Implicit null/suspend checks (oat version bump)

This adds the ability to use SEGV signals
to throw NullPointerException exceptions from Java code rather
than having the compiler generate explicit comparisons and
branches.  It does this by using sigaction to trap SIGSEGV and when triggered
makes sure it's in compiled code and if so, sets the return
address to the entry point to throw the exception.

It also uses this signal mechanism to determine whether to check
for thread suspension.  Instead of the compiler generating calls
to a function to check for threads being suspended, the compiler
will now load indirect via an address in the TLS area.  To trigger
a suspend, the contents of this address are changed from something
valid to 0.  A SIGSEGV will occur and the handler will check
for a valid instruction pattern before invoking the thread
suspension check code.

If a user program taps SIGSEGV it will prevent our signal handler
working.  This will cause a failure in the runtime.

There are two signal handlers at present.  You can control them
individually using the flags -implicit-checks: on the runtime
command line.  This takes a string parameter, a comma
separated set of strings.  Each can be one of:

none        switch off
null        null pointer checks
suspend     suspend checks
all         all checks

So to switch only suspend checks on, pass:
-implicit-checks:suspend

There is also -explicit-checks to provide the reverse once
we change the default.

For dalvikvm, pass --runtime-arg -implicit-checks:foo,bar

The default is -implicit-checks:none

There is also a property 'dalvik.vm.implicit_checks' whose value is the same
string as the command option.  The default is 'none'.  For example to switch on
null checks using the option:

setprop dalvik.vm.implicit_checks null

It only works for ARM right now.

Bumps OAT version number due to change to Thread offsets.

Bug: 13121132
Change-Id: If743849138162f3c7c44a523247e413785677370

21 files changed, 803 insertions, 14 deletions

diff --git a/runtime/Android.mk b/runtime/Android.mk
index e094850..983b48f 100644
--- a/runtime/Android.mk
+++ b/runtime/Android.mk
@@ -139,6 +139,7 @@ LIBART_COMMON_SRC_FILES := \
 	trace.cc \
 	transaction.cc \
 	profiler.cc \
+	fault_handler.cc \
 	utf.cc \
 	utils.cc \
 	verifier/dex_gc_map.cc \
@@ -207,7 +208,8 @@ LIBART_TARGET_SRC_FILES_arm := \
 	arch/arm/portable_entrypoints_arm.S \
 	arch/arm/quick_entrypoints_arm.S \
 	arch/arm/arm_sdiv.S \
-	arch/arm/thread_arm.cc
+	arch/arm/thread_arm.cc \
+	arch/arm/fault_handler_arm.cc
 
 LIBART_TARGET_SRC_FILES_x86 := \
 	arch/x86/context_x86.cc \
@@ -215,7 +217,8 @@ LIBART_TARGET_SRC_FILES_x86 := \
 	arch/x86/jni_entrypoints_x86.S \
 	arch/x86/portable_entrypoints_x86.S \
 	arch/x86/quick_entrypoints_x86.S \
-	arch/x86/thread_x86.cc
+	arch/x86/thread_x86.cc \
+	arch/x86/fault_handler_x86.cc
 
 LIBART_TARGET_SRC_FILES_x86_64 := \
 	arch/x86_64/context_x86_64.cc \
@@ -224,7 +227,8 @@ LIBART_TARGET_SRC_FILES_x86_64 := \
 	arch/x86_64/portable_entrypoints_x86_64.S \
 	arch/x86_64/quick_entrypoints_x86_64.S \
 	arch/x86_64/thread_x86_64.cc \
-	monitor_pool.cc
+	monitor_pool.cc \
+	arch/x86_64/fault_handler_x86_64.cc
 
 
 LIBART_TARGET_SRC_FILES_mips := \
@@ -233,7 +237,8 @@ LIBART_TARGET_SRC_FILES_mips := \
 	arch/mips/jni_entrypoints_mips.S \
 	arch/mips/portable_entrypoints_mips.S \
 	arch/mips/quick_entrypoints_mips.S \
-	arch/mips/thread_mips.cc
+	arch/mips/thread_mips.cc \
+	arch/mips/fault_mhandlerarm.cc
 
