diff --git a/include/backtrace/Backtrace.h b/include/backtrace/Backtrace.h
index 8c39acb..290682a 100644
--- a/include/backtrace/Backtrace.h
+++ b/include/backtrace/Backtrace.h
@@ -44,9 +44,6 @@
   uintptr_t func_offset;  // pc relative to the start of the function, only valid if func_name is not NULL.
 };
 
-// Forward declarations.
-class BacktraceImpl;
-
 #if defined(__APPLE__)
 struct __darwin_ucontext;
 typedef __darwin_ucontext ucontext_t;
@@ -72,7 +69,7 @@
   virtual ~Backtrace();
 
   // Get the current stack trace and store in the backtrace_ structure.
-  virtual bool Unwind(size_t num_ignore_frames, ucontext_t* context = NULL);
+  virtual bool Unwind(size_t num_ignore_frames, ucontext_t* context = NULL) = 0;
 
   // Get the function name and offset into the function given the pc.
   // If the string is empty, then no valid function name was found.
@@ -95,9 +92,9 @@
   virtual std::string FormatFrameData(size_t frame_num);
   virtual std::string FormatFrameData(const backtrace_frame_data_t* frame);
 
-  pid_t Pid() { return pid_; }
-  pid_t Tid() { return tid_; }
-  size_t NumFrames() { return frames_.size(); }
+  pid_t Pid() const { return pid_; }
+  pid_t Tid() const { return tid_; }
+  size_t NumFrames() const { return frames_.size(); }
 
   const backtrace_frame_data_t* GetFrame(size_t frame_num) {
     if (frame_num >= frames_.size()) {
@@ -117,7 +114,11 @@
   BacktraceMap* GetMap() { return map_; }
 
 protected:
-  Backtrace(BacktraceImpl* impl, pid_t pid, BacktraceMap* map);
+  Backtrace(pid_t pid, pid_t tid, BacktraceMap* map);
+
+  // The name returned is not demangled, GetFunctionName() takes care of
+  // demangling the name.
+  virtual std::string GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) = 0;
 
   virtual bool VerifyReadWordArgs(uintptr_t ptr, word_t* out_value);
 
@@ -130,10 +131,6 @@
   bool map_shared_;
 
   std::vector<backtrace_frame_data_t> frames_;
-
-  BacktraceImpl* impl_;
-
-  friend class BacktraceImpl;
 };
 
 #endif // _BACKTRACE_BACKTRACE_H
diff --git a/include/cutils/trace.h b/include/cutils/trace.h
index 59ff6c1..9d039e6 100644
--- a/include/cutils/trace.h
+++ b/include/cutils/trace.h
@@ -80,7 +80,6 @@
 #error ATRACE_TAG must be defined to be one of the tags defined in cutils/trace.h
 #endif
 
-#ifdef HAVE_ANDROID_OS
 /**
  * Opens the trace file for writing and reads the property for initial tags.
  * The atrace.tags.enableflags property sets the tags to trace.
@@ -248,19 +247,6 @@
     }
 }
 
-#else // not HAVE_ANDROID_OS
-
-#define ATRACE_INIT()
-#define ATRACE_GET_ENABLED_TAGS()
-#define ATRACE_ENABLED() 0
-#define ATRACE_BEGIN(name)
-#define ATRACE_END()
-#define ATRACE_ASYNC_BEGIN(name, cookie)
-#define ATRACE_ASYNC_END(name, cookie)
-#define ATRACE_INT(name, value)
-
-#endif // not HAVE_ANDROID_OS
-
 __END_DECLS
 
 #endif // _LIBS_CUTILS_TRACE_H
diff --git a/libbacktrace/Android.build.mk b/libbacktrace/Android.build.mk
index d7eaa68..35fed6d 100644
--- a/libbacktrace/Android.build.mk
+++ b/libbacktrace/Android.build.mk
@@ -19,28 +19,37 @@
 LOCAL_MODULE := $(module)
 LOCAL_MODULE_TAGS := $(module_tag)
 LOCAL_MULTILIB := $($(module)_multilib)
+ifeq ($(LOCAL_MULTILIB),both)
+ifneq ($(build_target),$(filter $(build_target),SHARED_LIBRARY STATIC_LIBRRARY))
+  LOCAL_MODULE_STEM_32 := $(LOCAL_MODULE)32
+  LOCAL_MODULE_STEM_64 := $(LOCAL_MODULE)64
+endif
+endif
 
 LOCAL_ADDITIONAL_DEPENDENCIES := \
     $(LOCAL_PATH)/Android.mk \
     $(LOCAL_PATH)/Android.build.mk \
 
 LOCAL_CFLAGS := \
-    $(common_cflags) \
+    $(libbacktrace_common_cflags) \
     $($(module)_cflags) \
     $($(module)_cflags_$(build_type)) \
 
+LOCAL_CLANG_CFLAGS += \
+    $(libbacktrace_common_clang_cflags) \
+
 LOCAL_CONLYFLAGS += \
-    $(common_conlyflags) \
+    $(libbacktrace_common_conlyflags) \
     $($(module)_conlyflags) \
     $($(module)_conlyflags_$(build_type)) \
 
 LOCAL_CPPFLAGS += \
-    $(common_cppflags) \
+    $(libbacktrace_common_cppflags) \
     $($(module)_cppflags) \
     $($(module)_cppflags_$(build_type)) \
 
 LOCAL_C_INCLUDES := \
-    $(common_c_includes) \
+    $(libbacktrace_common_c_includes) \
     $($(module)_c_includes) \
     $($(module)_c_includes_$(build_type)) \
 
diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
old mode 100755
new mode 100644
index f3b28dd..b875efd
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -16,16 +16,20 @@
 
 LOCAL_PATH:= $(call my-dir)
 
-common_cflags := \
+libbacktrace_common_cflags := \
 	-Wall \
 	-Werror \
 
-common_conlyflags := \
+libbacktrace_common_conlyflags := \
 	-std=gnu99 \
 
-common_cppflags := \
+libbacktrace_common_cppflags := \
 	-std=gnu++11 \
 
+# The latest clang (r230699) does not allow SP/PC to be declared in inline asm lists.
+libbacktrace_common_clang_cflags += \
+    -Wno-inline-asm
+
 build_host := false
 ifeq ($(HOST_OS),linux)
 ifeq ($(HOST_ARCH),$(filter $(HOST_ARCH),x86 x86_64))
@@ -37,20 +41,21 @@
 # The libbacktrace library.
 #-------------------------------------------------------------------------
 libbacktrace_src_files := \
-	BacktraceImpl.cpp \
+	Backtrace.cpp \
+	BacktraceCurrent.cpp \
 	BacktraceMap.cpp \
-	BacktraceThread.cpp \
+	BacktracePtrace.cpp \
 	thread_utils.c \
-
-libbacktrace_shared_libraries_target := \
-	libcutils \
-
-libbacktrace_src_files += \
+	ThreadEntry.cpp \
 	UnwindCurrent.cpp \
 	UnwindMap.cpp \
 	UnwindPtrace.cpp \
 
+libbacktrace_shared_libraries_target := \
+	libcutils \
+
 libbacktrace_shared_libraries := \
+	libbase \
 	libunwind \
 	libunwind-ptrace \
 
