thread to indicate it completed.");
+  }
 }
 
 bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) {
@@ -121,17 +137,15 @@ bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) {
   act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
   sigemptyset(&act.sa_mask);
   if (sigaction(THREAD_SIGNAL, &act, &oldact) != 0) {
-    BACK_LOGW("sigaction failed %s", strerror(errno));
-    entry->Unlock();
+    BACK_LOGE("sigaction failed: %s", strerror(errno));
     ThreadEntry::Remove(entry);
     pthread_mutex_unlock(&g_sigaction_mutex);
     return false;
   }
 
   if (tgkill(Pid(), Tid(), THREAD_SIGNAL) != 0) {
-    BACK_LOGW("tgkill %d failed: %s", Tid(), strerror(errno));
+    BACK_LOGE("tgkill %d failed: %s", Tid(), strerror(errno));
     sigaction(THREAD_SIGNAL, &oldact, nullptr);
-    entry->Unlock();
     ThreadEntry::Remove(entry);
     pthread_mutex_unlock(&g_sigaction_mutex);
     return false;
@@ -139,17 +153,42 @@ bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) {
 
   // Wait for the thread to get the ucontext. The number indicates
   // that we are waiting for the first Wake() call made by the thread.
-  entry->Wait(1);
-
+  bool wait_completed = entry->Wait(1);
+
+  if (!wait_completed && oldact.sa_sigaction == nullptr) {
+    // If the wait failed, it could be that the signal could not be delivered
+    // within the timeout. Add a signal handler that's simply going to log
+    // something so that we don't crash if the signal eventually gets
+    // delivered. Only do this if there isn't already an action set up.
+    memset(&act, 0, sizeof(act));
+    act.sa_sigaction = SignalLogOnly;
+    act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
+    sigemptyset(&act.sa_mask);
+    sigaction(THREAD_SIGNAL, &act, nullptr);
+  } else {
+    sigaction(THREAD_SIGNAL, &oldact, nullptr);
+  }
   // After the thread has received the signal, allow other unwinders to
   // continue.
-  sigaction(THREAD_SIGNAL, &oldact, nullptr);
   pthread_mutex_unlock(&g_sigaction_mutex);
 
-  bool unwind_done = UnwindFromContext(num_ignore_frames, entry->GetUcontext());
+  bool unwind_done = false;
+  if (wait_completed) {
+    unwind_done = UnwindFromContext(num_ignore_frames, entry->GetUcontext());
 
-  // Tell the signal handler to exit and release the entry.
-  entry->Wake();
+    // Tell the signal handler to exit and release the entry.
+    entry->Wake();
+
+    // Wait for the thread to indicate it is done with the ThreadEntry.
+    if (!entry->Wait(3)) {
+      // Send a warning, but do not mark as a failure to unwind.
+      BACK_LOGW("Timed out waiting for signal handler to indicate it finished.");
+    }
+  } else {
+    BACK_LOGE("Timed out waiting for signal handler to get ucontext data.");
+  }
+
+  ThreadEntry::Remove(entry);
 
   return unwind_done;
 }