 ifeq ($(TARGET_ARCH),arm64)
 $(info TODOArm64: $(LOCAL_PATH)/Android.mk Add Arm64 specific runtime files)
@@ -263,6 +268,7 @@ LIBART_HOST_SRC_FILES += \
 	arch/x86_64/portable_entrypoints_x86_64.S \
 	arch/x86_64/quick_entrypoints_x86_64.S \
 	arch/x86_64/thread_x86_64.cc \
+	arch/x86_64/fault_handler_x86_64.cc \
 	monitor_pool.cc
 else
 LIBART_HOST_SRC_FILES += \
@@ -271,6 +277,7 @@ LIBART_HOST_SRC_FILES += \
 	arch/x86/jni_entrypoints_x86.S \
 	arch/x86/portable_entrypoints_x86.S \
 	arch/x86/quick_entrypoints_x86.S \
+	arch/x86/fault_handler_x86.cc \
 	arch/x86/thread_x86.cc
 endif
 else # HOST_ARCH != x86
diff --git a/runtime/arch/arm/fault_handler_arm.cc b/runtime/arch/arm/fault_handler_arm.cc
new file mode 100644
index 0000000..c748ce9
--- /dev/null
+++ b/runtime/arch/arm/fault_handler_arm.cc
@@ -0,0 +1,148 @@
+/*
+ * Copyright (C) 2008 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 "fault_handler.h"
+#include <sys/ucontext.h>
+#include "base/macros.h"
+#include "globals.h"
+#include "base/logging.h"
+#include "base/hex_dump.h"
+#include "thread.h"
+#include "thread-inl.h"
+
+//
+// ARM specific fault handler functions.
+//
+
+namespace art {
+
+extern "C" void art_quick_throw_null_pointer_exception();
+extern "C" void art_quick_test_suspend();
+
+void FaultManager::GetMethodAndReturnPC(void* context, uintptr_t& method, uintptr_t& return_pc) {
+  struct ucontext *uc = (struct ucontext *)context;
+  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
+  uintptr_t* sp = reinterpret_cast<uint32_t*>(sc->arm_sp);
+  if (sp == nullptr) {
+    return;
+  }
+
+  // Work out the return PC.  This will be the address of the instruction
+  // following the faulting ldr/str instruction.  This is in thumb mode so
+  // the instruction might be a 16 or 32 bit one.  Also, the GC map always
+  // has the bottom bit of the PC set so we also need to set that.
+
+  // Need to work out the size of the instruction that caused the exception.
+  uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc);
+
+  uint16_t instr = ptr[0] | ptr[1] << 8;
+  bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800);
+  uint32_t instr_size = is_32bit ? 4 : 2;
+
+  // The method is at the top of the stack.
+  method = sp[0];
+
+  return_pc = (sc->arm_pc + instr_size) | 1;
+}
+
+bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) {
+  // The code that looks for the catch location needs to know the value of the
+  // ARM PC at the point of call.  For Null checks we insert a GC map that is immediately after
+  // the load/store instruction that might cause the fault.  However the mapping table has
+  // the low bits set for thumb mode so we need to set the bottom bit for the LR
+  // register in order to find the mapping.
+
+  // Need to work out the size of the instruction that caused the exception.
+  struct ucontext *uc = (struct ucontext *)context;
+  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
+  uint8_t* ptr = reinterpret_cast<uint8_t*>(sc->arm_pc);
+
+  uint16_t instr = ptr[0] | ptr[1] << 8;
+  bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800);
+  uint32_t instr_size = is_32bit ? 4 : 2;
+  sc->arm_lr = (sc->arm_pc + instr_size) | 1;      // LR needs to point to gc map location
+  sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_throw_null_pointer_exception);
+  LOG(DEBUG) << "Generating null pointer exception";
+  return true;
+}
+
+// A suspend check is done using the following instruction sequence:
+// 0xf723c0b2: f8d902c0  ldr.w   r0, [r9, #704]  ; suspend_trigger_
+// .. some intervening instruction
+// 0xf723c0b6: 6800      ldr     r0, [r0, #0]
+
+// The offset from r9 is Thread::ThreadSuspendTriggerOffset().
+// To check for a suspend check, we examine the instructions that caused
+// the fault (at PC-4 and PC).
+bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) {
+  // These are the instructions to check for.  The first one is the ldr r0,[r9,#xxx]
+  // where xxx is the offset of the suspend trigger.
+  uint32_t checkinst1 = 0xf8d90000 + Thread::ThreadSuspendTriggerOffset().Int32Value();
+  uint16_t checkinst2 = 0x6800;
+
+  struct ucontext *uc = (struct ucontext *)context;
+  struct sigcontext *sc = reinterpret_cast<struct sigcontext*>(&uc->uc_mcontext);
+  uint8_t* ptr2 = reinterpret_cast<uint8_t*>(sc->arm_pc);
+  uint8_t* ptr1 = ptr2 - 4;
+  LOG(DEBUG) << "checking suspend";
+
+  uint16_t inst2 = ptr2[0] | ptr2[1] << 8;
+  LOG(DEBUG) << "inst2: " << std::hex << inst2 << " checkinst2: " << checkinst2;
+  if (inst2 != checkinst2) {
+    // Second instruction is not good, not ours.
+    return false;
+  }
+
+  // The first instruction can a little bit up the stream due to load hoisting
+  // in the compiler.
+  uint8_t* limit = ptr1 - 40;   // Compiler will hoist to a max of 20 instructions.
+  bool found = false;
+  while (ptr1 > limit) {
+    uint32_t inst1 = ((ptr1[0] | ptr1[1] << 8) << 16) | (ptr1[2] | ptr1[3] << 8);
+    LOG(DEBUG) << "inst1: " << std::hex << inst1 << " checkinst1: " << checkinst1;
+    if (inst1 == checkinst1) {
+      found = true;
+      break;
+    }
+    ptr1 -= 2;      // Min instruction size is 2 bytes.
+  }
+  if (found) {
+    LOG(DEBUG) << "suspend check match";
+    // This is a suspend check.  Arrange for the signal handler to return to
+    // art_quick_test_suspend.  Also set LR so that after the suspend check it
+    // will resume the instruction (current PC + 2).  PC points to the
+    // ldr r0,[r0,#0] instruction (r0 will be 0, set by the trigger).
+
+    // NB: remember that we need to set the bottom bit of the LR register
+    // to switch to thumb mode.
+    LOG(DEBUG) << "arm lr: " << std::hex << sc->arm_lr;
+    LOG(DEBUG) << "arm pc: " << std::hex << sc->arm_pc;
+    sc->arm_lr = sc->arm_pc + 3;      // +2 + 1 (for thumb)
+    sc->arm_pc = reinterpret_cast<uintptr_t>(art_quick_test_suspend);
+
+    // Now remove the suspend trigger that caused this fault.
+    Thread::Current()->RemoveSuspendTrigger();
+    LOG(DEBUG) << "removed suspend trigger invoking test suspend";
+    return true;
+  }
+  return false;
+}
+
+bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+}       // namespace art
diff --git a/runtime/arch/mips/fault_handler_mips.cc b/runtime/arch/mips/fault_handler_mips.cc
new file mode 100644
index 0000000..8d494c1
--- /dev/null
+++ b/runtime/arch/mips/fault_handler_mips.cc
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2008 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 "fault_handler.h"
+#include <sys/ucontext.h>
+#include "base/macros.h"
+#include "globals.h"
+#include "base/logging.h"
+#include "base/hex_dump.h"
+
+
+//
+// Mips specific fault handler functions.
+//
+
+namespace art {
+
+void FaultManager::GetMethodAndReturnPC(void* context, uintptr_t& method, uintptr_t& return_pc) {
+}
+
+bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+
+bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+
+bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+}       // namespace art
diff --git a/runtime/arch/x86/fault_handler_x86.cc b/runtime/arch/x86/fault_handler_x86.cc
new file mode 100644
index 0000000..171a541
--- /dev/null
+++ b/runtime/arch/x86/fault_handler_x86.cc
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2008 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 "fault_handler.h"
+#include <sys/ucontext.h>
+#include "base/macros.h"
+#include "globals.h"
+#include "base/logging.h"
+#include "base/hex_dump.h"
+
+
+//
+// X86 specific fault handler functions.
+//
+
+namespace art {
+
+void FaultManager::GetMethodAndReturnPC(void* context, uintptr_t& method, uintptr_t& return_pc) {
+}
+
+bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+
+bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+
+bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+}       // namespace art
diff --git a/runtime/arch/x86_64/fault_handler_x86_64.cc b/runtime/arch/x86_64/fault_handler_x86_64.cc
new file mode 100644
index 0000000..3ef19fb
--- /dev/null
+++ b/runtime/arch/x86_64/fault_handler_x86_64.cc
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2008 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 "fault_handler.h"
+#include <sys/ucontext.h>
+#include "base/macros.h"
+#include "globals.h"
+#include "base/logging.h"
+#include "base/hex_dump.h"
+
+
+//
+// X86_64 specific fault handler functions.
+//
+
+namespace art {
+
+void FaultManager::GetMethodAndReturnPC(void* context, uintptr_t& method, uintptr_t& return_pc) {
+}
+