@@ -86,6 +91,7 @@
 module_tag := debug
 build_type := target
 build_target := SHARED_LIBRARY
+libbacktrace_test_multilib := both
 include $(LOCAL_PATH)/Android.build.mk
 build_type := host
 include $(LOCAL_PATH)/Android.build.mk
@@ -124,6 +130,7 @@
 module_tag := debug
 build_type := target
 build_target := NATIVE_TEST
+backtrace_test_multilib := both
 include $(LOCAL_PATH)/Android.build.mk
 build_type := host
 include $(LOCAL_PATH)/Android.build.mk
diff --git a/libbacktrace/Backtrace.cpp b/libbacktrace/Backtrace.cpp
new file mode 100644
index 0000000..91ca8b7
--- /dev/null
+++ b/libbacktrace/Backtrace.cpp
@@ -0,0 +1,138 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <ucontext.h>
+
+#include <string>
+
+#include <base/stringprintf.h>
+
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
+#include "BacktraceLog.h"
+#include "thread_utils.h"
+#include "UnwindCurrent.h"
+#include "UnwindPtrace.h"
+
+using android::base::StringPrintf;
+
+//-------------------------------------------------------------------------
+// Backtrace functions.
+//-------------------------------------------------------------------------
+Backtrace::Backtrace(pid_t pid, pid_t tid, BacktraceMap* map)
+    : pid_(pid), tid_(tid), map_(map), map_shared_(true) {
+  if (map_ == nullptr) {
+    map_ = BacktraceMap::Create(pid);
+    map_shared_ = false;
+  }
+}
+
+Backtrace::~Backtrace() {
+  if (map_ && !map_shared_) {
+    delete map_;
+    map_ = nullptr;
+  }
+}
+
+extern "C" char* __cxa_demangle(const char* mangled, char* buf, size_t* len,
+                                int* status);
+
+std::string Backtrace::GetFunctionName(uintptr_t pc, uintptr_t* offset) {
+  std::string func_name = GetFunctionNameRaw(pc, offset);
+  if (!func_name.empty()) {
+#if defined(__APPLE__)
+    // Mac OS' __cxa_demangle demangles "f" as "float"; last tested on 10.7.
+    if (func_name[0] != '_') {
+      return func_name;
+    }
+#endif
+    char* name = __cxa_demangle(func_name.c_str(), 0, 0, 0);
+    if (name) {
+      func_name = name;
+      free(name);
+    }
+  }
+  return func_name;
+}
+
+bool Backtrace::VerifyReadWordArgs(uintptr_t ptr, word_t* out_value) {
+  if (ptr & (sizeof(word_t)-1)) {
+    BACK_LOGW("invalid pointer %p", reinterpret_cast<void*>(ptr));
+    *out_value = static_cast<word_t>(-1);
+    return false;
+  }
+  return true;
+}
+
+std::string Backtrace::FormatFrameData(size_t frame_num) {
+  if (frame_num >= frames_.size()) {
+    return "";
+  }
+  return FormatFrameData(&frames_[frame_num]);
+}
+
+std::string Backtrace::FormatFrameData(const backtrace_frame_data_t* frame) {
+  const char* map_name;
+  if (BacktraceMap::IsValid(frame->map) && !frame->map.name.empty()) {
+    map_name = frame->map.name.c_str();
+  } else {
+    map_name = "<unknown>";
+  }
+
+  uintptr_t relative_pc;
+  if (BacktraceMap::IsValid(frame->map)) {
+    relative_pc = frame->pc - frame->map.start;
+  } else {
+    relative_pc = frame->pc;
+  }
+
+  std::string line(StringPrintf("#%02zu pc %" PRIPTR "  %s", frame->num, relative_pc, map_name));
+  if (!frame->func_name.empty()) {
+    line += " (" + frame->func_name;
+    if (frame->func_offset) {
+      line += StringPrintf("+%" PRIuPTR, frame->func_offset);
+    }
+    line += ')';
+  }
+
+  return line;
+}
+
+void Backtrace::FillInMap(uintptr_t pc, backtrace_map_t* map) {
+  map_->FillIn(pc, map);
+}
+
+Backtrace* Backtrace::Create(pid_t pid, pid_t tid, BacktraceMap* map) {
+  if (pid == BACKTRACE_CURRENT_PROCESS) {
+    pid = getpid();
+    if (tid == BACKTRACE_CURRENT_THREAD) {
+      tid = gettid();
+    }
+  } else if (tid == BACKTRACE_CURRENT_THREAD) {
+    tid = pid;
+  }
+
+  if (pid == getpid()) {
+    return new UnwindCurrent(pid, tid, map);
+  } else {
+    return new UnwindPtrace(pid, tid, map);
+  }
+}
diff --git a/libbacktrace/BacktraceCurrent.cpp b/libbacktrace/BacktraceCurrent.cpp
new file mode 100644
index 0000000..b7190e2
--- /dev/null
+++ b/libbacktrace/BacktraceCurrent.cpp
@@ -0,0 +1,144 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/param.h>
+#include <sys/ptrace.h>
+#include <sys/types.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+#include <string>
+
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
+#include "BacktraceCurrent.h"
+#include "BacktraceLog.h"
+#include "ThreadEntry.h"
+#include "thread_utils.h"
+
+bool BacktraceCurrent::ReadWord(uintptr_t ptr, word_t* out_value) {
+  if (!VerifyReadWordArgs(ptr, out_value)) {
+    return false;
+  }
+
+  backtrace_map_t map;
+  FillInMap(ptr, &map);
+  if (BacktraceMap::IsValid(map) && map.flags & PROT_READ) {
+    *out_value = *reinterpret_cast<word_t*>(ptr);
+    return true;
+  } else {
+    BACK_LOGW("pointer %p not in a readable map", reinterpret_cast<void*>(ptr));
+    *out_value = static_cast<word_t>(-1);
+    return false;
+  }
+}
+
+size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
+  backtrace_map_t map;
+  FillInMap(addr, &map);
+  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
+    return 0;
+  }
+  bytes = MIN(map.end - addr, bytes);
+  memcpy(buffer, reinterpret_cast<uint8_t*>(addr), bytes);
+  return bytes;
+}
+
+bool BacktraceCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
+  if (ucontext) {
+    return UnwindFromContext(num_ignore_frames, ucontext);
+  }
+
+  if (Tid() != gettid()) {
+    return UnwindThread(num_ignore_frames);
+  }
+
+  return UnwindFromContext(num_ignore_frames, nullptr);
+}
+
+static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+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());
+    return;
+  }
+
+  entry->CopyUcontextFromSigcontext(sigcontext);
+
+  // Indicate the ucontext is now valid.
+  entry->Wake();
+
+  // Pause the thread until the unwind is complete. This avoids having
+  // 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);
+}
+
+bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) {
+  // Prevent multiple threads trying to set the trigger action on different
+  // threads at the same time.
+  pthread_mutex_lock(&g_sigaction_mutex);
+
+  ThreadEntry* entry = ThreadEntry::Get(Pid(), Tid());
+  entry->Lock();
+
+  struct sigaction act, oldact;
+  memset(&act, 0, sizeof(act));
+  act.sa_sigaction = SignalHandler;
+  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();