+bool NullPointerHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+
+bool SuspensionHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+
+bool StackOverflowHandler::Action(int sig, siginfo_t* info, void* context) {
+  return false;
+}
+}       // namespace art
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index b709da3..b8d1493 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -573,6 +573,38 @@ bool ClassLinker::GenerateOatFile(const char* dex_filename,
   argv.push_back("-classpath");
   argv.push_back("--runtime-arg");
   argv.push_back(Runtime::Current()->GetClassPathString());
+
+  argv.push_back("--runtime-arg");
+  std::string checkstr = "-implicit-checks";
+
+  int nchecks = 0;
+  char checksep = ':';
+
+  if (!Runtime::Current()->ExplicitNullChecks()) {
+    checkstr += checksep;
+    checksep = ',';
+    checkstr += "null";
+    ++nchecks;
+  }
+  if (!Runtime::Current()->ExplicitSuspendChecks()) {
+    checkstr += checksep;
+    checksep = ',';
+    checkstr += "suspend";
+    ++nchecks;
+  }
+
+  if (!Runtime::Current()->ExplicitStackOverflowChecks()) {
+    checkstr += checksep;
+    checksep = ',';
+    checkstr += "stack";
+    ++nchecks;
+  }
+
+  if (nchecks == 0) {
+    checkstr += ":none";
+  }
+  argv.push_back(checkstr);
+
   if (!kIsTargetBuild) {
     argv.push_back("--host");
   }
diff --git a/runtime/fault_handler.cc b/runtime/fault_handler.cc
new file mode 100644
index 0000000..6399c0d
--- /dev/null
+++ b/runtime/fault_handler.cc
@@ -0,0 +1,181 @@
+/*
+ * Copyright (C) 2008 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 "fault_handler.h"
+#include <sys/mman.h>
+#include <sys/ucontext.h>
+#include "base/macros.h"
+#include "globals.h"
+#include "base/logging.h"
+#include "base/hex_dump.h"
+#include "thread.h"
+#include "mirror/art_method-inl.h"
+#include "mirror/class-inl.h"
+#include "mirror/dex_cache.h"
+#include "mirror/object_array-inl.h"
+#include "mirror/object-inl.h"
+#include "object_utils.h"
+#include "scoped_thread_state_change.h"
+#include "verify_object-inl.h"
+
+namespace art {
+// Static fault manger object accessed by signal handler.
+FaultManager fault_manager;
+
+// Signal handler called on SIGSEGV.
+static void art_fault_handler(int sig, siginfo_t* info, void* context) {
+  fault_manager.HandleFault(sig, info, context);
+}
+
+FaultManager::FaultManager() {
+  sigaction(SIGSEGV, nullptr, &oldaction_);
+}
+
+FaultManager::~FaultManager() {
+  sigaction(SIGSEGV, &oldaction_, nullptr);   // Restore old handler.
+}
+
+void FaultManager::Init() {
+  struct sigaction action;
+  action.sa_sigaction = art_fault_handler;
+  sigemptyset(&action.sa_mask);
+  action.sa_flags = SA_SIGINFO | SA_ONSTACK;
+  action.sa_restorer = nullptr;
+  sigaction(SIGSEGV, &action, &oldaction_);
+}
+
+void FaultManager::HandleFault(int sig, siginfo_t* info, void* context) {
+  bool handled = false;
+  if (IsInGeneratedCode(context)) {
+    for (auto& handler : handlers_) {
+      handled = handler->Action(sig, info, context);
+      if (handled) {
+        return;
+      }
+    }
+  }
+
+  if (!handled) {
+    LOG(INFO)<< "Caught unknown SIGSEGV in ART fault handler";
+    oldaction_.sa_sigaction(sig, info, context);
+  }
+}
+
+void FaultManager::AddHandler(FaultHandler* handler) {
+  handlers_.push_back(handler);
+}
+
+void FaultManager::RemoveHandler(FaultHandler* handler) {
+  for (Handlers::iterator i = handlers_.begin(); i != handlers_.end(); ++i) {
+    FaultHandler* h = *i;
+    if (h == handler) {
+      handlers_.erase(i);
+      return;
+    }
+  }
+}
+
+
+// This function is called within the signal handler.  It checks that
+// the mutator_lock is held (shared).  No annotalysis is done.
+bool FaultManager::IsInGeneratedCode(void *context) {
+  // We can only be running Java code in the current thread if it
+  // is in Runnable state.
+  Thread* thread = Thread::Current();
+  if (thread == nullptr) {
+    return false;
+  }
+
+  ThreadState state = thread->GetState();
+  if (state != kRunnable) {
+    return false;
+  }
+
+  // Current thread is runnable.
+  // Make sure it has the mutator lock.
+  if (!Locks::mutator_lock_->IsSharedHeld(thread)) {
+    return false;
+  }
+
+  uintptr_t potential_method = 0;
+  uintptr_t return_pc = 0;
+
+  // Get the architecture specific method address and return address.  These
+  // are in architecture specific files in arch/<arch>/fault_handler_<arch>.cc
+  GetMethodAndReturnPC(context, /*out*/potential_method, /*out*/return_pc);
+
+  // If we don't have a potential method, we're outta here.
+  if (potential_method == 0) {
+    return false;
+  }
+
+  // Verify that the potential method is indeed a method.
+  // TODO: check the GC maps to make sure it's an object.
+
+  mirror::Object* method_obj =
+      reinterpret_cast<mirror::Object*>(potential_method);
+
+  // Check that the class pointer inside the object is not null and is aligned.
+  mirror::Class* cls = method_obj->GetClass<kVerifyNone>();
+  if (cls == nullptr) {
+    return false;
+  }
+  if (!IsAligned<kObjectAlignment>(cls)) {
+    return false;
+  }
+
+
+  if (!VerifyClassClass(cls)) {
+    return false;
+  }
+
+  // Now make sure the class is a mirror::ArtMethod.
+  if (!cls->IsArtMethodClass()) {
+    return false;
+  }
+
+  // We can be certain that this is a method now.  Check if we have a GC map
+  // at the return PC address.
+  mirror::ArtMethod* method =
+      reinterpret_cast<mirror::ArtMethod*>(potential_method);
+  return method->ToDexPc(return_pc, false) != DexFile::kDexNoIndex;
+}
+
+//
+// Null pointer fault handler
+//
+
+NullPointerHandler::NullPointerHandler(FaultManager* manager) {
+  manager->AddHandler(this);
+}
+
+//
+// Suspension fault handler
+//
+
+SuspensionHandler::SuspensionHandler(FaultManager* manager) {
+  manager->AddHandler(this);
+}
+
+//
+// Stack overflow fault handler
+//
+
+StackOverflowHandler::StackOverflowHandler(FaultManager* manager) {
+  manager->AddHandler(this);
+}
+}   // namespace art
+
diff --git a/runtime/fault_handler.h b/runtime/fault_handler.h
new file mode 100644
index 0000000..9fe6e9a
--- /dev/null
+++ b/runtime/fault_handler.h
@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2008 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 ART_RUNTIME_FAULT_HANDLER_H_
+#define ART_RUNTIME_FAULT_HANDLER_H_
+
+#include <signal.h>
+#include <vector>
+#include <setjmp.h>
+#include <stdint.h>
+
+#include "base/mutex.h"   // For annotalysis.
+
+namespace art {
+class FaultHandler;
+
+class FaultManager {
+ public:
+  FaultManager();
+  ~FaultManager();
+
+  void Init();
+
+  void HandleFault(int sig, siginfo_t* info, void* context);
+  void AddHandler(FaultHandler* handler);
+  void RemoveHandler(FaultHandler* handler);
+
+ private:
+  bool IsInGeneratedCode(void *context) NO_THREAD_SAFETY_ANALYSIS;
+  void GetMethodAndReturnPC(void* context, uintptr_t& method, uintptr_t& return_pc);
+
+  typedef std::vector<FaultHandler*> Handlers;
+  Handlers handlers_;
+  struct sigaction oldaction_;
+};
+
+class FaultHandler {
+ public:
+  FaultHandler() : manager_(nullptr) {}
+  explicit FaultHandler(FaultManager* manager) : manager_(manager) {}
+  virtual ~FaultHandler() {}
+
+  virtual bool Action(int sig, siginfo_t* siginfo, void* context) = 0;
+ protected:
+  FaultManager* const manager_;
+};
+
+class NullPointerHandler FINAL : public FaultHandler {
+ public:
+  NullPointerHandler() {}
+  explicit NullPointerHandler(FaultManager* manager);
+
+  bool Action(int sig, siginfo_t* siginfo, void* context) OVERRIDE;
+};
+
+class SuspensionHandler FINAL : public FaultHandler {
+ public:
+  SuspensionHandler() {}
+  explicit SuspensionHandler(FaultManager* manager);
+
+  bool Action(int sig, siginfo_t* siginfo, void* context) OVERRIDE;
+};
+
+class StackOverflowHandler FINAL : public FaultHandler {
+ public:
+  StackOverflowHandler() {}
+  explicit StackOverflowHandler(FaultManager* manager);
+
+  bool Action(int sig, siginfo_t* siginfo, void* context) OVERRIDE;
+};
+
+// Statically allocated so the the signal handler can get access to it.
+extern FaultManager fault_manager;
+
+}       // namespace art
+#endif  // ART_RUNTIME_FAULT_HANDLER_H_
+
diff --git a/runtime/gc/space/image_space.cc b/runtime/gc/space/image_space.cc
index ca5b5a9..5480639 100644
--- a/runtime/gc/space/image_space.cc
+++ b/runtime/gc/space/image_space.cc
@@ -67,6 +67,37 @@ static bool GenerateImage(const std::string& image_file_name, std::string* error
   arg_vector.push_back("--runtime-arg");
   arg_vector.push_back("-Xmx64m");
 
+  arg_vector.push_back("--runtime-arg");
+  std::string checkstr = "-implicit-checks";
+  int nchecks = 0;
+  char checksep = ':';
+
+  if (!Runtime::Current()->ExplicitNullChecks()) {
+    checkstr += checksep;
+    checksep = ',';
+    checkstr += "null";
+    ++nchecks;
+  }
+  if (!Runtime::Current()->ExplicitSuspendChecks()) {
+    checkstr += checksep;
+    checksep = ',';
+    checkstr += "suspend";
+    ++nchecks;
+  }
+
+  if (!Runtime::Current()->ExplicitStackOverflowChecks()) {
+    checkstr += checksep;
+    checksep = ',';
+    checkstr += "stack";
+    ++nchecks;
+  }
+
+  if (nchecks == 0) {
+    checkstr += ":none";
+  }
+
+  arg_vector.push_back(checkstr);
+
   for (size_t i = 0; i < boot_class_path.size(); i++) {
     arg_vector.push_back(std::string("--dex-file=") + boot_class_path[i]);
   }
diff --git a/runtime/mirror/art_method.cc b/runtime/mirror/art_method.cc
index fe27992..e8a0891 100644
--- a/runtime/mirror/art_method.cc
+++ b/runtime/mirror/art_method.cc
@@ -157,7 +157,7 @@ uintptr_t ArtMethod::NativePcOffset(const uintptr_t pc) {
   return pc - reinterpret_cast<uintptr_t>(code);
 }
 