+    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));
+    sigaction(THREAD_SIGNAL, &oldact, nullptr);
+    entry->Unlock();
+    ThreadEntry::Remove(entry);
+    pthread_mutex_unlock(&g_sigaction_mutex);
+    return false;
+  }
+
+  // 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);
+
+  // 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());
+
+  // Tell the signal handler to exit and release the entry.
+  entry->Wake();
+
+  return unwind_done;
+}
diff --git a/libbacktrace/BacktraceCurrent.h b/libbacktrace/BacktraceCurrent.h
new file mode 100644
index 0000000..81ea81d
--- /dev/null
+++ b/libbacktrace/BacktraceCurrent.h
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBBACKTRACE_BACKTRACE_CURRENT_H
+#define _LIBBACKTRACE_BACKTRACE_CURRENT_H
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <ucontext.h>
+
+#include <backtrace/Backtrace.h>
+
+// The signal used to cause a thread to dump the stack.
+#if defined(__GLIBC__)
+// In order to run the backtrace_tests on the host, we can't use
+// the internal real time signals used by GLIBC. To avoid this,
+// use SIGRTMIN for the signal to dump the stack.
+#define THREAD_SIGNAL SIGRTMIN
+#else
+#define THREAD_SIGNAL (__SIGRTMIN+1)
+#endif
+
+class BacktraceMap;
+
+class BacktraceCurrent : public Backtrace {
+public:
+  BacktraceCurrent(pid_t pid, pid_t tid, BacktraceMap* map) : Backtrace(pid, tid, map) {}
+  virtual ~BacktraceCurrent() {}
+
+  size_t Read(uintptr_t addr, uint8_t* buffer, size_t bytes) override;
+
+  bool ReadWord(uintptr_t ptr, word_t* out_value) override;
+
+  bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext) override;
+
+private:
+  bool UnwindThread(size_t num_ignore_frames);
+
+  virtual bool UnwindFromContext(size_t num_ignore_frames, ucontext_t* ucontext) = 0;
+};
+
+#endif // _LIBBACKTRACE_BACKTRACE_CURRENT_H
diff --git a/libbacktrace/BacktraceImpl.cpp b/libbacktrace/BacktraceImpl.cpp
deleted file mode 100644
index 4650b6a..0000000
--- a/libbacktrace/BacktraceImpl.cpp
+++ /dev/null
@@ -1,283 +0,0 @@
-/*
- * Copyright (C) 2013 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#include <errno.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/param.h>
-#include <sys/ptrace.h>
-#include <sys/types.h>
-#include <ucontext.h>
-#include <unistd.h>
-
-#include <string>
-
-#include <backtrace/Backtrace.h>
-#include <backtrace/BacktraceMap.h>
-
-#include "BacktraceImpl.h"
-#include "BacktraceLog.h"
-#include "thread_utils.h"
-
-//-------------------------------------------------------------------------
-// Backtrace functions.
-//-------------------------------------------------------------------------
-Backtrace::Backtrace(BacktraceImpl* impl, pid_t pid, BacktraceMap* map)
-    : pid_(pid), tid_(-1), map_(map), map_shared_(true), impl_(impl) {
-  impl_->SetParent(this);
-
-  if (map_ == NULL) {
-    map_ = BacktraceMap::Create(pid);
-    map_shared_ = false;
-  }
-}
-
-Backtrace::~Backtrace() {
-  if (impl_) {
-    delete impl_;
-    impl_ = NULL;
-  }
-
-  if (map_ && !map_shared_) {
-    delete map_;
-    map_ = NULL;
-  }
-}
-
-bool Backtrace::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
-  return impl_->Unwind(num_ignore_frames, ucontext);
-}
-
-extern "C" char* __cxa_demangle(const char* mangled, char* buf, size_t* len,
-                                int* status);
-
-std::string Backtrace::GetFunctionName(uintptr_t pc, uintptr_t* offset) {
-  std::string func_name = impl_->GetFunctionNameRaw(pc, offset);
-  if (!func_name.empty()) {
-#if defined(__APPLE__)
-    // Mac OS' __cxa_demangle demangles "f" as "float"; last tested on 10.7.
-    if (func_name[0] != '_') {
-      return func_name;
-    }
-#endif
-    char* name = __cxa_demangle(func_name.c_str(), 0, 0, 0);
-    if (name) {
-      func_name = name;
-      free(name);
-    }
-  }
-  return func_name;
-}
-
-bool Backtrace::VerifyReadWordArgs(uintptr_t ptr, word_t* out_value) {
-  if (ptr & (sizeof(word_t)-1)) {
-    BACK_LOGW("invalid pointer %p", (void*)ptr);
-    *out_value = (word_t)-1;
-    return false;
-  }
-  return true;
-}
-
-std::string Backtrace::FormatFrameData(size_t frame_num) {
-  if (frame_num >= frames_.size()) {
-    return "";
-  }
-  return FormatFrameData(&frames_[frame_num]);
-}
-
-std::string Backtrace::FormatFrameData(const backtrace_frame_data_t* frame) {
-  const char* map_name;
-  if (BacktraceMap::IsValid(frame->map) && !frame->map.name.empty()) {
-    map_name = frame->map.name.c_str();
-  } else {
-    map_name = "<unknown>";
-  }
-
-  uintptr_t relative_pc;
-  if (BacktraceMap::IsValid(frame->map)) {
-    relative_pc = frame->pc - frame->map.start;
-  } else {
-    relative_pc = frame->pc;
-  }
-
-  char buf[512];
-  if (!frame->func_name.empty() && frame->func_offset) {
-    snprintf(buf, sizeof(buf), "#%02zu pc %0*" PRIxPTR "  %s (%s+%" PRIuPTR ")",
-             frame->num, (int)sizeof(uintptr_t)*2, relative_pc, map_name,
-             frame->func_name.c_str(), frame->func_offset);
-  } else if (!frame->func_name.empty()) {
-    snprintf(buf, sizeof(buf), "#%02zu pc %0*" PRIxPTR "  %s (%s)", frame->num,
-             (int)sizeof(uintptr_t)*2, relative_pc, map_name, frame->func_name.c_str());
-  } else {
-    snprintf(buf, sizeof(buf), "#%02zu pc %0*" PRIxPTR "  %s", frame->num,
-             (int)sizeof(uintptr_t)*2, relative_pc, map_name);
-  }
-
-  return buf;
-}
-
-void Backtrace::FillInMap(uintptr_t pc, backtrace_map_t* map) {
-  map_->FillIn(pc, map);
-}
-
-//-------------------------------------------------------------------------
-// BacktraceCurrent functions.
-//-------------------------------------------------------------------------
-BacktraceCurrent::BacktraceCurrent(
-    BacktraceImpl* impl, BacktraceMap* map) : Backtrace(impl, getpid(), map) {
-}
-
-BacktraceCurrent::~BacktraceCurrent() {
-}
-
-bool BacktraceCurrent::ReadWord(uintptr_t ptr, word_t* out_value) {
-  if (!VerifyReadWordArgs(ptr, out_value)) {
-    return false;
-  }
-
-  backtrace_map_t map;
-  FillInMap(ptr, &map);
-  if (BacktraceMap::IsValid(map) && map.flags & PROT_READ) {
-    *out_value = *reinterpret_cast<word_t*>(ptr);
-    return true;
-  } else {
-    BACK_LOGW("pointer %p not in a readable map", reinterpret_cast<void*>(ptr));