-uint32_t ArtMethod::ToDexPc(const uintptr_t pc) {
+uint32_t ArtMethod::ToDexPc(const uintptr_t pc, bool abort_on_failure) {
   if (IsPortableCompiled()) {
     // Portable doesn't use the machine pc, we just use dex pc instead.
     return static_cast<uint32_t>(pc);
@@ -183,9 +183,11 @@ uint32_t ArtMethod::ToDexPc(const uintptr_t pc) {
       return cur.DexPc();
     }
   }
-  LOG(FATAL) << "Failed to find Dex offset for PC offset " << reinterpret_cast<void*>(sought_offset)
-                     << "(PC " << reinterpret_cast<void*>(pc) << ", code=" << code
-                     << ") in " << PrettyMethod(this);
+  if (abort_on_failure) {
+      LOG(FATAL) << "Failed to find Dex offset for PC offset " << reinterpret_cast<void*>(sought_offset)
+             << "(PC " << reinterpret_cast<void*>(pc) << ", code=" << code
+             << ") in " << PrettyMethod(this);
+  }
   return DexFile::kDexNoIndex;
 }
 
diff --git a/runtime/mirror/art_method.h b/runtime/mirror/art_method.h
index a9da66c..84a3eb6 100644
--- a/runtime/mirror/art_method.h
+++ b/runtime/mirror/art_method.h
@@ -402,7 +402,8 @@ class MANAGED ArtMethod : public Object {
   uintptr_t NativePcOffset(const uintptr_t pc) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Converts a native PC to a dex PC.
-  uint32_t ToDexPc(const uintptr_t pc) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  uint32_t ToDexPc(const uintptr_t pc, bool abort_on_failure = true)
+      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   // Converts a dex PC to a native PC.
   uintptr_t ToNativePc(const uint32_t dex_pc) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
diff --git a/runtime/oat.cc b/runtime/oat.cc
index 454786d..d04514f 100644
--- a/runtime/oat.cc
+++ b/runtime/oat.cc
@@ -22,7 +22,7 @@
 namespace art {
 