-    *out_value = static_cast<word_t>(-1);
-    return false;
-  }
-}
-
-size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
-  backtrace_map_t map;
-  FillInMap(addr, &map);
-  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
-    return 0;
-  }
-  bytes = MIN(map.end - addr, bytes);
-  memcpy(buffer, reinterpret_cast<uint8_t*>(addr), bytes);
-  return bytes;
-}
-
-//-------------------------------------------------------------------------
-// BacktracePtrace functions.
-//-------------------------------------------------------------------------
-BacktracePtrace::BacktracePtrace(
-    BacktraceImpl* impl, pid_t pid, pid_t tid, BacktraceMap* map)
-    : Backtrace(impl, pid, map) {
-  tid_ = tid;
-}
-
-BacktracePtrace::~BacktracePtrace() {
-}
-
-#if !defined(__APPLE__)
-static bool PtraceRead(pid_t tid, uintptr_t addr, word_t* out_value) {
-  // ptrace() returns -1 and sets errno when the operation fails.
-  // To disambiguate -1 from a valid result, we clear errno beforehand.
-  errno = 0;
-  *out_value = ptrace(PTRACE_PEEKTEXT, tid, reinterpret_cast<void*>(addr), NULL);
-  if (*out_value == static_cast<word_t>(-1) && errno) {
-    BACK_LOGW("invalid pointer %p reading from tid %d, ptrace() strerror(errno)=%s",
-              reinterpret_cast<void*>(addr), tid, strerror(errno));
-    return false;
-  }
-  return true;
-}
-#endif
-
-bool BacktracePtrace::ReadWord(uintptr_t ptr, word_t* out_value) {
-#if defined(__APPLE__)
-  BACK_LOGW("MacOS does not support reading from another pid.");
-  return false;
-#else
-  if (!VerifyReadWordArgs(ptr, out_value)) {
-    return false;
-  }
-
-  backtrace_map_t map;
-  FillInMap(ptr, &map);
-  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
-    return false;
-  }
-
-  return PtraceRead(Tid(), ptr, out_value);
-#endif
-}
-
-size_t BacktracePtrace::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
-#if defined(__APPLE__)
-  BACK_LOGW("MacOS does not support reading from another pid.");
-  return 0;
-#else
-  backtrace_map_t map;
-  FillInMap(addr, &map);
-  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
-    return 0;
-  }
-
-  bytes = MIN(map.end - addr, bytes);
-  size_t bytes_read = 0;
-  word_t data_word;
-  size_t align_bytes = addr & (sizeof(word_t) - 1);
-  if (align_bytes != 0) {
-    if (!PtraceRead(Tid(), addr & ~(sizeof(word_t) - 1), &data_word)) {
-      return 0;
-    }
-    align_bytes = sizeof(word_t) - align_bytes;
-    memcpy(buffer, reinterpret_cast<uint8_t*>(&data_word) + sizeof(word_t) - align_bytes,
-           align_bytes);
-    addr += align_bytes;
-    buffer += align_bytes;
-    bytes -= align_bytes;
-    bytes_read += align_bytes;
-  }
-
-  size_t num_words = bytes / sizeof(word_t);
-  for (size_t i = 0; i < num_words; i++) {
-    if (!PtraceRead(Tid(), addr, &data_word)) {
-      return bytes_read;
-    }
-    memcpy(buffer, &data_word, sizeof(word_t));
-    buffer += sizeof(word_t);
-    addr += sizeof(word_t);
-    bytes_read += sizeof(word_t);
-  }
-
-  size_t left_over = bytes & (sizeof(word_t) - 1);
-  if (left_over) {
-    if (!PtraceRead(Tid(), addr, &data_word)) {
-      return bytes_read;
-    }
-    memcpy(buffer, &data_word, left_over);
-    bytes_read += left_over;
-  }
-  return bytes_read;
-#endif
-}
-
-Backtrace* Backtrace::Create(pid_t pid, pid_t tid, BacktraceMap* map) {
-  if (pid == BACKTRACE_CURRENT_PROCESS || pid == getpid()) {
-    if (tid == BACKTRACE_CURRENT_THREAD || tid == gettid()) {
-      return CreateCurrentObj(map);
-    } else {
-      return CreateThreadObj(tid, map);
-    }
-  } else if (tid == BACKTRACE_CURRENT_THREAD) {
-    return CreatePtraceObj(pid, pid, map);
-  } else {
-    return CreatePtraceObj(pid, tid, map);
-  }
-}
diff --git a/libbacktrace/BacktraceImpl.h b/libbacktrace/BacktraceImpl.h
deleted file mode 100755
index 18c3cb5..0000000
--- a/libbacktrace/BacktraceImpl.h
+++ /dev/null
@@ -1,78 +0,0 @@
-/*
- * Copyright (C) 2013 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#ifndef _LIBBACKTRACE_BACKTRACE_IMPL_H
-#define _LIBBACKTRACE_BACKTRACE_IMPL_H
-
-#include <backtrace/Backtrace.h>
-#include <backtrace/BacktraceMap.h>
-
-#include <sys/types.h>
-
-class BacktraceImpl {
-public:
-  virtual ~BacktraceImpl() { }
-
-  virtual bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext) = 0;
-
-  // The name returned is not demangled, Backtrace::GetFunctionName()
-  // takes care of demangling the name.
-  virtual std::string GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) = 0;
-
-  void SetParent(Backtrace* backtrace) { backtrace_obj_ = backtrace; }
-
-  inline pid_t Pid() { return backtrace_obj_->Pid(); }
-  inline pid_t Tid() { return backtrace_obj_->Tid(); }
-
-  inline void FillInMap(uintptr_t addr, backtrace_map_t* map) {
-    backtrace_obj_->FillInMap(addr, map);
-  }
-  inline std::string GetFunctionName(uintptr_t pc, uintptr_t* offset) {
-    return backtrace_obj_->GetFunctionName(pc, offset);
-  }
-  inline BacktraceMap* GetMap() { return backtrace_obj_->GetMap(); }
-
-protected:
-  inline std::vector<backtrace_frame_data_t>* GetFrames() { return &backtrace_obj_->frames_; }
-
-  Backtrace* backtrace_obj_;
-};
-
-class BacktraceCurrent : public Backtrace {
-public:
-  BacktraceCurrent(BacktraceImpl* impl, BacktraceMap* map);
-  virtual ~BacktraceCurrent();
-
-  size_t Read(uintptr_t addr, uint8_t* buffer, size_t bytes);
-
-  bool ReadWord(uintptr_t ptr, word_t* out_value);
-};
-
-class BacktracePtrace : public Backtrace {
-public:
-  BacktracePtrace(BacktraceImpl* impl, pid_t pid, pid_t tid, BacktraceMap* map);
-  virtual ~BacktracePtrace();
-
-  size_t Read(uintptr_t addr, uint8_t* buffer, size_t bytes);
-
-  bool ReadWord(uintptr_t ptr, word_t* out_value);
-};
-
-Backtrace* CreateCurrentObj(BacktraceMap* map);
-Backtrace* CreatePtraceObj(pid_t pid, pid_t tid, BacktraceMap* map);
-Backtrace* CreateThreadObj(pid_t tid, BacktraceMap* map);
-
-#endif // _LIBBACKTRACE_BACKTRACE_IMPL_H
diff --git a/libbacktrace/BacktraceLog.h b/libbacktrace/BacktraceLog.h
old mode 100755
new mode 100644
diff --git a/libbacktrace/BacktraceMap.cpp b/libbacktrace/BacktraceMap.cpp
index 82a4085..b0ada46 100644
--- a/libbacktrace/BacktraceMap.cpp
+++ b/libbacktrace/BacktraceMap.cpp
@@ -15,18 +15,15 @@
  */
 
 #include <ctype.h>
+#include <stdint.h>
 #include <sys/types.h>
 #include <unistd.h>
 
-#include <string>
-#include <vector>
-
 #include <backtrace/backtrace_constants.h>
 #include <backtrace/BacktraceMap.h>
 #include <log/log.h>
 
 #include "thread_utils.h"
-#include "BacktraceImpl.h"
 
 BacktraceMap::BacktraceMap(pid_t pid) : pid_(pid) {
   if (pid_ < 0) {
@@ -116,7 +113,7 @@
   snprintf(path, sizeof(path), "/proc/%d/maps", pid_);
   FILE* fp = fopen(path, "r");
 #endif
-  if (fp == NULL) {
+  if (fp == nullptr) {
     return false;
   }
 
@@ -142,7 +139,7 @@
   BacktraceMap* map = new BacktraceMap(pid);
   if (!map->Build()) {
     delete map;
-    return NULL;
+    return nullptr;
   }
   return map;
 }
diff --git a/libbacktrace/BacktracePtrace.cpp b/libbacktrace/BacktracePtrace.cpp
new file mode 100644
index 0000000..6134438
--- /dev/null
+++ b/libbacktrace/BacktracePtrace.cpp
@@ -0,0 +1,116 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/param.h>
+#include <sys/ptrace.h>
+#include <sys/types.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
+#include "BacktraceLog.h"
+#include "BacktracePtrace.h"
+#include "thread_utils.h"
+
+#if !defined(__APPLE__)
+static bool PtraceRead(pid_t tid, uintptr_t addr, word_t* out_value) {
+  // ptrace() returns -1 and sets errno when the operation fails.
+  // To disambiguate -1 from a valid result, we clear errno beforehand.
+  errno = 0;
+  *out_value = ptrace(PTRACE_PEEKTEXT, tid, reinterpret_cast<void*>(addr), nullptr);
+  if (*out_value == static_cast<word_t>(-1) && errno) {
+    BACK_LOGW("invalid pointer %p reading from tid %d, ptrace() strerror(errno)=%s",
+              reinterpret_cast<void*>(addr), tid, strerror(errno));
+    return false;
+  }
+  return true;
+}
+#endif
+
+bool BacktracePtrace::ReadWord(uintptr_t ptr, word_t* out_value) {
+#if defined(__APPLE__)
+  BACK_LOGW("MacOS does not support reading from another pid.");
+  return false;
+#else
+  if (!VerifyReadWordArgs(ptr, out_value)) {
+    return false;
+  }
+
+  backtrace_map_t map;
+  FillInMap(ptr, &map);
+  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
+    return false;
+  }
+
+  return PtraceRead(Tid(), ptr, out_value);
+#endif
+}
+
+size_t BacktracePtrace::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
+#if defined(__APPLE__)
+  BACK_LOGW("MacOS does not support reading from another pid.");
+  return 0;
+#else
+  backtrace_map_t map;
+  FillInMap(addr, &map);
+  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
+    return 0;
+  }
+
+  bytes = MIN(map.end - addr, bytes);
+  size_t bytes_read = 0;
+  word_t data_word;
+  size_t align_bytes = addr & (sizeof(word_t) - 1);
+  if (align_bytes != 0) {
+    if (!PtraceRead(Tid(), addr & ~(sizeof(word_t) - 1), &data_word)) {
+      return 0;
+    }
+    align_bytes = sizeof(word_t) - align_bytes;
+    memcpy(buffer, reinterpret_cast<uint8_t*>(&data_word) + sizeof(word_t) - align_bytes,
+           align_bytes);
+    addr += align_bytes;
+    buffer += align_bytes;
+    bytes -= align_bytes;
+    bytes_read += align_bytes;
+  }
+
+  size_t num_words = bytes / sizeof(word_t);
+  for (size_t i = 0; i < num_words; i++) {
+    if (!PtraceRead(Tid(), addr, &data_word)) {
+      return bytes_read;
+    }
+    memcpy(buffer, &data_word, sizeof(word_t));
+    buffer += sizeof(word_t);
+    addr += sizeof(word_t);
+    bytes_read += sizeof(word_t);
+  }
+
+  size_t left_over = bytes & (sizeof(word_t) - 1);
+  if (left_over) {
+    if (!PtraceRead(Tid(), addr, &data_word)) {
+      return bytes_read;
+    }
+    memcpy(buffer, &data_word, left_over);
+    bytes_read += left_over;
+  }
+  return bytes_read;
+#endif
+}
diff --git a/libbacktrace/BacktracePtrace.h b/libbacktrace/BacktracePtrace.h
new file mode 100644
index 0000000..1d49811
--- /dev/null
+++ b/libbacktrace/BacktracePtrace.h
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBBACKTRACE_BACKTRACE_PTRACE_H
+#define _LIBBACKTRACE_BACKTRACE_PTRACE_H
+
+#include <stdint.h>
+#include <sys/types.h>
+
+#include <backtrace/Backtrace.h>
+
+class BacktraceMap;
+
+class BacktracePtrace : public Backtrace {
+public:
+  BacktracePtrace(pid_t pid, pid_t tid, BacktraceMap* map) : Backtrace(pid, tid, map) {}
+  virtual ~BacktracePtrace() {}
+
+  size_t Read(uintptr_t addr, uint8_t* buffer, size_t bytes);
+
+  bool ReadWord(uintptr_t ptr, word_t* out_value);
+};
+
+#endif // _LIBBACKTRACE_BACKTRACE_PTRACE_H
diff --git a/libbacktrace/BacktraceThread.cpp b/libbacktrace/BacktraceThread.cpp
deleted file mode 100644
index 439cc3b..0000000
--- a/libbacktrace/BacktraceThread.cpp
+++ /dev/null
@@ -1,227 +0,0 @@
-/*
- * Copyright (C) 2013 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-#include <errno.h>
-#include <inttypes.h>
-#include <limits.h>
-#include <pthread.h>
-#include <signal.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/syscall.h>
-#include <sys/time.h>
-#include <sys/types.h>
-#include <ucontext.h>
-#include <unistd.h>
-
-#include <cutils/atomic.h>
-
-#include "BacktraceLog.h"
-#include "BacktraceThread.h"
-#include "thread_utils.h"
-
-//-------------------------------------------------------------------------
-// ThreadEntry implementation.
-//-------------------------------------------------------------------------
-ThreadEntry* ThreadEntry::list_ = NULL;
-pthread_mutex_t ThreadEntry::list_mutex_ = PTHREAD_MUTEX_INITIALIZER;
-
-// Assumes that ThreadEntry::list_mutex_ has already been locked before
-// creating a ThreadEntry object.
-ThreadEntry::ThreadEntry(pid_t pid, pid_t tid)
-    : pid_(pid), tid_(tid), ref_count_(1), mutex_(PTHREAD_MUTEX_INITIALIZER),
-      wait_mutex_(PTHREAD_MUTEX_INITIALIZER), wait_value_(0),
-      next_(ThreadEntry::list_), prev_(NULL) {
-  pthread_condattr_t attr;
-  pthread_condattr_init(&attr);
-  pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
-  pthread_cond_init(&wait_cond_, &attr);
-
-  // Add ourselves to the list.
-  if (ThreadEntry::list_) {
-    ThreadEntry::list_->prev_ = this;
-  }
-  ThreadEntry::list_ = this;
-}
-
-ThreadEntry* ThreadEntry::Get(pid_t pid, pid_t tid, bool create) {
-  pthread_mutex_lock(&ThreadEntry::list_mutex_);
-  ThreadEntry* entry = list_;
-  while (entry != NULL) {
-    if (entry->Match(pid, tid)) {
-      break;
-    }
-    entry = entry->next_;
-  }
-
-  if (!entry) {
-    if (create) {
-      entry = new ThreadEntry(pid, tid);
-    }
-  } else {
-    entry->ref_count_++;
-  }
-  pthread_mutex_unlock(&ThreadEntry::list_mutex_);
-
-  return entry;
-}
-
-void ThreadEntry::Remove(ThreadEntry* entry) {
-  pthread_mutex_unlock(&entry->mutex_);
-
-  pthread_mutex_lock(&ThreadEntry::list_mutex_);
-  if (--entry->ref_count_ == 0) {
-    delete entry;
-  }
-  pthread_mutex_unlock(&ThreadEntry::list_mutex_);
-}
-
-// Assumes that ThreadEntry::list_mutex_ has already been locked before
-// deleting a ThreadEntry object.
-ThreadEntry::~ThreadEntry() {
-  if (list_ == this) {
-    list_ = next_;
-  } else {
-    if (next_) {
-      next_->prev_ = prev_;
-    }
-    prev_->next_ = next_;
-  }
-
-  next_ = NULL;
-  prev_ = NULL;
-
-  pthread_cond_destroy(&wait_cond_);
-}
-
-void ThreadEntry::Wait(int value) {
-  timespec ts;
-  if (clock_gettime(CLOCK_MONOTONIC, &ts) == -1) {
-    BACK_LOGW("clock_gettime failed: %s", strerror(errno));
-    abort();
-  }
-  ts.tv_sec += 10;
-
-  pthread_mutex_lock(&wait_mutex_);
-  while (wait_value_ != value) {
-    int ret = pthread_cond_timedwait(&wait_cond_, &wait_mutex_, &ts);
-    if (ret != 0) {
-      BACK_LOGW("pthread_cond_timedwait failed: %s", strerror(ret));
-      break;
-    }
-  }
-  pthread_mutex_unlock(&wait_mutex_);
-}
-
-void ThreadEntry::Wake() {
-  pthread_mutex_lock(&wait_mutex_);
-  wait_value_++;
-  pthread_mutex_unlock(&wait_mutex_);
-
-  pthread_cond_signal(&wait_cond_);
-}
-
-void ThreadEntry::CopyUcontextFromSigcontext(void* sigcontext) {
-  ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(sigcontext);
-  // The only thing the unwinder cares about is the mcontext data.
-  memcpy(&ucontext_.uc_mcontext, &ucontext->uc_mcontext, sizeof(ucontext->uc_mcontext));
-}
-
-//-------------------------------------------------------------------------
-// BacktraceThread functions.
-//-------------------------------------------------------------------------
-static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;
-
-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());
-    return;
-  }
-
-  entry->CopyUcontextFromSigcontext(sigcontext);
-
-  // Indicate the ucontext is now valid.
-  entry->Wake();
-
-  // Pause the thread until the unwind is complete. This avoids having
-  // the thread run ahead causing problems.
-  entry->Wait(2);
-
-  ThreadEntry::Remove(entry);
-}
-
-BacktraceThread::BacktraceThread(BacktraceImpl* impl, pid_t tid, BacktraceMap* map)
-    : BacktraceCurrent(impl, map) {
-  tid_ = tid;
-}
-
-BacktraceThread::~BacktraceThread() {
-}
-
-bool BacktraceThread::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
-  if (ucontext) {
-    // Unwind using an already existing ucontext.
-    return impl_->Unwind(num_ignore_frames, ucontext);
-  }
-
-  // Prevent multiple threads trying to set the trigger action on different
-  // threads at the same time.
-  if (pthread_mutex_lock(&g_sigaction_mutex) < 0) {
-    BACK_LOGW("sigaction failed: %s", strerror(errno));
-    return false;
-  }
-
-  ThreadEntry* entry = ThreadEntry::Get(Pid(), Tid());
-  entry->Lock();
-
-  struct sigaction act, oldact;
-  memset(&act, 0, sizeof(act));
-  act.sa_sigaction = SignalHandler;
-  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();
-    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));
-    sigaction(THREAD_SIGNAL, &oldact, NULL);
-    entry->Unlock();
-    ThreadEntry::Remove(entry);
-    pthread_mutex_unlock(&g_sigaction_mutex);
-    return false;
-  }
-
-  // Wait for the thread to get the ucontext.
-  entry->Wait(1);
-
-  // After the thread has received the signal, allow other unwinders to
-  // continue.
-  sigaction(THREAD_SIGNAL, &oldact, NULL);
-  pthread_mutex_unlock(&g_sigaction_mutex);
-
-  bool unwind_done = impl_->Unwind(num_ignore_frames, entry->GetUcontext());
-
-  // Tell the signal handler to exit and release the entry.
-  entry->Wake();
-
-  return unwind_done;
-}
diff --git a/libbacktrace/GetPss.cpp b/libbacktrace/GetPss.cpp
index 442383b..09a721d 100644
--- a/libbacktrace/GetPss.cpp
+++ b/libbacktrace/GetPss.cpp
@@ -14,11 +14,10 @@
  * limitations under the License.
  */
 