 const uint8_t OatHeader::kOatMagic[] = { 'o', 'a', 't', '\n' };
-const uint8_t OatHeader::kOatVersion[] = { '0', '1', '7', '\0' };
+const uint8_t OatHeader::kOatVersion[] = { '0', '1', '8', '\0' };
 
 OatHeader::OatHeader() {
   memset(this, 0, sizeof(*this));
diff --git a/runtime/parsed_options.cc b/runtime/parsed_options.cc
index 37db462..5717689 100644
--- a/runtime/parsed_options.cc
+++ b/runtime/parsed_options.cc
@@ -15,6 +15,9 @@
  */
 
 #include "parsed_options.h"
+#ifdef HAVE_ANDROID_OS
+#include "cutils/properties.h"
+#endif
 
 #include "debugger.h"
 #include "monitor.h"
@@ -191,6 +194,36 @@ bool ParsedOptions::Parse(const Runtime::Options& options, bool ignore_unrecogni
   profile_backoff_coefficient_ = 2.0;
   profile_clock_source_ = kDefaultProfilerClockSource;
 
+  // Default to explicit checks.  Switch off with -implicit-checks:.
+  // or setprop dalvik.vm.implicit_checks check1,check2,...
+#ifdef HAVE_ANDROID_OS
+  {
+    char buf[PROP_VALUE_MAX];
+    property_get("dalvik.vm.implicit_checks", buf, "none");
+    std::string checks(buf);
+    std::vector<std::string> checkvec;
+    Split(checks, ',', checkvec);
+    for (auto& str : checkvec) {
+      std::string val = Trim(str);
+      if (val == "none") {
+        explicit_checks_ = kExplicitNullCheck | kExplicitSuspendCheck |
+            kExplicitStackOverflowCheck;
+      } else if (val == "null") {
+        explicit_checks_ &= ~kExplicitNullCheck;
+      } else if (val == "suspend") {
+        explicit_checks_ &= ~kExplicitSuspendCheck;
+      } else if (val == "stack") {
+        explicit_checks_ &= ~kExplicitStackOverflowCheck;
+      } else if (val == "all") {
+        explicit_checks_ = 0;
+      }
+    }
+  }
+#else
+  explicit_checks_ = kExplicitNullCheck | kExplicitSuspendCheck |
+    kExplicitStackOverflowCheck;
+#endif
+
   for (size_t i = 0; i < options.size(); ++i) {
     if (true && options[0].first == "-Xzygote") {
       LOG(INFO) << "option[" << i << "]=" << options[i].first;
@@ -470,6 +503,54 @@ bool ParsedOptions::Parse(const Runtime::Options& options, bool ignore_unrecogni
       if (!ParseDouble(option, ':', 1.0, 10.0, &profile_backoff_coefficient_)) {
         return false;
       }
+    } else if (StartsWith(option, "-implicit-checks:")) {
+      std::string checks;
+      if (!ParseStringAfterChar(option, ':', &checks)) {
+        return false;
+      }
+      std::vector<std::string> checkvec;
+      Split(checks, ',', checkvec);
+      for (auto& str : checkvec) {
+        std::string val = Trim(str);
+        if (val == "none") {
+          explicit_checks_ = kExplicitNullCheck | kExplicitSuspendCheck |
+            kExplicitStackOverflowCheck;
+        } else if (val == "null") {
+          explicit_checks_ &= ~kExplicitNullCheck;
+        } else if (val == "suspend") {
+          explicit_checks_ &= ~kExplicitSuspendCheck;
+        } else if (val == "stack") {
+          explicit_checks_ &= ~kExplicitStackOverflowCheck;
+        } else if (val == "all") {
+          explicit_checks_ = 0;
+        } else {
+            return false;
+        }
+      }
+    } else if (StartsWith(option, "-explicit-checks:")) {
+      std::string checks;
+      if (!ParseStringAfterChar(option, ':', &checks)) {
+        return false;
+      }
+      std::vector<std::string> checkvec;
+      Split(checks, ',', checkvec);
+      for (auto& str : checkvec) {
+        std::string val = Trim(str);
+        if (val == "none") {
+          explicit_checks_ = 0;
+        } else if (val == "null") {
+          explicit_checks_ |= kExplicitNullCheck;
+        } else if (val == "suspend") {
+          explicit_checks_ |= kExplicitSuspendCheck;
+        } else if (val == "stack") {
+          explicit_checks_ |= kExplicitStackOverflowCheck;
+        } else if (val == "all") {
+          explicit_checks_ = kExplicitNullCheck | kExplicitSuspendCheck |
+            kExplicitStackOverflowCheck;
+        } else {
+          return false;
+        }
+      }
     } else if (option == "-Xcompiler-option") {
       i++;
       if (i == options.size()) {
@@ -488,6 +569,7 @@ bool ParsedOptions::Parse(const Runtime::Options& options, bool ignore_unrecogni
                StartsWith(option, "-da:") ||
                StartsWith(option, "-enableassertions:") ||
                StartsWith(option, "-disableassertions:") ||
+               (option == "--runtime-arg") ||
                (option == "-esa") ||
                (option == "-dsa") ||
                (option == "-enablesystemassertions") ||
diff --git a/runtime/parsed_options.h b/runtime/parsed_options.h
index f07bba1..d6516a8 100644
--- a/runtime/parsed_options.h
+++ b/runtime/parsed_options.h
@@ -81,6 +81,11 @@ class ParsedOptions {
   double profile_backoff_coefficient_;
   ProfilerClockSource profile_clock_source_;
 