-#include <assert.h>
 #include <inttypes.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <stdint.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <fcntl.h>
@@ -46,13 +45,22 @@
 
 size_t GetPssBytes() {
   FILE* maps = fopen("/proc/self/maps", "r");
-  assert(maps != NULL);
+  if (maps == nullptr) {
+    return 0;
+  }
 
   int pagecount_fd = open("/proc/kpagecount", O_RDONLY);
-  assert(pagecount_fd >= 0);
+  if (pagecount_fd == -1) {
+    fclose(maps);
+    return 0;
+  }
 
   int pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
-  assert(pagemap_fd >= 0);
+  if (pagemap_fd == -1) {
+    fclose(maps);
+    close(pagecount_fd);
+    return 0;
+  }
 
   char line[4096];
   size_t total_pss = 0;
diff --git a/libbacktrace/ThreadEntry.cpp b/libbacktrace/ThreadEntry.cpp
new file mode 100644
index 0000000..e8b60c8
--- /dev/null
+++ b/libbacktrace/ThreadEntry.cpp
@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <pthread.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/types.h>
+#include <time.h>
+#include <ucontext.h>
+
+#include "BacktraceLog.h"
+#include "ThreadEntry.h"
+
+// Initialize static member variables.
+ThreadEntry* ThreadEntry::list_ = nullptr;
+pthread_mutex_t ThreadEntry::list_mutex_ = PTHREAD_MUTEX_INITIALIZER;
+
+// Assumes that ThreadEntry::list_mutex_ has already been locked before
+// creating a ThreadEntry object.
+ThreadEntry::ThreadEntry(pid_t pid, pid_t tid)
+    : pid_(pid), tid_(tid), ref_count_(1), mutex_(PTHREAD_MUTEX_INITIALIZER),
+      wait_mutex_(PTHREAD_MUTEX_INITIALIZER), wait_value_(0),
+      next_(ThreadEntry::list_), prev_(nullptr) {
+  pthread_condattr_t attr;
+  pthread_condattr_init(&attr);
+  pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
+  pthread_cond_init(&wait_cond_, &attr);
+
+  // Add ourselves to the list.
+  if (ThreadEntry::list_) {
+    ThreadEntry::list_->prev_ = this;
+  }
+  ThreadEntry::list_ = this;
+}
+
+ThreadEntry* ThreadEntry::Get(pid_t pid, pid_t tid, bool create) {
+  pthread_mutex_lock(&ThreadEntry::list_mutex_);
+  ThreadEntry* entry = list_;
+  while (entry != nullptr) {
+    if (entry->Match(pid, tid)) {
+      break;
+    }
+    entry = entry->next_;
+  }
+
+  if (!entry) {
+    if (create) {
+      entry = new ThreadEntry(pid, tid);
+    }
+  } else {
+    entry->ref_count_++;
+  }
+  pthread_mutex_unlock(&ThreadEntry::list_mutex_);
+
+  return entry;
+}
+
+void ThreadEntry::Remove(ThreadEntry* entry) {
+  pthread_mutex_unlock(&entry->mutex_);
+
+  pthread_mutex_lock(&ThreadEntry::list_mutex_);
+  if (--entry->ref_count_ == 0) {
+    delete entry;
+  }
+  pthread_mutex_unlock(&ThreadEntry::list_mutex_);
+}
+
+// Assumes that ThreadEntry::list_mutex_ has already been locked before
+// deleting a ThreadEntry object.
+ThreadEntry::~ThreadEntry() {
+  if (list_ == this) {
+    list_ = next_;
+  } else {
+    if (next_) {
+      next_->prev_ = prev_;
+    }
+    prev_->next_ = next_;
+  }
+
+  next_ = nullptr;
+  prev_ = nullptr;
+
+  pthread_cond_destroy(&wait_cond_);
+}
+
+void ThreadEntry::Wait(int value) {
+  timespec ts;
+  clock_gettime(CLOCK_MONOTONIC, &ts);
+  ts.tv_sec += 10;
+
+  pthread_mutex_lock(&wait_mutex_);
+  while (wait_value_ != value) {
+    int ret = pthread_cond_timedwait(&wait_cond_, &wait_mutex_, &ts);
+    if (ret != 0) {
+      BACK_LOGW("pthread_cond_timedwait failed: %s", strerror(ret));
+      break;
+    }
+  }
+  pthread_mutex_unlock(&wait_mutex_);
+}
+
+void ThreadEntry::Wake() {
+  pthread_mutex_lock(&wait_mutex_);
+  wait_value_++;
+  pthread_mutex_unlock(&wait_mutex_);
+
+  pthread_cond_signal(&wait_cond_);
+}
+
+void ThreadEntry::CopyUcontextFromSigcontext(void* sigcontext) {
+  ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(sigcontext);
+  // The only thing the unwinder cares about is the mcontext data.
+  memcpy(&ucontext_.uc_mcontext, &ucontext->uc_mcontext, sizeof(ucontext->uc_mcontext));
+}
diff --git a/libbacktrace/BacktraceThread.h b/libbacktrace/ThreadEntry.h
similarity index 70%
rename from libbacktrace/BacktraceThread.h
rename to libbacktrace/ThreadEntry.h
index 99a8638..94becf2 100644
--- a/libbacktrace/BacktraceThread.h
+++ b/libbacktrace/ThreadEntry.h
@@ -14,26 +14,13 @@
  * limitations under the License.
  */
 
-#ifndef _LIBBACKTRACE_BACKTRACE_THREAD_H
-#define _LIBBACKTRACE_BACKTRACE_THREAD_H
+#ifndef _LIBBACKTRACE_THREAD_ENTRY_H
+#define _LIBBACKTRACE_THREAD_ENTRY_H
 
-#include <inttypes.h>
 #include <pthread.h>
-#include <signal.h>
-#include <string.h>
 #include <sys/types.h>
 #include <ucontext.h>
 
-#include "BacktraceImpl.h"
-
-// The signal used to cause a thread to dump the stack.
-#if defined(__GLIBC__)
-// GLIBC reserves __SIGRTMIN signals, so use SIGRTMIN to avoid errors.
-#define THREAD_SIGNAL SIGRTMIN
-#else
-#define THREAD_SIGNAL (__SIGRTMIN+1)
-#endif
-
 class ThreadEntry {
 public:
   static ThreadEntry* Get(pid_t pid, pid_t tid, bool create = true);
@@ -81,12 +68,4 @@
   static pthread_mutex_t list_mutex_;
 };
 
-class BacktraceThread : public BacktraceCurrent {
-public:
-  BacktraceThread(BacktraceImpl* impl, pid_t tid, BacktraceMap* map);
-  virtual ~BacktraceThread();
-
-  virtual bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext);
-};
-
-#endif // _LIBBACKTRACE_BACKTRACE_THREAD_H
+#endif // _LIBBACKTRACE_THREAD_ENTRY_H
diff --git a/libbacktrace/UnwindCurrent.cpp b/libbacktrace/UnwindCurrent.cpp
old mode 100755
new mode 100644
index 372555b..12e2890
--- a/libbacktrace/UnwindCurrent.cpp
+++ b/libbacktrace/UnwindCurrent.cpp
@@ -14,41 +14,30 @@
  * limitations under the License.
  */
 
-#include <sys/types.h>
+#include <stdint.h>
 #include <ucontext.h>
 
-#include <backtrace/Backtrace.h>
-#include <backtrace/BacktraceMap.h>
+#include <memory>
+#include <string>
 
 #define UNW_LOCAL_ONLY
 #include <libunwind.h>
 
+#include <backtrace/Backtrace.h>
+
 #include "BacktraceLog.h"
-#include "BacktraceThread.h"
 #include "UnwindCurrent.h"
-#include "UnwindMap.h"
 
-//-------------------------------------------------------------------------
-// UnwindCurrent functions.
-//-------------------------------------------------------------------------
-UnwindCurrent::UnwindCurrent() {
-}
-
-UnwindCurrent::~UnwindCurrent() {
-}
-
-bool UnwindCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
-  if (!ucontext) {
-    int ret = unw_getcontext(&context_);
-    if (ret < 0) {
-      BACK_LOGW("unw_getcontext failed %d", ret);
-      return false;
-    }
+std::string UnwindCurrent::GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) {
+  *offset = 0;
+  char buf[512];
+  unw_word_t value;
+  if (unw_get_proc_name_by_ip(unw_local_addr_space, pc, buf, sizeof(buf),
+                              &value, &context_) >= 0 && buf[0] != '\0') {
+    *offset = static_cast<uintptr_t>(value);
+    return buf;
   }
-  else {
-    GetUnwContextFromUcontext(ucontext);
-  }
-  return UnwindFromContext(num_ignore_frames, false);
+  return "";
 }
 
 void UnwindCurrent::GetUnwContextFromUcontext(const ucontext_t* ucontext) {
@@ -76,54 +65,43 @@
 #endif
 }
 
-std::string UnwindCurrent::GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) {
-  *offset = 0;
-  char buf[512];
-  unw_word_t value;
-  if (unw_get_proc_name_by_ip(unw_local_addr_space, pc, buf, sizeof(buf),
-                              &value, &context_) >= 0 && buf[0] != '\0') {
-    *offset = static_cast<uintptr_t>(value);
-    return buf;
-  }
-  return "";
-}
-
-bool UnwindCurrent::UnwindFromContext(size_t num_ignore_frames, bool within_handler) {
-  // The cursor structure is pretty large, do not put it on the stack.
-  unw_cursor_t* cursor = new unw_cursor_t;
-  int ret = unw_init_local(cursor, &context_);
-  if (ret < 0) {
-    if (!within_handler) {
-      BACK_LOGW("unw_init_local failed %d", ret);
+bool UnwindCurrent::UnwindFromContext(size_t num_ignore_frames, ucontext_t* ucontext) {
+  if (ucontext == nullptr) {
+    int ret = unw_getcontext(&context_);
+    if (ret < 0) {
+      BACK_LOGW("unw_getcontext failed %d", ret);
+      return false;
     }
-    delete cursor;
+  } else {
+    GetUnwContextFromUcontext(ucontext);
+  }
+
+  // The cursor structure is pretty large, do not put it on the stack.
+  std::unique_ptr<unw_cursor_t> cursor(new unw_cursor_t);
+  int ret = unw_init_local(cursor.get(), &context_);
+  if (ret < 0) {
+    BACK_LOGW("unw_init_local failed %d", ret);
     return false;
   }
 
-  std::vector<backtrace_frame_data_t>* frames = GetFrames();
-  frames->reserve(MAX_BACKTRACE_FRAMES);
   size_t num_frames = 0;
   do {
     unw_word_t pc;
-    ret = unw_get_reg(cursor, UNW_REG_IP, &pc);
+    ret = unw_get_reg(cursor.get(), UNW_REG_IP, &pc);
     if (ret < 0) {
-      if (!within_handler) {
-        BACK_LOGW("Failed to read IP %d", ret);
-      }
+      BACK_LOGW("Failed to read IP %d", ret);
       break;
     }
     unw_word_t sp;
-    ret = unw_get_reg(cursor, UNW_REG_SP, &sp);
+    ret = unw_get_reg(cursor.get(), UNW_REG_SP, &sp);
     if (ret < 0) {
-      if (!within_handler) {
-        BACK_LOGW("Failed to read SP %d", ret);
-      }
+      BACK_LOGW("Failed to read SP %d", ret);
       break;
     }
 
     if (num_ignore_frames == 0) {
-      frames->resize(num_frames+1);
-      backtrace_frame_data_t* frame = &frames->at(num_frames);
+      frames_.resize(num_frames+1);
+      backtrace_frame_data_t* frame = &frames_.at(num_frames);
       frame->num = num_frames;
       frame->pc = static_cast<uintptr_t>(pc);
       frame->sp = static_cast<uintptr_t>(sp);
@@ -131,34 +109,18 @@
 
       if (num_frames > 0) {
         // Set the stack size for the previous frame.
-        backtrace_frame_data_t* prev = &frames->at(num_frames-1);
+        backtrace_frame_data_t* prev = &frames_.at(num_frames-1);
         prev->stack_size = frame->sp - prev->sp;
       }
 
-      if (!within_handler) {
-        frame->func_name = GetFunctionName(frame->pc, &frame->func_offset);
-        FillInMap(frame->pc, &frame->map);
-      } else {
-        frame->func_offset = 0;
-      }
+      frame->func_name = GetFunctionName(frame->pc, &frame->func_offset);
+      FillInMap(frame->pc, &frame->map);
       num_frames++;
     } else {
       num_ignore_frames--;
     }
-    ret = unw_step (cursor);
+    ret = unw_step (cursor.get());
   } while (ret > 0 && num_frames < MAX_BACKTRACE_FRAMES);
 
-  delete cursor;
   return true;
 }
-
-//-------------------------------------------------------------------------
-// C++ object creation function.
-//-------------------------------------------------------------------------
-Backtrace* CreateCurrentObj(BacktraceMap* map) {
-  return new BacktraceCurrent(new UnwindCurrent(), map);
-}
-
-Backtrace* CreateThreadObj(pid_t tid, BacktraceMap* map) {
-  return new BacktraceThread(new UnwindCurrent(), tid, map);
-}
diff --git a/libbacktrace/UnwindCurrent.h b/libbacktrace/UnwindCurrent.h
index 2375e6e..3023996 100644
--- a/libbacktrace/UnwindCurrent.h
+++ b/libbacktrace/UnwindCurrent.h
@@ -17,27 +17,32 @@
 #ifndef _LIBBACKTRACE_UNWIND_CURRENT_H
 #define _LIBBACKTRACE_UNWIND_CURRENT_H
 
+#include <stdint.h>
+#include <sys/types.h>
+#include <ucontext.h>
+
 #include <string>
 
-#include "BacktraceImpl.h"
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
+#include "BacktraceCurrent.h"
 
 #define UNW_LOCAL_ONLY
 #include <libunwind.h>
 
-class UnwindCurrent : public BacktraceImpl {
+class UnwindCurrent : public BacktraceCurrent {
 public:
-  UnwindCurrent();
-  virtual ~UnwindCurrent();
+  UnwindCurrent(pid_t pid, pid_t tid, BacktraceMap* map) : BacktraceCurrent(pid, tid, map) {}
+  virtual ~UnwindCurrent() {}
 
-  virtual bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext);
+  std::string GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) override;
 
-  virtual std::string GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset);
+private:
+  void GetUnwContextFromUcontext(const ucontext_t* ucontext);
 
-  bool UnwindFromContext(size_t num_ignore_frames, bool within_handler);
+  bool UnwindFromContext(size_t num_ignore_frames, ucontext_t* ucontext) override;
 
-  void GetUnwContextFromUcontext(const ucontext_t* context);
-
-protected:
   unw_context_t context_;
 };
 
diff --git a/libbacktrace/UnwindMap.cpp b/libbacktrace/UnwindMap.cpp
index 284a561..fa59d07 100644
--- a/libbacktrace/UnwindMap.cpp
+++ b/libbacktrace/UnwindMap.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include <pthread.h>
+#include <stdint.h>
 #include <stdlib.h>
 #include <sys/types.h>
 #include <unistd.h>
@@ -142,7 +142,7 @@
   }
   if (!map->Build()) {
     delete map;
-    return NULL;
+    return nullptr;
   }
   return map;
 }
diff --git a/libbacktrace/UnwindMap.h b/libbacktrace/UnwindMap.h
index be8855e..e292016 100644
--- a/libbacktrace/UnwindMap.h
+++ b/libbacktrace/UnwindMap.h
@@ -17,6 +17,9 @@
 #ifndef _LIBBACKTRACE_UNWIND_MAP_H
 #define _LIBBACKTRACE_UNWIND_MAP_H
 
+#include <stdint.h>
+#include <sys/types.h>
+
 #include <backtrace/BacktraceMap.h>
 
 // The unw_map_cursor_t structure is different depending on whether it is
diff --git a/libbacktrace/UnwindPtrace.cpp b/libbacktrace/UnwindPtrace.cpp
index efe758b..a7c3de5 100644
--- a/libbacktrace/UnwindPtrace.cpp
+++ b/libbacktrace/UnwindPtrace.cpp
@@ -14,35 +14,36 @@
  * limitations under the License.
  */
 
-#include <backtrace/Backtrace.h>
-#include <backtrace/BacktraceMap.h>
-
+#include <stdint.h>
 #include <sys/types.h>
-#include <string.h>
 #include <ucontext.h>
 
 #include <libunwind.h>
 #include <libunwind-ptrace.h>
 
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
 #include "BacktraceLog.h"
 #include "UnwindMap.h"
 #include "UnwindPtrace.h"
 
-UnwindPtrace::UnwindPtrace() : addr_space_(NULL), upt_info_(NULL) {
+UnwindPtrace::UnwindPtrace(pid_t pid, pid_t tid, BacktraceMap* map)
+    : BacktracePtrace(pid, tid, map), addr_space_(nullptr), upt_info_(nullptr) {
 }
 
 UnwindPtrace::~UnwindPtrace() {
   if (upt_info_) {
     _UPT_destroy(upt_info_);
-    upt_info_ = NULL;
+    upt_info_ = nullptr;
   }
   if (addr_space_) {
     // Remove the map from the address space before destroying it.
     // It will be freed in the UnwindMap destructor.
-    unw_map_set(addr_space_, NULL);
+    unw_map_set(addr_space_, nullptr);
 
     unw_destroy_addr_space(addr_space_);
-    addr_space_ = NULL;
+    addr_space_ = nullptr;
   }
 }
 