+  static constexpr uint32_t kExplicitNullCheck = 1;
+  static constexpr uint32_t kExplicitSuspendCheck = 2;
+  static constexpr uint32_t kExplicitStackOverflowCheck = 4;
+  uint32_t explicit_checks_;
+
  private:
   ParsedOptions() {}
 
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index d1c8370..1555bf2 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -123,7 +123,10 @@ Runtime::Runtime()
       system_thread_group_(nullptr),
       system_class_loader_(nullptr),
       dump_gc_performance_on_shutdown_(false),
-      preinitialization_transaction(nullptr) {
+      preinitialization_transaction(nullptr),
+      null_pointer_handler_(nullptr),
+      suspend_handler_(nullptr),
+      stack_overflow_handler_(nullptr) {
   for (int i = 0; i < Runtime::kLastCalleeSaveType; i++) {
     callee_save_methods_[i] = nullptr;
   }
@@ -170,6 +173,10 @@ Runtime::~Runtime() {
   // TODO: acquire a static mutex on Runtime to avoid racing.
   CHECK(instance_ == nullptr || instance_ == this);
   instance_ = nullptr;
+
+  delete null_pointer_handler_;
+  delete suspend_handler_;
+  delete stack_overflow_handler_;
 }
 
 struct AbortState {
@@ -515,6 +522,27 @@ bool Runtime::Init(const Options& raw_options, bool ignore_unrecognized) {
     GetInstrumentation()->ForceInterpretOnly();
   }
 
+  if (options->explicit_checks_ != (ParsedOptions::kExplicitSuspendCheck |
+        ParsedOptions::kExplicitNullCheck |
+        ParsedOptions::kExplicitStackOverflowCheck)) {
+    // Initialize the fault manager.
+    fault_manager.Init();
+
+    // These need to be in a specific order.  The null point check must be
+    // the last in the list.
+    if ((options->explicit_checks_ & ParsedOptions::kExplicitSuspendCheck) == 0) {
+      suspend_handler_ = new SuspensionHandler(&fault_manager);
+    }
+
+    if ((options->explicit_checks_ & ParsedOptions::kExplicitStackOverflowCheck) == 0) {
+      stack_overflow_handler_ = new StackOverflowHandler(&fault_manager);
+    }
+
+    if ((options->explicit_checks_ & ParsedOptions::kExplicitNullCheck) == 0) {
+      null_pointer_handler_ = new NullPointerHandler(&fault_manager);
+    }
+  }
+
   heap_ = new gc::Heap(options->heap_initial_size_,
                        options->heap_growth_limit_,
                        options->heap_min_free_,
diff --git a/runtime/runtime.h b/runtime/runtime.h
index 109f031..eeaaa2b 100644
--- a/runtime/runtime.h
+++ b/runtime/runtime.h
@@ -36,6 +36,7 @@
 #include "object_callbacks.h"
 #include "runtime_stats.h"
 #include "safe_map.h"
+#include "fault_handler.h"
 
 namespace art {
 
@@ -404,6 +405,18 @@ class Runtime {
     return fault_message_;
   }
 
+  bool ExplicitNullChecks() const {
+    return null_pointer_handler_ == nullptr;
+  }
+
+  bool ExplicitSuspendChecks() const {
+    return suspend_handler_ == nullptr;
+  }
+
+  bool ExplicitStackOverflowChecks() const {
+    return stack_overflow_handler_ == nullptr;
+  }
+
  private:
   static void InitPlatformSignalHandlers();
 
@@ -536,6 +549,9 @@ class Runtime {
 
   // Transaction used for pre-initializing classes at compilation time.
   Transaction* preinitialization_transaction;
+  NullPointerHandler* null_pointer_handler_;
+  SuspensionHandler* suspend_handler_;
+  StackOverflowHandler* stack_overflow_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(Runtime);
 };
diff --git a/runtime/stack.cc b/runtime/stack.cc
index 26b4de3..f397afa 100644
--- a/runtime/stack.cc
+++ b/runtime/stack.cc
@@ -92,11 +92,11 @@ StackVisitor::StackVisitor(Thread* thread, Context* context)
   DCHECK(thread == Thread::Current() || thread->IsSuspended()) << *thread;
 }
 