@@ -74,8 +75,6 @@
     return false;
   }
 
-  std::vector<backtrace_frame_data_t>* frames = GetFrames();
-  frames->reserve(MAX_BACKTRACE_FRAMES);
   size_t num_frames = 0;
   do {
     unw_word_t pc;
@@ -92,15 +91,15 @@
     }
 
     if (num_ignore_frames == 0) {
-      frames->resize(num_frames+1);
-      backtrace_frame_data_t* frame = &frames->at(num_frames);
+      frames_.resize(num_frames+1);
+      backtrace_frame_data_t* frame = &frames_.at(num_frames);
       frame->num = num_frames;
       frame->pc = static_cast<uintptr_t>(pc);
       frame->sp = static_cast<uintptr_t>(sp);
       frame->stack_size = 0;
 
       if (num_frames > 0) {
-        backtrace_frame_data_t* prev = &frames->at(num_frames-1);
+        backtrace_frame_data_t* prev = &frames_.at(num_frames-1);
         prev->stack_size = frame->sp - prev->sp;
       }
 
@@ -129,10 +128,3 @@
   }
   return "";
 }
-
-//-------------------------------------------------------------------------
-// C++ object creation function.
-//-------------------------------------------------------------------------
-Backtrace* CreatePtraceObj(pid_t pid, pid_t tid, BacktraceMap* map) {
-  return new BacktracePtrace(new UnwindPtrace(), pid, tid, map);
-}
diff --git a/libbacktrace/UnwindPtrace.h b/libbacktrace/UnwindPtrace.h
index 2fb7967..ab04abf 100644
--- a/libbacktrace/UnwindPtrace.h
+++ b/libbacktrace/UnwindPtrace.h
@@ -17,20 +17,26 @@
 #ifndef _LIBBACKTRACE_UNWIND_PTRACE_H
 #define _LIBBACKTRACE_UNWIND_PTRACE_H
 
+#include <stdint.h>
+#include <sys/types.h>
+
 #include <string>
 
-#include "BacktraceImpl.h"
-
+#ifdef UNW_LOCAL_ONLY
+#undef UNW_LOCAL_ONLY
+#endif
 #include <libunwind.h>
 
-class UnwindPtrace : public BacktraceImpl {
+#include "BacktracePtrace.h"
+
+class UnwindPtrace : public BacktracePtrace {
 public:
-  UnwindPtrace();
+  UnwindPtrace(pid_t pid, pid_t tid, BacktraceMap* map);
   virtual ~UnwindPtrace();
 
-  virtual bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext);
+  bool Unwind(size_t num_ignore_frames, ucontext_t* ucontext) override;
 
-  virtual std::string GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset);
+  std::string GetFunctionNameRaw(uintptr_t pc, uintptr_t* offset) override;
 
 private:
   unw_addr_space_t addr_space_;
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index b1e34bd..d408856 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -33,13 +33,14 @@
 #include <backtrace/BacktraceMap.h>
 
 // For the THREAD_SIGNAL definition.
-#include "BacktraceThread.h"
+#include "BacktraceCurrent.h"
 
 #include <cutils/atomic.h>
 #include <gtest/gtest.h>
 
 #include <algorithm>
 #include <memory>
+#include <string>
 #include <vector>
 
 #include "thread_utils.h"
@@ -83,15 +84,16 @@
   return static_cast<uint64_t>(t.tv_sec * NS_PER_SEC + t.tv_nsec);
 }
 
-void DumpFrames(Backtrace* backtrace) {
+std::string DumpFrames(Backtrace* backtrace) {
   if (backtrace->NumFrames() == 0) {
-    printf("    No frames to dump\n");
-    return;
+    return "   No frames to dump\n";
   }
 
+  std::string frame;
   for (size_t i = 0; i < backtrace->NumFrames(); i++) {
-    printf("    %s\n", backtrace->FormatFrameData(i).c_str());
+    frame += "   " + backtrace->FormatFrameData(i) + '\n';
   }
+  return frame;
 }
 
 void WaitForStop(pid_t pid) {
@@ -133,8 +135,8 @@
       break;
     }
   }
-  ASSERT_LT(static_cast<size_t>(0), frame_num);
-  ASSERT_LE(static_cast<size_t>(3), frame_num);
+  ASSERT_LT(static_cast<size_t>(0), frame_num) << DumpFrames(backtrace);
+  ASSERT_LE(static_cast<size_t>(3), frame_num) << DumpFrames(backtrace);
 
   ASSERT_EQ(backtrace->GetFrame(frame_num)->func_name, "test_level_one");
   ASSERT_EQ(backtrace->GetFrame(frame_num-1)->func_name, "test_level_two");
@@ -490,9 +492,13 @@
   // The SA_RESTORER flag gets set behind our back, so a direct comparison
   // doesn't work unless we mask the value off. Mips doesn't have this
   // flag, so skip this on that platform.
-#ifdef SA_RESTORER
+#if defined(SA_RESTORER)
   cur_action.sa_flags &= ~SA_RESTORER;
   new_action.sa_flags &= ~SA_RESTORER;
+#elif defined(__GLIBC__)
+  // Our host compiler doesn't appear to define this flag for some reason.
+  cur_action.sa_flags &= ~0x04000000;
+  new_action.sa_flags &= ~0x04000000;
 #endif
   EXPECT_EQ(cur_action.sa_flags, new_action.sa_flags);
 }
@@ -858,10 +864,15 @@
   // Tell the caller it's okay to start reading memory.
   android_atomic_acquire_store(1, &thread_data->state);
 
-  // Loop waiting for everything
+  // Loop waiting for the caller to finish reading the memory.
   while (thread_data->state) {
   }
 
+  // Re-enable read-write on the page so that we don't crash if we try
+  // and access data on this page when freeing the memory.
+  if (mprotect(&memory[pagesize], pagesize, PROT_READ | PROT_WRITE) != 0) {
+    return reinterpret_cast<void*>(-1);
+  }
   free(memory);
 
   android_atomic_acquire_store(1, &thread_data->state);
@@ -1005,6 +1016,7 @@
     delete backtrace;
   }
   size_t stable_pss = GetPssBytes();
+  ASSERT_TRUE(stable_pss != 0);
 
   // Loop enough that even a small leak should be detectable.
   for (size_t i = 0; i < 4096; i++) {
@@ -1014,6 +1026,7 @@
     delete backtrace;
   }
   size_t new_pss = GetPssBytes();
+  ASSERT_TRUE(new_pss != 0);
   size_t abs_diff = (new_pss > stable_pss) ? new_pss - stable_pss : stable_pss - new_pss;
   // As long as the new pss is within a certain amount, consider everything okay.
   ASSERT_LE(abs_diff, MAX_LEAK_BYTES);
diff --git a/libcutils/Android.mk b/libcutils/Android.mk
index d890319..9f32307 100644
--- a/libcutils/Android.mk
+++ b/libcutils/Android.mk
@@ -59,7 +59,8 @@
         sockets.c \
 
     commonHostSources += \
-        ashmem-host.c
+        ashmem-host.c \
+        trace-host.c
 
 endif
 
@@ -116,7 +117,7 @@
         partition_utils.c \
         properties.c \
         qtaguid.c \
-        trace.c \
+        trace-dev.c \
         uevent.c \
 
 LOCAL_SRC_FILES_arm += \
diff --git a/libcutils/trace.c b/libcutils/trace-dev.c
similarity index 100%
rename from libcutils/trace.c
rename to libcutils/trace-dev.c
diff --git a/libcutils/trace-host.c b/libcutils/trace-host.c
new file mode 100644
index 0000000..b87e543
--- /dev/null
+++ b/libcutils/trace-host.c
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <cutils/trace.h>
+
+#ifndef __unused
+#define __unused __attribute__((__unused__))
+#endif
+
+volatile int32_t        atrace_is_ready      = 1;
+int                     atrace_marker_fd     = -1;
+uint64_t                atrace_enabled_tags  = 0;
+
+void atrace_set_debuggable(bool debuggable __unused) { }
+void atrace_set_tracing_enabled(bool enabled __unused) { }
+void atrace_update_tags() { }
+void atrace_setup() { }
+void atrace_begin_body(const char* name __unused) { }
+void atrace_async_begin_body(const char* name __unused, int32_t cookie __unused) { }
+void atrace_async_end_body(const char* name __unused, int32_t cookie __unused) { }
+void atrace_int_body(const char* name __unused, int32_t value __unused) { }
+void atrace_int64_body(const char* name __unused, int64_t value __unused) { }