-uint32_t StackVisitor::GetDexPc() const {
+uint32_t StackVisitor::GetDexPc(bool abort_on_failure) const {
   if (cur_shadow_frame_ != NULL) {
     return cur_shadow_frame_->GetDexPC();
   } else if (cur_quick_frame_ != NULL) {
-    return GetMethod()->ToDexPc(cur_quick_frame_pc_);
+    return GetMethod()->ToDexPc(cur_quick_frame_pc_, abort_on_failure);
   } else {
     return 0;
   }
diff --git a/runtime/stack.h b/runtime/stack.h
index f840f67..4ee5de1 100644
--- a/runtime/stack.h
+++ b/runtime/stack.h
@@ -520,7 +520,7 @@ class StackVisitor {
     return cur_shadow_frame_ != nullptr;
   }
 
-  uint32_t GetDexPc() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
+  uint32_t GetDexPc(bool abort_on_failure = true) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   mirror::Object* GetThisObject() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
diff --git a/runtime/thread.cc b/runtime/thread.cc
index fbdf95f..f4b9d9a 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -302,6 +302,7 @@ void Thread::Init(ThreadList* thread_list, JavaVMExt* java_vm) {
   SetUpAlternateSignalStack();
   InitCpu();
   InitTlsEntryPoints();
+  RemoveSuspendTrigger();
   InitCardTable();
   InitTid();
   // Set pthread_self_ ahead of pthread_setspecific, that makes Thread::Current function, this
@@ -576,6 +577,7 @@ void Thread::ModifySuspendCount(Thread* self, int delta, bool for_debugger) {
     AtomicClearFlag(kSuspendRequest);
   } else {
     AtomicSetFlag(kSuspendRequest);
+    TriggerSuspend();
   }
 }
 
@@ -643,6 +645,7 @@ bool Thread::RequestCheckpoint(Closure* function) {
     checkpoint_functions_[available_checkpoint] = nullptr;
   } else {
     CHECK_EQ(ReadFlag(kCheckpointRequest), true);
+    TriggerSuspend();
   }
   return succeeded == 0;
 }
@@ -1774,6 +1777,7 @@ void Thread::DumpThreadOffset(std::ostream& os, uint32_t offset, size_t size_of_
   // DO_THREAD_OFFSET(top_of_managed_stack_);
   // DO_THREAD_OFFSET(top_of_managed_stack_pc_);
   DO_THREAD_OFFSET(top_sirt_);
+  DO_THREAD_OFFSET(suspend_trigger_);
 #undef DO_THREAD_OFFSET
 
   size_t entry_point_count = arraysize(gThreadEntryPointInfo);
diff --git a/runtime/thread.h b/runtime/thread.h
index eaffc3e..264a927 100644
--- a/runtime/thread.h
+++ b/runtime/thread.h
@@ -433,6 +433,10 @@ class PACKED(4) Thread {
     return ThreadOffset(OFFSETOF_MEMBER(Thread, state_and_flags_));
   }
 
+  static ThreadOffset ThreadSuspendTriggerOffset() {
+    return ThreadOffset(OFFSETOF_MEMBER(Thread, suspend_trigger_));
+  }
+
   // Size of stack less any space reserved for stack overflow
   size_t GetStackSize() const {
     return stack_size_ - (stack_end_ - stack_begin_);
@@ -824,6 +828,10 @@ class PACKED(4) Thread {
   PortableEntryPoints portable_entrypoints_;
   QuickEntryPoints quick_entrypoints_;
 
+  // Setting this to 0 will trigger a SEGV and thus a suspend check.  It is normally
+  // set to the address of itself.
+  uintptr_t* suspend_trigger_;
+
   // How many times has our pthread key's destructor been called?
   uint32_t thread_exit_check_count_;
 
@@ -838,6 +846,20 @@ class PACKED(4) Thread {
   mirror::Object* AllocTlab(size_t bytes);
   void SetTlab(byte* start, byte* end);
 
+  // Remove the suspend trigger for this thread by making the suspend_trigger_ TLS value
+  // equal to a valid pointer.
+  // TODO: does this need to atomic?  I don't think so.
+  void RemoveSuspendTrigger() {
+    suspend_trigger_ = reinterpret_cast<uintptr_t*>(&suspend_trigger_);
+  }
+
+  // Trigger a suspend check by making the suspend_trigger_ TLS value an invalid pointer.
+  // The next time a suspend check is done, it will load from the value at this address
+  // and trigger a SIGSEGV.
+  void TriggerSuspend() {
+    suspend_trigger_ = nullptr;
+  }
+
   // Thread-local rosalloc runs. There are 34 size brackets in rosalloc
   // runs (RosAlloc::kNumOfSizeBrackets). We can't refer to the
   // RosAlloc class due to a header file circular dependency issue.
diff --git a/runtime/thread_list.cc b/runtime/thread_list.cc
index ac5750b..ec610e1 100644
--- a/runtime/thread_list.cc
+++ b/runtime/thread_list.cc
@@ -753,6 +753,7 @@ void ThreadList::Register(Thread* self) {
   self->debug_suspend_count_ = debug_suspend_all_count_;
   if (self->suspend_count_ > 0) {
     self->AtomicSetFlag(kSuspendRequest);
+    self->TriggerSuspend();
   }
   CHECK(!Contains(self));
   list_.push_back(self);